Use method for porous film, diaphragm for alkaline water electrolysis, and electrolytic tank for alkaline water electrolysis

Abstract

The purpose of the present invention is to realize a diaphragm for alkaline water electrolysis having good airtightness even when a sheet-like gasket is used, and enabling execution of water electrolysis at a low cell voltage. A use method according to the present invention is characterized by using, as a diaphragm for alkaline water electrolysis, a porous film which contains a polyethylene, and in which the content of the polyethylene in resin components is 50 mass% or more, and the tortuosity is 3.00 or less.

Description

Method of using porous membrane, diaphragm for alkaline water electrolysis, and electrolytic cell for alkaline water electrolysis

[0001] The present invention relates to a method for using a porous membrane, a diaphragm for alkaline water electrolysis, and an electrolytic cell for alkaline water electrolysis.

[0002] In recent years, CO ２ Hydrogen produced using renewable energy is attracting attention as a clean energy source that can solve problems such as global warming caused by CO2 and dwindling fossil fuel reserves. Hydrogen production using renewable energy requires low costs comparable to those of conventional hydrogen production by reforming fossil fuels. Therefore, hydrogen production using renewable energy requires high levels of energy efficiency and inexpensive equipment that could not be achieved with conventional technologies.

[0003] One of the industrial methods for producing hydrogen is water electrolysis. This method has the advantage of producing hydrogen with higher purity than hydrogen production methods that involve reforming fossil fuels. In water electrolysis, an aqueous solution containing an electrolyte such as sodium hydroxide or potassium hydroxide is generally used as the electrolyte to increase conductivity. Water is electrolyzed by applying a direct current to this electrolyte between the cathode and anode.

[0004] Among these, alkaline water electrolysis can be carried out on a large scale and is inexpensive compared to other water electrolysis devices, and therefore has already been proven in commercial plants. Therefore, the development of a large-scale hydrogen production device using alkaline water electrolysis is expected. For example, several concepts have been proposed for producing large amounts of hydrogen by electrolysis of alkaline water using power generated by natural energy such as wind power or solar power, and then transporting and supplying the hydrogen to consumption areas.

[0005] An electrolytic cell for performing electrolysis (hereinafter sometimes referred to as "electrolysis") is divided into an anode chamber and a cathode chamber via a diaphragm, and oxygen gas is produced in the anode chamber, while hydrogen gas is produced in the cathode chamber. The diaphragm is required to have gas barrier properties to prevent mixing of the oxygen gas and hydrogen gas. In addition, in water electrolysis, the medium that carries electricity (electrons) is ions, and therefore, to perform electrolysis efficiently, the diaphragm is required to have high ion permeability. From this perspective, a diaphragm having a porous structure (hereinafter sometimes referred to as a "porous membrane") has been proposed as a diaphragm that has gas barrier properties and ion permeability.

[0006] In addition, in order to efficiently perform electrolysis, it is desirable to reduce the electrical resistance of the solution between the anode, cathode, and diaphragm, and it is considered preferable to have a structure in which the diaphragm is sandwiched between both electrodes (hereinafter, sometimes referred to as a "zero gap structure").

[0007] As technologies relating to such diaphragms, Patent Documents 1 and 2 disclose diaphragms for alkaline water electrolysis, which are porous membranes formed by mixing zirconium oxide or magnesium oxide into polysulfone, an aromatic polymer resin, and by a non-solvent-induced phase separation method.

[0008] However, the above-mentioned technologies still have room for improvement. For example, polyethersulfone and polysulfone, which are commonly used as diaphragms, contain ether groups in their repeating units and are therefore gradually hydrolyzed in acidic or alkaline environments. As hydrolysis progresses, the membrane structure changes, which can lead to a decrease in membrane function and mechanical strength. The rate of hydrolysis increases, particularly in high-temperature, highly acidic, or alkaline environments, making this problem even more pronounced.

[0009] On the other hand, the ion permeation efficiency is expressed by the electrical conductivity, which is closely related to the concentration and temperature of the electrolyte. For example, in a high temperature range of 80°C or higher, the electrical conductivity of an aqueous potassium hydroxide solution reaches a maximum at a concentration of approximately 30 mass%. Therefore, using a diaphragm under high electrical conductivity conditions in order to improve ion permeability may exacerbate the problem of the hydrolysis rate.

[0010] Meanwhile, polyethylene (hereinafter, sometimes referred to as "PE"), a polyolefin resin, is widely used as a highly chemical-resistant material and is known to have extremely high resistance even in alkaline environments. PE porous membranes made from PE maintain the properties of PE and are therefore used in applications such as filters in environments where mechanical strength and chemical resistance are required.

[0011] On the other hand, PE is known to be highly hydrophobic and has extremely poor wettability with an electrolyte solution. Therefore, if PE is used as a diaphragm without any treatment, the electrolysis efficiency will be extremely poor. Therefore, Patent Documents 3, 4, and 5 disclose methods of carrying out hydrophilization treatments, such as introducing a hydrophilic substance such as an inorganic oxide into the pores or introducing a hydrophilic resin or a hydrophilic group into the porous surface.

[0012] International Publication No. WO 93 / 15529 French Patent Application Publication No. 2546535 International Publication No. 2018-182006 International Publication No. 2014-119207 International Publication No. 2014-119208

[0013] However, in the conventional techniques disclosed in the above-mentioned Patent Documents 3, 4, and 5, the hydrophilization treatment of the porous surface of PE causes considerable blockage of the porous structure, resulting in a problem of reduced ion permeability, and further improvement in electrolysis performance is desired. Furthermore, in the conventional techniques disclosed in Patent Documents 1 and 2, when the diaphragm is sandwiched between the anode and the cathode, if the end of the diaphragm is exposed, airtightness cannot be ensured, so the entire outer periphery of the diaphragm needs to be covered with a gasket. Therefore, a gasket with a special structure that accommodates the outer periphery of the diaphragm needs to be used, and it is desired that airtightness can be ensured by stacking sheet-like gaskets, which are easier to work with.

[0014] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a diaphragm that has good airtightness even when a sheet-like gasket is used, and that enables water electrolysis at a low cell voltage.

[0015] Therefore, the present inventors have conducted extensive research to solve the above problems, and as a result have found that by using a porous membrane having a polyethylene content and a tortuosity within specific ranges, the porous structure at the portion fastened with the gasket is closed to ensure airtightness, while the portion sandwiched between the anode and cathode maintains a void structure with a tortuosity within the above specific range, thereby maintaining high ion permeability, and thereby enabling water electrolysis at a low cell voltage, which led to the completion of the present invention.

