GB2635061A

GB2635061A - Composite sheet

Info

Publication number: GB2635061A
Application number: GB2500173.6A
Authority: GB
Inventors: HOSOKAWA Junji; Goto Minoru; Yoneta Keitaro; Natsui Shohei
Original assignee: Kao Corp
Current assignee: Kao Corp
Priority date: 2023-07-12
Filing date: 2024-06-24
Publication date: 2025-04-30
Also published as: CN119731387A; GB202500173D0; FR3150963A1; WO2025013601A1; JP2025013206A; JP7608664B1

Abstract

Provided is a composite sheet which has a metal-organic framework supported in a sheet base material composed of fibers, which has high gas adsorption performance, and in which the metal-organic framework hardly collapses even during use. In the composite sheet, the metal-organic framework is dispersed throughout the sheet base material composed of fibers. The fibers include core-sheath fibers having a core-sheath structure composed of a core portion and a sheath portion. The metal-organic framework is supported by melting and fixing a resin of the sheath portion of the core-sheath fibers. The surface exposure ratio of the metal-organic framework supported in the sheath portion of the core-sheath fibers is 50% or more.

Description

Title of the Invention: COMPOSITE SHEET

Technical Field

[0001] The present invention relates to a composite sheet in which a metal organic framework is supported on a sheet base material.

Background Art

[0002] Attention has been focused on metal organic frameworks (MOFs) as high-performance gas adsorption materials because they have a uniform pore size, a high specific surface area, high separation performance, and the like. Meanwhile, MOF is known to be difficult to handle by itself because it is a micron-scale fine powder. In order to deal with this, a technology has been known that a base material such as a non-woven fabric supports MOFs to collectively handle a large number of MOFs (see, for example, Patent Literature 1). Citation List Patent Literature [0003] Patent Literature 1: Japanese Patent Application Laid-open No. 2021-191913 Patent Literature 2: US Patent Application Laid-open No. 2021/0189620 Patent Literature 3: Chinese Patent Application Laid-open No. 12002938

Disclosure of Invention Technical Problem

[0004] In order to enhance the gas adsorption performance, it is necessary to support a large number of MOFs by a non-woven fabric. For this purpose, it is advantageous to support MOFs by not only the surface layer portion of the non-woven fabric but also the inside thereof. However, each particle of the MOF tends to stay on the surface layer portion without entering the inside of the non-woven fabric in general methods such as a method of spraying particles of the MOF on the non-woven fabric and a method of impregnating the non-woven fabric with a dispersion liquid of the MOFs.

[0005] Fibers forming a non-woven fabric do not have a function of fixing the MOFs on their surfaces. For this reason, even if the non-woven fabric is tried to support a large number of MOFs, the MOFs that are not sufficiently fixed drop out of the non-woven fabric, which makes it difficult to exhibit sufficient gas adsorption performance during use.

A technology that uses binders for fixing MOFs on surfaces of fibers forming a non-woven fabric has been known. However, in the technology that mainly relies on the binders to fix MOFs, the binders adhered to the surfaces of the MOFs obstruct pores of the MOFs, and the original gas adsorption performance of the MOFs is easily impaired.

[0006] An object of the present invention is to provide a composite sheet in which a metal organic framework is supported in a sheet base material formed of a fiber, gas adsorption performance is high, and the metal organic framework is difficult to drop out during use.

Solution to Problem [0007] A composite sheet according to an embodiment of the present invention includes: a sheet base material formed of fibers; and metal organic frameworks dispersed in the sheet base material.

In an embodiment, the fibers include core-sheath fibers having a core-sheath structure that includes a core and a sheath.

In an embodiment, one metal organic framework is supported on the sheath of the core-sheath fibers where a resin of the sheath is molten and fixes the metal organic framework.

In an embodiment, a surface exposure ratio of the metal organic frameworks supported on the sheath of the core-sheath fiber is SO% or more.

Advantageous Effects of Invention [0008] In accordance with the present invention, it is possible to provide a composite sheet in which a metal organic framework is supported in a sheet base material formed of a fiber, gas adsorption performance is high, and the metal organic framework is difficult to drop out during use.

Brief Description of Drawings

[0009] [Fig. 1] Fig. 1 is a flowchart showing a method of producing a composite sheet according to an embodiment of the present invention.

Mode(s) for Carrying Out the Invention [0010] [Basic configuration of composite sheet] A composite sheet according to an embodiment of the present invention includes a sheet base material and a metal organic framework (MOE).

The sheet base material of the composite sheet according to this embodiment is a base material formed of a fiber in a sheet shape, which is typically a non-woven fabric, but may be a woven fabric, a knitted fabric, a mesh, or the like.

The MOF of the composite sheet according to this embodiment is typically a fine powder including a metal ion and an organic ligand, is dispersed in the sheet base material, and is supported on the surface of the fiber forming the sheet base material. Such a structure is referred to as a porous coordination polymer (PCP) in some cases, but is referred to as a metal organic framework (MOF) throughout the present specification.

[0011] In the composite sheet according to this embodiment, the fiber forming the sheet base material includes a core-sheath fiber. The core-sheath fiber is a composite fiber in which a resin that forms a core and a resin that forms a sheath are different from each other, and the sheath covers the core forming a surface of the fiber.

In the core-sheath fiber used in this embodiment, the melting point of the core is preferably higher than the melting point of the sheath. The difference between the melting point of the core and the melting point of the sheath is preferably 10°C or more and 200°C or less, more preferably 60°C or more, and still more preferably 100°C or more. With such a configuration, in the process of producing the composite sheet according to this embodiment, the form of the fiber is maintained by the core having a high melting point. That is, in Step SO5 described below, the sheath is more reliably molten, and melting of the core due to overshooting during heating can be more easily avoided. Further, the resin of the sheath having a low melting point is molten and fixed to the MOF, which allows the MOF to be supported.

In the core-sheath fiber used in this embodiment, the melting point of the core is preferably 160°C or more and 280°C or less, more preferably 200°C or more, and still more preferably 240°C or more. In the composite sheet according to this embodiment, by setting the melting point of the core of the core-sheath fiber included in the fiber forming the sheet base material to such a high temperature, it is possible to further expand the range of use. For example, gas in high-temperature exhaust gas generated in factories or the like can be collected.

In the core-sheath fiber used in this embodiment, the melting point of the sheath is preferably 70°C or more and less than 160°C, more preferably 80°C or more, and still more preferably 100°C or more. By raising the melting point of the sheath in the core-sheath fiber in this way, it is possible to raise the drying temperature in Step SO4 described below and perform drying in a shorter time.

The fiber forming the sheet base material in this embodiment preferably includes, for example, a core-sheath fiber that includes a core formed of polyethylene terephthalate and a sheath formed of polyethylene.

In the core-sheath fiber according to this embodiment, at least one of the core or the sheath may include two or more types of resin components. In this case, the melting point of the core indicates the melting point of one resin component included in the core, and the melting point of the sheath indicates the melting point of one resin component included in the sheath.

[0012] Each particle of the MOF used in the composite sheet according to this embodiment is typically porous with numerous pores having uniform pore sizes and functions as a gas adsorption material by adsorbing and holding gas molecules in each pore.

The composite sheet according to this embodiment collectively supports a large number of MOFs, by a sheet base material, in a state capable of effectively exhibiting gas adsorption performance. It allows the entire MOFs supported on the sheet base material to adsorb a large amount of gas.

[0013] In the composite sheet according to this embodiment, a MOF layer is typically formed on the surface of the fiber.

Here, the MOF layer means a state in which aggregates of MOF particles form a layer as a whole. Specifically, the MOF layer includes one or more forms in, for example, the following states: a plurality of MOFs in a fine powder shape or particle shape is deposited/stacked on the surface of the fiber; MOFs are generated to a fine powder shape or particle shape on the surface of the fiber and grow to cover the surface of the fiber; and particles of adjacent MOFs become unified in the course of its generation and growth to cover the surface of the fiber as a unified film.

The MOF layer is preferably in a state of covering the surface of the fiber as a unified film. This makes it more difficult for the MOF to drop out of the fiber.

In addition, it is possible to prevent, when the sheath of the core-sheath fiber melts, the resin forming the molten sheath from adhering to MOFs fixed to another core-sheath fiber.

In the composite sheet according to this embodiment, the particle size of the MOF may be larger or smaller than the fiber diameter of the sheet base material.

[0014] MOFs that can be used in the composite sheet according to this embodiment have various pore sizes depending on the combination of metal ions and organic ligands. Therefore, in the composite sheet according to this embodiment, the pore size of the MOF to be supported on the sheet base material can be determined in accordance with the molecular size of gas to be adsorbed. As a result, in the composite sheet according to this embodiment, it is possible to selectively adsorb a specific gas by the MOF supported on the sheet base material.

