Pollution Prevention in
Metal Painting and Coating Operations:
A Manual for Technical Assistance Providers
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Poll giipn -:. Pre ve nti o n
In Metal Painting and
ng
A Manual for
Pollution Prevention
Technical Assistance Providers
April 1998
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Printed.on Recycled Paper
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Acknowledgments
NEWMOA is indebted to the US. Environmental Protection Agency's Office of Pollution Prevention
for its support for this project. The Northeast states provided additional in-kind support.
NEWMOA would also like to thank those who provided advice and assistance^ especially those who
volunteered on the peer review committee: " .
Alan Buckley, Massachusetts Office of Technical Assistance
Mike Callahan, Jacobs Engineering Group Inc , .
Dean Cornstubble, Research Triangle Institute ...
Lynn Corson, Ph.D., Purdue University .
Mike Eck, U.S. Army Environmental Center
Tim Greiner, Gre.iner Environmental .
PaulPagel,MnTAP .
Jeff Palmer, The Powder Coating Institute ;
Alice Pincus, Pineus Associates
Paul Randall, U.S. EPA '
Alexander Ross, RadTech ,
Mike Simek, Rutgers
Rodger Taibert, Chemical Coaters Association International
David Liebl, Solid and Hazardous Waste Education Center ' /
Kathy Blake,:New Hampshire Department of Environmental Services
Project Staff/Contributors
Terri Goldberg, NEWMOA P2 Program Manager-Editor/Manager
Lisa Regenstein, NEWMOA P2 Project ManagerResearch/Writer
Jennifer Shearman, NEWMOA Technical StaffResearch/Writer
Beth Anderson, EPAEPA Project Manager , .
' Laurie Case, WMRCLayout and Desktop Publishing : :
Printed on Recycled Paper
Cover Photo courtesy Dean Cornstubble, Research Triangle Institute
NEWMOA welcomes users of this manual to cite and reproduce sections of it for use in providing assis-
tance to companies. However, the Association requests that users cite the document whenever reproducing.
orquoting^o that appropriate credit is give to original authors, NEWMOA and U.S. EPA. NEWMOA
thanks you for cooperating with this request.
. ' - - . /
".'"'' '-..'.- , ' in' ""'"-.' : . ' '-'
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Northeast Waste Management Officials1 Association
The Northeast Waste Management Officials' Association (NEWMOA) is a non-profit, nonpartisanj .
interstate governmental association. The membership is composed of state environmental agency
directors of the hazardous waste, solid waste, waste site cleanup and pollution prevention programs in
Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont.
NEWMOA's mission is to help states articulate, promote, and implement'economically sound regionaj
programs for the enhancement of environmental protection. The group fulfills this mission by providing
a variety of support services that facilitate communication and cooperation among member states and
between the states and EPA, and promote the efficient sharing of state and federal program resources.
NEWMOA was established by the governors of the New England states as an official interstate regional
organization, in accordance with Section 1005 of the Resource Conservation and Recovery Act
(RCRA). The organization was formally recognized by the U.S. Environmental Protection Agency
(EPA) in 1986. It is funded by state membership dues and EPA grants.
NEWMOA established the Northeast States Pollution Prevention Roundtable (NEP2 Roundtable) in
1989 to enhance the capabilities of member state environmental officials to implement effective source
reduction programs. The NE P2 Roundtable's program involves the following components: (1) manag-
ing a regional roundtable of state pollution prevention programs; (2) publishing a newsletter; (3) manag-
ing a resource center of books, reports, case studies, fact sheets, notices of upcoming meetings and
conferences, and a list of P2 experts; (4) organizing training; and (5) conducting research and publishing
reports and other documents. The resource center provides pollution prevention information to state and
local government officials, the public, industry, and others. Funding for theNE P2 Roundtable is
provided by the NEWMOA member states and the U.S. EPA. For more information contact: Terri
Goldberg, NEWMOA, 129PortlandStreet,6thfloor,Boston,MA02114,(617)367-8558x302
(Phone); (617) 367-0449 (Fax); newmoa@aol.com (e-mail). ' :;"
IV
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About This Manual
The Northeast Waste Management Officials' Association (NEWMOA) designed this manual to provide
environmental assistance staff with a basic reference on the metal coatings process. The purpose of the
manual is to enable assistance providers to rely on a single publication to jump start their research on
pollution prevention for companies with which they are working. The manual is explicitly designed to be
useful to assistance professionals with experience working with metal coating operations and those who
have never before encountered this process. The U.S. Environmental Protection Agency Pollution
Prevention Division funded this manual as a model of a comprehensive packet of pollution prevention
(P2) information on a single industry.
The Northeast Waste Management Officials' Association designed this manual to provide information
on P2 methods for paints and coatings processes. Specifically, the manual focuses on P2 methods for
reducing volatile organic compounds (VQCs) emitted during the coating of metal substrates. This
manual stresses the use of low-VOC paints and coatings (i.e., high-solids, waterborne and powder
coatings that contain lower solvent concentrations than conventional paints) as well as techniques that
can increase transfer efficiency (i.e., the percentage of paints actually put on the part compared to the
amount of paint used/sprayed). Methods for reducing the amount of solvents used during other stages
of the coatings process, particularly surface preparation and equipment cleaning, also.figure prominently.
NEWMOA collaborates with state and local environmental assistance programs in the Northeast; these
programs have requested this manual to help them provide more efficient and effective help to the .
numerous companies with metal coating operations. Assistance providers have reported frustration with
having to search databases for materials only to obtain a list of citations and case studies that they have
to spend considerable time finding in order to provide information to their client companies. In addition,
these officials rarely have the opportunity to check the accuracy of the information they find in data-
bases to determine whether the material is still current. To avoid duplicating efforts and to ensure that
the information companies receive is up-to-date and accurate, NEWMOA developed this manual as a
model "synthesized" information packet that includes an exhaustive compilation and synthesis of
existing materials oh P2 for the metal coatings process.
To compile this manual, NEWMOA reviewed many books,"articles,- fact sheets, reportsand guides on
P2 for metal coatings operations. NEWMOA staff also sent a draft of the manual to more than 15
expert reviewers for their comments and suggestions. The result is an up-to-date compilation of infor-
mation on P2 options for metal coatings. However, pollution prevention is a rapidly changing field, and
all users should check with the various centers identified in Appendix A to determine whether any new
information is available. , -
Overview of Manual
This manual is broken down into nine chapters as described below. Supporting case studies, tables,
figures and appendices are also provided.
+ Chapter 1 provides background information on paints and coatings, including a discussion of the
coatings process arid wastes generated.
* Chapter 2 presents an overview of federal regulations that affect coatings processes.
* Chapter 3 provides specific information on the role of technical assistance providers in promoting
pollution prevention.
-' * Chapter 4 is an overview .of pollution prevention options for surface preparation, coatings applica-
tion/curing and equipment cleaning. . ;
* Chapter 5 discusses surface preparation methods with an emphasis on reducing solvent use.
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* Chapter 6 presents alternatives to solvent-borne coatings, including high-solids, waterborne and
powder coatings.
+ Chapter 7 provides an overview of application techniques (i.e., spray painting and other methods)
along with a discussion of transfer efficiency.
« Chapter 8 presents information on curing methods.
4- Chapter 9 discusses alternatives to traditional equipment cleaning methods.
« Appendix A presents information resources for coatings.
*' Appendix B presents information on how to calculate VOC/HAP emissions.
« Appendix C provides information on conducting an economic analysis of paint costs.
* Appendix D presents purchasing guidelines for HVLP spray guns.
«- Appendix E presents information .on coatings testing. .
« Appendix F provides a glossary of terms pertaining to the coatings process.
* Appendix G provides information on calculating transfer efficiency.
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Audience
NEWMOA designed this manual for individuals who are involved in providing technical assistance to
firms seeking information on P2 for paint and coating processes. NEWMOA believes that the informa-
tion in this manual also would be useful for environmental inspectors and permit writers who are
involved in regulatory compliance activities. Comments and suggestions from manual users on content '
and format are welcomed. Please take-a moment and complete the evaluation form included with this
document to help us with future versions of this, manual and related manuals, or call NEWMOA at
(617) 367-8558 to speak with us directly.
Using This Manual
This manual is designed to serve as a complete reference on P2 methods for paint and coating pro-
cesses, however, it alone should not be used to advise companies on the selection of a particular coating
system. The selection of a coating system depends on a number of application-specific factors, including
the type of surface to be coated as well as the required perfotmancexharacteristics of the coating.
Companies that decide to adopt an alternative system should do so only after consultation with the
appropriate coating and equipment vendors, and careful in-house analyses of the costs and benefits as
well as technical feasibility of the alternative system.
Disclaimer
The views expressed in this report do not necessarily reflect those of NEWMOA, NEWMOA member
states, Waste Management and Research Center (WMRC), or U.S. EPA. Mention of any company,
process, or product name should not be considered .an endorsement by NEWMOA, NEWMOA mem-
ber states, WMRC, or U.S. EPA.
VI
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Table of Contents
Acknowledgments
,i
Chapter 1: Background ................................... v........... ...... 1
Definition of Terms'...: ....; ........... ...... ;.- 1.
Uses for Paints and Coatings - 1
Paint Composition........ :..-2-
Description of Coatings Processes.............. ..,- - -2
Examples of Typical Systems ............. ...4
.Sources of Wastes .......................: ..........4
Summary. -. .. 6
Chapter 2: Regulatory Overview......... ....:.;.7
Clean Air Act..... .........! .... .. 8
Resource Conservation and Recovery Act 9
Clean Water Act.......:................: - ...;.......,.... -12.
Chapter 3: Planning Pollution Prevention Programs at Coating
Facilities[[[ ........:............ 15
Characterizing a Facility........... '......................... -15
Planning ....... '.', - 16
Identify Pollution Prevention Opportunities ..... '. ,........; 22
* , --' .. . : ~ l~\ f~\
Analyze and Select Options'... ...; ^
Pilot Test or Validate Preferred Options.........,!........ -.- 23
' ' O Q
Procure and Implement New System ; -.. - ' ^J
Evaluate and Keep the Program. Going .-.'..., ':........ 23 ;
Chapter 4: Overview of Pollution Prevention in Coatings
Application Processes -25
Chapter 5: Surface Preparation v. 29
' " " --..- '99
.General Description ......;.....,..,;.. 47
' Pollution Problem .,......;.,.,.............,.... /........-................: ..-, 29
Mechanical Cleaning .....:.,.;. ., .........;: /V
Chemically-Assisted Cleaning .....'.: 30
Stripping ., , - _ ....... = ...-. o^
General P2 Options for Surface Preparation .......,...:.....,.. . -.- 30
Qeaning :......... ..',' ' ' -:,
Alternative Cleaning Methods ..."... ....."- , ; od
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Chapter 6: Alternatives to Solvent-Borne Coatings 57
Conventional Paint Composition ". 57
Switch to Surface-Free Coating '61
Alternative Coatings 61
High-Solids Coatings , - 62
Waterborne Coatings , '. 66
Powder Coating '69
Radiation Curing.. ' 75
Emerging Technologies , -79
Chapter 7: Application Techniques .83
General Description of Spray Systems -... 83
Pollution Problem , ..83
General P2 Options ' '. - --83
Strategies to Improve Transfer Efficiency 85
Conventional Air Spray (LVHP) .- 88
High-Volume/Low-Pressure (HVLP) Air Spray i 89
Low-Pressure/Low-Volume (LPLV) 91
Airless Spray . 91
Electrostatic Spray , 93
Other Methods ........'.... .95
Paint Booths...; .-..- : -101
Chapter 8: Curing Methods.... 109
Chapter 9: Equipment Cleaning 113
General Description 113
Pollution Problem '. ' '.. 1 1 3
P2 Options.^ :... -. '.... 11.3
References 117
Appendix A 123
Appendix B 127
Appendix. C .............: 129
Appendix D....'.. '...... ..'. 133
Appendix E 135
Appendix F 137
Appendix G '. 149
VIII
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List of Tables
Table 1. Common Solvents, Federal Regulatory Status v.. : 7
Table 2. Scheduled Date for MACT"Standards for Surface Coating .. 9
Table3. EPA Guidelines for Maximum VOC Content of Coatings ....'.... 10
Table'4. Hazardous Wastes Generated from Coatings Operations 13
Table 5. Overview of Assessment Information .....' 20
Table 6. Opportunities for .Improved Housekeeping in Coating Operations .:...... 26
Table 7. P2 Options for Coatings Processes .....: 27
Table 8. Alternatives to Chlorinated Solvent Cleaning 35.
Table 9. Advantages and'Disadvantages of Plastic Media Blasting \ 43
Table 10. Advantages and Disadvantages.of Vacuum Sanding. Systems... .-.. 44
Table 11. Advantages and Disadvantages of Sodium Bicarbonate 46
Table 12. Advantages and Disadvantages of Wheat Starch Blasting .........;.. 47
Table 1 3. Advantages and Disadvantages.of Carbon Dioxide Blasting .-.=-... 50
Table 14. Advantages and Disadvantages of Sponge Blasting Systems 51
' Table 15. Advantages and Disadvantages of Water Blasting Systems .................:... 52
Table 1 6. Advantages and Disadvantages of Fluidized Bed Stripping ....,..:. 53
Table 1 7. Overview of Alternative Surface Preparation Technologies...: 55
-Table 18. Health Effects of Solvents Used in Paint Formulations,. 58
Table 19, Overview of Alternatives to Solvent-Borne Coatings :...:.,-..:... ..... 63-
Table 20. Advantages and Disadvantages of High-Solids Coatings 66
Table 21. Advantages and Disadvantages of Waterborne Coatings 70
Table 22. Characteristics'of Powder Coating Techniques...... 73
Table 23. Advantages and Disadvantages of Powder Coatings .... 75
Table 24. Summary of Powder Coating Resin Properties 77
Table'25. Advantages and Disadvantages of Radiation-Cured.Coatings.. 79
Table 26. Advantages and Disadvantages of VIC ' - 80,
Table 27. Advantages and Disadvantages of Unicoat Paint Technology ...v.i: 81
table 28. Cost/Benefit Summary for Spray Application.Methods ...,...,...:.... 87.
Table 29. Advantages and Disadvantages of HVLP Spray Guns '..'. 90
Table 30. Advantages and Disadvantages of LPLV Spray Guns.... 91
Table 3.1. Advantages and Disadvantages of Airless Spray Systems,. 93
Table 32. Advantages and Disadvantages ol Electrostatic Spray Guns 95
Table 33. Advantages and.Disadvantages of E-Coat Systems ......: :;., 96
"Table 34. Advantages and Disadvantages of Autodeposition Systems... 97
Table 35. Advantages and Disadvantages of Dip Coating Systems , 97
Table 36. Advantages and Disadvantages of Flow Coating Systems , 98
Table 37.. Advantages arid Disadvantages of Curtain Coating Systems -.- '.-. 98
Table 38. Advantages and Disadvantages of Roll Coating Systems 99
Table'39. Advantages and Disadvantages of Plural Component '
Proportioning Systems ;...."............... 100
Table 40. Advantages and Disadvantages of-Supercritical Carbon Dioxide-...:.... .100
Table 41. Transfer Efficiencies of Various Application'Technologies ...:....... 101
Table 42. Overview of Application Technologies.....:..... - -.- 102
Table 43. Advantages and Disadvantages of Dry Filter Booths ."..- 1 06
IX
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Table 44.'Air/Force Dry Vs. Bake '. 109
Table 45. Typical RA'CT Limits for Miscellaneous Metal Parts Coating 1 1 1
List of Figures
Figure 1. Overview of the Coating Process ; 3
Figure 2. Coating Process and Waste Generation ,,... 5
Figure 3. Emissions vs. VOC Content ; 62
Figure 4. Major Resin Fluidization Methods 68
Figure 5. HVLP System V -....- 89
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Background
C imply statedpollution prevention makes .
O.good business sense. Faced with the increasing.
costs and liabilities associated with end-of-pipe
pollution control practices, many companies are
mming to pollution prevention as a cleaner, safer
and more cost-effective alternative.,
EPA defines pollution prevention as any practice-
which reduces or eliminates the amount or toxicity
of pollutants' entering the waste stream or the
environment prior to recycling, treatment or
disposal. Pollution prevention includes such
techniques as modification or redesign of pro-
cesses; reformulation or redesign of products;
product substitution; raw materials substitution;
and improved maintenance, housekeeping and
operating practices (EPAj, p. v).
Designed for technical assistance providers, this -
manual focuses on pollution prevention techniques
for reducing emissions of volatile organic con>
pounds (VOCs) from paint and coating processes,
including reducing the amount of solvents used in
coating formulations as well as in surface prepara-
tion and equipment cleaning. Most of the informa-
tion contained in this manual relates to the coating
of metal substrates used to manufacture metal
containers, automobiles, machinery (including
computers), metal furniture, appliances and other
consumer goods.
This Chapter presents the definitions of key terms,
discusses uses for paints and coatings and pro-
vides general information on paint composition £
and coatings processes. It also provides examples
of typical coating systems and discusses the
sources of wastes in the coatings process, includ-
" ing the specific pollution problems that are the
focus of this manual;
Definition of Terms
; . ' ' "'' ' j
The following terms are used throughout the . j
' manual. These terms are often used to mean a_.
variety of things. To clarify the use of the terms in
this document, we have provided the following
definitions.
Coating: This term refers only to organic or
polymer coatings and their associated application
techniques. In other words, although metal plating
does perform the function of a coating (e.g., it
improves appearance, corrosion resistance,
abrasion resistance, and electrical or optical
7 properties), this manual does not cover metal
"plating (i.e., zinc, aluminum, etc.) or related
processes (i.e., electroplating, conversion coating,
sputtering, ion plating, and plasma spraying).
Detailed information on P2 options for metal
plating can be found in NE WMO A's manual
Pollution Preventionjor the Metal Finishing
Industry. ,
Solvent: This term generally refers to hydrocar-
bon-based or organic solvents only; that is,
solvents made from petroleum that contain the
chemical elements hydrogen and carbon. In other
wordSj although water is a solvent in terms of
function (i.e., it is a liquid capable of dissolving
another substance); the use of the term solvent in
this manual, for the most part, does not apply to
water or other non-carbon compounds.
Uses for Paints and
Coatings
Paint is a generic term typically used to identify a
wide range of surface coating products, including
conventional solvent-borne formulations, var-
nishes, enamels, lacquers and water-based sys-
tems. Normally, painting is a process where a
liquid consisting of several components, when
applied, dries to athin plastic film. Traditionally,
major constituents of these paints are solvents.
However, non-liquid paints such as powder
coatings and high solids paints have also been .
developed. These newer materials have led to the
use of the term coating instead of/the term paint.
In general, the function of all paints and coatings
is to provide an aesthetically pleasing colored and/
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Chapter 1: Background
or glossy surface, as well as to help metal and
other substrates withstand exposure to both their
environment and everyday wear and tear (TURIb,
P-1).
Paints and coatings can be categorized according
to their use into three major groups:
* Architectural coatings include all shelf goods
and stock type coatings that are formulated for
normal environmental conditions and general
applications on new and existing structures.
These coatings include interior and exterior
house paints and stains, as well as
undercoaters, sealers and primers.
* Product coatings are paints sold to and used
by original equipment manufacturers (OEM).
Paint consumers in this sector include produc-
ers of wood furniture and fixtures, metal
containers, automobiles, machinery, metal
furniture, metal coil, appliances and other
consumer goods.
* Special purpose coatings are used in automo-
bile and machinery refinishing, high-perfor-
mance maintenance, bridge maintenance,
traffic paint, aerqsol applications and other
similar operations (TURIb, p. 1).
Coatings Sales
In 1995, sales by paints and coatings manu-
facturers were $15.9 billion. Architectural
coatings accounted for 38% of total surface
coating shipments, product coatings for 33%,
and special purpose coatings for 19%.
Miscellaneous paint products made up 9% of
the sales (NPCA). Most of the architectural
coatings sold are water-based (73%), while
the overriding majority of product and special
purpose coatings were still conventional
solvent-borne systems (TURIb, p. 1).
The intent of this manual is to provide information
on polludon prevention opportunities for users of
product coatings. Because product coatings are
used by a wide variety of industries, it is difficult
to accurately quantify these users. In addition, the
use of product coatings occurs not only in OEM
settings, but.also in contract job shops. The
pollution prevention opportunities identified in this
manual are not industry specific, but rather they
include general options available to a variety of
firms that coat metal substrates. Therefore, many
of the P2 opportunities identified in this manual
can be applied to users of architectural and
special-purpose coatings as well.
Paint Composition
The major components of solvent-borne paints
and coatings are solvents, binders, pigments, and
additives. In paint, the combination of the binder
and solvent is referred to as the paint "vehicle."
Pigment and additives are dispersed within the
vehicle (IHWRIC, p. 2). The amount of each
constituent varies with the particular paint, but
solvents traditionally make up about 60% of the
total formulation. Typical solvents include toluene,
xylene, MEK, and MIBK. Binders account for
30%, pigments for 7 to 8%, and additives for 2 to
3% (KSBEAP, p. 4). Environmental issues
surrounding paints usually center around solvents
and heavy metals used in the pigments. Binders
and other additives can also affect the toxicity of
the paint depending on the specific characteristics
of the paint. For more information on paint
composition, refer to chapter 6.
Description of
Coatings Processes
The coating of metal substrates can be broken up
into three major steps: surface preparation,.a two-
step paint application/curing process and equip-
ment cleaning. These steps are presented in figure
1. -, '
Surface Preparation
Although each of these steps can affect the
performance of the final finish, proper surface
preparation is essential.in ensuring the success of a
particular coating. In fact, as high as 80% or more
of all coating adhesion failures can.be directly
attributed to improper surface preparation
(Binksbj-p. 1).
In surface preparation, a variety of methods are
used to remove soils or other imperfections from
substrates, creating a surface that bonds well with
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Chapter 1 Background
Figure 1. Overview of the Coating, Process
Cleaning/
Surface
Preparation
fc
Application:
Spray or Dip
. .
Curing:
Air dry or
Oven
Stripping:
Racks-or
Rejects
Inspection:
the coating. The most common form of debris are
oils and/or greases that originate from mechanical
processing or oils and greases that are deliberately
applied for temporary storage or shipping (Kuhn,
p. 25). Other contaminants commonly include
oxidation, rust, corrosion, heat scale, tarnish, and
smut (SME, p. 27-1). In some cases, old paint
must also be removed prior to the application of a
new paint coat (MnTAP, p. 2). Traditionally,
halogenated solvents have been used as cleaning
and stripping agents to remove these substances.
As part of surface preparation, a conversion
coating might be applied to improve adhesion,
corrosion resistance, and thermal compatibility.
The processes used most often for the application
of conversion coatings on metal are phosphating
(using iron or zinc) and chromating. Anodizing
(i.e.,.the electrochemical deposition of an oxide
coating) is sometimes used on aluminum surfaces
(KSBEAP,p.2-3). '.''
In the phosphating process, acid attacks the metal
surface, forming a microcrystalline layer that
improves the surface for paint application.-Zinc
phosphate coatings are predominately used for
' metal substrates (Doren et al., p. 131). Combining
cleaning and phosphating in a single solution is -
possible; however this is not the case with zinc
phosphating (KSBEAP, p. 2-3). For more infor-
mation on conversion coatings consult, Pollution
Prevention for Metal Finishing: A Manual'for
Pollution Prevention Technical Assistance
Providers, published by the Northeast Waste
Management Officials'Association.
Coatings Application
Following surface preparation, paints and coatings
are applied to substrates using.a variety of meth-
ods, including:
* Dip coating] in which parts are dipped into
tanks of paint and the excess paint is allowed
to drain off; ,
« Roller^ in which paint is rolled onto a flat part;
.-* Curtain coating, flow coating;
* Electrodeposition, in which a part.is coated by
making it anodic or cathodic in a bath that is
generally an aqueous emulsion of the coating;
' and
* Various spray processes, in which paint is
sprayed from a gun onto a part.
Coatings are usually applied in a number of coats,
starting with a prime coat followed by subsequent
coats (basecoats and topcoats) and a finishing coat
(clearcoats). Given the different types of coatings
necessary to ensure adequate protection and
performance, coatings should always be consid-
ered as a system.
Curing
Once a paint has been applied, a curing process
takes place that converts the coating into a hard,
tough, and adherent film-. Coatings cure by
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Chapter 1: Background
chemical reaction or polymerization of the resins
(i.e., crosslinking). Mechanisms for initiating
curing generally include ambient temperature
oxidation, chemical reaction with another compo-
nent (two-component coating systems) or baking
in an oven. Radiation is an additional curing
mechanism (IHWRIC, p. 11).
Equipment Cleaning
The final stage of any coating operation is the
cleaning of equipment, such as spray guns and
hoses. This generally involves flushing solvent
through the coating system (Freeman, p. 483- .
484).
Examples of Typical
Systems
Although the basic process remains the same, the
particular coating system, coating formulation and
application method used, can vary considerably
from industry to industry. In the automotive
industry, for example, approximately 80% of all
painting starts with an electrocoat primer, usually
applied by electrodeposition. Visible indoor areas
of automobile bodies receive a topcoat, usually of
the same color as the overall body topcoat. In
addition, the underside of the hood and inside of
the engine compartment usually receive a topcoat
of black alkyd or acrylic paint which is sprayed
on; therefore, they carry a two-coat system.
Outside surfaces of the body receive a sandable
surface coat, which is either fully or partially
sprayed and is applied on either the wet or
incompletely baked electrocoat. Next, the color
topcoat, usually an acrylic resin, is sprayed on and
baked. In many cases, a clearcoat is sprayed over
the color coat to provide "depth" (SME, p. 29-4-
6).
The appliance industry, however, uses high-solids
paints to spray coat surfaces. These paints are
hardened with a crosslinking agent called
melamine. Some assembled appliance cabinets .
receive a 7-stage zinc phosphate metal preparation
and are then prime coated inside and out by
electrodeposition. The cabinets can also be spray
primed with a thermosetting epoxy-resin-based
paint, followed by a topcoat of acrylic melamine
paint, which is sprayed on. Other appliances carry
a powder coat, which is sprayed directly over the
metal preparation, plus a decorative acrylic
melamine coat (SME, p. 29-4-6).
Steel furniture for indoor use generally receives a
3- to 5-stage iron phosphate metal preparation,
plus a dip, spray, or electrodeposited prime coat.
The topcoat is usually an alkyd or acrylic. Steel
outdoor furniture and steel doors usually receive a
7- or 9-stage zinc phosphate treatment, plus a
prime coat of epoxy-based spray paint or an
electrocoat. The topcoats may be alkyds or
. polyesters, and are sometimes modified with
silicone. In some cases, powder coats are applied
over the iron phosphate preparation (SME, p. 29-
7).
Sources of Wastes
Traditionally, each step in the coating process
generates waste and emissions. Figure 2 presents a
process flow diagram that outlines the sources and
types of pollutants. Wastes occur in solid, liquid,
and gaseous forms and can include the following:
4 Scrubber water, paint sludge and filters from
air pollution control equipment
* Spent solvents, aqueous cleaners, wastewater
and paint sludge from equipment cleaning
* Aqueous waste and spent solvents from
surface pretreatment
+ VOC emissions during paint application,
curing and drying , '
* Empty raw material containers
* Obsolete or unwanted paint (IHWRIC, p. 38)
Inefficient paint transfer can be the largest source
of waste and VOC emissions from paint and
coating processes. Paint used but not applied to
the surface being coated (e.g.,-paint overspray)
generally becomes waste. A spray booth can be
used to remove the overspray .as it is generated
(IHWRIC, p. 38). However, the type of booth
selected can also affect the volume and type of
paint waste generated (MnTAP, p. 4). See chapter
4 for more information on spray booths and their
effect on waste generation.
Evaporation of organic solvents is an important
source of air emissions. During coating applica-
tion, solvents that are present in conventional
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, .". Chapter 1: Background
Figure 2. Coating Process and Waste Generation (IHWRIC, p. 34)
Inputs Processes Wastes
Abrasives
Solvents
Alkaline solutions
Water
Paints
Thinners
Brushes
Rollers
Rags
Solvents
Alkaline Solutions
Raw Material Inventory
I
Surface Preparation
Paint Application
Equipment Cleaning
Spills
VOCs .
Obsolete or leftover paint
Ground abrasive (e.g., sand.)
mixed with metal fines.
Spent solvents
Alkaline solutions
Wastewater .
Sludge with metals
VOCs
Containers
Paint scraps
Paint sludge
.Scrubber water
Filters
Rags, brushes, and rollers
VOCs
Containers
Wastewater
Spent solvents
Paint sludge
Alkaline solutions
VOCs
Containers
paint formulations evaporate and release VOCs
into the air (IHWRIC, p. 38). Emissions occur
during initial coating, as well as each time a
surface is recbated during the life of the object or
structure (EPAk). In addition, solvents used to
thin paint, to clean equipment, 'and to prepare
surfaces for coating can be sources of VOCs
(IHWRIC, p. 38)..
Specific estimates of the amount of solvents
released during coating application are difficult to
make as use is spread across numerous industry
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Chapter 1: Background
groups. However, EPA has developed air emission
factors for solvent losses from paint and coating
applications. EPA estimates that all toluene and
87% of the xylene isomers used in paints and
cpatings are emitted to the atmosphere when the
emissions are uncontrolled. No emission factors-
are available for MEK and MIBK used in paints
and coatings, but it can be assumed that, like
toluene and xylene, virtually all these solvents are
eventually released to the atmosphere (EPA, p.
157-158).
Cleaning of equipment is a third major source of
waste generation. Generally, all paint-application
equipment must be cleaned after each use to
prevent dry paint residue and avoid contaminating
batch processes. In addition, brushes and rollers
must be cleaned after each use to remain pliable
(IHWRIC, p.. 38).
Summary
The primary focus of this manual is on P2
methods for reducing pollutants generated during
coatings application and on reducing emissions of
VOCs in particular. VOCs can pose risks to
human health and the environment. These prob-.
lems have prompted the federal government and a
number of states to promulgate regulations to
control releases of solvent emissions and wastes
from paint and coating processes. For an overview
of applicable regulations, see chapter 2.
' Pollution prevention is an effective method for
reducing emissions of VOCs and other wastes,
and therefore, for reducing a firm's regulatory
compliance burden. General information on
promoting pollution prevention can be found in
chapter 3. An overview of specific P2 options for
coatings processes is discussed in chapter 4, with,
detailed technical information provided in chapters
5-9. See table 7 at the end of chapter 4 for a
complete list of P2 options.
-------
Regulatory Overview
The use of solvents in coating formulations and '.,
in other areas of the coating process poses a
number of risks, to human health and the environ-
ment. To reduce the risks resulting from exposure
to these substances, the federal government and
individual states have regulated the generation and
management of wastes from paint and coating,
operations. Applicable regulations dependon the
environmental medium to which the waste is
released (e.g., air, land, or water) and the regula-
tory status of the generator (IHWRIC, p. 10).
A discussion of individual state laws is beyond the
scope of this document. However, this chapter
provides an overview of the major federal statutes
'that affect coating processes, including the Clean
Air Act (CAA) and the Clean Air Act Amend-
ments of 1990 (CAAA), which regulate air
releases; the Resource and Conservation Recov^
eiy Act (RCRA), which regulates hazardous
wastes; and the Clean Water Act (CWA), which
regulates wastewaters. For an overview of the
regulatory status under the CAAA and RCRA for
particular solvents used in paint and coating
operations, see table 1 .Technical assistance
Table 1. Common Solvents, Federal Regulatory Status (IHWRIC, p. 5)
Solvent
Aliphatic Hydrocarbons
Mineral Spirits ,
Aromatic Hydrocarbons
Toluene , '
Xylene
Esters
Ethyl Acetate .
Butyl Acetate
Ketones
Acetone
Methyl Isobutyl Ketone
Methyl Ethyl Ketone
Glycol Ethers
Monoethyl Ether
Alcohols
Ethyl Alcohol
Butyl Alcohol --
RCRA Hazardous
- ,Yes . .
Yes
Yes
Yes
. Yes
Yes
Yes
Yes
-No
Yes
, Yes
Air Toxics Program a
- m Maybe b .
Yes
Yes ;
No
No ,
N6C '.'....
Yes
Yes . , '
. . No '
- No
No
0 Under the 1990 Clean Air Act Amendments. . '
b Depends on the composition of the mineral spirits; some cheaper blends may contain'aromatic
solvents such as benzene. . . -. .
; c Acetone has recently been delisted from the GAAA's Title III list of VOCs. However, technical
assistance providers should not promote the use of acetone to achieve environmental compliance.
Material substitution using acetone does not constitute a pollution prevention option.
-------
Chapter 2: Regulatory Overview
providers should check with their state regulatory
programs to see if their state has imposed require-
ments stricter than those developed under the
federal programs. Coating operations might also
be affected by a number of other federal and state
regulations. Many of these regulations are industry
specific rather than process specific.
Clean Air Act
The Clean Air Act and the Clean Air Act Amend-
ments of 1990 consist of 11 chapters or titles that
require EPA to establish national standards for
ambient air quality and to work with states to
implement, maintain, and enforce these standards.
Of these titles, none have attracted more attention
from industry than the Title IH air toxics program,
which brought many previously unregulated
companies and processes under legislative control
(Freeman, p. 34).,
Under Title III, EPA created a list of 189 hazard-
ous air pollutants (HAPs) of which 149 also are
VOCs. Surface coating operations of all kinds are
major users of these compounds. Commonly used
compounds include toluene, xylene, MEK and
MIBK. VOCs not regulated under the air toxics
program might be regulated under Title I provi-
sions for ozone non-attainment areas (Falcone, p.
35). Details of these titles are provided below.
Air Releases from Coatings Processes
* VOCs, which contribute to ozone pollution
* Heavy metal dust from pigments
* Atomized paint from spray applications
(IHWRIC, p. 10)
Air Toxics
Under Title HI, facilities that emit HAPs are
grouped into categories with similar operating
processes, including the process of surface
coating. Individual sources within a category are
considered "major" if they emit or have the
"potential to emit" 10 or more tons per year- of
any HAP on the list or 25 or more tons per year'
of a combination of HAPs. EPA defines "potential
to emit" as the amount of emissions that a facility
could release if it operated at maximum capacity
24 hours per day, 365 days per year.
Under Title III, major sources are subject to
maximum achievable control technology (MACT)
standards. MACT standards specify the maximum
degree of reduction in the emission of HAPs that
must he met through the use of traditional control
technologies as well as through pollution preven-
tion techniques. EPA has listed 16 surface coating
processes as source categories subject to MACT
standards, although not all of these surface coating
processes apply to the coating of metal substrates.
MACT standards are to be promulgated according
to the schedule in table 2. Existing sources gener-
ally will have up to 3 years from the effective date
of the standards to comply.
Ozone
Under Title I, EPA established national ambient air
quality standards (NAAQS) to limit levels of
"criteria pollutants," including carbon monoxide,
lead, nitrogen dioxide, particulate matter, ozone,
and sulfur dioxide. The federal government has.
developed control technique guidelines (CTGs)
which deal with a number of sources of air
pollution in nonattainment areas (i.e., geographic
areas that did not meet the NAAQS). These
guidelines require the use of reasonably available
control technologies (RACT).
For surface coating sources, the federal CTGs
generally define RACT in terms of the VOC
content limits of a coating; that is RACT is the
mass of VOC per unit volume of coating (minus
water) as applied (ready for application). In some
cases, however, RACT is defined in terms of the
percentage emission reduction achieved with add-
on control devices, equipment specifications,
record keeping, reporting requirements, and
exemption levels (EPAf, p. 2-1). While limits are -
based on specific industry groups and applications,
the VOC limit of 340 g/1 (2.81b/gal) can be consid-
ered an unofficial national standard (Freeman, p.
486). For more specific information on EPA
guidelines for VOCs in coatings, see table 3.
Other Requirements.
Under Title V, the permitting provision of the
CAAA, all major sources must apply for operating
permits. Accurate information on source pollutants
and emission quantities must be gathered before
application submittal (Falcone, p. 35). Information
about calculating VOC and HAP emissions from
8
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Chapter 2: Regulatory.Overview
Table 2. Scheduled Date for MAC! Standards for Surface Coating (EPAm, p. 1 -5)
Source Categories
Scheduled Date for
Emissions Standards
Aerospace Industries . "
Auto and Light Duty Truck (Surface Coating)
Flat Wood Paneling (Surface Coating)
Large Appliances (Surface'Coating)
Magnetic Tapes (Surface Coating)
Manufacture of Paints, Coatings,
and Adhesives
10/8/96 .', .
11/15/00- ,
11/15/00
11/15/00 ;
11/15/94 (final rule issued 12/15/96;
compliance 2 or 3 years) >
11/15/00 ,
Metal Can (Surface Coating) .
Metal Coil. (Surface Coating)
Metal Furniture (Surface Coating)
Miscellaneous Metal Parts and Products
(Surface Coating)
Paper-and Other Webs (Surface Coating)
11/15/00
11/15/00
11/15/00
11/15/00
11/15/00
Plastic Parts and Products (Surface Coating) .
Printing, Coating, and Dyeing -of Fabrics
Printing/Publishing (Surface Coating)
Shipbuilding and Ship Repair (Surface Coating
Wood Furniture (Surface Coating)
11/T5/00 ' ' :
11/15/00. v
11/15/94 (final rule 5/30/96;
compliance 3 years)
11 /15/94 (final rule issued 12/15/95;
compliance 1 year)
9/7/95 (final rule issued 2/9/96;
compliance 11/21/97)
NOTE: Work is beginning on the development of the 2000 regulations. Meetings were held in April of
1 997 and workgroups are organizing to further develop the regulations..
coatings processes can be found in appendix B.
State and local governments oversee, manage, and
enforce much of the permitting program and many
of the other requirements of the CAAA. For more
information pertaining to the CAA, see 40 CFR
'Parts 50-99. ' ' .' .
Resource
Conservation and
Recovery Act
Under the Resource Conservation and Recovery
Act Subtitle C, EPA has established a "cradle-to-
grave" system governing hazardous waste. Most .
RCRA requirements are not industry specific but
apply to any company that transports, treats,
stores, or disposes of hazardous waste. Wastes
generated during the application of paints and
coatings might be considered hazardous because
of the presence of solvents or toxic metals ,
(IHWRIC,p. iO). .
RCRA Wastes from Coating Processes
* Organic solvents commonly used in paint
formulations ,
* Waste paint containing heavy metals
* Materials used fprsurface preparation and-
equipment cleaning (IHWRIC, p.: 12)
Waste Characterization
A waste is considered hazardous if it is included
on one of the four EPA lists of hazardous wastes;
if it displays one or more of the characteristics of
-------
Chapter 2: Regulatory Overview
Table 3. EPA Guidelines for Maximum VOC Content of Coatings (SWR, p. 46)
Process ;
Can Coating
* Sheet basecoat and overvarnish; iwo-piece can exterior
VTwo-, three-piece can interior body spray; two-piece
can exterior end
+Side-seam seal
+End sealing compound
Coil Coating
Fabric Coating
Vinyl
Paper
Aut.o and Light-Duty Truck
+Prime
^Topcoat
^Repair
Metal Furniture
Magnet Wire
Large Appliance
Miscellaneous Metal Parts
Wood Paneling
^Printed interior
^Natural- finish hardwood'
*Class II hardwood
Limitation
(pounds per gallon)
2.0;' 2.8
3.6; 4.2
5.5
3.7
2.6
2.9
3.8
2.9 .
1.9
2.8
. ' 3.0
.3.0
1.7
2.8
0.4-4.4
1.7
3.2
2.7
hazardous waste (ignitability, corrosivity, reactivity
or toxicity); or if it is a mixture that contains a
listed hazardous waste.
* Listed wastes include acutely hazardous
commercial chemical products and toxic
commercial chemical products, designated
with the code "P" or "U," respectively; hazard-
o.us wastes from specific industries/sources,
designated with the code "K"; or hazardous
wastes from nonspecific sources, designated
with the code "F".
F wastes are of particular interest to paint and
coating operations because they are generic
wastes commonly produced during coating
application. Examples from this list include
spent solvents used in cleaning and used paint
thinners such as xylene and toluene (IVVRCb, p.
15).
^Characteristic wastes include those that are
ignitable, corrosive, reactive or toxic. Ignitable
wastes have a flashpoint of less than 140°F
and are easily combustible or flammable.
'Corrosive wastes have a pH of 2 or less, or of
12.5 or greater and can dissolve metals or
other materials. Reactive wastes are unstable,
or undergo rapid or violent chemical reaction
with water or other materials. Toxic wastes
contain concentrations of heavy metals, certain
solvents, or pesticides rn excess of correspond-
10
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Chapter 2: Regulatory Overview
ing regulatory parameters-determined by the
Toxicity Characteristic Leaching Procedure
(TCLP). Characteristic wastes are designated
with the ERA hazardous waste code "D," See ;
table 4 for more information on hazardous ,
wastes generated from coatings operations.
Generator Status
To determine what a facility must do to. comply
with RCRA requirements, the facility must first
determine its generator status. Generator status is
based on the amojunt of waste generated on a
monthly basis. The following criteria determine
the quantity of waste that is regulated by RCRA:
1) material remaining in a production process is
not counted as waste, until it is no longer being
used in that process.
2) waste discharged directly and legally to a
POTW in compliance with CWA pretreatment
standards is riot counted toward RCRA generation
total. '-.,'_.
3) any material that is characteristic or listed as a
hazardous waste, and is accumulating after
its removal from the process before being sent off
site for treatment, storage, or disposal, is counted
toward RCRA Subtitle C generation total-
Facilities that generate hazardous waste are
subject to certain waste accumulation, manifest-
ing, and record keeping standards based on the
amount of waste generated. RCRA specifies three
categories of waste generators. The following
outlines the basic guidelines for generator status;
be aware, however, that state guidelines may vary.
+ Conditionally exempt small quantity generators
(CESQGs) generate less than 220 pounds of
hazardous waste, or 2.2 pounds of acute
. hazardous waste (K wastes), per calendar
.month. CESQGs cannot accumulate more
than 2,200 pounds of nonacute hazardous
waste.(or 1-kilogram, of acute hazardous
waste). ' .
f Small quantity generators (SQGs) generate
220 to 2,200 p9unds of hazardous waste per
calendar month. SQGs cannot accumulate
more than 13,200 pounds. Storage time is
restricted to 180 days.' . -
* Large quantity generators (LQGs) generate
more than 2,200 pounds of hazardous waste
per calendar month. Storage time is restricted
to 90 days. ' ,
Each state has varying degrees of regulation for ,
the three generator classes. At a minimum,
however, EPA requires each class to comply with
the following requirements: ,
Large Quantity Generators
+ Notify the US EPA or state and obtain an EPA
ID number from the state regulatory agency
+ Store waste for no more than 90 days
'* Comply with container standards and tank
rules .
+ Prepare and retain a written contingency plan
* Prepare and retain a written training plan
which includes information on the annual
training of employees
+ Prepare a written waste minimization plan
* Dispose of hazardous materials only at a
RCRA permitted site
* Only use transporters with EPA ID numbers
* Use proper Department of Transportation
(DOT) packaging and labeling
«> Use the full Uniform Hazardous Waste Mani-
fest _..';, -
*Placea 24-hour emergency number on-all
manifests ;
* Report serious spills or fires to the National
Response Center , '
* Obtain a DOT registration number for ship- .
rrients over 5,000 pounds
* Keep ail records for 3 years :
* Make' sure that any treatment or recycling done
onsite is permitted . '
> Report missing shipments in writing
* Submit biennial reports of hazardous waste
activities, including waste minimization .
Small Quantity Generators
V Notify the US EPA or state and obtain an EPA
ID number from the state regulatory agency
* Store waste for no more than 1 80 days (270
days if the waste is shipped more than 200
miles) . " ..
11
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Chapter 2: Regulatory Overview
* Comply with container standards and tank
rules
* Dispose of hazardous materials only at a
RCRA permitted site
* Only use transporters with EPA ID numbers
* Use proper Department of Transportation
' (DOT) packaging and labeling
+ Use the full Uniform Hazardous Waste Mani- '
fest
* Place a 24-hour emergency number on all
manifests
* Post emergency response telephone numbers
near telephones
* Provide informql employee training
* Make sure that any treatment or recycling done
onsite is permitted
« Report missing shipments in writing
* Keep all records for 3 years
Conditionally Exempt Small Quantity
Generators
i
* Avoid accumulating more than 1,000 kilo-
grams (2,200 pounds) of hazardous waste
onsite at any one time
* Send waste to a facility that is at least ap-
proved to manage municipal.or industrial solid
waste
Toxics Release Inventory
Reporting
Some coating facilities may have to publicly report
many of the chemicals they use under the federal
Toxic Release Inventory (TRI) reporting require-
ment. Facilities report information on a TRI data
form (Form R) for each toxic chemical that is
used over the threshold amount. Basic information
that is reported in a Form R includes the follow-
.ing: . .
4- Facility identification
« Parent company information
« Certification by corporate official
* ' SIC code
4 Chemical activity and use information
* Chemical release and transfers
* Off-site transfer information
+ On-site waste treatment
* Source reduction and recycling activities
The releases and transfers, reported on a Form R
include the following:
* Emissions of gases or particulars to the air
* Wastewater discharges into rivers, streams,
and other bodies of water
* Releases to land onsite including landfill,
surface impoundment, land treatment, or other
mode of land disposal
* Disposal of wastes in underground injection
wells
* Transfers of wastewater to POTWs
* Transfers of wastes to other offrsite facilities for
treatment, storage, and disposal
A facility must fill out Form R if it meets the
following criteria:
* The facility is included in SIC codes 20 to 39
* The facility has 10 or more full-time employees
* The facility manufactures, processes, or
"otherwise uses" any listed material in quanti-
ties equal to or greater than the established
threshold for the calendar year
The manufacturing and processing thresholds
have dropped over the reporting years from
75,000 pounds in 1987 to 25,000 pounds in 1989.
For a chemical "otherwise used," the threshold
amount is 10,000 pounds. Technical assistance
providers can use TRI data to develop an aggre-
gate picture of the releases and transfers from a
facility.
Clean Water Act
The primary objective of the Federal Water
Pollution Control Act, cprnmonly referred to as
.the Clean Water Act (CWA), is to restore and
maintain the chemical, physical and biological
integrity of the nation's surface waters. Pollutants
regulated under the C WA are classified as "prior-
ity" pollutants. These include various toxic
pollutants; "conventional" pollutants, such as
biochemical oxygen demand (BOD), total sus-
pended solids (TSS), fecal chloroform, oil and
grease, and pH; and "non-conventional" pollut-
ants, including any pollutant not identified as
either conventional or priority.
National Pollutant Discharge
Elimination System (NPDES)
Under the CWA, most point sources of wastewa-
ter (e.g., discharge pipes or sewers) discharging to
waterways require a National Pollutant Discharge
Elimination System permit. Permits, issued by
12
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Chapter 2: Regulatory Overview
Table 4. Hazardous Wastes Generated from Coatings Operations (EPAb,
p. 96-97)
EPA Hazardous
Waste Number
Hazardous Waste
D006 (cadmium)
D007 (chromium)
D008 (lead)
D009 (mercury)
Wastes that are hazardous due to. the characteristic of toxicity for each of the
constituents. »
FOOl
Hafogenatedso/vents used in degreasing: tetrachloroethylene, methylene
chloride, 1,1,1 -trichloroethdne, carbon tetrachloride, and chlorinated
fluorocarbons; all spent solvent mixtures/blends used in degreasing con-
taining, before use, a total of 1 0 percent or more (by volume) of one or
more of the above, halogenated solvents or those solvents listed in F002,
F004, and F005; and still bottoms.from the recovery of these spent
solvents and spent solvent mixtures.
F002
Spent halogenated solvents: tetrachloroethylene, methylene chloride, frichlo-
roethylene, 1,1,1 -trichloroethane chlorobenzene, 1,1,,2-trichlorp-l ,2,2-
trifluoroethane, ortho-dichlorobenzene, trichlorofluoromethane, and 1,1,2-
trichloroethane; alUpent solvent mixtures/blends containing, before use, one
or more of'the above halogenated solvents or those listed in FOOl, F004 ,
F005; and still bottoms from the recovery of these spent solvents and spent
solvent mixtures. , .
F003
Spent nonha/ogenafed solvents: xylehe, acetone, ethyl acetate, ethyl ben-
zene/ethyl ether, .methyl isobutyl ketone, n-butyl alcohol, cyclohexanone, and
methanol; all spent solvent mixtures/blends containing, before use, only the
above spent nonhalogenated solvents; and all spent solvent mixtures/blends
containing, before use, one or more of the above nonhalogenated-solvents,
and a total of 10 percent or more (by\ volume) of one of those solvents listed
in FOOl, F002, F004, and F005; and still bottoms from the recovery of these
spent solvents and spent solvent mixtures. .
F004
Spenf ndnha/ogenafed solvents: cresols and cresylic acid, and nitrobenzene;
all spent solvent mixtures/blends containing, before use/a total of 10 ' .
percent or more (by volume) of one or more of the above nonhalogenated
solvents or those solvents listed in .FOOl, F002, and F005; and still bottoms
from the recovery of these spent solvents and spent solvent mixtures. - )
F005
Spenf npnha/ogenafed so/vents: toluene, methyl ethyl ketone, carbon disul-
fide, iso'butanol, pyridine, benzene, 2-ethoxyethanol, and 2-nitropropane; a
spent solvent r.iixtures/blends containing,.before use, a total of 10 percent o
more (by volume) of one or more of the above non-haldgenated solvents o
those solvents listed in FOOl, F002, or F004; and still bottoms from the
recovery of these spent solvents and spent solvent mixtures.
13
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Chapter 2: Regulatory Overview
Wastewaters from Coatings Processes
* Wastewaters from equipment cleaning and
surface preparation
* Rinsing of a surface after paint removal
(IHWRIC, p. 1.1)
either EPA or an authorized state (EPA has.
presently authorized 40 states to administer the
NPDES program), specify levels of toxicity and
other characteristics that must be achieved prior to
discharge. Pretreatment of the wastewatef is
generally necessary. Wastewater generated-from
coating application might be regulated because of
the presence of organic solvents or heavy metals
(IHWRIC, p. 11).
Pretreatment Program
Another type of discharge that is regulated by the
CWA is one that goes to a publicly-owned treat-
ment works (POTWs). The, national pretreatment
program controls the indirect discharge of pollut-
ants to POTWs by industrial users. Facilities
regulated under this program must meet certain
pretreatment standards. The goal of the pretreat-
ment program is (1) to protect municipal wastewa-
ter treatment plants from damage that can occur
when hazardous, toxic, or other wastes are
discharged into a sewer system and (2) to protect
the quality of sludge generated by these plants.
For more information about the CWA, see 40
CFR Part 433.
14
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Planning Pollution Prevention
Programs at Coating Facilities
How can assistance providers and regulatory
compliance staff sell pollution prevention
options to a facility? The most important point
that an assistance provider can make is that
pollution prevention can help the facility achieve
regulatory compliance while saving money. The
savjrigs associated with recapturing and reclaiming
materials is obvious; but the value of reducing the
regulatory burden and the expense from wasted
raw materials, can, in many cases, exceed the cost
of pollution prevention projects. Overall, the
benefits associated with pollution prevention
include: 7
"* Reduced Operating Costs/Overhead
. These savings can. result in reduced utility
charges, water/sewer fees, wastewater treat-
ment costs, wasfe disposal expenses, permit
discharge fees, analytical monitoring,-and
reporting costs.
« Reduced Manufacturing,Costs ; ,
Facilities can save money on reduced material
costs (paint and solvent purchases), water -'
costs, and energy costs.
V Product Quality Improvements
Pollution prevention techniques often increase
the'quality of the coating process. Improving
process controls makes coating operations
more efficient and allows the;m to run within
tighter operating parameters, often resulting in
decreased reject rates. ,
, * Environmental Risk Reduction
Pollution prevention projects can result in
reduced noncompliance enforcement actions;
reduced environmental and worker health
liability; and reduced risk of on-site contami-
. nation via spills, releases, and leaks.
Potentially, a facility can realize other benefits
from the implementation of a comprehensive
pollution.preventioh program. 'Source reduction
can lower insurance costs, protect property
values, and improve relationships with financial
institutions. Even though pollution prevention has
clear economic advantages and the techniques can
be simple, inexpensive, and time proven, many.
facilities still do not have significant source
reductionprograms (Haveman, 1995).
This chapter provides information on how to
conduct an assessment of a facility that has a
coating process. It provides information on a
general facility assessment as well as specific
information on assessing the coating process.
Technical assistance providers should be aware .
that while a facility may have one process or .
chemical that is of major concern, assessing the
entire facility is critical. In this way they can
identify processes that are impacting the coating
process and that might be increasing pollution
generation. >
Characterizing a
Facility
Numerous factors can influence whether a facility
adopts and implements pollution prevention
techniques. Understanding what,motivates a ,.
facility can help a technical assistance provider
develop a message for the facility that will influ-
ence their decision to implement pollution preven-
tion. The following list divides firms into
"categories and describes some characteristics of.
firms and their motivating factors:
> Environmentally proactive firms that
actively pursue and invest in strategic
"environmental management projects:
Most often these firms are incompliance with
environmental regulations. They actively
pursue and invest capital in continuous im-
' provement projects that go beyond compli-
ance in order to maintain their places as
environmental leaders in their sector. These
firms are often driven by public recognition,
' and pride in industry performance. They
15
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Chapter 3: Planning Pollution Prevention Programs at Coating Facilities
understand the economic payoffs of strategic
environmental investments and believe that
flexibility in compliance would promote inno-
vative approaches and increase their willing-
ness to help other firms.
