United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
EPA456/K-01-001
July 2001
Air
EPA
TECHNICAL BULLETIN
ULTRAVIOLET AND ELECTRON
BEAM (UV/EB) CURED COATINGS,
INKS AND ADHESIVES
C LEAN
A IR
T ECHNOLOGY
C ENTER
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EPA-456/K-01-001
July 2001
ULTRAVIOLET AND ELECTRON BEAM (UV/EB)
CURED COATINGS, INKS AND ADHESIVES
Prepared by
Clean Air Technology Center (MD-12)
Information Transfer and Program Integration Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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DISCLAIMER
This report has been reviewed by the Information Transfer and Program Integration
Division of the Office of Air Quality Planning and Standards, U.S. Environmental Protection
Agency and approved for publication. Approval does not signify that the contents of this report
reflect the views and policies of the U.S. Environmental Protection Agency. Mention of trade
names or commercial products is not intended to constitute endorsement or recommendation for
use. Copies of this report are available form the National Technical Information Service,
U.S. Department of Commerce, 5285 Port Royal Road, Springfield, Virginia 22161, telephone
number (800) 553-6847.
11
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FORWARD
The Clean Air Technology Center (CATC) serves as a resource on all areas of
emerging and existing air pollution prevention and control technologies, and provides public
access to data and information on their use, effectiveness and cost. In addition, the CATC will
provide technical support, including access to EPA's knowledge base, to government agencies
and others, as resources allow, related to the technical and economic feasibility, operation and
maintenance of these technologies.
Public Access and Information Transfer
INTERNET / World Wide Web Home Page
http ://www. epa.gov/ttn/catc/
Communications
CATC Info-Line: (919) 541-0800 (English)
CATC/CICA Info-Line: (919) 541-1800 (Spanish)
FAX: (919) 541-0242
E-Mail: catcmail@epamail.epa.gov
Data Resources
RACT/BACT/LAER Clearinghouse (RBLC)
Query, view and download data you select on
- Source Specific Technology Applications
- Air Pollution Regulatory Requirements
CATC PRODUCTS
download technical reports, cost information and software
Related Programs and Centers
• CICA - U.S.-Mexico Border Information Center on Air Pollution /
Centra de Information sobre Contamination de Aire Para la Frontera
entreEE.UU. Y Mexico
• SBAP - Small Business Assistance Program
• International Technology Transfer Center for Global Greenhouse Gasses
in
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ACKNOWLEDGMENTS
This technical bulletin was made possible through the diligent and persistent efforts of
Lyndon Cox, Senior Environmental Employee with the Clean Air Technology Center (CATC).
Lyndon did an exceptional job identifying information sources, gathering relevant data and putting
this bulletin together. The CATC also appreciates the helpful and timely comments and
cooperation of the following peer reviewers:
Dr. Alexander Ross, RADTECH International North America
Paul Almodovar, Coatings and Consumer Products Group, Emission Standards Division, Office
of Air Quality Planning and Standards, Office of Air and Radiation, U.S. EPA
Rhea Jones, Coatings and Consumer Products Group, Emission Standards Division, Office of Air
Quality Planning and Standards, Office of Air and Radiation, U.S. EPA
Candace Sorrell, Emissions, Monitoring and Analysis Division , Office of Air Quality Planning
and Standards, Office of Air and Radiation, U.S. EPA
Charles Darvin, Emissions Characterization and Prevention Branch, Air Pollution Prevention and
Control Division, National Risk Management Research Laboratory, Office of Research and
Development, U.S. EPA
In addition, the CATC thanks the individuals, companies and institutions who supplied
information on Ultraviolet and electron beam curing technology used to prepare this Technical
Bulletin. Contributors are indicated in the REFERENCES section of this bulletin.
IV
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TABLE OF CONTENTS
TOPIC Page
DISCLAIMER ii
FORWARD iii
ACKNOWLEDGMENTS iv
TABLE OF CONTENTS v
FIGURES viii
TABLES ix
ACRONYMS USED IN THIS REPORT x
INTRODUCTION 1
BACKGROUND 2
PART I: THE BASICS 3
WHAT ARE UV/EB-CURED MATERIALS? 3
Review of Conventional Coatings, Inks and Adhesives 4
UV/EB-Cured vs. Conventional Coatings, Inks and Adhesives 5
WHERE ARE UV/EB-CURED MATERIALS USED? 6
DO UV/EB FORMULATIONS USE CONVENTIONAL RESINS? 9
HOW ARE UV/EB MATERIALS CURED? 10
DO UV/EB-CURED MATERIALS NEED SPECIAL EQUIPMENT? 12
Curing Units 12
Printing and Roller Coating 13
Spray Painting 13
Other Application Techniques 14
PART II: THE DETAILS 15
UV/EB RADIANT ENERGY 15
HOW IS UV/EB RADIANT ENERGY GENERATED? 15
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TABLE OF CONTENTS (continued)
TOPIC Page
UV Sources 15
EB Sources 20
WHAT IS UV/EB IONIZING RADIATION? 22
HOW DEEPLY DOES IONIZING RADIATION PENETRATE? 24
UV Ionizing Radiation 24
EB Ionizing Radiation 24
UV/EB-CURING 26
HOW DO UV/EB COATINGS, INKS AND ADHESIVES FORM? 26
Free Radical Polymerization 27
Cationic Polymerization 28
Crosslinking 28
HOW DO PHOTOINITIATORS WORK? 29
DOES PRODUCTION RATE DEPEND ON COATING THICKNESS? 29
WHY HAS THERE BEEN GROWTH IN 3D CAPABILITIES? 30
HOW IS EXTENT OF CURING MEASURED? 31
IS THERE ANYTHING ELSE THAT AFFECTS CURING? 33
PART III: EMISSIONS, HEALTH AND SAFETY 34
WHAT AIR POLLUTANTS ARE EMITTED FROM UV/EB-CURED
MATERIALS? 34
VOC Emissions 34
Fine Particulate Emissions 35
HAP Emissions 35
Odorous Emissions 36
Ozone and NO, Emissions 36
VI
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TABLE OF CONTENTS (continued)
TOPIC Page
HOW ARE EMISSIONS FROM UV/EB-CURED MATERIALS MEASURED? . 36
WHAT ABOUT WORKER HEALTH AND SAFETY? 37
What Health and Safety Concerns Does UV/EB Radiant Energy Present? ... 37
How Can Workers Be Protected Against UV/EB Ionizing Radiation? 38
What Health and Safety Concerns Do Hazardous Components In
UV/EB-Cured Materials Present? 39
What About Worker Hygiene? 43
COST CONSIDERATIONS 46
ARE UV/EB-CURED MATERIALS MORE EXPENSIVE THAN
CONVENTIONAL COATINGS, INKS AND ADHESIVES? 46
SUMMARY 49
WHAT ARE THE ADVANTAGES OF USING UV/EB-CURED
COATINGS, INKS AND ADHESIVES? 49
WHAT ARE THE DISADVANTAGES OF USING UV/EB-CURED
COATINGS, INKS AND ADHESIVES? 50
CONCLUSIONS so
REFERENCES 51
GLOSSARY OF TERMS 55
APPENDIX A: ULTRAVIOLET AND ELECTRON BEAM RADIATION
VS. RADIOACTIVITY A-l
APPENDIX B: EXAMPLES OF UV/EB COATING AND INK USE B-l
APPENDIX C: EPA METHOD 24: DETERMINATION OF VOLATILE
MATTER CONTENT, WATER CONTENT, DENSITY, VOLUME
SOLIDS, AND WEIGHT SOLIDS OF SURFACE COATINGS ... C-l
vn
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TABLE OF CONTENTS (continued)
TOPIC Page
APPENDIX D DEFINITION OF VOLATILE ORGANIC COMPOUNDS (VOC) D-l
APPENDIX E: HAZARDOUS AIR POLLUTANTS (HAP) E-l
FIGURES
1. General Domains of the Electromagnetic Spectrum from Gamma Radiation to
Television and Frequency Modulated (FM) Wavelengths 5
2. UV Mercury Arc Lamp 16
3. Microwave Excited Bulb with Generator 17
4. UV Light reflectors 18
5. Spectrum of UV from a Mercury Vapor Lamp 19
6. Dichroic Coatings 20
7. Schematic of Electron Gun 21
8 Free Radical Polymerization 27
9. Cationic Polymerization 28
10. An Example of Crosslinking 29
11. Schematic of Optic Fiber 31
12. UV Coatings - Now used for Packaging Chocolates 36
13. Examples of Safety Equipment 45
14. Presses with UV-Curing Units 48
Vlll
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TABLES
1 UV/EB COATING, INK AND ADHESIVE APPLICATIONS 7
2. RADIATION-CURABLE MONOMERS in 1991 10
3. FAMILIES OF RADIATION-CURABLE MONOMERS IN 1999 11
4. PERMISSIBLE EXPOSURE LIMITS OF RADIATION-
CURABLE MATERIAL IN 1991 40
5. PERMISSIBLE EXPOSURE LIMITS (PEL) FOR ORGANIC SOLVENTS 42
IX
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ACRONYMS USED IN THIS REPORT
3D
Three Dimensional
ACGIH American Conference of Government Industrial Hygienists
AFP Association for Finishing Processes (an affiliate of SME)
AIM Architectural, Industrial and Maintenance
ASTM American Society of Testing Materials
C Centigrade
CAS Chemical Abstract Service
CATC Clean Air Technology Center
CD Compact Disk
CERCLA Comprehensive Environmental Response, Compensation and
Liability Act
CFR Code of Federal Regulations
cm Centimeter
cm2 Square Centimeters
cm3 Cubic Centimeters
DVD Digital Video Disk
EB Electron Beam
EPA U.S. Environmental Protection Agency
FDA U.S. Food and Drug Administration
FM Frequency Modulated
fpm Feet per minute
Gy Gray unit of energy absorption, equals one Joule per kilogram
HAP Hazardous Air Pollutants
hr Hour
HVAC Heating, Ventilating and Air Conditioning Equipment
in2 Square Inches
IR Infrared
kg Kilogram
LAER Lowest Achievable Emission Rate
LEL Lower Explosive Limit
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MBTU Millions of British Thermal Units
mm millimeters
MSDS Material Safety Data Sheets
NCS New Chemical Substance
NFPA National Fire Protection Association
nm Nanometers
NTIS National Technical Information Service, U.S. Department of
Commerce
OSHA Occupational Safety and Health Administration
P2 Pollution Prevention
PEL Permissible Exposure Limit
PMN Premanufacturing Notice
R Roentgen
REM Roentgen Equivalents for Mankind
SAMPE Society for Advancement of Material and Process Engineering
SME Society of Manufacturing Engineers
Tg Glass Transition Temperature
TV Television
TWA Time Weighted Average
TSCA Toxic Substance Control Act
UV Ultraviolet
VOC Volatile Organic Compounds
WEELS Workplace Environmental Exposure Levels
Z Atomic Number
XI
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xn
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ULTRAVIOLET AND ELECTRON BEAM (UV/EB)
CURED COATING S, INKS AND ADHESIVES
INTRODUCTION
The use of ultraviolet and electron beam (UV/EB) cured coatings, inks and adhesives has
increased dramatically over the last decade. Currently, this pollution prevention (P2) technique
is used in a wide variety of coating, printing and unique product applications. This Clean Air
Technology Center (CATC) Technical Bulletin provides basic information on UV/EB
technology and how it has advanced since the Control Technology Center (CATC predecessor)
published "Radiation-Curable Coatings" (EPA-600/2-91-035) in 1991.
Increasing numbers of coating and printing facilities are using or considering UV/EB
technology because it is effective and profitable for them to do so. In "Radiation-Cured
Coatings," three reasons were given for this: (1) a 75-90% energy savings; (2) a 50-75% savings
in floor space; and, (3) higher production rates. All three reasons are still valid and the
advantages may be even greater today. UV/EB-curing units are significantly more energy
efficient and compact than thermal drying/curing systems that are used with conventional
coatings, inks and adhesives. Also UV/EB-curing is extremely fast - almost instantaneous to a
few seconds at most. Because UV/EB systems emit only very small amounts of volatile organic
compounds (VOC; see Appendix D) and virtually no hazardous air pollutants (HAP; see
Appendix E), they generally require no add-on air pollution control equipment and are
considered environmentally friendly. In fact, the South Coast Air Quality Management District
in California classifies UV/EB coating and printing applications as "Super Clean Technology"
and has eliminated or minimized air pollution permitting procedures for facilities using this
technology.
UV/EB materials cure almost instantaneously when exposed to UV/EB radiant energy
(i.e., UV/EB radiation). Manufacturers of UV/EB equipment include shielding and safety
interlocks in their equipment that adequately protect workers from exposure to UV/EB radiant
energy. However, much confusion exists concerning worker safety. The term "radiation" has
been applied to many different types of energy sources that individually present significantly
different health and safety issues. For example, the term has been applied to nuclear radiation,
radioactivity, solar radiation, UV radiation, EB radiation, microwave radiation, fluorescent
lamp radiation, computer monitor radiation, television (TV) set radiation, TV and radio
broadcast radiation, and even illumination radiating from incandescent lamps. The unifying
attributes in all of these "radiation" sources are that energy (in some form) is emitted from a
source, propagated radially along a line-of-sight, and absorbed. However, the effects of these
various forms of "radiation" on humans are very different and depend on the type and source of
the energy. Because over-use and misuse of the term "radiation" has and continues to cause
confusion, we will use the term "UV/EB radiant energy" to describe the "radiation" that cures
UV/EB material. See the UV/EB Radiant Energy section of this report for more detailed
1
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information on that topic. Additional information can be found in Appendix A, Ultraviolet and
Electron Beam Radiation vs. Radioactivity.
When we refer to UV/EB material in this Technical Bulletin we are speaking of UV/EB-cured
coatings, paints, inks, adhesives, and similar products in general. We use the name of the
specific type of material (e.g., coating, ink, etc.) when information pertains to only that
material. Trade-names are not used because they are not descriptive of the chemistry of the
materials involved and might be misconstrued as a recommendation.
To fully understand and appreciate UV/EB technology and its advantages we need to consider
organic chemistry, physics, engineering, manufacturing processes and cost accounting. This
Technical Bulletin tries to bring all of these perspectives together.
BACKGROUND
Use of radiant energy cured coatings dates back at least 4,000 years. Ancient Egyptians used a
type of UV coating that cured when exposed to sunlight in preparing mummies (AFP/SME,
1986)30 Also, an asphalt-based oil coating that polymerized upon exposure to solar radiation
was used by ancient Egyptians as a sealant for ships (Decker, 1987).30
In the modern era, scientific interest in developing UV/EB-cured systems began in the 1940's.
At that time, the first patent was granted for an unsaturated polyester styrene printing ink that
polymerized under UV exposure. One of the first attempts at applying UV/EB-cured systems to
manufacturing was made in the late 1960's, but successful commercial application did not evolve
until the early 1970's. The publicized driving forces behind development of commercially viable
systems were the energy crisis of 1974 and growing environmental concerns about VOC
emissions resulting from conventional thermal-cure systems. However, the primary motivations
for use of UV/EB-cured systems were and still are improved product performance and increased
productivity.
Early applications of UV/EB-cured systems were limited to flat sheets, mainly in the wood
products and printing industries. Radiant energy cured processes of that time were limited by
the need for a line-of-sight energy source. Starting in 1974, UV-curable inks and varnishes
were used for decorating aluminum beverage cans. Improvements in plant engineering, such as
rotating conveyors, multiple UV sources and adjustments to curing equipment, have allowed
three-dimensional (3D) applications of UV/EB-cured materials. In addition, advances in
polymer science have provided a wide variety of UV/EB-cured materials that can exhibit
characteristics required by the end-user in specific applications.
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PART I: THE BASICS
This section summarizes basic information on UV/EB materials, including their use and
application. A more comprehensive discussion of important technical, safety and regulatory
issues is presented in "PART II: THE DETAILS" section of this report. A number of terms are
introduced that may not be familiar to you. To help you, a glossary of terms is provided at the
end of this report. Terms included in the glossary are in BOLD print within the body of the
report. Acronyms also are used for many terms or complex names. A list of acronyms is
provided at the front of this report, immediately after the table of contents.
WHAT ARE UV/EB-CURED MATERIALS?
UV and EB materials cure (polymerize) when exposed to UV and EB radiant energy,
respectively. Virtually all components of a UV/EB formulation become a solid part of a cured
coating, ink or adhesive. Generally, only small amounts of VOC may be emitted. For UV/EB
materials, curing means the interaction of liquid molecules (monomers, oligomers and
photoinitiators) to form polymers. This curing process is known as polymerization. It forms
long molecular chains that are the carbon backbone for a polymer molecule. After
polymerization the UV/EB-cured material is a solid, consisting of pigments and polymer
molecules that may be tangled together and interconnected by crosslinks.
Conventional VOC/solvent borne and waterborne coatings, inks and adhesives use thermal
energy to evaporate volatile components (i.e., organic solvent/VOC and/or water) and to cure.
As a result, most of the volatiles in a conventional coating, ink or adhesive are emitted to either
a control device or the atmosphere. Only the remaining non-volatile part in a conventional
material actually cures to form a final coating, printing or adhesive that remains on a substrate.
Some degree of polymerization may take place in the cure of a conventional material. The
amount of polymerization that occurs during the cure of a conventional material (as opposed to
polymerization/prepolymer formation that occurs during the paint/ink/adhesive manufacturing
process) varies depending on the type of material. For example, virtually no polymerization
occurs when curing a conventional lacquer; however, polymerization would be a critical
process when curing a conventional urethane, epoxy, or acrylic.
Since you are probably more familiar with conventional coatings, inks and adhesives and how
they are used, it may be helpful to compare UV/EB materials to conventional materials. So, we
will spend a little time here reviewing how conventional coating, ink and adhesive systems
work before elaborating on UV/EB coatings, inks and adhesives.
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Review of Conventional Coatings, Inks and Adhesives
Conventional oil/solvent based and waterborne coatings, inks and adhesives are evaporative
systems. They use suitable partially pre-polymerized monomers (alkyd, acrylic, epoxy, silicone,
etc.) and pigments dispersed in a solvent. These pre-polymers must further polymerize and
cross-link during the cure to become solids.
Conventional pre-polymers are formed by a chemical condensation reaction at elevated
temperatures. This reaction occurs at a chemical plant or coating, ink or adhesive
manufacturing facility, and not during the cure. Just before the rjre-polymer gets long enough to
form a gel, the temperature is reduced and the pre-polymer is dispersed in either an organic
solvent or water. The organic solvent is usually VOC and often accounts for more than half of
the volume of liquid coating. Water accounts for a similar fraction of the volume of water-
based coatings. Some conventional coatings even contain HAP.
When conventional materials are applied and the organic solvent or water evaporates, pre-
polymerized resin molecules are able to contact each other. Solidification of the coating occurs
as the pre-polymer further proceeds in its polymerization by a chemical reaction. This is a
relatively slow process because the temperature is now much lower than it was in pre-
polymerization and, in fact, it is a process that never ends. You may have observed that
conventional paints thicken in storage (even without evaporation), change their surface finish
and shrink over a period of years.
For lacquers, solvent can be much more than half of the final volume of coating as applied.
Lacquers simply solidify upon evaporation of the solvent. They are more fully polymerized
during their manufacture then other conventional coatings and no further polymerization is
needed when they are applied. However, there is no crosslinking and they melt or mar easily.
They shrink from loss of solvent and not because of further polymerization.
Conventional materials must be applied with sufficient air flow (ventilation) to keep the solvent
concentration in air below a quarter of the Lower Explosive Limit (LEL). This is required by
the National Fire Protection Association (NFPA) and the Occupational Safety and Health
Administration (OSHA). For spray applications, air flow of either 100 feet per minute (fpm) or
60 fpm (for electrostatic deposition) through the area in which vapors are generated is required.
In addition to explosion/fire safety issues, there also are health effects issues for humans that
breathe solvent vapors.
Conventional materials use infrared (IR) radiant energy (i.e., heat) to cure. IR energy is
emitted naturally from everything. It is electromagnetic radiation with a wavelength between
1000 nm and 11,000 nm. Visible light is electromagnetic radiation with wavelengths from 400
nm to 700 nm. Microwaves are electromagnetic radiation with wavelengths in meters (See
Figure 1). IR energy is sensed as radiant heat and its wavelength is based upon temperature.
Heat is used to evaporate organic solvent or water and to accelerate polymerization.
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At ambient temperatures, evaporation and polymerization can take from hours to days. Thermal
ovens can reduce evaporation and polymerization time to minutes. However, thermal ovens are
bulky, take up considerable floor space, and consume large amounts of energy because they
must heat the air flow through the oven, in addition to heating the coating, ink, or adhesive and
substrate.
THE ELECTROMAGNETIC SPECTRUM
x-ray visible microwave
gamma ultraviolet infrared TV/FM
I i . i i i H
-12 -10 -8-6-4_2 0
wavelength meters
Figure 1: General Domains of the Electromagnetic Spectrum from Gamma
Radiation to Television and Frequency Modulated (FM) Wavelengths
UV/EB-Cured vs. Conventional Coatings, Inks and Adhesives
UV/EB materials consist of pigments and the same monomers and oligomers that react to form
polymers in conventional coatings, but without being subjected to pre-polymerization.
Oligomers are created by joining about 3 to 5 monomer molecules, but this is not to be
confused with pre-polymerization. Acrylic groups or vinyl ether groups are reacted with
monomer and/or oligomer molecules in a UV/EB material, and become side-branching or
pendant groups to the carbon backbone. These are referred to as functional groups because
they are more reactive and, therefore, require less increase in energy to polymerize monomers
and oligomers. In addition, they are used to achieve desired properties and crosslinking
between polymer chains.
Polymerization is actually a chain reaction, in which monomers or oligomers are added to a
backbone of carbon atoms. Each monomer or oligomer molecule is added as another link in the
chain, or as another vertebra in the carbon backbone. A polymer chain can be thousands of
monomer or oligomer molecules in length.
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For UV/EB materials, polymerization actually is initiated by a compound included in the
formulation called a photoinitiator. A photoinitiator absorbs UV/EB radiant energy and
either forms free radicals or cations and anions. Until a photoinitiator receives UV/EB
radiant energy, a UV/EB-cured material does not have enough energy to initiate and complete
polymerization. Upon absorbing the UV/EB energy, photoinitiator molecules have enough
energy to split into either free radicals or cations and anions. These free radicals and cations
are energetic enough to create a polymer from monomers and oligomers.
