EPOXY RESIN COMPOSITION, CURED RESIN, PREPREG AND FIBER-REINFORCED COMPOSITE MATERIAL

Provided is an epoxy resin composition with improved heat resistance and resin elongation. Further provided is a fiber-reinforced composite material which uses the epoxy resin composition and thereby excels in compression strength in high-temperature environments and interlaminar toughness. The epoxy resin composition comprises the constituents [A], [B] and [C]. 8-40 mass% of [B] is contained in the epoxy resin composition. The number of moles of active hydrogen contained in [C] is 1.05-2.0 times the number of moles of epoxy groups contained in the entire epoxy resin composition. In a cured resin formed by curing the epoxy resin composition and having a degree of curing of at least 90% obtained by DSC (differential scanning calorimetry), [A], [B] and [C] form a monolayer structure, or a phase separation structure of less than 500nm. The rubber state modulus of elasticity Y (MPa) and glass transition temperature X (°C) obtained by DMA (dynamic mechanical analysis) of the cured resin satisfy formula (1). [A] amine type epoxy resin [B] thermoplastic resin [C] aromatic amine 0.19 X / °C ˆ’ 31.5 ‰¦ Y / MPa ‰¦ 0.19 / °C ˆ’ 27