Sizing agent-coated carbon fiber bundle, carbon fiber bundle production method, and prepreg

A carbon fiber bundle comprising a sizing agent coated on the carbon fiber bundle, wherein carbon fiber in the carbon fiber bundle exhibits, when measured by a single-fiber composite fragmentation method, a number of fiber breaks of at least 2.0/mm when apparent single-fiber stress is 15.3 GPa and the number of fiber breaks of up to 1.3/mm when the apparent single-fiber stress is 12.2 GPa.

A carbon fiber bundle comprising a sizing agent coated on the carbon fiber bundle having an average tearable length of 300 to 710 mm, a tensile strength of resin-impregnated strands of at least 5900 MPa, a tensile modulus of resin-impregnated strands of at least 320 GPa, and a number of broken single-filaments of 0.5 to 3/m, and which is substantially non-twisted.

A method of producing a carbon fiber bundle comprising subjecting a precursor fiber bundle comprising a polyacrylonitrile polymer to an oxidation process, a pre-carbonization process, and a carbonization process to obtain a carbon fiber bundle, wherein the carbonization process is conducted in an inert atmosphere at a temperature of 1200 to 2000° C. so that tension applied to the pre-carbonized fiber bundle produced by the pre-carbonization in the carbonization process satisfies relation (1):

• 9.8≦tension in the carbonization process (mN/dtex)≦−0.0225×(average tearable length of the pre-carbonized fiber bundle (mm))+23.5 (1),
• wherein the pre-carbonized fiber bundle is substantially non-twisted, and the pre-carbonized fiber bundle has an average tearable length of 150 to 620 mm.