Composite porous body and method for producing same

Abstract

A composite porous body comprising: a base material which has a first surface; a carbon nanotube layer which covers at least some of the first surface; and a hydrophilic polymer which bonds the base material and the carbon nanotube layer, wherein the base material includes a first layer comprising a polytetrafluoroethylene porous body having the first surface, and the peel strength T1 between the base material and the carbon nanotube layer is 0.4 N / 20 mm or more, the peel strength T1 being measured in accordance with JIS Z 0237:2009 in an atmosphere having a temperature of 25°C and a relative humidity of 50%.

Description

Composite porous body and method for producing the same

[0001] The present disclosure relates to a composite porous body and a method for producing the same. This application claims priority to Japanese Patent Application No. 2024-110977, filed on July 10, 2024. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] Porous materials made of polytetrafluoroethylene (PTFE) are used in various separation membranes such as filtration filters.

[0003] Non-Patent Document 1 discloses a composite membrane for solvent separation, which has a carbon nanotube intermediate layer and a polyamide layer laminated on a substrate made of a porous PTFE material. The carbon nanotube intermediate layer contains carbon nanotubes and polydopamine (PDA) as a binder component.

[0004] Non-Patent Document 2 discloses a composite membrane for membrane distillation in which a carbon nanotube-immobilized membrane is laminated on a substrate made of a porous PTFE material. The carbon nanotube-immobilized membrane contains carbon nanotubes and polyvinylidene fluoride as a binder component.

[0005] Mingjia Liao et al., Thin-Film Composite Membranes with a Carbon Nanotube Interlayer for Organic Solvent Nanofiltration, Membranes 2022,12,817Madihah Saud Humoud et al., Enhanced Performance of Carbon Nanotube Immobilized Membrane for the Treatment of HighSalinity Produced Water via Direct Contact Membrane Distillation, Membranes 2020,10,325

[0006] The composite porous body of the present disclosure is a composite porous body comprising a substrate having a first surface, a carbon nanotube layer covering at least a portion of the first surface, and a hydrophilic polymer bonding the substrate and the carbon nanotube layer, wherein the substrate includes a first layer made of a porous polytetrafluoroethylene body having the first surface, and the peel strength T1 between the substrate and the carbon nanotube layer is 0.4 N / 20 mm or more, and the peel strength T1 is measured in accordance with JIS Z 0237:2009 in an atmosphere at a temperature of 25°C and a relative humidity of 50%.

[0007] Fig. 1 is a schematic view of a composite porous body according to embodiment 1. Fig. 2 is a cross-sectional view of a composite porous body according to embodiment 1. Fig. 3 is a diagram schematically showing the state of existence of a cross-linked polymer. Fig. 4 is a schematic view of a test device used in a liquid flow test. Fig. 5 is a schematic view of a composite porous body according to embodiment 2. Fig. 6 is a flowchart showing the manufacturing process of a composite porous body according to embodiment 3.

[0008] In the field 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.

[0009] In the composite membrane of Non-Patent Document 1, the adhesion between the substrate made of porous PTFE and the carbon nanotube intermediate layer is weak, so when an external force is applied to the composite membrane, the carbon nanotube intermediate layer easily peels off from the substrate, causing problems when using the composite membrane.

[0010] In the composite membrane of Non-Patent Document 2, the carbon nanotube layer contains polyvinylidene fluoride as a binder component. Since polyvinylidene fluoride is hydrophobic, when the composite membrane of Non-Patent Document 2 is used as a water treatment membrane, the filtration efficiency decreases.

[0011] Therefore, the present disclosure aims to provide a composite porous body in which the adhesion between a substrate containing a polytetrafluoroethylene porous body and a carbon nanotube layer is improved and the surface of the carbon nanotube layer is hydrophilic, and a method for producing the same.

[0012] According to the present disclosure, it is possible to provide a composite porous body in which the adhesion between a substrate containing a polytetrafluoroethylene porous body and a carbon nanotube layer is improved and the surface of the carbon nanotube layer is hydrophilic, and a method for manufacturing the same.

[0013] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be described. (1) A composite porous body of the present disclosure is a composite porous body comprising a substrate having a first surface, a carbon nanotube layer covering at least a portion of the first surface, and a hydrophilic polymer bonding the substrate and the carbon nanotube layer, wherein the substrate includes a first layer made of a porous polytetrafluoroethylene body having the first surface, and the peel strength T1 between the substrate and the carbon nanotube layer is 0.4 N / 20 mm or more, and the peel strength T1 is measured in an atmosphere at a temperature of 25°C and a relative humidity of 50% in accordance with JIS Z 0237:2009.

[0014] According to the present disclosure, it is possible to provide a composite porous body in which the adhesion between a substrate containing a polytetrafluoroethylene porous body and a carbon nanotube layer is improved and the surface of the carbon nanotube layer is hydrophilic.

[0015] (2) In the above (1), the hydrophilic polymer may be crosslinked, which further improves the adhesion between the substrate and the carbon nanotube layer.

[0016] (3) In the above (1) or (2), the percentage (T2 / T1)×100 of the peel strength T2 between the substrate and the carbon nanotube layer after immersing the composite porous body in water at 25° C. for 3 minutes to the peel strength T1 may be 30% or more. The units of the peel strengths T1 and T2 are N / 20 mm. The peel strengths T1 and T2 are measured in an atmosphere at a temperature of 25° C. and a relative humidity of 50% in accordance with JIS Z 0237:2009.

[0017] According to this, the hydrophilic polymer is crosslinked, and the adhesive strength between the substrate and the carbon nanotube layer is further improved.

[0018] (4) In any one of the above (1) to (3), the hydrophilic polymer may contain at least one selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyethylene glycol, polyallylamine, polyethyleneimine, polyvinylpyrrolidone, polystyrene sulfonic acid, polyoxazoline, cellulose acetate, and ethylene-vinyl alcohol copolymer resin, thereby further improving the adhesion between the substrate and the carbon nanotube layer.

[0019] (5) In any of the above (1) to (4), the hydrophilic polymer may contain one or both of polyvinyl alcohol and polyethyleneimine, which further improves the adhesion between the substrate and the carbon nanotube layer.

[0020] (6) In any of (1) to (5) above, after immersing the carbon nanotube layer in N-methyl-2-pyrrolidone at 25°C for 45 days, the contact angle α2 on the surface of the carbon nanotube layer may be 25° or more and 65° or less, and the percentage of the difference α2-α1 between the contact angle α2 and the contact angle α1 on the surface of the carbon nanotube layer before the immersion, {(α2-α1) / α1}×100, may be 40% or less. This allows the composite porous body to have excellent solvent resistance.

[0021] (7) In any of (1) to (6) above, adhesion of carbon nanotubes to the polytetrafluoroethylene rod may not be confirmed in a peeling evaluation test conducted under the following conditions: Peeling Evaluation Test Conditions: A sample made of the composite porous body is attached to a stainless steel plate using waterproof double-sided tape. At this time, the waterproof double-sided tape is attached to the main surface of the sample facing the substrate. The sample is immersed in water for 2 minutes and then removed from the water. Within 30 seconds, the tip surface of a 5 mm diameter polytetrafluoroethylene rod is pressed against the surface of the carbon nanotube layer of the sample with a force of 7 gf, and the rod is slid 50 mm along the surface of the carbon nanotube layer. The rod is then removed from the surface of the carbon nanotube layer, and the tip surface of the rod is visually observed to confirm whether or not carbon nanotubes are attached to the rod.

