WO2023188872A1 - Composite porous body and method for producing composite porous body - Google Patents

Abstract

The present invention provides a composite porous body which comprises a base material that has a first surface and an inorganic layer that covers at least a part of the first surface, wherein: the base material is a porous body that is configured from a resin material; the inorganic layer is a multilayer body of a plurality of nanofibers; each one of the plurality of nanofibers is formed of an inorganic material that contains aluminum, oxygen and hydrogen; the average pore diameter of the first surface is 5 nm to 500 nm; the average thickness of the inorganic layer is 10 nm to 1,000 nm; and the average pore diameter of the inorganic layer is 1 nm to 50 nm.

Description

Composite porous body and method for manufacturing the composite porous body

The present disclosure relates to a composite porous body and a method for manufacturing the composite porous body. This application claims priority based on Japanese Patent Application No. 2022-052170, which is a Japanese patent application filed on March 28, 2022. All contents described in the Japanese patent application are incorporated herein by reference.

Patent Document 1 discloses an alumina composite separation membrane that includes a support made of a porous material and a porous thin film layer. Porous materials are typically composed of inorganic oxides such as alumina. The porous thin film layer is constructed by laminating a plurality of fibrous alumina particles. Hereinafter, the alumina composite separation membrane will be referred to as a composite porous body.

The composite porous body disclosed in the example of Patent Document 1 includes a support whose main component is alumina. A composite porous body comprising a support made of alumina and a porous thin film layer has excellent strength, heat resistance, and chemical resistance.

Japanese Patent Application Publication No. 2011-255303

The composite porous body of the present disclosure includes:
a base material having a first surface;
an inorganic layer covering at least a portion of the first surface,
The base material is a porous body made of a resin material,
The inorganic layer is a laminate of multiple nanofibers,
Each of the plurality of nanofibers is made of an inorganic material containing aluminum, oxygen, and hydrogen,
The average pore diameter on the first surface is 5 nm or more and 500 nm or less,
The average thickness of the inorganic layer is 10 nm or more and 1000 nm or less,
The average pore diameter of the inorganic layer is 1 nm or more and 50 nm or less.

The method for manufacturing a composite porous body of the present disclosure includes:
Step A of preparing a base material made of a porous body made of a resin material;
Step B of hydrophilizing the first surface of the base material;
Step C of preparing a dispersion containing a plurality of nanofibers;
a step D of applying the dispersion liquid to the first surface;
A step E of heat-treating the base material coated with the dispersion liquid in a heating atmosphere of 80° C. or more and 200° C. or less,
The average pore diameter of the first surface in the step A is 5 nm or more and 500 nm or less,
Each of the plurality of nanofibers in the step C is made of an inorganic material containing aluminum, oxygen and hydrogen,
The average length of the plurality of nanofibers in the step C is 10 times or more the average pore diameter.

FIG. 1 is a schematic configuration diagram of a sheet-shaped composite porous body according to Embodiment 1. FIG. 2 is an explanatory diagram schematically showing the structure of the composite porous body of FIG. 1. FIG. 3 is an explanatory diagram schematically showing the surface of the inorganic layer of the composite porous body of FIG. 2. FIG. 4 is a schematic configuration diagram of a cylindrical composite porous body according to a second embodiment. FIG. 5 is a schematic diagram of a test device used in the liquid passage test shown in the test example. FIG. 6 is a schematic explanatory diagram of the bending test shown in the test example.

[Problems to be solved by this disclosure]
A composite porous body having a support mainly composed of alumina has poor flexibility. Depending on how the composite porous body is used, the composite porous body may be bent. A composite porous body with poor flexibility is easily damaged by bending.

One of the objects of the present disclosure is to provide a composite porous body with excellent flexibility and a method for manufacturing the composite porous body with excellent flexibility.

[Effects of this disclosure]
The composite porous body of the present disclosure has excellent flexibility.

The method for producing a composite porous body of the present disclosure is suitable for producing the composite porous body of the present disclosure.

[Description of embodiments of the present disclosure]
Hereinafter, embodiments of the present disclosure will be listed and described.

<1> The composite porous body according to the embodiment is
a base material having a first surface;
an inorganic layer covering at least a portion of the first surface,
The base material is a porous body made of a resin material,
The inorganic layer is a laminate of multiple nanofibers,
Each of the plurality of nanofibers is made of an inorganic material containing aluminum, oxygen, and hydrogen,
The average pore diameter on the first surface is 5 nm or more and 500 nm or less,
The average thickness of the inorganic layer is 10 nm or more and 1000 nm or less,
The average pore diameter of the inorganic layer is 1 nm or more and 50 nm or less.

The composite porous body according to the embodiment has excellent flexibility. One of the reasons for this is that the base material is made of a porous body made of a flexible resin material. Another reason is that the inorganic layer is composed of a laminate of multiple nanofibers made of an inorganic material containing aluminum, oxygen, and hydrogen.

The composite porous body according to the embodiment has excellent heat resistance and chemical resistance. This is because the inorganic layer that the fluid to be filtered comes into contact with is composed of nanofibers of inorganic material. The fluid may be a liquid, a gas, a liquid mixed with a solid, or a gas mixed with a solid.

A composite porous body having a first surface with an average pore diameter of 5 nm or more has excellent liquid permeability. Liquid permeability refers to the ease with which fluid can pass through. A composite porous body with high liquid permeability can shorten filtration time. If the average pore diameter of the first surface is 500 nm or less, an inorganic layer is likely to be formed during production of the composite porous body.

A composite porous body comprising an inorganic layer with an average thickness of 10 nm has excellent filtration performance. A composite porous body including an inorganic layer with an average thickness of 1000 nm or less has excellent liquid permeability and flexibility.

A composite porous body comprising an inorganic layer with an average pore diameter of 1 nm or more has excellent liquid permeability. A composite porous body including an inorganic layer with an average pore diameter of 50 nm or less has excellent filtration performance.

The composite porous body according to the embodiment can remove nano-order impurities from the fluid to be filtered. This is because in an inorganic layer formed by stacking a plurality of nanofibers, gaps between adjacent nanofibers become pores through which fluid passes. Since the gaps between adjacent nanofibers are very small, the inorganic layer removes nano-order impurities from the fluid.

<2> In the composite porous body according to the embodiment,
The resin material may be a hydrophobic polymer.

Many hydrophobic polymers have excellent strength, heat resistance, or chemical resistance. Therefore, the strength, heat resistance, or chemical resistance of the composite porous body is improved.

<3> In the composite porous body described in <2> above,
The hydrophobic polymer may be polytetrafluoroethylene.

Polytetrafluoroethylene has excellent heat resistance and chemical resistance. Therefore, the heat resistance and chemical resistance of the composite porous body are improved.

<4> In the composite porous body according to the embodiment,
At least a portion of the first surface may include a hydrophilic material.

The hydrophilic material improves the adhesion between the first surface of the base material made of resin material and the inorganic layer. Therefore, even a thin inorganic layer is difficult to peel off from the first surface of the base material. As described in the method for producing a composite porous body described below, when producing a composite porous body, the first surface of the base material is made hydrophilic with a hydrophilic material. Here, at least a portion of the hydrophilic material may be decomposed by heat treatment during production of the composite porous body. It is possible that all of the hydrophilic material is decomposed by the above heat treatment. The presence of a hydrophilic material in the base material can be confirmed by, for example, XPS (X-ray Photoelectron Spectroscopy).

