JPS621749A - Prepreg for high-strength composite material - Google Patents

Abstract

PURPOSE:The titled prepreg capable of giving composite materials having respective specific values or above of tensile strength at breaking point and glass transition temperature and improved strength and heat resistance and molding the composite materials using an autoclave. CONSTITUTION:A prepreg capable of giving cured articles having >=320kg/mm<2> tensile strength at breaking point and >=160 deg.C glass transition temperature at 60% fiber volume fraction thereof. Preferably, carbon fibers having >=1.9% tensile strength at breaking point of a resin-impregnated strand are used. A resin having >=3% tensile elongation at breaking point and >=160 deg.C glass transi tion temperature is preferably used. Preferably, the basic weight of the carbon fibers is 100-200g/m<2> and the content of the resin is 30-45%.

Description

Detailed Description of the Invention "Industrial Application Fields" The present invention is directed to high-strength composite materials that provide composite materials with superior strength and heat resistance compared to conventionally known composite materials that use carbon fibers as reinforcing fibers. It concerns prepreg.

[Prior Art] Conventionally, composite materials made of carbon fiber and epoxy resin have been used for premium sports applications such as golf shirts and fishing rods, and for structural materials such as aircraft, by taking advantage of their high specific strength and specific modulus. widely used. However, in recent years, composite materials have been used for primary structural materials such as aircraft wings and wings, space structural materials, and various industrial applications, and from the perspective of further reducing weight, conventional composite materials have been Composite material 1'31 with far superior strength and excellent heat resistance
It is strongly desired that the

Several proposals have been made to date to improve the strength of composite materials. One of these concerns improving the strength and elongation of carbon fibers. For example, in order to improve the strength of carbon fibers themselves, carbon fibers are soaked in highly concentrated inorganic acids such as sulfuric acid, nitric acid, and phosphoric acid. A method has been proposed in which the fiber surface is etched by immersion for a long time, and then heat-treated in a high-temperature inert atmosphere to remove functional groups on the fiber surface generated by the inorganic acid treatment (for example, According to Japanese Patent Publication No. 54-59497, Japanese Patent Publication No. 52-35796@, and Japanese Patent Application Laid-Open No. 54-59497, scratches on the surface of carbon fibers formed in the manufacturing process of carbon fibers are removed by such etching treatment. is removed, which is said to improve the mechanical strength of carbon fibers.

However, according to the inventors' investigation,
When a fiber with extremely good chemical resistance, such as carbon fiber, is subjected to severe treatment that etches its surface, it damages not only the surface area of the fiber, that is, the surface layer, but also the internal structure of the fiber in some cases. However, the mechanical strength of the carbon fibers does not necessarily improve, and even if the mechanical strength improves, the strength and elongation of the resin-impregnated strands do not improve, and do not contribute to improving the tensile strength of the composite material. I discovered that.

As another method for improving the strength of composite materials, a method of using a high elongation epoxy resin as a matrix resin has been proposed (for example, Japanese Patent Laid-Open No. 59-2177
Publication No. 21).

However, although these techniques certainly improve the strength of composite materials, dramatic improvements in strength cannot be expected.

[Problems to be Solved by the Invention] The object of the present invention is to provide a prepreg for composite materials with excellent strength and heat resistance, and more specifically, to provide a prepreg for composite materials with excellent strength and heat resistance. The present invention provides a prepreg for high-strength composite materials with a high glass transition temperature.

[Means for Solving the Problems] The present invention provides: (1) A high-strength composite having a tensile strength at break of 320 kg/mm2 or higher at a fiber volume fraction of 60% and a glass transition temperature of 160°C or higher. Prepreg for materials.

(2) The prepreg using a high-strength composite material according to item (1) above, characterized in that carbon fibers of resin-impregnated strands having a tensile elongation at break of 1.9% or more are used.

(3) A prepreg for a high-strength composite material, characterized in that a resin having a tensile elongation at break of 3% or more and a glass transition temperature of 160° C. or more is used in items (1) and (2) above.

