Characterization of Mar – Scratch Resistance of Polymeric Coatings – Part ll

By Weidian Shen

This two-part article (Part I was published on pages 54-60 in the March 2006 issue of JCT COATINGSTECH) briefly reviews the development of mar/scratch characterization techniques, and focuses on single-probe tests with nano instruments which have been widely used recently. Quantitative measurements of micro mar resistance (MMR), different responses of the coatings to the marring stress (i.e., elastic response, plastic deformation, and abrasive wear), and critical forces for rough trough, cracking, delamination, and chipping are described, as are some complementary test methods.

Statistical investigation of damage on samples used in real environments, combined with laboratory mar/scratch tests on these samples, could determine the force distribution curve in the lab which is approximately equivalent to the field conditions. The curve is useful for development of new coatings, and it can predict the weights of different damage modes that are likely to occur at the surface of the coatings in the field.

The weights, combined with the quantification of the damage levels of different modes, allow calculation of a quantitative index to characterize the mar/scratch resistance of a coating in a specific environment comprehensively. To better understand the mar/scratch resistance behavior of tested materials,  a detailed stress-strain study is needed, utilizing theoretical analysis and finite element modeling to complement the experimental measurements described here as an integrated approach.

Measurements of micro mar resistance, the different responses to marring stress-elastic recovery, plastic deformation and abrasive wear, and critical forces for rough trough, cracking, delamination, and chipping-described in Part I of this article (JCT COATINGSTECH, March 2006) are commonly used in characterization of mar/scratch resistance of coatings. However, selecting a characterization technique must be based on the properties of the tested materials as well as their application conditions. Some complementary test methods are described in Part II.