Epoxy resin composition, prepreg, and fiber-reinforced plastic using the same

Abstract

The present invention provides an epoxy resin composition for improving the adhesion of a thermoplastic epoxy resin to a reinforcing fiber. The epoxy resin composition is a resin composition containing a bifunctional phenol compound, a bifunctional epoxy resin, and a polymerization catalyst, characterized in that, as the bifunctional epoxy resin, it contains 50% by weight or more of an epoxy resin (a) represented by the following formula (1), the molar ratio of the bifunctional epoxy resin / bifunctional phenol compound is 1.01 to 1.05 moles, the epoxy equivalent of a polymer obtained from the epoxy resin composition is 5,000 to 20,000 g / eq., the flexural strength is 70 MPa or more, and the tetrahydrofuran insoluble content is 10% by weight or less. (A is represented by formula (2), X is a single bond, an alkylene group, an arylene group, O, CO, or the like, and Y is an alkyl group or an aryl group.) 1 is an alkyl group or an aryl group.)

Description

TECHNICAL FIELD

[0001] The present application relates to an epoxy resin composition, an epoxy resin composition containing a reinforcing fiber, a prepreg, and a fiber-reinforced plastic using the same. BACKGROUND

[0002] A fiber-reinforced plastic (FRP) exhibits excellent physical properties such as light weight and high strength, and has been applied in many fields. Among them, a carbon fiber-reinforced plastic (CFRP) using carbon fiber as a reinforcing fiber is known to be particularly excellent in mechanical strength.

[0003] Since the balance of price and physical properties is excellent, an epoxy resin is mainly used as a matrix resin of FRP. In addition, since an epoxy resin has a secondary hydroxyl group, it is also known to form a good adhesive surface with a reinforcing fiber, and thus exhibits good mechanical properties as a CFRP matrix resin.

[0004] On the other hand, a plastic using a thermoplastic resin as a matrix resin is called FRTP, and is developed because it is excellent in mass productivity, moldability, and recyclability. As a matrix resin of FRTP, nylon, polypropylene, polycarbonate, and the like are mainly used.

[0005] As a problem of FRTP, since the adhesion of a reinforcing fiber to a resin is low, a problem of low bending strength in the 90-degree direction of a unidirectional material (UD material) can be cited. In order to improve the adhesion of a reinforcing fiber to a resin, various methods of modifying the surface of a reinforcing fiber by washing a sizing agent attached to the fiber, oxidizing the fiber surface with ozone or an acid, and the like have been studied, but all require additional processes and are not simple (Non-Patent Literature 1).

[0006] In order to improve the adhesion to a reinforcing fiber, as a thermoplastic resin, an in-situ polymerization type thermoplastic epoxy resin has been proposed. The in-situ polymerization type thermoplastic epoxy resin is impregnated in a fiber in a low viscosity state before polymerization, and thus has good impregnation properties and can increase the proportion of a reinforcing fiber. In addition, since a secondary hydroxyl group is present in the epoxy resin, good adhesion to a reinforcing fiber is expected.

[0007] In a conventional report on the adhesion of a thermoplastic epoxy resin to carbon fiber, it is reported that the interfacial shear strength between carbon fiber and a matrix increases as the molecular weight of the thermoplastic epoxy increases (Non-Patent Literature 2).

[0008] PRIOR ART DOCUMENTS

[0009] PATENT LITERATURE

[0010] Patent Literature 1: Japanese Patent Application Laid-Open No. 2006-321897

[0011] NON-PATENT LITERATURE

[0012] Non-Patent Literature 1: Improvement of Bending Strength of Carbon Fiber / Thermoplastic Epoxy Composites (Open Journal of Composite Materials, 2017, 7, 207-217)

[0013] Non-Patent Literature 2: Journal of the Adhesion Society of Japan VOL. 53 No. 11 (2017) 375-380 SUMMARY

[0014] However, according to the research by the present inventors, in order to sufficiently increase the molecular weight of the thermoplastic epoxy resin within the reinforcing fiber, it is necessary to spend a sufficient time for polymerization. In addition, if the backbone volume of the thermoplastic epoxy resin is made large in order to achieve high heat resistance, the steric hindrance of the reaction becomes large, and thus the curing time for polymerization further becomes long, and the productivity is poor. Therefore, there is a need for a method for improving the adhesion of the thermoplastic epoxy resin to the reinforcing fiber and increasing the bending strength in the 90-degree direction by a simple method with excellent productivity.

[0015] In order to exhibit the adhesion of the thermoplastic epoxy resin to the reinforcing fiber, the present inventors have conducted intensive research, and as a result, it has been found that the adhesion to the reinforcing fiber and the bending strength in the 90-degree direction can be improved by using a specific epoxy resin composition.

