Carbon fiber bundle, prepreg, and carbon fiber reinforced composite material

Abstract

The present invention addresses the problem of providing: a carbon fiber bundle that has good quality and has excellent strand tensile strength, strand tensile elastic modulus, and single-fiber compression strength; and a prepreg and a carbon fiber-reinforced composite material which are obtained using the carbon fiber bundle.　In order to achieve this purpose, a carbon fiber bundle according to the present invention has a strand tensile strength of 4.5-6.5 GPa, a strand tensile elastic modulus of not less than 400 GPa, a crystallite size of 4.0-4.7 nm, and a single-fiber diameter of 5.2-6.2 μm, and has substantially no twisting.

Description

Technical Field

[0001] The present invention relates to a carbon fiber bundle suitably used for sports applications such as golf shafts and fishing rods and other general industrial applications, a prepreg obtained using the carbon fiber bundle, and a carbon fiber reinforced composite material.

Background Art

[0002] Carbon fiber bundles have been increasingly used in various industrial fields in recent years as reinforcing fibers for fiber-reinforced composite materials due to their extremely high specific strength and specific modulus. In particular, in fields where weight reduction is emphasized, the replacement of conventional metal materials with carbon fiber composite materials has been accelerating. Among sports applications, weight reduction is required not only for golf shafts, fishing rods, and bicycles but also for rackets, and their applications are expanding more and more.

[0003] In the case of weight reduction for sports applications, it is required to have excellent physical property balance in a wide range, including further improvement of the mechanical properties of carbon fiber bundles centered on the resin-impregnated strand tensile elastic modulus (hereinafter sometimes simply referred to as the strand elastic modulus), and further improvement of the tensile and compressive strengths as carbon fiber reinforced composite materials. The most widely used polyacrylonitrile-based carbon fiber bundles are industrially manufactured through a flame-retardant conversion process of converting polyacrylonitrile-based precursor fiber bundles into flame-retardant fiber bundles in an oxidizing atmosphere at 200 to 300 °C, a pre-carbonization process of pre-carbonizing in an inert atmosphere at a maximum temperature of 500 to 1,000 °C, and a carbonization process of carbonizing in an inert atmosphere at a maximum temperature of 1,200 to 3,000 °C. It is known that the strand elastic modulus of carbon fiber bundles can be increased as the maximum temperature in the carbonization process is increased. However, it is generally said that carbon fiber bundles with a high strand elastic modulus obtained by increasing the maximum temperature of the carbonization process have a large crystallite size and a decrease in the compressive strength of the carbon fiber reinforced composite material (Patent Document 1), and there is generally a trade-off relationship between the compressive strength and the strand elastic modulus of the carbon fiber reinforced composite material. Therefore, studies have been conducted to improve the strand elastic modulus without increasing the crystallite size. For example, as a technique for reducing the crystallite size of carbon fiber bundles, a technique has been proposed in which ions are implanted on the surface of carbon fibers to reduce the crystallinity of the carbon fiber surface layer and improve the compressive strength of single fibers (Patent Document 1). Also, as a technique for improving the strand elastic modulus without increasing the crystallite size of carbon fiber bundles, it is known to increase the draw ratio in the carbonization process, and in order to increase the draw ratio in the carbonization process without reducing the processability, techniques have been proposed in which the precursor fiber bundles are entangled or twisted to improve the drawability in the carbonization process (Patent Documents 2 to 6). In addition, in order to improve the compressive strength of carbon fiber reinforced composite materials without relying on drawing, a technique has been proposed in which the flame-retardant structure is controlled to improve the single-fiber compressive strength of carbon fiber bundles (Patent Document 7).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, by implanting ions into carbon fibers as in Patent Document 1, although the crystallite size decreased and the apparent compressive strength measured by the loop method increased to as much as 10.0 GPa, it was not satisfactory from the viewpoint of the balance with the strand tensile elastic modulus (hereinafter sometimes simply referred to as the strand elastic modulus). Further, as in Patent Documents 2 to 6, by applying entanglement or twisting, it became possible not to break even when a high tension was applied in the carbonization process, and although the strand elastic modulus was improved, it was not possible to satisfy the single fiber compressive strength and the small number of fiber ends during prepreg processing. Further, according to the technique of Patent Document 7, the flame-resistant structure can be controlled to increase the single fiber compressive strength, but the level of the strand elastic modulus is low. When only the maximum temperature of the carbonization process is increased based on the technique of Patent Document 7, the decrease in the single fiber compressive strength is large, and it is not possible to simultaneously exhibit the resin-impregnated strand tensile strength, the strand elastic modulus, and the single fiber compressive strength at a high level. An object of the present invention is to obtain a carbon fiber bundle that simultaneously exhibits excellent strand strength, strand elastic modulus, and compressive strength with good quality in order to solve such problems.

Means for Solving the Problems

[0006] The inventors of the present invention have increased the fineness of the carbon fiber precursor fiber to improve productivity, and by controlling the stretching in the pre-carbonization process, the stretching, heating rate, and maximum temperature in the carbonization process, they have increased the single fiber diameter of the carbon fiber and reduced the crystallite size, thereby achieving both improvement in mechanical properties and maintenance of quality to a level that could not be achieved with conventional carbon fiber bundles, and thus arriving at the present invention.

[0007] In order to achieve the above object, the carbon fiber bundle of the present invention has the following characteristics. (1) A carbon fiber bundle having a strand tensile strength of 4.5 GPa or more and 6.5 GPa or less, a strand tensile modulus of elasticity of 400 GPa or more, a crystallite size of 4.0 nm or more and 4.7 nm or less, a single fiber diameter of 5.2 μm or more and 6.2 μm or less, and being substantially untwisted. (2) The carbon fiber bundle according to (1), having a number of unwound flyings of 0.3 pieces / m or less. (3) The carbon fiber bundle according to (1) or (2), having a number of drafting flyings of 6 pieces / 100 m or less. (4) The carbon fiber bundle according to any one of (1) to (3), having a density of 1.84 g / cm 3 or less. (5) The carbon fiber bundle according to any one of (1) to (4), having a single fiber diameter of 5.5 μm or more and 6.2 μm or less. (6) The carbon fiber bundle according to (1) or (2), having a strand tensile strength of 4.8 GPa or more and 6.5 GPa or less. (7) The carbon fiber bundle according to (1) or (2), having a strand tensile strength of 5.0 GPa or more and 6.5 GPa or less. (8) The carbon fiber bundle according to (1) or (2), having a strand tensile strength of 5.5 GPa or more and 6.5 GPa or less. (9) A prepreg in which the carbon fiber bundle according to any one of (1) to (8) is impregnated with a thermosetting resin, and the prepreg has a number of prepreg flying defects of 7 pieces / 100 m 2 or less. (10) A prepreg in which the carbon fiber bundle according to any one of (1) to (9) is impregnated with a thermosetting resin, and the cured product of the thermosetting resin has a modulus of elasticity of 3.0 GPa or more. (11) A prepreg obtained by impregnating a carbon fiber bundle according to any one of (1) to (10) with a thermosetting resin, wherein the elastic modulus of the cured product of the thermosetting resin is 3.8 GPa or more and 5.5 GPa or less. (12) A carbon fiber reinforced composite material comprising the carbon fiber bundle according to any one of (1) to (11) and a matrix resin. (13) Comprising the carbon fiber bundle according to any one of (1) to (12) and a matrix resin, A carbon fiber reinforced composite material having a composite 0° compression strength of 1200 MPa or more and 1350 MPa or less and a composite 0° tensile elastic modulus of 245 GPa or more and 270 GPa or less.

Advantages of the Invention

[0008] According to the present invention, the effect of simultaneously exhibiting the strand strength, strand elastic modulus, and compressive strength of the carbon fiber bundle while maintaining good quality can be obtained.

Embodiments for Carrying Out the Invention

[0009] The carbon fiber bundle of the present invention has a strand tensile strength of 4.5 GPa or more and 6.5 GPa or less. When the strand tensile strength of the carbon fiber bundle is 4.5 GPa or more, the balance with the high single fiber compressive strength of the carbon fiber bundle of the present invention is improved, and it is easy to sufficiently maintain the compressive strength when made into a carbon fiber reinforced composite material. Although the strand tensile strength cannot be too high, from the viewpoint of productivity, it is 6.5 GPa or less. The strand strength is the value evaluated by the strand tensile test described in the Examples section. To make the strand tensile strength within the above range, it is important to subject the polyacrylonitrile-based precursor fiber bundle to flame resistance while controlling the temperature, and to subject the flame-resistant fiber bundle to preliminary carbonization and carbonization while controlling the temperature and the draw ratio.

[0010] Also, such strand strength is preferably 4.8 GPa or more and 6.5 GPa or less. If it is 4.8 GPa or more, the tensile strength of the composite is further improved. Such strand strength can be adjusted mainly by controlling the maximum carbonization temperature and the draw ratio in the carbonization process.

