RU2784511C2 - Carbon fiber bundle, its production method, prepreg and composite material reinforced with carbon fiber - Google Patents

Abstract

FIELD: composite materials.

SUBSTANCE: invention relates to a carbon fiber bundle, which is used in sports fields of application, such as golf clubs and fishing rods, and to its production method, prepreg, and composite material reinforced with carbon fiber, obtained using the carbon fiber bundle. In the carbon fiber bundle, the ratio between a crystallite size Lc (nm), compressive strength of single fiber Fc (GPa), measured by a fragmentation method, when compressing composites containing fiber of one type, and an initial elasticity module E₀ (GPa), when testing tensile strength of resin-impregnated thread, simultaneously satisfies following formulas (1)-(3), and Lc has a value of 2.60 nm or more and 4.00 nm or less: Fc ≥ 1.3 × 10/Lc - 0.3 (1); E₀ ≤ 80 × Lc + 155 (2); E₀ ≥ 330 (3).

EFFECT: obtained carbon fiber bundle simultaneously shows high compressive strength of composite material reinforced by carbon fiber and high elasticity module, when tensioning thread of the carbon fiber bundle.

11 cl, 1 dwg, 3 tbl, 15 ex

Description

Technical field

[0001]

The present invention relates to a carbon fiber bundle, which is suitably used in sports applications such as golf clubs and fishing rods, as well as other general industrial fields, and to a method for its production, a prepreg and a carbon fiber reinforced composite material obtained using bundle of carbon fiber.

State of the art

[0002]

In recent years, carbon fiber bundles have been actively used in various industrial fields as reinforcing fibers for fiber-reinforced composite materials, since they have exceptionally high specific strength and tensile modulus. In particular, in areas where weight reduction is important, the replacement of conventional metal materials with carbon fiber composites is accelerating. Particularly in sports fields, weight reduction is required for golf clubs, fishing rods, bicycles, rackets, etc., and these applications are expanding more and more.

[0003]

Weight reduction in sports applications requires that the carbon fiber reinforced composite material have a high tensile modulus and be excellent in a wide range of physical properties such as tensile strength and compressive strength. The most widely used polyacrylonitrile carbon fiber bundle is produced commercially by a stabilization process to convert the polyacrylonitrile precursor fiber bundle into a stabilized fiber bundle in an oxidizing atmosphere at a temperature of 200 to 300°C; a pre-carbonization process for converting the stabilized fiber bundle into a pre-carbonized fiber bundle by pre-carbonization in an inert atmosphere at a maximum temperature of 500 to 1000°C; and a carbonization process to convert the pre-carbonized fiber bundle into a carbon fiber bundle by carbonization in an inert atmosphere at a maximum temperature of 1700 to 3000°C. It is known that the tensile modulus of a carbon fiber reinforced composite material improves substantially in proportion to the tensile modulus of the resin impregnated carbon fiber bundle filament (hereinafter simply referred to as the tensile modulus of the filament). It is known that such a filament tensile modulus can be increased by further increasing the maximum temperature during carbonization. However, experts agree that a carbon fiber bundle having a high filament elastic modulus obtained by increasing the maximum temperature of the carbonization process causes a decrease in the compressive strength of carbon fiber reinforced composites due to an increase in crystallite size (Patent Document 1), and there is usually a trade-off relationship between compressive strength and tensile modulus of a carbon fiber reinforced composite thread. Therefore, research has been carried out to improve the tensile modulus of a yarn without increasing the crystallite size. As a method for reducing the crystallite size of a carbon fiber bundle, for example, a method for improving the compressive strength of single fibers by injecting ions onto the surface of carbon fibers to break the crystallite of a surface layer of carbon fiber has been proposed (Patent Document 1). As a method of improving the tensile modulus of a yarn without increasing the crystallite size of a carbon fiber bundle, a method of increasing the carbonization stretch ratio is known, and methods have been proposed to improve the carbonization stretch ratio by interlacing or twisting the precursor fiber bundle so as to increase the carbonization stretch ratio without deterioration in processability (Patent Documents 2 and 3), and a method for increasing the molecular weight of a polyacrylonitrile copolymer (Patent Document 4). Also proposed is a method for improving the compressive strength of a single fiber of a carbon fiber bundle by adjusting the stabilized structure so as to improve the compressive strength of a carbon fiber reinforced composite material regardless of stretching (Patent Document 5).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1: JP 3-180514 A

Patent Document 2: JP 2014-141761 A

Patent Document 3: JP 2014-159665A

Patent Document 4: JP 2008-308776 A

Patent Document 5: JP 2015-10290A

The essence of the invention

Problems solved by the invention

[0005]

In Patent Document 1, although the crystallite size was reduced by incorporating ions into carbon fibers, resulting in an increase in the apparent compressive strength measured by the loop method to a maximum of 10.0 GPa, this was not satisfactory in terms of balance with the tensile modulus threads. According to the methods mentioned in Patent Documents 2 and 3 above, the precursor fiber bundle is not broken even when a high tension is applied in the carbonization process by weaving or twisting the precursor fiber bundle. However, the compressive strength of a single fiber was not satisfactory. According to the method mentioned in Patent Document 4, although the carbonization extensibility is improved and the tensile modulus of the yarn is improved by increasing the molecular weight of the polyacrylonitrile copolymer, the compressive strength of the single fiber was not satisfactory. According to the method mentioned in Patent Document 5, the compressive strength of a single fiber can be improved by adjusting the stabilized structure. However, the level of tensile modulus of the yarn is low, and when the maximum temperature of the carbonization process is simply increased based on the method of Patent Document 5, the compressive strength of the single fiber drops significantly, therefore, it is not possible to achieve a high level of both the tensile modulus of the yarn and compressive strength of a single fiber.

[0006]

To solve these problems, the object of the present invention is to obtain a carbon fiber bundle that simultaneously exhibits high compressive strength of a carbon fiber reinforced composite material and a high tensile modulus of a carbon fiber bundle yarn, as well as to develop a method for its production and create a prepreg obtained using a bundle carbon fiber.

Problem solving

[0007]

In order to solve the problems mentioned above, the present invention consists in the following technical solution. In other words, the carbon fiber bundle of the present invention is a carbon fiber bundle in which the ratio between the crystallite size Lc (nm), the compressive strength of a single fiber Fc (GPa) measured by the compressive fragmentation method of composites containing the same type of fiber, and the initial tensile modulus E ₀ (GPa) of the thread simultaneously satisfies the following formulas (1) to (3), and Lc is 4.00 nm or less:

Fc ≥ 1.3 × 10/Lc - 0.3 (1)

E ₀ ≤ 80 × Lc + 155 (2)

_E0 ≥ 330 (3).

[0008]

The method for producing a carbon fiber bundle of the present invention is a method for producing a carbon fiber bundle, which includes obtaining a substantially untwisted fiber bundle by a stabilization process in which a polyacrylonitrile precursor fiber is heat-treated in an oxygen-containing atmosphere; a pre-carbonization process in which the fiber bundle obtained in the stabilization process is subjected to heat treatment in an inert atmosphere at a maximum temperature of 500 to 1000°C; a carbonization process in which the fiber bundle obtained in the pre-carbonization process is subjected to heat treatment in an inert atmosphere at a maximum temperature of 1700 to 3000°C; and a process in which the fiber bundle obtained in the carbonization process is subjected to an oxidative treatment; where

the stabilization process is carried out until the ratio of the intensity of the peak at 1453 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum of the fiber beam is in the range from 0.60 to 0.70, and the ratio of the intensity of the peak at 1254 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum will not be in the range from 0.50 to 0.65; and

the tension of the fiber bundle during the carbonization process is 4.0 to 6.0 mN/dtex, and the carbonization process is carried out until the ratio between the crystallite size Lc (nm) in the fiber bundle and the maximum temperature T satisfies the following formula: Lc ≥ 2.00 x 10 ^-3 x T - 0.90.

[0009]

Another method for producing a carbon fiber bundle of the present invention is a method for producing a carbon fiber bundle, which includes obtaining a carbon fiber bundle through a stabilization process in which a polyacrylonitrile precursor fiber bundle is heat-treated in an oxygen-containing atmosphere; a pre-carbonization process in which the fiber bundle obtained in the stabilization process is subjected to heat treatment in an inert atmosphere at a maximum temperature of 500 to 1000°C; a carbonization process in which the fiber bundle obtained in the pre-carbonization process is subjected to heat treatment in an inert atmosphere at a maximum temperature of 1700 to 3000°C; and a process in which the fiber bundle obtained in the carbonization process is subjected to an oxidative treatment; where

the tension of the fiber bundle during the stabilization process is 1.0 mN/dtex or more;

the stabilization process is carried out until the ratio of the intensity of the peak at 1453 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum of the fiber beam is in the range from 0.60 to 0.70, and the ratio of the intensity of the peak at 1254 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum will not be in the range from 0.50 to 0.65; and

the number of twists of the fiber bundle in the carbonization process is 2 turns/m or more, or the twist angle of the surface of the fiber bundle is 0.2° or more, and the tension of the fiber bundle in the carbonization process is 4.0 mN/dtex or more.

Invention Effects

[0010]

According to the carbon fiber bundle of the present invention, the effect of achieving both the compressive strength of the carbon fiber reinforced composite material and the tensile modulus of the carbon fiber bundle yarn can be obtained at a high level. According to the prepreg of the present invention, the effect of achieving a high level of both compressive strength and tensile modulus of the carbon fiber reinforced composite material can be obtained.

Brief description of the drawings

[0011]

FIG. 1 is a view showing a breaking length measurement method.

Embodiments of the invention

[0012]

In the carbon fiber bundle of the present invention, the relationship between the crystallite size Lc (nm), the compressive strength of a single fiber Fc (GPa) measured by the compressive fragmentation method of composites containing fiber of the same type, and the initial elastic modulus E ₀ (GPa) when tested on stretching of the thread simultaneously satisfies the following formulas (1)-(3):

[0013]

Fc ≥ 1.3 × 10/Lc - 0.3 (1)

E ₀ ≤ 80 × Lc + 155 (2)

_E0 ≥ 330 (3).

[0014]

A carbon fiber bundle that simultaneously satisfies these three formulas can provide high levels of both the compressive strength of the carbon fiber reinforced composite material and the tensile modulus of the carbon fiber bundle filament, which is the object of the present invention. Each formula is described separately below.

