| 摘要 |
PURPOSE:To obtain a polyvinylidene fluoride resin porous film suitable for concentration and separation of substance such as reverse osmosis, ultrafiltration and precise filteration, by a method wherein the title film is constituted of at least five layer structure where there are at least three transmission layers possessing fine many holes and among the said transmission layers supporting layers possessing huge voids are interposed. CONSTITUTION:A stock solution obtained by dissolving polyvinylidene fluoride resin into a solvent mainly composed of dimethyl sulfoxide is extruded through a mouthpiece for 4 hollow thread along with an immersion liquid, solidified from both the inside and outside of the hollow thread by passing through a solidifying solution and then the hollow thread is wound up. Both the surfaces and inside of a film of this hollow thread film possess transmission layers 1a, 1b, 1c whose mean hole diameter is 0.01-1 muand five layer structure where supporting layers 2a, 2b containing huge voids whose mean hole diameter in the surface running parallel with a film surface is 1-20 muhave existed by placing them among those transmission layers 1a, 1b, 1c is observed. There is no difference on transmission capacity of this film from whichever side of the film the stock solution may be caused to flow and the film is excellent practically.
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