(4) In items (1) to (3> above, carbon fiber basis weight is 100 to 200C]/m2) resin weight content is 3
A prepreg for high-strength composite materials having a content of 0 to 45%.

(5) In paragraphs (1) to (4) above, the fiber has a surface layer having substantially the same level of crystal integrity as the fiber center, and the surface layer is located at the center of the fiber. A prepreg for high-strength composite materials characterized by using carbon fiber having an ultra-thin outermost layer with low crystal integrity.

(6) In item (5) above, the amount of pyrolyzable organic matter in the carbon fiber is within the range of about 0.05 to 0.5% by weight and the carbon detected by X-ray electron spectroscopy (ES, CA) The ratio of functional groups ffi (OIs/Q Is) on the fiber surface is 0.
．． A prepreg for a high-strength composite material, characterized in that carbon fiber is used within a range of 1 to 0.4.

It is related to.

The prepreg for high-strength composite materials of the present invention can be manufactured from high-elongation carbon fiber and 7-trix resin that has high elongation and excellent heat resistance. The carbon fiber used in the present invention is a carbon fiber whose resin-impregnated strand has a tensile elongation at break of 1.9% or more.

Here, the tensile elongation is measured according to the test method specified in JIS-R7601. As impregnating resins, "Chissonox" 221 (100 parts), boron trifluoride monoedylamine complex (3 parts) and acetone (42B
) is used and cured at 130° C./30 minutes to produce a strand. There are no particular limitations on the manufacturing method of the carbon fibers with a strand tensile elongation at break of 1.9% or more used in the present invention, but the surface layer has substantially the same level of crystal integrity as the center of the fiber. Preferably used is a carbon fiber having a surface layer having an ultra-thin outermost layer whose crystal integrity is lower than that of the center portion of the fiber. Further, the amount of thermally decomposable organic matter is within the range of about 0.05 to 0.5 type% and the functional lff1 (OIs/C1s) ratio on the carbon fiber surface detected by X-ray electron spectroscopy (ESCA) is 0.1. Carbon fibers within the range of 0.4(7) are preferred.

Here, the crystal integrity of the core, surface layer, and ultra-thin outermost layer of the fiber can be determined by transmission electron diffraction (TE).
M>, and specifically, as described later, when comparing the degree of crystal perfection of the fiber surface layer and the ultra-thin outermost layer of the surface layer with reference to the crystal perfection of the center of the fiber. , the surface layer exhibits substantially the same level of crystalline integrity relative to the fiber core, and the ultra-thin outermost layer of the surface layer exhibits less crystalline integrity relative to the fiber core. means. 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 content of pyrolyzable organic substances in the carbon fiber of the present invention is determined by the amount of chemical functional groups present on the surface and inside of the carbon fiber, especially the chemical functional groups mainly in the ultra-thin outermost layer. This is a scale of 0.05 to 0.5.
The amount of carbon must be within the range of 5%, preferably 0.1 to 0.4, more preferably 0.15 to 0.30%, and if this amount is less than 0.05%, carbon This is not preferred because the adhesion between the fiber and the resin decreases too much, and on the other hand, if it exceeds 0.5%, the elongation of the resin-impregnated strand decreases.

The carbon fiber of the present invention having such an ultra-thin outermost layer has a functional group St detected by X-ray electron spectroscopy.
(01s/C15) ratio is O, 1 to 0.4, preferably 0.15 to 0.4, more preferably 0.20 to 0.2
It is preferable that it is in the range of 5.

That is, the functionality of the surface layer of the inactivated carbon fiber is 1 m.
is outside the above range, carbon fibers with high resin-impregnated strand elongation cannot be used.

The prepreg resin used in the present invention is JIS-7.
The resin has a tensile elongation at break of 3.0% or more, as measured in accordance with the test method specified in No. 113.

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.

Note that the resin used in the present invention needs to have a glass transition temperature of 160° C. or higher in order for the composite material to exhibit sufficiently high heat resistance.

