A new approach to characterize scratch and mar resistance of automotive coatings

Mar damage is a major customer concern of the automotive coatings industry. Our study of mar performance can be separated into two distinct areas, a d etailed understanding of the damage formation mechanism, and an investigati on of the relationship between the damage morphology and appearance. We hav e developed a nanoscratch technique that can measure important physical qua ntities, such as penetration depth, normal force and tangential force durin g the formation of the scratch. Mar resistance of three coatings was evalua ted and compared based on the damage mechanisms: plastic flow and fracture. The different deformation mechanisms result in different damage morphologi es and a corresponding change in visual impact of the scratch. Statistical surveys of appearance of well-defined scratches indicate that in very short observation times, scratches where fracture has occurred are much more vis ible than those made by plastic deformation alone. However, with sufficient time and strong illumination a significant percentage of observers could s ee plastic deformation as well. (C) 2000 Elsevier Science S.A. All rights r eserved.