* Firms that are in compliance but do not
or cannot seek opportunities to improve
environmental performance because they
.lack the necessary resources: Regulatory
compliance is what drives this potentially large
middle tier. Barriers to proactive performance
include a lack of capital and information, and
a lack of positive reinforcement.
The barriers that generally apply to some or all of
these facilities are:
* Regulatory compliance and/or enforcement
actions: Many shops lack the personnel and
capital resources to move beyond compliance.
Liability may be a barrier to obtaining loans
for capital improvements. Existing liability can
overwhelm their ability to pay for remediation
or new, cleaner technologies.
* Development of safer products: In.some
cases, suppliers might be reluctant to suggest
environmentally proactive processes or prod-
uct changes becpuse these could result in
lower product sales.
» Uncertainty about future regulatory activity:
inconsistency in existing regulatory require-
ments and enforcement actions at the federal,
state, and local level creates uncertainty and,
at worst, competitive imbalances throughout
the industry. This climate generates distrust of
EPA and state programs and can inhibit
meaningful communication.
* Lack of awareness of changes in product/
process technology: Facilities .may hot have
the time or resources to research new tech-
nologies and the benefits these technologies
could provide them (Haveman, 1995). In
some cases, facilities may be aware of the new
technologies but are unwilling to implement
them because they cannot field test the new .
systems at their facility.
Planning
The key to developing a successful pollution
prevention program is planning. Assistance
providers can work with facilities to implement
planning programs, assist in establishing baseline
measures, and identify potential pollution preven-
tion projects. The key steps to starting a pollution
prevention program include: -
* Obtaining management support and involve-
ment
+ Establishing an in-house pollution prevention
team
* Attracting company wide involvement
The following pages outline an ideal planning
process. Often, there are issues and limitations
that inhibit a company's ability to carry out all of
the outlined activities. Therefore, this process
should be viewed as a flexible model.
Management Support
The support of company management is essential.
for developing a lasting and successful pollution
prevention program. The level of success that a
facility can achieve in reducing waste generation
appears to depend more on management interest
and commitment than on technical and economic
feasibility, particularly for source reduction
technologies that require process modifications or
housekeeping improvements. In some states, the
technical assistance programs will not work with a
facility until top management has shown that it is
willing to support a long-term pollution prevention
program.
At the outset of the P2 planning program, man- .
agement endorsement is needed to help identify
the pollution prevention team and give credence to
the planning effort. Throughout the program,
company management can support the team by
endorsing goals and implementation efforts,
communicating the importance of pollution
prevention, and encouraging and rewarding ,
employee commitment and participation in the
effort (Dennison, p. 61)".
At some companies, technical assistance providers
may find that employees see only the barriers they
16
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Chapter 3: Planning Pollution Prevention Programs at Coating Facilities
face in implementing a project, which they use as
excuses to not implement pollution prevention. At
other firms, motivated'employees are empowered
to find solutions to overcome obstacles, and the
compari ies cart reap the benefits of successful
pollution prevention projects. Technical assistance
providers should stress to management that a
successful program has a wide range of benefits.
These benefits include cost savings, reduced
liability, and enhanced company image as de-
scribed earlier.
Assistance providers should inform management
that some initial labor costs will be incurred as a
result of organizing and implementing a pollution
prevention program'. Usually, however, companies
find this up-front investment is repaid several
times over. Case studies often highlight the
benefits that other companies have realized from
implementing such programs.
Technical assistance providers can help facilitate
management support by developing a plan that
sells pollution prevention to a company's execu-
tives. Successful management initiatives that have
promoted pollution prevention include: developing
a corporate policy that makes pollution prevention
a mandate; incorporating pollution prevention
success into performance evaluations; and offering
financial incentives for meeting pollution preven- ,
tion goals or for finding pollution prevention
opportunities.
Obviously, each firm is different. The assistance
provider's approach to each company's leadership
should attempt to address their specific interests
and priorities as manifested by the Corporate
culture. Identifying these interests and priorities is
a challenge for any assistance team. On these
visits the teams discuss their priorities and pollu-
tion prevention in relation to those priorities.
Technical assistance providers should also stress
to management that planning is an ongoing task.
Once the initial plan is completed, the facility
should continue to reevaluate their operations to
identify areas that can be improved (CAMF,
1995). .'''
Establishing the Team
A successful pollution prevention program re-
quires not only support from management, but
CASE STUDY: .
Using Employee Participation to
Reduce Hazardous Waste
The VALSPAR company in Beaumont, Texas,
is a paint manufacturer with 45 employees.
The company produces solvent-based y
coatings for maintenance and marine use. To
reduce hazardous waste, VALSPAR instituted
a program in which solvent used to clean
mixing,.tanks is recycled back into batch
production. VALSPAR's pollution prevention
program also found innovative ways to elicit
valuable employee participation. The pro-
gram included forming P2 teams composed
of union workers and offering a 2% bonus
for each waste reduction goal attained.
Within the first months of the program, the
team found a way to recycle 60 gallons of
additional spent solvent per week, leading to
a 20% reduction in annual waste generation.
Eventually, the program was able to recycle
95% of all solvent used in the clean-up ,
process. In addition, VALSPAR accepted and
reworked unused paint into new batches. In
1993, the company recycled 52,000 gallons
of solvent and reworked an additional
20,000 gallons of returned paint. These
efforts resulted in a reduction of approxk,
rndtely 250 tons of hazardous waste at a cos-
savings of $103,000, not including savings
from reduced purchases of raw material.
'. (PPIPTI)
also input and participation from all levels of the
organization. To champion the effort, every
pollution prevention program needs an effective
pollution prevention coordinator. Assistance
providers can help identify the team leader, work
with the leader on developing their team, and
suggest ways for the facility to implement its
pollution prevention program.
A team approach allows tasks to be distributed
among several employees and enables staff from
different parts of the company to have input into
the planning process. Members of the team are
typically responsible for:
* Working with upper management to set
preliminary and long-term goals ,
17
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Chapter 3: Planning Pollution Prevention Programs at Coating Facilities
in
+ Gathering and analyzing information relevant
to the design and implementation of the
program
* Promoting the program to employees and
educating them on how they can participate i
the effort
+ Monitoring and reporting to management on
the progress of the program (Dennison,Lp. 61)
The pollution prevention team should include
employees who are responsible for planning,
designing, implementing, and maintaining the
program. The ideal size of the team depends on
the size of the organization. In small companies,
the team-can consist of one person who wears
many hats, or the company manager and a
technical person. In larger companies, the team
might includeenvironmental managers, building
supervisors^ technical staff, maintenance staff,
marketing staff, purchasing staff, and other
interested employees (Dennison, p. 63).
External personnel, such as technical assistance
providers or consultants, can complement the
team by providing technical or managerial exper-
tise. Often these people can offer auditing exper-
tise as well as knowledge of pollution prevention,
and environmental laws and regulations. However,
external contributors will be unfamiliar with the
facility's operation. Once the team is established,
assistance providers and regulatory staff should
encourage the facility to take the following steps
to properly evaluate the options for reducing
pollution:
* Define and Identify the Facility's Objectives:
Clearly identify, quantify, and rank the facility's
objectives. For example, at some facilities
compliance with air quality standards is a
primary concern while optimized worker
efficiency and cost are secondary concerns.
* Define Criteria for Evaluating Pollution Preven-
tion Options: Clearly define what constitutes a
feasible option. Items to consider in addition to
technical feasibility include economic feasibility,
quality standards, and the effect of the option
on the overall process.
The following pages provide'an overview of the
typical steps involved in assessing a facility and
coatings processes in particular. These steps
include: .
* Characterizing the facility
+ Gathering baseline facility data
* Analyzing work-place practices
* Developing process flow diagrams
+ Identifying pollution prevention options
> Analyzing and selecting options for further
investigation
* Pilot testing preferred options ,
* Implementing the new system
* Evaluating and maintaining the pollution
prevention program
While the facility may have brought in a technical
assistance provider to suggest methods for a single
process or problem, the entire facility must be
evaluated because the coating process will be
affected by outside issues. Consider the case of a
facility that wants to change from solvent cleaning
to aqueous cleaning but has problems with
removing cutting fluids. The machining process
would need to be examined to see if the facility
could use alternative cutting fluids that are easily
removed using aqueous cleaning.
Assess the Facility
Once the team has defined its objectives and
criteria for a pollution prevention program, the
next step is to assess the facility. Beyond the
facility tour, useful information for the assessment
can be obtained from sources such as:
* Engineering interviews and records
+Accounting interviews and records
* Manifest documents
* Vendor data
* Regulatory documents
* Sampling data
Map the Facility
Locate or prepare drawings of the layout of the
process and storage areas. These drawings should
be to scale, showing the location of all relevant
equipment and tanks, and identifying:
* Floor space of the facility
" * Coating and other process lines
* Gutters, sumps, and sewer lines .
* Water lines, control valves, and flow regulators
* Ventilation/exhaust systems
18
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Chapter 3: Planning Pollution Prevention Programs at Coating Facilities
Gather Baseline Information
The first step in P2 assessments of coatings
processes is to collect as much information as .,.
possible about the coating process from company
personnel. Background information should
establish the sources and nature of wastes gener-
ated, and can include:
* Specific information about emissions (e.g.,
current releases, desire'd reductions) and other
wastes generated from coatings operations
(e.g., wastewaters and paint wastes)
* Details about the type of coating used and
application techniques
* Information about the types of parts to be
coated and performance specifications of the
finish --..-.
* Details about the surface preparatiorTand
equipment cleaning processes (e.g., equip-
ment and methods used) ;
Technical assistance providers should also review
all operations of the facility that relate to chemical,
energy, or water use. Some of the information that
technical assistance providers'should request
includes:. . /
* Estimates of production units, such as square
me'ters coated and number of parts that pass
through a line sequence, or production.rates
(i.e., square feet processed per hour)
* Material purchases
* Material inventory ..
* Material use rates (where each material is
used and how much is used in each process)
* Waste management costs
* Raw material costs ' ' ,
* Compliance problems
* Control processes
* .Sampling and analysis information
* Process line design and condition
^Actual operating procedures
* Operating parameters .
The information listed above should be used in
conjunction with the information obtained in the
walk-through of the facility to determine what
pollution prevention options are technically and
economically feasible. This information should
also provide the technical assistance provider with
information to determine which processes in a
facility need to be addressed to reduce pollution
generation.
Analyze Workplace Practices
A great deal of data should be accumulated so that
assistance providers can determine the best
pollution prevention approaches for a facility. The
first pieces of information gathered should be
material/resource use, general operating proce-
dures, and facility information. This information
usually can be gathered prior to a facility tour and
used to start a facility map that will be valuable
' during the site visit. Table 5 provides an overview
of the basic operational information that technical
assistance providers should obtain from the
company prior to the technical assistance visit.
Additional information is gathered during the
facility tour. When touring the coatings operations
at a facility, technical assistance providers should
observe or ask employees about workplace
operating practices. Often, employees can provide
valuable insight both into why waste is being"
generated and into some of the obstacles a plant
may face in implementing new projects or meth-
ods. The following lists present some of the
questions technical assistance providers might
wanttoask(KSBEAP,p.33): s
Personnel
4 Do employees view overs'pray as lost product?
* Are paint and solvent records maintained for
each spray gun operator?
> Are gun operators or paint crews rewarded for
high quality work using less paint?
+ Are there written guidelines' on how much paint
should be prepared and used'for frequent
jobs?
* Are employees provided with proper devices
to measure the correct anrfount of paint? .
. * Are operators given spray gun training?
* Is technique training routinely provided? r
+ Are performance monitors in place?'
Housekeeping/Maintenance
* Is spray equipment maintained according to
manufacturer or vendor instructions? -
* Are paint containers tightly closed when not in
use? . : .
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Chapter 3: Planning Pollution Prevention Programs at Coating Facilities
Table 5. Overview of Assessment Information (BCDNRP)
Process
Data
Production Processes
and Operational Procedures
* Production rates
+ Process description and efficiencies
* Condition of process equipment
* Sources or potential sources of leaks/spills
* Operating procedures
* Maintenance procedures and schedules
+ Energy/utility use and costs
* Operating and maintenance costs
Material Use, Handling,
and Storage
Paint and solvent use
Raw material accounting (how much of the materialis
is used in the process, how much is lost through evapo-
ration or other means, and how much enters the waste
stream) ' . .
Raw material costs
Material transfer and handling procedures
Storage procedures '
Sources of leaks or spills in transfer and storage areas
Waste Stream
+ Activities, processes, or input materials that generate
waste streams '
* Physical and chemical characteristics of each stream
* Hazardous classification of each waste stream
* Rates of generation of each waste stream and variability
in these rates
Waste Management
Current treatment and disposal system for each waste
stream
Cost of managing waste stream (e.g., fees, labor, and
disposal costs) .
Efficiency of waste treatment units
Quantity and characteristics of all treated wastes
Waste stream mixing (hazardous wastes mixed with non-
hazardous waste)
Waste Reduction
Current waste reduction and recycling methods being
implemented
Effectiveness of those methods
* Are there regular inspections and repairs for Inventory Control
paint and solvent leaks?
4,Are tight-fitting spigots used?
* Are spigots orpumps used to transfer paint
from storage containers to smaller containers?
*'Are good records kept on paint inventory.and
use?
* Are paint purchase expenses allocated to the
painting department? .
* Are paint containers adequately labeled?
20
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Chapter 3: Planning Pollution Prevention Programs at Coating Facilities
* Are paints stored on the floor according to
- manufacturer's instructions? :
+ Are paints used on a first-in, first-out basis?
* Is access to the paint room controlled?
« Is access to solvents controlled?
» Are unused or expired paints returned to .
vendors or manufacturers?
^ Is a computerized paint-mixing system used?
Scheduling
* Are certain production runs scheduled around
the same time each month? - .
* Are jobs scheduled so that jobs using the same
color are scheduled together?
* Are production runs scheduled to go from
lighter to darker colors?
Equipment and Materials
+.Are efficient spray guns being used (e.g., HVLR
electrostatic)? ; ' ,
* Are paints maintained at proper viscosity?
« Is'the correct gun setup being used for the
paint and the workpiece?
* Is it possible to reduce gun pressure and
achieve an acceptable finish?
* Are gun operators keeping the spray pattern
over the workpiece?
+ Are gun operators holding the gun perpen-
dicular to the work surface?
* When part size allows, are operators making a
pass over the full length of the work surface?
* Are paints with less or no hazardous ingredi-
ents being used?
*Are high-solids or powder coatings used?
Rework
* Is touch up dpne.only on the imperfection or
: reworks?
+ If paint is stripped, are mechanical methods
being used instead of chemical ones?
* If using chemical stripping, are less toxic
strippers being used?
Cleanup and Disposal
* Are waste paint handling and solvent handling
charges allocated to the production units or
departments that incur them?
* Are guns, nozzles, and lines cleaned irfimedi-
ately-after use?
* Are enclosed paint gun cleaners used?
* Is compressed air used to clean lines instead
of sol vent? ,
* Are spatulas or scrapers used to clean equip-
ment and paint containers prior to using
solvents? ,
* Are polystyrene filters used?
* Is unused paint stored properly so that it can
be .used again? ,
* If waste paint cannot be used onsite, are there
potential employee or local uses?
+ Is solvent recycled onsite?
* Is solvent gravity separated from waste
sludge? ,
If the technical assistance provider uses the team.
approach described above, many individuals from
all areas of the company will have a chance to
share their perspective on pollution problems and
solutions. Working with this information, technical
assistance providers can develop a process map,
including data information. Using these tools, the
P2 team can go onto the plant floor to discuss the
process with those directly involved (e.g., supervi-
sors and front-line production workers) to deter-
mine appropriate P2 projects and develop a
baseline to measure all future efforts.
Develop a Process Flow Diagram
Once all the information has been gathered and a
map of the facility is drawn, technical assistance
providers can develop a process-flow diagram.
Process-flow diagrams break the facility down
into functional units, each of which can be
portrayed in terms of material inputs, outputs, and
losses. Developing a process map helps the facility
understand how the production process is orga-
nized, thereby providing a focal point for identify-
ing and prioritizing sources of emissions'and waste
(EPAp, 1996).
t
The process map should cover the main opera-'
tions of the facility and any ancillary operations
(e.g., shipping and receiving, chemical mixing
areas, and maintenance operations). Separate
maps can be generated for these ancillary opera-
tions. Another important area to cover is "inter-
mittent operations" or operations that do not occur
on a regular basis. The most common intermittent
operations are cleaning and maintenance. A great
many pollution prevention opportunities can be
found by examining these interm ittent operations
(EPAp, 1996).
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Chapter 3: Planning Pollution Prevention Programs at Coating Facilities
Assistance providers should also help the facility
to include operations that are upstream and
downstream of the coating operation. For ex-
ample, machining operations could have a major
impact on cleaning operations. Pollution and waste
issues often cross process boundaries. An under-
standing of the origins of the pollution can assist
the facility in identifying opportunities for pollution
prevention.
Identify Pollution
Prevention
Opportunities
Using the information obtained in the facility
assessment, the team should compile a list of P2
options that are technically feasible. Brainstorming
sessions with the P2 team can provide innovative
ideas. Researching case studies of other compa-
nies also can provide valuable information. Other
potential sources of ideas include suppliers and
consultants. At this point, all ideas should betaken
seriously, and none should be-rejected automati-
cally for reasons such as "that's already been
tried," or "it will never work," or "it's too expen-
sive."
After all options have been identified, the team
should screen the options based on the objectives
and criteria that were established in the assess-
ment phase. Each option'should fit into one of the
following categories:
+ Ideas that are impractical .
* Ideas that need more detailed information and
study
+ Ideas that can be implemented with a mini-
mum of effort and cost
This initial evaluation will assist the company in .
identifying a subset of options that deserve further
investigation. Generally, the number of options
requiring detailed information and study should be
pared to a minimum (Ferrari, 1994).
When screening ideas, assistance providers should
keep in mind that an important principle of
excellence in manufacturing is maximizing the
productivity of the coating process. Some pollu-
tion prevention options can increase productivity
while others can decrease productivity, sometimes
substantially. Technical assistance providers
should be aware of how their suggestions can
affect the productivity of the coatings process
when screening options. By gaining information
on these types of issues, technical assistance
providers can provide better suggestions on
pollution prevention options when assessing a .
facility.
Analyze and Select
Options
Once a short list of options has been identified,
the team should begin the process of deciding
which options are appropriate for the facility.
During this phase, the team should be clear on the
company's objectives and criteria. Depending on
the goals of the company, cost effectiveness might
not be the overriding goal. The following ques-
tions should be asked when screening options:
* Which options will best achieve the companies
waste/emissidns reduction goals?
> What are the main benefits to be gained by
implementing this option?
* Does the technology exist to implement the
option?
* How much does it cost?
* Can the option be implemented without major
disruptions in production?
* Does the option have a good track record?
* Does the option require additional space?
* What are other areas that might be affected by
implementation of the option?
In addition, a company thatbelieves cost effec-
tiveness is critical should consider the long-term
costs associated with a particular option. For
instance, the team might be inclined to disregard
an option because'the initial capital outlay is high;
however, upon examining the total cost associated
with the project, the team might find that the
measure could yield impressive savings in several
years (Dennison, p. 75). In order to identify the
total costs associated with both existing and new
processes, the facility could consider costs that
traditionally have not been incorporated into
capital acquisitions. For more information on
identifying these costs, assistance providers can
refer to Improving Your Competitive Position:
Strategic and Financial Assessment of Pollution
Prevention Projects, a training manual developed
by NEWMOA for conducting financial assess-
ments of pollution prevention projects.
22
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Chapter 3: Planning Pollution Prevention Programs at Coating Facilities
Pilot Test or Validate
Preferred Options
Once the facility has determined -its preferred
option(s), the facility can pilot test the program
prior to full facility implementation. A pilot test
c?.n highlight any installation or implementation
issues. At this point, the technical assistance
provider has completed most of his or her job.
However, if issues arise in the pilot test phase, he
or she can be called in to troubleshoot and suggest
other alternatives. The technical assistance
provider could brief the facility's P2 team on how
to anticipate and prevent problems and issues
during implementation of the new system. This
could be useful because the cost to correct a failed
system can greatly exceed the cost of proper initial
implementation." .
Procure and
Implement New
System
Once the new system is installed, the company's
employees should be informed about the project.
arid the importance of their cooperation and
involvement. Operators should be trained on how
to properly operate the system. Companies should
update employees on the expected benefits of and
the progress rriade in achieving the goals of the
new system. '
Frequent updates on the progress of the overall P2
program can increase a staff s stake in the pro-
gram. In orderto sustain ernployee interest in P2,
facilities should encourage staff to submit new
ideas for increasing the effectiveness of the
' program. ' -
A few critical rules should be kept in mind when
helping a company consider new projects: '
> No single system or process is right'for all
.applications. A vast range of variables can
affect the coatings process which, in turn,
affects the selection and performance of a :
. pollution prevention system..Specific variables
include work type, work loading rate,
workpiece geometry, substrate materials/ and
finish requirements. . .
f
+ Prior to investing m any new system, the team
, should take the time to evaluate and under-
stand the process, preferably including a
rigorous pilot test in the facility.
« The team, should, recognize that the provider of
any new system (including the designer and.
sales staff) is a new partner at .the facility
(Ferrari, 1994). '
Evaluate and Keep
the Program Going:
Assistance providers can suggest that the facility
develop a mechanism for soliciting input from all
employees in the future. Communicating the
success of the program also can keep employees
involved. The facility can use the baseline infor-
mation developed from the facility assessment
phase to communicate any progress that has been
made. Technical assistance programs can follow
up with a facility (usually within 6 months to one
year from their final visit) to report on the suc-
cesses and failures of the company's P2 program
and leam of new projects that the facility may
have implemented.
23
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24
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Overview of Pollution
Prevention in Coating
Application Processes
Q ignificaht amounts of pollutants are generated
O from paint and coatings processes. The exact
amount for the nation is difficult to calculate,
because use is spread across numerous industry
groups (EPA, p. 158), and companies do not
report-emissions by manufacturing process to
EPA. Wastes from paint application include
leftover paints, dirty thinner from the cleaning of
spray guns and paint cups, air emissions of VOCs
and HAPs, dirty spray booth filters, dirty rags,
debris from area wash downs, and outdated
supplies. Simple and cost-effective ways to reduce
these wastes include rigid inventory control, good
housekeeping practices, proper paint mixing,
increased operator training, high transfer effi-
ciency equipment, proper cleaning methods,
alternative coatings, reusable paint booth filters,
recycling solvents, and the use of waste exchanges
(KSBEAP, p. 21). This chapter presents an
overview of these techniques while detailed
information on specific technologies are covered
in subsequent chapters: Table 7 presents a broad
overview of pollution prevention opportunities in
coating operations.
Rigid Inventory Control
Rigid inventory control is an efficient and effective
way of reducing indiscriminate use of raw materi-
als. The facility should monitor employee opera-
tions and make verbal or written comments on
product use. Another option is to limit employee
access to storage areas containing raw materials.
This inaccessibility can force employees to stretch
the use of raw materials (EPAr, p.8). Rigid control
can reduce solvent use by as much as 50%.
Good Housekeeping
Improvements in better operating practices, or
. "good housekeeping" methods apply to all emis-
sions and waste streams, require minimal capital
outlays, and can be very effective in reducing
wastes and pollutants. Good housekeeping
includes the development of management initia-
tives to increase employee awareness of the need
for, and benefits of: pollution preventipn; preven-
tative maintenance to reduce the number of leaks
and spills; and efficient use of raw materials. .
Table 6 presents a summary of good housekeep-
ing measures that are described in detail in this
chapter.
Many methods are available to control and
minimize material losses. The following ap-
proaches to bulk material drum consolidation,
material transfer methods, evaporation, and drum
transport can effectively limit material loss:
* Control inventory by storing drums together in .
an area of limited accessibility
* Reduce leaks and spills by placing drums at
points of highest use
* Use spigots or pumps to transfer materials
from storage containers to "working" contain-
ers , . .
> Control evaporation by using tight-fitting lids
and spigots
+ Use drip pans
Use secondary containment in bulk storage
areas
* Move drums correctly to prevent damage or
punctures that could lead to leaks or ruptures
during future use (EPAr, p.8). " '
Paint Mixing
In many cases, facilities will mix a fixed amount of
paint for each job (e,g., one pint'or one quart). .
For small jobs especially, the amount of paint
prepared often exceeds the amount of paint
actually applied. Facilities can encourage the use
of the correct amount of paint by having various
size&bf paint-mixing and sprayer cups available to
limit overmixing. Any paint not used for a job is
25
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Chapter 4; Overview of Pollution Prevention in Coating Application Processes
Table 6. Opportunities for Improved Housekeeping in Coating Operations
(KSBEAP, p. 21)
Waste
Method
General
* Improve material handling and storage to avoid spills
* Segregate waste streams
* Perform preventative maintenance .
* Practice emergency preparedness
* Charge departments generating waste for costs associated with man-
agement and disposal '
Paint Waste
* Maintain rigid inventory control to reduce thinner use
* Initiate routine'mainfenance and training to reduce leaks and spills
*Mix paint according to need; document use
* Provide operator training to improve transfer efficiency
* Schedule jobs to maximize color runs
Solvent Waste
* Control inventory to reduce use
^Substitute coating material for one with low or no solvents
^Substitute cleaning solution for one with low or no solvents
+ Practice proper equipment cleaning methods
* Recycle solvents onsite
usually considered a hazardous waste and should
be disposed of as such. A disadvantage to this
technique is that if too little paint is mixed for the
job and more needs to be made, color matching
can be difficult (EPAr, p. 9).
Operator Training
Operators may be skilled in producing high quality
finishes but poorly trained in minimizing paint use.
Technical assistance providers can help operators
by teaching them to: "
* Avoid arcing the spray gun and blowing
paint into the air
+ Maintain a fixed distance from the painted
surface while triggering the gun
* Keep air pressure (which is often set too high)
low; this can increase transfer efficiency by 30
to 60%
+ Keep the gun perpendicular to the surface
being painted '
* Use proper on/off trigger technique (KSBEAP,
p.23)
High Transfer Efficiency
Equipment
Less overspray means reduced emissions. Trans-
fer efficiency is a measure of how much paint
actually goes on the product, compared to how
much paint is sprayed. Typical transfer efficiency
from conventional guns ranges from 20 to 40%,
making average overspray rates 60 to 80%. For
more information on high transfer efficiency
equipment, refer to chapter 7.
Alternative Coatings
Painting usually consists of applying a primer/
surfacer followed by one or more coats of paint.
VOC emissions are directly related to the types of
paints used. Technical assistance programs should
assist companies in identifying any potential
alternative coatings such as powder, waterborne,
or high-solids coatings'. For more information on
alternative coatings, refer to chapter 6.
Proper Cleaning Methods
Reducing solvent use in equipment cleaning can
significantly reduce pollution. This can include:
26
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Chapter 4: Overview of Pollution Prevention in Coating, Application Processes
> Scraping paint cups or tanks before rinsing
with solvent
« Making use of Teflon-lined metal paint con-
' tainers that are easier to clean
> Using an "enclosed gun-cleaning station .
* Spraying solvent through the gun into the
cleaning station where it is condensed for
recovery and reuse
* Scheduling jobs^so that large batches of
similar items are painted instead of scheduling
jobs so that small batches of custom items are
painted. This reduces the amount of solvent
and waste paint generated
* Scheduling jobs from light.to dark colors to
, minimize cleaning between colors (EPA, p..10)
For more information on proper equipment cleaning
methods, refer to chapter 8.
Filters
.Reducing the amount of filters used in painting can
reduce hazardous waste generation. Facilities
should handle filters as a hazardous waste if they
contain wet paint (e.g., solvents), due to their
Table 7. P2 Options for Coatings Processes (KSBEAP, p. 23 and IHWRIC, p.
39-40)
P2 Options
Description
Benefits
Use Low-VOC Paint
> Substitute waterborne, powder,
UV curable or high-solids paints
fqr solvent-borne paint
> Use paints that have less toxic pigments
+ Reduces VOC emissions
* Reduces toxicity of paint
. sludge
Increase Transfer
Efficiency
Use electrostatic spraying
Use flow coating, roller coating, or
: electrodeposition
Improve operating practices
Provide operator training
* Reduces pointless
due to oversprgy
Reduce Quantity and
Toxicity of Solutions
Used for Surface
Preparation
Reduce solvent evaporation by
installing tank lids,-increasing
freeboard space, and installing ,
freeboard chillers in conventional
solvent vapor degreasing unfts
Use aqueous solutions or mechanical
methods
Maximize mechanical or aqueous
cleaning processes
* Reduces spent solvents,
aqueous solutions and.
rinsewqter from surface
preparation
* Reduces VOG emissions
Reduce; Equipment
Cleaning Waste
> Use less toxic solvents
* Install gun washer
+ Adopt distillation/recycling practices
+ Use enclosed cleaning devices
* Reduces VOC emissions
* Reduces toxicity of
'cleaning wastes.
Adopt Better
Housekeeping
Practices
* Segregate waste stream's
* Implement rigid inventory control
+ Improve material handling and storage
* Mix paint according to need;
, document use
* Schedule jobs to maximize color runs
* Perform preventative maintenance
».Practice 'emergency preparedness
* Reduces paint waste '
>Reduces solvent use -
* Reduces'leaks and spills
27
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Chapter 4: Overview of Pollution Prevention in Coating Application Processes
flammability and the existence of toxics in the
paint. One method for reducing filter waste is to
use a cleanable polystyrene filter or a reusable
metal filter. When the filter is too clogged for use,
it can be cleaned by blowing compressed air over
the filter until it is clean.enough for reuse (paint ,
removed in this process would require collection
and may still be classified as a hazardous waste)
(EPAr,p. 13).
On-site Solvent Recycling
Several alternatives are available for recycling
solvents onsite. Gravity separation is inexpensive
and relatively easy to implement. This technique
enables a solvent/sludge mixture to separate under
quiescent conditions. The clear solvent can be
decanted with a drum pump and used for equip-
ment cleaning. This reduces the amount of wash
solvent purchased. Reclaimed solvent also can be
used for formulating primers and base coats, but
might create problems if it is not sufficiently pure.
For those facilities that generate large quantities of
waste solvent, on-site distillation may provide a
more cost-effective solution. Batch distillation of
all high-grade solvent wastes can virtually elimi-
nate the need to purchase lower-quality solvents
used in priming and cleaning operations. An
operator can reclaim 4.5 gallons of thinner, with
0.5 gallons left as sludge. This ratio will vary
depending on the specific operation (EPAf, p. 11).
For more information on solvent distillation, refer
to chapter 5.
Waste exchanges provide another alternative for
reducing waste disposal costs. Waste exchanges
are organizations that manage or arrange for the
transfer of wastes between companies, where one
producer's waste becomes another producer's
feedstock. Most exchanges exist as information
clearinghouses that provide information on
available wastes. Opportunities exist for these
exchanges to oversee direct transfer (without
processing) of waste solvents from one company
toanother(KSBEAP,p.24). ' .
28
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Surface Preparation
This chapter covers a variety of surface prepa-
ration methods along with technology-specific
suggestions for optimizing processes in order to
reduce waste. Detailed descriptions of techniques
for optimizing traditional cleaning methods and
alternative cleaning methods, eliminating pollutants
from conversion coatings, and modifying or
replacing traditional stripping operations are
provided below. For an overview of alternative
surface preparation technologies, refer to table 8.
General Description
Methods for surface preparation vary depending
on the material to be painted, the paint to be used
and the desired properties of the resulting finish .
(IHWRIC, p. 33). Many products require a
preparation step prior to painting. This step is
commonly called pretreatment for new products,
or paint stripping for products that need to be
reworked (Ohio EPA, p. 1). Pretreatment of a
metal surface can include chemical-assisted
cleaning, mechanical cleaning, and chemical or
abrasive blasting, application of conversion
coatings or stripping methods.
P2 Tips for Surface Preparation
* Improve current .operating practices
> Set standards for cleaning and stripping
* Use aqueous cleaners and/or mechanical -
methods when possible
* Maximize the cleaning capacity of current
methods
Halogenated solvents have traditionally been used
as cleaning and stripping agents. Conventional
surface preparation generally involves applying
some form of a solvent. However, environmental
problems with air emissions often arise from
solvent use. In addition, after surface preparation,
a waste stream composed of the solvent combined
with oil, debris and other contaminants is left for
disposal (EPAij p. 1). Fortunately, a number of
alternative methods are now widely available.
These are discussed in the cleaning section of this
chapter. Surface preparation can consist of a
variety of processes including several cleaning .
steps, conversion coatings, and a stripping opera-
tion.
Pollution Problem
Surface preparation can generate a number of
wastes, including spent abrasives, solvents and/or
aqueous cleaning baths, and surface treatment
baths; air emissions from abrasives and solvents;
rinsewaters following aqueous processing steps;
and solvent-soaked rags used for wiping parts
before painting. Depending on the complexity of
the operation and the nature of the chemicals
used, the volume and toxichy of wastes generated
can vary widely (Freeman, p. 484-485).
Removing old paints that contain lead, for ex-
ample, can be particularly problematic, as abrasive
stripping of these paints generates a fine lead dust
that is highly toxic to workers. The use of sand
and other silica-containing materials in stripping
processes also has been associated with lung
disease in workers (IHWRIC, p. 48).
Mechanical Cleaning
Usually, the first step in the surface preparation
process is to mechanically remove rust or debris
from the substrate. Wiping loose dust and dirt off
the part is an example of mechanical cleaning.
Typically, though, more aggressive mechanical
action is needed to remove rust or other contamii-
nates. Rust and metal scale can be removed
mechanically by sanding, brushing with a wire
brush or plastic "wool" pads, or by using abrasive
blasting techniques (KSBEAP, p. 1-2). Abrasive
blasting can also be used for removing old paint
from products; solvent-based chemical stripping is
another option. Environmental concerns and rising
chemical prices have pushed more companies into
using mechanical cleaning to accomplish a larger
portion of the cleaning process (KSBEAP, p. 1).
29
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Chapter 5: Surface Preparation
Chemically-Assisted
Cleaning
Traditionally, solvents have been used for remov-
ing contaminates such as oils and greases. Compa-
nies use various solvent-based methods to clean a
workpiece. For example, metal parts can be
immersed in a solvent tank (i.e., cold cleaning).
Solvents also can be wiped or sprayed onto the
parts, or solvent vapor degreasing units can be
used. There are environmental problems associ-
ated with all of these cleaning methods.,Dip tanks
get dirty as they are'used. Spraying can be
wasteful if too much solvent is used. Wiping is
labor intensive. Vapor degreasers are regulated
under the Clean Air Act and OSHA and pose
health hazards. Often a combination of techniques
can be used to reduce solvent use and still obtain a
properly cleaned workpiece. For example, a dip
tank can be used followed by wiping or confined
.spraying. The key to solvent cleaning is to have
the part as clean as possible before it enters the
solvent cleaning process (KSBEAP, p.2). Optimiz-
ing solvent cleaning systems and alternatives to
solvent cleaning are discussed in greater detail in
the cleaning section of this chapter.
Conversion Coatings
A conversion coating may be applied to the
workpiece prior to painting to improve adhesion,
corrosion resistance, and thermal capability.
Conversion coatings chemically react with the
metal surface to create a physical surface that
allows for better paint adhesion. In addition,
conversion coatings act as a buffer between the
coaling and the substrate, reducing the effects of
sudden temperature changes. Phosphate and
aluminum conversion coatings are usually con-
fined to large operations with elaborate waste
treatment facilities because of the extensive
regulations controlling the disposal of rinse waters
and sludges containing heavy metals. For more
information on conversion coatings, refer to the
section on conversion coatings in this chapter.
Stripping
When a part needs repainting, the old paint usually
must be removed "before a new coating can be
applied. The first thing a technical assistance
provider should do is determine why the piece
needs to be reworked. Reducing reject rates can
greatly reduce the amount of waste generated
from these processes. Once the need for rework
,has been reduced, alternative stripping methods
can be examined.
General P2 Options
for Surface
Preparation
This section covers general methods to improve
the efficiency of the surface preparation process
and to reduce the pollution generated during the
surface preparation processes. Detailed informa-
tion on alternative technologies/processes is
discussed. , . '
A cost-effective method for reducing these wastes
is to minimize the need for surface preparation by
(1) improving current operating practices and (2)
setting standards for cleaning and stripping. If the
need for surface preparation cannot be reduced by
these methods, alternative technologies must be
assessed (MnTAP, p. 1). Maximizing the cleaning
capacity of current methods also can help reduce
wastesr(KSBEAP, p. 2). Each of these options is
discussed below.
Improve Current Operating
Practices
To reduce the need for cleaning, technical assis-
tance providers can help companies examine the
sources of workpiece contamination. Technical
assistance providers should determine how
contaminants such as lubricants from machining,
dirt from the manufacturing environment, and
finger oil from handling by shop personnel are
contaminating the workpieces. Once the contami-
nation sources are identified, technical assistance
providers can help determine whether some or all
contamination sources can be eliminated by
improving current operating practices. For ex-
ample, proper storage of materials and just-irj-time
delivery of parts can keep contaminants from
becoming a problem (KSBEAP, p. 1): To elimi-
nate finger oil contamination, gloves can be used
in areas of parts handling; gloves can be made of
lint-free material, or lint can be removed with a
dry cloth (OH EPAe, p. 1).
30
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Chapter 5: Surface Preparation
In the case of paint stripping, technical assistance
providers can help firms examine what causes the
need for paint stripping. Possibilities include:
inadequate initial part preparation, defects in
coating application, improper time/temperature
cycle for the curing oven, and equipment prob-
lems or coating damage due to improper handling.,
While no process is perfect, reducing the need for
repainting can greatly reduce the volume of waste
generated from paint removal (MnTAP, p. 1 -2).
Set Standards for Cleaning and
Stripping
. Next, companies should determine the cleanliness
level or cleanliness standard that is needed.
Gleaning requirements are generally based on two
factors: process specifications and customer
requirements. A system to measure cleanliness
should be used to prevent over-cleaning arid
ensure efficient use of cleaning agents
(MnTAPe).' .
In the case of abrasive stripping, standards should
be set to avoid blasting a surface longer than
necessary, creating excess waste and reducing
productivity. Measuring devices can be used to
define the level of surface scratching or "profile"
. desired. Most standards use Structural Steel
Painting Council (SSPC) classifications for surface
cleanliness. There are two types pf standards
. available: visual disk and photographic. A surface
profiler instrument also can be used (Freeman, p.
490-491). ' .
. Pollution prevention approaches tends to favor
mechanical or aqueous cleaning methods, but
solvent vapor degreasing can be more economical
and suitable for certain types of parts (e.g., parts
that slide into each other to form a close fit,
preventing some surfaces from being exposed)
(MnTAP, p. 2). Advanced technologies have
made both of these processes more effective and
less harmful to the environment (Freeman, p.
469.). More information on this topic is found in
the cleaning section of this chapter.
Maximize Cleaning Capacity of
Current Methods2
The following practices should be implemented
where possible to maximize the cleaning capacity
of aqueous or solvent cleaners:
+ Use countercurrent cleaning (i.e., begin with
"dirty" cleaner, followed by "clean" cleaner)
* Add an additional rinse
* Recycle cleaning solvent and rinsewater
* For aqueous cleaners, control water tempera-
ture and pressure. For example, elevated
temperature solutions are more effective for
removing greases and oils (KSBEAP, p: 2)
The following sections provide more detail on
specific surface preparation processes including
solvent vapor degreasing, aqueous cleaning,
alternative solvents, phosphatizing, anodizing,
stripping, and abrasive blasting.
Cleaning
This section provides information on a variety of
conventional and alternative P2 technologies
typically used for cleaning and degreasing metal
parts prior to coating.
Solvent Vapor Degreasing
The conventional method used for cleaning most
metal parts is vapor degreasing using a variety of
halogenated solvents. In vapdr degreasing, parts
are usually suspended over a solvent tank. The
solvents are then heated to their boiling point,
which creates a vapor that condenses on the parts
and dissolves contaminants. The condensate drips
back into the tank along with the contain inants.
However, because the contaminants usually have
higher boiling points than the solvent, the vapor
itself remains relatively pure. The cleaning process
is complete when the parts reach the temperature
of the vapor, and no more condensate is generated
(EPAh,p.2).
Advantages and Disadvantages
Unlike other cleaning processes involving water,
solvent vapor degreasing does not require down-
' For m6re information on setting cleanliness standards, see Is it Clean? Testing for Cleanliness of Metal Surfaces by
Anselm Kuhn in the September 1993 issue of Metal Finishing.' '
2 For.more information on extending the life of aqueous cleaning solutions, see Extending fhet/fe of Aqueous Cleaning
Solutions a fact sheet developed by the Office of Pollution Prevention, Ohio Environmental Protection Agency.
31
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Chapter 5: Surface Preparation
CASE STUDY:
Crown Equipment Corporation
Crown Equipment Corporation of New
Bremen, Ohio, is a manufacturer of electric
lift trucks and antenna rotators. Between 1987
and 1991, Crown removed methyl ethyl
ketone (MEK), methyl chloride, toluene and
1', 1,1 -trichloroethane from its cleaning and
degreasing operations by changing over to
aqueous cleaning.
In painting operations, Crown has removed
lead and chromium from most paint formula-
tions, eliminating hazardous paint waste. Paint
sludge is recycled into building materials such
as quarry tile, asphalt, mastic, and binder.
Savings
Changing over to aqueous cleaning initially
cost Crown $78,000, but the company now
saves m ore tha n $ 103,000 per yea r
(OH EPAc).
stream drying because the solvent vaporizes from
the parts over time. However, solvents such as
TCE vaporize resulting in significant VOC emis-
sions and solvent losses (Freeman, p. 468). Other
common solvents are either toxic, HAPs, and/or
o.zone depleters. In fact, conventional vapor
degreasing units commonly lose 60% of their
solvents through evaporation (SHWEC, p. 1).
Solvent Vapor Degreasing Processes
Conventional vapor degreasing units or open-top
vapor cleaners (OTVC) use an open tank where a
layer of solvent vapor is maintained. Air emissions
from an OTVC occur during startup, shutdown,
working, idling, and downtime. However, move-
ment of the work load in and out of the vapor
degreaser is the main cause of air emissions (EPAi,
p. 7). During startup, losses occur as the solvent in
the sump is heated and a vapor layer is established
in the open tank. Shutdown losses occur when the
unit is switched off and this vapor layer subsides.
Downtime losses occur due to normal evaporation
of the solvent when the OTVCis not in use. Idling
losses occur by diffusion from the vapor layer in
the period between loads. Completely enclosed
vapor cleaners (CEVC) are available, although use
is generally confined to Europe (Freeman, p. 468-
474).
Process Optimization
A number of equipment-related and operational
changes can reduce solvent emissions from
traditional OTVCs by as much as 50%. Many of
these practices are required under the MACT
standard since solvent degreasers are regulated
under the NESHAP. These include:
+ Minimizing solvent drag-out by improving
parts drainage over the tank
* Superheating vapors
+ Minimizing convective losses by lowering and
raising parts with a hoist at a speed less than
11 feet per minute
« Rotating complex parts
* Building a degreaser enclosure
* Placing, a cover on the OTVC opening during
idling and shutdown
* Minimizing air movement over the degreaser
Degreasing with Liquid Solvents
(Cold Cleaning)
This method of cleaning uses traditional solvents
in their liqujd form rather than their vapor form to
clean the workpiece. This is a common practice in
painting operations. Typically, solvents such as
methyl isobutyl ketone (MIBK), methyl ethyl
ketone (MEK), or 1,1,1 trichloroethane are used.
The primary advantage of this method is its
versatility. Liquid solvents can be used to clean an
entire part by spraying or immersing the part in
the solvent, or by wiping with a rag. Typically,
this process is used to clean small workpieces
rather than parts that are large or have complex
geometries.
Like vapor degreasing, capital costs for cold-
solvent degreasing generally are low, and the
system requires minimal equipment, floor space, ,
and training. Also, spent solvent can be distilled
and recycled onsite. In states where the solvent is
regulated as hazardous material, however, most
facilities send'exhausted cleaning solution offsite
to commercial recycling operations. Assistance
providers should be aware that special safety
equipment is required by OSHA for distillation
systems.
32
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Chapter. 5: Surface Preparation
As with vapor degreasing, the principal limitation,
of cold solvent cleaning is that emissions from the
solvents can be damaging to the environment, and
may pose a threat to human health. Other limita-
tions include:
+ Moisture can form on the workpiece and
" cause rusting problems when solvent evapo-
rates too quickly.
* Same solvents can leave a residue that re-
duces the adhesion of the coating.
* Solvents with low flashpoints can be fire
hazards. ,-
Best Management Practices for Cold
Cleaning
Best management practices for enhancing effi-
ciency in the cold cleaning process include the
following: "
* To minimize emissions, cleaning operations
should be done in an enclosed area; if the
solvent used is heavier than water and not
miscible, a water cover should be used as a .
. vapor barrier.
* Solvent should be replenished using an
enclosed pump system. ,
* Consider recommending the use of several
tanks that extend the period belween solvent
changes (EPAr, p. 83).
+ Investigate alternative solvents. A variety of less
toxic solvents are available and are potentially
effective substitutes. A recent U.S. Army study
identified the .following odorless hydrocarbons
with d-limonene as alternatives to Stoddard
' solvent: Breakthrough, Electron 296;Skysol
100;Skysol,andPF.
- For many facilities, the most effective way to
reduce waste from cleaning operations is to invest
in a new cleaning method. The following section
provides information on alternatives to solvent
degreasing.
Alternative Gleaning
Methods
Aqueous Cleaning
Aqueous cleaning involves the use of solutions
which are largely made up of water, detergents,
and acidic or alkaline chemicals rather than
solvents. Typically, aqueous cleaning solutions
contain at least 95% water. Solutions that include
larger percentages of other compounds, including
terpenes and other solvents, typically are called
semiaqueous (Freeman, p. 707).
Both aqueous cleaning and semiaqueous cleaning
are usually more environmentally friendly than
traditional solvent cleaning and adapt to a wide
variety of cleaning needs. Aqueous cleaning is
usually used after mechanical cleaning. A spray,
dip, or a combination of both is typically used,
depending on the workpiece. The particular
solution selected depends on both the type of
contaminant and the type of process equipment
used (EPAli, p. 13). Elevating the temperature of
CASE STUDY:
Ball Metal Container Group,
^
Ball Metal Container Group of Findlay, Ohio,
produces 12-ounce aluminum beverage
cans, drawn and ironed containers, and
easy-opening ecology ends. The company
has virtually eliminated the use of solvent-
based materials by switching to .water-based
products, for its cleaning needs. In October
1990, Ball voluntarily stopped using 1,1,1-
trichloroethane to clean parts and printing
blankets, opting instead for a substitute qf
alcohol and a water-based Simple Green
solution (OH EPAd).
the solution can make it more effective in remov-
ing greases and oils, which have increased mobil-
ity at higher temperatures (KSBEAP,.p. 2).
However, solutions that have too high a tempera-
ture may set some soils and make them more
difficult to remove.
Advantages and Disadvantages
Aqueous cleaning can be used on a wide range of
substrates and is less toxic than solvent processes.
Some disadvantages include a high rate of water
consumption and hazardous wastewater discharge
(Freeman, p. 707). In addition, some acids used in
aqueous cleaning can cause hydrpgeri
embrittlement, reducing the strength of metal
substrates'(KSBEAP, p. 2). Ferrous parts need to
be dried rapidly to avoid rusting. .
33
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Chapter 5: Surface Preparation
Aqueous Cleaning Processes
The conventional aqueous cleaning processes are
vibratory deburring and hand-aqueous washing,
although automated and power washing processes
are available.
In vibratory deburring, soiled parts are placed in
an open vessel with an aqueous cleaning solution.
The vessel is then rotated, which rumbles the
parts. The cleaning solution is removed and clean
tap water is added to rinse the parts (Freeman, p.
470-472). In this method, the part is simulta-
neously cleaned and deburred.
In hand-aqueous washing, parts are dipped by
hand into a series of tanks containing surfactant
solutions and rinsewater. A continuous clean water
flow must be maintained in the final rinse tanks,
but the surfactant and other rinse tanks (also
known as drag-out tanks) can be used for an.
entire day without changing the solutions (Free-
man, p. 470-472).
The most common automated aqueous washer
used in coating operations is a 3- to 7-stage spray
washer which uses an overhead conveyor and
racks to move the parts. Belted conveyor spray
washers are also common, as are multistage
agitated immersion washers of various types.
Centrifugal washers can be part of an automated
aqueous system, but they are uncommon in
coating pretreatment systems (Callahan, 1997).
Process Optimization
A number of other processes used as part of an
aqueous c leaning system can enhance cleaning
effectiveness. These include high-pressure sprays,
mechanical agitation, and ultrasonic methods. In
fact, in the manufacturing environment, many
aqueous cleaning systems are multistaged and ,
include several different processes (Levitan et al.,
p. 54).
Ultrasonic cleaning uses high-frequency sound
waves to improve the efficiency of aqueous and
semiaqueous cleaners. By generating zones of
high and low pressures in the liquid, the sound
waves create microscopic vacuum bubbles that
implode when the sound waves move and the
zone changes from negative to positive pressure.
This process, called cavitation, exerts enormous
localized pressures (approximately 10,000 psi)and
temperatures (approximately 20,000°F on a
microscopic scale) that loosen contaminants and
actually scrub the workpiece (Freeman, p. 472). A
typical ultrasonic system moves the pieces through
three stages: an ultrasonic cleaning tank containing
a water-based detergent; two rinse tanks; and a
drying stage (Levitan et al., p. 57). Ultrasonic
cleaning can be used on ceramics, aluminum,
plastic, and glass, as well as electronic parts, wire,
cables, rods, and detailed items that might be
difficult to clean by other processes (Freeman, p.
472).
Other Cleaning Methods .
The methods described below are not widely used
to clean metal parts. However, they can be used
as substitutes for conventional solvent vapor
degreasing.
' Vacuum De-o///ng. This method uses a vacuum
furnace and heat to vaporize oils from parts.
Vacuum furnace de-oiling can be applied where
vapor degreasing typically is used to clean metal
parts. It also can remove oil from nonmetallic
parts. Although capital costs for vacuum de-oiling
are high, the operating costs are low. Unlike other
clean technologies, vacuum de-orling does not
leave the cleaned parts water soaked, so they do
not need to be dried. Because the time and
temperature of the de-oiling process depends on
the material to be cleaned and the oil to be
. removed, adjustments might be needed for each
new material, oil, or combination. Also, the parts
must be able to withstand the required tempera-
ture and vacuum pressure (Freeman, p. 478-479).
Laser Ablation. In this method, short pulses of
high-peak-power laser radiation are used to rapidly
heat and vaporize thin layers of material surfaces.
Laser ablation can perform localized cleaning in
small areas without affecting the entire part. Laser
ablation does not use solvents or aqueous solu-
tions and therefore generates little hazardous
waste. The only waste generated is the small
amount of material removed from the surface of
the item being cleaned (Freeman, p. 479). Laser
ablation has been used to strip paint from aircraft.
At the other extreme, it has been used to remove
sub-micron particles and thin fluid films from
semiconductor components (SHWEC, p. 16).
34
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Chapter 5: Surface Preparation
Table 8. Alternatives to Chlorinated Solvent Cleaning (NFESC)
Contaminant
Corrosion Inhibitors
Fats and Fatty Oils
Fingerprints
Ink Marks
Hydrocarbon Greases
and Oils
Machining (cutting fluids)
Polishing Compounds
Possible Alternatives ,
> Alkaline-soluble compounds
* Hand wipe or use alkaline cleaners .
'« Handle all fabricated parts with gloves ....
> Use alkaline compounds for hand wiping
* Use alcohols with hand wiping ,
« Use water-soluble inks and remove ink with water
* Use labels or tags until final marking is applied
> Institute the use of hand wiping stations to remove enough soil for
alkaline cleaning " ,
* Use water-soluble compounds
* Substitute water-soluble fluids for use in machining
* Use water-soluble compounds
* Clean at polishing station '",
Supercnf/ca/ Fluid Cleaning.This process
involves the application of fluids at temperatures .
and pressures above their critical point to remove
contaminants from parts. CO2 is the most com-
monly used fluid in this process because it is
widely available and considered to be nontoxic.
Supercritical fluid cleaning is compatible with
stainless steel, copper, silver, porous metals, and
silica. It leaves no solvent residue after cleaning
and has low pperating costs. However, capital
costs are high (e.g., $ 100,000 for small-capacity.
equipment) (Freeman, p. 708-709). Therefore,
supercritical fluid cleaning has been used mainly in
.precisioncleaning(EPAh,p.27). '
Alternative Cleaners
With the phase.out of chlorofluorocarbon (CFC)-
based cleaners, there has been an increased
interest in investigating alternatives to these
chemicals. Table 8 lists typical soils and alternative -
cleaning methods that are effective in reducing the
use of chlorinated solvents.
