GB1007050A - Coating substrates - Google Patents

Abstract

A process comprises coating a substrate with an aqueous dispersion of a polymer and thereafter drying the coating and gelling the polymer, in which process the polymer is a copolymer of at least 70% by weight of vinylidene chloride and from 4-30% by weight of a component which comprises at least one monoethylenically unsaturated monomer which is soluble in water to the extent of at least 0,5 gm. per 100 c.c. at the temperature of the polymerization, which copolymer has been prepared by polymerizing the vinylidene chloride and the water-soluble monomer or mixture of monomers in aqueous medium in the presence of (i) a water-soluble salt of a peroxyacid, and (ii) a sulphur-containing acid having reducing properties or an alkali metal salt thereof, and in the presence of less than 0,1% by weight, based on the total weight of the monomeric components, of any ionic emulsifying or dispersing agent and in the presence of less than 2% by weight based on the total weight of the monomeric components of any non-ionic surface active agent. Suitable substrates include metals such as aluminium foil, paper, cardboard, aluminium foil laminated to paper, regenerated cellulose and thermoplastic materials such as polypropylene, polyethylene, polyvinyl fluoride, vinyl chloride polymers and copolymers with up to 20% by weight of other monomers, cellulose acetate, and linear polyesters, e.g. polyethylene terephthalate. Monomers which are soluble to the desired extent in water include acrylonitrile, methacrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, acrylamide, methacrylamide, methyl vinyl ether, ethyl vinyl ether, methyl vinyl ketone, and acrolein. Specified water-soluble salts of peroxy acids are the alkali metal and ammonium peracetates, percarbonates and persulphates. Specified sulphur acids and salts thereof are sulphurous acid, sulphites, hydrosulphites, thiosulphates, formaldehyde, sulphoxylates and metabisulphites. Specified ionic emulsifying agents are the alkali metal salts of sulphated or sulphonated alcohols containing at least 12 carbon atoms e.g. sodium lauryl sulphate. Specified non-ionic surface active agents are the polyoxyethylated carboxylic acid esters of sorbitan in which the carboxylic acid contains at least 12 carbon atoms, for example polyoxyethylated sorbitan monostearate; polyoxyethylated alcohols or phenols such as polyoxyethylated nonyl phenol; polyoxyethylated octyl cresol; polyoxyethylated alkyl alcohols such as the polyoxyethylated oleyl and cetyl alcohols, and hydrolysed polyvinyl acetate and ethylene oxide / propylene oxide copolymers. Polymerization may be effected at 30-70 DEG C. Chain transfer agents may be added. The polymer dispersion, the particles of which may be less than 0,18 micron in size, may be applied direct to the substrate. The surface of plastic material substrates e.g. biaxially oriented polypropylene film may be activated to improve adhesion of the coating, for example, by corona discharge treatment. The coating may be applied by roller-coating, spraying, doctor-knife coating or air-knife coating. The coating may be dried and gelled at any temperature above 50 DEG C. Blocking may be prevented by incorporating additives e.g. an aqueous dispersion of fine particles of wax e.g. candelilla wax into the dispersion. The surface of the substrate may be that of a film, sheet, tube, or channel, and the coated surface may be shaped e.g. by vacuum forming or blow moulding into containers.