Epoxy resin composition for RTM, resin cured product, fiber-reinforced composite material, and methods for producing same

Abstract

The present invention addresses the problem of providing: an epoxy resin composition for RTM that achieves both short takt time and solvent resistance, and yields a resin cured product having an exceptional balance of elastic modulus under moist, hot conditions, heat resistance under wet conditions, and fracture toughness; and a large, high-Vf fiber-reinforced composite material composed of the epoxy resin composition. The present invention relates to an epoxy resin composition for RTM that contains an epoxy resin and a curing agent component, the epoxy resin composition for RTM containing component [A], component [C], and component [D] as the epoxy resin, and containing component [B] as the curing agent component. [A] A tetrafunctional glycidyl amine epoxy resin. [B] A curing agent that is liquid at 150°C. [C] A prescribed aniline epoxy resin. [D] An aminophenol epoxy resin.

Description

Epoxy resin composition for RTM, cured resin, fiber-reinforced composite material, and methods for producing the same

[0001] The present invention relates to an epoxy resin composition for RTM that is preferably used for aerospace components and general industrial applications, a cured resin product, a fiber-reinforced composite material using the same, and a method for producing the same.

[0002] Epoxy resin compositions, which have excellent heat resistance, adhesive properties, and mechanical strength, are widely used as matrix resins in fiber-reinforced composite materials. Fiber-reinforced composite materials are manufactured by integrating reinforcing fibers and matrix resins. Manufacturing methods include lamination molding of prepregs in which reinforcing fibers and matrix resins have been impregnated, and injecting a low-viscosity matrix resin into a shaped reinforcing fiber substrate and curing it. Generally, methods using intermediate substrates such as prepregs exhibit high mechanical properties and have been widely used in the industrial and aircraft fields. However, they have the disadvantage of requiring time-consuming manufacturing processes, such as the preparation and shaping of the prepregs.

[0003] In recent years, there has been an increasing demand for high productivity in structural component applications for aircraft, automobiles, etc., and there is a need for technology that can be applied to the high-speed production of large composite material components and obtain fiber-reinforced composite materials that have high mechanical properties and heat resistance. Therefore, there is an increasing demand for fiber-reinforced composite materials that can be applied to injection molding methods such as resin transfer molding (RTM) and that exhibit excellent properties.

[0004] In injection molding, shortening the takt time is effective by reducing the time lost during heating and cooling due to high-temperature injection and by shortening the curing time. To achieve this, the matrix resin must have low viscosity and volatility even at high temperatures and exhibit sufficient curing properties to achieve a high degree of cure in a short time. Furthermore, for fiber-reinforced composite materials to be used in applications involving paint removal, such as aircraft and automobiles, they must also be resistant to solvents used in cleaning. Therefore, there is a need for resin design technology that can achieve both short takt times and solvent resistance without sacrificing the mechanical properties required for structural applications, such as elastic modulus under wet heat, heat resistance, and fracture toughness.

[0005] Patent Document 1 discloses a technique for improving solvent resistance by using a phenolic curing agent with a specific structure as the curing agent.

[0006] Patent Document 2 discloses an epoxy resin composition that achieves both viscosity stability during injection and curability by combining a specific curing agent.

[0007] JP 2019-108491 A JP 2022-133796 A

[0008] The epoxy resin composition described in Patent Document 1 has excellent solvent resistance, but has high viscosity and poor impregnation properties, making it difficult to apply to the RTM method.

[0009] The epoxy resin composition described in Patent Document 2 has excellent viscosity stability during injection and curing properties, but has low solvent resistance, making it difficult to apply to applications that include a process of stripping paint.

[0010] An object of the present invention is to provide an epoxy resin composition for RTM, a cured resin, and a fiber-reinforced composite material using the same, which overcome the drawbacks of the prior art.

[0011] As a result of intensive research aimed at solving the above problems, the present inventors have discovered an epoxy resin composition for RTM having the following constitution, and have completed the present invention. That is, the epoxy resin composition for RTM of the present invention has the following constitution: [1] An epoxy resin composition for RTM comprising an epoxy resin and a curing agent component, wherein the epoxy resin comprises the following components [A], [C], and [D], and the curing agent component comprises component [B]. [A] tetrafunctional glycidylamine-type epoxy resin [B] curing agent that is liquid at 150°C [C] aniline-type epoxy resin represented by formula (I) [D] aminophenol-type epoxy resin

[0012]

[0013] (In formula (I), R １ and R ２ represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, n is an integer of 0 to 4, and m is an integer of 0 to 5. When n or m is 2 or more, R １ and R２ may be the same or different. X represents O or S.) [2] The epoxy resin composition for RTM according to [1], which contains 10 to 25 mass% of component [D] based on 100 mass% of the epoxy resin. [3] The epoxy resin composition for RTM according to [1] or [2], which contains tetraglycidyldiaminodiphenylmethane as component [A]. [4] The epoxy resin composition for RTM according to any one of [1] to [3], which contains methylenebisaniline as component [B]. [5] The epoxy resin composition for RTM according to any one of [1] to [3], which contains 4,4'-methylenebis(isopropyl-6-methylaniline) as component [B]. [6] The epoxy resin composition for RTM according to any one of [1] to [5], which contains 85 to 100 mass% of component [B] based on 100 mass% of the curing agent component. [7] The epoxy resin composition for RTM according to any one of [1] to [6], further comprising 1 to 20 parts by mass of core-shell type rubber particles as component [E] when the epoxy resin is taken as 100 parts by mass. [8] The epoxy resin composition for RTM according to any one of [1] to [7], which has a mass loss rate of 3.0% by mass or less when heated at 150°C for 30 minutes. [9] The epoxy resin composition for RTM according to any one of [1] to [7], further comprising 1 to 20 parts by mass of core-shell type rubber particles when the epoxy resin is taken as 100 parts by mass. １ The viscosity after holding for 30 minutes is η ３０ When this is done, T satisfies Equation 1 １ The epoxy resin composition for RTM according to any one of [1] to [8], wherein the maximum temperature is 160°C or higher. ３０ ≦100 cps... Formula 1

[10] The epoxy resin composition for RTM according to any one of [1] to [9], which has a degree of cure of 85% or more after heating at 180°C for 1 hour.