Free radicals produce a very fast reaction that occurs almost immediately and, for all practical
purposes, reaches completion. This results in a finished (cured) coating, ink or adhesive that is
almost completely polymerized and nearly ceases to polymerize further. Only trace quantities of
monomers, oligomers and photoinitiators remain trapped within the polymer after a free
radical reaction. These trace quantities may react with each other over time as they diffuse
through the polymer. However, this occurs very slowly.
When cations (Bronsted or Lewis acids) are formed, they generate more ions by spontaneously
breaking other photoinitiator molecules. These cations also initiate polymerization that can
spread, even in the absence of UV/EB radiant energy, after a UV/EB-cured material has
received enough radiant energy to start polymerization. These cationic photoinitiators cause
polymerization to occur somewhat more slowly; i.e., polymerization occurs in seconds. On
the other hand, being a chemical process, cationic polymerization can be completed in the dark
(without UV/EB radiant energy) once it has started.
In 1991, UV/EB materials used volatile components, but these are no longer needed or used.
UV/EB materials rarely use solvents. The only exception is to reduce viscosity and allow
application of a thinner coat (usually with adhesives) or to facilitate spray coating. Even when
a solvent is used with a UV/EB material, the amount of solvent and, therefore, the amount of
VOC emissions are generally much less than from conventional materials. In the typical case
where no solvent is used, only cure volatiles between 1-10% of the applied film weight might be
emitted. Usually cure volatiles are less than 5%. At this level, uncontrolled emissions are no
worse than that of a conventional operation equipped with very good emission capture and
control technology. However, no control technology is either needed or used with UV/EB
materials.
WHERE ARE UV/EB-CURED MATERIALS USED?
UV/EB coatings, inks and adhesives are used in a variety of applications such as printing inks,
overprint varnishes, release coatings, primers, pigmented paints, clear topcoats, bonding
coatings for magnetic tape, bonding for abrasives, encapsulates, pressure sensitive adhesives,
and permanent bond adhesives.5 The list of applications keeps growing; therefore, any static
list of applications should not be expected to be complete. However, in order to appreciate the
extent to which UV/EB technology is being applied, a list of UV/EB applications compiled from
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Envirosense 14 and the RadTech UV/EB-Curing Primer23 is provided in Table 1. Examples of
UV/EB material applications can also be found in Appendix B.
TABLE 1: UV/EB COATING, INK AND ADHESIVE APPLICATIONS
INDUSTRY
APPLICATION
AIM Coatings
(Architectural / Industrial /
Maintenance coatings
applied to protect from
corrosive environment)
metal and concrete structures
pipes
tanks
processing equipment
Aircraft
primers
color coats
topcoats
Automotive Parts
underbody paints
primers
color coats
topcoats
refinishing
Coil Coating
Applied to coiled sheet metal that is used in:
household appliance industries
transportation industries
construction industries
container industries
Dental
fillings
Electronics
microelectronics photomasks
solder masks
notations on circuit board
encapsulation of circuits or components
optical fiber coatings
compact disks (CDs)
digital video disks (DVD's)
Flexible Plastics
decals
decorative laminates
shrink film
magnetic recording media
abrasive films
release films
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TABLE 1: UV/EB COATING, INK AND ADHESIVE APPLICATIONS
INDUSTRY
APPLICATION
Highway
coatings used to mark lanes
coatings used to provide directional arrows on roadway
Leather
finishes
topcoats
Machinery and Equipment
farm equipment
construction equipment
electrical machinery
heating, ventilating, and air conditioning systems (HVAC)
industrial machinery
computers
office equipment
Marine
ships
offshore platforms
other steel and aluminum structures
Metal containers
beverage cans
lids and closures
food cans
Optics
eyeglass lenses
optical fibers
Paper and Paperboard
record albums
folding cartons
juice cartons
magazines
paperback books
business forms
bank notes and money
release paper
abrasive coated paper
Rigid Plastics
vinyl floor covering and tiles
bottles
credit cards
sports equipment
medical equipment
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TABLE 1 : UV/EB COATING, INK AND ADHESIVE APPLICATIONS
INDUSTRY
Textiles
Wire
Wood Furniture
Wood Products
APPLICATION
sizing
fill coats
topcoats
magnet wire
furniture
kitchen cabinets
doors
trim
moldings
hardboard panels
plywood panels
particle board panels
hardwood flooring
door laminates
DO UV/EB FORMULATIONS USE CONVENTIONAL RESINS?
All coatings, inks and adhesives (i.e., solvent borne, waterborne, or UV/EB-cured), regardless
of curing method, use basically the same resins. However, the resins used with UV/EB-cured
material have been modified by including functional groups and photoinitiators that trigger
polymerization. For UV/EB materials, different performance properties have been gained by
using acrylics, methacrylates, epoxies, polyesters, polyols, glycols, silicones, urethanes, vinyl
ethers, and combinations of these. Structurally different monomers or oligomers may be
blended together to adjust properties of a final polymer. The composition of a formulation is
usually considered proprietary and, therefore, is usually referred to by a trademarked name
which does not normally reveal its composition. Table 2 shows monomers and oligomers that
were available in 1991. Either acrylic or vinyl ether functional groups are included in these
monomers to enable them to be cured by UV/EB radiant energy.
The list of monomers and oligomers has grown to be quite large in 1999. See Table 3. This
listing is by generic types. Actual formulations are composed of these types of compounds in a
proprietary mix. The mix will be identified by a trademarked name that will give no clues as to
constituents.
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Table 2. RADIATION-CURABLE MONOMERS IN 1991
30
SYSTEM
Polyester/
styrene
Acrylates
Thiol-polyene
Cationic
Epoxies
REACTIVITY
Low
High
High
Medium
OXYGEN
INHIBITION
High
High
Low
Low
DURABILITY
Poor
Moderate
High
Fair
EB
CURABLE
No
Yes
Yes
No
UV
CURABLE
Yes
Yes
Yes
Yes
Source: Decker, C. "UV-Curing Chemistry: Past, Present, and Future", J. of Coatings Tech., 1987
Vrancken, A. "Market Trends for Irradiation Curable Coatings in Europe", Radiation Curing V,
Association of Finishing Processes of SME, Boston, 1980
HOWAREUV/EB MATERIALS CURED?
TJV7EB materials cure (change from a liquid to a solid) by a reaction that involves both
polymerization and crosslinking. UV-cured materials need UV radiant energy to polymerize
monomers and oligomers into a solid. EB-cured materials need EB radiant energy to
polymerize monomers and oligomers into a solid. There are many polymerization
mechanisms; however, currently only two polymerization mechanisms are used for curing
UV/EB materials: free radical polymerization and cationic polymerization. A free radical
cured UV material must be either very thin, clear, or both in order to let sufficient amounts of
UV radiant energy to (del) penetrate all the way through the material. A free radical cured EB
material can be filled, pigmented and thicker because EB penetrates more than UV. Cationic
photoinitiators, after UV/EB exposure, spontaneously form cations that trigger further cationic
polymerization. Once the cationic polymerization has been started, cationic reactions can
carry polymerization to completion in thicker, opaque materials, or even in the dark (i.e. after
radiant energy exposure stops).
In free radical polymerization, a monomer or oligomer joins with a free radical and, in
effect, forms a larger free radical. This larger free radical then acts upon another monomer or
oligomer and forms an even larger molecule, and so on. The process is a chain reaction (another
term used by chemists and physicists to mean a continuing reaction), that is endless until a
polymer molecule is terminated. Termination occurs when one polymer chain runs into the end
of another polymer chain, an oxygen atom reacts with the end of a chain, or a polymerization
becomes so nearly complete that further reactants are not available.
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Table 3. FAMILIES OF RADIATION-CURABLE MONOMERS IN 1999
Acrylated Aliphatic Oligomers
Acrylated Aromatic Oligomers
Acrylated Epoxy Monomers
Acrylated Epoxy Oligomers
Aliphatic Epoxy Acrylates
Aliphatic Urethane Acrylates
Aliphatic Urethane Methacrylates
Allyl Methacrylate
Amine-modified Oligoether Acrylates
Amine-modified Polyether Acrylates
Aromatic Acid Acrylate
Aromatic Epoxy Acrylates
Aromatic Urethane Methacrylates
Butylene Glycol Acrylate
Silanes
Silicones
Stearyl Acrylate
Cycloaliphatic Epoxides
Cyclohexyl Methacrylate
Ethylene Glycol Dimethacrylate
Epoxy Methacrylates
Epoxy Soy Bean Acrylates
Glycidyl Methacrylate
Hexanediol Dimethacrylate
Isodecyl Acrylate
Isooctyl Acrylate
Oligoether Acrylates,
Polybutadiene Diacrylate
Polyester Acrylate Monomers
Polyester Acrylate Oligomers
Polyethylene Glycol Dimethacrylate
Stearyl Methacrylate
Triethylene Glycol Diacetate
Vinyl Ethers
Note: These monomers/oligomers were cataloged in 1999. These can be blended to achieve desired properties. These can
be combined with any of a similar number of types of photoinitiators. The photoinitiators tend to be aromatic molecules
that are more sensitive to UV or EB than the monomers and oligomers are.
Cationic polymerization is an ionic process that is not inhibited by oxygen and, therefore, can
cure in air without a nitrogen blanket. Cationic polymerization will continue after exposure
to UV/EB radiant energy source ceases. Therefore, the only concerns are to initiate cationic
polymerization and to store the product for a few seconds to allow for the cure to complete.
UV/EB monomer and an oligomer molecules have functional groups that attach to the side of
a carbon chain. These also are referred to as pendant groups. Pendant groups aid in reducing
the energy that must be added to polymerize and to form crosslinks. Crosslinks interconnect
carbon chains and, as a result, provide greater mechanical strength, resistance to abrasion, higher
softening temperatures, and increased mar resistance.
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Polymerization and crosslinking are the critical processes that take place as a UV/EB material
cures. Free radical curing is very fast and may reach completion in a millisecond or less.
Cationic curing is slower and may take a few seconds to reach completion. Fortunately, cations
are more stable than free radicals and endure much longer.
Monomer and oligomer molecules are initially short enough to be mobile and, therefore, are in
a liquid state. As polymerization progresses, polymer chains grow in length, become less
mobile, and form a gel. In the gel state, a polymer solidifies, but has no significant mechanical
strength. As polymerization continues, crosslinking occurs and the polymer gains mechanical
strength. A material is fully cured when polymerization and crosslinking processes are
virtually completed.
DO UV/EB-CURED MATERIALS NEED SPECIAL EQUIPMENT?
For the most part, the same equipment that is used to apply conventional coatings, inks and
adhesives can be used to apply UV/EB-cured materials, although they may be adjusted
differently. The only major difference is how these materials are cured.
Curing Units
UV-curing units contain one or more UV lamps, a reflector for each lamp, a means of
dissipating heat from the lamps (which may be ventilating air flow), and shielding to protect
people from exposure to UV. All UV-curing unit manufacturers now include shielding as an
integral part of a curing unit.
An EB-curing unit contains an electron beam generator and shielding to attenuate x-rays that
are generated during the curing process. An EB-curing unit is heavier and larger than a UV-
curing unit because it has more massive shielding to absorb x-rays. All EB-curing unit
manufacturers include such shielding as an integral part of a curing unit.
For both UV/EB-curing units, production rates are determined by the composition and applied
thickness of the UV/EB-cured material, intensity of radiant energy in the curing unit, and
amount of radiance that is absorbed. UV/EB materials cure almost instantaneously to within a
few seconds when exposed to the appropriate radiant energy. Compared to thermal dryers used
with conventional coating, ink and adhesive applications, UV/EB-curing units provide for a 75-
90% savings in energy, 50-75% savings in floor space, and higher production rates.
By_contrast, for conventional coating, ink and adhesive applications, a thermal oven is used to
flash off organic solvent or water and to harden/cure the applied material enough for handling.
The oven is insulated to minimize heat loss (other than to the air flow that passes through it).
Air flow through a thermal oven must assure that the concentration of organic solvent does not
exceed one fourth of the LEL. Production rates are determined by the composition and applied
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thickness of the conventional material, path length through the thermal oven, temperature, and
air flow. Oven temperature, air flow, oven size, and production rate are inter-related factors in
conventional processes. The temperature must be high enough to evaporate the solvent or water
and to harden the coating enough for handling, but must not damage the substrate or the
coating. Air flow must remove and dilute solvent vapors to prevent excess concentrations from
occurring. The size of the oven is based upon the time required to dry, harden, and/or cure a
conventional coating, ink or adhesive at the desired production rate.
Printing and Roller Coating
Although printing presses and roller coaters that use UV/EB materials may differ in detail, they
are essentially the same as those that use conventional materials. The differences are mainly due
to the location, size and speed of the curing unit. For printing, UV/EB-curing units are often
mounted on a printing press after the application of each color. For roll-coating, the UV-curing
unit is a chamber with UV lamps arrayed to give the desired cure.
Rollers and print transfer surfaces for UV/EB material applications can be identical to those used
for conventional coatings, inks and adhesives. UV/EB material losses only occur when colors
are changed, mist is emitted, or a roller must be cleaned. If a roller and its pan are covered to
prevent UV/EB radiant energy from reaching them, a UV/EB coating will not cure on or in
them. As a result, a roller and pan used with UV/EB materials can be left for over a weekend
and used again without cleaning. This can minimize both the loss of UV/EB material, as a result
of cleaning and use of cleaning solvents that might be VOC.
Spray Painting
For spray coating, the same spray paint guns and related equipment used for conventional
coatings can be used for UV/EB coatings. Techniques for spraying viscous UV/EB paints
include: increased pressure to drive paint through spray gun nozzles; dilution with organic
solvent (VOC); dilution with water; or, some combination of heated spray paint guns and these
techniques. Viscosity in new UV/EB spray paints has been reduced, but still is higher than that
typically used for conventional paint spraying. Reactive diluents (i.e., diluents that become
part of the cured coating) reduce viscosity and are less toxic and volatile then they once were.
However, because UV/EB paints tend to be more viscous, heated spray guns may be needed to
bring UV/EB paint viscosity close to that of conventional paints. New UV/EB coatings
significantly reduce or eliminate coating decomposition, fumes, and/or smoke aerosol problems
experienced in the past when using heated spray guns. If used, organic solvents must be flashed
off before the UV/EB cure, and generally increase VOC emissions that may need to be
controlled by add-on emission control technology. Water can successfully lower viscosity of
some UV/EB-cured coatings without introducing VOC.40 However, when either an organic
solvent or water is used to adjust viscosity, additional drying time, space and energy is required.
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The same paint spray booth used to apply conventional coatings can be used for UV/EB
applications. A paint spray booth where conventional coatings are applied must have positive
air flow through it to avoid accumulation of combustible or explosive vapors, and to carry VOC
and overspray away from workers. Because UV/EB paints contain little or no VOC (unless
VOC is used to adjust viscosity), overspray is the primary concern in UV/EB applications. As a
result, if VOC is not present, less airflow may be needed. Overspray in a UV/EB application is
carried to an overspray arrester (a kind of air filter) to protect workers. Overspray collected
from an arrester can be reused because UV/EB coatings retain their fluidity and do not dry out.
However, if solvent was added to adjust viscosity, addition of solvent may be required before
reuse of captured overspray.
Transfer efficiency for a particular spray application technique is about the same for both
conventional and UV/EB coatings. However, collection and reuse of UV/EB overspray can
improve the overall effectiveness of a coating operation; that is, the ratio of coating solids
applied on a substrate to the total amount of coating solids consumed improves because reusing
the UV/EB coating overspray reduces overall coating consumption. For example, when
transfer efficiency is about 50%, the overall effectiveness of a coating operation may improve
to about 95% with UV/EB coatings by using an arrester that captures 90% of the overspray and
reuse of that overspray. Similarly, electrostatic spray guns normally have a 90% transfer
efficiency, but the overall effectiveness of a coating operation using electrostatic spray guns can
be about 99% for UV/EB coatings when the Overspray is captured and reused.
Other Application Techniques
High speed spinners are used to apply UV/EB coatings in microelectronics. A photoresist
coating is applied to the center of a substrate, that is then spun to leave only a thin coat on the
substrate. The UV/EB photoresist coating may contain a solvent or be heated to reduce
viscosity, if necessary to control coating thickness. (Note: Conventional photoresist contains a
solvent that must evaporate to allow this thin film.) The UV/EB coating is then cured in
selected areas by exposure to radiant energy. The uncured areas are then washed away by
solvent to expose uncured areas to etching, doping to change the electronic properties, oxidation
to form insulators, or deposition of metal to form conductors. The coating is then stripped off
and another coating applied for the next step in the process.
Flow or curtain coating is used with objects that move through a flowing curtain of coating
(similar to a waterfall). This technique is used to advantage with UV/EB coatings because they
lack volatile ingredients. Volatile ingredients in conventional coatings would require
replacement to compensate for evaporation from the flowing curtain.
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PART II: THE DETAILS
Now that you have a basic understanding of UV/EB coatings, inks and adhesives and how they
differ from conventional solvent borne and waterborne systems, you probably have some
insightful questions. In this section we attempt to answer those questions and provide details on
UV/EB technology and its application.
UV/EB RADIANT ENERGY
In this section UV/EB radiant energy is discussed in detail. Topics cover UV/EB radiant
energy sources, UV/EB ionizing radiation and UV/EB radiation penetration. As previously
noted, there has been a lot of confusion about the term radiation and we have tried to use the
term UV/EB radiant energy to avoid this confusion. However, as we discuss certain topics the
term radiation will be used. As you read these sections, keep in mind that UV/EB radiation
and radioactivity are not the same, and should not be confused. The only connection between
UV/EB radiation and radioactivity is purely linguistic (i.e., both radiation and radioactivity
use the root radi- to describe radial propagation of energy by particles and electromagnetic
waves from a source). Refer to Appendix A, Ultraviolet and Electron Beam Radiation vs.
Radioactivity, for additional information.
UV radiant energy does not penetrate the skin, but can cause sunburn and tanning of the top
layer of skin - just like sunlight. UV radiation from curing units can be much more intense than
that from sunlight and can burn or tan the skin quicker. When UV sources are properly shielded,
eye irritation, skin tanning and sunburn do not occur. EB produces x-rays as high velocity
electrons change speed and are absorbed by air, an EB coating, ink, or adhesive, the substrate,
or an absorbing part of a printing press or coating apparatus. X-rays can and do penetrate
human tissue, but proper shielding of EB-curing units reduces this hazard to below background
levels.
HOW IS UV/EB RADIANT ENERGY GENERATED?
Sources of UV and EB radiant energy are quite different. Therefore, each will be discussed
independently. In general, UV radiant energy sources have evolved for continuous and discrete
flat (2 dimensional) and 3D production, but EB has remained largely a continuous flat process
with only a few instances of use for discrete 3D production.
UV Sources
UV radiant energy is often generated by electric arcs in medium-pressure (about two
atmospheres) mercury vapor arc lamps, as shown in Figure 2. These lamps are generally made
of quartz formed into a long cylindrical tube to provide uniform illumination over the width of
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the web. The lamps also contain a gas, such as argon, that aids in ionizing mercury. When a
startup arc is operating, the mercury in the lamp has not yet fully vaporized and, for several
minutes, both the spectrum and intensity of radiation are changing. In addition, mercury vapor
arc bulbs have a very nonlinear current versus voltage characteristic. As a result, they require a
ballast - similar to fluorescent lamps, but at higher power. Various designs of these ballasts have
had their performance evaluated. There is truly no single answer for all applications, but ballast
selection is based on a tradeoff of cost, size, noise, and power.42 The length of the cylindrical
quartz tube with electrodes limits the width of the web that can be used. For mercury arc
lamps, this has a practical limit of about 5 feet.
1/2" DIA
13/16 OlA APPROX
5/16 DIA
Figure 2: UV Mercury Arc Lamp
Microwave excited bulbs, another source of UV radiation, are filled with mercury vapor and an
easily ionized starter gas such as argon or xenon (See Figure 3). Light is produced by a plasma
which is generated by microwave radiation and, as a result, these bulbs do not have electrodes
penetrating the quartz envelope. Because these electrodes are absent, microwave excited lamps
are not subject to leakage or breakage around such electrodes. Consequently, microwave excited
lamps tend to last much longer than arc lamps. Because space is not required for electrodes,
microwave excited bulbs can achieve cures on very wide webs (up to six meters or 20 feet) and
conceivably more. Microwave excited lamps can be shaped to give more uniform 3D curing and
are not constrained to a long cylindrical geometry. Therefore, they can assume any shape that
the optical designers have in mind and that lamp manufacturers can make. Microwave excited
lamps may be used intermittently because they start up nearly immediately. They also can be
operated continuously.
Recently, lamps have been developed which operate without elevated temperatures, are instant-
on, and produce a line spectrum in the near-UV which does not generate ozone.32
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MAGNETRON
WAVEGUIDE
ANTENNA
REFLECTOR
MAGNETRON
COOLING FINS
COOLING
HOLES
BULB
/
SCREEN
REFLECTOR
Figure 3: Microwave Excited Bulb with Generator
There are also xenon or argon arc lamps which use excimers to generate UV. These generate a
thermal plasma in xenon or argon gas which then excites an excimer. It appears that pulsed high
intensity radiance from these lamps can penetrate even better than a steady lower intensity
radiance from mercury vapor lamps. These arc lamps can be pulsed repetitively (strobed) to
give essentially continuous curing, or can be used for UV radiation which is required only
intermittently at a point (such as with hand-held sources). The rate and number of flashes can be
adjusted to give a required dose for curing. Hand-held UV point sources use much less power,
use a mirror to focus energy, and can use a wand or optical fiber to direct energy. Hand held
sources are used to splice optical fibers, bond lenses, bond items to printed circuit boards,
encapsulate small electronic components, or even bond artwork. These compact hand-held
sources produce less heat and consume less power with greater UV penetration than either
mercury arc lamps or microwave excited mercury vapor lamps.
