Heat-resistant high-toughness fiber, production method thereof, and heat-resistant high-toughness film

A production method of heat-resistant high-toughness fiber, comprising the following steps (1) to (6):

• (1) providing a copolymerized aramid polymer containing at least three monomer units selected from the group consisting of meta-phenylenediamine, para-phenylenediamine, isophthaloyl, and terephthaloyl, a molar ratio of monomer units of the meta-phenylenediamine and/or the isophthaloyl to monomer units of the para-phenylenediamine and/or the terephthaloyl being in the range of 10 or more and less than 70:90 or less and greater than 30, and having a weight average molecular weight of 400,000 to 1,000,000,
• (2) dissolving the copolymerized aramid polymer in a solvent to prepare a spinning dope,
• (3) spinning the spinning dope through a spinneret into a coagulation bath to obtain a coagulated yarn;
• (4) washing the coagulated yarn in an aqueous washing bath and drawing it at a draw ratio in the range of 1.1 to 5.0 times in a boiling water bath to obtain a fiber;
• (5) subjecting the fiber to dry heat treatment in the range of 100 to 250° C., and
• (6) after the dry heat treatment, heat-drawing the fiber at a draw ratio in the range of 2.0 to 10.0 times while heat-treating at 290 to 380° C.