[0015]

In the carbon fiber bundle of the present invention, the relationship between the crystallite size Lc (nm), the compressive strength of a single fiber Fc (GPa) measured by the compressive fragmentation method of composites containing a single type of fiber, and the initial elastic modulus E ₀ (GPa) when tested thread tension is in the range of the following formula (1):

Fc ≥ 1.3 × 10/Lc - 0.3 (1).

[0016]

In the carbon fiber bundle of the present invention, the right side of formula (1) is more preferably 1.3×10/Lc+0.1 and even more preferably 1.3×10/Lc+0.5. The crystallite size Lc is a measure indicating the thickness of the crystallites existing in the carbon fibers in the c-axis direction, and is estimated by wide-angle fiber beam X-ray diffraction discussed below. However, it is also possible to evaluate a single single fiber using wide-angle X-ray microbeam diffraction. In the fiber bundle of the present invention, wide-angle X-ray diffraction data and wide-angle X-ray microbeam diffraction data of a single fiber are equivalent. In general, it is known that the larger the crystallite size of carbon fibers, the more the compressive strength of a single fiber tends to drop. The above formula (1) means that the carbon fiber bundle of the present invention has a higher compressive strength of a single fiber than the value expected from conventional inferences regarding crystallite size. As a result, both the compressive strength and the tensile modulus of the carbon fiber-reinforced composite yarn, which are the effects of the present invention, can be achieved at a high level. In the carbon fiber bundle of the present invention, a value satisfying the compressive strength of the carbon fiber reinforced composite material can be obtained when the right side of the formula (1) becomes 1.3×10/Lc-0.3 or more. The higher the compressive strength of a single fiber, the better. When the right side of formula (1) is adjusted to a value of 1.3×10/Lc+1.0, more preferably to a value of 1.3×10/Lc+0.5, and even more preferably to a value of 1.3×10/Lc , as a rule, get a high effect.

[0017]

The “Compression Fragmentation Method for Composites Containing One Type of Fiber” used in the present invention is a method for studying the compressive strength of a single fiber of carbon fibers by counting the number of fiber breaks due to each compression strain when compressive strain is applied stepwise to a carbon fiber-reinforced composite material, comprising a single fiber of a carbon fiber bundle embedded in a resin (composites containing a single type of fiber). In order to convert the compressive strain of a composite containing a single type of fiber that occurs when the fibers break into the compressive strength of a single fiber, it is necessary to take into account the difference between the compressive strain of the composite containing a single type of fiber and the compressive strain of the fiber, and the non-linearity of the tensile modulus at each strain fiber compression. In the present invention, the compressive stress of a single fiber is obtained by fitting the stress-strain (S-S) curve obtained from the filament tensile test (details below) using a quadratic function with X-axis strain and Y-axis stress, followed by calculation using an approximating straight line passing to the compressive strain side. The compressive stress of a single fiber at the time when the number of broken fibers exceeds 1/10 mm is defined as the compressive strength of a single fiber. In order to control the carbon fiber bundle so that it satisfies formula (1), it is necessary that high tension be applied in the carbonization process discussed below, and the heat treatment be carried out while the crystallite size grows at a constant temperature during the carbonization process.

[0018]

In the carbon fiber bundle of the present invention, the ratio between the crystallite size Lc and the initial elastic modulus E ₀ (GPa) in the yarn tensile test is in the range of formula (2):

_E0 ≤80 × Lc + 155 (2).

[0019]

In the carbon fiber bundle of the present invention, the ratio of formula (2) is more preferably E ₀ ≤ 80×Lc+120, and even more preferably E ₀ ≤ 80×Lc+110. In general, the larger the crystallite size of the carbon fiber bundle, the more the crystallite orientation is made uniform, so that the initial tensile modulus of the yarn becomes higher. The initial filament tensile modulus measured with the carbon fiber bundle is almost the same as the initial single fiber carbon fiber elastic model. Despite the small size of the carbon fiber bundle crystallites, the carbon fiber bundle having a high initial modulus in the yarn tensile test can be produced by applying high tension during the carbonization process to make the crystallite orientation uniform. However, hairiness easily grows due to high tension, and deterioration of product quality may create a high-order processability problem when producing a carbon fiber-reinforced composite material. To prevent such deterioration in quality, it is usually necessary, by trial and error, to find production conditions under which an increase in hairiness is unlikely.

[0020]

As a result of the study, the present inventors have found that the initial tensile modulus of the yarn tensile test relative to the crystallite size can be maximized while suppressing the hairiness of the carbon fiber bundle by adjusting the initial tensile modulus and the crystallite size in the tensile test of the carbon fiber bundle yarn so that to satisfy the relation of formula (2). The lower limit of the right side of the formula (2) is not particularly limited, and when the lower limit is adjusted to 80 × Lc + 60, more preferably to 80 × Lc + 70, and even more preferably to 80 × Lc + 80, it is possible to improve the quality while an increase in the initial modulus of elasticity during a tensile test of the thread.

[0021]

The initial tensile modulus E ₀ of the yarn used in the present invention is determined as the factor "b" of the basic assumption when fitting the SS curve obtained from the tensile test of the carbon fiber bundle using a quadratic function (y=ax²+bx+ c) with "x" as strain and "y" as stress (GPa) in the range 0≤y≤3. In order to control the carbon fiber bundle so that it satisfies the relationship of formula (2), it is required that a high tension be applied in the carbonization process discussed below and a heat treatment be carried out while the crystallite size grows at a constant temperature. It is also possible to estimate Lc and E ₀ from a single fiber using the method described below.

[0022]

In the carbon fiber bundle of the present invention, the ratio of the initial elastic modulus E ₀ (GPa) in the tensile test of the thread is in the range of formula (3):

_E0 ≥ 330 (3).

[0023]

In the carbon fiber bundle of the present invention, the ratio of formula (3) is preferably E ₀ ≥ 340, and more preferably E ₀ ≥ 350. the carbon fiber-reinforced composite material obtained as a result grows, which is preferable. Although E ₀ is preferably as high as possible, the right hand side of formula (3) is adjusted so that the upper limit is preferably 450, more preferably 400, and even more preferably 380. In general, when the initial tensile modulus of the yarn increases, the compressive strength of a single fiber often falls, but the carbon fiber bundle of the present invention has sufficient compressive strength for practical purposes even when the initial tensile modulus of the filament is 330 GPa or more. The initial tensile modulus of the yarn can be estimated from the SS curve obtained in the tensile test of the carbon fiber bundles as mentioned above. In order to control the carbon fiber bundle to satisfy the relationship of formula (3), it is required to increase the degree of orientation of the polyacrylonitrile precursor fibers, apply high tension to the fiber bundle in the pre-carbonization process and the carbonization process mentioned below, increase the maximum temperature of the carbonization process, and increase the time heat treatment during carbonization.

[0024]

The carbon fiber bundle of the present invention has a crystallite size Lc of preferably 2.60 nm or more, more preferably 2.85 nm or more, and even more preferably 3.00 nm or more. If Lc is 2.60 nm or more, it is easy to satisfy both the compressive strength of the carbon fiber bundle and the initial modulus of elasticity in the tensile test of the yarn. If Lc is 2.85 nm or more, a higher industrial value can be achieved in terms of initial elastic modulus. The upper limit of Lc in the carbon fiber bundle of the present invention is 4.00 nm. If the crystallite size Lc is too large, the compressive strength of the compressive strength of a single fiber may fall, and high-order processability may deteriorate, for example, hairiness may easily occur. It is possible to suppress deterioration of these properties by setting the upper limit of Lc to 4.00 nm or less. Preferably Lc is 3.80 nm or less, and more preferably 3.60 nm or less. Generally, the compressive strength of a single fiber tends to decrease as the crystallite size of carbon fibers increases, but the carbon fiber bundle of the present invention has both a high crystallite size and a high compressive strength of a single fiber. Since high-order processability can be maintained, the effect of achieving both tensile modulus and compressive strength of carbon fiber-reinforced composites can be obtained, which is the effect of the present invention. Examples of the method for controlling the crystallite size of the carbon fiber bundle within the above range include increasing the maximum temperature of the carbonization process, increasing the heat treatment time in the carbonization process, and the like.

[0025]

In the carbon fiber bundle of the present invention, the amount of lint present in the carbon fiber bundle is preferably 2/m or less, more preferably 1.0/m or less, and even more preferably 0.5/m or less. When the number of filaments existing in the carbon fiber bundle increases, the high-order processability of the carbon fiber reinforced composite material deteriorates, and when the carbon fiber reinforced composite material is formed, the part where the fibers are destroyed under the compressive stress may become the starting point of failure, resulting in to reduce the compressive strength of the carbon fiber reinforced composite material. When the number of fibers in the carbon fiber bundle is 2/m or less, higher order processability and compressive strength of the carbon fiber reinforced composite material are generally kept at satisfactory values. The number of hairs is calculated by counting the number of (fluffy clumps)/hairs while the carbon fiber bundle is moving at a speed of 1 m/min per 10 m in one line, and then converting to their number per 1 m. m bundle of carbon fiber, within the above range include a reduction in the applied tension in the carbonization process mentioned below.

[0026]

The carbon fiber bundle of the present invention has an average breaking length of preferably 800 to 1100 mm, more preferably 850 to 1050 mm, and even more preferably 900 to 1000 mm. When the average breaking length is 800 mm or more, the carbon fiber bundle is sufficiently opened in the production of carbon fiber reinforced composite material, and the matrix resin is easily absorbed into the space between single fibers, resulting in uniform stress transmission in carbon fiber reinforced composites, therefore, makes it possible improving the compressive strength of carbon fiber reinforced composites. There is no particular limitation on the upper limit of the average breaking length of the carbon fiber bundle, and a sufficient effect is generally obtained if the upper limit is 1100 mm or less. The details of the method for measuring the mean breaking length can be evaluated using the method described below. As a means of controlling the average breaking length within the above range, any method can be used as long as the above range of numerical values can be achieved. Preferably, the average breaking length of the pre-carbonized fiber bundle is controlled in the range of 500 to 800 mm. For this, it is preferable to carry out the fluid weaving process in any of the polyacrylonitrile precursor fiber production process and the stabilization process, that is, at the point where the fiber bundle having a fiber elongation of 5% or more is processed.

