JPS6236427A - Unidirectionally carbon fiber-reinforced high-strength composite material - Google Patents

Abstract

PURPOSE:The titled lightweight composite material of excellent strength, comprising a specified carbon fiber and a matrix resin. CONSTITUTION:A prepreg is obtained by impregnation a carbon fiber having a 1.5mu-thick surface layer whose perfectness of crystal is on level with that of the fiber core, said surface layer having a 0.2mu-thick or below super-thin outer layer whose perfectness of crystal is low as compared with that of the fiber core,a tensile strength at a fiber volume rate of 70%>=370kg/mm<2>, a tensile strength of a resin-impregnated strand >=600kg/mm<2>, a content of heat- decomposable organic matter of 0.05-0.5wt%, and a ratio of functional group content (OIs/CIs) detected by X-ray photo-electron spectroscopy of 0.1-0.4 with a matrix resin (e.g.., epoxy resin) or a tensile elongation at break (JIS-K-7113)>=3.0 (e.g., epoxy resin). Several to several tens of such prepregs are laminated and heated to cure the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a carbon fiber-reinforced composite material that is lighter in weight and has superior strength compared to conventionally known composite materials using carbon fibers as reinforcing fibers.

[Conventional technology] Conventionally, composite materials using carbon fiber have been widely used for premium sports applications such as corfushafts and fishing rods, as well as for structural materials such as aircraft, due to their excellent specific strength and specific modulus. has been done. However, in recent years, composite materials have been used for primary building materials for aircraft, space structures, and various industrial applications, and from the perspective of further reducing the weight, they are much lighter and much lighter than conventional composite materials. The appearance of the composite material A'Mi1, which has excellent strength, is strongly observed.

Several proposals have been made to date to improve the strength of composite +41'3+. One of these concerns the improvement of the strength and elongation of carbon fiber itself.For example, in order to improve the strength of carbon fiber itself, carbon fiber with a high
The surface of the fiber is etched by immersing it in an inorganic acid such as sulfuric acid, nitric acid, or phosphoric acid at a temperature of 400°C for a long time, and then heat-treated in a high-temperature inert atmosphere to remove the functionality of the fiber surface generated by the inorganic acid treatment. Methods for removing groups have been proposed (for example, JP-A-54-59497, JP-A-52-3).
According to Japanese Unexamined Patent Publication No. 5796) and Japanese Patent Application Laid-Open No. 54-59497, this etching treatment removes scratches on the fiber surface formed during the carbon fiber manufacturing process, thereby improving the mechanical strength of the carbon fiber. is said to improve.

However, according to the inventors' investigation,
It was found that even if the mechanical strength of carbon fibers is improved, it does not necessarily contribute to the improvement of the tensile strength of composite materials.

As another method for improving the strength of composite materials, a method has been proposed in which a 6-elongation resin is used as a matrix resin (for example, Japanese Patent Application Laid-Open No. 59-217721@).

However, although these techniques certainly improve the strength of composite materials, there are limits to the strength improvement.

As a method for reducing the weight of a composite material, there is a method of reducing the resin content in the composite material, that is, increasing the VF of the composite material. However, according to the studies conducted by the present inventors, in conventionally commonly used carbon fibers with non-circular cross sections, when vF is set to a level of 70%, vF is 6.
Compared to the case of 0%, the strength utilization rate of the carbon fiber itself decreases.

[Problems to be Solved by the Invention] The inventors of the present invention have conducted extensive studies on carbon fiber reinforced composite materials that are lightweight and have excellent strength, and as a result, have arrived at the following invention. .

In particular, it is an object of the present invention to provide a carbon fiber-reinforced composite material in which the carbon fibers themselves have excellent strength, and the strength utilization rate does not decrease even at high vF.

Means for Solving the L Problem] The present invention has the configuration as described in the claims section.

The lightweight and high-strength composite material of the present invention can be manufactured by increasing the vF of the composite material using high-strength carbon fibers with a circular cross section and a matrix resin with high elongation.

The carbon fiber used in the present invention has a resin-impregnated strand having a tensile strength of 600 kCJ/mm2 or more.

