New Automated Evaluation Technique for Scratch and Mar Resistance in Automotive Clear Top Coatings: Optical Imaging Technique

The scratch and mar resistance of automotive clear topcoats is of great concern to automotive manufacturers, coatings suppliers and ultimately the end-use consumers. The clear topcoat serves as a functional, protective layer, as well as a layer that provides visual appeal through luster and gloss. Scratches and marring, whether induced by washing, polishing or common abrasion, affect visual texture and reflectivity of the clear coating layer. Conventional techniques for measuring scratch and mar resistance depend on human visual evaluation and/or photometric measurements. Human visual evaluation lacks the objectivity required for a routine evaluation, and photometric measurement, such as for gloss, does not characterize or quantify the change in texture resulting from common scratch and mar damage. The small field of view inherent to photometric measurement devices is not adequate for translating the overall appearance change apparent to the naked eye. Additionally, gloss measurements are inaccurate when applied to textured surfaces or those exhibiting orange peel. Optical imaging and grayscale analysis techniques may be used to overcome these limitations by eliminating the deleterious influences of human subjectivity and by capturing texture changes in two-dimensional data format. Regardless of the original surface texture or structure underlying the scratch or mar damage, optical imaging techniques can reliably measure and quantify scratch and mar characteristics and provide absolute parameters for use as evaluation criteria. This paper describes the deficiencies of conventional evaluation techniques and presents a new, more advanced methodology that exploits the advantages of optical imaging technology.