Multilayer body and filter element

Abstract

Disclosed is a multilayer body which comprises a porous film, wherein: the porous film contains a polytetrafluoroethylene as a main component; the multilayer body is in the form of a sheet; the average bubble point P1a of the multilayer body is 390 kPa or more, or the average bubble point P1b of the multilayer body is 780 kPa or more; the average bubble point P1a is determined by a bubble point method using a first a liquid; the surface tension of the first a liquid is 13 mN / m; the average bubble point P1b is determined by a bubble point method using a first b liquid; the surface tension of the first b liquid is 21 mN / m; the Gurley seconds of the multilayer body is 70 seconds or less; and in a test in which the multilayer body is left to stand at 120°C for 1 hour in a thermostatic chamber, the length X of the multilayer body in the MD direction before the test and the length X' of the multilayer body in the MD direction after the test satisfy the relationship of formula 1, and the length Y of the multilayer body in the TD direction before the test and the length Y' of the multilayer body in the TD direction after the test satisfy the relationship of formula 2.

Description

Laminate and filter element

[0001] The present disclosure relates to a laminate and a filter element including the laminate. This application claims priority to Japanese Patent Application No. 2023-084101, filed May 22, 2023, the entire contents of which are incorporated herein by reference.

[0002] Conventionally, porous films 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 5), and laminates including the porous films have been used (Patent Documents 4 and 5).

[0003] Japanese Patent Application Laid-Open No. 2022-78151 Japanese Patent Application Laid-Open No. 2021-54892 International Publication No. 2007 / 011492 International Publication No. 2020 / 251909 Japanese Patent Application Laid-Open No. 2015-226877

[0004] a Gurley second of the laminate is 70 seconds or less; and in a test in which the laminate is left to stand in a thermostatic chamber at 120°C for 1 hour, the length X in the MD direction of the laminate before the test and the length X' in the MD direction of the laminate after the test satisfy the relationship of Equation 1, The length Y of the laminate in the TD direction before the test and the length Y' of the laminate in the TD direction after the test satisfy the relationship of formula 2: |X'-X| / X≦0.10 formula 1 |Y'-Y| / Y≦0.05 formula 2

[0005] Fig. 1 is a schematic enlarged cross-sectional view showing an example of a laminate according to an embodiment of the present disclosure. Fig. 2 is a schematic enlarged cross-sectional view showing another example of a laminate according to an embodiment of the present disclosure. Fig. 3 is a schematic enlarged cross-sectional view showing yet another example of a laminate according to an embodiment of the present disclosure. Fig. 4 is a schematic enlarged cross-sectional view showing yet another example of a laminate according to an embodiment of the present disclosure. Fig. 5 is a perspective view of a filter element according to an embodiment of the present disclosure.

[0006] [Problem to be Solved by the Present Disclosure] In the precision filtration of dispersion media and substrates in fields such as semiconductors, a laminate including a porous membrane is required to have a high average bubble point in order to capture finer particles, etc. Here, the average bubble point is an index indicating the difficulty of particles, etc. passing through. The higher the average bubble point, the more difficult it is for particles, etc. to pass through.

[0007] Furthermore, in the microfiltration, it is required to increase the flow rate of the filtrate through the laminate including the porous membrane in order to increase the permeation efficiency.

[0008] Furthermore, when a laminate including a porous membrane is used as a pleated cartridge filter, the laminate is heated and heat-set after being folded into pleats. In this case, if the thermal stability of the laminate is low (in other words, if it is prone to thermal shrinkage), cartridge processing becomes difficult and the properties of the laminate (pore size and flow rate) are likely to change, so the laminate is required to have excellent thermal stability. Expanded polytetrafluoroethylene is inherently prone to shrinkage. By heating the expanded polytetrafluoroethylene in the sintering process, the polytetrafluoroethylene is melted, thereby releasing the internal stress generated by the stretching. Subsequent cooling and recrystallization impart thermal stability to the expanded polytetrafluoroethylene. Therefore, a laminate including a porous membrane containing such polytetrafluoroethylene as a main component will have excellent thermal stability through the sintering process. Here, excellent "thermal stability" means that "shrinkage of the laminate including the porous membrane due to heating" is unlikely to occur.

[0009] The laminate having a porous film containing polytetrafluoroethylene as a main component has excellent thermal stability due to the sintering process, but it tends to have a low average bubble point and a low flow rate due to the expansion of pores and the decrease in porosity (in other words, the ratio of the volume of pores to the total volume of the porous film) caused by the aggregation of fibers in the porous film.

[0010] For these reasons, it has sometimes been difficult to provide a laminate including a porous membrane with both excellent thermal stability and a high average bubble point, while also increasing the flow rate of filtrate through the laminate.

[0011] Therefore, an object of the present disclosure is to provide a laminate that has both excellent thermal stability and a high average bubble point, and that has a high filtrate flow rate, and a filter element including the laminate.

[0012] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a laminate and a filter element including the laminate that have excellent thermal stability, a high average bubble point, and a high filtrate flow rate.

[0013] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. [1] A laminate according to one aspect of the present disclosure is a laminate including a porous membrane, wherein the porous membrane contains polytetrafluoroethylene as a main component, and the laminate is in a sheet form, and the laminate has an average bubble point P1a of 390 kPa or more, or an average bubble point P1b of 780 kPa or more, the average bubble point P1a being measured by a bubble point method using a 1a liquid, and the 1a liquid has a surface tension of 13 mN / m, and the average bubble point P1b being measured by a bubble point method using a 1b liquid, and the 1b liquid has a surface tension of 21 mN / m, and the laminate has a Gurley second of 70 seconds or less, and in a test in which the laminate is left standing in a thermostatic bath at 120°C for 1 hour, a length X in the MD direction of the laminate before the test and a length X' in the MD direction of the laminate after the test satisfy the relationship of Formula 1, The length Y of the laminate in the TD direction before the test and the length Y' of the laminate in the TD direction after the test satisfy the relationship of Formula 2: |X'-X| / X≦0.10 Formula 1 |Y'-Y| / Y≦0.05 Formula 2

[0014] According to the present disclosure, it is possible to provide a laminate and a filter element including the laminate that have excellent thermal stability, a high average bubble point, and a high filtrate flow rate.

[0015] [2] In the above [1], the laminate may have a maximum tensile strength S1 in the MD direction and a maximum tensile strength S2 in the TD direction, and the maximum tensile strength S1 in the MD direction and the maximum tensile strength S2 in the TD direction may satisfy the relationship of Formula 3: 3.2≦S1 / S2≦5.0 Formula 3 This makes it possible to provide a laminate and a filter element including the laminate that have both better thermal stability and a higher average bubble point, and that have a higher filtrate flow rate.

[0016] [3] In the above [1] or [2], the laminate further includes a support film, which may be porous and contain polytetrafluoroethylene as a main component. This makes it possible to provide a laminate and a filter element including the laminate that have both better thermal stability and a higher average bubble point, and that have a higher filtrate flow rate.

[0017] [4] In the above [3], the support membrane may comprise a first support membrane and a second support membrane, the porous membrane and the second support membrane being disposed in this order on the first support membrane, and each of the first support membrane and the second support membrane may be a uniaxially stretched support membrane. This makes it possible to provide a laminate and a filter element including the laminate that have both superior thermal stability and a higher average bubble point, and that have a higher filtrate flow rate.

[0018] [5] In the above [3], the support membrane may comprise a first support membrane, a second support membrane, a third support membrane, and a fourth support membrane, the second support membrane, the porous membrane, the third support membrane, and the fourth support membrane being disposed in this order on the first support membrane, the second support membrane and the third support membrane each being a biaxially stretched support membrane, and the first support membrane and the fourth support membrane each being a uniaxially stretched support membrane. This makes it possible to provide a laminate and a filter element including the laminate that have both superior thermal stability and a higher average bubble point, and that have a higher filtrate flow rate.

[0019] [6] A filter element according to one aspect of the present disclosure includes the laminate according to any one of [1] to [5] above.

[0020] According to the present disclosure, it is possible to provide a filter element including a laminate that combines excellent thermal stability with a high average bubble point and a high filtrate flow rate.

[0021] [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.

[0022] 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.

[0023] [Embodiment 1: Laminate] A laminate 10 according to one embodiment of the present disclosure will be described with reference to Figures 1 to 4. One embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") is a laminate 10 including a porous membrane 1, the porous membrane 1 containing polytetrafluoroethylene as a main component, and the laminate 10 being in a sheet form.

