Novel process for spinning heat resistant polyamide fibers

摘要

1,106,190. Polyamide filaments. MONSANTO CO. 14 June, 1965 [19 June, 1964], No. 24982/65. Heading B5B. Shaped articles, especially fibres, are made from wholly aromatic polyamide solutions by extruding the solution in a downward direction as a stream by forcing the solution through a shaped orifice into a gaseous medium in which only a small amount of the solvent is evaporated from the stream; directing the stream through the medium for a short distance and into a coagulating bath comprising a liquid that is a precipitant for the polymer and an extractant for the solvent; withdrawing the thus-formed article from the coagulating bath; passing the article through a first wash liquid while relaxing or stretching; washing the article a second time; drying the article; and passing the article through a heated environment under tension to produce a shaped article. Preferably, the polyamide solution contains 10 to 30% polyamide by solution weight, the temperature of said solution is from 25‹ to 100‹ C.; said distance is from 1/8 inch to 1¢ inch, said coagulating bath comprises a liquid that is a precipitant for the polymer stream and an extractant for the solvent at ambient temperatures; said first wash liquid is boiling water, said relaxation or stretching is from less from one to four times; said stream is washed a second time with water at a temperature of from 15‹ to 65‹ C.; said fibre is dried at a temperature of from 120‹ to 160‹ C.; and said fibre is passed through a heated environment at a temperature of from 300‹ to 500‹ C. under sufficient tension to stretch said fibre to from one to four times its length. In such a preferred method, the polyamide may be dissolved in a lower dialkyl amide (e.g. dimethyl acetamide or dimethyl formamide), containing from 1% to 10% by weight of an alkali metal halide or an alkaline earth metal halide (e.g. lithium chloride, lithium bromide, or calcium chloride), said solution temperature is from 40‹ to 100‹ C.; said distance is from “ inch to 1 inch, said bath comprises from about 1% to 10% by weight of a lower dialkyl amide (e.g. those previously specified) and from about 99% to 90% by weight of water at ambient temperatitres; and said fibre is withdrawn from the coagulating bath at a rate sufficient to impart a jet stretch of from about 2 to 7 times its length. Suitably the polyamide solution has an inherent viscosity of from about 1À2 to 2À0; the coagulating bath is held at from about 10‹ to 30‹ C.; and comprises a mixture of from about 70% to 95% water by weight, and from about 30% to 5% of a polyalkalene glycol; said fibre is moved through a first wash liquid comprising water at a temperature of from about 15‹ C. to 60‹ C.; and said fibre is moved through a second wash liquid comprising water at a temperature of from about 15‹ to 65‹ C. Alternatively, the polyamide solution may contain from 10% to 22% polyamide by solution weight and have an inherent viscosity of from about 2.0 to 3.0; the coagulating bath may comprise from about 1% to 10% by weight of the solvent and from 99% to 90% by weight of water at ambient temperatures; and said fibre is washed a second time with water at a temperature of from about 15‹ to 65‹ C. Other solvents which may be used for spinning solution preparation include trifluoro acetic acid, dimethyl sulphoxide, N - methyl - 2 - pyrrolidone, and hexamethylphosphonic triamide. These solvents usually have their solvency power enhanced by adding the aforementioned metal salts to the spinning solution. Mixtures of two or more of these solvents may be used, and concentrated sulphuric acid may -also be used. Poly-N, N1 - m - - phenylene bis (m - benzamide)2, 6- naphthylene - dicarbonamide, Poly - N, N1 m - phenylene bis m - benzamide) terephthalamide, poly(m - phenyleneisophthalamide), poly - 3, 41 - diaminobenzanilide isophthalamide, and poly - N, N1 - m - phenylene bis (m - benzamide) 4,41 - biphenyldicarbonamide fibres may be made using an amide solution containing 15% to 22% by solution weight of polyamide, 70% to 98% dimethyl acetamide, 1% to 10% lithium chloride and 1% to 5% water, stretching being from 0.88 to 2.80 times the length of the fibre while passing through the hot wash liquid and the heated environment comprising a pre-heater oven at a temperature of from 300‹ to 500‹ C., and a shoe heated to a temperature of from 300‹ to 450‹ C. Poly-N, N1 - m - phenylene bis (m - benzamide) terephthalamide fibres having a tenacity of at least 6 d.p.f. may be made by extruding a solution of from 15% to 22% by solution weight of poly-N, N1-m-phenylene bis (m-benzamide) terephthalamide having an inherent viscosity of above 2.0, dissolved in a solvent comprising 70% to 80% dimethylacetamide, 1% to 10% lithium chloride and 1% to 5% by weight water, in a downward direction into a stream by forcing the solution through a shaped orifice into a gaseous medium comprising air in which only a small amount of the solvent is evaporated from the stream as a gas; directing the stream through the air for a distance of “ inch to 1 inch and into a coagulating bath comprising 99% to 90% by weight of water and 1% to 10% by weight of the solvent; withdrawing the thusformed fibre from the coagulating bath; passing the fibre through a first wash bath containing a solvent extraction agent selected from the group consisting of hydroxy compounds containing 1 to 3 hydroxyl groups and up to 6 carbon atoms, polyalkylene glycols of 600 to 2000 molecular weight, mixtures of water soluble amides with from 40% to 70% by weight water, and mixtures of the hydroxy compounds with up to 50% water, then through a wash liquid comprising water at 50‹ C. while stretching the fibre from 1.10 to 2À80 times its length to orient the polymer molecules thereof; washing the fibre with water at a temperature of from 15‹ to 65‹ C.; drying the fibre at a temperature of from about 120‹ to about 150‹ C; and subjecting the fibre to a hot draw by advancing the fibre over a shoe heated to a temperature of from 300‹ to 450‹ C., while stretching the fibre to from 1 to 4 times its length. By the processes described wholly aromatic polyamide fibres may be made having a birefringence of at least 0.150 and a zero strength temperature of at least 500‹ C., and tenacities of from 1.0 to 3.0 d.p.f. or of at least 6 d.p.f., according to the method used. Examples are given.