Composite porous body and method for producing same

Abstract

A composite porous body comprising a base material having a first surface and a polyvinyl alcohol layer covering at least a portion of the first surface, wherein the base material includes a first layer comprising a polytetrafluoroethylene porous body having the first surface, the polyvinyl alcohol layer comprises a nonporous body of polyvinyl alcohol, and the average pore diameter of the polyvinyl alcohol layer is 1 nm to 5 nm.

Description

Composite porous body and method for manufacturing the same

[0001] This disclosure relates to a composite porous body and a method for producing the same.

[0002] Polyvinyl alcohol (hereinafter also referred to as "PVA") porous membranes are used in various separation membranes such as filtration filters.

[0003] Patent Document 1 discloses a filtration filter in which a PVA porous membrane is arranged on a filter made of a porous polytetrafluoroethylene (hereinafter also referred to as "PTFE") material. The PVA porous membrane used in Patent Document 1 has physical pores that can be confirmed when observed at 100,000x magnification using a scanning electron microscope (SEM) (see Figures 10 and 11 of Patent Document 1, etc.). The diameter of these physical pores contributes to the separation performance of the filtration filter in Patent Document 1.

[0004] Japanese Patent Publication No. 2013-34973

[0005] The composite porous body of the present disclosure comprises a substrate having a first surface and a polyvinyl alcohol layer covering at least a portion of the first surface, wherein the substrate includes a first layer made of a polytetrafluoroethylene porous material having the first surface, and the polyvinyl alcohol layer is made of a non-porous polyvinyl alcohol material, and the average pore size of the polyvinyl alcohol layer is 1 nm or more and 5 nm or less.

[0006] Figure 1 is an overview view of the composite porous body according to Embodiment 1. Figure 2 is a cross-sectional view of the composite porous body according to Embodiment 1. Figure 3 is a schematic diagram of the test apparatus used for the liquid permeability test. Figure 4 is an overview view of the composite porous body according to Embodiment 2. Figure 5 is a flowchart showing the manufacturing process of the composite porous body according to Embodiment 3.

[0007] [Problems this disclosure aims to solve] In the fields of solvent separation membranes and water treatment membranes, there is a desire to further reduce the size of substances that can be removed from the fluid being filtered.

[0008] Therefore, the present disclosure aims to provide a composite porous body having high separation performance.

[0009] [Effects of this disclosure] According to this disclosure, it is possible to provide a composite porous body having high separation performance.

[0010] [Description of Embodiments of the Disclosure] Embodiments of the Disclosure will be described first by listing them. (1) The composite porous body of the Disclosure is a composite porous body comprising a substrate having a first surface and a polyvinyl alcohol layer covering at least a part of the first surface, wherein the substrate includes a first layer made of a polytetrafluoroethylene porous body having the first surface, the polyvinyl alcohol layer is made of a non-porous polyvinyl alcohol, and the average pore size of the polyvinyl alcohol layer is 1 nm or more and 5 nm or less.

[0011] The composite porous material of this disclosure includes a polyvinyl alcohol layer (hereinafter also referred to as the "PVA layer") made of a non-porous polyvinyl alcohol (hereinafter also referred to as the "PVA non-porous material"). The non-porous polyvinyl alcohol (non-porous membrane) is mainly composed of PVA and does not have any physical pores that can be confirmed when observed at 100,000x magnification using a SEM. The PVA non-porous material separates target substances by utilizing the gaps in the polymer network. The composite porous material of this disclosure includes a polyvinyl alcohol layer with an average pore diameter of 1 nm to 5 nm. As a result, the composite porous material of this disclosure can have high separation performance. The higher the separation performance, the smaller the substances that can be separated.

[0012] The composite porous material of this disclosure can be used as a nanofiltration membrane, a solvent nanofiltration membrane, or a solvent dehydration membrane. The solvent dehydration membrane may also be a permeable vaporization membrane, a vapor filtration membrane, or a solvent reverse osmosis membrane.

[0013] (2) In (1) above, the average pore size on the first surface of the substrate may be 20 nm or more and 2000 nm or less. When the average pore size on the first surface of the substrate is 20 nm or more, the composite porous body including the substrate has excellent liquid permeability. A composite porous body with high liquid permeability can shorten the filtration time. When the average pore size on the first surface of the substrate is 2000 nm or less, the non-porous polyvinyl alcohol constituting the polyvinyl alcohol layer is more likely to get caught on the first surface, and the polyvinyl alcohol layer is more likely to be properly formed on the first surface. When the average pore size on the first surface of the substrate is 2000 nm or less, the composite porous body has excellent strength. The average pore size on the first surface of the substrate is larger than the average pore size of the polyvinyl alcohol layer.