[0015] The composite sheet according to this embodiment may comprise the MOF capable of selectively adsorbing carbon dioxide, for example, to collect carbon dioxide known as a greenhouse gas, then collected carbon dioxide can be used as a raw material for chemicals. By using the MOF capable of selectively adsorbing, other than carbon dioxide, for example, a hydrocarbon (methane, ethane, propane, or the like), hydrogen, hydrogen sulfide, nitrogen, or oxygen, the composite sheet according to this embodiment can be configured as a gas adsorption sheet for these gases.

[0016] In the composite sheet according to this embodiment, it is possible to achieve the effects of the present invention even in the case where any of wide variety of MOFs is used. That is, the MOF is synthesized by self-assembly mainly through a coordination bond between a metal ion and an organic ligand. This reaction mechanism is the same regardless of the types of metal ion and organic ligand. Since the MOFs have, in principle, infinite combinations of metal ions and organic ligands, the combination of MOFs has infinite possibilities. At this time, the shape of the nano-space to be obtained can be arbitrarily tuned because the MOF can be synthesized by considering and selecting species of the metal ion, the shape, the length and the substituent group of a ligand, and the like in accordance with the type of gas to be adsorbed and the adsorption characteristics. Thus, the same effect of the present invention is obtainable for an arbitrary MOF.

[0017] [Basic configuration of method of producing composite sheet]

(Schematic description)

The basic configuration of a method of producing a composite sheet according to this embodiment will be described in accordance with the flowchart shown in Fig. 1. The method of producing a composite sheet according to Fig. 1 includes Step S01 (Prepare raw material solution), Step SO2 (Impregnate with first raw material solution), Step SO3 (Impregnate with second raw material solution), Step SO4 (Dry), and Step SO5 (Apply heat treatment). Hereinafter, Steps SO1 to SO5 according to this embodiment will be described.

[0018] (Step 501: Prepare raw material solution) In Step S01, each of a first raw material solution and a second raw material solution is prepared as a raw material solution of a MOF. The first raw material solution and the second raw material solution are each a solution including one of a metal ion and an organic ligand, which are raw materials of the MOF. When these solutions are mixed, the metal ion and the organic ligand react with each other to generate a MOF.

In this embodiment, the first raw material solution includes a metal ion as a solute, and the second raw material solution includes an organic ligand as a solute.

In this embodiment, the solvent of the first raw material solution preferably includes water.

In this embodiment, the solution of the second raw material solution preferably includes ethanol.

[0019] As an example of Step S01, in the case where the MOF is an ELM-11 (ELM = Elastic Layer-structured Metal organic framework), an aqueous solution of Cu(BF4)2 is prepared as a first raw material solution, and an ethanol solution of 4,4'-bipyridine (bpy) is prepared as a second raw material solution.

[0020] (Step S02: Impregnate with first raw material solution) In Step S02, a sheet base material is impregnated with the first raw material solution prepared in Step S01.

The method of impregnating the sheet base material with the first raw material solution in Step SO2 is not limited to a specific method. For example, a method of impregnating the sheet base material with a sufficient amount of the first raw material solution using one or two or more selected from dropping with a dropper, spraying, spray coating, die coating, curtain coating, and dip coating can be used. Of these, one or two or more selected from dropping with a dropper, spraying, spray coating, die coating, and curtain coating are preferably used from the viewpoint of preventing contamination in the first raw material solution.

In Step S02, the time for impregnating the sheet base material with the first raw material solution is preferably 0.1 minute or more from the viewpoint of allowing the first raw material solution to penetrate to the central region of the sheet base material. Further, the time for impregnating the sheet base material with the first raw material solution is preferably 30 minutes or less from the viewpoint of ensuring productivity.

In Step S02, it is preferable to uniformly disperse the metal ion included in the first raw material solution together with the solvent over the entire sheet base material.

[0021] (Step S03: Impregnate with second raw material solution) In Step S03, the sheet base material that has been impregnated with the first raw material solution in Step SO2 is impregnated with the second raw material solution prepared in Step SO1 before the first raw material solution dries.

This allows the reaction between the solute of the first raw material solution and the solute of the second raw material solution to proceed smoothly even in the case where the solute of the first raw material solution is difficult to dissolve in the solute of the second raw material solution.

Further, even in the case where the solute of the first raw material solution is dissolved in the solute of the second raw material solution, it is possible to uniformly proceed the reaction between the solute of the first raw material solution and the solute of the second raw material solution.

The state in which the first raw material solution has not dried in the sheet base material is a state in which the solvent of the first raw material solution remains in the sheet base material, more specifically a state in which 50, or more of the solvent of the first raw material solution remains in the sheet base material as compared with that before the impregnation.

The amount of the second raw material solution is preferably the amount corresponding to the amount of the first raw material solution with which the sheet base material is impregnated in Step S02.

In Step S03, the time for impregnating the sheet base material with the second raw material solution is preferably 0.1 minute or more from the viewpoint of allowing the second raw material solution to penetrate to the central region of the sheet base material.

Further, the time for impregnating the sheet base material with the second raw material solution is preferably 30 minutes or less from the viewpoint of ensuring productivity.

The method of impregnating the sheet base material with the second raw material solution in Step S03 is not limited to a specific method. For example, a method of adding dropwise a sufficient amount of the second raw material solution into the sheet base material using one or two or more selected from dropping with a dropper, spraying, spray coating, die coating, curtain coating, and dip coating can be used. Of these, one or two or more selected from dropping with a dropper, spraying, spray coating, die coating, and curtain coating are preferably used from the viewpoint of preventing contamination in the second raw material solution.

In Step S03, it is preferable to uniformly disperse the organic ligand included in the second raw material solution together with the solvent over the entire sheet base material.

This organic ligand reacts with the metal ion that has been previously dispersed in the sheet base material in Step SO2 to generate a MOF.

[0022] As an example of Step S03, in the case where MOF is ELM-11, Cu(l3Fd)2 contained in the first raw material solution and bpy contained in the second raw material solution react with each other by the following formula to generate ELM-11. Cu(BF4)2 + 2bpy -> Cu (bpy)2(BF4)2 [0023] In the general process of producing a composite sheet, a MOF generated in advance is supported on the sheet base material. For this reason, each particle of the MOF tends to stay on the surface layer portion in the vicinity of the surface of the sheet base material because it cannot penetrate the inside through gaps of the fiber forming the sheet base material. That is, in the general process of producing a composite sheet, the MOF tends to be unevenly distributed in the sheet base material and remain on the surface layer portion. Conversely, with a base material configuration in which the MOF is capable of penetrating the inside of the sheet base material, the MOF drops off quickly and it is difficult to increase the number of MOFs supported.

On the other hand, in the process of producing the composite sheet according to this embodiment, typically, raw materials before generating MOFs, i.e., a metal ion and an organic ligand, are dispersed into the sheet base material at the molecular level. By generating MOF particles after that, it is possible to cause not only the surface layer portion of the sheet base material but also the central region in the thickness direction to support a large number of MOFs.

The "central region in the thickness direction" refers to the middle part when the sheet base material is equally divided into three regions in the thickness direction.

In the process of producing the composite sheet according to this embodiment, the above advantage can be achieved even with a sheet base material with large thickness. Therefore, it is possible to support even more MOFs by using a sheet base material having a large thickness. From this viewpoint, in this embodiment, the thickness of the composite sheet is preferably 0.2 mm or more, more preferably 0.5 mm or more, and still more preferably 1 mm or more.

The thickness of the composite sheet is realistically 10 mm or less, preferably 5 mm or less.

The thickness of the composite sheet is obtained as an average of a total of 5 positions, i.e., 4 corner positions and 1 central region in plan view, measured with a weight of 3.7 gf/cm' and the area of the pressure surface of the probe of 10 cm in accordance with JIS K 6402.

[0024] In the above general process of producing a composite sheet, the amount of MOF particles that wrap around to the region on the opposite side of the fiber on the spraying surface or application surface is small in the process of spraying or applying MOFs to the sheet base material. For this reason, it is difficult to support the MOFs uniformly over the entire circumference of the surface of the fiber.

On the other hand, in the process of producing the composite sheet according to this embodiment, it is possible to disperse the metal ion and the organic ligand together with the solvent over the entire three-dimensional structure of the sheet base material. For this reason, it is possible to support the MOFs uniformly over the entire circumference of the surface of the fiber forming the sheet base material.

