JP7537162B2 - Epoxy resin composition, prepreg and fiber-reinforced composite material - Google Patents

Description

The present invention relates to an epoxy resin composition that is preferably used as a matrix resin for fiber-reinforced composite materials suitable for sports, aerospace, and general industrial applications, as well as to a substrate and a fiber-reinforced composite material that use the same as a matrix resin.

Taking advantage of their excellent mechanical properties, heat resistance and adhesiveness, epoxy resins are preferably used as matrix resins in fiber-reinforced composite materials in which they are combined with reinforcing fibers such as carbon fibers, glass fibers and aramid fibers.

In the manufacture of fiber-reinforced composite materials, a sheet-shaped intermediate substrate (prepreg) made of reinforcing fibers impregnated with epoxy resin is commonly used. After laminating the prepregs, molded products are obtained by heating to harden the epoxy resin. Because a wide variety of properties can be achieved by varying the lamination design of the prepregs, they are used in a variety of fields, including aircraft and sports. In recent years, they have also been increasingly used in industrial applications, such as in automobiles.

Molded products using prepregs are required to have excellent mechanical properties. In particular, in applications requiring tensile strength and rigidity, such as sports equipment such as bicycles and tennis rackets, and structural components of automobiles, there is a high demand for deformation ability and impact resistance. In addition, in transportation equipment used in various environments, such as aircraft and automobiles, resistance to water absorption and deterioration is also required. Furthermore, current prepregs usually require freezing for storage, and prepregs that are easier to store and handle are required, and there is also a high demand for storage stability of epoxy resins. The types of curing agents that can be used with current prepregs are limited from the viewpoint of storage stability, and dicyandiamide and diaminodiphenyl sulfone are commonly used. In response to this, improvement technologies that focus on the chemical structure of curing agents that can be applied to prepregs have been attracting attention in recent years in order to meet the demand for improved performance.

Patent Document 1 discloses a technology that improves the storage stability of an epoxy resin composition by using 4,4'-dimethyl-3,3'-diaminodiphenyl sulfone as a curing agent.

Patent Document 2 discloses a technology that uses 2,2'-diaminodiphenyl sulfone as a curing agent to improve the flexural modulus of a cured epoxy resin and the storage stability of an epoxy resin composition.

Patent Document 3 discloses a technology that uses 3,3'-diamino-4,4'-difluorobenzophenone to improve the moldability and adhesion of polyimide.

JP 2012-153746 A International Publication No. 2018/021146 Japanese Patent Application Publication No. 5-194736

However, the epoxy resin composition disclosed in Patent Document 1 did not provide sufficient deformation ability, fracture toughness, water resistance, and storage stability for the cured resin.

The epoxy resin composition disclosed in Patent Document 2 has excellent storage stability, but the deformation ability, fracture toughness, and water resistance of the cured resin are not sufficient.

Patent Document 3 discloses a polyimide using 3,3'-diamino-4,4'-difluorobenzophenone, but makes no mention of the effects of combining it with an epoxy resin composition or its application to fiber-reinforced composite materials.

In light of the above, there is a demand for an epoxy resin composition that has high levels of deformation ability, fracture toughness, and water resistance of the cured product, as well as good storage stability.

As a result of intensive research aimed at solving the above problems, the inventors of the present invention discovered an epoxy resin composition having the following composition, and completed the present invention. That is, the present invention has the following composition.

1) An epoxy resin composition comprising an epoxy resin [A] and a curing agent [B] represented by chemical formula [I], and satisfying conditions [a] to [c].

(Note that R ₁ to R ₁₀ are either an amino group, an alkyl group, a halogen atom, or a hydrogen atom, and each aromatic ring contains one amino group and one halogen atom.)
[a]: The bending strain at break of the cured resin obtained by curing the epoxy resin composition at 180° C. for 120 minutes is 7.0% or more.

[b]: The epoxy resin composition is cured at 180°C for 120 minutes, and the cured resin has a water absorption rate of 3.0% or less when immersed in hot water at 98°C for 48 hours.

[c]: The change in Tg of the epoxy resin composition after storage at 40°C and 75% RH for 14 days is less than 10°C.

2) The epoxy resin composition according to 1), in which the curing agent [B] is a curing agent [B1] in which the halogen atom is a fluorine atom.

3) An epoxy resin composition according to either 1) or 2), in which the number of moles of active hydrogen in the curing agent [B]/the number of moles of active groups in all epoxy resins in the epoxy resin composition is 1.0 or more and 1.2 or less.

4) A prepreg consisting of the epoxy resin composition described in any one of 1) to 3) and reinforcing fibers.