[0014] (3) In (1) or (2) above, the porosity of the first surface of the substrate may be 10% or more and 60% or less. If the porosity of the first surface of the substrate is 10% or more, the composite porous body including the substrate has excellent liquid permeability. A composite porous body with high liquid permeability can shorten the filtration time. If the porosity of the first surface of the substrate is 60% or less, the non-porous polyvinyl alcohol constituting the polyvinyl alcohol layer is more likely to catch on the first surface, and the polyvinyl alcohol layer is more likely to be properly formed on the first surface. If the porosity of the first surface of the substrate is 60% or less, the composite porous body has excellent strength.

[0015] (4) In any of (1) to (3) above, the average thickness of the polyvinyl alcohol layer may be 10 nm or more and 2000 nm or less. If the average thickness of the polyvinyl alcohol layer is 10 nm or more, the polyvinyl alcohol layer can be formed uniformly, and the composite porous body can separate smaller substances. If the average thickness of the polyvinyl alcohol layer is 2000 nm or less, the flux of the composite porous body is improved.

[0016] (5) In any of (1) to (4) above, the shape of the base material may be a sheet. This makes it possible to obtain a sheet-like composite porous body. The sheet-like composite porous body is easy to process into various shapes and can be applied to various types of filtration devices. Because the composite porous body has excellent flexibility, it is not easily damaged even when subjected to processing such as bending.

[0017] (6) In (5) above, the average thickness of the substrate may be 1 μm or more and 1000 μm or less. When the average thickness of the substrate is 1 μm or more, the composite porous body has excellent strength. When the average thickness of the substrate is 1000 μm or less, the composite porous body has excellent flexibility. In addition, the filtration time by the composite porous body does not become too long.

[0018] (7) In any of (1) to (4) above, the shape of the base material is a tube, and the first surface may be the outer surface of the tube.

[0019] The overall shape of a composite porous body comprising a tubular substrate is tubular. The tubular substrate also includes a hollow fiber membrane. In a tubular composite porous body, fluids containing impurities flow to the outside of the tubular composite porous body. Fluids that have permeated the composite porous body flow to the inside of the tubular composite porous body. The above composite porous body can constitute a fluid flow path within itself. Multiple of these composite porous bodies can be bundled together to form a module for a purification device.

[0020] (8) In (7) above, the average thickness of the substrate may be 50 μm or more and 1000 μm or less. When the average thickness of the substrate is 50 μm or more, the composite porous body has excellent strength. When the average thickness of the substrate is 1000 μm or less, the composite porous body has excellent flexibility. In addition, the filtration time by the composite porous body does not become too long.

[0021] (9) The substrate comprises the first layer and a second layer adjacent to the first layer, wherein the average pore size of the second layer may be larger than the average pore size of the first layer. The liquid permeability of a substrate having a second layer with a larger average pore size is superior to that of a substrate having the same thickness as the substrate and consisting only of the first layer. Therefore, by having the substrate composed of a first layer and a second layer, the filtration time of the composite porous body does not tend to increase even if the substrate is made thicker.

[0022] (10) A method for producing a composite porous body according to the present disclosure is a method for producing a composite porous body according to any one of (1) to (9) above, comprising the steps of: preparing a substrate including the first layer made of the polytetrafluoroethylene porous body having the first surface; preparing a first liquid containing polyvinyl alcohol; and applying the first liquid to at least a part of the first surface to form the polyvinyl alcohol layer made of a non-porous polyvinyl alcohol to obtain the composite porous body, wherein the average pore size of the polyvinyl alcohol layer is 1 nm or more and 5 nm or less.

[0023] According to this disclosure, it is possible to manufacture a composite porous body having high separation performance.

[0024] (11) In the above (10), the first liquid further contains a crosslinking agent, and the polyvinyl alcohol in the polyvinyl alcohol layer may be crosslinked.

[0025] According to this, the leaching of polyvinyl alcohol is suppressed, and the durability of the polyvinyl alcohol layer is improved.

[0026] [Details of Embodiments of the Disclosure] Specific examples of the composite porous body and method for manufacturing the same of the Disclosure will be described below with reference to the drawings. In the drawings of the Disclosure, the same reference numerals represent the same part or a corresponding part. In addition, dimensional relationships such as length, width, thickness, and depth have been appropriately modified for clarity and simplification of the drawings and do not necessarily represent actual dimensional relationships.

[0027] In this disclosure, the notation "A to B" means A or greater and B or less. If no unit is specified for A, and only a unit is specified for B, then the unit for A and the unit for B are the same.

[0028] In this disclosure, when compounds and the like are represented by chemical formulas, unless otherwise specified, the atomic ratios should include all conventionally known atomic ratios and should not necessarily be limited to those within the stoichiometric range.

[0029] In this disclosure, if one or more numerical values ​​are listed as the lower limit and upper limit of a numerical range, any combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit shall also be disclosed.

[0030] In this disclosure, “equipment,” “includes,” “possesses,” and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the essential elements. The statement “consists of” is a closed term. However, even a configuration expressed in closed terms may include additional elements that are usually incidental or irrelevant to the subject technology.

