-------
these areas is conditioned to remove dust particles and to adjust the
temperature and humidity. In some cases, "clean room" conditions are
rigorously maintained.
1 8
Emissions And Controls-1"0 - The significant VOC emission sources in a
magnetic tape manufacturing plant include the coating preparation equipment,
the coating application and flashoff area, and the drying ovens. Emissions
from the solvent storage tanks and the cleanup area are generally only a
negligible percentage of total emissions.
In the mixing or coating preparation area, VOCs are emitted from the
individual pieces of equipment during the following operations: filling of
mixers and tanks; transfer of the coating; intermittent activities, such as
changing the filters in the holding tanks; and mixing (if equipment is not
equipped with tightly fitting covers). Factors affecting emissions in the
mixing areas include the capacity of the equipment, the number of pieces of
equipment, solvent vapor pressure, throughput, and the design and performance
of equipment covers. Emissions will be intermittent or continuous, depending
on whether the preparation method is batch or continuous.
Emissions from the coating application area result from the evaporation
of solvent during use of the coating application equipment and from the
exposed web as it travels from the coater to the drying oven (flashoff).
Factors affecting emissions are the solvent content of the coating, line width
and speed, coating thickness, volatility of the solvent(s), temperature,
distance between coater and oven, and air turbulence in the coating area.
Emissions from the drying oven are of the remaining solvent that is
driven off in the oven. Uncontrolled emissions at this point are determined
by the solvent content of the coating when it reaches the oven. Because the
oven evaporates all the remaining solvent from the coating, there are no
process VOC emissions after oven drying.
Solvent type and quantity are the common factors affecting emissions
from all operations in a magnetic tape coating facility. The rate of
evaporation or drying depends on solvent vapor pressure at a given temperature
and concentration. The most commonly used organic solvents are toluene,
methyl ethyl ketone, cyclohexanone, tetrahydrofuran, and methyl isobutyl
ketone. Solvents are selected for their cost, solvency, availability, desired
evaporation rate, ease of use after recovery, compatibility with solvent
recovery equipment, and toxicity.
Of the total uncontrolled VOC emissions from the mixing area and coating
operation (application/flashoff area and drying oven), approximately 10
percent is emitted from the mixing area, and 90 percent from the coating
operation. Within the coating operation, approximately 10 percent occurs in
the application/flashoff area, and 90 percent in the drying oven.
A control system for evaporative emissions consists of two components, a
capture device and a control device. The efficiency of the control system is
determined by the efficiencies of the two components.
9/90 Evaporation Loss Sources 4.2.2.13-3
-------
A capture device is used to contain emissions from a process operation
and direct them to a stack or to a control device. Room ventilation systems,
covers, and hoods are possible capture devices from coating preparation
equipment. Room ventilation systems, hoods, and partial and total enclosures
are typical capture devices used in the coating application area. A drying
oven can be considered a capture device, because it both contains and directs
VOC process emissions. The efficiency of a capture device or a combination of
capture devices is variable and depends on the quality of design and the
levels of operation and maintenance.
A control device is any equipment that has as its primary function the
reduction of emissions to the atmosphere. Control devices typically used in
this industry are carbon adsorbers, condensers and incinerators. Tightly
fitting covers on coating preparation equipment may be considered both capture
and control devices, because they can be used either to direct emissions to a
desired point outside the equipment or to prevent potential emissions from
escaping.
Carbon adsorption units use activated carbon to adsorb VOCs from a gas
stream, after which the VOCs are desorbed and recovered from the carbon. Two
types of carbon adsorbers are available, fixed bed and fluidized bed. Fixed
bed carbon adsorbers are designed with a steam-stripping technique to recover
the VOCs and to regenerate the activated carbon. The fluidized bed units used
in this industry are designed to use nitrogen for VOC vapor recovery and
carbon regeneration. Both types achieve typical VOC control efficiencies of
95 percent when properly designed, operated and maintained.
