CN117999385A - Carbon fiber bundle and method for producing same - Google Patents
Carbon fiber bundle and method for producing same Download PDFInfo
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- CN117999385A CN117999385A CN202280063686.1A CN202280063686A CN117999385A CN 117999385 A CN117999385 A CN 117999385A CN 202280063686 A CN202280063686 A CN 202280063686A CN 117999385 A CN117999385 A CN 117999385A
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- carbon fiber
- fiber bundle
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- carbonization step
- polyacrylonitrile
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- 229920000049 Carbon (fiber) Polymers 0.000 title claims abstract description 125
- 239000004917 carbon fiber Substances 0.000 title claims abstract description 125
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 119
- 238000004519 manufacturing process Methods 0.000 title claims description 26
- 229920005989 resin Polymers 0.000 claims abstract description 15
- 239000011347 resin Substances 0.000 claims abstract description 15
- 239000013078 crystal Substances 0.000 claims abstract description 13
- 238000005470 impregnation Methods 0.000 claims abstract description 11
- 238000005259 measurement Methods 0.000 claims abstract description 11
- 238000009864 tensile test Methods 0.000 claims abstract description 11
- 238000004736 wide-angle X-ray diffraction Methods 0.000 claims abstract description 7
- 238000012887 quadratic function Methods 0.000 claims abstract description 3
- 239000000835 fiber Substances 0.000 claims description 112
- 238000010438 heat treatment Methods 0.000 claims description 65
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 52
- 238000000034 method Methods 0.000 claims description 50
- 238000009656 pre-carbonization Methods 0.000 claims description 44
- 238000003763 carbonization Methods 0.000 claims description 43
- 239000002243 precursor Substances 0.000 claims description 43
- RNFJDJUURJAICM-UHFFFAOYSA-N 2,2,4,4,6,6-hexaphenoxy-1,3,5-triaza-2$l^{5},4$l^{5},6$l^{5}-triphosphacyclohexa-1,3,5-triene Chemical compound N=1P(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP=1(OC=1C=CC=CC=1)OC1=CC=CC=C1 RNFJDJUURJAICM-UHFFFAOYSA-N 0.000 claims description 35
- 239000003063 flame retardant Substances 0.000 claims description 35
- 239000012298 atmosphere Substances 0.000 claims description 12
- 230000001590 oxidative effect Effects 0.000 claims description 4
- 238000012545 processing Methods 0.000 abstract description 24
- 238000009987 spinning Methods 0.000 description 11
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 10
- 229920000642 polymer Polymers 0.000 description 10
- 239000002131 composite material Substances 0.000 description 8
- 230000015271 coagulation Effects 0.000 description 7
- 238000005345 coagulation Methods 0.000 description 7
- 238000005406 washing Methods 0.000 description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 6
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 230000003647 oxidation Effects 0.000 description 6
- 238000007254 oxidation reaction Methods 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 229910052799 carbon Inorganic materials 0.000 description 5
- 239000003795 chemical substances by application Substances 0.000 description 5
- 238000001035 drying Methods 0.000 description 5
- 239000003733 fiber-reinforced composite Substances 0.000 description 5
- 239000011208 reinforced composite material Substances 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- 239000002904 solvent Substances 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 239000007791 liquid phase Substances 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000000280 densification Methods 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 229920001296 polysiloxane Polymers 0.000 description 3
- 238000010248 power generation Methods 0.000 description 3
- 230000001737 promoting effect Effects 0.000 description 3
- 238000004513 sizing Methods 0.000 description 3
- JAHNSTQSQJOJLO-UHFFFAOYSA-N 2-(3-fluorophenyl)-1h-imidazole Chemical compound FC1=CC=CC(C=2NC=CN=2)=C1 JAHNSTQSQJOJLO-UHFFFAOYSA-N 0.000 description 2
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- FXHOOIRPVKKKFG-UHFFFAOYSA-N N,N-Dimethylacetamide Chemical compound CN(C)C(C)=O FXHOOIRPVKKKFG-UHFFFAOYSA-N 0.000 description 2
- 239000003677 Sheet moulding compound Substances 0.000 description 2
- 238000005299 abrasion Methods 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- LVHBHZANLOWSRM-UHFFFAOYSA-N methylenebutanedioic acid Natural products OC(=O)CC(=C)C(O)=O LVHBHZANLOWSRM-UHFFFAOYSA-N 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 230000003014 reinforcing effect Effects 0.000 description 2
- 239000011342 resin composition Substances 0.000 description 2
- 229920002545 silicone oil Polymers 0.000 description 2
- 238000002166 wet spinning Methods 0.000 description 2
- 238000004804 winding Methods 0.000 description 2
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical compound [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 description 2
- YXALYBMHAYZKAP-UHFFFAOYSA-N 7-oxabicyclo[4.1.0]heptan-4-ylmethyl 7-oxabicyclo[4.1.0]heptane-4-carboxylate Chemical compound C1CC2OC2CC1C(=O)OCC1CC2OC2CC1 YXALYBMHAYZKAP-UHFFFAOYSA-N 0.000 description 1
- HRPVXLWXLXDGHG-UHFFFAOYSA-N Acrylamide Chemical compound NC(=O)C=C HRPVXLWXLXDGHG-UHFFFAOYSA-N 0.000 description 1
- 238000012935 Averaging Methods 0.000 description 1
- CERQOIWHTDAKMF-UHFFFAOYSA-N Methacrylic acid Chemical compound CC(=C)C(O)=O CERQOIWHTDAKMF-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 230000005260 alpha ray Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- JDVIRCVIXCMTPU-UHFFFAOYSA-N ethanamine;trifluoroborane Chemical compound CCN.FB(F)F JDVIRCVIXCMTPU-UHFFFAOYSA-N 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 238000010528 free radical solution polymerization reaction Methods 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000001891 gel spinning Methods 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 239000000543 intermediate Substances 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 239000012778 molding material Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000012783 reinforcing fiber Substances 0.000 description 1
- VGTPCRGMBIAPIM-UHFFFAOYSA-M sodium thiocyanate Chemical compound [Na+].[S-]C#N VGTPCRGMBIAPIM-UHFFFAOYSA-M 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 235000005074 zinc chloride Nutrition 0.000 description 1
- 239000011592 zinc chloride Substances 0.000 description 1
Classifications
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
- D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
- D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
- D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
- D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
- D01F9/21—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D01F9/22—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Textile Engineering (AREA)
- Inorganic Fibers (AREA)
Abstract
A carbon fiber bundle which has high total fineness and excellent strength, elastic modulus and operability for high-order processing, is produced by satisfying the relationship between the coefficient A obtained from the nonlinear approximation formula (1) and the crystal orientation n (%) in the wide-angle X-ray diffraction measurement in the stress sigma-strain epsilon curve in the resin impregnation harness tensile test in the stress range of 0 to 3GPa and the formula (2), wherein the initial elastic modulus of the carbon fiber bundle is 240 to 279GPa, the filament number is 24,000 ～ 72,000, and the carbon fiber bundle is substantially untwisted. epsilon=Aσ 2+Bσ+C…(1);-410≤(0.0000832Π2 -0.0184n+1.00)/A is less than or equal to-310 (2); wherein A, B, C is a coefficient of a quadratic function of stress σ and strain ε, and ε is a degree of crystal orientation.