[0031] In this disclosure, it has been confirmed that, as long as the measurements are taken on the same sample, there is almost no variation even if the measurement location is arbitrarily selected.

[0032] [Embodiment 1: Composite Porous Body] A composite porous body according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") will be described with reference to Figures 1 and 2. As shown in Figures 1 and 2, the composite porous body 1 according to Embodiment 1 is in the shape of a sheet. The composite porous body 1 according to Embodiment 1 is a composite porous body 1 comprising a base material 2 having a first surface 21 and a polyvinyl alcohol layer 3 covering at least a part of the first surface 21. The base material 2 includes a first layer 2A made of a polytetrafluoroethylene porous body having a first surface 21. The polyvinyl alcohol layer 3 is made of a non-porous polyvinyl alcohol body. The average pore size of the polyvinyl alcohol layer 3 is 1 nm or more and 5 nm or less.

[0033] The composite porous body of Embodiment 1 may consist of a substrate 2 having a first surface 21 and a polyvinyl alcohol layer 3 covering at least a portion of the first surface 21.

[0034] <Substrate> In Embodiment 1, the substrate 2 includes a first layer 2A made of a polytetrafluoroethylene porous material having a first surface 21. As shown in Figure 2, the substrate 2 is in the shape of a sheet. As shown in Figure 2, the substrate 2 has a plurality of pores 2h. Since Figure 2 is a cross-sectional view, each pore 2h of the substrate 2 appears to be independent, but each pore 2h is connected to other pores 2h, forming countless channels from the first surface 21 to the second surface 22. Countless channels are formed in the substrate 2, extending from the first surface 21 to the second surface 22.

[0035] PTFE has excellent heat resistance and chemical resistance. Therefore, a composite porous body comprising a polytetrafluoroethylene porous body can have excellent heat resistance and chemical resistance. The first layer 2A may contain components other than polytetrafluoroethylene, as long as the effects of the present disclosure are not impaired. Examples of such components include perfluoroalkoxyalkanes (PFAs) and tetrafluoroethylene-hexafluoropropylene copolymers (FEPs).

[0036] The surface of the substrate 2 includes the inner circumferential surface of the pores 2h of the substrate 2. Polyvinyl alcohol may be present in the pores 2h of the substrate 2.

[0037] The thickness of the substrate 2 is the length between the first surface 21 and the second surface 22. The average thickness of the substrate 2 may be 1 μm or more and 1000 μm or less, 10 μm or more and 900 μm or less, or 20 μm or more and 500 μm or less. If the substrate 2 comprises multiple layers, the average thickness of the first layer having the first surface may be 1 μm or more. As shown in Figure 2, the substrate 2 comprises a first layer 2A and a second layer 2B, and the average thickness of the first layer 2A may be 1 μm or more, 1 μm or more and less than 1000 μm, 10 μm or more and 900 μm or less, or 20 μm or more and 500 μm or less.

[0038] The average thickness of the substrate 2 is the average of the thicknesses of three different locations on the composite porous body 1 minus the average thickness of the polyvinyl alcohol layer 3. The thickness of the composite porous body 1 is measured using a micrometer. The method for measuring the average thickness of the polyvinyl alcohol layer 3 is described below.

[0039] The average pore diameter on the first surface 21 of the base material 2 may be 20 nm or more and 2000 nm or less, may be 50 nm or more and 1000 nm or less, or may be 100 nm or more and 500 nm or less.

[0040] A plurality of pores 2h are formed on the first surface 21. When the polyvinyl alcohol layer 3 is formed on the first surface 21, it is difficult to measure the average pore diameter of the pores 2h on the first surface 21. In the present disclosure, the average pore diameter of the first surface 21 is obtained from a SEM image of a cross section along the thickness direction of the base material 2. In the present disclosure, the thickness direction of the base material 2 means the direction from the first surface 21 toward the second surface 22. The magnification of the SEM image is 50,000 times. The size of the SEM image is 1 μm in the thickness direction and 10 μm in the width direction. The SEM image is acquired at a position sufficiently close to the first surface of the base material 2. The SEM image is binarized using image processing software (ImageJ), and each pore 2h in the SEM image is extracted. The equivalent circle diameter of each pore 2h in the SEM image is obtained, and the arithmetic mean of the equivalent circle diameters of all the pores 2h is obtained. The equivalent circle diameter is the diameter of a perfect circle having the same area as the pore 2h. This arithmetic mean of the equivalent circle diameters is regarded as the average pore diameter on the first surface 21 of the base material 2.

