JP7287171B2 - Prepregs and carbon fiber reinforced composites - Google Patents

Description

TECHNICAL FIELD The present invention relates to an epoxy resin composition for a carbon fiber reinforced composite material that provides a carbon fiber reinforced composite material having both excellent mode I interlaminar toughness and 0° compressive strength, and a prepreg and a carbon fiber reinforced composite material using the same. It is.

Conventionally, fiber-reinforced composite materials made of reinforcing fibers such as carbon fibers and glass fibers and thermosetting resins such as epoxy resins and phenolic resins are lightweight, yet have mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. Because of its superiority, it has been applied in many fields such as aerospace, automobiles, railroad vehicles, ships, civil engineering and construction, and sporting goods. In particular, for applications that require high performance, fiber-reinforced composite materials using continuous reinforcing fibers are used. Carbon fibers with excellent specific strength and specific elastic modulus are used as reinforcing fibers, and thermosetting resins are used as matrix resins. In particular, epoxy resins, which have excellent adhesion to carbon fibers, are widely used.

A carbon fiber reinforced composite material is a heterogeneous material having reinforcing fibers and a matrix resin as essential components, and therefore there is a large difference in physical properties in the direction in which the reinforcing fibers are arranged and in the other directions. For example, it is known that the interlaminar toughness, which indicates how difficult it is for reinforcing fiber interlaminar fractures to progress, cannot be drastically improved simply by improving the strength of the reinforcing fibers. In particular, a carbon fiber reinforced composite material using a thermosetting resin as a matrix resin has the property of being easily destroyed by stresses from directions other than the direction in which the reinforcing fibers are arranged, reflecting the low toughness of the matrix resin. Therefore, for applications that require high strength and reliability, such as aircraft structural materials, it is necessary to ensure strength in the direction of the fiber while also responding to stresses other than the alignment direction of the reinforcing fibers, such as interlaminar toughness. Various techniques have been proposed for the purpose of improving physical properties of composite materials.

In recent years, the application of carbon fiber reinforced composite materials to aircraft structural materials has expanded, and the application of carbon fiber reinforced composite materials to wind turbine blades and various turbines aimed at improving power generation efficiency and energy conversion efficiency. Also, application to thick members and members having three-dimensional curved surfaces is being studied. When tensile or compressive stress is applied to such a thick member or curved member, a peeling stress in the out-of-plane direction between the prepreg fiber layers is generated, cracks are generated between the layers due to the open mode, and the cracks Due to the progress of this, the strength and rigidity of the entire member may decrease, leading to total destruction. Interlaminar toughness in the open mode, or Mode I, is required to counteract this stress. In order to obtain a carbon fiber reinforced composite material with high mode I interlayer toughness, the matrix resin itself must have high toughness. In order to improve the toughness of the matrix resin, a method of blending a rubber component into the matrix resin (see Patent Document 1) and a method of blending a thermoplastic resin (see Patent Document 2) have been known. In addition, a method of inserting a kind of adhesive layer or shock absorbing layer called interleaf between layers (see Patent Document 3) and a method of reinforcing the interlayer with particles (see Patent Document 4) have been proposed.

In addition, high compressive strength of carbon fiber reinforced composite materials is also required for application to aircraft structural materials. In fiber-reinforced composite materials, it is known that the compressive strength is lowered due to buckling of the fibers. In order to suppress the buckling of the fibers, it is effective to increase the elastic modulus of the matrix resin that fills the periphery of the fibers. However, in general, increasing the elastic modulus of a resin tends to reduce the elongation of the resin, resulting in a cured resin with low toughness. Therefore, it has been very difficult to satisfy high levels of mode I interlaminar toughness and compressive strength in the resulting fiber-reinforced composite material.

Japanese Patent Application Laid-Open No. 2001-139662 JP-A-7-278412 JP-A-60-231738 Japanese Patent Publication No. 6-94515

However, the methods described in Patent Literature 1 and Patent Literature 2 are not sufficiently effective in improving the toughness of the matrix resin. Moreover, although the methods described in Patent Documents 3 and 4 are effective for the mode II interlaminar toughness, they are not sufficiently effective for the mode I interlaminar toughness. Moreover, it was very difficult to achieve both 0° compressive strength and mode I interlaminar toughness. Accordingly, an object of the present invention is to provide a prepreg and a carbon fiber reinforced composite material from which a carbon fiber reinforced composite material having excellent mode I interlaminar toughness and 0° compressive strength can be obtained.

The prepreg of the present invention that solves the above problems is a prepreg that includes the following components [A] to [C] and satisfies the conditions [I] and [II].
[A]: carbon fiber [B]: epoxy resin [C]: curing agent having a structure represented by general formula (1)

(In general formula (1), X ¹ is a single bond or one selected from group (I). P ¹ and P ² may be the same or different, and are shown in group (II). Each W in group (II) is independently an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an aliphatic alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, represents a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group, and each n independently represents an integer of 0 to 4. The substituents W may all be the same or different, or X ² in group (II) is one selected from group (I), F ¹ and F ² are active groups capable of reacting with epoxy groups, and directly attached to a six-membered ring selected from

[I]: The surface oxygen concentration O/C of [A] measured by X-ray photoelectron spectroscopy is 0.10 or more.
[II]: A cured product of an epoxy resin composition containing components [B] and [C] contains a resin region having molecular anisotropy that exhibits an interference pattern when observed with a polarizing microscope in a crossed Nicols state.

Further, the carbon fiber reinforced composite material of the present invention is obtained by curing the prepreg.

According to the present invention, a carbon fiber reinforced composite material excellent in mode I interlayer toughness, 0° compressive strength, and heat resistance can be obtained.

FIG. 3 shows a method for measuring Mode I interlaminar toughness (G _IC ).

The carbon fiber, which is the component [A] of the present invention, is not limited in fiber form or arrangement, and examples thereof include long fibers aligned in one direction, single tows, woven fabrics, knits, and braids. of fiber structures are used. It may be used in combination with two or more types of carbon fibers or other reinforcing fibers such as glass fibers, aramid fibers, boron fibers, PBO fibers, high-strength polyethylene fibers, alumina fibers and silicon carbide fibers.

Specific examples of carbon fibers include acrylic, pitch, and rayon carbon fibers, and acrylic carbon fibers having high tensile strength are preferably used.

Such acrylic carbon fibers can be produced, for example, through the steps described below. A spinning dope containing polyacrylonitrile obtained from a monomer containing acrylonitrile as a main component is spun by a wet spinning method, a dry-wet spinning method, a dry spinning method, or a melt spinning method. The coagulated yarn after spinning can be made into a precursor through a spinning process, followed by processes such as flameproofing and carbonization to obtain carbon fibers.

As the form of the carbon fiber, twisted yarn, untwisted yarn, non-twisted yarn, etc. can be used. Untwisted yarn or untwisted yarn, which has a good balance between the moldability and strength characteristics of the carbon fiber reinforced composite material, is preferably used because it causes a decrease in the mechanical properties of the carbon fiber reinforced composite material.

In order to improve the adhesiveness to the matrix resin, the carbon fiber of the present invention is usually preferably subjected to oxidation treatment to introduce oxygen-containing functional groups. Gas-phase oxidation, liquid-phase oxidation, and liquid-phase electrolytic oxidation are used as the oxidation treatment method. Liquid-phase electrolytic oxidation is preferably used from the viewpoint of high productivity and uniform treatment.

In the present invention, the electrolytic solution used in the liquid-phase electrolytic oxidation includes an acidic electrolytic solution and an alkaline electrolytic solution. From the viewpoint of adhesion, it is preferable to apply a sizing agent after liquid-phase electrolytic oxidation in an alkaline electrolytic solution. is more preferred.

Examples of acidic electrolytes include inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, and carbonic acid; organic acids such as acetic acid, butyric acid, oxalic acid, acrylic acid, and maleic acid; or ammonium sulfate and ammonium hydrogen sulfate. and the like. Among them, sulfuric acid and nitric acid, which are strongly acidic, are preferably used.

Specific examples of alkaline electrolytes include aqueous solutions of hydroxides such as sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide and barium hydroxide, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, Aqueous solutions of carbonates such as barium carbonate and ammonium carbonate, aqueous solutions of carbonates such as sodium hydrogencarbonate, potassium hydrogencarbonate, magnesium hydrogencarbonate, calcium hydrogencarbonate, barium hydrogencarbonate and ammonium hydrogencarbonate, ammonia, tetraalkylammonium hydroxide and an aqueous solution of hydrazine. Among them, an aqueous solution of ammonium carbonate and ammonium hydrogencarbonate, or an aqueous solution of tetraalkylammonium hydroxide exhibiting strong alkalinity is preferably used from the viewpoint that it does not contain an alkali metal that inhibits curing of the matrix resin.

In the present invention, the total amount of electrolytic electricity used in the electrolytic treatment is preferably 3 to 300 coulombs per 1 g of carbon fiber. When the total amount of electrolyzed electricity is 3 coulomb/g or more, sufficient functional groups can be imparted to the surface of the carbon fibers, resulting in excellent interfacial adhesion between the matrix resin and the carbon fibers. On the other hand, when the total amount of electrolyzed electricity is 300 coulomb/g or less, it is possible to suppress the expansion of defects on the surface of the carbon fiber single fiber and reduce the decrease in the strength of the carbon fiber.

The carbon fiber used in the present invention preferably has a tensile modulus in the range of 200 to 440 GPa. The tensile elastic modulus of carbon fibers is affected by the crystallinity of the graphite structure that constitutes the carbon fibers, and the higher the crystallinity, the higher the elastic modulus. This range is preferable because the rigidity and strength of the carbon fiber reinforced composite material are well balanced at a high level. More preferably, the elastic modulus is in the range of 230-400 GPa, more preferably in the range of 260-370 GPa. Here, the tensile modulus of carbon fiber is a value measured according to JIS R7601 (2006).

Commercially available carbon fibers include "Torayca (registered trademark)" T800G-24K, "Torayca (registered trademark)" T300-3K, "Torayca (registered trademark)" T700G-12K, and "Torayca (registered trademark)" T1100G. -24K (manufactured by Toray Industries, Inc.) and the like.

The carbon fiber used in the present invention preferably has a single fiber fineness of 0.2 to 2.0 dtex, more preferably 0.4 to 1.8 dtex. If the single fiber fineness is less than 0.2 dtex, the carbon fibers may be easily damaged by contact with guide rollers during twisting, and similar damage may occur during the resin composition impregnation process. If the single fiber fineness exceeds 2.0 dtex, the carbon fibers may not be sufficiently impregnated with the resin composition, resulting in a decrease in fatigue resistance.

The number of filaments in one fiber bundle of carbon fibers used in the present invention is preferably in the range of 2,500 to 50,000. If the number of filaments is less than 2,500, the fiber arrangement tends to meander, which tends to cause a decrease in strength. Also, if the number of filaments exceeds 50,000, it may be difficult to impregnate the prepreg with the resin during fabrication or molding. The number of filaments is more preferably in the range of 2800-40000.

As the condition [I] to be satisfied by the prepreg of the present invention, the constituent element [A] carbon fiber is the atomic ratio of oxygen (O) and carbon (C) on the fiber surface measured by X-ray photoelectron spectroscopy. A certain surface oxygen concentration (O/C) is 0.10 or more. Furthermore, it is preferably within the range of 0.10 to 0.50, more preferably within the range of 0.14 to 0.30, and still more preferably within the range of 0.14 to 0.20. It is a thing. When the surface oxygen concentration (O/C) is 0.10 or more, the oxygen-containing functional groups on the surface of the carbon fiber can be secured and strong adhesion to the matrix resin can be obtained. Further, a surface oxygen concentration (O/C) of 0.50 or less is preferable because it is possible to suppress a decrease in the strength of the carbon fiber itself due to oxidation.

