An In-mold Application of Adhesion Promoters to Polyolefin Substrates


Several different treatments of polyolefinic plastics are used to improve adhesion to their low energy surfaces. One conventional method is that of tie-coating, e. g., chlorinated polyolefins applied to the polyolefinic parts as a solution or dispersion and dried as a thin, well-adhered film. Another potential process would involve application of similar coatings at the time of part fabrication, e.g., during a molding process, utilizing the process heat instead of solvents to provide a reduced viscosity and adhesion to the polymer surface. Several commercial chlorinated polyolefins (CPOs) were applied as films using the transfer from a dry mold surface or by a conventional (control) wet film application of the adhesion promoter onto the surfaces of polypropylene (PP) and a commercial thermoplastic polyolefin (TPO). Injection molding conditions were optimized for the neat polymers in a standard ASTM dogbone mold profile. Adhesion of a polyurethane acrylic coating to the molded parts was then tested by a cloth peel method. Results showed that in-mold process coatings' adhesion was significant but less than that obtained for conventionally applied films. the magnitudes of adhesion were dependent on the composition of the CPO used, as well as of the substrate. a single treatment of CPO to the mold surface was shown to transfer coating to the injection molded polymer surface during each of several consecutive injection mold cycles, although film thickness and adhesion to the applied CPO film gradually decreased over the successive injection cycles. a correlation between adhesion values and the amount of chlorine transferred as a CPO coating during the molding process was observed.



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© 2007 CRC Press, All rights reserved.

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01 Jan 2007