Scratch resistance of automobile clearcoats : Chemistry and characterization on the micro- and nanoscale

The scratch resistance of polymeric clearcoats intended for automobile exterior surfaces was tested with scanning 3D nanoindentation and laboratory car wash simulation (AMTEC). It could be shown by using "real world" samples with comparable scratch resistance that the applied methods were suitable for discriminating even small differences in scratch resistance with high accuracy. In the area of physical characterization of scratch resistance, the results of this investigation demonstrate the ability of microscopic, single-contact testing methods to reproduce the macroscopically experienced results. By using a combination of different scratch methods, insight into the fundamentals, e.g., chemistry, that are responsible for good or bad scratch resistance, is achieved. One key for this goal is the imaging and analytical evaluation of the damage pattern after the indent, which leads to additional results and models presented in this article. It was found that an essential key to obtaining scratch resistant surfaces is a strengthening of rubber-like elasticity as well as minimizing interactions between individual polymeric chains.