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

Abstract

To provide an epoxy resin composition for RTM (resin transfer molding) having low volatility at an injection temperature and giving a cured resin having well-balanced elastic modulus in wet heat, heat resistance in wet heat and fracture toughness and provide a large-sized fiber-reinforced composite material having high Vf and produced by using the epoxy resin composition.SOLUTION: An epoxy resin composition for RTM comprising the following components [A], [B], [C], and [D], and satisfying all of the following conditions 1 to 4: [A]: 4-functional glycidyl amine type epoxy resin [B]: selected from the group consisting of alkyl benzene diamine and methylene bisaniline. At least one aromatic amine curing agent [C]: Condition 1: Viscosity at 110 °C. is 1mPa·s or more and 200mPa·s or less Condition 2: Mass loss rate after being heated at 110 °C. for 30 minutes is 0.3% by mass or less Condition 3: Rubbery state modulus of a resin-cured product obtained by being cured at 180 °C. for 2 hours is 2MPa or more and 8MPa or less Condition 4: Water absorption of a resin-cured product obtained by being cured at 180 °C. for 2 hours is 1.0% or more and 3.0% or less SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[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 laminating 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 prepregs have been widely used in the industrial and aircraft fields because they exhibit high mechanical properties. However, they have the drawback of requiring time-consuming manufacturing processes, such as the preparation and shaping of the prepregs.

[0003] In recent years, the demand for high productivity has increased in structural applications such as aircraft and automobiles, and there is a demand for technology that can rapidly produce large composite material components and obtain fiber-reinforced composite materials with high mechanical properties and heat resistance. Therefore, there is a growing demand for fiber-reinforced composite materials that can be used with injection molding methods such as resin transfer molding (RTM) and that exhibit excellent properties.

[0004] In the injection molding method, two-component epoxy resin compositions are often used from the perspective of molding processability. A two-component epoxy resin composition is an epoxy resin composition that is composed of an epoxy base liquid containing an epoxy resin as its main component and a hardener liquid containing a hardener as its main component, and is obtained by mixing the two liquids, the epoxy base liquid and the hardener liquid, immediately before use. In contrast, an epoxy resin composition in which all components, including the base resin and hardener, are mixed into one is called a one-component epoxy resin composition.

[0005] To obtain large fiber-reinforced composites using injection molding, the matrix resin must have low viscosity during the injection process. Furthermore, for use in primary structural components such as aircraft, fiber-reinforced composites must have a well-balanced combination of hygrothermal modulus, heat resistance, and fracture toughness. One method for achieving low viscosity while simultaneously achieving both hygrothermal modulus and heat resistance is to incorporate a large amount of multifunctional, low-molecular-weight epoxy resins. However, this approach results in excessively high crosslink density in the cured resin, which reduces fracture toughness and impact resistance of the fiber-reinforced composite. Furthermore, volatilization of low-molecular-weight resin components during the molding process reduces the fiber volume fraction (Vf) of the molded product, hindering the development of mechanical properties. Therefore, the development of resin design technology for obtaining large, high-Vf fiber-reinforced composites through injection molding without compromising hygrothermal modulus, heat resistance, and fracture toughness is highly desirable.

[0006] Patent Document 1 describes a technique for obtaining a cured epoxy resin product with high fracture toughness by using a thermoplastic resin and core-shell rubber particles in combination at a specific ratio.

[0007] Patent Document 2 discloses a technology that combines a low-viscosity epoxy resin and core-shell rubber particles to obtain a cured resin product with high fracture toughness and to achieve good impregnation of the epoxy resin composition into a reinforcing fiber substrate in the resin injection step.

[0008] Patent Document 3 discloses a technology in which 4,4-methylenebis(isopropyl-6-methylaniline) and core-shell rubber particles are used together as a curing agent for epoxy resin, thereby increasing the fracture toughness of the cured resin compared to when neither is used.

[0009] Patent Document 4 discloses an epoxy resin composition containing the low-volatility N,N-diglycidyl-4-phenoxyaniline, which gives a prepreg that produces molded articles with few voids, and also gives a general example that resin transfer molding methods and the like can be used. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 5808057 [Patent Document 2] International Publication No. 2021 / 241734 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-150310 [Patent Document 4] International Publication No. 2010 / 109929 Summary of the Invention [Problem to be solved by the invention]

[0011] The epoxy resin composition described in Patent Document 1 has excellent fracture toughness in the cured resin product obtained by curing the epoxy resin composition, but has the problem of a slow curing reaction due to the use of M-CDEA as a curing agent, resulting in a long production cycle for the fiber-reinforced composite material. Also, the elastic modulus under wet heat conditions is insufficient.

[0012] The epoxy resin composition described in Patent Document 2 can give a cured resin product that has low viscosity and high heat resistance in the resin injection step, but the elastic modulus under wet heat conditions is significantly insufficient.

[0013] The epoxy resin composition described in Patent Document 3 has low viscosity in the resin injection step and is excellent in impregnation ability into a reinforcing fiber substrate. However, the elastic modulus of the cured resin obtained by curing the epoxy resin composition is extremely low, and although the fracture toughness is improved, it does not reach the desired level.

