Heat-curable pulverulent coating agent consisting of a mixture of copolymers containing glycidyl groups, dicarboxylic acid anhydrides and curing anhydrides

Abstract

The invention relates to heat-curable pulverulent coating agents, frequently also called powder lacquers, which are suitable for applying a coherent coating which possesses excellent properties after heat-curing.

What is claimed is: 
     
       1. Pulverulent coating agent of a mixture of A. a copolymer of relatively low molecular weight, which contains glycidyl groups and is a copolymer of several ethylenically unsaturated compounds,   B. at least one dicarboxylic acid anhydride in an amount corresponding to 0.4-1.0 anhydride groups per epoxy group (glycidyl group) of the copolymer and   C. a curing accelerator in the form of an organic base,   D. a flow control agent in an amount of at least 0.05 per cent by weight of the mixture, which agent is a polymer of molecular weight (M n ) of at least 1,000 and has a glass transition temperature which is at least 50° C lower than the glass transition temperature of the copolymer (A), characterised in that the component (A) consists of 84 to 94 per cent by weight of copolymers containing epoxide groups and hydroxyl groups, which copolymers have Duran softening points of about 90°-120° C and are soluble in organic solvents and consist essentially of:   a. 6-24 per cent by weight of ethylenically unsaturated epoxide monomers with 6-12 carbon atoms, of the general formula ##EQU1## wherein   R.sub.1 and R.sub.2 = H-- or --CH.sub.3 ##SPC3##       b. 4-20 per cent by weight of hydroxyalkyl esters of acrylic acid or methacrylic acid, with the hydroxyalkyl ester group being saturated and containing 2-4 C atoms,   c. 25-50 per cent by weight of methyl methacrylate and   d. 25-45 per cent by weight of other acrylic acid esters or methacrylic acid esters of aliphatic saturated monoalcohols with 1 to 8 carbon atoms, the component (B) consisting of 6-16 per cent by weight of at least one dicarboxylic acid anhydride with melting points of about 60°-140° C, the component (C) .[.consisting of 0.15-1.8 per cent by weight of N',N'-bis-.]. .Iadd.consisting of 0.5-1.8 per cent by weight of N',N'-bis-.Iaddend.(dimethylaminoisobutylidene)-melamine and the optional component (D) consisting of a flow control agent and other customary additives.     
     
     
       2. Pulverulent coating agent according to claim 1, characterised in that the component (A) consists of a copolymer formed of: a. 12 to 16 per cent by weight of glycidyl methacrylate,   b. 14 to 18 per cent by weight of hydroxyethyl methacrylate,   c. 34 to 44 per cent by weight of methyl methacrylate and   d. 25 to 35 per cent by weight of ethyl acrylate.   
     
     
       3. Pulverulent coating agent according to claim 1, characterised in that component (A) consists of a copolymer formed of a. 12 to 16 per cent by weight of glycidyl methacrylate,   b. 14 to 18 per cent by weight of hydroxyethyl methacrylate,   c. 34 to 44 per cent by weight of methyl methacrylate and   d. 30 to 40 per cent by weight of butyl methacrylate.   
     
     
       4. A pulverulent coating agent according to claim 1 wherein the copolymer component (A) contains as ethylenically unsaturated epoxide monomer (a) a compound selected from the group consisting of glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methallyl glycidyl ether, glycidyl crotonate, vinyl glycidyl ether, allyl glycidyl maleate, allyl glycidyl phthalate and butadiene monoxide. 
     
     
       5. A pulverulent coating agent mixture according to claim 1 wherein the copolymer component (A) contains as hydroxy alkyl ester component (b) a compound selected from the group consisting of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxybutyl acrylate. 
     
     
       6. A pulverulent coating agent according to claim 1 wherein the copolymer component (A) contains as component (d) a C 1  to C 8  -aliphatically saturated monoalcohol ester of acrylic or methacrylic acid selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2 ethylhexylmethacrylate, isobutyl acrylate and butyl methacrylate.