Composite porous body and method for producing composite porous body

Abstract

This composite porous body comprises a substrate which is a porous body configured from a fluororesin, a polymer crosslinked body which is fixed to at least a part of a surface of the porous body, and a coating layer which is bonded to the polymer crosslinked body to cover a first surface of the substrate, wherein: the polymer crosslinked body comprises a crosslinked body of a first polymer having an amino group; and the coating layer comprises graphene oxide.

Description

Composite porous body and method for producing composite porous body

[0001] The present disclosure relates to a composite porous body and a method for manufacturing a composite porous body. This application claims priority to Japanese Patent Application No. 2023-115247, filed on July 13, 2023. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] As global environmental problems become more serious, various measures are being implemented, such as the use of renewable energy, with the aim of achieving carbon neutrality. In the chemical industry, for example, many fossil fuels are used as energy sources for distillation processes aimed at refining organic solvents. ２ Emissions are CO ２ It accounts for 10% of total CO emissions. ２ As a measure to reduce emissions, separation membranes that enable separation and purification without heating are expected. Separation membranes for organic solvents require nano-level separation performance. To achieve nano-level separation performance, numerous studies have been conducted on composite separation membranes using graphene-based materials, one of the promising materials, particularly graphene oxide. A composite separation membrane comprises a substrate and a coating layer provided on the substrate. The substrate is porous. The coating layer contains graphene oxide.

[0003] International Publication No. 2019 / 155946 JP 54-017978 JP 53-134871 JP 54-008669 JP 5-301034

[0004] The composite porous body of the present disclosure comprises a substrate that is a porous body made of a fluororesin, a polymer crosslinked body fixed to at least a portion of the surface of the porous body, and a coating layer that is bonded to the polymer crosslinked body and covers a first surface of the substrate, wherein the polymer crosslinked body includes a crosslinked body of a first polymer having an amino group, and the coating layer includes graphene oxide.

[0005] Fig. 1 is a schematic diagram of a sheet-shaped composite porous body according to embodiment 1. Fig. 2 is a plan view schematically showing nodes and fibrils of a substrate provided in the composite porous body of Fig. 1. Fig. 3 is an explanatory view schematically showing the structure of the composite porous body of Fig. 1. Fig. 4 is a plan view schematically showing solid particles provided in the composite porous body of Fig. 1. Fig. 5 is a schematic diagram of a cylindrical composite porous body according to embodiment 2.

[0006] [Problem to be Solved by the Present Disclosure] Although much research has been conducted on composite separation membranes, they have not yet been put to practical use, particularly for the separation of organic solvents. This is primarily due to issues related to the substrate. When the separation target includes organic solvents, the entire composite separation membrane must be solvent-resistant. Graphene oxide itself is solvent-resistant. However, the solvent resistance of the substrate is insufficient. As a result, the substrate itself undergoes structural changes such as swelling. As a result, the long-term stability of the composite separation membrane cannot be ensured. On the other hand, when a solvent-resistant material such as polyethylene, polypropylene, or polytetrafluoroethylene is used as the substrate, the substrate itself is chemically stable. However, because of this chemical stability, it is difficult to form chemical bonds with graphene oxide, especially stable covalent bonds. This results in weak adhesion, making reliable composite formation difficult. As a result, research reports often focus on separation performance itself without considering stability, and most performance evaluations are based on short-term evaluations. Patent Document 1 discloses an example of an attempt to improve adhesion by treating the substrate with silane coupling agents. However, silane coupling causes hydrolysis, which limits its application to treating solutions containing water in organic solvents. A new composite separation membrane with high solvent resistance and long-term stability is desired, which can withstand use in treating organic solvents.

[0007] An object of the present disclosure is to provide a composite porous body in which a substrate and a coating layer containing graphene oxide are stable for a long period of time in the presence of a solvent.

[0008] [Effects of the Present Disclosure] In the composite porous body of the present disclosure, the substrate and the coating layer containing graphene oxide have long-term stability in the presence of a solvent.

[0009] Description of Embodiments of the Present Disclosure Research has been conducted on composite porous bodies having a coating layer containing graphene oxide. When composite porous bodies are used in industrial materials and equipment such as fluid separation membrane modules, particularly when used to separate solvents and various chemicals, excellent chemical resistance and heat resistance are required for the porous body as a substrate and for the contact area between the substrate and the coating layer containing graphene oxide. Therefore, the porous substrate is made of a fluororesin, which has excellent chemical resistance. In particular, polytetrafluoroethylene (PTFE) has outstanding chemical resistance and heat resistance, making it ideal for the substrate.

[0010] To achieve thermally and chemically stable composite formation between a graphene oxide-containing coating layer and a substrate, it is important to form chemical bonds, particularly stable covalent bonds, between the substrate and graphene oxide. Graphene oxide has a thin, planar molecular structure. It is aligned parallel to the substrate surface and stacked along its thickness to form a layered coating layer. Therefore, when chemically reacting the first graphene oxide layer, which comes into direct contact with the substrate, with the substrate surface, it is desirable to utilize the epoxy groups present within the plane of the planar graphene oxide molecules. Therefore, it is desirable for the substrate surface to contain functional groups that readily react with epoxy groups. However, fluororesins, which are chemically stable and desirable as substrates, do not contain functional groups, and functional groups cannot be easily introduced. PTFE, in particular, is unreactive with most chemicals, making the introduction of functional groups extremely difficult.

[0011] Patent Literature 2 discloses a method for impregnating a porous PTFE body with various water-soluble hydrophilic polymers and then crosslinking the hydrophilic polymers themselves to make them water-insoluble. The hydrophilic polymers are placed around the fibers and nodes that make up the porous body, and then crosslinked to immobilize the hydrophilic polymers, allowing for the introduction of functional groups. Therefore, the inventors initially believed that the technology described in Patent Literature 2 could be used to create strong chemical bonds and achieve stable composite formation by introducing, for example, amino groups, which are highly reactive with the epoxy groups in graphene oxide.

[0012] However, even with the technology of Patent Document 2, there were important factors to consider in obtaining a suitable substrate for a separation membrane. To ensure fluid permeability, it was necessary to crosslink and fix a very small amount of hydrophilic polymer while maintaining the original microstructure of the PTFE membrane, such as the number and size of pores. The inventors discovered that there was an important factor for this. Specifically, among the many hydrophilic polymers available, they found the need to identify the affinity with the substrate in water, i.e., the type of chemical structure and molecular weight of the hydrophilic polymer, and further control the concentration conditions in the crosslinking reaction. According to their investigations, the crosslinking process involves three steps: (1) a linear hydrophilic polymer dissolved in water is adsorbed onto the PTFE microfibers, (2) a crosslinking agent dissolved in water diffuses near the hydrophilic polymer, and (3) a crosslinking reaction occurs, if necessary, in the presence of a catalyst, to produce a crosslinked hydrophilic polymer surrounding the PTFE microfibers. The inventors conducted extensive research into the fixation and conjugation of a crosslinked hydrophilic polymer containing amino groups to the microstructure of a PTFE membrane. As a result, the present inventors have discovered a new technical finding that there are appropriate concentration conditions depending on the molecular structure and molecular weight of the hydrophilic polymer containing an amino group.

