Nano mechanical properties of an automotive clear-coats containing nano silica particles with different surface chemistries

Different nano-silica particles were incorporated in an automotive OEM clear-coat based on acrylic-melamine chemistry. A neat and three silane-treated nano-silica particles were added to the clear-coat. Treated grades were coated by dimethyl dichloro silane, hexamethyl disilane and methacryl silane, respectively. The scratch/mar resistances of the heat-cured films were investigated using nano-indentation hardness measurements. It was found that there is a close relationship between the surface chemistry of silica nano-particles and nano mechanical behavior of the baked films. Adding the above-mentioned nano-silica particles to the clear coat resulted in higher elastic modulus and indentation hardness. The most significant effect was observed in samples containing silica particles coated with dimethyl dichloro silane and carrying acidic surface hydroxyl groups.