Chemistry of surface modification with UV/ozone for improved intercoat adhesion in multilayered coating systems

Surface modification using UV/ozone was explored as an approach towards ens uring robust intercoat adhesion in multilayered automotive coating systems, This study was directed toward reducing the variability in adhesion perfor mance 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 comm ercially available epoxy layer, which is known to become surface-enriched b y a polyether-based crater-control additive (CCA) in its formulation. X-ray photoelectron spectroscopy established that UV/ozone treatment oxidizes th e epoxy CCA overlayer and forms carboxyl species. Contact angle measurement s identified a concomitant increase in surface wettability. Epoxy-to-polyes ter adhesion improved slightly after exposure to ozone alone and dramatical ly after exposure to UV/ozone, X-ray photoelectron spectroscopy of interfac ial epoxy surfaces, exposed by delamination of the polyester coating, discl osed that bond-line fracture occurs within a CCA-enriched region, with a tr end of decreasing CCA concentrations in proportion to the UV/ozone exposure time initially received by the epoxy, Copyright (C) 2000 John Wiley & Sons , Ltd.