Epoxy resin composition, cured resin product, fiber-reinforced composite material, and method for producing fiber-reinforced composite material

Abstract

Provided by the present invention is an epoxy resin composition which contains at least: an epoxy resin [A] constituted from an epoxy compound having four or more glycidyl groups; and an aromatic polyamine [B] that is a liquid at 25ºC. In a differential scanning calorimetry curve obtained by subjecting the epoxy resin composition to differential scanning calorimetric measurements at a temperature increase rate of 20ºC / min, if an exothermic onset temperature, which is determined from the intersection of a base line and a tangent of an inflection point on the low temperature side of a hardening exothermic peak, is denoted by S (ºC) and the temperature at which the degree of curing, as determined from the integrated value of the hardening exothermic peak on the differential scanning calorimetry curve, is 95% is denoted by R (ºC), then both relationships shown by numerical formula (1) and numerical formula (2) are satisfied. Numerical formula (1): 10≤S-T≤30; numerical formula (2): R-T<98 (in the numerical formula (1) and numerical formula (2), T is any value selected from within the range 125-180, and the value of T in the numerical formula (1) and numerical formula (2) are the same. The numerical formula (1) and numerical formula (2) should be satisfied for any value of T that is selected from within the range 125-180).

Description

Epoxy resin composition, cured resin, fiber-reinforced composite material, and method for producing fiber-reinforced composite material

[0001] The present invention relates to an epoxy resin composition, a cured resin, a fiber-reinforced composite material, and a method for producing the fiber-reinforced composite material. More specifically, the present invention relates to an epoxy resin composition, a cured resin, a fiber-reinforced composite material, and a method for producing the fiber-reinforced composite material, which have a long pot life at curing temperatures and fast curing properties.

[0002] Fiber-reinforced composite materials are lightweight, strong, and rigid, and are therefore used in a wide range of fields, including sports and leisure applications such as fishing rods and golf shafts, and industrial applications such as automobiles and aircraft. Known molding methods for composite materials that use a thermosetting resin as the matrix resin include the resin transfer molding (RTM) method, in which a reinforcing fiber substrate placed in a mold is impregnated with a liquid resin composition and then the resin composition is cured to obtain a fiber-reinforced composite material, and a method in which a reinforcing fiber substrate is impregnated with a resin composition in advance and formed into a sheet-like prepreg (intermediate substrate) is molded.

[0003] In recent years, the RTM method has been attracting attention as a low-cost, highly productive production method for fiber-reinforced composite materials, requiring fewer steps and no expensive equipment such as an autoclave. The resin composition used in the RTM method mainly contains an epoxy resin and a curing agent, with other additives added as needed. An aromatic polyamine is used as the curing agent in order to obtain a cured resin or fiber-reinforced composite material with high mechanical properties.

[0004] When an epoxy resin composition used in the RTM method is impregnated into a reinforcing fiber substrate, it is necessary to prevent solids in the epoxy resin composition from being filtered out by the reinforcing fiber substrate. Therefore, it is common to dissolve the curing agent and additives in the epoxy resin beforehand. An epoxy resin composition in which the curing agent and additives are pre-dissolved in the epoxy resin is called a one-component epoxy resin composition. In one-component epoxy resin compositions, the reaction between the epoxy resin and the curing agent proceeds relatively easily because the curing agent is dissolved in the epoxy resin, which poses the problem of a short shelf life for the epoxy resin composition. Therefore, one-component epoxy resin compositions require refrigerated storage to inhibit the reaction between the epoxy resin and the curing agent, and they are not particularly easy to handle.

[0005] To solve this problem, two-component epoxy resin compositions have been investigated, in which an epoxy resin and a curing agent are mixed immediately before use. A two-component epoxy resin composition is an epoxy resin composition that is composed of a base liquid containing an epoxy resin as a main component and a curing agent liquid (curing agent composition) containing a curing agent as a main component, and that is used by mixing these two liquids immediately before use.

[0006] In two-component epoxy resin compositions, the base liquid and the curing agent liquid are mixed immediately before use, so ease of mixing is important. Although it is possible to use the curing agent used in one-component epoxy resin compositions as the curing agent for two-component epoxy resin compositions, as described in Patent Document 1, aromatic polyamine curing agents used in one-component epoxy resin compositions are usually solids, which can easily cause poor mixing with the base liquid. In order to prevent poor mixing with the base liquid, it is desirable for the curing agent composition to be in a liquid form.

[0007] Epoxy resin compositions using a liquid aromatic polyamine as a curing agent are described in Patent Documents 2 and 3. However, the cured resin products obtained by curing the epoxy resin compositions described in Patent Documents 2 and 3 do not have the mechanical properties such as elastic modulus and fracture toughness required for industrial applications such as automobiles and aircraft, and there is a demand for improvements in these properties.

[0008] In the RTM process, shortening the curing time of the resin composition (fast curing) is required for highly efficient production of fiber-reinforced composite materials. Patent Document 4 proposes a fast-curing two-component epoxy resin composition using a compound having two or more aromatic rings with phenolic hydroxyl groups. However, when a compound having a phenolic hydroxyl group is added to an epoxy resin composition, its high reactivity causes a rapid increase in viscosity of the resin composition, significantly shortening its usable life in the RTM process. This makes it difficult to impregnate a sufficient amount of the epoxy resin composition into the reinforcing fiber substrate. As a result, fiber-reinforced composite materials produced using such epoxy resin compositions tend to have many inherent defects such as voids, resulting in problems such as reduced compressive performance and damage tolerance of the fiber-reinforced composite structure. In the RTM method described in Patent Document 4, a fiber-reinforced composite material is produced by injecting a resin composition into a mold preheated to a temperature (80°C) lower than the curing temperature (130°C) of the resin composition, impregnating a reinforcing fiber substrate placed in the mold with the liquid resin composition, and then heating the mold at a constant temperature increase rate (1.5°C / min) up to the curing temperature (130°C) of the resin composition to pre-cure the resin composition. Therefore, it takes a long time to increase the temperature from the injection temperature of the resin composition to the curing temperature.

[0009] Thus, there has not been a two-component epoxy resin composition available to date that has sufficiently fast curing properties to achieve high productivity for fiber-reinforced composite materials, and that can give cured resin products that have high levels of heat resistance and mechanical properties required for industrial applications such as automobiles and aircraft.

[0010] JP 2014-148572 A JP 2015-193713 A WO2009 / 119467 A Japanese Patent No. 6617559 A

[0011] As mentioned above, in conventional RTM processes, a fiber-reinforced composite material is produced by injecting a resin composition into a mold preheated to a temperature (e.g., 80-100°C) lower than the curing temperature (e.g., 125-180°C). The liquid resin composition is then impregnated into a reinforcing fiber substrate placed in the mold, and the mold is then heated to the curing temperature of the resin composition to cure the resin composition. When the mold preheating temperature is low, the pot life of the resin composition is maintained relatively long, but production efficiency is reduced. On the other hand, when the mold preheating temperature is increased to rapidly cure the resin composition, the pot life of the resin composition is extremely short. As a result, the resulting fiber-reinforced composite material contains many inherent defects, such as voids. With conventional epoxy resin compositions, if the pot life is too short during RTM molding, gelation occurs before the injection into the mold is completed, resulting in molding defects. On the other hand, if the pot life is too long, the curing time is extended, resulting in reduced production efficiency. In particular, it is difficult to adjust the curing speed, and the technical challenge is to optimize the balance between in-mold fluidity and curing characteristics.

[0012] The present invention aims to solve the above-mentioned problems of the conventional art by providing an epoxy resin composition that has low viscosity, ensures a sufficient pot life at the curing temperature of the resin composition, and has fast curing properties. Another object of the present invention is to provide a cured resin and a fiber-reinforced composite material that have heat resistance and excellent mechanical properties.

[0013] As a result of investigations aimed at solving the above-mentioned problems, the present inventors have found that the balance between pot life and rapid curing property can be controlled and the above-mentioned problems can be solved by using an epoxy resin composition which is composed of a combination of a predetermined epoxy resin, a curing agent, and a resin particle component and which is prepared so that the heat generation onset temperature S (°C) and the temperature R (°C) at which the degree of cure is 95% have a predetermined relationship, thereby achieving the present invention.

[0014] The present invention that achieves the above object is described below.

[0015] [1] An epoxy resin composition comprising at least an epoxy resin [A] composed of an epoxy compound containing four or more glycidyl groups, and an aromatic polyamine [B] that is liquid at 25 (°C), wherein the epoxy resin composition is subjected to differential scanning calorimetry at a heating rate of 20 (°C / min), and the exothermic onset temperature calculated from the intersection of the tangent to the inflection point on the low-temperature side of the curing exothermic peak and the baseline in a differential scanning calorimetry curve is S (°C), and the temperature at which the degree of cure calculated from the integrated value of the curing exothermic peak in the differential scanning calorimetry curve is 95 (%) is R (°C), the following mathematical formulas (1) and (2) are satisfied: 10 ≦ S − T ≦ 30 ... mathematical formula (1) R − T < 98 ... mathematical formula (2) (wherein in formula (1) and formula (2), T is any value selected from the range of 125 to 180, and T is the same value in formula (1) and formula (2). It is sufficient that formula (1) and formula (2) are satisfied when T is any value selected from the range of 125 to 180.)

[0016] [2] The epoxy resin composition according to [1], further comprising an epoxy resin [C] composed of an epoxy compound containing two or three glycidyl groups.

[0017] [3] The epoxy resin composition according to [1], wherein the epoxy resin [A] is tetraglycidyl-4,4'-diaminodiphenylmethane.

[0018] [4] The epoxy resin composition according to [2], wherein the epoxy resin [C] is an epoxy resin containing a diglycidylamino group.

[0019] [5] The epoxy resin composition according to [2], wherein the epoxy resin [C] is N,N-diglycidylaniline.

[0020] [6] The epoxy resin composition according to [2], wherein the epoxy resin [C] is an epoxy resin having a bisphenol structure in its main skeleton.

[0021] [7] The epoxy resin composition according to [1], wherein the proportion of the epoxy resin [A] contained in the epoxy resin composition is 50 mass% or more of the total mass of the epoxy resins contained in the epoxy resin composition.

[0022] [8] The epoxy resin composition according to [1], wherein the aromatic polyamine [B] includes an aromatic polyamine having a substituent at the ortho position relative to the amino group.

[0023] [9] The epoxy resin composition according to [1], wherein the aromatic polyamine [B] is a phenylenediamine derivative or a derivative of a compound having a diaminodiphenyl skeleton.