The surface oxygen concentration of the carbon fiber under condition [I] is determined by X-ray photoelectron spectroscopy according to the following procedure. First, _after removing the dirt adhering to the surface of the carbon fiber with a solvent, cut the carbon fiber into 20 mm, spread it on a copper sample support, and then arrange it. The chamber was maintained at 1×10 ⁻⁸ Torr and measured at a photoelectron escape angle of 90°. The binding energy value of the main peak (peak top) of C _1s is adjusted to 284.6 eV as a peak correction value associated with charging during measurement. The C _1s peak area is determined by drawing a linear baseline in the range 282-296 eV, and the O _1s peak area is determined by drawing a linear baseline in the range 528-540 eV. The surface oxygen concentration (O/C) is represented by an atomic number ratio calculated by dividing the O _1s peak area ratio by the apparatus-specific sensitivity correction value. When ESCA-1600 manufactured by ULVAC-Phi, Inc. is used as the X-ray photoelectron spectroscopy apparatus, the sensitivity correction value peculiar to the apparatus is 2.33.

The carbon fiber of the present invention is preferably a sizing agent-coated carbon fiber. By using the sizing agent-coated carbon fiber, the handling property of the carbon fiber is excellent, and the interfacial adhesion between the carbon fiber and the matrix resin is excellent, and it is suitable for use as a carbon fiber composite material.

In the present invention, the sizing agent preferably contains an epoxy resin compound. Epoxy compounds contained in the sizing agent include, for example, aliphatic epoxy compounds and aromatic epoxy compounds, and these may be used alone or in combination.

It has been confirmed that a carbon fiber coated with a sizing agent consisting only of an aliphatic epoxy compound has high adhesiveness to a matrix resin. Although the mechanism is not clear, aliphatic epoxy compounds are derived from flexible skeletons and structures with a high degree of freedom, and functional groups with carboxyl groups and hydroxyl groups on the carbon fiber surface form strong interactions with aliphatic epoxy compounds. It is considered possible to

Carbon fibers coated with a sizing agent consisting only of an aromatic epoxy compound have the advantage that the reactivity between the sizing agent and the matrix resin is low, and physical property changes are small when the prepreg is stored for a long period of time. There is also the advantage that a rigid interface layer can be formed.

When an aliphatic epoxy compound and an aromatic epoxy compound are mixed, the more polar aliphatic epoxy compound is unevenly distributed on the carbon fiber side, and the less polar aromatic epoxy compound is in the outermost layer of the sizing layer on the opposite side of the carbon fiber. is likely to be unevenly distributed. As a result of this gradient structure of the sizing layer, the aliphatic epoxy compound has a strong interaction with the carbon fibers in the vicinity of the carbon fibers, thereby enhancing the adhesion between the carbon fibers and the matrix resin. In addition, the aromatic epoxy compound, which is abundantly present in the outer layer, plays a role of shielding the aliphatic epoxy compound from the matrix resin when the sizing agent-coated carbon fiber is made into a prepreg. As a result, the reaction between the aliphatic epoxy compound and the highly reactive component in the matrix resin is suppressed, so stability during long-term storage is exhibited.

In a fiber-reinforced composite material comprising sizing agent-coated carbon fibers and a matrix resin, the so-called interface layer in the vicinity of the carbon fibers may be affected by the carbon fibers or the sizing agent and have properties different from those of the matrix resin. When the epoxy compound has one or more aromatic rings, a rigid interfacial layer is formed, the stress transmission ability between the carbon fiber and the matrix resin is improved, and the mechanical properties such as 0° tensile strength of the fiber-reinforced composite material are improved. improves. In addition, since the aromatic ring improves the hydrophobicity, it has a weaker interaction with the carbon fiber than the aliphatic epoxy compound, and can cover the aliphatic epoxy compound and exist in the outer layer of the sizing layer. As a result, when the sizing agent-coated carbon fiber is used for the prepreg, it is possible to suppress deterioration over time when stored for a long period of time, which is preferable. Having two or more aromatic rings is preferable because the aromatic rings improve long-term stability. There is no particular upper limit to the number of aromatic rings, but 10 is sufficient from the viewpoint of mechanical properties and suppression of reaction with the matrix resin.

In the present invention, the epoxy equivalent of the sizing agent applied to the carbon fibers is preferably 350-550 g/mol. When the amount is 550 g/mol or less, the adhesiveness between the carbon fiber coated with the sizing agent and the matrix resin is improved, which is preferable. In addition, when the sizing agent-coated carbon fiber is used in the prepreg, the reaction between the resin component used in the prepreg and the sizing agent can be suppressed by being 350 g / mol or more, so the prepreg can be stored for a long time. It is also preferable because the physical properties of the obtained carbon fiber reinforced composite material are improved even when it is carried out. The epoxy equivalent of the carbon fiber coated with the sizing agent in the present invention is eluted from the fiber by immersing the sizing agent-coated fiber in a solvent represented by N,N-dimethylformamide and performing ultrasonic cleaning. After that, the epoxy group is ring-opened with hydrochloric acid, and it can be determined by acid-base titration. The epoxy equivalent is preferably 360 g/mol or more, more preferably 380 g/mol or more. Also, it is preferably 530 g/mol or less, more preferably 500 g/mol or less. The epoxy equivalent of the sizing agent applied to the carbon fibers can be controlled by the epoxy equivalent of the sizing agent used for application and the heat history during drying after application.

In the present invention, the amount of the sizing agent adhered is preferably 0.1 parts by mass or more, more preferably 0.1 to 3.0 parts by mass, and still more preferably 0.1 part by mass with respect to 100 parts by mass of the carbon fiber. It is in the range of 2 to 3.0 parts by mass. When the amount of the sizing agent adhered is within such a range, high shear toughness can be exhibited. 2±0.5 g of sizing-coated carbon fiber was sampled and subjected to heat treatment at 450° C. for 15 minutes in a nitrogen atmosphere. It is the weight percent of the value divided by the previous weight.

In the present invention, it is preferable that the amount of the sizing agent remaining on the carbon fiber after washing with a mixed solution of acetonitrile and chloroform at a volume ratio of 9:1 is 0.08% by mass or more relative to the sizing agent-coated carbon fiber. , more preferably 0.08 to 3.0% by mass, and still more preferably 0.14 to 0.30% by mass. When the adhesion amount of the sizing agent after washing is within such a range, the interfacial adhesion between the carbon fibers and the sizing agent is improved, and high shear toughness can be exhibited when a fiber-reinforced composite material is produced. The "amount of sizing agent adhered after washing" in the present invention is measured and calculated as follows. 2 ± 0.5 g of the sizing agent-coated carbon fiber is immersed in 10 ml of a solution in which acetonitrile and chloroform are mixed at a volume ratio of 9:1, and ultrasonically cleaned for 20 minutes to elute the sizing agent from the fiber. Dry and weigh. Further, after washing, the carbon fibers are heat-treated at 450° C. for 15 minutes in a nitrogen atmosphere. The amount of change in mass before and after the heat treatment at this time is divided by the mass of the sizing agent-coated carbon fiber before the heat treatment, and the value in mass % is defined as the sizing agent adhesion amount after washing.

The carbon fibers in the prepreg of the present invention preferably have an interfacial shear strength (IFSS) of 25 MPa or more, more preferably 30 MPa or more, and still more preferably 40 MPa or more, as defined by the following method. When the interfacial shear strength is high, the adhesion between the carbon fiber and the epoxy resin tends to be high. Here, the "interfacial shear strength" in the present invention means the interfacial shear strength between a single fiber of carbon fiber and a bisphenol A type epoxy resin, and is a value calculated by measuring as follows.

A method for measuring the interfacial shear strength will be described below. Drzal, L. et al. T. , Master, Sci, Eng. A126, 289 (1990).

That is, 100 parts by mass of a bisphenol A type epoxy compound "jER (registered trademark)" 828 (manufactured by Mitsubishi Chemical Corporation) and 14.5 parts by mass of metaphenylenediamine (manufactured by Sigma-Aldrich Japan Co., Ltd.) were placed in a container. After that, it is heated at a temperature of 75° C. for 15 minutes in order to reduce the viscosity of the jER828 and dissolve the metaphenylenediamine. After that, both are well mixed, and vacuum defoaming is performed at a temperature of 80° C. for about 15 minutes.

Next, a single fiber is extracted from the carbon fiber bundle, and both ends are fixed with an adhesive while a constant tension is applied to the single fiber in the longitudinal direction of the dumbbell mold. Thereafter, vacuum drying is performed at a temperature of 80° C. for 30 minutes or more in order to remove the water adhering to the carbon fibers and the mold. The dumbbell mold is made of silicone rubber, and the shape of the casting part is 5 mm wide at the center, 25 mm long, 10 mm wide at both ends, and 150 mm long.

The prepared resin is poured into the mold after the above vacuum drying, and the temperature is raised to 75 ° C. at a temperature increase rate of 1.5 ° C./min using an oven, and after holding for 2 hours, the temperature increase rate is 1.5 ° C. /min to a temperature of 125°C, held for 2 hours, and then lowered to a temperature of 30°C at a cooling rate of 2.5°C/min. After that, the mold is removed to obtain a test piece.

Tensile force was applied to the test piece obtained by the above procedure at a strain rate of 0.3% / sec in the fiber axis direction (longitudinal direction) to cause a strain of 12%. Measure the number of fiber breaks N (pieces) in the range. Next, the average broken fiber length la is calculated by the formula la (μm)=22×1000 (μm)/N (pieces). Next, the critical fiber length lc is calculated from the average broken fiber length la by the formula lc (μm)=(4/3)×la (μm). Furthermore, the strand tensile strength σ and the diameter d of the carbon fiber single yarn are measured, and the value calculated from the following equation is defined as the "interfacial shear strength" in the present invention.
- Interfacial shear strength IFSS (MPa) = σ (MPa) x d (μm) / (2 x lc) (μm).

The carbon fiber-reinforced composite material of the present invention exhibits surprisingly excellent mode I interlaminar toughness because the cured epoxy resin composition has a higher-order structure. This is presumably because when cracks develop in the carbon fiber reinforced composite material, a large amount of energy is required to destroy the higher-order structure present in the cured product of the resin composition.

The term "higher-order structure" as used herein means a state in which molecules are aligned after curing or semi-curing of the epoxy resin composition, for example, a state in which a crystalline structure or liquid crystal structure exists in the cured product. .

Condition [II] to be satisfied by the prepreg of the present invention will be described below. The presence or absence of a higher-order structure in the cured product of the resin composition can be confirmed by examining the presence or absence of optical anisotropy using a polarizing microscope. When the size of the structure having optical anisotropy is equal to or larger than the visible light wavelength order, an interference pattern (bright field) is observed with a polarizing microscope in the crossed Nicols state. When no higher-order structure is formed, or when the size of the formed higher-order structure is smaller than the visible light wavelength order, a dark field is observed due to no optical anisotropy. That is, satisfying the condition [II] of the present invention means that an interference pattern (bright field) is observed when the cured product of the resin composition is observed with a crossed Nicol polarizing microscope. In the case of a liquid crystal structure, it is known that the observed interference pattern varies depending on the type of liquid crystal phase to be formed. Specific examples of the observed interference patterns include schlieren textures, filamentous textures, sandy textures, and droplet textures when the higher-order structure is a nematic phase structure. Examples include focal conic fan tissue and oily streak tissue.

In the prepreg or carbon fiber reinforced composite material of the present invention, a transmission method is used as a polarizing microscope observation method for confirming whether the condition [II] is satisfied. In the case of polarizing microscope observation by the transmission method, if the target test piece is too thick, visible light is not sufficiently transmitted, making it difficult to determine the presence or absence of an interference pattern. In order to transmit visible light, a test piece obtained by curing one ply of prepreg or a test piece obtained by shaving a carbon fiber reinforced composite material in the fiber direction to reduce the thickness to about 10 μm is used. With respect to the test piece, the cured product of the epoxy resin composition, excluding the component [A], is observed with a polarizing microscope, and the presence or absence of the interference pattern can be used to confirm the presence or absence of formation of a higher-order structure.