[0024] (a) The laminate 10 has an average bubble point P1a of 390 kPa or more, or an average bubble point P1b of 780 kPa or more. The laminate 10 can have a high average bubble point.

[0025] 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. "P1a" measured by the bubble point method using "liquid 1a" and "P1b" measured by the bubble point method using "liquid 1b" are defined. Furthermore, "P2a" and "P2b" (described later), as well as "P3a" and "P3b" (described later) are defined.

[0026] (b) The Gurley seconds of the laminate 10 are 70 seconds or less. The laminate 10 can exhibit a high filtrate flow rate.

[0027] (c) On the other hand, in such a laminate, due to the “ease of shrinkage of the fibers of the laminate” caused by the residual stress of the laminate, the laminate 10 tends to have difficulty in having excellent thermal stability.

[0028] In the laminate 10 of the present disclosure, in a test in which the laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour, the length X in the MD (Machine Direction) direction of the laminate 10 before the test and the length X' in the MD direction of the laminate 10 after the test satisfy the relationship of Equation 1, and the length Y in the TD (Transverse Direction) direction of the laminate 10 before the test and the length Y' in the TD direction of the laminate 10 after the test satisfy the relationship of Equation 2: |X' - X| / X≦0.10 Equation 1 |Y' - Y| / Y≦0.05 Equation 2 This suppresses deformation of the fibers of the porous membrane due to heating, allowing the laminate 10 to have excellent thermal stability without compromising the above-mentioned high average bubble point and high filtrate flow rate.

[0029] <Laminate> <Structure of Laminate> The laminate 10 includes a porous membrane 1. The laminate 10 may further include a support membrane 2. In this way, the support membrane 2 functions as a protective material for the porous membrane 1, thereby improving the capture performance of the laminate 10 and increasing the mechanical strength and lifespan of the laminate 10.

[0030] The support membrane 2 may be, for example, in a form (form 1) consisting of a first support membrane 21 and a second support membrane 22, with the porous membrane 1 and the second support membrane 22 arranged in this order on the first support membrane 21. Alternatively, the support membrane 2 may be in a form (form 2) consisting of a first support membrane 21, a second support membrane 22, a third support membrane 23, and a fourth support membrane 24, with the second support membrane 22, the porous membrane 1, the third support membrane 23, and the fourth support membrane 24 arranged in this order on the first support membrane 21. Alternatively, the porous membrane 1 may be composed of a first porous membrane and a second porous membrane, and the support membrane 2 may be composed of a first support membrane 21, a second support membrane 22, a third support membrane 23, a fourth support membrane 24, and a fifth support membrane 25, with the second support membrane 22, the first porous membrane, the third support membrane 23, the second porous membrane, the fourth support membrane 24, and the fifth support membrane 25 being arranged in this order on the first support membrane 21 (form 3). Alternatively, the porous membrane 1 may be composed of a first porous membrane, a second porous membrane, and a third porous membrane, and the support membrane 2 may be composed of a first support membrane 21, a second support membrane 22, a third support membrane 23, a fourth support membrane 24, a fifth support membrane 25, and a sixth support membrane 26, with the second support membrane 22, the first porous membrane, the third support membrane 23, the second porous membrane, the fourth support membrane 24, the third porous membrane, the fifth support membrane 25, and the sixth support membrane 26 being arranged in this order on the first support membrane 21 (form 4). Furthermore, the support membrane 2 may be either a uniaxially stretched support membrane described later or a biaxially stretched support membrane described later.

[0031] The laminate 10 is in a sheet form. Here, "sheet form" means a thin plate form. 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. The shape of the laminate 10 is long.

[0032] The thickness of the laminate 10 can be determined by a method similar to the measurement method for the "thickness of the porous membrane 1" described below, except that the measurement is performed on the laminate 10. It has been confirmed that similar results can be obtained when different measurement points are arbitrarily selected on the same laminate 10 and the above measurement is performed at those measurement points.

[0033] <Length in MD Direction and Length in TD Direction> The length X in the MD direction of the laminate 10 before a test in which the laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour is not particularly limited as long as the relationship of Formula 1 is satisfied, but may be, for example, 0.010 m or more and 1.000 m or less, 0.020 m or more and 0.500 m or less, or 0.025 m or more and 0.250 m or less. In this embodiment, the "MD direction" can be rephrased as the longitudinal direction.

[0034] The length X of the laminate 10 in the MD direction can be determined by the following method. First, the laminate 10 is prepared before a test in which the laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour. Next, the length of the laminate 10 in the MD direction is measured at any five points. Next, the average value of the lengths in the MD direction is calculated, thereby determining the length X of the laminate 10 in the MD direction.

[0035] The length X' of the laminate 10 in the MD direction after a test in which the laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour is not particularly limited as long as the relationship of Equation 1 is satisfied, but can be, for example, 0.010 m or more and 1.000 m or less, 0.020 m or more and 0.500 m or less, or 0.025 m or more and 0.250 m or less.

[0036] The length X' of the laminate 10 in the MD direction can be determined in the same manner as the "length X of the laminate 10 in the MD direction," except that the measurement is performed on the "laminated body 10 after a test in which the laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour."

[0037] The length Y in the TD direction of the laminate 10 before the test in which the laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour is not particularly limited as long as the relationship in Equation 2 is satisfied, but it can be, for example, 0.010 m or more and 1.000 m or less, 0.020 m or more and 0.500 m or less, or 0.025 m or more and 0.250 m or less. In this embodiment, the "TD direction" of the laminate 10 is the direction perpendicular to the "MD direction" and the thickness direction of the laminate 10.

[0038] The length Y of the laminate 10 in the transverse direction can be determined by the following method. First, the laminate 10 is prepared before a test in which the laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour. Next, the length of the laminate 10 in the transverse direction is measured at five arbitrary positions. Next, the average value of the lengths in the transverse direction is calculated, thereby determining the length Y of the laminate 10 in the transverse direction.

[0039] The length Y' of the laminate 10 in the TD direction after a test in which the laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour is not particularly limited as long as the relationship of Equation 2 is satisfied, but can be, for example, 0.010 m or more and 1.000 m or less, 0.020 m or more and 0.500 m or less, or 0.025 m or more and 0.250 m or less.

[0040] The MD length Y' of the laminate 10 can be determined in the same manner as the TD length Y of the laminate 10, except that the measurement is performed on the laminate 10 after a test in which the laminate 10 is left standing in a constant temperature bath at 120°C for 1 hour.

[0041] In a test in which laminate 10 is left standing in a thermostatic chamber at 120°C for 1 hour, the length X in the MD direction of laminate 10 before the test and the length X' in the MD direction of laminate 10 after the test satisfy the relationship of Formula 1, and the length Y in the TD direction of laminate 10 before the test and the length Y' in the TD direction of laminate 10 after the test satisfy the relationship of Formula 2. |X' - X| / X≦0.10 Formula 1 |Y' - Y| / Y≦0.05 Formula 2 This allows laminate 10 to have excellent thermal stability without compromising its high average bubble point and high filtrate flow rate.

[0042] The upper limit of "|X'-X| / X" may be 0.09 or less, 0.08 or less, or 0.07 or less. The lower limit of "|X'-X| / X" may be 0.01 or more, 0.02 or more, or 0.03 or more. "|X'-X| / X" may be 0.01 or more and 0.10 or less, 0.02 or more and 0.09 or less, or 0.03 or more and 0.08 or less.

[0043] The upper limit of |Y'-Y| / Y may be 0.09 or less, 0.08 or less, or 0.07 or less. The lower limit of |Y'-Y| / Y may be 0.01 or more, 0.02 or more, or 0.03 or more. |Y'-Y| / Y may be 0.01 or more and 0.10 or less, 0.02 or more and 0.09 or less, or 0.03 or more and 0.08 or less.

[0044] <Density> 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. ３If 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 more ３ It may be the following:

[0045] The density of the laminate 10 can be determined by a method similar to the method for measuring the "density of the porous membrane 1" described below, 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.

[0046] <Weight> The weight per unit area 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 ２The 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:

[0047] The basis weight of the laminate 10 can be determined by a method similar to the measurement method for the "basis weight of the porous membrane 1" described below, 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.

