Effect of primer curing conditions on basecoat-primer adhesion - A LIDS study

摘要

We present a new technique, laser induced decohesion spectroscopy (LIDS), which is capable of measuring the practical work of adhesion G between a transparent polymer coating and an opaque coating or substrate. In LIDS, a laser pulse directed onto the sample creates a blister at the transparent/opaque interface. The blister's internal pressure depends on the laser pulse energy, and at a critical pressure the sample fractures, creating an annular debond similar to that obtained in the standard blister test. By measuring physical variables such as the curvature of the blister, and its radius and thickness, it is possible to deduce G. Here, we have investigated the effect of primer baking conditions on the fracture of automotive panels, with the goal of understanding the physical factors that affect resistance to stone chipping. Good adhesion can be achieved by not overbaking the primer. For melamine-formaldehyde systems, this implies that the self-condensation of mela-mine should be avoided. Current baking temperature of 140℃ is adequate. For good fracture resistance, the coating thicknesses should be substantially greater than the plastic zone sizes, which are measured here for the first time in such systems and are generally ～20-35 μm.