[0011] And such strand strength is more preferably 5.0 GPa or more and 6.5 GPa or less. If it is 5.0 GPa or more, the tensile strength of the composite is further improved. Such strand strength can be adjusted mainly by controlling the maximum carbonization temperature, the heating rate of the carbonization process, and the draw ratio of the carbonization process.

[0012] Furthermore, such strand strength is particularly preferably 5.5 GPa or more and 6.5 GPa or less. If it is 5.5 GPa or more, the tensile strength of the composite is particularly improved. Such strand strength can be adjusted by controlling the carbonization process and, mainly based on the density of the flame-resistant fiber bundle, controlling the flame-resistant temperature and treatment time so that the structure of the flame-resistant yarn falls within a specific range from the peak ratio in the infrared spectrum of each flame-resistant fiber bundle after the first and second flame-resistant processes. The control of such conditions will be described in detail in the manufacturing method. More preferably, it is 5.8 GPa or more.

[0013] The carbon fiber bundle of the present invention has a strand tensile modulus of elasticity of 400 GPa or more, preferably 420 GPa or more, more preferably 430 GPa or more, and particularly preferably 440 GPa or more. If the strand modulus of elasticity is 400 GPa or more, it is preferable for increasing the tensile modulus of elasticity of the carbon fiber reinforced composite material. Also, although the higher the strand modulus of elasticity is, the more preferable it is, it is preferably adjusted so that 500 GPa is the upper limit from the viewpoint of compressive strength. Usually, when the strand modulus of elasticity in the strand tensile test increases, the single fiber compressive strength decreases, but in the present invention, both can be achieved even under this premise. To make the strand modulus of elasticity within the above range, it is necessary to increase the orientation degree of the polyacrylonitrile-based precursor fiber, and control while increasing the draw ratio and the maximum temperature of the carbonization process in the preliminary carbonization treatment process and the carbonization process described later.

[0014] The carbon fiber bundle of the present invention has a crystallite size of 4.0 nm or more, preferably 4.1 nm or more, more preferably 4.2 nm or more. When the crystallite size is less than 4.0 nm, it is necessary to perform high drawing in the carbonization process to increase the orientation degree in order to satisfy the elastic modulus, and the quality may deteriorate. If the crystallite size is 4.0 nm or more, the compressive strength of the carbon fiber bundle, the strand elastic modulus in the strand tensile test, and the hairiness quality of the carbon fiber can be satisfied simultaneously. Further, if the crystallite size is too large, the single fiber compressive strength may decrease, so it is adjusted to be 4.7 nm or less, preferably 4.5 nm or less, more preferably 4.4 nm or less. That is, the crystallite size is 4.0 nm or more and 4.7 nm or less, preferably 4.1 nm or more and 4.5 nm or less, more preferably 4.2 nm or more and 4.4 nm or less.

[0015] Generally, as the crystallite size of carbon fiber increases, the single fiber compressive strength tends to decrease. However, the carbon fiber bundle of the present invention shows that both the crystallite size and the single fiber compressive strength are high. The crystallite size in the present invention can be evaluated by the wide-angle X-ray diffraction method described in the Examples section. In order to control the conditions within the above range of the crystallite size, it is necessary to increase the maximum temperature of the carbonization process, increase the draw ratio of the carbonization process, and the like.

[0016] The single fiber diameter of the carbon fiber bundle of the present invention is 5.2 μm or more. The single fiber diameter of the carbon fiber bundle is evaluated by the method described in the Examples section. When the cross-sectional shape of the single fiber is not a perfect circle, it is substituted with the equivalent circular diameter. The equivalent circular diameter refers to the diameter of a perfect circle having the same cross-sectional area as the actually measured cross-sectional area of the single fiber.

[0017] When manufacturing a prepreg, since the impregnation property depends on the single fiber diameter, a large single fiber diameter enables efficient production of a composite material. Further, since the breaking load per single fiber is determined from the strand strength and the single fiber cross-sectional area, the single fiber diameter affects the breaking load per single fiber. In addition, as the single fiber diameter increases, the tendency of hairiness due to rubbing during the process decreases, which affects the quality.

[0018] If the single fiber diameter is 5.2 μm or more, the quality is likely to be good when producing carbon fiber bundles or making carbon fiber composite materials. The single fiber diameter is preferably 5.3 μm or more, more preferably 5.5 μm or more. If the single fiber diameter becomes too large, in the firing process, the reaction within the single fiber becomes non-uniform, and the strand strength and strand elastic modulus may decrease. Therefore, it is adjusted to be 6.2 μm or less. That is, the single fiber diameter is 5.2 μm or more and 6.2 μm or less, preferably 5.3 μm or more and 6.2 μm or less, more preferably 5.5 μm or more and 6.2 μm or less.

[0019] The single fiber diameter can be adjusted by controlling the discharge amount from the die during the spinning of the carbon fiber precursor fiber bundle and the draw ratio in each process.

[0020] The carbon fiber bundle of the present invention is substantially untwisted. That the carbon fiber bundle is substantially untwisted means that there is no twist at all, or even if there is twist, it is 0.5 turns or less per meter. When the carbon fiber bundle is untwisted, when used as a reinforcing fiber for a carbon fiber reinforced composite material, it has excellent spreadability of the carbon fiber bundle, and the physical properties and quality of the carbon fiber reinforced composite material are often excellent.

[0021] In the present invention, the density of the carbon fiber bundle is preferably 1.84 g / cm 3 or less. The lower the density, the better the specific strength and specific elastic modulus, so that a carbon fiber composite material can be efficiently produced. If the density is 1.84 g / cm 3 or less, it is likely to be efficient in producing a carbon fiber composite material. More preferably, it is 1.83 g / cm 3 or less, and even more preferably 1.82 g / cm 3 or less.

[0022] The carbon fiber bundle of the present invention preferably has a number of protruding flyers of 0.3 or less per meter, more preferably 0.2 or less per meter, and even more preferably 0.1 or less per meter. When the number of protruding flyers of the carbon fiber bundle increases, the high-order processability of the carbon fiber reinforced composite material may be reduced, and the compressive strength of the carbon fiber reinforced composite material may decrease. If the number of protruding flyers of the carbon fiber is 0.3 or less per meter, the high-order processability and compressive strength of such a carbon fiber reinforced composite material tend to be maintained at satisfactory values.

[0023] The number of protruding flyers is measured by the method described in the Examples section. In order to adjust the number of protruding flyers per meter of the carbon fiber bundle to the above range, it is necessary to control the draw ratio in the carbonization process while controlling the draw ratio in the preliminary carbonization process described later.

[0024] The carbon fiber bundle of the present invention preferably has a number of unravelling flyers of 6 or less per 100 meters, more preferably 5 or less per 100 meters, and even more preferably 4 or less per 100 meters. When the number of unravelling flyers of the carbon fiber bundle increases, the high-order processability of the carbon fiber reinforced composite material may be reduced, and when it is made into a carbon fiber reinforced composite material, the compressive strength of the carbon fiber reinforced composite material may decrease due to fiber breakage at the fracture origin caused by compressive stress. If the number of unravelling flyers of the carbon fiber bundle is 6 or less per 100 meters, the high-order processability and compressive strength of such a carbon fiber reinforced composite material tend to be maintained at satisfactory values.

[0025] The number of unravelling flyers is measured by the method described in the Examples section. In order to adjust the number of unravelling flyers per 100 meters of the carbon fiber bundle to the above range, it is necessary to control the draw ratio in the carbonization process while controlling the draw ratio in the preliminary carbonization process described later.

[0026] The prepreg of the present invention is a prepreg in which the above carbon fiber bundle is impregnated with a thermosetting resin. As the prepreg, the number of prepreg flyer defects is preferably 7 or less per 100 meters 2 or less, more preferably 3 or less per 100 meters 2The following, more preferably 1 piece / 100 m 2 The following. When the number of prepreg fluff defects increases, when made into a carbon fiber reinforced composite material, the locations where the fibers are broken may become fracture initiation points, and the tensile strength and compressive strength of the carbon fiber reinforced composite material may decrease. The number of prepreg fluff defects in the carbon fiber bundle is 7 pieces / 100 m 2 If it is below this, the high-order processability, tensile strength, and compressive strength of such a carbon fiber reinforced composite material tend to be maintained at satisfactory values.

[0027] The number of prepreg fluff defects is measured by the method described in the Examples section. For 100 m of prepreg 2 In order to adjust the number of prepreg fluff defects per 100 m of prepreg to the above range, it is necessary to control the draw ratio in the carbonization process and the carbonization temperature while controlling the draw ratio in the preliminary carbonization process described later.