[0014] The epoxy resin composition described in Patent Document 4 has a high water absorption rate in the cured resin obtained by curing the epoxy resin composition, and the elastic modulus and glass transition temperature decrease significantly under wet heat conditions. In addition, the composition has a high viscosity during the resin injection process, which results in poor impregnation into reinforcing fiber substrates, making it difficult to apply the composition to the RTM method.

[0015] An object of the present invention is to provide an epoxy resin composition for RTM, a cured resin product, and a fiber-reinforced composite material using the same, which overcome the drawbacks of the prior art. [Means for solving the problem]

[0016] 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 containing the following components [A], [B], [C], and [D], and satisfying all of the following conditions 1 to 4: [A]: tetrafunctional glycidylamine epoxy resin [B]: at least one aromatic amine curing agent selected from the group consisting of alkylbenzenediamine and methylenebisaniline [C]: Core-shell rubber particles [D]:Thermoplastic resin Condition 1: Viscosity at 110°C is 1 mPa·s or more and 200 mPa·s or less Condition 2: Mass loss rate after heating at 110°C for 30 minutes is 0.3% by mass or less Condition 3: The rubber-state elastic modulus of the resin cured product obtained by curing at 180°C for 2 hours is 2 MPa or more and 8 MPa or less. Condition 4: The water absorption rate of the resin cured product obtained by curing at 180°C for 2 hours is 1.0% or more and 3.0% or less. [2] The epoxy resin composition for RTM according to [1], which contains 1 to 10 parts by mass of polyethersulfone or polyetherimide as component [D] relative to 100 parts by mass of the total epoxy resin. [3] The epoxy resin composition for RTM according to [1] or [2], which contains an aniline-type epoxy resin represented by formula (I) as component [E].

[0017] [ka] (In formula (I), R 1 and R 2R represents at least one aliphatic hydrocarbon group having 1 to 4 carbon atoms. 1 and R 2 When there are multiple, they may be the same or different. n is an integer of 0 to 4, and m is an integer of 0 to 5. X represents -O- or -S-. [4] A cured resin product obtained by thermally curing the epoxy resin composition for RTM according to any one of [1] to [3]. [5] A fiber-reinforced composite material comprising the cured resin according to [4] and a reinforcing fiber substrate. [6] The fiber-reinforced composite material according to [5], wherein the reinforcing fiber substrate is a carbon fiber substrate. [7] A method for producing a fiber-reinforced composite material, comprising injecting the epoxy resin composition for RTM according to any one of [1] to [3] into a reinforcing fiber substrate placed in a molding die heated to 70°C or higher and 190°C or lower, allowing the composition to impregnate the substrate, and curing the composition in the molding die. [8] The method for producing a fiber-reinforced composite material according to [7], wherein the reinforcing fiber substrate is a carbon fiber substrate. [Effects of the Invention]

[0018] According to the present invention, there is provided an epoxy resin composition for RTM that can yield a cured resin product having an excellent balance of elastic modulus, heat resistance, and fracture toughness under humid and hot environments. Furthermore, the epoxy resin composition for RTM of the present invention maintains the above-mentioned properties in the cured resin product while exhibiting low viscosity and low volatility in the resin injection process, making it suitable for use as an epoxy resin composition for RTM that is suitable for producing large, high-Vf fiber-reinforced composite materials by injection molding. DETAILED DESCRIPTION OF THE INVENTION

[0019] An epoxy resin composition for RTM is one aspect of the present invention. The epoxy resin composition for RTM of the present invention contains, as essential components, [A] a tetrafunctional glycidylamine-type epoxy resin, [B] at least one aromatic amine curing agent selected from the group consisting of alkylbenzenediamine and methylenebisaniline, [C] core-shell rubber particles, and [D] a thermoplastic resin. It is also preferable to include, as component [E], an aniline-type epoxy resin represented by formula (I). First, these components will be described.

[0020] (Component [A]) The epoxy resin composition for RTM of the present invention must contain a tetrafunctional glycidylamine-type epoxy resin as component [A]. By containing component [A], the cured resin obtained by curing the epoxy resin composition for RTM of the present invention will exhibit high heat resistance and an excellent wet heat modulus. If component [A] is not contained, the cured resin obtained by curing the epoxy resin composition will have insufficient heat resistance.

[0021] Examples of such component [A] include tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, and the like.

[0022] Commercially available products of the above-mentioned tetraglycidyldiaminodiphenylmethane include "Sumiepoxy (registered trademark)" ELM-434, "Sumiepoxy (registered trademark)" ELM-434VL (both 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.).

[0023] Commercially available products of the above tetraglycidyldiaminodiphenyl sulfone include TG3DAS (manufactured by Konishi Chemical Industry Co., Ltd.).

[0024] (Component [E]) The epoxy resin composition for RTM of the present invention preferably contains, as component [E], an aniline-type epoxy resin represented by formula (I). By containing component [E], it is possible to lower the rubber-state elastic modulus of the cured resin obtained by curing the epoxy resin composition for RTM of the present invention while maintaining the elastic modulus.

[0025] Examples of such component [E] 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 (in formula (I), n = 0, m = 0, X = -O-) with a small molecular weight is preferably used in the resin injection process due to its low viscosity.

[0026] Commercially available products of such diglycidyl-p-phenoxyaniline include "TOREP (registered trademark)" A-204E (diglycidyl-p-phenoxyaniline) (manufactured by Toray Fine Chemicals Co., Ltd.).

