United States
Environmental Protection
Agency
Air Quality and Planning
Standards '
EPA340/1-91-009
August 1991 —
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Report on Compliance Coatings
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EPA 340/1-91-009
REPORT ON COMPLIANCE COATINGS FOR THE
MISCELLANEOUS METAL PARTS INDUSTRY
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Radiation
Stationary Source Compliance Division
401 M. Street S.W.
Washington, D.C. 20460
August 1991
CM
OJ
HEADQUARTERS LIBRARY
ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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i$ 1$
DISCLAIMER
This report was furnished to the U.S. Environmental Protection Agency's Stationary
Source Compliance Division by Alliance Technologies Corporation in fulfillment of
Contract No. 68-02-4465, Task 90-143. The opinions, findings, and conclusions
expressed are those of the authors and not necessarily those of the U.S.
Environmental Protection Agency. Mention of company, process, or product name is
not to be considered as an endorsement by the U.S. Environmental Protection
Agency.
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TABLE OF CONTENTS
Chapter Page
1 INTRODUCTION AND USE OF THIS MANUAL 1-1
1.1 INTRODUCTION 1-1
1.2 HOW TO USE THIS MANUAL 1-1
2 DESCRIPTION OF COATING PROCESSES 2-1
2.1 INTRODUCTION 2-1
2.2 PRIMARY METAL INDUSTRIES (Major SIC Group 33) 2-2
2.2.1 Coating Process 2-2
2.2.2 Appropriate VOC-Compliant Technology 2-6
2.2.3 Requirements for Conversion to Compliant
Coatings 2-6
2.3 FABRICATED METAL PRODUCTS, EXCEPT MACHINERY AND
TRANSPORTATION PRODUCTS (Major SIC Group 34) 2-6
2.3.1 Coating Process 2-6
2.3.2 Appropriate VOC-Compliant Technology 2-14
2.3.3 Requirements to Convert to Compliant Coatings 2-15
2.4 INDUSTRIAL AND COMMERCIAL MACHINERY AND
COMPUTER EQUIPMENT (Major SIC Group 35) 2-15
2.4.1 Coating Process 2-15
2.4.2 Appropriate VOC-Compliant Coatings 2-19
2.4.3 Requirements for Conversion to Compliant
Coatings 2-21
2.5 ELECTRONICS AND OTHER ELECTRICAL EQUIPMENT
EXCEPT COMPUTER EQUIPMENT (Major SIC Group 36) 2-21
2.5.1 Coating Process 2-21
2.5.2 Appropriate VOC-Compliant Technology 2-22
2.5.3 Requirements to Convert to Compliant Coatings 2-22
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TABLE OF CONTENTS - (Continued)
Chapter
Page
2.6 TRANSPORTATION EQUIPMENT (Major SIC Group 37) 2-23
2.6.1 Coating Process 2-24
2.6.2 Appropriate VOC-Compliant Technology 2-24
2.6.3 Requirements for Conversion to Compliant
Coatings 2-25
2.7 MEASURING, ANALYZING AND CONTROLLING INSTRUMENTS
(Major SIC Group 38) 2-25
2.7.1 Coating Process 2-25
2.7.2 Appropriate VOC-Compliant Coating Technology 2-28
2.7.3 Requirements to Convert to Compliant Coatings 2-28
2.8 MISCELLANEOUS MANUFACTURING (Major SIC Group 39) ... 2-28
2.8.1 Coating Process . . 2-29
2.8.2 Appropriate VOC-Compliant Technology 2-30
2.8.3 Requirements for Conversion to Compliant .
Coatings 2-31
2.9 RAILROAD TRANSPORTATION (Major SIC Group 40) 2-31
2.10 LOCAL AND SUBURBAN AND INTERURBAN HIGHWAY
PASSENGER TRANSPORTATION (Major SIC Group 41) 2-32
3 STATE VOC LIMITS 3-1
4 TYPICAL PHYSICAL AND CHEMICAL PROPERTIES OF
VOC-COMPLAINT COATINGS v. 4-1
4.1 INTRODUCTION 4-1
4.2 GENERAL PURPOSE INDOOR AND OUTDOOR EXPOSURE,
WATER-BORNE PRIMERS, AIR/FORCE DRY 4-1
4.3 GENERAL PURPOSE INDOOR AND OUTDOOR EXPOSURE,
WATER-BORNE TOPCOATS, AIR/FORCE DRY 4-1
4.4 HIGH PERFORMANCE WATER-BORNE COATINGS,
BAKE >250°F 4-4
4.5 GENERAL PURPOSE, SOLVENT-BORNE COATINGS,
AIR/FORCE DRY 4-6
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TABLE OF CONTENTS - (Continued)
Chapter
Page
4.6 HIGH PERFORMANCE, SOLVENT-BORNE COATINGS,
BAKE >250°F 4-8
4.7 HIGH PERFORMANCE COATINGS, TWO-COMPONENT,
EPOXY AND POLYURETHANE 4-9
4.8 POWDER COATINGS: EPOXY, POLYESTER, AND
POLYESTER TGIC 4-12
5 RESIN SYSTEMS USED IN THE MISCELLANEOUS METAL
PARTS INDUSTRY 5-1
5.1 INTRODUCTION 5-1
5.2 FILM FORMATION MECHANISMS 5-1
5.2.1 Class I Film Formation by Solvent Evaporation 5-1
5.2.2 Class II Film Formation by Evaporation Followed by
Auto-Oxidation 5-3
5.2.3 Class III Film Formation by Cross-Unking 5-3
5.2.4 Class IV Film Formation by Coalescence 5-4
5.3 RESIN TECHNOLOGIES 5-5
5.3.1 Water-Reducible, Air/force'Dry, <194°F(90°C)
Alkyds and Modified Alkyds 5-7
5.3.2 Water-Borne Air/Force Dry Acrylic Latex 5-7
5.3.3 Water-Borne, Air/Force Dry Acrylic Epoxy Hybrids 5-11
5.3.4 Water-Borne, Air/Force Dry Epoxy 5-12
5.3.5 Water-Borne, Air/Force Dry, Polyurethane Dispersions .... 5-13
5.3.6 Water-Borne, Bake/Alkyd, Modified Alkyd and Acrylic 5-13
5.3.7 Solvent-Borne, Air/Force Dry, Alkyd and Modified Alkyd . . . 5-13
5.3.8 Solvent-Borne, Air/Force Dry Epoxy Esters 5-17
5.3.9 Solvent-Borne, Air/Force Dry Catalyzed Epoxies 5-19
5.3.10 Solvent-Borne, Air/Force Dry Catalyzed Polyurethane 5-21
5.3.11 Solvent-Borne, Bake Alkyd and Modified Alkyds 5-28
5.3.12 Silicone Coatings 5-30
5.3.13 Autodeposited Coatings 5-30
5.3.14 Electrodeposition 5-33
5.3.15 Radiation Cured Coatings 5-35
5.3.16 Vapor Injection Cure 5-37
5.3.17 Powder Coatings 5-37
HI
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TABLE OF CONTENTS - (Continued)
Chapter Page
5.4 BIBLIOGRAPHY 5-40
6 HOW TO SELECT A COMPLIANT COATING ..., 6-1
6.1 INTRODUCTION 6.1
6.2 APPEARANCE CONSIDERATIONS 6.1
6.3 ENVIRONMENTAL CONSIDERATIONS 6.5
6.4 PHYSICAL AND CHEMICAL PERFORMANCE CONSIDERATIONS . . 6.6
6.5 PART SIZE, SHAPE, AND MATERIAL CONSIDERATIONS 6.12
6.6 SURFACE PREPARATION 6-14
6.7 PRODUCTION, APPLICATION, AND FACILITY
REQUIREMENTS 6-15
6.8 QUALITY CONTROL 6-17
6.9 COST 6-20
7 COATING MANUFACTURERS AND AVAILABLE COMPLIANT
COATINGS 7-1
8 CASE HISTORIES 8-1
8.1 INTRODUCTION 8-1
8.2 CASE HISTORY NO. 1 - COMPANY MANUFACTURING
STEEL BRACKETS FOR THE BUILDING SUPPLY INDUSTRY 8-3
8.3 CASE HISTORY NO. 2 - SMALL COMPANY WHICH
MANUFACTURES TRAILERS FOR RECREATIONAL BOATS 8-4
8.4 CASE HISTORY NO. 3 - FENCE POST MANUFACTURING
FACILITY 8-6
8.5 CASE HISTORY NO. 4 - MANUFACTURER OF DECORATIVE
LIGHTING FIXTURES FOR THE CONSUMER INDUSTRY 8-7
8.6 CASE HISTORY NO. 5 - MANUFACTURER OF LAMP
HOUSINGS BURIED IN SOIL 8-9
8.7 CASE HISTORY NO. 6 - MANUFACTURER OF CUSTOM
DESIGNED MACHINERY FOR INDOOR AND EXTERIOR EXPOSURE8-10
8.8 CASE HISTORY NO. 7 - COMPANY WHICH MANUFACTURES
LARGE TOTE TANKS FOR STORAGE OF CHEMICALS 8-13
8.9 CASE HISTORY NO. 8 - COMPANY MANUFACTURING AIRCRAFT
LOADING MACHINES FOR USE AT AIRPORTS 8-15
8.10 CASE HISTORY NO. 9 - MAINTENANCE OPERATION OF
AIRLINE GROUND SUPPORT EQUIPMENT 8-17
IV
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TABLE OF CONTENTS - (Continued)
Chapter ' Page
8.11 CASE HISTORY NO. 10 - MANUFACTURER OF LABORATORY
AND MEDICAL ELECTRONIC EQUIPMENT 8-18
8.12 CASE HISTORY NO. 11 - MANUFACTURER OF LAWN AND
GARDEN TRACTORS 8-21
8.13 CASE HISTORY NO. 12 - MILITARY CONTRACTOR FACILITY
WHICH MAKES TRACKED VEHICLES FOR THE U.S. ARMY 8-23
8.14 CASE HISTORY NO. 13 - MILITARY CONTRACTOR FACILITY
WHICH MAKES MICROWAVE COMMUNICATION SYSTEMS
FOR THE U.S. NAVY, ARMY, AND AIR FORCE 8-25
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TABLE OF CONTENTS (Continued)
Figure Page
2-1 Assembly, priming and topcoating line spray or
dipcoating primer and spray-applied coatings 2-8
2-2 Assembly, and powder coating operation 2-9
2-3 Typical iron and zinc phosphating processes 2-11
2-4 Typical 7-stage iron and zinc phosphating processes 2-17
Table
2-1 Miscellaneous Metal Parts Industry Sectors 2-1
2-2 Coating Categories 2-3
2-3 Example of Industries Potentially Subject to MMP Rules in Major
Group 33, SIC Code 3312-3399 ...... 2-5
2-4 Example of Industries Potentially Subject to MMP Rules in Major
Group 34, SIC Code 3411-3499 2-7
2-5 Most Common Manual Spray Guns 2-12
2-6 Most Common Automated Coating Processes 2-13
2-7 Reasons for Poor Spray Booth Efficiency 2-13
2-8 Example of Industries Potentially Subject to MMP Rules in Major
Group 35, SIC Code 3511-3599 2-16
2-9 Example of Industries Potentially Subject to MMP Rules in Major
Group 36, SIC Code 3612-3699 2-22
2-10 Example of Industries Potentially Subject to MMP Rules in Major
Group 37, SIC Code 3711-3799 2-23
2-11 Example of Industries Potentially Subject to MMP Rules in Major
Group 38, SIC Code 3812-3973 . 2-26
VI
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TABLE OF CONTENTS (Continued)
Table Page
2-12 Example of Industries Potentially Subject to MMP Rules in Major
Group 39, SIC Code 3911-3999 2-29
2-13 Example of Industries Potentially Subject to MMP Rules in Major
Group 40, SIC Code 4011-4013 2-32
2-14 Example of Industries Potentially Subject to MMP Rules in Major
Group 41, SIC Code 4111-4173 2-32
3-1 Compliant Coating Regulations by State 3-3
3-2 California VOC Compliant Coatings 3-4
4-1 Typical Properties of General Purpose Indoor and Outdoor
Exposure Water-Borne Primers, Air/Force Dry 4-2
4-2 Typical Properties of General Purpose Indoor and Outdoor
Exposure Water-Borne Topcoats, Air/Force Dry 4-3
4-3 Typical Properties of General Purpose Indoor and Outdoor
Exposure Water-Borne Coatings, Bake >250°F 4-5
4-4 Typical Properties of General Purpose Indoor and Outdoor Exposure
Solvent-Borne Coatings, Air/Force Dry 4-6
4-5 Typical Properties of High Performance Solvent-Borne Coatings ... 4-8
4-6 Typical Properties of High Performance Indoor and Outdoor Exposure
High Solids Epoxy and Polyurethane Coatings 4-10
4-7 Typical Performance Properties of Powder Coatings 4-13
5-1 Film Formation Mechanisms 5-2
5-2 Resin Technologies 5-6
5-3 Water-Reducible Air/Force Dry Alkyd and Modified Alkyds 5-8
5-4 Water-Borne, Air/Force Dry Acrylic Latexes 5-9
Vil
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TABLE OF CONTENTS (Continued)
Table Page
5-5 Water Borne, Air/Force Dry Acrylic Epoxy Hybrids 5-11
5-6 Water-Borne, Air/Force Dry Epoxies 5-14
5-7 Water-Borne, Air/Force Dry Polyurethane Dispersions 5-15
5-8 Water-Borne, Bake Alkyd, Modified Alkyd and Acrylics 5-16
5-9 Solvent-Borne, Air/Force Dry Alkyds and Modified Alkyds 5-18
5-10 Solvent-Borne, Air/Force Dry Epoxy Esters 5-20
5-11 Solvent-Borne, Air/Force Dry, Catalyzed Epoxies 5-22
5-12 Solvent-Borne, Air/Force Dry Two-Component Catalyzed
Polyurethane Coatings 5-23
5-13 Moisture Cured Polyurethane Coatings 5-25
5-14 Typical Polyurethane Applications 5-27
5-15 Solvent-Borne, Bake Alkyd and Modified Alkyd Coatings 5-29
5-16 Silicon Coatings 5-31
5-17 Autodeposited Coatings 5-32
5-18 Electrodeposited Coatings 5-34
5-19 Radiation Cured Coatings 5-36
5-20 Powder Coatings 5-38
6-1 Criteria for Selecting a Compliant Coating 6-2
7-1 Available VOC Compliant Coatings 7-3
7-2 Coating Manufacturers 7-25
VIII
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CHAPTER 1
INTRODUCTION AND USE OF THIS MANUAL
1.1 INTRODUCTION
This manual has been prepared with a focus on the surface coating of Miscellaneous
Metal Parts, as defined by those industries which fall into the Standard Industrial
Codes (SIC) 33 to 40, inclusive.
The objectives of the manual are as follows:
1. To serve as a guide for industrial coating users and coating
manufacturers, as well as inspectors and engineers with EPA who need
to understand VOC compliance as it applies to surface coating
operations.
To enable coating facilities to identify the most likely strategies for getting
into compliance using low-VOC coating technologies.
To provide the reader with a comprehensive listing of the most common
VOC-compliant coating technologies used in the Miscellaneous Metal
Parts industries, and to describe the advantages and disadvantages of
each.
4. To provide the reader with a listing of a wide range of VOC-compiiant
coatings, as well as the names and addresses of the coating
manufacturers.
5. To provide the reader with an understanding of the process of selecting
compliant coatings.
1.2 HOW TO USE THIS MANUAL
This manual assumes that the reader has little or no previous knowledge of
miscellaneous metal parts coatings. Therefore, Chapter 2 lists all of the major SIC
categories covered by this manual, and assumes that, by definition, the affected facility
will fall into one of them. For each SIC category, a brief description of a typical
coating process is described. Thereafter, a fairly-detailed analysis is provided which
guides the reader to the coating technologies which are most applicable for each
industry.
2.
3.
1-1
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The reader will then continue to Chapter 3, in which tables provide the VOC
requirements of ail States. Armed with this information, the reader can then select
only those technologies which meet the regulatory VOC limits.
Clearly, the selected coating must be able to satisfy the physical and chemical
performance properties required by the product which is to be coated. Chapter 4,
provides the reader with the typical properties of the most common coatings.
By now, the reader should have narrowed his/her choice of compliant technology to
perhaps three or four possible coatings. Chapter 5 presents detailed information
about each technology. The chapter not only describes the curing mechanism of
each technology but, more importantly, lists the major advantages and disadvantages
of each.
Chapter 6 addresses the real-life problem of fitting the coating technology to the
production line application. This chapter gives the reader an opportunity to confirm
the coating selection. Simple questions such as "Must the coating be able to provide a
texture pattern?", or "Musi the coating dry within a 15-30 minute period?", or "What
minimum surface preparation is required to apply the coating?" are answered for each
technology.
Chapter 7 comprises a listing of some coatings currently being offered for sale by
coating manufacturers. The tables are the result of a questionnaire sent to many
coating manufacturers, requesting details of their compliant formulations. While it must
be understood that the listing is not complete, and for practical reasons could not list
all of the compliant coatings currently available from each and every coating
manufacturer in the United States, it nevertheless provides the reader with a starting
point.
Several case histories of companies which have converted to VOC compliant coatings
are discussed in Chapter 8.
Finally, there Is a word of caution! Despite every effort to compile this manual so
that it is a useful reference guide, the reader must understand that final selection of a „
compliant coating can only occur after the coating has been tried and tested under
actual production line conditions. Moreover, while the coating from one manufacturer
may not be suitable, it is quite possible that a coating of the same technology type,
but formulated by a competitive manufacturer, may suffice. There is no substitute for
shopping around and then testing each product under real-life conditions.
1-2
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CHAPTER 2
DESCRIPTION OF COATING PROCESSES
2.1 INTRODUCTION
This chapter describes the typical coating processes which take place in several types
of Miscellaneous Metal Parts industries listed in Table 2-1 together with their
appropriate Standard Industrial Codes (SIC).
TABLE 2-1. MISCELLANEOUS METAL PARTS INDUSTRY SECTORS
Industry Sector
SIC Code
Major Group
Primary Metal Industries
Fabricated Metal Products, Except
Machinery & Transportation Equipment
Industrial and Commercial Machinery and
Computer Equipment
Electronics and other Electrical
Equipment except Computer Equipment
Transportation Equipment
Measuring, Analyzing and Controlling
Instruments
Miscellaneous Manufacturing Industries
Railroad Transportation
Local and Suburban and Interurban
Highway Passenger Transportation
33
34
35
36
37
38
39
40
41
2-1
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For each industry sector, processes typical to that sector and VOC-comp!iant
technologies most suitable for use in that sector are discussed under the following
headings:
1. Surface Preparation
2. Coating Application
3. Spray Booths and Ovens
4. Typical Facility Layout
5. Most likely VOC-compliant Technology
6. Requirements for Conversion to Compliant Coatings
Table 2-2 lists the types of coatings commonly used in the Miscellaneous Metal Parts
industries. Throughout the chapter, references are made to the listed categories of
coatings when discussing most likely VOC-compliant technology and requirements for
conversion to compliant coatings.
2.2 PRIMARY METAL INDUSTRIES (MAJOR SIC GROUP 33)
This sector is characterized by industries which make products that are sold to
manufacturing industries. As shown in Table 2-3, typical products include car wheels,
railroad crossings, spikes, wire carts, wrought pipe and tubes, and others.
These industries essentially do not use coatings; they ship their products as-is. The
customers receiving the products rework them into final products. For those products
which are coated before shipping, surface preparation is minimal, and the coating itself
is fast drying and inexpensive.
2.2.1 Coating Process
\
Because of the minimal requirements for coatings used in the industries covered by
major SIC Group 33, the typical coating process is likely to be fairly simple. Cleaning
is followed by coating application by spray, dip or flow coating, and drying.
2.2.1.1 Surface Preparation
The steel or aluminum substrate receives a cursory solvent wipe for the purpose of
removing excess oil and grease. Alternatively, the parts may be cleaned with an
aqueous detergent cleaner applied through a high pressure hot water system. In
some cases, a light phosphate will be added to the rinse water to provide a minimal
etch to the surface.
Any rust or scale present will remain and will not be removed.
2-2
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TABLE 2-2. COATING CATEGORIES
Coating Type
No. of
Components
Category 1
Water-borne, air dry/force dry,
(<194°F, 90°C):
Alkyd, and modified alkyds,
water-reducible
Acrylic latex
Acrylic epoxy hybrids
Epoxy water-reducible
Polyurethane dispersions
Category 2
Water-borne, Bake,
(>194°F, 90°C):
Alkyds and modified alkyds
Acrylics
Category 3
Solvent-borne, air dry/force dry,
(<194°Ff90'C):
Alkyds (alkyd modified: acrylic,
vinyl toluene, styrene, silicone)
Epoxy esters
Epoxy catalyzed
Single
Single
Two or three
Two or three
Single
Single
Single
Single
Single
Two
2-3
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TABLE 2-2 (Continued)
Coating Type
No. of
Components
Polyurethane catalyzed:
Polyester-urethane
Acrylic-urethane
Moisture cure
Category 4
Solvent-borne, Bake,
(>194T90°C):
Alkyds (alkyd modified: melamine,
urea-formaldehyde, phenolic)
Acrylic
Polyester (oil free)
Category 5
Specialty Coatings
Siiicone
Autophoretic
Electrodeposited
Anodic
Cathodic
Radiation Cure (UV and EB)
Vapor Injection Cure
Powder
Two
Two
Single
Single
Single
Single
Single
Single
Single
Single
Single
Three
Single
2-4
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TABLE 2-3. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 33, SIC CODE 3312-3399
SIC CODE 3312-3399: PRIMARY METAL INDUSTRIES
Axles, rolled or forged
Car wheels
Railroad crossings
Sheet steel
Steel baskets made in wire-drawing plants
Chain link fencing, made in wire-drawing plants
Spikes
Steel wire cages
Wire carts, household, grocery, made in wire-drawing plants
Conduit
Well casings
Wrought pipe and tubes
Cast iron cooking utensils [
2.2.1.2 Coating Application
Coatings, typically primers, are usually an inexpensive, fast drying alkyd or modified
alkyd, such as a styrenated alkyd. They can be applied by spray, dip or flow coating.
The primary function of the coating is to prevent corrosion of the metal for a short
duration, until the customer has fabricated a new product and is ready to recoat or
topcoat with a new system. Color and gloss are relatively unimportant; a low or semi-
gloss finish is usually chosen so that the customer can apply a topcoat directly over
tiie primer coat Special chemical and physical properties are usually not required.
A thermoset coating, which cures at elevated temperatures, such as 250°F (121°C) is
rarely used. Also, catalyzed coatings, such as a two-component epoxy or
polyurethane are not likely; these coatings can be very difficult to remove. The
customer will be reworking the product, and may need to remove the coatings before
applying a completely new system.
2.2.13 Spray Booths and Ovens
Depending on the amount of coating used, the booths may be of the dry filter or
water-wash type. The coatings will be air or force dried at temperatures less than
194°F (90°C).
2-5
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2.2.2 Appropriate VOC-Compliant Technology
The preferred compliance coating is inexpensive and fairly tolerant to contaminated
surfaces. It should be capable of being dip- or flow-coated, and should dry fairly
rapidly.
The coatings which are likely to be considered are the water-borne air/force dry
coatings of Category 1 (see Table 2-2), such as the alkyds, modified alkyds or
acrylics.
The most likely technologies in Category 3 (see Table 2-2) are the alkyds, modified
aikyds and epoxy esters. They are reasonably inexpensive and can easily be spray or
dip-applied. Also, similar to the Category 1 coatings, they are supplied as a single
component and do not require sophisticated application techniques.
The coatings in Categories 2 and 4 (see Table 2-2) are unsuitable because they are
too expensive and require curing at elevated temperatures. Category 5 (see Table 2-
2) coatings are not used because they are too sophisticated for use by this group.
2.2.3 Requirements for Conversion to Compliant Coatings
Converting from a solvent-borne system to a water-borne system can be expensive,
particularly if the drying time is increased. Water-borne coatings often require an
oven; whereas, the coated parts may currently be dried at ambient temperature. If the
conversion involves a new dipping application, then there is a cost associated with the
additional space requirement. Dip tanks, conveyor lines or racks, and a drainage area
must be provided.
On the other hand, if all of the necessary capital equipment is currently in use,
changeover may be very simple and inexpensive.
2.3 FABRICATED METAL PRODUCTS, EXCEPT MACHINERY AND
TRANSPORTATION EQUIPMENT (MAJOR SIC GROUP 34)
As shown in Table 2-4, this SIC group covers a wide variety of Industries ranging from
the manufacture of shipping containers, drums and pails, to the production of hedge
shears and trimmers. Operations manufacturing such items as bathroom fixtures,
swimming pool heaters, industrial gate valves, bombs rifles, and torsion bars are also
included in this group.
2.3.1 Coating Process
Clearly, the spectrum of products is too varied to suggest one scenario which can
describe the type of coating facility required to finish every one of these fabricated
2-6
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TABLE 2-4. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 34, SIC CODE 3411-3499
SIC Code 3411-3499: Fabricated Metal Products,
Except Machinery and Transportation Equipment
Shipping containers
Drums and pails
Hedge shears and trimmers
Hand and edge tools
Saw blades and handsaws
Fabricated iron and steel brackets
Fireplace equipment
ice chests or coolers
Ladder jacks
Trunk hardware
Bathroom fixtures
Lawn sprinklers
Room gas heaters
Swimming pool heaters
Radiators
Wood and coal burning stoves
Door and jamb assemblies
Liquid oxygen tanks
Sheet metal hoods
Bombs and parts
Mortar fin assemblies
Rifles
Industrial gate valves
Torsion bars
products. Therefore, a facility which will typify most of the industries in this SIC
category is described.
Figures 2-1 and 2-2 depict typical large-scale operations in SIC Group 34. Coatings
may be spray applied or dip coated (Figure 2-1), or powder coated (Figure 2-2).
Smaller facilities may combine the first and second topcoat into one booth, or apply
the primer and topcoat in one booth.
2-7
-------
STEAM CLEAN
OB SOLVENT
WIPE
PBETBEATIHON
OR3NCPHOS
(Figure 2-5.)
FORCE DRY
OR
BAKING OVEN
PACKAGING
AND
SHIPPING
PRIME BOOTH
OR DIP COATING
PRIMER
SECOND
TOPCOAT
SOOTH
2-8
Figure 2-1. Assembly, priming and topcoating line spray or dipcoating
primer and spray-applied coatings.
