JP7260298B2 - Diaphragm for alkaline water electrolysis - Google Patents

Description

The present invention relates to a diaphragm for alkaline water electrolysis.

Conventionally, the introduction of renewable energy using natural energy such as sunlight, wind power, and geothermal heat has been promoted toward the realization of a low-carbon society. Among renewable energies, the amount of power generated by wind power generation, solar power generation, and the like fluctuates depending on weather conditions, so the power supply and demand balance cannot be maintained, resulting in surplus power. A technique called Power to Gas for storing and utilizing such surplus electric power in the form of energy has been attracting attention in recent years. Specifically, the above technology is a technology for converting surplus electric power into gaseous fuel such as hydrogen or methane by electrolysis of water, and storing and using the surplus electric power.

Electrolysis of water is known as one of the industrial production methods of hydrogen. is performed by applying For such electrolysis of water, an electrolytic cell having an anode compartment and a cathode compartment separated by a diaphragm is used.

Electrolysis of water is performed by the transfer of electrons (or ions). Therefore, in order to perform electrolysis efficiently, the diaphragm is required to have high ion permeability. In addition, it is required to have gas barrier properties capable of blocking oxygen generated in the anode chamber and hydrogen generated in the cathode chamber. In the electrolysis of water, a high-concentration alkaline aqueous solution of about 30% is used, and the electrolysis is carried out at about 80 to 90° C., so the diaphragm is required to be resistant to high temperatures and alkalis.

Various diaphragms for alkaline water electrolysis have been proposed so far.
For example, Patent Document 1 discloses a porous ion-permeable diaphragm composed of a hydrophilic inorganic material and an organic binding material, further comprising first and second porous reinforcing material layers. The second porous reinforcing material layer is an ion-permeable diaphragm that is separated from each other in the thickness direction of the diaphragm and is buried in the diaphragm from one main surface and the other main surface of the diaphragm, respectively. It is
Further, in Patent Document 2, an ion-permeable diaphragm used for alkaline water electrolysis, wherein an organic non-woven fabric is incorporated in a mixture of a hydrophilic inorganic material and an organic binding material. A sex septum is described.

Furthermore, Patent Document 3 describes a microporous membrane having an average pore diameter of 0.1 μm or more and 1 μm or less, a maximum pore diameter of 0.2 μm or more and 2 μm or less, and a porosity of 30% or more and 80% or less. Patent Document 3 discloses that polyethersulfone and polysulfone, which are commonly used as microporous membranes, have ether bonds in their repeating units, so they are gradually hydrolyzed in an acidic or alkaline environment, and when hydrolysis proceeds, , the pore size and porosity change, which may cause a decrease in the function as a porous membrane and a decrease in mechanical strength. It is described that problems such as the film becoming brittle may occur.

In a diaphragm in which a large number of coarse macrovoids exist, the membrane in the macrovoid portions becomes thin, and the effect of suppressing gas permeation is lowered, and defects are likely to occur. As a result, there is a problem that the membrane has low durability in a high-temperature alkaline environment even though it exhibits a high value of ionic conductivity.
As a diaphragm for alkaline water electrolysis, a diaphragm that achieves both higher gas barrier properties and higher durability has been desired.

JP 2017-106056 A JP 2011-117056 A JP 2017-066184 A

An object of the present invention is to provide a diaphragm for alkaline water electrolysis that exhibits high ionic conductivity and simultaneously achieves higher gas barrier properties and higher durability.

The present inventors have found that as a result of controlling the size of macrovoids generated during the production of a diaphragm for alkaline water electrolysis, a diaphragm for alkaline water electrolysis that exhibits high ionic conductivity and achieves both higher gas barrier properties and higher durability. The present inventors have found that they can provide the above, and completed the present invention.

That is, the diaphragm for alkaline water electrolysis of the present invention is ^a diaphragm for alkaline water electrolysis containing an organic polymer and inorganic particles, and is observed by irradiating the membrane with transmitted light. The area ratio of the total area to the total area of the diaphragm is 1% or more, and the ratio of the number of bright areas with an area of 10,000 μm ² or more to the total number of bright areas with an area of 12 μm ² or more is 10% or less. is.

INDUSTRIAL APPLICABILITY The diaphragm for alkaline water electrolysis of the present invention exhibits high ionic conductivity, achieves both higher gas barrier properties and higher durability, and can be suitably used for electrolysis of alkaline water.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically one form of the cross section of the diaphragm for alkaline water electrolysis of this invention. FIG. 4 is a diagram schematically showing a bright portion observed by applying transmitted light to one embodiment of the diaphragm for alkaline water electrolysis of the present invention.

The present invention will be described in detail below.
A combination of two or more of the individual preferred embodiments of the invention described below is also a preferred embodiment of the invention.

1. Diaphragm for alkaline water electrolysis The diaphragm for alkaline water electrolysis of the present invention is a diaphragm for alkaline water electrolysis containing an organic polymer and inorganic particles, and has an area of 12 μm ² or more observed by exposing the membrane to transmitted light. The area ratio of the total area of the bright portions to the total area of the diaphragm (hereinafter sometimes simply referred to as the area ratio of the bright portions) is 1% or more, and the total number of bright portions with an area of 12 μm ² or more ( The ratio of the number of bright portions having an area of 10,000 μm ² or more (hereinafter sometimes simply referred to as large bright portions) to the total number of bright portions is 10% or less.
The diaphragm for alkaline water electrolysis of the present invention is a diaphragm that exhibits high ionic conductivity and achieves both higher gas barrier properties and higher durability. In this specification, the description of "A to B" means "A or more and B or less".

1-1 Organic Polymer The diaphragm for alkaline water electrolysis of the present invention contains an organic polymer. The organic polymer holds the inorganic particles. The organic polymer functions as a partition that holds the inorganic particles, and can suppress the inorganic particles from falling off from the partition in an alkaline solution while minimizing the decrease in the hydrophilic surface of the inorganic particles, which will be described later.

The organic polymer is not particularly limited as long as it is a resin (R) that retains the particle surfaces of the inorganic particles, preferably does not swell in an alkaline solution, and exhibits the effects of the present invention. Examples of the resin (R) include fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene; olefin-based resins such as polypropylene; and aromatic hydrocarbon-based resins such as polysulfone and polystyrene. These may be used individually by 1 type, and may be used in combination of 2 or more type. Among them, aromatic hydrocarbon-based resins are preferable in that they can be used as a diaphragm for alkaline water electrolysis with further excellent heat resistance and alkali resistance.

