Hard polyurethane coatings on compliant polycarbonate: An application of the 3D deformation response model to scratch visibility

The present investigation deals with the design of a transparent protective coating and its application on flat substrates in polycarbonate. The experimental analyses looked into the formulation of the coating material, the best strategy to deposit it as well as the characterization of the coated substrates. Visual appearance and morphological features of the coatings were studied by combined scanning electron microscope and contact gauge surface profiler. Their scratch and wear endurance were assessed by progressive and constant load scratching procedure and dry sliding linear reciprocating tribological tests. Imaging analyses were also used to evaluate the deformation response of the coating material to scratch and wear. Analytical modeling was developed accordingly, thus allowing to establish a strict relation between the design criteria of the coatings, the overall (coating + substrate) material performance and the loading conditions. The experimental findings showed the organic coatings were able to significantly improve the micro-mechanical and tribological response of the bare polycarbonate, thus making it available for a large share of applications where high performant, scratch and wear resistant materials are an ineluctable pre-requisite.