Coating Solvent Effects Producing Adhesion to Molded Plastic Parts


While adhesion is of paramount importance to ensure durability and quality of a coating system, solvents have long been known to affect coating adhesion to molded plastics, including polyolefins. Varions research group in their characterizations of interfaces and/or adhesion to plastics, have produced much understanding of the role played by solvents in adhesion to plastics. However, the 'goodness' of a coating solvent for the plastic, defined as a small Flory interaction parameter chi12, was not indicative of the quality of the coating adhesion to the molded plastic substrates under consideration. For instance, coating adhesion to either polypropylene or ethylene-styrene interpolymer substrates, as affected by the coating solvent, was poorly related to the solvent-polymer miscibility, the magnitude of solubility parameter mismatch, or the ability of the solvent to swell the polymer bulk, except where such swelling produced a topographical change to the polymer surface. Though the topographical change was different for polypropylene compared to the interpolymer surface, if a coating solvent induced little or no change in the topography of a molded plastic then little or no coating adhesion to the plastic was observed. Polymer surface crystallinity reduced the amount of topographical change caused by a solvent and, likewise, reduced adhesion of a coating containing the solvent. the alteration of topographical features by solvent provides an adhesion mechanism and an explanation for the reported formation of diffuse interfaces and how a coating solvent could expose sub-surface domains within a polymer substrate.



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