Patent GB-807914-A (GB)
Title: Improvements in or relating to coatings on metal
IPC: B32B15/08
Filed: 1955-12-30
Abstract: A metal article is provided with a coating consisting of a layer of primer in contact with the article, a layer of undercoat comprising a phosphated copolymer of methyl methacrylate and glycidyl methacrylate, and a top coat layer of a methyl methacrylate lacquer. The primer layer may consist of coats of two or more different primers.  The weight ratio of the methyl methacrylate to the glycidyl methacrylate in the copolymer may be between 85 : 15 and 99 : 1 preferably 95 : 5, and the copolymer may be phosphated by reacting it with orthophosphoric acid or other acid of phosphorus such as metaor pyro-phosphoric acid, or a partial ester of an acid of phosphorus, such as methyl or butyl acid phosphate, in a ratio of 0.8 to 2.5, preferably substantially 1, mol. per mol. of the glycidyl methacrylate.  The undercoat may also contain a homopolymer of methyl methacrylate, plasticizers, solvents and diluents, pigments, and organophilic cation-modified clay, such as bentonite or montmorillonite, wherein the cation is an ammonium, phosphonium, oxonium, sulphonium, arsonium, stibonium or telluronium group having at least one alkyl substituent containing at least 10 carbon atoms in a straight chain, e.g. dimethyl dioctadecyl ammonium bentonite. The top-coat lacquer may comprise a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate with a minor proportion of e.g. acrylic acid, methacrylic acid, the C1 to C4 alkyl esters of acrylic acid, the C2 to C4 alkyl esters of methacrylic acid, vinyl acetate acrylonitrile or styrene; pigments, plasticizers, inhibitors for preventing pigment floating or settling, viscosity change, sagging, &c., dispersing agents and flow-control agents may be included. Examples describe the preparation of the phosphated copolymer and of the undercoat compositions.  Tests are described on metal panels, some of them treated with a rust-proofing composition, which were coated with conventional primers having as film-forming constituents (A) linseed oil modified glycerol phthalate alkyl resin and linseed oil modified phenol-formaldehyde resin varnish; (B) soya oil modified glycerol phthalate alkyd resin, linseed and chinawood oil modified glycerol phthalate alkyd resin, linseed oil modified phenol-formaldehyde resin varnish and butylated urea-formaldehyde resin; (c) soya oil modified glycerol phthalate alkyd resins and butylated urea-formaldehyde resin; (D) soya oil modified glycerol phthalate alkyd resins; and (E) linseed oil modified ester gum varnish and boiled linseed oil.  After baking, undercoats containing the phosphated copolymers were applied to half of each panel and dried, and a methyl methacrylate lacquer applied to both halves by spraying, the wet panels then being baked. Specifications 759,863, 763,158 and 807,895, [both in Group IV (a)], are referred to.ALSO:A metal article is coated with a layer of primer, an undercoat comprising a phosphated copolymer of methyl methacrylate and glycidyl methacrylate, and a top coat layer of a methyl methacrylate lacquer. The weight ratio of the methyl methacrylate to the glycidyl methacrylate in the copolymer may be between 85:15 and 99:1, preferably 95:5; the copolymer may be phosphated by reacting it, preferably in a solution containing a ketone, e.g. acetone, methyl ethyl ketone or methyl isobutylketone with orthophosphoric acid or other acid of phosphorus, such as meta- or pyrophosphoric acid, or a partial ester of an acid of phosphorus, such as methyl or butyl acid phosphate, in a ratio of 0.8 to 2.5, preferably substantially 1, mol. per mol. of the glycidyl methacrylate.  The undercoat composition may also contain a homopolymer of methyl methacrylate, plasticizers, e.g. benzyl butyl phthalate, dibutyl phthalate, triphenyl phosphate, 2-ethylhexyl benzyl phthalate, dicyclohexyl phthalate, diallyl phthalate, dibenzyl phthalate, butyl cyclohexyl phthalate, mixed benzoic acid and fatty oil acid esters of pentaerythritol, poly (propylene adipate) dibenzoate, diethylene glycol dibenzoate, tetrabutylthiodisuccinate, butyl phthalyl butyl glycollate, acetyl tributyl citrate, dibenzyl sebacate, tricresyl phosphate, p-toluene N-ethyl sulphonamide, the di-2-ethylhexyl ester of hexamethylene diphthalate and di(methylcyclohexyl) phthalate; solvents and diluents, e.g. ethyl acetate, butyl acetate or ethylene glycol monoethyl ether acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl or isopropyl alcohol, ethylene glycol monobutyl ether, toluene, xylene and naphtha; pigments, e.g. titanium dioxide, iron oxide, zinc chromate, carbon black, phthalocyanine blue or green, barytes, whiting, talc, china clay; and an organophilic cation-modified clay, such as bentonite or monotmorillonite, wherein the cationic group in an ammonium, phosphonium, oxonium, sulphonium, arsonium, stibonium or telluronium group having at least one alkyl substituent containing at least 10 carbon atoms in a straight chain, e.g. dimethyl dioctadecyl ammonium bentonite.  Specifications 759,863, 763,158 and 807,895 are referred to.