[0022] According to this, even when the composite porous body is wet with water, the adhesive strength between the substrate and the carbon nanotube layer is improved.

[0023] (8) The method for producing a composite porous body of the present disclosure is a method for producing a composite porous body according to any one of (1) to (7) above, comprising the steps of preparing a substrate including a first layer made of a polytetrafluoroethylene porous body having a first surface, mixing a hydrophilic polymer with a carbon nanotube dispersion to obtain a carbon nanotube mixture, and applying the carbon nanotube mixture to the first surface of the substrate to form a carbon nanotube layer and obtain a composite porous body.

[0024] According to the present disclosure, it is possible to provide a composite porous body in which the adhesion between a substrate containing a polytetrafluoroethylene porous body and a carbon nanotube layer is improved and the surface of the carbon nanotube layer is hydrophilic.

[0025] (9) In the above (8), the step of obtaining the composite porous body may include a step of immersing the substrate on which the carbon nanotube layer has been formed in a hydrophilic polymer, or a step of applying a hydrophilic polymer to the carbon nanotube layer, which further improves the adhesion between the substrate and the carbon nanotube layer.

[0026] (10) In the above (8), the step of obtaining the composite porous body may include a step of crosslinking the hydrophilic polymer after the step of immersing the substrate in the hydrophilic polymer or after the step of applying the hydrophilic polymer, which further improves the adhesion between the substrate and the carbon nanotube layer.

[0027] [Details of the embodiments of the present disclosure] Specific examples of the composite porous body and its manufacturing method of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0028] In this specification, the notation in the form of "A to B" means 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.

[0029] 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.

[0030] In the present disclosure, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be disclosed.

[0031] In this disclosure, "comprises," "includes," "has," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even a configuration expressed in closed terms may include additional elements that are normally incidental impurities or unrelated to the subject technology.

[0032] [Embodiment 1: Composite Porous Body (1)] 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 FIGS. 1 and 2. As shown in FIGS. 1 and 2, the composite porous body 1 according to Embodiment 1 is in the form of a sheet. The composite porous body 1 according to Embodiment 1 is a composite porous body comprising a substrate 2 including a first layer 2A made of porous polytetrafluoroethylene having a first surface 21, a carbon nanotube layer 3 covering at least a portion of the first surface 21, and a hydrophilic polymer 5 bonding the substrate 2 and the carbon nanotube layer 3. The peel strength T1 between the substrate 2 and the carbon nanotube layer 3 is 0.4 N / 20 mm or greater. The peel strength T1 is measured in an atmosphere at a temperature of 25°C and a relative humidity of 50% in accordance with JIS Z 0237:2009.

[0033] The composite porous body of embodiment 1 may be composed of a substrate, a carbon nanotube layer, and a hydrophilic polymer. The composite porous body of embodiment 1 may contain inevitable impurities in addition to the substrate, the carbon nanotube layer, and the hydrophilic polymer, as long as the effects of the present disclosure are not impaired. Examples of inevitable impurities include metal elements derived from catalysts such as cobalt and iron used in carbon nanotube production, and substances such as silicon and aluminum derived from dust.

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

[0035] The substrate 2 includes a first layer 2A made of a polytetrafluoroethylene porous body. PTFE has excellent heat resistance and chemical resistance. Therefore, the heat resistance and chemical resistance of the composite porous body are improved. 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 perfluoroalkoxyalkane (PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP).

[0036] 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 100 μm or less, 10 μm or more and 90 μm or less, or 20 μm or more and 50 μm or less. A composite porous body 1 including a substrate 2 having an average thickness of 1 μm or more has excellent strength. A composite porous body 1 including a substrate 2 having an average thickness of 100 μm or less has excellent flexibility. In addition, the filtration time using the composite porous body 1 is not too long.

[0037] The average thickness of the substrate 2 is determined by SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy). The magnification of the SEM image is 10,000 times. The size of the SEM image is 8 μm × 11 μm. The average thickness of the substrate 2 is the average of thicknesses at five or more different points on the substrate 2. As the scanning electron microscope (SEM), a "JSM-7800F" (trademark) manufactured by JEOL Ltd. can be used. The acceleration voltage during measurement is 3.0 kV. As the energy dispersive X-ray analyzer (EDX), an "OCTANE PLUS-A" (trademark) manufactured by AMETEK Corporation can be used. The same device can be used for measurements using SEM and EDX, which will be described later.

[0038] The average pore size on the first surface 21 of the substrate 2 may be 20 nm or more and 2000 nm or less, 50 nm or more and 450 nm or less, or 200 nm or more and 350 nm or less. When the average pore size on the first surface 21 of the substrate 2 is 20 nm or more, the composite porous body 1 including the substrate 2 has excellent liquid permeability. A composite porous body 1 with high liquid permeability can shorten the filtration time. When the average pore size on the first surface 21 of the substrate 2 is 2000 nm or less, the carbon nanotubes 6 that make up the carbon nanotube layer 3 are easily caught on the first surface 21, making it easier to properly form the carbon nanotube layer 3 on the first surface 21. When the average pore size on the first surface 21 of the substrate 2 is 2000 nm or less, the composite porous body 1 including the substrate 2 has excellent strength. The average pore size on the first surface 21 of the substrate 2 is larger than the average pore size of the carbon nanotube layer 3.

[0039] A plurality of pores 2h are formed on the first surface 21. When a carbon nanotube 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 this disclosure, the average pore diameter of the first surface 21 is determined from an SEM image of a cross section along the thickness direction of the substrate 2. In this disclosure, the thickness direction of the substrate 2 refers to the direction from the first surface 21 toward the second surface 22. The magnification of the SEM image is 5000 times. The size of the SEM image is 8 μm × 11 μm. The SEM image is binarized to extract each pore 2h in the SEM image. The circle-equivalent diameter of each pore 2h in the SEM image is calculated, and the arithmetic mean of the circle-equivalent diameters of all the pores 2h is calculated. The circle-equivalent diameter is the diameter of a perfect circle with the same area as the pore 2h. The arithmetic mean of these circle-equivalent diameters is considered to be the average pore diameter on the first surface 21 of the substrate 2.

[0040] The average minor axis of the pores 2h in 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 axis of 4 nm or more improves the liquid permeability of the composite porous body 1. If the average minor axis of the pores 2h in the first surface 21 is 400 nm or less, the carbon nanotubes 6 constituting the carbon nanotube layer 3 are easily caught on the first surface 21, and the carbon nanotube layer 3 is easily formed on the first surface 21. The average minor axis of the pores 2h in the first surface 21 may be, for example, 10 nm or more and 300 nm or less.

[0041] In the present disclosure, the average minor axis of the pores 2h on the first surface 21 is determined from an SEM image of a cross section along the thickness direction of the substrate 2. The magnification of the SEM image is 5000 times. The size of the SEM image is 8 μm × 11 μm. The SEM image is binarized, and each pore 2h in the SEM image is extracted. In the SEM image, the smallest rectangle circumscribing each pore 2h is determined. The average of the minor axes of all the rectangles in the SEM image is the average minor axis of the pores 2h.

