Carbon fiber bundle and method of producing carbon fiber bundle

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/mm.sup.2 or greater. This method of producing carbon fibers having knot strength of 298 N/mm.sup.2 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.

Claims

1. A carbon fiber bundle having a single fiber fineness of at least 0.8 dtex to no more than 2.5 dtex, and a knot strength of at least 298 N/mm.sup.2, wherein the carbon fiber bundle is prepared by a heat treatment of a polyacrylonitrile-based precursor fiber bundle having a single fiber fineness of at least 1.7 dtex to no more than 5.0 dtex, wherein the polyacrylonitrile-based precursor fiber bundle consists of a polyacrylonitrile-based copolymer and a copolymer comprising 1 to 4.0 mole % of hydroxyalkyl methacrylate units.

2. The carbon fiber bundle according to claim 1, wherein the polyacrylonitrile-based precursor fiber bundle consists of a polyacrylonitrile-based copolymer and a copolymer comprising 1.2 to 4.0 mole % of hydroxyalkyl methacrylate units.

3. The carbon fiber bundle according to claim 1, wherein the polyacrylonitrile-based precursor fiber bundle consists of a polyacrylonitrile-based copolymer and a copolymer comprising 1.5 to 4.0 mole % of hydroxyalkyl methacrylate units.

4. The carbon fiber bundle according to claim 1, wherein the polyacrylonitrile-based precursor fiber bundle consists of a polyacrylonitrile-based copolymer and a copolymer comprising 1.5 to 3.0 mole % of hydroxyalkyl methacrylate units.

Description

EXAMPLES

(1) Although the present invention will be explained in further detail by showing Examples in the following, the present invention is not to be limited in any way by these Examples, etc.

(2) <Constant Velocity Temperature Rising Exothermic Curve of Precursor Fiber Bundle>

(3) The constant velocity temperature rising exothermic curve of the precursor fiber bundle was measured as follows by way of a heat flux-type differential scanning calorimeter. First, the precursor fiber bundle was cut to a length of 4.0 mm, 4.0 mg was precisely weighed, loaded into a 50 l-hermetically sealed sample container made of Ag manufactured by SII Inc. (trade name: P/N SSC000E030), and was covered by a mesh cover made of Cu manufactured by SII Inc. (trade name: P/N 50-037) (heat treated in air at 450 C. for 15 minutes). Next, it was measured from room temperature (30 C.) to 450 C. at conditions of heating rate of 10 C./min and air supply rate of 100 ml/min (standard of air supply rate: 30 C., 0.10 MPa) using a heat flux-type differential scanning calorimeter: DSC/220 (trade name) manufactured by SII Inc. The heat generation of 230 C. to 260 C. of the obtained constant velocity temperature rising exothermic curve was defined as heat amount Ja, and the heat generation of 260 C. to 290 C. was defined as heat amount Jb.

(4) <Measurement of Knot Strength of Carbon Fiber Bundle>

(5) The measurement of knot strength was implemented as follows. Gripping parts of 25 mm length were mounted to both ends of a 150-mm long carbon fiber bundle to make a test piece. Upon preparation of the test piece, doubling of carbon fiber bundles is performed by applying a load of 0.110.sup.3 N/denier. A knot was formed at substantially the center in this test piece, and a crosshead speed during pulling was implemented at 100 mm/min, and the maximum load value thereof was measured. Next, a value arrived at by dividing this maximum load value by the cross-sectional area of the carbon fiber bundle is defined as knot strength. The number of tests conducted was 12, the minimum and maximum values were discarded, and the average value of 10 was defined as the measured value of knot strength.

(6) <Measurement of Strand Strength and Strand Modulus of Elasticity>

(7) The strand strength and strand modulus of elasticity measured the tensile property of an epoxy resin impregnated strand based on the method of ASTM D4018.

(8) <Roundness of Carbon Fiber Bundle>

(9) (1) Preparation of Sample

(10) A carbon fiber bundle cut to a length of 5 cm was embedded in epoxy resin (Epomount base resin: Epomount hardener=100:9 (mass ratio)), then cut to 2 cm to expose a cross section, and mirror surface processed.

