Curable resin composition and fiber-reinforced composite material using the same

Abstract

To provide a curable resin composition that can give a molding having resistance to oxidative degradation, barely shows a deterioration of strength even after long-term thermal hysteresis, and can improve the heat-resistant reliability of a fiber-reinforced composite material.SOLUTION: A curable resin composition contains an epoxy resin (A), an alicyclic amine compound (B), and an antioxidant (C) as essential components, the antioxidant being a naphthol-based or aromatic amine-based antioxidant, and the amount of addition of the antioxidant (C) being 0.05-3 pts.mass relative to 100 pts.mass of the total of the components (A)-(C).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a curable resin composition having excellent heat resistance, and to a matrix resin for a fiber-reinforced composite material that retains high strength even after long-term thermal history. [Background technology]

[0002] Fiber-reinforced composite materials are generally composed of reinforcing fibers such as glass fibers, aramid fibers, and carbon fibers, and thermosetting matrix resins such as unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic resins, benzoxazine resins, cyanate resins, and bismaleimide resins. Fiber-reinforced composite materials are lightweight and have excellent mechanical properties, such as strength, corrosion resistance, and fatigue resistance, and are therefore widely used as structural materials for aircraft, automobiles, civil engineering and construction, sporting goods, and other applications.

[0003] Fiber-reinforced composite materials are manufactured by methods such as autoclave molding or press molding using prepregs in which reinforcing fibers have been previously impregnated with a thermosetting matrix resin, resin transfer molding, liquid compression molding, wet layup molding, pultrusion molding, or filament winding molding, which include a step of impregnating reinforcing fibers with a liquid matrix resin and a molding step by thermosetting.

[0004] Liquid thermosetting resins such as unsaturated polyester resins, vinyl ester resins, urethane resins, and epoxy resins have been used in resin transfer molding, liquid compression molding, wet layup molding, pultrusion molding, and filament winding molding. One example of a thermosetting resin composition made from epoxy resin is a resin composition that uses an epoxy resin as the base resin and an amine compound as the curing agent, and is widely used in applications that require easy handling at the work site, fast curing, and heat resistance and strength after curing.

[0005] Resin compositions using epoxy resins and amine compounds as curing agents are fast-curing and produce cured products with high strength and toughness. However, they have the drawback of being subject to decomposition reactions caused by oxidation when exposed to high temperatures for long periods, resulting in discoloration of the cured product and a decrease in strength and toughness.

[0006] Attempts have been made to add antioxidants to epoxy resin compositions in order to suppress oxidative degradation. Patent Document 1 discusses the addition of a phenol novolac compound as a curing agent to an epoxy resin, and a hindered phenol or a phosphorus-based compound as an antioxidant. Patent Documents 2 and 3 discuss the addition of an acid anhydride compound as a curing agent to an epoxy resin, and a hindered phenol, a phosphorus-based compound, a sulfur-based compound, or an amine-based compound as an antioxidant. Patent Document 4 discusses the addition of dicyandiamide as a curing agent to an epoxy resin, and a hindered phenol, a sulfur-based compound, a sulfur-based compound, or a hindered amine-based compound as an antioxidant.

[0007] The matrix resin of fiber-reinforced composite materials is used outdoors or in high-temperature environments, and is therefore required to maintain not only its initial physical properties after curing but also its strength properties after long-term thermal history. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 7-309998 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-236893 [Patent Document 3] Patent No. 6501359 [Patent Document 4] Patent No. 6163763 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a curable resin composition that can give a molded product resistant to oxidative degradation and that can improve the heat resistance reliability of a fiber-reinforced composite material with little decrease in strength even after long-term thermal history. [Means for solving the problem]

[0010] As a result of investigations to solve the above-mentioned problems, the present inventors have found that by using a specific epoxy resin, an amine compound and an antioxidant, strength properties can be maintained even after long-term thermal history, and have thus completed the present invention.

[0011] That is, the present invention provides a curable resin composition characterized in that the essential components are an epoxy resin (A), an alicyclic amine compound (B), and an antioxidant (C), the antioxidant is a naphthol-based or aromatic amine-based antioxidant, and the amount of antioxidant (C) added is 0.05 to 3 parts by mass per 100 parts by mass of the total of components (A), (B), and (C).

[0012] Preferred examples of the antioxidant (C) include compounds represented by the following formula (1) or (2). [ka] (In the formula, R1 represents a hydrocarbon group having 1 to 4 carbon atoms.) [ka] (In the formula, R2 and R3 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms.)

[0013] The weight ratio of the epoxy resin (A) to the alicyclic amine compound (B) is more preferably in the range of 90:10 to 70:30.