[0042] As shown in FIG. 2 , the substrate 2 may include multiple layers. The substrate 2 may include a first layer 2A and a second layer 2B. In FIG. 2 , the boundary between the first layer 2A and the second layer 2B is schematically indicated by a two-dot chain line. The first layer 2A includes a first surface 21. The second layer 2B is adjacent to the first layer 2A. In the first embodiment, the second layer 2B includes a second surface 22. The average pore size of the second layer 2B is larger than that of the first layer 2A. The liquid permeability of a substrate 2 including a second layer 2B with a larger average pore size is superior to that of a substrate 2 having the same thickness as the substrate 2 but consisting only of the first layer 2A. Therefore, by configuring the substrate 2 with the first layer 2A and the second layer 2B, the filtration time of the composite porous body 1 is unlikely to be prolonged even if the substrate 2 is thick. 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 carbon nanotube layer 3. When the substrate 2 is composed of three or more layers, the average pore size may be larger the further from the first surface 21. Unlike this example, the substrate 2 may be composed of only the first layer 2A. In this case, the first layer 2A includes the first surface 21 and the second surface 22.

[0043] The average pore diameter of the first layer 2A and the average pore diameter of the second layer 2B can be determined from an SEM image of a cross section along the thickness direction of the substrate 2. The first layer 2A and the second layer 2B are heat-fused when the substrate 2 is produced. 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 circle-equivalent diameters of the pores 2h present 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 circle-equivalent diameters of the pores 2h present in the region adjacent to the first layer 2A across the boundary is the average pore diameter of the second layer 2B.

[0044] 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, or polyphenylene sulfide.

[0045] <Carbon Nanotube Layer> In the first embodiment, the carbon nanotube layer 3 includes a plurality of carbon nanotubes 6. The carbon nanotube layer 3 may cover at least a portion of the first surface 21 of the substrate 2, or may cover the entire first surface 21 of the substrate 2. The carbon nanotube layer 3 may be disposed directly on the first surface 21 of the substrate 2. Although only the carbon nanotube layer 3 is provided on the substrate 2 in FIGS. 1 and 2 , other layers may be provided on the carbon nanotube layer 3 as long as the effects of the present disclosure are not impaired.

[0046] The carbon nanotubes 6 may be single-walled carbon nanotubes, which have a single cylindrical carbon layer (graphene), double-walled or multi-walled carbon nanotubes, which have a cylindrical carbon layer formed by stacking multiple carbon layers, or cup-stacked nanotubes, which have a structure in which graphene is stacked in the shape of a paper cup with an open bottom. The presence of carbon nanotubes 6 in the carbon nanotube layer 3 can be confirmed by observation with a scanning electron microscope. The magnification of the scanning electron microscope is 10,000 times, and the acceleration voltage is 3.0 kV.

[0047] The length of the carbon nanotubes 6 is not particularly limited. The length of the carbon nanotubes 6 may be, for example, 0.1 μm or more and 50 μm or less, or 0.5 μm or more and 30 μm or less. The length of the carbon nanotubes can be measured by observation with an atomic force microscope or a scanning electron microscope. As the atomic force microscope, an "SPI4000" (trademark) manufactured by Hitachi High-Tech Corporation can be used.

[0048] The diameter of the carbon nanotubes 6 is not particularly limited. The diameter of the carbon nanotubes 6 may be, for example, 1 nm or more and 100 nm or less, or 3 nm or more and 80 nm or less. The diameter of the carbon nanotubes means the average outer diameter of a single carbon nanotube. The average outer diameter of a single carbon nanotube can be measured and calculated by directly observing a projected image of the carbon nanotube using a scanning electron microscope or a transmission electron microscope. As the transmission electron microscope, an "HF-2000" (trademark) manufactured by Hitachi Ltd. can be used. The measurement condition for the transmission electron microscope is an acceleration voltage of 200 kV.

[0049] The average pore size of the carbon nanotube layer 3 is not particularly limited as long as it is equal to or smaller than the average pore size on the first surface 21 of the substrate 2. The average pore size of the carbon nanotube layer 3 may be, for example, 1 nm or more and 100 nm or less, 5 nm or more and 80 nm or less, or 20 nm or more and 60 nm or less. When the average pore size of the carbon nanotube layer 3 is 1 nm or more, the flexibility of the carbon nanotube layer 3 is ensured. In addition, the filtration time by the composite porous body 1 does not become too long. When the average pore size of the carbon nanotube layer 3 is 100 nm or less, impurities can be efficiently separated by the carbon nanotube layer 3.

[0050] Because the average pore diameter of the carbon nanotube layer 3 is very small, it is difficult to determine it from an SEM image of the cross section of the carbon nanotube layer 3. In the present disclosure, the average pore diameter of the carbon nanotube layer 3 is determined by a liquid flow test. FIG. 4 is a schematic diagram of a test apparatus 7 used in the liquid flow test. The test apparatus 7 includes a flask 70 that can be evacuated and a cylindrical chamber 71 that is open at both ends. The composite porous body 1 is sandwiched between a lower opening 71D of the chamber 71 and an upper opening 70U of the flask 70. The carbon nanotube layer 3 of the composite porous body 1 faces the chamber 71.

[0051] The procedure for determining the average pore size of the carbon nanotube layer 3 is as follows. First, a test solution containing a plurality of polymers or particles having known average particle sizes is prepared. Here, the average particle size means the Stokes diameter value in the case of polymers, and the mode value of the number distribution in the case of particles. The average molecular weight of the polymer or the concentration of particles (g / cm) in the test solution is used to determine the average pore size. ３ As will be described later, the average particle size (Stokes diameter) of the polymer is calculated based on the average molecular weight of the polymer.

[0052] A plurality of test solutions with different average particle sizes are prepared. For example, when the average particle size is between 0.8 nm and 5 nm, test solutions of polymers with average molecular weights of 200, 300, 600, 1000, 2000, 4000, or 6000 are prepared. When the average particle size is between 5 nm and 20 nm, test solutions of particles at 5 nm intervals are prepared. When the average particle size is between 20 nm and 60 nm, test solutions of particles at 10 nm intervals are prepared. When the average particle size is between 60 nm and 100 nm, test solutions of particles at 20 nm intervals are prepared.

[0053] Polyethylene glycol (hereinafter also referred to as "PEG") is used as the polymer having an average particle size of 0.8 nm to 5 nm contained in the test solution. The average particle size (Stokes diameter) of polyethylene glycol is calculated based on the molecular weight using the following formula: r [nm] = 2 × 16.73 × 10 －３ ×M ｗ ０．５５７ In the above formula, M ｗ is the average molecular weight, and r is the Stokes diameter. For example, based on the above formula, the Stokes diameter of polyvinyl alcohol particles with an average molecular weight of 600 is 1.2 nm, and the Stokes diameter of polyvinyl alcohol particles with an average molecular weight of 2000 is 2.3 nm.

[0054] As particles having an average particle size of 5 nm to 100 nm contained in the test solution, "gold nanoparticles" manufactured by Aldrich Corporation are used.

