Epoxy resin composition for fiber-reinforced composite material, epoxy resin film for fiber-reinforced composite material, prepreg and fiber-reinforced composite material

Abstract

To provide an epoxy resin composition, a resin film and a prepreg which can obtain good low pressure sticking properties of prepregs, are excellent in mechanical characteristics and heat resistance of a cured product, and are suitable for a fiber-reinforced composite material.SOLUTION: An epoxy resin composition for a fiber-reinforced composite material contains components [A] to [D], and satisfies conditions (1) to (4). [A] Epoxy resin, [B] a polyamine curing agent, [C] a thermoplastic resin having a glass transition temperature of 120°C or higher, and [D] a compound which has no epoxy group in the molecule and does not substantially have reactivity with the epoxy resin and the polyamine curing agent, and has a boiling point of 150°C or higher and a molecular weight of 250 or less. The epoxy resin composition contains, with respect to 100 pts.mass of the compound [A], (1) 5 to 20 pts.mass of [C] and (2) 2 to 12 pts.mass of [D], and has (3) a mass ratio [D] / [C] of 0.2 to 0.6, and (4) storage elastic modulus G' at 25°C and 0.5 Hz in dynamic viscoelasticity of 10 to 500 kPa, and storage elastic modulus G' at 50°C and 0.5 Hz of 0.1 to 5 kPa.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an epoxy resin composition, an epoxy resin film, a prepreg, and a fiber-reinforced composite material, which are suitably used for fiber-reinforced composite materials for aerospace applications, general industrial applications, sports applications, and the like.

Background Art

[0002] Fiber-reinforced composite materials using carbon fibers, aramid fibers, etc. as reinforcing fibers utilize their high specific strength and specific modulus of elasticity, and are widely used as structural materials for aircraft and automobiles, and for sports and general industrial applications such as tennis rackets, golf shafts, fishing rods, bicycles, and casings. As the resin composition used for this fiber-reinforced composite material, thermosetting resins are mainly used from the viewpoints of heat resistance and productivity, and among them, epoxy resins are preferably used from the viewpoint of mechanical properties such as adhesiveness to reinforcing fibers.

[0003] Conventionally, various methods have been used for manufacturing fiber-reinforced composite materials, but a method using a prepreg, which is a sheet-like intermediate substrate impregnated with a resin composition, is widely used. In this method, after laminating a plurality of prepregs, a fiber-reinforced composite material can be obtained as a molded product by heating this.

[0004] When using a prepreg impregnated with a resin composition, the adhesiveness between prepregs often becomes a problem, which greatly affects the workability when handling the prepreg. For example, if the adhesiveness between prepregs is poor, when forming a cylindrical fiber-reinforced composite material, even if the prepreg is wound around a mandrel (core bar), it will immediately peel off.

[0005] The adhesiveness between prepregs is related to the wettability of the resin present on the prepreg surface and the resistance to the force that gradually tries to peel off after sufficient wetting (hereinafter referred to as peel strength). If the wettability of the prepreg surface resin and / or the peel strength is too small, the stacked prepregs will easily peel off during the lamination of the prepregs or when winding around a mandrel, which will hinder the work. Conversely, if the wettability of the prepreg surface resin, the peel strength, or both are too large, it will be difficult to correct the situation when they are accidentally stacked.

[0006] As another problem, in order to apply fiber-reinforced composite materials to applications that require weight reduction, it is necessary to improve the elastic modulus, elongation, and strength of the epoxy resin used as the matrix resin. However, cured epoxy resins having a high elastic modulus are generally brittle and tend to have a low elongation. Therefore, it has been a technical problem to simultaneously improve the high elastic modulus and elongation.

[0007] Various studies have been conducted to improve these problems. For example, by using a resin composition containing an epoxy resin containing an isocyanuric acid type epoxy resin, a dicyandiamide curing agent, and a polysulfone having a weight average molecular weight within a specified range, an epoxy resin composition excellent in the resin elastic modulus and strength after curing and the tackiness of the prepreg has been studied (Patent Document 1).

[0008] In addition, an epoxy resin composition excellent in the resin strength after curing and the tackiness of the prepreg has been studied by blending a compound that improves the solubility of the curing agent dicyandiamide during resin curing and adjusting the viscosity (Patent Document 2).

[0009] On the other hand, a method of optimizing the viscoelasticity of the resin composition and improving the adhesiveness between prepregs by controlling the blending ratio of a liquid epoxy resin, a solid epoxy resin, and a thermoplastic resin soluble in the epoxy resin has been studied (Patent Document 3).