[0014] The curable resin composition preferably contains core-shell rubber particles (D) in addition to the epoxy resin (A), the alicyclic amine compound (B), and the antioxidant (C), and the amount of the core-shell rubber particles (D) is 1 to 8 parts by mass per 100 parts by mass of the total of the components (A), (B), (C), and (D).

[0015] Furthermore, it is desirable that the tensile strength retention ratio (T2 / T1) of a cured product (I) obtained by heat-treating the curable resin composition at 130°C for 1 hour and a cured product (II) obtained by further heat-treating the cured product (I) at 170°C for 20 hours be 90% or more. Here, T1 is the tensile strength of the cured product (I), and T2 is the tensile strength of the cured product (II).

[0016] Another aspect of the present invention is a resin composition for a fiber-reinforced composite material, characterized by blending reinforcing fibers with the above-mentioned curable resin composition. Also, a fiber-reinforced composite material obtained from this resin composition for a fiber-reinforced composite material. [Effects of the Invention]

[0017] The curable resin composition of the present invention is suitable for use in a fiber-reinforced composite material or molded article obtained by curing a material containing the curable resin composition, which exhibits excellent heat resistance and little loss in strength even after long-term thermal history. The curable resin composition is particularly suitable as a curable resin composition used to produce a molded article by resin transfer molding or liquid compression molding. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail. The curable resin composition of the present invention is a curable resin composition comprising an epoxy resin (A), an alicyclic amine compound (B), and an antioxidant (C). Here, the epoxy resin (A), the alicyclic amine compound (B), and the antioxidant (C) are also referred to as component (A), component (B), and component (C), respectively.

[0019] The epoxy resin (A) used in the present invention is preferably a compound having two or more epoxy groups in one molecule, and examples thereof include bisphenol type epoxy resins such as bisphenol F type epoxy resin, bisphenol E type epoxy resin, bisphenol S type epoxy resin, bisphenol Z type epoxy resin, and isophorone bisphenol type epoxy resin; halides, alkyl-substituted products, hydrogenated products, and high molecular weight products having multiple repeating units, including but not limited to monomers, of these bisphenol type epoxy resins; glycidyl ethers of alkylene oxide adducts; novolac type epoxy resins such as phenol novolac type epoxy resin, cresol novolac type epoxy resin, and bisphenol A novolac type epoxy resin; and 3,4-epoxy-6-methylcyclohexylmethyl- ... Examples of epoxy resins that can be used include alicyclic epoxy resins such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and 1-epoxyethyl-3,4-epoxycyclohexane; aliphatic epoxy resins such as trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, and polyoxyalkylene diglycidyl ether; glycidyl esters such as phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, and dimer acid glycidyl ester; and glycidyl amines such as tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenyl sulfone, triglycidylaminophenol, triglycidylaminocresol, and tetraglycidylxylylenediamine. These may be used alone or in combination of two or more. Among these epoxy resins, from the viewpoints of economy and heat resistance, the use of bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, etc., which have two or more epoxy groups in one molecule, can improve the heat resistance of molded articles.

[0020] The alicyclic amine compound (B) used in the present invention is an amine compound having an alicyclic structure. Alicyclic amines have excellent reactivity and can improve heat resistance during curing.

[0021] Specific examples of the alicyclic amine compound (B) include polyamines having an alicyclic structure, such as bis(aminomethyl)cyclohexane, methylenebis(cyclohexylamine), methylenebis(2-methylcyclohexylamine), 1,3,6-trisaminomethylcyclohexane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro[5.5]undecane, bis(aminomethyl)norbornane, and N-(2-aminoethyl)piperazine, as well as derivatives of these alicyclic structures substituted with alkyl groups. The alicyclic amine compound (C) can be used alone or in combination with two or more. Among these, the alicyclic amine compound represented by the following formula (3) is preferred, with bis(aminomethyl)cyclohexane or bis(aminomethyl)norbornane being more preferred in terms of heat resistance and strength after curing. X-(CH2NH2) n (3) (In the formula, X represents an n-valent organic group having 1 to 16 carbon atoms and an alicyclic structure, and n represents 2 or 3.)

[0022] The antioxidant (C) used in the present invention is naphthol-based or aromatic amine-based. Common antioxidants include hindered phenol-based antioxidants, but their antioxidant ability is less effective in cured products made from epoxy resins and amine compounds, and they tend to reduce strength due to oxidative degradation over long-term thermal history. In contrast, the present invention has found that naphthol-based or aromatic amine-based antioxidants function as radical traps to prevent oxidation even in cured products made from epoxy resins and amine compounds, thereby maintaining strength by suppressing oxidative degradation over long-term thermal history.