<5> In the composite porous body described in <4> above,
The hydrophilic material may be a hydrophilic polymer coated on at least a portion of the surface of the base material including the first surface.

The surface of the base material also includes the inner peripheral surface of the pores of the base material. That is, the hydrophilic material may enter the pores of the base material and coat the inner circumferential surfaces of the pores. The hydrophilic material coated on the surface of the base material improves the adhesion between the base material and the inorganic layer.

<6> In the composite porous body described in <5> above,
The hydrophilic polymer may be polyvinyl alcohol.

Polyvinyl alcohol (PVA) easily adheres to the base material. PVA particularly tends to adhere to a base material made of polytetrafluoroethylene (PTFE). The hydrophilic resin made of PVA firmly adheres the base material and the inorganic layer during production of the composite porous body.

<7> In the composite porous body described in <6> above,
The resin material is polytetrafluoroethylene,
The first surface containing the hydrophilic polymer includes a plurality of chemical structures derived from the polyvinyl alcohol and the polytetrafluoroethylene,
Among the plurality of chemical structures, the content of CH ₂ -O-R bonds in the chemical structure detected by the C1s spectrum obtained by XPS may be 3% or more and 15% or less.

A hydrophilic polymer containing a CH ₂ -O-R bond in the above range improves the adhesion between the base material and the inorganic layer.

<8> In the composite porous body according to the embodiment,
The shape of the base material may be a sheet.

The overall shape of the composite porous body including a sheet-like base material is a sheet shape. A sheet-shaped composite porous body can be easily processed into various shapes and can be applied to various types of filtration devices. Since the composite porous body according to the embodiment has excellent flexibility, it is not easily damaged even when subjected to processing such as bending.

<9> In the composite porous body described in <8> above,
The average thickness of the base material may be 1 μm or more and 100 μm or less.

If the average thickness of the sheet-like base material is 1 μm or more, the strength of the composite porous body including the base material is ensured. When the average thickness of the base material is 100 μm or less, the flexibility of the composite porous body including the base material is ensured, and the filtration time using the composite porous body does not become too long.

<10> In the composite porous body described in any one of <1> to <7> above,
The shape of the base material is a tube,
The first surface may be an outer peripheral surface of the tube.

The overall shape of the composite porous body including a tubular base material is a tube shape. The tubular substrate also includes hollow fiber membranes. In the tube-shaped composite porous body, a fluid containing impurities is passed to the outside of the tube-shaped composite porous body. The fluid that has passed through the composite porous body is circulated inside the tube-shaped composite porous body. With the configuration described in <10> above, the fluid flow path can be configured by the composite porous body itself. A module of a purification device can be constructed by bundling a plurality of these composite porous bodies.

<11> In the composite porous body described in <10> above,
The average thickness of the base material may be 50 μm or more and 1000 μm or less.

If the average thickness of the tubular base material is 50 μm or more, the strength of the composite porous body including the base material is ensured. When the average thickness of the base material is 1000 μm or less, the flexibility of the composite porous body including the base material is ensured, and the filtration time using the composite porous body does not become too long.

<12> In the composite porous body according to the embodiment,
The base material includes a first layer including the first surface and a second layer adjacent to the first layer,
The average pore size of the second layer may be larger than the average pore size of the first layer.

The thicker the base material, the higher the strength of the base material, that is, the strength of the composite porous body. On the other hand, the liquid permeability of the base material, ie, the liquid permeability of the composite porous body, decreases. The liquid permeability of the base material X, which includes the second layer with a large average pore diameter, is superior to the liquid permeability of the base material Y, which has the same thickness as the base material X and is composed of only the first layer. Therefore, since the base material is composed of the first layer and the second layer, even if the base material is made thicker, the filtration time of the composite porous body is not easily increased.

<13> In the composite porous body according to the embodiment,
The inorganic layer includes an Al-OH bond and an Al-O-Al bond,
The ratio X/Y between the content X of the Al--OH bonds and the content Y of the Al-O-Al bonds may be 0.3 or more and 1.0 or less.

Boehmite containing Al-OH bonds is softer than alumina containing Al-O-Al bonds. The inorganic layer with high boehmite content is resistant to bending stress. Therefore, the composite porous body described in <13> above is easy to bend.

<14> In the composite porous body according to the embodiment,
The average short diameter of the pores on the first surface may be 4 nm or more and 400 nm or less.

The first surface having pores with an average minor axis of 4 nm or more improves the liquid permeability of the composite porous body. If the average short diameter of the pores on the first surface is 400 nm or less, nanofibers can be easily formed on the first surface during production of the composite porous body. Therefore, a thin inorganic layer is likely to be formed.

<15> In the composite porous body according to the embodiment,
The inorganic layer has an opening opening on the surface of the inorganic layer,
The average pore diameter of the open pores is 2 nm or more and 200 nm or less,
The average short diameter of the opening pores may be 1 nm or more and 100 nm or less.

A composite porous body comprising an inorganic layer with an average pore diameter and an average short diameter within the above range has excellent filtration performance and liquid permeability.

<16> A method for manufacturing a composite porous body according to an embodiment,
Step A of preparing a base material made of a porous body made of a resin material;
Step B of hydrophilizing the first surface of the base material;
Step C of preparing a dispersion containing a plurality of nanofibers;
a step D of applying the dispersion liquid to the first surface;
A step E of heat-treating the base material coated with the dispersion liquid in a heating atmosphere of 80° C. or more and 200° C. or less,
The average pore diameter of the first surface in the step A is 5 nm or more and 500 nm or less,
Each of the plurality of nanofibers in the step C is made of an inorganic material containing aluminum, oxygen and hydrogen,
The average length of the plurality of nanofibers in the step C is 10 times or more the average pore diameter.

The method for manufacturing a composite porous body according to the embodiment is suitable for manufacturing the composite porous body according to the embodiment.
Nanofibers made of an inorganic material containing aluminum are difficult to adhere to, for example, a base material made of a resin material. Therefore, in order to form an inorganic layer consisting of a laminate of a plurality of nanofibers on a substrate, a dispersion containing a large amount of nanofibers must be applied onto the substrate. In that case, since the thickness of the inorganic layer is several tens of micrometers or more, a composite porous body with excellent flexibility cannot be obtained. To address this problem, in the method for manufacturing a composite porous body according to the embodiment, the first surface of the base material is hydrophilized in step B, and the nanofibers are attached to the first surface in step D. It becomes easier. Furthermore, since the average length of the nanofibers is 10 times or more the average pore diameter of the first surface, the nanofibers are unlikely to fall into the pores of the first surface in step D. As described above, since nanofibers are difficult to fall into the pores of the first surface and easily adhere to the first surface, according to the method for manufacturing a composite porous body according to the embodiment, the inorganic layer having an average thickness of 1000 nm or less A composite porous body can be manufactured.

[Details of embodiments of the present disclosure]
Hereinafter, specific examples of the composite porous body and the method for manufacturing the composite porous body of the present disclosure will be described based on the drawings. Hereinafter, the same reference numerals in the figures indicate the same or corresponding parts. The sizes of parts shown in each drawing are shown for clarity of explanation and do not necessarily represent actual dimensions. Note that the present invention is not limited to these examples, but is indicated by the scope of the claims, and is intended to include all changes within the meaning and scope equivalent to the scope of the claims.