5) A fiber-reinforced composite material obtained by curing the prepreg described in 4).

By using the epoxy resin composition described in the present invention, it is possible to provide prepregs and fiber-reinforced composite materials that are excellent in mechanical properties, fracture toughness, water resistance, and storage stability.

The epoxy resin composition of the present invention contains the following essential components: [A]: epoxy resin; [B]: curing agent represented by chemical formula [I]. First, these components will be described.

(Epoxy resin [A])
The epoxy base resin contained in the epoxy resin composition of the present invention is not particularly limited, and can be bisphenol A type, bisphenol F type, bisphenol S type, phenol novolac type, cresol novolac type, dicyclopentadiene type, biphenyl novolac type, naphthalene novolac type, amine type, isocyanuric acid type, etc. epoxy resins having a fluorene skeleton, monofunctional epoxy resins, etc. Among them, from the viewpoint of increasing bending fracture strain, bisphenol A type, bisphenol F type, phenol novolac type, cresol novolac type, dicyclopentadiene type, biphenyl novolac type, and naphthalene novolac type epoxy resins are preferably used.

Commercially available bisphenol A type epoxy resins include jER (registered trademark) 825, 827, 828, 828EL, 828US, 828XA, 801N, 801PN, 802, 811, 813, 816A, 819, 1001, 1002, 1003, 1003F, 1004, 1004F, 1004AF, 1004FS, 1005F, 1006FS, 1007, 1007FS, 1009, 1009F, and 1010 (manufactured by Mitsubishi Chemical Corporation), and EPICLON (registered trademark) Examples include "840, 840-S, 850, 850-S, EXA-850CRP, 850-LC, 860, 2050, 3050, 4050, and 7050 (manufactured by DIC Corporation), "Epotohto (registered trademark)" YD-115, YD-115CA, YD-127, YD-128, YD-128G, YD-128S, YD-128CA, and YD-134 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and DER330, DER331, DER332, and DER383 (manufactured by The Dow Chemical Company).

Commercially available bisphenol F type epoxy resins include jER (registered trademark) 806, 806H, 807, 4005P, 4007P, and 4010P (manufactured by Mitsubishi Chemical Corporation), EPICLON (registered trademark) 830, 830-S, 835, EXA-830CRP, EXA-830LVP, and EXA-835LV (manufactured by DIC Corporation), Epotohto (registered trademark) YDF-170, YDF-170N, YDF-2001, YDF-2004, and YDF-2005RD (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and DER354 (manufactured by The Dow Chemical Company).

Commercially available products of the phenol novolac type epoxy resin include "jER (registered trademark)" 152, 154 (manufactured by Mitsubishi Chemical Corporation), "EPICLON (registered trademark)" N-730A, N-740, N-770, N-775 (manufactured by DIC Corporation), "Epotec (registered trademark)" YDPN-638 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), DEN431, DEN438, DEN439 (manufactured by The Dow Chemical Company), PY307-1, EPN1179, EPN1180 (manufactured by Huntsman Advanced Materials), EPPN-201, EPPN-201-55, EPPN-201-80 (manufactured by Nippon Kayaku Co., Ltd.), etc.

Commercially available cresol novolac epoxy resins include EPICLON (registered trademark) N-660, N-665, N-670, N-673, N-680, N-690, and N-695 (manufactured by DIC Corporation), Epotec (registered trademark) YDCN-700-3, YDCN-700-7, YDCN-700-10, YDCN-704, and YDCN-704A (manufactured by Nippon Steel Chemical & Material Co., Ltd.), ECN1273, ECN1280, ECN1285, ECN1299, and ECN9511 (manufactured by Huntsman Advanced Materials), and EOCN-1020, EOCN-102S, EOCN-103S, and EOCN-104S (manufactured by Nippon Kayaku Co., Ltd.).

Commercially available dicyclopentadiene type epoxy resins include "EPICLON (registered trademark)" HP-7200-L, HP-7200, HP-7200-H, HP-7200-HH, HP-7200-HHH (manufactured by DIC Corporation), and XD-1000 (manufactured by Nippon Kayaku Co., Ltd.).

Commercially available biphenyl novolac epoxy resins include NC-3000, NC-3000-L, NC-3000-H, and NC-3100 (manufactured by Nippon Kayaku Co., Ltd.).

Commercially available products of the naphthalene novolac type epoxy resin include NC-7000-L and NC-7300-L (manufactured by Nippon Kayaku Co., Ltd.).

(Curing agent [B])
The epoxy resin composition of the present invention contains a curing agent [B].

The curing agent [B] in the present invention is a compound represented by the chemical formula [I].

