Matrix resin composition, prepreg and method for producing the same, and fiber-reinforced composite material

1. A method for producing a prepreg which contains reinforcing fibers and a matrix resin composition with the weight per square meter of the reinforcing fibers being 250-2,000 g/m 2 , the production method comprising the following steps (1)-(3):

(1) a matrix resin composition blending step for obtaining a matrix resin composition having a viscosity of 12 Pa·s to 3,000 Pa·s at 30° C. by mixing an epoxy resin, a radically polymerizable unsaturated compound, an epoxy resin curing agent and a polymerization initiator that generates radicals, in said step the content of the radically polymerizable unsaturated compound relative to 100% by mass of the total of the epoxy resin and the radically polymerizable unsaturated compound being 10-25% by mass;

(2) a matrix resin composition impregnating step for obtaining a prepreg precursor by impregnating a reinforcing fiber assembly being 250-2,000 g/m 2 in weight with the matrix resin composition; and

(3) a surface viscosity increasing step of obtaining a prepreg in which viscosity of the matrix resin composition is increased more in a superficial part than in a central part, by letting the polymerization initiator present in the superficial part of the prepreg precursor generate a radical, while not letting the polymerization initiator present in the central part generate a radical, wherein

the step (2) includes the following steps (2-i) to (2-iii):

(2-i) a matrix resin composition applying step comprising applying the matrix resin composition only to one face of a first reinforcing fiber sheet A 1 composed of consecutive reinforcing fiber bundles;

(2-ii) a reinforcing fiber matrix laminating step comprising laminating a second reinforcing fiber sheet A 2 composed of consecutive reinforcing fiber bundles onto the face of the fiber sheet A 1 to which the matrix resin composition has been applied, wherein the matrix resin composition is only present on the A 1 fiber sheet; and

(2-iii) a pressurizing step comprising impregnating the A 1 and the A 2 fiber sheets with the matrix resin composition by pressurizing the A 1 and A 2 fiber sheets so that the matrix resin composition migrates outward from inside the A 1 and the A 2 fiber sheets to form the prepreg precursor.

2. The method for producing a prepreg according to claim 1 , wherein a means for letting the polymerization initiator generate a radical in the above described step (3) is the following method (3-i):

(3-i) a method of irradiating the prepreg precursor with an energy wave selected from a group consisting of: ultraviolet; infrared; visible light; and electron beam, with an incident intensity no greater than such an incident intensity that transmittance becomes 0% at a depth of 40% from a surface of the prepreg precursor with respect to a thickness of the prepreg precursor being 100%.

3. The method for producing a prepreg according to claim 2 , wherein the polymerization initiator is α-aminoalkyl phenone or α-hydroxyalkyl phenone.

4. The method for producing a prepreg according to claim 1 , wherein a means for letting the polymerization initiator generate a radical in the above described step (3) is the following method (3-ii):

(3-ii) a method of heating the prepreg precursor from the outside in a non-contact state, for such a time period that a rate of temperature change becomes 0% at a depth of 40% from a surface of the prepreg precursor with respect to a thickness of the prepreg precursor being 100%.

5. The method for producing a prepreg according to claim 4 , wherein the method (3-ii) is realized by high frequency heating.

6. The method for producing a prepreg according to claim 1 , wherein the weight per square meter of the reinforcing fibers is 400-2,000 g/m 2 .

7. The method for producing a prepreg according to claim 1 , wherein the weight per square meter of the reinforcing fibers is 500-2,000 g/m 2 .

8. The method for producing a prepreg according to claim 1 , wherein in step (2-i), the matrix resin composition is applied only to one face of the first reinforcing fiber sheet A 1 by: (i) a touch roller method in which the one face of the first reinforcing fiber sheet A 1 contacts with the touch roller so that the matrix resin composition is applied only to the one face of the first reinforcing fiber sheet A 1 ; or (ii) a die coating method in which the matrix resin composition is extruded from a resin bath and applied to the one face of the first reinforcing fiber sheet A 1 .