Condition [III] that the prepreg of the present invention preferably satisfies will be described below. The prepreg and carbon fiber reinforced composite material of the present invention contain a higher-order structure in the cured product of the resin composition, and in particular, exhibit high mode I interlaminar toughness because the higher-order structure is a smectic phase structure. When a smectic phase structure is formed, in addition to the above condition [II], a peak derived from a higher-order structure is generally observed in the region of the diffraction angle 2θ≦10° in X-ray diffraction. The presence or absence of a smectic phase structure can be confirmed by the presence or absence of peaks in this range. In the present invention, a mesogenic structure (biphenyl group, terphenyl group, terphenyl analogous group, anthracene group, azomethine group, or It corresponds to a periodic structure (higher-order structure) based on a group connected by an ester group, etc.), and has a peak in the range of the diffraction angle 2θ=1.0 to 6.0°. That is, when the condition [III] is satisfied, a peak in the range of diffraction angle 2θ = 1.0 to 6.0°, which is a peak derived from a smectic phase structure formed by a mesogenic structure, is observed by wide-angle X-ray diffraction. means that It is important that the diffraction angle 2θ range of peaks observed by X-ray diffraction be 1.0 to 6.0°, preferably 2.0 to 4.0°. A measurement sample having a length of 20 mm and a width of 10 mm is prepared using a carbon fiber reinforced composite material molded with a thickness of 1 mm. A prepared measurement sample is measured using a wide-angle X-ray diffraction device under the following conditions.
・X-ray source: CuK _α ray (tube voltage 45 kV, tube current 40 mA)
・Detector: goniometer + monochromator + scintillation counter ・Scanning range: 2θ = 1 to 90°
• Scanning mode: step scan, step unit 0.1°, counting time 40 seconds.

X-ray diffraction measurements are made parallel (0°), perpendicular (90°) and 45° to the carbon fiber axis within the carbon fiber reinforced composite.

The higher-order structure of the cured product of the resin composition may be oriented in any direction with respect to the carbon fibers of the component [A]. Due to the strong peak derived from the resin composition, the peak derived from the resin composition may not be observed in X-ray diffraction. In that case, the presence or absence of the periodic structure can be confirmed by performing X-ray diffraction measurement on a cured plate of the resin composition excluding the carbon fiber. As another confirmation method, use of synchrotron radiation is also effective. By narrowing down the beam diameter to about several μm, it becomes possible to measure only the cured resin composition containing the constituent elements [B] and [C], excluding the constituent element [A]. It is possible to check the presence or absence.

In the prepreg and carbon fiber reinforced composite material of the present invention, the cured resin composition preferably contains a resin region exhibiting molecular anisotropy. The term “anisotropic resin region” as used herein refers to an oriented domain in which molecules are arranged in one direction and have a diameter of 1 μm or more. As a confirmation method, for example, for 5 to 10 locations in the resin region in the carbon fiber reinforced composite material, an arbitrary orientation is set to 0 °, and the polarization orientation is changed at intervals of 30 ° from 0 ° to 150 °, and polarized IR or It can be confirmed by measuring the polarization Raman spectroscopy and checking the presence or absence of change in the signal intensity with respect to the polarization direction. In a resin composition having no anisotropy, no intensity change is observed with respect to the polarization direction.

Condition [IV] that the prepreg of the present invention preferably satisfies will be described below. In the prepreg and carbon fiber composite material of the present invention, the cured product obtained by curing the resin composition has an endothermic peak due to liquid crystal phase transition at 250° C. or higher in differential scanning calorimetry. It is more preferably in the range of 280°C or higher, still more preferably in the range of 300°C or higher. By reaching a temperature at which the endothermic peak due to the liquid crystal phase transition of the cured resin material occurs, the temperature range in which the cured resin material maintains the liquid crystal phase is widened, and a cured resin material that exhibits excellent mechanical properties even at high temperatures can be obtained. . In addition, since the higher the liquid crystal phase transition temperature, the stronger the higher-order structure is formed, the cured resin and the carbon fiber composite material tend to exhibit excellent mechanical properties. As a confirmation method, differential scanning calorimetric analysis of the resin cured product is performed in a nitrogen atmosphere, and the presence or absence of an endothermic peak in the heat flow when the temperature is raised from 50 ° C. to 400 ° C. at a temperature increase rate of 5 ° C./min is confirmed. be able to. For confirmation of liquid crystallinity by differential scanning calorimetry, a resin cured product or a carbon fiber composite material may be used. Regarding whether or not the endothermic peak observed by differential scanning calorimetry is caused by the liquid crystal phase transition, a test piece obtained by curing one ply of prepreg or a carbon fiber reinforced composite material was scraped in the fiber direction and thinned to about 10 μm. It can be determined by confirming whether or not there is a change in the interference pattern near the endothermic peak of interest when observing the test piece with crossed Nicols under a polarizing microscope. If there is a change in the interference pattern, it can be determined to be due to the liquid crystal phase transition.

The molding conditions for the carbon fiber reinforced composite material of the present invention are particularly limited to the extent that the resin composition after curing has a higher-order structure derived from the diffraction angle 2θ = 1.0° to 6.0° observed by X-ray diffraction. Although not limited, if the molding temperature is too high, the equipment and secondary materials used will need to have high heat resistance, and the production cost of the carbon fiber reinforced composite material will be high. On the other hand, if the molding temperature is too low, it takes a long time for the components [B] and [C] to react, which may also lead to an increase in production costs. The maximum temperature used for molding is preferably 100 to 220°C, more preferably 120 to 200°C.

The epoxy resin of the component [B] has a mesogenic structure and exhibits liquid crystallinity because the cured product of the resin composition in the prepreg and carbon fiber reinforced composite material of the present invention has a higher-order structure, so-called liquid crystal. curable epoxy resins are preferred. By having a mesogenic structure (biphenyl group, terphenyl group, terphenyl analogous group, anthracene group, azomethine group, group connected by an ester group, etc.), a higher-order structure derived from the structure (also called a periodic structure ) is formed.

As the mesogenic structure when the component [B] is a liquid crystalline epoxy resin, an epoxy resin having a structure represented by the following general formula (2) is preferable.

(Q ¹ , Q ² and Q ³ in general formula (2) each contain one structure selected from group (III). R ¹ and R ² in general formula (2) each have 1 to 1 carbon atoms. represents an alkylene group of 6. Each Z in the general formula (2) is independently an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an aliphatic alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine represents an atom, an iodine atom, a cyano group, a nitro group, or an acetyl group, n is each independently an integer of 0 to 4. Y ¹ , Y ² and Y ³ in general formula (2) and group (III). is selected from a single bond or group (IV).)

Z in group (III) each independently represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, an aliphatic alkoxy group having 1 to 4 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, A nitro group or an acetyl group is preferable, a methyl group, an ethyl group, a methoxy group, an ethoxy group or a chlorine atom is more preferable, and a methyl group or an ethyl group is even more preferable. Each n in group (III) is preferably an integer of 0 to 2, more preferably 0 or 1, independently.

When the constituent element [B] is a liquid crystalline epoxy resin, the mesogenic structure tends to form a higher-order structure after curing when the proportion is large, but when the proportion is too large, the softening point increases and the handling property decreases. . Therefore, the number of mesogenic structures in general formula (2) is particularly preferably two. Here, the softening point in the present invention means that a sample cast into a ring is heated in a bath according to the ring and ball method specified in JIS-K7234 (1986), and the ball set in the sample crosses the optical sensor. indicates the temperature of

When Q ¹ , Q ² , and Q ³ in the general formula (2) contain a benzene ring, the structure of the component [B] becomes rigid, which facilitates the formation of a higher-order structure, which is advantageous for improving toughness, which is preferable. . In addition, when Q ¹ , Q ² and Q ³ in the general formula (2) contain an alicyclic hydrocarbon, the softening point is lowered and the handleability is improved, so this is also a preferred embodiment. The epoxy resin of the component [B] may be used singly or in combination of two or more.

The component [B] can be produced by a known method, and can be produced by the following methods: Japanese Patent No. 4619770; Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 42, 3631 (2004) and the like can be referred to.

