| 摘要 |
Sheet wrapping material comprises a base film of a highly moistureproof relatively difficultly fusible polymer of vinylidene chloride, or of a copolymer of vinylidene chloride with up to 12 per cent (based on the total weight of the monomers) of one or more of the following monomeric ethylenic compounds, viz., acrylonitrile, methyl methacrylate, ethyl acrylate, vinyl chloride, vinyl acetate and styrene, coated with one or more coatings of a more readily fusible copolymer or copolymers formed by the copolymerization of monomeric vinylidene chloride with one or more of the said compounds in total proportion greater than that of such compounds in the mixture from which the material of the base film is formed, when this is a copolymer. The coatings may be of a copolymer or copolymers formed from monomeric vinylidene chloride (90 to 50 per cent) with one or more of the above ethylenic monomers (5 to 50 per cent) with or without one or more of the following monomeric ethylenic acidic compounds in total proportion of 2 to 5 per cent:-citraconic acid or its anhydride, mesaconic acid, itaconic acid or its anhydride, acrylic acid, methacrylic acid, butacrylic acid, or maleic acid or its anhydride. Examples describe the preparation of copolymer emulsions from vinylidene chloride and acrylonitrile, with or without itaconic acid, or from vinylidene chloride and vinyl chloride or methyl methacrylate, in the presence of ammonium persulphate, sodium metabisulphite, the ammonium or sodium salts of long-chain alkyl sulphates, and water. Specification 680,709 is referred to. |