<Embodiment 1>
≪Overall composition≫
The composite porous body 1 of the embodiment has a sheet shape shown in FIG. 1, for example. The composite porous body 1 includes a base material 2 and an inorganic layer 3. The shape of the base material 2 is a sheet. The base material 2 includes a first surface 21 and a second surface 22, as shown in FIGS. 1 and 2. The inorganic layer 3 is arranged on the first surface 21 of the base material 2. As described later, the average pore diameter of the inorganic layer 3 is smaller than the average pore diameter of the base material 2. The composite porous body 1 may be required to have resistance to bending. For example, the composite porous body 1 constitutes a filter of a module of a purification device when rolled into a cylindrical shape. In a cylindrical module, the inorganic layer 3 is arranged on the outer peripheral side of the cylinder. Hereinafter, each structure of the composite porous body 1 will be explained in detail.

[Base material]
The base material 2 is a porous body. As shown in FIG. 2, the base material 2 includes a plurality of holes 2h. Since FIG. 2 is a cross-sectional view, each hole 2h of the base material 2 appears to be independent, but each hole 2h is connected to other holes 2h. Numerous channels are formed in the base material 2 from the first surface 21 to the second surface 22.

The base material 2 is made of a resin material. The resin material is appropriately selected depending on the use of the composite porous body 1. The resin material is, for example, a hydrophobic polymer. Many hydrophobic polymers have excellent strength, heat resistance, or chemical resistance. Examples of hydrophobic polymers include polypropylene (PP), polyethylene (PE), polyvinylidene difluoride (PVDF), and polyethylene terephthalate. thalate: PET) or polytetrafluoroethylene (PTFE). In particular, PTFE has excellent heat resistance and chemical resistance.

The thickness of the base material 2 is the length between the first surface 21 and the second surface 22. The average thickness of the base material 2 in this example is 1 μm or more and 100 μm or less. The composite porous body 1 including the base material 2 having an average thickness of 1 μm or more has excellent strength. The composite porous body 1 including the base material 2 having an average thickness of 100 μm or less has excellent flexibility. Moreover, the filtration time using the composite porous body 1 does not become too long. The lower limit of the average thickness may be 5 μm, 10 μm, 15 μm, or 20 μm. The upper limit of the average thickness may be 90 μm, 80 μm, or 50 μm. The range of the average thickness of the base material 2 may be, for example, 10 μm or more and 90 μm or less, or 20 μm or more and 50 μm or less.

The average thickness of the base material 2 is determined by SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy). The boundary between the base material 2 and the inorganic layer 3 is determined by line analysis of the detected intensity of aluminum (Al) in the depth direction from the surface 30 of the base material 2 using EDX. In the SEM image, the location where the detection intensity of Al sharply decreases is the boundary between the base material 2 and the inorganic layer 3. The distance from this boundary to the second surface 22 of the base material 2 is the thickness of the base material 2. The average thickness of the base material 2 is, for example, the average of the thicknesses at five different points on the base material 2.

The average pore diameter on the first surface 21 of the base material 2 is 5 nm or more and 500 nm or less. The composite porous body 1 including the base material 2 having an average pore diameter of 5 nm or more has excellent liquid permeability. The composite porous body 1 with high liquid permeability can shorten the filtration time. The base material 2 having an average pore diameter of 500 nm or less has excellent strength. The lower limit of the average pore diameter may be 50 nm, 100 nm, or 200 nm. The upper limit of the average pore diameter may be 450 nm, 400 nm, or 350 nm. The range of the average pore diameter of the base material 2 may be, for example, 50 nm or more and 450 nm or less, or 200 nm or more and 350 nm or less.

A plurality of holes 2h are formed in the first surface 21. When the inorganic 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. The average pore diameter of the first surface 21 in this specification is determined from an SEM image of a cross section of the base material 2 along the thickness direction. Specifically, a SEM image of a cross section along the thickness direction of the base material 2 is subjected to a binarization process, and each hole 2h in the SEM image is extracted. The equivalent circle diameter of each hole 2h is determined, and the average of the equivalent circle diameters of all the holes 2h is determined. The equivalent circle diameter is the diameter of a perfect circle having the same size as the area of the hole 2h. In this specification, this average equivalent circle diameter is regarded as the average pore diameter of the first surface 21.

The average short diameter of the pores 2h on the first surface 21 is, for example, 4 nm or more and 400 nm or less. The average short diameter of the pores 2h is determined from an SEM image of a cross section of the base material 2 along the thickness direction. The smallest rectangle circumscribing each hole 2h in the SEM image is determined. The average of the short axes of all the rectangles is the average short axis of the holes 2h. The first surface 21 having the pores 2h having an average minor axis of 4 nm or more improves the liquid permeability of the composite porous body 1. If the average short diameter of the pores 2h on the first surface 21 is 400 nm or less, the nanofibers 4 are easily formed on the first surface 21 during production of the composite porous body 1. Therefore, a thin inorganic layer 3 is easily formed. The average short diameter of the holes 2h on the first surface 21 may be, for example, 10 nm or more and 300 nm or less.

The base material 2 may include multiple layers, as shown in FIG. 2. The base material 2 includes, for example, a first layer 2A and a second layer 2B. The first layer 2A includes a first surface 21. The second layer 2B is adjacent to the first layer 2A. The average pore size of the second layer 2B is larger than the average pore size of the first layer 2A. For example, the average pore diameter of the second layer 2B is 2 times or more and 2000 times or less, more preferably 10 times or more and 1000 times or less, than the average pore diameter of the first layer 2A. Here, when the base material 2 is composed of three or more layers, the layers farther from the first surface 21 have a larger average pore diameter. Of course, the base material 2 may be composed only of the first layer 2A.

The average pore diameter of the first layer 2A and the average pore diameter of the second layer 2B are determined from the SEM image of the cross section of the base material 2 along the thickness direction. The first layer 2A and the second layer 2B are thermally fused together when the base material 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 average of the circular equivalent diameters of the pores 2h existing 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 average of the equivalent circular diameters of the pores 2h existing in the region adjacent to the first layer 2A across the boundary is the average pore diameter of the second layer 2B.

At least a portion of the first surface 21 of the base material 2 may contain the hydrophilic material 5. In other words, the hydrophilic material 5 may be present on at least a portion of the surface of the porous body. The hydrophilic material 5 in FIG. 2 is shown exaggerated. The hydrophilic material 5 improves the adhesion between the first surface 21 of the base material 2 and the nanofibers 4 made of an inorganic material in the method for manufacturing the composite porous body 1 described later. It is difficult to confirm the hydrophilic material 5 in the SEM image. The presence of the hydrophilic material 5 can be confirmed by, for example, XPS. The hydrophilic material 5 may disappear due to heat treatment during the manufacturing process of the composite porous body 1. Therefore, the hydrophilic material 5 may not be detected by XPS.

The hydrophilic material 5 is, for example, a hydrophilic polymer that coats at least a portion of the surface of the base material 2 including the first surface 21. The hydrophilic polymer is a layered body formed on the surface of the base material 2. The surface of the base material 2 also includes the inner peripheral surface of the pores of the base material 2. In this example, the hydrophilic polymer has entered the pores of the base material 2. That is, the hydrophilic polymer covers not only the first surface 21 but also at least a portion of the inner peripheral surface of the hole. Since the hydrophilic polymer layer is extremely thin, the pore size of the base material 2 hardly changes depending on the presence or absence of the hydrophilic polymer.