[0048] <Average Bubble Point> The average bubble point P1a of the laminate 10 is 390 kPa or more, and the average bubble point P1b of the laminate 10 is 780 kPa or more. The average bubble point P1a is measured by a bubble point method using a 1a liquid, and the surface tension of the 1a liquid is 13 mN / m. The average bubble point P1b is measured by a bubble point method using a 1b liquid, and the surface tension of the 1b liquid is 21 mN / m. The laminate 10 can have a high average bubble point. The lower limit of the average bubble point P1a of the laminate 10 may be 400 kPa or more, 410 kPa or more, or 420 kPa or more. The upper limit of the average bubble point P1a of the laminate 10 may be 900 kPa or less, 890 kPa or less, or 880 kPa or less. The average bubble point P1a of the laminate 10 may be 390 kPa or more and 900 kPa or less, 400 kPa or more and 890 kPa or less, or 410 kPa or more and 880 kPa or less.

[0049] More specifically, the average bubble point P1a of the laminate 10 is determined by the following method. That is, except that the measurement is performed on the "laminate 10", the average bubble point P1a is determined by the same method as the measurement method for the "average bubble point P2a of the porous membrane 1" described below.

[0050] The lower limit of the average bubble point P1b of the laminate 10 may be 790 kPa or more, 800 kPa or more, or 810 kPa or more. The upper limit of the average bubble point P1b of the laminate 10 may be 1400 kPa or less, 1390 kPa or less, or 1380 kPa or less. The average bubble point P1b of the laminate 10 may be 780 kPa or more and 1400 kPa or less, 790 kPa or more and 1390 kPa or less, or 800 kPa or more and 1380 kPa or less.

[0051] More specifically, the average bubble point P1b of the laminate 10 is determined by the following method. That is, except that the measurement is performed on the "laminated body 10", the average bubble point P1b is determined by the same method as the measurement method for the "average bubble point P2b of the porous membrane 1" described later.

[0052] <Gurley Second> The Gurley second of the laminate 10 is 70 seconds or less. This allows the flow rate of the filtrate to be increased, thereby increasing the permeation efficiency. The lower limit of the Gurley second of the laminate 10 may be 1 second or more, 3 seconds or more, or 5 seconds or more. The upper limit of the Gurley second of the laminate 10 may be 45 seconds or less, 40 seconds or less, or 35 seconds or less. The Gurley second of the laminate 10 may be 1 second or more and 68 seconds or less, 3 seconds or more and 66 seconds or less, or 5 seconds or more and 40 seconds or less.

[0053] The Gurley second of the laminate 10 is determined by the following method. That is, except that the measurement is performed on the "laminate 10", it can be determined by the same method as the measurement method of the "Gurley second of the porous membrane 1" described later.

[0054] <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 the laminate 10 to have a higher average bubble point and a higher filtrate flow rate. 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.

[0055] The mean flow pore size of the laminate 10 can be determined in the same manner as the measurement method for the "mean flow pore size of the porous membrane 1" described below, except that the measurement is performed on the "laminated body 10."

[0056] <Maximum tensile strength> The laminate 10 has a maximum tensile strength S1 in the MD direction and a maximum tensile strength S2 in the TD direction, and the maximum tensile strength S1 in the MD direction and the maximum tensile strength S2 in the TD direction may satisfy the relationship of Formula 3: 3.2≦S1 / S2≦5.0 Formula 3 This suppresses deformation of the fibers of the porous membrane 1 due to heating, so the laminate 10 has both better thermal stability and a higher average bubble point, and can exhibit a higher filtrate flow rate.

[0057] The maximum tensile strength S1 in the MD direction of the laminate 10 can be determined by the following method. First, a rectangular sample of 50 mm in the MD direction by 5 mm in the TD direction is obtained by cutting the laminate 10 at any one location into a rectangle of 50 mm in the MD direction by 5 mm in the TD direction. Using an autograph "AGS-X" (trademark) manufactured by Shimadzu Corporation, the sample is then pulled in the MD direction at a chuck distance of 10 mm and a speed of 100 mm / min. The maximum tensile stress value applied until the sample breaks is measured as the maximum tensile strength S1 in the MD direction. Furthermore, the maximum tensile strength S2 in the TD direction of the laminate 10 can be determined by the following method. The maximum tensile strength S2 in the TD direction can be determined by the same method as the measurement method for the maximum tensile strength S1 in the MD direction, except for the points that "pulling is performed in the TD direction" and "the maximum tensile stress value applied until the sample breaks is measured as the maximum tensile strength S2 in the TD direction."

[0058] <Porous Membrane> <Composition> 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.

[0059] 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.

[0060] <Shape> 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.

[0061] 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.

[0062] It has been confirmed that similar results can be obtained when different measurement points are arbitrarily selected on the same porous membrane 1 and the above measurement is carried out at those measurement points.

[0063] <Density> 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 ３ or 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:

[0064] The density of the porous membrane 1 can be determined by the following method. That is, the density of the porous membrane 1 can be determined by the formula "density [g / cm ３ ] = [{(basis weight [mg / mm ２ ]) / 1000} / {(thickness [mm]) / 10}] / (1 / 100)" based on the basis weight and thickness.

[0065] <Weight> The weight per unit area 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 ２or 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:

[0066] The basis weight of the porous membrane 1 can be determined by the following method. First, an evaluation sample is obtained by punching out a hole with a diameter of 60 mm at any one location of the porous membrane 1 in the film thickness direction. Next, the mass [g] of the evaluation sample is measured using an analytical balance "AP224X" (trademark) manufactured by Shimadzu Corporation. Next, the mass and the formula "basis weight [mg / mm ２ ] = {1000 × (mass of the evaluation sample [g])} / {(60 / 2) ２ × π}" to calculate the basis weight of the porous membrane 1.

[0067] 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.

[0068] <Average Bubble Point> The average bubble point P2a of the porous membrane 1 may be 300 kPa or more and 900 kPa or less, or the average bubble point P2b of the porous membrane 1 may be 780 kPa or more and 1400 kPa or less. This allows the laminate 10 to have a higher average bubble point and a higher filtrate flow rate. The lower limit of the average bubble point P2a of the porous membrane 1 may be 300 kPa or more, 310 kPa or more, or 320 kPa or more. The upper limit of the average bubble point P2a of the porous membrane 1 may be 900 kPa or less, 890 kPa or less, or 880 kPa or less. The average bubble point P2a of the porous membrane 1 may be 310 kPa or more and 890 kPa or less, or 320 kPa or more and 880 kPa or less.

[0069] The average bubble point P2a of the porous membrane 1 is measured by the bubble point method using liquid 1a, and the surface tension of liquid 1a is 13 mN / m. More specifically, the average bubble point of 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 (1a liquid) manufactured by Mitsui-Chemours Fluoroproducts, Inc., for about 5 minutes at about 25°C, and then removed from the hydrofluoroolefin (1a liquid), thereby obtaining a porous membrane 1 wet with hydrofluoroolefin (1a liquid). Next, for the porous membrane 1 wet with hydrofluoroolefin (1a liquid), 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 differential pressure on the horizontal axis and the air flow rate on the vertical axis. Next, the differential pressure at the intersection of the first curve and the second curve is identified as the average bubble point P2a of the porous membrane 1.

[0070] The lower limit of the average bubble point P2b of the porous membrane 1 may be 780 kPa or more, 790 kPa or more, or 800 kPa or more. The upper limit of the average bubble point P2b of the porous membrane 1 may be 1400 kPa or less, 1390 kPa or less, or 1380 kPa or less. The average bubble point P2b of the porous membrane 1 may be 790 kPa or more and 1390 kPa or less, or 800 kPa or more and 1380 kPa or less.

[0071] In the porous membrane 1, the average bubble point P2b 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, the average bubble point P2b is determined by a method similar to the method for measuring P2a, except that isopropyl alcohol (liquid 1b) manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. is used instead of liquid 1a.

[0072] <Gurley seconds> The Gurley seconds of the porous membrane 1 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 the Gurley seconds of the porous membrane 1 may be 1 second or more, 3 seconds or more, or 5 seconds or more. The upper limit of the Gurley seconds of the porous membrane 1 may be 100 seconds or less, 80 seconds or less, or 60 seconds or less. The Gurley seconds of the porous membrane 1 may be 3 seconds or more and 80 seconds or less, or 5 seconds or more and 60 seconds or less.

