Coatings with organic polymeric fillers for molded SMC articles
AssigneeGM Global Technology Operations LLC
InventorHamid G. Kia
Life of this patent
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Abstract
Filler particles of a moisture-permeable, organic polymeric material are used in a polymeric coating composition, and this composition can be applied to a surface of a molded, fiber-reinforced polymeric material, such as sheet molding compound (SMC), to enable the electrostatic application of a layer of a powder primer to the same surface overlying the polymeric coating. And, when the molded SMC is heated to cure the powder primer layer, the out-gassing of moisture from the heated SMC does not result in defects on the surface of the molded SMC.
Claims18
A method of coating a moisture-absorbing, molded sheet molding compound (SMC) article to produce at least two coating layers on a surface of the SMC article so that the coating layers are substantially free of visual defects, the method comprising the following steps in the sequence set forth:
- applying a thin film of a polymeric coating composition to the surface of the SMC article to enable the subsequent electrostatic application of a layer of a powder primer, the polymeric coating composition comprising moisture-permeable, organic polymeric filler particles and electrically conductive particles dispersed within a polymeric binder resin precursor material;
- the filler particles having an average particle size of less than one micron, a melting point above a baking temperature of the polymeric coating composition and the powder primer, and being present in a sufficient amount to provide a cured polymeric coating with a coefficient of linear thermal expansion compatible with that of the SMC article,
- heating the SMC article to cure the polymeric coating composition and form a solid adherent polymeric coating on the surface of the SMC article,
- electrostatically applying the layer of powder primer overlying the polymeric coating on the surface of the SMC article;
- and
- baking the SMC article to melt and cure the powder primer without melting the organic polymeric filler particles and form a smooth primer layer on the surface of the SMC article, the composition of the polymeric coating and the amount of organic polymeric filler particles therein being such that moisture driven from the baked SMC article diffuses through the polymeric coating and into the overlying primer layer without forming bubbles or voids in the primer layer.
A method of coating a moisture-absorbing, molded sheet molding compound (SMC) article comprising:
- applying a thin film of a polymeric coating composition to a surface of the SMC article by spray application, the polymeric coating composition comprising moisture-permeable, organic polymeric filler particles and electrically conductive particles dispersed within a binder resin precursor material,
- heating the SMC article to polymerize the binder resin precursor material and form a polymeric binder resin without melting the organic polymeric filler particles and form a solid adherent polymeric coating on the surface of the SMC article,
- electrostatically applying a layer of a powder primer overlying the polymeric coating on the surface of the SMC article;
- and, thereafter
- baking the SMC article to form a smooth solid primer layer on the surface of the SMC article.
Dependencies are inferred from the claim text.