Porous film, laminate, and filter element

Abstract

This porous film contains a polytetrafluoroethylene as a main component. The porous film has Gurley seconds and an average bubble point. The Gurley seconds and the average bubble point satisfy the relationship of formula 1 or formula 2.　Formula 1: G1 < 0.035×P1a, formula 2: G1 < 0.020×P1b. In formula 1 and formula 2, G1 is the Gurley seconds of the porous film. In formula 1, P1a is the average bubble point of the porous film. P1a is measured using a bubble point method in which a first a liquid is used. The surface tension of the first a liquid is 13 mN / m. In formula 2, P1b is the average bubble point of the porous film. P1b is measured using a bubble point method in which a first b liquid is used. The surface tension of the first b liquid is 21 mN / m.

Description

Porous membranes, laminates, and filter elements

[0001] The present disclosure relates to a porous membrane, a laminate, and a filter element. This application claims priority to Japanese Patent Application No. 2023-084099, filed May 22, 2023. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] Conventionally, porous membranes containing polytetrafluoroethylene as a main component have been used as dispersion media and substrate precision filters in the semiconductor-related field and the like (Patent Documents 1 to 6, Non-Patent Document 1).

[0003] Japanese Patent Application Publication No. 2021-54892 International Publication No. 2007 / 011492 International Publication No. 2020 / 251909 International Publication No. 2020 / 251912 Japanese Patent Application Publication No. 2015-226877 Japanese Patent Application Publication No. 2021-178948

[0004] Collection of Polymer Papers (Kobunshi Ronbunshu), Vol. 66, No. 12, pp. 585-590 (Dec., 2009)

[0005] A porous membrane according to one embodiment of the present disclosure is a porous membrane comprising polytetrafluoroethylene as a main component, the porous membrane having a Gurley second and an average bubble point, the Gurley second and the average bubble point satisfying the relationship of Equation 1 or Equation 2: G1<0.035×P1a Equation 1 G1<0.020×P1b Equation 2 In Equation 1 and Equation 2, G1 is the Gurley second of the porous membrane, In Equation 1, P1a is the average bubble point of the porous membrane, P1a is measured by a bubble point method using liquid 1a, and the surface tension of liquid 1a is 13 mN / m, and In Equation 2, P1b is the average bubble point of the porous membrane, P1b is measured by a bubble point method using liquid 1b, and the surface tension of liquid 1b is 21 mN / m.

[0006] Fig. 1 is a schematic enlarged cross-sectional view of a porous membrane according to an embodiment of the present disclosure. Fig. 2 is a schematic enlarged cross-sectional view of a laminate according to an embodiment of the present disclosure. Fig. 3 is a perspective view of a filter element (1) according to an embodiment of the present disclosure. Fig. 4 is a perspective view of a filter element (2) according to an embodiment of the present disclosure.

[0007] [Problem to be Solved by the Present Disclosure] In the microfiltration of dispersion media and substrates in the semiconductor-related field and the like, from the viewpoint of capturing finer particles and the like, a porous membrane having a high average bubble point and a laminate including a porous membrane are required as filters for the microfiltration. Note that the average bubble point here is an index indicating the difficulty of particles and the like passing through. The higher the average bubble point, the more difficult it is for particles and the like to pass through. Therefore, having a high average bubble point means that the ability to capture fine particles is excellent.

[0008] Furthermore, in the microfiltration, in order to increase the permeation efficiency, it is required to increase the flow rate of the filtrate through the porous membrane and the laminate including the porous membrane (in other words, to decrease the Gurley seconds of the porous membrane and the laminate including the porous membrane).

[0009] However, it is known that in porous membranes and laminates comprising porous membranes, if the average bubble point is high, the flow rate of the filtrate through the porous membranes and laminates comprising porous membranes tends to be low (in other words, the Gurley second of the porous membranes and laminates comprising porous membranes tends to be high).Therefore, it has sometimes been difficult to increase the average bubble point and reduce the Gurley second of porous membranes and laminates comprising porous membranes.In other words, it has sometimes been difficult for porous membranes and laminates comprising porous membranes to have both excellent particle capture performance and excellent permeation efficiency.

[0010] Therefore, an object of the present disclosure is to provide a porous membrane that combines excellent particulate capture performance and excellent permeation efficiency, a filter element including the porous membrane, a laminate that combines excellent particulate capture performance and excellent permeation efficiency, and a filter element including the laminate.

[0011] [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a porous membrane that combines excellent particulate capture performance and excellent permeation efficiency, a filter element including the porous membrane, a laminate that combines excellent particulate capture performance and excellent permeation efficiency, and a filter element including the laminate.

[0012] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. [1] A porous membrane according to one aspect of the present disclosure is a porous membrane containing polytetrafluoroethylene as a main component, the porous membrane having a Gurley second and an average bubble point, and the Gurley second and the average bubble point satisfy the relationship of Formula 1 or Formula 2. G1<0.035×P1a Equation 1 G1<0.020×P1b Equation 2 In Equation 1 and Equation 2, G1 is the Gurley second of the porous membrane, In Equation 1, P1a is the average bubble point of the porous membrane, P1a is measured by a bubble point method using liquid 1a, and the surface tension of liquid 1a is 13 mN / m, In Equation 2, P1b is the average bubble point of the porous membrane, P1b is measured by a bubble point method using liquid 1b, and the surface tension of liquid 1b is 21 mN / m.

[0013] According to the present disclosure, it is possible to provide a porous membrane that combines excellent particulate capture performance and excellent permeation efficiency, and a filter element including the porous membrane.

[0014] [2] In the above [1], P1a may be 450 kPa or more, and P1b may be 900 kPa or more. This makes it possible to provide a porous membrane having both superior fine particle capture performance and superior permeation efficiency, and a filter element including the porous membrane.

[0015] [3] In the above [1] or [2], the porous film has crystallites, each of which has a length X along the MD direction of the porous film and a length Y along the TD direction of the porous film, and the product XY of the length X and the length Y is 1200 nm. ２ This makes it possible to provide a porous membrane that has both superior fine particle capture performance and superior permeation efficiency, and a filter element that includes the porous membrane.

[0016] [4] A filter element according to one embodiment of the present disclosure includes the porous membrane described in [1] to [3] above.

[0017] According to the present disclosure, it is possible to provide a filter element including a porous membrane that combines excellent particulate capture performance and excellent permeation efficiency.

[0018] [5] A laminate according to one aspect of the present disclosure is a laminate comprising one or more porous membranes according to the above-mentioned [1] to [3], and a support membrane located on one or both sides of at least one of the porous membranes, wherein the support membrane is porous, and contains polytetrafluoroethylene as a main component, and the laminate has a Gurley second and an average bubble point, and the Gurley second and the average bubble point of the laminate satisfy the relationship of Equation 3 or Equation 4. G2<0.040×P2a Equation 3 G2<(0.025×P2b)-6 Equation 4 In the equations 3 and 4, G2 is the Gurley second of the laminate, In the equation 3, P2a is the average bubble point of the laminate, The P2a is measured by a bubble point method using a second a liquid, The surface tension of the second a liquid is 13 mN / m, In the equation 4, P2b is the average bubble point of the laminate, The P2b is measured by a bubble point method using a second b liquid, The surface tension of the second b liquid is 21 mN / m.

[0019] According to the present disclosure, it is possible to provide a laminate that combines excellent fine particle capture performance and excellent permeation efficiency, and a filter element including the laminate.

[0020] [6] In the above [5], the P2a may be 510 kPa or more, and the P2b may be 1000 kPa or more. This makes it possible to provide a laminate having both better fine particle capture performance and better permeation efficiency, and a filter element including the laminate.

[0021] [7] A filter element according to one embodiment of the present disclosure includes the laminate described in [5] or [6] above.

[0022] According to the present disclosure, it is possible to provide a filter element including a laminate that combines excellent particulate capture performance and excellent permeation efficiency.

[0023] [Details of the embodiment of the present disclosure] Hereinafter, one embodiment of the present disclosure (hereinafter referred to as "the present embodiment") will be described. However, the present embodiment is not limited thereto. In this specification, an expression in the form of "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0024] In the present specification, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is understood to include any conventionally known atomic ratio, and is not necessarily limited to only those within the stoichiometric range.

[0025] [Embodiment 1: Porous Membrane] A porous membrane 1 according to one embodiment of the present disclosure will be described with reference to Fig. 1. One embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") is a porous membrane 1 containing polytetrafluoroethylene as a main component, and the porous membrane 1 has a Gurley second and an average bubble point.