-------
STEAM CLEAN
OR SOLVENT
WIPE
PRETREATIRON
OR2NCPHOS
(Figure 2-5.)
WELD AND
ASSEMBLE
DRY-
OFF
OVEN
POWDER
COATING
PACKAGING
AND
SHIPPING
OVEN
BAKE
325-400' F
Figure 2-2. Assembly, and powder coating operation.
2-9
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2.3.1.1 Surface Preparation
Prior to welding and fabrication, the incoming steel is often degreased by one of the
following methods: vapor, steam or high pressure hot water detergent cleaning, or
abrasive blast cleaning. This cleaning is not related to the priming which will take
place later.
Rather, the degreasing is carried out so that the welds are not contaminated. Vapor
degreasing is usually carried out on light metal fabrications while the other methods
are used for the heavier or larger stock. After the component parts have been
fabricated (i.e., welding, machining, drilling, etc.), they will be degreased again and
treated before receiving the primer coat. Once again, a vapor degreaser is typical.
Abrasive blasting is common for heavy welds, particularly those which are too large to
be treated with a chemical system.
After the second degreasing, further surface preparation is often necessary. A three-
stage iron phosphate process, Figure 2-3(a), is typically employed for steel. For
excellent corrosion resistance, either a five-stage iron or zinc phosphate process,
Figure 2-3(b) may be used. If a step-by-step process is desired, a batch process in
which the parts are immersed successively into each of the tanks can be employed.
Alternatively, if the material handling considerations favor a continuous process, the
treatment tanks can be covered by a sheet metal tunnel, and the parts will move from
tank to tank via conveyor. Instead of being immersed in each tank, the parts pass
through a series of high or low pressure sprays. Each spray zone contains the next
solution in the sequence. The solutions are then recirculated for reuse.
Aluminum parts are cleaned and treated in a similar process (immersion or spray), but
the chemicals used are considerably different. Rgure 2-3 (c) is a schematic of a typical
aqueous conversion coating line. After treatment, the wet parts are immediately
transferred into a high temperature dry-off oven, the temperature of which is set above
the boiling point of water. If the parts are heavy and bulky, the oven temperature may
be as high as 400°F (204°C). The sole purpose of this oven is to evaporate off the
water as quickly as possible to prevent flash rusting.
2.3.1.2 Coating Application
The majority of facilities prime their products in a spray booth using manual spray
guns shown in Table 2-5.
Conventional air atomized spray, air-assisted airless and airless spray applications are
not suitable to meet the 65 percent minimum transfer efficiency necessary for control
application. Therefore, facilities which are regulated to such a minimum may not use
these spray devices. On the other hand, high volume, low pressure (HVLP),
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Degrease
Iron Phosphate
(120° F)
Water
Rinse
(Ambient)
Seal
Rinse
(Ambient)
Rgure 2-3(a). Three stage iron phosphating.
Degrease
(120° F)
Water
Rinse
(Ambient)
Iron or Zinc
Phosphate
(120° F)
Water
Rinse
(Ambient)
Seal
Rinse
(Ambient)
Figure 2-3(b). Rve stage iron phosphating.
Degrease Water Rinse Deoxidize Water . Chromateor Water Seal
(120° F) (Ambient) (120° F) Rinse Other Conversion Rinse Rinse
(Ambient) (120° F) (Ambient) (Ambient)
Figure 2-3(c). Seven stage conversion process for aluminum.
Figure 2-3. Typical iron and zinc phosphating processes.
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electrostatic, dip, flow, brush and roller applications are considered to meet the
minimum.
TABLE 2-5. MOST COMMON MANUAL SPRAY GUNS
Conventional air atomizing
Air-assisted airless
Airless
High volume, low pressure, (HVLP)
Electrostatic (low voltage)
air atomizing
air-assisted airless
airless
(currently, electrostatic HVLP is not available)
Electrostatic powder application
In facilities which coat large volumes of metal, automated coating application is
common. The application methods can vary depending on the size and shape of the
parts, the number of parts being coated per hour and whether or not there are long
runs of one part geometry. If the runs are short and part sizes vary significantly
between runs, manual spray application may be chosen. When conditions favor
automation, or when the primer does not need to have a high appearance finish, any
of the methods specified in Table 2-5 can be used for primer application.
Topcoats are applied using any of the hand-held spray guns listed in Table 2-5 and
automatic guns listed in Table 2-6. Automated spray guns can be in the fixed position,
or can be mounted on reciprocators or robots.
Topcoat application is fairly demanding, particularly when the final finish is expected to
have a high quality appearance. Under such circumstances dip and flow coating are
unlikely to be used, although electrodeposftion remains a viable option.
2.3.1.3 Spray Booths and Ovens
Spray booths can either be of the dry filter or water-wash type. Dry filter spray booths
are used when the volume of coating used per surface area of fitter medium is
relatively small.
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TABLE 2-6. MOST COMMON AUTOMATED COATING PROCESSES
Dip coating
Row coating
Electrodeposition
Autodeposition (primarily for priming steel)
Electrostatic turbo bells and discs
Automatic spray guns, using any of the delivery and atomization mechanisms
listed in Table 2-5, except that electrostatic guns will usually be of the high
voltage type.
If only a few gallons of coating are used on a daily basis, but the spray booth filter
area is large, then the loading of overspray on the filters will be small. This situation
would indicate the selection of a dry filter spray booth. On the other hand, if the
volume of coating used within the booth is large and the loading of overspray on the
filters is also large, then a water-wash spray booth might be the better choice.
The primary function of the spray booth is to capture the paniculate and to provide a
safe environment for the paint operator. Neither the dry or wet booths reduce VOC
emissions to the atmosphere. In the wet booths, a small amount of VOC may
dissolve in the water trough. But this amount is so slight, it may be of no real
consequence with regard to total VOC emissions to the atmosphere. A spray booth
which is improperly maintained, will allow paniculate to escape into the air. The most
common reasons for poor capture of paniculate are presented in Table 2-7.
TABLE 2-7. REASONS FOR POOR SPRAY BOOTH EFFICIENCY
Dry Filters
Water-Wash Booth
Missing filters
Excessive overspray on filters
Excessive air velocity
Insufficient filters in
filter bank
Excessive paint sludge floating
on surface of water in trough
Incorrect water level in trough
Excessive air velocity in trough
booth
Incorrect chemicals used;
insufficient level of chemicals
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Regardless of whether the filter medium is dry or wet, the spray booth may be open,
and of the "walk-in" type, or closed and of the "drive-in" type. From an air quality
perspective, the type of booth in the facility makes little difference, as long as the
booth is properly maintained and effectively traps the overspray, preventing it from
escaping into the outside atmosphere.
Facilities which fall into SIC Group 34, primarty use the walk-in type spray booths.
Smaller facilities may combine the first and second topcoat into one booth, or may
even perform the priming and topcoat applications in one booth. Ovens can be
electric or gas-fired convection, infrared, or combinations of convection and infrared.
2.3.2 Appropriate VOC-Compiiant Technology
2.3.2.1 Primers
Because of the variety of applications which fall into this SIC group, it is impossible to
predict what type of primer will be used. Some will require excellent corrosion
resistance, while for others a general purpose shopcoat will suffice. Also, some
facilities wil! prefer to use air/force dry primers while others will select baking finishes.
Information about specific primer characteristics is available in Section 5.4 Resin
Technologies.
• ' >
2.3.2.2 Topcoats
A wide variety of topcoats are in use in this industry. Where products, such as
shipping containers, are exposed outdoors, and need to withstand corrosive
environments, the more corrosion resistant compliant coatings will be selected.
Typically, the cross-linked coatings (either baking or two-component, air/force dried)
described in Section 5.4 will be the most likely choices.
For products such as drums and pails, which are also subjected to outdoor
environments, less stringent performance requirements may suffice. Ladder jacks,
door and jamb assemblies, and swimming pool heaters do not require sophisticated
finishes, so less expensive compliant coatings can be chosen. Products, such as
rifles, bombs and parts, and mortar fin assemblies are usually coated with military
specification coatings, for which compliant alternatives may already be available.
Numerous facilities of this SIC group use powder coatings. Apart from the extremely
low VOC emitted from powders (approximately 1-4 percent by weight), powders serve
as both the primer and topcoat in one application.
Products which require excellent chemical resistance (such as industrial gate valves,
the internal passages of industrial pumps, and other industrial equipment which comes
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into contact with chemicals and solvents), may be coated with compliant epoxies,
poiyurethanes, vinyls, phenolics and similar coatings.
2.3.3 Requirements to Convert to Compliant Coatings
No major equipment changes are required to bring an existing operation into
compliance if the technology to be implemented is similar to the one already in use.
However, major facility changes are required to implement technologies such as
powder coating, auto deposition or electrodeposition.
2.4 INDUSTRIAL AND COMMERCIAL MACHINERY AND COMPUTER
EQUIPMENT (MAJOR SIC GROUP 35)
As shown in Table 2-8, this industry sector includes companies which manufacture
machinery such as windmills for generating power, steam engines, combines, road
graders, machine tools, and many more.
Although the operations which fall into this industry sector are diverse and have
different finishing requirements, they can be distinguished from the Primary Metal
Industry operations (see Section 2.2) in that the component parts are primed prior to
assembly of the machines. After assembly, the fully assembled and tested machines
receive their finishing coats. In the Fabricated Metal Products operation (Section 2.3),
the component parts are often primed before assembly and topcoated after assembly.
Considerable similarities exist between the industries described in this and Section 2.3,
the major differences being in the size of the equipment which is coated.
It is not uncommon for the component parts to be pre-treated and primed in one
location, while the assembled and tested equipment is finish coated in another area.
For example, in some cases, these two operations (priming and finishing) take place in
different cities or States. Several large corporations manufacture, pretreat and prime
coat the component parts in one facility. These are then shipped to another facility
operated by the corporation where assembly, inspection, testing, and final finishing
take place.
2.4.1 Coating Process
Facility layout for operations covered by SIC Code 35 is similar to that of SIC Code 33,
Primary Metal Industries (Section 2.2).
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TABLE 2-8. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 35, SIC CODE 3511-3599
SIC Code 3511-3599 - Industrial and Commercial Machinery and Computer
Equipment
Windmills for generating power
Steam engines, except locomotives
Engine and engine parts ,
Marine engines
Agricultural implements and machinery
Blowers and cutters
Farm elevators
Greens mowing equipment
Combines (harvesters and threshers)
Spraying machines
Construction cranes
Road graders
Logging equipment
Tractors
Vibrators for concrete construction
Mining machinery and equipment
Elevators and moving stairways
Conveyors and conveying equipment
Machine tools
Power-driven hand tools
Textile machinery
Woodworking machinery
Printing trade machinery
Computer Equipment
2.4.7.7 Surface Preparation
Substrate preparation is similar to that used in SIC Group 34 (See Section 2.3.1). For
extra corrosion protection and to improve on the three- and five-stage processes
shown in Figures 2-3(a) and 2-3(b), a seven-stage process, such as that shown in
Figure 2-4, may be selected.
In the seven-stage process, the various components are brought together onto the
assembly line where the machine is assembled at well-defined stations. A few
components may be assembled at Station 1, then a few more components added at
Station 2, and so on until the entire machine is assembled.
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Degrease
(120° F)
(Ambient)
Water
Rinse
(Ambient)
Acid
Pickle
(120° F)
Water
Rinse
(Ambient)
Iron or Zinc
Phosepnate
(120°F)
Water
Rinse
(Ambient)
Seal
Rinse
Figure 2*4. Typical 7-stage iron and zinc pnospnating processes.
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After assembly, the machine, including ail hydraulic systems, will be tested to ensure
that it meets all of its performance requirements. Motorized machines such as
vehicles, combines, and others may require a test drive.
2.4.1.2 Coating Application
2.4.1.2.1 Priming
in most cases, the primer is applied by manual spray guns (see Table 2-5), but there
are facilities which employ automated systems (see Table 2-6). The coating may also
be applied by dip or flow coating, in which case it must be specially formulated for the
application.
Primers are often air/force dried in a low temperature oven (<194°F) (90°C), after
which the components are removed from the conveyor line, stacked into baskets or
placed on pallets, and then taken to storage. As discussed earlier, the primed parts
may then be shipped to another factory to await assembly and final finishing.
2.4.1.2.2 Rnishing
The machine must be cleaned in preparation for topcoat application to remove oil,
grease, and hydraulic fluids contaminating the surface. Cleaning is usually carried out
by steam or high pressure hot water detergent cleaning or solvent wiping.
At this point, the damaged areas or areas which show signs of corrosion (rust), will be
sanded back to bare metal either by hand or with pneumatic power tools. The
sanding dust is removed by solvent wiping or by means of sticky tack-rags. The
machine now enters the finishing spray booth where it receives one or two coats of
the topcoat. The topcoat is usually applied by one of the manual spray guns listed in
Table 2-5. Large facilities may employ robots or reciprocators to apply topcoats with
the use of manual operators for coating hidden and damaged or otherwise defective
areas.
The topcoat is then dried, by either taking the machine into a staging area where it is
flash dried in ambient air, or driving it into a low temperature oven where it is force
dried at temperatures below 194°F (90°C). If heat sensitive materials, such as plastics,
rubber hoses, hydraulic hoses, etc. have already been assembled into the machine,
then topcoats requiring force drying are unsuitable.
After the coating is force dried, the machine is driven out of the oven and left to cool
down. Subsequently, glass, decals, striping and other add-ons are applied to the
machine to prepare it for shipment. Damaged areas are repaired by applying the
coating by means of a small siphon gun, paint brush or aerosol can.
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2.4.1.3 Spray Booths and Ovens
The prime booth has three sides, with the back open. A typical booth may be 10-20 ft
wide, 6-8 ft deep, and 8 ft high. Depending on size, the prime booth may have the
water-wash or dry fitter design discussed in Section 2.3.1.3.
The topcoating spray booth differs from the prime booth in that it is much larger and
can be closed off. Depending on the size of the assembled machine, the finishing
booth may be 16 ft wide, 20 ft long and 12 ft high. Filtered air is often drawn into the
down draft spray booth to prevent excessive dust and overspray from settling on the
freshly painted surfaces. In northern climates where the weather is cold in winter and
hot in summer, the make-up air might be heated to a consistent temperature, above
ambient levels. Extraction of the VOC and participate may be through dry filter banks
or a water curtain.
2.4.2 Appropriate VOC-Compiiant Coatings
In Chapter 6, a detailed discussion is provided which will aid the end-user in selecting
the most appropriate VOC-compliant coating. This section is limited to more broad
generalizations, although several factors such as appearance and environmental
considerations and physical and chemical performance are discussed.
2.4.2.1 Priming
The choice of VOC-compliant primer depends on many factors including:
size and complexity of weids and subassemblies
drying speed
surface area throughput of components
degree of corrosion resistance required
compatibility with topcoat
type of application equipment to be used
Because of large component parts and welds, the primer is likely to be of the air/force
drying type, rather than a high temperature baking formulation. This, therefore, limits
the choice to the water-borne coatings, or high solids, solvent-borne coatings which
require no baking (for example, Category 1 or 3 coatings in Table 2-2).
Epoxy water reducible coatings (Category 1 in Table 2-2) are currently in use for
coating parts requiring salt-spray resistance. These epoxies require stringent surface
preparation. For lesser corrosion resistance requirements, the alkyds, modified
alkyds, and acrylics (Category 1 in Table 2-2) can be used. Once again, the surfaces
must be properly cleaned if a water-bome primer is to be used.
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Air dry solvent-borne coatings can also be used (Category 3 in Table 2-2). The high
solids alkyds, modified alkyds, 1,1,1-trichloroethane, and epoxy esters are all
commonly used as primers in this industry sector.
The high solids epoxy is also being used, primarily by military contractors.
Polyurethanes are not used as primers.
Autodeposited and electro-deposited coatings are also feasible; but, the throughput of
component parts must justify the space requirements, capital outlay, and operating
expenses required of these more sophisticated processes.
Powder coatings are generally not used as primers in these types of applications.
They are more commonly used in a single coat system to perform as both the primer
and topcoat.
2.4.2.2 Topcoats
The most likely topcoats are similar to the primers. Coatings with high baking
temperature requirements are unsuitable for large assembled machines consisting of
any heat sensitive materials.
High performance water-reducible alkyds or modified alkyds will do well, particularly if
the assembled machine is not expected to be exposed outdoors for lengthy periods.
If the resin is formulated for outdoor exposure, then this limitation does not apply.
The epoxy water-reducible coatings are not used as topcoats. They are primarily
formulated as primers, and are not intended for direct exposure to sunlight.
The polyurethane dispersions are a viable option, but few are on the market.
The high solids alkyds, modified alkyds, 1,1,1-trichloroethane alkyds and the catalyzed
pofyurethanes are the most likely choices. Of the polyurethanes, the polyester version
is appropriate where chemical resistance is more important than sunlight resistance.
The reverse is true for the acrylic version.
The moisture-cure camouflage polyurethane, in accordance with MIL-C-53039 (a
military specification coating), is currently being used in this industry sector on military
vehicles. Unfortunately, this technology is not generally available in a range of colors
and gloss levels.
In coating Category 5 (Table 2-2), the only likely technology is the cathodic
electrocoat. Radiation and vapor cure topcoats may be available. Powder coatings
are generally not used.
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2.4.3 Requirements for Conversion to Compliant Coatings
f
Once a preliminary coating selection is made, extensive laboratory and field testing
must be conducted to determine actual coating suitability. As always, selection of a
coating technology similar to the one currently in use requires the least expensive
process modifications. However, if a sophisticated electrocoat is chosen, a complete
facility renovation may be necessary.
2.5 ELECTRONICS AND OTHER ELECTRICAL EQUIPMENT EXCEPT
COMPUTER EQUIPMENT (MAJOR SIC GROUP 36)
As shown in Table 2-9, the industries represented in this group manufacture general
purpose electronic and electrical equipment such as power distribution transformers,
switch gear, switchboard apparatus, motors and generators, electric dehumidifiers,
household fans, electric conduits and fittings, etc.
The components coated are usually the steel and aluminum cabinets of electronic and
electrical equipment. The electronic components are installed either before or after the
cabinets are coated, depending on the complexity of the instrument and the
manufacturing process flow.
2.5.7 Coating Process
If the products are primed and coated in one continuous process then the coating
operations are similar to those for the Primary Metals Industry (Major SIC Group 33).
In this case the parts may be primed and topcoated either before or after assembly.
If the products are primed, assembled, and the assembled item is then topcoated, the
coating operations will be similar to those described for Industrial and Commercial
Machinery (Major SIC Group 35), Section 2.4.
2.5.1.1 Surface Preparation
The surface preparation processes carried out for electronics and other electrical
equipment are the same as those for Fabricated Metal Products and Industrial and
Commercial Machinery described in Sections 2.3.1 and 2.4.1, respectively.
2.5.1.2 Coating Application
The coating application options are similar to those described for Fabricated Metal
Products in Section 2.3.1. However, motors and generators must be handled
differently. In these cases, the armatures will often be dip coated in an insulation
varnish and then baked.
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TABLE 2-9. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 36, SIC CODE 3612-3699
SIC Code 3612-3699: Electronics and Other Electrical Equipment and
Components, Except Computer Equipment
Power distribution and specialty transformers
Switch gear and switchboard apparatus
Motors and generators
Relays and Industrial controls
Battery chargers
Barbecues, grills and braziers
Portable air purifiers
Electric dehumidifiers
Household fans
Electric wall heaters
Vacuum cleaners
Floor waxers and polishers
Electric wiring boxes
Electric conduits and fittings
Residential electric lighting fixtures
Commercial, industrial and institutional lighting fixtures
Household audio and video equipment
2.5.1.3 Spray Booths and Ovens
The spray booths used in these industries are the same as those described for
Fabricated Metal Products in Section 2.3.1.3.
2.5.2 Appropriate VOC-Compllant Technology
With the exception of special electrical insulating coatings needed for applications such
as motor and generator armatures, and coatings requiring special UV resistance, the
coating requirements of this industry group are the same as those discussed in
Sections 2.3.2 and 2.3.3.
2.5.3 Requirements to Convert to Compliant Coatings
The requirements to convert to compliant coatings for electronics and other electrical
equipment are the same as those discussed in Section 2.3.3 under Fabricated Metal
Products.
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2.6 TRANSPORTATION EQUIPMENT (MAJOR SIC GROUP 37)
This industry sector, presented in Table 2-10, applies to: fully assembled vehicles
such as ambulances, personnel carriers, campers for trucks, street sweepers, tractors,
etc., and vehicle accessories such as exhaust mufflers, trailer hitches, oil air and fuel
filters, and others. Bicycles and parts, wheel barrows, etc. are also included in this
industry sector. As far as coating facilities are concerned, the accessories and smaller
items such as bicycles and wheel barrows are coated much like items in Group 34
(Fabricated Metal Products) discussed in Section 2.3.
TABLE 2-10. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 37, SIC CODE 3711-3799
SIC Code 3711-3799: Transportation Equipment
Ambulances
Car bodies
Fire department vehicles
Motor homes
Personnel carriers
Tractors
Motor vehicle parts and accessories
Oil, air and fuel filters
Motor vehicle homs
Exhaust mufflers
Motor vehicle radiators
Patrol boats
Floating radar towers
Steam engines (locomotives)
Trolley buses
Bicycles and parts
Motor scooters and parts
Campers for mounting on trucks
Military tanks
Trailer hitches
Wheel barrows
The assembled vehicles are similar to some of the large machinery of SIC Group 35
(industrial and Commercial Machinery) discussed in Section 2.4. The manufacturing
and coating processes are not as sophisticated as those found in the automotive
assembly plants.
2-23
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2.6.1 Coating Process
The process operations in SIC Group 37 are similar to those for Groups 34 and 35,
described in Sections 2.3.2 and 2.4.2, respectively.
2.6.1.1 Surface Preparation
Steam cleaning or vapor degreasing is usually carried out prior to welding, as was the
case for SIC Group 34. Surface preparation of the vehicle component parts prior to
priming comprise three- or five-stage iron- or zinc-phosphate immersion or convey-
orized continuous processes, described in Section 2.3.1 and 2.4.1. Aqueous
chromate conversion coatings are usually specified for use on military vehicles.
After the components are primed and assembled into the completed vehicle, the entire
surface is steam cleaned with high pressure hot water to remove grease, oil and other
contaminants which were deposited during the assembly process. Refer to Section
2.4.1 for details.
2.6.1.2 Coating Application
The priming and topcoating processes are no different for this industry than for the
machinery industries described in Sections 2.3.1.2 and 2.4.1.2.
2.6.1.3 Spray Booths and Ovens
The spray booths used in this industry sector are similar to those described in
Sections 2.3.1.3 and 2.4.1.3. Where particular emphasis is placed on a blemish-free
final finish, such as on fire engines, bicycles, motor homes, ambulances, etc., a large
closed, drive-in water-wash down draft spray booth with filtered air make-up may be
more suitable. Although such booths are more sophisticated than those used by the
general metals industry, they are not as dust-free as the ones used in automotive
assembly plants. The paint operators and others working in the paint area are usually
not required to pass through an air knife before entering the coating facility.
2.6.2 Appropriate VOC-CompJiant Technology
for the component parts industries, the choice of compliant coatings is the same as
for SIC Category 34, discussed in Section 2.3.2. Similarly, the choice of coatings for
the assembled vehicles will be very similar to that for SIC Group 35, discussed in
Section 2.4.2.
The predominant compliant topcoat for vehicles is the two-component, catalyzed
polyurethane, of which the acryiic-isocyanate formulations are more popular than the
poiyester-isocyanate formulations. The acryiic-isocyanate coatings are preferred when
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sunlight resistance takes precedence over chemical resistance. The polyester-
isocyanate formulations are more suitable where chemical resistance takes
precedence. Thus, ambulances, street sweepers and motor homes will be coated with
the acrylic polyols, while fire engines, personnel carriers and patrol boats will receive
the polyester versions. Chapter 5 provides a detailed discussion on compliant
polyurethane technologies.
2.6.3 Requirements for Conversion to Compliant Coatings
As in any industry, major changes in production methods will require major plant
modifications. However, coating application processes currently in use can be«
adapted to new compliant coatings, thus minimizing conversion expenses. Major
facility changes will however be required to implement technologies such as powder
coatings, auto deposition, or electrodeposition.
2.7 MEASURING, ANALYZING AND CONTROLLING INSTRUMENTS (MAJOR
SIC GROUP 38)
This industry segment is comprised of computer interface equipment, laboratory
scales and instruments, laboratory furniture, photographic developing machines, etc.
and other analytical devices. Example of industries in this group are shown in
Table 2-11.
In this market, product finish is critical. Unlike many of the other Miscellaneous Metal
Parts market segments, the finishes used by SICs Group 38 are required to have a
very high quality appearance.
2.7.1 Coating Process
Figure 2-1 shows a coating operation typical of the Major Group 38 industries. To
maintain these standards, many companies, particularly in the computer and
instruments industries, do not apply the coatings in-house. Rather, parts are sent to
outside custom coaters Qob shops).
2.7.1.1 Surface Preparation
Most parts manufactured by this category are made of cold rolled steel sheet metal
and tubing, and aluminum sheet stock and extrusions. Mainframe computers may be
constructed out of hot rolled steel sections, but this is not common. Surface
preparation of the steel can be accomplished by various methods. The most common
are iron or zinc phosphating and vapor degreasing.
Iron phosphating is generally more popular than zinc phosphating for economic
reasons. Zinc phosphating is carried out only where severe corrosion of the substrate
is expected during the service life of the final product. Military specifications for field
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radios, and other communication instruments may require the application of zinc
phosphates; but, where service life is not expected to be severe, an iron phosphate
may suffice.
TABLE 2-11. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 38, SIC CODE 3812-3973
SIC Code 3812-3973: Measuring, Analyzing, and Controlling Instruments;
Photographic, Medical and Optical Goods; Watches and Clocks
Air traffic control radar systems
Distance measuring equipment
Gyroscopes
Hydrophones
Nautical instruments
Laboratory balances
Laboratory hotplates
Laboratory furniture
Clothes dryer controls
Thermostats
Computer interface equipment
Differential pressure instruments
Magnetic flow meters
Speedometers
Spark plug testing equipment
X-ray equipment
Photographic developing machines
Photographic enlargers
Appliance timers
A typical iron or zinc phosphating line comprises various stages. Three or five stage
processes are common. Figures 2-3(a), 2-3{b), and 2-4 illustrate these processes.
