JP2020029553A - Prepreg and carbon fiber-reinforced composite material - Google Patents

Abstract

To provide a prepreg that makes it possible to obtain a carbon fiber-reinforced composite material being excellent in mode I interlayer toughness, 0° compression strength, and heat resistance, and a carbon fiber-reinforced composite material.SOLUTION: A prepreg contains the following components [A]-[C] and satisfies conditions [I] and [II]. [A]: carbon fiber, [B]: epoxy resin, and [C]: a specific curing agent having a mesogen structure.SELECTED DRAWING: None

Description

  The present invention relates to an epoxy resin composition for a carbon fiber reinforced composite material, which can provide a carbon fiber reinforced composite material having both excellent mode I interlayer toughness and 0 ° compressive strength, and a prepreg and a carbon fiber reinforced composite material using the same. Things.

  Conventionally, fiber-reinforced composite materials consisting of reinforcing fibers such as carbon fiber and glass fiber and thermosetting resins such as epoxy resin and phenol resin are lightweight, yet have mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. Due to its superiority, it has been applied to many fields such as aerospace, automobiles, railway vehicles, ships, civil engineering and sporting goods. In particular, in applications where high performance is required, 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 is used as matrix resin. In particular, epoxy resins having excellent adhesiveness to carbon fibers have been widely used.

  A carbon fiber reinforced composite material is a non-uniform material containing a reinforcing fiber and a matrix resin as essential components, and therefore, there is a great difference between the physical properties of the reinforcing fibers in the arrangement direction and the physical properties in other directions. For example, it is known that interlaminar toughness, which indicates the difficulty of interlaminar fracture of a reinforcing fiber, does not lead to a drastic improvement only by improving the strength of the reinforcing fiber. In particular, a carbon fiber reinforced composite material using a thermosetting resin as a matrix resin reflects the low toughness of the matrix resin and has a property of being easily broken by stress from a direction other than the arrangement direction of the reinforcing fibers. Therefore, for applications requiring high strength and reliability, such as aircraft structural materials, it is necessary to secure the strength in the fiber direction and to cope with stress from other than the arrangement direction of the reinforcing fibers such as interlayer toughness. Various techniques have been proposed for the purpose of improving the physical properties of composite materials.

  In recent years, the application area of carbon fiber reinforced composite materials to aircraft structural materials has been expanding, 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 Application to a thick member or a member having a three-dimensional curved surface shape is being studied. When tensile or compressive stress is applied to such a thick member or a curved surface member, an out-of-plane peeling stress is generated between the prepreg fiber layers, and a crack is generated between the layers by an opening mode. As a result, the strength and rigidity of the entire member are reduced, which may lead to total destruction. To cope with this stress, an interlayer mode, that is, an interlayer toughness in the mode I, is required. To obtain a carbon fiber reinforced composite material having a high mode I interlayer toughness, the matrix resin itself needs to have high toughness. In order to improve the toughness of the matrix resin, a method of blending a rubber component with the matrix resin (see Patent Document 1) and a method of blending a thermoplastic resin (see Patent Document 2) have been known. Further, a method of inserting a kind of an adhesive layer or a shock absorbing layer called an interleaf between layers (see Patent Document 3) and a method of reinforcing the layers with particles (see Patent Document 4) have been proposed.

  In addition, for application to aircraft structural materials, high compressive strength of carbon fiber reinforced composite materials is also required. It is known that in a fiber reinforced composite material, compressive strength is reduced due to buckling of a fiber. In order to suppress the buckling of the fiber, it is effective to increase the modulus of the matrix resin filling the periphery of the fiber. However, generally, increasing the elastic modulus of the resin causes a decrease in the elongation of the resin, and tends to result in a cured resin having low toughness. Therefore, in the obtained fiber-reinforced composite material, it was very difficult to satisfy mode I interlayer toughness and compressive strength at a high level.

JP 2001-139662 A 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 do not have a sufficient effect of improving the toughness of the matrix resin. Further, the methods described in Patent Documents 3 and 4 have an effect on the mode II interlayer toughness, but do not provide a sufficient effect on the mode I interlayer toughness. Also, it was very difficult to achieve both 0 ° compression strength and mode I interlayer toughness. Then, an object of the present invention is to provide a prepreg from which a carbon fiber reinforced composite material excellent in mode I interlayer toughness and 0 ° compression strength can be obtained, and a carbon fiber reinforced composite material.

A 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 the general formula (1)

(In the general formula (1), X ¹ is a single bond or one selected from the group (I). P ¹ and P ² may be the same or different, and are represented by group (II). W in group (II) is each 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 each independently represents an integer of 0 to 4. The substituents W may be all the same or different, or X ² in group (II) is selected from group (I), and F ¹ and F ² are active groups capable of reacting with an epoxy group, and group (II) Directly bonded 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 the epoxy resin composition containing the components [B] and [C] includes a resin region having molecular anisotropy showing an interference pattern when observed under 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 ° compression strength, and heat resistance can be obtained.

It is a diagram showing a measurement method of the mode I interlayer toughness (G _IC).

  The form and arrangement of the carbon fibers as the constituent element [A] of the present invention are not limited, and examples thereof include long fibers aligned in one direction, a single tow, a woven fabric, a knit, and a braid. Is used. It may be used in combination with two or more kinds of carbon fibers or other reinforcing fibers such as glass fiber, aramid fiber, boron fiber, PBO fiber, high-strength polyethylene fiber, alumina fiber and silicon carbide fiber.

  Specific examples of the carbon fiber include acryl-based, pitch-based, and rayon-based carbon fibers, and acryl-based carbon fibers having particularly high tensile strength are preferably used.

  Such an acrylic carbon fiber can be manufactured, for example, through the following steps. A spinning solution 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 processed into a precursor through a spinning process, and then a carbon fiber can be obtained through processes such as flame resistance and carbonization.

  As the form of the carbon fiber, twisted yarn, untwisted yarn and non-twisted yarn can be used, but in the case of twisted yarn, the orientation of the filaments constituting the carbon fiber is not parallel, so the obtained carbon fiber reinforced composite material Untwisted or non-twisted yarns having a good balance between the moldability and strength characteristics of the carbon fiber reinforced composite material are preferably used because they cause a decrease in the mechanical properties of the carbon fiber reinforced composite material.

  It is preferable that the carbon fiber of the present invention is usually subjected to an oxidation treatment and an oxygen-containing functional group is introduced in order to improve the adhesiveness with the matrix resin. As the oxidation treatment method, gas-phase oxidation, liquid-phase oxidation and liquid-phase electrolytic oxidation are used, but liquid-phase electrolytic oxidation is preferably used from the viewpoint of high productivity and uniform treatment.

  In the present invention, examples of the electrolytic solution used in the liquid phase electrolytic oxidation include an acidic electrolytic solution and an alkaline electrolytic solution. From the viewpoint of adhesiveness, after performing liquid phase electrolytic oxidation in an alkaline electrolytic solution, applying a sizing agent. Is more preferred.

  Examples of the acidic electrolyte 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 showing strong acidity are preferably used.

  Specific examples of the alkaline electrolyte 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 solution of carbonate such as barium carbonate and ammonium carbonate, aqueous solution of hydrogen carbonate such as sodium hydrogen carbonate, potassium hydrogen carbonate, magnesium hydrogen carbonate, calcium hydrogen carbonate, barium hydrogen carbonate and ammonium hydrogen carbonate, ammonia, tetraalkylammonium hydroxide And an aqueous solution of hydrazine. Of these, aqueous solutions of ammonium carbonate and ammonium bicarbonate or aqueous solutions of tetraalkylammonium hydroxide showing strong alkalinity are preferably used from the viewpoint that they do not contain alkali metals that cause curing inhibition of the matrix resin.

  In the present invention, the total amount of electrolytic electricity employed in the electrolytic treatment is preferably 3 to 300 coulombs per gram of carbon fiber. When the total amount of electrolytic electricity is 3 coulombs / g or more, a sufficient functional group can be imparted to the carbon fiber surface, and the interfacial adhesion between the matrix resin and the carbon fiber becomes excellent. On the other hand, when the total amount of electrolytic electricity is 300 coulombs / g or less, the expansion of defects on the surface of the carbon fiber single fiber can be suppressed, and a decrease in strength of the carbon fiber can be reduced.

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

  Commercially available carbon fibers include "Treca (registered trademark)" T800G-24K, "Treca (registered trademark)" T300-3K, "Treca (registered trademark)" T700G-12K, and "Treca (registered trademark)" T1100G. -24K (all 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 fiber may be easily damaged by the contact with the guide roller during the twisting, and the same damage may be caused in the impregnation process of the resin composition. If the single fiber fineness exceeds 2.0 dtex, the carbon fiber may not be sufficiently impregnated with the resin composition, and as a result, fatigue resistance may be reduced.