[0073] The Gurley seconds of the porous membrane 1 can be determined by the following method. That is, 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 the porous membrane 1 to permeate at a differential pressure of 1.22 kPa is measured. The time is specified as the Gurley seconds of the porous membrane 1.

[0074] <Mean flow pore diameter> The mean flow pore diameter of the porous membrane 1 may be 25 nm or more and 70 nm or less. This allows the laminate 10 to have a higher average bubble point and a higher filtrate flow rate. 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 70 nm or less, 67 nm or less, or 65 nm or less. The mean flow pore diameter may be 26 nm or more and 67 nm or less, or 27 nm or more and 65 nm or less.

[0075] 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 the differential pressure and the vertical axis is the 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) of Porous Materials, Inc. for about 5 minutes at about 25 ℃, and then taken out from this GALWICK (fourth liquid), thereby obtaining the porous membrane 1 wet with GALWICK (fourth liquid). Next, for a porous membrane 1 wetted with GALWICK (fourth liquid), 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 fourth curve showing the relationship between the differential pressure and the air flow rate is obtained on a coordinate system with the differential pressure on the horizontal axis and the air flow rate on the vertical axis. Next, the differential pressure P' at the intersection of the third curve and the fourth curve is identified. Next, the mean flow pore diameter [nm] of the porous membrane 1 is determined by dividing the product of the constant 2860 and the surface tension of the fourth liquid, 16 mN, 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.

[0076] <<Support membrane>> <Structure> The support membrane 2 is porous. Here, "porous" means having a fibrous skeleton in which pores are connected in a three-dimensional network. The mean flow pore size of the support membrane 2 is larger than the mean flow pore size of the porous membrane 1, and the support membrane 2 does not have to excessively inhibit the permeation efficiency of the porous membrane 1. The fact that "the support membrane 2 is porous" can be determined by observing the surface state and cross-sectional state of the support membrane 2 using a scanning electron microscope.

[0077] 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 to demonstrate its function as a protective material for the porous membrane 1, 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 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. In embodiments 1 to 4, the thicknesses of the first to sixth support films may be within the ranges described above.

[0078] 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 above, except that the measurement is performed on the support membrane 2. It has been confirmed that similar results can be obtained when different measurement points are arbitrarily selected on the same support membrane 2 and the above measurement is performed at those measurement points.

[0079] <Uniaxially stretched support membrane and biaxially stretched support membrane> The support membrane 2 can be a uniaxially stretched support membrane or a biaxially stretched support membrane. In particular, when the support membrane 2 is a biaxially stretched support membrane, the fibers (polytetrafluoroethylene) of the support membrane 2 and the fibers (polytetrafluoroethylene) of the porous membrane 1 are likely to be entangled with each other, so the mean flow pore size of the laminate 10 can be made smaller (in other words, the mean bubble point of the laminate 10 can be made higher). In particular, when the support membrane 2 is a uniaxially stretched support membrane, the fibers of the support membrane 2 are aligned only in the MD direction, which is the stretching direction, so the thermal stability of the laminate 10 can be made higher.

[0080] When the support membrane 2 is composed of a first support membrane and a second support membrane, each of the first support membrane and the second support membrane may be a uniaxially stretched support membrane, which suppresses deformation of the fibers of the porous membrane due to heating, and therefore the laminate 10 has both superior thermal stability and a higher average bubble point, and can exhibit a higher filtrate flow rate.

[0081] In the case where the support membrane 2 is composed of a first support membrane, a second support membrane, a third support membrane, and a fourth support membrane, the second support membrane and the third support membrane may each be a biaxially stretched support membrane, and the first support membrane and the fourth support membrane may each be a uniaxially stretched support membrane. This suppresses deformation of the fibers of the porous membrane due to heating, and the fibers of the support membrane 2 and the porous membrane 1 are easily entangled with each other, so that the laminate 10 has both superior thermal stability and a higher average bubble point, and can exhibit a higher filtrate flow rate.

[0082] In the case where the support membrane 2 is composed of a first support membrane, a second support membrane, a third support membrane, a fourth support membrane, and a fifth support membrane, the second support membrane, the third support membrane, and the fourth support membrane may each be a biaxially stretched support membrane, and the first support membrane and the fifth support membrane may each be a uniaxially stretched support membrane. This suppresses deformation of the fibers of the porous membrane due to heating, and the fibers of the support membrane 2 and the porous membrane 1 are easily entangled with each other, so that the laminate 10 has both superior thermal stability and a higher average bubble point, and can exhibit a higher filtrate flow rate.

[0083] In the case where support membrane 2 is composed of first support membrane, second support membrane, third support membrane, fourth support membrane, fifth support membrane, and sixth support membrane, each of the second support membrane, the third support membrane, the fourth support membrane, and the fifth support membrane may be a biaxially stretched support membrane, and each of the first support membrane and the sixth support membrane may be a uniaxially stretched support membrane. This suppresses deformation of the fibers of the porous membrane due to heating, and the fibers of support membrane 2 and porous membrane 1 are easily entangled with each other, so that laminate 10 has both superior thermal stability and a higher average bubble point, and can exhibit a higher filtrate flow rate.

[0084] When the uniaxially stretched support film has a maximum tensile strength S5 in the MD direction and a maximum tensile strength S6 in the TD direction, "the support film 2 is a uniaxially stretched support film" means that "the maximum tensile strength S5 in the MD direction and the maximum tensile strength S6 in the TD direction satisfy the relationship of Formula 5." 2.0≦S5 / S6≦50 Formula 5

[0085] The maximum tensile strength S5 in the MD direction and the maximum tensile strength S6 in the TD direction can be determined by a method similar to the measurement method for the "maximum tensile strength S1 in the MD direction and the maximum tensile strength S2 in the TD direction in the laminate 10," except that the measurement is performed on a uniaxially stretched support film.

[0086] When the biaxially stretched support film has a maximum tensile strength S3 in the MD direction and a maximum tensile strength S4 in the TD direction, the statement "the support film 2 is a biaxially stretched support film" means that "the maximum tensile strength S3 in the MD direction and the maximum tensile strength S4 in the TD direction satisfy the relationship of Formula 4." 0.5≦S3 / S4<2.0 Formula 4

[0087] The maximum tensile strength S3 in the MD direction and the maximum tensile strength S4 in the TD direction can be determined by a method similar to the method for measuring the maximum tensile strength S1 in the MD direction and the maximum tensile strength S2 in the TD direction in the laminate 10, except that the measurement is performed on a biaxially stretched support film.

[0088] <Density> 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 / cm３ 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 In embodiments 1 to 4, the densities of the first to sixth support films may be in the above ranges.

[0089] The density of the support membrane 2 can be determined by a method similar to the method 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 by arbitrarily selecting a different measurement range for the same support membrane 2 and performing the above measurement in that measurement range.

[0090] <Weight> 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 ２ When 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 In the first to fourth embodiments, the basis weights of the first to sixth support membranes may be within the above ranges.

[0091] The basis weight of the support membrane 2 can be determined by a method similar to the method for measuring the "basis weight of the porous membrane 1" described below, 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 laminate 10 and the above measurement is performed in that measurement range.

[0092] <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 laminate 10 to have a higher average bubble point. The lower limit of the average bubble point P3a of the support film 2 may be 5 kPa or more, 7 kPa or more, or 10 kPa or more. The upper limit of the average bubble point P3a of the support film 2 may be 400 kPa or less, 350 kPa or less, or 300 kPa or less. The average bubble point P3a of the support film 2 may be 7 kPa or more and 350 kPa or less, or 10 kPa or more and 300 kPa or less. In embodiments 1 to 4, the average bubble points P3a of the first to sixth support films may be in the above-mentioned ranges.

[0093] The average bubble point P3a of the support membrane 2 is measured by a bubble point method using the 1a liquid, and the surface tension of the 1a liquid is 13 mN / m. More specifically, the average bubble point P3a of the laminate 10 is determined by the following method. That is, it is determined by a method similar to the measurement method for the "average bubble point P2a of the porous membrane 1" described above, except that the measurement is performed on the "support membrane 2."

[0094] The lower limit of the average bubble point P3b of the support film 2 may be 5 kPa or more, 7 kPa or more, or 10 kPa or more. The upper limit of the average bubble point P3b of the support film 2 may be 800 kPa or less, 700 kPa or less, or 600 kPa or less. The average bubble point P3b of the support film 2 may be 7 kPa or more and 700 kPa or less, or 10 kPa or more and 600 kPa or less. The average bubble point P3b of the support film 2 may be within the above range.

