Patent GB-602533-A (GB)
Title: Improvements in or relating to the production of crinkled viscose filaments
IPC: D01F2/06
Filed: 1945-10-16
Abstract: Viscose is spun into a coagulating bath in which slow regeneration is effected while the filaments are under "low tension" and the regenerated filaments are subjected to "high tension" stretching while wet, causing them to develop the property of crinkling spontaneously when wet with water.  By "low tension" is meant such positive tension as is sufficient to draw the filaments through the bath at a speed in excess of the extrusion speed, i.e. a torsion of less than 0.3 g./denier. "High tension" stretching refers to tensions of above 0.5 g./denier and especially to tensions of 0.75 to 1.0 g./denier, the upper limit being the point at which the filaments become damaged. The slow regeneration is effected either by using a viscose of special composition with an ordinary Muller coagulating bath, or by an ordinary viscose with a regenerating bath of special composition.  The special composition viscose comprises a viscose of cellulose content 9-13 per cent, a caustic soda content 8-13 per cent and a cellulose to caustic soda ratio of 0.833 to 1.13 (the best results are obtained using a viscose containing 10 per cent of each and a ratio of 1.0), and this is spun into a bath comprising 125-145 g./litre sulphuric acid, 235-330 g./litre sodium sulphate and 12.5 g./litre zinc sulphate with or without 50 g./litre glucose.  When using an ordinary viscose (i.e. of cellulose content 7-8.5 per cent, caustic soda content 6-7.4 per cent and cellulose/caustic soda ratio about 1.15), the spinning bath comprises 90 g./litre sulphuric acid, 300 g./litre sodium sulphate and 42 g./litre zinc sulphate.  The regenerated filaments are subjected to a high degree of stretching in any appropriate manner and at any convenient time, for example while wet with the spinning bath, during or after washing, during or after bleaching, or after drying and re-wetting.  Dried filaments should be re-wetted in an aqueous swelling bath containing, say 1 per cent caustic soda or 5 per cent of dibenzyl dimethyl ammonium hydroxide (a wetting agent) before stretching.  The stretched filaments may be led while under tension through a bath containing saturated ammonium sulphate solution, which inhibits crinkling, and then they may be cut into staple, opened and dropped into water, whereupon they crinkle. The process is particularly applicable to the spinning of wool-like staple fibre having filament denier of 1-7 or lower.  The crinkled filaments are stable and repeated boiling does not impair the crinkles.  In an example, a viscose with a cellulose content 10 per cent and caustic soda content 10 per cent and salt point 5.8 is spun into an ordinary coagulating bath (140 g./litre H2SO4, 245 g./litre Na2SO4, 50 g./litre glucose and 12.5 g./litre ZnSO4) at 47 DEG  C. using a 100-hole spinneret having holes 0.0020 inch diameter.  The filaments are drawn out of the bath at a speed of 85 metres per minute and wound on a bobbin, washed acid free, stretched 30 per cent on a slasher and dried under tension. The dried yarn is skeined and immersed in a hot-water desulphurizing bath containing 1 per cent caustic soda, whereupon crinkling occurs immediately.  The crinkled skeins are bleached, oiled and dried.  In another example, a wood-pulp viscose having a 10 per cent cellulose content and a cellulose/caustic soda ratio of 1.0 and a salt point of 5.3 is spun at 47.5 DEG  C. into a coagulating bath of composition as in the previous example, but without glucose, and using a 480-hole spinneret, each hole being of 0.0030 inch diameter.  The filaments are drawn through the bath for a distance of 100 inches under a tension of 200 grams and wound on a bobbin at a speed of 85 metres per minute.  After being washed free from acid, the bobbins are stretched 30 per cent on a slasher and led through a bath containing 50 per cent (NH4)2SO4, excess solution being removed by a squeeze roll.  The bundle of filaments is cut into 4-inch staples, opened and dropped into water, crinkling immediately and spontaneously into 1-inch lengths.