[0016] That is, the present application is an epoxy resin composition characterized by containing, as essential components, a bifunctional phenol compound, a bifunctional epoxy resin, and a polymerization catalyst,

[0017] As the bifunctional epoxy resin, 50% by weight or more of a bifunctional epoxy resin (a) represented by the following formula (1) is contained,

[0018] The bifunctional epoxy resin is 1.01 to 1.05 moles per 1 mole of the bifunctional phenol compound,

[0019] The polymer obtained from the above-described epoxy resin composition is a thermoplastic epoxy resin having an epoxy equivalent weight of 5000 g / eq. to 20000 g / eq. and a bending strength of 70 MPa or more, and when it is dissolved in tetrahydrofuran, the insoluble component is 10% by weight or less in the polymer.

[0020] [Chemical Formula 1]

[0021]

[0022] Here, A in equation (1) is represented by equation (2), n is the number of repetitions and its average value is 0 to 5. X is any one of a single bond, a hydrocarbon group with 1 to 13 carbon atoms, -O-, -CO-, -COO-, -S-, and -SO2-, and Y... 1 Y is independently any one of an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 10 carbon atoms. 2 and Y 3 Each is independently one of hydrogen atom, alkyl group having 1 to 4 carbon atoms, or aryl group having 6 to 10 carbon atoms.

[0023] In addition, the present invention is an epoxy resin composition containing reinforcing fibers or a prepreg obtained by mixing the above-mentioned epoxy resin composition with reinforcing fibers.

[0024] The aforementioned reinforcing fiber is preferably PAN-based carbon fiber, and is preferably contained in the resin composition or prepreg at a ratio of 50% to 80% by weight.

[0025] In addition, the present invention is a fiber-reinforced plastic obtained by using the above-described epoxy resin composition containing reinforcing fibers or the above-described prepreg.

[0026] According to the present invention, a thermoplastic epoxy resin composition with excellent adhesion to reinforcing fibers can be provided.

[0027] The reason why the adhesion between the reinforcing fiber and the resin can be brought into play is that by controlling the composition ratio of the raw materials, it is possible to obtain epoxy resin with low epoxy equivalent and high epoxy group concentration, which can form good adhesion with the functional groups on the surface of the reinforcing fiber and the sizing agent.

[0028] Furthermore, due to reasons such as incomplete polymerization, the composite material can exhibit sufficient strength by achieving a flexural strength of 70 MPa or higher. Previously, the adhesiveness of epoxy resins was thought to be caused by secondary hydroxyl groups, and the influence of the epoxy group concentration in the polymer had not been reported. According to the present invention, the adhesiveness to reinforcing fibers can be achieved through a simple method of adjusting the feed ratio of the raw materials. Detailed Implementation

[0029] The present invention will now be described in detail according to its preferred embodiments.

[0030] The epoxy resin composition of the present invention is a composition containing a bifunctional phenolic compound, a bifunctional epoxy resin, and a polymerization catalyst as essential components, and capable of polymerization by heating. It may also contain additives such as organic solvents, fillers, and flame retardants.

[0031] The above-mentioned difunctional epoxy resin contains 50% by weight or more of the above-mentioned epoxy resin (a) represented by the above-mentioned formula (1) as an essential component. It is preferable to be 66% by weight or more, more preferable to be 75% by weight or more, and further preferable to be 80% by weight or more. The epoxy resin (a) constitutes a part of the difunctional epoxy resin.

[0032] Further, the epoxy equivalent of the difunctional epoxy resin is preferably 150 to 350 g / eq.

[0033] In formula (1), A is a divalent group represented by the above-mentioned formula (2). n is a repeating number and its average value is 0 to 5, preferably 0 to 1.

[0034] In formula (2), X is any one of a single bond, a hydrocarbon group having 1 to 13 carbon atoms, -O-, -CO-, -COO-, -S-, -SO2-.

[0035] As the hydrocarbon group having 1 to 13 carbon atoms, an alkylene group having 1 to 9 carbon atoms or an arylene group having 6 to 13 carbon atoms is preferable, and for example, -CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -CHPh-, -C(CH3)Ph-, 1,1-cyclopropylene, 1,1-cyclobutylene, 1,1-cyclopentylene, 1,1-cyclohexylene, 4-methyl-1,1-cyclohexylene, 3,3,5-trimethyl-1,1-cyclohexylene, 1,1-cyclooctylene, 1,1-cyclononylene, 1,2-ethylene, 1,2-cyclopropylene, 1,2-cyclobutylene, 1,2-cyclopentylene, 1,2-cyclohexylene, 1,2-phenylene, 1,3-propylene, 1,3-cyclobutylene, 1,3-cyclopentylene, 1,3-cyclohexylene, 1,3-phenylene, 1,4-butylene, 1,4-cyclohexylene, 1,4-phenylene, 1,1-fluorene, 1,2-biphenylene, 1,4-biphenylene, tetrahydrodicyclopentadienyl, tetrahydrotricyclopentadienyl, and the like can be mentioned.