Hydrophilic polymers are, for example, polyvinyl alcohol (PVA), ethylene vinyl alcohol copolymer, polyvinylpyrrolidone, polyethyleneimine, or carboxylic acid. It is a polyacrylic acid containing a boxyl group. In particular, PVA improves the adhesion between the base material 2 and the inorganic layer 3.

When the base material 2 is PTFE and the hydrophilic polymer is PVA, the first surface 21 containing the hydrophilic polymer includes a plurality of chemical structures derived from PVA and PTFE. The CH ₂ -O-R bond, which is a type of chemical structure, improves the adhesion between the base material 2 and the inorganic layer 3. Among the plurality of chemical structures, the content of CH ₂ -O-R bonds in the chemical structure detected by the C1s spectrum obtained by XPS is, for example, 3% or more and 15% or less. The content of CH ₂ -O-R bonds is determined by XPS. Details of the XPS conditions are shown in Test Example 3 described later.

[Inorganic layer]
The inorganic layer 3 is a layer facing the fluid filtered by the composite porous body 1. The inorganic layer 3 is a laminate of a plurality of nanofibers 4. In FIG. 2, some nanofibers 4 are illustrated. These nanofibers 4 are arranged generally along the plane direction of the inorganic layer 3.

Each nanofiber 4 is made of an inorganic material containing aluminum (Al), oxygen (O), and hydrogen (H). Nanofiber 4 is mainly composed of boehmite and alumina. Boehmite is softer than alumina. Therefore, when the proportion of boehmite in the nanofibers 4, that is, the proportion of boehmite in the inorganic layer 3 is high, the inorganic layer 3 is less likely to crack or chip.

Boehmite contains Al-OH bonds. The presence of boehmite in the inorganic layer 3 can be confirmed by detecting Al--OH bonds on the surface 30 of the inorganic layer 3 using XPS. Alumina contains Al-O-Al bonds. The presence of alumina in the inorganic layer 3 can be confirmed by detecting Al-O-Al bonds on the surface 30 of the inorganic layer 3 by XPS. The ratio X/Y of content X of Al-OH bonds to content Y of Al-O-Al bonds is, for example, 0.3 or more and 1.0 or less. In this specification, the integrated intensity of the Al(OH) ₃ peak in the spectrum obtained by XPS is regarded as the Al--OH bond content X. Further, the integrated intensity of the Al ₂ O ₃ peak in the spectrum is regarded as the content Y of Al--O--Al bonds.
Details of the XPS conditions are shown in Test Example 3 described later.

The average thickness of the inorganic layer 3 is 10 nm or more and 1000 nm or less. If the average thickness of the inorganic layer 3 is 10 nm or more, impurities can be efficiently separated by the inorganic layer 3. If the average thickness of the inorganic layer 3 is 1000 nm or less, the flexibility of the inorganic layer 3 can be easily ensured. Moreover, the filtration time using the composite porous body 1 does not become too long. The lower limit of the average thickness may be 15 nm, 50 nm, 100 nm, or 200 nm. The upper limit of the average thickness may be 900 nm, 800 nm, or 500 nm. The range of the average thickness of the inorganic layer 3 may be, for example, 15 nm or more and 900 nm or less, or 200 nm or more and 500 nm or less.

The average thickness of the inorganic layer 3 is determined by SEM-EDX. The boundary between the base material 2 and the inorganic layer 3 is determined by measuring the detected intensity of Al using EDX. In the SEM image, the location where the detection intensity of Al sharply decreases is the boundary between the base material 2 and the inorganic layer 3. The distance from this boundary to the surface of the inorganic layer 3 is the thickness of the inorganic layer 3. The average thickness of the inorganic layer 3 is, for example, the average of the thicknesses at five different points in the inorganic layer 3.

The inorganic layer 3 formed by laminating a plurality of nanofibers 4 is a porous body. In this inorganic layer 3, gaps between adjacent nanofibers 4 become pores through which fluid passes. The average pore diameter of the pores in the inorganic layer 3 is 1 nm or more and 100 nm or less. If the average pore diameter of the inorganic layer 3 is 1 nm or more, the flexibility of the inorganic layer 3 is ensured. Moreover, the filtration time using the composite porous body 1 does not become too long. If the average pore diameter of the inorganic layer 3 is 100 nm or less, impurities can be efficiently separated by the inorganic layer 3. The lower limit of the average pore diameter may be 2 nm, 5 nm, 10 nm, or 20 nm. The upper limit of the average pore diameter may be 45 nm, 40 nm, or 30 nm. The range of the average pore diameter of the inorganic layer 3 may be, for example, 2 nm or more and 45 nm or less, or 20 nm or more and 30 nm or less.

Since the average pore diameter in the inorganic layer 3 is very small, it is difficult to obtain it from a SEM image of the cross section of the inorganic layer 3. The average pore diameter of the inorganic layer 3 in this example is determined by a liquid passage test. FIG. 5 shows the test device 7 used for the liquid passage test. The test device 7 includes a flask 70 that can be evacuated and a cylindrical chamber 71 with both ends open. The composite porous body 1 is sandwiched between the lower end opening 71D of the chamber 71 and the upper end opening 70U of the flask 70. The inorganic layer 3 of the composite porous body 1 faces the chamber 71 .

The procedure for determining the average particle size of the inorganic layer 3 is as follows. First, a test liquid containing a plurality of particles having a known average particle size is prepared, and the test liquid is placed in the chamber 71. The concentration of particles in the test solution (g/cm ³ ) is known. By evacuating the inside of the flask 70, the filtrate that has passed through the composite porous body 1 is stored in the flask 70. The degree of vacuum is 80 Pa or less. The concentration (g/cm ³ ) of particles contained in the filtrate is measured. The concentration of the particles is calculated from the measured volume of the filtrate and the mass of the particles remaining after the filtrate is evaporated. When the concentration of particles in the filtrate is 10% or less of the concentration of particles in the test liquid, the average particle size of the particles contained in the test liquid is regarded as the average pore size of the inorganic layer 3.

Although it is difficult to measure the average pore diameter of the pores in the entire inorganic layer 3, it is possible to measure the size of the openings 3h opened in the surface 30 of the inorganic layer 3. The opening hole 3h is formed by a gap between adjacent nanofibers 4, and is relatively large. FIG. 3 is a schematic diagram schematically showing a SEM image of the surface 30. The average pore diameter of the open pores 3h is, for example, 2 nm or more and 200 nm or less. The average diameter of the open holes 3h may be 5 nm or more and 100 nm or less. The average short diameter of the opening hole 3h is, for example, 1 nm or more and 100 nm or less. The average short diameter of the opening hole 3h may be 2 nm or more and 50 nm or less. The average pore diameter and average minor axis of the opening holes 3h are determined by image analysis, similarly to the average pore diameter and average minor axis of the first surface 21. Specifically, a SEM image of the surface 30 is acquired, and the apertures 3h are identified by binarization processing. The average circular equivalent diameter of the opening hole 3h is the average hole diameter of the opening hole 3h. The average minor axis of the smallest rectangle circumscribing the opening hole 3h is the average minor axis of the opening hole 3h.