[0026] In the porous membrane 1 according to this embodiment, the Gurley second and the average bubble point satisfy the relationship of formula 1 or formula 2. G1<0.035×P1a Formula 1 G1<0.020×P1b Formula 2 By making the fibers of the porous membrane thinner, even if the fiber density increases (in other words, even if the average bubble point of the porous membrane increases), the pore ratio increases. Therefore, the porous membrane 1 can suppress the improvement of the Gurley second that accompanies an increase in the average bubble point. As a result, the porous membrane 1 can have both excellent particle capture performance and excellent permeation efficiency.

[0027] The average bubble point is measured by a bubble point method using a specific liquid. The numerical value of the average bubble point varies depending on the surface tension of the specific liquid. In view of the difficulty of obtaining the specific liquid, Equation 1 is defined for "P1a" measured by the bubble point method using "liquid 1a," and Equation 2 is defined for "P1b" measured by the bubble point method using "liquid 1b."

[0028] <Composition of Porous Membrane> The porous membrane 1 contains polytetrafluoroethylene as a major component. Here, "major component" refers to the component with the largest content in terms of mass, for example, a component with a content of 90% by mass or more, preferably 95% by mass or more. The porous membrane 1 may be made of polytetrafluoroethylene. The phrase "the porous membrane 1 is made of polytetrafluoroethylene" means that the porous membrane 1 may contain unavoidable impurities, as long as the effects of the present disclosure are achieved. In the present application, "polytetrafluoroethylene" refers to a polymer of tetrafluoroethylene, and is a concept that encompasses both a homopolymer of tetrafluoroethylene and a modified product of the "homopolymer of tetrafluoroethylene." Examples of such modified products include tetrafluoroethylene-hexafluoropropylene copolymer (in other words, perfluoroethylenepropene copolymer; hereinafter, also referred to as "FEP"), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), etc. The modified product may contain hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (FVE), or the like in an amount of 0.1 mol % or less.

[0029] In the porous membrane 1, the content of polytetrafluoroethylene is indicated by "-CF ２ -" absorbance at an absorption wavelength of 4.25 μm, and "-CH" indicating FEP ３ The absorbance at the absorption wavelength of 10.18 μm of the "CF group" and the absorbance at the absorption wavelength of 10.18 μm of the "CF group" ３ It can be identified based on the absorbance of the "O-group" at an absorption wavelength of 10.07 μm. It has been confirmed that similar results can be obtained even if different measurement ranges are arbitrarily selected for the same porous membrane 1.

[0030] <Shape of porous membrane> The thickness of the porous membrane 1 may be 0.002 mm or more and 0.100 mm or less. If the thickness is less than 0.002 mm, the strength of the porous membrane 1 tends to be insufficient. If the thickness is more than 0.100 mm, the pressure loss during permeation of the filtrate tends to be large. The lower limit of the thickness of the porous membrane 1 may be 0.002 mm or more, 0.005 mm or more, or 0.010 mm or more. The upper limit of the thickness of the porous membrane 1 may be 0.100 mm or less, 0.090 mm or less, or 0.080 mm or less. The thickness of the porous membrane 1 may be 0.005 mm or more and 0.090 mm or less, or 0.010 mm or more and 0.080 mm or less.

[0031] The thickness of the porous membrane 1 can be determined by the following method. First, the thickness is measured at one arbitrary location using a standard digital thickness gauge. Next, the thickness is measured at other arbitrary nine locations using the same standard digital thickness gauge. Next, the average value of the thicknesses at all 10 locations is calculated, thereby determining the thickness of the porous membrane 1.

[0032] It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same porous membrane and the above measurement is carried out in that measurement range.

[0033] The porous membrane 1 has an elongated shape.

[0034] <Density of porous membrane> The density of the porous membrane 1 is 0.05 g / cm ３ 2.00g / cm or more ３ The density may be 0.05 g / cm or less. ３ When the density is less than 2.00 g / cm, the strength of the porous membrane 1 tends to be insufficient. ３ If the density is greater than 0.05 g / cm3, the permeation efficiency of the porous membrane 1 tends to decrease. ３ or more, and 0.10 g / cm ３ or more, and 0.15 g / cm ３ The upper limit of the density of the porous membrane 1 is 2.00 g / cm ３or less, 1.70 g / cm ３ or less, 1.50 g / cm ３ The density of the porous membrane 1 may be 0.10 g / cm or less. ３ 1.70g / cm or more ３ or less, and 0.15 g / cm ３ 1.50g / cm or more ３ It may be the following:

[0035] The density of the porous membrane 1 can be determined by a method in accordance with ASTM-D-792. It has been confirmed that similar results can be obtained when different measurement ranges are arbitrarily selected for the same porous membrane 1 and the above measurements are performed within those measurement ranges.

[0036] <<Weight of porous membrane>> The weight of the porous membrane 1 is 0.002 mg / mm ２ 0.100mg / mm or more ２ The weight per unit area of ​​the porous membrane 1 may be 0.002 mg / mm ２ When the weight per unit area of ​​the porous membrane 1 is less than 0.100 mg / mm ２ If the permeation efficiency of the porous membrane 1 is more than 0.002 mg / mm ２ or more, and ２ or more, and ２ The upper limit of the basis weight of the porous membrane 1 is 0.100 mg / mm ２ or less, 0.080 mg / mm ２ or less, 0.060 mg / mm ２ The basis weight of the porous membrane 1 may be 0.003 mg / mm ２ 0.080mg / mm or more ２ or less, 0.004 mg / mm ２ 0.060mg / mm or more ２ It may be the following:

[0037] The basis weight of the porous membrane 1 can be determined by the following method. First, an evaluation sample is obtained by cutting an arbitrary portion of the porous membrane 1 into a circle with a diameter of 60.0 mm. Next, the mass of the evaluation sample is determined using an analytical balance "AP224X" (trademark) manufactured by Shimadzu Corporation. Next, the mass of the evaluation sample is multiplied by the area of ​​the evaluation sample (in other words, 30.0 mm). ２ × π) to determine the basis weight. Next, the basis weights of any other 9 locations are determined in the same manner as above. Next, the basis weight of the porous membrane 1 can be determined by calculating the average value of the basis weights of the total 10 locations.

[0038] It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same porous membrane 1 and the above measurement is carried out in that measurement range.

[0039] <Average Bubble Point and Gurley Second> <Average Bubble Point> The porous membrane 1 has an average bubble point (P1a and P1b). P1a may be 450 kPa or more. This allows the fibers of the porous membrane 1 to be formed thin and densely, so that the porous membrane 1 can have both a higher average bubble point and a lower Gurley second. The lower limit of P1a may be 450 kPa or more, 470 kPa or more, or 500 kPa or more. The upper limit of P1a may be 900 kPa or less, 890 kPa or less, or 880 kPa or less. P1a may be 470 kPa or more and 890 kPa or less, or 500 kPa or more and 880 kPa or less.

[0040] P1b may be 900 kPa or more. This allows the fibers of the porous membrane 1 to be formed thin and dense, so that the porous membrane 1 can have both a higher average bubble point and a lower Gurley second. The lower limit of P1b may be 910 kPa or more, or 920 kPa or more. The upper limit of P1b may be 1600 kPa or less, 1500 kPa or less, or 1400 kPa or less. P1b may be 900 kPa or more and 1600 kPa or less, or 910 kPa or more and 1500 kPa or less.

[0041] In the porous membrane 1, P1a is measured by the bubble point method using the 1a liquid, and the surface tension of the 1a liquid is 13 mN / m. More specifically, P1a in the porous membrane 1 is determined by the following method. First, for a dry porous membrane 1, the differential pressure applied to the porous membrane 1 and the air flow rate permeating the porous membrane 1 are measured based on the bubble point method (ASTM F316-86, JIS K3832). Next, on a coordinate system with the differential pressure on the horizontal axis and the air flow rate on the vertical axis, a first curve is obtained showing the relationship between the differential pressure and the numerical value obtained by dividing the air flow rate by 2. Next, the porous membrane 1 is immersed in "Opteon SF70" (trademark), a hydrofluoroolefin (liquid 1a) manufactured by Mitsui Chemours Fluoroproducts, Inc., for 5 minutes at 25°C, and then removed from the hydrofluoroolefin (liquid 1a), thereby obtaining a porous membrane 1 wet with hydrofluoroolefin (liquid 1a). Next, for the porous membrane 1 wet with hydrofluoroolefin (liquid 1a), the differential pressure applied to the porous membrane 1 and the air flow rate permeating the porous membrane 1 are measured based on the bubble point method. Next, a second curve showing the relationship between the differential pressure and the air flow rate is obtained on a coordinate system with the horizontal axis representing the differential pressure and the vertical axis representing the air flow rate. Next, the differential pressure at the intersection of the first curve and the second curve is determined as the average bubble point P1a. The surface tension of the hydrofluoroolefin (liquid 1a) is 13 mN / m.