[11] The SP value of the cured resin obtained by heating at 180°C for 2 hours is 11.7 (cal / cm ３ ) １／２The epoxy resin composition for RTM according to any one of [1] to

[10] , wherein the epoxy resin composition for RTM according to any one of [1] to

[11] is an epoxy resin composition in a rubber state having a modulus of elasticity of 4 MPa or more, and the cured resin has a modulus of elasticity in a rubber state of 4 MPa or more.

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

[11] .

[13] A fiber-reinforced composite material comprising the cured resin according to

[12] and a reinforcing fiber substrate.

[14] The fiber-reinforced composite material according to

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

[15] A structural member comprising the fiber-reinforced composite material according to

[13] or

[14] .

[16] A method for producing a fiber-reinforced composite material, comprising injecting the epoxy resin composition for RTM according to any one of [1] to

[11] into a reinforcing fiber substrate placed in a molding die heated to 70°C or higher and 190°C or lower, impregnating the reinforcing fiber substrate, and curing the reinforcing fiber substrate in the molding die.

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

[16] , wherein the reinforcing fiber substrate is a carbon fiber substrate.

[0014] According to the present invention, it is possible to provide an epoxy resin composition for RTM that exhibits an excellent balance of elastic modulus, heat resistance, and fracture toughness in a humid and hot environment in the form of a cured resin product. Furthermore, the epoxy resin composition for RTM of the present invention achieves both short takt time and solvent resistance while maintaining the above properties, and therefore can be suitably used as an epoxy resin composition for RTM that is suitable for producing large, high Vf fiber-reinforced composite materials by injection molding.

[0015] One aspect of the present invention is an epoxy resin composition for RTM. The epoxy resin composition for RTM of the present invention contains an epoxy resin and a curing agent component, and the epoxy resins include component [A]: a tetrafunctional glycidylamine-type epoxy resin, component [C]: an aniline-type epoxy resin represented by formula (I), and component [D]: an aminophenol-type epoxy resin, and the curing agent component includes component [B]: a curing agent that is liquid at 150°C as an essential component. First, these components will be described.

[0016] (Component [A]) The epoxy resin composition for RTM of the present invention must contain component [A], a tetrafunctional glycidylamine-type epoxy resin. By including component [A], the epoxy resin composition exhibits an excellent balance between viscosity stability during injection and curing properties, and the cured epoxy resin exhibits high heat resistance and an excellent elastic modulus under wet heat. Without component [A], both viscosity stability during injection and curing properties cannot be achieved, and the resulting cured epoxy resin exhibits low elastic modulus under wet heat and heat resistance. It is preferable that component [A] be contained in an amount of 20 to 60% by mass based on 100% by mass of the epoxy resin. When component [A] is 20% by mass or more, a cured resin with sufficient heat resistance can be obtained. Furthermore, when component [A] is 60% by mass or less, the resulting epoxy resin composition exhibits low viscosity and excellent impregnation properties.

[0017] Examples of such component [A] include tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenyl sulfone, etc. The use of tetraglycidyldiaminodiphenylmethane is preferred from the viewpoint of improving the balance between viscosity stability during injection and curing properties.

[0018] Examples of the tetraglycidyldiaminodiphenylmethane that can be used include "Sumiepoxy (registered trademark)" ELM-434 and "Sumiepoxy (registered trademark)" ELM-434VL (all manufactured by Sumitomo Chemical Co., Ltd.), YH434L (manufactured by Nippon Steel Chemical & Material Co., Ltd.), "jER (registered trademark)" 604 (manufactured by Mitsubishi Chemical Corporation), "Araldite (registered trademark)" MY720, and "Araldite (registered trademark)" MY721 (all manufactured by Huntsman Japan Co., Ltd.).

[0019] As the tetraglycidyldiaminodiphenyl sulfone, TG3DAS (manufactured by Konishi Chemical Industry Co., Ltd.) or the like can be used.

[0020] (Component [C]) The epoxy resin composition for RTM of the present invention must contain component [C], which is an aniline-type epoxy resin represented by formula (I).

[0021]

[0022] (In formula (I), R１ and R ２ represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, n is an integer of 0 to 4, and m is an integer of 0 to 5. When n or m is 2 or more, R １ and R ２ may be the same or different. X represents O or S.) By including component [C], an epoxy resin composition having excellent viscosity stability during injection can be obtained, and a cured epoxy resin product having a good balance between fracture toughness and moist heat elastic modulus can be obtained. Without component [C], an epoxy resin composition having poor viscosity stability during injection can be obtained, and a cured epoxy resin product having a low elastic modulus can be obtained. Furthermore, component [C] is preferably contained in an amount of 20 to 60% by mass per 100% by mass of epoxy resin. When component [C] is 20% by mass or more, an epoxy resin composition having excellent viscosity stability during injection can be obtained, and a cured epoxy resin product having a sufficient moist heat elastic modulus can be obtained. Furthermore, when component [C] is 60% by mass or less, an epoxy resin composition having high heat resistance can be obtained.

[0023] Examples of such component [C] include diglycidyl-p-phenoxyaniline, diglycidyl-4-(4-methylphenoxy)aniline, diglycidyl-4-(4-tert-butylphenoxy)aniline, diglycidyl-4-(4-phenoxyphenoxy)aniline, etc. Among these, diglycidyl-p-phenoxyaniline (n=0, m=0, X=0) with a small molecular weight is preferably used in the resin injection process, taking advantage of its low viscosity characteristics.

[0024] As such diglycidyl-p-phenoxyaniline, "TOREP (registered trademark)" A-204E (manufactured by Toray Fine Chemicals Co., Ltd.) or the like can be used.

[0025] (Component [D]) The epoxy resin composition for RTM of the present invention must contain component [D], which is an aminophenol-type epoxy resin. By containing component [D], a fiber-reinforced composite material with excellent solvent resistance can be obtained. If component [D] is not contained, a fiber-reinforced composite material with poor solvent resistance can be obtained.