Specific examples of the component [B] include 1,4-bis{4-(oxiranylmethoxy)phenyl}cyclohexane, 1-{3-methyl-4-(oxiranylmethoxy)phenyl-4-{4 -(oxiranylmethoxy)phenyl}cyclohexane, 1,4-bis{4-(oxiranylmethoxy)phenyl}-1-cyclohexene, 1-{3-methyl-4-(oxiranylmethoxy)phenyl}- 4-{4-(oxiranylmethoxy)phenyl}-1-cyclohexene, 1-{2-methyl-4-(oxiranylmethoxy)phenyl}-4-{4-(oxiranylmethoxy)phenyl}- 1-cyclohexene, 1-{3-ethyl-4-(oxiranylmethoxy)phenyl}-4-{4-(oxiranylmethoxy)phenyl}-1-cyclohexene, 1-{2-ethyl-4-( oxiranylmethoxy)phenyl}-4-{4-(oxiranylmethoxy)phenyl}-1-cyclohexene, 1-{3-n-propyl-4-(oxiranylmethoxy)phenyl}-4-{4 -(oxiranylmethoxy)phenyl}-1-cyclohexene, 1-{3-isopropyl-4-(oxiranylmethoxy)phenyl}-4-{4-(oxiranylmethoxy)phenyl}-1-cyclohexene, 1,4-bis{4-(oxiranylmethoxy)phenyl}-2-cyclohexene, 1-{3-methyl-4-(oxiranylmethoxy)phenyl}-4-{4-(oxiranylmethoxy) Phenyl}-2-cyclohexene, 1,4-bis{4-(oxiranylmethoxy)phenyl}-2,5-cyclohexadiene, 1-{3-methyl-4-(oxiranylmethoxy)phenyl}-4 -{4-(oxiranylmethoxy)phenyl}-2,5-cyclohexadiene, 1,4-bis{4-(oxiranylmethoxy)phenyl}-1,5-cyclohexadiene, 1-{3-methyl -4-(oxiranylmethoxy)phenyl}-4-{4-(oxiranylmethoxy)phenyl}-1,5-cyclohexadiene, 1,4-bis{4-(oxiranylmethoxy)phenyl}- 1,4-cyclohexadiene, 1-{3-methyl-4-(oxiranylmethoxy)phenyl}-4-{4-(oxiranylmethoxy)phenyl}-1,4-cyclohexadiene, 1,4- Bis{4-(oxiranylmethoxy)phenyl}-1,3-cyclohexadiene, 1-{3-methyl-4-(oxiranylmethoxy)phenyl}-4-{4-(oxiranylmethoxy)phenyl }-1,3-cyclohexadiene, 1,4-bis{4-(oxiranylmethoxy)phenyl}benzene, 1-{3-methyl-4-(oxiranylmethoxy)phenyl}-4-{4- (oxiranylmethoxy)phenyl}benzene, 1,4-phenylene-bis{4-(2,3-epoxypropoxy)benzoate}, 1,4-phenylene-bis{4-(2,3-epoxypropoxy)- 2-methylbenzoate}, 1,4-phenylene-bis{4-(2,3-epoxypropoxy)-3-methylbenzoate}, 1,4-phenylene-bis{4-(2,3-epoxypropoxy)- 3,5-dimethylbenzoate}, 1,4-phenylene-bis{4-(2,3-epoxypropoxy)-2,6-dimethylbenzoate}, 2-methyl-1,4-phenylene-bis{4-( 2,3-epoxypropoxy)benzoate}, 2-methoxy-1,4-phenylene-bis(4-hydroxybenzoate), 2-methyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy) -2-methylbenzoate}, 2-methyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)-3-methylbenzoate}, 2-methyl-1,4-phenylene-bis{4- (2,3-epoxypropoxy)-3,5-dimethylbenzoate}, 2-methyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)-2,6-dimethylbenzoate}, 2, 6-dimethyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)benzoate}, 2,6-dimethyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)- 3-methylbenzoate}, 2,6-dimethyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)-3,5-dimethylbenzoate}, 2,3,6-trimethyl-1,4 -phenylene-bis{4-(2,3-epoxypropoxy)benzoate}, 2,3,6-trimethyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)-2,6-dimethyl benzoate}, 2,3,5,6-tetramethyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)benzoate}, 2,3,5,6-tetramethyl-1,4- Phenylene-bis{4-(2,3-epoxypropoxy)-3-methylbenzoate} and 2,3,5,6-tetramethyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy) -3,5-dimethylbenzoate}, 2-methyl-1,4-phenylene-bis{4-(3-oxa-5,6-epoxyhexyloxy)benzoate} 4-{4-(2,3-epoxypropoxy ) phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate, 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)-2-methylbenzoate, 4- {4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)-3-methylbenzoate, 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2 ,3-epoxypropoxy)-3-ethylbenzoate, 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)-2-isopropylbenzoate and 4-{4-( 2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)-3,5-dimethylbenzoate, 1,4-bis{4-(3-oxa-5,6-epoxyhexyloxy)phenyl }-1-cyclohexene, 1-{4-(3-oxa-5,6-epoxyhexyloxy)-3-methylphenyl}-4-{4-(3-oxa-5,6-epoxyhexyloxy)phenyl }-1-cyclohexene, 1,4-bis{4-(5-methyl-3-oxa-5,6-epoxyhexyloxy)phenyl}-1-cyclohexene, 1-{4-(5-methyl-3- oxa-5,6-epoxyhexyloxy)-3-methylphenyl}-4-{4-(5-methyl-3-oxa-5,6-epoxyhexyloxy)phenyl}-1-cyclohexene, 1,4- bis{4-(4-methyl-4,5-epoxypentyloxy)phenyl}-1-cyclohexene, 1,4-bis{4-(3-oxa-5,6-epoxyhexyloxy)phenyl}benzene, 1 -{4-(3-oxa-5,6-epoxyhexyloxy)-3-methylphenyl}-4-{4-(3-oxa-5,6-epoxyhexyloxy)phenyl}benzene, 1,4- bis{4-(5-methyl-3-oxa-5,6-epoxyhexyloxy)phenyl}benzene, 1-{4-(5-methyl-3-oxa-5,6-epoxyhexyloxy)-3- methylphenyl}-4-{4-(5-methyl-3-oxa-5,6-epoxyhexyloxy)phenyl}benzene, 1,4-bis{4-(4-methyl-4,5-epoxypentyloxy ) phenyl}benzene, 1,4-bis{4-(3-oxa-5,6-epoxyhexyloxy)phenyl}cyclohexane, 1-{4-(3-oxa-5,6-epoxyhexyloxy)-3 -methylphenyl}-4-{4-(3-oxa-5,6-epoxyhexyloxy)phenyl}cyclohexane, 1,4-bis{4-(5-methyl-3-oxa-5,6-epoxyhexyl) oxy)phenyl}cyclohexane, 1-{4-(5-methyl-3-oxa-5,6-epoxyhexyloxy)-3-methylphenyl}-4-{4-(5-methyl-3-oxa-5 ,6-epoxyhexyloxy)phenyl}cyclohexane, 1,4-bis{4-(4-methyl-4,5-epoxypentyloxy)phenyl}cyclohexane, among others, formation of higher-order structures after curing , 1-(3-methyl-4-oxiranylmethoxyphenyl)-4-(4-oxiranylmethoxyphenyl)-1-cyclohexene, 2-methyl-1,4 -phenylene-bis{4-(2,3-epoxypropoxy)benzoate}, 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate, 4-{4 -(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)-3-methylbenzoate is particularly preferred.

The component [B] may contain a prepolymer partially polymerized with a curing agent or the like. The epoxy resin of the component [B] generally tends to crystallize, and many require a high temperature to impregnate the reinforcing fibers. Containing a prepolymer obtained by polymerizing at least a part of the component [B] tends to suppress crystallization, thus improving handleability, which is a preferred embodiment.

As a method for partially polymerizing the component [B], polymerization may be performed using an anionic polymerization catalyst such as tertiary amines or imidazoles, or a cationic polymerization catalyst such as a Lewis acid such as a boron trifluoride-amine complex. , a prepolymerizing agent having a functional group capable of reacting with epoxy may be used. When the component [B] is partially polymerized, a method using a prepolymerizing agent is preferable because the molecular weight of the prepolymer to be produced can be easily controlled. If the molecular weight of the prepolymer is too large, the crosslink density of the resin in the carbon fiber reinforced composite material will decrease, possibly impairing heat resistance and mechanical properties.

The prepolymerizing agent for partially polymerizing the component [B] is not particularly limited as long as it is a compound having 2 to 4 active hydrogens capable of reacting with epoxy. Examples include phenol compounds, amine compounds, amide compounds, sulfide compounds, and acid anhydrides. Here, active hydrogen means a highly reactive hydrogen atom that is bound to nitrogen, oxygen, and sulfur in an organic compound. When there is one active hydrogen, the crosslink density of the epoxy resin cured product using the prepolymer is lowered, so that the heat resistance and mechanical properties may be lowered. If the number of active hydrogen groups is 5 or more, it becomes difficult to control the reaction during prepolymerization of the component [B], and gelation may occur. A phenolic compound having 2 to 3 active hydrogens is particularly suitable as a prepolymerizing agent because of its suppression of gelation during the prepolymerization reaction and the storage stability of the prepolymer.

Among phenolic compounds having 2 to 4 active hydrogens, phenolic compounds having 1 to 2 benzene rings have a rigid structure of the prepolymerized constituent element [B], which makes it easier to form a higher-order structure. In addition to tending to improve toughness, it is possible to keep the viscosity of the resin composition containing the prepolymer, component [B], and curing agent low, thereby improving handleability.

Phenolic compounds having 2-3 active hydrogens include, for example, catechol, resorcinol, hydroquinone, bisphenol A, bisphenol F, bisphenol G, bisphenol Z, tris(4-hydroxyphenyl)methane and derivatives thereof. Derivatives include compounds in which a benzene ring is substituted with an alkyl group having 1 to 8 carbon atoms or the like. These phenol compounds may be used singly or in combination of two or more.

The molecular weight of the prepolymer contained in component [B] is not particularly limited. From the viewpoint of fluidity of the resin composition, the number average molecular weight is preferably 15,000 or less, preferably 10,000 or less, and more preferably 350 to 5,000. The number average molecular weight of the present invention indicates the molecular weight converted using standard polystyrene by GPC (gel permeation chromatography, also referred to as SEC: size exclusion chromatography).

The method for partially polymerizing and prepolymerizing the component [B] is not particularly limited. For example, the component [B] and the prepolymerizing agent are dissolved in a synthetic solvent and heated. can be synthesized by stirring while A catalyst may be used as long as it does not cause gelation during the prepolymerization reaction. Although it is possible to synthesize without using a solvent, the component [B] has a high melting point and requires a high temperature for the prepolymerization reaction without a solvent, so a synthetic solvent was used from the viewpoint of safety. Synthetic methods are preferred.

When the constituent element [B] contains a prepolymer, crystallization tends to be suppressed, so the handling property is improved. becomes too high, impregnating the reinforcing fibers may become difficult. When the component [B] contains a prepolymer, its content is preferably 80 parts by mass or less, more preferably 5 to 60 parts by mass with respect to the total 100 parts by mass of the component [B] and the prepolymer. is. The ratio of the prepolymer-derived peak area to the total epoxy resin-derived peak area in the resin composition in the above-mentioned GPC or HPLC (High performance Liquid chromatography) measurement (peak area derived from the prepolymer/total epoxy resin composition The peak area derived from the resin) is preferably 0.80 or less, more preferably in the range of 0.05 to 0.60.

The epoxy resin composition containing component [B] and component [C] preferably transitions from a crystalline phase to a liquid crystal phase or an isotropic liquid at a temperature of less than 180°C. When the temperature at which the crystalline phase transitions to the liquid crystal phase or the isotropic liquid is less than 180°C, the fluidity of the resin is improved when molding the carbon fiber reinforced composite material, and the impregnation of the carbon fiber is improved. Therefore, it becomes easier to obtain a carbon fiber reinforced composite material with few defects such as voids.

In the present invention, epoxy resins that do not exhibit liquid crystallinity, thermosetting resins other than epoxy resins, copolymers of epoxy resins and thermosetting resins, and the like may be included.

Examples of the above thermosetting resins include unsaturated polyester resins, vinyl ester resins, epoxy resins, benzoxazine resins, phenol resins, urea resins, melamine resins and polyimide resins. These resin compositions and compounds may be used alone or may be used by blending them as appropriate. Blending at least an epoxy resin or a thermosetting resin that does not exhibit liquid crystallinity provides both fluidity of the resin and heat resistance after curing.

Among the epoxy resins that do not exhibit liquid crystallinity in the component [B], glycidyl ether type epoxy resins that use phenol as a precursor are preferably used as the bifunctional epoxy resins. Examples of such epoxy resins include bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol S-type epoxy resins, naphthalene-type epoxy resins, biphenyl-type epoxy resins, urethane-modified epoxy resins, hydantoin-type and resorcinol-type epoxy resins. be done.

In the component [B], by containing an epoxy resin that does not exhibit liquid crystallinity by itself, the viscosity of the resin composition is reduced, and the wettability between the epoxy resin and the surface of the component [A] is improved, resulting in interfacial adhesion. is improved, resulting in a fiber reinforced composite with better Mode I interlaminar toughness. Here, the epoxy resin "does not exhibit liquid crystallinity" means that when the temperature is raised from 10 ° C. to 250 ° C. at a rate of temperature increase of 10 ° C./min in differential scanning calorimetry in a nitrogen atmosphere, from 20 ° C. to After confirming the presence or absence of an endothermic peak in the temperature range up to 240 ° C., if there is no endothermic peak, the state at 30 ° C. If there is an endothermic peak, 10 ° C. before and after the endothermic peak (phase transition) This means that a nematic phase structure is not formed in any of the states in the temperature range of . Specifically, it is confirmed that no interference patterns peculiar to the nematic phase structure, such as schlieren texture, filamentous texture, sandy texture, and droplet texture, are observed.

Epoxy resins that do not exhibit liquid crystallinity by themselves are particularly liquid at room temperature (25° C.), while reducing the viscosity of the resin composition and preventing smectic structure formation in the cured product of the resin composition. It is suitable from the point that. The term "liquid" as used herein means that a piece of metal having a specific gravity of 7 or more, which is at the same temperature as the non-liquid crystalline epoxy resin alone, is placed on the non-liquid crystalline epoxy resin alone and is instantly buried by gravity. , the epoxy resin alone that does not exhibit liquid crystallinity is defined as liquid. Examples of metal pieces having a specific gravity of 7 or more include iron (steel), cast iron, and copper.

In the component [B], the content of the epoxy resin that does not exhibit liquid crystallinity by itself is preferably in the range of 1 to 25 parts by mass, and 3 to 25 parts by mass with respect to 100 parts by mass of the entire component [B]. A range is more preferable, and a range of 3 to 20 parts by mass is even more preferable. Within this range, the interfacial adhesion between the epoxy resin and the constituent element [A] is improved without reducing the smectic structure ratio in the cured product of the resin composition, so that the fiber has better mode I interlayer toughness. A reinforced composite material is obtained.