[0042] In the porous membrane 1, P1b is measured by a bubble point method using liquid 1b, and the surface tension of liquid 1b is 21 mN / m. More specifically, in the porous membrane 1, P1b is determined by a method similar to the method for measuring P1a, except that isopropyl alcohol (liquid 1b) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. is used instead of liquid 1a.

[0043] <Gurley seconds> The porous membrane 1 has a Gurley second (G1). In the porous membrane 1, G1 may be 1 second or more and 100 seconds or less. This allows the flow rate of the filtrate to be increased, thereby increasing the permeation efficiency and improving the ability to capture fine particles contained in the filtrate. The lower limit of G1 may be 1 second or more, 3 seconds or more, or 5 seconds or more. The upper limit of G1 may be 100 seconds or less, 80 seconds or less, or 60 seconds or less. G1 may be 3 seconds or more and 80 seconds or less, or 5 seconds or more and 60 seconds or less.

[0044] In the porous membrane 1, G1 can be determined by the following method: In accordance with JIS P 8117, 100 ml of air is suctioned to a membrane with an effective membrane area of ​​6.42 cm. ２ The time required for permeation at a differential pressure of 1.22 kPa is measured and is identified as G1.

[0045] <Relationship between Gurley seconds and average bubble point> The Gurley seconds and the average bubble point satisfy the relationship of formula 1 or formula 2. G1<0.035×P1a Formula 1 G1<0.020×P1b Formula 2 In formula 1 and formula 2, G1 is the Gurley seconds of porous membrane 1, In formula 1, P1a is the average bubble point of porous membrane 1, P1a is measured by the bubble point method using liquid 1a, and the surface tension of liquid 1a is 13 mN / m, In formula 2, P1b is the average bubble point of porous membrane 1, P1b is measured by the bubble point method using liquid 1b, and the surface tension of liquid 1b is 21 mN / m. As a result, the porous membrane 1 can have both a high average bubble point and a low Gurley second, and therefore can have both excellent particle capture performance and excellent permeation efficiency. In Equation 1, "0.035" means the slope of the linear function. In Equation 2, "0.020" means the slope of the linear function.

[0046] <<Mean flow pore size>> The mean flow pore size of the porous membrane 1 may be 25 nm or more and 70 nm or less. This allows for both high permeation efficiency and high capture performance of fine particles contained in the filtrate. The lower limit of the mean flow pore size may be 25 nm or more, 26 nm or more, or 27 nm or more. The upper limit of the mean flow pore size may be 70 nm or less, 67 nm or less, or 65 nm or less. The mean flow pore size may be 26 nm or more and 67 nm or less, or 27 nm or more and 65 nm or less.

[0047] The mean flow pore size of porous membrane 1 can be determined by the following measurement method. That is, first, for dry porous membrane 1, the differential pressure applied to porous membrane 1 and the air flow rate passing through porous membrane 1 are measured based on bubble point method. Next, in a coordinate system where the horizontal axis is differential pressure and the vertical axis is air flow rate, obtain a third curve showing the relationship between the differential pressure and the numerical value obtained by dividing the air flow rate by 2. Next, the porous membrane 1 is immersed in GALWICK (propylene, 1,1,2,3,3,3-hexafluorofluoric acid oxide, fourth liquid) manufactured by Porous Materials for 5 minutes at 25 ° C., and then removed from the GALWICK (fourth liquid), thereby obtaining the porous membrane 1 wet with the GALWICK (fourth liquid). Next, for the porous membrane 1 wet with the GALWICK (fourth liquid), the differential pressure applied to porous membrane 1 and the air flow rate passing through porous membrane 1 are measured based on bubble point method. Next, a fourth curve showing the relationship between the differential pressure and the air flow rate is obtained on a coordinate system with the horizontal axis representing the differential pressure and the vertical axis representing the air flow rate. Next, the differential pressure P' at the intersection of the third curve and the fourth curve is identified. The mean flow pore size [nm] of the porous membrane 1 is then determined by dividing the product of the constant 2860 and the surface tension of the fourth liquid, 16 mN / m, by the differential pressure P'. In the bubble point method, for example, a Perm Porometer "CFP-1500A" manufactured by PMI is used as the pore diameter distribution measuring device.

[0048] <Crystallite> <Crystallite Structure> The porous membrane 1 has a crystallite, and the crystallite has a length X along the MD direction of the porous membrane 1 and a length Y along the TD direction of the porous membrane 1. In the present disclosure, "crystallite" refers to the smallest unit portion of a crystal grain that can be regarded as a single crystal. The upper limit of the length X along the MD direction of the porous membrane 1 may be less than 60 nm. When the length X along the MD direction of the porous membrane 1 is 60 nm or more, the average bubble point tends to decrease and the particle capture performance tends to be easily reduced. The upper limit of the length X along the MD direction of the porous membrane 1 may be less than 59 nm or less than 58 nm. The lower limit of the length X along the MD direction of the porous membrane 1 is not particularly limited, but can be, for example, 5 nm or more, 7 nm or more, or 10 nm or more. In this embodiment, the "MD direction" can be rephrased as the longitudinal direction. In this embodiment, the “TD direction” can be rephrased as a direction perpendicular to the “MD direction” and the thickness direction of the porous membrane 1 .

[0049] The length X of the porous membrane 1 along the MD direction can be determined by X-ray diffraction measurement. For X-ray diffraction measurement, BL16 at the Synchrotron Radiation Facility SAGA-LS was used. At the beamline, a double-crystal spectrometer using Si (111) diffraction was used to monochromatize the X-rays to a wavelength of 0.124 nm. Measurements were performed using the transmission method, with a NaI scintillation counter as the detector and a double-slit optical system. The receiving slits were all 0.5 mm long (in the direction of diffraction angle measurement) and 3 mm wide (perpendicular to the direction of diffraction angle measurement). Using the peak integral width B1 of the polytetrafluoroethylene (100) diffraction line in the obtained XRD profile and θ1, which is half the Bragg angle 2θ1 and the peak position, the length X was calculated based on the Scherrer equation (Equation 5 below) with a Scherrer constant of 1. λ1 represents the wavelength of the X-rays and is 0.124 nm. X = λ1 / (B1 cos θ1) Equation 5

[0050] The upper limit of the length Y of the porous membrane 1 along the TD direction may be less than 60 nm. When the length Y of the porous membrane 1 along the TD direction is 60 nm or more, the average bubble point becomes small (i.e., the particle capture performance becomes low), and the permeation efficiency tends to be easily reduced. The upper limit of the length Y of the porous membrane 1 along the TD direction may be less than 59 nm or less than 58 nm. The lower limit of the length Y of the porous membrane 1 along the TD direction is not particularly limited, but can be, for example, 5 nm or more, 7 nm or more, or 10 nm or more.

[0051] The length Y of the porous membrane 1 along the TD direction can be determined by X-ray diffraction measurement. For X-ray diffraction measurement, BL16 of the Synchrotron Radiation Facility SAGA-LS was used. At the beamline, a double-crystal spectrometer using Si (111) diffraction was used to monochromatize the X-rays to a wavelength of 0.124 nm. Measurements were performed using the transmission method, with a NaI scintillation counter as the detector and a double-slit optical system. The receiving slits were all 0.5 mm vertically (in the direction of diffraction angle measurement) and 3 mm horizontally (perpendicular to the direction of diffraction angle measurement). X-ray diffraction measurement was performed after measuring the "length X of the porous membrane 1 along the MD direction," and then rotating the porous membrane 1 by 90° along a virtual plane perpendicular to the film thickness direction of the porous membrane 1. Using the peak integral width B2 of the polytetrafluoroethylene (100) diffraction line in the obtained XRD profile and θ2, which is 1 / 2 of the Bragg angle "2 × θ2" at the peak position, the length Y is calculated based on the Scherrer equation (Equation 6 below) with the Scherrer constant set to 1. λ2 represents the wavelength of the X-rays and is 0.124 nm. Y = λ2 / (B2 cos θ2) Equation 6

[0052] The product XY of length X and length Y is 1200 nm ２ As a result, the fibers of the porous membrane become thinner, and even if the fiber density increases, the pore ratio increases, so that the porous membrane 1 can have both a higher average bubble point and a lower Gurley second. The upper limit of the product XY of the length X and the length Y is 1100 nm. ２ may be less than 1000 nm ２ The lower limit of the product XY of the length X and the length Y is not particularly limited, but may be, for example, 30 nm.２ Above, 50nm ２ More than 100 nm ２ It can be more than that.

