Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/30—Polyalkenyl halides
  • B01D71/32—Polyalkenyl halides containing fluorine atoms
  • B01D71/36—Polytetrafluoroethylene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0002—Organic membrane manufacture
  • B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
  • B01D67/0018—Thermally induced processes [TIPS]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0002—Organic membrane manufacture
  • B01D67/002—Organic membrane manufacture from melts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/10—Supported membranes; Membrane supports
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/12—Composite membranes; Ultra-thin membranes
  • B01D69/1213—Laminated layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
  • B32B27/322—Layered products comprising a layer of synthetic resin comprising polyolefins comprising halogenated polyolefins, e.g. PTFE
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
  • C08J7/04—Coating
  • C08J7/0427—Coating with only one layer of a composition containing a polymer binder
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
  • C08J7/04—Coating
  • C08J7/056—Forming hydrophilic coatings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/02—Details relating to pores or porosity of the membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/02—Details relating to pores or porosity of the membranes
  • B01D2325/0283—Pore size
  • B01D2325/02833—Pore size more than 10 and up to 100 nm
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/20—Specific permeability or cut-off range
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/22—Thermal or heat-resistance properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/34—Molecular weight or degree of polymerisation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
  • B32B5/22—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
  • B32B5/32—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed at least two layers being foamed and next to each other
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2429/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
  • C08J2429/02—Homopolymers or copolymers of unsaturated alcohols
  • C08J2429/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids

Definitions

• Porous membranes using polytetrafluoroethylene have the properties of polytetrafluoroethylene such as high heat resistance, chemical stability, weather resistance, nonflammability, high strength, non-adhesiveness, and low coefficient of friction, as well as properties such as flexibility, dispersion medium permeability, particle trapping, and low dielectric constant due to porosity. Therefore, porous films containing polytetrafluoroethylene as a main component are widely used as dispersion media and gas precision filters in the semiconductor-related, liquid-crystal-related, and food and medical-related fields.
• a porous membrane according to an aspect of the present disclosure is a porous membrane containing polytetrafluoroethylene as a main component, having an average flow pore size E of 75 nm or less, and a pore size difference (GE) between the maximum pore size G and the average flow pore size E of 20 nm or less.
• E average flow pore size
• GE pore size difference
• FIG. 1 is a schematic partial cross-sectional view showing a porous membrane according to one embodiment of the present disclosure.
• FIG. 2 is a schematic partial cross-sectional view showing an example of a porous membrane laminate according to an embodiment of the present disclosure.
• FIG. 3 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 4 is a photograph of test no. 1 is a cross-sectional image of the porous membrane laminate of No. 1.
• FIG. FIG. 5 is a photograph of test no. 2 is a cross-sectional image of the porous membrane laminate of No. 2.
• FIG. FIG. 6 is a photograph of test no. 3 is a cross-sectional image of the porous membrane laminate of No. 3.
• FIG. 7 is a photograph of test no. 4 is a cross-sectional image of the porous membrane laminate of No. 4.
• FIG. FIG. 8 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 9 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 10 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 11 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 12 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 13 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 14 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 15 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• FIG. 16 is a schematic partial cross-sectional view showing another example of the porous membrane laminate according to one embodiment of the present disclosure.
• the present disclosure has been made based on such circumstances, and aims to provide a porous membrane having excellent fine particle trapping performance.
• a porous membrane according to one aspect of the present disclosure is a porous membrane containing polytetrafluoroethylene as a main component, having an average flow pore size E of 75 nm or less, and a pore size difference GE between the maximum pore size G and the average flow pore size E of 20 nm or less.
• the main component of the porous membrane is polytetrafluoroethylene (hereinafter also referred to as PTFE), and the pore diameter is the gap between the polytetrafluoroethylene.
• PTFE polytetrafluoroethylene
• the pore diameter difference is 20 nm or less, the pore diameter variation is small and the accuracy of the filtration process is good.
• main component refers to a component having the largest content in terms of mass, for example, a component having a content of 90% by mass or more, preferably 95% by mass or more.
• the porous membrane preferably has a pore size difference of 15 nm or less between the maximum pore size G and the average flow pore size E.
• the pore size difference between the maximum pore size G and the average flow pore size E of the porous membrane is 15 nm or less, the pore size variation can be further reduced and the accuracy of the filtration process can be improved.
• the ratio of the pore size difference between the maximum pore size G and the average flow pore size E with respect to the average flow pore size E ⁇ (GE)/E ⁇ 100 (hereinafter also referred to as pore size ratio) is preferably 35% or less.
• the pore diameter ratio of the porous membrane is 35% or less, the variation in pore diameter can be further reduced, and the accuracy of filtration can be improved.
• Average flow rate pore diameter "pore diameter difference (GE)” and “pore diameter ratio ⁇ (GE)/E ⁇ x 100” are measured using propylene, 1,1,2,3,3,3 oxide hexafluoric acid with a surface tension of 15.9 mN/m as reagents in accordance with ASTM F316-03 and JIS-K3832 (1990), as described later, using a pore diameter distribution measuring device (for example, PMI's Palm Polo It can be calculated from the pore size distribution measured by a meter "CFP-1500A").
• a pore diameter distribution measuring device for example, PMI's Palm Polo It can be calculated from the pore size distribution measured by a meter "CFP-1500A").
• a porous membrane laminate according to another aspect of the present disclosure preferably includes one or more of the porous membranes described in (1) to (3) above, has an average flow pore diameter K of 75 nm or less, and preferably has a pore diameter difference JK between the maximum pore diameter J and the average flow pore diameter K of 20 nm or less. Since the porous membrane laminate includes the porous membrane, it is excellent in capturing fine particles and is suitable as a microfiltration filter. When the upper limit of the average flow pore diameter of the porous membrane laminate is 75 nm, fine particles easily collide with the fibers, and thus the porous membrane laminate has excellent fine particle trapping performance.
