Core-sheath composite fiber, production method therefor, and fiber structure

Abstract

Provided are a core-sheath composite fiber, a production method therefor, and a fiber structure. The core-sheath composite fiber includes: a core component (12) including a melt-anisotropic aromatic polyester (a polymer A); and a sheath component having an islands-in-the-sea structure and including a flexible thermoplastic polymer (a polymer B) and a melt-anisotropic aromatic polyester (a polymer C). The polymer B and the polymer C constitute a sea component and an island component of the islands-in-the-sea structure, respectively. The island component includes a plurality of islands (18) dispersed in a sea (14) that is formed of the sea component.

What is claimed is: 
     
         1 . A core-sheath composite fiber comprising:
 a core component including a melt-anisotropic aromatic polyester (a polymer A); and   a sheath component having an islands-in-the-sea structure and including a flexible thermoplastic polymer (a polymer B) as a sea component and a melt-anisotropic aromatic polyester (a polymer C) as an island component, the islands-in-the-sea structure being provided with a plurality of islands formed of the island component dispersed in a sea formed of the sea component, wherein   the sheath component has a proportion of the island component of more than wt %;   among the islands in a cross section cut along a longitudinal direction of the core-sheath composite fiber, an island represented by having a largest width along a direction perpendicular to the fiber has a maximum width W of 0.65 μm or shorter;   the island having the maximum width W has a maximum diagonal length L1 which is a longest length in the island overlapped with a diagonal line drawn in the sheath component at a fixed angle of 10° relative to the longitudinal direction of the fiber along one end to another end thereof, and has a ratio L1/W of the maximum diagonal length L1 to the maximum width W of said island being 5.0 or more.   
     
     
         2 . The core-sheath composite fiber of  claim 1 , wherein the maximum diagonal length L1 is 1.0 μm or longer. 
     
     
         3 . The core-sheath composite fiber of  claim 1 , wherein said island in the sheath component has a length L2 along the longitudinal direction of the fiber of from 450 to 1000 μm, in the cross section cut along the longitudinal direction of the core-sheath composite fiber. 
     
     
         4 . The core-sheath composite fiber of  claim 1 , wherein the sheath component has a thickness of from 0.8 to 5.0 μm. 
     
     
         5 . The core-sheath composite fiber of  claim 1 , wherein the polymer A and the polymer C comprise a melt-anisotropic aromatic polyester of same species as each other. 
     
     
         6 . The core-sheath composite fiber of  claim 1 , wherein a ratio of the core component/the sheath component in terms of a weight ratio of the core component to the sheath component is from 20/80 to 97/3. 
     
     
         7 . The core-sheath composite fiber of  claim 1 , wherein the core-sheath composite fiber has a single fiber fineness of from 1 to 120 dtex. 
     
     
         8 . A method for producing a core-sheath composite fiber, the core-sheath composite fiber comprising: a core component including a melt-anisotropic aromatic polyester (a polymer A); and a sheath component having an islands-in-the-sea structure and including a flexible thermoplastic polymer (a polymer B) as a sea component and a melt-anisotropic aromatic polyester (a polymer C) as an island component, the islands-in-the-sea structure being provided with a plurality of islands formed of the island component dispersed in a sea formed of the sea component, the method at least comprising:
 kneading the polymer B and the polymer C for the sheath component in a twin-screw extruder at a temperature which is equal to Mb° C. or higher, is equal to (Mc−20°) C. or higher, and is lower than Mc° C., where Mb is a melting point of the polymer B and Mc is a melting point of the polymer C, and melt-kneading the polymer A for the core component in an extruder different from the twin-screw extruder used for the sheath component;   discharging an as-spun composite fiber of the kneaded sheath component and the kneaded core component; and   taking up the discharged as-spun fiber at a draft value of from 13 to 50, the draft value being a ratio of a winding speed to a discharging speed.   
     
     
         9 . The production method for the core-sheath composite fiber of  claim 8 , further comprising:
 subjecting the spun fiber to a heat treatment.   
     
     
         10 . A fiber structure comprising, at least in a part thereof, a core-sheath composite fiber recited in  claim 1 .