[0055] The test liquid is placed in the chamber 71. The flask 70 is evacuated, and the filtrate that has permeated the composite porous body 1 is stored in the flask 70. The degree of vacuum is 80 Pa or less. The concentration of particles contained in the filtrate is measured.

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

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

[0058] The liquid flow test is performed in the above procedure, starting with the test liquid with the smallest average particle size. Among the average particle sizes of the test liquids whose particle concentration in the filtrate is 10% or less of the particle concentration in the test liquid, the smallest average particle size is considered to be the average pore size of the carbon nanotube layer 3. For example, if the particle concentration in the filtrate is 90% of the particle concentration in the test liquid for a test liquid with an average particle size of 10 nm, if the particle concentration in the filtrate is 5% of the particle concentration in the test liquid for a test liquid with an average particle size of 15 nm, or if the particle concentration in the filtrate is 5% of the particle concentration in the test liquid for a test liquid with an average particle size of 25 nm, then the average pore size of the carbon nanotube layer 3 is 15 nm.

[0059] The ratio of the average pore size of the carbon nanotube layer 3 to the average pore size on the first surface 21 of the substrate 2 is, for example, 0.01 or more and 1 or less. When the ratio is 0.01 or more, the difference between the average pore size on the first surface 21 of the substrate 2 and the average pore size of the carbon nanotube layer 3 is not too large, making it easier to properly form the carbon nanotube layer 3 on the first surface 21. When the ratio is 1 or less, the average pore size of the carbon nanotube layer 3 is the same as or smaller than the average pore size on the first surface 21 of the substrate 2, improving the filtration performance of the carbon nanotube layer 3. The ratio may be 0.05 or more and 0.8 or less, 0.1 or more and 0.5 or less, or 0.2 or more and 0.4 or less.

[0060] The average thickness of the carbon nanotube layer 3 may be 100 nm or more and 10,000 nm or less, 500 nm or more and 5,000 nm or less, or 1,000 nm or more and 3,000 nm or less. When the average thickness of the carbon nanotube layer 3 is 100 nm or more, it is easy for the carbon nanotube layer 3 to efficiently separate impurities, that is, it is easy to improve filtration performance. When the average thickness of the carbon nanotube layer 3 is 10,000 nm or less, the filtration time by the composite porous body 1 including the carbon nanotube layer 3 is not too long, that is, it is easy to improve liquid permeability. When the average thickness of the carbon nanotube layer 3 is 5,000 nm or less, the composite porous body 1 including the carbon nanotube layer 3 has excellent flexibility.

[0061] The average thickness of the carbon nanotube layer 3 is determined in the same manner as the average thickness of the substrate 2. The distance from the boundary between the substrate 2 and the carbon nanotube layer 3 to the surface 30 of the carbon nanotube layer 3, as determined by SEM-EDX, is the thickness of the carbon nanotube layer 3. The magnification of the SEM image is 10,000 times. The size of the SEM image is 8 μm × 11 μm. The average thickness of the carbon nanotube layer 3 is the average of thicknesses at five different points on the carbon nanotube layer 3. If it is difficult to measure the thickness of the carbon nanotube layer using SEM-EDX, the distance from the boundary between the substrate 2 and the carbon nanotube layer 3 to the surface 30 of the carbon nanotube layer 3 is measured using FIB-SEM. This distance corresponds to the thickness of the carbon nanotube layer 3. The image magnification is set appropriately depending on the carbon nanotube film thickness. For example, the image magnification is ×8,000, ×15,000, or ×30,000.

[0062] The carbon nanotube layer 3 may include, for example, a carbon nanotube sheet formed by forming a plurality of carbon nanotubes into a sheet. The carbon nanotube sheet may include components other than carbon nanotubes as long as the effects of the present disclosure are not impaired. Examples of such components include dispersants and binder components. Examples of dispersants include compounds that disperse carbon nanotubes in a medium, such as sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, carboxymethyl cellulose, and polycarboxylic acid. Examples of binder components include acrylic and silicone resins.

[0063] The carbon nanotube layer 3 may contain carbon nanotubes and a hydrophilic polymer. The carbon nanotube layer 3 may be made of carbon nanotubes and a hydrophilic polymer. The carbon nanotube layer 3 may contain carbon nanotubes, a hydrophilic polymer, and the above-mentioned binder component. The carbon nanotube layer 3 may be made of carbon nanotubes, a hydrophilic polymer, the above-mentioned dispersant, and a binder component.

[0064] <Hydrophilic Polymer> In embodiment 1, the composite porous body 1 includes a hydrophilic polymer 5 that bonds the substrate 2 and the carbon nanotube layer 3. In the present disclosure, whether the composite porous body 1 includes the hydrophilic polymer 5 that bonds the substrate 2 and the carbon nanotube layer 3 is confirmed by measuring the peel strength T1 between the substrate 2 and the carbon nanotube layer 3. In the present disclosure, the peel strength T1 between the substrate and the carbon nanotube layer is measured by conducting a 90° peel test in accordance with JIS Z 0237:2009 "Test methods for pressure-sensitive adhesive tapes and pressure-sensitive adhesive sheets." When the composite porous body is in the form of a sheet, the measurement conditions are as follows.

[0065] <<Measurement Conditions for Peel Strength T1 (When the Composite Porous Body is in Sheet Form)>> Measurement Temperature: 25°C Relative Humidity: 50% Substrate: BASUS Plate (SUS Plate with BA Finish) Release Tape: Acrylic Adhesive Tape Measurement Size (Release Tape Size): 20 mm Width, 100 mm Length Bonding Conditions: Double-sided tape with acrylic adhesive is attached to the BASUS plate, and the carbon nanotube layer 3 of a sample made of a composite porous body is attached thereon. The release tape is then attached to the main surface of the sample opposite the carbon nanotube layer 3 (i.e., the main surface on the substrate side), and a 2 kg roller is rolled back and forth three times. The bonding speed is 50 mm / sec. Time from bonding to measurement: Measured within 1 minute. Measurement Data: The initial 25 mm is ignored, and the subsequent 50 mm is measured at all points at 1 mm intervals. Peel Speed: 5 mm / sec. The peel strength (unit: N) is measured for each of the 10 samples, and the arithmetic average of the peel strengths of the 10 samples is calculated. The arithmetic mean (unit: N) is divided by the width of the sample (20 mm) to obtain a value (unit: N / 20 mm) which is defined as the peel strength T1 of the composite porous body.

[0066] When the composite porous body is tubular, the measurement conditions are as follows: <<Measurement Conditions for Peel Strength T1 (When the Composite Porous Body is Tubular)>> Measurement Temperature: 25°C Relative Humidity: 50% Substrate: BASUS Plate (SUS Plate with BA Finish) Release Tape: Acrylic Adhesive Tape Measurement Size (Release Tape Size): 3 mm Width, 100 mm Length Pressing Conditions: Double-sided tape with acrylic adhesive is attached to the BASUS plate, and the carbon nanotube layer 3 of a sample made of a composite porous body is attached thereon. The release tape is then attached to the sample, and a 0.2 kg roller is rolled back and forth three times. Pressing Speed: 50 mm / sec. Time from Pressing to Measurement: Measured within 1 minute. Measurement Data: The initial 25 mm is ignored, and the subsequent 50 mm is measured at all points at 1 mm intervals. Peel Speed: 5 mm / sec. Peel strength (unit: N) is measured for each of the 10 samples. For each sample, the width (unit: mm) of the carbon nanotubes attached to a 3 mm wide release tape is evaluated using a microscope. The peel strength (unit: N) is divided by the width of the carbon nanotubes attached to the tape, and the result is multiplied by 20 to determine the peel strength (unit: N / 20 mm). The arithmetic average of the peel strengths (unit: N / 20 mm) of the 10 samples is calculated. This arithmetic average corresponds to the peel strength T1 of the composite porous body.

