Metal Finishing Guide Book

2012-2013

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6. Wood Coatings Figure 9. Extensive solvent entrapment on the underside of an epoxy coating, resulting in poor wetting and inadequate adhesion to the substrate. Figure 10. Top of epoxy coating showing extensive pinholes and craters. A cabinet maker applied a lacquer from Company A for finishing kitchen cabinets. After the cabinets were installed, several customers complained the coating easily chipped off when something was dropped onto the wood. The problem was exacerbated when someone bumped into the corners or edges of the wood. The cabinet maker then changed to a different lacquer and clear coat from Company B and the results appeared to be fine. Upon microscopic investigation, it was clear that the original finish was so brittle that when the paint consultant touched it with the tip of an X-Acto�� knife, the coating shattered into small pieces and there was essentially no adhesion between the lacquer and the wood (see Figure 8). When the replacement coating was examined, some of the clear coat broke away from the underlying lacquer, but the coating system remained in good condition. There were no complaints that the new coating system failed in the field. Figure 11. Top coat blistering due to extensive solvent entrapment in the under coat. 7. Delamination of epoxy primer Figure 12. Multiple layers of paint leads to tremendous internal pressures. One of the most common reasons for paint delamination is solvent entrapment. Figure 9 illustrates a micrograph taken with a stereomicroscope showing extensive solvent entrapment on the underside of the coating. Although this was barely visible with the naked eye, it became obvious under approximately 15X magnification. To highlight the cavities, the paint consultant chose to illuminate the sample paint chip at a shallow oblique angle of approximately 10 to 15 degrees. Using oblique lighting, the top of the coating clearly showed pinholes filled 586

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