CPC D01F 8/14 (2013.01) [D01D 5/08 (2013.01); D10B 2331/04 (2013.01)] | 6 Claims |
1. An ultrafine fiber having a fiber diameter (D) of 100 to 5000 nm, a ratio (L/D) of a fiber length (L) to the fiber diameter (D) of 3000 to 6000, and a carboxyl terminal group amount of 40 eq/ton or more,
wherein at least a part of a surface layer of the ultrafine fiber is formed of polyester, when the ultrafine fiber is dispersed in an aqueous medium to obtain a fiber dispersion liquid having a solid content concentration of 0.01 to 10% by weight, a dispersion index measured by the following method is 20 or less,
method of measuring the dispersion index: a fiber dispersion liquid is prepared such that the solid content concentration is 0.01% by weight with respect to a total amount of the fiber dispersion liquid, an image of the obtained fiber dispersion liquid at a magnification of 50 times is captured with a microscope under transmitted illumination, the image is converted into a monochrome image by using an image processing software, then a luminance histogram is formed with 256 grades, and a standard deviation obtained from the luminance histogram is used as the dispersion index.
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