[0024]

[10] The epoxy resin composition according to [1], wherein the gel time of the epoxy resin composition at any temperature of 125 to 180 (°C) is within the range of 300 to 600 (seconds).

[0025]

[11] The epoxy resin composition according to [1], wherein when the epoxy resin composition is heated at any temperature of 125 to 180°C for 15 minutes, the degree of cure of the cured resin product of the epoxy resin composition reaches 90% or more.

[0026]

[12] A cured resin product obtained by curing the epoxy resin composition according to any one of [1] to

[11] .

[0027]

[13] A fiber-reinforced composite material comprising a cured resin obtained by curing the epoxy resin composition according to any one of [1] to

[11] , and a reinforcing fiber substrate.

[0028]

[14] The fiber-reinforced composite material according to

[13] , wherein the reinforcing fiber substrate is a reinforcing fiber substrate made of carbon fiber.

[0029]

[15] A method for producing a fiber-reinforced composite material, comprising compounding a reinforcing fiber substrate with the epoxy resin composition according to any one of [1] to

[11] , and curing the resulting composite.

[0030]

[16] A method for producing a fiber-reinforced composite material, comprising impregnating a reinforcing fiber substrate placed in a molding die with the epoxy resin composition according to any one of [1] to

[11] , and then curing the composition.

[0031]

[17] The method for producing a fiber-reinforced composite material according to

[16] , wherein the mold is preheated to 125 to 180°C.

[0032] According to the present invention, an epoxy resin composition having low viscosity, sufficient pot life at the curing temperature, and rapid curing properties is provided. It also provides a cured resin product and a fiber-reinforced composite material having heat resistance and high mechanical properties. In conventional technology, the correlation between S, R, and T was unknown, and no guidelines existed for optimizing these ranges. Therefore, the present invention goes beyond simply optimizing the numerical ranges and is based on new findings derived from an analysis of the curing mechanism of epoxy resins.

[0033] FIG. 1 is a differential scanning calorimetric curve obtained by subjecting the epoxy resin composition of Example 1 described below to differential scanning calorimetry at a temperature rise rate of 20° C. / min.

[0034] The epoxy resin composition, cured resin, and fiber-reinforced composite material of the present invention, as well as their production methods, will be described below. Fiber-reinforced composite material may be abbreviated as "FRP," and carbon fiber-reinforced composite material may be abbreviated as "CFRP." Furthermore, unless otherwise specified, the various physical properties are measured at 25°C and atmospheric pressure.

[0035] 1. Epoxy Resin Composition The epoxy resin composition of the present invention comprises at least an epoxy resin [A] composed of an epoxy compound containing four or more glycidyl groups, and an aromatic polyamine [B] that is liquid at 25°C. The aromatic polyamine [B] that is liquid at 25°C functions as a curing agent for the epoxy resin [A].

[0036] (1) Curing Agent The curing agent contains, as an essential component, an aromatic polyamine [B] that is liquid at 25°C. By containing, as an essential component, an aromatic polyamine that is liquid at 25°C, the viscosity of the epoxy resin composition can be reduced to a level that allows it to be appropriately handled during casting in the RTM method. Being liquid at 25°C means that the composition has fluidity at 25°C, and includes the case where the composition is in a paste state. Specifically, this means that the viscosity at 25°C is 90,000 mPa s or less.

[0037] As the aromatic polyamine [B], a phenylenediamine derivative or a derivative of a compound having a diaminodiphenyl skeleton can be used. Specific examples include compounds represented by the following chemical formula (1) or (2).

[0038]

[0039] However, in the chemical formula (1), R １ ~R ４ are each independently a hydrogen atom, an aliphatic substituent, an alkoxy group, or a thioalkoxy group, and at least one of the substituents is an aliphatic substituent having 1 to 6 carbon atoms or a thioalkoxy group.

[0040]

[0041] However, in the chemical formula (2), R ５ ~R ６ are each independently an aliphatic substituent, a methoxy group, an alkoxy group, or a thioalkoxy group. ２ -, -CH(CH ３ ) -, -C(CH ３ ) ２ -, -S-, -O-, -SO ２ -, -CO-, -CONH-, -NHCO-, or -C(=O)-.

[0042] More specific examples of the compounds represented by the above chemical formula (1) or (2) include compounds represented by the following chemical formulas (3) to (7), which may be used alone or in combination.

[0043]

[0044]

[0045]

[0046]

[0047]

[0048] As the aromatic polyamine [B], it is preferable to use an aromatic polyamine having a substituent at the ortho position relative to the amino group, and it is more preferable to use an aromatic polyamine having a substituent at at least two of the ortho positions relative to the amino group. The substituent is selected from an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, an alkoxy group, or a halogen atom. When these curing agents are used, a cured resin product can be obtained that has excellent mechanical properties such as heat resistance, elastic modulus, and fracture toughness. In addition to the above chemical formulas (1) to (7), examples of aromatic polyamines having a substituent at the ortho position relative to the amino group include derivatives of compounds having a diaminodiphenyl skeleton represented by the following chemical formula (8).

[0049]

[0050] However, in the chemical formula (8), R ７ ~R １０ are each independently an aliphatic substituent, an aromatic substituent, an alkoxy group, or a halogen atom, and at least one of the substituents is an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, an alkoxy group, or a halogen atom. X is —CH ２ -, -CH(CH ３ ) -, -C(CH ３ ) ２ -, -S-, -O-, -SO ２ -, -CO-, -CONH-, -NHCO-, or -C(=O)-.

[0051] In chemical formula (8), examples of the aliphatic substituent having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a neopentyl group, an n-hexyl group, and a cyclohexyl group. Examples of the aromatic substituent include a phenyl group and a naphthyl group.

[0052] The derivative of the compound having the diaminodiphenyl skeleton of chemical formula (8) is particularly preferably a 4,4'-diaminodiphenylmethane derivative. Specific examples of this aromatic polyamine [B] include compounds represented by the following chemical formulas (9) to (12). These may be used alone or in combination.

[0053]

[0054]

[0055]

[0056]

[0057] The curing agent in the epoxy resin composition of the present invention may contain a curing agent other than the aromatic polyamine [B] that is liquid at 25° C. Examples of other curing agents include various isomers of aliphatic polyamines and aromatic amine-based curing agents, aminobenzoic acid esters, and acid anhydrides.

[0058] Examples of aliphatic polyamines include 4,4'-diaminodicyclohexylmethane, isophoronediamine, and m-xylylenediamine. Examples of aminobenzoic acid esters include trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate. Cured products and fiber-reinforced composite materials cured using these curing agents have high tensile elongation. Examples of acid anhydrides include 1,2,3,6-tetrahydrofuran phthalic anhydride, hexahydrophthalic anhydride, and 4-methylhexahydrophthalic anhydride. The use of these curing agents can extend the usable life of the resin composition. In addition, cured resin products with a good balance of electrical, chemical, and mechanical properties can be obtained.

[0059] In the present invention, when two or more components are mixed and used as a curing agent liquid, the curing agent liquid becomes a homogeneous liquid by heating to a temperature of 200°C or less, and thereafter maintains the homogeneous liquid state at room temperature. The period during which the homogeneous liquid state is maintained at room temperature is preferably one week or more, more preferably three weeks or more, and particularly preferably one month or more. If the period during which the homogeneous liquid state is maintained at room temperature is less than one week, it becomes difficult to handle the composition as a substantially liquid curing agent composition for thermosetting resins, and poor mixing with the epoxy base liquid is likely to occur.

[0060] The total amount of curing agent contained in the epoxy resin composition of the present invention is an amount appropriate for curing all of the epoxy resins blended in the epoxy resin composition in a short period of time, and is adjusted appropriately depending on the types of epoxy resins and curing agents used. Specifically, the ratio (H / E) of the active hydrogen equivalent H (g / eq) of the curing agent to the epoxy equivalent E (g / eq) of the epoxy resin is preferably 0.5 to 5.0, more preferably 0.5 to 2.0, particularly preferably 0.6 to 1.4, and most preferably 1.1 to 1.4. If the ratio (H / E) is outside the range of 0.5 to 5.0, poor curing may occur.

[0061] The content of the aromatic polyamine [B] that is liquid at 25°C is preferably 50% by mass or more, more preferably 70% by mass or more, based on the total mass of the curing agent contained in the epoxy resin composition of the present invention. If the content of the aromatic polyamine [B] that is liquid at 25°C is less than the above lower limit, it becomes difficult for the epoxy resin composition to maintain its liquid state at room temperature, which is not preferred. Furthermore, the mechanical properties such as heat resistance, elastic modulus, and fracture toughness of the obtained cured resin are likely to be insufficient, which is not preferred.

[0062] (2) Epoxy Resin (2-1) Tetrafunctional Epoxy Resin The epoxy resin composition of the present invention contains, as an essential component, an epoxy resin [A] composed of an epoxy compound containing four or more glycidyl groups (hereinafter also referred to as "tetrafunctional epoxy resin"). The tetrafunctional epoxy resin may be a homopolymer having an epoxy compound containing four or more glycidyl groups as a repeating unit, or a copolymer containing two or more types of epoxy compounds containing four or more glycidyl groups, or a mixture thereof.

[0063] A preferred example of the tetrafunctional epoxy resin is an epoxy resin composed of an epoxy compound represented by the following chemical formula (13).

[0064]

[0065] However, in the chemical formula (13), R １１ ~R １４ each independently represents one selected from the group consisting of a hydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and a halogen atom, and X is —CH ２ -, -O-, -S-, -CO-, -C(=O)O-, -OC(=O)-, -NHCO-, -CONH-, -SO ２ - represents one selected from.

[0066] R １１ ~R １４ When R is an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, it preferably has 1 to 4 carbon atoms. １１ ~R １４ is preferably a hydrogen atom, since this does not inhibit the formation of a special three-dimensional structure in the cured resin.

[0067] Specific examples of the epoxy compound represented by the above chemical formula (13) include tetraglycidyl-4,4'-diaminodiphenyl ether, tetraglycidyl-4,4'-diaminodiphenylmethane, tetraglycidyl-3,4'-diaminodiphenyl ether, and tetraglycidyl-3,3'-diaminodiphenylmethane. These may be used alone or in combination.

