Surface modification using UV/ozone was explored as an approach towards ensuring robust intercoat adhesion in multilayered automotive coating systems. This study was directed toward reducing the variability in adhesion performance associated with changes in coating surface chemistry that can result from the surface migration of formulation additives. The evaluated coating system included a melamine-cross-linked polyester layer applied over a commercially available epoxy layer, which is known to become surface-enriched by a polyether-based crater-control additive (CCA) in its formulation. X-ray photoelectron spectroscopy established that UV/ozone treatment oxidizes the epoxy CCA overlayer and forms carboxyl species. Contact angle measurements identified a concomitant increase in surface wettability. Epoxy-to-polyester adhesion improved slightly after exposure to ozone alone and dramatically after exposure to UV/ozone. X-ray photoelectron spectroscopy of interfacial epoxy surfaces, exposed by delamination of the polyester coating, disclosed that bond-line fracture occurs within a CCA-enriched region, with a trend of decreasing CCA concentrations in proportion to the UV/ozone exposure time initially received by the epoxy.
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Haack et al. (2000) studied this question.
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