Abstract: Provided are carbon fiber bundles which have high knot strength even if the single fiber fineness is large, and which have excellent handling properties and processability. The carbon fiber bundles have a single fiber fineness of 0.8-2.5 dtex, knot strength of 298 N/mm2 or greater. This method of producing carbon fibers having knot strength of 298 N/mm2 or greater involves a heat treatment step for heat treating, for 50-150 minutes, specific polyacrylonitrile-based precursor fiber bundles described in the description in an oxidizing atmosphere rising in temperature in the temperature range of 220-300° C.

Abstract: Provided are carbon fiber bundles which have high knot strength even if the single fiber fineness is large, and which have excellent handling properties and processability. The carbon fiber bundles have a single fiber fineness of 0.8-2.5 dtex, knot strength of 298 N/mm2 or greater. This method of producing carbon fibers having knot strength of 298 N/mm2 or greater involves a heat treatment step for heat treating, for 50-150 minutes, specific polyacrylonitrile-based precursor fiber bundles described in the description in an oxidizing atmosphere rising in temperature in the temperature range of 220-300° C.

Abstract: Provided are carbon fiber bundles which have high knot strength even if the single fiber fineness is large, and which have excellent handling properties and processability. The carbon fiber bundles have a single fiber fineness of 0.8-2.5 dtex, knot strength of 298 N/mm2 or greater. This method of producing carbon fibers having knot strength of 298 N/mm2 or greater involves a heat treatment step for heat treating, for 50-150 minutes, specific polyacrylonitrile-based precursor fiber bundles described in the description in an oxidizing atmosphere rising in temperature in the temperature range of 220-300° C.

Abstract: Provided are carbon fibers which have a thicker single fiber fineness of the polyacrylonitrile-based precursor fiber bundles and lower production costs, and which have excellent mechanical properties. Also provided are: carbon fiber bundles having a single fiber fineness of 0.8-2.1 dtex, a strand strength of 4.9 GPa or greater, and a strand elastic modulus of 200 GPa or greater; carbon fiber bundles having a single fiber fineness of 0.8-2.5 dtex, a strand strength of 3.0 GPa or greater, and a strand elastic modulus of 240 GPa or greater; and an optimal method for producing said carbon fiber bundles. carbon fiber bundles having a single fiber fineness of 0.8-2.5 dtex, a strand strength of 3.0 GPa or greater, and a strand elastic modulus of 240 GPa or greater; and an optimal method for producing said carbon fiber bundles.

Abstract: Provided are: chopped carbon fiber bundles which have high fluidity without decreasing the dispersibility of carbon fibers and the physical properties of a molded product; and a method for producing chopped carbon fiber bundles with high productivity. Chopped carbon fiber bundles, each of which contain a carbon fiber bundle having a total fineness of from 25,000 dtex to 45,000 dtex (inclusive) and a sizing agent in an amount of from 1% by mass to 5% by mass (inclusive) relative to the total mass of the chopped carbon fiber bundle. The length (L) of each chopped carbon fiber bundle along the fiber direction of the carbon fiber bundle is from 1 mm to 50 mm (inclusive); the ratio of the longest diameter (Dmax) to the shortest diameter (Dmin) of a cross section perpendicular to the fiber direction of each chopped carbon fiber bundle, namely Dmax/Dmin is from 6.0 to 18.0 (inclusive); and the orientation parameter of the single fibers present in the surface of each chopped carbon fiber bundle is 4.0 or less.

Abstract: Provided is a carbon fiber manufacturing method including a surface treatment step of ejecting an ozone solution in which ozone is dissolved in solvent from a fluid ejecting port toward a carbon fiber bundle and causing the ozone solution to pass between single fibers of the carbon fiber bundle so as to contact surfaces of the single fibers so that the surfaces of carbon fibers are treated by the ozone solution. Also, provided is a carbon fiber subjected to a surface treatment by the carbon fiber manufacturing method.

Abstract: Provided are: chopped carbon fiber bundles which have high fluidity without decreasing the dispersibility of carbon fibers and the physical properties of a molded product; and a method for producing chopped carbon fiber bundles with high productivity. Chopped carbon fiber bundles, each of which contain a carbon fiber bundle having a total fineness of from 25,000 dtex to 45,000 dtex (inclusive) and a sizing agent in an amount of from 1% by mass to 5% by mass (inclusive) relative to the total mass of the chopped carbon fiber bundle. The length (L) of each chopped carbon fiber bundle along the fiber direction of the carbon fiber bundle is from 1 mm to 50 mm (inclusive); the ratio of the longest diameter (Dmax) to the shortest diameter (Dmin) of a cross section perpendicular to the fiber direction of each chopped carbon fiber bundle, namely Dmax/Dmin is from 6.0 to 18.0 (inclusive); and the orientation parameter of the single fibers present in the surface of each chopped carbon fiber bundle is 4.0 or less.

