Powder coating with metallic and chromatic pigments and method for preparing the same

#The invention relates to a two-part powder coating system that produces a chromatic and metallic effect surface coating. More specifically, the invention relates to a two-part powder coating system in which a first part incorporates at least one chromatic pigment and at least one metallic effect pigment while the second part is substantially free of chromatic pigment.

#Powder coatings may be used as an alternative to solvent-based coatings. They are applied to various articles for protecting and/or decorating the article. Although applied in powder form, powder coatings generally undergo a process during which the powder form material is transformed into a substantially continuous polymer film. Typically, the polymer material in the powder coatings is a thermosetting polymer, and the transformation into a substantially continuous polymer film coincides with a cross-linking, or cure, of the thermosetting polymer.

#Powder coatings may be formed by intimately mixing ingredients in dry or molten form, by mixing in liquid suspension, or by methods involving solution polymerization. Application of the resultant powder form materials to a desired article is achieved by a variety of mechanisms, including electrostatic spray, or fluidized bed immersion. In an electrostatic spray process, particles of a powder coating composition are electrostatically charged, and the charged particles are attracted to the article that is grounded or oppositely charged. In a fluidized bed immersion process, powdered or particulate coating material is contained within a dipping tank. A flow of gas or liquid through the coating material fluidizes the material to form a fluidized bed. This allows easy passage of the article through the fluidized bed. Typically, a pre-heated article is put into the fluidized bed. As the powdered or particulate coating material contacts the heated article, the coating material adheres to at least one surface of the article where it forms a more or less continuous coating. It is known to prepare a powder coating composition in which a powdered or particulate thermosetting coating material is provided as part of a blend or mixture that further includes leafing or non-leafing metallic flake pigments. U.S. Pat. No. 6,166,123 describes reflective powder coating compositions and the method of preparing the same. The reflective powder coating compositions include a thermally softenable resin powder and highly reflective particles, such as non-leafing or leafing metallic flake, mica, and the like. The reflective powder coating compositions provide, after cure, shiny, reflective metallic coatings with high-gloss ranging from sparkling, to specular or mirror-like. The resultant coatings exhibit metallic coloration including e.g., silver or other metallic colors depending on the particular metallic pigment incorporated in the powder coating compositions.

#FIG. 1 is a mode of the process of the invention in flow chart form for making an article including dry blending of chromatic pigment according to one aspect of the invention.

#FIG. 2 is an alternative mode of the process of the invention in flow chart form for making an article including melt mixing of chromatic pigment according to another aspect of the invention.

#FIG. 3 is an alternative mode of the process of the invention in flow chart form for making an article including high shear blending of chromatic pigment according to another aspect of the invention.

#The two-part powder coating system of the invention includes a first part and a second part. The first part includes a first substantially uniform powder mixture and is substantially free of solvent including, e.g., organic solvent and water. The powder mixture includes at least one film-forming polymer, at least one chromatic pigment, and at least one metallic-effect pigment.

#The film-forming polymers include thermosetting polymers or resins used in powder coating compositions. Examples of useful thermosetting polymers or resins include, e.g., epoxy resins such as diglycidyl ethers of bisphenol A and epoxy cresol/novolacs; phenolic resins such as novolacs and resols; polyurethanes such as polyester resins with blocked isocyanate groups; saturated polyesters such as saturated terephthalic acid based polyesters and carboxylated polyesters; acrylics based on crosslinkable acrylate resins such as carboxyl terminated resins; polysilaxanes and other silicon resins; self-crosslink etherified methoxylated resins based on acrylamides and/or methacrylamides. Polyester resins such as those derived from isophthalic anhydride/glycol and trimellitic anhydride/glycol are also examples of useful materials as well as those disclosed in U.S. Pat. No. 6,166,123, which is hereby incorporated by reference in its entirety.

#Useful chromatic pigments include any chromatic pigments used in conventional powder coating compositions, such as organic and inorganic pigments. Preferably, chromatic pigments are organic pigments such as organo reds, phthalocyanine blues and greens, organic yellows and violets, and other organic dyes. Examples of useful organic chromatic pigments include, e.g., Diarylide Yellow (C.I. Pigment Yellow 14), Monoazo Orange (C.I Pigment Orange 67), Benzimidazole Derivative Yellow (C.I Pigment Yellow 151), Azo Yellows (C.I Pigment Yellow 194, 191 and 83), Pyrazolone Orange (C.I Pigment Orange 34), Metalized Organic Yellow (C.I Pigment Yellow 153), Quinacridone Violet (C.I Pigment Violet 19), Azo Red (C.I Pigment Red 187), Dis Azo Orange (C.I Pigment Orange 34, and Carbazole Violet (C.I Pigment Violet 23).