JP2023149614A - Epoxy resin composition, fiber-reinforced composite material, and molding - Google Patents

Abstract

To provide an epoxy resin composition with excellent mechanical properties of moldings while maintaining impregnation into carbon fiber and immediate curing.SOLUTION: An epoxy resin composition comprises an epoxy resin (A), an aromatic epoxy resin (B), an alicyclic amine (C) and a core-shell rubber (D) as essential components, where the aromatic epoxy resin (B) has a structure represented by the general formula (1) in the figure, and has a viscosity of 100 to 5000 mPa s at 25°C.SELECTED DRAWING: None

Description

The present invention relates to a fiber reinforced composite material and an epoxy resin composition used therein.

Conventionally, fiber-reinforced composite materials made of reinforcing fibers such as carbon fibers and glass fibers and thermosetting resins such as epoxy resins and phenolic resins are lightweight, yet have excellent mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. Because of its excellent properties, it has been applied to many fields such as aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods. In particular, in applications that require high performance, fiber-reinforced composite materials using continuous reinforcing fibers are used.The reinforcing fibers are carbon fibers with excellent specific strength and specific modulus, and the matrix resin is thermosetting. Among these resins, epoxy resins are often used because of their excellent adhesion to carbon fibers.

The epoxy resin composition is required to have a low viscosity since it is used by impregnating reinforcing fibers with the resin. In addition, when fiber-reinforced resin molded products are used for structural parts in automobiles, etc. or wire core materials, fiber-reinforced resin molded products are exposed to harsh environments, so resins with excellent heat resistance and mechanical strength are used. Certain things are also required.

In addition to heat resistance and mechanical strength, short curing time is also important. This is because the shorter curing time makes it possible to improve productivity within limited production equipment.

As a low-viscosity epoxy resin composition, an epoxy resin composition containing a bisphenol type epoxy resin, an acid anhydride, and an imidazole compound is widely known (Patent Document 1). Furthermore, an epoxy resin composition is also known in which a glycidyl ether of dihydric phenol and a glycidylamine type epoxy resin are used in combination with a curing agent (Patent Document 2). An epoxy resin composition containing an amine curing agent and an amine curing agent is also known (Patent Document 3). However, the epoxy resin compositions provided in Patent Documents 1, 2, and 3 have high impregnation properties into reinforcing fibers and exhibit a certain level of performance in terms of heat resistance and mechanical strength in the cured product; It took a long time to complete the process, and it did not meet the ever-increasing performance requirements.

As a method to improve the mechanical strength of epoxy resins, methods such as blending rubber components and thermoplastic resins with excellent toughness are being tried. For example, it has been studied since the 1970s and is generally well known that the toughness of epoxy resins can be improved by incorporating a rubber component such as acrylonitrile-butadiene rubber containing carboxyl groups into epoxy resins. However, the rubber component causes a decrease in heat resistance and elastic modulus, and in order to sufficiently obtain the toughness-modifying effect of the rubber component, it is necessary to blend a large amount of the rubber component. As a result, the viscosity increases and the heat resistance and mechanical properties inherent to the epoxy resin deteriorate, making it impossible to obtain a composite material with good physical properties.

To address this problem, a method using polymer particles that are substantially insoluble in epoxy resins has been proposed. Among these, a method has been proposed in which a particulate core part whose main component is a polymer is blended with core-shell rubber particles that cover part or all of the surface of the core part by a method such as graft polymerization with a polymer different from the core part. (Patent Document 4). It is known that this method can suppress an increase in the viscosity of the epoxy resin composition and a decrease in the Tg of the cured epoxy resin.

However, in order to obtain a sufficient toughness improvement effect, it is necessary to incorporate a large amount of core-shell rubber particles, which not only increases the viscosity but also reduces the elastic modulus of the cured epoxy resin, which ultimately impairs the mechanical properties of the fiber-reinforced composite material. The problem of causing a decline still remained.

