Extra-fine fiber sheet

An extra-fine fiber sheet comprising an extra-fine fiber assembly, wherein the assembly consists essentially of:

• a solvent-spinnable polymer (A) having a weight average molecular weight of 5,000 to 100,000 as a main component;
• a polymer (B) having a weight average molecular weight equal to or more than 10 times as large as that of the polymer (A) as an accessory component;
• and
• optionally one or more additives selected from the group consisting of a plasticizer, an antioxidant, a slip additive, an ultraviolet absorber, a light stabilizer, an antistatic agent, a flame retardant, a lubricant, a crystallization speed retarder, and a colorant;
• wherein:
• the polymer (A) is (i) an ethylene-vinyl alcohol copolymer or (ii) a polyamide including a 1,9-nonanediamine unit, a 2-methyl-1,8-octanediamine unit or both, as a diamine unit;
• the polymer (B) is a polyethylene oxide, a polyethylene glycol or a polyacrylamide;
• the sheet has a composition ratio of the polymer (A) to the polymer (B) of (A):(B)=10:1 to 10,000:1;
• the assembly comprises constituent fibers having an average fiber diameter of 10 to 500 nm;
• and
• the assembly has 5 or fewer beads generated per 100 μm2 on a cross section of the extra-fine fiber assembly photographed at a magnification of 5,000, and the beads are unfiberized particulate material having a size equal to or greater than 5 times as large as the average fiber diameter.