≪Characteristics of composite porous material≫
In the composite porous body 1 of this example, the inorganic layer 3 that comes into contact with the fluid to be filtered first is made of an inorganic material containing aluminum. Inorganic materials are difficult to be denatured by heat and also by chemicals. Therefore, the composite porous body 1 of this example has excellent heat resistance and chemical resistance. Since the base material 2 is made of PTFE which has excellent heat resistance and chemical resistance, the heat resistance and chemical resistance of the composite porous body 1 are further improved.

In the composite porous body 1 of this example, the base material 2 is made of a resin material with excellent flexibility. Further, the inorganic layer 3 is constituted by a laminate of a plurality of nanofibers 4. When the inorganic layer 3 is bent, each nanofiber 4 deforms minutely and absorbs the stress acting on the inorganic layer 3. Therefore, the inorganic layer 3 of this example has a predetermined flexibility. The composite porous body 1 including such a base material 2 and an inorganic layer 3 has excellent flexibility and is difficult to break when bent.

The flexibility of the composite porous body 1 is evaluated, for example, by the bending test shown in FIG. 6. In the bending test shown in FIG. 6, the composite porous body 1 is placed along the curved surface of the approximately semi-cylindrical test stand 8, and it is examined whether the inorganic layer 3 of the composite porous body 1 breaks. The bending test will be explained in detail in Test Example 2 below.

≪Method for producing composite porous body≫
The composite porous body 1 of Embodiment 1 is obtained, for example, by a manufacturing method including the following steps.
-Step A: A base material 2 made of a porous body made of a resin material is prepared.
- Step B...The first surface 21 of the base material 2 is subjected to a hydrophilic treatment.
-Step C... A dispersion containing a plurality of nanofibers 4 is prepared.
- Step D...Apply the dispersion liquid to the first surface 21.
- Step E: The base material 2 coated with the dispersion liquid is heat-treated in an atmosphere of 80° C. or higher and 200° C. or lower.
The order of process B and process C can be interchanged. Each step will be explained in detail below.

[Process A]
The base material 2 is the same as the base material 2 provided in the composite porous body 1 described above. That is, the average pore diameter of the first surface 21 of the base material 2 is 50 nm or more and 500 nm or less. The average pore diameter of the first surface 21 can be determined from the SEM image of the first surface 21.

The method for producing the base material 2 is not particularly limited. For example, the base material 2 made of a porous body made of PTFE may be manufactured by a manufacturing method disclosed in JP-A No. 2010-94579. Specifically, by stretching a thin film made of PTFE, the thin film becomes porous. As a result, a base material 2 made of a porous PTFE material is obtained. The average pore diameter of the base material 2 changes depending on the stretching conditions.

[Process B]
In step B, at least the first surface 21 of the base material 2 is subjected to a hydrophilic treatment. Specifically, the first surface 21 of the porous base material 2 is composited with a hydrophilic polymer. The hydrophilic polymer is preferably one that undergoes dehydration condensation or hydrogen bonding with the hydroxyl group of alumina. Hydrophilic polymers include, for example, polyvinyl alcohol (PVA) and ethylene vinyl alcohol copolymers having many hydroxyl groups. The hydrophilic polymer may be polyvinylpyrrolidone containing an amide group, polyethyleneimine containing an imino group, polyacrylic acid containing a carboxyl group, or the like. In particular, PVA has a hydrophobic group, and the hydrophobic group tends to adhere to the surface of the porous PTFE body. Therefore, PVA is easily composited into the base material 2.

The surface of the porous PTFE body can be made hydrophilic, for example, by the following procedure. First, a porous PTFE body is immersed in IPA, and then immersed in a PVA aqueous solution adjusted to an appropriate concentration. The PVA is then gelled by chemical crosslinking or electron beam crosslinking. In chemical crosslinking, a crosslinking agent is added to the PVA aqueous solution. An acid catalyst may be added to the PVA aqueous solution if necessary. After crosslinking the PVA, the porous body is washed with pure water and dried. The PVA concentration in the PVA aqueous solution changes depending on the porosity of the base material 2 and the like. For example, the PVA concentration in the PVA aqueous solution is 0.8% by mass or more and 10% by mass or less. The immersion time of the porous body in the PVA aqueous solution varies depending on the porosity of the base material 2 and the like. For example, the immersion time of the porous body in the PVA aqueous solution is 2 minutes or more and 24 hours or less. Crosslinking agents include, for example, glutaraldehyde or terephthalaldehyde, which form acetal bonds. The dose of the electron beam is, for example, about 6 megarad.

[Process C]
The dispersion liquid is a liquid in which a plurality of nanofibers 4 are dispersed in a dispersion medium. The dispersion medium is mainly water. The dispersion medium may contain isopropyl alcohol (IPA) in addition to water, and may further contain a surfactant. IPA improves the wettability of the dispersion medium to the surface of the base material 2. The concentration of IPA is preferably 5% by mass or less when the mass of the dispersion liquid is 100.

The concentration of nanofibers 4 in the dispersion medium is preferably 0.1% by mass or more and 5% by mass or less. If the concentration of the nanofibers 4 is 0.1% by mass or more, the concentration of the nanofibers 4 in the dispersion medium is sufficient, so that the nanofibers 4 are easily stacked on the first surface 21 in step D. If the concentration of nanofibers 4 is 5% by mass or less, the concentration of the dispersion liquid will not become too high. If the concentration of the dispersion liquid is too high, it is difficult to apply the dispersion liquid thinly and uniformly onto the first surface 21.

The average length of the nanofibers 4 is 10 times or more the average pore diameter of the first surface 21 of the base material 2. The average length is, for example, 100 nm or more and 10000 nm or less. The lower limit of the average length may be 500 nm, or even 1000 nm. The upper limit of the average length may be 7000 nm, or even 5000 nm. The range of the average length may be, for example, 500 nm or more and 7000 nm or less, or 1000 nm or more and 5000 nm or less. The average width of the nanofibers 4 is, for example, 1 nm or more and 10 nm or less. The width and length of the nanofibers 4 are orthogonal to each other. The lower limit of the average width may be 2 nm, and further may be 3 nm. The upper limit of the average width may be 7 nm, or even 5 nm. The range of the average width may be, for example, 2 nm or more and 7 nm or less. The average aspect ratio, which is the average length divided by the average width, is, for example, 30 or more and 5000 or less. The average aspect ratio may be, for example, 100 or more and 500 or less, or 100 or more and 300 or less. The size of the nanofibers 4 does not change even in the inorganic layer 3 of the composite porous body 1.

[Process D]
The method of applying the dispersion liquid onto the first surface 21 is not particularly limited. The coating method is, for example, spin coating, bar coating, dip coating, or die coating. Alternatively, the tube-shaped or sheet-shaped base material 2 may be fixed to a rotating shaft, and the dispersion liquid may be applied by spraying or the like while rotating the base material 2. The inorganic layer 3 of the composite porous body 1 according to the embodiment is very thin. In order to form the thin inorganic layer 3, spin coating is preferable. Spin coating, in which the dispersion liquid is dropped onto the base material 2 while rotating the base material 2, allows the thickness of the dispersion liquid to be thin and uniform. The peripheral speed of spin coating is, for example, 10,000 mm/min or more.

