JP2010047865A - Carbon fiber for composite material and composite material produced by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber having improved surface characteristics, strength and elastic modulus and giving a composite material having high composite characteristics, especially high open hole tensile strength. <P>SOLUTION: The carbon fiber for composite materials has tensile strength of ≥6,000 MPa, elastic modulus of ≥340 GPa and surface oxygen concentration of 7-17%, and gives a composite material having open hole tensile strength of ≥600 MPa using the carbon fiber. More preferably, the carbon fiber has a BET specific surface area of 0.65-2.5 m<SP>2</SP>/g measured by krypton adsorption, and an intensity ratio (D/G) of 1.00-1.25 wherein D is intensity of D band developing near 1,350 cm<SP>-1</SP>and G is intensity of G band developing near 1,580 cm<SP>-1</SP>of a Raman spectrum. The composite material produced using such carbon fiber has excellent open hole tensile strength. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a carbon fiber suitably used for a composite material for aircraft and the like, and a composite material using the carbon fiber.

In recent years, composite materials using carbon fibers as reinforcing fibers are light and have excellent mechanical properties such as high strength, and thus have been widely used as composite materials for aircraft and the like. These composite materials are molded, for example, from a prepreg, which is an intermediate product in which a reinforcing fiber is impregnated with a matrix resin, through molding and processing steps such as heating and pressing. Therefore, in order to obtain a desired composite material, it is necessary to adopt an optimum material or molding / processing means for each, and various properties are also required for carbon fibers which are reinforcing fibers.

For example, in aircraft composite materials, one of the important physical properties is perforated tensile strength (Open Hole
Tensile, OHT), and the higher this value, the better. In general, carbon fibers are more brittle as the elastic modulus increases, so even a slight surface defect becomes a starting point of breakage, which significantly affects the strength. As described above, since the surface defects of the carbon fibers adversely affect the tensile strength, it is very difficult to obtain an excellent composite material having composite properties of high elasticity and high strength. Conventionally, in a medium to high elasticity carbon fiber, surface treatment by electrolytic oxidation or gas phase oxidation is strengthened, and surface defects of the fiber are removed by etching. However, if the surface treatment is strengthened, as the surface oxygen concentration (O / C) of the carbon fiber increases, the adhesion to the matrix resin becomes excessive and the stress dispersibility decreases, resulting in a porous tensile strength. There is a problem that decreases.

In addition, by combining materials with high adhesion between the carbon fiber surface and the matrix resin, and dispersing the matrix resin and the carbon fiber more uniformly, the strength, elasticity, impact resistance, etc. of the composite material are improved. Various attempts have been proposed in the past (see, for example, Patent Documents 1 to 6). However, the performance of conventional carbon fibers has not yet been sufficient to obtain a composite material having high composite properties used for aircraft and the like, in particular, high porous tensile properties.
JP-A-5-214614 Japanese Patent Laid-Open No. 10-25627 JP-A-11-217734 JP2003-73932A JP 2005-133274 A JP 2004-277192 A

An object of the present invention is to provide a carbon fiber with improved surface characteristics, strength, and elastic modulus, which can obtain a composite material having higher composite characteristics than conventional ones, particularly high perforated tensile characteristics. .

In order to obtain a composite material having high composite properties, particularly excellent porous tensile strength (OHT), the present inventor has conducted extensive research focusing on the surface oxygen concentration (O / C) and specific surface area value of carbon fiber. As a result, the inventors have found that by controlling the surface oxygen concentration and the specific surface area to appropriate values, particularly the porous tensile strength of the composite material can be improved, and the present invention has been achieved.

Among the present inventions, the invention described in claim 1 uses a carbon fiber having a tensile strength of 6000 MPa or more, an elastic modulus of 340 GPa or more, and a surface oxygen concentration of 7 to 17%. It is a carbon fiber for composite materials in which the porous tensile strength of the composite material is 600 MPa or more.

