Epoxy resin composition

An epoxy resin composition, comprising:

• components (A2), (B2) and (D2), wherein a content of the component (B2) is 8 to 20 parts by mass relative to 100 parts by mass of the component (A2), and a content of the component (D2) is 1 to 50 parts by mass relative to 100 parts by mass of the component (A2),
• wherein component (A2) is an epoxy resin, component (B2) is a boron trihalide-amine complex, component (D2) is a polymer which is compatible with an epoxy resin composition comprising the components (A2) and (B2), and
• wherein the epoxy resin composition comprising component (D2) has a characteristic of forming a phase separation structure when cured.

An epoxy resin composition, comprising:

• an epoxy resin, an epoxy resin curing agent which is a boron trihalide-amine complex, and a thermoplastic resin;
• wherein the epoxy resin composition has a characteristic of forming, when cured, a phase separation structure 1 in which a phase of a cured product of the epoxy resin composition and a phase of the thermoplastic resin constitute a sea-island phase separation structure in the cured product, and a phase separation structure 2 which is a sea-island phase separation structure, by taking the island structure in the phase separation structure 1 as a sea structure.