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.
This paper describes the balancing of developing a robust high chipping performance body primer with lower glass transition temperature (Tg) and higher damping efficiency (tan delta), while maintaining critical process parameters such as reparability and indirect material compatibility performance.