Seven-stage processes are not widely used, but may be necessary if the incoming
steel has already started to show signs of corrosion. In this case, an acid pickling
bath, followed by a water rinse would precede the iron or zinc phosphate tank. As
can be expected, the more stages in the system, the more thorough the surface
preparation, and the higher the cost.
2.7.7.2 Coating Application
When "Class A" finishes without blemishes are required, all surface imperfections must
be sanded off the part before coating. Casting lines, scratches, and swirl patterns can
2-26
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be removed from metal and plastic in this way. The surface preparation discussed
below describes the sanding process.
For "Class A" finishes, a primer is sprayed directly over the pretreated substrates.
Typically, a conventional air atomizing or a High Volume, Low Pressure (HVLP) spray
gun is used for this application. Next, a primer surface is applied to ensure a smooth
surface for topcoating. This surface is formulated to be applied by spray to yield a
reasonably high film build usually in excess of 2 mils. After the primer surfacer has
been allowed to dry, it is sanded with progressively finer abrasive paper, until all of the
substrate defects have been obliterated and a blemish-free finish has been attained. A
good primer surfacer is not too hard to sand, and does not cause the abrasive paper
to clog. If a smooth finish is desired, then one or two basecoats will be applied before
topcoating or texturing. After topcoating, the item is flash dried (not cured) either at
ambient temperature or, more frequently, in a low temperature oven, less than 194*F
(90°C).
Many of the finishes in this market sector are textured. To achieve this, the spray
operator applies the same coating as was used for the basecoat. However, instead of
finely atomizing the coating, the operator turns down the atomizing air pressure to
produce unatomized particles. The lower the air pressure, the coarser the texture
pattern.
The reader will find it interesting to look at the finish on computer housings and
typewriters manufactured by different companies. Some have a very fine, almost
imperceptible texture, while others have a coarse pattern. Control of the pattern is
accomplished primarily by the atomizing air at the spray gun.
For those parts which do not require a "Class A" finish, there is no need for either a
primer or primer surfacer. For these items, the basecoat is applied directly to the
pretreated metal. If necessary, another coat of the basecoat is applied, followed by
the texture coat.
2.7.1.3 Spray Booths and Ovens
The coatings are applied by a spray gun in a dry filter or water-wash spray booth.
These coatings are rarely applied by dipcoating.
Not all facilities cure their coatings in an oven; many allow the coatings to dry and
cure while standing in a staging area of the facility at room temperature. These wet
coatings can collect dust which will mar the surface. Moreover, the absence of heat
precludes the possibility that the coating will flow out to form a smoother finish.
However, heat curing, either by force drying at temperatures below 194°F (90°C), or
baking at temperatures in excess of 250T (121°C), allows most surface defects in the
2-27
-------
coating to flow out into a very smooth finish. Also, the coating achieves excellent
hardness and can be handled and packaged sooner.
2.7.2 Appropriate VOC-Compliant Coating Technology
Many companies which have already switched to compliant coatings are using the
following:
• Water-borne air/force dry primers, primer surfacers and topcoats for
plastic substrates. (Refer to Category 1 in Table 2-2). While some
companies also use these coatings on metal substrates, the performance
is not as good as other available compliant coatings.
• Water-borne bake primers and topcoats for metal substrates (refer to
Category 2 in Table 2-2).
• Two-component, catalyzed epoxy primers from either Category 1 or
Category 3 (Table 2-2); high solids, two-component polyurethane
topcoats from Category 3; usually, the polyester-urethane will be
specified.
In addition, Category 4 (see Table 2-2) coatings might also be used.
In Category 5 (Table 2-2), probably the most popular technology is the powder
coating, which is available in a variety of resin formulations, depending on end-use.
Clearly, powders will be used on metal and not plastic substrates, due to the high
temperatures at which the powders are cured (325-400°F [163-204°C]). The powder
coatings are applied as a one-coat system in which the powder acts as both the
primer and the topcoat. The other technologies listed in Category 5 are unsuitable for
this SIC group.
2.7.3 Requirements to Convert to Compliant Coatings
Most of the compliant coatings can be applied with the same equipment as is currently
being used. However, the existing electrostatic spray gun must be changed to
another type which is more compatible with water-borne coatings. The costs
associated with these changes should be relatively small.
2.8 MISCELLANEOUS MANUFACTURING (MAJOR SIC GROUP 39)
This industry sector includes a wide variety of products, including music stands,
rowing machines, treadmills, advertising displays, name plates, neon signs, costume
ornaments, artist frames, paint rollers, and more. Table 2-12 lists several industries of
this sector.
2-28
-------
TABLE 2-12. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 39, SIC CODE 3911-3999
SIC Code 3911-3999: Miscellaneous Manufacturing Industries
Electronic musical instruments
Music stands
Games, toys
Rsh and bait buckets
Exercising machines
Rowing machines
Treadmills
Penholders and parts
Artist frames
Easels
Stamp pads
Hand stamps (time, date, etc.)
Costume jewelry
Costume ornaments
Paint rollers
Street sweeping brooms
Advertising displays
Name plates
Neon signs
2.8.7 Coating Process
The facility layout and coating processes for this group are similar to those used by
SIC Group 34, described in Section 2.3.
2.8.1.1 Surface Preparation
Unlike the metal fabrications described in Section 2.3, the industries comprising SIC
Group 39 use light gage metal (steel, aluminum, stainless steel, copper, brass, etc.).
Because of the large quantities small parts (\.e., costume jewelry, stamp pads, pen
holders and parts), surface preparation may simply consist of thorough vapor
degreasing or perhaps a three stage cleaning/ treating iron phosphate process. Refer
to Section 2.3.1 for more detail.
2.8.1.2 Coating Application
Because of the consumer products manufactured in this industry sector, blemish-free
finishes are more prevalent than in many other industry sectors. Moreover, large
2-29
-------
volumes of components of similar geometry are coated facilitating the use of
automation. Therefore, the most likely application methods are:
conventional spray
high volume, low pressure (HVLP) (still an emerging technology)
electrostatic low and high voltage (for liquid coatings)
electrostatic (for powder)
electrodeposition
dipcoating
Coating application by airless or air-assisted airless spray are unsuitable due to high
fluid delivery which could excessively coat the part. In some States, such as
California, in which a minimum transfer efficiency is required, conventional air atomized
spray may be outlawed.
2.8.1.3 Spray Booths and Ovens
Unless special spray booths or capturing devices are designed to accommodate the
automated applicators, the common walk-in type spray booths are likely to be used.
These may be dry filter or water-wash, depending on the throughput of parts and the
surface area of the filter medium.
To save time in drying the large volumes of parts coated, it is likely that baked
coatings will be chosen over air-dried coatings. The ovens required can be
convection or infrared type, or combinations of the two. UV ovens are used in
combination with UV-curable coatings for a few applications.
2.8.2 Appropriate VOC-Comptiant Technology
i
Due to the high quality finish required, a baked finish or a powder coating is most
suitable. Other coatings which may be used include:
Water-borne (Category 2)
Alkyds and modified alkyds
Acrylics
Solvent-borne (Category 4)
Alkyds and modified alkyds
Acrylics
Polyesters (oil free)
2-30
-------
Sophisticated Technologies (Category 5)
Electrodeposfted
Radiation cure
Vapor cure
Powder
Air dry coatings are used to a lesser degree than baked or thermoset coatings. Clear
-coatings are used on items such as costume jewelry, costume ornaments, and
advertising displays.
Powder coatings are popular for many of the industries in this sector, specifically
exercising machines, treadmills, paint rollers, artist frames, and similar tubular or wire
products.
UV curable coatings known for their extremely low VOC contents, are popular for
items with relatively simply geometry (i.e., flat or uniformly round). Typical items
include lipstick containers and flat metal signs. Because of chemical and physical
hazards, industrial hygiene and safety are serious considerations when using UV
curable technologies.
2.8.3 Requirements for Conversion to Compliant Coatings
In this industry sector, very low VOC technologies, such as powder coatings or UV
curables are often chosen; but, such technologies require a significant capital
investment as well as major modifications to the coating facility. A long testing period
is required to identify the most suitable compliant coating, and to select the most
appropriate application equipment. Major facility changes will however be required to
implement technologies such as powder coatings, auto deposition or
electrodeposition.
2.9 RAILROAD TRANSPORTATION (MAJOR SIC GROUP 40)
Table 2-13 presents the industries represented by this group. They are comprised of
electric railroads, interurban railways, railroad terminals, and others. In general, they
do not manufacture machines. Manufacture is covered by one of the previously
described industry
2-31
-------
TABLE 2-13. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 40, SIC CODE 4011-4013
SIC CODE 4011-4013: Railroad Transportation
Establishments furnishing transportation by line-haul railroad, and switching and
terminal services. Therefore, this category is generally not concerned with the coating
of manufactured parts. Examples include: electric railroads, interurban railways, and
railroad terminals.
2.10 LOCAL AND SUBURBAN AND INTERURBAN HIGHWAY PASSENGER
TRANSPORTATION (MAJOR SIC GROUP 41)
The types of operations of this group (Major SIC Group 41, SIC Code 4111-4173) are
shown in Table 2-14. They include airport limousine services, city suburban bus line
operations, and streetcar operations. Painting within this group generally is of a
maintenance nature.
TABLE 2-14. EXAMPLE OF INDUSTRIES POTENTIALLY SUBJECT TO MMP
RULES IN MAJOR GROUP 41, SIC CODE 4111-4173
SIC Code 4111-4173: Local and Suburban Transit and Interurban Highway
Passenger Transportation
Establishments primarily engaged in furnishing road or rail passenger transportation
services. Therefore, this category is generally not concerned with the coating of
manufactured parts. Examples include:
• airport limousine service
• city suburban bus line operation
• streetcar operation
2-32
-------
CHAPTER 3
STATE VOC LIMITS
The majority of the States have elected to conform with the VOC limits for compliant
coatings which are stated in the CTG for Miscellaneous Metal Parts. (Control of
Volatile Organic Emissions from Existing Stationary Sources - Volume VI: Surface
Coating of Miscellaneous Metal Parts and Products; EPA-450-2-78-015, June 1978.}
However, other States have chosen to regulate the industry, or specific industry
segments more stringently. California regulations are determined not only by the
industry type, but also by the plant location. The regulations for those States which
have specified VOC limits for compliant miscellaneous metal parts coating, as well as
those in the CTG, are presented in Table 3-1. Regulations for four California Air
Pollution Control Districts are presented in Table 3-2. (Please note that these
regulations are current as of 4/90, but are subject to change.)
3-1
-------
THIS PAGE INTENTIONALLY LEFT BLANK
3-2
-------
TABLE 3-1. COMPLIANT COATING REGULATIONS BY STATE
State
Alabama
Arkansas
California
Colorado
Connecticut
Delaware
D.C.
Florida
Georgia
Illinois
Indiana
Kansas
Kentucky
Maryland
Massachusetts
Michigan
Missouri
New Hampshire
New Jersey
New York
North Carolina
Ohio
Oregon
Pennsylvania
South Carolina
Tennessee
Texas
Utah
Virginia
Washington
Wisconsin
Federal-CTG
Regulation
ID
335^6-11-11
Section 5.5
See Table 3-2
Regulation *7,DC
Sec 228-174-20(8)
24 Section 9
24 Section 9
17'2.650(1)(f)14
391 -3-02 (ii)
215.202
326IAC8-2-9
28-19-73
401KAR59:225
10.18.21.13
7.18(11}
R336.1621
10 CSR 10-5.330
1204.17
7:27-16.5
Part 228.8
Sec. 0934
3745-21-09
340-22-170
129.52
62.5 Std 5 Sec II F
1200-3-18-21
115.191 (a)
4.9.6 (g)
1200444
WAC 173-490-205
NR 422.15
EPA-450/2-78-015
Compliance Coatings: IbVI
Applicability
Limits dear
100 t/yr, 800 Ib/mon
none
Non-attainment areas
15 Ibs/day/plant
40 Ibs/day
40 Ibs/day
40 t/yr, A
25 t/yr
251/yr
B.C.
3 t/yr
20 t/yr
20 Ibs/day
25 t/yr
D
10 t/yr
100 t/yr
1 gal/hr, 5 gal/day
100 t/yr & all NYC
I5lb/day, 100 t/yr
100 t/yr, E
40 t/yr
500 Ibs/day, 50 t/yr
550 tbs/day. B
Urban: 25 t/yr. Rural: 100
t/yr
Non-attainment areas
10 t/yr
7 t/yr
106 kg/day
10 t/yr. B.E
44
44
44
44
44
44
44
4.3
4.3
4.3
4.3
4.3
4.3
10.342 (vi)
4.75
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
4.3
44
4.3
44
iJC/Qfftl CXMra flQj 1
Air Dried A
EjUfMltQ
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
6.674 (vi)
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.S
nlnus water as applied
Special
Coalings Other
0.4(11!)
0.4(iii)
6-20)
(ii)
0.4(111}
0.4(iil),3.0(h/)
44(v)
4.8(vil)
5-90)
0.40ii)
(viii)
6.20)
4.3(ix)
3.5 (x)
0.4(iM)
5.40)
0.40H,
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
5064**}
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
Applicability Limit Notes:
A: For non-attainment areas and non-attainment Impact areas.
B: Dependant on site location.
O» Dopftftoflnt on CGfistfuCDOfi uttte.
D: 2000 Ibs/month or 10 t/yr per operation or 30 t/yr per site.
E: Additional regulations tor non-attainment areas.
Special Coating Notes:
yj; HiQn pOf lUI'l I'l&ftCB BfCniteCtUfifti GOdullQS
(ii): Nail coatings
(ill): Powder coatings
(rv): First coat on ferrous substrate
(v): Drum interiors
(vi): Umit is expressed in Ib VOC/gal solids as applied
(vii): Truck repair
(viii): Zinc Primer 4.0 Ib VOC/gal
Steel drum interiors: 5.0 Ib VOC/gal
Steel Drum Exteriors: 3.5 Ib VOC/gal
Motor Vehicle interior above catalytic converter: 4.8 Ib VOC/gal
Architectural aluminum: 6.2 Ib VOC/gal
Ox): Pail and drum coatings, topcoat for locomotive and heavy duty trucks, hopper and tank car interiors
(x): Aircraft primer
3-3
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CHAPTER 4
TYPICAL PHYSICAL AND CHEMICAL PROPERTIES
OF VOC-COMPLIANT COATINGS
4.1 INTRODUCTION
This chapter provides the reader with details of the physical and chemical properties of
VOC-compliant coatings. Typically, coating selection is based on required coating
properties which are determined by the specific chemical make-up of the coating as
well as the resin system.
Specifications obtained from several manufacturers' product data sheets are provided
for the following types of coatings:
general purpose, water-borne primers, air/force dry;
general purpose, water-borne top-coats, air/force dry;
high performance, water-borne coatings, bake;
general purpose, solvent-borne coatings, air/force dry;
high performance, solvent-borne coatings, bake;
high performance coating, two-component epoxy and polyurethane; and
powder coatings.
4.2 GENERAL PURPOSE INDOOR AND OUTDOOR EXPOSURE, WATER-
BORNE PRIMERS, AIR/FORCE DRY
A large number of water-borne primers are available for general purpose applications.
They are formulated for use under strenuous conditions. Most of them are formulated
for spray application; some products are also applied by dipping. Typical applications
include: sheet metal cabinets, tool boxes, garden implements, inexpensive household
tools and furniture. Table 4-1 lists physical and chemical performance properties of
the air/ force dry alkyds and acrylic primers.
A few of the air/force dry primers exhibit better than usual corrosion and chemical and
solvent resistance when used in more demanding applications. Manufacturers' data
sheets do not provide much information regarding corrosion resistance.
4.3 GENERAL PURPOSE INDOOR AND OUTDOOR EXPOSURE, WATER-
BORNE TOPCOATS, AIR/FORCE DRY
The coatings in this category are used for general purpose applications where
superior physical and chemical performance is not required. These coatings can be
used for both interior and exterior exposure, although they will not perform as well as
some of the more sophisticated technologies, such as two component polyurethanes,
4-1
-------
electrodeposited coatings, or powder coatings. Typical applications include sheet
metal cabinets, tool boxes, garden implements, inexpensive household tools and
furniture. Table 4-2 lists physical and chemical properties of air/force dry alkyds and
acrylics topcoats. These coatings are formulated for spray and dip applications.
A few of the air/force dry products are formulated to exhibit better than usual chemical
and solvent resistance for use on computer components and laboratory equipment.
TABLE 4-1. TYPICAL PROPERTIES OF GENERAL PURPOSE INDOOR AND
OUTDOOR EXPOSURE WATER-BORNE PRIMERS, AIR/FORCE DRY
Volume solids (%)
Weight solids (%)
Viscosity
60° Gloss
VOC (g/l minus water)
Dry film (mils)
Spraying viscosity
Dipping viscosity
Dry to touch (minutes)
Force dry (minutes)
(temp. °F)
Taber abrasion, 1000 cps/1000
grams weight CS17 wheel
Pencil hardness
Salt spray 5% (hours)
Humidity 100%, 100°F, 100 hours
Water immersion
25-50
40-50
25-50 (Zahn No. 3)
3-15
150-340
1.0-1.5
20-35 (Zahn No. 3)
Some are formulated for
dipping
10-20
15-30
130-150 °F
Generally not reported
HB-F
100->200
Pass
Not reported
4-2
-------
TABLE 4.1 (Continued)
Chemical resistance
Solvent resistance
Stain resistance
Mandrel flexibility (in.)
Direct/reverse impact (in-lbs)
Package life (months)
Generally not reported
Generally not reported
Generally not reported
1/8-1/4
100/30
6-12
TABLE 4-2. TYPICAL PROPERTIES OF GENERAL PURPOSE INDOOR AND
OUTDOOR EXPOSURE WATER-BORNE TOPCOATS, AIR/FORCE DRY
Volume solids (%)
Weight solids (%)
Viscosity
60° gloss
VOC (g/l minus water)
Dry film (mils)
Spraying viscosity
Dipping viscosity
Dry to touch (minutes)
Force dry (minutes)
(temp.°F)
Taber abrasion 1000 cycles
1000 grams weight CS17 wheel
25-40
33-50
70-80 (Zahn #2)
Full range available
210-340
0.8-1.5
20-45 (Zahn #3)
30-50 (Zahn #2) (if available)
10-30
10-20
150-180
<100
4-3
-------
TABLE 4-2. (Continued)
Pencil Hardness
Salt spray 5% (hours)
Humidity 100%, 100°F, 100 hours
Water immersion
Chemical resistance
Solvent resistance
Stain resistance
Package life (months)
Other Properties
B-HB
>100
Pass
Pass
Fair to good
Fair
Pass
6-12
Low VOC
Low degree of
flammability
Corrosion resistance
Chemical and solvent
resistance.
4.4 HIGH PERFORMANCE WATER-BORNE COATINGS, BAKE >250°F
These coatings are used when high performance and low VOC are required. Though
they are formulated for spray application, some products can also be applied by
dipping. Typical applications include better quality office furniture, shelving, filing
cabinets, better quality tool boxes, patio furniture, appliances, and lawnmowers.
These coatings can be used for both interior and exterior exposure. However, for
exposure outdoors, the resin system must be selected for exterior durability and
sunlight resistance.
Compared to other coatings, these coatings have fair to poor flexibility and impact
resistance. Table 4-3 lists physical and chemical performance properties of water-
borne bake systems.
4-4
-------
TABLE 4-3. TYPICAL PROPERTIES OF GENERAL PURPOSE INDOOR AND
OUTDOOR EXPOSURE WATER-BORNE COATINGS, BAKE >250°F
Volume solids (%)
Weight solids (%)
Viscosity
60° gloss
VOC (g/1 minus water)
Dry film (mils)
Spraying viscosity
Dipping viscosity
Baking schedule (minutes)
(temp.'F)
Taber abrasion 1000 cycles
1000 mg weight CS17 wheel
Direct/reverse impact
resistance (m-lbs)
Mandrel flexibility (in.)
Pencil hardness
Salt spray 5% (hours)
Humidity 100%, 100°F, 100 hours
Water immersion
32-40
44-56
Varies among products
Full range, from flat to
gloss
137-250
0.8-1.5
22" Zahn #2, to 45" Zahn
#4
Depends on specific
product
15-30
275-350
<100
10-80
10-40
1/8 - 1/4
H-4H
72-350
>200
Excellent
4-5
-------
TABLE 4-3. (Continued)
Chemical resistance
Solvent resistance
Stain resistance
Package life (months)
Good
Good
Good
6-12
A few products are formulated to exhibit better than usual chemical and solvent
resistance when used on computer components and laboratory equipment.
4.5 GENERAL PURPOSE, SOLVENT-BORNE COATINGS, AIR/FORCE DRY
The coatings in this category are among the more commonly used solvent-borne
VOC-complying coatings. They are used for general purpose applications when high
performance is not a requirement.
These coatings can be used indoors and outdoors; however, for outdoor exposure,
sunlight resistance will not be as good as for some of the more sophisticated resin
systems, such as polyurethanes and acrylic electrocoats. Table 4-4 provides a
general list of physical and chemical performance properties, which are based on
manufacturer data sheets.
TABLE 4-4. TYPICAL PROPERTIES OF GENERAL PURPOSE INDOOR AND
OUTDOOR EXPOSURE SOLVENT-BORNE COATINGS, AIR/FORCE DRY
Volume solids (%)
Weight solids (%)
Viscosity
60° gloss
VOC (g/l minus water)
45-60
41-71
60-100", Ford #4
Full range, from flat to gloss
436-428
4-6
-------
TABLE 4-4. (Continued)
Dry film (mils)
Spraying viscosity (Zahn #2)
Dipping viscosity (Zahn #2)
Dry to touch (minutes)
Force dry (minutes)
(temp.°F)
Taber abrasion 100X3 cycles
1000 grams weight CS17 wheel
Direct/reverse impact
resistance (in-lbs)
Mandrel flexibility
Pencil hardness
Salt spray 5% (hours)
Humidity 100%, 100°F, 100 hours
Water immersion
Chemical resistance
Solvent resistance
Stain resistance
Package life (months)
1.2-2.0
Usually about 30-40", Zahn
#2
Generally not used for
dipping
20-120
20-30
140-180
Not reported
30
10
Not reported
Usually HB-H
Generally not reported
Not reported
Not reported
Not reported
Not reported
Not reported
12
4-7
-------
4.6 HIGH PERFORMANCE, SOLVENT-BORNE COATINGS, BAKE >250°F
This group of coatings is comprised of a range of resins and resin blends including
alkyds, modified alkyds, oil-free polyesters, and urea-, melamine- and phenol
formaldehydes. They are used in industries where hardness, abrasion resistance, and
color fastness are more important than chemical and solvent resistance. Not all of the
baking enamels perform well when exposed to sunlight. Due to high baking
temperatures, they are popular for end-uses such as metal office furniture, metal
cabinetry, electronic enclosures, shelving for supermarkets, and metal appliances.
These coatings can provide smooth or textured finishes, and are available in a
multitude of color coats and clear coats. Table 4-5 presents typical physical and
chemical properties of high performance solvent borne coatings.
TABLE 4-5. TYPICAL PROPERTIES OF HIGH PERFORMANCE SOLVENT
BORNE COATINGS
Solids (% volume); (% weight)
Viscosity
60° gloss
Color
VOC (g/l minus water)
Dry film (mils)
Spraying viscosity
Dipping viscosity (Zahn #2)
Dry to touch (minutes)
Force dry (minutes)
(temp.°F)
Taber abrasion 1000 cycles
1000 grams weight, CS17 wheel
50-72; 60-77
45" Zahn #2 - 55" Ford #4
Full range available
Full range available
<257 - 420
0.8-1.2
20" Zahn #2 - 55" Ford #4
No data was available. But
dipping enamels are
available.
N/A as these coatings must
heat cure.
5-20
400 - 325
Not reported
4-8
-------
TABLE 4-5. (Continued)
Direct/reverse impact
resistance (in-lbs)
Mandrel flexibility, in.
Pencil Hardness
Salt spray 5% (hours)
Humidity 100%, 100°F, 100 hours
Water Immersion
Chemical resistance
Solvent resistance
Stain resistance
Package life (months)
80/40
1/8 - 3/4
H-5H
>100
Up to 1000
Good - Excellent
Not generally reported
Generally not reported,
Probably good
Pass 100 double rubs MIBK
Generally good-excellent
12
Some baking enamels have been formulated to meet the chemical and solvent
resistance specifications of the computer industry.
4.7 HIGH PERFORMANCE COATINGS, TWO-COMPONENT, EPOXY AND
POLYURETHANE
Table 4-6 presents typical physical and chemical properties of high performance
indoor and outdoor high solids epoxy and polyurethane coatings.
epoxy Coatings - High solids epoxies are available at low VOC contents and are used
for a variety of end-use applications. Many high solids epoxies are formulated for
heavy duty corrosion resistance, such as for coating and protection of water tanks,
pipe lines, vessels used in chemical plants, bridges, off-shore drilling platforms, and
others.
4-9
-------
TABLE 4-6. TYPICAL PROPERTIES OF HIGH PERFORMANCE INDOOR AND
OUTDOOR EXPOSURE HIGH SOLIDS EPOXY AND POLYURETHANE
COATINGS
Volume solids (%)
Viscosity
60° gloss
VOC (g/l minus water)
Dry film (mils)
Spraying viscosity (Zahn #2)
Dipping viscosity (Zahn #2)
Dry to touch
Force dry (minutes)
(temp.°F)
55-60 for general purpose
> 70 for industrial
maintenance
Not reported
Wide range for epoxies
Full range for polyurethanes
340 - 383 for many epoxies
<250 for some epoxy
industrial maintenance
coatings
<340 for polyurethanes
1.5-2
> 5 for industrial
maintenance epoxies
Not reported for epoxies
25-23# Zahn #2 for
polyurethanes
N/A because they are
2-component systems
Up to 9 hour for industrial
maintenance epoxies
1-3 hours for general
purpose epoxies
25-60 mins for
polyurethanes
90 for epoxies and 30-45 for
polyurethanes
1208-140°
4-10
-------
TABLE 4-6, (Continued)
Taber abrasion 1000 cycles
1000 grams weight CS17 wheel
Direct/reverse impact
Salt spray 5% (hours)
Humidity 100%, 100°F, 100 hours
Water immersion
Chemical resistance
Acids
Alkalines
Solvent resistance
Stain resistance
Package Life (months)
Not reported for epoxies
<100 for polyurethanes
Not reported for epoxies
> 100 for general purpose
epoxies and polyurethanes
> 1000 for high
performance, high build
epoxies
100-168 for general purpose
>1000 for high performance
epoxies
\
Not reported for general
purpose coatings
Up to 1 year for high
performance epoxies
Good to excellent
Good to excellent
Good to excellent
Excellent (mainly for
polyurethanes)
12
4-11
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While they are more commonly classified as maintenance coatings and generally fall
into the architectural coatings category, they can also fall under the Miscellaneous
Metal Parts category if a structure is coated in a fabrication shop prior to being
shipped to the construction site.