[0027] (component [C]) The epoxy resin composition for RTM of the present invention must contain core-shell rubber particles as component [C]. Preferably, the component contains 1 to 10 parts by mass of the total epoxy resins, based on 100 parts by mass of the total epoxy resins. "Containing 1 to 10 parts by mass of the total epoxy resins, based on 100 parts by mass of the total epoxy resins, "means containing 1 to 10 parts by mass of the total epoxy resins contained in the epoxy resin composition for RTM of the present invention, based on 100 parts by mass (the same applies hereinafter)." By including component [C] within the above range, the fracture toughness of the cured resin obtained by curing the epoxy resin composition for RTM of the present invention can be improved without impairing the elastic modulus. Therefore, by using the epoxy resin composition for RTM of the present invention as the matrix resin, a fiber-reinforced composite material with excellent compression properties and impact resistance can be obtained. If the blending amount of component [C] is less than 1 part by mass, the toughness of the resulting cured resin may not be sufficiently improved. If the blending amount of component [C] is more than 10 parts by mass, the elastic modulus of the resulting cured resin may be reduced.

[0028] Commercially available products of component [C] 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 Dow Chemical Company), etc.

[0029] The fracture toughness value of the cured epoxy resin material of the present invention can be evaluated, for example, from the K1c value obtained from the SENB test described in ASTM D5045-99.

[0030] (Component [D]) The epoxy resin composition for RTM of the present invention must contain a thermoplastic resin as component [D]. By including component [D], the fracture toughness of the cured resin obtained by curing the epoxy resin composition for RTM of the present invention can be increased without impairing the elastic modulus. Therefore, by using the epoxy resin composition for RTM of the present invention as the matrix resin, a fiber-reinforced composite material with improved compressive properties and impact resistance can be obtained. The thermoplastic resin used for this purpose is generally preferably a thermoplastic resin having in its main chain a bond selected from the group consisting of carbon-carbon bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, thioether bonds, sulfone bonds, and carbonyl bonds.

[0031] The thermoplastic resin may have a partially crosslinked structure and may be crystalline or amorphous. Component [D] may be mixed or dissolved in the epoxy resin composition for RTM, but it is preferable for it to be at least partially dissolved in order to ensure uniformity in the properties of the cured product. Preferred thermoplastic resins that can be used in a dissolved state in the epoxy resin composition for RTM include polycarbonate, polyacetal, phenylene oxide, polyphenylene sulfide, polyarylate, polyester, polyamideimide, polyimide, polyetherimide, polyimide having a phenyltrimethylindane structure, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, polyaramid, polyethernitrile, and polybenzimidazole. Among these, polyethersulfone and polyetherimide are preferred due to their good compatibility with epoxy resins. Furthermore, it is preferable for the component [D] to be present in an amount of 1 to 10 parts by mass per 100 parts by mass of the total epoxy resin.

[0032] Commercially available products of such component [D] include commercially available polyethersulfone products such as "Sumikaexcel (registered trademark)" PES3600P, "Sumikaexcel (registered trademark)" PES5003P, "Sumikaexcel (registered trademark)" PES5200P, and "Sumikaexcel (registered trademark)" PES7600P (all manufactured by Sumitomo Chemical Co., Ltd.), "Virantage (registered trademark)" VW-10200RFP, and "Virantage (registered trademark)" VW-10700RFP (all manufactured by Alternatively, a copolymer oligomer of polyethersulfone and polyetherethersulfone as described in JP-A-2004-506789, or commercially available polyetherimide products such as "Ultem (registered trademark)" 1000, "Ultem (registered trademark)" 1010, and "Ultem (registered trademark)" 1040 (all manufactured by Solvay Advanced Polymers) can be used.

[0033] (Component [B]) Component [B] in the present invention is at least one aromatic amine curing agent selected from the group consisting of alkylbenzenediamines and methylenebisanilines.

[0034] Such alkylbenzenediamines are aromatic amine compounds having one or more alkyl groups and two amino groups on the benzene ring, and toluenediamines such as diethyltoluenediamine and dimethylthiotoluenediamine are preferably used. By using an alkylbenzenediamine as a curing agent for an epoxy resin, it is possible to obtain a cured resin product with an excellent elastic modulus while suppressing the viscosity of the epoxy resin composition for RTM in the resin injection process. Among these, dimethylthiotoluenediamine is particularly preferred because it can obtain a cured resin product with an excellent balance between elastic modulus and toughness.

[0035] Commercially available alkylbenzene diamines include jER Cure (registered trademark) WA (manufactured by Mitsubishi Chemical Corporation), Ethacure (registered trademark) 100 (manufactured by Albemarle), Heartcure (registered trademark) 10 (manufactured by Kumiai Chemical Industry Co., Ltd.), Lonzacure (registered trademark) DETDA80 (manufactured by Lonza), Ethacure (registered trademark) 300 (manufactured by Albemarle), and Heartcure (registered trademark) 30 (manufactured by Kumiai Chemical Industry Co., Ltd.).

[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, it is possible to obtain cured resin products with low water absorption and excellent toughness.