Addition of excimers to mercury vapor arc lamps, microwave excited lamps, or argon or xenon
filed arc lamps can generate more radiant output in selected near-UV or actinic portions of the
spectrum. For example, a Fusion UV Systems "D" filled bulb has an excimer that can produce a
broad spectrum with peak intensity at 370-380 nm. Excimers are excited dimers. These
molecules get excited, separate, and recombine while releasing energy in a given and sometimes
narrow band of wavelengths. Excimers can emit shorter wavelengths than that of photons used
to excite them. This happens because more than one photon can excite a dimer molecule to
cause it to separate, but only one photon is emitted when the molecule recombines. The
excimer is not consumed in this process. By comparison, the phenomenon of fluorescence
always produces longer wavelengths than that of an absorbed photon. Fluorescence is caused
by a molecule absorbing a photon and reradiating the energy at a defined longer wavelength.
Whenever mercury vapor or excimers are used, bulbs that have reached their end of life should
be disposed of properly. This may require crushing lamps to recover mercury, recycling of
quartz, capture of any excimers that may be hazardous pollutants, and recovery of electrodes.
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A lamp is often backed by a semi-elliptical mirror to focus radiation and obtain the highest
intensity (See Figure 4). An ellipse has two foci. By placing a source at one focus, the image of
that source appears at the other focus. The reflected UV radiation is focused to achieve as
much intensity as possible because both wavelength and intensity play a role in curing. Intensity
is the energy flow or rate at which photons are being absorbed. More than one photon can be
absorbed by a molecule and the absorbed photon energies are available for ionization. This
allows other longer (del) wavelengths to play a part in curing too.
Ultraviolet Light Reflectors
Elliptical Parabolic
Figure 4: UV Light Reflectors
Lamps also can be backed by parabolic reflectors. As shown in Figure 4, parabolic reflectors
have only one focus that sends light from the focus as parallel rays away from the reflector. A
wide variety of dimpled reflectors and diffusing surfaces also are used where a sharp focus and
high intensity are not needed. All types of reflectors are used, but for different types of cures.
More than one UV lamp may be required in a UV-curing unit. The dose that objects (e.g., web
in printing, or furniture in a 3D cure) receive from UV lamps is determined by the power of the
lamps, intensity of radiation, absorption of radiation through an ink, coating, or adhesive,
absorption of the UV radiant energy spectrum by the photoinitiator, and the speed that objects
flow through UV radiant energy in a curing unit. In printing and web coating, web speed (rate
at which a substrate passes through a curing unit) determines production rate. Production rates
with UV-curing have been increasing as lamps become more efficient and powerful and as
advances in UV-cured material chemistry have enhanced polymerization.
The UV radiant energy source must be selected to match the absorption requirements of the
photoinitiator that the lamps are to activate. The source must also provide UV radiant energy
over the entire surface of the applied film, given the configuration of the product. Therefore,
the intensity of UV radiant energy must penetrate well enough to cure a UV ink, coating or
adhesive all the way through; the UV material must cure with the chosen photoinitiator; and,
the UV radiant energy source must be compatible with the photoinitiator and the shape of the
substrate. For all UV lamps, a large portion of their spectrum (See Figure 5) fails to match the
absorption of either the UV-cured material or the photoinitiator that is being used. Lamps and
excimers are selected on the basis that their output peaks at the wavelength of maximum
absorption of the photoinitiator. Lamps and excimers should be selected on the basis of their
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output of an emitted energy intensity peak that the photoinitiator absorbs, because the
photoinitiator is used to gain sensitivity and minimize the UV radiant energy dose required for
curing. When energy consumption must be addressed, the photoinitiator must be a concern.
Figure 5: Spectrum of UV From a Mercury Vapor Lamp
(having no excimer)
UV is generally transmitted a short distance (up to 25-50 cm or 10-20 inches) through air or a
nitrogen atmosphere to minimize ozone formation. Because air and nitrogen are essentially
transparent to UV, and aerosol particles that would cause UV scattering are sparse, this distance
is not critical. Direct ozone and NO2 generation is not a problem if an oxygen-free nitrogen
blanket, an ozone-free lamp, or a quartz filter is used. Ozone-free mercury bulbs are made of a
type of quartz that strongly absorbs energy below 260 nm in wavelength.
Mercury vapor arc lamps can take several minutes to warm up. A shutter is usually provided to
protect the web and prevent fires during warm up. If there is no shutter, a printing or coating
line is kept running to prevent the web from melting or catching fire while the lamps warm up.
A substrate or web that passes through a press or coater during bulb warmup becomes solid
waste with uncured UV ink or coating on it. This can be hazardous solid waste because the UV
ink and/or coating is not cured. It can be converted to solid non-hazardous waste simply by
exposing it to enough sunlight. A shutter that remains closed also can protect a stationary web
until mercury vapor arc lamps are warmed up and minimizes such waste.
Both mercury vapor arc lamps and microwave excited lamps normally operate at about 800°C.
IR radiant energy from each is proportional to their surface areas. Mercury vapor arc lamps
have over twice the surface area for the same UV radiance and, therefore, over twice the IR
radiant energy compared to microwave excited lamps. As a result, mercury vapor arc lamps
will cause a greater temperature rise in a substrate for the same UV dose.
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To prevent web damage from heat (highly focused IR radiant energy) and a fire hazard when a
web breaks or stops, UV-curing devices are usually equipped with one of the following:
(1) deionized water in tubes to absorb IR radiant energy; (2) a dichroic optical system (See
Figure 6) (3) a shutter that automatically closes when the web stops; or (4) a cold light source.
In option (1), flowing de-ionized water transmits UV while absorbing the IR. A dichroic optical
system (2) uses coatings on the reflector that transmit UV with much lower interference losses
than they do for IR radiant energy and, therefore, reduce incidental IR reaching the web. A
properly ventilated shutter (3) absorbs all radiation while the web is moving too slowly. In
option (4), the light source lacks any IR that would ignite a web.
Wf-
DtotecWc
Sodas
Transparent
Substrata
IR TRANSMITTING
DICHROIC REFLECTOR
Dielectric Series
Abaoebing Layer
Thermally Conductive
Substrate
IR ABSORBING
DICHROIC REFLECTOR
Figure 6: Dichroic Coatings
EB Sources
Electron guns are used to generate electron beams in a manner similar to a TV picture tube.
These beams can be deflected, just like a beam that forms a raster on a TV screen or computer
monitor. A beam from these electron guns can be focused magnetically to create a small spot
that moves rapidly. Electron beams also may be generated by linear filaments and cathodes
that are then directed by electrostatic electrodes to form their image on a substrate, as in Figure
7. Multiple filaments or cathodes can be used when higher currents for higher production speeds
are required.
An EB is capable of curing printing ink within a very short length of curing unit (excluding
those parts required for shielding and baffles), and has sufficient curing capability to allow high
web speeds. Older EB-curing units often had more production capacity than was needed.
Because of the cost of shielding and handling high voltages, as well as improvements in EB
inks, coatings, adhesives and photoinitiators, there has been a trend to produce smaller
electron guns with lower voltages. Although Photoinitiators are frequently not needed for EB
cures, they have been used to cure thick films on three-dimensional objects with a lower EB
voltage.
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Structur* terminal (T)
Electron gun (G)
Chamber
Vacuum
Figure 7: Schematic of Electron Gun
Early EB-curing units used with (and usually attached to) printing presses were relatively large
compared to UV-curing units because, EB units had to include much more shielding (some even
used concrete vaults to enclose a press). These early EB units had much greater production
(curing) capacity than early UV units and used up to 10 MV to accelerate electrons. Current
state-of-the-art electron guns use about 35 kV in a package about 3 inches in diameter by 12
inches long. As a result of this substantial reduction in energy, current EB-curing units do not
require as massive a shield. Excess production capacity associated with EB in past years is
becoming smaller, and production capacity for both UV and EB is converging to a point
originally between the two techniques. In addition, greater efficiency in EB power use is
obtained by using cationic photoinitiators and has resulted in lower voltage sources.
Electron beams are sensitive to the density of the gas between an EB source and an object to be
cured. An EB will ionize oxygen in air to create ozone and nitrogen oxide; therefore, a nitrogen
blanket is highly recommended to avoid nitrogen oxide and ozone formation.
Electrons are slowed down by multiple impacts with gas molecules surrounding a substrate
(presumably nitrogen, but the same is true of oxygen). This causes an electron beam to
degenerate into a diffuse multiple scattering of electrons. Scattered electrons are much more
numerous than electrons in the original beam, because they result from an avalanche effect.
Scattering occurs because nuclei are surrounded by numerous electrons that have the same mass
as electrons in the beam. To minimize this problem, a sealed evacuated space is provided from
the EB source to within a small distance from the substrate. A titanium foil window forms the
air-tight seal to maintain a vacuum for the evacuated space.
Titanium is chosen for the window because: (1) it has a low atomic number (Z) and is a low
density metal that heats up by absorbing about half of the electrons in the beam, but does not
heat up enough to lose its strength; (2) it can be made as a foil that is thin enough to minimize
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losses of electrons; (3) it is strong enough to allow a thin foil to hold against atmospheric
pressure, even when an electron beam is on; and (4) it is very corrosion resistant so it will not
readily oxidize when moderately heated. Until titanium foil could be made (circa. 1970), there
was no suitable window material and, therefore, no energetic electron beam in air was possible.
The electrons are directed at the foil window because they would lose too much energy going
through a thicker
metal wall. They would even lose too much energy by going through enough glass to provide an
adequate seal for a vacuum.
When the electrons stream through the window, they encounter their first air or nitrogen
molecules and are scattered rather strongly. Nevertheless, an intact stream of electrons continues
for several millimeters (depending upon the initial velocity). This intact electron stream
becomes more and more diffuse as the distance becomes greater. After only a few centimeters,
the electron stream is scattered and diffuse. As the electron beam loses energy by impacts and
capture, it generates x-rays. Finally only ions remain, with x-rays radiating from where the
electron beam had been.
Electron beams are sensitive to the density of the gas surrounding the object to be cured and to
ionizing oxygen in air (oxygen ions create ozone). After passing through a foil window,
electrons are slowed down and scattered by impacts with molecular gases in air. As a result, a
foil window must be placed very near (~ 1 mm) to a material that is to be cured at atmospheric
pressure.
Vacuum chambers have been built to EB-cure filament reinforced plastic objects.18 These
vacuum chambers are suitable for curing fiber reinforced composite objects that are small
enough to fit within a chamber. These chambers are also suitable for EB-curing of coatings on
the exterior of such objects. These chambers are not well-suited to continuous coating
applications as in either rotogravure printing or coating optical fibers.
WHAT IS UV/EB IONIZING RADIATION?
Ionizing radiation is radiation that can ionize a molecule. Because all molecules are not
ionized by the same amount of energy, the question becomes what molecule? The term ionizing
radiation usually refers to the amount of radiation that will ionize oxygen in air; that is,
radiation with a wavelength shorter than 253 nm (this includes actinic UV radiant energy
generated in UV-curing systems and electrons and x-rays generated in EB-curing systems).
UV/EB-cured inks, coatings and adhesives also contain other molecules that can be ionized by
radiation at these wavelengths.
UV energy is selective in the molecules that it can ionize. On the other hand, EB energy ionizes
anything in its path until all electrons are absorbed. EB systems generate x-rays when the
electrons are absorbed. These x-rays also can ionize molecules.
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Ionizing radiation can even mean visible light if a photoinitiator that is sensitive to a visible
wavelength is used to ionize molecules. Even IR energy can ionize when it is intense enough to
set an object on fire.
Both UV and EB radiation have photons or particles that are energetic enough to break
molecular bonds. It is important to realize that photons of a given wavelength (or color if they
are visible) are all at the same energy level and that energy level increases as the radiated
wavelength gets smaller. The amount of energy in each photon is determined by the following
formula:
energy = hf = hc/A
where h = Planck's Constant
f = frequency
c = speed of light
A = wavelength
Intensity indicates the number of photons striking a detector per unit of time. Photons have
wavelength-defined energy until they are absorbed. Contrast this with the concept in quantum
physics that views photons as massless particles that are used as an alternative to wave behavior.
Describing the phenomenon as both a wave and a particle is not logical. How can a particle be
everywhere a wave goes? How can a photon have only one energy, while a particle's energy
varies. Yet both are used to describe the wave and particle characteristics of radiation.
Knowing that this is the case, we now must deal with ionizing radiation that is used for
UV/EB-curing.
OSHA does not include UV in its definition of ionizing radiation, although UV can ionize
oxygen in air when the wavelength is below 253 nm. From an EPA viewpoint, ionizing
radiation can be any wavelength shorter than blue light; therefore, ionizing radiation is any
wavelength shorter than 400 nm. It can be near-UV radiation (315 - 400 nm wavelength),
actinic or far-UV radiation (180 - 315 nm wavelength),1 x-rays (0.1- 40 nm wavelength), or
gamma rays (<0.1 nm wavelength).
Some sources define ionizing radiation having wavelengths between 40 nm and 180 nm as UV.
However, the ozone generation capability of electromagnetic waves with wavelengths under
253 nm and the difficulty in generating these waves greatly restricts use of these wavelengths for
curing UV/EB materials.
Another definition of ionizing radiation splits the UV spectrum into parts. It defines UV-A as
315-400nm, UV-B as 280-315 nm, UV-C as 200-280 nm, and Vacuum UV as 100-200 nm. In
this scheme, UV-A is the lower wavelength limit for human vision, is transmitted by window
glass, and can increase pigmentation of tissues. UV-B is primarily erythrogenic energy; that is,
it will cause reddening of skin, increase pigmentation of tissue, and cause eye irritation. The
most common effect of UV-B exposure is erythema (sunburn) that generally appears within
three hours and becomes most severe about twelve hours after exposure. UV-C is filtered from
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sunlight by ozone but, when man-made, has important sterilizing properties and other industrial
uses. Use of UV-C or Vacuum UV requires an oxygen-free atmosphere to prevent formation of
ozone.
Some materials need more energy to ionize than that supplied by a collision with one photon of
available radiation in a brief period of time and are, therefore, dependent on the intensity of
radiation for ionization. Intensity is the rate at which photons are absorbed. Even long
wavelength IR radiation can ionize molecules if it is sufficiently intense. However, IR
radiation is not usually considered ionizing radiation for curing because it either melts or
burns substrates. Only photons of shorter wavelengths and electrons actually have enough
energy to cause ionization of UV/EB-cured ink, coating and adhesive molecules to happen
without damaging a substrate.
The intensity of UV is measured in Watts per square centimeter. Doses of x-rays and gamma
rays are measured in either Roentgens (IRoentgen; R = 100 ergs/gram) or the Roentgen
Equivalent for Mankind (REM, which is the integral over the whole spectrum of Roentgens
times the adsorption factor for human tissue).2 The dose of electron beams is measured in Gray
absorbed radiation units (1.0 Gy = 1.0 Joule/kg).
HOW DEEPLY DOES IONIZING RADIATION PENETRATE?
UV Ionizing Radiation
UV radiant energy penetrates to only a shallow depth in a coating, ink or adhesive, clothing,
or human skin. Therefore, UV radiant energy is usually used for thin film applications such as
printing ink, pressure sensitive adhesives, permanent adhesive assembly, or some paints. UV
radiant energy is absorbed by pigments, monomers, oligomers and photoinitiator sensitive to
that UV wavelength to break molecular bonds. Air or nitrogen is essentially transparent to UV.
However, an ink, coating or adhesive will deplete UV radiant energy within a shallow depth,
often less than a thousandth of an inch.
EB Ionizing Radiation
In EB-curing, electrons have a limited range before scattering in air. They also have a limited
range (1 - 20 mm) within the material to be cured. This range is a function of the speed of the
electrons (usually measured in electron volts) at the surface of the material being cured, the
density of that material, and the atomic number (Z) of the molecules that make up the material.
As EB voltage increases electrons move faster and, as electrons move faster, they penetrate more
deeply. For electrons and x-rays, higher Z materials have greater absorption potential because
an EB is attenuated by reacting with orbital electrons. Most nuclei in EB-cured materials have
about the same low capture cross-section for scattered electrons as they do for high energy
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electrons. An EB ionizes (changes the electronic balance of) atoms and molecules that capture
it. Electrons in a beam lose energy to electrons that they impact and slow down. Electrons are
captured more readily (i.e., the capture cross-section is greater) when they are moving slower.
These fast moving electrons in a beam are retarded by impacts with the orbiting electrons of
atoms and the positive charge on the nuclei. This happens with air molecules as well as
molecules in the EB-cured material. Electrons that are impacted may either gain escape velocity
or go into larger orbits. Electrons that gain escape velocity are referred to as being scattered.
Scattered electrons, and those that go into larger orbits, cause the atom to radiate energy as x-
rays. Scattered electrons impact other atoms and produce an avalanche of lower energy electrons
that replace electrons that were lost.
As electrons in a beam slow down, they generate x-rays. These x-rays are called
brehmsstrahlung, which is a German word meaning "braking radiation" or "radiation caused
by retardation." This results from the slowing of electrons, scattering of electrons, acceleration of
orbiting electrons, and cyclotron radiation are caused by larger electron orbits. Cyclotron
radiation produces a characteristic narrow band x-ray spectrum emission of brehmsstrahlung at
wavelengths that depend upon the particular capturing atoms. Low Z materials generate longer
wavelength x-rays that do not penetrate as much. Collisions with high Z materials tend to
produce more energetic x-rays that can penetrate more readily. Electrons that escape orbit
produce a broad spectrum of x-rays. All man-made x-rays are generated in this way.
The extent to which x-rays from EB radiation penetrate is related to the Z of the material, and
the density that is penetrated. X-rays generally penetrate lower Z materials to a greater depth.
Higher material density places more atomic cross-sections along the trajectory, which causes a
greater attenuation. Attenuation is the term that is used to describe the amount that x-rays are
absorbed. X-rays resulting from older EB systems with significant excess capacity have required
a concrete vault or other appropriate shielding around the printing press to contain and attenuate
them.
Most substrates and EB-cured materials are composed of oxygen, hydrogen, carbon, and
nitrogen atoms. These are all low Z materials. Some pigments and additives contain high Z
materials, but the effect of these is mitigated by a thin film of material. Therefore, penetration of
low energy x-rays through the EB-cured materials and substrates is usually very great. When
higher Z atoms are excited by EB, a higher penetration x-ray is generated. These x-ray
generated photons also can ionize molecules in EB-cured materials, just as an electron beam
and UV radiant energy do more directly.
Because an EB will be absorbed and x-rays will be generated, x-rays will have to be attenuated.
This is now done by insertion of dense heavy metal shields in a curing unit. It also can be done
by enclosing a press within a concrete vault. The walls of such a vault might be made thinner by
addition of insoluble heavy, metal salts as a filler.
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UV/EB-CURING
In this section more details are provided on UV/EB coating, ink and adhesive formation,
photoinitiators, the relationship between film (applied coating, ink or adhesive) thickness and
production rate, 3D capabilities, measuring the extent of curing, and anything else that you need
to know about UV/EB-curing
HOW DO UV/EB COATINGS, INKS AND ADHESIVES FORM?
UV/EB materials cure (form a solid film) by polymerization and crosslinking. There are many
polymerization mechanisms; however, currently only two polymerization mechanisms are
used for UV/EB-curing: free radical polymerization and cationic polymerization. Except for
powder coatings, most UV/EB coatings start out as a liquid. UV/EB-cured powder coatings
start out as solid particles that are applied to a substrate, subjected to infrared radiant energy
(heat) to melt them, and then exposed to UV/EB radiant energy to polymerize the coating.
UV/EB radiant energy breaks the photoinitiator molecule in the UV/EB material by either
homolytic fission (to make free radicals), or heterolytic fission (to make cations and anions).
This fission refers to breaking a molecule rather than an atom. (It does not mean the same thing
as the term used for nuclear reactions.) These free radicals and cations then combine with
monomer or oligomer molecules to form a polymer.
The properties of a polymer are the result of: (1) monomer and oligomer molecules that have
become part of the polymer chain; (2) crosslinking that is accomplished by pendant groups; and
(3) the length of the polymer chain before termination. A polymer molecule can be terminated
in one of three ways:
1. One chain bonds endwise to another, which creates a pair of electrons that will not react
further, or
2. An oxygen atom reacts with the free electron in a free radical and creates a pair of
electrons that will not react further, or
3. Polymer molecules limit the mobility of monomer molecules so that the reaction stops
due to the unavailability of reactants, and the free radical reaches the end of its lifetime.
The second termination mechanism is also referred to as oxygen inhibition. Note that this is
only an issue in free radical polymerization, not cationic polymerization. Oxygen inhibition
is avoided by blanketing the reaction area with dry nitrogen to exclude oxygen that would
otherwise be present in ambient air. The presence of oxygen molecules could cause polymer
chains to be terminated too short, or limit crosslinking.
The types of monomers or oligomers define the structure of the polymer and, therefore, its
properties. The basic properties are modified by crosslinking that molecularly bonds the
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polymer chains together.
While we might like to think that a time integrated dose of UV/EB radiant energy causes a
cure, intensity (the rate at which photon energy is absorbed) is also important. Molecules at the
surface (the topmost level) may receive 100 or more times the intensity of UV/EB energy as
molecules at the bottommost level adjacent to the substrate. As a result, adhesion failure may
occur if bottommost coating molecules do not receive enough radiant energy to cure.
Free Radical Polymerization
A free radical is a molecular fragment that has a single free valence electron (See Figure 8).
Photoinitiators are unsaturated molecules (having aromatic or aryl carbon rings) that form free
radicals very readily. Valence electrons are unreactive when paired with another valence
electron; however, a single valence electron always seeks a second valence electron. A free
valence electron is formed by homolytic fission. This occurs when sufficient UV/EB radiant
energy is absorbed by the photoinitiator molecule. Homolytic fission means that both
fragments are free radicals with single electrons available. Free radicals exist for a limited
time and must find and react with monomers and oligomers within their lifetime.
Free radical polymerization contains the following steps:
UVor
Initiation R > R'
electrons
Propagation R* + Ri > RR^
Chain Transfer RR'n + AH > RRnH + A*
Termination R • + R'm > RRm
Initiation
Figure 8: Free Radical Polymerization
When a free radical captures an electron from a monomer or oligomer, that monomer or
oligomer becomes part of the free radical. A single valence electron is always left free after
this joining and this new expanded free radical reacts again and again as it forms a polymer.
