METHOD OF PRODUCING HIGH-ORIENTATION FLAME-RESISTANT FIBER

PROBLEM TO BE SOLVED: To provide a method of producing a polyacrylonitrile-based flame-resistant fiber which has high crystal orientation without requirement of complex tension control.SOLUTION: In a step of imparting flame resistance to a polyacrylonitrile-based carbon fiber precursor fiber, a flame resistance treatment is carried out under the condition of - ≥-3(%), where is the crystal orientation of the precursor fiber determined from a peak in the vertical direction (2 =17°) relative to the fiber axis, by the wide-angle X-ray diffraction measurement; (%) is the crystal orientation before the flame resistance treatment; and (%) is the crystal orientation when the density of the precursor fiber reaches 1.3 g/cm. In the step of imparting flame resistance to the polyacrylonitrile-based flame-resistant fiber, a heating treatment is carried out under conditions (1) and (2). (1) The temperature of the atmosphere for the flame resistance treatment is 200°C or higher and 300°C or lower. (2) The precursor fiber is kept in a state with no tension applied when the fiber temperature of the precursor fiber during the flame resistance treatment is 170°C or lower. 【課題】複雑な張力制御をすることなく、結晶配向度が高いポリアクリロニトリル系耐炎化繊維を製造する方法を提供する。【解決手段】ポリアクリロニトリル系炭素繊維前駆体繊維の耐炎化工程において、広角Ｘ線回折測定による繊維軸に対して垂直方向（２θ=１７?）のピークから求まる同前駆体繊維の結晶配向度をπとして、耐炎化処理前の結晶配向度をπ１（％）、前躯体繊維の密度が１．３ｇ／ｃｍ３に達した際の結晶配向度をπ２（％）とした場合、π２-π１≧−３（％）となる条件で耐炎化処理を行う。また、ポリアクリロニトリル系耐炎化繊維の耐炎化工程において、以下（１）（２）の条件で加熱処理を行う。（１）耐炎化処理の雰囲気温度が２００℃以上、３００℃以下（２）耐炎化処理中の前駆体繊維の繊維温度が１７０℃以下では、該前駆体繊維は、張力が負荷されない状態に維持される【選択図】なし