[0041] The average minor diameter of the pores 2h on the first surface 21 may be 4 nm or more and 400 nm or less. The first surface 21 having pores 2h with an average minor diameter of 4 nm or more on the first surface 21 improves the liquid permeability of the composite porous body 1. If the average minor diameter of the pores 2h on the first surface 21 is 400 nm or less, the non-porous body of polyvinyl alcohol constituting the polyvinyl alcohol layer 3 is likely to be caught on the first surface 21, and the polyvinyl alcohol layer 3 is likely to be appropriately formed on the first surface 21. The average minor diameter of the pores 2h on the first surface 21 may be, for example, 10 nm or more and 300 nm or less.

[0042] In the present disclosure, the average minor diameter of the pores 2h on the first surface 21 is determined from a SEM image of a cross-section along the thickness direction of the base material 2. The magnification of the SEM image is 50,000 times. The size of the SEM image is 1 μm in the thickness direction and 10 μm in the width direction. The SEM image is acquired at a position sufficiently close to the first surface of the base material 2. The SEM image is binarized using image processing software (ImageJ), and each pore 2h in the SEM image is extracted. The minor diameter of an ellipse approximating each pore 2h is determined in the SEM image. The average of the minor diameters of all the ellipses in the SEM image is the average minor diameter of the pores 2h.

[0043] The porosity on the first surface 21 of the base material 2 may be 10% or more and 60% or less, may be 10% or more and 50% or less, or may be 10% or more and 40% or less.

[0044] In the present disclosure, the porosity on the first surface 21 of the base material 2 is measured based on a SEM image of a cross-section along the thickness direction of the base material 2. The magnification of the SEM image is 50,000 times. The size of the SEM image is 1 μm in the thickness direction and 10 μm in the width direction. The SEM image is acquired at a position sufficiently close to the first surface of the base material 2. The SEM image is binarized using image processing software (ImageJ), and each pore 2h in the SEM image is extracted. The porosity on the first surface 21 of the base material 2 is obtained by dividing the total area of all the pores 2h in the SEM image by the area of the entire SEM image.

[0045] The substrate 2 may comprise multiple layers, as shown in Figure 2. The substrate 2 may comprise a first layer 2A and a second layer 2B. In Figure 2, the boundary between the first layer 2A and the second layer 2B is schematically shown by a dashed line. The first layer 2A includes a first surface 21. The second layer 2B is adjacent to the main surface of the first layer 2A opposite to the first surface 21. In Embodiment 1, the second layer 2B includes a second surface 22. The average pore diameter of the second layer 2B is larger than the average pore diameter of the first layer 2A. The liquid permeability of the substrate 2 comprising the second layer 2B with a larger average pore diameter is superior to that of the substrate 2 having the same thickness as the substrate 2 and consisting only of the first layer 2A. Therefore, by having the substrate 2 comprised of a first layer 2A and a second layer 2B, the filtration time of the composite porous body 1 does not tend to increase even if the substrate 2 is made thicker. The average pore size of the second layer 2B may be, for example, 2 to 2000 times or 10 to 1000 times the average pore size of the first layer 2A. The average pore size of the first layer 2A is larger than the average pore size of the polyvinyl alcohol layer 3. If the substrate 2 consists of three or more layers, the average pore size may be larger for layers further away from the first surface 21. Unlike this example, the substrate 2 may consist only of the first layer 2A. In this case, the first layer 2A includes the first surface 21 and the second surface 22.

[0046] The average pore diameter of the first layer 2A and the average pore diameter of the second layer 2B are determined from SEM images of the cross-section along the thickness direction of the substrate 2. The first layer 2A and the second layer 2B are heat-fused together during the fabrication of the substrate 2. Therefore, the boundary between the first layer 2A and the second layer 2B can be confirmed in the SEM image. In the SEM image, the arithmetic mean of the equivalent circular diameters of each void 2h in the region including the first surface 21 across the boundary is the average pore diameter of the first layer 2A. Similarly, in the SEM image, the arithmetic mean of the equivalent circular diameters of each void 2h in the region adjacent to the first layer 2A across the boundary is the average pore diameter of the second layer 2B.

[0047] The second layer 2B may be made of a porous polytetrafluoroethylene material. The second layer 2B may be made of a nonwoven fabric made of polyethylene terephthalate, polypropylene, polyethylene, polytetrafluoroethylene, or polyphenylene sulfide.

[0048] <Polyvinyl Alcohol Layer> In Embodiment 1, the polyvinyl alcohol layer 3 is made of a non-porous polyvinyl alcohol material. The polyvinyl alcohol layer 3 may cover at least a portion of the first surface 21 of the substrate 2, or it may cover the entire first surface 21 of the substrate 2. The polyvinyl alcohol layer 3 is placed directly on the first surface 21 of the substrate 2.

[0049] The polyvinyl alcohol layer 3 consists of a non-porous polyvinyl alcohol. The polyvinyl alcohol layer 3 may also contain other components in addition to the non-porous polyvinyl alcohol, as long as the effects of the present disclosure are not impaired. Other components include glutaraldehyde, silica, titania, and epoxy. Furthermore, the polyvinyl alcohol may have functional groups. Examples of functional groups include carboxyl groups, sulfonic acid groups, amino groups, ethylene oxide groups, and acetoacetyl groups.