[0013] Patent Document 2 discloses that crosslinked materials can be crosslinked and fixed to PTFE membranes, but does not disclose a technique for achieving uniformity and optimal performance in separation membranes. To achieve separation membrane performance, it is necessary to maintain the original PTFE membrane microstructure with numerous pores. However, excessive fixation results in poor flow rate and practical problems. Furthermore, if aggregates remain on the membrane surface, the layered structure of the coating layer is disrupted, and the disrupted portions become defects, often affecting separation performance.

[0014] In response to this, the present inventors discovered that among hydrophilic polymers containing amino groups, (1) those with -C-C- bonds in the main chain and amino groups in the side chains, and (2) those with -C-C-N- bonds in the main chain, there are molecular structures, molecular weights, and concentrations of polymers that can produce appropriate separation membranes. That is, polymers that have amino groups in the side chains but have units of -C-C- bonds consisting only of carbon atoms and no N atoms in the main chain are more likely to adsorb to PTFE membranes due to van der Waals forces between carbon atoms and can be crosslinked at lower concentrations. On the other hand, they found that reactions within the polymer itself tend to proceed, resulting in reactions between polymers containing amino groups on the membrane surface, which can easily lead to the formation of aggregates. After extensive investigations, they found that the above problem can be solved by setting the number-average molecular weight of the polymer to between 1,000 and 100,000 and the concentration of the polymer to between 0.05% by mass and 5% by mass. In other words, they discovered that by fixing a small amount of hydrophilic polymer crosslinked material to the PTFE microfibers, the microstructure has sufficient pores that are the same as those of the original PTFE membrane, and the filtration capacity is also maintained.

[0015] On the other hand, polyethyleneimine (PEI), which contains nitrogen atoms in a linear chain, such as a -C-C-N- bond, is hydrophilic due to the N atoms in its main chain, and therefore does not adequately adsorb to hydrophobic PTFE microfibers at low concentrations. Therefore, a high concentration and high polymer are required. However, in this case, a large amount of crosslinked polymer surrounds the PTFE microfibers due to the chain reaction of crosslinking during crosslinking. This significantly reduces the porosity, resulting in a membrane with lower filtration capacity than the original PTFE membrane. Furthermore, at high concentrations and high polymers, the polymer aqueous solution is difficult to impregnate into the porous membrane, and the solution crosslinks independently on the surface of the porous membrane, resulting in the formation of aggregates. However, the present inventors have discovered that, even if a N atom is contained in the main chain, a small amount of crosslinked polymer can be obtained with an amine-based hydrophilic polymer having a network structure by appropriately selecting a combination of conditions within the range of a polymer number-average molecular weight of 300 to 70,000 and a polymer concentration of 0.1% by mass to 5% by mass, resulting in a microstructure with sufficient porosity comparable to the original PTFE membrane, while maintaining filtration capacity.

[0016] The present inventors have conducted extensive research into the relationship between the molecular structure and molecular weight of a hydrophilic polymer having amino groups highly reactive with graphene oxide, the concentration conditions for crosslinking and immobilizing the polymer to a PTFE membrane, and the quality of the composite porous body. As a result, they have found that a specific polymer can be easily adsorbed into a porous body made of a fluororesin even at a low concentration, and can be immobilized by crosslinking without blocking the pores of the composite porous body. First, embodiments of the present disclosure will be described.

[0017] (1) A composite porous body according to one aspect of the present disclosure includes: a substrate that is a porous body made of a fluororesin; a crosslinked polymer immobilized on at least a portion of the surface of the porous body; and a coating layer that is bonded to the crosslinked polymer and thereby covers a first surface of the substrate, wherein the crosslinked polymer includes a crosslinked polymer of a first polymer having an amino group, and the coating layer includes graphene oxide. The first surface of the substrate is one of two outermost surfaces that face each other in a direction along the thickness of the substrate. In this specification, an amino group is defined as "-NH ２ " includes not only " but also substituted amino groups such as "-NHR" or "-NRR'" in which hydrogen atoms of primary or secondary amines are replaced. "R" is a hydrocarbon group.

[0018] The coating layer of the composite porous body is resistant to peeling. The reasons for this are as follows: Amino groups easily react with graphene oxide to form bonds. Therefore, the first polymer has excellent adhesion to the coating layer. The first polymer has a three-dimensional network structure due to crosslinking, which stably integrates it with the substrate, thereby enabling adhesion between the coating layer and the substrate to be achieved. Therefore, the composite porous body has long-term stability between the substrate and the coating layer in the presence of a solvent. Furthermore, the coating layer of the composite porous body is resistant to peeling even when subjected to processing such as bending.

[0019] The composite porous body has excellent flexibility because the substrate is a flexible porous body made of a fluororesin.

[0020] The composite porous body can remove nano-order impurities from the raw liquid, i.e., the fluid to be filtered. The coating layer includes graphene oxide. In this coating layer, the fluid passes through the gaps between adjacent graphene oxides or the gaps present as a layered stack. Because the gaps between adjacent graphene oxides are very small, the coating layer removes nano-order impurities from the fluid. The fluid may be a mixture of a liquid or gas and a solid, a mixture of gases with different molecular weights or molecular sizes, or a liquid in which a solid or liquid substance is dissolved.

[0021] The composite porous body has excellent heat resistance and chemical resistance for the following reasons: the substrate is a porous body made of a fluororesin, which has excellent heat resistance and chemical resistance, and the coating layer contains graphene oxide, which has excellent heat resistance and chemical resistance.

[0022] (2) In the composite porous body of (1), the first polymer contains a —C—C— bond in the main chain and —NH ２ The polymer may be a polymer containing:

[0023] The first polymer has a high adsorption property to a porous body made of a fluororesin even at a low concentration, and therefore the first polymer can easily form an adsorbed state and be fixed by crosslinking even at a low concentration, and since a small amount of crosslinked polymer is formed, the first polymer is unlikely to clog the pores of the porous body.

[0024] (3) In the composite porous body of (2), the first polymer may be polyallylamine.

[0025] Polyallylamine has excellent adhesion to graphene oxide.

[0026] (4) In the composite porous body of (1) above, the first polymer may be a polymer having a network structure containing —C—C—N— bonds in the main chain.

[0027] A network structure containing -C-C-N- bonds in the main chain is a structure in which easily adsorbed C atoms are arranged two-dimensionally. Therefore, the first polymer has high adsorption properties to a porous body made of fluororesin even at low concentrations. Therefore, the first polymer can easily form an adsorbed state even at low concentrations and be fixed by crosslinking. Therefore, the first polymer is less likely to clog the pores of the porous body. A network structure refers to a structure branched at multiple locations.

[0028] (5) In the composite porous body of (4), the first polymer may have a primary amine and a secondary amine.

[0029] The first polymer having a primary amine has particularly excellent adhesion to graphene oxide.

[0030] (6) In the composite porous body of (4) or (5), the first polymer may be polyethyleneimine or polydopamine.

[0031] Polyethyleneimine or polydopamine has excellent adhesion to graphene oxide.

[0032] (7) In any one of the composite porous bodies (1) to (6), the crosslinked polymer may include a crosslinked second polymer having at least one functional group selected from the group consisting of a hydroxy group and an ester group.