(11) (2) Etching Process of Observed Face

(12) Furthermore, in order to make the profile of a fiber clear, the cross section of the sample was etching processed by the following method.

(13) Apparatus Used: JEOL, JP-170 (trade name), plasma etching apparatus

(14) Treatment conditions: (atmospheric gas: Ar/O.sub.2=75/25 (volume ratio), plasma output: 50 W, vacuum: about 120 Pa, treatment time: 5 min)

(15) (3) SEM Observation

(16) The cross section of the sample obtained by (1) and (2) was observed using an SEM (PHILIPS FEI-XL20 (trade name)), and five photographs in which at least five fiber cross sections were captured on the screen were arbitrarily imaged.

(17) Roundness Measurement of Single Fiber of Carbon Fiber Bundle

(18) Using image analysis software (trade name: Image-Pro PLUS, produced by Nippon Roper K.K.), the profile of the fiber cross sections were traced, and the periphery L and surface area S were measured. Selecting 20 from five photographs arbitrarily, provided that at three fiber cross sections are from one photograph, each sample was measured, and the roundness was calculated according to the formula below:
Roundness=(4S)/L.sup.2

Example 1

(19) An acrylonitrile-based copolymer consisting of acrylonitrile units/2-hydroxyethyl methacrylate units=98.5/1.5 (mol %) was obtained by copolymerizing under the presence of acrylonitrile, 2-hydroxyethyl methacrylate, ammonium persulfate-ammonium hydrogensulfite and ferric sulfate by way of aqueous suspension polymerization. This polyacrylonitrile-based copolymer was dissolved in dimethylacetoamide to prepare a 21% by mass spinning dope. Through a spinneret with 24,000 holes and a hole diameter of 60 m (spinning nozzle), the spinning dope was discharged into a coagulation bath consisting of a dimethylacetoamide aqueous solution of 45% by mass concentration at a temperature of 35 C., and received at a rate 0.32 times the discharge linear velocity from the spinneret to obtain a fiber bundle (swollen line of thread). Next, this fiber bundle was drawn to 5.4 times simultaneously with water rinsing, was led to a first oil bath tank consisting of an oil-based treatment liquid in which an oil-based composition of amino-modified silicone/polyoxyethylene(6)lauryl ether=91/9 (mass ratio) had been dispersed in water at a concentration of 1.5% by mass, the oil-based treatment liquid was imparted to the fiber bundle, and after temporarily wringing out with a guide, it was successively led to a second oil bath tank consisting of the same composition and concentration as the first oil bath tank to impart the oil-based treatment liquid to the fiber bundle again. The fiber bundle imparted with the oil-based treatment liquid again was dried using a heated roller, and dry drawing at 1.34 times was done between heated rollers for which the rotational speed was adjusted to predetermined conditions. The overall draw ratio from the swollen line of thread at this time was 7.4 times. Subsequently, the moisture percentage was adjusted by imparting water to the fiber bundle with a touch roller to obtain a precursor fiber bundle with a single fiber fineness of 2.5 dtex.

(20) The above-mentioned precursor fiber bundle was subjected to flameproofing treatment under a temperature distribution of 220 to 260 C. for 70 minutes at an elongation rate of 5.0% to obtain a flameproof fiber bundle with a density of 1.35 g/cm.sup.3. The obtained flameproof fiber bundle was further pre-carbonization treated for 1.1 minutes under a nitrogen atmosphere at 700 C. with an elongation rate of 3%, then carbonization treated for 1.0 minute in a nitrogen atmosphere at 1,300 C. with an elongation rate of 4.0% to obtain a carbon fiber bundle. Subsequently, surface treatment was performed on the carbon fiber bundle by way of an electrolytic oxidation method, and thereafter a sizing agent was imparted. The sizing agent used was an aqueous dispersion prepared by mixing 80 parts by mass of Epikote 828 (trade name) manufactured by Japan Epoxy Resin Co., Ltd. as a base compound, and 20 parts by mass of Pluronic F88 (trade name) manufactured by ADEKA Corp. as an emulsifier, and phase-transfer emulsifying. This sizing agent was adhered at 1% by mass relative to the carbon fiber bundle, and after passing through the drying process, a carbon fiber bundle was obtained. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.4 Gpa and the strand modulus of elasticity was 233 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.82, and the knot strength was 417 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 170 kJ/kg, and the heat amount Jb was 725 kJ/kg.

