Epoxy resin composition, reinforcing fiber-containing epoxy resin composition, prepreg, thermoplastic resin, and fiber-reinforced plastic using the same

Abstract

To provide an in-situ polymerizable epoxy resin composition and a prepreg, being suitable for in-situ polymerizable fiber-reinforced thermoplastic resins, and exhibiting excellent handling and polymerization characteristics through a simplified process.SOLUTION: An epoxy resin composition comprises, as essential components, (A) an epoxy resin having two epoxy groups per molecule, (B) a compound having two phenolic groups per molecule, and (D) a polymerization catalyst, wherein the number-average molecular weight of the uncured resin composition is 300 or more and less than 1500; the blending ratio of the epoxy resin (A) to the phenolic compound (B) is 0.90-1.10 mol of the compound (B) per 1 mol of the epoxy resin (A); the terminal epoxy content of the epoxy resin (A) is within a predetermined range; and the content of the polymerization catalyst (D), in molar ratio, is 0.008 or more and less than 0.0020 times relative to the amount of epoxy groups.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermoplastic resin, an epoxy resin composition, a reinforcing fiber-containing epoxy resin composition, a prepreg, and a fiber-reinforced plastic using these. [Background technology]

[0002] Fiber-reinforced plastics (FRP) exhibit excellent physical properties such as light weight and high strength, and among them, those using carbon fiber as the reinforcing fiber (CFRP) are known to have particularly excellent mechanical strength. Among CFRPs, those that use thermoplastic resin as the base resin are called CFRTPs, and are expected to have excellent secondary processability and recyclability.

[0003] Epoxy resins are primarily used as the base material (matrix) resin for FRP due to their excellent balance of cost and physical properties. Patent Document 1 proposes a method for molding a fiber-reinforced thermoplastic resin by premixing an epoxy resin and a phenolic hydroxyl group-containing compound with reinforcing fibers and polymerizing them by a polyaddition reaction using a polymerization catalyst and a reaction retarder. Patent Document 2 proposes the polyaddition reaction of a bifunctional epoxy resin with a bifunctional compound containing a functional group selected from the group consisting of a phenolic hydroxyl group, an amino group, a carboxyl group, a mercapto group, an isocyanate group, and a cyanate ester group. Such epoxy resins are also known as in-situ polymerization thermoplastic epoxy resins, and FRPs using these are expected to have excellent mass productivity, moldability, and recyclability. In-situ polymerization thermoplastic epoxy resins are impregnated into fibers in a low-viscosity state before polymerization, which allows for a higher proportion of reinforcing fibers. They also offer superior impact strength and toughness compared to conventional thermosetting epoxy resins. However, Patent Document 1 only discloses a method for producing a prepreg by the so-called "wet method," in which a solvent is added to reduce the viscosity of the resin so that the resin can be sufficiently impregnated into the reinforcing fiber bundles. However, with prepregs produced by such a wet method, it is difficult to control the amount of solvent remaining in the prepreg, resulting in variations in the amount of remaining solvent. Therefore, there are problems with unstable quality of molded products, such as the generation of voids due to evaporation of the remaining solvent during molding and variations in mechanical properties.

[0004] Patent Document 2 discloses a method for producing a prepreg of an in-situ polymerized thermoplastic epoxy resin by a hot melt method. In order to obtain a prepreg with suitable tackiness and drapeability, the document describes a step of adjusting the molecular weight to 300 or more by curing the prepreg at 20 to 40°C for 50 to 240 hours. However, such a process requires a long time and is therefore less productive. Although it is possible to shorten the curing time by increasing the curing temperature, the inventors have found that if the polymerization reaction is carried out at a temperature lower than the optimum curing temperature, undesirable side reactions occur, making the polymer more likely to undergo three-dimensional crosslinking, which adversely affects thermoplasticity.

[0005] One known method for controlling the tackiness of resins is to add solid epoxy resins. Solid epoxy resins are classified into one-stage and two-stage methods based on their manufacturing method, and the proportion of terminal group impurities varies depending on the method of use and manufacturing.

[0006] Non-Patent Document 1 lists impurities contained in epoxy resins, such as inorganic chlorine, chlorine-containing compounds such as 1,2-chlorohydrin, 1,3-chlorohydrin, and 1-chloromethyl-2-glycidyl ether, and 1,2-glycol (α-diol). Patent Document 3 indicates that in the production of an epoxy resin cured product with excellent mechanical properties, the terminal group impurities of the epoxy resin, typified by α-diol and hydrolyzable chlorine, must be kept below a certain level.

[0007] The type and amount of polymerization catalyst are important for the polymerization of epoxy resins, but excessive use of polymerization catalyst shortens the pot life and makes the resin less easy to handle. Reducing the amount of polymerization catalyst added can extend the pot life of the resin, but this can also reduce reactivity and slow in-situ polymerization, potentially reducing productivity. Furthermore, there is a risk of deactivation due to side reactions before the target molecular weight is reached. The optimal amount of catalyst added varies depending on the amount of epoxy groups present in the epoxy resin. The process of creating prepreg involves coating the resin to form a film. Coating requires heating the resin and adjusting the viscosity to a level suitable for coating. If the resin is highly reactive and has a short usable life, the viscosity will fluctuate during coating, making it difficult to obtain a uniform resin film. In particular, epoxy resin compositions with adjusted tackiness tend to have higher viscosities, so coating temperatures must be high, and it is becoming increasingly important to ensure the usable life of the resin. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-321897 [Patent Document 2] WO2017 / 94633 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-37917 [Non-patent literature]

[0009] [Non-Patent Document 1] Review of Epoxy Resins, Basics II, pp. 99-104, Epoxy Resin Technology Association Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide an in situ polymerization type epoxy resin composition and a prepreg which are suitable for use in in situ polymerization type fiber reinforced thermoplastic resins and which have excellent handleability and polymerizability through a simple process. [Means for solving the problem]

[0011] The inventors have found that adjusting the molecular weight of the epoxy resin composition within a certain range is effective in controlling the tackiness of the prepreg appropriately, but using an epoxy resin with low terminal group purity in the epoxy resin composition has an adverse effect on polymerization. Furthermore, in order to achieve both polymerization ability and usable life, it is important to select the catalyst type and amount. As a result of intensive research conducted by the present inventors to solve the above problems, they have found that a fiber-reinforced thermoplastic resin and a prepreg that are excellent in handleability and polymerizability can be obtained by using an epoxy resin composition in which the number average molecular weight of the resin composition before curing is 300 or more and less than 1500, the epoxy end group purity of the contained epoxy resin is 97.0% or more, and the content of polymerization catalyst (D) is 0.0008 or more and less than 0.0020 times the amount of epoxy groups in molar terms, and have thus completed the present invention.