Description
Technical Field
The present invention relates to a carbon fiber bundle having high total fineness and excellent strength, elastic modulus and handleability for high-order processing, and a method for producing the same.
Background
Since carbon fiber bundles have high specific strength and specific elastic modulus, they are widely used as reinforcing fibers for composite materials, such as for aerospace applications. Recently, the present invention has been developed and applied to industrial applications such as automobile parts and wind power generation. In particular, in wind power generation, since lightweight and rigidity are required, carbon fiber bundles having a higher modulus than that of elasticity are often used, and in recent years, the demand for carbon fiber bundles for wind power generation has been expanding.
In industrial applications, there is a strong demand for cost reduction, and carbon fiber bundles having 24,000 filaments or more are excellent in productivity. In addition, high-order processability is important in the production of carbon fiber composite materials such as prepregs, tow-impregnated materials, fabrics, intermediate substrates such as Sheet Molding Compounds (SMC), and pultrusions from carbon fiber bundles. In order to improve the high-order processability, it is particularly important that the carbon fiber bundles have less fluff and excellent fiber opening properties, and that the carbon fiber bundles as a whole or the carbon fiber single fibers do not break and that the handling properties are good when the carbon fiber bundles are unwound from the bobbins and run in the manufacturing process.
Generally, carbon fiber bundles are produced by the following steps: a flame-retardant step in which a polyacrylonitrile-based precursor fiber obtained by fiberizing a polyacrylonitrile-based copolymer is oxidized in air at 200-300 ℃; a pre-carbonization step of heating in an inert atmosphere having a maximum temperature of 500 to 1,200 ℃; and a carbonization step of heating in an inert atmosphere having a maximum temperature of 1,200 to 3,000 ℃.
Heretofore, a technique for producing a carbon fiber having high strength, high elastic modulus, and excellent high-order processability for industrial use has been proposed (patent documents 1 to 4). Patent document 1 discloses the following technique: when flame-resistant treatment is performed on a polyacrylonitrile-based precursor fiber bundle having a total fineness of 40,000dtex or more, twisting of the precursor fiber bundle during traveling in a flame-resistant furnace is suppressed by defining the shape and arrangement of the folding rollers, whereby the morphology of the fiber bundle can be stably maintained, yarn breakage and fuzzing in the flame-resistant process can be suppressed, and further, a high-quality carbon fiber bundle can be stably produced. Patent document 2 discloses a technique for improving resin impregnation and expansibility in molding a composite material by controlling the diameter and surface state of carbon fibers within specific ranges. Patent document 3 discloses a carbon fiber bundle having a semi-permanent twist and an elastic modulus of 200GPa or more, and discloses a carbon fiber bundle which is excellent in handling properties and high-order processability as a fiber bundle and has a high reinforcing effect of a fiber-reinforced composite material. Patent document 4 discloses that a carbon fiber bundle of a high-performance carbon fiber reinforced composite material having excellent tensile strength can be obtained by controlling the nonlinearity of the stress σ -strain ε curve in a resin impregnation wire harness tensile test within a specific range.
Prior art literature
Patent literature
Patent document 1: japanese patent application laid-open No. 2014-214386
Patent document 2: japanese patent laid-open No. 2002-69754
Patent document 3: japanese patent application laid-open No. 2019-151956
Patent document 4: international publication No. 2016/068034
Disclosure of Invention
Problems to be solved by the invention
However, the following problems exist in the background art.
In patent document 1, the effect of suppressing the occurrence of twisting and "jump-out" (the yarn coming off from the roller) in the flame-retardant process is exhibited by setting the yarn density in the flame-retardant process to a specific range, but the obtained carbon fiber bundle does not exhibit the effect of improving the quality, nor can the operability at the time of the process for higher-order processing be improved.
Patent document 2 discloses that the strength of a molding material having resin impregnation properties can be improved when a pressure vessel is molded, but the operability of the obtained carbon fiber bundles in a process for high-order processing cannot be improved.
Patent document 3 discloses that the operability can be improved by leaving the carbon fiber bundles semi-permanently twisted, but does not disclose or suggest a specific effect on the operability of the obtained carbon fiber bundles in the process for high-order processing, and has a problem that the orientation of fibers in the obtained carbon fiber-reinforced composite material is disturbed and mechanical properties are hardly exhibited due to the presence of twisting.
In patent document 4, the nonlinear characteristic of the stress σ -strain ε curve in the resin-impregnated wire harness tensile test is controlled to a specific range by controlling the heat treatment method in the flame-retarding step, so that the fracture toughness value effective for improving the strength is improved, but there is no teaching about the operability of the high-total-fineness carbon fiber bundle in the high-order processing process, and the initial elastic modulus in the resin-impregnated wire harness tensile test is as high as 315GPa, and the operability in the high-order processing process cannot be expected to be improved. Further, although it is effective to increase the total fineness of the polyacrylonitrile-based precursor fiber bundles to obtain carbon fiber bundles having excellent productivity, there is a limit in the heat treatment method in the flame-retarding step due to thermal runaway or the like, and in the method described in the patent document, there is a problem that it is difficult to stably control the nonlinearity of the stress σ -strain ε curve.