Therefore, there has been a need for an epoxy resin composition that has low viscosity, good impregnating properties into fibers, and even better Tg, elastic modulus, and instant curing properties.

Japanese Patent Application Publication No. 2010-163573 International Publication No. 2016/148175 International Publication No. 2020/022950 Japanese Patent Application Publication No. 5-65391

The present invention provides an epoxy resin composition that maintains impregnability into carbon fibers and instant curing properties, and has excellent mechanical properties of molded products.

（ただし、ｎは０以上４以下の整数、Ｒｍは０～４個の置換基でありそれぞれ独立して水素原子、炭素数４以下の脂肪族炭化水素基のいずれかを表す） That is, the present invention includes an epoxy resin (A), an aromatic epoxy resin (B), an alicyclic amine (C), and a core shell rubber (D) as essential components, and the aromatic epoxy resin (B) has the general formula ( This is an epoxy resin composition having the structure represented by 1) and having a viscosity of 100 to 5000 mPa·s at 25°C.

(However, n is an integer of 0 to 4, and Rm is 0 to 4 substituents, each independently representing either a hydrogen atom or an aliphatic hydrocarbon group having 4 or less carbon atoms)

Another aspect of the present invention is a fiber-reinforced composite material, characterized in that the epoxy resin composition is blended with reinforcing fibers. The volume content of reinforcing fibers is preferably 30 to 75%.

The epoxy resin composition of the present invention has a low viscosity and good impregnating properties into fibers, is instantly curable, and the resulting cured product exhibits excellent heat resistance and mechanical properties.

Embodiments of the present invention will be described in detail below.
The epoxy resin composition of the present invention includes an epoxy resin (A), an aromatic epoxy resin (B), an alicyclic amine (C), and a core-shell rubber (D) as essential components. Hereinafter, epoxy resin (A), aromatic epoxy resin (B), alicyclic amine (C), and core shell rubber (D) will be described as (A) component, (B) component, (C) component, and (D), respectively. Also called ingredients.

The amount of the epoxy resin (A) used in the present invention is 45 to 85 parts by weight, preferably 45 to 80 parts by weight, more preferably 55 to 80 parts by weight, out of the total of 100 parts by weight of components (A) to (D). It is 75 parts by mass.
Examples of the epoxy resin (A) include bisphenol A type epoxy resin having two epoxy groups in one molecule, bisphenol F type epoxy resin, bisphenol E type epoxy resin, bisphenol S type epoxy resin, bisphenol Z type epoxy resin, and isophorone bisphenol. Bisphenol-type epoxy resins such as type epoxy resins, halogen- and alkyl-substituted products, hydrogenated products of these bisphenol-type epoxy resins, high molecular weight products having multiple repeating units not limited to monomers, and glycidyl ethers of alkylene oxide adducts. and novolac type epoxy resins such as phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, and 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexane. Alicyclic epoxy resins such as carboxylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 1-epoxyethyl-3,4-epoxycyclohexane, trimethylolpropane polyglycidyl ether, penta Aliphatic epoxy resins such as erythritol polyglycidyl ether and polyoxyalkylene diglycidyl ether, glycidyl esters such as phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, and dimer acid glycidyl ester, tetraglycidyldiaminodiphenylmethane, and tetraglycidyl ester. Glycidyl amines such as glycidyl diaminodiphenylsulfone, triglycidylaminophenol, triglycidylamino cresol, and tetraglycidyl xylylene diamine can be used. These may be used alone or in combination of two or more.
Preferred are liquid bisphenol epoxy resins such as bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol E epoxy resin, bisphenol S epoxy resin, and bisphenol Z epoxy resin.

The epoxy equivalent of the epoxy resin (A) is preferably 130 to 220 g/eq. More preferably 140 to 200 g/eq. It is.
The epoxy resin (A) is desirably liquid and has a viscosity at 25°C of preferably 1,000 to 20,000 mPa·s, more preferably 1,000 to 15,000 mPa·s.

