JP2001310957A - Intermediate material for composite and fiber reinforced composite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intermediate material for a fiber reinforced composite having high mechanical strength and excellent weatherability owing to a strong adhesion between the carbon fiber and the resin maintained even under a wet and hot environment, and to provide such a fiber reinforced composite. SOLUTION: This intermediate material comprises carbon fibers and a resin composition comprising a benzoxazine compound containing within the molecule a structural unit I expressed by the following structural formula (I) in which cross section of the single fiber of the carbon fibers is substantially circular (I) wherein R1 represents an aliphatic alkyl group having 1-12 carbons, a cycloalkyl group having 3-8 carbons, a phenyl group or a substituted phenyl group; and to the aromatic ring, a hydrogen atom is bound to at least one carbon at ortho- or para-position to the carbon bound with oxygen atom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to molding a composite material for obtaining a fiber reinforced composite material which can be suitably applied to sports applications such as golf shafts, fishing rods, etc., as well as aircraft structural materials. The present invention relates to an intermediate and a fiber-reinforced composite obtained therefrom.

[0002]

2. Description of the Related Art Carbon fiber reinforced composite materials are widely used for sports applications such as golf shafts and fishing rods and structural materials for aircraft because of their excellent mechanical strength such as specific strength and specific elastic modulus.

[0003] As the resin constituting such a composite material, a thermosetting resin having excellent impregnation and heat resistance is often used, and the thermosetting resin has excellent adhesiveness with carbon fiber, moldability, and the like. It is necessary to exhibit high mechanical strength even in a high-temperature, humid environment (hereinafter abbreviated as a moist heat environment).

As the thermosetting resin, phenol resin, melamine resin, bismaleimide resin, unsaturated polyester resin, epoxy resin and the like are used.

[0005] Above all, epoxy resins are widely used because they are excellent in heat resistance, moldability and adhesion to carbon fibers, and are thermosetting resins which provide fiber-reinforced composite materials having high mechanical strength.

A fiber-reinforced composite material obtained from a prepreg composed of carbon fiber as a reinforcing fiber and tetraglycidyldiaminodiphenylmethane and diaminodiphenylsulfone as a resin component is used for sports applications such as golf shafts and fishing rods and structural materials for aircraft. Widely used for structural members such as.

[0007] In such a fiber-reinforced composite material, under normal circumstances such as room temperature, the adhesiveness between the carbon fiber and the matrix resin is sufficiently high and the mechanical strength is good.
Once placed in a humid environment, the mechanical strength is impaired due to a decrease in adhesiveness, and thus improvement in wet heat resistance is strongly desired.

[0008] Therefore, as a measure to suppress the intrusion of water into the inside of the composite material, the porosity of the composite material is reduced,
Attempts have been made to reduce the polarity of the resin.

To reduce the polarity of the resin, it is necessary to introduce a side chain such as an alkyl group into a polymer molecule constituting the resin, lengthen the alkyl chain of the main chain, increase the epoxy equivalent, and reduce the amine equivalent. A method is conceivable.

However, when a side chain such as an alkyl group is introduced, the heat resistance is reduced, and when the main chain alkyl chain is lengthened, the elastic modulus and the heat resistance are reduced, and the epoxy equivalent is increased and the amine equivalent is reduced. When the amount is reduced, the adhesion to carbon fiber is reduced, and the resulting composite material has a problem that the mechanical strength such as the compressive strength in the fiber direction, the tensile strength in the non-fiber direction, the shear strength, and the peel strength is greatly reduced. there were.

Examples of the use of a benzoxazine compound having excellent wet heat resistance include Polymer Composites, 17,
5 (1996), P710, proposes a method for obtaining a carbon fiber reinforced composite material having high bending rigidity by using a prepreg composed of a carbon fiber having a bean-shaped cross section and a benzoxazine compound.

However, such a technique has a problem that the interface between the carbon fiber and the resin is deteriorated due to moisture absorption because the specific surface area of the carbon fiber is large.

