FIBER HAVING SEA-ISLAND-TYPE COMPOSITE CROSS SECTION, AND METHOD FOR PRODUCING SAME

摘要

Provided are: a fiber having a sea-island-type composite cross section, whereby it becomes possible to prevent the detachment at a composite interface and it also becomes possible to greatly improve the occurrence of fluffing, thread breakage and the like; and an ultrafine polyamide fiber which is produced by dissolving and removing a polyester contained in the fiber having a sea-island-type composite cross section. A fiber having a sea-island-type composite cross section, in which a sea component comprises a polyester capable of eluting readily with an alkaline component and an island component comprises a polyamide, wherein the polyester contains an isophthalic acid component, which is a component having a main repeating unit composed of ethylene terephthalate and containing a metal sulphonate group, in an amount of 2.0 to 5.5 mol% relative to the total amount of all of acid components and an adipic acid component in an amount of 3.0 to 6.0 mol% relative to the total amount of all of the acid components.