Patent GB-1193170-A (GB)
Title: Manufacture of Industrial Acrylic Fibers
IPC: D01F6/18
Filed: 1967-12-11
Abstract: 1,193,170. Industrial acrylic fibres. MONSANTO CO. 11 Dec., 1967 [12 Dec., 1966], No. 56243/67. Heading B5B. A method for the manufacture of an industrial filament of an acrylonitrile polymer having a tenacity of at least 3 grams per denier and an elongation at break of at least 15% at linear take-up speeds of at least 800 ft. per minute, is characterized by extruding a solution of a polymer of acrylonitrile into an inert gaseous medium for a distance of from # to 4 inches (0À32 to 10 cms.) to form a filamentary shaped polymer solution and then passing the thus formed filamentary shaped solution into a coagulation bath; passing the filament from the coagulation bath to a first godet and into a hot water bath at 50‹ to 100‹ C. for a distance sufficient to elevate the temperature of the filament to the temperature of the bath and then passing the filament to a first stretch godet having a peripheral speed of from 2 to 5 times the peripheral speed of said first godet to stretch the filament from 2 to 5 times the coagulated length; applying an antistatic finish to said filament and thereafter passing the filament over a series of rolls wherein the temperature is incrementally elevated from temperatures below about 100‹ C. up to about 170‹ C. to dry and collapse the filamentary structure and thereafter passing the filamentary structure to rolls at from 180‹ to 200‹ C. and passing the filament from rolls in the latter temperature range to a second stretch godet having a peripheral speed of from 2 to 5 times the speed of said first stretch godet to further stretch the filament to from 2 to 5 times, with the proviso that the total stretch imparted to the filament by said first and second stretch rolls is at least 9 times the length of the coagulated filament; and thereafter passing said filament to a heat relaxation zone wherein the filament is allowed to shrink at least about 10% of its length. Preferably, the coagulated filament is washed with water on said first godet and the first stretch lies between 3 and 4 times the coagulated length and the further stretch lies between 3 and 4 times the length of the filament after the first stretch. By acrylonitrile polymer is meant polyacrylonitrile, copolymers, and terpolymers of acrylonitrile, and blends of polyacrylonitrile and copolymers of acrylonitrile with other polymerizable mono-olefinic materials, as well as blends of polyacrylonitrile and such copolymers with small proportions of other polymeric materials, such as polystyrene. In general a polymer may be used which is made from a monomeric mixture of which acrylonitrile is at least 70% by weight of the polymerisable content. Besides polyacrylonitrile, useful copolymers are those of 80 or more per cent of acrylonitrile and 1 or more percent of other mono-olefinic monomers. A wide variety of suitable polymeric compositions is listed. Of particular utility are blends of polyacrylonitrile or a copolymer of more than 90% acrylonitrile and up to 10% vinyl acetate, and a copolymer of vinyl pyridine or an alkylsubstituted vinyl pyridine and acrylonitrile. Of particular utility also are blends of copolymers of 90 to 98% acrylonitrile and 10 to 2% vinyl acetate and sufficient copolymer of 10 to 70% acrylonitrile and 90 to 30% vinyl pyridine to produce a blended composition of a total of 2 to 10 weight per cent vinyl pyridine. Preferred spinning solvents include N,N-dimethyl formamide, butyrolactone, dimethyl sulphoxide and N,N-dimethylacetamide. Ethylene carbonate, and concentrated aqueous solutions of zinc chloride, calcium chloride, lithium bromide, cadmium bromide, or sodium thiocyanate, may also be used. The spinning solution may be maintained prior to and at extrusion at temperatures from about 20‹ to 180‹ C. A solution containing at least 10% acrylonitrile polymer is desirable. Preferably, the spinneret is positioned so that its face is between # and 1¢ inches (0À32 to 3À8 cms.) above the bath, and the gas between the spinneret and the coagulating bath through which the streams of polymer travel is normally air. The coagulating baths suitable for use in the invention normally contain a non-solvent for the acrylonitrile polymer e.g. water, or a mixture of a solvent and a non-solvent. Preferably, the solvent used in the coagulating bath is the same as that used in preparing the polymer solution. Desirably, the coagulating bath contains 20% to 80% solvent, and its temperature range is suitably from -40‹ to + 80‹ C. Baths at the lower temperatures should contain high concentrations of solvent. The filaments may be given a travel in the coagulating bath, e.g. from 2 to 24 inches (5À08 to 61 cms.) or more by employment of two suitably spaced guides and withdrawal rolls. Between the spinneret and the withdrawal rolls, the filaments are subjected to a desired substantial attenuation. Washing may be accomplished either by spraying water on the filaments travelling around positively driven rolls as the tow leaves the coagulation bath, or may be accomplished in the hot water stretch bath. Examples are given.