[0013]

SUMMARY OF THE INVENTION The present invention maintains a high level of adhesion between a carbon fiber and a resin even in a wet heat environment, thereby exhibiting excellent weather resistance and exhibiting high mechanical strength. It is an object of the present invention to provide an intermediate for molding a composite material that provides a fiber-reinforced composite material to be formed, and such a fiber-reinforced composite material.

[0014]

The present invention has the following arrangement to solve the above-mentioned problems. That is, a composite material molding intermediate comprising a carbon fiber and a resin composition containing a benzoxazine compound having a structural unit I represented by the following structural formula (I) in a molecule, Intermediate for molding a composite material in which the cross-sectional shape of a single fiber of the fiber is substantially a perfect circle

[0015]

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(Wherein R ₁ is a chain alkyl group having 1 to 12 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, a phenyl group or a substituted phenyl group, and an oxygen atom is contained in the aromatic ring. Hydrogen is bonded to at least one of the ortho and para carbon atoms of the bonded carbon atom.).

The present invention has the following configuration in order to solve the above-mentioned problems. That is, the composite material molding intermediate is a fiber reinforced composite material obtained by heating and curing.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In view of the above problems, the present inventors have conducted intensive studies, and as a result, have found that a resin composition containing a carbon fiber having a substantially perfect circular cross section and a benzoxazine compound is used. The present inventors have found that a fiber-reinforced composite material exhibiting a high degree of mechanical strength can be obtained even under a moist heat environment by using a composite material molding intermediate having the following components.

In the present invention, the benzoxazine compound is a compound represented by the structural unit I represented by the structural formula (I).
Or more compounds.

[0020]

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(Wherein, R ₁ is a chain alkyl group having 1 to 12 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, a phenyl group or a substituted phenyl group, and an oxygen atom is contained in the aromatic ring. Hydrogen is bonded to at least one of the ortho and para carbon atoms of the bonded carbon atom.) From the viewpoint of further improving the wet heat resistance of the obtained composite material, the benzoxazine compound has the following structure: Structural formula (I
I)

[0022]

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It is preferable that the compound does not have the structural unit II represented by the formula or that it has the structural unit II within a range satisfying the following formula (1).

X ₁ ≧ X ₂ (1) X ₁ : the number of structural units II represented by the following structural formula (III) present in the molecule X ₂ : the following structural formula (III) present in the molecule Number of structural units II not represented by

[0025]

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(In the formula, R ₁ is a chain alkyl group having 1 to 12 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, a phenyl group, or a substituted phenyl group.) In the present invention, a benzoxazine compound Is synthesized from the corresponding phenol, primary amine and formaldehyde or a derivative thereof according to the reaction route represented by the following reaction formula (2) according to the method described in Japanese Patent No. 2595437 or Japanese Patent Publication No. 9-502452. can do.

[0027]

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(Wherein, R ₁ is a chain alkyl group having 1 to 12 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, a phenyl group, or a substituted phenyl group.) In the present invention, a benzoxazine compound is used. Examples include at least one selected from the group consisting of compounds represented by the following structural formula (IV).

[0029]

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The benzoxazine compound may be composed of only a monomer, or may be formed by oligomerizing several molecules by polymerization.

In the present invention, the resin composition preferably further contains a curing agent for the benzoxazine compound, a curing aid for the compound, and / or a curing catalyst. This allows
The handleability and curability of the resulting composite material intermediate are improved, and a fiber-reinforced composite material having excellent mechanical properties can be obtained.

Further, the resin composition according to the present invention can contain components such as thermosetting resin, thermoplastic resin and the like, and organic particles and inorganic particles.

A curing aid for benzoxazine compounds and / or
Alternatively, it is preferable to use an acid such as a phenol compound or a carboxylic acid, or an aromatic amine as the curing catalyst. Among them, a phenol compound and an aromatic amine can be preferably used since a fiber-reinforced composite material having excellent mechanical properties can be obtained. Specific examples of the phenol compound include monofunctional phenols and polyfunctional phenols such as bisphenol A as disclosed in International Publication WO0027921, resorcinol compounds as disclosed in JP-A-11-21336, and the like. Can be used. Further, as the aromatic amine, diaminodiphenylmethane, diaminodiphenylsulfone (DDS) and the like can be used.