More specifically, the aromatic hydrocarbon resins include, for example, polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polystyrene, polysulfone, polyethersulfone, polyarylene sulfide resins such as polyphenylene sulfide, and polyphenylsulfone. , polyarylate, polyetherimide, polyimide, polyamideimide, and the like. Among them, at least one selected from the group consisting of polysulfone, polyethersulfone, and polyphenylsulfone is preferable in terms of being able to impart even better alkali resistance. Ethersulfone is more preferred.
By using at least one selected from the group consisting of polysulfone, polyethersulfone, and polyphenylsulfone, for example, when producing a diaphragm using a non-solvent-induced phase separation method or a vapor-induced phase separation method, Since the sulfonyl group has an appropriate affinity with the inorganic particles described later, it becomes easier to adjust the phase separation conditions, and the area ratio of the bright areas and the ratio of the number of large bright areas to the total number of bright areas can be controlled more appropriately. easier to do. For this reason, the resistance value of the obtained diaphragm for alkaline water electrolysis is further lowered, and the alkali resistance is further increased, so that the size, mass, and resistance value stability and newness when used in an alkaline solution for a long time. It becomes excellent due to the effect of suppressing the generation of voids.

The content of the resin (R) is preferably 3 to 40% by mass based on 100% by mass of the diaphragm for alkaline water electrolysis. When the content of the resin (R) is within the above range, the ion permeability and toughness of the diaphragm for alkaline water electrolysis are good, but inorganic components are not eluted from the diaphragm for alkaline water electrolysis in an alkaline solution. It is even more suppressed. In addition, the diaphragm for alkaline water electrolysis exhibits high ion conductivity and is also excellent in ion permeability, gas barrier properties, heat resistance, and alkali resistance. The content of the resin (R) is more preferably 5 to 35% by mass, still more preferably 7 to 30% by mass, based on 100% by mass of the diaphragm for alkaline water electrolysis.
The content of the resin (R) is preferably 5 to 40% by mass based on 100% by mass of the diaphragm for alkaline water electrolysis when the diaphragm for alkaline water electrolysis of the present invention does not contain a porous support, which will be described later. , more preferably 10 to 35% by mass, more preferably 15 to 30% by mass. When the diaphragm for alkaline water electrolysis of the present invention contains a porous support described later as an organic polymer, the content of the resin (R) is preferably 3 to 20% by mass in 100% by mass of the diaphragm for alkaline water electrolysis, More preferably 5 to 18% by mass, still more preferably 7 to 15% by mass.

The diaphragm for alkaline water electrolysis of the present invention preferably contains 10 to 40 parts by mass, more preferably 12 to 35 parts by mass, more preferably 15 to 33 parts by mass of the resin (R) with respect to 100 parts by mass of the inorganic particles described later. It is more preferable to include parts by mass. When the content ratio of the inorganic particles and the resin (R) is within the range described above, the elution of inorganic components from the diaphragm for alkaline water electrolysis in an alkaline solution is further suppressed. In addition, the diaphragm for alkaline water electrolysis exhibits high ion conductivity and is also excellent in ion permeability, gas barrier properties, flexibility, heat resistance, and alkali resistance.

1-1-1 Porous Support The diaphragm for alkaline water electrolysis of the present invention comprises a membrane containing the above-described organic polymer and inorganic particles described below, and contains a porous support as the organic polymer. good too. The porous support is a porous organic polymer, and is a member that does not inhibit ion permeability and can serve as a support for a diaphragm for alkaline water electrolysis. The porous support is preferably a sheet-like member.

Examples of materials for the porous support include polyarylene sulfide resins such as polyethylene, polypropylene, polysulfone, polyethersulfone, polyphenylsulfone, and polyphenylene sulfide, and resin materials such as polyketone, polyimide, polyetherimide, and fluororesin. are mentioned. These may be used individually by 1 type, and may be used in combination of 2 or more type. Among them, it preferably contains at least one resin material selected from the group consisting of polypropylene, polyethylene, and polyphenylene sulfide in that it can exhibit excellent heat resistance and alkali resistance, and the group consisting of polypropylene and polyphenylene sulfide. More preferably, it contains at least one more selected resin material.

Examples of the form of the porous support include nonwoven fabric, woven fabric (fabric), knitted fabric, mesh, porous membrane, felt, and mixed fabric of nonwoven fabric and woven fabric. Nonwoven fabric and woven fabric are preferred. Examples include cloth, mesh, or felt, and more preferably non-woven fabric, woven fabric, and mesh.

As the porous support, nonwoven fabric, woven fabric, mesh, or felt containing at least one resin selected from the group consisting of polypropylene, polyethylene, and polyphenylene sulfide is preferred. Furthermore, non-woven fabrics, meshes, or felts containing polyphenylene sulfide are preferred as porous supports. The total content of polypropylene, polyethylene, and polyphenylene sulfide in the porous support is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

When the porous support is in the form of a sheet, the thickness of the porous support is not particularly limited as long as the diaphragm for alkaline water electrolysis of the present invention can exhibit the effects of the present invention. , more preferably 50 to 1000 μm, still more preferably 80 to 500 μm, and most preferably 80 to 250 μm.

1-2 Inorganic Particles The diaphragm for alkaline water electrolysis of the present invention contains inorganic particles. The diaphragm for alkaline water electrolysis of the present invention can exhibit ion permeability by filling the gaps between the inorganic particles and the organic polymer with the electrolytic solution. In addition, by including inorganic particles, the diaphragm for alkaline water electrolysis becomes hydrophilic, and oxygen gas and hydrogen gas generated in the electrolysis of water can be prevented from adhering to the diaphragm and interfering with the electrolysis.

Examples of inorganic particles used in the present invention include hydroxides or oxides of magnesium, zirconium, titanium, zinc, aluminum and tantalum, sulfates of calcium, barium, lead, strontium and the like. Among them, magnesium hydroxide, zirconium hydroxide, titanium hydroxide, zirconium oxide, titanium oxide, calcium sulfate, and barium sulfate are preferable in terms of dispersibility of inorganic particles and stability in alkaline solutions. Magnesium oxide, zirconium oxide, titanium oxide and barium sulfate are more preferred. The inorganic particles may be used singly or in combination of two or more.

The inorganic particles may be natural or synthetic. Moreover, the surface may be untreated, or the surface may be treated with a silane coupling agent, stearic acid, oleic acid, phosphate ester, or the like. The shape of the inorganic particles is not particularly limited as long as it is particulate, and may be amorphous; spherical such as a perfect sphere or oblong sphere; plate-like such as flaky or hexagonal plate-like; or fibrous. However, it is preferably spherical, plate-shaped, or fibrous in terms of ease of dispersion in a solvent and ease of preparation of a resin composition. A plate-like shape is more preferable.