In the invention described in claim 2, the specific surface area value according to the BET method by krypton adsorption of carbon fibers is in the range of 0.65 to ^2.5 m ² / g, and in the vicinity of 1350 cm ^{−1 of} the Raman spectrum. The carbon fiber for a composite material according to claim 1, wherein the intensity ratio D / G of the D band that appears and the G band that appears in the vicinity of 1580 cm ^-1 is in the range of 1.00 to 1.25.

In the invention described in claim 3, the tensile strength of the carbon fiber is 6000 MPa or more, the elastic modulus is 340 GPa or more, the surface oxygen concentration is in the range of 7 to 17%, and the composite material using the carbon fiber is It is a composite material comprising a carbon fiber having a porous tensile strength of 600 MPa or more and a matrix resin.

In the invention described in claim 4, the specific surface area value in the BET method by krypton adsorption of carbon fibers is in the range of 0.65 to ^2.5 m ² / g, and 1350 cm ^{−1 of} the Raman spectrum. The composite material according to claim 3, wherein the intensity ratio D / G of the D band appearing in the vicinity and the G band appearing in the vicinity of 1580 cm ^-1 is in the range of 1.00 to 1.25.

Since the carbon fiber of the present invention has high strength and elastic modulus and the surface oxygen concentration is in an appropriate range, the adhesiveness with the matrix resin is moderate. As a result, the composite material using this carbon fiber is Excellent perforated tensile strength. Therefore, the composite material composed of the carbon fiber and the matrix resin of the present invention can be used as a highly safe and lightweight composite material in the aerospace field, the automobile field, and the like.

In the present invention, the tensile strength of the carbon fiber is 6000 MPa, preferably 6100 MPa or more, the elastic modulus is 340 GPa, preferably 343 GPa, and the surface oxygen concentration (O / C) is 7 to 17%, preferably 10 to 17%. In addition, the composite material using the carbon fiber has a porous tensile strength (OHT) of 600 MPa, preferably 700 MPa or more.

In order to obtain a carbon fiber reinforced composite material having a high porous tensile strength, conventionally, a carbon fiber having a medium strength and elastic modulus, for example, a material having a strength of about 5680 MPa and a modulus of elasticity of about 294 GPa is used. Those having a tensile strength of about 600 to 700 MPa were obtained. However, in the field of aircraft, higher performance composite materials have been required mainly for the purpose of reducing the weight of the aircraft. In order to respond to this requirement, development of carbon fiber that achieves both high strength and high elastic modulus has been carried out, but it was obtained because the elongation of carbon fiber decreased as the elastic modulus increased. There was a problem that the porous tensile strength of the composite material was lowered.

In the present invention, the carbon fiber is prevented from becoming brittle by removing the portion that becomes the break start point of the carbon fiber, and the adhesion between the fiber and the matrix resin is controlled within a certain range by controlling the surface state of the carbon fiber. As a result, it is intended to improve particularly the porous tensile strength of the composite material.

In the present invention, the perforated tensile strength is measured by a test method according to EN 6035 using a laminate of carbon fiber composite material. It is an evaluation physical property that is often used in the field of aircraft materials as a basic strength value of a structure including a hole, and is used as a measure of a damage tolerance value of a composite material, similar to a compressive strength after impact (CAI). The measuring method will be described in the section of the examples.

In the present invention, the surface oxygen concentration means an O / C value of carbon fiber measured by an X-ray photoelectron spectrometer, and the O / C value needs to be in a range of 7 to 17%, preferably 10 to 17%. There is. When the O / C value is less than 7%, the adhesion between the carbon fiber and the matrix resin is too low, and the resulting composite material has only a porous tensile strength of less than 600. On the other hand, if the O / C value exceeds 17%, the adhesiveness with the matrix resin is too strong, and when made into a composite, the brittleness of the carbon fiber is strongly influenced, and only those having a porous tensile strength of less than 600 are obtained. It is inappropriate because it is not possible.

