Interactions between basecoats and clearcoats in car refinish systems

The introduction of VOC compliant waterborne basecoats and solventborne basecoats on one hand and the introduction of VOC compliant clearcoats on the other hand forces to look to the interactions between the two systems. As well known from studies in the automotive OEM area small molecules like HALS and UV-absorbers additives diffuse from the clearcoat into the basecoat. This influences the durability performance of the system.The main question addressed in this paper is the interaction of the binder system of the basecoat and clearcoat. In general crosslinkers (e.g. poly-urethane coatings) are rather low molecular weight materials which may diffuse between layers as well. Also the lower molecular weight functional resins of the binder may move throughout the system.The interactions of basecoat/clearcoat combinations were investigated by means of chemical and physical techniques. The effect of a medium solid clearcoat, a VOC compliant p-urethane clearcoat and UV-clearcoat on interpenetration, physical and paint properties were studied.Also some attention is paid to the diffusion of HALS and UV-absorbers from the clearcoat into the basecoat.