Patent GB-858532-A (GB)
Title: Improvements in the manufacture of artificial filamentary material
Inventor: GROOMBRIDGE DENIS WILLIAM
IPC: D01F2/28
Filed: 1956-08-23
Abstract: <PICT:0858532/IV(a)/1> An acetic acid solution of cellulose triacetate is wet-spun into a coagulant bath of aqueous acetic acid, the filaments are withdrawn from the coagulant after a time sufficient to give them coherence but insufficient to allow them to attain equilibrium with the coagulant, and are then stretched while still wet with liquor carried from the coagulant bath and after the acetic acid content of the liquor has been considerably increased by diffusion into it of acetic acid from the filaments. The acetic acid solution of cellulose triacetate obtained by acetylation of cellulose may be used as a spinning solution, after hydrolysis of excess acetic anhydride with water and neutralization of the sulphuric acid catalyst, e.g. with magnesium carbonate or acetate, the solution then being heat treated prior to spinning according to Specification 858,533.  The coagulant is preferably an aqueous acetic acid of not over 25% by weight concentration, at a temperature such that its swelling action on cellulose triacetate is not greater than that of an 18% by weight aqueous acetic acid at 18 DEG C.  Preferably the filaments are not stretched until the acetic acid content of the filaments and the acetic acid content of the liquid carried by them have attained substantial equilibrium, and desirably the acetic acid concentration of the liquid carried by the filaments when they are stretched is 40-55% by weight.  After the filaments have left the coagulant bath part of the liquid which they carry may be removed mechanically, the amount so removed being such that, when the equilibrium between the acetic acid content of the filaments and that of the liquid carried by them has been established, the concentration of the acetic acid in the liquid is from 40-55% by weight.  The coagulant may be contained in a vessel of small capacity (i.e. of cross-section little more than sufficient to accomodate the spinning jet), and the coagulant carried away from the vessel by the filaments may be compensated for by introducing into the vessel either water or aqueous acetic acid of lower concentration than the bulk of the coagulant in the vessel, the coagulant becoming enriched to the desired concentration in the vessel with acetic acid from the spinning solution.  Apparatus as shown comprises a vessel 33 for coagulant, means 34 for feeding liquid into the vessel, a spinning jet 35 near the bottom of the vessel and facing upwards, means 39 for drawing filamentary material from the vessel, the vessel being of small capacity as defined above, and means 19, 20 spaced from the vessel for stretching filamentary material after it has left the vessel. Preferably the vessel is substantially vertical and its upper edge is 1-8 inches higher than the face of the spinning jet. Adjustable means may also be provided whereby a predetermined amount of liquid can be removed from filamentary material after it has emerged from the vessel and before it reaches the stretching means (e.g. a yarn guide 37, or squeeze rolls).