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

The use of thermoplastic poly(olefins) in the automotive industry continues to proliferate due to their decreased,,cost and weight and increased recyc lability in comparison to thermoplastics such as poly(carbonate) alloys or poly(urethanes), An attribute that continues to hamper the widespread intro duction of thermoplastic poly(olefins), in particular thermoplastic olefin (TPO, a blend of impact copolymer and elastomer), into additional automotiv e components, however, is its poor surface wettability and adhesion. Adhesi on promoter formulation, both in terms of resin composition and solvent var iation, has been known to influence the adhesive propensity of topcoats whe n analyzed by typical tests such as peel strength. It has long been dispute d, however, that peel strength is not a true measure of paint adhesion sinc e it artificially introduces a film between the paint and the adhesion prom oter to enable one to perform the test. In contrast, this paper discusses t he 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 chl orinated poly(olefin) (CPO) adhesion promoting resin on the adhesion/cohesi on of topcoats to ` TPO is described. Chlorinated poly(olefin) type,followe d by solvent variation, was shown to have the most significant impact on th e adhesion/cohesion of topcoats. This newly described CSD protocol for dete rmining the weak link in painted plastic may have a significant impact on t he choice of topcoat, adhesion promoting primer formulation, and substrate in particular automotive applications.