（ただし、ｎは０以上４以下の整数、Ｒｍは０～４個の置換基でありそれぞれ独立して水素原子、炭素数４以下の脂肪族炭化水素基のいずれかを表す）
具体的には、グリシジルエーテル基が、２つのベンゼン環ユニットをつなぐ脂肪族鎖の両端のエーテル酸素原子に対し、どの位置（オルト位、メタ位、パラ位）でベンゼン環に結合するかによって、オルト位にグリシジルエーテル基を有するカテコール型、メタ位にグリシジルエーテル基を有するレゾルシノール型、パラ位にグリシジルエーテル基を有するヒドロキノン型の異性体が挙げられる。
二量体（ｎ＝１）でも、分子鎖の屈曲性を利用した硬化物の自由体積減少による弾性率向上効果の観点から、カテコール型、レゾルシノール型が好ましい。また、二量体ではユニット間連結部分に水酸基を有するため、分子鎖間相互作用が強く、硬化物の弾性率向上のためには、より好ましい。
さらに、それぞれのユニットの芳香環の置換基Ｒｍについて、水素原子または脂肪族炭化水素基いずれかであるが、脂肪族炭化水素基の場合、他の成分との相溶性を保ち、高い機械特性を得るため炭素数４以下であり、より好ましくは炭素数２以下である。 The aromatic epoxy resin (B) is an epoxy resin represented by the general formula (1), and needs to have a viscosity of 100 to 5000 mPa·s at 25°C.

(However, n is an integer of 0 to 4, and Rm is 0 to 4 substituents, each independently representing either a hydrogen atom or an aliphatic hydrocarbon group having 4 or less carbon atoms)
Specifically, depending on where the glycidyl ether group is bonded to the benzene ring (ortho position, meta position, para position) with respect to the ether oxygen atoms at both ends of the aliphatic chain connecting the two benzene ring units, Examples include catechol type isomers having a glycidyl ether group at the ortho position, resorcinol type having a glycidyl ether group at the meta position, and hydroquinone type isomers having a glycidyl ether group at the para position.
Even in the dimer (n=1), catechol type and resorcinol type are preferable from the viewpoint of improving the elastic modulus by reducing the free volume of the cured product using the flexibility of the molecular chain. Further, since the dimer has a hydroxyl group in the connecting portion between the units, the interaction between molecular chains is strong, which is more preferable for improving the elastic modulus of the cured product.
Furthermore, the substituent Rm on the aromatic ring of each unit is either a hydrogen atom or an aliphatic hydrocarbon group, but in the case of an aliphatic hydrocarbon group, it maintains compatibility with other components and has high mechanical properties. The number of carbon atoms is 4 or less, more preferably 2 or less.

In the aromatic epoxy resin (B), n is preferably an integer of 0 or more and 4 or less, more preferably 0 or more and 3 or less. If n is 5 or more, the viscosity will increase significantly, so it is not suitable for this study.

The epoxy equivalent of the aromatic epoxy resin (B) is preferably 100 to 170 g/eq. , more preferably 110 to 150 g/eq. It is.
The aromatic epoxy resin (B) needs to have a viscosity of 100 to 5000 mPa·s at 25°C. It is preferably 100 to 1000 mPa·s, preferably 200 to 700 mPa·s.

The aromatic epoxy resin (B) can be obtained, for example, by the following manufacturing method. First, epichlorohydrin and isopropyl alcohol are dissolved in dihydroxybenzenes, heated, and an aqueous sodium hydroxide solution is added dropwise. Next, the saline solution is separated and removed, and excess epichlorohydrin, isopropyl alcohol, and water are distilled and recovered to obtain a crude resin. Further, this is dissolved in toluene, a basic aqueous solution is added, and the mixture is heated and stirred. Thereafter, salts and alkalis generated by water washing are removed by oil/water separation, and toluene can be distilled and recovered through dehydration and filtration.