[0016] That is, the present invention is as follows. [1] A method for use, characterized in that a porous membrane containing polyethylene, wherein the polyethylene content in a resin component is 50 mass% or more and the tortuosity is 3.00 or less, is used as a diaphragm for alkaline water electrolysis. [2] The method for use according to [1], wherein the porous membrane has a thickness of 40 μm or more and 1000 μm or less. [3] The method for use according to [1] or [2], wherein the tortuosity of the porous membrane is 0.30 or more and 2.50 or less. [4] The method for use according to [1] or [2], wherein the tortuosity of the porous membrane is 1.00 or more and 2.50 or less. [5] The method for use according to any of [1] to [4], wherein the porosity of the porous membrane is 20% or more and 95% or less. [6] The method for use according to any of [1] to [5], wherein the water permeability of the porous membrane is 0.1 g / 2 min or more and 500 g / 2 min or less. [7] The method for use according to any one of [1] to [6], wherein the air permeability of the porous membrane is 10 seconds or more and 4,000 seconds or less, calculated on a 100 μm basis. [8] The method for use according to any one of [1] to [7], wherein the viscosity average molecular weight of the polyethylene is 300,000 or more and 7,500,000 or less. [9] A diaphragm for alkaline water electrolysis, comprising a porous membrane containing polyethylene, wherein a polyethylene content in a resin component of the porous membrane is 50 mass% or more, and the tortuosity of the porous membrane is 3.00 or less.

[10] The diaphragm for alkaline water electrolysis according to [9], having a membrane thickness of 40 μm or more and 1,000 μm or less.

[11] The diaphragm for alkaline water electrolysis according to [9] or

[10] , wherein the tortuosity of the porous membrane is 0.30 or more and 2.50 or less.

[12] The diaphragm for alkaline water electrolysis according to [9] or

[10] , wherein the tortuosity of the porous membrane is 1.00 or more and 2.50 or less.

[13] The diaphragm for alkaline water electrolysis according to any one of [9] to

[12] , wherein the porosity of the porous membrane is from 20% to 95%.

[14] The diaphragm for alkaline water electrolysis according to any one of [9] to

[13] , wherein the water permeability of the porous membrane is from 0.1 g / 2 min to 500 g / 2 min.

[15] The diaphragm for alkaline water electrolysis according to any one of [9] to

[14] , wherein the air permeability of the porous membrane is from 10 seconds to 4,000 seconds, converted into 100 μm.

[16] The diaphragm for alkaline water electrolysis according to any one of [9] to

[15] , wherein the viscosity average molecular weight of the polyethylene is 300,000 or more and 7,500,000 or less.

[17] An electrolytic cell for alkaline water electrolysis, comprising: the diaphragm for alkaline water electrolysis according to any one of [9] to

[16] , an anode, and a cathode, wherein the diaphragm for alkaline water electrolysis is disposed between the anode and the cathode.

[18] An electrolytic cell for alkaline water electrolysis, comprising: the diaphragm for alkaline water electrolysis according to any one of [9] to

[16] , a sheet-like gasket, an anode, and a cathode, wherein the diaphragm for alkaline water electrolysis is disposed between the anode and the cathode.

[19] An electrolytic cell for alkaline water electrolysis, comprising: the diaphragm for alkaline water electrolysis according to any one of [9] to

[16] ; two sheet-like gaskets; an anode; and a cathode, wherein the diaphragm for alkaline water electrolysis is disposed between the anode and the cathode and the two sheet-like gaskets are disposed to sandwich the diaphragm for alkaline water electrolysis.

[0017] The present invention makes it possible to provide a diaphragm for alkaline water electrolysis that can ensure airtightness of an electrolytic cell even when a sheet-like gasket is used, and that enables alkaline water electrolysis to be performed at a low cell voltage.

[0018] Fig. 1 is a side view illustrating the entirety of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment; Fig. 2 is a side view illustrating the zero-gap structure of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment, in the part enclosed by a dashed square frame; Fig. 3 is a plan view illustrating an electrode chamber part of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment; Fig. 4 is a diagram illustrating an outline of an alkaline water electrolysis device including an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment;

[0019] Hereinafter, an embodiment of the present invention (hereinafter, the present embodiment) will be described in detail. Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention.

[0020] <Diaphragm for alkaline water electrolysis> The diaphragm for alkaline water electrolysis of the present embodiment is characterized by comprising the porous membrane of the present embodiment, which contains 50% by mass or more of polyethylene in the resin component and has a tortuosity of 3.00 or less. The diaphragm for alkaline water electrolysis of the present embodiment comprises at least the porous membrane of the present embodiment, and may further comprise other components such as a support. In particular, the diaphragm for alkaline water electrolysis of the present embodiment preferably consists solely of the porous membrane of the present embodiment. In this specification, the diaphragm for alkaline water electrolysis may also be referred to simply as the "diaphragm".

[0021] In an electrolytic cell, the diaphragm is disposed between an anode and a cathode and serves to allow an ion-containing electrolyte to pass through while blocking gas generated at both electrodes. The porous membrane of this embodiment is preferably a membrane prior to being incorporated into an alkaline water electrolysis diaphragm. For example, the porous membrane may be one free of conductive members (e.g., an anode, a cathode) disposed on both surfaces. The diaphragm for alkaline water electrolysis of this embodiment is preferably a membrane prior to being disposed in an electrolytic cell. For example, the diaphragm for alkaline water electrolysis may be one free of conductive members (e.g., an anode, a cathode of an electrolytic cell) disposed on both surfaces.

[0022] The porous membrane included in the diaphragm for alkaline water electrolysis of the present embodiment is preferably formed from a resin composition containing polyethylene. The resin composition may further contain other components, such as additives described below, in addition to polyethylene. In particular, the resin composition preferably contains polyethylene as the only resin component, and may be a resin composition consisting solely of polyethylene.

[0023] Polyethylene has a main chain skeleton that is resistant to hydrolysis, so it is less likely to dissolve or decompose in an alkaline environment. However, adding a substance to impart hydrophilicity to an alkali-resistant resin such as polyethylene may result in performance degradation such as a decrease in strength or deterioration in permeability, so it is preferable that the porous membrane be made solely of an alkali-resistant resin. Specific examples of alkali-resistant resins other than polyethylene include polyphenylene sulfide (PPS) resin and polyether ether ketone (PEEK) resin. Examples of polyethylene include low-density PE (density 0.910 g / cm ３ 0.930g / cm or more ３ less than 0.910 g / cm ３ 0.940g / cm or more ３ less than 0.930 g / cm ３ 0.942g / cm or more ３ less than), high density PE (density 0.942 g / cm ３These can be used alone or in combination of two or more. Among them, using PE alone is preferred from the viewpoint of obtaining a porous membrane with uniform physical properties. From the viewpoint of improving resistance to decomposition under high temperature conditions in a concentrated alkaline aqueous solution, the content of PE in the resin component contained in the porous membrane is 50% by mass or more, preferably 65% ​​by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, still more preferably 80% by mass or more, even more preferably 85% by mass or more, still more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 99% by mass or more, and may even be 100% by mass (composed only of PE). The content of the resin component in the porous membrane is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and may be 100% by mass (consisting only of the resin component). Also, from the viewpoint of improving resistance to decomposition under high temperature conditions in a concentrated alkaline aqueous solution, the content of PE in the porous membrane is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and may be 100% by mass (consisting only of PE). Here, the proportion of the resin contained in the porous film can be measured, for example, by measuring the weight change using a thermogravimetric analyzer or by combining a pyrolysis GC-MS and a thermogravimetric analyzer.

