Analysis of scratch characteristics of automotive clearcoats containing silane modified blocked isocyanates via carwash and nano-scratch tests

The aim of this study was to investigate the scratch characteristics of automotive clearcoats based on an acrylic polyol resin, with butylated melamine and silane modified blocked isocyanates, using car-wash and nano-scratch tests.To scrutinize the effect of silane modified blocked isocyanate on the chemical and mechanical properties of clearcoats, with respect to changes in the crosslinking networks inside the clearcoats due to the curing reaction, dynamic mechanical analysis (DMA) and FT-IR analysis were performed. The scratch behaviors were analyzed via Amtec-Kistler car-wash and nano-scratch tests, accompanied with scratch images simultaneously visualized using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The basic properties of various automotive clearcoats such as impact resistance, pencil hardness, solvent resistance, and stone-chip resistance, were also compared. The results showed that a close correlation existed between the scratch resistance data obtained from the car-wash and nano-scratch tests for clearcoats made from acrylic polyol resin, with melamine and silane modified blocked isocyanates. Also, all the mechanical properties, including scratch resistance, noticeably improved due to the increased crosslinking networks via the formation of urethane bonds, when the portion of silane modified blocked isocyanates was increased. This was verified from the surface profiles and images of the scratched clearcoats captured using AFM and SEM.