Condensers control VOC emissions by cooling the solvent-laden gas to the
dew point of the solvent(s) and then collecting the droplets. There are two
condenser designs commercially available, nitrogen (inert gas) atmosphere and
air atmosphere. These systems differ in the design and operation of the
drying oven (i. e., use of nitrogen or air in the oven) and in the method of
cooling the solvent-laden air (i. e., liquified nitrogen or refrigeration).
Both design types can achieve VOC control efficiencies of 95 percent.
Incinerators control VOC emissions by oxidation of the organic compounds
into carbon dioxide and water. Incinerators used to control VOC emissions may
be of thermal or catalytic design and may use primary or secondary heat
recovery to reduce fuel costs. Thermal incinerators operate at approximately
890°C (1600°F) to assure oxidation of the organic compounds. Catalytic
incinerators operate in the range of 400° to 540°C (750° to 1000°F) while
using a catalyst to achieve comparable oxidation of VOCs. Both design types
achieve a typical VOC control efficiency of 98 percent.
Tightly fitting covers control VOC emissions from coating preparation
equipment by reducing evaporative losses. The parameters affecting the
efficiency of these controls are solvent vapor pressure, cyclic temperature
change, tank size, and product throughput. A good system of tightly fitting
covers on coating preparation equipment reduces emissions by as much as 40
percent. Control efficiencies of 95 or 98 percent can be obtained by venting
the covered equipment to an adsorber, condenser or incinerator.
4.2.2.13-4 EMISSION FACTORS 9/90
-------
When the efficiencies of a capture device and control device are known,
the efficiency of the control system can be computed by the following
equation:
capture control device control system
efficiency x efficiency = efficiency
The terms of this equation are fractional efficiencies rather than
percentages. For instance, a system of hoods delivering 60 percent of VOC
emissions to a 90 percent efficient carbon adsorber would have control system
efficiency of 54 percent (0.60 x 0.90 - 0.54). Table 4.2.2.13-1 summarizes
control system efficiencies, which may be used to estimate emissions in the
absence of measured data on equipment and coating operations.
TABLE 4.2.2.13-1. TYPICAL OF CONTROL EFFICIENCIES3
Control technology Control Efficiency
Coating Preparation Equipment
Uncontrolled 0
Tightly fitting covers 40
Sealed covers with
carbon adsorber/condenser 95
Coating Operation0
Local ventilation with
carbon adsorber/condenser 83
Partial enclosure with
carbon adsorber/condenser 87
Total enclosure with
carbon adsorber/condenser 93
Total enclosure with incinerator 95
aReference 1.
"To be applied to uncontrolled emissions from indicated process area, not from
entire plant.
clncludes coating application/flashoff area and drying oven.
~l O Q
Emission Estimation Techniques ' - In this industry, realistic
emission estimates require solvent consumption data. The variations found in
coating formulations, line speeds' and products mean that no reliable
inferences can be made otherwise.
9/90 Evaporation Loss Sources 4.2.2.13-5
-------
In uncontrolled plants and in those where VOCs are recovered for reuse
or sale, plantwide emissions can be estimated by performing a liquid material
balance based on the assumption that all solvent purchased replaces that which
has been emitted. Any identifiable and quantifiable side streams should be
subtracted from this total. The liquid material balance may be performed
using the following general formula:
solvent quantifiable VOC
purchased " solvent output = emitted
The first term encompasses all solvent purchased, including thinners, cleaning
agents, and any solvent directly used in coating formulation. From this
total, any quantifiable solvent outputs are subtracted. Outputs may include
reclaimed solvent sold for use outside the plant or solvent contained in waste
streams. Reclaimed solvent that is reused at the plant is not subtracted.
The advantages of this method are that it is based on data that are
usually readily available, it reflects actual operations rather than
theoretical steady state production and control conditions, and it includes
emissions from all sources at the plant. Care should be taken not to apply
this method over too short a time span. Solvent purchase, production and
waste removal occur in cycles which may not coincide exactly.