Chemical Alternatives
Many alternatives to methylchlorofluorocarbons
(MCF) and CFC-113 are available for use in cold
cleaning and vapor degreasing applications such as
wipe cleaning, dip cleaning, immersion soaking,
pressure washing, and vapor degreasing. Some
solvents are recommended only for specific
applications while others are used for many .
applications. In general, the following properties
are desirable when considering solvent alterna-
tives: low surface tension to penetrate small .
spaces, high density to remove small particles,
high volatility to provide rapid drying, non-VOC,
good solvency to readily improve organic soils,
low cost, low toxicity, nonflammable, little resi-
due, and easy cleanup and disposal (NFESC).
' Drop-in solvent replacements for traditional
solvents such as MCF and CFC-113 usually are
not possible. However, because vapor degreasing
is effective in cleaning delicate parts,_some
facilities might want to consider maintaining the
process with a substitute solvent. Some possible
CFC-free alternatives include:
''* D-Limonene
Common D-limonene solvent blends have
flashpoints higher than T40°F. Therefore, they
do not pose an ignitability hazard.
35
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Chapter 5: Surface Preparation
N-methyl-2-pyrolidone
Also known as M-pyrol or NMP, N-methyl-2-
pyrolidone has high purity, a high flash point,
and low volatility. It is very effective in ultra-
sonic applications'.
Volatile Methyl Siloxanes
Volatile methyl siloxanes (VMS) compounds are
relative newcomers to solvent cleaning. They
are low molecular-weight silicone fluids
available in a variety of blends, exhibiting
good compatibility with plastics and elas-
tomers. However, all blends are either flam-
mable or combustible, and somewhat toxic.
Advantageous characteristics of VMS include
good cleaning capabilities for a wide variety
of contaminants, rapid drying without leaving
residue on the workpiece, rapid spreading,
and good penetration into tight spaces. Also
VMS can use existing equipment. Finally, VMS
fluids can be distilled for reuse.
* Hydrochlorofluorocarbons
While hydrochlorofluorocarbons (HCFCs) are
similar to CFC-113 and MCF in solvency and
, cleaning effectiveness, the use of HCFCs is
severely restricted because of their ozone-
depleting potential and negative health effects.
A production ban on HCFCs is scheduled for
the year 2010, and could be accelerated at
any time. Emission controls are also required
for safe operating conditions (NFESC).
^Aliphatic Hydrocarbons
Aliphatic compounds comprise a wide range
of solvents such as mineral sprrits and kero-
.sene. These solvents' have superior cleaning
ability and are compatible with most plastics,
rubbers, and metals, and are reusable when
distilled. However, aliphatic hydrocarbons are
flammable, slow to dry, and have low occupa-
tional-exposure limits. Because of this fact,
aliphatics have not been considered a desir-
able substitute for traditional solvents.
*Other Organic Solvents ,
Organic solvents, such as ketones; alcohols,
ether, and esters, are effective but dangerous.
Many are HAPS while others have very low
flash points. For example, acetone has a
flashpoint of 0°F. Extreme caution is required
when handling these organic solvents. In
addition, organic solvents can be toxic and
malodorous and, as a result, are not generally
used in vapor degreasing. Another major
concern is fire danger. Also,' in development
are hydrofluoroethers (HFE) and
perfluorocarbons. These contain no VOCs '
and are not considered ozone depleting
chemicals (ODC). EPA has approved them for
use underthe Significant-New Alternatives
Program (SNAP). These chemicals are more
volatile than 1,1,1 trichloroethane and CFC-
11 3 and would serve as an ideal replacement
when quick drying, is important (EPAq, p. 32).
Some companies have begun using other HCFC
solvents such as trichlofoethylene, perchloroethyl-
ene, and methylene chloride. These solvents have
been used often in vapor degreasing because of
their similarity to CFC solvents in both physical
properties and cleaning effectiveness. However,
using these alternatives has significant disadvan-
tages for the facility. All of the above three
alternatives have been classified as Hazardous Air
Pollutants (HAPs) by EPA and are targeted by the
Emergency Planning and Community Right-to- .
Know Act as well. Furthermore, these spent
solvents are classified as a hazardous waste. As a
result, handling and disposal of these solvents is
complicated and more expensive.
Once a part has been cleaned,.it can receive a
conversion coating prior to the painting process.
The next section provides information on conver-
sion coatings and techniques to reduce waste-from
these processes.
Conversion Coatings
Chemical and electrochemical conversion treat-
ments provide a coating on metal surfaces to
prepare the surfaces for painting. These conver-
sion treatments include anodizing and phosphat-
ing. Conversion coatings are usually confined to
large operations with elaborate, waste-treatment
facilities because of extensive regulations control-
ling disposal of rinse water and sludges containing
heavy metals.
Anodizing
Anodizing is a specialized electrolytic surface
finish for aluminum that imparts hardness and
36
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Chapter 5: Surface Preparation
P2 Tips for Conversion Coatings
* Avoid soiling the substrate prior to the
cleaning process.
* Analyze water for hardness and dissolved
solids. Use alkaline cleaners or phosphate
compounds with hard-water stabilizers .
when necessary.
* Use fow-temperature, energy-conserving,
alkaline cleaners or phosphate compounds.
corrosion resistance, increases paint adhesion^
provides electrical insulation, imparts decorative
characteristics, and aids in the detection of surface
flaws on the aluminum. This process employs
electrochemical means to develop a surface oxide
film on the workpiece, enhancing corrosion _
resistance. Anodizing is a similar process to
electroplating but it differs in two ways. First, the
workpiece is the anode rather than the cathode as
in electroplating. Second, rather than adding
another layer of metal to the substrate, anodizing
converts the surface of the metal to form an oxide
that is integral to the substrate (SME, 1985).
Industry uses three principal types of anodizing:
chromic-acid anodizing (called Type I anodizing),
sulfuric-acid anodizing (called Type II anodizing),
and hard-coat anodizing, which is a combination
of sulfurie acids with an organic a'cid such as
. oxalic acids (called Type III anodizing). Because
of the structure, the anodized surface can be dyed
easily. These dyes include organic or organometal-
lic dyes and often contain chrome in the trivalent
state. Whether the pieces are dyed, they need to
be sealed. Sealing can be performed withhot
water, nickel acetate, or sodium dichrpmate, .
depending on the required properties (SME,
1985),
VType 1 (Chromic Acid) Anodizing: Chromic-
acid anodizing takes place in a solution of
. chromic acid. The hexavalent chrome solution
creates a thin hard coating (Ford, 1 994).
,+ Type II (Sulfurie Acid) Anodizing: Sulfuric-acid
anodizing takes place in a 15% solution of
, sulfurie acid. During the anodizing process,
aluminum dissolves,off the surfdce of the part
and changes the surface characteristics to an
' oxide coating. This process creates a surface
structure that is. both porous arid harder than
the base aluminum. Sealing of this coating
provifjes greater corrosion protection. When
the aluminum concentration in the bath solu-
tion builds up to a certain level ,(-15 to 20
grams per liter), the process becomes less
. efficient and requires treatment (Ford, 1994).
*Type.ll) (Hard Coat) Anodizing: Hard-coat ,,
anodizing is'a form of sulfuric-acid anodizing'
in which the acid-content is slightly higher
(20%) and an organic additive is added to the
bath. This additive helps to create a tighter
pore structure that increases the hardness of
the oxide coating. Hard-coat anodizing has a
high resistance to abrasion, erosion, and
corrosion. This type of coating also can be '
applied in much thicker layers than'Type I or
Type II anodizing (Ford, 1994).
Various methods are used to treat wastes gener-
ated from anodizing bath solutions. Technologies
that have been employed successfully include:
evaporation systems operating under reduced
pressure, sedimentation, reverse osmosis, filtra-
tion, and anion and cation exchangers.
Substituting.Type I Chromic-Acid Anod-
izing with Type II Sulfuric-Acid Anodizing
Because of federal and state mandates imposed on
operations using hexavalent chrome, researchers
have investigated the feasibility of substituting
Type I anodizing with Type II sulfuric-acid
anodizing. A NASA study found that in applica-
tions where anodizing is used to impart corrosion
protection on aluminum, Type II sulfuric-acidj
anodizing is superior to Type I chromic-acid
anodizing (Danford, 1992). '
According to suppliers, conversion from chromic-
acid to sulfuric'-acid anodizing is not a simple
chemical substitution: The conversion requires a
complete-changeover of anodizing equipment and
partial modifications to downstream waste-
treatment facilities. Replacement of the anodizing.
tank often is required because of the differences in
material compatibility between the tank (and tank
liner) and sulfurie acid and chromic acid. Sulfuric-
acid anodizing processes also have different
voltage and amperage requirements, necessitating
replacement of the rectifier. The operating tem-
perature of the;electrolytic bath also is different
for the two processes. The chromic process is
37
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Chapter 5: Surface Preparation
CASE STUDY:
Substituting Chromic Anodizing with
SulfuricAcid
In December 1 988, General Dynamics
replaced a 35-year-old chromic-acid/alumi-
num-anodizing system with a new sulfuric-aeid
anodizing system that used computerized
hoists and on-demand rinsing. The new
system, supplied by NAPCO, Inc., enabled
General Dynamics to eliminate a major
source of chromium emissions. In addition to
the chemical substitution which eliminated
chromium releases, automated hoist and on-
demand water rinse systems helped to reduce
wastewater treatment requirements.. The
computerized automated hoists'monitor the
time intervals during which the parts are
treated and allowed to drain. Compared vyith
manual immersion and draining of parts, this
system reduces treatment requirements by
avoiding unnecessary dragout of immersion
fluids to downstream rinse tanks. Subse-
quently, the on-demand water system reduces
rinsewater use and wastewater treatment
requirements by reducing water consumption
and monitoring the conductivity of the
rinsewater in the tank. Unlike manually-
operated rinse tanks, which have constant
overflows, the on-demand system adds water
only when the conductivity of the tank exceeds
a set value (US EPA 1995). '
usually maintained by steam heat at an operating
temperature of 90 to 1.00°F whereas the sulftiric
acid process must be chilled.using cooling water to
an operating temperature of 45 to 70°F.
Operation and maintenance costs are typically
mUch lower for sulfuric-acid anodizing than for
chromic-acid anodizing because of lower energy
requirements. Wastewater treatment costs are
lower as well because sulfuric acid only requires
removal of copper whereas chromic acid requires
more complex chrome reduction techniques. The
change in materials also means that the cost of
sludge disposal is greatly reduced.
Sulfuric-Acid Anodize Regeneration with
Ion Exchange
Traditionally, facilities use'ion exchange to remove
metallic contaminants from wastewater streams.
However, ion exchange resins also remove the
hydrogen and sulfate components of the sulfuric
acid/aluminum anodizing solution. As the solution
passes through the columns, the acid is removed.
Then the waste stream, which consists of a small
amount of acid plus all the aluminum from the
anodizing solution, flows to the wastewater
treatment system. To recover the acid, platers use
water to flush the acid components from the resin.
This forms a sulfuric acid solution that is low in
dissolved aluminum and can be used again in the
anodizing process (Ford, 1994).
Sulfuric-Acid Anodize Regeneration with
Electrodialysis
Electrodialysis removes metal ions (cations) from
solutions using a selective membrane, an electrical
current, and electrodes. This technology uses a
chemical mixture (catholyte) as a capture and '
transport media for metal ions. This catholyte
forms a metal sludge and requires periodic
change-outs. The recovered sludge is hazardous,
and companies might want to work with an
outside firm to recover the metal in the sludge.
Using electrodialysis, facilities can remove all the
metal impurities from the anodizing bath, main-
taining the bath indefinitely. By keeping the
concentration of contaminants in the process bath
low, the rinsewater potentially can be recycled
back to the bath, closing the loop on the process.
The cost to operate this system depends on the
size of the acid anodizing bath, the level of metal
concentration, the metal removal capacity of the
electrodialysis unit, and the company's ability to
reclaim metals in the sludge.
Alodine
Alodine is a nonelectrolytic process used to create
a chrome oxide film similar to anodizing. It is
widely used in military and aerospace applications.
Phosphate Coatings
Phosphating is used to treat various metals
(mainly steel and iron) to impart corrosion resis-
tance and to promote the adhesion of finishes
., such as paint and lacquers. Phosphating treat-
ments provide a coating of insoluble metal-
phosphate crystals that adhere strongly to the base
metal. Generally,-phosphating solutions are
prepared from liquid concentrations containing
38
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Chapter 5: Surface Preparation
one or more divalent metal's, free phosphoric acid,
and an accelerator (Ford, 1994).
The phosphating process consists of a series of
application and rinse stages typically involving the
application of either an iron, manganese, or zinc
phosphate solution to a substrate. A simple iron
phosphating system is composed of two stages: an
iron phosphate .bath that both.cleans the part and
applies the conversion coating followed by a rinse
bath to remove dissolved salts from the treated
surface. An advanced zinc phosphating line might
feature seven stages of spray/dip and rinse baths.
.-In addition, a final rinse in a low-concentrate
acidic ehromate or an organic nonchromate
solution is often used to further enhance corrosion
resistance and seal the coating. Following the
conversion application, the parts are dried to
prevent flash rusting (Ford, 1994).
Iron and zinc phosphate coatings often are used as
paint bases, and manganese phosphate coatings
are applied chiefly to ferrous parts for break-in
and galling (e.g., to engine parts). The choice of
iron or zinc phosphate coating depends on product,
specifications. In general,"the more extensive
multistage zinc phosphate processes provide better
paint adhesion, corrosion protection, and rust
protection than iron phosphate processes. Zinc .
phosphate baths, however, tend to.be more
expensive, require more maintenance, and often
result in more sludge disposal (SME, 1985).
Phosphate Coatings for Steel
Iron or zinc phosphate coatings are usually used
- for steel. In the phosphating process, acid attacks
the metal surface, forming a protective coating of.
iron or zinc phosphate salts. Zinc phosphate forms
finer, denser crystals than iron phosphate.and has
better corrosion resistance and paint adhesion.
Accelerators and oxidizers are added to the
phosphating solution to improve its effectiveness.
Molybdic acid, added for corrosion inhibition,
gives a purple cast to iron phosphate coatings. A
clean surface is critical to successful application of
the phosphate coating (KSBEAP. p.3). .
Process time, temperature, and chemical concen-
tration affect the acid's reaction with the steel
part. Process time is usually fixed because the line
must run at a certain speed, however, temperature
can have a great effect on the phosphating pro-
cess. In order for ithe process to run at optimum
efficiency, the temperature/preceding the phos-
phating process should be higher than the tem- ,
perature required for phosphating. This allows the
part to become heated prior to entering the
phosphating process. If the part is not heated prior
to phosphating, process efficiency is reduced. For
example, if deposition efficiency is reduced,
additional chemicals may be required, and more .
sludge could be generated. Iron phosphating
solutions typically operate between 120 and
140°F, but can also be operated at room tempera-
ture.
Cleaning and irbaphosphating can be combined in
a single solution, however, this is usually success-
ful only when the parts are lightly soiled. It is not
possible to use a combination process with zinc
phosphating (KSBEAP, p. 3).
Phosphate Coatings for'
Aluminum
Iron and zinc phosphate coatings are used on
aluminum parts or products. The choice of
solution largely depends on the volume of alumi-
num in the process. When a company is process-
ing a small amount of aluminum, the same
phosphating solution is typically used for all metals
that are processed. For instance, if a company
processes mainly steel and a small volume of .
aluminum, iron phosphating will be the' only
process used.
Iron phosphating solutions can effectively clean
the surface of aluminum and improve paint
adhesion. However, they leave little or no c.oating
on the substrate. In order to etch the aluminum, a
fluoroborate or fluoride additive is required.
Companies often use chromium phosphate coating
for small volumes of aluminum. Often, no.-rinse
, chromium phosphate solutions are'us'ed because
. they have the advantage of not being classified as
a hazardous waste. However, they typically . .
provide less corrosion resistance due to incom-
plete coverage. Chromic acid sealers can be used
but they contain hexavalent chromium (KSBEAP,
P-3)-- , . -..'.
39
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Chapter 5: Surface Preoaration
Issues with Pretreatment Coatings
The most common problems associated with
chemical pretreatment systems are poor adhesion
and premature corrosion failure. Frequently these
problems are caused by the following:
Residual soils: These soils may be caused by
(1) conveyer line speed that exceeds the design
limits of the cleaning system, causing low dwell
time, (2) inappropriate cleaner for the soils
present, and (3) incorrect temperature for the
cleaner being used. Generally, high temperatures,
120 to 13 0°F, are best for good cleaning unless
the facility is using a low-temperature cleaner. In
that case, high temperatures can be detrimental.
To determine the cleaning temperature that
removes the soil from the parts, the operator can
immerse an uncleaned part into a container of
water and begin heating it. The operator should
use a thermometer tp watch the temperature rise
while keeping an eye on the point where the water
line touches the part. At some point, the water will
become hot enough to visibly loosen the soils,
causing globules to float to the surface (CAGE).
1 Flash rust: This can be caused by (1) excessive
line speeds that prevent adequate exposure to the
sealer in the final rinse, (2) line stops that overex-
pose parts to chemicals or allow them to dry off
between stages, and (3) lack of sealer in the final
rinse. When using a solvent-type cleaning systenj
or an iron phosphate conversion process, wiping
with a clean, white cloth is an ideal way to check
a part's cleanliness before coating (CAGE).
Aluminum oxide: A natural oxide is present on
the surface of aluminum parts. This oxide
interferes with adhesion if it is not rempved. If a
facility is using a combination of iron phosphate
and cleaner to remove this oxide, they should be
certain that the combination is made for steel and
aluminum. Their chemical supplier can discuss
this with them in more detail (CAGE).
Inadequate rinsing: This is one of the most
common mistakes made in metal cleaning. It is
caused by both increased line speeds that reduce
rinse-s.tage dwell time and inadequate rinsewater
overflow. Simple tests for inadequate rinsing can.
include slowing down the production line or hand-
rinsing parts in deionized water. If the technical
assistance provider suspects that the company's
surface preparation system is causing a problem,
they should suggest that the company clean test
parts with clean rags dipped in a solvent, instead
of running the parts through their normal cleaning
process. If this fixes the problem, the firm should
focus their investigation on the surface preparation
system. If they are getting premature and massive
lifting of the coating after exposure to water due to
exterior weather elements, or after slat-fog tests,
this can indicate inadequate rinsing. Water-soluble
crystals (salts) are probably present at the coating
and metal interface. Moisture can dissolve these
salts quickly. When this happens, rapid undercut-
ting of the film occurs and significant rust forms
(CAGE).
Pollution Prevention in the
Phosphating Process / .
Reduced water use is the primary waste reduction
option for phosphatizing. The water added to
maintain the solution in the phosphatizing bath can
be reduced by analyzing and controlling the
solution's temperature, chemical concentration,
and pH level in each step, and recirculating
solution or rinse water from one bath to others
when possible. This option also reduces chemical
use (Ohio EPA, p. 1). A facility should analyze
incoming water quality. City water can bring in
considerable amounts of dissolved solids, and
these contaminants can vary seasonally. The .
contaminant can have a damaging effect on
control regimes. Determining control set points,
and treating and conditioning incoming water is a
good idea.
Properly matching the phosphating chemicals with
the metal substrate is another key issue in mini-
mizing waste from phosphating operations. This
can significantly minimize sludge generation. For
example, processing galvanized steel in an iron
phosphate solution results in excess generation of
zinc sludge because the acid reacts with the zinc in
the substrate.
Ultrafiltration to Maintain Phosphating
Baths
PrecipitateS'Continuously form in phosphating
operations, primarily on the heating coils in the
tanks. This presents challenges in maintaining the
baths and often results in dumping of the solution.
40
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Chapter 5: Surface Preparation
When the solution is removed from the tank, this
accumulation of sludge must be manually re-
moved. The solution should be decanted back into
the tank to minimize waste, but because this
requires space and time, it is rarely done. A more
efficient system involves the use of a continuous '
recirculation system through a clarifier with gentle .
agitation in the sludge blanket zone. This allows .
for indefinite use of the solution and e.asy removal
of dewatered sludge from the bottom of the
'clarifier (Steward, 1985). ?
Stripping
Various methods are available for removing old
paint from metal substrates. In some cases,
stripping also functions as a cleaning method to
remove oils, greases, or other contaminants.
Chemical stripping has been used in a number of
applications, but there are alternative methods that
are less toxic and less costly! Alternatives to
chemical stripping include plastic media, sodium
bicarbonate, wheat-starch, and carbon-dioxide
blasting, as well as high-pressure water, high-
energy light, mechanical, cryogenic, and high-
temperature thermal stripping. Key factors that
must be considered when selecting a paint-
stripping method include: the characteristics of the
substrate to be stripped; the type of paint to be
removed; and the volume and type of waste
produced. Waste type and volume can have a
major impact on the cost and.benefits associated
with a change (MnTAP, p. 2). The following
section describes conventional chemical stripping
and the-alternatives. / .
Chemical Stripping
The conventional method for removing paints
from metal surfaces is chemical stripping. This
process may involve applying solvents by hand
directly to a coated surface. The solvents soften
or dissolvethe coatings and are usually scraped
- away or otherwise mechanically removed (Free-
man, p. 704-705). Facilities often use a water
rinse for final cleaning of the part (EPAg, p. 2).-
Disassembled parts may be stripped in an immer-
sion tank. Immersion strippers are advantageous
because they can strip paint from recessed and
hidden areas. This is not possible with abrasive .
blasting methods. . ,
Chemical-based paint strippers are either hot (i.e.,
heated) or cold. Many hot strippers use sodium
hydroxide and other organic additives. Most cold
strippers are formulated with methylene chloride
and other additives such as phenolic acids, '
cosolvents, water-soluble solvents, thickeners, and
sealants. Handling and disposal of spent baths and
rinses is a major problem for facilities employing
both types of strippers (Freeman, p. 704-705).
Many new stripping formulations have been
developed including strippers based on formula-
tions ofN-methyl-2-pyrollidone (NMP) and
dibasic esters (DBE). Althpugh these new strip-
pers are used in the consumer market, they have
not been accepted for use in.industrial stripping
operations because their effectiveness varies from
paint to paint. Compared to the stripping achieved.
. with formulations containing methylene chloride
and phenol, many of the substitutes suffer from
one or more of the following disadvantages:
effectiveness varies with type of paint and extent
of cure; elevated temperature is required; and
increased stripping time is required. In selecting
art alternative, technical assistance providers
should make sure that the stripper does not attack
the substrate or react with the substrate (i.e., is
flammable, combustible, or photochemically
reactive) (Freeman, p. 491-492).
Abrasive Blasting
Many facilities have reduced their reliance on
chemical-based strippers by converting to abrasive
blasting. Abrasive blasting uses mechanical energy
to hurl particles at high speed, removing paints
and other organic coatings from metallic and
nonmetallic surfaces (Freeman, p. 704).
Abrasives commonly used for stripping include'
steel grit, alumina, garnet, and glass beads. Steel
gritcreates a rough surface profile on the substrate
which aids coating adhesion. Because it is so hard
and durable, steel grit can be reused repeatedly,
and it generates the least amount of waste per unit
of surface area stripped. To maximize the reuse of
steel grit, companies must keep the blast media
dry to avoid rusting. Alumina is considered to be a
multipurpose material that is less aggressive and
less durable than steel grit, and it results in a
smoother surface profile and less removal of
substrate material. Garnet and glass beads are the
41
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Chapter 5: Surface Preparation
least aggressive abrasive and often are used in a
single-pass operation (i.e., the abrasive is not
recycled). Use of garnet and glass beads is most .
suitable for preparation of soft materials that are
easily damaged, and for maintenance of the
dimensional tolerance of the part (Freeman, p.
490-491).
Types of Abrasive Blasting
Companies can use abrasive blasting to remove
paint from larger metal structures in the field (field
stripping) or from smaller metal structures in a
hanger, booth, or blasting cabinet.
Field stripping can be performed in an open
area. Operators must wear self-contained breath-
ing equipment in order to be protected from the
stripping dust. After blasting, the used abrasive
can be shoveled or vacuumed from the area and
processed through the reclaimer. Some systems
combine dust control and abrasive recovery by
including a vacuum collection pickup device with
the blasting nozzle (Freeman, p. 490-491).
Blast stripping in cabinets is often performed
using manual blast cabinets and automated
blasting chambers to remove paint from parts.
'The abrasive is fed into the cabinet or chamber
and directed against the part being stripped. Used
abrasive and removed paint are then pneumati-
cally conveyed to a reclaimer. Reusable abrasive is
separated from the waste and fines (broken-down
abrasives and paint chips) are collected in a dust
collector (Freeman, p. 490-491).
Process Optimization
Because the main advantage of chemical-based
strippers is their inability to scratch or damage the
substrate, most of the abrasives that companies
consider as feasible substitutes are relatively soft
materials. Glass-bead blasting has become popular
because it is the least aggressive of the commonly
used abrasives. New alternatives include plastic
media, wheat starch, ice crystals, carbon dioxide
pellets and sodium bicarbonate slurry (Freeman,
p. 490-491). The major disadvantage with these
processes is that they can only be used for line-of-
sight stripping.
Plastic media blasting
Plastic media blasting (PMB) is an abrasive
blasting process designed to replace chemical
paint-stripping operations and conventional sand
blasting. This process uses soft, angular plastic
particles as the blasting medium. PMB is .per-
formed in ventilated enclosures such as small
cabinets (a glove box), a walk-in booth, a large
room, or airplane hangers. The PMB process
blasts the plastic media at a much lower pressure -
(less than 40 psi) than conventional blasting. PMB
is well suited for stripping paints, because the low
pressure and relatively soft plastic medium have a
minimal effect on the surfaces beneath the paint
(TSPPO).
Plastic media are manufactured in 6 types and a
variety of sizes and hardness. Military specifica-
tions (MIL-P-85891) have been developed for
plastic media. The specifications provide general
information on the types and characteristics of
plastic media. The plastic media types are:
Type I Polyester (T-hermoset)
Type II Urea formaldehyde (Thermoset)
Type 111 Melamirie formaldehyde (Thermoset)
Type IV Phenol formaldehyde (Thermoset)
TypeV Acrylic (Thermoplastic)
Type VI Polyallyl diglycol carbonate (Thermoset)
Facilities typically use a single type of plastic
media for all of their PMB work. The majority of.,
DOD PMB facilities use either Type II or Type V
media. Type V media is notas.hard as Type II
media and is gentler on substrates. Type V media
is more commonly used on aircraft. Type II is
better suited for steel-only surfaces (TSPPO).
After blasting, the PMB media is passed through a
reclamation system that consists of a cyclone
centrifuge, a dual adjustable air wash, multiple
vibrating classifier screen decks, and a magnetic
separator. In addition, some manufacturers
provide dense particle separators as a reclamation
. system. The denser particles, such as paint chips,
are separated from the reusable blast media, and
the reusable media is returned to the blast pot.
Typically, media can be recycled 10 to 12 times
before becoming too small to remove paint
effectively (TSPPO).
42
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Chapter 5: Surface Preparation
Waste material consists of blasting media and
paint chips. The waste material may be classified
as a RCRA hazardous waste, because of the
presence of certain metals (primarily lead and
chrome from paint pigments). An alternative
solution to handling the potential hazardous waste'
is to recycle the media to recapture the metals.
progress in accordance with OSHA requirements
as specified in 29 CFR 1910.94 (TSPPO).
PMB systems can range in cost from $7,000 for a
small portable unit to $ 1,400,000 for a major
facility for aircraft stripping.
Vacuum Sanding Systems
Reusing the plastic blasting media greatly reduces A vacuum sanding system is essentially a dry-
the volume of spent media generated as compared abrasive blasting process (e.g., sand blasting or
to that generated in sand blasting. When compared plastic media blasting) with a vacuum system
to chemical paint stripping, this technology
eliminates the generation of waste solvent. PMB'is
also cheaper and quicker than chemical stripping.
The U.S. Air Force and airlines have found PMB
effective for field stripping of aircrafts, but PMB
could also be used to strip vehicles, ships, and
.engine parts (IHWRICf). However, PMB can
cover fatigue cracks at high blast pressures and
prevent their detection. ,
As with any blasting operations, airborne dust is a
safety and health concern with PMB. Proper
precautions should be taken to ensure that person-
nel do not inhale dust and particulate matter.
Additional protective measures should be taken
, when stripping lead chromate- or zinc chromate-
based paints, as these compounds may be hazard-
ous. Inhalation of lead and zinc compounds can
irritate the respiratory tract, and other paint
compounds are known to be carcinogenic. Inhala-
tion of paint solvents can irritate the lungs and
mucous membranes. Prolonged exposure can
affect respiration and the central nervous system.
Operators must wear continuous-flow airline
respirators when blasting operations are in
attached to the blast head that collects the blast
media and the removed coating material (paint or
rust). The unit then separates the used blast media
from the removed coating material. The remaining
blast material is recycled for further use, and the
coating material is disposed. ' , '
This system is designed to replace chemical paint
stripping, and has three added advantages. The
first advantage is its collection of both the blasting
media (sand, PMB, or other media) and its .
collection of the waste coating material being
removed. The second advantage is that it sepa-
rates the media from the waste material by a
reverse pulse filter, and the media is reused in the
system, thereby minimizing the quantity of media
required. The third advantage is that, due to the
confinement of the blast material, this technology
may be used when it is impractical to use tradi-
tional sand blasting or chemical stripping
(TSSOP).
Vacuum sanding is a stand-alone system, including
the air compressor to drive the system. The units
are portable (skid, mounted) and can be moved by
Table 9. Advantages and Disadvantages of Plastic Media Blasting
Advantages
Disadvantages
* Can be recycled for use (10-12
.recycling events) ,
Eliminates wastewater disposal costs (typical
in chemical paint-stripping operations)
Eliminates production of waste solvents when
compared to chemical paint stripping
Has a high stripping rate '
Has no'si'ze limitations
^Requires substantial capital equipment investment
*May generate hazardous waste
*May require different operator time, maintenance
requirements, and handling and disposal methods
' for waste depending upon material stripped
*May limit quality depending on skill and
experience level of the operator
*May not be used in certain military applications
because of limits in specifications'
* May not remove corrosion
43
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Chapter 5: Surface Preparation
a forklift. The air compressor is a trailer unit (2-
wheeled). The waste material may be classified as
a RCRA hazardous waste because of the presence
of metals in the waste (TSSOPj.
This technology reduces pollution because the
portable vacuum sander removes coatings and
corrosion from composite or metal structures
while capturing the media and solid waste.
Vacuum sanding eliminates airborne particulate
matter and potential lead-dust exposure hazards.
When compared to chemical paint stripping, this
technology eliminates the generation of waste
solvent (TSSOP).
Storage and handling of sand or plastic media and
blast waste- associated with vacuum sanding pose
no compatibility problems. Collection systems
should not mix different types of waste, and
should ensure that the most economic disposal
method can be obtained for each. Prior to using
plastic media for de-painting operations, personnel
should check applicable military specifications
[such as (MIL-P-85891)] and operations manuals
for the PMB systems. Some military specifica-
tions do not allow PMB for de-painting certain
types of materials (e.g., fiberglass, certain Com-
posites, honeycomb sandwich structures, and
some applications with thin-skinned aircraft
components). In certain cases, PMB can inhibit
crack detection on softer alloys used for aircraft
components (e.g.; magnesium) (TSSOP).
Airborne dust, which is an important safety and
health concern with any blasting operation, is
essentially eliminated using the vacuum blasting
system. However, in order for the vacuum system
to be effective, the vacuum and blasting head
must be kept in contact with the material being
stripped of paint or corrosion. Therefore, training
operators in the proper use of the equipment is
essential. In addition, eye protection and hearing
protection are recommended (TSSOP).
Vacuum sanding systems can range in cost from
$ 17,000 to $40,000, excluding the portable
generator to operate the system.
Sodium Bicarbonate
Sodium bicarbonate is another media that compa-
nies can use to remove paint. The process that
Table 10. Advantages and Disadvantages of Vacuum Sanding Systems
Advantages
Disadvantages
* Improves personnel safety by eliminating
airborne particulate matter and potential
lead dust exposure hazards
* Eliminates the need for the use of respirators
while blasting
* Separates waste material from blasting media,
therefore, the media can be recycled
« Is versatile and can use multiple media types
« Eliminates wastewater disposal costs (typical in
chemical paint-stripping operations)
* Eliminates the production of waste solvents
when compared to chemical paint stripping
* Can be portable
*Has self-supplied power/air compressor
* Minimizes emissions from portable (mobile
source) diesel air compressors so no air
permit required
» Minimizes the clean-up time because blast
material is contained
* Contains contaminated coatings
* Requires substantial capital equipment
investment
* Requires disposal of used blasting materials
and waste coating as a hazardous waste
4 Requires operator training .
+May vary operator time, maintenance
requirements, and handling and disposal
methods depending upon material to be
stripped
* May vary quality of stripping depending on
skill and experience level of the operator
44
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Chapter 5: Surface Preparation
uses sodium bicarbonate cart be used with or
without water. However, it is most frequently
applied with water, which acts as a dust suppres-
sant. The water-based process uses a compressed
air delivery system that transfers the sodium
bicarbonate from a pressure pot to a nozzle^
where the sodium bicarbonate mixes with a stream
of water. The soda/water mixture impacts the
coated surface and removes old coatings Trom the
substrate. The water dissipates the heat generated
by the abrasive process, reduces the amount of
dust in the air, and assists in paint removal through
hydraulic action. Workers do not have to prewash
or mask the surface of the material being stripped.
The solid residue from the wastewater generated
can be' separated by filtration or settling (NFESC).
/ ' ' '
The effectiveness of sodium bicarbonate stripping
depends on optimizing a number of operating
parameters such as nozzle pressure, standoff
distance, angle of impingement, flow rate, water
pressure, and traverse speed. In general, sodium
.bicarbonate stripping systems remove paint more
slowly than chemical stripping. The type of
equipment used may also bring about significantly
different results,
i ' " " -
Use of sodium bicarbonate in its dry form (or
when it is not fully mixed with water) can create a
cloud of dust that requires monitoring and may
require containment to meet air-quality standards.
The dust is not an explosive hazard nor is it toxic,
but air particulates generated from stripping
operations can contain toxic elements. This
process should be conducted in areas where
.exhau'st particulates can be contained and/or .
ventedto ventilation systems to remove hazardous
airborne particulates.
Approximately 150 to 200 pounds of bicarbonate
is needed per hour, while PMB requires 800
pounds. In the end, bicarbonate is,cheaper than
PMB because it neither generates large amounts
of waste nor damages the metal. Nevertheless,
sodium bicarbonate can have long-term corrosive
effects because alkaline compounds that remain
on the metal can foster corrosion or interfere with
the paint bonding. Corrosion inhibitors can be
added; however, the waste .might then become
hazardous, depending on the type of inhibitor used
(IHWRICf).
Wastewater disposal methods and sodium bicar-
bonate waste disposal methods will dependpn the,
toxicity of the coatings and pigments that are
removed in the stripping process. The waste
generated from bicarbonate of soda stripping
systems in the wet form is a slurry consisting of
sodium bicarbonate media, water, paint chips, and
residues such as grease and oil. Some facilities are
using centrifuges to separate the water from the
contaminated waste stream, reducing the amount
of hazardous waste. Filtered wastewater contain-
ing dissolved sodium bicarbonate may be treated
at industrial wastewater treatment plants. In its dry
form, the waste includes nuisance dust, paint
chips, and residues of grease and oil. This waste
may be disposed of in a solid waste landfill;
however, due to the possibility of toxics in the
paints and the presence of oils, the material should
be tested prior to landfill disposal (NFESCa, p.4).
Wheat starch blasting . :
Wheat starch blasting is a user-friendly blasting
process where wheat starch.is used in systems
designed for plastic media blasting, as well as
systems.specifically designed for wheat starch
blasting. The wheat starch abrasive media is a
crystallized form of wheat starch that is nontoxic,
biodegradable, and made from renewable re-
sources. The media is similar in appearance to .
plastic media, but it is softer (TSSPO). >
The wheat starch blasting process propels the
media at less than a 3 5 psi nozzle pressure for
most applications. The low pressure and relatively
soft media have minimal effects on the surfaces
beneath the paint.' For this reason, wheat starch is -
.well suited for stripping paints without risking
damage to the substrate. Examples of suitable
applications include removing paint from alumi-
. num alloys and composites like graphite and
fiberglass (Kevlar).
The wheat starch blasting process can remove a
variety of coatings: Coating types range from
resilient rain ero^ionrresistant coatings found on
radar absorbing materials to the tougher polyure-
thane and ep'oxy paint systems.'The wheat starch
system has been shown to be effective in remov-
ing bonding adhesive flash .(leaving the metal-to-
metal bond primer intact), vinyl coatings, and
sealants. It has also been found to.be effective in
45
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Chapter 5: Surface Preparation
Table 11. Advantages and Disadvantages of Sodium Bicarbonate (NFESCa p. 4)
Advantages
Disadvantages
* Significantly reduces the amount of hazardous
waste generated when compared to chemical
stripping
* Reduces the number of hours required for
stripping when compared to chemical
I stripping
Selectively removes individual coating layers
Does not require prewashing and masking in
most applications
* Avoids size limitations for parts being stripped
Enables wastewater stream to be centrifuged
to reduce waste volume or to be treated at an
industrial wastewater facility
* Reduces costs because blast media is usually
less expensive than plastic media, wheat
starch, and carbon dioxide pellets
* Requires subsequent washing of the item; thus
electrical components cannot be exposed to this
stripping process
* Although the water can be separated for
" disposal, cannot recycle sodium bicarbonate
solution
* May require monitoring
* May require containment
removing the paint from cadmium parts, while
leaving the cadmium plating intact (TSSPO).
Wheat starch blasting is mainly known for its
gentle stripping action and is particularly suited for
stripping operations on soft substrates,, such as
aluminum, very soft alloysj anodized surfaces, or
sensitive composites.
There are several important components in wheat
starch systems. First, a moisture control system is
needed to control the storage conditions of the
medium. This is especially important when the
" system is shut down for extended periods of time.
Second, to remove contaminants from the wheat
starch media, the spent wheat starch residue is
dissolved in water and then either filtered or
separated in a dense particle separator/centrifuge.
The wheat starch media is recycled in the system
and may be used for up to 15 to 20 cycles. Low
levels of dense particle contamination in the media
may result in a rough surface finish on delicate
substrates. The waste stream produced from this
process consists of sludge generated from the
wheat starch recycling system. This system
produces approximately 85% less waste sludge '
compared to the waste sludge produced in chemi-
cal stripping (TSSPO).
Wheat starch blasting can be used on metal and
composite surfaces. Direct contact of wheat starch
with water must be avoided to maintain the
integrity of the blast media. Wheat starch blasting
requires explosion protection. If conditions are
right, a static electrical charge developed by a high
velocity wheat starch particle in the air could ignite
the material. Preventive measures must be taken.
As with other blasting procedures, airborne dust is
a safety and health concern. Proper precautions
should be taken to ensure that personnel do not
inhale dust and particulate matter. Additional
protective measures should be taken when
stripping lead, chromate, ziric chromate, or .
solvent-based paints, as these components may be
hazardous. Inhalation of lead and zinc compounds
can irritate the respiratory system and some
compounds are known to be carcinogenic. Inhala-
tion of paint solvents can irritate the lungs and .
mucous membranes. Prolonged exposure to these
emissions can affect respiration and the central
nervous system. Proper personal protective
equipment should be used (TSSPO).
Capital costs for wheat starch blasting systems
vary depending upon the application. A PMB
system for a small application can be modified for
a cost of approximately $10,000: An automated,
closed, dust-free system for a large application
(e.g., aircraft) can cost up to $'1.5 million. The
operating costs for wheat starch blasting systems
46
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Chapter 5: Surface Preparation
Table 12. Advantages and Disadvantages of Wheat Starch Blasting (TSSPO)
Advantages
Disadvantages
4\'s biodegradable '
<»Can treat in a bioreactor
Lowers waste volume to an estimated 5%
of original volume
* Can be used for removing coatings from both
metallic and composite materials
+ Is easily controlled . -
* Can be used to selectively remove from one to
all coating layers - .
* Does not cause fatigue to the substrate surface
4> Can achieve moderate stripping rates while
maintaining a gentle stripping action
* Is safe on'soft-ciad aluminum-
* Has inexpensive .and non-toxic material
* Eliminates water use
ho size limitations on parts being stripped
* Has high capital'invesfment cost ""'
+ Requires complex subsystems for media
recovery and recycling and dust collection
and control . _:.'
^Requires operator training - .
*May result in a rough surface finish on delicate
substrates if low levels of dense particle
contamination exist
*May require high disposal costs
4 Typically slow to moderate stripping rate
* Requires operators to wear personal
protective equipment . . '
require an air dryer for humidity control
have been estimated to be 50% less than those for
chem ical paint stripping (such as methylene
chloride)!
Carbon dioxide
Carbon dioxide (CO2) blasting is an alternative
^process to chem.ical cleaning and stripping. The
obvious advantage of GO2 blasting over chemical
stripping is the introduction of inert media that
dissipates, in this case CO2. There are two basic
types of CO, blasting systems: pellet blasting for ,
heavy cleaning and snow blasting for precision
cleaning.- . . " ,
CO2 Pellet Blasting .
. CO, pellets are uniform in shape and the effec-
tiveness of the pellets as a blast medium is similar
to abrasive blasting. However, the pellets do not
affect the substrate; therefore, CO2 pellet blasting
is technically not an abrasive operation. This
process can be used for cleaning, degreasing,.
some de-painting applications,-surface preparation,
and de-flashing (flashing is the excess material .
formed on the edges of molded parts).
' The process starts with liquid CO2 stored under
pressure (-850 psig). The liquid CO, is fed to a
. pelletizer, which converts the liquid into solid CO2
snow (dry ice flakes), and then compresses the
dry ice flakes into.pellets at about -110°F. The
pellets are metered into a compressed air stream
and applied to a surface by manual or automated
cleaning equipment with specially-designed
Blasting nozzles. The CO2 pellets are projected
onto the target surface at high speed. As the dry
ice pellets strike the surface, they induce an
extreme difference in temperature (thermal shock)
between the coating or contaminant and the
underlying substrate, weakening the chemical and
physical bonds between the surface materials and ,
f/ie substrate. Immediately after impact, the pellets
begin to sublimate (i.e., vaporize directly from the
solid phase to a gas), releasing CO2 gas at a high
velocity along the surface to be cleaned'. The high
velocity-is caused by the extreme difference in
density between the gas and solid phases. This
kinetic energy dislodges the contaminants (e.g.,
. coating systems and flash), resulting in a clean
surface. Variables that facilitate process optimiza-
tion include the following: pellet density, mass
flow, pellet velocity, and propellant stream tem-
perature.
C02.pellet blasting is effective in removing some
paints, sealants, carbon and corrosion deposits,
_ grease, oil, and adhesives, as well as solder and
flux from printed circuit board assemblies-. Fur-
thermore, because CO, pellet blasting is not an
abrasive operation, it is excellent for components
'with tight tolerances. This process also provides
excellent surface preparation prior to application
of coatings or adhesive and is suitable for most .
47
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Chapter 5: Surface Preparation
metals and some composite materials. However,
thin materials may be adversely affected. Blasting
efficiency is approximately equal to that of other
blasting operations. CO2 blasting can be done at
various velocities: subsonic, sonic, and even
supersonic. Therefore, equipment noise levels are
high (between 95 and 130 dB). This operation
always requires hearing protection.
Waste cleanup and disposal are minimized be-
cause only the coating or contaminated residue
remains after blasting. No liquid waste is created
because CO2 pellets sublimate to CO2 gas. They
pass from a liquid to a gaseous state, leaving no
spent media residue. With regard to air pollution
control, small quantities of coating particles are
emitted to the air. A standard air filtration system
should be utilized.
CO2 Snow Blasting
In contrast to CO2 pellet blasting, CO2 snow
blasting is a low impact process. This process
applies primarily to precision cleaning. A typical
precision cleaning operation must clean small
contaminant particles that, due to electrostatic
attraction, attach to surfaces and/or surface layers
of adsorbed moisture or soil. These particles are
so smalt that a large fraction of their surface area
attaches to the surface layers. CO2 snow blasting
is mos.t effective in breaking the adhesive forces
and dislodging particles from the substrate surface.
Small flakes of dry ice transfer their kinetic energy
to submicron particulate contaminants and then
sublimate; lifting the particulate matter from the
substrate surface as the adhesive bonds are
broken. This process is often used as a final
cleaning process for submicron particulate re-
moval and light soils removal.
CO, snow is generated from liquid CO2, and is
discharged directly front the nozzle of the blasting
device. The liquid CO2is partially vaporized as it
passes through the nozzle, while the rest of the
stream solidifies as pressure is reduced. The fine
particles of "snow" are propelled by the fraction
of CO, that vaporizes. No compressed air or other
inert gas is needed to propel the snow.
Many of the blasting media described in the
previous sections cannot be used in precision
cleaning because either they are too aggressive, or
they contaminate the component with media
residue. CO2 snow, however, is ideal for this
application because it is relatively gentle in appli-
cation, leaves no media residue, is highly purified,
and does not introduce new contaminants. CO2.
snow blasting is often done in a clean room or
cabinet purged with nitrogen to provide a dry
atmosphere, minimizing moisture buildup on the
component (TSSOP).
As a completely oxidized compound, CO2 is a
nonreactive gas, and thus is compatible with most
metals and nbnmetals. Dry ice processes are cold
and can cause thermal fracture of a component. In
addition, prolonged use in one spot will cause
condensation and ice buildup. However, this is
rarely a problem for CO2 blasting because it is a
fast-acting, nonstationary process. Particulate and
organic contamination is either quickly removed or
unable to be removed by continued blasting.
Therefore, the component temperature does not
change much, because contact time is short.
Nevertheless, should component temperature drop
below the dew point of the surrounding atmo-
sphere, moisture will accumulate on the compo-
' nent. This problem can be mitigated by heating
the component in some manner so that its tem-
perature remains above the surrounding
atmosphere's dew point after blasting. If compo-
nents cannot take heat, then blasting can be done
in an enclosed space purged with a dry gas to
lower or eliminate the dew point problem
(TSSOP).
CO2 does not support combustion and it is
nontoxic; however, it is an asphyxiant. CO2 will
displace air because its density is greater than that
of air, causing CO2 to accumulate at the lower
level of enclosed spaces. When blasting with CO2
pellets, additional ventilation should be provided
for workers in enclosed spaces. Companies should
also require use of personal protection equipment
(PPE) when blasting (TSSOP).
Static energy can.build up if grounding is not
provided. CO2 blasting should not be done in
flammable or explosive atmospheres. High-
pressure gases should be handled with great care.
Companies should always chain or secure high-
.pressure cylinders to a stationary support such as
a column.
48
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Chapter 5: Surface Preparation
CQ2 Pellet Blasting:
1. Units come in several different configura-
tions. ' . ' ',,-_''
2. The'blasting.unitcanbe purchased. Prices ;
' range from $25,000 to $50,000.
3. The blasting unit can also be rented.
Monthly payments range from $ 1,500 to
$2,500.
,4. Units that combine pelletizing and blasting
are also available, but generally are not'
economical unless the blasting operation is
performed 24 hours/day, 7 days/week.
5. Pellet blasting jobs can,be done on a
contract basis for a cost between $200 to
$300 per hour including labor, pellets,
and equipment (not including travel time
or'travel expenses). '
6. A stand-alone pelletizer can be purchased
for between $50,000 to $ 130,000
(the cost to make pe.llets. from delivered
liquid carbon dioxide is about $0.10 to
0.15/lb), '..
"Purchased directly from a manufacturer for between
$0.10 and $0.50/lb delivered, depending on the purify
and the distance from the manufacturer (pelletizer
purchase is reported to be economical only if blasting is
done more than 40 hours/week). (TSPPO)
CO2 Snow Blasting:
Units'are much lower in cost and operation as'
compared to CO2 pellet blasting, and again
there are several different configurations to
choose from: . = > '
1 . All manual units'cost about $2,000.'
2.. Semi-automated units, which can also be
used in assembly applications, cost
' between $3,000 and $5,000.
3. For the highest quality of precision clean-
sing with substantial volume requirements,
CO2 purifiers are also available. Units .
that can purify commercial grade liquid
:. CO2 start at about $5,000. (TSPPO) -.-
Sponge Blasting
Sponge blasting systems are a class of abrasive
blasting that uses (1) grit-impregnated foam and
(2) nonabrasive blasting media using foam without
grit. These systems incorporate various grades of
water-based urethane-foam cleaning media. Firms
use the nonabrasive media grades to clean delicate
substrates.. The abrasive media grades are used to
remove surface contaminants, paints, protective
coatings, and rust from a variety of surfaces. In
addition, the abrasive grades can be used to
roughen concrete and metallic surfaces. A variety
of grit types are used in abrasive media including
aluminum oxide, steel, plastic, or garnet (TSPPO).
The foam cleaning medium is absorptive and can"
be used either dry or wet with various cleaning
agents and surfactants to capture, absorb, and
remove a variety of surface contaminants such as
oils, greases, lead compounds, chemicals, and
radionuclides. The capability.of using the foam
cleaning medium in a!wet form provides for dust
control without excessive dampening of the
/surface being cleaned. The equipment consists of
three transportable modules, which include .the
feed unit,-the classifier unit, and the wash unit
(TSPPO).
The feed unit is pneumatically powered for.
propelling the foam cleaning medium. The unit is
portable and produced in several sizes. A hopper,
mounted at the top of the unit, holds the foam
medium. The medium is fed into a metering ,
chamber that mixes the foam cleaning medium
with compressed air. By varying the feed-unit air
pressure and type of cleaning medium used,
sponge blasting can remove a range of coatings
from soot on wallpaper to high-performance
protective coatings on,steel. and concrete surfaces -
(TSPPO). "'.'".
The classifier unit removes large debris and
powdery residues from the foam medium after
each use. The used medium is collected and
placed into an electrically-powered.sifter. The
vibrating sifter classifies the used medium with a
stack of progressively finer screens. Coarse
contaminants, such as paint flakes and rust
particles, are collected on the. coarse' screens.
The reusable foam medium is collected on the
corresponding screen size. The dust and finer
particles fall through the sifter and are collected
for disposal. After classifying, the reclaimed foam
medium can be reused immediately in the feed
unit. The abrasive medium can be recycled
approximately six times and the nonabrasive -
49
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Chapter 5: Surface Preparation
Table 13. Advantages and Disadvantages of Carbon Dioxide Blasting
(TSPPO)
Advantages
Disadvantages
* Significantly reduces the amount of hazardous
waste and hazardous air emissions generated
compared to chemical stripping.
* Reduces the time required for cleaning/
stripping processes by 80 to 90%
* Leaves no residue on the component surface
* Is effective in precision cleaning
* Introduces no new contaminants
* Is not always a one-pass operation; an effective
blasting operation usually requires multiple
passes to achieve the desired effect
* Requires operator training
* Can have high capital costs
* Can damage the components surface in
fixed position blasting operations
» Generates solid waste containing coating chips
that are potentially hazardous; media does not
add to the volume of solid waste
* May carry coating debris that can contaminate
workers and work area ,
*Mdy redeposit some coating debris on substrate
* Can increase workers fatigue in non-automated
systems because of cold temperature, weight/
arid thrust of the blast nozzle
+ Can increase potential hazards from
compressed air or high velocity CO2 pellets
medium can be recycled approximately 12 times
(TSPPO).
During degreasing applications, the foam medium
must be washed every 3 to 5 cycles. The washing
of the foam medium takes place in the wash unit,
which is a'po'rtable centrifuge, closed-cycle
device. The contaminated wash water is collected,
filtered, and reused within the wash unit
(TSPPO).
Thjs system removes paint, surface coatings, and
surface'contaminants' from a variety of surfaces.
Waste streams produced from this system include:
coarse contaminants, such as paint flakes and rust
particles; dust and finer particles; and the concen-
trated residue from the bottom of the wash unit.,
This technology helps prevent pollution for two
reasons: the stripping media can be recycled (i.e.,
every 10 to 15 events), and the quantity of
wastewater that is typically generated using
conventional methods (e.g., chemical stripping) is
greatly reduced. -Sponge blasting systems are
compatible in most situations where other types
of blasting media have been used.
As with any blasting operations, airborne dust is a
safety and health concern. Proper precautions
should be taken to ensure that inhalation of dust
and particulate matter is avoided. Additional
protective measures should be taken when
stripping lead chromate- or zinc chromate-based
paints, as these compounds may be hazardous.
Inhalation of lead and zinc compounds can irritate
the respiratory tract, and some compounds are
known to be carcinogenic. Proper personal
protective equipment should be used.
