Scratch Resistance of Automotive Plastic Coatings

The scratch resistance of automotive plastic coatings has been studied extensively over the past few years. Most testing methodology to correlate damage of the coating to field conditions has been in the form of small particulate wearing, e.g., alumina oxide abrasive, or indentation resistance of the coating to an external probe, e.g., a nanoindentation device. The subsequent damage imparted to the coating has generally been analyzed by the amount of coating mass lost in the wear event or through a ratio of optical reflectance of the damaged area to the undamaged surface. In this paper, we attempt to delineate surface damage resistance of several automotive clearcoats through an optical interferometry methodology developed to measure volume and depth of damage incurred with small particle alumina oxide erodents in a simulated wear environment. The effect of coating attributes such as film thickness, pigment to volume ratio, and chemical structure variation in the coating formulation are related to damage imparted with the erodent. These damage criteria are then cross-correlated with other scratch damage estimators, e.g., method of essential work and gloss retention after damage.