| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a flameproof fiber strand which has a reduced variation in physical properties among single fibers constituting the strand and is suitable for producing a carbon fiber having high strand strength.SOLUTION: A polyacrylonitrile-based (PAN-based) precursor fiber strand, which comprises 1000-30000 single fibers and has a strand flatness ratio of 0.5-0.95 after passing through a groove roller as necessary and then through a flat roller, is introduced into a flameproofing treatment oven after passing through the groove roller as necessary and then through the flat roller. In the flameproofing treatment oven, stretching of 1.0-1.15 times is performed while an oxidizing gas of 200-300°C is supplied to the flat surface of the precursor fiber strand from the vertical direction at a wind velocity of 0.1 m/s or higher and lower than 1.0 m/s. In a flameproof fiber strand obtained by the production method, a variation in strength among single fibers constituting the strand is 7.0% or less, and the difference between the maximum value and the minimum value of the slope values of load-elongation curves for the single fibers, which are obtained by measuring the tensile strengths of the single fibers, is 0.01 N/mm or less. |