[0023] The amount of antioxidant (C) added is 0.05 to 3 parts by mass per 100 parts by mass of the total of components (A), (B), and (C). If it is less than 0.05 part by mass, the antioxidant ability will be insufficient, and if it exceeds 3 parts by mass, it will cause a decrease in the initial physical properties of the cured product.

[0024] Examples of naphthol-based antioxidants include, but are not limited to, 1,4-naphthoquinone, 2-hydroxy-1,4-naphthoquinone, 4-methoxy-1-naphthol, 4-ethoxy-1-naphthol, 4-benzyloxy-1-naphthol, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 5-hydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, and 2,5-dihydroxy-1,4-naphthoquinone.

[0025] Examples of aromatic amine antioxidants include, but are not limited to, phenothiazine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N'-diphenyl-1,4-phenylenediamine, N,N'-di-sec-butyl-1,4-phenylenediamine, and N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine.

[0026] Preferred antioxidants (C) include naphthol-based antioxidants represented by the above formula (1) and aromatic amine-based antioxidants represented by the formula (2). In formula (1), R1 represents a hydrocarbon group having 1 to 4 carbon atoms, and is preferably an alkyl group having 1 to 3 carbon atoms. In formula (2), R2 and R3 each independently represent a hydrogen atom or a hydrocarbon residue having 1 to 4 carbon atoms, and is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

[0027] The weight ratio of the epoxy resin (A) to the alicyclic amine compound (B) is preferably in the range of 90:10 to 70:30, which is preferable from the viewpoints of initial heat resistance after curing and maintaining strength after thermal history. If the weight ratio of the epoxy resin exceeds 90, heat resistance decreases, and if it is less than 70, the alicyclic amine structure becomes relatively more abundant, which makes it prone to oxidative degradation due to thermal history and reduces strength.

[0028] As the curing agent, other epoxy resin curing agents besides the alicyclic amine compound (B) can also be used. In this case, the amount is preferably less than 10 parts by mass per 100 parts by mass of the total of components (A), (B), and (C). Examples of such other epoxy resin curing agents include phenol-based and thiol-based epoxy resin curing agents. In addition, it may contain a curing accelerator, a viscosity modifier, an internal mold release agent, etc.

[0029] The phenolic curing agent used as the curing agent for the other epoxy resin is not particularly limited, and examples thereof include bisphenol A, bisphenol F, substituted or unsubstituted biphenol, phenol novolac resin, triazine skeleton-containing phenol novolac resin, naphthol novolac resin, naphthol aralkyl resin, triazine skeleton-containing naphthol resin, biphenyl aralkyl phenolic resin, etc. One or more types of phenolic curing agents may be used in combination.

[0030] A curing catalyst or curing accelerator may be used together with the alicyclic amine compound (B) or a curing agent consisting of the compound and other epoxy resin curing agents to accelerate the curing reaction. Examples of the curing catalyst or curing accelerator include tertiary amines, carboxylic acids, Lewis acid complexes, onium salts, imidazole, alcohols, phenol, cresol, allylphenol, nitrophenol, paraaminophenol, metaaminophenol, mono-t-butylphenol, di-t-butylphenol, hydroquinone, methylhydroquinone, dimethylhydroquinone, trimethylhydroquinone, tetramethylhydroquinone, isopropylhydroquinone, methylisopropylhydroquinone, mono-t-butylhydroquinone, di-t-butylhydroquinone, and mono-t-amylhydroquinone. Phenol compounds such as quinone, di-t-amylhydroquinone, nitrohydroquinone, phenylhydroquinone, diphenylhydroquinone, chlorohydroquinone, dichlorohydroquinone, trichlorohydroquinone, tetrachlorohydroquinone, bromohydroquinone, dibromohydroquinone, tribromohydroquinone, tetrabromohydroquinone, catechol, t-butylcatechol, resorcinol, pyrogallol, dinitropyrogallol, and 1,2,4-benzenetriol can be used, and these curing catalysts and curing accelerators may be used alone or in combination of two or more.

[0031] The curable resin composition of the present invention may contain core-shell rubber particles (D) in addition to the epoxy resin (A), alicyclic amine compound (B), and antioxidant (C). In this case, the amount of the core-shell rubber particles (D) is preferably 1 to 8 parts by mass per 100 parts by mass of the total of the components (A), (B), (C), and (D). Within this range, the initial toughness after curing can be improved, and a cured product can be obtained that maintains strength and toughness even after long-term thermal history.