[0050] The average pore size of the polyvinyl alcohol layer 3 is 1 nm or more and 5 nm or less, and may be 1.0 nm or more and 5.0 nm or less, 1.2 nm or more and 3 nm or less, or 1.6 nm or more and 1.7 nm or less.

[0051] Because the average pore size of the polyvinyl alcohol layer 3 is very small, it is difficult to determine from an SEM image of the cross-section of the polyvinyl alcohol layer 3. In this disclosure, the average pore size of the polyvinyl alcohol layer 3 is determined by a liquid permeability test. Figure 3 is a schematic diagram of the test apparatus 7 used for the liquid permeability test. The test apparatus 7 comprises a beaker 70, a pressurized cylindrical chamber 71, and a holder 72. The composite porous body 1 is sandwiched between the lower end opening 71U of the chamber 71 and the upper end opening 72D of the holder 72. The polyvinyl alcohol layer 3 of the composite porous body 1 faces the chamber 71.

[0052] The procedure for determining the average pore size of the polyvinyl alcohol layer 3 is as follows. First, a test solution is prepared containing polyethylene glycol particles (hereinafter also referred to as "PEG particles"), vitamin B12, or gold nanoparticles having the average particle size listed in Table 1. Here, the average particle size refers to the Stokes diameter for PEG particles, the Stokes diameter for vitamin B12 as described in the literature (e.g., Sungil Jeon et al., RSC Adv., 2018, 8, 19879-19882), and the manufacturer's stated value for gold nanoparticles. The average particle sizes of the test solutions to be prepared are as shown in Table 1. As described below, the average particle size (Stokes diameter) of PEG particles is calculated based on the average molecular weight of the PEG particles. Average molecular weight of PEG particles in the test solution, concentration of vitamin B12 (g / cm³) ３ ), or the concentration of gold nanoparticles (g / cm³) ３ ) is known.

[0053]

[0054] The particle size (Stokes diameter) of PEG particles is calculated based on the average molecular weight using the following formula: r ｓ [nm]=(0.262×M ｗ ０．５ -0.3) × 0.2 In the above formula, M ｗ is the molecular weight, r ｓ This is the Stokes diameter.

[0055] Next, a liquid permeability test is performed. The test liquid is placed in the chamber 71. By pressurizing the chamber 71, the filtrate that has permeated through the composite porous body 1 is collected in the beaker 70. The pressurization conditions are between 0.6 MPa and 6 MPa. The concentration of particles contained in the filtrate is measured.

[0056] If the particles in the test solution are PEG particles, the test solution used is a solution with a PEG mass-based concentration of 3000 ppm. In this case, the concentration of particles in the filtrate (hereinafter also referred to as "filtrate concentration") is calculated using the following formula based on the amount of carbon [mg / L] obtained by total organic carbon measurement of the test solution and the filtrate: Filtrate concentration [%] = Test solution concentration [%] × Filtrate carbon amount [mg / L] / Test solution carbon amount [mg / L]

[0057] If the particles in the test solution are vitamin B12 or gold nanoparticles, the concentration of particles in the filtrate is calculated based on the absorbance of the test solution and the filtrate at a wavelength of 550 nm using ultraviolet-visible-near-infrared spectroscopy, using the following formula: Filtrate concentration [%] = Test solution concentration [%] × (Filtrate absorbance at 550 nm) / (Test solution absorbance at 550 nm)

[0058] The liquid flow test is performed using the above procedure, starting with the test solution having the smallest average particle size. The average particle size of the smallest particle among the test solutions whose particle concentration in the filtrate is 10% or less of the particle concentration in the test solution is considered to be the average pore size of the polyvinyl alcohol layer 3. For example, in a test solution with an average particle size of PEG particles of 1.0 nm, the particle concentration in the filtrate is 50% of the particle concentration in the test solution; in a test solution with an average particle size of PEG particles of 1.2 nm, the particle concentration in the filtrate is 10% of the particle concentration in the test solution; and in a test solution with an average particle size of vitamin B12 of 1.7 nm, the particle concentration in the filtrate is 5% of the particle concentration in the test solution. In these cases, the average pore size of the polyvinyl alcohol layer 3 is 1.2 nm.

[0059] In the composite porous body of Embodiment 1, the average pore size of the polyvinyl alcohol layer 3 is smaller than the average pore size of the substrate 2.

[0060] In a non-porous polyvinyl alcohol material, the polyvinyl alcohol may be crosslinked. Examples of crosslinking agents include glutaraldehyde, silica, and alkoxysilane, and titania (TiO2). ２ ) and titanium alkoxides, titanium chelates, or epoxides may also be used.

[0061] If the rate of change in flux before and after immersion of the composite porous material in 80°C hot water for 20 minutes is within 20%, it can be confirmed that the polyvinyl alcohol is cross-linked in the non-porous polyvinyl alcohol material.