The inorganic particles preferably have an aspect ratio of 1.0 to 8.0. When the aspect ratio is within the above range, the membrane can have even better ion permeability and excellent uniformity. The aspect ratio is more preferably 1.5 to 7.0, even more preferably 2.0 to 6.0.
In the present specification, the aspect ratio means the ratio (a/b) between the longest diameter a and the shortest diameter b, and powdery inorganic particles are observed with SEM, and any 10 particles of the obtained image are In the above, using analysis software or the like, the ratio (a/b) between the longest diameter a and the shortest diameter b of each particle is measured, and the simple average value of these ratios can be obtained as the aspect ratio of the particle. .

As the maximum diameter a, for example, when the shape of the particle is plate-like, the length of the plate surface of the particle is used, and when the particle is fibrous, the length of the fiber is used. The shortest diameter among the diameters passing through the midpoint of the longest diameter a and perpendicular to the longest diameter is defined as the shortest diameter b. As the shortest diameter b, for example, when the shape of the particles is plate-like, the thickness of the particles is used, and when the shape is fibrous, the thickness of the fibers is used. As the thickness of the particles and the thickness of the fibers, the thickness and thickness at the midpoint of the longest diameter a are employed, respectively.

The average particle diameter of the inorganic particles is preferably 0.01 to 2.0 μm, more preferably 0.05 to 1.0 μm, from the viewpoint of further improving the dispersibility of the inorganic particles. It is more preferably 0.08 to 0.7 μm. The average particle size is obtained from particle size distribution measurement by a laser diffraction/scattering method using an inorganic particle dispersion liquid that has been subjected to dispersion treatment using inorganic particles and a 0.2% by mass sodium hexametaphosphate aqueous solution. Average particle size (d50). When the average particle size of the inorganic particles is within the above range, the membrane can exhibit high ion conductivity, ion permeability, and gas barrier properties.

The specific surface area of the inorganic particles is preferably from 5 to 35 m ² /g, more preferably from 5.5 to 25 m ² /g, and more preferably from 6 to 20 m ² /g, in that the ion permeability of the diaphragm is further improved. is more preferable. The above specific surface area is a specific surface area measured by the BET method using liquid nitrogen for powdery inorganic particles. Since the ion path in the diaphragm for alkaline water electrolysis is formed by the highly hydrophilic surface of the inorganic particles, the specific surface area of the inorganic particles within the above range can provide a diaphragm with even better ion permeability.

The content of the inorganic particles is preferably 30 to 95% by mass in 100% by mass of the diaphragm for alkaline water electrolysis. When the content of the inorganic particles is within the above range, the elution of the inorganic component in the alkaline solution is further suppressed, exhibiting high ion conductivity, ion permeability, gas barrier properties, heat resistance and alkali resistance. An excellent diaphragm can be obtained. The content of the inorganic particles is more preferably 32 to 92% by mass, still more preferably 35 to 90% by mass, based on 100% by mass of the diaphragm for alkaline water electrolysis.
When the diaphragm for alkaline water electrolysis of the present invention does not contain the porous support, the content of the inorganic particles is preferably 60 to 95% by mass in 100% by mass of the diaphragm for alkaline water electrolysis, more preferably. is 65 to 92% by mass, more preferably 75 to 90% by mass.
When the diaphragm for alkaline water electrolysis of the present invention contains the porous support, the content of the inorganic particles is preferably 30 to 50% by mass, more preferably 32 to 48%, based on 100% by mass of the diaphragm for alkaline water electrolysis. % by mass, more preferably 35 to 45% by mass.

FIG. 1 schematically shows one embodiment of the diaphragm for alkaline water electrolysis of the present invention. A diaphragm 1 for alkaline water electrolysis includes a single membrane layer 2 and a support layer 3 . The single layer 2 is a layer containing the resin (R) and inorganic particles, and the support layer 3 is a layer containing the resin (R), inorganic particles and a porous support. 4 is a void, and 5, 51, 52 are the thicknesses of the solid portions in the monolayer 2. FIG. When a plurality of voids 4 exist in the thickness direction, the total thickness of the solid portions in the single film layer 2 in the thickness direction is the sum of 51 and 52 .

In the diaphragm for alkaline water electrolysis of the present invention, the single membrane layer 2 may be formed on one surface of the support layer 3 or may be formed on both surfaces.
Further, the diaphragm for alkaline water electrolysis of the present invention may not have the above-described single layer 2, and a composite as a support layer 3 in which the inorganic particles, the resin (R), and the porous support are integrated. It can be a body. By forming the above composite, the strength and toughness of the diaphragm for alkaline water electrolysis can be improved.

1-3 Light Area The diaphragm for alkaline water electrolysis of the present invention has a bright area area ratio of 1% or more, and the number of large bright areas to the total number of bright areas observed by irradiating the membrane with transmitted light. The number ratio is 10% or less. The bright part is, for example, the surface of the diaphragm for alkaline water electrolysis, using a digital microscope (model: VH-5500, manufactured by Keyence) and a lens (model: VH-Z100, manufactured by Keyence), by transmitted illumination, A magnified photograph was taken at a magnification of 100, and analysis software (Image-Pro Premier) was used on the resulting transmitted light image to perform conversion processing from pixel units to actual size values and processing to eliminate non-uniformity in dark area luminance. After that, the bright and dark portions are binarized so that when the brightness is represented by 256 gradations, the portions showing brightness with a gradation value of 66 or more become bright portions, and formed based on the difference between light and dark. A closed area is indicated by a contour line. The area of the bright part is calculated by calculating the area inside the contour including the pixels of the contour.

FIG. 2 schematically shows a bright portion in one embodiment of the diaphragm for alkaline water electrolysis of the present invention. 1 is a diaphragm for alkaline water electrolysis, 21 is the surface of the diaphragm for alkaline water electrolysis, and 41 and 42 are bright portions. 41 is a bright portion with an area of 12 μm ² or more, and 42 is a bright portion (large bright portion) with an area of 10,000 μm ² or more.
FIG. 1 schematically shows a cross section taken along line XX in FIG. As shown in FIG. 1, when voids 4 are present inside the diaphragm for alkaline water electrolysis, the total thickness, which is the sum of the thickness 5 of the solid portion in the single membrane layer 2 and the thicknesses 51 and 52 of the solid portions, is becomes smaller, and bright portions 41 and 42 are observed. The light portions 41 and 42 can be evaluated as portions having a small total thickness in the thickness direction of the solid portions containing the organic polymer and the inorganic particles of the diaphragm 1 for alkaline water electrolysis.
When the area ratio of the portion having a small total thickness (that is, the bright portion) is less than 1%, the flexibility of the diaphragm is lowered, and defects occur during handling, resulting in a diaphragm with low durability.
Moreover, if the ratio of the number of the bright portions 42 to the total number of the bright portions 41 and 42 is more than 10%, the total thickness of the diaphragm is reduced in many parts, and the gas barrier property is lowered and defects are likely to occur.
In the present invention, by controlling the light portion, the total thickness in the thickness direction of the solid portion of the diaphragm can be controlled more appropriately, exhibiting high ion conductivity, and achieving both higher gas barrier properties and higher durability. membrane can be provided. The light area can be controlled by the combination of the resin and the non-solvent, contact conditions with the non-solvent, etc. in the method of bringing the coating film into contact with the non-solvent, which will be described later.