[0012] That is, the present invention provides an epoxy resin composition which contains, as essential components, an epoxy resin (A) having two epoxy groups in one molecule, a compound (B) having two phenol groups in one molecule, and a polymerization catalyst (D), and which becomes a thermoplastic resin through a polymerization reaction, The number average molecular weight of the resin composition before curing is 300 or more and less than 1500, The blending amounts of the epoxy resin (A) and the compound (B) are 0.90 to 1.10 moles of the phenol compound (B) per mole of the epoxy resin (A), the terminal epoxy content of the epoxy resin (A) calculated from formula (1) is 97.0% or more and 100% or less, The epoxy resin composition does not contain any organic solvent, or if it contains an organic solvent, the content of the organic solvent is 0.01% by weight or more and 10% by weight or less of the epoxy resin composition; The content of the polymerization catalyst (D) is 0.0008 to less than 0.0020 times the amount of epoxy groups in terms of moles. The epoxy resin composition is characterized by the following: Here, the terminal epoxy content of the epoxy resin can be calculated by the following formula.

number

[0013] The present invention also provides a reinforcing fiber-containing epoxy resin composition, characterized by containing the above epoxy resin composition and reinforcing fibers (F). The present invention also relates to a prepreg made from the above-mentioned reinforcing fiber-containing epoxy resin composition, a fiber-reinforced plastic using the above-mentioned reinforcing fiber-containing epoxy resin composition, and a fiber-reinforced plastic using the above-mentioned prepreg. [Effects of the Invention]

[0014] The prepreg obtained from the epoxy resin composition of the present invention can provide a fiber reinforced plastic (FRTP) that is easy to handle and has excellent mechanical properties. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below based on preferred embodiments thereof. The epoxy resin composition (E) of the present invention is an epoxy resin composition that contains, as essential components, an epoxy resin (A) having two epoxy groups in one molecule, a compound (B) having two functional groups reactive with epoxy groups in one molecule, and a polymerization catalyst (D), and becomes a thermoplastic resin through a polymerization reaction.

[0016] The epoxy resin (A) used in the epoxy resin composition (E) preferably has an epoxy equivalent ranging from 100 g / eq. to 2000 g / eq. The lower limit is preferably 150 g / eq., more preferably 180 g / eq. The upper limit is preferably 1000 g / eq., more preferably 800 g / eq.

[0017] In the epoxy resin composition of the present invention, it is essential that the epoxy resin (A) has a terminal epoxy content calculated from the following formula (1) of 97.0% or more and 100% or less, preferably 98.0% or more. Each coefficient in the formula is converted into g / meq units for each functional group (epoxy group, α-diol group, chlorine).

number

[0018] Examples of the epoxy resin (A) include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol E type epoxy resins, bisphenol Z type epoxy resins, bisphenol S type epoxy resins, bisphenol AD ​​type epoxy resins, bisphenol acetophenone type epoxy resins, bisphenol trimethylcyclohexane type epoxy resins, bisphenol fluorene type epoxy resins (e.g., ZX-1201 (manufactured by Nippon Steel Chemical & Material Co., Ltd.)), biscresol fluorene type epoxy resins (e.g., OGSOL Bisphenol type epoxy resins such as tetramethylbisphenol A type epoxy resin, tetramethylbisphenol F type epoxy resin (e.g., YSLV-80XY (Nippon Steel Chemical & Material Co., Ltd.)), tetra-t-butylbisphenol A type epoxy resin, tetramethylbisphenol S type epoxy resin, dihydroxydiphenyl ether type epoxy resin, thiodiphenol type epoxy resin, tetrabromobisphenol A type epoxy resin, etc., biphenol type epoxy resin, tetramethylbiphenol type epoxy resin (e.g., YX4000 (Mitsubishi Chemical Co., Ltd.)), etc. Examples of epoxy resins that can be used include epoxy resins manufactured by Epoxy Research & Development Co., Ltd.), biphenol-type epoxy resins such as dimethylbiphenol-type epoxy resins and tetra-t-butylbiphenol-type epoxy resins, benzenediol-type epoxy resins such as hydroquinone-type epoxy resins, methylhydroquinone-type epoxy resins, dibutylhydroquinone-type epoxy resins, resorcinol-type epoxy resins and methylresorcinol-type epoxy resins, dihydroxyanthracene-type epoxy resins, hydroanthrahydroquinone-type epoxy resins, dihydroxynaphthalene-type epoxy resins, bisnaphtholfluorene-type epoxy resins, and diphenyldicyclopentadiene-type epoxy resins.

[0019] In particular, it is preferable to contain an epoxy resin (a) represented by the following general formula (1): The epoxy resin (a) constitutes a part of the epoxy resin (A). [ka] In formula (1), A is a divalent group represented by the following formula (2): n is the number of repetitions, and its average value is 0 to 5, preferably 0.2 to 5. [ka] In formula (2), X is a single bond, a hydrocarbon group having 1 to 13 carbon atoms, -O-, -CO-, -COO-, -S-, or -SO2-. Y 1 , Y 2 , Y 3 , Y 4 are independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0020] Such epoxy resins can be obtained by a conventionally known one-step or two-step process: a process in which a bifunctional phenol compound is reacted with an epihalohydrin in the presence of an alkali metal compound (one-step process), or a process in which a bifunctional epoxy resin is reacted with a bifunctional phenol compound in the presence of a catalyst (two-step process). The weight average molecular weight and epoxy equivalent of the epoxy resin can be produced within the desired range by appropriately adjusting the molar ratio of the epihalohydrin and the bifunctional phenolic compounds charged in the one-stage process, or by appropriately adjusting the molar ratio of the bifunctional epoxy resins and the bifunctional phenolic compounds charged in the two-stage process. Furthermore, two or more types of epoxy resins obtained by such a one-stage or two-stage method can be mixed together and used as a mixed epoxy resin in order to adjust the properties to the desired level. Since the epoxy resin composition of the present invention is used as an in-situ polymerization prepreg, it is preferable to mix a solid epoxy resin with the liquid epoxy resin to adjust tackiness. The amount of the solid epoxy resin mixed is preferably 1.0 to 50 parts by weight, more preferably 5.0 to 45 parts by weight, and even more preferably 10.0 to 40 parts by weight, per 100 parts by weight of the total epoxy resin. Generally, epoxy resins obtained by the one-stage method with a high molecular weight tend to have a lower terminal epoxy content than epoxy resins obtained by the two-stage method. Therefore, in order to obtain the desired tackiness and polymerizability for an in-situ polymerization prepreg, it is important to control the blending ratio of the mixed epoxy resins and the terminal epoxy content. It is essential that the terminal epoxy content of the epoxy resin represented by formula (1) falls within a predetermined range.