As the carbon fiber of the present invention, one having a specific surface area value in the range of 0.65 to ^2.5 m ² / g by BET method by krypton adsorption of the carbon fiber is further preferable. The specific surface area value in the BET method by krypton adsorption is a value indicating the surface state of the carbon fiber, and gas molecules whose adsorption occupation area is known are adsorbed to the sample, and the value of the monomolecular layer adsorption amount at that time Is calculated by the following equation.

S = ([Vm × N × Acs] M) / w
S: Specific surface area Vm: Monolayer adsorption amount N: Avogadro constant Acs: Adsorption cross section M: Molecular weight w: Sample weight

The carbon fiber of the present invention preferably has a specific surface area value of 0.65 to 2.5 m ² / g, and more preferably 1.3 to 2.4 m ² / g. Specifically, this value varies depending on the degree of etching effect by the surface treatment of the carbon fiber surface. That is, the specific surface area value in the BET method by krypton adsorption is caused by the etching action by the surface treatment, and as the index value increases, the surface area of the carbon fiber increases and the unevenness difference increases. Etching by surface treatment also affects the surface oxygen concentration.

The carbon fiber of the present invention preferably has an intensity ratio D / G of a D band appearing near 1350 cm ⁻¹ and a G band appearing near 1580 cm ^{−1 in} the Raman spectrum in the range of 1.00 to 1.25. More preferably, it is in the range of 1.05-1.20. This D / G varies depending on the degree of surface treatment. That is, when the value of D / G is high, it means that the graphite on the surface of the carbon fiber is oxidized by the surface treatment, and the crystallinity is lowered. Therefore, the strength decreases.

Methods and means for carbon fiber surface treatment (etching treatment) include liquid phase oxidation using chemicals, electrolytic oxidation using carbon fiber as an anode in an electrolytic solution, and vapor phase oxidation by plasma treatment in a gas phase. Etc. For example, when the etching process is performed by electrolytic oxidation, the fragile portion generated in the firing step that becomes the surface defect of the carbon fiber is preferentially removed by the etching, and the strength of the carbon fiber itself is improved. Further, with the removal of the fragile portion, fine irregularities are generated on the fiber surface, the surface area of the carbon fiber is increased, and sufficient contact can be obtained between the carbon fiber and the matrix resin. Furthermore, a functional group such as a carboxyl group or a hydroxyl group having an effect of improving the affinity with the matrix resin is introduced. As a result, the adhesion between the carbon fiber and the matrix resin is improved by the anchor effect. On the other hand, if the surface treatment is excessively performed, the excessively scraped portion becomes a physical defect such as a new crack or void, and becomes a starting point for breaking the carbon fiber. Accordingly, in order to form an optimum surface state, appropriate etching is necessary.

The carbon fiber of the present invention can be produced, for example, by the following method.

[Precursor fiber]
In the present invention, as the precursor fiber used in the carbon fiber production method, conventionally known fibers such as pitch fibers and acrylic fibers can be used without any limitation. Among them, acrylic fibers are preferable, and acrylic fibers having an orientation degree by wide-angle X-ray diffraction (diffraction angle 17 °) of 90.5% or less are more preferable. Specifically, a spinning solution obtained by polymerizing a monomer containing 90% by mass or more, preferably 95% by mass or more of acrylonitrile is spun to obtain a carbon fiber raw material. As the spinning method, either a wet or dry wet spinning method can be used, but considering the adhesiveness to the resin, the wet spinning method is more preferable. Moreover, after solidifying, it is preferable to wash with water, dry and stretch to obtain a carbon fiber raw material.

[Flame resistance treatment]
The obtained precursor fiber is subsequently flameproofed in a temperature range of 200 to 280 ° C., preferably 240 to 250 ° C. in heated air. The treatment at this time is generally carried out in the range of a draw ratio of 0.85 to 1.30, but 0.95 or more is more preferable in order to obtain a carbon fiber with high strength and high elastic modulus. This flameproofing treatment is to make a flameproof fiber having a fiber density of 1.3 to 1.5 g / cm ³ , and the tension applied to the yarn at the time of flameproofing is not particularly limited.