[0032] From the viewpoint of long-term storage, it is desirable that the curable resin composition of the present invention be stored separately as a base agent containing an epoxy resin (A) and a curing agent containing an alicyclic amine compound (B), and then mixed on-site or immediately before use to form the curable resin composition. The above-mentioned base agent and curing agent may also be appropriately blended with other components such as plasticizers, dyes, organic pigments, inorganic fillers, polymeric compounds, coupling agents, surfactants, and solvents. Other curable resins may also be blended. Examples of such curable resins include, but are not limited to, unsaturated polyester resins, curable acrylic resins, curable amino resins, curable melamine resins, curable urea resins, curable cyanate ester resins, curable urethane resins, curable oxetane resins, and curable epoxy / oxetane hybrid resins. These may be blended with either the base agent or curing agent, taking into consideration their reactivity with the components contained therein, viscosity, and other factors. Compounds that react with the components contained in the base agent or curing agent should be avoided.

[0033] The curable resin composition of the present invention may contain a coupling agent, conductive particles such as carbon particles or metal-plated organic particles, thermosetting resin particles, or inorganic fillers such as silica gel, nanosilica, alumina fiber, or clay, or a conductive filler. The use of conductive particles or conductive fillers can improve the conductivity of the resulting cured resin product or fiber-reinforced composite material.

[0034] Examples of conductive fillers include carbon black, carbon nanotubes, fullerenes, and metal nanoparticles, which may be used alone or in combination. Among these, the incorporation of carbon nanotubes is particularly well known for its ability to not only improve conductivity but also increase the impact strength of fiber-reinforced composite materials even when incorporated in an amount of less than 1 wt% of the fiber-reinforced composite material, and is therefore suitable for use.

[0035] The curable resin composition of the present invention is cured by heat treatment at 130°C for 1 hour to obtain a cured product (I), which is then further subjected to a thermal history at 170°C for 20 hours to obtain a cured product (II), and the tensile strength retention rate after this is desirably 90% or more. When the tensile strength retention rate is 90% or more, stable physical properties are exhibited even after a long period of thermal history, making the composition desirable as a matrix resin for fiber-reinforced composite materials.

[0036] The curable resin composition of the present invention can be blended with reinforcing fibers to form a fiber-reinforced composite material composition. The reinforcing fibers are selected from glass fibers, aramid fibers, carbon fibers, boron fibers, etc., with carbon fibers being preferred for obtaining a fiber-reinforced composite material with excellent strength.

[0037] The volume content of the reinforcing fibers in the resin composition for fiber-reinforced composite materials of the present invention is preferably in the range of 45 to 70%, more preferably 48 to 62%. By setting it in this range, a molded product with few voids and a high volume content of the reinforcing fibers can be obtained, resulting in a fiber-reinforced composite material with excellent strength. This resin composition for fiber-reinforced composite materials can be used as a prepreg.

[0038] The method for producing a fiber-reinforced composite material from the curable resin composition or resin composition for a fiber-reinforced composite material of the present invention is not particularly limited, but is preferably the RTM (Resin Transfer Molding) method or the LCM (Liquid Compression Molding) method. The RTM method involves placing a fiber substrate or preform made of reinforcing fibers in a molding die, injecting a liquid curable resin composition into the mold to impregnate the reinforcing fibers, forming a resin composition for a fiber-reinforced composite material, and then heating and curing the composition to obtain a molded product. The LCM method involves placing a fiber substrate or preform made of reinforcing fibers that have already been blended with a resin in the molding die with the molding pressure released, clamping the die to simultaneously impregnate and mold the fiber-reinforced composite material precursor, and then heating the die to cure the precursor to obtain a fiber-reinforced composite material (molded product). [Example]

[0039] Next, the present invention will be described in detail based on examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. Parts indicating blend amounts are parts by mass unless otherwise specified.

[0040] The abbreviations for the components used in the examples are as follows: Component (A) YD-128: Bisphenol A epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd.) YDF-170: Bisphenol F epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd.) YDPN-638: Phenol novolac epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd.) (B) Component CHDA: 1,3-bis(aminomethyl)cyclohexane NBDA: Bis(aminomethyl)norbornane (mixture of isomers) BCDA: Methylenebis(cyclohexylamine) (mixture of isomers) (B') component TETA: Triethylenetetramine (aliphatic amine curing agent) (C) Component HMN: 4-Methoxy-1-naphthol (naphthol-based antioxidant) PTZ: Phenothiazine (aromatic amine antioxidant) (C') component BHT: Dibutylhydroxytoluene (hindered phenol antioxidant) (D) Component MX-154: A bisphenol A epoxy resin (manufactured by Kaneka Corporation) containing 40 wt% core-shell rubber particles, including core-shell rubber particles (MX-CSR) and a bisphenol A epoxy resin component (MX-EP). MX-EP is counted as component (A).