[0027]

The carbon fiber bundle of the present invention has a filament tensile strength of preferably 3.5 GPa or more, more preferably 4.0 GPa or more, even more preferably 4.8 GPa or more, even more preferably 5.2 GPa or more, and particularly preferably 5.6 GPa or more. From the viewpoint of an increase relative to the tensile elongation of the obtained carbon fiber reinforced composite material, it is preferable to increase the tensile strength of the yarn. If the tensile strength of the thread is 3.5 GPa or more, the tensile elongation of the obtained carbon fiber-reinforced composite material is generally industrially significant. When the tensile strength of the yarn is low, even if the compressive strength of a single fiber of a carbon fiber bundle is high, the outer side of the bend where the tensile load acts may cause final failure when bending deformation is applied to the obtained carbon fiber reinforced composite material. If the tensile strength of the carbon fiber bundle is 4.8 GPa or more, the carbon fiber bundle of the present invention is well balanced in the high compressive strength of a single fiber, so that it is easy to sufficiently maintain the compressive strength of the obtained carbon fiber reinforced composite material. Although the tensile strength of the yarn is preferably as high as possible, it is preferably 9.0 GPa or less, more preferably 8.7 GPa or less, and even more preferably 8.5 GPa or less in terms of balance with the compressive strength of a single fiber. . The tensile strength of a yarn can be evaluated using the yarn tensile test described below. In order to keep the tensile strength of the yarn in the above range, it is important to oxidize the polyacrylonitrile precursor fiber bundle while simultaneously controlling the infrared parameters, and pre-carbonize and carbonize the stabilized fiber bundle.

[0028]

In the carbon fiber bundle of the present invention, it is preferable that the diameter of a single fiber is 5.0 μm or more, and the ratio between the crystallite size Lc (nm) and the specific gravity (SG) determined by the method of Archimedes satisfies formulas (4) and (5 ). Each formula is described below.

SG ≥ 0.0633 × Lc + 1.565 (4)

2.85 ≤ Lc ≤ 4.00 (5).

[0029]

In the carbon fiber bundle of the present invention, the specific gravity SG is preferably 0.0633×Lc+1.565 or more, more preferably 0.0633×Lc+1.567 or more, and even more preferably 0.0633×Lc+1.569 or more. In general, the larger the crystallite size of a carbon fiber bundle, the more the compressive strength of a single fiber tends to decrease. As a result of careful study by the present inventors, it has been found that a carbon fiber bundle having a high compressive strength of a single fiber relative to the crystallite size is obtained by controlling the specific gravity in the range of formula (4) relative to the crystallite size. Although the cause is not clear, it is believed that crystallite warping causes compression failure in carbon fibers, therefore, the formation of a structure having a high specific gravity, ie, a dense structure, is believed to increase the compression stress required for crystallite warping. To control the relationship between crystallite size and specific gravity in the range of formula (4), it is effective if the heat treatment is carried out for a time in the carbonization process mentioned below.

[0030]

In the carbon fiber bundle of the present invention, it is preferable that the specific gravity SG satisfies formula (4) and the crystallite size Lc is in the range of 2.85 nm or more and 4.00 nm or less shown by formula (5). The reason why the crystallite size preferably satisfies such a range, and the method of controlling it, have been discussed above.

[0031]

The single fiber diameter of the carbon fiber bundle of the present invention is preferably 5.0 µm or more, more preferably 6.0 µm or more, even more preferably 6.5 µm or more, even more preferably 6.9 µm or more, and most preferably 7 .2 µm or more. The diameter of a single fiber is estimated by observation with a scanning electron microscope. If the cross-sectional shape of a single fiber is not a perfect circle, the diameter is replaced by the diameter of an equivalent circle. The equivalent circle diameter refers to an ideal circle having a cross-sectional area equal to the measured cross-sectional area of a single fiber. If the diameter of a single fiber is 5.0 µm or more, the resin impregnation of the fiber bundle during the molding of the composite material is effectively increased, and a high-quality composite material with a small amount of voids is easily obtained. As a result, the tensile modulus of the obtained composite material is effectively increased. If the diameter of the single fiber is 6.0 µm or more, the single fiber is less prone to warp, so that the compressive strength of the single fiber is effectively increased. There is no particular upper limit on the diameter of a single fiber, and the upper limit is approximately 15 µm for manufacturing reasons. The diameter of a single fiber can be controlled in a known manner, for example, by the amount of precursor polymer extruded from a spinneret when spinning a bundle of precursor fibers for carbon fibers, and by the stretch ratio in each process.

[0032]

The prepreg of the present invention is a prepreg comprising a carbon fiber bundle impregnated with a thermosetting resin. The thermosetting resin is preferably a thermosetting resin whose cured product has a tensile modulus of preferably 3.0 GPa or more, more preferably 3.2 GPa or more, and even more preferably 3.5 GPa or more. When the cured thermosetting resin product has a high tensile modulus, it can sufficiently exhibit the compressive strength of a single fiber of the carbon fiber bundle in the obtained carbon fiber reinforced composite material, thereby making it possible to improve the compressive strength of the entire carbon fiber reinforced composite material. If the tensile modulus of the cured thermosetting resin product is 3.0 GPa or more, the requirement for the compressive strength value of the carbon fiber reinforced composite material can be satisfied. Although the tensile modulus of the cured thermosetting resin product should preferably be as high as possible, it is sufficient when it is 7.0 GPa, more preferably 6.7 GPa, and even more preferably 6.5 GPa. The type of thermosetting resin is not particularly limited, and examples thereof include epoxy resin, vinyl ester resin, phenolic resin, benzoxazine resin, bismaleimide resin, cyanate ester resin, polyimide resin, etc. Of these, epoxy resin is preferable from the standpoint of excellent handling and curability in the pre-cured state.

[0033]

Examples of the epoxy resin include a bisphenol A-based epoxy resin, a bisphenol F-based epoxy resin, a bisphenol S-based epoxy resin, a bisphenyl-type epoxy resin, a naphthalene-type epoxy resin, a novolac epoxy resin, an epoxy resin having a fluorene skeleton, an epoxy resin obtained of a phenol compound and dicyclopentadiene as a raw material, a glycidyl ether type epoxy resin such as resorcinol diglycidyl ether, tetrakis(glycidyloxyphenyl)ethane or tris(glycidyloxyphenyl)methane, and a glycidylamine type epoxy resin such as tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, triglycidylaminocresol or tetraglycidyl-xylenediamine. Such epoxy resins may be used singly or many types may be used in combination.

[0034]

The epoxy resin curing agent is not particularly limited as long as it causes the epoxy resin to cure, and examples thereof include amines such as an aromatic amine and an alicyclic amine, acid anhydrides, polyaminoamides, organic acid hydrazides, isocyanates, and the like. An amine curing agent is preferred because the resulting cured resin product has excellent mechanical properties and excellent heat resistance. As the amine curing agent, aromatic amines such as diaminodiphenyl sulfone and diaminodiphenylmethane, aliphatic amines such as dicyandiamide or derivatives thereof, a hydrazide compound, and the like can be used.

[0035]

The curing agent may be used in combination with a curing accelerator. Examples of the curing accelerator that are used in combination include ureas, imidazoles, Lewis acid type catalysts, and the like. Of these, the urea compound is preferably used from the viewpoint of the balance between storage stability and catalytic ability. Can be used as urea compound N, N-dimethyl-N'-(3,4-dichlorophenyl)urea, toluene-bis(dimethylurea), 4,4'-methylene-bis(phenyldimethylurea), 3-phenyl-1,1 -dimethylurea and the like.

[0036]

The prepreg includes a carbon fiber bundle and a thermosetting resin. Such a prepreg can be obtained by impregnating a carbon fiber bundle with a thermosetting resin. Examples of the impregnation method include the wet method and the hot melt method (dry method).

[0037]

The wet method is a method in which the carbon fiber bundle is immersed in a solution prepared by dissolving a thermosetting resin in a solvent such as methyl ethyl ketone or methanol, after pulling out the carbon fiber bundle, the solvent is evaporated from the carbon fiber bundle using an oven, etc., thus impregnating a bundle of carbon fiber with an epoxy resin composition. The hot melt method is a method in which a carbon fiber bundle is directly impregnated with a thermosetting resin having a viscosity reduced by heating, or a method in which, after making a film by coating a thermosetting resin on release paper, the film is laminated on both sides or one side carbon fiber bundle, and then heat and pressure are applied, thereby impregnating the carbon fiber bundle with resin. Only one carbon fiber bundle may be used, or a plurality of aligned carbon fiber bundles may be used.

[0038]

The carbon fiber-reinforced composite material of the present invention is a composite material including the above-described carbon fiber bundle and a matrix resin. As the matrix resin, a cured product of a thermosetting resin, a thermoplastic resin, or mixtures thereof can be used. When using a thermosetting resin, the composite material can be produced through the prepreg described above. In this case, as mentioned above, it is preferable to use a thermosetting resin whose cured product has a tensile modulus of 3.0 GPa or more from the viewpoint of improving the compressive strength of the carbon fiber reinforced composite material. The type of thermosetting resin is not particularly limited, and the thermosetting resin can be appropriately used in combination with the resins mentioned above.

[0039]

The following describes the production method of the carbon fiber bundle of the present invention.

[0040]

In the production of a carbon fiber bundle, a precursor fiber based on polyacrylonitrile is first produced. The polyacrylonitrile copolymer is preferably used as the raw material used for the production of the polyacrylonitrile precursor fiber bundle. In the present invention, a polyacrylonitrile copolymer refers to copolymers in which at least acrylonitrile is a major constituent of the copolymer. The main constituent usually refers to the constituent component, which has from 90 to 100% of the mass. polymer. As a monomer that can be used as a copolymerization component, a monomer having one or more carboxyl groups or amide groups is preferably used from the point of view of promoting oxidation. Examples of the monomer having carboxyl groups include acrylic acid, methacrylic acid, itaconic acid, their alkali metal salts and ammonium salts. Examples of a monomer having amide groups include acrylamide.

[0041]

In the method for producing the polyacrylonitrile precursor fiber bundle, the method for producing the polyacrylonitrile copolymer may be selected from known polymerization methods.

[0042]

In the production of the polyacrylonitrile precursor fiber bundle, dry-wet spinning or wet spinning may be used as the fiber production method, but dry-wet spinning, effective in terms of tensile strength of the filament of the obtained carbon fiber bundle, use preferably. The fiber manufacturing process includes a spinning process by extruding a spinning solution from a spinneret into a coagulation bath, a water bath process for washing the fibers produced by the spinning process, a water bath drawing process for drawing the fiber bundle obtained from the water bath washing process, a dry heat treatment process in which the fiber bundle obtained by the water bath drawing process is subjected to a dry heat treatment; and, optionally, a steam drawing process for steam stretching the fiber bundle obtained by the dry heat treatment. It should be noted that the order of any process can be changed depending on the situation.