As described above, although a technique for improving the mechanical properties of the carbon fiber bundles and a technique for improving the operability in the production of the carbon fiber bundles have been proposed in the prior art, there is no disclosure of a technique capable of suppressing the problems such as fluff caused by friction with rolls or guides during high-order processing, breakage of a part or the whole of the carbon fiber bundles, and the like in the carbon fiber bundles having a large total fineness. The invention aims at: provided are a carbon fiber bundle which has high total fineness, excellent strength and elastic modulus, is excellent in handling properties for high-order processing, is substantially untwisted, and easily exhibits mechanical properties when produced into a carbon fiber-reinforced composite material, and a method for producing the same.
Means for solving the problems
In order to achieve the object of the present invention, the present invention mainly has the following constitution.
Specifically, the present invention provides a carbon fiber bundle having an initial elastic modulus of 240 to 279GPa and a filament number of 24,000 ～ 72,000, wherein the relationship between a coefficient A obtained from a nonlinear approximation formula (1) and a crystal orientation degree pi (%) in wide-angle X-ray diffraction measurement in a stress sigma-strain epsilon curve in a resin impregnation wire harness tensile test and the coefficient A is obtained from a nonlinear approximation formula (1) in a stress range of 0 to 3GPa satisfies formula (2).
ε＝Aσ2+Bσ+C…(1)
-410≤(0.0000832Π2-0.0184Π+1.00)/A≤-310· · · (2)
Wherein A, B, C is a coefficient of a quadratic function of stress σ and strain ε, and ε is a degree of crystal orientation.
The present invention also provides a method for producing the carbon fiber bundle, comprising:
A flame-retardant step of heat-treating a substantially untwisted polyacrylonitrile-based precursor fiber bundle having a filament number of 24,000 ～ 72,000 at a temperature of 220 to 280 ℃ in an oxidizing atmosphere; and a pre-carbonization step of heat-treating the flame-resistant fiber bundles obtained in the flame-resistant step in an inert atmosphere at a maximum temperature of 300 to 1,000 ℃; and a carbonization step of heat-treating the pre-carbonized fiber bundles obtained by the pre-carbonized fiber bundles at a maximum temperature of 1,000 to 1,600 ℃ in an inert atmosphere,
The stretching ratio in the pre-carbonization step is 1.05-1.20, the stretching ratio in the carbonization step is 0.960-0.990, the product of the stretching ratio of the pre-carbonization step and the stretching ratio of the carbonization step is 1.020-1.180,
In the flame-retardant step, heat treatment is performed stepwise on the polyacrylonitrile-based precursor fiber bundles in a plurality of heat treatment furnaces set to different temperatures from each other or in a plurality of heat treatment sections set to different temperatures from each other in the heat treatment furnaces, and in the flame-retardant step, the temperature of the heat treatment furnace or the heat treatment section having the lowest temperature is set to less than 230 ℃, and the temperature of the heat treatment furnace or the heat treatment section having the highest temperature is set to 280 ℃ or less.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, a carbon fiber bundle having high total fineness, excellent strength and elastic modulus, excellent handleability for high-order processing, and easy mechanical properties when produced into a carbon fiber reinforced composite material can be obtained.
Detailed Description
In order to achieve the above object, the present invention has the following constitution.
In the carbon fiber bundle of the present invention, the value of the coefficient a obtained by introducing the stress σ -strain ε curve obtained by measuring the carbon fiber bundle by the resin impregnation strand tensile test into the following nonlinear approximation formula (1) satisfies the following formula (2).
ε＝Aσ2+Bσ+C…(1)
-410≤(0.0000832Π2-0.0184Π+1.00)/A≤-310· · · (2)
Where, pi represents the degree of crystal orientation (%) obtained by measuring the carbon fiber bundle by wide-angle X-ray diffraction measurement. The degree of crystal orientation is obtained by a method of measuring the degree of crystal orientation pi of the carbon fiber described later.
The value of the central term in the above formula (2) is-410 to-310, preferably-406 to-343, and more preferably-386 to-352.
In the formula (1), the coefficient A represents the nonlinearity of the stress sigma-strain epsilon curve. The coefficient A is obtained by fitting a stress sigma-strain epsilon curve obtained by measuring a carbon fiber bundle by a resin impregnation wire harness tensile test to an approximate formula (1) within a stress range of 0 to 3 GPa. As described above, since the stress σ -strain ε curve of the carbon fiber bundle is generally a curve that protrudes downward when the stress σ (GPa) is on the vertical axis and the strain ε (-) is on the horizontal axis, the coefficient A obtained by the above-described approximation formula (1) takes a negative value. That is, the closer the coefficient a is to 0, the smaller the nonlinearity is.
The inventors of the present application found that, in terms of the nonlinearity of the stress σ -strain ε curve, the correlation with the shear elastic modulus of Carbon fibers is not necessarily sufficient, and theories concerning the stress and deformation in Carbon fibers are described, for example, in "Carbon" (Netherlands), esculer (Elsevier), 1991, volume 29, volume 8, p.1267-1279, and the like. However, this is an academic study, and is difficult to apply in practical studies for controlling the shear elastic modulus of carbon fibers. The inventors of the present application have conducted studies based on these theories, and as a result, have found that the value (0.0000832 pi 2 -0.0184 pi+1.00)/a of the central term of the formula (2) derived from the coefficient a of the approximate formula (1) and the shear elastic modulus of the carbon fiber have extremely high correlation with each other. More specifically, the larger the value of the central term of formula (2), the lower the shear elastic modulus; the smaller the value of the central term of formula (2), the greater the shear modulus of elasticity.
The shear modulus is an index of the formability of a single fiber when stress in the bending and compression directions is applied, and is important for improving the operability in a high-order processing step. When the value of the central term in the above formula (2) is-410 to-310, the fiber is moderately deformed when subjected to bending and compressive stress in the high-order processing step, and breakage of the single fiber and winding of the roll or guide continuous thereto can be suppressed. The coefficient a of the above formula (1) can be controlled by the stretch ratio in the flame retardant step, the stretch ratio in the pre-carbonization step, and the stretch ratio in the carbonization step. The degree of crystal orientation pi may be controlled by the stretch ratio of the pre-carbonization step, the stretch ratio of the carbonization step, and the temperature of the carbonization step.