[0041] Example 1 83 parts of YD-128 as component (A) and 0.3 parts of HMN as component (C) were placed in a 150 mL plastic container and stirred for 5 minutes using a vacuum mixer "Awatori Rentaro" (Thinky Corporation) to uniformly dissolve the HMN. Next, 17 parts of CHDA as component (B) was added, and the mixture was stirred for 2 minutes using a vacuum mixer to obtain a curable resin composition.

[0042] Examples 2 to 16, Comparative Examples 1 to 8 Components (A) to (C) are shown in Table 1. Tables 2 and 3A curable resin composition was prepared under the same mixing conditions as in Example 1, except that the raw materials were used in the composition described in 1.

[0043] The measurement or test methods for each strength property are as follows.

[0044] (Preparation of test specimens for measuring tensile strength) The obtained curable resin composition was poured into a mold hollowed out in the shape specified in JIS K-7161, and cured by heating at 130°C for 1 hour in a hot air circulating oven to obtain a test piece for tensile test.

[0045] (Measurement of tensile strength retention rate) Using an autograph AGS-X (Shimadzu Corporation), the tensile test specimens were measured according to a method in accordance with JIS K-7161, and the maximum tensile stress (MPa) was taken as the initial tensile strength (T1). After subjecting the tensile test specimens to a thermal history of 170°C for 20 hours in an oven, the specimens were removed and subjected to a tensile test according to JIS K-7161. The maximum tensile stress (MPa) was taken as the tensile strength after the thermal history (T2). The tensile strength retention rate was then calculated using the following formula: Tensile strength retention rate = 100 x (T2 / T1)

[0046] (Preparation of test specimens for fracture toughness measurement) A mold was prepared by sandwiching a 4 mm thick U-shaped spacer between two 150 mm long x 150 mm wide x 8 mm thick steel plates, and the resin composition was cured by heating at 130°C for 1 hour in a hot air circulating oven to obtain a molded product measuring 140 mm x 130 mm x 4 mm thick. The product was then cut into 80 mm x 10 mm pieces using a bench band saw and used for measuring fracture toughness, as described below.

[0047] (Measurement of fracture toughness) The fracture toughness test specimens were measured using an Autograph AGS-X (Shimadzu Corporation) according to the method described in ASTM D5045, and the initial fracture toughness value was recorded. After the test specimens were subjected to a thermal history at 170°C for 20 hours in an oven, they were removed and subjected to a fracture toughness test according to ASTM D5045, and the resulting value was recorded as the fracture toughness after thermal history.

[0048] The test results of the examples and comparative examples are shown in Tables 1 and 2, respectively. and Table 3 Shown below. The blend amount is in parts by weight, the tensile strength is in MPa, and the fracture toughness is in MPa m 0.5 is.

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3]

Claims

1. A curable resin composition comprising, as essential components, an epoxy resin (A), an alicyclic amine compound (B), and an antioxidant (C), wherein the alicyclic amine compound (B) is an alicyclic amine compound having two or more primary amino groups, the antioxidant is a naphthol-based or aromatic amine-based compound represented by the following formula (1) or (2), and the amount of the antioxidant (C) added is 0.05 to 3 parts by mass per 100 parts by mass of the total of the components (A), (B), and (C): 【Chemical 1】 (wherein R 1 represents a hydrocarbon group having 1 to 4 carbon atoms). 【Chemistry 2】 (In the formula, R 2 and R 3 each independently represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms.)

2. 2. The curable resin composition according to claim 1, wherein the weight ratio of the epoxy resin (A) to the alicyclic amine compound (B) is in the range of 90:10 to 70:

30.

3. 3. The curable resin composition according to claim 1, further comprising: an epoxy resin (A), an alicyclic amine compound (B), an antioxidant (C), and core-shell rubber particles (D), wherein the amount of the core-shell rubber particles (D) is 1 to 8 parts by mass per 100 parts by mass of the total of the components (A), (B), (C), and (D).

4. 4. The curable resin composition according to claim 1, wherein a cured product (I) obtained by heat-treating the curable resin composition at 130°C for 1 hour and curing the curable resin composition, and a cured product (II) obtained by further heat-treating the cured product (I) at 170°C for 20 hours, have a tensile strength retention rate of 90% or more.

5. A resin composition for fiber-reinforced composite materials, characterized by comprising the curable resin composition according to any one of claims 1 to 4 and reinforcing fibers blended therein.

6. A fiber-reinforced composite material obtained from the resin composition for a fiber-reinforced composite material according to claim 5.

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