Patent GB-689407-A (GB)
Title: Spinning artificial filamentary materials
IPC: D01D5/04
Filed: 1950-11-13
Abstract: <PICT:0689407/IV (a)/1> Filaments, yarns, tow, ribbon and like products are made by extruding a solution of a filament-forming material in a volatile solvent through a spinneret into an evaporative medium in a spinning cell comprising a setting zone nearest to and a drying zone furthest from the spinneret, causing the medium to flow through the setting zone in counter-current to the extruded solution, whereby a large proportion of the solvent is evaporated and the solution is set in the form of filaments, causing the medium to flow through the drying zone concurrently with the filaments, whereby most or all of the remaining solvent is evaporated, and drawing the filaments from the drying zone at a rate of over 600 metres per minute, the rate of flow of the medium through the drying zone being such that the force required to draw the filaments from the drying zone does not exceed 0.2 gram per denier and is preferably between 0.02 and 0.2 gram per denier. The filamentary material is preferably cellulose acetate but may be cellulose propionate, butyrate, acetate propionate or acetate butyrate, ethyl cellulose, polyvinyl acetate, polyvinyl chloride, or a vinyl acetate vinyl chloride copolymer.  The volatile solvent is preferably acetone but may be ethylene dichloride, methylene chloride and ethyl alcohol, or chloroform and methyl or ethyl alcohol.  The evaporative medium may be air, nitrogen or carbon dioxide.  As shown, a heated acetone solution of cellulose acetate is fed under pressure to a spinneret 41 from which the solution is extruded in the form of filaments 44.  The upper part 45 of the spinning cell 46 constitutes the setting zone while the lower and much longer part 57 constitutes the drying zone.  Air is drawn through the zone 45 from the inlet duct 48 to the exhaust duct 47 leading to a solvent recovery plant and is heated by the coil 49. The lower end of the zone 45 is closed by means of a plate 53 having an aperture 56 for the passage of the filaments and carried by legs 54.  The zone 57 is unheated and is considerably smaller in cross-section than the zone 45.  The filaments 44, after passing from the aperture 56 through the open air, enter the zone 57 through the opening 58 and are drawn by means of the feed roll 63 through the chamber 59 and the aperture 62.  Air is drawn into the zone 57 through the opening 58 and is sucked out through the exhaust duct 65.  The filaments in their travel from the aperture 56 to the opening 58 may pass through a longitudinally split tube 66 and the upper end of the zone 57 may be provided with an air inlet 64.  The spinning speed may be 800 metres per minute or more and 60-80 per cent of the acetone may be removed in the zone 45.  In a modification the setting and drying zones are joined by a very short narrow duct through which the filaments pass and the drying zone is provided near its upper end with an air inlet duct.  The process enables high spinning speeds to be used without substantial reduction in the quality of the filaments or increase in the occurrence of filament breakages. Specification 683,403 is referred to.