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, and this epoxy group may be present as a terminal group or may be internal to the molecule. The polyepoxide may be a saturated or unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic compound, and may further contain a halogen atom, a hydroxyl group, an ether group, etc.

Examples thereof include glycidyl compounds of bisphenols A, F, and S, glycidyl compounds of cresol novolak or phenol novolak, 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-boxybroboxy)diphenyl ether.

Another example of a polyepoxide is a glycidyl compound of polyhydric phenol. Examples of polyhydric phenols that can be used for this purpose include resorcinol, catechol, hydroquinone, 2.2-bis(4-hydroxyphenyl)propane (bisphenol A), 2.2-bis(4-hydroxyphenyl)butane, and bis(4-hydroxyphenyl)butane. 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-te1helaoxaspiro[5,5]undecane, and also 2,2-bis as a halogen-containing phenol. (4-hydroxytetrabromphenyl)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-(
Examples include 3,4-epoxy)cyclohexane hydroxylate.

Another example of a polyepoxide is a diglycidyl compound of an aromatic amine. Aromatic amines that can be used for this purpose include diaminodiphenylmethane, metaxylylene diamine, m-amine phenol, p-amine phenol, and the like.

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

The curing agents used in the present invention include aromatic amine 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.

In addition, curing catalysts such as boron trifluoride/amine complexes, imidazole compounds, and urea compounds obtained by the addition reaction of toluene diisocyanate-1 and dimethylamine may be used alone or in combination with the above curing agents. I can do it.

The epoxy resin used in the present invention with a tensile elongation at break of 3% or more and a glass transition temperature of 160°C or more contains one or more of the above-mentioned polyepoxides, and u% of the above-mentioned curing agent or curing catalyst alone. Gtl number 8 combinations t!
Epoxy resin having desired physical properties can be prepared by a method well known in the industry by combining these epoxy resins. Typical examples are revealed 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 71-Rix resin and improving the moldability, or increasing the toughness of the composite material. Ru. Examples of the resins included include polyvinyl acetal, polyamide, polyester, polysulfone, polyethersulfone, polyetherimide, polyarylate, polyamideimide, polyetheramide, polyetherester, and 21-lyru rubber.

There are no particular limitations on the method for producing the prepreg of the present invention, and various methods known in the art can be used. A typical example is a method in which carbon fiber yarn is impregnated with a matrix resin, and carbon fiber yarn is impregnated with a matrix resin solvent, and then all or an appropriate amount of the solvent is removed to produce prepreg. There is a way to do it.

There is no particular limit to the carbon fiber basis weight and resin content of the prepreg of the present invention, but each is 100 to 200 Q/m.
2.30-45% prepreg is most preferred for producing high strength composites. In the prepreg of the present invention, other high modulus reinforcing fibers such as polyaramid fibers can be used in combination with carbon fibers as long as the purpose of the present invention is not impaired.

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

Transmission electron diffraction method Carbon fibers are aligned in the fiber axis direction, embedded in a room temperature curing epoxy resin, and cured. After rimming 10 pieces of cured carbon fiber embedding to expose at least 2-3 of the embedded carbon fibers, use a micrometer equipped with a die lemon knife to cut the 150 mm thick -2
Ultrathin sections of 00 Onges 1 to Loam (A) are prepared.

This ultrathin section is placed on a gold-deposited microglue and subjected to electron beam diffraction using a high-resolution electron microscope.

In this case, in order to detect the difference in drawing between the inside and outside of the carbon fiber,
Examine the electron diffraction image from a specific area using selected area electron diffraction.

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. @shadow in the state. 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 of the fiber center near the center of the fiber, the diffraction intensity in the equatorial direction for (002) of these electron diffraction images was 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.

Note that the electron beam diffraction image (0
Examples of measurement charts of the scanning profile of the diffraction intensity in the equatorial direction in 02) are shown in FIGS. 1 and 2.

