Patent ID: 8324338

Claim:
A method of dyeing polyester-based fiber materials comprising: preparing a dyeing bath that contains a dye and an oligomer removing agent comprising a polyester copolymer which is obtained by polycondensation of a dibasic acid component containing 15-65 mol % of a sulfonate group-containing dibasic acid and a dihydric alcohol component containing polyethylene glycol, the polyethylene glycol having a molecular weight of 1000-3500, the polyester copolymer having a 200° C. melt viscosity of 5000-23,000 mPa·s and 10-40 mass % polyoxyethylene chain in the molecule; and dyeing the polyester-based fiber materials in the dyeing bath at a temperature of 100° C. to 140° C. to produce a dyed polyester-based fiber material that is substantially free of the oligomer removing agent.