  In the carbon fiber used in the present invention, the number of filaments in one fiber bundle is preferably in the range of 2,500 to 50,000. If the number of filaments is less than 2500, the fiber arrangement tends to meander, which tends to cause a decrease in strength. On the other hand, if the number of filaments exceeds 50,000, it may be difficult to impregnate the resin during the preparation or molding of the prepreg. The number of filaments is more preferably in the range of 2800 to 40,000.

  As the condition [I] to be satisfied by the prepreg of the present invention, the component [A] carbon fiber is expressed by the ratio of the number of atoms 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 in the range of 0.10 to 0.50, more preferably in the range of 0.14 to 0.30, and still more preferably in the range of 0.14 to 0.20. Things. When the surface oxygen concentration (O / C) is 0.10 or more, an oxygen-containing functional group on the carbon fiber surface can be secured, and strong adhesion to the matrix resin can be obtained. Further, when the surface oxygen concentration (O / C) is 0.50 or less, a decrease in the strength of the carbon fiber itself due to oxidation can be suppressed, which is preferable.

The surface oxygen concentration of the carbon fiber under the condition [I] is determined by X-ray photoelectron spectroscopy according to the following procedure. First, carbon fibers, etc. to remove dirt adhering to the surface of the carbon fibers with a solvent was cut into 20 mm, after aligned spread on copper sample holder, using AlK _.alpha.1,2 as X-ray source, the sample The inside of the chamber was kept at 1 × 10 ⁻⁸ Torr, and the measurement was performed at a photoelectron escape angle of 90 °. The binding energy value of the main peak (peak top) of C _{1 s} is adjusted to 284.6 eV as a correction value of the peak due to charging during measurement. The C _1s peak area is obtained by drawing a linear base line in the range of 282 to 296 eV, and the O _1s peak area is obtained by drawing a linear base line in the range of 528 to 540 eV. The surface oxygen concentration (O / C) is represented by the atomic ratio calculated by dividing the ratio of the O _1s peak area by the sensitivity correction value specific to the device. When using ESCA-1600 manufactured by ULVAC-PHI, Inc. as an X-ray photoelectron spectroscopy device, the sensitivity correction value specific to the device is 2.33.

  The carbon fiber of the present invention is preferably a sizing agent-coated carbon fiber. By using a sizing agent-coated carbon fiber, the handling properties of the carbon fiber are excellent, and the interfacial adhesion between the carbon fiber and the matrix resin is excellent.

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

  It has been confirmed that a carbon fiber coated with a sizing agent consisting of only an aliphatic epoxy compound has high adhesiveness to a matrix resin. Although the mechanism is not certain, the aliphatic epoxy compound is derived from its flexible skeleton and highly flexible structure, and the functional group of carboxyl group and hydroxyl group on the carbon fiber surface forms a strong interaction with the aliphatic epoxy compound. It is considered possible.

  A carbon fiber coated with a sizing agent consisting of only an aromatic epoxy compound has the advantages of low reactivity between the sizing agent and the matrix resin and a small change in physical properties when the prepreg is stored for a long period of time. There is also an advantage that a rigid interface layer can be formed.

  When the aliphatic epoxy compound and the aromatic epoxy compound are mixed, the more polar aliphatic epoxy compound is unevenly distributed on the carbon fiber side, and the lower polar aromatic epoxy compound is formed on the outermost layer of the sizing layer opposite to the carbon fiber. Are likely to be unevenly distributed. As a result of the inclined structure of the sizing layer, the aliphatic epoxy compound has a strong interaction with the carbon fiber in the vicinity of the carbon fiber, so that the adhesion between the carbon fiber and the matrix resin can be enhanced. In addition, the aromatic epoxy compound, which is often present in the outer layer, plays a role of blocking the aliphatic epoxy compound from the matrix resin when the sizing agent-coated carbon fiber is prepreg. As a result, the reaction between the aliphatic epoxy compound and the highly reactive component in the matrix resin is suppressed, and stability during long-term storage is exhibited.

  In a fiber-reinforced composite material comprising a carbon fiber coated with a sizing agent and a matrix resin, the so-called interface layer near the carbon fiber may be affected by the carbon fiber or the sizing agent and have different properties from the matrix resin. When the epoxy compound has one or more aromatic rings, a rigid interface layer is formed, the ability to transmit stress between the carbon fiber and the matrix resin is improved, and the mechanical properties such as the 0 ° tensile strength of the fiber reinforced composite material are improved. improves. Further, since the hydrophobicity is improved by the aromatic ring, the interaction with the carbon fiber is weaker than that of the aliphatic epoxy compound, and the aliphatic ring covers the aliphatic epoxy compound and can be present in the outer layer of the sizing layer. Thus, when the sizing agent-coated carbon fiber is used for a prepreg, it is possible to suppress a change with time when stored for a long period of time, which is preferable. It is preferable to have two or more aromatic rings since the long-term stability by the aromatic rings is improved. There is no particular upper limit on 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 sizing agent applied to the carbon fibers preferably has an epoxy equivalent of 350 to 550 g / mol. The content of 550 g / mol or less is preferable because the adhesion between the carbon fiber coated with the sizing agent and the matrix resin is improved. 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 using the prepreg at 350 g / mol or more. This is also preferable because the physical properties of the obtained carbon fiber reinforced composite material are improved. The epoxy equivalent of the carbon fiber coated with the sizing agent in the present invention means that the sizing agent-coated fiber is immersed in a solvent typified by N, N-dimethylformamide and eluted from the fiber by performing ultrasonic cleaning. Thereafter, the epoxy group can be opened with hydrochloric acid, and the epoxy group can be determined by acid-base titration. The epoxy equivalent is preferably 360 g / mol or more, more preferably 380 g / mol or more. Further, it is preferably at most 530 g / mol, more preferably at most 500 g / mol. The epoxy equivalent of the sizing agent applied to the carbon fiber can be controlled by the epoxy equivalent of the sizing agent used for application, the heat history in drying after application, and the like.

  In the present invention, the amount of the sizing agent attached is preferably at least 0.1 part by mass, more preferably 0.1 to 3.0 parts by mass, and still more preferably 0.1 part by mass, per 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. The method of measuring the amount of the sizing agent adhered is as follows: 2 ± 0.5 g of the sizing-coated carbon fiber is sampled, and the amount of mass change before and after the heat treatment at 450 ° C. for 15 minutes in a nitrogen atmosphere is measured by the heat treatment. It is% by mass divided by the previous mass.

  In the present invention, it is preferable that the 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 based on 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 amount of the sizing agent adhered after the washing is within the above range, the interfacial adhesion between the carbon fiber and the sizing agent is improved, and a high shear toughness can be exhibited when a fiber-reinforced composite material is obtained. The “sizing agent adhesion amount after cleaning” in the present invention is measured and calculated as follows. After immersing 2 ± 0.5 g of the sizing agent-coated carbon fiber in 10 ml of a solution obtained by mixing acetonitrile and chloroform at a volume ratio of 9: 1 and performing ultrasonic cleaning for 20 minutes, the sizing agent is eluted from the fiber. Dry and weigh. Further, after the washing, the carbon fiber is subjected to a heat treatment at 450 ° C. for 15 minutes in a nitrogen atmosphere. The mass change of the mass before and after the heat treatment divided by the mass of the sizing agent-coated carbon fibers before the heat treatment is defined as the sizing agent adhesion amount after washing.

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

  Hereinafter, a method for measuring the interface shear strength will be described. In the measurement, Drzal, L. et al. T. , Master, Sci, Eng. A126, 289 (1990).

  That is, 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.) are put in respective containers. Then, the mixture is heated at a temperature of 75 ° C. for 15 minutes for decreasing the viscosity of jER828 and dissolving metaphenylenediamine. Then, both are well mixed and vacuum degassed at a temperature of 80 ° C. for about 15 minutes.

  Next, the 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 attached to the carbon fiber and the mold. The dumbbell mold is made of silicone rubber, and the shape of the casting portion is 5 mm in width at the center, 25 mm in length, 10 mm in width at both ends, and 150 mm in overall length.

  Pour the prepared resin into the mold after the above vacuum drying, raise the temperature to 75 ° C. using an oven at a rate of 1.5 ° C./min, hold for 2 hours, and then increase the rate of 1.5 ° C. The temperature is raised to a temperature of 125 ° C./min and maintained for 2 hours, and then the temperature is lowered to a temperature of 30 ° C. at a rate of 2.5 ° C./min. Thereafter, the mold is removed to obtain a test piece.

A tensile force is applied to the test piece obtained in the above procedure at a strain rate of 0.3% / sec in the fiber axis direction (longitudinal direction) to generate a strain of 12%. The number of broken fibers N (pieces) in the range is measured. 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 of lc (μm) = (4/3) × la (μm). Further, 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 “interface 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 interlayer toughness because the cured product of the epoxy resin composition has a higher-order structure. This is presumably because, when a crack develops in the carbon fiber reinforced composite material, much energy is required to break the higher-order structure present in the cured product of the resin composition.

