GB890559A - Method of annealing synthetic organic filamentary material and apparatus therefore - Google Patents

Abstract

A filametary tow of synthetic organic polymeric material such as acrylonitrile polymer is heat-relaxed or annealed by continuously moving it in a path through a heat treatment zone in which heat is applied momentarily to contiguous and preferably very short portions of the tow only during its movement to raise the temperature of the portions to 130 DEG -150 DEG C., whereafter <PICT:0890559/IV (a)/1> <PICT:0890559/IV (a)/2> <PICT:0890559/IV (a)/3> the tow is moved through a relaxing zone in the form of an unsupported free-running horizontal length of tow so as to permit the internal strains in the filaments to be relieved. As shown in Fig. 1, a tow 10 of continuous polyacrylonitrile filaments which have been stretched and are therefore in an internally strained condition is advanced in the direction of the arrow H by a pair of co-operating driven nip rolls 11, 12 of which roll 11 is covered with a layer of resilient material 24. The lower roll 12 contains a central bore 16 (Figs. 2 and 3) and a number of radial passages 17 in its peripheral wall 18. A heating medium such as superheated steam is supplied through a pipe 22 into a stationary chamber 19 centrally positioned within the roll bore 16 by bearings 21. A longitudinal slot 23 in the wall of the chamber 19 is arranged to communicate successively with each longitudinal row of passages 17 as the roll 12 is rotated and is positioned so that it communicates with a single longitudinal row of passages 17 only when the outlet ends of the passages are in alignment with the nip 14 of the rolls 11, 12, the inlet ends of the remaining passages 17 being closed by the peripheral wall of the chamber 19. The tow 10 moving out of the nip of the rolls 11, 12 is taken up by a pair of nip rolls 26, 27 which are driven at a lower peripheral speed than that of the rolls 11, 12 in order to compensate for the shrinkage of the reach of the tow 10 in the relaxing area 28. The tow is subjected in the nip 14 to the action of steam at 130 DEG -150 DEG C. for about 0,1 second. The tow may be heated successively by a number of pairs of processing rolls, e.g. 3 pairs, each identical in construction and operation with the processing rolls 11, 12. The tow is then allowed to sag in three relaxing areas, two between the three pairs of processing rolls and the third between the third pair of the processing rolls and a pair of take-up rolls, the amount of sag in the tow decreasing as it passes through the system of rolls. The temperature of the tow may be raised prior to the annealing operation by passing it through a steam conditioner during its passage from the stretching to the annealing zone. The process prevents the discoloration of polyacrylonitrile filaments.