The epoxy maintenance coatings are easily identified by their high film build. Typically,
a single coat can be applied to a film thickness of 5-8 mils. General purpose high
solids epoxies are also available in VOC compliant formulations. Their film thickness is
usually in the 1.5 - 2.5 mil range.
Epoxies are used primarily for adhesion on a wide range of substrates. They have
very good to excellent chemical and solvent resistance. They should not be used as
the final topcoat if resistance to sunlight exposure is a requirement
Polyurethanes - High solids polyurethanes are very popular for a wide range of end-
uses. Like the epoxies, they have good to excellent chemical and solvent resistance.
They also exhibit outstanding resistance to sunlight. Unlike epoxies, their adhesion to
substrates is generally poor. For this reason, epoxy primers are usually specified
under polyurethane topcoats.
4.8 POWDER COATINGS: EPOXY, POLYESTER, AND POLYESTER TGIC
Powder coatings are in use for a variety of purposes. Different resins are used
depending on the end use and whether or not the product is exposed to sunlight.
Table 4-7 lists physical and chemical performance properties of powder coatings.
Common uses of various powder coating types are shown below:
Epoxies - They are used primarily for computer parts, microwave ovens, office
equipment and furniture, hospital equipment, tool boxes, screening, wire racks, room
air conditioners, automotive under-the-hood components, appliance cavities, irrigation
equipment. Epoxies are not recommended for outdoor exposure.
4-12
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TABLE 4-7. TYPICAL PERFORMANCE PROPERTIES OF POWDER COATINGS
Specific gravity
60° gloss
Colors
Texture finishes
Dry film (mils)
Curing (minutes)
(temp.°F)
Direct/reverse impact
resistance (in-lbs)
Mandrel flexibility (in.)
Pencil hardness
Salt spray 5% (hours)
Humidity 100%, 100°F, 100 hours
Water immersion
Chemical resistance
Solvent resistance
Stain resistance
1.2-1.8
Full range
Full range
Available
1.0-2.5
Dependent on resin
5-20
450 - 325
160
Not reported
1/8-1/4
H-3H
> 1,000
> 1,000
Excellent, although not
reported
Dependent on resin
Dependent on resin
Dependent on resin
4-13
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-------
CHAPTER 5
RESIN SYSTEMS USED IN THE MISCELLANEOUS
METAL PARTS INDUSTRY
5.1 INTRODUCTION
In order to better understand coating technology used in the Miscellaneous Metal
Parts industry, an understanding of film curing mechanisms is necessary. Many
coating properties are determined by their curing process. For example, coatings
which cure by chemical reaction are stronger than those which cure by solvent
evaporation.
»
Coatings are typically composed of three parts: binders, solvents, and colorizers.
Binders are liquid or solid resins that form the backbone of the coating. Binders
determine the physical and chemical properties of the coatings such as: adhesion,
hardness, abrasion resistance, flexibility, chemical resistance, solvent resistance,
ultraviolet resistance, and water resistance. A single resin, or a combination of resins
can be used to provide maximum performance.
Solvents are used as a base for liquid coatings. Water, organic solvents, or a
combination of the two can be used, and volumes can be varied to control viscosity.
Coating color is altered by the addition of other chemicals, either liquid or solid, which
do not adversely affect coating performance.
This Chapter is divided into two parts. The first provides a description of basic curing
mechanisms. The second part provides information regarding properties of individual
coating types.
5.2 FILM FORMATION MECHANISMS
Table 5-1 lists a number of ways in which coatings can cure. Most coatings will fall
into only one of these classes, but a few may be hybrids of two or more.
5.2.1 Class I Film Formation by Solvent Evaporation
The coatings in this class are made of very viscous, high molecular weight resins and
large volumes of solvent. Large solvent volumes are required to dissolve the resins,
and to control viscosity. Once these coatings are exposed to air, the solvent begins
to evaporate, and the coating cures to a hard film. Depending on the solvents used,
baking may be necessary for complete drying.
5-1
-------
TABLE 5-1 FILM FORMATION MECHANISMS
Class
Discussion Location
Class I: Solvent Evaporation
Class II: Evaporation Followed by
Auto-Oxidation
Class ill: Cross-linking
Class HI a - At elevated
temperatures
Class III b - Two component
cross-linking at
ambient temperatures
Class III c - Moisture curing
^
Class III d - Radical polymerization
Class IV: Coalescence
Class IV a - Latex resins
Class IV b - Water-soluble resins
Section 5.2.1
Section 5.2.2
Section 5.2.3
Section 5.2.3.1
Section 5.2.3.2
Section 5.2.3.3
Section 5.2.3.4
Section 5.2.4
Section 5.2.4.1
Section 5.2.4.2
There is no chemical reaction involved in this curing process. As a result, any solvent
which is capable of dissolving the original resin will also dissolve the cured coating.
Because the Class I coatings can be diluted to a variety of viscosities, they are
suitable for a number of application methods; for example, spray, dip or brush
applications. Typical polymer resins are nitrocellulose, vinyl, and chlorinated rubber.
Due to the large volumes of solvent needed, Class I coatings are not usually available
in VOC-compliant formulations. For this reason, compliant coating alternatives have
been difficult to find for replacement of coatings such as nitrocellulose lacquers.
5-2
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5.2.2 Class II Film Formation by Evaporation followed by Auto-Oxidation
These coatings contain reactive, low molecular weight resins suspended in solvent.
As in Class I systems, the solvents evaporate, and deposit a film on the substrate.
However, the Class II coatings do not cure simply by evaporation. Once the resin film
is exposed to the oxygen in the air, a reaction begins. The polymer resins, which
contain carbon=carbon double bonds react with oxygen and cross-link to form long
chains of resin molecules. These long chains are very stable, and have increased
physical and chemical properties. Typical polymer resins include oil based coatings,
alkyds, epoxy esters, and urethane alkyds.
Generally, VOC-compliant coatings are available as high-solids alkyds or modified
aikyds, coatings diluted with 1,1,1-trichloroethane (an exempt solvent), or water-borne
coatings. In some cases, the high solids coatings may be hard to apply because of
their high viscosities.
5.2.3 Class III Film Formation by Cross-Linking
Coatings in this category undergo cross-linking similar to that exhibited by Class II
coatings, and form large stable molecules. The exception is that Class III coatings do
not require the presence of oxygen to react. Instead, the cross-linking agent is
supplied as part of the coating. These coatings can come as two separate packages,
or as a one package system where both the resin and the cross-linking agent are
present, but the reaction is inhibited. Reactions between the iow-moiecular weight
resin and the cross-linking agent can take place under a number of different
conditions, as discussed below.
5.2.3.7 Class Ilia Cross-linking at Elevated Temperatures
This class includes many of the baked coatings. These coatings can be supplied as
either one package, resin and cross-linking agent premtxed, or two package systems.
However, the resin and cross-linking agent will not completely react at ambient
conditions; baking is required. Typical cure temperatures range from 230°F (110°C) to
350°F (176°C). EPA regulations define bake coatings as those which cure at
temperatures above 194°F (90°C).
Baking aikyds, polyesters, and thermosetting acrylics which are used for appliances,
metal furniture and computer cabinets are often based on alkyd resins plus melamine
formaldehyde, alkyd resins plus urea formaldehyde, and acrylics.
Coatings are available which meet the 3.0 Ib VOC/gal (360 g/l) coating minus water
limit specified in most State regulations.
5-3
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5.2.3.2 Class Mb Cross-linking at Room Temperature (Two Component System)
Cross-linking coatings are often packaged in two containers. The first contains the
low molecular weight resin, and the majority of the solvent and colorizers; the second
contains the cross-linking agent that will react with the resin. The two components
must be mixed in the correct proportions immediately before application. As soon as
the resin and the cross-linking agent are mixed, the reaction begins and cross-linking
starts.
The most common coatings which fall into this category are polyurethanes and
epoxies. Both types are available in VOC-compliant formulations.
Since these coatings cure at ambient temperatures, they are classified as air/force dry
coatings, and must meet limits of 3.5 Ib VOC/gal (420 g/l) coating minus water in
most States, and 2.8 Ib VOC/gal (340 g/l) coating minus water in California.
5.2.3.3 Class flic Moisture Cure Coatings
Moisture cure coatings are similar to Class II coatings, as they both undergo
automatic reactions in air. Whereas Class II coatings react with oxygen, moisture cure
coatings react with atmospheric water in order to cross-link. They are supplied as one
package free from water. As soon as the coating comes into contact with water, it
begins to cure. Because of this, proper storage is necessary to keep the coating dry
and unreacted. Moisture cure coatings may not cure properly when used in very dry
areas.
A limited range of colors or gloss levels of these coatings are available in VOC-
compliant formulations. This technology is still relatively new, and only a few coating
manufacturers are able to produce pigmented coatings. The most commonly available
coating is a camouflage topcoat used by the military.
5.2.3.4 Class Hid Radical Polymerization
These coatings are supplied as low-molecular weight resins contained in a reactive
base. In the presence of ultraviolet or electron-beam radiation, the polymers react to
form large stable molecular chains. The most common resins used in this type of
coatings are acrylates, and acrylated oligomers. This technology produces coatings
with very low VOC levels. However, the radiation-based curing mechanism can cause
safety and financial problems.
While these technologies are popular for printing and paper coating, they are not yet
practical for most of the Miscellaneous Metal Parts industries.
53.4 Class N Film Formation by Coalescence
Class IV coatings contain resins, solvents, and co-solvents. Typically the solvent is
water, and the co-solvent is an organic compound. As the coating is applied, the
5-4
-------
water evaporates faster than the co-solvent. After all the water has evaporated, the
resin particles are suspended close together in the co-solvent. Capillary action causes
them to come even closer in a loose crystal structure. As all the co-solvent continues
to evaporate, a tight structure is formed and remains.
However, unlike the Class II and Class III coatings, no chemical change takes place
with Class IV coatings. Any solvent which is capable of dissolving the original resin
can also dissolve the cured coating. If the co-solvent evaporates before ail the water
has evaporated, the coating will not cure. This is possible in areas of high humidity
and additional equipment may be needed to supply dry air to prevent poor curing.
5.2.4.7 Class IVa Latex Resins
Latex coatings are usually high solids dispersions in a water base. The most common
resins in this category are polyvinyl alcohol and acrylic latexes. Polyvinyl alcohol
latexes are common in architectural applications. Because so little co-solvent is
necessary, water-borne latex coatings have some of the lowest VOC-contents of liquid
coatings.
5.2.4.2 Class IVb Water-Soluble Resins
These coatings contain relatively lower volume solids than the latexes. They are
composed of 20 percent solids and 80 percent water and co-solvent. Although they
do contain more co-solvent than similar latex coatings, these coatings are also
available in VOC-compliant formulations.
Alkyds and modified alkyds are the most popular resins used in water-soluble
coatings. Depending on the specific resin chosen, they can be formulated as air/force
dry coatings, or can cross-link at elevated temperatures. They are widely used in
Miscellaneous Metal Parts industries where medium to high quality finishes are
required.
5.3 RESIN TECHNOLOGIES
This section provides information about properties of individual coating types. It is
organized according to solvent, drying conditions and resin technology. Table 5-2
serves as an index to this section. In the table, the first column lists the coating type,
the second refers to the film formation class from Table 5-1, and the third column
indicates in which section of this manual additional information can be found.
Most technologies cure by only one film formation mechanism, but in a few cases,
different coatings of the same type may cure slightly differently. The double notations
in column 2 of Table 5-2 reflect this.
5-5
-------
TABLE 5-2. RESIN TECHNOLOGIES
Technology
Class
Location In
This Section
Water-borne, Air/Force Dry
Alkyd and Modified Alkyd
Acrylic Latex
Acrylic Epoxy Hybrid
Water-reducible Epoxy
Polyurethane Dispersion
Water-borne, Bake
Alkyd and Modified Alkyd
Solvent-borne, Air/Force Dry
Alkyd and Modified Alkyd
Epoxy Ester
Catalyzed Epoxy
Catalyzed Polyurethane
Solvent-borne, Bake
Alkyd and Modified Alkyd
Specialty Coatings
Silicons
Autophoretic
Electrodeposited
Radiation Cure
Vapor Injection Cure
Powder
Class IVb
Class IVa
Class Nib or
Class IVa
Class 1Mb
Class IV
Class Ilia
Class II
Class II
Class Ilib
Class Ilib or
Class life
Class Ilia
Class II or
Class Ilia
Class II or
Class Ilia
Class Ilia
Class Hid
Class Ilib
Class Ilia
5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
5.3.6
5.3.7
5.3.8
5.3.9
5.3.10
5.3.11
5.3.12
5.3.13
5.3.14
5.3.15
5.3.16
5.3.17
5-6
-------
5.3.1 Water-Reducible, Air/Force Dry, < 194°F (MTC) Alkyds and Modified Alkyds
These coatings belong to film Class IVb - water-reducible resins described in Section
5.2.4.2. They coalesce into hard films by the evaporation of water and co-solvent.
These types of coatings are extremely versatile. Since they can be thinned with water
to almost any viscosity, they are suitable for either dip or spray application. They have
generally good physical properties, and can be used for both interior and exterior
applications. However, they are not quite as durable as their baking counterparts, or
the more sophisticated two-component epoxies or polyurethanes. The low VOC
content of these alkyd coatings and their simple application often make them the idea!
choice when extreme physical or chemical durability are not required.
However, these coatings take longer to dry and cure than the water-borne latexes
discussed in Section 5.3.2. Also, in areas of high humidity, the water-borne alkyds
must be force dried to allow the water to evaporate before the co-solvent. Failure to
do so may result in poor film quality. A wide range of colors and gloss levels are
currently available. General properties of these coatings are delineated in Table 5-3.
5.3.2 Water-borne Air/Force Dry Aery lie Latex
This category includes polymers such as vinyl acrylics and styrene acrylics supplied as
latexes. These coatings cure by evaporation and coalescence. This film formation
mechanism is discussed in Section 5.2.4.1 (Class IVa coatings) of this Manual. Most
latexes are supplied as a blend of resins. The desired film characteristics can be built
into the final product by the types of polymers used.
Acrylic latexes are resistant to ultraviolet degradation; they retain their gloss and color
over long periods of exterior exposure. These coatings are generally used as primers
and topcoats where high performance is not required, such as on farm implements,
hand tools and general purpose metal fabrications.
Both temperature and humidity affect the drying time of latex paints. Some means of
forced drying is necessary in areas of high humidity or low temperature. Also, proper
surface preparation is critical. Surface contamination or improper paint mixing can
cause edge pull or cratering. Coating unprimed ferrous surfaces will cause flash
rusting.
Latex finishes are available in a wide range of colors at low VOC content. General
properties of these coatings are delineated in Table 5-4.
5-7
-------
TABLE 5-3. WATER-REDUCIBLE AIR/FORCE DRY ALKYD AND MODIFIED
ALKYDS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
Texture
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Cure Time
Number of Components
Solvent
Clean-up
General purpose primers and
topcoats
< 2.0 Ib/gal (240 g/l) of coating
minus water
Steel, aluminum, plastics
Better than for solvent-borne
alkyds
Good
Good
Does not meet standards
Primers poorer than solvent-
borne alkyds
Can be used for texture coats
Wide range available
Wide range available
Dip or conventional spray
More sensitive than solvent-
borne systems
Low<194°F(90°C)
Must be force dried in high
humidity areas
One
Primarily water with co-solvent
Water or solvent and water
5-8
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TABLE 5-3. (Continued)
Pot Life
Touch-up
Rammability
Toxicity
No limitations
Self touch-up possible
Low
Lower than solvent-borne alkyds
TABLE 5-4. WATER-BORNE, AIR/FORCE DRY ACRYLIC LATEXES
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance'
UV Resistance
Texture
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
< 2.0 Ib/gal (240 g/l) of coating
minus water
Most clean surfaces, topcoat
only on iron
Poor
Poor
Poor
Does not meet requirements
NA
NA
NA
Wide range available
Wide range available
Conventional spray
Must be oil and grease free
Low < 194°F (90°C)
5-9
-------
TABLE 5-4. (Continued)
Cure Time
Number of Components
Solvent
Clean-up
solvent
Pot Life
containers
Storage
Rammability
Toxicity
Must be force dried in high
humidity, low temperature
One
Primarily water with co-solvent
Water when wet, other times
Unlimited life for sealed
Protect from extreme
temperatures, and bacterial
growth
Low
NA
NA - Not available
5-10
-------
5.3.3. Water-borne, Air/Force Dry Acrylic Epoxy Hybrids
This is a less common two or three package system in which emulsified epoxies are
used to cross-link aqueous acrylics. It combines elements of Class Illb and Class IVa
film formation mechanisms. Like the Class IV coatings, these hybrids contain small
amounts of co-solvent which must evaporate before final curing can take place.
However, the final cure step involves a chemical change like those in Class III.
Common hybrid coatings are corrosion resistant and produce finishes with good
gloss, hardness, and abrasion resistance. The acrylic portion provides resistance to
ultraviolet radiation, and the epoxy portion improves adhesion and alkali resistance.
Pot-life can exceed 36 hours for some formulations.
As in most aqueous systems, substrates must be free of contaminants which could
impede adhesion. Drying can be hampered by high humidity or low temperature.
These coatings are corrosive and can damage application equipment. Storage is also
critical, as hybrids are subject to fungal and bacterial growth.
These coatings are used in applications where the hardness, flexibility and chemical
resistance of an epoxy is desired. Thus, they are ideal for general metal finishing
applications. General properties of these coatings are provided in Table 5-5.
TABLE 5-5. WATER-BORNE, AIR/FORCE DRY ACRYLIC EPOXY HYBRIDS
VOC
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
< 2.0 Ib/gal (240 g/l) of coating
minus water
Good
Good
Good
NA
NA
Good
NA
NA
5-11
-------
TABLE 5-5. (Continued)
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Cure Time
Number of Components
Solvent
Clean-up
Pot Life
Storage
Flammabilrty
High gloss available
Conventional spray
Must be free from oil and grease
< 194T (90°C)
Varies with humidity and
temperature
Two or three
Primarily water with co-solvent
Water
Up to 36 hours after mixing
Protect from extremes in
temperature and bacterial
growth
Low
NA - Not available
5.3.4 Water-borne, Air/Force Dry Epaxy
These coatings are supplied as a three package system. Components A and B cross
link as a Class (lib coating, and water is added to control viscosity (see Section 5.2.3).
Unlike Class IV coatings, these epoxies can cure rapidly even in high humidity.
These coatings are predominately sold as primers because of their poor resistance to
ultraviolet light. The most commonly available water-reducible epoxies are formulated
as primers to meet military specifications. They are used where good corrosion-
resistance is required. The performance of the epoxy is superior to that of alkyl
primers. The epoxy primers are commonly topcoated with polyurethanes.
5-12
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Primers are available in a smalt range of colors. Topcoats can be made in a wide
range of colors, but only in large quantities. General coating properties are described
in Table 5-6.
5.3.5 Water-borne, Air/Force Dry, Potyurethane Dispersions
These are relatively new coatings (see Section 5.2.1) which consist of polyurethane
lacquers dispersed in water. As the water evaporates, the film is formed.
These coatings can be used on non-metal as well as metal parts and, therefore, are
suitable as topcoat on assemblies containing plastic or rubber parts. The coatings
can be applied by conventional spray, and can achieve hardnesses from 3B to 2H.
Like most lacquers, the non-volatile content of these coatings is low (35-40%) and
multiple coats are often necessary. Unlike solvent-borne lacquers where the topcoat
partially dissolves the previous layers, care must be taken to ensure good intercoat
adhesion. General properties of these coatings are described in Table 5-7.
5.3.6 Water-borne, Bake Alkyd, Modified AJkyd and Acrylic
These coatings cure by cross-linking at elevated temperatures. Section 5.2.3.1
discusses the curing mechanism.
The resin, which is the backbone of these coatings, is equally soluble in water or
organic solvent. Therefore, these coatings are similar to the solvent-borne alkyds.
They show excellent performance properties, and meet industry standards for many
top of the line applications such as computers, business machines, lighting fixtures,
appliances and automobiles.
Uniform thin layers of coatings are difficult to achieve. Thus, alkyd and acrylic bake
coatings are not suitable for application of machined surfaces with tight dimensional
tolerances. However, they can be used in situations where parts are assembled prior
to coating. Table 5-8 provides general information on coating properties.
5.3.7 Solvent-borne, Air/Force Dry, Alkyd and Modified Alkyd
These coatings cure by evaporation of the diluent solvent followed by auto-oxidation
(see Section 5.2.2.) Historically, high VOC alkyd coatings have been the backbone of
the coating industry, and have been used for a number of applications. Now that new
low VOC resins are available, the popularity of alkyds is on the wane. However, low-
VOC alkyds and modified alkyds are becoming available. The most common of these
low VOC coatings are modified alkyds. Common alkyd modifiers for air dried coatings
include acrylics, vinyl toluene, styrenes, and siiicone.
5-13
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TABLE 5-6. WATER-BORNE, AIR/FORCE DRY EPOXIES
Availability
VOC
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
Gloss
Application Methods
Cure Temperature
Cure Time
Number of Components
Solvent
Clean-up
Primarily available as military
primers. Some topcoats are
also available.
<2.8 Ib/gal (340 g/i) of coating
minus water
NA
NA
NA
NA
NA
Poor
NA
Primers - small range,
Topcoats - large range
NA
Conventional spray
< 194°F (90°C)
Cure quickly even in high
humidity. Can recoat in less
than 30 min.
Three: base, curing agent, water
Water
May be difficult
5-14
-------
TABLE 5-6. (Continued)
Pot Life
Touch-up
Flammabiiity
Toxicity
Six to eight hours after mixing
NA
NA
NA
NA - Not available
TABLE 5-7. WATER-BORNE, AIR/FORCE DRY POLYURETHANE DISPERSIONS
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Colors
Application Methods
Cure Temperature
Cure Time
Number of Components
Solvent
Metals, textiles, leather, wood,
glass, paper, plastics
Excellent color and gloss
retention
Poor
Poor
Poor
Few now available
Conventional spray
Must be grease and oil free
Dependant on temperature and
humidity
One
Primarily water, small amounts of
organic solvent
5-15
-------
TABLES-?. (Continued)
Clean-up
Pot Life
Touch-up
Rammabiltty
Toxicity
Water
Unlimited for sealed container!
Self touch-up possible
NA
NA
NA - Not available
TABLE 5-8. WATER-BORNE, BAKE ALKYD, MODIFIED ALKYD AND ACRYLICS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
Primer and topcoat
<2.0 Ib/gal (240 g/l) of coatinj
minus water
Metals only
Good
Good
Good
Meets requirements for some
industries
Good
Good
Some coatings are suitable
Large range available
5-16
-------
TABLE 5-8. (Continued)
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Cure Time
Number of Components
Solvent
Clean-up
Pot Life
Storage
Touch-up
Flammability
ToxicHy
Large range of levels available
Conventional spray
Must be grease and oil free
>350°F (176°C)
Approximately 10 min.
One
Water
Water
No limitations
No specific requirements
Self touch-up may require
second bake
Low
Lower than solvent
Because they are among the least expensive compliant coatings, alkyd and modified
alkyds are still among the most popular systems for use as general purpose topcoats.
They can be used for either indoor or outdoor applications provided that extreme
chemical or physical properties are not required, and long term exposure to ultraviolet
radiation is not expected. Over exposure to ultraviolet light leads to chalking, and a
loss of cohesiveness. General properties of these coatings are provided in Table 5-9.
5.3.8 Sotvent-bome, Air/Force Dry Epaxy Esters
Like alkyd coatings, epoxy esters cure by evaporation followed by auto-oxidation. See
Section 5.2.2 for information on curing mechanism for these coatings.
5-17
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TABLE 5-9. SOLVENT-BORNE, AIR/FORCE DRY ALKYDS AND MODIFIED ALKYDS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Cure Time
Number of Components
Solvent
Primers and topcoats
<3.5 Ib/gal (420 g/l) of coating
minus water
Most - not recommended for
direct coating on Zinc
Limited
Limited
Limited
Does not meet requirements
Poor
Poor
Not generally used for texture
coatings
Large range, but not in small
quantities
High gloss available
Conventional and electrostatic
spray
Less sensitive than most
<194°F (90°C), some at ambient
Six to eight hours
One
Organic solvent
5-18
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TABLE 5-9. (Continued)
Pot Life
Storage
Touch-up
Flammability
Toxicity
Unlimited for sealed containers
No specific requirements
Self touch-up possible, but long
drying time is required between
coats
May be high, depends on
solvent
Higher than water-borne
Epoxy esters have better chemical resistance and hardness than alkyd coatings and
some have gained FDA approval for use on food and beverage containers. Some
epoxy esters, however, require metallic drying agents to effect total curing. These
curing agents, which are supplied as part of the one package system, lose their
potency with age. The coating will not cure properly if stored for an excessive period
of time. General properties of these coatings are provided in Table 5-10.
5.3.9 Sotvent-bome, AJr/Force Dry Catalyzed Epades
Catalyzed epoxy coatings are usually supplied as two discrete packages. When
mixed, they begin to react in a Class I lib mechanism (see in Section 5.2.3.2)
producing a tough, flexible cross-linked film.
Epoxy coatings and adhesives are well known for their excellent adhesion to
substrates. However, epoxies should not be applied at temperatures lower than GOT
(15°C). They are used where resistance to alkalis such as soaps, and some
chemicals and solvents, is desired. They are very resistant to fresh and salt water, so
they are used on off-shore drilling rigs, ships and bridges. They are also used to coat
tanks and pipelines for potable water.
Epoxies chalk in ultraviolet (UV) light. Although this makes them unsuitable for exterior
applications where appearance is important, the chalking takes place primarily on the
coating surface, and does not effect the chemical properties. Epoxy primers are
usually topcoated with more resistant coatings. Other properties may depend on the
specific coating formulation.