[0021] The bifunctional phenol compound (B) used in the epoxy resin composition (E) preferably has a hydroxyl equivalent ranging from 80 g / eq. to 500 g / eq. The lower limit is preferably 100 g / eq., more preferably 110 g / eq. The upper limit is preferably 300 g / eq., more preferably 250 g / eq. The physical properties of the bifunctional phenol compound (B), i.e., specific values ​​of the hydroxyl equivalent, softening point, and melting point, can be obtained from a catalog of a commercially available material. The hydroxyl equivalent can also be calculated from the charge ratio or measured in accordance with JIS K0070.

[0022] The purity of the bifunctional phenol compound (B) is preferably 95% by weight or more. If monofunctional impurities are present, the molecular weight after polymerization may not increase, which may result in poor mechanical properties of the produced thermoplastic resin. Therefore, the monofunctional impurities are preferably 2% by weight or less relative to the bifunctional compound (B). If trifunctional or higher functional impurities are present, crosslinking structures are likely to form starting from the impurities, which may increase the dispersion of the polymer and may cause gelation, resulting in loss of thermoplasticity. Therefore, the trifunctional or higher functional impurities are preferably 1% by weight or less relative to the bifunctional compound (B). As long as the purity of the bifunctional phenol compound (B) is high, positional isomers may be present. The bifunctional phenol compound (B) may be used alone or in combination of multiple types.

[0023] Examples of diphenol compounds include bisphenol compounds such as bisphenol A, bisphenol F, bisphenol E, bisphenol Z, 2,4'-bisphenol S, bisphenol AP, bisphenol C, bisphenolacetophenone, bisphenoltrimethylcyclohexane, tetramethylbisphenol A, tetramethylbisphenol F, tetra-t-butylbisphenol A, dihydroxydiphenyl ether, dihydroxydiphenylmethane, thiodiphenol, and dihydroxystilbene; benzenediol compounds such as hydroquinone, methylhydroquinone, dibutylhydroquinone, resorcin, and methylresorcin; and phosphorus-containing phenol compounds such as dihydroxynaphthalene and diphenylphosphinylhydroquinone. In particular, when used in a reinforcing fiber-containing epoxy resin composition, a bisphenol compound is preferred. Furthermore, a phosphorus-containing phenol compound may be used for the purpose of imparting flame retardancy. If necessary, an ester compound may be added.

[0024] In the epoxy resin composition (E), the proportion of the bifunctional phenol compound (B) is 0.90 to 1.10 mol, preferably 0.95 to 0.99 mol, and more preferably 0.97 to 0.98 mol, per 1.00 mol of the bifunctional epoxy resin (A). In the epoxy resin composition (E), the bifunctional epoxy resin (A) and the bifunctional phenol compound (B) react sequentially to form a linear structure, resulting in thermoplasticity. If there is an excess of the bifunctional epoxy resin (A), the polymer will be terminated with an epoxy group, whereas if there is an excess of the bifunctional phenol compound (B), the polymer will be terminated with a phenol group, and the reaction will terminate. If the ratio of the bifunctional phenol compound (B) exceeds 0.99 mol, the polymer will terminate with phenol groups, which may make it difficult to achieve a high molecular weight. On the other hand, if the ratio of the bifunctional phenol compound (B) is less than 0.95 mol, the excess epoxy groups may cause a side reaction, which may cause the polymer to gel and impair its thermoplasticity.

[0025] When a phosphorus-containing epoxy resin or a phosphorus-containing bifunctional compound is used to impart flame retardancy to the epoxy resin composition (E), the phosphorus content is preferably from 1 to 6 wt%, more preferably from 1.5 to 5 wt%, and even more preferably from 2 to 4 wt%, relative to 100 wt% of the total amount of the epoxy resin (A) and the compound (B). Furthermore, instead of blending a phosphorus-containing compound as the bifunctional epoxy resin (A) or the bifunctional compound (B), or in addition to such a phosphorus-containing compound, various other known phosphorus-containing compounds may be blended into the epoxy resin composition (E).

[0026] Furthermore, impurity components that do not have active groups reactive with either the bifunctional epoxy resin (A) or the bifunctional compound (B) and that do not inhibit the polymerization reaction by themselves, such as non-reactive impurities derived from the raw materials, may also result in a small molecular weight after polymerization if present in large amounts. Therefore, it is preferable that the amount of such impurity components be 2% by weight or less relative to both the bifunctional epoxy resin (A) and the bifunctional compound (B).

[0027] In an epoxy resin composition, it is preferable that the epoxy resin (A) and the phenolic compound (B) are uniformly dissolved. If the phenolic compound (B) is present in a crystalline state in the epoxy resin (A), the molar ratio will deviate from the design when viewed microscopically. If the reaction is initiated in this state, polymerization may not proceed sufficiently. To ensure sufficient polymerization, an epoxy resin composition (E) in which the phenolic compound (B) and the epoxy resin (A) are uniformly compatible with each other is preferred. Furthermore, it is desirable for the epoxy resin composition before the addition of reinforcing fibers or other components to be completely compatible or in a homogeneous liquid state. For example, if a bubble-free molten mixture is placed in a glass Petri dish to a thickness of 2 mm and the haze value in the thickness direction is measured, a haze value of less than 30% can be determined to indicate that the mixture has dissolved to a level that does not affect the polymerization reaction or has become a homogeneous liquid state.

[0028] To obtain an epoxy resin composition (E) in which the phenolic compound (B), epoxy resin (A), and polymerization catalyst (D) are uniformly compatible with one another, it is recommended to achieve compatibility by heating. Methods for achieving compatibility by heating include heating a mixture of epoxy resin (A) and phenolic compound (B) containing polymerization catalyst (D), or heating a mixture of epoxy resin (A) and phenolic compound (B) without a polymerization catalyst to obtain a uniformly compatible epoxy resin composition, followed by adding polymerization catalyst (D). Heating a mixture of epoxy resin (A) and phenolic compound (B) containing polymerization catalyst (D) to a temperature at which the phenolic compound (B) is compatible may result in a runaway polymerization reaction. While heating a mixture of epoxy resin (A) and phenolic compound (B) without polymerization catalyst (D) does not result in a reaction, excessive heat history in the absence of a catalyst may produce by-products that become multifunctional components that are the source of branching, potentially increasing the degree of branching in the polymer. Therefore, when obtaining the epoxy resin composition (E), it is preferable to employ a method in which a mixture of the phenol compound (B) and the epoxy resin (A) is heated in advance with a minimum thermal history to obtain an epoxy resin composition in which they are uniformly dissolved, and then the polymerization catalyst (D) is added.