The carbon fibers used in the present invention have a surface layer having substantially the same level of crystalline perfection as the center of the fiber, and the surface layer has crystallization compared to the center of the fiber. The carbon fiber has an ultra-thin outermost layer with low integrity, and further has a pyrolyzable organic content ω in the range of 0.05-0.5% by weight and detected by X-ray electron spectroscopy (ESCA). The amount of functional groups on the surface' (01s/C15) ratio is 0.1 to 0.4
carbon fiber within the range of

Here, crystal perfection is a property determined by the crystal dimensions and the orderliness of the carbon network arrangement that make up the carbon fiber. It is said that the greater the orderliness of the crystal, the greater the perfection of the crystal.

Here, the crystal integrity of the core, surface layer, and ultra-thin outermost layer of the fiber can be determined by transmission electron diffraction (T
EM>, specifically as described below,
When comparing the degree of crystal perfection of the surface layer of the fiber and the ultra-thin outermost layer of the surface layer with reference to the perfection of the crystals in the center of the fiber, the surface layer is substantially lower than the center of the fiber. The fibers exhibit the same level of crystalline perfection, and the ultra-thin outermost layer at the surface layer exhibits less crystalline integrity than the fiber core. According to the measurement method described below, the surface layer is a layer with an average thickness of 1.5 microns from the surface of the carbon fiber, and the ultra-thin outermost layer has an average thickness of 0.2 microns from the surface of the fiber, and more preferably 0.1 microns from the surface of the fiber. A layer in the micron or smaller region.

In addition, the term "substantially the same level of crystal perfection as in the center of the fiber" means that the ratio of the crystal perfection in the surface layer to that in the center of the fiber is approximately the same or greater. When expressed numerically, it means about 0.98 or more, preferably 1°0 or more.

In general, the pyrolyzable organic substance content of the carbon fiber used in the present invention is determined by the amount of chemical functional groups present on the surface and inside of the carbon fiber, especially the amount of chemical functional groups mainly in the ultra-thin outermost layer. It is a scale that indicates the amount, and this is 0.05 to
It is necessary that the amount is within the range of 0.5% by weight, preferably 0.1-0.4%, more preferably 0.15-0.30%, and this amount is less than 0.05%. This is not preferable because the adhesion between the carbon fiber and the resin decreases too much. On the other hand, when it exceeds 0.5%, the inactivation becomes insufficient and the tensile strength of the composite material decreases, which is not preferable.

Carbon fiber with such an ultra-thin outermost layer is
Amount of functional groups detected by line electron spectroscopy (01s/C
1s> ratio of 0.1 to 0.4, preferably 0.20 to 0.
It is preferably within the range of 25. That is, if the amount of functional groups in the surface layer of the deactivated carbon fiber is outside the above range, a composite material with high tensile strength cannot be obtained.

The carbon fibers used in the present invention have such structural characteristics, and only by doing so can their mechanical strength be significantly expressed as the strength of the composite material. Such a fiber structure indicates that the physical strain formed in the carbon fiber during the manufacturing process of the carbon fiber structure has been alleviated, and the structural defects on the carbon fiber surface have been repaired. It is thought that this plays an advantageous role in reflecting the mechanical strength of the fibers in the mechanical strength of the composite material.

Carbon fibers having such structural characteristics and having a tensile strength of resin-impregnated strands of 600 ki/mm2 or more are difficult to obtain by conventionally known electrolytic treatment or etching treatment with concentrated inorganic acid-deactivation treatment. It is preferable to obtain it by the method described below. That is, first, carbon fibers are electrolytically treated in a high-temperature electrolytic aqueous solution containing nitrate ions as an essential component.
By chemically oxidizing, only the very limited outermost surface of the fiber, i.e., the ultra-thin outermost layer, is selectively amorphized, i.e., the center of the carbon fiber, without compromising the crystalline integrity of the carbon fiber as much as possible. The integrity of the crystal is small compared to the
Formation of a layer that is easy to defunctionalize, followed by heat treatment in an inert atmosphere to substantially inactivate, i.e., defunctionalize, the functional groups formed in the ultra-thin outermost layer region by the oxidation. More specifically, the amount of the thermally decomposable organic matter is 0.05 to 0.5 weight percent, and the (01 s/C1s) ratio detected by X-ray electron spectroscopy is about 0.1 to 0.0. 4
The carbon fibers used in the present invention are easily deactivated by a method of substantially removing functional groups formed in the ultra-thin outermost layer of the fibers by inactivating the fibers so that the carbon fibers are within the range of 1q.

