Scratch Resistance Behavior of Model Coating Systems

By Rose A. Ryntz, B.D. Abell, G.M. Pollano, L.H. Nguyen, W.C. Shen

Coatings are often subjected to physical deformations caused by car wash brushes, tree limbs, keys, fingernails, and the like, which may result in mechanical abrasion. The resistance of the coat-ing to scratches imposed by such mechanical abrasions has been studied through the utilization of laboratory tests such as nanoindentors, crockmeters, scanning probe microscopes, and taber abraders.

Little emphasis, however, has been placed on the influence of coating attributes on measured scratch resistance. In this study we attempt to relate the effect of coating glass transition temperature, crosslink density, and crosslink type in a series of formulated waterborne polyurethane dispersion clearcoats on resultant scratch resistance.

Methods utilized to impart the scratches, e.g., scanning probe microscopy, weighted fingernail, and crockmeter, as well as related coating physical properties measured, e.g., viscoelastic behavior, hardness, and tensile strength, are discussed.

The scratch resistance of model coating systems analyzed was found to be dependent upon the base resin Tg, which affected the surface hardness of the coating and the toughness of the crosslinked network, as measured by the method of essential work. Coatings that exhibited both hard surfaces and tough-elastic net-work integrity afforded the optimized scratch resistance behavior.