Production method for obtaining fiber-reinforced composite material, and epoxy resin composition used therein

1. A production method for obtaining a fiber-reinforced composite material by impregnating a fiber assembly with an epoxy resin composition and curing, the method comprising

preparing the epoxy resin composition including a constitutional element [A], a constitutional element [B], and a constitutional element [C] by blending at a temperature of at least 60° C. and no higher than 80° C., wherein, given that a blending amount of the constitutional element [B] is b parts by mass and a blending amount of the constitutional element [C] is c parts by mass with respect to 100 parts by mass of the constitutional element [A], wherein the epoxy resin composition satisfies equation (2) when the constitutional element [A] has a molecular weight in a range of equation (1), the epoxy resin composition satisfies equation (4) when the constitutional element [A] has a molecular weight in a range of equation (3), and the epoxy resin composition satisfies equation (6) when the constitutional element [A] has a molecular weight in a range of equation (5), wherein

the constitutional element [A] is an epoxy resin of a converted molecular weight a;

the constitutional element [B] is 3,3′-diaminodiphenyl sulfone; and

the constitutional element [C] is 4,4′-diaminodiphenyl sulfone,

150<a≦200   (1)

0 <b /( b+c )<1   (2)

200<a≦350   (3)

0.002 a− 0.35 ≦b /( b+c )≦−0.002 a+ 1.35   (4)

350<a   (5)

0.35 ≦b /( b+c )≦0.65   (6),

the converted molecular weight a being defined as follows:

in a case of using only one kind of epoxy resin as the epoxy resin [A], the converted molecular weight a is a product of an epoxy equivalent of the epoxy resin used and the number of epoxy groups in a molecule of the epoxy resin;

and in a case of using a plurality of kinds of epoxy resin as the epoxy resin [A], the converted molecular weight a is a value obtained by: obtaining a product of an epoxy equivalent and the number of epoxy groups in a molecule of the epoxy resin for each epoxy resin component; and then weighted-averaging, per blending ratios of components composing the epoxy resin [A], the product of the epoxy equivalent and the number of epoxy groups thus obtained for each epoxy resin component.

2. The production method according to claim 1 , wherein the epoxy resin composition further satisfies equation (7):

15≦( b+c )≦70   (7).

3. The production method according to claim 1 , wherein the temperature is at least 65° C. and no higher than 80° C.

4. An epoxy resin composition comprising a constitutional element [A], a constitutional element [B], and a constitutional element [C], wherein,

given that a blending amount of the constitutional element [B] is b parts by mass and a blending amount of the constitutional element [C] is c parts by mass with respect to 100parts by mass of the constitutional element [A] included in the epoxy resin composition,

wherein the epoxy resin composition satisfies equation (9) when the constitutional element [A] has a molecular weight in a range of equation (8), the epoxy resin composition satisfies equation (11) when the constitutional element [A] has a molecular weight in a range of equation (10), and the epoxy resin composition satisfies equation (13) when the constitutional element [A] has a molecular weight in a range of equation (12),

wherein

the constitutional element [A] is an epoxy resin of a converted molecular weight a;

the constitutional element [B] is 3,3′-diaminodiphenyl sulfone; and

the constitutional element [C] is 4,4′-diaminodiphenyl sulfone,

150<a≦200   (8)

0 <b /( b+c )<1   (9)

200<a≦350   (10)

0.002 a− 0.35 ≦b /( b+c )≦−0.002 a+ 1.35   (11)

350<a   (12)

0.35 ≦b /( b+c )≦0.65   (13)

the converted molecular weight a being defined as follows:

in a case of using only one kind of epoxy resin as the epoxy resin [A], the converted molecular weight a is a product of an epoxy equivalent of the epoxy resin used and the number of epoxy groups in a molecule of the epoxy resin;

and in a case of using a plurality of kinds of epoxy resin as the epoxy resin [A], the converted molecular weight a is a value obtained by: obtaining a product of an epoxy equivalent and the number of epoxy groups in a molecule of the epoxy resin for each epoxy resin component; and then weighted-averaging, per blending ratios of components composing the epoxy resin [A], the product of the epoxy equivalent and the number of epoxy groups thus obtained for each epoxy resin component, and

wherein the epoxy resin composition is obtained by being blended at a temperature of at least 60° C. and no higher than 80° C.

5. The epoxy resin composition according to claim 4 , wherein the epoxy resin composition satisfies equation (15) when the constitutional element [A] has a molecular weight in a range of equation (14), the epoxy resin composition satisfies equation (17) when the constitutional element [A] has a molecular weight in a range of equation (16), and the epoxy resin composition satisfies equation (19) when the constitutional element [A] has a molecular weight in a range of equation (18):

150<a≦190   (14)

0.1 ≦b /( b+c )≦0.9   (15)

190<a≦365   (16)

0.002 a− 0.28 ≦b /( b+c )≦−0.0017 a+ 1.23   (17)

365<a   (18)

0.45 ≦b /( b+c )≦0.60   (19).

6. The epoxy resin composition according to claim 4 , wherein the epoxy resin composition further satisfies equation (20):

150<a<800   (20).

7. The epoxy resin composition according to claim 4 , wherein the epoxy resin composition further satisfies equations (21) and (22):

150≦a≦357   (21)

0.00169 a− 0.103 ≦b /( b+c )≦−0.0019 a+ 1.19   (22).

8. The epoxy resin composition according to claim 4 , wherein the epoxy resin composition further satisfies equations (23) and (24):

150≦a≦300   (23)

0.00169 a− 0.103 ≦b /( b+c )≦−0.0010 a+ 0.90   (24).

9. The epoxy resin composition according to claim 4 , wherein the epoxy resin composition further satisfies equation (25):

15≦( b+c )≦70   (25).

10. The epoxy resin composition according to claim 4 , wherein the temperature is at least 65° C. and no higher than 80° C.

11. The epoxy resin composition according to claim 5 , wherein the epoxy resin composition further satisfies equation (20):

150<a<800   (20).

12. The epoxy resin composition according to claim 5 , wherein the epoxy resin composition further satisfies equations (21) and (22):

150≦a≦357   (21)

0.00169 a− 0.103 ≦b /( b+c )≦−0.0019 a+ 1.19   (22).

13. The epoxy resin composition according to claim 5 , wherein the epoxy resin composition further satisfies equations (23) and (24):

150≦a≦300   (23)

0.00169 a− 0.103 ≦b /( b+c )≦−0.0010 a+ 0.90   (24).

14. The epoxy resin composition according to claim 5 , wherein the epoxy resin composition further satisfies equation (25):

15≦( b+c )≦70   (25).