The carbon fiber used in the present invention has a circular cross-sectional shape. In order to reduce the weight of a composite material, there is a method of reducing the resin content in the composite material, that is, increasing the resin content. Conventionally, composite materials are often used in the region where vF is 60% or less, and in order to roughly reduce the weight, it is necessary to increase V to 65% or more, but with carbon fiber, it is possible to increase V The present inventors have found that there are cases where the strength utilization rate decreases and there are cases where the strength utilization rate remains the same. The carbon fibers used in the present invention have a circular cross-sectional shape,
■The strength utilization rate of carbon fiber grains does not decrease even if V becomes 70%, but the strength utilization rate decreases when V increases to 65% or more in the case of conventionally commonly used carbon fibers whose cross section is not circular. However, it does not improve the strength of the composite material, so it cannot be used for weight reduction. .

Specifically, the ratio of the major axis to the minor axis (degree of cross-sectional deformation) of the cross section is 1.
It needs to be 4 or less, preferably 1.2 or less. 1.1 or less is particularly preferable.

If the shape is close to a perfect circle, the decrease in strength utilization at high V4 will be smaller, making it possible to manufacture high-strength composite materials that were previously unimaginable.

The resin used in the present invention has a tensile elongation at break of 3.0% when measured according to the test method specified in JIS-7113.
These are the above resins. When using a brittle resin with a tensile elongation at break of 3.0% or less, it is not possible to obtain the high-strength composite material aimed at by the present invention. As the matrix resin, epoxy resins, bismaleimide resins, unsaturated polyester resins, vinyl ester resins, etc. can be used, and among them, epoxy resins are most preferred.

The epoxy resin used in the present invention is prepared by combining the polyepoxide described below with a curing agent and/or a curing catalyst.

Polyepoxides are compounds having on average more than one epoxy group in the molecule, which epoxy groups may be present as terminal groups or internal to the molecule. The polyepoxide may be a saturated or unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic compound, and may also be a compound containing a halogen atom, a hydroxyl group, an ether group, etc., such as bisphenol △ , glycidyl compounds of F and S, glycidyl compounds of talezol novolak or phenol novolak,
Examples include glycidyl compounds of aromatic amines and cycloaliphatic epoxy resins.

Specific examples of such polyepoxides include 1,4-bis(2,3-epoxypropoxy)benzene, 4,4'-
Bis(2,3-epoxypropoxy)diphenyl ether.

Another example of a polyepoxide is a glycidyl compound of polyhydric phenol. Polyhydric phenols that can be used for this purpose include, for example, resorcinol, catechol, hydroquinone, 2,2-bis(4-hydroxyphenyl)propane (to bisphenol), 2,2-bis(4-hydroxyphenyl)butane, bis( 4-hydroxyphenyl)
Sulfone (bisphenol S), bis(4-hydroxyphenyl)methane, tris(4-hydroxyphenyl)
Methane, 3,9-bis(3-me1-xy,4-hydroxyphenyl)-2,4,8,10-te1-laoki1naspiro[5,5]undecane, and further 2.2 as halogen-containing phenol. -bis(4-hydroxyte1-labromphenyl)propane, and the like.

Another example of a polyepoxide is a glycidyl compound of a polyhydric alcohol. Alcohols that can be used for this purpose include, for example, glycerol, ethylene glycol,
Examples include pentaerythritol and 2°2-bis(4-hydroxycyclohexyl)propane.

Examples of polyepoxides with internal epoxy groups include 4
-(1,2-epoxyethyl) -1,2-epoxycyclohexane, bis(2,3-epoxycyclopentyl) ether, 3,4-epoxycyclohexylmethyl-(3,4-epoxy)cyclohexanecarboxylate, etc. It will be done.

