Surface Chemistry of an Acrylosilane-Melamine Based Automotive Clearcoat

The surface chemistry of an acrylosilane-melamine-based automotive clearcoat was studied using multiple analytical techniques. A prototype system was prepared which had a chemical composition similar to the commercial formulation. The objective was to analyze how inert or reactive the clearcoat surface is under various environmental conditions that are relevant to the automobile manufacturing process. The elemental composition of the surface region, the surface energy, the surface-exposed alkyl/hydroxyl groups, and the indentation modulus and adhesion force were analyzed. The clearcoat surface was found to be inert (free of reactive functional groups) under ambient conditions, regardless of humidity levels to which it is exposed. The alkyl group orientation changed slightly upon heating the sample above the glass transition temperature (T_g). The surface T_g appeared to be much lower than that of the bulk T_g. The exposure to organic solvent (N-methyl pyrrolidone) swelled the surface, but upon blow-drying, the surface chemistry of the clearcoat appeared to have returned to its original state. The methoxysilyl groups at the surface could be converted to silanol groups through acid- or base-catalyzed hydrolysis, but not in neutral conditions (such as exposure to DI water or high humidity conditions). The surface chemistry information found in this study will help better understand surface changes when the coating is exposed to different environments and may be useful in guiding clearcoat formulation improvements.