| 摘要 |
Transparent moisture resistant flexible self-supporting films are obtained by casting a solution of a mixture of a butadiene-acrylonitrile type elastomer, a vinyl resin and 0.2-2.0 per cent of the solids content of an amorphous or micro-crystalline paraffin or vegetable wax melting in the range 51.7-93.3 DEG C. dissolved in a solvent mixture containing a major proportion of a relatively rapidly evaporating solvent for the film constituents together with a minor proportion of a relatively slowly evaporating solvent for the wax. In addition, the casting solution may contain a proportion of a resinous gum, e.g. up to 30 per cent of the weight of the film; specified are ester gum, elemi, mastic, sandarac, dammar and garentula gums and rosin and linseed, fish, sod and palm oils. Suitable elastomers are obtained by copolymerisation of butadiene, isoprene, 1-methyl-1.3-butadiene, 2.3-dimethyl-1.3-butadiene or 2-chloro-1.3-butadiene with acrylonitrile or methyl, ethyl, propyl or chloro-acrylonitriles. Listed vinyl resins are polyvinyl chloride and copolymers of vinyl chloride and vinyl acetate, methyl methacrylate or other alkyl methacrylates, vinyl cyanide or vinylidene chloride. Specified waxes are carnauba, p candelilla, ozokerite, montan, paraffin and halogenated paraffin waxes, including that sold under the trade name "Aristowax". Rapidly evaporating solvents are those which evaporate at least as fast as isopropanol, e.g. methyl ethyl ketone, acetone, benzene, methanol and isopropanol. Slowly evaporating solvents evaporate at least as slowly as toluene, e.g. xylene, toluene and turpentine. In examples a film having reduced moisture permeability is obtained by casting the solutions onto a fabric belt coated with polyvinyl alcohol.
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