[0028] The prepreg of the present invention is a prepreg in which the above carbon fiber bundle is impregnated with a thermosetting resin. As the thermosetting resin, those having a cured product elastic modulus of preferably 3.0 GPa or more, more preferably 3.2 GPa or more, and even more preferably 3.8 GPa or more are preferred. When the elastic modulus of the cured product of the thermosetting resin is high, the single fiber compressive strength of the carbon fiber bundle in the obtained carbon fiber reinforced composite material can be sufficiently exhibited, and the compressive strength of the entire carbon fiber reinforced composite material can be increased. If the elastic modulus of the cured product of the thermosetting resin is 3.0 GPa or more, the value of the compressive strength of the carbon fiber reinforced composite material can be satisfied. Although it is preferable that the elastic modulus of the cured product of the thermosetting resin is higher, 7.0 GPa, more preferably 6.7 GPa, and even more preferably 5.5 GPa are sufficient. The type of thermosetting resin is not particularly limited, and examples include epoxy resins, vinyl ester resins, phenolic resins, benzoxazine resins, bismaleimide resins, cyanate ester resins, polyimide resins, etc. Among them, epoxy resins are preferred from the viewpoint of excellent handleability and curability in the state before curing.

[0029] Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, novolac type epoxy resins, epoxy resins having a fluorene skeleton, epoxy resins made from copolymers of phenolic compounds and dicyclopentadiene, glycidyl ether type epoxy resins such as diglycidyl resorcinol, tetrakis (glycidyloxyphenyl) ethane, and tris (glycidyloxyphenyl) methane, and glycidyl amine type epoxy resins such as tetraglycidyl diaminodiphenylmethane, triglycidyl aminophenol, triglycidyl aminocresol, and tetraglycidyl xylylenediamine. These epoxy resins may be used alone or in combination of two or more.

[0030] The curing agent for the epoxy resin is not particularly limited as long as it can cure the epoxy resin, and examples include amines such as aromatic amines and alicyclic amines, acid anhydrides, polyaminoamides, organic acid hydrazides, isocyanates, etc. Amine curing agents are preferred because they are excellent in the mechanical properties and heat resistance of the resulting resin cured product. As the amine curing agent, diamino diphenyl sulfone, diamino diphenyl methane which are aromatic amines, dicyandiamide or its derivatives which are aliphatic amines, hydrazide compounds, etc. can be used.

[0031] Also, the curing agent may be used in combination with a curing accelerator. Examples of the curing accelerator to be combined include ureas, imidazoles, Lewis acid catalysts, etc. Among them, urea compounds are preferably used in view of the balance between storage stability and catalytic ability. Examples of such urea compounds include N,N-dimethyl-N'-(3,4-dichlorophenyl) urea, toluene bis (dimethylurea), 4,4'-methylenebis (phenyldimethylurea), 3-phenyl-1,1-dimethylurea, etc.

[0032] A prepreg is a sheet-like intermediate substrate containing carbon fiber bundles and a thermosetting resin. Such a prepreg can be obtained by impregnating carbon fiber bundles with a thermosetting resin. Examples of the impregnation method include the wet method and the hot melt method (dry method).

[0033] The wet method is a method in which carbon fiber bundles are immersed in a solution obtained by dissolving a thermosetting resin in a solvent such as methyl ethyl ketone or methanol, then the carbon fiber bundles are pulled up, and the solvent is evaporated from the carbon fiber bundles using an oven or the like to impregnate the carbon fiber bundles with an epoxy resin composition. The hot melt method is a method in which a thermosetting resin whose viscosity has been reduced by heating is directly impregnated into carbon fiber bundles, or a film coated with a thermosetting resin on a release paper or the like is prepared, and then the film is overlaid from both sides or one side of the carbon fiber bundles, and the carbon fiber bundles are impregnated with the resin by heating and pressing. Here, only one carbon fiber bundle may be used, or a plurality of carbon fiber bundles may be aligned and used.

[0034] The carbon fiber reinforced composite material of the present invention is a composite material containing the above carbon fiber bundles and a matrix resin. As the matrix resin, a cured product of a thermosetting resin, a thermoplastic resin, or a mixture thereof can be used. When a thermosetting resin is used, it may be produced via the prepreg described above. In that case, it is preferable to use a thermosetting resin having a cured product elastic modulus of 3.0 GPa or more from the viewpoint of increasing the compressive strength of the carbon fiber reinforced composite material. The type of thermosetting resin is not particularly limited, and they can be appropriately combined and used from those described above.

[0035] The carbon fiber composite material of the present invention is a carbon fiber composite material manufactured using a prepreg in which the above carbon fiber bundle is impregnated with a thermosetting resin. The composite 0° compression strength is preferably 1200 MPa or more, more preferably 1220 MPa or more, still more preferably 1240 MPa or more, and the composite 0° tensile elastic modulus is preferably 245 GPa or more, more preferably 250 GPa or more, still more preferably 255 GPa or more. When the composite 0° compression strength and the composite 0° tensile elastic modulus of the carbon fiber composite material are high, the molded body manufactured from the obtained carbon fiber composite material can be made lighter and have higher physical properties. If the composite 0° compression strength is 1200 MPa or more and the composite 0° tensile elastic modulus is 245 GPa or more, the weight reduction and property improvement by the carbon fiber composite material can be satisfactory. Although it is preferable that the composite 0° compression strength is higher, 1350 MPa, more preferably 1330 MPa, still more preferably 1310 MPa is also sufficient. Also, although it is preferable that the composite 0° elastic modulus is higher, 270 GPa, more preferably 265 GPa, still more preferably 260 GPa is also sufficient.

[0036] Next, the manufacturing method for manufacturing the carbon fiber bundle of the present invention will be described.

[0037] In the production of the carbon fiber bundle, a polyacrylonitrile-based precursor fiber bundle is obtained. As the raw material used for the production of the polyacrylonitrile-based precursor fiber bundle, it is preferable to use a polyacrylonitrile copolymer. In the manufacturing method for manufacturing the carbon fiber bundle of the present invention, the polyacrylonitrile copolymer refers to a copolymer in which at least acrylonitrile is the main constituent component of the copolymer. The main constituent component usually refers to a constituent component that occupies 90 to 100% by mass of the polymer. As the monomer that can be used as the copolymerization component, from the viewpoint of promoting flame resistance, a monomer containing one or more carboxylic acid groups or amide groups is preferably used. For example, as the monomer containing a carboxylic acid group, acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts, and ammonium salts, etc. can be mentioned. Also, as the monomer containing an amide group, acrylamide, etc. can be mentioned.

[0038] In the production of a polyacrylonitrile-based precursor fiber bundle, as a method for producing a polyacrylonitrile copolymer, it can be selected from known polymerization methods.

[0039] In producing a polyacrylonitrile-based precursor fiber bundle, either a dry-wet spinning method or a wet spinning method may be used as the spinning method, but it is preferable to use the dry-wet spinning method, which is advantageous for the strand strength of the resulting carbon fiber bundle. The spinning process includes a spinning step of discharging a spinning dope from a spinneret into a coagulation bath for spinning, a water washing step of washing the fibers obtained in the spinning step in a water bath, a water bath stretching step of stretching the fiber bundle obtained in the water washing step in a water bath, and a dry heat treatment step of dry heat-treating the fiber bundle obtained in the water bath stretching step. If necessary, it includes a steam stretching step of steam stretching the fiber bundle obtained in the dry heat treatment step. It should be noted that the order of each step can also be appropriately changed.

[0040] The spinning dope is obtained by dissolving the above-mentioned polyacrylonitrile copolymer in a solvent in which the polyacrylonitrile copolymer is soluble, such as an organic solvent such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, or an aqueous solution such as nitric acid, zinc chloride, and rhodan soda.

[0041] It is preferable to include in the coagulation bath a solvent such as dimethyl sulfoxide, dimethylformamide, and dimethylacetamide used as a solvent for the spinning dope and a coagulation promoting component. As the coagulation promoting component, those that do not dissolve the polyacrylonitrile copolymer and are compatible with the solvent used in the spinning solution can be used. Specifically, it is preferable to use water as the coagulation promoting component.

[0042] As the water washing bath in the water washing step, it is preferable to use a multi-stage water washing bath with a temperature of 30 to 98°C. Also, the stretching ratio in the water bath stretching step is preferably 2 to 6 times.

[0043] After the water bath stretching process, for the purpose of preventing fusion between single fibers, it is preferable to apply an oil agent composed of silicone or the like to the fiber bundle. Such a silicone oil agent preferably uses a modified silicone, and preferably uses one containing a highly heat-resistant amino-modified silicone.

[0044] The dry heat treatment process can utilize a known method. For example, the drying temperature is exemplified as 100 to 200°C.

[0045] After the above-described water washing process, water bath stretching process, oil agent application process, and dry heat treatment process, if necessary, by performing steam stretching, a polyacrylonitrile-based precursor fiber bundle suitable for obtaining the carbon fiber bundle of the present invention can be obtained. In steam stretching, in pressurized steam, the stretching ratio is preferably 2 to 6 times.