(wherein R ₁ to R ₁₀ are either an amino group, an alkyl group, a halogen atom, or a hydrogen atom, and each aromatic ring contains one amino group and one halogen atom).

From the viewpoint of increasing fracture toughness, the curing agent [B] is preferably a curing agent [B1] in which the halogen atom is a fluorine atom. The compound represented by the chemical formula [I] may be used alone or in combination with other curing agents as long as the effect of the present invention is not lost.

Here, the resin toughness value of the cured resin can be evaluated, for example, by the KIc value obtained from the SENB test described in ASTM D5045-99.

The epoxy resin composition of the present invention satisfies the following condition [a].

[a]: The bending break strain of the cured resin obtained by curing the epoxy resin composition at 180°C for 120 minutes is 7.0% or more.

Here, the deformation ability of the cured resin can be evaluated by the breaking strain in a three-point bending test according to the JIS K7171 (1994) standard.

When the epoxy resin composition of the present invention satisfies condition [a], a fiber-reinforced composite material with excellent strength is obtained. From the viewpoint of the balance with the flexural modulus and toughness, the flexural break strain is preferably 7.0% to 25.0%.

The epoxy resin composition of the present invention also satisfies the following condition [b].

[b]: The epoxy resin composition is cured at 180°C for 120 minutes, and the cured resin has a water absorption rate of 3.0% or less when immersed in hot water at 98°C for 2 days.

When the epoxy resin composition of the present invention satisfies condition [b], that is, when the water absorption rate of the cured resin is less than 3.0%, a fiber-reinforced composite material with excellent water resistance is obtained. The smaller the water absorption rate of the cured resin, the more preferable it is, but in reality, the lower limit is 1.0%.

The water absorption rate of the cured resin can be evaluated, for example, by tracking the change in mass of the cured resin. Specifically, a test piece cut to a specified size from the cured resin is dried, and then immersed in water for a specified period of time in a thermostatic water bath or the like, and the change in mass before and after immersion is tracked to determine the water absorption rate.

The epoxy resin composition of the present invention satisfies the following condition [c].

[c]: The change in Tg of the epoxy resin composition after storage at 40°C and 75% RH for 14 days is less than 10°C.

When the epoxy resin composition of the present invention satisfies condition [c], that is, when the change in Tg when stored for 14 days at 40°C and 75% RH is less than 10°C, the prepreg made of the epoxy resin composition exhibits excellent storage stability even at room temperature. On the other hand, when the change in Tg is 10°C or more, the tack of the prepreg changes significantly when stored at room temperature, and storage in a precise temperature and humidity environment is required. Note that the smaller the change in Tg when stored for 14 days at 40°C and 75% RH, the more preferable, and 0°C is more preferable.

The storage stability of the epoxy resin composition of the present invention, i.e., whether or not it satisfies condition [c], can be evaluated, for example, by tracking the change in Tg using differential scanning calorimetry (DSC). Specifically, the epoxy resin composition prepared by the above method can be stored for a predetermined period of time in a thermo-hygrostat or the like, and the change in Tg before and after storage can be measured using DSC to determine the storage stability.

The epoxy resin composition of the present invention may contain a thermoplastic resin for the purpose of improving mechanical properties and toughness, adjusting viscoelasticity, improving the tack and drape properties of the prepreg, etc., within the scope of the present invention. As the thermoplastic resin, a thermoplastic resin soluble in the epoxy resin, or organic particles such as rubber particles and thermoplastic resin particles can be selected.

Thermoplastic resins that are soluble in epoxy resins include polyacetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, phenoxy resins, polyamides, polyimides, polyvinylpyrrolidone, and polysulfones.

Examples of rubber particles include crosslinked rubber particles and core-shell rubber particles in which a different polymer is graft-polymerized onto the surface of crosslinked rubber particles.

The epoxy resin composition of the present invention contains a curing agent [B], so that the cured resin exhibits excellent deformation ability, fracture toughness, and water resistance, and the epoxy resin composition exhibits storage stability. These characteristics are believed to be due to the planarity of the benzophenone skeleton and the properties of the halogen atoms.

From the viewpoint of enhancing the deformation ability of the resin cured product, the epoxy resin composition of the present invention preferably has the number of moles of active hydrogen in the curing agent [B]/the number of moles of active groups in all epoxy resins in the epoxy resin composition of 1.0 or more and 1.2 or less.

Here, the number of moles of active groups in all epoxy resins in an epoxy resin composition is the sum of the number of moles of active groups in each epoxy resin, and is calculated by the following formula.
Number of moles of active groups in all epoxy resins in an epoxy resin composition=mass of epoxy resin [A]/epoxy equivalent of epoxy resin [A].

