Studies on Scratch and Mar Resistance of Polyurethane Coatings

This paper investigates two critical properties, scratch and mar resistance and environmental etch resistance, of automotive clearcoats, the top layer of a “basecoat/ clearcoat” automobile finish. Polyurethane clearcoats based on two commercially available polyisocyanates and two developmental polyisocyanates were tested for scratch and mar resistance by two different methods: a car wash test and a dry abrasion test. In addition, outdoor acid etch resistance of the same clearcoat systems was tested by summer outdoor exposure in Vero Beach, Florida, and in Pittsburgh, Pennsylvania. Results of the scratch and mar testing and the environmental etch studies are evaluated and compared. Structure/property relationships associated with the different polyisocyanate crosslinkers are analyzed.