[0033] The second polymer contains a -C-C- bond in its main chain, and during the manufacturing process, it easily forms an adsorbed state on the hydrophobic fluororesin or PTFE porous body, and by crosslinking, the porous body can be made hydrophilic. When hydrophilized, the presence of hydrophilic groups on the surface of the porous body makes it easier for the polymer containing amino groups to form an adsorbed state. Therefore, it can be immobilized by crosslinking even at lower concentrations.

[0034] (8) In the composite porous body of (7), the second polymer may be polyvinyl alcohol.

[0035] Polyvinyl alcohol contains -C-C- bonds in its main chain, and during the manufacturing process, it easily forms an adsorbed state on hydrophobic fluororesin and PTFE porous bodies, and crosslinking can make the porous bodies hydrophilic. When hydrophilized, hydrophilic groups, i.e., hydroxyl groups and ester groups, are present on the surface of the porous body, making it easier for polymers containing N in the main chain, such as polyethyleneimine, to form an adsorbed state. Therefore, polyethyleneimine can be immobilized by crosslinking even at low concentrations.

[0036] (9) In the composite porous body according to any one of (1) to (8), the fluororesin may be polytetrafluoroethylene.

[0037] The flexibility of the composite porous body is improved because the substrate is made of flexible polytetrafluoroethylene.The heat resistance and chemical resistance of the composite porous body are improved because the substrate is made of polytetrafluoroethylene, which has excellent heat resistance and chemical resistance.

[0038] (10) The composite porous body according to any one of (1) to (9) above may further comprise a plurality of solid particles held inside the porous body on the surface portion of the substrate.

[0039] The solid particles can reinforce the substrate, and therefore the substrate can withstand the filtration pressure more easily by including the solid particles. Therefore, the composite porous body of (10) above has better pressure resistance.

[0040] (11) In the composite porous body of (10), the solid particles may be made of one material selected from the group consisting of fluororesins and ceramic materials.

[0041] The composite porous body of (11) above is superior in pressure resistance.

[0042] (12) In the composite porous body of (10) or (11), the solid particles may have an average particle size of 10 nm or more and 500 nm or less.

[0043] If the average particle size of the solid particles is 10 nm or more, they can easily reinforce the substrate. If the average particle size of the solid particles is 500 nm or less, they can easily be disposed inside the porous body and are less likely to clog the pores of the porous body.

[0044] (13) In the composite porous body according to any one of (10) to (12), at least a part of the surface of the solid particles may be covered with the crosslinked polymer.

[0045] The crosslinked first polymer contained in the crosslinked polymer exhibits hydrophilicity because it contains an amino group. If solid particles covered with a crosslinked polymer that reacts with the coating layer are held in a porous body, chemical bonds are formed between the solid particles and the coating layer, making it easier to form a more stable coating layer.

[0046] (14) A method for producing a composite porous body according to one embodiment of the present disclosure includes the steps of: preparing a substrate made of a porous body made of a fluororesin; impregnating the substrate with a first liquid containing a first polymer having an amino group, and immobilizing the first polymer on at least a portion of a surface of the porous body by adsorbing and crosslinking the first polymer on the porous body; and applying a second liquid containing graphene oxide to at least a portion of the surface of the first polymer immobilized on the substrate, and reacting the first polymer with the graphene oxide.

[0047] The method for producing a composite porous body according to (14) above can produce a composite porous body that is chemically stable and has a coating layer that is difficult to peel off.

[0048] (15) The method for producing a composite porous body according to (14) above may further include, before the step of fixing the first polymer, a step of impregnating the substrate with a third liquid containing a second polymer having a hydroxy group, and causing the second polymer to be adsorbed and crosslinked onto the porous body, thereby fixing the second polymer to at least a portion of the surface of the porous body.

[0049] In the method for producing a composite porous body described in (15), a second polymer containing a hydroxy group, which is more likely to adsorb an amine that can form a chemically stable bond with graphene oxide, is crosslinked and immobilized to a hydrophobic fluororesin in advance, thereby enabling the composite porous body, whose coating layer is less likely to peel off, to be produced more stably.

[0050] <<Details of the Embodiments of the Present Disclosure>> Specific examples of the composite porous body and the method for manufacturing the composite porous body of the present disclosure will be described below with reference to the drawings. Hereinafter, the same reference numerals in the drawings indicate the same or corresponding parts. The sizes of the components shown in each drawing are expressed for the purpose of clarifying the explanation and do not necessarily represent the actual dimensions.

[0051] Embodiment 1 Composite Porous Body A composite porous body 1 of Embodiment 1 will be described with reference to FIGS. 1 to 4. The composite porous body 1 of Embodiment 1 includes a substrate 2, a crosslinked polymer 3, and a coating layer 4. The composite porous body 1 has a sheet shape, for example, as shown in FIG. 1. The substrate 2 is a porous body 20 made of a fluororesin. As shown in FIGS. 1 and 3, the substrate 2 has a first surface 21 and a second surface 22. The first surface 21 and the second surface 22 are outermost surfaces facing each other in the thickness direction of the substrate 2. As shown in FIG. 2, the crosslinked polymer 3 is fixed to the surface of the porous body 20 so as to cover at least a portion of the surface of the porous body 20. The coating layer 4 is bonded to the crosslinked polymer 3, thereby covering the first surface 21 of the substrate 2, as shown in FIG. 1. One of the features of the composite porous body 1 of this embodiment is that the crosslinked polymer 3 includes a crosslinked polymer 3a of a specific first polymer. The composite porous body 1 of the first embodiment is suitable for applications such as separation of solutes in a solvent, removal of water in a solvent, and treatment of water containing a solvent.

[0052] [Substrate] The substrate 2 is a porous body 20. The substrate 2 of this embodiment has a sheet-like shape. As shown in FIG. 2, the porous body 20 of this embodiment has a plurality of nodes 25 and a plurality of fibrils 26. For ease of explanation, the nodes 25 and fibrils 26 in FIG. 2 are hatched. This also applies to FIG. 4. The nodes 25 and fibrils 26 exist to form a three-dimensional network structure. The nodes 25 and fibrils 26 exist in the direction along the thickness of the substrate 2. The nodes 25 and fibrils 26 are also present on the first surface 21. The plurality of nodes 25 are dispersedly arranged. The plurality of nodes 25 are scattered in an island-like manner in three-dimensional space. Each fibril 26 connects the nodes 25 together. Each fibril 26 is configured in a linear shape. The porous body 20 has a plurality of pores 2h as shown in FIG. 3. 3 is a cross-sectional view, each pore 2h in the porous body 20 appears to be independent, but each pore 2h is connected to other pores 2h. The pores 2h are provided between the nodes 25 and fibrils 26 shown in FIG.

[0053] The porous body 20 is made of a fluororesin. Fluororesin has excellent heat resistance and chemical resistance. Therefore, the heat resistance and chemical resistance of the composite porous body 1 are improved. Furthermore, since fluororesin has excellent flexibility, the substrate 2 also has excellent flexibility. An example of the fluororesin is polytetrafluoroethylene (PTFE). Polytetrafluoroethylene is particularly excellent in heat resistance, chemical resistance, and flexibility.