[0068] The proportion of the tetrafunctional epoxy resin in the total mass of the epoxy resin is preferably 50% by mass or more, more preferably 70% by mass or more. The upper limit is 100% by mass. By ensuring that the proportion of the tetrafunctional epoxy resin is equal to or greater than the lower limit, the heat resistance and elastic modulus of the resulting cured resin can be further improved. As a result, various mechanical properties of the resulting fiber-reinforced composite material can also be improved.

[0069] (2-2) Other Epoxy Resins The epoxy resin composition of the present invention may further contain an epoxy resin [C] (hereinafter also referred to as a "bifunctional epoxy resin" and a "trifunctional epoxy resin") composed of an epoxy compound having two or three glycidyl groups. The inclusion of a bifunctional or trifunctional epoxy resin reduces the viscosity of the epoxy resin composition, improving the resin's ability to impregnate a reinforcing fiber substrate, extending the usable time and increasing the design freedom of the mold used in the RTM method. Furthermore, the use of a tetrafunctional epoxy resin in combination with a bifunctional or trifunctional epoxy resin improves the resin's ability to impregnate a reinforcing fiber substrate, and allows for the production of cured resins and fiber-reinforced composite materials that maintain high heat resistance and a high elastic modulus.

[0070] The difunctional or trifunctional epoxy resin is preferably an aromatic epoxy resin. Examples of difunctional epoxy resins include N,N-diglycidylaniline and its derivatives, such as diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-xylidine, diglycidyl-mesidine, diglycidyl-anisidine, diglycidyl-phenoxyaniline, and diglycidyl-naphthylamine, as well as their derivatives. Diglycidylaniline, diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, and diglycidyl-phenoxyaniline are particularly preferred, with diglycidylaniline or diglycidyl-o-toluidine being even more preferred. The glycidyl group is preferably a diglycidylamino group. By using an epoxy resin containing a diglycidylamino group, a sufficient working life can be achieved. Examples of trifunctional epoxy resins include triglycidyl isocyanurate, triglycidyl aminophenol, triglycidyloxyphenylmethane, triglycidyl aminotriazine, and triglycidyl glycerol.

[0071] As the difunctional or trifunctional epoxy resin, it is also preferable to use an epoxy resin having a polycyclic aromatic hydrocarbon skeleton. Examples of polycyclic aromatic hydrocarbon skeletons include a naphthalene skeleton and an anthracene skeleton, with the naphthalene skeleton being preferred from the viewpoint of the physical properties of the cured resin. The polycyclic aromatic hydrocarbon skeleton may have a substituent in addition to the glycidyl group. Examples of monomers having a naphthalene skeleton include 1,6-bis(glycidyloxy)naphthalene, 1,5-bis(glycidyloxy)naphthalene, 2,6-bis(glycidyloxy)naphthalene, 2,7-bis(glycidyloxy)naphthalene, 2,2'-bis(glycidyloxy)-1,1'-binaphthalene, and 2,7-bis(glycidyloxy)-1-[2-(glycidyloxy)-1-naphthylmethyl]naphthalene. The use of these difunctional or trifunctional epoxy resins can reduce the viscosity of the epoxy resin composition and improve the heat resistance of the cured resin. Furthermore, using an epoxy resin having a polycyclic aromatic hydrocarbon skeleton as the difunctional or trifunctional epoxy resin is preferable because it prevents excessive increase in the crosslink density of the cured product and suppresses a decrease in toughness of the cured resin. Among the difunctional or trifunctional epoxy resins, it is preferable to use an aromatic trifunctional epoxy resin. Examples of aromatic trifunctional epoxy resins include triglycidylaminophenol derivative epoxy resins. Specific examples include triglycidyl-m-aminophenol and triglycidyl-p-aminophenol. The inclusion of such an epoxy resin can reduce the viscosity of the epoxy resin composition and further improve the heat resistance of the cured resin.

[0072] It is also preferable to use a trifunctional epoxy resin composed of a heteroaromatic compound. That is, it is also preferable to use a triglycidyl isocyanurate-derived epoxy resin. Examples of triglycidyl isocyanurate-derived epoxy resins include 1,3,5-triglycidyl isocyanurate, 1,3,5-tri(ethylglycidyl)isocyanurate, and 1,3,5-tri(pentylglycidyl)isocyanurate. By using a trifunctional epoxy resin composed of a heteroaromatic compound in combination with an epoxy resin composed of a monomer containing four or more glycidyl groups, it is possible to obtain a cured resin and a fiber-reinforced composite material that maintain heat resistance and a high elastic modulus.

[0073] Other examples of difunctional or trifunctional epoxy resins include epoxy resins having a bisphenol structure in the main skeleton, such as bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, phenol novolac epoxy resins, and cresol novolac epoxy resins.

[0074] (3) Resin Particles The epoxy resin composition of the present invention may contain resin particles. The resin particles are present in a dispersed state in the epoxy resin composition without dissolving, and are also present in the cured resin product after the epoxy resin composition is cured in a dispersed state. When the cured resin product of the epoxy resin is a sea component, the resin particles are present in the cured resin product of the epoxy resin as island components. The inclusion of resin particles can impart high fracture toughness and impact resistance to the cured resin product and fiber-reinforced composite material.

[0075] Examples of resin particles that can be used include thermoplastic resin particles, thermosetting resin particles, and rubber particles. Rubber particles are preferred. Examples of rubber particles include silicone rubber, butadiene rubber, styrene-butadiene rubber, and methyl methacrylate-butadiene-styrene rubber. Commercially available rubber particles used as resin particles include MX-153 (a bisphenol A type epoxy resin with 33% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-257 (a bisphenol A type epoxy resin with 37% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-154 (a bisphenol A type epoxy resin with 40% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-960 (a bisphenol A type epoxy resin with 25% by mass of silicone rubber dispersed therein, manufactured by Kaneka Corporation), MX-136 (a bisphenol F type epoxy resin with 25% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), and MX-965 (a bisphenol F type epoxy resin with 25% by mass of silicone rubber dispersed therein, manufactured by Kaneka Corporation). Examples of epoxy resins include MX-217 (phenol novolac epoxy resin with 25% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-227M75 (bisphenol A novolac epoxy resin with 25% by mass of styrene butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-334M75 (brominated epoxy resin with 25% by mass of styrene butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-416 (tetrafunctional glycidylamine epoxy resin with 25% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), and MX-415 (trifunctional glycidylamine epoxy resin with 25% by mass of styrene butadiene rubber dispersed therein, manufactured by Kaneka Corporation).

[0076] The average particle size of the resin particles is preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.3 μm or less. The average particle size is preferably 0.03 μm or more, more preferably 0.05 μm or more, and particularly preferably 0.08 μm or more. When the average particle size is below the upper limit, in the step of impregnating the reinforcing fiber substrate with the epoxy resin composition, the resin particles are filtered on the surface of the reinforcing fiber substrate and do not accumulate on the surface, so that the impregnation of the resin into the reinforcing fiber substrate is not hindered, and the impregnation of the resin into the reinforcing fiber substrate is facilitated. This makes it possible to prevent poor resin impregnation and obtain a fiber-reinforced composite material with excellent physical properties.

[0077] The content of resin particles in the epoxy resin composition of the present invention is preferably 0.1 to 50% by mass, more preferably 0.5 to 20% by mass, and particularly preferably 1 to 15% by mass, of the total amount of the epoxy resin composition. By ensuring a content equal to or greater than the lower limit, the fracture toughness and impact resistance of the cured resin product and fiber-reinforced composite material can be sufficiently improved. On the other hand, a content greater than the upper limit is undesirable because it increases the viscosity of the resin composition, making casting difficult and tending to result in insufficient mechanical properties, such as the modulus of elasticity, of the cured resin product and fiber-reinforced composite material. The resin particles can also be used as a masterbatch in which they are dispersed at a high concentration in an epoxy resin. In this case, it becomes easier to uniformly disperse the resin particles in the epoxy resin composition.

[0078] (4) Other Optional Components The epoxy resin composition of the present invention may contain epoxy resins other than the above-mentioned epoxy resins, thermosetting resins other than epoxy resins, thermoplastic resins other than resin particles, and other additives. Examples of other epoxy resins that can be used include monofunctional epoxy resins. Among these, epoxy resins containing aromatic groups are preferred, and epoxy resins containing either a glycidyl amine structure or a glycidyl ether structure are preferred. Alicyclic epoxy resins can also be suitably used. These epoxy resins may have non-reactive substituents in the aromatic ring structure, etc., as necessary. Examples of non-reactive substituents include alkyl groups such as methyl, ethyl, and isopropyl groups; aromatic groups such as phenyl groups; alkoxyl groups; aralkyl groups; and halogen groups such as chlorine and bromine.

[0079] Examples of thermosetting resins other than epoxy resins include vinyl ester resins, benzoxazine resins, bismaleimide resins, and bismaleimide-triazine resins.

[0080] In addition to the resin particles described above, the epoxy resin composition of the present invention may contain a thermoplastic resin as a component dissolved in the epoxy resin composition. The thermoplastic resin improves the fracture toughness and impact resistance of the resulting fiber-reinforced composite material. The thermoplastic resin may be dissolved in the epoxy resin composition during the curing process of the epoxy resin composition. Specific examples of the thermoplastic resin include polyethersulfone, polysulfone, polyetherimide, and polycarbonate. These may be used alone or in combination of two or more.

[0081] The thermoplastic resin is preferably polyethersulfone or polysulfone having a weight-average molecular weight (Mw) of 8,000 to 100,000 as measured by gel permeation chromatography. A weight-average molecular weight (Mw) of 8,000 or more ensures sufficient impact resistance for the resulting FRP, while a weight-average molecular weight (Mw) of 100,000 or less prevents the viscosity from becoming significantly high, resulting in an epoxy resin composition with good handleability. The thermoplastic resin preferably has a uniform molecular weight distribution, and the polydispersity (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), is preferably 1 to 10, more preferably 1.1 to 5.0.

[0082] The thermoplastic resin preferably has a reactive group reactive with the epoxy resin or a functional group that forms a hydrogen bond. Such a thermoplastic resin can improve the dissolution stability of the epoxy resin during the curing process. Furthermore, it can impart fracture toughness, chemical resistance, heat resistance, and moist heat resistance to the fiber-reinforced composite material obtained after curing. Preferred reactive groups reactive with the epoxy resin include hydroxyl groups, carboxyl groups, imino groups, and amino groups. Hydroxyl-terminated polyethersulfone is preferred because the resulting fiber-reinforced composite material exhibits particularly excellent impact resistance, fracture toughness, and solvent resistance. The content of the thermoplastic resin in the epoxy resin composition is adjusted appropriately depending on the viscosity. When a thermoplastic resin is included, from the viewpoint of impregnation into the reinforcing fiber substrate, the content is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the epoxy resin included in the epoxy resin composition. By including 0.1 part by mass or more, the resulting fiber-reinforced composite material exhibits sufficient fracture toughness and impact resistance. When the content is 10 parts by mass or less, the viscosity of the epoxy resin composition does not increase significantly, and the impregnation into the reinforcing fiber substrate becomes easy, and various physical properties of the obtained fiber-reinforced composite material are improved.

