Surface and interface analysis of complex polymeric paint formulations

Abstract

Complex model formulations of coil coatings have been investigated by X-ray photoelectron spectroscopy (XPS), angle resolved X-ray photoelectron spectroscopy (ARXPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). High-resolution monochromated XPS C 1s spectra have been peak fitted and can account for all the carbon functionalities of the components included in these complex paint formulations. The addition of small quantities of additives such as flow agents is shown to induce significant changes in the surface composition of these coatings, and ARXPS reveals the additive outer layer to be 1-2 nm thick. Furthermore, in our investigation of a poly(vinylidene difluoride) (PVdF)-based topcoat, analysis of the high binding energy background of the XPS F 1s peak indicates that the PVdF component of the topcoat formulation is to be found below a surface segregated flow agent layer. Use of a silicone-based flow agent in a polyurethane (PU)-based primer formulation is shown to result in the migration of the flow agent into and through the PVdF topcoat. The silicone-based flow agent is ultimately observed at the PVdF topcoat's air-coating surface. XPS analysis of a PVdF topcoat-PU primer interface buried 20 μm below the topcoat's air-coating surface, exposed by ultra-low-angle microtomy (ULAM), suggests diffusion of fluorine-bearing materials from the topcoat into the top few nanometres of the underlying PU primer. Imaging ToF-SIMS analysis of a PVdF-PU interface exposed by ULAM reveals that a substantial fraction of an acrylic co-polymer included in the topcoat formulation segregates to the topcoat-primer interface where it enhances the adhesive properties exhibited by the PVdF topcoat towards the PU primer. Copyright © 2006 John Wiley & Sons, Ltd.