Abstract: Provided are carbon fiber bundles which have high knot strength even if the single fiber fineness is large, and which have excellent handling properties and processability. The carbon fiber bundles have a single fiber fineness of 0.8-2.5 dtex, knot strength of 298 N/mm2 or greater. This method of producing carbon fibers having knot strength of 298 N/mm2 or greater involves a heat treatment step for heat treating, for 50-150 minutes, specific polyacrylonitrile-based precursor fiber bundles described in the description in an oxidizing atmosphere rising in temperature in the temperature range of 220-300° C.

Abstract: Provided are carbon fibers which have a thicker single fiber fineness of the polyacrylonitrile-based precursor fiber bundles and lower production costs, and which have excellent mechanical properties. Also provided are: carbon fiber bundles having a single fiber fineness of 0.8-2.1 dtex, a strand strength of 4.9 GPa or greater, and a strand elastic modulus of 200 GPa or greater; carbon fiber bundles having a single fiber fineness of 0.8-2.5 dtex, a strand strength of 3.0 GPa or greater, and a strand elastic modulus of 240 GPa or greater; and an optimal method for producing said carbon fiber bundles. carbon fiber bundles having a single fiber fineness of 0.8-2.5 dtex, a strand strength of 3.0 GPa or greater, and a strand elastic modulus of 240 GPa or greater; and an optimal method for producing said carbon fiber bundles.

Abstract: Provided is a carbon fiber manufacturing method including a surface treatment step of ejecting an ozone solution in which ozone is dissolved in solvent from a fluid ejecting port toward a carbon fiber bundle and causing the ozone solution to pass between single fibers of the carbon fiber bundle so as to contact surfaces of the single fibers so that the surfaces of carbon fibers are treated by the ozone solution. Also, provided is a carbon fiber subjected to a surface treatment by the carbon fiber manufacturing method.

Abstract: Provided are: a carbon fiber bundle which has a large value of single-fiber fineness and excellent productivity and which, despite this, contains few interlaced single fibers therein and has excellent spreadability; and precursor fibers which are suitable for use in producing the carbon fiber bundle. The precursor fibers are a carbon-fiber-precursor acrylic fiber bundle which comprises a polyacrylonitrile copolymer comprising 95-99 mol % acrylonitrile units and 1-5 mol % hydroxyalkyl (meth)acrylate units and which has a single-fiber fineness of 1.5-5.0 dtex. In the acrylic fiber bundle, the cross-section of each single fiber which is perpendicular to the fiber axis has a shape that has a roundness of 0.9 or less.

Abstract: It is an object of the present invention to provide a package in an optimal form obtained by winding a carbon fiber bundle having a fineness of 25,000 to 35,000 deniers, which has a high wound density and is less apt to become loose, and a method for producing the same. The present invention is a carbon fiber package obtained by winding a carbon fiber bundle having a fineness of 25,000 to 35,000 deniers on a bobbin in a square-end type, wherein the width per unit fineness of the carbon fiber bundle is in the range of 0.30×10?3 to 0.63×10?3 mm/denier, the traverse angle in the beginning of winding is in the range of 13 to 14°, the traverse angle in the end of winding is 3° or larger, and the fractional portion W0 of the winding ratio W is in the range of 0.07 to 0.08.

Abstract: It is an object of the present invention to provide a package in an optimal form obtained by winding a carbon fiber bundle having a fineness of 25,000 to 35,000 deniers, which has a high wound density and is less apt to become loose, and a method for producing the same. The present invention is a carbon fiber package obtained by winding a carbon fiber bundle having a fineness of 25,000 to 35,000 deniers on a bobbin in a square-end type, wherein the width per unit fineness of the carbon fiber bundle is in the range of 0.30×10?3 to 0.63×10?3 mm/denier, the traverse angle in the beginning of winding is in the range of 13 to 14°, the traverse angle in the end of winding is 3° or larger, and the fractional portion W0 of the winding ratio W is in the range of 0.07 to 0.08.