Patent GB-683403-A (GB)
Title: Improvements in the manufacture of artificial filaments and related articles
IPC: D01D5/04
Filed: 1949-12-16
Abstract: Filamentary materials are produced by extruding a solution of filament-forming substance in a volatile solvent into an evaporative medium in a spinning zone, <PICT:0683403/IV (a)/1> drawing the material from the zone at a speed exceeding 800 metres per minute and, by means of pressure or vacuum generated outside the spinning zone, causing the medium to travel through the whole or nearly the whole length of the spinning zone in contact with, and in the same direction as, the material at such a speed that the force required to draw the filamentary material from the spinning zone is 0.02-0.2 grams per denier.  The filamentary p  materials may be continuous fibres of the type commonly used in the production of yarns of moderate denier, coarse fibres, or artificial straw, braid or ribbon, of regular or irregular cross-section.  The speed of the evaporative medium may be 35-95 per cent of the spinning speed, but in no case more than 600 metres per minute below the spinning speed.  The evaporative medium may be admitted under pressure into the spinning cell at or near the spinning jet or may preferably be drawn from the other end of the spinning cell by suction.  The concentration of solvent vapour in the air leaving the spinning cell should be above 1.2 per cent, e.g. about 1.5 per cent.  The spinning cell may have a square, rectangular or elliptical cross-section, but preferably a circular cross-section.  The filament-forming material may be a cellulose derivative such as cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetatepropionate, cellulose acetate-butyrate, ethyl cellulose, or a polyvinyl compound such as polyvinyl acetate, polyvinyl chloride or a vinyl acetate-vinyl chloride copolymer.  The solvents may be acetone, ethylene dichloride, methylene chloride or ethyl alcohol.  The evaporative medium may be nitrogen, carbon dioxide, or (preferably) air.  In an illustrated example, a hot solution of cellulose acetate in acetone is extruded from a spinning jet 11 in the form of a bundle of filaments 13 into the spinning cell 14 through which flows a stream of air having a mean velocity through the narrower section 17 of the cell of 1200 metres per minute. Steam at 175 DEG  C. is admitted into the jackets 19, 21 and 22.  The filaments are drawn from the cell through the aperture 33 by means of the feed roller 34 at 1400 metres per minute.  The filaments pass through a region of relatively still air before entering the cell and owing to the relatively low air velocity in the short upper wide diameter section of the cell 16 and the intermediate tapered section 18, the air flows smoothly past the filaments during the first portion of their travel through the cell and increases gradually in velocity without turbulence before entering the long, narrow section of the cell 17.  The air is exhausted from the cell to a solvent recovery system (not shown) by means of the pipe 36.  The invention enables higher spinning speeds to be used than hitherto without breakage of or detriment to the filaments.  The Specification as open to inspection under Sect. 91 discloses also the extrusion of a solution of the filament-forming substance in a volatile solvent into an evaporative medium at a rate such that, in the absence of movement of the evaporative medium, the force required to draw the filaments from the spinning zone would exceed 0.2 grams per denier, and causing the evaporative medium to travel in contact with, and in the same direction as, the filaments at a velocity such that the force required is 0.02-0.2 gram per denier.  Alternatively, the velocity of the evaporative medium may be equal to 35-95 per cent of the spinning speed (no limits being, however, specified for the latter).  This subject-matter does not appear in the Specification as accepted.