Patent ID: 7569145

Claim:
A porous hollow fiber, comprising a stretched single layer of a vinylidene fluoride resin having a weight-average molecular weight of at least 3×10 5 , having a water permeation rate F (m 3 /m 2 ·day) measured at a pressure difference of 100 kPa and at a water temperature of 25° C. in a range of test length L=0.2-0.8 (m) and expressed in a linear relationship with the test length L of: F=C·L+F 0 (formula 1) and satisfying requirements (a)-(d) shown below: (a) an average slope C (/day) of: −20≦C≦0, (b) an intercept (basic permeability) F 0 (m 3 /m 2 ·day) of: F 0 ≦30, (c) a relation between F 0 (m 3 /m 2 ·day) and an average pore diameter P (μm) according to half-dry method of F 0 /P≧500, (d) an outer diameter of at most 3 mm, (e) a porosity of 65-80%, and (f) a relationship of: F 0 /D i 4 ≦75 between the basic permeability F 0 (m 3 /m 2 ·day) and an inner diameter D i (mm) of the hollow fiber; wherein the vinylidene fluoride resin comprises 2-49 wt. % of a first vinylidene fluoride resin having a weight-average molecular weight (Mw 1 ) of 4×10 5 -12×10 5 and 51-98 wt. % of a second vinylidene fluoride resin having a weight-average molecular weight (Mw 2 ) of 1.5×10 5 -6×10 5 provided that the weight-average molecular weight (Mw 1 ) of the first vinylidene fluoride resin and the weight-average molecular weight (Mw 2 ) of the second vinylidene fluoride resin satisfy a ratio Mw 1 /Mw 2 of at least 1.2.