• the average flow pore diameter K of the porous membrane laminate is 75 nm or less, and the pore size difference JK between the maximum pore diameter J and the average flow pore diameter K is 20 nm or less, the pore diameter variation is small, and the accuracy of the filtration process is improved.
• the ratio of the pore diameter difference between the maximum pore diameter J and the average flow pore diameter K to the average flow pore diameter K ⁇ (JK)/K ⁇ 100 is preferably 35% or less.
• the pore diameter ratio of the porous membrane laminate is 35% or less, the variation in pore diameter can be reduced, and the accuracy of the filtration treatment of the porous membrane laminate can be further improved.
• the porous membrane laminate preferably includes one or more porous support membranes containing polytetrafluoroethylene as a main component, and the support membranes are laminated on one or both sides of the porous membrane.
• the porous membrane laminate includes one or more porous support membranes, and the support membrane is laminated on one or both sides of the porous membrane, so that the support membrane functions as a protective material for the porous membrane. Therefore, the porous membrane laminate can increase the mechanical strength and life of the porous membrane laminate while improving the trapping performance. Moreover, heat resistance, chemical stability, etc. can be improved by using polytetrafluoroethylene as a main component of the support film.
• the average flow pore size of the support membrane is 200 nm or less.
• the average flow pore diameter of the support film is 200 nm or less, the fine particle trapping performance of the porous film laminate can be further improved.
• the porous membrane laminate includes a plurality of the porous membranes and a plurality of the supporting membranes, the porous membranes and the supporting membranes being alternately laminated, and the supporting membranes being laminated at both ends.
• the porous membrane laminate the porous membranes and the support membranes are alternately laminated, and the support membranes are laminated on both ends, so that the trapping performance, mechanical strength and life of the porous membrane laminate can be further enhanced.
• the average flow pore diameter K of the porous membrane laminate is 60 nm or less.
• the average flow pore size of the porous membrane laminate is 60 nm or less, the fine particle trapping performance of the porous membrane laminate can be further improved.
• FIG. 1 is a schematic partial cross-sectional view showing a porous membrane according to one embodiment of the present disclosure.
• the porous membrane 1 is composed of a biaxially stretched porous membrane containing polytetrafluoroethylene as a main component. This biaxially stretched porous membrane is obtained by stretching the surface of a sheet containing PTFE as a main component in two orthogonal directions to make it porous.
• the porous membrane 1 allows the filtrate to permeate in the thickness direction while preventing permeation of fine impurities.
• the PTFE powder one with a high molecular weight is preferable.
• the use of high-molecular-weight PTFE powder can promote the growth of the fibrous skeleton while preventing excessive expansion of pores and tearing of the sheet during stretching.
• the PTFE powder one with a high molecular weight is preferable.
• the use of high-molecular-weight PTFE powder can promote growth of the fibrous skeleton while preventing excessive pore expansion and membrane cleavage during stretching.
• the lower limit of the number average molecular weight of the PTFE powder forming the porous membrane 1 is preferably 12 million, more preferably 20 million.
• the upper limit of the number average molecular weight of the PTFE powder forming the porous membrane 1 is preferably 50 million, more preferably 40 million. If the number-average molecular weight of the PTFE powder forming the porous membrane 1 is less than the above lower limit, the pore size of the porous membrane 1 may become large and the accuracy of the filtration process may deteriorate. On the other hand, if the number average molecular weight of the PTFE powder forming the porous membrane 1 exceeds the upper limit, formation of the membrane may become difficult.
• the "number-average molecular weight" is obtained from the specific gravity of the molded article, but the molecular weight of PTFE varies greatly depending on the measurement method and is difficult to measure accurately.
• the lower limit of the average thickness of the porous membrane 1 is preferably 2 ⁇ m, more preferably 5 ⁇ m.
• the upper limit of the average thickness of the porous membrane 1 is preferably 50 ⁇ m, more preferably 40 ⁇ m. If the average thickness is less than the lower limit, the strength of the porous membrane 1 may be insufficient. On the other hand, if the average thickness exceeds the upper limit, the porous membrane 1 becomes unnecessarily thick, which may increase the pressure loss when the filtrate is permeated. When the average thickness of the porous membrane 1 is within the above range, both strength and filtration efficiency of the porous membrane 1 can be achieved.
• Average thickness refers to the average value of ten arbitrary thicknesses, measured using a standard digital thickness gauge.
• the upper limit of the average flow pore diameter E of the porous membrane 1 is 75 nm or less, more preferably 70.0 nm or less. When the upper limit of the average flow pore size E of the porous membrane 1 is 75 nm or less, the fine particle trapping performance of the porous membrane 1 is excellent.
• the lower limit of the average flow pore size of the porous membrane 1 is preferably 25.0 nm or more, more preferably 35.0 nm or more. If the average flow pore size E of the porous membrane 1 is less than the above lower limit, the pressure loss of the porous membrane 1 may increase.
• the average flow pore diameter E of the porous membrane 1 is, for example, the molecular weight of PTFE as a raw material, the 1st.
• the average flow pore diameter E of the porous membrane 1 is preferably 25.0 nm or more and 75 nm or less, more preferably 35.0 nm or more and 70.0 nm or less.
• the upper limit of the pore size difference GE between the maximum pore size G and the average flow pore size E of the porous membrane 1 is 20 nm or less, and may be 15 nm or less.
