Patent GB-936758-A (GB)
Title: Method and apparatus for wet spinning polyacrylonitrile filaments
IPC: D06B3/04
Filed: 1961-05-16
Abstract: <PICT:0936758/IV(a)/1> Freshly wet-spun polyacrylonitrile filaments are washed by moving a tow of the filaments through an elongated washing zone and flowing a wash liquid through the zone counter to the direction of tow movement therein while maintaining regions of wash liquid turbulence at spaced intervals along the zone.  The process may be carried out in an apparatus comprising a sloping trough, means for causing the tow to travel upwards through the trough, means for introducing a wash liquid into the upper portion of the trough and allowing it to flow under the action of gravity down the trough in a direction counter to the travel of the tow and in intimate contact therewith and means for maintaining regions of liquid turbulence at spaced points along the trough.  As shown in the drawing, the two 10 is delivered to the lower end of a washer 11 by a pair of draw rollers 12 and is withdrawn from the upper end of the washer by pairs of draw rollers 13 and 14.  The washer 11 comprises a sloping trough with sides high enough to confine a body of wash liquid such as water flowing down the trough and supplied to the upper end of the trough from the nozzle 16.  The wash liquid is discharged from the lower end of the trough into the receiver 15 from which it is led to a solvent recovery unit. The outlet of the nozzle 16 is in the form of a slot adapted to p  supply the wash liquid in the form of a flat stream covering the full width of the trough 11. Additional wash liquid is introduced at spaced points along the bottom of the trough from conduits 20 fed from a header 21 and provided with valves 22.  The conduits 20 define with the bottom of the trough 11 an acute angle such that the entering wash liquid flows partly in the same direction of travel as the tow and partly across the tow between adjacent filaments.  The cross-sections of the apertures of the conduits 20 in the bottom of the trough 11 are such as fully to cover the width of the tow.  The wash liquid is introduced from the conduits 20 at a velocity in excess of the velocity of the flow of wash liquid down the trough 11.  The pairs of rollers 13, 14 may be driven at a peripheral speed higher than that of the pair of rollers 12, for example at five times the peripheral speed of the latter, so that the tow is stretched as well as washed while travelling through the trough.  The tow may thereafter be caused to by-pass the hot water bath trough 17 and pass direct through a finish bath in trough 18 on its way to the drying rolls 19. Under these conditions the water supplied to the nozzle 16 and header 21 must be at a temperature of about 95\s2. Preferably the tow may be stretched between the draw rollers 14 and the drying rollers 19 while being passed through water at not less than 90\s2. in the short trough 17.  The trough is continuously replenished from a spout 23 and the water overflowing from the trough through funnels 24 and 25 into the header 26 is pumped by the pump 31 through pipe 27 to the valved delivery pipe 28 at the upper end of the trough 11.  Finish solution is supplied to the trough 18 through outlet 29 and is drained off for recycle through the conduit 30.  In this arrangement the tow in the trough 11 is not under tension and is very much more efficiently washed therein than when stretched in the trough.  The temperature of the wash liquid in the trough is preferably 20 DEG  to 60\s2.  A list is furnished of copolymers of acrylonitrile and blends of acrylonitrile polymers with other polymers which may be used for producing the tow, the overall polyacrylonitrile content of these copolymers and mixtures being at least 80%.  The invention enables polyacrylonitrile filaments to be washed at higher speeds than is possible in conventional cascade washers.