GB340437A - Improvements in the production of artificial materials by wet spinning processes - Google Patents

Abstract

The wet-coagulation processes of the parent Specification and of Specification 340,436, for the manufacture of filaments, threads, films &c., from solutions of cellulose acetate or other organic esters of cellulose or of cellulose esters in which processes the solutions are extruded into coagulation baths in the presence of such quantities of solvent for the cellulose derivative that the coagulated products emerge in a plastic state, are modified by first coagulating the filaments &c. and thereafter immediately bringing them into a plastic state as by passage through a secondary bath containing solvents for the cellulose derivative in relatively high concentration, for example by using baths identical in composition with those referred to in the parent Specification. The filaments emerging from the secondary baths may have acquired such a state of plasticity that if brought together they will coalesce. The following may be employed as non-solvents in the secondary baths,-water; methyl and ethyl alcohols and their homologues; hydrocarbons such as benzene, toluene, gasoline and kerosene. Organic solvents less volatile than the non-solvent liquid are preferably employed in the secondary bath; for example with water or alcohol as the non-solvent there may be used diacetone-alcohol, diethyl tartrate, mono- or diacetin, and ethyl lactate; and mixtures of solvents of low volatility may be employed, or the solvent of high volatility such as acetone may be used in conjunction with a solvent of low volatility such as diacetone-alcohol. The concentration of the solvent in the secondary bath depends on the conditions of spinning and the product desired; in general 25-65 per cent solutions are suitable. Before collecting the products, excess of solvent should be washed out or otherwise removed to prevent coalescence of the filaments, for example, by washing with water, salt solutions or solutions of solvent of lower concentration, conveniently by using solutions of decreasing concentrations. The washing may be effected by spraying or in a centrifugal spinning box. The solvents employed are preferably such that by reason of their innocuous properties a residue of solvent may be permitted to remain in the washed products. As coagulation baths, water or the other above-specified non-solvent liquids may be used, and the non-solvent liquid selected should be the same as that of the secondary bath or one readily mixible therewith; and the coagulation baths may also contain solvents, preferably organic solvents, for the cellulose derivative as is referred to in Specifications 177,868 and 179,234, [both in Class 2 (ii), Cellulose &c.]. A convenient arrangement is to employ a coagulation bath containing a solvent for the cellulose derivative, and a secondary bath consisting of the same constituents but containing a higher proportion of the solvent medium. The further treatment may also be applied to products which have been made according to the processes of the parent Specification and of Specification 340,436. The filaments &c. may be stretched during their passage through the coagulation and secondary baths, to produce fine denier filaments. The secondary bath may contain a lubricant such as an oil, present either in the form of an emulsion or as a layer on the bath. According to the Provisional Specification non-solvent media may be added to the spinning solutions.