Among the epoxy resins that do not exhibit liquid crystallinity, tri- or higher functional glycidylamine type epoxy resins include, for example, diaminodiphenylmethane type, diaminodiphenylsulfone type, aminophenol type, metaxylenediamine type, and 1,3-bisaminomethylcyclohexane. and isocyanurate-type epoxy resins. Among them, diaminodiphenylmethane-type and aminophenol-type epoxy resins are particularly preferably used because of their well-balanced physical properties.

Examples of trifunctional or higher glycidyl ether type epoxy resins include phenol novolak type, ortho cresol novolak type, trishydroxyphenylmethane type and tetraphenylolethane type epoxy resins.

The component [C] of the present invention is an epoxy resin curing agent having a structure represented by the general formula (1).

(In general formula (1), X ¹ is a single bond or one selected from group (I). P ¹ and P ² may be the same or different, and are shown in group (II). Each W in group (II) is independently an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an aliphatic alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, represents a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group, and each n independently represents an integer of 0 to 4. The substituents W may all be the same or different, or X ² in group (II) is one selected from group (I), F ¹ and F ² are active groups capable of reacting with epoxy groups, and is directly bonded to a six-membered ring selected from If the structure of the substituent W is too large, the viscosity of the epoxy resin composition becomes too high, impairing the handleability, or interfering with other components in the epoxy resin composition. The effect of improving the mechanical properties of the reinforced fiber composite material obtained may be reduced due to the loss of compatibility, etc. In addition, from the viewpoint of flame retardancy, the substituent W is a halogen atom such as Cl or Br. Substituted ones are also preferred.)

In the case of a molecular structure having three or more six-membered rings in the molecular structure of the constituent element [C], the compatibility with the epoxy resin of the constituent element [C] is poor, and in the cured product of the epoxy resin composition, Undissolved curing agents tend to remain. The strength of the cured resin may be lowered because the portion of the undissolved powder becomes the starting point of destruction. For this reason, it is preferable to have two six-membered rings in the molecular structure of the component [C].

Constituent element [C] contained in the epoxy resin composition of the present invention preferably has a structure represented by general formula (1) in which X ¹ is -C(=O)NH-. By introducing an amide skeleton in the center of the molecular structure, a hydrogen bond is formed with the surrounding functional groups having hydrogen bonding properties, so that the skeleton tends to be rigid, and a cured resin product having an excellent resin elastic modulus can be obtained. can be done. In addition, the formation of planar hydrogen bonds between the curing agents into which the amide skeleton is introduced allows the curing agents to be aligned, thereby enhancing the liquid crystallinity, which can also contribute to the increase in the elastic modulus and the increase in heat resistance.

Commercially available products of component [C] include 4,4′-diaminobenzanilide (4,4′-DABAN), 3,4′-diaminobenzanilide (3,4′-DABAN), 4-aminobenzoic acid 4-aminophenyl (4,4'-BAAB), o-tolidine, (bis (4-aminophenyl) terephthalamide (4,4'-APTP) (manufactured by Nippon Junryo Yakuhin Co., Ltd.) and the like. These curing agents may be used singly or in combination, and an epoxy resin and a curing agent, or a product obtained by pre-reacting a part of them, may be blended into the composition. This method may be effective in adjusting viscosity and improving storage stability.

In the present invention, a curing agent other than the component [C] may be used in combination as long as the effect of the invention is not impaired. Curing agents other than component [C] include, for example, diaminodiphenyl sulfone, diaminodiphenyl ether, diaminobenzophenone, dicyandiamide, aminobenzoic acid esters, various acid anhydrides, phenol novolak resins, cresol novolak resins, polyphenol compounds, and imidazole derivatives. , aliphatic amines, and the like.

The optimum amount of curing agent to be added varies depending on the type of epoxy resin and curing agent. For example, an aromatic polyamine curing agent is preferably added in a stoichiometrically equivalent amount. By setting the ratio to 0.0, it is possible to obtain a resin having a higher elastic modulus than when the equivalent weight is used, which is a preferred embodiment. On the other hand, when the ratio of the amount of active hydrogen in the aromatic polyamine curing agent to the amount of epoxy groups in the epoxy resin is 1.0 to 1.6, in addition to improving the curing speed, a resin with high elongation may be obtained. This is also a preferred embodiment. Therefore, the ratio of the amount of active hydrogen in the curing agent to the amount of epoxy groups in the epoxy resin is preferably in the range of 0.7 to 1.6.

In the present invention, a thermoplastic resin may be mixed or dissolved in the epoxy resin composition containing the components [B] and [C] and used. By using a thermoplastic resin, it is possible to control the tackiness of the obtained prepreg and the fluidity of the resin composition when molding the carbon fiber reinforced composite material, so it is preferably used. Such thermoplastic resins generally have a main chain consisting of a carbon-carbon bond, an amide bond, an imide bond, an ester bond, an ether bond, a carbonate bond, a urethane bond, a thioether bond, a sulfone bond and a carbonyl bond. Thermoplastic resins with selected bonds are preferred. Further, this thermoplastic resin may have a partially crosslinked structure, and may be crystalline or amorphous. In particular, polyamides, polycarbonates, polyacetals, polyphenylene oxides, polyphenylene sulfides, polyarylates, polyesters, polyamideimides, polyimides, polyetherimides, polyimides having a phenyltrimethylindane structure, polysulfones, polyethersulfones, polyetherketones, polyetherethers At least one resin selected from the group consisting of ketones, polyaramids, polyethernitrile and polybenzimidazole is preferably mixed or dissolved in any one of the epoxy resins contained in the epoxy resin composition. be.

Above all, in order to obtain good heat resistance, the glass transition temperature (Tg) of the thermoplastic resin is at least 150°C or higher, preferably 170°C or higher. If the glass transition temperature of the thermoplastic resin to be blended is less than 150° C., deformation due to heat may easily occur when used as a molded article. Furthermore, as terminal functional groups of this thermoplastic resin, hydroxyl groups, carboxyl groups, thiol groups, acid anhydrides and the like can react with the cationic polymerizable compound and are preferably used. Specifically, commercially available polyethersulfone products "Sumika Excel (registered trademark)" PES3600P, "Sumika Excel (registered trademark)" PES5003P, "Sumika Excel (registered trademark)" PES5200P, "Sumika Excel (registered trademark)" "PES7600P (manufactured by Sumitomo Chemical Co., Ltd.), Virantage (registered trademark)" VW-10200RFP, "Virantage (registered trademark)" VW-10700RFP (manufactured by Solvay Advanced Polymers Co., Ltd.), etc. Also, a copolymer oligomer of polyether sulfone and polyether ether sulfone as described in JP-T-2004-506789, and "Ultem (registered trademark)" 1000, which is a commercial product of polyetherimide, "Ultem (registered trademark)" 1010, "Ultem (registered trademark)" 1040 (manufactured by Solvay Advanced Polymers Co., Ltd.), etc. An oligomer is a finite number of monomers of about 10 to 100 bound together. It refers to polymers with relatively low molecular weights.

In the present invention, the epoxy resin composition containing the constituent elements [B] and [C] may further contain an elastomer. Such an elastomer is blended for the purpose of forming a fine elastomer phase within the epoxy matrix phase after curing. As a result, the plane strain that occurs when stress is applied to the cured resin can be eliminated by breaking voids (cavitation) in the elastomer phase, and plastic deformation of the epoxy matrix phase is induced, resulting in large energy absorption. This leads to further improvement in interlayer toughness as a carbon fiber reinforced composite material.

Elastomers are polymeric materials having domains with a glass transition temperature below 20°C, including liquid rubbers, solid rubbers, crosslinked rubber particles, core-shell rubber particles, thermoplastic elastomers, and blocks with a glass transition temperature below 20°C. and block copolymers having Above all, the elastomer is preferably selected from block copolymers containing blocks having a glass transition temperature of 20° C. or less and rubber particles. As a result, it is possible to introduce a fine elastomer phase while minimizing the compatibility of the elastomer with the epoxy resin, so it is possible to greatly improve the interlayer toughness as a carbon fiber reinforced composite material while suppressing the deterioration of heat resistance and elastic modulus. can be made

As the rubber particles, crosslinked rubber particles and core-shell rubber particles obtained by graft-polymerizing a different polymer on the surface of crosslinked rubber particles are preferably used from the viewpoint of handleability and the like. The primary particle size of such rubber particles is preferably in the range of 50 to 300 nm, particularly preferably in the range of 80 to 200 nm. Moreover, it is preferable that such rubber particles have good affinity with the epoxy resin to be used and do not cause secondary agglomeration during resin preparation and molding curing.

Commercial products of crosslinked rubber particles include FX501P (manufactured by Nippon Synthetic Rubber Industry Co., Ltd.), which is a crosslinked product of carboxyl-modified butadiene-acrylonitrile copolymer, and CX-MN series (Nippon Shokubai Co., Ltd.), which is composed of acrylic rubber fine particles. ), YR-500 series (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) and the like can be used.

Commercially available core-shell rubber particles include, for example, "Paraloid (registered trademark)" EXL-2655 (manufactured by Kureha Co., Ltd.) composed of a butadiene/alkyl methacrylate/styrene copolymer, and an acrylic acid ester/methacrylic acid ester copolymer. "Staphyloid (registered trademark)" AC-3355 and TR-2122 (manufactured by Takeda Pharmaceutical Co., Ltd.) composed of coalescence, "PARALOID (registered trademark)" EXL-2611 composed of butyl acrylate/methyl methacrylate copolymer , EXL-3387 (manufactured by Rohm & Haas), "Kane Ace (registered trademark)" MX series (manufactured by Kaneka Corporation), and the like can be used.

In the present invention, it is also suitable to blend thermoplastic resin particles into the epoxy resin composition of the present invention. By blending the thermoplastic resin particles, the toughness of the resin composition is improved and the impact resistance is improved when it is made into a carbon fiber reinforced composite material.

As the raw material for the thermoplastic resin particles used in the present invention, the same thermoplastic resins as those exemplified above can be used as thermoplastic resins that can be used by mixing or dissolving them in the epoxy resin composition. From the viewpoint of providing stable adhesive strength and impact resistance when made into a carbon fiber reinforced composite material, it is preferable that the particles retain their shape. Among them, polyamide is the most preferable, and among polyamides, polyamide 12, polyamide 11, polyamide 6, polyamide 66 and polyamide 6/12 copolymer, semi-IPN ( Polymer interpenetrating network structure) polyamide (semi-IPN polyamide) and the like can be preferably used. The shape of the thermoplastic resin particles may be spherical particles, non-spherical particles, or porous particles. This is a preferred embodiment in terms of imparting high impact resistance. The number average particle diameter of the thermoplastic resin particles is preferably in the range of 1 μm to 100 μm, more preferably in the range of 5 μm to 40 μm, and even more preferably in the range of 10 μm to 30 μm. If the number average particle size is too small, the particles may enter between the fibers of the carbon fiber and reduce the impact resistance and other mechanical properties. On the other hand, if the number average particle diameter is too large, the arrangement of carbon fibers is disturbed due to the presence of large diameter particles, and the thickness of the carbon fiber reinforced composite material obtained by laminating prepregs becomes thick, resulting in a relatively large number of fibers. It can lower the volume fraction and degrade its mechanical properties. Here, the number-average particle size is obtained by observing the thermoplastic particles with a laser microscope (ultra-depth color 3D shape measuring microscope VK-9510: manufactured by Keyence Corporation) at a magnification of 200 times or more, and 50 arbitrary particles. For the above particles, after measuring the diameter of the circle circumscribing the particle as the particle size, the average value is used. The amount of the thermoplastic resin particles to be blended is preferably 1 to 50 parts by mass, preferably 3 to 25 parts by mass, per 100 parts by mass of the total resin composition. If the amount of the thermoplastic resin added is too small, there is a possibility that a sufficient effect of improving impact resistance cannot be obtained in the carbon fiber reinforced composite material.