5-19
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TABLE 5-10. SOLVENT-BORNE, AIR/FORCE DRY EPOXY ESTERS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
UV Resistance
Texture
Colors
Application Methods
Substrate Cleanliness
Cure Temperature
Number of Components
Solvent
Pot Life
Storage
Touch-up
Primers, Topcoats for internal
use only
<2.0 Ib/gal (240 g/l) of coating
minus water
Most clean surfaces
Poor
Good
Good
Does not meet requirements
Poor
Not generally used for texturing
applications
Wide range available
Conventional spray
Less important than for water-
based coatings
<194°F(90°C)
One
Organic solvent
Depends on drying agent
No specific requirements
Self touch-up possible
5-20
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Polyfunctional amine epoxy coatings have excellent chemical resistance, but show less
flexibility than most other epoxies. They are used in applications where chemical
resistance is of primary importance. Unfortunately, these coatings can cause severe
dermatitis if the fumes come into contact with skin; therefore, strict safety procedures
are necessary. Additionally, their pot life tends to be short.
Polyamide epoxy coatings are harder and more flexible, do not cause dermatitis, and
have a longer pot-life. However, their chemical resistance is not as good as the
polyfunctional amine coatings.
Several coating vendors supply epoxies to meet military specifications. General
information on these coatings is provided in Table 5-11.
5.3.10 Soivent-bome, Air/Force Dry Catalyzed Poiyur&hane
Like many VOC-compliant coatings, catalyzed polyurethanes cure by cross linking.
Polyurethane coatings may be supplied as either one or two package systems. The
one package coatings react with atmospheric moisture (see Section 5.2.3.3.). The two
components of the two-package system react with each other as described in Section
5.2.3.2.
Two component polyurethanes must be mixed just prior to application. No equipment
is required to mix coatings manually, and this is ideal for small quantities of different
colors where much waste is expected. For large runs of a limited number of colors,
automation assures consistent mixing of components, and may justify the initial
expense. Once two-component coatings are mixed, they can be applied by
conventional spray equipment.
Two-component polyurethanes may be difficult to use. Substrate cleanliness is more
important than in most solvent-based systems and uniform film thickness may be
difficult to achieve. Also, these coatings are expensive. For health and safely
reasons, respirators must be worn by painters. General properties of two-component
polyurethanes are provided in Table 5-12.
One component polyurethanes have all the advantages of two-component
polyurethanes, and they do not require complicated mixing. However, the moisture
cured coatings do not have much field history and only a small range of colors is
currently available. Those coatings which are currently on the market are more
expensive than their two-component counterparts, and are available through only a
few suppliers. General properties of moisture cured polyurethanes are provided in
Table 5-13. Typical end uses of polyurethane are provided in Table 5-14.
5-21
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TABLE 5-11. SOLVENT-BORNE, AIR/FORCE DRY, CATALYZED EPOXIES
Availability
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Cure Time
Number of Components
Clean-up
Pot Life
Toxicity
Primers
Most clean surfaces
Poor
Good to excellent
Good to excellent
Does not meet requirements
Good
Poor
Wide range of colors available
only in large quantities
Wide range available
Spray
Less critical than for water-borne
coatings
<194°F(90°)
Air dry: 3 to 5 hours
Force dry: 30 minutes
Two
Equipment must be cleaned
before coating sets
4 to 6 hours after mixing
May cause dermatitis
5-22
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TABLE 5-12. SOLVENT-BORNE, AIR/FORCE DRY TWO-COMPONENT
CATALYZED POLYURETHANE COATINGS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Number of Components
Primer and topcoat Topcoat
must be applied over epoxy
primer.
To meet most regulations
Steel, Aluminum and Plastics
Excellent
Excellent
Excellent
Meets requirements for some
industries
Good
Excellent
Can be used to achieve textured
coatings
Wide range available in smalt
quantities
High gloss available only in large
amounts
Conventional spray
Must be clean, pretreated or
primed surface
<194°F(90°C)
Two
5-23
-------
TABLE 5-12. (Continued)
Clean-up
Pot Life
Touch-up
Toxiclty
Equipment must be cleaned
before coating sets
May be less than 4 hours,
particularly for high solids
Self touch-up possible
Respirators necessary for
painters
5-24
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TABLE 5-13. MOISTURE CURED POLYURETHANE COATING COATINGS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Cure Time
Primers and topcoats. Topcoats
must be applied over epoxy
primers.
<3.5 Ib/gal (420 g/l) of coating
minus water
Steel, aluminum and plastics
Excellent
Excellent
Excellent
Meets qualifications for some
industries
Good
Excellent
Can be used for textured
coatings
Limited number of colors
available
High gloss coatings may not be
available
Conventional spray
Must be clean, pretreated or
primed surface
<194T(90°C) ,
Depends on humidity. May dry
slowly in dry areas
5-25
-------
TABLE 5-13. (Continued)
Number of Components
Pot Life
Storage
Touch-up
Rammability
Toxlclty
One
Shelf life six months
Must be kept dry
Self touch-up possible
Low
Lower than for two-component
polyurethanes
5-26
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TABLE 5-14. TYPICAL POLYURETHANE APPLICATIONS
TRANSPORTATION
Aircraft skins
Missiles and other aerospace products
Over-the -road trucks
Busses
Railcars
Automotive refinishing
Chip-resistant primer surfacers (baked)
MILITARY
Ground support equipment such as tanks, personnel carriers, vehicles, etc. with
exposure to live chemical agents
ARCHITECTURAL AND MAINTENANCE
Structures and vessels in chemical plants
Offshore drilling rigs
Bridge maintenance
Topcoats for urethane roofs
Anti-graffiti coatings
Pipelines
PRODUCT FINISHING
Machine tools
Garden lawnmowers, snowblowers, tractors
Computer and Business machines
Medical and laboratory equipment
5-27
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5.3.11
Sotvent-bome, Bake Alkyd and Modified Alkyds
The primary difference between these coatings and air dry alkyds, described in
Section 5.3.7, is that the chemical and physical properties of these coatings develop
only after exposure to temperatures above 230T (110°C). Also, baked coatings have
better physical properties than air dried alkyds. .They cure by cross-linking at elevated
temperatures as described in Section 5.2.3.2. These coatings are easily adapted to
high speed lines and uniform film thicknesses of less than 1 mm can be achieved.
Modification to the basic alkyd resin can improve coating properties. In white baking
enamels, used for metal shelving and metal furniture, urea formaldehyde improves
color retention as well as resistance to soap and water. Alkyd coatings modified with
melamine formaldehyde have increased hardness, chemical resistance and shorter
drying time. Melamine formaldehyde coatings are used to coat refrigerators, washing
machines, light fixtures and automobile parts. General information concerning coating
properties is provided in Table 5-15.
5-28
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TABLE 5-15. SOLVENT-BORNE, BAKE ALKYD AND MODIFIED ALKYD COATINGS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Primers and topcoats
<2.3 Ib/gal (275 g/l) of coating
minus water
Metals
Good
Good
Good
Meets requirements for some
industries
Good
Good
Not usually used for textured
coatings
Wide range of colors available
High gloss coatings available
Spray. Some high viscosity
coatings may require special
equipment
Less critical than with water-
borne systems
>194°F (90°C)
5-29
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5.3.12
Silicons Coatings
Silicone coatings are specifically formulated to withstand high temperatures. They are
hybrids of glass and organic resins, and are extremely stable.
The properties of silicons coatings vary depending on specific resins used.
Unmodified silicones are known primarily for their heat resistance. They also retain
color and gloss when exposed outdoors, but require curing at temperatures in excess
of 500 °F (90°C). The silicone-organic copolymers can be cured at ambient
temperatures. Methyl silicones retain their hardness at high temperatures. They cure
quickly and have good low-temperature properties (e.g., they do not react poorly at
low temperatures). Phenyl silicones have better heat resistance and better shelf life,
but are less thermoplastic.
Most silicon coatings are available only in black and shades of gray. Colored coatings
have poorer heat resistance. Silicon resins are used on exhaust manifolds, mufflers,
heat stacks, furnaces, boilers, ovens, heat exchangers and aerospace components.
General properties of silicone coatings are provided in Table 5-16.
5.3.13
Autodeposited Coatings
Autodeposition is a process in which a resin, in the form of a latex, is chemically
deposited on steel. Final film curing results from auto-oxidation and cross-linking at
elevated temperatures. Auto-oxidation is described detail in Section 5.2.2 and cross-
linking at elevated temperatures is explained in Section 5.2.3.1.
Autodeposition is currently limited to coating steel substrates. The coating resins are
dispersed in a bath. Steel is immersed in the bath, and a chemical reaction takes
place between the resins and the surface of the steel. Coating thickness is
determined by the length of immersion time. After sufficient coating is deposited, the
item is removed from the bath and rinsed. It is then baked to ensure total curing.
Transfer efficiencies of 98 percent are possible with this method. Although no
phosphate pre-treatment is necessary, the steel must be free from grease for proper
adhesion.
Unlike electrodeposited coatings, described in Section 5.3.14, no electrical current is
necessary for deposition. Electrical shielding cannot take place, and the coating will
be deposited on all surfaces. Thus, holes, crevices and other inaccessible areas are
coated.
Autodeposited coatings act as both primers and topcoats in one application, but they
can also be topcoated with a wide range of coatings. They are very hard, and have
excellent corrosion resistance and flexibility. Uniform coating thicknesses from 0.6 to
1.0 mm are possible.
5-30
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TABLE 5-16. SILICON COATING COATINGS
Availability
VOC
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Colors
Gloss
Substrate Cleanliness
Cure Temperature
Number of Components
Solvent
Usually used as primer and
topcoat
<3.5 Ib/gal (420 g/l) of coating
minus water
Excellent
Excellent
Excellent
Meets requirements for some
- industries
Excellent
Excellent for modified siiicones
High temperature coatings
available in black and gray
High gloss available
Requires excellent surface
preparation
Varies with formulation
One
None
Autodeposited coatings, however, are only available from one supplier (Parker-
Amchem). They are produced in black and shades of gray, and are only suitable for
production shops with high steel throughput. Parts hanging is important for uniform
appearance. Additional information is provided in Table 5-17.
5-31
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TABLE 5-17. AUTODEPOSITED COATINGS
Availability
vex:
Possible Substrates
Exterior Durability
Chemical Resistance
t
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Number of Components
Clean-up
Pot Life
Rammability
Toxicity
Primer and topcoat. Only one
supplier.
< 1.6 to/gal (192 g/l) of coating
minus water
Steel
Excellent
Excellent
Excellent
Meets requirements for some
industries
Good
Excellent
Not applicable as texture coat ,
Black and gray only
High gloss not available
Large space requirements
Requires degreasing, but not
phosphatizing
200 to 356°F
One
May be difficult
Limited bath life. Must be
monitored.
Low
Non-toxic
5-32
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5.3.14 Electrofeposition
Electrodeposited coatings are resins dispersed in water which can accept an electrical
charge. The metal part to be coated is immersed in the coating bath and connected
to one terminal of a DC power supply. An electrode is connected to the other terminal
and immersed in the tank to complete the circuit. An electric current is passed
between the two terminals, and the coating plates onto the surface of the part.
The chemical reaction which plates resin onto the metal drives water out of the
coating. The coating then cures by coalescence (see Section 5.2.4.). When the part
is removed from the tank, excess coating is rinsed off and recycled. After several
rinsings, the part is baked to ensure total curing.
Surface preparation is critical to good film formation. For coating steel, an iron or zinc
phosphate treatment is necessary. The minimum preparation is the three stage
process described in Figure 2-3 (a), but more thorough cleaning is usually
recommended. Aluminum requires conversion pretreatment illustrated in Figure 2-3(c).
If the substrate is given a positive charge, it becomes the anode in the circuit.
Negatively charged paint particles are deposited. Anodic electrocoats can serve as
both primers and topcoats, although their corrosion resistance and color retention are
not as good as for cathodic deposition coatings.
If the parts are connected to the negative terminal, they become the cathode, and
positively charged paint particles are deposited. Because of their excellent chemical
and physical
properties, cathodic electrocoats are often used as both primers and topcoats.
Cathodic topcoats cannot be used to cover anodic primers.
The electrodeposition process requires fairly high voltages, but low currents. This
generates heat, and the coating solution must be cooled in heat exchangers.
Initially, the deposition process takes place rapidly, but as the coating film develops,
the process slows down resulting in very even film thicknesses.
As is the case in all processes in which an electric field influences the coating
deposition, sharp edges usually receive slightly thicker films than other areas. This is
advantageous because sharp edges are often the first to show signs of wear. On the
other hand, interior surfaces, which are shielded from the electric field often form
"Faraday cages" and cause poor coating distribution. If recesses in the parts are too
deep, then no coating will be deposited. Under such conditions, electrocoating may
not be feasible.
5-33
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Electrocoating is a sophisticated coating method, and several parameters must be
closely controlled by trained technical staff. These parameters include bath
temperature, pH, content and conductivity.
While the final coating can provide outstanding properties, the conversion process is
too capital intensive for most operations. The technology is more suitable for facilities
with large tonnage metal throughput. Both anodic and cathodic coatings are currently
in use by the Miscellaneous Metal Parts industry. Typical uses include: truckbeds,
engine blocks, water coolers, microwave ovens, dryer drums, compressors, furnace
parts, housings for the automotive industry, shelving, washers, air conditioners, file
cabinets, switch boxes, refrigerators, transmission housings, lighting fixtures, and farm
machinery.
Table 5-18 presents properties of electrodeposited coatings.
TABLE 5-18. ELECTRODEPOSITED COATINGS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Usually used as both primer and
topcoat
<2.3 Ib/gal (276 g/l) of coating
minus water
Steel, galvanized steel and
aluminum
Excellent
Excellent
Excellent
Meets requirements for some
industries
Excellent
Good
Not recommended for texture
coating
5-34
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TABLE 5-18. (Continued)
Colors
Gloss
Application Methods
Substrate Cleanliness
Cure Temperature
Cure Time
Number of Components
Solvent
Wide range available
High gloss available
Electrodeposition
Must be grease and oil free,
must be pretreated
350 to 400°F (177 to 232°C)
15 to 30 minutes
One
Water
5.3.15
Radiation Cured Coatings
Radiation cured coatings cross-link when they are exposed to either ultraviolet (UV)
light or electron beam (EB) radiation. These coatings cure without any solvent
evaporation, and so release very little VOC.
The energy for the UV cured coatings is generated from low pressure mercury arc
lamps located just a few inches from the coated surface. Electron beams can be
further from the substrate. These coatings are primarily applied to flat metal stock,
such as clear coatings applied to metal signs. Clear coatings are also applied as
over-varnishes to beverage cans, aerosol cans and lipstick containers. Radiation
cured coatings cannot be used on parts with complex shapes.
Safety is an important concern when using radiation cured coatings, which can cause
skin irritation and can be inhalation hazards. Proper training and suitable protective
equipment are a must for personnel dealing with these coatings.
Radiation cure coatings typically have VOC contents under 0.5 Ib/gal (60 g/l) of
coating less water. Additional information about these coatings is provided in
Table 5-19.
5-35
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TABLE 5-19. RADIATION CURED COATING COATINGS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
Salt Resistance
UV Resistance
Texture
Gloss
Application Methods
Cure Temperature
Number of Components
Storage
Touch-up
Toxicrty
Used as both primer and topcoat
<0.5 Ib/gal (60 g/l) of coating
minus water
Flat metal stock and cans
Excellent
Good
Good
Good
Excellent
Not suitable for texture coating
High gloss available
Curtain, roll, dip, spray, flow coat
EB or UV light to cure
One
No special requirements
Self touch-up possible
Potential contact and inhalation
hazard
5-36
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5.3. re
Vapor Injection Cure
The Vapor Injection Curing (VIC) process is patented and marketed by the Ashland
Chemical Company. This is a process for excellerating the curing rate of two-
component polyurethanes.
Two-component polyurethanes normally begin to cross-link as soon as they are
mixed, as described in Section 5.2.3.2. In the VIC process, a catalyst, dimethyl
ethanol, is introduced into the spray gun, and speeds up film curing. Most types of
spray guns can be used to apply VIC coatings, although modifications may be
necessary if components are sensitive to the catalyst. The amine is heated in a metal
container to produce vapor. The vapor is conducted through heated lines to the air
inlet of the spray gun.
The VIC coatings are an improvement over standard two-component polyurethanes.
Since the curing rate is determined by the catalyst added during application, the pot
life of the polyurethane can be increased. Before development of the catalyst, pot life
had to be short to reduce curing time. With use of the VIC system, polyurethanes with
longer pot life are feasible. According to Ashland, potltfe can be extended to 24 hours.
The VIC system is just a means of facilitating curing. Conventional polyurethane
coatings can be used for this application method. Two-component polyurethanes are
discussed in Section 5.3.10.
5.3.17
Powder Coatings
As the name implies, powder coatings are organic coatings supplied in dry powder
form. There are few solvents in powder coatings. Curing takes place by heating the
powder-covered part in an oven at temperatures between 325 and 400°F (163 and
204°C); the coating melts and coats the item. The fully cured coating is extremely
hard and abrasion resistant. Depending on the resin system, the coating may also be
resistant to chemicals, solvents, and ultraviolet light.
These coatings require specialized application methods. In electrostatic coating, parts
are suspended from a conveyor which is electrically grounded. A special spray gun,
designed to charge the powder to a very high electrostatic potential is used to
discharge the powder in the form of a cloud. The charged particles adhere loosely to
the grounded part. The coated part then enters an oven where the powder melts and
fuses. As soon as the part leaves the oven and cools to ambient temperature, it can
be handled, worked on and shipped.
Curing can take place in either convection or infrared ovens. In convection ovens,
curing time is determined by part size and shape. In infrared ovens, curing and
cooling time are not if concern, since only the part surfaces are heated.
5-37
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Start-up costs for powder coating application technology are high due to major
modifications required to existing application equipment. New ovens may be required,
particularly if infrared curing is used to minimize cooling time. The powder coatings
themselves are more expensive than conventional coatings. Since powder coatings
are cured at elevated temperatures, energy costs are also high. Since transfer
efficiencies are almost 100 percent, there is little waste associated with powder
coatings. Any excess of conventional coatings must be disposed of as hazardous
waste.
General properties of powder coatings are provided in Table 5-20. As with any
specialty coating, specific properties depend on the exact chemical structure of the
resins selected.
TABLE 5-20. POWDER COATINGS
Availability
VOC
Possible Substrates
Exterior Durability
Chemical Resistance
Solvent Resistance
High Performance
Salt Resistance
UV Resistance
Texture
Colors
Gloss
Application Methods
Used as both topcoat and primer
<5 percent by weight
Any non-heat sensitive substrate
i
Excellent
Excellent
Excellent
Meets requirements for some
industries
Good
Depends on resin system
Can be used for texture coats
Large range available
High gloss available
Electrostatic or Ruidized bed
5-38
-------
TABLE 5-20. (Continued)
Substrate Cleanliness
Cure Temperature
Cure Time
Number of Components
Solvent
Clean-up
Pot Life
Storage
Must be degreased
325 to 450T
Depends on resin system
One
None
Compressed air
No limitations
No special requirements
5-39
-------
BIBLIOGRAPHY
1. Ashland Chemicals, "High Performance, Fast Curing Coatings"
2. Bailey, Jane; "Winnebegos Sport a New Two-Tone Look", Industrial Finishing,
July 1989
3. Deft, Inc. Trade literature, Untitied
4. Dow Coming, "Silicons Based Maintenance Coatings Outlast Organic Paints
Two to One;" "Information about Silicone Resins"; and "Selection Guide to
Silicone Paint Resins"
5. Federation of Coating Societies, "Silicone Resins for Organic Coatings", January
1970
6. Glidden, "Electrocoating of Organic Finishes"
7. Gordon, John A., "Introduction to Coatings Technology • A Short Course",
8. Industrial Finishing, "Cathodic Electrocoating for Automotive Parts", June 1980
9. Jones, David K., "Vapor Curing Coatings for Plastics", SME Finishing, December
1988
10. Joseph, Ron, "Production Painting Training Program" "Environmental Paints and
Coating Training Program"
11. Loved, George; "Electrocoat Basics", Production Finishing, April 1990
12. Mobay Chemicals Corp., "Chemistry for Coatings" "Weatherability of Urethane
Coatings" "Aliphatic Urethane Coatings"
13. Parr, Lynne M. and William A. Finzel, "Water-borne Silicone Alkyds and
Acrylics", Journal of Water-borne Coatings, Vol. 3, No. 2, May 1979
14. Potter, T.A. and J.L Williams, Article, Journal of Coating Technology, Vol. 59,
No. 749, June 1987, p. 69
15. PPG "Electrodeposition Coatings"
16. Praenti, Ray, etal., "Industrial Finishing ", September 1987
5-40
-------
17. Prane, Joseph A., "Introduction to Polymers and Resins", Federation of Coating
Societies, July 1986
18. Saunders, J.H. and K.C. Frisch, "Polyurethane Chemistry and Technology -
Part II" John Wiley and Sons, NY; 1964
19. Steinhebel, Fred W., "Electrocoat Rinsing", Product Finishing, April 1990
20. Tool and Manufacturing Engineers' Handbook", Society of Manufacturing
Engineers, Dearborn, Ml
21. Wicks, Zeno W., "Rim Formation ", Federation of Coating Societies, June 1986
5-41
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-------
CHAPTER 6
HOW TO SELECT A COMPLIANT COATING
6.1 INTRODUCTION
Selecting a compliant coating is a complex process because many parameters
determine the suitability of coatings. First, it is necessary to identify all of the
properties required of the new coating. Tests on existing coatings in a laboratory may
be necessary to establish what properties are currently present.
Next, the appropriate compliant technologies must be identified. The guidance given
in this chapter and the information in Chapter 5 may be useful in this regard. Most of
the technologies presented in Chapter 5 will be eliminated from consideration for one
reason or another, but usually two or three remain.
Laboratory tests must be conducted to confirm the quality of the selected coating.
Despite the information available from manuals or vendor data sheets, there is no
substitute for laboratory testing of specific coating formulations. Production line tests
or trials must be conducted to confirm that the VOC-compliant technology will perform
in the manner expected. These tests will check the coating properties and will also
allow the facility's production engineers to plan for ultimate implementation.
Once the final selection of a new coating has been made, any necessary modifications
must be made to the current operation. The coating should then be purchased,
tested for compliance, and implemented.
Clearly, the most important step in the compliance project is to identify the most likely
compliant coating. To assist in this process, this chapter lists 29 common questions
which need to be addressed. These questions have been divided into the nine
categories listed in Table 6-1, and further discussed in the following sections.
6.2 APPEARANCE CONSIDERATIONS
Question 1. Will the coating be used solely for appearance purposes?
Answer: Many industries coat their products solely for appearance, and corrosion
resistance or other chemical or physical properties are of no consequence. Examples
include fabricated steel or aluminum which will be repainted by the customer, parts
which are hidden from public view, and parts which will be used indoors. If
appearance is the only factor affecting coating selection, then an inexpensive, fast air
drying coating technology is the most likely choice.
6-1
-------
Water-borne, air/force dry, < 194°F (90°C) - The most likely technologies to be
chosen are the aJkyd and modified alkyd water-reducible coatings and the acrylic
latexes.. These air dry fairly rapidly, and are relatively inexpensive.
it is unlikely that the hybrid acrylic latex/epoxy emulsion, the epoxy water-reducible, or
the polyurethane dispersion would be selected, because these are probably too
expensive for the intended application.
Water-borne, bake, >194°F (90°C) - It is unlikely that any of these technologies would
be chosen because they require curing at temperatures in excess of 250°F (121°C),
which adds to the cost.
Solvent-borne, air/force dry, < 194°F (90°C) - The alkyds and epoxy esters are likely
choices. Compliant alkyds are available in two types: high solids and low solids
diluted with 1,1,1-trichioroethane, an exempt solvent. The high solid alkyds take
longer to dry than those which are reduced with 1,1,1-trichloroethane.
TABLE 6-1. CRITERIA FOR SELECTING A COMPLIANT COATING
Coating Selection Considerations
Section
Appearance 6.2
Environmental 6.3
Physical and chemical performance 6.4
Part size, shape and material 6.5
Surface preparation 6.6
Production, application and facility requirements 6.7
Quality control 6.8
Cost 6.9
The remaining air dried solvent-borne coatings are all considerably more expensive
and probably would not be selected for appearance only.
6-2
-------
Solvent-borne, bake, > f 94T (SOPC) - It is unlikely that any of these technologies
would be chosen since they, too, would require temperatures in excess of 250T
(120°C) to cure.
Specialty Coatings - It is unlikely that any of the technologies in this category would
be chosen because they all require excellent surface preparation and fairly
sophisticated facilities.
Question 2. Must the coating produce a smooth finish?
Answer; Orange-peel is a coating defect which causes the finish to have, a fairly
coarse appearance, much like the peel of an orange. Almost any coating can be used
in applications where "orange-peel" can be tolerated. However, if a smooth surface is
necessary, there are fewer options for compliant coatings.
Water-Dome, air/force dry, <194°F (90°CJ - These coatings can be considered, but
the paint operator must go through a lengthy learning process before a smooth finish
can be guaranteed.
Water-borne, bake, >194°F (9O°C) - These coatings can be used, but a lengthy
operator learning curve is necessary to guarantee a smooth finish.
Solvent-borne, air/force dry, <194°F (90°Q) - The high solids alkyds are unlikely to
produce a smooth surface and, therefore, this technology would be unsuitable.
Alkyds reduced with 1,1,1-trichloroethane can be applied to produce smooth finishes,
but should only be considered as short-term solutions.
The remaining solvent-borne air dry coatings have high solids contents and thus are
unsuitable when a smooth finish is required, unless they can be force dried at elevated
temperatures. At elevated temperatures, the coating may melt and flow over the
substrate. Whether a smooth finish is possible can only be determined by testing of
the potential coating.
Sotvent-bome, bake, >194°F (9O°C) - Due to the high baking temperature, all of
these technologies are suitable.
Specialty Coatings — Silicone coatings can produce smooth finishes; however, they
are only used if high temperature resistance is required. The autodeposited and
electrodeposrted coatings also provide smooth finishes and some radiation cured and
vapor cured coatings may meet the requirements for a smooth finish. Many powder
coatings do not provide perfectly smooth finishes and testing is needed to determine
which will comply with the requirements.
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Question 3. Will the coated parts be texture-coated?
Answer: With liquid coatings, the textured finish is achieved by first applying a
smooth basecoat, and allowing it to flash dry or pre-bake. This is followed with a
textured finish of the same material.
In order to achieve the texture pattern, the coating is improperly atomized as it leaves
the spray gun, so that fine droplets of coating are deposited on the surface. Before
the droplets can flatten out and blend with the basecoat, the solvent flashes off or the
coated part enters a low temperature oven, so that the droplets set in position.