[0029] Examples of the polymerization catalyst (D) that can be used in the present invention include N-substituted aminopyridine compounds, phosphine compounds, quaternary phosphonium salt compounds, imidazole compounds, and tertiary amine compounds. These polymerization catalysts (D) may be used alone or in combination. Among these, phosphine compounds are particularly preferred, and phosphine compounds having a melting point of 100°C or less are particularly preferred.

[0030] Examples of phosphine compounds include triphenylphosphine, tris(paratolyl)phosphine, tri-(m-tolyl)phosphine, dicyclohexylphenylphosphine, tris(ortho-tolyl)phosphine, tris(para-methoxyphenyl)phosphine, etc. Among these, triphenylphosphine, tri-(m-tolyl)phosphine, and dicyclohexylphenylphosphine are particularly preferred because of their excellent solubility in epoxy resins.

[0031] Examples of quaternary phosphonium salt compounds include tributyl(methyl)phosphonium dimethyl phosphate, tributyl(ethyl)phosphonium diethyl phosphate, methyltributylphosphonium dimethyl phosphate (e.g., Hishicolin PX-4MP (manufactured by Nippon Chemical Industry Co., Ltd.)), methyltrioctylphosphonium dimethyl phosphate, and tetrabutylphosphonium o,o-diethylphosphorodithioate (e.g., Hishicolin PX-4ET (manufactured by Nippon Chemical Industry Co., Ltd.)). Examples of imidazole compounds include 4-methylimidazole, Curesol 1B2MZ, Curesol 1B2PZ, and Curesol TBZ (all manufactured by Shikoku Chemicals Corporation). Examples of tertiary amine compounds include triethylamine and tributylamine. Other examples of the polymerization catalyst include crown ether complexes such as 18-crown-6 (18-C-6) / AcOK complex and 18-C-6 / KF complex, and metal chlorides.

[0032] The amount of polymerization catalyst (D) is preferably 0.01 to 10 parts by weight per 100 parts by weight of the total amount of components other than component D constituting the epoxy resin composition (e.g., the total amount of epoxy resin (A) and phenolic compound (B), or the total amount including component (S) if a small amount of solvent (S) is used). If the amount is less than 0.01 part by weight, in-situ polymerization may take too long, resulting in reduced productivity. Furthermore, the catalyst may be deactivated for some reason before the target molecular weight is reached. On the other hand, if the amount exceeds 10 parts by weight, the polymerization reaction may proceed quickly, but storage stability may be impaired, resulting in process compatibility problems. Since the catalyst (D) is a component that participates in the reaction but is not incorporated into the backbone, post-polymerization physical properties may be impaired. Furthermore, the catalyst (D) is expensive, which is economically disadvantageous. The amount is preferably 0.05 to 5.0 parts by weight, more preferably 0.1 to 3.0 parts by weight, and even more preferably 0.1 to 1.0 parts by weight. The optimum amount of the polymerization catalyst to be blended can be appropriately selected by comprehensively considering the balance between the usable time and the polymerization time, taking into account the concentration of epoxy groups in the epoxy resin. The amount of the polymerization catalyst (D) added is, in molar terms, 0.0008 to 0.0020 times the amount of epoxy groups, and more preferably 0.0015 times or less.

[0033] In the epoxy resin composition (E) of the present invention, other catalysts may be used in combination with the phosphine-based compound as the polymerization catalyst (D). The other catalysts are not particularly limited as long as they are catalysts that can be used in the two-stage epoxy resin production process. Examples include alkali metal compounds, organic phosphorus compounds, tertiary amines, quaternary ammonium salts, cyclic amines, and imidazole-based compounds. These other catalysts may be used alone or in combination of two or more. When used in a reinforcing fiber-containing epoxy resin composition, it is preferable that the other catalysts are not used.

[0034] The epoxy resin composition (E) preferably does not contain an organic solvent. However, if necessary, an organic solvent may be contained as a solvent for the polymerization catalyst (D) or for viscosity adjustment. The organic solvent is not particularly limited as long as it does not inhibit the reaction between the epoxy resin (A) and the compound (B). However, hydrocarbons, ketones, and ethers are preferred due to their availability. Specific examples include toluene, xylene, acetone, methyl ethyl ketone, isobutyl ketone, cyclopentanone, cyclohexanone, and diethylene glycol dimethyl ether. However, the presence of a large amount of organic solvent during the reaction may inhibit the polymerization reaction, and residual organic solvent in the polymer may deteriorate mechanical properties and heat resistance. Therefore, when an organic solvent is added, its proportion is 0.01% by weight or more and 10% by weight or less of the epoxy resin composition (E), preferably 4% by weight or less, and more preferably 2% by weight or less. When an organic solvent is added, there is no lower limit, but it is usually 0.01% by weight or more and more preferably 0.5% by weight or more.

[0035] From the viewpoint of workability when made into a prepreg, the epoxy resin composition (E) preferably has a glass transition temperature of 0°C or higher and lower than 20°C. If the glass transition temperature is 0°C or lower, the tackiness will be too strong, and the resin will be more likely to remain on the release paper or to adhere to the worker's hands, resulting in poor workability. If the glass transition temperature is 20°C or higher, the tackiness will be lost, making it difficult for PPg sheets to bond together during lamination, and drapeability will also be impaired, resulting in poor workability.

[0036] The epoxy resin composition (E) preferably has a low viscosity in order to maintain its ability to impregnate reinforcing fibers. The viscosity (Pa s) when heated to 60°C is 100 or less, preferably 80 or less, more preferably 50 or less, and even more preferably 40 or less. The lower limit of the viscosity is 0.1 or more, preferably 1 or more. The time required for the viscosity to double from the initially measured viscosity (viscosity doubling time) is preferably 30 minutes or more, more preferably 60 minutes or more.