[0043]

A dope is prepared by dissolving the above-described polyacrylonitrile copolymer in a solvent in which the polyacrylonitrile copolymer is soluble. Examples of the solvent in which the polyacrylonitrile copolymer is soluble include organic solvents such as dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, and aqueous solutions of nitric acid, zinc chloride, and sodium thiocyanate.

[0044]

Preferably, a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a solvent for the dope and a coagulation aid are included in the coagulation bath. As the coagulation aid component, a component that does not dissolve the polyacrylonitrile copolymer and is compatible with the solvent used in the dope can be used. More specifically, it is preferable to use water as the coagulation aid.

[0045]

It is preferable to use as a water washing bath in the water washing process a water washing bath comprising a plurality of steps at a temperature of 30 to 98°C. The stretching ratio in the water bath drawing process is preferably 2 to 6 times.

[0046]

After the water bath drawing process, it is preferable to apply an oily agent derived from silicone to the fiber bundle in order to prevent adhesion between single fibers. It is preferable to use modified silicone as the silicone oil agent, and agents containing amino-modified silicone having high temperature resistance are preferably used.

[0047]

For the dry heat treatment process, a known method can be used. For example, the drying temperature is 100 to 200°C.

[0048]

After the dry heat treatment process, fluid interlacing of the fiber bundle is preferably applied. The fluid used in fluid weaving may be a gas or a liquid, and the use of air or nitrogen is preferred due to low cost. In fluid weaving, the fluid is preferably sprayed onto the fiber bundle using a nozzle, and the shape of the nozzle used in fluid spraying is not particularly limited, although a nozzle having 2 to 8 injection holes is preferred. Although the location of the injection holes is not particularly limited, an even number of injection holes are preferably arranged around the fiber bundle so that the longitudinal direction of the fiber bundle and the fluid spray direction are at an angle in the range of 88 to 90° and each injection hole faces the other injection hole. on opposite sides of the fiber bundle to form a pair of injection holes.

[0049]

After the above-described water washing process, the water bath drawing process, the oil agent application process, and the dry heat treatment process, steam stretching is optionally carried out to obtain a polyacrylonitrile precursor fiber bundle to obtain a carbon fiber bundle of the present invention. Steam stretching is preferably carried out with pressurized steam at a stretch ratio of 2 to 6.

[0050]

The single fiber fineness of the polyacrylonitrile precursor fiber bundle is preferably 0.5 to 1.5 dtex, more preferably 0.7 to 1.5 dtex, and even more preferably 0.9 to 1.5 dtex in terms of increase tensile strength of a carbon fiber bundle thread.

[0051]

In the carbon fiber bundle production method, the polyacrylonitrile precursor fiber bundle is subjected to a stabilization process, a pre-carbonization process, and a carbonization process to obtain a carbon fiber bundle.

[0052]

In the present invention, the stabilization process refers to a process in which a bundle of a precursor fiber based on polyacrylonitrile is subjected to heat treatment at a temperature of 200 to 300°C in an atmosphere containing oxygen. In the carbon fiber bundle production method of the present invention, in order to improve the initial modulus and compressive strength of a single fiber in a carbon fiber bundle tensile test, especially when a polyacrylonitrile precursor fiber bundle is subjected to a stabilization process, it is preferable to control the peak intensity ratio at 1453 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum of the obtained stabilized fiber bundle, so that it is in the range from 0.60 to 0.70, and the ratio of the intensity of the peak at 1254 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum so that it is in the range from 0.50 to 0.65. The peak at 1453 cm ^-1 in the infrared spectrum is a peak derived from alkene, and decreases with the development of the stabilization reaction. The peak at 1370 cm ^-1 and the peak at 1254 cm ^-1 are peaks derived from the stabilized structure (which is considered to be the structure of the naphthyridine ring and the structure of the hydrogenated naphthyridine ring, respectively), and increase with the development of the stabilization reaction. The stabilization process usually reduces the peak obtained from polyacrylonitrile as much as possible in order to increase the carbonization yield. However, in the present invention, the conditions of the stabilization process are intentionally set so that a large amount of alkenes remains. It has been found that if stabilized fibers having such a structure are subjected to a pre-carbonization process, the effect of increasing the initial modulus of elasticity and compressive strength of a single fiber is manifested when a tensile test of a thread of the obtained carbon fiber bundle is manifested. It is important to set the stabilization conditions so that the ratio of the peak intensity at 1254 cm ^-1 to the peak intensity at 1370 cm ^-1 is between 0.50 and 0.65. The peak intensity referred to in this case is the absorption at each wavelength after correction for the background of the spectrum obtained by measuring the infrared spectrum after sampling a small amount of stabilized fiber, and no particular separation of the peaks is carried out. The concentration of the sample is measured after dilution with KBr so that it is 0.67% of the mass. In order to control the infrared spectrum of the stabilized fibers within the above range, the production conditions can be studied depending on the suitable production method described below.

[0053]

In the present invention, the processing time in the stabilization process can be appropriately selected in the range of preferably 10 to 100 minutes. In order to improve the initial elastic modulus and compressive strength of a single fiber in a tensile test of a filament of the obtained carbon fiber bundle, the treatment time in the stabilization process is set so that the specific gravity of the obtained stabilized fiber is preferably in the range of 1.30 to 1.36 and more preferably from 1.31 to 1.35. More preferably, the stabilization treatment time depends on the stabilization temperature. If the specific gravity of the stabilized fiber is 1.30 or more, physical properties such as the tensile modulus of the carbon fiber bundle thread can be sufficiently developed, and if the specific gravity is 1.36 or less, the compressive strength of the single fiber may be increased. The specific gravity of the stabilized fiber is controlled by the stabilization treatment time and the stabilization temperature. In the present invention, in order to oxidize the polyacrylonitrile precursor fiber, it is preferable to control the stabilization temperature so that the intensity ratio of the infrared spectrum peaks falls within the above range. Specifically, the stabilization temperature is preferably controlled in air in the range of 200 to 300°C, more preferably 210 to 280°C and even more preferably 220 to 280°C. The preferred stabilization treatment time and stabilization temperature varies depending on the properties of the polyacrylonitrile precursor fiber bundle and the polyacrylonitrile copolymer copolymerization composition.

[0054]

In the present invention, when a twisted fiber bundle is used in the carbonization process, the tension of the fiber bundle in the stabilization process is set to 1.0 mN/dtex or more. The tension is preferably 1.2 mN/dtex or more, and more preferably 1.4 mN/dtex or more. The tension of the fiber bundle during the stabilization process is obtained by dividing the tensile force (mN) of the fiber bundle, measured at the output side of the stabilization oven, by the total fineness (dtex), which is the product of the single fiber fineness (dtex) of the carbon fiber precursor bundle used and the number of elementary threads. By adjusting the tension, the degree of crystal orientation of the stabilized fiber bundle is effectively increased, and when tension is applied to the fiber bundle in the subsequent carbonization process, the tensile modulus of the obtained carbon fibers is effectively increased, so that a carbon fiber bundle having an excellent balance with compressive strength is easily obtained. . If the tension of the fiber bundle during the stabilization process is 1.0 mN/dtex or more, the degree of crystal orientation of the stabilized fiber bundle can be significantly increased.

[0055]

In the pre-carbonization process, in the pre-carbonization of the fiber bundle obtained in the stabilization process, the resulting stabilized fiber is subjected to heat treatment at a maximum temperature of 500 to 1000° C. in an inert atmosphere. If the maximum temperature for the pre-carbonization temperature is 500° C. or higher, the pre-carbonized fiber bundle can be carbonized in the subsequent carbonization process without breaking due to thermal degradation. There is no particular limitation on the upper limit of the maximum temperature for the pre-carbonization temperature, but it is preferably 1000° C. or lower in order to keep the temperature below the carbonization temperature of the subsequent carbonization process.

[0056]

In the carbonization process in the carbonization of the pre-carbonized fiber bundle, the obtained pre-carbonized fiber bundle is subjected to heat treatment in an inert atmosphere at a maximum temperature T of 1700 to 3000°C. The maximum temperature is preferably 1700 to 2900°C and more preferably 1900 to 2800°C. In general, the higher the maximum temperature in the carbonization process, the larger the crystallite size and the more uniform the crystallite orientation becomes, so that the initial modulus of elasticity in the tensile test of the resulting carbon fiber bundle is improved, while the compressive strength of a single fiber of the carbon bundle decreases. fibers. If the carbonization temperature is 1700°C, it is a temperature sufficient for full development of carbonization to increase the crystallite size, and if it is 3000°C or lower, it is a temperature sufficient to maintain the compressive strength of a single fiber bundle of carbon fibers.

[0057]

In the carbonization process in the carbonization of a pre-carbonized fiber bundle, when a substantially non-twisted fiber bundle is used, the obtained pre-carbonized fiber bundle is carbonized in an inert atmosphere until the ratio between the crystallite size Lc (nm) and the maximum temperature T (°C) is satisfy the ratio Lc ≥ 2.00 × 10 ^-3 × T - 0.90. In the present invention, "substantially untwisted" means that although there is no twist in the fiber bundle or twist is present locally, S-twist and Z-twist exist equivalently and the net twist number in the entire carbonization process is less than 1 turn/m. By using a substantially non-twisted fiber bundle, it becomes easy to expand the fiber bundle when forming a carbon fiber reinforced composite material, and it is easy to obtain a high quality prepreg and carbon fiber reinforced composite material. The conditions preferably correspond to the ratio Lc ≥ 2.00 x 10 ^-3 x T - 0.87 and even more preferably Lc ≥ 2.00 x 10 ^-3 x T - 0.83. The upper limit of Lc is not particularly limited, but if it is too large, the compressive strength of a single fiber may fall so that the following ratios Lc ≤ 2.00×10 ^-3 ×T - 0.50, preferably Lc ≤ 2.00××T - 0.60 and more preferably Lc ≤ 2.00 × 10 ^-3 × T - 0.70 can satisfy the requirement for compressive strength of a single fiber of a carbon fiber bundle. In general, the larger the crystallite size of the carbon fibers, the lower the compressive strength of the single fiber tends to fall, and the carbon fiber bundle of the present invention shows that both the crystallite size and the compressive strength of the single fiber are high. As a result, the effect of achieving both the tensile modulus and the compressive strength of the carbon fiber reinforced composite material can be successfully obtained, which is the effect of the present invention. When the condition Lc ≥ 2.00 x 10 ^-3 x T - 0.90 is satisfied, the initial tensile modulus of the yarn and the single fiber compressive strength can be compatible at a high level. To improve the crystallite size, it is sufficient to increase the carbonization temperature, but only increasing the carbonization temperature lowers the compressive strength of a single fiber of a carbon fiber bundle. In order to improve the crystallite size without reducing the compressive strength of the single fiber, the residence time at the maximum temperature during the carbonization process can be extended. The relationship between residence time and crystallite size is in fact a linear relationship, and the residence time can be selected by extrapolating the expression of the relationship between residence time and crystallite size.