The carbon fiber bundles of the present invention have an initial elastic modulus of 240 to 279GPa, preferably 245 to 269GPa, and more preferably 245 to 260GPa. The initial elastic modulus is an index of initial deformability when stress in the tensile direction is applied to the filaments, and is important for improving the operability in the high-order processing step. When the initial elastic modulus is 240 to 279GPa, the fibers are moderately deformed when subjected to stress in the stretching direction in the high-order processing step, and breakage of the single fibers and winding of the rolls and guides connected thereto can be suppressed. The initial elastic modulus is calculated as the reciprocal 1/B of the coefficient B when the stress σ -strain ε curve measured by the resin impregnation wire harness tensile test described later is fitted to the approximate formula (1). The initial elastic modulus can be controlled by the stretch ratio in the flame-retardant step, the stretch ratio in the pre-carbonization step, the stretch ratio in the carbonization step, and the temperature in the carbonization step.
The number of filaments of the carbon fiber bundle of the present invention is 24,000 ～ 72,000, preferably 36,000 ～ 60,000, more preferably 48,000 ～ 50,000. The number of filaments is the number of single fibers constituting the carbon fiber bundle, and as the number of filaments increases, the productivity of the carbon fiber reinforced composite is more excellent, but when the number of filaments is too large, the mechanical properties of the obtained carbon fiber reinforced composite may be lowered from the viewpoints of expansibility of the carbon fiber bundle and resin impregnation. If the filament number is 24,000 ～ 72,000, the productivity in molding the composite material is excellent, and the composite material can be suitably used for industrial applications. The number of filaments can be controlled by the number of holes of a spinneret, the division of sliver, and the spinning in the step of producing the polyacrylonitrile-based precursor fiber bundle.
The carbon fiber bundles of the present invention are substantially untwisted. The term "substantially untwisted" as used herein means that the number of turns (turns) of the carbon fiber bundles is not more than 0.5 per 1 m. If the carbon fiber bundles are not substantially twisted, disturbance of the orientation of the fibers in the carbon fiber-reinforced composite material can be suppressed, and the reinforcing effect of the carbon fiber-reinforced composite material is improved.
The crystallite size Lc of the carbon fiber bundles of the present invention is preferably 1.80 to 2.20nm. The crystallite size Lc is the [002] direction size of the crystal of graphite in the carbon fiber. When the crystallite size Lc is 1.80 to 2.20nm, a carbon fiber having more excellent balance between strength and elastic modulus can be obtained. The crystallite size Lc can be evaluated by a measurement method of crystallite size Lc described below by wide-angle X-ray diffraction measurement. The crystallite size Lc can be controlled by the temperature of the carbonization process.
The single fiber fineness of the carbon fiber bundle of the present invention is preferably 0.63 to 1.35dtex, more preferably 0.67 to 1.35dtex, and still more preferably 0.74 to 1.20dtex. The single fiber fineness is the mass per unit length of a single fiber. When the single fiber fineness is 0.63 to 1.35dtex, productivity and mechanical properties can be simultaneously achieved. The single fiber fineness can be evaluated by measuring the mass per unit length by a method described later. The single fiber fineness can be controlled by the ejection amount and the stretching ratio of the polyacrylonitrile-based polymer in the filament-making process of the polyacrylonitrile-based precursor fiber bundles.
The degree of roundness of the single fiber cross section of the carbon fiber bundle of the present invention is preferably 0.86 to 0.98, more preferably 0.87 to 0.96, and even more preferably 0.87 to 0.93. The roundness of the cross section of the filament is defined as follows based on the perimeter L and the area a cs of the cross section of the filament.
(True circle) =4pi a cs/L2.
When the degree of roundness of the single fiber cross section is 0.86 to 0.98, the bundling property and the abrasion resistance at the time of high-order processing can be more reliably combined, and the operability at the time of high-order processing is more excellent. The roundness of the cross section of the single fiber can be evaluated by a method described later based on an image of a cut surface obtained by cutting the single fiber vertically. The roundness of the single fiber cross section can be controlled by the shape of the ejection hole of the spinneret in the filament-making process and the conditions of the coagulation process.
Next, a preferred method for producing the carbon fiber bundles of the present invention will be described.
In the production of carbon fiber bundles, polyacrylonitrile-based precursor fiber bundles are spun. As a raw material for the production of the polyacrylonitrile-based precursor fiber bundle, a polyacrylonitrile-based polymer is preferably used. In the present invention, the polyacrylonitrile-based polymer means a polymer in which at least acrylonitrile is the main component of the polymer skeleton, and the main component generally means a component constituting 90 to 100% by mass of the polymer skeleton. From the viewpoint of improving the thread forming property, and the like, the polyacrylonitrile-based polymer preferably contains a copolymerized component such as itaconic acid, acrylamide, methacrylic acid, and the like, from the viewpoint of performing flame-retardant treatment efficiently. The method for producing the polyacrylonitrile-based polymer may be selected from known polymerization methods. In the production of the polyacrylonitrile-based precursor fiber bundle, the spinning solution is a solution obtained by dissolving the above-mentioned polyacrylonitrile-based polymer in a polyacrylonitrile-soluble solvent such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, or nitric acid/zinc chloride/sodium thiocyanate aqueous solution.
The method for producing the polyacrylonitrile-based precursor fiber bundle used in the present invention is not particularly limited, but it is preferably obtained by using wet spinning, and then, by the steps of stretching, washing with water, applying an oil, drying and densification, post-stretching as needed, and the like. In order to achieve the above-mentioned filament count of the carbon fiber bundle, the number of holes of the spinneret for producing the polyacrylonitrile-based precursor fiber bundle is preferably 3,000 ～ 200,000 holes, and the polyacrylonitrile-based precursor fiber bundle having a predetermined filament count can be obtained by dividing and spinning.
In the production of the polyacrylonitrile-based precursor fiber bundle, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, which are used as solvents for the spinning dope, and a so-called coagulation promoting component. As the coagulation promoting component, a component which does not dissolve the polyacrylonitrile-based polymer and has compatibility with a solvent used for the spinning dope can be used. Preferably, water is used as the solidification promoting ingredient.