[0024] From the viewpoint of achieving both ion permeability and the mechanical strength of the membrane, it is preferable to use high-density PE with a viscosity average molecular weight of 300,000 or more, more preferably high-density PE with a viscosity average molecular weight of 900,000 or more, and even more preferably ultra-high molecular weight PE with a viscosity average molecular weight of 2,000,000 or more. On the other hand, from the viewpoint of membrane formability, it is preferable to use PE with a viscosity average molecular weight of 10,000,000 or less, more preferably PE with a viscosity average molecular weight of 7,500,000 or less, and even more preferably PE with a viscosity average molecular weight of 4,000,000 or less. Setting the viscosity average molecular weight of PE to 300,000 or more is preferable from the viewpoint of maintaining high melt tension during melt molding to ensure good moldability, or from the viewpoint of imparting sufficient entanglement to the resin to increase the mechanical strength of the porous membrane. On the other hand, setting the viscosity average molecular weight of PE to 10,000,000 or less is preferable from the viewpoint of achieving uniform melt kneading and improving sheet moldability, particularly thickness moldability. Furthermore, setting the viscosity average molecular weight to 7,500,000 or less is preferable from the viewpoint of further improving thickness moldability. The viscosity average molecular weight Mv of PE can be calculated by determining the intrinsic viscosity [η] (dl / g) at 135°C in decalin solvent according to ASTM-D4020 and then using the following formula: [η] = 6.77 × 10 -４ Mv ０．６７

[0025] In addition, the resin composition containing PE used in producing the porous membrane may be mixed with various known additives, such as phenol-based, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments, as needed.

[0026] The porous membrane included in the diaphragm for alkaline water electrolysis of the present embodiment has a tortuosity of 3.00 or less, preferably 2.70 or less, more preferably 2.50 or less, even more preferably 2.40 or less, still more preferably 2.20 or less, and still more preferably 2.00 or less, from the viewpoint of achieving good ion permeability and a low electrolysis voltage. There is no particular lower limit for the tortuosity, but, for example, from the viewpoint of achieving a good pin puncture strength per 100 µm of thickness of the porous membrane, the tortuosity is preferably more than 0, more preferably 0.30 or more, still more preferably 0.50 or more, still more preferably 0.60 or more, and still more preferably 1.00 or more.

[0027] In alkaline water electrolysis, it is common knowledge among those skilled in the art that, unlike the use of nonaqueous electrolytes, it is difficult for the electrolyte to enter the pores of a porous membrane containing PE (a PE porous membrane), making it difficult to achieve a low cell voltage. In studying the present invention, for example, a PE porous membrane can be pre-immersed in a hydrophilic solvent (e.g., ethanol) and then immersed in a solvent (e.g., water (distilled water)) to replace the hydrophilic solvent in the pores with the solvent (e.g., water), thereby filling the pores with the solvent (e.g., water). It was found that if the pores are pre-filled with the solvent (e.g., water), when electrolysis is performed using a PE membrane equipped with the PE porous membrane, the electrolyte flows into and is retained in the pores, even if ions move due to the electrolysis reaction. However, it was found that when the tortuosity of the PE porous membrane exceeds 3.00, the initial cell voltage increases rapidly during electrolysis, a level that cannot be explained solely by an increase in the distance of the ion conduction path. Although the mechanism is unclear, in the case of a PE porous membrane, when the tortuosity exceeds 3.00, even when a hydrophilic solvent such as ethanol is used, some of the pores (voids) of the PE porous membrane are not filled with the solvent or hydrophilic solvent, leaving areas unfilled with the electrolyte, which is thought to result in a sudden increase in cell voltage. Meanwhile, a PE porous membrane, which is a PE porous body, is easily deformed by applying pressure in a direction perpendicular to the membrane surface (thickness direction). This is because the fibrous portion of the PE porous membrane undergoes plastic deformation at room temperature, causing the pores (voids) to close. In light of these findings, the present inventors have found that, since the pores are closed and good airtightness is obtained at the portion fastened (pressured) by the sheet-like gasket, while the tortuosity is maintained at the portion sandwiched between the anode and the cathode (where no pressure is applied by the sheet-like gasket), a low cell voltage can be achieved by setting the tortuosity of the PE porous membrane to 3.00 or less; that is, by using a diaphragm including a PE porous membrane having a tortuosity of 3.00 or less, both airtightness (sealing properties) and a low cell voltage can be achieved even when a sheet-like gasket is used.The tortuosity can be adjusted by adjusting the viscosity average molecular weight of PE, the proportion of PE in the resin composition in the mixing step (a) described later, and the stretching temperature and stretching ratio in the primary stretching step (d) of the method for producing a porous membrane containing polyethylene described later, and / or by adjusting the temperature and stretching ratio in the heat setting step (f) (stretching and relaxation operation) described later.

[0028] The porous membrane of this embodiment has a final membrane thickness of preferably 40 μm or more, more preferably 50 μm or more, even more preferably 70 μm or more, and preferably 1000 μm or less, more preferably 650 μm or less, even more preferably 300 μm or less, and most preferably 250 μm or less. The diaphragm for alkaline water electrolysis of this embodiment has a final membrane thickness of preferably 40 μm or more, more preferably 50 μm or more, even more preferably 70 μm or more, and preferably 1000 μm or less, more preferably 650 μm or less, even more preferably 300 μm or less, and most preferably 250 μm or less. A membrane thickness of 40 μm or more is suitable from the viewpoints of preventing initial short-circuiting of the diaphragm and improving the mechanical strength. On the other hand, a diaphragm thickness of 1000 μm or less is advantageous for reducing the distance between electrodes and is preferred because it tends to reduce the cell voltage during electrolysis.

[0029] The porosity of the porous membrane of this embodiment is preferably 20% or more, more preferably 30% or more, even more preferably 45% or more, and preferably 95% or less, more preferably 80% or less, and even more preferably 70% or less. A porosity of 20% or more is preferable from the viewpoint of reducing the cell voltage when the porous membrane is used for alkaline water electrolysis. On the other hand, a porosity of 95% or less is preferable from the viewpoint of ensuring high pin puncture strength and from the viewpoint of avoiding a decrease in ion permeability due to excessive stretching of the membrane in the stretching and / or heat setting steps. The porosity can be adjusted by adjusting the stretching temperature, stretching ratio, and stretching strain rate in the primary stretching step (d) described below, and / or by adjusting the temperature and stretching ratio in the heat setting step (stretching and relaxation operation) described below (f).

[0030] The water permeability of the porous membrane of this embodiment is preferably 0.1 g / 2 min or more, more preferably 0.5 g / 2 min or more, and even more preferably 1.0 g / 2 min or more, from the viewpoint of good ion permeability and reducing cell voltage, and from the viewpoint of good pin puncture strength, it is preferably 500 g / 2 min or less, more preferably 100 g / 2 min or less, and even more preferably 10 g / 2 min or less. Note that the water permeability can be adjusted by adjusting the stretching temperature, stretching ratio, and stretching strain rate in the primary stretching step (d) described below, and / or by adjusting the temperature and stretching ratio in the heat setting step (stretching and relaxation operation) described below (f).

[0031] The air permeability of the porous membrane of this embodiment is, in terms of 100 μm thickness, preferably 10 seconds or more, more preferably 20 seconds or more, even more preferably 50 seconds or more, and particularly preferably 100 seconds or more, from the viewpoint of maintaining the mechanical strength and gas barrier properties of the porous membrane. On the other hand, from the viewpoint of lowering the cell voltage during electrolysis, it is preferably 4000 seconds or less, more preferably 3000 seconds or less, and even more preferably 2500 seconds or less. The air permeability can be adjusted by adjusting the temperature and magnification of the heat setting step (stretching and relaxation operation) described later in (f).

