Patent ID: 7846544

Claim:
A sheath-core type composite polyester monofilament in which 80 mol % or more of a structural unit is polyethylene terephthalate, wherein the following A to F are satisfied: A. A polyester of a core component has an intrinsic viscosity of 0.70 dL/g or more, and a polyester of a sheath component has an intrinsic viscosity of 0.55 to 0.60 dL/g; B. The weight ratio of the core component in the sheath-core type composite polyester monofilament is from 50% to 70%; C. Fine metal particles are contained in polyethylene terephthalate constituting at least a sheath component in an amount of 0.2 to 0.4% by weight; D. When the monofilament has a fineness of 5 to 15 dtex, the modulus at an elongation of 5% is from 3 to 4.5 cN/dtex, and the breaking elongation is from 20 to 40%; E. The degree of free shrinkage of the monofilament in a most inner layer portion of a taken-up package measured 10 days after winding up is 0.3% or less; and F. The number of slub portions per 100,000 meters in a filament longitudinal direction, which are 10 μm or more thicker than a filament diameter, is 1 or less.