[First carbonization treatment]
In the first carbonization step, the flame-resistant fiber is primarily stretched at a stretching ratio of 1.03 to 1.06 within a temperature range of 300 to 900 ° C., preferably 300 to 550 ° C., in the first carbonization step. Next, a secondary stretch treatment is performed at a draw ratio of 0.9 to 1.01 to obtain a first carbonized fiber having a fiber density of 1.40 to 1.70 g / cm ³ . In the first carbonization step, in the primary stretching treatment, the range from the time when the elastic modulus of the flameproof fiber decreases to a minimum value until it increases to 9.8 GPa, until the density of the fiber reaches 1.5 g / cm ^3. In this range, it is preferable to perform the stretching treatment at a stretching ratio of 1.03 to 1.06. In the secondary stretching process, it is preferable to perform the stretching process at a stretching ratio of 0.9 to 1.01 within a range in which the density of the fiber after the primary stretching process continues to rise during the secondary stretching process. When such conditions are employed, the crystals are densified without growing, the formation of voids can be suppressed, and finally high-strength carbon fibers having high density can be obtained. The first carbonization step can be performed continuously or separately in one furnace or two or more furnaces.

[Second carbonization treatment]
The first carbonized fiber is subjected to a primary treatment and a secondary treatment in an inert atmosphere within a temperature range of 800 to 2100 ° C., preferably 1000 to 1450 ° C., in the second carbonization step. Separately, it is stretched to obtain a second carbonized fiber. In the primary treatment, it is preferable to stretch the fiber in a range where the density of the first carbonized fiber continues to increase during the primary treatment, and in a range where the nitrogen content of the fiber is 10% by mass or more. In the secondary treatment, it is preferable to stretch the fiber in a range where the density of the primary treated fiber does not change or decreases. The elongation of the second carbonized fiber is 2.0% or more, more preferably 2.2% or more. Moreover, it is preferable that the diameter of a 2nd carbonization processing fiber is 5-6.5 micrometers. Moreover, these baking processes can be processed continuously with a single facility or with several facilities, and are not particularly limited.

[Third carbonization treatment]
In the third carbonization treatment, the second carbonization-treated fiber is further carbonized or graphitized at 1500 to 2100 ° C, preferably 1650 to 1950 ° C.

[surface treatment]
The third carbonized fiber is subsequently subjected to a surface treatment. For the surface treatment, a gas phase or a liquid phase treatment can be used, but surface treatment by electrolytic treatment is preferable from the viewpoint of easy process control and productivity. As the electrolytic solution used in the surface treatment, an inorganic acid, an inorganic acid salt, or the like can be used, but an inorganic acid such as sulfuric acid, nitric acid, or hydrochloric acid is more preferable. The amount of these electrolytes is 1 to 25% by mass, the temperature is 10 to 80 ° C., more preferably 20 to 50 ° C., and the amount of electricity is 10 to 2000 coulombs per 1 g of fiber, more preferably 10 to 500 coulombs. It is better to carry out chemical and electrical oxidation treatment. By increasing the amount of electricity, the amount of etching increases and the removal of the fragile portion proceeds. However, if the amount of electricity is too large, defects will be created on the surface due to excessive etching, which is not preferable because the fiber strength decreases. On the other hand, if the amount of electricity is too small, the removal of the fragile portion is insufficient and the fiber strength decreases, which is not preferable.

It is preferable to use nitric acid as the electrolytic solution because nitric acid enters and reacts between the layers of the carbon fiber graphite structure, so that etching can be performed more efficiently. In this case, an electrolytic oxidation reaction takes place in the interlayer part of the graphite structure, so that a gap is formed between the layers. This gap is considered to occur along a part having a large crystallite size and a low electrical resistance. Then, along with the electrolytic treatment, the surface layer is covered with the electric double layer, and the electric resistance value of the interface portion becomes high. For this reason, it is considered that the electrolytic treatment is performed only up to the extreme surface layer portion with a low amount of electricity.