In the figure, the noise in the scanning profile is determined by taking the midpoint of the noise amplitude to create a smooth profile, and as shown in the figure, by subtracting the baseline and dividing the smoothed diffraction peak and the baseline by half according to the usual method. I asked for a price tag. Particularly, as shown in FIG. 1, when the half height of the peak was lower than the valley of the peak, the half width was determined by extending the line of the diffraction peak.

A carbon fiber (sample) with an amount of pyrolyzable organic matter of about 20 m () was washed with a solvent,
Removal of "reising" etc. that adheres to the fiber surface, using a CHN coder M-3 model manufactured by Yanagimoto Seisakusho,
Measurements were made on the following strip A′.

CHN coder sample combustion furnace at 950℃, oxidation furnace at 85℃
5. Raise the temperature of the reduction furnace to 0°C and 550°C. Edge r
The cum was flowed at a rate of 180 ml/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 through the oxidation furnace and reduction furnace for about 5 minutes using a suction pump,
C0 by the thermal conductivity type detector of the C)-I N coder.
Quantitate as 2FL, and calculate the amount of thermally decomposable organic matter as C (wt%) with respect to the sample by calibration. The characteristics of this measurement method are ordinary C, H.

By heating the carbon fiber in an atmosphere of helium gas only without flowing oxygen gas in the N elemental analyzer, it is possible to quantify the amount of thermally decomposable substances such as Co, CO2) CH4, etc. in the carbon fiber. be.

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

After cleaning the carbon fiber (sample) with a solvent and removing surface deposits such as sizing, the carbon fiber is cut,
After spreading and arranging the specimens on a copper specimen rat support stand, using AIKα1,2 as an X-ray source, the inside of the specimen chamber was 1*1
Maintain at 0E (-8) Torr. and C1S peak area with kinetic energy of 955 cV and 1202 eV
The ratio of surface oxygen atoms/surface carbon atoms (OIs/CIs) is determined from the ratio of C1S peak areas.

[Function] In the present invention, by combining a specific carbon fiber and a specific resin, a prepreg for composite material with high strength and excellent heat resistance can be obtained.

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

Reference Example 1 A having an intrinsic viscosity [η] of 1.80, consisting of acryloni 1-lyl (AN>99.5 mol% and itacon 10.5 mol%)
Ammonia is blown into a dimethyl sulfoxide (DMSO) solution of a N copolymer, and the polymer is modified by substituting the carboxyl terminal group of the copolymer with an ammonium hydrogen group, and the concentration of the modified polymer is 20% by weight in a DMS○ solution. It was created.

This solution was filtered using a sintered metal filter with an opening of 5 μm as a filter medium, and then exposed to the air through a spinneret with a pore diameter of 0.15 mm and 1500 holes. The discharged fiber yarn was coagulated by introducing it into a DMSO aqueous solution at 130%. 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-swellable fiber thread is made of polyethylene glycol (PEG).
) A 0.8% aqueous solution of modified polydimethylsiloxane (PEG modification amount: 50% by weight), 85 parts of amino-modified polydimethylsiloxane (amino modification amount: 1 wt. %), and 15 parts of a nonionic surfactant. After being immersed in a mixed oil bath containing an 8% aqueous dispersion, it was dried and densified on a heated roll with a surface temperature of 130°C. The dried and densified fiber yarn was drawn three times in heated steam to obtain an acrylic fiber yarn with a single filament fineness of 0.8 denier (d) and l-tal denier 1200 (D>).

Three of these acrylic fiber yarns with a total denier of 1200D were combined, and using a ring nozzle, the pressure was 0.7
kCJ/- air opening treatment, 240-260℃
Heated in air at a stretching ratio of 1.05 to a moisture content of 4.
A 5% oxidized fiber yarn was prepared.

Next, this oxidized fiber yarn was heated in a nitrogen atmosphere with a maximum temperature of 1400°C at a heating rate of about 250°C/min in the temperature range of 300 to 700°C, and at a heating rate of about 400°C in the temperature range of 1000 to 1200°C. The carbon fiber yarn was carbonized at a temperature of 19 °C/min.

