Use and interpretation of scratch tests on ductile polymer coatings

The use and interpretation of contact scratch tests on polymer coatings has been investigated. The influences from test parameters such as scratch speed, contact geometry and load on the deformation response were examined. Two ductile polymer coatings of commercial grade tailored for pre-painted steel applications were used as model systems. The residual deformation pattern was examined with optical microscopy, white-light interferometry, and atomic force microscopy. Free-standing coating films were also subjected to static, transient and dynamic tensile testing to find a correlation between the intrinsic coating properties and the scratch behavior. The results indicate that the use of a single set of contact parameters is insufficient to reflect the overall response of a coating material to real contact conditions. A well-designed scratch test will however give a substantial amount of useful information.