Water-tome, air/force dry, <194°F (90°C) - Some of these coatings are currently in
use on computers and business machines in which textured finishes of varying texture
patterns are required. The water-reducible epoxies are more commonly used as
primers; therefore, they are unlikely to be used as textured topcoats.
Polyurethane dispersion is a new technology and may satisfy texturing requirements.
It will be necessary to experiment with each formulation to determine which will work
best.
Water-borne, bake, >194°F (90°C) - The alkyds and modified alkyds, and the acrylics
are currently being used in the computer and business machines industries where
texture coatings are required.
Solvent-borne, air/force dry, <194°F (90°C) - The high solids alkyds are not usually
used for texturing because they dry slowly and the texture pattern tends to melt into
the basecoat. On the other hand, the low solid alkyds, reduced with 1,1,1-
trichioroethane, can be texture coated. The epoxy ester is generally used as a primer
and would not be texture coated. The two-component catalyzed epoxy is a high
solids coating and is usually not texture coated. The two-component polyester-
urethane is currently being used as the standard coating in the computer and
business machines industries, where texturing is the norm.
The acrylic-uretnane is often used as an exterior coating on transportation equipment,
such as trucks, buses and airplanes where a smooth rather than texture finish is
usually desired.
The moisture cure poiyurethane is a high solids material and is currently sold primarily
as a camouflage coating in the military equipment industry. While it is possible that
this technology can be texture coated, it is unlikely at the present time that this coating
will be chosen for such purposes. Once again, the coating vendor should be
consulted.
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Solvent-borne, bake, >194°F (9CTC) - All the coating technologies in this category
can be applied to achieve a textured finish; however, it may be necessary to first pre-
bake the smooth basecoat before applying the texture coat.
Specialty Coalings - The only technology in this category which is likely to produce a
texture finish is a powder coating. Unlike any of the liquid coating technologies, the
texture can be built into the coating formulation.
6.3 ENVIRONMENTAL CONSIDERATIONS
Question 4. Must the coating have an extremely low VOC content?
Answer: A few technologies are available which emit VOC less than 1 Ib/gal (120 g/l)
coating less water.
Water-borne, air/force dry, <194°F (9p°C) - Alkyd and acrylic water-borne coatings
have very low VOC contents. In particular, the acrylic latexes use small quantities of
co-solvents, and therefore their VOC contents are often below 1 Ib/gal (120 g/l)
coating less water.
Polyurethane dispersions are also available at low VOC content.
The water-reducible epoxy coatings, typically used as primers, have VOC contents of
approximately 2.0 - 2.8 Ibs/gal (240-340 g/l) coating less water.
The hybrid acrylic latex/epoxy emulsion normally has a VOC content below 2.8 Ibs/gal
(340 g/l) coating less water.
Water-borne, bake, >194°F (9O°C) - None of the bake coatings currently available
have extremely low VOC contents.
Solvent-borne, air/force dry, <194°F (9(TC) - Extremely low VOC content coatings
are rare in this category.
Solvent-borne, bake, >194°F (90°C) - None of these coatings commonly have
extremely low VOC contents, although they are available to meet the regulatory limits.
Specialty Coatings - Depending on the formulation, the autodeposited coatings may
be available with very low VOCs, below 2 ibs/gal (240 g/l) coating less water.
Radiation cured coatings are available with extremely low VOC contents, but these
coatings need to be specifically formulated for metal end-use application.
The vapor cured coating is generally available only to meet the VOC limits.
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Powder coatings have VOC contents of approximately 3 percent by weight of the
powder. This translates into an equivalent VOC of less than 0.3 Ibs/gal (36 g/l)
coating less water.
Question 5. Are there environmental or economic reasons for limiting substrate
pro-treatment?
s
Answer Some companies are reluctant to introduce aqueous pretreatment systems,
particularly if they are located in areas where the water must be pretreated before it is
discharged to sanitary sewer. Vapor degreasing may not be desirable if potential
solvent emissions are high and if permitting the solvent degreaser is difficult. Similarly,
abrasive blasting operations may not be attractive due to permitting difficulties.
The alternative to the use of sophisticated surface pretreatment systems is to select
coatings which are reasonably tolerant of surface contaminants, such as light layers of
oil, grease, or scale.
Water-borne, air/force dry, <194°F (90°C) - The water-borne coatings are generally
sensitive to oil and grease; however, acrylic latexes may be used where a low level of
corrosion performance is adequate. Most of the other water-borne coatings are not
generally used on untreated metal.
Water-borne, bake, >194°F (MFC) - The alkyds and acrylics may be suitable for
untreated metal, but extensive testing will be needed to confirm selection. The
polyurethanes are not suitable for application to unprepared surfaces.
Sofvent-bome, air/force dry, <194°F (90°C) - The epoxy esters, high solids alkyds,
and low solid alkyds reduced with 1,1,1 trichioroethane may provide adequate
adhesion to untreated metal. Unmodified epoxies and polyurethanes should not be
applied to untreated metal.
Solvent-borne, bake, >19fT (90PC) - These coatings do not adhere well to untreated
steel.
Specialty Coalings - None of the specialty coatings should be applied to untreated
steel.
6.4 PHYSICAL AND CHEMICAL PERFORMANCE CONSIDERATIONS
Question 6. Will the coated product be exposed outdoors for lengthy periods?
Answer: Some resin systems are particularly sensitive to UV, or sunlight exposure.
While they may be used as primers, they are rarely suitable as topcoats where
appearance is a consideration.
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Alkyds, in general have reasonably good exterior durability. Acrylics have particularly
good exterior durability, and polyurethanes lead the field in their ability to withstand
many years of exterior exposure without showing any sign of degradation, loss of
color or ioss of gloss. Epoxies may be used as primers, but are notorious for their
extremely poor exterior durability, as can be seen by their readiness to chalk.
Water-tome, air/force dry, <194°F (90°C) - Alkyds and acrylics are used for genera!
purpose exterior topcoats, while the polyurethanes are selected where superior
exterior durability is required. The epoxy systems are generally used as primers but
not as topcoats.
Water-borne, bate, > 194°F (90°C) - Exterior durability will be better for the water
borne, bake coatings than for the air dry water-borne systems. The acrylics and
polyurethanes are the most likely candidates for consideration.
Solent-borne, air/force dry, <194°F (90°C) - The same rationale applied to the
water-borne coatings also applies to this category. While the alkyds and modified
alkyds perform quite well, the polyurethanes are the preferred choice. The high solids
epoxy is not suitable as an exterior topcoat.
Sotvent-bome, bake, >194°F (9O°C) - All of these coatings have reasonably good
exterior durability.
Specialty Coatings — The silicons coatings are specifically used for high heat
resistance, but they are also known to have excellent exterior durability.
The autodeposited coatings are usually used as primers, or as one-coat systems in
situations where appearance is not critical. Some show good exterior durability.
Electrodeposited coatings, particularly the cathodic type, are well known for their ability
to withstand sunlight for many years. For this reason, many well known companies
such as Deere & Co. use cathodic electrocoats for finishing garden tractors and
mowers.
The vapor cure and radiation cure coatings have fairly good exterior durability;
however, few cases have been cited in which either coating has been used for the
finishing of exterior machinery.
With regard to powder coatings, it is necessary to select a resin which can resist
sunlight for lengthy periods. In this category, polyurethanes and polyester powders
are normally chosen for long-term exterior durability.
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Question 7. Must the coating have superior hardness and abrasion resistance?
Answer: All of the alkyds and alkyd modified coatings have good hardness. These
formulations usually have pencil hardnesses on the order of HB, while acrylics are
slightly harder with a pencil hardness of approximately H to 2H. Epoxies and
polyurethanes lead the field with pencil hardnesses exceeding 3H.
Water-borne, air/force dry, < 194T (9O°C) and Water-borne, bake, > 194°F (9O°C) -
The air/force dried alkyds and modified alkyds generally have lower hardnesses than
the baked alkyds and modified alkyds, because during cross-linking at elevated
temperatures, the alkyds tend to acquire a considerably harder finish.
Sotvent-bome, air/force dry, <194°F (90°C) - The high solids alkyds tend to retain
their softness for several days and eventually achieve a hardness of HB. All of the
other coatings in that category can be used where superior hardness is required.
Solvent-tome, bake, >194°F (90*0) - As is the case with water-bome baked
coatings, cross-linking at elevated temperatures results in extremely hard finishes.
Specialty Coatings — All of the specialty coatings have excellent hardness.
Question 8. Does the coated part need to meet any specified corrosion
resistance requirements?
Answer: Usually this question implies that a minimum salt spray resistance is
required. Typically, primers, must withstand less than 400 hours, whereas, topcoats
may be exposed for more than 1000 hours.
Generally, the single-component air dry systems have lower corrosion resistance than
two-component systems, or coatings which bake at elevated temperatures.
Water-bome, air/force dry, <194°F (9O°C) — The epoxy water-reducible coatings of
this category are commonly used as primers because they meet most requirements
for salt spray resistance. Other water-bome coatings are used as primers, but they
generally do not possess long-term corrosion resistance.
Water-bome, bate, > 194V (90°C) - These coatings, when used as primers, will
exhibit higher corrosion resistance than air dried water-bome coatings. Polyurethanes
are generally not used as primers; however, as topcoats applied over epoxies, they
will provide excellent corrosion resistance.
Sotvent-bome, air/force dry, <194T (9O°C) - The epoxy esters and the catalyzed
epoxies are generally used where long-term corrosion performance is necessary. The
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alkyds and modified alkyds are also available as corrosion resistant primers, but they
do not perform as well as the epoxies.
Polyurethanes are generally not used as primers, but as topcoats applied over
epoxies, they will provide excellent corrosion resistance.
Solvent-borne, bake, > 194°F (90°C) - All of these coatings, when used as primers,
will provide good corrosion resistance. When used as both primer and topcoat, they
also provide excellent corrosion resistance.
Specialty Coatings — The silicons coatings are not recommended for corrosion
resistance because their primary purpose is heat resistance.
The autodeposited coatings, when properly applied, provide excellent corrosion
resistance, and the electrodeposited coatings, both anodic and cathodic, exhibit
superior salt spray resistance.
With regard to radiation cured and vapor cured coatings, the coating supplier must be
consulted as to the type of corrosion resistance that can be expected.
Powder coatings are usually applied as a one-coat, primer/topcoat system. Provided
that the appropriate resin is selected, corrosion resistance up to and exceeding 1000
hours of salt spray can be achieved.
Question 9. Is the coated part expected to meet any specific chemical
resistance requirements, such as to acids, alkalis, detergents, or strong salts?
Answer: As a general rule, the alkyds, modified alkyds and other non-cross-linking
coatings do not provide the same superior chemical resistance as the highly cross-
linked technologies. Therefore, epoxies and polyurethane out-perform the alkyds,
acrylics, epoxy esters, and other similar resin systems.
Water-borne, air/force dry, <194°F (90°C) - Only the polyurethane dispersion
provides relatively good chemical resistance of the coatings in this category.
Water-borne, bake, >194°F (90°C) - All of the coatings in this category exhibit
relatively good chemical resistance.
Sotvent-bome, air/force dry, <194°F (90°C) - The alkyds and epoxy esters may not
provide the chemical resistance required. However, the epoxy catalyzed system is
excellent for chemical resistance as are the polyurethanes within this category.
Sotvent-bome, bake, >194°F, (90°C) - All of the solvent-borne, bake technologies
may well satisfy the chemical resistance, but testing is necessary to confirm this.
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Specialty Coalings - Due to the variety of coatings in this category, the coating
supplier must be consulted for information about specific coatings. Some of the
powder coating resins may satisfy the chemical resistance requirements, but testing is
required to confirm this.
Question 10. Must the coating be resistant to specific solvents?
Answer: Consultations with the paint vendor or laboratory testing are necessary to
confirm the solvent resistance of any particular coating.
Question 11. Will the coating need to withstand any sustained elevated
temperature?
Answer: Most organic coatings can withstand temperatures up to approximately
250°F (120°C). However, as the temperature increases, the resin will start to degrade
and lose its chemical and physical properties; colors may also change.
Epoxies and poiyurethanes, if properly formulated, can withstand temperatures up to
approximately 250T (121°C), but they tend to harden and embrittle if elevated
temperatures are sustained for too long.
Coatings which contain silicone tend to exhibit higher temperature resistance than any
other coatings, often withstanding sustained temperatures in excess of 1000T (540°C).
However, even with silicone resin formulations, the coating manufacturer must be
consulted regarding which resin system should be used.
Question 12. Can out-gassing be tolerated?
Answer Out-gassing relates primarily to the evaporation of plasticizers from the resin.
These vapors may cause corrosion of other parts or may be deposited as a fog on
critical surfaces. In the aerospace industry where work is performed in ultra-clean
rooms, or where surfaces such as mirrors must retain extreme clarity, out-gassing can
be a major problem.
Of all the coating technologies available, the specially formulated polyurethane best
resists out gassing. Therefore air dried solvent-borne coatings are most likely to be
selected for testing purposes.
Question 13. Will the coated part be immersed in water for lengthy periods?
Answer: This question is particularly relevant to items exposed outdoors in wet
environments for several weeks or months. These requirements are common for
outdoor equipment used in States in which rainfall is relatively high and internal
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coatings are applied to the water tanks, and other products used in wet environments.
Most water-borne technologies are not suitable for these applications.
Solvent-borne, air/force dry, <194?F (90°C) - Perhaps the best performing coatings
are two-component catalyzed epoxies, modified epoxies, coal tar epoxies and
phenolics. A wide range of two-component epoxies is available specifically for this
type of application. They are generally sold by coating vendors which specialize in
industrial "maintenance" coatings. Several products are listed in Chapter 7.
Sotvent-bome, bake, > 194V (90°C) - Some of the phenolic alkyds in this category
might perform adequately for this purpose.
Specialty Coatings - Some powder coatings may also satisfy the water-immersion
requirements.
Question 14. If a VOC-compliant primer and topcoat are to be used, what
guidelines are there for intercoat compatibility and adhesion?
Answer: When selecting VOC-compliant primer and topcoat system, it is imperative
that thorough laboratory tests be carried out to confirm intercoat compatibility and
adhesion. The following guidelines are useful when selecting the VOC-compliant
systems:
Primers based on water-borne coatings can be topcoated with solvent-based
formulations, provided that all of the water has evaporated from the primer film.
Solvent-borne primers are usually compatible with water-borne topcoats.
Primers based on air/force dry technologies may not always be compatible with
topcoats which are cured at elevated temperatures, because the primer may be
unable to withstand the elevated oven temperatures necessary for topcoat curing.
Testing is required. However, primers which are baked, will generally be compatible
with topcoats which are air/force dried.
Alkyd and alkyd modified topcoats are usually compatible with alkyd and alkyd
modified primers.
Acrylic topcoats are usually compatible with alkyd or acrylic primers.
Topcoats which are based on two-component technologies such as epoxies and
polyurethanes are generally not compatible with single-component alkyd and acrylic
primers. Topcoats which are based on two-component technologies are generally
compatible with primers which are based on two-component systems, specifically
epoxy primers.
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Silicones (unmodified), which are used for high heat resistance, are usually not applied
over any other primer.
Autodeposited coatings are almost exclusively applied as primers and will accept
topcoats of most types.
Electrodeposrted coatings are used as primers and one-coat systems in which they
function as both the primer and topcoat. When electrodeposrted coatings are used as
primers, they can be topcoated with most other non-specialty coatings.
Electrocoatings can generally not be applied as topcoats over primers from other
technologies.
Radiation cured and vapor cured coatings should only be applied after consultation
with the coating vendors.
Powder coatings can function as primers, topcoats, or single-coat systems in which
they serve as both the primer and topcoat When a powder coating is used as a
topcoat, it will generally not be compatible with any of the liquid coating technologies.
Once again, the facility will need to check with the powder coating vendor before
trying to incorporate powder coating as a topcoat applied over a liquid coating primer.
6.5 PART SIZE, SHAPE, AND MATERIAL CONSIDERATIONS
Question 15. Does the part to be coated include heat-sensitive materials, such
as plastics, rubber or upholstery as well as metal?
Answer: Many assembled parts or machines are comprised of a number of different
materials. For instance, assembled fire trucks, tractors, harvesters and other vehicles
contain plastic and rubber hoses, hydraulic tubing, and other heat-sensitive materials.
Therefore, the field is limited to air/force dried coatings.
Since Silicones are intended specifically for high temperature applications, they are
unlikely to be used.
Autodeposited coatings will adhere only to steel and not to any of the other substrates.
Electrodeposited coatings will adhere to steel and aluminum and some other metals,
but will not adhere to non-metal substrates.
Both radiation cure and vapor cure coatings, cure at elevated temperatures and
therefore may not be suitable.
Powder coatings, which are applied at temperatures between 325-400"F (163-204'C)
are not suitable for use on heat-sensitive composite assemblies.
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Question 16. Is the part geometry very simple, or does it consist of many
critical recesses or difficult to reach areas, such as "Faraday Cages"?
Answer: "Faraday Cages" are areas such as deep recesses and the interior surfaces
of acute angles which are shielded from electric fields. Electrostatic paint or powder
coating application and electrodeposition are all applied under the influence of an
electric current and are affected by such shielding. Coating deposition is hindered in
these areas. Therefore, if the part consists of critical recesses and "Faraday Cages"
which must be coated, this usually precludes the use of technologies which are
applied by an electrostatic field.
Electrodeposited and powder coatings will almost invariably be excluded from the
choice of compliant coating technologies.
Autodeposited coatings can be used in most situations where a complex shaped part
includes "Faraday Cages".
If the geometry is very complex, and requires a substantial paint operator flexibility,
then solvent-based high solids coatings may be difficult to apply, particularly if uniform
thin film thicknesses is important.
Question 17. Does the part lend itself to a dipcoating application?
Answer: For a large-scale continuous operation coating items with simple shapes,
dipcoating is often the preferred method of application. The following guidelines will
be helpful for selecting a compliant dipcoating.
Dipcoating must be of a single-component formulation, because two-component
coatings such as epoxies and polyurethanes will cure while in the dip tank. Water-
borne coatings have an advantage over the solvent-bomes in that evaporation of the
water and co-solvents results in considerably lower VOC emissions than with solvent-
borne coatings. High viscosity coatings are usually unsuitable for dipcoating
applications because rapid drainage is hindered. The solvent-borne alkyds and epoxy
esters could be considered, provided that they have sufficiently low viscosity to allow
for dipping.
The moisture-cured polyurethanes, although single-component, will be unsuitable
because they rapidly absorb moisture from the air and will cure prematurely in the
diptank.
The autodeposited and electrodeposited coatings are formulated specifically for
dipcoating applications.
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The silicone, radiation cure, and vapor cure coatings are not suitable for this type of
application.
Question 18. Can the metal or alloy tolerate temperatures up to 350-400°F (176
to 204°C), without undergoing metallurgical changes?
Answer: Some alloys, particularly high strength alloys, can be detrimentally affected if
exposed to these high temperatures for sustained periods. Under such conditions,
they have been known to lose some of their strength and tensile properties. Due to
elevated curing temperatures, these metals should not be coated with electrodeposited
or powder coatings. However, many other baked coatings may be suitable because of
tower baking temperatures. If a coating is to be applied and cured at an elevated
temperature, then it is strongly advised that the alloys be subjected to laboratory
testing to confirm the applicability of the candidate VOC-compliant coating.
6.6 SURFACE PREPARATION
Question 19. Are existing pretreatment methods sufficient?
Answer: Most of the coatings used by the Miscellaneous Metals Parts industry
require clean surfaces in order to provide good adhesion. The following guidelines will
assist in determining whether the surface pretreatment needs to be upgraded.
Water-borne Coatings - Water-borne coatings are more sensitive to surface
contamination than solvent-borne coatings. For general purpose applications, steel
surfaces should undergo a minimum of a three-stage iron phosphate coating, while for
more sophisticated applications, a five-stage iron phosphate or five-stage zinc
phosphate is preferable.. Abrasive blasting is acceptable provided that the blast-
cleaned surface is primed within a few hours. Aluminum surfaces must be conversion
coated before application of water-borne coatings.
High Performance Coatings - Degreasing is the minimum surface preparation
necessary for baked coatings and two-component coatings such as catalyzed epoxies
and potyurethanes. However, further pretreatment, either with an iron or zinc
phosphate, hi the case of steel, or a conversion coating in the case of aluminum is
preferable. Abrasive blasting is acceptable provided that the blast-cleaned surface is
primed within a few hours.
Sillcones must be applied over well pretreated surfaces particularly if they are intended
for very high temperature applications.
Electrodeposited coatings are extremely sensitive to surface preparation and only the
very best cleaning and pretreatment system should be considered; iron and zinc
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phosphating of steel, or conversion coatings of aluminum must be followed by at least
one or two rinses with deionized water.
Radiation and vapor cured coatings must be applied to clean surfaces.
Powder coatings should be handled the same way as other high performance
coatings, and require a stringent precleantng.
6.7 PRODUCTION, APPLICATION, AND FACILITY REQUIREMENTS
Question 20. Must the coating dry or cure in a short time?
Answer: If short drying and curing times are required, then many compliant coating
technologies may not be suitable.
Water-borne, air/force dry, <194°F ffXTC) - Most of the coatings can air dry to touch
within approximately 15 minutes, but for all of the technologies drying is enhanced if
movement of air and elevated temperatures in excess of 150"F (66*C) are present.
The acrylic latexes are probably the fastest drying and the most suitable if the parts
need to be off-loaded from the conveyor and packaged within half an hour.
The epoxy water-reducible coatings, if used as primers, will flash dry within 15
minutes, but should not be topcoated for up to 90 minutes.
Water-oome, bake, > 194°F (9O°C) - All of these coatings will need to be oven baked
for a minimum of 10 minutes, depending on oven temperatures, and an adequate
cooling off period will be required before the parts can be off-loaded from the
conveyor. It should be noted that even after the parts have cooled down, some of
these coatings may still remain too soft for packaging for up to 2 hours.
Soivent-bome, air/force dry, <194°F (90°C) - The high solids alkyds do not dry or
cure in a short time. On the other hand, the low solids alkyds which are formulated
with 1,1,1-trichloroethane may satisfy the short drying time requirement. Al! of the
other solvent-borne, air dry coatings will need an hour or more before they can be
off-loaded from the conveyor and packaged.
Solvent-borne, bake, > 194°F (90°C) - These coatings may need up to 2 hours to
completely harden.
Specialty Coatings — The silicone coatings may air dry, but often need high
temperatures in order to cure. This is particularly relevant where very high heat
resistance is necessary.
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The autodeposited coatings might satisfy a 15-minute drying time requirement,
provided that the oven temperature is high enough to evaporate the water in the
coating.
The electrodeposited coatings may require a lengthy hardening period, while radiation
cured coatings cure within seconds.
Vapor cured coatings cure in much the same time as solvent-borne, air dried coatings.
High solids coatings take longer to dry than those formulated with 1,1,1-
trichloroethane.
Powder coatings usually cure within a period of 10 to 20 minutes at temperatures
between 325-400'F (163-204*C); however an adequate cool off time is required
before the parts can be off-loaded and packaged. The cool off time is dependent on
the size and mass of the coated parts.
Question 21. Does the facility have sufficient space to expand?
Answer: In general, the machinery for the application of VOC-compIiant coatings
does not require any more space than that used for non-compliant coatings based on
the same technologies. In other words, if a company is currently using coating similar
to the compliant coating under consideration, very few equipment changes may be
necessary in order to accommodate the new technology. However, if a company is
upgrading from a liquid coating technology to autodeposited, electrodeposited or
powder coatings, then it is very likely that more space will be required.
Radiation cure coatings will require special ovens; these may be more space-
consuming than what the company already has in place.
Vapor cure coatings will also require a special booth in which the curing agent is
applied to the basecoat. This booth may require additional space.
Question 22. Is the facility sufficiently sophisticated to cope wtth two-
component coatings?
Answer: Many production facilities specifically do not want to use two-component
coatings because they do not have the quality control procedures or staffing to
monitor the correct mixing of the two components.
One solution to this is to purchase plural component mixing equipment which mixes
the two components of the coating immediately prior to the application. These
systems however, are not foolproof, and require good maintenance in order to ensure
proper functioning.
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Question 23. If the facility can accommodate two-component coatings, is there
a requirement for the two components to be premixed prior to the application?
Answer: Facility needs dictate whether a two-component coating should be premixed
by the operator prior to coating applications, or if a plural component equipment can
be used to mix the coating immediately before it enters the spray gun.
For instance, if a small quantity of each of a number of coatings are used in one day,
then the operator should measure out the two components immediately prior to paint
application to avoid waste of pre-mixed coatings. On the other hand, if a large volume
of only a few coatings are used on a daily basis, then it is more cost-effective to
purchase plural component spray equipment.
With low VOC, two-component coatings, the pot-life is often too short to be practical
for a desired coating method. Therefore a facility must pay special attention to
selecting two-component coatings which have relatively long pot-lives. Epoxy water-
reducible primers have acceptable pot-lives of between 6 to 8 hours. Some water-
borne, bake pofyurethane coatings have sufficient pot-lives for most applications.
VOC-compliant high solids, two-component catalyzed solvent-borne air dried epoxies
and potyurethanes have considerably shorter pot-lives and, therefore, the facility will
need to check with various coating vendors to find a two-component mix with an
appropriate pot-1'rfe.
Pot-life is not an issue for the other technologies.
Question 24. Will large or small quantities be required of each color per run?
Answer The choice of VOC-compliant coating technology is strongly dependent on
how many colors will be used, and whether the quantities per run will be large or
small. If small amounts of coatings are required for each run, it is necessary to select
coatings, which are available in small quantities.
Water-borne, air/force dry, < 194°F (90°C) - The alkyd, acrylic, and hybrid
technologies can be purchased in small quantities and, since they are all single-
component systems, no major disruption in production will take place if only a small
quantity is used for each color in any one production run.
However, the epoxy water-reducible is only available in a few colors, and requires
complex mixing. It may therefore be too time consuming to mix up small quantities.
The pofyurethane dispersion is a new technology, and it is unlikely that a large number
of colors will be available.
6-17
-------
Wafer-dome, bake, >194°F (9O°C) - All three technologies are available in a multitude
of colors, but usually these coatings are sold in large quantities only.
Solvent-borne, air/force dry, < 194V (9194°F (9O°C) - These coatings are available in a wide range of
colors but, for the most part, large quantity orders are required.
Specialty Coatings - The silicons coatings are generally not available in a wide variety
of colors, since they are intended for high temperature applications. These coatings
must be ordered in large quantities.