[0053] <Crystallite Composition> The crystallite may be made of polytetrafluoroethylene. This makes it easy for the crystallite density of the porous membrane 1 to be high in crystallinity and high in permeability efficiency, and therefore it is possible to have both a higher permeability efficiency and a higher ability to capture fine particles contained in the filtrate. Here, the term "made of polytetrafluoroethylene" is not limited to an embodiment made of polytetrafluoroethylene only, but also encompasses an embodiment containing components other than polytetrafluoroethylene (for example, inevitable impurities) as long as the effects of the present disclosure are achieved.

[0054] <<Method for manufacturing porous film>> The method for manufacturing porous film according to this embodiment includes the steps of: 1-1 step of obtaining a kneaded product of polytetrafluoroethylene powder and liquid lubricant; 1-2 step of obtaining a sheet-like molded body by extrusion molding the kneaded product; 1-3 step of obtaining an elongated body by biaxially stretching the molded body; and 1-4 step of obtaining a porous film by heat treatment of the elongated body. In addition, the step 1-4 is carried out under the condition of less than 345°C.

[0055] <Step 1-1> Step 1-1 is carried out by kneading polytetrafluoroethylene powder and a liquid lubricant to obtain a kneaded product. More specifically, first, polytetrafluoroethylene powder and a liquid lubricant are mixed to obtain a mixture. Next, the mixture is compression-molded into a block shape using a compression molding machine to obtain the kneaded product.

[0056] The polytetrafluoroethylene powder refers to a powder consisting of fine particles of polytetrafluoroethylene. Examples of the polytetrafluoroethylene powder include "PTFE (polytetrafluoroethylene) fine powder" produced by emulsion polymerization and "PTFE molding powder" produced by suspension polymerization.

[0057] The number-average molecular weight of polytetrafluoroethylene in the polytetrafluoroethylene powder may be 12 million or more and 50 million or less, from the viewpoint of being able to promote the growth of the fibrous skeleton while preventing excessive pore size expansion and rupture of the porous film during stretching. Furthermore, the second heat of fusion in the polytetrafluoroethylene powder may be 10 J / g or more and 25 J / g or less, from the viewpoint of being dependent on the number-average molecular weight of the polytetrafluoroethylene powder. Here, the second heat of fusion can be determined by the following method. The polytetrafluoroethylene powder is heated from room temperature to 380°C at a rate of 10°C / min (Pattern 1 (1st Run)), then cooled from 380°C to 100°C at a rate of -1°C / min (Pattern 2), and then heated from 100°C to 380°C at a rate of 10°C / min (Pattern 3 (2nd Run)). The endothermic heat obtained by integrating the 48°C section from the end set temperature of the peak in the range of 300°C to 360°C of the melting curve of Pattern 3 is defined as the second heat of fusion.

[0058] As the liquid lubricant, various lubricants conventionally used in the extrusion method can be used. Examples of the liquid lubricant include petroleum solvents such as solvent naphtha and white oil, hydrocarbon oils such as undecane, aromatic hydrocarbons such as toluene and xylol, alcohols, ketones, esters, silicone oil, fluorochlorocarbon oil, solutions of polymers such as polyisobutylene and polyisoprene dissolved in these solvents, and water or aqueous solutions containing surfactants. These can be used alone or in combination of two or more. However, from the viewpoint of uniform mixing, a single-component liquid lubricant can also be used.

[0059] The mass ratio of the liquid lubricant to 100 parts by mass of the polytetrafluoroethylene powder may be 10 parts by mass or more and 40 parts by mass or less. If the mass ratio of the liquid lubricant is less than 10 parts by mass, extrusion tends to be difficult. If the mass ratio of the liquid lubricant is more than 40 parts by mass, compression molding tends to be difficult.

[0060] In addition to the polytetrafluoroethylene powder and the liquid lubricant, other additives may be used as materials for the kneaded product. Examples of other additives include pigments for coloring, inorganic fillers such as carbon black, graphite, silica powder, glass powder, glass fiber, silicates and carbonates, metal powder, metal oxide powder, and metal sulfide powder, which are used to improve wear resistance, prevent low-temperature flow, and facilitate pore formation. Furthermore, to aid in the formation of a porous structure, substances that can be removed or decomposed by heating, extraction, dissolution, etc., such as ammonium chloride, sodium chloride, plastics other than polytetrafluoroethylene, rubber, etc., may be used in the form of powder or solution.

[0061] <Step 1-2> Step 1-2 is carried out by extrusion molding the kneaded material to obtain a sheet-like molded body. More specifically, the kneaded material is extruded into a sheet at room temperature (for example, 25°C) or higher and 50°C or lower, and at a speed of, for example, 10 mm / min to 30 mm / min, to obtain a precursor of the sheet-like molded body. Furthermore, the precursor is rolled using a calender roll or the like to obtain a sheet-like molded body having an average thickness of 0.250 mm to 0.400 mm. The average thickness can be determined in the same manner as the thickness of the porous membrane 1, except that the measurement is carried out on the molded body.

[0062] Furthermore, before carrying out Steps 1-3 described below, the liquid lubricant contained in the compact may be removed. The liquid lubricant can be removed by heating, extracting, dissolving, or the like the compact. When heating, the liquid lubricant can be removed from the compact by rolling the compact with a heated roll at a temperature of 130°C or higher and 220°C or lower. When a liquid lubricant with a relatively high boiling point, such as silicone oil or fluorochlorocarbon oil, is used, removal by extraction is preferred.

[0063] Step 1-3 is carried out by biaxially stretching the molded body to obtain a stretched body. Here, biaxial stretching means stretching the sheet-like molded body in the MD direction (in other words, the flow direction of the molded body) and the TD direction perpendicular to the MD direction.

[0064] The temperature in step 1-3 may be 60°C or higher and 300°C or lower. If the temperature is higher than 300°C, the pore size of the porous membrane tends to be too large (in other words, the average bubble point of the porous membrane tends to be too small). If the temperature is lower than 60°C, the pore size tends to be too small (in other words, the average bubble point of the porous membrane tends to be too large). By adjusting the temperature in step 1-3 within the range of "60°C or higher and 300°C or lower," the average bubble point P1 and the product XY of length X and length Y can be adjusted to desired ranges.

[0065] The stretching ratio in MD direction may be 1.5 times or more and 20 times or less.The stretching ratio in MD direction means the value obtained by dividing the average length in MD direction immediately after stretching in MD direction by the average length in MD direction immediately before stretching in MD direction.If the stretching ratio in MD direction is less than 1.5 times, the thickness of the porous film may be outside of the desired range.If the stretching ratio in MD direction is more than 20 times, the thickness of the porous film may be outside of the desired range.In addition, here, "average length in MD direction" means the average value of the length in MD direction at any 10 positions.

[0066] The stretching ratio in TD direction may be 1.5 times or more and 100 times or less. Note that, the stretching ratio in TD direction means the value obtained by dividing the average length in TD direction immediately after stretching in TD direction by the average length in TD direction immediately before stretching in TD direction. If the stretching ratio in TD direction is less than 1.5 times, the thickness of the porous film may be out of the desired range. If the stretching ratio in TD direction is more than 100 times, the thickness of the porous film may be out of the desired range. Note that, here, "average length in TD direction" means the average value of the length in TD direction at any 10 positions.

[0067] <Step 1-4> Step 1-4 is performed by subjecting the stretched body to heat treatment to obtain a porous membrane. Step 1-4 is performed under conditions of less than 345°C. This allows the porous membrane to satisfy the relationship of the above formula 1 or 2. It also makes it possible to prevent the porous membrane from shrinking over time. In Step 1-4, by adjusting the heat treatment temperature to the range of "less than 345°C," it is possible to adjust the Gurley seconds, average bubble point, and the product XY of length X and length Y to the desired ranges.

