POLLUTION PREVENTION OPPORTUNITY DATASHEET

POWDER COATING TECHNOLOGY

Revision: 4/94
Process / Product: Powder Painting
Process Code: ID-05-03, ID-05-04
Substitute For: Conventional Solvent-based, Waterborne, or High Solids Painting
Waste Stream: Solvents, Paint Sludges, VOC Emissions
Applicable EPA Hazardous Waste Codes: D008, D035
Applicable EPCRA Targeted Constituents: Acetone, n-Butanol, Lead, Methyl Ethyl Ketone,
Toluene, and Xylene

Introduction: In conventional paint spray systems, paint atomization occurs via high-
velocity air jets, forcing paint through small air holes in the paint gun
face caps. Air pressures used range from 40 to 80 psi, with air volumes
of 8 to 30 sqfm. The atomized paint particles travel at high velocities
and tend to bounce off the object being painted, rather than adhering
to the surface. In addition, the expanding high-pressure air (as high as
70 psi) passes through the small face cap openings, causing turbulent
flow of the paint stream following air currents within the paint booth.
The amount of paint that bypasses the workpiece (overspray) is
relatively high for air pressure atomized spray painting. Transfer
efficiencies of 15 to 30 percent are associated with conventional
painting systems.

Description: Thin film powder coating, also referred to as a ‘dry painting” process,
e428nates volatile organic compounds (VOCs), hazardous air
pollutants (HAPS), and solvents, and produces superior surface finish.
There are four basic powder coating application processes: e4ectrostatic
spraying, fluidized bed, e4ectrostatic fluidized bed, and flame spray.
Electrostatic spraying is the most commonly used powder application
method. For all application methods, surface preparation (i.e., cleaning
and perhaps application of a conversion coating) is required to develop
good coating adhesion to the workpiece surface. Characteristics of the
four different powder coating application techniques are summarized
in Table 1 and described be4ow.

In e4ectrostatic spraying, an e4ectrical charge is applied to the dry

powder particles while the component to be painted is e4ectrically
grounded. The charged powder and grounded workpiece create an
electrostatic fie4d that pulls the paint particles to the workpiece. The
coating deposited on the workpiece retains its charge, which holds the
powder to the workpiece. The coated workpiece is placed in a curing
oven, where the paint particles are melted onto the surface and the
charge is dissipated.

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Table 1. Characteristics of Powder Coating Techniques

Fluidized Bed
Characteristic Electrostatic and
of Workpiece Spray Electrostatic Flame Spray
Fluidized Bed
Size Larger Smaller Not limited
Material Metallic, must Any, not Any, not
be conductive necessarily necessarily
conductive conductive
Temperature Relatively high High Not relevant
Resistance
Aesthetic High Low, not Low, not
Value suitable for suitable for
decorative decorative
purposes purposes
Coating Thinner films Thick high- Thick high-
Thickness build films with build films;
excellent uniformity
uniformity dependent on
the operator
Type of Thermoplasts Thermoplastic Thermoplasts
Coatings and thermosets and thermosets only
Color Change Difficult Relatively Easy
difficult
Capital Moderate to LOW Very low
Investments high
Labor Low since Moderate Relatively high
highly depending on
automated the
automatization
Energy Only post- Preheating and Low, no
Consumption heating often preheating and
postheating postheating
Coating Waste Very little Very little Dependent on
the workpiece
geometry
From Miser, Tosko A. 1991. Powder Coatings: Chemistry and Technology, Table 6.4, p. 350.

In a fluidized bed, powder particles are kept in suspension by an air

stream. A preheated workpiece is placed in the fluidized bed where the
powder particles coming in contact with the workpiece melt and adhere
to its surface. Coating thickness is dependent on the temperature and
heat capacity of the workpiece and its residence time in the bed. Post
heating is generally not required when applying thermoplastic powder
coatings. However, post heating is required to completely cure
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thermoset powder coatings.

Electrostatic fluidized beds are similar in design to conventional

fluidized beds, but the air stream is electrically charged as it enters the
bed. The ionized air charges the powder particles as they move upward
in the bed, forming a cloud of charged particles. The grounded
workpiece is covered by the charged particles as it enters the chamber.
No preheating of the workpiece is required. Curing of the coating is,
however, necessary. This technology is most suitable for coating small
objects with simple geometry.

The flame-spray technique was recently developed for application of

thermoplatic powder coatings. The thermoplastic powder is fluidized
by compressed air and fed into a flame gun where it is injected through
a flame of propane, and the powder melts. The molten coating
particles are deposited on the workpiece, forming a film on
solidification. Since no direct heating of the workpiece is required, this
technique is suitable for applying coatings to most substrates. Metal,
wood, rubber, and masonry can be successfully coated by this
technique. This technology is also suitable for coating large or
permanently-fixed objects.

The choice of powders is dependent on the end-use application and

desired properties. Powders are typically individually formulated to
meet specific finishing needs. Nevertheless, powder coatings fall into
two basic categories: thermoplastic and thermosetting. The choice is
application dependent. However, in general, thermoplastic powders are
more suitable for thicker coatings, providing increased durability, while
thermosetting powders are often used when comparatively thin coatings
are desired, such as decorative coatings. The principal resins used in
thermoplastic powders are vinyl, nylon, and fluoropolymer.
Thermosetting powders use primarily epoxy, polyester, and acrylic
resins.

