Porous membrane and method for manufacturing the same

A porous membrane manufacturing method comprising:

• a process (A) of manufacturing a raw material resin mixture containing 10 to 90 parts by weight of a solid-type paraffin wax having a weight-average molecular weight of 100 to 5,000 and 10 to 90 parts by weight of a liquid-type paraffin oil having a weight-average molecular weight of 300 to 1,500 relative to 100 parts by weight of a polyethylene resin;
• a process (B) of extruding and cooling the raw material resin mixture;
• a process (C) of stretching the raw material resin mixture extruded in the process (B);
• and
• a process (D) of immersing the raw material resin mixture stretched in the process (C) in an organic solvent to extract the solid-type paraffin wax and the liquid-type paraffin oil;
• and
• wherein the raw material resin mixture is obtained by mixing the solid-type paraffin wax and the liquid-type paraffin oil into the polyethylene resin in a state in which the solid-type paraffin wax and the liquid-type paraffin oil are previously mixed.

A porous membrane manufacturing method comprising the steps of:

• a) manufacturing a raw material resin mixture containing 10 to 90 parts by weight of a solid-type paraffin wax having a weight-average molecular weight of 100 to 5,000, 10 to 90 parts by weight of a liquid-type paraffin oil having a weight-average molecular weight of 300 to 1,500 as a pore-forming additive, and 6 to 10 parts by weight of an antioxidant relative to 100 parts by weight of a polyethylene resin having a melt index of 0.01 to 0.6 g/10 minutes and a weight-average molecular weight of no less than 300,000 and less than 500,000;
• b) mixing the raw material resin mixture into an extrusion screw to melt the raw material resin mixture at a temperature of 180 to 250° C. and extrude a gelatinous sheet having a thickness of 1,000 to 6,000 μm, and making the gelatinous sheet pass between a casting roll and a nip roll, respective surface temperatures of which are adjusted to 30 to 60° C., to cool the gelatinous sheet, in which for the nip roll, a nip roll having a diameter (D1) of a center region thereof that is smaller than a diameter (D2) of each of end parts on opposite sides of the nip roll and including a surface having an arc-like inverse gradient formed in an axial direction is used;
• c) sequentially stretching the cooled sheet in a machine direction and then in a transverse direction by approximately 5 to 15 times, respectively, to manufacture a stretched film having a thickness of 6 to 50 μm;
• and
• d) immersing the stretched film in an extraction solvent to remove the pore-forming additive, and then thermally fixing the stretched film at a temperature of 110 to 150° C.

A porous membrane manufacturing method comprising the steps of:

• A) melting and mixing 10 to 90 parts by weight of a solid-type paraffin wax having a weight-average molecular weight of 100 to 5,000 and 10 to 90 parts by weight of a liquid-type paraffin oil having a weight-average molecular weight of 300 to 1,500 at a temperature of 80 to 100° C. to manufacture a paraffin wax mixture;
• B) putting the paraffin wax mixture in a high-temperature state into an extrusion screw together with 100 parts by weight of a polyethylene resin having a weight-average molecular weight of no less than 300,000 and less than 500,000 to be melted and kneaded at a temperature of 180 to 250° C., and then extruding and cooling the resulting mixture to manufacture a gelatinous sheet, and biaxially stretching the gelatinous sheet and then immersing the gelatinous sheet in an organic solvent to manufacture a porous base material;
• C) mixing 0.1 to 30% by weight of a water-soluble polymer and 1 to 40% by weight of a non-water-soluble particulate polymer manufactured by emulsion polymerization or suspension polymerization, 1 to 50% by weight of an inorganic filler and 20 to 70% by weight of water to manufacture aqueous-dispersion ceramic slurry;
• and
• D) applying the aqueous-dispersion ceramic slurry to one surface or both of opposite surfaces of the porous base material in a thickness of 1 to 5 μm to form a ceramic coating layer.