Powder coating compositions for forming multi layer coatings

Claim 1

A multi-layer forming powder coating composition comprising: (1) at least one of finely divided thermosetting addition copolymers having a glass transition of 35° to 75° C. and comprising as comonomers a wt. % of a hardness imparting monomer which, when singly polymerized, will have a glass transition temperature of higher than 80° C. and b wt. % of a softness imparting monomer which, when singly polymerized, will have a glass transition temperature of up to 10° C. based on the copolymer wherein a+b≦60, b≦a and b≦20, said hardness imparting monomer being at least one species selected from the group consisting of styrene, methyl methacrylate, acrylonitrile, methacrylic acid, acrylic acid, indene, isobornyl acrylate, 2-chlorostyrene, 2-methylstyrene, t-butyl vinyl ether, vinyl chloride and acrylamide, and said softness monomer being at least one species selected from the group consisting of 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, 2-ethylhexyl methacrylate, isobutyl acrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, lauryl methacrylate, t-butyl acrylate, p-nonylstyrene, n-butyl vinyl ether, vinyl fluoride and isopropyl acrylate, and (2) at least one of finely divided thermosetting resinous materials selected from the group consisting of epoxy resin, acrylic resin and polyester having incompatibility or low compatibility with the copolymer and a substantially greater surface tension than the copolymer when melted at the same temperature and substantially differing from the copolymer in composite parameter ht, the ratio of the composite parameter of said resinous material to said copolymer being at least 1.3, wherein the affinity parameter P between said copolymer and resinous material, calculated by the following equation ##EQU3## A and B: the weights (g) of the two resins in the solvent mixture, C: the weight (g) of the solvent in the mixture before the addition of the good or poor solvent, ΔD: the weight (g) of the good or poor solvent added, K: modification factor which is 1 when P is negative, or 100/45 when P is positive, is positive, zero or negative number of less than 0.1, the composite parameter ht is calculated by the following equation ht=Ht×ρ HT: the height (cm) of creeping of the resin in a molten state, ρ: density (g/cm 3 ) of the molten resin, and the proportion of each finely divided resinous material is at least 10 wt. % based on the composition.