[0025] As a comparative configuration example to this embodiment, a production process using a method of drying the sheet base material impregnated with the first raw material solution before Step S03 will be described. In the process of producing a composite sheet according to the comparative configuration example, the solvent is removed by evaporating from the surface layer side of the sheet base material in the process of drying the sheet base material before Step 503. For this reason, the solvent in the central region in the thickness direction of the sheet base material disperses to the surface layer side together with the metal ion and solidifies. As a result, in the process of producing the composite sheet according to the comparative configuration example, the solute of the first raw material solution is unevenly distributed on the surface layer portion in the sheet base material before being impregnated with the second raw material solution. For this reason, the number of MOFs that can be generated in the central region in the thickness direction of the sheet base material is small. Further, in the process of producing the composite sheet according to the comparative configuration example, the solute of the first raw material solution is generated as a solid in the sheet base material before being impregnated with the second raw material solution. For this reason, even if the sheet base material is Impregnated with the second raw material solution, it is difficult for the solute of the first raw material solution to dissolve in the solvent of the second raw material solution to form metal ions. As a result, metal ions do not react with the organic ligand and tend to remain as unreacted products.

[0026] In the process of producing the composite sheet according to this embodiment, it is preferable that the sheet base material impregnated with the first raw material solution in Step SO2 is not dried and the sheet base material in a state in which the solvent of the first raw material solution is present is impregnated with the second raw material solution in Step S03.

This eliminates the above problem that occurs in the process of producing the composite sheet according to the comparative configuration example. That is, in the process of producing the composite sheet according to this embodiment, the metal ion included in the first raw material solution can be caused to react with the organic ligand included in the second raw material solution while being uniformly dispersed in the sheet base material.

Further, in the process of producing the composite sheet according to this embodiment, the metal ion and the organic ligand, that are present in the solvent without being subjected to binding force, efficiently bond to each other to proceed the reaction. For this reason, the metal ion and the organic ligand are unlikely to remain as unreacted products.

Therefore, in the process of producing the composite sheet according to this embodiment, it is possible that the sheet base material supports MOFs more than in the process of producing the composite sheet according to the comparative configuration example.

[0027] In the process of producing the composite sheet according to this embodiment, it is conceivable that the reaction between the metal ion and the organic ligand proceeds with heterogeneous nucleation at the interface of the fiber forming the sheet base material. Intermolecular forces act between the MOF generated with heterogeneous nucleation in this way and the interface of the fiber. The MOF generated in Step S03 is supported directly on the interface of the fiber by the intermolecular forces without any other component. Therefore, in the process of producing the composite sheet according to this embodiment, it is unnecessary to use a binder as an adhesive component to support the MOF on the surface of the fiber.

In the present specification, the phrase "the MOF is supported directly on the surface of the fiber" refers to that the MOF is fixed to the surface of the fiber without any other component other than the MOF and the fiber material. Typically, the MOF is fixed by intermolecular forces as described above, hydrophobic interactions described below, and/or the resin on the surface of the fiber, which is molten and fixed to the MOF.

The fact that the resin on the surface of the fiber is molten and fixed to the MOF can be determined by observing the cross section of the fiber forming the composite sheet with a scanning electron microscope (SEM). In the case where the resin of the sheath of the core-sheath fiber is molten and fixed to the MOF, the MOF becomes embedded in the sheath of the core-sheath fiber. Thus, the contour of the core-sheath fiber, which is originally circular, is observed to be distorted at the boundary between the MOF and the core-sheath fiber.

As a result, in the composite sheet according to this embodiment, performance degradation due to the presence of binders, such as a decrease in gas adsorption performance of the MOF due to adhesion of the binder and a decrease in flexibility due to the binder, is less likely to occur. For this reason, in the composite sheet according to the present invention, it is preferable that the MOF is supported directly on the surface of the fiber. Such an effect is achieved mainly by generation of the MOF by the reaction between the metal ion and the organic ligand as described above and can be effectively achieved with not only the configuration exemplified in Examples described below but also other configurations.

[0028] In the composite sheet according to this embodiment, the distance between fibers defined as the dimension of the gap between fibers forming the sheet base material is preferably 1 um or more, more preferably 10 pm or more, still more preferably 50 um or more, and still more preferably 100 um or more. This ensures structure flexibility of the MOF supported on the surface of the fiber and prevent the MOF from dropping off. That is, it is more easily achieve high flexibility of the composite sheet and it is possible to provide a space where the MOF is formed to increase the support ratio.

Further, the distance between fibers is preferably 1 000 pm or less, more preferably 500 pm or less, still more preferably 400 pm or less, and still more preferably 300 pm or less. This suppresses homogeneous nucleation and more effectively generates heterogeneous nucleation during the reaction between the metal ion and the organic ligand. That is, the portion where the MOF is formed can be controlled to be the surface of the fiber.

A method of measuring the distance between fibers of the sheet base material in the composite sheet according to this embodiment will be described. First, an arbitrary surface of the composite sheet to be measured is observed with a SEM to obtain an enlarged image of the surface. In the enlarged image, 50 gaps formed by the respective fibers are selected, and the total area of the gaps is measured and divided by the number of gaps (50) to obtain an average gap area per gap. An average fiber-to-fiber diameter when the gap is converted into a circle is obtained on the basis of the average gap area per gap obtained in this way using the following formula, and the average fiber-to-fiber diameter is used as the distance between fibers. Average fiber-to-fiber diameter = 2 x (average gap area / 3.14)1(1/2) Further, in the composite sheet according to this embodiment, the basis weight of the sheet base material is preferably 10 g/m1 or more, more preferably 20g/m' or more, and preferably 100 g/M. or less, more preferably 80g/m2 or less. Note that in the case where sheet base materials are stacked and used as one sheet base material, it is preferable that the total basis weight of the sheet base material exceeds 100 g/i111.

[0029] (Step SO4: Dry) In Step SO4, the sheet base material on which the MOF is supported in Step S03 is dried.

In Step 504, in the process of drying, the solvent is removed by evaporating from the surface layer side of the sheet base material, and the solvent in the central region in the thickness direction of the sheet base material disperse to the surface layer side.

However, the MOF that has been fixed to the surface of the fiber in the central region in the thickness direction of the sheet base material stays on the surface of the fiber without moving together with the solvent. For this reason, in the method of producing a composite sheet according to this embodiment, the dispersed state of the MOF supported on the sheet base material in Step SO4 is maintained.

[0030] In the method of producing a composite sheet according to the present invention, the total number of times to perform the series of processes of Step SO2 to SO4 may be one. That is, it does not necessarily need to repeat the series of processes.

Meanwhile, by repeating the processes of Steps SO2 to SO4, it is possible to increase the number of MOFs to be supported on the sheet base material. From this viewpoint, the total number of times to perform the processes of Step SO2 to SO4 is preferably 2 or more, more preferably 3 or more.

Since there is a limit to the amount of MOFs that can be supported on the sheet base material, the total number of times to perform Step SO2 to SO4 is preferably 20 or less in the method of producing a composite sheet according to this embodiment from the viewpoint of the production cost and the like.

[0031] (Step S05: Apply heat treatment) In Step S05, heat treatment is applied to the sheet base material dried in Step SO4. The heat treatment in Step SO5 is performed at preferably a temperature equal to or greater than the melting point of the sheath and less than the melting point of the core. For example, the heat treatment in Step S05 can be performed by holding at 140°C for 2 hours.

Since the MOF generated in Step S03 is in a hydrated state, it does not have a gas adsorption function.

In Step SO5, it is preferable that the solvent component remaining in the sheet base material is completely removed.

In Step SO5, by dehydrating the MOF, it is possible to exhibit the gas adsorption function of the MOF. In this way, the composite sheet according to this embodiment is obtained.

[0032] In Step 505, by performing heat treatment within the above temperature range, only the sheath, having a low melting point in the core-sheath fiber included in the fiber forming the sheet base material, melts or softens. As a result, in the composite sheet after heat treatment, the MOF is supported on the surface of the core-sheath fiber by the melting and fixing. That is, in the composite sheet according to this embodiment, it is possible to fix the sheath of the core-sheath fiber to the MOF without adding a binder separately as an adhesive component.

Meanwhile, in Step 505, the core having a high melting point is less likely to melt or soften in the process of heat treatment. For this reason, even in the composite sheet after heat treatment, the form of the fiber forming the sheet base material is maintained in the core.

In the sheet base material used in this embodiment, the more the number of the core-sheath fibers is, the more effectively it is possible to prevent MOFs from dropping off. From this viewpoint, in the sheet base material used in this embodiment, the content of the core-sheath fiber is preferably 3 mass% or more, more preferably 10 mass or more, and still more preferably 30 mass% or more.

The content of the core-sheath fiber in the sheet base material is less than 100 massi, preferably 90 mass% or less, and more preferably 80 mass% or less.

The content of the core-sheath fiber in the composite sheet is preferably 1 mass% or more, more preferably 2 mass% or more.

