EPOXY RESIN COMPOSITION, CURED EPOXY RESIN PRODUCT, PREPREG, AND FIBER-REINFORCED COMPOSITE MATERIAL

Abstract

Provided are: an epoxy resin composition having exceptional performance with regard to impregnating reinforcing fibers, enabling optimal control of resin flow during molding, and having exceptional in-plane shear strength; a cured epoxy resin product; and a prepreg. An epoxy resin composition comprising at least the following constituent elements [A], [B], and [C]: [A] an epoxy resin, [B] a polyether sulfone having a weight-average molecular weight of 2000-20000 g/mol, [C] a curing agent

Claims

1. An epoxy resin composition comprising at least components [A], [B], and [C] listed below: [A] epoxy resin, [B] polyethersulfone having a weight-average molecular weight of 2,000 to 20,000 g/mol, and [C] curing agent.

2. An epoxy resin composition as set forth in claim 1, wherein the storage elastic modulus G′ and complex viscosity η* at 80° C. meets the relation 0.20≦G′/η*≦2.0.

3. An epoxy resin composition as set forth in either claim 1 , wherein component [B] accounts for 20 to 60 mass % of the epoxy resin composition.

4. An epoxy resin composition as set forth in claim 1, wherein the hydroxyphenyl group accounts for 60 mol % or more of the end groups in component [B].

5. An epoxy resin composition as set forth in claim 1, wherein component [A] contains polyfunctional amine type epoxy resin.

6. An epoxy resin composition as set forth in claim 1, wherein component [A] contains bifunctional amine type epoxy resin.

7. Cured epoxy resin produced by curing an epoxy resin composition as set forth in claim 1 and characterized by having either a 400 nm-or-less phase-separation structure or a uniform phase structure.

8. Prepreg produced by impregnating reinforcement fiber with an epoxy resin composition as set forth in claim 1.

9. Prepreg as set forth in claim 8, wherein the reinforcement fiber is carbon fiber.

10. Fiber reinforced composite material comprising either cured epoxy resin formed by curing an epoxy resin composition as set forth in claim 1 or cured epoxy resin as set forth in claim 7, and reinforcement fiber.

Description

EXAMPLES

[0076] The epoxy resin composition according to the present invention is described more specifically below with reference to Examples. Described first, below are the resin material preparation procedures and evaluation methods used in Examples.

[0077] <Epoxy Resin [A]>

[0078] <Polyfunctional Amine Type Epoxy Resin> [0079] SUMI-EPDXY (registered trademark) ELM434 (tetraglycidyl diaminodiphenyl methane, manufactured by Sumitomo Chemical Co., Ltd.) [0080] jER (registered trademark) 630 (triglycidyl aminophenol, manufactured by Mitsubishi Chemical Corporation) [0081] Araldite (registered trademark) MY0600 (triglycidyl aminophenol, manufactured by Huntsman Advanced Materials)

[0082] <Bifunctional Amine Type Epoxy Resin> [0083] GAN (diglycidyl aniline, manufactured by Nippon Kayaku Co., Ltd.) [0084] GOT (diglycidyl toluidine, manufactured by Nippon Kayaku Co., Ltd.)

[0085] <Epoxy Resins Other Than the Above> [0086] jER (registered trademark) 828 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation) [0087] EPICLON (registered trademark) 830 (bisphenol F type epoxy resin, manufactured by DIC) [0088] jER (registered trademark) 1004 (bisphenol F type epoxy resin, manufactured by Mitsubishi Chemical Corporation)) [0089] EPICLON (registered trademark) HP7200H (epoxy resin containing dicyclopentadiene backbone, manufactured by DIC)

[0090] <Polyethersulfone>

[0091] <Polyethersulfone [B] With a Weight-Average Molecular Weight of 2,000 to 20,000 g/mol> [0092] Polyethersulfone ([B]) synthesized by the following procedure (Method for production of [B]: based on Japanese Unexamined Patent Publication No. HEI-5-86186. A detailed procedure for the production is described in Reference example 1.)

