Micro or nano porous membrane, manufacturing method of same, porous resin membrane complex, and filter element

A method of manufacturing a micro or nano porous membrane composed of a stretched membrane obtained by stretching a non-porous membrane material of fluororesins, the method comprising:

• shaping a plurality of core-shell particles containing the fluororesins into a membrane;
• sintering the plurality of core-shell particles by heating the membrane obtained by the shaping to its melting point or more to obtain a sintered body, which is the non-porous membrane material of the fluororesins;
• and
• stretching the non-porous membrane material of the fluororesins obtained by the sintering,
• wherein the core-shell particles include cores and shells covering outer surfaces of the cores,
• wherein an average particle size of the core-shell particles before the sintering is greater than or equal to 100 nm and less than or equal to 1,000 nm,
• wherein a ratio of a volume of the shells to a volume of the cores in the core-shell particles before the sintering is greater than or equal to 2/98 and less than or equal to 50/50,
• wherein a fluororesin of the cores is a tetrafluoroethylene-hexafluoropropylene copolymer or a combination of the tetrafluoroethylene-hexafluoropropylene copolymer and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and a fluororesin of the shells is polytetrafluoroethylene,
• wherein the tetrafluoroethylene-hexafluoropropylene copolymer does not include any monomer other than tetrafluoroethylene and hexafluoropropylene,
• wherein the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer does not include any monomer other than tetrafluoroethylene and perfluoroalkyl vinyl ether,
• wherein a first heat of fusion of the fluororesins in the core-shell particles is less than or equal to 68 J/g, and
• a Gurley in the micro or nano porous membrane is 25 seconds or less.