| 摘要 |
Threads, which may be endless silk-like threads or shorter wool-like or cotton-like fibres, are produced by spinning a solution of an undecomposed polymer consisting wholly or mainly of polyacrylonitrile in a 56-65% by weight aqueous solution of nitric acid through a nozzle into a precipitation bath having a nitric acid content of 45/sB1% by weight, and withdrawing the resulting thread at a speed greater than the theoretical discharge speed of the polymer solution from the spinning nozzle. The theoretical discharge speed V1 in m./min. is defined by the equation: <FORM:0867846/IV (a)/1> in which Q is the quantity of solution in cc./min. delivered by the spinning pump to the nozzle, Z is the number of nozzle apertures and D is their diameter in mm. The freshly spun threads are preferably stretched in several stages, the stretching treatment being combined with the recovery of the precipitation both by washing the threads several times with more dilute acid and simultaneously stretching so that the total stretch between the extrusion nozzle and the final washing with water is at least 400% of the theoretical discharge speed. The precipitation bath is preferably maintained at a temperature of -5 DEG to -7 DEG C. but the subsequent more dilute acid washing baths, which may contain successively 15-20%, 4-6% and 0,5-2% by weight of nitric acid, and the washing water may be maintained at 20 DEG -30 DEG C. The threads may subsequently be hot stretched, shrunk, crimped, cut into fibres and dried. Specification 701,652 is referred to. |