[0054] The composite porous body 1 may further include solid particles 6, as shown in FIG. 4. For ease of explanation, the solid particles 6 are hatched in FIG. 4. The solid particles 6 can reinforce the substrate 2. By including the solid particles 6, the substrate 2 is more likely to withstand filtration pressure. Therefore, the composite porous body 1 has superior pressure resistance. The solid particles 6 are held inside the porous body 20 including the surface portion 28 of the substrate 2 shown in FIG. 3. The surface portion 28 refers to a region extending from the first surface 21 to the second surface 22 of the substrate 2 up to 1 μm, and may further extend to 5 μm. The solid particles 6 are held inside the porous body 20 in the surface portion 28 covered by the coating layer 4.

[0055] The solid particles 6 have an average particle size of, for example, 10 nm or more and 500 nm or less. If the average particle size of the solid particles 6 is 10 nm or more, the substrate 2 is easily reinforced. If the average particle size of the solid particles 6 is 500 nm or less, the pores 2h of the porous body 20 are less likely to be blocked. The average particle size of the solid particles 6 may further be 100 nm or more and 400 nm or less, particularly 150 nm or more and 250 nm or less.

[0056] The average particle size of the solid particles 6 is determined as follows. A cross section of the substrate 2 is taken along the thickness of the substrate 2. The cross section of the substrate 2 is obtained by cutting the substrate 2 using a focused ion beam (FIB). An SEM image of the cross section is obtained using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX). The magnification of the SEM image is 10,000 times. The size of the SEM image is 9 μm × 12 μm. The equivalent circle diameter of the cross section of each solid particle 6 in the SEM image is determined, and the average of the equivalent circle diameters of all the solid particles 6 is determined. The equivalent circle diameter is the diameter of a perfect circle having the same size as the cross-sectional area of ​​the solid particle 6. In this specification, this average equivalent circle diameter is considered to be the average particle size of the solid particles 6.

[0057] The solid particles 6 are made of, for example, one material selected from the group consisting of fluororesin and ceramic-based materials. Examples of the fluororesin include PTFE and tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA). Examples of the ceramic-based material include alumina. The plurality of solid particles 6 may include only one type of solid particles 6, or two types of solid particles 6, of solid particles 6 made of fluororesin and solid particles 6 made of ceramic-based materials.

[0058] At least a portion of the surface of the solid particle 6 may be covered with the crosslinked polymer 3. Only a portion of the surface of the solid particle 6 may be covered with the crosslinked polymer 3, or the entire surface of the solid particle 6 may be covered with the crosslinked polymer 3. If the solid particle 6 covered with the crosslinked polymer 3 is held inside the porous body 20, which is covered with the coating layer 4 in the surface portion 28, the coating layer 4 also forms a chemical bond with the solid particle 6, thereby further improving pressure resistance. The solid particle 6 covered with the crosslinked polymer 3 may be located not only inside the porous body 20, but also in a portion between the porous body 20 and the coating layer 4, i.e., at least a portion between the first surface 21 of the substrate 2 and the coating layer 4. The solid particle 6 covered with the crosslinked polymer 3 may be located only in a portion of the region between the first surface 21 and the coating layer 4, or in the entire region between the first surface 21 and the coating layer 4. The crosslinked polymer 3 covering at least a portion of the surface of the solid particle 6 is directly bonded to the crosslinked polymer 3 and the coating layer 4 fixed on the surface of the porous body 20. The crosslinked polymer 3 covering at least a part of the surface of the solid particle 6 may be continuously connected to the crosslinked polymer 3 fixed on the surface of the porous body 20 .

[0059] The average thickness of the substrate 2 is, for example, 5 μm or more and 500 μm or less. A composite porous body 1 having a substrate 2 with an average thickness of 5 μm or more has excellent strength. A composite porous body 1 having a substrate 2 with an average thickness of 500 μm or less has excellent flexibility. The composite porous body 1 may be required to have resistance to bending. For example, the composite porous body 1 is rolled into a cylindrical shape to form a filter for a module of a purification device. In a cylindrical module, the coating layer 4 is arranged proximal to the surface that comes into contact with the raw water. The composite porous body 1, which has excellent flexibility, is suitable for a filter for a module of a purification device.

[0060] The average thickness of the substrate 2 is determined by SEM-EDX. The magnification of the SEM image is 200x. The size of the SEM image is 450 μm × 600 μm. Because the thicknesses of the crosslinked polymer 3 and the coating layer 4 are much thinner than the thickness of the substrate 2, the thicknesses of the crosslinked polymer 3 and the coating layer 4 are ignored when determining the thickness of the substrate 2. In other words, the thickness of the composite porous body 1 is considered to be the thickness of the substrate 2. Five or more line analyses at different positions are performed. The line analysis determines the distance between the surface 40 of the coating layer 4 and the second surface 22 of the substrate 2. This distance is the thickness of the composite porous body 1, i.e., the thickness of the substrate 2. The average thickness of the substrate 2 is the average of the above distances at five or more different points.

[0061] The average pore size on the first surface 21 of the substrate 2 is, for example, 0.01 μm or more and 2 μm or less. A composite porous body 1 including a substrate 2 having an average pore size of 0.01 μm or more has excellent liquid permeability. Liquid permeability refers to the ease with which a fluid passes through. A composite porous body 1 with excellent liquid permeability has excellent filtration performance. In other words, a composite porous body 1 with high liquid permeability can shorten the filtration time. A substrate 2 having an average pore size of 2 μm or less has excellent strength. The average pore size may be 0.05 μm or more, 0.1 μm or more, or 0.15 μm or more. The average pore size may be 1.5 μm or less, 1.45 μm or less, or 1.4 μm or less. The average pore size of the substrate 2 may be in the range of, for example, 0.05 μm or more and 1.5 μm or less, 0.1 μm or more and 1.45 μm or less, or 0.15 μm or more and 1.4 μm or less.

[0062] A plurality of pores 2h are formed on the first surface 21. When a coating layer 4 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 specification, the average pore diameter of the first surface 21 is determined from an SEM image of a cross section cut along the thickness of the substrate 2. The magnification of the SEM image is 5000x. The size of the SEM image is 18 μm × 24 μm. The SEM image is binarized, and each pore 2h in the SEM image is extracted. The image processing software "ImageJ" is used for the binarization process. The threshold value for the binarization process is 127. The circle-equivalent diameter of each pore 2h is calculated, and the average of the circle-equivalent diameters of all pores 2h is calculated. The circle-equivalent diameter is the diameter of a perfect circle with the same area as the pore 2h. In this specification, this average circle-equivalent diameter is considered to be the average pore diameter of the pores 2h on the first surface 21.

[0063] [Crosslinked Polymer] The crosslinked polymer 3 includes a crosslinked polymer 3a of a first polymer. The crosslinked polymer 3a of the first polymer is exaggerated in FIG. 3 . The crosslinked polymer 3 may further include a crosslinked polymer 3b of a second polymer. It is not essential that the crosslinked polymer 3 include a crosslinked polymer 3b of the second polymer. The crosslinked polymer 3b of the second polymer is also exaggerated in FIG. 3 .

[0064] The crosslinked polymer 3 is formed on at least a portion of the surface of the porous body 20. "At least a portion of the surface of the porous body 20" may refer to a portion or the entire surface of the porous body 20. The surface of the porous body 20 includes the first surface 21 shown in FIGS. 1 and 3 in addition to the surfaces of the nodes 25 and fibrils 26 shown in FIG. 2. The crosslinked polymer 3 in this example is a network layer formed on the surface of the porous body 20. The crosslinked polymer 3 in this example covers at least a portion of the surfaces of the nodes 25 and fibrils 26 present on the first surface 21, as well as at least a portion of the surfaces of the nodes 25 and fibrils 26 present between the first surface 21 and the second surface 22. Note that the crosslinked polymer 3 is sufficient as long as it covers the surfaces of the nodes 25 and fibrils 26 present on the first surface 21, and may also cover the surfaces of the nodes 25 and fibrils 26 present between the first surface 21 and the second surface 22.

