Patent ID: 7351338

Claim:
A hollow yarn porous membrane of vinylidene fluoride resin for water filtration, comprising a hollow yarn-form porous membrane of: (A) a vinylidene fluoride resin having a weight-average molecular weight of at least 200,000 and a ratio of weight-average molecular weight/number-average molecular weight of at least 2.5, or (B) a vinylidene fluoride resin comprising 2-75 wt. % of a first vinylidene fluoride resin having a weight-average molecular weight of 400,000-1,200,000 and 25-98 wt. % of a second vinylidene fluoride resin having a weight-average molecular weight of 150,000-600,000 giving a ratio of the weight-average molecular weight of the first vinylidene fluoride resin/the weight-average molecular weight of the second vinylidene fluoride resin of at least 1.2, wherein a crystalline oriented portion and a crystalline non-oriented portion are present in mixture as confirmed by X-ray diffraction.