The ratio of the number of bright areas to the total number of bright areas is obtained by the following formula.
(Ratio of the number of bright areas to the total number of bright areas) (%)
= [(number of bright parts) / (total number of bright parts)] x 100
The ratio of the number of large bright areas to the total number of bright areas is 10% or less, preferably 8.0% or less, more preferably 6.0% or less, and even more preferably 2.0% or less. When the ratio of the number of large light areas to the total number of light areas is within the above range, the film can exhibit high ion conductivity and achieve both higher gas barrier properties and higher durability.

In addition, the area ratio of the total area of the bright part with an area of 12 μm ² or more to the total area of the diaphragm is the ratio of the total area of the bright part with an area of 12 μm ² or more to the total area of the diaphragm (area where image analysis was performed). area ratio. The area ratio of the bright portion is 1% or more, preferably 5% or more, more preferably 10% or more, further preferably 13% or more, and particularly preferably 15% or more. . If the area ratio of the bright portion is less than 1%, the flexibility of the membrane is reduced, and defects occur during handling, resulting in a diaphragm with low durability.

Among them, a diaphragm having a light area ratio of 15 to 25% and a ratio of the number of large light areas to the total number of light areas of 2.5% or less has higher membrane flexibility and better handleability. It is particularly preferable because it is highly durable, exhibits high ionic conductivity, and achieves both high gas barrier properties and high durability.

1-4 Porosity The diaphragm for alkaline water electrolysis of the present invention preferably has a porosity of 25 to 80%. The porosity is obtained by the following formula from the measured density value of the diaphragm measured by the method shown below, and the calculated density value of the diaphragm calculated using the density value (true density) and composition ratio of each component constituting the diaphragm. can be calculated from
Porosity (%) = [1 - (measured density value) / (calculated density value)] × 100
The measured density value can be calculated by measuring the mass and volume of a test piece cut from an arbitrary location of the obtained diaphragm and dividing the mass by the volume. The volume can be calculated by measuring the vertical and horizontal lengths of the test piece using calipers, and measuring the film thickness based on the film thickness measurement method described above. Also, the mass of the test piece can be measured using a precision balance with four decimal places for the test piece whose volume has been measured.
The porosity of the diaphragm for alkaline water electrolysis of the present invention is more preferably 30 to 75%, more preferably 35 to 70%. When the porosity is in the above range, the electrolyte solution is continuously filled in the voids in the diaphragm, so that the membrane can exhibit high ion conductivity, excellent ion permeability, and excellent gas barrier properties. can.

1-5 Ionic Conductivity The ionic conductivity of the diaphragm for alkaline water electrolysis of the present invention can be calculated by the method described in Examples. The ion conductivity of the diaphragm for alkaline water electrolysis of the present invention is preferably more than 100 mS/cm. In this case, the efficiency of electrolysis in alkaline water electrolysis can be increased.

1-6 Durability The durability of the diaphragm for alkaline water electrolysis of the present invention can be evaluated, for example, by the difference in air permeability resistance of the diaphragm before and after immersion in a 30 mass % potassium hydroxide aqueous solution for 60 days. Specifically, the air permeability resistance of the diaphragm is obtained by the method described in the Examples using a digital type Oken type air permeability tester (model: EGBO-S-1MR, manufactured by Asahi Seiko Co., Ltd.). can be done. The difference in air resistance of the diaphragm is preferably less than 50%, more preferably less than 30%, and even more preferably less than 15% of the value before immersion in the aqueous potassium hydroxide solution.

1-7 Thickness The thickness of the diaphragm for alkaline water electrolysis of the present invention is not particularly limited, and may be appropriately selected according to the size of the equipment to be used, the handleability, etc. 50 to 2000 μm is preferable, 100 to 1000 μm is more preferable, 100 to 500 μm is still more preferable, and 150 to 350 μm is most preferable from the viewpoint of ion permeability and strength.
Further, when the porous support described above is included, the thickness of the diaphragm for alkaline water electrolysis of the present invention is preferably 50 to 2000 μm, more preferably 100 to 1000 μm, still more preferably 100 to 500 μm, most preferably 150 to 300 μm. is.

2. Method for Producing Diaphragm for Alkaline Water Electrolysis A method for producing the diaphragm for alkaline water electrolysis will be described.
The method for producing the diaphragm for alkaline water electrolysis is not particularly limited, and known methods can be applied. Further, the non-solvent induced phase separation method and the vapor induced phase separation method are preferable in terms of efficiently producing a diaphragm for alkaline water electrolysis having excellent ion permeability and gas barrier properties.

Specifically, the method for producing the alkaline water electrolysis membrane preferably includes the following steps (1) to (3).
(1) preparing a dispersion containing inorganic particles and a solvent;
(2) a step of mixing the dispersion and the resin (R) as the organic polymer to prepare a resin mixture;
(3) Step of Forming a Film Using the Resin Mixture Below, each step will be described.

(1) Step of preparing a dispersion containing inorganic particles and a solvent In the above production method, when the inorganic particles are mixed with the resin (R), the inorganic particles may be mixed in solid form or dispersed in the solvent. Although a dispersion (slurry) may be prepared and then mixed, it is preferable to prepare a dispersion in a solvent and then mix. By preparing a dispersion of inorganic particles and then mixing it with the resin (R), the inorganic particles and the resin (R) can be mixed more uniformly. ) uniformly distributed and immobilized within the partition walls formed by the method ), thereby obtaining a diaphragm for alkaline water electrolysis in which the elution of inorganic components is more sufficiently suppressed. A dispersant may be added to the dispersion liquid.

The content of inorganic particles in the dispersion liquid is preferably 20 to 70% by mass, more preferably 30 to 65% by mass, and still more preferably 50 to 65% by mass. By doing so, the average pore size defined above of the finally obtained membrane can be more easily controlled within the range of 0.05 μm to 0.6 μm, and alkaline water with both ion conductivity and gas barrier properties It can be used as a diaphragm for electrolysis.