[0065] By attaching the crosslinked bodies 3 a of the first polymer and the crosslinked bodies 3 b of the second polymer to the surfaces of the nodes 25 and the fibrils 26, water, which is a solvent for a second liquid containing graphene oxide 5 (described later) during the manufacturing process, can easily penetrate into the substrate 2, and when the second liquid is applied, the graphene oxide 5 can easily come into contact with the surfaces of the nodes 25 and fibrils 26 present on the first surface 21. The coating layer 4 containing graphene oxide 5 becomes dense, and excellent filtration properties can be achieved.

[0066] Because the layers of the crosslinked bodies 3a of the first polymer and the crosslinked bodies 3b of the second polymer are extremely thin, the presence of the crosslinked bodies 3a of the first polymer and the crosslinked bodies 3b of the second polymer makes it difficult for the pore diameter of the pores 2h to become small. In this embodiment, a mesh-like layer made of the crosslinked bodies 3b of the second polymer is present in a position of the crosslinked polymer 3 close to the surface of the porous body 20. A mesh-like layer made of the crosslinked bodies 3a of the first polymer is present in a position of the crosslinked polymer 3 far from the surface of the porous body 20, i.e., close to the coating layer 4.

[0067] The crosslinked body 3a of the first polymer has an amino group. Therefore, the crosslinked body 3a of the first polymer easily bonds to the graphene oxide 5. Therefore, the crosslinked body 3a of the first polymer has excellent adhesion to the coating layer 4. The coating layer 4 of the composite porous body 1 is unlikely to peel off from the substrate 2 even when the composite porous body 1 is subjected to processing such as bending. The composite porous body 1 is suitable for use as a filter in a module of a purification device. The presence of amines can be confirmed by XPS (X-ray Photoelectron Spectroscopy).

[0068] The first polymer contains a —C—C— bond in the main chain and —NH ２ The first polymer may include, for example, polyallylamine (PAA). PAA easily clings to the porous body 20 and has excellent adhesion to the graphene oxide 5. Nitrogen atoms derived from PAA can be confirmed by XPS. The first polymer includes a -C-C- bond in the main chain and an -NH ２When the first polymer contains the polymer, the number average molecular weight of the first polymer is, for example, 1,000 or more and 100,000 or less. A first polymer having a number average molecular weight of 1,000 or more easily clings to the porous body 20. A first polymer having a number average molecular weight of 100,000 or less can suppress a decrease in the pore size of the porous body 20. Therefore, a composite porous body 1 in which the number average molecular weight of the first polymer is 100,000 or less has excellent liquid permeability.

[0069] Alternatively, the first polymer may have a mesh-like network structure containing -C-C-N- bonds in the main chain. The first polymer is, for example, polyethyleneimine (PEI). PEI easily clings to the porous body 20 and has excellent adhesion to the graphene oxide 5. Nitrogen atoms derived from PEI can be confirmed by XPS. When the first polymer has a mesh-like network structure containing -C-C-N- bonds in the main chain, the number-average molecular weight of the first polymer is, for example, 300 or more and 70,000 or less. A first polymer having a number-average molecular weight of 300 or more easily clings to the porous body 20. A first polymer having a number-average molecular weight of 70,000 or less can suppress a decrease in the pore size of the porous body 20. Therefore, a composite porous body 1 in which the number-average molecular weight of the first polymer is 70,000 or less has excellent liquid permeability.

[0070] The first polymer may contain a primary amine and a secondary amine. A crosslinked body 3 a of the first polymer containing a primary amine has excellent adhesion to graphene oxide 5. The first polymer may further contain a tertiary amine.

[0071] The second polymer is a polymer containing at least one functional group, a hydroxy group or an ester group, in its side chain and a methylene chain in its main chain. The methylene chain in the main chain of this second polymer is hydrophobic. Therefore, the second polymer easily clings to the hydrophobic porous body 20 and is easily crosslinked and immobilized. The crosslinked form 3b of the second polymer has a highly hydrophilic hydroxy group in its side chain, which forms a hydrogen bond with the amino group in the first polymer, resulting in excellent adhesion to the crosslinked form 3a of the first polymer. The presence of the hydroxy group and the ester group can be confirmed by FTIR (Fourier Transform Infrared Spectroscopy).

[0072] The second polymer is, for example, polyvinyl alcohol (PVA). PVA easily forms an adsorbed state in the porous body 20 during the manufacturing process, and by crosslinking, the porous body 20 can be made hydrophilic. When the porous body 20 is made hydrophilic, the first polymer is more likely to form an adsorbed state because a hydrophilic polymer is present on the surface of the porous body 20. Therefore, PVA can be fixed by crosslinking even at low concentrations. PVA can be confirmed by FTIR.

[0073] [Coating Layer] The coating layer 4 is a layer that faces the fluid to be filtered, such as raw water, by the composite porous body 1. The coating layer 4 is bonded to the crosslinked polymer 3 to cover the first surface 21 of the substrate 2. In the present disclosure, "the coating layer 4 covers the first surface 21 of the substrate 2" means either that the coating layer 4 covers the entire first surface 21 of the substrate 2 or that the coating layer 4 covers a portion of the first surface 21 of the substrate 2, as long as the effects of the present disclosure are achieved. When the above-mentioned solid particles 6 are disposed only in a partial region between the first surface 21 and the coating layer 4, the coating layer 4 includes a region directly bonded to the crosslinked polymer 3 fixed on the surface of the porous body 20 and a region directly bonded to the crosslinked polymer 3 fixed on the surface of the solid particles 6. When the above-mentioned solid particles 6 are disposed in the entire region between the first surface 21 and the coating layer 4, the coating layer 4 is directly bonded to the crosslinked polymer 3 fixed on the surface of the solid particles 6. In the region where the coating layer 4 and the crosslinked polymer 3 fixed to the surface of the solid particle 6 are directly bonded, the coating layer 4 and the crosslinked polymer 3 fixed to the surface of the porous body 20 are indirectly bonded by the crosslinked polymer 3 covering the solid particle 6.

[0074] The coating layer 4 includes graphene oxide 5. The graphene oxide 5 has epoxy groups and carboxyl groups. The epoxy groups or carboxyl groups strongly bond with amino groups. Therefore, the graphene oxide 5 has excellent adhesion to the crosslinked body 3a of the first polymer. As shown in FIG. 3 , the coating layer 4 may include a stack of multiple graphene oxides 5. Each graphene oxide 5 has a flake shape. FIG. 3 illustrates only a portion of the graphene oxides 5. In the coating layer 4 including a stack of multiple graphene oxides 5, fluid passes through the gaps between adjacent graphene oxides 5. The coating layer 4 may include an organic material that bonds the graphene oxides 5 together. The organic material is disposed between the stacked graphene oxides 5. The interlayer distance of the graphene oxides 5 can be changed by varying the thickness of the organic material. The organic material is crosslinked. The organic material is, for example, ethylenediamine. Unlike the example shown in FIG. 3 , the coating layer 4 may have a single-layer structure of graphene oxide 5, although this is not shown. In this case, a plurality of thin graphene oxide 5 flakes are arranged on the first surface 21 to form one layer.

