GB645969A - Improvements in and relating to the production of viscose rayon threads - Google Patents

Abstract

Artificial threads are produced from viscose by extruding viscose into a coagulating bath and subjecting the thread thus formed without any break to liquid treatment and to drying and winding on to a package wherein a liquid containing a bleaching agent and which will be destroyed, before any appreciable degradation of the cellulose occurs, by reaction with impurities present and by heat under the conditions prevailing immediately preceding and during the drying step, is applied to the thread and the thread containing the agent is dried. The preferred bleaching agent is chlorine which may be in the form of an aqueous solution of chlorine or of a hypochlorite such as sodium hypochlorite, or may be an aqueous suspension of calcium chloro-hypochlorite (bleaching powder). The bleaching liquid may also contain a mild alkali and/or a small proportion of a soft finishing agent such as an emulsified oil. The liquid may contain from below 20 to over 100 parts, e.g. 500 parts, per million of available chlorine. In an illustrated example viscose is extruded from a jet 1 into a coagulating bath 2 containing sulphuric acid, sodium sulphate and zinc sulphate to form a thread which is withdrawn from the bath by a thread-advancing reel 5 and passes from thence over a series of thread-advancing reels 6, 9, 12 and 15 arranged in echelon and driven by gearing 18. The thread 4 is treated on reel 6 with an aqueous 1 per cent sulphuric acid solution at 85 DEG C. <PICT:0645969/IV (a)/1> applied from the pipe 7, the used liquid being collected in the drip pan 8, and similarly on reel 12 with an aqueous bleaching solution at 25 DEG C. containing 0.02 per cent of sodium bicarbonate and an amount of sodium hypochlorite equivalent to 25 parts of available chlorine per million parts of solution. The thread is then passed immediately to a steam-heated drying reel 15 at 110 DEG C. and finally collected on a cap-spinning device 17. Prior to the application of the bleach solution the thread may be washed on the reel 9 with hot water. The bleaching agent may be partially removed by a washing treatment before the thread is dried. Data are furnished showing the effect on the tensile properties of threads of bleaching with various concentrations of available chlorine. Specifications 413,413, [Group IV], 413,414, [Group IX], 474,973, [Group IV], and 645,171 are referred to.