[Problem] To provide: a carbon fiber precursor fiber that can efficiently produce a carbon fiber at a low cost which is excellent in mechanical strengths even without an infusibilization treatment; a carbon fiber; and a method for producing the carbon fiber.

[Solution] A carbon fiber precursor fiber of the present invention includes a polymer containing a constituent unit represented by General Formula (1) below:

##STR00001## where in the General Formula (1), X and Y each independently represent a divalent substituent, a single bond, or a structure forming a fused ring by sharing one side of two adjacent rings, and the divalent substituent is selected from the group consisting of —O—, —S—, —OSO—, —NH—, —CO—, —CH.sub.2—, and —CH(CH.sub.3).sub.2—.

The present invention relates to a method for manufacturing carbon composite fibers and carbon nanofibers, and more particularly, to a method for manufacturing carbon composite fiber with greatly improved specific tensile strength, specific modulus, electrical conductivity, and thermal conductivity.

The present invention relates to a method for manufacturing carbon composite fibers and carbon nanofibers, and more particularly, to a method for manufacturing carbon composite fiber with greatly improved specific tensile strength, specific modulus, electrical conductivity, and thermal conductivity.

To provide a carbon fiber precursor fiber that can efficiently produce a carbon fiber excellent in mechanical strength without an infusibilization treatment; a carbon fiber; and a method for producing the carbon fiber. The carbon fiber precursor fiber includes a polymer represented by General Formula (1) below: ##STR00001## where in the General Formula (1), Ar.sub.1 represents an aryl group expressed by any one of Structural Formulas (1) to (5) below, and Ar.sub.2 represents an aryl group expressed by Structural Formula (6) or (7) below: ##STR00002##

To provide a carbon fiber precursor fiber that can efficiently produce a carbon fiber excellent in mechanical strength without an infusibilization treatment; a carbon fiber; and a method for producing the carbon fiber. The carbon fiber precursor fiber includes a polymer represented by General Formula (1) below: ##STR00001## where in the General Formula (1), Ar.sub.1 represents an aryl group expressed by any one of Structural Formulas (1) to (5) below, and Ar.sub.2 represents an aryl group expressed by Structural Formula (6) or (7) below: ##STR00002##

Disclosed is a method for producing a hollow fiber carbon membrane using a hollow fiber carbon membrane-forming material by means of a dry method or dry-wet method comprising a spinning step, a drying step, an infusibilization step, and a carbonization step as basic steps; wherein in the infusibilization step, heat treatment is performed at least two times at different temperatures, with the second temperature being higher than the first temperature. It is preferable that the second heat treatment is performed directly after the first treatment is performed, without once cooling to room temperature. The obtained hollow fiber carbon membrane has improved permeability, without reducing its separation coefficient.

Disclosed is a method for producing a hollow fiber carbon membrane using a hollow fiber carbon membrane-forming material by means of a dry method or dry-wet method comprising a spinning step, a drying step, an infusibilization step, and a carbonization step as basic steps; wherein in the infusibilization step, heat treatment is performed at least two times at different temperatures, with the second temperature being higher than the first temperature. It is preferable that the second heat treatment is performed directly after the first treatment is performed, without once cooling to room temperature. The obtained hollow fiber carbon membrane has improved permeability, without reducing its separation coefficient.

A hollow fiber carbon membrane is produced by preparing a membrane-forming dope for carbon membranes by dissolving polyphenylene oxide in an amount giving a concentration of 15 to 40 wt. % in the membrane-forming dope, and sulfur in an amount giving a ratio of 0.2 to 3.0 wt. % based on the polyphenylene oxide, in a solvent capable of dissolving these components; preparing the membrane-forming dope for carbon membranes into a hollow shape by means of a spinning method in accordance with a non-solvent induced separation method using a double annular nozzle; performing a crosslinking treatment at 200 to 240° C. in the air; then performing an infusibilization treatment by heating at 250 to 350° C.; and further performing a carbonization treatment by heating at 450 to 850° C. in an inert atmosphere or under vacuum.

A hollow fiber carbon membrane is produced by preparing a membrane-forming dope for carbon membranes by dissolving polyphenylene oxide in an amount giving a concentration of 15 to 40 wt. % in the membrane-forming dope, and sulfur in an amount giving a ratio of 0.2 to 3.0 wt. % based on the polyphenylene oxide, in a solvent capable of dissolving these components; preparing the membrane-forming dope for carbon membranes into a hollow shape by means of a spinning method in accordance with a non-solvent induced separation method using a double annular nozzle; performing a crosslinking treatment at 200 to 240° C. in the air; then performing an infusibilization treatment by heating at 250 to 350° C.; and further performing a carbonization treatment by heating at 450 to 850° C. in an inert atmosphere or under vacuum.

The present invention provides a porous carbon fiber which has an excellent permeation amount and excellent pressure resistance, which is prevented from the occurrence of detachment or cracking at an interface, and which can exhibit excellent properties needed for use as a support for a fluid separation membrane. The present invention is a porous carbon fiber having a bicontinuous porous structure, wherein

the average value R.sub.ave of the R value of the outer surface and the R value of the inside is 1.0 or more and 1.8 or less,

the absolute value ΔR of the difference between the R value of the outer surface and the R value of the inside is 0.05 or less, and

R value is a carbonization progression degree calculated from a Raman spectrum in accordance with the following formula:

R value=(intensity of scattering spectrum at 1360 cm.sup.−1)/(intensity of scattering spectrum at 1600 cm.sup.−1).