[0075] [Method for manufacturing a composite porous body] The method for manufacturing a composite porous body of embodiment 1 includes the following steps. The method for manufacturing a composite porous body of embodiment 1 can manufacture the composite porous body 1 of embodiment 1. In step A, a substrate 2 made of a porous body 20 made of a fluororesin is prepared. In step B, a crosslinked polymer 3 is formed on at least a portion of the surface of the porous body 20. In step C, a coating layer 4 including graphene oxide 5 is formed on the crosslinked polymer 3.

[0076] [Step A] The substrate 2 is the same as the substrate 2 provided in the composite porous body 1 described above. The substrate 2 can be obtained, for example, by stretching a rolled material made of a fluororesin. The rolled material can be produced by rolling an extruded material. The extruded material can be produced by extrusion molding a resin paste. The resin paste can be produced by mixing a fluororesin powder with an auxiliary agent. The auxiliary agent is, for example, a lubricant. The stretching process may include, for example, a first stretching process and a second stretching process. The first stretching process stretches the rolled material along the rolling direction to produce a first stretched material. The second stretching process stretches the first stretched material in a direction perpendicular to the rolling direction to produce a second stretched material.

[0077] The substrate 2 having the solid particles 6 held inside the porous body 20 can be obtained as follows. When the solid particles 6 are made of a fluororesin, the solid particles 6 are applied to the porous body 20, and the applied porous body 20 is heated. The application of the solid particles 6 to the porous body 20 may be performed after step B and before step C. When the solid particles 6 are made of a ceramic material, a mixture containing the solid particles 6 and an organic binder is applied to the porous body 20, and the applied porous body 20 is heated. The organic binder is a first polymer such as polyethyleneimine.

[0078] [Step B] In step B, a crosslinked polymer 3 having both crosslinked bodies 3b of the second polymer and crosslinked bodies 3a of the first polymer may be formed on the surface of the porous body 20, or a crosslinked polymer 3 having crosslinked bodies 3a of the first polymer without crosslinked bodies 3b of the second polymer may be formed. When forming a crosslinked polymer 3 having both crosslinked bodies 3b of the second polymer and crosslinked bodies 3a of the first polymer, the crosslinked bodies 3b of the second polymer and the crosslinked bodies 3a of the first polymer are formed in that order on the surface of the porous body 20. When forming a crosslinked polymer 3 having crosslinked bodies 3a of the first polymer without crosslinked bodies 3b of the second polymer, the crosslinked bodies 3a of the first polymer are formed on the surface of the porous body 20 without forming crosslinked bodies 3b of the second polymer.

[0079] The procedure for sequentially forming the crosslinked bodies 3b of the second polymer and the crosslinked bodies 3a of the first polymer on the surface of the porous body 20 is, for example, as follows: The porous body 20 is impregnated with a hydrophilic organic solvent such as isopropyl alcohol (IPA). Next, the porous body 20 impregnated with the hydrophilic organic solvent is impregnated with a third liquid containing the second polymer, thereby adsorbing the second polymer into the porous body 20. Next, the porous body 20 with the adsorbed second polymer is immersed in a crosslinking liquid to crosslink the second polymer. When the porous body 20 is impregnated with the third liquid, the hydrophilic organic solvent adhering to the surface of the porous body 20 is replaced with the third liquid. Therefore, substantially no hydrophilic organic solvent remains between the surface of the porous body 20 and the crosslinked bodies 3b of the second polymer. Next, the porous body 20 with the crosslinked bodies 3b of the second polymer is impregnated with a first liquid containing the first polymer, thereby adsorbing the first polymer onto the crosslinked bodies 3b of the second polymer. Next, the porous body 20 with the first polymer adsorbed onto the crosslinked bodies 3b of the second polymer is immersed in a crosslinking liquid to crosslink the first polymer. The procedure for forming crosslinked bodies 3a of the first polymer on the surface of the porous body 20 without forming crosslinked bodies 3b of the second polymer is as follows: After impregnating the porous body 20 with the hydrophilic organic solvent, the porous body 20 is impregnated with the first liquid without impregnating with the third liquid, and the first polymer is adsorbed into the porous body 20. The porous body 20 with the adsorbed first polymer is immersed in a crosslinking liquid to crosslink the first polymer. When the substrate 2 is impregnated with the first liquid, the hydrophilic organic solvent adhering to the surface of the porous body 20 is replaced with the first liquid. Therefore, substantially no hydrophilic organic solvent remains between the surface of the porous body 20 and the crosslinked bodies 3a of the first polymer.

[0080] The second polymer contained in the third liquid has at least one functional group selected from the group consisting of a hydroxyl group and an ester group. The amino group may be introduced into the hydroxyl group or the ester group of the PVA by chemically reacting with a molecule having an amino group.

[0081] The method for impregnating the substrate 2 with the hydrophilic organic solvent, the third liquid, and the first liquid is not particularly limited. Examples of impregnation methods include spin coating, bar coating, immersion, and die coating. The concentration of the second polymer in the third liquid and the concentration of the first polymer in the first liquid can be appropriately selected depending on the porosity of the substrate 2, for example. The concentration of the second polymer in the third liquid and the concentration of the first polymer in the first liquid may each be, for example, 0.05% by mass or more and 5% by mass or less. The impregnation time of the substrate 2 with each of the third liquid and the first liquid can be appropriately selected depending on the porosity of the substrate 2, for example. The impregnation time of the substrate 2 with each of the third liquid and the first liquid may be, for example, 10 minutes or more and 180 minutes or less. The crosslinking of the second polymer is performed by chemical crosslinking or electron beam crosslinking. A crosslinking agent used in chemical crosslinking is, for example, glutaraldehyde.

[0082] When the substrate 2 is immersed in the third liquid and then the first liquid, a crosslinked polymer 3 composed of crosslinked polymers 3b of the second polymer and crosslinked polymers 3a of the first polymer is formed on at least a portion of the surfaces of the nodes 25 and fibrils 26 present on the first surface 21, as well as on at least a portion of the surfaces of the nodes 25 and fibrils 26 present between the first surface 21 and the second surface 22. When the substrate 2 is immersed only in the first liquid, a crosslinked polymer 3 composed of crosslinked polymers 3a of the first polymer is formed on at least a portion of the surfaces of the nodes 25 and fibrils 26 present on the first surface 21, as well as on at least a portion of the surfaces of the nodes 25 and fibrils 26 present between the first surface 21 and the second surface 22. This crosslinked polymer 3 does not include crosslinked polymers 3b of the second polymer. Note that in step B, it is sufficient that the crosslinked polymer 3 is formed on the surfaces of the nodes 25 and fibrils 26 present on the first surface 21. Furthermore, the crosslinked polymer 3 may also be formed on the surfaces of the nodes 25 and fibrils 26 present between the first surface 21 and the second surface 22.