[0095] The average bubble point P3b of the support film 2 is measured by a bubble point method using the 1b liquid, and the surface tension of the 1b liquid is 13 mN / m. More specifically, the average bubble point P3b of the laminate 10 is determined by the following method. That is, it is determined by a method similar to the measurement method for the "average bubble point P2b of the porous film 1" described above, except that the measurement is performed on the "support film 2."

[0096] <Gurley seconds> The Gurley seconds of the support membrane 2 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. The lower limit of the Gurley seconds of the support membrane 2 may be 0.5 seconds or more, 0.7 seconds or more, or 1.0 second or more. The upper limit of the Gurley seconds of the support membrane 2 may be 60 seconds or less, 50 seconds or less, or 40 seconds or less. The Gurley seconds of the support membrane 2 may be 0.7 seconds or more and 50 seconds or less, or 1.0 second or more and 40 seconds or less. In embodiments 1 to 4, the Gurley seconds of the first to sixth support membranes may be in the above-mentioned ranges.

[0097] The Gurley seconds of the support membrane 2 are determined by the following method. That is, except that the measurement is performed on the "support membrane 2", it can be determined by the same method as the measurement method for the "Gurley seconds of the porous membrane 1" described above.

[0098] <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 excellent strength and excellent permeation efficiency. 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. In embodiments 1 to 4, the mean flow pore diameters of the first to sixth support membranes may be in the above-mentioned ranges.

[0099] The mean flow pore size of support membrane 2 can be determined in the same manner as the measurement method for the "mean flow pore size of porous membrane 1" described above, except that the measurement is performed on "support membrane 2."

[0100] <Composition> The support film 2 contains polytetrafluoroethylene as a main component. This can improve the heat resistance and chemical stability 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.

[0101] The polytetrafluoroethylene content in the support membrane 2 can be determined by a method similar to the method for measuring the "polytetrafluoroethylene content in the porous membrane 1" of the vapor, 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.

[0102] [Embodiment 2: Manufacturing Method of Laminate] A manufacturing method of the laminate according to the above-mentioned embodiment 1 will be described. However, the manufacturing method of the laminate is not limited to the following method. The manufacturing method of the laminate according to embodiment 2 can include, for example, a first step of preparing a porous film and a support film, and a second step of laminating the porous film and the support film. Furthermore, the first step can include a 1-1 step of preparing a porous film and a 1-2 step of preparing a support film. Furthermore, the 1-1 step can include a 1-1-a step of obtaining a kneaded product of polytetrafluoroethylene powder and a liquid lubricant, a 1-1-b step of extrusion-molding the kneaded product to obtain a sheet-like molded product, a 1-1-c step of biaxially stretching the molded product to obtain an elongated product, and a 1-1-d step of heat-treating the elongated product to obtain a porous film. Step 1-2 can include Step 1-2-a of obtaining a kneaded product of polytetrafluoroethylene powder and a liquid lubricant, Step 1-2-b of obtaining a sheet-like molded body by extrusion molding the kneaded product, Step 1-2-c of obtaining an elongated body by uniaxially or biaxially stretching the molded body, and Step 1-2-d of obtaining a support film by heat treating the elongated body.

[0103] <<Step 1>> <Step 1-1> (Step 1-1-a) Step 1-1-a is carried out by kneading polytetrafluoroethylene powder and a liquid lubricant to obtain a kneaded mixture. More specifically, first, a mixture is obtained by mixing polytetrafluoroethylene powder and a liquid lubricant. Next, the mixture is compression-molded into a block shape using a compression molding machine to obtain the kneaded mixture.

[0104] 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.

[0105] 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 preventing excessive pore expansion and rupture of the porous film during stretching and facilitating the growth of the fibrous skeleton. 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 depending 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 quantity obtained by integrating a 48°C section starting from the end set temperature of a peak in the range of 300°C to 360°C in the melting curve of Pattern 3 is defined as the second heat of fusion. Here, the "end set temperature" refers to the temperature at the end of melting associated with a temperature rise in the relationship between the melting curve and the peak.

[0106] 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.

[0107] 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.

[0108] In addition to the polytetrafluoroethylene powder and 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.

[0109] <Step 1-1-b> Step 1-1-b is carried out by extrusion molding the kneaded mixture to obtain a sheet-like molded body. More specifically, the kneaded mixture is extruded into a sheet at room temperature (e.g., 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 0.200 mm to 0.400 mm. The average thickness can be determined by the same method as the measurement method for the "thickness of porous membrane 1" above, except that the measurement is carried out on the molded body.

[0110] Furthermore, before carrying out the step 1-1-c 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 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.

[0111] <Step 1-1-c> Step 1-1-c is carried out by biaxially stretching the molded body to obtain a stretched body. Here, biaxial stretching means stretching a 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. Here, stretching in the MD direction is carried out, and then stretching in the TD direction is carried out.

[0112] The temperature in step 1-1-c may be 60° C. or higher and 300° C. or lower. If the temperature exceeds 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).

[0113] 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.

[0114] 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.

[0115] <Step 1-1-d> Step 1-1-d is performed by subjecting the stretched body to heat treatment to obtain a porous membrane. Step 1-1-d is performed under the conditions of 140°C to 345°C for 0.01 to 120 minutes.

[0116] The lower limit of the temperature in step 1-1-d may be 140°C or higher. If the temperature is lower than 140°C, the residual stress due to stretching is not sufficiently relaxed, and the laminate tends to be prone to thermal shrinkage. The upper limit of the temperature in step 1-1-d may be 345°C or lower. If the temperature is higher than 345°C, the mean flow pore size of the laminate tends to be excessively enlarged (in other words, the average bubble point of the laminate tends to be excessively reduced).

[0117] The lower limit of the time for step 1-1-d may be 0.01 minutes or more. If the time is less than 0.01 minutes, the thermal stability of the laminate tends to be insufficient. The upper limit of the time for step 1-1-d may be 120 minutes or less. If the time is more than 120 minutes, the mean flow pore size of the laminate tends to be excessively enlarged (in other words, the mean bubble point of the laminate tends to be excessively reduced).

[0118] <Step 1-2> (Step 1-2-a) Step 1-2-a is carried out by kneading polytetrafluoroethylene powder and a liquid lubricant to obtain a kneaded mixture. More specifically, first, the polytetrafluoroethylene powder and the 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 mixture.

[0119] Examples of polytetrafluoroethylene powder include "CD145E" (trademark) manufactured by AGC Inc., "CD123E" (trademark) manufactured by AGC Inc., "F-104" (trademark) manufactured by Daikin Industries, Ltd., and "6-J" (trademark) manufactured by Mitsui-Chemours Fluoroproducts, Inc.

[0120] The number-average molecular weight of polytetrafluoroethylene in the polytetrafluoroethylene powder may be 1,000,000 or more and 20,000,000 or less from the viewpoint of preventing the pores from becoming excessively small and the porous film from cracking during stretching, and facilitating the growth of the fibrous skeleton. Also, the second heat of fusion in the polytetrafluoroethylene powder may be 20 J / g or more and 45 J / g or less from the viewpoint of depending on the number-average molecular weight of the polytetrafluoroethylene powder.

[0121] 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.

[0122] As the material of the kneaded product, in addition to the polytetrafluoroethylene powder and the liquid lubricant, the above-mentioned other additives may also be used.

[0123] <Step 1-2-b> Step 1-2-b is carried out by extrusion molding the kneaded mixture to obtain a sheet-like molded product. More specifically, the kneaded mixture is extruded into a sheet at room temperature (e.g., 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 product. Furthermore, the precursor is rolled using a calendar roll or the like to obtain a sheet-like molded product having an average thickness of 0.200 mm to 0.400 mm. The average thickness can be determined by the same method as the measurement method for the "thickness of porous membrane 1" above, except that the measurement is performed on the molded product.

[0124] Furthermore, before carrying out the step 1-2-c 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 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.