[0058]

When a non-twisted fiber bundle is used in the carbonization process in the carbonization of a pre-carbonized fiber bundle, the carbonization is carried out while adjusting the tension in the range of 4.0 to 6.0 mN/dtex. The tension during carbonization is preferably 4.5 to 6.0 mN/dtex and more preferably 4.5 to 5.5 mN/dtex. By applying tension carbonization during the carbonization process, the crystallite orientation can be made uniform, thereby improving the initial tensile modulus of the filament of the resulting carbon fiber bundle. If the tension is 4.0 mN/dtex or more, the initial modulus of elasticity in the tensile test of the carbon fiber bundle yarn is sufficiently developed, and if the tension is 6.0 mN/dtex or less, the formation of lint during carbonization can be suppressed. , even when a bundle of substantially untwisted fiber is used. In the carbonization process, there is a need to apply tension while maintaining both the maximum temperature and the residence time at the maximum temperature. When the maximum temperature in the carbonization process is low or the residence time at the maximum temperature is short, the initial tensile modulus of the filament of the obtained carbon fiber falls. When the tension in the carbonization process is increased to increase the initial modulus of elasticity, fluff is formed and wound on the windrow, resulting in a significant deterioration in productivity. In addition, if the tension in the carbonization process is low, the initial tensile modulus of the filament of the obtained carbon fiber bundle will be low. If the maximum temperature in the carbonization process or the residence time at the maximum temperature is increased to increase the initial elastic modulus, the compressive strength of a single fiber of a carbon fiber bundle falls. Tension during carbonization is measured by interleaving a moving carbon fiber bundle immediately after exiting the heating furnace during carbonization using a strain gauge. The tension can be adjusted by adjusting the swath speed before and after the carbonization process.

[0059]

When a twisted fiber bundle is used in the carbonization process in the carbonization of a pre-carbonized fiber bundle, the number of twists in all processes during the passage through the carbonization process is controlled to 2 turns/m or more. The number of twists is preferably 5 threads/m or more, more preferably 16 threads/m or more, even more preferably 20 threads/m or more, even more preferably 31 threads/m or more, and particularly preferably 46 threads/m or more. The number of twists is preferably 120 turns/m or less, and more preferably 80 turns/m or less. By controlling the number of twists to 2 threads/m or more, hairiness during the carbonization process is suppressed, so that a higher tension can be applied than in the absence of twisting, and the tensile modulus of the obtained carbon fiber bundle effectively increases. As the number of twists increases, the axial direction of the single fibers in the fiber bundle is inclined with respect to the tension direction of the fiber bundle, and fluff can be generated quite easily during the carbonization process. If their number is adjusted to 120 threads/m or less, the formation of fluff can be suppressed to such an extent that there are no problems in the process. The number of twists of the fiber bundle in the carbonization process means the number of twists in all carbonization heat treatment application processes, and the carbonization process is carried out in a state in which the fiber bundle has a twist of 2 twists/m or more before it is subjected to the carbonization process. When the tension in the carbonization process is increased without twisting, single fiber breakage occurs and the number of filaments increases so that the permeability of the carbonization process may deteriorate or the entire fiber bundle may break, resulting in not maintaining the necessary tension. The number of twists can be controlled by a method in which a bundle of precursor fibers for carbon fibers, or a bundle of stabilized fibers, or a bundle of pre-carbonized fibers, is wound around a bobbin once, and when the fiber bundle is unwound, the bobbin is turned to a surface orthogonal to the direction bobbin unwinding, or the twisting method by bringing a rotating roll or belt into contact with a moving fiber bundle without being wound onto a bobbin. Although there is no clear upper limit on the number of twists, approximately 500 threads/m can be considered as a practical upper limit in terms of processability.

[0060]

When a twisted fiber bundle is used in the carbonization process in the carbonization of a pre-carbonized fiber bundle, the surface layer 4 of the fiber bundle in all processes during passing through the carbonization process is controlled at 0.2° or more. The twist angle is preferably 0.7° or more, more preferably 2.0° or more, and even more preferably 2.5° or more. The twist angle is preferably 41.5° or less, more preferably 30.5° or less, even more preferably 24.0° or less, and particularly preferably 12.5° or less. By controlling the twisting angle at 0.2° or more, hairiness during the carbonization process is suppressed, so that it becomes possible to apply a higher tension than in the case without twisting, and the tensile modulus of the obtained carbon fiber bundle effectively increases. As the twisting angle increases, the axial direction of the single fibers in the fiber bundle forms an inclination with respect to the tension direction of the fiber bundle, and the formation of lint during the carbonization process can occur quite easily. If the twisting angle is controlled at 41.5° or less, the formation of lint can be suppressed to such an extent that there are no problems in the process. The twist angle of the fiber bundle during carbonization can be calculated from the number of twists and the number of filaments of the fiber bundle and the single fiber diameter, as discussed below. Although there is no clear upper limit on the twist angle, approximately 52.5° can be considered to represent a practical upper limit in terms of processability.

[0061]

When a stranded fiber bundle is used in the carbonization process in the carbonization of a pre-carbonized fiber bundle, it is carbonized while controlling the tension at 4.0 mN/dtex or more. The tension during carbonization is preferably 4.5 mN/dtex or more, more preferably 5.0 mN/dtex, and even more preferably 7.0 mN/dtex. By carbonizing while applying tension in the carbonization process, the crystallite orientation can be made uniform, and the initial tensile modulus of the filament of the obtained carbon fiber bundle is improved. If the tension is 4.0 mN/dtex or more, the initial modulus of elasticity in the tensile test of the carbon fiber bundle is sufficiently exhibited, and when the twisted fiber bundle is used, even if the tension is 6.0 mN/dtex or more, lint is generated. in the carbonization process, a high tension can be suppressed and applied, so that the crystallite orientation can be effectively made uniform, and a carbon fiber bundle having an excellent balance between the tensile modulus of the yarn and the compressive strength is easily obtained.

[0062]

The carbon fiber bundle thus obtained is preferably subjected to an oxidative treatment. By oxidative treatment, the oxygen-containing functional group is introduced into the carbon fiber bundle. As the oxidation treatment, vapor phase oxidation, liquid phase oxidation, and liquid phase electrolytic oxidation can be used. From the viewpoint of high productivity and the ability to perform uniform processing, liquid-phase electrolytic oxidation is preferably used. In the present invention, the liquid-phase electrolytic oxidation method is not particularly limited, and a known method can be used.

[0063]

A sizing agent may also be applied after the liquid phase electrolytic oxidation to impart converging properties to the resulting carbon fiber bundle. As for the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected depending on the type of the matrix resin used in the composite material.

[0064]

Methods for measuring various physical properties used in the present invention are as follows.

[0065]

Mean breaking length measurement method

The breaking length measurement method is shown in FIG. 1. First, fiber bundle 1 is cut to a length of 1160 mm and one end is fixed on a horizontal table with adhesive tape so that this end is stationary. This point (2) is designated as fixed point A. The other unfixed end of the fiber bundle is divided into two bundles with fingers and one bundle is attached to the table with adhesive tape in a slightly stretched state. This point (3) is designated as fixed point B. The other end of the split bundle is rotated on the table without sagging around fixed point A, and this end is left in a position where the distance in a straight line from fixed point B is 500 mm and fixed on the table with adhesive tape . This point (4) is designated as fixed point C. The area surrounded by fixed points A, B and C is visually assessed, and after determining the entanglement point 5 furthest from fixed point A, record the length projected on a straight line between fixed point A and fixed point B, using a ruler with a minimum scale of 1 mm. This length means a breaking length of 6. This measurement is repeated 30 times and the arithmetic mean of the measurements is used as the average breaking length. In such a measurement method, the entanglement point 5 furthest from the fixed point A is the point furthest from the fixed point A at a straight line distance where three or more single fibers without slack are intertwined with each other.

[0066]

Infrared intensity ratio

After freezing and pulverizing the stabilized fiber to be evaluated, 2 mg of the pulverized powder was accurately weighed and collected, and then mixed with 300 mg of KBr. The mixture thus obtained was placed in a molding tool, and then pressed at 40 MPa for 2 minutes using a press machine to obtain a tablet for measurement. The tablet thus obtained is mounted in a Fourier transform infrared spectrophotometer to measure the spectrum in the range from 1000 to 2000 cm ⁻¹ . The background correction is made by lowering the minimum value in the range from 1700 to 2000 cm ⁻¹ of each intensity so that the minimum value corresponds to "0". In the Examples and Comparative Examples below, a PARAGON 1000 manufactured by Perkin Elmer Co., Ltd. was used as the Fourier transform infrared spectrophotometer.

[0067]

Carbon fiber bundle tensile test

The tensile modulus of a carbon fiber bundle yarn and the tensile strength of the yarn are determined according to the "Strand Test Method" defined in JIS R7608 (2008). The initial tensile modulus E ₀ of the thread used in the present invention is determined as the coefficient "b" of the main assumption when fitting the SS curve obtained from the thread tensile test using the quadratic function y=ax²+bx+c with "x" as strain and "y" as stress (GPa) ranging from 0≤y≤3. The strain is measured using an extensometer. The number of threads to be measured is seven, and the arithmetic mean of the measurement results determines both the initial elastic modulus E ₀ and the tensile strength of the carbon fiber bundle thread. In the examples and comparative examples described below, test samples were prepared as follows. Test specimens are prepared by impregnating a carbon fiber bundle with the resin composition below, followed by curing by heat treatment at 130° C. for 35 minutes.

[0068]

resin composition

3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (100 mass)

Boron trifluoride monoethylamine (3 mass parts)

Acetone (4 parts by mass).

