Patent ID: 8790554

Claim:
A method for preparing meta-aramid fibers, the method comprising: i) polymerizing m-phenylenediamine with isophthaloyl chloride in a polar organic amide solvent at a low temperature to give a solution of polymer polyisophthaloyl metaphenylene diamine and hydrogen chloride; ii) neutralizing hydrogen chloride given in operation i) with a neutralizing agent in a twin-screw extruder to give a spin dope of polyisophthaloyl metaphenylene diamine; iii) extruding the spin dope obtained in operation ii) through the twin-screw extruder, spinning the extruded spin dope through a spinneret into a precipitation bath to precipitate spun filaments which are meta-aramid primary fibers; and iv) washing the meta-aramid primary fibers obtained in operation iii) at least once, drying and drawing the fibers to obtain the finished meta-aramid fibers, wherein in operation ii) the neutralizing agent is added in an amount that is sufficient only for neutralizing a part of hydrogen chloride, so that the resultant spin dope of polyisophthaloyl metaphenylene diamine contains salts produced by the neutralization reaction and a part of unneutralized hydrogen chloride, and the neutralizing agent is added at 5% to 50% of an equal molar ratio of the neutralization reaction, and wherein the twin screw extruder is directly followed by and connected to a metering pump through which the spin dope containing the unneutralized hydrogen chloride and the salts produced by the neutralization reaction is dosed and then fed into the spinneret to be extruded into the precipitation bath, and that the twin screw extruder includes a two-stage jacket configuration, wherein water at room temperature is introduced into a front stage of the jacket for exchanging with heat generated by the neutralization reaction, and constant temperature water is introduced into a rear stage of the jacket to ensure the temperature of the spin dope.