[0037] Examples of such 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, 4,4-methylenebis(isopropyl-6-methylaniline) is particularly preferred because it can give a cured resin having an excellent balance between elastic modulus and toughness.

[0038] Commercially available products of such methylenebisaniline 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), and "Kayahard (registered trademark)" AA(PT) (manufactured by Nippon Kayaku Co., Ltd.).

[0039] In the present invention, the component [B] is preferably an alkylbenzenediamine, and it is also preferable that the component [B] contains both an alkylbenzenediamine and methylenebisaniline.

[0040] When component [B] in the present invention is an alkylbenzenediamine, it is preferable in that it is possible to obtain a cured resin product with an excellent elastic modulus while sufficiently suppressing the viscosity of the epoxy resin composition for RTM in the resin injection step.

[0041] On the other hand, when component [B] in the present invention contains both alkylbenzenediamine and methylenebisaniline, it is preferable in that it is possible to obtain a cured resin product that has an excellent balance of elastic modulus, low water absorption, and toughness while suppressing the viscosity of the epoxy resin composition for RTM in the resin injection step.

[0042] The epoxy resin composition for RTM of the present invention must satisfy all of the following conditions 1 to 4. Condition 1: Viscosity at 110°C is 1 mPa·s or more and 200 mPa·s or less Condition 2: Mass loss rate after heating at 110°C for 30 minutes is 0.3% by mass or less Condition 3: The rubber-state elastic modulus of the resin cured product obtained by curing at 180°C for 2 hours is 2 MPa or more and 8 MPa or less. Condition 4: The water absorption of the cured resin obtained by curing at 180°C for 2 hours is 1.0% or more and 3.0% or less.

[0043] Regarding the above condition 1, the epoxy resin composition for RTM of the present invention must have a viscosity of 1 mPa·s or more and 200 mPa·s or less at 110°C. When the viscosity is in this range, the epoxy resin composition for RTM of the present invention has excellent impregnation properties into reinforcing fiber substrates in the resin injection step, and therefore the epoxy resin composition for RTM of the present invention can be suitably used for large structural materials.

[0044] The viscosity of the epoxy resin composition for RTM was measured using a dynamic viscoelasticity apparatus under the following conditions: measurement mode: parallel plate (25 mmφ, gap 1.0 mm), shear rate: 100 s -1 The measurement is performed under the condition of a set temperature of 110°C. In this case, the epoxy resin composition is set on parallel plates heated to 110°C so that the gap is 1.0 mm within 5 minutes after preparation, and the measurement is started. The complex viscosity at the point when the sample temperature rises and reaches 110°C is taken as η0.

[0045] Regarding the above condition 2, the epoxy resin composition for RTM of the present invention must have a mass loss rate of 0.3% by mass or less, preferably 0.2% by mass or less, after heating for 30 minutes at 110°C. By keeping the mass loss rate within this range, volatilization of the resin component during the molding process is suppressed, thereby enabling the production of a fiber-reinforced composite material with high Vf and excellent mechanical properties.

[0046] The mass loss rate of such an epoxy resin composition for RTM can be obtained by placing approximately 2 g of the epoxy resin composition in an aluminum cup having an inner diameter of 50 mm, weighing it on an electronic balance, heating it in a fan oven set at 110°C, removing it after 30 minutes, cooling it to room temperature, and then reweighing it to calculate the mass loss rate of the epoxy resin composition.

[0047] Regarding condition 3 above, the rubber-state elastic modulus of the epoxy resin composition for RTM of the present invention, obtained by curing the epoxy resin composition at 180°C for 2 hours, must be in the range of 2 MPa to 8 MPa. By satisfying this range, the cured resin obtained by curing the epoxy resin composition for RTM of the present invention will exhibit excellent fracture toughness while maintaining its elastic modulus and heat resistance, resulting in excellent impact resistance for fiber-reinforced composite materials obtained using the epoxy resin composition as a matrix resin. If the rubber-state elastic modulus is greater than 8 MPa, the above effect cannot be achieved. If the rubber-state elastic modulus is less than 2 MPa, the fracture toughness will be improved, but the elastic modulus and heat resistance of the cured epoxy resin will be reduced, resulting in reduced compressive strength under wet heat and other conditions for the fiber-reinforced composite material.

[0048] The rubber-state modulus of the cured resin can be determined by DMA (dynamic viscoelasticity measurement). Specifically, a dynamic viscoelasticity measuring device is used to measure a test piece 2.0 mm thick, 12.7 mm wide, and 45 mm long mounted on a solid torsion jig, with a temperature rise rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.08% over a temperature range of 40°C to 260°C. The rubber-state modulus is the storage modulus at a temperature 50°C above the glass transition temperature in the resulting graph of storage modulus vs. temperature. The glass transition temperature is the temperature at the intersection of a tangent drawn to the glassy state and a tangent drawn to the glass transition temperature region in the resulting graph of storage modulus vs. temperature.

[0049] Regarding condition 4 above, the water absorption of the epoxy resin composition for RTM of the present invention, a cured resin obtained by curing the epoxy resin composition at 180°C for 2 hours, must be in the range of 1.0% to 3.0%. By satisfying this range, the cured resin obtained by curing the epoxy resin composition for RTM of the present invention will have a high wet heat modulus, and thus fiber-reinforced composite materials obtained using the epoxy resin composition as a matrix resin will have excellent wet heat compressive strength. If the water absorption is greater than 3.0%, the above effect cannot be achieved. If the water absorption is less than 1.0%, the adhesion between the cured epoxy resin and the reinforcing fibers in the fiber-reinforced composite material will be reduced, resulting in a decrease in the impact resistance of the fiber-reinforced composite material.