In the production of the polyacrylonitrile-based precursor fiber bundle, the water washing step preferably uses a water washing bath having a temperature of 30 to 98 ℃ and comprising a plurality of stages. In the washing step, the stretching ratio is preferably set to 2 to 6 times.
After the washing step, an oil solution containing silicone or the like is preferably applied to the sliver for the purpose of preventing the filaments from adhering to each other. The silicone oil agent is preferably a modified silicone, and is preferably an oil agent containing an amino-modified silicone having high heat resistance.
The drying heat treatment step (the drying densification step) may be performed by a known method. For example, the drying temperature may be 100 to 200 ℃.
The single fiber fineness of the polyacrylonitrile-based precursor fiber bundle in the method for producing a carbon fiber bundle of the present invention is preferably 1.20 to 2.40dtex, more preferably 1.20 to 2.20dtex, and even more preferably 1.40 to 1.80dtex. The single fiber fineness is the mass per unit length of a single fiber. When the single fiber fineness is 1.20dtex or more, a carbon fiber bundle can be obtained with a sufficiently high productivity; when the single fiber fineness is 2.40dtex or less, the unevenness in treatment in the heat treatment after the flame-retardant treatment step is reduced, and a carbon fiber bundle having high mechanical properties can be obtained. The single fiber fineness can be controlled by the ejection amount and the draw ratio in the filament-making process.
In the polyacrylonitrile-based precursor fiber bundle in the method for producing a carbon fiber bundle of the present invention, the true roundness of the single fiber cross section is preferably 0.86 to 0.98, more preferably 0.87 to 0.96, and even more preferably 0.87 to 0.93. The roundness of the cross section of the filament is defined as follows based on the perimeter L and the area A cs of the cross section of the filament.
(True circle) =4pi a cs/L2.
When the degree of roundness of the single fiber cross section is 0.86 to 0.98, the bundling property and the abrasion resistance of the obtained carbon fibers can be more reliably combined, and the workability of the obtained carbon fiber bundle at the time of high-order processing can be more excellent. The roundness of the single fiber cross section of the polyacrylonitrile-based precursor fiber bundle can be evaluated by the method described below from an image of a cross section obtained by cutting the single fibers vertically. The roundness of the single fiber cross section of the polyacrylonitrile-based precursor fiber bundle can be controlled by the shape of the discharge hole of the spinneret in the filament-making process and the conditions of the coagulation process.
The number of filaments of the polyacrylonitrile-based precursor fiber bundle in the method for producing a carbon fiber bundle of the present invention is preferably 24,000 ～ 72,000, more preferably 36,000 ～ 60,000, and still more preferably 48,000 ～ 50,000. The number of filaments is the number of single fibers constituting the polyacrylonitrile-based precursor fiber bundle, and as the number of filaments increases, the productivity of carbon fiber bundle production and the productivity of the carbon fiber reinforced composite material using the obtained carbon fiber bundle are more excellent, but when the number of filaments is too large, the uneven treatment in the flame-retardant step, the pre-carbonization step, and the carbonization step may increase, and the mechanical properties of the obtained carbon fiber reinforced composite material may decrease from the viewpoints of the expansibility and resin impregnation of the obtained carbon fiber bundle. When the filament number of the polyacrylonitrile-based precursor fiber bundle is 24,000 ～ 72,000, the productivity of the carbon fiber bundle and the carbon fiber reinforced composite material is excellent, and a carbon fiber bundle suitable for industrial use can be obtained. The number of filaments of the polyacrylonitrile-based precursor fiber bundle can be evaluated by counting the number of single fibers constituting the polyacrylonitrile-based precursor fiber bundle. The number of filaments can be controlled by the number of holes of the spinneret, the number of divisions of the fiber bundle discharged from the spinneret, and the number of filaments to be combined in the filament-making step.
In the method for producing a carbon fiber bundle of the present invention, the above-mentioned substantially untwisted polyacrylonitrile-based precursor fiber bundle is subjected to a heat treatment in an oxidizing atmosphere at a temperature of 220 to 280 ℃ (flame-retardant step). The temperature in the flame-retarding step is preferably 220 to 280 ℃. When the temperature of the flame-resistant treatment is 220 ℃ or higher, a flame-resistant fiber bundle having sufficient flame resistance can be produced, and therefore, generation of fluff due to insufficient flame resistance can be suppressed, and the obtained carbon fiber bundle is excellent in operability at the time of high-order processing. When the temperature at which the flame-retardant treatment is performed is 280 ℃ or less, the heat generation rate does not become excessively high, so that the temperature unevenness in the flame-retardant fiber bundle can be reduced, and a carbon fiber bundle excellent in mechanical properties can be obtained. The temperature of the flame retardant treatment may be measured by inserting a thermometer such as a thermocouple into the flame retardant furnace, and when the temperature in the furnace is measured at a predetermined point, a simple average temperature is calculated when there is a temperature unevenness or a temperature distribution. The temperature of the above-mentioned flame retardant treatment can be controlled by the output of heating in a heating method used in a known flame retardant furnace. As an example, in the case of a hot air circulating type flame retardant furnace, the output of a heater for heating an oxidizing atmosphere may be changed.
In the flame-retardant step, heat treatment is performed stepwise on the polyacrylonitrile-based precursor fiber bundle using a plurality of heat treatment furnaces set to different temperatures from each other or a plurality of heat treatment sections set to different temperatures from each other in the heat treatment furnaces (hereinafter, such heat treatment furnaces and heat treatment sections may be referred to as "heat treatment furnaces/heat treatment sections"). In the present invention, among the plurality of heat treatment furnaces/heat treatment sections, the temperature may be different between at least 2 heat treatment furnaces/heat treatment sections, for example, 2 heat treatment furnaces/heat treatment sections among 3 heat treatment furnaces/heat treatment sections may be the same temperature. In the present invention, the temperature of the heat treatment furnace or heat treatment section which is the lowest in the flame retardant treatment step is set to less than 230 ℃, preferably 225 ℃ or less, and more preferably 223 ℃ or less. By setting the temperature of the lowest heat treatment furnace or heat treatment zone to less than 230 ℃, the heat treatment unevenness easily occurring in the polyacrylonitrile-based precursor fiber bundle of high total fineness can be reduced, and high quality can be maintained in the stretching in the pre-carbonization step and carbonization step described later. When the temperature of the lowest heat treatment furnace or heat treatment section is 230 ℃ or higher, the heat treatment unevenness in the flame-retardant process increases, and the quality is reduced by stretching in the pre-carbonization process and carbonization process.
