GB900134A - A process for improving the properties of viscose rayon yarn or filaments and staple fibre - Google Patents

Abstract

Viscose filaments, after emerging from the coagulating bath, are subjected to heat-treatment while they are being stretched, and are maintained in a stretched condition and in contact with hot water and/or steam for at least 10 seconds. Heat-treatment may be effected at a temperature higher than that at which the filaments emerge from the bath, this higher temperature being 65 DEG C. or above. Where hot water is used, the water temperature may be 85 DEG -92 DEG C. and the duration of treatment from 30 to 90 seconds. Heat-treatment may be effected in a single step or treating zone or in more than one step or treating zone, in such a way that the combined treatment takes at least 10 seconds and preferably 30-90 seconds. Filaments may be made to travel during treatment at a speed higher than 50 m./min. Filaments may be fully stretched by a quick pass through a stretch trough in which hot acidic water or steam is circulated and the stretched filaments led to a device where they are held under tension for a period such that the total duration of contact with the treating medium is at least 10 seconds and preferably 30-90 seconds, the speed of the filaments being 50 m./min. or more. In a preferred method, a viscose solution is used containing, by weight, 5,5-8,5% caustic soda, 6,0-9,0% of cellulose, 0,5-4% (based on the cellulose) of polyethylene oxide of molecular weight 1,000-4,000 or other known modifier which improves the tenacity of the filaments and enables filaments having a non-serrated, smooth cross-section to be obtained, and is spun at a degree of ripeness above 10 DEG Hottenroth (salt point about 4), at a viscosity of 40 to 200 poises (at 20 DEG C.) into a coagulating bath containing by weight, 6-10% sulphuric acid, 2,5-12,0% anhydrous zinc sulphate, and 12,0-25,0% anhydrous sodium sulphate, and of specific gravity 1,260-1,310 at 35 DEG C. The coagulating bath may also contain a modifier, e.g. polyethylene oxide of molecular weight 1,000-4,000, and may be maintained at 45 DEG -65 DEG C. Spinning may be effected in a trough giving a horizontal immersion of above 50 cms. or vertical or inclined immersion of more than 30 cms. On emerging from the coagulating bath the filaments may be led into a trough or other convenient treating device in which they are stretched while remaining in contact with hot water which may be acidic at 65 DEG C. or above, or with steam, the travel of the filaments in the treating device being so arranged that they are held under tension for from 30-90 seconds while being heated by the hot water or steam. Filaments so made are characterized by a high wet and conditioned tenacity, and a high ratio of wet to conditioned tenacity. In examples, staple fibres made from such filaments of denier 1,5-2 have wet tenacities of 2,76-3,04 g./denier, conditioned tenacities of 3,28-3,70 g./denier, and ratios of wet to conditioned tenacity of 80-84%.