[0062] The rate of change in flux is expressed as {(T2-T1) / T1} × 100, based on the flux T1 before immersion and the flux T2 after immersion. The flux of the composite porous material is measured by the following filtration test. A sample of the composite porous material is placed in the sample holder of a test apparatus consisting of a chamber and a sample holder. The test liquid is added to the chamber and pressurized to 0.6 MPa. The amount passing through the inspection surface per unit time is calculated from the weight change of the filtrate permeating from the sample holder, and the flux is obtained. The test liquid is water.

[0063] The average thickness of the polyvinyl alcohol layer 3 may be 10 nm to 2000 nm, 50 nm to 1500 nm, or 100 nm to 1000 nm.

[0064] The average thickness of the polyvinyl alcohol layer 3 is determined by SEM-EDX or FIB-SEM. The distance from the interface between the substrate 2 and the polyvinyl alcohol layer 3 to the surface 30 of the polyvinyl alcohol layer 3 is the thickness of the polyvinyl alcohol layer 3. The average thickness of the polyvinyl alcohol layer 3 is the average of the thicknesses of five different points on the polyvinyl alcohol layer 3. The image magnification is set appropriately according to the thickness of the polyvinyl alcohol layer 3. For example, the image magnification may be ×10000, ×20000, or ×50000.

[0065] [Embodiment 2: Composite Porous Body] A composite porous body according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") will be described with reference to Figure 4. As shown in Figure 4, the shape of the composite porous body 1 according to Embodiment 2 is a tube. The composite porous body 1 according to Embodiment 2 can have the same configuration as the composite porous body 1 of Embodiment 1, except that the shape of the base material 2 is a tube and the overall shape of the composite porous body 1 is a tube.

[0066] In Embodiment 2, the first surface 21 of the base material 2 constitutes the outer surface of the tube-shaped base material 2. The polyvinyl alcohol layer 3 constitutes the outer surface of the tube-shaped composite porous body 1.

[0067] In Embodiment 2, the average thickness of the substrate 2 may be 50 μm or more and 1000 μm or less, 100 μm or more and 900 μm or less, or 200 μm or more and 500 μm or less. If the substrate 2 comprises multiple layers, the average thickness of the first layer having the first surface may be 1 μm or more.

[0068] [Embodiment 3: Method for Manufacturing a Composite Porous Body] A method for manufacturing a composite porous body according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 3") will be described. The method for manufacturing a composite porous body of Embodiment 3 is a method for manufacturing the composite porous body of Embodiment 1 or Embodiment 2. As shown in Figure 5, the method for manufacturing a composite porous body of Embodiment 3 comprises the steps of: preparing a substrate including a first layer made of a polytetrafluoroethylene porous body having a first surface (hereinafter also referred to as "substrate preparation step S1"); preparing a first liquid containing polyvinyl alcohol (hereinafter also referred to as "first liquid preparation step S2"); and applying the first liquid to at least a part of the first surface to form a polyvinyl alcohol layer made of a non-porous polyvinyl alcohol to obtain a composite porous body (hereinafter referred to as "step S3 for obtaining a composite porous body"). The average pore size of the polyvinyl alcohol layer is 1 nm or more and 5 nm or less. The substrate preparation step S1 and the first liquid preparation step S2 may be performed either first or simultaneously.

[0069] <Substrate Preparation Step S1> In the substrate preparation step S1, a substrate 2 is prepared, which includes a first layer 2A made of a polytetrafluoroethylene porous material having a first surface 21. The substrate 2 is the same as the substrate 2 described in Embodiment 1 or Embodiment 2.

[0070] The base material 2 is obtained, for example, by stretching a rolled material made of PTFE. The rolled material can be made by rolling an extruded material. The extruded material can be made by extruding a resin paste. The resin paste can be made by mixing PTFE powder and an auxiliary agent. The auxiliary agent is, for example, a lubricant. When the rolled material made of PTFE is stretched, the rolled material becomes porous. As a result, a first layer 2A made of a porous PTFE body is obtained.

[0071] The stretching process may include, for example, a first stretching process and a second stretching process. In the first stretching process, the rolled material is stretched along the rolling direction to produce a first stretched material. In the second stretching process, the first stretched material is stretched in a direction perpendicular to the rolling direction to produce a second stretched material. By changing the stretching ratio in the stretching process, the average pore diameter and porosity on the first surface 21 of the base material 2 can be adjusted. For example, the first stretching ratio, which is the stretching ratio in the first stretching process, and the second stretching ratio, which is the stretching ratio in the second stretching process, may each be changed. The first stretching ratio is, for example, 1.5 times or more and 10 times or less. The second stretching ratio is, for example, 2 times or more and 40 times or less.

[0072] The first layer 2A may be used as the base material 2 as is. Alternatively, the first layer 2A may be bonded to the second layer 2B to produce the base material 2. Details of the second layer 2B are as described in Embodiment 1.