[0050] The water absorption rate of such a cured resin product is calculated by immersing a test piece having a thickness of 2.0 mm, a width of 10 mm and a length of 60 mm in boiling water for 48 hours, and calculating the difference in mass before and after immersion.

[0051] The epoxy resin composition for RTM of the present invention is characterized in that the wet heat resistance (wet Tg) of the cured resin obtained by curing the epoxy resin composition at 180°C for 120 minutes decreases less than the dry heat resistance (dry Tg). When applying a fiber-reinforced composite material as a structural material, such as for aircraft, the smaller the decrease in wet Tg, the better. As an indicator of this, the ratio of wet Tg to dry Tg (wet Tg / dry Tg) can be used to express the rate of decrease, and the wet Tg / dry Tg ratio is preferably in the range of 0.9 to 1.0. The wet Tg can be evaluated, for example, by the DMA measurement described above using a test piece obtained by immersing the cured resin in boiling water for 48 hours.

[0052] Furthermore, the epoxy resin composition for RTM of the present invention has a flexural modulus (E 82 ) is the flexural modulus (E 23 ), it also has the characteristic that the degree of decline is small compared to E 82 and E 23 The ratio (E 82 / E 23 ) can be used to express the rate of decline, but E 82 / E 23 is preferably 0.75 or more, more preferably 0.80 or more.

[0053] The epoxy resin composition for RTM used in the present invention may contain an epoxy resin different from the components [A] and [E] as component [F], as long as the effects of the present invention are not lost.

[0054] Examples of such epoxy resins include dicyclopentadiene-type epoxy resins, biphenyl-type epoxy resins, phenol aralkyl-type epoxy resins, naphthalene-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, phenol novolac-type epoxy resins, triglycidylaminophenol-type epoxy resins, etc. These may be used alone or in combination.

[0055] Commercially available products of the dicyclopentadiene type epoxy resin include "EPICLON (registered trademark)" HP-7200L, "EPICLON (registered trademark)" HP-7200, and "EPICLON (registered trademark)" HP-7200H (all manufactured by DIC Corporation).

[0056] Commercially available biphenyl type epoxy resins include "jER (registered trademark)" YX-4000 (manufactured by Mitsubishi Chemical Corporation).

[0057] Commercially available products of the phenol aralkyl epoxy resin include NC-3000H, NC-3000, NC-3000L, NC-7000, NC-7300, NC-2000, and NC-2000L (all manufactured by Nippon Kayaku Co., Ltd.).

[0058] Commercially available bisphenol A epoxy resins include jER (registered trademark) 828 and jER (registered trademark) 825 (both manufactured by Mitsubishi Chemical Corporation).

[0059] Commercially available bisphenol F epoxy resins include "EPICLON (registered trademark)" 830 and "EPICLON (registered trademark)" 807 (both manufactured by DIC Corporation), and "jER (registered trademark)" 806 (manufactured by Mitsubishi Chemical Corporation).

[0060] Commercially available products of the phenol novolac epoxy resin include "jER (registered trademark)" 152, "jER (registered trademark)" 154, and "jER (registered trademark)" 180S (all manufactured by Mitsubishi Chemical Corporation).

[0061] Commercially available examples of the triglycidyl aminophenol type epoxy resin include "Sumiepoxy (registered trademark)" ELM100 and ELM120 (manufactured by Sumitomo Chemical Co., Ltd.), "Araldite (registered trademark)" MY0500, "Araldite (registered trademark)" MY0510, and "Araldite (registered trademark)" MY0600 (all manufactured by Huntsman Advanced Materials), and "jER (registered trademark)" 630 (manufactured by Mitsubishi Chemical Corporation).

[0062] 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 or the like, provided that uniform kneading is possible.

[0063] The epoxy resin composition for RTM of the present invention exhibits viscosity stability over long periods at relatively high temperatures and has excellent impregnation properties for reinforcing fiber substrates, making it particularly suitable for use in the RTM method. The RTM method involves placing a reinforcing fiber substrate or a preform in a molding die, injecting a liquid matrix resin into the die to impregnate the reinforcing fibers, and then heating to cure the epoxy resin composition, thereby obtaining a molded fiber-reinforced composite material.

[0064] One aspect of the present invention is a method for producing a fiber-reinforced composite material. The method for producing a fiber-reinforced composite material of the present invention is a method for producing a fiber-reinforced composite material in which a reinforcing fiber substrate is placed in a molding die heated to 70°C or higher and 190°C or lower, the epoxy resin composition for RTM of the present invention is impregnated, and the composition is cured in the molding die. Preheating the molding die is preferred because it reduces the viscosity of the epoxy resin composition and shortens the injection time, thereby improving mass productivity. The heat curing temperature does not need to be the same as the temperature during injection, and the time required for heat curing can be shortened by appropriately raising the temperature.

