| 摘要 |
PROBLEM TO BE SOLVED: To provide an ultrafine fiber excellent in industrial continuous productivity, useful for a filter use, an isolation membrane, a clothing use and the like as a web, and especially useful for the use as blood-separating filter. SOLUTION: This ultrafine fiber is composed of a polyester and/or a copolyester, obtained by polycondensing an ester or an oligoester by using a coprecipitation product of titanium dioxide and silicon dioxide having (90:20)-(20:80) mol/mol composition of TiO2:SiO2 as a polycondensation catalyst, and having 0.3-1.5 intrinsic viscosity and 4,000-20,000 weight average molecular weight expressed in terms of polystyrene, and has 0.7-5 μm average fiber diameter.
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