Prior Art Documents

Patent Documents

[0010] [Patent Document 1] International Publication No. 2021 / 177089 [Patent Document 2] International Publication No. 2019 / 181402 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2003 - 2990 [Summary of the Invention] [Problems to be Solved by the Invention]

[0011] When using the technology of Patent Document 1 or Patent Document 2, although it has excellent mechanical properties of epoxy resins and fiber - reinforced composite materials and sufficient tackiness as a prepreg can be obtained, a higher level is required for the adhesiveness when the prepregs are lightly laminated together.

[0012] When using the technology of Patent Document 3, the adhesiveness of the obtained prepreg is improved, but further improvement in the balance with the mechanical properties of the cured product is required.

[0013] Therefore, an object of the present invention is to provide an epoxy resin composition, a resin film, and a prepreg that can be suitably used for fiber - reinforced composite materials, which can obtain excellent adhesiveness between prepregs, that is, good low - pressure adhesiveness, even when lightly laminated, and also have excellent mechanical properties and heat resistance when formed into a cured product. [Means for Solving the Problems]

[0014] The present invention adopts the following means to solve such problems. 1. That is, an epoxy resin composition for fiber - reinforced composite materials, which contains the following constituent elements [A] to [D] and satisfies the following conditions (1) to (5). [A]: Epoxy resin, [B]: Polyamine curing agent, [C]: A thermoplastic resin having a glass transition temperature of 120°C or higher, [D]: A compound that does not have an epoxy group in the molecule and is substantially non-reactive with any of the epoxy resin and the polyamine curing agent, having a boiling point of 150 °C or higher and a molecular weight of 250 or less. (1): Component [C] is included in an amount of 5 to 20 parts by mass with respect to 100 parts by mass of component [A]. (2): Component [D] is included in an amount of 2 to 12 parts by mass with respect to 100 parts by mass of component [A]. (3): The mass ratio of component [D] to component [C] ([D] / [C]) is 0.2 to 0.6. (4): The storage modulus G' at 25 °C and 0.5 Hz in dynamic viscoelasticity measurement is 10 to 500 kPa. (5): The storage modulus G' at 50 °C and 0.5 Hz in dynamic viscoelasticity measurement is 0.1 to 5 kPa. 2. The epoxy resin composition for a fiber-reinforced composite material according to 1 above, wherein component [D] is at least one compound selected from alcohols, amides, ethers, sulfoxides, imides, and esters. 3. The epoxy resin composition for a fiber-reinforced composite material according to 1 or 2 above, wherein 25 parts by mass or more of the 100 parts by mass of component [A] is a glycidylamine type epoxy resin. 4. An epoxy resin film for a fiber-reinforced composite material, comprising the epoxy resin composition for a fiber-reinforced composite material according to any one of 1 to 3 above. 5. A prepreg in which a reinforcing fiber layer is at least partially impregnated with the epoxy resin composition for a fiber-reinforced composite material according to 4 above. 6. A fiber-reinforced composite material obtained by laminating the prepreg according to 5 above and curing the epoxy resin composition.

Advantages of the Invention

[0015] According to the present invention, it is possible to obtain excellent adhesion between prepregs, that is, good low-pressure adhesion, even when laminated thinly, and at the same time, it is possible to obtain excellent mechanical properties and heat resistance when cured, thereby obtaining an epoxy resin composition, a resin film, and a prepreg that can be suitably used for fiber-reinforced composite materials.

Mode for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail.

[0017] The epoxy resin composition for fiber-reinforced composite materials of the present invention contains components [A] to [D]. In the present invention, "component" means an individual compound contained in the composition. Also, for a certain physical property, characteristic or composition ratio, any upper limit value and any lower limit value within the numerical range described below can be arbitrarily combined (for example, for H / E described below, a combination of 0.30 or more and 1.10 or less can be taken as a preferable range) unless otherwise specified.

[0018] Component [A] in the present invention is an epoxy resin. It is preferable that component [A] contains two or more epoxy groups in one molecule because it can increase the glass transition temperature of the cured product obtained by heat-curing the resin composition and improve the heat resistance. Also, an epoxy resin containing one epoxy group in one molecule may be blended. These epoxy resins may be used alone or in an appropriate combination.

[0019] Examples of the epoxy resin of component [A] include glycidylamine type epoxy resins such as diaminodiphenylmethane type, diaminodiphenylsulfone type, aminophenol type, metaxylenediamine type, 1,3-bisaminomethylcyclohexane type, glycidyl ether type epoxy resins such as bisphenol type, phenol novolac type, orthocresol novolac type, trishydroxyphenylmethane type, tetraphenylol ethane type, glycidyl ester type epoxy resins such as terephthalic acid type, phthalic acid type, and isocyanurate type epoxy resins. Among them, glycidylamine type epoxy resins and glycidyl ether type epoxy resins are particularly preferably used because of their good balance of physical properties.

