Measuring adhesion to poly(olefins): The role of adhesion promoter and substrate

Abstract

The use of thermoplastic poly(olefins) in the automotive industry continues to proliferate due to their decreased cost and weight and increased recyclability in comparison to thermoplastics such as poly(carbonate) alloys or poly(urethanes). An attribute that continues to hamper the widespread introduction of thermoplasticpoly(olefins), in particular thermoplastic olefin (TPO, a blend of impact copolymer and elastomer), into additional automotive components, however, is its poor surface wettability and adhesion. Adhesion promoter formulation, both in terms of resin composition and solvent variation, has been known to influence the adhesive propensity of topcoats when analyzed by typical tests such as peel strength. It has long been disputed, however, that peel strength is not a true measure of paint adhesion since it artificially introduces a film between the paint and the adhesion promoter to enable one to perform the test. In contrast, this paper discusses the use of a newly developed in-situ adhesion test, described as compressive shear delamination (CSD), to quantify the adhesive/cohesive propensity of coatings to a variety of TPO substrates. The effect of solvent type and chlorinated poly(olefin) (CPO) adhesion promoting resin on the adhesion/cohesion of topcoats to TPO is described. Chlorinated poly(olefin) type, followed by solvent variation, was shown to have the most significant impact on the adhesion/cohesion of topcoats. This newly described CSD protocol for determining the weak link in painted plastic may have a significant impact on the choice of topcoat, adhesion promoting primer formulation, and substrate in particular automotive applications.