• the pore diameter ratio of the porous membrane 1 is determined, for example, by the molecular weight of PTFE as a raw material and the 1st. It can be adjusted by selecting the difference between the onset temperature and the endset temperature of the peak in the range of 300° C. or higher and 360° C. or lower on the run melting curve, the drawing speed, and the like.
• the upper limit of the ratio of the difference between the maximum pore diameter G and the average flow pore diameter E with respect to the average flow pore diameter E of the porous membrane 1 ⁇ (GE)/E ⁇ 100 may be 35% or less, or 20% or less.
• the lower limit of the pore diameter ratio can be 10% or more and 15% or more.
• the pore size ratio can be 10% or more and 35% or less, or 10% or more and 20% or less.
• the pore diameter ratio of the porous membrane 1 is determined, for example, by the molecular weight of PTFE as a raw material and the 1st. It can be adjusted by selecting the difference between the onset temperature and the endset temperature of the peak in the range of 300° C. or higher and 360° C. or lower on the run melting curve, the drawing speed, and the like.
• the upper limit of the Gurley seconds of the porous membrane 1 is preferably 100 seconds, more preferably 80 seconds. If the Gurley second exceeds the above upper limit, the filtration efficiency of the porous membrane 1 may decrease. On the other hand, the lower limit of the Gurley second is preferably 1 second, more preferably 3 seconds. If the Gurley second is less than the above lower limit, the pore size of the porous membrane 1 may become too large and the fine particle trapping performance may deteriorate. "Gurley second" is measured according to JIS-P8117 (2009) and means the time for 100 cm 3 of air to pass through a 6.42 cm 2 sample with an average pressure difference of 1.22 kPa.
• the upper limit of the porosity of the porous membrane 1 is preferably 90%, more preferably 85%.
• the lower limit of the porosity of the porous membrane 1 is preferably 40%, more preferably 50%. If the porosity of the porous membrane 1 exceeds 90%, there is a risk that the ability of the porous membrane 1 to capture fine particles will be insufficient. On the other hand, if the porosity of the porous membrane 1 is less than 40%, the pressure loss of the porous membrane 1 may increase.
• the "porosity” refers to the ratio of the total volume of pores to the volume of the object, and can be obtained by measuring the density of the object according to ASTM-D-792.
• the porous membrane 1 may contain other fluororesins and additives within a range that does not impair the desired effects of the present disclosure.
• the method for producing the porous membrane includes the steps of forming a kneaded product of PTFE powder and liquid lubricant, and stretching the formed body.
• a kneaded product of PTFE powder produced by emulsion polymerization or the like and a liquid lubricant is extruded to produce a sheet-like molded body.
• the raw material PTFE particles are powder composed of fine PTFE particles.
• Examples of the PTFE powder include PTFE fine powder, which is a powder composed of fine particles of PTFE and produced by emulsion polymerization, and PTFE molding powder produced by suspension polymerization.
• liquid lubricant Various lubricants conventionally used in the extrusion method can be used as the liquid lubricant.
• the liquid lubricant include petroleum solvents such as solvent naphtha and white oil, hydrocarbon oils such as undecane, aromatic hydrocarbons such as toluol and xylol, alcohols, ketones, esters, silicone oils, fluorochlorocarbon oils, solutions obtained by dissolving polymers such as polyisobutylene and polyisoprene in these solvents, water or aqueous solutions containing surfactants, and the like.
• solvents such as solvent naphtha and white oil
• hydrocarbon oils such as undecane
• aromatic hydrocarbons such as toluol and xylol
• alcohols ketones, esters
• silicone oils fluorochlorocarbon oils
• solutions obtained by dissolving polymers such as polyisobutylene and polyisoprene in these solvents, water or aqueous solutions containing surfactants,
• the lower limit of the amount of the liquid lubricant mixed with 100 parts by mass of the PTFE powder is preferably 10 parts by mass, more preferably 16 parts by mass.
• the upper limit of the mixed amount of the liquid lubricant is preferably 40 parts by mass, more preferably 25 parts by mass. If the mixed amount of the liquid lubricant is less than the above lower limit, extrusion may become difficult. On the other hand, if the mixed amount of the liquid lubricant exceeds the above upper limit, there is a possibility that compression molding, which will be described later, becomes difficult.
• the material for forming the porous film may contain other additives in addition to the liquid lubricant, depending on the purpose.
• additives include pigments for coloring, carbon black, graphite, silica powder, glass powder, glass fiber, inorganic fillers such as silicates and carbonates, metal powders, metal oxide powders, and metal sulfide powders for improving wear resistance, preventing cold flow, and facilitating pore formation.
• substances that can be removed or decomposed by heating, extraction, dissolution, etc. such as ammonium chloride, sodium chloride, plastics other than PTFE, rubber, etc., may be blended in the form of powder or solution.
• the PTFE powder and the liquid lubricant are mixed, and then compression-molded into a block body, which is a primary molded body, by a compression molding machine.
• this block is extruded into a sheet at a temperature of room temperature (eg, 25° C.) to 50° C. at a speed of, for example, 10 mm/min to 30 mm/min.
• a PTFE sheet having an average thickness of 250 ⁇ m or more and 350 ⁇ m or less is obtained.
• the porous membrane has excellent liquid lubricant permeability, and the extrusion pressure during manufacturing is reduced.
• the liquid lubricant contained in the PTFE sheet may be removed after stretching the sheet, but it is preferably removed before stretching.
• the liquid lubricant can be removed by heating, extraction, dissolution, or the like. When heating, for example, the liquid lubricant can be removed by rolling the PTFE sheet with a hot roll at 130° C. or higher and 220° C. or lower.
• a liquid lubricant having a relatively high boiling point such as silicone oil or fluorochlorocarbon oil, removal by extraction is suitable.