As the thermosetting resin, epoxy resin, polyester resin, polyurethane resin, urea resin, phenol resin, melamine resin, cyanate ester resin and the like can be used. In addition, the thermosetting resin may partially contain an oligomer.

Among these thermosetting resins, an epoxy resin can be preferably used as a resin which gives a resin composition having good handleability and excellent curability and mechanical properties.

As the epoxy resin, bisphenol A
Epoxy resin (epoxy resin obtained by reaction of bisphenol A and epichlorohydrin), bisphenol F epoxy resin (epoxy resin obtained by reaction of bisphenol F and epichlorohydrin), bisphenol S epoxy resin (bisphenol S) Such as epoxy resin obtained by the reaction of novolak and epichlorohydrin), novolak-type epoxy resin (epoxy resin obtained by the reaction of novolak and epichlorohydrin), and tetrakis (glycidyloxyphenyl) ethane and tris (glycidyloxy) methane. Glycidyl ether type epoxy resin, glycidylamino such as tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, triglycidylaminocresol, and tetraglycidylxylylenediamine Type epoxy resins, and alkyl group or a halogen substituted derivatives such as they can be used. Among them, since a fiber-reinforced composite material having particularly excellent mechanical properties and heat resistance can be obtained, tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol,
Glycidylamine type epoxy resins such as triglycidylaminocresol and tetraglycidylxylylenediamine are used as the optimal resin.

In the present invention, when the epoxy resin is blended in the resin composition, it is preferable to further blend a curing agent for the epoxy resin. This makes it possible to obtain a resin composition that gives a cured product that is tougher and has excellent curability. Examples of the curing agent include aromatic amines such as diaminodiphenylmethane and diaminodiphenylsulfone (DDS), aliphatic amines such as triethylenetetramine and isophoronediamine, imidazole derivatives, dicyandiamide, tetramethylguanidine and methylhexahydrophthalic anhydride. Such carboxylic anhydrides, carboxylic acid hydrazides such as adipic hydrazide, carboxylic acid amides, polyphenol compounds, polymercaptan, and Lewis acid complexes such as boron trifluoride ethylamine complex name can be used.

In the present invention, as a resin component, an adduct having a curing activity and obtained by reacting these curing agents with an epoxy resin can also be used. Also, those obtained by microencapsulating the above-mentioned various curing agents can be preferably used from the viewpoint of further improving the storage stability of the prepreg.

Further, these curing agents can be combined with a curing accelerator in order to enhance the curing activity. For example, examples include combining dicyandiamide with a urea derivative or an imidazole derivative as a curing accelerator, and combining carboxylic anhydride or a polyphenol compound with a tertiary amine or imidazole derivative as a curing accelerator.

As the urea derivative, a compound obtained by reacting a secondary amine with an isocyanate, for example, 3
-Phenyl-1,1-dimethylurea, 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCM
U), 3- (3-chloro-4-methylphenyl) -1,
1-dimethylurea, 2,4-bis (3,3-dimethylureido) toluene and the like can be preferably used.

As the thermoplastic resin, a nylon resin, a polyester resin, a polyether ketone resin, a polyphenylene sulfide resin, a polyether sulfone resin and the like can be preferably used. Among them, thermoplastic polyimide polyetherimide and polyether sulfone can be particularly preferably used from the viewpoint of improving heat resistance and mechanical properties of the obtained fiber-reinforced composite material.

In the present invention, rubber particles and thermoplastic resin particles are preferable as the organic particles to be added to the resin composition. These particles have the effect of improving the toughness of the resin and the impact resistance of the fiber-reinforced composite material.