The number of moles of active hydrogen in the curing agent [B] is calculated by the following formula.
Number of moles of active hydrogen in curing agent [B] = mass of curing agent [B] / active hydrogen equivalent of curing agent [B].

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

When preparing a fiber-reinforced composite material using the epoxy resin composition of the present invention, it is preferable to prepare a prepreg consisting of the epoxy resin composition of the present invention and reinforcing fibers in advance. The prepreg is a material form in which the fiber arrangement and the resin ratio can be precisely controlled, and the properties of the composite material can be maximized. The prepreg can be obtained by impregnating a reinforcing fiber substrate with the epoxy resin composition of the present invention. Examples of the impregnation method include the hot melt method (dry method). The hot melt method is a method in which the epoxy resin composition, which has been reduced in viscosity by heating, is directly impregnated into the reinforcing fibers, or a film coated with the epoxy resin composition is prepared on release paper or the like, and then the film is placed on both sides or one side of the reinforcing fibers, and the reinforcing fibers are impregnated with the resin by heating and pressurizing.

Methods for molding the laminated prepregs include press molding, autoclave molding, bagging molding, wrapping tape method, and internal pressure molding, as appropriate.

Next, the fiber-reinforced composite material will be described. The fiber-reinforced composite material of the present invention is obtained by curing the prepreg of the present invention. More specifically, a fiber-reinforced composite material containing the cured resin product of the epoxy resin composition of the present invention as a matrix resin can be obtained by laminating prepregs made of the epoxy resin composition of the present invention and then heating and curing them.

The reinforcing fibers used in the present invention are not particularly limited, and examples include glass fibers, carbon fibers, aramid fibers, boron fibers, alumina fibers, and silicon carbide fibers. Two or more of these fibers may be mixed together. From the viewpoint of obtaining a lightweight and highly rigid fiber-reinforced composite material, it is preferable to use carbon fibers.

The resin cured product of the epoxy resin composition of the present invention and a fiber-reinforced composite material containing reinforcing fibers are preferably used in sports, aerospace, and general industrial applications. More specifically, in sports applications, they are preferably used for golf shafts, fishing rods, tennis and badminton rackets, hockey sticks, and ski poles. In aerospace applications, they are preferably used for primary aircraft structural materials such as main wings, tails, and floor beams, and secondary structural materials such as interior materials. In general industrial applications, they are preferably used for structural materials for automobiles, bicycles, ships, and railroad cars.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the description of these examples.

The components used in this example are as follows:

<Materials used>
Component [A]: Epoxy resin [A]-1 "jER (registered trademark)" 828 (liquid bisphenol A type epoxy resin, average epoxy equivalent: 189 g/eq, manufactured by Mitsubishi Chemical Corporation),
[A]-2 "jER (registered trademark)" 1001 (solid bisphenol A type epoxy resin, average epoxy equivalent: 475 g/eq, manufactured by Mitsubishi Chemical Corporation),
[A]-3 "EPICLON (registered trademark)" 830 (liquid bisphenol F type epoxy resin, average epoxy equivalent: 172 g/eq, manufactured by DIC Corporation),
[A]-4 "Epotohto (registered trademark)" YDF-2001 (solid bisphenol F type epoxy resin, average epoxy equivalent: 485 g/eq, manufactured by Nippon Steel Chemical & Materials Co., Ltd.),
[A]-5 “EPICLON (registered trademark)” N-740 (phenol novolac type epoxy resin, average epoxy equivalent: 182 g/eq, average number of functional groups: 3.6/molecule, manufactured by DIC Corporation),
[A]-6 “EPICLON (registered trademark)” N-695 (cresol novolac type epoxy resin, average epoxy equivalent: 215 g/eq, average number of functional groups: 7.6/molecule, manufactured by DIC Corporation),
[A]-7 NC-3000-L (biphenylaralkyl type epoxy resin, average epoxy equivalent: 272 g/eq, average number of functional groups: 2.0/molecule, manufactured by Nippon Kayaku Co., Ltd.),
[A]-8 NC-7300-L (naphthalene novolac type epoxy resin, average epoxy equivalent: 214 g/eq, average number of functional groups: 3.8/molecule, manufactured by Nippon Kayaku Co., Ltd.),
[A]-9 "EPICLON (registered trademark)" HP-7200-H (dicyclopentadiene type epoxy resin, average epoxy equivalent: 278 g/eq, average number of functional groups: 3.0/molecule, manufactured by DIC Corporation),
[A]-10 "Sumiepoxy (registered trademark)" ELM434 (diaminodiphenylmethane type epoxy resin, average epoxy equivalent: 120 g/eq, manufactured by Sumitomo Chemical Co., Ltd.).