In the present invention, the temperature of the heat treatment furnace or heat treatment section that is the highest in the flame retardant treatment step is 280 ℃ or lower, preferably 275 ℃ or lower, and more preferably 270 ℃ or lower. By setting the temperature of the highest heat treatment furnace or heat treatment section to 280 ℃ or lower, the heat treatment unevenness easily occurring in the polyacrylonitrile-based precursor fiber bundle of high total fineness can be reduced, and high quality can be maintained in the pre-carbonization step and the stretching of the carbonization step, which will be described later. When the temperature of the heat treatment furnace or the heat treatment section exceeds 280 ℃, the heat treatment unevenness in the flame-retardant process increases, and the quality decreases due to the stretching in the pre-carbonization process and the carbonization process.
The pre-carbonization is performed after the polyacrylonitrile-based precursor fiber bundle production step and the flame-retardant step. In the pre-carbonization step, the flame-retardant fiber bundles obtained as described above are heat-treated in an inert atmosphere at a maximum temperature of 300 to 1,000 ℃, preferably to a density of 1.5 to 1.8g/cm 3.
And continuing the pre-carbonization to perform carbonization. In the carbonization step, the pre-carbonized fiber bundle is heat-treated at a maximum temperature of 1,000 to 1,600 ℃ in an inert atmosphere.
In the present invention, in the pre-carbonization step and the carbonization step, a plurality of heat treatment furnaces or heat treatment sections may be used and may be set at different temperatures from each other. Therefore, the temperature of the heat treatment furnace or the heat treatment section having the highest temperature in each step is referred to as "highest temperature".
In the method for producing a carbon fiber bundle of the present invention, the stretch ratio in the pre-carbonization step is 1.05 to 1.20, the stretch ratio in the carbonization step is 0.960 to 0.990, and the product of the stretch ratio in the pre-carbonization step and the stretch ratio in the carbonization step is 1.020 to 1.180.
The stretching ratio in the pre-carbonization step is preferably 1.10 to 1.20, more preferably 1.10 to 1.15.
The stretching ratio in the carbonization step is preferably 0.975 to 0.990, more preferably 0.975 to 0.985.
The product of the stretching ratio in the pre-carbonization step and the stretching ratio in the carbonization step is preferably 1.040 to 1.130, more preferably 1.070 to 1.130.
The values of the central term of the above formula (2) and the initial elastic modulus of the obtained carbon fiber bundles can be controlled to be in appropriate ranges by controlling the stretching ratio in the pre-carbonization step to be 1.05 or more, the stretching ratio in the carbonization step to be 0.960 or more, and the product of the stretching ratio in the pre-carbonization step and the stretching ratio in the carbonization step to be 1.020 or more. On the other hand, by controlling the draw ratio in the pre-carbonization step to be 1.20 or less, the draw ratio in the carbonization step to be 0.990 or less, and the product of the draw ratio in the pre-carbonization step and the draw ratio in the carbonization step to be 1.180 or less, breakage due to drawing can be suppressed, and a decrease in operability at the time of producing carbon fibers and an increase in the fluff number of the obtained carbon fiber bundles can be suppressed.
In order to improve the adhesion to the matrix resin, the carbon fiber bundles obtained as described above are preferably oxidized to introduce oxygen-containing functional groups. As the oxidation treatment method, gas phase oxidation, liquid phase oxidation and liquid phase electrolytic oxidation can be used, but from the viewpoint of high productivity and uniform treatment, liquid phase electrolytic oxidation is preferably used. The method of the liquid-phase electrolytic oxidation is not particularly limited, and a known method may be used.
After the above electrolytic treatment, a sizing treatment may be performed to give bundling properties to the obtained carbon fiber bundles. As for the sizing agent, a sizing agent which is good with Xiang Rongxing of the matrix resin can be appropriately selected according to the kind of the matrix resin used in the composite material.
Examples
The present invention will be described in more detail with reference to examples. But the present invention is not limited thereto.
< Resin impregnated strand tensile test of carbon fiber bundles >
The tensile elastic modulus (strand elastic modulus E (GPa)) of the resin-impregnated strand of the carbon fiber strand, the tensile strength (strand strength (GPa)) of the resin-impregnated strand, and the stress σ -strain epsilon curve were obtained according to JIS R7608 (2008) "resin-impregnated strand test method". The elastic modulus E of the wire harness is measured in a strain range of 0.1 to 0.6%. The test piece was produced by impregnating the carbon fiber bundles with the following resin composition under curing conditions of heat treatment at 130℃for 35 minutes.
[ Resin composition ]
3, 4-Epoxycyclohexylmethyl-3, 4-epoxy-cyclohexane-carboxylate (100 parts by mass)
3 Boron fluoride monoethylamine (3 parts by mass)
Acetone (4 parts by mass)
The number of strands was 6, and the arithmetic average of the measurement results was used as the strand elastic modulus and strand strength of the carbon fiber strands.
< Analysis of stress sigma-Strain epsilon Curve >
The stress σ -strain ε curve obtained by the tensile test of the resin-impregnated wire harness was analyzed, and the coefficient A, B, C was calculated by fitting the curve with the strain ε (-) on the vertical axis and the stress σ (GPa) on the horizontal axis. Fitting was performed in a range of 0 to 3GPa in the stress sigma-strain epsilon curve obtained by measurement. Regarding fitting, fitting based on a 2-degree function was performed using Microsoft "Excel".
ε＝Aσ2+Bσ+C···(1)。
< Initial elastic modulus (GPa) >)
The initial elastic modulus of the carbon fiber bundle was calculated as follows using the coefficient B obtained by analyzing the stress σ -strain ε curve and fitting the curve by the formula (1).
Initial elastic modulus (GPa) =1/B.