• Step of stretching In this step, the PTFE sheet, which is a molded body, is biaxially stretched. Through this step, pores are formed and a porous membrane can be obtained. In this step, a biaxially stretched porous membrane is obtained by sequentially stretching the PTFE sheet in the machine direction (flow direction) and the transverse direction (width direction) perpendicular to the machine direction.
• the lower limit of the temperature during stretching is preferably 60°C, more preferably 120°C.
• the upper limit of the temperature during stretching is preferably 300°C, more preferably 280°C. If the temperature during stretching is less than the above lower limit, the pore size may become too large. On the other hand, if the stretching temperature exceeds the above upper limit, the pore size may become too small.
• the biaxially stretched porous membrane is preferably heat-set after stretching.
• heat setting shrinkage of the biaxially stretched porous membrane can be prevented, and the porous structure can be more reliably maintained.
• a specific method of heat setting for example, a method of fixing both ends of the biaxially stretched porous membrane and holding at a temperature of 200° C. or higher and 500° C. or lower for 0.1 minute or longer and 20 minutes or shorter can be used.
• heat setting is preferably performed after each stage.
• the porous membrane since it is excellent in capturing fine particles, it can be suitably used as a filter or the like that requires high filtration accuracy.
• the porous membrane laminate includes one or more of the porous membranes described above. Since the porous membrane laminate includes the porous membrane, it is excellent in capturing fine particles and is suitable as a microfiltration filter.
• the upper limit of the average flow pore size K of the porous membrane laminate is preferably 75 nm or less, more preferably 60 nm or less, and even more preferably 55 nm or less.
• the lower limit of the average flow pore size K of the porous membrane laminate is preferably 25 nm or more, more preferably 30 nm or more. If the average flow pore size K of the porous membrane laminate is less than the above lower limit, the pressure loss of the porous membrane laminate may increase.
• the average flow pore size K of the porous membrane laminate is preferably 25 nm or more and 75 nm or less, more preferably 25 nm or more and 60 nm or less, and even more preferably 30 nm or more and 55 nm or less.
• the upper limit of the pore size difference JK between the maximum pore size J and the average flow pore size K in the porous membrane laminate is preferably 20 nm or less, more preferably 18 nm or less.
• the lower limit of the pore size difference JK can be 17 nm or more and 15 nm or more.
• the pore size difference JK can be 17 nm or more and 20 nm or less, or 15 nm or more and 18 nm or less.
• the upper limit of the ratio of the difference between the maximum pore diameter J and the average flow pore diameter K with respect to the average flow pore diameter K in the porous membrane laminate ⁇ (JK)/K ⁇ 100 is preferably 35% or less, more preferably 33% or less.
• the lower limit of the pore diameter ratio can be 20% or more and 23% or more.
• the pore size ratio can be 20% or more and 35% or less, or 23% or more and 33% or less.
• the upper limit of the Gurley seconds of the porous membrane laminate is preferably 75 seconds, more preferably 70 seconds, and even more preferably 65 seconds.
• the lower limit of the Gurley seconds of the porous membrane laminate is preferably (1) seconds. If the Gurley second of the porous membrane laminate exceeds 75 seconds, the filtration cost of the porous membrane laminate may not be sufficiently reduced. On the other hand, if the Gurley second of the porous membrane laminate is less than the above lower limit, the pore diameter of the porous membrane laminate may become too large and the fine particle trapping performance may deteriorate.
• the porous membrane laminate preferably includes one or more porous support membranes, and the support membrane is laminated on one side or both sides of the porous membrane. Since the support film is laminated on one side or both sides of the porous membrane, the support film functions as a protective material for the porous membrane, so that the porous membrane laminate can improve the trapping performance while increasing the mechanical strength and life of the porous membrane laminate.
• the support film preferably contains polytetrafluoroethylene as a main component. By using polytetrafluoroethylene as a main component of the support film, heat resistance, chemical stability, etc. can be improved.
• the upper limit of the average flow pore size of the support membrane is preferably 200 nm or less, more preferably 180 nm or less. If the average flow pore diameter of the support membrane exceeds 3000 nm, the strength of the support membrane 2 may be insufficient.
• the lower limit of the mean flow pore diameter of the support membrane is preferably 80 nm or more, more preferably 100 nm or more. If the average flow pore size of the support membrane is less than the above lower limit, the pressure loss of the porous membrane laminate may increase.
• the average flow pore size of the support membrane is preferably 80 nm or more and 200 nm or less, more preferably 100 nm or more and 180 nm or less.
• the upper limit of the average thickness of the support film is preferably 20 ⁇ m, more preferably 15 ⁇ m.
• the lower limit of the average thickness of the support film is preferably 2 ⁇ m, more preferably 5 ⁇ m. If the average thickness of the support membrane exceeds the above upper limit, the pressure loss of the porous membrane laminate may increase. On the other hand, if the average thickness of the support film 2 is less than the above lower limit, the strength of the porous membrane laminate may be insufficient.
• FIG. 2 is a schematic partial cross-sectional view showing a porous membrane laminate according to one embodiment of the present disclosure.
• a porous membrane laminate 10 shown in FIG. 2 includes a porous membrane 1 and a porous support membrane 2 laminated on one side of the porous membrane 1 .
• the porous membrane laminate 10 includes the porous membrane 1 and the porous support film 2 laminated on one side of the porous membrane 1” can be rephrased as “the porous membrane laminate 10 comprises the first porous membrane 1 made of the porous membrane 1 and the first support film 2 mainly composed of polytetrafluoroethylene, and the first porous membrane 1 is arranged on one main surface of the first support film 2.”
