Abstract: Acrylic fiber comprising an acrylonitrile-based copolymer comprising 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units and 0.5% by weight or more of methacrylic acid units, the percentage by weight (A) of acrylamide units and the percentage by weight (M) of methacrylic acid units in the copolymer satisfying the following equations (I) and (II), and adsorbed iodine in an amount of 1% by weight or less based on the weight of the copolymer:X=0.21 to 0.23 (I)M+A.sup.x =1.82 to 2.18 (II)A copolymer having the above-mentioned composition is spun by a wet process, while adjusting the modulus in tension of coagulated fiber to approximately 2.0-3.0 g/d, wherein d means denier in terms of the weight of polymer in the coagulated fiber. There is provided acrylic fiber which permits production of carbon fiber with a high tensile strength and a high tensile modulus by pyrolysis for a shorter time.

Abstract: A carbon fiber of a high tenacity and a high modulus of elasticity having a fiber diameter of 1 to 6 .mu.m, a strand tenacity of 430 kg/mm.sup.2 or more, a strand modulus of elasticity of 28 ton/mm.sup.2 or more and a density of 1.755 g/cm.sup.3 or more, and a process for producing the same.The above-mentioned carbon fiber has extremely useful properties as a raw material for composite materials to be used not only for sporting goods such as fishing rods or golf clubs but also in aerospace industries.

Abstract: A flameresisting apparatus in which two sections, referred to as roller compartments, enclosing a series of rollers provided face to face with one another for transferring precursor fiber, are separated from a heat treatment section by two walls facing each other. The walls include apertures for passage of the precursor fiber. Significantly, the two walls facing each other are provided at a distance which enables the precursor fiber to pass from one wall to the other in 5 to 60 seconds. The surface temperature of the rollers and the temperature of the roller compartments are maintained at a temperature of 10.degree. to 80.degree. C. lower than the temperature of the heat treatment compartment, but not lower than 180.degree. C. In addition, heated air is blown against the precursor fiber into the heat treatment compartment.

Abstract: Acrylonitrile precursor fibers are subjected to a flame-resisting treatment, in an oxidizing atmosphere, while being elongated at least 3%, until a density of 1.22 g/cm.sup.3 is reached. The fibers are further treated to increase density up to 1.40 g/cm.sup.3, and then heat treated while undergoing further elongation, followed by higher temperature heat treatment while under tension. The resulting fibers have excellent properties, including high strand tenacity, high strand modulus, and high density.

Abstract: The invention relates to a process for producing carbon fibers which comprises a continuous flame-resisting treatment of acrylic fibers in bundle form containing at least 90% by weight of acrylonitrile in an oxidizing atmosphere at temperatures of 250.degree. to 350.degree. C. by using a plurality of flame-resisting furnace different in heat treatment temperature under such conditions that the fiber density .rho.n after each stage of flame-resisting treatment may be maintained on the level defined by a specific conditional expression and so that the fiber density .rho.k after completion of the flame-resisting treatment may be from 1.34 to 1.40 g/ml, and successively are subjected to carbonizing treatment in an inert atmosphere.

Abstract: A process for producing a carbon fiber having a tenacity of 450 kg/mm.sup.2 or more, preferably 500 kg/mm.sup.2 or more, and a modulus of elasticity of 25 ton/mm.sup.2 or more which comprises subjecting a polyacrylonitrile-type fiber to a flame-resisting treatment in a flame-resisting treatment furnace provided with a plural number of driving rolls in an oxidizing atmosphere at 200.degree. to 400.degree. C. under application of multistep elongation, during said treatment the respective percentage of elongation in said multistep elongation being set respectively at a value which is equal to or within .+-.3% of the value of the percentage of elongation En indicating an inflection point Pn obtainable from the load and the percentage of elongation determined in advance by experimental measurements, and then subjecting the treated fiber to carbonization.