The effect of basecoat pigmentation on mechanical properties of an automotive basecoat/clearcoat system during weathering

The aim of this study is to elucidate the effect of basecoat pigmentation on mechanical aspects of an automotive basecoat/clearcoat (BC/CC) system during artificial weathering exposures. A silver basecoat as the most reflective and a black basecoat as the most absorptive basecoat were selected. These two extreme behaviored basecoats were chosen with hopes that other basecoats would behave somewhere between the silver and the black extremes. The structural and mechanical properties of the coatings were investigated after various weathering exposure times (0, 150, 300, 450, 600 h). Dynamic mechanical thermal analysis (DMTA) was carried out to study variations in structure and basic characteristics of the system such as cross-linking density and T_g during weathering. In order to investigate variations in mechanical properties of the system, nano indentation, nano scratch, and tensile tests were also utilized.It was found that although both silver and black systems experienced post-curing reactions (dominant at earlier stages of weathering) and degradation reactions (dominant at later stages of weathering), but basecoat pigmentation affected the post-curing and degradation reaction rates of the BC/CC system, leading to variations in mechanical properties. It was concluded that post-curing occurred to a greater extent in the black pigmented system whilst in the silver pigmented system weathering degradation was much more sever.