The Effect of Solvent on Adhesion of Coatings to Plastics
Options available to alter the appearance of a molded polymer material are either homogeneous blending of colorant into the polymer or coating of the polymer surface. Advantages of using coatings include reduced pigmentation costs, added surface protection, and optimal control of surface appearance. Molded polymer items such as toys, home appliances, furniture, and building materials also benefit from the improved manufacturing flexibility of a post-applied surface coating rather than an as-molded surface finish. Adhesion is of paramount importance to durability and quality of any coating system, and specific applications such as toys require 100% crosshatch adhesion retention. the trend toward waterborne coatings accentuates wetting and adhesion challenges as polymer surfaces are inherently hydrophobic. What is the role of solvent in adhesion to plastics? Information presented by Ryntz et al., Stoffer et al., Foster et al., Clemens et al., and Winnik et al. in the characterization of polymer interfaces or adhesion to plastics or both has led to some understanding of the role played by solvents in surface adhesion development and wetting. Our approach studied how adhesion-promoting solvents generated surface topology differently from the as-molded interface, compared to nonadhesion promoting solvents that resulted in swelling but little topographical change. These other solvents, considered “good” solvents for polymers, yielded smooth, unaltered, as-molded surface topography. Measured improvements in adhesion thus appeared to result from improved surface- area contact and altered fracture mechanics, and not necessarily improved polymer chain mobility such as through reptation mechanisms resulting in polymer entanglement.
T. P. Schuman, "The Effect of Solvent on Adhesion of Coatings to Plastics," University of Southern Mississippi, Jan 2004.
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