To obtain a latent crimp-expressing polyester fiber which has an improved crimp-expressing ability under a condition restrained in a woven fabric and is useful for a fabric or the like by melt-spinning polybutylene terephthalate and polyethylene terephthalate having a lower intrinsic viscosity than that of the polybutylene terephthalate under specific conditions, wherein both the polyesters have a difference of prescribed value or larger between their intrinsic viscosities.
Polybutylene terephthalate having an intrinsic viscosity [η] of ≥1.20 and polyethylene terephthalate having an intrinsic viscosity [η] of ≥0.55 are melted and spun in the form of a side-by-side conjugate fiber or an eccentric sheath-core conjugate fiber to obtain a latent crimp-expressing polyester fiber having a crimp extension-retaining rate of ≥5% and a shrinking stress of ≥0.20 CN/dtex. Both the polyesters has an intrinsic viscosity difference Δ[η] of ≥0.60. It is preferable that middle twisted or strongly twisted latent crimp-expressing polyester fibers having a twist coefficient K of 8,000-25,000 are used to produce a polyester fabric having excellent stretchability, and it is also preferable that a polyester blended yarn is produced from the latent crimp-expressing polyester fibers and low shrinkable polyester fibers having a boiling water rate of ≤3%.
KIDAI AKIRA
SATO MASAYUKI