[0065] 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, including metals such as steel and aluminum, fiber-reinforced plastics (FRP), wood, and plaster. Materials for the flexible film include polyamide, polyimide, polyester, fluororesin, and silicone resin.

[0066] One aspect of the present invention is a cured resin product, which is obtained by thermally curing the epoxy resin composition for RTM of the present invention.

[0067] One aspect of the present invention is a fiber-reinforced composite material. The fiber-reinforced composite material of the present invention is a fiber-reinforced composite material composed of the cured resin of the present invention and a reinforcing fiber substrate.

[0068] 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, and glass fibers, carbon fibers, aramid fibers, boron fibers, alumina fibers, silicon carbide fibers, etc. can be used. Two or more of these fibers may 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.

[0069] 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. [Example]

[0070] 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.

[0071] The materials, sample preparation methods, and evaluation methods used in the present examples are as follows.

[0072] <Materials used> (1) Component [A]: tetrafunctional glycidylamine epoxy resin [A]-1 "Sumiepoxy (registered trademark)" ELM434VL (manufactured by Sumitomo Chemical Co., Ltd., epoxy equivalent: 115 g / eq), [A]-2 “Araldite (registered trademark)” MY721 (manufactured by Huntsman Japan Co., Ltd., epoxy equivalent: 115 g / eq).

[0073] (2) Component [B]: at least one aromatic amine curing agent selected from the group consisting of alkylbenzenediamines and methylenebisanilines (2-1) Alkylbenzenediamine [B]-1 "jER Cure (registered trademark)" WA (manufactured by Mitsubishi Chemical Corporation, active hydrogen equivalent: 45 g / eq), [B]-2 "Ethacure (registered trademark)" 300 (manufactured by Albemarle, active hydrogen equivalent: 54 g / eq), (2-2) Methylenebisaniline [B]-3 "Lonzacure (registered trademark)" M-MIPA (manufactured by Lonza, active hydrogen equivalent: 78 g / eq).

[0074] (3) Component [C]: A mixture of core-shell rubber particles and component [A] Kane Ace (registered trademark) MX-416 (glycidylamine type epoxy resin (corresponding to component [A]) 75% by mass, butadiene-based core-shell type rubber particles 25% by mass, epoxy equivalent: 148 g / eq).

[0075] (4) Component [D]: Thermoplastic resin [D]-1 "Sumika Excel (registered trademark)" PES2603MP (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.) [D]-2 "Sumika Excel (registered trademark)" PES5003P, manufactured by Sumitomo Chemical Co., Ltd.) [D]-3 "Ultem (registered trademark)" 1000 (polyetherimide, manufactured by SABIC Co., Ltd.).

[0076] (5) Component [E]: Glycidylaniline type epoxy resin represented by formula (I) "TOREP (registered trademark)" A-204E (manufactured by Toray Fine Chemical Co., Ltd., epoxy equivalent: 162 g / eq).

[0077] (6) Component [F]: Other epoxy resins [F]-1 "EPICLON (registered trademark)" HP-7200L (manufactured by DIC Corporation, epoxy equivalent: 246 g / eq) [F]-2 NC-3000L (manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 272 g / eq).

[0078] [F]-3 "jER (registered trademark)" YX-4000 (manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 186 g / eq) <Method for preparing RTM epoxy resin composition> Into a stainless steel beaker, put the components other than component [B] in a predetermined amount, heat up to 130 - 150 °C, and knead appropriately until each component is compatible to obtain an epoxy main agent solution.

[0079] Into another container, put component [B] in a predetermined amount, heat it as necessary to make it compatible, and obtain a curing agent solution.

[0080] Mix a predetermined amount of the epoxy main agent solution and the curing agent solution at about 60 °C, and knead for 3 minutes with a planetary mixer to obtain an RTM epoxy resin composition. The composition was as shown in Table 1.

[0081] <Evaluation method> The evaluation methods in the following examples are described. For those with a measurement number \(n = 1\), the description of the measurement number \(n\) is omitted.

[0082] (1) Evaluation method for the viscosity (\(\eta_0\)) of the RTM epoxy resin composition at 110 °C The RTM epoxy resin composition obtained according to the above <Preparation method of RTM epoxy resin composition> was set to a thickness of 1.0 mm on a parallel plate set at 110 °C in the following device within 5 minutes after mixing, and measurement was started under the following conditions. The complex viscosity when the RTM epoxy resin composition reached 110 °C was taken as \(\eta_0\). Measuring device: Dynamic viscoelasticity measuring device (Discovery HR-2, manufactured by TA Instruments) Measurement mode: Parallel plate (25 mm φ, gap 1.0 mm) Shear rate: 100 s -1 Set temperature: 110 °C.

[0083] (2) Evaluation method for the mass loss rate of the RTM epoxy resin composition at 110 °C About 2 g of the RTM epoxy resin composition obtained according to the above <Preparation method of RTM epoxy resin composition> was put into an aluminum cup with an inner diameter of 50 mm, weighed with an electronic balance, then heated in a forced-air oven (DKM400, manufactured by Yamato Scientific Co., Ltd.) set at 110 °C, taken out after 30 minutes, cooled to room temperature, and weighed again to calculate the mass loss rate. The number of samples \(n = 5\), and the average value was adopted as the value of the mass loss rate.