[0037] The progress of the polymerization of the epoxy resin composition (E) can be judged by the change in the weight-average molecular weight of the polymer (thermoplastic resin). If the weight-average molecular weight tends to increase, the polymerization reaction may not be complete. The polymerization conditions for obtaining a thermoplastic resin from the epoxy resin composition are a temperature of preferably 100 to 200°C, more preferably 150 to 180°C, and a time of preferably 30 minutes to 2 hours, more preferably within 1 hour.

[0038] The progress of polymerization of the reinforcing fiber-containing epoxy resin composition can also be judged from the change in weight-average molecular weight of the polymer. The polymerization conditions for obtaining a fiber-reinforced thermoplastic resin polymer from the reinforcing fiber-containing epoxy resin composition are preferably a temperature of 100 to 200°C and a time of 2 to 5 hours.

[0039] When a phosphorus-containing compound is used as a raw material, the phosphorus content of the polymer is preferably 1 to 6% by weight, more preferably 1.5 to 5% by weight, and even more preferably 2 to 4% by weight.

[0040] Diluting the epoxy resin composition of the present invention with various organic solvents can facilitate impregnation into fibers and adjust tackiness, and this can be adjusted by the solids concentration. When an organic solvent is used to adjust the solids concentration, it is preferable to remove the organic solvent by drying or other methods after impregnation. The drying temperature should be such that the substrate used does not deform, and the drying time is preferably 1 hour or less from the viewpoint of productivity. There are no restrictions on the thermal curing temperature, but a temperature of 20 to 100°C is preferred, and 40 to 80°C is more preferred. The dilution amount is preferably 0.01% by weight or more and 10% by weight or less.

[0041] Specific examples of the organic solvent that can be used include known organic solvents, such as aromatic organic solvents such as toluene and xylene; ketone organic solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester organic solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate and isobutyl acetate; alcohol organic solvents such as methanol, ethanol, n-propanol, isopropanol and n-butanol; and glycol ether organic solvents such as propylene glycol monomethyl ether.

[0042] The epoxy resin composition (E) may contain additives. Examples of additives include fillers such as fumed silica, flame retardants such as aluminum hydroxide and red phosphorus, modifiers such as core-shell rubber, and viscosity adjusters such as xylene resin. From the viewpoint of stabilizing the polymerization reaction, it is preferable that the additives be different from those in the resin phase. However, plasticizers and compatible flame retardants may also be included as long as they do not affect the reaction.

[0043] The epoxy resin composition (E) becomes a high molecular weight thermoplastic resin (phenoxy resin) by polymerization, which is an excellent resin component for fiber-reinforced plastics. The weight-average molecular weight (Mw) of the thermoplastic resin (phenoxy resin) obtained by polymerizing the epoxy resin composition (E) is preferably 40,000 or more and 200,000 or less. If the Mw of the thermoplastic resin is below the lower limit of the range, it will contain a large amount of compounds that have not fully polymerized, which may result in a deterioration in mechanical strength. On the other hand, if the Mw of the thermoplastic resin is above the upper limit of the range, crosslinking reactions may have progressed, which may result in a loss of thermoplasticity. The Mw is preferably 50,000 or more and 170,000 or less, more preferably 70,000 or more and 150,000 or less. The epoxy equivalent of the thermoplastic resin is preferably 10,000 g / eq. or more. If the epoxy equivalent is less than 10,000 g / eq., polymerization may not proceed sufficiently. The epoxy equivalent is more preferably 20,000 g / eq. or more, and even more preferably 25,000 g / eq. or more. The glass transition temperature (Tg) of the thermoplastic resin is preferably 80°C or higher, more preferably 90°C or higher. The proportion of gel components that are insoluble in organic solvents (gel fraction) in the thermoplastic resin is preferably less than 10%. If the gel fraction is 10% or more, the resin contains a large amount of crosslinking components, which may impair the thermoplasticity.

[0044] An epoxy resin composition film can be obtained by coating the epoxy resin composition (E) on release-treated paper or plastic film and, if necessary, adding a release-treated cover film. Known release papers, release plastic films, and cover films can be used and are not particularly limited. The thickness of the epoxy resin composition film is determined by the design thickness and resin ratio of the prepreg, but is typically 1 μm or more and 300 μm or less. If the thickness is less than 1 μm, the fiber mesh will become noticeable unless the reinforcing fibers are properly defibrated. If the thickness exceeds 300 μm, it will be difficult to uniformly impregnate the reinforcing fibers. The thickness is preferably 5 μm or more and 150 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0045] The reinforcing fiber-containing epoxy resin composition of the present invention can be obtained by mixing or impregnating the above-mentioned epoxy resin composition (E) with reinforcing fibers (F). The prepreg can be obtained as follows. The reinforcing fibers (F) used in the present invention are intended to reinforce plastics, such as carbon fibers, aramid fibers, cellulose fibers, and basalt fibers, and are not particularly limited. The fiber form may include UD sheets, woven fabrics, tows, chopped fibers, nonwoven fabrics, and paper, each of which has a length of 1 mm or more. However, from the viewpoint of impregnation, the thickness of each fiber bundle is 1 mm or less, preferably 0.5 mm or less, and more preferably 0.2 mm or less.

[0046] The reinforcing fiber-containing epoxy resin composition or prepreg of the present invention is obtained from the above-mentioned epoxy resin composition and / or epoxy resin composition film and reinforcing fibers. The weight ratio of reinforcing fibers to epoxy resin composition is preferably 2:8 to 8:2. In terms of resin content (Rc), it is 20 to 80 wt %, and the proportion of reinforcing fibers can be increased, and if necessary, Rc can be set to 35 wt % or less. If the proportion of reinforcing fibers is too low, the strength required for fiber-reinforced materials may not be fully achieved, while if the proportion of reinforcing fibers is too high, defects such as voids may occur.

[0047] In order for the reinforcing fiber-containing epoxy resin composition or prepreg of the present invention to exhibit appropriate tackiness, the glass transition temperature is preferably 0°C or higher but lower than 20°C, and particularly preferably 5°C or higher but lower than 15°C. If the glass transition temperature is 0°C or lower, the tackiness will be strong, making it easier for the resin to adhere to the release paper, resulting in a decrease in the resin content below the designed value and causing voids. If the glass transition temperature is 20°C or higher, the tackiness will be weak, weakening the adhesion to the prepreg of the lower layer and adversely affecting lamination. [Example]

[0048] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples. Unless otherwise specified, "parts" means parts by weight, and "%" means % by weight. Furthermore, the unit of various equivalents is "g / eq." The raw materials, polymerization catalysts, solvents, and reinforcing fibers used in the examples are as follows.