High- and Medium-Pressure Water Stripping
High- and medium-pressure water blast systems
are used for paint stripping surfaces with low-
volume water streams at pressures ranging from
3,000 to 15,000 psi (medium-pressure opera-
tions), and 15,001 to 55,000 psi (high-pressure.
operations). These systems remove paint by
spraying a stream of high-pressure water at the
surface of the part. The advantages of this process
include a readily available medium (water), an
easily treatable waste stream, and an absence of
fume and hazardous-waste production. A disad- ,
vantage of this process is the necessity for an
automated system that usually uses robotics.
Robotics is required for application due to the
50
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Chapter 5: Surface Preparation
Table 14. Advantages and Disadvantages of Sponge Blasting Systems
(TSPPO)
Advantages
Disadvantages
* Is safer for operators compared to other':
blasting media and chemi'cal stripper systems
* Is1 easily transportable .. ,
> Achieves waste minimization by recycling the'
sponge media (i.e., can recycle sponge media
an average of 10 to 15 times)
* Absorbs and removes contaminants
* Reduces dust generation
« Costs are more expensive than sand blasting
media . " '
> Requires reasonably large capital investment
extremely high pressure of the water stream
(Freeman, p, 491).
Medium-pressure systems may be augmented. For
example, sodium.bicarbonate may be added to the
water stream, or environmentally compliant
chemicals may be applied to painted surfaces prior
to water blasting. High-pressure systems typically
use pure water streams. With both medium- and
high-pressure water systems, specialized nozzles
can be used to achieve varying effects. A rela-
tively gentle, layer-by-layer process may be used
for removal of organic paints versus the use of a
different nozzle for the removal of metal flame
spray coating and other tough, tightly adherent.
coatings! The process water, paint, and residue are
collected by an effluent-recovery system that.
filters the paint and residue. The recovery system
removes leached ions (e.g., copper, cadmium, and
lead), microparticulates, chlorides, sulfates,
nitrates, and other contaminants from the water.
The water is then passed through a coalescing
tank for removal of oils and film, then through
charcoal filters, microfilters, and finally, a deion-
ization system to ensure that the water is Grade A
deionized water. The recovered deionized water is
recycled back into the process (TSSOP).
No material compatibility problems have been
documented for use of high- and medium-pressure
water processes to de-paint metallic surfaces. The
. use of specific chemicals to augment medium-
pressure water processes must be evaluated on a
case-by-case basis. The automotive industry
.currently uses high-pressure water jets to remove
paint from the floor of painting booths
(IHWRICf). . . .,-
The capital costs for high- and medium-pressure
water processes vary considerably depending on
the process and its application. Capital costs for
medium-pressure systems range from $40,000 to
$70,000, and capital costs for high-pressure
"systems range from $850;QOO to $1,500,000.
Fluidized Bed Stripping .
The fluidized bed paint removal process is an
alternative method to chemical paint stripping and
degreasing of nonaluminum and nonheat sensitive
metal parts. In fluidized bed stripping, an air
stream is pumped into a tank of quartz sand or
aluminum oxide, making it a fluid. Natural gas is
mixed with the air and ignited above the tank,
creating temperatures of approximately 800°F.
Objects to be stripped are lowered in a basket into
the tank. The paint is vaporized, and the gases
and unburned natural gas are burned in a
postcombustion chamber above the^ank. A wet
scrubber removes the solids from the final exhaust
before it is vented into the air. The;most notable
advantage of this process is that it produces no
solvent wastes. This method works for steel parts
but not for aluminum parts (IHWRICf). Technical
assistance providers should not recommend the
fluidized bed paint stripping (FBPS) process for
use with aluminum and aluminum alloy parts
because these materials lose essentially all of their
hardness or temper when exposed to the 700 to
, 800°F process temperatures (TSSOP).
The FBPS process typically consists of the
following four components: 1) fluidized bed
furnace'or retort, 2) fluidized bed cooling system,
3 ) off-gas treatment system cons isting of a
cyclone, afterburner and :scrubber, and 4) low
51
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Chapter 5: Surface Preparation
Table 15. Advantages and Disadvantages of a Water Blasting System
(TSPPO)
Advantages
Disadvantages
4- Reduces hazardous.waste by 90%
* Selectively removes individual coating layers
* Does not need pre-washing, and masking is not'
needed in most applications
* Are no size limitations for parts being stripped
* Generates wastewater stream that is compatible
with conventional industrial wastewater plants
located at many installations
* Has low implementation cost utilizing simple
robust equipment
* Reduces the process material costs significantly
« Reduces labor hours for the stripping process
by 50%
4 Generates no dust or airborne contaminants
* Requires-no cleanup after stripping
* Has high capital costs
* Removes one layer at a time
+ May not remove corrosion
* Must consider the substrates to be, removed
for impact on personal protection and
waste collection/disposal
* Generates a potential hazardous
waste stream
* Requires review of wastewater disposal
requirements for toxicity of the coating
being removed
* Must protect employees from direct
impingement of water jet
* Requires operator training
*Can damage joints, seals, and bonded
areas &y. water penetration
^-Requires additives to the water that may
have an adverse effect (i.e., flash rusting) on
the surfaces being cleaned
* Has variable stripping rates from differ-
ences in type of paint, coating condition and
coating thickness
energy shot-blast unit. The fluidized bed furnace
or hot bed is where pyrolysis of the coatings takes
place. A granular material, aluminum oxide
(alumina) in most cases, is used as a heat-transfer
medium. Air passing through the bed keeps the.
medium fluidized. Parts to be cleaned are lowered
into the fluidized bed, which quickly heats the part
and its surface coatings (e.g., paint, grease, and
oil) to a temperature at which organic components
of the surface material pyrolyze into carbon.
oxides, other gaseous combustion products, and
char. The fluidized bed cooling system, or cold
bed, is used to cool the parts after the organics
have been pyrolyzed. Carbon monoxide and
volatiie organic compounds (VOCs) generated
during pyrolysis are burned in the afterburner. The
thermal decomposition of paint leaves some
carbon and inorganic char on the part. Most of the
char may be removed in the fluidiz'ed bed; how-
ever, most parts require further cleaning before
they can be repainted. The shot-blast unit is used
to remove the inorganic coatings and char to
prepare the parts forrepain.ting (TSSOP).
This process removes and destroys paint and
grease from nonaluminum or nonheat sensitive
materials. Waste streams from this process include
spent heat-transfer medium, spent blast media,
exhaust air from the afterburner and scrubber,
water discharge from the scrubber, and dust from
the cyclone separator. The heat-transfer medium,
. blast media, and.cyclone dust contain metals from
the stripped paint. .. .
Assistance providers should also inform facilities
that this blasting method requires employees to
wear equipment to protect them from toxics in the
paint. For example, inhalation of lead and zinc
chromate paints can lead to irritation of the
respiratory tract; some lead compounds are
carcinogenic; solvent-based'paints-can irritate the
lungs and mucous membranes; and prolonged
exposure can affect respiration and the central
nervous system.
52
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Chapter 5: Surface Preparation
Costs for fluidized bed paint strippers can range
from $7,000 for a small parts stripper to $800,000
for ah industrial scale stripper. ..'.-.
Other Methods
The methods that follow can also be used to strip
old paints from metal parts. . ,
High-energy Light. High-energy light uses-
optically directed beams of photon energy emitted
by lasers or flash lamps (typically xenon lamps) to
ablate the paint. Using high-energy light to remove
paint decreases operating cost, minimizes the
waste stream, and lowers the possibility of
material damage. The disadvantages of this
process are its high capital cost and precision
robotics requirements (Freeman, p. 490)
Cryogenic Methods. Cryogenic methods
generally use liquid nitrogen immersion at approxi-
mately r200°F, which causes the paint to contract,
breaking the adhesive bond with the substrate. For
small components, a tumbler design normally is
used, where the parts can impact and abrade each
other to assist in removing the paint. If the parts
have complex shapes, tumbling media might be
added (Freeman, p. 491). Cryogenic stripping has
a harder time removing epoxy and urethanei
coatings than other coatings. Also, this stripping
method removes thick coatings more efficiently
than thin coatings. In addition, this method may
^ damage or distort parts because of the extreme
temperatures needed in the process (IHWIRCf).
High-temperature Thermal Methods.
High-temperature thermal methods, such as
burnoffovens and molten salt baths, are some-
times used to strip paint. In general, these meth-
ods are labor intensive, and result in emissions of
burned paint and metal surfaces that are fouled^
by heat scale. This heat scale, subsequently, must
be removed by abrasive methods,.such as
sanding or wire brushing. Most thermal methods
are limited to heavy metal parts that will not warp
because of thermal expansion and distortion
(Freeman, p. 490). In burnoff ovens, the ovens
simply burn off the paints. This method is limited
to steel parts (IHWRiCf).
Molten salt baths remove paint easily from metal.
Baths that are only 500 to 700°F significantly
reduce any problems with heat distortion. Objects
to be stripped are lowered into the salt bath",
removed, rinsed with water, lowered in dilute acid,
and immersed in water agajn. Care must be taken
in stripping aluminum parts; leaving the parts in
the bath for more than 60 seconds could, soften
the metal and make the parts unusable. Also, salt
can solidify or get trapped in an area that cannot
be thoroughly rinsed, causing corrosion at a later
time(IHWRICf).
Burnoff ovens and molten salt baths often are
» used to remove paint overspray from hooks,
racks, grates, and body carriers used in automo-
tive plants. Stripped parts are left with a residue of
ash, which can be removed by rinsing (Freeman,
p. 491). ..'--./
Table 16. Advantages and Disadvantages of Fluidized Bed Stripping (TSPPQ)
Advantages
Disadvantages
,* Leaves practically no waste.paint residue,
thus eliminating significant waste sludge
disposal costs.as well as avoiding the future
liability associated with the hazardous
components of the'paint sludge
+ Uses an inert medium to clean parts of any
shape, size, or geometry which are coated
with any type of paint; the rapid changes in
coating technology do not affect the
' performance of the system
* Provides cleaning to the bare metal
O Is not suitable for removal of paint from
aluminum and aluminum alloy parts
* Is not suitable for parts with crevices, channels,
or cavities (e.g. engine blocks) that would
retain FBPS media and be difficult to clean
after treatment
« Has little or no effect on corrosion'removal
»May require secondary cleaning to remove
char and inorganic coatings from parts
« May generate more waste than a caustic
stripping system
53
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Chapter 5: Surface Preparation
Table 17. Overview of Alternative Surface Preparation Technologies (EPAh, p. 7-
10, EPAi, p. 5-6, 24, EPAg, p. 7-9 and IHWRICf)
;
Technology
Cleaning
Aqueous
Cleaning
'
Ultrasonic
Cleaning
Supercritical
Fluids
<
Vacuum
De-oiling
Laser Ablation
'ollution
Prevention
Benefits >
Reported
Application
Operational
Benefits
Limitations
* Eliminates solvent
use by using
water-based
cleaners
+ Eliminates solvent
use by making
aqueous cleaners
more effective
4>Nonpollutingwhen
CO2 is used as the
supercritical fluid .
* Eliminates solvent
use for cleaning
* Eliminates solvent
use for cleaning
» Used to remove
light oils and
residues left by
other cleaning
processes
* Used to remove
heavy oils, greases,
and waxes at
elevated temp-
eratures
* Cleaning of ceramic,
aluminum, plastic
and metal parts,
electronics, glass-
ware, wire, cable
and rods
* Precision cleaning
. of stainless steel,
copper, silver,
porous metals, and
silica
* Removal of oils
from metals
* Cleans metallic or
nonmetallic surfaces
^Cleaning
performance
changes with
concentration and
temperature, so
process can be
tailored to
individual need
+ Cavitate Using
ultrasonics
*Can clean in small
crevices '
* No solvent residue
left on parts
* Low operating
costs
* Low operating costs
+ Does not leave the
cleaned parts water-
soaked, therefore
parts do not need to
be dried
* Localized cleaning
* May generate
significant amounts
of hazardous
wastewater
*Some acids can
cause hydrogen
embrittlement . .
* High capital cost
* Parts must be"
able to withstand'
the required
' . temperature and.
vacuum pressure
VHigh capital costs
* Adjustments might
be needed for
each application
because the time
and temperature of
the de-oiling
process depends
on the material to
be, cleaned and the
oil to be removed
'
' ' 1
(continued on next page}
54
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Chapter 5: Surface Preparation
Table 17. Overview of Alternative Surface Preparation Technologies (EPAh, p.
7-10, EPAi, p. 5-6, 24, EPAg, p. 7-9 and IHWRICf) '(continued)
Technology
Pollution
Prevention
Benefits
Reported
Application
/
Operational
Benefits
Limitations
Stripping
Abrasive
Blasting
High-energy
Light
, ^Lasers
+Flash lamps
Cryogenic
Stripping
High-pressure
Water
Thermal
Stripping
* Fluidized bed
stripping
* Molten salt
baths
* Burnoff ovens
* Eliminates solvent,
use in stripping
* Eliminates solvent
use in stripping
* Eliminates solvent
use in stripping
* Eliminates solvent
use in stripping
+ Water can be
processed and
recycled during
stripping, reducing
wastewater volume
+ Eliminates solvent .
use in stripping
* Removes thick
coatings from
a variety of .
coating line
fixtures and tools
'* Fluidized- bed
stripping and
molten salt baths
, can be used only
on steel parts .
* Blast substitutes
available: plastic
media, sodium bi-
carbonate, carbon
dioxide, and wheat
starch
+ Lovv chance of "
material damage
*High stripping rate
/ " '
*Can process
complex shapes
* Harder materials
can damage
metals
= f
* High capital costs
^Precision robotics
required
* Does. not remove
epoxy or urethane
coats as well as
other types.
* Does not remove
thin coats as well
as thick ones
* Extreme tempera-
tures can damage
or distort parts
* Misapplied water
jet may damage ,
substrate
* Blasting generates
high noise levels
* Water can enter
cavities penetrat-
ing and/or
damaging joints,
seals, and bonds
* Fluidized bed-'
stripping cannot .
be used on
aluminum
55
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Chapter 5: Surface Preparation
56
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6
Alternatives to
Solvent-Borne Coatings
The majority of conventional coatings are
solvent borne, traditionally containing about
25% solids and a relatively high organic solvent
content. These materials generally have been
applied with conventional air spray, which uses
compressed air at high pressures to atomize paint,
a technique known as low-volume/high-pressure
(LVHP). LVHP and other application techniques
are discussed in chapter 7. This chapter covers the
composition of conventional metal coatings, low-
to-no solvent alternatives, and lower toxicity
alternatives. The US EPA's Coatings Alternative
Guide (CAGE) (available via the Internet at http://
cage.rti.ofg) is a helpful tool for assistance provid-
ers to use in identifying specific alternative
coatings for facilities.
Conventional Paint
Composition
The major components of paints and coatings are
solvents, binders, pigments, and additives. In
paint, the combination of the binder and solvent is
referred to as the paint"vehicle." Pigment and
additives are dispersed within the vehicle
(IHWRIC, p. 2). The amount of each constituent
varies with the particular paint, but solvents
traditionally make up about 60% of the total
formulation. Binders account for 30%, pigments
for 7 to 8%, and additives for 2 to 3% (KSBEAP,
p. 4). '_:.
'^Solvents are added to coatings to disperse
the other constituents of the formulation and to
reduce viscosity, thereby enabling application
of the coating. A wide variety of solvents are
used in paints, including aliphatic hydrocar-
bons, aromatic hydrocarbons (toluene, xylene,
and the tri methyl benzenes), ketones (methyl
ethyl ketone (MEK) and methyl isobutyl ketone
(MIBK)), alcohols, esters, and glycol ethers
''.. {IHWRIC, p. 5).
A Few Words About Solvents
A solvent is typically selected based on its
ability to dissolve binder components
(resins), and its evaporation rate. Its ability to
dissolve binder components is often referred
to as solvent power. Combinations of -.
different solvents are often found in paint
formulations. The most widely used solvents :
are toluene, xylene, MEK and MIBK.
* Toluene will dissolve a large number of
resins. Toluene is miscible with drying oils
like linseed oil or king oil that are often
used in oil-based paints and with most
other solvents.
*Xy/ene has high solvent power with a
wide range of resins'and a high rate of
evaporation. As a result, xylene is widely
used in both heat-cured and rapid air-
drying coatings.
> MEK. and MIBK are solvents used with a
wide range of resins. MIBK is extensively
used in both heat-cured enamels and
lacquers (EPA, p. 154-155).
Solvents are a major source of environmental
concern because at normal temperatures and
pressures they, can volatilize (i.e., the liquid
solvent becomes a vapor). Exposure to these
solvent vapors is dangerous for a number of
reasons. In the workplace, solvent vapors can
result in a number of human health risks. Table 18
presents information on the health effects of
solvents used in paint formulations. Solvent
vapors also can pose fire/explosion hazards,
necessitating careful storage and handling proce-
. dures. ;
When solvent vapors arereleased, they emit
volatile organic compounds (VOCs) and hazard-
57
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Chapter 6: Alternatives to Solvent-Borne Coatings
Table 18. Health Effects of Solvents Used in Paint Formulations0 (EPAe)
Solvents Used
in Paint
Formulations
Health Effects
Toluene
The central nervous system (CNS) is the primary target organ for toluene toxicity in both
humans and animals for acute (short-term) and chronic (long-term) exposures. CNS
'dysfunction (which is often reversible) and narcosis have been frequently observed in
humans acutely exposed to low or moderate levels of toluene by inhalation; symptoms
include fatigue, sleepiness, headaches and nausea. Cardiac arrhythmia has also been
reported in humans acutely exposed to toluene.
>CNS depression has been reported to occur in. people chronically exposed'to high levels of
toluene. Symptoms include ataxia; tremors; cerebral atrophy; nystagmus (involuntary eye
movements); and impaired speech, hearing and vision. Chronic inhalation exposure of
humans to toluene also causes irritation of the upper respiratory tract, eye irritation, sore
throat, nausea, skin conditions, dizziness, headache and difficulty with sleep.
> None of the available data suggest that toluene is carcinogenic. Two epidemiological
studies did not detect a statistically significant increased risk of cancer due to inhalation .
exposure to toluene. However, these studies had many confounding factors. Animal studies
have also been negative for carcinogenicity. EPA has classified toluene as not classifiable
as to human carcinogenicity.
Xylene
* Acute (short-term) exposure to mixed xylenes in humans results in irritation of the nose and
throat; gastrointestinal effects such as nausea, vomiting, and gastric irritation; mild
transient eye irritation; and neurological effects.
* Chronic (long-term) inhalation exposure of humans to mixed xylenes results primarily in
central nervous system (CNS) effects, such as headache, dizziness, fatigue, tremors and
incoordination. Other effects noted include labored breathing and impaired pulmonary
function, increased heart palpitation, severe chest pain and an abnormal EKG, and
possible" effects on the blood and kidney.
> Insufficient data are available on the developmental or reproductive effects of mixed
xylenes on humans. Animal studies have reported developmental effects such as an
increased incidence of skeletal variations in fetuses and fetal resorptions via inhalation.
>No information is available on the carcinogenic effects of mixed xylenes in humans, and
animal studies have reported negative results from exposure through gavage (experimen-
tally placing the chemical in the stomach). EPA has classified mixed xylenes as not
classifiable as to human carcinogenicity. . .
Methyl Ethyl
Ketone
* Acute (short-term) exposure to methyl ethylketone in humans, via inhalation, results,in.
irritation to the eyes, nose and throat; and, central nervous system depression.
No information is available on the developmental or reproductive effects of methyl ethyl
ketone in humans. Reduction of fetal development and fetal malformations has been
reported in mice exposed to methyl ethyl ketone in the air.
Limited data are available on the carcinogenic effects of methyl ethyl ketone. No human
data are available and the only available animal study did not report skin tumors from
dermal exposure to methyl ethyl.ketone. EPA has classified methyl ethyl ketone as not
classifiable as to human-carcinogenicity. .
These solvents are nonha/ogenated hydrocarbons; that is, they do not contain chlorine or related elements. Nonhalogenated hydrocarbon
solvents are often used in paint formulations as well as in surface preparation and equipment cleaning. Ha/ogenated hydrocarbons are hydrocar-
bon solvents that contain one or more of the halogens (i.e., fluorine, chlorine, bromine, iodine and astatine). Examples include tnchloroetnylene
(TCE), perchloroethylene (PERQ, 1,1, Hrichloroethane (TCA), carbon tetrachloride, methylene chloride (METH) and CFC-1 13. The halogenqted
hydrocarbon solvents are preferred foryapordegreasing operations because their flashpoints are in a higher range than those of the.
nonhalogenated solvents; therefore, they are usually not ignitable. However, halogenated solvents, in general, are more toxic to humans and
capable of causing greater environmental damage (IWRC, p. 13-14). . '
58
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Chapter 6: Alternatives to Solvent-Borne Coatings
ous air pollutants (HAPs) into the atmosphere.
VOCs combine with nitrogen oxides in the pres-
ence'of sunlight to form ground-level ozone.
Ground-level ozone is a precursor to smog, a
major pollutant in urban and industrial areas.
Smog poses a number of human health risks to
respiratory function, particularly among persons
with asthma or allergies.
+ Binders are liquid polymeric or resinous
materials that are used in coatings to hold the
pigment and additives together, to provide
adhesion, and to enable the coating to cure
into a thin plastic film, The binder provides the
working properties of the'coating and deter-
mines the performance of the film, including
flexibility, durability and chemical resistance
(EPA, p. 152-154). Most binders are named
for their main resin. The resins most commonly
used in paints and coatings are natural oils or
vegetable oils, alkyds, polyesters, arhinoplasts,
phenolics, polyurethanes, epqxies, silicones,
acrylics, vinyls, cellulpsics and fluorocarbons
(SME, p. 26-3-4). See "A Few Words About
Binders" for more, information.
A '
V Pigments are insoluble particles of organic
or inorganic materials (either natural or
synthetic) that are dispersed in a C9ating in
order to confer color and opacity to a sub-
strate, or to improve the substrate's envirph-
'.mental resistance and the flow properties of
the paint. The type of pigment in the paint
. . determines the color and color stability of the
paint or coating, while the amount of pig-
ment determines the gloss, hiding power and
permeability of the coating (EPA, p. 1.52-.
1 54). Inorganic pigments have high thermal
stability and ultraviolet light stability. Organic
pigments are ^brighter and clearer than
inorganic pigments (KSBEAP, p. 5).
Many pigments still contain lead, chromium,
cadmium, or other heavy metals. These paints
cannot be disposed of in a landfill and must be
handled as a hazardous waste because the heavy
metals can leach out of latidfills and contaminate
' groundwater. Production of paints containing
these heavy metals is being phased out due to
their toxicity (KSBEAP, p.5). EPA banned the
production of certain paints containing lead and
A few Words About Pigments
The four commonly recognized classes of .
pigments are:"colored pigments; white
pigments, which include the primary and .
extender pjgments; metallic pigments; and
functional pigments, which provide corrosion
resistance, antifouling protection, slip .
resistance or other desired properties.
Colored pigments are available in both
inorganic and organic compounds (SME, p.
26-9). Inorganic pigments have high thermal
stability and ultraviolet (UV) light stability.
Organic pigments are brighter and clearer
than inorganic pigments (KSBEAP, p: 5).
Examples of each type follow: .
'4 Colored pigments: red/yellow/black iron
oxide, blue/green phtalocyanine and
gilsonite
« White pigments: lithopone and titanium
'. dioxide
> Metallic pigments: yemniculite (texture),
flake aluminum (sparkle/metallic appear-
.. ance), and titqnid and surface-modified
talc (pearlescence)
> Functional pigments: limestone and clay
(fillers); barium metaborate (preservatives
against mold, mildew or bacteria);
lithopone and zinc sulfide (UV stabilizers);
nickel/copper/silver powders and barium
titanate (conductive ability); and carbon
black, silica, Attapulgus clay and fibers
(reinforcement) (Athey, p. .59)
mercury several years ago. However, some-
facilities may still have these paints in use if they
purchased the paints prior to the phaseout..
* Additives are materials that improve the
physical and chemical properties of the
coating; Additives include surfactants, colloids
and thickeners, biocides and fungicides,
freeze/thaw stabilizers, coalescing agents,
defoamers, plqsticizers, flattening ag«nts, flow
modifiers, stabilizers, catalysts and antiskinnihg
agents (SME/p. 26-13). A coating's character-
istics can change significantly depending on .
which-additives are included.
59
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Chapter 6: Alternatives to Solvent-Borne Coatings
A Few Words About Binders
Binders are chosen based on what physical and chemical properties are desired of the finished film. In
general, metal coatings are dominated by alkyds; however, water-based acrylics, epoxies, polyure-
thanes and polyesters also are used for certain applications (MPCa, p. 34).
4Acry//cs and alkyds contain suspended polymer particles. These materials produce a shiny, hard
finish that has good weather resistance. Alkyds are made from chemically modified vegetable oils
and are relatively low in cost. They are easily modified in order to change the properties of a paint.
They also can react with other chemicals in the curing process to change the finish. In ambient
conditions, they react with oxygen to form cross-linked films, making them functional for a wide
variety of applications. Because of the versatility and moderate cost, they are considered "general
purpose paint" (KSBEAP, p.4). Both acrylics and alkyds are widely used for farm equipment and
industrial products that require good corrosion protection at a moderate .cost. Silicone modification
of these resins improves overall weatherability and durability. These finishes are often used on space
heaters, clothes dryers and barbecue grills.
4 Urethanes combine high gloss and flexibility with chemical and stain resistance. They are also
characterized by toughness, durability and corrosion resistance. They require little or no heat to cure.,
These materials usually cost 2 to 5 times more than other paints so they are often used in applications
where high performance justifies the cost (KSBEAP, p.4). Typical uses are on conveyor equipment,
pircraft radome's, tugboats, road-building machinery and motorcycle parts.
Urethanes are produced by a reaction between isocyanate and alcohol. The components can be
mixed in a "pot" priorto application or can be mixed in the atomizing portion of the spray gun.
Once mixed, urethanes have a limited "pot life," which is the amount of time the components can be
mixed before crosslinking occurs. Often, pot life can be adjusted to meet process requirements;
typical ranges available commercially are a few minutes to 16 hours (KSBEAP, p.5).
4 Epoxies provide excellent water and chemical resistance. They have better adhesion to metal
substrates than most other materials. Epoxies are attractive economically because they are more
effective'against corrosion in thinner films than most other finishing materials. They are often used
as primers under other materials that have good barrier properties but marginal adhesive charac-
teristics. They can be formulated in a variety of ways, from one-component formulations requiring
elevated temperature curing to two-component systems that cure at or below ambient tempera-
ture conditions. Epoxies lose their gloss from ultraviolet exposure but the damage is rarely struc-
tural (KSBEAP, p.4).
^Polyesters, are similar to alkyds in chemical structure but require heat to cure. They are used exten-
sively in powder coatings. Polyesters, such as Nylon 11, provide an attractive appearance as well as
protection from chemicals, abrasion and impact. Nylon coatings are used on office and outdoor
furniture, hospital beds, bending machine parts and building railings. Heavier coats can be used to
protect dishwasher baskets, food-processing machinery, farm and material-handling equipment, and
industrial equipment such as pipes/fittings and valves (MD, p. 703-704).
' + Ofher Binders, such as silicones have high heat resistance and superior resistance to. weather and
water. They are used alone or blended with acrylics or alkyds. Vinyls are another binder that can
have a wide range of flexibility. They are used extensively in marine applications, interior metal can
liners (e.g., polyvinylchloride), or structural wood finishes (e.g., polyvinylacetgte) (KSBEAP, p.5).
60
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Chapter 6: Alternatives to Solvent-Bome.Coatings
Switch to Surface-
Free Coating
Many manufacturers are finding that they can
eliminate unnecessary paints and coatings that are.
used only for appearance. Ijfotpnly does this
reduce capital, operating and maintenance costs, it
also reduces potential liability from toxic chemical
use (EPA, p. 1-59). The use of injection-molded
. plastic sheets in place of painted metal cabinets in
the electronics industry is one example of this
trend (Freeman, p. 485). Manufacturers that are
considering product redesign to eliminate unneces-
sary coatings must consider the substrate and its
characteristics without a coating. If the coating is
needed to provide an engineering function, such as
improved corrosion resistance, one option may be
to change to a base material that does not require
a coating (EPA, p. 160). Currently available
materials that are free of surface coats include
plastics, aluminum, titanium and other .metals. \
Other materials that are under development for a
wide range of industries include: cement-bonded
particle boards, pultruded products from fiber-
glass-reinforced plastic, uncoated metals, weath-
CA5E STUDY:
Chrysler Corporation
The Chrysler Corporation's manufacturing-
plant in Belvidere, Illinois, ho longer needs -
to apply zinc-rich primers to car bodies:
Chrysler now uses galvanized metal (zinc-
plated) instead,* a move that has saved the
company $7,000 per year and eliminated
nearly 1 50 gallons of waste paint. Chrysler
also has begun to use more waterborne
paints in its production lines.
^Savings
Chrysler estimates that its pollution preven-
tion efforts so far have saved the company
$350,000,
*Althbugh substituting galvanized metal might
reduce the amount of VOGs generated, a lifecycle
analysis could reveal that zinc plating produces a
number of other wastes. If a company chooses to
purchase galvanized metals from outside firms,:they
could simply be passing along a different pollution
burden to their supplier rather than achieving
pollution prevention. ' .' (IHWRICd)
ering steel and polymer film coatings (TORI, p.
2>-'. '' " :' - ; .
Alternative Coatings
The primary advantage of conventional solvent-
borne paints is their versatility. However, due to
the low solids content of conventional solvent-
borne paints, a high volume of paint is required to
supply a small amount of coverage. In addition, ,
because the paint solvent is highly atomized along
with the paint solids in LVHP application, VOC
emissions are high (MnTAP, p. 3-4), See figure 3 .
for more information.
Vendors have developed a number of alternative
coating technologies. Environmental compliance
remains the principal driver for the development
of new technologies (Tilton). These new technolo-
gies include:
* High-solids coatings - .
> Waterborne coatings ; ' .
. * Powder coatings
+ Radiation-cured coatings '. .
> Emerging technologies such as vapor perme-
' atioh of injection coatings and supercritical
carbon dioxide
These^coating alternatives can reduce emissions of
VOCs and, in so doing,- reduce the generation of
hazardous wastes and decrease worker exposure
to toxic air emissions (EPAd, p. 1-5). Each of the
alternatives is discussed on the following pages.
Generally, the P2 alternatives are not one-to-one
substitutions. In some cases, an alternative
requires a process change using a specific applica-
tion and/or curing method (e.g., powder coating).
Alternatives also can raise other issues (e.g., less
solvent in the coating generally requires more
thorough surface preparation). For an overview of
alternatives to solvent-borne coatings, see table
19. Firms should consult with coatings suppliers
for more detailed information on product -offer-
ings, as a number of hybrid technologies and
different chemistries have recently been intro- '
duced (Tilton).
The relationship between emissions and VOG
content, though obviously direct, is not linear; in
other words, the transfer efficiency of the applica-
tion method also can have a significant impact on
61
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Chapter 6: Alternatives to Solvent-Borne Coatings
Figure 3. Emissions versus VOC Content (EPA-450/2-77/008)
Solvent content
of original
coating (Ibs/gal)
12 3 4 5
Pounds of solvent per gallon
of replacement coatings (less water)
solvent density = 7.36 Ibs/gal
the amount of VOCs emitted. This issue is
explored in chapter 7 (Falcone, p. 35).
High-Solids Coatings
General Description
High-solids coatings have a higher percentage of
paint solids and a lower percentage of solvent
carriers than conventional solvent-borne coatings
(MnTAP, p. 4). EPA defines high-solids paints as
systems with volatile organic contents of less than
2.8 pounds per gallon. Paints with more than 85%
solids content by weight are also generally referred
to in the coatings industry as high-solids paints. In
practice, paints with a solids content of 60 to 80%
can be called high-solids paints per EPA's defini-
tion, especially if the equivalent solvent-borne
paint contains more than 50% solvent (EPA, p.
162).
modified so that it has a much lower intrinsic
viscosity than binders of conventional solvent-
borne paints. To overcome performance limita-
tions, additives often are used to increase
crosslinking during curing (EPAd, p. 15). The
binders in high-solids paints include alkyd resins,
polyester resins, polyurethanes, acrylic resins,
epoxy resins and poly vinyl chloride plastisols.
Nondrying alkyd resins crosslinked with melamine
during heat curing are often used for industrial
coatings (EPA, p. 162-163).'
Advantages and Disadvantages
Because high-solids coatings contain less solvent
than traditional formulations, VOC and HAP
emissions are reduced in this process (e.g., up to
50%, in some cases) (VT DEC). High-solids
paints also provide higher layer thicknesses per
application cycle than conventional coatings,
resulting in a savings in time. Despite past issues
with viscosity, today's high-solids paints can be
applied with conventional spray equipment (EPA,
p. 162-163). However, surface preparation of the
substrate remains a critical issue. This is because a
To achieve solids contents exceeding 70%, the
binder in a high-solids paint must be chemically
1 For more information see, "High So/ids, Low VOC, So/venf-hased Coatings," by Ron Joseph; part of the Metal Finishing
Special: Organics Finishing Guidebook and Directory that provides detailed information on the advantages/disadvan-
tages of specific resin types.
62 ' :
-------
Chapter 6: Alternatives to Solvent-Borne Coatings
Table 19. Overview of Alternatives to Solvent-Borne Coatings (EPAd, p. 12
andKSBEAP, p. 12)
Technology
High-Solids"
Waterborne
^ ' '
\ ' i
L -. - ,
Pollution
Prevention
Benefits
* Reduces solvent
in coatings (low
- voq,_ .
* Has less over-
spray compared
to conventional
coatings
'-. ' ' . .
>Eiiminatesor
reduces solvent
in coating (little
ornoVOC)
> Uses water for
cleanup
.
. ' -. .
Reported
Application
* Zinc-coated
steel doors "
* Miscellaneous
metal parts
+ Same as
conventional
coatings
i .
4 Wide range
4 Architectural
trade finishes,
* Wood furniture
* Damp concrete
' e
Operational
Benefits
*Gan apply thick
orthin'coat
* Has easy color
blending or
changing
4 Is compatible
with conventiona
and electrostatic
equipment
* Can apply thick
orthin'coat
* Has«asy color
blending or
changing
* Is compatible
with conventional
and electrostatic
application
equipment
>
-
Limitations
* Does not eliminate
solvent completely
+ Has shorter pot life
than conventional
coatings -
4 Must be heated
v ' '
. '
4 Has coating flow
properties and drying
rates that can change
With humidity, affect-
ing coating
application
* Is sensitive to humidity;
workplace humidity
control required
4 May have poor flow
characteristics 'due to
high surface tension of
water
* Needs special equip-
ment for electrostatic
application
4 Has water in paint that
can cause corrosion of
storage tanks and ,
- transfer piping, and
"flash rusting" of metal
' substrates
(continued on next ptige)
63
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Chapter 6: Alternatives to Solvent-Borne Coatings
Table 19. Overview of Alternatives to Solvent-Borne Coatings (EPAd, p. 12
and KSBEAP, p. 12) (continued)
Technology
Powder
Radiation-
cured
Pollution
Prevention
Benefits
^Eliminates solvent
in coating (no.
VOC) in most
cases
^Reduces solvent
in cleanup
^Reduces need for
solid paint waste .
disposal
* Eliminates solvent
in coating (no
VOC)
*ls 100%
reactive liquid
,
Reported
Application
+ Steel
^Aluminum
*Zinc and- brass
castings
* Some metal
applications
* Filler for
chipboard
+Wood
>" Wet look"
finishes.
.,
Operational
Benefits
* Can apply thick
coat in one
application
+ Requires no
mixing or
stirring.
* Has efficient
material use
(i.e., nearly
1 00% transfer
efficiency)
* Can apply thin
coat
* Has easy color
blending or
changing
4- Has efficient
material use
(i.e., nearly
100% transfer
, efficiency)
Limitations
* Requires special"
handling of heated
parts
* Has electrostatic
application systems
that must be
electrically
conductive; complex
. shapes difficult fb.coal.
+ Needs special equip-
ment or extra effort to
make color changes
* Is difficult to incorpo-
'.rate metal flake
pigments
* Has styrene volatility
* Is typically best
applied to flat
materials
* Is limited te thin
coatings
*Has high capital
cost of equipment
+ Can have yellow
. color
"High-solids formulations do reduce solvent in the coating when compared with low-solids formulations. In many cases,
however, high-solids coatings represent the baseline for regulatory limits, and low-solids no longer comply. For this reason,
high-solids are considered the baseline for solvent content, and consequently do not have a reduced solvent content '
even though they qualify as a cleaner technology compared to traditional low-solids coatings.
smaller amount of solvent in the coating mixture
means a smaller amount will be available to clean
the substrate (TURIb, p. 9).
Types of High-Solids Coatings
High-solids coatings fit into 3 general categories:
air/force dry, baking and two-component.
Air/force dry coatings cure by exposure to
moisture or oxygen at temperatures less than
194*F. Alkyd resins are most common in air-dry
coatings. Air-dry alkyds are often termed oxidizing
of auto-oxidizing because they cure in air without
baking or the addition of a catalyst. However,
. low-temperature ovens can be used to speed cure.
The recent development of new acrylic resins has
resulted in a range of fast-drying high-solids paints
suitable for general metal finishing applications,-
both indoor and outdoor. These coatings are
inexpensive, offer excellent flow and drying
properties, good hardness, durability, color and
gloss stability, and do not suffer from air entrap-
ment or sagging (EPAd,.p.'16).
64
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Chapter 6: Alternatives to Solvent-Borne Coatings
Bake coatings predominately use acrylic and
polyester resins, although some alkyds and
modified alkyds.are also used. These resin
systems cure in an oven at high temperatures (350
to 400°F) to form a crosslinked film. Crpsslinking
agents, such as melamine-formaldehyde (MF) or
blocked isocyanates, are commonly used. MF
coatings are usually one-pack systems, catalyzed
by a strong acid, such a p-toluenesulfonic acid.
Latent of blocked catalysts are used for fast cure
and good pot life. Blocked isocyanates, such as
aliphatic polyisocyanates, are recommended for
coatings requiring superior weathering properties .
and resistance to yellowing (EPAd, p. 16-17).
In a fwo-componenf reactive liquid coating
system, two low-viscosity liquids are mixed just
before application. One liquid contains reactive
resins, and the other contains an activator or
catalyst that promotes polymerization of the resins
(NCP2P, p. 4). However, once the two compo-
nents are brought together, curing starts; therefore,
these coatings have very short pot lives after
mixing. Short pot life can be overcome by using a
twin-headed sprayer that is fed from two different
pots. This spray head can proportion the flow of
each component to achieve the desired ratio of
liquids. Thus, the two components mix both on
the way to the workpiece and on the workpiece
itself (VT DEC). ..
Two-component coatings cure at low tempera-
tures, and do not require heating in ovens
(MnTAP, p. 4). Epoxies and polyurethanes are the
most-common two-component systems. Epoxies
are the oldest form of high-solids coatings,
producing thick films for specialty applications.
Two-component polyurethane coatings are
suitable for use in the automotive and machine
tool industries because of their excellent resistance
to solvents, lubricants, cutting oils and other
chemicals However, polyurethane coatings do,
pose some health and safety concerns. For
example, polyisocyanates used as crosslinking
agents in polyurethane coatings can impair the
respiratory function, causing sensitization and in
some.cases, permanent lung damage (EPAd, p.
17-18).
Application Methods
High-solids coatings usually are applied by con-
ventional spray guns. Traditionally, the high
viscosity of high-solids coatings have made them
difficult to atomize, making it difficult to achieve a
uniform film thickness. Today, emerging formula-
tions are tending toward lower viscosities and,
therefore, easier spraying. These new formula-
tions might be based on new resin systems, or
additives that modify viscosity and rheology for
easier spraying (EPAd, p. 18-19). In addition, the
use of a heated spraying system can also reduce
viscosity (VT DEC). ,
Paint Heaters
If the viscosity of the paint needs adjustment
before it can be sprayed, companies generally thin
the coating with solvents. Using solvents for
thinning increases air emissions and requires the
purchase of additional materials. An alternative
method for reducing viscosity.is to use heat. The
benefits from the purchase of paint heaters can
include lower solvent use, lower solvent emis-
sions, more consistent viscosities and faster curing
rates (MnTAP, p, 3).
Most heaters are stainless steel and are placed
between the pump and spray gun. The heaters
work best on recirculating systems that return
heated material to the container when operators
are not spraying. These systems keep the tem-
perature and viscosity constant and avoid cooking
the material when spraying stops (MnTAPc, p. 6).
Markets
With the exception of two-component liquid
coatings, which are widely used for auto and
appliance painting (IWRCb, p, 26), high-solids
paints have not made the inroads that other
systems (such as powder coatings) have hi .
replacing conventional coatings in product coatings
applications. Particular problems have included
high viscosity, viscosity changes due to tempera-
ture variation, and storage stability, as well as the
control of film thickness and the drying character-
istics of the film (EPAd, p. 15). A variety of new
formulations, however, could mean increased
growth in a wider variety of markets.
65
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Chapter 6: Alternatives to Solvent-Home Coatings
New Developments
100% So/ids Coatings. Because these materials
are basically solids, their most distinguishing
feature is their viscosity. The 100% solids coatings
have a viscosity at room temperature that is
approximately 10 times greater than other paint
coatings. These materials are not formulated with
heavy metals, HAPs or added solvents. Further- .
more, once cured, they can be disposed of as
nonhazardous solid waste. Because 100% solids
coatings have very high viscosities, conventional
handling and application methods are ineffective.
Instead, mechanical agitation is needed to reduce
the viscosity of the coating, making it easy to
apply. Increasing the temperature can also reduce.
viscosity as these coatings are extremely heat
sensitive (e.g., an additional 20T can reduce
viscosity by.50%). Application techniques include
electrostatic spraying, airless application, roller
application and dip tanks. Using these methods the
material can be applied in thin layers, providing
excellent coverage of the painted object (APC, p.
1.12).
Cost and Implementation Issues
The high-solids coatings that are currently avail-
able are generally similar to low-solids coatings in
their application, curing and final film properties,
and the capital cost for application equipment is
approximately the same. The high-solids coatings
themselves are slightly more expensive; however,
pollution control costs may be lower. In addition,
a paint heater might be required (EPAd, p. 15-21).
In many cases, high-solids coatings represent the
baseline for regulatory limits, and conventional
solvent-based, low-solids coatings no longer
comply (EPAd, p. 12).
Waterborne Coatings
General Description
The term waterborne refers to coating systems
that primarily use water as the solvent to disperse
the resin (IHWRIC, p. iv). Usually, they contain
up to 80% water with small amounts of other
solvents, such as glycol ethers (TURI, p. 1). Most
regulations require waterborne coatings to have a
CASE STUDY:
Freightliner Truck Manufacturing
In 1989, Freightliner Truck Manufacturing's
plant in North Carolina substituted high-solids
paints for conventional solvent-borne coat-
ings. This increased transfer efficiency while
reducing VOC emissions and paint wastes by
30%.
* Savings
The substitution resulted in savings of $28,000
in paint purchases and paint disposal costs ,
(TURIb,p.9).
Table 20. Advantages and Disadvantages of High-Solids Coatings
(NCP2P, p. 2)
Advantages
Disadvantages
Reduces VOC and HAP emissions
* Reduces solvent use
Reduces inventory
Reduces fire hazards
Reduces number of spray applications to
achieve a given film thickness
Improves abrasion and mar resistance
Reduces environmental, safety and
odor problems
Compatible for use with conventional
spray equipment
Decreases energy costs associated with
reduced curing times
. 4 Generally requires high cure temperatures
* Is sensitive to inadequate cleaning of substrate
* Is extremely sensitive to temperature and humidity
* Is difficult to control film thickness
4 Has tacky overspray; difficult to clean
'» Might require paint heater in system
* Is difficult to control sagging
*Has narrow "time-temperature-cure" window.
* Cannot use dip or flow coating
*ls difficult to repair.
* Solvent use not completely eliminated
* Has shorter potrlife than conventional coatings
66
-------
VOC content of less than 3:5 pounds per gallon ,
'less water (EPAd, p. 47).,
Advantages and Disadvantages
In addition to reducing VOC emissions during.
application, waterborne coatings reduce risk of
fire, are easier to clean up (creating less hazardous
residues) "and result in reduced worker exposure to
organic vapors (EPAd, p. 46-52). However,
special equipment might be required for applica-
tion, as water in the formulation can cause
corrosion. For instance, water-based paints can
rust plain steel or attack aluminum; therefore,
application equipment must be constructed of a
' corrosion-resistant material such as 316 stainless
steel. Humidity, must .also be controlled to achieve
the best film formation"; a microprocessor-con-
trolled water-spray system is one method for
doing so (EPAd, p. 52), For more information on
other advantages and disadvantages.of waterborne
coatings, see the box at the end of this section.
Types of Waterborne Coatings
Almost all types of resins are available in a
waterborne version, including vinyls, two-compo-
nent acrylics, epoxies, polyesters, styrene-butadi-
ene, amine-solubilized, carboxyl-terminated alkyd
and urethanes (EPAd, p. 47-48). Waterborne
coatings are classified based on how the'resin is
fluidized (KSBEAP, p. 6). The three main types
.are:, water-soiuble/water-reducible (solutions),
water-dispersible/colloidal (dispersions) and
emulsions (latex) paints (the most commonly used
form) (TURI j. Within each category, physical
properties and performance depend on which ;
resins, are used (KSBEAP, p. 6).2
Water-solub/e paints are paints whose individual
molecules of water-soluble resins dissolve com-
pletely in waten Water-soluble resins are generally
produced via polycondensation or polymerization
reactions in an organic medium. As a result, they .
generally contain organic co-solvents like alcohols,
glycol ethers or other oxygen-containing solvents
. that are soluble or rniscible with water (organic
content less than 10 to 15%). Because of viscosity
anomalies, waterborne paints made with water-
. soluble binders have only about 30 to 40% solids
Chapter 6: Alternatives to Solvent-Borne .Coatings
content by weight. Resins include alkyds, polyes-
ters, polyacrylates, epoxies and epoxy esters.
Despite their sensitivity to water, water-soluble
paints have a high gloss and a high level of
corrosion protection, along with good pigment,
wetting and stabilization (EPA, p. 160).
Wafer-d/spersib/e paints, or colloidal coatings, are
paints that have small clusters of insoluble resin
particles that are suspended in water. Mechanical
agitation is sufficient to suspend the clusters
(KSBEAP, p. 7). Small amounts of organic
solvents (usually less than 5% by weight) are used
as coalescing agents that evaporate on drying,
Resins used in dispersion paints include vinyl
acetate copolymers, vinyl propionate copolymers,
acrylate-methacrylate copolymers, and styrerie-
butadiene copolymers and polymers (EPA, p. .
161). Colloidal dispersions are used mainly to coat
porpus materials such as paper or leather (EPAd,
P-'49). /. ' -
Emulsions, or as they are more commonly known,
latex paints, are similar to water-dispersibles.
However, resin clusters;in emulsions tend to be
larger, and an emulsifier is required to keep the
clusters in suspension (KSBEAP, p. 7). Emulsion
paints are manufactured using a variety of resins
including styrene-butadiene copolymers, poly vinyl
acetate (the most common), acrylics, alkyds and
polystyrene. Emulsion paints are widely used in
the architectural market segment (IHWRIC, p; 6).
The increased permeability of latex paints allows
these coatings to "breathe," reducing the chances
for blistering or peeling (EPA, p. 16-1).
Wafer-based alkyds may take longer to dry than
solvent-borne coatins, but the resulting coatings
have similar gloss, flow and leveling properties.
These coatings are extremely versatile because
they are thinned with water to almost any viscos-
ity. They can be applied with spray or dip applica-
tions and are among the least expensive VOC
compliant coatings (CAGE).
Application Methods
Application technology for waterborne coatings is
comparable to that of conventional solvent-borne
2 For more information on the advantages and disadvantages of each resin type see, "High-Solids, Low VOC, Solvent-
based Coatings," by Ron Joseph, part of. the Mefal Finishing Special: Organics Finishing Guidebook and Directory.
67
-------
Qupter 6: Alternatives to Solvent-Borne Coatings
Figure 4. Major Resin Fluidization Methods (KSBEAP p.8)
Solution
Paint
Individual separate
molecules
Emulsion
Paint
Large 'clustered*
groups of 50-75
molecules, each
coated with a layer
of emulsifying agent
Dispersion
Paint
Small 'clustered*
groups of 10-25
molecules
coatings. If a facility is using a water wash booth,
overspray is easily recovered and reused if colors
are appropriately segregated. Uncured waterborne
coatings can be cleaned from equipment with
water (TURI, p. 1).
Electrostatic spray can be used if the electrically
conductive waterborne paint is isolated from the
electrostatic system. Three methods can be used
to avoid grounding out the electrostatics in a
waterborne system. The facility can (1) isolate the
entire paint system from electrical grounds; (2)
isolate a small part of the wetted system with a
voltage blocking device; and (3) indirectly charge
the paint particles away from any wetted equip-
ment. Each method has its own advantages and
disadvantages and should be evaluated for the
specific application. The use of a voltage blocking
device at each atomizer is often the most cost-
effective method (EPAd, p. 51) (VT DEC).
Waterborne coatings can also be applied by
electrodeposition for corrosion resistance and
coating of hard-to-reach areas (TURI, p. 1).
However, some formulations or substrates might
require special pumps and piping to prevent
corrosion from water in the formulation. In '
addition, for product finishing, coatings need to
dry or cure at elevated temperatures to ensure
complete cure in a reasonable period of time.
Therefore ovens are required with this process
(EPAd, p. 52).
Markets
Waterbome coatings have quickly taken hold in
some product-coating market segments; for more
than two decades, copiers, fax machines, type-
writers, printers and computers have been painted
with various combinations of waterborne emulsion
and other coatings (McBree et al., p. 35). How-
ever, waterborne coatings have been less accepted
in market sectors with requirements that are
exceptionally high for appearance and engineering.
In recent years, however, the automotive OEM
sector has increased its use of water-based paints
and coatings in all but the heaviest coat applica-
. tions. An estimated 20% of this sector now uses
water-based paints, and that percentage is growing
each year. With improved water-based paint
technology, manufacturers have been able to
change from solvent-borne paint systems and
meet emissions regulations while maintaining their
ultrahigh finish standards (EPA; p. 162).
New Developments
Waferborne Two-Comp.onenf Technology. With
this new technology, coatings manufacturers can
formulate high-performance coatings without
cosolvents and achieve the same appearance,
properties and ease of use that manufacturers
have with the solvent-borne analogs. For example,
an epoxy curing agent for water-based epoxy
coating formulations has been designed for use
with solid epoxy dispersions. This epoxy curing
68
-------
Chapter 6: Alternatives to Solvent-Borne Coating-
agent provides corrosion resistance when used as
a primer in general metal applications (Iceman, p.
27). ' ''''".'
Cost and Implementation Issues
Waterborne coatings are more expensive than
conventional^coatings per unit of reactive resins.
In addition, the capital costs for application
equipment tends to be greater (e.g., stainless steel
is required to protect against corrosion in storage
tanks and transfer piping). However, water-based
coatings generally use less organic solvents,
reducing environmental and human health risks
(EPAd, p. 58-60). Technical assistance providers
should remember that, despite the use of water in
waterjrarne formulations, discharge of wastes
from coatings must still be in compliance with
federal and state wastewater discharge regulations.
Paint manufacturers, however, are developing
methods for recycling waterborne paints col-
CASi STUDY:
ESCO Elevators
ESCO Elevators is an elevator manufacturer
with 225 employees located in Forth Worth,
Texas. They identified a waterborne coating
that could reduce VOC emissions and
maintain production quality! To ensure that
the coating complied with all environmental
standards, ESCO asked the Fort Worth Water
Department to determine if the waste gener-
-ated by this coating could be discharged to
the city's sewer system. The waste was tested
and approved by the city; -which noted that
the waste helped balance the sewer system's
pH level. To ensure that dust generated from
the water-based paint could be disposed of
in landfills, ESCO also had to administer a
1C.L.R test for the paint dust.
* Savings
By substituting waterborne coatings for
solvent-based coatings, ESCO Elevators was
able to reduce its VOC emissions by 10,764
pounds per year. ESCO also saved between
$20,000 and $30,000 peryearby elimina-
tion of hazardous waste disposal costs.
Additional savings came from lower fire
insurance premiums and reductions in
reporting requirements for EPA (PPIFTI). -
CASE STUDY:
Metal Lab Furniture Manufacturer
This facility is a manufacturer of metah
laboratory furniture, including base cabinets,
wall cases and fume hoods. The facility
produces 3,500 units of furniture a year with
sales of $3,000,000 annually. Production
processes include punching, forming,
cleaning, phosphatizing and painting. Waste
streams generated by these processes
included solvent waste and paint sludge. The
facility implemented a switch from solvent-
based paints to qqueo'us-based paints to
minimize both the volume-ahd toxicity of their
waste streams. The company chose an
acrylic enamel paihtfor use that is not only
nonhazardous but has a longer shelf life
than conventional solvent-based paints.
* Savings -.'-.-.