  The higher-order structure referred to herein means a state in which molecules are aligned after curing or semi-curing of the epoxy resin composition, and for example, a state in which a crystal structure or a liquid crystal structure is present in a cured product. .

  Hereinafter, the condition [II] to be satisfied by the prepreg of the present invention will be described. 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 order of visible light wavelength, an interference pattern (bright field) is observed with a polarizing microscope in a crossed Nicols state. When no higher-order structure is formed, or when the size of the formed higher-order structure is smaller than the order of visible light wavelength, a dark field is observed because it has no optical anisotropy. That is, satisfying the condition [II] of the present invention means that an interference pattern (bright field) is observed when a 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 interference patterns observed vary depending on the type of liquid crystal phase to be formed. Specific examples of the observed interference pattern include, when the higher-order structure is a nematic phase structure, a schlieren structure, a thread-like structure, a sandy structure, a droplet structure, and a smectic phase structure, a Batne structure, Focal conic fan organization and oily streak organization.

  In the prepreg or carbon fiber reinforced composite material of the present invention, a transmission method is used as a technique of observation with a polarizing microscope to confirm the satisfaction of the condition [II]. In the case of observation by a polarizing microscope using a transmission method, if the target test piece is too thick, visible light does not sufficiently pass therethrough, 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 a prepreg or a test piece obtained by shaving a carbon fiber reinforced composite material in the fiber direction and thinning it to about 10 μm is used. With respect to the test piece, a 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 confirmed by the presence or absence of the interference pattern.

Hereinafter, the condition [III] suitable for satisfying the prepreg of the present invention will be described. The prepreg and the carbon fiber reinforced composite material of the present invention exhibit high mode I interlayer toughness by including a higher-order structure in the cured product of the resin composition, and in particular, by having a smectic phase structure as the higher-order structure. When a smectic phase structure is formed, in addition to the condition [II], a peak derived from a higher-order structure is generally observed in a region where the diffraction angle is 2θ ≦ 10 ° in X-ray diffraction. The presence or absence of a peak in this range can confirm the presence or absence of a smectic phase structure. In the present invention, the mesogen structure (biphenyl group, terphenyl group, terphenyl analog group, anthracene group, or azomethine group) present in the component [C] or in both the components [B] and [C] is used. In a periodic structure (higher-order structure) based on a group connected by an ester group, etc., the compound has a peak at a diffraction angle 2θ of 1.0 to 6.0 °. That is, satisfying the condition [III] means that a peak at a diffraction angle 2θ = 1.0 to 6.0 °, which is a peak derived from the smectic phase structure formed by the mesogenic structure, is observed by wide-angle X-ray diffraction. Means that It is important that the range of the diffraction angle 2θ of the peak observed by X-ray diffraction is from 1.0 to 6.0 °, and preferably from 2.0 to 4.0 °. Using a carbon fiber reinforced composite material molded to a thickness of 1 mm, a measurement sample having a length of 20 mm and a width of 10 mm is prepared. The prepared measurement sample is measured using a wide-angle X-ray diffractometer 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 = 1-90 °
Scan mode: step scan, step unit 0.1 °, counting time 40 seconds.

  The measurement of the X-ray diffraction is performed with respect to the parallel (0 °), perpendicular (90 °), and 45 ° to the carbon fiber axis in the carbon fiber reinforced composite material.

  The higher-order structure of the cured product of the resin composition may be oriented in any direction with respect to the carbon fiber of the component [A]. Due to a strong peak derived from the resin composition, a 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 measurement by X-ray diffraction 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 a cured product of the resin composition containing the constituent elements [B] and [C] excluding the constituent element [A], and to form a higher-order structure. The presence or absence can be confirmed.

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

  Hereinafter, the condition [IV] suitable for satisfying the prepreg of the present invention will be described. In the prepreg and the carbon fiber composite material of the present invention, a cured product obtained by curing the resin composition has an endothermic peak at 250 ° C. or higher due to liquid crystal phase transition in differential scanning calorimetry. More preferably, it is in the range of 280 ° C. or more, further preferably 300 ° C. or more. When the temperature at which the endothermic peak due to the liquid crystal phase transition of the cured resin is applied is applied, the temperature range in which the cured resin maintains the liquid crystal phase is widened, and the cured resin exhibiting excellent mechanical properties even at high temperatures can be obtained. . In addition, the higher the liquid crystal phase transition temperature is, the stronger the higher-order structure is formed. Therefore, the cured resin and the carbon fiber composite material tend to exhibit excellent mechanical properties. As a confirmation method, a 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 a heat flow rate when the temperature is increased from 50 ° C. to 400 ° C. at a rate of 5 ° C./min is confirmed. be able to. For confirming the liquid crystallinity by differential scanning calorimetry, a cured resin may be used, or a carbon fiber composite material may be used. Whether the endothermic peak observed by differential scanning calorimetry was caused by the liquid crystal phase transition was determined by cutting a test piece obtained by curing one ply of prepreg or a carbon fiber reinforced composite material in the fiber direction and thinning it to about 10 μm. It can be determined by observing whether or not there is a change in the interference pattern near the endothermic peak of the target when the specimen thus obtained is observed with a polarizing microscope in a crossed Nicols state. When there is a change in the interference pattern, it can be determined that the interference pattern is derived from the liquid crystal phase transition.

  The molding condition of the carbon fiber reinforced composite material of the present invention is particularly limited within a range that the resin composition after curing has a higher order structure derived from a diffraction angle 2θ = 1.0 ° to 6.0 ° observed by X-ray diffraction. Although not limited, when the molding temperature is too high, high heat resistance is required for the equipment and auxiliary materials to be used, and the production cost of the carbon fiber reinforced composite material increases. On the other hand, if the molding temperature is too low, the reaction of the components [B] and [C] takes a long time, which may also increase the production cost. The maximum temperature used for molding is preferably from 100 to 220C, more preferably from 120 to 200C.

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

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

(In the general formula (2), Q ¹ , Q ² and Q ³ each include one kind of structure selected from the group (III). In the general formula (2), R ¹ and R ² each have 1 to 1 carbon atoms. And Z represents an alkylene group of formula 6. Z in the general formula (2) is each 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, iodine atom, cyano group, nitro group, or acetyl group, and n independently represents an integer of 0 to 4. Y ¹ , Y ² , Y ^{3 in the} general formula (2) and group (III) Is selected from a single bond or group (IV).)

  Z in group (III) is each independently 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, It is preferably a nitro group or an acetyl group, more preferably a methyl group, an ethyl group, a methoxy group, an ethoxy group, or a chlorine atom, and still more preferably a methyl group or an ethyl group. N in group (III) is preferably independently an integer of 0 to 2, and more preferably 0 or 1.

  In the case where the component [B] is a liquid crystalline epoxy resin, the higher the proportion of the mesogen structure, the easier the resin is to form a higher-order structure after curing, but if the ratio is too large, the softening point increases and the handling property decreases. . Therefore, the number of mesogen structures in the general formula (2) is particularly preferably two. Here, the softening point in the present invention is defined as a temperature at which a sample cast in a ring is heated in a bathtub by a ring and ball method specified in JIS-K7234 (1986), and a ball set in the sample crosses the optical sensor. Shows the temperature.

When Q ¹ , Q ² , and Q ^{3 in the} general formula (2) include a benzene ring, the structure of the constituent element [B] becomes rigid, so that a higher-order structure is easily formed, which is advantageous in improving toughness. . Further, when Q ¹ , Q ² , and Q ³ in the general formula (2) include an alicyclic hydrocarbon, the softening point is lowered and the handling properties are improved, so this is also a preferable embodiment. The epoxy resin of the constituent element [B] may be used alone or in combination of two or more.

  The component [B] can be manufactured by a known method, and Japanese Patent No. 4619770, JP-A-2005-268814, JP-A-2010-241797, JP-A-2011-98952, JP-A-2011-74366, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 42, 3631 (2004) and the like.

  Specific examples of the component [B] include 1,4-bis {4- (oxiranylmethoxy) phenyl} cyclohexane and 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- { -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- (oxira) Nilmethoxy) 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-epoxy) Propoxy) -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-dimethylbenzoate}, 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-epoxyprop) (Ropoxy) -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-epoxy Propoxy) 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) C) 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- , 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-epoxyhexyl) Oxy) phenyl} cyclohexane, 1,4-bis {4- (5-methyl-3-oxa-5,6-epoxyhexyloxy) 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 and the like. Among them, from the viewpoint of formation of a higher-order structure after curing, handleability, and availability of raw materials, 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-methyl benzoate are particularly preferred.