As the rubber particles, crosslinked rubber particles, core-shell rubber particles obtained by graft-polymerizing a different polymer on the surface of the crosslinked rubber particles, and the like can be preferably used. Commercially available crosslinked rubber particles include XER-91 (manufactured by Nippon Synthetic Rubber Industries, Ltd.) composed of a crosslinked product of a carboxyl-modified butadiene-acrylonitrile copolymer, and CX-M composed of acrylic rubber fine particles.
N series (manufactured by Nippon Shokubai Co., Ltd.) and YR-500 series (manufactured by Toto Kasei Co., Ltd.) can be used.

Commercially available core-shell rubber particles include, for example, “PARALOID” EXL-2655 (available from Kureha Chemical Industry Co., Ltd.) made of butadiene / alkyl methacrylate / styrene copolymer, acrylic acid ester / methacrylic acid ester copolymer “Staphyroid” AC-3355, TR-212
2 (Takeda Pharmaceutical Co., Ltd.) "PARALOID" EXL-261 consisting of butyl acrylate / methyl methacrylate copolymer
1, EXL-3387 (Rohm & Haas) or the like can be used.

As the thermoplastic resin particles, polyamide or polyimide particles are preferably used. As commercially available polyamide particles, SP-500 manufactured by Toray Industries, Inc., and “Orgasol” manufactured by ATOCHEM can be used.

In the present invention, silica, alumina, smectite, synthetic mica and the like can be preferably used as the inorganic particles to be blended in the resin composition.

These inorganic particles mainly have the effect of controlling rheology such as thickening of the resin composition and imparting thixotropic properties.

In the present invention, an elastomer can be used as another additive. Especially CTB
N (carboxyl group-terminated butadiene nitrile rubber)
It is effective for improving the fracture toughness G _IC .

In the present invention, the benzoxazine compound is used in an amount of 10 to 100 parts by weight based on 100 parts by weight of the total resin composition.
It is good to mix the resin composition by weight, preferably 50 to 100 parts by weight, more preferably 70 to 100 parts by weight. If the amount is less than 10 parts by weight, the adhesiveness between the carbon fiber and the resin is reduced, and the wet heat resistance of the obtained composite material may be impaired.

In the present invention, the resin composition contained in the intermediate for molding a composite material is in an uncured state. Here, the uncured state refers to a state in which the resin composition has not been completely cured and the resin has fluidity remaining.

In the present invention, since the fiber-reinforced composite material exhibits a high degree of wet heat resistance, specific strength, and specific elastic modulus required in the field of aircraft use, the cross-sectional shape of the monofilament of carbon fiber used is substantially It is necessary to be perfectly circular.

Here, that the cross-sectional shape of a single fiber is substantially a perfect circle means that the radius R of a circle circumscribing the cross-sectional shape of the single fiber
And the radius R of the inscribed circle is in the range of 1 to 1.1, preferably 1 to 1.05. If the cross-sectional shape of the single fiber of the carbon fiber is a shape other than a perfect circle, for example, an elliptical shape, an egg shape, a soybean shape, a three-leaf shape, or the like, the resulting composite material may have insufficient mechanical strength in the fiber direction. .

As the carbon fiber having a substantially perfect circular cross-sectional shape of a single fiber, PAN-based carbon fibers include “Treca (registered trademark)” T700S (manufactured by Toray Industries, Inc.) and “Treca (registered trademark)”. "M30S (manufactured by Toray Industries, Inc.) and the like. Also, so-called pitch-based carbon fibers can be used.

The tensile strength of the carbon fiber is 3800 MPa or more, preferably 4000 MPa or more, and more preferably 4 MPa or more.
The pressure is preferably 500 MPa or more. If it is less than 3800 MPa, the tensile strength of the obtained composite material may be insufficient, and it may be difficult to apply the composite material to aircraft structural materials requiring high mechanical strength. In addition, if the tensile strength of the carbon fiber is 7000 MPa, it is often sufficient to achieve the effects of the present invention.

The tensile modulus of the carbon fiber is 200 to 8
It is good to be 00 GPa, preferably 220 to 800 GPa. By using such high modulus carbon fiber,
Since a fiber-reinforced composite material having sufficient product rigidity can be obtained with a small amount of material, lightweight and high-rigidity aircraft members, leisure goods, and general industrial members can be obtained, which is preferable.