Example 2

(21) A carbon fiber bundle was obtained similarly to Example 1, except for copolymerizing under the presence of acrylonitrile, 2-hydroxyethyl methacrylate, ammonium persulfate-ammonium hydrogensulfite and ferric sulfate by way of aqueous suspension polymerization, and setting to acrylonitrile units/2-hydroxyethyl methacrylate units=98.0/2.0 (mol %). Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.3 GPa and the strand modulus of elasticity was 233 GPa. In addition, the single fiber fineness of the carbon fiber was 1.26 dtex, the roundness was 0.82, and the knot strength was 410 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 168 kJ/kg, and the heat amount Jb was 722 kJ/kg.

Example 3

(22) A carbon fiber bundle was obtained similarly to Example 2, except for setting the coagulation bath concentration of 45% by mass (concentration of dimethylacetoamide) and a coagulation bath temperature of 25 C. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.2 GPa and the strand modulus of elasticity was 232 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.79, and the knot strength was 420 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 175 kJ/kg, and the heat amount Jb was 740 kJ/kg.

Example 4

(23) A carbon fiber bundle was obtained similarly to Example 2, except for setting the coagulation bath concentration of 50% by mass and a coagulation bath temperature of 35 C. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.3 GPa and the strand modulus of elasticity was 232 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.86, and the knot strength was 420 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 170 kJ/kg, and the heat amount Jb was 725 kJ/kg.

Example 5

(24) A carbon fiber bundle was obtained similarly to Example 2, except for setting the coagulation bath concentration of 50% by mass and a coagulation bath temperature of 40 C. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.2 GPa and the strand modulus of elasticity was 233 GPa. In addition, the single fiber fineness of the carbon fiber was 1.26 dtex, the roundness was 0.88, and the knot strength was 422 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 172 kJ/kg, and the heat amount Jb was 727 kJ/kg.

Example 6

(25) A carbon fiber bundle was obtained similarly to Example 1, except for setting the coagulation bath concentration of 60% by mass and a coagulation bath temperature of 45 C. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.2 GPa and the strand modulus of elasticity was 233 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.93, and the knot strength was 450 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 168 kJ/kg, and the heat amount Jb was 722 kJ/kg.

Example 7

(26) A carbon fiber bundle was obtained similarly to Example 1, except for setting the coagulation bath concentration of 67% by mass and a coagulation bath temperature of 35 C. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.2 GPa and the strand modulus of elasticity was 233 GPa. In addition, the single fiber fineness of the carbon fiber was 1.26 dtex, the roundness was 0.95, and the knot strength was 490 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 163 kJ/kg, and the heat amount Jb was 710 kJ/kg.

Example 8

(27) A carbon fiber bundle was obtained similarly to Example 1, except for copolymerizing under the presence of acrylonitrile, 2-hydroxyethyl methacrylate, ammonium persulfate-ammonium hydrogensulfite and ferric sulfate by way of aqueous suspension polymerization, and setting to acrylonitrile units/2-hydroxyethyl methacrylate units=97.5/2.5 (mol %), the coagulation bath concentration of 67% by mass and coagulation bath temperature of 45 C. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.2 GPa and the strand modulus of elasticity was 233 GPa. In addition, the single fiber fineness of the carbon fiber was 1.26 dtex, the roundness was 0.98, and the knot strength was 510 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 159 kJ/kg, and the heat amount Jb was 698 kJ/kg.

