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Chipping performance of body paint on a vehicle has become increasingly important in harsher climates such as North America and Russia. Stones can cause body paint to chip down to substrate and expose bare metal, which can then lead to corrosion. The primer layer serves not only as the adhesion promoter between metal substrate and topcoat, but also secures overall chipping performance of the coating system. The benefits of a softer body primer have been established and described in Bock and Engbert’s SAE paper “Waterborne Polyurethane Based Paint Materials for the Automotive Industry - Present Situation and Future Possibilities - ,”[1], however, the challenge exists in accommodating various application process conditions.

Automotive clearcoats have many purposes, from providing a glossy finish to protecting the underlying paint layers from UV radiation. Yellowing of clearcoats is a natural phenomenon during weathering processes, as well as from extreme baking conditions, due to polymer degradation. However, occasionally yellowing may be caused by unexpected chemical reactions occurring in the clearcoat. These reactions may happen very quickly (within hours or days) or take years to manifest, as other chemicals migrate into the clearcoat. We have investigated one family of these unexpected reactions which occur with certain UV absorbers, as well as how to prevent the reactions from occurring. We found that certain benzotriazole UV absorbers react readily with some common metals, including copper and zinc, provided that the UV absorber is not in its excited state. The conformational change that occurs within the benzotriazole when it absorbs UV radiation effectively inhibits the reaction with metals.