Patent GB-453156-A (GB)
Title: Improvements in the production and treatment of artificial filaments, threads, yarns, foils and similar materials containing organic derivatives of cellulose
IPC: D01F2/28
Filed: 1935-03-07
Abstract: In processes wherein artificial filaments, threads, yarns, ribbons and similar materials having a base of organic derivatives of cellulose are treated with a mixture of a swelling agent and a non-solvent for the cellulose derivative, the materials are subjected in the presence of the said mixture to treatment with acid salts adapted to decrease the solubility of the said swelling agent in the said non-solvent The term acid salt is used to mean a polybasic acid salt still containing replaceable hydrogen and having an acid reaction in solution.  The acid salt is preferably highly soluble in the nonsolvent and insoluble in the swelling agent.  Examples of suitable salts are ammonium, sodium and potassium dihydrogen phosphates, bisulphates, bisulphites which are acidic, and acid salts of polybasic organic acids, e.g. sodium and potassium hydrogen tartrates and acid sodium and potassium citrates and oxalates.  A coagulating solution may consist of a strong, preferably aqueous solution of a swelling agent to which an acid salt has been added, or a solution of an organic derivative of cellulose in a neutral organic medium containing a swelling agent of higher boiling point than the nonsolvent of the coagulating solution may be extruded into a coagulating medium consisting of a solution of a swelling agent in water or other non-solvent containing an acid salt.  When spinning acetone solutions of cellulose acetate, aqueous coagulating media containing 25--65 per cent of solvents such as diacetone alcohol, diethyl tartrate or ethyl lactate may be employed.  The acid salt may be in any suitable concentration provided that it does not cause actual separation of the swelling agent from the non-solvent. Suitable proportions are 1--10 per cent.  Products produced by web spinning may also be softened continuously with coagulation, by media containing swelling agents, non-solvents and acid salts, and stretched if desired very rapidly and to a high degree, e.g. 500 or 1000 per cent of their unstretched length. Formed products may also be softened for stretching according to the invention.  The mixture of solvent and non-solvent used for softening may contain the acid salt or the salt may be applied to the products after they have been wetted with the mixture.  The mixtures may be applied by bath, roller or wick treatment or by spraying.  Or the softening mixture may be applied in vapour form. The material may be in the form of hanks but the treatments are preferably applied in a bobbin to bobbin winding operation.  The stretching operation may take place in one or more stages. Suitable solvents are acetone, diacetone alcohol, ethyl lactate, diethyl tartrate, dioxane or esters and ether-esters of olefine glycols, e.g. glycol monoacetate and methyl glycol mono-acetate. The non-solvent is preferably water but may be an ether, alcohol or hydrocarbon.  The process may be effected at normal temperature and pressures or at super-atmospheric temperatures and/or pressures.  Stretching may be to a low degree, e.g. 150--200 per cent of the original length or to a higher degree, e.g. 400--600 per cent. The lustre of the products may be altered by adjusting the conditions of the process.  Products of low lustre produced according to this invention are not relustred by treatments such as are described in Specifications 259,265 and 259,266, [both in Class 2 (ii)].  In an example a 25 per cent solution of cellulose acetate in acetone is spun through orifices of 0,08 mm. diameter into a coagulating bath consisting of 45 parts by weight of diacetone alcohol, 8 parts by weight of sodium bisulphate and 47 parts by weight of water.  The filaments are withdrawn from the bath at a speed of 60--70 metres per minute, the supply of solution being so adjusted that the products are stretched to 7 or 8 times their unstretched length.  After washing the filaments are wound on bobbins or collected in a centrifugal box. Specifications 343,062, 391,158, and 391,480 also are referred to. According to the Provisional Specification, foils and similar materials may be treated according to the invention, and the term acid salt is used in a wider sense and includes acid salts of fatty acids and alkali metals, e.g. acid potassium acetate.