Evaluation of durability of nano-silica containing clear coats for automotive applications

In automotive application, multilayer coating systems are typically used to guarantee protection from corrosion phenomena and aesthetic properties. A coating system's appearance and its durability is becoming increasingly important for automotive original equipment manufacturers. Clear coats are required to maintain long term aesthetic appearance, color and gloss stability to weathering and mechanical damage. One key property is scratch and mar resistance. The use of nano-fillers is a promising strategy to increase the abrasion resistance without affecting the optical clarity of high gloss coatings. In this work, the influence of nano-silica particles on properties of clear coats has been studied. Three different 2 component isocyanate/polyol clear coats were chosen: one without any fillers, and two with nano-silica particles disposed in the surface layer of the coating. One of these at a normal crosslinker level and one with enhanced crosslinking. The samples were exposed to artificial weathering. The stability of clear coats was evaluated by color and gloss measurements to evaluate aesthetic changes, by FTIR analysis to determine any degradation of the polymer bonds. Taber test and falling abrasive test have been used to simulate coating abrasion and erosion respectively. Gloss retention was measured for the different clear coats. Environmental scanning electron microscopy has been used to study the surface morphology after the damage. Artificial weathering (UV radiation, salt spray chamber, thermal treatment) and abrasion tests were combined to investigate the influence of weathering on mar resistance of the clear coatings. (C) 2011 Elsevier B.V. All rights reserved.