Another example of a polyepoxide is a glycidyl compound of an aromatic amine. Aromatic amines used for this purpose include diaminodiphenylmethane, metaxylylene diamine, m-aminophenol, and p-aminophenol.

Among these polyepoxides, diglycidyl ether of bisphenol A, glycidyl compounds of talesol novolak or phenol novolak, glycidyl compounds of diaminodiphenylmethane, and glycidyl compounds of aminophenol are preferably used.

Curing agents used in the present invention include aromatic amine based curing agents such as metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, diglycol esters of meta- or para-aminobenzoic acid, dicyandiamide and bis(parahydroxyphenyl)sulfone. Typical examples include phenolic curing agents.

Furthermore, curing catalysts such as boron trifluoride/amine complexes, imidazole compounds, and urea compounds obtained by the addition reaction of 1- to luene diisocyanate and dimethylamine can be used alone or in combination with the above-mentioned curing agents.

The epoxy resin having a tensile elongation at break of 3% or more used in the present invention can be prepared by combining one or more of the polyepoxides mentioned above with one or more of the curing agents or curing catalysts mentioned above. Using these combinations U, an epoxy resin having desired physical properties can be prepared by a method well known in the industry. Typical examples of such epoxy resins are clarified in the Examples.

The epoxy resin used in the present invention is often preferably one containing a thermoplastic resin or an elastomer for the purpose of appropriately increasing the viscosity of the matrix resin to improve moldability or increasing the toughness of the composite material. Examples of the resins contained include polyvinyl acetal, polyamide, polyester, polysulfone, polyethersulfone, polyetherimide, polyarylate, polyamideimide, polyetheramide, polyetherester, and nitrile rubber.

There are no particular limitations on the method for producing the composite material of the present invention, and various methods known in the art may be used. Typical examples include impregnating carbon fiber yarn with an uncured matrix resin to create an intermediate prepreg (prepreg), which is then laminated with several to dozens of sheets (prepreg), and curing in an autoclave or heat press. There is a way to manufacture it.

The properties of the carbon fiber used in the present invention are measured by the following method.

Transmission electron diffraction method (TEM) Carbon fibers are aligned in the fiber axis direction, embedded in room temperature curing epoxy resin, and cured. Using a microtome equipped with a diamond knife, trimmed so that 2 to 3 fibers are exposed, an ultrathin section with a thickness of 150 to 200 angstroms (A>) is prepared. The carbon fiber is placed on top of the carbon fiber and subjected to electron beam diffraction using a high-resolution electron microscope.In this case, in order to detect the structural differences between the inside and outside of the carbon fiber, selected area electron diffraction is used to detect the difference in the structure from a specific part. Examine the electron diffraction image.

The measurement conditions were an electron microscope H-80 manufactured by Hitachi, Ltd.
0 type (transmission type), acceleration voltage 200KV, diameter 0.
With a 2 micron selected field aperture, the edge of the ultrathin section (ed
qe) to the core.

The ultra-thin outermost layer is approximately 0.1 micron deep from the fiber surface, more precisely, half of the selected area aperture with a diameter of 0.2 microns is on the outermost fiber layer, and the other half is outside the fiber. Becomes an enemy in certain situations. In addition, the surface layer is about 1 inch from the fiber surface.
．． Using an electron diffraction photograph of a portion within 5 microns, and using an electron diffraction photograph near the center of the fiber for the center of the fiber, the diffraction intensity in the equatorial direction for (002>) of these electron diffraction images is determined. Create scanning profiles, and then calculate the half width using these scanning profiles.

Since the reciprocal of the half-width is a measure of crystal integrity, the ratio of the reciprocal of the half-width of the ultra-thin outermost layer and the surface layer to the center of the fiber was determined.

A carbon fiber (sample) containing approximately 20 mg of pyrolyzable organic matter was washed with a solvent to remove sizing etc. adhering to the fiber surface, and was washed using a CI-I N coder model MT-3 bag neck manufactured by Yanagimoto Seisakusho.
Measurements were made under the following conditions.

CHN coder sample combustion furnace at 950'C, oxidation furnace at 8
The temperature was raised to 50'C and the reduction furnace to 550C, helium was flowed at a rate of 180ml/min, and the washed carbon fibers were accurately weighed and placed in the sample combustion furnace.