[0069]

In the Examples and Comparative Examples described below, CELLOXIDE P2021P (manufactured by Daicel Corporation) was used as the above 3,4-epoxycyclohexyl-methyl-3,4-epoxycyclohexanecarboxylate.

[0070]

Specific gravity of a carbon fiber bundle

After sampling a 1 m carbon fiber bundle to be evaluated, the specific gravity is measured by the method of Archimedes using o-dichloroethylene as the heavy liquid for measuring the specific gravity. The measurements are carried out in a constant temperature environment at room temperature 25°C, the number of samples is 3 and their average value is used.

[0071]

Compressive Strength of Single Fiber Carbon Fibers

The compressive strength of a single fiber, determined by the method of fragmentation in compression of composites containing one type of fiber, is measured using the following methods (1)-(5).

[0072]

(1) Resin preparation

190 mass.h are loaded into the container. epoxy resin based on bisphenol A "EPOTOHTO (registered trademark)" YD-128 (manufactured by Nippon Steel Chemical Co., Ltd.) and 20.7 mass. diethylenetriamine (manufactured by Wako Pure Chemical Industries, Ltd.), then stirred using a spatula, and further defoamed using an automatic vacuum defoamer.

[0073]

(2) Sampling a single carbon fiber fiber and fixing for molding

A carbon fiber bundle having a length of approximately 20 cm is substantially evenly divided into four bundles and single fibers are sampled in order from four bundles. In this case, the fibers are selected as evenly as possible from all bundles. Then, a double-sided adhesive tape is applied to both ends of the perforated paper substrate, and the selected single fibers are fixed on the perforated paper substrate in a state where a constant tension is applied to the single fibers. Then, a glass plate was prepared with a "LUMIRROR (registered trademark)" polyester film (manufactured by Toray Industries, Inc.) attached on the plate, and a spacer having a thickness of 2 mm to control the thickness of the test sample was fixed on the film. A perforated paper substrate with single fibers fixed thereon is placed on a spacer, and additionally, a glass plate with a film similarly attached thereon is placed on the paper substrate so that its side with the film attached thereon faces down. Meanwhile, in order to control the depth of fiber embedding, a tape having a thickness of approximately 70 µm is attached to both ends of the film.

[0074]

(3) Resin curing casting

The resin prepared by the method of (2) above is poured into the mold (the space surrounded by the spacer and the film) obtained by the method (1) described above. The mold containing the resin poured into it is heated for 5 hours using an oven preheated to 50°C, and the temperature is then lowered to 30°C at a temperature reduction rate of 2.5°C/min. After being released from the mold and cut, a 2 x 7.5 x 0.2 cm test sample is obtained. The test sample is cut so that single fibers are located on an area having a width of 0.5 cm, centered in the width direction of the test sample.

[0075]

(4) Depth measurement

The fiber embedment depth was measured for the test sample obtained by the method of (3) above, using a JASCO Corporation NRS-3200 laser Raman laser spectrophotometer) and a 532 nm notch filter. First, the surface of a single fiber is irradiated with a laser beam and the stage height is adjusted to minimize the diameter of the laser beam. This stage height is referred to as "A" (µm). The surface of the test specimen is then irradiated with a laser beam and the stage height is adjusted to minimize the diameter of the laser beam. This table height is referred to as "B" (µm). The embedment depth d (µm) of the fiber is calculated using the refractive index of 1.732 of the resin measured using a laser as mentioned above, according to the following formula (4):

d = (A-B)×1.732 (4).

[0076]

(5) 4-point bend test

A compressive strain is applied to the test specimen obtained by the above procedure (3) using the 4-point bending test method using a clamp having external indenters at 50 mm intervals and internal indenters at 20 mm intervals. The voltage is applied in steps of 0.1%, and the test sample is examined using a polarizing microscope to measure the number of broken single filaments in a 5 mm wide area centered in the longitudinal direction of the test sample. The double value of the measured number of breaks is determined as the number of broken fibers (filaments/10 mm), and the compressive stress calculated from the compressive strain when the average number of broken samples for test number 30 exceeds 1 (filament)/10 mm, is determined, as the compressive strength of a single fiber. The strain ε(%) of the single fiber composites is also measured using a strain gauge attached at a position of approximately 5 mm in the width direction from the center of the test sample. The ultimate compressive strain ε _c of single fiber composites is calculated considering the calibration factor κ of the strain gauge, the embedded depth d (µm) of the fiber measured by the method of (4) above, and the permanent strain of 0.14(%) by the following formula (5) :

ε _c \u003d ε × (2 / κ) × (1-d / 1000) -0.14 (5).

[0077]

Crystallite size Lc

The carbon fiber bundle used in the measurement is aligned and fixed using an alcohol solution of collodion to obtain a quadrangular prism measurement sample (length 4 cm; side length 1 mm). The sample thus obtained is evaluated using a wide-angle X-ray diffractometer under the following conditions:

X-ray source: CuKα radiation (tube voltage 40 kV, lamp current 30 mA),

Detector: goniometer + monochromator + scintillation counter,

Scan range: 2Ɵ = 10 to 40°

Scan mode: step scan; pitch unit 0.01°; scanning speed 1°/min.

[0078]

In the diffraction pattern thus obtained, the peak is approximated using a Gaussian model with respect to the peak around 2Ɵ = 25 to 26°. The full linewidth at half height is determined and the crystallite size is calculated from this value using the following Scherrer equation:

Crystallite size (nm) = Kλ/β ₀ cosθ _B ,

provided that

K: 1.00; λ: 0.15418 nm (X-ray wavelength)

β ₀ : (βE ² -β ₁ ² ) ^1/2

β _E : apparent full width at half height (measurement) rad,

β ₁ : 1.046×10 ^-2 rad

Ɵ _B : Bragg diffraction angle.

[0079]

The measurement is carried out ten times per level and the average of the obtained values is determined as the size of the crystallite. In the Examples and Comparative Examples discussed below, an XRD-6100 manufactured by SHIMADZU CORPORATION is used as a wide-angle X-ray diffractometer.

[0080]

When measuring from a single carbon fiber, a single fiber is randomly removed from the carbon fiber bundle and wide-angle X-ray diffraction measurements are taken with an instrument capable of using an x-ray µ beam. The measurement is carried out using a microbeam having a wavelength of 0.1305 nm, located in the form of 3 μm in the direction of the fiber axis and 1 μm in the direction of the fiber diameter, scanning single fibers in the direction of the fiber diameter with an advance of 1 μm. The irradiation time for each advance is 2 sec. The length of the chamber, which is the distance between the detector and the sample, is set to fall within the range of 40 to 200 mm. The chamber length coordinates and beam center are obtained by measuring cerium oxide as a standard. By subtracting the 2D diffraction pattern obtained by removing a sample of the determined 2D diffraction pattern, dark noise due to the detector and scattering noise due to air are eliminated to obtain a corrected 2D diffraction pattern. By adding the corrected 2D diffraction patterns at each position in the fiber diameter direction of the single fiber, an average 2D diffraction pattern in the fiber diameter direction of the single fiber is obtained. This average two-dimensional diffraction pattern is sector-integrated at an angle of ±5° centered on a direction orthogonal to the fiber axis to obtain a diffraction intensity profile in the 2Ɵ direction. A least-squares fit of the diffraction intensity profile in the 2Ɵ direction is performed using two Gaussian functions, and the angle 2Ɵ _m (°) of the 2Ɵ angle at which the diffraction intensity is maximum and the full width at half-height FWHM (°) of the combined function of the two Gaussian functions are calculated . Then circumferential integration is carried out with a width of ±5° around the angle 2Ɵ _m (°), when the diffraction intensity profile in the 2Ɵ direction becomes maximum, and the diffraction intensity profile in the circumferential direction is obtained. The crystallite size Lc of a single fiber is obtained by the following formula, and the results for each of the three single fibers are averaged and calculated.

Lc (nm) = Kλ/FWHMcos(2Ɵ _m /2),

where the Scherrer coefficient K is 1.0, the X-ray wavelength λ is 0.1305 nm, and the full linewidth at half height FWHM and 2Ɵ _m is used after converting the unit to radians (rad) from angle (°).

[0081]

Measurement of Tensile Modulus of a Cured Thermoplastic Resin Product

The resin component of the thermosetting resin was loaded into a kneader, and the temperature was raised to 150° C. while kneading, followed by kneading at the same temperature for 1 hour. The temperature is then lowered to 60° C. with stirring. Then, a curing agent and a curing accelerator are added, followed by further kneading to obtain an uncured thermosetting resin. After defoaming the uncured thermosetting resin in a vacuum, the uncured thermosetting resin is cured in a mold in which a 2mm thick "Teflon (Registered Trademark)" pad is used to set the thickness to 2mm at 130°C for 2 hours to obtain a cured product. thermosetting resin having a thickness of 2 mm. A test piece having a width of 10 mm and a length of 60 mm is cut from this cured product, and then a 3-point bend test is performed with a length between spaces of 32 mm and a traverse speed of 2.5 mm/min in accordance with JIS-K7171 (1994) for measuring the tensile modulus of elasticity. The number of samples is five, and their average is determined as the tensile modulus of the cured resin product.

[0082]

Measurement of 0° Compressive Strength of a Carbon Fiber Reinforced Composite Material

The resin raw material for the thermosetting resin, excluding the curing agent and the curing accelerator, was mixed with a kneader, followed by stirring for 1 hour, to obtain a resin composition. Then, the resin composition thus obtained is applied to the silicone surface of the silicone-coated release paper to form a resin film. The obtained resin film is wound around the surface of a steel drum having a circumference of approximately 2.7 m, and the temperature is controlled at 60-70° C., with the surface of the resin composition facing outward. Then, the bundle of carbon fiber unwound from the creel is placed on the surface of the resin composition wound around the steel drum by means of a traverse. The surface of the resin composition is covered with a resin film on the side of the carbon fiber bundle, and the separately prepared roll is pressed against the surface of the outer resin film while rotating it in contact to impregnate the fiber bundle with resin, resulting in a unidirectional prepreg 300 mm wide and 2.7 mm long. m. The basic weight of the fiber in the prepreg is controlled in the range from 190 to 200 g/m ² by adjusting the speed of rotation of the drum and the feed rate of the traverse. A plurality of obtained prepregs were laminated with the fiber direction aligned in one direction, treated at a temperature of 130°C and a pressure of 0.3 MPa for 2 hours to cure the resin, resulting in a laminate having a thickness of 1 mm (fiber-reinforced composite material). A test specimen is cut from the laminate having a thickness of 1 ± 0.1 mm, a width of 12.7 ± 0.13 mm, a length of 80 ± 0.013 mm and a length of the test part of 5 ± 0.13 mm. At both ends of the test specimen (37.5 mm from each of both ends), fix the reinforcing platinum with adhesive, thus setting the length of the test piece to 5 ± 0.13 mm. In accordance with ASTM D695 (1996), the compressive strength is measured for a number of test specimens under conditions of a strain rate of 1.27 mm/min, and the resulting compressive strength is converted to a fiber volume fraction of 60%. The measurements are taken at n=6 and in the present invention their average is defined as 0° compressive strength of the carbon fiber reinforced composite material.