[0036] Among them, a single bond, -O-, -CO-, -COO-, -S-, -SO2-, -CH2-, -CH(CH3)-, -C(CH3)2-, -CHPh-, -C(CH3)Ph-, 1,1-cyclohexylene, 4-methyl-1,1-cyclohexylene, 3,3,5-trimethyl-1,1-cyclohexylene, 1,4-cyclohexylene, 1,4-phenylene, 1,1-fluorene are preferable, and a single bond, -O-, -CO-, -COO-, -S-, -SO2-, -CH2-, -CH(CH3)-, -C(CH3)2-, -C(CH3)Ph-, 1,1-cyclohexylene, 3,3,5-trimethyl-1,1-cyclohexylene, 1,1-fluorene are more preferable.

[0037] It should be noted that Ph represents a phenyl group. Alkylene includes the meaning of alkylidene.

[0038] Y 1 is independently any one of an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0039] As the alkyl group having 1 to 4 carbon atoms, for example, there can be mentioned a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a t-butyl group, and the like.

[0040] As the aryl group having 6 to 10 carbon atoms, for example, there can be mentioned a phenyl group, a tolyl group, an ethylphenyl group, a xylyl group, an n-propylphenyl group, an isopropylphenyl group, a mesityl group, a naphthyl group, and the like.

[0041] Among them, a methyl group, an ethyl group, an n-propyl group, an n-butyl group, a t-butyl group, a phenyl group, a tolyl group, a xylyl group, or a naphthyl group is preferred, and a methyl group, an ethyl group, an n-propyl group, an n-butyl group, a t-butyl group, a phenyl group, or a tolyl group is more preferred.

[0042] Y 2 is independently any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and is preferably a group other than a hydrogen atom. As examples of the alkyl group and the aryl group, the same groups as those exemplified in Y 1 are given. A preferred Y 2 is the same as Y 1 .

[0043] Y 3 is independently any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms. As examples of the alkyl group and the aryl group, the same groups as those exemplified in Y 1 are given. A preferred Y 3 is a hydrogen atom or the same group as that exemplified in Y 1 .

[0044] As the bifunctional epoxy resin (a), for example, there can be mentioned a tetramethyl bisphenol F type epoxy resin (for example, YSLV-80XY (manufactured by Nitobo Chemical Co., Ltd.), and the like), a tetramethyl diphenol type epoxy resin (for example, YX-4000 (manufactured by Mitsubishi Chemical Corporation), and the like), a bisphenol fluorene type epoxy resin (for example, OGSOL CG-500 (manufactured by Osaka Gas Chemicals Co., Ltd.), and the like), and the like.

[0045] In addition, even if an epoxy resin other than the epoxy resin (a) is used, it is acceptable as long as it is a difunctional epoxy resin, and the purity thereof is preferably 95% or more. Furthermore, as long as the purity of the difunctional epoxy resin is high, position isomers and oligomers can also be included. As the epoxy resin that can be used in combination with the epoxy resin (a), for example, there are mentioned bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenol phenylacetone type epoxy resins, diphenyl sulfide type epoxy resins, diphenyl ether type epoxy resins, bisphenol fluorene type epoxy resins, and the like, but they are not limited thereto.

[0046] The difunctional epoxy resin that can be used in combination with the epoxy resin (a) is preferably less than 50% by weight of the total epoxy resins, and desirably less than 30% by weight. If it is more than 50% by weight, gelation occurs to produce a component that is difficult to dissolve in a solvent, and thus the reworkability can be deteriorated.

[0047] In the case where a monofunctional impurity is included in the difunctional epoxy resin, the molecular weight after polymerization does not increase, and thus the mechanical properties of the obtained thermoplastic resin product can be deteriorated. Therefore, the monofunctional impurity is preferably 2% by weight or less relative to the difunctional epoxy resin.

[0048] In the case where a trifunctional or higher impurity is included, a crosslinked structure is easily formed starting from the impurity, and thus in addition to the increase in the dispersion of the polymer, gelation can occur to deteriorate the thermoplasticity. Therefore, the trifunctional or higher impurity is preferably 1% by weight or less relative to the difunctional epoxy resin.

[0049] It should be noted that in the case of an impurity that does not have a reactive group that reacts with either of the epoxy resin and the phenolic hydroxyl group and does not hinder the polymerization reaction in the monomer, if the amount thereof is increased, the molecular weight after polymerization can be decreased. Therefore, it is preferably 2% by weight or less relative to the difunctional epoxy resin.

[0050] The difunctional phenol compound used in the epoxy resin composition of the present application is a compound having two phenolic hydroxyl groups in one molecule, and the purity thereof is preferably 95% by weight or more. Furthermore, as long as the purity of the difunctional phenol compound is high, position isomers can also be included.