Example 9

(28) A precursor fiber bundle was obtained by the same method as Example 1 except for obtaining a fiber bundle (swollen line of thread) by discharging the spinning dope into a coagulation bath consisting of dimethylacetoamide aqueous solution of 45% by mass concentration at a temperature of 35 C., through a spinneret with 36,000 holes and a hole diameter of 60 m (spinning nozzle), and receiving at a rate 0.45 times the discharge linear velocity from the spinneret. Carbon fiber was produced by the same method as Example 1 except for setting the flameproofing elongation rate to 4%. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.8 GPa and the strand modulus of elasticity was 235 GPa. In addition, the single fiber fineness of the carbon fiber was 1.04 dtex, the roundness was 0.82, and the knot strength was 480 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 190 kJ/kg, and the heat amount Jb was 745 kJ/kg.

Example 10

(29) A precursor fiber bundle was obtained by the same method as Example 1 except for obtaining a fiber bundle (swollen line of thread) by discharging the spinning dope into a coagulation bath consisting of dimethylacetoamide aqueous solution of 45% by mass concentration at a temperature of 35 C., through a spinneret with 24,000 holes and a hole diameter of 60 m (spinning nozzle), and receiving at a rate 0.40 times the discharge linear velocity from the spinneret. Carbon fiber was produced by the same method as Example 1 except for setting the flameproofing elongation rate to 2.0%. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.7 GPa and the strand modulus of elasticity was 235 GPa. In addition, the single fiber fineness of the carbon fiber was 0.95 dtex, the roundness was 0.82, and the knot strength was 460 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 185 kJ/kg, and the heat amount Jb was 740 kJ/kg.

Example 11

(30) The spinning dope was discharged into a coagulation bath consisting of a dimethylacetoamide aqueous solution of 45% by mass concentration at a temperature of 35 C., and received at a rate 0.35 times the discharge linear velocity of the spinning dope to obtain a fiber bundle (swollen line of thread). Next, this fiber bundle was drawn to 5.3 times simultaneously with water rinsing, was led to a first oil bath tank consisting of an oil-based treatment liquid in which an oil-based composition of amino-modified silicone/polyoxyethylene(6)lauryl ether=91/9 (mass ratio) had been dispersed in water at a concentration of 1.5% by mass, the oil-based treatment liquid was imparted to the fiber bundle, and after temporarily wringing out with a guide, it was successively led to a second oil bath tank consisting of the same composition and concentration as the first oil bath tank to impart the oil-based treatment liquid to the fiber bundle again. This fiber bundle was dried using a heated roller, and dry drawing at 1.7 times was done between heated rollers for which the rotational speed was adjusted to predetermined conditions. The overall draw ratio from the swollen line of thread at this time was 9.0 times. A precursor fiber bundle with a single fiber fineness of 2.3 dtex was obtained by the same method as Example 1 except for this.

(31) Carbon fiber was produced by the same method as Example 1 except for setting the flameproofing elongation rate of 1.0% for the above-mentioned precursor fiber bundle. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 5.0 GPa and the strand modulus of elasticity was 235 GPa. In addition, the single fiber fineness of the carbon fiber was 1.12 dtex, the roundness was 0.85, and the knot strength was 490 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 175 kJ/kg, and the heat amount Jb was 730 kJ/kg.

Example 12

(32) A precursor fiber bundle with a single fiber fineness of 3.5 dtex was obtained similarly to Example 1 except for obtaining a fiber bundle (swollen line of thread) by discharging the spinning dope into a coagulation bath consisting of dimethylacetoamide aqueous solution of 45% by mass concentration at a temperature of 35 C., through a spinneret with 15,000 holes and a hole diameter of 60 m (spinning nozzle), and receiving at a rate 0.23 times the discharge linear velocity from the spinneret.

(33) The above-mentioned precursor fiber bundle was subjected to flameproofing treatment under a temperature distribution of 220 to 260 C. for 120 minutes at an elongation rate of 5% to obtain a flameproof fiber bundle. The obtained flameproof fiber bundle was further pre-carbonization treated for 1.2 minutes under a nitrogen atmosphere at 700 C. with an elongation rate of 3.0%, then carbonization treated for 1.2 minutes in a nitrogen atmosphere at 1,350 C. with an elongation rate of 4.0%. A carbon fiber bundle was obtained similarly to Example 1 except for these. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.0 GPa and the strand modulus of elasticity was 235 GPa. In addition, the single fiber fineness of the carbon fiber was 1.69 dtex, the roundness was 0.84, and the knot strength was 360 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 150 kJ/kg, and the heat amount Jb was 690 kJ/kg.

