| 摘要 |
Compositions for priming polyethylene surfaces to receive polyvinylidene chloride films comprise (1) an aqueous emulsion of a butadiene-styrene copolymer comprising 20 to 80% by weight butadiene and 80 to 20% by weight styrene and (2) an aqueous emulsion of a vinyl acetate copolymer comprising 30 to 50% by weight vinyl acetate and 70 to 50% by weight of (a) a dialkyl ester of an alpha, beta-ethylenically-unsaturated dicarboxylic acid, (b) a monoalkyl ester of an alpha, beta-ethylenically unsaturated monocarboxylic acid or (c) a mixture of esters (a) and (b), the emulsions (1) and (2) being in such proportion that the butadiene-styrene copolymer comprises 70 to 98% by weight and the vinyl acetate copolymer 30 to 2% by weight of the total solids content of (1) and (2) taken together. The dialkyl esters (a) preferably have 4 to 12 carbon atoms in each alkyl radical and may be derived from dicarboxylic acids having 4 to 6 carbon atoms, e.g. itaconic, citraconic, maleic and fumaric acids. The monoalkyl esters preferably have 8 to 12 carbon atoms in the alkyl radical and may be derived from carboxylic acids having 3 to 6 carbon atoms, e.g. acrylic, methacrylic and crotonic acids. As copolymers for the aqueous emulsion (2), there are illustrated in the examples vinyl acetate-diisooctyl maleate-2-ethylhexyl acrylate, vinyl acetate-2-ethylhexyl acrylate, vinyl acetate-diisooctyl maleate, vinyl acetate-di(2-ethylhexyl) maleate, vinyl acetate-2-ethylhexyl acrylate-di-n-butyl maleate and vinyl acetate-2-ethylhexyl acrylate-di(2-ethylhexyl) maleate copolymers.ALSO:A composite film substantially impervious to water vapour, organic vapours and gases comprises a polyethylene substrate having a surface which has been conditioned to enhance adhesion, a primer composition deposited and dried on said surface, and a film of a vinylidene chloride copolymer disposed on and bonded to the primer composition, said primer composition comprising (1) an aqueous emulsion of a butadiene-styrene copolymer and (2) an aqueous emulsion of a coplymer of vinyl acetate with an alkyl ester of an alpha,beta-ethylenically-unsaturated mono- and/or dicarboxylic acid. (For a more detailed description of the primer compositions see Division C3.) The polyethylene substrate may be a polyethylene film per se or a film incorporated in a paper product, such as kraft paper or boxboard. The surface of the film can be conditioned, to promote adhesion, by treatment such as electrostatic discharge, contact with an oxidizing flame, exposure to ultra-violet light, or subjecting to a matted roller to provide a matt finish. Any type of device may be used for depositing the primer composition on the polyethylene surface, e.g. air knife coater, horizontal and vertical size presses, trailing blade, transfer roll, reverse roll, roller coater, gravure, bead coat, metering bar, spray coater, or curtain coater. The dried primer film thickness should preferably be from 0,002-0,06 mil; drying may be effected in air or in an oven. The vinylidene chloride copolymer may then be applied from a latex thereof in a similar manner as described for the primer composition. The thickness of the dried vinylidene chloride copolymer film should preferably be from 0,02-1 mil. |