After sucking a part of the cracked gas in the sample combustion furnace for about 5 minutes using a water suction pump via the oxidation furnace and reduction furnace,
It is quantified as 002m by the heat transfer type 1 detector of the CHN coder, and the amount of thermally decomposable organic matter is determined as C (wt%) with respect to the sample by calibration. The feature of this measurement method is that by heating the carbon fiber in an atmosphere of helium gas only without flowing oxygen gas, Go, CO2 in the carbon fiber, and CH4
It is possible to quantify the amount of pyrolyzable organic substances such as

X-ray photoelectron spectroscopy (FSC△) A specific device is model ES- manufactured by Kokusai Denki Co., Ltd.
200 was used.

After cleaning the carbon fibers (sample) with a solvent and removing surface deposits such as sizing, the carbon fibers were cut and spread out on a copper sample support stand.
1:10E in the sample chamber using IKα1,2
Maintain at (-8) Torr.

And 015 peak surface with kinetic energy of 9556V!
? The ratio of surface oxygen atoms/surface carbon atoms (015/C1s>) is determined from the ratio of the C1S peak areas of 1 and 1202 eV.

Resin Impregnated Strand 1 - Land Strength Measurement Method Measured according to the resin impregnated strand test method specified in Jl5-R-7601. In this case, the following resin formulation and curing conditions were used for testing.

Resin formulation: 100 parts of Pa'Tissonox" 221, 3 parts of 3-fluoroboronoethylamine (BF3MEA), acetone
4-part curing conditions = 130° C., 30 minutes Each strand was tested 10 times, and the results were averaged.

[Function] In the present invention, by combining a specific carbon fiber and a specific resin, a lightweight and strong composite material can be obtained.

The reason is not clear, but only when carbon fibers have a circular cross section can they take advantage of the characteristics of high strength and high shape.

[Example] The present invention will be explained in further detail by the following example. In the examples below, ♀ for each component represents parts by weight.

Example 1 AN having an intrinsic viscosity [η] of 1.80, consisting of acrylonitrile (ΔN>99.5 mol%, itaconic acid 0.5 mol%)
Ammonia is blown into the dimethyl sulfoxide (DMSO) solution of the copolymer, and the carboxyl end of the copolymer is OHM.
The polymer was modified by replacing hydrogen with ammonium groups, and a DMSO solution containing the modified polymer at a concentration of 20% by weight was prepared.

After visually filtering this solution using a 5μ sintered metal filter as a door material, it was discharged into the air through a spinneret with a pore diameter of 0.15 mm and a number of holes of 1500.
After traveling through the space, the discharged fiber yarn was introduced into a 30% DMSO aqueous solution at about 30° C. to coagulate it. The obtained coagulated fiber thread was washed with water and stretched 4 times in hot water to obtain a water-swollen fiber thread. This water-swollen fiber yarn is made of polyethylene glycol (PEG) modified polydimethylsiloxane (P
EG modified modified ff1 car 0 modified polydimethylsiloxane (amino modified amount 1% by weight)
0.8% consisting of 85 parts and 15 parts of nonionic surfactant
After being immersed in a water dispersion mixed oil bath, the surface temperature was 130°C.
Dry and densify on heated rolls at ℃. The dried and densified fiber yarn is stretched three times in heated steam, and the single yarn fineness is 0.8 denier (d) and the total denier is 1200.
(The acrylic fiber thread of D> is 19.

Three of these acrylic fiber yarns with a total denier of 1200D were combined, and a ring-shaped nozzle was used to combine them under a pressure of 0.
7 was subjected to +1/- air opening treatment, 240 to 260
An oxidized fiber yarn having a moisture content of 4.5% was produced by heating in air at a temperature of 'C' at a draw ratio of 1.05.

Next, this oxidized fiber yarn was heated in a nitrogen atmosphere with a maximum temperature of 140°C at a heating rate of about 250°C/min in a temperature range of 1000 to 1200°C. The temperature rate was set at about 400'C/min to carbonize the carbon fiber yarn.