The content of the core-sheath fiber in the composite sheet is preferably 20mass% or less, more preferably 18 mass% or less.

In the general process of producing a composite sheet, as described above, in which a sheet base material is caused to support a MOF generated in advance, molten sheaths in a plurality of core-sheath fibers adjacent to one MOF particle tend to adhere to the one MOF particle during heat treatment. On the other hand, in the process of producing the composite sheet according to this embodiment, since the sheath forming the surface of the core-sheath fiber is covered by the MOF in the stage of Step S03, the molten sheath in the core-sheath fiber is difficult to adhere to a MOF supported on another core-sheath fiber in Step S05.

As a result, in the composite sheet according to this embodiment, the MOF supported on the sheet base material is capable of more effectively exhibiting original gas adsorption performance.

Further, in the composite sheet according to this embodiment, high supportability for MOFs is easily achieved and the MOF is less likely to drop out of the core-sheath fiber as compared with a composite sheet obtained by the process of producing a general composite sheet. This also contributes to effectively exhibiting gas adsorption performance.

[0033] The relationship between the drying temperature in Step SO4, the heat treatment temperature in Step S05, and the configuration of the core-sheath fiber in the method of producing a composite sheet according to this embodiment will be summarized below.

In the core-sheath fiber according to this embodiment, it is preferable that the melting point of the core is higher than the heat treatment temperature in Step S05.

Further, in the core-sheath fiber, it is preferable that the melting point of the sheath is higher than the drying temperature in Step SO4 and lower than the heat treatment temperature in Step S05. In the method of producing a composite sheet according to this embodiment, by setting the melting point of the sheath of the core-sheath fiber to be higher than the drying temperature in Step SO4, it is possible to prevent the sheath from melting to take the reaction product into the fiber in Step 504. For this reason, it is possible to firmly proceed the reaction of generating MOFs and increase the reactivity of the reaction of generating MOFs.

Further, by setting the melting point of the sheath of the core-sheath fiber to be lower than the heat treatment temperature in Step S05, it is possible to fix the MOF more reliably to the surface of the fiber. Further, by setting the melting point of the core of the core-sheath fiber to be higher than the heat treatment temperature in Step SO5, the fiber shape is maintained by the core that does not melt in Step 505. For this reason, the gaps between the fibers of the sheet base material are maintained, and it is possible to increase the reactivity of the reaction of generating MOFs.

[0034] [Another configuration example of method of producing composite sheet] The method of producing a composite sheet according to this embodiment is not limited to the above basic configuration. For example, in the method of producing a composite sheet according to this embodiment, it is preferable that in Step 501, one of the metal ion and the organic ligand, which are raw materials of a MOF, is included in the first raw material solution, and the other is included in the second raw material solution.

In Step S01, it is preferable that the first raw material solution includes the metal ion and the second raw material solution includes the organic ligand as described above.

In addition to this, the first raw material solution may include the organic ligand and the second raw material solution may include the metal ion.

[0035] In the method of producing a composite sheet according to this embodiment, it is preferable that in Step 501, one of the first raw material solution and the second raw material solution includes water as a solvent, and the other includes an organic solvent as a solvent.

In Step 501, it is preferable that water is included as the solvent of the first raw material solution and an organic solvent is included as the solvent of the second raw material solution as described above.

In addition to this, an organic solvent may be included as the solvent of the first raw material solution and water may be included as the solvent of the second raw material solution.

Further, in Step 501, a solvent other than ethanol may be used as the organic solvent. For example, methanol, isopropanol, or acetone may be included.

The organic solvent is preferably one that can be mixed with water in arbitrary ratio.

[0036] In the method of producing a composite sheet according to this embodiment, it is preferable that in Step S01, the content of water included in one of the first raw material solution and a second raw material solution, which includes water as a solvent, is 30 mass% or more and 99 mass% or less. Further, in the method of producing a composite sheet according to this embodiment, it is preferable that in Step 501, the content of an organic solvent included in one of the first raw material solution and the second raw material solution, which includes the organic solvent as a solvent, is 30 mass% or more and 99 mass% or less. Within these numeral ranges, it is easier for the raw material solution to penetrate to the sheet base material and for MOFs to fix uniformly in the thickness direction of the composite sheet.

[0037] The method of producing a composite sheet according to this embodiment may include, as necessary, an additional Step in addition to the above Steps. Further, in the method of producing a composite sheet according to this embodiment, some of the above Steps may be changed or omitted as necessary.

For example, in the drying in Step SO4, the treatment time can be shortened by performing the heat treatment at a temperature higher than room temperature and lower than the heat treatment temperature in Step S05.

Further, for example, by providing a process of drying the sheet base material in the heat treatment in Step SO5, Step SO4 immediately before Step SO5 (the last Step SO4 in the case where Steps SO2 to SO4 are repeated) can be omitted.

[0038] In the method of producing a composite sheet according to this embodiment, as the fiber forming the sheet base material, a fiber other than the core-sheath fiber may be included. In this case, it is preferable that the fiber other than the core-sheath fiber also includes an organic fiber. As a result, in the method of producing a composite sheet according to this embodiment, hydrophobic interactions between molecules act between the organic ligand of the MOF and a group present on the surface of the organic fiber, which allows the MOF to be fixed more firmly to the surface of the organic fiber.

Such hydrophobic interactions appear not only in hydrophobic organic fibers but also in hydrophilic organic fibers. That is, hydrophobic interactions appear even in the organic fiber that is hydrophilic as a whole if it has a hydrophobic portion at a micro level. For example, in a cellulose fiber that is a hydrophilic organic fiber, hydrophobic interactions appear because a C-H group forming an axial group of the glucopyranose ring is hydrophobic.

Whether the fiber forming the sheet base material in the composite sheet is hydrophilic or hydrophobic is determined by the actual property of the surface of the fiber regardless of the original property of the fiber itself. That is, in the case of the fiber that has been subjected to surface treatment, the determination is made for the fiber in the state after the surface treatment. For example, the hydrophobic fiber whose surface has been subjected to hydrophilic treatment is determined to be a hydrophilic fiber, and the hydrophilic fiber whose surface has been subjected to hydrophobic treatment is determined to be a hydrophobic fiber.

To evaluate whether the fiber forming the sheet base material in the composite sheet is hydrophilic or hydrophobic, deionized water is sprayed on the composite sheet, and the contact surface between each fiber and deionized water is observed using a microscope or a digital microscope. It is determined that the surface of the fiber is hydrophilic in the case where the contact angle between the fiber and deionized water is less than 60°, and it is determined that the surface of the fiber is hydrophobic in the case where the contact angle is 60° or more.

In the case where a fiber other than the core-sheath fiber is included as the fiber forming the sheet base material, the mass of only the core-sheath fiber can be obtained as follows. That is, the type of fiber can be identified by identifying the structural formula of the fiber forming the sheet base material in the composite sheet using time-of-flight secondary ion mass spectrometry (TOF-SIMS), infrared spectroscopy (IR), nuclear magnetic resonance (NMR), energy dispersive X-ray spectroscopy (EDX), or the like, and measuring the melting point thereof using DSC. After that, the mass of the core-sheath fiber included in the composite sheet can be calculated on the basis of the intensity ratio of the NMR spectrum obtained from the aggregate of 100 of the corresponding core-sheath fiber and the spectrum obtained from the composite sheet.

[0039] In the method of producing a composite sheet according to this embodiment, it is preferable to use a sheet base material including both a hydrophilic fiber and a hydrophobic fiber. That is, in the sheet base material used in this embodiment, at least a hydrophilic fiber other than the core-sheath fiber that is a hydrophobic fiber is preferably included, and a hydrophobic fiber other than the core-sheath fiber may be included. As a result, in Step 503, the penetration speed of one of water and the organic solvent into the sheet base material impregnated with the other increases, and thus, the MOFs are less likely to be unevenly distributed in the sheet base material.

[0040] The sheet base material according to this embodiment preferably includes, as a hydrophilic organic fiber, one or two or more selected from a cellulose fiber, a regenerated cellulose fiber, a thermoplastic fiber whose surface has been hydrophilized, and the like.

The regenerated cellulose fiber more preferably includes one or two or more selected from a rayon, a cupra, and the like.

Examples of the method of hydrophilizing the surface of the thermoplastic fiber include applying a hydrophilizing agent and performing plasma treatment.

The thermoplastic fiber preferably includes one or two or more selected from a polyolefin resin, a polyester resin, a vinyl resin, an acrylic resin, a fluoropolymer, a polyamide resin, and the like.

The polyolefin resin preferably includes one or two or more selected from polyethylene, polypropylene, and the like.

The polyester resin preferably includes one or two or more selected from polyethylene terephthalate and the like.

The vinyl resin preferably includes one or two or more selected from polyvinyl chloride, polystyrene, and the like.

