Patent GB-1042897-A (GB)
Title: Coated films
Inventor: STEAD BRIAN DOUGLAS
IPC: C08J7/052
Filed: 1963-11-20
Abstract: A heat sealable coated olefine polymer film is produced by subjecting uncoated film to a chemical or physical treatment resulting in oxidation of the film surface to improve the bonding properties of its surface, after which a coating of a heat-curable water-insoluble condensation product of melamine and formaldehyde, which has been prepared by reacting at least three moles of formaldehyde with each mole of melamine, and a monohydric alcohol, is applied to the film by solution coating and evaporation of the solvent, the film is then overcoated with an aqueous dispersion of a polymer or copolymer which enables the film to which it is applied to be heat sealed using standard heat sealing equipment which is then dried off on the film and heated to cure the condensation product so that it becomes adhesively bonded to the heat-sealable coating and to the base film. The oxidation of the film surface may be by treatment with chromic acid in sulphuric acid or with hot nitric acid; exposure to ozone e.g. at a temperature above 100 DEG C.; exposure to high voltage electric stress accompanied by corona discharge; exposure to ionizing radiation e.g. ultraviolet, X-, a -, b - or g - radiation particularly at temperatures above 100 DEG C.; exposure to a flame; to give the film a water contact angle at 65 to 75 degrees.  The monohydric alcohol may be an alkanol containing between 3 and 6 carbon atoms.  The condensation product may be prepared by reacting the formaldehyde with the melamine in the presence of the monohydric alcohol, or by first reacting the melamine and formaldehyde to produce a water-soluble heat curable condensation product and then reacting the product with the monohydric alcohol.  The condensation product may have a petroleum ether tolerance (defined) of at least 2. Before applying the heat sealable coating the thermosetting resin is partially but not completely cured.  The thermosetting resin may be set in the presence of an acid catalyst.  The thermosetting resin may contain a plasticizer.  The sealable coating polymer may be a copolymer of vinylidene chloride and acrylonitrile, which may contain 80 to 95% by weight vinylidene chloride, polyvinyl acetate which may be partially hydrolysed, butadiene-acrylonitrile, -styrene, and/or -methyl methacrylate, methyl methyacrylate-methacrylic acid, copolyesters of terephthalic acid and an other dicarboxylic acid e.g. sebacic acid, with a glycol, vinylidene chloride -vinyl chloride, -methyl, -butyl or -octyl acrylate, vinyl acetate -vinyl chloride, or -ethylene, and vinyl chloride-ethylene copolymers. The copolymer may be applied as an aqueous emulsion using as the emulsifying agent a cationic surface active agent, examples of which are given, thereby to confer antistatic properties on the film.  The heat sealable coating dispersion may also contain additives other than cationic surface agents, examples of which are given.  The olefine polymer may be polymers and copolymers of ethylene, a -olefines having at least 3 carbon atoms e.g. propylene, butene 1.  The olefine polymer film may be oriented in one or both directions in the plane of the film, e.g. biaxially oriented with a substantially equal degree of orientation in each direction, and may be heat set either before or after the coating treatment.