[0051] In the case where a monofunctional impurity is included, the molecular weight after polymerization does not increase, and thus the mechanical properties of the manufactured thermoplastic resin can be deteriorated. Therefore, the monofunctional impurity is preferably 2% by weight or less relative to the difunctional phenol compound.

[0052] In the case of containing a tri-functional or more impurity, a crosslinked structure is easily formed from the impurity as a starting point, and thus, in addition to the increase in the dispersion of the polymer, gelation can occur, which can impair the thermoplasticity. Therefore, the tri-functional or more impurity is preferably 1% by weight or less relative to the di-functional phenol compound.

[0053] It should be noted that, in the case of an impurity that does not have a reactive group that reacts with either of the epoxy resin and the phenolic hydroxyl group and does not hinder the polymerization reaction in the monomer, if the amount is large, the molecular weight after polymerization can be small. Therefore, the impurity is preferably 2% by weight or less relative to the di-functional phenol compound.

[0054] The di-functional phenol compound is preferably a bisphenol compound or a diphenol compound. As the bisphenol compound, for example, bisphenol A, bisphenol F (both manufactured by Nippon Steel Chemical Co., Ltd.), bisphenol fluorene (manufactured by Osaka Gas Chemical Co., Ltd.), Bis-E, Bis-Z, BisOC-FL, BisP-AP, BisP-CDE, BisP-HTG, BisP-MIBK, BisP-3MZ, S-BOC (all manufactured by Hokuriku Chemical Industry Co., Ltd.), bisphenol S, and the like can be given. As the diphenol compound, for example, diphenol, dimethyl diphenol, tetramethyl diphenol, and the like can be given. As the di-functional phenol compound other than these, for example, hydroquinone, methyl hydroquinone, dibutyl hydroquinone, resorcinol, methyl resorcinol, catechol, methyl catechol, and the like can be given. Among these, the bisphenol compound or the diphenol compound is preferred.

[0055] The ratio of the di-functional epoxy resin contained in the epoxy resin composition of the present application is 1.01 to 1.05 moles relative to 1 mole of the di-functional phenol compound, and is preferably 1.02 to 1.03 moles. In the case of a thermoplastic epoxy resin, a straight chain structure is obtained by sequentially reacting the epoxy resin and the phenol compound, and thermoplasticity is exhibited. If the epoxy resin is in excess, an epoxy group terminal is formed, and if the phenol compound is in excess, a phenol group terminal is formed, and the reaction is terminated.

[0056] When the ratio of the epoxy resin is less than 1.01 moles, the polymer easily becomes a phenol group terminal, and it can be impossible to exhibit adhesion to the reinforcing fiber.

[0057] When the ratio of the epoxy resin is more than 1.05 moles, after the polymerization reaction is terminated, the presence of the unreacted epoxy resin component in the resin can adversely affect the strength of the resin.

[0058] In the epoxy resin composition, if the phenol compound exists in the epoxy resin in a crystalline state, the molar ratio deviates from the design when observed microscopically. If the reaction is initiated in this state, sometimes the polymerization does not proceed sufficiently. In order to make the polymerization proceed sufficiently, an epoxy resin composition in which the phenol compound and the epoxy resin are uniformly dissolved (compatible) with each other is preferred.

[0059] Further, it is preferred that the epoxy resin composition before compounding with a reinforcing fiber or the like is completely dissolved or becomes a uniform liquid, for example, when a molten mixture is added to a glass-made petri dish in a state free of air bubbles so that the thickness is 2 mm and the haze value in the thickness direction is measured, if the haze value in the thickness direction is less than 30%, it is judged that the epoxy resin composition has been dissolved or become a uniform liquid to a level that does not affect the polymerization reaction. The haze value is more preferably less than 20%, and further preferably less than 10%.

[0060] There is no limitation on the polymerization catalyst used in the epoxy resin composition, and a publicly known polymerization catalyst can be used. Specifically, phosphorus-based polymerization catalysts such as triphenylphosphine, tris(p-tolyl)phosphine, tris(o-tolyl)phosphine, tris(p-methoxyphenyl)phosphine, and the like can be given. As polymerization catalysts other than these, imidazole compounds such as 1B2MZ, 1B2PZ, and TBZ (manufactured by Shikoku Chemicals Corporation) can be given.

[0061] The above polymerization catalyst is preferably 0.05 to 5% by weight relative to the total amount of the resin composition composed of the difunctional epoxy resin and the difunctional phenol compound. In the case of less than 0.05% by weight, the time taken for in-situ polymerization is long, and thus the productivity can be reduced, and in addition, the catalyst can be deactivated for some reason before reaching the target molecular weight. In the case of more than 5% by weight, the polymerization reaction proceeds rapidly, and on the other hand, the storage stability can be impaired to cause problems in processability, and since it is a component that participates in the reaction but is not incorporated into the skeleton, the properties after polymerization can be impaired in addition to the simple expense being economically disadvantageous.