[0125] <Step 1-2-c> Step 1-2-c can be carried out to obtain a stretched body by uniaxially stretching the molded body. In the production of any of the support membranes provided in the laminate, step 1-2-c is carried out by uniaxially stretching the molded body, thereby suppressing the expansion of pores and the decrease in porosity associated with the aggregation of fibers in the porous membrane, and while keeping the average bubble point and Gurley seconds of the laminate within the desired range, "the ratio of the absolute value of the difference between the MD length X' and the MD length X relative to the MD length X is 10% or less, and the ratio of the absolute value of the difference between the TD length Y' and the TD length Y relative to the TD length Y is 5% or less." Here, uniaxial stretching means stretching a sheet-like molded body in the MD direction (in other words, the flow direction of the molded body). Biaxial stretching means stretching a sheet-like molded body in the MD direction (in other words, the flow direction of the molded body) and in the TD direction perpendicular to the MD direction.

[0126] The temperature in step 1-2-c may be 60° C. or higher and 300° C. or lower. If the temperature exceeds 300° C., the pore size of the support film tends to be too large (in other words, the average bubble point of the support film 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 support film tends to be too large).

[0127] When stretching a sheet-like molded body in the MD direction, the stretching ratio in the MD direction may be 1.5 times or more and 20 times or less. The stretching ratio in the MD direction means the value obtained by dividing the average length in the MD direction immediately after stretching in the MD direction by the average length in the MD direction immediately before stretching in the MD direction. If the stretching ratio in the MD direction is less than 1.5 times, the thickness of the support film may be outside the desired range. If the stretching ratio in the MD direction is more than 20 times, the thickness of the support film may be outside the desired range. Here, the "average length in the MD direction" means the average value of the MD direction length at any 10 points.

[0128] When stretching a sheet-like molded body in the TD direction, the stretching ratio in the TD direction may be 1.5 times or more and 100 times or less. The stretching ratio in the TD direction means the value obtained by dividing the average length in the TD direction immediately after stretching in the TD direction by the average length in the TD direction immediately before stretching in the TD direction. If the stretching ratio in the TD direction is less than 1.5 times, the thickness of the support film may be outside the desired range. If the stretching ratio in the TD direction is more than 100 times, the thickness of the support film may be outside the desired range. Here, the "average length in the TD direction" means the average value of the length in the TD direction at any 10 points.

[0129] <Step 1-2-d> Step 1-2-d is carried out by subjecting the stretched body to heat treatment to obtain a support film.

[0130] The lower limit of the temperature in step 1-2-d may be 345°C or higher. If the temperature is lower than 345°C, the thermal stability of the laminate tends to decrease. The upper limit of the temperature in step 1-2-d may be 800°C or lower. If the temperature is higher than 800°C, the mechanical strength of the laminate tends to decrease due to thermal decomposition of polytetrafluoroethylene.

[0131] The lower limit of the time for step 1-2-d may be 0.01 minutes or more. If the time is less than 0.01 minutes, the thermal stability of the support film tends to be easily reduced. The upper limit of the time for step 1-2-d may be 120 minutes or less. If the time is more than 120 minutes, the mechanical strength of the support film tends to be easily reduced due to thermal decomposition of polytetrafluoroethylene.

[0132] The second step is carried out by laminating the porous membrane and the support membrane. Examples of a method for laminating the porous membrane and the support membrane include a method in which adjacent membranes of the support membrane and the porous membrane are pressure-bonded to each other.

[0133] Specifically, the method for pressing adjacent support membranes and porous membranes together includes, for example, overlapping the support membrane and the porous membrane to obtain a laminate precursor. Next, the laminate precursor is pressed from above and below with flat plates, or the laminate precursor is sandwiched between rotating rollers and sent out. The method for pressing adjacent support membranes and porous membranes together may be performed by pressing at a pressure of 10 kgf or more and 2000 kgf or less. If the pressure is less than 10 kgf, the adhesive strength between adjacent support membranes and porous membranes tends to be insufficient. If the pressure is more than 2000 kgf, the pores of the support membrane or porous membrane tend to be crushed, resulting in a decrease in permeation efficiency.

[0134] Thus, there is provided a laminate comprising a porous membrane, the porous membrane containing polytetrafluoroethylene as a main component, the laminate being in a sheet form, the laminate having an average bubble point P1a of 390 kPa or more, or an average bubble point P1b of 780 kPa or more, the average bubble point P1a being measured by a bubble point method using a liquid 1a, the surface tension of the liquid 1a being 13 mN / m, and the average bubble point P1b being measured by a bubble point method using a liquid 1b, the surface tension of the liquid 1a being 13 mN / m, and the average bubble point P1b being measured by a bubble point method using a liquid 1b, the surface tension of the liquid 1a being 13 mN / m, and the average bubble point P1a being measured by a bubble point method using a liquid 1b ... The surface tension of the 1b liquid is measured by a bubble point method using a liquid 1b, and the surface tension of the 1b liquid is 21 mN / m, the Gurley seconds of the laminate is 70 seconds or less, and in a test in which the laminate is left to stand in a thermostatic chamber at 120°C for 1 hour, the length X in the MD direction of the laminate before the test and the length X' in the MD direction of the laminate after the test satisfy the relationship of Formula 1 above, and the length Y in the TD direction of the laminate before the test and the length Y' in the TD direction of the laminate after the test satisfy the relationship of Formula 2 above.

[0135] [Embodiment 3: Filter Element] A filter element according to one embodiment of the present disclosure will be described with reference to Figure 5. A filter element 500 according to this embodiment includes the laminate 670 according to embodiment 1. The filter element 500 according to this embodiment is not particularly limited as long as it includes the laminate 670 according to embodiment 1, but for example, in the filter element 500, the laminate 670 may have a pleated structure.

[0136] The present disclosure provides a filter element including a laminate that combines excellent thermal stability with a high average bubble point and high filtrate flow rate.

[0137] FIG. 5 shows a filter element 500 including a pleated laminate 670. The laminate 670 is sandwiched between two protective materials 520 and 540, then pleated and wrapped around a core 550 with multiple liquid collection ports 590. An outer peripheral guard 510 protects the laminate 670. End plates 560a and 560b seal the laminate 670 at both ends of the cylinder. 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 in the core 550 and recovered through an outlet 580. Filter elements with outlets at both ends and those at one end are known. Typically, when outlets are provided at both ends, one end is sealed with a fixture to allow the filtered liquid to be recovered through the outlet at the other end.

[0138] [Embodiment 4: Method for manufacturing a filter element] A method for manufacturing a filter element according to this embodiment can be carried out in the same manner as a conventionally known method, except that the laminate according to embodiment 1 is used.

[0139] Hereinafter, the present disclosure will be specifically described based on examples, but the present invention is not limited to the following examples.

[0140] Example 1 <<Production of Laminate>> Laminates according to Samples 1-1 to 1-4 and Samples 1-101 to 1-103 were produced as follows.

[0141] <Production of porous film> <Step 1-1-a> 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 polytetrafluoroethylene powder and "Supersol FP-25" (trademark) which is 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 shape using a compression molding machine, thereby obtaining a kneaded product.

[0142] <Step 1-1-b> 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.

[0143] <Step 1-1-c> The above molded body was biaxially stretched under the conditions shown in Table 1 to obtain a stretched body.

[0144] <Step 1-1-d> The stretched body was subjected to a heat treatment under the conditions shown in Table 1 to obtain a porous membrane.

[0145] In this manner, porous membranes according to Samples 1-1 to 1-4 and Samples 1-101 to 1-103 were produced.

[0146] <Production of First Support Film> <Step 1-2> First support films were produced for Samples 1-1 to 1-4 and Samples 1-101 to 1-103 as follows. First, a mixture was obtained by mixing "PTFE Fine Powder B (second heat of fusion 26.5 J / g, molecular weight approximately 4 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 2. Next, the mixture was compression-molded into a block using a compression molding machine, thereby obtaining a kneaded product.

[0147] The kneaded material was extruded into a sheet under the conditions shown in Table 2 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 2.

[0148] The above molded body was stretched under the conditions shown in Table 2 to obtain a stretched body.

[0149] The stretched body was subjected to a heat treatment under the conditions shown in Table 2 to obtain a porous first support film.

[0150] In this manner, porous first support films for Samples 1-1 to 1-4 and Samples 1-101 to 1-103 were prepared.

[0151] <Production of second support film> <Step 1-2> A second support film was produced for Samples 1-1 to 1-4 and Samples 1-101 to 1-103 as follows. First, a mixture was obtained by mixing "PTFE Fine Powder C (second heat of fusion 26.0 J / g, molecular weight approximately 5 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 3. Next, the mixture was compression molded into a block using a compression molding machine, thereby obtaining a kneaded product.