9. A method for producing a prepreg which contains reinforcing fibers and a matrix resin composition with the weight per square meter of the reinforcing fibers being 250-2,000 g/m 2 , the production method comprising the following steps (1)-(3):

(1) a matrix resin composition blending step for obtaining a matrix resin composition having a viscosity of 12 Pa·s to 3,000 Pa·s at 30° C. by mixing an epoxy resin, a radically polymerizable unsaturated compound, an epoxy resin curing agent and a polymerization initiator that generates radicals, in said step the content of the radically polymerizable unsaturated compound relative to 100% by mass of the total of the epoxy resin and the radically polymerizable unsaturated compound being 10-25% by mass;

(2) a matrix resin composition impregnating step for obtaining a prepreg precursor by impregnating a reinforcing fiber assembly being 250-2,000 g/m 2 in weight with the matrix resin composition; and

(3) a surface viscosity increasing step of obtaining a prepreg in which viscosity of the matrix resin composition is increased more in a superficial part than in a central part, by letting the polymerization initiator present in the superficial part of the prepreg precursor generate a radical, while not letting the polymerization initiator present in the central part generate a radical,

wherein the step (2) includes the following steps (2-iv) to (2-vi):

(2-iv) a matrix resin composition applying step comprising applying the matrix resin composition only to one face of a first reinforcing fiber sheet A 1 composed of consecutive reinforcing fiber bundles or applying the matrix resin composition only to both a first face and a second face of the first reinforcing fiber sheet A 1 ;

(2-v) a reinforcing fiber matrix laminating step comprising laminating a second reinforcing fiber sheet A 2 composed of consecutive reinforcing fiber bundles, and a third reinforcing fiber sheet A 3 composed of consecutive reinforcing fiber bundles, onto the first face of the A 1 fiber sheet and the second face of the A 1 fiber sheet respectively, wherein the matrix resin composition is only present on the A 1 fiber sheet; and

(2-vi) a pressurizing step comprising impregnating the A 1 fiber sheet, the A 2 fiber sheet, and the A 3 fiber sheet with the matrix resin composition by pressurizing the A 1 , the A 2 , and the A 3 fiber sheets so that the matrix resin composition migrates outward from inside of the A 1 , the A 2 and the A 3 fiber sheets to obtain the prepreg precursor.

10. The method for producing a prepreg according to claim 9 , wherein a means for letting the polymerization initiator generate a radical in the above described step (3) is the following method (3-i):

(3-i) a method of irradiating the prepreg precursor with an energy wave selected from a group consisting of: ultraviolet; infrared; visible light; and electron beam, with an incident intensity no greater than such an incident intensity that transmittance becomes 0% at a depth of 40% from a surface of the prepreg precursor with respect to a thickness of the prepreg precursor being 100%.

11. The method for producing a prepreg according to claim 9 , wherein the weight per square meter of the reinforcing fibers is 400-2,000 g/m 2 .

12. The method for producing a prepreg according to claim 9 , wherein the weight per square meter of the reinforcing fibers is 500-2,000 g/m 2 .

13. The method for producing a prepreg according to claim 9 , wherein in step (2-iv), the matrix resin composition is applied to only one face of the first reinforcing fiber sheet A 1 .

14. The method for producing a prepreg according to claim 9 , wherein in step (2-iv), the matrix resin composition is applied only to the first reinforcing fiber sheet A 1 by: (i) a touch roller method in which the one face or the both first and second faces of the first reinforcing fiber sheet A 1 contacts the touch roller so that the matrix resin composition is applied to the one face or the both first and second faces of the first reinforcing fiber sheet A 1 ; or (ii) a die coating method in which the matrix resin composition is extruded from a resin bath and applied to the one face or the both first and second faces of the first reinforcing fiber sheet A 1 .