Commercially available polyamide particles include SP-500, SP-10, TR-1, TR-2, 842P-48, 842P-80 (manufactured by Toray Industries, Inc.), and "Orgasol (registered trademark)" 1002D. , 2001UD, 2001EXD, 2002D, 3202D, 3501D, 3502D, (manufactured by Arkema Co., Ltd.), "Grilamid (registered trademark)" TR90 (manufactured by Mzawerke Co., Ltd.), "TROGAMID (registered trademark)" CX7323, CX9701 , CX9704 (manufactured by Degussa Corporation) and the like can be used. These polyamide particles may be used alone or in combination.

The epoxy resin composition of the present invention contains a coupling agent, thermosetting resin particles, thermoplastic resins soluble in epoxy resin, silica gel, carbon black, clay, carbon nanotubes, as long as the effects of the present invention are not hindered. , inorganic fillers such as metal powder, etc. can be blended.

The prepreg of the present invention preferably has a carbon fiber mass fraction of 40 to 90% by mass, more preferably 50 to 80% by mass. If the carbon fiber mass fraction is too low, the resulting composite material will have an excessive mass, and the advantage of the carbon fiber reinforced composite material, which is excellent in specific strength and specific elastic modulus, may be impaired. If it is too high, impregnation of the resin composition will be imperfect, the resulting composite material will tend to have many voids, and the mechanical properties will be greatly reduced.

The prepreg of the present invention can be produced by a wet method in which the epoxy resin composition of the present invention is dissolved in a solvent such as methyl ethyl ketone or methanol to reduce the viscosity and impregnated into carbon fibers, and a wet method in which the epoxy resin composition is heated to reduce the viscosity. It can be suitably produced by a hot-melt method or the like in which fibers are impregnated.

The wet method is a method of obtaining a prepreg by immersing carbon fibers in a solution of an epoxy resin composition, pulling them out, and evaporating the solvent using an oven or the like.

The hot melt method is a method of directly impregnating the carbon fiber with an epoxy resin composition whose viscosity has been reduced by heating, or a resin film is prepared by coating the epoxy resin composition on release paper or the like, and then the carbon fiber This is a method of obtaining a prepreg by superimposing the resin film from both sides or one side of the sheet and applying heat and pressure to transfer and impregnate the epoxy resin composition. This hot-melt method is a preferred embodiment because substantially no solvent remains in the prepreg.

When the prepreg is produced by the hot-melt method, the viscosity of the resin composition is preferably 0.01 to 30 Pa·s as the minimum viscosity measured by the method described later. The minimum viscosity of the resin composition referred to here is measured using a dynamic viscoelasticity measuring device (ARES, manufactured by TA Instruments) using a parallel plate, while increasing the temperature at a rate of 2° C./min. The complex viscosity η ^* measured at 5 Hz and a plate interval of 1 mm shows the lowest value in the temperature range of 40-180°C.

The prepreg preferably has a carbon fiber content of 50 to 1000 g/m ² per unit area. If the amount of carbon fiber is less than 50 g/m ² , the number of layers to be laminated must be increased in order to obtain a predetermined thickness when molding the carbon fiber reinforced composite material, and the work may become complicated. On the other hand, when the amount of carbon fibers exceeds 1000 g/m ² , the drapeability of the prepreg tends to deteriorate.

The carbon fiber reinforced composite material of the present invention can be produced by laminating the prepregs of the present invention described above in a predetermined form, pressing and heating, and molding as an example. Methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape, and internal pressure molding. In particular, the wrapping tape method and the internal pressure molding method are preferably used for molding sporting goods.

The wrapping tape method is a method of winding a prepreg around a metal core such as a mandrel to form a tubular body made of a carbon fiber reinforced composite material, and is a suitable method for producing rod-shaped bodies such as golf shafts and fishing rods. be. More specifically, a prepreg is wound around a mandrel, a wrapping tape made of a thermoplastic resin film is wound around the prepreg for fixing and applying pressure to the prepreg, and the epoxy resin is heated and cured in an oven. In this method, the core is removed to obtain a tubular body.

In the internal pressure molding method, a preform obtained by winding a prepreg around an internal pressure imparting body such as a thermoplastic resin tube is set in a mold, and then a high-pressure gas is introduced into the internal pressure imparting body to apply pressure. At the same time, the mold is heated to form a tubular body. This internal pressure molding method is particularly preferably used when molding complex shapes such as golf shafts, bats, and rackets for tennis, badminton, and the like.

The carbon fiber reinforced composite material of the present invention can also be produced using the epoxy resin composition described above by a method that does not involve prepreg.

Such methods include, for example, a method in which carbon fibers are directly impregnated with the resin composition of the present invention containing the constituent elements [B] and [C] and then heat-cured, that is, a hand lay-up method and filament winding. method, pultrusion method, resin film infusion method in which a resin composition is impregnated and cured in a continuous fiber base material preformed into a member shape, resin injection molding method and resin transfer molding (RTM) Laws, etc. are used.

The epoxy resin composition according to the present invention can be used for VARTM (Vaccum-assisted Resin Transfer Molding) and VIMP (Variable Infusion Molding Process), which are listed in the review on the RTM method (SAMPE Journal, Vol. 34, No. 6, pp. 7-19). ), TERTM (Thermal Expansion RTM), RARTM (Rubber-Assisted RTM), RIRM (Resin Injection Recirculation Molding), CRTM (Continuous RTM), CIRTM (Co-injection Resin Transfer Molding) , RLI (Resin Liquid Infusion), SCRIMP ( It is also suitable for molding methods such as Seeman's Composite Resin Infusion Molding Process).

EXAMPLES The present invention will be described in detail below with reference to examples. However, the scope of the present invention is not limited to these examples. In addition, the unit "part" of a composition ratio means a mass part unless there is a comment in particular. In addition, measurements of various properties (physical properties) were performed under an environment of 23° C. temperature and 50% relative humidity unless otherwise noted.

<Raw materials used in Examples and Comparative Examples>
(1) Component [A]
・Carbon fiber 1
A polyacrylonitrile copolymer mainly composed of acrylonitrile is spun and baked, and the total number of filaments is 24,000, the total fineness is 1,000 tex, the specific gravity is 1.8, the strand tensile strength is 6.6 GPa, and the strand tensile modulus is 324 GPa. A carbon fiber was obtained. Next, the carbon fibers were subjected to an electrolytic surface treatment using an ammonium hydrogen carbonate aqueous solution as an electrolytic solution with an amount of electricity of 80 coulombs per 1 g of the carbon fibers. The electrolytic surface-treated carbon fibers were then washed with water and dried in hot air to obtain carbon fibers as a raw material. The surface oxygen concentration O/C was 0.16 when measured according to the method described in (5) below.

A sizing agent prepared by mixing "jER (registered trademark)" 152 (manufactured by Mitsubishi Chemical Corporation) and polyglycerin polyglycidyl ether is applied to the surface-treated carbon fiber by an immersion method, followed by heat treatment and application of the sizing agent. A carbon fiber bundle was obtained. The adhesion amount of the sizing agent was adjusted so as to be 0.6% by mass with respect to the sizing agent-coated carbon fiber.

When the carbon fiber thus produced was measured according to the method described in (7) below, the sizing agent adhesion amount after washing was 0.16% by mass, which was a preferable adhesion amount. Further, the interfacial adhesion strength measured by the method described in (8) below was 44 MPa.

・Carbon fiber 2
A polyacrylonitrile copolymer mainly composed of acrylonitrile is spun and baked, and the total number of filaments is 12,000, the total fineness is 1,000 tex, the specific gravity is 1.8, the strand tensile strength is 4.9 GPa, and the strand tensile modulus is 230 GPa. A carbon fiber was obtained. Next, the carbon fibers were subjected to an electrolytic surface treatment using an ammonium hydrogen carbonate aqueous solution as an electrolytic solution with an amount of electricity of 80 coulombs per 1 g of the carbon fibers. The electrolytic surface-treated carbon fibers were then washed with water and dried in hot air to obtain carbon fibers as a raw material. At this time, the surface oxygen concentration O/C was 0.15.

Using this carbon fiber, a sizing agent-coated carbon fiber bundle was obtained in the same manner as the carbon fiber 1. The adhesion amount of the sizing agent was adjusted so as to be 0.6% by mass with respect to the sizing agent-coated carbon fiber. The sizing agent adhesion amount after washing was 0.17% by mass, which was a preferable adhesion amount. Moreover, the interfacial adhesive strength was 43 MPa.

・Carbon fiber 3
A polyacrylonitrile copolymer mainly composed of acrylonitrile is spun and baked, and the total number of filaments is 24,000, the total fineness is 1,000 tex, the specific gravity is 1.8, the strand tensile strength is 5.9 GPa, and the strand tensile modulus is 294 GPa. A carbon fiber was obtained. Then, the carbon fibers were subjected to an electrolytic surface treatment using an aqueous solution of ammonium hydrogen carbonate as an electrolytic solution with an amount of electricity of 120 coulombs per 1 g of the carbon fibers. The electrolytic surface-treated carbon fibers were then washed with water and dried in hot air to obtain carbon fibers as a raw material. At this time, the surface oxygen concentration O/C was 0.20.

Using this carbon fiber, a sizing agent-coated carbon fiber bundle was obtained in the same manner as the carbon fiber 1. The adhesion amount of the sizing agent was adjusted so as to be 0.6% by mass with respect to the sizing agent-coated carbon fiber. The sizing agent adhesion amount after washing was 0.19% by mass, which was a preferable adhesion amount. Moreover, the interfacial adhesive strength was 45 MPa.

・Carbon fiber 4
A sizing agent-coated carbon fiber bundle was obtained in the same manner as the carbon fiber 3, except that the electrolytic surface treatment was performed with an amount of electricity of 80 coulombs per gram of carbon fiber. The surface oxygen concentration O/C was 0.15. The adhesion amount of the sizing agent was adjusted so as to be 0.6% by mass with respect to the sizing agent-coated carbon fiber. The sizing agent adhesion amount after washing was 0.16% by mass, which was a preferable adhesion amount. Moreover, the interfacial adhesive strength was 43 MPa.

・Carbon fiber 5
A sizing agent-coated carbon fiber bundle was obtained in the same manner as in carbon fiber 3, except that the electrolytic surface treatment was performed with an amount of electricity of 40 coulombs per 1 g of carbon fiber. The surface oxygen concentration O/C was 0.13. The adhesion amount of the sizing agent was adjusted so as to be 0.6% by mass with respect to the sizing agent-coated carbon fiber. The sizing agent adhesion amount after washing was 0.12% by mass, which was a preferable adhesion amount. Moreover, the interfacial adhesive strength was 29 MPa.

・Carbon fiber 6
A sizing agent-coated carbon fiber bundle was obtained in the same manner as the carbon fiber 3, except that the electrolytic surface treatment was performed with sulfuric acid as an electrolyte and an amount of electricity of 20 coulombs per 1 g of carbon fiber. The surface oxygen concentration O/C was 0.12. The adhesion amount of the sizing agent was adjusted so as to be 0.6% by mass with respect to the sizing agent-coated carbon fiber. The sizing agent adhesion amount after washing was 0.13% by mass, which was a preferable adhesion amount. Moreover, the interfacial adhesive strength was 27 MPa.

・Carbon fiber 7
A sizing agent-coated carbon fiber bundle was obtained in the same manner as carbon fiber 6, except that the electrolytic surface treatment was performed with an amount of electricity of 10 coulombs per 1 g of carbon fiber, and ethylene glycol was used instead of polyglycerin polyglycidyl ether. The surface oxygen concentration O/C was 0.09. The adhesion amount of the sizing agent was adjusted so as to be 0.6% by mass with respect to the sizing agent-coated carbon fiber. The sizing agent adhesion amount after washing was 0.05% by mass. Moreover, the interfacial adhesive strength was 21 MPa.

