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
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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
Penalty for Private Use $300
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EPA/600/SR-93/077

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