The solvent for dispersing the inorganic particles is not particularly limited as long as it has the property of dissolving the resin (R) to be mixed later. Examples include N-methyl-2-pyrrolidone and N,N-dimethyl. Acetamide, N,N-dimethylformamide, dimethylsulfoxide, methyl ethyl ketone, toluene and the like. These solvents may be used singly or in combination of two or more. Among them, N-methyl-2-pyrrolidone is preferable in terms of good dispersibility of the inorganic particles. The amount of the solvent used for the inorganic particles in the dispersion is preferably 50 parts by mass or more and less than 100 parts by mass, more preferably 50 parts by mass or more and 90 parts by mass or less, and 50 parts by mass or more and 80 parts by mass with respect to 100 parts by mass of the inorganic particles. More preferably less than parts by mass. By doing so, the average pore size defined above of the finally obtained membrane can be more easily controlled within the range of 0.05 μm to 0.6 μm, and alkaline water with both ion conductivity and gas barrier properties It can be used as a diaphragm for electrolysis.

Dispersants include water-soluble polymers such as polyvinylpyrrolidone, polyethylene glycol, ethylene glycol, polyethyleneimine, polyacrylic acid and dextran; cationic surfactants; anionic surfactants; carboxy groups, phosphoric acid groups, sulfonic acid groups conventionally known pigment dispersants having functional groups such as The amount of the dispersant used for the inorganic particles in the dispersion liquid is preferably more than 0.5 parts by mass and 8.0 parts by mass or less, and 0.8 parts by mass or more and 6.0 parts by mass or less with respect to 100 parts by mass of the inorganic particles. is more preferable, and 1.0 parts by mass or more and 5.0 parts by mass or less is even more preferable. By doing so, it becomes possible to control and improve the particle size of the inorganic particles in the dispersion liquid and the dispersion stability of the inorganic particles in the diaphragm forming step, and the finally obtained membrane can be improved. In addition, the area ratio of the bright portions and the ratio of the number of large bright portions to the total number of bright portions can be easily controlled within the above ranges, and a diaphragm for alkaline water electrolysis having both ion conductivity and gas barrier properties can be obtained.

The method for dispersing the inorganic particles in the solvent is not particularly limited, and known mixing and dispersing means such as a method using a mixer, ball mill, jet mill, disper, sand mill, roll mill, pot mill, bead mill, paint shaker, etc. are applied. be able to.

The average particle size of the inorganic particles in the dispersion liquid is preferably 0.1 to 1.0 μm, more preferably 0.15 to 0.8 μm, still more preferably 0.15 to 0.5 μm. The average particle size of the inorganic particles in the dispersion can be determined by particle size distribution measurement using a dynamic light scattering method, and can be specifically measured by the method described in Examples.

(2) A step of mixing the dispersion liquid and the resin (R) as the organic polymer to prepare a resin mixed liquid. The method for mixing is not particularly limited as long as it is a method capable of sufficiently mixing the dispersion liquid and the resin (R), and the resin (R) may be mixed as it is in the dispersion liquid. Alternatively, a resin solution may be prepared in advance by dissolving the resin (R) in a solvent, and the resin solution and the dispersion may be mixed. Among them, the method of preparing the resin solution and mixing the resin solution and the dispersion liquid is preferable in that the inorganic particles and the resin (R) can be dispersed and mixed more uniformly.

The solvent used for preparing the resin solution is not particularly limited as long as it has the property of dissolving the resin (R). Examples include N-methyl-2-pyrrolidone and N,N-dimethylacetamide. , N,N-dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, toluene and the like. Among them, the same solvent as the solvent used for preparing the dispersion liquid is preferable in that the inorganic particles and the resin (R) can be dispersed and mixed more uniformly.

The content of the resin (R) in the resin solution is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, even more preferably 15 to 40% by mass.
Examples of the mixing method include the same means as the mixing and dispersing means described in step (1).

The dispersion liquid and the resin (R) are preferably 10 to 40 parts by mass, more preferably 12 to 35 parts by mass, still more preferably 15 to 33 parts by mass, based on 100 parts by mass of the inorganic particles. It is preferable to mix so that it becomes a mass part. When the content ratio of the inorganic particles and the resin (R) is within the range described above, the elution of the inorganic component in the obtained diaphragm for alkaline water electrolysis in the alkaline solution is further suppressed. In addition, it is possible to produce a diaphragm for alkaline water electrolysis that exhibits high ion conductivity and is also more excellent in ion permeability, gas barrier properties, heat resistance and alkali resistance.

When the dispersion of the inorganic particles and the solution of the resin (R) are mixed, the total content of the solvent in the dispersion of the inorganic particles and the solvent in the solution of the resin (R) is the dispersion of the inorganic particles. It is preferably 30 to 75% by mass with respect to 100% by mass of the total mass of the liquid and the solution of the resin (R). More preferably 35 to 70% by mass, still more preferably 40 to 65% by mass. In order to adjust the porosity of the diaphragm for alkaline water electrolysis to a preferable range, it is preferable to use the solvent in such a ratio.

A compound that dissolves in both the solvent of the resin mixture and the non-solvent of the resin (R) may be added as an additive to the resin mixture for the purpose of adjusting the average pore size of the diaphragm. good. Examples of the above additives include water-soluble polymers such as polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, polyethyleneimine, polyacrylic acid, and dextran; surfactants; glycerin; organic compounds such as sugars; calcium chloride, magnesium chloride, and chloride; Examples include inorganic compounds such as lithium.

(3) Step of Forming a Film Using the Resin Mixture A film is formed using the resin mixture obtained in step (2).
As the method for forming the membrane, the following steps (3-a), ( 3-b) is preferably included.
(3-a) forming a coating film of the resin mixture, and
(3-b) contacting the coating film with a non-solvent to solidify the coating film to obtain a porous film;

(3-a) Step of forming a coating film of the resin mixed solution Examples of the method of forming a coating film of the resin mixed solution include a method of applying the resin mixed solution obtained above on a substrate, and a method of applying the resin mixed solution obtained above on a substrate. A method of obtaining a substrate impregnated with the resin mixture by immersing the substrate in the resin mixture can be used. Among them, the method of applying the above-mentioned resin mixed solution onto a base material is preferable in that a coating film can be easily formed.

The method of applying the resin mixture onto the substrate is not particularly limited, and known coating means such as methods using die coating, spin coating, gravure coating, curtain coating, spray, applicator, bar coater, etc. are applied. can do.

The substrate is not particularly limited as long as it can be coated with the resin mixture to form a coating film. Examples include polyethylene terephthalate, polyethylene naphthalate, polypropylene, polyethylene, polyvinyl chloride, and polyvinyl. A film or sheet made of a resin such as acetal, polymethyl methacrylate, polycarbonate, or the like, a glass plate, or the like can be used. Among them, polyethylene terephthalate is preferable because it is easy to handle and the material cost can be reduced.
Moreover, when manufacturing the diaphragm for alkaline water electrolysis containing the porous support mentioned above, you may use the said porous support as said base material.

