Optimization of a 2K primer for polypropylene substrates with different flame conditions

Abstract

The demand for a higher plastic content in automobiles in order to increase gas mileage by decreasing vehicle weight creates a need to develop coatings that will adhere to these materials. Adhesion to thermoplastic olefin (TPO) substrates, like blends of polypropylene (PP), is often difficult to attain due to the low surface energy and the nonpolar nature of the surface. One always specifies, therefore, that the surface of the substrate must be pretreated. Pretreatment methods can vary, from oxidation of the surface, e.g., plasma or flame, to diffusion and mechanical interlocking of an applied polymer to the surface. Mechanical interlocking to the nonpolar TPO surface can be achieved through the use of an adhesion promoter, namely a chlorinated polyolefin (CPO). The type of CPO used, in addition to the types of solvents and flame treatments used, can substantially influence the degree of adhesion/cohesion obtained within the CPO/TPO system. PP is a TPO that is used in automobile construction. In this report it is described a set of experiments that provide quantitative information about how CPOs optimize the adhesion of a commercial primer coating to PP. The study was performed according to eight CPOs and two different ways of flame treatment. The CPOs were prepared by mixing them with a standard primer in order to investigate what type of CPO optimized better the adhesion of the primer to a PP substrate. On the other hand, the experiments were started with non ideal parameters for the flame treatment and were changed for the final experiment to work at its best. To study the paint adhesion a steam jet test was used. This consists of an assay based in high pressure cleaners. A hot water jet impacts into the paint system during a specific time and tests the paint adhesion to the substrate.