・Carbon fiber 8
A sizing agent-coated carbon fiber bundle was obtained in the same manner as the carbon fiber 7, except that the electrolytic treatment was not performed. The surface oxygen concentration O/C was 0.02. The adhesion amount of the sizing agent was adjusted so as to be 0.6% by mass with respect to the sizing agent-coated carbon fiber. The sizing agent adhesion amount after washing was 0.02% by mass. The interfacial adhesive strength was 18 MPa.

(2) Component [B]
<Epoxy resin that exhibits liquid crystallinity by itself>
・Epoxy resin 1
Compound name: 2-methyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)benzoate}, see JP-A-2010-241797, epoxy equivalent: 245 g/eq) is heated and melted at 200 ° C. Then, resorcinol (hydroxyl equivalent: 55 g/eq) was added as a prepolymerizing agent so that the ratio of epoxy equivalents:hydroxyl equivalents was 100:25, and the mixture was heated at 200°C for 3 hours in a nitrogen atmosphere to form epoxy resin. Resin 1 was obtained. The content of the prepolymer is 53 parts by mass with respect to a total of 100 parts by mass of 2-methyl-1,4-phenylene-bis{4-(2,3-epoxypropoxy)benzoate and its prepolymer, and conforms to JIS K7236. When the epoxy equivalent was measured according to the method, it was 353 g/eq.

・Epoxy resin 2
Compound name: 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate, see Japanese Patent No. 5471975, epoxy equivalent: 213 g/eq) is heated to 200°C. It was melted, resorcinol (hydroxyl equivalent: 55 g/eq) was added as a prepolymerizing agent so that the ratio of epoxy equivalents:hydroxyl equivalents was 100:25, and heated at 200°C for 3 hours in a nitrogen atmosphere. Epoxy resin 2 was obtained. The content of the prepolymer is 53 parts by mass with respect to a total of 100 parts by mass of 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate and its prepolymer. The epoxy equivalent was measured according to JIS K7236 and found to be 320 g/eq.

・Epoxy resin 3
Compound name: 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate, see Japanese Patent No. 5471975, epoxy equivalent: 213 g/eq) is heated to 200°C. Melt, add bisphenol F (hydroxyl equivalent: 100 g/eq) as a prepolymerizing agent to the mixture so that the ratio of epoxy equivalents to hydroxyl equivalents is 100:15, and heat at 200°C for 3 hours in a nitrogen atmosphere. Epoxy resin 3 was thus obtained. The content of the prepolymer is 38 parts by mass with respect to a total of 100 parts by mass of 4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate and its prepolymer. The epoxy equivalent was measured according to JIS K7236 and found to be 309 g/eq.

<Epoxy resin that does not show liquid crystallinity>
・ “Araldite (registered trademark)” MY0610 (triglycidyl-m-aminophenol, manufactured by Huntsman Japan Co., Ltd.)
・ “jER (registered trademark)” YX4000H (biphenyl type epoxy resin, manufactured by Mitsubishi Chemical Corporation)
・ “jER (registered trademark)” 604 (tetraglycidyldiaminodiphenylmethane, manufactured by Mitsubishi Chemical Corporation)
- "jER (registered trademark)" 828 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation).

(3) Component [C]
· 4,4'-DABAN (4,4'-diaminobenzanilide, manufactured by Nippon Junryo Pharmaceutical Co., Ltd.)
· 3,4'-DABAN (3,4'-diaminobenzanilide, manufactured by Nippon Junryo Pharmaceutical Co., Ltd.)
・ o-Tolidine (3,3′-dimethylbenzidine, manufactured by Nippon Junryo Yakuhin Co., Ltd.)
· 4,4'-BAAB (4-aminophenyl 4-aminobenzoate, manufactured by Nippon Junryo Yakuhin Co., Ltd.))
- 4,4'-APTP (bis(4-aminophenyl)terephthalamide, manufactured by Nippon Junryo Yakuhin Co., Ltd.).

(4) Other components/components Curing agent other than [C] “Seikacure (registered trademark)”-S (4,4′-diaminodiphenylsulfone, manufactured by Wakayama Seika Co., Ltd.)
- Thermoplastic resin "Virantage (registered trademark)" VW-10700RFP (polyethersulfone, manufactured by Solvay Advanced Polymers Co., Ltd.).

<Various evaluation methods>
(5) Measurement of Surface Oxygen Concentration O/C of Carbon Fiber The surface oxygen concentration (O/C) of carbon fiber was obtained by X-ray photoelectron spectroscopy according to the following procedure. First, the carbon fiber, from which dirt adhering to the surface was removed with a solvent, was cut to about 20 mm and spread on a copper sample support. Next, the sample support was set in the sample chamber, and the inside of the sample chamber was maintained at 1×10 ⁻⁸ Torr. Subsequently, AlK _{α1, 2} was used as the X-ray source, and the photoelectron escape angle was set to 90° for measurement. The binding energy value of the main peak (peak top) of C1s was adjusted to 284.6 eV as a peak correction value associated with charging during measurement. The C _1s main area was determined by drawing a straight baseline in the range 282-296 eV. The O _1s peak area was obtained by drawing a straight baseline in the range of 528-540 eV. Here, the surface oxygen concentration is calculated as an atomic number ratio from the ratio of the O _1s peak area to the C _1s peak area using the apparatus-specific sensitivity correction value. As an X-ray photoelectron spectroscopy apparatus, ESCA-1600 manufactured by ULVAC-Phi, Inc. was used, and the sensitivity correction value unique to the apparatus was 2.33.

(6) Measurement of sizing agent adhesion amount The sizing agent adhesion amount of the sizing-coated carbon fiber was determined according to the following procedure. First, 2±0.5 g of sizing-coated carbon fiber was sampled and heat-treated at 450° C. for 15 minutes in a nitrogen atmosphere. The mass % of the value obtained by dividing the amount of change in mass before and after the heat treatment by the mass before the heat treatment was defined as the adhesion amount of the sizing agent.

(7) Measurement of sizing agent adhesion amount after washing The adhesion amount of the sizing agent after washing was measured as follows. First, 2 ± 0.5 g of sizing agent-coated carbon fibers are immersed in 10 ml of a solution in which acetonitrile and chloroform are mixed at a volume ratio of 9:1, and ultrasonically cleaned for 20 minutes to elute the sizing agent from the fibers. It was dried and weighed. Further, after washing, the carbon fibers were heat-treated at 450° C. for 15 minutes in a nitrogen atmosphere. The amount of change in mass before and after the heat treatment was divided by the mass before the heat treatment, and the mass % of the value was taken as the adhesion amount of the sizing agent after cleaning.

(8) Measurement of interfacial shear strength (IFSS) Interfacial shear strength (IFSS) was measured by the following procedures (a) to (d).

(B) Preparation of resin 100 parts by mass of bisphenol A type epoxy compound "jER (registered trademark)" 828 (manufactured by Mitsubishi Chemical Corporation) and 14.5 parts by mass of metaphenylenediamine (manufactured by Sigma-Aldrich Japan Co., Ltd.) placed in each container. After that, it was heated at a temperature of 75° C. for 15 minutes in order to reduce the viscosity of jER828 and dissolve the meta-phenylenediamine. After that, both were well mixed and vacuum defoaming was performed at a temperature of 80° C. for about 15 minutes.

(b) Fixing carbon fiber single yarn to special mold A single fiber was pulled out from the carbon fiber bundle, and both ends were fixed with an adhesive while a constant tension was applied to the single fiber in the longitudinal direction of the dumbbell-shaped mold. Thereafter, vacuum drying was performed at a temperature of 80° C. for 30 minutes or longer in order to remove water adhering to the carbon fibers and the mold. The dumbbell mold was made of silicone rubber, and the shape of the cast part was 5 mm wide at the center, 25 mm long, 10 mm wide at both ends, and 150 mm long.

(C) From resin casting to curing Pour the resin prepared in the above procedure (A) into the mold after vacuum drying in the above procedure (B), and use an oven to raise the temperature at a rate of 1.5 ° C./ After the temperature was raised to 75°C at 1.5°C/min and held for 2 hours, the temperature was raised to 125°C at a temperature rise rate of 1.5°C/min and held for 2 hours. The temperature has dropped. After that, the mold was removed to obtain a test piece.

(D) Measurement of interfacial shear strength (IFSS) A tensile force is applied to the test piece obtained by the procedure in (C) above at a strain rate of 0.3% / sec in the fiber axis direction (longitudinal direction), and the strain is 12%. After forming, the number of fiber breakages N (pieces) in the range of 22 mm from the center of the test piece was measured with a polarizing microscope. Next, the average broken fiber length la was calculated by the formula la (μm)=22×1000 (μm)/N (pieces). Next, the critical fiber length lc was calculated from the average broken fiber length la by the formula lc (μm)=(4/3)×la (μm). The strand tensile strength σ and the diameter d of the carbon fiber single yarn were measured, and the interfacial shear strength IFSS, which is an index of the adhesive strength between the carbon fiber and the resin interface, was calculated by the following formula. In the examples, the average of the number of measurements n=5 was used as the test result.
- Interfacial shear strength IFSS (MPa) = σ (MPa) x d (μm) / (2 x lc) (μm).

(9) Preparation of epoxy resin composition In a kneader, a predetermined amount of components other than the curing agent and the curing accelerator are added at the compounding ratio (parts by mass) shown in Table 1, and the mixture is heated to 160°C while kneading. By kneading at 160° C. for 1 hour, a transparent viscous liquid was obtained. After the temperature was lowered to 80° C. while kneading, a predetermined amount of a curing agent was added and further kneaded to obtain an epoxy resin composition.

(10) Production of prepreg The epoxy resin composition was applied onto release paper using a knife coater to produce a resin film. Next, two resin films are superimposed on the carbon fibers of the component [A] arranged in one direction in a sheet form from both sides of the carbon fibers, and the carbon fibers are impregnated with the resin by heating and pressing, and the basis weight of the carbon fibers is obtained. was 190 g/m ² and the weight fraction of the resin composition was 35%.

(11) Preparation of composite material flat plate for mode I interlaminar toughness (G _IC ) test and measurement of G _IC According to JIS K7086 (1993), a composite material for G _IC test is manufactured by the following operations (a) to (e). A flat plate was produced.

(a) 20 plies of the unidirectional prepreg produced in (10) were laminated with the fiber direction aligned. However, a fluororesin film having a width of 40 mm and a thickness of 50 μm was sandwiched between the lamination center plane (between the 10th ply and the 11th ply) perpendicularly to the fiber arrangement direction.

(b) The laminated prepregs were covered with a nylon film without gaps, and cured by heating and pressing in an autoclave at 180° C. for 2 hours at an internal pressure of 0.59 MPa to form a unidirectional carbon fiber reinforced composite material.

(c) The unidirectional carbon fiber reinforced composite material obtained in (b) was cut into a width of 20 mm and a length of 195 mm. The fiber direction was cut so as to be parallel to the length side of the test piece.

(d) Since the pin loading block (25 mm in length, made of aluminum) described in JIS K7086 (1993) had its adhesive part peeled off during the test, a triangular grip was used instead (Fig. 1). Notches with a length of 1 mm were made at both ends in the width direction at a position 4 mm from the end of the test piece (the side on which the fluororesin film was sandwiched), and a triangular grip was hooked. In the test, a load was applied to the test piece by pulling a triangular jig with a crosshead of an Instron universal testing machine (manufactured by Instron).

(e) White paint was applied to both sides of the test piece to facilitate observation of crack growth.

