Dominant Mechanisms for Forming Surface Profile of Automotive Topcoats

Abstract

The surface profile of automotive topcoats, which affects the appearance such as orange peel and gloss, is determined by two mechanisms.

The surface irregularity with wavelength of about 1-5 mm is formed on the paint film during spraying, since the volume of paint droplets deposited on the substrate is not uniform along the substrate surface. Though the irregularity is reduced during drying and baking, it does not disappear, resulting in the unevenness like orange peel.

The irregularities of substrate surface, interface between wet film layers by wet-on-wet processing, and pigment distribution in the films are transcribed on the surface of top layer (clearcoat in many cases), resulting in the unevennesses with various wavelengths, after the top layer cannot flow along the substrate surface. It is because the irregularities make the shrinkage of the film thickness ununiform along the substrate surface.