Example 13

(34) A precursor fiber bundle with a single fiber fineness of 4.5 dtex was obtained similarly to Example 1 except for discharging the spinning dope into a coagulation bath consisting of dimethylacetoamide aqueous solution of 45% by mass concentration at a temperature of 35 C., through a spinneret with 12,000 holes and a hole diameter of 60 m (spinning nozzle), and receiving at a rate 0.18 times the discharge linear velocity from the spinneret.

(35) The above-mentioned precursor fiber bundle was subjected to flameproofing treatment under a temperature distribution of 220 to 260 C. for 150 minutes at an elongation rate of 5% to obtain a flameproof fiber bundle. The obtained flameproof fiber bundle was further pre-carbonization treated for 1.8 minutes under a nitrogen atmosphere at 700 C. with an elongation rate of 3.0%, then carbonization treated for 1.6 minutes in a nitrogen atmosphere at 1,300 C. with an elongation rate of 4.0%. A carbon fiber bundle was obtained similarly to Example 1 except for these. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 3.0 GPa and the strand modulus of elasticity was 230 GPa. In addition, the single fiber fineness of the carbon fiber was 2.43 dtex, the roundness was 0.83, and the knot strength was 345 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 135 kJ/kg, and the heat amount Jb was 660 kJ/kg.

Example 14

(36) Carbon fiber was produced by the same method as Example 1 except for setting a flameproofing treatment time of 50 minutes. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.0 GPa and the strand modulus of elasticity was 235 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.82, and the knot strength was 390 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 170 kJ/kg, and the heat amount Jb was 725 kJ/kg.

Example 15

(37) Carbon fiber was produced by the same method as Example 1 except for setting a flameproofing treatment time of 120 minutes. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 5.2 GPa and the strand modulus of elasticity was 235 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.82, and the knot strength was 480 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 170 kJ/kg, and the heat amount Jb was 725 kJ/kg.

Example 16

(38) Carbon fiber was produced by the same method as Example 1 except for setting a flameproofing treatment time of 150 minutes. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 5.2 GPa and the strand modulus of elasticity was 235 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.82, and the knot strength was 500 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 170 kJ/kg, and the heat amount Jb was 725 kJ/kg.

Example 17

(39) A carbon fiber bundle was obtained similarly to Example 1 except for obtaining a fiber bundle (swollen line of thread) by discharging the spinning dope into a coagulation bath consisting of dimethylacetoamide aqueous solution of 45% by mass concentration at a temperature of 35 C., through a spinneret with 40,000 holes and a hole diameter of 60 m (spinning nozzle), and receiving at a rate 0.32 times the discharge linear velocity from the spinneret. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 3.9 GPa and the strand modulus of elasticity was 225 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.82, and the knot strength was 298 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 170 kJ/kg, and the heat amount Jb was 725 kJ/kg.

Example 18

(40) A carbon fiber bundle was obtained similarly to Example 1, except for copolymerizing under the presence of acrylonitrile, 2-hydroxyethyl acrylate, ammonium persulfate-ammonium hydrogensulfite and ferric sulfate by way of aqueous suspension polymerization, and setting to acrylonitrile units/2-hydroxyethyl acrylate units=98.5/1.5 (mol %). Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 4.2 GPa and the strand modulus of elasticity was 233 GPa. In addition, the single fiber fineness of the carbon fiber was 1.26 dtex, the roundness was 0.85, and the knot strength was 415 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 198 kJ/kg, and the heat amount Jb was 850 kJ/kg.