[0026] Component [D] is preferably contained in an amount of 10 to 25% by mass based on 100% by mass of the epoxy resin. When component [D] is 10% by mass or more, a fiber-reinforced composite material having sufficient solvent resistance is obtained. When component [D] is 25% by mass or less, the epoxy resin composition has excellent viscosity stability during injection, and a cured epoxy resin product having excellent fracture toughness is obtained.

[0027] Examples of such component [D] include triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, etc. Among these, triglycidyl-p-aminophenol is preferred because of its excellent balance between viscosity stability during injection and solvent resistance.

[0028] As such triglycidyl-p-aminophenol, "jER (registered trademark)" 630 (manufactured by Mitsubishi Chemical Corporation), "Araldite (registered trademark)" MY0500, "Araldite (registered trademark)" MY0510 (all manufactured by Huntsman Japan Co., Ltd.) and the like can be used.

[0029] As such triglycidyl-m-aminophenol, "Araldite (registered trademark)" MY0600, "Araldite (registered trademark)" MY0610 (both manufactured by Huntsman Japan Co., Ltd.), etc. can be used.

[0030] (Component [E]) The epoxy resin composition for RTM of the present invention preferably contains 1 to 20 parts by mass of core-shell rubber particles as component [E], based on 100 parts by mass of epoxy resin. By including component [E] in the above range, the fracture toughness of the cured epoxy resin product can be increased without impairing the elastic modulus, thereby obtaining a fiber-reinforced composite material with excellent compression properties and impact resistance. If the amount of component [E] is less than 1 part by mass, the obtained cured epoxy resin product may not have sufficient fracture toughness. If the amount of component [E] is more than 20 parts by mass, the viscosity of the epoxy resin composition for RTM may increase, and the elastic modulus of the cured epoxy resin product may be insufficient.

[0031] Examples of such component [E] that can be used include "Kane Ace (registered trademark)" MX-125, "Kane Ace (registered trademark)" MX-150, "Kane Ace (registered trademark)" MX-154, "Kane Ace (registered trademark)" MX-257, "Kane Ace (registered trademark)" MX-267, "Kane Ace (registered trademark)" MX-416, and "Kane Ace (registered trademark)" MX-451 (all manufactured by Kaneka Corporation), "PARALOID (registered trademark)" EXL-2655, and "PARALOID (registered trademark)" EXL-2668 (all manufactured by The Dow Chemical Company).

[0032] (Component [B]) The epoxy resin composition for RTM of the present invention must contain, as component [B], a curing agent that is liquid at 150°C. Here, the curing agent refers to a curing agent for the epoxy resin contained in the epoxy resin composition for RTM of the present invention, and is a compound having an active group capable of reacting with an epoxy group. Specific examples of curing agents that are liquid at 150°C include imidazoles such as 2-methylimidazole and 2-ethyl-4-methylimidazole, acid anhydrides such as phthalic anhydride and maleic anhydride, aliphatic amines such as isophoronediamine and m-xylenediamine, and aromatic amines such as alkylbenzenediamines and methylenebisaniline. Of these, aromatic amines are preferred in that they impart excellent mechanical properties to the cured resin. The inclusion of a curing agent that is liquid at 150°C reduces the viscosity of the epoxy resin composition for RTM, facilitating injection and impregnation into a reinforcing fiber substrate during RTM molding.

[0033] As the component [B], alkylbenzenediamine and methylenebisaniline are preferred, and methylenebisaniline is more preferred.

[0034] Such alkylbenzenediamines are aromatic amine compounds having one or more alkyl groups and two amino groups on a benzene ring, and toluenediamines such as diethyltoluenediamine and dimethylthiotoluenediamine are preferably used. By using an alkylbenzenediamine as a curing agent, it is possible to reduce the viscosity of the epoxy resin composition for RTM, while obtaining a cured epoxy resin product with an excellent elastic modulus and a fiber-reinforced composite material with excellent solvent resistance.

[0035] Commercially available alkylbenzene diamines include jER Cure (registered trademark) WA (manufactured by Mitsubishi Chemical Corporation), Ethacure (registered trademark) 100, Ethacure (registered trademark) 300 (all manufactured by Albemarle), Heartcure (registered trademark) 10, Heartcure (registered trademark) 30 (all manufactured by Kumiai Chemical Industry Co., Ltd.), and Lonzacure (registered trademark) DETDA 80 (manufactured by Lonza).

[0036] Such methylene bisaniline is an aromatic amine compound in which two aniline compounds are linked by a methylene bridge, and various substituents may be present on each benzene ring. By using methylene bisaniline as a curing agent for epoxy resins, an epoxy resin composition for RTM that has an excellent balance between viscosity stability during injection and curing properties can be obtained, and a cured resin product that has excellent low water absorption and fracture toughness can be obtained.

[0037] Suitable methylene bisanilines include 4,4'-methylenebis(isopropyl-6-methylaniline) (M-MIPA), methylenebis(diethylaniline) (M-DEA), methylenebis(chlorodiethylaniline) (M-CDEA), methylene(methylethylaniline)-(chlorodiethylaniline) (M-MEACDEA), etc. Among these, the use of 4,4'-methylenebis(isopropyl-6-methylaniline) is particularly preferred in that it results in an RTM epoxy resin composition that exhibits an excellent balance between viscosity stability during injection and curing properties, and also in that it produces a cured epoxy resin product that exhibits an excellent balance between elastic modulus and fracture toughness.

[0038] Commercially available products of such methylene bisaniline include MDA-220 (manufactured by Mitsui Chemicals, Inc.), "Lonzacure (registered trademark)" M-MIPA, "Lonzacure (registered trademark)" M-DEA, "Lonzacure (registered trademark)" M-CDEA, "Lonzacure (registered trademark)" M-DIPA (all manufactured by Lonza Chemical), "Kayahard (registered trademark)" A-A (PT) (manufactured by Nippon Kayaku Co., Ltd.), and the like.