[0083]

Average diameter of single fiber carbon fibers

The cross-section of the single fiber to be evaluated is examined using a scanning electron microscope to determine the cross-sectional area. Calculate the diameter of an ideal circle having the same cross-sectional area and determine as the diameter of a single fiber. The acceleration voltage is 5 keV.

[0084]

In the Examples and Comparative Examples discussed below, a scanning electron microscope (SEM) "S-4800" manufactured by Hitachi High-Technologies Corporation was used as the scanning electron microscope.

[0085]

Twisting angle of the surface layer of the fiber bundle

The angle of twist (°) of the surface layer of the fiber bundle during carbonization is determined as follows: the diameter (µm) of the entire fiber bundle is calculated from the number of twists (turns/m) of the fiber bundle during carbonization, the number of filaments and the diameter (µm) of a single fiber of the obtained carbon fibers using the formula below, followed by a calculation using the diameter of the entire fiber bundle as follows.

Diameter (µm) of the entire fiber bundle = {(single fiber diameter) ² ×(number of filaments)} ^0.5

Remaining twist angle (°) of the surface layer of the fiber bundle=atan (diameter of the entire fiber bundle × 10 ^-6 × π × number of twists).

EXAMPLES

[0086]

The present invention is more specifically described below with the help of examples. The measurement method used in the examples is the method described above.

[0087]

Reference Examples 1-4

The polyacrylonitrile copolymer is produced by polymerizing a polyacrylonitrile copolymer copolymerized with itaconic acid by a solution polymerization method using dimethyl sulfoxide as a solvent. The coagulated yarn is produced by the "dry jet" wet spinning method, where the resulting dope is once extruded into air from a spinneret, passed through a space of approximately 4 mm, and then introduced into a coagulation bath with a 35% aqueous dimethyl sulfoxide solution at a temperature of 3°C. This coagulated yarn is washed in the usual way and then stretched in a bath of hot water from 2 containers 3.5 times in a water bath. An amino-modified silicone oil agent is applied to this fiber bundle after being stretched in a water bath, and a densification treatment is carried out by drying using a heat roller at 160°C. After combining two yarns together so that the number of single fibers in the fiber bundle is 12,000, the fiber bundle is stretched 3.7 times in high pressure steam so that the total stretch after spinning is 13 times. The fiber bundle is then interlaced to form a polyacrylonitrile precursor fiber bundle containing 12,000 single fibers each having a degree of crystal orientation of 93%. The weave treatment is carried out using a fluid spray nozzle having eight injection holes arranged around the fiber bundle so that the direction of the fluid spray is at a 90° angle with the longitudinal direction of the fiber bundle and each injection hole faces another injection hole on opposite sides of the bundle. fibers, forming a pair of injection holes. In weaving, the conditions are adjusted so that the fiber bundle tension is 3 mN/dtex and the fluid ejection pressure is 0.35 MPa. Then, the precursor fiber bundle is subjected to a stabilization treatment at a stabilization temperature of 210 to 280° C. to obtain a stabilized fiber bundle. The stabilization treatment is carried out by adjusting the stabilization time so that the stabilized structure shown in Table 1 is formed, while stretching the polyacrylonitrile precursor fiber bundle at a stretch ratio of 1 in an oven under nitrogen atmosphere.

[0088]

Reference Example 5

In the same manner as in Reference Examples 1 to 4, a polyacrylonitrile precursor fiber bundle was prepared, and the tension was controlled by adjusting the stabilization time and stretching ratio at a stabilization temperature of 210 to 280°C to form a stabilized structure shown in Table 1 and then the polyacrylonitrile precursor fiber bundle is subjected to a stabilizing treatment in an oven under a nitrogen atmosphere to obtain a stabilized fiber bundle.

[0089]

Examples 1-8 and 12, Comparative Examples 1-7

The stabilized fiber bundle obtained in the Reference Examples was subjected to a pre-carbonization treatment under nitrogen at a temperature of 300 to 800°C to obtain a pre-carbonized fiber bundle. The pre-carbonized fiber bundle thus obtained is subjected to a carbonization treatment under nitrogen atmosphere at the maximum temperature, tension and residence time shown in Table 2. The carbon fiber bundle thus obtained is subjected to surface treatment and sizing agent application treatment to obtain fibers. Using this carbon fiber bundle, a prepreg and a carbon fiber reinforced composite were prepared with the resin composition shown below. The physical properties of the carbon fiber bundle thus obtained and the fiber-reinforced composite material are shown in Table 3. The tensile modulus of the cured resin product with the same resin composition is measured, and the tensile modulus is found to be 4.4 GPa.

[0090]

resin composition

Bisphenol A liquid 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), 50 parts by mass;

Phenolic novolac epoxy resin ("jER (registered trademark)" 154, manufactured by Mitsubishi Chemical Corporation), 30 parts by mass;

Curing agent:

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

[0091]

Comparative Example 8

Using "TORAYCA (registered trademark)" M40S carbon fiber bundle (filament tensile modulus 380 GPa, single fiber compressive strength 3.0 GPa (manufactured by Toray Industries, Inc.)), a prepreg and a carbon fiber reinforced composite were produced. material with the resin composition shown below. The 0° compressive strength was measured and found to be 1.3 GPa, which is lower than the 0° compressive strength of the composite materials of Examples 1-8. The tensile modulus of the cured resin product with the same resin composition was measured, and the tensile modulus was found to be 3.3 GPa.

[0092]

resin composition

Bisphenol A diglycidyl ether liquid resin ("jER (registered trademark)" 1001, manufactured by Mitsubishi Chemical Corporation), 20 parts by mass, 30 parts by mass;

Bisphenol A liquid epoxy resin ("jER (registered trademark)" 828, manufactured by Mitsubishi Chemical Corporation), 30 parts by mass;

Phenolic novolac based on polyglycidyl ether ("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;

Curing agent:

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

[0093]

Comparative Example 9

Using "TORAYCA (registered trademark)" M40S carbon fiber bundle (filament tensile modulus 380 GPa, single fiber compressive strength 3.0 GPa (manufactured by Toray Industries, Inc.)), prepreg and carbon fiber reinforced composite material with the same resin composition as in Example 1. The 0° compressive strength was measured and found to be 1.3 GPa. 0° The compressive strength of the fiber-reinforced composite material is the same as the compressive strength of Comparative Example 8 despite the high tensile modulus of the resin. As a result, it is found that the 0° compressive strength of the carbon fiber composite does not improve even when only the tensile modulus of the resin increases.

[0094]

Examples 9 and 10, Comparative Examples 10 and 11

The stabilized fiber bundle obtained in Reference Example 5 was twisted to obtain a twist of 50 twists/m, and then subjected to pre-carbonization treatment under a nitrogen atmosphere at a temperature of 300 to 800°C to obtain a pre-carbonized fiber bundle. The pre-carbonized fiber bundle thus obtained is subjected to carbonization treatment under nitrogen atmosphere at the maximum temperature, tension, and residence time shown in Table 2. The physical properties of the resulting carbon fiber bundle and the fiber-reinforced composite material are shown in Table 3. With regard to size crystallite Lc and initial modulus E ₀ of Example 9, the results evaluated from the carbon fiber bundle are as follows: Lc=2.98 nm and E ₀ =331 GPa; and the results evaluated for a single fiber are as follows: Lc=3.00 nm and E ₀ =320 GPa; the difference is 1% and 3%, respectively.

[0095]

Example 11

In the same manner as in Example 10, except that a twist of 20 twists/m was used in the twisting process, a carbon fiber bundle was obtained. The physical properties of the carbon fiber bundle thus obtained and the fiber-reinforced composite material are shown in Table 3.

[0096]

Example 13

In the same manner as in Example 11, except that a twist of 10 twists/m was used in the twisting process, a carbon fiber bundle was obtained. The physical properties of the carbon fiber bundle thus obtained and the fiber-reinforced composite material are shown in Table 3.

[0097]

Example 14

In the same manner as in Example 13, except that the number of single fibers in the polyacrylonitrile precursor fiber bundle subjected to the stabilizing treatment is 24,000, and a twist of 30 twists/m is applied in the twisting process, a carbon fiber bundle is obtained. fibers. The physical properties of the carbon fiber bundle thus obtained and the fiber-reinforced composite material are shown in Table 3.

[0098]

Example 15

In the same manner as in Example 14, except that a twist of 10 twists/m was used in the twisting process, a carbon fiber bundle was obtained. The physical properties of the resulting carbon fiber bundle and the fiber-reinforced composite material are shown in Table 3.