Occasionally, a liquid material balance may be possible on a scale
smaller than the entire plant. Such an approach may be feasible for a single
coating line or group of lines, if served by a dedicated mixing area and a
dedicated control and recovery system. In this case, the computation begins
with total solvent metered to the mixing area, instead of with solvent
purchased. Reclaimed solvent is subtracted from this volume, whether or not
it is reused on the site. Of course, other solvent input and output streams
must be accounted, as previously indicated. The difference between total
solvent input and total solvent output is then taken to be the quantity of
VOCs emitted from the equipment in question.
Frequently, the configuration of meters, mixing areas, production
equipment, and controls will make the liquid material balance approach
impossible. In cases where control devices destroy potential emissions, or
where a liquid material balance is inappropriate for other reasons, plantwide
emissions can be estimated by summing the emissions calculated for specific
areas of the plant. Techniques for these calculations are presented below.
Estimating VOC emissions from a coating operation (application/flashoff
area and drying oven) starts with the assumption that the uncontrolled
emission level is equal to the quantity of solvent contained in the coating
applied. In other words, all the VOC in the coating evaporates by the end of
the drying process.
Two factors are necessary to calculate the quantity of solvent applied,
solvent content of the coating and the quantity of coating applied. Coating
solvent content can be either directly measured using EPA Reference Method 24
or estimated using coating formulation data usually available from the plant
owner/operator. The amount of coating applied may be directly metered. If it
is not, it must be determined from production data. These data should be
4.2.2.13-6 EMISSION FACTORS 9/90
-------
available from the plant owner/operator. Care should be taken in developing
these two factors to assure that they are in compatible units. In cases where
plant-specific data cannot be obtained, the information in Table 4.2.2.13-2
may be useful in approximating the quantity of solvent applied.
When an estimate of uncontrolled emissions is obtained, the controlled
emissions level is computed by applying a control system efficiency factor:
(uncontrolled VOC) x (1-control system efficiency) = (VOG emitted).
TABLE 4.2.2.13-2. SELECTED COATING MIX PROPERTIES3
Parameter
Unit
Range
Solids
VOC
Density of coating
Density of coating solids
Resins/binder
Magnetic particles
Density of magnetic material
Viscosity
Coating thickness
Wet
Dry
weight %
volume %
weight %
volume %
kg/1
Ib/gal
kg/1
Ib/gal
weight % of' solids
weight % of solids
kg/1
Ib/gal
Pa-s
lbf-s/ft2
//m
mil
/urn
mil
15-50
10-26
50-85
74-90
1.0-1.2
8-10
2.8-4.0
23-33
15-21
66-78
1.2-4.8
10-40
2.7-5.0
0.06-0.10
3.8-54
0.15-2.1
1.0-11
0.04-0.4
aReference 9. To be used when plant-specific data are unavailable.
As previously explained, the control system efficiency is the product of the
efficiencies of the capture device and of the control device. If these values
are not known, typical efficiencies for some combinations of capture and
9/90
Evaporation Loss Sources
4.2.2.13-7
-------
control devices are presented in Table 4.2.2.13-1. It is important to note
that these control system efficiencies apply only to emissions that occur
within the areas serviced by the systems. Emissions from sources such as
process wastewater or discarded waste coatings may not be controlled at all.
In cases where emission estimates from the mixing area alone are
desired, a slightly different approach is necessary. Here, uncontrolled
emissions will consist of only that portion of total solvent that evaporates
during the mixing process. A liquid material balance across the mixing area
(i.e., solvent entering minus solvent content of coating applied) would
provide a good estimate. In the absence of any measured value, it may be
assumed, very approximately, that 10 percent of the total solvent entering the
mixing area is emitted during the mixing process. When an estimate of
uncontrolled mixing area emissions has been made, the controlled emission rate
can be calculated as discussed previously. Table 4.2.2.13-1 lists typical
overall control efficiencies for coating mix preparation equipment.