[Sizing process]
The surface-treated fiber is subsequently subjected to sizing treatment. The sizing method can be carried out by a conventionally known method, and the sizing agent is preferably used after changing its composition as appropriate according to the application, and after uniformly adhering.

By passing through the above steps, the carbon fiber of the present invention, that is, the tensile strength is 6000 MPa or more, the elastic modulus is 340 GPa or more, the surface oxygen concentration is in the range of 7 to 17%, and the carbon fiber is Carbon fiber for composite material having a porous tensile strength of 600 MPa or more of the composite material used, and the specific surface area value by BET method by krypton adsorption of carbon fiber is in the range of 0.65 to ^2.5 m ² / g. There is obtained a carbon fiber for a composite material having an intensity ratio D / G of D band appearing in the vicinity of 1350 cm ^{−1 of} the Raman spectrum and G band appearing in the vicinity of 1580 cm ⁻¹ of 1.00 to 1.25. It is done. Specific manufacturing conditions will be described in Examples.

Another aspect of the present invention is a composite material obtained by using the carbon fiber of the present invention obtained as described above as a reinforcing fiber and a matrix resin. In the present invention, the composite material means, for example, a prepreg, an intermediate molded product or a molded product produced from carbon fiber and various matrix resins by various known methods such as a hot melt method and a filament winding method.

Carbon fiber is usually used as a sheet-like reinforcing fiber material. The sheet-like material is a material in which fiber materials are arranged in a sheet shape in one direction, these are laminated in an orthogonal manner, a fiber material is formed into a fabric such as a woven or knitted fabric or a non-woven fabric, or a strand-like material. All things, including multi-axis fabrics. As the fiber form, long fiber monofilaments or bundles of these are preferably used.

The matrix resin used in the present invention is not particularly limited. Specific examples of thermosetting matrix resins include epoxy resins, unsaturated polyester resins, phenol resins, vinyl ester resins, cyanate ester resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins and cyanate ester resins. And a prepolymerized resin, bismaleimide resin, polyimide resin and polyisoimide resin having an acetylene terminal, and polyimide resin having a nadic acid terminal. These can also be used as one type or a mixture of two or more types. Of these, epoxy resins and vinyl ester resins excellent in heat resistance, elastic modulus, and chemical resistance are particularly preferable. These thermosetting resins may contain commonly used colorants and various additives in addition to the curing agent and the curing accelerator.

Examples of the thermoplastic resin used as the matrix resin include polypropylene, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, aromatic polyamide, aromatic polyester, aromatic polycarbonate, polyetherimide, and polyarylene. Examples thereof include oxide, thermoplastic polyimide, polyamide, polyamideimide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyacrylonitrile, polyaramid, and polybenzimidazole.

The content of the matrix resin in the composite material is 10 to 90% by weight, preferably 20 to 60% by weight, and more preferably 25 to 45% by weight. As the composite material, those having a perforated tensile strength of 600 MPa or more, more preferably 700 MPa or more, measured by the method described in detail in Examples, are preferable.

Hereinafter, although an example explains the present invention in detail, the present invention is not limited to this. The measuring method of various physical property values in the examples is as follows.

The surface oxygen concentration (O / C) of the carbon fiber can be determined by XPS (ESCA) according to the following procedure. After cutting the carbon fibers and spreading them on a stainless steel sample support table, the photoelectron escape angle was set to 90 degrees, MgKα was used as the X-ray source, and the inside of the sample chamber was vacuumed at 1 × 10 ⁻⁶ Pa. Keep it up. As correction of the peak accompanying charging during measurement, first, the binding energy value B. of the main peak of C1s. E. Is adjusted to 284.6 eV. The O1s peak area is obtained by drawing a straight base line in the range of 528 to 540 eV, and the C1s peak area is obtained by drawing a straight base line in the range of 282 to 292 eV. The surface oxygen concentration O / C on the surface of the carbon fiber is determined by calculating the ratio of the O1s peak area to the C1s peak area.

