Properties of Chlorinated and Non-Chlorinated Polyolefin Adhesion Promoters and Blends for TPO Substrates
Non-chlorinated polyolefin (N-CPO) adhesion promoters have been developed to promote adhesion of coatings applied to PP and TPO substrates, but studies are limited on their use and mechanism for promoting adhesion. The performance properties of a solventborne, non-chlorinated adhesion promoter applied under both melamine-cured and two-part urethane coatings are described in a study conducted by Templeton et.al.5 Results from this study showed that a non-chlorinated adhesion promoter provided excellent adhesion and gasoline resistance performance under two-part urethane coatings, but showed poor humidity resistance properties under the melamine-cured coating system. The use of low-viscosity functionalized olefinic polymers in color coats has also been examined.10 Results from this study suggest that low-viscosity functionalized olefinic polymers can be formulated into basecoats that can be directly applied to TPOs with good adhesion and performance properties. Waterborne, non-chlorinated adhesion promoters for PP and TPO substrates have also been reported.11 These materials provide good adhesion of coatings to both PP and TPO. Similar materials were also investigated by Jackson et al., although these materials were utilized in thermoset adhesion promoter systems.12 Polyacrylic-grafted polyolefin dispersions have also been investigated by Hintze-Bruning and Borgholte.13 These materials provided good adhesion of a commercial basecoat/two-part urethane clearcoat system applied over TPO. In this study, adhesion was found to be highly dependant on the nature of the grafted polyolefin and the type of substrate coated.
CPOs provide excellent adhesion to a wide variety of coating types applied over both PP and TPO substrates. These materials have been tested and used in commercial adhesion-promoter systems for several years. With recent advancements in N-CPOs that provide good adhesion and superior resistance properties, one becomes interested in developing a better understanding of how N-CPOs promote adhesion to PP and TPO. Of particular interest is the performance properties of blends of CPOs with N-CPOs, since each of these materials have certain superior performance properties. In this study, the adhesion and gasoline resistance performance properties of CPOs, N-CPOs, and various blends of a CPO/N-CPO are investigated using standard automotive test methods and other analytical techniques. Adhesion properties were quantified by measuring 90o and 180o peel strength of adhesion promoters through the use of a universal tensile testing machine. Surface characteristics of the adhesion promoters applied over a TPO substrate were examined, as a function of curing temperature, using AFM (atomic force microscopy).