[0073] <First Liquid Preparation Step S2> In the first liquid preparation step S2, the first liquid containing polyvinyl alcohol is prepared. As the first liquid, for example, a polyvinyl alcohol dispersion can be prepared using at least one selected from the group consisting of water, ethanol, isopropyl alcohol, acetone, dimethyl sulfoxide, butyl acetate, and methyl ethyl ketone as the dispersion medium.

[0074] The polyvinyl alcohol content of the first liquid is 0.1% by mass or more and 5% by mass or less. If the polyvinyl alcohol content of the first liquid is 0.1% by mass or more, the amount of polyvinyl alcohol in the first liquid is sufficient, and the polyvinyl alcohol is easily deposited on the substrate 2. If the polyvinyl alcohol content of the first liquid is 5% by mass or less, the dispersibility of the polyvinyl alcohol is not impaired, and the first liquid can be uniformly coated onto the substrate 2.

[0075] The degree of polymerization of the polyvinyl alcohol contained in the first liquid may be between 100 and 5000. If the degree of polymerization of the polyvinyl alcohol is 100 or higher, the viscosity is high and the first liquid can be retained on the substrate 2. If the degree of polymerization of the polyvinyl alcohol is 500 or lower, the viscosity is low and the first liquid can be uniformly coated onto the substrate 2.

[0076] The first liquid may further contain a crosslinking agent in addition to polyvinyl alcohol. According to this, the polyvinyl alcohol in the polyvinyl alcohol layer formed by applying the first liquid to at least a part of the first surface is crosslinked, the elution of polyvinyl alcohol is suppressed, and the durability of the polyvinyl alcohol layer is improved.

[0077] A crosslinking liquid containing a crosslinking agent may be added to the polyvinyl alcohol dispersion liquid to prepare a first liquid containing polyvinyl alcohol and a crosslinking agent. The crosslinking liquid can be prepared by adding a crosslinking agent to a solvent such as water, ethanol, or isopropyl alcohol. The crosslinking agent may be, for example, glutaraldehyde, silica and alkoxysilane, titania (TiO ２ ), titanium alkoxide, titanium chelate, or epoxide.

[0078] When the first liquid contains a crosslinking agent, the content of the crosslinking agent in the first liquid may be 0.1% by mass or more and 10% by mass or less.

[0079] <Process S3 of obtaining a composite porous body> In process S3 of obtaining a composite porous body, the first liquid is applied to at least a part of the first surface 21 to form a polyvinyl alcohol layer 3 made of a non-porous body of polyvinyl alcohol, and the composite porous body 1 is obtained. The application method of the first liquid is not particularly limited. For example, the first liquid may be applied to the first surface 21 of the first layer 2A using a bar coater, an applicator, a dip coater, a spin coater, a spray coater, or a die coater. Alternatively, the first liquid may be coated on another substrate, and the first surface 21 may be placed downward on it and the first liquid may be transferred and coated on the first surface 21. Alternatively, the first liquid may be dropped on the first surface 21 and spread evenly for coating.

[0080] When the first liquid contains a crosslinking agent, after forming the polyvinyl alcohol layer, the crosslinking reaction may be advanced by adding a reaction catalyst such as sulfuric acid, nitric acid, or hydrochloric acid, or the crosslinking reaction may be advanced by heating. When polyvinyl alcohol is crosslinked after coating, the crosslinking network becomes dense and the pore diameter of the polyvinyl alcohol layer becomes smaller. The higher the degree of polymerization of polyvinyl alcohol, the denser the crosslinking network and the smaller the pore diameter of the polyvinyl alcohol layer.

[0081] In step S3, which is the step of obtaining a composite porous body, the step of applying the first liquid to at least a portion of the first surface 21 may be repeated two or more times. In this case, the composition of the first liquid may be the same in all steps, or it may be different.

[0082] [Note 1] A composite porous body comprising a substrate having a first surface and a polyvinyl alcohol layer covering at least a part of the first surface, wherein the substrate includes a first layer made of a polytetrafluoroethylene porous body having the first surface, the polyvinyl alcohol layer is made of a non-porous polyvinyl alcohol body, and the average pore size of the polyvinyl alcohol layer is 1 nm or more and 5 nm or less.

[0083] This embodiment will be described in more detail by reference to examples. However, this embodiment is not limited by these examples.

[0084] [Preparation of Composite Porous Materials] Composite porous materials were prepared for each sample using the following procedure.

[0085] <Substrate Preparation Process S1> A substrate made of a porous polytetrafluoroethylene material was prepared. The shape of the substrate, average thickness, average pore diameter of the first surface, and porosity of the first surface are as shown in Table 2.