[0062] The epoxy resin composition can contain an organic solvent for a solvent for the polymerization catalyst or adjustment of the viscosity. The organic solvent used is not particularly limited as long as it does not hinder the reaction of the epoxy resin and the phenol compound, but from the viewpoint of easy availability, a hydrocarbon-based, ketone-based, or ether-based solvent is preferred. Specifically, toluene, xylene, acetone, methyl ethyl ketone, isobutyl ketone, cyclopentanone, cyclohexanone, diethylene glycol dimethyl ether, and the like can be given. However, if a large amount of the organic solvent is present in the reaction, the polymerization reaction is hindered. Further, if the organic solvent remains in the polymer, the mechanical properties and heat resistance are deteriorated. Therefore, the proportion of the organic solvent is preferably 5% by weight or less relative to the total weight of the epoxy resin composition.

[0063] The progress of polymerization of the epoxy resin composition can be judged by the change in the epoxy equivalent of the polymer. If heating is less than 1 hour, the epoxy equivalent is in a tendency to increase, and it is likely that the polymerization is not sufficiently progressed. When heating is 1 hour or more, the epoxy equivalent hardly increases from the value at 1 hour, and it is judged that the polymerization is sufficiently progressed. Thus, the polymerization condition for obtaining a polymer from the epoxy resin composition is heating at 160°C for 1 hour. In the present application, the polymer for measuring the tetrahydrofuran (THF) insoluble component means a polymer obtained by polymerization under this condition.

[0064] The progress of polymerization of the epoxy resin composition and the prepreg containing a reinforcing fiber is also judged by the change in the epoxy equivalent as in the case of the confirmation of the progress of the polymer. If heating is less than 4 hours, the epoxy equivalent is in a tendency to increase, and it is likely that the polymerization is not sufficiently progressed. When heating is 4 hours or more, the epoxy equivalent hardly increases from the value at 4 hours, and it is judged that the polymerization is sufficiently progressed. It should be noted that, in the case of the epoxy resin composition for fiber composite, the epoxy equivalent becomes almost equivalent by setting the heating time to 4 times the monomer of the epoxy resin composition. It is considered that this is because the reaction is inhibited in the fiber. Thus, the curing condition for obtaining a fiber reinforced plastic from the epoxy resin composition containing a reinforcing fiber or the prepreg is heating at 160°C for 4 hours.

[0065] It is important that the flexural strength of the polymer obtained by polymerizing the epoxy resin composition of the present application in the state of not containing a filler such as a reinforcing fiber and an additive is 70 MPa or more. If the flexural strength of the polymer is below the lower limit of the range, the mechanical strength as a fiber reinforced plastic cannot be sufficiently exhibited. The higher the strength, the better the mechanical strength as a fiber reinforced plastic, and thus the upper limit value is not particularly specified.

[0066] The epoxy equivalent of the polymer obtained by polymerizing the epoxy resin composition of the present application is 5000 g / eq. to 20000 g / eq. When the epoxy equivalent of the polymer is less than the lower limit of the range, many epoxy resins in which polymerization is not sufficiently progressed are contained, and it is likely that the mechanical strength is deteriorated. When the epoxy equivalent of the polymer exceeds the upper limit of the range, the terminal group becomes a phenolic group, and thus it is likely that the adhesion of the reinforcing fiber is deteriorated.

[0067] The epoxy resin composition of the present application can contain an additive. As the additive, for example, a filler such as fumed silica, a flame retardant such as aluminum hydroxide and red phosphorus, a modifier such as a core-shell rubber, and the like can be given. From the viewpoint of stabilizing the polymerization reaction, it is preferable that the additive is a substance different from the resin, but a plasticizer, a compatible flame retardant can also be contained within the range not affecting the reaction.

[0068] The epoxy resin composition of the present application can be made into a thermoplastic epoxy resin by polymerization. The thermoplastic epoxy resin is excellent as a resin component of fiber-reinforced plastic.

[0069] The epoxy resin composition containing a reinforcing fiber of the present application is obtained by mixing or impregnating the above-mentioned epoxy resin composition and a reinforcing fiber. In addition, a prepreg can be obtained as follows.

[0070] An epoxy resin composition film can be obtained by coating the epoxy resin composition of the present application on a release-treated paper or a plastic film, and, if necessary, imparting a release-treated cover film. As to the release paper, the release plastic film, and the cover film, known materials can be used without particular limitation. The thickness of the epoxy resin composition film is determined depending on the design thickness and the resin ratio of the prepreg, and the usual thickness is 1 μm to 300 μm. If less than 1 μm, there is a problem that the mesh of the fiber is noticeable if the reinforcing fiber is not completely fibrillated, and if more than 300 μm, it is difficult to impregnate uniformly in the reinforcing fiber. It is preferred to be 5 μm to 150 μm, and more preferred to be 10 μm to 100 μm.