[0083] The thermoplastic resin preferably contains a reactive aromatic oligomer (hereinafter simply referred to as "aromatic oligomer") having amine end groups. During heat curing, the epoxy resin composition undergoes a curing reaction between the epoxy resin and the curing agent, resulting in a high molecular weight. As the two-phase region expands due to the high molecular weight, the aromatic oligomer dissolved in the epoxy resin composition undergoes reaction-induced phase separation. This phase separation results in the formation of a two-phase structure within the matrix resin, in which the epoxy resin and the aromatic oligomer are co-continuous after curing. Furthermore, since the aromatic oligomer has amine end groups, it also reacts with the epoxy resin. The phases in this co-continuous two-phase structure are firmly bonded to each other, improving solvent resistance. This co-continuous structure absorbs external impacts on the fiber-reinforced composite material and suppresses crack propagation. As a result, fiber-reinforced composite materials prepared using epoxy resin compositions containing a reactive aromatic oligomer having amine end groups exhibit high impact resistance and fracture toughness. Known amine-terminated polysulfones and amine-terminated polyethersulfones can be used as the aromatic oligomer. The amine end group is a primary amine (-NH ２ ) terminal group is preferred. When an aromatic oligomer is blended into the epoxy resin composition, the aromatic oligomer preferably has a weight-average molecular weight of 8,000 to 40,000 as measured by gel permeation chromatography. A weight-average molecular weight of 8,000 or more is effective in improving the toughness of the matrix resin. Furthermore, a weight-average molecular weight of 40,000 or less provides processing advantages such as the resin composition being more easily impregnated into a reinforcing fiber substrate without the viscosity of the resin composition becoming too high. As the aromatic oligomer, commercially available products such as "Virantage DAMS VW-30500 RP (registered trademark)" (manufactured by Solvay Specialty Polymers) can be preferably used.

[0084] The thermoplastic resin is preferably in the form of particles before being blended into the epoxy resin composition, as the particulate thermoplastic resin can be blended and dissolved uniformly in the resin composition.

[0085] The epoxy resin composition of the present invention may contain other additives, such as conductive particles, flame retardants, inorganic fillers, and internal mold release agents. Examples of conductive particles include conductive polymer particles such as polyacetylene particles, polyaniline particles, polypyrrole particles, polythiophene, polyisothianaphthene particles, and polyethylenedioxythiophene particles; carbon particles, carbon fiber particles, metal particles, and particles with an inorganic or organic core coated with a conductive substance. Examples of flame retardants include phosphorus-based flame retardants. Phosphorus-based flame retardants may be any flame retardant containing a phosphorus atom in the molecule, such as organic phosphorus compounds such as phosphate esters, condensed phosphate esters, phosphazene compounds, and polyphosphates, as well as red phosphorus. Examples of inorganic fillers include aluminum borate, calcium carbonate, silicon carbonate, silicon nitride, potassium titanate, basic magnesium sulfate, zinc oxide, graphite, calcium sulfate, magnesium borate, magnesium oxide, and silicate minerals. The use of silicate minerals is particularly preferred. An example of a commercially available silicate mineral is THIXOTROPIC AGENT DT 5039 (manufactured by Huntsman Japan Co., Ltd.). Examples of internal release agents include metal soaps, vegetable waxes such as polyethylene wax and carnauba wax, fatty acid ester-based release agents, silicone oil, animal wax, and fluorine-based nonionic surfactants. When these internal release agents are added, the amount added is preferably 0.1 to 5 parts by mass, and more preferably 0.2 to 2 parts by mass, per 100 parts by mass of the epoxy resin. Within this range, the mold release effect is particularly favorably exhibited. Examples of commercially available internal mold release agents include MOLD WIZ (registered trademark) INT1846 (manufactured by AXEL PLASTICS RESEARCH LABORATORIES INC.), Licowax S, Licowax P, Licowax OP, Licowax PE190, and Licowax PED (manufactured by Clariant Japan), and stearyl stearate (SL-900A, manufactured by Riken Vitamin Co., Ltd.).

[0086] (5) Thermal Properties of Epoxy Resin Composition The epoxy resin composition of the present invention has the following thermal properties, as determined by differential scanning calorimetry of an uncured epoxy resin composition at a heating rate of 20°C / min, where S (°C) is the heat-up onset temperature calculated from the intersection of the tangent to the inflection point on the low-temperature side of the curing exothermic peak in a differential scanning calorimetry curve and the baseline, and R (°C) is the temperature at which the degree of cure is 95% calculated from the integrated value of the curing exothermic peak in the differential scanning calorimetry curve. (However, in formula (1) and formula (2), T is any value selected from the range of 125 to 180, and T is the same value in formula (1) and formula (2). Formula (1) and formula (2) only need to be satisfied when T is any value selected from the range of 125 to 180.) In other words, if T is taken to be any value between 125 and 180, S-T will be in the range of 10 to 30, and R-T will be less than 98. In other words, the following formula (3) is satisfied: ∃T∈[125, 180]:(10≦S-T≦30) ∧(R-T<98) ... formula (3).

[0087] The inflection point on the low-temperature side of the curing exothermic peak in a differential scanning calorimetry curve obtained by subjecting an uncured epoxy resin composition to differential scanning calorimetry at a heating rate of 20°C / min refers to the point at which the curing exothermic peak has a maximum gradient. The point at which the curing exothermic peak has a maximum gradient can be determined directly from the obtained differential scanning calorimetry curve or by processing using analytical software. In the present invention, the exothermic onset temperature S refers to the temperature at the intersection of the baseline and the tangent to the maximum gradient point of the exothermic peak. FIG. 1 shows a differential scanning calorimetry curve obtained by subjecting the epoxy resin composition of Example 1 described below to differential scanning calorimetry at a heating rate of 20°C / min. The exothermic onset temperature calculated from the intersection of the tangent to the inflection point on the low-temperature side of the curing exothermic peak with the baseline is 208.79°C. When the exothermic onset temperature S is 208.79°C, Equation (1) is satisfied if T in the above formula (1) is 178.79 to 198.79. However, since T is a value selected from the range of 125 to 180, in Example 1, the value of T that satisfies formula (1) is in the range of 178.79 to 180. In this way, formula (1) only needs to be satisfied when T is any value selected from the range of 125 to 180.

[0088] The temperature R (°C) at which the degree of cure is 95% as determined from the integrated value of the exothermic curing peak in a differential scanning calorimetry curve refers to the temperature at which the curing reaction reaches a 95% reaction rate, calculated by dividing the exothermic curing peak by the reaction fraction. The reaction fraction can be calculated based on the area of ​​the exothermic curing peak. FIG. 1 shows a differential scanning calorimetry curve obtained by performing differential scanning calorimetry on the epoxy resin composition of Example 1 described below at a heating rate of 20°C / min. The temperature R at which the degree of cure reaches 95% is 262.29°C (not shown). When the temperature R at which the degree of cure reaches 95% is 262.29°C, the formula (2) is satisfied if T in the formula (2) is 164.29 or greater. However, since T is a value selected from the range of 125 to 180, the value of T that satisfies the formula (2) in Example 1 is in the range of 164.29 to 180. Thus, it is sufficient that formula (2) is satisfied when T is any value selected from the range of 125 to 180. Note that T selected in formula (1) and T selected in formula (2) must be the same value. In the case of Example 1 of the present invention, T in formula (1) may be 178.79 to 180, and T in formula (2) may be 164.29 to 180. Since both formulas partially overlap and both formulas (1) and (2) are satisfied in the range of T = 178.79 to 180, it is determined that this is within the scope of the present invention. Note that T is preferably a value selected from the range of 140 to 180.

[0089] In formula (1), if the value of S-T (the value obtained by subtracting T from S) is less than 10, the pot life of the epoxy resin composition will be insufficient, and gelation of the epoxy resin composition will occur before the injection of the resin into the mold during RTM is completed, which is undesirable. In formula (1), if S-T exceeds 30, the time required to complete curing will be long, and rapid curing properties will be impaired, which is undesirable. In formula (2), if R-T (the value obtained by subtracting T from R) is 98 or more, the time required to complete curing will be long, and rapid curing properties will be impaired, which is undesirable.

[0090] The heat generation initiation temperature S and the temperature R at which the degree of cure reaches 95% can be adjusted by adjusting the amounts of the components blended by referring to the descriptions in the Examples of the present application or by referring to the differential scanning calorimetry curves of several epoxy resin compositions with different compositions, and no excessive trial and error is required.

[0091] The curing temperature of the epoxy resin composition of the present invention is any temperature in the range of 125 to 180°C. The curing temperature is preferably any temperature in the range of 140 to 180°C. A more preferred curing temperature is a temperature around the range of the value of T that satisfies the above-mentioned mathematical formula (1) and mathematical formula (2). Specifically, the curing temperature is preferably a temperature within ±10°C of the range of the value of T that satisfies mathematical formula (1) and mathematical formula (2), more preferably a temperature within ±5°C, and particularly preferably within the range of the value of T that satisfies mathematical formula (1) and mathematical formula (2).

[0092] The epoxy resin composition of the present invention preferably achieves a degree of cure of 90% or more, and more preferably 95% or more, when heated for 15 minutes at a temperature between 125 and 180°C. Here, the degree of cure refers to the degree of cure of the cured resin obtained after heating the epoxy resin composition for 15 minutes at a temperature between 125 and 180°C. The degree of cure of the cured resin is evaluated by measuring the calorific value when the cured resin is reheated after heating for 15 minutes at a temperature between 125 and 180°C using a differential scanning calorimetry (DSC) (see the Examples section below). A degree of cure of less than 90% is likely to result in poor rapid curing, leading to reduced productivity of the cured resin and fiber-reinforced composite material.

