Characterizing the surface structure of plastics coatings

Excellent appearance of the coated exterior car parts is one of the aims at the applications of plastics for automotive painting. The painted plastics parts and the metal car body should have comparable surface structures not depending on the different substrate materials (steel or plastics) used. Against this background parameters influencing the surface of plastics parts are becoming recently more important. To characterize the overall appearance of a coating system mainly two different techniques are used in the automotive and paint industry. The mechanical profilometry yields a detailed information of the topography so that substrate influences and other effects on the final coating appearance can be described. In addition to mechanical methods several optical methods are existing to describe the surface structure. Especially the “wave-scan” (Byk-Gardner) should be named, which was developed to transfer the visual impression into detectable measuring data. The measuring principle is based on the modulation of the light of a small laser diode reflected by the surface structures of the sample. These methods (mechanical profilometry and wave-scan), in the past mainly used for coated steel substrates, are demonstrated showing typical examples with focus on plastics applications.