[0039] The content of component [B] is preferably 85 to 100% by mass based on 100% by mass of the curing agent component. By including component [B] in the above range, an epoxy resin composition for RTM having a good balance between viscosity stability during injection and rigidity during demolding can be obtained.

[0040] The epoxy resin composition for RTM of the present invention preferably exhibits a mass loss rate of 3.0% by mass or less, more preferably 2.0% by mass or less, when heated for 30 minutes at 150° C. When the mass loss rate is in this range, volatilization of the resin component during the molding step is suppressed, and a fiber-reinforced composite material having high Vf and excellent mechanical properties can be obtained.

[0041] The mass loss rate of such an epoxy resin composition for RTM is measured by the following procedure. First, about 2 g of the epoxy resin composition for RTM is placed in an aluminum cup with an inner diameter of 50 mm and weighed on an electronic balance. Next, the composition is heated for 30 minutes in a fan oven set at 150°C, removed, cooled to room temperature, and then reweighed. The mass loss rate of the epoxy resin composition is then calculated.

[0042] The epoxy resin composition for RTM of the present invention has a T satisfying formula 1 １ The maximum temperature of the epoxy resin composition for RTM is preferably 160°C or higher, and more preferably 165°C or higher. １ Viscosity after holding for 30 minutes at η ３０ When the temperature is in this range, injection into the reinforcing fiber substrate during RTM molding becomes easy. １ By satisfying the condition that the maximum temperature of η is applied, the difference between the injection temperature and the curing temperature becomes small, and molding with excellent productivity and less time spent on heating becomes possible. ３０ ≦100cps...Formula 1.

[0043] The epoxy resin composition for RTM is heated to a temperature T １ Viscosity η after holding for 30 minutes ３０ is measured using a dynamic viscoelasticity measuring device (Discovery HR-2, manufactured by TA Instruments). The measurement conditions are: measurement mode: parallel plate (25 mmφ, gap 1.0 mm), temperature T １, shear rate: 100s －１ The temperature T １ The higher the temperature, the more the reaction of the epoxy resin composition for RTM progresses, and the higher the viscosity after 30 minutes. Therefore, the T １ If the maximum temperature is known, it can be considered that the formula 1 is satisfied even at temperatures below that temperature.

[0044] The epoxy resin composition for RTM of the present invention preferably has a degree of cure of 85% or more, more preferably 90% or more, after heating for 1 hour at 180° C. By satisfying these conditions, curing can be completed in a short time, and the takt time can be shortened.

[0045] The degree of cure of the epoxy resin composition for RTM after heating at 180°C for 1 hour was calculated using the following formula from the calorific value (Q1) of the epoxy resin composition measured using a DSC (DSC25, manufactured by TA Instruments) at 30 to 280°C and a rate of 3°C / min, and the residual calorific value (Q2) after heating at 180°C for 1 hour: degree of cure = (1 - Q2 / Q1) x 100.

[0046] The epoxy resin composition for RTM of the present invention has an SP value of 11.7 (cal / cm) for a cured resin obtained by curing the epoxy resin composition for RTM at 180°C for 2 hours. ３ ) １／２ It is preferable that the calorie content is 11.8 (cal / cm ３ ) １／２It is more preferable that the modulus of elasticity in the rubber state of the cured resin is 4 MPa or more, and more preferably 5 MPa or more. The SP value is an index of the polarity of the cured resin, and when the SP value satisfies such conditions, the affinity with solvents decreases, and a fiber-reinforced composite material with excellent solvent resistance is obtained. The modulus of elasticity in the rubber state is an index of the crosslink density of the cured resin, and when the modulus of elasticity in the rubber state satisfies such conditions, the crosslink density is high, the space for solvent penetration is small, and a fiber-reinforced composite material with excellent solvent resistance is obtained. Since a high modulus of elasticity in the rubber state deteriorates the fracture toughness of the cured resin, it is preferably 9.0 MPa or less, and more preferably 7.0 MPa or less. When both the SP value and the modulus of elasticity in the rubber state satisfy the above ranges, a fiber-reinforced composite material with sufficient solvent resistance is obtained.

[0047] The SP value of the cured resin obtained by heating an epoxy resin composition for RTM at 180°C for 2 hours can be calculated using the Fedors estimation method, assuming that there are no side reactions and that crosslinks are ideally formed by the reaction of amine and epoxy in accordance with the stoichiometric ratio of each component.

[0048] The rubber-state elastic modulus of the cured resin obtained by curing an RTM epoxy resin composition at 180°C for 2 hours is measured by the following method. A test piece is set on a solid torsion jig using a dynamic viscoelasticity measuring device (ARES-G2, manufactured by TA Instruments) and the measurement is performed. The measurement conditions are a temperature rise rate of 5°C / min, a frequency of 1 Hz, a strain of 0.1%, and a temperature range of 30 to 280°C. In the obtained graph of storage modulus vs. temperature, the storage modulus at a temperature 50°C above the glass transition temperature is taken as the rubber-state elastic modulus.

[0049] In the present invention, the ratio (Mh / Me) of the number of moles of active hydrogen (Mh) in the curing agent component to the number of moles of active epoxy groups (Me) in the epoxy resin in the epoxy resin composition for RTM is preferably in the range of 0.8 to 1.2, more preferably 0.9 to 1.1. By setting the ratio in this range, both the wet heat elastic modulus and fracture toughness of the cured resin can be achieved, and the solvent resistance of the fiber-reinforced composite material can be improved.

[0050] The number of moles of active epoxy groups (Me) of the epoxy resin in the epoxy resin composition for RTM is the sum of the number of moles of each active group in the epoxy resin, and is expressed by the following formula: Me = (mass of epoxy resin A / epoxy equivalent of epoxy resin A) + (mass of epoxy resin B / epoxy equivalent of epoxy resin B) + ... + (mass of epoxy resin W / epoxy equivalent of epoxy resin W).

