Patent GB-729472-A (GB)
Title: Improvements in and relating to the production of artificial threads, fibres, filaments and the like
Inventor: NEVILLE ALBERT WALTER BENNETT
IPC: D01F6/18
Filed: 1952-08-05
Abstract: A solution of an acrylonitrile polymer in a solvent mixture consisting essentially of water, a water-miscible diluent and one or more highly water-soluble salts selected from the alkali metal, alkaline earth metal, ammonium and guanidine thiocyanates, lithium bromide, lithium and sodium iodides and zinc chloride, the salt constituting at least 35 per cent by weight of the solvent mixture, is extruded into a coagulant bath consisting of an aqueous solution containing the same salt and the same diluent in substantially the same relative proportions as they are present in the polymer solution such that the bath contains at least 10 per cent by volume of the solvent mixture, and the concentrations of the salt and the diluent in the coagulating bath are maintained below the value at which spinning would break down.  The diluent may be a water-miscible aliphatic liquid containing not more than 6 carbon atoms and one alcoholic hydroxyl group in the molecule, e.g. methyl or ethyl alcohol, ethylene glycol mono methyl or ethyl ether, ethyl lactate or diacetone alcohol, or it may be acetone or acetonitrile.  The filaments which are obtained may be dried and then heated under conditions such that they can relax freely so that they become crimped.  Yarns in continuous length may be passed under very little tension through a heated block and the crimped yarns so obtained may be cut into staple fibres. Alternatively, the dried threads may be cut into staple fibres and the fibres may be crimped by treating them with boiling water or with steam.  The drying of the thread may be effected on a heated thread-advancing reel so as to obtain fibres of lustrous appearance.  If the drying is effected partly on a heated reel and is then completed at ordinary temperature, the fibres after crimping are generally of a dull appearance.  To maintain the desired concentration of diluent and salt, water or a wash liquor may be added to the coagulating bath at a controlled rate during the spinning operation.  When methyl alcohol is used as the diluent, recovery of the constituents in the excess spinning bath can be effected by distilling off first the methyl alcohol and then water, usually under reduced pressure, until the point is reached when, on adding the recovered methyl alcohol to the residue, the required solvent mixture is produced.  In an example, a copolymer of 94 per cent of acrylonitrile and 6 per cent of methyl acrylate (M.W. 100,000) is dissolved to form a 15 per cent solution in a solvent mixture consisting of 27.5 parts by weight of water, 27.5 parts of methyl alcohol and 45 parts of sodium thiocyanate.  The solution is extruded into a coagulating bath consisting of 80 volumes of water and 20 volumes of the solvent mixture at 5 DEG  C.  The resultant thread is washed and then stretched 1000 per cent in steam.  It is dried on a drying reel, relaxed 5 per cent by passage through a block heated to 350 DEG  C., and then collected.  Specifications 714,530 and 718,997 are referred to.