Investments in this system included purchas-
ing electrostatic spray equipment and
| retraining operators. The enamel paint is .
more expensive than the solvent-based
paint, but because it can be dried at lower
temperatures the company has realized
savings in energy costs. The company has
also reduced its hazardous waste generation
by 75%, and because the paint has a longer
shelf life, less obsolete paint is disposed (VT
DEC).
lected from communities and industry (EPA, p.
162), ', . .,. -.
Powder Coating:
General Description
Powder coating uses 100% resin in a dry, pow-
dered form (MnTAP, p. 4). Powder coating works
on the principle that opposite charges attract. The
powder is pneumatically fed from a reservoir
through a spray gun where the powder gains a low
amperage, high-voltage positive charge. Parts to
.be painted are electrically grounded so that the
positively charged powder particles are strongly .
attracted to the parts' surfaces. The powder-
' coated part is then pulled through an oven where
69
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Chapter 6: Alternatives to Solvent-Borne Coatings'
Table 21. Advantages and Disadvantages of Waterborne Coatings
(NCP2P, p. 2)
Advantages
Disadvantages
Reduces VOC and HAP emissions
* Can use conventional application processes
Reduces toxiciry and odor, resulting in
improved worker safety and comfort
good storage life
* Is easy to clean up
* Minimizes or eliminates disposal of
hazardous waste. '
+ Has good to excellent surface properties,
including gloss, rub resistance, anti-sealing
effects and non-yellowing film
|+ Can recover and reuse some waterborne
paints, increasing transfer efficiency
* Some dried waterborne paint waste may be
disposed of in a landfill as non-hazardous
waste
* Has tendency to foam
Requires clean surface for high quality
application; surface must be free of oil and dust
+ Requires longer drying times or increased
oven temperatures
*Has difficulty obtaining high gloss finish
* Has difficult cleanup once coating is cured
+ Has great susceptibility to dirt pickup
+ Has higher cost per gallon on an equivalent
solids basis compared with conventional coating
*Does not have many resins available for
waterborne formulations
*ls complex to convert solvent-borne coating line,
i.e., stainless steel, plastic lines, valves and
other ancillary equipment are needed ,
*Has problems with atomization, i.e., reduced
paint transfer efficiencies
* Increases runs and sags
* Requires good temperature/humidity control
* Requires storage area enclosure and heating
(i.e., repeated freezing and thawing will damage
the coating).
* Is difficult to refinish .
* Has reduced temperature resistance
Can have poor penetration and adhesion proper-
ties, particularly with emulsion coatings on porous
surfaces'
the powder melts and fiases into a smooth coating
(IHWRICe). Substrates must generally be able to
withstand temperatures of 260T or higher (EPAd,
p-33).
the pomplete conversion of a coating line, which
can be costly. For more information on other
advantages and disadvantages of powder coating,
see table 23 at the end of this section.
Advantages and Disadvantages Types of Powder Coatings
Powder-coating materials can provide a high-
quality, durable, corrosion-resistant coating.
Powder coatings do not produce hazardous
overspray wastes or wastewater sludges, and most
' do not release VOCs when cured (some powder
coatings will release VOCs, such as caprolactam, a
former HAP). With powder coating, users can
collect the powder overspray and reuse it, result-
ing in transfer efficiencies of up to 99% (MnTAP,
p. 4). However, powder coating systems require
Product manufacturers can specify the properties
required in a finish (such as resistance to ultravio-
let light, high durability, corrosion resistance and
color) to a powder coating manufacturer who then
formulates the appropriate powder (HIWRICe).
Coating powders are frequently separated into
decorative and functional grades; decorative
grades generally have a finer particle size than
functional grades. Powders are also divided
between thermpset and thermoplastic resins
(EPA, p. 163-164).
70
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Chapter 6: Alternatives to Sotvent-Bome Coatings
Thermoset resins crosslink to form a permanent
film that withstands heat and cannot be remelted.
They are used for decorative and protective
coatings for architectural structures, on appliances
and furniture, and elsewhere. Thermosetting
resins are characterized by their excellent adhesion
to metal; they are one-coat systems and do not
requires primer (Farrelr, p. 81). The five basic
families of thermoset resins are epoxies, hybrids,
urethane polyesters, acrylics and triglycidyl
: isocyanurate (TGIC) polyesters as described
below:
* Epoxies are used for both functional and
decorative coatings. Their functional properties
, include outstanding corrosion resistance and
electrical insulation. Decorative epoxies offer
attractive finishes that are flexible, tough, and
have excellent corrosion-resistance and-high-
impact strength. However, these coatings lack
ultraviolet resistance and, therefore, are not
recommended for outdoor use. In prolonged
exposure to sunlight, they tend to chalk and
' discolor. Various types of hardeners are used
with epoxy powder to optimize its properties.
* Epoxy polyester hybrid coatings are mainly
used for decorative applications. They are
more resistant to chalking and over-bake . . .
' yellowing than pure epoxies, but have a lower
surface-hardness and; are I ess-resistant to
solvents. They exhibit better transfer efficiency "
.. and a greater degree of penetration into
recessed areas of a part than other resins.
* Urethane polyesters are formulated with
polyester hydroxyl resin combined with blocked
isocyanate hardeners. They exhibit outstanding
thin film appearance and toughness as well as
good weathering properties.
+Acry/ic-urefhane coatings are formulated with
acrylic resins crosslinked with blocked isocyan-
qtes. They have excellent color, gloss, hard--
ness, weatherability and chemical resistance,
.and have an excellentth'rn film appearance.
However, they are less flexible than polyesters.
. * TGIC polyesters contain a polyester resin
crosslinked with TGIC as a -curing agent.
They offer very good mechanical properties, .
impact strength and weather resistance. They-
a re'resistant to chalking and are often used
for outdoor parts, such as patio furniture,
lawn mowers, as well as aluminum extrusions
and panels for large commercial buildings. In
Europe, reduced occupational-exposure
limits were recommended for TGIC powders
as a result of in vivo mutagenjcify tests (EPAd,
P-28}. ; - . .
Thermop/asfic resins form a coating, but do not
undergo a change in molecular structure. These
resins can be remelted after they have been
applied. Thermoplastic powder coatings melt and
flow when heat is applied, but retain the same
chemical composition when they .are cool and
solidified (KSBEAP, p,: 10). Although Some
thermoplastic materials provide adhesion to metal,
.most require a primer (Farrell, p. 81). Thermo-
plastic resins are mainly used in functional coat-
ings, such as thick, protective coatings on
dishwasher trays. Examples of thermoplastic ' '
resins useci in powder coating are polyethylene,:
polypropylene, nylon, polyvinyl chloride (PVC),
and thermoplastic polyester. These examples are
described below:
* Po/yefhy/ene provides excellent chemical
resistance and outstanding electrical insulation
properties. These coatings are smooth, and
have a medium gloss and good release,
properties that allow sticky materials to be
cleaned from their surfaces. These are often
used as coatings for laboratory equipment.
* Po/ypropy/ene produces a surface that is very
inert and is often used in applications where
the part that is powder coated might be
exposed to chemicals.
VNy/on offers excellent abrasion, wear and "
impact resistance, and a low coefficient of
friction. Nylon is commonly used as a me-
chanical coating for sliding and rotating
bearing applications-in appliances, farm
equipment and textile machinery.
* PVC provides good durability as well as
flexibility; dishwasher trays are an example of
a product coated with PVC. .
* Thermoplastic polyester offers good exterior
durability and weatherability. The coating does
71
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Chapter 6: Alternatives to Solvent-Borne Coating
not usually require a primer for good adhe-
sion to most metals. These materials are
often used on outdoor metal furniture (EPAd,
p. 26 and PCI, p. 6-7).
See table 24 for a summary of powder coating
resin properties.
Application Methods
There are five powder coating processes: electro-
static spraying, fluidized bed, electrostatic fluid-
ized bed, flame spray, and tribocharge.
Electrostatic Spraying
The main method in use today for the application
of powder coatings is the electrostatic process. In
the electrostatic process, electrostatic spray guns
impart an electrostatic charge to the powder being
sprayed via a charging electrode that is located at
the front of the spray gun. This technique is called
"corona charging," and these guns generate a
high-voltage, low-amperage electrostatic field
between the electrode and the product being
coated. The charge on the electrode can be
controlled by the operator. Powder particles
become charged as they pass through the ionized
electrostatic field, which controls the deposition
' rate and the powder's location on the part. The
field can be adjusted to direct the powder's flow,
control pattern size, shape, and powder density as
it is released from the gun (KSBEAP, p. 14). The
particles are attracted and held to the grounded
substrate through electrostatic forces. The sub-
strate subsequently is heated in an oven, or
through chemical activation (e.g., by infrared), to
fuse the particles to the substrate and to each
other to create a continuous film (EPA, p. 164).
This method has made it possible to apply thin
layers of coatings for higher quality decorative
finishes, and has allowed powders to be used on
parts that should not be dipped in a fluidized bed.
Powder is supplied to the electrostatic spray gun
by the powder delivery system. This system
consists of a powder storage container, or feed
hopper, and a pumping device that transports a
stream of powder into hoses or feed tubes.
Compressed air is often used as a pump because
aids in separating the powder into individual
particles for easier transport. The powder
delivery system is usually capable of supplying
powder to one or several guns. Delivery systems
are used in many different sizes, depending on
the application, number of guns to be supplied,
and volume of powder to be sprayed in a given
time period. Recent improvements in powder
delivery systems, coupled with better powder
.chemistries that reduce clumping, have made
delivery of a consistent flow of particles to the'
spray gun possible. Agitating or fluidizing the.
powder in the feed hopper also helps prevent
clogging or clumping of the powder before it
enters the transport lines (KSBEAP, p. 9).
Innovations in powder delivery systems also .
allow the powder supply reservoir to be switched
easily to another, color when necessary. Systems
are also available for segregating colors so that
several colors can be applied.in the same booth
(EPAd, p. 36).
Fluidized Bed
Initially, powder was applied using a fluidized bed
process in which heated parts were dipped into a
. vat-with the suspended coating powders. As
these particles came in contact with heated parts
they softened and began to "flow" into other
particles to create a coating. The coatings .were
. thick, usually vinyl or epoxy, and demonstrated
functional rather than decorative qualities
(KSBEAP, p. 9). However, several methods for
powder coating exist now, which makes powder
coating a more versatile option, however fluidized
bed is still used in certain operations.
In a fluidized bed, powder particles are kept in
suspension by an air stream. A preheated
workpiece is placed in the fluidized bed where
the particles coming in contact with the
workpiece melt and adhere to its surface. Coat-
ing thickness depends on the temperature and
heat capacity of the workpiece, and its residence
time in the bed. Postheating is generally not
required when applying thermoplastic powder
coatings. However, postheating is required to
cure thermoset powder coatings completely
(NEFSC).
Electrostatic Fluidized Bed
{ An electrostatic fluidized bed is similar in design
to conventional fluidized beds, but its air stream is
electrically charged as it enters the bed. The
ionized air charges the particles as they move
72
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Chapter 6: Alternatives to Sgtvent-Bome Coatings
Table 22. Characteristics of Powder Coating Techniques (Misev, p. 350)
Characteristic
of Workpiece
Size
Material
Temperature
Resistance
Aesthetic Value-
Coating Thickness
Type of Coatings
Color Change
Capital Investment
Labor
Energy
Consumption
Coating Waste
Electrostatic
Spray
Larger .
Metallic, must be
co'nductive
Relatively high ,
High
Thinner films
Therrnoplasts and
thermosets
Difficult
Moderate to high
low because highly
automated
Only postheating
Very little
Fluidized Bed
or Electrostatic
Fluidized Bed
Smaller-
Any, except wood, rtot
necessarily conductive
' High.
Low, not suitable for '
decorative purposes
Thjck high-build films -
.with excellent uniformity
Thermoplastic and
thermosets
Relatively difficult
Low
Moderate depending on
the automatization
Preheating and often
, postheating.
Very little
." . t
Flame Spray
Not limited
Any, not necessarily
conductive
Not relevant .
Low, not suitable for
decorative purposes
Thick high-build films;
uniformity depends'
on the operator
Thermoplastsbnly ,
Easy
Very low
Relatively high
Low, no preheating
or postheating
Depends on the
workpiece geometry
upward in the bed, forming a cloud of charged
particles. The grounded workpiece is covered by
the charged particles as it enters the chamber.
No preheating of .the workpiece is required.
However, curing of the coating is necessary. This
technology is mcst suitable for coating small
objects with simple geometries (NEFSC).
Flame Spray
Flame spray was recently developed for applica-
tion of thermoplastic powder coatings. The
thermoplastic powder is fluidized by compressed
air and fed into a flame gun where it is injected
through a flame of propane, which melts the . ..
powder. The molten coating particles are depos-
ited on the workpiece and form a film upon
solidification. Because no direct heating of the
workpiece is required, this technique is suitable for
applying coatings to most substrates. Metal, wood,
rubber and masonry can be coated successfully
using this technique. This technology is also
suitable for coating large or permanently fixed
objects (NEFSC). - .
Tribocharge
Tribocharging relies on friction between the
powder and the spray gun. The. action of the
powder flowing through the barrel of the gun
73
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Chapter 6: Alternatives to Solvent-Borne Coatings
generates a frictional charge on the powder. The
charged powder is carried by the air stream to the
substrate, where it adheres due to electrostatic
attraction. Because no high-voltage system is
used, the electric field is substantially smaller and
the powder tends to follow air currents rather than
field lines. The smaller electric field results in a
much reduced Faraday cage effect3. Conse-
quently, tribo guns produce smoother finishes,
allow deposition of thicker films, and provide
better coverage of intricately-shaped objects
(EPAd.p. 31).
Markets
Currently, 85% of the total market for powder
coatings is represented by four industrial areas:
metal finishing (53%), appliances (21%), lawn and
garden (8%), and architectural applications (3%)
(EPA, p. 164).
Since 1986, all ormost automotive manufacturers,
have powder coated engine blocks, the largest
volume job in the history of the powder industry.
Now powder has come out from "under the
hood" and is being used on a wide range of trim
and accent parts. Polyester and acrylic powders
are used in these coatings. For example, the
"metallic look" powders are delivering luster to
aluminum wheels. However, there remains great
potential for more powder use in the automotive
industry; its use as a primer surface and anti-chip
coating on body panels is becoming more com-
mon. Powder coatings have undergone extensive
testing both as a primer surfacer and antichip
coating and have met OEM standards for chip
resistance, adhesion, durability, and heat and
humidity exposure.
In addition, clear powders over liquid base coats
are currently being tested for exterior auto body
finishing. The advent of clearcoat finishes for base
coats in the mid-1980s made it more economically
feasible to use powder as an automotive topcoat.
Using specially formulated acrylic and polyester
powders, manufacturers are working to meet the
automotive industry standard for clearcoats of
absolute smoothness, clarity, perfection and
performance (Bocchi, p. 21).
New Developments
Con Coating. Development of powder coatings
for the coating of can interiors, tops, ends and lids
is well underway. In addition, application equip-
ment is now available to apply, recover and
recycle the very small particle size powders
required to maintain thin films and run at line
speeds common in this industry. Food and Drug
Administration approval is still pending.
Lower-Temperature Cures, Powder coatings with
very high reactivity have been developed to cure
at temperatures as low as 121°C (250°F). Such
low-curing powders will allow more types of
products to be coated with powder, including
plastics and preassembled products that contain
heat-sensitive fluids or gaskets. In addition,
manufacturers can run higher line speeds with the
lower-cure powders, thereby increasing produc^
tion capacity.
Weathering Capabilities. Significant advances
have been made in the development of polyester
and acrylic resin systems with excellent long-term
weatherability, which is needed to meet the
extended warranties being offered by manufactur-
ers. Also under development are fluorocarbon-
based powders that will match or exceed the
weatherability of liquid fluorpcarbons, with
application costs similar to or lower than conven-
tional powder coatings.
Thinner Films. Powder manufacturers are continu-
ally working to develop powders that can form
films that are thinner than those previously
attainable, resulting in a savings of material and
money. Based on epoxy-polyester hybrids, these-
powder coatings provide applications in the range
of 1. to 1.2 mils for colors with good hiding
powder. These thin coatings are currently suitable
only for indoor applications (Moore, p. 66 and
Bocchi, p. 32-34). '
Cost and Implementation Issues
Powder coating emits no VOCs and offers ~
several performance advantages. However, to
, introduce powder coating to an existing paint line,
3 The Faraday cage effect occurs when the electrostatic-field force limits the entry of paint particles in
recessed areas. To achieve coating in the recessed area, overpainting of the nonrecessed area or manual
touchup often is required. In this situation, real transfer efficiency is less than the quoted transfer efficiency.
74
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Chapter 6: Alternatives to Solvent-Borne Coatings
a capital investment in special equipment must be
made. Pretreatment of the part to.be coated also
needs to be quite thorough, which can add to the
overall cost (EPAd, p; 35), For entirely newrlines,
however, investment in powder application
equipment is comparable to that of equipment for
liquid coatings (VT DEC). In addition, the cost of
producing a finished coating is typically lower with
-powder coating than conventional coating because
maintenance and operating costs are less, particu-
larly for operations that use a single color (EPAd,
Radiation Curing:
General Description
. Radiation curing uses ultraviolet (UV) and
electron beam (EB) electromagnetic radiation to
polymerize specially formulated coatings directly
on a substrate. Galled photopolymerization, the
UV-cu,ring process is a photochemical reaction.
Specially formulated coatings mixed with a small
amount of materials called photoinitiators are
exposed to a UV-light source, initiating
crosslinking. The rate of polymerization depends
on the intensity of the radiation used (Radtech, p.
40), EB curing crosslinks coatings by exposing
them to low-energy electrons; however, because
of the high cost associated with EB generators,
this method of radiation curing accounts for only
about 10 to 15% of the total radiation curing
market (Lucas, p. 29). .
Advantages and Disadvantages
Radiation curing produces high-performance
protective and decorative finishes. Radiation-
curable coatings can be 100% reactive liquids,
completely eliminating the use of solvents. How-
ever, some of the resins in these coatings can
volatilize, resulting in VOCs; Although emissions
are usually low, the amount of VOCs emitted
from radiation curing depends entirely upon the
coating formulation (EPAd, p. 68). In addition, the
shape of the part will affect the curing; flat
surfaces are easiest to cure: Capital investments
for UV-curing systems' are usually lower than
Table 23. Advantages and Disadvantages of Powder Coatings (NCP2P, p. 3)
Advantages
Disadvantages
* Reduces cost due to: ; .' ..
'.-no solvent flash required . .. ' -
-no.coatings mix room needed
-minimal oven length required,
-low ventilation required
-less floor space required, i.e., system
requires two-thirds to three-quarters of
. wet paint'systems
-VOC and HAP,compliant, i.e.; no solvents
* Improves finish quality
* Improves finish durability
* Has good corrosion resistance
+ Has coating utilization efficiencies that
reach 95 to 99%
* Saves energy
* Requires little operator expertise
*.Has quick "packageabiiity"
'* Has a variety of resins available .
* Has, no hazardous overspray, waste sludge
or contaminated water
* Reduces worker exposure to solvent vapors
* Has heat requirements that restrict application of
powder to metal finishing surfaces - ,
* Has powder manufacturing limitations:
-difficult to make small amounts . . .
-control of texture size and distribution limited
-metallic powder coatings not as attractive
as wet metallic finishes .
* Has recirculating system that creates negative .
pressure in booth
* Needs gentle air stream to apply powder
+ Enhances Faraday cage effect (VT DEC) .
* Is difficult to achieve thin films below 1.0 to 1.5 mils
* May cause powder clumping
> Is difficult to change colors
* Needs cool, dry storage area
* Must pretreat substrate .''.'.
75
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Chapter 6: Alternatives to Solvent-Borne Coatings
CASE STUDY:
Knoll Group
The Knoll Group in East Greenville, Pennsyl-
vania, manufactures office furnishings includ-
ing office systems, desks, credenzas and
chairs. Originally, the company applied
solvent-borne coatings using conventional
spray techniques. Solvents in the paints
included toluene and methyl ethyl ketone
(MEK). When Knoll studied the paint process,
the company found that paint material loss
was nearly 80%.
As a result, Knoll decided to develop a
powder coating that would give a high-quality
finish. Knoll engineers and scientists experi-
mented with resin and other powder-paint
components from various national and
international suppliers to develop the new
coating. The result was a new powder system
.that uses approximately 98% of the raw
coating material. Excess powder is collected,
cleaned and reused.
+ Savings
The Knoll group realized a payback of its
$500,000 investment in less than a year with
total savings of $639,000 per year. Other
bonuses included easier compliance with
more stringent environmental regulations, anc
elimination of fees for incineration of solid
and liquid hazardous waste (OH DEP).
investments for conventional ovens and use
considerably less space. The cost of the coating is
generally higher on a per pound basis, but not
always on a coverage basis (RadTech). For more
information on other ad vantages .and disadvan- .
tages of radiation curing, see table 25 at the end of
this section.
Types of Radiation-Curable
Coatings
A complete formulation for a radiation-curable
coating consists of a blend or mixture of ojigo-
mers (low molecular weight polymers), mono-
mers, additives, pigments, and photoinitiators. The
oligomer used in the formulation plays an irhpor-.
tant role in determining the final properties of the
CASE STUDY:
Swing-N-Slide Corporation
Swing-N-Slide Corporation's Newco Fabrica-
tion Division in Janesville, Wisconsin, is a
leading manufacturer of build-it-yourself
swing sets. In 1 989, Newco installed a liquid
spray system for coatings to replace the dip
coating .operation that had been used there
since 1 987. However, company officials
quickly realized that, while more efficient,
spray painting resulted in an increase in air
emissions and hazardous waste generation.
The Wisconsin Department of Natural
Resources began enforcement for ai-r permit
noncompliance and classified the facility as a
large quantity generator.
As a result, in 1993, Newco installed a
powder system to replace the liquid paint
system. The system features 1 0 automatic
and 2 manual electrostatic spray paint guns.
The facility has reduced hazardous waste
generation from 38,350 pounds per year to
4,800 pounds and has been reclassified as a
small quantity generator. At the same time,
production output has tripled.
* Savings
The capital costs for the powder system were
$200,000 with a payback period of 14
months. Newco estimates savings of
$ 140,670 annually ($41,000 from elimina-
tion of hazardous wastestreams, $99,670
from savings on labor and materials, and'
$23,000 from savings on paint filter clean-
ing) (Wl DNR).
finish (Radtech, p. 40). Resins used in conven-
tional solvent-based coatings can be'chemically
modified for use in radiation-cured systems by
introducing acrylate functionality. The general
physical and chemical characteristics of the resins
are retained after modification (EPAd, p. 71.).
The oligomers most commonly found in today's
. radiation-curable formulations are acrylated
urethanes, epoxies, polyesters and silicones
(Radtech, p. 40). Coatings that use acrylated -
resins cure by free radical polymerization and
comprise 8'5% of the total radiation-curable
coatings market (Lucas, p. 28). ,
76
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, Chapter 6: Alternatives to Solvent-Borne Coatings
Table 24. Summary of Powder Coating Resin Properties (EPAd, p. 27)
Coating
Property
Hardness
Flexibility
Resistance
to Overbaking
Exterior
Durability
Corrosion '
Protection
Chemical
Resistance
Thin Coat
Colors
Available
Clears
Available
Textures
Available
Epoxies
Excellent
Excellent
Fair
Poor
"V '
Excellent
Excellent
No.
All
Yes
Yes.
Epoxy-
Urethane
Hybrids
Excellent
Excellent
Very good
Poor.
Excellent
.Excellent -
No
All .'/
No
Yes.
Urethahe
Polyesters
Very good
Yery good
Very good
Very good
Very good
Very good
Yes
All
Yes
Yes
TGIC
Polyesters
Excellent
Excellent
Excellent
Excellent
Excellent
Very good
No
All
')
Yes
Yes
Acrylics
Very good
Fair
Good
Very good
Fair
Very good
No
All '
Yes
No
Coatings can also cure by cationic curing, the
polymerization of cycloaliphatic epoxies or vinyl
ethers. Cationic curing is an attractive option
because it withstands pasteurization and promotes
adhesion to metals, even during postforming
operations (Lucas, p. 28-29).
Application Methods
UVrcured coatings can be applied using tradi-
tional-spray methods, but roll-coating is often
used on flat s,tock'(KSBEAP, p. 11). Varnishes on
two-piece cans, are applied using an offset
process, while curtain coating is used in some
specialty applications (RadTech).
Markets
The use of TJV-inks and overprint coatings on
two-piece metal cans has been commercially
successful for more than 10 years! Coating of
three-piece composite and metal-can ends has
been a commercial reality since the 1970s
(RadTeeh.p. 14). UV-cured coatings are;widely
used to provide corrosion resistance to galvanized
metal tubing. It is also used on metallized plastics.
In addition, UV-cured coatings have been
formulated for coil coating, in which outstanding
resistance and flexibility have been achieved.
Significant growth in other metal markets could
occur in the next decade as environmental and
77
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Chapter 6: Alternatives to Sotvent-Bome Coatings
CASE STUDY:
Replacing Solvent-Based Paints with Powder Paint
Miller Electric Manufacturing Company in Appleton, Wisconsin, is the world's largest manufac-
turer of arc welding equipment and systems. Founded in 1 929, the company employs more than
1,600 people and operates 1,000,000 square feet of manufacturing space. Responding to
environmental concerns and a desire to improve corrosion resistance of painted parts, Miller
modified their liquid painting conveyor line for metal parts by replacing four of their electrostatic
disk applicator booths with two powder booths.
The previous system used high-sotids paint and achieved a relatively high transfer efficiency.
However, in 1 994, nearly 30 tons of VOCs were generated from liquid spray painting opera-
tions, and paint-related wastes were disposed of at a cost of approximately $20,000.
* Savings . . ' '
The new system reduced annual feed stock needs from'13,000 gallons of liquid paint to 80,000
pounds of powdered paint (equivalent to 9,000 gallons'of liquid paint). Annual waste genera-
tion was reduced from 60,000'pounds per year of paint-related wastes to 1 5,000 pounds per
year of paint-related wastes (90% of the remaining waste was from liquid paint processes).
Additional reductions include 50,000 pounds of VOC air emissions, 40,000 pounds of waste
paint filters and 5,000 pounds of hazardous waste paint and solvents.
The new powder painting process cost $545,000 to purchase and install. The new system
included a powder paint system, an environmentally controlled application room, oven up-
grades, and improvements to metal preparation and cleanup. The. new system reduced opera-
tion and maintenance costs by $87,000 per year. This figure includes savings-in purchasing and
disposal costs. Due to higher transfer efficiency, the total cost of painting was reduced by 25%
on a square foot of painting surface, resulting in a payback period of 6.3 years.
This project was approved based on predicted improvements in quality and environmental
benefits. Powder painting of parts has significantly improved corrosion resistance and surface
' finish quality. Employees have also benefited from the elimination of solvent, use and the powder
booth's effective dust control system (SHWEC). '
productivity requirements increase. The use of
UV curing is growing rapidly for wood finishes,
medical appliances, consumer products, automo-
tive head lamp assemblies, optical fibers and
electronics. Growth will be further enhanced with
the development of cationic-cured epoxies, which
provide improved adhesion to, and protection of,
metal substrates (MFC, p.. 29-36).4
New Developments
Wafer-Redudb/e, UV-/EB-Curable Formula-
tions. These formulations have been developed
for a number of coatings and products, including
flexo and gravure inks, clear coatings for wood
furniture, and dip-coated or spray-coated plastics.
Water dilution of a compatible resin system
provides lower viscosity, thinner films, improved
flow and leveling, lower applied costs and lower
amounts of monomers and solvents. The use of
water as a viscosity reducer'can minimize or
eliminate the use of lower molecular weight
diluents, which tend to be skin irritants. Some
research has indicated that small amounts of water
(1"% of water) can reduce the viscosity of .
oligomers substantially, and larger amounts of
water can be used as a formulation tool to vary
gloss and reduce web temperatures in critical
applications. Disadvantages include the increased
time and energy required to remove, any added
water, as well as the negative effects of water on
4 For more information on the use of radiation curing in can manufacturing, refer to the EPA document Project
Summary: Evaluation of Barriers to the Use of Radiation-Cured Coatings in Can Manufacturing.
78
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Chapter 6: AltematWes to Solvent-Borne Coatings
the drying and curing system-and the substrate to
which it is applied. If the material is cured before
the water is fully evaporated, then the film
properties will be reduced (Lawson, p. 16).
Cost and Implementation Issues
The UV-radiation source most commonly used in
industry is the medium-pressure mercury-elec-
trode arc lamp. These lamps can be retrofitted
easily to existing production lines, but they require
an extraction system to remove excess heat and
ozone that is generated by UV action on oxygen in
the air (EPAd, p. 72). The cost of an electrode arc
system is approximately $6,400 for a 10:inch
lamp, shields to contain the UV light waves that
are harmful to skin and eyes, reflectors, snutters,
a high-voltage power supply, arid an air cooling
fan (EPRI). An alternative UV system produces
UV radiation through microwave excitation of the
mercury vapor (EPAd, p. 72). A microwave- ,
powered UV-curing system costs approximately
$7,500. This system includes a standard-length
lamp, a power supply, an air cooling system, a
cable, and a detector to ensure that microwave
radiation leaks do not occur (EPRI).
EB generators are expensive, complex and large.
In addition, oxygen has an inhibiting effect on
crossliriking initiated by EB; therefore, companies
must establish an inert atmosphere of nitrogen,
with oxygen concentrations of less than 100 parts
per million (ppm) if adequate curing is to be
achieved (EPAd, p. 72).. .-
Emerging
Technologies
This section presents coating systems that have:
only recently become commercially available..
Knowledge of cither technologies that are still
under research and development is important for
technical assistance providers. However, present-
ing information on experimental systems is not
within the scope of this manual. Technologies
covered in this section include vapor permeation
of injection-cured coatings, supercritical carbon
dioxide and unicoat paint. For more information
on coating research and development, consult the
trade journals listed in appendix A.
Vapor Permeation of /n/ecf/bn-Cured- Coatings
" (VIC). After a.reactive resin is applied as a liquid,
curing is induced by exposing the liquid to a .
vapor-containing compound that initiates polymer-
ization. Examples are polyol-isocyanate coatings
that cure by tertiary amine vapor injection
(NCP2P, p. 4). The amine vapor is made by an
amine generator in a predetermined concentration
and is dispersed in an air stream channel in-the
spray gun. The generator uses dried and filtered
air at 90 to 120 psi. The coating material and
catalyst are mixed as they leave the spray gun.
Table 25. Advantages and Disadvantages of Radiation-Cured Coatings
(NCP2P,p. 4)
Advantages
Disadvantages
* Uses coatings with lower VOC and HAP
content than conventional coatings
* Has lower capital investment than
' .conventional pveris
* Increases production rates because
curing periods are reduced to seconds
* Has low .energy costs
> Has consistent performance
«> Requires small ovens
+ Has low air movement that reduces dust
and dirt contamination
+ js easily installed/retrofitted
+ Reduces fire and explosion hazard
* Can have interference of photocy re by
pigments
> Has higher costs for EB and UV coatings
* Has potential problems with acrylate skin
irritation if proper safety techniques are not used
* Has shrinkage and adhesion problems with
'acrylate .
* Is not applicable to all finish types because
it produces a specific "look"
* Has curing sensitive to shape of part
79
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Chapter 6: Alternatives to Solvent-Borne Coatings
CASE STUDY:
Adolph Coors Company
The Coors can manufacturing plant,
located in Golden, Colorado, is the largest
single aluminum can manufacturing plant in
the world, producing approximately 4
billion cans a year. The plant currently
produces aluminum cans exclusively for the
beer beverage market.
Since 1975, Coors has been using UV
curing in full-scale can production. The
initial push to convert to UV was caused by
a desire to increase can printing speeds,
reduce e.nergy consumption and lower air
emissions.
* Savings
According to company estimates, the UV
system saves the firm $90,000 per billion
cans produced versus conventional technol-
ogy. In addition, Coors estimates that since
1975, VOC emissions have been reduced'
by 1,740 tons (Donhowe). For additional
information on Coors use of UV curing, see
EPRIb.
This technology is a high-solids coating system
because the coating still uses solvent in the
formulation. However, its ease of use and rapid
cure times can improve production efficiency
(EPAd, p. 80).
Advantages and Disadvantages
VIC can produce a variety of finishes with good
performance characteristics including chemical,
solvent, and stain resistance; high humidity and
water resistance; high mar and abrasion resistance;
and color and gloss retention. These coatings can
be used on a broad range of substrates including
plastic, steel, aluminum, wood and castings. Heat-
sensitive parts such as thermoplastics and thermo-
sets are ideally suited to the low-temperature cure
used with VIC (EPAd, p. 80). For other advan-
tages and disadvantages of VIC, see table 26.
Cost and Implementation Issues
VIC is compatible with LVHP, HVLP, electrostatic
and airless spray systems. However, electrostatic
equipment might need to be modified to accom-
modate the amine generator. In addition, some
types of spray guns might have rubber or plastic
seals that degrade when exposed to the amine.
Capacity is limited to two spray guns (EPAd, p.
80).
UN/COAT Paint Technology: The UNICOAT
technology is a one-coat painting system for
aircraft that replaces the combination of a coat
primer system and a top coat system. .Since only
one coat is applied instead of two coats, VOC
emissions- and waste generated from cleanup
operations can be reduced by 50 to 70%. This
technology, developed by the Naval Warfare
Center (NAWC), consists of a self-priming
topcoat for aircraft and other industrial parts. It is
applied directly to the metal substrate Without
priming (NFESC).
UNICOAT, which is formulated without lead or
chrome, replaces the two-coat system with a
blend of organic and inorganic zinc compounds
that are non-toxic. UNICOAT contains polyure-
thane as do traditional coatings-, however; corro-
sion inhibitors and adhesion promoters have been
added to UNICOAT.
UNICOAT has performed at levels equivalent to,
and superior to, the performance levels for
Table 26. Advantages and Disadvantages of VIC (NCP2P, p. 4)
Advantages
Disadvantages
* Eliminates or reduces solvent
* Has low-temperature processing
* Has unreacted pverspray that can be
collected for reuse
* Can be used on heat-sensitive substrates
>Has limited industrial experience
+ Has a highly.complex process
« Requires high level of operator skill
* Has high capital cost
80
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Chapter 6: Alternatives to Solvent-Borne Coatings
Table 27. Advantages and Disadvantages of Unicoat Paint Technology
(NFESC)
Advantages
Disadvantages
* Contains no toxic pigments (e.g./ chromate,
, lead)
* Reduces VOC emissions a'nd hazardous
waste generation ;
* Reduces paint and primer costs ,
* Reduces paint weight on equipment and aircraft
* Reduces labor costs because.one coat
is applied ,
V Reduces stripping cost due to less paint
on workpiece ' ^
May not be suitable for all applications
conventional paints (in applications by the U.S.
Navy and U.S. Air Force). To avoid adverse
reactions, freshly painted wet surfaces must not
come in contact with alcohols, amines, water or'
acids. Costs for the UNICOAT system varies
depending on the specific application (NFESC).
81
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82
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Application Techniques
Various application methods are available to
coat metal, the most common being spray
painting and electrodeposition (EPAb,p. 20). :
Coatings also can be applied by dipping parts into
tanks filled with paint and then allowing the excess
paint to drain off, or by direct application methods
such as roller coating and flow coating. This
chapter provides information on: conventional air-
spray guns; high-volume/low-pressure spray
guns;'airless spray guns; electrostatic spray guns;
electrodeposition; roll coating; flow coating; and
plural component systems. Which paint applica-
tion process is chosen depends on the type of
substrate to be coated, the type of coating, and the
size and shape of the surface (IHWRIC, p..35).
General Description
of Spray Systems
Paints and coatings can be applied to surfaces in a
number of ways. Industrial coatings often are
applied on a production line using spray applica-
tion techniques. Curing is done usually by an
accelerated curing operation involving heat,
surface catalysts or radiation (EPA, p. 15 5-156).
In general, spray methods use specially designed
guns to atomize paint into a fine spray. For
industrial applications, the paint is typically
contained in a pressure vessel and fed to the spray
, gun using compressed air. Traditionally, hand-held
or automated guns (mounted on a mechanical-
control arm) have been used to apply liquid paints
to metal substrates. .
.Although spray systems are easy to operate and
- have low equipment costs, they have a certain
amount of overspray and rebound from the .
sprayed surface and, therefore, are unable to
transfer a substantial portion of the paint to the
part (Freeman, p. 710). Spray booths with an
open front and exhaust at the rear are generally
used to remove the overspray as.it is generated
(EPA,p. 155). '
P2 Tips for Coatings Application
* Eliminate the need to paint by using
surface-free-coatings materials
* Substitute low-VOC paints for solvent-
borne paints
* Increase transfer efficiency
* Train operators to practice proper spray
painting techniques .<- '
> Improve housekeeping, maintenance and
operating practices
Use a paint heater to adjust viscosity
* Set application standards
Pollution Problem
During conventional spray painting, some of the
paint is deposited on the surface being painted;
while much of it, in the form of overspray, is
sprayed into the air. As the paint dries, the solvent
evaporates into the air in the form of VOCs. Often
exhaust from paint booths is run through dry
filters to capture the particulates. Though it can be
run through a water scrubber that separates the
paint from the air, scrubber water is normally
recycled, and paint solids are concentrated in the
scrubber sump. Wheathe sump fills with paint
sludge, it is removed and put in drums for dis-
posal. Paint sludge that fails the TCLP test must
be disposed of as a hazardous waste (Higgins, p.
118).
General P2 Options
.Emissions of VOCs from coatings application can
be significantly reduced by substituting a paint
with a lower solvent content (e.g., high-solids,
waterborne or powder), and by increasing transfer
efficiency. The type of coating and the application'
method selected can have a significant effect on
. transfer efficiency (MnTAP, p. 2). For more
information on alternatives to solvent-borne
coating formulations, see chapter 6. ^ J
83
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Chapter 7: Application Techniques
Whatever type of paint and application method is
chosen, the best environmental solution may be to
redesign the product to eliminate unnecessary
coating. This is a P2 option known as surface-free
coating. Many of the resins used in alternative
paints are made from regulated chemicals, and
surface-free coating can eliminate the use of these
substances (EPA, p. 165).
A number of other P2 techniques in coating
applications also are available. For coating opera-
tions that involve manual spray application, for
example, training operators to practice proper
spray techniques is a cost-effective method for
reducing VOC emissions and other wastes. Wastes
generated during the application of paints and
coatings (as well as during surface preparation and
equipment cleaning) can also be reduced by
adopting improved housekeeping, maintenance
and operating practices. Additional P2 options
include: installing a paint heater to reduce the need
for paint thinning with solvents, and setting
application standards to avoid unnecessary
coating. Each of these options is discussed below.
Transfer Efficiency and Paint
Application
Improvements in transfer efficiency can lead to
less paint waste and lower emissions of VO.Cs.
Transfer efficiency depends on a large number of
parameters. Some of these parameters are under
the control of the operator, while others are not.
Important parameters that should be considered
when optimizing spray gun application include:
* Spray application technique.
* Target configuration and size. Higher transfer
efficiency rates are easier to obtain on large
flat objects than on small complex parts.
* Spray booth configuration. Stray crossdrafts
and downdrafts may reduce transfer efficiency
by deflecting the paint away from the target.
Temperature control and humidity control in a
facility can significantly affect the transfer
efficiency of electrostatic systems.
^Paint characteristics.
+ Paint/airflow rates. Spray guns are designed
to operate at maximum optimum flow rates.
Exceeding these flow rates can reduce
transfer efficiency by increasing the amount
of blowback (paint bouncing off part) and
overshoot. Excessive air pressure can also
lead to premature drying of the paint before it
reaches the target (paint fog).
* Spray gun distance from part. When the gun is
placed too close to the part, bounceback
increases and can result in poor finish quality
(i.e., sags and runs). Too much distance results
in overshoot and paint fog.
> Operator error (Jacobs, p. 7-8).
By definition, transfer efficiency is the amount of
paint solids deposited on an object, divided by the
amount of paint solids sprayed at the object,
multiplied by 100%. The definition of transfer
efficiency does omit some related factors for
optimum material use. Minimizing waste is not
necessarily achieved by simply using the applica-
tion technique that has the highest rated transfer
efficiency. "Real" transfer efficiency depends on a
number o'f other factors including:
+ Quality of finish. The quality of the finish
generally improves as the size of spray par-
ticles is reduced. Unfortunately, as the size of
spray particles decreases, transfer efficiency
also decreases. Some of the finest particle
sizes are achieved with conventional LVHP air
spray; however, this is the least efficient means
of applying paint. To meet finish requirements,
a compromise must be reached between'
transfer efficiency and quality.
* Production rate. A desired production rate
shpuld be established before determining the
- transfer efficiency of the coating system,
especially if coating is being done on a
conveyorized system that includes other
operations. This is because the efficiency of
spray devices will vary with the rate of applica-
tion.
> Desired film thickness. To determine real
transfer efficiency, the thickness of the applied
film versus the thickness desired should be
established. For example, if a l-mi,l-thickfilm is
specified, but the spray method can only
deliver a quality film of 2 mils or greater, then
at least 50% of the paint is wasted. Even if all
84
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Chapter-7; Application Techniques
of the paint used is applied to the workpiece,
; the real transfer efficiency is only 50%.
* Uniformity of applied film thickness. Aflat, fan-
shaped spray.pattern can hold film thickness
variations to within 1 0% of the ideal in a well-
engineered painting system. However, a round
doughnut-shaped pattern is used in some .
spray systems. This type of pattern delivers a -
film thickness variation ©{approximately 1 mil.
In other words, if the desired film thickness is T
mil, the coating can have areas that are 2 mils
thick. Even when all-the paint is applied, 25%
is wasted. Therefore, at best the real transfer
efficiency is 75%.
>Edge buildup. In electrostatic painting, edges
.of parts can attract paint spray that would
normally pass by the workpiece. Paint builds
up oh the edges, which represents wasted
paint even though the point is transferred to '
the workpiece. This buildup may have to be
sanded down and the edges may have to be
touched up manually. .
;+ Need for manual touchup/Faraday cage
effects (in electrostatic spraying). In addition, in
electrostatic painting, the electrostatic field
force can prevent paintparticles from reaching
recessed areas. To coat these areas com-
pletely, overpainting or manual touchup of the
nonrecessed areas often is required. In this
situation, real transfer efficiency is less than the
quoted transfer efficiency.
In summary, real transfer efficiency depends on
the particular coating situation. Replacing a system
(manual or automatic) will not reduce VOC
' 'emissions by improving transfer efficiency alone,
hence another step must be taken to use less
paint. This may require changing the flow rates,
triggering times, and/or spray tip sizes. For
instance, electrostatic can be added to increase
transfer efficiency, but if nothing else is changed,
VOC emissions will stay the same and paint
thickness on the part will increase. A study by the
Research Triangle Institute found that real transfer
efficiency depends heavily on solids content, wet
film thickness, application equipment and operator
experience. Therefore, if a firm is considering a
change in paint application methods to improve
transfer efficiency, careful testing should be done
to ensure that paint and solvent waste are truly
being minimizejd. When comparing application
techniques for possible use in a particular plant,
spray efficiency and the above factors should all
be considered (VT DEC)!
Strategies to Improve
Transfer Efficiency
Following are methods that facilities can use to
increase their transfer efficiencies:
* Stand closer to the workpiece. A typical gun-
target distqnce is 8 to 12 inches. In general, as
the distqnce increases, transfer efficiency
diminishes. As the distance decreases, how-
, ever/the operator needs to reduce the fluid
and/or air pressure to avoid applying too
much coating to the part. '
^'Optimize fan size. The operator must appro-
priately size the fan for the workpiece on a
regular basis. A spray painter uses a fan size
of 6 to 8 inches .when paintirig small- or
narrow-shaped parts such as metal tubing or
angle brackets. Adjusting fan size is not a
major problem for operators who work on
production lines that coat one type of part or
work in long production runs. For those
facilities whose parts continuously change size,
the most practical strategy is to purchase a cap
that the operator can change quickly and
easily. Because not all spray guns can be fitted,
. with adjustable caps, facilities may need to
contact a variety of vendors to locate this
equipment.
O Reduce atomizing air pressure (where appli-
cable). In HVLP, conventional air atomizing,
arid electrostatic'guns reduce air pressure to
the lowest possible levels, which results in
marked improvements in transfer efficiency .
rates. For airless', and in some cases, air-
assisted airless guns, using a smaller orifice
can achieve the same atomizing results.
* Reduce fluid pressure. If the fluid pressure and
corresponding fluid flow rate are high, the
stream of paint emerging from the spray gun
travels a relatively long distance before .
bending and fajling to.the ground. Such a flow
rate has a very short residence time within the
85
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Chapter 7: Application Techniques
spray gun and requires a large amount of
energy for atomization. As fluid pressure
decreases, the stream emerging from the
spray gun shortens and less energy is needed
for atamization. Longer residence times lead to
more efficient atomization, which in turn leads
to higher transfer efficiencies.
Many spray painters argue that lowering fluid
delivery rates slows down production speed
and raises the cost of painting. This argument
is true only for a very small percentage of
facilities that have already optimized their fluid
delivery rates. At most facilities, fluid delivery
rates are considerably higher than the job
requires.
+ Space workpieces closer together. Many
facilities that use conveyor systems suspend
parts on hooks that are spaced 18 to 24
inches apart. This spacing is appropriate for
medium or large parts but reduces transfer
efficiency on small parts. Facilities should try to
use hooks and racks specifically designed for
the parts they are coating. This will result in
increased transfer efficiency and an optimized
speed for the process line.
Operators, however, cannot always work well
with close spacing. For instance, parts with
complex geometries often require the operator
to access .the part at a variety of angles to
ensure the quality of the coating. Also, when
using electrostatic spray guns, painters must
"provide sufficient spacing to allow for some
wrap to take place.
+ Reduce air turbulence in spray booth. Paint
facilities that use several spray booths that all
pull from one air make-up system may experi-
ence violently turbulent air velocities that
change direction from one second to the next.
Correcting this problem can be difficult and
often requires air conditioning and airventila-
' tion consultants. While this remedy can be
costly, having a uniform, laminar air flow
through a spray booth improves transfer
efficiency and significantly reduces overspray
and booth maintenance.
* Reduce the air velocity in the spray booth (not
below recommended OSHA limits). OSHA
requires a minimum air velocity of 1 00 to
120 feet per minute through spray booths in
which .operators use manual spray guns (the
automated electrostatic gun's minimum air
velocity is 60 feet per minute). Many paint
facilities inadvertently run their booths at
velocities well above the limit because they
are unaware of the effect this can' have on
transfer efficiency. Lower air velocities are
especially important in electrostatic opera-
tions because too high a velocity can prevent
the coating from wrapping the parts,
* Reduce leading and trailing edges. In cases
where a high-quality finish is required, trailing
edges are needed to ensure that there are no
fat edges. In many cases, however, operators
' set the spray guns so that they trigger .sooner
than is necessary, and/or cease too long after
the part has passed. When painting small- or
medium-sized parts, even a small decrease in .
leading and trailing edges results in significant
improvements in transfer efficiency.
. * Select the most efficient spray gun for the
intended application. Selecting a spray gun
that meets finish requirements and has the
highest transfer efficiency is important in
optimizing the efficiency of a coating system.
Before deciding whether an operation can improve
transfer efficiency, determine the current transfer
efficiency rates. Appendix G provides information
on how to estimate current transfer efficiency
(EPAq,p.74-76).
Table 28 provides an overview of the relative
costs and'benefits of the different spray applica-
tion methods relative to conventional air spray
guns. .,
Set Application Standards
The monitoring of applied film thickness is critical
. to ensure that a uniform and consistent coating of
paint is being applied. Too thin a coat will result in
premature failure in the field, while too thick a
coat represents excess cost and waste. Other
standards that should be established include the
levels of Crosshatch adhesion, film hardness and
solvent resistance. Specification of and adherence
to'standards can do much to minimize the level of
86
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Chapter 7: Application Techniques*
Table 28. Cost/Benefit Summary for Spray Application Methods
Method of
Application
HVLP Spray
Air-Assisted
Airless Spray
Electrostatic
Spray
Powder
Coating
Capital Cost
Low
Low
Medium
Medium
Process
Complexity
Low
Low
Medium
Medium
Waste and
Emissions
.Medium/High
Medium/High
Medium
Low
Additional
Considerations
Only conductive parts
can be painted
Extensive parts' wash-
ing and a curing oven
are required >
NOTE: Capital cost refers to the cost of the system in comparison to conventional air spray. The higher the process complexity, thefiigher
the associated costs (i.e., training for employees-and maintenance) ;
rejects and ease troubleshooting when problems
arise (Freeman, p. 487). Different tests have been -
used over the years for liquid arid cured paints. A
consistent system should be used for evaluating
coating properties. The American Society for
Testing Materials (A§TM) standards has devel-
oped many useful standards; see appendix'E for
more information (KSBEAP, p. 25).
Adopt Proper Manual- Spray
Techniques
Untrained and hurried workers using poorly
maintained equipment can contribute to the need
' to rework products and to clean up and dispose of
wasted coatings, thereby increasing costs. A well-
trained operator is far more important than the
type of gun used. By training operators on proper
equipment setup, application techniques and
maintenance, companies can reduce the use of
materials by 20 to 40% (Callahan). These savings
will depend on the parts coated, material sprayed,
and operator technique and experience level
(MnTAPd, p. 6). The fundamentals of effective
spray technique that o'peratprs can follow are:
* Proper gun setup. Use the paint gun :
manufacturer's suggested air cap and fluid tip
; combination for the viscosity of the product
being sprayed. Check the spray gun to see that
it produces a proper spray pattern, and keep '
the air and fluid pressures at the lowest - .
possible settings. ,
* Spray distance and angle. Keep the distance
between the gun and the part being sprayed
, as close as possible to the manufacturer's
recommendations at all times (e.g.,.6 to 8
inches for conventional spraying, 12 to 15
inches for airless spraying, and 1 0 to 12,
inches for'electrostatfc spraying). Move the
spray gun parallel to the. work, keeping the
gun at a right angle. ' , '_
^Triggering and overlap. Overlap each succes-
sive stroke (e.g., 50% for conventional spray-
ing or 25% for airless spraying), using a
Crosshatch overlap when required. Trigger the
v spray gun at the beginning and end of each
stroke, making sure that the gun is in motion
before triggering. In so doing, operators can .
minimize the lead (i.e., the distance between
where the gun is triggered and the point where
the gun pattern hits the part) and the lag (i.e.,
the distance between the point where the
pattern leaves the part and the point where the
gun is untriggered), thereby reducing
overspray (Binb and iWRC, p. 2-8),
Whenever helping companies adjust the spray
technique of operators, technical assistance
providers should keep in mind that, over a period
87
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Chapter 7: Application Techniques
of time, the firm may have selected a coating and
application equipment to conform to an incorrect
technique. Equipment settings and materials might
need to be changed to conform to an improved
technique (De Vilbiss).
Improve Current Operating
Practices
Improving operating practices is another cost-
effective pollution prevention method for reducing
the amount of wastes generated. The following
methods require minimal capital outlays, and can
be very effective (KSBEAP, p. 21):
* Segregate waste streams to prevent mixing of
hazardous and nonhazardous waste
* Perform preventative maintenance for quality
control of finishes
* Improve materials handling and storage to
dvoid spills
* Practice emergency preparedness to minimize
loss during accidents
* Schedule jobs to maximize color runs
* Implement strict inventory control by purchas-
ing only the amount of paint required
* Standardize paints and colors to minimize the
number of different types of paint used
* Return expired materials to suppliers for
reblending (KSBEAR p. 21, EPAc, p. 84-85
and Freeman, p. 487-489)
The following sections provide more detailed
information on specific application equipment and
on methods to optimize their performance.
Conventional Air
Spray (LVHP)
General Description
Conventional air spray technology, which has
been the standard for the past 40 years, uses a
specially designeii gun and air at high pressures
(i.e., 40 to 90 psi) to atomize a liquid stream of
paint into a fine spray. This technology is known
as low-volume/high-pressure (LVHP) but is
commonly referred to as conventional air spray.
Air is usually supplied to the LVHP gun by an air
compressor, and paint is supplied via a pressure
feed system (siphon and gravity systems are also
used). A typical picture of an air spray gun
features clouds of overspray around the part.
Conventional air spray produces a smooth finish,
and can be used on many surfaces. It offers the
best control of spray pattern and the best degree
of atomization. This system produces the finest
atomization and, therefore, the finest finishes. It
also sprays the widest range of coating materials
(CAGE). However, this technology produces a
great deal of overspray, resulting in low transfer
efficiencies (i.e., 30 to 60%) and uses large
amounts of compressed air (7 to 35 cfm at 100
psi). In addition, because the solvent in the paint is
highly atomized along with the paint solids,
transfer efficiency is low and VOC emissions are
high(MnTAP,p.3).