This is a chain reaction. In this way, monomers and oligomers form polymers that contain
long chains of monomer molecules.
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Cationic Polymerization
Cationic photoinitiators are unsaturated molecules that break apart by heterolytic fission under
UV/EB radiant energy to form cations and anions. Heterolytic fission means that the
fragments are different. Cation fragments initiate and sustain the polymerization process, as in
Figure 9. The anions do not contribute much to polymerization. The cations are either
Bronsted acids or Lewis acids. These strong organic acids are positive ions that either donate
protons or absorb electrons and are attracted to a cathode just as hydrogen ions are. The cations
also cause fission to continue until all available photoinitiator molecules have ionized.
Therefore, once started, polymerization will spread throughout the UV/EB material. Unlike
free radical polymerization, cationic polymerization is an ionic reaction that cannot be
terminated by a reaction with oxygen molecules. Because anions are also formed, the overall
state of the polymer is neutral, even though polymerization occurs because cations are present.
Because cationic photoinitiators now exist, the list of potential applications that can be served
changes and expands. These cationic photoinitiators can be used to polymerize coatings that,
because of absorption, shadowing, or pigmentation, cannot receive enough radiant energy
throughout their depth. Once cationic polymerization starts, it will continue to completion,
even in the dark.
CF
.. p. p. p. p
Figure 9: Cationic Polymerization
Crosslinking
Crosslinking can result from either free radical polymerization or cationic polymerization.
It occurs as part of polymerization when pendant groups on one chain connect with pendant
groups on another chain. Crosslinking produces mechanical hardness, resistance to melting,
resistance to mechanical deformation, greater strength, and mar resistance (See Figure 10).
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Figure 10: An Example of Crosslinking
HOW DO PHOTOINITIATORS WORK?
Photoinitiators are unsaturated, aromatic, aryl compounds that are more sensitive to UV/EB
radiant energy than monomers and oligomers Compared to monomers and oligomers,
photoinitiators represent a small percentage of the weight of a coating, ink or adhesive that is
being applied. Most absorption of UV/EB radiant energy in a UV/EB-cured material is
accomplished by a photoinitiator.
Photoinitiator molecules fission (break apart) in predictable ways when they receive UV/EB
radiant energy. They either form free radicals or cations as fragments. Therefore,
photoinitiators play a critical role in initiating free radical or cationic polymerization in
UV/EB materials. The type of photoinitiator must be selected with care. The energy absorption
potential of a photoinitiator must be matched to the wavelength of peak radiant energy that is
generated by the UV/EB source in order for the photoinitiator to do its job properly. If radiant
energy is not sufficiently intense, a photoinitiator may not receive enough energy to form free
radicals or cations Photoinitiators also are major absorbers of UV/EB radiant energy
DOES PRODUCTION RATE DEPEND ON COATING THICKNESS?
Coating thickness does affect production rate. Because the thickness of material applied by
spray and roller methods (>0.001 inch) are typically much greater than that of printing («0.001
inch), they require a larger dose of radiation to cure. Therefore, for a constant radiant energy
source, production rate must decrease as film thickness increases in order to provide adequate
exposure to radiant energy needed to cure the material. In reality, the intensity is adjusted to
cure the coating at the production rate.
This is exacerbated by absorption of radiant energy by the UV material itself, because the
intensity of UV radiant energy will decrease severely with film thickness. This may be offset
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with more intense UV. However, IR radiant energy (heat) is absorbed along with UV energy.
Therefore, the limit in UV intensity is determined by the IR energy that is absorbed by the
substrate and coating.
Thin material applications (as used in printing and adhesive coating) can cure almost
immediately. Production rates for these applications can be much higher than for thicker
applications. Printing production speeds of over 1,000 feet per minute can be achieved with
complete curing in a UV-curing unit that is only a few feet long.
Cure times for thicker applications using spray or roller techniques may be measured in seconds.
3D fiber reinforced composite structures contain fibers that shadow much of the UV/EB coating
that bonds the fibers together. Curing a coating in this type of structure can require EB radiant
energy, cationic curing, or both. Cure time may be greatly extended, though 3D cures can be
accomplished in seconds.
WHY HAS THERE BEEN GROWTH IN 3D CAPABILITIES?
As previously stated, UV/EB-cured materials were first used in printing processes because this
technology is well suited to a thin coating of ink on a flat surface. UV/EB technology was also
well suited to coating sheet metal before it was coiled and flat wood product panels for the same
reasons. However, other applications arose, such as optical fibers, that were not flat. These 3D
applications have the ability to cast shadows that hide portions of the surface from the radiant
energy needed to cure the UV/EB material. By 3D capabilities we mean the ability to cure
coatings on 3D objects.
Figure 11 shows a cross-section of an optical fiber used for transmission of digital signals and
the special coatings that are crucial to its performance. Without these coatings, fiber optics
could not be a long-distance medium. The innermost coating must have a low index of
refraction, and not absorb the wavelength of the laser that is being used to send the digital
signals. The next coating must provide strength. The outermost coating must strongly absorb
the wavelength that is being used to prevent "cross-talk" between fibers. The development and
availability of these UV/EB coatings were crucial to the success of fiber optic cable, because no
other technology could provide the rapid cure with 100% integrity. As a result, equipment and
UV/EB coating developers and manufacturers cooperated to produce this product and the other
products that use UV/EB materials.
Because efforts to minimize the effect of the shadow in 3D applications succeeded in optical
fiber manufacturing, the advancement of 3D capabilities in other applications became only a
matter of time. Currently the effects of shadows can be minimized for wood furniture and even
automobile bodies. This has been achieved by multiple radiant energy sources, dimpled
reflectors, and myriad other optical design techniques.
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strong coating low inclex °f refraction
opaque coating
Figure 11: Schematic of Optical Fiber
Manufacturing plants now spray or roller coat UV sealers, primers, finish, and topcoats on
panels and furniture and rapidly cure these materials within 25°C of room temperature.
Conventional coatings on a wood substrate can not be heated enough to cure in less than an
hour. Because the curing time is so short for UV materials, fine furniture manufactures use UV
coatings to avoid dust blemishes. In addition, because there are no flammable VOC to cause a
fire hazard, at least one insurance company has decreased the fire insurance premiums by 15%
where UV material are used.
Use of a computer guided UV optical fiber or laser has allowed layer-by-layer construction of
objects using a polymer. The polymer object that is formed can be either a model or the final
part. This technique is referred to as stereo lithography. This is done by retreating a platform
beneath the surface of a monomer or oligomer while a computer guided UV source operates
like a printer tracing a raster with the UV source "on" over the solid portion, and "off over open
spaces or cavities in the structure of each successive cross-section. In this way, a scale model
(any scale including life size) of a complex part can be made - even body parts can be generated
from a CAT or MRI scan. This technique allows for troubleshooting of designs. It can even
allow surgeons to practice on life-size models of the patient.
HOW IS EXTENT OF CURING MEASURED?
The extent of a UV/EB coating cure has been measured by adhesion, solvent-rub, stain tests, ion
mobility, glass transition temperature, mechanical properties such as elastic modulus or tensile
strength, Taber abrasion, a fluorescent indicator, or by minimum volatility. The measure is
selected based on some performance measure that is germane to endurance, and no correlation
has been made between the various cure measurement techniques. A few of the main tests are
discussed here.
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Adhesion of a coating is measured by the force per inch of edge that is peeled. When the
coating is liquid, this force is near zero. It becomes a finite amount as curing progresses. When
it approaches a maximum force, the slope of the peel force with increased UV/EB exposure
approaches zero. Further exposure is said to overcure the material. Overcuring is thought to
accomplish further crosslinking between molecules and react some additional monomer.
Taber abrasion tests the resistance to abrasion. It is based on the use of a weight (250 gram, 500
gram, or 1 kilogram) bearing down on an abrasive disk while the specimen is rotated against it.
The abrasive disk can be any of a large number of types, based upon the purpose for which a
coating is intended.
Solvent-rub is a modification of abrasion that requires a specified solvent to be present. This
test measures the effect of the solvent on the cured coating. Presumably, an uncured or
shallowly-cured coating would be readily removed by the solvent.
Ion mobility is measured by placing two electrodes on a coating, applying a voltage and
measuring the current. Both the amount of current and the time response to switching the
voltage on are measured. Both of these measurements provide diagnostics as to the ion mobility.
Presumably, the ion mobility is least in an overcured coating. A minimum ion mobility that is
acceptable to the usage is specified.
Elastic modulus is based on the slope of the stress-strain curve. This test requires a specimen to
be coated for measurement of stress versus strain. Stress is the force per unit area to achieve the
strain. Strain is the elongation per unit length that results. A higher elastic modulus requires
more stress to achieve a given strain.
Tensile strength is the maximum stress that can be achieved before breaking. Typically, this
occurs when a discontinuity in the stress versus strain curve occurs.
Minimum volatility is measured by weighing a specimen of cured coating to determine weight
loss. Curing is done in increments with weight measurements at each increment. Between
increments, temperature can be elevated to drive off volatile ingredients. A minimum volatility
cure is the point at which weight loss reaches a minimum.
Glass transition is a property of the amorphous portion of a semi-crystalline solid. It is measured
as the temperature at which the solid changes from a glassy deformation to a rubbery
deformation. This is determined by measuring the elastic modulus at different temperatures, and
finding the temperature interval in which the glass transition to a higher modulus occurs. A
higher glass transition temperature (Tg) can be used as evidence of greater crosslinking.
Alternatively, the minimum Tg can be specified and the elastic modulus is then determined at
that temperature to determine whether it is glass-like or rubber-like.
The other methods are used less often because: they are more suited to research; are more
expensive; or take too long to obtain a result while production is running. While each method
ostensibly shows that curing is complete, the correlation of one method to another is seldom if
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ever done. Whether food contact could or should be allowed is not determined by these tests
(with the possible exception of ion mobility).
IS THERE ANYTHING ELSE THAT AFFECTS CURING?
You may have noticed that we have hardly mentioned temperature. UV/EB materials cure
nearly instantaneously and cure even faster as temperature increases. Temperature is a measure
of the kinetic energy of molecules. If the temperature gets above a critical level (a different
level is critical for each UV/EB material) polymerization can occur in the absence of UV/EB
radiant energy. The temperature of UV/EB-cured materials needs to be kept between 60°F and
80°F to preclude depletion of inhibitors in the material. This temperature range usually is not a
problem, but air conditioning may be required in some cases.
Other factors are UV lamp variation during use, variations in power line voltage, oxidation
effects and infrared effects. All of these vary with time and the effect of each may be different.
Therefore, we should recognize that the cure will vary as a combined effect of all of these
factors.
UV/EB materials can vary. To minimize variability, UV/EB-cured materials should not be
exposed to peroxides, iron particles, or other free radical sources. In addition, they should be
stored away from sunlight or other sources of radiant energy that could cause polymerization.
If a UV/EB-curing unit promoting free radical polymerization is exposed to atmospheric
oxygen or atmospheric oxygen invades a "nitrogen blanket" used in the process, oxygen
inhibition will occur. Oxygen can inhibit the curing of acrylics, polyesters, and styrenes. The
effects of oxygen inhibition may result in the use of a far greater dose of radiant energy than
expected to obtain a cure. This would be especially true if the "nitrogen blanket" were not
used. On a positive note, oxygen inhibition is intentionally used to retain tack in some pressure
sensitive adhesives.
Humidity can affect the curing time of UV/EB materials that use cationic photoinitiators.
This effect differs for various coatings, coating thicknesses, coating permeabilities and water
vapor concentrations.38 In some cases, water can inhibit polymerization similar to oxygen
inhibition. This can be corrected by using an IR dryer or an extended dry nitrogen blanket.
Monomers, oligomers, photoinitiators, fibers, and pigments in a coating, ink or adhesive can
all absorb UV/EB radiant energy. The extent to which all of these materials absorb radiant
energy can inhibit curing of the material, especially in thicker applications. Fibers and pigments
can cast UV/EB shadows that prevent radiant energy from reaching monomers, oligomers, and
photoinitiators. Materials that contain cationic photoinitiators do not have this problem.
Material containing cationic photoinitiators only have to receive enough radiant energy to
decompose the photoinitiator in the top layer and curing will be spontaneous after that.
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PART III: EMISSIONS, HEALTH AND SAFETY
WHAT AIR POLLUTANTS ARE EMITTED FROM UV/EB-CURED MATERIALS?
UV/EB-curing is a very low emitter of air pollutants, but some emission do occur. This section
discusses potential emissions of VOC, fine paniculate, HAP, odors, ozone and NO2.
VOC Emissions:
UV/EB-cured coatings, inks and adhesives have a reputation for being VOC-free, but they
actually do emit some cure volatiles that may be VOC. Although VOC emissions are extremely
low from many applications using modern UV/EB materials (i.e., VOC emissions can be less
than 1% of the weight of the coating, ink or adhesive used), cure volatile emissions for a typical
application usually are in the 1-5% range. (Note that no solvent diluent is used in the typical
case.) However, for a small number of applications, cure volatile emissions can approach 10%
of the applied film weight. Even at the 10% level, uncontrolled VOC emissions are no worse
than that of a conventional coating or printing operation equipped with good emission capture
and control technology. Typically, no add-on control technology is either needed or used with
UV/EB-cured materials.
UV/EB-cured materials are ready to use as provided by the manufacturer. No additives or
blending is required after the UV/EB-cured materials leave the manufacturer. The one exception
may be adding a solvent (VOC or water) to adjust viscosity in some spray or special
applications. UV/EB-cured materials will not dry up unless subjected to sufficient UV/EB
radiant energy. If diluents are present, uncured UV/EB coatings may simply become more
viscous as the diluent evaporates. However, normally VOC diluents are not present.
Acrylates have been measured at a concentration of approximately 10 ppm in the space
immediately above a coating (a headspace measurement) during cure. Concentrations of VOC
in the same space were even lower.28 Concentrations in a subsequent emission stream would tend
to be even lower as a result of mixing and dilution with air in the exhaust stream. Such small
emission concentrations are the desired goal of add-on emission control technology used with
conventional processes, but they can be achieved by using UV/EB-cured coatings, inks and
adhesives without a add-on emission control device.
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EXAMPLE: Calculation of VOC Emissions
Source type: Printing
Application: Overcoating a 5 foot Web running at 1000 feet/minute
Coating characteristics: 0.8% specific gravity
Film thickness: 100 microns
VOC emissions: 1% of the film weight as applied
In this example, the source would produce 0.000163 pounds of VOC per square foot, or about
1.0 pound of VOC per 6,124 square feet. One pound of VOC would be emitted from
overcoating 100% of a 5 foot web for 1.2 minutes at 1,000 feet/minute. This would provide a
maximum of 72 pounds of VOC per hour, 576 pounds per 8 hour shift, or 52 tons per year per
shift. In most cases UV/EB technology would qualify as a Lowest Achieved Emission Rate
(LAER) technology. (LAER is required by the Clean Air Act on new and modified major
sources locating in areas that are not attaining National Ambient Air Quality Standards.) In
comparison, a conventional overcoating operation using VOC solvent would emit 2,600 - 3,600
tons per year of VOC for the same level of operation.
Note that the previous calculation was based on the amount of material that actually is applied to
the substrate. In reality, some losses due to misting, spills, splatter, transfer efficiency, etc.
may occur. Therefore, it would be preferable to use the mass of the total amount of UV/EB-
cured material (coating, ink, etc.) that is consumed when calculating potential emissions from
UV/EB printing and/or coating processes.
Fine Particulate Emissions:
When UV/EB materials are used on high speed printing presses and roll coaters, they will emit
some mist. Mist is generated when UV/EB material that is between rollers and substrate
rapidly separates in high speed applications. (Conventional materials also would mist if they
were applied at as high a speed.) Misting of UV/EB ink in high speed printing has been
measured at between 1% and 50% of the ink consumed. Many of the droplets were found to be
under 2.5 |im (PM-2.5). Where misting is severe, users and suppliers can work together to
minimize the problem.
HAP Emissions:
Unless HAP solvents are added, UV/EB coatings are HAP-free (i.e., do not contain any a HAP
listed in Appendix E). However, fine droplets in mist generated by high speed rollers (see
above) may contain toxic chemical compounds. You should check Material Safety Data Sheets
(MSDS), review the HAP list, and/or contact the supplier to determine to what extent toxicity is
an issue with a particular UV/EB-cured material.
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Odorous Emissions:
Overall, the UV/EB-cured material used today have much less of an odor problem then material
used 10 years ago. In fact, restaurant menus, packages for fine perfumes and boxes for
chocolates can now be printed and coated with UV/EB (See Figure 12). However, UV/EB
materials have historically emitted some objectionable odor, some even after curing. Odor
generating UV/EB materials containing amines or sulfur compounds should be avoided where
odor is an issue.
Figure 12: UV Coatings - Now Used for
Packaging Chocolates
Ozone and NO-, Emissions:
Each form of ionizing radiation can ionize oxygen and generate ozone. Also, there is suspicion
that NO2 can be generated, too. However, total emission of ozone and NO2 are relatively small
and should not significantly affect concentrations of these pollutants in the atmosphere.
Equipment manufacturers have reduced the potential for ozone and NO2 generation from
processes that use UV/EB radiant energy. Nitrogen blankets exclude air from the
polymerization areas and, therefore, exclude oxygen as a reactant in these areas. However, air
ventilation is used to remove heat from UV lamps; therefore, these pollutants still can be
generated. Quartz filters that strongly absorbs wavelengths below 260 nm (the wavelengths that
form ozone) can be used to reduce ozone generation.
HOW ARE EMISSIONS FROM UV/EB-CURED MATERIALS MEASURED?
VOC content of coatings is measured by EPA Reference Test Method 24. This method can be
found in Title 40, Code of Federal Regulations, Part 60, Appendix A. For your convenience,
Method 24 is provided in Appendix C of this report. Section 3.2 of Method 24 addresses non-
thin-film UV Radiation-cured Coatings. This method is based on an American Society for
Testing Materials (ASTM) test method (D 5403-93). If the amount of UV coating or ink as
applied to the sample substrate is less than 0.2 grams (based on manufactures recommended
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film thickness) and the area of the sample substrate is equal to or greater than 35 in2 (225 cm2)
then the coating is considered a thin-film UV radiation-cured coating for determining
applicability of ASTM D 5403-93. No test method is specified for thin-film UV coatings, inks
or adhesives or any EB-cured materials.
In considering and evaluating the modifications to Test Method 24 that eventually added
procedures for testing non-thin-film UV coatings, minimum VOC content was found when a
resin was UV-cured well beyond the manufacturers recommendation.16 The supporting paper
evaluating this modification did not state whether the recommended cure was intended for an
oxygen-free atmosphere, or whether an oxygen-free atmosphere was used. Because it made no
mention of a nitrogen blanket to exclude air from the curing process to minimize oxygen
inhibition, we assume that one was not used. Oxygen inhibition of a cure in atmospheric air
would explain the need for a higher UV dose (i.e., the amount of UV radiant energy required to
complete the cure and assure minimum VOC emissions). The report also stated that lamp output
power in the test apparatus was not measured, and that there is no easy relationship between the
power input level and UV light output at the specific wavelengths that cause a coating to cure.
Therefore, low lamp output at the desired wavelength also could have increased the cure time.
Manufacturers of UV radiant energy cured materials believe that Method 24 overstates VOC
emissions because it subjects a cured UV material to excessive heat (110 +/- 5°C) after a cure.
Manufacturers suggest that excessive heat causes a UV coating to decompose and that a
resultant loss of coating mass is being reported as VOC. EPA is aware of these concerns, but
has no plans to revise the test method or develop a new method at this time.
WHAT ABOUT WORKER HEALTH AND SAFETY?
There are three major worker health and safety issues that need to be addressed: (1) potential
exposure to UV/EB radiation; (2) potential exposure to hazardous components that are part of
UV/EB-cured materials; and (3) hygiene to protect workers. This section will discuss all of
these issues and significant changes and improvements made over the past ten years to minimize
potential hazards.
What Health and Safety Concerns Does UV/EB Radiant Energy Present?
UV radiant energy is ultraviolet light. This is the same type of ultraviolet light that is
received from the sun. It cannot penetrate the skin, but can cause sunburn and tanning of the top
layer of skin or can cause eye irritation. When properly shielded, UV does not cause even these
to occur.
EB radiant energy consists of high velocity electrons and subsequent x-rays. Electrons are
generated in an accelerator or gun that projects them toward the coating, ink or adhesive and
the substrate. Electrons generate x-rays as their speed is retarded in these materials, and by any
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molecules between the EB source and the target film and substrate. Manufacturers of this EB
equipment install shielding to reduce x-radiation to below background level.
According to OSHA regulations (Code of Federal Regulations (CFR) part 1910.96), no
employer shall possess, use, or transfer sources of ionizing radiation (OSHA's definition
excludes UV) in such a manner as to cause any individual to receive, in any quarter of a calendar
year, more than:
Whole body, head and trunk, active blood-forming organs, or gonads 1.25 REM
Hands and forearms, feet and ankles 18.75 REM
Skin of whole body 7.5 REM
An individual can receive a dose greater than this if:
1. During any calendar quarter the dose equivalent of the whole body does not exceed 3
REM
2. The dose equivalent to the whole body when added to the accumulated dose equivalent to
the whole body shall not exceed 5(N-18) REM, where N equals the individuals age in
years.
3. The employer maintains past and current records which show that the addition of such
dose equivalent will not cause the individual to exceed the above tabulated amounts.
Additional limitations may exist in the form of local, state, or subsequent federal regulations. It
is the responsibility of the employer to determine what regulations apply and to assure that
employees are not exposed to ionizing radiation that exceeds statutory and regulatory limits.
How Can Workers Be Protected Against UV7EB Ionizing Radiation?
The principal means of protection from all ionizing radiation is shielding. This shielding is
integrated into UV/EB-curing equipment in most cases. In the event of UV leakage, clothing is
a backup to shielding and wearing full sleeved and full legged garments is recommended. Eye
protection with side-shields is also recommended for the same reason.
With near-UV, far-UV, and actinic radiation, shielding consists of opaque barriers and baffles.
