Patent ID: 8486518

Claim:
A prepreg obtained from an epoxy resin composition as a matrix resin impregnated in a reinforced fiber, wherein the epoxy resin composition comprises a sulfur-containing thermosetting component; (C) a urea compound, which is a solid substance having an average particle diameter of no greater than 150 μm, and (D) a dicyandiamide; wherein: the sulfur containing thermosetting component is selected from the group consisting of: a blend of (A) an epoxy resin excluding glycidylamine type epoxy resins and (B-1) an amine compound having at least one sulfur atom in its molecule; a reaction product (B-2) of (A) and (B-1); and a blend of (B-2) and one of (A) and (B-1); the content of the urea compound in the epoxy resin composition is 1 to 15% by mass; the prepreg has a gel time at 130° C. of no more than 200 seconds; the prepreg has a usable period of at least 21 days; the epoxy resin composition does not contain a polyvinylacetal resin; and the epoxy resin composition has a sulfur atom content in the range of 1.17 to 7% by mass.