  The component [B] may include a prepolymer partially polymerized by a curing agent or the like. The epoxy resin of the component [B] is generally easily crystallized, and many require high temperatures to impregnate the reinforcing fibers. It is a preferable embodiment to include a prepolymer obtained by polymerizing at least a part of the constituent element [B], since crystallization tends to be suppressed and handling properties are improved.

  As a method of partially polymerizing the component [B], the polymerization may be performed using an anionic polymerization catalyst such as a tertiary amine or imidazole, or a cationic polymerization catalyst such as a Lewis acid such as boron trifluoride-amine complex. Alternatively, 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 is 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, and heat resistance and mechanical properties may be impaired.

  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. For example, a phenol compound, an amine compound, an amide compound, a sulfide compound, and an acid anhydride are mentioned. Here, active hydrogen refers to a highly reactive hydrogen atom bonded to nitrogen, oxygen, and sulfur in an organic compound. When the number of active hydrogens is one, the crosslink density of the epoxy resin cured product using the prepolymer is reduced, so that heat resistance and mechanical properties may be reduced. When the number of active hydrogen groups is 5 or more, it is difficult to control the reaction when the component [B] is prepolymerized, which may cause gelation. As the prepolymerizing agent, a phenol compound having 2 to 3 active hydrogens is particularly suitable from the viewpoint of suppressing gelation during the prepolymerization reaction and the storage stability of the prepolymer.

  Among phenol compounds having 2 to 4 active hydrogens, phenol compounds having 1 to 2 benzene rings are easy to form a higher-order structure because the structure of the prepolymerized component [B] is rigid, This is preferable because the viscosity of the resin composition containing the prepolymer, the component [B], and the curing agent can be suppressed to a low level, and the handling properties are improved, in addition to the tendency to improve the toughness.

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

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

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

  When the component [B] contains a prepolymer, the crystallization tends to be suppressed, so that the handleability is improved. However, when the content is too large, the melt viscosity of the resin composition containing the component [B] and the curing agent is increased. May be too high, making it difficult to impregnate the reinforcing fibers. When the component [B] contains a prepolymer, the content is preferably 80 parts by mass or less, more preferably 5 to 60 parts by mass, based on 100 parts by mass of the total of the component [B] and the prepolymer. It is. The ratio of the prepolymer-derived peak area to the total epoxy resin-derived peak area in the resin composition in the above-described GPC or HPLC (High Performance Liquid Chromatography) measurement (peak area derived from prepolymer / total epoxy content in the resin composition) (Peak area derived from resin) is preferably 0.80 or less, more preferably in the range of 0.05 to 0.60.

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

  In the present invention, an epoxy resin which does not exhibit liquid crystallinity, a thermosetting resin other than the epoxy resin, a copolymer of an epoxy resin and a thermosetting resin, or the like may be included.

  Examples of the thermosetting resin include an unsaturated polyester resin, a vinyl ester resin, an epoxy resin, a benzoxazine resin, a phenol resin, a urea resin, a melamine resin, and a polyimide resin. These resin compositions and compounds may be used alone or may be appropriately blended and used. Mixing at least an epoxy resin or a thermosetting resin that does not exhibit liquid crystal properties has both the fluidity of the resin and the heat resistance after curing.

  Among the constituent resins [B], a glycidyl ether type epoxy resin having phenol as a precursor is preferably used as a bifunctional epoxy resin among epoxy resins used as an epoxy resin having no liquid crystallinity. Examples of such an epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, urethane modified epoxy resin, hydantoin type and resorcinol type epoxy resin. Can be

  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, so that the interfacial adhesion is improved. And a fiber-reinforced composite material having better mode I interlayer toughness can be obtained. Here, the epoxy resin “does not exhibit liquid crystallinity” means that when the temperature is increased from 10 ° C. to 250 ° C. at a rate of 10 ° C./min in a differential scanning calorimetry under a nitrogen atmosphere, 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 is 30 ° C. If there is an endothermic peak, 10 ° C. before and after the endothermic peak (phase transition) For the state in the temperature range described above, a polarizing microscope observation in a crossed Nicols state was performed, and it means that no nematic phase structure was formed in any case. Specifically, it is confirmed that no interference pattern unique to the nematic phase structure, such as a schlieren structure, a thread-like structure, a sand-like structure, or a droplet structure, is observed.

  As an epoxy resin that does not exhibit liquid crystallinity when used alone, it is particularly difficult for the epoxy resin that is liquid at room temperature (25 ° C.) to inhibit the formation of a smectic structure in a cured product of the resin composition while reducing the viscosity of the resin composition. This is preferable from the viewpoint. The term liquid refers to a case where a metal piece having a specific gravity of 7 or more in the same temperature state as a single epoxy resin that does not exhibit liquid crystal properties is placed on the single epoxy resin that does not exhibit liquid crystal properties, and is instantly buried by gravity. The single epoxy resin that does not exhibit liquid crystallinity is defined as a liquid. Examples of the metal piece 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 more preferably 3 to 25 parts by mass based on 100 parts by mass of the entire component [B]. The range is more preferred, and the range of 3 to 20 parts by mass is even more preferred. Within this range, the interfacial adhesion between the epoxy resin and the component [A] is improved without lowering the ratio of the smectic structure in the cured product of the resin composition. A reinforced composite is obtained.

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

  Examples of the glycidyl ether type epoxy resin having three or more functional groups include epoxy resins such as phenol novolak type, orthocresol novolak type, trishydroxyphenylmethane type and tetraphenylolethane type.

  The constituent element [C] of the present invention is a curing agent for an epoxy resin, and has a structure represented by the general formula (1).

(In the general formula (1), X ¹ is a single bond or one selected from the group (I). P ¹ and P ² may be the same or different, and are represented by group (II). W in group (II) is each 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 each independently represents an integer of 0 to 4. The substituents W may be all the same or different, or X ² in group (II) is selected from group (I), and F ¹ and F ² are active groups capable of reacting with an epoxy group, and group (II) The substituent W is too large in structure when the epoxy resin composition is too large. Viscosity may be too high to impair handleability, or the effect of improving the mechanical properties of the reinforced fiber composite material obtained by impairing the compatibility with other components in the epoxy resin composition may be reduced. Also, from the viewpoint of flame retardancy, those in which the substituent W is substituted with a halogen atom such as Cl or Br are also preferable.)

  In the case of a molecular structure having three or more six-membered rings in the molecular structure of the constituent [C], the compatibility with the epoxy resin of the constituent [C] is poor, and the cured product of the epoxy resin composition has Residual residues of these curing agents tend to occur. In some cases, the strength of the resin cured product may be reduced because the unmelted powder portion serves as a starting point of destruction. For this reason, the molecular structure of the component [C] preferably has two six-membered rings.

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

  Commercially available products of the component [C] include 4,4′-diaminobenzanilide (4,4′-DABAN), 3,4′-diaminobenzanilide (3,4′-DABAN), and 4-aminobenzoic acid 4-aminophenyl (4,4'-BAAB), o-tolidine, (bis (4-aminophenyl) terephthalamide (4,4'-APTP) (all manufactured by Nippon Pure Chemicals Co., Ltd.) and the like. These curing agents may be used alone or in combination of two or more, and an epoxy resin and a curing agent, or a product obtained by preliminarily reacting a part of them, may be added to the composition. This method may be effective for 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 effects of the present invention are not impaired. Examples of the curing agent other than the component [C] include diaminodiphenyl sulfone, diaminodiphenyl ether, diaminobenzophenone, dicyandiamide, aminobenzoic acid esters, various acid anhydrides, phenol novolak resins, cresol novolak resins, polyphenol compounds, and imidazole derivatives. And aliphatic amines.

  The optimum value of the amount of the curing agent varies depending on the type of the epoxy resin and the curing agent. For example, in the case of an aromatic polyamine curing agent, it is preferable to add it so that it becomes stoichiometrically equivalent, but the ratio of the active hydrogen amount of the aromatic amine curing agent to the epoxy group amount of the epoxy resin is 0.7 to 1 By setting to 0.0, a resin having a high elastic modulus may be obtained as compared with a case where the resin is used in an equivalent amount, which is a preferable embodiment. On the other hand, when the ratio of the amount of the active hydrogen of the aromatic polyamine curing agent to the amount of the epoxy group of the epoxy resin is 1.0 to 1.6, in addition to the improvement of the curing speed, a high elongation resin 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 above components [B] and [C]. The use of a thermoplastic resin is preferably used because the tackiness of the obtained prepreg can be controlled and the fluidity of the resin composition at the time of molding the carbon fiber reinforced composite material can be controlled. As such a thermoplastic resin, generally, a main chain has 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. Preferably, it is a thermoplastic resin having the selected bond. The thermoplastic resin may have a partially crosslinked structure, and may have a crystalline property or an amorphous property. In particular, polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyester, polyamideimide, polyimide, polyetherimide, polyimide having a phenyltrimethylindane structure, polysulfone, polyethersulfone, polyetherketone, polyetherether It is preferable that at least one resin selected from the group consisting of ketone, polyaramid, polyether nitrile and polybenzimidazole is mixed or dissolved in any one of the epoxy resins contained in the above epoxy resin composition. is there.