[0067] When the peel strength T1 between the substrate 2 and the carbon nanotube layer 3 is 0.4 N / 20 mm or more, it is confirmed that the composite porous body 1 contains a hydrophilic polymer 5 that bonds the substrate 2 and the carbon nanotube layer 3. Furthermore, in the present disclosure, when the peel strength T1 is 0.4 N / 20 mm or more, it is determined that the adhesion between the substrate and the carbon nanotube layer is improved.

[0068] When the carbon nanotube layer 3 is disposed directly on the substrate 2 made of porous polytetrafluoroethylene and no hydrophilic polymer 5 is present to bond the substrate 2 and the carbon nanotube layer 3, the peel strength T1 between the substrate 2 and the carbon nanotube layer 3 is less than 0.4 N / 20 mm or 0.3 N / 20 mm or less. When the carbon nanotube layer 3 is disposed directly on the substrate 2 made of porous polytetrafluoroethylene and the carbon nanotube layer 3 contains polydopamine as a binder component, as in Non-Patent Document 1, the peel strength T1 between the substrate 2 and the carbon nanotube layer 3 is 0.3 N / 20 mm or less.

[0069] In embodiment 1, the peel strength T1 between the substrate and the carbon nanotube layer is 0.4 N / 20 mm or more, or may be 0.6 N / 20 mm or more, 0.7 N / 20 mm or more, 1.0 N / 20 mm or more, or 1.1 N / 20 mm or more. The peel strength T1 may be 4.0 N / 20 mm or less, 3.0 N / 20 mm or less, 2.8 N / 20 mm or less, 2.5 N / 20 mm or less, or 2.2 N / 20 mm or less. The peel strength T1 may be 0.4 N / 20 mm or more to 4.0 N / 20 mm or less, 0.7 N / 20 mm or more to 3.0 N / 20 mm or less, or 1.0 N / 20 mm or more to 2.5 N / 20 mm or less.

[0070] To deepen understanding of the present disclosure, the form of the hydrophilic polymer 5 will be described with reference to FIG. 3 . For ease of explanation, carbon nanotubes are not shown in FIG. 3 . As shown in FIG. 3 , the hydrophilic polymer 5 exists across the interface between the substrate 2 and the carbon nanotube layer 3 (corresponding to the first surface 21 in FIG. 3 ), thereby bonding the substrate 2 and the carbon nanotube layer 3. The presence of the hydrophilic polymer 5 across the interface between the substrate 2 and the carbon nanotube layer 3 can also be expressed as meaning that the substrate 2 and the carbon nanotube layer 3 contain the hydrophilic polymer 5, and that the hydrophilic polymer 5 exists continuously across the interface between the carbon nanotube layer 3 and the substrate 2.

[0071] The hydrophilic polymer 5 may be present throughout the substrate 2 and the carbon nanotube layer 3. Alternatively, the hydrophilic polymer 5 may not be present in at least a portion of the substrate 2, as long as the effects of the present disclosure are not impaired.

[0072] The hydrophilicity of the polymer contained in the composite porous body 1 is confirmed by measuring the contact angle α1 on the surface of the carbon nanotube layer 3. In the present disclosure, when the contact angle α1 on the surface of the carbon nanotube layer 3 is 65° or less, it is confirmed that the polymer contained in the composite porous body 1 is hydrophilic and that the surface of the carbon nanotube layer 3 is hydrophilic. In the present disclosure, the contact angle α1 on the surface of the carbon nanotube layer 3 is measured on the main surface of the carbon nanotube layer 3 in accordance with JIS R 3257:1999 "Static Method." The volume of the water droplet is 1 μl, and the contact angle is measured at 10 points 1 second after the droplet lands on the carbon nanotube layer 3. The arithmetic average of these measured values ​​is defined as the contact angle α1 on the surface of the carbon nanotube layer 3.

[0073] In the composite porous body 1, if another layer is formed on the carbon nanotube layer 3 and the main surface of the carbon nanotube layer 3 is not exposed to the outside, the other layer is removed to expose the main surface of the carbon nanotube layer 3 to the outside, and then the contact angle α1 of the surface of the carbon nanotube layer 3 is measured. Methods for removing the other layer include, for example, chemical removal or polishing removal using a microtome or ion milling.

[0074] The hydrophilic polymer 5 may be crosslinked. Whether the hydrophilic polymer 5 is crosslinked can be confirmed by measuring the percentage (T2 / T1) x 100 of the peel strength T2 between the substrate and the carbon nanotube layer after immersing the composite porous body in water at 25°C for 3 minutes relative to the peel strength T1 between the substrate and the carbon nanotube layer. In the present disclosure, if the percentage (T2 / T1) x 100 is 30% or more, it is confirmed that the hydrophilic polymer 5 is crosslinked. Here, the units of peel strength T1 and peel strength T2 are N / 20 mm, and peel strength T1 and peel strength T2 are measured by conducting a 90° peel test in an atmosphere at a temperature of 25°C and a relative humidity of 50% in accordance with JIS Z 0237:2009, "Test Methods for Pressure-Sensitive Adhesive Tapes and Pressure-Sensitive Adhesive Sheets."

[0075] The peel strength T1 is measured before the composite porous body is immersed in water at 25°C for 3 minutes, and the measurement conditions are as described above under the measurement conditions for peel strength T1. The measurement conditions for peel strength T2 are basically the same as those for peel strength T1, except that the measurement is performed after the composite porous body is immersed in water at 25°C for 3 minutes. Double-sided tape made of an acrylic adhesive is attached to a BASUS plate, and the carbon nanotube layer 3 of a sample made of a composite porous body removed from water is attached thereto. The sample is attached to the double-sided tape immediately after being removed from the water. Further, a release tape is attached to the sample, and a 2 kg roller is rolled back and forth three times. The peel strength T2 is measured within 3 minutes after the sample is attached to the double-sided tape.

[0076] In embodiment 1, the percentage (T2 / T1) x 100 may be 30% or more, 40% or more, 50% or more, or 60% or more. The percentage (T2 / T1) x 100 may be 90% or less, 81% or less, 80% or less, or 75% or less. The percentage (T2 / T1) x 100 may be 30% or more and 90% or less, 40% or more and 80% or less, or 50% or more and 75% or less.

[0077] The hydrophilic polymer 5 may contain at least one selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyethylene glycol, polyallylamine, polyethyleneimine, polyvinylpyrrolidone, polystyrene sulfonic acid, polyoxazoline, cellulose acetate, and ethylene-vinyl alcohol copolymer resin. The hydrophilic polymer 5 may consist of at least one selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyethylene glycol, polyallylamine, polyethyleneimine, polyvinylpyrrolidone, polystyrene sulfonic acid, polyoxazoline, cellulose acetate, and ethylene-vinyl alcohol copolymer resin.