Reference Example 1

[0093] In a L flask equipped with a stirrer, thermometer, cooler, distillate separator, and nitrogen supply tube, 4,4′-dihydroxy diphenyl sulfone (hereinafter abbreviated as DHDPS) (50.06 g, 0.20 moles), toluene (100 ml), 1,3-dimethyl-2-imidazolidinone (250.8 g), and 40% potassium hydroxide aqueous solution (56.0 g, 0.39 moles) were weighed out and, while stirring, nitrogen gas was supplied to achieve nitrogen substitution of the entire reaction system. Heating was performed up to 130° C. while supplying nitrogen gas. As the temperature of the reaction system rises, reflux of toluene was started to remove water from the reaction system through azeotropic distillation with toluene, and azeotropic dehydration was continued at 130° C. for 4 hours while recovering toluene back to the reaction system. Subsequently, 4,4′-dichlorodiphenyl sulfone (hereinafter abbreviated as DCDPS) (57.40 g, 0.20 moles) was added to the reaction system together with 40 g of toluene, and the reaction system was heated to 150° C. The reaction was continued for 4 hours while distilling out toluene to provide a high-viscosity, dark brown solution. The temperature of the reaction liquid was lowered by cooling to room temperature, and the reaction solution was poured into 1 kg of methanol to precipitate polymer powder. The polymer powder was recovered by filtration and 1 kg of water was added, followed by further adding 1 N hydrochloric acid and adding a slurry solution to adjust the pH value to 3 to 4 to make the solution acidic. After recovering the polymer powder by filtration, the polymer powder was washed twice with 1 kg of water. It was further washed with 1 kg of methanol and vacuum-dried at 150° C. for 12 hours. The polymer powder obtained was white powder and the yield weight was 88.3 g (yield rate 99.9% calculated from the following equation: yield rate =(92.8/464.53 (molecular weight of intermediate product for polyethersulfone component synthesis)/0.2×100).

[0094] Then, in a 300 mL three-neck flask equipped with a stirrer, nitrogen supply tube, thermometer, and cooling pipe, DHDPS (1.25 g, 4.35 mmol), N-methyl-2-pyrolidone (NMP) 200 ml, and anhydrous potassium carbonate (0.6 g, 4.34 mmol) were weighed with the intermediate product for polyethersulfone component synthesis (5 g, 10.7 mmol (calculated as 5/464.53×1,000), and the reaction temperature was increased to 150° C. while stirring the NMP reaction solution, followed by ending the reaction after a 1 hour reaction period, pouring the reaction solution into 500 ml of methanol, crushing the solid precipitate, washing it twice with 500 ml of water, and vacuum-drying it at 130° C. The polymer powder obtained was white powder, and the yield weight and yield rate were 7.2 g and 96%, respectively (yield rate was calculated as: weight of polyethersulfone, i.e. recovered polyethersulfone component/(feed weight of intermediate product for polyethersulfone component synthesis+feed weight of DHDPS)×100).

[0095] Component [B] is substantially identical to the polyethersulfone described in Japanese Unexamined Patent Publication No. HEI-5-86186 except that the weight-average molecular weight of the polyethersulfone disclosed in Japanese Unexamined Patent Publication No. HEI-5-86186 is larger than that of component [B]. Thus, polyethersulfone samples, referred to as B-1 to B-4, which differ in weight-average molecular weight and end group conversion rate, were synthesized according to the procedure specified in the above reference example while varying the quantity of DHDPS, quantity of the alkali metal, and reaction time, and the samples were used in Examples. The weight-average molecular weight was measured using, as detector, an R-401 differential refractometer manufactured by WATERS and a 201 D type GPC-5 gel permeation chromatograph manufactured by WATERS. The measuring conditions included: the use of o-chlorophenol/chloroform (volume ratio 2/8) as eluant, column temperature of 23° C., and injection of 0.1 ml of a solution with a specimen concentration of 1 to 2 mg/nil. Two Shodex 80M columns manufactured by Showa Denko K.K. and one Shodex 802 column manufactured by Showa Denko K.K. were connected in series and an eluant was supplied at a rate of 1.0 ml/min. The molecular weight of the polymer was determined by conversion based on a calibration curve for standard polymethyl methacrylate.

