The Use of Blocked Isocyanates in Automotive OEM Clearcoats

Automotive OEM clearcoats have been developed and commercialized using blocked isocyanates which offer good etch resistance. The key technical problems are yellowing, sag resistance and the high cure temperatures needed when blocking agents such as oximes are used. Yellowing of coatings that contain blocked isocyanates was a major problem that limited their introduction in automotive clearcoats. Sag resistance and other physical properties have been improved by incorporating high imino functional melamines into the clearcoat formulation.