[0083] [Step C] In step C, a second liquid containing graphene oxide 5 is applied to at least a portion of the surface of the crosslinked polymer 3, causing a reaction between the graphene oxide 5 and the crosslinked first polymer 3a. The second liquid is a liquid in which a plurality of graphene oxides 5 are dispersed in a dispersion medium. The dispersion medium is mainly water. The concentration of graphene oxide 5 in the second liquid may be, for example, 0.001% by mass or more and 2% by mass or less. When the concentration of graphene oxide 5 is 0.001% by mass or more, the concentration of graphene oxide 5 in the second liquid is sufficient, making it easy to deposit graphene oxide 5 on the first surface 21. When the concentration of graphene oxide 5 is 2% by mass or less, the concentration of graphene oxide 5 in the second liquid is not too high. A second liquid with an excessively high concentration of graphene oxide 5 makes it difficult to deposit a thin, uniform layer on the first surface 21. The second liquid may contain the organic material described above in addition to water. The organic material can improve adhesion between the deposited graphene oxides 5 and change the interlayer distance of the graphene oxides 5. The concentration of the organic material may be 0.001% by mass or more and 2% by mass or less, where the mass of the second liquid is taken as 100. The method for applying the second liquid to the first surface 21 is not particularly limited. The method for applying the second liquid is the same as the impregnation method described above. The reaction between the graphene oxide 5 and the crosslinked body 3a of the first polymer can be carried out, for example, by heating the member to which the second liquid has been applied. The heating temperature is, for example, 80°C.

[0084] [Others] Step C may be performed multiple times. Performing step C multiple times facilitates the formation of a coating layer 4 composed of a laminate of graphene oxide 5. The thickness of the coating layer 4 can be changed by appropriately selecting the number of times step C is performed. Step C may be performed, for example, two or more times and five or less times. Performing step C two or more times can prevent the formation of an area on the first surface 21 where no coating layer 4 is formed. When crosslinked bodies 3a of the first polymer are contained within the substrate 2, the second liquid containing graphene oxide 5 easily penetrates into the substrate 2, so that even when step C is performed fewer times, the same filtration performance can be achieved as when step C is performed more times. When crosslinked bodies 3a of the first polymer are contained within the substrate 2, the graphene oxide 5 is attracted to the substrate 2, so that even when step C is performed fewer times, the same filtration performance can be achieved as when step C is performed more times.

[0085] <<Embodiment 2>> [Composite porous body] A composite porous body 1 of embodiment 2 will be described with reference to Fig. 5. The composite porous body 1 of embodiment 2 differs from the composite porous body 1 of embodiment 1 in that the substrate 2 has a tubular shape. The tubular substrate 2 is also called a hollow fiber membrane. When a plurality of composite porous bodies 1 are bundled together, a hollow fiber membrane module is formed.

[0086] In this example, the first surface 21 of the substrate 2 constitutes the outer peripheral surface of the substrate 2. The coating layer 4 formed on the first surface 21 constitutes the outer peripheral surface of the composite porous body 1. The second surface 22 constitutes the inner peripheral surface of the composite porous body 1. When this composite porous body 1 is used to filter a mixed fluid, for example, a liquid or gas mixed with a solid, the mixed fluid is introduced to the outer peripheral side of the composite porous body 1. The mixed fluid passes through the coating layer 4 and the substrate 2 and flows into the internal space of the composite porous body 1. The mixed fluid that has flowed into the internal space is discharged to the outside of the composite porous body 1 along the axis of the composite porous body 1. Unlike this example, the first surface 21 of the substrate 2 may constitute the inner peripheral surface of the substrate 2. The coating layer 4 formed on the first surface 21 constitutes the inner peripheral surface of the composite porous body 1. The second surface 22 constitutes the outer peripheral surface of the composite porous body 1. When this composite porous body 1 is used to filter a mixed fluid, for example, a liquid or gas mixed with a solid, the mixed fluid is introduced to the inner peripheral side of the composite porous body 1. The mixed fluid passes through the coating layer 4 and the substrate 2 and is discharged to the outside of the composite porous body 1 .

[0087] The average thickness of the tubular substrate 2 may be set appropriately depending on the required inner diameter, design strength, etc. The average thickness of the tubular substrate 2 may be, for example, 0.1 mm or more and 3 mm or less. If the average thickness of the tubular substrate 2 is 0.1 mm or more, the strength of the composite porous body 1 including the substrate 2 is ensured. If the average thickness of the substrate 2 is 3 mm or less, the flexibility of the composite porous body 1 including the substrate 2 is ensured, and the filtration time by the composite porous body 1 does not become too long. The average thickness of the tubular substrate 2 may be, for example, 0.3 mm or more and 2 mm or less.

[0088] Test Example In the test example, the effect of the inclusion of a crosslinked product of a first polymer having an amino group on the first surface of the substrate on improving the adhesion between the substrate and the coating layer was investigated.

[0089] [Sample No. 1] The composite porous body of Sample No. 1 was produced by sequentially carrying out steps A to C described in the method for producing the composite porous body of Embodiment 1.

[0090] [Step A] A substrate made of a porous material composed of PTFE was prepared. The substrate was in the form of a sheet. The thickness of the substrate was 15 μm. A nonwoven fabric was fused to the second surface of the substrate to reinforce the substrate. The nonwoven fabric was composed of polyethylene terephthalate. The thickness of the nonwoven fabric was 90 μm. The average pore diameter of the pores on the first surface of the substrate was 210 nm. The average pore diameter of the pores on the first surface of the substrate was determined as follows: The substrate was cut using an FIB, and the cross section cut along the thickness of the substrate was observed using an SEM. The magnification of the SEM image was 5000x. The size of the SEM image was 18 μm x 24 μm. The SEM image was binarized using the image processing software "ImageJ." The threshold for the binarization was 127. The average pore diameter of the substrate was determined by averaging the circle-equivalent diameter of each pore in the binarized image. The average pore diameter of the substrate was considered to be the average pore diameter of the pores on the first surface of the substrate.

[0091] [Step B] The substrate was immersed in IPA. Next, the substrate was immersed in a third liquid containing a second polymer. The second polymer had a hydroxy group. Specifically, the second polymer was PVA. The concentration of PVA in the third liquid was 0.5% by mass. The immersion time was 120 minutes. Next, the second polymer attached to the surface of the porous body was crosslinked. The crosslinking of the second polymer was performed by immersing the substrate to which the second polymer was attached in an aqueous solution containing glutaraldehyde and sulfuric acid. The concentration of glutaraldehyde in the aqueous solution was 2% by mass. The concentration of sulfuric acid in the aqueous solution was 5% by mass.

[0092] The substrate with the crosslinked second polymer fixed thereto was immersed in a first liquid containing a first polymer. The first polymer had an amino group. Specifically, the first polymer was branched PEI. The branched PEI contained all of primary amines, secondary amines, and tertiary amines. The molecular weight of the branched PEI was 8,000. The concentration of branched PEI in the first liquid was 2% by mass. The immersion time was 120 minutes. Next, the first polymer attached to the substrate was crosslinked. The crosslinking of the first polymer was performed by immersing the substrate with the attached first polymer in an aqueous solution containing glutaraldehyde and sulfuric acid. The concentration of glutaraldehyde in the aqueous solution was 2% by mass. The concentration of sulfuric acid in the aqueous solution was 0.05% by mass.