In the case of producing a diaphragm for alkaline water electrolysis, which is a composite in which a membrane containing inorganic particles, the resin (R), and a porous support are integrated, the resin mixed solution is applied onto the base material. Then, the porous support may be placed on the coating liquid to impregnate the porous support with the coating liquid.

The amount of the resin mixed solution to be applied is not particularly limited, and may be appropriately set so that the diaphragm has a thickness capable of exhibiting the above-described effects.

(3-b) A step of solidifying the coating film by contacting the coating film with a non-solvent, whereby the non-solvent diffuses in the coating film and dissolves in the non-solvent. The resin (R) that does not solidify. On the other hand, the solvent in the coating film that is soluble in the non-solvent is eluted from the coating film. Due to the occurrence of phase separation in this manner, the resin (R) (and the inorganic particles) is solidified to form a porous film.

Examples of the method of bringing the coating film into contact with the non-solvent include a method of immersing the coating film in the non-solvent (coagulation bath), and a method of exposing the coating film to the non-solvent vapor atmosphere. Alternatively, after the coating film is exposed to the non-solvent vapor atmosphere, it may be subsequently immersed in the non-solvent. In this case, the exposure time to the non-solvent vapor atmosphere can be about 3 to 60 seconds, and the time to be immersed in the non-solvent can be about 1 to 15 minutes.

The temperature of the non-solvent in which the coating film is immersed is preferably 10°C or higher, more preferably 15°C or higher, and even more preferably 20°C or higher. Moreover, 55 degrees C or less is preferable, 50 degrees C or less is more preferable, and 45 degrees C or less is more preferable. By setting the temperature to such a temperature, the ratio of the number of large bright portions to the total number of bright portions having an area of 12 μm ² or more observed by irradiating the membrane with transmitted light is more reliably 10% or less. Thus, it is possible to more easily produce a diaphragm for alkaline water electrolysis that exhibits high ionic conductivity and has both higher gas barrier properties and higher durability.

The non-solvent is not particularly limited as long as it has the property of not substantially dissolving the resin (R). A mixed solvent or the like can be preferably used. Ion-exchanged water is preferable from the viewpoint of economy and waste liquid treatment. In addition to the components described above, the non-solvent may contain a small amount of the same solvent as the solvent contained in the coating film.

The amount of the non-solvent used is preferably 50 to 10,000 parts by mass with respect to 100 parts by mass of the coating film, ie, 100 parts by mass of the solid content of the resin mixture used for forming the coating film. It is more preferably 100 to 5000 parts by mass, still more preferably 200 to 1000 parts by mass. It is preferable to use the non-solvent in such a ratio in order to adjust the porosity of the membrane to be obtained within a preferable range and to completely extract the solvent in the coating film into the non-solvent.

Furthermore, in order to remove the non-solvent, the coating film solidified in the above step may be dried to obtain the diaphragm.
The drying temperature for the coating film is preferably 60 to 120°C.
The drying time is preferably 0.5 to 120 minutes, more preferably 1 to 60 minutes, even more preferably 1 to 30 minutes.

As described above, the diaphragm for alkaline water electrolysis of the present invention can be easily produced by the steps (1) to (3) described above.

3. Applications The diaphragm for alkaline water electrolysis of the present invention exhibits high ion conductivity, and simultaneously achieves higher gas barrier properties and higher durability. Therefore, the diaphragm for alkaline water electrolysis of the present invention can be suitably used as a diaphragm for water electrolysis using an alkaline aqueous solution as an electrolyte. In addition to the diaphragm for alkaline water electrolysis described above, it can also be used for battery separators such as alkaline fuel cell separators, primary battery separators, secondary battery separators, and salt electrolysis separators.

4. Alkaline Water Electrolysis Apparatus The diaphragm for alkaline water electrolysis of the present invention is used as a member of an alkaline water electrolysis apparatus. Examples of the alkaline water electrolysis apparatus include those including an anode, a cathode, and the diaphragm for alkaline water electrolysis arranged between the anode and the cathode. More specifically, the alkaline water electrolysis apparatus has an anode chamber in which an anode exists and a cathode chamber in which a cathode exists, which are separated by the diaphragm for alkaline water electrolysis.
The anode and cathode include known electrodes such as conductive substrates containing nickel, nickel alloys, and the like.

5. Electrolyzing Method The method of electrolyzing water using the alkaline water electrolysis apparatus provided with the diaphragm for alkaline water electrolysis of the present invention is not particularly limited, and a known method can be used. For example, it can be carried out by filling an electrolytic solution into an alkaline water electrolysis apparatus provided with the above-described diaphragm for alkaline water electrolysis of the present invention and applying an electric current in the electrolytic solution.
As the electrolytic solution, an alkaline aqueous solution in which an electrolyte such as potassium hydroxide or sodium hydroxide is dissolved is used. Although the concentration of the electrolyte in the electrolytic solution is not particularly limited, it is preferably 20 to 40% by mass from the viewpoint of further improving the electrolysis efficiency.
The temperature for electrolysis is preferably 50 to 120° C., more preferably 80 to 90° C., since the ion conductivity of the electrolytic solution can be further improved and the electrolysis efficiency can be further improved. Current application conditions can be performed by known conditions and methods.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited only to these examples. Unless otherwise specified, "part" means "mass part" and "%" means "mass %".

In the present examples, the measurement conditions for various physical properties are as follows.

<Average particle size of inorganic particles (powder)>
A laser diffraction/scattering particle size distribution analyzer (product Name: LA-920, manufactured by Horiba Ltd.) was used to measure the particle size distribution, and the median diameter (d50) in the obtained volume-based particle size distribution was defined as the average particle size (μm) of the inorganic particles.

<Average particle size of inorganic particles in inorganic particle dispersion>
0.1 part by mass of the obtained inorganic particle dispersion was diluted with 2 parts by mass of a dispersion medium, and the diluted solution of the inorganic particle dispersion was measured with a particle size distribution analyzer (trade name: FPAR-1000, Otsuka Electronics) using a dynamic light scattering method. Co., Ltd.), the particle size of the inorganic particles dispersed in the inorganic particle dispersion is measured, and the average particle size obtained by the cumulant method analysis is the average particle size of the inorganic particles dispersed in the inorganic particle dispersion. bottom.

<Film thickness>
The thickness of the obtained diaphragm for alkaline water electrolysis was measured using a digimatic micrometer (manufactured by Mitutoyo Corporation). Ten arbitrary points were measured, and the average value was taken as the film thickness.

<Porosity>
The porosity of the obtained diaphragm for alkaline water electrolysis was calculated from the calculated density value calculated from the composition ratio using the measured density value of the diaphragm measured by the method shown below and the density value of each composition component, as shown below. Calculated from the formula.
(Porosity) (%) = [1 - (measured density value) / (calculated density value)] × 100
The measured density value was calculated by measuring the mass and volume of a test piece cut out from an arbitrary location of the obtained diaphragm and dividing the mass by the volume. The volume was calculated by measuring the vertical and horizontal lengths of the test piece using vernier calipers, and measuring the film thickness based on the film thickness measurement method described above. In addition, the mass of the test piece was measured using a precision balance with 4 decimal places for the test piece whose volume was measured.