[0078] From the viewpoint of productivity, the hydrophilic polymer 5 may contain one or both of polyvinyl alcohol (PVA) and polyethyleneimine (PEI). The hydrophilic polymer 5 may be made of one or both of polyvinyl alcohol and polyethyleneimine.

[0079] The hydrophilic polymer 5 may contain a crosslinked product of polyethyleneimine.The hydrophilic polymer 5 may be made of a crosslinked product of polyethyleneimine.

[0080] As long as the effects of the present disclosure are not impaired, unavoidable impurities may be contained, such as metal elements derived from catalysts such as cobalt and iron used in carbon nanotube production, or substances such as silicon and aluminum derived from dust.

[0081] The composition ratio of the hydrophilic polymer 5 is measured by a combination of X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and solid-state NMR analysis. The X-ray photoelectron spectroscopy (XPS) measurement device can be a "PHI Quantera SXM" (trademark) manufactured by ULVAC-PHI, Inc. Measurement conditions are a beam diameter of 100 μmφ and an acceleration voltage of 15 kV. The time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement device can be a "PHI nano TOF II" (trademark) manufactured by ULVAC-PHI, Inc. Measurement conditions are Bi primary ions, an acceleration voltage of 30 kV, and an irradiation area of ​​100 μm square. The solid-state NMR measurement device can be an "ECA700" (trademark) manufactured by JEOL Ltd.

[0082] <Change in Contact Angle of Carbon Nanotube Layer> In the first embodiment, after immersing the carbon nanotube layer in N-methyl-2-pyrrolidone at 25°C for 45 days, the contact angle α2 on the surface of the carbon nanotube layer may be 25° or more and 65° or less, and the percentage of the difference α2-α1 between the contact angle α2 and the contact angle α1 relative to the contact angle α1 on the surface of the carbon nanotube layer before immersion, {(α2-α1) / α1}×100, may be 40% or less. In the present disclosure, when the contact angles α1 and α2 satisfy the above condition, the composite porous body is determined to have excellent solvent resistance.

[0083] The contact angle α2 may be 30° or more and 60° or less, or 35° or more and 60° or less, or 41° or more and 60° or less. The percentage {(α2-α1) / α1}×100 may be 3% or more and 40% or less, or 5% or more and 30% or less, or 10% or more and 25% or less.

[0084] The contact angles α1 and α2 are measured on the main surface of the carbon nanotube layer 3 in accordance with JIS R 3257:1999 "Static Method." The contact angle α2 is measured on a sample that has been removed from N-methyl-2-pyrrolidone, replaced with pure water, and then dried. For sheet-shaped samples, a "DMo-502" (trademark) manufactured by Kyowa Interface Science Co., Ltd. can be used. Measurement conditions include a temperature of 25°C and a relative humidity of 50%, and the contact angle is measured one second after 1 μL of water contacts the sample. For tube-shaped samples, a "MCA-4" (trademark) manufactured by Kyowa Interface Science Co., Ltd. can be used. Measurement conditions include a temperature of 25°C and a relative humidity of 50%, and the contact angle is measured one second after 300 pL of water contacts the sample.

[0085] <Peeling Evaluation Test> In the composite porous body of embodiment 1, adhesion of carbon nanotubes to a polytetrafluoroethylene round rod may not be confirmed in a peeling evaluation test performed under the following conditions. Peeling Evaluation Test Conditions: A sample made of a composite porous body is attached to a stainless steel plate using waterproof double-sided tape. At this time, the waterproof double-sided tape is attached to the main surface of the sample facing the substrate. The sample is immersed in water for 2 minutes and then removed from the water. Within 30 seconds, the tip surface of a 5 mm diameter polytetrafluoroethylene round rod is pressed against the surface of the carbon nanotube layer of the sample with a force of 7 gf, and the round rod is slid 50 mm along the surface of the carbon nanotube layer. The round rod is then removed from the surface of the carbon nanotube layer, and the tip surface of the round rod is visually observed to confirm whether or not carbon nanotubes are attached to the round rod.

[0086] The stainless steel plate is not particularly limited, and a conventionally known stainless steel plate can be used. The waterproof double-sided tape is not particularly limited, and a conventionally known waterproof double-sided tape can be used. An example of the waterproof double-sided tape is "Strong Double-Sided Tape (Waterproof)" (trademark) manufactured by Nitoms.

[0087] The PTFE rod is pressed against the carbon nanotube layer so that the tip end surface of the rod comes into contact with the carbon nanotube layer.

[0088] When the composite porous body is in the form of a sheet, the direction in which the PTFE rod is slid on the surface of the carbon nanotube layer is not particularly limited. As described in the second embodiment below, when the composite porous body is in the form of a tube, the direction in which the PTFE rod is slid on the surface of the carbon nanotube layer is the direction along the longitudinal direction of the composite porous body.

[0089] [Embodiment 2: Composite porous body (2)] 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 Fig. 5. As shown in Fig. 5, the composite porous body 1 according to Embodiment 2 has a tubular shape. The composite porous body 1 according to Embodiment 2 can have the same configuration as the composite porous body 1 of Embodiment 1, except for its tubular shape.

[0090] The substrate 2 of the composite porous body 1 has a tubular shape. A first surface 21 of the tubular substrate 2 constitutes the outer peripheral surface of the substrate 2. A carbon nanotube layer 3 formed on the first surface 21 constitutes the outer peripheral surface of the tubular composite porous body 1.

[0091] The outer diameter and inner diameter of the tubular substrate can be appropriately set depending on the application. The outer diameter of the tubular substrate may be, for example, 1.0 mm or more and 2.5 mm or less. The inner diameter of the tubular substrate may be, for example, 0.3 mm or more and 1.5 mm or less.

[0092] [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 Fig. 6, the method for manufacturing a composite porous body of Embodiment 3 includes the steps of preparing a substrate having a first surface and including a first layer made of porous polytetrafluoroethylene (hereinafter also referred to as "substrate preparation step S1"); mixing a hydrophilic polymer with a carbon nanotube dispersion to obtain a carbon nanotube mixture (hereinafter also referred to as "carbon nanotube mixture preparation step S2"); and applying the carbon nanotube mixture to the first surface of the substrate to form a carbon nanotube layer to obtain a composite porous body (hereinafter also referred to as "composite porous body obtaining step S3").

[0093] <Substrate Preparation Step S1> In the substrate preparation step S1, a substrate 2 including a first layer 2A made of a porous polytetrafluoroethylene body is prepared. The substrate 2 is the same as the substrate 2 described in the first embodiment.

[0094] The method for producing the substrate 2 is not particularly limited. For example, a first layer made of porous polytetrafluoroethylene may be produced by the production method disclosed in Japanese Patent Application Laid-Open No. 2010-94579. A thin film made of PTFE is stretched to make the thin film porous. As a result, a first layer 2A made of porous PTFE is obtained. The average pore size of the substrate 2 varies depending on the stretching conditions. The first layer 2A may be used as the substrate 2 as is. The first layer 2A may be bonded to a second layer 2B to produce the substrate 2. Details of the second layer 2B are as described in embodiment 1.