[0086]

[0087] <First Solution Preparation Step S2> A polyvinyl alcohol dispersion was prepared by dispersing polyvinyl alcohol in water. A crosslinking solution, which was water with glutaraldehyde added as a crosslinking agent, was added to the polyvinyl alcohol dispersion to prepare the first solution. For each sample, the polyvinyl alcohol content and the crosslinking agent content of the first solution are as shown in Table 2. The degree of polymerization of the polyvinyl alcohol used in each sample is as shown in Table 2. For sample 3, two types of first solutions were prepared (indicated in the "1st time" and "2nd time" columns in Table 2).

[0088] <Step S3 to obtain a composite porous body> The first liquid was applied to the first surface of the substrate using an applicator to form a polyvinyl alcohol layer consisting of a non-porous polyvinyl alcohol, thereby obtaining a composite porous body. In sample 3, the first liquid described in the "1st application" column of Table 2 was applied first, and then the first liquid described in the "2nd application" column was applied.

[0089] [Measurement of Composite Porous Materials] For each sample, the average thickness of the polyvinyl alcohol layer and the average pore diameter of the polyvinyl alcohol layer were measured using the method described in Embodiment 1. The results are shown in Table 3. The average pore diameter of the polyvinyl alcohol layer corresponds to the average pore diameter of the composite porous material. The smaller the average pore diameter of the polyvinyl alcohol layer, the more the composite porous material can separate smaller substances, indicating higher separation performance.

[0090]

[0091] [Fluid Measurement] The flux of each composite porous material was measured using the following filtration test. A sample of each composite porous material was placed in the sample holder of a test apparatus consisting of a chamber and a sample holder. The test liquid was added to the chamber and pressurized to 0.6 MPa. The amount passing through the inspection surface per unit time was calculated from the weight change of the filtrate permeating from the sample holder, and the flux was obtained. The test liquid was water. The results are shown in Table 3. The flux of the composite porous materials of samples 1 to 3 was 0.01 L / (m ２ The flux was found to be above h·bar, confirming that it had sufficient flux.

[0092] [Discussion] Samples 1 to 3 are examples. Sample 4 is a comparative example. It was confirmed that the composite porous materials of Samples 1 to 3 can separate smaller particles and have higher separation performance compared to the composite porous material of Sample 4.

[0093] While embodiments and examples of this disclosure have been described above, it is intended from the outset that the configurations of each of the embodiments and examples described above may be combined or modified in various ways as appropriate. The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the scope of the claims are intended to be included in the meaning of equivalences.

[0094] 1 Composite porous body, 2 Substrate, 2h Cavities, 2A First layer, 2B Second layer, 3 Polyvinyl alcohol layer, 7 Test apparatus, 21 First surface, 22 Second surface, 30 Surface, 70 Beaker, 72D Upper opening, 71 Chamber, 71U Lower opening.

Claims

1. A composite porous body comprising a substrate having a first surface and a polyvinyl alcohol layer covering at least a portion of the first surface, wherein the substrate includes a first layer made of a polytetrafluoroethylene porous material having the first surface, the polyvinyl alcohol layer is made of a non-porous polyvinyl alcohol material, and the average pore size of the polyvinyl alcohol layer is 1 nm or more and 5 nm or less.

2. The composite porous body according to claim 1, wherein the average pore diameter on the first surface of the substrate is 20 nm or more and 2000 nm or less.

3. The composite porous body according to claim 1 or claim 2, wherein the porosity of the first surface of the substrate is 10% or more and 60% or less.

4. The composite porous body according to any one of claims 1 to 3, wherein the average thickness of the polyvinyl alcohol layer is 10 nm or more and 2000 nm or less.

5. The composite porous body according to any one of claims 1 to 4, wherein the shape of the substrate is a sheet.

6. The composite porous body according to claim 5, wherein the average thickness of the substrate is 1 μm or more and 1000 μm or less.

7. The composite porous body according to any one of claims 1 to 4, wherein the shape of the substrate is a tube, and the first surface is the outer surface of the tube.

8. The composite porous body according to claim 7, wherein the average thickness of the substrate is 50 μm or more and 1000 μm or less.

9. The composite porous body according to any one of claims 1 to 8, wherein the substrate comprises the first layer and a second layer adjacent to the first layer, and the average pore diameter of the second layer is greater than the average pore diameter of the first layer.

10. A method for producing a composite porous body according to any one of claims 1 to 9, comprising the steps of: preparing a substrate including the first layer made of the polytetrafluoroethylene porous body having the first surface; preparing a first liquid containing polyvinyl alcohol; and applying the first liquid to at least a portion of the first surface to form the polyvinyl alcohol layer made of a non-porous polyvinyl alcohol to obtain the composite porous body, wherein the average pore size of the polyvinyl alcohol layer is 1 nm or more and 5 nm or less.

11. The method for producing a composite porous body according to claim 10, wherein the first liquid further comprises a crosslinking agent, and the polyvinyl alcohol in the polyvinyl alcohol layer is crosslinked.

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