Using the composite material flat plate thus produced, _GIC measurement was performed according to the following procedure. According to JIS K7086 (1993) Annex 1, the test was performed using an Instron universal testing machine (manufactured by Instron). The crosshead speed was 0.5 mm/min until the crack growth reached 20 mm, and 1 mm/min after reaching 20 mm. The test was conducted until the crack propagated by 100 mm, and the G _IC was calculated from the area of the load-displacement diagram obtained during the test.

(12) 0° compressive strength measurement Cut a unidirectional prepreg into a predetermined size, laminate 6 sheets in one direction, vacuum bag, and use an autoclave at a temperature of 180 ° C and a pressure of 0.59 MPa for 2 hours. to obtain a unidirectional reinforcing material (carbon fiber composite material). After bonding the tab to this unidirectional reinforcing material in accordance with SACMA-SRM 1R-94, a rectangular test piece having a length of 80.0 mm and a width of 15.0 mm was prepared with the 0 ° direction as the length direction of the test piece. cut out. The obtained 0° direction compression test piece was placed in a 23° C. environment according to SACMA-SRM 1R-94, and a material universal testing machine (manufactured by Instron Japan Co., Ltd., “Instron (registered trademark)” 5565 type P8564 ) at a test speed of 1.0 mm/min.

(13) Observation with a polarizing microscope Cut the unidirectional prepreg prepared in (10) into a width of 50 mm and a length of 50 mm. It was cured for 2 hours to obtain a carbon fiber reinforced composite material specimen for observation. The resin region of the specimen was observed with a polarizing microscope (manufactured by Keyence Corporation; VHX-5000, with a polarizing filter). A case in which formation of a higher-order structure such as a fan-shaped structure or a focal conic structure was observed (bright field) was rated as "A", and a case in which no higher-order structure was observed (dark field) was rated as "B".

(14) Measurement of diffraction angle 2θ by X-ray diffraction After laminating the unidirectional prepregs produced in (10) to a thickness of about 1 mm, the laminated prepregs are covered with a nylon film without any gaps, and placed in an autoclave. At 180° C. for 2 hours, the mixture was cured by heating and pressurizing at an internal pressure of 0.59 MPa to form a unidirectional carbon fiber reinforced composite material. Using the molded carbon fiber reinforced composite material, it was cut into a length of 20 mm and a width of 10 mm to obtain a test piece. Measurements were made parallel (0°), perpendicular (90°), and 45° to the carbon fiber axis in the carbon fiber composite material under the following conditions.
・Apparatus: X'PertPro (manufactured by Spectris Co., Ltd. PANalytical Division)
・X-ray source: CuKα ray (tube voltage 45 kV, tube current 40 mA)
・Detector: goniometer + monochromator + scintillation counter ・Scanning range: 2θ = 1 to 90°
Scanning mode: step scan, step unit 0.1°, counting time 40 seconds Moreover, when it does not have a peak, it described as "B."

(15) Measurement of Molecular Anisotropy in Cured Resin Material by Polarized Raman Spectroscopy A test piece was obtained by cutting a 2 cm square from the carbon fiber composite material produced in (10). The measurement was performed under the following conditions at five arbitrary locations on the resin portion in the carbon fiber composite material.
・ Apparatus: PDP320 (manufactured by PHOTO Design Co., Ltd.)
・Beam diameter: 1 μm
・Light source: YAG laser/1064 nm
・Diffraction grating: Single 300gr/mm
・Slit: 100 μm
・Detector: CCD: Jobin Yvon 1024×256
- Objective lens: x100.

Polarized Raman spectroscopy was measured by changing the polarization direction from 0° to 150 at intervals of 30°, with the arbitrary direction of the measured test piece set to 0°. Regarding the Raman band intensity near 1600 cm ⁻¹ derived from the C=C stretching vibration of the aromatic ring, if it has a polarization orientation that varies by ±20% or more, it is considered anisotropic in Tables 1 and 2. If the fluctuation width was 20% or less at any of the five measured points in the range of 0° to 150° of the polarization direction, it was indicated as "B" in Tables 1 and 2 as no anisotropy.

(16) Measurement of heat resistance Cut a unidirectional prepreg into a predetermined size, laminate 12 prepregs in one direction, vacuum bag, and cure in an autoclave at a temperature of 180 ° C. and a pressure of 0.59 MPa for 2 hours. to obtain a unidirectional reinforcing material (carbon fiber composite material). A rectangular test piece having a length of 50.0 mm and a width of 12.7 mm was cut from the unidirectional reinforcing material with the 0° direction as the longitudinal direction of the test piece. The resulting 0° direction test piece was subjected to torsional strain DMA measurement during the heating process at 5°C/min from 40°C to 300°C. The glass transition temperature was defined as the point of intersection obtained by extending the two linear portions of the obtained storage modulus change curve. The two linear portions are a linear portion before the rapid decrease in storage modulus and a linear portion appearing in the process of rapid decrease in storage elastic modulus.

(Examples 1 to 16, Comparative Examples 1 to 5)
Epoxy resin compositions for carbon fiber reinforced composite materials were prepared according to the compounding ratios shown in Tables 1 and 2 by the procedure of (9) Epoxy resin composition preparation. Using the obtained epoxy resin composition, a prepreg was obtained according to the procedure of (10) Preparation of prepreg. Using the obtained prepreg, the above (11) preparation of composite material flat plate for mode I interlaminar toughness (G _IC ) test and G _IC measurement, and (12) preparation of composite material flat plate for 0° tensile strength test (13) observation with a polarizing microscope, (14) measurement of diffraction angle 2θ by X-ray diffraction, and (15) measurement of anisotropy in the resin composition by polarized Raman spectroscopy. Table 1 shows the results.

Various measurement results of Examples are shown in Table 1, and various measurement results of Comparative Examples are shown in Table 2. As in Examples 1 to 16, carbon fibers having a resin composition having a higher-order structure and a preferable surface oxygen concentration , excellent mode I interlaminar toughness G _IC , 0° compressive strength, and heat resistance were obtained.

Comparative Example 1 uses the constituent elements [A], [B], and [C] of the present invention, but the cured product of the resin composition does not form a higher-order structure. Compared to Example 1 using the same components [A] and [C], Comparative Example 1 has a substantially lower Mode I interlaminar toughness G _IC while having an equivalent 0° compressive strength. It can be seen that the mode I interlaminar toughness G _IC is dramatically improved.

In Comparative Examples 2 and 3, the constituent elements [B] and [C] of the present invention were used, and the cured product of the resin composition formed a higher-order structure, but the surface of the constituent element [A] This is the case where the oxygen concentration is low and does not satisfy the requirements of the component [A] of the present invention. In this case, components [B] and [C] have significantly lower Mode I interlaminar toughness G _IC compared to identical Examples 1 and 7, respectively, satisfying the component [A] requirements of the present invention. Therefore, it can be seen that the mode I interlaminar toughness _GIC is dramatically improved.

Comparative Examples 4 and 5 are cases in which the constituent elements [A] and [B] of the present invention are used and the cured product of the resin composition forms a higher-order structure, but the requirements for the constituent element [C] are satisfied. This is the case when using a curing agent that does not have Due to the formation of a higher-order structure, the mode I interlaminar toughness G _IC is a higher value than in the case of no formation of a higher-order structure, but the same constituent elements [A] and [B] were used, respectively. Compared to Examples 4 and 3, the 0° compressive strength and heat resistance are particularly low, and it can be seen that the 0° compressive strength and heat resistance can be improved by the curing agent that satisfies the component [C] of the present invention.

Example 9 is a case of using a curing agent having three six-membered rings in its molecular structure as the component [C] of the present invention. In this case, it was found that due to the formation of higher-order structures, the high mode I interlaminar toughness G _IC and the rigid skeleton hardener developed a high 0° compressive strength when compared to Comparative Example 5, but the same constituent [A ] and [B], the 0° compressive strength was lower than that of Example 6. The reason for this is considered to be the constituent element [C] that remains slightly undissolved in the cured product of the resin composition. From the viewpoint of not leaving undissolved residue, the constituent element [C] preferably has two six-membered ring structures in its molecular structure.

Comparing Example 10 with Examples 1, 13, and 15, as the constituent element [B], in addition to the epoxy resin that shows liquid crystallinity by itself, the epoxy resin that does not show liquid crystallinity by itself is used as constituent element [B]. By including 1 to 25 parts by mass with respect to parts by mass, mode I interlaminar toughness (G _IC ) and 0° compressive strength are improved while maintaining heat resistance.

Claims (10)

A prepreg that contains the following components [A] to [C] and satisfies the conditions [I] and [II].
[A]: Carbon fiber [B]: Epoxy resin [C]: Curing agent having a structure represented by general formula (1).

(In general formula (1), X ¹ is a single bond or one selected from group (I). P ¹ and P ² may be the same or different, and are shown in group (II). Each W in group (II) is independently an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an aliphatic alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, represents a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group, and each n independently represents an integer of 0 to 4. The substituents W may all be the same or different, or X ² in group (II) is one selected from group (I), F ¹ and F ² are active groups capable of reacting with epoxy groups, and directly attached to a six-membered ring selected from

[I]: The surface oxygen concentration O/C of [A] measured by X-ray photoelectron spectroscopy is 0.10 or more.
[II]: A cured product of an epoxy resin composition containing components [B] and [C] contains a resin region having molecular anisotropy that exhibits an interference pattern when observed with a polarizing microscope in a crossed Nicols state. The prepreg according to claim 1, which satisfies the following condition [III].
[III]: The cured product of the epoxy resin composition containing the components [B] and [C] has a high degree of It has the following structure. The prepreg according to claim 1 or 2, which satisfies the following condition [IV].
[IV]: The cured product of the epoxy resin composition containing the components [B] and [C] was raised from 50°C to 400°C at a temperature elevation rate of 5°C/min in differential scanning calorimetry under a nitrogen atmosphere. When heated, it has an endothermic peak in the range of 250° C. or higher, which is derived from the phase transition of the higher-order structure. The prepreg according to any one of claims 1 to 3, wherein the component [B] contains an epoxy resin having a structure represented by general formula (2).

(Q ¹ , Q ² and Q ³ in general formula (2) each contain one structure selected from group (III). R ¹ and R ² in general formula (2) each have 1 to 1 carbon atoms. 6. Each Z in group (III) is independently an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an aliphatic alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom , an iodine atom, a cyano group, a nitro group or an acetyl group, n is each independently an integer of 0 to 4. Y ¹ , Y ² and Y ³ in general formula (2) and group (III) are , a single bond or one selected from Group (IV).)

The prepreg according to any one of claims 1 to 4, wherein the constituent element [B] contains an epoxy resin in which a part of the epoxy resin having the structure represented by general formula (2) is prepolymerized. The prepreg according to any one of claims 1 to 5 , wherein the component [C] is selected from diaminophenylbenzoate, diaminobenzanilide, diaminobenzylideneaniline, diaminodiphenylacetylene and diaminobiphenyl. Component [A] has a sizing agent adhesion amount remaining on the carbon fiber after washing with a solution in which acetonitrile and chloroform are mixed at a volume ratio of 9:1 is 0.08% by mass or more,
7. The prepreg according to any one of claims 1 to 6 , wherein the component [B] contains 1 to 25 parts by mass of an epoxy resin that does not exhibit liquid crystallinity by itself with respect to 100 parts by mass of the entire component [B]. 8. The prepreg according to claim 7, wherein the component [B] contains 3 to 25 parts by mass of an epoxy resin that does not exhibit liquid crystallinity by itself with respect to 100 parts by mass of the entire component [B]. Claim 1, wherein the constituent element [A] has a sizing agent adhesion amount remaining on the carbon fiber after washing with a solution in which acetonitrile and chloroform are mixed at a volume ratio of 9:1 is 0.14 to 0.30% by mass or more. 9. The prepreg according to any one of 1 to 8. A carbon fiber reinforced composite material obtained by curing the prepreg according to any one of claims 1 to 9.

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