[0095] <Carbon nanotube mixture liquid preparation step S2> In the carbon nanotube mixture liquid preparation step S2, a hydrophilic polymer is mixed with a carbon nanotube dispersion liquid to obtain a carbon nanotube mixture liquid. The substrate preparation step S1 and the carbon nanotube mixture liquid preparation step S2 may be performed either first or simultaneously.

[0096] In the carbon nanotube dispersion, carbon nanotubes are dispersed in a dispersion medium. The dispersion medium may be, for example, at least one selected from the group consisting of water, ethanol, isopropyl alcohol, acetone, dimethyl sulfoxide, butyl acetate, and methyl ethyl ketone. The dispersion medium may further contain a surfactant. The carbon nanotube content in the carbon nanotube dispersion medium may be 0.01% by mass or more and 15% by mass or less.

[0097] The hydrophilic polymer is the same as the hydrophilic polymer described in embodiment 1. The content of the hydrophilic polymer in the carbon nanotube mixture may be 0.01% by mass or more and 0.5% by mass or less. When the content of the hydrophilic polymer in the carbon nanotube mixture is 0.01% by mass or more, the carbon nanotube layer is less likely to peel off from the porous polytetrafluoroethylene body. When the content of the hydrophilic polymer in the carbon nanotube mixture is 0.5% by mass or less, aggregation of the carbon nanotubes in the mixture is suppressed, making it easier to obtain a uniform carbon nanotube layer.

[0098] The carbon nanotube content in the carbon nanotube mixture may be 0.01% by mass or more and 0.5% by mass or less. When the carbon nanotube content is 0.01% by mass or more, the amount of carbon nanotubes in the carbon nanotube mixture is sufficient, making it easy for the carbon nanotubes to be deposited on first surface 21. When the carbon nanotube content is 0.5% by mass or less, the carbon nanotubes can be uniformly coated on first surface 21 without impairing their dispersibility.

[0099] <Step S3 of Obtaining Composite Porous Body> In step S3 of obtaining a composite porous body, a carbon nanotube mixture is applied to first surface 21 of substrate 2 to form a carbon nanotube layer 3 (hereinafter also referred to as "CNT layer formation step S31"), thereby obtaining a composite porous body 1. The carbon nanotube mixture can be applied to first surface 21 using, for example, a bar coater.

[0100] The step S3 of obtaining a composite porous body may include a step of immersing the substrate 2 on which the carbon nanotube layer 3 has been formed in the CNT layer forming step S31 in a hydrophilic polymer, or a step of applying a hydrophilic polymer to the carbon nanotube layer (hereinafter also referred to as the "immersion or application step S32"). This allows the hydrophilic polymer to penetrate into the pores of the substrate 2 and the carbon nanotube layer. The hydrophilic polymer used here is the same as the hydrophilic polymer in the carbon nanotube mixture.

[0101] The step S3 of obtaining a composite porous body may include a step of crosslinking the hydrophilic polymer (also referred to as a "crosslinking step S33").

[0102] The step S3 of obtaining a composite porous body may include a step of crosslinking the hydrophilic polymer ("crosslinking step S33") after the step of immersing in the hydrophilic polymer or after the step of applying the hydrophilic polymer (after the immersion or application step S32). Even if the step S3 of obtaining a composite porous body does not include the immersion or application step S32, the crosslinking step S33 can be performed after the carbon nanotube layer is formed.

[0103] In the crosslinking step S33, a crosslinking agent may be added to the hydrophilic polymer in which the substrate 2 has been immersed, thereby crosslinking the hydrophilic polymer. Alternatively, in the crosslinking step S33, after the step of immersing the substrate 2 in the hydrophilic polymer or the step of applying the hydrophilic polymer (after the immersion or application step S32), the hydrophilic polymer may be crosslinked by immersing the substrate 2 in a crosslinking liquid containing a crosslinking agent.

[0104] The type of crosslinking agent is appropriately selected depending on the type of hydrophilic polymer. The crosslinking agent may be, for example, glutaraldehyde or an epoxy compound. The epoxy compound may be ethylene glycol diglycidyl ether. Specifically, the epoxy compound may be "Denacol" (trademark) manufactured by Nagase ChemteX Corporation.

[0105] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0106] [Preparation of Composite Porous Body] Each sample composite porous body was prepared according to the following procedure.

[0107] <Substrate Preparation Step S1> In the substrate preparation step S1, a substrate made of a porous polytetrafluoroethylene body was prepared. The average thickness of the substrate was 130 μm. The average pore diameter of the substrate was 300 nm. The shape of the substrate for each sample is as shown in Table 1. When the substrate was tubular, the outer diameter of the substrate was 1.6 mm.

[0108] <Carbon nanotube mixture preparation step S2> In the carbon nanotube mixture preparation step S2, a hydrophilic polymer was mixed with a carbon nanotube dispersion to obtain a carbon nanotube mixture. The dispersion medium of the carbon nanotube dispersion was water. The carbon nanotube content in the carbon nanotube dispersion medium was 3 mass %. The hydrophilic polymer content in the carbon nanotube dispersion medium was 0.03 mass %.

[0109] The type of hydrophilic polymer used in each sample is as shown in Table 1. Note that in Sample 1-1, polydopamine (PDA) was used instead of the hydrophilic polymer. Although polydopamine is not a hydrophilic polymer, for convenience it is listed in the "hydrophilic polymer" column in Table 1.

[0110] <Step S3 of Obtaining Composite Porous Body> The carbon nanotube mixture was applied to the first surface of the substrate to form a carbon nanotube layer. The carbon nanotube mixture was applied to the first surface using a bar coater.

[0111] For samples marked with "Yes" in the "Immersion in hydrophilic polymer" column in Table 1, a composite porous body was obtained by immersing the substrate 2 on which the carbon nanotube layer 3 was formed in a hydrophilic polymer (except for sample 1-1, which was polydopamine). The hydrophilic polymer used here was the same as the hydrophilic polymer in the carbon nanotube mixture. For samples marked with "No" in the same column, this step was not carried out.

[0112] Next, for samples marked "Yes" in the "Immersion in crosslinking liquid" column of Table 1, the composite porous body was immersed in a crosslinking liquid containing a crosslinking agent (Denacol (trademark) manufactured by Nagase ChemteX Corporation when the hydrophilic polymer was PEI, or glutaraldehyde when the hydrophilic polymer was PVA) to crosslink the hydrophilic polymer. For samples marked "No" in the same column, this step was not carried out.

[0113]

[0114] [Evaluation] <Thickness and average pore diameter of carbon nanotube layer> The thickness and average pore diameter of the carbon nanotube layer of each sample were measured by the method described in embodiment 1. The measurement results of the thickness of the carbon nanotube layer are shown in Table 2. In all samples, the average pore diameter of the carbon nanotube layer was within the range of 20 to 60 nm.

[0115] <Change in Contact Angle of Carbon Nanotube Layer> For each sample composite porous body, the contact angle α2 of the surface of the carbon nanotube layer after immersion in N-methyl-2-pyrrolidone at 25°C for 45 days and the contact angle α1 of the surface of the carbon nanotube layer before immersion were measured by the method described in embodiment 1. Based on the measured values, the percentage of the difference α2 - α1 between the contact angles α2 and α1, {(α2 - α1) / α1} x 100, was calculated relative to the contact angle α1. The results are shown in Table 2. When the contact angle α1 is 65° or less, it is confirmed that the surface of the carbon nanotube layer is hydrophilic. When the contact angle α2 is 25° or more and 65° or less and the percentage {(α2 - α1) / α1} x 100 is 40% or less, the composite porous body is determined to have excellent solvent resistance.