Baffles are needed because UV radiation can readily scatter from sub-micron aerosols and
become a diffuse glow reflected and re-radiated from aerosols and surfaces. UV can scatter
much more readily than visible light can, because its wavelength is shorter and sub-micron
aerosols in air can readily scatter UV. These aerosols are invisible (too small to be seen)
because they fail to efficiently scatter visible light. Multiple baffles are needed to reduce the
leakage produced by this scattering before it reaches human tissue. OSHA allows up to 1
milliwatt/square centimeter of near-UV radiation for exposure times over 16 minutes. OSHA
allows only up to 0.1 milliwatt/square centimeter of actinic radiation for 8 hour exposures.1
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Unlike UV with coexisting visible wavelengths, electron beams and x-rays have no visible
component to alert a human being to their existence. Because human genes (just like the
photoinitiator, monomer, and oligomer molecules) are sensitive to molecular breakage under
ionizing radiation, workers need to be shielded from EB radiation. Ideally, radiation intensity
should be reduced to near background radiation level by shielding. The background radiation
level is the intensity of x-ray and gamma radiation that would exist if no radiation source
(except for trace sources of naturally radioactive materials) were close enough to affect the
radiation intensity. There are many of these low-level natural sources (such as wood, wood-fiber,
paper, metals, and masonry) and therefore the background level can never reach absolute zero.
At wavelengths of x-ray and shorter, scattering becomes pronounced and there is no truly
opaque material. The mass of a shield will attenuate (reduce) the intensity of radiation that
penetrates that shield, as will the atomic number (Z) of the material Higher Z materials
attenuate penetrating radiation more than low Z ones of equal mass. However, the first solid to
be encountered by radiation should be a low Z material, both to minimize generation of x-rays
and to absorb x-rays that are generated from the higher Z materials that are encountered later in
a multiple layer shield.
X-ray and shorter wavelengths are usually shielded by lead, other heavy metals, concrete, or
distance. In the absence of shielding, radiation intensity is reduced by the square of the distance
between the source and the point of the measurement. Obviously, nobody can afford to place an
operator a kilometer or even a hundred meters away from a source just to attenuate the intensity
and limit the dose they receive. Shielding which places a high-Z mass between a source and a
person is used to attenuate (reduce or weaken) x-rays within a reasonable distance. This
shielding must include baffles to limit leakage of scattered or re-radiated x-rays because even air
molecules and aerosols can scatter x-rays. The effectiveness of shielding must be tested by
measuring the radiation level to assure that radiation leakage is near background levels while
an electron beam is operating.
What Health and Safety Concerns Do Hazardous Components in
UV/EB-Cured Materials Present?
The toxicity of constituents that are vapors and gases are determined from the MSDS that are
required to be supplied with a coating. According to OSHA regulation 1910.1000:
E = C(a) T(a) + C(b) T(b) + C(n) T(n) divided by 8
Where:
E is the exposure in terms of effective concentration.
C is the concentration during any time period T where the concentration remains consistent.
T is the duration in hours of the exposure at concentration C.
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The value of E shall not exceed the 8-hour time weighted average specified in Subpart Z of 29
CFR Part 1910 for the substance involved. Table Z-l (which is too large to insert here) gives
the permissible exposure limits (PELs) which are 8-hour time weighted averages (TWAs) unless
otherwise noted. A "C" designation on concentration in the table denotes a ceiling limit on the
concentration.
When monomers, oligomers and photoinitiator have become part of a polymer, they no
longer have the toxicity that they previously had. Therefore, the UV/EB radiant energy can be
considered as transforming the composition of a liquid material and thereby changing its
toxicological properties. This transformation generally reduces toxicity by making the
contribution of each component to overall toxic dosage unavailable.
Monomers that were used with acrylic functional groups over 20 years ago were toxic at a
dose of milligrams per kilogram of body weight. Everything is toxic, it just depends on the
dose. You can be killed by ingesting even pure water or table salt if the dose is large enough.
Acrylates in use today have a greatly increased toxic dose (which means a lower toxicity) when
compared to monomers and photoinitiators used in the past. However, these formulations
should still be used with adequate hygiene (safety precautions). Table 4 lists some allowable
emissions that were found in 1991.
Additional compounds could have been listed in Table 4, but no PEL standards were available
for them in 1991. These unlisted compounds include: acetophenone, benzophenone,
caprolactone acrylate, 2,2 dimethyltrimethylene acrylate, epoxy acrylate,
ethoxyethoxyethacrylate, ethoxyethyl acrylate, 2 ethylhexyl methacrylate,
glycerolpropoxytriacrylate, hexandiol acrylate, methylcarbamoyloxyethyl acrylate,
pentaerythritol triacrylate, trimethylolpropane triacrylate, trimethylolpropane
tri(3-mercaptopropionate, tripropyleneglycoldiacrylate, n-vinyl pyrrolidone. The fact that there
were no standards available indicates the infancy of UV/EB materials in 1991.
Table 4 Permissible Exposure Limits of Radiation-Curable Material in 1991
Compound
1,4 divinyl benzene
2-ethylhexyl acrylate
hydroxypropyl acrylate
phenyl glycidyl ether
styrene
vinyl cyclohexene dioxide
8 hour time
averaged permissible exposure limit (PEL)
10 ppm
50 ppm
0.5 ppm *
10 ppm
100 ppm
lOppm
Note: * - There were no federal standards available, values recommended by American Conference of Government Industrial
Hygienists (ACGIH). OSHA determined the PEL.
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Ten years ago, many photoinitiators were VOC and leached out after polymerization.30
Because these photoinitiators also were toxic, they were undesirable and not allowed to contact
food. As a result, new photoinitiators were developed that replaced the old ones. These new
photoinitiators have a lower toxicity in an uncured state and become an integral part of the
polymer molecule. Therefore, toxic compounds can no longer migrate or leach out. After
polymerization they are no longer separate and toxic molecules.
The Toxic Substance Control Act (TSCA) of 1977 gave EPA broad authority to assess risks to
human health. Most of the radiation-curable materials were subject to TSCA. Section 5 of
TSCA required manufacturers or importers of a new chemical substance to submit a
Pre-Manufacturing Notice (PMN) for a new chemical substance (NCS) 90 days prior to its
manufacture or import. During the 90 day period, EPA had to decide whether or not the NCS
presented an unreasonable risk. In 1991, questions about acrylic material caused few if any
acrylates to clear the PMN step of the regulatory process. This inhibited the development of
acrylates and also inhibited the development of alternatives. However, a study by the Specialty
Acrylates and Methacrylates Panel of the Chemical Manufacturers Association changed that
situation. Based on that study, the EPA's position changed and the EPA no longer automatically
considers newer acrylates and methacrylates as significant health risks. However, if a new
acrylate is structurally similar to a substance for which EPA has positive toxicity data, EPA
may regulate that substance on the basis of its potential risk. This change in EPA policy has
helped to introduce new acrylates and methacrylates, especially those with higher molecular
weight. Therefore, the toxicity of UV/EB-cured monomers, oligomers and photoinitiators are
much less of a concern today then they were in the past.
The American Industrial Hygiene Association has published Workplace Environmental
Exposure Levels (WEELs) for several monomers used in UV/EB-curable coating technology.1
Table 5 shows the PELs for organic solvents that could be used for cleanup or dilution.
When applying a coating by spray painting, about 50% of the coating is carried away in air
flow as overspray. This amount of overspray can be as small as 10% if electrostatic deposition
is used. This is true of both conventional paints and UV paints. The conventional and UV
paints can have a comparable toxicity prior to curing. However, all of the overspray of a
conventional paint must be disposed of, because it has flashed off its volatile components
(mainly the VOC) and changed its viscosity. The UV paint that is captured by the arrester can
be reused because it typically contains no volatile solvent and, therefore, has not changed its
viscosity.
Paint overspray arresters (filters in the air exhaust from a paint spray booth) capture 90% to
99% of the overspray droplets. Reuse of overspray droplets that drain off of a UV/EB paint
overspray arrester can increase the overall effectiveness of a spray coating operation. Various
types of paint overspray arresters, when used with conventional paints, allow droplets with
aerodynamic diameters from 3 to 7 microns or less unimpeded passage. However, a filter to
capture droplets down to 1 micron in diameter could be used with UV paints. This is practical
because drainage from the filter in a UV process can be reused and the cost realized, as a
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TABLE 5: PERMISSIBLE EXPOSURE LIMITS (PEL) FOR ORGANIC SOLVENTS
Compound
n-butoxyethanol
butyl acetate
n-butyl glycidyl ester
butyl lactate
p-tert-butyl toluene
carbon tetrachloride
di-isopropyl ether
n,n dimethylacetamide
dipropylene glycol methyl ether
dipropyl ketone
2 ethoxyethanol
2 ethoxyethyl acetate
ethyl acetate
ethyl butyl ketone
ethyl ether
sec-hexyl acetate
isophorone
isopropanol
isopropyl acetate
mesityl oxide
methyl acetate
methylal
methyl alcohol
methyl n-amyl ketone
methyl n-butyl ketone
methylcyclohexane
methyl ethyl ketone
5-methyl-3-heptane
methyl isoamyl ketone
n-propyl alcohol
propylene glycol monomethyl ether
1 , 1 ,2,2-tetrachloroethane
tetrahydrofuran
toluene
xylenes
8 hour time weighted average permissible exposure limit (PEL)
50 ppm
1 50 ppm
50
5 ppm*
10 ppm
10 ppm
500 ppm
10 ppm
1 00 ppm
50 ppm
200 ppm
1 00 ppm
400 ppm
50 ppm
400 ppm
50 ppm
25 ppm
400 ppm
250 ppm
25 ppm
200 ppm
1,000 ppm
200 ppm
100 ppm
100 ppm
500 ppm
500 ppm
25 ppm
50 ppm
200 ppm
100 ppm*
5 ppm
200 ppm
200 ppm
100 ppm
* Note: No Federal Standard, value recommended by ACGIH
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result of the greater pressure, would be less than the cost of the paint saved.
To minimize potential exposure to uncured UV droplets that do pass through the arrester, a UV-
curing unit should be installed on an arrester exhaust. If a UV-curing unit is used to cure the
droplets that pass through the filter before they are exhausted to the atmosphere, the aerosol in
the exhaust air would not be toxic. In addition, the cured exhaust stream would be less likely to
mark a neighbor's roof than an aerosol from a conventional spray booth.
A paint overspray arrester is typically removed when it is "fully loaded" with uncured
conventional paint. "Fully loaded" means that a filter has too great a pressure drop when
passing the required air flow. In addition to a "fully loaded" filter (and the paint it contains),
paint that has drained off the overspray arrester must be considered. When a conventional paint
is used, this drainage cannot by reused because it has flashed off its volatile components and is
more viscous than the sprayed paint. Therefore, with conventional paints, a greater amount of
waste must be handled and this poses a greater threat of adverse health effects. This threat of
adverse health effects can be minimized by using and reusing UV paint.
The aerosol emission of mist was noted in 1991 as "monomer emissions", for which the
quantity
and composition of emissions were to be researched. It has since been discovered that this
aerosol or mist is emitted not only from spray guns, but from rollers and printing presses
(especially high speed operations). Misting varies from 1% to 50% of the total consumed
UV/EB coating or ink. If misting is a problem, the equipment, process and materials suppliers
can work with operators to minimize emissions.
Conventional coatings can range from 40% to 80% solvent by volume. This solvent is
frequently a combination of VOC. Ingredients in conventional coatings that cause health effects
include HAP, VOC, and pigments. HAP include ingredients that are toxic, neurotoxic, and
carcinogenic. UV/EB materials essentially do not contain VOC or HAP (Currently available
UV/EB coatings may have HAP as a very minor ingredient that becomes part of the polymer).
Some pigments have displayed toxicity.
Currently available UV/EB coatings emit only 1% - 5% by weight, while older coatings could
emit up to 10% as curing volatiles. These values are based on Method 24 results. Method 24
bakes the coating after the cure to drive off any residual VOC, but this may cause some
decomposition to occur.
What About Worker Hygiene?
Hygiene is the procedure that is followed to keep from getting injured, sick, or otherwise having
health problems. It is contrasted with therapy, the procedure followed to recover or to get well
after you have gotten injured, sick, or developed a health problem. Hygiene is safety
precautions. Therefore, it is a good idea to follow good hygiene, even though you may not agree
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that it is necessary, or understand why it is required.
Several regulations or laws have been enacted, including the Federal Hazard Communication
Standard, plus federal, state, and local laws and regulations requiring workmen to be informed
of risk factors in a job. Parts of these standards regulate product warning labels, MSDS,
worker education, and training. These standards should help you understand why hygiene needs
to be practiced, why specific hygienic practices are required, and how to communicate hygiene
requirements to employees.
Although UV/EB-curable materials, in their modern form, have not been in use long enough to
demonstrate long-term toxic effects, some older UV/EB materials have demonstrated short-term
toxic effects. These short-term effects have abated somewhat with development of less toxic
materials over intervening years since these effects were observed.
Because the same base monomers and oligomers are used in conventional coatings, inks and
adhesives for painting or printing, UV/EB materials are subject to the same conventional
painting or printing hygiene with some additions. Some of these additional safety precautions
are attributed to the acrylic group (or other functional group) which has been attached to an
UV/EB-curable molecule. An acceptable risk of occupational contact dermatitis (inflammation
of the skin and mucous membranes) and eye irritation can be achieved with proper protective
clothing, proper handling procedures of UV/EB-curable materials and proper shielding from
UV/EB radiation. Contact dermatitis also may be caused by an allergic reaction to a substance
in a UV/EB material that is only present in trace amounts.
It is important to remember that UV/EB-curable materials remain spreadable and not necessarily
in one place until they are cured or cleaned up. They do not evaporate, cure, or dry up like
conventional materials do. They may travel based on contact, first from a contaminated site and
then on contact to any other site. Equipment touched by contaminated gloves will remain
contaminated and a source of exposure until it is either exposed to UV/EB radiation or cleaned
up.
UV/EB-curable materials should never be allowed to come in contact with the eyes. For eye
protection, safety glasses, goggles, or a full face shield should always be worn when handling
any chemicals or solvents (See Figure 13). This was especially true of older UV/EB chemicals,
but you should use this precaution even though newer UV/EB chemicals cause less eye irritation
and are less toxic.
You should never look directly at UV lamps or strong reflections, even with eye protection. All
eye protection materials should have side shields and absorb sufficient UV light to prevent
unintentional exposure and the resulting eye irritation.1
You should never adjust UV or EB shielding without qualified supervision.1
You should always eat or drink in a designated lunch area, and never in the work area. You
should be alert to any contamination of this area and avoid such contamination. You should also
wash thoroughly before touching any food or drink.24 You should apply a barrier cream after
eating and before returning to work.
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Figure 13: Examples of Safety Equipment
Direct skin contact with all coatings, inks and adhesives should be avoided.1 Always wash
hands thoroughly before using restroom facilities. Barrier cream should subsequently be
reapplied after washing hands and before returning to work.24 Barrier creams should be applied
to clean skin before exposure and not applied after exposure. Barrier creams can protect against
material that might penetrate through defects in the protective equipment.
Typically, fabric or non-woven long sleeved and full leg clothing or coveralls are worn. Rubber
gloves should always be worn when direct contact with radiation curable materials is possible.
It is appropriate to use the same hygiene for UV/EB materials that you would use for a solvent,
a corrosive chemical, or a toxic chemical. Wearing protective clothing for a full shift may also
require that air temperature be controlled to allow workers to remain comfortable. Use of a
rubber apron or rubber suit is appropriate when there is a possibility that you could be splashed
with solvent, corrosive, or toxic material. Shoes must provide full foot coverage. Rubber boots
should be worn when there is danger of a spill or when walking where a solvent or toxic
material has spilled.
Contaminated leather objects (shoes, belts, etc.) should be discarded because they cannot be
decontaminated. Always change work clothes before leaving the plant. Never wear the work
clothes or the work shoes away from the plant.
Contaminated clothing can be laundered at a commercial laundry, but not in a home laundry.
After cleaning, they may be worn again. Heavily contaminated clothing should be discarded.24
Rags used for clean up should immediately be placed in a container for either disposal or
laundering and should never be placed in your pocket.1
Some coatings use monomers and amine photoinitiators that may have strong odors. Vapor
inhalation is usually an odor problem, but could also become a toxicity problem. Therefore,
ventilation for odor control is strongly advised. Although odoriferous amines are falling out of
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use, ventilation should also be used for mist aerosols, ozone, and HAP that might result when
UV/EB radiation cured materials are applied and cured. Odors can reach concentration levels
that require controls for the comfort and, perhaps, health of workers.
Misting occurs in high speed presses, at liquid ink transfer points, when paints are sprayed and
during application with high speed rollers. Mist is an aerosol that is probably toxic and possibly
carcinogenic. Misting forms deposits in UV lamp enclosures. Such deposits reduce UV output
and increase heating within an enclosure. Electrical arcing can occur at lamp electrode contacts
as a result of powder accumulating due to misting. This can cause slower curing speeds and
result in higher operating costs. Deposits must be removed from ovens and lamp enclosures
with a mild detergent to avoid these problems.
The droplet size of mist aerosol is often smaller than 3 microns, but can be larger for sprayed
paints. In both cases, its existence is well-known. Since uncured UV/EB materials have a
toxicity, prudence would require that you not breathe this aerosol. A suitable filter mask or
supplied air mask is recommended when there is no ventilation. If an aerosol has been cured by
sufficient exposure to UV or EB radiant energy, it no longer is toxic. Operations that produce
such aerosols or mists should be enclosed and well ventilated. Ventilation should carry air to an
ultraviolet light source or sunlight to cure a UV coating or ink aerosol, because droplets are
frequently too small to be filtered out. Such aerosols should not be emitted after sundown unless
cured by a curing unit before being emitted. Aerosols can also form in a fire, or with
uncontrolled polymerization of bulk materials. A mask providing fresh air or an organic vapor
respirator should be worn under such potential exposure conditions.1
Make sure that you do not exceed the allowed exposure to ionizing radiation. While the OSHA
definition only applies to x-rays, care must be taken to assure that workers do not receive a UV
dose that would irritate either their skin or eyes.
COST CONSIDERATIONS
ARE UV/EB-CURED MATERIALS MORE EXPENSIVE THAN CONVENTIONAL
COATINGS, INKS AND ADHESIVES?
Conventional coatings, inks and adhesives can emit 50% to 80% of their volume as VOC. This
VOC evaporates and is carried away by ventilating air flow from application processes and/or
from thermal ovens that dry and cure this material. VOC emissions from UV/EB-cured
materials are much less, ranging from 1% to 10% of the weight of the UV/EB material.
Typically, VOC emissions from most UV/EB material applications are less than 5% of the
applied material weight. Also note that virtually every component in a UV/EB-cured material
becomes part of the cured coating ink or adhesive, but only 20%-50% of a conventional
material (i.e., the resin and pigments, not the solvent) becomes applied coating solids. Less
gallons of UV/EB material are needed to cover the same amount of area at the same film
thickness. Therefore, the best way to compare the cost of UV/EB and conventional materials is
on a solid film basis instead of cost per gallon.
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More effective use of UV/EB-cured materials (based on reuse of overspray) can make UV/EB
operations more cost effective then conventional operations. In addition, more cost savings
result when using UV/EB technology as a result of lower energy requirements, reduced floor
space, increased productivity and absence of add-on control equipment. Overspray of UV/EB
materials can be effectively captured and reused because they generally lack volatiles, and will
not cure unless exposed to UV/EB radiant energy. If recirculation of UV/EB material is a
viable alternative, the cost of UV/EB materials could actually be about 30% - 60% of the cost of
a conventional coating on a comparable solid film basis (this is for material cost only).
The cost of "as applied" UV/EB-cured coatings is about 15% greater than conventional coatings
on a per gallon basis. However, as noted above, over half of a conventional coating evaporates
and does not become part of the final cured coating. Because UV/EB-cured coatings have only
a 1 to 10 % loss, they cost about 45 % less than conventional coatings per square foot on a solid
film basis. The 1991 CTC report stated that UV/EB coatings cost as much as four times the cost
of conventional coatings on a per gallon basis, and twice as much on a solid film basis. Over
the past 10 years these differences are no longer valid because of reductions in price of UV/EB-
cured materials. When higher production rates (along with a resulting reduction of inventory
in-process), lower energy consumption and reduced floor space requirements are considered,
economic considerations greatly favor UV/EB over conventional coating technologies in most
cases. Similar economic advantages are found in the printing industry.
Higher production rates for UV/EB processes are based on shorter (faster) cure time. Shorter
cure times result in smaller curing units (compared to conventional thermal dryers) that require
less floor space (See Figure 14). Also, there may be additional space savings because UV/EB-
cured products do not require conditioning time in storage. For conventional processes that use
thermal ovens, product exiting an oven may have to be held for several hours (8 to 24 hours or
possibly more) in storage if conditioning of the substrate is necessary (e.g., to reduce
brittleness after a paper substrate has been subjected to heat and drying in an oven). This
conditioning often requires storage at controlled temperature and humidity. This type of storage
is not needed for products after UV/EB-curing. Therefore, UV/EB processes may have an
additional space and productivity advantage over conventional operations that require product
conditioning after exiting a thermal oven.
As an example, consider two printing lines with 10 foot wide webs and operating at 1,000 feet
per minute. One printing line uses UV technology and print leaves the curing unit completely
cured. The other printing line uses conventional technology and print leaving the oven is
sufficiently cured (i.e., it will no longer smudge). In this comparison, the conventional material
must reach that point in 6 seconds in an oven that extends 100 feet. This may be optimistic. The
conventional process may have to run slower than this, but we will assume that the conventional
material will cure sufficiently in 6 seconds. By comparison, the UV cure will take a fraction of a
second and the UV-curing unit only takes up 100 square feet. The thermal oven will need to use
1,000 square feet (10 x 100) of rental floor space at $0.50 per square foot per month ($6.00 per
square foot per year), for a total of $6,000 per year. The UV-curing unit will use only 100
square feet (10 x 10), and the rental cost is $600 per year.
