Production of artificial filaments by wet spinning

摘要

An apparatus for the production of filaments by wet spinning comprises a spinning vessel 11 provided with an inlet 14 for admission of coagulant and housing a spinneret 12 for the extrusion of a spinning solution supplied thereto through a conduit 13. The vessel 11 communicates directly with a spinning tube 15 of smaller cross-sectional area than vessel 11 and is provided near its open top with a liquid run off 16 to carry away coagulant. The tube 15 is provided with an annular insert 17 to define a restricted passageway for the flow of coagulant. The filaments 18 pass upwardly from the spinneret 12 through insert 17 and then the remainder of tube 15 to pass about a positively driven feed roll 19 and idler 20. In the constricted zone 17 the coagulant accelerates and travels at a linear speed greater than the linear extrusion speed of the spinning solution, while in the zone constituted by the unrestricted part of the tube 15 the coagulant travels at a linear speed slower than that of the filaments in this zone. Stretching tension is applied to the filaments leaving the tube 15 by the feed roll 19 against the hydraulic drag applied by the slower flowing coagulant in the unrestricted part of the tube 15. The apparatus and process of the invention is particularly suitable for the wet spinning of cellulose derivatives, especially cellulose acetate of acetyl value at least 59% and preferably at least 61% calculated as acetic acid. The cellulose triacetate may be dissolved to an extent of about 18 to 26% by weight in methylene chloride which may be blended with up to 15% by weight of the total solvent of a lower alkanol, preferably methanol. The coagulant is preferably a methylene chloride/methanol mixture containing 75 1/4 -T/sB5% by weight of methanol, where T is the temperature of the coagulant in DEG C. The spinning tube may be disposed horizontally or inclined but is preferably arranged vertically with the filaments and coagulant moving upwardly. In either case, the tube may be of uniform diameter and a portion of the coagulant withdrawn at the end of the high coagulant velocity zone so that the linear velocity of the coagulant which is not withdrawn will be reduced in its passage through the second zone. The linear speed of extrusion may be about 5 to 50 metres per minute and the filaments are preferably taken up at about 5 to 10 times the extrusion speed. The coagulant is preferably fed to the tube at such a volumetric rate that its linear rate of flow in the first zone ranges from about 50 to 80% of the filament take-up speed and at least three times the extrusion speed. The invention permits the production of cellulose triacetate filaments of tenacities of 2,5 or more grams per denier with elongations not below 20%. Specification 826,098 is referred to.