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 ------- 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. ------- ------- 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 BULK RATE POSTAGE & FEES PAID EPA PERMIT NO. G-35 EPA/600/SR-93/077 ------- |