• the porous membrane laminate 10 is provided with the porous support membrane 2 laminated on one side of the porous membrane 1, and the porous membrane 1 is supported by the support membrane 2, so that the mechanical strength can be improved and clogging of the filter can be suppressed.
• the porous membrane laminate may have a three-layer structure, and may have a total of three layers, for example, a pair of support membranes arranged as the outermost layers and a porous membrane arranged between the pair of support membranes. Also, the porous membrane laminate may have a structure of four or more layers.
• the porous membrane laminate includes a plurality of the porous membranes and a plurality of the supporting membranes, the porous membranes and the supporting membranes being alternately laminated, and the supporting membranes being laminated at both ends.
• the porous membrane laminate the porous membrane and the support membrane are alternately laminated, and the support membranes are laminated on both ends, so that the trapping performance, mechanical strength, and life of the porous membrane laminate can be further enhanced.
• FIG. 3 is a schematic partial cross-sectional view showing a porous membrane laminate according to another embodiment of the present disclosure.
• the porous membrane laminate 20 shown in FIG. 3 has a five-layer structure in which two layers of the porous membrane 1 are laminated between the pair of support membranes 2 of the outermost layer, and the support membrane 2 is further laminated between the pair of porous membranes 1.
• the porous membrane laminate 20 has a five-layer structure in which two layers of the porous membrane 1 are laminated between the pair of outermost support films 2 and the support film 2 is laminated between the pair of porous membranes 1
• the porous membrane laminate 20 includes the first porous membrane 1 composed of the porous membrane 1, the second porous membrane 1 composed of the porous membrane 1, the first support membrane 2 mainly composed of polytetrafluoroethylene, and polytetrafluoroethylene. and a third support film 2 mainly composed of polytetrafluoroethylene, and on one main surface of the first support film 2, the first porous film 1, the second support film 2, the second porous film 1, and the third support film 2 are arranged in the above order.
• the porous membrane 1 and the support membrane 2 are alternately laminated, and the support membrane 2 is laminated on both ends, so that the trapping performance, mechanical strength and life of the porous membrane laminate 20 can be further enhanced.
• the first porous film 1 and the second porous film 1 may have the same structure or different structures.
• the first supporting film 2, the second supporting film 2, and the third supporting film 2 may have the same structure or different structures.
• the porous membrane laminate 10 can be composed of a first porous membrane 1 made of the porous membrane 1 and a second porous membrane 1 made of the porous membrane 1, and the second porous membrane 1 can be arranged on one main surface of the first porous membrane 1.
• the mechanical strength of the porous membrane laminate 10 can be improved, and the fine particle trapping performance (probability of trapping particles by fibers) can be improved.
• the first porous film 1 and the second porous film 1 may have the same structure or different structures.
• the porous membrane laminate 20 is composed of a first porous membrane 1 made of the porous membrane 1, a first supporting membrane 2 mainly composed of polytetrafluoroethylene, and a second supporting membrane 2 mainly composed of polytetrafluoroethylene.
• the mechanical strength of the porous membrane laminate 20 can be improved, filter clogging can be suppressed, and deterioration of particle trapping performance due to trauma can be suppressed.
• the first support film 2 and the second support film 2 may have the same structure or different structures.
• the porous membrane laminate 20 is composed of a first porous membrane 1 made of the porous membrane 1, a second porous membrane 1 made of the porous membrane 1, and a first support membrane 2 containing polytetrafluoroethylene as a main component.
• the mechanical strength of the porous membrane laminate 20 can be improved, filter clogging can be suppressed, and the fine particle trapping performance (probability of trapping particles by fibers) can be improved.
• the first porous film 1 and the second porous film 1 may have the same structure or different structures.
• the porous membrane laminate 20 comprises a first porous membrane 1 made of the porous membrane 1, a second porous membrane 1 made of the porous membrane 1, a first supporting membrane 2 mainly composed of polytetrafluoroethylene, and a second supporting membrane 2 mainly composed of polytetrafluoroethylene.
• the membrane 1 and the second support membrane 2 can be arranged in the above order.
• the mechanical strength of the porous membrane laminate 20 can be improved, filter clogging can be suppressed, the fine particle trapping performance (probability of trapping particles by fibers) can be improved, and deterioration of the particle trapping performance due to trauma can be suppressed.
• the first porous film 1 and the second porous film 1 may have the same structure or different structures.
• the first support film 2 and the second support film 2 may have the same structure or different structures.
• the porous membrane laminate 20 includes a first porous membrane 1 made of the porous membrane 1, a second porous membrane 1 made of the porous membrane 1, a third porous membrane 1 made of the porous membrane 1, and a first support membrane 2 containing polytetrafluoroethylene as a main component.
• the membrane 1 and the third porous membrane 1 can be arranged in the above order.
• the mechanical strength of the porous membrane laminate 20 can be improved, filter clogging can be suppressed, and the fine particle trapping performance (probability of trapping particles by fibers) can be improved.
• the first porous film 1, the second porous film 1, and the third porous film 1 may have the same configuration or different configurations.
• the porous membrane laminate 20 includes a first porous membrane 1 made of the porous membrane 1, a second porous membrane 1 made of the porous membrane 1, a third porous membrane 1 made of the porous membrane 1, a first supporting membrane 2 mainly composed of polytetrafluoroethylene, and a second supporting membrane 2 mainly composed of polytetrafluoroethylene.
• the first porous membrane 1, the second porous membrane 1, the third porous membrane 1, and the second support membrane 2 can be arranged in the above order.
• the mechanical strength of the porous membrane laminate 20 can be improved, filter clogging can be suppressed, the fine particle trapping performance (probability of trapping particles by fibers) can be improved, and deterioration of the particle trapping performance due to trauma can be suppressed.
