Quantification of Coating Adhesion Using Laser Induced Decohesion Spectroscopy

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 measure G between an automotive clearcoat and four opaque basecoats of various pigmentations (black, white, red, metallic green) as a function of clearcoat thickness. We find that G depends on pigmentation due to the various pigment volume concentrations (PVC's) and specific pigment-binder interactions. Also, G depends on the clearcoat thickness when the thickness is comparable with the size of the plastic zone, R_p.