Nanofiber structure and manufacturing method thereof

Abstract

In a nanofiber structure in which a nanofiber A and a nanofiber B are tangled with each other, the softening point of the nanofiber A is different from that of the nanofiber B, a cross-section along a surface of the nanofiber A orthogonal to a longitudinal direction thereof has a shape having a concave portion, and the nanofiber A and the nanofiber B are fused with each other at this concave portion.

What is claimed is: 
     
         1 . A nanofiber structure comprising:
 a nanofiber A; and   a nanofiber B tangled with the nanofiber A, wherein:   the softening point of the nanofiber A is different from the softening point of the nanofiber B,   a cross-section along a surface of the nanofiber A orthogonal to a longitudinal direction thereof has a shape having a concave portion, and   at the concave portion, the nanofiber A and the nanofiber B are fused with each other.   
     
     
         2 . The nanofiber structure according to  claim 1 , wherein the concave portion is provided in an edge portion of the cross-section in a direction orthogonal to a longitudinal direction thereof. 
     
     
         3 . The nanofiber structure according to  claim 1 , wherein the concave portion is provided in an edge portion of the cross-section in a longitudinal direction thereof. 
     
     
         4 . The nanofiber structure according to  claim 1 , wherein:
 the average width of the cross-section of the nanofiber A is from 1 nm to 8×10 4  nm,   the cross-section of the nanofiber A at which the width thereof is from 1 nm to 8×10 4  nm has a shape having at least two convex portions,   the height of the convex portion is equal to or more than the average height of the cross-section of the nanofiber A and is equal to or less than the maximum height of the cross-section of the nanofiber A, and   the average fiber diameter of the nanofiber B is from 1 nm to 3,000 nm.   
     
     
         5 . The nanofiber structure according to  claim 1 , wherein a ratio L/Y of an average value L of the width of the cross-section of the nanofiber A to an average value Y of the fiber diameter of the nanofiber B is from 3.3×10 −4  to 8×10 3 . 
     
     
         6 . The nanofiber structure according to  claim 1 , wherein constituent materials of the nanofiber A and the nanofiber B are each a thermoplastic resin, and
 the difference in softening point between the constituent material of the nanofiber A and the constituent material of the nanofiber B is from more than 0° C. to less than 100° C.   
     
     
         7 . The nanofiber structure according to  claim 1 , wherein the difference in average solubility parameter between a constituent material of the nanofiber A and a constituent material of the nanofiber B is from 0 to 25 (J/cm 3 ) 1/2 . 
     
     
         8 . The nanofiber structure according to  claim 1 , wherein an average presence rate of nanofibers on the surface of the nanofiber structure is from 10% to 60%. 
     
     
         9 . The nanofiber structure according to  claim 1 , wherein:
 the nanofiber structure is a sheet-shaped structure, and   the thickness of the sheet-shaped structure is from 1 μm to 1 mm.   
     
     
         10 . A method for manufacturing a nanofiber structure, wherein the nanofiber structure comprises:
 a nanofiber A; and   a nanofiber B tangled with the nanofiber A, wherein:   the softening point of the nanofiber A is different from the softening point of the nanofiber B,   a cross-section along a surface of the nanofiber A orthogonal to a longitudinal direction thereof has a shape having a concave portion, and   at the concave portion, the nanofiber A and the nanofiber B are fused with each other,   the method comprising:   forming a precursor by tangling at least the nanofiber A and the nanofiber B; and   heating the precursor.   
     
     
         11 . The method according to  claim 10 , wherein the nanofiber A or the nanofiber B contains an organic resin material and a low molecular weight organic compound having a chemical reactivity. 
     
     
         12 . The method according to  claim 10 , wherein in the heating, the precursor is heated without pressure application.