[Process E]
The temperature of the heating atmosphere is preferably 80°C or more and 200°C or less. The heating atmosphere is not particularly limited, and is, for example, an air atmosphere, an inert gas atmosphere, a steam atmosphere, or a reduced pressure atmosphere. The dispersion medium is evaporated by the heating atmosphere, and a stack of nanofibers 4 is formed on the first surface 21. As the temperature of the heating atmosphere becomes higher, the evaporation time of the dispersion medium becomes faster, and the productivity of the composite porous body 1 improves. Further, as the temperature of the heating atmosphere increases, the nanofibers 4 are more likely to bond with each other, and the nanofibers 4 are less likely to fall off from the composite porous body 1. However, if the temperature of the heating atmosphere is too high, the boehmite contained in the nanofibers 4 tends to change to alumina. If the proportion of alumina in the inorganic layer 3 increases, the inorganic layer 3 may become brittle. For example, if the temperature of the heating atmosphere is less than 130° C., the proportion of alumina will not become too large.

[others]
It is preferable that the film-forming cycle consisting of Step D and Step E is repeated multiple times. It is preferable that the repeat number k of the film forming cycle is 2 or more and 5 or less. In this case, in the kth step D, the dispersion liquid is applied onto the laminate formed in the k-1st step E. By performing the film formation cycle twice or more, it is possible to suppress the formation of a region on the first surface 21 where the inorganic layer 3 is not formed.

<Embodiment 2>
In Embodiment 2, a tube-shaped composite porous body 1 will be described based on FIG. 4. The shape of the base material 2 of this composite porous body 1 is a tube. The first surface 21 of the tube-shaped base material 2 constitutes the outer peripheral surface of the base material 2 . The inorganic layer 3 formed on the first surface 21 constitutes the outer peripheral surface of the tube-shaped composite porous body 1.

The tube-shaped composite porous body 1 may be placed in a bent state, for example, in a module of a purification device. Therefore, the tube-shaped composite porous body 1 may also be required to have resistance to bending. The bending resistance of the tube-shaped composite porous body 1 can be evaluated, for example, by wrapping the composite porous body 1 around the outer peripheral surface of a cylinder having a predetermined radius.

The average thickness of the tube-shaped base material 2 is, for example, 50 μm or more and 1000 μm or less. If the average thickness of the tubular base material 2 is 50 μm or more, the strength of the composite porous body 1 including the base material 2 is ensured. If the average thickness of the base material 2 is 1000 μm or less, the flexibility of the composite porous body 1 including the base material 2 is ensured, and the filtration time by the composite porous body 1 does not become too long. The average thickness of the tube-shaped base material 2 may be, for example, 100 μm or more and 500 μm or less.

<Test Example 1>
In Test Example 1, the influence of the relationship between the average pore diameter of the first surface 21 of the base material 2 and the average length of the nanofibers 4 on the formation of the inorganic layer 3 was investigated. Specifically, the following Sample A, Sample B, and Sample C were produced.

≪Sample A≫
A base material 2 made of PTFE was prepared. The average thickness of the base material 2 was 30 μm, and the average pore diameter was 130 nm. The average pore diameter was determined by cutting the base material 2 using a focused ion beam (FIB) and observing the cross section of the base material 2 using an SEM. The magnification of the SEM image was 5000 times, and the image processing software was "ImageJ". The average pore diameter of the base material 2 was determined by binarizing the SEM image and averaging the equivalent circular diameters of the pores 2h. The threshold value for the binarization process was 127. In this specification, the average pore diameter of the base material 2 is considered to be the average pore diameter of the first surface 21 of the base material 2.

The base material 2 was immersed in IPA for 90 minutes, and then in a PVA solution for 150 minutes. The PVA concentration in the PVA solution was 0.6% by mass. Next, the base material 2 was immersed in pure water for 1 minute, and then the PVA was crosslinked by electron beam irradiation. Finally, the base material 2 was dried in an atmosphere at 25° C. to make the surface of the base material 2 hydrophilic.

A dispersion containing nanofibers 4 was prepared. The dispersion medium was water containing 4% by weight IPA. The concentration of nanofibers 4 in the dispersion was 5% by mass. The average length of the nanofibers 4 was 1400 nm, the average width was 4 nm, and the average aspect ratio was 350. The average length of the nanofibers 4 was 10 times or more the average pore diameter of the first surface 21 of the base material 2.

The dispersion liquid was dropped onto the first surface 21 of the substrate 2 by spin coating. The peripheral speed of spin coating was 10,000 mm/min. The base material 2 coated with the dispersion liquid was left in a heated atmosphere at 100° C. for 30 minutes. Dropping of this dispersion liquid and heating were repeated once again to complete sample A.

When the surface of sample A was observed by SEM, it was found that an inorganic layer 3 made of a laminate of a plurality of nanofibers 4 was formed on the first surface 21 of the base material 2.

In order to measure the average pore diameter of the inorganic layer 3 of Sample A, a liquid flow test was conducted using the testing device 7 of FIG. 5. In the liquid flow test, multiple test liquids were prepared. The average particle size of particles contained in each test liquid is known. As a result of the liquid passage test, the average pore diameter of the inorganic layer 3 of Sample A was 20 nm.

≪Sample B≫
The method for producing sample B was the same as sample A except that the average length of nanofibers 4 was 3000 nm. The average width of the nanofibers 4 was 4 nm, and the average aspect ratio of the nanofibers 4 was 750. The average length of the nanofibers 4 was about 23 times the average pore diameter of the first surface 21 of the base material 2. Although no SEM image is shown in this specification, an inorganic layer 3 made of a laminate of a plurality of nanofibers 4 was formed on the surface of sample B.

The average pore diameter of the inorganic layer 3 of Sample B was measured by the same liquid passage test as Sample A. As a result, the average pore diameter of the inorganic layer 3 of sample B was 20 nm.

≪Sample C≫
The method for producing sample C was the same as sample A except that the average pore diameter of base material 2 was 260 nm. The average length of the nanofibers 4 was 1400 nm, which was about 5.4 times the average pore diameter of the first surface 21 of the base material 2.

When the surface of Sample C was observed by SEM, it was found that the nanofibers 4 were attached to the surface of the porous base material 2 and were unable to close the pores on the first surface 21 of the base material 2. It is presumed that the reason why the pores were not filled was because the average length of the nanofibers 4 was short.

<Test Example 2>
In Test Example 2, a bending test was conducted to examine the flexibility of Sample A and Sample B. Figure 6 shows an overview of the bending test. As shown in FIG. 6, the bending test procedure is as follows. A test stand 8 having a substantially semi-cylindrical shape was prepared. The radius of curvature of the curved surface of test stand 8 was 10 cm. The composite porous body 1 of Sample A and the composite porous body 1 of Sample B were placed along the curved surface of the test table 8, fixed with tape 80, and left for a predetermined period of time. The inorganic layer 3 of the composite porous body 1 was arranged radially outward of the test stand 8. As a result of the bending test, no defects such as cracks were observed in the inorganic layer 3 in either the composite porous body 1 of Sample A or the composite porous body 1 of Sample B. From the results of Test Example 2, it was found that the composite porous body 1 having the configuration of Embodiment 1 had sufficient bending properties.

<Test Example 3>
In Test Example 3, it was investigated whether the composite porous body 1 of this example could withstand the pressure of practical desalination treatment. Specifically, Sample A, Sample B, Sample D, and Sample E were produced.