[0032] The pin puncture strength of the porous membrane of this embodiment is preferably 90 gf / 100 μm or more, more preferably 200 gf / 100 μm or more, and even more preferably 500 gf / 100 μm or more, per 100 μm of membrane thickness, from the viewpoint of suppressing membrane rupture during assembly of the electrolytic cell and suppressing short circuits due to contact between the electrodes and the diaphragm caused by vibrations occurring during electrolysis. On the other hand, from the viewpoint of reducing width shrinkage of the diaphragm during electrolysis, it is preferably 10,000 gf / 100 μm or less, more preferably 8,000 gf / 100 μm or less, and even more preferably 6,000 gf / 100 μm or less. The pin puncture strength can be adjusted by adjusting the molecular weight of PE, the proportion of PE in the resin composition in the mixing step (a) described below, and the stretching temperature and stretch ratio in the primary stretching step (d) described below, and / or by adjusting the temperature and stretch ratio in the heat setting step (stretching and relaxation operation) described in (f) described below.

[0033] (Gas barrier property evaluation) One of the evaluation indexes of the gas barrier property of the porous membrane of this embodiment is the evaluation of the bubble point of the porous membrane.The bubble point in this evaluation method is measured by wetting the porous membrane thoroughly with pure water, filling the pores with pure water, then pressurizing one side of the porous membrane with nitrogen, and measuring the pressure when bubbles start to continuously generate at a rate of 150 mL / min from the other side of the porous membrane.The lower the gas barrier property of the porous membrane, the smaller the bubble point value, and the higher the gas barrier property of the porous membrane, the more difficult it is for gas to pass through, so the bubble point value becomes larger.

[0034] The bubble point of the porous membrane of this embodiment is preferably 0.1 MPa or more. When the bubble point of the porous membrane is 0.1 MPa or more, the separation ability of the porous membrane can be ensured. Furthermore, when the porous membrane is used as a diaphragm for electrolysis, even if a pressure difference occurs between the cathode chamber and the anode chamber, the generated gas cannot easily permeate the diaphragm, so that mixing of oxygen and hydrogen can be effectively suppressed. From this viewpoint, the bubble point of the porous membrane is more preferably 0.2 MPa or more, further preferably 0.4 MPa or more, and most preferably 0.6 MPa or more. The bubble point can be measured by the following method. A sample of the porous membrane is wetted with pure water to impregnate the pores of the membrane with pure water, and then set in a pressure-resistant container for measurement. Next, the pressure vessel is held in a thermostatic chamber set to a predetermined temperature, and once the interior of the pressure vessel has reached the predetermined temperature, measurement is initiated using an integrity tester (e.g., Sartocheck Junior BP-Plus manufactured by Sartorius Stedim Japan). When measurement begins, the upper surface of the sample is pressurized with nitrogen. The nitrogen pressure at which bubbles begin to continuously emerge from the lower surface of the sample at a rate of 150 mL / min is taken as the bubble point pressure (MPa).

[0035] The diaphragm for alkaline water electrolysis of the present embodiment can perform continuous water electrolysis for long periods of time at a low cell voltage without substantially damaging the original porous structure, as long as the pores of the porous membrane are pre-filled with a solvent at a certain volume fraction or more, even without any special hydrophilization treatment. Although not particularly limited, for example, pre-filling 40% or more of the pores of the porous membrane with a solvent such as water is preferable because, even if ions or the electrolyte move as the water electrolysis reaction progresses, a continuous layer of the electrolyte in the pores is maintained without interruption, allowing for more continuous water electrolysis. In particular, a porous membrane having a porous structure with high ion permeability is considered to enable water electrolysis at a low cell voltage. From the viewpoint of high ion permeability, it is more preferable to pre-fill 54% or more of the pores of the porous membrane with a solvent (e.g., water), even more preferably to pre-fill 68% or more of the pores with a solvent (e.g., water), and even more preferably to pre-fill 88% or more of the pores with a solvent (e.g., water).

[0036] The method for filling the pores of a porous membrane with a solvent (e.g., water) is not particularly limited, but a preferred method is to impregnate the porous membrane with a hydrophilic solvent, fill the pores with the hydrophilic solvent, and then impregnate the porous membrane with a solvent (e.g., water), thereby replacing the hydrophilic solvent in the pores with the solvent (e.g., water), and filling the pores with the solvent (e.g., water). Since it is difficult to sufficiently fill the pores of a porous membrane with a hydrophilic solvent having a high surface tension, it is more preferable to use a hydrophilic solvent with a surface tension of 34 mN / m or less. This is particularly preferable for porous membranes with a contact angle with water of greater than 70°. The contact angle of a porous membrane with water is the angle between the surface of the flat plate when water is dropped onto the surface of a porous membrane that has been hot-pressed to form a flat plate, and a tangent is drawn to the surface of the water droplet from the point where the water droplet contacts the flat plate surface. The contact angle between the plate and water can be measured by the θ / 2 method using a commercially available contact angle meter.

[0037] Examples of the hydrophilic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and butanol, as well as acetone and acetonitrile. Alternatively, a method in which the hydrophilic solvent is used as an aqueous solution mixed with water rather than alone is also preferably used. In this case, it is preferable to use an aqueous solution with a surface tension of 34 mN / m or less. For example, a 30% by mass aqueous solution of ethanol (surface tension 33 mN / m) or a 50% by mass aqueous solution of ethanol (surface tension 28 mN / m) can be used. The hydrophilic solvent preferably contains one or more solvents selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, acetone, and acetonitrile. Furthermore, the hydrophilic solvent is preferably an aqueous solution containing 30% by mass or more of one or more solvents selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, acetone, and acetonitrile. Furthermore, the hydrophilic solvent is not particularly limited, but is more preferably an organic solvent with a solubility in water of 50 g / L or more at 20°C. The solubility of the organic solvent in water is more preferably 100 g / L or more, and further preferably 200 g / L or more, from the viewpoint that when the solvent in the pores of the porous membrane is water, replacement with water is rapid.

[0038] The proportion of the solvent (e.g., water) filling the pores of the porous membrane can be adjusted by appropriately adjusting the time for impregnating the porous membrane with the hydrophilic solvent or the time for impregnating the porous membrane with the solvent (e.g., water). In some cases, the proportion of the solvent filling the pores may be adjusted by providing a step of drying the porous membrane after impregnating the porous membrane with the solvent (e.g., water).

[0039] Examples of the solvent that fills the pores of the porous membrane include water; the hydrophilic solvents (preferably, hydrophilic solvents having a surface tension of 34 mN / m or less); alkaline aqueous solutions such as an aqueous NaOH solution and an aqueous KOH solution (for example, alkaline aqueous solutions having an alkali salt concentration of more than 0% by mass and not more than 40% by mass (preferably more than 0% by mass and not more than 35% by mass)); and combinations thereof. Among these, hydrophilic solvents (more preferably, hydrophilic solvents having a surface tension of 34 mN / m or less) and water are preferred, from the viewpoints of facilitating replacement with an electrolytic solution during alkaline water electrolysis and further extending the period during which continuous electrolysis is possible.

[0040] The various parameters described above are measured according to the measurement methods in the examples described below, unless otherwise specified.