[0071] The reinforcing fiber used in the present application is a material for reinforcing plastic such as carbon fiber, aramid fiber, cellulose fiber, and the like, and is not particularly limited. In addition, as to the form of the fiber, UD sheet, fabric, tow, short fiber, nonwoven fabric, papermaking, and the like can be mentioned, and are not particularly limited. 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.

[0072] The epoxy resin composition containing a reinforcing fiber of the present application or the prepreg is obtained from the reinforcing fiber and the above-mentioned epoxy resin composition and / or epoxy resin composition film.

[0073] The ratio of the reinforcing fiber to the epoxy resin composition is preferably 5:5 to 8:2 in terms of weight ratio. If the reinforcing fiber is too small, it can not be sufficient to satisfy the strength required for the fiber-reinforced material, and if the reinforcing fiber is too large, there is a possibility that defects such as voids are generated.

[0074] Example

[0075] Hereinafter, the present application will be more specifically described based on examples, but the present application is not limited to the following examples. Unless otherwise specified, "parts" means parts by weight, and "%" means % by weight.

[0076] The raw materials, catalysts, solvents, and reinforcing fibers used in the examples are described below.

[0077] [Epoxy Resin]

[0078] A1: Tetramethyl biphenol type epoxy resin (manufactured by Mitsubishi Chemical Corporation, YX-4000, epoxy equivalent 188)

[0079] A2: Bisphenol A type epoxy resin (manufactured by JFE Chemicals Corporation, YD-8125, epoxy equivalent 173)

[0080] [Phenolic compound]

[0081] B1: Bisphenol A (manufactured by JFE Chemicals Corporation, hydroxyl equivalent 114)

[0082] B2: 4,4'-Bis(3,3,5-trimethylcyclohexylidene) bisphenol (manufactured by Hokoku Chemical Industry Co., Ltd., BisP-HTG, hydroxyl equivalent 155)

[0083] [Polymerization catalyst]

[0084] C1: Tris(p-methoxyphenyl) phosphine (manufactured by Kitagawa Chemical Industry Co., Ltd., TPAP)

[0085] C2: 2,3-Dihydro-1 H-pyrrolo-[1,2-a]benzimidazole (manufactured by Shikoku Chemicals Corporation, TBZ)

[0086] [Solvent]

[0087] D1: Cyclohexanone

[0088] [Reinforcing fiber]

[0089] E: PAN-based carbon fiber (manufactured by Toray Corporation, T700-12K-50C)

[0090] The evaluation method of the examples is as follows.

[0091] Epoxy equivalent:

[0092] Determined according to the Japanese Industrial Standard JIS K7236 standard, and the unit is "g / eq.".

[0093] The polymer is directly determined, and the reinforcing fiber plastic is extracted for the resin component in the following order, and the obtained resin component is used for the determination.

[0094] About 4 g of the sample is weighed in a 110 mL Erlenmeyer flask, 100 mL of tetrahydrofuran (THF) is added, and after ultrasonic diffusion at room temperature for 1 hour, dissolution is performed at room temperature for 23 hours or more. The obtained THF solution is filtered under reduced pressure using a 5 μm filter paper, and the filtrate is recovered. The recovered filtrate is dried in a silicon tank at 20°C for 24 hours or more, and then dried in an oven set to 110°C for 5 hours or more, thereby obtaining the resin component after film formation.

[0095] Hydroxyl equivalent:

[0096] Determined according to the JIS K0070 standard, and the unit is "g / eq.". Note that the hydroxyl equivalent weight of the phenol resin means the phenolic hydroxyl equivalent weight, unless otherwise specified.

[0097] Uniformity:

[0098] The uniformity of the phenolic compound in the epoxy resin was determined by the haze value. The epoxy resin composition was added to a colorless transparent glass petri dish to a thickness of 2 mm, and the haze value was evaluated with reference to the standard plate for the haze value prepared by Murakami Color Research Laboratory, using five levels of "less than 5% (<5)", "less than 10% (<10)", "less than 20% (<20)", "less than 30% (<30)", and "30% or more (30≤)". If the haze value was less than 30%, it was determined that the phenolic compound was uniformly dissolved in the epoxy resin, and was marked as O, and if it was 30% or more, it was determined that it was not uniformly dissolved, and was marked as X.

[0099] Gel fraction:

[0100] About 1 g of the sample was accurately weighed in a 100 mL erlenmeyer flask, 50 mL of tetrahydrofuran was added, and after ultrasonic diffusion for 1 hour at room temperature, dissolution was performed at room temperature for 23 hours or more. Separately, a 325 mesh metal mesh was dried in an oven at 100°C for 1 hour, and the weight was measured. The metal mesh was folded into a funnel shape, and the sample solution was poured into the funnel. The funnel was washed with tetrahydrofuran until no insoluble material of the sample remained in the erlenmeyer flask, and after pouring into the funnel, the insoluble material on the metal mesh was further washed with tetrahydrofuran, and then dried in an oven at 100°C for 4 hours or more. The dried weight of the sample and the metal mesh was subtracted from the dried weight of the metal mesh, and divided by the weight of the sample to obtain the gel fraction in weight % and evaluate it. The gel fraction is equal to the weight % of the THF-insoluble component.