The essential components of an air atomizing
system are gun body, fluid inlet, fluid nozzle, fluid
needle assembly, fluid control assembly, air inlet,
air nozzle, air valve, fan control and trigger. Other
parts of the spray coating system may include a
compressed air supply, fluid supply and paint
heater. Recirculation booths are often used with
these systems. These booths are designed to ,
reduce process exhaust volumes while maintaining
minimum ventilation flow rates in order to lower
operating costs for both emission control systems
and the facility in general (e.g., heating, ventilation
and air conditioning). These systems have built-in
safety limits that are based on the concentration of
hazardous constituents present in the recirculated
stream.
Advantages and Disadvantages
The main advantages of conventional air spray
systems are the high level of control that the
operator has of the gun and the versatility of the
systems. Disadvantages of this system include
high air emissions, low transfer efficiencies and
high compressed air use. However, using proper
training and setting the gun at low pressure (20
psi), transfer rates similar to HVLP can be
achieved (Eck).
Costs
The capital investment for a new conventional air
spray system that includes spray gun, two-gallon
pressure pot, hoses and fittings can range from
$500 to $1,500.
88
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Chapter 7: Application Techniques
Safety
Painters are required to wear respirators to
prevent inhalation of overspray, hazardous vapors
and toxic fumes. Depending on the noise level in
the spray booth, ear protection may also be
required. .
Alternative Methods
There are a number of alternative spray gun
systems, including high-volume/low-pressure
(HVLP) air spray, airless spray, and electrostatic
spray. There are also variations on each of these
techniques. Of the many available methods,
electrostatic air-assisted airless spray is considered
to have the best'transfer efficiency (IWRCb, p.
39). Other available paint application methods
include electrodeposition, and dip, roll and flow
coating. ,.--'
High-Volume/Low-
Pressure (HVLP) Air
Spray
General Description
As the name suggests, this technology uses a high-
volume of air at low pressures (i.e., 0.1 to 10 psi)
to atomize paint. This technology reduces
overspray and improves.transfer efficiency. HVLP
guns have nozzles with larger diameter openings
than LVHP guns for atomizing air. They can be
bleeder (i.e., controls only the fluid flow to the
gun) or non-bleeder (i.e., controls air flow and
Figure 5. HVLP System (VT DEC)
Spray Gun
fluid flow to the gun by use ofa trigger) types,
and may require airflows of 10 to 30 cubic feet
per minute. Air can be supplied to the sprayer by
turbine air blowers or conventional shop compres-
sors (KSBEAP, 13). Typical transfer efficiencies ,
with HVLP systems are 65 to 75%. Figure 5
shows a typical configuration for a HVLP system.
Advantages and Disadvantages
An HVLP gun is portable and easy to clean, and
has a lower risk of blowback to the worker. In
many cases, HVLP guns are mandated to comply
with state air regulations (KSBEAP, p. 14).
~ However, the atomization of HVLP guns might
not be good enough for fine finishes, and produc-
tion rates might not be as high as with conven-
tional LVHP spray. Generally, fluid delivery rates
of up to 10 ounces per minute with low viscosity
paints work best with HVLP guns (MnTAP, p, 3).
For more information on other advantages and
disadvantages of HVL'P, see table 29.
Types of HVLP Systems
Several different configurations of HVLP systems
are available. The specific air supply (i.e., turbine
or compressor) and fluid delivery system (de-
scribed below) will affect the efficiency, ease of
use, cost and versatility of the particular system
(KSBEAP, p. 13). : . -
In a siphon-fed system, air pressure to the
sprayer is used to pull paint from a cup located
below the gun, producing a fully atomized pattern
for even surface coverage. The simple design of
Extractor
Turbine
Motor
Pressure Tank
89
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Chapter 7: Application Techniques
siphon-fed guns.has made it possible to buy
conversion kits for conventional siphon sprayers,
making HVLP technology very affordable for
small shop owners (KSBEAP, p. 13).
Gravity-fed systems are well adapted to high
viscosity paints such as clears, water-based paints,
high-solids paints and epoxy primers because of
the design of the system. The cup, located on top
of the gun, allows paint to completely drain,
minimizing paint waste (KSBEAP, p. 13).
The pressure assist cup system uses a cup that is
mounted beneath the gun with a separately
regulated air line to feed paint to the gun. This
design increases transfer efficiency and makes it
possible for the operator to spray evenly while the
gun is inverted, offering maximum flexibility in
application techniques (KSBEAP, p. 13-14).
Although covering every aspect of equipment
selection is not possible in this manual, see
appendix D for a list of some of the more impor-
tant points to consider when evaluating HVLP
spray equipment.
Cost and Implementation Issues
HVLP paint spray systems can be used in a
variety of painting applications. The finer atomiza-
tion of HVLP systems produce smoother finishes.
There are many paint gun models with a variety
of tip sizes to accommodate most coatings includ-
ing solvent-based paints, water-based coatings,
fine finish metallic, high-solids polyurethane,
contact adhesives, varnish, top coats, lacquer,
enamel primer, latex primer, epoxy and vinyl
fluids. The efficiency of these systems is greatly
reduced if the painting is done in an exposed area.
LVHP systems can be easily converted to HVLP
by retrofitting the air gun and installing the appro-
priate diameter air hoses (5/16 in. I.D.); however,
the air supply system must be able to deliver 10 to
30 cubic feet per minute of airflow at 10 psi or
lower. If a firm has a large investment in high-
pressure air compressors, conversion air systems
(CAS) can be used. The CAS reduces high-
pressure compressed air in two ways: 1) by using
an air-restricted HVLP gun that is specially ',
equipped to restrict air pressure within the gun
body, and 2) by using a small air conversion unit
that takes in high-pressure compressed air and
restricts its flow, delivering low-pressure air to the
HVLP gun (CC and Binksd). Costs can vary
depending on specific applications, painting/
coating type, paint volume, workpiece specifica-
tions and technique. Generally, costs for HVLP
paint-spray system equipment range from $500 to
$ 1,500 for a gun, hose and paint pot.
Safety
Painters are required to wear respirators to
prevent inhalation of overspray, hazardous vapors
and toxic fumes when using HVLP equipment.
Depending on the noise level in the spray booth,
ear protection may also be required.
Table 29. Advantages and Disadvanfages of HVLP Spray Guns (NCP2P, p. 5.)
Advantages
Disadvantages
Reduces overspray
Increases transfer efficiency
* Reduces paint waste
Lowers booth cleanup costs
Reduces filter replacement costs
* Decreases waterwash reservoir treatment costs
* Reduces VOC and HAP emissions
* Is portable'and easy to clean
* Sprays well into recesses and cavities
« Reduces worker exposure to blowback
Has atomization that may not be sufficient for
fine finishes
May not be able to operate with high
production rates
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Chapter 7: Application Techniques
CASE STUDY:
Lily Company
Lily.Company Drum Reconditioning in
Thomasville, North Carolina has experienced
a 38% reduction in lacquer paint ysage by
switching to HVLP guns. Converting to HVLP
has sayed the company approximately
$3,500 a month in materials and reduced
paint booth cleanup. The cost of the HVLP .
equipment was the same as it would have
been to purchase conventional spray gun
equipment (VT DEC). \
Low-Pressure/
Low-Volume
General Description
tow-pressure/low-volume paint spraying, which is
similar to air^assisted airless, is a relatively new
.development. Paint and air separately exit through
the spray nozzle into a secondary fluid tip assem-
bly. The exiting paint stream is of low pressure
(less than 100 psig), flattened by the spray nozzle,
but unatomized. Atomization occurs by impinging
low amounts of compressed air (5-35 psig) from :
two small holes in the fluid tip assembly into the
flattened paint stream. Table 30 presents an
overview of the advantages and disadvantages of
LPLV Systems. ,
Airless Spray
General Description
Airless spray does not use compressed air. In-
stead, paint is pumped at increased fluid pressures
(500 to 6,500 psi) through a small opening at the
tip of the spray gun to achieve atomization".
Pressure is generally supplied to the gun by an air-
driven reciprocating fluid pump (KSBEAP, p. 16).
When the pressurized paint enters the low pres-
sure region in front of the gun, the sudden drop in
pressure causes the paint to atomize. Airless
systems are most widely used by painting contrac-
tors and maintenance painters (Binksc).
Advantages and Disadvantages
Airless spraying has several distinct advantages
over air spray methods. This method is more
efficient than the air spray because the airless
spray is softer and less turbulent, thus less paint is
lost in bounce back. The droplets formed are
generally larger than conventional spray guns and
produce a heavier paint coat in a single pass. This
system is also mpre portable. Production rates are
nearly double^ and transfer efficiencies are usually
greater (65 to 70%). Other advantages include the
ability to utilize high-viscosity coatings (without
thinning with solvents) and its ability to have good
penetration in recessed areas of a workpiece.
Table 30. Advantages and Disadvantages of LPLV Spray Guns (Jacobs,
P-15)
Advantages
Disadvantages
* Reduces overspray
* Increases transfer efficiency
* Reduces paint waste
* Lowers booth cleanup costs
> Reduces filter replacement costs
+ Decreases waterwash reservoir treatment costs
4 Reduces VOC and HAP emissions
* Sprays well into recesses and cavities
* Has moderate capital cost
* Low operating costs
Does not have a proven track record
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Chapter 7: Application Techniques
The major disadvantage of the airless spray is
that the quality of the applied coating is not as
good as conventional coatings, unless a thicker
coating is required. Airless spray is limited to
painting large areas and requires a different
nozzle on the spray gun to change spray patterns.
In addition, the nozzle tends to clog and can be
dangerous to use or clean because of the high
pressures involved (IHWRICb). For more
information on other advantages and disadvan-
tages of airless spray, see table 31.
Application Considerations
Small fluid nozzle orifices limit the coating
materials that can be sprayed with airless sys-
tems to those that are finely ground. This rules
out fiber-filled and heavily pigmented materials.
In addition, airless spraying lacks the feather
capability that air guns have. This can result in
flooding of the surface and sags or runs if gun
movement is too slow. The high pressures used
with airless spray deliver a high rate of paint flow
through the nozzle, tending to enlarge the orifice,
increase flow rates and change spray pattern
characteristics. This is especially true at very
high pressures and with paints containing high
amounts of pigments or abrasive pigments. Strict
maintenance is required for this system. Foreign
objects in the fluid that are larger than the nozzle ,
tips can block or shut off the system. Equipment
maintenance on pumps is high .because of the
high pressures used (CAGE).
Economics
The capital investment required for a new airless
spray system consisting of an airless spray gun,
carted mount pump, hoses, and fittings, can range
from $3,500 to $7,500.
Safety
The high velocity of the fluid stream and spray
pattern as it exits the gun and hose is a potential
hazard. Operators should never allow any part of
their body to come into contact with this high-
pressure material. Failure to keep several inches
away from the coating as it exits the gun will result
in serious injury. As with other spray systems,
respirators are required, and hearing protection
may be required as well.
Types of Airless Systems
Air-assisted airless systems are a variation of
airless spraying. These systems use supplemental
air jets to guide the paint spray and to boost the
level of atomization. Approximately 150 to 800 psi
of fluid pressure and 5 to 30 psi of air pressure are
used. Air-assisted airless spray systems atomize
paint well, although not as well as air spray
methods. The use of air-assisted airless systems
improves the quality of the finish, presumably
because finer paint particles are formed. The
transfer efficiency of the airless, air-assisted spray
gun is greater in comparison to airless, and with
proper operator training, the manufacturer can
obtain finishes comparable to conventional guns
(Batelle, p. III-5). This system has the same
dangers as airless spraying, but it also requires
more maintenance and operator training and has a
higher capital cost (IHWRICb).
The major difference in gun construction between
an air-assisted airless gun and an air-atomized gun
is found in the atomizing tip. The air-atomized tip
incorporates a fluid nozzle and an air nozzle. The
fluid orifice in the center of the tip is surrounded
by a concentric atomizing ring of air. The air-
assisted tip delivers a flat fan spray of partially
atomized paint. Jets of atomizing air, exiting from
ports in small projections on each side of the tip
impacts at a 90 degree angle into the spray. The
air jets break up the large droplets and complete
the atomization, assisting the airless spray process.
Economics
The capital investment required for a new air-
assisted airless spray system, including an air-
assisted airless spray guri, 10:1 ratio carted mount
pump, hoses and fittings, can range from $2,500
to $5,000.
Advantages
* Low equipment maintenance. The reduced
fluid pressures in comparison with airless spray
cut down on pump and fluid nozzle wear.
*Good atomization. The atomization quality of
an air-assisted airless gun is rated as superior
compared to an airless gun but it is not nearly
as good as with an .air-atomized gun.
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Chapter 7: Application Techniques
* Low bpunceback. The extremely low atomiz-
ing air pressure allows air-assisted airless.
guns to spray into.corners and hard-to-reach
areas better than with air-atomized spray.
* Varied fluid delivery. The" paint flow rates can
' vary considerably from about 5 to 50 ounces '
, 'perminute. . ... ,
+ High'paint transfer efficiency. With a low-end
delivery rate of 5 ounces per minute versus 25
/ounces for airless, air-assisted transfer effi-
ciency is even higher than airless.
' Table 31 presents an overview of the advantages
and disadvantages of airless spray systems.
Air and air-assisted electrostatic spray guns
resemble nonelectrpstatic guns. An electrostatic
gun has a wire charging electrode positioned in
front to ionize the air. The ionized air passes its
qharge to the paint particles exiting the gun. Some
guns have no external electrode. Instead, an
internal electrode located inside the gun barrel is
used to charge the paint. In another variation, a
metal electrode is situated in the paint tank, and
the paint is delivered to the gun already charged.
Cost and Implementation Issues
LVHP systems cannot be converted to airless
systems. Therefore, the capital cost for imple-
menting airless spray is usually high. However,
this cost might be offset by the number of advan-
tages that airless spray provides.
Electrostatic Spray
General Description
This spray method is based on the principle that
negatively charged objects are attracted to-pqsi-
, lively charged objects. Atomized paint droplets are
charged at the tip of the spray gun by a charged
.. electrode;:the electrode runs 30 to 140 kV through
the paint at 0 to 225 microamperes (CAGE). Pairit
can be atomized using conventional air, airless, or
rotary systems. The electrical force needed to
guide paint particles to the workpiece is 8,000 to .
10,000 volts per inch of .air between the gun and
its workpiece. The part to be painted, which is
attached to a grounded conveyor, is electrically
neutral, and the charged paint droplets are at-
tracted to that part. If the charge difference is
strong enough, the paint particles normally fly
past the part and reverse direction, coating the
edges and.back of the part. This effect is called
"wraparound" and increases transfer efficiency
(KSBEAP, p. L5). Electrostatic spray is used by
most appliance manufacturers (Binksc).
Advantages and Disadvantages
The major advantage of using electrostatic
spraying is that it saves in material costs and labor.
The labor savings is often associated with a
changeover to automated lines, although labqr
savings for cleanup is significantly reduced in
either automated or manual lines. Another benefit
of electrostatic is its ability to completely cover an
object with a uniform thickness, including areas
that are normally inaccessible (Batelle, p. Ill-10).
Table 31. Advantages and Disadvantages of Airless Spray Systems (NCP2P,
p. 5)
Advantages
Disadvantages
* Has high rates of "paint flow
*Has relatively high transfer efficiency
* Has versatile gun handling (no air-hose)
* Has ability to apply highly viscous fluids
* Has relatively poor atornizatiori .
* Has an expensive nozzle
* Reduces fan pattern control
> Has coatings limitations
+ Has a tendency for tip plugging
* Has a skin injection danger
<> Requires increased operator training
* Requires increased maintenance
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Chapter 7: Application Techniques
The initial capital investment for electrostatic
systems is high (EPA, p. 155). In addition;
electrostatic systems must be properly grounded at
all stages of paint delivery in order to reduce
injuries and fire hazards that can result from
shorting or sparking (KSBEAP, p. 15-16). An-
other problem with electrostatic spray is that the
paint is attracted to all grounded objects, including
the conveyor and conveyor protection systems in
assembly line painting, the paint booth ceiling, the
spray gun and the spray gun handler. Work has
been done on developing an electrically charged
paint repelling panel to protect against stray paint.
Such repelling panels are not 100% effective, but
they can cut down on problems from stray paint
(IHWRICb). For more information on other
advantages/disadvantages of electrostatic spray,
see table 32.
Types of Electrostatic Systems
Rotary atomization is a variation of electrostatic
spraying that uses centrifugal force generated by
discs or bells to atomize paint, which drives it
from the nozzle. The atomization of this method
is excellent as is the transfer efficiency. This
method also can be used with paints of different
viscosity. However, the equipment needed for this
type of application is very specialized and usually
requires a major conversion of a painting line
(IHWRICb). Typical costs for a new rotary
atomization system consisting of a rotary atom-
izer, 2-gallon pressure-pot, and hoses and fittings
may range from $5,000 to $7,500 .
Implementation Issues
An LVHP air spray system can be converted to an
electrostatic system. In most cases, however,
airless, air-assisted airless, or rotary atomization is
used with electrostatic spray. This is because
LVHP air-afomized electrostatic spray has a
transfer efficiency of only 60 to 70%. Airless,
however, runs from 70 to 95%, and rotary runs
from 80 to 90% (IHWRICb).
Part and gun cleanliness are essential for efficient
electrostatic operation. Dirt or oversprayed paint
can form on a conductive track on the plastic gun
tip and short out the system. For top efficiency, '
the part to be coated should be the closest
grounded object to the charging needle on the
spray gun. The charged paint particles are at-
tracted to the nearest electrically grounded item;
the larger the item, the greater the attraction.
Ungrounded objects in the vicinity of the charged
gun electrode can pick up a considerable electrical
charge. The charge buildup can arc over or spark
if a grounded object is brought near. The intense
heat of the arc may be sufficient to ignite the .
solvent-laden atmosphere typically found in a
paint booth'.
Paint buildup on hooks or hangers can act as an
insulator and block the flow of electric current in
the electrostatic circuit. Hangers and hooks should
be regularly stripped or otherwise cleaned of paint
buildup to maintain good grounding-contact
between the parts and the conveyor.
Because of high transfer efficiencies, air velocity
in spray booths may be reduced from 100 to 60
feet/minute. This results in a 40% reduction in
make-up air costs and reduces emissions.
Safety
In 1995, the National Fire Protection Association
(NFPA) rewrote the NFPA 33 Standard to require
fast-acting flame detectors for all automatic
electrostatic liquid painting applications. These are
also required for automatic electrostatic powder
coating applications. All electrically conductive
materials near the spray area such as material
supply, containers and spray equipment should be
grounded as well.
Cost
The capital investment for a new liquid electro- .
static spray system consisting of an electrostatic
spray gun, 2-gallon pressure pot, and hoses and
fittings can range from $4,900 to $7,500. The
capital investment required for a new electrostatic
powder coating spray system, including powder
application equipment, powder booth, cleaning
system and bake oven, may range from $75,000
to $1,000,000. (CAGE). . '
Other Methods
This section presents brief descriptions of a
variety of other paint application methods, includ-
ing electrodeposition, various dip processes, and
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Chapter 7: Application Techniques
Table 32. Advantages and Disadvantages of Electrostatic Spray Guns
(NCP2P, p. 6)
Advantages
Disadvantages
'+Has high transfer efficiency
*Has good edge cover
* Has good wraparound
* Has uniform film thickness
*Has guns that tend to be bulky and delicate,
* Requires extra cleanliness -...-.
* Creates Faraday cage effect
* Can be safety/fire hazard
^Requires all parts*to be conductive (however,/
- special conductive precoatings on nonconductive
workpieces can be used to permit electrostatic
spray) .
+ Has high equipment and maintenance cost
direct application methods such as roller and flow
coating.
Electrodepositipn/Electrocoating (E-coat). This
process applies paint in a method that is similar to
electroplating. In the E-coat process, a paint film
from a waterborne solution is electrically depos-
ited onto a part. Parts are usually made primarily
of steel. An E-coat bath contains resin, pigment
(unless it is a clearcoat), solvent (water and a
cosolvent) and additives. The most commonly
used resins in this process are epoxies and acryl-
ics. These systems have no or low VOC emissions
and produce little toxic waste.
. The liquid is a very dilute emulsion of waterborne
paint. Reactions between the paint particles and
certain bath components cause the resin to be
ionic. The electric current causes the paint par-
ticles to migrate to the metal surface. As more and
more particles collect, water is squeezed out and
cross linking of the resin particles occurs. TJie
transfer efficiency of electrodeposition is greater
""'than 90%. High production rates are possible, and
production can be automated. However, this
method is costly and requires a lot of energy.
Also,.employees need a high level of training to
use this system (IHWRICc). "... .
E-coat is extremely efficient, depositing a mostly
uniform coating on all surfaces that can be
reached by electricity. Waterborne electrocoating
systems may be used to apply uniform, pinhole- '
' free coatings. For films that require high appear-
ance.standards, E-coat uses acrylic resins.
Electrocoatings are resistant to attack'by UV light
CASE STUDY:
Navistar International Transportation
Corporation
Navistar International. Transportation
Corporation's assembly plant in Springfield,
Ohio, is the site of painting and final assembly
of Navistar's medium-and heavy-duty trucks
and school bus chassis. The plant's compre-
hensive pollution.prevention efforts have
resulted in significant reductions in environmen-
tal releases.
Many of the'pollution prevention activities have.
taken place in^Navistar's painting operations.
In the prime coating operation, conventional
air-atomized, low-solids paint was replaced
with waterborne paint, resulting in a 50%"
reduction in.VOC emissions. Electrostatic
robotic application of paint has increased
transfer efficiency of equipment in topcoat
operations. For almost all colors of topcoat,
Navistar was able to change from applying two
coats of paint to only one coat of paint without
lowering product quality, reducing the amount
of paint wasted by 65,000 gallons and the
amount of solvent used by 138,000 gallons
annually.
Other raw material, process and equipment
changes have resulted in annud reductions
exceeding 65 tons of VOC emissions, 82 tons
of HAPs and 2^600 gallons of hazardous
waste. ,
* Savings-
Navistar reports savings in excess of $3.5
million. (OH EPAb)
95
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Chapter 7: Application Techniques
and have good weatherability. Typical applica-
tions include truck beds, engine blocks, water
coolers, microwave ovens, dryer drums, com-
pressors, furnace parts, housings for the automo-.
tive industry, shelving, washers, air conditioners,
file cabinets, switch boxes, refrigerators, trans-
mission housings, lighting fixtures, farm machin-
ery, and fasteners.
One drawback to the electrocoating system is
that it is limited to one color at a time. Each color
requires its own tank.
Autodeposition. Autodeposition is a process used
to deposit organic paint films Onto iron-, steel-,
zinc- and zinc alloy-plated substrates.
Autodeposition is typically an 6-step process,
including alkaline cleaning, rinsing with plant water
and deionized water, autodeposition (immersion),
immersion sealing rinse and curing. The part is
immersed into a solution containing paint conv-
pounds, usually a vinyl emulsion, hydrofluoric
acid and hydrogen peroxide. When the part is
submersed, the paint compound precipitates out of
the solution and coats the part. The part is then
removed from the tank, rinsed and cured
(KSBEAP,p.20).
Autodeposition is an effective method for achiev-
ing corrosion resistance and coverage of objects.
Autodeposited films also provide extremely
uniform thicknesses, typically 13 to 30 microme-
ters (0.6 to 1.2 mils). These resins also have
excellent hardness, formability and adhesion
characteristics. Two other advantages of
autodeposition are that organic solvents are not
needed, and little or no VOCs are emitted.
Autodeposited films have high transfer efficiencies
(approximately 95%), further reducing environ-
mental impacts. This system also does not have'
CASE STUDY:
Emerson Electronics
In 1977, the Emerson Electronic plant in
Murphy, North Carolina,,was faced with a
decision concerning the type of paint line to
install for producing a quality finish on die-
cast aluminum, bench power tool parts.
Emerson compared an electrostatic spray
process for coating solvent-based paint to an
electrocoating process applying a water-
based paint.
Emerson found that the electrocoating system
offered the following advantages:
Lower VOC emissions, 70 pounds per day
versus 3,040 pounds per day
Lower hazardous paint waste, 0 pounds
per day versus 160 pounds per day
> Production cost savings of $1,080,000 per
year
> Raw material cost savings of $600,000 per
year (VT DEC)
Table 33. Advantages and Disadvantages of E-Coat Systems (NCP2P, p.7)
Advantages
Disadvantages
« Utilizes over 90 percent of coating material
« Has very thick, uniform coating on all surfaces
that can be reached by electricity
* Has high production rates
I * Produces corrosion-resistant coating
+ Has low VOC and HAP emissions
I * Can be fully automated
*Can apply seiond coat on uncured
electrocodt
* Has substrate limitation
* Requires separate lines for each color
* Requires high cost to install
* Has masking problems
* Requires sophisticated maintenance
* Has air-entrapment pockets
* Has difficulty coating bulky, small parts
* Requires corrosion-resistant equipment
* Requires de-ionized water .
+ Has difficulty sanding/stripping
* Has high energy demands
+ Is restricted to large volume finishing
* Has coating thickness limitation
+ Requires high level of training for employees
96
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Chapter 7: Application Techniques
fire hazards. However, autodeposition produces a
dull or low gloss finish and has few available
colors (IHWRICc). The largest application for
autodeposition coatings have been for nonappeaf-
ance and under-hood parts in cars and trucks due
to their excellent anticorrosion properties.,It is also
used on drawer slides for office furniture, replac-
ing zinc-plating: '....'
Dip Coating. With this process, parts are dipped
(usually by conveyor) into a tank of paint. Dip '
coating allows for a high production rate and high
transfer efficiency and requires relatively little
labor. The effectiveness of dip coating depends
greatly on the viscosity of the paint, which
thickens with exposure to air unless it is. carefully.
managed. The viscosity of the paint in a dip tank
mustremain practically constant if the deposited
film quality is to remain high. To maintain viscos-
ity, solvent must be routinely added as makeup.
This results in higher VOC per gallon ratios.
Dip coating is not suitable for objects with hollows
'or cavities, and generally the finish is of lower
quality (IHWRICc). Color change is slow and not
feasible for most dip operations. This process is
usually used to apply primers and to coat items
whose appearance is not vitally important. Top
coats are not commonly applied by dipping.
Coatings applied by dipping have only a poor to
fair appearance unless parts are rotated during
drippage.'Dipping is well suited for automation
with conveyerized paint lines.
Capital investment required for dip coating is
minimal. All that is required is a tank for the
coating. The parts may be dipped manually, or -
automatically with a conveyor. Given the large
surface area of the dip tank, adequate ventilation
must be provided to prevent buildup of fumes and
vapors. An efficient fire-extinguishing system must.
be installed as a safety measure if flammable
paints are. used (CAGE).
Flow Coating. In a flow coat system, 10 to 80
separate streams of paint coat all surfaces of the
parts as they are carried through the flow-coater
on a conveyor. This system has the advantages of
dip coating along with low installation costs and
low maintenance requirements. The quality of the
Table 34. Advantages and Disadvantages of Autodeposition Systems
(NCP2P, p. 7)
Advantages
Disadvantages
Has excellent anticorrosion properties
(no phosphate coating required)
* Wets T 00% coverage of surfaces
(no Faraday cage areas)
Uses waterborne material
» Requires no.external source of electricity
Has dull or low gloss appearance
Has few colors available
Table 35. Advantages and Disadvantages of Dip Coating Systems
(NCP2P, p. 7)
Advantages
Disadvantages
Has high production rates.
Requires low labor
Has high transfer efficiency
Can closely rack parts
* Coating thickness does not depend on
operator skill , .
Is well suited to automated applications
> Is extremely dependent on viscosity of the paint
V Is not suitable for items with hollows or cavities
* Has slow color change
>Can be a fire hazard
* Has poor to fair appearance
+ High VOC emissions relative to the amount
of coating applied in low VQC applications
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Chapter 7: Application Techniques
finish is also comparable to dip coating
(IHWRICc).
Flow coating is usually used for large or oddly
shaped parts that are difficult or impossible to dip
coat. Coatings applied by flow coating have only a
poor to fair appearance unless the parts are
rotated during drippage. Flow coating is fast and
easy, requires little space, involves relatively low
installation cost, requires low maintenance, and
has a low labor requirement. Required operator
skill is also low. Flow coating achieves a high paint
transfer efficiency, often 90% and higher (CAGE).
Principal control of dry-film thickness depends, on
the paint viscosity. If viscosity is too low, insuffi-
cient paint will be applied. If the paint viscosity
rises, extra paint will be applied. This can increase
paint costs and also plug small holes in the part
(CAGE).
Curtain Coating. Instead of the multiple streams
of paint found in flow coating, curtain coating uses
a waterfall flow of paint to coat parts on a con-
veyor belt. The paint flows at a controlled rate
from a reservoir through a wide variable slot.
Curtain coating has a high transfer efficiency and
covers parts uniform ly, but is suitable only for flat
work. The quality of the finish depends on the
viscosity of the paint (IHWRICc).
Roll Coating. Roll coating is the process of
applying a coating to a flat substrate by passing it
between rollers. Paint is applied by one or more
auxiliary rolls onto an application roll, which rolls
across the conveyed flat work. After curing, the
coated substrate is then shaped or formed into the
final shape without damaging the coating. The
paint-covered rollers have large surface areas that
contribute to heavy solvent evaporation. This can
pose a fire hazard from flammable solvents in
solvent-borne formulations.
Roll coating is divided into two types: direct and
reverse roll coating. In direct roll coating, the
applicator roll rotates in the same direction as the
substrate moves. In reverse roll coating, metal .
feed stock is fed between the rolls as a continuous.
coil. The applicator roll rotates in the opposite
direction of the substrate.
Roll coating is limited to flatwork and is extremely
viscosity dependent. Coating properties should be
checked often to ensure proper results. These
tests should include adhesion, impact resistance,
flexibility and hardness. A well-known application
of roll coating is coil coating, in which coiled metal
strip is uncoiled, pretreated, roller coated with
paint, cured and then recoiled (IHWRIC, p. 36).
Roll coaters are typically custom made for each
application. Roll coaters can be made-to-order to
Table 36. Advantages and Disadvantages of Flow Coating Systems
(NCP2P, p.7)
Advantages
+ Has high transfer efficiency
* Has low installation cost
* Requires little maintenance
* Has high production rates "
* Requires less labor.
Disadvantages
* Has poor to fair appearance
* Requires principal control of dry-film
thickness to control viscosity of pajnt
Table 37. Advantages and Disadvantages of Curtain Coating Systems
(NCP2P, p. 7)
Advantages
* Has high transfer efficiency
+ Enables uniform coating thickness
Disadvantages
* Is suitable only for flat work
+ls highly dependent on viscosity
98
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Chapter 7: Application Techniques
Tabte 38. Advantages and Disadvantages of Roll Coating Systems
(NCP2P, p. 6)
Advantages
«' Has high transfer efficiency
> Has high production rates
Disadvantages
* Cannot paint hard-to-reach areas
* Is limited to flat work
accommodate widths ranging from 14 to 100
inches. .
Plural Component Proportioning System for
Epoxy Paints. Plural component proportioning
systems are self-contained epoxy paint measuring
and mixing systems. These systems accurately
mix the epoxy paint components, produce the
precise amount of paint required by an applica-
tion, and consequently minimize waste.
'''.. "*"
Epoxy paint mixtures are prepared by premixing a
base and a catalyst and then combining them in
appropriate proportions in a separate container.
After mixing and waiting the specified time,
application of the paint to the workpiece may
proceed. Once mixed, epoxy paints have a limited
pot-life that cannot be exceeded without affecting
the characteristics of the paint. If the pot life is
exceeded, the mixture must be disposed of, and
the application equipment must be cleaned. Under
conventional methods, these mixtures are pre-
pared by hand, a process that frequently leads to
the generation of excess paint. The solvents used
to cleanup and dispose of excess paint generates
hazardous waste consisting of spent solvents and
waste paint.
Plural component proportioning systems are used
in conjunction with application devices. A typical
proportioning and application system layout
includes the following components: proportioning
pump module, mix manifold, mixer, application
device, materials supply module, and purge or
flush module. These systems optimize painting
'operations by maximizing efficiency and minimiz-
ing waste generation.
The plural component proportion system for
epoxy paints provides for total control of materials
from containers) to application. The system is
accurate and can provide more consistent material
quality than hand mixing,These systems can also
keep pace with higher production requirements.
The systems mix the coating on demand (i.e., as
the gun is triggered); This does not result in
significant quantities of waste materials because
no excess paint is mixed. Material cleanup requires
less labor and maintenance, and generates less
waste because the mixed material can be purged
with solvent from the mix manifold, mixer, hose,
and applicator before it cures. The plural compo-
nent system is a closed system and, as a result,
there are fewer spills, less contamination or waste
to cleanup, and less exposure of toxic materials to
personnel.-In addition, the proportioning system
makes bulk purchase of material practical.
If an epoxy paint requires significant induction
time (i.e., 15 minutes or longer), the plural
component system can still be used, provided that
the mixed paint is allowed to stand in a separate
.container prior to application.
Capital costs for plural component proportioning
systems can range from $6,000 to $7,500 for
basic units that mix two materials, up to $50,000
. to $70,000 for systems that mix multiple materi-
als. Application systems are an additional compo-
nent, and their capital costs can range from $500
to $5,000. Each application needs to be evaluated
on a case-by-case basis with respect to material
and labor costs and savings.
Supercritical Carbon Dioxide (CQ2).
Supercritical fluid spray application allows substi-
tution of supercritical carbon dioxide for up to
two-thirds of conventional solvents concentration
in spray-applied coatings, reducing VOC emissions
by 30 to 70%. The proportioning and supply
system from Union Carbide (UNICARB) mixes
supercritical CO2 solvent with coating concentrate
and supplies the material to a specially designed
spray gun (i.e., internal mixing). The CQ2 solvent
is compatible with high molecular weight resins
and existing painting facilities and procedures;
99
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Chapter 7: Application Techniques
Table 39. Advantages and Disadvantages of Plural Component
Proportioning Systems (NCP2P, p. 7)
Advantages
Disadvantages
« Provides total control of materials from
container to application
* Generates paint on an as-needed basis,
eliminating the generation of excess paint
(Under conventional methods, this excess
paint is frequeritly disposed of as hazardous
waste)
* Minimizes solvent cleanup
* Reduces chance of spills
* Reduces worker exposure
Needs to be designed for specific applications
therefore, mis-compatibility enables the use of
solvent-borne formulations with substantial VOC
reductions.
Advantages and Disadvantages
In the supercritical CO2 spray process, the sol-
vent-like properties of supercritical CO2 are .
exploited to replace a portion of the solvent in the
conventional solvent-borne coating formulation.
The addition of supercritical CO2 acts as a diluent
solvent to thin the viscous coating just before
application, so that the coating can be atomized
and applied with a modified spray gun (EPA1).
Supercritical fluid spray application can be used to
coat metal and plastics. The applied coating has a
higher viscosity that allows thicker coatings
without runs or sags. However, care is required in
working with high-pressure gas at high operating
temperatures (100 to 150°F) (TURI, p. 2).
Cost and Implementation Issues
This system requires investment in hew equip-
ment for paint mixing, handling and spraying. In
1991, five coating formulators were licensed to
develop, manufacture and market UNICARB
systems, including Akzo (automotive components,
furniture), BASF (automotive), Guardsman
(furniture), Lilly (furniture, plastics, heavy
equipment) and PPG Industries (automotive, >
heavy equipment) (EPAd, p. 82).
Paint Booths
A paint booth is an enclosure that directs
overspray and solvent emissions from painting .
operations away from the painter and toward an
entrainment device. Spray booths are designed to
capture particulate matter that is released into the
air during coating operations. The'y are not
Table 40. Advantages and Disadvantages of Supercritical Carbon Dioxide
(NCP2P, p. 3)
Advantages
+ Has high quality finish
* Needs fewer coating applications
+ Reduces VOCs and HAPs
* Reduces operating costs
+ Is easy to retrofit
+ Has high transfer efficiency
* Reduces worker exposure for solvent vapors
Disadvantages
+ Has limited industrial experience
* Has lower fluid delivery rates than airless or air
spray guns
* Has bulky gun and supply tubing
* Has royalty costs '
100
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Chapter 7: Application Techniques
Table 41. Transfer Efficiencies of Various Application Technologies
(IHWRIC> p. 37, KSBEAP, p. 23 and CC)
Technology
Conventional Air Spray
HVLP Spray
LPLV Spray
Airless Spray
Electrostatic Spray
Electrodeposition
Transfer
Efficiency
30 to 60%
50 to 90%
60 to 80%
65 to 70%
65 to 95%
90 to 99% ,
Operating
Cost
Low
Low
Low
Medium/high
Medium/high
NA
Finish
Quality
'High
High
. Unknown
Low
Low.
NA
Recess
Coverage
Good
Good
Good
Good " '
Poor
NA - '
NA=not applicable
abatement devices for VOCs. A spray booth's
primary function is to protect the painter and
other employees from exposure to potentially
toxic vapors and particulates. Another function of
the booth is to prevent fires within a facility by
venting high concentrations of flammable solvent
vapors out of the building (EPAq, p. 149).
Pollution Problems
Discharges from paint booths consist of particulate
matter and organic solvent vapors. Particulates
result from solids in the paint that are not trans-
ferred t"o the part. Organic solvent vapors are from
the solvent, diluent or thinner that is used with the
coating to reduce the viscosity of the paint. Much
of the particulate matter is captured by a dry,
water-wash or baffle filter (these are discussed
belo.vv). Solvent vapors are controlled or recov-
ered by the application of control technologies
such as condensation, compression, absorption,
adsorption or combustion. Solvent vapors can be
minimized by using more efficient equipment, and
low or no VOC materials. Increasing the transfer
efficiency of the painting operation can result in
both reduced particulate and solvent emissions
(EPAq, p. 149).
Types of Paint Booths
There are two basic types of enclosures that are
used in most painting applications: dry booths and
wet booths. The key difference between the two
is that a dry booth depends on a filter of paper,
fiberglass or polystyrene to collect overspray,
while the wet booth uses water with chemical
additives to collect overspray. The type of booth
selected can affect the volume and type of paint
wasted A third type of booth is used exclusively in
powder coating operations. '.''.
Although a spray booth is generally thought of as
an enclosed.painting area, this is not always the
case. For instance, facilities that paint very large
pieces may have a booth that only has one side,
consisting of an exhaust plenum that draws
solvent and particulates away from the operator. It
is also not uncommon to see two spray booths
opposite one another. This set-up allows for very
large workpieces to be transported in between the -
booths either by a conveyor or a forklift truck that
runs between the booths. Often neither booth has
a ceiling, and they draw air from the surrounding
factory (EPAq, p. 149).
Regardless of the size or design of the booth, they
consist of one of three basic designs for directing
, airflow.
>Cross-draft. In a cross-draft booth, air moves.
from behind the operator toward the dry filter ,
or water curtain (parallel to the floor). This type
of booth is ideal for systems where the parts
are moved through the facility in a rack or ..
conveyor system, and the painter applies the
, coating from only one direction. However,
these types of systems can be used if the paint
must be applied .in more than one direction.
This type of ventilation system is usually the
least expensive. . p
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Chapter 7: Application Techniques
Table 42. Overview of Application Technologies (IHWRIC, p. 36-37;
IHWRICb,c; and Binksc)
Technology
HVLP Spray
LPLV Spray
Airless Spray
Air- Assisted
Airless Spray
Rotary
Atomization
Pollution
Prevention
Benefits
* Reduces overspray,
increasing transfer
efficiency
4 Reduces VOC and
HAP emissions
> Lowers risk of
blowback to the
worker
* Has a .high transfer
efficiency rate
+ Has low operating
costs
* Has moderate
capital costs
* Has a transfer
efficiency of 65
to 70%
* Cuts overspray by
more than half,
and is cleaner and
more economical
* Has higher transfer
efficiency and lower
chance of blowback
* Has excellent
efficiency
Reported
Application
*Can be used on
many surfaces
^.Hydraulic
atomization used
most widely by
painting
contractors and
maintenance
painters
+ Heated
atomization usec
by furniture
manufacturers
and industrial
finishers
*Used by furniture
and industrial
finishers
Operational
benefits
*ls portable and
easy to clean
^Allows'operator
to vary the air
pressure, air
volume, paint
pressure and
spray pattern
* Is twice as fast
as air spray and
produces a
higher film build;
is more portable
than air spray
* Has material
savings that are
50% better
than air spray
*Has higher film
build per pass
than air spray
+ Can be used
with paints of
different viscosity
Limitations
*Has production
rates that are
not as high as
conventional air
spray
*ls widely used
* Is limited to
painting large
areas, requires
a different
nozzle to change
spray patterns;
nozzle tends to
clog and can be
dangerous to use
. or clean because
of the high
pressures
involved
*Has same
dangers as
airless, but'
requires more
maintenance and
operator training,
. and has a higher
initial capital cost
* Requires high
degree of
cleanliness
, - (continued on next page)
102
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Chapter 7: Application Techniques
Table 42. Overview of Application Technologies (IHWRIC, p. 36-37;
mWRICb,c; and Binksc) (continued)
|r
Technology
Electrostatic
Spray
V
Auto-
deposition
Electro-
deposition
t
; p
Pollution
Prevention
Benefits
* Has high transfer
efficiency
* Produces little over-
spray and uses
' i ' .
relatively little paint
0 '
' . > ' .
* Uses water-borne
.paints
v:
* Has transfer
efficiency of more
than 90% . '
Reported
Application
* Is good for .
. painting oddly
shaped objects
* Is used by most
appliance
manufacturers
/
,
* Is limited to iron,
steel, zinc and
zinc-alloy plated
materials
4> Is limited to
metallic or other
electrically con-
ductive objects
(e.g., autobody
coating)
. ' '
Operational
Benefits
* Produces a
uniform coat
because the
paint itself acts
as an insulator
#
« Is effective for
anti-corrosion
properties and
coverage of the
objects
V Uses no
electricity
* Can accommo-
, date high
production rates,
production can
be automated
'v ;
Limitations
* Has limited
coverage with
complicated
' parts because
of Faraday cage
effects
+Can paint only
conductive parts
* Presents a
possible shock
hazard
*ls limited to only
-one coat
*ls more expen-
sive^ slower and
has higher
" maintenance
costs than air
spray
* Is limited to
chargeable paints
* Surface of the
object must be
extremely clean
>ls limited to dull
or low gloss
finish'; few
available colors
* Requires that
objects be metallic
or electrically
conductive
» Is costly and
requires a lot of
eher,gy ,
* Requires that
employees receive
high level training to
use this system
[continued .on next page)
103
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Chapter 7: Application Techniques
Table 42. Overview of Application Technologies (IHWRIC, p. 36-37;
IHWRICb,c; and Binksc) (continued)
Technology
Dip, Flow and
Curtain
Coating
Roll Coating.
Pollution
Prevention
Benefits
* Has high transfer ,
efficiency
+ Has high transfer
efficiency
Reported
Application
* Is well suited
for parts that
are always the
same color and
have minimum
decorative finish
requirements,
such as
agricultural
equipment
-
> Is limited to sheet
materials (e.g.,
'strip metal and
boards); used to
decorate cans
and other metal'
objects
Operational
Benefits
> Has high
production rate
* Requires
relatively little
labor
+ Has high
production
rates
Limitations
* Depends
greatly on the
viscosity of the
paint, which
thickens with
exposure to air
unless. carefully
managed
Vis not suitable
for objects with
hollows or
cavaties .
*Has lower
quality finish
* Is limited to flat
work .
» Down-draft. Down-draft booths move air
from the cejling of the booth vertically down-
ward toward an exhaust plenum in the floor.
This type of booth is preferred when the paint
operator must be able.to walk around the
part, particularly in the case of painting large
machines. These booths usually cost more than
cross-draft booths because they require
building' a pit beneath the booth. The operat-
ing expenses with a down-draft are also
usually higher because these systems draw
more air.
* Semidown-drdft. This type of booth moves the
air down and then to the side where the
exhaust is located. Semidown-draft booths
offer a compromise between the cross-draft
and down-draft configurations (EPAq, p.
149). ' ..
Decisions about equipment should be made based
on the type and volume of painting done and the
volume of waste generated.
Choosing between a dry filter, water-wash or
baffle spray booth encompasses many different
issues. The following section provides informa-
tion on these three systems. Analysts estimate that
80% or more of the spray booths in use today are
of the dry filter type (EPAq, p. 151). Inrecent
years, however, many facilities have switched to
water-wash booths because of their lower mainte-
nance and hazardous waste costs. However, there
are other concerns with these booths. The follow.-
ing section provides more detail on dry filter and
water-wash booths.
Dry Filter Booths
There are many types of dry filter systems,
however, they all operate on the same principle:
104
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Chapter 7: Application Techniques
i
participate- laden air flowing toward the filter ,
medium is forced to change directions rapidly.
The particulate, having more inertia than the
surrounding air, impacts the filter medium and is
removed from the air flow. The scrubbed air is
then vented to the atmosphere.
There are four general types of filters currently
used; fiberglass cartridges, multilayer honey-
combed paper rolls or pads, accordion-pleated
paper sheets, and cloth rolls or pads. Each type of
filter has different characteristics for particulate
capacity, removal efficiency, cost and replacement
time. Filter performance is characterized by three
basic parameters: particulate capacity, resistance
to air'flow and particulate removal efficiency.
Filter replacement is required when the filter
becomes heavily laden with captured particles,
resulting in a reduction in removal efficiency and
an increase in the pressure differential across the
filter face. The primary waste stream generated
by dry booths is spent filters. When using lead or
. zinc chromate paints, the dry filter will eliminate
5 0 to 90% of the hazardous waste generated by
water-curtain paint booths.
Generally, small-volume painting operations find
' that the lower cost of a dry-filter booth meets their
requirements. This equipment requires a low
capital investment relative to wet-booths and are
simple in design. The filters act to remove paint in
airborne particles by capturing them as they are *
forced through the filter. Ease of replacing a
relatively low number of filters produced by small
operations makes such an approach attractive. As
paint volume increases, though, filter replacements
must be made more often. This may increase
costs for labor and materials significantly
. (Mitchell, p. 10).. -
Dry filters effectively remove up to 95 to 99% of
particulates. These systems are also versatile.
They can be used in booths of all designs (small,
large, cross-draft, down-draft and semidown-
draft). These booths can also be operated for a
variety of coating technologies, including polyure-
thanes, epoxies and alkyds. However, they cannot
be used for nitrocellulose paints and some
waterborne coatings (proper filter selection is
critical in these cases). They are inexpensive to
purchase, and depending on the nature of the
paint (i.e., pass or fail TCLP test), they are also
inexpensive to operate.
A disadvantage of dry filter booths is that they
are generally not appropriate for facilities with
high coating use (i.e;, greater than 5 gallons per
square foot of filter areas per day). They also
have problems with VOC emissions, since they
do not remove VOCs. .
Regarding safety, dry filters are a potential fire
hazard, especially if dry overspray is allowed to
Jjuild up. Typically, the majority of this waste is
the filter media, which can be contaminated by a
relatively small amount of paint. Reusable filters
may decrease waste volume and reduce disposal .
cost. In some applications, such as powder
coatings, overspray can be reused. ,
Choosing the proper type of dry filter is important
for a facility's operations. Dry filter characteris-
tics that should be considered include:
* Efficiency-its ability to remove particulates
before they enter the stack
*Resistance-this is the pressure differential that
ensues when the high velocity of air passes
across the filter bank
* Holding capacity-the amount of overspray that
a filter can hold or retain during its service life
* Incineration profile-can spent filters be
burned?
* Biodegradability-does the product degrade
naturally? :
* Landfill option profile-does it meet landfill
standards?
* Flammability-does it meet the National Fire
Protection Bulletin number 33 requirement and '
Underwriter's Laboratories Approved Class 2
list? .
* Suitability for various coatings-some water-
borne coatings may complicate filter choice; .
facilities should check to make sure filter is
compatible with all/coatings that will be used
Filters made from expanded polystyrene are also
available. Facilities can reuse these types of filters
after carefully brushing the overspray off the
surface with a bristle brush. Hence, the same
filters can be used several times until they break
or become unusable. Manufacturers have pro-
moted the practice of dissolving the filter in a
105
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Chapter 7: Application Techniques
drum of solvent and paint waste when a facility is
ready to scrap the filter. The solvents dissolve the
filter into the waste, which must then be treated as
a hazardous waste. Some facilities have argued
that this is counterproductive due to disposal costs
o'f liquids versus solids. Others argue that this
qualifies as treatment of a hazardous waste and
therefore is a violation of RCRA regulations1
(EPAq.p. 151).
Water-Wash Booths
Water-wash booths capture overspray paint by
using positive air pressure to force the particles .
into a cascading curtain of water. As a result of
being captured in the water curtain, uncured
particles of paint accumulate in a wash-water pit,
located either beneath a grating that the painters
stand on or above ground behind the booth itself.
When overspray enters the Water, it remains
sticky and can plug up holes, nozzles, pipes and
. pumps. In addition, it can form a deposit on the
water curtain, slowly building up a layer that
eventually impedes the smooth water flow down
the water curtain's face. With time, the water
becomes contaminated with bacteria and requires
disposal. To prevent this from occurring, the
water needs to be treated with chemicals designed
to de-tack overspray particles (EPAq, p. 152).
If overall .painting volume can justify the invest-
ment, a water-wash booth has substantial advan-
tages. This type of booth eliminates disposal of
filter media and allows waste to be reduced in
weight and volume. This is achieved by separat-
ing the paint from the water through settling,
drying, or using a centrifuge or cyclone. How-
ever, the primary disadvantage of this technology
is the resulting generation of large quantities of
wastewater and paint sludge. Typically, spent
wastewater and sludge requires offsite treatment,
and the paint sludge is disposed of as a hazardous
waste. Depending on the amount of coating used,
this option could use more energy, require more
maintenance time, add to chemical use for water
treatment, and/or result in additional cost to
dispose of "wet," low BTU value, heavy paint
sludges than a dry filter booth. These units are
also more expensive to install and to operate than
dry filter booths. ' .
The water-wash booth design faces substantial
challenges and more restrictive landfill regulations
than they have in the past. Prior to 1993, some
liquid nonhazardous special wastes could be
disposed of in a landfill with little or no treatment..
EPA's decision to redefine liquid wastes and ban
certain materials from landfill disposal pertains to
sludge generated from water-wash booths.2 This
material still can be disposed of, however, the
material must be.processed prior to disposal,
resulting in a significant increase in waste treat-
ment costs (Mitchell, p. 10).
Baffle Booths
A baffle spray booth is an uncommon alternative
to both dry filter and water-wash booths. In a
baffle spray booth, the face of the booth has steel
Table 43. Advantages and Disadvantages of Dry Filter Booths (NFESC, p. 3)
Advantages
Disadvantages
* Decreases operating costs when compared
to water curtain spray booths due to reduced
chemical, electrical, sewer and water costs
* Reduces waste generation of wastewater
and sludge . "
+ Eliminates need for daily skimming and
removal of sludge from the booth
Increases efficiency of particulate removal
Is not compatible with powder paint application:
« Has filter selection that depends on paint type
and application
Requires frequent downtimes if improper filter is
used
'For more information, see the May 1995 issue of Metal Finishing.
2EPA's definition of "liquid wastes" is: any material that will exude droplets of liquid through a standard
conical paint filter within a prescribed period of time.
V06
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Chapter 7: Application Techniques
. baffles that run the height of the booth and are
several inches wide. The baffles usually overlap
each other, forcing the air .that passes through the
booth to change direction in order to reach .the^
back of the booth. When the air does reach the
entrainment section in the back, the paint particu-
lates that the air is carrying fall into the trough for
reuse. These booths are used less frequently
because unless the facility is reclaiming paint, this
type of booth offers no advantages,
Powder Coating Booths
In most powder coating operations, the coating is
reclaimed and reused in the process, optimizing
material use. Powder coating booths have smooth
sides with steep, hopper-like sloping bottoms that
empty into collectors and an exhaust system that
removes powder'suspended in the air. The
powder is drawn into a cylindrical chamber that
has a centrifugal blower to force the powder to the
outside walls where the powder collects and then
falls through an opening in the cone-shaped
bottom. The air flows,through a filter at the top to
remove any. fine suspended powder particles. The
reclaimed powder can then be blended with fresh
material.
Best Management Practices to
Minimize Coating Defects from
Paint Booths
', There are a number of'steps that a company can
take to minimize the defects that result in rejected
work. Most of the defects require painters to
perform rework or, in some cases, completely
reject a part: Higher reject rates result in increased
waste generation and reduced profits. The most
common coating defects that relate topaint booths
include:
* Poor wrap when using electrostatic paints.'
Poor wrap can happen for a variety of rea-
sons. However as they relate to paint booths,
assistance providers should ensure that the
spray booth has a proper ground. Wrap may
: also occur as a result of turbulent air flow. .
« Dust and dirt in the finish. This is probably
the most comrrion cause for reworks and '
rejects. Facilities can take several steps to
avoid this including: avoid having sanding or
other dirty operations take place immediately
outside the booth; make sure that air filters '
' at air intakes of the booth are not dirty,_or ,
have too large of a mesh size; make sure
.thatjfhe booth is operating under negative
, pressure; make sure that the air make-up
system draws fresh air into'the booth and -
that the intake stack is not too close to the
exhaust ducts from sanding -or other dirty
operations; keep booth walls, floor and
ceiling free of .loose, dry, oyerspray or the
booth blowers may pry particles loose,
allowing them to fall onto freshly"painted .
surfaces; and make sure that proper booth
size is selected.