[0041] The porous membrane of this embodiment may contain an inorganic compound. The content of the inorganic compound in the porous membrane is not particularly limited as long as it does not block the porous structure and impair ion permeability, but may be, for example, 10% by mass or more, 20% by mass or more, 30% by mass or more, 90% by mass or less, 80% by mass or less, or 70% by mass or less. Here, it is preferable that the inorganic compound does not dissolve or decompose in an alkaline environment. In addition, the inorganic compound may be attached to the surface of the porous membrane, or may be partially or completely embedded in the resin constituting the porous membrane.

[0042] Examples of inorganic compounds include at least one inorganic substance selected from the group consisting of oxides or hydroxides of zirconium, titanium, bismuth, and cerium; oxides of Group IV elements of the periodic table; hydroxides of Group IV elements of the periodic table; nitrides of Group IV elements of the periodic table; and carbides of Group IV elements of the periodic table. Among these, from the viewpoint of chemical stability, oxides of zirconium, titanium, bismuth, and cerium, and oxides or hydroxides of Group IV elements of the periodic table are preferred, and zirconium oxide (ZrO ２ ), zirconium hydroxide (Zr(OH) ４ ), titanium oxide (TiO ２ ), titanium hydroxide (Ti(OH) ４) is more preferred. These may be used alone or in combination of two or more. As the electrolyte for alkaline water electrolysis, alkaline aqueous solutions such as aqueous NaOH solutions and aqueous KOH solutions are often used. When titanium oxide is exposed to such an environment, it may change into titanates such as sodium titanate and potassium titanate. Therefore, titanates may be used in advance.

[0043] The size of the inorganic compound is not particularly limited, but in the case of a particulate substance, the average primary particle size is preferably 10 nm or more and 300 nm or less, and more preferably 25 nm or more and 250 nm or less. The average primary particle size of the particulate inorganic compound in the porous membrane (hereinafter sometimes referred to as "inorganic particles") can be determined by the following method. The measurement sample is observed with a scanning electron microscope (SEM) from the perpendicular direction to the porous membrane surface, and an image is taken at a magnification at which the particulate inorganic compound can be observed. The image is binarized using image analysis software (ImageJ), and the absolute maximum length is measured for each of 10 non-aggregated points of the particulate inorganic compound, and the number average is determined. Note that if the particulate inorganic compound is present only inside the porous membrane and not on the surface, the cut cross section can be observed with an SEM.

[0044] The porous membrane of the present embodiment contains polyethylene, and the content of polyethylene in the resin component is 50% by mass or more (65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, or 100% by mass), the tortuosity is 3.00 or less (2.70 or less, 2.50 or less, 2.40 or less, 2.20 or less, 2.00 or less, or more than 0, 0.30 or more, 0.50 or more, 0.60 or more, 1.00 or more), the membrane thickness is 40 μm or more and 1000 μm or less (50 μm or more, 70 μm or more, or 650 μm or less, 300 μm or less, 250 μm or less), It is preferable that the porosity is 20% or more and 95% or less (can be 30% or more, 45% or more, or 80% or less, 70% or less), the water permeability is 0.1 g / 2 min or more and 500 g / 2 min or less (can be 0.5 g / 2 min or more, 1.0 g / 2 min or more, or 100 g / 2 min or less, 10 g / 2 min or less), the air permeability is 10 seconds or more and 4,000 seconds or less (can be 20 seconds or more, 50 seconds or more, 100 seconds or more, or 3,000 seconds or less, 2,500 seconds or less) converted into 100 μm, and the viscosity average molecular weight of the polyethylene is 300,000 or more and 10,000,000 or less (can be 900,000 or more, 2,000,000 or more, or 7,500,000 or less, 4,000,000 or less).

[0045] The diaphragm for alkaline water electrolysis of the present embodiment may have a single-layer structure consisting of a porous membrane only, or may have a layered structure including other layers in addition to the porous membrane.

[0046] From the viewpoints of suppressing swelling due to the electrolytic solution, preventing clogging of the porous structure, and ensuring good ion permeability, it is preferable that the inner surface (pore surfaces) of the diaphragm for alkaline water electrolysis of the present embodiment is not modified with a monomer having an anion-exchangeable functional group, specifically an amino group, an amide group, a cyano group, an imidazole group, etc. The presence or absence of the surface modification can be evaluated, for example, by measuring the FT-IR of the diaphragm surface and the cross section of the fibrous portion at the center of the cross section of the diaphragm.

[0047] The diaphragm for alkaline water electrolysis of this embodiment may have a support. The support may be porous or non-porous as long as it has ion permeability. Among these, a porous support is preferred from the viewpoint of not substantially reducing ion permeability. The porous support mainly serves as a core material in the diaphragm for alkaline water electrolysis and improves the mechanical strength of the diaphragm. It is preferred that the porous support does not substantially reduce ion permeability. The material of the porous support is not particularly limited, and examples include polyphenylene sulfide, polyethylene, polypropylene, fluorine-based resin, polyparaphenylene benzobisoxazole, polyketone, polyimide, and polyetherimide. These may be used alone, or two or more types may be used simultaneously. The porous support may have a shape such as a sheet. Examples of the porous support include a membrane-like porous body, a nonwoven fabric, a woven fabric, and a composite fabric containing a nonwoven fabric and a woven fabric embedded in the nonwoven fabric. These may be used alone, or two or more types may be used simultaneously. On the other hand, from the viewpoint of ion permeability, the diaphragm for alkaline water electrolysis of the present embodiment preferably does not include a porous support, and more preferably does not include a support. When the diaphragm for alkaline water electrolysis does not include a support, the area that can contribute to ion permeability increases by the volume of the support, and water electrolysis with high ion permeability and low cell voltage may be achieved.

[0048] The diaphragm for alkaline water electrolysis of the present embodiment comprises a porous membrane containing polyethylene, wherein the resin component of the porous membrane has a polyethylene content of 50 mass% or more (optionally 65 mass% or more, 70 mass% or more, 75 mass% or more, 80 mass% or more, 85 mass% or more, 90 mass% or more, 95 mass% or more, 99 mass% or more, or 100 mass%), the tortuosity of the porous membrane is 3.00 or less (optionally 2.70 or less, 2.50 or less, 2.40 or less, 2.20 or less, or 2.00 or less, or alternatively, more than 0, 0.30 or more, 0.50 or more, 0.60 or more, or 1.00 or more), and the membrane thickness of the diaphragm for alkaline water electrolysis is 40 μm or more to 1000 μm or less (optionally 50 μm or more, 70 μm or more, or alternatively 650 μm or less, 300 μm or less, or 250 μm or less). The porosity of the porous membrane is 20% or more and 95% or less (may be 30% or more, 45% or more, or 80% or less, 70% or less), the water permeability of the porous membrane is 0.1 g / 2 min or more and 500 g / 2 min or less (may be 0.5 g / 2 min or more, 1.0 g / 2 min or more, or 100 g / 2 min or less, 10 g / 2 min or less), the air permeability of the porous membrane is 10 seconds or more and 4000 seconds or less (20 seconds or more, 50 seconds or more, 100 seconds or more, or 3000 seconds or less, 2500 seconds or less) in terms of 100 μm, and the viscosity average molecular weight of the polyethylene contained in the porous membrane is 300,000 or more and 10 million or less (may be 900,000 or more, 2 million or more, or 7.5 million or less, 4 million or less).

