method for the manufacture of a multilayer lackaufbaus with layers of polymethacrylsaeuremethylester adjusted on metal

摘要

Metal articles are provided with a hard, adherent multiple-layer coating comprising a pigmented primer in adherent contact with the metal, a layer of undercoat, consisting of lacquer-grade nitrocellulose, 0 to 50 per cent, based on the weight of the nitrocellulose, of a plasticizer therefor, and 0 to 45 per cent of pigment, based on the total weight of nitrocellulose and plasticizer, and a top coat layer of methyl methacrylate lacquer. The primer may be of either the air-drying or baking type; in examples conventional car-body finishing primers, viz. modified drying oil primers, are used. The preferred nitrocellulose compositions do not contain any plasticizer, but if one is used dicyclohexyl phthalate or benzyl butyl phthalate is preferred. Suitable pigments for use in the invention include titanium dioxide, zinc oxide, iron oxide, zinc chromate, carbon black, iron blue, phthalocyanine blue or green, barytes, whiting, talc, china clay, organic maroons, and chromium tetrahydrate. The top coat may comprise a homopolymer of methyl methacrylate or a copolymer of this substance with a minor proportion of e.g. acrylic and methacrylic acids, alkyl esters of acrylic acid in which the alkyl group contains 1 to 4 carbon atoms, alkyl esters of methacrylic acid of which the alkyl group contains 2 to 4 carbon atoms, vinyl acetate, acrylonitrile or styrene. In examples, steel car body panels, some treated with a rustproofing composition such as a phosphate coating, are coated by spraying, the drying of the primer and top coats being accelerated by baking, and the nitrocellulose undercoat being omitted over parts of the panels for comparative purposes; in these portions the adhesion of the top coat was poor when fresh, and failed badly after outdoor exposure, whereas it remained adherent where applied over a nitrocellulose undercoat. Specifications 763,158 and 807,895, [both in Group IV (a)], are referred to.