The blending amount of the aromatic epoxy resin (B) used in the present invention is 5 to 30 parts by weight, preferably 5 to 25 parts by weight, more preferably The amount is 5 to 20 parts by mass.

The alicyclic amine (C) is a curing agent for epoxy resin, and those with low viscosity can be used. The viscosity at 25° C. is preferably 1 to 100 mPa·s, more preferably 3 to 50 mPa·s, and still more preferably 5 to 30 mPa·s.
Examples of the alicyclic amine (C) include 4,4'-methylenebiscyclohexylamine, diaminodicyclohexylmethane, bis(4-amino-3-methylcyclohexyl)methane, bis(aminomethyl)cyclohexane, isophoronediamine, Examples include norbornene dimethylamine, N-aminoethylpiperazine, and epoxy adducts of these cycloaliphatic amines.
Among these, 1,3-bis(aminomethyl)cyclohexane is preferred because it has high reactivity and low viscosity.

The active hydrogen equivalent ratio of the alicyclic amine (C) to the epoxy equivalent in the epoxy resin composition is 0.7 to 1.2, preferably 0.8 to 1.2, more preferably 0.8. ~1.1. If the active hydrogen equivalent ratio is lower than 0.7, the Tg of the cured product will decrease significantly, and if it is higher than 1.2, the heat resistance will be significantly impaired.

The core-shell rubber (D) is produced by graft polymerizing a shell component polymer different from the core component onto the surface of a particulate core component whose main component is a crosslinked rubbery polymer or elastomer. Part or all of the shell is coated with a shell component.

When a core-shell polymer is applied to the epoxy resin composition of the present invention, the average particle diameter of the core-shell polymer is preferably 1 to 500 nm in volume average particle diameter, more preferably 3 to 300 nm. Note that the volume average particle diameter can be measured using a Nanotrac particle size distribution analyzer (manufactured by Nikkiso Co., Ltd.). If the volume average particle size of the core-shell polymer used in the present invention is 1 nm or less, it is difficult to produce or it becomes extremely expensive and cannot be practically used, and if the volume average particle size is 500 nm or more, it is difficult to produce. In the prepreg manufacturing process, the reinforcing fibers are bundles of fibers with a diameter of about 1 μm, so this becomes like a net and is separated without passing through the core-shell polymer of the same size, which affects the dispersion state of the core-shell polymer. This is not preferable because it may result in non-uniformity.

The core shell rubber (D) is preferably blended in an amount of 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass, in 100 parts by mass of the epoxy resin composition. If the blending amount is 0.5 parts by mass or more, it is easy to obtain the fracture toughness required for the fiber-reinforced composite material after molding, and if the blending amount is 15 parts by mass or less, the resulting fiber-reinforced composite material Since the epoxy resin composition is prevented from increasing in viscosity and can be easily impregnated into reinforcing fibers, it is more suitable for fiber-reinforced composite materials.

The epoxy resin composition of the present invention may further contain other stabilizers, modifiers, etc. A preferred stabilizer is a boric acid compound represented by B(OR) ₃ (wherein R represents a hydrogen atom, an alkyl group, or an aryl group). The amount of the boric acid compound to be blended is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 3 parts by weight, based on 100 parts by weight of the entire resin composition. If the amount added is less than 0.01 parts by mass, stability during storage cannot be ensured, and if it exceeds 10 parts by mass, the effect of inhibiting the curing reaction becomes greater, leading to poor curing.

An antifoaming agent and a leveling agent can be added to the epoxy resin composition of the present invention as additives for the purpose of improving surface smoothness. These additives can be blended in an amount of preferably 0.01 to 3 parts by weight, more preferably 0.01 to 1 part by weight, based on 100 parts by weight of the entire resin composition. If the amount is less than 0.01 parts by mass, the effect of smoothing the surface will not be exhibited, and if it exceeds 3 parts by mass, the additive will bleed out on the surface, which will conversely become a factor that impairs the smoothness.

Other curable resins can also be blended into the epoxy resin composition of the present invention. Such curable resins include 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, Examples include, but are not limited to, curable epoxy/oxetane composite resins.

