Abstract: A method for producing a highly permeable microporous polyolefin membrane including the steps of preparing a polyolefin solution containing 5-40 weight % of a polyolefin or a polyolefin composition and 95-60 weight % of a solvent, the polyolefin having a weight-average molecular weight of not less than 3.times.10.sup.5 and less than 1.times.10.sup.6 and a weight-average molecular weight/number-average molecular weight of 5-300, and the polyolefin composition having a weight-average molecular weight of not less than 3.times.10.sup.5 and less than 1.times.10.sup.6 and a weight-average molecular weight/number-average molecular weight of 5-300 as a whole, extruding the polyolefin solution, stretching the extrudate uniaxially at a draft ratio of 3-50 in a molten state, cooling the stretched extrudate to solidify to a gel-like sheet, removing residual solvent, drying the resultant sheet, and heat-setting at a temperature of 80.degree. C. or higher and its melting point or lower.

Abstract: A microporous polyolefin composite membrane, preferably for use as a battery separator, comprising a microporous polyolefin membrane and a polyolefin nonwoven fabric laminated on at least one surface of the microporous polyolefin membrane. The composite membrane has a thickness of 25 to 200 .mu.m, a porosity of 30 to 70%, an air permeability of 100 to 2000 sec/100 cc and a surface opening area ratio of 50 to 90% on at least one outer surface thereof. The microporous polyolefin membrane comprises a matrix polyolefin component which is a polyolefin having a weight average molecular weight of 5.times.10.sup.5 or more or a polyolefin mixture containing the polyolefin having a weight average molecular weight of 5.times.10.sup.5 or more, and has a porosity of 30 to 95%, an air permeability of 100 to 2000 sec/100 cc, an average open pore diameter of 0.001 to 1 .mu.m and a tensile strength at break of 500 kg/cm.sup.2 or more.

Abstract: A method of producing a microporous thermoplastic resin membrane of excellent permeability having uniform and fine micropores without filling stress concentrators to the thermoplastic resin is provided. Namely, there is provided a method of producing a microporous thermoplastic resin membrane, in which a thermoplastic resin foam incorporating fine cells having a ratio B/A between a cell size (A) and a wall thickness (B) of the cells of less than 0.5 and having a void ratio of not less than about 50% is subjected to plastic deformation of the boundaries of the cells themselves sufficient to cause shape deformation of the cells, thereby breaking the boundaries of the cells. Also there is provided a microporous thermoplastic resin membrane of excellent permeability having uniform and fine micropores produced by the method as described above.

Abstract: An efficient method of producing a microporous polyolefin membrane having improved tensile strength and pierce strength is provided, in which a solution having dissolved therein 5% by weight to 50% by weight of a polyolefin whose weight-average molecular weight is in the range of 5.times.10.sup.5 to 2.5.times.10.sup.6 and whose weight-average molecular weight to number-average molecular weight ratio is less than 10, is extruded and rapidly cooled to obtain a gel-like product which is then stretched and has remaining solvent removed therefrom.

Abstract: A method of producing a microporous polyolefin membrane having a relatively large pore size and a high permeability, the membrane being suitable for use in water treatment, microfiltration, etc. The method comprises dissolving a polyolefin composition in a solvent to prepare a solution, extruding the solution through a die lip into a form of gel-like sheet, rapidly cooling the gel-like sheet, removing a residual solvent in the cooled sheet by a washing solvent, and drying the resultant sheet to remove the washing solvent. The polyolefin composition is a mixture of (A) an ultra high molecular weight polyolefin having a weight average molecular weight of 5.times.10.sup.5 or more and (B) a polyolefin having a weight average molecular weight less than 5.times.10.sup.5, and a weight ratio of (B)/(A) is 0.2 to 20.

Abstract: A method of manufacturing a polyolefin solution continuously and in a stable manner with a high yield which comprises heading a polyolefin resin with a liquid composed of a solvent for the polyolefin resin, and is characterized in that; (1) a continuous kneader having a self-cleaning action is used, and (2) a starving state is maintained in the internal sections of the header at a polyolefin resin feed section, a liquid feed section, and the section in which the kneading of the polyolefin resin and the liquid is initially carried out.

Abstract: A microporous polyolefin membrane made of a polyolefin composition containing 1 weight % or more of an ultra-high-molecular-weight polyolefin having a weight-average molecular weight of 7.times.10.sup.5 or more and having a weight-average molecular weight/number-average molecular weight ratio of 10-300, the microporous membrane having a thickness of 0.1-25 .mu.m, a porosity of 35-95%, an average pore diameter of 0.001-0.2 .mu.m and a breaking strength of 0.2 kg or more per 15 mm width is produced by (a) preparing a solution comprising 10-50 weight % of the polyolefin composition and 50-90 weight % of a solvent; (b) extruding the solution through a die; (c) cooling the extruded solution to form a gel-like article; (d) stretching the gel-like article at a temperature equal to or lower than a melting point of the polyolefin composition +10.degree. C; and (e) removing the remaining solvent.