| 摘要 |
<p>1385196 Laminated films W R GRACE & CO 23 June 1972 [23 June 1971 14 Jan 1972] 29532/71 and 1986/72 Headings B5B and B5N A heat shrinkable laminate having an oxygen permeability of less than 70 cc. 25 microns/m<SP>2</SP>. 24 hours. atm. at 23‹ C. which comprises an oxygen barrier layer (A) of a vinylidene chloride polymer and a plasticizer therefor, the oxygen barrier layer being laminated on each side to layers (B 1 and B 2 ) of another polymer or mixture of polymers, is made by extruding a film of a vinylidene chloride polymer containing a plasticizer, stretching the film to orient it and render it heat shrinkable, and before or after said stretching, laminating both sides of the film to other polymeric layers which will absorb plasticizer from the vinylidene chloride polymer and which have a combined thickness of at least 75% of the thickness of the film of vinylidene chloride polymer. In a preferred method, a vinylidene chloride polymer containing plasticizer in an amount which gives a film with an initial oxygen permeability of at least 130, preferably at least 200 is extruded, and each side thereof is laminated to another polymeric layer which will absorb plasticizer from the vinylidene chloride polymer and thus reduce the oxygen permeability of the barrier layer to below 70. The laminate may be made by melt-extrusion of the three layers through a single extrusion head having three extrusion orifices to form a tubular extrudate, followed by orientation of the extrudate by internal gaseous pressure. Specified plasticizers include dibutyl sebacate, desirably present in a proportion of 7 to 10% of the vinylidene chloride polymer, and diisobutyl adipate, 2-ethylhexyldiphenylphosphate, and acetyl tri-n-butyl citrate, desirably present in a proportion of 7 to 12%. The vinylidene chloride polymer may contain 90 to 65 % by weight of units derived from vinylidene chloride and 10 to 35% of units derived from vinyl chloride, and the layers B 1 and B 2 may comprise either a compatible blend of ethylene/vinyl acetate copolymer and a minor proportion of the vinylidene chloride polymer used in layer A, or a copolymer of ethylene with up to 40%, especially 10 to 30% by weight of vinyl acetate; a chlorinated polyethylene containing 25 to 50% by weight of chlorine; a methacrylate-butadiene-styrene terpolymer; or a mixture of polyethylene and polyisobutylene. Other suitable polymers are listed. Up to 15% by weight, based on the weight of the blend, of the ethylene/vinyl acetate copolymer used in layers B 1 and B 2 may be present. Scrap laminate may be recycled and used in the production of layers, A, B 1 or B 2 . In the oriented laminate, the combined thickness of the layers, B 1 and B 2 may be at least 100%, but not more than 400%, of the thickness of layer A. Layer A may be 20 to 30 microns thick and the layers B 1 and. B 2 each 15 to 30 microns thick.</p> |