[0051] The number of moles of active hydrogen (Mh) of the curing agent component in the epoxy resin composition for RTM is the sum of the masses of each curing agent divided by the active hydrogen equivalent of each curing agent, and is expressed by the following formula: Mh = (mass of curing agent A / active hydrogen equivalent of curing agent A) + (mass of curing agent B / active hydrogen equivalent of curing agent B) + ... + (mass of curing agent W / active hydrogen equivalent of curing agent W).

[0052] The epoxy resin composition for RTM used in the present invention may contain, as the epoxy resin, an epoxy resin (component [F]) different from components [A], [C], and [D], as long as the effects of the present invention are not lost.

[0053] Examples of such epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, triglycidylaminophenol epoxy resins, dicyclopentadiene epoxy resins, biphenyl epoxy resins, phenol aralkyl epoxy resins, and naphthalene epoxy resins. These may be used alone or in combination. Dicyclopentadiene epoxy resins and naphthalene epoxy resins are preferred because they have an excellent balance between elastic modulus and fracture toughness. Dicyclopentadiene epoxy resins are particularly preferred. In addition to reducing the water absorption of the cured epoxy resin, they can also increase the fracture toughness of the cured resin.

[0054] The epoxy resin composition for RTM of the present invention may be prepared by kneading using a machine such as a kneader, a planetary mixer, a three-roll mill, or a twin-screw extruder, or by hand using a beaker and a spatula, etc., provided that uniform kneading is possible.

[0055] The cured resin product of the present invention is a cured resin product obtained by curing the epoxy resin composition for RTM of the present invention.

[0056] A fiber-reinforced composite material is also an aspect of the present invention. The fiber-reinforced composite material of the present invention refers to a fiber-reinforced composite material composed of the cured resin of the present invention and a reinforcing fiber substrate.

[0057] A structural member is also one aspect of the present invention. The structural member of the present invention refers to a structural member made of the fiber-reinforced composite material of the present invention.

[0058] The epoxy resin composition for RTM of the present invention exhibits viscosity stability at relatively high temperatures, excellent impregnation properties for reinforcing fiber substrates, and its Tg easily increases at relatively low temperatures, resulting in excellent rigidity upon demolding. Therefore, it is particularly suitable for use in the RTM method, which requires a small temperature rise from injection to curing. The RTM method is a molding method consisting of the following steps: First, a reinforcing fiber substrate or a preform is placed in a molding die. Next, a liquid matrix resin is injected into the molding die to impregnate the reinforcing fibers. The matrix resin is then cured to obtain a molded product, a fiber-reinforced composite material.

[0059] A method for producing a fiber-reinforced composite material is also an aspect of the present invention, and the method for producing a fiber-reinforced composite material of the present invention refers to a method in which the epoxy resin composition for RTM of the present invention is injected into a reinforcing fiber substrate placed in a molding die heated to 70° C. or higher and 190° C. or lower, impregnated, and cured in the molding die. Heating the molding die in advance is preferred because it reduces the viscosity of the epoxy resin composition for RTM and shortens the injection time, thereby providing excellent mass productivity.

[0060] The mold used in the method for producing a fiber-reinforced composite material of the present invention may be a closed mold made of a rigid material, or an open mold made of a rigid material and a flexible film (bag). In the latter case, the reinforcing fiber substrate can be placed between the open mold made of a rigid material and the flexible film. Various existing rigid materials can be used, such as metals such as steel and aluminum, fiber-reinforced plastics (FRP), wood, and gypsum. Materials for the flexible film include polyamide, polyimide, polyester, fluororesin, and silicone resin.

[0061] The reinforcing fibers used in the fiber-reinforced composite material of the present invention and the reinforcing fiber substrate used in the manufacturing method for the fiber-reinforced composite material of the present invention are not particularly limited, but glass fibers, carbon fibers, aramid fibers, boron fibers, alumina fibers, silicon carbide fibers, etc. can be used. Two or more of these fibers can also be mixed and used. From the viewpoint of obtaining a lightweight and highly rigid fiber-reinforced composite material, it is preferable to use carbon fibers. That is, it is preferable to use a carbon fiber substrate as the reinforcing fiber substrate.

[0062] The fiber-reinforced composite material of the present invention has excellent mechanical properties, compressive strength under wet heat and impact resistance, and therefore can be preferably used for many structural materials, including aircraft parts such as fuselages, main wings, tail parts, moving surfaces, fairings, cowls, doors, seats, and interior materials; spacecraft parts such as motor cases and main wings; artificial satellite parts such as bodies and antennas; automobile parts such as outer panels, chassis, aerodynamic parts, and seats; railway vehicle parts such as bodies and seats; and ship parts such as hulls and seats.

[0063] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the descriptions of these examples.

[0064] The components used in this embodiment are as follows:

[0065] <Materials Used> Component [A]: tetrafunctional glycidylamine-type epoxy resin [A]-1 "Sumiepoxy (registered trademark)" ELM434VL (tetraglycidyldiaminodiphenylmethane) (manufactured by Sumitomo Chemical Co., Ltd.) [A]-2 "Araldite (registered trademark)" MY721 (tetraglycidyldiaminodiphenylmethane) (manufactured by Huntsman Corporation) [A]-3 "Sumiepoxy (registered trademark)" ELM434 (tetraglycidyldiaminodiphenylmethane) (manufactured by Sumitomo Chemical Co., Ltd.) Component [B]: curing agent that is liquid at 150°C [B]-1: "jER Cure (registered trademark)" WA (diethyltoluenediamine) (manufactured by Mitsubishi Chemical Corporation) (liquid at room temperature) [B]-2: "Ethacure (registered trademark)" 300 (dimethylthiotoluenediamine) (manufactured by Albemarle) (liquid at room temperature) [B]-3: "Lonzacure (registered trademark)" M-MIPA (4,4'-methylenebis(isopropyl-6-methylaniline)) (manufactured by Lonza) (melting point: 72°C).

[0066] Component [C]: Aniline-type epoxy resin represented by formula (I) [C]-1 "TOREP (registered trademark)" A-204E (diglycidyl-p-phenoxyaniline) (manufactured by Toray Fine Chemicals Co., Ltd.).

