Method for producing polyester fibers

Claim 1

A method for producing polyester fibers having excellent dyeability, and capable of being dyed with basic or disperse dyes at a temperature of less than 100° C. with no deterioration of said fibers, which comprises melt-spinning a polyester comprising predominantly repeating units of ethylene terephthalate and containing 0.5% by mol or more of an ester unit derived from a dicarboxylic acid or diol containing at least one metal sulfonate group under the condition of being highly oriented so as to give filaments having a birefringence (Δn) of 0.015 to 0.100 and drawing the resulting filaments at a temperature of less than the melting point of the polymer and satisfying the following equation (1): 100 ≦ T ≦ 4 × (Δn × 10.sup.3) + 70 (1) wherein T is the drawing temperature (° C) and Δn is the birefringence of the filaments obtained after the melt-spinning, and at a draw ratio of from 1.05 times up to the maximum draw ratio of the following equations (2) and (3): ##EQU2## wherein Δn is as defined above, DR max .sbsb.1 and DR max .sbsb.2 are each the maximum draw ratio, and IV f is the intrinsic viscosity of the filaments obtained after the melt-spinning which is measured at 30° C in a mixed solvent of phenol:tetrachloroethane = 3:2.

Claim 2

A method for producing polyester fibers having excellent dyeability, and capable of being dyed with basic or disperse dyes at a temperature of less than 100° C. with no deterioration of said fibers, which comprises melt-spinning a polyester comprising predominantly repeating units of ethylene terephthalate and containing 0.5% by mol or more of an ester unit derived from a dicarboxylic acid or diol containing at least one metal sulfonate group under the condition of being highly oriented so as to give filaments having a birefringence (Δn) of 0.015 to 0.100 and drawing the resulting filaments at a temperature of less than the melting point of the polymer and satisfying the following equation (1): 100 ≦ T ≦ 4 × (Δn × 10.sup.3) + 70 (1) wherein T is the drawing temperature (° C) and Δn is the birefringence of the filaments obtained after the melt-spinning, and at a draw ratio of from 1.05 times up to the maximum draw ratio of the following equations (2) and (3): ##EQU2## wherein Δn is as defined above, DR max .sbsb.1 and DR max .sbsb.2 are each the maximum draw ratio, and IV f is the intrinsic viscosity of the filaments obtained after the melt-spinning which is measured at 30° C in a mixed solvent of phenol:tetrachloroethane = 3:2.