[0096] In regard to the glass transition temperature Tg, a 10 mg specimen was taken from the material for component [B] synthesized above, and subjected to measurement at a heating rate of 10° C./min in the temperature range from 30° C. to 350° C. using a DSC2910 (model) apparatus manufactured by TA Instruments. The midpoint temperature determined according to JIS K7121-1987 was assumed to represent the glass transition temperature Tg and used for heat resistance evaluation. [0097] B-1 (polyethersulfone, weight-average molecular weight 4,000, hydroxyphenyl end group 100 mol %, Tg 204° C.) [0098] B-2 (polyethersulfone, weight-average molecular weight 7,000, hydroxyphenyl end group 100 mol %, Tg 206° C.) [0099] B-3 (polyethersulfone, weight-average molecular weight 14,000, hydroxyphenyl end group 94 mol %, Tg 211° C.) [0100] B-4 (polyethersulfone, weight-average molecular weight 18,000, hydroxyphenyl end group 86 mol %, Tg 214° C.)

[0101] <Polyethersulfone Polymers Other Than the Above> [0102] Virantage (registered trademark) VW-10700RP (polyethersulfone, manufactured by. Solvay Advanced Polymers, weight-average molecular weight 21,000) [0103] Sumikaexcel (registered trademark) PES5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd., weight-average molecular weight 47,000) [0104] D-1 (polyethersulfone, weight-average molecular weight 22,000, hydroxyphenyl end group 100 mol %, Tg 217° C.)

[0105] (Method for production of [D-1]: based on Japanese Unexamined Patent Publication No. HEI-5-86186. It was synthesized according to the aforementioned production procedure for component [B] and subjected to evaluation.)

[0106] <Components Other Than Constituents [A], [B], and [C]> [0107] Virantage (registered trademark) VW-30500RP (polysulfone, manufactured by Solvay Advanced Polymers, weight-average molecular weight: 14,000) [0108] Matsumoto Microsphere (registered trademark) M (polymethyl methacrylate, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., weight-average molecular weight 1,000,000) [0109] Particle 1 (thermoplastic resin particle prepared from Grilamide (registered trademark) TR55 used as feed)

[0110] (Production method for particle 1: according to International Publication WO 2009/142231) In a 100 ml four-neck flask, 2.5 g of amorphous polyamide (Grilamide (registered trademark) TR55 manufactured by Emser Werke, Inc., weight-average molecular weight 18, 000) used as polymer A, 42.5 g of N-methyl-2-pyrolidone used as organic solvent, and 5 g of polyvinyl alcohol (Gohsenol (registered trademark) GL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) used as polymer B were fed and heated at 80° C. and stirred to ensure dissolution of the polymers. After lowering the temperature of the system back to room temperature, 50 g of ion-exchanged water, which was used as poor solvent, was dropped through a water supply pump at a rate of 0.41 g/min while stirring the solution at 450 rpm. The solution turned to white when the amount of ion-exchanged water added reached 12 g. After finishing the addition of the total quantity of water, stirring was continued for 30 min, and the resulting suspension liquid was filtered, followed by washing with 100 g of ion-exchanged water and vacuum-drying at 80° C. for 10 hours to provide 2.2 g of a white solid material. The resulting powder was observed by scanning electron microscopy and found to be formed of fine particles of polyamide with an average particle diameter of 16.1 μm.

[0111] <Curing Agent [C]> [0112] 3,3′-DAS (3,3′-diaminodiphenyl sulfone, manufactured by Mitsui Fine Chemical, Inc.) [0113] SEIKACURE-S (4,4′-diaminodiphenyl sulfone, manufactured by Wakayama Seika Kogyo Co., Ltd.) [0114] DICY-7 (dicyandiamide, manufactured by Mitsubishi Chemical Corporation)

[0115] <Curing Accelerator> [0116] DCMU99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, curing accelerator, manufactured by Hodogaya Chemical Co., Ltd.)

[0117] (1) Preparation of Epoxy Resin Composition

[0118] Predetermined amounts of epoxy resin, polyethersulfone, and other components were put in a kneader and heated to 160° C. while kneading, followed by kneading at 160° C. for 1 hour to provide a transparent viscous liquid. After cooling to 80° C. while kneading, a predetermined amount of <curing agent [C] was added, followed by further kneading to provide an epoxy resin composition.