The concentration of powder in air must be controlled to maintain a

safe working environment. Despite the absence of flammable solvents,
any finely divided organic material, such as dust or powder, can form
an explosive mixture in air. This is normally controlled by maintaining
proper air velocity across face openings in the spray booth. In the dust
collector, where the powder concentration cannot be maintained below
the lower explosive limit, either a suppression system or a pressure
relief device must be considered.

Materials
Compatibility: Only workpieces that can be oven heated can be coated by the

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electorostatic, the fluidized bed, and the electrostatic fluidized bed

application methods. These technologies are, therefore, most suitable
for relatively small, metal objects. The flame-spray method allows
powder coatings to be applied to other substrates such as wood,
rubber, and plastic, and to large or stationary structures.

Safety and Health: Powder and air mixtures, in the correct concentrations, can be a fire
hazard when an ignition source is introduced. Inhalation of the powders
should be avoided, as this can cause irritation to the lungs and mucous
membranes. proper personal protective equipment should be used.

Consult your local Industrial Health specialist, your local health and
safety personnel, and the appropriate MSDS prior to implementing any
of these technologies.

Benefits: Powder coating eliminates the need for expensive and often toxic
solvents, as well as the control equipment, employee exposure, and the
disposal requirements and liabilities associated with liquid coating (wet
solvent) use. Because the powder is dry when sprayed, any overspray
can be readily retrieved and recycled, regardless of the complexity of
the system, resulting in shorter cleanup times. In all cases, the dry
powder is separated from the air stream by various vacuum and
filtering methods and returned to a feed hopper for reuse. Powder
efficiency (powder particles reaching the intended surface) approaches
100 percent. Other advantages over conventional spray painting include
greater durability; improved corrosion resistance; and elimination of
drips, runs, and bubbles.

Economic Analysis: Analysis of capital costs for a typical coating installation (two wash
booths, one dry filter booth, four automatic guns, one manual gun, and
two reciprocators) associated with a powder system totals
approximately $120,000. This compares favorably to the conventional
solvent-based system, which costs approximately $150,000. However,
the powdered system is more expensive than waterborne or high solids
coating systems, which cost approximately $110,000. Material costs are
also substantially lower for powder coating systems ($27,300 per
1,000,000 square feet) than conventional solvent-based systems ($34,900
per l,000,000 square feet) or waterborne systems ($35,600 per
l,000,000 square feet), while high solids systems are the least expensive
($24,400 per l,000,000 square feet). Overall, powder coating is the
most cost effective when annual operating costs are included (cleanup,
disposal, and power). On an applied basis, conventional systems are
most expensive, followed by waterborne, high solids, and finally
powdered, with approximate costs of $5.66/100 square feet, $5.64/100
square feet, $4.41/100 square feet, and $3.80/100 square feet,

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respectively.

Major Assumptions: Economic data and basis provided by the Powder Coating
Institute, Powder Coating Today, 1987, p 10.

Points of Contact: Powder Coating Institute

1800 Diagonal Road, Suite 600
Alexandria, VA 22314
(703) 684-1770

Tony Gomes
Code 422
Naval Facilities Engineering Service Center
560 Center Drive
Port Hueneme, CA 93042-4328
(805) 982-3425 or DSN 551-3425

Vendors: The following is a list of powder coating system manufacturers. This is

not meant to be a complete list, as there may be other manufacturers
of this type of equipment.

Coating Manufacturers:

Cardinal Industrial Finishes

Powder Coating Division
901 Stimson Avenue
City of Industry, CA 91745
Phone: (818) 336-3345, Fax: (818) 336-0410

EVTECH
9103 Forsyth Park Drive
Charlotte, NC 28273
Phone: (704) 588-2112, Fax: (704) 588-2280

Farboil Company
8200 Fischer Road
Baltimore, MD 21222
Phone: (410) 477-8200, Fax: (410) 477-8995

Plastic Flamecoat Systems, Inc.

3400 West Seventh Street
Big Spring, TX 79720
Phone: (800) 753-5263, Fax: (915) 267-1318

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Pratt & Lambert Inc.

Powder Coatings Division
40 Sonwil Drive
Cheektowaga, NY 14225
Phone: (716) 683-6831, or Customer Service (800) 777-6831
Fax: (716) 683-6204

Equipment Manufacturers:

Nordson Corp.
555 Jackson Street
Amherst, OH 44001
Phone: (216) 988-9411, Fax: (216) 985-1417

Sames Electrostatic, Inc.

555 Lordship Blvd.
Stratford, CT 06497
(203) 375-1644

Gema
3939 W. 56th Street
Indianapolis, IN 46208
Phone: (317) 298-5001, Fax: (317) 298-5059

Contact NAVAIR Code 530 (Ref. R 1820022) for further approval

authority for use on aircraft and aircraft components. Phone is (703)
692-6025; DSN 222-6025.

This recommendation should be implemented only after engineering

approval has been granted by cognizant authority.

Source: Powder Coating Institute, 1987, Powder Coating Today p.l0

Miser, Toako A. 199l. Powder Coatings Chemistry and Technology, Chapter 6, Powder Application Techniques.
‘Reducing Waste in Railcar Coating Operation Graco Equipment and Emissions Update, June 1994 pp. 8-9.

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