Acrylonitrile swollen fiber for carbon fiber, precursor fiber bundle, stabilized fiber bundle, carbon fiber bundle and production methods thereof

Abstract

Provided is a carbon fiber bundle for obtaining a fiber-reinforced plastic having high mechanical characteristics. An acrylonitrile swollen fiber for a carbon fiber having openings of 10 nm or more in width in the circumference direction of the swollen fiber at a ratio in the range of 0.3 openings/μm2 or more and 2 openings/μm2 or less on the surface of the swollen fiber, and the swollen fiber is not treated with a finishing oil agent. A precursor fiber obtained by treating the swollen fiber with a silicone-based finishing oil agent has a silicon content of 1700 ppm or more and 5000 ppm or less, and the silicon content is 50 ppm or more and 300 ppm or less after the finishing oil agent is washed away with methyl ethyl ketone by using a Soxhlet extraction apparatus for 8 hours. The fiber is preferably an acrylonitrile copolymer containing acrylonitrile in an amount of 96.0 mass % or more and 99.7 mass % or less and an unsaturated hydrocarbon having at least one carboxyl group or ester group in an amount of 0.3 mass % or more and 4.0 mass % or less.

1 - 3 . (canceled) 
     
     
         4 . A method of producing a swollen fiber, comprising:
 (i) preparing a dope at a temperature of 50° C. or more and 70° C. or less by dissolving an acrylonitrile-based copolymer, which is obtained by copolymerizing acrylonitrile in an amount of 96.0 mass % or more and 99.7 mass % or less and an unsaturated hydrocarbon having at least one carboxyl group or ester group in an amount of 0.3 mass % or more and 4.0 mass % or less, as essential components, in an organic solvent in a concentration in the range of 20 mass % or more and 25 mass % or less;   (ii) obtaining a coagulated fiber bundle containing the organic solvent by ejecting the dope from ejection holes into the air by use of a dry-wet spinning method, followed by coagulating in a coagulation bath constituted of an aqueous solution containing an organic solvent in a concentration of 78.0 mass % or more and 82.0 mass % or less, at a temperature of −5° C. or more and 20° C. or less;   (iii) drawing the coagulated fiber bundle in the air at a ratio in the range of 1.0 time or more and 1.25 times or less, followed by further drawing in a warm aqueous solution containing an organic solvent, a total draw ratio of both drawing processes being 2.6 times or more and 4.0 times or less; and   (iv) subsequently removing the solvent with warm water and further drawing in hot water at a ratio of 0.98 times or more and 2.0 times or less.   
     
     
         5 . The method according to  claim 4 , wherein the organic solvent is either dimethyl formamide or dimethyl acetamide. 
     
     
         6 . The method according to  claim 4 , wherein a draw ratio in the warm aqueous solution is 2.5 times or more and 4.0 times or less. 
     
     
         7 - 8 . (canceled) 
     
     
         9 . A method of producing a precursor fiber bundle for a carbon fiber, comprising applying a finishing oil agent containing silicone compounds as main components to a bundle of the swollen fiber obtained by  claim 4 , in an amount of 0.8 mass % or more and 1.6 mass % or less based on 100 mass % of the swollen fiber, followed by drying and then drawing by a heat drawing method or a steam drawing method at a ratio in the range of 1.8 times or more and 6.0 times or less. 
     
     
         10 . The method according to  claim 9 , wherein as the silicone compound, an amino-modified silicone compound satisfying the following conditions (1) and (2) is used:
 (1) kinematic viscosity at 25° C. is 50 cSt or more and 5000 cSt or less, and   (2) amino equivalent mass is 1,700 g/mol or more and 15,000 g/mol or less.   
     
     
         11 . A method of producing a precursor fiber bundle for a carbon fiber by applying a finishing oil agent containing silicone compounds as main components to a bundle of an acrylonitrile swollen fiber for a carbon fiber having openings of 10 nm or more in width in the circumference direction of the swollen fiber at a ratio in the range of 0.3 openings/μm 2  or more and 2 openings/μm 2  or less on the surface of the swollen fiber, and that is not treated with a finishing oil agent. 
     
