| 摘要 |
A porous membrane, made of polyvinylidene fluoride which is excellent in fractionating capability, permeating capability and physical strength and suitable for use in water treatment such as water purification, preparation of drinking water, preparation of water for industrial use and wastewater treatment, and which can be manufactured inexpensively and easily. The porous membrane has one surface formed with round or oval micropores and the opposite surface formed with substantially slit shaped micropores. The round or oval micropores have an average ratio between the major axis and the minor axis, which is within the range of 1:1 to 5:1, and the substantially slit shaped micropores have an average ratio between the major axis and the minor axis, which is not smaller than 5:1 and the particle cutoff of the membrane is not smaller than 0.2 μm.
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