Patent GB-652594-A (GB)
Title: Improvements in and relating to the production of viscose rayon threads
IPC: D01F11/02
Filed: 1948-12-24
Abstract: A continuous process for the production of viscose rayon thread comprises the steps of extruding viscose through a jet into a coagulating bath, withdrawing the resultant thread from the coagulating bath, and while it is being passed without a break over one or more thread-advancing devices, treating the thread with an aqueous acid solution at a temperature not lower than 65 DEG  C. to continue the regeneration of the cellulose in the thread, treating the thread while still in an acid condition with an aqueous solution containing an oxidizing agent, washing the thread substantially free from the oxidizing agent and subsequently drying the thread.  The term "thread" is used to include threads, filaments, fibres, yarns, strips, films and the like. The process may be applied to pot or spool spinning processes but is preferably carried out over a series of thread-advancing reels or over one multistage reel.  It is preferable to advance the threads over a reel before treatment with the aqueous acid solution.  This acid solution may be of the same composition as the coagulating bath, or it may be a solution of, say, sulphuric acid of concentration equal to or less than that of the coagulating bath, preferably 1-5 per cent by weight.  The amount of dissolved salts should be less than that in the coagulating bath. The oxidizing agent should be chosen so that under the conditions obtaining the cellulose is not degraded.  Suitable oxidizing agents are hypochlorous, hypobromous, hypoiodous, chlorous, bromous and iodous acids, their alkali and alkaline earth salts and chloride of lime.  Water-soluble per compounds such as peroxides, permanganates, perborates, persilicates, percarbonates and persulphates may also be used, hydrogen peroxide, alkali and alkaline earth peroxides, sodium and ammonium persulphates and the alkali permanganates being specified. Hypochlorite solutions containing 0.005 to 0.01 per cent available chlorine at a pH range of 6.0 to 10.0 are satisfactory. Chlorite solutions should have pH of 3.0 to 7.0.  The washing may be carried out with water between 30 DEG  and 90 DEG  C.  The threads may be stretched before or during the treatment with hot aqueous acid to about 10-50 per cent.  In an example, viscose containing 6.5 per cent sodium hydroxide and 8.0 per cent cellulose at a salt point of 4.0 is extruded through a multi-hole spinneret into a coagulating bath containing 12 per cent sulphuric acid, 22 per cent sodium sulphate, 1.5 per cent zinc sulphate and 0.1 per cent of a cation-active agent.  The wet thread is stored on a reel from which it is led to a second reel rotating at a higher speed to give a 25 per cent stretch.  A solution of 2.5 per cent sulphuric acid and 5 per cent sodium sulphate at 70 DEG  C. is applied to the discharge end of the reel and owing to the tilting thereof flows to the delivery end and off into a trough beneath the reel from whence it may be recovered if desired.  The thread is then passed to another reel upon which it is treated with a dilute solution of sodium hypochlorite at pH 9.0 and 50 DEG  C. containing 0.01 per cent available chlorine.  This solution is likewise fed to the discharge end but is allowed to run to waste.  On the third reel the thread is washed with soft water at 90 DEG  C., the water running off at the delivery end being used to make up the sodium hypochlorite solution. Finally, it is led to a drying reel enclosed in a chamber and thence to a cap-spinning device. Example 5 describes the application of the process to a multistage reel.  Specifications 413,413, 413,414. [Group IX], and 618,633, are referred to.