[0049] <Method of using porous membrane> A method of using a porous membrane according to the present embodiment is characterized in that the porous membrane contains polyethylene in a resin component of 50 mass% or more and has a tortuosity of 3.00 or less, and is used as a diaphragm for alkaline water electrolysis. The porous membrane used in the method of use is preferably the porous membrane according to the present embodiment. Furthermore, the diaphragm for alkaline water electrolysis preferably does not include a support. The porous film contains polyethylene, and the content of polyethylene in the resin component is 50% by mass or more (which may be 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, or 100% by mass), the tortuosity is 3.00 or less (which may be 2.70 or less, 2.50 or less, 2.40 or less, 2.20 or less, or 2.00 or less, or may be greater than 0, 0.30 or more, 0.50 or more, 0.60 or more, or 1.00 or more), the film thickness is 40 μm or more and 1000 μm or less (which may be 50 μm or more, 70 μm or more, or may be 650 μm or less, 300 μm or less, or 250 μm or less), and the porosity is is 20% or more and 95% or less (may be 30% or more, 45% or more, or 80% or less, 70% or less), the water permeability is 0.1 g / 2 min or more and 500 g / 2 min or less (may be 0.5 g / 2 min or more, 1.0 g / 2 min or more, or 100 g / 2 min or less, 10 g / 2 min or less), the air permeability is 10 seconds or more and 4,000 seconds or less (may be 20 seconds or more, 50 seconds or more, 100 seconds or more, or 3,000 seconds or less, 2,500 seconds or less) converted into 100 μm, and the viscosity average molecular weight of the polyethylene is preferably 300,000 or more and 10,000,000 or less (may be 900,000 or more, 2,000,000 or more, or 7,500,000 or less, 4,000,000 or less).

[0050] <Method of using diaphragm for alkaline water electrolysis> A method of using a diaphragm for alkaline water electrolysis according to the present embodiment is characterized by using a diaphragm for alkaline water electrolysis, comprising a porous membrane containing polyethylene, wherein the resin component of the porous membrane has a polyethylene content of 50 mass% or more and a tortuosity of 3.00 or less. The porous membrane used for the diaphragm for alkaline water electrolysis in the above-mentioned method is preferably the porous membrane according to the present embodiment. Furthermore, the diaphragm for alkaline water electrolysis preferably does not include a support. The diaphragm for alkaline water electrolysis comprises a porous membrane containing polyethylene, wherein the polyethylene content in a resin component of the porous membrane is 50 mass% or more (optionally 65 mass% or more, 70 mass% or more, 75 mass% or more, 80 mass% or more, 85 mass% or more, 90 mass% or more, 95 mass% or more, 99 mass% or more, or 100 mass%), the tortuosity of the porous membrane is 3.00 or less (optionally 2.70 or less, 2.50 or less, 2.40 or less, 2.20 or less, or 2.00 or less, or alternatively, more than 0, 0.30 or more, 0.50 or more, 0.60 or more, or 1.00 or more), and the membrane thickness of the diaphragm for alkaline water electrolysis is 40 μm or more to 1000 μm or less (optionally 50 μm or more, 70 μm or more, or alternatively 650 μm or less, 300 μm or less, or 250 μm or less). The porosity of the porous membrane is 20% or more and 95% or less (may be 30% or more, 45% or more, or 80% or less, 70% or less), the water permeability of the porous membrane is 0.1 g / 2 min or more and 500 g / 2 min or less (may be 0.5 g / 2 min or more, 1.0 g / 2 min or more, or 100 g / 2 min or less, 10 g / 2 min or less), the air permeability of the porous membrane is 10 seconds or more and 4000 seconds or less (20 seconds or more, 50 seconds or more, 100 seconds or more, or 3000 seconds or less, 2500 seconds or less) converted to 100 μm, and the viscosity average molecular weight of the polyethylene contained in the porous membrane is 300,000 or more and 10 million or less (may be 900,000 or more, 2 million or more, or 7.5 million or less, 4 million or less).

[0051] <Method for producing diaphragm for alkaline water electrolysis> The diaphragm for alkaline water electrolysis of the present embodiment can be produced by any known method without any particular limitation, but preferably includes the following steps. The order of these steps is not limited and can be selected as appropriate.

[0052] [Method for producing a porous membrane containing polyethylene] The method for producing the porous membrane containing polyethylene of this embodiment (hereinafter sometimes referred to as "polyethylene porous membrane") is not particularly limited, and can be produced by, for example, a known dry film-forming method, melt film-forming method, wet film-forming method, etc. For example, a method including a mixing step (a) of mixing a resin composition containing polyethylene and a pore-forming material, an extrusion step (b) of melt-kneading and extruding the mixture obtained in step (a), a sheet-forming step (c) of forming the extrudate obtained in step (b) into a sheet, a primary stretching step (d) of stretching the sheet-shaped molded product obtained in step (c) at least once in at least one axial direction, an extraction step (e) of extracting the pore-forming material from the stretched membrane obtained in step (d), and a heat-setting step (f) of heat-setting the extracted membrane obtained in step (e) at a predetermined temperature may be mentioned. In addition, in the above method, a secondary stretching step (g) may be further performed after the extraction step (e) and then the heat-setting step (f). The sheet forming step (c) may be immediately followed by the extraction step (e), followed by the primary stretching step (d) and the heat setting step (f).

[0053] The above-mentioned method for producing a polyethylene porous membrane can provide a polyethylene porous membrane that exhibits excellent performance in a high-temperature, high-concentration alkaline environment when used as a diaphragm for an alkaline water electrolysis cell or other electrochemical device. Among these, the method of stretching in MD and TD in the first stretching step (d), followed by heat setting in TD in the heat setting step (f) after the extraction step (e) tends to produce a membrane that can perform water electrolysis at a low cell voltage. Note that MD refers to the machine direction of continuous molding, and TD refers to the direction perpendicular to the MD. Other examples include a method (so-called dry method) in which polyethylene alone or a mixture of polyethylene and a crystal nucleating agent is melt-kneaded and extruded, and then uniaxially stretched and oriented at a high draw ratio immediately after extrusion, followed by heat treatment and stretching to produce a porous membrane. Note that the method for producing the polyethylene porous membrane of this embodiment is not limited to the above-mentioned production method, and various modifications are possible within the scope of the invention.

[0054] [Mixing step (a)] The mixing step (a) is a step of mixing a resin composition containing polyethylene and a pore-forming material. In the mixing step (a), other components may be mixed as necessary.

[0055] The pore-forming material may be any material as long as it is distinguishable from polyethylene and inorganic particle materials. Examples of pore-forming materials include non-volatile solvents capable of forming a homogeneous solution at or above the melting point of polyethylene, such as hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate, dibutyl phthalate, and diisononyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. These pore-forming materials may be recovered and reused by operations such as distillation after extraction. Among pore-forming materials, liquid paraffin is preferred because it has high compatibility with polyethylene, making it less likely for interfacial peeling to occur between the resin and the pore-forming material even when the molten mixture is stretched, and therefore tends to facilitate uniform stretching.

