Patent GB-1136928-A (GB)
Title: Oriented acrylonitrile polymer films
IPC: B29C55/00
Filed: 1965-12-24
Abstract: 1,136,928. Acrylonitrile polymer films. STANDARD OIL CO. 24 Dec., 1965 [28 Dec., 1964], No. 54800/65. Heading B5B. [Also in Division C3] A process for preparing a biaxially oriented polymer film comprises forming a film from a solution in a polar solvent or mixture of polar solvents of a polymer composed primarily of at least one alpha, beta-olefinically unsaturated nitrile, stretching the film at an elevated temperature in a longitudinal and a transverse direction and drying the film at an elevated temperature while it is retained in its biaxially stretched condition. Preferably the alpha, beta-olefinically unsaturated nitrile is acrylonitrile or methacrylonitrile. Polymers most useful in the present invention are those resulting from the polymerization of at least one alpha, beta-mono-olefinically unsaturated nitrile monomer having three or four carbon atoms and a terminal CH 2 = C = group. From 5-15% by weight of the alpha, beta-monoolefinically unsaturated nitrile may be replaced with one or more polymerizable monoalkenyl monomers copolymerizable therewith, e.g. acrylate esters, methacrylate esters, vinyl esters, vinyl aromatics, vinyl amides, vinyl halides, vinylidene chloride, vinylidene fluoride, dichlorodifluoroethylene and tetrafluoroethylene, and olefines. Many such compounds are listed. Specified alpha, beta-mono-olefinically unsaturated nitrile monomers include in addition to acrylonitrile and methacrylonitrile, alphachloroacrylonitrile, crotononitrile, vinylidene cyanide, cinnamonitrile and atroponitrile. Polymer solutions suitable for casting or otherwise forming films may be prepared by dissolving from 10-75% by weight of the polymers in one or a combination of volatile polar solvents, e.g. dimethylformamide, dimethyl thioformamide, N - methyl - beta - cyano - ethyl formamide, alpha-cyano acetamide, N-methyl pyrrolidone, gamma - butyrolactone, ethylene carbonate, tetramethyl oxamide, epsiloncyanolactone, 1,3,3,5 - tetracyanopentane, dimethyl cyanamide, dimethyl methoxy acetamide, N-formyl morpholine, N-formyl hexamethylene imine, dimethyl sulphoxide, propiolactone, N,N-dimethyl acetamide, dimethyl sulphone, tetramethylene cyclic sulphone, ethylene cyanohydrin, nitromethane, acetonitrile, malononitrile, tris - dimethylamino phosphine oxide or N,N<SP>1</SP>-tetramethylmethane phosphonamide. Solvents used in examples include a 90/10 by weight mixture of dimethyl formamide and ethylene carbonate; dimethyl formamide; and methyl ethyl ketone. In a preferred method, the film formed before stretching is effected contains from 8-70% by weight of the polar solvent, preferably from 25-45% by weight solvent; and, after stretching and before drying, the film suitably contains about one half the weight of polar solvent that it contained immediately before stretching. After casting, partial removal of the solvent by volatilization is effected, whereafter the film is longitudinally stretched, e.g. by drafting on a four-roll apparatus having two hot rolls and two cold rolls. In drafting, temperatures of 100- 260 F., preferably from 135-220 F. on the hot rolls are used, the cold rolls being maintained at or near room temperature. Longitudinal stretch ratios are suitably from 1.2: 1 to 10 : 1, especially 2 :1 to 4 1. Transverse stretching may be effected by tentering using either a disc or a chain tenter. Tentering is suitably effected at 100-260 F., especially 160-210 F., the ratio of stretching in tentering being about the same as that in drafting. Alternatively, drafting and, tentering may be effected simultaneously in a suitable apparatus at 100-260 F. After stretching, the film is heat set, suitably at 125-250 C. for up to five minutes, and is thereafter cooled.