Fundamentals and characterizations of scratch resistance on automotive clearcoats
Li Piin Sung, Linqian Feng, Nadia Benhamida, Pierre Morel, Andrew T. Detwiler, Jon M. Skelly, Leslie T. Baker, Deepanjan Bhattacharya
As original equipment manufacturers (OEMs) strive to deliver improved coating performance with a sustainable footprint, opportunities for innovation are emerging, particularly on improving mechanical properties, appearance, and solids content. Resistance to scratch and mar damage is one of the key performance attributes that has been emphasized by both OEMs and consumers to maintain a vehicles appearance and corrosion resistance over its service lifetime. Fundamental methodologies including instrumented scratch measurements at multiple size scales are used in this work as part of a product development strategy to better understand the scratch and mar behavior of automotive topcoats. This study compares physical properties of several melamine and isocyanate cured clearcoats over the appropriate basecoats. Micro and nano scratch techniques were employed in combination with industry standard methods: Amtec-Kistler car-wash and crockmeter, to identify performance differences under different scratch conditions. Mechanical and viscoelastic properties of the coatings were studied using tensile tests and dynamic mechanical thermal analysis (DMTA) to better understand the failure mechanisms associated with plastic deformation and fracture at different scratch scales. The information gathered from the above testing protocols is used to analyze coatings performance in terms of the contact strain, transitions between elastic plastic behavior, coefficient of friction and stress localization.