[0020] As component [A] in the present invention, it is preferable that 25 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more of a glycidylamine type epoxy resin be contained in 100 parts by mass of component [A]. By containing 25 parts by mass or more of the glycidylamine type epoxy resin in 100 parts by mass of component [A], the compatibility with component [C]: a thermoplastic resin having a glass transition temperature of 120°C or higher is good, and a cured product that is uniform and excellent in strength can be easily obtained.

[0021] In addition, other epoxy compounds may be appropriately blended in the epoxy resin composition of the present invention.

[0022] Component [B] in the present invention is a polyamine curing agent. The polyamine curing agent has a plurality of amino groups (including two modes of amino groups) that can react with epoxy groups and functions as a curing agent.

[0023] Examples of the polyamine curing agent include aliphatic polyamines and aromatic polyamines. These polyamine curing agents may be used alone or in appropriate combination.

[0024] Those classified as aliphatic polyamines include chain aliphatic polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and diethylaminopropylamine, cycloaliphatic polyamines such as isophoronediamine and bis(4-aminocyclohexyl)methane, aliphatic aromatic polyamines such as ortho-xylenediamine, meta-xylenediamine, and para-xylenediamine, and dicyandiamide.

[0025] Those classified as aromatic polyamines include diethyltoluenediamines such as 2,2'-diethyldiaminodiphenylmethane, 2,4-diethyl-6-methyl-m-phenylenediamine, 4,6-diethyl-2-methyl-m-phenylenediamine, 4,6-diethyl-m-phenylenediamine, etc.; 4,4'-methylenebis(N-methylaniline), 4,4'-methylenebis(N-ethylaniline), 4,4'-methylenebis(N-sec-butylaniline), N,N'-di-sec-butyl-p-phenylenediamine, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-t-butyl-4,4'-diaminodiphenylmethane, and the like.

[0026] From the point that the pot life can be effectively improved, it is a preferred embodiment to use a solid curing agent, and it is preferable to contain at least one of dicyandiamide, 3,3'-diaminodiphenylsulfone, and 4,4'-diaminodiphenylsulfone.

[0027] As the blending amount of the polyamine curing agent in the present invention, it is preferable that the ratio H / E of the number of moles E of the epoxy group of component [A] to the number of moles H of the active hydrogen of the polyamine curing agent is 0.20 or more and 1.30 or less, more preferably 0.30 or more and 1.20 or less, and even more preferably 0.50 or more and 1.10 or less. By setting H / E within such a range, a crosslinked structure can be appropriately formed by the reaction between the epoxy resin and the polyamine curing agent, and a resin cured product excellent in strength and elongation can be obtained.

[0028] In particular, when diaminodiphenyl sulfone is applied as component [B] in the present invention, it is preferable that H / E is 0.50 or more and 1.30 or less. By making it more preferably 0.70 or more and 1.20 or less, and even more preferably 0.80 or more and 1.10 or less, the balance of the heat resistance and mechanical properties of the epoxy resin composition of the present invention may be improved.

[0029] Also, when dicyandiamide is applied as component [B] in the present invention, it is preferable that H / E is 0.20 or more and 1.20 or less, more preferably an amount in the range of 0.30 or more and 1.00 or less, and most preferably an amount in the range of 0.50 or more and 0.80 or less. When the amount of the active hydrogen group is within this range, an epoxy resin cured product excellent in the balance between heat resistance and mechanical properties may be obtained.

[0030] Component [C] is a thermoplastic resin having a glass transition temperature of 120°C or higher. Component [C] is an essential component from the viewpoints of adjusting the viscoelasticity of the resin composition, particularly optimizing the storage elastic modulus G' at 50°C described later, and the heat resistance of the cured product.

[0031] As the thermoplastic resin that can be used in the present invention as the constituent element [C], examples of those having a glass transition temperature of 120°C or higher include polyamide, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyamideimide, polyimide, polyetherimide, polysulfone, polyethersulfone, polyether ketone, polyetherether ketone, polyether nitrile, etc. Among them, polyetherimide, polysulfone, and polyethersulfone are preferably used because they have good compatibility with epoxy resin and are likely to obtain a uniform cured product.

[0032] The glass transition temperature of the constituent element [C] is 120°C or higher. When the glass transition temperature of the constituent element [C] is less than 120°C, the heat resistance of the cured product is likely to be insufficient. From the viewpoint of enhancing the heat resistance of the cured product, the glass transition temperature of the constituent element [C] is preferably 150°C or higher, and more preferably 180°C or higher. Also, there is no particular upper limit to the boiling point of the constituent element [C], but the boiling points of the compounds usually used in the present invention are mostly 400°C or lower.