[0068] The time for step 1-4 may be 0.1 minutes or more and 20 minutes or less. If the time is less than 0.1 minutes, it tends to be difficult to prevent the porous membrane from shrinking over time. If the time is more than 20 minutes, the average bubble point of the porous membrane tends to increase excessively. By adjusting the time for step 1-4 within the range of "0.1 minutes or more and 20 minutes or less," the average bubble point and the product XY of length X and length Y can be adjusted to the desired range.

[0069] As a result of the above, a porous membrane containing polytetrafluoroethylene as a main component, which has a Gurley second and an average bubble point, and which satisfies the relationship of the above formula 1 or 2, can be obtained.

[0070] [Embodiment 2: Filter element (1)] A filter element (1) according to one embodiment of the present disclosure will be described with reference to Figure 3. A filter element 500 according to this embodiment includes the porous membrane 570 according to embodiment 1. The filter element 500 according to this embodiment is not particularly limited as long as it includes the porous membrane 570 according to embodiment 1, but for example, in the filter element 500, the porous membrane 570 may have a pleated structure.

[0071] The present disclosure provides a filter element including a porous membrane that combines a high average bubble point with a low Gurley second.

[0072] FIG. 3 shows a filter element 500 equipped with a porous membrane 570 having a pleated structure. The porous membrane 570 is sandwiched between two protective materials 520 and 540, then pleated and wrapped around a core 550 having multiple liquid collection ports 590. An outer peripheral guard 510 protects the porous membrane 570. The porous membrane 570 is sealed at both ends of the cylinder by end plates 560a and 560b. The end plates interface with the seals of the filter housing (not shown) via gaskets 600. The filtered liquid is collected through the liquid collection ports 590 of the core 550 and recovered through an outlet 580. Filter elements with outlets at both ends and those at one end are known. Generally, when outlets are provided at both ends, one end is sealed with a fixture, allowing the filtered liquid to be recovered through the outlet at the other end.

[0073] <<Method for manufacturing filter element (1)>> The method for manufacturing the filter element according to this embodiment can be carried out by a method similar to a conventionally known method, except that the porous membrane according to embodiment 1 is used.

[0074] [Embodiment 3: Laminate] A laminate 10 according to this embodiment will be described with reference to Fig. 2. The laminate 10 according to this embodiment is a laminate 10 comprising one or more porous membranes 1 according to embodiment 1 and a support membrane 2 located on one or both sides of at least one of the porous membranes 1, wherein the support membrane 2 is porous, the support membrane 2 contains polytetrafluoroethylene as a main component, and the laminate 10 has a Gurley second and an average bubble point.

[0075] In the laminate 10 according to this embodiment, the Gurley second of the laminate 10 and the average bubble point of the laminate 10 satisfy the relationship of Equation 3 or Equation 4. G2<0.040×P2a Equation 3 G2<(0.025×P2b)-6 Equation 4 As a result, even if the fiber density of the laminate increases (in other words, even if the average bubble point of the laminate increases) due to the thinner fibers of the laminate, the void ratio increases. Therefore, the laminate 10 can suppress the improvement in the Gurley second that accompanies an increase in the average bubble point. As a result, the porous membrane 1 can combine excellent particle capture performance with excellent permeation efficiency.

[0076] The average bubble point is measured by a bubble point method using a specific liquid. The numerical value of the average bubble point varies depending on the surface tension of the specific liquid. In view of the difficulty of obtaining the specific liquid, Equation 3 is defined for "P2a" measured by the bubble point method using "liquid 2a," and Equation 4 is defined for "P2b" measured by the bubble point method using "liquid 2b."

[0077] <<Laminate Structure>> The laminate 10 includes one or more porous membranes 1 according to embodiment 1 and a support membrane 2 located on one or both sides of at least one of the porous membranes 1. The support membrane 2 thereby functions as a protective material for the porous membrane 1 according to embodiment 1, thereby improving the capture performance of the laminate 10 and increasing the mechanical strength and lifespan of the laminate 10.

[0078] The thickness of the laminate 10 may be 0.010 mm or more and 0.200 mm or less. If the thickness is less than 0.010 mm, the strength of the laminate 10 tends to be insufficient. If the thickness is more than 0.200 mm, the pressure loss during permeation of the filtrate tends to be large. The lower limit of the thickness of the laminate 10 may be 0.010 mm or more, 0.013 mm or more, or 0.015 mm or more. The upper limit of the thickness of the laminate 10 may be 0.200 mm or less, 0.150 mm or less, or 0.100 mm or less. The thickness of the laminate 10 may be 0.013 mm or more and 0.150 mm or less, or 0.015 mm or more and 0.100 mm or less.

[0079] The thickness of the laminate 10 can be determined by a method similar to the method for measuring the thickness of the porous membrane 1, except that the measurement is performed on the "laminate 10." It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same laminate 10 and the above measurement is performed in that measurement range.

[0080] <Density of Laminate> The density of the laminate 10 is 0.10 g / cm ３ 2.00g / cm or more ３ The density may be 0.10 g / cm or less. ３ If the density is less than 2.00 g / cm3, the strength of the laminate 10 tends to be insufficient. ３ If the density exceeds 0.10 g / cm3, the permeability of the laminate 10 tends to decrease. ３ or more, and 0.13 g / cm ３ or more, and 0.15 g / cm ３ The upper limit of the density of the laminate 10 is 2.00 g / cm ３ or less, 1.70 g / cm ３ or less, 1.50 g / cm ３ The density of the laminate 10 may be 0.13 g / cm or less. ３ 1.70g / cm or more ３ or less, and 0.15 g / cm ３ 1.50g / cm or more３ It may be the following:

[0081] The density of the laminate 10 can be determined by the same method as the "method for measuring the density of the porous film 1" described in embodiment 1, except that the measurement is performed on the "laminated body 10." It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same laminate 10 and the above measurement is performed in that measurement range.

[0082] <Basis Weight of Laminate> The basis weight of the laminate 10 is 0.005 mg / mm ２ 0.100mg / mm or more ２ The basis weight of the laminate 10 may be 0.005 mg / mm ２ When the weight per unit area of ​​the laminate 10 is less than 0.100 mg / mm, the strength of the laminate 10 tends to be insufficient. ２ If the weight of the laminate 10 exceeds 0.005 mg / mm ２ or more, and ２ or more, and ２ The upper limit of the basis weight of the laminate 10 is 0.100 mg / mm ２ or less, 0.080 mg / mm ２ or less, 0.060 mg / mm ２ The basis weight of the laminate 10 may be 0.007 mg / mm ２ 0.080mg / mm or more ２ or less, 0.008 mg / mm ２ 0.060mg / mm or more ２ It may be the following:

[0083] The basis weight of the laminate 10 can be determined by the same method as the "method for measuring the basis weight of the porous membrane 1" described in embodiment 1, except that the measurement is performed on the "laminated body 10." It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same laminate 10 and the above measurement is performed in that measurement range.

[0084] <Average Bubble Point and Gurley Second> <Average Bubble Point> The laminate 10 has an average bubble point (P2a and P2b). P2a may be 510 kPa or more. This allows the fibers of the laminate to be formed thin and dense, so that the laminate 10 can have both a higher average bubble point and a lower Gurley second. The lower limit of P2a may be 510 kPa or more, 520 kPa or more, or 530 kPa or more. The upper limit of P2a may be 1000 kPa or less, 990 kPa or less, or 980 kPa or less. P2a may be 510 kPa or more and 1000 kPa or less, or 520 kPa or more and 990 kPa or less.

[0085] P2b may be 1000 kPa or more. This allows the fibers of the laminate 10 to be formed thin and dense, so that the laminate 10 can have both a higher average bubble point and a lower Gurley second. The lower limit of P2b may be 1020 kPa or more, or 1040 kPa or more. The upper limit of P2b may be 1600 kPa or less, 1500 kPa or less, or 1465 kPa or less. P2b may be 1000 kPa or more and 1600 kPa or less, or 1020 kPa or more and 1500 kPa or less.

[0086] In the laminate 10, P2a is measured by a bubble point method using the 2a liquid, and the surface tension of the 2a liquid is 13 mN / m. More specifically, in the laminate 10, P2a is determined in a manner similar to that for measuring P1a, except that the measurement is performed on the "laminate" and the name of the liquid "1a liquid" is replaced with "2a liquid."