• the first porous film 1, the second porous film 1, and the third porous film 1 may have the same configuration or different configurations.
• the first support film 2 and the second support film 2 may have the same structure or different structures.
• the porous membrane laminate 20 comprises a first porous membrane 1 made of the porous membrane 1, a first support film 2 mainly composed of polytetrafluoroethylene, a second support film 2 mainly composed of polytetrafluoroethylene, a third support film 2 mainly composed of polytetrafluoroethylene, and a fourth support film 2 mainly composed of polytetrafluoroethylene.
• the second support film 2, the first porous film 1, the third support film 2, and the fourth support film 2 can be arranged in the above order.
• the mechanical strength of the porous membrane laminate 20 can be improved, filter clogging can be suppressed, and deterioration of particle trapping performance due to trauma can be suppressed.
• the first supporting film 2, the second supporting film 2, the third supporting film 2, and the fourth supporting film 2 may have the same configuration or different configurations.
• the porous membrane laminate 20 includes a first porous membrane 1 composed of the porous membrane 1, a second porous membrane 1 composed of the porous membrane 1, a third porous membrane 1 composed of the porous membrane 1, a first supporting membrane 2 composed mainly of polytetrafluoroethylene, a second supporting membrane 2 composed mainly of polytetrafluoroethylene, a third supporting membrane 2 composed mainly of polytetrafluoroethylene, and a polytetrafluoroethylene.
• the first porous film 1, the second porous film 1, and the third porous film 1 may have the same configuration or different configurations.
• the first supporting film 2, the second supporting film 2, the third supporting film 2, and the fourth supporting film 2 may have the same configuration or different configurations.
• the porous membrane laminate 20 includes a first porous membrane 1 composed of the porous membrane 1, a second porous membrane 1 composed of the porous membrane 1, a third porous membrane 1 composed of the porous membrane 1, a fourth porous membrane 1 composed of the porous membrane 1, a fifth porous membrane 1 composed of the porous membrane 1, a first support membrane 2 composed mainly of polytetrafluoroethylene, and polytetrafluoroethylene. and a second support film 2 containing fluoroethylene as a main component, wherein the first porous film 1, the second porous film 1, the third porous film 1, the fourth porous film 1, the fifth porous film 1, and the second support film 2 are arranged in the above order on one main surface of the first support film 2.
• the mechanical strength of the porous membrane laminate 20 can be improved, filter clogging can be suppressed, the fine particle trapping performance (probability of trapping particles by fibers) can be improved, and deterioration of the particle trapping performance due to trauma can be suppressed.
• the first porous film 1, the second porous film 1, the third porous film 1, the fourth porous film 1, and the fifth porous film 1 may have the same configuration or different configurations.
• the first support film 2 and the second support film 2 may have the same structure or different structures.
• the porous membrane laminate is formed by, for example, laminating the porous membrane on one side of the support membrane and heating them.
• Examples of the method of laminating the porous membrane on the support membrane include a method of fusion bonding by heating, a method of bonding using an adhesive or a pressure-sensitive adhesive, and the like.
• the porous membrane is first laminated on one side of a support film, for example, and this laminate is heated to thermally fuse and integrate each layer at the boundary to obtain a porous membrane laminate.
• the lower limit of the heating temperature is preferably 327°C, which is the glass transition point of PTFE, and more preferably 360°C.
• the upper limit of the heating temperature is preferably 400°C. If the heating temperature is less than 327° C., there is a possibility that the layers will be insufficiently heat-sealed. On the other hand, if the heating temperature exceeds 400°C, each layer may be deformed.
• the heating time is preferably 0.5 minutes or more and 3 minutes or less.
• fluororesin or fluororubber having solvent solubility or thermoplasticity is preferable as the adhesive or adhesive in the method of bonding using an adhesive or adhesive.
• Hydrophilization treatment may be performed on the porous membrane laminate obtained as described above.
• the porous membrane laminate is impregnated with a hydrophilic material and crosslinked.
• the hydrophilic material include polyvinyl alcohol (PVA), ethylene vinyl alcohol copolymer (EVOH), acrylate resin, and the like.
• PVA polyvinyl alcohol
• EVOH ethylene vinyl alcohol copolymer
• acrylate resin acrylate resin
• PVA polyvinyl alcohol
• PVA polyvinyl alcohol
• EVOH ethylene vinyl alcohol copolymer
• acrylate resin acrylate resin
• the hydrophilization treatment can be performed, for example, by the following procedure.
• the porous membrane laminate is immersed in isopropyl alcohol (IPA) for 0.25 to 2 minutes, and then immersed in an aqueous PVA solution having a concentration of 0.5 to 0.8 mass % for 5 to 10 minutes.
• the porous membrane laminate is immersed in pure water for 2 minutes or more and 5 minutes or less, and then crosslinking is performed by adding a crosslinking agent or irradiating electron beams.
• the porous membrane laminate is washed with pure water and dried at room temperature (25° C.) or higher and 80° C. or lower to make the surface of the porous membrane laminate hydrophilic.
• cross-linking agent for example, one that forms glutaraldehyde cross-linking, terephthalaldehyde cross-linking, or the like is used.
• electron beam for example, an electron beam of 6 Mrad can be used.
• the porous membrane laminate by including one or a plurality of the porous membranes, it has excellent fine particle trapping performance. Therefore, it is suitable for a dispersion medium and gas precision filtration filter used for cleaning, peeling, chemical supply, etc. in the semiconductor-related field, the liquid crystal-related field, and the food and medical-related field.
• Appendix 2 The porous membrane according to appendix 1, wherein the pore size difference between the maximum pore size G and the average flow pore size E is 15 nm or less.