In the epoxy resin composition of the present invention, the components (A), (B) and (D) excluding the alicyclic amine (C) preferably have a viscosity of 1 at 25°C as measured using an E-type viscometer. ~80 Pa·s, more preferably 1 – 50 Pa·s, particularly preferably 1 – 10 Pa·s. If the viscosity is too high, impregnation into carbon fibers will deteriorate, and if the viscosity is too low, the resin will flow and the RC of the cured product will be low, making it impossible to exhibit sufficient performance.

The reinforcing fibers used in the epoxy resin composition of the present invention are selected from glass fibers, aramid fibers, carbon fibers, boron fibers, etc., but carbon fibers are used to obtain a fiber-reinforced composite material with excellent strength. is preferable.

In the molded article composed of the epoxy resin composition of the present invention and reinforcing fibers, the volume content of the reinforcing fibers is preferably 30 to 75%, more preferably 45 to 75%, and within this range, voids are reduced. Since a molded article with a small amount of reinforcing fibers and a high volume content of reinforcing fibers can be obtained, a molding material with excellent strength can be obtained.

The epoxy resin composition of the present invention can be heated at any temperature of 80 to 180°C for any time in the range of 20 minutes to 1 hour to advance the crosslinking reaction and obtain a cured product. The heating conditions may be one step or may be multistep conditions combining a plurality of heating conditions. Especially when assuming a high-pressure container filled with hydrogen gas, etc. used in fuel cells, heat curing can be performed at any temperature in the range of 80 to 150°C and for any time in the range of 20 minutes to 1 hour. By doing so, desired physical properties of the cured product can be obtained.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples. The following resin raw materials were used to obtain the resin compositions of each example.

(A) Epoxy resin/liquid bisphenol F type epoxy resin: YDF-170 (manufactured by Nippon Steel Chemical & Materials Co., Ltd.) Epoxy equivalent: 160 to 180 g/eq. , viscosity 3000mPa・s
・Liquid bisphenol A type epoxy resin: YD-128 (manufactured by Nippon Steel Chemical & Materials Co., Ltd.) Epoxy equivalent: 184 to 194 g/eq. , viscosity 13000mPa・s
(B) Aromatic epoxy resin/resorcinol diglycidyl ether: DE-703 (Kokuto Kagaku Co., Ltd.) Epoxy equivalent 115 to 135 g/eq. , viscosity 360mPa・s
(B') Comparative epoxy resin/trimethylolpropane triglycidyl ether: YH-300 (Nippon Steel Chemical & Materials Co., Ltd.) Epoxy equivalent 140 to 155 g/eq. , viscosity 145mPa・s
(C) Alicyclic amine/1,3-bis(aminomethyl) cyclohexane: 1,3-BAC (manufactured by Mitsubishi Gas Chemical) Viscosity 9 mPa・s
・Norbornene diamine: NBDA (Mitsui Fine Co., Ltd.) Viscosity 20 mPa・s
(D) Core shell rubber (CSR)
・Master batch "MX-154" in which core shell rubber (CSR) is dispersed in bisphenol A type epoxy resin: core shell rubber (CSR) content 40 wt%, BPA type epoxy resin content 60 wt%, average particle size 200 nm (Co., Ltd.) (Manufactured by Kaneka) Viscosity 30000mPa・s (50℃)