Component [B]: Curing agent represented by chemical formula [I]: [B]-1 3,3'-diamino-4,4'-difluorobenzophenone [B]-2 3,3'-diamino-4,4'-dichlorobenzophenone Curing agent [B]-1 was prepared by the method described below.

[First step] Method for producing 3,3'-dinitro-4,4'-difluorobenzophenone 4,4'-difluorobenzophenone (6.0 kg, 27.3 mol) was dissolved in concentrated sulfuric acid (14.7 L) and cooled to 0°C. The temperature of the reaction solution was kept at 7°C, and concentrated nitric acid (3.4 L) was added dropwise over 1 hour, followed by stirring at room temperature overnight. The reaction solution was then cooled to 6°C, and ice (32.0 kg) was added over 2 hours while maintaining the temperature at 15°C or lower. The precipitated solid was collected by filtration, and the residue was washed with water (23.9 L) and 50% methanol (10.9 L). The obtained solid was dried under reduced pressure at 50°C to obtain 8.2 kg of 3,3'-dinitro-4,4'-difluorobenzophenone.

[Second step] Method for producing 3,3'-diamino-4,4'-difluorobenzophenone At room temperature, 3,3'-dinitro-4,4'-fluorodiaminobenzophenone (3.0 kg, 9.7 mol) was dissolved in ethanol (17.1 L), and then ammonium chloride (2.87 kg, 53.6 mol) and water (8.6 L) were added and stirred until homogenous. Subsequently, iron powder (4.2 kg, 75 mol) was added in four portions, and the mixture was stirred at 70°C for 4 hours, and then cooled to 40°C. Thereafter, ethyl acetate (25.1 L) and water (8.8 L) were added to the reaction liquid, and the mixture was filtered with radiolight. The residue was washed with ethyl acetate (4.4 L) and 10% by mass saline (14.1 kg), and then dried with sodium sulfate (6.8 kg), and concentrated under reduced pressure at 60°C to precipitate a solid. The obtained solid was dissolved in ethyl acetate (8.6 L), and then amine silica gel (1.8 kg) was added and stirred for 1 hour. The mixture was filtered, washed, and dried at 60° C. under reduced pressure to obtain a crude product (2.2 kg).

[Third step] Purification method of 3,3'-diamino-4,4'-difluorobenzophenone The crude product was partially dissolved in isopropyl alcohol (4.3 L) at 80°C, and purified water (5.1 L) was added dropwise, and the mixture was stirred at 20°C for 1 hour, followed by washing with a 50% by mass aqueous isopropyl alcohol solution (5.0 L) and drying at 50°C to obtain a solid. Subsequently, the obtained solid was back-extracted with 2.0 mol/L hydrochloric acid, neutralized with an aqueous sodium hydroxide solution, and filtered and washed to obtain 1.48 kg of 3,3'-diamino-4,4'-difluorobenzophenone.

Hardener [B]-2 was synthesized using 4,4'-dichlorobenzophenone as the raw material in the same manner as hardener [B]-1.

Component [C]: Other hardener [C]-1 3,3'-diaminobenzophenone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
[C]-2 "jER Cure (registered trademark)" DICY7 (dicyandiamide, manufactured by Mitsubishi Chemical Corporation)
[C]-3 2,2'-Diaminodiphenylsulfone Curing agent [C]-3 was prepared by the method described below.

[First step] Method for producing 2,2'-diaminodiphenyl sulfone At room temperature, 2,2'-diaminodiphenyl sulfide (1.1 kg, 5.1 mol) was dissolved in N,N-dimethylformamide (DMF) (10.1 L), potassium peroxymonosulfate (4.7 kg, 7.6 mol) was added, and the mixture was stirred at room temperature for 20 hours. Subsequently, water (22 L) and toluene (22 L) were added to the reaction solution, and the mixture was stirred for 30 minutes, and then the mixture was filtered through Celite, and the residue was washed with toluene (10 L). The filtrate was separated, and the aqueous layer was extracted with toluene (10 L). The obtained organic layer was washed with water (10 L), a saturated aqueous sodium thiosulfate solution (10 L), and saturated saline (10 L) in that order, and concentrated under reduced pressure to obtain a crude product.
[Second step] Purification method of 2,2'-diaminodiphenyl sulfone The obtained crude product was dissolved in ethanol (2.5 L), water (0.8 L) was added, and the precipitated solid was collected by filtration. The collected solid was then dissolved in ethyl acetate, silica gel (150 g) was added, and the mixture was stirred for 30 minutes, and then the mixture was filtered under reduced pressure on 150 g of silica gel, and the filtrate was concentrated to obtain a crude product. Furthermore, methanol (0.8 L) was added to the obtained crude product, and the mixture was stirred for 30 minutes, and the solid was collected by filtration and dried at 40°C under reduced pressure to obtain 2,2'-diaminodiphenyl sulfone (0.43 kg).