Solvent storage tanks of the size typically found in this industry are
regulated by only a few states and localities. Tank emissions are generally
small (130 kilograms per year or less). If an emissions estimate is desired,
it can be computed using the equations, tables and figures provided in Section
4.3.2.
References For Section 4.2.2.13
1. Magnetic Tape Manufacturing Industry - Background Information For
Proposed Standards. EPA-450/3-85-029a, U. S. Environmental Protection
Agency, Research Triangle Park, NC, December 1985.
2. Control of Volatile Organic Emissions From Existing Stationary Sources -
Volume II: Surface Coating Of Cans. Coils. Paper. Fabrics. Automobiles,
And Light Duty Trucks. EPA 450/2-77-008, U. S. Environmental Protection
Agency, Research Triangle Park, NC, May 1977.
3. C. Beall, "Distribution Of Emissions Between Coating Mix Preparation
Area And The Coating Line", Memorandum file, Midwest Research Institute,
Raleigh, NC, June 22, 1984.
4. C. Beall, "Distribution Of Emissions Between Coating Application/
Flashoff Area And Drying Oven", Memorandum to file, Midwest Research
Institute, Raleigh, NC, June 22, 1984.
5. Control Of Volatile Organic Emission From Existing Stationary Sources -
Volume I: Control Methods For Surface-coating Operations. EPA-450/2-76-
028, U. S. Environmental Protection Agency, Research Triangle Park, NC,
November 1976.
6. G. Crane, Carbon Adsorption For VOC Control. U. S. Environmental
Protection Agency, Research Triangle Park, NC, January 1982.
4.2.2.13-8 EMISSION FACTORS 9/90
-------
7. D. Mascone, "Thermal Incinerator Performance For NSPS", Memorandum,
Office Of Air Quality Planning And Standards, U. S. Environmental
Protection Agency, Research Triangle Park, NC, June 11, 1980.
8. D. Mascone, "Thermal Incinerator Performance For NSPS, Addendum",
Memorandum, Office Of Air Quality Planning And Standards, U. S.
Environmental Protection Agency, Research Triangle Park, NC, June 22,
1980.
9. C. Beall, "Summary Of Nonconfidential Information On U. S. Magnetic Tape
Coating Facilities", Memorandum, with attachment, to file, Midwest
Research Institute, Raleigh, NC, June 22, 1984.
9/90 Evaporation Loss Sources 4.2.2.13-9
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4.2.2,14 Surface Coating Of Plastic Parts For Business Machines
4.2.2.14.1 General1'2
Surface coating of plastic parts for business machines is defined as the
process of applying coatings to plastic business machines parts to improve the
appearance of the parts, to protect the parts from physical or chemical
stress, and/or to attenuate electromagnetic interference/radio frequency
interference (EMI/RFI) that would otherwise pass through plastic housings.
Plastic parts for business machines are synthetic polymers formed into panels,
housings, bases, covers, or other business machine components. The business
machines category includes items such as typewriters, electronic computing
devices, calculating and accounting machines, telephone and telegraph
equipment, photocopiers and miscellaneous office machines.
The process of applying an exterior coating to a plastic part can include
surface preparation, spray coating, and curing, with each step possibly being
repeated several times. Surface preparation may involve merely wiping off the
surface, or it could involve sanding and puttying to smooth the surface. The
plastic parts are placed on racks or trays, or are hung on racks or hooks from
an overhead conveyor track for transport among spray booths, flashoff areas
and ovens. Coatings are sprayed onto parts in partially enclosed booths. An
induced air flow is maintained through the booths to remove overspray and to
keep solvent concentrations in the room air at safe levels. Although low
temperature bake ovens (140° F or less) are often used to speed up the curing
process, coatings also may be partially or completely cured at room
temperature.