[0116]

[0117] <Measurement of Peel Strength T1> For each sample of composite porous body, the peel strength T1 between the substrate and the carbon nanotube layer was measured by the method described in embodiment 1. The results are shown in Table 3. When the peel strength T1 is 0.4 N / 20 mm or more, it is confirmed that the composite porous body contains a hydrophilic polymer that bonds the substrate and the carbon nanotube layer, and that the adhesion between the substrate and the carbon nanotube layer is improved.

[0118] When the peel strength T1 between the substrate 2 and the carbon nanotube layer 3 is 0.4 N / 20 mm or more, it is confirmed that the composite porous body 1 contains a hydrophilic polymer 5 that bonds the substrate 2 and the carbon nanotube layer 3. Furthermore, in the present disclosure, when the peel strength T1 is 0.4 N / 20 mm or more, it is determined that the adhesion between the substrate and the carbon nanotube layer is improved.

[0119] <Measurement of peel strength T2 after immersion in water> For each sample composite porous body, the peel strength T2 between the substrate and the carbon nanotube layer after immersing the composite porous body in water at 25°C for 3 minutes was measured by the method described in embodiment 1. Based on the measured value, the percentage of peel strength T2 relative to peel strength T1, (T2 / T1) x 100, was calculated. The results are shown in Table 3. If the percentage (T2 / T1) x 100 is 30% or more, it is confirmed that the hydrophilic polymer is crosslinked.

[0120]

[0121] <Peeling Evaluation Test> A peeling evaluation test was performed on each sample composite porous body under the following conditions. <Peeling Evaluation Test Conditions> A sample made of a composite porous body was attached to a stainless steel plate using waterproof double-sided tape. At this time, the waterproof double-sided tape was attached to the main surface of the sample facing the substrate. The sample was immersed in water for 2 minutes and then removed from the water. Within 30 seconds, the tip surface of a 5 mm diameter polytetrafluoroethylene rod was pressed against the surface of the carbon nanotube layer of the sample with a force of 7 gf, and the rod was slid 50 mm along the surface of the carbon nanotube layer. The rod was then removed from the surface of the carbon nanotube layer, and the tip surface of the rod was visually observed to confirm whether or not carbon nanotubes were attached to the rod.

[0122] The results are shown in Table 4.

[0123]

[0124] [Discussion] The composite porous bodies of Samples 1 to 6 correspond to Examples. The composite porous body of Sample 1-1 corresponds to a Comparative Example. It was confirmed that the composite porous bodies of Samples 1 to 6 have improved adhesion between the substrate made of porous polytetrafluoroethylene and the carbon nanotube layer, and that the surface of the carbon nanotube layer is hydrophilic.

[0125] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples 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 examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0126] 1 Composite porous body, 2 Substrate, 2h Holes, 2A First layer, 2B Second layer, 3 Carbon nanotube layer, 5 Hydrophilic polymer, 6 Carbon nanotubes, 7 Test apparatus, 21 First surface, 22 Second surface, 30 Surface, 70 Flask, 70U Upper opening, 71 Chamber, 71D Lower opening.

Claims

1. A composite porous body comprising: a substrate having a first surface; a carbon nanotube layer covering at least a portion of the first surface; and a hydrophilic polymer bonding the substrate and the carbon nanotube layer, wherein the substrate includes a first layer made of a porous polytetrafluoroethylene body having the first surface; and the peel strength T1 between the substrate and the carbon nanotube layer is 0.4 N / 20 mm or more, and the peel strength T1 is measured in accordance with JIS Z 0237:2009 in an atmosphere at a temperature of 25°C and a relative humidity of 50%.

2. The composite porous body according to claim 1, wherein the hydrophilic polymer is crosslinked.

3. The composite porous body according to claim 1 or 2, wherein the percentage (T2 / T1) x 100 of the peel strength T2 between the substrate and the carbon nanotube layer after immersing the composite porous body in water at 25°C for 3 minutes relative to the peel strength T1 is 30% or more, the units of the peel strengths T1 and T2 are N / 20 mm, and the peel strengths T1 and T2 are measured in accordance with JIS Z 0237:2009 in an atmosphere at a temperature of 25°C and a relative humidity of 50%.

4. A composite porous body according to any one of claims 1 to 3, wherein the hydrophilic polymer comprises at least one selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyethylene glycol, polyallylamine, polyethyleneimine, polyvinylpyrrolidone, polystyrene sulfonic acid, polyoxazoline, cellulose acetate, and ethylene-vinyl alcohol copolymer resin.

5. A composite porous body according to any one of claims 1 to 4, wherein the hydrophilic polymer comprises one or both of polyvinyl alcohol and polyethyleneimine.

6. A composite porous body according to any one of claims 1 to 5, wherein the contact angle α2 on the surface of the carbon nanotube layer after immersion in N-methyl-2-pyrrolidone at 25°C for 45 days is 25° or more and 65° or less, and the percentage of the difference α2-α1 between the contact angle α2 and the contact angle α1 on the surface of the carbon nanotube layer before immersion, {(α2-α1) / α1} x 100, is 40% or less.

7. The composite porous body according to any one of claims 1 to 6, wherein no adhesion of carbon nanotubes to a polytetrafluoroethylene rod is confirmed in a peeling evaluation test conducted under the following conditions. Peeling Evaluation Test Conditions: A sample made of the composite porous body is attached to a stainless steel plate using waterproof double-sided tape. At this time, the waterproof double-sided tape is attached to the main surface of the sample facing the substrate. The sample is immersed in water for 2 minutes and then removed from the water. Within 30 seconds, the tip surface of a 5 mm diameter polytetrafluoroethylene rod is pressed against the surface of the carbon nanotube layer of the sample with a force of 7 gf, while the rod is slid 50 mm along the surface of the carbon nanotube layer. The rod is then removed from the surface of the carbon nanotube layer, and the tip surface of the rod is visually observed to confirm whether or not carbon nanotubes are attached to the rod.

8. A method for producing a composite porous body according to any one of claims 1 to 7, comprising the steps of: preparing a substrate including a first layer made of a polytetrafluoroethylene porous body having a first surface; mixing a hydrophilic polymer with a carbon nanotube dispersion to obtain a carbon nanotube mixture; and applying the carbon nanotube mixture to the first surface of the substrate to form a carbon nanotube layer and obtain a composite porous body.

9. A method for producing a composite porous body as described in claim 8, wherein the process for obtaining the composite porous body includes a process for immersing the substrate on which the carbon nanotube layer is formed in a hydrophilic polymer, or a process for applying a hydrophilic polymer to the carbon nanotube layer.

10. A method for producing a composite porous body according to claim 9, wherein the step of obtaining the composite porous body includes a step of crosslinking the hydrophilic polymer after the step of immersing in the hydrophilic polymer or after the step of applying the hydrophilic polymer.

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