GB693496A - Improvements in or relating to the production of aqueous dispersions of vinylidene chloride copolymers and of moistureproof sheet wrapping material produced therefrom - Google Patents

Abstract

Aqueous dispersions of vinylidene chloride copolymers are made by emulsifying a mixture of vinylidene chloride and another monomer or monomers in which not more than 80 parts are vinylidene chloride, in an aqueous medium containing a water-soluble or water-dispersible dispersing agent selected from alkali metal or ammonium salts of long straight-chain alkyl or alkylene sulphates or sulphonates, comprising between 18 and 28 carbon atoms in the alkyl or alkylene group, maintaining the emulsion at a polymerization temperature, either under visible reflux action or in an autoclave, and preferably in the presence of a polymerization catalyst, until polymerization is substantially complete, then adding another dispersing agent selected from alkali metal or ammonium salts of an alkyl aryl sulphonate comprising between 4 and 12 carbon atoms in the alkyl group, or a water-soluble or water - dispersible condensation product of formaldehyde with a naphthalene sulphonic acid or alkali or ammonium salts thereof, or similar salts of straight-chain alkyl sulphates or sulphonates comprising between 8 and 12 carbon atoms in the alkyl group or alkyl sulphates or sulphonates comprising more than 12 carbon atoms in an alkyl group which comprises one or more branched chains. The comonomer may be acrylonitrile, vinyl chloride, methyl methacrylate, ethyl acrylate, alone or admixed with mesaconic acid, citraconic acid, or citraconic anhydride, or mixtures, or itaconic acid or anhydride or mixtures, or mixtures of citraconic and itaconic anhydrides obtainable from citric acid by distillation. The catalyst may be a mixture of ammonium persulphate and sodium metabisulphite. Specified dispersing agents are ammonium n-octadecyl sulphate, sodium n-octadecyl sulphate and/or sodium n-hexadecyl sulphate, sodium octadecenyl sulphate, sodium dodecyl benzene sulphonate, the condensation product of formaldehyde with sodium naphthalene beta-sulphonate, ammonium dodecyl sulphate, and ammonium 3,10-diethyl dodecyl sulphate. The dispersions may be used for coating organic, non-fibrous, hydrophilic films or sheets (see Group VIII) or made into self-supporting films by depositing the dispersed vinylidene chloride particles on to a base and stripping off the deposit, e.g. by the processes described in Specifications 669,907 and 680,709. Specification 663,645, [Group VIII], also is referred to.