[0067] Component [D]: Aminophenol-type epoxy resin [D]-1 "jER (registered trademark)" 630 (triglycidyl-p-aminophenol) (manufactured by Mitsubishi Chemical Corporation) [D]-2 "Araldite (registered trademark)" MY0600 (triglycidyl-m-aminophenol) (manufactured by Huntsman Japan) Component [E]: Core-shell type rubber particles [E]-1 "Kane Ace (registered trademark)" MX-416 (75% by mass of tetrafunctional glycidylamine-type epoxy resin and 25% by mass of butadiene-based core-shell type rubber particles).

[0068] Component [F]: Other epoxy resins [F]-1 "EPICLON (registered trademark)" HP-7200L (dicyclopentadiene type epoxy resin) (manufactured by DIC Corporation) [F]-2 "EPICLON (registered trademark)" 830 (bisphenol F type epoxy resin) (manufactured by DIC Corporation) [F]-3 GAN (glycidyl aniline) (manufactured by Nippon Kayaku Co., Ltd.).

[0069] Other curing agent components [H]-1: "Seikacure (registered trademark)" S (4,4'-diaminodiphenyl sulfone) (manufactured by Seika Corporation) (melting point: 170 to 173°C, solid at 150°C).

[0070] <Method for preparing an epoxy resin composition for RTM> A stainless steel beaker was charged with predetermined amounts of components other than component [B] and other curing agent components, and the temperature was raised to 60-150°C. The components were then mixed appropriately until they were compatible, yielding an epoxy base liquid. Component [B] and other curing agent components were charged into a separate container, and heated as necessary to achieve compatibility, yielding a curing agent liquid. Predetermined amounts of the epoxy base liquid and curing agent liquid were mixed and kneaded for 3 minutes using a planetary mixer, yielding an epoxy resin composition for RTM. The composition of the epoxy resin composition is as shown in Tables 1 to 3.

[0071] <Method for evaluating the mass loss rate of an epoxy resin composition for RTM at 150°C> Approximately 2 g of the epoxy resin composition for RTM obtained according to the above <Method for preparing an epoxy resin composition for RTM> was placed in an aluminum cup with an inner diameter of 50 mm and weighed on an electronic balance. Next, the composition was heated under vacuum for 30 minutes in a fan oven (DKM400, manufactured by Yamato Scientific Co., Ltd.) set to 150°C, then removed and cooled to room temperature. The composition was then reweighed, and the mass loss rate of the epoxy resin composition for RTM was calculated from the difference in mass before and after the reweighing.

[0072] <η of epoxy resin composition for RTM ３０ The complex viscosity η of the epoxy resin composition for RTM obtained according to the above <Method for preparing epoxy resin composition for RTM> was evaluated. ０was measured using a dynamic viscoelasticity measuring device (Discovery HR-2, manufactured by TA Instruments) under the following conditions: measurement mode: parallel plate (25 mmφ, gap 1.0 mm), temperature T １ , shear rate: 100s －１ The value after 30 minutes is the η of the epoxy resin composition for RTM. ３０ It was decided.

[0073] <Method for evaluating the degree of cure of an epoxy resin composition for RTM use after heating at 180°C for 1 hour> 4 to 10 mg of the epoxy resin composition for RTM use obtained according to the above <Method for preparing an epoxy resin composition for RTM use> was weighed into a pan, and the degree of cure was calculated using the following formula from the calorific value (Q1) of the uncured resin measured using a DSC (DSC25, manufactured by TA Instruments) at 30 to 280°C and a rate of 3°C / min, and the residual calorific value (Q2) measured using a DSC after heating at 180°C for 1 hour and then at 30 to 280°C and a rate of 3°C / min: degree of cure = (1 - Q2 / Q1) x 100.

[0074] <Method for calculating the SP value of a cured resin obtained by curing an epoxy resin composition for RTM at 180°C for 2 hours> The SP value was calculated using the Fedors estimation method, assuming that there were no side reactions and that crosslinks were ideally formed by the reaction between the amine and the epoxy in accordance with the stoichiometric ratio of each component.

[0075] <Method for evaluating the rubber-state elastic modulus of cured resin obtained by curing an epoxy resin composition for RTM use at 180°C for 2 hours> The epoxy resin composition for RTM use obtained according to the above <Method for preparing an epoxy resin composition for RTM use> was degassed in a vacuum and then cured at 180°C for 2 hours in a mold set to a thickness of 2 mm using a 2 mm Teflon (registered trademark) spacer, yielding a 2 mm thick plate-like cured resin. A test piece measuring 12.7 mm wide and 45 mm long was cut out from this cured resin, and measurements were performed using a dynamic viscoelasticity measuring device (ARES-G2, manufactured by TA Instruments) with the test piece set in a solid torsion jig at a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.1% over a temperature range of 30 to 280°C. In the resulting graph of storage modulus vs. temperature, the storage modulus at a temperature 50°C above the glass transition temperature was taken as the rubber-state elastic modulus. The glass transition temperature (dry Tg) was determined as the temperature at the intersection of a tangent drawn to the glass state and a tangent drawn to the glass transition temperature region in the obtained graph of storage modulus vs. temperature.

[0076] <Preparation of Reinforced Fiber Substrate with Nonwoven Fabric> A plain weave fabric (fiber basis weight: 285 g / m) consisting of carbon fiber "Torayca (registered trademark)" T700G-12K-31E was used as the reinforcing fiber. ２ ) on one side of which is a nonwoven fabric made of polyamide 12 (fiber basis weight: 6 g / m ２ Thereafter, the nonwoven fabric was fused using a far-infrared heater to obtain a reinforcing fiber substrate with a nonwoven fabric attached to one surface of the substrate.

