Epoxy resin composition for fiber-reinforced composite material

1. An epoxy resin composition for fiber-reinforced composite materials, comprising, 100 parts by weight of an epoxy resin (A), 25 to 50 parts by weight of an amine curing agent (B) selected from aliphatic polyamines, alicyclic polyamines and aromatic polyamines; and 1 to 20 parts by weight of an organic acid dihydrazide compound (C) of a melting point of between 185 and 200° C.; and a thermosetting resin (E) that is solid at room temperature does not completely dissolve in the epoxy resin (A) at a temperature of less than 90° C. and has a softening point of 120° C. or higher, wherein

the thermosetting resin (E) is dispersed in a particulate form in the epoxy resin composition;

wherein the composition further comprises a thermoplastic resin (F) and the thermoplastic resin (F) is in a particle state and is dissolved at a temperature of 90° C. or higher; and wherein the fracture toughness value measured in accordance with ASTM D5045-91 after curing of the epoxy resin composition is 1.8 MPa·√m or higher.

2. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , comprising:

dicyandiamide (D), wherein

the organic acid dihydrazide compound (C) is dispersed in a particulate form.

3. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein

the organic acid dihydrazide compound (C) is any one of a dibasic acid dihydrazide and a carboxylic acid dihydrazide compound expressed by Formula (I):

wherein X represents a phenyl group or an aliphatic hydrocarbon group having 2 to 18 carbon atoms.

4. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein the average particle diameter of the organic acid dihydrazide compound (C) is 100 μm or less.

5. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein

the amine curing agent (B) is 3,3′-diaminodiphenylsulfone and/or 4,4′-diaminodiphenylsulfone.

6. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein the thermoplastic resin (F) is any one of a polyethersulfone resin and a polyetherimide resin.

7. The epoxy resin composition for fiber-reinforced composite materials according to claim 2 , comprising 1 to 5 parts by weight of the dicyandiamide (D) with respect to 100 parts by weight of the epoxy resin (A).

8. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , comprising 20 to 60 parts by weight of the thermoplastic resin (F) with respect to 100 parts by weight of the epoxy resin (A).

9. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein the minimum viscosity of the epoxy resin composition measured by dynamic viscoelasticity measurement at a temperature rise rate of 2° C./minute is from 10 to 150 Pa·s.

10. A method of producing an epoxy resin composition for fiber-reinforced composite material according to claim 1 , comprising:

dissolving the thermoplastic resin (F) in the epoxy resin (A) at 95 to 150° C. to make a mixture resin,

cooling the mixture resin to 60 to 90° C., and then

adding other blending components including the amine curing agent (B) and the organic acid dihydrazide compound (C) into the mixture resin.

11. A fiber-reinforced prepreg, comprising the epoxy resin composition according to claim 1 as a matrix resin in complex with a reinforcing fiber.

12. The fiber-reinforced prepreg according to claim 11 , wherein a content of the matrix resin is from 30 to 50% by weight.

13. The fiber-reinforced prepreg according claim 11 , wherein the reinforcing fiber is carbon fiber.

14. A honeycomb sandwich panel, comprising the fiber-reinforced prepreg according to claim 11 and a honeycomb core that are laminated to each other.

15. The honeycomb sandwich panel according to claim 14 , wherein the honeycomb core is any one selected from the group consisting of aramid honeycombs, aluminum honeycombs, paper honeycombs, and glass honeycombs.