Procédé de coagulation de copolymères de chlorure de vinylidène

A method of coagulating vinylidene chloride polymers from aqueous emulsions thereof comprises adding the emulsion at not more than 10 DEG C. to a 5%, or more dilute, aqueous coagulant solution at at least 20 DEG C. Polymers specified are copolymers of vinylidene chloride with vinyl chloride and other ethylenically unsaturated monomers such as acrylonitrile, styrene, vinyl acetate and esters of acrylic and methacrylic acids, especially copolymers of 65%-90% vinylidene chloride with 35%-10% vinyl chloride and terpolymers of 75%-80% vinylidene chloride, 15%-20% vinyl chloride and 5%-10% of a C8-18 alkyl acrylate. Suitable coagulants are solutions of bi- and tri-valent metal salts, e.g. calcium chloride and nitrate, magnesium and barium chlorides, and aluminium chloride and sulphate. Emulsifiers mentioned are dihexyl sodium sulphosuccinate and dodecyl benzene sodium sulphonate. In the preferred mode of operation, streams of emulsion and coagulant are simultaneously stirred into a bath of coagulant. The coagulated resin may be grained (or crystallized) by heating the slurry formed at 60 DEG C. for at least half an hour. The bulk density of the product varies inversely with the coagulation temperature. Examples show the effect of varying the temperatures within and without the specified range for a copolymer of 75% vinylidene chloride with 25% vinyl chloride, the bulk density of the product varying from 0,25-0,73. The products obtained are particularly suitable for extrusion into packaging film. Specification 866,895 is referred to.