Final Report: Near-Zero VOC General OEM Bake EnamelEPA Contract Number: 68D03023
Title: Near-Zero VOC General OEM Bake Enamel
Investigators: Slama, Francis J.
Small Business: Finishes Unlimited Inc.
EPA Contact: Manager, SBIR Program
Project Period: April 1, 2003 through September 1, 2003
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2003) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , SBIR - Air Pollution , Small Business Innovation Research (SBIR)
Finishes Unlimited, Inc., develops, produces, and markets paints for general-purpose original equipment manufacturer (OEM) applications. This market includes such sundry metal products as lockers, light fixtures, toolboxes, compressors, metal office furniture, folding chairs, storage racks, etc. It does not include high-end applications such as automobiles, refrigerators, washers, dryers, etc. Costs of general-purpose OEM paints are moderate compared to those for paints used in automotive and appliance applications. In 1993, Finishes Unlimited, Inc., discontinued its solvent-borne and high-solids lines of paint and now produces only waterborne products. The company produces both air-dry and baking enamels. This Phase I research project involved a waterborne bake enamel. The goal was to develop a waterborne bake enamel with a very low level of volatile organic compound (VOC) emissions. The project envisioned a maximum VOC of 0.5 lb/gallon without water. Typical waterborne paints have VOC levels of approximately 1.9-3.0 lb/gallon.
The project was based on the results of an extensive preliminary study in which some promising developments had been observed. Finishes Unlimited, Inc.'s Research and Development Team developed two separate products, based on two different binder systems, and coatings from both of those products had exhibited acceptable properties. However, in field tests at customers' shops, both products produced coatings that exhibited a certain surface roughness that was attributed to poor overspray melt-in (this phenomenon is not the same as poor gloss). This application problem is not observed with any of the company’s higher-VOC products.
A great hindrance in the earlier study was that the Research and Development Team had been unable to reproduce the poor overspray melt-in in their laboratory spraying operation. That is, all specimens sprayed in the laboratory exhibited excellent appearance, and the technicians were unable to elicit the poor overspray melt-in that was being observed in field tests. The only way to determine whether a given low-VOC candidate would produce an acceptable film on a commercial paint line was to conduct a field test, either by purchasing line time or by accepting it as a gift from a valued customer. This cumbersome situation made further development work practically impossible. One of the goals of this project was to develop a laboratory test that would predict the application performance on a full-scale paint line. The second goal was to develop a very low-VOC paint with good overspray melt-in, a product that would perform acceptably on commercial-size paint lines.
A laboratory test was developed that reproduces the application problem observed in the field. The predictive ability of the test was validated by contracting a metal fabricator to make custom boxes and paint them with paints that had been tested with the newly developed bench-scale test. In terms of overspray melt-in, the paints ranked the same on that commercial paint line as they did in the laboratory. The test employs air-assisted airless equipment, with a properly chosen interval between initial spraying and application of overspray, and with properly chosen fluid and fan pressures for the overspray (specifically, low fluid pressure and high fan pressure). With this test, it became possible to evaluate four 800-g samples in the laboratory in one-half of a day, instead of negotiating for time at a distant site to test one or two 10-gallon samples.
Facilitated by the availability of a method for evaluating the application performance in the laboratory, several hypotheses were proposed and tested as possible explanations for the poor overspray melt-in. As a result of that testing, some of the hypotheses had to be discarded, but two of them did provide clues as to how to solve the application problem. Low-VOC paints were developed that performed well in the laboratory application test, and there was no sacrifice in coating properties such as hardness, toughness, or durability.
Although the overspray of the new development products melted in well, a new problem arose that was not exhibited by the precursor paints from the preliminary study before this Phase I project. There was an unusual type of popping—a fine, dense "micropopping"—unlike classical popping that occurs when a coating is too thick. What was especially unusual was that this "micropopping" was exaggerated when a specimen was flashed under a fan instead of in still air, exactly the opposite of what was expected (flashing sometimes is conducted under a fan to reduce popping by forcing more evaporation before a specimen is baked).
In an attempt to understand the reason for the unusual "micropopping," a hypothesis was developed that attempted to: (1) explain the unexpected fan effect in the newly developed, low-VOC products that exhibit good overspray melt-in; and (2) explain why the earlier low-VOC products (those with poor overspray melt-in) did not exhibit this "micropopping." Working with this hypothesis, a modification was made that resulted in a coating with greatly reduced "micropopping."
Ultimately, two paints were chosen for field testing on a large commercial paint line. One of the paints was the version that had exhibited "micropopping" in the laboratory when it was flashed under a fan, but not when it was flashed in still air. It was hoped that the unusual popping might not occur under the conditions of that plant. The VOC of that version was 0.3 lb/gallon without water. The other paint was the modified version that largely, but not entirely, overcame the "micropopping" when flashed under a fan. That paint had a VOC of 0.7 lb/gallon without water, quite low but not as low as the proposed goal of 0.5 lb/gallon.
Despite the potential popping problem, the field test was successful for both paints. Overspray melted in much better than had been observed in earlier tests with the paints from the preliminary study. The customer's quality control department approved all of the products painted with those two paints, and all of the products were shipped. Nevertheless, upon very close inspection, Finishes Unlimited, Inc., did observe some "micropopping" on all of the finished products.
A laboratory-scale technique was developed that reproduces the problem of poor overspray melt-in that was the subject of this investigation. The use of that test allowed the development of paints that do not exhibit that application problem. Two paints yielded results that were acceptable to a customer who evaluated those paints on a large commercial paint line, although there was a minor amount of the unusual "micropopping" on all of the finished products. Although the customer was satisfied with the trial, Finishes Unlimited, Inc., realizes that refinements are necessary to achieve long-term, trouble-free performance. Additional studies to minimize the unusual popping should result in a technology that will allow for a large reduction in VOC emissions from paint lines that apply bake enamels.