Dyeability improver for polyester-based fiber material and disperse dye combination

The invention provides a dyeability improver for a polyester-based fiber material excellent in dispersibility of a dye from a low temperature to a high temperature and having good dyeability. It is apolyester copolymer which consists of a dibasic acids component unit which contains 10-40 mol% of dibasic acids components which have a sulfonate group, and a dihydric alcohol component unit of with amolecular weight of less than 48 to 900 dihydric alcohol origin, This dyeability improver for a polyester-based fiber material comprises a polyester copolymer having a molecular weight of 3,000-20,000 and an intramolecular content ratio of 2 to 75% by mass of the dibasic acid constituent unit of the polyester copolymer of 50. 本发明提供从低温到高温的染料的分散性优异并且染色性良好的聚酯系纤维材料用染色性提高剂。聚酯系纤维材料用染色性提高剂，其包含聚酯共聚物，该聚酯共聚物包含：含有10～40摩尔％的具有磺酸盐基的二元酸成分的二元酸成分单元、和来自分子量48以上且不到900的二元醇的二元醇成分单元，分子量为3000～20000，并且该二元酸成分单元的分子内含有比率为50～75质量％。