< Degree of Crystal orientation of carbon fiber bundle pi (%) >
A measurement sample having a length of 4cm and a length of 1mm on each side of the quadrangular prism was prepared by aligning carbon fiber bundles to be measured and fixing the carbon fiber bundles with a collodion/ethanol solution. The prepared measurement sample was measured using a wide-angle X-ray diffraction apparatus under the following conditions.
X-ray source: cuK alpha ray (tube voltage 40kV, tube current 30 mA)
Detector: goniometer + monochromator + scintillation counter
Peaks appearing in the vicinity of 2θ=25 to 26 ° are scanned in the circumferential direction, and the half-value width H (°) of the obtained diffraction intensity distribution is obtained by using the following formula.
Crystal orientation degree pi (%) = [ (180-H)/180 ] ×100
In the examples, XRD-6100 manufactured by Shimadzu corporation was used as the wide-angle X-ray diffraction device.
< Crystallite size Lc (nm) >)
X-ray source: cuK alpha line (tube voltage 40kV, tube current 30 mA)
Detector: goniometer + monochromator + scintillation counter
Scan range: 2θ=10 to 40°
Scanning mode: step scan, step unit 0.02 °, count time 2 seconds.
In the obtained diffraction pattern, the half width was obtained for peaks appearing in the vicinity of 2θ=25 to 26 °, and the crystallite size was calculated from the value by the following equation of Scherrer (Scherrer).
Crystallite size (nm) =kλ/β 0cosθB
Wherein,
K:1.0, λ:0.15418nm (wavelength of X-ray)
β0：(βE 2-β1 2)1/2
Beta E: apparent half-value width (measured value) rad
β1：1.046×10-2rad
Θ B: diffraction angle of Bragg.
< Measurement of roundness (-) >
The polyacrylonitrile-based precursor fiber bundle or carbon fiber bundle was cut perpendicularly to the fiber axis direction with a single blade razor, and the resulting cross section was observed from the perpendicular direction of the fiber cross section using a Scanning Electron Microscope (SEM) "S-4800" manufactured by HITACHI HIGH-technologies company. The acquired image was analyzed using image analysis software "ImageJ", and the circularity was calculated from the perimeter and area of the cross section of the single fiber contained in the fiber cross section as defined below. In 1 cross section, this measurement was repeated for 25 single fibers at random, and the value obtained by averaging the roundness was taken as the roundness of the single fiber cross section.
The roundness of the cross section of the filament is defined as follows based on the perimeter L and the area a cs of the cross section of the filament.
(True circle) =4pi a cs/L2.
< Evaluation of high-order processability >
The carbon fiber bundle tube was set in a creel, pulled out at a tension of 1.6mN/dtex, passed through 10 free rolls, rubbed against 5 fixed guides, pulled by a driving roll at a speed of 10 m/min, and wound by a winder. At this time, the fluff generated was counted for 10 minutes immediately before the driving roller, and evaluated by the following index.
A: less than 10/m
B: more than 10 and less than 50/m
C:50 or more per m.
Examples 1 to 4
The polyacrylonitrile copolymer formed by acrylonitrile and itaconic acid is polymerized by a solution polymerization method by taking dimethyl sulfoxide as a solvent to prepare the polyacrylonitrile copolymer, so as to obtain spinning solution. The obtained dope was coagulated by a wet spinning method in which the dope was introduced into a coagulation bath containing an aqueous solution of dimethyl sulfoxide from a spinneret for producing filaments having a pore number of 50,000, and a fiber bundle was produced. The fiber bundle is subjected to water washing at 30 to 98℃by a conventional method, and then stretched. Then, the fiber bundle after the water washing and stretching was given an amino-modified silicone oil agent, and a drying densification treatment was performed by using a heated roll at 130℃to obtain a polyacrylonitrile-based precursor fiber bundle having 50,000 filaments and a single fiber fineness of 1.50 dtex. The polyacrylonitrile-based precursor fiber bundles were not subjected to twisting treatment.
The obtained polyacrylonitrile-based precursor fiber bundles were treated with a flame-retardant step, a pre-carbonization step, and a carbonization step under the conditions shown in table 1, to obtain carbon fiber bundles. In the flame-retardant step, the pre-carbonization step, and the carbonization step, the heat treatment is performed by stepwise increasing the temperature in a plurality of heat treatment furnaces having different temperatures. In addition, in the flame-retardant step, the pre-carbonization step, and the carbonization step, twisting treatment is not performed. The properties of the obtained carbon fiber bundles are shown in table 2.
Example 5
The same procedure as in example 1 was carried out except that the discharge amount of the spinning dope was changed to obtain a polyacrylonitrile-based precursor fiber bundle having a single fiber fineness of 1.65dtex, and the conditions of the subsequent pre-carbonization step and carbonization step were changed as shown in table 1.
Example 6
The same procedure as in example 1 was carried out except that the discharge amount of the spinning dope was changed to obtain a polyacrylonitrile-based precursor fiber bundle having a single fiber fineness of 2.40dtex, and the conditions of the subsequent pre-carbonization step and carbonization step were changed as shown in table 1.
Example 7
The same procedure as in example 1 was carried out except that the flame retardant temperature, the stretch ratio in the pre-carbonization step, and the stretch ratio in the carbonization step were changed to the conditions shown in table 1.
Comparative example 1
A carbon fiber bundle was obtained in the same manner as in example 1, except that the stretching ratio in the pre-carbonization step was changed to 1.00, the stretching ratio in the carbonization step was changed to 0.960, and the product of the stretching ratios was changed to 0.960. The central term of the obtained carbon fiber bundle of formula (2) had a value of-307, an initial elastic modulus of 213GPa, and poor operability at the time of high-order processing.
Comparative example 2
A carbon fiber bundle was obtained in the same manner as in example 1, except that the stretching ratio in the pre-carbonization step was 1.01, the stretching ratio in the carbonization step was 0.955, and the product of the stretching ratios was 0.965. The central term of the obtained carbon fiber bundle of formula (2) had a value of-286, an initial elastic modulus of 215GPa, and poor operability at the time of high-order processing.