[0033] The glass transition temperature of the constituent element [C] is determined according to JIS K 7121:1987 by the method for obtaining the midpoint glass transition temperature in differential scanning calorimetry (DSC). Examples of the measuring device include Pyris1 DSC (manufactured by Perkin Elmer). The sample is taken in an aluminum sample pan, and the measurement is performed at a heating rate of 40°C / min in a nitrogen atmosphere, and the midpoint glass transition temperature in the region where the baseline in the obtained DSC curve shifts to the endothermic side is adopted.

[0034] The content of component [C] in the present invention contains 5 to 20 parts by mass of component [C] with respect to 100 parts by mass of component [A], more preferably 8 to 20 parts by mass, and still more preferably 8 to 18 parts by mass. When the above content is less than 5 parts by mass, the adhesiveness between prepregs is insufficient. When it exceeds 20 parts by mass, a coarse phase separation structure is formed after curing, resulting in insufficient mechanical properties, insufficient wettability of the resin on the prepreg surface, and poor adhesiveness between prepregs.

[0035] In addition, the epoxy resin composition of the present invention may contain a thermoplastic resin other than component [C] as long as the physical properties are not impaired.

[0036] Component [D] is a compound that does not have an epoxy group in its molecule and is substantially non-reactive with either component [A]: epoxy resin and component [B]: polyamine curing agent. That is, component [D] is present in the voids of the crosslinked structure formed by the reaction of the epoxy resin and the polyamine curing agent without being incorporated into the crosslinked structure, and its state is maintained even after curing. By including component [D], the elastic modulus of the obtained cured epoxy resin becomes higher, and a cured epoxy resin with high elongation and high strength can be obtained. The reason for this is not clear, but it is considered that component [D] is not constrained by a covalent bond with the crosslinked structure formed by the reaction of the epoxy resin and the polyamine curing agent, and is appropriately retained in the voids of the crosslinked structure, effectively filling the voids in the cured product and increasing the elastic modulus of the cured product. It is also an essential component from the viewpoint of optimizing the storage elastic modulus G' at 25°C described later.

[0037] Whether it substantially has reactivity with the epoxy resin and the polyamine curing agent can be confirmed by DSC of a mixture obtained by mixing component [D] and component [A]: epoxy resin, or component [D] and component [B]: polyamine curing agent in equimolar amounts. As a measuring device, for example, Pyris1 DSC (manufactured by Perkin Elmer) can be used. The above mixture is sampled into an aluminum sample pan and measured at a heating rate of 10°C / min from 0°C to 150°C under a nitrogen atmosphere. In the obtained DSC curve, the presence or absence of reactivity can be determined by checking whether an exothermic reaction is observed. However, when a compound having a boiling point of less than 150°C is included in the above components, it is confirmed by whether an exothermic reaction is observed from 0°C to its boiling point.

[0038] Component [D] is preferably a compound having at least one functional group selected from the group consisting of alcoholic hydroxyl group, amide group, ketone group, ether group, sulfoxide group, imide group, and ester group in the molecule. Among them, a compound having at least one functional group selected from the group consisting of alcoholic hydroxyl group, amide group, and ketone group is more preferable. When component [D] has a highly polar functional group as described above in the molecule, a strong intermolecular interaction acts between the hydroxyl group in the crosslinked structure formed by component [A] and component [B], and component [D] is likely to be appropriately retained in the voids of the crosslinked structure. Therefore, an especially excellent effect of improving elongation and strength can be obtained. From such a viewpoint, as the type of the compound, component [D] is preferably at least one compound selected from alcohols, amides, ketones, ethers, sulfoxides, imides, and esters.

[0039] Specifically, examples of component [D] include amides such as N-methylformamide, N-methylacetamide, 2-pyrrolidone, N-methylpropionamide, N-ethylacetamide, N-methylacetanilide, N,N'-diphenylacetamide, and diols such as ethanediol, propanediol, butanediol, pentanediol, hexanediol, and heptanediol.

[0040] Component [D] may be a single compound or a mixture of multiple compounds used as appropriate.

[0041] The boiling point of component [D] is 150°C or higher. When the boiling point of component [D] is less than 150°C, component [D] is likely to volatilize when the epoxy resin composition cures, and the mechanical properties of the cured product are likely to be inferior. From the perspective of suppressing the generation of voids and the degradation of mechanical properties in the cured product, the boiling point of component [D] is preferably 190°C or higher, more preferably 230°C or higher. Also, from the perspective of compatibility with the epoxy resin and curing agent, the boiling point of component [D] is preferably 400°C or lower. In the present invention, the boiling point is the value at normal pressure (101 kPa). Also, when the boiling point at normal pressure cannot be measured, the converted boiling point converted to 101 kPa using a boiling point conversion chart can be used.