Dry filters or water curtains (in water wash spray booths) are used to
remove overspray particles from the booth exhaust. In waterwash spray booths,
most of the insoluble material is collected as sludge, but some of this
material is dispersed in the water along with the soluble overspray
components. Figure 4.2.2.14-1 depicts a typical dry filter spray booth, and
Figure 4.2.2.14-2 depicts a typical water wash spray booth.
Many surface coating plants have only one manually operated spray gun per
spray booth, and they interchange spray guns according to what type of
coating is to be applied to the plastic parts. However, some larger surface
coating plants operate several spray guns (manual or robotic) per spray booth,
because coating a large volume of similar parts on conveyor coating lines
makes production more efficient.
Spray coating systems commonly used in this industry fall into three
categories, three coat, two coat, and single coat. The three coat system is
the most common, applying a prime coat, a color or base coat, and a texture
coat. Typical dry film thickness for the three coat system ranges from 1 to
3 mils for the prime coat, 1 to 2 mils for the color coat, and 1 to 5 mils for
the texture coat. Figure 4.2.2.14-3 depicts a typical conveyorized coating
line using the three-coat system. The conveyor line consists of three
separate spray booths, each followed by a flashoff (or drying) area, all of
9/90 Evaporation Loss Sources 4.2.2.14-1
-------
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EMISSION FACTORS
9/90
-------
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Evaporation Loss Sources
4.2.2.14-3
-------
which is followed by a curing oven. A two coat system applies a color or base
coat, then a texture coat. Typical dry film thickness for the two coat system
is 2 mils for the color (or base) coat and 2 to 5 rails for the texture coat.
The rarely used single coat system applies only a thin color coat, either to
protect the plastic substrate or to improve color matching between parts whose
color and texture are molded in. Less coating solids are applied with the
single coat system than with the other systems. The dry film thickness
applied for the single coat system depends on the function of the coating. If
protective properties are desired, the dry film thickness must be at least 1
mil (.001 inches). For purposes of color matching among parts having
molded-in color and texture, a dry film thickness of 0.5 mils or less is
needed to avoid masking the molded-in texture. The process of applying 0.5
mils of coating or less for color matching is commonly known as "fog coating",
"mist coating", or "uniforming".
The three basic spray methods used in this industry to apply
decorative/exterior coatings are air atomized spray, air-assisted airless
spray, and electrostatic air spray. Air atomized spray is the most widely
used coating technique for plastic business machine parts. Air-assisted
airless spray is growing in popularity but is still not frequently found.
Electrostatic air spray is rarely used, because plastic parts are not
conductive. It has been used to coat parts that have been either treated with
a conductive sensitizer or plated with a thin film of metal.
Air atomized spray coating uses compressed air, which may be heated and
filtered, to atomize the coating and to direct the spray. Air atomized spray
equipment is compatible with all coatings commonly found on plastic parts for
business machines.
Air-assisted airless spray is a variation of airless spray, a spray
technique used in other industries. In airless spray coating, the coating is
atomized without air by forcing the liquid coating through specially designed
nozzles, usually at pressures of 7 to 21 megapascals (MPa) (1,000 to 3,000
pounds per square inch). Air-assisted airless spray atomizes the coating by
the same mechanism as airless spray, but at lower fluid pressures (under 7
MPa). After atomizing, air is then used to atomize the coating further and to
help shape the spray pattern, reducing overspray to levels lower than those
achieved with airless atomization alone. Figure 4.2.2.14-4 depicts a typical
air-assisted airless spray gun. Air-assisted airless spray has been used to
apply prime and color coats but not texture coats, because the larger size of
the sprayed coating droplet (relative to that achieved by conventional air
atomized spray) makes it difficult to achieve the desired surface finish
quality for a texture coat. A touch-up coating step with air atomized
equipment is sometimes necessary to apply color to recessed and louvered areas
missed by air-assisted airless spray.
