| 摘要 |
PROBLEM TO BE SOLVED: To provide a sea-island type composite cross-section fiber capable of suppressing separation at a composite interface and substantially improving a fluff and thread breakage, etc., and an ultra fine polyamide fiber obtained by dissolving and removing a polyester included in the sea-island type composite fiber.SOLUTION: The sea-island type composite cross section fiber uses an alkali easily leachable polyester having a main repeating unit formed of ethylene terephthalate and comprising 2.0-5.5 mol% of an isophthalic acid component including a metal sulfonate group and 3.0-6.0 mol% of an adipic acid component to a total acid component as a sea component, and a polyamide as an island component. In the sea-island type composite cross section fiber, a unit reaction rate of terephthalic acid caused by an ester/amide exchange reaction is 0.0005-0.0025%/mm. |
