Patent GB-1423441-A (GB)
Title: Production of polyamide fibres
IPC: C07D207/267
Filed: 1973-05-17
Abstract: 1423441 Aromatic polyamide filaments TEIJIN Ltd 17 May 1973 [18 May 1972 13 June 1972] 23693/73 Heading B5B Wholly aromatic polyamide fibres are made by extruding a spinning solution of a wholly aromatic polyamide in an amide solvent into an aqueous coagulating bath containing an inorganic salt, the process comprising feeding an aqueous coagulating liquid containing calcium chloride and having an amide solvent concentration of not more than 3% by weight to the vicinity of a spinneret, flowing the coagulating liquid at an average velocity not more than 0À1 times that of the take-up of the yarn, (preferably from 0À04 to 0À1 times), discharging the coagulating liquid having an amide solvent concentration of not less than 4% by weight from said bath, treating the coagulating liquid with an organic solvent consisting substantially of methylene chloride, and extracting and recovering the amide solvent from the coagulating liquid. Suitable solvents for the polyamides, which should contain at least 75 mol. per cent of units derived from m-phenylene isophthalamide include N-methyl-2-pyrrolidone, N,N<SP>1</SP>- dimethylacetamide, N,N<SP>1</SP>-dimethylformamide, and hexamethyl phosphoramide. The concentration of the polyamide in the spinning solution is suitably 15 to 30% by weight. Extrusion may be upward from a spinneret disposed horizontally towards the bottom of the coagulating bath as in Figs. 1 and 2, or an inclined spinneret may be used, the filaments being taken up obliquely upwardly as in Fig. 3. A spinneret having at least 5000 holes is preferred, and a yarn take-up velocity of 1 to 5 m./min., and preferably the distance H(cms.) between the spinneret face and the top surface of the coagulating bath satisfies the condition expressed by where S is the velocity in m./min. of taking up the filaments from the coagulating bath, D is the single filament denier of the final filaments, and 1#D#30 and 1#S#5. The coagulating liquid may be used at a temperature of at least 60‹ C. and preferably contains not less than 20% by weight of calcium chloride, based on the solution, the total salt concentration being at least 35%, and the proportion of calcium chloride being at least 65% of the entire salts. An aqueous solution of calcium chloride of concentration at least 35% may be used; additional salts, where used, may include magnesium chloride, calcium nitrate and zinc chloride. Preferably the coagulating liquid is discharged when it has a specific gravity, measured at 60‹ C., of at least 1À36, and extracted countercurrently with methylene chloride or with a mixed solvent containing at least 85% by weight of methylene chloride, the balance being another organic solvent having a specific gravity of not more than 1À3 and being soluble in methylene chloride and the amide solvent and being insoluble in water. In apparatus as shown, the spinning solution is extruded through spinneret 1 into coagulating bath 2 and the filaments 3 are taken up by roller 4, washed in water bath 5 and then fed to a drawing step. The coagulating liquid is fed from the feed inlet 5 rearward of the spinneret and flows in the direction of the arrows in Figs. 2 and 3. It overflows into trough 6 and is led through exhaust port 7 into reservoir 8 where it is cooled to about 50‹ C., and supplied by pump 10 to the upper part of the extracting tower 11. Methylene chloride is fed from the lower part of the tower and within the tower the amide solvent in the coagulating liquid is extracted and transferred into the methyl chloride. The coagulating liquid after extraction is taken out by pump 12 and returned to the coagulating bath via reservoir 13. The methylene chloride containing the amide solvent is taken out from the upper part of the tower and led to an evaporation device where the methylene chloride is evaporated and separated from the amide solvent. The amide solvent is further distilled under reduced pressure to purify and recover it, and is re-used for the preparation of the spinning solution, the methylene chloride being re-used as an extracting agent. In examples, filaments after washing are drawn up to 3À2 times in water at 95‹ C., dried, drawn up to 1À9 times using a plate at up to 340‹ C., heat-treated, crimped, and cut to staple fibres.