[0093] The epoxy resin composition of the present invention preferably has a viscosity at 100°C of 300 mPa·s or less, more preferably 0.1 to 100 mPa·s, and particularly preferably 0.5 to 50 mPa·s. If the viscosity at 100°C is below the above upper limit, the epoxy resin composition can be easily impregnated into a reinforcing fiber substrate, and the formation of voids that cause a decrease in the physical properties of the resulting fiber-reinforced composite material can be prevented. The relationship between viscosity and impregnation ability also depends on the composition of the reinforcing fiber substrate.

[0094] The pot life of the epoxy resin composition of the present invention at the curing temperature varies depending on the molding conditions for the composite material. For example, when the composite material is impregnated into a fiber substrate using resin transfer molding (RTM) at a relatively low impregnation pressure, it is preferably 300 seconds or more, more preferably 300 to 600 seconds, and particularly preferably 420 to 600 seconds or more. The pot life refers to the gel time when maintained at the curing temperature. If the gel time when maintained at the curing temperature is below the lower limit, the epoxy resin composition will gel before injection into the mold during RTM is completed, which is undesirable. The gel time measurement temperature varies depending on the composition of the epoxy resin composition, but it is sufficient that the gel time at any temperature between 125 and 180°C is within the above range. Furthermore, it is preferable that the gel time be within the above range at a temperature (unit: °C) within the range of values ​​of T that satisfy both the aforementioned mathematical formulas (1) and (2).

[0095] (6) Manufacturing Method of Epoxy Resin Composition The epoxy resin composition of the present invention can be produced by mixing an epoxy resin base liquid, a curing agent liquid, and resin particles. The order of mixing is not important. The resin particles may be premixed with the epoxy resin base liquid and / or the curing agent liquid. The epoxy resin composition may be in the form of a slurry in which some components are dispersed as solids, but a single-liquid state in which all components are uniformly mixed is preferred. Any conventionally known method may be used to manufacture the epoxy resin composition. The mixing temperature is, for example, 40 to 190°C, preferably 50 to 160°C, and more preferably 50 to 100°C. If the temperature exceeds the upper limit, the viscosity increases as the curing reaction progresses, which tends to reduce the impregnation ability into the reinforcing fiber substrate. As a result, the physical properties of the cured product may be reduced, which is undesirable. If the temperature is below the lower limit, the viscosity of the epoxy resin base liquid may be so high that mixing may be virtually impossible.

[0096] Conventionally known mixing machines can be used. Specific examples include a roll mill, a planetary mixer, a kneader, an extruder, a Banbury mixer, a mixing vessel equipped with stirring blades, and a horizontal mixing tank. The components can be mixed in the air or in an inert gas atmosphere. When mixing in the air, an atmosphere in which the temperature and humidity are controlled is preferred. For example, mixing is preferably performed at a temperature controlled to a constant temperature of 30°C or less, or in a low-humidity atmosphere with a relative humidity of 50% RH or less.

[0097] (6-1) Method for Producing Curing Agent Liquid The curing agent liquid is prepared by mixing, as an essential component, an aromatic polyamine [B] that is liquid at 25°C, with other components as necessary. The state of this curing agent liquid may be a single liquid state in which the components are uniformly mixed, or a slurry state in which some components are dispersed as solids. Any conventionally known method may be used for producing the curing agent liquid. The mixing temperature is, for example, 50 to 200°C, preferably 50 to 150°C, and more preferably 80 to 120°C. If the upper limit temperature is exceeded, the added components may thermally decompose. On the other hand, if the temperature is below the lower limit temperature, the solid curing agent components are difficult to dissolve in the aromatic polyamine [B] that is liquid at 25°C, making it difficult to obtain a liquid curing agent liquid.

[0098] (6-2) Method for Producing Epoxy Resin Base Liquid The epoxy resin base liquid is prepared by mixing an epoxy resin [A] composed of an epoxy compound containing four or more glycidyl groups with, as necessary, resin particles and other optional components. The order of mixing is not important. The epoxy resin base liquid may be in a single-liquid state in which the components are uniformly mixed, or in a slurry state in which some components are dispersed as solids. Any conventionally known method may be used to produce the epoxy resin base liquid. The mixing temperature is, for example, 40 to 200°C, preferably 50 to 100°C, and more preferably 50 to 90°C. If the upper temperature limit is exceeded, the self-polymerization reaction of the epoxy resin may progress partially, reducing the impregnation ability of the reinforcing fiber substrate and / or reducing the physical properties of the cured resin produced using the resulting epoxy resin base liquid. If the temperature limit is less than the lower temperature limit, the viscosity of the epoxy resin base may be high, making mixing substantially difficult.

[0099] (7) Cured Resin Product A cured resin product can be obtained by curing the epoxy resin composition of the present invention. The obtained cured resin product can have the following properties.

[0100] The degree of cure of the cured resin is preferably 90% or more, and more preferably 95% or more. Here, the degree of cure is as described above.

[0101] The glass transition temperature (dry-Tg) of the cured resin in a dry state is preferably 140°C or higher, more preferably 150°C or higher, and particularly preferably 180°C or higher. If the glass transition temperature (dry-Tg) in a dry state is equal to or higher than the above-mentioned lower limit temperature, the cured resin and fiber composite material can exhibit sufficient mechanical properties even in a high-temperature environment, which is preferable. The glass transition temperature (wet-Tg) of the cured resin when saturated with water absorption is preferably 110°C or higher, more preferably 150°C or higher. If the glass transition temperature (wet-Tg) at saturated with water absorption is equal to or higher than the above-mentioned lower limit temperature, the cured resin and fiber composite material can exhibit sufficient mechanical properties even in a wet environment, which is preferable.

[0102] The room temperature dry flexural modulus (RTD-FM) of the cured resin product measured according to JIS K 7171 is preferably 3.0 GPa or more, more preferably 3.3 to 10.0 GPa. By exceeding the lower limit, the fiber reinforced composite material obtained using the epoxy resin composition of the present invention has better mechanical properties.

[0103] The critical stress intensity factor KIc of deformation mode I of the cured resin measured by ASTM D5045 is 0.6 MPa m １／２ It is preferable that the viscosity is 0.7 MPa m or more. １／２ When the epoxy resin composition of the present invention is used in a fiber-reinforced composite material, the fiber-reinforced composite material obtained by using the epoxy resin composition of the present invention has better impact properties.

[0104] (8) Fiber-reinforced composite material The fiber-reinforced composite material of the present invention is formed by combining a cured resin obtained by curing an epoxy resin composition with a reinforcing fiber substrate.

[0105] Examples of fibers for the reinforcing fiber substrate include carbon fibers, glass fibers, aramid fibers, silicon carbide fibers, polyester fibers, ceramic fibers, alumina fibers, boron fibers, metal fibers, mineral fibers, rock fibers, and slag fibers. Among these reinforcing fibers, carbon fibers, glass fibers, and aramid fibers are preferred. Carbon fibers are more preferred because they have good specific strength and specific modulus, and can produce lightweight, high-strength fiber-reinforced composite materials. Among carbon fibers, polyacrylonitrile (PAN)-based carbon fibers are particularly preferred because they have excellent tensile strength.

[0106] When PAN-based carbon fibers are used as the reinforcing fibers, the tensile modulus is preferably 100 to 600 GPa, more preferably 200 to 500 GPa, and particularly preferably 230 to 450 GPa. The tensile strength is preferably 2,000 to 10,000 MPa, and more preferably 3,000 to 8,000 MPa.

[0107] When carbon fibers are used as reinforcing fibers, the diameter of the carbon fibers is preferably 4 to 20 μm, more preferably 5 to 10 μm. By using such carbon fibers, the mechanical properties of the resulting fiber-reinforced composite material can be improved.

[0108] In the present invention, the reinforcing fibers are preferably treated with a sizing agent. In this case, the amount of sizing agent attached is preferably 0.01 to 10 mass%, more preferably 0.05 to 3.0 mass%, and particularly preferably 0.1 to 2.0 mass%, relative to the mass of the reinforcing fibers to which the sizing agent is attached. A larger amount of sizing agent attached tends to strengthen the adhesion between the reinforcing fibers and the matrix resin. On the other hand, a smaller amount of sizing agent attached tends to result in superior interlaminar toughness of the resulting composite material.

[0109] The reinforcing fiber substrate preferably uses a reinforcing fiber sheet formed from reinforcing fibers in a sheet form. Examples of reinforcing fiber sheets include sheets in which a large number of reinforcing fibers are aligned in one direction, bidirectional fabrics such as plain weave and twill weave, multiaxial fabrics, nonwoven fabrics, mats, knits, braids, and paper made from reinforcing fibers. Among these, unidirectionally aligned sheets, bidirectional fabrics, and multiaxial fabric substrates formed from continuous reinforcing fibers are preferred because they yield fiber-reinforced composite materials with superior mechanical properties. The bidirectional fabric and multiaxial fabric substrates may be formed by stacking and stitching multiple unidirectionally aligned sheets. In this case, to improve the interlaminar toughness of the resulting fiber-reinforced composite material, a thermoplastic resin nonwoven fabric layer may be disposed on one side of the unidirectionally aligned sheet and then laminated to form a woven fabric. Examples of thermoplastic resin nonwoven fabric layers include polyester resin fibers, polyamide resin fibers, polyethersulfone resin fibers, polysulfone resin fibers, polyetherimide resin fibers, polycarbonate resin fibers, and fibers composed of mixtures of these resins. The basis weight and number of layers of the unidirectionally aligned sheets can be appropriately set depending on the application of the fiber-reinforced composite material. The basis weight of the unidirectionally aligned sheets is, for example, 100 to 300 g / m ２ , preferably 150 to 250 g / m ２The thickness of each layer of the unidirectionally aligned sheet of reinforcing fiber substrate is preferably 0.01 to 3 mm, more preferably 0.05 to 1.5 mm.

[0110] The reinforcing fiber substrate according to the present invention may contain a binder resin. The use of a binder resin can improve the handleability of the reinforcing fiber substrate. The resin material used as the binder resin is not particularly limited, and thermosetting resins such as epoxy resins and vinyl ester resins, thermoplastic resins such as polyamides and polyethersulfones, and mixtures thereof can be used as appropriate. These binder resins may be used by scattering powder and sintering and fixing, or may be formed into a sheet, nonwoven fabric, or the like and laminated on the reinforcing fiber substrate. Alternatively, they may be attached in advance to each yarn constituting the reinforcing fiber substrate of the present invention.

