Multilayer Coatings for Polycarbonate Glazing: Influence of Mechanical Properties on the Abrasion Performance of the Coating System

Coated polycarbonate (PC) is a leading engineering thermoplastic used in automotive glazing for replacing laminated glass. Mechanical properties of multi-layer coating systems were investigated using a nano-indenter and the fracture behavior of coating during nano-scratch was studied employing scanning electron and atomic force microscopy. A set of coated samples was prepared, with two layers, namely Layer-1 and Layer-2. Layer-1 was applied directly to the PC substrate and used as adhesion promoter. Layer-2 was prepared with different mechanical properties. Abrasion performance of the coated system was characterized using an ASTM abrasion test methodology. Regression analysis was performed to establish correlation between the mechanical properties of the coating system and its abrasion performance. Fracture behavior of the coating systems and their plausible relationship with abrasion performance was also discussed. From the above study, it was observed that the abrasion performance of a 2-layer coating system mostly depends on mechanical properties of the sufficiently thick Layer-2. For multilayer coating it was observed that the hardness, hardness over modulus and critical load to fracture are the dominant factors for optimum coating performance.