Abstract: A knife cylinder for a rotary cutter capable to accommodate to increased cutting speed and width of a corrugated cardboard sheet in recent years and low in weight and rotatory inertia and having enough tensile strength, flexural and torsional rigidity, is provided. The cylinder body of the knife cylinder is a hollow cylindrical body consisting of layers of carbon fiber reinforced plastic and has tensile elastic modulus of 206 GPa or higher in axial direction thereof. Preferably the innermost layer is of a CFRP layer 41 with carbon fibers arranged to extend in circumferential direction of the cylinder body, and a plurality of sets of CFRP layers consisting of a layer 42 with carbon fibers arranged to extend in axial direction and layers 42, 44 with carbon fibers arranged to extend in directions inclined by ±30°˜±60° to axial direction of the cylinder are laminated on the innermost layer.

Abstract: Pitch based carbon fiber wherein the spread La of graphite crystallites constituting a fiber in the direction of layer plane is 1000 angstroms or less; the orientation angle &PSgr; in the direction of fiber axis is 10° or less, and the following relationship formulas (1) and (2) are satisfied: 0.70La−46&PSgr;>50  (1) 0.55La−76&PSgr;<500  (2).

Abstract: A short carbon fiber bundling mass is disclosed, which can provide a high-modulus fiber-reinforced resin composition and comprises short carbon fibers bundled by using a sizing agent and heated to a maximum temperature ranging from 1,600° C. to 3,300° C. in an inert gas atmosphere so as to be graphitized.

Abstract: A short carbon fiber bundling mass is disclosed, which can provide a high-modulus fiber-reinforced resin composition and comprises short carbon fibers bundled by using a sizing agent and heated to a maximum temperature ranging from 1,600.degree. C. to 3,300.degree. C. in an inert gas atmosphere so as to be graphitized.

Abstract: A carbon fiber woven fabric constituted by carbon fibers having a thermal conductivity of at least 400 W/m.multidot.K in the fiber axial direction, which has a FAW (weight per unit area of fabric) of at lest 400 g/m.sup.2.

Abstract: Pitch based carbon fibers characterized in that their thermal conductivity is at least 1,000 W/m.multidot.K as measured at room temperature, their electrical resistivity is at most 1.2 .mu..OMEGA.m, their tensile modulus is at least 95 ton/mm.sup.2, their compression strength is at least 30 kg/mm.sup.2, and the ratio of crack-free fibers to cracked fibers is from 5/95 to 30/70, where the crack-free fibers are fibers having no cracks in their cross section, and the cracked fibers are fibers having cracks in their cross section.

Abstract: A pitch based carbon fiber, having a thermal conductivity in the direction of the fiber axis of from 500 to 1,500 W/m.multidot.K, a tensile modulus of at least 85 ton/mm.sup.2, a compression strength of at least 35 kg/mm.sup.2, a laminated layer thickness, Lc, of graphite crystallites of from 30 to 50 nm, and a ratio thereto of a spread, La, of graphite crystallites in the direction of the layer plane, of at least 1.5, has high thermal conductivity, excellent compression strength and an excellent tensile modulus of elasticity. When a cross section of said fiber in the direction of the fiber axis is observed by a polarization microscope with 1,000 X magnifications, the domain size as observed is at most 500 nm.

Abstract: A pitch-type carbon fiber made from a pitch having 1 a glass transition temperature width of at most 40.degree. C. as measured by a differential scanning calorimeter, 2 a proportion of the optically anisotropic phase of at least 10% by volume, and 3 a quinoline-insoluble content of at most 5% by weight, as a spinning raw material pitch.

Abstract: A pitch-type carbon fiber made from a pitch having 1 a glass transition temperature width of at most 40.degree.C. as measured by a differential scanning calorimeter, 2 a proportion of the optically anisotropic phase of at least 10% by volume, and 3 a quinoline-insoluble content of at most 5% by weight, as a spinning raw material pitch.

Abstract: A process for producing carbon fibers having high strand strength, which comprises subjecting pitch fibers obtained by melt-spinning pitch, followed by gathering, to infusible treatment to obtain infusible fibers, followed by carbonization treatment, and if necessary, graphitization treatment, to obtain carbon fibers, wherein the infusible fibers or the carbon fibers are heat-treated in an atmosphere containing steam or carbon dioxide at a temperature of from 500.degree. to 1,800.degree. C.

Abstract: Spinning pitch for carbon fibers, which (1) has a glass transition temperature width of at most 60.degree. C. as measured by a differential scanning calorimeter, (2) contains at least 80% by volume an optically anisotropic phase, and (3) shows a shear viscosity of 200 poise at a temperature of from 270.degree. to 370.degree. C.