| 摘要 |
<PICT:0839595/IV (a)/1> Threads are produced from homopolymers of acrylonitrile and from copolymers containing at least 80% of acrylonitrile by extruding downwards a solution of the polymers in a concentrated aqueous or aqueous alcoholic salt solution into a concurrently moving stream of an aqueous coagulating bath which is miscible in all proportions with the spinning solvent, the rate of feed of the bath being adjusted so that a substantially horizontal, stationary liquidliquid interface constituting a boundary between an upper stratum of coagulant of relatively low salt content and a lower stratum of relatively high salt content is formed and maintained in the coagulant stream, and withdrawing the freshly coagulated thread so formed, associated with at least part of the coagulant, from the coagulant stream at a point below the interface, the rate of feed of the coagulant to the spinning cell above the interface being the same as the rate of discharge of the coagulant from the cell below the interface. The coagulant may be water or a dilute aqueous solution of the salt which is present in the spinning solution, and may be the wash liquor obtained by washing the threads free from the spinning solution salt, said liquor containing usually about 0.5 to 2% of the salt. The salt in the spinning solution may be sodium or calcium thiocyanate or zinc or lithium chloride. In an example, and as shown, 12.5 parts of a 94/6% acrylonitrile/methyl acrylate copolymer in 87.5 parts of a 51.5% aqueous sodium thiocyanate solution is fed through a supply line 15 to a downward facing spinning jet 16 mounted in a jet holder 17. The spinning solution is extruded from the jet into a stream of 1% aqueous sodium thiocyanate solution which is supplied to a spinning cell 1 through pipes 12 which are an air-tight fit in the steel plate 5 and gasket 4 which form an air-tight closure at the top of the cell. The tow 18 and a mixture of diluted spinning solvent and coagulant are withdrawn through an aperture 11 defined by adjustable shutters 8 held between the fixed plates 9, 10 at the bottom of the cell 1. The top of the cell is provided with an air and liquor release valve 13 which is normally closed during spinning. The coagulant is fed into the cell 1 through the pipes 12 at a controlled rate such that a liquid-liquid interface 19 is formed below the jet 16 between the denser spinning solution-coagulant mixture and the lighter coagulant. The coagulated tow 18 is withdrawn from the cell 1 and is stretched, washed and dried. The liquor flowing from the cell with the tow and containing 14% sodium thiocyanate is passed to an evaporator in which it is concentrated to 51.5% salt content. The relatively high salt concentration in the liquor withdrawn from the cell facilitates further concentration of the solution or recovery of the salt. Specifications 714,530, 768,708 and 796,294 are referred to.
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