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Figure 14: Presses With UV-Curing Units
For the same example, energy consumption for a thermal oven is 1.5 MBTU/hr plus blowers at
56 kW. We will assume that natural gas consumption will be at $3.00 /MBTU and electric
consumption will be at $0.07/kW-hr. If the plant operates 300 days per year for two shifts, the
total energy cost for the thermal oven would be $21,600 per year and the cost of electricity for
the blowers would be $18,816 per year. In comparison, the UV-curing unit would use 5.6
kW/lamp times 12 lamps times $0.07/kW-hr to cost $22,579 per year and ventilation would cost
$336 per year on the same basis.
In summary, the cost of operating a conventional printing line in the example would be $6,000 +
$21,600 + $18,816 = $46,416. The cost of operating the UV printing line would be $600 +
$22.579 + $336 = $23,415. This is a savings in operating cost for the UV line over the
conventional line of at least $23,001 ($46,416 - $23,415), or about 50% for this hypothetical
example.
The capital cost of a thermal oven is significant. The capital cost of a UV-curing unit is almost
trivial by comparison. Even an EB-curing unit should cost less.
As previously indicated, UV/EB-cured coatings, inks and adhesives cure rapidly and can go on
to the next finishing operation in the production process immediately. The only exception (at
this time) is if cationic photoinitiators are used. Cationic curing takes a few seconds compared
to almost instantaneous cures when using free radical photoinitiators
The cost of add-on emission control technology for conventional solvent (i.e., VOC) based
coatings, inks and adhesives can be from $250,000 to over $3,000,000. UV/EB-cured coatings
have minimal VOC emissions; therefore, add-on controls are not required. The capital and
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operation and maintenance costs of the emission controls needed for conventional applications
should be included in any comparative cost analysis.
When UV/EB materials are used, fire insurance premiums should be reduced due to the lack of
inflammable VOC. (One insurance company reported a 5% reduction). The absence of
inflammable VOC at facilities using UV/EB technology should reduce accidents that lead to fire
or explosion.
Protective equipment and safety measures that must be used with UV/EB materials are typical of
the chemical, printing, painting, and coating industries in general. Although there may be some
variation in safety precautions between facilities that use UV/EB materials compared to
conventional materials, the variations should not greatly influence cost.
The actual costs for implementing UV/EB technology for a particular operation will vary with
time and circumstances. Actual cost estimates should be obtained for each facility and process at
the time a change is being considered. The net cost of a change to UV/EB-cured technology
usually allows payback within two years.
SUMMARY
WHAT ARE THE ADVANTAGES OF USING UV/EB-CURED
COATINGS, INKS AND ADHESIVES?
* Cures Fast - Runs at higher rates and cures in a shorter time than evaporative coatings.
* Low Energy Consumption - Uses much less energy to cure than evaporative coatings.
^Compact Design - Uses much less floor space than conventional evaporative coatings.
* Low Emissions - Less emissions without controls than most conventional evaporative
coatings systems with emissions controls.
"^Regulatory Advantage - Easily meets most regulatory requirements and eliminates some.
"A" Cost Effective - Reduces initial costs and payback times. No conditioning required.
"A" Produces High Quality Finish - Used for quality furniture, magazines, microelectronics.
"A" Ready-to Go - Materials supplied ready to use - no blending/mixing required.
"A" Reusable/Recyclable - No volatiles lost in application, can be reused immediately.
"A" Cures in Curing Unit - Does not cure on equipment, can be left over a weekend.
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* Less Worker Exposure to HAP/VOC - Absence of HAP/VOC in UV/EB materials.
* Less Flammable - Greater safety, lower fire insurance premiums.
* Able to Recycle Product - Paper from UV/EB products can be recycled, even to higher grade
WHAT ARE THE DISADVANTAGES OF USING UV/EB-CURED
COATINGS, INKS AND ADHESIVES?
• Misting/Overspray - Spray and high speed roller and printing applications can produce
aerosol that can be inhaled.
• Aerosol Toxicity - Aerosol is uncured, toxic, and will not go away without cleanup.
• Worker Hygiene/Sensitization - Similar to other processes, but different. Has different
results.
• Workplace Contamination/Cleanup - Contamination will persist and spread until cleaned up.
• Persistent in Environment - Uncured material will persist in shade.
• UV/EB Radiant Energy - Can injure if used improperly.
• Customer Resistance - Historic risk of not meeting need. This may now be past.
CONCLUSIONS
1. UV/EB-cured coatings, inks and adhesives are widely used and are expected to be more
widely used as people become more familiar with this material and developers produce new,
safer, and better coatings, inks and adhesives to apply to specific objects or substrates.
2. Toxicity of UV/EB-cured coatings has gone from very toxic to only mildly toxic. Further
advances in toxicity reduction are anticipated. Conventional coatings are considered mildly
toxic. Cured coatings of all types are usually free of toxicity.
3. Use of UV/EB-cured coatings, inks and adhesives requires good hygiene in handling and
disposal of waste. This hygiene is similar to what is already used in the coating, printing, and
chemical industries. However, each situation requires somewhat different equipment.
4. Using UV/EB radiant energy to cure instead of heat to evaporate VOC from coatings and
inks reduces energy consumption, fire hazard, need for control technology, in-process product
storage requirements, floor space needs and, probably, insurance premiums. These reductions
should provide potentially significant economic benefits.
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REFERENCES
1. Safety and Handling of UV/EB-curing Materials, R. Golden, Journal of Coatings
Technology, Vol. 69 No. 871, August 1997, pp 83-89
2. Occupational Safety and Health Administration (OSHA) Standards 29CFRNo. 1910.1096,
Ionizing Radiation
3. AP-42, Clearinghouse for Inventory and Emission Factors, Environmental Protection
Agency, Chapter 4 Section 9, General Graphic Printing
4. Stork Sheds Light on UV Inks, D. Lanska, Converting Magazine, June 1997
5. Acrylate Formulations for a Solventless Magnetic Tape Manufacturing Process; M. Ellison,
J. Huh, A. Power, J. Purse, and D. Nikles, Proceeding of the Polymeric Materials Science and
Engineering, American Chemical Society, pp 115-116
6. Ultra Low Voltage Curing of Acrylic Hot Melt PSA's, R. Ramharack, R. Chandran, S. Shah,
D. Hariharan, J. Orloff, and P. Foreman, Adhesives Age, December 1996, pp 40-43
7. Deco-Chem Education Center
www.decochem.com/educntr.htm
8. Coating Types and Curing Characteristics, Small Business Environmental Assistance
Program
sbeap.niar.twsu.edu/docs/pntch2.html
9. Electron-beam Curable Structural Adhesives. Part 1: Study of acrylic resins for adhesive
applications, N. Cadinot, B. Boutevin, AJ. Parisi, D. Beziers and E. Chataignier, International
Journal of Adhesion and Adhesives, Volume 14 Number 4, 1994, pp 237-241
10. Design for the Environment, Flexography Project, Focusing on Flexo Inks,
EPA 744-F-95-006, February 1996
11. Coating Alternatives Guide, CAGE
cage.rti.org/altern_data.cfm?id=radcure&cat=summary
12. European Coatings Net: New Coating Technologies for Wood Products, M. Tavakoli, S.
Riches, J. Shipman, and M. Thomas
www.coatings.de/articles/tava/TAVA.htm
13. Alternatives to Solvent-Borne Coatings, University of Illinois at Urbana-Champaign
nuclear.hazard.uiuc.edu/packets/coatings/alternat.htm
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14. Guide to Cleaner Technologies: Organic Coating Replacements, R. Joseph, O. Stanley, C.
Danick, L. Melgery, Envirosense/Environmental Protection Agency
es.epa.gov/program/epaorgs/ord/org-coat.html
15. Polyallyl Glycidal Ether Resins for Very Fast Curing High Performance Coatings,
J. Knapczyk, Solutia Inc.
www.coatings-solutia.com/docs/TechPubs/211x.htm
16 Volatile Organic Compounds from Electron Beam Cured and Partially Electron Beam
Cured Packaging Using Automated Short Path Thermal Desorption, V. Das, J. Manura, T.
Hartman, Scientific Instrument Services Application Note No.79
www. si sweb. com/referenc/applnote/app-79 .htm
17. Advanced Electron Beam Curing Systems and Recent Composite Armored Vehicle
Results, D. Goodman, C. Byrne, G. Palmese, 42nd International SAMPE Symposium, May 1997
18. E-Beam Processing of Composite Structures, R. Vastava, 42nd International SAMPE
Symposium, May 1997
19. Layer by Layer E-Beam Curing of Filament Wound Composite Materials with Low Energy
Beam Accelerators, F. Guasti, N. Kutufa, G. Mattacari, E. Rosi, SAMPE Journal, Vol.34 No.2,
March/April 1998
20. Low Energy Electron Beam Curing for Thick Composite Production, F. Guasti and E. Rosi,
Composites - Part A: Applied Science and Manufacturing, Vol. 28 No. 11, 1997, pp. 965-969
21. Toughened Epoxy Resins Cures by Electron Beam Radiation, C. Jahnke, G. Dorsey, S.
Havens, V. Lopata, 28th International SAMPE Technical Conference, November 1996
22. Electron Curing of Epoxy Resins: Initiator and Concentration Effects on Curing Dose and
Rheological Properties, V. Lopata, M. Chung, C. Jahnke, and S. Havens, 28th International
SAMPE Technical Conference, November 1996
23. UV/EB-curing, Primer 1, RadTech International North America, 1995
24. UV-curing Technical Information, Health Safety and the Environment
www.uvcuring.com/uvguide/chap4_8/chap4_8.htm
25. Coatings R&D, Paint and Powder Magazine Online, Dr. Harvest L. Collier, University of
Missouri-Rolla www.ippmagazine.com/news/0499col3.htm
26. UV, EB and Aqueous Coatings: Technical Basics, Elmer W. Griese, GATFWorld,
May/June 1998
27. Radiation Curing in the Printing Industry, CEPE Position Paper of June 1997
www.cepe.org/RadCurePS0697.html
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28 Volatile Organic Compounds from Electron Beam Cured Packaging Using Automated
Short Path Thermal Desorption, V. Das, J. Manura, T. Hartman, PittaCon99 Meeting, Orlando,
FL, March 1999
29. UV Systems - Technology and Technique, R. Stowe, Fusion Systems at the National
Association of Graphic and Product Identification Manufacturers, Coronado Island Marriott
Resort, CA, October 25-28 1998
30. Radiation-Curable Coatings, Control Technology Center, U.S. Environmental Protection
Agency, April 1991
31. Characteristics and Performance of Radiation Curable Powder Coatings, S. Udding-
Louwrier, E. Sjord de Jong, R. Baijards, RadTech Proceedings, April 19-22 1998, Chicago, pp
106-111
32. Excimer UV Lamps - The real cold alternative in UV-curing, Dr. A. Roth, M. Honig,
RadTech Proceedings, April 19-22 1998, Chicago, pp 112-116
33. UCB Chemicals Corporation/Radcure - An Overview, M. Philips, D. Nack, RadTech
Proceedings, April 19-22 1998, Chicago, pp 120-124
34. Waterbased radiation-curable systems - newest investigations, W. Reich, P. Enenkel, E.
Keil, M. Lokai, K. Menzel, w. Schrof, RadTech Proceedings, April 19-22 1998, Chicago, pp
258-265
35. Radiation Curable Binder Matrices of Interest in Manufacturing Energetic Materials, S.
Stiles, Dr C. Clark, RadTech Proceedings, April 19-22 1998, Chicago, pp 266-284
36. Characterization of Radiation Curable Formulations Using a Fluorescence Monitoring
Technique, R. Buehner, pp 337-347
37. New Developments in Fluorescence Probe Technology for Cure Monitoring, K. Specht, R.
Popielarz, S. Hu, d. Neckers, RadTech Proceedings, April 19-22 1998, Chicago, pp 348-355
38. The Effect of Moisture on the Cationic Polymerization, P. Hupfield, S. Hurford, J.
Tonge, pp 468-475
39. Low Viscous Maleate/Vinyl Ether Resins as Reactive Diluents In Conventional Acrylate
Based Wood Coating Formulations For UV-curing, E. Meij, A. Dias, L. de Cocq, pp 585-589
40. Water Thinnable UV-Curable Coatings, M. Bernard, RadTech Proceedings, April 19-22
1998, Chicago, pp 590-596
41. UV Lamp Performance Over Time, S. Siegel, RadTech Proceedings, April 19-22 1998,
Chicago, pp 685-691
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42. A Performance Comparison of Electronic vs. Magnetic Ballast for Powering Gas-Discharge
UV Lamps, E. Persson, D. Kuuisisto, RadTech Proceedings, April 19-22 1998, Chicago, pp
692-700
43. Deinking Trials for RadTech International, Beloit Corporation, Pittsfield Research Center,
Pittsfield, Mass., January 1992
44. Personal communication, Gary Jones, Graphic Arts Technical Foundation, January 31, 2000
54
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GLOSSARY OF TERMS
Acrylate(s)
An organic salt (an ester) produced by the reaction of acrylic
acid with an organic molecule. It is any molecule that has an
acrylic radical attached to it.
Actinic UV
Actinic or far-UV (both terms mean the same thing) is the UV
radiant energy between 180 - 315 nanometers in wavelength. It
is used mainly for sterilization. Also see UV Radiant Energy.
Adhesive(s)
Specialty coating designed applied to a material to make it cling
or stick fast to another surface (e.g., the coating applied to make
pressure sensitive tape and labels).
Arrhenius Acid(s)
S. Arrhenius of Sweden defined an acid as a hydrogen ion
donor. Since the hydrogen ion is a proton and a neutron, this is
very close to a Bronsted acid. Also see Lewis acid.
Atomic Number (Z)
The number of protons in the nucleus of each atom of an
element. The atomic numbers for naturally occurring elements
range from 1 to 89. Man-made elements exist above this range.
Brehmsstrahlung
In German, Brehmsstrahlung is literally retarding or braking
radiation. Brehmsstrahlung is the energy lost in the elastic
impact of electrons, or the energy lost when an electron goes
from a larger orbit to a smaller orbit. It is radiated as x-rays.
Bronsted Acid(s)
J. N. Bronsted of Denmark defined an acid as a proton donor.
This definition allows an organic radical or a zeolite to be
included with the acids. It replaced the concept of a hydrogen
ion donor for chemicals that do not hydrolyze or generate
hydrogen ions. See also Arrhenius acids, Lewis acids
Catalyst(s)
There are two types of catalysts, heterogenous and
homogenous. Both affect the rate of chemical reactions. A
heterogenous catalyst is a substance within another phase (solid,
liquid or gas). A homogeneous catalyst is a substance within
the same phase. Heterogenous catalysts do not enter into the
reaction, but homogeneous catalysts may enter into the
reaction.
Cationic/Cationic
Polymerization
A positive valence ion that is attracted to the cathode in
electrolysis. A cationic photoinitiator is one that decomposes
under UV/EB radiant energy or from Bronsted Acids to form
cations that cause polymerization to occur by an ionic
mechanism.
Coating(s)
A protective, adhesive, or decorative film applied in a layer to a
surface. The coating can be applied as either a liquid or a solid.
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Crosslinking
The interconnecting of one polymer molecule with another by
molecular bonds. Crosslinking raises the glass transition
temperature and gives mechanical strength and abrasion
resistance to the polymer.
Diluent(s)
A low viscosity chemical that is added to a mixture to reduce
overall viscosity. This includes reactive diluents that become
part of the polymer molecule upon polymerization. Reactive
diluents may be VOC prior to polymerization, but cease to be
VOC after polymerization
Dimer(s)
Two identical molecules link together to form one molecule.
An example is a hydrogen peroxide molecule which is two
hydroxyl radicals linked together.
Electromagnetic Wave(s)
Radially propagating energy in the form of photons or waves,
traveling away from a source. These photons or waves are
characterized by wavelength or frequency, amplitude, intensity,
and quantum parameters. Wavelength is the speed of
propagation divided by frequency. Amplitude of a wave is a
measure of the strength of the energy. Intensity is measured as
the rate at which the energy is absorbed.
Electron Beam (EB)
EB Radiant Energy
Electron beams are produced by a high potential gradient
between electrodes. When the gradient is high enough,
electrons stream from the negative electrode. A positive
electrode having a hole in the middle attracts the electrons.
Because an electron has mass, electrons that are directed toward
the hole continue through as an electron beam.
Excimer(s)
An excimer is an excited dimer It is a molecule that is split
apart by photons. It gives a defined spectrum of
electromagnetic energy when the dimer reassembles. If two or
more photons caused the split, the emitted spectrum can even
be at a shorter, more energetic wavelength.
FarUV
See Actinic UV
Fluorescence
The phenomenon of a single photon exciting a molecule and
causing that molecule to emit a longer wavelength.
Free Radical / Free
Radical Polymerization
A free radical is a molecular fragment having a single unpaired
electron. It causes polymerization by transfer of an electron
from a monomer molecule. When this transfer occurs, the free
radical and the monomer molecule become one. This new
molecule is a larger free radical that can then transfer an
electron from still another monomer molecule. This process
can continue in a chain reaction that will form a seemingly
endless polymer molecule (one composed of many monomers).
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Functional Group(s)
A radical that has been attached to a monomer or oligomer
molecule. A functional group causes a molecule to become
excited more easily in the presence of free radicals and radiant
energy. The most commonly used functional groups are the
acrylic, methacrylic, vinyl ether, and methoxyacrylic radicals.
Gray
A unit of absorbed radiant that is equal to one Joule per
kilogram.
Hazardous Air Pollutants
(HAP)
A list of 189 chemicals identified in the Clean Air Act
Amendments of 1990 as Hazardous Air Pollutants. See
Appendix E
Ionizing Radiation
Radiation that can ionize a molecule. The term usually refers
to the amount of radiation that will ionize oxygen in air; that is,
radiation with a wavelength shorter than 253 nm (this includes
actinic UV radiant energy generated in UV-curing systems and
electrons and x-rays generated in EB-curing systems).
Infrared (IR)
IR Radiant Energy
Electromagnetic radiant energy that is emitted by any body
above absolute zero in temperature. It is absorbed and sensed as
heat. It is emitted as a spectrum, which shifts its peak to shorter
wavelengths as the temperature increases. The non-luminous
portion of that spectrum is in the range from 700 to ~11,000 nm.
Ink(s)
A pigmented fluid or paste that is used as a writing fluid or the
visible result in printing.
Lewis Acid(s)
G. N. Lewis defined an acid as a electron pair acceptor. See
also the Arrhenius Acid and Bronsted acid definitions.
Monomer(s)
A molecule that self-assembles into a polymer. Each monomer
is another vertebra in a polymer's carbon backbone. The types
of monomer that are available will define the properties of a
polymer. Monomer molecules are named for their chemical
structure (e.g., epoxy, polyester, urethane, silicone, etc).
Near-UV
UV radiant energy between 315 nm and 400 nm. Also see UV
Radiant Energy.
Nitrogen Blanket
Nitrogen gas that covers the substrate like a blanket to exclude
oxygen in the ambient atmosphere. It is used to avoid ozone
generation, nitrogen oxide generation and oxygen inhibition of
polymerization
Oligomer(s)
A group of 3 to 5 monomer molecules that have been joined
together to form a larger molecule. It behaves as a monomer
would, but is usually less toxic.
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Overspray
The solids potion of a coating from a spray applicator which
fails to adhere to the part being sprayed or coated. UV/EB
overspray may be droplets of liquid because virtually all of the
UV/EB material can become a solid.
Oxygen Inhibition
The premature termination of a polymer molecule caused by the
reaction of oxygen molecules with free radicals. When
polymerization is terminated prematurely, polymer molecules
are shorter and perform differently.
Photoinitiator(s)
A compound that forms free radicals or cations when subjected
to UV/EB radiant energy. A photoinitiator is sensitive to a
specific wavelength of radiant energy. Photoinitiators now
become part of the polymer that is formed.
Photon(s)
According to quantum theory, a hypothetical massless particle
that is used to explain some aspects of an electromagnetic
wave. In quantum theory, the electromagnetic wave and the
particle are the same.
Polymer(s)
A chain of many monomer molecules linked together. This
chain can be thousands to millions of monomers long. The
polymer chain tangles and bonds to other polymer chains.
Commonly, a polymer is known as a plastic.
Polymerization
The process that forms a polymer from monomers and
oligomers.
Radiation
Energy (in some form) emitted from a source, propagated
radially along a line-of-sight, and absorbed. However,
depending on the type and source of the energy, the effects of
radiation on humans are very different
Radical
An ionized portion of a molecule. Normally these are anions
and cations, depending upon whether they have a surplus or
deficiency of electrons.
Radioactivity
A property of some atoms in which electromagnetic energy is
emitted. The energy comes from an unstable ratio of neutrons
to protons in the nucleus of these atoms. The nucleus will either
spontaneously fission or fuse to reduce the energy. This occurs
spontaneously and the energy is radiated away as gamma rays,
x-rays, or other particles. Half of the atoms having such
identity will fission or fuse within a well defined half life.
Reactive Diluent(s)
see Diluents
Resin(s)
A term used interchangeably with polymer.
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Roentgens (R)
A unit of absorbed radiation. One Roentgen equals 100 ergs
per gram.
Roentgen Equivalent for
Mankind (REM)
A unit of absorbed dose for the human body. It is expressed in
Roentgens (see above). It is the absorbed dose over the
spectrum up to 100 nm. Since the REM is an integral (the sum)
of all these wavelengths multiplied by the absorption at that
wavelength, there are no conversion factors from other
measurements.
Solvent
A liquid used in a paint, coating or ink to dissolve or disperse
film-forming constituents and to adjust viscosity. It evaporates
during drying/curing and does not become part of the dried film.
Substrate
The surface to which a coating is applied.
Three-Dimensional (3D)
Any object that has length, width, and depth dimensions. Such
objects are capable of casting a shadow over some portion of
their surface. With regard to UV/EB technology, this refers to
the ability to minimize the effect of such shadows to provide for
curing of the entire coating.
Toxic Dose
The lethal dose for 50% of laboratory animals (rats) that
ingested the substance. It can also refer to the concentration that
if inhaled leads to 50% death of laboratory animals.
Transfer Efficiency
The ratio of the amount of coating solids deposited onto the
surface of the coated part to the total amount of coating solids
used.