[0046] From the viewpoint of increasing the strand strength of the carbon fiber bundle, the single fiber fineness of the polyacrylonitrile-based precursor fiber bundle is preferably 0.4 to 1.5 dtex, more preferably 0.5 to 1.4 dtex, and even more preferably 0.6 to 1.3 dtex.

[0047] In a method for producing a carbon fiber bundle, a polyacrylonitrile-based precursor fiber bundle is subjected to a flame retardant treatment process, a pre-carbonization process, and a carbonization process to obtain a carbon fiber bundle.

[0048] In the manufacturing method for producing the carbon fiber bundle of the present invention, the flame resistance improvement step means heat-treating a polyacrylonitrile-based precursor fiber bundle at 200 to 300°C in an atmosphere containing oxygen. The treatment time of the flame resistance improvement step can be appropriately selected preferably in the range of 10 to 100 minutes. However, for the purpose of improving the strand tensile strength in the strand tensile test of the obtained carbon fiber bundle, the specific gravity of the obtained flame resistance improved fiber is preferably in the range of 1.30 to 1.36, more preferably in the range of 1.31 to 1.35, and the treatment time of the flame resistance improvement step is set accordingly. A more preferable treatment time for flame resistance improvement depends on the flame resistance improvement temperature. If the specific gravity of the flame resistance improved fiber is 1.30 or more, physical properties such as the strand elastic modulus of the carbon fiber bundle can be sufficiently exhibited, and if the specific gravity is 1.36 or less, the strand tensile strength can be increased. The specific gravity of the flame resistance improved fiber is controlled by the treatment time and the flame resistance improvement temperature of the flame resistance improvement step.

[0049] In the manufacturing method of the carbon fiber bundle of the present invention, in order to increase the strand tensile strength in the strand tensile test of the carbon fiber bundle, especially when the polyacrylonitrile-based precursor fiber bundle is subjected to the flame resistance improvement step, the obtained flame resistance improved fiber bundle has a ratio of the peak intensity at 1453 cm -1 to the peak intensity at 1370 cm -1 in the infrared spectrum in the range of 0.70 to 0.75, and a ratio of the peak intensity at 1254 cm -1 to the peak intensity at 1370 cm -1 in the infrared spectrum in the range of 0.50 to 0.65. It is preferable to control the conditions so that this is achieved. The peak at 1453 cm -1 in the infrared spectrum is a peak derived from alkene and decreases as the flame resistance improvement progresses. The peaks at 1370 cm -1 and 1254 cm -1 are peaks derived from the flame resistance improved structure and increase as the flame resistance improvement reaction progresses. Further, the ratio of the peak intensity at 1254 cm -1 to the peak intensity at 1370 cm -1It is preferable to set the flame-retardant conditions so that the ratio of the peak intensities is 0.50 to 0.65. Such a peak intensity ratio decreases as the flame-retardant treatment progresses, and the initial decrease is particularly large. However, depending on the flame-retardant conditions, the peak intensity ratio may not fall below 0.65 even if the time is increased.

[0050] In order to make both of these peak intensity ratios compatible within the target range, basically, the amount of the copolymer component contained in the polyacrylonitrile-based polymer constituting the precursor fiber bundle should be small, the crystal orientation degree of the precursor fiber bundle should be high, the single fiber fineness of the precursor fiber bundle should be small, and attention should be mainly paid to setting the conditions such that the flame-retardant temperature is increased in the latter half. The polyacrylonitrile-based carbon fiber precursor fiber bundle is subjected to flame retardancy for 8 to 25 minutes until the ratio of the peak intensity at 1453 cm -1 to the peak intensity at 1370 cm -1 in the infrared spectrum is in the range of 0.98 to 1.10 (first flame-retardant step). Subsequently, at a temperature higher than that in the first flame-retardant step, until the ratio of the peak intensity at 1453 cm -1 to the peak intensity at 1370 cm -1 in the infrared spectrum is in the range of 0.70 to 0.75, and until the ratio of the peak intensity at 1254 cm -1 to the peak intensity at 1370 cm -1 in the infrared spectrum is in the range of 0.50 to 0.65, it is preferably flame-retarded for 5 to 20 minutes (second flame-retardant step). In order to shorten the flame-retardant time in the second flame-retardant step, the flame-retardant temperature can be adjusted higher, but the appropriate flame-retardant temperature depends on the characteristics of the precursor fiber bundle. It is preferable to set the flame-retardant temperature to preferably 260 to 290 °C in order to adjust to the above-mentioned range of the ratio of the peak intensities in the infrared spectrum. The flame-retardant temperature does not have to be constant, and a multi-stage temperature setting may be used. In order to increase the strand strength of the obtained carbon fiber bundle, it is preferable that the flame-retardant temperature is high and the flame-retardant time is short. The first flame-retardant step is preferably carried out with a flame-retardant time of preferably 10 to 25 minutes at a flame-retardant temperature such that it is within the above-mentioned range.

[0051] The charring time described herein means the time during which the fibers stay in the charring furnace, and the charred fiber bundle means the fiber bundle after the charring process and before the pre-carbonization process. Also, the peak intensity described herein refers to the absorbance at each wavelength after baseline correction of the spectrum obtained by measuring the infrared spectrum of a small sample of the charred fiber bundle, and in particular, no peak splitting or the like is performed. Further, the sample is diluted with KBr so that the concentration is 0.67% by mass and then measured. Thus, the infrared spectrum is measured each time the charring conditions are changed, and the conditions can be examined. By controlling the conditions so that the peak intensity ratio of the infrared spectrum of the charred fiber bundle is within an appropriate range, the strand strength of the obtained carbon fiber bundle can be adjusted.

[0052] In the present invention, the charring process means heat-treating the precursor fiber bundle at 200 to 300°C in an oxygen-containing atmosphere. The total treatment time of the charring process can preferably be appropriately selected in the range of 15 to 40 minutes. Also, for the purpose of improving the strand strength of the obtained carbon fiber bundle, the treatment time of charring is preferably set so that the specific gravity of the obtained charred fiber is preferably 1.28 to 1.32. The more preferable treatment time of the charring process depends on the charring temperature. If the specific gravity of the charred fiber bundle is less than 1.28, the strand strength of the carbon fiber bundle may decrease. If the specific gravity of the charred fiber bundle is 1.32 or less, the strand strength can be increased. The specific gravity of the charred fiber bundle is adjusted by controlling the treatment time and the charring temperature of the charring process. Also, the timing of switching from the first charring process to the second charring process is preferably such that the specific gravity of the fiber bundle is in the range of 1.21 to 1.23. Also in this case, priority is given to satisfying the range of the infrared spectrum intensity ratio to control the conditions of the charring process. The preferable ranges of these charring treatment times and charring temperatures vary depending on the characteristics of the precursor fiber bundle and the copolymer composition of the polyacrylonitrile-based polymer.

[0053] In the pre-carbonization process of pre-carbonizing the fiber bundle obtained in the flame-resistant treatment process, the obtained flame-resistant fiber bundle is heat-treated in an inert atmosphere at a maximum temperature of 500 to 1,000 °C. If the maximum temperature of the pre-carbonization temperature is 500 °C or higher, the pre-carbonized fiber bundle can be carbonized without breaking due to thermal decomposition in the subsequent carbonization process. Although there is no particular upper limit for the maximum temperature of the pre-carbonization temperature, it is preferably 1,000 °C or lower in order to be lower than the carbonization temperature in the subsequent carbonization process. Also, the draw ratio in the pre-carbonization process is preferably 1.020 to 1.090. More preferably, it is 1.030 to 1.050. Generally, the higher the draw ratio in the pre-carbonization process, the more the strand strength and strand elastic modulus of the carbon fiber are improved, but the formation of fluff is likely to occur. If it is 1.020 or more, it is a sufficient draw ratio to increase the strand strength and strand elastic modulus of the carbon fiber bundle.

[0054] In the carbonization process of carbonizing the pre-carbonized fiber bundle, the obtained pre-carbonized fiber bundle is heat-treated in an inert atmosphere at a maximum temperature preferably of 2,300 to 2,500 °C, more preferably 2,310 to 2,400 °C, and even more preferably 2,330 to 2,380 °C.

[0055] Generally, the higher the maximum temperature of the carbonization process, the larger the crystallite size and the more aligned the orientation, so the strand elastic modulus is improved, and the single-fiber compressive strength of the carbon fiber bundle decreases. If the carbonization temperature is 2,300 °C, it is a sufficient temperature for the carbonization to proceed sufficiently and increase the crystallite size, and if it is 2,500 °C or lower, it is a sufficient temperature to maintain the single-fiber compressive strength of the carbon fiber bundle.