The acrylic resin preferably includes one or two or more selected from polyacrylic acid, polymethylmethacrylate, and the like.

The fluoropolymer preferably includes one or two or more selected from polyperfluoroethylene and the like.

Further, the sheet base material according to this embodiment preferably includes, as a hydrophobic organic fiber, one or two or more selected from a synthetic fiber and the like.

The synthetic fiber preferably includes one or two or more selected from a polyolefin fiber, a polyester fiber, a fluorine fiber, a polyamide fiber, and the like.

Further, in this embodiment, part or all of the fiber forming the sheet base material may be an inorganic fiber. The sheet base material according to this embodiment preferably includes, as an inorganic fiber, one or two or more selected from a glass fiber, a ceramic fiber, a metal fiber, a carbon fiber, and the like.

[0041] [Detailed configuration of composite sheet] (Surface coverage) In the composite sheet according to this embodiment, the MOF can be supported on the entire three-dimensional structure of the sheet base material including the fiber in Step 503. That is, in the composite sheet according to this embodiment, a large number of MOFs can be supported on not only the surface layer portion of the sheet base material but also the central region in the thickness direction.

Specifically, in the composite sheet according to this embodiment, the surface coverage defined as the ratio of the region covered by the MOF on the surface of the fiber in the central region in the thickness direction of the composite sheet is preferably 60% or more, more preferably 70% or more, still more preferably 80% or more, and realistically 100% or less.

[0042] The surface coverage by the MOF in the fiber forming the sheet base material of the composite sheet can be obtained using SEM and EDX. Specifically, the composite sheet is split, and unsupported MOFs are removed by a blower or the like. A microstructure photograph of the entire split surface is taken by SEM. In the obtained microstructure photograph, a perpendicular line to a straight line along the width direction of the composite sheet is drawn, and the midpoint between both end portions in the thickness direction of the composite sheet is determined on the perpendicular line. The portion on the straight line along the width direction passing through the midpoint is defined as the central region in the thickness direction of the composite sheet. Attention is paid on one arbitrary fiber present in the central region in the thickness direction of the composite sheet, a microstructure photograph of the one fiber is taken by SEM, and an element mapping image is generated by EDX.

As a result, a region where the fiber is present can be identified by the microstructure photograph, and a region where metal is present can be identified as a region where a MOF is present by the element mapping image. The surface coverage can be calculated as a ratio of the region where a MOF is present to the entire region where a fiber is present.

[0043] (Circumferential coverage) In the composite sheet according to this embodiment, the MOF can be supported uniformly on the entire circumference of the surface of the fiber forming the sheet base material. As a result, in the composite sheet according to this embodiment, it is possible to increase the circumferential coverage defined as the ratio of the region covered by the MOF, of the surface of the fiber observed as the contour of the fiber in the cross section orthogonal to the longitudinal direction of the fiber forming the sheet base material. Specifically, in the composite sheet according to this embodiment, the circumferential coverage by the MOE in at least part of the fiber forming the sheet base material is preferably 80(., or more, more preferably 85% or more, still more preferably 90% or more, and realistically 100 or less. Still more preferably, the circumferential coverage by the MOF in at least part of the fiber forming the middle region when the cross section of the composite sheet is equally divided into three regions is or more. The shape of the contour of the fiber is not particularly limited, and may be circular, rectangular, triangular, star-shaped, or the like. In any case, the circumferential coverage can be calculated by obtaining the length of the entire circumference of the surface of the fiber using a known method.

[0044] The circumferential coverage by the MOF on the surface of the fiber forming the sheet base material of the composite sheet can be obtained by SEM and EDX. Specifically, a microstructure photograph in the field of view in which the cross section orthogonal to the longitudinal direction of the fiber in the cross section of the composite sheet can be observed is taken by SEM, and an element mapping image is generated by EDX. The length of the entire region of the surface of the fiber observed as the contour of the fiber in the cross section orthogonal to the longitudinal direction of the fiber and the length of the region covered by the MOF of the surface of the fiber observed as the contour of the fiber are measured, and the circumferential coverage can be used as the ratio thereof by the following formula.

Circumferential coverage (5) by MOF = 100 x (length of region covered by MOF of surface of fiber / length of entire region of surface of fiber) [0045] (Thickness of MOF layer covering fiber) Whether or not the MOF covers the surface of the fiber and the thickness of the MOF layer covering the fiber are measured as follows. A two-component curable liquid epoxy resin and a curing agent are mixed, and a sheet to be measured is impregnated with the mixture. After that, the obtained mixture is degassed by vacuuming and then subjected to heat treatment to cure the epoxy resin and the curing agent. In this way, a cured sample with the positions of the fiber and the MOF fixed is obtained.

The obtained cured sample is cut along the thickness direction of the sheet, and the surface thereof is observed by SEM. A cross-sectional portion of the fiber covered by the MOF is extracted from the obtained cross-sectional image of the composite sheet. An average value of the thicknesses in the fiber radial direction of the MOF layer of the portion covering the fiber is used as the thickness of the MOF layer.

[0046] (Content ratio of MOF) In the composite sheet according to this embodiment, by increasing the surface coverage and the circumferential coverage by the MOF in the fiber forming the sheet base material as described above, it is possible to support more MOFs on the sheet base material, i.e., increase the content of MOFs. Specifically, in the composite sheet according to this embodiment, the content ratio of the MOF defined as the ratio of the mass of the MOF to the mass of the entire composite sheet is preferably 80 mass% or more, more preferably 85 mass% or more. Further, in the composite sheet according to this embodiment, the content ratio of the MOF is preferably 99 mass% or less.

[0047] The content ratio of the MOF in the composite sheet can be obtained by analyzing the composite sheet.

Specifically, first, gas adsorption measurement, X-ray diffraction (XRD), EDX, NMR, IR, elemental analysis, and the like are performed to obtain a pore structure, a crystal lattice size, a crystal structure, and a constituent element. The type of MOF, i.e., the metal ion and the organic ligand are identified by checking these results against a publicly available database of MOFs. The composite sheet is then thermally decomposed, and the amount of metal included in the remaining ash is measured. Next, the mass of the MOF included in the composite sheet is obtained on the basis of the measured amount of metal and the content of metal in the identified MOF. The content ratio of the MOF is obtained by dividing the obtained mass of the MOF by the mass of the composite sheet.

[0048] (Surface exposure ratio of MOF) In the composite sheet according to this embodiment, it is unnecessary to rely on mainly a binder as an adhesive component. For this reason, in the composite sheet according to this embodiment, it is possible to increase the surface exposure ratio without causing a binder to cover the surface of the MOF. The surface exposure ratio is defined as the ratio of the area of the region where the surface of the MOF is exposed to the area of the region occupied by the MOF supported on the sheath of the core-sheath fiber forming the sheet base material when the composite sheet is viewed in plan (100 x (area of the region where the surface of the MOF is exposed) / (area of the region occupied by the MOF supported on the sheath of the core-sheath fiber forming the sheet base material)). Specifically, in the composite sheet according to this embodiment, the surface exposure ratio of the MOF is preferably 50% or more and 100% or less, more preferably 70% or more, and still more preferably 90% or more.

[0049] In order to measure the surface exposure ratio of the MOF in the composite sheet, first, MOFs that are not supported on the sheath of the core-sheath fiber forming the sheet base material in the composite sheet are removed by a blower or the like.

Subsequently, the surface of the MOF supported on the sheath of the core-sheath fiber forming the sheet base material is analyzed using TOF-SIMS, micro IR, or the like and can be evaluated by mapping. Specifically, a portion of the MOF to be observed is identified, the area thereof (area of the region occupied by the MOF) is measured, and the surface of the MOF is analyzed. The area of the region where a spectrum derived from a substance other than MOF is detected on the MOF is measured by analyzing the surface of the MOF. The substance other than the MOF is derived from, for example, a binder. The area of the region where a spectrum derived from a substance other than MOF is detected is subtracted from the rea occupied by the MOF. The area of the difference is divided by the surface area of the MOF, and thus, the surface exposure ratio of the MOF can be calculated.

[0050] (Gas adsorption amount per unit volume of composite sheet) Similarly, in the composite sheet according to this embodiment, the surface of the MOF is not covered by adhesion of a binder. For this reason, the surface exposure ratio of the MOF is high. In addition, in the composite sheet according to this embodiment, there are few unreacted products of the MOF as described by comparison with the comparative configuration example in the above "Step 503: Impregnate with second raw material solution". For this reason, the gas adsorption performance is less inhibited. As a result, in the composite sheet according to this embodiment, the MOF supported on the sheet base material is capable of effectively exhibiting the original gas adsorption performance. Further, it is possible to fix the MOF also to the fiber in the central region of the composite sheet, and the air permeability is high. For this reason, in the composite sheet according to this embodiment, it is possible to increase the gas adsorption amount per unit volume of the composite sheet. Specifically, in the composite sheet according to this embodiment, for example, in the case of using a MOF selectively adsorbing carbon dioxide, the gas adsorption amount per unit volume of the composite sheet is preferably 2 mL/cm3 or more, more preferably 3 mL/cri0 or more, and still more preferably 5 mL/cm? or more.

