| 摘要 |
Filaments, films, and like shaped products of polyacrylonitrile are produced by shaping a solution of polyacrylonitrile in a mixture of nitromethane and water containing at least 6, and preferably about 7-12, per cent by weight of water, and setting the shaped solution by means of a coagulating bath which consists essentially of nitro-methane and the water-content of which does not at any time during the process rise above 4 per cent by weight. The process is preferably effected at 75-100 DEG C. The concentration of polyacrylonitrile in the solution may be 5-25 per cent, e.g. 8-14 per cent. The coagulating bath may consist of substantially dry nitromethane, or it may contain up to 4, but preferably less than 3, per cent by weight of water, including water derived from the spinning solution. Its temperature is preferably above 50 DEG C., especially about 70-90 DEG C. Advantageously the polyacrylonitrile solution and the coagulating bath are at about the same temperature between 75 DEG and 90 DEG C. The composition of the coagulating bath may be kept substantially constant by continuously removing from the bath water derived from the polyacrylonitrile solution. The filaments are preferably stretched about 3-15 times their unstretched length as they pass through the coagulating bath and also stretched at a high temperature, but below their melting-point, very soon after they have left the bath. For example, they may be stretched by about 3-10 times their length while they pass over a hot surface at about 150-220 DEG C., and especially about 170-210 DEG C., or while they are heated by means of hot air, wet steam, or water at over 80 DEG C., as described in Specification 636,476. The stretched filaments may then be heated, e.g. to about 140-200 DEG C., while free from tension or under a tension insufficient to prevent them from shrinking. Instead of polyacrylonitrile there may be used such copolymers of acrylonitrile with other unsaturated compounds as contain at least 85 per cent of acrylonitrile and have substantially the same solubility in aqueous nitromethane as has polyacrylonitrile itself. Examples of such unsaturated compounds are methacrylonitrile, vinyl esters such as vinyl chloride and vinyl acetate, styrene and its derivatives, and vinylidene chloride. The copolymers are used in the same manner as polyacrylonitrile, but the water-content of the coagulating bath is preferably kept below about 2 per cent by weight. In the example a polyacrylonitrile is dissolved at 85 DEG C. in about 9 times its weight of a mixture of nitromethane and water containing 8 per cent by weight of water, and the solution is spun at about 85 DEG C. into a bath of dry nitromethane at the same temperature. The filaments are stretched by about 800 per cent in the bath and then by 500 per cent while passing over a metal plate at 190 DEG C. Specifications 665,004 and 720,199 also are referred to.
|