The measurement method is shown below.
(1) Epoxy equivalent:
It was measured in accordance with the JIS K 7236 standard. Specifically, a potentiometric titration device was used, tetrahydrofuran was used as a solvent, a brominated tetraethylammonium acetic acid solution was added, and a 0.1 mol/L perchloric acid-acetic acid solution was used.
(2) Viscosity:
Conforms to JISK7117-1. Specifically, the viscosity at 25° C. of the pre-cured resin composition excluding the aliphatic amine as a curing agent was measured using an E-type viscometer.
(3) Gel time: Using a rheometer MCR-102 made by Anton Paar, time-dispersive measurements were performed in vibration mode at a temperature of 90°C, a strain of 0.1%, and a frequency of 1 Hz, and the storage modulus G' and loss modulus G were measured. "The time of intersection was defined as gel time.
(3) Glass transition temperature (Tg):
The temperature was expressed as the temperature of the DSC extrapolated value when the measurement was performed using a differential scanning calorimeter (EXSTAR6000 DSC6200 manufactured by SII Nanotechnology Co., Ltd.) at a temperature increase of 20° C./min.
(4) Fracture toughness (K1c):
According to ASTM E399. Specifically, a test piece with a width of 10 mm, a thickness of 2 mm, and a length of 50 mm was prepared and measured at a room temperature of 23° C. and a crosshead speed of 0.5 mm/min.
(5) Tensile modulus, tensile strength, tensile elongation:
Conforms to JIS K7161. Specifically, a universal material testing machine (Autograph AGS-H manufactured by Shimadzu Science Co., Ltd.) was used. At room temperature, a dumbbell test piece with dimensions of 215 mm in total length including the gripping part, 10 mm in width, and 2 mm in thickness was held at a chuck distance of 114 mm and a speed of 50 mm/min. A tensile test was conducted, and the tensile strength, tensile modulus, and tensile elongation were determined from the stress-strain diagram obtained.

Examples 1 to 3, Comparative Examples 1 to 5
(1) Preparation of epoxy resin composition Put epoxy resin (A), aromatic epoxy resin (B), and core shell rubber (D) in a container in the proportions shown in Table 1, and add them to a THINKY PLANETARY VACUUM MIXER (manufactured by THINKY Co., Ltd.). ) for 2 minutes at 2000 rpm and 4.0 mmhg. Thereafter, alicyclic amine (C) was added and kneaded for 20 seconds at 2000 rpm and 4.0 mmhg to prepare an epoxy resin composition having the composition shown in Table 1.
(2) Preparation of test piece The epoxy resin composition prepared in (1) above was injected into a mold heated to 90°C, heated in an oven at 90°C for 8 minutes, and then heated to 150°C. It was cured in an oven for 20 minutes to produce a plate-shaped cured resin product with a thickness of 2 mm. Next, the obtained plate-shaped cured resin material was cut out and used for test analysis. The results are shown in Table 1.

Claims (9)

Epoxy resin (A), aromatic epoxy resin (B), alicyclic amine (C), and core shell rubber (D) are essential components, and aromatic epoxy resin (B) is represented by the following general formula (1). An epoxy resin composition having a structure having a viscosity of 100 to 5000 mPa·s at 25°C.

(However, n is an integer of 0 to 4, and Rm is 0 to 4 substituents, each independently representing either a hydrogen atom or an aliphatic hydrocarbon group having 4 or less carbon atoms) The epoxy resin composition according to claim 1, wherein the active hydrogen equivalent ratio of the alicyclic amine (C) is in the range of 0.7 to 1.2 with respect to the epoxy equivalent in the epoxy resin composition. The epoxy resin composition according to claim 1, wherein the resin composition excluding the alicyclic amine (C) has a viscosity of 5 to 80 Pa·s at 25°C. The epoxy resin composition according to claim 1, wherein the aromatic epoxy resin (B) represented by general formula (1) is resorcinol diglycidyl ether. The epoxy resin composition according to claim 1, wherein the aromatic epoxy resin (B) represented by general formula (1) is catechol diglycidyl ether. The epoxy resin composition according to claim 1, which has a fracture toughness of 1.3 or more, a glass transition temperature of 130° C. or more, and a tensile modulus of 2 GPa or more. A fiber-reinforced composite material, characterized in that the epoxy resin composition according to claim 1 is blended with reinforcing fibers. The fiber reinforced composite material according to claim 7, wherein the volume content of the reinforcing fibers is 30 to 75%. A molded article obtained by curing the fiber reinforced composite material according to claim 7.