[0051] The gas adsorption amount per unit volume of the composite sheet is obtained by dividing the gas adsorption amount measured for the composite sheet by the area of the measured composite sheet. The gas adsorption amount is measured using a high accuracy gas adsorption amount measurement instrument "BELSORPminiII" manufactured by MicrotracBEL Corp. [0052] (Dropout ratio of MOF) In the composite sheet according to this embodiment, it is possible to fix the MOF firmly to the surface of the fiber by intermolecular forces acting between the surface of the fiber and the MOF, and it is unnecessary to mainly rely on a binder as an adhesive component for fixing the MOF to the surface of the fiber.

In the composite sheet according to this embodiment, since the MOF is fixed by the molten sheath forming the surface of the core-sheath fiber, particularly high fixing strength can be achieved on the surface of the core-sheath fiber. For this reason, in the composite sheet according to this embodiment, the MOF is less likely to drop out of the sheet base material.

[0053] In the composite sheet according to this embodiment, the dropout ratio of the MOF by shaking evaluation in which the composite sheet is grabbed by hand and shaken up and down is preferably 0 mass% or more and 20 mass% or less, more preferably la mass% or less, still more preferably 15 mass% or less, and still more preferably 9 mass% or less.

As a result, in the composite sheet according to this embodiment, since the amount of the MOF supported on the sheet base material is easily maintained during transportation and use, the gas adsorption performance is less likely to deteriorate. Further, in the composite sheet according to this embodiment, it is possible to prevent the MOF that had dropped off during use from entering the facility as a foreign substance.

The dropout ratio of the MOF is obtained by dividing the mass of the MOF that has dropped off in shaking evaluation by the mass of the MOF included in the composite sheet before the shaking evaluation.

[0054] (Maximum bending stress of composite sheet) In the composite sheet according to this embodiment, high flexibility can be easily achieved with the configuration that does not rely on mainly a binder as an adhesive component for fixing the MOF to the surface of the fiber. As a result, the composite sheet according to this embodiment can achieve high workability and can be preserved and transported in a rolled form.

In the composite sheet according to this embodiment, the maximum bending stress is preferably 0 MPa or more and 5 MPa or less, more preferably 3 MPa or less, still more preferably 1 MPa or less, still more preferably 0.1 MPa or less.

[0055] The maximum bending stress in the composite sheet can be measured using a measuring apparatus (universal testing machine AG-X plus manufactured by SHIMADZU CORPORATION) in accordance with the three-point bending test of JIS K7017. At this time, the composite sheet used as a measurement sample is cut as a sample with the dimension of 100 mm (length) x 100 mm (width) and measured.

In the three-point bending evaluation, the sample is placed on a jig with a distance between fulcrums of 40 mm, the central region between the fulcrums is pressed at a speed of 10 ram/min, and the amount of pressing and the bending load are measured. The maximum value of the bending stress obtained by this evaluation is used as the maximum bending stress.

The bending stress is a physical property value calculated by the moment (product of a load and a distance) applied to the sample during the three-point bending test by the section modulus of the sample and is calculated by the following formula.

Bending stress (MPa) = 3 x bending load (N) x distance between fulcrums (m) / 2 / sample thickness (m) / (sample width (m)2) / 10 In the case where the sample cannot cut out due to the dimension of the composite sheet to be measured, a sample having an arbitrary dimension may be cut out and measured.

[0056] (Gurley air permeability of composite sheet) It is preferable that the composite sheet according to this embodiment is configured to allow gas to pass therethrough with low pressure loss such that gas is easily supplied also to the MOF supported on the central region in the thickness direction of the composite sheet. Specifically, in the composite sheet according to this embodiment, the Gurley air permeability is preferably 0 sec/100 mL or more and 10 sec/100 mL or less, more preferably 5 sec/100 mL or less, and still more preferably 0.5 sec/100 mL or less. The Gurley air permeability of the composite sheet can be obtained using a Gurley type air permeability tester in accordance with JIS P8117:2009.

In the composite sheet according to this embodiment, since the Gurley air permeability is high, it is possible to suppress a decrease in the number of supported MOFs due to fixing by the contact between sheaths of the core-sheath fiber in the process of heat treatment in Step S05.

[0057] (Identification of type of fiber forming sheet base material) The type of fiber forming the sheet base material in the composite sheet can be identified using TOF-SIMS, IR, NMR, EDX, differential scanning calorimetry (DSC), and the like. Specifically, the type of fiber can be identified by identifying the structural formula of the fiber forming the sheet base material in the composite sheet using TOF-SIMS, IR, NMR, EDX, or the like and measuring the melting point thereof by DSC.

[0058] [Other embodiments] Although an embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to only the above-mentioned embodiment and various modifications can be made without departing from the essence of the present invention.

[0059] For example, in the method of producing a composite sheet according to this embodiment, although it is preferable that one of solvents used in the first raw material solution and the second raw material solution prepared in Step SO1 includes water and the other includes an organic solvent from the viewpoint of the penetration speed of the first raw material solution and the second raw material solution to the sheet base material, a configuration different from this may be adopted from another viewpoint. For example, in the method of producing a composite sheet according to this embodiment, both the solvents used in the first raw material solution and the second raw material solution prepared in Step SO1 may include water or an organic solvent.

[0060] Although it is preferable that the composite sheet according to this embodiment does not include a binder, it may include a small amount of binder in the case where, for example, it is necessary to fix the MOF even more firmly to the sheet base material. However, in the composite sheet according to this embodiment, it is preferable that the ratio of the mass of the binder to the total mass of the MOF and the binder is 0 mass% or more and 5 mass% or less from the viewpoint of ensuring high gas adsorption performance of the MOF and high flexibility.

Further, in the composite sheet according to this embodiment, the content of the binder to the mass of the entire composite sheet is 0 masse or more and 10

SO

mass% or less, preferably 5 mass% or less, and more preferably 1 mass% or less.

[0061] [Examples and Comparative Examples]

(Examples 1 and 2)

As Examples of the present invention, samples of composite sheets were prepared using the above production method.

As a sheet base material, an air laid non-woven fabric (basis weight of 40 g/Mj including a hydrophilic fiber and a hydrophobic fiber in the mass ratio shown in Table 1 was used. In both Examples 1 and 2, softwood chemical pulp (NBKP) that was a cellulose fiber was used as a hydrophilic organic fiber. Further, as a hydrophobic organic fiber, a core-sheath fiber in which a core was formed of polyethylene terephthalate (PET) having a melting point of 260°C and a sheath was formed of polyethylene (PE) having a melting point of 130°C was used. The content of the core-sheath fiber in the sheet base material was 70 mass%.

As a MOF, ELM-11 capable of selectively adsorbing carbon dioxide was used.

Table 1 shows the thickness of the composite sheet, the number of times to perform Steps SO2 to SO4, and the heat treatment temperature in Step S05.

[0062] The specific configurations of Steps S01 to SO5 are as follows.

As Step 501, a Cu(BF,i)c aqueous solution was diluted with deionized water to be 0.125 mol/L to prepare a first raw material solution. Further, bpy was dissolved with ethanol to be 1 mol/L to prepare a second raw material solution.

As Step S02, 14 g of the first raw material solution was applied to the sheet base material of 100 100 mm using a dropper.

As Step S03, 2.4 g of the second raw material solution was applied to the sheet base material to which the first raw material solution had been applied in Step SO2 using a dropper before the sheet base material dries.

As Step SO4, the sheet base material to which the second raw material solution had been applied in Step S03 was dried by draft overnight.

Steps SO2 to SO4 were repeated the number of times shown in Table 1.

As Step S05, after repeating Steps SO2 to SO4 the number of times shown in Table 1, the sheet was placed in a drying furnace for two hours at the heat treatment temperature shown in Table 1.

[0063] The content ratio of the MOF, the circumferential coverage, the surface exposure ratio, and the gas adsorption amount per unit volume in each sample of the composite sheet were obtained using the above analysis method. The circumferential coverage was obtained for the fiber forming the central region in the thickness direction of the composite sheet. In more detail, the content ratio of the MOF and the gas adsorption amount per unit volume were obtained as follows.