[0111] The fiber-reinforced composite material provided by the present invention preferably has a compressive strength after impact CAI (impact energy 30.5 J) measured by ASTM D7136 of 150 MPa or more, and more preferably 150 to 400 MPa. The fiber-reinforced composite material provided by the present invention preferably has a room-temperature dry open-hole compressive strength (RTD-OHC) measured by SACMA SRM3 of 260 MPa or more, more preferably 280 to 450 MPa, and particularly preferably 300 to 400 MPa. The fiber-reinforced composite material provided by the present invention preferably has a heated open-hole compressive strength after water absorption (HTW-OHC) measured by SACMA SRM3 of 200 MPa or more, more preferably 220 to 400 MPa, and particularly preferably 240 to 350 MPa.

[0112] (9) Method for Producing Fiber-Reinforced Composite Material The fiber-reinforced composite material of the present invention is produced by compounding a reinforcing fiber substrate with the epoxy resin composition of the present invention and then curing the composite, or by curing the composite while compounding. Examples of compounding methods include resin transfer molding (RTM), hand layup, filament winding, and pultrusion. Examples of methods for producing a fiber-reinforced composite material using the epoxy resin composition of the present invention include known molding methods such as RTM, autoclave molding, and press molding. The epoxy resin composition of the present invention is particularly suitable for the RTM method. The RTM method is a method for obtaining a fiber-reinforced composite material by impregnating a reinforcing fiber substrate placed in a mold with a liquid epoxy resin composition and curing it. In the present invention, the mold used in the RTM method may be a closed mold made of a rigid material, or a combination of an open mold made of a rigid material and a flexible film (bag). In the latter case, the reinforcing fiber substrate can be placed between the open mold made of a rigid material and the flexible film. Rigid materials include metals such as steel and aluminum, fiber-reinforced plastics, wood, and gypsum. Flexible film materials include polyamide, polyimide, polyester, fluororesin, and silicone resin. When a closed mold made of a rigid material is used in the RTM method, the epoxy resin composition is typically injected into the clamped mold under pressure. A suction port may be provided in addition to the injection port and connected to a vacuum pump for suction. The epoxy resin composition may be injected under atmospheric pressure without using special pressurizing means. This method is advantageous because it allows the production of large components by providing multiple suction ports. When a combination of an open mold made of a rigid material and a flexible film is used in the RTM method, the epoxy resin composition may be injected under atmospheric pressure without using special pressurizing means for suction. To achieve good impregnation with injection under atmospheric pressure alone, it is effective to use a resin diffusion medium. Furthermore, it is preferable to apply a gel coat to the surface of the rigid material prior to placing the reinforcing fiber substrate.

[0113] In the RTM method, the epoxy resin composition is impregnated into a reinforcing fiber substrate and then heat-cured. From the viewpoint of productivity, it is preferable that the mold be preheated. The mold temperature (curing temperature) during heat-curing is generally selected to be the same as or higher than the mold temperature (preheating temperature) of the mold when the epoxy resin composition is injected. The preheating temperature and curing temperature of the mold are preferably 100 to 200°C, more preferably 125 to 180°C, and particularly preferably 140 to 180°C. These preferred temperatures vary depending on the composition of the epoxy resin composition, but in the present invention, temperatures (units: °C) around the range of T satisfying the aforementioned mathematical formulas (1) and (2) are preferred. Specifically, a temperature within the range of T satisfying mathematical formulas (1) and (2) ±10°C is preferred, a temperature within the range of T satisfying mathematical formulas (1) and (2) ±5°C is more preferred, and a temperature within the range of T satisfying mathematical formulas (1) and (2) is particularly preferred.

[0114] The heat curing time is preferably 1 minute to 20 hours. After heat curing is complete, the fiber-reinforced composite material is removed from the mold and removed. The resulting fiber-reinforced composite material may then be post-cured by heating at a higher temperature. The post-curing temperature is preferably 150 to 200°C, and the time is preferably 1 minute to 4 hours. The impregnation pressure when impregnating the reinforcing fiber substrate with the epoxy resin composition by the RTM method is determined appropriately taking into account the viscosity and resin flow of the resin composition. Specific impregnation pressures are, for example, 0.001 to 10 MPa, preferably 0.01 to 1 MPa. When obtaining a fiber-reinforced composite material using the RTM method, the viscosity of the epoxy resin composition at 120°C is preferably 1 to 200 mPa·s.

[0115] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The components and evaluation methods used in these examples and comparative examples are described below.

[0116] <Evaluation Method> Evaluations performed in the examples and comparative examples are as follows.

[0117] (1) Preparation of Epoxy Resin Composition An epoxy resin base liquid was prepared by weighing out the epoxy resin and resin particles in the proportions shown in Table 1 and mixing them at 80°C for 30 minutes using a stirrer. A curing agent liquid was prepared by weighing out the curing agent components in the proportions shown in Table 1 and mixing them at 80°C for 30 minutes using a stirrer. The epoxy resin base liquid and curing agent liquid, which had been prepared separately, were mixed at 80°C for 30 minutes using a stirrer to prepare an epoxy resin composition.

[0118] (2) Properties of the cured resin (2-1) Preparation of the cured resin The epoxy resin composition prepared in (1) above was degassed in a vacuum for 60 minutes, and then poured into a stainless steel mold set to a thickness of 4 mm using a 4 mm Teflon (registered trademark) resin spacer. The composition was heated and cured for 15 minutes at the curing temperature shown in Table 1 to obtain a 4 mm thick cured resin plate.

[0119] (2-2) Glass transition temperature (dry-Tg) Measurement was carried out in accordance with the SACMA 18R-94 method. Using the resin-cured plate obtained in (2-1) above, a resin test piece measuring 50 mm x 6 mm x 2 mm was prepared. Using a dynamic viscoelasticity measuring device Rheogel-E400 manufactured by UBM, the storage modulus E' of the resin test piece was measured from 50 ° C to the rubber elastic region under the conditions of a measurement frequency of 1 Hz, a heating rate of 5 ° C / min, and a strain of 0.0167%, with the distance between the chucks set to 30 mm. Log E' was plotted against temperature, and the temperature obtained from the intersection of the approximation line of the flat region of log E' and the approximation line of the region where E' transitions was recorded as the glass transition temperature (dry-Tg).

[0120] (2-3) Glass transition temperature after water absorption (wet-Tg) Measurement was performed according to the SACMA 18R-94 method. Resin test pieces measuring 50 mm x 6 mm x 2 mm were prepared using the cured resin plates obtained in (2-1) above. Using a pressure cooker (HASTEST PC-422R8, manufactured by Espec Corporation), the prepared resin test pieces were subjected to a water absorption treatment at 121 ° C for 24 hours. Using a dynamic viscoelasticity measuring device Rheogel-E400 manufactured by UBM, the storage modulus E' of the water-absorbed resin test pieces was measured from 50 ° C to the rubber elastic region under the conditions of a measurement frequency of 1 Hz, a heating rate of 5 ° C / min, and a strain of 0.0167%, with a chuck distance of 30 mm. Log E' was plotted against temperature, and the temperature determined from the intersection of the approximate line of the plateau region of log E' with the approximate line of the transition region of E' was recorded as the glass transition temperature (wet-Tg).

[0121] (2-4) Room temperature dry resin flexural modulus (RTD-FM) Testing was performed in accordance with JIS K7171. Resin test pieces with dimensions of 80 mm x 10 mm x 4 mm (thickness h) were prepared using the resin cured plates obtained in (2-1) above. A bending test was performed at an ambient temperature of 25°C, with a support distance L of 16 x h mm, and a test speed of 2 mm / min, to measure the flexural strength and flexural modulus.

[0122] (2-5) Toughness of cured resin (deformation mode I critical stress intensity factor KIc) Toughness (KIc) was measured using a universal testing machine (Shimadzu Autograph) according to ASTM D5045. Resin test pieces with dimensions of 50 mm x 8 mm (width W) x 4 mm were prepared using the cured resin plates obtained in (2-1) above. The crack length a was adjusted to 0.45≦a / W≦0.55. The crack length a was determined by observing the fracture surface after the fracture test using an optical microscope, and the length to the tip of the crack and the average value of the crack lengths on both surfaces of the test piece were used.

[0123] (2-6) Gel Time Using a Discovery HR-2 manufactured by TA Instruments, an epoxy resin composition was placed on a 25 mm parallel plate, and viscoelasticity measurements were carried out at a strain of 0.1% and an angular frequency of 10 rad / sec at the curing temperature shown in Table 1. From the obtained data, the gel time was determined as the time required for the complex viscosity to reach 1000 times the complex viscosity immediately after the start of measurement.

[0124] (2-7) Degree of Cure DSC measurement (heating rate: 20°C / min) was performed on the epoxy resin composition prepared in (1) to obtain the total heat release amount. Separately, DSC measurement was performed on the epoxy resin composition prepared in (1). First, the temperature was raised from 25°C to the curing temperature listed in Table 1 at 100°C / min, and the curing temperature listed in Table 1 was maintained for 15 minutes. Thereafter, the temperature was lowered to 25°C at 100°C / min, and the composition was maintained at 25°C for 20 minutes. Subsequently, this epoxy resin composition (cured resin) was reheated from 25°C to 350°C at 10°C / min. The post-cure heat release amount was obtained from the heat release amount during the re-heating from 25°C to 350°C. The degree of cure was calculated from the total heat release amount and the post-cure heat release amount according to the following formula: Degree of cure [%] = (total heat generation [J / g] - heat generation after cure [J / g]) / total heat generation [J / g] × 100

[0125] (2-8) Difference between exotherm onset temperature and curing temperature The epoxy resin composition prepared in (1) was subjected to DSC measurement (heating rate: 20°C / min), and the exotherm onset temperature was obtained from the intersection of the baseline and the tangent to the inflection point on the low-temperature side of the curing exotherm peak. The difference between the obtained exotherm onset temperature and the curing temperature when the resin composition was cured was calculated.

[0126] (2-9) Difference between the temperature at which the degree of cure is 95%, determined from the integrated value of the exothermic peak, and the curing temperature DSC measurement (heating rate: 20°C / min) was carried out on the epoxy resin composition prepared in (1). The obtained exothermic peak was integrated with respect to temperature, and the temperature at which the cumulative 95% of the total heat release was obtained was defined as the temperature at which the degree of cure is 95%. The difference between the temperature at which the degree of cure is 95%, determined from the integrated value of the exothermic peak, and the curing temperature listed in Table 1 was calculated.