[0099]

Table 1

Ratio of IR peaks 1453 cm ^-1 /1370 cm ^-1 Ratio of IR peaks 1.254 cm ^-1 /1.370 cm ^-1 Tension during stabilization mN/dtex Reference Example 1 0.63 0.60 1.1 Reference Example 2 0.70 0.61 1.3 Reference Example 3 0.64 0.62 1.1 Reference Example 4 0.80 0.64 1.5 Reference Example 5 0.63 0.60 1.5

[0100]

table 2

Maximum carbonization temperature T 2.00×10 ^-3 ×T-0.90 Tension during carbonization Number of twists during carbonization Twisting angle of the surface layer of the fiber bundle during carbonization The residence time in the carbonization process, when the residence time of example 1 is taken as 1 °C - mN/dtex turns/m ° - Example 1 2050 3.20 4.9 0 0.0 1.0 Example 2 2000 3.10 4.8 0 0.0 1.0 Example 3 2100 3.30 5.7 0 0.0 1.0 Example 4 1800 2.70 4.3 0 0.0 1.5 Example 5 1800 2.70 5.5 0 0.0 1.5 Example 6 1900 2.90 4.7 0 0.0 1.1 Example 7 2000 3.10 4.3 0 0.0 1.1 Example 8 2050 3.20 4.0 0 0.0 1.1 Example 9 1900 2.90 6.0 fifty 7.3 1.5 Example 10 1900 2.90 10.0 fifty 7.4 1.5 Example 11 1900 2.90 10.0 twenty 2.8 1.5 Example 12 2050 2.90 4.9 0 0.0 0.9 Example 13 1900 2.90 10.0 ten 1.4 1.5 Example 14 1900 2.90 10.0 thirty 6.0 1.5 Example 15 1900 2.90 10.0 ten 2.0 1.5 Comparative Example 1 1490 2.08 4.8 0 0.0 1.0 Comparative Example 2 2000 3.10 4.3 0 0.0 0.3 Comparative Example 3 1800 2.70 3.5 0 0.0 1.5 Comparative Example 4 1350 1.80 13.0 0 0.0 0.9 Comparative Example 5 1800 2.70 6.5 0 0.0 1.5 Comparative Example 6 1800 2.70 6.0 0 0.0 0.6 Comparative Example 7 2000 3.10 6.0 0 0.0 0.6 Comparative Example 10 1900 2.90 1.0 fifty 5.3 0.7 Comparative Example 11 1900 2.90 1.0 fifty 5.3 1.5

[0101]

Table 3

Stabilization conditions Specific gravity
SG Right side of formula (4)
0.0633×Lc+1.565 Single fiber diameter Single fiber compressive strength
Fc Crystal size
Lc Right side of formula (1)
1.3×10/Lc (nm) - 0.3 Initial modulus in the thread tensile test
_E0 Right side of formula (2)
80*Lc(nm) +155 Number of villi in a carbon fiber bundle Breaking length Tensile strength of thread Tensile modulus of yarn 0° Compressive Strength of Unidirectional Fiber Reinforced Composite - - micron GPa nm - GPa - villi/m mm GPa GPa GPa Example 1 Ref. example 1 1.775 1.774 5.5 4.4 3.30 3.6 338 419 1.0 960 5.7 377 1.6 Example 2 Ref. example 1 1,770 1.768 5.5 4.7 3.20 3.8 341 411 1.0 900 5.8 370 1.7 Example 3 Ref. example 1 1.786 1,780 5.5 4.2 3.39 3.5 350 426 1.0 940 5.7 382 1.6 Example 4 Ref. example 2 1.774 1.743 5.0 4.7 2.81 4.3 345 380 1.0 1000 7.6 380 1.8 Example 5 Ref. example 2 1,770 1.743 5.0 4.8 2.81 4.3 359 380 2.0 1000 7.7 395 1.8 Example 6 Ref. example 3 1.768 1.757 5.4 4.7 3.03 4.0 342 397 1.0 1000 5.5 373 1.7 Example 7 Ref. example 3 1.777 1.769 5.4 4.5 3.23 3.7 356 413 1.0 1000 5.2 389 1.7 Example 8 Ref. example 3 1.788 1.776 5.4 4.3 3.33 3.6 352 421 0.5 1000 5.4 390 1.6 Example 9 Ref. example 5 1.720 1.745 7.4 4.9 2.84 4.3 331 382 1.0 - 4.1 367 1.8 Example 10 Ref. example 5 1.738 1.751 7.5 4.5 2.94 4.1 357 390 2.0 - 4.3 392 1.7 Example 11 Ref. example 5 1,740 1.751 7.2 4.3 2.94 4.1 374 390 2.0 - 4.5 408 1.6 Example 12 Ref. example 1 1,760 1.773 5.5 4.2 3.29 3.7 338 418 1.0 900 5.7 377 1.5 Example 13 Ref. example 5 1,740 1.751 7.2 4.3 2.94 4.1 380 390 5.0 - 4.6 396 1.6 Example 14 Ref. example 5 1.739 1.751 7.2 4.3 2.94 4.1 375 390 2.0 - 4.2 389 1.6 Example 15 Ref. example 5 1.739 1.751 7.2 4.2 2.94 4.1 376 390 5.0 - 4.0 390 1.6 Wed example 1 Ref. example 3 1,800 1.704 5.5 4.8 2.20 5.6 285 331 0.5 1000 7.2 320 1.9 Wed example 2 Ref. example 3 1.690 1.756 5.4 4.4 3.01 4.0 311 396 0.5 1000 5.3 354 1.4 Wed example 3 Ref. example 2 1,770 1.743 5.1 4.6 2.81 4.3 310 380 0.0 1000 7.8 350 1.3 Wed example 4 Ref. example 3 1,800 1.673 5.4 5.2 1.70 7.3 334 291 5.0 600 6.9 365 1.6 Wed example 5 Ref. example 2 1,770 1.743 5.1 4.7 2.81 4.3 390 380 10.0 1000 5.5 420 1.5 Wed example 6 Ref. example 4 1.744 1.723 4.9 4.5 2.50 4.9 325 355 0.5 650 7.1 365 1.7 Wed example 7 Ref. example 4 1,740 1.742 4.9 4.2 2.80 4.3 340 379 0.5 650 6.9 385 1.6 Wed example 8 - 1,800 1.827 5.4 3.0 4.14 2.8 350 486 - - 4.9 380 1.3 Wed example 9 - 1,800 1.827 5.4 3.0 4.14 2.8 350 486 - - 4.9 380 1.3 Wed example 10 Ref. example 5 1.703 1.742 7.5 4.1 2.80 4.3 254 379 0.0 - 4.3 294 1.6 Wed example 11 Ref. example 5 1.720 1.742 7.4 4.1 2.98 4.1 294 393 0.5 - 4.4 330 1.6

Wed example - Comparative example; Ref. Example - Reference Example

Explanation of reference positions

[0102]

1: Fiber bundle

2: Fixed point A

3: Fixed point B

4: Fixed point C

5: Plexus point

6: Breaking length

Claims (21)

1. A carbon fiber bundle in which the ratio between the crystallite size Lc (nm), the compressive strength of a single fiber Fc (GPa) measured by the compressive fragmentation method of composites containing fibers of the same type, and the initial elastic modulus E ₀ (GPa) when tested tensile strength of the resin-impregnated yarn simultaneously satisfies the following formulas (1) to (3), and Lc is 2.60 nm or more and 4.00 nm or less: Fc ≥ 1.3 x 10 / Lc - 0.3 (1) E ₀ ≤ 80 x Lc+155 (2) _E0 ≥ 330 (3). 2. The carbon fiber bundle of claim 1, which is substantially untwisted. 3. The carbon fiber bundle according to claim 1 or 2, wherein the number of lint existing in the carbon fiber bundle is 2/m or less. 4. A bundle of carbon fiber according to any one of paragraphs. 1-3, in which the average breaking length is from 800 to 1100 mm. 5. A bundle of carbon fiber according to any one of paragraphs. 1-4, in which the tensile strength of the yarn is 4.8 GPa or more and 9.0 GPa or less. 6. A bundle of carbon fiber according to any one of paragraphs. 1-5, in which the single fiber diameter is 5.0 µm or more and 15 µm or less, and the ratio between the crystallite size Lc (nm) and the specific gravity (SG) determined by the method of Archimedes satisfies the following formulas (4) and ( 5): SG ≥ 0.0633 x Lc+1.565 (4) 2.85 ≤ Lc ≤ 4.00 (5). 7. A bundle of carbon fiber according to any one of paragraphs. 1-6, wherein the single fiber diameter is 6.0 µm or more and 15 µm or less. 8. Prepreg containing a carbon fiber bundle according to any one of paragraphs. 1-7 impregnated with a thermosetting resin, wherein the cured thermosetting resin product has a tensile modulus of 3.0 GPa or more and 7.0 GPa or less. 9. Reinforced with carbon fiber composite material containing a bundle of carbon fiber according to any one of paragraphs. 1-7 and matrix resin. 10. Method for the production of a carbon fiber bundle according to any one of paragraphs. 1-7, which includes obtaining a bundle of substantially untwisted carbon fiber through a stabilization process in which a bundle of precursor fiber based on polyacrylonitrile is subjected to heat treatment in an atmosphere containing oxygen; a pre-carbonization process in which the fiber bundle obtained in the stabilization process is subjected to heat treatment in an inert atmosphere at a maximum temperature of 500 to 1000°C; a carbonization process in which the fiber bundle obtained in the pre-carbonization process is subjected to heat treatment in an inert atmosphere at a maximum temperature of 1700 to 3000°C; and a process in which the fiber bundle obtained in the carbonization process is subjected to an oxidative treatment; where the stabilization process is carried out until the ratio of the intensity of the peak at 1453 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum of the fiber beam is in the range from 0.60 to 0.70, and the ratio of the intensity of the peak at 1254 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum will not be in the range from 0.50 to 0.65; and the tension of the fiber bundle during the carbonization process is 4.0 to 6.0 mN/dtex, and the carbonization process is carried out until the ratio between the crystallite size Lc (nm) in the fiber bundle and the maximum temperature T satisfies the following formula: Lc ≥ 2.00 x 10 ^-3 x T - 0.90. 11. Method for the production of a carbon fiber bundle according to any one of paragraphs. 1-7, which includes obtaining a carbon fiber bundle through a stabilization process in which a polyacrylonitrile precursor fiber bundle is subjected to heat treatment in an atmosphere containing oxygen; a pre-carbonization process in which the fiber bundle obtained in the stabilization process is subjected to heat treatment in an inert atmosphere at a maximum temperature of 500 to 1000°C; a carbonization process in which the fiber bundle obtained in the pre-carbonization process is subjected to heat treatment in an inert atmosphere at a maximum temperature of 1700 to 3000°C; and a process in which the fiber bundle obtained in the carbonization process is subjected to an oxidative treatment; where the tension of the fiber bundle during the stabilization process is 1.0 mN/dtex or more; the stabilization process is carried out until the ratio of the intensity of the peak at 1453 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum of the fiber beam is in the range from 0.60 to 0.70, and the ratio of the intensity of the peak at 1254 cm ^-1 to the intensity of the peak at 1370 cm ^-1 in the infrared spectrum will not be in the range from 0.50 to 0.65; and the number of twists of the fiber bundle in the carbonization process is 2 turns/m or more, or the twist angle of the surface of the fiber bundle is 0.2 or more, and the tension of the fiber bundle in the carbonization process is 4.0 mN/dtex or more.

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