Autodeposited coatings are formulated in only a handful colors, most of them black or
shades of gray. The required application methods are only applicable if large volumes
of steel are to be processed.
Unlike autodeposited coatings, the electrodeposited coatings are available in a wide
range of colors. However, because the electrocoating tanks usually hold many
thousands of gallons, these coatings are inappropriate for facilities which need small
amounts of a wide range of colors. Typically, a facility which elects electrodeposited
coatings uses only two or three colors.
Powder coatings are available in a wide range of colors and gloss or texture finishes.
Until recently, most powder coatings vendors required minimum orders of 1,500
pounds per color. Now, however, several powder coating companies have dedicated
themselves to small quantity orders. A facility may need to shop around for a coating
vendor which can accommodate this requirement.
6-18
-------
Question 25. Must the coating system satisfy unsophisticated application
requirements?
Answer: Many facilities are reluctant to change from the coating application methods
they are currently using. Any such change could be costly, and require retraining of
key employees.
Most liquid coatings can be applied with relatively unsophisticated equipment.
However, the specialty coatings, with the exception of the silicons coatings, require
both sophisticated equipment and specially trained personnel to maintain and monitor
tine processes. Therefore, any facility wishing to consider autodeposrted,
electrodepos'rted, radiation cure, vapor cure or powder coatings must be prepared to
invest in relatively sophisticated equipment and also commit to a maintenance and
quality control program.
Question 26. Will "critical recoating" time be a problem?
Answer: Some coatings are very sensitive to being repair-coated or over coated
within a specific time period. For instance, some acrylic air dry coatings cannot be
recoated for 2 to 8 hours from the application of the first coat. If these coatings are
recoated too early, the basecoat may lift and ruin the coating. In general, fast drying,
single-component acrylic modified coatings tend to be sensitive to this problem and,
therefore, should be avoided.
6.8 QUALITY CONTROL
Question 27. Is there a requirement for low film thickness?
Answer: Some companies have a definite requirement for uniformly low film
thicknesses, less than 1.0 mm. The requirement is often a result of parts with close
tolerances. A low solids coating is best for such uses. Most water-borne coatings will
satisfy these requirements.
Solvent-borne, Air/Force Dry < 194°F (9CPC) - The high solid alkyds, high solids two-
component catalyzed epoxies, high solids two-component polyurethanes and the high
solids moisture cure polyurethanes, may result in too high film thickness.
Some formulations of the high solids, two component polyurethanes are available in
very tow viscosities and, therefore, uniform film build may be possible.
Solvent-borne, Bake > 194°F (90°C) - These coatings may be difficult to apply at
uniform film thicknesses.
6-19
-------
Specialty Coatings - Depending on the formulation, silicones may result in uneven film
thickness. Typically, autodeposition, and electrodeposition apply extremely uniform
low film thicknesses. The radiation cure and vapor cure coatings also generally
provide relatively uniform film thicknesses.
Powder coatings can usually be applied at uniform film thicknesses, because the
principle of application is based on an electrostatic field set up between the grounded
part and the positively charged powder coating gun. However, most powders can
only be applied at film thicknesses above 1.0 to 1.5 mm.
Question 28. Must colors and gloss levels meet low batch-to-batch tolerances?
Answer: In some facilities it is vital that color and gloss levels exactly match from
batch to batch. In the Miscellaneous Metal Parts industries, machines are often
assembled from several different components which may be manufactured and coated
at different times. Color and gloss mismatches are often a major production problem.
The electronics industry, manufacturing computers, business machines, laboratory and
medical instruments, and the automotive industry are particularly sensitive to this
problem.
Of ail of the VOC-compliant technologies available, perhaps the ones which cause the
greatest color and gloss matching problems are powder coatings. Once the powder .
coating has been manufactured, it is very difficult, if not impossible to make minor
changes, particularly after the coating user has received the batch. Unlike liquid
coatings, the gloss or color of powders cannot be modified after they have been
delivered to the customer.
6.9 COST
Question 29. Is the part to be coated so price-sensitive that no increase in
finishing cost can be tolerated?
Answer: Many low priced articles, such as hand tools, wire products, and building
supply items, are so price sensitive that even small cost increases cannot be tolerated.
Thus price is a primary concern.
Water-borne, Air/Force Dry — The alkyds, acrylic latexes and hybrids are potential
coating choices.
Water-borne, Bake - These coatings may prove to be slightly too expensive.
Solvent-borne, Air/Force Dry - The high solids alkyds and epoxy esters may be
suitable for these markets.
Solvent-borne, Bake - It is likely that all of these technologies will be too expensive.
Specialty Coatings - Almost unquestionably, all of these coatings can be eliminated.
6-20
-------
CHAPTER 7
COATING MANUFACTURERS AND AVAILABLE COMPLAINT
COATINGS
As State and Federal VOC regulations grow more stringent, the demand for VOC
complaint coatings increases. New technologies are discovered and developed, and
new methods of achieving compliance become available. Table 7-1 presents specific
VOC compliant coatings which are presently available. This table is organized
according to coating type: Primers; Topcoats; Specialty Coatings; Powders;
Conductive Coatings; and Military Specification Coatings. Each of these categories is
subdivided by dispersion and drying methods. Information is included on VOC
content (including and excluding water), percent solids by volume, and theoretical
coverage. Where the manufacturer has indicated an optimal coating dilution or mix,
the VOC content, solids and coverage information cited is the coating as mixed. Table
7-2 presents the addresses of each coating supplier contacted. Since not every
vendor contacted chose to become involved with this project, some vendors listed in
Table 7-2 are not represented in Table 7-1.
7-1
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THIS PAGE INTENTIONALLY LEFT BLANK
7-2
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CHAPTERS
CASE HISTORIES - CONVERSION TO COMPLIANT COATINGS
8.1 INTRODUCTION
This chapter provides case histories of companies which have converted to compliant
coatings. Details of the processes which several companies have used to pretreat
and coat their products are discussed. In some cases, the pretreatment and coating
process are unsophisticated. In others, no expense has been spared to pretreat the
metal and provide the finished product with a high quality finish.
The case histories presented in this chapter have been selected to cover the full
spectrum of requirements. Three case histories are included which involve the use of
military specification coatings which were selected through a qualification process in
order to convert to alternative coatings.
AH the case histories described are successful conversions to compliant coatings, as
opposed to the use of add-on control equipment for compliance. Most of the case
histories cover a period from the early 1980's to the present.
While powder coating technologies are becoming increasingly popular as a means for
complying with State regulations, most of the companies described in this chapter
opted for other methods. Many tested powder coatings, however, they did not want
to make the major facility changes and incur the expenses required to implement the
powder coatings.
This chapter is divided into three major sections:
• Category 1 describes companies which have minimal performance
requirements due to the low cost products which they manufacture.
• Category 2 describes the wide spectrum of industries which require
anything from a relatively unsophisticated finish to a high performance
product.
• Category 3 deals with military contractors who are contractually bound
by military coating specifications.
CATEGORY 1
The companies in this category are fabricators of metal products for which the market
is very price sensitive. Generally, no surface preparation is performed prior to coating
8-1
-------
application. The coatings are intended simply to provide a pleasing finish to the
products. Corrosion resistance or any other chemical or physical properties are not
required. The three case histories in these categories include:
1. Company manufacturing steel brackets for the building supply industry
2. Small company manufacturing trailers for recreational boats.
3. Company manufacturing fence posts.
CATEGORY 2
In this category, the companies require both corrosion resistance and high quality
appearance. Case histories have been selected which cover a range of performance
requirements. Some companies may make great efforts to provide a high quality
finish, while other companies will compromise in order to keep the costs reasonable.
The case histories in this category include:
4. Manufacturer of decorative lighting fixtures for the consumer industry.
Products are generally for indoor use.
5. Manufacturer of lamp housings buried in soil.
6. Manufacturer of custom designed machinery for indoor or exterior
exposure.
7. Company which makes large tote tanks storage of chemicals.
8. Company manufactures aircraft loading machines used at airports.
9. Maintenance operation of airline ground support equipment.
10. Manufacturer of laboratory medical electronic instruments.
11. Manufacturer of lawn and garden tractors.
CATEGORY 3
This category comprises companies.which are required to coat their products in
accordance with military specifications:
12. Military contractor who manufactures tracked vehicles for the U.S. Army.
8-2
-------
13. Military contractor who manufactures microwave communications
systems for the U.S. Navy, Army, and Air Force.
8.2 CASE HISTORY NO. 1 - COMPANY MANUFACTURING STEEL BRACKETS
FOR THE BUILDING SUPPLY INDUSTRY
Process Description
This company specializes in the manufacture of steel tie-down brackets for the building
industry. Typical products are used to tie together wooden beams, such as attaching
a 2 in. x 4 in. beam to a 2 in. x 6 in. beam.
The metal ties are made of mild steel and, in some cases, also galvanized steel.
Some of the company's products are sold without any decorative coating; however,
the steel ties are coated primarily to give the product a colored finish. Corrosion
resistance is of minor importance to the company, because the consumer usually
repaints the ties after the building has been erected.
Previously, the company performed no surface preparation because the solvent-based
coating used was tolerant to most contaminants on the surface. The coating was
applied by dipping the parts in a large steel tank. High solvent losses from the dip
tank were noticed; but, since the company did not violate any regulations, no special
attention was given to this problem. In fact, the entire coating process was carried out
under a lean-to, which was attached to the main fabrication building.
Regulations were then implemented which required the company to convert to
coatings with a VOC-content of less than 2.8 Ibs/gal, less water and exempt solvent
Compliance Strategy
The first task was to define the exact performance properties required of the coating,
e.g., color, gloss, drying time, and minimum salt spray resistance. After evaluation of
the advantages and disadvantages of water-borne versus solvent-borne coatings, the
company decided to confine the search to water-borne compliant coatings which
could dry at temperatures less than 120°F.
One potential choice was a water-borne autodeposited coating. Company
representatives visited the vendor and soon established that their parts would require
extremely good cleaning before entering the autodeposttion tank. This would require
the installation of a large washing system, the cost of which would be prohibitive if the
finished products were to remain competitive. The concept of autodeposition was
therefore eliminated from the choice of available coatings.
8-3
-------
After a considerable amount of research, the company procured samples of water-
borne dip coatings from 10 vendors. Trials were conducted using each of the 10
coatings received. To carry out the tests, small parts, representative of the actual
products, were dip coated in one-gallon containers. Tests were conducted to check
for the ease with which the coating could drain from the part, for the absence of a
thick edge at the bottom of the part, and for total drying time to handle.
One coating was selected for implementation. Results from the tests provided
sufficient information to allow the company to design a conveyorized dip coating line,
complete with a three-stage alkaline degreasing spray washer, a dip tank and a
convection oven.
Permits to construct were submitted to the local agency, and building and installation
commenced.
Time to Implement
One year after initiation of the project, the coating line was completed and the
company was able to convert to the low-VOC product. The water-borne coating had a
VOC of approximately 1.5 Ibs/gal of coating less water.
8.3 CASE HISTORY NO. 2 - SMALL COMPANY WHICH MANUFACTURES
TRAILERS FOR RECREATIONAL BOATS
Process Description
Automobile trailers were manufactured by a relatively small company with a total
employment of less than 25 people.
*.
The trailers were fabricated from hot rolled tubular steel, which was welded together
into tiie trailer frames. Immediately after fabrication the trailers were moved to the
spray booth where one operator was responsible for surface preparation and painting.
Surface preparation was comprised of a cursory solvent wipe-down. An electrostatic
spray gun was used to apply the alkyd air-dry coatings directly to the poorly prepared
steel. Each trailer required less than one quart of paint, and the colors varied
according to customer request
After the coating had been spray applied, the trailer was placed in a staging area,
where the coating would air dry overnight. Shipment took place the following day.
The company was cited by the local air pollution agency for noncompliance with a rule
requiring a VOC content of 2.8 Ibs/gal of coating less water.
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Compliance Strategy
The most likely alternative technologies for compliance for this facility included:
• water-reducible alkyd air drying primer followed by a water-reducible, air
drying alkyd enamel
• water-reducible epoxy primer followed by a two-component polyurethane
topcoat
* high solids alkyd enamel
• air drying alkyd formulated with exempt solvent 1,1,1 trichloroethane
(TCA).
The company tentatively rejected a water-borne alkyd primer and topcoat because the
existing electrostatic spray equipment could not be used without making some safety
modifications, in any case, the company did not want to apply a primer and wanted
to maintain the current practice of applying only two coats of topcoat even after being
advised that the absence of a primer would render the surface more susceptible to
corrosion.
The company rejected the suggestion for use of the water-reducible epoxy primer and
the two-component polyurethane top coats. The company's argument was that
painters could not be relied on to properly mix the two components. Nor did the
company want to incur the waste costs which are often associated with pre-mixed
two-component coatings.
The high solids alkyd enamel was rejected because this coating requires a minimum 8-
hour drying time, provided that the film thickness can be controlled within a range of
approximately 1.0-1.5 mils. This option required a purchase of an oven to accelerate
the drying time.
The company was informed of the potential disadvantages of chlorinated solvents,
such as 1,1,1 trichloroethane (TCA). These include cost, potential danger when using
spray equipment with aluminum parts in the fluid line, and the possibility of elimination
of the exemption for 1,1,1 TCA within a few years. But the fact that the coating was
readily available and would not require the painter to go through another learning
curve was very attractive for one company.
The owner decided on this last alternative, as he was able to procure the coatings
from a supplier located within 3 miles from his facility.
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Since solvent wiping often does not render clean surfaces, and solvents are
expensive, the owner was advised to clean the metal with a high pressure hot water
wand to which detergent is added.
Time to implement
The entire implementation process took less than 1 week. Immediately after the
decision was made, the owner called the coating vendor and made arrangements for
the compliant coatings to be manufactured and delivered. The VOC content of the
fast drying alkyd was 2.8 ibs/gal coating less water and exempt solvent.
8.4 CASE HISTORY NO. 3 - FENCE POSTS MANUFACTURING FACILITY
Process Description
Fence posts are often manufactured from steel stock which has been rolled at a steel
mill. During the hot rolling process, scale builds up on the surface of the metal. If the
rolling temperature is too high, then the scale can delaminate from the surface, or
loosely adhere.
The company in question applied a fast drying solvent-borne alkyd coating with a VOC
content of approximately 5.4 Ibs/gal coating less water by dip coating. The high VOC
content was not unusual, because dip coatings have low viscosities, and the volume
of solids is often fairly low.
In order to obtain permits operating, the company was required to lower its emissions.
Compliance Strategy
T
The company worked with two paint vendors to develop a water-borne, air drying dip
coating with a VOC content less than 3.5 Ibs/gal coating less water, formulated in the
company's two standard colors. The coating required a small amount of reduction
with water before the viscosity was acceptable for dip coating.
Though water-borne coatings are very sensitive to surface preparation, the company
does not clean the metal posts before applying the coating. This is, apparently,
consistent with the practices of other competitive companies. Because the posts
require no machining, the only major contamination is the loose scale. Generally, oils
and greases are not present The water-borne coating adheres surprisingly well to the
substrate, and corrosion resistance meets the expectations for this industry.
Some of the problems which were experienced from this change included a longer
drainage time than was previously necessary with the solvent-borne coating. This
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resulted in higher dragoirt from the dip tank, and more dripping of the water-borne
coating from the posts onto the floor under the conveyor line.
Time to Implement
The task of finding applicable compliance coatings took several weeks. For the most
part, the water-borne coating simply replaced the solvent bome coating in the dip
tank. The company is now trying to resolve the drainage and dripping problem.
8.5 CASE HISTORY NO. 4 - MANUFACTURER OF DECORATIVE LIGHTING
FIXTURES FOR THE CONSUMER INDUSTRY
Process Description
The company manufactures lamp housings from aluminum sheet stock. Some of the
interior components comprise zinc die castings. Although they are coated, they are
not exposed to view. All of the aluminum and zinc die-cast parts were cleaned and
treated in a three-stage conveyorized spray washing machine comprised of a
degreaser and phosphate in the first stage, followed by two water rinse stages.
The company was using a combination of water-borne therrnoset acrylic baking
enamels and solvent-based acrylic baking enamels to coat all of its products; however,
the VOC contents were in excess of the regulated 2.3 Ibs/gal coating less water
requirement.
Most of the lamp housings were coated by means of conventional air atomizing spray
guns. White fluorescent light fixtures, similar to those sold in hardware and building
supply stores, were also coated by spray application. Large recessed lighting
housings, which are not exposed to view and, therefore, have a lower appearance
requirement were dip coated in a water reducible acrylic baking enamel. Baking
temperature was approximately 300-325°F for 5 - 7 minutes.
The company used 15-20 standard colors, and numerous custom colors, as many
as were specified by customers.
Compliance Plan
The company hired a consultant to assist in preparing a plan to identify compliant
coatings. First, the consultant suggested that a list of all the performance and
application requirements be compiled. As is often the case, the company did not have
a paint specification and, therefore, submitted samples of their coatings to an outside
laboratory to determine the minimum performance and application properties of the
existing coatings.
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Then, a search for the most likely technologies began. Those which seemed most
appropriate for this operation were:
* thermoplastic, water-borne coatings which air or force dry and are
available with VOC contents less than 1.8 Ibs/gal coating less water;
* thermoset water-reducible coatings which are cured at temperatures of
approximately 250 - 350°F for 15 minutes, and are available with VOC
contents of 2.3 Ibs/gal coating less water;
two-component polyurethanes which will air dry or can be force dried,
and are available at 2.8 Ibs/gal coating less water;
• powder coatings.
Tests were conducted with all the above types of coatings to determine their ability to
withstand metal skin temperatures of SOOT for 48 hours, to simulate typical conditions
to which lamp housings are subjected by high wattage light bulbs.
The air-drying water-borne alkyds failed this test on two counts. Rrst, they
delaminated from the metal surfaces and charred badly. Second, they discolored from
light pastel colors to dark browns. Both the polyurethanes and the thermoset water-
borne acrylics withstood the high temperature test
Although polyurethanes provide an excellent-looking finish, they were ruled out
because too many small batches were required to be mixed on a daily basis, and
coating wastage would incur excessive hazardous waste costs. Moreover,
polyurethanes are expensive, with some colors selling for more than $50 per gallon.
Powder coatings would have been the ideal choice, because they emit negligible
VOCs and generate little hazardous waste. However, too many colors would have
been required, and any one coating run only comprised a few component parts.
Moreover, many of the lamp housings were coated in two colors; reflective white on
the interior and a decorative color on the exterior.
The thermoset acrylic baking enamels performed very well, and were chosen to
replace the existing non-complying coatings. The paint operators were already familiar
with the application of water-borne coatings and, therefore, did not require a large
learning curve.
Time to Comply
The entire conversion process took approximately 18 months. At least 6 months were
required to conduct the initial laboratory tests and then sample and test alternative
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coating technologies. The next time-consuming step involved the reformulation of the
coatings to match the existing colors. This process commenced with converting the
standard colors used in the largest quantities followed by the smaller volume colors.
The coating for the recessed housings was difficult to formulate, because as a housing
was withdrawn from the dip coating tank, drops of paint falling back into the tank
created air bubbles on the surface of the tank. When the next housing entered the
tank, the air bubble adhered to the metal surface and remained all the way into the
drying oven. During tine curing process the bubble would burst, leaving an
unacceptable coating defect.
This company has recently converted the fluorescent fixture line to powder coatings,
and they hope to convert some of their spray coated lamp housings to the same
technology in the near future. It is unlikely that the recessed housings will be changed
from the dip coating to a powder coating.
8.6 CASE HISTORY NO. 5 MANUFACTURER OF LAMP HOUSINGS BURIED IN
SOIL
,~
Process Description
This company manufactures lamp casings for fixtures which light up the exterior of
buildings, bridges, pathways, etc. The casings are made of aluminum, and are
assembled with stainless steel nuts and bolts. They resemble cylinders of
approximately 12 inches in diameter and 18 inches deep. Customers who purchase
these products bury them in the soil, so that only the outer flange (approximately one
inch thick) is visible.
The casings are cleaned and treated in a three-stage conveyorized spray washer,
comprising a degreaser/phosphate in the first stage, followed by two water rinses.
The entire exterior assembly was dip coated with a very high VOC plastisol vinyl
coating to prevent corrosion by aggressive soils. At least two coats were applied, and
the coating was then oven cured.
The primary performance requirement is corrosion resistance. Because the units are
buried in the soil, only the top flange required both a corrosion resistant and a
decorative finish. Due to the high VOC content of the plastisol, the company was
required to convert to a technology that would meet a 3.5 Ibs/gal coating less water
regulation.
Compliance Plan
Before undertaking this program, the company first subjected its existing coated
casings to laboratory tests to establish the minimum corrosion resistance which a new
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technology would need to meet. No definitive test data was on hand, although the
company knew that its existing product satisfied most exposure conditions.
Three technologies were suggested for use by their coating consultant: a high solids,
low VOC plastisol vinyl coating; a fluidized bed powder coating; and an electrostatically
spray applied powder coating. The project commenced with a search for custom
coaters who could apply the high solids plastisol vinyl.
The high solids plastisol vinyl was rejected based on trial runs which indicated that too
many large air bubbles were entrapped during the dipping process, causing large
areas in which no coating had deposited in the final finish. Further, the applied
coating was uneven.
The company then examined a fluidized bed epoxy coating. This coating penetrated
too many holes and other recessed areas which required cleaning before the
electronic components were assembled into the casing. Moreover, due to the varying
heat sink of the cylinder, the powder coating was uneven and visually unacceptable.
Electrostatic spray application of an epoxy powder coating proved to be successful.
Because epoxies have poor resistance to sunlight, the top flange needed to be coated
with a decorative finish to resist long-term exposure to sunlight. A polyester powder,
applied over the epoxy powder, accomplished this goal.
Time to Implement
The entire compliance project was conducted over an 8-month period. The initial
laboratory tests took approximately 2-3 months. The first set of laboratory data
produced inconclusive results; thus an additional series of tests was required.
Identifying custom coaters and arranging to have the casings coated took
approximately 3 months. The electrostatically spray applied powder was determined
to be the best after all three types were tested, including the high solids plastisol and
the fluidized bed epoxy. Further laboratory tests were undertaken to verify that the
powder could withstand the aggressive exposure conditions of some soils. Next,
arrangements were made for all production cylinders to be coated by a custom coater.
Finally, the epoxy and polyester powder coatings were ordered.
8.7 CASE HISTORY NO. 6 - MANUFACTURER OF CUSTOM DESIGNED
MACHINERY FOR INDOOR AND EXTERIOR EXPOSURE
Process Description
This company specializes in custom designing machinery, such as postal sorters, food
packaging machines, large computer printers, etc. The machines are unique and, in
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some cases, only one machine is built for the customer. More often than not, the
machines will contain complex mechanical components and sophisticated electronic
circuitry.
The machines themselves are housed in sheet metal cabinets, comprising side, back
and top panels, and sheet metal doors. In some cases, the metal is cold rolled steel;
in others they will use aluminum sheet stock.
The surface preparation consisted of a solvent wipe and cleaning with a high pressure
hot water wand. An alkaline detergent was added to the water, and final rinsing
consisted of a wash down with clean water. To enhance adhesion, a pretreatment
primer, or "wash primer" was used. These vinyl butyryl coatings have approximately
12 percent volume soiids and a VOC content of 6.5 Ibs/gal coating less water. This
coating was applied to a dry film thickness of 0.3 - 0.5 mils.
It was customary for the company to apply the primer and first basecoat to all
component parts. After the machine was assembled, a final coat of basecoat,
followed by a texture coat was applied. (Texture coats are applied by reducing the
atomizing pressure to the spray gun so that incomplete atomization takes place and
small paint droplets land on the surface.)
The standard finish offered to customers was comprised of a smooth basecoat of a
quick drying medium oil alkyd with a VOC content of approximately 4.5 Ibs/gal coating
less water followed by an application of a texture coat, using the same material.
Some times at the customer's request, the coating system was consisted of a two-
component epoxy primer followed by one or two coats of a two-component
polyurethane, both of which had VOC contents of 4.5 - 5.4 Ibs/gal coating less water.
The company was required to reduce its VOC contents to the following levels:
* primers to 2.8 Ibs/gal coating minus water;
• gloss topcoats to 3.5 Ibs/gal coating minus water; and
• semi-gloss or flat topcoats to 2.8 Ibs/gal coating minus water.
Compliance Strategy
The company decided to upgrade the standard finish from an alkyd to a two-
component polyurethane. In order to assure good adhesion, it also decided to install
a three-stage iron phosphate immersion process, in which the first stage comprised a
degreaser and iron phosphate combination; the second and third stages were water
rinses. A convection oven was installed to dry off the component metal parts.
8-11
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After performing some spray application tests with coatings from three local vendors,
the company was able to select the coatings which provided the best application
properties. The biggest problem was excessive orange peel. At a VOC content of 2.8
Ibs/gal less water, it was not possible to achieve a smooth basecoat finish with the
pofyurethanes. Fortunately, the texture coat tended to hide imperfections in the
basecoat.
Because of the iron phosphate pretreatment, the "pretreatmerrt wash primer" was no
longer necessary.
For machines which were to be exposed indoors, the polyurethane basecoat was
applied directly over the pretreatment. For machines which were to be exposed to
exterior environments, a water-reducible epoxy primer with a VOC content of 2.8
Ibs/gal less water was applied. The vendor had qualified the primer to that of military
specification MIL-P-85582.
Because the polyurethane can air dry without the need for oven assist, the company
decided not to install a curing oven. They could allow the time required for the metal
panels to cure hard overnight
It was understood that the epoxy/polyurethane systems were more expensive than the
previously used alkyds, but the company was willing to pay the extra price for several
reasons: the cost of the coatings was relatively small when compared against the cost
of the assembled machines; the quality of the finish (color, hardness, abrasion
resistance, reduction in rework and rejects, and improved corrosion resistance) was
improved distinctively; and compliance was achieved with the low VOC products.
Time for Implementation
The first phase of the program, consisting of selection of coating vendors and field
testing, took approximately 3 months.
The paint facility was modified to accommodate the immersion tanks, and the
company used this opportunity to replace their old spray booth with a new and larger
dry filter booth. Permits to construct and operate were required. This phase took
approximately 5 months.
After the coatings had been identified, the selected vendor was required to match the
company's standard colors. This delayed implementation by a few weeks. The entire
project was completed within 9 months.
