Epoxy resin composition, molded article, prepreg, fiber-reinforced composite material and structure

1. An epoxy resin composition, comprising:

Component (A): an organic phosphinic acid metal salt;

Component (B): an epoxy resin;

Component (C): dicyandiamide or a derivative thereof;

Component (D): a curing accelerator having a dimethylureido group; and

Component (E): at least one selected from the group consisting of an imidazole adduct, an imidazole clathrate compound, an imidazole compound coordinated with a stabilizer, and an imidazole compound per se, which has a curing initiation temperature of 100° C. or higher as measured by a method comprising:

preparing a sample resin composition by mixing 10 parts by mass of at least one selected from the group consisting of an imidazole adduct, an imidazole clathrate compound, an imidazole compound coordinated with a stabilizer, and an imidazole compound per se with 100 parts by mass of a bisphenol A type epoxy resin having an epoxy equivalent of 180 to 220;

measuring a calorific value of the sample resin composition using a differential scanning calorimeter at a rate of temperature increase of 10° C./min, and

designating a temperature at the intersection point of the tangent line at the inflection point of the DSC curve thus obtained and the baseline as the curing initiation temperature,

wherein the epoxy resin composition comprises the Component (A) in an amount such that a phosphorus atom content becomes 0.3% to 5.0% by mass in 100% by mass of the epoxy resin composition, with the proviso that in a case in which the epoxy resin composition comprises a metal hydroxide, 100% by mass of the epoxy resin composition excluding the metal hydroxide, and

wherein the epoxy resin composition has an index of determination in shear rate sweep measurement of 0.98 or more.

2. The epoxy resin composition according to claim 1 , wherein the Component (D) is at least one compound selected from the group consisting of phenyldimethylurea, methylenebis(phenyldimethylurea), and tolylenebis(dimethylurea).

3. The epoxy resin composition according to claim 1 , wherein the epoxy resin composition comprises the Component (C) in an amount of 1 to 15 parts by mass, the Component (D) in an amount of 1 to 30 parts by mass, and the Component (E) in an amount of 1 to 30 parts by mass, with respect to 100 parts by mass of the Component (B).

4. The epoxy resin composition according to claim 1 , further comprising:

Component (G): a metal hydroxide.

5. The epoxy resin composition according to claim 4 , wherein the epoxy resin composition comprises the Component (G) in an amount of 70% by mass or less in 100% by mass of the epoxy resin composition, and when the phosphorus atom content in 100% by mass of the epoxy resin composition excluding the Component (G) is designated as x, and the content of the Component (G) in 100% by mass of the epoxy resin composition comprising the Component (G) is designated as y, satisfying the following Expression (1):

y≥− 4.5 x+ 39.8  (1).

6. The epoxy resin composition according to claim 1 , wherein the Component (B) comprises a bisphenol F type epoxy resin.

7. The epoxy resin composition according to claim 1 , wherein the Component (B) comprises a trifunctional or higher-functional epoxy resin having an epoxy equivalent of 350 or less.

8. The epoxy resin composition according to claim 1 , further comprising:

Component (F): a thermoplastic resin.

9. The epoxy resin composition according to claim 8 , wherein the Component (F) is at least one selected from the group consisting of a phenoxy resin and a polyvinylformal resin.

10. A molded article, obtained by molding the epoxy resin composition according to claim 1 .

11. A prepreg, obtained by impregnating a reinforcing fiber bundle with the epoxy resin composition according to claim 1 .

12. A fiber-reinforced composite material, obtained by curing the prepreg according to claim 11 .

13. A structure having a portion or the entirety thereof constructed from the fiber-reinforced composite material according to claim 12 .

14. The structure according to claim 13 , wherein the structure comprises at least two pieces of the fiber-reinforced composite material, and a core material comprising at least one material selected from hollow glass microspheres and foamed plastic beads, the core material being sandwiched between the pieces of the fiber-reinforced composite material such that the at least two pieces of the fiber-reinforced composite material and the core material are integrated together.

15. The epoxy resin composition according to claim 1 , wherein the epoxy resin composition comprises the Component (C) in an amount of 2 to 14 parts by mass, the Component (D) in an amount of 1 to 30 parts by mass, and the Component (E) in an amount of 2 to 25 parts by mass, with respect to 100 parts by mass of the Component (B).