Comparative Example 1

(41) An acrylonitrile-based copolymer consisting of acrylonitrile units/acrylamide units/methacrylate units=96/3/1 (mol %) was obtained by copolymerizing acrylonitrile, acrylamide and methacrylic acid under the presence of ammonium persulfate-ammonium hydrogensulfite and ferric sulfate by way of aqueous suspension polymerization. This polyacrylonitrile-based copolymer was dissolved in dimethylacetoamide to prepare a 21% by mass spinning dope. Through a spinneret with 24,000 holes and a hole diameter of 60 m (spinning nozzle), the spinning dope was discharged into a coagulation bath consisting of a dimethylacetoamide aqueous solution of 60% by mass concentration at a temperature of 35 C., and received at a rate 0.32 times the discharge linear velocity from the spinneret to obtain a fiber bundle (swollen line of thread). Next, this fiber bundle was drawn to 5.4 times simultaneously with water rinsing, was led to a first oil bath tank consisting of an oil-based treatment liquid in which an oil-based composition of amino-modified silicone/polyoxyethylene(6)lauryl ether=91/9 (mass ratio) had been dispersed in water at a concentration of 1.5% by mass, the oil-based treatment liquid was imparted to the fiber bundle, and after temporarily wringing out with a guide, it was successively led to a second oil bath tank consisting of the same composition and concentration as the first oil bath tank to impart the oil-based treatment liquid to the fiber bundle again. The fiber bundle imparted with the oil-based treatment liquid again was dried using a heated roller, and dry drawing at 1.3 times was done between heated rollers for which the rotational speed was adjusted to predetermined conditions. The overall draw ratio from the swollen line of thread at this time was 7.3 times. Subsequently, the moisture percentage was adjusted by imparting water to the fiber bundle with a touch roller to obtain a precursor fiber bundle with a single fiber fineness of 2.5 dtex.

(42) The above-mentioned precursor fiber bundle was subjected to flameproofing treatment under a temperature distribution of 220 to 260 C. for 180 minutes at an elongation rate of 2.0% to obtain a flameproof fiber bundle. The obtained flameproof fiber bundle was further pre-carbonization treated for 2.2 minutes under a nitrogen atmosphere at 700 C. with an elongation rate of 3.0%, then carbonization treated for 2.0 minutes in a nitrogen atmosphere at 1,300 C. with an elongation rate of 4.0%. A carbon fiber bundle was obtained similarly to Example 1 except for these. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 3.8 Gpa and the strand modulus of elasticity was 231 GPa. In addition, the single fiber fineness of the carbon fiber was 1.37 dtex, the roundness was 0.85, and the knot strength was 297 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 190 kJ/kg, and the heat amount Jb was 1151 kJ/kg.

Comparative Example 2

(43) Carbon fiber was produced by the same method as Comparative Example 1 except for setting the flameproofing treatment time to 120 minutes and the flameproofing elongation ratio to 5.0%. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 3.2 GPa and the strand modulus of elasticity was 230 GPa. In addition, the single fiber fineness of the carbon fiber was 1.37 dtex, the roundness was 0.85, and the knot strength was 275 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 190 kJ/kg, and the heat amount Jb was 1151 kJ/kg.

Comparative Example 3

(44) Carbon fiber was produced by the same method as Comparative Example 1 except for setting the flameproofing treatment time to 60 minutes and the flameproofing elongation ratio to 5.0%. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 3.0 GPa and the strand modulus of elasticity was 225 GPa. In addition, the single fiber fineness of the carbon fiber was 1.40 dtex, the roundness was 0.85, and the knot strength was 259 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 190 kJ/kg, and the heat amount Jb was 1151 kJ/kg.

Comparative Example 4

(45) Carbon fiber was produced by the same method as Example 1 except for setting the flameproofing treatment time to 30 minutes. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 3.0 GPa and the strand modulus of elasticity was 235 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.82, and the knot strength was 290 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 170 kJ/kg, and the heat amount Jb was 725 kJ/kg.

Comparative Example 5

(46) Copolymerization was performed under the presence of acrylonitrile, 2-hydroxyethyl methacrylate, ammonium-persulfate-ammonium hydrogensulfite and ferric sulfate by way of aqueous suspension polymerization, establishing acrylonitrile units/2-hydroxyethyl methacrylate units=95/5 (mol %). Otherwise, a carbon fiber bundle was produced similarly to Example 1. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 3.0 GPa and the strand modulus of elasticity was 229 GPa. In addition, the single fiber fineness of the carbon fiber was 1.21 dtex, the roundness was 0.85, and the knot strength was 275 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 139 kJ/kg, and the heat amount Jb was 650 kJ/kg.