  Among them, in order to obtain good heat resistance, the glass transition temperature (Tg) of the thermoplastic resin is at least 150 ° C., preferably 170 ° C. or more. When the glass transition temperature of the thermoplastic resin to be blended is less than 150 ° C., the resin may be easily deformed by heat when used as a molded article. Further, as the terminal functional group of the thermoplastic resin, those having a hydroxyl group, a carboxyl group, a thiol group, an acid anhydride or the like can react with the cationically polymerizable compound, and are preferably used. Specifically, “SUMIKAEXCEL (registered trademark)” PES3600P, “SUMIKAEXCEL (registered trademark)” PES5003P, “SUMIKAEXCEL (registered trademark)” PES5200P, and “SUMIKAEXCEL (registered trademark)” are commercially available products of polyether sulfone. Use of “PES7600P (all manufactured by Sumitomo Chemical Co., Ltd.), Virtage (registered trademark)” VW-10200RFP, “Virantage (registered trademark)” VW-10700RFP (all manufactured by Solvay Advanced Polymers Co., Ltd.), etc. And polyethersulfone and polyetherethersulfone copolymer oligomers as described in JP-T-2004-506789, and “Ultem (registered trademark)” 1000, which is a commercial product of polyetherimide, “Ultem (Registered trademark) "1010 and" Ultem (registered trademark) "1040 (all manufactured by Solvay Advanced Polymers Co., Ltd.) Oligomers are relatively molecular weights in which about 10 to 100 finite monomers are bonded. Indicates a low polymer.

  Further, in the present invention, an elastomer may be further added to the epoxy resin composition containing the above components [B] and [C]. Such an elastomer is blended for the purpose of forming a fine elastomer phase in the cured epoxy matrix phase. As a result, the plane distortion generated when a stress is applied to the cured resin can be eliminated by breaking cavitation (cavitation) of the elastomer phase, and the 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.

  Elastomer is a polymer material having a domain whose glass transition temperature is lower than 20 ° C. Liquid rubber, solid rubber, crosslinked rubber particles, core shell rubber particles, thermoplastic elastomer, and a block whose glass transition temperature is lower than 20 ° C Block copolymers and the like. Among them, the elastomer is preferably selected from a block copolymer including a block having a glass transition temperature of 20 ° C. or lower and rubber particles. As a result, a fine elastomer phase can be introduced while minimizing the compatibility of the elastomer with the epoxy resin, and the interlayer toughness as a carbon fiber reinforced composite material is greatly improved while suppressing a decrease in heat resistance and elastic modulus. Can be done.

  As the rubber particles, crosslinked rubber particles and core-shell rubber particles obtained by graft-polymerizing a heterogeneous polymer on the surface of the 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. Further, it is preferable that such rubber particles have good affinity with the epoxy resin to be used and do not cause secondary aggregation during resin preparation or molding and curing.

  Commercially available crosslinked rubber particles include FX501P (manufactured by Nippon Synthetic Rubber Industries, Ltd.) composed of a crosslinked product of a carboxyl-modified butadiene-acrylonitrile copolymer, and CX-MN series composed of acrylic rubber fine particles (Nippon Shokubai Co., Ltd.) And YR-500 series (manufactured by Nippon Steel & Sumitomo Metal Corporation).

  Examples of commercially available core-shell rubber particles include, for example, “PARALOID (registered trademark)” EXL-2655 (manufactured by Kureha Corporation) comprising butadiene / alkyl methacrylate / styrene copolymer, acrylic acid ester / methacrylic acid ester copolymer “STAPHYLOID (registered trademark)” AC-3355, TR-2122 (manufactured by Takeda Pharmaceutical Co., Ltd.) composed of coalesced products, and “PARALOID (registered trademark)” EXL-2611 composed of butyl acrylate / methyl methacrylate copolymer EXL-3387 (manufactured by Rohm & Haas), "Kaneace (registered trademark)" MX series (manufactured by Kaneka Corporation), or the like.

  In the present invention, it is also preferable to mix thermoplastic resin particles with the epoxy resin composition of the present invention. By blending the thermoplastic resin particles, when a carbon fiber reinforced composite material is formed, the toughness of the resin composition is improved and the impact resistance is improved.

  As the material of the thermoplastic resin particles used in the present invention, the same thermoplastic resins as those exemplified above can be used as the thermoplastic resin that can be used by being mixed or dissolved in the epoxy resin composition. From the viewpoint of providing stable adhesive strength and impact resistance when the carbon fiber reinforced composite material is used, it is preferable that the shape be maintained in the particles. Among them, polyamides are most preferable. Among the polyamides, polyamide 12, polyamide 11, polyamide 6, polyamide 66, polyamide 6/12 copolymer, and semi-IPN (Epoxy) in the epoxy compound described in Example 1 of JP-A-1-104624. Polyamide (semi-IPN polyamide) having a polymer interpenetrating network structure or the like can be suitably used. The shape of the thermoplastic resin particles may be spherical particles or non-spherical particles, or may be porous particles, but the spherical shape is excellent in viscoelasticity because it does not reduce the flow characteristics of the resin, and there is no starting point of stress concentration, This is a preferred embodiment in that high impact resistance is provided. 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 still more preferably in the range of 10 μm to 30 μm. If the number average particle size is too small, particles may enter between the fibers of the carbon fibers, which may reduce impact resistance and other mechanical properties. Also, if the number average particle size is too large, the arrangement of the carbon fibers is disturbed by the presence of large-diameter particles, and the thickness of the carbon fiber reinforced composite material obtained by laminating the prepregs becomes relatively thick, and the fibers become relatively thick. May lower the volume fraction and its mechanical properties. Here, the number average particle diameter of the thermoplastic particles was observed at a magnification of 200 times or more with a laser microscope (ultra-depth color 3D shape measuring microscope VK-9510: manufactured by KEYENCE CORPORATION), and 50 arbitrary particles were observed. For the above particles, the average value is used after measuring the diameter of the circle circumscribing the particle as the particle size. The amount of the thermoplastic resin particles is preferably 1 to 50 parts by mass, more preferably 3 to 25 parts by mass, based on 100 parts by mass of the whole resin composition. If the addition amount of the thermoplastic resin is too small, there is a possibility that a sufficient impact resistance improving effect 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 (all manufactured by Toray Industries, Inc.) and "Orgasol (registered trademark)" 1002D. , 2001UD, 2001EXD, 2002D, 3202D, 3501D, 3502D (all manufactured by Arkema Co., Ltd.), "Grillamide (registered trademark)" TR90 (manufactured by Mazaverke Co., Ltd.), "TROGAMID (registered trademark)" CX7323, CX9701 , CX9704 (manufactured by Degussa Co., Ltd.) and the like can be used. These polyamide particles may be used alone or in combination of two or more.

  The epoxy resin composition of the present invention may be a coupling agent, a thermosetting resin particle, a thermoplastic resin soluble in an epoxy resin, or silica gel, carbon black, clay, or a carbon nanotube as long as the effects of the present invention are not impaired. And an inorganic filler such as a metal powder.

  The carbon fiber mass fraction of the prepreg of the present invention is preferably 40 to 90% by mass, and more preferably 50 to 80% by mass. If the carbon fiber mass fraction is too low, the mass of the obtained composite material becomes excessive, and the advantage of the carbon fiber reinforced composite material having excellent specific strength and specific elastic modulus may be impaired. If it is too high, impregnation failure of the resin composition occurs, the resulting composite material tends to have many voids, and its mechanical properties may be significantly reduced.

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

  The wet method is a method in which carbon fibers are immersed in a solution of an epoxy resin composition, then pulled up, and the solvent is evaporated using an oven or the like to obtain a prepreg.

  The hot melt method is a method of directly impregnating carbon fibers with an epoxy resin composition whose viscosity has been reduced by heating, or a method of preparing a resin film in which the epoxy resin composition is coated on release paper or the like, and then forming a carbon fiber. This method is to obtain a prepreg by transferring and impregnating the epoxy resin composition by laminating the resin films from both sides or one side of the resin composition and applying heat and pressure. This hot melt method is a preferred embodiment because there is substantially no solvent remaining in the prepreg.

When a prepreg is prepared by a hot melt method, the viscosity of the resin composition is preferably 0.01 to 30 Pa · s as a minimum viscosity measured by a method described later. The term "minimum viscosity of the resin composition" as used herein means that a dynamic viscoelasticity measuring device (ARES, manufactured by TA Instruments) using a parallel plate is used, and the temperature is raised to 0.degree. The lowest value in the temperature range of 40 to 180 ° C is shown for the complex viscosity η ^* measured under the conditions of 5 Hz and a plate interval of 1 mm.

