Acid etch resistance of automotive clearcoats. I: Laboratory test method development

This paper reports on the development of a laboratory test procedure for th e evaluation of the environmental etch resistance of clearcoats. The test e valuates the bulk acid hydrolysis resistance of clearcoats by gravimetrical ly following material weight loss as a function of exposure time to a sulfu ric acid solution, under conditions that simulate outdoor exposure. The bul k hydrolysis resistance of five production clearcoat technologies including acrylic melamine, acrylic melamine-silane, carbamate, acrylic urethane, an d epoxy acid were evaluated. Results from the weight loss measurements were consistent with those anticipated based on the coating systems bulk chemis try and inherent hydrolysis resistance, for clearcoat systems processed und er nominal processing conditions. The relative rankings from the laboratory test were found to correlate with field etch ratings. The test method is i nexpensive, quantitative, and generates repeatable results that are not sub ject to environmental variations associated with current field etch testing .