In electrostatic air spray, the coating is usually charged electrically,
and the parts being coated are grounded to create an electric potential
between the coating and the parts. The atomized coating is attracted to the
part by electrostatic force. Because plastic is an insulator, it is necessary
to provide a conductive surface that can bleed off the electrical charge to
maintain the ground potential of the part as the charged coating particles
accumulate on the surfaces. Electrostatic air spray has been demonstrated for
application of prime and color coats and has been used to apply texture coats,
4.2.2.14-4 EMISSION FACTORS 9/90
-------
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Evaporation Loss Sources
4.2.2.14-5
-------
Figure 4.2.2.14-4. Typical air assisted airless spray gun.5
but this technique does not function well with the large size particles
generated for the texture coat, and it offers no substantial improvement over
air atomized spray for texture coating. A touch-up coating step with air
atomized spray is sometimes necessary to apply color and texture to recessed
and louvered areas missed by electrostatic spray.
The coatings used for decorative/exterior coats are generally solvent-
based and waterborne coatings. Solvents used include toluene, methyl ethyl
ketone, methylene chloride, xylene, acetone and isopropanol. Typically,
organic solvent-based coatings used for decorative/exterior coats are two
types of two-component catalyzed urethanes. The solids contents of these
coatings are from 30 to 35 volume percent (low solids) and 40 to 54 volume
percent (medium solids) at the spray gun (i.e., at the point of application,
or as applied). Waterborne decorative/exterior coatings typically contain no
more than 37 volume percent solids at the gun. Other decorative/exterior
coatings being used by the industry include solvent-based high solids coatings
(i.e., equal to or greater than 60 volume percent solids) and one-component
low solids and medium solids coatings.
The application of an EMI/RFI shielding coat is done in a variety of
ways. About 45 percent of EMI/RFI shielding applied to plastic parts is done
by zinc-arc spraying, a process that does not emit volatile organic compounds
(VOC). About 45 percent is done using organic solvent-based and waterborne
metal-filled coatings, and the remaining EMI/RFI shielding is achieved by a
variety of techniques involving electroless plating, and vacuum metallizing or
sputtering (defined below), and use of conductive plastics, and metal inserts.
Zinc-arc spraying is a two-step process in which the plastic surface
(usually the interior of a housing) is first roughened by sanding or grit
blasting and then sprayed with molten zinc. Grit blasting and zinc-arc
spraying are performed in separate booths specifically equipped for those
activities. Both the surface preparation and the zinc-arc spraying steps
currently are performed manually, but robot systems have recently become
available. Zinc-arc spraying requires a spray booth, a special spray gun,
pressurized air and zinc wire. The zinc-arc spray gun mechanically feeds two
zinc wires into the tip of the spray gun, where they are melted by an electric
4.2.2.14-6
EMISSION FACTORS
9/90
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arc. A high pressure air nozzle blows the molten zinc particles onto the
surface of the plastic part. The coating thickness usually ranges from 1 to 4
mils, depending on product requirements.
Conductive coatings can be applied with most conventional spray equipment
used to apply exterior coatings. Conductive coatings are usually applied
manually with air spray guns, although air-assisted airless spray guns are
sometimes used. Electrostatic spray methods can not be used because of the
high conductivity of EMI/RFI shielding coatings.
Organic solvent-based conductive coatings contain particles of nickel,
silver, copper or graphite, in either an acrylic or an urethane resin.
Nickel-filled acrylic coatings are the most frequently used, because of their
shielding ability and their lower cost. Nickel-filled acrylics and urethanes
contain from 15 to 25 volume percent solids at the gun. Waterborne nickel-
filled acrylics with between 25 and 34 volume percent solids at the gun
(approximately 50 to 60 volume percent solids, minus water) are less
frequently used than,are organic-solvent-based conductive coatings.
The application of a conductive coating usually involves three steps:
surface preparation, coating application, and curing. Although the first step
can be eliminated if parts are kept free of mold-release agents and dirt, part
surfaces are usually cleaned by wiping with organic solvents or detergent
solutions and then roughened by light sanding. Coatings are usually applied
to the interior surface of plastic housings, at a dry film thickness of 1 to
3 mils. Most conductive coatings can be cured at room temperature, but some
must be baked in an oven.
