Abstract: Disclosed are carbon fibers consisting of a plurality of single filaments, wherein the carbon fibers as a resin impregnated strand are characterized by satisfying the following relations: &sgr;≧11.1−0.75 d where &sgr; is the tensile strength of said carbon fibers as a resin impregnated strand in GPa, and d is the average diameter of said single filaments in &mgr;m, and RD≦0.05 where RD is the difference in crystallinity between the inner and outer layers of each of the single filaments evaluated with RAMAN, and an acrylic fibers for producing the carbon fibers and a process for producing the acrylic fibers.

Abstract: Disclosed are carbon fibers consisting of a plurality of single filaments, wherein the carbon fibers as a resin impregnated strand are characterized by satisfying the following relations: &sgr;≧11.1-0.75d where &sgr; is the tensile strength of said carbon fibers as a resin impregnated strand in GPa, and d is the average diameter of said single filaments in &mgr;m, and RD≧0.05 where RD is the difference in crystallinity between the inner and outer layers of each of the single filaments evaluated with RAMAN, and an acrylic fibers for producing the carbon fibers and a process for producing the acrylic fibers.

Abstract: Disclosed are carbon fibers consisting of a plurality of single filaments, wherein the carbon fibers as a resin impregnated strand are characterized by satisfying the following relations: &sgr;≧11.1−0.75d where &sgr; is the tensile strength of said carbon fibers as a resin impregnated strand in GPa, and d is the average diameter of said single filaments in &mgr;m, and RD≦0.05 where RD is the difference in crystallinity between the inner and outer layers of each of the single filaments evaluated with RAMAN, and an acrylic fibers for producing the carbon fibers and a process for producing the acrylic fibers.

Abstract: Disclosed are carbon fibers consisting of a plurality of single filaments, wherein the carbon fibers as a resin impregnated strand are characterized by satisfying the following relations: &sgr;≧11.1−0.75 d where a is the tensile strength of said carbon fibers as a resin impregnated strand in GPa, and d is the average diameter of said single filaments in &mgr;m, and RD≦0.05 where RD is the difference in crystallinity between the inner and outer layers of each of the single filaments evaluated with RAMAN, and an acrylic fibers for producing the carbon fibers and a process for producing the acrylic fibers.

Abstract: Disclosed are carbon fibers consisting of a plurality of single filaments, wherein the carbon fibers as a resin impregnated strand are characterized by satisfying the following relations: &sgr;≧11.1−0.75 d where &sgr; is the tensile strength of said carbon fibers as a resin impregnated strand in GPa, and d is the average diameter of said single filaments in &mgr;m, and RD≦0.05 where RD is the difference in crystallinity between the inner and outer layers of each of the single filaments evaluated with RAMAN, and an acrylic fibers for producing the carbon fibers and a process for producing the acrylic fibers.

Abstract: The object of the present invention is to provide carbon fibers with high tensile strength as a resin impregnated strand even if the single filaments constituting the carbon fibers are thick. The carbon fibers of the present invention consisting of a plurality of single filaments are characterized by satisfying the following relation:.sigma..gtoreq.11.1-0.75dwhere .sigma. is the tensile strength of the carbon fibers as a resin impregnated strand (in GPa) and d is the average diameter of the single filaments (in .mu.m). The carbon fibers can be preferably used as a material for forming energy-related apparatuses such as CNG tanks, fly wheels, wind mills and turbine blades, a material for reinforcing structural members of roads, bridge piers, etc., and also a material for forming or reinforcing architectural members such as timber and curtain walls.

Abstract: There is disclosed a prepreg including noncircular cross-section carbon fibers and a matrix resin having a flexural elastic modulus of 2.7 GPa or more and a water absorption of 3.4% or less under hot-wet conditions after curing; and another prepreg including carbon fibers and a matrix resin having an open-hole compression strength under hot-wet conditions and a compression strength after impact under room-temperature conditions of a quasi-isotropic material after curing of each 275 MPa or more. Carbon fiber-reinforced composite materials produced by curing these prepregs are excellent in open-hole compression strength under hot-wet conditions and in compression strength after impact, and can be suitably used especially as an aircraft primary structure material.

Abstract: Carbon fibers with a surface oxygen concentration (O/C ratio) of 0.20 or less as measured by X-ray photoelectron spectroscopy, a surface concentration of hydroxyl groups (C--OH/C ratio) of 0.5% or greater as measured by chemical modification X-ray photoelectron spectroscopy and a surface concentration of carboxylic groups (COOH/C ratio) of 2.0% or less as measured by chemical modification X-ray photoelectron spectroscopy, and an aliphatic compound applied as a sizing agent which has multiple epoxy groups or an aromatic compound which has multiple epoxy groups, the number of atoms between the epoxy groups and an aromatic ring being 6 or greater.

Abstract: A process for preparing carbon fibers including electrolyzing a carbon fiber in an alkaline aqueous solution, or electrolyzing a carbon fiber in an acidic aqueous solution followed by washing with an alkaline aqueous solution, and then applying a sizing agent of an aliphatic compound with multiple epoxy groups or an aromatic compound with multiple epoxy groups in which the number of atoms between the epoxy groups and an aromatic ring is 6 or greater. Alternatively, the carbon fibers are prepared by electrolyzing a carbon fiber in an aqueous solution of an ammonium salt and then applying a sizing agent of an aliphatic compound with multiple epoxy groups or an aromatic compound with multiple epoxy groups in which the number of atoms between the epoxy groups and an aromatic ring is 6 or greater.

Abstract: Carbon fibers with a surface oxygen concentration (O/C ratio) of 0.20 or less as measured by X-ray photoelectron spectroscopy, a surface concentration of hydroxyl groups (C-OH/C ratio) of 0.5% or greater as measured by chemical modification X-ray photoelectron spectroscopy and a surface concentration of carboxylic groups (COOH/C ratio) of 2.0% or less as measured by chemical modification X-ray photoelectron spectroscopy, and an aliphatic compound applied as a sizing agent which has multiple epoxy groups or an aromatic compound which has multiple epoxy groups, the number of atoms between the epoxy groups and an aromatic ring being 6 or greater.

Abstract: Carbon fibers with a surface oxygen concentration (O/C ratio) of 0.20 or less as measured by X-ray photoelectron spectroscopy, a surface concentration of hydroxyl groups (C--OH/C ratio) of 0.5% or greater as measured by chemical modification X-ray photoelectron spectroscopy and a surface concentration of carboxylic groups (COOH/C ratio) of 2.0% or less as measured by chemical modification X-ray photoelectron spectroscopy, and comprising applied as a sizing agent an aliphatic compound which has multiple epoxy groups or an aromatic compound which has multiple epoxy groups, the number of atoms between the epoxy groups and an aromatic ring being 6 or greater.

Abstract: Disclosed is a carbon fiber made from an acrylic fiber, the carbon crystal of which has a crystal size Lc of 15 to 65 .ANG. as determined by the wide angle X-ray diffractometry. This carbon fiber has regions with a lower crystallinity in the surface layer portion thereof than that of the central portion thereof, and the compressive strength .sigma..sub.cf (GPa) of the single filament thereof determined by the loop method satisfies formula (I):.sigma..sub.cf .gtoreq.10.78-0.1176.times. Lc (I).The carbon fiber is produced by ionizing in vacuo an atom or molecule which is solid or gaseous at normal temperature, accelerating the ionized atom or molecule by an electric field, and implanting the accelerated ionized atom or molecule in a bundle of carbon fibers.