Comparative Example 6

(47) A precursor fiber bundle with a single fiber fineness of 5.5 dtex was obtained similarly to Example 1 except for discharging the spinning dope into a coagulation bath consisting of a dimethylacetoamide aqueous solution of 45% by mass concentration at a temperature of 35 C., through a spinneret with 12,000 holes and a hole diameter of 60 m (spinning nozzle), and receiving at a rate 0.15 times the discharge linear velocity from the spinneret.

(48) The above-mentioned precursor fiber bundle was subjected to flameproofing treatment under a temperature distribution of 220 to 260 C. for 150 minutes at an elongation rate of 5.0% to obtain a flameproof fiber bundle. The obtained flameproof fiber bundle was further pre-carbonization treated for 1.8 minutes under a nitrogen atmosphere at 700 C. with an elongation rate of 3.0%, then carbonization treated for 1.6 minutes in a nitrogen atmosphere at 1,300 C. with an elongation rate of 4.0%. A carbon fiber bundle was obtained similarly to Example 1 except for these. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 2.5 GPa and the strand modulus of elasticity was 225 GPa. In addition, the single fiber fineness of the carbon fiber was 2.78 dtex, the roundness was 0.82, and the knot strength was 250 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 130 kJ/kg, and the heat amount Jb was 650 kJ/kg.

Reference Example 1

(49) Carbon fiber was produced by the same method as Example 1 except for setting the flameproofing treatment time to 180 minutes. Upon measuring the strand properties of the obtained carbon fiber bundle, the strand strength was 5.3 GPa and the strand modulus of elasticity was 238 GPa. In addition, the single fiber fineness of the carbon fiber was 1.27 dtex, the roundness was 0.82, and the knot strength was 510 N/mm.sup.2. Furthermore, the heat amount Ja obtained by heat flux-type differential scanning calorimetry measurement was 170 kJ/kg, and the heat amount Jb was 725 kJ/kg.

(50) Although the knot strength can be raised when lengthening the flameproofing time, since the flameproofing time lengthens, the productivity declines compared to the Examples.

(51) The test conditions of the Examples and Comparative Examples and the properties of the obtained carbon fiber bundles are shown in Tables 3 and 4.