≪Sample A≫
Sample A is the same as Sample A of Test Examples 1 and 2. The average thickness of the inorganic layer 3 of sample A was 100 nm.

≪Sample B≫
Sample B is the same as Sample B in Test Examples 1 and 2. The average thickness of the inorganic layer 3 of sample B was 100 nm.

≪Sample D≫
The method for producing sample D was based on the method described in JP-A-2010-105846. A dispersion containing nanofibers 4 was poured into a container coated with polytetrafluoroethylene and heated in an oven to obtain a self-supporting film. The average thickness of the obtained free-standing membrane was 0.1 μm.

≪Sample E≫
The method for preparing sample E was the same as sample D except that the amount of the dispersion containing nanofibers 4 was 1000 times larger. The average thickness of the obtained free-standing membrane was 100 μm.

Sample A, Sample B, Sample D, and Sample E were each subjected to a pressure filtration test. In the pressure filtration test, water at a pressure of 7 MPa, which is the pressure for practical desalination treatment, was supplied to each sample. As a result, cracks occurred in Samples D and E. On the other hand, no cracking occurred in Sample A and Sample B. The reason why cracks did not occur in Samples A and B, in which the average thickness of the inorganic layer 3 is thin, is that the inorganic layer 3 is formed on the base material 2 made of a flexible resin material, and the resin material is It is assumed that this is because it played the role of a cushion.

<Test Example 4>
In Test Example 4, Sample 4-14 was prepared from Sample 4-1 with different average pore diameters on the first surface 21, etc. Table 1 shows data on the physical properties of each sample. Performance data for each sample is shown in Table 2. The physical property data and performance data are as follows.

[Material]
The material of the base material 2 was PP or PTFE. All materials have been treated to make them hydrophilic. "PTFE*" shown in Table 1 is PTFE in which only a portion, specifically 50% of the surface of PTFE, has been made hydrophilic.

[shape]
The shape of the base material 2 is a round bar, a sheet, or a tube. In the round bar-shaped and tube-shaped base materials 2, the outer peripheral surface of the base material 2 is the first surface 21, and the inorganic layer 3 is provided on the outer peripheral surface.

[Average thickness]
The average thickness of the sheet-shaped base material 2 was determined from an SEM image of a cross section of the sheet-shaped composite porous body 1 cut in the thickness direction. The average thickness of the tube-shaped base material 2 was determined from an SEM image taken of a cross section of the composite porous body 1 cut in a direction perpendicular to the stretching direction of the tube-shaped composite porous body 1. The average thickness was the average of 5 points. The average thickness of a round bar is the diameter of the round bar.

[Average pore diameter on the first surface of the base material]
The average pore diameter of the first surface 21 was determined by image analysis of a SEM image of a cross section of the composite porous body 1. The conditions for image analysis are the same as in Test Example 1.

[Average short axis of first surface of base material]
The average short axis of the first surface 21 was measured from image data acquired when measuring the average pore diameter. The average short axis of the smallest rectangle circumscribing each hole in the image data is the average short axis of the first surface 21 .

[Average pore diameter of second layer]
Samples listed as "none" in Table 1 do not include the second layer 2B shown in FIG. 2. The samples whose numerical values are listed in Table 1 are provided with the second layer 2B. The average pore diameter of the second layer 2B was determined from the SEM image of the cross section of the base material 2. The conditions for image analysis are the same as in Test Example 1.

[Average thickness of inorganic layer]
The average thickness of the inorganic layer 3 was measured from a SEM image of the cross section of the composite porous body 1. The average thickness was the average of 5 points.

[Average pore diameter of inorganic layer]
The average pore diameter of the inorganic layer 3 was determined by the liquid passage test shown in Test Example 1.

[Average pore diameter of open pores in inorganic layer]
The average pore diameter of the open pores 3h of the inorganic layer 3 was measured from a SEM image taken of the surface 30 of the inorganic layer 3. The average hole diameter is the average value of the equivalent circular diameters of the opening holes 3h. The magnification of the SEM image was 100,000 times.

[Average pore diameter of inorganic layer]
The average short axis of the openings 3h of the inorganic layer 3 was measured from a SEM image of the surface 30 of the inorganic layer 3. The average short axis is the average short axis of the smallest rectangle circumscribing the opening hole 3h.

[Al-OH ratio in inorganic layer]
The "Al-OH ratio" is the ratio X/Y between the content X of Al-OH bonds and the content Y of Al-O-Al bonds. Content X and content Y were determined by XPS. The measuring instrument was a QuanteraSXM manufactured by ULVAC PHI. The measurement conditions were as follows.
・X-ray source: MONO Al Kα
・Beam conditions: 100μm, φ100W, 25kV HP
・Transmission energy: 55eV (narrow), 280eV (wide)
・Analysis elements: C, O, F, Al, Si, S
・Charge correction: All element charge correction with F1s as 689.67eV

It was assumed that two components, _Al2O3 and Al(OH) ₃ , were present in the _Al2p3 peak of the spectrum obtained by XPS. The difference between the binding energy of Al ₂ O ₃ and that of Al(OH) ₃ is defined as 0.6 eV, and the above peak is separated into the peak of Al ₂ O ₃ and the peak of Al(OH) ₃ . did. The integrated intensity of the Al ₂ O ₃ peak is the Al-OH bond content X, and the integrated intensity of the Al(OH) ₃ peak is the Al-O-Al bond content Y.

[Material of hydrophilic material]
Each of the hydrophilic materials 5 is a layer of a hydrophilic polymer that covers at least a portion of the surface of the base material 2.

[CH ₂ -O-R content in hydrophobic material]
“CH ₂ —O—R content” is the content of CH ₂ —O—R bonds in the plurality of chemical structures derived from PVA and PTFE contained in the first surface 21 expressed as a percentage. The CH ₂ -O-R bond is a type of chemical structure derived from PVA and PTFE. The CH ₂ -O-R content was determined by XPS. The measuring instrument was a QuanteraSXM manufactured by ULVAC PHI. The measurement conditions were as follows.
・X-ray source: MONO Al Kα
・Beam conditions: 100μm, 100W, 20kV HP
・Transmission energy: 55eV (narrow), 280eV (wide)
・Analysis elements: C, O, F
・Photoelectron extraction angle: 45°

Assuming that 12 components were present in the peak of the C1s spectrum obtained by XPS, the peaks were separated, and the integrated intensity of the peak of each component was determined. The binding energies of the 12 components are 284.0eV, 285.0eV, 285.8eV, 286.6eV, 287.5eV, 288.4eV, 289.1eV, 289.9eV, 290.7eV, 291.8eV, 292. 6 eV, and 293.6 eV. The chemical structure containing the CH ₂ -O-R bond is assigned to the peak at 286.6 eV. The above peak was separated into 12 component peaks, and the integrated intensity of each component peak was determined. The CH ₂ -O-R content is {(integrated intensity of peak with binding energy of 286.6 eV)/(sum of integrated intensities of peaks of 12 components)}×100.

Next, the performance of each sample shown in Table 2 will be explained.

[Flexibility]
The flexibility of each sample was determined by the bending test shown in FIG. The radius of curvature of the curved surface of test stand 8 was 5 cm. The round bar-shaped sample and the tube-shaped sample were placed along the curved surface of the test stand 8. A sample in which no cracks occurred in the inorganic layer 3 was rated A.

