Method for producing polyurethane elastic fiber

A method for producing a polyurethane elastic fiber, comprising the steps of:

• (1) producing a polyurethane urea polymer (A) represented by general formula (1) described below, which has a number average molecular weight calculated in terms of polystyrene ranging from 12,000 to 50,000, and has tertiary nitrogen groups at the terminal groups, by adding a diamino compound (2) represented by general formula (2) described below in a ratio ranging from 0.01 to 15 parts by mass with respect to 100 parts by mass of a solid content of a polyurethane urea polymer (B), and subsequently heating, wherein said polyurethane urea polymer (B) is produced by reacting a urethane prepolymer having a terminal isocyanate group which is obtained by a reaction between a high-molecular diol and diisocyanate in an excess amount with respect to said high-molecular diol, with a bifunctional active hydrogen-containing compound which is able to form a urea group by reacting with an isocyanate group;
• {wherein R1 and R2 each independently represent an alkyl group or a hydroxyalkyl group, having 1 to 5 carbon atoms, or R1 and R2 are bonded to form a heterocyclic group together with the nitrogen atom to which they are bonded, and R3 represents a linear or branched alkylene group having 1 to 5 carbon atoms}
• {wherein R1 and R2 are the same or different and represent a linear or branched alkyl group or hydroxyalkyl group having 1 to 5 carbon atoms, or R1 and R2 are bonded to form a heterocyclic group together with the nitrogen atom to which they are bonded, R3 is a linear or branched alkylene group having 1 to 5 carbon atoms, X is a urea bond, R4, R5 and R6 are the same or different diisocyanate residue, P is a diol residue, Q is a diamine residue, UT is a urethane bond, UA is a urea bond, each of k, 1, m and n is a positive number, 1 is 1}
• (2) preparing a spinning dope containing a solvent by adding a solid content of said polyurethane urea polymer (A) in a ratio of 0.01 to 20 parts by mass with respect to 100 parts by mass of a solid content of another polyurethane urea polymer (B) which is obtained by reacting a prepolymer obtained by a reaction between a high-molecular diol and diisocyanate, with an active hydrogen-containing compound;
• and
• (3) spinning a polyurethane elastic fiber using said spinning dope.