The average single fiber strength of the obtained carbon fiber yarn was 45OkCJ
/mm2) The resin-impregnated strand elongation was 1.97%. In addition, ultra-thin sections of the longitudinal cross section of this carbon fiber yarn single fiber were prepared, and the central part of the fiber was determined using selected area electron diffraction.
The completeness of the crystals was measured in a region approximately 0.1μ deep from the fiber surface (ultra-thin outermost layer region) and a region approximately 0.4 micrometers from the fiber surface (surface layer region), and the crystals in the center of the fiber were measured. The ratio of the crystal perfection in the 0.1 micron and 0.4 micron deep regions from the fiber surface to the perfection of the fiber was found to be 1.05 and 1°03, respectively.
The crystal integrity of the approximately 0.1 micron deep region (ultra-thin outermost layer) exhibits greater crystallinity than that of the fiber core;
The crystal integrity of the approximately 0.4 micron deep region (surface layer) showed substantially the same crystallinity as that of the fiber core.

The raw carbon fiber yarn thus obtained was introduced into a treatment bath containing a 5N nitric acid aqueous solution swirled at a temperature of 80°C via a Keramix guide, and the yarn speed was 0.3.
The carbon fiber yarn was run continuously at a speed of m/min, and a positive voltage was applied to the carbon fiber yarn by a metal guide roller placed just before the processing bath, and a voltage of 0.00 m/min was applied between the carbon fiber yarn and the cathode plate placed in the processing bath.
A current of 12A was applied. Here, the immersion length of the carbon fiber yarn into the processing bath is about 0.2 m, the processing time is about 40 seconds,
The amount of electricity per 10 carbon fibers was 150 coulombs.

After washing the electrochemically oxidized carbon fiber yarn with water and drying it in heated air at about 200"C,
Heating in a nitrogen atmosphere at 0° C. for about 1 minute defunctionalized the functional groups in the fibers formed by the treatment. As a result of measuring the average single fiber strength and resin-impregnated strand elongation of the 1q carbon fiber yarn, each was found to be 550/mm.
2 and 2.34%.

An ultra-thin section of the carbon fiber yarn obtained in this way was prepared, and crystallization was performed in the same manner as described above at a depth of approximately 0.1 micron and approximately 0.4 micron from the fiber center and fiber surface, respectively. The ratio of the crystal perfection in the region of about 0.1 micron and about 0.4 micron from the surface to the crystal perfection in the center of the fiber was determined to be 0.92 and 1.0 microns, respectively. 03, the region at a depth of about 0.1 microns from the surface (ultra-thin outermost layer) shows low crystal integrity, and the region at a depth of about 0.4 microns from the surface (surface layer) shows fiber center The crystallinity was substantially the same as that of the other parts.

Example 1 35 parts of bisphenol △ diglydyl ether (Epicote 828, manufactured by Yuka Shell Epoxy Co., Ltd.), 35 parts of a tetraglycidyl compound of diaminodiphenylmethane (ELM434, manufactured by Sumitomo Chemical Co., Ltd.), and tetrabromo bisphenol △ diglycidyl Ether (Dainippon Ink Co., Ltd.)
A prepreg resin was prepared by adding and mixing 32 parts of diaminodiphenylsulfone to an epoxy compound mixture consisting of 30 parts of Epiclon 152) manufactured by Epiklon. This epoxy resin was cured in an oven at 180℃ for 12 hours to a thickness of 2mm.
A transparent cured resin plate was obtained. Glass transition temperature of cured product (
(Measured using a differential calorimeter at a heating rate of 40°C/min) was 220°C, and the tensile elongation at break measured according to JIS-7113 test method was 4.4%. .