[0077] <Preparation of Fiber-Reinforced Composite Material> The reinforcing fiber substrate with nonwoven fabric obtained according to the above <Preparation of Reinforcing Fiber Substrate with Nonwoven Fabric> was cut into a 400 mm x 400 mm piece so that the fiber direction was 45° / -45°. The cut reinforcing fiber substrate with nonwoven fabric was stacked in a [45° / -45°] configuration in a mold having a plate-shaped cavity of 400 mm x 40 mm x 0.8 mm. Next, the mold was heated to 110°C, and the epoxy resin composition for RTM obtained according to the above <Preparation Method of Epoxy Resin Composition for RTM>, which had been preheated to 110°C, was poured into the mold. The temperature was then raised to 180°C at a rate of 1.5°C / min and cured at 180°C for 2 hours to obtain a fiber-reinforced composite material.

[0078] <Measurement of IPSM Retention Rate of Fiber-Reinforced Composite Material After MEK Absorption> A rectangular specimen measuring 304.8 mm in the 0° direction and 25.4 mm in the 90° direction was cut from the fiber-reinforced composite material obtained according to the above <Preparation of Fiber-Reinforced Composite Material> to obtain a test specimen. The in-plane shear modulus (IPSM) of this test specimen was measured using an Instron universal testing machine (manufactured by Instron Corporation) in accordance with ASTM-D3518. The number of samples (n = 5) was used, and the retention rate calculated from the average value was designated as the in-plane shear modulus E1 under untreated conditions. The test specimens obtained as described above were immersed in MEK (methyl ethyl ketone) at 23°C for 6 days, and then the in-plane shear modulus after methyl ethyl ketone absorption was measured in the same manner. The number of samples (n = 5) was used, and the retention rate calculated from the average value was designated as the in-plane shear modulus E2 after MEK absorption. The IPSM retention rate after MEK absorption was calculated using E1 and E2 according to the following formula: IPSM retention after MEK absorption = (E2 / E1) x 100.

[0079] Example 1 An epoxy resin composition for RTM was prepared in accordance with the above <Method for preparing epoxy resin composition for RTM> using 55 parts by mass of Sumiepoxy (registered trademark) ELM-434VL (component [A]-1), 40 parts by mass of TOREP (registered trademark) A-204E (component [C]-1), 5 parts by mass of jER (registered trademark) 630 (component [D]-1), and 60.5 parts by mass of Lonzacure (registered trademark) M-MIPA (component [B]-3) as epoxy resins.

[0080] The SP value of this epoxy resin composition for RTM was calculated according to the above <Calculation of SP value of epoxy resin composition for RTM>, and it was 11.7 (cal / cm ３ ) １／２ The rubbery state elastic modulus was evaluated in accordance with the above-mentioned <Method for evaluating the rubbery state elastic modulus of a cured resin obtained by curing an epoxy resin composition for RTM at 180°C for 2 hours>, and was found to be 4 MPa, indicating sufficient crosslinking.

[0081] Furthermore, when the mass loss rate was evaluated according to the above-mentioned <Method for evaluating the mass loss rate of an epoxy resin composition for RTM at 150°C>, it was found to be 1.3 mass%, which is sufficiently low. ３０ According to the evaluation method of ３０ When evaluated, T satisfying Eq. １ The maximum temperature was 170°C, which allowed for sufficiently high-temperature injection. The degree of cure was evaluated according to the above-mentioned <Method for evaluating the degree of cure of an epoxy resin composition for RTM after heating at 180°C for 1 hour>, and was found to be 96%, indicating excellent curability.

[0082] Furthermore, a fiber-reinforced composite material was prepared using this epoxy resin composition for RTM in accordance with the above <Preparation of fiber-reinforced composite material>. The IPSM retention of this fiber-reinforced composite material was evaluated in accordance with the above <Measurement of IPSM retention of fiber-reinforced composite material after MEK absorption>, and it was found to be 85%, which was sufficient solvent resistance.

[0083] Examples 2 to 11 Epoxy resin compositions for RTM and fiber reinforced composite materials were prepared in the same manner as in Example 1, except that the resin compositions were changed as shown in Tables 1 and 2, respectively.

[0084] The SP value of the epoxy resin composition for RTM in each example, the rubber-state elastic modulus of the cured resin obtained by curing at 180°C for 2 hours, the mass loss rate after heating at 150°C for 30 minutes, and the T satisfying Equation 1 １ The degree of cure was evaluated after heating for 1 hour at the highest temperature of 180°C. The SP was 11.7 (cal / cm) for all levels. ３ ) １／２The rubber-state elastic modulus of the cured resin obtained by curing at 180°C for 2 hours is 4 MPa or more, the mass loss rate after heating at 150°C for 30 minutes is 3.0% or less, and the T satisfying formula 1 １ The maximum temperature was 160°C or higher, and the degree of cure after heating at 180°C for 1 hour was 85% or higher.

[0085] Furthermore, when the IPSM retention rate of the fiber reinforced composite material of each Example after absorbing MEK was evaluated, it was 85% at all levels, indicating sufficient solvent resistance.

[0086] Comparative Example 1 An epoxy resin composition for RTM was prepared in the same manner as in Example 1, except that the resin composition was changed as shown in Table 3.

[0087] When the rubbery state modulus of this epoxy resin composition for RTM was evaluated in accordance with the above-mentioned <Method for evaluating the rubbery state modulus of a cured resin obtained by curing an epoxy resin composition for RTM at 180°C for 2 hours>, it was found to be 2 MPa, which was an insufficient crosslink density. When a fiber-reinforced composite material was prepared using this epoxy resin composition for RTM in accordance with the above-mentioned <Preparation of fiber-reinforced composite material>, and the IPSM retention of this fiber-reinforced composite material was evaluated in accordance with the above-mentioned <Measurement of IPSM retention of fiber-reinforced composite material after MEK absorption>, it was found to be 70%, which was a low solvent resistance.

[0088] Comparative Example 2 An epoxy resin composition for RTM was prepared in the same manner as in Example 1, except that the resin composition was changed as shown in Table 3.