[0056] In addition, in the manufacturing method for producing the carbon fiber bundle of the present invention, it is preferable to control the heating rate (°C / min) in the carbonization temperature range of 1,000°C to 2,400°C in the carbonization step to 250 to 500°C / min. When the heating rate in the carbonization step is 250 to 500°C / min, it becomes easier to control the structure formation in the carbonization step. Therefore, tension can be uniformly applied to the yarn bundle, and it becomes easier to stretch in the carbonization step without impairing the quality. Here, the heating rate (°C / min) can be defined by the formula: {the maximum temperature reached in the carbonization furnace (°C) - the inlet temperature of the carbonization furnace (°C)} / treatment time (min).

[0057] The heating rate in the carbonization step is preferably 250 to 500°C / min, more preferably 300 to 400°C / min. When the heating rate in the carbonization step is less than 250°C / min, it becomes difficult to improve productivity. When the heating rate in the carbonization step is greater than 500°C / min, the heat treatment of the yarn bundle becomes non-uniform, and as a result, a tension distribution occurs within the fiber yarn bundle, making it easy for the quality to deteriorate and making it difficult to achieve both quality and grade.

[0058] In addition, in the manufacturing method for producing the carbon fiber bundle of the present invention, it is preferable to control the treatment time at the maximum temperature in the carbonization step to 120 to 300 seconds. When the treatment time at the maximum temperature in the carbonization step is 120 to 300 seconds, it becomes easier to control the crystallite structure formation in the carbonization step. Therefore, the elastic modulus can be improved without impairing the quality. The treatment time at the maximum temperature in the carbonization step is preferably 150 seconds to 280 seconds, more preferably 180 to 250 seconds. When the treatment time at the maximum temperature in the carbonization step is less than 120 seconds, the growth of the crystallite size becomes insufficient and the quality becomes difficult. When the treatment time at the maximum temperature in the carbonization step is greater than 300 seconds, the growth of the crystallite size tends to be excessive, and it becomes difficult to achieve both quality and grade.

[0059] And, the draw ratio in the carbonization process of the preliminarily carbonized fiber bundle is preferably 0.940 to 0.995. More preferably, it is 0.945 to 0.980. Generally, the higher the draw ratio in the carbonization process, the higher the strand strength and strand elastic modulus of the carbon fiber, but the generation of hairiness becomes easier. If it is 0.940 or more, it is a temperature sufficient to increase the strand strength and strand elastic modulus of the carbon fiber bundle. By controlling in combination with the heating rate in the carbonization process, it is possible to achieve both an increase in strand strength and strand elastic modulus and the quality of the carbon fiber bundle.

[0060] The carbon fiber bundle obtained as described above is preferably subjected to an oxidation treatment, and oxygen-containing functional groups are introduced. In the production method for producing the carbon fiber bundle of the present invention, gas-phase oxidation, liquid-phase oxidation, and liquid-phase electrolytic oxidation are used for the surface treatment. From the viewpoint of high productivity and uniform treatment, liquid-phase electrolytic oxidation is preferably used. In the production method for producing the carbon fiber bundle of the present invention, there are no particular restrictions on the method of liquid-phase electrolytic oxidation, and it may be carried out by a known method.

[0061] After such electrolytic treatment, in order to impart bundling properties to the obtained carbon fiber bundle, it is preferable to perform a sizing treatment. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of the matrix resin used in the composite material. In order to achieve both abrasion resistance and resin impregnation properties, when the entire carbon fiber bundle containing the sizing agent is 100% by mass, the adhesion amount of the sizing agent is preferably 0.5 to 2.0% by mass.

Examples

[0062] The measurement methods of various physical property values used in the evaluation of the present invention are as follows.

[0063] <Strand Tensile Test of Carbon Fiber Bundle> The strand tensile elastic modulus and strand tensile strength of the carbon fiber bundle were determined according to JIS R7608 (2008) "Strand Test Method". The number of strands measured was 7, and the arithmetic mean value of the measurement results was taken as the strand strength, strand elastic modulus, and initial elastic modulus in the strand tensile test of the carbon fiber bundle. At this time, the strand elastic modulus was measured in the strain range of 0.1 to 0.6%. Also, the initial elastic modulus in the strand tensile test was the coefficient b of the first-order term when the S-S curve obtained by tensile testing the strand was fitted with the quadratic function y = ax 2 + bx + c in the range of 0 ≤ y ≤ 3, with strain as x and stress as y (GPa). The strain was measured using an extensometer. Test specimens were prepared as follows. The test specimens were made by impregnating the carbon fiber bundle with the following resin composition and subjecting it to heat treatment curing conditions at a temperature of 130°C for 35 minutes.

[0064] [Resin Composition] · 3,4-Epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate (100 parts by mass) · Boron trifluoride monoethylamine (3 parts by mass) · Acetone (4 parts by mass).

[0065] As the above 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate, Celoxide P2021P (manufactured by Daicel Corporation) was used.

[0066] <Crystallite Size> The carbon fiber bundles to be measured were aligned and hardened using a collodion-alcohol solution to prepare a measurement sample in the shape of a quadrangular prism with a length of 4 cm and a side length of 1 mm. For the prepared measurement sample, measurements were carried out under the following conditions using a wide-angle X-ray diffractometer. · X-ray source: CuKα ray (tube voltage 40 kV, tube current 30 mA) · Detector: Goniometer + Monochromator + Scintillation Counter · Scanning range: 2θ = 10 to 40° · Scanning mode: Step scan, step unit 0.01°, scan speed 1° / min.

[0067] For the peak that appears around 2θ = 25 - 26° in the obtained diffraction pattern, peak fitting was performed using Gaussian. The full width at half maximum was obtained, and from this value, the crystallite size was calculated using the following Scherrer's equation.

[0068] Crystallite size (nm) = Kλ / β0cosθ B However, K: 1.00, λ: 0.15418 nm (wavelength of X-ray) β0: (βE 2 -β1 2 ) 1 / 2 β E : Apparent full width at half maximum (measured value) rad, β1: 1.046×10 -2 rad θ B : Bragg diffraction angle That is. This measurement was performed 10 times for each level, and the average value of the obtained values was taken as the crystallite size. As a wide-angle X-ray diffractometer, XRD-6100 (manufactured by Shimadzu Corporation) was used.

[0069] <Single fiber diameter of carbon fiber bundle> For a carbon fiber bundle composed of a large number of carbon filaments to be measured, the mass A f (g / m) and density B f (g / cm 3 ) were obtained. The number of filaments of the carbon fiber bundle to be measured was C f , and assuming that the cross-section of the carbon fiber is a perfect circle, the single fiber diameter (μm) of the carbon fiber was calculated using the following formula. Single fiber diameter of carbon fiber (μm) = ((A f / B f / C f ) / π) (1 / 2) ×2×10 3 .

[0070] <Intensity ratio of infrared spectrum> The flame-retardant fibers to be subjected to measurement were precisely weighed and sampled at 2 mg after cryogenic pulverization, thoroughly mixed with 300 mg of KBr, placed in a forming jig, and a measurement tablet was produced by applying pressure at 40 MPa for 2 minutes using a press machine. This tablet was set in a Fourier transform infrared spectrophotometer, and the spectrum was measured in the range of 1000 - 2000 cm -1 . For background correction, the minimum value in the range of 1700 - 2000 cm -1 was subtracted from each intensity so that the minimum value became 0. In the examples and comparative examples described later, Paragon1000 manufactured by PerkinElmer was used as the Fourier transform infrared spectrophotometer.

[0071] <Measurement of the density of the flame-retardant fiber bundle and the carbon fiber bundle> The density B of the flame-retardant fiber bundle and the carbon fiber bundle f (g / cm 3 ) is calculated by the Archimedes method using o-dichlorobenzene as the specific gravity liquid. The measurement was performed with 3 samples.

[0072] <Adhesion amount of sizing agent> After weighing (reading to the fourth decimal place) a carbon fiber bundle coated with 2.0 ± 0.5 g of sizing agent (W1), it was left in an electric furnace (capacity 120 cm 3 ) set at a temperature of 450 °C for 15 minutes in a nitrogen gas stream of 50 milliliters per minute to completely thermally decompose the sizing agent. Then, it was transferred to a container in a dry nitrogen gas stream of 20 liters per minute, and after cooling for 15 minutes, the carbon fiber bundle was weighed (W2) (reading to the fourth decimal place), and the weight loss on heating was determined by W1 - W2. The value obtained by converting this weight loss on heating to mass% when the carbon fiber bundle coated with the sizing agent was 100 mass% (rounding to the third decimal place) was taken as the adhesion amount (mass%) of the adhered sizing agent. The measurement was performed twice, and the average value was taken as the adhesion amount of the sizing agent.