Ultraviolet (UV)
UV Radiant Energy
That portion of the electromagnetic spectrum between 180 nm
and 400 nm. This can be broken into near-UV (315 nm - 400
nm) and far-UV or actinic (180 nm - 315 nm). It can also be
broken into UV-A ( 315 nm - 400 nm), UV-B (290nm -315
nm), and UV-C (220nm - 290 nm). Near-UV, UV-a, and UV-B
are used for curing UV materials. Sunburn is caused by UV-A
and UV-B. Actinic UV or UV-C is used for sterilization.
Volatile Organic
Compounds (VOC)
Any compound of carbon, excluding carbon monoxide, carbon
dioxide, carbonic acid, metallic carbides or carbonates, and
ammonium carbonate, which participates in atmospheric
photochemical reactions. This includes any such organic
compound other than those that the Administrator of EPA has
determined to have negligible photochemical reactivity.
See Appendix D
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Web Any fabric, paper, plastic film, metallic foil, coiled sheet metal,
or other products which are flexible enough to be unrolled from
a large roll, coated by blade, roll coating, or rotogravure as a
continuous sheet and, after cured, rerolled
X-Ray(s)
Electromagnetic radiation having a wavelength ranging from
0.1 nm to 40 nm. X-rays have a relatively low absorption, and
therefore pass through solids. The attenuation (reduction) in
intensity varies with the mass along that path, the atomic
number of the material along the path, and the wavelength of
the x-ray. Some high Z materials can reduce the x-ray to
background levels with only a short path.
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APPENDIX A
ULTRAVIOLET AND ELECTRON BEAM RADIATION
VS.
RADIOACTIVITY
Radiation is a very broad term. It can refer to the emission of rays of heat, light, radio waves,
or sounds; however, it can also may refer to the emissions of rays by a radioactive substance.
Ultraviolet (UV) and electron beam (EB) radiation are not the same as radioactivity and
should not be confused. Hopefully this appendix will help you understand the difference. Niels
Bohr's concept of the atom (i.e., a nucleus of protons and neutrons surrounded by orbiting
electrons) is the basis for this appendix. We do not need to go any deeper into the realm of
atomic structure.
RADIOACTIVITY
Radioactivity is a property of atoms that have an unstable ratio of neutrons to protons in their
nucleus (i.e., have more than the minimum energy in the nucleus). Because these atoms have
more energy than atoms with a stable nuclide (i.e., a favorable ratio of neutrons to protons),
these atoms are unstable. The nuclei of these atoms spontaneously divide (fission, when the
number of protons is greater than 82, which is the atomic number of lead) or combine (fusion,
when the number of protons is less than 82) with well-defined half-lives. These fissions and
fusions cause emission of electrons, alpha particles (two protons and two neutrons, a helium
nucleus), beta particles (a positron or an electron), neutrons, protons, x-rays, and gamma rays.
The half-life is defined as the time for half of the atoms to undergo either fission or fusion.
Half-lives range from almost instantaneous to millennia.
Fission or fusion of these atoms can be greatly accelerated when they are bombarded by neutrons
from a chain reaction. This happens when neutrons are sufficiently conserved within a critical
mass. As far as we know, a critical mass occurs only in man-made nuclear reactors and in nature
in the core of each star and planet. Even the Earth has a radioactive core and, therefore, we
cannot totally avoid all radioactivity.
There are naturally occurring radioactive isotopes of elements (atoms having a defined atomic
number, but having various atomic weights). These isotopes exist in trace quantities and are
radioactive. UV/EB radiation does not change the concentration, rate of reaction, or number of
such isotope atoms. Therefore, UV/EB radiation does not change naturally occurring
radioactivity. UV/EB radiant energy does not make atoms radioactive.
Gamma rays are not used for curing UV/EB materials because they require much more shielding
to attenuate the intensity of radiation to near background radiation levels.35
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UV/EB RADIATION
UV/EB radiation refers to electromagnetic energy moving radially (i.e., radiating) from a
source. This energy is normally transmitted over a line of sight, but it experiences scattering
when it strikes an object. Ultraviolet radiation exists in sunlight and is emitted, very weakly,
by radioactive materials (except when they undergo a chain reaction - as in the sun or Earth's
core - and elevate their temperature). Our principal natural source of ultraviolet radiation is
sunlight.
The energy of a photon is inversely proportional to its wavelength. Scattering is a function of
wavelength and the size of the object that produces scattering. When the diameter of an object
(scatterer) is less than a tenth of the wavelength of the radiant energy, scattering is negligible.
When the size of the scatterer becomes comparable to or larger than the wavelength of the
radiated energy, scattering is enhanced. You can see an example of this with visible light in a
smoky room. Visible light rays (400-700 nm wavelength) go radially as directed until they
strike a scatterer (e.g., a smoke particle of about 1000 nm) that scatters the radiation. Each
scatterer acts like a point source in scattering waves of radiation and, therefore, each scatterer
appears to be a luminous source. All wavelengths of radiation behave like this, regardless of
the source. X-rays have a short enough wavelength that even oxygen and nitrogen molecules
become scatterers like the smoke described above.
Electron beams are composed of particles (electrons) that collide with other electrons and
scatter, too. Electrons do not actually collide with electrons, but repel each other in close
encounters that resemble collisions. Electron beams, in scattering electrons and impacting
nuclei, generate x-rays similar to those emitted from radioactive materials, but these x-rays (like
medical x-rays) cease to be emitted when the electron beam is turned off.
CONCLUSION
Since UV/EB radiation does not supply neutrons, the UV/EB-cured material does not have any
change in radioactivity or half-life. Therefore, the only connection between UV/EB radiation
and radioactivity is purely linguistic. Both radiation and radioactivity use the root radi- to
describe radial propagation of energy by quantum particles or electromagnetic waves.
We hope that this clarifies more misconceptions than it may cause, for as Alfred North
Whitehead once said, "All truths are only half-truths." This is true because the human mind
cannot understand or accept whole truths. We all function on half-truths that we can understand.
We can act intelligently only when we have the capability to understand what we are doing.
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APPENDIX B
EXAMPLES OF UV/EB COATING AND INK USE
ABRASIVES
Abrasives can be permanently bonded instantly. This eliminates an energy-intensive 8 hour or
longer curing that is required for conventional evaporative coatings under controlled
temperature and ventilation. It also eliminates storage of a day's production under these
controlled conditions. UV-cured abrasives are instantly ready for use.
DENTISTRY
Dental fillings are another application area. After preparing a tooth, a suitably sized lump of
oligomers, photoinitiators, pigments and fillers is mixed and inserted into a clean dry hole in
the tooth. After insertion and molding, an intense UV light source (with readily apparent visible
light) is directed at it by a wand. In about a minute the UV and visible light cures the filling and
the person can use their teeth immediately after finishing operations are completed. While this
seems slow, it is a much faster cure than silver amalgam fillings. The use of a radiation-cured
dental filling has an additional benefit in that it avoids ingestion of mercury from silver amalgam
fillings.
FIBER REINFORCED PLASTICS
Coatings have also been used as the cement to hold fibers or particles together. These fiber-
reinforced-polymer items are used to construct 3D objects. Penetration of EB radiation
becomes a significant factor when coating depth is over 1 centimeter. These thick applications
have been cured by EB either in a vacuum chamber or with a cationic photoinitiator. In these
types of applications, coatings are not limited to a surface, but also may be found on interfaces
at any depth within the object.
FOOD PACKAGING / MENUS
Ten years ago strong odors associated with some monomers and photoinitiators precluded their
use with foods and perfumes. This has been overcome to a large extent, by purification to
eliminate malodorous impurities, using a less odiferous photoinitiator, or using other
alternatives to odiferous additives, monomers, or oligomers. These deodorized materials have
made both printing and overprint coatings suitable for packages for fine perfumes, chocolates,
and food, and even for restaurant menus.23
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MAGNETIC MEDIA
Printing of magnetic media by orienting magnetic particles of a coating to lock magnetic
domains of particles in a preferred position before EB-curing has benefitted the high density
floppy disk and tape manufacturing industry. EB-curing also allows a more durable surface
after bonding. Such coatings must be applied in a clean room to control coating thickness,
insure surface smoothness, and to eliminate dust particles. EB-curing allows these needs to be
easily met.
MICROELECTRONICS
In the microelectronics industry, electron beams have been focused and used to trace circuits on
coated substrates. Alternatively, UV has been used to cure a coating through a mask. The
coating (which is referred to as a photoresist) is cured by the focused EB along a path where a
substrate must be protected from the next step in the process. The coating is then "developed"
by washing any uncured resin away with a solvent. This leaves uncured parts of the substrate
unprotected from reagents used to subsequently etch, deposit a dopant (an atomic species that
changes the electronic properties of the substrate), or deposit metal conductors. It has been
found that for very sharp demarcation of edges of a cured polymer, a coating thickness has to
be no thicker than the width of a line on the microelectronics. Microelectronics now uses lines
only 0.18 microns wide. This thin layer of monomer is applied by diluting or heating the
coating to reduce viscosity and then spreading it by high-speed spinning of the substrate to
centrifuge most of the coating away. The substrate is usually a sliced and polished section of a
purified silicon ingot (called a boule') about 4 inches in diameter.
To be able to use UV, the wavelength must be shorter. This is referred to as extreme UV. This
process requires a thin film that can be either UV-cured through a mask, or EB-cured along a
path. For a UV cure, UV radiant energy must be at a wavelength that the photoinitiator can
adsorb and that delineates a clear image (edge), even if the path is obstructed. For an EB cure,
EB radiant energy must be focused to a spot no larger than the finest line that must be
produced. This produces an EB that cures the thin film instantly at low voltage.
After the cured coating has performed its function of providing a mask for reagents, the cured
polymer is stripped off and another thin coating of photoresist is applied before the next step of
the process is performed. This is repeated several times when an integrated circuit is created.
Integrated circuits are used as central processor units, as memory, as programmable gate arrays,
and as various logic components that are used on circuit boards to make digital circuits.
On printed circuit boards, features such as solder masks, notations, encapsulates and conformal
coatings all use a thicker UV/EB-curable coating than that used in making integrated circuits.
Although curing of UV/EB coatings on circuit boards is fast, it is not as rapid as EB-curing for
microelectronics (extremely rapid). However, the time required for curing microelectronics is
per unit length along the track within the mask, while curing for circuit board coatings occurs all
at once.
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OPTICAL FIBERS
3D techniques have been applied to cure coatings on optical fibers. The inner coating on
optical fibers has a low index of refraction that redirects light (the signal) back into the fiber. An
overcoat for these fibers provides abrasion resistance and adds to mechanical strength. An
optically absorbent final coating prevents undesirable "crosstalk" between fibers. Without these
radiation-cured coatings, long distance optical fiber communications could not have come into
existence.
PRESSURE SENSITIVE ADHESIVES
Use of UV/EB coatings with pressure sensitive adhesives is seldom advertised. Pressure
sensitive adhesives are used to bond metallization to wrappings, for tapes and labels, and to
laminate. Advantages include: (1) use of single-component materials that can be dispensed with
automated equipment; (2) long open time without losing volatile ingredients; (3) fast cures after
dispensing; (4) low energy requirement for curing; and (5) ability to be used on temperature
sensitive substrates such as paper and plastic films.
PRINTING
UV/EB coatings had their start in printing and many terms from printing are genetically used -
such as web that refers to a continuous flexible substrate that is unrolled, passes through the
printing press and drying ovens, and is then re-rolled. Radiation-cured printing inks are used
for lithographic, rotogravure, screen, and flexographic printing.3'4 All of these types of printing
are in a state of rapid evolution with former distinctions between them becoming blurred. As a
result, any generalization may have already become obsolete. For example, flexography has
historically used a low viscosity ink. While UV/EB-cured inks are more viscous than the
traditional flexographic inks, UV/EB-cured inks are used in flexography anyway. UV/EB
radiation-cured inks allow printing presses to have web speeds of 400-1000 feet per minute.
The advent of ultraviolet lasers has allowed UV-curing of photopolymer printing plates without
need for a negative transparency. The ultraviolet laser is computer controlled, and can be used
to make any number of identical plates at any number of sites. These plates can then make
identical impressions on any number of presses. This eliminates the need for printing plates that
can make a million impressions and adds to the capacity to reproduce images.
RELEASE COATINGS
Release coatings are usually silicones applied to plastic or paper. Silicone resin producers
worked with equipment producers and flexible packaging printers to produce desired UV/EB
radiation-cured release coatings. Labels and double-sided tapes with pressure sensitive
adhesive coatings are normally placed on a release coating until they are applied.
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SPRAY COATING
UV/EB-cured paints are suitable for spray-coating and can realize up to 99% overall
effectiveness in applying a coating to a substrate when capture and reuse of overspray are
considered. Coatings have been applied to materials that are porous (such as wood or ceramics)
or impervious (such as plastics or metal). This overall effectiveness is significantly greater than
that for conventional coatings because captured TJV7EB droplets can be reused. This can be
done because UV coatings can have essentially zero VOC content and do not cure unless
exposed to an appropriate radiation source.
VINYL FLOORING
Vinyl floor coatings are second only to paper coatings in use of UV/EB-cured coatings.
Premium grade no-wax vinyl flooring uses a UV/EB topcoat consisting of two layers. The first
layer is a barrier coat to seal the vinyl and provide better adhesion for the final layer. The final
layer is an abrasion resistant coating to improve wear characteristics.
WOOD PRODUCTS
UV wood product coatings have been used for a long time. They were used first to coat panels
with polyester resins. Acrylic and urethane-acrylic coatings have since been used on panels for
greater durability. Further developments have included 3D cure of sealers and primers for wood
furniture. UV radiation curing of topcoats for fine furniture allows a shorter cure time (a few
seconds) with fewer dust flaws in the wet surface.
The example given for emissions in the 1991 reference is now outdated. The use of VOC as
thinners in furniture coatings is now obsolete. In 1999, wood furniture used water thinned UV-
cured coatings, monomer thinned UV-cured coatings, heat and reactive diluents when
temperature alone could not sufficiently control viscosity.
B-4
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APPENDIX C
EMISSION MEASUREMENT TECHNICAL INFORMATION CENTER
NSPS TEST METHOD
(EMTIC -24, 9/11/95)
Method 24 - Determination of Volatile Matter Content,
Water Content, Density, Volume Solids, and
Weight Solids of Surface Coatings
1. APPLICABILITY AND PRINCIPLE
1.1 Applicability. This method applies to the determination of
volatile matter content, water content, density, volume solids,
and weight solids of paint, varnish, lacquer, or related surface
coatings.
1.2 Principle. Standard methods are used to determine the
volatile matter content, water content, density, volume solids,
and weight solids of the paint, varnish, lacquer, or related
surface coatings.
2. APPLICABLE STANDARD METHODS
Use the apparatus, reagents, and procedures specified in the
standard methods below:
2.1 ASTM D 1475-60 (Reapproved 1980), Standard Test Method for
Density of Paint, Varnish, Lacquer, and Related Products.
2.2 ASTM D 2369-81, Standard Test Method for Volatile Content of
Coatings.
2.3 ASTM D 3792-79, Standard Test Method for Water Content of
Water Reducible Paints by Direct Injection into a Gas
Chromatograph.
2.4 ASTM D 4017-81, Standard Test Method for Water in Paints and
Paint Materials by the Karl Fischer Titration Method.
2.5 ASTM 4457-85 Standard Test Method for Determination of
Dichloromethane and 1,1,1-Trichloroethane in Paints and Coatings
by Direct Injection into a Gas Chromatograph (incorporated by
reference--see §60.17).
2.6 ASTM D 5403-93 Standard Test Methods for Volatile Content of
Radiation Curable Materials (incorporated by reference--see
§60.17) .
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3. PROCEDURE
3.1 Multicomponent Coatings. Multicomponent coatings are
coatings that are packaged in two or more parts, which are
combined before application. Upon combination a coreactant from
one part of the coating chemically reacts, at ambient conditions,
with a coreactant from another part of the coating. To determine
the total volatile content, water content, and density of
multicomponent coatings, follow the procedures in section 3.8.
3.2 Non Thin-film Ultraviolet Radiation-cured Coating. To
determine volatile content of non thin-film ultraviolet
radiation-cured (UV radiation-cured) coatings, follow the
procedures in Section 3.9. Determine water content, density and
solids content of the UV-cured coatings according to Sections
3.4, 3.5, and 3.6, respectively. The UV-cured coatings are
coatings which contain unreacted monomers that are polymerized by
exposure to ultraviolet light. To determine if a coating or ink
can be classified as a thin-film UV cured coating or ink, use the
following equation:
C=FAD Eq.
where:
A = Area of substrate, in2, cm2.
C = Amount of coating or ink added to the substrate, g.
D = Density of coating or ink, g/in3 (g/cm3)
F = Manufacturer's recommended film thickness, in (cm).
If C is less than 0.2 g and A is greater than or equal to 35 in2
(225 cm2) then the coating or ink is considered a thin-film UV
radiation-cured coating for determining applicability of
ASTM D 5403-93. NOTE: As noted in Section 1.4 of
ASTM D 5403-93, this method may not be applicable to radiation
curable materials wherein the volatile material is water. For
all other coatings not covered by Sections 3.1 or 3.2 analyze as
follows:
3.3 Volatile Matter Content. Use the procedure in ASTM D 2369-
81 to determine the volatile matter content (may include water)
of the coating.
3.3.1 Record the following information:
W± = Weight of dish and sample before heating, g.
W2 = Weight of dish and sample after heating, g.
W3 = Sample weight, g.
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3.3.2 Run analyses in pairs (duplicate sets) for each coating
until the criterion in Section 4.3 is met. Calculate the weight
fraction of the volatile matter (Wv) for each analysis as
follows:
Wv = (Wx - W2)/W3 Eq. 24-2
Record the arithmetic average (Wv) .
3.4 Water Content. For waterborne (water reducible) coatings
only, determine the weight fraction of water (Ww) using either
ASTM D 3792-79 or ASTM D 4017—81. A waterborne coating is any
coating which contains more than 5 percent water by weight in its
volatile fraction. Run duplicate sets of determinations until
the criterion in Section 4.3 is met. Record the arithmetic
average (Ww) .
3.5 Coating Density. Determine the density (D0, kg/liter) of
the surface coating using the procedure in ASTM D 1475-60. Run
duplicate sets of determinations for each coating until the
criterion in Section 4.3 is met. Record the arithmetic average
(D0).
3.6 Solids Content. Determine the volume fraction (Vs) solids
of the coating by calculation using the manufacturer's
formulation.
3.7 Exempt Solvent Content. Determine the weight fraction of
exempt solvents (WE) by using ASTM Method D4457-85 (incorporated
by reference--see §60.17). Run a duplicate set of determinations
and record the arithmetic average (WE) .
3.8 To determine the total volatile content, water content, and
density of multicomponent coatings, use the following procedures:
3.8.1 Prepare about 100 ml of sample by mixing the components in
a storage container, such as a glass jar with a screw top or a
metal can with a cap. The storage container should be just large
enough to hold the mixture. Combine the components (by weight or
volume) in the ratio recommended by the manufacturer. Tightly
close the container between additions and during mixing to
prevent loss of volatile materials. However, most manufacturers
mixing instructions are by volume. Because of possible error
caused by expansion of the liquid when measuring the volume, it
is recommended that the components be combined by weight. When
weight is used to combine the components and the manufacturer's
recommended ratio is by volume, the density must be determined by
section 3.5.
3.8.2 Immediately after mixing, take aliquots from this 100 ml
sample for determination of the total volatile content, water
content, and density. To determine water content follow
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section 3.4. To determine density, follow section 3.5. To
determine total volatile content, use the apparatus and reagents
described in ASTM D2369-81, sections 3 and 4, respectively
(incorporated by reference, and see §60.17) the following
procedures:
3.8.2.1 Weigh and record the weight of an aluminum foil weighing
dish. Add 3±1 ml of suitable solvent as specified in ASTM
D2369-81 to the weighing dish. Using a syringe as specified in
ASTM D2369-81, weigh to 1 mg, by difference, a sample of coating
into the weighing dish. For coatings believed to have a volatile
content less than 40 weight percent, a suitable size is
0.3 +. 0.10 g, but for coatings believed to have a volatile
content greater than 40 weight percent, a suitable size is
0.5 ± 0.1 g.
NOTE: If the volatile content determined pursuant to
section 5 is not in the range corresponding to the sample size
chosen repeat the test with the appropriate sample size. Add the
specimen dropwise, shaking (swirling) the dish to disperse the
specimen completely in the solvent. If the material forms a lump
that cannot be dispersed, discard the specimen and prepare a new
one. Similarly, prepare a duplicate. The sample shall stand for
a minimum of 1 hour, but no more than 24 hours prior to being
oven fried at 110 +. 5°C, for 1 hour.
3.8.2.2 Heat the aluminum foil dishes containing the dispersed
specimens in the forced draft oven for 60 min at 110±5°C.
Caution -- provide adequate ventilation, consistent with accepted
laboratory practice, to prevent solvent vapors from accumulating
to a dangerous level.
3.8.2.3 Remove the dishes from the oven, place immediately in a
desiccator, cool to ambient temperature, and weigh to within
1 mg.
3.8.2.4 Run analyses in pairs (duplicate sets) for each coating
mixture until the criterion in section 4.3 is met. Calculate Wv
following Equation 24-2 and record the arithmetic average.
3.9 UV-cured Coating's Volatile Matter Content. Use the
procedure in ASTM D 5403-93 (incorporated by reference--see
§60.17) to determine the volatile matter content of the coating
except the curing test described in NOTE 2 of ASTM D 5403-93 is
required.
4. DATA VALIDATION PROCEDURE
4.1 Summary. The variety of coatings that may be subject to
analysis makes it necessary to verify the ability of the analyst
and the analytical procedures to obtain reproducible results for
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the coatings tested. This is done by running duplicate analyses
on each sample tested and comparing results with the within-
laboratory precision statements for each parameter. Because of
the inherent increased imprecision in the determination of the
VOC content of water-borne coatings as the weight percent water
increases, measured parameters for water-borne coatings are
modified by the appropriate confidence limits based on between-
laboratory precision statements.