The BET specific surface area of carbon fiber by krypton gas adsorption is calculated by analyzing the relative pressure range of about 0.1 to 0.25 in the BET plot according to the BET theory using carbon fiber cut to about 1 m in length. did. For gas adsorption, a fully automatic gas adsorption device “AUTOSORB-1” manufactured by Yuasa Ionics Co., Ltd. was used under the following conditions.

Adsorption gas: Kr
Dead volume: He
Adsorption temperature: 77K (liquid nitrogen temperature)
Measuring range: Relative pressure (P / Po) = 0.05-0.3
P: Measurement pressure, Po: Kr saturated vapor pressure

As the Raman spectroscope, a single microscope laser Raman spectroscope T64000 manufactured by Joban Yvon was used. An Ar ⁺ laser (λ = 514.5 nm) was used as an excitation light source, and the output was 20 mW. From the resulting chart, a baseline correction, and peak separation the G band appearing in the vicinity of D band and 1580 cm ^-1 appearing near 1350 cm ^-1, was calculated peak intensity determined intensity ratio D / G of each band. The same measurement was repeated three times, and the average value was obtained.

For the measurement of OHT, carbon fiber after sizing and epoxy resin (No. 133) resin manufactured by Toho Tenax Co., Ltd. are used, and a unidirectional prepreg with a carbon fiber basis weight of 270 g / m ² and a resin content of 33% is used. It was fabricated and laminated in a pseudo isotropic direction of [+ 45 ° / 0 ° / −45 ° / 90 °] _2s . After the laminated specimen (sample) was cured at 180 ° C. for 2 hours, a hole having a diameter of 6.35 mm was formed in the center portion to prepare a specimen (sample) having a size of 30 × 280 × 4.3 mm.

The specimen (sample) was subjected to measurement of the dimensions of each test piece, and the load was applied until the specimen was broken at a crosshead speed of 2.0 mm / min of a tester (Autograph AG-100TB type manufactured by Shimadzu Corporation).

The resin-impregnated strand strength and elastic modulus of carbon fiber were measured by the method defined in JIS R 7608. The carbon fiber sizing agent was removed by Soxhlet treatment with acetone for 3 hours, and then the fiber was air-dried. The density was measured by the Archimedes method, and the sample fiber was measured after degassing in acetone.

[Example 1]
A copolymer spinning stock solution of 95% by mass of acrylonitrile / 4% by mass of methyl acrylate / 1% by mass of itaconic acid is wet-spun by a conventional method so that the total draw ratio becomes 14 times after washing with water, oiling and drying. Steam stretching was performed to obtain a precursor fiber having a filament number of 12,000 having a fineness of 0.65 denier.

While the obtained precursor fiber is stretched in heated air, flameproofing treatment is performed within a temperature range of 240 to 250 ° C, and then in a nitrogen atmosphere, the first, second, and A third carbonization treatment was performed to obtain unelectrolyzed carbon fibers.

The non-electrolytically treated carbon fiber was subjected to electrolytic treatment using a 6.3 mass% nitric acid aqueous solution as an electrolyte solution, using three tanks under conditions of an electrolytic solution temperature of 35 ° C. and an electric quantity of 250 coulomb / g. The carbon fiber subjected to electrolytic treatment was subjected to sizing treatment by a conventional method and dried to obtain carbon fiber having a density of 1.77 g / cm ³ and 0.31 denier. Table 1 shows the measured carbon fiber strength (resin impregnated strand strength), elastic modulus, surface oxygen concentration, specific surface area value, D / G and perforated tensile strength.