[C]-4 3,3'DAS (3,3'-diaminodiphenyl sulfone, manufactured by Mitsui Fine Chemicals, Inc.)
[C]-5 Seikacure-S (4,4'-diaminodiphenyl sulfone, manufactured by Seika Co., Ltd.)
[C]-6 4,4'-Dimethyl-3,3'-diaminodiphenylsulfone Curing agent [C]-6 was prepared by the method described below.

[First step] Manufacturing process of 4,4'-dimethyl-3,3'-dinitrodiphenylsulfone 4,4'-dimethyldiphenylsulfone (1.4 kg, 5.7 mol) was dissolved in concentrated sulfuric acid (2.3 L, 4.2 mol) and then cooled to 4°C. The temperature of the reaction solution was kept at 11°C, and concentrated nitric acid (0.76 L, 17.1 mol) was added dropwise over 4 hours, and the mixture was stirred at room temperature overnight. The reaction solution was then cooled to 6°C, and ice water (1.4 L) was added over 2 hours while maintaining the temperature at 15°C or less. The precipitated solid was collected by filtration, and the filtrate was washed with water. The obtained solid was dried under reduced pressure at 50°C to obtain 1.8 kg of a white solid. The obtained white solid was dissolved in chloroform (25 L), stirred, and then heptane (25 L) was added. After stirring for 30 minutes, the precipitated solid was collected by filtration. The filtered solid was dried under reduced pressure to obtain 1.6 kg of 4,4'-dimethyl-3,3'-dinitrodiphenyl sulfone.

[Second step] Manufacturing process of 4,4'-dimethyl-3,3'-diaminodiphenylsulfone 4,4'-dimethyl-3,3'-dinitrodiphenylsulfone (0.55 kg, 1.64 mol) was dissolved in methanol (5.0 L) and the system was replaced with argon gas. In a separate container, 5% palladium carbon (0.13 kg, 50% wet) was added to methanol (1.0 L) degassed with argon gas to prepare a suspension of palladium carbon, which was added to the methanol solution of 4,4'-dimethyl-3,3'-dinitrodiphenylsulfone, and then methanol (0.6 L) was added. Next, the reaction system was replaced with hydrogen gas and stirred for two days while replenishing hydrogen. After that, the reaction solution was filtered through Celite, and the filter cake was washed with methanol (13.0 L). The same operation was performed three times, and the methanol was distilled off under reduced pressure to obtain a solid (1.1 kg).

The resulting solid was suspended in ethyl acetate (6.4 L), stirred for 5 minutes, and then diluted with heptane (2
5.0 L) was added and stirred for 20 minutes. The precipitated solid was collected by filtration and dried under reduced pressure to obtain 4,4'-dimethyl-3,3'-diaminodiphenylsulfone (1.08 kg).

Component [D]: Other components [D]-1 DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Industry Co., Ltd.)
[D]-2 "Sumikaexcel (registered trademark)" PES5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.).

<Method for preparing epoxy resin composition>
Predetermined amounts of components other than the curing agent were placed in a stainless steel beaker, and the mixture was heated to 150° C. while being appropriately kneaded with a spatula to obtain a transparent viscous liquid. After the viscous liquid was cooled to 60° C., the curing agent was added and kneaded at 60° C. for 30 minutes to obtain an epoxy resin composition.

The method for preparing an epoxy resin composition using dicyandiamide as a curing agent is as follows. That is, a predetermined amount of [A]-1 ("jER (registered trademark)" 828) and [C]-2 ("jER Cure (registered trademark)" DICY7) were added to a polyethylene cup, and the mixture was passed twice between the rolls of a three-roll mill to prepare a dicyandiamide master. The viscous liquid prepared above was cooled to 60°C, and then the viscous liquid and the dicyandiamide master were kneaded until homogenous. After kneading, [D]-1 (DCMU99) was added, and the mixture was kneaded at 60°C for 30 minutes to obtain an epoxy resin composition.