[0084] (3) Flexural modulus of the resin cured product (23 °C, 50% RH): E 23 Evaluation method The RTM epoxy resin composition obtained according to the above <Method for Preparing RTM Epoxy Resin Composition> was degassed in vacuo, and then cured at a temperature of 180 °C for 2 hours in a mold set to a thickness of 2 mm with a 2-mm-thick "Teflon (registered trademark)" spacer to obtain a plate-like resin cured product with a thickness of 2 mm. From this resin cured product, a test piece with a width of 10 mm and a length of 60 mm was cut out, and using an Instron universal testing machine (manufactured by Instron Corporation), with a span of 32 mm and a crosshead speed of 10 mm / min, three-point bending was carried out at room temperature (23 °C, 50% RH) according to JIS K7171 (1994), and the flexural modulus (23 °C, 50% RH) was measured. At this time, the number of samples n = 6, and the average value was adopted as the value of the flexural modulus.

[0085] (4) Flexural modulus of resin cured product (humid heat 82 °C): E 82 And evaluation method of water absorption rate The flexural modulus of the resin cured product in (3) above (23 °C, 50% RH): E 23 A resin cured product was obtained in the same manner as the evaluation method in , and after cutting out a test piece with a width of 10 mm and a length of 60 mm, it was immersed in boiling water for 48 hours. The taken-out test piece was used with an Instron universal testing machine (manufactured by Instron Corporation), with a span of 32 mm and a crosshead speed of 10 mm / min, and three-point bending was carried out at a high temperature environment (82 °C) according to JIS K7171 (1994), and the flexural modulus (humid heat 82 °C) was measured. In addition, the mass of the above test piece was measured before and after immersion in boiling water for 48 hours, and the water absorption rate was calculated from the difference in mass. At these times, the number of samples n = 6, and the average value was adopted as the values of the flexural modulus and the water absorption rate.

[0086] (5) Evaluation method for glass transition temperature (dry Tg) and rubbery state modulus of resin cured product The RTM epoxy resin composition obtained according to the above <Method for Preparing RTM Epoxy Resin Composition> was degassed in vacuo in an uncured state, and then cured at a temperature of 180 °C for 2 hours in a mold set to a thickness of 2 mm with a 2-mm-thick "Teflon (registered trademark)" spacer to obtain a resin cured product in the form of a 2-mm-thick plate. From this resin cured product, a test piece with a width of 12.7 mm and a length of 45 mm was cut out. Using a dynamic viscoelasticity measuring device (ARES-G2, manufactured by TA Instruments), the test piece was set in a solid torsion jig with a chuck-to-chuck distance of 30 mm. The test piece was set in the solid torsion jig, and measurements were performed in the temperature range of 40 to 260 °C at a heating rate of 5 °C / min, a frequency of 1 Hz, and a strain of 0.08%. At this time, the glass transition temperature (dry Tg) was defined as the temperature at the intersection of the tangent line drawn in the glassy state and the tangent line drawn in the glass transition temperature region in the graph of the obtained storage modulus and temperature. The rubbery state modulus was defined as the storage modulus at a temperature 50 °C higher than the glass transition temperature in the graph of the obtained storage modulus and temperature.

[0087] (6) Method for Evaluating Glass Transition Temperature (Wet Tg) of Resin Cured Product A resin cured product was obtained in the same manner as in the above (5) Method for Evaluating Glass Transition Temperature (Dry Tg) of Resin Cured Product. After cutting out a test piece with a width of 12.7 mm and a length of 45 mm, it was immersed in boiling water for 48 hours. Viscoelasticity measurement was performed in the same manner as in the above <Method for Evaluating Glass Transition Temperature (Dry Tg) of Resin Cured Product> to obtain the glass transition temperature (wet Tg).

[0088] (7) Method for Evaluating Fracture Toughness Value (K1c) of Resin Cured Product The RTM epoxy resin composition obtained according to the above <Method for Preparing RTM Epoxy Resin Composition> was degassed in vacuo, and then cured at a temperature of 180 °C for 2 hours in a mold set to a thickness of 6 mm with a 6-mm-thick "Teflon (registered trademark)" spacer to obtain a resin cured product in the form of a 6-mm-thick plate. After processing the obtained resin cured product into the test piece shape described in ASTM D5045-99, a SENB test was performed according to ASTM D5045-99. At this time, the number of samples n = 16, and the average value was adopted as K1c.

[0089] The method for preparing samples, the properties of the cured resin, and the measurement results of the properties of the uncured resin in each example are described below.

[0090] (Example 1) As the epoxy resin, 25 parts by mass of "Sumiepoxy (registered trademark)" ELM-434VL (Component [A]), 30 parts by mass of "TOREP (registered trademark)" A-204E (Component [E]), 30 parts by mass of "EPICLON (registered trademark)" HP-7200L (Component [F]), 20 parts by mass of "Kaneka (registered trademark)" MX-416 (5 parts by mass of Component [C] and 15 parts by mass of Component [A]), 9.5 parts by mass of "jER Cure (registered trademark)" WA (Component [B]), and 28.4 parts by mass of "Lonzacure (registered trademark)" M-MIPA (Component [B]) were used, and an epoxy resin composition for RTM was prepared according to the above <Method for Preparing Epoxy Resin Composition for RTM>.