The prepreg preferably has an amount of carbon fibers per unit area of 50 to 1000 g / m ² . When the amount of the carbon fibers is less than 50 g / m ^2, it is necessary to increase the number of laminations to obtain a predetermined thickness when molding the carbon fiber reinforced composite material, which may complicate the operation. On the other hand, when the amount of carbon fibers exceeds 1000 g / m ² , the drapability of the prepreg tends to be poor.

  The carbon fiber reinforced composite material of the present invention can be manufactured by laminating the above-described prepreg of the present invention in a predetermined form, and pressing and heating the prepreg as an example. As a method for applying heat and pressure, a press molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, an internal pressure molding method, and the like are used. In particular, a wrapping tape method and an internal pressure molding method are preferably used for molding sports equipment.

  The wrapping tape method is a method in which a prepreg is wound on a core metal such as a mandrel to form a tubular body made of a carbon fiber reinforced composite material, and is a method suitable for producing a rod-shaped body such as a golf shaft or a fishing rod. is there. More specifically, a prepreg is wound around a mandrel, and a wrapping tape made of a thermoplastic resin film is wound around the outside of the prepreg for fixing and applying pressure to the prepreg, and after the epoxy resin is cured by heating in an oven, This is a method of obtaining a tubular body by removing the cored bar.

  In the internal pressure forming method, a preform obtained by winding a prepreg on an internal pressure applying body such as a tube made of a thermoplastic resin is set in a mold, and then a high pressure gas is introduced into the internal pressure applying 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 complicated shapes such as golf shafts, bats, and rackets such as tennis and badminton.

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

  As such a method, for example, a method of directly impregnating a carbon fiber with the resin composition of the present invention including the constituent elements [B] and [C] and then heating and curing the resin composition, that is, a hand lay-up method, a filament winding method Method, pultrusion method, resin film infusion method in which a resin composition is impregnated and cured in a continuous fiber base material previously formed into a member shape, resin injection molding method, and resin transfer molding (RTM) Method is used.

  The epoxy resin composition according to the present invention includes VARTM (Vaccum-assisted ResinTransfer Molding) and VIMP (Variable Infusion Molding Process) which are listed in a 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 (ContinuousRTM), and CIRTM (Co-injectRinRiteRinRiteRinRiteRinRiteRin). sion), suitably used in molding method such as SCRIMP (Seeman's Composite Resin Infusion Molding Process).

  Hereinafter, the present invention will be described in detail with reference to examples. However, the scope of the present invention is not limited to these examples. The unit “parts” of the composition ratio means parts by mass unless otherwise specified. The measurement of various properties (physical properties) was performed in an environment at a temperature of 23 ° C. and a relative humidity of 50% unless otherwise specified.

<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 has a total filament count of 24,000, a total fineness of 1,000 tex, a specific gravity of 1.8, a strand tensile strength of 6.6 GPa, and a strand tensile elastic modulus of 324 GPa. A carbon fiber was obtained. Next, the carbon fiber was subjected to electrolytic surface treatment using an aqueous solution of ammonium hydrogen carbonate as an electrolytic solution at an electric quantity of 80 coulombs per gram of the carbon fiber. Subsequently, the carbon fiber subjected to the electrolytic surface treatment was washed with water and dried in heated air to obtain a carbon fiber as a raw material. When measured according to the method described in (5) below, the surface oxygen concentration O / C was 0.16.

  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, and then heat-treated to apply the sizing agent. A carbon fiber bundle was obtained. The amount of the sizing agent attached was adjusted to be 0.6% by mass based on the sizing agent-coated carbon fibers.

  When the carbon fiber thus produced was measured according to the method described in (7) described below, the sizing agent adhesion amount after washing was 0.16% by mass, which was a preferable adhesion amount. The interfacial adhesive 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 has a total filament number of 12,000, a total fineness of 1,000 tex, a specific gravity of 1.8, a strand tensile strength of 4.9 GPa, and a strand tensile elastic modulus of 230 GPa. A carbon fiber was obtained. Next, the carbon fiber was subjected to electrolytic surface treatment using an aqueous solution of ammonium hydrogen carbonate as an electrolytic solution at an electric quantity of 80 coulombs per gram of the carbon fiber. Subsequently, the carbon fiber subjected to the electrolytic surface treatment was washed with water and dried in heated air to obtain a carbon fiber 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 for the carbon fiber 1. The amount of the sizing agent attached was adjusted to be 0.6% by mass based on the sizing agent-coated carbon fibers. The sizing agent adhesion amount after washing was 0.17% by mass, which was a preferable adhesion amount. The interfacial adhesive strength was 43 MPa.

・ Carbon fiber 3
A polyacrylonitrile copolymer mainly composed of acrylonitrile is spun and baked, and has a total filament number of 24,000, a total fineness of 1,000 tex, a specific gravity of 1.8, a strand tensile strength of 5.9 GPa, and a strand tensile modulus of 294 GPa. A carbon fiber was obtained. Next, the carbon fiber was subjected to electrolytic surface treatment using an aqueous solution of ammonium hydrogen carbonate as an electrolytic solution at an electric quantity of 120 coulombs per gram of the carbon fiber. Subsequently, the carbon fiber subjected to the electrolytic surface treatment was washed with water and dried in heated air to obtain a carbon fiber 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 for the carbon fiber 1. The amount of the sizing agent attached was adjusted to be 0.6% by mass based on the sizing agent-coated carbon fibers. The sizing agent adhesion amount after washing was 0.19% by mass, which was a preferable adhesion amount. 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 amount of electricity was subjected to electrolytic surface treatment at 80 coulombs per gram of carbon fiber. The surface oxygen concentration O / C was 0.15. The amount of the sizing agent attached was adjusted to be 0.6% by mass based on the sizing agent-coated carbon fibers. The sizing agent adhesion amount after washing was 0.16% by mass, which was a preferable adhesion amount. The interfacial adhesive strength was 43 MPa.

・ Carbon fiber 5
A sizing agent-coated carbon fiber bundle was obtained in the same manner as for the carbon fiber 3 except that the amount of electricity was subjected to electrolytic surface treatment at 40 coulombs per gram of carbon fiber. The surface oxygen concentration O / C was 0.13. The amount of the sizing agent attached was adjusted to be 0.6% by mass based on the sizing agent-coated carbon fibers. The sizing agent adhesion amount after washing was 0.12% by mass, which was a preferable adhesion amount. The interfacial adhesive strength was 29 MPa.

・ Carbon fiber 6
A sizing agent-coated carbon fiber bundle was obtained in the same manner as for the carbon fiber 3, except that sulfuric acid was used as an electrolytic solution and the amount of electricity was subjected to electrolytic surface treatment at 20 coulombs per gram of carbon fiber. The surface oxygen concentration O / C was 0.12. The amount of the sizing agent attached was adjusted to be 0.6% by mass based on the sizing agent-coated carbon fibers. The sizing agent adhesion amount after washing was 0.13% by mass, which was a preferable adhesion amount. The interfacial adhesive strength was 27 MPa.

・ Carbon fiber 7
A sizing agent-coated carbon fiber bundle was obtained in the same manner as in the case of the carbon fiber 6, except that the amount of electricity was subjected to electrolytic surface treatment at 10 coulombs per gram of carbon fiber, and that ethylene glycol was used instead of polyglycerin polyglycidyl ether. The surface oxygen concentration O / C was 0.09. The amount of the sizing agent attached was adjusted to be 0.6% by mass based on the sizing agent-coated carbon fibers. The sizing agent adhesion amount after washing was 0.05% by mass. The interfacial adhesive strength was 21 MPa.

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

(2) Component [B]
<Epoxy resin showing liquid crystal properties 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. Then, resorcinol (hydroxyl equivalent: 55 g / eq) was added thereto as a prepolymerizing agent so that the epoxy equivalent number: hydroxyl equivalent number became 100: 25, and the mixture was heated at 200 ° C. for 3 hours in a nitrogen atmosphere to obtain epoxy. Resin 1 was obtained. The content of the prepolymer is 53 parts by mass based on 100 parts by mass of the total of 2-methyl-1,4-phenylene-bis {4- (2,3-epoxypropoxy) benzoate and its prepolymer, and is JIS K7236. The epoxy equivalent was determined to be 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) heated to 200 ° C It is melted, and resorcinol (hydroxyl equivalent: 55 g / eq) is added thereto as a prepolymerizing agent so that the epoxy equivalent number: hydroxyl equivalent number becomes 100: 25, and the mixture is heated at 200 ° C. for 3 hours in a nitrogen atmosphere. Epoxy resin 2 was obtained. The content of the prepolymer was 53 parts by mass based on 100 parts by mass of 4- {4- (2,3-epoxypropoxy) phenyl} cyclohexyl 4- (2,3-epoxypropoxy) benzoate and the prepolymer in total. When the epoxy equivalent was measured according to JIS K7236, it was 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) heated to 200 ° C Melt, add bisphenol F (hydroxyl equivalent: 100 g / eq) as a prepolymerizing agent so that the epoxy equivalent number: hydroxyl equivalent number becomes 100: 15, and heat at 200 ° C. for 3 hours under a nitrogen atmosphere. Thus, an epoxy resin 3 was obtained. The content of the prepolymer was 38 parts by mass with respect to 100 parts by mass of 4- {4- (2,3-epoxypropoxy) phenyl} cyclohexyl 4- (2,3-epoxypropoxy) benzoate and the prepolymer in total. When the epoxy equivalent was measured according to JIS K7236, it was 309 g / eq.