[0073] <Number of protruding flyings> A bobbin of carbon fiber bundles was placed on a creel, drawn by a roller at a speed of 2 m / min under a tension of 1.6 mN / dtex, and wound up by a winder. At this time, the flyers defined as follows generated between the creel and the roller were counted for 5 minutes, and the number of flyers unwound was calculated by the following formula. The number of measurement bobbins for the number of flyers unwound was 10, and the arithmetic mean value of the measurement results was taken as the number of flyers unwound. Unwound flyers: Those in which the broken carbon fiber filaments are exposed from the carbon fiber bundle by 5 mm or more are called flyers, and those in which there are 2 or less such flyers within a test length of 10 mm.

[0074] <Number of flyers for unwinding> A bobbin of carbon fiber bundles was placed on a creel, drawn by a roller at a speed of 2 m / min under a tension of 1.6 mN / dtex, and wound up by a winder. At this time, the grouped flyers and fluff balls defined as follows generated between the creel and the roller were counted for 50 minutes, and the number of flyers for unwinding was calculated by the following formula. The number of measurement bobbins for the number of flyers for unwinding was 10, and the arithmetic mean value of the measurement results was taken as the number of flyers for unwinding. Number of flyers for unwinding (pieces / 100 m) = Number of flyer counts (grouped flyers + fluff balls) (pieces) / Measurement length (m) × 100 Grouped flyers: Those in which the broken carbon fiber filaments are exposed from the carbon fiber bundle by 5 mm or more are called flyers, and those in which there are 3 or more such flyers within a test length of 10 mm Fluff ball: Those in which the broken carbon fiber filaments are exposed from the carbon fiber bundle and entangled to form a lump with a diameter of 5 mm or more. Here, the diameter of the fluff ball is the length of the longest line segment from end to end of the fluff ball.

[0075] <Measurement test of single fiber compressive strength of carbon fiber> The measurement of the single fiber compressive strength by the compression fragmentation method of the single fiber composite was carried out according to the following procedures (A) to (E).

[0076] (A) Preparation of resin 190 parts by mass of bisphenol A type epoxy resin compound "Epoto (registered trademark)" YD-128 (manufactured by Nippon Steel Chemical Co., Ltd.) and 20.7 parts by mass of diethylenetriamine (manufactured by Wako Pure Chemical Industries, Ltd.) were placed in a container and stirred with a spatula, and then degassed using an automatic vacuum degassing device.

[0077] (B) Sampling of carbon fiber single fibers and fixing to the mold A carbon fiber bundle about 20 cm long was divided into approximately four equal parts, and single fibers were sampled in order from the four bundles. At this time, sampling was performed as evenly as possible from the entire bundle. Next, double-sided tape was attached to both ends of the perforated cardboard, and the single fibers were fixed to the perforated cardboard while applying a certain tension to the sampled single fibers. Next, a glass plate pasted with polyester film "Lumirror (registered trademark)" (manufactured by Toray Industries, Inc.) was prepared, and a 2-mm-thick spacer for adjusting the thickness of the test piece was fixed on the film. The perforated cardboard with the single fibers fixed was placed on the spacer, and then another glass plate pasted with the film in the same way was set with the film-pasted surface facing down. At this time, in order to control the embedding depth of the fibers, tapes with a thickness of about 70 μm were attached to both ends of the film.

[0078] (C) From resin casting to curing The resin prepared in the procedure of (A) was poured into the mold (the space surrounded by the spacer and the film) in the procedure of (B). The mold into which the resin was poured was heated for 5 hours using an oven preheated to 50 °C, and then cooled to a temperature of 30 °C at a cooling rate of 2.5 °C / min. Then, demolding and cutting were performed to obtain a test piece of 2 cm × 7.5 cm × 0.2 cm. At this time, the test piece was cut so that the single fibers were located within a 0.5-cm width in the center of the test piece width.

[0079] (D) Measurement of fiber embedding depth For the test piece obtained in the procedure (C) above, the embedding depth of the fiber was measured using a laser of a laser Raman spectrophotometer (JASCO NRS-3200) and a 532 nm notch filter. First, the laser was applied to the surface of a single fiber, and the stage height was adjusted so that the beam diameter of the laser was minimized. The height at that time was designated as A (μm). Next, the laser was applied to the surface of the test piece, and the stage height was adjusted so that the beam diameter of the laser was minimized. The height at that time was designated as B (μm). The embedding depth d (μm) of the fiber was calculated using the refractive index 1.732 of the resin measured using the above laser by the following formula (1). d = (A - B) × 1.732 ···(1).

[0080] (E) Four-point bending test For the test piece obtained in the procedure (C) above, a compressive strain was applied by four-point bending using a jig with an outer load cell interval of 50 mm and an inner load cell interval of 20 mm. The strain was applied stepwise at 0.1% intervals, and the test piece was observed with a polarized light microscope. The number of breaks in the 5 mm center part in the longitudinal direction of the test piece was measured. Twice the measured number of breaks was defined as the fiber breakage number (pieces / 10 mm), and the compressive stress calculated from the compressive strain and the initial elastic modulus at which the average fiber breakage number of 30 tests exceeded 1 piece / 10 mm was defined as the single fiber compressive strength. Also, the single fiber composite strain ε (%) was measured using a strain gauge attached at a position approximately 5 mm away from the center of the test piece in the width direction. c The final compressive strain ε of the carbon fiber single fiber was calculated by the following formula (2) considering the gauge factor κ of the strain gauge, the fiber embedding depth d (μm) measured in the procedure (D) above, and the residual strain of 0.14 (%). ε c = ε × (2 / κ) × (1 - d / 1,000) - 0.14 ···(2).

[0081] The measured single fiber compressive strength was evaluated using the following criteria. S: 3.1 GPa or more A: 3.0 GPa or more and less than 3.1 GPa B: 2.9 GPa or more and less than 3.0 GPa C: Less than 2.9 GPa.

[0082] <Preg Quality - Preg Fuzz Defect Count> Observe 50 m of the preg in the longitudinal direction and convert it to the number per 100 m 2 to evaluate the preg defect count (pieces / 100 m 2 ) using the following criteria. A preg fuzz defect is a fluff ball with a diameter of 10 mm or more. Here, the diameter of the fluff ball is the length of the longest line segment from end to end of the fluff ball. S: 3 pieces / 100 m 2 Below A: Exceeding 3 pieces / 100 m 2 and up to 7 pieces / 100 m 2 Below B: Exceeding 7 pieces / 100 m 2 and up to 30 pieces / 100 m 2 Below C: Exceeding 30 pieces / 100 m 2

[0083] <Measurement of Elastic Modulus of Thermosetting Resin Cured Product> Add the resin component of the thermosetting resin into a kneader, raise the temperature to 150 °C while kneading, and knead for 1 hour at the same temperature. Then, lower the temperature to 60 °C while kneading. After that, add a curing agent and a curing accelerator and further knead to obtain an uncured thermosetting resin. After degassing this uncured thermosetting resin in a vacuum, set it in a mold so that the thickness becomes 2 mm with a 2 mm thick "Teflon (registered trademark)" spacer, and cure it at a temperature of 130 °C for 2 hours to obtain a cured product of a thermosetting resin with a thickness of 2 mm. Cut out a test piece with a width of 10 mm and a length of 60 mm from this cured product, set the span length to 32 mm and the crosshead speed to 2.5 mm / min, and perform three-point bending according to JIS-K7171 (1994) to measure the elastic modulus. With the number of samples n = 5, the average value was taken as the elastic modulus of the resin cured product.

[0084] <Measurement of 0° Compressive Strength of Carbon Fiber Reinforced Composite Material and Measurement of 0° Tensile Elastic Modulus of Carbon Fiber Reinforced Composite Material> ​The raw material resin of the thermosetting resin excluding the curing agent and the curing accelerator was mixed with a kneader and stirred for 1 hour to obtain a resin composition. Next, the obtained resin composition was applied onto the silicone surface of the release paper coated with silicone to obtain a resin film. The obtained resin film was wound around the surface of a steel drum having a circumference of about 2.7 m and temperature-controlled at 60 to 70°C with the surface of the resin composition facing outward. Next, a carbon fiber bundle unwound from a creel was arranged via a traverse on the surface of the resin composition wound around the steel drum. Further, the resin film was placed thereon to cover the resin composition with the surface of the resin composition facing the carbon fiber bundle side, and pressure was applied while contacting and rotating a roll prepared separately with the surface of the outer resin film to impregnate the resin into the fiber bundle, thereby producing a unidirectional prepreg having a width of 300 mm and a length of 2.7 m. Here, the fiber areal weight of the prepreg was adjusted to 190 to 200 g / m by adjusting the rotation speed of the drum and the feed rate of the traverse. 2It was adjusted to. A plurality of the obtained prepregs were laminated with their fiber directions aligned in one direction, and treated at a temperature of 130 °C and a pressure of 0.3 MPa for 2 hours to cure the resin, thereby obtaining a laminate (fiber-reinforced composite material) with a thickness of 1 mm. From such a laminate, test pieces with a thickness of 1 ± 0.1 mm, a width of 12.7 ± 0.13 mm, a length of 80 ± 0.013 mm, and a gauge part length of 5 ± 0.13 mm were cut out. Note that reinforcing plates were fixed to both ends of the test piece (37.5 mm each from both ends) with an adhesive or the like to make the gauge part length 5 ± 0.13 mm. In accordance with ASTM D695 (1996), the compressive strength was measured for the number of test pieces under the condition of a strain rate of 1.27 mm / min, and the obtained compressive strength was converted to a fiber volume fraction of 60%. It was measured with n = 6, and the average value was taken as the 0° compressive strength of the carbon fiber-reinforced composite material in the present invention. Also, as described in JIS K7017 (1999), a unidirectional reinforcing material was cut into a width of 12.7 mm and a length of 230 mm, and tabs made of glass fiber-reinforced plastic with a length of 50 mm and a thickness of 1.2 mm were adhered to both ends to obtain a test piece. For the test piece thus obtained, a tensile test was performed at a crosshead speed of 1.27 mm / min using a universal testing machine manufactured by Instron Corporation, the 0° tensile elastic modulus was measured, and the obtained tensile elastic modulus was converted to a fiber volume fraction of 60%. It was measured with n = 6, and the average value was taken as the 0° tensile elastic modulus of the carbon fiber-reinforced composite material in the present invention.