[0042] The molecular weight of component [D] is 250 or less. When the molecular weight of component [D] exceeds 250, it becomes difficult for component [D] to be appropriately retained in the voids of the cross-linked structure formed by the reaction of the epoxy resin and polyamine, and the mechanical properties of the resulting cured product are likely to be inferior. From the perspective of obtaining a cured product with excellent flexural modulus, strength, and elongation, the molecular weight of component [D] is preferably 150 or less, more preferably 120 or less. Also, from the perspective of component [D] being appropriately retained in the voids of the cross-linked structure, the molecular weight of component [D] is preferably 70 or more, more preferably 80 or more.

[0043] The melting point of component [D] is preferably 140°C or lower, more preferably 120°C or lower, and even more preferably 80°C or lower. When the melting point is 140°C or lower, component [D] has good compatibility with other components in the epoxy resin composition, and it is easy to obtain an effect of improving the mechanical properties when made into a cured product. Also, from the perspective of preventing the viscosity of the resin composition from becoming too low, the melting point of component [D] is preferably -50°C or higher.

[0044] In the epoxy resin composition of the present invention, component [D] is contained in an amount of 2 parts by mass or more and 12 parts by mass or less with respect to 100 parts by mass of component [A]. When the content is less than 2 parts by mass, the mechanical properties of the cured product are insufficient, and the adhesiveness when lightly bonding prepregs together deteriorates. Further, when the content exceeds 12 parts by mass, even if the prepregs are bonded, they are easily peeled off. From the viewpoints of the mechanical properties of the cured product and the adhesiveness when lightly bonding prepregs together, it is preferable that component [D] is contained in an amount of 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of component [A], and more preferably 3 parts by mass or more and 8 parts by mass or less.

[0045] Further, the mass ratio of [D] to [C] ([D] / [C]) in the present invention is in the range of 0.2 or more and 0.6 or less. When [D] / [C] is outside this range, the resin composition is likely to be outside the optimum storage elastic modulus G' range at 25°C and 50°C described later, and sufficient adhesiveness when lightly bonding prepregs together cannot be obtained. Further, from the viewpoint of obtaining more excellent adhesiveness, it is preferable that [D] / [C] is 0.2 or more and 0.5 or less, and more preferably 0.3 or more and 0.5 or less.

[0046] The epoxy resin composition of the present invention may be blended with a curing accelerator from the viewpoint of controlling the curing rate. Examples of the curing accelerator include urea compounds and imidazole compounds, and urea compounds can be particularly preferably used from the viewpoint of the storage stability of the epoxy resin composition.

[0047] Examples of the urea compound include 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, phenyldimethylurea, and toluenebisdimethylurea.

[0048] The epoxy resin composition of the present invention has a storage elastic modulus G' at 25°C and 0.5 Hz, determined by dynamic viscoelasticity measurement, of 10 kPa or more and 500 kPa or less. When G' at 25°C and 0.5 Hz is less than 10 kPa, the stickiness of the resin composition at room temperature is too high, resulting in poor handleability when made into a prepreg. On the other hand, when it exceeds 500 kPa, the resin composition at room temperature is too hard, and the wettability is insufficient just by lightly laminating prepregs together, making it difficult to laminate in the first place. Also, from the perspective of optimizing the wettability between prepregs, G' at 25°C and 0.5 Hz is preferably 10 kPa or more and 300 kPa or less, and more preferably 30 kPa or more and 200 kPa or less.

[0049] Further, the epoxy resin composition of the present invention has a storage elastic modulus G' at 50°C and 0.5 Hz, determined by dynamic viscoelasticity measurement, of 0.1 kPa or more and 5 kPa or less. When G' at 50°C and 0.5 Hz is less than 0.1 kPa, the resistance to peeling is small even when the resins are sufficiently wet, resulting in insufficient peel strength. On the other hand, when it exceeds 5 kPa, the peel strength becomes too strong when the resins are wet, making repair difficult after once laminating. Also, from the perspective of optimizing the peel strength after the resins are wet, G' at 50°C and 0.5 Hz is preferably 0.1 kPa or more and 3 kPa or less, and more preferably 0.2 kPa or more and 2 kPa or less.

