Quantitative method for evaluating fingernail induced mar damage of coatings

Abstract

A traditional method of coating qualification, known as fingernail mar resistance, historically has been practiced in industry where the back of a fingernail is “flicked” across a coating surface. Any resulting permanent mark from this qualitative analysis is deemed a failure. Lack of quantitative analysis and control over experimental parameters in this type of test limits its utility as an analytical test. Fundamental understanding of this specific type of mar damage is hindered, and research efforts to find unique solutions based on changes in polymer structure are frustrated by the binary response of the test. In an attempt to rectify the situation, a high speed mar tester was developed to mimic and quantify the effects of the fingernail flick test. The work described in this report demonstrates the applicability of this tester to produce similar damage to that of the fingernail test. In addition, a quantitative method enabling differentiation of the degree of mar damage of different coatings is described. Finally, the method is demonstrated by differentiating mar resistance of coatings that show similar qualitative results in fingernail flick testing.