Electroless plating is a dip process in which a film of metal is
deposited in aqueous solution onto all exposed surfaces of the part. In the
case of plastic business machine housings, both sides of a housing are
coated. No VOC emissions are associated with the plating process itself.
However, coatings applied before the plating step, so that only selected areas
of the parts are plated, may emit VOCs. Wastewater treatment may be necessary
to treat the spent plating chemicals.
Vacuum metallizing and sputtering are similar techniques in which a thin
film of metal (usually aluminum) is deposited from the vapor phase onto the
plastic part. Although no VOC emissions occur during the actual metallizing
process, prime coats often applied to ensure good adhesion and top coats to
protect the metal film may both emit VOCs.
Conductive plastics are thermoplastic resins that contain conductive
flakes or fibers of materials such as aluminum, steel, metallized glass or
carbon. Resin types currently available with conductive fillers include
acrylonitrile butadiene styrene, acrylonitrile butadiene styrene/polycarbonate
blends, polyphenylene oxide, nylon 6/6, polyvinyl chloride, and polybutyl
terephthalate. The conductivity, and therefore the EMI/RFI shielding
effectiveness, of these materials relies on contact or near contact between
the conductive particles within the resin matrix. Conductive plastic parts
usually are formed by straight injection molding. Structural foam injection
molding can reduce the EMI/RFI shield effectiveness of these materials because
air pockets in the foam separate the conductive particles.
9/90 Evaporation Loss Sources 4.2.2.14-7
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4.2.2.14.2 Emissions And Controls
The major pollutants from surface coating of plastic parts for business
machines are VOC emissions from evaporation of organic solvents in the
coatings used, and from reaction byproducts when the coatings cure. VOC
sources include spray booth(s), flashoff area(s), and oven(s) or drying
areas(s). The relative contribution of each to total VOC emissions from a
from plant to plant, but for an average coating operation, about 80 percent is
emitted from the spray booth(s), 10 percent from the flashoff area(s), and 10
percent from the oven(s) or drying area(s).
Factors affecting the quantity of VOC emitted are the VOC content of the
coatings applied, the solids content of coatings as applied, film build
(thickness of the applied coating), and the transfer efficiency (TE) of the
application equipment. To determine of VOC emissions when waterborne coatings
are used, it is necessary to know the amounts of VOC, water and solids in the
coatings.
«
The TE is the fraction of the solids sprayed that remains on a part. TE
varies with application technique and with type of coating applied.
Table 4.2.2.14-1 presents typical TE values for various application methods.
TABLE 4.2.2.14-1. TRANSFER EFFICIENCIES'
Application methods
Transfer
efficiency
Type of coating
Air atomized spray
Air-assisted airless spray
Electrostatic air spray
25
40
40
Prime, color, texture,
touchup and fog coats
Prime, color coats
Prime, color coats
"As noted in the promulgated standards, values are presented solely to
aid in determining compliance with the standards and may not reflect
actual TE at a given plant. For this reason, table should be used with
caution for estimating VOC emissions from any new facility. For a more
exact estimate of emissions, the actual TE from specific coating
operations at a given plant should be used.1
Volatile organic compound emissions can be reduced by using low
VOC-content coatings (i.e., high solids or waterborne coatings), using surface
finishing techniques that do not emit VOC, improved TE, and/or added controls.
Lower VOC content decorative/exterior coatings include high solids-content
(i.e., at least 60 volume percent solids at the spray gun) two-component
catalyzed urethane coatings and,waterborne coatings (i.e., 37 volume percent
solids and 12.6 volume percent VOC at the spray gun). Both of these types of
exterior/decorative coatings contain less VOC than conventional urethane
4.2.2.14-8
EMISSION FACTORS
9/90
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