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8.8 CASE HISTORY NO. 7 - COMPANY WHICH MANUFACTURES LARGE
TOTE TANKS FOR STORAGE OF CHEMICALS
Process Description
Large and small tote tanks are used by several industries to store chemicals, liquids,
powders, and more. Often, the tote tanks are shipped from the primary manufacturer
(such as a supplier of resins) to their customer (such as the paint manufacturer).
When the tote tank is empty, the tanks are returned to the primary manufacturer for
reuse. Therefore, the tote tanks are shipped across country many times during their
life. As the coating finish deteriorates, the primary manufacturer may repaint the tank
for improved aesthetic appeal. Depending on the primary manufacturer's
requirements, the tanks may need to be coated with a corrosion resistant finish, or
simply with one which will withstand normal exterior exposures.
The manufacturer of the tote tanks in this case fabricated them from hot rolled steel,
on which very little scale was evident. Surface preparation comprised a thorough
steam clean, to which an iron phosphate had been added for extra protection. The
wet tanks entered a drying oven to evaporate off the water.
After leaving the oven, the tanks were transported by lift truck to the paint booth where
a corrosion resistant, fast drying acrylic-modified alkyd primer was applied by means
of an air-assisted airless spray gun.
Soon after the primer had dried ready for re-coating, a fast-drying acrylic-modified
alkyd enamel was applied using the same spray gun. In some cases, both the inside
and outside of the tanks were coated. In all cases, at least the outside was coated.
In a few cases, customers specified epoxy and/or polyurethane finishes.
All of the coatings used by the company had VOC contents in excess of 4.5 Ibs/gal
coating less water at application viscosity, and all of the coatings were required to air
dry as they did not have a coating oven.
The company experienced premature corrosion on some of its products which were
exposed to aggressive marine environments. Also, the appearance of the alkyd
finishes was unsatisfactory. VOC-compliance was not an issue, as they are located in
an attainment area for ozone.
The company decided to make changes to their current coating system. These
changes included voluntarily switching to coatings with VOC content less than 3.5
Ibs/gal coating less water.
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Compliance Strategy
The company planned to conduct a series of application trials using a combination of
technologies as follows:
• water-reducible epoxy primer (VOC < 2.8 Ibs/gai coating less water)
followed by thermoplastic water-borne, air dry alkyd enamel (VOC < 2.0
Ibs/gal coating less water)
• water-borne epoxy primer followed by water-borne thermoset baking
acrylic enamel (VOC < 3.0 Ibs/gal coating less water)
• epoxy water-reducible primer followed by a two-component high solids
polyurethane enamel (VOC < 3.5 Ibs/gal coating less water)
• high solids epoxy primer (VOC less than 3.5 Ibs/gal coating less water)
followed by a two-component high solids polyurethane enamel
• hybrid powder coating
Several paint manufacturers were contacted for sample coatings, so that several of the
systems were comprised of more than one coating vendor. The tests were conducted
using high volume, low pressure spray equipment (HVLP) for the liquid coatings. All
metal parts were pretreated in a five-stage iron phosphate immersion tank process.
This consisted of the following:
Stage 1: Heated alkaline degreaser
Stage 2: Water rinse
Stage 3: Iron phosphate pretreatment
Stage 4: Water rinse
Stage 5: Water rinse with seal coat
The most important findings of these trials are: an air dried thermoplastic water-bome
coating, applied over an epoxy primer, but dried in an oven at a temperature less than
180T, would yield the desired results; the surface preparation must be improved from
the current wand cleaning to a three or five-stage iron phosphate pretreatment if
powder coatings are to be applied; and an oven capable of curing powders at 400°F is
required.
Time for Implementation
Information relative to implementation time is not available for this case history.
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8.9 CASE HISTORY NO. 8 - COMPANY MANUFACTURES AIRCRAFT
LOADING MACHINES FOR USE AT AIRPORTS
Process Description
Aircraft baggage loaders are fabricated from hot rolled steel sections which are welded
into frames. The frames are assembled into scissor lifts, which then operate under
hydraulic pressure. A driver's cab made from sheet metal forms the front end of the
machine.
The company, already manufacturing such machines, wanted to build a new facility in
an ozone non-attainment area. Regulations limited the VOC emissions to 3.5 Ibs/gal
coating less water.
The existing coating process at the facility is described as follows. All hot rolled steel
sections were mechanically wire brushed to remove loose rust and scale. Next, high
pressure hot water cleaning by means of a hand-held wand, was carried out. A mild
iron phosphate was added to the water. To accelerate drying of the steel,
compressed air was used to blow off excess water which had collected in channels,
crevices, etc. The hot water had heated the steel to a sufficient temperature to
promote rapid drying of the substrate. All steel sheet stock, which was used for the
drivers cab, was pretreated in a five-stage iron phosphate immersion system.
Prior to assembly, the component subassemblies were primed with a fast drying aikyd-
modified zinc chromate primer, with a VOC content of approximately 5.0 Ibs/gal
coating less water. In some cases, the sheet stock was treated with a pretreatment
"wash primer." The components then received the first coat of an alkyd-modified air
drying, automotive refinishing enamel, with a VOC content of 4.5 - 5.0 Ibs/gal coating
less water. They were next placed in a flash-off staging area where they were allowed
to air dry at ambient temperature. After overnight drying, they were placed into
storage awaiting assembly.
After assembly of the machine, final testing took place. This included high pressure
testing of the hydraulic equipment and, therefore, often resulted in hydraulic oil
contamination of the painted surfaces. Also, during assembly, the already-painted
surfaces were sometimes damaged.
Before entering the water-wash spray booth for a second time, the entire machine was
prepped. This included a thorough cleaning with high pressure hot water to which
detergent was added, followed by a blow off with compressed air. Where necessary,
damaged areas were prepped with fine abrasive paper, and a touch-up coat of primer
was applied.
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The entire machine then received at least one more application of the topcoat Due to
the complexity of the operation, this final operation could take at least 8 hours. The
finish-coated machines were allowed to air dry in the spray booth overnight, and were
then taken outdoors for final glazing, and to receive decals, etc. prior to shipping.
Compliance Strategy
Numerous meetings were held to discuss all of the options for the new facility, and to
calculate the cost impact of each option. Surface preparation of the hot rolled steel
was considered to be of paramount importance, and it was decided to shot blast all of
the weldments. They were to be primed within a few hours of blasting.
The sheet stock was to be treated in a seven-stage immersion process which was to
comprise the following:
Stage 1: Degrease in hot alkaline bath
Stage 2: Water rinse
Stage 3: Acid pickle only of steel stock which had already shown signs of
corrosion. All other steel was to bypass stages 3 and 4.
Stage 4: Water rinse
Stage 5: Iron phosphate at elevated temperature
Stage 6: Water rinse
Stage 7: Water rinse, with non-chromate seal coat.
All steel which will be passed through the pretreatment tanks will be oven dried at a
temperature of approximately SOOT. All steel will receive a high solids alkyd primer,
with a VOC content of 3.5 Ibs/gal coating less water, followed by the first of two coats
of a high solids, air drying alkyd enamel, also with a VOC content of 3.5 Ibs/gal
coating less water. The subassemblies will be handled in much the same way as was
being done in the existing facility. After final assembly and propping (similar to the
existing facility), at least one final coat will be applied.
Coating vendors were solicited for their compliant primers and topcoats. Reid trials
were arranged to fit into production schedules at the existing facility.
In each trial, problems were encountered. The most notable were:
• The high solids alkyd could not be applied to a smooth finish without
demonstrating excessive orange peel.
* Due to the configuration of the weldments, it was impossible to achieve
uniform film thicknesses; these varied from 1.5 mils to 5.5 mils.
• Gloss patches were evident wherever film thickness varied.
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• Drying times varied wherever film thickness varied. In areas where the
film thickness was low (1.5 mils), the coating dried in 6 - 8 hours; but, in
those areas where film thickness exceeded 3 mils, acceptable drying
took well over 24 hours.
• Areas of the machine which needed to be recoated due to damage, were
incompatible with the touch-up coat. Particularly where film build-up was
high, the touch-up coat lifted from the previous coat.
The problems encountered were so significant, that company representatives
researched other manufacturing companies who were also using high solids alkyds, to
see how the coatings were being applied. Apparently, this was a special case due to
the complexity of the weldments. Additionally, other companies were curing their
machines in ovens; whereas, this company could not do so because the large size of
the machines, and the heat-sensitive hydraulic components.
As an alternative, the company started testing a water-reducible epoxy primer with a
VOC content of 2.8 Ibs/gal coating less water and a two-component polyurethane with
a VOC content of 3.5 Ibs/gal coating less water. The tests for these coatings were
successful and, when the new facility was built, the epoxy/polyurethane system was
successfully introduced.
Time for Implementation
The first phase of the project, to establish a design philosophy and test the alkyd
coatings, took approximately 10 months. The testing phase was slow because field
tests had to be arranged to fit into the current production schedule. Also, after each
test series, the coating vendor required at least 4 weeks to make a new batch of
material for the next trial.
Selection of the shot blasting equipment, immersion tanks, conveyor lines, ovens, etc.
took at least 10 months. Retesting with the epoxy/polyurethane system also took
several months, and the newly hired paint operators had to be trained to use these
sophisticated coatings. The entire conversion process took 18 - 24 months.
8.10 CASE HISTORY NO. 9 - MAINTENANCE OPERATION OF AIRLINE
GROUND SUPPORT EQUIPMENT
Process Description
The maintenance shop of this company repaints all ground support equipment, such
as trucks, baggage carts, scissor lifts, electric generators, and all other equipment
commonly used on the airport concourse. Repainting was carried out by means of a
conventional air atomizing spray gun, and quick-drying, alkyd enamels, or alkyd-
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modified automotive refinishing enamels, (all of which had VOC contents in excess of
4.5 Ibs/gal coating less water) were primarily used. The shop was required to
introduce compliant coatings with a VOC content of less than 3.5 Ibs/gal coating less
water.
Because the ground support equipment had already been painted by the original
manufacturer, the shop manager was not concerned about long term performance.
Furthermore, he knew that he could repaint the machinery if the new VOC compliant
coatings did not perform as well as the non-compliant coatings.
Compliance Strategy
Samples of several water-reducible air drying alkyds were solicited, and cursory tests
were conducted. The shop manager was satisfied that the new coatings would suffice
for his application needs, and the conversion was made.
Time for Implementation
The entire conversion process took 3 to 4 weeks at most
8.11 CASE HISTORY NO. 10 - MANUFACTURER OF LABORATORY AND
MEDICAL ELECTRONIC EQUIPMENT
Process Description
The most important properties coatings must possess for the protection of laboratory
and medical electronic equipment are:
• They must withstand strong chemicals and solvents used by the
consumer.
* They must be resistant to frequent washing and cleaning, particularly if
used in hospitals and operating theaters.
• They must be hard and abrasion resistant.
• Computer consoles, keyboards and other surfaces frequently touched by
the operators must be resistant to commonly encountered products such
as nail polish, nail polish remover, juices, nicotine stains from cigarettes,
and food.
From a manufacturing viewpoint, the coatings must be easy to apply, should be useful
as a smooth basecoat and a texture coat, and achieve excellent adhesion to
substrates.
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The company in this case manufactured a wide range of products, including laboratory
instalments, medical equipment and electronic products for the industrial community
by the following process:
• Light gage steel panels were vapor degreased with 1,1,1 trichloroethane
(TCA).
• Light gage aluminum panels were treated with a seven stage chromate
conversion coating, complying with MIL-C-5541.
* Plastic substrates were lightly scuff-sanded and then wiped with a mixture
of water and isopropanol (I PA).
» Prior to assembly of the instruments, all metal and plastic components
were coated with a two-component polyurethane smooth basecoat,
followed by a texture coat of the same material.
• The metal parts were force dried at an oven temperature of 180°F, and
the plastic parts were force dried at 120°F.
• The components were then sent to the assembly area.
* After assembly, areas where product coating was damaged were
touched up with the same polyurethane. Small areas were repaired with
a small artists brush. Larger areas were coated with an air brush or a
conventional air atomizing spray gun.
For component parts which were to have a high visibility smooth appearance
(commonly referred to as a "Class A" finish), a primer surfacer was applied over the
treated metal or plastic. Once dry, all minor defects in the substrate were sanded
using No. 200, and No. 400 grit abrasive paper. The sanded surfaces were cleaned
with a tack-rag prior to topcoat application. The company used approximately 10
standard corporate colors.
Local air pollution regulations limited the VOC to 3.5 Ibs/gal coating less water.
However, the company anticipated that the limits would be lowered down to
2.8 Ibs/gal coating less water within 2 years.
Compliance Strategy
Because time was running out, the company applied to their air pollution control
district for a variance, which would legally allow them to continue operating with the
non-compliant coatings for an agreed-upon period of 9 months.
8-19
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With the assistance of a consultant, the company conducted a series of laboratory
tests to determine exactly what properties are required of the coating finishes. Their
experience had shown that the existing coatings were more than satisfactory, but no
specifications had ever been written to quantify the properties of the coatings in use.
Samples of the following compliant coatings, all of which were at or below the VOC
limits of the regulation were trial tested in the water-wash spray booths of the paint
shop. They comprised the following:
• Water-borne alkyds, air or force drying.
• Water-reducible acrylics, oven cured at 250 - 350°F for 10 - 20 minutes.
* Two-component polyurethanes with a gloss of 18 - 22% as read on a 60°
specular gloss meter.
• Two-component primer surfacer.
A detailed test specification was written, following wherever possible, ASTM methods.
Test panels were submitted to a laboratory for some of the more difficult tests, such
as salt spray and humidity resistance, while the simpler ones were conducted within
the paint shop.
The air drying water-borne alkyds, sampled from more than one vendor, were soon
eliminated because they failed many of the chemical and solvent resistant tests.
Staining, loss of gloss, and even total destruction were evident on some of the panels.
The oven-cured, high temperature baked acrylics performed extremely well. However,
initially they were difficult to apply. Typical problems included cratering, low film build
which photographed the surface finish of the underlying metal substrate, and pulling
away from edges and other discontinuities, such as punched or tapped holes in the
substrate.
The operators had difficulty establishing the correct application viscosities and other
application properties. After they had gone through the required learning curve and
understood the sensitivity of the water-borne coating, these problems could be
avoided.
The two-component high solids polyurethane performed almost as well as the existing
non-compliant polyurethane, but was more difficult to apply, particularly when a "Class
A" smooth finish was required. Typical of most high solids products, the polyurethane
produced a somewhat acceptable orange peel finish.
8-20
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The final selection was to use the water-reducible, bake coating on the metal
substrates, and the two-component polyurethane on the plastic substrates. Although
the water-borne coating produced the better finish, the plastic parts could not be
subjected to the high curing temperatures.
Time for Implementation
The company was able to comply with the 3.5 Ib/gal coating less water VOC limit
within a 6-month period. The testing phase, which included the writing of the test
specification, laboratory tests and the application trials, were completed within
approximately 4 months.
One of the major problems encountered during implementation program concerned
color matching. Not only did the new coatings have to match the existing standard
colors, but the water-borne coating had to exactly match the polyurethane. The fully
assembled instruments often have metal and plastic components adjacent to each
other, and exact color matches are critical.
Before the color matching could take place, it was first necessary for the company to
make new color standards of their existing coatings, ensuring that the problem of
"metamerism" did not occur. (Metamerism is a phenomenon in which two colors may
appear to exactly match each other when viewed in one light source, but be different
when viewed in one or more other light sources.)
8.12 CASE HISTORY NO. 11
TRACTORS
MANUFACTURER OF LAWN AND GARDEN
Process Description
The company, a manufacturer of lawn and garden tractors, was applying alkyds by
dipping and acrylic enamels by spray guns. A water-borne alkyd flowcoat was also
used. These coatings did not meet upgraded performance requirements for edge
corrosion protection, overall corrosion resistance, and aesthetic appeal, in addition,
the VOC content did not meet local environmental regulations.
Compliance Strategy
The company decided to convert to an electro-deposition priming technology and
selected a cationic eiectrocoat primer for that purpose. After a series of tests, a
triglycidal isocyanurate (TGIC) powder coating was used as the topcoat, which was
applied over the electrocoated primer.
8-21
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To ensure that they fully understood the complex system, the company first
constructed a pilot facility for testing purposes, and later went into full-scale
implementation,
Pretreatment consisted of a seven-stage process which comprised the following:
Alkaline dwell
Water rinse
Water rinse
Iron phosphate
Water rinse
Chrome seal
01 water rinse
Dry off
Cool down
90 sec at 150T
30 sec at ambient
30 sec at ambient
60 sec at 120°F
30 sec at ambient
30 sec at ambient
30 sec at ambient
5 mins at 250°F
5 mins at ambient
The electro-coating tank is comprised of 23,000 gallons of a cationic electrocoat with a
VOC-content of 2.8 Ibs/gal coating less water. Immersion of the parts in the coating
is for 3 minutes with a potential of 200 volts. Dry film thickness of the electrocoat is
0.8 mils.
Dragout from the bath and post rinsing is accomplished with two counterflow stages
supplied with uftrafilter permeate. Stainless steel alloy 316 anodes are used in the
bath, and they are of a tubular design to allow for easy conversion to an acolyte
solution.
Draining and flash-off is accomplished in 7 minutes, and the parts then enter a gas-
fired oven with three temperature zones:
10 mins at 200°F
15 mins dwell to 375°F
15 mins at 375°F
From the oven, the parts are cooled down in a forced air tunnel, where they are
allowed to cool to 180°F prior to entering the powder coating booths.
One of three colors, green, yellow or black are applied to a film thickness of 2.5 - 3.0
mils. The VOC content of the powder is approximately 0.03 Ibs/ib of powder. A final
manual operation is required to ensure overall quality of finish. The powder is cured in
ovens which have two temperature zones, and which heat the parts to a metal
temperature of 375°F.
A high gloss, high solids baking enamel, with a VOC content of 4.3 fbs/gal is used for
the non-metal hoods of the lawn tractors.
8-22
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Reference
Christopher Daniels, "Focused on Quality", Product Finishing, November 1989, p 54.
8.13 CASE HISTORY NO. 12 - MILITARY CONTRACTOR FACILITY WHICH
MAKES TRACKED VEHICLES FOR THE U.S. ARMY
Process Description
Armored personnel carriers are manufactured from 1-1/4 inch thick aluminum plates
which are welded into the hull of the vehicle. Thousands of medium and small parts,
such as brackets, handles, stowage boxes, hinges, hatch covers, etc, are fabricated
separately and then painted prior to assembly of the vehicle. Military contractors are
contractually bound to use military specification coatings in the finishing process.
The company in question was using a conventional alkyd system, comprised of one
primer and two topcoats. The primer was a zinc chromate formulation, and the
interior topcoat was a semi-gloss alkyd enamel. The exterior topcoat required infrared
camouflage properties, and was also an alkyd.
Local surface coating regulations required the company to convert from the high VOC
products (generally in the range of 4.5 * 5.0 Ibs/gal coating less water) to 3.5 Ibs/gal
coating less water for the primer and topcoats.
Also during this time, the U.S. Army had decided to convert their alkyd systems to
epoxies and polyurethanes. It was, therefore, prudent for the military contractor to
immediately evaluate low-VOC epoxies and polyurethanes.
Compliance Strategy
The Army's coatings laboratory worked closely with both the contractor and potential
coating manufacturers to develop compliant formulations.
The company contacted the primary suppliers of military specification coatings, and
set the application parameters for the VOC-compliant primers and topcoats. (Existing
military specifications already existed for the high-VOC products, and these were to
remain intact for the new compliant coatings.)
Extensive laboratory tests were conducted by the paint manufacturers and the military
contractor. Not only was it necessary for the coatings to pass all the chemical and :
physical performance tests, but they also had to be compatible with the production
finishing lines on which they would be used. This meant that properties such as those
listed below had to be met:
8-23
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• Drying time to be compatible with conveyor line speed.
• Ability to recoat with the other coatings in the system, as well as with
itself.
• Ease of application with conventional air atomizing spray and air-assisted
airless spray.
• No major coating defects such as orange peeling and cratering.
• No premature pigment settling in 55-gallon drums.
• Easy mixing of the two components, namely the base and curing agent.
Reasonable material handling properties (for instance, the two-
component products were not to be over sensitive to moisture in the 55-
gallon drums, or moisture in the spray hoses, otherwise they would have
gelled in the coating lines).
• Batch-to-batch color and gloss consistency, within the specified range
(this is often a major problem).
Laboratory testing was conducted over a 2-year period to ensure that all problems
were worked out of the system before the coatings were applied to production
vehicles. There were no case histories of other companies which had gone through
the same procedure.
After many months of laboratory and field testing, countless trips across the country to
participate in meetings with vendors and the Army coatings laboratory, numerous in-
house meetings to plan for the required facility modifications, the establishment of new
quality control procedures, preparation of new health and safety requirements, and
implementation of painter training programs, the company was ready to convert to the
new technologies.
Before being able to make the switch, however, it was necessary to negotiate
contractual modifications with the customer. It should be noted that while the Army
coatings laboratory worked closely with all of the parties involved, they had no
contractual authority to approve the switch to compliant coatings.
The negotiation phase of the project took several months. Several trips by company
personnel to meet with the customer and explain the need for VOC compliance, and
the consequences to the manufacturing and production procedures, had to be
accomplished before approval could be given.
8-24
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Implementation went smoothly because much preliminary work had been carried out.
Hie overwhelming success of the program was due to the very close cooperation
between the contractor and its vendors, as well as with the Army laboratory. More
importantly, the close working relationship between company personnel in different
departments, such as the Materials Laboratory, Methods Engineering, Production
Engineering, Process Control, Environmental Management, Quality Control,
Purchasing, Contracts, etc. was crucial to the program.
Time for Implementation
The entire program was conducted over a 24 - 36 month period. Implementation was
phased in. The primer, a water-reducible epoxy to MIL-P-53030, was the first to be
introduced. Ten months later, the Epoxy interior coat, MIL-C-22750, and the two-
component polyurethane camouflage and "Chemical Agent Resist" (CARC) topcoat,
MIL-C-46168, were introduced.
The company had applied to the local air pollution control agency for a variance,
which legally allowed the company to continue using non-compliant coatings for a
negotiated period. The company was able to meet its obligations because they had
prepared time-lines, and religiously followed the progress of the project.
8.14 CASE HISTORY NO. 13 - MILITARY CONTRACTOR FACILITY WHICH
MAKES MICROWAVE COMMUNICATION SYSTEMS FOR THE U.S. NAVY,
ARMY AND AIR FORCE
Process Description
Microwave communication systems are made of various substrates, but particularly
light gage aluminum, light gage steel and various plastics. The company involved in
this case history supplies communication systems to all branches of the Department of
Defense, and is contractually obligated to use military specification coatings. It mostly
used non-compliant alkyds and epoxies. The most common specifications were:
TT-P-1757 - zinc chromate alkyd primer, MIL-P-23377 - strontium chromate epoxy
primer, TT-E-529 - semi-gloss alkyd enamel, TT-E-489 - gloss alkyd enamel, TT-E-527
- low-gloss alkyd enamel, and M1L-E-15090 - alkyd machinery enamel. The VOC
contents of these coatings were in the 4.5-5.0 Ib/gal range.
This company was out of compliance with the local regulation of 3.5 Ibs VOC per
gallon coating less water. A reduction of this limit to 2.8 Ibs VOC per gallon coating
less water was a possibility within 2 years. At the advice of a consultant, the company
filed for a variance which allowed them to legally use the non-compliant coatings
during an agreed-upon period of time.
8-25
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Compliance Strategy
An extensive laboratory testing program was conducted to demonstrate that the
performance properties of the complying coatings would qualify against the existing
specifications.
Although interested in the laboratory results, the customers' coating laboratories did
not accept the work, and requested samples of the same coatings, so that the test
results could be confirmed.
The major problem presented by the high solids alkyds was that they were slow to
dry. On the other hand, high solids polyurethanes, although more expensive than
alkyds, could meet all of the performance and application requirements, of both the
military specifications and the painting facility.
Time for Implementation
The first phase of the program, which consisted of the initial laboratory testing, took
approximately 6 months.
The second phase, in which the Army's laboratory conducted Hs tests, took
approximately 6 months, and receiving customer approval took between 6-8 months.
Implementation was phased in on a contract by contract basis, and total compliance
was achieved after approximately 18 months.
8-26
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TECHNICAL REPORT DATA
(f!tss* naa Iiatrucaons on Ott rvttrs* lit fort eomnitsnj}
EPA 340/1-91-009
4. TITU5 AND SU8T1TLS
S.eport on Compliance Coarir
Metal Parts Industry
,gs for the Miscellaneous
John D. Jeffery, Lysa Modica
Alliance Technologies Corpo
Boott Mills South
Foot of John Street
Lowell, MA. 01852
12. SPONSORING AGENCY NAME ANC ACS
U.S. Environmental Protacti
Stationary Source Complianc
4C1 M Street SV
Washington. DC -fUfin
ration
MESS
on Agency
e Division
x fttcimNT-s AcssssiON NO.
August 1991
68-02-4465
WA# 90-143
13.TYI»6 Qf REPORT ANO PERIOD COVERED
Draft
1*. SPONSORING AGENCY C2OE
EFA Technical Contact - Vishnu Katari, (703) 308-8717, PIS, 398-8717.
id* AfeS » flACT
This manual has been prepared with a focus on the surface coating of Miscellaneous Metal
Parts, as defined by those industries which fall into the Standard Industrial Codes (SIC) 33-
40, inclusive.
The objectives of the manual are: to serve as a guide for industrial coating users and coating
manufacturers, as well as inspectors and engineers with EPA who need to understand VOC
compliance as it applies to surface coating operations; to enable coating facilities to identify
the most likely strategies for getting into compliance using low-VOC coating technologies; to
prcvide the reader with a comprehensive listing of, the most common VOC-complaint coating
technologies used in the Miscellaneous Metal Parts industries, and to describe the advantages
and disadvantages of each; to provide the reader with a listing of a wide range of VOC-
complaint coatings, as well as the names and addresses of the coating manufacturers; and to
provide the reader with an understanding of the process of selecting complaint coatings.
17.
L DESCRIPTORS
KEY WORDS ANO DOCUMENT ANALYSIS
b.JOBNTIFISRS/0»SN ENDED TERMS
Miscellaneous K«tal Parts
VOCs
Coatings
18. DISTRIBUTION STATEMENT
Released Public
19. SECURITY CLASS iTilit Atfen)
Unclassified
20. SECURITY CLASS ,-iuJW/t;
Unclassified
e. COSATt Field/Group
21. NO. OF PACES
1C-3
22. PRICE
Form 2220—1 (R«». i-77) Pncviou* BQITIOM
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