[0049] [Epoxy resin] A1: Epoxy resin described in Synthesis Example 1 Bisphenol A type epoxy resin (epoxy equivalent weight 187, liquid) [ka] A2: Epoxy resin described in Synthesis Example 2 Bisphenol A type epoxy resin (epoxy equivalent 650, solid) A3: Epoxy resin described in Synthesis Example 3 (bisphenol A type epoxy resin, epoxy equivalent 950, solid) A4: Epoxy resin described in Synthesis Example 4 Bisphenol A type epoxy resin (epoxy equivalent weight 475, solid) A5: Epoxy resin described in Synthesis Example 5 Bisphenol F type epoxy resin (epoxy equivalent 170, liquid) [ka] A6: Epoxy resin described in Synthesis Example 6 Bisphenol A type epoxy resin (epoxy equivalent weight 215, liquid)

[0050] [Phenol compounds] B1: Bisphenol A (Nippon Steel Chemical & Material Co., Ltd., hydroxyl equivalent 114, melting point 158°C) [ka]

[0051] [Polymerization catalyst] D1: Triphenylphosphine (Hokko Chemical Industry Co., Ltd., TPP, molecular weight 262) [ka]

[0052] [others] S1: Cyclohexanone F: PAN-based carbon fiber (Toray Industries, Inc., Torayca T700-12K-60E)

[0053] The evaluation methods used in the examples are as follows. (1) Epoxy equivalent: Measurements were carried out in accordance with JIS K7236 and expressed in units of g / eq. Specifically, a potentiometric titrator (Hiranuma Sangyo Co., Ltd., COM-1600ST) was used, and chloroform was used as the solvent, to which tetraethylammonium bromide acetate solution was added, and a 0.1 mol / L perchloric acid-acetic acid solution was used. (2) α-diol content Measurements were carried out in accordance with the JIS K7146 standard and expressed in units of "meq. / 100g." Specifically, epoxy resin was dissolved in chloroform, and a standard orthoperiodine oxygen solution was added to cause a reaction. After cooling with water, sulfuric acid and potassium iodide solutions were added, and titration with sodium thiosulfate was carried out while stirring. When the titration reached the end point, starch solution was added, and the time when the black color disappeared was taken as the end point. (3) Total chlorine content Measurements were carried out in accordance with JIS K7243-3 standard and expressed in units of "wt%". Specifically, the epoxy resin was dissolved in butyl carbitol, a specified propylene glycol solution of potassium hydroxide was added, and the mixture was heated under reflux for 30 minutes. The amount of chloride ions released was measured by silver nitrate titration.

[0054] (4) Viscosity at 60°C and viscosity doubling time The viscosity and viscosity doubling time at 60°C were measured in accordance with JIS K6870 and JIS K5600-2-3 standards. Measurements were performed using an Anton Paar MCR 102. The viscosity was measured at 60°C under the following conditions: a measurement frequency of 3 Hz, a load strain of 1%, flat plates of 20 mm diameter, and a gap between the plates of 0.5 mm. The viscosity was measured after heating to 60°C. The time required for the viscosity to double from the initial viscosity after heating to 60°C was also measured and used as the viscosity doubling time. If the viscosity remains less than double the initial viscosity even after heating for 60 minutes or more, it is determined that sufficient potential exists, and the measurement time was limited to 60 minutes. In such cases, the viscosity was recorded as ">60." (5) Glass transition temperature (Tg·DSC): Measurements were performed in accordance with JIS K7121 standard. Specifically, a differential scanning calorimeter EXSTAR6000 DSC6200 (Hitachi High-Tech Science Corporation) was used to measure one cycle in the range of -20 to 50°C at a temperature increase rate of 10°C / min, and the glass transition temperature was expressed as the midpoint glass transition temperature (Tmg; the midpoint temperature of the transition curve relative to the tangent line between the glassy and rubbery states) of the obtained measurement chart. (6) Weight average molecular weight The weight-average molecular weight (Mw) and number-average molecular weight (Mn) were determined by GPC measurement. Specifically, a Tosoh HLC8320 GPC (Tosoh Corporation) was used, equipped with columns (TSKgel SuperH-H, SuperH2000, SuperHM-H, and SuperHM-H, all manufactured by Tosoh Corporation) in series. The column temperature was 40°C. The eluent was tetrahydrofuran (THF) at a flow rate of 0.3 mL / min, and a refractive index detector was used. The measurement sample was prepared by dissolving 0.1 g of solid content in 10 mL of THF and filtering through a 0.45 μm membrane filter. The injection volume was 20 μL. Mw and Mn were calculated from a calibration curve obtained from standard polystyrenes (Tosoh Corporation, PStQuick A, PStQuick B, and PStQuick C). Data processing was performed using a Tosoh GPC8020 Model II version 6.00. (7) Gel fraction of polymer Approximately 1 g of sample was weighed into a 100 mL vial, 50 mL of tetrahydrofuran was added, and the mixture was subjected to ultrasonic diffusion at room temperature for 1 hour, followed by standing at room temperature for at least 23 hours for dissolution. A 500-mesh wire mesh was then dried in an oven at 100 °C for 1 hour and its weight was measured. The 500-mesh wire mesh was folded into a funnel, and the entire sample solution was poured onto the funnel. The vial was washed with tetrahydrofuran until no undissolved sample remained, and then poured into the funnel. The insoluble material on the mesh and the mesh were then further washed with tetrahydrofuran and dried in an oven at 100 °C for at least 4 hours. The gel fraction was calculated as a weight percent by subtracting the dry weight of the mesh from the weight of the dried sample and mesh and dividing this by the sample weight.

[0055] (8) Tackiness of prepreg The prepreg was peeled from the release paper and protective film at 23°C and 50% RH, and the workability when laminating 7 ply prepreg was evaluated. The amount of resin remaining on the release paper and the adhesion to the lower prepreg when the prepreg was attached were evaluated. The meaning of the evaluation results of the tackiness of the prepreg is as follows: 〇: The resin does not adhere to the release paper, and the prepreg is not easily peeled off when bonded together, and there is moderate adhesiveness ×1: Some resin adheres to the release paper, making it very sticky ×2: Prepreg is easily peeled off when bonded together, and adhesiveness is very weak (9) Flexural strength of FRP: Measurements were performed in a 90-degree direction using a three-point bending test (Method A) according to JIS K7074. The test was performed using a Shimadzu Science Autograph AGS-X, with sample dimensions of 2 mm thick, 100 mm long, and 15 mm wide, a bending span of 70 mm, and a test speed of 1 mm / min.