[0089] When the rubbery state modulus of this epoxy resin composition for RTM was evaluated in accordance with the above-mentioned <Method for evaluating the rubbery state modulus of a cured resin obtained by curing an epoxy resin composition for RTM at 180°C for 2 hours>, it was found to be 3 MPa, which was an insufficient crosslink density. When a fiber-reinforced composite material was prepared using this epoxy resin composition for RTM in accordance with the above-mentioned <Preparation of fiber-reinforced composite material>, and the IPSM retention of this fiber-reinforced composite material was evaluated in accordance with the above-mentioned <Measurement of IPSM retention of fiber-reinforced composite material after MEK absorption>, it was found to be 70%, which was a low solvent resistance.

[0090] Comparative Example 3 An epoxy resin composition for RTM was prepared in the same manner as in Example 1, except that the resin composition was changed as shown in Table 3.

[0091] The mass loss rate of this epoxy resin composition for RTM was evaluated according to the above <Method for evaluating mass loss rate of epoxy resin composition for RTM at 150°C>, and was found to be as high as 5.0%.

[0092] Comparative Example 4 An epoxy resin composition for RTM was prepared in the same manner as in Example 1, except that the resin composition was changed as shown in Table 3.

[0093] When the rubbery state elastic modulus of this epoxy resin composition for RTM was evaluated according to the above-mentioned <Method for evaluating the rubbery state elastic modulus of a cured resin obtained by curing an epoxy resin composition for RTM at 180°C for 2 hours>, it was found to be 10 MPa, which was a high crosslink density, and the plastic deformation capacity was insufficient. ３０ According to the evaluation method of ３０ When the temperature was lower than 160°C, the initial viscosity exceeded 100 cps, and when the temperature was higher than 160°C, the viscosity increased significantly and exceeded 100 cps within 30 minutes. １ Furthermore, when the degree of cure was evaluated according to the above-mentioned <Method for evaluating the degree of cure of an epoxy resin composition for RTM after heating at 180°C for 1 hour>, it was found to be insufficient at 82%.

[0094] Comparative Example 5 An epoxy resin composition for RTM was prepared in the same manner as in Example 1, except that the resin composition was changed as shown in Table 3.

[0095] The SP value of this epoxy resin composition for RTM was calculated according to the above-mentioned <Method for calculating the SP value of an epoxy resin composition for RTM>, and was found to be 11.5 (cal / cm ３ ) １／２ and the polarity is insufficient, and the above-mentioned <η of the epoxy resin composition for RTM ３０ According to the evaluation method of ３０ When evaluated, T satisfying Eq. １The maximum temperature was as low as 155° C. Furthermore, a fiber-reinforced composite material was produced using this epoxy resin composition for RTM according to the above <Production of fiber-reinforced composite material>, and the IPSM retention of this fiber-reinforced composite material was evaluated according to the above <Measurement of IPSM retention of fiber-reinforced composite material after MEK absorption>, and the solvent resistance was low at 83%.

[0096]

[0097]

[0098]

[0099] The units of each component in the table are parts by mass.

[0100] The epoxy resin composition for RTM of the present invention has low viscosity and low volatility, and can provide a cured resin product that has high elastic modulus and fracture toughness under wet heat conditions. Fiber-reinforced composite materials using this epoxy resin composition for RTM also have excellent compressive properties under wet heat conditions, impact resistance, and solvent resistance, making them suitable for use in aerospace components and general industrial structural components.

Claims

1. An epoxy resin composition for RTM containing an epoxy resin and a curing agent component, the epoxy resin containing the following components [A], [C], and [D], and the curing agent component containing component [B]: [A] tetrafunctional glycidylamine-type epoxy resin; [B] a curing agent that is liquid at 150°C; [C] an aniline-type epoxy resin represented by formula (I); [D] an aminophenol-type epoxy resin. (In formula (I), R １ and R ２ represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, n is an integer of 0 to 4, and m is an integer of 0 to 5. When n or m is 2 or more, R １ and R ２ may be the same or different. X represents O or S.

2. The epoxy resin composition for RTM according to claim 1, which contains 10 to 25 mass % of component [D] based on 100 mass % of the epoxy resin.

3. The epoxy resin composition for RTM according to claim 1, which contains tetraglycidyldiaminodiphenylmethane as component [A].

4. The epoxy resin composition for RTM according to claim 1, which contains methylenebisaniline as component [B].

5. The epoxy resin composition for RTM according to claim 1, which contains 4,4'-methylenebis(isopropyl-6-methylaniline) as component [B].

6. The epoxy resin composition for RTM according to claim 1, which contains 85 to 100% by mass of component [B] relative to 100% by mass of the curing agent component.

7. The epoxy resin composition for RTM according to claim 1, further comprising 1 to 20 parts by mass of core-shell type rubber particles as component [E], relative to 100 parts by mass of the epoxy resin.

8. An epoxy resin composition for RTM according to claim 1, which has a mass loss rate of 3.0 mass% or less when heated at 150°C for 30 minutes.

9. The epoxy resin composition for RTM is heated to a temperature T １ The viscosity after holding for 30 minutes is η ３０ When this is done, T satisfies Equation 1 １ The epoxy resin composition for RTM according to claim 1, wherein the maximum temperature in the step (h) is 160°C or higher. ３０ ≦100cps...Formula 1 10. The epoxy resin composition for RTM according to claim 1, which has a degree of cure of 85% or more after heating at 180°C for 1 hour.

11. The SP value of the cured resin obtained by heating at 180°C for 2 hours is 11.7 (cal / cm ３ ) １／２ 2. The epoxy resin composition for RTM according to claim 1, wherein the cured resin has a rubber-state elastic modulus of 4 MPa or more.

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

13. A fiber-reinforced composite material comprising the cured resin of claim 12 and a reinforcing fiber substrate.

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

15. A structural member made of the fiber-reinforced composite material according to claim 14.

16. A method for producing a fiber-reinforced composite material, comprising injecting the epoxy resin composition for RTM described in claim 1 into a reinforcing fiber substrate placed in a mold heated to 70°C or higher and 190°C or lower, allowing it to impregnate, and then curing it in the mold.

17. The method for producing a fiber-reinforced composite material according to claim 16, wherein the reinforcing fiber substrate is a carbon fiber substrate.

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