# US 2014/0196840 A1 · Method for producing porous polytetrafluoroethylene membrane > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0196840 A1 - Document ID: US20140196840A1 - Status: Published application - Kind: A1 - Application number: 14/130,816 - Filed: 2012-07-04 - Published: 2014-07-17 - Earliest claimed: 2011-07-05 - Assignees: Nitto Denko Corporation - Inventors: Kyoko Ishii; Seiji Aizawa - Web page: https://patentgrep.com/patent/US20140196840A1 ## CPC - B01D 69/107: {Organic support material} - B01D 39/1692: {Other shaped material, e.g. perforated or porous sheets} - B01D 67/00041: {by sintering} - B01D 67/00042: {by deposition of fibres, nanofibres or nanofibrils} - B01D 67/0027: {by stretching} - B01D 71/36: Polytetrafluoroethylene - B32B 5/022: {Non-woven fabric} - B32B 5/30: one layer {being formed of particles, e.g. chips,} granules, powder - B32B 27/12: next to a fibrous or filamentary layer - B32B 27/322: {comprising halogenated polyolefins, e.g. PTFE} - C08J 5/18: Manufacture of films or sheets - B29C 55/005: {characterised by the choice of materials} - B29C 55/02: of plates or sheets - B32B 2262/12: Conjugate fibres, e.g. core/sheath or side-by-side - B32B 2264/0257: Polyolefin particles, e.g. polyethylene or polypropylene homopolymers or ethylene-propylene copolymers - B32B 2307/718: Weight, e.g. weight per square meter - B32B 2307/724: Permeability to gases, adsorption - B32B 2307/7265: Non-permeable - C08J 2327/18: Homopolymers or copolymers of tetrafluoroethylene - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) - B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM - C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29) - B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00) ## Abstract Provided is a method including: a step A of extruding a mixture containing a polytetrafluoroethylene (PTFE) fine powder having a standard specific gravity (SSG) of 2.19 or less and a liquid lubricant into a sheet using a flat die so as to obtain a PTFE sheet; a step B of rolling the PTFE sheet by passing the sheet between a pair of rolls in a longitudinal direction of the sheet; a step C of stretching the rolled PTFE sheet in a transverse direction of the sheet; a step D of removing the liquid lubricant from the PTFE sheet; and a step E of stretching the PTFE sheet, from which the liquid lubricant has been removed, both in the longitudinal direction of the sheet and in the transverse direction of the sheet, for example, at an area stretch ratio of 150 to 700, so as to make the sheet porous. According to this production method, it is possible to increase the PF value of the porous PTFE membrane. ## Claims ### Claim 1 A method for producing a porous polytetrafluoroethylene membrane, comprising: a step A of extruding a mixture containing a polytetrafluoroethylene fine powder having a standard specific gravity of 2.19 or less and a liquid lubricant into a sheet using a flat die so as to obtain a polytetrafluoroethylene sheet; a step B of rolling the polytetrafluoroethylene sheet by passing the sheet between a pair of rolls in a longitudinal direction of the sheet that is a direction of the extrusion in the step A; a step C of stretching the polytetrafluoroethylene sheet in a transverse direction perpendicular to the longitudinal direction of the sheet; a step D of removing the liquid lubricant from the polytetrafluoroethylene sheet that has been rolled in the step B and stretched in the step C; and a step E of stretching the polytetrafluoroethylene sheet, from which the liquid lubricant has been removed in the step D, both in the longitudinal direction of the sheet and in the transverse direction of the sheet so as to obtain a porous polytetrafluoroethylene membrane. ### Claim 2 (depends on 1) The method for producing a porous polytetrafluoroethylene membrane according to claim 1, further comprising a step F of sintering the porous polytetrafluoroethylene membrane at a temperature equal to or higher than a melting point of polytetrafluoroethylene. ### Claim 3 (depends on 1) The method for producing a porous polytetrafluoroethylene membrane according to claim 1, wherein in the step B, the polytetrafluoroethylene sheet is rolled, with a length of the polytetrafluoroethylene sheet in the transverse direction being maintained unchanged. ### Claim 4 (depends on 1) The method for producing a porous polytetrafluoroethylene membrane according to claim 1, wherein a mixing ratio of the polytetrafluoroethylene fine powder and the liquid lubricant in the mixture is adjusted so that the mixture contains 5 to 50 parts by mass of the liquid lubricant per 100 parts by mass of the polytetrafluoroethylene fine powder. ### Claim 5 (depends on 1) The method for producing a porous polytetrafluoroethylene membrane according to claim 1, wherein the flat die is a fishtail die. ### Claim 6 (depends on 1) The method for producing a porous polytetrafluoroethylene membrane according to claim 1, wherein in the step E, a product of a stretch ratio in the longitudinal direction and a stretch ratio in the transverse direction is 4 or more and less than 150. ### Claim 7 (depends on 1) The method for producing a porous polytetrafluoroethylene membrane according to claim 1, wherein in the step E, a product of a stretch ratio in the longitudinal direction and a stretch ratio in the transverse direction is 150 or more and 700 or less. ### Claim 8 (depends on 7) The method for producing a porous polytetrafluoroethylene membrane according to claim 7, wherein in the step E, a product of a stretch ratio in the longitudinal direction and a stretch ratio in the transverse direction is 300 or more and 700 or less. ### Claim 9 (depends on 1) A method for producing a waterproof air-permeable member, comprising a step of connecting a fixing member to a connecting region of a porous polytetrafluoroethylene membrane, the connecting region surrounding an air-permeable region of the porous polytetrafluoroethylene membrane, wherein the method further comprises a step of preparing the porous polytetrafluoroethylene membrane, the step being the method for producing a porous polytetrafluoroethylene membrane according to claim 1. ### Claim 10 (depends on 1) A method for producing an air filter medium, comprising a step of bonding a porous polytetrafluoroethylene membrane and an air-permeable support member, wherein the method further comprises a step of preparing the porous polytetrafluoroethylene membrane, the step being the method for producing a porous polytetrafluoroethylene membrane according to claim 1.