• Appendix 6 Equipped with one or more porous support films containing polytetrafluoroethylene as a main component, The porous membrane laminate according to appendix 4 or appendix 5, wherein the support film is laminated on one side or both sides of the porous membrane.
• Appendix 7 The porous membrane laminate according to appendix 6, wherein the support membrane has an average flow pore size of 200 nm or less.
• Appendix 8 comprising a plurality of the porous membranes and a plurality of the support membranes, The porous membrane laminate according to appendix 6 or appendix 7, wherein the porous membranes and the support films are alternately laminated, and the support films are laminated on both ends.
• Appendix 10 A first porous film made of the porous film according to any one of Appendices 1 to 3, and a second porous film made of the porous film according to any one of Appendices 1 to 3, A porous membrane laminate in which the second porous membrane is arranged on one main surface of the first porous membrane.
• Appendix 12 A first porous film made of the porous film according to any one of Appendices 1 to 3, a second porous film made of the porous film according to any one of Appendices 1 to 3, and a first support film containing polytetrafluoroethylene as a main component, A porous membrane laminate in which the first porous membrane and the second porous membrane are arranged in the order described above on one main surface of the first support membrane.
• a first porous film comprising the porous film according to any one of Appendices 1 to 3; a second porous film comprising the porous film according to any one of Appendices 1 to 3; a third porous film comprising the porous film according to any one of Appendices 1 to 3; A porous membrane laminate in which the first porous membrane, the second porous membrane, the third porous membrane, and the second supporting membrane are arranged in the order described above on one main surface of the first supporting membrane.
• a first porous film comprising the porous film according to any one of Appendices 1 to 3; a second porous film comprising the porous film according to any one of Appendices 1 to 3; a third porous film comprising the porous film according to any one of Appendices 1 to 3; and a fourth support film mainly composed of polytetrafluoroethylene, A porous membrane laminate in which the first porous membrane, the second supporting membrane, the second porous membrane, the third supporting membrane, the third porous membrane, and the fourth supporting membrane are arranged in the order described above on one main surface of the first supporting membrane.
• a first porous film comprising the porous film according to any one of Appendices 1 to 3; a second porous film comprising the porous film according to any one of Appendices 1 to 3; a third porous film comprising the porous film according to any one of Appendices 1 to 3; a fourth porous film comprising the porous film according to any one of Appendices 1 to 3; A fifth porous film made of the porous film according to item 1, a first support film containing polytetrafluoroethylene as a main component, and a second support film containing polytetrafluoroethylene as a main component, A porous membrane laminate in which the first porous membrane, the second porous membrane, the third porous membrane, the fourth porous membrane, the fifth porous membrane, and the second supporting membrane are arranged in the order described above on one main surface of the first supporting membrane.
• PTFE fine powder A (second heat of fusion: 15.8 J/g, molecular weight: about 28,000,000) shown in Table 1 was used as the raw material powder.
• the PTFE fine powder A used here is a powder obtained by drying and granulating PTFE particles (primary particles) produced by emulsion polymerization of tetrafluoroethylene (emulsion polymerization product).
• Table 1 shows the specific gravity of PTFE fine powder A and the results of differential scanning calorimetry using a differential scanning calorimeter (“DSC-60A” manufactured by Shimadzu Corporation). In addition, differential scanning calorimetry by a differential scanning calorimeter was performed by the above-mentioned method.
• PTFE fine powder 100 parts by mass of PTFE fine powder was kneaded with 18 parts by mass of solvent naphtha (“Supersol FP-25” manufactured by Idemitsu Oil Co., Ltd., boiling point: 50° C. to 180° C.) as a liquid lubricant.
• solvent naphtha (“Supersol FP-25” manufactured by Idemitsu Oil Co., Ltd., boiling point: 50° C. to 180° C.) as a liquid lubricant.
• the kneaded product was placed in a molding machine and compression molded to obtain a block-shaped molding.
• the block-shaped molding was continuously extruded into a sheet, passed through a rolling roller, passed through a heating roll (130° C. to 220° C.) to remove the liquid lubricant, and wound around a roll to form a PTFE sheet having an average thickness of 320 ⁇ m.
• the film was stretched 4 times in the machine direction (machine direction) at a roll temperature of 250°C to 280°C. Subsequently, both ends of the longitudinally stretched film in the width direction were gripped with chucks, and the film was stretched 25 times in the transverse direction, which is the direction perpendicular to the machine direction, in an atmosphere at 150°C. Heat fixation was carried out by holding it at 285° C. for 0.25 to 1 minute. By this stretching, test no. 1 and test no. No. 2 porous membrane was obtained. The sheet thus stretched was passed through a heating furnace at 360° C. and sintered for 1.5 minutes. 1 and test no. No. 2 porous membrane was obtained.
• PTFE fine powder (second heat of fusion 26.0 J/g, molecular weight about 5 million) was used as the raw material powder, and a PTFE sheet was produced according to the following procedure to form a support film.
• 100 parts by mass of PTFE fine powder was kneaded with 23 parts by mass of solvent naphtha (“Supersol FP-25” manufactured by Idemitsu Oil Co., Ltd.) as a liquid lubricant.
• the kneaded product was placed in a molding machine and compression molded to obtain a block-shaped molding.
• the block-shaped molding was continuously extruded into a sheet, passed through a rolling roller, passed through a heating roll (130° C.
• the film was stretched 3.5 times in the machine direction (machine direction) at a roll temperature of 250°C to 280°C. Subsequently, both ends of the longitudinally stretched film in the width direction were gripped with chucks, and the film was stretched 23 times in the transverse direction, which is the direction perpendicular to the machine direction, in an atmosphere at 150°C. Heat fixation was carried out by holding it at 285° C. for 0.25 to 1 minute. The thus stretched sheet was passed through a heating furnace at 360° C. and sintered for 1.5 minutes.