[0085] Hereinafter, the present invention will be described more specifically with reference to examples.

[0086] (Example 1) A polyacrylonitrile copolymer copolymerized with itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent to produce a polyacrylonitrile copolymer. The spinning solution obtained from the produced polyacrylonitrile copolymer was once discharged into the air from a spinneret, passed through a space of about 4 mm, and then introduced into a coagulation bath composed of an aqueous solution of 35% by mass of dimethyl sulfoxide controlled at 3°C by a dry-wet spinning method to form a coagulated yarn. This coagulated yarn was washed with water by a conventional method and then stretched 3.5 times in a warm water bath of two tanks. Subsequently, an amino-modified silicone-based silicone oil agent was applied to the fiber bundle after the stretching in the water bath, and a drying densification treatment was performed using a heating roller at 160°C. After combining two yarns to make the number of single fibers 12,000, the total draw ratio of yarn production was set to 13 times by stretching 3.7 times in pressurized steam, and then an entangling treatment was performed to obtain a polyacrylonitrile-based precursor fiber bundle with a crystal orientation degree of 93%, a single fiber fineness of 0.75 dtex, and 12,000 single fibers. Next, the first flameproofing step was carried out at a flameproofing temperature of 240°C, and the second flameproofing step was carried out at 244°C. The flameproofing time was adjusted so that the density of the flameproofed yarn became 1.30 g / cm 3 . While stretching the polyacrylonitrile-based precursor fiber bundle at a draw ratio of 1 in an oven in an air atmosphere, a flameproofing treatment was performed to obtain a flameproofed fiber bundle. Here, the step of performing flameproofing in the "first furnace" corresponds to the first flameproofing step, and the step of performing flameproofing in the "second furnace" corresponds to the second flameproofing step. In addition, in the present invention, there is no limitation on the number of flameproofing furnaces for performing the first flameproofing step and the second flameproofing step. The ratio of the peak intensity at 1,453 cm -1 to the peak intensity at 1,370 cm -1 in the infrared spectrum of the fiber after the first flameproofing step was 0.68. The ratio of the peak intensity at 1,453 cm -1 to the peak intensity at 1,370 cm -1 in the infrared spectrum of the fiber after the second flameproofing step was 0.49, and the ratio of the peak intensity at 1,254 cm -1 to the peak intensity at 1,370 cm -1The ratio of peak intensities was 0.55. The obtained flame-resistant fiber bundle was placed in a nitrogen atmosphere at a temperature of 300 to 800 °C to obtain a pre-carbonized fiber bundle. The obtained pre-carbonized fiber bundle was carbonized in a nitrogen atmosphere while controlling the maximum temperature, heating rate, and draw ratio. The flame-resistant conditions, pre-carbonization conditions, and carbonization conditions are summarized in Table 1.

[0087]

Table 1-1

[0088]

Table 1-2

[0089] The obtained carbon fiber bundle was subjected to surface treatment and sizing agent coating treatment to obtain the final carbon fiber bundle. The adhesion amount of sizing was adjusted to be 1.2% by mass. The carbon fiber bundle thus obtained had a single fiber diameter of 5.3 μm, a density of 1.82 g / cm 3 , a crystallite size of 4.2 nm, a strand tensile strength of 4.8 GPa, a strand tensile elastic modulus of 438 GPa, and a single fiber compressive strength of 3.0 GPa, indicating high mechanical properties. Also, the number of protruding flyers was 0.5 pieces / m, the number of unwinding flyers was 10.0 pieces / 100 m, and the number of prepreg flyer defects was 28 pieces / 100 m 2 , indicating that the quality was sufficiently high. The above results are summarized in Table 2.

[0090]

Table 2-1

[0091]

Table 2-2

[0092] (Example 2) A carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the heating rate, the treatment time at the maximum temperature, and the draw ratio in the carbonization process were changed as shown in Table 1. The results are as summarized in Table 2, and a carbon fiber bundle with high quality and high mechanical properties was obtained.

[0093] (Example 3) A carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the draw ratio in the pre-carbonization process, the maximum temperature, the treatment time at the maximum temperature, and the heating rate and draw ratio in the carbonization process were changed as shown in Table 1. The results are as summarized in Table 2, and a carbon fiber bundle with sufficiently high quality and high mechanical properties was obtained.

[0094] (Example 4) A carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the draw ratio in the pre-carbonization process, the heating rate, the treatment time at the maximum temperature, and the draw ratio in the carbonization process were changed as shown in Table 1. The results are as summarized in Table 2, and a carbon fiber bundle with very high quality and high mechanical properties was obtained.

[0095] (Example 5) A carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the draw ratio in the pre-carbonization process, the maximum temperature, the treatment time at the maximum temperature, the heating rate, and the draw ratio in the carbonization process were changed as shown in Table 1. The results are as summarized in Table 2, and a carbon fiber bundle with very high quality and very high mechanical properties was obtained.

[0096] (Example 6) A carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the draw ratio in the pre-carbonization process, the maximum temperature, the treatment time at the maximum temperature, the heating rate, and the draw ratio in the carbonization process were changed as shown in Table 1. The results are as summarized in Table 2, and a carbon fiber bundle with sufficiently high quality and sufficiently high mechanical properties was obtained.

[0097] (Example 7) A carbon fiber bundle was obtained and various evaluations were performed in the same manner as in Example 1, except that the draw ratio in the preliminary carbonization step was changed as shown in Table 1. The results are as summarized in Table 2, and a carbon fiber bundle with sufficiently high quality and high mechanical properties was obtained.

[0098] (Example 8) In the flame retardant treatment in the flame retardant step, the flame retardant temperature and the flame retardant time were controlled so as to have the flame retardant structure shown in Table 1, the draw ratio in the preliminary carbonization step was changed as shown in Table 1, and the draw ratio in the carbonization step was changed as shown in Table 1. A carbon fiber bundle was obtained and various evaluations were performed in the same manner as in Example 1, except for the change. The results are as summarized in Table 2, and a carbon fiber bundle with high quality and high mechanical properties was obtained.

[0099] (Example 9) In the flame retardant treatment in the flame retardant step, the flame retardant temperature and the flame retardant time were controlled so as to have the flame retardant structure shown in Table 1, the draw ratio in the preliminary carbonization step was changed as shown in Table 1, and the maximum temperature, the treatment time at the maximum temperature, the heating rate, and the draw ratio in the carbonization step were changed as shown in Table 1. A carbon fiber bundle was obtained and various evaluations were performed in the same manner as in Example 1, except for the change. The results are as summarized in Table 2, and a carbon fiber bundle with high quality and high mechanical properties was obtained.

[0100] (Example 10) In the flame retardant treatment in the flame retardant step, the flame retardant temperature and the flame retardant time were controlled so as to have the flame retardant structure shown in Table 1, the draw ratio in the preliminary carbonization step was changed as shown in Table 1, and the maximum temperature, the treatment time at the maximum temperature, the heating rate, and the draw ratio in the carbonization step were changed as shown in Table 1. A carbon fiber bundle was obtained and various evaluations were performed in the same manner as in Example 1, except for the change. The results are as summarized in Table 2, and a carbon fiber bundle with high quality and high mechanical properties was obtained.

[0101] (Example 11) Using the carbon fiber bundle obtained in Example 4, prepregs and carbon fiber reinforced composite materials were produced with the resin compositions shown below, and the 0° tensile modulus was measured to be 259 GPa, and the 0° compressive strength was measured to be 1240 MPa. The physical properties of the carbon fiber reinforced composite material thus obtained are shown in Table 3. In addition, when the elastic modulus of the resin cured product having the same resin composition was measured, the elastic modulus was 4.4 GPa.

