Scratch tests to contribute designing performance maps of multilayer polymeric coatings

Abstract

The scratching technique has gained interest in recent times because of the numerous inherent properties implied (adherence, hardness, elasticity, visco-elasticity, cohesion, etc.) during tests. Some singular mechanical responses have been noticed (cyclical slips and unsticking, degradation modes, etc.) and valued on multilayers polymeric coatings. The results allow differentiating them and illustrating the mare resistance for part. Scratch test is identified as one of the most efficient to build coating performance maps. The main purpose of our work related to the characterization of multilayers polymeric coatings, is to determine a set of experiments in order to compare their mar resistance. Experiments are made by indentation (hardness, creep, stress relaxation), scratch test (determination of the critical load), glossy reflection and wear. In this paper we describe the scratch experiments used to compare the mar resistance of the coatings. The parameters recorded are used to build a performance map relative to a specimen and this performance map is used to compare all characteristics of different multilayers coatings. Two organic systems are taken as samples to illustrate it. They are composed of three layers with a common steel sheet substrate and a common PET topcoat. The intermediary layer is soft and thick for the first product while it is hard and thin for the second one. The scratch results combined with other test results in performances maps underline the role of an intermediary layer in order finally to better design multilayer polymeric coatings.