[0152] The kneaded material was extruded into a sheet under the conditions shown in Table 3 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 3.

[0153] The molded body was stretched under the conditions shown in Table 3 to obtain a stretched body.

[0154] The stretched body was subjected to a heat treatment under the conditions shown in Table 3 to obtain a porous second support film.

[0155] In this manner, porous second support films for Samples 1-1 to 1-4 and Samples 1-101 to 1-103 were prepared.

[0156] <Second Step> The first support membrane, the porous membrane, and the second support membrane were laminated in this order under the conditions shown in Table 4 to obtain a sheet-like laminate.

[0157] As described above, sheet-shaped laminates according to Samples 1-1 to 1-4 and Samples 1-101 to 1-103 were produced.

[0158]

[0159]

[0160]

[0161]

[0162]

[0163]

[0164]

[0165]

[0166] <<Evaluation of porous membrane properties>> For the porous membrane in the laminate of each sample, the polytetrafluoroethylene content, thickness, basis weight, density, average bubble point, Gurley seconds, and mean flow pore size were determined by the method described in embodiment 1. The obtained results are shown in Table 6.

[0167] <Evaluation of Support Film Properties> For the first support film in the laminate of each sample, the polytetrafluoroethylene content, thickness, maximum tensile strength and stretching directionality, basis weight, density, average bubble point, Gurley seconds, and mean flow pore size were determined by the method described in embodiment 1. The results obtained are shown in Table 5. For the second support film in the laminate of each sample, the polytetrafluoroethylene content, thickness, maximum tensile strength and stretching directionality, basis weight, density, average bubble point, Gurley seconds, and mean flow pore size were determined by the method described in embodiment 1. The results obtained are shown in Table 7. In the "Uniaxially Stretched / Biaxially Stretched" column, "uniaxially stretched" means that the support film is a "uniaxially stretched support film," and "biaxially stretched" means that the support film is a "biaxially stretched support film."

[0168] <<Evaluation of Laminate Properties>> The laminates of each sample were evaluated for thickness, basis weight, density, mean flow pore size, maximum tensile strength, mean bubble point, Gurley seconds, and thermal stability by the methods described in "Embodiment 1." The results are shown in Table 8.

[0169] The laminates of Samples 1-1 to 1-4 correspond to Examples, while the laminates of Samples 1-101 to 1-103 correspond to Comparative Examples. The laminates of Samples 1-1 to 1-4 have higher average bubble points than the laminate of Sample 1-102.

[0170] A Gurley value of 70 seconds or less for the laminate means that the laminate exhibits a high filtrate flow rate.

[0171] The laminates according to Samples 1-1 to 1-4 exhibit high filtrate flow rates.

[0172] The ratio of the absolute value of the difference between X' and X to X being 10% or less, and the ratio of the absolute value of the difference between Y' and Y to Y being 5% or less means that the thermal stability of the laminate is excellent.

[0173] The laminates of Samples 1-1 to 1-4 have significantly superior thermal stability compared to the laminates of Samples 1-101 and 1-103.

[0174] Therefore, compared to the laminates of Samples 1-101 and 1-103, the laminates of Samples 1-1 to 1-4 exhibit exceptionally excellent effects, such as having excellent thermal stability, a high average bubble point, and a high filtrate flow rate.

[0175] From the above, it was found that the laminates of Samples 1-1 to 1-4 exhibited exceptionally excellent effects, such as excellent thermal stability, a high average bubble point, and a high filtrate flow rate.

[0176] Example 2 <<Production of Laminate>> Laminates according to Samples 2-1 to 2-4 and Samples 2-101 to 2-103 were produced as follows.

[0177] <Production of porous film> <Step 1-1-a> 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 polytetrafluoroethylene powder and "Supersol FP-25" (trademark) which is solvent naphtha (liquid lubricant) manufactured by Idemitsu Oil Co., Ltd. in the parts by mass shown in Table 9. Next, the mixture was compression molded into a block shape using a compression molding machine, thereby obtaining a kneaded product.

[0178] <Step 1-1-b> The kneaded mixture was extruded into a sheet under the conditions shown in Table 9 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 9.

[0179] <Step 1-1-c> The above molded body was biaxially stretched under the conditions shown in Table 9 to obtain a stretched body.

[0180] <Step 1-1-d> The stretched body was subjected to a heat treatment under the conditions shown in Table 9 to obtain a porous membrane.

[0181] In this manner, porous membranes according to Samples 2-1 to 2-4 and Samples 2-101 to 2-103 were produced.

[0182] <Production of first support film> <Step 1-2> As described below, a first support film was produced for Samples 2-1 to 2-4 and Samples 2-101 to 2-103. First, a polytetrafluoroethylene powder "PTFE fine powder B (second heat of fusion 26.5 J / g, molecular weight approximately 4 million)" and a solvent naphtha (liquid lubricant) manufactured by Idemitsu Oil Co., Ltd., "Supersol FP-25" (trademark), were mixed in the parts by mass shown in Table 10 to obtain a mixture. Next, the mixture was compression molded into a block using a compression molding machine to obtain a kneaded product.

[0183] The kneaded material was extruded into a sheet under the conditions shown in Table 10 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 10.

[0184] The above molded body was stretched under the conditions shown in Table 10 to obtain a stretched body.

[0185] The stretched body was subjected to a heat treatment under the conditions shown in Table 10 to obtain a porous first support film.

[0186] In this manner, porous first support films for samples 2-1 to 2-4 and samples 2-101 to 2-103 were prepared.

[0187] <Production of second support film> <Step 1-2> A second support film was produced for Samples 2-1 to 2-4 and Samples 2-101 to 2-103 as follows. First, a polytetrafluoroethylene powder "PTFE fine powder C (second heat of fusion 26.0 J / g, molecular weight approximately 5 million)" and a solvent naphtha (liquid lubricant) manufactured by Idemitsu Oil Co., Ltd. "Supersol FP-25" (trademark) were mixed in the parts by mass shown in Table 11 to obtain a mixture. Next, the mixture was compression molded into a block using a compression molding machine to obtain a kneaded product.

[0188] The kneaded material was extruded into a sheet under the conditions shown in Table 11 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 11.

[0189] The molded body was stretched under the conditions shown in Table 11 to obtain a stretched body.

[0190] The stretched body was subjected to a heat treatment under the conditions shown in Table 11 to obtain a porous second support film.

[0191] In this manner, porous second support films for samples 2-1 to 2-4 and samples 2-101 to 2-103 were prepared.

[0192] <Production of third support film> <Step 1-2> As described below, a third support film was produced for Samples 2-1 to 2-4 and Samples 2-101 to 2-103. First, a mixture was obtained by mixing "PTFE fine powder C (second heat of fusion 26.0 J / g, molecular weight approximately 5 million)" which is a polytetrafluoroethylene powder and "Supersol FP-25" (trademark), which is solvent naphtha (liquid lubricant) manufactured by Idemitsu Oil Co., Ltd., in the parts by mass shown in Table 12. Next, the mixture was compression molded into a block using a compression molding machine, thereby obtaining a kneaded product.

[0193] The kneaded material was extruded into a sheet under the conditions shown in Table 12 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 12.

[0194] The molded body was stretched under the conditions shown in Table 12 to obtain a stretched body.

[0195] The stretched body was subjected to a heat treatment under the conditions shown in Table 12 to obtain a porous third support film.

[0196] In this manner, the porous third support films for Samples 2-1 to 2-4 and Samples 2-101 to 2-103 were prepared.

[0197] <Production of Fourth Support Film> <Step 1-2> As described below, a fourth support film was produced for Samples 2-1 to 2-4 and Samples 2-101 to 2-103. First, a mixture was obtained by mixing "PTFE Fine Powder B (second heat of fusion 26.5 J / g, molecular weight approximately 4 million)" which is a polytetrafluoroethylene powder and "Supersol FP-25" (trademark), which is solvent naphtha (liquid lubricant) manufactured by Idemitsu Oil Co., Ltd., in the parts by mass shown in Table 13. Next, the mixture was compression molded into a block using a compression molding machine, thereby obtaining a kneaded product.

[0198] The kneaded material was extruded into a sheet under the conditions shown in Table 13 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 13.

[0199] The molded body was stretched under the conditions shown in Table 13 to obtain a stretched body.

[0200] The stretched body was subjected to a heat treatment under the conditions shown in Table 13 to obtain a porous fourth support membrane.