<Method for evaluating bending fracture strain of cured epoxy resin>
The epoxy resin composition obtained in the <Preparation method of epoxy resin composition> was degassed in a vacuum, and then cast into a 2 mm thick mold sandwiching a 2 mm thick "Teflon (registered trademark)" spacer. After casting, the epoxy resin composition inside the mold was cured by heating at 180°C for 120 minutes to obtain a 2 mm thick cured resin. Six test pieces with a width of 10 mm and a length of 60 mm were cut out from the cured resin obtained, and a three-point bending test was performed using an Instron universal testing machine (Instron Corporation). After setting the span to 32 mm and the crosshead speed to 10 mm/min, the bending break strain was measured by performing a three-point bending test in accordance with the JIS K7171 (1994) standard. The average of the measured values of each sample was used as the measurement result of bending break strain.

<Method for evaluating fracture toughness of cured epoxy resin>
The epoxy resin composition obtained in <Preparation of epoxy resin composition> was degassed in a vacuum and then cast into a 6 mm thick mold with a 6 mm thick Teflon (registered trademark) spacer sandwiched therebetween. After casting, the epoxy resin composition inside the mold was cured by heating at 180°C for 120 minutes to obtain a 6 mm thick cured resin product. The obtained highly cured resin plate was processed into a test piece shape described in ASTM D5045-99, and then an SENB test was carried out according to ASTM D5045-99. At this time, the number of samples n=16 was used, and the average value was adopted as the KIc value.

<Method for evaluating water absorption of cured epoxy resin>
A resin cured product was prepared using the same method as in <Method for evaluating bending fracture strain of cured epoxy resin product>, and then a test piece with a width of 10 mm and a length of 60 mm was cut out and the initial mass W1 was measured. The obtained test piece was placed in a water tank and immersed in hot water at 98°C for 48 hours, after which the moisture adhering to the surface was removed and the mass W2 after immersion was measured. Based on the obtained values of W1 and W2, the water absorption was calculated according to the following formula:

Water absorption rate (%) = 100 x (W2-W1)/W1.

<Method for evaluating storage stability of epoxy resin composition>
The initial epoxy resin composition obtained in <Preparation method of epoxy resin composition> was weighed in an aluminum cup in an amount of 3 g, and then the glass transition temperature after standing in a thermo-hygrostat for 14 days under an environment of 40°C and 75% RH was defined as T1, and the initial glass transition temperature was defined as T0. The change in glass transition temperature was defined as ΔTg=T1-T0, and the storage stability was determined based on the value of ΔTg. The glass transition temperature was measured by weighing 3 mg of the epoxy resin after storage into a sample pan and raising the temperature from -20°C to 150°C at a rate of 5°C/min using a differential scanning calorimeter (Q-2000: manufactured by TA Instruments). The midpoint of the inflection points of the obtained heat generation curve was taken as Tg.

Example 1
An epoxy resin composition was prepared according to the above <Preparation method of epoxy resin composition> using 100 parts by mass of liquid bisphenol A type epoxy resin “jER (registered trademark)” 828 as component [A] and 32.9 parts by mass of 3,3′-diamino-4,4′-difluorobenzophenone as component [B].

The bending strain at break of this epoxy resin composition was measured according to the <Method for evaluating bending strain at break of epoxy resin cured product>, and the bending strain at break was 12.5%, which was a good value (condition [a]). The fracture toughness was measured according to the <Method for evaluating fracture toughness of epoxy resin cured product>, and the fracture toughness was 0.88 MPa·m ^1/2 , which was good. The water absorption was measured according to the <Method for evaluating water absorption of epoxy resin cured product>, and the water absorption was 2.9%, which was good (condition [b]). Finally, the ΔTg was measured according to the <Method for evaluating storage stability of epoxy resin composition>, and the ΔTg was 8.7° C., which was a good value (condition [c]).

(Examples 2 to 13)
Epoxy resin compositions and cured epoxy resin materials were prepared in the same manner as in Example 1, except that the resin compositions were changed as shown in Table 1.

The resin compositions obtained all had good bending strain at break, fracture toughness, water resistance, and storage stability when cured, similar to those in Example 1.

(Examples 14 to 16)
Epoxy resin compositions were prepared in the same manner as in Example 1, except that the resin compositions were changed as shown in Table 1.

Although the resin compositions obtained were inferior to those of Examples 1 to 13, the bending strain at break, fracture toughness, water resistance, and storage stability of the cured products were good.

(Comparative Example 1)
An epoxy resin composition and a cured epoxy resin material were prepared in the same manner as in Example 1, except that 3,3'-diaminobenzophenone was used instead of component [B]. The resin composition and the evaluation results are shown in Table 2. The bending strain at break and water absorption of the cured material were 11.4% and 2.9%, respectively, satisfying the conditions [a] and [b]. On the other hand, the ΔTg of the resin composition was 50.8°C, which did not satisfy the condition [c] and the storage stability was insufficient.