[0050] The epoxy resin composition of the present invention can be made into a sheet in various ways to produce an epoxy resin film. For example, a method of dissolving the epoxy resin composition in an organic solvent such as acetone, methyl ethyl ketone, and methanol to reduce the viscosity, coating it on a release paper, and then evaporating the organic solvent to obtain a resin film, or a method of reducing the viscosity by heating without using an organic solvent and coating it on a release paper to obtain a resin film can be used.

[0051] The basis weight of the above-mentioned resin film is preferably 15~150 g / m 2 . The basis weight of the resin film is 15~150 g / m2 By setting it within the range, when impregnating the reinforcing fibers to obtain a prepreg, a sufficient amount of resin can be ensured in the prepreg, so that sufficient adhesiveness between the prepregs can be easily obtained.

[0052] Examples of the reinforcing fibers used in the prepreg of the present invention preferably include carbon fibers, graphite fibers, aramid fibers, glass fibers, etc., and carbon fibers are particularly preferred. The form and arrangement of the reinforcing fibers are not limited. For example, long fibers aligned in one direction, single tows, woven fabrics, knits, and fiber structures such as braids are used. Two or more types of carbon fibers, glass fibers, aramid fibers, boron fibers, PBO fibers, high-strength polyethylene fibers, alumina fibers, and silicon carbide fibers may be used in combination as the reinforcing fibers.

[0053] Specific examples of the carbon fibers include acrylic-based, pitch-based, and rayon-based carbon fibers, and acrylic-based carbon fibers with particularly high tensile strength are preferably used.

[0054] As the form of the carbon fibers, twisted yarns, untwisted yarns, and non-twisted yarns can be used. However, in the case of twisted yarns, since the orientation of the filaments constituting the carbon fibers is not parallel, it causes a decrease in the mechanical properties of the obtained carbon fiber-reinforced composite material. Therefore, untwisted yarns or non-twisted yarns with a good balance between the moldability and strength characteristics of the carbon fiber-reinforced composite material are preferably used.

[0055] The carbon fibers preferably have a tensile elastic modulus of 200 GPa or more and 440 GPa or less. The tensile elastic modulus of the carbon fibers is affected by the crystallinity of the graphite structure constituting the carbon fibers, and the higher the crystallinity, the higher the tensile elastic modulus. This range is preferable because all of the rigidity and strength of the carbon fiber-reinforced composite material are balanced at a high level. A more preferable tensile elastic modulus is 230 GPa or more and 400 GPa or less, and even more preferably 260 GPa or more and 370 GPa or less. Here, the tensile elastic modulus of the carbon fibers is a value measured according to JIS R7608 (2008).

[0056] The prepreg of the present invention is in a form in which an epoxy resin composition is impregnated in reinforcing fibers in advance, and can be manufactured by various known methods. For example, the prepreg can be manufactured by a hot melt method in which the resin composition is made low-viscosity by heating without using an organic solvent and impregnated in the reinforcing fibers. The hot melt method is preferred because voids are less likely to occur in the molded product compared to the wet method using an organic solvent.

[0057] In the hot melt method, methods such as directly impregnating the reinforcing fibers with the resin composition made low-viscosity by heating, or first preparing a resin film with a release paper on which the resin composition is once coated on the release paper and then stacking the resin film side on both sides or one side of the reinforcing fibers and heating and pressing to impregnate the reinforcing fibers with the resin composition can be used.

[0058] Note that the prepreg of the present invention is not limited to only those in which the epoxy resin composition is completely impregnated to the inside of the reinforcing fiber layer. Those in which the reinforcing fiber layer is partially impregnated, more specifically, those in which the surface layer of the reinforcing fiber layer or the reinforcing fiber layer is partially impregnated and the epoxy resin composition and the reinforcing fibers can be handled integrally are regarded as prepregs. That is, those in which the reinforcing fiber layer is at least partially impregnated with the epoxy resin composition are regarded as prepregs in the present invention.

[0059] The content of the reinforcing fibers in the prepreg is preferably 30% by mass or more and 90% by mass or less. By setting it to 30% by mass or more, more preferably 35% by mass or more, and still more preferably 65% by mass or more, it is easy to obtain the advantages of a fiber-reinforced composite material excellent in specific strength and specific modulus. Further, by setting the fiber content within the above range, it is possible to suppress an excessive increase in the heat generation amount during curing when molding into a fiber-reinforced composite material. On the other hand, by setting the above content to 90% by mass or less, more preferably 85% by mass or less, it is easy to suppress the generation of voids in the composite material due to poor resin impregnation, and it is also easy to maintain the adhesiveness between prepregs.

[0060] The fiber-reinforced composite material of the present invention can be manufactured, for example, by laminating the prepreg of the present invention described above in a predetermined form and applying pressure and heat to cure the resin. Here, methods for applying heat and pressure include a press molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, an internal pressure molding method, and the like.