[0201] In this manner, fourth porous support films for samples 2-1 to 2-4 and samples 2-101 to 2-103 were prepared.

[0202] <Second step> The first support membrane, the second support membrane, the porous membrane, the third support membrane, and the fourth support membrane were laminated in this order under the conditions shown in Table 14 to obtain a sheet-like laminate.

[0203] As described above, sheet-shaped laminates according to Samples 2-1 to 2-4 and Samples 2-101 to 2-103 were produced.

[0204]

[0205]

[0206]

[0207]

[0208]

[0209]

[0210]

[0211]

[0212]

[0213]

[0214]

[0215]

[0216] <<Evaluation of porous membrane properties>> For the porous membrane in the laminate of each sample, the polytetrafluoroethylene content, thickness, basis weight, density, average bubble point, Gurley seconds, and mean flow pore size were determined by the method described in embodiment 1. The obtained results are shown in Table 17.

[0217] <Evaluation of Support Film Properties> For the first to fourth support films in the laminates of each sample, the polytetrafluoroethylene content, thickness, maximum tensile strength and stretch directionality, basis weight, density, average bubble point, Gurley seconds, and mean flow pore size were determined by the method described in Embodiment 1. The results obtained are shown in Tables 15 to 19.

[0218] <<Evaluation of Laminate Properties>> For each sample laminate, the evaluation items of thickness, basis weight, density, mean flow pore size, maximum tensile strength, average bubble point, Gurley seconds, and thermal stability evaluation test were determined by the method described in embodiment 1. The obtained results are shown in Table 20.

[0219] The laminates of Samples 2-1 to 2-4 correspond to Examples, while the laminates of Samples 2-101 to 2-103 correspond to Comparative Examples. The laminates of Samples 2-1 to 2-4 have higher average bubble points than the laminate of Sample 2-102.

[0220] A Gurley number of 70 seconds or less means that the laminate exhibits a high filtrate flow rate.

[0221] The laminates of samples 2-1 to 2-4 exhibit higher filtrate flow rates than the laminate of sample 2-103.

[0222] The ratio of the absolute value of the difference between X' and X to X being 10% or less, and the ratio of the absolute value of the difference between Y' and Y to Y being 5% or less means that the thermal stability of the laminate is excellent.

[0223] The laminates of Samples 2-1 to 2-4 have significantly superior thermal stability compared to the laminates of Samples 2-101 to 2-103.

[0224] Therefore, compared to the laminates of samples 2-101 to 2-103, the laminates of samples 2-1 to 2-4 exhibit exceptionally excellent effects, such as having excellent thermal stability, a high average bubble point, and a high filtrate flow rate.

[0225] From the above, it was found that the laminates of Samples 2-1 to 2-4 exhibited exceptionally excellent effects, such as excellent thermal stability, a high average bubble point, and a high filtrate flow rate.

[0226] In addition, the above-mentioned Examples 1 and 2 only show a laminate in which "the support membrane is composed of a first support membrane and a second support membrane, and a porous membrane and the second support membrane are arranged in this order on the first support membrane" and a laminate in which "the support membrane is composed of a first support membrane, a second support membrane, a third support membrane, and a fourth support membrane, and the second support membrane, the porous membrane, the third support membrane, and the fourth support membrane are arranged in this order on the first support membrane." However, there is also a description of a laminate including a porous membrane, the porous membrane containing polytetrafluoroethylene as a main component, the laminate being in the form of a sheet, the laminate having an average bubble point P1a of 390 kPa or more, or an average bubble point P1b of 780 kPa or more, the average bubble point P1a being measured by a bubble point method using a 1a liquid, the surface tension of the 1a liquid being 13 mN / m, the average bubble point P1b being measured by a bubble point method using a 1b liquid, the surface tension of the 1b liquid being 21 mN / m, The Gurley seconds of the laminate is 70 seconds or less, and in a test in which the laminate is left standing in a thermostatic chamber at 120°C for 1 hour, the length X in the MD direction of the laminate before the test and the length X' in the MD direction of the laminate after the test satisfy the relationship of the above formula 1, and the length Y in the TD direction of the laminate before the test and the length Y' in the TD direction of the laminate after the test satisfy the relationship of the above formula 2. As long as the Gurley seconds of the laminate is 70 seconds or less, and in a test in which the laminate is left standing in a thermostatic chamber at 120°C for 1 hour, the length X in the MD direction of the laminate before the test and the length Y' in the TD direction of the laminate after the test satisfy the relationship of the above formula 2, it is expected that the same effect will be achieved in the laminates shown in (i) and (ii) below, for example, in which the porous membrane and the biaxially stretched support membrane are alternately laminated and the uniaxially stretched support membrane is located on the surface of the laminate. (i) A laminate (FIG. 3) in which the porous membrane comprises a first porous membrane and a second porous membrane, and the support membrane comprises a first support membrane, a second support membrane, a third support membrane, a fourth support membrane, and a fifth support membrane, and the second support membrane, the first porous membrane, the third support membrane, the second porous membrane, the fourth support membrane, and the fifth support membrane are arranged in this order on the first support membrane, and the second support membrane, the third support membrane, and the fourth support membrane are each a biaxially stretched support membrane, and the first support membrane and the fifth support membrane are each a uniaxially stretched support membrane.(ii) A laminate (FIG. 4) in which the porous membrane comprises a first porous membrane, a second porous membrane, and a third porous membrane, and the support membrane comprises a first support membrane, a second support membrane, a third support membrane, a fourth support membrane, a fifth support membrane, and a sixth support membrane, and the second support membrane, the first porous membrane, the third support membrane, the second porous membrane, the fourth support membrane, the third porous membrane, the fifth support membrane, and the sixth support membrane are arranged in this order on the first support membrane, and the second support membrane, the third support membrane, the fourth support membrane, the third porous membrane, the fifth support membrane, and the sixth support membrane are each biaxially stretched support membranes, and the first support membrane and the sixth support membrane are each uniaxially stretched support membranes.

[0227] 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.

[0228] 1 porous membrane, 2 support membrane, 10 laminate, 21 first support membrane, 22 second support membrane, 23 third support membrane, 24 fourth support membrane, 25 fifth support membrane, 26 sixth support membrane, 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, 670 laminate.

Claims

1. A laminate comprising a porous membrane, The porous membrane contains polytetrafluoroethylene as a main component, The laminate is in a sheet form, The average bubble point P1a of the laminate is 390 kPa or more, or The average bubble point P1b of the laminate is 780 kPa or more, The average bubble point P1a is measured by a bubble point method using a 1a liquid, The surface tension of the first liquid is 13 mN / m; The average bubble point P1b is measured by a bubble point method using a 1b liquid, The surface tension of the first liquid is 21 mN / m. The Gurley second of the laminate is 70 seconds or less, In a test in which the laminate is left standing in a thermostatic chamber at 120°C for 1 hour, a length X in the MD direction of the laminate before the test and a length X' in the MD direction of the laminate after the test satisfy the relationship of Formula 1, A laminate, wherein a length Y in the TD direction of the laminate before the test and a length Y' in the TD direction of the laminate after the test satisfy the relationship of Equation 2. |X'-X| / X≦0.10 Formula 1 |Y'-Y| / Y≦0.05 Formula 2

2. The laminate has a maximum tensile strength S1 in the MD direction and a maximum tensile strength S2 in the TD direction, The laminate according to claim 1 , wherein the maximum tensile strength S1 in the MD direction and the maximum tensile strength S2 in the TD direction satisfy the relationship of Equation 3. 3.2≦S1 / S2≦5.0 Formula 3

3. The laminate further comprises a support film, the support membrane is porous; The laminate according to claim 1 or 2, wherein the support film contains polytetrafluoroethylene as a main component.

4. the support film includes a first support film and a second support film; the porous membrane and the second support membrane are disposed in this order on the first support membrane; The laminate according to claim 3 , wherein each of the first support film and the second support film is a uniaxially stretched support film.

5. the support film includes a first support film, a second support film, a third support film, and a fourth support film; the second support membrane, the porous membrane, the third support membrane, and the fourth support membrane are disposed in this order on the first support membrane; each of the second support film and the third support film is a biaxially stretched support film; The laminate according to claim 3 , wherein each of the first support film and the fourth support film is a uniaxially stretched support film.

6. A filter element comprising the laminate according to claim 1 or 2.