[0102] Resin composition: · Liquid bisphenol A type epoxy resin (“jER (registered trademark)” 828: manufactured by Mitsubishi Chemical Corporation): 20 parts by mass · Triglycidyl-m-aminophenol (“Araldite (registered trademark)” MY0600: manufactured by Huntsman Advanced Materials Co., Ltd.): 50 parts by mass · Phenol novolac type epoxy (“jER (registered trademark)” 154: manufactured by Mitsubishi Chemical Corporation): 30 parts by mass Hardener: · Dicyandiamide (manufactured by Mitsubishi Chemical Corporation): 6 parts by mass Curing accelerator: · 3-(3,4-dichlorophenyl)-1,1-dimethylurea (manufactured by Hodogaya Chemical Co., Ltd.): 3 parts by mass.

[0103] (Comparative Example 1) A carbon fiber bundle was obtained in the same manner as in Example 1 except that the draw ratio in the pre-carbonization step and the draw ratio in the carbonization step were changed as shown in Table 1, and various evaluations were performed. The results are as summarized in Table 2, and the obtained carbon fiber bundle had high mechanical properties but a small single fiber diameter and insufficient quality.

[0104] (Comparative Example 2) A carbon fiber bundle was obtained in the same manner as in Example 1 except that the draw ratio in the pre-carbonization step, the maximum temperature in the carbonization step, the heating rate, and the draw ratio were changed as shown in Table 1, and various evaluations were performed. The results are as summarized in Table 2, and the obtained carbon fiber bundle had high mechanical properties but a high density, a large crystallite size, insufficient strand strength and single fiber compressive strength, and insufficient quality.

[0105] (Comparative Example 3) A carbon fiber bundle was obtained in the same manner as in Example 1 except that the draw ratio in the pre-carbonization step and the draw ratio in the carbonization step were changed as shown in Table 1, and various evaluations were performed. The results are as summarized in Table 2. The obtained carbon fiber bundle had high mechanical properties but a small single fiber diameter and insufficient quality.

[0106] (Comparative Example 4) A carbon fiber bundle was obtained in the same manner as in Example 1 except that the draw ratio in the pre-carbonization step, the maximum temperature in the carbonization step, the treatment time at the maximum temperature, and the heating rate and draw ratio were changed as shown in Table 1, and various evaluations were performed. The results are as summarized in Table 2. The obtained carbon fiber bundle had very high quality, but due to the low maximum carbonization temperature, the strand elastic modulus was insufficient.

[0107] (Comparative Example 5) A carbon fiber bundle was obtained in the same manner as in Example 1 except that the draw ratio in the pre-carbonization step, the heating rate in the carbonization step, and the treatment time at the maximum temperature were changed as shown in Table 1, and various evaluations were performed. The results are as summarized in Table 2. The obtained carbon fiber bundle had insufficient mechanical properties and quality due to the high carbonization heating rate.

[0108] (Comparative Example 6) A carbon fiber bundle was obtained in the same manner as in Example 1 except that the draw ratio in the pre-carbonization step, the maximum temperature in the carbonization step, the treatment time at the maximum temperature, and the draw ratio were changed as shown in Table 1, and various evaluations were performed. The results are as summarized in Table 2. The obtained carbon fiber bundle had high mechanical properties but insufficient quality because the carbonization temperature was low and the draw ratio in the carbonization step was high.

[0109] (Comparative Example 7) A carbon fiber bundle was obtained and various evaluations were conducted in the same manner as in Example 1, except that the draw ratio in the preliminary carbonization step and the maximum temperature, heating rate, treatment time at the maximum temperature, and draw ratio in the carbonization step were changed as shown in Table 1. The results are as summarized in Table 2. The obtained carbon fiber bundle had insufficient mechanical properties and quality because the carbonization temperature was low and the draw ratio in the carbonization step was high.

[0110] (Comparative Example 8) A carbon fiber bundle was obtained and various evaluations were conducted in the same manner as in Example 1, except that the draw ratio in the preliminary carbonization step and the maximum temperature, heating rate, treatment time at the maximum temperature, and draw ratio in the carbonization step were changed as shown in Table 1. The results are as summarized in Table 2. The obtained carbon fiber bundle had insufficient mechanical properties and quality because the carbonization temperature was low and the draw ratio in the carbonization step was high.

[0111] (Comparative Example 9) Using the carbon fiber bundle "Torayca (registered trademark)" M46J (strand elastic modulus: 434 GPa, manufactured by Toray Industries, Inc.), a prepreg and a carbon fiber reinforced composite material were produced with the resin composition shown below, and the 0° tensile elastic modulus was measured to be 256 GPa. When the 0° compressive strength was measured, it was 1060 MPa, which was about the same value as the 0° tensile elastic modulus of the composite material of Example 10, but the 0° compressive strength was low. In addition, when the elastic modulus of a resin cured product having the same resin composition was measured, the elastic modulus was 3.3 GPa.

[0112] (Comparative Example 10) Using the carbon fiber bundle "Torayca (registered trademark)" M40S (strand elastic modulus: 380 GPa, manufactured by Toray Industries, Inc.), a prepreg and a carbon fiber reinforced composite material were produced with the resin composition shown below, and the 0° tensile elastic modulus was measured to be 223 GPa. When the 0° compressive strength was measured, it was 1240 MPa, which was about the same value as the 0° compressive strength of the composite material of Example 11, but the 0° tensile elastic modulus was low. In addition, when the elastic modulus of a resin cured product having the same resin composition was measured, the elastic modulus was 3.3 GPa.

[0113] Resin composition: · Liquid bisphenol A diglycidyl ether resin (“jER (registered trademark)” 1001: manufactured by Mitsubishi Chemical Corporation): 20 parts by mass: 30 parts by mass · Liquid bisphenol A type epoxy resin (“jER (registered trademark)” 828: manufactured by Mitsubishi Chemical Corporation): 30 parts by mass · Phenol novolac polyglycidyl ether resin (“EPICLON” (registered trademark) N740 (manufactured by DIC Corporation)): 27 parts by mass · Polyvinyl formal resin (“Vinylec (registered trademark)” PVF-K, manufactured by JNC Corporation): 5 parts by mass Hardening agent: · Dicyandiamide (manufactured by Mitsubishi Chemical Corporation): 6 parts by mass Hardening accelerator: · 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (manufactured by Hodogaya Chemical Co., Ltd.): 3 parts by mass.

[0114]

Table 3

Claims

1. A carbon fiber bundle having a strand tensile strength of 4.5 GPa or more and 6.5 GPa or less, a strand tensile modulus of 400 GPa or more, a crystallite size of 4.0 nm or more and 4.7 nm or less, a single fiber diameter of 5.2 μm or more and 6.2 μm or less, and being substantially untwisted.

2. 2. The carbon fiber bundle according to claim 1, wherein the number of unwinding fluffs is 0.3 fluffs / m or less.

3. 3. The carbon fiber bundle according to claim 1, wherein the number of unwound fluffs is 6 or less per 100 m.

4. Density is 1.84 g / cm ３ The carbon fiber bundle according to claim 1 or 2, wherein:

5. 3. The carbon fiber bundle according to claim 1, wherein the single fiber diameter is 5.5 μm or more and 6.2 μm or less.

6. 3. The carbon fiber bundle according to claim 1 or 2, having a strand tensile strength of 4.8 GPa or more and 6.5 GPa or less.

7. 3. The carbon fiber bundle according to claim 1 or 2, having a strand tensile strength of 5.0 GPa or more and 6.5 GPa or less.

8. 3. The carbon fiber bundle according to claim 1 or 2, having a strand tensile strength of 5.5 GPa or more and 6.5 GPa or less.

9. A prepreg obtained by impregnating the carbon fiber bundle according to claim 1 or 2 with a thermosetting resin, the prepreg having a fluff defect count of 7 / 100 m. ２ The prepreg is as follows:

10. 3. A prepreg comprising the carbon fiber bundle according to claim 1 or 2 impregnated with a thermosetting resin, the thermosetting resin having a cured product with an elastic modulus of 3.0 GPa or more.

11. 3. A prepreg comprising the carbon fiber bundle according to claim 1 or 2 impregnated with a thermosetting resin, the thermosetting resin having a cured product with an elastic modulus of 3.8 GPa or more and 5.5 GPa or less.

12. A carbon fiber reinforced composite material comprising the carbon fiber bundle according to claim 1 or 2 and a matrix resin.

13. A composite material comprising the carbon fiber bundle according to claim 1 or 2 and a matrix resin, A carbon fiber reinforced composite material having a composite 0° compressive strength of 1200 MPa or more and 1350 MPa or less, and a composite 0° tensile modulus of 245 GPa or more and 270 GPa or less.

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