[0093] [Step C] A second liquid containing graphene oxide was applied to the substrate on which the first polymer was fixed. The graphene oxide was in the form of flakes. The graphene oxide had an average thickness of 1.4 nm and an average length of 4 μm. The graphene oxide concentration in the second liquid was 0.5 mass%. An automatic applicator device manufactured by BEVS was used to apply the second liquid. The automatic applicator device had a bar with multiple grooves. The bar had a length of 200 mm, a diameter of 10 mm, and a groove depth of 10 μm. 5 ml (milliliters) of the second liquid was dropped onto the first surface of the substrate using the automatic applicator. The second liquid was applied once. After applying the second liquid once, the substrate on which graphene oxide had been attached was heated at 80°C for 1 hour.

[0094] [Observation and Analysis] The cross section of the produced composite porous body was observed by SEM and analyzed by XPS. Although SEM images are not shown, a coating layer composed of multiple graphene oxide laminates was formed on the first surface of the substrate.

[0095] The produced composite porous body was examined by XPS. The measuring device used was a Quantera SXM manufactured by ULVAC PHI. ２ -NH bond, at 399.3 eV (C) ３ A peak due to a -N bond was confirmed, which means that the first polymer and graphene oxide contained a bonded portion.

[0096] The average pore size of the first surface of the substrate in the composite porous body, i.e., the average pore size of the first surface of the substrate after the coating layer was formed, was determined. The method for determining the average pore size of the first surface was the same as the average pore size of the first surface determined before the coating layer was formed, as described above. The average pore size of the first surface of the substrate after the coating layer was formed was the same as the average pore size of the first surface of the substrate before the coating layer was formed.

[0097] [Sample No. 2] The composite porous body of Sample No. 2 was produced in the same manner as Sample No. 1, except that the first polymer contained in the first liquid contained only primary amines, without containing secondary amines or tertiary amines. Specifically, the first polymer contained in the first liquid was polyallylamine. The composite porous body of Sample No. 2 was observed and analyzed in the same manner as Sample No. 1.

[0098] A coating layer was formed on the first surface of the substrate of Sample No. 2. The coating layer was composed of a plurality of graphene oxide laminates. The first polymer and the graphene oxide included a bonded portion.

[0099] [Sample No. 3] The composite porous body of Sample No. 3 was produced in the same manner as Sample No. 1, except that the first polymer contained in the first liquid contained only secondary amines, without any primary or tertiary amines. Specifically, the first polymer contained in the first liquid was linear PEI. The composite porous body of Sample No. 3 was observed and analyzed in the same manner as Sample No. 1.

[0100] A coating layer was formed on the first surface of the substrate of Sample No. 3. The coating layer was composed of a plurality of graphene oxide laminates. The first polymer and the graphene oxide included a bonded portion.

[0101] [Sample No. 101] The composite porous body of Sample No. 101 was produced in the same manner as Sample No. 1, except that the substrate was subjected to the silane coupling treatment without performing Steps B and C.

[0102] [Adhesion] The adhesion of each composite porous body sample was examined as follows. Each composite porous body sample was placed in a cross-flow permeation device in which the fluid to be filtered flows parallel to the composite porous body. The effective area of ​​the composite porous body in the permeation device was 3.84 × 10 －３ m ２ The results were as follows. Ultrapure water containing 200 ppm by mass of vitamin B12 was supplied to the water permeation device at a flow rate of 5 L / min. The pressure on the supply side, which is the primary side, was varied. At each pressure, the vitamin B12 concentration X in the aqueous solution before passing through the composite porous body and the vitamin B12 concentration Y in the filtrate after passing through the composite porous body were measured. The rejection rate of the composite porous body for each sample was determined at each pressure. The rejection rate is calculated by (1-Y / X) x 100. Peeling of the coating layer from the substrate reduces the rejection rate. The pressure α of the aqueous solution at which the rejection rate decreased by 10% was compared to the rejection rate at the minimum aqueous solution pressure. A higher pressure α indicates better adhesion between the substrate and the coating layer.

[0103] The composite porous bodies of Samples No. 1 to No. 3 had a higher pressure α than Sample No. 101. That is, it was found that the composite porous bodies of Samples No. 1 to No. 3 had better adhesion between the substrate and the coating layer than Sample No. 101. The composite porous bodies of Samples No. 1 and No. 2 had a higher pressure α than Sample No. 3. That is, it was found that the composite porous bodies of Samples No. 1 and No. 2 had better adhesion between the substrate and the coating layer than Sample No. 3.

[0104] The present invention is not limited to these examples, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0105] 1 Composite porous body, 2 Substrate, 20 Porous body, 2h Pore, 21 First surface, 22 Second surface, 25 Node, 26 Fibril, 28 Surface portion, 3 Polymer crosslinked body, 3a Crosslinked body of first polymer, 3b Crosslinked body of second polymer, 4 Coating layer, 40 Surface, 5 Graphene oxide, 6 Solid particles.

Claims

1. A substrate which is a porous material made of fluororesin, A polymer crosslinked body fixed to at least a portion of the surface of the porous body, A coating layer that covers the first surface of the substrate by being bonded to the polymer crosslinked material, Equipped with, The aforementioned polymer crosslinked material includes a crosslinked material of a first polymer having an amino group, The coating layer comprises graphene oxide, Composite porous material.

2. The first polymer contains -C-C- bonds in its main chain and -NH in its side chains. ２ The composite porous body according to claim 1, wherein the polymer contains a polymer.

3. The composite porous body according to claim 2, wherein the first polymer is polyallylamine.

4. The composite porous body according to claim 1, wherein the first polymer is a polymer having a network structure including a -C-C-N- bond in its main chain.

5. The composite porous body according to claim 4, wherein the first polymer comprises a primary amine and a secondary amine.

6. The composite porous body according to claim 4, wherein the first polymer is polyethyleneimine or polydopamine.

7. The composite porous body according to any one of claims 1 to 6, wherein the polymer crosslinked body comprises a crosslinked body of a second polymer having at least one functional group of a hydroxyl group and an ester group.

8. The composite porous body according to claim 7, wherein the second polymer is polyvinyl alcohol.

9. The composite porous body according to any one of claims 1 to 6, wherein the fluororesin is polytetrafluoroethylene.

10. The composite porous body according to any one of claims 1 to 6, further comprising a plurality of solid particles held inside the porous body on the surface of the substrate.

11. The composite porous body according to claim 10, wherein the solid particles are composed of one selected from the group consisting of fluororesins and ceramic materials.

12. The composite porous body according to claim 10, wherein the average particle size of the solid particles is 10 nm or more and 500 nm or less.

13. The composite porous body according to claim 10, wherein at least a portion of the surface of the solid particles is covered with the polymer crosslinking material.

14. A step of preparing a substrate made of a porous material composed of fluororesin, A step of impregnating the substrate with a first liquid containing a first polymer having an amino group, and fixing the first polymer to at least a part of the surface of the porous body by adsorbing and crosslinking the first polymer onto the porous body, The process includes the steps of applying a second liquid containing graphene oxide to at least a portion of the surface of the first polymer fixed to the substrate, and reacting the first polymer with the graphene oxide. A method for manufacturing a composite porous body.

15. The method for producing a composite porous body according to claim 14, further comprising the step of impregnating the substrate with a third liquid containing a second polymer having a hydroxyl group, and fixing the second polymer to at least a portion of the surface of the porous body by adsorbing and crosslinking the second polymer onto the porous body, prior to the step of fixing the first polymer.