Improvements in or relating to the production of aqueous dispersions of copolymers and of moistureproof sheet wrapping materials coated therewith

Abstract

Abstract Amorphous copolymers of vinylidene chloride and acrylonitrile are made by heating until polymerization is substantially complete, an aqueous emulsion comprising a mixture of more than 75 parts by weight of vinylidene chloride and 25 parts by weight of acrylonitrile in the presence of 0.5 to 8 per cent by weight of a dispersing agent consisting of the condensation product of formaldehyde with a naphthalene or alkyl substituted naphthalene sulphonic acid or with an alkali metal salt or ammonium salt thereof. The alkyl substituent contains 1 to 4 carbon atoms in the molecule. The emulsion may contain a polymerization catalyst, e.g. ammonium persulphate and an activator, e.g. sodium metabisulphite. Specified dispersing agents are formaldehyde with sodium naphthalene beta-sulphonate, or with naphthalene beta-sulphonic acid, or ammonium naphthalene beta-sulphonate, or sodium isopropyl-naphthalene beta-sulphonate, or isopropyl - naphthalene - beta - sulphonic acid. The aqueous dispersion of the copolymers may be used for coating non-fibrous hydrophilic sheets or films (see Group VIII). The dispersions may include natural or artificial ester-type waxes such as carnauba, spermaceti, candellila, palm, hydrogenated castor oil, benzyl stearate, pentaerythritol distearate, pentaerythritol tetrastearate and octadecyl stearate, or the wax agents described in Specification 655,006, and softeners for the film such as ethylene glycol and glycerol. The coated films are used as wrapping materials.

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