[0119] (2) Viscosity of Epoxy Resin Composition (G′/η*)

[0120] The viscosity of an epoxy resin composition was determined from the storage elastic modulus G′ and complex viscosity η* at 80° C. measured by simply heating a specimen at a heating rate of 1.5° C./min and taking measurements under the conditions of a frequency of 1 Hz and a gap of 1 mm using a dynamic viscoelasticity measuring apparatus (ARES, manufactured by TA Instruments) equipped with parallel plates with a diameter of 40 mm. From the value of storage elastic modulus G′ at 80° C. and the value of complex viscosity η* at 80° C., the ratio G′/η* between the storage elastic modulus G′ at 80° C. and the complex viscosity η* at 80° C. was calculated.

[0121] (3) Bending Elastic Modulus of Cured Epoxy Resin

[0122] The epoxy resin composition prepared in section (1) above was deaerated in a vacuum and injected in a mold which was set up so that the thickness would be 2 mm by means of a 2 mm thick Teflon (trademark) spacer. Curing was performed at a temperature of 180° C. for 2 hours to provide cured epoxy resin with a thickness of 2 mm. Then, the resulting cured epoxy resin plate was cut to prepare a test piece with a width of 10 mm and length of 60 mm, and it was subjected to three-point bending test with a span of 32 mm, followed by calculation of the bending elastic modulus according to JIS K7171-1994.

[0123] (4) Nominal Strain at Compression Fracture of Cured Epoxy Resin

[0124] The epoxy resin composition prepared in section (1) above was deaerated in a vacuum and injected in a mold which was set up so that the thickness would be 6 mm by means of a 6 mm thick Teflon (trademark) spacer, followed by curing at a temperature of 180° C. for 2 hours to provide a cured epoxy resin with a thickness of 6 mm. This cured epoxy resin was cut to prepare a test piece with a size of 6×6 mm. A plate of cured epoxy resin with a thickness of 6 mm was prepared using an lnstron type universal tester (manufactured by lnstron Corporation). Then, a cubic specimen 6 mm on each side was cut out of the cured epoxy resin plate and subjected to measurement of the nominal strain at compression fracture under the same conditions as specified in JIS K7181 except for a test speed of 1±0.2 mm/min.

[0125] (5) Structural Period of Cured Epoxy Resin

[0126] The cured epoxy resin obtained above was dyed, sliced to produce a thin section, and examined by transmission electron microscopy (TEM) under the following conditions to provide a transmission electron microscopic image. As the dyeing agent, either OsO.sub.4 or RuO.sub.4 suitable for the resin composition was selected to ensure an adequate contrast to permit easy morphological examination. [0127] Equipment: H-7100 transmission electron microscope (manufactured by Hitachi, Ltd.) [0128] Accelerating voltage: 100 kV [0129] Magnification: 10,000

[0130] Under these conditions, the structural period of [A]-rich phase regions and [B]-rich phase regions was observed. Results on the phase structural period of cured epoxy resin are given in the column for phase structure size (pm) in Tables 1 to 3.

[0131] (6) Preparation of Prepreg

[0132] An epoxy resin composition was spread over a piece of release paper with a knife coater to prepare a resin film. Then, carbon fibers of TORAYCA (registered trademark) T800G-24K-31E manufactured by Toray Industries, Inc. were paralleled in one direction to form a sheet, and two resin films were used to cover both sides of the carbon fiber sheet and pressed under heat to impregnate the carbon fiber sheet with the resin to provide a unidirectional prepreg sheet with a carbon fiber metsuke of 190 g/m.sup.2 and a matrix resin mass fraction of 35.5%. Here, in cases where an epoxy resin composition containing thermoplastic resin particles was used, two-step impregnation was carried out as described below to produce prepreg sheets in which the thermoplastic resin particles were highly localized near the surface.

[0133] First, primary prepreg that was free of thermoplastic resin particles was prepared. An epoxy resin composition was prepared by the procedure described in section (1) above using component materials listed in Tables 1 to 3 excluding thermoplastic resin particles insoluble in epoxy resin. This epoxy resin composition for primary prepreg was spread over a piece of release paper with a knife coater to provide a resin film for primary prepreg with a metsuke of 30 g/m.sup.2, which corresponds to 60 mass % of the normal value. Then, carbon fibers of TORAYCA (registered trademark) T800G-24K-31E manufactured by Toray Industries, Inc. were paralleled in one direction to form a sheet, and two of the resin films for primary prepreg were used to cover both sides of the carbon fiber sheet and pressed under heat using heating rollers at a temperature of 100° C. and an air pressure of 1 atm to impregnate the carbon fiber sheet with the resin to provide primary prepreg.

