A method for producing polyacrylonitrile (PAN) fiber, the method comprising: (i) mixing PAN with an ionic liquid in which the PAN is soluble to produce a PAN composite melt in which the PAN is dissolved in the ionic liquid; (ii) melt spinning the PAN composite melt to produce the PAN fiber; and (iii) washing the PAN fiber with a solvent in which the ionic liquid is soluble to substantially remove the ionic liquid from the PAN fiber. Also described herein is a method for producing carbon fiber from the PAN fiber as produced above, the method comprising oxidatively stabilizing the PAN fiber produced in step (iii), followed by carbonizing the stabilized PAN fiber to produce the carbon fiber. The initially produced PAN fiber, stabilized PAN fiber, resulting carbon fiber, and articles made thereof are also described.

Provided is a resin composition including carbon fibers and a thermoplastic resin, in which the carbon fibers have a tensile elastic modulus E of 350 to 500 GPa, and the tensile elastic modulus E (GPa) and a loop fracture load A (N) satisfy the relationship of A≥−0.0017×E+1.02. This resin composition not only has a high moldability into a member of a complex shape by injection molding, but also can yield a molded article having excellent flexural modulus and excellent impact characteristics.

The present invention provides a method for producing a carbon fiber bundle, the method including steps (b) to (e) described below: (b) an oil agent application step of applying a silicone oil agent to a precursor fiber bundle to produce an oil-agent-attached precursor fiber bundle; (d) a stabilization step of subjecting the oil-agent-attached precursor fiber bundle to an oxidization treatment to produce an oxidized fiber bundle; and (e) a carbonization step of carbonizing the oxidized fiber bundle, wherein the silicone oil agent has a skin over time at 250° C. of less than 40 minutes.

A flexible, ignition resistant, non-electrically conductive biregional fiber is disclosed. The biregional fiber comprising an inner core region of a partially oxidized thermoplastic polymeric composition and a surrounding outer sheath region of a thermoset carbonaceous material.

Carbon fiber precursor treatment agents include a nonionic surfactant, an amino-modified silicone, and a dimethyl silicone with a kinematic viscosity at 25° C. of 5 to 200 mm.sup.2/s. The mass ratio of the content of the amino-modified silicone with respect to the content of the dimethyl silicone is 99.9/0.1 to 90/10. Alternatively, when the total content of the nonionic surfactant, the amino-modified silicone, and the dimethyl silicone is taken as 100 parts by mass, the nonionic surfactant is contained at a ratio of 9 to 85 parts by mass, the amino-modified silicone is contained at a ratio of 10 to 90.9 parts by mass, and the dimethyl silicone is contained at a ratio of 0.1 to 5 parts by mass.

A method of producing a carbon fiber bundle is provided, involving performing a flame-proof treatment to a carbon-fiber-precursor acryl fiber bundle having a single-fiber fineness of 1.5 dtex or more and 5.0 dtex or less, and having a roundness of 0.7 or more and 0.9 or less in a cross-section shape perpendicular to a fiber axis of the single fiber to obtain a flame-proofed fiber bundle; and performing a carbonization treatment to the flame-proofed fiber bundle.

A carbon fiber bundle is characterized in that a ratio (n/N) of a number n of pairs wherein a flaw of 50 nm in size or more is present on at least one of the fracture surfaces forming the pair to a total number N of pairs of fiber fracture surfaces selected at random after performing a single fiber tensile test for a gauge length of 10 mm is 35% or less, and in that a single-fiber diameter d is 4.3 μm or more.

A drawing method is provided which enables a pressurized steam drawing of an acrylonitrile-based fiber bundle used as the precursor fiber of the carbon fiber bundle. In particular, a drawing method is provided which realizes a high processability when this treatment is conducted at a high draw ratio and high speed. This invention is a method for producing an acrylonitrile-based fiber bundle which includes the steps of spinning a spinning solution containing an acrylonitrile-based copolymer, and subjecting the fiber bundle to a pressurized steam drawing in a pressurized steam drawing apparatus (A) having at least two zones which are a preheating zone on the fiber bundle inlet side and a heating zone on the fiber bundle exit side, the two zones being separated by a seal member. The preheating zone is in a pressurized steam atmosphere at 0.05 to 0.35 MPa, the heating zone is in a pressurized steam atmosphere at 0.45 to 0.70 MPa, temperature difference ΔT1 in the preheating zone of the steam drawing apparatus in the fiber bundle-moving direction defined in the specification is up to 5° C., and temperature difference ΔT2 in the preheating zone of the steam drawing apparatus in the cross-sectional direction of the steam drawing apparatus defined in the specification is up to 5° C.

Carbon fiber precursor treatment agents include a nonionic surfactant, an amino-modified silicone, and a dimethyl silicone with a kinematic viscosity at 25° C. of 5 to 200 mm.sup.2/s. The mass ratio of the content of the amino-modified silicone with respect to the content of the dimethyl silicone is 99.9/0.1 to 90/10. Alternatively, when the total content of the nonionic surfactant, the amino-modified silicone, and the dimethyl silicone is taken as 100 parts by mass, the nonionic surfactant is contained at a ratio of 9 to 85 parts by mass, the amino-modified silicone is contained at a ratio of 10 to 90.9 parts by mass, and the dimethyl silicone is contained at a ratio of 0.1 to 5 parts by mass.

The present invention relates to a method for producing an acrylonitrile-based fiber, the method including: providing a polymer solution including an acrylonitrile-based copolymer containing a carboxylic acid group; mixing 100 parts by weight of the polymer solution with 1 to 6 parts by weight of a hydrophilization solution containing an organic solvent and ammonia water in a weight ratio of 95:5 to 60:40 to prepare a spinning stock solution; and spinning the spinning stock solution. The method controls the viscosity of the spinning stock solution to improve the stretchability and strength of the acrylonitrile-based fiber, and suppresses the occurrence of gelation.