In the present invention, the carbon fibers can be used in combination with other types of reinforcing fibers, ie, inorganic fibers such as glass fibers and boron fibers, and organic fibers such as aramid fibers and nylon fibers.

In the present invention, the form and arrangement of the reinforcing fibers containing carbon fibers are not particularly limited, and can be appropriately selected from woven fabric, nonwoven fabric, mat, knit, braid, unidirectional strand, roving, chopped, etc. In order to obtain a fiber reinforced composite material having a higher level of durability, the reinforcing fibers are preferably in the form of continuous fibers such as woven fabrics, unidirectional strands, rovings and the like. Here, a conventionally known two-dimensional fabric can be applied to the fabric. As the woven structure, plain weave, twill weave, entangled weave, and satin weave are preferred. Note that the surface of the woven fabric is preferably a woven fabric made of carbon fiber, since the woven fabric is given an aesthetic appearance such as color and luster.

The composite material molding intermediate according to the present invention has a fiber volume fraction of 10 to 75%, preferably 30 to 65%.
% Is good. If it is less than 10%, the weight of the obtained composite material becomes excessively large, and the advantage of the fiber-reinforced composite material having excellent specific strength and specific elastic modulus may be impaired.
When the ratio exceeds the above range, impregnation failure of the resin occurs, and the obtained composite material tends to have many voids, and the mechanical strength thereof may be largely reduced.

In the present invention, the composite material molding intermediate is produced by a method such as a hand lay-up method, a FW method (filament winding method), a pultrusion method, and an RTM method (resin injection molding method). Can be.

The hand lay-up method is a method in which a reinforcing fiber is impregnated with a resin and a predetermined number of the fibers are laminated to obtain an intermediate. The FW method is a method in which a fiber bundle in which a resin is impregnated in a mandrel or the like is wound in a predetermined direction to obtain an intermediate.
The pultrusion method is a method in which a resin is immersed in a reinforcing fiber and then impregnated in a mold to obtain an intermediate. The RTM method is
This is a method in which reinforcing fibers are arranged in a mold in advance, and then a resin is injected to obtain an intermediate.

The intermediate for molding a composite material according to the present invention is an intermediate obtained by impregnating a reinforcing fiber with an uncured matrix resin in the form of a sheet, ribbon, cloth, tape or the like in which the fibers are aligned in one direction. It can also be used as a so-called prepreg.

The prepreg is prepared by dissolving the resin in a solvent to reduce the viscosity and impregnating the resin, by coating the resin on a release paper, arranging reinforcing fibers on the release paper, and applying the heated and melted resin to a roll or doctor blade. It can be produced by a hot melt method (dry method) in which pressure impregnation is carried out with the method and the like and then the mixture is allowed to cool. The wet method can be suitably used for a prepreg made of a glass fiber fabric.

These production methods can be appropriately used depending on the production amount, scale, shape, etc. of the target composite material.
For example, when a composite material having a relatively simple shape is mass-produced in a short time, a pultrusion method or a hot melt method is suitable.

Further, each of these production methods has a suitable resin viscosity range, for example, 450 to 550 mP · s for the hand lay-up method and 10 to 100 mP · s for the pultrusion method. . In addition,
The viscosity of the resin can be adjusted by adding an additive or a diluent or controlling the impregnation temperature.

In the present invention, a fiber-reinforced composite material can be obtained by heating and curing the intermediate having a predetermined shape.

[0066]

The present invention will be described more specifically with reference to the following examples. <Example 1> 228 of bisphenol A was used without using a solvent.
Parts by weight, 186 parts by weight of aniline, and 120 parts by weight of paraformaldehyde were charged into a flask, respectively, immersed in an oil bath and dissolved by stirring with a mechanical stirrer at 110 to 120 ° C for 20 minutes, and then stirred at 130 to 140 ° C for 20 minutes. Thereafter, the flask was cooled in an ice bath to synthesize a benzoxazine compound represented by the following structural formula (V).