[0134] To prepare resin films for two-step impregnation, the procedure described in section (1) above was carried out by using a kneader to produce an epoxy resin composition containing thermoplastic resin particles insoluble in epoxy resin, which is among the component materials listed in Tables 1 to 3, in a quantity 2.5 times the specified value. This epoxy resin composition for two-step impregnation was spread over a piece of release paper with a knife coater to provide a resin film for two-step impregnation with a metsuke of 20 g/m.sup.2, which corresponds to 40 mass % of the normal value. Such films were used to cover both sides of a primary prepreg sheet and pressed under heat using heating rollers at a temperature of 80° C. and an air pressure of 1 atm to provide prepreg in which thermoplastic resin particles were extremely localized near the surface.

[0135] (7) In-Plane Shear Strength of Fiber Reinforced Composite Material

[0136] A required number of unidirectional prepreg sheets were stacked in a lamination structure of [+45/−45].sub.5S with a fiber direction of ±45° so as to form a molded product with a thickness of 2 mm, and cured by heating at a temperature of 180° C. under a pressure of 6 kg/cm.sup.2 for 2 hours in an autoclave to provide unidirectional composite material. Then, the resulting material was examined according to JIS K7079 (1991) to determine the in-plane shear strength. Measurements were taken from five samples (n =5) and their average was, adopted.

Example 1

[0137] In a kneading machine, 50 parts by mass of SOMI-EPDXY (registered trademark) ELM434 (polyfunctional amine type epoxy resin), 50 parts by mass of GAN (bifunctional amine type epoxy resin), and 180 parts by mass of B-1 (polyethersulfone [B] with a weight-average molecular weight of 2,000 to 20,000 g/mol) were kneaded, followed by further kneading with 50 parts by mass of 3,3′-DAS added as curing agent [C] to prepare an epoxy resin composition. Table 1 lists the components and proportions (figures in Table 1 are in parts by mass). The resulting epoxy resin composition was examined to determine the viscosity of the epoxy resin composition (′G′/η*) (section (2)), bending elastic modulus of cured epoxy resin (section (3)), nominal strain at compression fracture of cured epoxy resin (section (4)), structural period of cured epoxy resin (section (5)), and in-plane shear strength of fiber reinforced composite material (section (7)). Results are given in Table 1.

Examples 2-10

[0138] Except that the epoxy resin, polyethersulfone, other components, curing agent, and their quantities were as specified in Tables 1 and 2, the same procedure as in Example 1 was carried out to produce an epoxy resin composition. The resulting epoxy resin composition was examined to determine the viscosity of the epoxy resin composition (′G′/η*) (section (2)), bending elastic modulus of cured epoxy resin (section (3)), nominal strain at compression fracture of cured epoxy resin (section (4)), structural period of cured epoxy resin (section (5)), and in-plane shear strength of fiber reinforced composite material (section (7)). Results are given in Table 1 and Table 2.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 epoxy resin [A] (polyfunctional amine type epoxy resin) SUMI-EPOXY ® ELM434 50 60 70 jER ® 630 40 10 80 Araldite ® MY0600 30 (bifunctional amine type epoxy resin) GAN 50 30 40 60 90 10 GOT 5 10 (epoxy resin other than above) jER ® 828 15 10 20 EPICLON ® 830 10 jER ® 1004 EPICLON ® HP7200H 10 polyethersulfone [B] (polyethersulfone with weight-average molecular weight of 2,000 to 20,000 g/mol) B-1 180 230 B-2 125 100 B-3 80 60 B-4 38 (polyethersulfone other than above) Virantage ® VW-10700RP SUMI-EPOXY ® PES5003P D-1 other component Virantage ® VW-30500RP Matsumoto Microsphere  ® M particles 1 30 curing agent [C] 3,3′-DAS 50 50 50 SEIKACURE-S 50 50 55 50 DICY-7 curing accelerator DCMU99 resin composition characteristics 80° C. G/η* 0.23 0.31 0.28 0.20 0.22 0.25 0.24 cured resin characteristics bending elastic modulus (GPa) 4.3 4.3 4.1 4.2 4.0 4.1 4.2 nominal strain at compression fracture (%) 61 62 55 52 60 58 55 phase structure size (μm) uniform uniform uniform uniform uniform uniform uniform fiber reinforced composite material characteristics in-plane shear strength (MPa) 146 148 140 131 146 142 137