[0056] In step (a), any additive may be added to the polyethylene-containing resin composition. The additives are not particularly limited, but examples thereof include polymers other than polyethylene; antioxidants such as phenolic compounds, phosphorus compounds, and sulfur compounds; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. The total amount of these additives added is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of polyethylene.

[0057] The mixing method in step (a) is not particularly limited, but examples thereof include a method in which some or all of the raw materials are premixed as necessary using a Henschel mixer, ribbon blender, tumbler blender, etc. Among these, a method in which mixing is performed using a Henschel mixer is preferred.

[0058] Alternatively, the step (a) may be omitted and each raw material may be fed separately to the next step (b). For example, the polyethylene and the porous material may be fed separately to the twin-screw extruder from separate feeders or liquid addition pumps, or a mixture may be prepared from the polyethylene and any additives, and this mixture and other components may be fed to the twin-screw extruder from separate feeders.

[0059] [Extrusion step (b)] The extrusion step (b) is a step of melt-kneading and extruding a resin composition containing polyethylene and a pore-forming material. In the extrusion step (b), other components may be mixed with the resin composition as needed.

[0060] The method of melt-kneading in step (b) is not particularly limited, and examples thereof include a method in which all raw materials including the mixture mixed in step (a) are melt-kneaded using a screw extruder such as a single-screw extruder or a twin-screw extruder, a kneader, a mixer, etc. Among these, it is preferable to perform the melt-kneading using the screws of a twin-screw extruder.

[0061] The mass fraction of polyethylene in the resin composition containing polyethylene and a pore-forming material is preferably 12% by mass or more and less than 40% by mass, more preferably 15% by mass or more and less than 35% by mass, and even more preferably 18% by mass or more and less than 33% by mass. When the mass fraction of polyethylene is less than 40% by mass, the energy required during kneading does not increase too much, and a decrease in molecular weight due to excessive entanglement between polymers can be suppressed, so that the properties of the polyethylene porous film are not impaired. On the other hand, when the mass fraction of polyethylene is 12% by mass or more, sufficient energy can be applied during melt kneading, and the polymers are entangled uniformly, so that even when the mixture of polyethylene and a pore-forming material is stretched at a high ratio, the polyethylene molecular chains do not become entangled, and it is easy to form a uniform and fine pore structure and the mechanical strength is also easy to increase.

[0062] Furthermore, when melt-kneading, the pore-forming material may be added in its entirety at once using a liquid addition pump, or may be added in portions at multiple locations using multiple liquid addition pumps. When adding the additive in portions multiple times, it is preferable to adjust the amount added in the first portion to 80% by mass or less of the total amount added, from the viewpoint of suppressing aggregation of the polyethylene and inorganic particles and uniformly dispersing them.

[0063] As described above, uniform dispersion of polyethylene or inorganic particles improves the viscosity of the polyethylene-containing porous membrane near its melting point, making pore clogging less likely to occur, leading to a lower cell voltage during alkaline water electrolysis and improved output characteristics, etc. Furthermore, uniform dispersion of polyethylene or inorganic particles reduces variation in membrane properties. This makes it possible to suppress performance variation within a cell even in a diaphragm with a large area, and also makes it possible to suppress performance variation among individual cells when electrolysis is performed by combining multiple cells to form a stack, which is preferable from the viewpoint of improving the uniformity of cell performance.

[0064] When a pore-forming material is used in step (b), the temperature of the melt-kneading section is preferably 250° C. or lower, more preferably 230° C. or lower, and even more preferably 210° C. or lower, in terms of dispersibility and suppression of molecular weight reduction in the case of polyethylene. The lower limit of the temperature of the melt-kneading section is preferably equal to or higher than the melting point of the polyethylene used, in terms of uniformly dissolving the polyethylene in the pore-forming material.

[0065] In the present embodiment, the kneading temperature is not particularly limited, but it is preferable to mix the raw polyethylene with an antioxidant at a predetermined concentration, then replace the atmosphere around the mixture with a nitrogen atmosphere, and perform melt-kneading while maintaining the nitrogen atmosphere. The temperature during melt-kneading is preferably 160°C or higher, more preferably 180°C or higher, and preferably lower than 300°C.

[0066] In step (b), the kneaded product obtained through the above kneading is extruded using an extruder such as a T-die, a circular die, or a slit nozzle. The conditions for extrusion are not particularly limited, and known methods can be used, for example. When a T-die is used to obtain the extrudate, from the viewpoint of easy control of the thickness of the diaphragm of the final product, the die slit gap is preferably 1.2 to 7 mm, more preferably 1.5 to 6 mm, and even more preferably 2 to 5 mm, and the extrusion is preferably heated to 150 to 250°C.

[0067] In step (b), moisture and volatile components contained in the raw materials may be mixed into the molten mixture during melt-kneading and adversely affect the mixture extruded from the extruder. Therefore, it is preferable to provide the extruder with a degassing vent and a vacuum pump to remove moisture and volatile components vaporized during melt-kneading.

[0068] [Sheet Molding Step (c)] The sheet molding step (c) is a step of molding the extrudate obtained in the extrusion step (b) into a sheet. The sheet-shaped product obtained in the sheet molding step (c) may be a single layer or a laminate, but is preferably a single layer. The sheet molding method is not particularly limited, but examples include a method of solidifying the extrudate by compression cooling. The compression cooling method is not particularly limited, but examples include a method of directly contacting the extrudate with a cooling medium such as cold air or cooling water; and a method of contacting the extrudate with a metal roll, a press, or the like cooled with a refrigerant. Among these, the method of contacting the extrudate with a metal roll, a press, or the like cooled with a refrigerant is preferred in terms of easy film thickness control. After the melt-kneading step (b), the set temperature in the step of molding the molten product into a sheet is preferably set to the same or higher than the set temperature of the extruder. From the viewpoint of thermal degradation of polyethylene, the upper limit of the set temperature is preferably 300°C or less, more preferably 260°C or less, and even more preferably 240°C or less. For example, when continuously producing a sheet-shaped molded product using an extruder, if the set temperatures of the path from the extruder outlet to the T-die and the T-die in the sheet-forming step after the melt-kneading step, i.e., the set temperatures of the path from the extruder outlet to the T-die, are set higher than the set temperatures in the extrusion step, this is preferred because it makes it possible to form the molten material into a sheet without re-agglomeration of the inorganic particles finely dispersed in the melt-kneading step. In particular, when inorganic particles having a small average primary particle size are added, the effect of suppressing aggregation is remarkable.

[0069] [Primary Stretching Step (d)] The primary stretching step (d) is a step of stretching the sheet-like molded product obtained in the sheet molding step (c) at least once in at least one axial direction. This stretching step (a stretching step performed before the next extraction step (e)) is referred to as "primary stretching," and the film obtained by primary stretching is referred to as "primary stretched film." In the primary stretching, the sheet-like molded product can be stretched in at least one direction, and may be performed in both MD and TD, or only in MD or TD. MD refers to the machine direction of continuous molding, and TD refers to the direction perpendicular to MD.

[0070] The stretching method for the primary stretching is not particularly limited, and examples thereof include uniaxial stretching using a roll stretching machine; TD uniaxial stretching using a tenter; sequential biaxial stretching using a roll stretching machine and a tenter or a combination of multiple tenters; simultaneous biaxial stretching using a simultaneous biaxial tenter or inflation molding; etc. Among these, in order to balance the ion permeability and mechanical strength of the resulting porous membrane, sequential biaxial stretching or simultaneous biaxial stretching is preferred.