[0061] The fiber-reinforced composite material of the present invention can be widely used in aerospace applications, general industrial applications, and sports applications. More specifically, in general industrial applications, it is suitably used for structures such as automobiles, ships, and railway vehicles. In sports applications, it is suitably used for golf shafts, fishing rods, and rackets for tennis and badminton.

Examples

[0062] Hereinafter, the present invention will be described by way of examples. However, the scope of the present invention is not limited to these examples. The unit “part” of the composition ratio means parts by mass unless otherwise noted. In addition, the measurement of various properties (physical properties) was carried out in an environment of a temperature of 23°C and a relative humidity of 50% unless otherwise noted.

[0063] <Materials used in Examples and Comparative Examples> (1) Component [A]: Epoxy resin · “jER (registered trademark)” 828 (liquid bisphenol A type epoxy resin, epoxy equivalent: 189 g / eq, manufactured by Mitsubishi Chemical Corporation) · “jER (registered trademark)” 1001 (solid bisphenol A type epoxy resin, epoxy equivalent: 475 g / eq, manufactured by Mitsubishi Chemical Corporation) · “Sumiepoxy (registered trademark)” ELM-434 (tetraglycidyl diaminodiphenylmethane, epoxy equivalent: 119 g / eq, manufactured by Sumitomo Chemical Co., Ltd.).

[0064] (2) Component [B]: Polyamine curing agent · DICY7 (dicyandiamide, active hydrogen equivalent: 21 g / eq, number of active hydrogens: 4, manufactured by Mitsubishi Chemical Corporation).

[0065] (3) Other component [B']: Curing accelerator · DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Co., Ltd.).

[0066] (4) Component [C]: Thermoplastic resin with a glass transition temperature of 120°C or higher · "Sumika Excel (registered trademark)" PES5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.).

[0067] (5) Other component [C']: Thermoplastic resin with a glass transition temperature of less than 120°C · "Vinylec (registered trademark)" K (polyvinyl formal, manufactured by JNC Corporation).

[0068] (6) Component [D]: Compound having no epoxy group in the molecule and substantially non-reactive with either epoxy resin or polyamine curing agent, with a boiling point of 150°C or higher and a molecular weight of 250 or less · N-ethylacetamide (boiling point: 206°C, melting point: -32°C, molecular weight m: 73 g / mol, manufactured by Tokyo Chemical Industry Co., Ltd.) · 1,2-propanediol (boiling point: 188°C, melting point: -59°C, molecular weight: 76, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0069] <Method for preparing epoxy resin composition> (1) Preparation of curing agent master Component [A]: Prepare 10 parts by mass of "jER (registered trademark)" 828 (10 parts by mass based on 100 parts by mass of all epoxy resins), and add Component [B]: DICY7 in the amounts shown in the table respectively, and knead at room temperature to obtain a mixture. The mixture was passed through a three-roll mill twice to prepare a curing agent master.

[0070] (2) Preparation of epoxy resin composition The remaining 90 parts by mass of component [A] excluding 10 parts by mass of “jER (registered trademark)” 828 and component [C] used in the above (1) were put into a beaker, heated at 150 °C and uniformly dissolved, and then cooled to 60 °C or lower. After cooling, the curing agent master and the curing accelerator prepared in the above (1) and component [D] were each added in the amounts shown in the table, and stirred well at 60 °C or lower to obtain an epoxy resin composition.

[0071] The following measuring methods were used to measure the epoxy resin compositions of each example.

