Heat-curable resin composition, prepreg, and method for producing fiber-reinforced composite using each of same

1. A heat-curable resin composition comprising:

(1) a heat-curable resin mixture containing a heat-curable resin (a) formed of an epoxy resin and thickener particles (b) dispersed in the heat-curable resin (a) and having a content of 8 to 20 parts by mass with respect to 100 parts by mass of the heat-curable resin (a), and exhibiting a viscosity S as a viscosity (150° C.) obtained after the heat-curable resin mixture is held at a temperature of 150° C. for 30 seconds, and

(2) a curing agent having a content of 7 to 20 parts by mass with respect to 100 parts by mass of the heat-curable resin (a),

wherein

the heat-curable resin composition exhibits a lowest viscosity R at a temperature of 80 to 120° C., and the lowest viscosity R is from 0.5 to 8 Pa·s,

the viscosity S and the lowest viscosity R satisfy the following formula (1)

8 ≤S/R≤ 107  formula (1),

the thickener particles (b) are capable of increasing the viscosity of the heat-curable resin composition by 10 times or more, measured at 150° C. after the heat-curable mixture is held at 150° C. for 30 seconds, when the thickener particles (b) are contained in the composition with 10% by mass,

the thickener particles (b) do not have core-shell structure,

the curing agent contains dicyandiamide and an urea curing agent selected from phenyl dimethyl urea and toluene bis-dimethyl urea,

a gel time of the heat-curable resin composition is from 40 to 200 seconds at a temperature of 150° C., and

the viscosity of the heat-curable resin composition is from 70 to 700 Pa·s at a temperature of 50° C., and the thickener particles (b) are formed of a polymer constituted by one or more polymerization units selected from the group consisting of a methacrylate compound, an acrylate compound, and a vinyl compound.

2. The heat-curable resin composition according to claim 1 , wherein the viscosity S is from 15 to 250 Pa·s.

3. A prepreg comprising: a reinforced fiber material; and the heat-curable resin composition according to claim 1 , wherein the reinforced fiber material is impregnated with a part of the heat-curable resin composition or the heat-curable resin composition in its entirety.

4. The prepreg of claim 3 , wherein the reinforced fiber material is a mat formed of short fibers having a fiber length of 5 to 100 mm.

5. A method for producing a fiber-reinforced composite, comprising: heating and pressurizing the prepreg according to claim 3 in a molding die at a temperature of 130 to 170° C. at a pressure of 0.2 to 10 MPa for 1 to 10 minutes.

6. A method for producing a fiber-reinforced composite, comprising:

stacking the prepreg of claim 3 outside a bag-shaped inner pressure bag to obtain a preform having the inner pressure bag therein;

disposing the preform in a molding die; and

heating and pressurizing the preform in the molding die at a temperature of 130 to 170° C. at a pressure of 0.2 to 2 MPa for 1 to 10 minutes.

7. A method for producing a fiber-reinforced composite; comprising:

stacking the prepreg of claim 3 and a film bag in a molding die sequentially to seal the prepreg between the molding die and the film bag;

vacuuming a space formed by the molding die and the film bag; and

pressurizing an inside of a cavity of the molding die formed by clamping the molding die with the air so as to have a pressure of 0.2 to 2 MPa, heating the prepreg to 130 to 170° C. at a temperature rising rate of 2 to 100° C./min in the molding die, and heating and pressurizing the prepreg at the temperature for 1 to 10 minutes.