[Example 2]
The unelectrolyzed carbon fiber obtained in Example 1 was subjected to electrolytic treatment using 7.0 mass% nitric acid aqueous solution, using an electrolytic solution temperature of 40 ° C. and an electric quantity of 250 coulomb / g in three tanks. The carbon fiber subjected to electrolytic treatment was subjected to sizing treatment by a conventional method and dried to obtain carbon fiber having a density of 1.77 g / cm ³ and 0.31 denier. Table 1 shows measured values of the strength and elastic modulus, surface oxygen concentration, specific surface area value, D / G and perforated tensile strength of the obtained carbon fiber.

[Comparative Example 1]
The electrolessly treated carbon fiber obtained in Example 1 was subjected to electrolytic treatment using a 6.3 mass% nitric acid aqueous solution in four tanks under the condition of an electric quantity of 110 coulomb / g, and then the polarity was changed to 10 coulomb. The electrolytic treatment was performed using 2 tanks under the conditions of / g. Thereafter, sizing treatment was performed by a conventional method, followed by drying to obtain carbon fibers having a density of 1.77 g / cm ³ and 0.31 denier. Table 1 shows measured values of the strength and elastic modulus, surface oxygen concentration, specific surface area value, D / G and perforated tensile strength of the obtained carbon fiber.

[Comparative Example 2]
The unelectrolyzed carbon fiber obtained in Example 1 was electrolytically treated using a 6.3 mass% nitric acid aqueous solution in 12 tanks under the condition of a total electricity of 100 coulomb / g, and sizing treatment by a conventional method. It was carried out and dried to a density 1.77 g ^/ cm 3, to obtain a 0.31 denier carbon fibers. Table 1 shows measured values of the strength and elastic modulus, surface oxygen concentration, specific surface area value, D / G and perforated tensile strength of the obtained carbon fiber.

[Comparative Example 3]
The unelectrolyzed carbon fiber obtained in Example 1 was subjected to electrolytic treatment using a 6.3% by mass nitric acid aqueous solution under the condition that the total electricity was 50 coulomb / g, and sizing treatment by a conventional method. And dried to obtain a carbon fiber having a density of 1.77 g / cm ³ and a denier of 0.31. Table 1 shows measured values of the strength and elastic modulus, surface oxygen concentration, specific surface area value, D / G and perforated tensile strength of the obtained carbon fiber.

[Comparative Example 4]
The electrolessly treated carbon fiber obtained in Example 1 was subjected to electrolytic treatment using a 6.3 mass% nitric acid aqueous solution in four tanks under a total electric charge of 5 coulomb / g, and sizing treatment by a conventional method. And dried to obtain a carbon fiber having a density of 1.77 g / cm ³ and a denier of 0.31. Table 1 shows measured values of the strength and elastic modulus, surface oxygen concentration, specific surface area value, D / G and perforated tensile strength of the obtained carbon fiber.

Claims (4)

For composite materials in which the tensile strength of the carbon fiber is 6000 MPa or more, the elastic modulus is 340 GPa or more, the surface oxygen concentration is in the range of 7 to 17%, and the porous tensile strength of the composite material using the carbon fiber is 600 MPa or more Carbon fiber. Specific surface area in BET method by krypton adsorption of the carbon fibers is in the range of 0.65~2.5m ² / g, and, appearing in the vicinity of D band and 1580 cm ^-1 appearing near 1350 cm ^-1 in the Raman spectrum The carbon fiber for composite materials according to claim 1, wherein the G band intensity ratio D / G is in the range of 1.00 to 1.25. A carbon fiber having a tensile strength of 6000 MPa or more, an elastic modulus of 340 GPa or more, a surface oxygen concentration of 7 to 17%, and a porous material having a porous tensile strength of 600 MPa or more using the carbon fiber; A composite material consisting of a matrix resin. Specific surface area in BET method by krypton adsorption of the carbon fibers is in the range of 0.65~2.5m ² / g, and, appearing in the vicinity of D band and 1580 cm ^-1 appearing near 1350 cm ^-1 in the Raman spectrum The composite material according to claim 3, wherein the G band intensity ratio D / G is in the range of 1.00 to 1.25.