The resin-impregnated strand strength of the obtained carbon fiber yarn was 56
It was 0ki/mm2. In addition, an ultra-thin section of the longitudinal cross-section of this carbon fiber single fiber was prepared, and selected area electron diffraction was performed on the fiber center and a region approximately 0.1μ deep from the fiber surface (ultra-thin outermost layer region). The completeness of the crystals was measured in a region of approximately 0.4 microns from the fiber surface (surface layer region), and the depth of 0.1 micron and 0.4 micron from the fiber surface was measured relative to the crystal perfection in the center of the fiber. The ratio of crystal perfection in the region of 1°05 and 1.03, respectively, is 1°05 and 1.03.
The crystal integrity of the ultra-thin outermost layer (ultra-thin outermost layer) exhibits greater crystallinity than that of the fiber core, and the crystal integrity of the approximately 0.4 micron deep region (surface layer) is similar to that of the fiber core. They exhibited virtually the same crystallinity.

The raw carbon fiber yarn thus obtained was heated to a temperature of 806C,
The yarn was introduced into a processing bath filled with a nitric acid aqueous solution with a concentration of 5N through a ceramic guide, and the yarn was run continuously at a speed of 0.3 m/min, and by a metal guide roller installed just before the processing bath. A positive voltage was applied to the carbon fiber yarn, and a current of 0.12 was passed between it and an electrode plate installed in the treatment bath.

Here, the immersion length of the carbon fiber yarn in the treatment bath is approximately 0.
．． 2 m, the processing time was about 40 seconds, and the amount of electricity per gram of carbon fiber was 150 coulombs.

After washing the electrochemically oxidized carbon fiber yarn with water and drying it in heated air at about 200°C,
Heat for about 1 minute in a nitrogen atmosphere at 0'C.

Heating was applied to defunctionalize the functional groups in the fibers formed by the treatment. The resin-impregnated strand strength of the obtained carbon fiber yarn was measured and found to be 6701/mm 2 .

An ultra-thin section of the carbon fiber yarn thus obtained was prepared, and cut into sections at depths of about 0.1 micron and about 0.4 micron from the fiber center and fiber surface, respectively, in the same manner as described above. The crystalline perfection in the region was determined, and the ratio of the crystalline perfection in the region of about (L) 1 micron and about 0.4 micron from the surface to the crystalline perfection in the center of the fiber was determined to be 0.92, respectively. and 1.03, the region approximately 0.1 microns deep from the surface (ultra-thin outermost layer) exhibits low crystal integrity, and the region approximately 0.4 microns deep from the surface (surface layer) It showed substantially the same crystallinity as the fiber center.

In addition, the cross-sectional shape of this carbon fiber has an average cross-sectional deformation of 1.0
It was less than 5 and was a perfect circle.

Next, regarding the matrix resin, 35 parts of bisphenol A diglycidyl ether (Epicote 828 manufactured by Yuka Shell Epoxy Co., Ltd.) and a tetraglycidyl compound of diaminodiphenylmethane (ELM434 manufactured by Sumitomo Chemical Co., Ltd.)
35 parts and tetrabromobisphenol△diglycidyl ether (Epiclon 152, manufactured by Dainippon Ink Co., Ltd.)
A prepreg resin was prepared by adding and mixing 32 parts of diaminodiphenylsulfone to a 30 part epoxy compound mixture. This epoxy resin was heated to 180'C1 in an oven.
The resin was cured for 2 hours to obtain a transparent cured resin plate having a thickness of 2ITII11. The tensile elongation at break measured according to the JIS-7113 test method was 4.4%.

The carbon fibers were aligned in one direction and impregnated with the prepreg resin to obtain a prepreg with a carbon 11i fiber density of 145 q/m2 and a resin content of 34%. Eight sheets of this prepreg were laminated and molded using an autoclave at 180°C for 2 hours at a pressure of 6kCJ/- to a thickness of 0.91mm, v
, 70.3% composite material is 19.