<Epoxy resin that does not exhibit liquid crystal properties by itself>
"Araldite (registered trademark)" MY0610 (triglycidyl-m-aminophenol, manufactured by Huntsman Japan KK)
-"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 Pure Chemicals Co., Ltd.)
-3,4'-DABAN (3,4'-diaminobenzanilide, manufactured by Nippon Pure Chemicals Co., Ltd.)
O-Tolidine (3,3'-dimethylbenzidine, manufactured by Nippon Pure Chemicals Co., Ltd.)
・ 4,4′-BAAB (4-aminophenyl 4-aminobenzoate, manufactured by Nippon Pure Chemicals Co., Ltd.)
4,4'-APTP (bis (4-aminophenyl) terephthalamide, manufactured by Nippon Pure Chemicals Co., Ltd.).

(4) Other components and curing agent other than component [C] “Seika Cure (registered trademark)”-S (4,4′-diaminodiphenyl sulfone, manufactured by Wakayama Seika Co., Ltd.)
-Thermoplastic resin "Virantage (registered trademark)" VW-10700RFP (polyether sulfone, 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 determined by X-ray photoelectron spectroscopy according to the following procedure. First, the carbon fiber from which dirt attached to the surface was removed with a solvent was cut into 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, measurement was performed using AlK _α1 , 2 as the X-ray source and setting the photoelectron escape angle to 90 °. In addition, the binding energy value of the main peak (peak top) of C1s was adjusted to 284.6 eV as a correction value of the peak accompanying the charging at the time of measurement. The C _1s main area was determined by drawing a linear baseline in the range of 282 to 296 eV. The O _1s peak area was determined by drawing a straight-line baseline in the range of 528 to 540 eV. Here, the surface oxygen concentration is calculated as an atomic ratio using a sensitivity correction value specific to the apparatus from the above ratio of the O _1s peak area to the C _1s peak area. An ESCA-1600 manufactured by ULVAC-PHI, Inc. was used as an X-ray photoelectron spectroscopy apparatus, and the sensitivity correction value specific to the apparatus was 2.33.

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

(7) Measurement of sizing agent adhesion amount after washing The sizing agent adhesion amount after washing was measured as follows. First, 2 ± 0.5 g of the sizing agent-coated carbon fiber was immersed in 10 ml of a solution in which acetonitrile and chloroform were mixed at a volume ratio of 9: 1, and ultrasonic cleaning was performed for 20 minutes to elute the sizing agent from the fiber. And the mass was measured. Further, after the washing, the carbon fiber was subjected to a heat treatment at 450 ° C. for 15 minutes in a nitrogen atmosphere. The mass change of the mass before and after the heat treatment at this time divided by the mass before the heat treatment was defined as the amount of the sizing agent attached after washing.

(8) Measurement of Interfacial Shear Strength (IFSS) The measurement of the interfacial shear strength (IFSS) was performed according to the following procedures (a) to (d).

(A) 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) Each was placed in a container. Thereafter, the mixture was heated at a temperature of 75 ° C. for 15 minutes in order to lower the viscosity of jER828 and dissolve metaphenylenediamine. Then, both were mixed well and vacuum degassing was performed at a temperature of 80 ° C. for about 15 minutes.

(B) Fixing the carbon fiber single yarn to the exclusive mold The single fiber was extracted from the carbon fiber bundle, and both ends were fixed with an adhesive while applying a constant tension to the single fiber in the longitudinal direction of the dumbbell type mold. Thereafter, in order to remove the water adhering to the carbon fiber and the mold, vacuum drying was performed at a temperature of 80 ° C. for 30 minutes or more. The dumbbell mold was made of silicone rubber, and the shape of the casting part was 5 mm in width at the center, 25 mm in length, 10 mm in width at both ends, and 150 mm in overall length.

(C) From resin casting to curing The resin prepared in the above procedure (a) is poured into the mold after vacuum drying in the above procedure (b), and the temperature is raised at a rate of 1.5 ° C. / After raising the temperature to 75 ° C in 2 minutes and holding for 2 hours, increasing the temperature to 125 ° C at a rate of 1.5 ° C / minute and holding it for 2 hours, then reducing the temperature to 30 ° C at a rate of 2.5 ° C / minute. The temperature has dropped. Thereafter, the mold was removed to obtain a test piece.

(D) Measurement of interfacial shear strength (IFSS) A tensile force was applied to the test piece obtained in the above procedure (c) at a strain rate of 0.3% / sec in the fiber axis direction (longitudinal direction) to reduce the strain by 12%. After the formation, the number N (pieces) of fiber breaks in a range of 22 mm in the center of the test piece was measured by 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 of 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 interface shear strength IFSS, which is an index of the adhesive strength between the carbon fiber and the resin interface, was calculated by the following equation. In the examples, the average of the number of measurements n = 5 was taken 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 a component other than a curing agent and a curing accelerator is added at a mixing ratio (parts by mass) shown in Table 1, and the temperature is raised 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) Preparation of prepreg The epoxy resin composition was applied on release paper using a knife coater to prepare a resin film. Next, two resin films are stacked on both sides of the carbon fiber of the component [A] arranged in one direction in a sheet shape from both sides of the carbon fiber, and the resin is impregnated into the carbon fiber by heating and pressing. Was 190 g / m ² , and the weight fraction of the resin composition was 35% to obtain a unidirectional prepreg.

(11) Mode I according to interlayer toughness _{(G IC)} Preparation of the test composite made flat and _{G IC} measurement JIS K7086 (1993), the following (a) ~ composite material for _{G IC} test by the operation of (e) A flat plate was prepared.

  (A) The unidirectional prepregs prepared in (10) were laminated by 20 ply in the same fiber direction. However, a fluororesin film having a width of 40 mm and a thickness of 50 μm was interposed at right angles to the fiber arranging direction on the laminating center plane (between the 10th and 11th plies).

  (B) The laminated prepreg was covered with a nylon film without any gap, and cured by heating and pressurizing 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) In the pin load block (length 25 mm, made of aluminum) described in JIS K7086 (1993), the adhesive portion was peeled off at the time of the test, so a triangle grip was used instead (FIG. 1). Notches having a length of 1 mm were placed at both ends in the width direction at positions 4 mm from the end of the test piece (the side sandwiching the fluororesin film), and a triangle grip was hooked. In the test, a load was applied to the test piece by pulling a triangle-shaped jig with a crosshead of an Instron universal testing machine (manufactured by Instron).

  (E) To facilitate observation of crack growth, white paint was applied to both sides of the test piece.

Using the composite material-made flat plate prepared by the following procedure was performed G _IC measurement. 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 20 mm. Testing crack performed until the evolution 100 mm, load obtained during the test - was calculated G _IC from the area of the displacement diagram.

(12) Measurement of 0 ° compressive strength One-way prepreg was cut into a predetermined size, and six sheets were laminated in one direction. Then, a vacuum bag was performed, and a temperature of 180 ° C. and a pressure of 0.59 MPa were used for 2 hours using an autoclave. To obtain a unidirectional reinforcing material (carbon fiber composite material). After bonding this one-way reinforcing material to a tab 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 obtained by setting the 0 ° direction to the length direction of the test piece. I cut it out. The obtained 0 ° directional compression test piece was subjected to a material universal testing machine (“Instron (registered trademark)” 5565 type P8564, manufactured by Instron Japan Co., Ltd.) at 23 ° C. in accordance with SACMA-SRM 1R-94. ), A compression test was performed at a test speed of 1.0 mm / min.

(13) Observation with a polarizing microscope The unidirectional prepreg prepared in (10) was cut into a width of 50 mm and a length of 50 mm, and the fiber interval was manually widened so that the prepreg became 80 mm or more in width. The composition was cured under the conditions of 2 hours to obtain a test specimen of the carbon fiber reinforced composite material for observation. The resin region of the specimen was observed with a polarizing microscope (Keyence Corporation; VHX-5000, with a polarizing filter). The case where a higher-order structure such as a fan-shaped structure or a focal conic structure was observed (bright field) was designated as “A”, and the case where no higher-order structure was observed (dark field) was designated as “B”.