[0087] In the laminate 10, P2b is measured by a bubble point method using the second liquid b, and the surface tension of the second liquid b is 21 mN / m. More specifically, in the porous film 1, P2b is determined by a method similar to that for measuring P1a, except that isopropyl alcohol (second liquid b) manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. is used instead of the first liquid a.

[0088] <Gurley seconds> The laminate 10 has a Gurley second (G2). In the laminate 10, G2 may be 1 second or more and 100 seconds or less. This allows the flow rate of the filtrate to be increased, thereby increasing the permeation efficiency and improving the ability to capture fine particles contained in the filtrate. The lower limit of G2 may be 1 second or more, 3 seconds or more, or 5 seconds or more. The upper limit of G2 may be 100 seconds or less, 80 seconds or less, or 70 seconds or less. G2 may be 3 seconds or more and 80 seconds or less, or 5 seconds or more and 70 seconds or less.

[0089] In the laminate 10, G2 is determined by the following method. It can be determined by the same method as the "method for measuring G1 of the porous membrane 1" in embodiment 1, except that the measurement is performed on the "laminated body".

[0090] <Relationship between Gurley seconds and average bubble point> The Gurley seconds and average bubble point of the laminate 10 satisfy the relationship of Equation 3 or Equation 4. G2<0.040×P2a Equation 3 G2<(0.025×P2b)-6 Equation 4 In Equation 3 and Equation 4, G2 is the Gurley seconds of the laminate 10, In Equation 3, P2a is the average bubble point of the laminate 10, P2a is measured by a bubble point method using liquid 2a, and the surface tension of liquid 2a is 13 mN / m, In Equation 4, P2b is the average bubble point of the laminate 10, P2b is measured by a bubble point method using liquid 2b, and the surface tension of liquid 2b is 21 mN / m. As a result, the laminate 10 can have both a high average bubble point and a low Gurley second, and therefore can have both excellent fine particle capture performance and excellent permeation efficiency. In Equation 3, "0.040" means the slope of the linear function. In Equation 4, "0.025" means the slope of the linear function, and "-6" means the intercept of the linear function.

[0091] <<Mean Flow Pore Diameter>> The mean flow pore diameter of the laminate 10 may be 25 nm or more and 100 nm or less. This allows for both higher permeation efficiency and higher capture performance of fine particles contained in the filtrate. The lower limit of the mean flow pore diameter may be 25 nm or more, 26 nm or more, or 27 nm or more. The upper limit of the mean flow pore diameter may be 100 nm or less, 60 nm or less, or 55 nm or less. The mean flow pore diameter may be 26 nm or more and 60 nm or less, or 27 nm or more and 55 nm or less.

[0092] The mean flow pore size of the laminate 10 can be determined in the same manner as the "Method for measuring the mean flow pore size of the porous membrane 1" in embodiment 1, except that the measurement is performed on the "laminated body 10".

[0093] <<Support Membrane>> <Structure of Support Membrane> The support membrane 2 is porous. Here, "porous" means having a fibrous skeleton in which pores are connected in a three-dimensional network. The support membrane 2 has a larger pore size than the porous membrane, and does not necessarily inhibit the permeation efficiency. The fact that "the support membrane 2 is porous" can be determined by observing the surface and any cross section of the support membrane 2 using a scanning electron microscope.

[0094] The thickness of the support membrane 2 may be 0.002 mm or more and 0.050 mm or less. If the thickness of the support membrane 2 is less than 0.002 mm, it tends to be difficult for the porous membrane 1 to function as a protective material, and it tends to be difficult to improve the mechanical strength and lifespan of the laminate 10. If the thickness of the support membrane 2 exceeds 0.050 mm, it tends to be difficult for the porous membrane 1 to achieve both the capture performance of the laminate 10 and the permeation efficiency of the laminate 10. The lower limit of the thickness may be 0.002 mm or more, 0.004 mm or more, or 0.006 mm or more. The upper limit of the thickness may be 0.050 mm or less, 0.045 mm or less, or 0.040 mm or less. The thickness may be 0.004 mm or more and 0.045 mm or less, or 0.006 mm or more and 0.040 mm or less.

[0095] The thickness of the support membrane 2 can be determined by the same method as the measurement method for "the thickness of the porous membrane 1" described in embodiment 1, except that the measurement is performed on the support membrane 2. It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same support membrane 2 and the above measurement is performed in that measurement range.

[0096] <Density of Support Film> The density of the support film 2 is 0.10 g / cm ３ 2.00g / cm or more ３ The density may be 0.10 g / cm or less. ３ If the density is less than 2.00 g / cm3, the strength of the laminate 10 tends to be insufficient. ３ If the density exceeds 0.10 g / cm3, the permeation efficiency of the laminate 10 tends to decrease. ３ or more, and 0.13 g / cm ３ or more, and 0.15 g / cm ３ The upper limit of the density of the support film 2 is 2.00 g / cm ３ or less, 1.70 g / cm ３ or less, 1.50 g / cm ３ The density of the support film 2 may be 0.13 g / cm or less. ３ 1.70g / cm or more ３ or less, and 0.15 g / cm ３ 1.50g / cm or more ３ It may be the following:

[0097] The density of the support membrane 2 can be determined by a method similar to that for measuring the density of the porous membrane 1, except that the measurement is performed on the "support membrane 2." It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same support membrane 2 and the above measurement is performed in that measurement range.

[0098] <Weight of Support Film> The weight of the support film 2 is 0.005 mg / mm ２ 0.100mg / mm or more ２ The weight per unit area of ​​the support film 2 may be 0.005 mg / mm ２When the weight per unit area of ​​the support film 2 is less than 0.100 mg / mm, the strength of the laminate 10 tends to be insufficient. ２ If it exceeds 0.005 mg / mm, the permeation efficiency of the laminate 10 tends to decrease. ２ or more, and ２ or more, and ２ The upper limit of the basis weight of the support film 2 is 0.100 mg / mm ２ or less, 0.080 mg / mm ２ or less, 0.060 mg / mm ２ The basis weight of the support film 2 may be 0.006 mg / mm ２ 0.080mg / mm or more ２ or less, 0.007 mg / mm ２ 0.060mg / mm or more ２ It may be the following:

[0099] The basis weight of the support membrane 2 can be determined by the following method. Except that the measurement is performed on the "support membrane 2", it can be determined by the same method as the method for measuring the basis weight of the porous membrane 1. It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same support membrane 2 and the above measurement is performed in that measurement range.

[0100] <Average Bubble Point and Gurley Second> <Average Bubble Point> The average bubble point P3a of the support film 2 may be 5 kPa or more and 400 kPa or less, or the average bubble point P3b of the support film 2 may be 5 kPa or more and 800 kPa or less. This allows the fibers of the support film 2 to be formed thin and dense, so that the laminate 10 can have both a higher average bubble point and a lower Gurley second.

[0101] The average bubble point is measured by a bubble point method using a specific liquid. The numerical value of the average bubble point varies depending on the surface tension of the specific liquid. In view of the difficulty of obtaining the specific liquid, "P3a" measured by the bubble point method using a "third a liquid" described below and "P3b" measured by the bubble point method using a "third b liquid" described below are defined.

[0102] The average bubble point P3a of the support film 2 may be 5 kPa or more and 400 kPa or less. This allows the fibers of the support film 2 to be formed thin and densely, allowing the laminate 10 to have both a higher average bubble point and a lower Gurley second. The lower limit of P3a may be 5 kPa or more, 7 kPa or more, or 10 kPa or more. The upper limit of P3a may be 400 kPa or less, 350 kPa or less, or 300 kPa or less. P3a may be 7 kPa or more and 350 kPa or less, or 10 kPa or more and 300 kPa or less.

[0103] The average bubble point P3b of the support film 2 may be 5 kPa or more and 800 kPa or less. This allows the fibers of the support film 2 to be formed thin and densely, allowing the laminate 10 to have both a higher average bubble point and a lower Gurley second. The lower limit of P3b may be 5 kPa or more, 7 kPa or more, or 10 kPa or more. The upper limit of P3b may be 800 kPa or less, 700 kPa or less, or 600 kPa or less. P3b may be 7 kPa or more and 700 kPa or less, or 10 kPa or more and 600 kPa or less.

[0104] For the support film 2, P3a is measured by the bubble point method using the 3a liquid, and the surface tension of the 3a liquid is 13 mN / m. More specifically, for the support film 2, P3a is determined in a manner similar to that for measuring P1a, except that the measurement is performed on the "support film 2" and the name of the liquid "1a liquid" is replaced with "3a liquid."

