United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-93/077
November 1994
&EPA Project Summary
Evaluation of Innovative
Painting Processes
Krish Pandalai and Gopinadhan Pandalai
This report gives results of an evalu-
ation of two novel spray painting tech-
niques that may decrease volatile or-
ganic compound (VOC) emissions as-
sociated with the application of sur-
face coatings. One technique uses
supercritical carbon dioxide (CO2) as a
solvent and a propel Ian t to deliver and
disperse the coating. The second sys-
tem utilizes pressurized nitrogen to de-
liver a constant-flow, very soft spray
through the gun nozzle. This technol-
ogy is called the Ultra Low Volume
(ULV) process. The CO, system encoun-
tered problems in delivering urethane
topcoats and was eliminated from field
testing.
Data were gathered on VOC emis-
sions, paint consumption, coating thick-
ness, and workplace exposure during
application of an epoxy primer and a
silica-filled chemical agent resistant
(CARC) topcoat to a fleet of trucks at
Warner Robins AFB, GA. The ULV pro-
cess was compared to a conventional
air atomizing gun system.
Results revealed a 50% decrease in
VOC emissions, and a 30% decrease in
paint consumption when using the ULV
system. Also no increase in exposure
was detected when compared to the
conventional gun.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Objective
The objective of the project was to per-
form a practical evaluation of two innova-
tive spray painting technologies that can
decrease volatile organic compound (VOC)
emissions associated with the application
of surface coatings.
Background
Solvents added to decrease the viscos-
ity of coatings to levels compatible with
application methods are a major source of
VOCs. These VOCs are subject to regula-
tion under environmental codes, including
Title 3 of the Clean Air Act Amendments.
While end-of-pipe technology exists to cap-
ture or destroy these volatiles from the
spray booth emissions air stream, it is
expensive to maintain and operate. A more
desirable alternative, when practical, is to
decrease the solvent content (i.e., raise
the solids content) of the coating as ap-
plied. Practicality depends on the avail-
ability of a delivery system that can apply
a high-solids coating formulation at the
viscosity supplied. This approach, defined
as pollution prevention, reduces the
amount of solvent available for emission
to the atmosphere.
This study initially addressed two ap-
proaches to spraying high viscosity coat-
ings. Unicarb technology is based on use
of supercritical carbon dioxide (CO2), a
relatively nontoxic, nonpolluting material,
as both a solvent to adjust viscosity and
as the propellant to deliver and disperse
the paint. The embodiment of this tech-
nology at the time of this study proved
incompatible with current two-component
urethane topcoat formulations, and thus
Printed on Recycled Paper
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was not evaluated in the field. However
the principle remains valid, and reexami-
nation of the Unicarb process as a way to
apply urethane topcoat can be reexam-
ined when it is compatible.
The second approach is a low-tech de-
vice employing a portable pressure cell
consisting of two connected chambers,
one pressurized with nitrogen gas, and
the second isolated from the first by a
floating piston that transmits the gas pres-
sure to a charge of paint. Flow of paint
from the second chamber through a nozzle
results in a constant-flow, very soft deliv-
ery of a paint spray. This technology, called
the Ultra Low Volume (ULV) spray pro-
cess, is available from commercial outlets
under license from Air Compliance Tech-
nologies.
Scope
During this study, the ULV gun was
qualified to apply MIL-C-83286 and MIL-
C-85285 urethane topcoats and was sub-
sequently used in the field to apply MIL-P-
23377 epoxy primer and a silica-filled
chemical agent resistant (CARC) topcoat,
MIL-C53039. Data were gathered on VOC
emissions, paint consumption, coating
thickness, and work place exposure dur-
ing application of prime and top coats to
two equivalent (same number of each size)
sets of trucks. One set was painted with
the ULV gun, and the other with a con-
ventional air atomizing gun, by paint shop
staff at Warner Robins AFB, GA.
Methodology
Standard procedures were changed as
little as possible for the test. Painters wore
air respirators, and the airflow through the
booths was verified by the Warner Robins
bioenvironmental engineering (BEE) sur-
vey. BEE personnel also monitored repre-
sentative painting sessions. Viscosity was
measured, using a Zahn viscometer cup,
at intervals roughly corresponding to refill-
ing. Film thickness was measured using a
thickness gauge (Inspector, Elcometer In-
struments) and is reported as the aver-
age of 10 determinations for each truck.
Paint consumption was measured by
weighing the paint gun systems after fill-
ing and after delivery, on a scale accurate
to ±0.02 Ib (9 g). Consumption was the
net weight loss. VOC concentrations were
measured with a flame ionization detector
(FID Rosemount Model 400A Hydrocar-
bon Analyzer). Stack samples were deliv-
ered to the FID by ADI 01320T dual-head,
TeflonR-diaphragm pumps. Continuous
VOC measurements were recorded on
strip charts. A second set of VOC data
was collected in tabular form at regular
15-second intervals. The time integral of
the VOC data was estimated by applica-
tion of the trapezoid rule and compared to
the mechanically integrated strip chart data
to confirm calibration.
Test Descriptions
The test consisted of measuring paint
consumption, VOC emissions, and paint
coating thickness during the painting of
14 trucks. However, experimental irregu-
larities eliminated the data from the first
weekend, leaving only two 2.5 ton (2268
kg) and two 5 ton (4535 kg) trucks as the
sample population for each treatment
group. Personal exposure was sampled
by the BEE group during one of the tests
performed with each of the guns. The
painters and shop supervisor were sur-
veyed afterward for impressions of the
two guns.
Results
After correcting for differences in coat-
ing thickness, paint consumption for the
CARC topcoat averaged 20% less when
applied with the ULV gun than with the
conventional unit. The ULV gun decreased
VOC emissions by about 50%, through a
combination of the greater transfer effi-
ciency noted above and the capability of
the ULV gun to deliver undiluted, high
viscosity paint. A qualitative decrease in
density of overspray was evident during
the study. Personal exposure data are
complicated by a solvent spill during the
exposure test for the ULV gun, but still
show that the ULV gun creates no in-
crease in exposure compared to the con-
ventional gun. Impressions of the ULV
gun were uniformly favorable, relating to
both its handling and the coating deliv-
ered.
Conclusions
The ULV gun delivered satisfactory
prime and top coats. Transfer efficiency
was significantly better than for the con-
ventional gun. Both of the latter observa-
tions have potential to lower the rate of
VOC emission associated with spray paint-
ing.
Further examination of the ULV gun
should help determine its suitability for
specific applications to ground equipment,
aircraft, parts, etc., and establish optimal
viscosities for application to minimize VOC
emissions consistent with satisfactory coat-
ing thickness and characteristics.
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Krish Pandalai and Gopinadhan Pandalai are with Pandalai Coatings Co.,
Brackenridge, PA 15014.
Bobby E. Daniel is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Innovative Painting Processes," (Order
No. ADA 279 762; Cost: $17.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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EPA/600/SR-93/077
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