Abstract: A flat permeable membrane of polyolefin 10 to 500 .mu.m in thickness, which membrane has compact layers of intimately bound fine particles of polyolefin formed one each in the opposite surface regions of the membrane and a layer of an aggregate of fine discrete particles of an average diameter of 0.01 to 5 .mu.m formed between the compact layers and, consequently, has fine through pores labyrinthically extended in the direction of thickness of the membrane to establish communication between the opposite surfaces of the membrane and a method for the manufacture of the permeable membrane.

Abstract: A flat permeable membrane of polyolefin 10 to 500 .mu.m in thickness, which membrane has compact layers of intimately bound fine particles of polyolefin formed one each in the opposite surface regions of the membrane and a layer of an aggregate of fine discrete particles of an average diameter of 0.01 to 5 .mu.m formed between the compact layers and, consequently, has fine through pores labyrinthically extended in the direction of thickness of the membrane to establish communication between the opposite surfaces of the membrane and a method for the manufacture of the permeable membrane.

Abstract: A method of manufacture of flat permeable membrane comprises the steps of mixing a polyolefin, an organic filler uniformly dispersible in the polyolefin in the molten state, and crystal seed forming agent for the polyolefin; discharging the resultant mixture in the molten state through a die; bringing one surface of the discharged molten membrane into contact with a cooling roll; placine the cooled and solidified flat membrane into contact with an extractant capable of dissolving and extracting the organic filler and capable of dissolving the polyolefin; and subjecting the cooled and solidified flat membrane in a fixed state in longitudinal and lateral directions to a heat treatment at a temperature 20.degree. to 50.degree. C. lower than the melting point of the polyolefin.

Abstract: A flat permeable polyolefin membrane 10 to 500 .mu.m in thickness, which has in one surface thereof a compact layer formed of intimately bound fine polyolefin particles and possessed of fine pores and in the interior and the other surface thereof a layer formed of an aggregate of fine discrete polyolefin particles of an average diameter in the range of 0.01 to 5 .mu.m so adjoined as to form fine labyrinthically continuing through pores and which, therefore, establishes communication between the opposite surfaces of said membrane.

Abstract: A porous hollow fiber membrane, comprising a polyolefin hollow fiber membrane of an annular cross section of substantial circle 150 to 300 .mu.m in inside diameter and 10 to 150 .mu.m in wall thickness, said hollow fiber membrane forming on the inner wall side thereof a tight layer of intimately bound fine polyolefin particles and on the outer wall side thereof a porous texture of fine polyolefin particles bound in chains and containing fine pores extended continuously form said inner wall side to said outer wall side.