[0064] Content ratio of MOF The content ratio of the MOF was calculated on the basis of the mass of the obtained composite sheet and the mass of the base material sheet alone before supporting the MOF using the following formula. Content ratio of MOF (")) = 100 x (mass of composite sheet -mass of base material sheet alone) / mass of sample [0065] .Gas adsorption amount per unit volume The sample of the composite sheet was cut into an arbitrary size. BELSORP-miniTT (manufactured by MicrotracBEt Corp.) was used to evaluate the gas adsorption amount. Vacuum degassing treatment was performed at 100°C for 12 hours as pre-processing, and then, the adsorption isotherm of carbon dioxide was measured. The resulting adsorption amount as the adsorption amount of carbon dioxide was divided by the area of the measured sample of the composite sheet to calculate the gas adsorption amount per unit volume.

[0066] Table 2 shows the analysis results of the samples of the composite sheets. As shown in Table 2, in both samples of the composite sheets according to Examples 1 and 2, the circumferential coverage was 100%. As a result, both samples had the high content ratio of the MOF of 80 mass% or more.

Further, in both samples, the surface exposure ratio of the MOF was 100% and the gas adsorption amount of the MOF per unit volume was also high. Therefore, it was presumed that a decrease in the gas adsorption performance of the MOF due to supporting by the sheet base material was suppressed.

Further, the form of any fiber was maintained. The fact that the MOF was fixed to the sheath by the molten and fixed resin of the sheath in the core-sheath fiber was determined. In addition, a MOF layer was formed on the surface of the fiber.

[0067] Next, the dropout ratio of the MOF, the maximum bending stress, the uniformity of the MOF, the workability, and Gurley air permeability in each sample were evaluated. For the workability, filling property evaluation and MOF retention evaluation were performed. In more detail, the uniformity of the MOF and the workability were evaluated as follows.

[0068] .Uniformity of MOF The sample of the composite sheet was cut along the thickness direction to create a cross-sectional observation surface. After that, a microstructure photograph by SEM and an element mapping image by EDX were generated. At this time, respective regions obtained by dividing the sample of the composite sheet into three in the thickness direction were made to fall in the observation/analysis region. The content of metal that is the main component of the MOF was quantified from the obtained element mapping image, and an average value of the contents of the metal that is the main component of the MOF in the three divided regions and an evaluation value of the uniformity were calculated by the following formula.

Evaluation value of uniformity (5) = 100 x (maximum value of the content of the metal that is the main component of the MOF -minimum value of the content of the metal that is the main component of the MOF) / average value of the contents of the metal that is the main component of the MOF in the three divided regions.

The numerical value obtained by rounding off the evaluation value of the uniformity obtained above to the nearest 10 was used as the evaluation result of the uniformity of the MOF. That is, it can be seen that in the sample of each composite sheet, the smaller the numerical value of the evaluation result is, the higher the uniformity of the MOF is, and the larger the numerical value of the evaluation result is, the lower the uniformity of the MOF is.

[0069] .Workability As evaluation of workability, filling property evaluation and MOF retention evaluation were performed.

(1) Filling property evaluation The composite sheet was cut into a width of 5 cm and a length of 10 cm, and the cut sample was wound around a cylinder having a diameter of 1.5 mm along the outer periphery of the circumference.

The stacked state of the obtained wound sample was determined and the state of the gaps of the stacked sample of composite sheet was determined. For the sample of each composite sheet, the maximum value of the gaps was used as the evaluation result of filling property. That is, it can be seen that in the sample of each composite sheet, the smaller the value of the evaluation result is, the higher the obtained filling property of the wound sample is.

(2) MOF retention evaluation The mass of the composite sheet was measured before and after the filling property evaluation test, and the MOF retention ratio was calculated by the following formula.

MOF retention ratio (5) = 100 x (mass of the composite sheet after the filling property evaluation test / mass of the composite sheet before the filling property evaluation test) This MOF retention ratio was used as the evaluation result of MOF retention evaluation. That is, it can be seen that in the sample of each composite sheet, the larger the value of the evaluation result is, the better the state in which the MOF is supported on the surface of the fiber when being processed into a wound sample is maintained.

[0070] As shown in Table 2, in both samples, the dropout ratio of the MOF was small, i.e., 10 mass% or less, and the maximum bending stress was small, i.e., 0.03 MPa. As a result, in both samples, preferable evaluation results for workability were obtained, i.e., the gap in the filling property evaluation was less than 2 mm and the MOF retention evaluation was 97 or more. Further, in both samples, the numerical value of the uniformity of the MOF was 20% or less, and it was found that the MOF was dispersed with high uniformity over the entire sheet base material. In addition, in both samples, the Gurley air permeability was small, i.e., 0.1 sec/100 mL, and it was found that high air permeability could be achieved. It is conceivable that the high air permeability in each sample contributes to the increase in the gas adsorption amount per unit volume.

[0071] In all Examples, the gas adsorption amount per unit volume was higher than that in the following Comparative Example 1. This is presumably because the MOF could exhibit the original gas adsorption function without being covered by a resin. Further, in all Examples, the maximum bending stress was smaller, the gap in the filling property evaluation was smaller, and the Gurley air permeability was larger than those in the following Comparative Example 1. These are presumably because they were not adversely affected by the melting of the resin.

[0072] It was found that in all Examples, the numerical value of the uniformity of the MOF was smaller and the dispersibility of the MOF was higher than those in the following Comparative Example 2. This is presumably because the MOF was uniformly disposed on the entire sheet base material by forming MOF particles on the sheet base material. It is conceivable that as a result of this, in all Examples, the circumferential coverage in the central region in the thickness direction of the composite sheet was higher than that in Comparative Example 2.

[0073] In all Examples, the gas adsorption amount per unit volume was higher than that in the following Comparative Example 3. This is presumably because the MOF supported on the surface of the fiber could exhibit the original gas adsorption function without being covered by a resin.

Further, in all Examples, the maximum bending stress was smaller and the gaps in the filling property evaluation for workability was smaller than those in Comparative Example 3. These are presumably because they were not adversely affected by the melting of the resin.

Further, it was found that in all Examples, the numerical value of the uniformity of the MOF was smaller and the dispersibility of the MOF were higher than those in Comparative Example 3. This is presumably because the MOF was uniformly disposed on the entire sheet base material by forming MOF particles on the sheet base material.

[0074] In all Examples, the gas adsorption amount per unit volume was significantly higher than that in Comparative Example 4. This is presumably because the MOF could exhibit the original gas adsorption function without being covered by a resin.

Further, it was found that in all Examples, the numerical value of the uniformity of the MOF was smaller and the dispersibility of the MOF was higher than those in Comparative Example 4. This is presumably because the MOF was uniformly disposed on the entire sheet base material by forming MOF particles on the sheet base material. It is conceivable that as a result of this, in all Examples, the circumferential coverage in the central region in the thickness direction of the composite sheet was higher than that in Comparative

Example 4.

[0075] (Comparative Examples 1 to 4) Samples of composite sheets according to Comparative Examples were prepared under the conditions shown in Table 1. Further, for each sample, analysis and evaluation same with those in Examples 1 and 2 were performed. Table 2 shows the analysis result and the evaluation result of each sample. Comparative Examples 1 to 4 will be described below in detail.

[0076] Comparative Example 1 In Comparative Example 1, an air-through non-woven fabric (basis weight of 40 g/m2) formed of a polyethylene (PE) fiber was used as a sheet base material. The content of the core-sheath fiber in the sheet base material was 0 mass%.

Instead of Steps SO2 to SO4 according to the above embodiment, MOF particles (average particle size of 5 pm) generated in advance were spread on both surfaces of the sheet base material such that the MOF content ratio in Table 2 was obtained, pressed at room temperature, and then subjected to heat treatment at 140°C for 2 hours. In the obtained composite sheet, the PE fiber formed of only PE having a low melting point melted by the heat treatment, the form of the fiber was not maintained, and the molten resin partially covered the MOF.

[0077] Comparative Example 2 In Comparative Example 2, a non-woven fabric same with that in Example 1 was used as a sheet base material.

Instead of Steps SO2 to SO4 according to the above embodiment, MOF particles (average particle size of 5 pm) generated in advance were spread on both surfaces of the sheet base material such that the MOF content ratio in Table 2 was obtained, pressed at room temperature, and then subjected to heat treatment at 140°C for 2 hours.

In Comparative Example 2, the form of the fiber in the composite sheet was maintained.

[0078] Comparative Example3 In Comparative Example 3, a non-woven fabric same with that in Example 1 was used as a sheet base material.

