Patent GB-870437-A (GB)
Title: Coating of polystyrene
IPC: C08J7/054
Filed: 1959-12-07
Abstract: A coating composition comprises an aqueous emulsion of from 15% to 40% by weight of thermoplastic polymer, (1); and 0,2% to 4% by weight of an intermediate-stage, watersoluble thermosetting aldehyde-amine resin, (II), (I) being a copolymer of (a) vinylidene chloride, vinyl chloride, vinyl acetate or mixtures thereof, in proportions of 58% to 98% of the total copolymer, with (b) acrylonitrile, an alkyl acrylate or methacrylate or mixtures thereof, in proportions of 2% to 42% of the copolymer; each 100 parts by weight of the emulsion containing 0,004 to 0,046 equivalents of carboxyl groups present in the form of (1) a free saturated or unsaturated carboxylic acid having less than 8 carbon atoms per molecule or (2) such an unsaturated carboxylic acid which has been copolymerized with the monomeric units making up the copolymer (1), or is partly from free acid and partly from such copolymerized acids.  The aldehyde-amine resin may be a urea-, melamine-, urea-melamine-, aniline-, thiourea-, or biuret-formaldehyde resin.  Preferred carboxylic acids are itaconic, acrylic, maleic, fumaric, citric, adipic, acetic, propionic and oxalic acids.  The alkyl acrylate or methacrylate preferably contains less than 10 carbon atoms in the alkyl group, such as methyl, ethyl, propyl, butyl, isobutyl, 2-ethyl hexyl or octyl acrylate or methacrylate.  Examples describe the production of the copolymers by aqueous emulsion polymerization in the presence of sodium lauryl sulphate, ammonium persulphate and sodium metabisulphite; if desired, a required proportion of saturated carboxylic acid may be incorporated before polymerization.  The coating composition may contain a plasticizer such as dibutyl phthalate.ALSO:An article of polystyrene or a copolymer of styrene and another polymerizable compound, such as acrylonitrile, in which at least 70% of the monomeric units are styrene, is coated by applying and then drying an aqueous emulsion of from 15 to 40% by weight of thermoplastic polymer (I), and 0.2 to 4% by weight of an intermediate-stage, water-soluble thermosetting aldehyde-amine resin, (II), (I) being a copolymer of (a) vinylidene chloride, vinyl chloride, vinyl acetate or mixtures thereof, in proportions of 58% to 98% of the total copolymer, with (b) acrylonitrile, an alkyl acrylate or methacrylate or mixtures thereof, in proportions of 2% to 42% of the copolymer; each 100 parts by weight of the emulsion containing 0.004 to 0.046 equivalents of carboxyl groups present in the form of (1) a free saturated or unsaturated carboxylic acid having less than 8 carbon atoms per molecule or (2) such an unsaturated carboxylic acid which has been copolymerized with the monomeric units making up the copolymer (1), or is partly from free acid and partly from such copolymerized acid. The aldehyde-amine resin may be a urea-, melamine-, urea-melamine-, aniline-, thiourea- or biuret-formaldehyde resin, and the carboxylic acid may be itaconic, acrylic, maleic, fumaric, citric, adipic, acetic, propionic or oxalic acid.  The coating may be applied by passing the article through a bath containing the coating composition, by spraying or by manual brushing, and the surface of the article may be rendered hydrophilic prior to coating by treatment such as contacting the surface with a flame, with ozone, with a sulphuric acid-potassium dichromate solution or with sulphuric acid.