Coating of untreated polypropylene with halogen free aqueous materials

Abstract Substrates made out of polypropylene (PP) or it’s blends with ethylene-propylene rubbers (PP-EPR) which are typically used for exterior automotive parts are either pretreated before they are coated or the primary coating layer consists of or at least comprises a chlorinated polyolefin (CPO) as an adhesion promoter — most often applied as an organic solution. The presentation describes the approaches for the development of a halogen free aqueous adhesion promoter. While chemical bonding via catalytic oxidation of the unactivated CH bonds as well as via insertion of a nitrene into the CH bonds proved to be ineffective, excellent adhesive strengths similar to those known from the state-of-art could be obtained via physical interactions with polyacrylic grafted polyolefins which have been applied as aqueous dispersions. The correlation of adhesive strengths with process parameters and analytical results obtained from model systems leads to the assumption that the adhesion is effected by amphiphilic polymers interacting with the outermost polypropylene at the surface rather than by penetrating deeply into the substrate.