[0056] Synthesis Example 1 190 parts of bisphenol A and 490 parts of epichlorohydrin were placed in a separable flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, a dropping device, and an oil-water separator having a cooling tube, and dissolved by heating to 60°C under a nitrogen atmosphere. Next, 35 parts of a 49% aqueous sodium hydroxide solution was added to this solution, and the mixture was reacted at 60°C for 2 hours. Next, while maintaining the temperature in the reaction system at 60°C, the pressure was gradually reduced to form an azeotrope between epichlorohydrin and water, the upper layer of water was removed via an oil-water separator, and the lower layer of epichlorohydrin was returned to the system as reflux. While maintaining this state, 119 parts of a 49% aqueous sodium hydroxide solution were added dropwise over 3 hours. After completion of the dropwise addition, the system was maintained under reflux at 60°C and 100 mmHg for 30 minutes. Thereafter, while the refluxed epichlorohydrin was removed from the system, the temperature and degree of vacuum in the system were gradually increased, and epichlorohydrin was evaporated and recovered until the final pressure reached 150°C and 5 mmHg. The system was then returned to atmospheric pressure, and 250 parts of MIBK was added to dissolve the crude resin. 500 parts of water was added to this solution to separate and remove the by-product salt. This solution was then washed several times with 300 parts of water, and this was repeated until the wash water became neutral. The solution was heated to 150°C under a reduced pressure of 5 mmHg to remove the MIBK, yielding liquid epoxy resin A1.

[0057] Synthesis Example 2 173 parts of bisphenol A and 478 parts of epoxy resin E1 were placed in a separable flask equipped with a stirrer, thermometer, nitrogen inlet tube, dropping device, and cooling tube, and dissolved in a nitrogen atmosphere by heating to 120°C. Next, 0.2 parts of TPP was added to this solution, and the reaction was carried out at 160°C for 5 hours. After the reaction was completed, the resin was extracted, quickly cooled, and solidified to obtain epoxy resin A2.

[0058] Synthesis Example 3 194 parts of bisphenol A and 456 parts of epoxy resin E1 were placed in a separable flask equipped with a stirrer, thermometer, nitrogen inlet tube, dropping device, and cooling tube, and dissolved under a nitrogen atmosphere by heating to 120°C. Next, 0.2 parts of TPP was added to this solution, and the reaction was carried out at 180°C for 5 hours. After the reaction was completed, the resin was removed, quickly cooled, and solidified to obtain epoxy resin A3.

[0059] Synthesis Example 4 A separable flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, a dropping device, and an oil-water separator having a cooling tube was charged with 360 parts of bisphenol A, 228 parts of epichlorohydrin, and 265 parts of MIBK, and the mixture was heated to 40°C under a nitrogen atmosphere to dissolve. Next, 519 parts of a 21% aqueous sodium hydroxide solution was added dropwise over 1 hour while maintaining the temperature inside the reaction system at 40° C. After completion of the dropwise addition, the temperature was maintained at 95° C. under a nitrogen atmosphere for 1 hour. Then, 300 parts of MIBK and 300 parts of water were added, and by-product salt was separated and removed. The mixture was then washed several times with 300 parts of water until the wash water became neutral. The solution was heated to 180°C under a reduced pressure of 5 mmHg to remove the MIBK, and the resin was extracted, cooled, and solidified to obtain Epoxy Resin A4.

[0060] Synthesis Example 5 The same reaction as in Example 1 was carried out except that 175 parts of bisphenol F was used instead of bisphenol A, to obtain epoxy resin A5.

[0061] Synthesis Example 6 The same reaction as in Example 1 was carried out except that the amount of epichlorohydrin charged was 420 parts by weight and the amount of 49% aqueous sodium hydroxide solution added dropwise over 3 hours was 73 parts by weight, to obtain an epoxy resin A6.

[0062] Synthesis Example 7 (Mixing Example) 159 parts of the bisphenol A epoxy resin (A1) obtained in Synthesis Example 1 and 29 parts of the bisphenol A epoxy resin (A2) obtained in Synthesis Example 2 were weighed, heated and mixed using a planetary mixer, and a mixed epoxy resin (A7) was obtained. Mixed epoxy resins (A7 to A10) were obtained by compounding the ingredients in the amounts (parts) shown in Table 1 and performing the same procedure.

[0063] For the epoxy resins (A1 to A10), the epoxy equivalent, α-diol content, and total chlorine content were measured, and the terminal epoxy content was calculated based on the following formula (1). The calculation results are shown in Table 1.

number

[0064] Example 1 188 parts of the epoxy resin (A7) obtained in Synthesis Example 7 and 100 parts of bisphenol A (B1) were weighed out and mixed using a planetary mixer while heating to 105°C. At 105°C, the bisphenol A dissolved in the epoxy resin, forming a transparent, homogeneous compound. After reaching 105°C, the mixture was quickly cooled to 60°C, and a polymerization catalyst solution prepared by dissolving 2.4 parts of triphenylphosphine (D1) as a polymerization catalyst in 2.4 parts of cyclohexanone (S1) as an organic solvent was added to the planetary mixer and mixed in. After mixing, the mixture was quickly removed and immediately cooled to below 40°C, yielding an epoxy resin composition (E1).

[0065] The number average molecular weight and epoxy equivalent of the epoxy resin composition (E1) were measured. The molar ratio of catalyst to epoxy groups was calculated from the amount of catalyst charged and the epoxy equivalent. The viscosity and viscosity doubling time at 60°C were measured using a rheometer.

[0066] The resulting epoxy resin composition (E1) was heated to approximately 60°C and stirred, then poured into a chrome-plated iron mold container with a pre-set clearance of 4 mm, and thermally polymerized in a hot air circulating oven at 160°C for 60 minutes to obtain a polymer (resin plate). The weight-average molecular weight of the resulting polymer was measured to be 130,000, and the gel fraction was measured to be 3%.