[0067]

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Next, a liquid obtained by adding ethyl acetate to this benzoxazine compound was subjected to a carbon fiber woven fabric (Toray Industries, Inc.) having a substantially perfect cross section of a single fiber at room temperature of 25 ° C. ), Carbon fiber "Treca (registered trademark)" T
700S), and ethyl acetate was removed under reduced pressure and vacuum to obtain an intermediate for molding a composite material.

Six intermediates were laminated, placed on a metal plate having a thickness of 5 mm, covered with a heat-resistant film, vacuum-sealed, and heated by an autoclave at 200 ° C. and a pressure of 0.6 MPa for 2 hours to form a molded body. Obtained.

A 12.7 mm wide strip-shaped test piece was cut out from the molded article, and the bending strength of the test piece before water absorption was measured according to JIS.
It was measured according to K6911. Here, the ratio of the span (l) to the sample thickness (d) was l / d = 32, and the crosshead speed of the bending tester was 2.5 mm / min.

On the other hand, the bending strength of the test piece after water absorption was determined by immersing the test piece in boiling water for 20 hours and then measuring the strength according to JIS K691.
According to No. 1, it was measured by a 120 ° C. bending test. <Example 2> A benzoxazine compound represented by the following structural formula (VI) was synthesized in the same manner as in Example 1 except that 186 parts by weight of 4,4'-biphenol was used instead of bisphenol A. .

[0072]

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The obtained benzoxazine compound was crushed in a mortar and pulverized to adhere to a carbon fiber fabric (manufactured by Toray Industries, Inc., carbon fiber “Treca (registered trademark)” using T700S). The fabric was heated at 150 ° C. by a heating press to impregnate the fabric while melting the benzoxazine compound to obtain an intermediate for molding a composite material.

This intermediate was placed on a metal plate having a thickness of 5 mm,
After being covered with a heat-resistant film and vacuum-sealed, it was heated by an autoclave at 210 ° C. and a pressure of 0.6 MPa for 2 hours to obtain a molded body. From this molded body, in the same manner as in Example 1,
The bending strength of the test piece before and after water absorption was measured. <Example 3> Bisphenol A type glycidyl ether type epoxy resin (YD-128, manufactured by Toto Kasei Co., Ltd.) was added to 100 parts by weight of the benzoxazine compound represented by the structural formula (V).
100 parts by weight and 33 parts by weight of 4,4'-DDS were blended and melt-kneaded to obtain a resin composition.

Next, after obtaining a molded body in the same manner as in Example 1, the bending strength of the test piece before and after water absorption was measured. <Example 4> 100 parts by weight of N, N, N ', N'-tetraglycidyldiaminodiphenylmethane (ELM434, manufactured by Sumitomo Chemical Co., Ltd.) was added to 100 parts by weight of the benzoxazine compound represented by the structural formula (V). , 4,4′-DDS were blended and melt-kneaded to obtain a resin composition.

Next, after obtaining a molded body in the same manner as in Example 1, the bending strength of the test piece before and after water absorption was measured. <Example 5> Triglycidyl m-methyl p was added to 100 parts by weight of the benzoxazine compound represented by the structural formula (V).
-100 parts by weight of aminophenol and 58 parts by weight of 3,3'-DDS were blended and melt-kneaded to obtain a resin composition.

Next, the bending strength of the test piece was measured in the same manner as in Example 1. Comparative Example 1 Bisphenol A type glycidyl ether type epoxy resin (YD-128, manufactured by Toto Kasei Co., Ltd.) 10
33 parts by weight of 4,4'-diaminodiphenylsulfone (hereinafter, abbreviated as 4,4'-DDS) was blended with 0 parts by weight, and melt-kneaded to obtain a resin composition.

Next, after obtaining a molded body in the same manner as in Example 1, the bending strength of the test piece before and after water absorption was measured. <Comparative Example 2> N, N, N ', N'-tetraglycidyldiaminodiphenylmethane (ELM434, Sumitomo Chemical Co., Ltd.)
100 parts by weight) and 52 parts by weight of 4,4'-DDS were blended and melt-kneaded to obtain a resin composition.