[0105] For the support film 2, P3b is measured by a bubble point method using the 3b liquid, and the surface tension of the 3b liquid is 21 mN / m. More specifically, for the support film 2, P3b is determined in a manner similar to that for measuring P1a, except that the measurement is performed on the "support film 2" and that isopropyl alcohol (3b liquid) manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. is used instead of the 1a liquid.

[0106] <Gurley seconds> The support membrane 2 has a Gurley second (G3). In the support membrane 2, G3 may be 0.5 seconds or more and 60 seconds or less. This allows the flow rate of the filtrate to be increased, thereby increasing the permeation efficiency and improving the ability to capture fine particles contained in the filtrate. The lower limit of G3 may be 0.5 seconds or more, 0.7 seconds or more, or 1.0 second or more. The upper limit of G3 may be 60 seconds or less, 50 seconds or less, or 40 seconds or less. G3 may be 0.7 seconds or more and 50 seconds or less, or 1.0 second or more and 40 seconds or less.

[0107] In the support membrane 2, G3 is determined by the following method. Except that the measurement is performed on the "support membrane 2", it can be determined by the same method as the "method for measuring G1 of the porous membrane 1" in embodiment 1.

[0108] <Mean flow pore diameter> The mean flow pore diameter of the support membrane 2 may be 45 nm or more and 600 nm or less. This allows the laminate 10 to have both higher permeation efficiency and higher trapping performance for fine particles contained in the filtrate. The lower limit of the mean flow pore diameter may be 45 nm or more, 50 nm or more, or 55 nm or more. The upper limit of the mean flow pore diameter may be 600 nm or less, 550 nm or less, or 500 nm or less. The mean flow pore diameter may be 50 nm or more and 550 nm or less, or 55 nm or more and 500 nm or less.

[0109] The mean flow pore size of the support membrane 2 can be determined by the following measurement method. Except that the measurement is performed on the "support membrane 2", it can be determined by the same method as the "method for measuring the mean flow pore size of the porous membrane 1" in embodiment 1.

[0110] <Composition of Support Film> The support film 2 contains polytetrafluoroethylene as a main component. This can improve the heat resistance, chemical stability, and the like of the support film 2. Here, the term "main component" refers to the component with the largest content in terms of mass, for example, a component with a content of 90 mass% or more, preferably 95 mass% or more. The support film 2 may be made of polytetrafluoroethylene. Note that "the support film 2 is made of polytetrafluoroethylene" means that the support film 2 may contain unavoidable impurities as long as the effects of the present disclosure are achieved.

[0111] The polytetrafluoroethylene content in the support membrane 2 can be determined by a method similar to the measurement method for "the polytetrafluoroethylene content in the porous membrane 1" described in embodiment 1, except that the measurement is performed on the support membrane 2. It has been confirmed that similar results can be obtained when a different measurement range is arbitrarily selected for the same support membrane 2 and the above measurement is performed in that measurement range.

[0112] <<Method for manufacturing laminate>> The method for manufacturing a laminate includes step 2-1 of preparing the porous membrane according to embodiment 1 and a support membrane, and step 2-2 of laminating the porous membrane on the support membrane. Step 2-1 consists of step 2-1-a of preparing the porous membrane and step 2-1-b of preparing the support membrane.

[0113] <Step 2-1> (Step 2-1-a) Step 2-1-a is carried out by preparing a porous membrane. The porous membrane 1 can be prepared by the method described in the first embodiment.

[0114] (Step 2-1-b) Step 2-1-b is carried out by preparing a support film, which can be prepared by a conventionally known method.

[0115] <Step 2-2> Step 2-2 is carried out by laminating a porous membrane on one or both sides of a support membrane. Examples of a method for laminating a porous membrane on one or both sides of a support membrane include a method in which the support membrane and the porous membrane are pressure-bonded together.

[0116] Specifically, the method for pressure-bonding the support membrane and the porous membrane is, for example, first to obtain a laminate precursor by overlapping the support membrane and the porous membrane. Next, the laminate precursor is pressed from above and below with flat plates, or the laminate precursor is sandwiched from above and below with rotating rollers and sent out. The method for pressure-bonding the support membrane and the porous membrane is carried out by pressure bonding at 100 kgf or more and 700 kgf or less. If the force is less than 100 kgf, the adhesive strength between the support membrane and the porous membrane tends to be insufficient. If the force is more than 700 kgf, the pores of the support membrane or the porous membrane tend to be crushed, and the permeation efficiency tends to be reduced.

[0117] As a result of the above, a laminate 10 can be obtained, which includes one or more porous membranes according to embodiment 1 and a support membrane 2 located on one or both sides of at least one of the porous membranes, wherein the support membrane is porous and the support membrane 2 contains polytetrafluoroethylene as a main component, and the laminate 10 has a Gurley second and an average bubble point, and the Gurley second and the average bubble point of the laminate satisfy the relationship of the above formula 3 or the above formula 4.

[0118] [Embodiment 4: Filter element (2)] A filter element (2) according to one embodiment of the present disclosure will be described with reference to Fig. 4. The filter element 500 according to this embodiment includes the laminate 670 according to embodiment 3. The filter element 500 according to this embodiment is not particularly limited as long as it includes the laminate 670 according to embodiment 3, but for example, in the filter element 500, the laminate 670 may have a pleated structure.

[0119] The present disclosure provides a filter element including a laminate that combines a high average bubble point with a low Gurley second.

[0120] 4 shows a filter element 500 including a laminate 670 having a pleated structure. The structure of the filter element 500 in FIG. 4 is the same as that of the filter element 500 in FIG. 3, except that the porous membrane 570 is replaced with the laminate 670.

[0121] <<Method for manufacturing filter element (2)>> The method for manufacturing the filter element according to this embodiment can be carried out by a method similar to a conventionally known method, except that the laminate according to embodiment 3 is used.

[0122] Hereinafter, the present disclosure will be specifically described based on examples, but the present invention is not limited to the following examples.

[0123] Example 1 <<Production of Porous Membrane>> In Example 1, porous membranes according to Samples 1-1 to 1-8 and Samples 1-101 to 1-105 were produced as follows.

[0124] <Step 1-1> First, a mixture was obtained by mixing "PTFE Fine Powder A (second heat of fusion 15.8 J / g, molecular weight approximately 28 million)," which is a polytetrafluoroethylene powder, and "Supersol FP-25" (trademark), which is a solvent naphtha (liquid lubricant) manufactured by Idemitsu Oil Co., Ltd., in the parts by mass shown in Table 1. Next, the mixture was compression molded into a block using a compression molding machine, thereby obtaining a kneaded product.

[0125] <Step 1-2> The kneaded material was extruded into a sheet under the conditions shown in Table 1 to obtain a precursor of a sheet-like molded product. Next, the precursor was rolled using a calendar roll to obtain a sheet-like molded product having an average thickness as shown in Table 1.

[0126] <Step 1-3> The above molded body was biaxially stretched under the conditions shown in Table 1 to obtain a stretched body.

[0127] <Step 1-4> The stretched body was subjected to a heat treatment under the conditions shown in Table 1 to obtain a porous membrane.

[0128] In this manner, porous membranes according to Samples 1-1 to 1-8 and Samples 1-101 to 1-105 were produced.

[0129]

[0130]

[0131]

[0132] <<Evaluation of porous membrane properties>> For the porous membrane of each sample, the polytetrafluoroethylene content, thickness, basis weight, density, crystallite structure, mean flow pore size, mean bubble point, and Gurley second were determined by the method described in embodiment 1. The results obtained are shown in Tables 2 and 3. Relatively high P1a and P1b mean relatively excellent fine particle capture performance. Relatively low Gurley second means relatively excellent permeation efficiency.

[0133] <Fine particle capture performance and permeation efficiency> The porous membranes of samples 1-1 to 1-8 correspond to examples. On the other hand, the porous membranes of samples 1-101 to 1-105 correspond to comparative examples. The porous membranes of samples 1-1 to 1-8, which satisfy the relationship of formula 1 or 2, have exceptionally excellent "fine particle capture performance" compared to the porous membranes of samples 1-101 to 1-105, which do not satisfy the relationship of formula 1 or 2. Furthermore, the porous membranes of samples 1-1 to 1-8, which satisfy the relationship of formula 1 or 2, have exceptionally excellent permeation efficiency compared to the porous membranes of samples 1-101 to 1-103, which do not satisfy the relationship of formula 1 or 2. That is, the porous membranes of samples 1-1 to 1-8, which satisfy the relationship of the above formula 1 or 2, can exhibit exceptionally excellent effects of combining excellent "particle capture performance" and excellent permeation efficiency, compared to the porous membranes of samples 1-101 to 1-105, which do not satisfy the relationship of the above formula 1 or 2.