TABLE-US-00002 TABLE 2 Example 8 Example 9 Example 10 epoxy resin [A] (polyfunctional amine type epoxy resin) SUMI-EPOXY ® ELM434 60 40 50 jER ® 630 50 Araldite ® MY0600 (bifunctional amine type epoxy resin) GAN 30 40 GOT (epoxy resin other than above) jER ® 828 20 Epicron ® 830 10 jER ®1004 Epicron ® HP7200H polvethersulfone [B] (polyethersulfone with weight- average molecular weight of 2,000 to 20,000 g/mol) B-1 B-2 50 30 B-3 65 B-4 (polyethersulfone other than above) Virantage ® VW-10700RP SUMIKAEXCEL ® PES5003P D-1 other component Virantage ® VW-30500RP Matsumoto Microsphere ® M particles 1 curing agent [C] 3,3'-DAS SEIKACURE-S 50 50 35 DICY-7 curing accelerator DCMU99 resin composition characteristics 80° C. G’/η* 0.22 0.24 0.20 cured resin characteristics bending elastic modulus (GPa) 4.3 4.1 4.0 nominal strain at 50 53 51 compression fracture (%) phase structure size (μm) uniform 0.35 uniform fiber reinforced composite material characteristics in-plane shear strength (MPa) 128 135 130

[0139] The cured epoxy resin samples obtained in Examples 1 to 10 had either a non-phase-separated uniform structure or a 400nm-or-less phase-separated structure and they all had good mechanical characteristics. Each of the resulting epoxy resin compositions had a dynamic viscoelasticity in a specific range, resulting in high moldability in fiber reinforced composite material production. It was also found that all fiber reinforced composite material samples obtained had sufficiently high in-plane shear strength.

Comparative Example 1

[0140] Except for using polyethersulfone not meeting the requirements for component [B], the same procedure as in Example 3 was carried out to provide an epoxy resin composition. The resulting epoxy resin composition was examined to determine the viscosity of the epoxy resin composition (G′/η*) (section (2)), bending elastic modulus of cured epoxy resin (section (3)), nominal strain at compression fracture of cured epoxy resin (section (4)), structural period of cured epoxy resin (section (5)), and in-plane shear strength of fiber reinforced composite material (section (7)). As seen from the results given in Table 3, the resulting epoxy resin composition were too high in viscosity and failed to form cured epoxy resin.

Comparative Example 2

[0141] Except for using polyethersulfone not meeting the requirements for component [B], the same procedure as in Example 4 was carried out to provide an epoxy resin composition and fiber reinforced composite material. The resulting epoxy resin composition was examined to determine the viscosity of the epoxy resin composition (G′/η*) (section (2)), bending elastic modulus of cured epoxy resin (section (3)), nominal strain at compression fracture of cured epoxy resin (section (4)), structural period of cured epoxy resin (section (5)), and in-plane shear strength of fiber reinforced composite material (section (7)). As seen from the results given in Table 3, the resulting resin composition was considerably low in G′/η*, resulting in deteriorated moldability in fiber reinforced composite material production. The resulting cured epoxy resin had a slightly large phase-separation structural period and accordingly, it was impossible to obtain a stable nominal strain at compression fracture, resulting in fiber reinforced composite material with insufficient in-plane shear strength.

[0142] Comparison between Example 3 and Comparative example 1 and comparison between Example 4 and Comparative example 2 show that the use of polyethersulfone alone is not sufficiently helpful to solve the problem, but the addition of polyethersulfone [B] with a weight-average molecular weight in a specific range is required to realize the intended effect.

Comparative Examples 3 to 7

[0143] Except that the epoxy resin, polyethersulfone, other components, curing agent, and their quantities were as specified in Table 3, the same procedure as in Example 1 was carried out to produce an epoxy resin composition. The resulting epoxy resin composition was examined to determine the viscosity of the epoxy resin composition (G′/η*) (section (2)), bending elastic modulus of cured epoxy resin (section (3)), nominal strain at compression fracture of cured epoxy resin (section (4)), structural period of cured epoxy resin (section (5)), and in-plane shear strength of fiber reinforced composite material (section (7)).

