GB934519A - Process for preparing spandex yarn - Google Patents

Abstract

A coalesced multifilament spandex yarn is made by extruding a solvent-containing solution of a spandex polymer through a spinneret having a plurality of orifices into a spinning cell to form a plurality of separate filaments forwarding said filaments in an unsupported fashion through the cell while simultaneously introducing into the cell a gaseous medium, withdrawing the filaments from the cell through an outlet remote from the orifices and thence through a zone of centrifugally circulating gas wherein the gas exerts a torque on the filaments imparting a false twist thereto, the false twist extending back along the line of the filaments into the cell to a point at which the filaments are in a sufficiently plasticized state to adhere to each other thereby forming a false-twisted coalesced multifilament, and passing the twisted multifilament from the circulating gas zone into contact with forwarding means under sufficient tension to counteract the torque imparted by the circulating gas zone thereby removing the false twist. The false twist may be imparted by a jet twister having an aperture for receiving the filaments and an annular plenum chamber surrounding the aperture into which a gas, preferably air, is introduced tangentially to provide a lubricating layer of centrifugally circulating gas about said filaments. In apparatus as shown, the filaments 16 extruded from spinneret 10 are met by a co-current stream of hot inert gas introduced at inlet 14 of dry spinning cell 12. A counter-current stream of inert gas may also be introduced at inlet 18 to minimize dripping of solvent from the cell. The two streams of gas meet and are drawn off through an aspiration device 20. The filament bundle leaves the cell at 30 and passes through <FORM:0934519/IV(a)/1> <FORM:0934519/IV(a)/2> jet twister 22 to feed roll 28. Jet twister 22 consists essentially of a doughnut shaped plenum chamber supplied with a tangential air inlet 24. The yarn passes through orifice 23 and is twisted by a swirling sheet of air issuing perpendicularly to the thread line from orifice 25. The flow of air to the jet is adjusted so that this twist backs up into the cell to a point 27 which is the first point of filament-to-filament contact. The multifilament then passes over a finish roll 32 for application of a lubricant, thence to a second feed roll 34 to traversing guide 36, drive roll 38 and bobbin 40. Spandex multifilaments of about 70-600 denier may be made by coalescing individual filaments of about 2-20 denier. Multiple-thread spinning may be effected by gathering the filaments issuing from the spinneret into separate groups and conducting each group to a separate air jet twister. The spandex filaments are made from segmented polyurethanes, prepared from hydroxylterminated prepolymers, e.g. low-molecular weight polyethers and polyesters. Reaction of the prepolymer with a molar excess of organic diisocyanate, preferably an aromatic diisocyanate, produces an isocyanate-terminated material which may be chain-extended with a difunctional, active-hydrogen containing compound, e.g. water hydrazine, organic diamines, glycols and aminoalcohols. The crystalline high-melting segment may be derived from, e.g. a polyurea, polyurethane, polyamide or bisureylene polymer, and the low-melting amorphous segment may be derived from, e.g. a polyester, a polyether or an N-alkylated polyurethane. The segmented polyurethanes may be prepared by carrying out the polymerization reaction in the solvent to be used for spinning. Specified spinning solvents include N,N-dimethylformamide, N,N-dimethylacetamide, tetramethylenesulphone, formic acid, and mixtures of 1,1,2-trichloroethane with formic acid. In an example, an isocyanate terminated polyether, made by capping polytetramethylene ether glycol with 2 mols. of p-p1-methylenediphenyl diisocyanate, is mixed with N,N-dimethylformamide and then reacted with a mixture of hydrazine (in water) and diethylamine (in dimethylformamide). The polymer solution so made is treated with a slurry of titanium dioxide in dimethylformamide and a solution of poly(N,N-diethyl-beta-amino ethyl methacrylate) in dimethylformamide to form a spinning solution containing 5% of each additive based on the elastomeric solids. Specifications 796,041, 849,154, 910,543 and U.S.A. Specifications re-issue 24,689, 2,929,801, 2,929,802, 2,929,804, 2,962,470 and 2,965,437 are referred to.