• a support film having an average thickness of 8 ⁇ m, a maximum pore size of 235 nm, an average flow rate pore size of 194 nm, a pore size ratio of 21.1%, and a Gurley second of 13 seconds was obtained.
• Test No. having a five-layer structure comprising two layers of support membranes shown in FIG. 3, two layers of porous membranes disposed between the pair of support membranes, and one layer of support membrane laminated between the pair of porous membranes. 1 and test no. No. 2 porous membrane laminate was produced.
• Test no. 1 and test no. In the step of laminating the porous membrane of Test No. 2 on the support membrane, 1 and test no. The porous membrane and the support membrane of the two tests were respectively laminated and heated at 370° C. for 100 seconds to heat-seal the boundaries of each layer to integrate them.
• the average thickness of the porous membrane laminate of No. 1 was 34 ⁇ m.
• the average thickness of the porous membrane laminate of No. 2 was 36 ⁇ m.
• PTFE fine powder B (second heat of fusion: 17.0 J/g, molecular weight: about 23,000,000) having a specific gravity and differential scanning calorimetry results shown in Table 1 was used as the raw material powder, and 100 parts by mass of the PTFE fine powder was kneaded with 16 parts by mass of solvent naphtha as a liquid lubricant.
• Test No. 1 having an average thickness of 45 ⁇ m was manufactured by the same process as the porous membrane laminate of No. 1. No. 3 porous membrane laminate was obtained.
• PTFE fine powder C (second heat of fusion: 16.8 J/g, molecular weight: about 22,000,000) having a specific gravity and differential scanning calorimetry results shown in Table 1 was used as raw material powder, and 100 parts by mass of PTFE fine powder was kneaded with 16 parts by mass of solvent naphtha as a liquid lubricant.
• Test No. 1 having an average thickness of 31 ⁇ m was manufactured by the same process as the porous membrane laminate of No. 1. 4 porous membrane laminates were obtained.
• the first heat of fusion was taken as the first heat of fusion. Further, similarly to the first heat of fusion, the end set temperature of the peak in the range of 300 ° C. or higher and 360 ° C. or lower of the melting curve of pattern 3 was used as the starting point, and the endothermic value obtained by integrating the section of 48 ° C. was taken as the second heat of fusion.
• Test no. 1 to test No. The pore diameter ratios of the porous membrane and the porous membrane laminate of No. 4 were calculated by the following procedure.
• test no. 1 to test No. For the porous membrane and porous membrane laminate of No. 4, propylene, 1,1,2,3,3,3 hexafluoric acid with a surface tension of 15.9 mN/m ("GALWICK” manufactured by PMI) was used as a reagent in accordance with ASTM F316-03 and JIS-K3832 (1990), and the pore size distribution was measured using a pore size distribution measuring instrument (perm porometer "CFP-1500A" manufactured by PMI). did.
• GALWICK 1,1,2,3,3,3 hexafluoric acid with a surface tension of 15.9 mN/m
• Pore size difference of porous membrane [nm] maximum pore size G - average flow pore size
• Pore size difference [nm] of the porous membrane laminate maximum pore size J - average flow pore size K
• Pore diameter ratio of porous membrane [%] ⁇ (GE) / E ⁇ ⁇ 100
• Pore diameter ratio of porous membrane laminate [%] ⁇ (JK) / K ⁇ ⁇ 100
• Polystyrene particle capture rate Test no. 1 to test No.
• the polystyrene particle capture rate [%] of the porous membrane laminate of No. 4 was measured by passing an aqueous solution of 0.1% octoxynol ("Triton X-100" manufactured by Dow Chemical Co.) containing polystyrene particles G40 (nominal diameter 0.04 ⁇ m) manufactured by Thermo Fisher Scientific at a concentration of 12 ppb, and collecting 500 ml of the filtrate after passage.
• the concentration of polystyrene particles in the filtrate was calculated from the fluorescence intensity of the polystyrene particle filtrate measured by a spectrofluorophotometer (Shimadzu Corporation, "Spectrofluorophotometer RF-6000").
• Test No. 1 to test No. Table 1 shows the evaluation results of the average flow pore size, pore size ratio, Gurley second, and polystyrene particle capture rate of the porous membrane laminate of No. 4.
• test No. photographed using a scanning electron microscope is shown in FIG.
• FIG. 5 shows a surface image of the porous membrane of Test No. 1 taken using a scanning electron microscope.
• a surface image of the porous membrane of Test No. 2 is shown
• FIG. 3 shows a surface image of the porous membrane of No. 3.
• Test No. photographed using a scanning electron microscope in FIG. 4 shows a surface image of the porous membrane of FIG.
• Test No. 1 has a porous membrane having an average flow pore size E of 75 nm or less and a difference (pore size difference GE) between the maximum pore size G and the average flow pore size E of 20 nm or less. 1 and test no.
• the porous membrane laminate of Test No. 2 comprises a porous membrane having an average flow pore size E of greater than 75 nm. 3 and the porous membrane with a pore size difference GE greater than 20 nm.
• the polystyrene particle trapping rate was superior to that of the porous membrane laminate of No. 4.
• FIGS. 1 and test no The porous membrane of Test No. 2 was tested. 3 and test no. Compared with the porous membrane of No.
• the porous membrane laminate provided with the porous membrane has excellent fine particle trapping performance. Therefore, the porous membrane laminate can be suitably used as a filter or the like that requires high-precision filtering performance.

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