Patent GB-1082899-A (GB)
Title: A proces for the production of viscose rayon
IPC: D01F2/06
Filed: 1965-10-19
Abstract: 1,082,899. Regenerated cellulose filaments. TACHIKAWA RESEARCH INSTITUTE. Oct. 19, 1965 [Nov. 2, 1964; Dec, 23, 1964], No. 44324/65. Heading B5B. In a process for the production of highly polymerized viscose rayon filaments or fibres which are obtained by spinning a high viscosity viscose having a ball-fall viscosity of more than 250 seconds at room temperature into a low acid concentration spinning bath containing less than 50 g./1. of sulphuric acid, stretching the spun filaments or fibres thus obtained and then heat-setting the same, the step of relaxing the spun filaments or fibres is effected by one or more of the following treatments: (a) relaxing the spun filaments or fibres during stretching at a temperature of less than 30 C. with an aqueous solution of an acid having a pH of 1À4 or more, (b) relaxing the spun filaments or fibres at a temperature of from 10 to 40 C. between stretching and heat-setting with water or an aqueous solution having a pH of about 7 containing an extremely small quantity of an acid, an alkali or a salt, and (c) relaxing the spun filaments or fibres at a temperature of from 30 to 80 C. just prior to heat-setting with an aqueous solution of an acid salt or a normal salt giving an alkaline solution having a pH of from 8 to 10À5. Desirably, the pH of the aqueous medium employed is dependent on the degree of development of the fibre structure of the filaments or fibres, and the aqueous solution, or at least one of the aqueous solutions, may contain a quaternary ammonium salt in a concentration of less than 1 g./1. In general, the stages of the spun filaments from the spinning bath to prior to the heat-setting stage are divided into three main categories, viz. the stretching stage, the stage immediately after the stretching, and the stage where the fibre structure has developed a fair amount after travelling a certain distance in air after the stretching. At a stage where the development of the fibre structure is still fairly low, for instance, at the stretching stage, the filaments or fibres must be treated with a diluted acid liquor whose pH is more than 1À4 in order to obtain the desired improvement. The acid concentration of this relaxing liquor is lower than that of the liquor previously attached to the fibres. Thus the acid concentration in the liquor surrounding the fibres is lowered, and accordingly the strain which is to occur at stretching is restrained. The relaxing-liquor in this case must be acidic, as water or an alkaline liquor is too strong for the relaxation of the fibre structure (vide Example 1). At a time when the cellulose molecules have a parallel orientation, and hydrogen-bond formation in the amorphous regions has been advanced to a certain extent, for instance at a time immediately after the stretching, the filaments or fibres must be treated using water or a solution whose pH- value is 7 or thereabouts containing extremely small quantities of acids, alkalies, or salts. By this treatment the amorphous regions only are relaxed and the desired improvement is obtained. At this stage, acid liquors have no improving effect but on the other hand the relaxing action of alkaline liquors is still too strong (vide Example 2). At a time when the fibre structure in crystal regions as well as in amorphous regions has been so advanced that the heat-setting may be applied, the improving effect is obtained by treating the filaments or fibres using an alkaline solution whose pH value is from 8 to 10À5. In this case, neutral salts or acid salts, whose aqueous solutions are alkaline, are suitable as the treating agents, especially such acid salts as sodium bicarbonate and disodium hydrogen phosphate (vide Examples 3, 4 and 5). The application of a multi-step treatment at various stages is also possible; a two-step treatment is illustrated in Example 6, and a three-step treatment in Example 7. By means of the process of the invention it is possible to obtain an improvement in the loop and knot tenacities, of the highly-polymerized rayon filament or fibre without any material deterioration of its so-called polynosic characteristics.