[0127] (3) Characteristics of Fiber Reinforced Composite Material (3-1) Preparation of Fiber Reinforced Composite Material Carbon fiber multiaxial fabric 1 and carbon fiber multiaxial fabric 2 were each cut to 300 mm x 300 mm, and a total of 16 sheets of carbon fiber multiaxial fabric 1 and 8 sheets of carbon fiber multiaxial fabric 2 were layered on a 500 mm x 500 mm release-treated aluminum plate so that the angles of the reinforcing fibers were [(+45 / -45) (0 / 90) (-45 / +45) (90 / 0)] [(+45 / -45) (0 / 90) (-45 / +45) (90 / 0)] [(0 / 90) (+45 / -45) (90 / 0) (-45 / +45)] [(0 / 90) (+45 / -45) (90 / 0) (-45 / +45)] to form a laminate. Furthermore, a peel cloth substrate, Release Ply C (manufactured by AIRTECH), which is a substrate with a release function, and a resin diffusion substrate, Resin Flow 90HT (manufactured by AIRTECH), were laminated on this laminate. Then, hoses for forming a resin inlet and a resin outlet were placed, the entire structure was covered with a nylon bag film, sealed with sealant tape, and the inside was evacuated. The aluminum plate was then heated to 120°C, and the pressure inside the bag was reduced to 5 torr or less. The epoxy resin composition prepared in (1) above was then heated to 100°C and injected into the vacuum system through the resin inlet. The injected epoxy resin composition filled the bag and impregnated the laminate. The temperature was then raised to the curing temperature listed in Table 1 and maintained at that temperature for 15 minutes to obtain a carbon fiber reinforced composite material (CFRP).

[0128] (3-2) Compressive Strength After Impact (CAI) The CFRP obtained in (3-1) above was cut to a size of 101.6 mm wide x 152.4 mm long to obtain a test piece for a compressive strength after impact (CAI) test. The test was carried out in accordance with ASTM D7136. An impact energy of 30.5 J was applied to this test piece using a drop weight impact tester (Dynatup, manufactured by Instron). After the impact, the damage area of ​​the test piece was measured using an ultrasonic flaw detector (SDS3600, HIS3 / HF, manufactured by Krautkramer). The strength test was carried out by attaching one strain gauge to each of the left and right sides of the test specimen after impact, 25.4 mm from the top and 25.4 mm from each side, and similarly attaching one to the back side, for a total of four strain gauges per test specimen on the front and back.The crosshead speed of the testing machine (Shimadzu Autograph) was then set to 1.27 mm / min, and a load was applied until the test specimen broke.

[0129] (3-3) Room-Temperature Dry Open-Hole Compression Strength (RTD-OHC) The CFRP obtained in (3-1) above was cut to a size of 38.1 mm wide x 304.8 mm long, and a hole with a diameter of 6.35 mm was drilled in the center of the test piece to obtain a test piece for a room-temperature dry open-hole compression strength (RTD-OHC) test. The test was conducted at an ambient temperature of 25°C in accordance with SACMA SRM3, and the room-temperature dry open-hole compression strength was calculated from the maximum point load.

[0130] (3-4) Open-hole compressive strength after heating and water absorption (HTW-OHC) The test piece for the room temperature dry open-hole compressive strength (RTD-OHC) test obtained in (3-3) above was immersed in hot water at 70°C for two weeks to obtain a test piece for the open-hole compressive strength after heating and water absorption (HTW-OHC) test. The test was carried out at an ambient temperature of 90°C in accordance with SACMA SRM3, and the open-hole compressive strength after heating and water absorption was calculated from the maximum point load.

[0131] <Components> The components used in the examples and comparative examples are as follows.

[0132] (1) Aromatic polyamines that are liquid at 25°C: Diethyltoluenediamine (Heartcure 10 (product name), manufactured by Kumiai Chemical Co., Ltd.; hereinafter abbreviated as "DETDA"; liquid at 25°C); 4,4'-diamino-3,3'-diethyldiphenylmethane (Kayahard AA (product name), manufactured by Nippon Kayaku Co., Ltd.; hereinafter abbreviated as "Kayahard AA"; liquid at 25°C);

[0133] (2) Other curing agents 4,4'-diamino-3,3'-diisopropyl-5,5'-dimethyldiphenylmethane (Lonzacure M-MIPA (product name) manufactured by Lonza, hereinafter abbreviated as "M-MIPA". Melting point 70°C, solid at 25°C.) 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane (MED-J (product name) manufactured by Kumiai Chemical Co., Ltd., hereinafter abbreviated as "MED-J". Melting point 76°C, solid at 25°C.) m-phenylenediamine (Tokyo Chemical Industry Co., Ltd., hereinafter abbreviated as "MPD". Melting point 65°C, solid at 25°C.)

[0134] (3) Epoxy compounds containing four or more glycidyl groups: Tetraglycidyl-4,4'-diaminodiphenylmethane (Araldite MY721 (product name) manufactured by Huntsman, hereinafter abbreviated as "4,4'-TGDDM")

[0135] (4) Epoxy compounds containing two or three glycidyl groups N,N-diglycidylaniline (GAN (product name) manufactured by Nippon Kayaku Co., Ltd.; hereinafter abbreviated as "GAN") Triglycidyl-p-aminophenol (Araldite MY0510 (product name) manufactured by Huntsman Chemical Industries, Ltd.; hereinafter abbreviated as "TG-pAP") Bisphenol A-diglycidyl ether (jER828 (product name) manufactured by Mitsubishi Chemical Corporation; hereinafter abbreviated as "TGEBA") Bisphenol F-diglycidyl ether (jER806 (product name) manufactured by Mitsubishi Chemical Corporation; hereinafter abbreviated as "TGEBF") N,N-diglycidyl-o-toluidine (GOT (product name) manufactured by Nippon Kayaku Co., Ltd.; hereinafter abbreviated as "GOT") Oxazolidone ring-containing epoxy resin (TSR-400 (product name) manufactured by DIC Corporation, hereinafter abbreviated as "TSR-400")

[0136] (5) Resin particles MX-416 (MX-416 (product name) manufactured by Kaneka Corporation, a masterbatch in which a particulate butadiene rubber component is dispersed in a glycidylamine-type tetrafunctional epoxy resin to a concentration of 25% by mass) MX-154 (MX-154 (product name) manufactured by Kaneka Corporation, a masterbatch in which a particulate butadiene rubber component is dispersed in bisphenol A-diglycidyl ether to a concentration of 40% by mass)

[0137] (6) Carbon fiber strand Carbon fiber 1: Tenax (registered trademark) HTS45 E23 12K 800tex (carbon fiber strand, tensile strength 4.5 GPa, tensile modulus 240 GPa, sizing agent adhesion amount 1.3 mass%, manufactured by Teijin Carbon Europe GmbH)

[0138] (7) Binder particles Binder 1: EP05311 (manufactured by Westlake Epoxy B.V.)

[0139] (8) Carbon fiber multiaxial fabric Carbon fiber multiaxial fabric 1: 194 g / m per layer of carbon fibers 1 aligned in one direction ２ Two sheets were stacked at an angle of (+45 / -45) and stitched together, and Binder 1 was applied to one side at 10 g / m ２ (total carbon fiber basis weight of woven fabric substrate: 388 g / m ２ ) Carbon fiber multiaxial fabric 2: Carbon fiber 1 aligned in one direction, 194 g / m per layer ２ Two sheets were laminated at an angle of (-45 / +45) and stitched together (the total weight of the carbon fiber in the woven fabric substrate was 388 g / m ２ ).

[0140] Example 1 (Preparation of Epoxy Resin Composition) Epoxy resin and resin particles were weighed out in the proportions listed in Table 1 and mixed using a stirrer at 80°C for 30 minutes to prepare an epoxy resin base liquid. Curing agent components were weighed out in the proportions listed in Table 1 and mixed using a stirrer at 80°C for 30 minutes to prepare a curing agent liquid. The separately prepared epoxy resin base liquid and curing agent liquid were mixed using a stirrer at 80°C for 30 minutes to prepare an epoxy resin composition. (Preparation of Cured Resin Product) The epoxy resin composition obtained above was degassed in vacuum for 60 minutes and then poured into a stainless steel mold set to a thickness of 4 mm using a 4 mm Teflon (registered trademark) resin spacer. Heat curing was performed at the curing temperature of 180°C for 15 minutes to obtain a 4 mm thick cured resin plate. The properties of the obtained cured resin product are shown in Table 1. The gel time was 5 minutes or more and the degree of cure was 90% or more, demonstrating excellent handleability and rapid curing properties. The cured resin has a wet Tg of 110°C or higher, a flexural modulus of 3.0 GPa or higher, and a KIc of 0.7 MPa m １／２The carbon fiber multiaxial fabric 1 and the carbon fiber multiaxial fabric 2 were cut into 300 mm x 300 mm pieces, and eight sheets of the carbon fiber multiaxial fabric 1 and eight sheets of the carbon fiber multiaxial fabric 2, a total of 16 sheets, were stacked on a 500 mm x 500 mm release-treated aluminum plate so that the angles of the reinforcing fibers were [(+45 / -45) (0 / 90) (-45 / +45) (90 / 0)] [(+45 / -45) (0 / 90) (-45 / +45) (90 / 0)] [(0 / 90) (+45 / -45) (90 / 0) (-45 / +45)] [(0 / 90) (+45 / -45) (90 / 0) (-45 / +45)] to form a laminate. Furthermore, a peel cloth substrate, Release Ply C (manufactured by AIRTECH), with a release function, and a resin diffusion substrate, Resin Flow 90HT (manufactured by AIRTECH), were laminated on the laminate. Hoses were then placed to form the resin inlet and resin outlet, and the entire structure was covered with nylon bag film and sealed with sealant tape to create a vacuum. The aluminum plate was then heated to 120°C, and the pressure inside the bag was reduced to 5 torr or less. The epoxy resin composition prepared above was then heated to 100°C and injected into the vacuum system through the resin inlet. Once the injected epoxy resin composition filled the bag and impregnated the laminate, the temperature was raised to the curing temperature of 180°C and heat-cured at that temperature for 15 minutes to obtain a carbon fiber reinforced composite material (CFRP). The properties of the resulting CFRP are shown in Table 1. It exhibited a high CAI of 150 MPa or more, a high and excellent RTD-OHC of 300 MPa or more, and an excellent HTW-OHC of 250 MPa or more.

[0141] Examples 2 to 9, 11 were carried out in the same manner as in Example 1, except that the composition was changed as shown in Table 1. The evaluation results are shown in Table 1. In all cases, the gel time was 5 minutes or more and the degree of cure was 90% or more, demonstrating excellent handleability and fast curing properties. In addition, the wet-Tg of the cured resin was 110°C or more, the flexural modulus was 3.0 GPa or more, and the KIc was 0.7 MPa m １／２ The fiber-reinforced composite materials also exhibited high CAI of 150 MPa or more, excellent RTD-OHC of 300 MPa or more, and excellent HTW-OHC of 250 MPa or more.