(52) TABLE-US-00003 TABLE 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Precursor fiber fineness 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 1.8 (dtex) Thread number of 24,000 24,000 24,000 24,000 24,000 24,000 24,000 24,000 36,000 precursor fiber bundles Acrylonitrile (mol %) 98.5 98.0 98 98 98 98.5 98.5 97.5 98.5 2-hydroxyethyl 1.5 2.0 2.0 2.0 2.0 1.5 1.5 2.5 1.5 methacrylate (mol %) 2-hydroxyethyl acrylate (mol %) Acrylamide (mol %) Methacrylic acid (mol %) Coagulation bath 45 45 45 50 50 60 67 67 45 concentration (Mass %) Coagulation bath 35 35 25 35 40 45 35 45 35 temperature ( C.) Flameproofing time (min) 70 70 70 70 70 70 70 70 70 Flameproofing elongation 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 4.0 rate (%) Area weight of carbon 3.04 3.03 3.04 3.04 3.03 3.04 3.03 3.02 3.73 fiber bundle (g/m) Density of carbon fiber 1.81 1.81 1.81 1.81 1.81 1.81 1.81 1.81 1.81 bundle (g/cm.sup.3) Circularity 0.82 0.82 0.79 0.86 0.88 0.93 0.95 0.98 0.82 Carbon fiber single fiber 1.27 1.26 1.27 1.27 1.26 1.27 1.26 1.26 1.04 fineness (dtex) Knot strength (N/mm.sup.2) 417 410 420 420 422 450 490 510 480 Strand strength (GPa) 4.4 4.3 4.2 4.3 4.2 4.2 4.2 4.2 4.8 Strand module of elasticity 233 233 232 232 233 233 233 233 235 (GPa) Heat flux-type differential 170 168 175 170 172 168 163 159 190 scanning calorimeter Ja (kJ/kg) Heat flux-type differential 725 722 740 725 727 722 710 698 745 scanning calorimeter Jb (kJ/kg) Example Example Example Example Example Example Example Example Example 10 11 12 13 14 15 16 17 18 Precursor fiber fineness 2.0 2.3 3.5 4.5 2.5 2.5 2.5 2.5 2.5 (dtex) Thread number of 24,000 24,000 15,000 12,000 24,000 24,000 24,000 40,000 24,000 precursor fiber bundles Acrylonitrile (mol %) 98.5 98.5 98.5 98.5 98.5 98.5 98.5 98.5 98.5 2-hydroxyethyl 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 methacrylate (mol %) 2-hydroxyethyl acrylate 1.5 (mol %) Acrylamide (mol %) Methacrylic acid (mol %) Coagulation bath 45 45 45 45 45 45 45 45 45 concentration (Mass %) Coagulation bath 35 35 35 35 35 35 35 35 35 temperature ( C.) Flameproofing time (min) 70 70 120 150 50 120 150 70 70 Flameproofing elongation 2.0 1.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 rate (%) Area weight of carbon 2.27 2.68 2.54 2.91 3.05 3.05 3.05 5.07 3.03 fiber bundle (g/m) Density of carbon fiber 1.81 1.81 1.81 1.82 1.81 1.81 1.81 1.81 1.81 bundle (g/cm.sup.3) Circularity 0.82 0.85 0.84 0.83 0.82 0.82 0.82 0.82 0.85 Carbon fiber single fiber 0.95 1.12 1.69 2.43 1.27 1.27 1.27 1.27 1.26 fineness (dtex) Knot strength (N/mm.sup.2) 460 490 360 345 390 480 500 298 415 Strand strength (GPa) 4.7 5.0 4.0 3.0 4.0 5.2 5.2 3.9 4.2 Strand module of elasticity 235 235 235 230 235 235 235 225 233 (GPa) Heat flux-type differential 185 175 150 135 170 170 170 170 198 scanning calorimeter Ja (kJ/kg) Heat flux-type differential 740 730 690 660 725 725 725 725 850 scanning calorimeter Jb (kJ/kg)

(53) TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Comparative Comparative Comparative Reference Example Example 2 Example 3 Example 4 Example 5 Example 6 Example 1 Precursor fiber fineness 2.5 2.5 2.5 2.5 2.5 5.5 2.5 (dtex) Thread number of 24,000 24,000 24,000 24,000 24,000 12,000 24,000 precursor fiber bundles Acrylonitrile (mol %) 96.0 96.0 96.0 98.5 95.0 98.5 98.5 2-hydroxyethyl 1.5 5.0 1.5 1.5 methacrylate (mol %) Acrylamide (mol %) 3.0 3.0 3.0 Methacrylic acid (mol %) 1.0 1.0 1.0 Coagulation bath 60 60 60 45 45 45 45 concentration (Mass %) Coagulation bath 35 35 35 35 35 35 35 temperature ( C.) Flameproofing time (min) 180 120 60 30 70 150 180 Flameproofing elongation 2.0 5.0 5.0 5.0 5.0 5.0 5.0 rate (%) Areal weight of carbon 3.29 3.29 3.35 3.05 2.9 3.34 3.05 fiber bundle (g/m) Density of carbon fiber 1.82 1.82 1.82 1.81 1.81 1.81 1.81 bundle (g/cm.sup.3) Circularity 0.85 0.85 0.85 0.82 0.85 0.82 0.82 Carbon fiber single fiber 1.37 1.37 1.40 1.27 1.21 2.78 1.27 fineness (dtex) Knot strength (N/mm.sup.2) 297 275 259 290 275 250 510 Strand strength (GPa) 3.8 3.2 3.0 3.0 3.0 2.5 5.3 Strand module of elasticity 231 230 225 235 229 225 238 (GPa) Heat flux-type differential 190 190 190 170 139 130 170 scanning calorimeter Ja (kJ/kg) Heat flux-type differential 1151 1151 1151 725 650 650 725 scanning calorimeter Jb (kJ/kg)