* Water spots in the finish. When using a water-
wash booth, operators must properly clean the
nozzles above the water curtain. Omitting this
step creates the opportunity for water droplets
to settle on the painted finish. \ .
* Haziness (blushing) that reduces gloss. This
problem occurs when humidity is high and .
moisture condenses on freshly painted sur-
faces. This is more likely to occur in a water-
wash booth than a dry-filter booth. To avoid,
this, parts should be moved out of the booth
shortly after painting is completed.
* Dry overspray on the finish. The most common
reason for this dry overspray is that the solvent
is too fast. As the solvent flashes off during
application, the overspray loses its wetness.
This problem is usually not-a result of the
booth but a result of high air velocity. Proper
monitoring and control of booth air flow
should assist in reducing this problem. Dry
overspray'on the finish also arises when.more
than one dry filter spray booth is being-
operated at the same time. If the- air flow
within the larger spray room is not uniform,
overspray from one booth can settle on .the
freshly painted surfaces in another booth.
Maintaining proper air flow between the two
booths or providing each booth with its own
air make-up system can solve this problem.
*Nonuniform coating finish with gloss,
patches, orange peel and voids. Numerous
causes exist for this defect, however, .causes
solely associated with spray booths are often
related to poor lighting. Investment in ad-
T07
-------
Chapter 7: Application Techniques
equate lighting and regular cleaning of the
cover plates can have quick payback in the
form of better looking finishes and fewer
touchups (EPAq, p. 154).
108
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Curing Methods
Once a coating is applied to the workpiece it
then undergoes a curing or drying process.
While the terms drying or baking are commonly
used in the painting industry to refer to curing,
there is a distinction between drying (baking) and
curing. In curing, the resin must be converted into
a new resin, while drying refers to the loss of the
solvent so that the resin remains the same. Curing
and drying both use the two same methods to
harden a coating: air/force dry and baking (newer
curing methods such as radiation curing are
discussed as they apply to specific coatings in the
preceding,chapters). Table 44 compares air/force
dry and bake methods.
* Air Drying. In air drying, a coating film is
Jbrmed by the evaporation of solvent, which
leaves behind a solid film. The rate of drying is
governed by how quickly the solvent evapo-
rates. Moderate heat (below 194T) can be
applied to accelerate evaporation (called force
drying), however,, the process still basically
remains one of air drying.
^Elevated Temperature Curing/Baking. El-
evated temperature curing uses one of three
rneans: conduction, convection or radiation to
apply heat to the coated part (SME, p. 28-7).
Selecting air/force dry or bake coating (baked at
elevated temperatures above 250°F) is an impor-
tant consideration in choosing a P2 alternative. .
Baked coatings usually have better physical and
' chemical-resistant properties, but they also have
some limitations. Air/force dried coatings (defined
by EPA as those that cure below 194°F) have
special VOC limits that are usually higher than
baked coatings (EPAq, p. 92). Table 45 lists the'
typical RACT VOC limits for metal part coating.
Table 44. Air/Force Dry vs. Bake (EPAq, p.91)
Air/Force Dry
Bake
Curing
Time
* Takes longer to achieve thorough
hardness, which can affect
production schedules -
* After baking and cool-down, the coated .parts
are usually ready for assembly or shipping
Clean-Up
Requirements
* Overspray dries on spray booth
filters, floors and walls; therefore,
maintenance is not a significant
problem.
* Uncured overspray remains sticky, making it
awkward to walk on spray booth floors
+ Maintenance is more costly because of
difficulty handling-the sticky material
(continued on next page)
109
-------
ChapcerS: Curing Methods
Table 44. Air/Force Dry vs. Bake (EPAq, p.91) (continued)
Air/Force Dry
Bake
Substrate
Versatility
Can be applied to all substrates
(e.g., metal, plastics, wood,
rubber and masonry)
Can be applied over porous
materials such as sand castings,
wood and paper
Can only be applied on metals and
substrates that can withstand high baking
temperatures. Generally not suitable for
heat-sensitive products such as plastics,
wood and rubber.
Should not be applied over machined or
other surfaces that are sensitive to warpage,
unless taking adequate precautions .
Can cause outgassing on sand castings and
other porous substrates. Preheating
workpiece can often overcome problem but
adds an additional step to the process
RACT
Regulations
*Some regulations have higher
VOC limits for air/force-dry than
for bake coatings
Heating
Requirements
dry and cure at temperatures
from ambient up to 194°F by
EPA definition
* Solvent-borne coatings do not
require an oven, although a low
temperature oven will speed up the
drying process
* Water-borne coatings would
benefit from a low temperature
oven that will speed up the drying
process .
Offers lower energy use
Generally must cure at a minimum of 250°F.
A typical curing schedule is 10 minutes at
350°F. Curing times are inversely
proportional to temperature. A cool-down
staging area is required.
Requires high temperature oven, and
therefore greater energy use
Physical/
Chemical
Requirements
Most single-component coatings,
such as alkyds and modified
alkyds, do not exhibit superior
physical and chemical properties
< Single-component moisture-cured
polyurethanes, however, do
perform comparably to Iwo-
component polyurethanes and
baked coatings.
* Often have excellent physical and chemical-
resistant properties, sometimes similar to
two-component polyurethanes
Appearance
Defects
* Surface defects, such as orange
peel, often do no? flow out during
the drying and curing process. .
Force drying at elevated
temperatures below 194°Fcan
partially alleviate this.
+ Films tend to flow out better when in the oven
providing smooth finishes and eliminating
surface defects such as orange peel.
110
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Chapter 8: Curing Methods
Table 45. Typical RACT Limits for Miscellaneous Metal Parts Coating
(EPAq,p.93)
'
California
Most other states .
Air/Force Dry
Ib/gal g/L
2.8 ' 340
' 3.5 420 ' '
Bake
Ik/gal g/L
2.3 ' '275'
..; 3.0 . 36.0
Ill
-------
112
-------
Equipment Cleaning
When a painting process is completed, a color
change is needed, or maintenance is
required, the metal cbater must clean the equip-
ment. There are numerous P2 opportunities for
reducing waste and air emissions in equipment
cleaning operations.
General Description
All coating practices require some type of equip-
ment cleaning. For spray painting, the most
common coating1 operation, spray guns and
accessories must be cleaned between color
changes, when orifices clog and often at shift
changes (IWRC,P: 15).
Pollution Problem
External equipment surfaces generally are cleaned
by soaking, wiping or flushing with solvent. If
equipment cleaning is done in an open container, a
significant quantity of solvent is lost to evapora-
tion. Internal parts and passageways as well as
paint guns are commonly cleaned by flushing
solvent through the gun and orifice. This practice
also results in significant evaporation and loss of
. usable product (IWRC, p. 15).
P2 Options
A cost-effective method for reducing wastes is to
eliminate unnecessary cleaning. For equipment
that requires cleaning, making improvements in
operating practices that minimize solvent use and
reduce evaporation should be implemented
wherever practical. Using a gun washer to clean
spray guns is one example. Various solvent
recovery and reuse technologies are also available.
In addition, alternative cleaning solutions can be
used. Each of these options is discussed below.
Scheduling Improvements
Implementing better operating practices and
scheduling can significantly reduce waste gener-
P2 Tips for Equipment Cleaning
,* Eliminate unnecessary cleaning
* Improve current operating practices
* Use a gun washer
« Recover and reuse spent solvents
* Use alternative nontoxic cleaning solutions
ated from cleaning operations. The amount of
waste generated is directly related to the number
of times paint color or paint types are made. For
this reason, scheduling improvements have
perhaps the largest effect on the volume of waste
produced from cleaning equipment. Making large
batches of similarly produced items instead of
small batches of custom items, increases the time
between cleaning. Additionally, scheduling paint
jobs so that they move from the lightest color to
the darkest can also reduce the need to clean.
Eliminate Unnecessary Cleaning
When assessing the cleaning process, all the
typical cleaning tasks should be reviewed to learn
whether cleaning is necessary. While most coaters
assume that spray guns, tips and lines must be
cleaned for reuse, cleaning some low-cost items
mightnot be advisable; Costs from cleaning
solvent purchases, solvent waste disposal and
solvent emissions could be higher than simply
replacing the item being cleaned. However, the .
.costs of proper disposal must be factored into any
decision (MnTAP, p. 5).
Improve Current Operating
Practices
A technical assistance provider should also help a
client company review the ways in whichcleaning
solvents are handled. All solvents should be stored
. in covered containers when npt in use. Leaving
solvents in the open air creates unnecessary
. solvent waste and VOC emissions. In addition, the
company should set a standard for the minimum
113
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Chapter 9: Equipment Cleaning
CASE STUDY:
Crenlo, Inc. - Spray Nozzle Selection Reduces Solvent Waste Volume
Crenlo, Inc. manufactures products from steel and aluminum. Finished products are coated with
saked enamel paint. Most colors are prepared onsite. Paint from any batch may be stored for
uture reuse. To ensure proper quality, the paint is remixed and strained to remove solids larger
han the 90 mesh screen size, before delivery to spray booths.
n the past, the straining equipment was cleaned using fresh solvent sprayed from a hose fitted
with a nozzle spraying a flat fan of solvent from a 0.1 72 inch diameter orifice. This nozzle is rated
or 4.3 gallons per minute (gpm) flow with a 30 pounds per square inch (psi) supply pressure.
Annual cleaning of the straining equipment produced about 14,000 gallons of waste costing at
east $ 16,000 per year. The cleanup solvent is a recycled blend that is distilled offsite and re-
umed to Crenlo. A single charge covers both purchase and processing costs. The.4.3 gpm
nozzle was originally selected because this size nozzle was already in use on an aqueous spray
wash line at the plant, so a supply was available onsite. A technical assistance assessment identi-
fied that nozzle size was the key factor affecting the volume of solvent used.
Three nozzles were purchased and tested in the cleaning system. Flow rates for these nozzles
ranged 'from one-fourth to one-fiftieth of the original flow rate. The smallest of these nozzles'
orifices (0.026 inches) cleaned the equipment at an acceptable level in 60 to 90 seconds at 30
psi, and used 80% less solvent than the original nozzle. Waste accumulation,from this source was
mo'nitored over the next two months and confirmed the improved efficiency using the new nozzle.
Foreign particles (such as rust) in the solvent feed line plugged the nozzle orifice frequently over
the first 2 weeks of operation. Plugging was eliminated by installing a small in-line basket filter to
remove solids before they reached the nozzle. Cleaning time with the low-flow nozzle was
doubled or tripled compared with the original nozzle. The 60 to 90 second cleaning time was
judged acceptable, although operators were not pleased with this change. Cleaning time was
reduced by 30 seconds by instituting a presoak step. The presoak used a dirty solvent bath to
remove or loosen most of the paint. The equipment was then sprayed with fresh solvent for a final
rinse. The presoak resulted in additional waste reduction.
^Savings
There was no capital investment for this project. Supplies included the purchase of three nozzles
for testing ($70) and a small, in-line basket filter ($50). Six hours of labor were needed to test the
nozzles, and approximately 4 hours were spent unclogging the nozzle orifice for the first 2 weeks
of operation. Total implementation costs were approximately $270. Reduction in waste resulting
from the new nozzles came to about 11,000 gallons less of spent solvent waste generated per
year with'savings of approximately $13,500 per year. ,
(MnTap 6/91-83]
strength necessary for cleaning in order to ensure The paint gun is partially disassembled and placed
that used solvent is disposed of or recycled only in the unit. Cleaning is accomplished by recirculat-
when it loses its cleaning effectiveness, not just ing solvent sprays. These units reportedly reduce
because it looks dirty (MnTAP, p. 5). solvent waste by 50 to 75%. VOC emissions can
be reduced by up to 20%, and a 60% labor time
Use a Gun Washer savings can be achieved (IWRC, p. 15).
The use of a gun washer can also help to reduce § c Q Q() ^ ^ tQ
wastes generated during equipment cleaning. An ^VJJ^ $1 5QO for industrial ^ units
automatic gun washer operates like a dishwasher. approximately * , jvy jv
114
-------
(i.e.. gun and paint hose wash). Similar units may
also be leased through various chemical suppliers
and waste management companies at a cost of
$ 165 to $ 195, per 5 gallon waste solvent change.
out interval (lWRC,'p. 15-17). . ;
Pressure Pot Liners .'"'.'
For maintenance of pressure pots, many compa-
nies use a polyethylene inner liner with the
pressure pot. The main advantage of this practice
is that only a small amount of paint comes into
contact with the steel or stainless steel body, and
cleaning the liner requires only a small amount of
solvent. After pouring-solvent into the liner, the
operator should swirl it around for a few seconds.
The operator can then discard the spent solvent
into a hazardous waste drum and the liner is ready
to be reused. -
Some operators choose to allow the paint that
sticks to the side of the liner to dry out, which
causes it to flake off with ease. If the solid paint is
shown to be hazardous per RCRA guidelines the
facility must manage it as a hazardous waste. If it
CASE STUDY:
Solvent Reclaimer
The Mormon Motor Company of Garland,
Texas, spent $ 10,000 to. install a solvent still
that reclaims thinners from paint-related
wastes. By installing this standard technol-
ogy, MaVmon reduced its disposal of
thinners from 34 drums to 3 drums and cut,
procurement of new'thinner from 4,000
gallons to 2,000 gallons per year.
4 . ' ' . '
* Savings. '.'-
As a result, waste disposal costs were
reduced from $6,200 to $1,400 per year.
Purchasing costs for new thinner decreased
from $9,500 to $4,750 per year. Even with'
additional labor costs at about $5,000 a
year, the annual savings were approxi- '
mately $4,500 with a 2.2 year payback
period (PPIFTil 994). .'-...
Chapter 9: Equipment Cleaning;
is not hazardous, it can be discarded with the rest of
the solid waste. The liner should then be reused
(EPAq,p. 137). "
Use Alternative Cleaning
Solutions
Because of the increased need to reduce VOC
emissions, alternative cleaning solutions are avail-
able. They include dibasic esters (DBE), N-methyl-
2-pyrolidone (NMP), and a variety of other
alkaline-, citric-, and water-based solvents suchas
d-liminone, naptha, and terpenes. These chemicals
have reduced VOC emissions due to their lower
evaporation rate. Although toxicology information
specific to these chemicals is relatively limited at
this.time, many researchers believe that the relative
safety of similar chemicals indicate that they are a
feasible alternative to organic solvents in certain -
applications (MnTAP, p. 5-6).'
Recover and Reuse Spent Solvents
Orisite recycling of used solvent is another way to
reduce waste and save ihoney. Savings come from
reducing the amount of solvent purchased and the
volume of spent solvent that must be sent offsite for
costly disposal. Two common methods of solvent
recycling are settling and distilling (MnTAP, p. 5-6).
Settling involves putting used solvent in a container
and letting the particulate matter settle out. The
container should be designed to allow for removal
of solvent without shaking up the sludge mat has
settled out (MnTAP, p. 5-6). Solvents can be used
for gun cleaning and then can be placed back into
the storage container for subsequent settling and
reuse. Eventually, sludge will make up the majority
of the container and offsite hazardous waste
'disposal will be necessary. At this point, the pro-
cesses can be repeated using a different container.
Solvent waste reduction of up to 33% can be
accomplished with this.simple method (IWRC, p.
15-17). Filtering equipment, which removes the
particulate matter from solvents, also is available
(MnTAP, p. 5-6).
Waste solvent also can be collected and processed
through distillation equipment. Approximately 80%
1 For more information on these alternative solvents, see Project Summary: SAGE 2.1, Solvent Alternatives
Guide: User's Guide. Research Triangle Park, NC: Air and Energy Engineering Research Laboratory. EPA/
600/SR-95/049: . ..'..'. . '. ' .
115
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Chapter 9: Equipment Cleaning
CASE STUDY:
Paint Gun Cleaning
Thermon is a electronics manufacturer in
San Marcos, Texas, with 300 employees. To
clean paint guns, the company traditionally
soaked the guns in solvent. This method
generated significant amounts of solvent.
waste and even clogged the guns when
inexperienced personnel performed the
cleaning.
To remedy this situation, Thermon purchased-
a spray gun cleaning system that circulates
solvent through the gun. The cleaning solvent
is filtered to remove particles that clog the .
paint gun, enabling the solvent to be reused
several times before disposal. The system
decreases solvent purchases and effectively
cleans the paint spray gun even when
inexperienced personnel perform the clean-
ing. -
To prepare the paint guns for the cleaning
system, the remaining paint is emptied from
the canister and the canister is washed with a
small amount of solvent (Vz pint). The
remaining solvent is poured out before the
gun is loaded in the cleaning system. This
extra rinsing step significantly reduces solvent
use.
* Savings
With the new cleaning system and methods,
Thermon reduced solvent use by 60%.
The cost of the spray gun system was $700.
The system was found to be very economical
due to reduced solvent costs and, more
importantly, improved spray gun perfor-
mance due to increased cleaning effective-
ness. Despite the fact that Thermon does a
relatively small amount of painting, the cost
of the unit was recovered in 6 to 8 months
(PPIFTI1994).
of the used solvent is recovered with basically the
same cleaning properties as a new product. The
remaining 20% sludge (still bottoms) must be
collected for offsite hazardous waste disposal. To
help maintain the cleaning properties of the
recycled thinner, certain paint and solvent wastes
should be segregated. Waste gun wash solvent and
any waste lacquer paint and thinner mixtures can
be included for recycling. All waste urethanes,
enamels and enamel reducers should be placed in
a separate container; enamel and urethane prod-
ucts will not clean as well as pure lacquer thinner.
By segregating the two, the reclaimed solvent will
possess cleaning properties like a virgin thinner.
This waste management technique has the advan-
tage of reducing the volume of virgin thinner
purchased as well as. the amount of waste thinner
generated (IWRC, p. 15-17).
Onsite distillation equipment comes in a wide .
range of capacities, from 5 gallons per 8 hour shift
batch operations to more than 100 gallons per
hour flow-through units. Costs for 5 gallon batch
units start at approximately^ 1,500 with an
average cost of $3,000 (IWRC, p. 15-17).
116
-------
Index
Symbols
100% solids coatings 66
1, ], 1 -trichloroethane 58;
2-ethoxyethanol 13
2-nitropropane 13
139
A ' ..' ' ' - "
abrasives 29
acetone 7, 13, 36, 141,148 ~. ;
acidic chromate 39 .
acrylic melamine paint 4
acrylic paint'; 4 .
acrylic resin 4, 74-
acrylic-urethane'coatings 71 ' .
acrylics 59, 60, 67, 71, 77,95, 137
additives 2, 41, 52, 57, 59, 62, 65, -* '
76, 95, 101, 137, 138, 140
adhesion 2, 30/33, 37, 38,-39, 41,
59; 60, 70," 71,. 72, 74, 77, 78, 79,
80, 86, 97, 98, 135, 136, 142, 144, 146
air drying 109
air emissions 4, 25, 50, 61, 65, 76, 78,80,
88,' 113,127
air releases 7, 8 /
air-assisted airless systems 92
air/force dry coatings 64
airless 66, 85, 87, 91, 92, 93, 94,-123,
102, 131,137
airless spray 80, 83, 87, 89, 91,92,93,131,
137
alcohols 7, 35, 36, ^57, 67, 80, 137,141,
144
aliphatic hydrocarbons 36, 57
glkyd resins 62
alkyds 4, 60, 110, 137 ' .
alternative coating^ 57, 61,123
alternative solvents 31, 33, 115
alumina 41, 52
aluminum alloys 46 ',-''
aminoplasts 59
anodizing 3, 31, 36, 37,38, 117,124
antiskinning agents 59
application standards 83, 84, 86
application techniques 1, -19, 83
applied film thickness 85
-.aqueous cleaning 18, 32, 119,120,137, 139
architectural coatings 2
aromatic hydrocarbons 57
autodeposition 96, 97, 138
automated aqueous washer 34
B
baffle/spray booth -104, 107
bake coatings 65,110
barriers 16, 17, 81, 118.
ba'secoats 3
baseline 16, 18, 19, 21, 23, 64, 66
. benzene 7, 13, 138
binders 2; 57, 59, 60, 62, 67, 138, 141
'biocides 59, 138
black alkyd 4 '
blast stripping 42
blasting cabinet 42
bonding adhesive flash 46
brushes 6, 139 - .
burnoff ovens 53,54
cadmium 13, 46, 51, 59
can coating 10, 74
carbon dioxide blasting 50
carbon dioxide pellets 42, 46
carbon oxides 52
carbon tetrachloride 13
case studies 1 7, 22; 1.18,119,124
catalysts 59, 65, 83
cation exchangers 37
cellulosics 59 '
CESQGs 11 ' . . .
CFC-11335, 36, 58, 148
chemical and electrochemical conversion 36
chemical stripping 21, 29, 41, 43, 45, 46,
47, 50 ' . .
chemical use 40, 6\
chromating 3 . ' .
chromic acid 37, 38, 39
chromium 13, 32, 38, 39, 59
Clean Air Act 7, 8, 9, 30
'Clean Air Act Amendments 7, 8, 9
Clean Water Act 7, 12
cleaning 113
cleaning capacity 31
cleaning methods 25, 26
cleanup and disposal '35, 48
clearcoat finishes 74
CO2 pellet blasting 47, 48, 49
117
-------
CO, snow blasting 48, 49
coating process 3, 4, 5, 7, 15, 18, 22
Coatings Alternative Guide 57, 117, 123
coatings application 14, 83
cold cleaning 30, 32, 33, 35
cold-solvent degreasing 32
colloidal coatings 67
colloids 59
colored pigments 59 .
completely enclosed vapor cleaners 32 '
compliance 6, 7, 9, 11, 15, 16, 61, 69,
76,117,118, 124
compressed air 21, 28, 45, 47, 48, 49,50,
83, 88, 90, 91, 117,123,137, 145
Conditionally Exempt Small Quantity
Generators 11,12
conduction 109
contamination sources 30
control equipment 4
control technique guidelines 8
convection 109
conventionaLair atomizing 85 ,
conventional air spray 57, 86, 87, 88, 101,
131
conversion airsystems 90
conversion coatings 3, 29, 30, 36, 37
corrosion resistance 1, 3, 30, 37, 38, 39,
59, 60, 61, 68, 69, 70, 71, 75, 77, 78,
96, 142, 143, 144
cosolvents 41, 68, 140
countercurrent cleaning 31.
cresols 13
cresylicacid 13
cryogenic stripping 53
curing 2, 3, 4, 31
curing methods 109
curtain coating 3, 77, 98
cutting fluids 18, 35
CWA7, 11, 12, 14
cyclohexanone 13
cyclone centrifuge 42, 44
D
d-limonene 33,35
defoamers 59 '
dense particle separators 42, 44
dip coating 3, 76^.89, 97, 98/138,
140, 141
dip tank 30
dirt 29, 30, 70, 79,94, 107
distillation/recycling practices 27
dry booths 101, 105
dual adjustable air wash 42, 44
E-coat95, 96, 138, 141, 143, 147, 148
economic feasibility 16, 18
edge buildup 85
electrocoat 4, 96
electrocoat primer 4
electrodeposition 27, 68, 83, 89, 95, 101,
138, 139, 141
electrodialysis 38
electrostatic 21, 27, 48, 63, 64, 66, 68,
69, 72, 73,74, 76, 78, 80, 81, 83, 84,
85, 86, 87, 89, 93, 94, 95, 96, 101,
. 103,107,123,131, 141, 143,148/149
electrostatic fluidized bed 72
electrostatic spray 68, 69, 72, 76, 83, 86,
89, 93, 94, 96,101, 141, 143
emerging technologies 61,79
emissions 1, 4, 6, 8, 19, 21, 22, 25, 26,
27-, 29, 32, 33, 38, 44, 47, 50, 53, 61,
62, 65, 66, 67, 68; 69, 70, 75, 76, 78,
80, 81, 84, 85t 88, 90, 91, 94, 95, 96,
97, 99, 101, 102, 105, 113, 114, 115,
127, 130, 131, 133
employee participation 17
emulsions 148
epoxies59, 60/65, 67, 71, 76, 77, 78,
95,105, 137,141 ,
epoxy polyester hybrid coatings 71
epoxy resins 141
equipment cleaning 1, 2, 4, 9, 14, 19, 26,
27, 28, 58, 84, 113, 114
esters 7, 36, 41, 57, 67, .115, 137, 144
. ether 7,13, 36, 139, 144 -
ethyl acetate 7, 13
ethyl ether 13
evaporation systems 37 -'..-
Faraday cage effect 75, 95, 141 . .
. federal regulatory status 7
Federal Water Pollution Control Act 12
fiberglass 44, 46, 61, 101/ 1.05
field stripping 42, 43
' film thickness 65, 66, 84, 85, 86, 95, 98,
129, 130, 151
- filters 25
filtration 37, 45, 48, 147
flamespray 51, 73 .
118
-------
flash lamps 53 ,.
flash rust 40
flattening agents. 59
flow coating 3, 27, 66, 83, .89,',95, 98,
141, 142' '
flow modifiers 59
fluidized bed paint removal 51
.fluidized bed stripping 51, 53
fluorocarbons 13, 59, 74
freeze/thaw stabilizers 59
functional pigments 59
fungicides 59, 1 37
garnet 41 , 42, 49 .
glass beads 41, 42 -, ...
glove box 42 ' . : ,
glycol ethers 7
good housekeeping practices 25
graphite 46
gravity separation 28
gun setup 87
gun washer 27, 1 1 3, 1 1 4 -
H
halogenated solvents 3, 13, 29, 31, 58, 142
hanger 42
HAPs 95, 100, 127
hazardous air pollutants 8, 36, 59, 1 1 8
hazardous wastes 7, 9, 10, 11, 13,20, 61
health effects ofsolvents 57, 58
heavy metals 2, 9, 10, 14, 30, 36, 59, 66
high solids 1, 21, 62, 64, 66, 67,117, 133
high transfer efficiency equipment 25, 26
high-solids coatings 26, 61,62,64,65, 66
high-temperature thermal methods" 53
HVLP 21, 80, 85, 87, 88, 89, 90, 91,
101,102, 117, 123, 130, 131,133
hydrochlorofluorocarbohs 36
hydrofluoroethers 36
.
ice crystals 42
immersion strippers 41 .
inventory control 21-, 25, 26, 27, 88
ion exchange 38
iron phosphating 39
isobutanol 13
K ,
ketones 7,36, 57, 144
lamp 78, 79
large quantity generators 1,1
laser ablation 34, 55
lasers 53
latex paints 67
lead 8, 13, 2'5, 29, 32, 43, 44, 46, 49, 50,
51, 53, 59,. 80, 81, .84, 86, 87, 105,
136, 149
low pressure, low volume paint spraying 91
'low-volume high-pressure 57
lower-temperature cures 74
LQGs 11 '-.'.-
LVHP 57, 61, 80, 84, 88, 89, 90, 93, 94
M
M-pyrol 36 .
machining 1 8, 22, 30, 35
machining operations 22
MACT standards 8, 9/32
magnetic separator 42, 44
manganese phosphate coatings 39
material handling 26, 27 __ .
maximum achievable control technology 8 .
measure cleanliness 31
mechanical cleaning 29, 33
medium-pressure mercury-electrode arc 79
MEK 57, 76 . . - , . '
melamine 4, 42., 62, 65
melamine-formaldehyde 65 / . ...
metal filter 28
metal scale 29 .
methanol 13
methyl ethyl ketone 7, 1 3, 32, 57, 58, 76 ^
methyl isobutyl ketone 57
methylchlqrofluorocarbons 35
methylene chloride 13, 36, 41, 47, 58, 139,
148
MIBK2, 6, 8, 32, 57 ;
molten salt baths 53, 54, 56
molybdicacid 39 - - .
monomers 76, 7.8
multiple vibrating classifier screen decks 42, 44
n-butyl alcohol 13
n-methyl-2-pyrolidone 36, 115
119
-------
national ambient air quality standards 8
National Pollutant Discharge Elimination System
12
natural oils 59
nitrobenzene 13
nitrogen oxides 59
NMP 36, 41, 115
nozzles 21, 47, 51, 89, 106, 107, 114, ,133,
141 .
nylon 60, 71 .
o
obstacles 17, 19
oils and greases. 3, 30
oligomers 76, 78
on-site distillation 28, 116
open-top vapor cleaners 32
operating parameters 15,19
operating practices 1,19, 25, 27, 29, 30,
83, 84, 88, 113
operator error 84 . .
operator training 26, 27, 44, 47, 50, 52,
92, 93/102
organic solvents 9,14, 36, 67, 69, 97,115,
139, 140
ortho-dichlorobenzene 13
OSHA30, 32, 43, 86, 123
overspray 4, 10, 26, 54, 66, 75, 80, 83,
86, 87, 88, 89, 90, 91, 101, 102, 105,
106,107,108, 109, 129, 144,147
ozone 8, 32, 36, 59, 79, 141, 145, 148
P2 options 1, 6, 22, 27, 30, 83, 84, 113,
.129
paintbooth 91, 94, 101, 129
paint characteristics 84
paint heaters 65
paint mixing 25
paint overspray 54
paint sludge 4, 32, 53, 69, 83, 106
paint stripping 29, 31, 42, 43, 44, 47, 51,
139
paint thinners 10
perfluoroccrbons 36
performance monitors 20
personal protection equipment 49
phenol formaldehyde 42
phenolic acids 41
phenoiics 59
phosphate coatings 3,-39, 140
phosphating 3, 36, 38, 39, 40, 1 42, 1 44
phosphoric acid 39, 144
photoinitiators 75, 76
photopolymerization 75
pigments 2, 8, 27, 43, 45, 59, 64, 79, 81,
92, 141
pilot testing 18
plastic media blasting 42, 43, 45, 56
plasticizers 59, 137
plural component proportioning systems 99
PMB 42, 43, 44, 45, 46, 47
pollution prevention 1 , 2, 3, 6, 7, 8/15,1 6,
17, 18, 19, 22, 23, 25, 31,40,61,88,
95, 1 1 7, 1 1 8, 11 9, 1 20, 1 21 , 1 24, 1 26,
133
pollution prevention options 15, 18, 19, 22
polyester 42, 62, 65, 71, 72, 74, 144; 146 .
polyol-isocyanate coatings 79
polypropylene 71
* polystyrene 101, 106, 148
polyurethanes 59, 60, 62, 65', 105, 110, 143
polyvinyl acetate 67, 1 47
polyvinyl chloride 62, 71, 147
POTW 11
powder coating resin properties 72, 77
pressure assist cup system 90
pressure pot liners 115
pressurewashing 35
pressure water blast systems 51
pressure water stripping 5 1
pretreatment 4, 11, 14, 29, 34, 40,74,131,
141, 144
pretreatment coatings 40
prime coat 3, 4
process flow diagrams 1 8
product coatings 2, 65
production rate 84, 97, 104 . '
publicly-owned treatment works 14
pumps 21, 25, 68, 92, 106
pyridine 13 , .
quality of finish 84
quality standards 8, 18, 45
RACTLimits 8, 111
radiation 61, 64, 75, 76, 79, 81,83,
109, 118, 119,140
radiation curing 75, 76, 109,119
RCRA7, 9, 11, 12, 43, 44, 115
120
-------
records: 11, 12, 18, 19/21, 127
recover and reuse spent solvents 1 13, 115
recycle cleaning solvent 31 ' -
recycling solvents'25, 28
regulations 6, 7, 8, 9, 1 5, 18, 30, 36, 66, "
68, 69, 76, 89, 106, 110, 117,124, 133
reverse osmosis 37, 145
rework 30, 87, 107 ' ' ;
rinsing 14,. 27, 38, '40, 54, 96, 116
roll coating 83, 98, 99, 104, 145
roller 3, 27, 66, 83, 89, 95, 99
rotary atomization 94
rust 3, 29, 39, 40,,43, 49, 50, 67, 114,
.-145 "-''
sand 29, 42, 43, 44, 51, 110
scheduling improvements 113
scrubber water 4, 83
sealants 41 r 46, 48-
sedimentation 37.
.Significant New Alternatives Program 36
silica-containing materials 29
silicone 4, 36,.60, 142,. 146 :
siphon-fed system 89
sludge 4, 14-, 19, 21, 27, 28, 32, 38, 39,
40, 41, 46, 53, 69, 75, 83, 106, 115,
116
soda stripping systems 45
sodium bicarbonate 41, 42, 45, 46, 51, 56
sodium'brcarbonate slurry 42'
sodium hydroxide 41, 143
solvent cleaning systems 30
solvent distillation 28
solvent emissions 6, 32, 65, 101, 113
s'olvent gravity separated 21 .
solvent vapor degreasing 27, 30, 31, 32,34
solvent-based chemical stripping 29 .
solvents 1, 2, 3, 4, 5, 6, 7, 9, 10, 13, 14,
17, 21, 25/26, 27, 28, 29, 30, 31, 32,
33, 34, 35, 36, 41, 43, 44, 47, 57;. 58,
65, 66, 67, 69, 71, 75, 76,78, 84, 91,.^
97, 98, 99, 106,. 113, 115, 118,127,
133, 137, 138, 139, 140, 142, 144,145,
146, 147,148
source reduction 16
spatulas. 21 . .
special purpose coatings 2
.spentsolvents 4, JO, 13, 27, 36, 113,115'
spigots 21, 25 ,
sponge blasting systems 49, 50, 51
sp'ray.application technique 84
spray booth 4, 25, 109, 139, T49
spray booth configuration 84 .
spray booth filters 25
spray distance 84,87
spray guns 4/ 21, 25, 83, 84, 85, 86, 88,
-90, 91, 93,95, '100, 113, 133/'l38, 149
SQGs 11 '.;.-, ; ' :
stabilizers 37, 59 ' ..
steel grit 41 . . t . ''
storage 3, 11, 12, 18, 20, 21/25, 26, 27,
30, 44, 46, 57, 63, 65, 69, 70, 72, 75,
88, 115 . " ' ' . ' .
stripping operations 29, 41, 42, 43, .44, 43,
,46 ; . ' .
styrene-butqdiene copolymers 67
sulfuric acid anodizing '117
supercritical carbon dioxide 79, 99, 100;.1 18
supercritical fluid cleaning 35
surface coat 138
surface preparation 1, 2, 3, 9, 14, 1 9, 29,. ,
30, 31, 40, 47, 48, 55, 56, 58, 61,
62, 84/117,123, 135, 145
surface treatment baths 29 .
surfactants 49 ", '
T ' : - ", " :
TCLP 11 ,
team approach 18, 21 .
technique training 20- ,
terpenes 33, 115,146
testing 18, 31, 74/85, 87, 114,119,135,"
136. .
tetrachloroethylene 13
TGIC polyesters 71
thermal capability 30 :
thermoplastic polyester 71,72
thermoplastic powder coatings 71, 72, 73, 147
. thermoplastic resins 71, .144,146
thermoset resins 71 . -
thermosetting epoxy-resin-based paint 4
'thickeners 41, 59
Title III air toxics program 8
toluene 2, 6, 7, 8, .10, 13, 32,-57, 58, 76,
'138. . ' - .. - :
topcoats' 3, 4,141 .
Toxic Release Inventory 12
-Toxicity Characteristic Leaching Procedure 11 .'
training 11,12, 20, 23, 25, 26, 27, 32,
44,45,47, 50, 52, 87, 93, 96, 102,
103,117,119,120, 123, 131
121
-------
TRI 12
trichloroethylene-36, 58
trichlorofluoromethane 13, 148
triggering 85, 87
trimethyl benzenes 57
two-component reactive liquid coating 65
two-step paint application/curing 2
Type I'anodizing 37
Type II anodizing 37
Type III anodizing 37 . .
u
ultrafiltration 40,144, 147
ultrasonic cleaning 34,147
unicoat Paint 79, 80, 81
urea formaldehyde 42
urethane polyesters 71
water-soluble solvents -41'
water-wash booths 104, 105, 106, 107
wet booths 101
wheatstarch 42, 45, 46, 47,56
wheat starch blasting 45, 46, 47 ,
white pigments 59
wipe cleaning 35
wraparound 93, 95
X
xenon lamps 53
xylene 2, 6, 7, 8, 10, 1.3, 57,58, 138
xylene isbmers 6 .
zinc phosphating 3, 39, 142
vacuum de-oiling 34
vacuum sanding system 43, 44
vegetable oils 59, 60
vibratory deburring 34
vinyl coatings 46
vinyls 59, 60, 67
viscosity 21, 57, 62, 65, 66, 67, 78, 83,
87, 89, 90, 91, 94, 97, 98,100,101,
102,104, 123,140, 147, 148, 149
VOC content of coatings 10
VOC emissions 4, 26, 27, 32, 66, 69, 80,
81, 84, 85, 88, 95, 96, 97, 99, 105,
113, 114, 115, 11.7,131
w
waste exchanges 25, 28 ,
waste management 19, 20, 1,19,120,125,
126
waste minimization plan 11
waste reduction 17, 20, 40, 114, 115,119,
120,121,126
waste stream 1, 20, 29, 38, 45, 46, 51, 53
wastes 1,4
wastewater4, 12, 14, 15, 33, 38, 43, 44,
45, 46, 50, 52, 55, 56, 69, 70, 106,
118
water use 19,' 40, 47 \ .
water-based alkyds 67
water-based Coatings 69
water-dispersible paints 67
water-soluble paints 67
122
-------
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127
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128
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Appendix A
Information Resources
Trade journals .
The following trade journals can provide up-to-date
information on coating developments. Many of these
journals have annual guidebooks and directories,
issues with articles on coatings technologies, and
vendor listings.
Journal of Coatings Technology
Surface Coatings international
American Paint and Coatings Journal :
Modern Paints and Coatings .
Metal Finishing , , '
Chemicalweek
Chemical Marketing Reporter
Manufacturers/Literature
Binks Training Division (Franklin Park, IL) offers a
variety of training materials on spray painting and
related topics, including seminars, videotapes and
literature: For more information, contact:
Binks Manufacturing Company
9201 W. Belmont Ave.
Franklin Park, IL 60103
Attn: Training Division
the following is a list of literature available from
Binks: ' , -'- ~ .
'Material Supply. TD2-1R-6.
Hose and'Fittings. TD3-1R-2. ; "''.'"-
Compressed Air Supply. TD4-1 R-6.
Automatic Spray Equipment. TD5-1R-4.
Spray Booths. TD6-1R-5. ,
Compressed,Air Spray Gun Principles. TD10-1 R-4.
High Volume Low Pressure-HVLR TD10-4R.
Airless Spraying. TD11-1R-4.
Air Assisted Airless Spraying. TD11-3R-2.
Plural Cofnponent'Spray Systems. TD16-1R-4.
Electrostatic Spraying. TD17-1R-4.
Electrostatics Safety Manual for Liquid and
Powder Finishing Systems. TD1 7-2R-.
Hot Spraying: TD42-1R-5. .
Operator Techniques. TD49-1R-3.
Spray Application Processes. TD49-2R-4.
Paint Curing by Infrared Catalytic Thermoreactors.
TD10Q-7.''.v
Viscosity. TD100-1R-3. . ' ' . '
Finish Problems-Solvent Base Coatings. TDtOO-2R-3.
Safety Considerations in Paint Applications. TD100-
3R-5. . . " . -.-
OSHA Safety and Health Standards. TD100-4R-4
Coating Materials. TD100-5R.
'Surface Preparation. TD100-6.
Other equipment manufacturers that technical assis-
tance providers should contact include:
DeVilbiss (800)338-4448
Graco (800)328-0211
Internet Links
The following Internet links can provide valuable
information on coatings: -
The ASTM Home Page
http://www.astm.org/index.html
ASTM has developed and published over 10,000
technical standards which are used by industries
worldwide. ASTM members develop the standards
within the ASTM consensus process. Technical
publications, training courses, and Statistical Quality
Assurance Programs are other ASTM products; .
ASTM services include The ASTM Institute for
Standards Research. ,
CAGE . ' : .
http://cage.rti.org/
CAGE (Coatings Alternative Guide) is a tool devel-
oped by the Research Triangle Institute to assist ,
companies or technical assistance providers in select-
ing appropriate alternative coatings or coatings equip-
ment.
Chemical Coaters Association International
http://www.finishing.com/CCAI/index.html
The Chemical Coaters Association International is the
finishing industry's educational arid networking asso-
ciation.
129
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Corrosion Coatings & Linings Information
Server
http://www.corrosion.com/index.html
Corrosion Coatings & Linings Information Server
Protective Coatings, Linings and Related Re-
sources is devoted to providing up to date,
relevant information about products and services
for the Protective Coatings, Linings, Painting and
Corrosion Industry.
Envirolink
http://www.envirolink.org
EnviroLink is an online environmental information
resource. This non-profit organization unites
hundreds of organizations and volunteers around
the world and provides comprehensive, up-to-date
environmental resources.
EPA'sEnviroSenSe
http://www.epa.gov/envirosense/index.html
Enviro$en$e attempts to provide a single reposi-
tory for pollution prevention, compliance assur-
ance, and enforcement information and data-
bases. Included are pollution: prevention case
studies, technologies, points of contact, environ-
mental statutes, executive orders, regulations, and
compliance and enforcement policies and guide-
lines. A major component of EnviroSense is the
database for "solvent alternatives."
Federation of Societies for Coatings Technol-
ogy
http://www2.coatingstech.org/coatingstech/
An individual member organization of over 7,200
international professionals in the coatings manu-
facturing industry. .
Finishing
http://wwW.finishing.com
F5nishing.com contains links to commerce, current
events, and technical reference materials pertinent
to anodizing, plating, powder coating, and surface
finishing. Also located at this site is a link to a
caller participation area where visitors can pose or
respond to finishing industry questions.
The Golden Gate Society for Coatings Tech-
nology
http://www.kudonet.com/~paintman/ggsct.htm
The GGSCT site contains a comprehensive
bibliography of coating industry issues.
National Paint & Coatings Association
(NPCA)
http://www.paint.org
NPCA is the preeminent organization representing
the paint and coatings industry in the United
States. A voluntary, nonprofit trade association,
NPCA represents some 500 paint and coatings
manufacturers, raw material suppliers and distribu-
tors.
P2Gems
http://www.turi.org/P2GEMS
P2Gems is a search tool for facility planners,
engineers, managers, and technical assistance
providers who are looking for technical process
and materials management information. The site
contains a database, searchable by keyword or by
four categories: product or industry, chemical or
waste, management tools, or process.
P2Tech
http://www.great-lakes.net/
P2 Tech contains information on the economy,
ecosystem, government, and environmental issues
in the Great Lakes region. .
The Paint/Coatings Net
http://www.horizonweb.com/pcn/pcnmain.htm
Paint/Coatings Net includes directories of manu-
facturers, distributers, contractors, and consultants
as well as a collection of paint/coatings articles.
The site also contains two discussion areas, a
coatings clinic and an environmental clinic.
Pacific Northwest Pollution Prevention Re-
search Center
http://pprc.pnl.gov/pprc/p2tech/p2tech.html
The Pacific Northwest PPRC provides technology
reviews for manufacturers, researchers and others
interested in the details of new cleaning technolo-
gies. Each review includes an overview of the
technology as well as links to relevant Internet
sites and bibliographies on each pollution preven-
tion technology.
Paint Research Association (PRA) Home Page
http://www.pra.org.uk
" PRA, the Paint Research Association was estab-
lished atTeddingtoh, Middlesex, UK in 1926 and
is now the largest independent research center for
the coatings industry worldwide. PRA is a mem-
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her based organization currently with over 20~0
members.
RadTech Ultraviolet (UV) and Electron (EB)
Beam Curing Home Page <
http://www.radtech.com/
RadTech International North America is a npn- ,
profit trade association'with members from
companies that supply UV/EB equipment, raw
materials and formulated' products, and other
indiv iduals interested in or involved in UV/EB ,
curing technology. .
SAE Home Page
http://www.sae.org/ . . ' , '
The home page of the Society of Automotive ,
Engineers is your one-stop resource for all aspects
of vehicle design/engineering, safety, and manu-
facturing information. A non-profit, educational
organization, SAE has nearly 70,00,0 members in
over 80 countries. . . .
Society of Manufacturing Engineers
http:///www.sme.org/
SME is an international professional society
dedicated to serving its members and the manu-
facturing community through the advancement of
professionalism, knowledge, and learning. SME
has more than 70,000 members in 70 countries.
The society also sponsors some 300 chapters,
districts, and regions, as well as.240 student
chapters worldwide. .
Trade Associations
The following trade associations can be contacted
for more information:
Air & Waste Management Association
1 Gateway Center, 3rd Floor
Pittsbury, PA 15222 .
(412)232-3444 . ,
American Institute of Chemical Engineers
. 345 East 47th Street
New York, NY 10017 .
-(212)705-7338
The Association for Finishing Processes
OneSMEDrive
P.O. Box 930 '-.-
Dearborne,MI48121
(3,13)271-1500
ASTM ; '"'..
100 Barr Harbor Drive
West Conshphocken, PA 19428
(610)832-9500 ' -.'...
Can Manufacturers Institute
1625 Massachusetts Ave. NW, 5th Floor
Washington, DC 20036 ,
(202)232-4677 .
Chemical Coaters Association International
PO Box 54316 -
Cincinnati, OH 45254
(513)624-6767 . '
Color Association of the United States
409 West 44th St.
New York, NY 1003 6
(212)582-6884
Federation of Societies for Coatings Technology'
492 Norf is Town Road
Blue Bell, PA 19422
(610)940-0777
National Association of Architectural Metal
Manufacturers
8 South Michigan Street, Suite 100
Chicago, IL 60603
(312)782-4951
National Coil Coaters Association
401 N.Michigan Ave.
Chicago, IL 60611-4267
(312)321-6894. ' ' .
National Decorating Products Association
1050 N.Lindbergh Blvd. .
St. Louis, MO 63132-2994 .
(314)991-3470
National Paint and Coatings Association, Inc.
1500 Rhode Island Ave. NW-
Washington, DC 2005
(202)462-6272 . ' . .
Paint Research Association
8 Waidegrave Road
Teddington, Middlesex
TW118LD,UK
+44(181)977-4427
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Powder Coating Institute
2121 Eisenhower Av.e., Suite 401
Alexandria, VA 22314
(703)684-1770
RadTech International-North America
60 Revere Drive, Suite 500
Northbrook, IL 60062
(708)480-9576
Society of Manufacturing Engineers for Finishing
Processes
1 SME Dr., P.O. Box 930
Dearborn, MI 48121
(3l3)271-1500ext.544
Steel Structures Painting Council
40 24th Street, 6th Floor
Pittsburgh, PA 15213
(412)281-2331
Synthetic Organic Chemical Manufacturers
Association '
1850 M Street NW
Washington, DC 20036-0700
(202)296-8577
Clearinghouses
Center for Environmental Research Information
(CERI)
U.S. EPA . '
Cincinnati, OH 45268
(513)569-7562
EPA's Pollution Prevention Information Clearing-
house
401M Street, SWMC 7409
Washington, DC 20460
202260-1023
Great Lakes P2 Information Clearinghouse
One East Hazelwood Drive
Champaign, Illinois 61820
'217333-8940
The Northeast Pollution Prevention Clearing- .
house
129 Portland Street, 6th Floor
Boston, MA 02114
617367-8558
Toxics Use Reduction Institute
One University Avenue
Lowell, MA 01854
(508)934-3275 ' '
Waste Reduction Resource Center
3 825 Barrett Drive, Suite 3 00
PO Box 27687
Raleigh, NC 27611-7687 '
(919)715-6500
The Pacific Northwest Pollution Prevention
Research Center (PPRC)
1218 Third Ave., Ste. 1205
Seattle, WA 98101 ...
206-223-11151
Technical Assistance Programs with
Expertise in Metal Coating
Illinois Waste Management and Research Center
One East Hazelwood Drive
Champaign, Illinois 61820
(217)3:33-8940
Maine Metal Products Association
190 Riverside Street
Portland, ME 04103-1073
(207)871-8254
Massachusetts Office of Technical Assistance
100 Cambridge Street, Room 2019
Boston, MA 02202
(617)727-3260
MnTAP
1315 5th Street SE, #207 ' -'
Minneapolis, MN 55414
-(612)627-4646
http://www.umn.edu/mntap
North Carolina Division of Pollution Prevention
and Environmental Assistance
PO Box 29569
Raleigh, NC 27626-9569
(919)715-6500
Great Lakes Pollution Prevention Centre
265 N. Front St., Suite 112
Sarnia^ ON N7T 7X1 CANADA
Tel: (519) 337-3423
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Toxics Use Reduction.Institute
University of Massachusetts/Lowell
One University Place
Lowell,'MA 01854
133
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134
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Appendix B
VOC/HAP Calculation
Air emissions that result from the evaporation of solvents such as those in paints can be calculated
using a material balance approach. To calculate the pounds 'of HAPs or VOCs emitted, a firm needs
tO'know: " . . ' ' . '. '
+ Quantity of product used annually ;
* Total density of the product
* Weight percent HAPs or VOCs '.'.'- " . -.
1 .
Calculating the Quantity of Product Used
The quantity of product used can be taken from purchasing records provided a company maintains an
essentially constant inventory. If the firm is disposing of waste materials and has records to show the
amount of HAPs or VOCs .in the waste, that amount can be subtracted from the total used since it was
not emitted into the air. -; .
Calculating the Total Density .
The total density of the product can be found on the Material Safety Data Sheet (MSDS). Sometimes it
is listed as a specific gravity, calculated by using the ratio of product density/density of water. If specific
gravity is given, multiply by 8.314 pounds per gallon (the density of water),'to get the density of the
product. '
Calculating Weight Percent ;
The HAP content in the paint can be found on the MSDS. HAP content may be listed as a volume
percent (vol %) or weight percent (wt %). VOC or solids content also may be listed. If the paint does
not contain water or exempt VOCs, the VOC content can be calculated from the weight content using
the following relationship: ; . .' .
wt % VOC = 100 - wt % solids - '. . .- ' ']
If the paint contains water or an exempt VOC, the amount of VOCs in the paint is calculated as follows:
wt % VOC = 1 00 - wt % solids - Wt % water - wt % exempt VOC , .
Calculating HAPs and VOCs
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136
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Appendix C
Economic Analysis
Selection of a particular paint system (paint and application method) for a specific application depends
primarily upon the products to be coated and production requirements. Before selecting a system, a
comprehensive economic analysis considering the following items should be performed:
1 ) . '.
* Cost per volume of the nonvolatile fraction of the paint ,
* Transfer efficiency versus paint cost . . .
* Relative costs of various coating process equipment , ' ,
* Energy consumption
The following section provides one method for conducting a comprehensive economic analysis that
considers all four factors. Technical assistance providers can help companies conduct this analysis to
compare P2 options for painting operations. :
Conventional liquid paints are comprised of both volatile and nonvolatile components. When paint is
applied to the part, the volatile components evaporate, leaving the nonvolatile components to form the '
actual finish. In order to evaluate a coat of an applied finish, one must consider: 1) the nonvolatile
fraction of the paint versus the product cost and 2) the efficiency of the paint application method (i.e.,.
transfer efficiency). ...
Cost per Volume of the Nonvolatile Fraction of the Paint
The cost of a paint based on its nonvolatile (solid) fraction can be calculated from product information
(generally the product Material Safety Data Sheets [MSDS]). For example, a paint that costs $ 15 per
gallon and contains 33% solids actually costs $15 divided by 0.33 or $45.45 per gallon of solids.'
If a desired film thickness is known, this cost can be further broken down into a cost per applied surface
area using the following equation':
Cost of paint solids per gallon x film thickness in milsx 0.0006233 = paint cost per square foot of -
applied finish (where 0.0006233'is a unit conversion factor)
Usingmepamtcostof$45.45pergallonofsolidsanda2mil(l mil =-'6.001 inch) finished film thick-
ness, the paint cost per square foot of applied finish (assuming a 100% transfer efficiency) would be:
$45.54x2x0.0006233 = $0.057 per square foot (ideal) -
Transfer Efficiency Versus Paint Cost
The above calculation gives the minimum or ideal cost of paint per square foot of applied finish
because it assumes that 100% of the paint product adheres to the part being painted. In order to get an
actual cost, one must also include transfer efficiency. In most spray painting operations only a portion
of the product reaches the part to be painted. The remainder (overspray) is collected in the paint booth
filters or settles to the floor of the paint area. The amount 6f paint reaching the product versus the
total amount of paint sprayed is referred to as transfer efficiency. A 50% transfer efficiency means
. half the paint adheres to the product and the other half is wasted. To calculate the actual cost of paint
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per square foot of applied finish, one must include the estimated transfer efficiency of the paint
operation into trie-above formula as follows:
(Ideal paint cost per square foot x 1 00)/TE = Actual paint cost per square foot
where: TE equals transfer efficiency .
Using the previous example and a transfer efficiency of 50%, the actual paint cost would be:
($0.057 x 100)/50 = $0.114 per square foot (actual) (IWRC, p. 10-12)
Example ..
A small manufacturer of metal cases for consumer electronics currently coats its products with conven-
tional solvent-borne coatings. The firm is considering changing its current coating and application system
to one containing lower VOC content and higher transfer efficiency, and they want to know what the
coverage, total reduction in emissions and materials cost would be for the new system.
