| 摘要 |
PROBLEM TO BE SOLVED: To provide a carbon fiber which provides a composite material excellent in impact resistance and is excellent in compression strength in the fiber cross section direction.SOLUTION: To provide a carbon fiber which has a carbon fiber density A(g/cm), measured by the helium filling method in a filament state, and a carbon fiber density B(g/cm), measured by the helium filling method including crushing a carbon fiber to a vol. average particle size of 0.5 μm or smaller, meeting the inequality condition (1) A/B≤0.9 and a crystal orientation degree of 80% or lower. A method of producing the carbon fiber is based on carbonization treatment of a flame-resistant fiber obtained by a flame-resistant treatment of a polyacrylonitrile-based precursor fiber and comprises subjecting the flame-resistant fiber to a first carbonization treatment at a treatment temperature of 350-550°C with a draw ratio lower than 1.00 time to obtain a first carbonization fiber and subjecting the first carbonization fiber to a second carbonization treatment at a treatment temperature of 650-850°C with a draw ratio lower than 1.00 time and then to a third carbonization treatment at a treatment temperature of 1,000°C or higher. |
