Composite fiber, hollow fiber and multifilament

Abstract

A composite fiber includes: two or more kinds of polymers that have different dissolution rates in a solvent and are laminated in a direction from a fiber center to a fiber surface in a fiber cross section, in which an innermost layer including the fiber center includes an easily soluble polymer, and two kinds of hardly soluble polymers having different melting points are unevenly distributed in at least one layer other than the innermost layer.

1 .- 10 . (canceled) 
     
     
         11 . A composite fiber comprising:
 two or more polymers having different dissolution rates in a solvent and laminated in a direction from a fiber center to a fiber surface in a fiber cross section, wherein   an innermost layer including the fiber center comprises an easily soluble polymer, and   two hardly soluble polymers having different melting points are unevenly distributed in at least one layer other than the innermost layer.   
     
     
         12 . The composite fiber according to  claim 11 , wherein a relationship between an inscribed circle diameter RA and a circumscribed circle diameter RB of the fiber is 1.2≤RB/RA≤2.4 in the fiber cross section. 
     
     
         13 . The composite fiber according to  claim 11 , wherein in the fiber cross section, the easily soluble polymer communicates from the fiber center to the fiber surface, and a communication width is 10% or less of a fiber diameter. 
     
     
         14 . The composite fiber according to  claim 11 , wherein in the fiber cross section, an outermost layer comprises the easily soluble polymer. 
     
     
         15 . A hollow fiber obtained by removing the easily soluble polymer from the composite fiber according to  claim 11 . 
     
     
         16 . A multifilament comprising:
 a flat hollow fiber, wherein   a variation coefficient CV of a rotation angle of a long axis of the flat hollow fiber is 15% to 50%.   
     
     
         17 . The multifilament according to  claim 16 , wherein the flat hollow fiber has a flatness of 1.2 or more in a fiber cross section. 
     
     
         18 . The multifilament according to  claim 16 , wherein the flat hollow fiber is made of at least two kinds of polymers having different melting points in a fiber cross section. 
     
     
         19 . The multifilament according to  claim 16 , wherein
 the flat hollow fiber includes an opening portion formed in a direction from a fiber center to a fiber surface, and   a width of the opening portion is 10% or less of a fiber diameter.   
     
     
         20 . A fiber product partially comprising the composite fiber according to  claim 11 . 
     
     
         21 . A fiber product partially comprising the hollow fiber according to  claim 15 . 
     
     
         22 . A fiber product partially comprising the multifilament according to  claim 16 .