[0144] As seen from the results given in Table 3, the use of polyethersulfone not meeting the requirements for component [B] in Comparative examples 3 and 4 results in cured epoxy resin with characteristics in deteriorated balance. In particular, the cured epoxy resin had an insufficient nominal strain at compression fracture, resulting in fiber reinforced composite material with insufficient in-plane shear strength.

[0145] As seen from the results given in Table 3, the use of a polymethyl methacrylate component with a large weight-average molecular weight instead of component [B] in Comparative example 5 led to an epoxy resin composition with a dynamic viscoelasticity out of the specific range, resulting in deterioration in the capability to impregnate reinforcement fiber. In addition, the resulting fiber reinforced composite material had insufficient in-plane shear strength.

[0146] Comparative example 6 adopts substantially the same resin components as in Example 7 of Patent document 2 (Japanese Unexamined Patent Publication No. SHO-61-228016). As seen from the results given in Table 3, the use of polysulfone instead of component [B] in Comparative example 6 resulted in cured epoxy resin with a largely decreased heat resistance. In addition, the resin composition obtained had a low G′/η* ratio, leading to deterioration in moldability in production of fiber reinforced composite material. Furthermore, the cured epoxy resin had a slightly large phase-separation structural period and the fiber reinforced composite material had insufficient in-plane shear strength.

[0147] Comparative example 7 adopts substantially the same resin components as in Example 6 of Patent document 1 (Japanese Unexamined Patent Publication No. 2009-167333). As seen from the results given in Table 3, the use of a polyethersulfone component that differs in molecular weight instead of component [B] in Comparative example 7 leads to cured epoxy resin with deteriorated mechanical characteristics. In addition, the resin composition obtained had a low G′/η* ratio, leading to deterioration in moldability in production of fiber reinforced composite material.

TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Comparative Comparative Comparative Comparative example 1 example 2 example 3 example 4 example 5 example 6 example 7 epoxy resin [A] (polyfunctional amine type epoxy resin) SUMI-EPOXY ® ELM434 50 jER ® 630 40 50 Araldite ® MY0600 30 40 90 100 (bifunctional amine type epoxy resin) GAN 40 60 GOT 5 10 (epoxy resin other than above) jER ® 828 15 50 Epicron ® 830 60 jER ® 1004 50 Epicron ® HP7200H 10 polyethersulfone [B] (polyethersulfone with weight-average molecular weight of 2,000 to 20,000 g/mol) B-1 B-2 B-3 B-4 (polyethersulfone other than above) Virantage ® VW-10700RP 65 40 Sumikaexcel ® PES5003P 80 38 D-1 30 other component Vintage ® VW-30500RP 100 Matsumoto Microsphere ® M 5 particles 1 curing agent [C] 3,3′-DAS 50 60 SEIKACURE-S 50 60 75 35 DICY-7 4 curing accelerator DCMU99 2 resin composition characteristics 80° C. G/η* 0.10 0.062 0.13 0.080 2.1 0.18 0.14 cured resin characteristics bending elastic modulus (GPa) — 4.0 3.5 4.0 3.0 3.9 3.8 nominal strain at compression — 50 48 45 60 55 47 fracture (%) phase structure size (μm) — 3 uniform uniform uniform 5 uniform fiber reinforced composite material — characteristics in-plane shear strength (MPa) — 119 118 114 145 126 116

INDUSTRIAL APPLICABILITY

[0148] The present invention provides an epoxy resin composition that can efficiently impregnate reinforcement fiber, enables an appropriate resin flow during molding, and serves to produce fiber reinforced composite material with high in-plane shear strength, and also provide cured epoxy resin material, prepreg, and fiber reinforced composite material that in particular can serve favorably for production of structural members. Preferred applications in the aerospace industry include, for instance, primary structural members of aircraft such as main wing, tail unit, and floor beam; secondary structural members such as flap, aileron, cowl, fairing, and other interior materials; and structural members of rocket motor cases and artificial satellites. Preferred applications in general industries include structural members of vehicles such as automobile, ship, and railroad vehicle; and civil engineering and construction materials such as drive shaft, plate spring, windmill blade, various turbines, pressure vessel, flywheel, roller for paper manufacture, roofing material, cable, reinforcing bar, and mending/reinforcing materials. Preferred applications in the sporting goods industry include golf shafts, fishing rods, rackets for tennis, badminton, squash, etc., hockey sticks, and skiing poles.