(Comparative Example 2)
An epoxy resin composition was prepared according to the above <Preparation method of epoxy resin composition> using 70 parts by mass of liquid bisphenol A type epoxy resin "jER (registered trademark)" 828 as component [A], 30 parts by mass of diaminodiphenylmethane type epoxy resin "Sumiepoxy (registered trademark)" ELM434 as component [A], 7.4 parts by mass of "jER Cure (registered trademark)" DICY7 as component [C], and 4.9 parts by mass of DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea) as component [D]. The resin composition and evaluation results are shown in Table 2. The bending strain at break of the cured product and ΔTg of the resin composition were 8.9% and 4.5°C, respectively, satisfying conditions [a] and [c]. However, the water absorption rate was 6.8%, which did not satisfy condition [b], and the water resistance was insufficient.

(Comparative Example 3)
An epoxy resin composition and a cured epoxy resin were prepared in the same manner as in Example 1, except that 2,2'-diaminodiphenylsulfone was used instead of the curing agent [B]. The resin composition and the evaluation results are shown in Table 2. The bending break strain of the cured product was 5.7%, which did not satisfy the condition [a], and the deformability of the cured product was insufficient. In addition, the water absorption rate was a high value of 4.0%, which did not satisfy the condition [b], and the water resistance was insufficient. The ΔTg of the resin composition was 1.7°C.

(Comparative Example 4)
An epoxy resin composition and a cured epoxy resin were prepared in the same manner as in Example 1, except that 3,3'-diaminodiphenylsulfone was used instead of the curing agent [B]. The resin composition and the evaluation results are shown in Table 2. The bending break strain of the cured product was 11.7%, satisfying the condition [a]. However, the water absorption and ΔTg were 3.5% and 39.6°C, respectively, which did not satisfy the conditions [b] and [c], and the water resistance and storage stability were insufficient.

(Comparative Example 5)
An epoxy resin composition and a cured epoxy resin product were prepared in the same manner as in Example 1, except that 4,4'-diaminodiphenylsulfone was used instead of the curing agent [B]. The resin composition and the evaluation results are shown in Table 2. The bending break strain of the cured product and the ΔTg of the resin composition were 8.4% and 5.9°C, respectively, satisfying the conditions [a] and [c]. However, the water absorption was 3.7%, which did not satisfy the condition [b], and the water resistance was insufficient.

(Comparative Example 6)
An epoxy resin composition and a cured epoxy resin product were prepared in the same manner as in Example 4, except that 4,4'-dimethyl-3,3'-diaminodiphenylsulfone was used instead of the curing agent [B]. The resin composition and the evaluation results are shown in Table 2. The bending break strain, water absorption and ΔTg of the cured product were 4.0%, 3.4% and 53.0°C, respectively, which did not satisfy any of the conditions [a] to [c], and the deformation ability, water resistance and storage stability of the cured product were insufficient.

Note that the units for each ingredient in the table are parts by mass.

Claims (6)

An epoxy resin composition comprising an epoxy resin [A] and a curing agent [B] represented by chemical formula [I], and satisfying conditions [a] to [c].

(Note that R ₁ to R ₁₀ are either an amino group, a halogen atom, or a hydrogen atom, and each aromatic ring contains one amino group and one halogen atom.)
[a]: The bending strain at break of the cured resin obtained by curing the epoxy resin composition at 180° C. for 120 minutes is 7.0% or more.
[b]: The epoxy resin composition is cured at 180° C. for 120 minutes, and the cured resin has a water absorption rate of 3.0% or less when immersed in hot water at 98° C. for 48 hours.
[c]: The change in Tg of the epoxy resin composition after storage at 40° C. and 75% RH for 14 days is less than 10° C. The epoxy resin composition according to claim 1, wherein the curing agent [B] is 3,3'-diamino-4,4'-difluorobenzophenone or 3,3'-diamino-4,4'-dichlorobenzophenone. The epoxy resin composition according to claim 1, wherein the curing agent [B] is a curing agent [B1] in which the halogen atom is a fluorine atom. A prepreg comprising the epoxy resin composition according to any one of claims 1 to 3 and reinforcing fibers. A fiber-reinforced composite material obtained by curing the prepreg according to claim 4 . An epoxy resin composition comprising an epoxy resin [A] and 3,3'-diamino-4,4'-difluorobenzophenone or 3,3'-diamino-4,4'-dichlorobenzophenone as a curing agent [B].