4.2 Analytical Precision Statements. The within-laboratory and
between-laboratory precision statements are given below:
Within- Between-
laboratory Laboratory
Volatile matter content, Wv 1.5% Wv 4.7% Wv
Water content, Ww 2.9% Ww 7.5% Ww
Density, D0 001 kg/liter 0.002 kg/liter
4.3 Sample Analysis Criteria. For Wv and Ww, run duplicate
analyses until the difference between the two values in a set is
less than or equal to the within-laboratory precision statement
for that parameter. For D0 run duplicate analyses until each
value in a set deviates from the mean of the set by no more than
the within-laboratory precision statement. If after several
attempts it is concluded that the ASTM procedures cannot be used
for the specific coating with the established within-laboratory
precision, the Administrator will assume responsibility for
providing the necessary procedures for revising the method or
precision statements upon written request to: Director, Emission
Standards and Engineering Division, MD-13, Office of Air Quality
Planning and Standards, U.S. Environmental Protection Agency,
Research Triangle Park, NC 27711.
4.4 Confidence Limit Calculations for Waterborne Coatings.
Based on the between-laboratory precision statements, calculate
the confidence limits for waterborne coatings as follows: To
calculate the lower confidence limit, subtract the appropriate
between-laboratory precision value from the measured mean value
for that parameter. To calculate the upper confidence limit, add
the appropriate between-laboratory precision value to the
measured mean value for that parameter. For Wv and D0, use the
lower confidence limits, and for Ww, use the upper confidence
limit. Because Vs is calculated, there is no adjustment for this
parameter.
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5. CALCULATIONS
5.1 Nonaqueous Volatile Matter.
5.1.1 Solvent-borne Coatings.
W0 = Wv Eq. 24-3
where: W0 = Weight fraction nonaqueous volatile matter, g/g.
5.1.2 Waterborne Coatings.
W0 = Wv - Ww Eq. 24-4
5.2 Weight Fraction Solids.
Ws = 1 - Wv. Eq. 24-5
where: Ws = Weight solids, g/g.
C-6
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APPENDIX D
Definition of Volatile Organic Compounds (VOC)
As of 2/25/99
40 CFR 51 100(s) - Definition - Volatile organic compounds (VOC)
"Volatile organic compounds (VOC)" means any compound of carbon, excluding carbon
monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium
carbonate, which participates in atmospheric photochemical reactions.
(1) This includes any such organic compound other than the following, which have been
determined to have negligible photochemical reactivity:
methane
ethane
methylene chloride (dichloromethane)
1,1,1-trichloroethane (methyl chloroform)
l,l,2-trichloro-l,2,2-trifluoroethane (CFC-113)
trichlorofluoromethane (CFC-11)
dichlorodifluoromethane (CFC-12)
chlorodifluoromethane (HCFC-22)
trifluoromethane (HFC-23)
1,2-dichloro 1,1,2,2-tetrafluoroethane (CFC-114)
chloropentafluoroethane (CFC-115)
1,1,1-trifluoro 2,2-dichloroethane (HCFC-123)
1,1,1,2-tetrafluoroethane (HFC-134a)
1,1-dichloro 1-fluoroethane (HCFC-141b)
1-chloro 1,1-difluoroethane (HCFC-142b)
2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124)
pentafluoroethane (HFC-125)
1,1,2,2-tetrafluoroethane (HFC-134)
1,1,1-trifluoroethane (HFC-143a)
1,1-difluoroethane (HFC-152a)
parachlorobenzotrifluoride (PCBTF)
cyclic, branched, or linear completely methylated siloxanes
acetone
perchloroethy 1 ene (tetrachloroethy 1 ene)
3,3-dichloro-l,l,l,2,2-pentafluoropropane(HCFC-225ca)
1,3-dichloro-1,1,2,2,3-pentafluoropropane (HCFC-225cb)
1,1,1,2,3,4,4,5,5,5-decafluoropentane (HFC 43-10mee)
difluoromethane (HFC-32)
ethylfluoride (HFC-161)
l,l,l,3,3,3-hexafluoropropane(HFC-236fa)
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1,1,2,2,3-pentafluoropropane (HFC-245ca)
1,1,2,3,3-pentafluoropropane (HFC-245ea)
l,l,l,2,3-pentafluoropropane(HFC-245eb)
1,1,1,3,3-pentafluoropropane (HFC-245fa)
1,1,1,2,3,3-hexafluoropropane (HFC-236ea)
l,l,l,3,3-pentafluorobutane(HFC-365mfc)
chlorofluoromethane (HCFC-31)
1 -chloro-1 -fluoroethane (HCFC-151 a)
1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a)
l,l,l,2,2,3,3,4,4-nonafluoro-4-methoxy-butane(C4F9OCH3)
2-(difluoromethoxymethyl)-l,l,l,2,3,3,3-heptafluoropropane((CF3)2CFCF2OCH3)
l-ethoxy-l,l,2,2,3,3,4,4,4-nonafluorobutane(C4F9OC2H5)
2-(ethoxydifluoromethyl)-l,l,l,2,3,3,3-heptafluoropropane((CF3)2CFCF2OC2H5)
methyl acetate and perfluorocarbon compounds which fall into these classes:
o (i) cyclic, branched, or linear, completely fluorinated alkanes,
o (ii) cyclic, branched, or linear, completely fluorinated ethers with no
unsaturations,
o (iii) cyclic, branched, or linear, completely fluorinated tertiary amines with no
unsaturations, and
o (iv) sulfur containing perfluorocarbons with no unsaturations and with sulfur
bonds only to carbon and fluorine.
(2) For purposes of determining compliance with emissions limits, VOC will be measured by
the test methods in the approved State implementation plan (SIP) or 40 CFR Part 60, Appendix
A, as applicable. Where such a method also measures compounds with negligible photochemical
reactivity, these negligibly-reactive compounds may be excluded as VOC if the amount of such
compounds is accurately quantified, and such exclusion is approved by the enforcement
authority.
(3) As a precondition to excluding these compounds as VOC or at any time thereafter, the
enforcement authority may require an owner or operator to provide monitoring or testing
methods and results demonstrating, to the satisfaction of the enforcement authority, the amount
of negligibly-reactive compounds in the source's emissions.
(4) For purposes of Federal enforcement for a specific source, the EPA shall use the test methods
specified in the applicable EPA-approved SIP, in a permit issued pursuant to a program
approved or promulgated under Title V of the Act, or under 40 CFR Part 51, Subpart I or
Appendix S, or under 40 CFR Parts 52 or 60. The EPA shall not be bound by any State
determination as to appropriate methods for testing or monitoring negligibly-reactive compounds
if such determination is not reflected in any of the above provisions.
Note to reader: This has been formatted to make it easier for the user to read.
D-2
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APPENDIX E
HAZARDOUS AIR POLLUTANTS (HAP)
This appendix contains the original list of hazardous air pollutants from the Clean Air
Act Amendments of 1990 followed by a list of final and proposed modifications to the list.
HAP LIST FROM THE CLEAN AIR ACT AMENDMENTS OF 1990
CAS Number
75070
60355
75058
98862
53963
107028
79061
79107
107131
107051
92671
62533
90040
133221
71432
92875
98077
100447
92524
117817
542881
75252
106990
156627
105602
133062
63252
75150
56235
463581
Chemical Name
Acetaldehyde
Acetamide
Acetonitrile
Acetophenone
2-Acetylaminofluorene
Acrolein
Aery 1 amide
Acrylic acid
Acrylonitrile
Allyl chloride
4-Aminobiphenyl
Aniline
o-Anisidine
Asbestos
Benzene (including benzene from gasoline)
Benzidine
Benzotri chloride
Benzyl chloride
Biphenyl
Bis(2-ethylhexyl)phthalate (DEHP)
Bis(chloromethyl)ether
Bromoform
1,3-Butadiene
Calcium cyanamide
Caprolactam (See Modification)
Captan
Carbaryl
Carbon disulfide
Carbon tetrachloride
Carbonyl sulfide
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CAS Number
Chemical Name
120809
133904
57749
7782505
79118
532274
108907
510156
67663
107302
126998
1319773
95487
108394
106445
98828
94757
3547044
334883
132649
96128
84742
106467
91941
111444
542756
62737
111422
121697
64675
119904
60117
119937
79447
68122
Catechol
Chloramben
Chlordane
Chlorine
Chloroacetic acid
2-Chloroacetophenone
Chlorobenzene
Chlorobenzilate
Chloroform
Chloromethyl methyl ether
Chloroprene
Cresols/Cresylic acid (isomers and mixture)
o-Cresol
m-Cresol
p-Cresol
Cumene
2,4-D, salts and esters
DDE (See technical note)
Diazomethane
Dibenzofurans (See technical note)
1,2-Dibromo-3 -chloropropane
Dibutylphthalate
l,4-Dichlorobenzene(p)
3,3-Dichlorobenzidene (See technical note)
Dichloroethyl ether (Bis(2-chloroethyl)ether)
1,3 -Di chl oropropene
Dichlorvos
Diethanolamine
N,N-Diethyl aniline (N,N-Dimethylaniline) (See technical note)
Diethyl sulfate
3,3-Dimethoxybenzidine (See technical note)
Dimethyl aminoazobenzene
3,3'-Dimethyl benzidine (See technical note)
Dimethyl carbamoyl chloride (See technical note)
Dimethyl formamide
E-2
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CAS Number
Chemical Name
57147 1,1-Dimethyl hydrazine (See technical note)
131113 Dimethyl phthalate
77781 Dimethyl sulfate
534521 4,6-Dinitro-o-cresol, and salts
51285 2,4-Dinitrophenol
121142 2,4-Dinitrotoluene
123911 1,4-Dioxane (1,4-Diethyleneoxide)
122667 1,2-Diphenylhydrazine
106898 Epichlorohydrin (l-Chloro-2,3-epoxypropane)
106887 1,2-Epoxybutane
140885 Ethyl acrylate
100414 Ethyl benzene (See technical note)
51796 Ethyl carbamate (Urethane)
75003 Ethyl chloride (Chloroethane)
106934 Ethylene dibromide (Dibromoethane)
107062 Ethylene dichloride (1,2-Dichloroethane)
107211 Ethylene glycol
151564 Ethylene imine (Aziridine)
75218 Ethylene oxide
96457 Ethylene thiourea
75343 Ethylidene dichloride (1,1-Dichloroethane)
50000 Formaldehyde
76448 Heptachlor
118741 Hexachlorobenzene
87683 Hexachlorobutadiene
77474 Hexachlorocyclopentadiene
67721 Hexachloroethane
822060 Hexamethylene-l,6-diisocyanate
680319 Hexamethylphosphoramide
110543 Hexane
302012 Hydrazine
7647010 Hydrochloric acid (See technical note)
7664393 Hydrogen fluoride (Hydrofluoric acid)
7783064 Hydrogen sulfide (See Modification)
123319 Hy droquinone
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CAS Number
Chemical Name
78591 Isophorone
58899 Lindane (all isomers)
108316 Maleic anhydride
67561 Methanol
72435 Methoxychlor
74839 Methyl bromide (Bromomethane)
74873 Methyl chloride (Chloromethane)
71556 Methyl chl or oform (1,1,1 -Tri chl oroethane)
78933 Methyl ethyl ketone (2-Butanone)
60344 Methyl hydrazine
74884 Methyl iodide (lodomethane)
108101 Methyl isobutyl ketone (Hexone)
624839 Methyl isocyanate
80626 Methyl methacrylate
1634044 Methyl tert butyl ether(See technical note)
101144 4,4-Methylene bis(2-chloroaniline)(See technical note)
75092 Methylene chloride (Dichloromethane)
101688 Methylene diphenyl diisocyanate (MDI)
101779 4,4~'-Methylenedianiline
91203 Naphthalene
98953 Nitrobenzene
92933 4-Nitrobiphenyl
100027 4-Nitrophenol
79469 2-Nitropropane
684935 N-Nitroso-N-methylurea
62759 N-Nitrosodimethylamine
59892 N-Nitrosomorpholine
56382 Parathion
82688 Pentachloronitrobenzene (Quintobenzene)
87865 Pentachlorophenol
108952 Phenol
106503 p-Phenylenediamine
75445 Phosgene
7803512 Phosphine
7723140 Phosphorus (See technical note)
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CAS Number
Chemical Name
85449 Phthalic anhydride
1336363 Polychlorinated biphenyls (Aroclors)
1120714 1,3 -Propane sultone
57578 beta-Propiolactone
123386 Propionaldehyde
114261 Propoxur (Baygon)
78875 Propylene dichloride (1,2-Dichloropropane)
75569 Propylene oxide
75558 1,2-Propylenimine (2-Methyl aziridine)
91225 Quinoline
106514 Quinone
100425 Styrene
96093 Styrene oxide
1746016 2,3,7,8-Tetrachlorodibenzo-p-dioxin
79345 1,1,2,2-Tetrachloroethane
127184 Tetrachloroethylene (Perchloroethylene)
7550450 Titanium tetrachloride
108883 Toluene
95807 2,4-Toluene diamine
584849 2,4-Toluene diisocyanate
95534 o-Toluidine
8001352 Toxaphene (chlorinated camphene)
120821 1,2,4-Trichlorobenzene
79005 1,1,2-Trichloroethane
79016 Trichloroethylene
95954 2,4,5-Trichlorophenol
88062 2,4,6-Trichlorophenol
121448 Triethylamine
1582098 Trifluralin
540841 2,2,4-Trimethylpentane
108054 Vinyl acetate
593602 Vinyl bromide
75014 Vinyl chloride
75354 Vinylidene chloride (1,1-Dichloroethylene)
1330207 Xylenes (isomers and mixture)
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CAS Number
95476
108383
10642
Chemical Name
o-Xylenes (See technical note)
m-Xylenes (See technical note)
p-Xylenes (See technical note)
Antimony Compounds
Arsenic Compounds (inorganic including arsine)
Beryllium Compounds
Cadmium Compounds
Chromium Compounds
Cobalt Compounds
Coke Oven Emissions
Cyanide Compounds1
Glycol ethers2
Lead Compounds (See technical note)
Manganese Compounds
Mercury Compounds
Fine mineral fibers3 (See technical note)
Nickel Compounds
Polycylic Organic Matter4 (See technical note)
Radionuclides (including radon)5
Selenium Compounds
NOTE: For all listings above which contain the word "compounds" and for glycol ethers, the
following applies:
Unless otherwise specified, these listings are defined as including any unique chemical substance
that contains the named chemical (i.e., antimony, arsenic, etc.) as part of that chemical's
infrastructure.
1. X'CN where X = H' or any other group where a formal dissociation may occur. For example
KCN or Ca(CN)2
2. Includes mono- and di- ethers of ethylene glycol, diethylene glycol, and triethylene glycol
R-(OCH2CH2)n -OR'
where
n= 1,2, or 3
R = alkyl or aryl groups
R = R, H, or groups which, when removed, yield glycol ethers with the structure:
R-(OCH2CH)n-OH. Polymers are excluded from the glycol category.(See Modification)
3. Includes mineral fiber emissions from facilities manufacturing or processing glass, rock, or
slag fibers (or other mineral derived fibers) of average diameter 1 micrometer or less.
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4. Includes organic compounds with more than one benzene ring, and which have a boiling
point greater than or equal to 100 °C.
5. A type of atom which spontaneously undergoes radioactive decay.
Technical Note: Minor editorial/technical issue - call (919) 541-5347 for details.
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Modifications To The 112(b)l Hazardous Air Pollutants
Authority for modifications:
Section 112 of the Act contains a mandate for EPA to evaluate and control emissions of
hazardous air pollutants Section 112(b)(l) includes an initial list of hazardous air pollutants
that is composed of specific chemical compounds and compound classes to be used to identify
source categories for which the EPA will promulgate emissions standards. The listed categories
are subject to emission standards subsequently developed under Section 112. The EPA must
periodically review the list of hazardous air pollutants and, where appropriate, revise this list
by rule. In addition, any person may petition EPA under Section 112(b)(3) to modify the list by
adding or deleting one or more substances. A petitioner seeking to delete a substance must
demonstrate that there are adequate data on the health and environmental effects of the substance
to determine that emissions, ambient concentrations, bioaccumulation, or deposition of the
substance may not reasonably be anticipated to cause any adverse effects to human health or the
environment. To demonstrate the burden of proof, a petitioner must provide a detailed
evaluation of the available data concerning the substance's potential adverse health and
environmental effects, and estimate the potential exposures through inhalation or other routes
resulting from emissions of the substance.
Modifications:
Glycol Ethers - Proposed
On January 12, 1999 (FR64:1780), EPA proposed to modify the definition of glycol ethers to
exclude surfactant alcohol ethoxylates and their derivatives (SAED). This proposal was based on
EPA's finding that emissions, ambient concentrations, bioaccumulation, or deposition of SAED
may not reasonably be anticipated to cause adverse human health or environmental effects. EPA
also proposed to make conforming changes in the definition of glycol ethers with respect to the
designation of hazardous substances under the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA). The proposal reads as follows:
"The definition of the glycol ethers category of hazardous air pollutants, as established by 42
U.S.C. 7412(b)(l) includes mono- and di-ethers of ethylene glycol, diethylene glycol, and
triethylene glycol R-(OCH2CH2)n-OR Where:
n= 1,2, or 3
R= alkyl C7 or less, or phenyl or alkyl substituted phenyl
R'= H, or alkyl C7 or less, or carboxylic acid ester, sulfate, phosphate, nitrate, or
sulfonate."
Methyl Ethyl Ketone(MEK) - Notices of Review
Hazardous Air Pollutant list - Methyl Ethyl Ketone(MEK); receipt of a complete petition
to delist Citation: 64 FR 33453; Date: 06/23/99
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Caprolactam
On July 19, 1993, EPA received a petition from AlliedSignal, Inc., BASF Corporation, and
DSM Chemicals North America, Inc. to delete caprolactam (CAS No. 105-60-2) from the
hazardous air pollutant list in Section 112(b)(l), 42 U.S.C., Section 7412(b)(l). A Notice of
Receipt was published (58FR45081, August 26, 1993) noting that the data filed were adequate to
support decision making. After a comprehensive review of the data submitted, the EPA
published a proposal to delist caprolactam (60FR48081, September 18, 1995). In order to help
address public concern, on March 13, 1995, EPA executed two detailed agreements with
AlliedSignal concerning the Irmo, South Carolina manufacturing facility and another facility
located in Chesterfield, Virginia, copies of which are included in the public docket for this
rulemaking. AlliedSignal agreed that, if caprolactam was delisted pursuant to the proposal,
AlliedSignal would install emissions controls which EPA believed would be equivalent to the
controls which would have been required had EPA issued a standard to control these sources
under Section 112. The agreed emissions controls are incorporated in federally enforceable
operating permits for the affected facilities, and will be in place years earlier than controls would
have otherwise been required. In addition, AlliedSignal has agreed to establish a citizen advisory
panel concerning the Irmo facility in order to improve communications with the community and
to assure that citizens have an ongoing role in implementation of the agreed emission reductions.
The public requesting a public hearing. On November 28, 1995, the EPA published a notice of
public hearing and an extension of the comment period (60FR58589). After considering all
public comments, the EPA published a final rule delisting caprolactam (61FR30816, June 18,
1996).
All information associated with this rule making is located in Docket Number A-94-33 at the
Central Docket Section (A-130), Environmental Protection Agency, 401 M St. SW.,
Washington, D.C. 20460. phone 202-260-7548, fax 202-260-4400, email
a-and-r-docket@epamail.epa. gov. The docket includes complete index to all papers filed in this
docket, a copy of the original petition, comments submitted, and additional materials supporting
the rule. A reasonable fee may be charged for copying. The docket may be inspected in person
between 8:00 a.m. and 4:30 p.m. on weekdays at EPA's Central Docket Section, West Tower
Lobby, Gallery 1, Waterside Mall, 401 M St., SW, Washington, D.C. 20460.
Hydrogen Sulfide
A clerical error led to the inadvertent addition of hydrogen sulfide to the Section 112(b) list of
Hazardous Air Pollutants. However, a Joint Resolution to remove hydrogen sulfide from the
Section 112(b)(l) list was passed by the Senate on August 1, 1991 (Congressional Record page
SI 1799), and the House of Representatives on November 25, 1991 (Congressional Record pages
HI 1217-H11219). The Joint Resolution was approved by the President on December 4, 1991.
Hydrogen Sulfide is included in Section 112(r) and is subject to the accidental release
provisions. A study (see citation below) was required under Section 112(n)(5).
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Hydrogen Sulfide Air Emissions Associated with the Extraction of Oil and Natural Gas,
EPA-453/R-93-045, (NTIS publication # is PB94-131224, $36.50 hard copy, $17.50
microfiche).
National Technical Information Services (NTIS)
5285 Port Royal Road
Springfield, VA 22161
703-487-4650 800-426-4791
703-487-4807 8:30-5:30 EST M-F
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing.)
1. REPORT NO.
'EPA 456/K-01-001
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Ultraviolet and Electron Beam (UV/EB) Cured Coatings, Inks,
and Adhesives
5. REPORT DATE
July 2001
6. PERFORMING ORGANIZATION CODE
CATC/ITPID/OAQPS/OAR/EPA
7. AUTHOR(S)
Clean Air Technology Center
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Clean Air Technology Center
ITG, ITPID, OAQPS
MD-12, U.S. EPA
RTP, NC 27711
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This document is a Technical Bulletin which is intended to enlighten the state air
pollution authorities about a relatively new technology. This document defines UV/EB coat-
ings, explains why they are important, explains how the technology works, what degree of
pollution prevention is afforded, what industries could use UV/EB coatings, and the cost
analysis of using UV/EB coatings. It even describes stereolithography, which makes a part
out of a coating. UV/EB coatings were previously called UV/EB radiation cured coatings, but
"radiation" has been dropped from the name because it is a term that is used too freely.
UV/EB cured coatings are used in many applications, and should become useful in more when
the results and risks of using them are fully understood. The intent is to make them fully
understandable.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
COSATI Field Group
coatings, inks, adhesives, ultraviolet, electron
beam, electromagnetic radiation, mercury vapor
lamps, organic polymers, free radical polymeriza-
tion, cationic polymerization, polymer, curing,
cure of conventional coatings, visible spectrum,
extreme ultraviolet, ozone
Air Pollution Con-
trol, Pollution
Prevention, Volatile
Organic Compounds,
Hazardous Air Pol-
lutants
18. DISTRIBUTION STATEMENT
Release Unlimited, Available from NTIS
5285 Port Royal Rd.
Springfield, VA 22161
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This Page)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION IS OBSOLETE
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