Clearcoat analysis in isolated and multi-layer paint systems by confocal Raman microscopy

Confocal Raman microscopy has been used to characterize the chemical composition of clearcoats in three paint systems: weathered and unweathered samples of isolated acrylic/melamine and acrylic/urethane clearcoats, polyester urethane clearcoats in weathered and unweathered samples of a complete paint system on plastic, and ultraviolet-light-cured acrylic clearcoats on polycarbonate substrates. The increase in the carbonyl peak intensity was found to be an excellent means to follow the progress of photo-oxidation in isolated clearcoats as well as in a clearcoat in a complete paint system. Similar measurements on basecoats were less successful; some samples produced intense fluorescence, which obscured the Raman lines. The technique was most useful for examining the interface formed between an ultraviolet-light-cured acrylic hardcoat and a polycarbonate. Spatial profiles of this interface with a resolution of similar to 1 mu m revealed that different cure conditions can produce either an abrupt (< 1 mu m) transition between the two materials or a thick (similar to 10 mu m) blended transitional region in which the two materials are completely mixed. (C) 1997 Elsevier Science Limited.