The carbon fibers described in Reference Example 1 were aligned in one direction and impregnated with the above prepreg resin to obtain a carbon fiber fabric weight of 145 g/
Tr12) A prepreg with a total resin loss of 34% was obtained. Laminated 8 sheets of this prepreg and used an autoclave to
It was molded at 0° C. for 12 hours at a pressure of 6 and 57 m′ to obtain a composite material with a thickness of 1 mm and a carbon fiber volume fraction of 58.2%. A tensile test piece with a length of 230 mm and a width of 12.72 mm (7) was cut out from this composite material in the fiber direction. The length of this test piece is 5 qmm and the width is 12.72 m at both the upper and lower ends.
A glass cloth/epoxy resin tab with a 10 mm taper was glued to one end at m. This test piece is 1 mm
As a result of a tensile test at a tensile speed of /min, the tensile strength was 319.
kg/mm2. From this tensile strength, the carbon fiber volume fraction is converted to 60%, which gives a tensile strength of 329 kv/mm2.
1 q.

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-te1-laokirispi[5,5]unde, and tetrabrome, etc. A prepreg resin was prepared by adding and mixing 24 parts of diaminodiphenylsulfone to an epoxy compound mixture consisting of 30 parts of Suphenol A diglycidyl ether (Epiclon 152). When this epoxy resin was cured in the same manner as in Example 1, the glass transition temperature was 180°C.
The 1-tensile elongation at break was 6.1%. Furthermore, the tensile strength of the carbon fiber composite material produced in the same manner as in Example 1 was 350
kl/mm2 (carbon fiber volume fraction 60%).

Comparative Example 1 Diaminodiphenylmethane tetraglycidyl compound (
ELM434) 62 parts, N,N,O-triglycidylmethaminephenol (ELM120 manufactured by Sumitomo Chemical Co., Ltd.)
A prepreg resin was prepared by mixing 17 parts of a phenol novolak type epoxy compound (DEN485 manufactured by Dow Chemical Co., Ltd.), 22 parts, and 45 parts of diaminodiphenylsulfone.

The glass transition temperature of this cured epoxy resin is 23O'C
The 1-tensile elongation at break was 2.7%. A prepreg was produced from the above prepreg resin and the carbon fiber of Reference Example 1 in the same manner as in Example 1, and the tensile strength of the molded product was measured. It was 285 kCJ/mm2 (carbon fiber volume fraction 60%).
).

[Effect of the invention] (1) Extremely high strength composite vJ19 can be obtained.

(2) Composite materials with high heat resistance can be obtained.

(3) Prepreg and composite materials of stable quality can be obtained.

(4) Composite materials can be molded using an autoclave, which requires special striations.

[Brief explanation of drawings]

Figures 1 and 2 are scans of diffraction intensities in the equatorial direction of electron diffraction images in electron micrographs of ultrathin sections of carbon fibers used to measure crystal integrity by electron diffraction, respectively. Char 1 showing an example of a profile.
It is.

Claims (6)

[Claims] (1) A prepreg for high-strength composite materials whose cured product has a tensile strength at break of 320 kg/mm^2 or higher at a fiber volume fraction of 60% and a glass transition temperature of 160° C. or higher. (2) A prepreg for a high-strength composite material according to claim (1), characterized in that carbon fibers in which resin-impregnated strands have a tensile elongation at break of 1.9% or more are used. (3) A prepreg for high-strength composite materials according to claims (1) and (2), characterized in that a resin having a tensile elongation at break of 3% or more and a glass transition temperature of 160°C or more is used. . (4) A prepreg for high-strength composite material according to claims (1) to (3), having a carbon fiber basis weight of 100 to 200 g/m^2 and a resin weight content of 30 to 45%. (5) In claims (1) to (4), the fiber has a surface layer portion having substantially the same level of crystal integrity as the center portion of the fiber, and the surface layer portion is A prepreg for high-strength composite materials, characterized by using carbon fibers having an ultra-thin outermost layer whose crystal integrity is small compared to the center part. (6) In claim (5), the amount of pyrolyzable organic matter in the carbon fiber is within the range of about 0.05 to 0.5% by weight and detected by X-ray electron spectroscopy (ESCA). The ratio of the amount of functional groups (O1s/C1s) on the carbon fiber surface is 0.
A prepreg for a high-strength composite material, characterized by using carbon fiber having a carbon fiber content within the range of 1 to 0.4.