VOC Content (pounds per gallon)
Solids Content
Dry Film Thickness (mils)
Equipment Transfer Efficiency
Cost (qallon)
Paint Use (gallons per year)
Existing System
3.5
35%
0.8
28% (air atomized)
$15
4,4.00
Proposed System
2.5
' 30%
<1.0
65% (HVLP)
$20
(to be determined)
Calculating Material Savings and Emission Reductions
Coverage = (paint volume x % volume solids x % transfer efficiency)/dry film thickness
If the surface to be covered is the same for both production scenarios, then:
(G2 (gallons) x % VS2.x %TE2)/FT2 (mils) = [(G, (gallons) x % VS, x % TE,)/FT, (mils)]/FT, (mils)
or
G2 (gallons) = (G, (gallons) x FT2 (mils)% VS, x % TE,)/(FT2 (mils) x % VS2 x % TE2)
Where: '
G, = amount of coating currently used fora given application
G2 = amount of coating used in riew method for the same application
%VS, =%voiume solids of the original coating - .
%VS2 = %volume solids of coating used in new applications method
%TE*= % transfer efficiency of existing.applicatio'ns method
, % TE2 = % transfer efficiency of new applications method
FT, .= film thickness achieved in existing applications method
FT2 = film thickness achieved in new applications method
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Emissions = -pgint volume used x-VOC content of paint
or,1
E (pounds) = G (gallons) x VOC (poGnds per gallon) , ' ;
'?Tofa/mafen'a/s cost = paint volume used x cost per gallon of paint
TMC($) = G (gallons) xC($ per gallon) . , . ,
where:
c = cost per gallon of alternative coating / ' . ' : '
TMC. = total paint materials cost of new application method
Substituting values, we get: G2 = 4400 x 1x35x287.8 x30x 65 = 2764'gallons ,
VOC emissions (E) = G (gallons) x VOC (pounds per gallon)
Current system: 4400-gallons x 3.5 pounds per gallon = 15,400 pounds per year VOC
,Prpposed system: 2764 gallons x 2,5 pounds per gallon = 6910 pounds per year VOC
Reduction in VOC: 8490 pounds per year VOC (NJTAP, p. U)
Relative Costs of Various Coating Process Equipment
Because of the various painting requirements present in the broad category of metal manufacturers,
providing a realistic cost comparison between one paint application method and another is nearly
impossible. In order to provide some degree of comparative information the following table is offered.
Cost/Benefit Summary for Spray Application Methods
Method of
Application
HVLP Spray
Air-Assisted
Airless Spray .
Electrostatic
Spray
Powder
Coating
Capital
Cost
Low
Low
Me.dium
High
Process
Complexity
Low
Low
Medium
High ,
Waste and
Emissions
Medium/High
Medium/High
Medium
Low
Additional
Considerations
Only conductive parts
can be painted
Extensive parts wash-..
ing and a curing oven
are required
NOTE: Capital cost refers to the cost of the system in comparison 'to conventional air spray. The higher the
. process complexity, the higher the associated costs (he., training for employees and maintenance).
Energy consumption should also be a consideration when selecting a paint and.application method.
Energy consuming operations include pretreatment (i.e., parts washing), ventilation, and makeup air/
heat for curing. All three of these factors are directly related to the type of paint and application method
selected. For comparative purposes, powder coating and waterbprne paints might have higher energy
requirements because of increased curing demands (I WRC, p. 10-12). .
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140
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Appendix D
HVLP Spray Gun Purchasing
Guidelines
The Wisconsin Department of Natural Resources
developed the following list of purchasing consid-
erations for HVLP guns to help Wisconsin
businesses identify and evaluate current pollution
prevention opportunities. Although this list does
not cover every aspect of equipment selection, it
includes some of the more important points and
provides considerations for evaluating HVLP
equipment. ' ;
* Would a cup-fed or a tank-fed sprayer be best
for the applications? r
+ A cup-fed sprayer is an excellent choice for
small jobs because it can be loaded with only the
amount of paint that is needed.
* A tank-fed sprayer would be more effective for,
continuous, large volume operations inwhich the
tank would need to provide a substantial supply of
paint.
* Would the firm want to add an air heater to the
HVLP system?
* Air heaters may decrease the drying time.
* Air heaters will increase the transfer efficiency
of high solids coating material. -
* Air heaters reduce the moisture condensation
inside the system. , .-
* Can the firm adapt any part ofthe existing
system to the HVLP system or will they need to
replace the system as a whole?
* Is the spray equipment warranted for use with
the material thai you want to apply?
. * Are the electrical controls and components UL
listed, and do they meet the firm's standards for
. safety at their facility?
* What is the weight of the spray gun?
« If the gun is used for an entire shift, the weight
pf the-gun could affect the productivity of the
worker using it.
4 A spray gun made from composite materials
may,be lighter than a gun made from metal.
* What are the available sizes and shapes of the
nozzles that can be used on the spray gun? Are
the nozzles compatible with the material that must
be applied?
* Is the equipment easy to disassemble (and
reassemble) for the cleaning and maintenance of
critical parts?
* Gun washers are considered by some to be an
effective means of cleaning spray equipment..
Some services rent these gun washers and sell the
solvents that are used in them. When the washing
solvent is dirty, the service will pick up the old
solvent for recycling and drop off new cleaner.
+ If you need to supply multiple HVLP spray guns
simultaneously, will the operation of the spray
equipment be affected significantly?
* Can an automatic positioner be added to the
HVLPsystem?
* An automatic positioner holds the spray gun in
the desired position while the material is applied. .
This reduces worker fatigue and improves repro-
ducibility.
* Are there any local, state or federal health and
safety or environmental quality regulations that
apply to the use of this equipment?
* What are the electrical power requirements for
the HVLP system? Is the system energy efficient?
. (MnTAPb, p. 1-3)
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142
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Appendix E
Testing
A variety of quality assurance tests are used on
cured.paints for characteristics including thickness,
adhesion, chemical resistance, color match and
cure. Companies generally select.tests based on
customer requirements. For example, applications
that involve high exposure to water and/or weather
require certain performance standards from the
coating. Whether the coating supplier provides this
information or the manufacturer does the tests at
their facility, the customer must be assured that
the coating can perform according to specifica-
tions. This appendix provides brief descriptions of
tests that are commonly performed by coatef s.
Thickness
The thickness of both wet and dry films are often
measured.
Wet Films
. The purpose of measuring wet films is to deter-
mine if they are sufficiently thick to develop the
required thickness when dry. Gauges used to
measure the thickness of wet coatings cut through
the film. The two most extensively used gauges
. include a wheel gauge and a tooth gauge. Wheel
gauges are rolled through the wet film to contact
the base material. A tooth gauge is simply pressed
into the wet coating to measure the thickness
Dry Films
A wide variety of gauges are used to determine the
thickness of dry films. Thickness measurements
can be performed on substrates containing iron by
using a magnetic "pull-off' type gauge. Magnetic
attraction decreases in proportion to the coating
thickness. Pencil and banana gauges are two types
of pull-off gauges. For other substrates,'microme-
ters can be used to measure coating thickness.
Destructive thickness methods include placing a
piece of tape on the substrate prior to painting,
removing it, and measuring the difference between
the tape thickness before and after painting.
Adhesion
Adhesion is defined in ASTM Designation D907
' as the state in which two surfaces are held to-
gether by interfacial forces which consist of either
valence forces or interlocking action, or both. It
would be difficult or even impossible to measure
these forces. Often it is difficult to determine the
true adhesion of a coating due to issues such as
voids in the surface profile, improper surface
preparation and surface contamination. Marty
factors other than substrate and paint properties
may influence adhesion. As a result, the type of
test used should be.selected according to the
-modes, of failure observed in service. The most
common adhesion tests include film removal and
cross-hatch. Inertia tests that use vibration to lift
the coating are rarely used.
Film removal
Tools used to test film removal vary from pocket
knives to mechanically operated cutting edges,
blades, or points. Gauges are used on some
devices to measure the force needed to remove
the coating.
Cross-Hatch
This test requires that two sets of parallel cuts are
made at 90 degree angles to each other, forming a
checker-board grid. The percent of paint remain-
ing on the substrate is estimated. In' some cases,
additional 45-degree cuts are made. . .
Abrasion Resistance
Several properties are involved in the measure-
ment of abrasion resistance. These include mar
resistance, hardness, elasticity and tensile strength.
Flexibility
Flexibility (bend or impact) is usually measured by
removing a piece of tape applied prior to painting..
ASTMD-3359 provides details about this simple
test, including a rating scale for evaluating results.
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It is critical to perform this test consistently. The
actual method may vary, but the procedure must
be performed identically every time.
Hardness
A wide variety of devices are used to measure
the hardness of paint films, including scratch or
pendulum mechanisms.
Scratch
Scratch tests on paint films maybe performed
using mechanically operated styli or knives. The
pencil hardness test is also widely used. In this .
test, pencil lead with specified hardness is pushed
against the paint. The hardest lead that does not
mar the paint is considered the paint hardness.
Pencils are available in 17 different grades of
hardness ranging from 9H, the hardest, to 6B, the
softest (SME, p. 30-3). As with other subjective
tests, procedures must be followed consistently so
test results are meaningful.
Extent of Cure
(Solvent Resistance)
Extent of cure can be determined via hardness
testing or a "solvent rub" test. The solvent rub test
. involves rubbing the cured coating a prescribed
number of times with a cloth saturated with a
specific solvent. If no color appears on the cloth,
the paint is considered cured.
Weather Resistance
Water and weather resistance can be measured in
a variety of ways. Immersion, humidity resistance,
and accelerated weathering tests are typical
methods. Accelerated weathering tests combine
UV light exposure with elevated temperatures and
humidity or salt sprays. In addition to predicting
field performance, the accelerated weathering test
used evaluates different coatings' performance.
It is an effective screening tool for choosing
alternate formulations.
Color Matching
Color matching is challenging because it requires
the manipulation of many variables which contrib-
ute to the test's outcome. Reflected light is the
basis for interpreting color. Light sources (sunlight
or specific artificial sources) vary in intensity, thus
the amount of reflected light may vary. Conduct
color matching, whether visual or instrumental,
under several light sources. The Munsell system
and the Cffi. systems are commonly used and
employ three different light sources to determine
color ( KSBEAP, p. 26-27). For a summary of
various tests, see the table below.
Summary of Paint Tests (KSBEAP, p. 27)
Attribute Measure
Thickness
Flexibility
Paint Adhesion
Hardness
Extent of Cure
Water or Weather
Resistance
Color Matching
Test
Pencil or banana gauge
Micrometer
Tape thickness
Bend or impact
Tape adhesion
Pencil hardness
Solvent rub
Immersion
Humidity resistance
Accelerated weathering
Munsell or CIE
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Appendix F
Glossary=
Acrylic : A resin resulting from the polymeriza-
tion of derivatives of acrylic acids, including
esters of acrylic acid, methacrylic acid, acryloni-
trile, and their copolymers. Acrylics are also used
in powder coatings in their thermoplastic form.
Active solvent: A liquid which dissolves a.binder.
Additives: Any substance added in small quanti-
ties to another substance, usually to improve
properties. Examples of additives include plasticiz-
ers, fungicides, and dryers.
Adhesive: A substance capable of holding materi-
als together by surface attachment. Various
descriptive adjectives are used with the term
adhesive to indicate certain characteristics: physi-
cal (liquid adhesive, tape adhesive), chemical type
(silicate adhesive, resin adhesive), materials
bonded (paper adhesive), and conditions of use
(hot-set adhesive). '
Air-assisted airless spray: Paint spray application
system using fluid pressure to atomize the paint
and low pressure air to adjust the shape of the fan
pattern.
Air-bearings: A stream of air used to support a
spinning shaft. Air bearings have limited load
carrying capacity but require no lubricants,,
Air-dried coatings: Coatings which are not
heated above 194°F (90°C) for coating or drying.
In the South Coast Air Quality Management .
District, curing also must be done below (rather
than at or below) 194°F (90°C) to qualify as air
dried. Air-dried coatings also include forced-air
dried coatings.
Air-dryers: Used to remove moisture.from
compressed air. Dryers have three basic styles of
operation: 1 .deliquescent types have disposable .
drying agents and tend to be marginally effective
for painting; 2. refrigerated dryers cool the air to
condense and remove the water. Most paint
systems use this type; 3. desiccant types have a
double bed dryer and are able to achieve the
lowest dew point air. The beds are alternately on-
stream and back-flushed to regenerate their
moisture absorbing qualities. Some plants with
critical finish requirements use this style of dryer
to reach dew points of-40°F.
Air knife: A slotted jet of compressed air quickly
blows superfluous water from parts, often before
they enter a dryoff oven.
Airless spray: A paint spray application system .
using high fluid pressure to atomize paint by
forcing it through a small orifice.
Air spray: A paint spray application system using
air at high velocity and pressure to atomize the
paint.
Air turbine: 1: Electric motor driven fans that
create volumes of relatively low-pressure atomiz-
ing air for spraying. Their output is referred to as
turbine air; 2. An air-driven-precision fan that is
used to spin a paint atomizing disk or bell head.
Aliphatic solvent: A solvent comprised primarily.
of straight chain hydrocarbons, including mineral
spirits, kerosene, and hexane. These solvents are
characterized as volatile organic compounds.
Alkali: Any substance that neutralizes acids.
Alkalis are helpful in aqueous cleaning to speed
. soil removal and suspension. Alkali is synonymous
with caustic.
Alkyd: A binder based on resins formed by the
condensation of polyhydric alcohols with polyba-
sic acids. They may be regarded as complex
polyesters (Thermoset).
Amino resins: Resins used to crosslink polyes-
ters, epoxies, acrylics, and alkyds to enhance their
durability.
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Amperes (AMPS): An electrodynamic unit of
measure for the quantity of current in a steady
electric flow.
Anode: The electrode at which chemical oxidation
takes place. In electrodeposition (E-coating) the
anode is indicated on diagrams fay the positive (+)
marking.
Anoltye: The water used to flush solubilizer
molecules that form inside an ejectrocoating anode
box. If used to flush a cathode box, it is termed
catholyte.
Aromatic solvents: Hydrocarbon solvents which
contain an unsaturated ring of carbon atoms,
including benzene, naphthalene, anthracene and
their derivatives. Toluene (toluol) and xylene
(xylol) are commonly used aromatics. These
solvents are characterized as volatile organic
compounds.
Atomization: The formation of tiny liquid
droplets during the spraying of coatings.
Autodeposition: Dip coating application method
which depends on a chemical reaction to plate out
the coating film.
Autodeposition (autophoretic): A precipitation
reaction of an organic resin that occurs by the
action of an acid etching a metallic substrate. The
ions of the oxidized metal codeposit with the vinyl
emulsion resin.
Azeotrope: A liquid mixture that distills with out
change in composition. Azeotropes are character-
ized by a constant minimum or maximum boiling
point which.is lower or higher than any of the
components. '
Baked coatings: Coatings that are cured or dried
at or above an oven air temperature of 194°F
(90°C).
Barytes: Colorless crystalline solids, which are a
form of barium sulfate (also called barite). Barytes
are used as an extender pigment in primers and
coatings.
Bells: A rotating head that is shaped to deliver
paint forward in a circular pattern. The bell may
be directed at any angle and be moved on robots
orreciprocatorsjustasspray'gunsare. " .
Bentonite: A type of clay derived from volcanic
ash, which is often used as a paint pigment.
Binder: The solid (non-volatile) material in a
coating that binds the pigment and additive
particles together to form a film. In general,
binders are resins.
Biocide: A chemical agent capable of killing
organisms responsible for microbial degradation.
Biocides are sometimes added to wqterborne
coatings.
Bituminous coating: An asphalt or tar compound
used to provide a protective finish for a surface.
Bleeding: Discoloration which occurs when '
colorants frdm a lower coat diffuse into a surface
coat.
Blistering: The formation of hollow bubbles in
the paint film caused by air, moisture, or solvents
trapped under the film.
Blocked isocyanates (blocking agent): Isocyan-
ates, normally extremely reactive with water, can
only be used in waterborne coatings if they can be
prevented from reacting before the water is baked'
out of the paint film. This is done by capping or
blocking the isocyanate group with a thermally
decomposable chemical. In a bake oven, the water
evaporates! the chemical cap decomposes and the
isocyanate crosslinks the paint. Blocked isocyan-
ates are often employed for E-coat curing.
Blocking: Undesirable sticking together of painted
surfaces when pressed together under normal
conditions. Sticking or blocking can be reduced by
anti-block paint additives.
Blooming: Powder-like deposit forming on the
surface of the film often resulting from partial
dissolving and redepositing of pigment by a
solvent component.
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Blushing: Whitish, milky area which develops on
.the film'and may be caused by absorption of
water vapor by the drying film.
Bounce-off, bounceback: Paint droplets from
air-ato.mized application that rebound or bounce
away from the surface due to the blasting effect of
the air.
Brush coating: Manual application of coatings
using brushes and rollers.
Bulk coating: The painting of large masses of
small unchangeable parts by a variety of possible
techniques such as dip-spin and dipping.
Burn-off ovens: A paint stripping method accom-
plished by combustion of the coating in gas-fired,
burn-off ovens in which high temperatures are
controlled by. injecting of water spray into the
oven.
CARC: Chemical Agent Resistant Coatings. The
polyurethane-based coatings are highly crosslinked
to resist chemical attack. CARC is often used on
military equipment that might become contami-
nated by nuclear, biological, or chemical sub-
stances.
Cathode: The cathode is defined as the electrode :
at which'chemical reduction takes place. In
,electrodeposition (E-C6ating) the cathode is
indicated on diagrams by the, negative (-) marking.
Caustic: A substance that neutralizes acids.
Caustics are used in aqueous cleaning to speed soil
removal and increase soil suspension. Caustic is
synonymous with alkali. :
Cellosolve: The generic term for the solvent
family of mono-alkyl ethers of ethylene glycol.
For example, a widely-used solvent is butyl
cellosolve, which chemically is ethylene glycol
monobutyl ether.
Centrifugal coater: see dip-spin coater
Chalking: The degradation of a paint film by
gradual erosion of the binder, usually due to
' weathering.
Checking: Slight breaks in the film that do not ..'
penetrate to the substrate surface. If the substrate
surface is exposed it is called cracking.
Chipping: Total or partial removal of a dried paint
film in flakes by damage or wear during service.
Chlorinated solvents: Organic solvents that
contain chlorine. Examples include 1,1,1-
trichloroethane and methylene^chloride. These
solvents are characterized as volatile organic
compounds. Their use is regulated and heavily,
restricted. , ,
Coating: A liquid or mastic composition which is
converted to a solid protective, decorative, 6r
functional adherent film. The South Coast Air
Quality Management District defines coatings as
materials which are applied to a surface and
which form a continuous film in order to beautify
and/or protect the surface.
Coating line: Coating lines are all operations
involved in the application, and/or drying of
surface coatings. However, this definition does not
specificly delineate what separates coating lines in
a source, especially when a single oven may cure
parts from multiple spray booths. For most rules,
where the exemption level of the rule is not related
to the volume of coating applied per coating line,
this definition does not apply.
Cobwebbiag: The tendency of spray paint to
form strands rather than droplets as it leaves the
spray gun. Cobwebbing may be caused by too
volatile a solvent or too little air pressure.
Continuous coater: An enclosed automatic spray !
booth that recovers and reuses oversprayed paint.
A continuous coater is suitable for coating large
volumes of similarly-sized parts.
Conversion coating: A chemical or electrochemi-
cal treatment of a metal surface to convert it to
another form, which provides an insulaiting barrier
of exceedingly low solubility between the metal
and its environment, and is an integral part of the
metallic substrate. Examples are phosphate coating
of steel and zinc and chromate anodizing of
aluminum.
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Cosolvents: Water-miscible organic solvents.
Waterborne paints frequently require cosolvents in
addition to water for easier manufacturing and
improved application properties.
Cracking: The splitting of a dry paint film, usually
the result of aging. This includes: hair cracking,
checking, crazing, and alligatoring (crocodiling).
Cratering: Small round depressions in a paint film
which may or may not expose the underlying
surface.
Crawling: A defect in wet paint or varnish film .
where it recedes from small areas of the surface,
leaving them apparently uncoated. Crawling is
caused by an-incompatible film on the surface.
Crazing: The formation of fine surface cracks,
often as a network, which do not penetrate to the
underlying surface.
Crosslinking: The setting up of chemical links
between the molecular chains of a resin to form a
three-dimensional network polymer system.
Crosslinking generally toughens and stiffens
coatings.
Cup gun: A spray gun used with a siphon cup.
Cure: Using heat, radiation, or reaction with
chemical additives to change the properties of a
polymeric system into a more stable, usable
condition. For liquid coatings, it is the process by
which the liquid is converted into a solid film.
Current density: A measure of the total electrical
flow across a given area, frequently expressed in
units of amps/square foot.
Cyclone separator: A funnel-bottomed enclosure
that rapidly moves particulate-laden streams of air
in a circular path. As the relatively high mass of
particles are thrown to the sides of the enclosure,
they slide down through the funnel'into a con-,
tainer for reuse. Cyclone separators are commonly
used for powder coating applications.
Deionized water: Water resulting from the
removal of contaminants by a double-bed ion
exchanger. The ion exchanger replaces positive.
impurity ions with H+ (hydrogen) ions and
negative impurity ions and OH-(hydroxide) ions.
The hydrogen ions and hydroxide ions then
combine to form HOH (H20). Deionized water is '
comparable in purity to distilled water but is
much less costly to produce.
Diluent: Liquids which increase the capacity of a
solvent for the binder. Diluents cannot dissolve the
binder themselves, but are used to control viscos-
ity, flash time, or cost. While true solvents can be
added in unlimited amounts to lower paint viscos-
ity, it may be more economical to lower viscosity
With less costly diluent solvents. When added to a
prepared paint, a diluent will lower the viscosity
just as effectively'as a true solvent. However, if
too much diluent is added, the resin will separate
out of solution and the paint becomes unusable.
Dip coating: The process in which a substrate is
immersed in a solution (or dispersion) containing
the coating material and withdrawn.
Dip-spin icoater: Bulk painting of small and
unchangeable parts accomplished by dipping a
mesh basket of parts, followed by rapid rotation of
the basket to remove excess paint. Parts from the
dip-spin cpater Eire dumped onto a belt for curing.
Disks (discs): Rotating heads that deliver paint
using a horizontal 360 degrees motion and an
omega loop conveyer line. A disk is usually
mounted horizontally on a vertical reciprocator.
Dispersion coating: A type of coating in which
the binder molecules are present as colloidal
particles and spread uniformly throughout the
formulation as a stable mixture.
Doctor blade: Device used to prepare paint and
varnish films of even and predetermined thick-
nesses.
Drier: An additive which accelerates the drying of
coatings.
E-coating (electrodeposition): A dip coating
application method where the paint solids are
given an electrical charge opposite to the part
being coated. In this method, which closely
parallels electroplating, paint is deposited using
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direct electrical current. The electrochemical
reactions that occur cause water-soluble resins to
become insolubilized onto parts which are elec-
trodes in the E-coating paint tank. Subsequent
resin curing is required. y-
Eductor: Nozzles located along E-coat return
.headers, and spaced laterally at intervals across the
tank. These nozzles help to agitate the paint and
prevent settling of pigments, which results in
cleaner film deposits. ,
Electrostatic spray: Method of spray application
of coating where an electrostatic potential is
created between the part to be coated and the
paint particles. . ' . .
Emulsion: A two-phase liquid system in which
small droplets of one liquid (the internal phase) are
immiscible in, and are dispersed uniformly
throughout, a second continuous liquid phase (the
external phase). This contrasts with latex, which
consists of solids dispersed in a liquid.
Emulsion paint: A coating comprised of an
emulsion of a resin binder in water.
Enamels: Topcoats which are characterized by
their ability to form a smooth surface; originally
associated with a high gloss, but may also include
a lower degree of gloss. Also a class of substances
having similar composition to glass with the
addition of stannic oxide, or other infusible
substances to render the enamel opaque. Can be
used to describe a coating which forms a film
through chemical union of its component mol-
ecules during curing. In shop termiriology can be
used to describe paint which is no longer a
lacquer. All paints, powder or liquid, that form
crosslinking chemical bonds during curing are
considered enamels. The majority of industrial
finishes fall into this category.
Epoxies: Binders based on epoxy resins. Epoxy
'crosslinking is based on the reaction of the epoxide
groups with other materials such as amines,
alcohols, phenols, carboxylic acids, and unsatur- -
ated compounds. Also used as a thermoset
powder coating.
Etching: A chemical solution used to remove a
layer of base metal to prepare a surface for ,
coating or binding.
Etching filler: Coatings that contain less.than
23% solids by weight, and at least 0.5% acid by
weight, and are used instead of applying a pre-
treatment coating followed by a primer.
Exempt compounds: Hydrocarbon compounds
excluded from the definition of volatile organic
compound, as defined by the U. S. Environmental
Protection Agency, on the basis that these com-
. pounds have negligible contribution to tropo-
' spheric ozone formation. Acetone is an exempt
compound.
Extender (pigments): White powders used to
give body to the coating. >
Fading: The loss of color in a pigmented coating
film, over time, following exposure to light, heat,
etc. ''-.
Faraday cage: Electrostatic application causes
paint particles to be attracted to the nearest
grounded object. This attraction force is often
strong enough to pull paint particles out of their
intended flight direction. Recessed areas on parts
often receive insufficient paint coverage since they
require a slightly longer path for paint particles. As
a result, these Faraday Cage areas may need
touch-up painting with non-electrostatic spray.
Faraday cage effect: The phenomenon by which
charged particles are prevented from entering
recessed areas during the electrostatic application
of coatings.
Fatty edge: An.excess bead of paint that forms on
the bottom edges of parts when they are in the
drippage zone following dip or flow coating.
Film: One or more layers of coating covering an
object or surface.
Fisheye: A paint defect resulting in a pattern of
small surface depressions' or craters in the wet
film, often caused by surface contamination such
as oil or silicone materials.
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Flash point: The lowest temperature of a liquid
at which it gives off sufficient vapor to form an
ignitable mixture with air.
Flash-off time: The time required between
application of wet-on-wet coatings or between
application and baking to allow the bulk of the
solvents to evaporate. In baked coatings, the flash-
off time helps to prevent solvent boil off and film
blistering.
Flat coatings: Coatings with a gloss reading of
less than 15 on an 85-degree meter or less than 5
on a 60-degree meter. This definition is usually
found in architectural, coating rules.
Flocculation: The formation of loose clusters of
dispersed pigment particles in liquid coatings.
Flooding, floating, or mottle: Tendency of
pigment particles to separate and concentrate in an
area such as the surface.
Flow coating: A coating application system where
paint flows over the part and the excess coating
drains back into a collection system.
Fluidized bed: Finely divided powders can be
made into a fluid-like state by passing air through
the porous plate bottom of a powder hopper. This
permits powder particles to.be used in dip tanks
and to be transported in a manner similar to
liquids.
Flushable electrode: An anode in cathodic E-
coating placed inside a semi-permeable membrane
enclosure. Excess solubilizer generated at the
anode can be continuously removed by water
pumped into the bottom of the enclosure.
Flushable electrodes in anodic E-coating can also
be used (but rarely are needed) for the cathode.
Free radical polymerization: Reactive electrons
that chemically bond to adjacent molecules and
produce a cured paint film. Certain organic
compounds will form highly reactive electron
configurations by the action of UV light (or other
activation sources). These reactive species are
called free radicals because, to an extent, 'free'
electrons are available for bonding.
Fusion: The melting of a powder coating into a
solid film.
Grain refiners: Agents used in water rinses prior
to zinc phosphating or in the zinc phosphatizing
bath itself to produce smaller crystals. Finer grain
zinc phosphate crystals provide superior corrosion
resistance and paint adhesion.
Ground (electrical ground): An object so
massive that it can lose or gain overwhelmingly .
large numbers of electrons without becoming
perceptibly charged.
Halogenated hydrocarbons (halogenated
solvents): Formed by substituting one of the
halogen elements (chlorine, bromine, or fluorine)
into a chemical compound to change both the
physical and chemical nature of the compound..
Heat-resistant coatings: Designed to resist
degradation upon continuous or intermittent
exposures to a predetermined elevated tempera-
ture. A San Diego Air Pollution Control District
rule stipulates that the coating must withstand
temperatures of 400°F during normal use as
determined by ASTM Method D-2485.
High boilers: Solvents with a boiling point above
212°F (tail-end solvents). These solvents usually
evaporate during baking.
High-solids: Solvent-borne coatings that contain
greater than 50% solids by volume or greater than
62%(69% for baked coatings) solids by weight.
High temperature coatings: Coatings certified to
withstand a temperature of 1000°F for 24 hours.
High volume low pressure spray: Spray equip-
ment used to apply coating by means of a gun
which operates between 0.1 and 10.0 psig air
pressure. The high volume of air is produced by a
turbine.
Hot water curing: A curing procedure which
involves immersing parts in 180°F water. Hot
water curing is faster than oven curing for parts
that act as a large heat sink, but is normally not
used since it results in reduced corrosion resis-
tance.
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Hydrocarbon solvent: An organic compound
consisting exclusively of the elements carbon and
hydrogen. They are principally derived from
petroleum and coal tar, arid include aliphatic,
aromatic, and napthenic solvents.
Hydroxides: The chemical opposites of acids.
Also known as caustics and alkalis.'Examples are
sodium hydroxide and potassium hydroxide.
Hygroscopic: A material property defined by the
ability of a substance to readily absorb moisture
from the air. Hygroscopic materials, such as silica
gel and calcium chloride, arejised as desiccants.
Thinly spread deposits of hygroscopic materials .
can absorb enough water to completely dissolve.
Inhibitor: A chemical additive that retards
undesired chemical reactions such as corrosion,
oxidation, drying, and skinning.
Initiator: A chemical used to help start a chemical
reaction such as polymerization. Its action is
similar to that of a catalyst, except that it is usually
consumed in the reaction.
Inorganic polymers: Substances whose principal
structural features are made up of homopolar
interlinkages between multivalent elements other
than carbon. This does not preclude the presence '
of carbon-containing groups in the side branches,
or in interlinkages between principal structural
members. Examples of such polymers are ethyl
and butyl silicates, mica, clays, and talc.
Ionized air cloud: A cloud of air molecules that
have picked up excess electrons around the tip of .
an operating electrostatic spray gun. The elec-
trons from the power pack flow off the end of the
needle electrode at the gun tip. When paint
droplets pass through the ionized air cloud they
accumulate electrons that enable electrostatic
attraction of the droplets to parts being coated.
Isocyanate: A compound containing the func-
tional group -N=C=O. Isocyanates are crosslinked
. with hydroxyls to form polyurethanes.
. Kick-out: .The portion of binder that comes out of
solution as small lumps.
Lacquer: Coating composition based on syn-
thetic thermoplastic film-forming material dis-
solved in organic solvent and dried primarily, by
solvent evaporation. Typical lacquers include .
those based on nitrocellulose, other cellulose
derivatives, vinyl resins, and acrylic resins.
Latent solvent: A liquid which cannot itself
dissolve a binder but which increases the tolerance
of the coating for a diluent.
Latex: Stable dispersion of polymeric solids in an
aqueous medium.
. - x
MEQ (milliequivalents): The concentration of E-
coat solubilizer in the bath.,
MHO: Unit of conductance equal to the reciprocal
of the ohm.
Molecule: The smallest particle of a substance
that retains all the properties of that substance and
is composed of one or more atoms. Water, for
example, consists of molecules having 2 hydrogen
atoms and 1 oxygen atom. The chemical formula,
H2O, indicates the composition of a water mol-
ecule. Organic polymers often have many thou-
sands of atoms per molecule.
Molten salt bath: A mixture of inorganic salts
melted at temperatures between 650° and 900°F.
Painted items immersed in these are rapidly
stripped by combustion of the paint.
Nitrocellulose:, A binder (resin) based on a
polymer from cotton cellulose. Nitrocelluloses
were primarily used in lacquers, and were widely
used from the 1920's to the 50's on automobiles.
v
OHM: A standard unit of resistance to electrical
flow. . .
Ohmeter: A device that measures (in units of
ohms) electrical resistance in a circuit.
Oil base: Coatings which form films through .
crosslinking of unsaturated plant oil (drying oils) in
the presence of oxygen.
Omega loop: The conveyor for rotating disk
paint applicators that is shaped to produce a
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circular path around the vertically oriented disk to
deliver paint from all 360 degrees of its circum-
ference. The term was derived because the
shape of the conveyor resembles the capitalized
form of the Greek letter.
Orange peel: An irregularity in the surface of a
paint film resulting from the inability of the wet
film to level out after being applied.
Overbake or overcure: Exposure of the coating
to a temperature higher or for a longer period of
time, or both, than recommended for optimal
curing; the condition may adversely affect the
appearance and properties of the coating.
Overspray: Any portion of a spray-applied
coating which does not land on a part.
Oxygenated solvents: Volatile organic com-
pounds which contain oxygen in addition to
carbon and hydrogen. Includes alcohols, esters,
ketones, and ether-alcohols.
Peeling: Failure of a coating film to maintain
adhesion with its substrate. Sheets or ribbons of
the film detach from the substrate. The condition
results from contaminated surfaces or excessive
differences in polarity and thermal expansion
characteristics between the surface and the film.
Permeate: The output from ultrafiltration, also
called ultrafiltrate.
pH: The measure of the acidity or alkalinity of a
solution and defined as the logarithm of the
reciprocal of the hydrogen-ion concentration of a
solution. The scale ranges from 2 for highly acidic
solutions to 14 for highly basic or alkaline solu-
tions. Neutral solutions have a pH of 7. Because
the scale is logarithmic, the intervals are exponen-
tial.
Phenolic resins: Resins formed by condensation
of phenols and aldehydes.
Phosphating: A pretreatment for steel or certain
other metal surfaces by chemical solutions con-
taining metal phosphates and phosphoric acid as
the main ingredients. A thin, inert adherent,
corrosion-inhibiting phosphate layer forms which
serves as a good base for subsequent paint coats.
Pigment: Finely ground insoluble particles
dispersed in coatings to influence properties such.
as color, corrosion resistance, mechanical strength,
hardness, durability, etc. Particles may be natural
or synthetic, and inorganic or organic.
Polar: Descriptive of molecules where the atoms
and their electrons and nuclei are so arranged that
one end of the molecule has a positive electrical
charge and the other end of the molecule has a
negative electrical charge. The greater the distance
between the two charged ends, the higher the
polarity. Polar molecules ionize in solution and
impart electrical conductivity. .
Polyester: A polymer in which the monomer units
are linked by the functional group -COO-. Polyes-
ter has been used as thermoplastic powder
coating, and in the following thermosetting powder
coatings: epoxy polyester hybrid powder, urethane
polyester powder, and polyester TGIC powder.
Polyethylenes: Thermoplastic resins composed of
polymers of ethylene (CH2CH2). Polyethylenes
are normally translucent, tough, waxy solids that
are unaffected by water and a large range of
chemicals. Frequently used in powder coatings.
Polymers: A high molecular weight organic
compound, natural or synthetic, with a structure
that can be represented by a repeated small unit,
or mer.
Polypropylenes: Tough lightweight thermoplastic
resins composed of polymers of propylene
(CH3CHCH2). They are commonly used in
powder coating.
Popping: Eruptions in a coating film after it has
become partially set, causing craters to remain in
thefilm.
Pot life: The length of time a coating material is
useable after the original package is opened or
after a catalyst or other ingredient is added.
Powder coatings: Any coating applied as a dry
(without solvent or other carrier), finely divided
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'solid which adheres to the substrate as a continu-
ous film when melted and fused.
Power-and-free conveyor: A separate pusher
chain unattached to paint hooks and riding freely
on a separate-support beam (as distinguished from
a continuous power conveyor). This conveyor
allows parts spacing to vary and parts to be held
stationary even when the pusher chain is moving.
.Power conveyor (continuous): Electrically
driven cables or .chains mechanically attached to
hoods which are used to hang parts to be painted.
The conveyor is used to carry parts through the
painting process. When the line is operating, all
individual hooks on the line will continue to move
and maintain theirspacing. _
Precursor: A chemical compound which is
released into the atmosphere, undergoes a chemi-
cal change, and leads to a new (secondary)
pollutant. Volatile organic compounds are precur-
sors to ozone.
Pressure pot: Various-sized paint tanks containing
delivery tubes which extend to the bottom of the
tank. These tanks are pressurized with com-
pressed air to force paint to the application device.
Primers: Coatings which are designed for applica-
tion to a surface to provide a firm bond between
the substrate and subsequent coatings.
Reactive diluent: A liquid which is a VOC during
application, and through chemical reaction, such
as polymerization, 20% or more of the VOC
becomes an integral part of the finished coating.
Reciprocatqr: An automated device which moves
a paint-applying tool in alternating directions along
a straight or slightly curved horizontal or vertical
path.
Resin: The polymer (plastic) component of a
paint that cures to form a paint film. Also known
as binder or vehicle.
Retarders: Solvents added to a coating to slow
. down a chemical or physical change, such as the
rate of evaporation.
Reverse osmosis: In reverse osmosis, high
pressures are applied to force water out of the
concentrated solution, often to obtain pure (or
purer) water. Solvent is driven through a semi-
permeable membrane separating solutions of
different concentrations.
Ringing: The occurrence of circular spots in a
sprayed repair area (spotting).
Roll coating: .Process by which a film is applied
mechanically to sheet or strip material.
Rusting (face and/or scratch): The appearance
of metal oxidation (corrosion) on the surface of
damaged paint.
Sagging: The downward flow of a coating film as
a result of the film being applied too heavily or
fluid-like.
Sandscratch swelling: A paint defect where
solvent from a repair coat soaks into scratches in
the initial coat and causes paint swelling.
Sealers: A liquid coat applied to a porous sub-
strate such as wood or plaster, to prevent the
substrate from absorbing subsequent coatings.
Shelf life: The length of time a coating may
normally be stored without losing any chemical/
physical properties. Manufacturers typically
specify the shelf life. -
Silicone release: A coating which contains
silicone resins and is intended to prevent food "
from sticking to metal surfaces such as baking
pans.
Silicones: Resins consisting of silicon-oxygen
linkages, unlike organic resins which contain
carbon.
Silking: A surface defect which results in parallel'
flew lines in the paint film. '
Siphon cup (suction cup):'When a special air
spray tip is employed; a partial vacuum is created
by the atomizing air just outside the fluid orifice.
As a result, atmospheric pressure on the paint in a
container connected to the fluid line(such as a
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siphon cup) will force paint out of the container
into the fluid line. The term siphon is actually a
misnomer; suction is a more accurate description
of the action.
Skinning: The formation of a surface skin on
coating liquids formed by the coating reacting with
air or rapidly loosing solvent.
Slitting: Cutting wide coils of roll-coated materials
into narrower widths.
Solubilizer: Compound that forms polar polymer
ions when mixed with water-insoluble resins. .
Since water is a pojar solvent and resins are
usually non-polar, the resins must be treated to
increase their polarity if they are to be used in
waterbome paints.
Solution paint: Resin molecules fully dissolved
by solvents in the paint.
Solvency: The degree to which a solvent holds a
resin or other paint binder in solution.
Solvent: The liquid or blend of liquids used to
dissolve or disperse the film forming particles in a
coating which evaporate during drying. A true
solvent is a single liquid which can dissolve the
coating. The term solvent is often used to describe
terpenes, hydrocarbons, oxygenated, ftirans,
nitroparaffiins, and chlorinated solvents.
Solvent-borne: Coatings in which volatile organic
compounds are the major solvent or dispersant.
Specific gravity: Weight of a given volume of any
substance compared with the weight of an equal
volume of water. Also known as relative density.
Static electricity (electrostatics): Electrons
temporarily removed from various items can cause
static charges. Whatever has excess electrons has
a negative charge; the object from which electrons
have been taken will be positively charged.
Electrons will tend to jump from a negatively
charged object to a positively charged object.
Stencil coating: Ink or other coating which is
rolled or brushed onto a template or stamp
in order to add identifying letters and/or numbers
to metal parts and products.
Surface tension: The energy required to expand
a liquid surface by one unit area. Liquids reduce
their surface area to bring intermolecular attrac-
tive forces into equilibrium. A low degree of
surface tension is preferred for liquid coatings to
maximize minimize wetting and spreading and
minimize edge-pull'and fish-eye effects.
Surfacer: Easily sanded coating used to fill
surface irregularities.
Terpene solvents: Volatile organic compounds
obtained from pine tress and are the oldest
solvents used in coatings. Includes turpentine,
dipentene, and pine oil.
TGIC (triglycidyl isocyanurate): A complex
chemical used to crosslink paint, especially
polyester powders, to increase exterior durability.
Thermoplastic: Resin capable of being repeatedly
softened by heat and hardened by cooling. These
materials, when heated, undergo a substantial '
physical, rather than chemical, change. Thermo-
plastic resins can be completely dissolved with
appropriate solvents.
Thermoset: Resin that, when cured by application
of heat or chemical means, changes into a sub-
stantially infusible and insoluble material. Thermo-
setting resins will soften but will not dissolve in
any solvent.
Thinning: The process of adding volatile liquid to
a coating to reduce its viscosity. This liquid may
be a solvent, diluent or a mixture of both. Thin-
'ning may also be called reducing or "adding m'aike-
up solvent".
Thixotrope: Substance that temporarily causes
high paint viscosities by forming loosely-held
three-dimensional particle networks within paint
fluids. Agitation of the paint by stirring, pumping,
spraying, etc., quickly destroys the networks and
viscosity drops sharply. When agitation is halted,
the networks rapidly reform and paint viscosity
rises again.
154
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.Thixotvopy. The tendency for the viscosity of a
liquid to be shear-rate dependent. When a liquid is
rapidly shaken, brushed, or otherwise mechani-
cally disturbed the viscosity decreases rapidly.
Throwing power: The ability of electro-deposited
coatings to cover interior surfaces.
Topcoat: The final coating film or multiple layers
of the same coating film applied to the surface.
Touch-up: The portion of the coating which is
incidental to the main coating process but is
necessary to cover minor imperfections.
Transfer efficiency: The ratio of solids adhering
to a surface, to the total amount of coating solids
used in the application process, expressed as a ,
percentage.
Undertake or undercure: Exposure of the
coating to a temperature lower or for a shorter
period of time, or both, than recommended for
optimal curing; the condition may cause tackiness,
softness, and inferior film durability.
Ultrafiltation: Ultrafiltration uses low-pressure
membrane filtration to separate small molecules
from large molecules arid fine particulates. For
example, E-coat rinse water is extracted from the
paint bath by ultrafiltation. ' .
Ultrafiltrate: The output from an ultrafiltration
unit; also called permeate.
Ultrasonic cleaning: Vibrational frequencies
slightly higher than those audible used to agitate
' immersion cleaning tanks. Microbubble formation
in the liquid accelerates dislodgement of soils.
Undercoats: Coatings formulated and applied to
substrates to provide a smooth-surface for
subsequent coats.
Urethanes: Materials based on resjns made by the
condensation of organic isocyanates with com-
pounds or resins containing hydroxyl groups.
Categories of polyurethane coatings include: single
. component prereacted-uretharie coatings; single
component moisture-cured urethane coatings;
single component heat-cured urethane coatings;
two. component catalyst-urethane coatings; two .
component polyurethane coatings; and one ,
component nonreactive lacquer-urethane solution
coatings. ,
Vacuum metallizing: Process in which surfaces
are thinly coated by exposing them to metal vapor
under a vacuum.
Varnish: Clear or pigmented coatings formulated
with various resins and designed to dry by chemi-
cal reaction on exposure to air. These coatings are
intended to provide a durable transparent or
translucent solid protective film.
Vehicle: The liquid portion of a coating in which
the pigment is dispersed; it is composed of binder,
solvent and diluent.
Vinyl chloride polymers: Polymers formed by
' the polymerization of vinyl chloride or copolymer-
ization of vinyl chloride with other unsaturated .
compounds, the vinyl chloride being in greatest
amount by weight. Can be used in thermoplastic
powder coatings.
Vimyl resins: Resins which contain the unsatur-,
ated vinyl group, (CH2=CH-) including polyvinyl
acetate, polyvinyl chloride,:copolymers of these,
the acrylic and methacrylic resins, the polystyrene
resins, etc. ,-.'.<
Viscosity: The property of a fluid whereby it
tends to resist relative motion within itself. A thick
liquid such as syrup has a high viscosity. Viscosity
is often measured using an efflux type cup which
gives the time required for a given quantity of
paint to flow through a hole in the bottom- of the
metal cup at a given temperature (See Zahn Cup).
Volatile organic compound (VOC): Any
organic compound, not specifically exempted by
the U.S. EPA, that participates in atmospheric
photochemical reactions. VOCs may be emitted
during the application and/or drying of coatings.
In calculating the VOC content of the coating,
exempt compounds and water are excluded.
Exempt compounds are acetone, ethane, meth-
ane, carbon monoxide, carbon dioxide, carbonic
acid, metallic carbides, metallic carbonates,
ammonium carbonate, methylene chloride, 1,1,1
155
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trichloroethane (methyl chloroform), 1,1,2
trichlorolotrifluproethane (CFC-113),
trichlorofluoromethane (CFC-11), dichlorodifluo-
romethane (CFC-12),- dichlorotetrafluoroethane
(CFC-1 HXchloropentafluoroethane (CFC-115),
trifluoromethane (CFC-23), and
chlorodifluoromethane (CFC-22). Although many
of these compounds are exempt under the VOC
rule, they may contribute to upper atmosphere
ozone destruction:
Volatility: The tendency of a liquid to evaporate.
Liquids with high boiling points have low volatility
and vice versa.
Voltage: measure of the potential difference
(force or pressure) in electrical systems.
Waterborne coatings: Coatings in which water is
the major solvent or dispersant. Solvents or
dispersants include water soluble polymers (water
reducible), water soluble colloidal dispersions, and
emulsions (including latex).
Water-reducible coatings: see waterbome
coatings.
Weir: The (often adjustable) barrier that controls
the paint depth in an E-coat tank over which the
paint flows to the circulation pump, to be filtered,
We't-on-wet finishing: Applying a new coat over
an earlier applied coat which has been allowed to
flash-off but not cure.
Wrap around: Electrostatic effect where charged
coating particles curve around the part and are
deposited onto the rear side of the part.
Wrinkling: Distortion in a paint film appearing as
ripples.
Zahn cup: Commonly used efflux cup used for
measuring the viscosity of coatings. Other widely
used viscosity cups are the Fischer cup and the
Ford cup. These instruments measure the time
required for a given quantity of paint to flow .
through a hole in the bottom'of a metal cup at a
given temperature.
156
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Appendix G
Measuring Transfer Efficiency
Before conducting any transfer efficiency test,
several parameters need to be established:
+ What part will the test focus on?
* Which coatings and spray guns will the test
use? ,
+ Who will apply the coatings? ,
« How will the test simulate day-to-day produc-
tion conditions?
After identifying the basic parameters, the paint
operator mustestablish a fluid flow rate that is
representative of day-to-day production. The
operator needs to set the optimum air pressure for
coating atomization and to adjust the coating
viscosity and temperature to be representative of
typical operating conditions. If the operator is
using electrostatic equipment, they must confirm
that the parts are properly grounded, the coating is
adjusted so that resistivity meets manufacturers
recommendations, and the air velocity through the
spray booth is neither too high nor too low. A
decision also needs to be made in selecting the
proper transfer efficiency test.
Guidelines for Choosing Transfer
Efficiency Methods !
* If workpieces are small and lightweight (less
than 70 pounds each), use the weight'(mass)
method.
* If workpieces are small and heavy (greater
than 70 pounds each) with simple geometry,
use the weight method by "wallpapering" with
aluminum foil. ' .
+ If workpieces are small with complex geometry
but the surface area can still be calculated, use
the-volume method. .
* If workpieces are small with a complex geom- .
etry where the surface area cannot be calcu-
lated, a special protocol may need to be
- designed. '
* If workpieces are too large to fit onto a
balance and have a simple geometry, use the
weight method by "wallpapering" with alymi- .
num foil.
V
* If workpieces are too large to fit onto a
balance and have a complex geometry, but the
surface area can still be calculated, use the
volume method.
* If workpieces are large with a complex geom-
etry where the surface area cannot'be calcu-
lated,^ special protocol may need to be
designed.
The Weight (Mass) Method
Determining transfer efficiency on a weight or
mass basis, as is usually the case, requires pur-
chasing or renting an electronic balance capable of
measuring within 0.5 grams. There are balances
available that can weigh parts up to 70 pounds
(154 kilograms) with this accuracy. The balance
must sit on a hard surface, such as a metal table,
concrete floor, or cement slab. Operators should
never place a piece of cardboard under the
balance, as this will lead to inaccurate results.
In addition, the operator must shield the balance
from all drafts that occur on a factory floor (this
can be accomplished by surrounding the balance
with cardboard walls). The operator must also
ensure that the pressure pot or coating reservoir is
not-tod heavy for the balance and that the part to
be coated falls within the acceptable limits of the
balance.
The balance should be set so that the air bubble in
the bubble glass falls within the center of the glass.
In addition, all four feet of the balance must be in
firm contact with the ground or surface. Finally,
.the operator must calibrate the balance using
standard weights, which are often supplied by.the
balance manufacturer.
157
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The paint operator should follow the steps below
to determine the weight of coating used during the
operation. This process begins by measuring the
liquid coating, then calculating the weight of the
solid coating.
1. Before beginning the test, appropriately label
each part and then accurately weigh the parts on
the balance. Record the weights.
2. Place the pressure pot or coating reservoir oh
the balance and slowly fill it with coating, ensuring
not to exceed the limit of the balance even after
tightening the pressure pot cover.
3. Before commencing the actual test, apply the
coating to several dummy parts to ensure that the
coating process is representative of actual operat-
ing conditions.
4. To begin the test, disconnect the fluid and air
hoses from the pressure pot. Do not allow any
paint to drip to the floor, as it is imperative that the
coating fills the line all the way up to the spray
gun. Record the coating weight and then replace
the air and fluid hoses and begin the spraying
operation.
5. For accurate results continue spraying until at
least one quart of paint has been used (approxi-
mately 2.2 pounds or 1 kg). After applying the
coating to the selected parts, immediately discon-
nect the fluid and air hoses from the pressure pot,
weigh the pot and record the second reading.
Repeating this entire procedure three times will
help determine an average transfer efficiency.
At any time during the test, the operator should
take a small grab sample (approximately one pint
of the coating) from the pressure pot. The opera-
tor should be sure to close the container to prevent
solvent evaporation. The facility should send the
sample to an analytical laboratory that will conduct
a percent weight solids test in accordance with
A STM D2369 (this is the standard test method For
volatile coatings).
The company should not bypass the sampling
procedure by simply calling the coating manufac-
turer to request information on the percent weight
solids or referring to the MSDS. Even a small .
discrepancy between the manufacturer's value and
the actual value obtained from the pressure pot
sample will make a large difference in the transfer
efficiency calculations.
The weight of solids used is calculated by following
this equation:
Wt of Liquid Coating x % Wt. Solids
Wt of Solids Used =
TOO
As noted earlier, before starting the transfer efficiency
test, each part must be labeled and weighed. After
applying the coating, the operator should allow
thorough curing before weighing the part again, If the
coating is normally air or force-dried, allow extra time
for all of the solvent to evaporate. Curing the parts in
an oven set at 230°F will result in a more accurate
transfer efficiency reading, even if this is not the
normal method for curing. This oven curing schedule
is identical to what a laboratory will use to determine
the percent weight solids of the one pint sample taken
earlier.
After the coating has thoroughly cured, the operator
should weigh the parts. The difference between the
weights of coated and uncoated parts represents the
weight of solid coating deposited. Knowing the weight
of solid coating used, and the weight of solid coating
deposited, the operator can calculate the transfer
efficiency as follows:
Transfer efficiency =
Mass of solid coa'ting deposited
Mass of solid coa'ting used
The credibility of the results depends entirely on the
accuracy of the weighing. If the factory has drafts or
vibrations that could affect the balance, the operator
may wish to take two or three readings before record*
ing any one weight. In addition, the laboratory deter-.
mination of percent weight solids must be accurate.
Finally, the accuracy of the results will increase if a
number of parts are coated during any one test.
When using this method for a large part with a
.relatively simple geometry the operator can still use
. the weight method by "wallpapering" the surface with
pre-weighed aluminum foil. At the conclusion of the
test, the operator should weigh the dried coating on
the foil to complete the calculations. ,
158
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Costs .
The cost to conduct a transfer efficiency test can
be minimal. Companies can usually rent an
electronic balance for less than $300/week. A
laboratory charge might be $ 1507 sample. The
other "in-house" expense is labor., If a consultant
is retained costs might range from $3,000 to
$5,000, depending on the complexity of the
operation. '
The Volume Method
The volume method is not as accurate as the
weight method. To measure transfer efficiency
using the volume method, a laboratory must
determine the percent solids of the coating as
applied, as described in the weight method. To
determine the volume of solid coating deposited, a
lab measures the average film thickness of the
deposited coating; as well as the total surface area
of the coated parts. '
159
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