[0101] Bending test:

[0102] The bending strength of the polymer was measured according to JIS K7171. The test equipment used was an Autograph AGS-X (manufactured by Shimadzu Seisakusho), and the sample size was 4 mm in thickness, 100 mm in length, and 15 mm in width, the bending span was 70 mm, and the test was performed at a test speed of 1 mm / min.

[0103] The 90 degree direction bending strength of the unidirectional reinforced fiber plastic was measured according to JIS K7074. The test equipment used was an Autograph AGS-X (manufactured by Shimadzu Seisakusho), and the sample size was 2 mm in thickness, 100 mm in length, and 15 mm in width, the bending span was 70 mm, and the test was performed at a test speed of 1 mm / min.

[0104] Resin adhesion amount:

[0105] The cross section of the fiber-reinforced plastic after the bending test was observed using an SEM (JSM-7900F, manufactured by JEOL Ltd.), and the resin adhesion amount on the fiber was confirmed. If the adhesion between the fiber and the resin is good, it can be confirmed that the resin is well adhered to the fiber surface on the fracture surface. The observation was performed using an SEM on 10 fibers, and the number of fibers on the fiber surface on which the resin was adhered by 80% or more was evaluated.

[0106] 9 or more: O, 8 or less: X

[0107] Example 1

[0108] A1 2913 parts, B1 1000 parts, and B2 1000 parts were separately pulverized and mixed using a Henschel mixer. Subsequently, melt mixing was performed using an S1KRC kneader (manufactured by Kurihira Seisakusho Co., Ltd.) whose cylinder temperature was preheated to 170°C, and the entire amount was recovered in a metal can, and cooled while stirring to obtain a precursor mixture (F1) of an epoxy resin composition.

[0109] C1 (polymerization catalyst) 5 parts was previously dissolved in D1 (organic solvent) 5 parts. The precursor mixture (F1) was put into a planetary mixer set to 60°C, and the polymerization catalyst solution before the mixing was added and mixed. After the mixing, it was quickly extracted, and immediately cooled to 40°C or less to obtain an epoxy resin composition (G1).

[0110] The obtained epoxy resin composition (G1) was heated to about 70°C and stirred, and poured into an iron plated chromium metal mold container in which the gap was previously set to 4 mm, and heat-polymerized at 160°C for 60 minutes in a hot air circulation oven to obtain a polymer.

[0111] The epoxy equivalent of the obtained polymer was measured, and the result was 9900 g / eq.

[0112] The bending strength of the obtained polymer was measured, and the result was 87 MPa.

[0113] The gel fraction of the obtained polymer was measured, and the result was 1%.

[0114] Examples 2 to 3, Comparative Examples 1 to 4

[0115] The epoxy resin composition and the polymer were obtained under the conditions described in Table 1 in the same manner as in Example 1. The epoxy equivalent, the bending strength, and the gel fraction of the obtained polymer were measured in the same manner as in Example 1, and the evaluation results are shown in Table 1.

[0116] In the case of Comparative Examples 3 and 4, the mixing was performed by stirring in a planetary mixer set at 60°C instead of the pulverizing mixing using the Henschel mixer.

[0117] In the case of Comparative Example 3, the temperature of the cylinder at the time of the melt mixing was set to 80°C. In this case, the haze value of the obtained epoxy resin composition was 30% or more, and the melt state of the phenol compound was judged as X.

[0118] Further, the gel fraction of the polymer of Comparative Example 4 was 95%, and since the polymer could not be dissolved in the solvent, the determination of the epoxy equivalent was not performed.

[0119] [Table 1]

[0120] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 A1 2947 2947 2920 2804 3148 A2 2277 2713 B1 1000 1000 1000 1000 1000 1000 B2 1000 1000 1000 1000 1000 2000 1000 C1 5.0 4.9 4.3 4.8 C2 5.0 2.4 2.5 D1 5.0 5.0 2.4 4.9 2.5 4.3 4.8 Molar ratio 1.03 1.03 1.02 0.98 1.10 1.02 1.03 Epoxy resin composition G1 G2 G3 G4 G5 G6 G7 Uniformity ○ ○ ○ ○ ○ × ○ Gel fraction (%) 1 3 2 2 0 0 95 Epoxy equivalent (g / eq.) 9900 11000 14000 120000 2500 3000 - Resin strength (MPa) 99 100 98 100 50 29 103

[0121] Example 4

[0122] The release paper subjected to the release treatment was fixed on a hot plate preheated to 70°C with the release surface facing upward, and the epoxy resin composition (Gl) obtained in Example 1 was placed on the release paper, and then coated using a bar coater preheated to 70°C so that the area weight of the resin was 79 g / m 2 . Immediately after the coating, the hot plate was removed to perform air cooling, and an epoxy resin composition sheet was obtained.