[0091] Regarding this epoxy resin composition for RTM, for the evaluation method of the flexural modulus of the cured resin (23°C, 50% RH): E 23 and the evaluation method of the flexural modulus of the cured resin (humid heat 82°C): E 82 and according to the evaluation method of water absorption rate, when the flexural properties were obtained, E 23 was 3.65 GPa, E 82 was 3.10 GPa, and E 82 / E 23 showed an excellent humid heat elastic modulus of 0.85. Also, according to the evaluation method of the glass transition temperature (dry Tg) and the rubbery state elastic modulus of the cured resin (5) and the evaluation method of the glass transition temperature (wet Tg) of the cured resin (6), when the heat resistance was evaluated, the dry Tg was 176°C, the wet Tg was 168°C, and the wet Tg / dry Tg showed an excellent heat resistance of 0.95. The water absorption rate was extremely good at 1.6%, and the rubbery state elastic modulus was 4.0 MPa. Also, according to the evaluation method of the fracture toughness value (K1c) of the cured resin (7), when the fracture toughness value was evaluated, it was 1.25 MPa·m 0.5 and was good.

[0092] The viscosity (η0) was evaluated according to the above (1) Method for evaluating the viscosity (η0) of an epoxy resin composition for RTM at 110°C, and was found to be 90 mPa·s. The mass loss rate was evaluated according to the above (2) Method for evaluating the mass loss rate of an epoxy resin composition for RTM at 110°C, and was found to be 0.12% by mass.

[0093] Examples 2 to 6 Epoxy resin compositions for RTM and cured resins were prepared in the same manner as in Example 1, except that the resin compositions were changed as shown in Table 1.

[0094] For the RTM epoxy resin compositions of each example, E 23 , E 82 The dry Tg, wet Tg, water absorption, and K1c were evaluated, and good physical properties were obtained at all levels. Furthermore, the η0 of each example was in the range of 32 mPa s to 190 mPa s, the mass loss rate was in the range of 0.07 mass% to 0.20 mass%, and the rubber-state elastic modulus was in the range of 3.5 MPa to 6.0 MPa.

[0095] (Comparative Example 1) Epoxy resin compositions for RTM and cured resins were prepared in the same manner as in Example 1, except that the resin compositions were changed as shown in Table 1.

[0096] The fracture toughness of this epoxy resin composition for RTM was evaluated according to the above (7) method for evaluating fracture toughness (K1c) of cured resins, and was found to be 0.65 MPa m 0.5 Because the K1c value was low, other evaluations were not performed.

[0097] [Table 1] [Industrial Applicability]

[0098] The epoxy resin composition for RTM of the present invention can provide a cured epoxy resin product that has low viscosity and low volatility at injection molding temperatures, and has high elastic modulus and fracture toughness under wet and hot conditions. Fiber-reinforced composite materials made from this epoxy resin composition also have excellent compressive properties and impact resistance under wet and hot conditions, making them suitable for use in aerospace components and general industrial structural components.

Claims

1. An epoxy resin composition for RTM containing the following components [A], [B], [C], and [D] and satisfying all of the following conditions 1 to 4: [A]: tetrafunctional glycidylamine type epoxy resin [B]: At least one aromatic amine curing agent selected from the group consisting of alkylbenzenediamines and methylenebisanilines [C]: Core-shell rubber particles [D]: Thermoplastic resin Condition 1: Viscosity at 110°C is 1 mPa·s or more and 200 mPa·s or less Condition 2: The mass loss rate after heating at 110°C for 30 minutes is 0.3 mass% or less Condition 3: The rubber-state elastic modulus of the cured resin obtained by curing at 180°C for 2 hours is 2 MPa or more and 8 MPa or less. Condition 4: The water absorption rate of the cured resin obtained by curing at 180°C for 2 hours is 1.0% or more and 3.0% or less.

2. 2. The epoxy resin composition for RTM according to claim 1, which contains 1 to 10 parts by mass of polyethersulfone or polyetherimide as component [D] relative to 100 parts by mass of the total epoxy resin.

3. 2. The epoxy resin composition for RTM according to claim 1, comprising an aniline-type epoxy resin represented by formula (I) as component [E]. 【Chemistry 1】 (In formula (I), R １ and R ２ R represents at least one selected from aliphatic hydrocarbon groups having 1 to 4 carbon atoms. １ and R ２ When there are multiple of each, they may be the same or different. n is an integer of 0 to 4, and m is an integer of 0 to 5. X represents -O- or -S-.

4. A cured resin obtained by thermally curing the epoxy resin composition for RTM according to any one of claims 1 to 3.

5. A fiber-reinforced composite material comprising the cured resin according to claim 4 and a reinforcing fiber substrate.

6. The fiber-reinforced composite material according to claim 5, wherein the reinforcing fiber substrate is a carbon fiber substrate.

7. A method for producing a fiber-reinforced composite material, comprising injecting the epoxy resin composition for RTM according to any one of claims 1 to 3 into a reinforcing fiber substrate placed in a molding die heated to 70°C or higher and 190°C or lower, allowing the composition to impregnate the substrate, and curing the composition in the molding die.

8. The method for producing a fiber-reinforced composite material according to claim 7, wherein the reinforcing fiber substrate is a carbon fiber substrate.

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