Epoxy resin composition for fiber-reinforced composite material

1. An epoxy resin composition for fiber-reinforced composite materials, comprising:

an epoxy resin (A) that is in a liquid state at room temperature;

a thermoplastic resin (B) that dissolves in the epoxy resin (A) at a temperature not less than 90° C.;

thermosetting resin particles (C) that do not completely dissolve in the epoxy resin (A) at a temperature less than 90° C., but completely dissolve in the epoxy resin (A) upon heating of the composition and have a softening point of not less than 120° C.; and

a curing agent (D), wherein the thermosetting resin particles (C) are made of an epoxy-based resin comprising bisphenol A-type epoxy resin that is in a solid state at room temperature, and wherein the epoxy resin composition contains, with respect to 100 parts by weight of the epoxy resin (A), 30 to 50 parts by weight of the thermoplastic resin (B) and 2 to 20 parts by weight of the thermosetting resin particles (C).

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

the thermoplastic resin (B) is both or any one of a polyethersulfone resin particle and a polyetherimide resin particle, and

the particle diameter thereof is 200 μm or less.

3. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein the thermosetting resin particles (C) has a particle diameter of 100 μm or less.

4. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein the curing agent (D) is both or any one of 3,3′-diaminodiphenylsulfone and 4,4′-diaminodiphenylsulfone.

5. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein the curing agent (D) is used in combination with a latent curing agent.

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

7. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 , wherein a fracture toughness value measured according to ASTM D5045-91 after curing of the epoxy resin composition is 1.8 MPa·√m or larger.

8. A method for producing the epoxy resin composition for fiber-reinforced composite materials according to claim 1 , comprising:

dissolving the thermoplastic resin (B) in the epoxy resin (A) at a temperature of from 95 to 150° C. followed by cooling to a temperature of from 60 to 90° C.; and,

thereafter, adding thereto the thermosetting resin particles (C) and the curing agent (D).

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

10. The fiber-reinforced prepreg according to claim 9 , wherein a content of the matrix resin is from 30 to 50 weight %.

11. The fiber-reinforced prepreg according to claim 9 , wherein the reinforcing fiber is carbon fiber.

12. A honeycomb sandwich panel, comprising the fiber-reinforced prepreg according to claim 1 and a honeycomb core that are laminated to each other.

13. The honeycomb sandwich panel according to claim 12 , wherein the honeycomb core is any one selected from the group consisting of aramid honeycombs, aluminum honeycombs, paper honeycombs, and glass honeycombs.

14. The epoxy resin composition for fiber-reinforced composite materials according to claim 2 , wherein the thermosetting resin particles (C) has a particle diameter of 100 μm or less.

15. The epoxy resin composition for fiber-reinforced composite materials according to claim 2 , wherein the curing agent (D) is both or any one of 3,3′-diaminodiphenylsulfone and 4,4′-diaminodiphenylsulfone.

16. The epoxy resin composition for fiber-reinforced composite materials according to claim 3 , wherein the curing agent (D) is both or any one of 3,3′-diaminodiphenylsulfone and 4,4′-diaminodiphenylsulfone.