[0142] Example 10 (Preparation of Epoxy Resin Composition) Epoxy resin and resin particles were weighed out in the proportions listed in Table 1 and mixed using a stirrer at 80°C for 30 minutes to prepare an epoxy resin base liquid. Curing agent components were weighed out in the proportions listed in Table 1 and mixed using a stirrer at 80°C for 30 minutes to prepare a curing agent liquid. The separately prepared epoxy resin base liquid and curing agent liquid were mixed using a stirrer at 80°C for 30 minutes to prepare an epoxy resin composition. (Preparation of Cured Resin Product) The epoxy resin composition obtained above was degassed in vacuum for 60 minutes and then poured into a stainless steel mold set to a thickness of 4 mm using a 4 mm Teflon (registered trademark) resin spacer. The composition was heated and cured at the curing temperature of 140°C for 15 minutes to obtain a 4 mm thick cured resin plate. The properties of the resulting cured resin product are shown in Table 1. The gel time was 5 minutes or more and the degree of cure was 90% or more, demonstrating excellent handleability and rapid curing properties. The cured resin has a wet Tg of 110°C or higher, a flexural modulus of 3.0 GPa or higher, and a KIc of 0.7 MPa m １／２The carbon fiber multiaxial fabric 1 and the carbon fiber multiaxial fabric 2 were cut into 300 mm x 300 mm pieces, and eight sheets of the carbon fiber multiaxial fabric 1 and eight sheets of the carbon fiber multiaxial fabric 2, a total of 16 sheets, were stacked on a 500 mm x 500 mm release-treated aluminum plate so that the angles of the reinforcing fibers were [(+45 / -45) (0 / 90) (-45 / +45) (90 / 0)] [(+45 / -45) (0 / 90) (-45 / +45) (90 / 0)] [(0 / 90) (+45 / -45) (90 / 0) (-45 / +45)] [(0 / 90) (+45 / -45) (90 / 0) (-45 / +45)] to form a laminate. Furthermore, a peel cloth substrate, Release Ply C (manufactured by AIRTECH), with a release function, and a resin diffusion substrate, Resin Flow 90HT (manufactured by AIRTECH), were laminated on the laminate. Hoses for forming the resin inlet and resin outlet were then installed, the entire structure was covered with nylon bag film, sealed with sealant tape, and a vacuum was created inside. The aluminum plate was then heated to 120°C, and the pressure inside the bag was reduced to 5 torr or less. The epoxy resin composition prepared above was then heated to 100°C and injected into the vacuum system through the resin inlet. Once the injected epoxy resin composition filled the bag and impregnated the laminate, the temperature was raised to the curing temperature of 140°C and heat-cured at that temperature for 15 minutes to obtain a carbon fiber reinforced composite material (CFRP). The properties of the resulting CFRP are shown in Table 1. It exhibited a high CAI of 150 MPa or more, a high and excellent RTD-OHC of 300 MPa or more, and an excellent HTW-OHC of 250 MPa or more.

[0143] Comparative Examples 1 to 4 and 6 were carried out in the same manner as in Example 1, except that the compositions were changed as shown in Table 1. The evaluation results are shown in Table 1. The degree of cure was 90% or less in all cases, and sufficient rapid curing properties were not exhibited.

[0144] Comparative Example 5 (Preparation of Epoxy Resin Composition) Epoxy resin and resin particles were weighed out in the proportions listed in Table 1 and mixed using a stirrer at 80°C for 30 minutes to prepare an epoxy resin base liquid. Curing agent components were weighed out in the proportions listed in Table 1 and mixed using a stirrer at 80°C for 30 minutes to prepare a curing agent liquid. The separately prepared epoxy resin base liquid and curing agent liquid were mixed using a stirrer at 80°C for 30 minutes to prepare an epoxy resin composition. (Preparation of Cured Resin Product) The epoxy resin composition obtained above was degassed in a vacuum for 60 minutes and then poured into a stainless steel mold set to a thickness of 4 mm using a 4 mm Teflon (registered trademark) resin spacer. Heat curing was performed at 160°C for 15 minutes to obtain a 4 mm thick cured resin plate. The properties of the resulting cured resin product are shown in Table 1. The gel time was 5 minutes or less, indicating insufficient handleability.

[0145]

[0146]

[0147] In Example 1, the heat generation initiation temperature S is 208.79°C. Therefore, if T in formula (1) is 178.79 to 198.79, formula (1) is satisfied. However, since T is a value selected from the range of 125 to 180, in Example 1, the value of T that satisfies formula (1) is in the range of 178.79 to 180. In Example 1, the temperature R at which a degree of cure of 95% is achieved is 262.29°C. Therefore, if T in formula (2) is 164.29 or higher, formula (2) is satisfied. However, since T is a value selected from the range of 125 to 180, in Example 1, the value of T that satisfies formula (2) is in the range of 164.29 to 180. In Example 1, the value of T that satisfies both formulas (1) and (2) is in the range of 178.79 to 180.

[0148] Calculating in the same manner, in Example 2, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 179.52 to 180. In Example 3, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 177.03 to 180. In Example 4, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 177.69 to 180. In Example 5, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 167.88 to 180. In Example 6, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 167.16 to 180. In Example 7, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 170.48 to 180. In Example 8, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 177.44 to 180. In Example 9, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 174.35 to 180. In Example 10, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 123.89 to 143.89. In Example 11, the value of T that satisfies both the formula (1) and the formula (2) is in the range of 174.96 to 180.

[0149] In Examples 1 to 11, by setting the curing temperature (°C) within the range of T that satisfies both the formula (1) and the formula (2), molding with a long pot life and excellent rapid curing properties could be performed.

[0150] In Comparative Example 1, the heat generation initiation temperature S is 210.00°C. Therefore, if T in formula (1) is 180.00 to 200.00, formula (1) is satisfied. However, since T is a value selected from the range of 125 to 180, the value of T that satisfies formula (1) in Comparative Example 1 is 180. In Comparative Example 1, the temperature R at which a degree of cure of 95% is achieved is 299.75°C. Therefore, if T in the above formula (2) is 201.75 or higher, formula (2) is satisfied. However, since T is a value selected from the range of 125 to 180, there is no value of T in Comparative Example 1 that satisfies both formulas (1) and (2). In Comparative Example 1, there is no value of T that satisfies both formulas (1) and (2).

[0151] When calculated in the same manner, in Comparative Examples 2 to 6, there is no value of T that satisfies both the formula (1) and the formula (2).

[0152] In Comparative Examples 1 to 6, there was no value of T that satisfied both the mathematical formula (1) and the mathematical formula (2), and therefore the pot life was short (Comparative Example 6) or the rapid curing property was poor (Comparative Examples 1 to 5).

Claims

1. An epoxy resin composition comprising at least an epoxy resin [A] composed of an epoxy compound containing four or more glycidyl groups, and an aromatic polyamine [B] that is liquid at 25°C, wherein the epoxy resin composition is subjected to differential scanning calorimetry at a heating rate of 20°C / min. The differential scanning calorimetry curve is obtained by measuring the epoxy resin composition using differential scanning calorimetry, and the exothermic onset temperature is determined from the intersection of the tangent to the inflection point on the low-temperature side of the curing exothermic peak and the baseline, where S (°C) is the exothermic onset temperature, and the temperature at which the degree of cure is 95% is determined from the integrated value of the curing exothermic peak on the differential scanning calorimetry curve is R (°C), and the following formulas (1) and (2) are satisfied: 10 ≦ S − T ≦ 30 ... formula (1) R − T < 98 ... formula (2) (wherein in formula (1) and formula (2), T is any value selected from the range of 125 to 180, and T is the same value in formula (1) and formula (2). It is sufficient that formula (1) and formula (2) are satisfied when T is any value selected from the range of 125 to 180.) 2. The epoxy resin composition according to claim 1, further comprising an epoxy resin [C] composed of an epoxy compound containing two or three glycidyl groups.

3. The epoxy resin composition according to claim 1, wherein the epoxy resin [A] is tetraglycidyl-4,4'-diaminodiphenylmethane.

4. The epoxy resin composition according to claim 2, wherein the epoxy resin [C] is an epoxy resin containing a diglycidylamino group.

5. The epoxy resin composition according to claim 2, wherein the epoxy resin [C] is N,N-diglycidylaniline.

6. The epoxy resin composition according to claim 2, wherein the epoxy resin [C] is an epoxy resin having a bisphenol structure in its main skeleton.

7. The epoxy resin composition according to claim 1, wherein the proportion of the epoxy resin [A] contained in the epoxy resin composition is 50 mass % or more of the total mass of the epoxy resins contained in the epoxy resin composition.

8. The epoxy resin composition according to claim 1, wherein the aromatic polyamine [B] comprises an aromatic polyamine having a substituent at the ortho position relative to the amino group.

9. The epoxy resin composition according to claim 1, wherein the aromatic polyamine [B] is a phenylenediamine derivative or a derivative of a compound having a diaminodiphenyl skeleton.

10. The epoxy resin composition according to claim 1, wherein the gel time of the epoxy resin composition at any temperature between 125 and 180°C is within the range of 300 to 600 seconds.

11. The epoxy resin composition according to claim 1, wherein when the epoxy resin composition is heated at a temperature of 125 to 180°C for 15 minutes, the degree of cure of the cured resin of the epoxy resin composition reaches 90% or more.

12. A cured resin product obtained by curing the epoxy resin composition according to any one of claims 1 to 11.

13. A fiber-reinforced composite material comprising a cured resin obtained by curing the epoxy resin composition according to any one of claims 1 to 11, and a reinforcing fiber substrate.

14. The fiber-reinforced composite material according to claim 13, wherein the reinforcing fiber substrate is made of carbon fiber.

15. A method for producing a fiber-reinforced composite material, comprising compounding a reinforcing fiber substrate with the epoxy resin composition according to any one of claims 1 to 11, and curing the compound.

16. A method for producing a fiber-reinforced composite material, comprising impregnating a reinforcing fiber substrate placed in a molding die with the epoxy resin composition according to any one of claims 1 to 11, and then curing the composition.

17. The method for producing a fiber-reinforced composite material according to claim 16, wherein the mold is preheated to 125 to 180°C.

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