<Ratio of number of large bright portions to total number of bright portions and area ratio of bright portions>
The surface of the obtained diaphragm for alkaline water electrolysis is magnified at a magnification of 100 by transmitted illumination using a digital microscope (model: VH-5500, manufactured by Keyence) and a lens (model: VH-Z100, manufactured by Keyence). Photographs were taken to obtain transmitted light images.
For the obtained transmitted light image, using analysis software (Image-Pro Premier), conversion processing from pixel units to actual size values and processing for eliminating non-uniform dark area luminance are performed. A range equivalent to ^6mm2 is selected, and when the brightness is expressed in 256 gradations, the bright and dark portions are binarized so that the portions showing brightness with a gradation value of 66 or more are bright. A region closed by a contour line formed based on the difference between the two was extracted as a bright portion.
Next, for each bright area obtained, the area inside the outline including the pixels of the outline is calculated, and the number of bright areas with an area of 12 μm ² or more obtained is counted as the “total number of bright areas”. bottom. In addition, from the area of each bright portion obtained, the number of bright portions (large bright portions) with an area of 10,000 μm ² or more was counted as “the number of bright portions”. The ratio (%) of the number of parts was obtained.
(Ratio of the number of bright areas to the total number of bright areas) (%)
= [(number of bright parts) / (total number of bright parts)] x 100
Further, the sum of the areas of the bright portions with an area of 12 μm ² or more was calculated, and the ratio of the total area of the bright portions with an area of 12 μm ² or more to the entire analysis area of the image was obtained, and was defined as the area ratio (%) of the bright portions.

<Air resistance>
The air permeability resistance (seconds) of the resulting diaphragm for alkaline water electrolysis was measured using a digital type Oken type air permeability tester (model: EGBO-S-1MR, manufactured by Asahi Seiko Co., Ltd.) according to JIS P8117: 2009. Measured according to

<Ionic conductivity>
The ionic conductivity of the obtained diaphragm for alkaline water electrolysis was measured by the following method.
After leaving the cell formed with the following cell configuration in a constant temperature bath at 25° C. for 30 minutes, AC impedance measurement was performed under the following measurement conditions. Using the intercept component (Rb) and the film thickness obtained by the above film thickness measurement method, the ion conductivity was calculated as the average value of two measurement points according to the following formula.
[Ionic conductivity (mS / cm)] = [film thickness (cm)] ÷ [(Ra-Rb) × 1000 × 1.77]
(Measurement condition)
・Cell configuration Working electrode: Ni plate Counter electrode: Ni plate Electrolyte solution: 30% by mass potassium hydroxide aqueous solution Sample pretreatment: immersed overnight in the above electrolyte solution Effective area for measurement: 1.77 cm ²
- AC impedance measurement conditions Applied voltage: 10 mV vs. Open circuit voltage Frequency range: 100kHz to 100Hz

<Handleability>
After the obtained diaphragm for alkaline water electrolysis was wound around a cylinder with a diameter of 10 mm, the presence or absence of cracks on the surface of the diaphragm in the part wound around the cylinder was observed, and the handleability was evaluated based on the following criteria.
(Handling evaluation criteria)
3: No cracks were observed 2: Several small cracks were observed 1: Many cracks were observed throughout 0: Peeling occurred on the surface of the film

<Durability>
The resulting diaphragm for alkaline water electrolysis was immersed in a 30% by mass aqueous potassium hydroxide solution adjusted to 90° C. for 60 days, and the air resistance of the diaphragm before and after immersion in the aqueous potassium hydroxide solution was measured. Evaluated based on criteria. Regarding the measurement of the air resistance after immersion in potassium hydroxide, the membrane immersed in potassium hydroxide was thoroughly washed with pure water until there was no remaining potassium hydroxide, and then dried at 80°C x 30 in a dryer. Measurement was performed using a film dried for 1 minute as a sample.
(Evaluation criteria for durability)
3: The difference in air resistance values before and after immersion was less than 15% of the value before immersion. 2: The difference in air resistance values before and after immersion was 15% of the value before immersion. Above, less than 30% 1: The difference in air resistance before and after immersion was 30% or more and less than 50% of the value before immersion 0: Air resistance before and after immersion The difference in value was 50% or more of the value before immersion

[Preparation Example 1]
200 parts by mass of magnesium hydroxide particles (plate-like, average particle size 0.36 μm), 200 parts by mass of N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Corporation), and 3 parts by mass of polyvinylpyrrolidone as a dispersing agent are mixed to form zirconia beads. was dispersed for 30 minutes with a bead mill, and then the zirconia beads were removed to obtain a magnesium hydroxide particle dispersion. The average particle size of the magnesium hydroxide particles in the resulting magnesium hydroxide particle dispersion was 280 nm.
200 parts by mass of the obtained magnesium hydroxide particle dispersion, polysulfone resin (trade name: Ultrason S3010, manufactured by BASF) at a concentration of 30% by mass at 100 ° C. N-methyl-2-pyrrolidone (Wako Pure Chemical Industries, Ltd. 100 parts by mass of the polysulfone resin solution obtained by thermally dissolving it in (manufactured by Thinky Corporation) is weighed and rotated at room temperature using a rotation and revolution mixer (trade name: Awatori Mixer ARE-500, manufactured by Thinky Corporation). After mixing for about 10 minutes at several thousand min ⁻¹ , filtration was performed to obtain a film-forming composition.

[Example 1]
The film-forming composition of Preparation Example 1 was applied to a polyethylene terephthalate (PET) film with an applicator so that the weight value was 35 mg/cm ² . ² , thickness: 205 μm), the nonwoven fabric was completely impregnated with the film-forming composition. After that, the nonwoven fabric impregnated with the film-forming composition is immersed in a coagulation bath made of pure water at 25° C. for 10 minutes to coagulate the coating film, and then the coating film is peeled off from the PET film together with the nonwoven fabric in water. By doing so, a water-containing film composed of magnesium hydroxide particles, polysulfone resin and non-woven fabric was obtained. The obtained membrane was dried at 80° C. for 30 minutes in a dryer to obtain a diaphragm for alkaline water electrolysis.
The obtained diaphragm for alkaline water electrolysis had a thickness of 270 μm, a porosity of 50%, a ratio of the number of large bright portions to the total number of bright portions of 0.4%, an area ratio of the bright portions of 19.0%, and air permeability. The resistance was 111 seconds, the ionic conductivity was 130 mS/cm, the handling evaluation was 3, and the durability evaluation was 3.