Next, after obtaining a molded body in the same manner as in Example 1, the bending strength of the test piece before and after water absorption was measured. <Comparative Example 3> Example 1 was repeated except that a carbon fiber woven fabric having a hollow bean-like cross section of monofilament (manufactured by Toray Industries, Inc., using carbon fiber "Treca (registered trademark)" T300B) was used as the carbon fiber woven fabric. After obtaining the molded body in the same manner as described above, the bending strength of the test piece before and after water absorption was measured.

From Table 1, it can be seen that a molded article (Examples 1 to 5) obtained from a resin composition containing a carbon fiber having a substantially circular cross section and a benzoxazine compound has a monofilament shape. Compared with the molded article obtained from the resin composition containing no benzoxazine compound (Comparative Examples 1 and 2), the water resistance using the bending strength retention as an index is improved, and the bending strength before and after water absorption is improved. It can be seen that all of them are excellent.

From Table 2, it can be seen that the molded product (Example 1) obtained from a resin composition containing a carbon fiber and a benzoxazine compound in which the cross-section of a single fiber is substantially a perfect circle is obtained. Compared with a molded article obtained from a resin composition containing a hollow bean-like carbon fiber and a benzoxazine compound (Comparative Example 3), the water resistance using the flexural strength retention as an index is almost the same, and the flexural strength It can be seen that is excellent before and after water absorption.

[0082]

[Table 1]

[0083]

[Table 2]

[0084]

According to the present invention, a fiber-reinforced composite material which maintains a high level of adhesion between a resin and a carbon fiber and exhibits a high mechanical strength even in a wet heat environment is provided. An intermediate for molding a composite material is obtained.

The fiber-reinforced composite material according to the present invention can be particularly suitably used as a structural material for aircraft which requires a high level of heat and moisture resistance, specific strength and specific elastic modulus.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C08L 65/00 B29C 67/14 X (72) Inventor Takeshi Terashita 1515 Tsutsui, Oaza, Matsumae-cho, Iyo-gun, Ehime Prefecture East F-term in the Ehime Plant Co., Ltd.F-term (reference) GC00 GF00

Claims (8)

[Claims] An intermediate for molding a composite material, comprising carbon fiber and a resin composition containing a benzoxazine compound having a structural unit I represented by the following structural formula (I) in a molecule: An intermediate for molding a composite material, wherein the cross-sectional shape of a single fiber of the carbon fiber is substantially circular. Embedded image (Wherein, R ₁ is a chain alkyl group having 1 to 12 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, a phenyl group, or a substituted phenyl group, and an oxygen atom is bonded to the aromatic ring. Hydrogen is bonded to at least one of the ortho and para positions of the carbon atom. 2. The benzoxazine compound has the following structural formula (II) in the molecule: The composite material molding intermediate according to claim 1, wherein the intermediate does not contain the structural unit II represented by the formula or at least one of the units containing the structural unit II within a range satisfying the following formula (1). X ₁ ≧ X ₂ (1) X ₁ : number of structural units II present in the molecule represented by the following structural formula (III) X ₂ : present in the molecule, not represented by the following structural formula (III) Number of structural units II (In the formula, R ₁ is a chain alkyl group having 1 to 12 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, a phenyl group, or a substituted phenyl group.) 3. The content of the benzoxazine compound is:
The composite material molding intermediate according to claim 1 or 2, which is 10 to 100 parts by weight based on 100 parts by weight of the whole resin composition. 4. The composite material molding intermediate according to claim 1, wherein said resin composition contains an epoxy resin. 5. The intermediate for molding a composite material according to claim 4, wherein the resin composition contains a curing agent for a benzoxazine compound and / or an epoxy resin. 6. The carbon fiber has a tensile strength of 3800 MPa.
The composite material molding intermediate according to any one of claims 1 to 5, which is as described above. 7. The composite material molding intermediate according to claim 1, wherein the fiber volume fraction is 10 to 75%. 8. A fiber-reinforced composite material obtained by heating and curing the intermediate for molding a composite material according to claim 1.