A review and comparative study of release coatings for optimised abhesion in resin transfer moulding applications

Abstract

In this study, a number of abhesion-promoting coatings were considered in terms of their physicochemical and release properties. The techniques used to further this study include; field emission gun scanning electron microscopy, atomic force microscopy (AFM), profilometry, X-ray photoelectron spectroscopy, Auger electron spectroscopy, static secondary ion mass spectrometry, Fourier transform infra-red analysis and contact angle analysis for coating physical and chemical characterisation along with pulsed force mode atomic force microscopy (PF-AFM) and other adhesion and mechanical tests to determine surface release properties. These coatings were applied to metal substrates and were based upon silicone, fluoropolymer or metal–PTFE composite chemistry, all being potentially useful as release films for resin transfer moulding applications. The semi-permanent Frekote B15/710 NC mould release coating system, which is based on PDMS, proved extremely effective in terms of release against a cured epoxide applied under pressure. Although fluoroalkylsilane coatings offer a number of technological advantages for release applications, they generally produce very thin coatings which conform to any existing surface topography and adhesion through mechanical interlocking. The commercial PTFE-based coatings were found to provide poor release properties due to the presence of surface microcracks which allowed epoxide penetration when cured under elevated pressure and temperature. Electroless Ni/PTFE composite coatings comprise a hard nickel–phosphorus matrix containing a very fine dispersion of PTFE particles. The matrix proved sufficiently robust for industrial applications and the low friction and surface energy provided by the embedded PTFE combined with macroscopic-scale surface roughness provided efficient mould release.