Instead of Steps SO2 to SO4 according to the above embodiment, a dispersion liquid of a MOF generated in advance was spread on both surfaces of the sheet base material and then subjected to heat treatment at 140°C for 2 hours. The configuration of the dispersion liquid of the MOF used in Comparative Example 3 is as follows. Average particle size of MOF: 5 um Binder: water-soluble PVA MOF/binder ratio: 1/1 Solvent: deionized water Solid content: 20% [0079] In the sample of the composite sheet according to Comparative Example 3, the MOF was not supported directly on the surface of the fiber. In all samples of the composite sheets, the surface of the MOF was partially covered by melting of the sheath of the core-sheath fiber or contact with the binder.

[0080] .Comparative Example 4 In Comparative Example4, a non-woven fabric same with that in Example 1 was used as a sheet base material.

Instead of Steps SO2 to SO4 according to the above embodiment, MOF particles (average particle size of 5 um) generated in advance were spread on both surfaces of the sheet base material such that the MOF content ratio in Table 2 was obtained.

[0081] In Comparative Example 4, since no heat treatment was performed, MOF particles were not fixed by melting of the sheath of the core-sheath fiber. In the obtained composite sheet, a large number of MOFs dropped off during processing and preparation of the sample when measuring the gas adsorption amount per unit volume.

[0082] (Table 1)

Example Comparative Example 1 2 i 2 3 4 Hydrophilic fiber (mass%) 30 30 0 30 30;0 Fiber Hydrophobic fiber (mass%) 70 70 100 70 70 70 Thickness of composite sheet (mm) 1.5 i.5 1.4 1.5 1.5 1.5 Steps S02 to SO4 (times) 3 g-

J

Heat treatment temperature CC) 140 140 140 140 100

[0083] (Table 2)

Example Comparative Example 1 2 1 2 3 4 MOF content ratio 86 90 90 87 48 12 (mass%) Circumferential coverage 100 100 60 50 10 (%) MOF surface exposure ratio 100 100 100 0 100 (%) Gas adsorption ratio 6.2 9.7 0.3 6.0 0.1 0.2 (mL/cm3) With or without MOF With With Without With Without Wth fixed on sheath portion MOF dropout ratio 4 10 16 33 0 97 (%) Maximum bending stress (MPa) 0.03 0.03 10 0.03 0.60 0.06 MOF uniformity 20 10 60 70 90 (%) Filling property Viasns Workability or o5r more Less o5r Less evaluation (mm) 2 than 2 more ' 2 2 MOF retention 99 97 95 85 100 80 evaluation (%) Gurley air permeability (sec/100 mL) 0.1 0.1 15 0.1 0.3 0.1

Claims

Claims [1] A composite sheet, comprising: a sheet base material formed of fibers; and metal organic frameworks dispersed in the sheet base material, wherein the fibers include core-sheath fibers having a core-sheath structure that includes a core and a sheath, one metal organic framework is supported on the sheath of the core-sheath fibers where a resin of the sheath is molten and fixes the metal organic framework, and a surface exposure ratio of the metal organic frameworks supported on the sheath of the core-sheath fibers is 50% or more.[2] The composite sheet according to claim 1, wherein the fibers have a circumferential coverage of 80% or more and 100% or less, preferably 85% or more, and more preferably 90% or more, by the metal organic frameworks, in at least part of one fiber in a cross section orthogonal to a longitudinal direction of the fiber.[3] The composite sheet according to claim 1 or 2, wherein the core of the core-sheath fibers includes a resin component having a melting point of 160°C or more and 280°C or less, preferably 200°C or more, and more preferably 240°C or more.[4] The composite sheet according to any one of claims 1 to 3, wherein the sheath of the core-sheath fibers includes a resin component having a melting point is 70°C or more and less than 160°C, preferably 80°C or more, and more preferably 100°C or more.[5] The composite sheet according to any one of claims 1 to 4, wherein the core of the core-sheath fibers includes a resin component having a melting point higher than that of the resin component included in the sheath, and a difference between the melting point of the resin component included in the core and the melting point of the resin component included in the sheath is preferably 10°C or more and 200°C or less, more preferably 60°C or more, and still more preferably 100°C or more.[6] The composite sheet according to any one of claims 1 to 5, wherein the resin component included in the core of the core-sheath fibers has the melting point higher than the melting point of the resin component included in the sheath by 10°C or more.[7] The composite sheet according to any one of claims 1 to 6, having a dropout ratio of the metal organic frameworks by shaking evaluation of 20 mass or less.[8] The composite sheet according to any one of claims 1 to 7, having a dropout ratio of the metal organic frameworks by shaking evaluation of 0 mass% or more and mass% or less, preferably 18 mass% or less.[9] The composite sheet according to any one of claims 1 to 8, having a maximum bending stress of 5 MPa or less.[10] The composite sheet according to any one of claims 1 to 9, having a maximum bending stress of 0 MPa or more and 5 MPa or less, preferably 3 MPa or less, and more preferably 1 MPa or less.[11] The composite sheet according to any one of claims 1 to 10, having a thickness of the composite sheet of 0.2 mm or more and 10 mm or less, preferably 0.5 mm or more and 5 mm or less, and more preferably 1 mm or more.[12] The composite sheet according to any one of claims 1 to 11, having a Gurley air permeability of the composite sheet of 0 sec/100 mL or more and 10 sec/100 mL or less, preferably 5 sec/100 mL or less, more preferably 0.5 sec/100 mL or less.[13] The composite sheet according to any one of claims 1 to 12, having a content ratio of the metal organic frameworks to a mass of the entire composite sheet of mass% or more and 99 mass% or less, preferably 85 mass% or more.[14] The composite sheet according to any one of claims 1 to 13, having fibers forming a central region in a thickness direction of the composite sheet, wherein the fibers forming the central region have a surface coverage by the metal organic frameworks of 60% or more and 100% or less, preferably 70% or more, and more preferably 80% or more.[15] The composite sheet according to any one of claims 1 to 14, wherein a surface exposure ratio of the metal organic frameworks is 50% or more and 100% or less, preferably 70% or more, and more preferably 90% or more.[16] The composite sheet according to any one of claims 1 to 15, comprising one fiber having a layer of the metal organic frameworks formed on a surface of the fiber.[17] The composite sheet according to claim 16, wherein the layer of the metal organic frameworks is a film of the metal organic frameworks covering the surface of the fiber as a unified film.[18] The composite sheet according to any one of claims 1 to 17, wherein the metal organic frameworks are capable of selectively adsorbing carbon dioxide.[19] The composite sheet according to any one of claims 1 to 18, wherein the composite sheet includes no binder.[20] The composite sheet according to any one of claims 1 to 19, wherein the sheet base material is a non-woven fabric.[21] The composite sheet according to any one of claims 1 to 20, wherein a form of a fiber is maintained in the core of the core-sheath fibers.[22] A method of producing a composite sheet in which metal organic frameworks are supported on a sheet base material formed of fibers including core-sheath fibers, comprising: preparing a first raw material solution and a second raw material solution, wherein the first raw material solution includes either a metal ion or an organic ligand that are raw materials of the metal organic framework, and the second raw material solution includes the other; impregnating the sheet base material with the first raw material solution; then impregnating the sheet base material with the second raw material solution before the first raw material solution with which the sheet base material is impregnated dries; and applying heat treatment to the sheet base material impregnated with the second raw material solution.[23] The method of producing a composite sheet according to claim 22, wherein one of the first raw material solution and the second raw material solution includes water of 30 mass% or more and 99 mass% or less, and the other includes an organic solvent of 30 mass% or more and 99 mass% or less.[24] The method of producing a composite sheet according to claim 22 or 23, wherein the first raw material solution includes the metal ion and the second raw material solution includes the organic ligand.[25] The method of producing a composite sheet according to claim 24, wherein a solvent of the first raw material solution includes water and a solvent of the second raw material solution includes an organic solvent.[26] The method of producing a composite sheet according to any one of claims 22 to 25, comprising drying the sheet base material that has been impregnated with the second raw material solution before the heat treatment.[27] The method of producing a composite sheet according claim 26, wherein a total number of times to perform a series of processes before the heat treatment is 1 or more and 20 or less, preferably 2 or more, and more preferably 3 or more, and the series of processes includes, impregnating a sheet base material with the first raw material solution; then impregnating the sheet base material with the second raw material solution before the first raw material solution with which the sheet base material is impregnated dries; and drying the sheet base material that has been impregnated with the second raw material solution.[28] The method of producing a composite sheet according to any one of claims 22 to 27, comprising dehydrating the metal organic frameworks by the heat treatment.[29] The method of producing a composite sheet according to any one of claims 22 to 28, wherein a resin component included in a core of the core-sheath fibers has a melting point being higher than a temperature of the heat treatment, and a resin component included in a sheath of the core-sheath fibers has a melting point being higher than a temperature of the drying and being lower than the temperature of the heat treatment.[30] A composite sheet produced by the method of producing a composite sheet according to any one of claims 22 to 29.