[0134] From the above, it was found that the porous membranes of Samples 1-1 to 1-8 can exhibit the exceptionally excellent effect of combining excellent "particle capture performance" with excellent permeation efficiency.

[0135] Example 2 <<Production of Laminate>> In Example 2, laminates according to Samples 2-1 to 2-5 and 2-101 to 2-105 were produced as follows.

[0136] <Step 2-1-a> One porous film was produced for each sample as follows. First, a mixture was obtained by mixing "PTFE Fine Powder A (second heat of fusion 15.8 J / g, molecular weight approximately 28 million)," which is a polytetrafluoroethylene powder, and "Supersol FP-25" (trademark), a solvent naphtha (liquid lubricant) manufactured by Idemitsu Oil Co., Ltd., in the parts by mass shown in Table 4. Next, the mixture was compression-molded into a block using a compression molding machine, thereby obtaining a kneaded product.

[0137] The kneaded material was extruded into a sheet under the conditions shown in Table 4 to obtain a precursor of a sheet-like molded product. Next, the precursor was rolled using a calendar roll to obtain a sheet-like molded product having an average thickness as shown in Table 4.

[0138] The molded body was biaxially stretched under the conditions shown in Table 4 to obtain a stretched body.

[0139] The stretched body was subjected to a heat treatment under the conditions shown in Table 4 to obtain a porous membrane.

[0140] As described above, porous membranes according to Samples 2-1 to 2-5 and Samples 2-101 to 2-105 were prepared.

[0141] <Step 2-1-b> Two support films were produced for each sample as follows. First, a mixture was obtained by mixing "PTFE Fine Powder B (second heat of fusion 26.0 J / g, molecular weight approximately 5 million)," which is a polytetrafluoroethylene powder, and "Supersol FP-25" (trademark), a solvent naphtha (liquid lubricant) manufactured by Idemitsu Oil Co., Ltd., in the parts by mass shown in Table 5. Next, the mixture was compression-molded into a block using a compression molding machine, thereby obtaining a kneaded product.

[0142] The kneaded material was extruded into a sheet under the conditions shown in Table 5 to obtain a precursor of a sheet-like molded product. Next, the precursor was rolled using a calendar roll to obtain a sheet-like molded product having an average thickness as shown in Table 5.

[0143] The molded body was biaxially stretched under the conditions shown in Table 5 to obtain a stretched body.

[0144] The stretched body was subjected to a heat treatment under the conditions shown in Table 5 to obtain a porous support film.

[0145] In this manner, porous support films for samples 2-1 to 2-5 and samples 2-101 to 2-105 were prepared.

[0146] <Step 2-2> A support membrane and a porous membrane were laminated in the order of support membrane-porous membrane-support membrane under the conditions shown in Table 6 to obtain a laminate.

[0147] In this manner, laminates according to Samples 2-1 to 2-5 and Samples 2-101 to 2-105 were produced.

[0148]

[0149]

[0150]

[0151]

[0152]

[0153]

[0154]

[0155]

[0156] <<Evaluation of porous membrane properties>> For the porous membrane in the laminate of each sample, the content of polytetrafluoroethylene, thickness, basis weight, density, crystallite structure, mean flow pore size, mean bubble point and Gurley seconds were measured by the method described in embodiment 1. The results obtained are shown in Table 7 and Table 8.

[0157] <Evaluation of Support Film Properties> For the support film in the laminate of each sample, the polytetrafluoroethylene content, thickness, basis weight, density, mean flow pore size, average bubble point, and Gurley seconds were determined by the method described in embodiment 3. The results obtained are shown in Table 9.

[0158] <<Evaluation of Laminate Properties>> The thickness, basis weight, density, mean flow pore size, average bubble point, and Gurley second of each sample laminate were determined by the method described in "Embodiment 3." The results are shown in Tables 10 and 11. Relatively high P2a and P2b indicate relatively excellent fine particle capture performance. Relatively low Gurley second indicates relatively excellent permeation efficiency.

[0159] <Fine Particle Capture Performance and Transmission Efficiency> The laminates of Samples 2-1 to 2-5 correspond to Examples. On the other hand, the laminates of Samples 2-101 to 2-105 correspond to Comparative Examples. The laminates of Samples 2-1 to 2-5, which satisfy the relationship of Formula 1 or 2 and the relationship of Formula 3 or 4, have significantly superior "fine particle capture performance" compared to the laminates of Samples 2-101, 2-102, 2-103, and 2-104, which do not satisfy at least one of the relationships of Formula 1 or 2 and Formula 3 or 4. Furthermore, the laminates of Samples 2-1 to 2-5, which satisfy the relationship of Formula 1 or 2 and Formula 3 or 4, have significantly superior transmission efficiency compared to the laminates of Samples 2-102 and 2-105, which do not satisfy at least one of the relationships of Formula 1 or 2 and Formula 3 or 4. That is, the laminates of samples 2-1 to 2-6, which satisfy the relationship of formula 1 or 2 and the relationship of formula 3 or 4, can exhibit exceptionally excellent effects of combining excellent "particle capture performance" and excellent permeation efficiency, compared to the laminates of samples 2-101 to 2-105, which do not satisfy at least one of the relationships of formula 1 or 2 and formula 3 or 4.

[0160] From the above, it was found that the laminates according to Samples 2-1 to 2-5 exhibited the exceptionally excellent effect of being able to combine excellent "particle capture performance" with excellent permeation efficiency.

[0161] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include any modifications within the scope of the claims and meanings equivalent to the claims.

[0162] 1 porous membrane, 2 support membrane, 10 laminate, 500 filter element, 520, 540 protective material, 590 liquid collection port, 550 core, 510 outer periphery guard, 560a, 560b end plate, 600 gasket, 580 outlet, 570 porous membrane, 670 laminate.

Claims

1. A porous membrane containing polytetrafluoroethylene as a main component, The porous membrane has a Gurley second and an average bubble point, The porous membrane, wherein the Gurley second and the average bubble point satisfy the relationship of Equation 1 or Equation 2. G1<0.035×P1a Formula 1 G1<0.020×P1b Formula 2 In the formula 1 and the formula 2, G1 is the Gurley second of the porous membrane, In the formula 1, P1a is the average bubble point of the porous membrane, The P1a is measured by a bubble point method using a 1a liquid, The surface tension of the first liquid is 13 mN / m; In the formula 2, P1b is the average bubble point of the porous membrane, The P1b is measured by a bubble point method using a 1b liquid, The surface tension of the first liquid is 21 mN / m.

2. The P1a is 450 kPa or more, The porous membrane of claim 1, wherein P1b is 900 kPa or more.

3. the porous membrane has crystallites, The crystallite has a length X along the MD direction of the porous membrane and a length Y along the TD direction of the porous membrane, The product XY of the length X and the length Y is 1200 nm ２ 3. The porous membrane of claim 1 or claim 2, wherein the porous membrane is less than 1000 .mu.m.

4. A filter element comprising the porous membrane of claim 1 or claim 2.

5. 10. A laminate comprising one or more porous membranes according to claim 1 or claim 2 and a support membrane located on one or both sides of at least one of the porous membranes, The support membrane is porous, the support film contains polytetrafluoroethylene as a main component, The laminate has a Gurley second and an average bubble point, A laminate, wherein the Gurley second of the laminate and the average bubble point of the laminate satisfy the relationship of Equation 3 or Equation 4. G2<0.040×P2a Formula 3 G2<(0.025×P2b)-6 Equation 4 In the formulas 3 and 4, G2 is the Gurley second of the laminate, In the formula 3, P2a is the average bubble point of the laminate, The P2a is measured by a bubble point method using a 2a liquid, The surface tension of the second liquid is 13 mN / m; In the formula 4, P2b is the average bubble point of the laminate, The P2b is measured by a bubble point method using a 2b liquid, The surface tension of the second liquid is 21 mN / m.

6. The P2a is 510 kPa or more, The laminate according to claim 5 , wherein P2b is 1000 kPa or more.

7. A filter element comprising the laminate of claim 5 .