[0123] Next, carbon fibers (E) were attached to the obtained epoxy resin composition sheet so that the area weight of the fibers was 153 g / m 2 , and a hot press preheated to 90°C was used to apply pressure at a surface pressure of 0.5 MPa, and after 1 minute, the hot press was removed to perform air cooling, and a prepreg with Rc = 34% was obtained.

[0124] Further, the obtained prepreg was stacked in such a manner that the orientation directions of the fibers were the same, and a release film was interposed, and a unidirectional fiber reinforced plastic was obtained by vacuum pressing. Note that the conditions of the vacuum pressing were 160°C, 0.1 MPa, and 240 minutes.

[0125] The 90-degree bending strength of the obtained unidirectional fiber reinforced plastic was measured, and the result was 86 MPa. The resin component of the obtained unidirectional fiber reinforced plastic was measured for the epoxy equivalent, and the result was 9800 g / eq.

[0126] In the case of Examples 5 to 6 and Comparative Examples 5 to 8, the same operation as in Example 4 was performed to obtain a unidirectional fiber reinforced plastic. Note that in Comparative Example 8, since many insoluble matters were generated at the time of the determination of the epoxy equivalent, the determination of the epoxy equivalent was not performed.

[0127] [Table 2]

[0128] Example 4 Example 5 Example 6 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Epoxy resin composition G1 G2 G3 G4 G5 G6 G7 Epoxy equivalent (g / eq.) 9800 12000 15000 110000 2500 2800 - Strength (MPa) 86 95 88 46 51 21 47 Resin adhesion amount ○ ○ ○ × ○ ○ ○

[0129] From Tables 1 and 2, it can be confirmed that if the epoxy equivalent of the polymer is 5,000 g / eq. to 20,000 g / eq. and the resin strength is 70 MPa or more, the 90 degree bending strength of the fiber reinforced plastic reaches 80 MPa or more.

[0130] From Comparative Example 5 (Comparative Example 1), it can be confirmed that if the epoxy equivalent of the polymer is high, the adhesion of the fiber-resin is weak, and the 90 degree bending strength cannot be sufficiently exhibited.

[0131] From Comparative Examples 6 and 7 (Comparative Examples 2 and 3), it can be confirmed that if the resin strength of the polymer is not strong enough, the 90 degree bending strength cannot be sufficiently exhibited.

[0132] From Comparative Example 8 (Comparative Example 4), it can be confirmed that if the insoluble component in the polymer is high, the 90 degree bending strength cannot be sufficiently exhibited. It is considered that the minimum melt viscosity of the resin containing many gel components in the polymerization reaction is in a tendency to be high, and as a CFRP molding, voids are easily left, which adversely affects the 90 degree bending strength.

Claims

1. An epoxy resin composition, characterized in that, It contains bifunctional phenolic compounds, bifunctional epoxy resins, and polymerization catalysts as essential components. The difunctional epoxy resin contains 50% by weight or more of the difunctional epoxy resin a represented by the following formula (1), Regarding the mixing ratio of bifunctional phenolic compounds to bifunctional epoxy resins, the ratio is 1.01 to 1.05 moles of bifunctional epoxy resin relative to 1 mole of bifunctional phenolic compound. The polymer obtained from the epoxy resin composition is a thermoplastic epoxy resin with an epoxy equivalent of 5000 g / eq. to 20000 g / eq., a flexural strength of 70 MPa or higher, and when dissolved in tetrahydrofuran, the insoluble component is less than 10% by weight. Here, A is the divalent group represented by formula (2), n is the number of repetitions with an average value of 0 to 5, X is a single bond, a hydrocarbon group with 1 to 13 carbon atoms, -O-, -CO-, -COO-, or -S-, and Y is a divalent group represented by formula (2). 1 Y is independently an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms. 2 and Y 3 Each is independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

2. An epoxy resin composition containing reinforcing fibers, characterized in that, It comprises the epoxy resin composition of claim 1 and reinforcing fibers.

3. The epoxy resin composition containing reinforcing fibers according to claim 2, wherein, It contains PAN-based carbon fiber as a reinforcing fiber in a proportion of 50% to 80% by weight.

4. A prepreg, characterized in that, It is composed of a mixture comprising the epoxy resin composition of claim 1 and reinforcing fibers.

5. The prepreg according to claim 4, wherein PAN-based carbon fiber is contained as reinforcing fiber in a proportion of 50% to 80% by weight.

6. A fiber-reinforced plastic obtained using the prepreg as described in claim 4 or 5.

7. A fiber-reinforced plastic obtained using the epoxy resin composition containing reinforcing fibers as described in claim 2 or 3.

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