[0072] <Various evaluation methods> (1) Measurement of the storage modulus G' of the epoxy resin composition The prepared uncured epoxy resin composition was used as a sample and measured by dynamic viscoelasticity measurement. ARES-G2 (manufactured by TA Instruments) was used as the measuring device. The sample was set on a 25 mm parallel plate, a tensile cycle of 0.5 Hz was applied, and the storage modulus G' in the range of 25 °C and 50 °C was measured. (2) Evaluation of the low-pressure sticking property of the epoxy resin composition The prepared epoxy resin composition was coated on a release paper, and a resin film with a resin basis weight of 50 g / m 2 was prepared as a sample. ARES-G2 (manufactured by TA Instruments) was used as the measuring device. Two 8 mm parallel plates were prepared, and double-sided tapes were attached to the surfaces of each plate. Then, the resin film was transferred from the release paper to the double-sided tapes to set the resin film on the surface of the parallel plate. The parallel plate with the transferred resin film was set on the upper and lower jigs of ARES-G2, and the measurement was carried out in the test mode of Axial Test. A load of 10 gf was applied for 2 seconds to press the upper and lower resin films against each other, and then the maximum load generated when peeling at a rate of 0.5 mm / min was read. When such a maximum load was 15 gf or more, it was regarded as good sticking property and marked as “○”, and when it was less than 15 gf, it was regarded as insufficient sticking property and marked as “×”. (3) Preparation of an epoxy resin cured plate The prepared uncured epoxy resin composition was degassed in a vacuum, and then sandwiched between "Teflon (registered trademark)" spacers with a thickness of 2 mm and cast into a mold set to a thickness of 2 mm. Thereafter, the temperature was raised from 30°C at a rate of 1.7°C / min and held at 90°C for 60 minutes, and then the temperature was raised at a rate of 2.0°C / min and cured at 135°C for 120 minutes to obtain a resin cured plate with a thickness of 2 mm. (4) Three-point bending measurement of the resin cured plate From the resin cured plate obtained in (3), test pieces with a width of 10 mm and a length of 60 mm were cut out. Using an Instron universal testing machine (manufactured by Instron Corporation), with a span of 32 mm, a crosshead speed of 2.5 mm / min, and a sample number of n = 6, the average values of the elastic modulus and elongation when three-point bending was performed according to JIS K7171 (1994) were taken as the bending elastic modulus and elongation of the resin cured product, respectively. (5) Glass transition temperature (Tg) measurement of the resin cured plate From the resin cured plate obtained in (3), test pieces with a width of 12.7 mm and a length of 55 mm were cut out. According to SACMA SRM18R-94, the glass transition temperature was determined by the DMA method. In the curve showing the transition of the storage elastic modulus G' with respect to temperature, the intersection temperature value of the tangent line in the region indicating that the target cured product is in a glassy state and the tangent line in the region indicating that it is in a transition state was taken as the glass transition temperature. Here, the measurement was performed at a heating rate of 5°C / min and a frequency of 1 Hz.

[0073] <Examples 1 to 6, Comparative Examples 1 to 4> Resin compositions prepared by mixing components in the ratios as described in Table 1 were prepared by the above method, and the storage elastic modulus G' of the resin composition was measured and the low-pressure adhesion property was evaluated by the above method. In addition, three-point bending measurement and glass transition temperature measurement of the epoxy resin cured product were performed.

[0074] Examples 1 to 6 were all resin compositions excellent in low-pressure adhesiveness, and also excellent in the balance of flexural modulus, elongation, and Tg in terms of the cured product properties. When not containing component [C] or [D] as in Comparative Examples 1 and 2, the low-pressure adhesiveness was insufficient. In Comparative Example 3, component [C'] was used instead of component [C], but the heat resistance of the resin cured product was particularly insufficient. Comparative Example 4 had a large composition with [D] / [C] = 1.0, but the low-pressure adhesiveness was insufficient.

[0075]

Table 1

Claims

1. An epoxy resin composition for a fiber-reinforced composite material, comprising the following components [A] to [D] and satisfying the following conditions (1) to (5): [A]: epoxy resin, [B]: Polyamine curing agent, [C]: a thermoplastic resin having a glass transition temperature of 120° C. or higher; [D]: a compound having a boiling point of 150° C. or higher and a molecular weight of 250 or lower, which does not have an epoxy group in the molecule and is substantially unreactive with either the epoxy resin or the polyamine curing agent; (1): The component [C] is contained in an amount of 5 to 20 parts by mass per 100 parts by mass of the component [A]. (2): The component [D] is contained in an amount of 2 to 12 parts by mass per 100 parts by mass of the component [A]. (3): The mass ratio of component [D] to component [C] ([D] / [C]) is 0.2 to 0.

6. (4): The storage modulus G' at 25° C. and 0.5 Hz in dynamic viscoelasticity measurement is 10 to 500 kPa. (5): The storage modulus G' at 50° C. and 0.5 Hz in dynamic viscoelasticity measurement is 0.1 to 5 kPa.

2. 2. The epoxy resin composition for fiber-reinforced composite materials according to claim 1, wherein the component [D] is at least one compound selected from the group consisting of alcohols, amides, ketones, ethers, sulfoxides, imides, and esters.

3. 3. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 or 2, wherein, of 100 parts by mass of the component [A], 25 parts by mass or more is a glycidyl amine-type epoxy resin.

4. 3. An epoxy resin film for fiber-reinforced composite materials, comprising the epoxy resin composition for fiber-reinforced composite materials according to claim 1 or 2.

5. A prepreg comprising a reinforcing fiber layer at least partially impregnated with the epoxy resin composition for fiber-reinforced composite materials according to claim 1 or 2.

6. A fiber-reinforced composite material obtained by laminating the prepreg according to claim 5 and curing the epoxy resin composition.

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