(14) Measurement of diffraction angle 2θ by X-ray diffraction After the unidirectional prepreg prepared in (10) is laminated so as to have a thickness of about 1 mm, the laminated prepreg is covered with a nylon film without any gap, and is placed in an autoclave. At 180 ° C. for 2 hours under an internal pressure of 0.59 MPa for curing to form a unidirectional carbon fiber reinforced composite material. The molded carbon fiber reinforced composite material was cut into a length of 20 mm and a width of 10 mm to obtain a test piece. The measurement was performed in parallel (0 °), perpendicular (90 °), and 45 ° with respect to the carbon fiber axis in the carbon fiber composite material under the following conditions.
・ Apparatus: X 'PertPro (manufactured by SPECTALIS Corporation, PANalytical Division)
・ X-ray source: CuKα ray (tube voltage 45 kV, tube current 40 mA)
・ Detector: Goniometer + Monochromator + Scintillation counter ・ Scanning range: 2θ = 1-90 °
Scanning mode: step scan, step unit 0.1 °, counting time 40 seconds The peak of the diffraction angle 2θ in the range of 1 to 10 ° is shown in Table 1. In addition, when there was no peak, it was described as "B".

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

An arbitrary direction of the measured test piece was set to 0 °, and polarization Raman spectroscopy was measured while changing the polarization direction from 0 ° to 150 at 30 ° intervals. Regarding the Raman band intensity around 1600 cm ⁻¹ derived from the C = C stretching vibration of the aromatic ring, if the polarization direction fluctuated by ± 20% or more, described as “A” in Tables 1 and 2 as anisotropic, When the fluctuation range of any of the measured polarization directions from 0 ° to 150 ° was 20% or less, “B” is described in Tables 1 and 2 as “no anisotropy”.

(16) Measurement of heat resistance One-way prepreg is cut to a predetermined size, and after laminating 12 sheets in one direction, a vacuum bag is performed, and cured at a temperature of 180 ° C. and a pressure of 0.59 MPa for 2 hours using an autoclave. Then, a unidirectional reinforcing material (carbon fiber composite material) was obtained. A rectangular test piece having a length of 50.0 mm and a width of 12.7 mm was cut out from the unidirectional reinforcing material with the 0 ° direction as the length direction of the test piece. The obtained 0 ° direction test piece was subjected to a torsional strain DMA measurement in the temperature rising process at 5 ° C./min at 40 ° C. to 300 ° C. With respect to the obtained storage elastic modulus change curve, the intersection between the two linear portions was defined as the glass transition temperature. The two straight portions are a straight portion before the storage elastic modulus sharply decreases and a straight portion appearing in the process where the storage elastic modulus sharply decreases.

(Examples 1 to 16, Comparative Examples 1 to 5)
An epoxy resin composition for a carbon fiber reinforced composite material was prepared in accordance with the procedure (9) for preparing the epoxy resin composition according to the mixing ratios in Tables 1 and 2. Using the obtained epoxy resin composition, a prepreg was obtained by the procedure of the above-mentioned (10) Preparation of prepreg. Using the obtained prepreg, the above (11) Mode I Interlaminar toughness (G _IC) Preparation and G _IC measurement of the test composite made flat, (12) 0 ° tensile Preparation of strength test composite material made flat and Measurement, (13) observation with a polarizing microscope, (14) measurement of a 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 the examples are as shown in Table 1 and various measurement results of the comparative examples are as shown in Table 2. As in Examples 1 to 16, a resin composition having a higher-order structure and a carbon fiber having a preferable surface oxygen concentration are provided. By the combination of the above, excellent mode I interlayer toughness G _IC , 0 ° compression strength, and heat resistance were obtained.

Comparative Example 1 is a case where the constituent elements [A], [B], and [C] of the present invention are used, but the cured product of the resin composition does not form a higher-order structure. Comparative Example 1 has significantly lower mode I interlaminar toughness G _IC while having the same 0 ° compressive strength as Example 1 using the same components [A] and [C]. mode I interlayer toughness G _IC it can be seen that has been dramatically improved.

In Comparative Examples 2 and 3, the components [B] and [C] of the present invention were used, and the cured product of the resin composition had a higher-order structure. This is the case where the oxygen concentration is low and the requirement of the component [A] of the present invention is not satisfied. In this case, the mode I interlayer toughness G _IC is significantly lower than those of Examples 1 and 7 in which the components [B] and [C] are the same, respectively, and satisfies the requirement of the component [A] of the present invention. it can be seen that the mode I interlayer toughness G _IC is dramatically improved by.

Comparative Examples 4 and 5 are cases in which the cured product of the resin composition forms a higher-order structure using the components [A] and [B] of the present invention, but satisfies the requirements of the component [C]. This is the case when no curing agent is used. By that conformation formed, mode I interlayer toughness G _IC is a high value as compared with the case of non-conformational form, respectively the same components [A] with [B] Compared with Examples 4 and 3, it can be seen that the 0 ° compressive strength and the heat resistance are particularly improved by the curing agent satisfying the component [C] of the present invention because of the low 0 ° compressive strength and the heat resistance.

Example 9 is a case where a curing agent having three six-membered rings in the molecular structure was used as the component [C] of the present invention. In this case, the higher-order structure formation, was found to express high 0 ° compression strength when compared with Comparative Example 5 by the high mode I interlayer toughness G _IC and rigid skeleton curing agent, the same elements [A ] And [B], the 0 ° compressive strength was lower than that of Example 6. It is considered that the component [C] slightly dissolved in the cured product of the resin composition is the cause. From the viewpoint of not causing undissolved residue, the constituent element [C] preferably has two six-membered ring structures in the molecular structure.

Comparing Example 10 with Examples 1, 13 and 15, it can be seen that, as a component [B], an epoxy resin that does not exhibit liquid crystallinity alone as well as an epoxy resin that exhibits no liquid crystallinity alone is used as the component [B]. By including 1 to 25 parts by mass with respect to the parts by mass, the mode I interlayer toughness (G _IC ) and 0 ° compression strength are improved while maintaining the heat resistance, and it can be seen that this is more preferable.

Claims (10)

A prepreg comprising the following components [A] to [C] and satisfying the conditions [I] and [II].
[A]: carbon fiber [B]: epoxy resin [C]: a curing agent having a structure represented by the general formula (1).
(In the general formula (1), X ¹ is a single bond or one selected from the group (I). P ¹ and P ² may be the same or different, and are represented by group (II). W in group (II) is each 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 each independently represents an integer of 0 to 4. The substituents W may be all the same or different, or X ² in group (II) is selected from group (I), and F ¹ and F ² are active groups capable of reacting with an epoxy group, and group (II) Directly bonded 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 the epoxy resin composition containing the components [B] and [C] includes a resin region having molecular anisotropy showing an interference pattern when observed under 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 angle derived from the diffraction angle 2θ = 1.0 ° to 6.0 ° confirmed by wide-angle X-ray diffraction. 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 constituent elements [B] and [C] is heated from 50 ° C. to 400 ° C. at a rate of 5 ° C./min in a differential scanning calorimetry under a nitrogen atmosphere. When heated, it has an endothermic peak in the range of 250 ° C. or higher due to a phase transition of a higher-order structure. The prepreg according to any one of claims 1 to 3, wherein the component [B] includes an epoxy resin having a structure represented by the general formula (2).
(In the general formula (2), Q ¹ , Q ² and Q ³ each include one kind of structure selected from the group (III). In the general formula (2), R ¹ and R ² each have 1 to 1 carbon atoms. And Z represents an alkylene group of 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, or a bromine atom. , Iodine atom, cyano group, nitro group, or acetyl group, n independently represents an integer of 0 to 4. In the general formula (2) and group (III), Y ¹ , Y ² , and Y ³ represent , One selected from a single bond or group (IV).)
The prepreg according to any one of claims 1 to 4, wherein the component [B] includes an epoxy resin in which a part of an epoxy resin having a structure represented by the general formula (2) is prepolymerized. The prepreg according to any one of claims 1 to 5, wherein both F ¹ and F ² in the general formula (1) of the constituent element [C] are amino groups. The prepreg according to any one of claims 1 to 6, wherein the number of six-membered rings contained in the molecular structure of the constituent element [C] is two. The prepreg according to any one of claims 1 to 7, wherein the component [C] is selected from diaminophenylbenzoate, diaminobenzanilide, diaminobenzylideneaniline, diaminodiphenylacetylene, and diaminobiphenyl. The prepreg according to any one of claims 1 to 8, 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]. A carbon fiber reinforced composite material obtained by curing the prepreg according to claim 1.