Resinous coating compositions

摘要

Metal surfaces are prime coated with a composition comprising a solvent having dissolved therein (I) a copolymer of acrylonitrile, an ethylenically unsaturated carboxylic acid and at least one other CH2 =C< group containing monomer, (II) a copolymer of a vinyl halide and a vinyl ester, e.g. a vinyl chloride/acetate copolymer, (III) an epoxide resin and, preferably, (IV) a urea-formaldehyde resin. Copolymers (I) specified are derived from acrylonitrile and methacrylic acid with one or more of methyl methacrylate, ethyl acrylate, 2-ethylhexyl acrylate, lauryl methacrylate and styrene. Other optional monomers are listed, and details are provided of suitable epoxide and urea-formaldehyde resins (see Group IV(a) ). The compositions may also contain pigments, e.g. iron oxide, carbon black, lithopone, magnesium silicate, chrome yellow, calcium, zinc and lead chromates, chromic phosphate, titanium dioxide, soapstone, talc and clays. In preferred modes of operation the composition is sprayed on a metal surface, e.g. a phosphated steel panel and is then either (i) air dried, coated with an alkyd resin-based filler composition, baked and then provided with a finishing p coating, or (ii) baked and then provided with a finishing coating, e.g. a polymethylmethacrylate lacquer, a nitrocellulose lacquer or an alkyd-melamine enamel.ALSO:A resinous composition useful as a coating material when combined with a solvent comprises (I) a copolymer of acrylonitrile, an ethylenically unsaturated carboxylic acid and at least one other group containing monomer, (II) a copolymer of a vinyl halide and a vinyl ester of a saturated aliphatic carboxylic acid, (III) an epoxide resin and, preferably, (IV) a urea-formaldehyde resin. Acid and vinylidene monomers specified for use in copolymer (I) are acrylic, methacrylic, crotonic, butenoic, angelic, tiglic, maleic and fumaric acids, styrene, alphamethyl, -ethyl and -chlorostyrenes, vinyl toluene, isobutylene, methyl, ethyl, butyl 2-ethylhexyl and trimethylhexyl acrylates, methyl, propyl, butyl and lauryl methacrylates, vinyl acetate, propionate, butyrate and isobutyrate, isopropenyl acetate and propionate, allyl chloride, bromide, acetate and butyrate, methyl chloroacrylate, vinyl and vinylidene chlorides, dibutyl itaconate, methacrylonitrile, ethacrylonitrile, acrylamide, methacrylamide and N-tert.-butyl acrylamide. Preferred copolymer (II) is one derived from vinyl chloride and vinyl acetate in which a proportion of the acetate groups may be hydrolysed to hydroxyl groups. Preferred epoxide resins (III) are those formed by the reaction of dihydric phenols (listed) and epoxy halogen compounds (listed), e.g. epichlorohydrin, and preferably have molecular weights of below 500. The ureaformaldehyde resin (IV) may be one prepared by condensing dimethylol urea in butanol or other alkanol which has been slightly acidified. Other specified ingredients of the compositions are solvents, e.g. toluene, xylene, ethyl alcohol, methyl ethyl ketone, methyl isobutyl ketone, ethyl amyl ketone, isobutyl acetate, the ethyl ether of ethylene glycol monoacetate, aromatic naphthas, acetone and mixtures thereof, titanium dioxide, magnesium silicate, lithopone, carbon black, chromic phosphate, iron oxide, lead and zinc chromates and soapstone. The preparation of a copolymer of methyl methacrylate, ethyl acrylate, acrylonitrile and methacrylic acid is described by a process which involves the gradual addition of the monomer mixture and benzoyl peroxide to a high boiling aromatic solvent followed by the intermittent addition of further quantities of benzoyl peroxide. In Example (1) a top-coat composition comprised an alkyd resin, iron oxide, barium sulphate, Mg and Al silicates, kerosene, mixed naphthenic solvents and anti-skinning agents.