Patent GB-989110-A (GB)
Title: Production of artificial filaments of cellulose triacetate
IPC: D01D5/06
Filed: 1962-01-17
Abstract: 989,110. Wet-spun cellulose triacetate filaments. CELANESE CORPORATION OF AMERICA. Jan. 17, 1962 [Jan. 25, 1961], No. 1707/62. Heading B5B. A solution of cellulose triacetate is extruded into a liquid coagulant exerting a swelling action on cellulose triacetate and containing both an organic solvent and an organic non- solvent for the cellulose triacetate and collecting the filaments coming from the coagulant at a linear speed several times the linear speed of extrusion, and the filaments are withdrawn from the coagulant, washed with a countercurrent stream of an organic non-solvent for cellulose triacetate, miscible both with water and with the coagulant, thereby reducing the solvent content of the filaments to below 10% based on their dry weight, the non-solvent removed and the filaments dried, filaments so obtained being substantially free from coalescence. Preferably the filaments are washed with the organic non-solvent in a plurality of stages with the effluent from one stage forming the washing liquid for the preceding stage, suitably until their solvent content is below 2% based on their dry weight, and with expression of liquid from the filaments to a value below 225% based on their dry weight before each stage. Effluent from the first stage of washing with the organic non-solvent may be mixed with spent coagulant and the mixture, after adjustment of the concentration of its ingredients, returned to the process for re-use as coagulant. The organic non-solvent may be washed from the filaments with water before the filaments are dried. Washing with water may be effected in a pluraity of stages with the effluent from one stage forming the washing liquid for the preceding stage, and with expression of liquid from the filaments to a value below 225% based on their dry weight before each stage. In a preferred method, a solution of cellulose triacetate in methylene chloride containing 5-10% by weight methanol is extruded into a mixture of methylene chloride and methanol containing a higher proportion by weight of methanol and the filaments washed with methanol. Other specified solvents are chlorinated lower alkanes, especially ethylene dichloride, and other specified non-solvents include methanol, ethanol, propanol and tertiary butyl alcohol. Suitably, the same solvent and non-solvent are present in both spinning solution and coagulant, and the spinning solvent may comprise up to 15% by weight, especially 5-10% of the non-solvent. In apparatus as shown, a cellulose triacetate spinning solution is extruded from spinneret 12 in spin pot 13, into which coagulant is introduced at 14. Spent coagulant overflows from the spinning column 16 into collector 17. Filaments 15 pass around pin 18 and excess spent coagulant is extracted by driven squeeze rolls 19, 20, falling into collector 17. The filaments then undergo six washing stages in vessels 21-26 and six extraction stages in the further six pairs of squeeze rolls, and finally pass to a dryer 29. Water is introduced at 30 to vessel 26, becoming enriched with methanol from the filaments and overflowing into vessel 25. Effluent from 25, containing a higher concentration of methanol is withdrawn at 31 and passes to distillation column 32. Underflow from column 32, water relatively free of methanol, is recycled at 30 to vessel 26. Distillate from 32, methanol, passes to collector 33, and together with make-up methanol introduced at 34 is withdrawn to be admitted at 35 to vessel 24. Methanol in 24 cascades successively into vessels 23, 22 and 21, from which it overflows into collector 17. Effluent from 17, chiefly spent coagulant, is treated at 36 for re-use, part being withdrawn at 37 to compensate for spinning solvent extracted from the filaments and methanol added to the first washing stage. The remainder is forwarded to receiver 38 to which make-up liquid is added at 39 to adjust the composition of the effluent fed at 14 into spin pot 13 by pump 40. Liquids introduced at 30 and 35 are preferably directed at the filaments to wash down into the baths, thereby improving the efficiency of washing.