[chemical resistance]
After each sample was immersed in ethanol, the surface of each sample was observed by SEM. A sample in which the peeled area of the inorganic layer 3 was 10% or less in the observation field was evaluated as A, and a sample in which the peeled area exceeded 10% was evaluated as B.

[Flow velocity ratio]
The flow rate ratio is the flow rate of each sample when the flow rate of sample 4-1 is set to 1. The flow rate is the flow rate of the filtrate passing through the sample. The stock solution flow rate is the same for all samples. In the sheet-shaped composite porous body 1, the filtrate flows from the surface 30 of the inorganic layer 3 toward the second surface 22. In the tube-shaped composite porous body 1, the filtrate flows from the outer peripheral surface of the tube toward the inner space of the tube. The filtrate that has flowed into the internal space is discharged to the outside of the tube along the extending direction of the tube. In the round rod-shaped composite porous body 1, the filtrate flows inward from the outer peripheral surface of the round rod. The filtrate that has flowed into the round bar moves along the extending direction of the round bar and is discharged from the end face of the round bar to the outside of the round bar. The higher the flow rate ratio, the higher the liquid permeability of the composite porous body 1.

[Separation rate of 20 nm particles]
The separation rate of 20 nm particles indicates the ability to separate particles contained in the stock solution. The dispersion medium was water, and the average particle size of the particles was 20 nm. The particle concentration X (mass %) in the stock solution and the particle concentration Y (mass %) in the filtrate are measured. A sample in which (1-Y/X)×100 is 10% or more is rated A.

[Separation rate of PEG1000]
The separation rate of PEG1000 indicates the ability to separate PEG1000 particles contained in the stock solution. PEG1000 is polyethylene glycol with an average molecular weight of around 1000. The dispersion medium is ethanol. The concentration X (mass%) of PEG1000 in the stock solution and the concentration Y (mass%) of PEG1000 in the filtrate are measured. A sample in which (1-Y/X)×100 is 10% or more is rated A.

[IPA separation rate]
The IPA separation rate indicates the ability to separate IPA from a stock solution that is a mixed solution of water and IPA. The concentration X (mass %) of IPA in the stock solution and the concentration Y (mass %) of IPA in the filtrate are measured. A sample in which (1-Y/X)×100 is 10% or more is rated A.

[Separation rate of NaCl]
The NaCl separation rate indicates the ability to separate NaCl from a stock solution of NaCl dissolved in water. The concentration X (mass %) of NaCl in the stock solution and the concentration Y (mass %) of NaCl in the filtrate are measured. Samples in which (1-Y/X)×100 is 10% or more are rated A, and samples in which it is less than 10% are rated B.

From the results in Tables 1 and 2, it was found that all samples had excellent flexibility. Furthermore, it was found that all the samples were excellent in the performance of separating 20 nm particles, the performance of separating PEG1000, and the performance of separating IPA. Furthermore, it was found that only sample 4-14, which included the inorganic layer 3 with an average pore diameter of 5 nm, had the ability to separate NaCl.

From the results in Tables 1 and 2, it was found that Samples 4-4 to 4-14, which included the base material 2 made of PTFE, had excellent chemical resistance.

From the results in Tables 1 and 2, it was found that the thinner the average thickness of the inorganic layer 3, the higher the flow velocity ratio. Since there is no large difference in the separation ability of each sample, the average thickness of the inorganic layer 3 may be reduced in order to shorten the filtration time.

1 Composite porous body, 2 Base material, 2h Holes, 2A First layer, 2B Second layer, 21 First surface, 22 Second surface, 3 Inorganic layer, 3h Open pores, 30 Surface, 4 Nanofiber, 5 Hydrophilic resin, 7 test device, 70 flask, 70U top opening, 71 chamber, 71D bottom opening, 8 test stand, 80 tape.

Claims (16)

1. a base material having a first surface;
   an inorganic layer covering at least a portion of the first surface,
   The base material is a porous body made of a resin material,
   The inorganic layer is a laminate of multiple nanofibers,
   Each of the plurality of nanofibers is made of an inorganic material containing aluminum, oxygen, and hydrogen,
   The average pore diameter on the first surface is 5 nm or more and 500 nm or less,
   The average thickness of the inorganic layer is 10 nm or more and 1000 nm or less,
   The average pore diameter of the inorganic layer is 1 nm or more and 50 nm or less,
   Composite porous material.
2. The composite porous body according to claim 1, wherein the resin material is a hydrophobic polymer.
3. The composite porous body according to claim 2, wherein the hydrophobic polymer is polytetrafluoroethylene.
4. The composite porous body according to any one of claims 1 to 3, wherein at least a portion of the first surface contains a hydrophilic material.
5. The composite porous body according to claim 4, wherein the hydrophilic material is a hydrophilic polymer coated on at least a portion of the surface of the base material including the first surface.
6. The composite porous body according to claim 5, wherein the hydrophilic polymer is polyvinyl alcohol.
7. The resin material is polytetrafluoroethylene,
   The first surface containing the hydrophilic polymer includes a plurality of chemical structures derived from the polyvinyl alcohol and the polytetrafluoroethylene,
   The composite pore according to claim 6, wherein the content of CH ₂ -O-R bonds in the chemical structure detected by the C1s spectrum obtained by XPS among the plurality of chemical structures is 3% or more and 15% or less. Substantive body.
8. The composite porous body according to any one of claims 1 to 7, wherein the base material has a sheet shape.
9. The composite porous body according to claim 8, wherein the average thickness of the base material is 1 μm or more and 100 μm or less.
10. The shape of the base material is a tube,
    The composite porous body according to any one of claims 1 to 7, wherein the first surface is an outer peripheral surface of the tube.
11. The composite porous body according to claim 10, wherein the average thickness of the base material is 50 μm or more and 1000 μm or less.
12. The base material includes a first layer including the first surface and a second layer adjacent to the first layer,
    The composite porous body according to any one of claims 1 to 11, wherein the average pore size of the second layer is larger than the average pore size of the first layer.
13. The inorganic layer includes an Al-OH bond and an Al-O-Al bond,
    Any one of claims 1 to 12, wherein the ratio X/Y of the content X of the Al-OH bond and the content Y of the Al-O-Al bond is 0.3 or more and 1.0 or less. Composite porous body described in section.
14. The composite porous body according to any one of claims 1 to 13, wherein the average short diameter of the pores on the first surface is 4 nm or more and 400 nm or less.
15. The inorganic layer has an opening opening on the surface of the inorganic layer,
    The average pore diameter of the open pores is 2 nm or more and 200 nm or less,
    The composite porous body according to any one of claims 1 to 14, wherein the average short diameter of the open pores is 1 nm or more and 100 nm or less.
16. Step A of preparing a base material made of a porous body made of a resin material;
    Step B of hydrophilizing the first surface of the base material;
    Step C of preparing a dispersion containing a plurality of nanofibers;
    a step D of applying the dispersion liquid to the first surface;
    A step E of heat-treating the base material coated with the dispersion liquid in a heating atmosphere of 80° C. or more and 200° C. or less,
    The average pore diameter of the first surface in the step A is 5 nm or more and 500 nm or less,
    Each of the plurality of nanofibers in the step C is made of an inorganic material containing aluminum, oxygen and hydrogen,
    The average length of the plurality of nanofibers in the step C is 10 times or more the average pore diameter.
    Method for manufacturing a composite porous body.