Comparative example 3
A carbon fiber bundle was obtained in the same manner as in example 1, except that the stretching ratio in the pre-carbonization step was 1.02, the stretching ratio in the carbonization step was 0.950, and the product of the stretching ratios was 0.969. The central term of the obtained carbon fiber bundle of formula (2) had a value of-287, an initial elastic modulus of 220GPa, and poor operability in high-order processing.
Comparative example 4
A carbon fiber bundle was obtained in the same manner as in example 1, except that the ejection amount of the spinning dope was changed to obtain a polyacrylonitrile-based precursor fiber bundle having a single fiber fineness of 0.80dtex, and further, the stretching ratio in the pre-carbonization step was changed to 1.05, the stretching ratio in the carbonization step was changed to 0.950, and the product of the stretching ratios was changed to 0.998. The central term of the obtained carbon fiber bundle of formula (2) had a value of-290, an initial elastic modulus of 218GPa and poor operability in high-order processing.
Comparative example 5
A carbon fiber bundle was obtained in the same manner as in example 1, except that the ejection amount of the spinning dope was changed to obtain a polyacrylonitrile-based precursor fiber bundle having a single fiber fineness of 3.00dtex, and further, the stretching ratio in the pre-carbonization step was changed to 1.00, the stretching ratio in the carbonization step was changed to 0.955, and the product of the stretching ratios was changed to 0.955. The central term of the obtained carbon fiber bundle of formula (2) had a value of-277, an initial elastic modulus of 225GPa, and poor operability at the time of high-order processing.
Comparative example 6
A carbon fiber bundle was obtained in the same manner as in example 1, except that a polyacrylonitrile-based precursor fiber bundle was obtained in the same manner as in example 1, except that the dry-wet spinning method in which the spinning dope was once discharged from the spinneret into the air and then introduced into the coagulation bath containing an aqueous solution of dimethyl sulfoxide was used, and the draw ratio of the pre-carbonization step was changed to 1.01, the draw ratio of the carbonization step was changed to 0.965, and the product of the draw ratios was changed to 0.975. The central term of the obtained carbon fiber bundle represented by formula (2) had a value of-290, an initial elastic modulus of 223GPa, and poor operability in high-order processing.
Comparative example 7
As a result of the same operation as in example 1 except that the stretch ratio in the pre-carbonization step was changed to 1.23, the fiber bundles were broken in the pre-carbonization step, and carbon fiber bundles could not be obtained.
Comparative example 8
The same procedure as in example 1 was repeated except that the stretching ratio in the pre-carbonization step was 1.05, the stretching ratio in the carbonization step was 1.000, and the product of the stretching ratios was 1.050, whereby the fiber bundles were broken in the carbonization step, and carbon fiber bundles could not be obtained.
Comparative example 9
The same procedure as in example 1 was repeated except that the temperature in the flame-retardant step was changed to the conditions shown in table 1 and the draw ratio in the pre-carbonization step was 1.05, and as a result, fluff of the pre-carbonized fiber bundles was increased and the quality was greatly deteriorated, so that the operation of the subsequent step was not performed, and carbon fiber bundles were not obtained.
Comparative example 10
The same procedure as in example 1 was repeated except that the temperature in the flame-retardant step was changed to the conditions shown in table 1 and the draw ratio in the pre-carbonization step was 1.05, and as a result, fluff of the pre-carbonized fiber bundles was increased and the quality was greatly deteriorated, so that the operation of the subsequent step was not performed, and carbon fiber bundles were not obtained.
TABLE 1
TABLE 2
/>
Claims (6)
1. A carbon fiber bundle having an initial elastic modulus of 240 to 279GPa and a filament number of 24,000 ～ 72,000, wherein a relation between a coefficient A obtained from a nonlinear approximation formula (1) in a stress sigma-strain epsilon curve in a tensile test of a resin impregnation strand and a crystal orientation degree pi (%) in a wide-angle X-ray diffraction measurement satisfies formula (2) in a stress range of 0 to 3GPa, wherein the carbon fiber bundle is substantially untwisted,
ε＝Aσ2+Bσ+C…(1)
-410≤(0.0000832Π2-0.0184Π+1.00)/A≤-310···(2)
Wherein A, B, C is a coefficient of a quadratic function of stress σ and strain ε, and ε is a degree of crystal orientation.
2. The carbon fiber bundle according to claim 1, wherein the single fiber fineness is 0.63 to 1.35dtex.
3. The carbon fiber bundle according to claim 1 or 2, wherein the roundness of the single fiber section is 0.86 to 0.98.
4. A method for producing the carbon fiber bundle according to any one of claims 1 to 3, wherein the method comprises:
A flame-retardant step of heat-treating a substantially untwisted polyacrylonitrile-based precursor fiber bundle having a filament number of 24,000 ～ 72,000 at a temperature of 220 to 280 ℃ in an oxidizing atmosphere; and a pre-carbonization step of heat-treating the flame-resistant fiber bundles obtained in the flame-resistant step in an inert atmosphere at a maximum temperature of 300 to 1,000 ℃; and a carbonization step of heat-treating the pre-carbonized fiber bundles obtained by the pre-carbonized fiber bundles at a maximum temperature of 1,000 to 1,600 ℃ in an inert atmosphere,
The stretching ratio in the pre-carbonization step is 1.05-1.20, the stretching ratio in the carbonization step is 0.960-0.990, the product of the stretching ratio of the pre-carbonization step and the stretching ratio of the carbonization step is 1.020-1.180,
In the flame-retardant step, heat treatment is performed stepwise on the polyacrylonitrile-based precursor fiber bundles in a plurality of heat treatment furnaces set to different temperatures from each other or in a plurality of heat treatment sections set to different temperatures from each other in the heat treatment furnaces, and in the flame-retardant step, the temperature of the heat treatment furnace or the heat treatment section having the lowest temperature is set to less than 230 ℃, and the temperature of the heat treatment furnace or the heat treatment section having the highest temperature is set to 280 ℃ or less.
5. The method for producing a carbon fiber bundle according to claim 4, wherein the polyacrylonitrile-based precursor fiber bundle has a single fiber fineness of 1.20 to 2.40dtex.
6. The method for producing a carbon fiber bundle according to claim 4 or 5, wherein the polyacrylonitrile-based precursor fiber bundle has a single fiber cross section with a roundness of 0.86 to 0.98.
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