This composite material has a length of 230 mm and a width of 12°7 in the fiber direction.
A 2 mm tensile test piece was cut out. Glass cloth/epoxy resin tabs with a length of 5 Q mm and a width of 12.72 mm and a taper section of 1 Q mm at one end were adhered to both upper and lower surfaces of both ends of this test piece. This test piece was pulled at a tensile rate of 1 mm/min. As a result of the tensile test, the tensile strength was 386 kg/m
m 2 Tea Tsuta.

At this time, the strength utilization rate of the composite material with respect to the strand strength was 82.0%. Similarly, VF5.8.2%
As a result of making a composite material of
%Met.

Comparative Example 1 Using carbon fiber with a cocoon-shaped cross section having a strand strength of 5301 q/mm2 and an average cross-sectional deformation of 1.60, V was 69. 9% and 59.3% composites were made. The tensile strength was measured using the same test method as in Example 1, and the results were 283) cq/mm2, ct, j, and 282 k, respectively.
i/mm2. At this time, the high and low utilization rates were 76.1% and 89.7%, respectively. The strength utilization rate is clearly lowered, and the lightweight effect due to high VE cannot be expected.

Example 2 Bisphenol A diglycidyl ether (Epicote 8
28) 40 parts, 30 parts of 3,9-bis(3-methoxy,4-hydroxyphenyl)-2,4,8,10-tetraoxaspiro[5,5]underichon and tetrabromobisphenol A diglycidyl ether (Epicron 1
52) A prepreg resin was prepared by adding and mixing 24 parts of diaminodiphenylsulfone to 30 parts of an epoxy compound mixture. When this epoxy resin was cured in the same manner as in Example 1, the tensile elongation at break was 6.1%.

Using the above resin and the same carbon fiber as in Example 1, Example 1
Composite materials of two types of V were prepared in the same manner. The VF at this time was 70.1% and 57.3%.

A tensile test was conducted in the same manner as in Example 1, and the tensile strength was 413 ki/mm 2 and 338 kq/m
It was m2. The strength utilization rate at this time was 87.9.
%, and 88.1%.

Comparative Example 2 The same test as in Example 1 was conducted using the same prepreg resin as in Example 2 and the same carbon fiber as in Comparative Example 1. The V' of the prepared composite material was 69.6%, and 56.
It was 9%. The tensile strength is 293kq/
mm 2 and 281 kq/mm 2 , and the strength utilization rates were 79.4% and 93.2%.

[Effects of the invention] ■ Composite materials with extremely high strength and light weight can be obtained.

■ Composite materials with stable quality can be obtained.

Claims (8)

[Claims] (1) A unidirectional carbon fiber-reinforced high-strength composite material made of carbon fibers and a matrix resin and having a tensile strength of 370 kg/mm^2 or more when the fiber volume fraction (V_F) in the composite material is 70%. (2) A unidirectional carbon fiber-reinforced high-strength composite material according to claim (1), characterized in that the resin-impregnated strands are made of carbon fibers having a tensile strength of 600 kg/mm^2 or more. (3) A unidirectional carbon fiber-reinforced high-strength composite material according to claims (1) and (2), characterized in that carbon fibers having a circular cross-sectional shape are used. (4) A unidirectional carbon fiber-reinforced high-strength composite material according to claims (1) to (3), characterized in that the fiber volume fraction is 65% or more. (5) A unidirectional carbon fiber-reinforced high-strength composite material according to claims (1) to (4), characterized in that a matrix resin having a tensile elongation at break of 3% or more is used. (6) In claims (1) to (5), the fiber has a surface layer portion having substantially the same level of crystal integrity as the center portion of the fiber; A unidirectional carbon fiber reinforced high strength composite material characterized by the use of carbon fibers having an ultra-thin outermost layer with less crystalline integrity compared to the central part. (7) In claims (1) to (6), the unidirectional carbon fiber reinforcement is characterized in that the ultra-thin outermost layer uses carbon fiber having an average thickness of 0.2 microns or less. High strength composite material. (8) In claims (1) to (7), the amount of thermally decomposable organic matter is within the range of about 0.05 to 0.5% by weight and detected by X-ray electron spectroscopy (ESCA). A unidirectional carbon fiber-reinforced high-strength composite material characterized by using carbon fibers having a surface functional group content (O1s/C1s) ratio within the range of 0.1 to 0.4.