     
         12 . A method of producing a stabilized fiber bundle comprising feeding the precursor fiber bundle obtained by the method according to  claim 11  to a hot-air circulation type oven for stabilization at a temperature of 220 to 260° C. for 30 minutes or more and 100 minutes or less, thereby applying heat treatment at an extension rate of 0% or more and 10% or less under an oxidizing atmosphere, and the method satisfying the following conditions:
 (1) intensity ratio (B/A) of peak A (2θ=25°) and peak B (2θ=17°) in the equatorial-line direction, which is determined by wide angle x-ray diffraction measurement of the fiber bundle, is 1.3 or more, 
 (2) orientation degree of peak B is 80% or more, 
 (3) orientation degree of peak A is 79% or more, and 
 (4) density is 1.335 g/cm 3  or more and 1.360 g/cm 3  or less. 
 
     
     
         13 . A method of producing a stabilized fiber bundle comprising feeding a precursor fiber bundle to a hot-air circulation type oven for stabilization at a temperature of 220 to 260° C. for 30 minutes or more and 100 minutes or less, thereby applying heat treatment at an extension rate of 0% or more and 10% or less under an oxidizing atmosphere, and the method satisfying the following conditions:
 (1) intensity ratio (B/A) of peak A (2θ=25°) and peak B (2θ=17°) in the equatorial-line direction, which is determined by wide angle x-ray diffraction measurement of the fiber bundle, is 1.3 or more, 
 (2) orientation degree of peak B is 80% or more, 
 (3) orientation degree of peak A is 79% or more, and 
 (4) density is 1.335 g/cm 3  or more and 1.360 g/cm 3  or less, 
 wherein, prior to the feeding, the precursor fiber bundle is obtained by copolymerizing acrylonitrile in an amount of 96.0 mass % or more and 99.7 mass % or less and an unsaturated hydrocarbon having at least one carboxyl group or ester group in an amount of 0.3 mass % or more and 4.0 mass % or less, as essential components, and having a silicon content of 1700 ppm or more and 5000 ppm or less when the fiber bundle is treated with a finishing oil agent containing silicone compounds as main components, wherein the silicon content is 50 ppm or more and 300 ppm or less after the finishing oil agent is washed away with methyl ethyl ketone by using a Soxhlet extraction apparatus for 8 hours. 
 
     
     
         14 . The method of producing the stabilized fiber bundle according to  claim 12 , wherein extension treatment is separately performed in at least three sets of conditions: an extension rate of 3.0% or more and 8.0% or less at a fiber density in the range of 1.200 g/cm 3  or more and 1.260 g/cm 3  or less; an extension rate at 0.0% or more and 3.0% or less at a fiber density in the range of 1.240 g/cm 3  or more and 1.310 g/cm 3  or less; and an extension rate of −1.0% or more and 2.0% or less at a fiber density in the range of 1.300 g/cm 3  or more and 1.360 g/cm 3  or less. 
     
     
         15 - 20 . (canceled) 
     
     
         21 . A method of producing a carbon fiber bundle, comprising treating the precursor fiber bundle obtained by the method according to  claim 9  with heat under an oxidizing atmosphere to obtain a stabilized fiber bundle having a density of 1.335 g/cm 2  or more and 1.355 g/cm 3  or less; then performing heating in a first carbonization furnace having a temperature gradient of 300° C. or more and 700° C. or less under an inert atmosphere while extending the extension rate to a rate of 2% or more and 7% or less for 1.0 minute or more to 3.0 minutes or less; and subsequently performing a heat treatment in at least one carbonization furnace having a temperature gradient from 1000° C. to a desired temperature under an inert atmosphere while extending the extension rate to a rate of −6.0% or more and 2.0% or less for 1.0 minute or more and 5.0 minutes or less.