Epoxy resin composition and prepreg made with the epoxy resin composition

1. An epoxy resin composition, comprising

(a) an epoxy resin;

(b) a latent curing agent with curing power at 100° C. or below; and

(c) an aromatic amine-based curing agent and/or an alicyclic amine-based curing agent, wherein

the mixing proportion of component (a), component (b) and component (c) is 3-40 parts by weight of component (b) and 10-40 parts by weight of component (c) to 100 parts by weight of component (a).

2. A composition according to claim 1 , wherein the epoxy resin of component (a) is an epoxy resin composed mainly of a trifunctional or greater epoxy resin.

3. A composition according to claim 2 , wherein the trifunctional or greater epoxy resin is an epoxy resin containing at least one selected from novolac-type epoxy resins represented by chemical formula (1) below,

wherein n represent a number of 0 or greater: novolac-type epoxy resins represented by chemical formula (2) below,

wherein n represents a number of 0 or greater; and tetralglycidyldiaminodiphenylmethane.

4. A composition according to claim 1 , wherein the latent curing agent as component (b) is an amine adduct-type curing agent.

5. A composition according to claim 1 , wherein the latent curing agent as component (b) is a microcapsular curing agent.

6. A composition according to claim 1 , wherein the aromatic amine-based curing agent as component (c) is diaminodiphenylsulfone or diaminodiphenylmethane.

7. A composition according to claim 1 , which further comprises a curing accelerator as component (d).

8. A composition according to claim 1 , wherein the viscosity of the epoxy resin composition prepared and allowed to stand at 25° C. for 3 weeks is no greater than twice the viscosity immediately after preparation of the resin composition.

9. A composition according to claim 1 , which either gives a cured product with a curing degree of at least 70% when obtained by primary curing for no more than 10 hours at a temperature of 100° C. or below, or gives a cured product with a tensile shear strength (adhesive strength) of at least 10 MPa according to JIS-K-6848 and JIS-K-6850.

10. A prepreg comprising a reinforcing fiber material impregnated with an epoxy resin composition according to claim 1 .

11. A method of making a prepreg, the method comprising impregnating a reinforcing fiber material with an epoxy resin composition; and producing the prepreg of claim 10 .

12. A method of using an epoxy resin composition to produce a fiber-reinforced composite material, the method comprising

(1) impregnating a reinforcing fiber material with the epoxy resin composition of claim 1 to obtain a prepreg; and

(2) subjecting the prepreg to primary curing in a molding die and, after releasing from the molding die, subjecting the primary cured molded article to secondary curing to obtain a fiber-reinforced composite material.

13. A method of making an epoxy resin composition, the method comprising

mixing (a) an epoxy resin, (b) a latent curing agent with curing power at 100° C. or below and (c) an aromatic amine-based curing agent and/or an alicyclic amine-based curing agent; and

producing the epoxy resin composition of claim 1 .

14. A process for producing a fiber-reinforced composite material comprising the steps of:

(1) impregnating a reinforcing fiber material with an epoxy resin composition comprising (a) an epoxy resin, (b) a latent curing agent with curing power a 100° C. or below and (c) an aromatic amine-based curing agent and/or an alicyclic amine-based curing agent to obtain a prepreg; and

(2) subjecting the prepreg to primary curing in a molding die and, aft r releasing from the molding die, subjecting the primary cured molded article to secondary curing to obtain a fiber-reinforced composite material.