[0067] A release-treated release paper was fixed on a hot plate preheated to 60°C with the release side facing up, and the epoxy resin composition (E1) was placed on the release paper. Then, a bar coater preheated to 60°C was used to coat the epoxy resin composition until the area weight of the resin was 79 g / m. 2 Immediately after coating, the sheet was removed from the hot plate and air-cooled to obtain an epoxy resin composition sheet. Subsequently, a fiber sheet having an area weight of 153 g / m was applied to the obtained epoxy resin composition sheet. 2 A protective film was then placed over the PAN-based carbon fiber (F), and pressure was applied to the PAN-based carbon fiber (F) so that the surface pressure was 0.5 MPa using a hot press preheated to 90°C. After 1 minute, the PAN-based carbon fiber (F) was removed and air-cooled to obtain a prepreg with an Rc of 34%. The glass transition temperature of the obtained prepreg was measured.

[0068] After laminating 13 sheets of prepreg (I1) with the fiber orientation in the same direction, release film was attached to the top and bottom surfaces and the sheet was sandwiched between 3 mm thick aluminum plates. The aluminum plates sandwiching the prepreg and the coupler were then wrapped in bag film, after which the coupler was connected to a vacuum pump and the air inside the bag film was removed. The bag was then placed in a hot air circulating oven preheated to 160°C and cured while maintaining the vacuum, resulting in the molding of a 2 mm thick unidirectional fiber-reinforced plastic (J1). The curing conditions were 160°C and 240 minutes.

[0069] When the prepreg was laminated, its tackiness was evaluated and it was rated as good. The flexural strength of the obtained unidirectional fiber reinforced plastic (J1) was measured and found to be 110 MPa.

[0070] Examples 2 to 4, Comparative Examples 1 to 6 Epoxy resin compositions (E2 to E10), polymers, epoxy resin composition sheets, prepregs, and unidirectional fiber-reinforced plastics were obtained by compounding the ingredients in the amounts (parts) shown in Table 1 and performing the same operations as in Example 1. In Comparative Example 2 (E6), the catalyst was added at 80°C, and the mixture was heated and stirred at 80°C for 2 hours, after which the resin was extracted. The physical properties of the obtained epoxy resin composition, polymer, prepreg and unidirectional fiber reinforced plastic were measured in the same manner as in Example 1, and the evaluation results are shown in Table 1.

[0071] In Examples 1 to 4, the molecular weight of the epoxy resin composition was in the range of 300 or more and less than 1500, and when made into a prepreg, a prepreg with appropriate tackiness could be obtained. Because a high-content epoxy resin with a terminal epoxy content that satisfies the specified range of formula (1) was used, the molecular weight was sufficiently increased and the mechanical properties of the CFRP were also fully exhibited. Because an appropriate amount of polymerization catalyst was used relative to the epoxy resin, i.e., the polymerization catalyst amount / epoxy group amount (molar ratio) was 0.008 or more and less than 0.02, the molecular weight was sufficiently increased while ensuring sufficient usable time. In Table 2, the amount of polymerization catalyst / amount of epoxy groups (molar ratio) is calculated as (2.4 / 262 / 288) / (1 / 322)=0.0104 in the case of Example 1. Here, 2.4 is the amount of polymerization catalyst added, 262 is the molecular weight of the polymerization catalyst, 288 is the weight of the resin composition, and 322 is the epoxy equivalent of the resin composition. In Comparative Example 1, the molecular weight of the epoxy resin composition was 300 or less, and the tackiness when made into a prepreg was too strong, resulting in poor workability when laminating the prepreg. In Comparative Example 2, the molecular weight of the epoxy resin composition was 1500 or more, and the tackiness of the prepreg was weak, resulting in poor workability during lamination of the prepreg. Furthermore, the polymerized product contained a large amount of gel components, resulting in poor secondary processability as a CFRTP. In Comparative Example 3, the epoxy resin used was a direct process epoxy resin, and therefore the terminal epoxy content was low, the polymerizability was poor, and the mechanical strength as a CFRTP was poor. In Comparative Example 4, the amount of polymerization catalyst was small relative to the epoxy resin, resulting in poor polymerization properties and poor mechanical strength as a CFRTP. In Comparative Example 5, the amount of polymerization catalyst was excessive relative to the epoxy resin, so the usable time at 60° C. was short, making it difficult to produce a uniform resin film. In Comparative Example 6, an epoxy resin with a high chlorine content and a low terminal epoxy content was used, resulting in poor polymerizability and poor mechanical strength as a CFRTP.

[0072] [Table 1]

[0073] [Table 2] [Industrial Applicability]

[0074] The epoxy resin composition and prepreg of the present invention are useful as a matrix resin for fiber-reinforced plastics (FRP), and are particularly suitable for use as in-situ polymerized thermoplastic epoxy resins.

Claims

1. An epoxy resin composition comprising, as essential components, an epoxy resin (A) having two epoxy groups in one molecule, a compound (B) having two phenol groups in one molecule, and a polymerization catalyst (D), The number average molecular weight of the resin composition before curing is 300 or more and less than 1500, The blending amounts of the epoxy resin (A) and the compound (B) are 0.90 to 1.10 moles of the phenol compound (B) per mole of the epoxy resin (A), the terminal epoxy content of the epoxy resin (A) calculated from formula (1) is 97.0% or more and 100% or less, An epoxy resin composition characterized in that the content of the polymerization catalyst (D) is 0.008 or more and less than 0.020 times the amount of epoxy groups in terms of moles. [Equation 1] W: Epoxy equivalent (g / eq.) α: α-diol group (meq. / 100g) Cl: Total chlorine (g / 100g)

2. 2. The epoxy resin composition according to claim 1, wherein the polymerization catalyst (D) is a phosphorus compound having a melting point of 100° C. or less.

3. 2. The epoxy resin composition according to claim 1, wherein the polymerization catalyst (D) is triphenylphosphine.

4. 2. The epoxy resin composition according to claim 1, further comprising an organic solvent (S) in an amount of 0.01% by weight to 10% by weight based on the epoxy resin composition.

5. A reinforcing fiber-containing epoxy resin composition comprising the epoxy resin composition according to any one of claims 1 to 4 and reinforcing fibers (F).

6. 6. The reinforcing fiber-containing epoxy resin composition according to claim 5, wherein the reinforcing fiber (F) is a continuous fiber.

7. 6. The reinforcing fiber-containing epoxy resin composition according to claim 5, wherein the reinforcing fiber (F) is carbon fiber in an amount of 20 to 80% by weight.

8. A prepreg comprising the reinforcing fiber-containing epoxy resin composition according to claim 5.

9. 9. The prepreg according to claim 8, having a glass transition temperature of 0°C or higher but lower than 20°C.

10. A fiber-reinforced plastic using the reinforcing fiber-containing epoxy resin composition according to claim 5.

11. A fiber reinforced plastic using the prepreg according to claim 8.

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