[Example 2]
A diaphragm for alkaline water electrolysis was obtained in the same manner as in Example 1, except that the coagulation bath was changed from pure water to 50% by mass isopropyl alcohol aqueous solution.
The obtained diaphragm for alkaline water electrolysis had a thickness of 260 μm, a porosity of 52%, a ratio of the number of large bright portions to the total number of bright portions of 1.3%, an area ratio of the bright portions of 17.5%, and air permeability. The resistance was 96 seconds, the ionic conductivity was 158 mS/cm, the handling evaluation was 3, and the durability evaluation was 3.

[Example 3]
A diaphragm for alkaline water electrolysis was obtained in the same manner as in Example 1, except that the temperature of the pure water in the coagulation bath was changed to 40°C.
The obtained diaphragm for alkaline water electrolysis had a thickness of 285 μm, a porosity of 51%, a ratio of the number of large bright portions to the total number of bright portions of 2.6%, an area ratio of the bright portions of 17.9%, and air permeability. The resistance was 108 seconds, the ionic conductivity was 211 mS/cm, the handling evaluation was 2, and the durability evaluation was 3.

[Example 4]
The film-forming composition of Preparation Example 1 was applied to a polyethylene terephthalate (PET) film with an applicator so that the basis weight was 40 mg/cm ² , and a non-woven fabric made of polyphenylene sulfide fibers (basis weight: 100 g/m2) was applied thereon. ² , thickness: 205 μm), the nonwoven fabric was completely impregnated with the film-forming composition. Thereafter, the nonwoven fabric impregnated with the film-forming composition is exposed to steam of pure water at 40°C for 10 seconds, and then immersed in a coagulation bath of pure water at 40°C for 10 minutes to solidify the coating film. After that, the coated film was peeled off from the PET film together with the nonwoven fabric in water to obtain a water-containing film composed of magnesium hydroxide particles, polysulfone resin and nonwoven fabric. The obtained membrane was dried at 80° C. for 30 minutes in a dryer to obtain a diaphragm for alkaline water electrolysis.
The obtained diaphragm for alkaline water electrolysis had a thickness of 280 μm, a porosity of 48%, a ratio of the number of large bright portions to the total number of bright portions of 6.6%, an area ratio of the bright portions of 19.9%, and air permeability. The resistance was 97 seconds, the ionic conductivity was 212 mS/cm, the handling evaluation was 3, and the durability evaluation was 2.

[Comparative Example 1]
The film-forming composition of Preparation Example 1 was applied to a polyethylene terephthalate (PET) film with an applicator so that the weight value was 35 mg/cm ² . ² , thickness: 205 μm), the nonwoven fabric was completely impregnated with the film-forming composition. Thereafter, the nonwoven fabric impregnated with the film-forming composition is exposed to steam of pure water at 60°C for 10 seconds, and then immersed in a coagulation bath of pure water at 60°C for 10 minutes to solidify the coating film. After that, the coated film was peeled off from the PET film together with the nonwoven fabric in water to obtain a water-containing film composed of magnesium hydroxide particles, polysulfone resin and nonwoven fabric. The obtained membrane was dried at 80° C. for 30 minutes in a dryer to obtain a diaphragm for alkaline water electrolysis.
The obtained diaphragm for alkaline water electrolysis had a thickness of 255 μm, a porosity of 51%, a ratio of the number of large bright portions to the total number of bright portions of 18.7%, an area ratio of the bright portions of 12.6%, and air permeability. The resistance was 42 seconds, the ionic conductivity was 208 mS/cm, the handling evaluation was 2, and the durability evaluation was 0.

[Comparative Example 2]
A diaphragm for alkaline water electrolysis was obtained in the same manner as in Example 1, except that the coagulation bath was changed from pure water to a 50% by mass N-methyl-2-pyrrolidone aqueous solution.
The obtained diaphragm for alkaline water electrolysis had a film thickness of 240 μm, a porosity of 46%, a ratio of the number of large bright portions to the total number of bright portions of 0.0%, an area ratio of the bright portions of 0.0%, and air permeability. The resistance was 190 seconds, the ionic conductivity was 126 mS/cm, the handling evaluation was 0, and the durability evaluation was 2.

Based on the above results, the diaphragms for alkaline water electrolysis of Examples 1 to 3, which were prepared so that the ratio of the number of large bright portions to the total number of bright portions having an area of 12 μm ² or more to the total number of bright portions having an area of 12 μm 2 or more was 10% or less, had a clear area of 12 μm ² or more. Compared to the diaphragm of Comparative Example 1, in which the ratio of the number of large bright parts to the total number of bright parts exceeds 10%, and the diaphragm of Comparative Example 2, in which no bright parts were observed, high ionic conductivity and high gas barrier properties are exhibited. It was confirmed that the diaphragm achieved both high durability.

1 Diaphragm for alkaline water electrolysis 2 Single membrane layer 3 Support layer 4 Voids 5, 51, 52 Thickness of solid portion in single membrane layer 21 Surfaces 41, 42 of diaphragm for alkaline water electrolysis Light area

Claims (1)

A diaphragm for alkaline water electrolysis containing an organic polymer and inorganic particles,
The inorganic particles contain at least one selected from magnesium hydroxide and barium sulfate,
In the transmitted light image obtained by the method (1) below , which is observed by irradiating the film with transmitted light, the bright areas and the bright areas defined by the methods (2) and (3) below Regarding the area, the area ratio of the total area of the bright portions with an area of 12 μm ² or more to the total area of the diaphragm is 1% or more, and the total area of the bright portions with an area of 12 μm ² or more is 10,000 μm. A diaphragm for alkaline water electrolysis, wherein the ratio of the number of the bright portions to ² or more is 10% or less.
(1) The transmitted light image is an image obtained by taking an enlarged photograph of the surface of the diaphragm for alkaline water electrolysis at a magnification of 100 under transmitted illumination using a digital microscope and a lens,
(2) The bright area is defined by analyzing the transmitted light image using analysis software.
Perform conversion processing from pixel units to actual size values and processing to eliminate non-uniformity in dark area luminance, and then
For all the pixels, the luminance of the pixel with the lowest luminance is set to a gradation value of 1 and the luminance of the pixel with the highest luminance is set to a gradation value of 256, and the luminance is specified in 256 gradations.
performing a binarization process in which pixels exhibiting luminance with a gradation value of 66 or more are set as light area pixels and pixels with a gradation value of less than 66 are set as dark area pixels;
A group of the bright area pixels inside the outline including the outline, with the bright area pixels that are in contact with the dark area pixels identified as a result as a outline,
(3) The area of the bright portion is calculated as the area inside the outline including the pixels of the outline.

Images