[0071] The stretching ratio in MD and / or TD of the primary stretching is preferably 2 times or more, more preferably 3 times or more, and even more preferably 4 times or more. When the stretching ratio in MD and / or TD of the primary stretching is 2 times or more, the mechanical strength of the obtained porous film tends to be further improved. Furthermore, the stretching ratio in MD and / or TD of the primary stretching is preferably 10 times or less, more preferably 8 times or less, and even more preferably 6 times or less. When the stretching ratio in MD and / or TD of the primary stretching is 10 times or less, stretching breakage tends to be further suppressed. When performing biaxial stretching, either sequential stretching or simultaneous biaxial stretching may be used, and the stretching ratio in each axial direction is preferably 2 times or more and 10 times or less, more preferably 3 times or more and 8 times or less, and even more preferably 4 times or more and 6 times or less.

[0072] In the simultaneous biaxial or sequential biaxial stretching of the primary stretching, the stretching strain rate in MD and TD is preferably 0.5% / sec or more and 50% / sec or less, more preferably 1% / sec or more and 45% / sec or less, even more preferably 1.5% / sec or more and 40% / sec or less, and most preferably 2% / sec or more and 35% / sec or less. Without wishing to be bound by theory, it is presumed that if the stretching strain rate in MD and TD is 0.5% / sec or more, the entanglement of the polymers in the sheet-like molded body is maintained while stretching, so the porous film has high mechanical strength and uniform pore size, and the occurrence of large pores that may cause a decrease in gas purity during electrolysis can be suppressed. If the stretching strain rate in MD and TD is 50% / sec or less, the residual stress of the resulting polyethylene porous film is reduced, which tends to reduce the shrinkage rate, which is preferable.

[0073] The primary stretching temperature is not particularly limited and can be selected with reference to the composition and concentration of the raw material resin contained in the polyethylene resin composition. The stretching temperature is preferably in the range from a temperature 30°C lower than the melting point Tm of the porous membrane to the melting point Tm (Tm-30°C to Tm°C) from the viewpoint of preventing breakage due to excessive stretching stress and balancing mechanical strength and thermal shrinkage. In the case of the porous membrane of this embodiment, in which 50% by mass or more of the porous membrane is PE, the stretching temperature is preferably 100°C or higher, and preferably 135°C or lower from the viewpoint of increasing the mechanical strength of the porous membrane. Specifically, the stretching temperature is preferably 100 to 135°C, more preferably 110 to 130°C, and even more preferably 120 to 128°C.

[0074] [Extraction step (e)] The extraction step (e) is a step of extracting the pore-forming material from the first stretched membrane obtained in the first stretching step (d) to obtain an extracted membrane. As a method for removing the pore-forming material, for example, a method of immersing the first stretched membrane in an extraction solvent to extract the pore-forming material and then thoroughly drying it can be mentioned. The method for extracting the pore-forming material may be either a batch method or a continuous method. In addition, it is preferable that the amount of the pore-forming material, particularly the amount of the pore-forming material remaining in the porous membrane, is less than 1 mass%.

[0075] The extraction solvent used to extract the pore-forming material is preferably a poor solvent for polyethylene and a good solvent for the pore-forming material or pore-forming material, and has a boiling point lower than the melting point of polyethylene. Examples of such extraction solvents include, but are not limited to, hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorinated halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered by distillation or other procedures and reused.

[0076] [Heat setting step (f)] The heat setting step (f) is a step of heat setting the extracted film obtained in the extraction step (e) at a predetermined temperature. The heat treatment method at this time is not particularly limited, but may be a heat setting method using a tenter or roll stretching machine to perform stretching and relaxation operations.

[0077] The stretching operation in the heat-setting step (f) is an operation of stretching the porous membrane in at least one direction of MD and TD, and may be performed in both MD and TD, or only in MD or TD. The stretching ratios in MD and TD in the heat-setting step (f) are preferably 1.0 times or more, more preferably 1.1 times or more, even more preferably 1.2 times or more, and even more preferably 1.5 times or more. The upper limit of the stretching ratios in MD and TD in the heat-setting step (f) is not particularly limited, but is preferably 2.5 times or less. If the stretching ratio is outside the above range, shrinkage stress near the melting point tends to remain, which tends to worsen heat shrinkage. In addition, when the stretching ratio is within the above range, the mechanical strength and porosity of the porous membrane tend to be further improved.

[0078] The stretching temperature in this stretching operation is not particularly limited, but is preferably a temperature 30°C lower than the melting point Tm of the porous membrane (i.e., stretching temperature ≥ Tm - 30°C), more preferably a temperature higher than the melting point Tm - 25°C of the porous membrane, and even more preferably a temperature in the range from the melting point Tm - 20°C of the porous membrane to the melting point Tm (i.e., Tm - 20°C to Tm). In the case of the porous membrane of this embodiment in which 50% by mass or more of the porous membrane is PE, the stretching temperature is preferably 110°C or higher, and preferably 136°C or lower from the viewpoint of increasing the mechanical strength of the porous membrane. Specifically, the stretching temperature is 110 to 136°C, more preferably 115 to 134°C, and even more preferably 120 to 133°C. By having the stretching temperature within the above range, the heat shrinkage rate of the obtained porous membrane tends to be further reduced, and the porosity and mechanical strength tend to be further improved.

[0079] The relaxation operation in the heat setting step (f) is an operation of shrinking the porous membrane in at least one direction of MD and TD, and may be performed in both MD and TD, or only in MD or TD. The relaxation rate in the heat setting step (f) is preferably 2% or more, more preferably 3% or more, even more preferably 4% or more, and even more preferably 5% or more. A relaxation rate of 2% or more in the heat setting step (f) tends to improve the heat shrinkage rate. In addition, from the viewpoint of membrane quality, the relaxation rate is preferably 30% or less, and more preferably 25% or less is preferred from the viewpoint of increasing the relaxation temperature. Here, the "relaxation rate" refers to the value obtained by subtracting the dimension of the membrane after the relaxation operation from the dimension of the membrane before the relaxation operation, divided by the dimension of the membrane before the relaxation operation. When both MD and TD are relaxed, it refers to the value obtained by multiplying the relaxation rate in MD and the relaxation rate in TD. Relaxation rate (%)=(membrane dimension (m) before relaxation operation−membrane dimension (m) after relaxation operation) / (membrane dimension (m) before relaxation operation)×100

[0080] The relaxation ratio in the heat setting step (f) is not particularly limited, but is preferably 1.0 to 1.8 times, more preferably 1.1 to 1.7 times, and even more preferably 1.2 to 1.6 times. When the relaxation ratio in the heat setting step (f) is 1.0 times or more, the cell voltage becomes good, and when it is 1.8 times or less, excessive increase in pore size can be suppressed. Here, the relaxation ratio is the value obtained by dividing the dimension of the membrane after the relaxation operation by the dimension of the membrane before stretching.

[0081] The relaxation temperature in the relaxation operation is not particularly limited, but in order to obtain a porous membrane according to the present embodiment and a diaphragm for alkaline water electrolysis including the same, the relaxation temperature is preferably equal to or lower than the melting point (Tm) of the porous membrane, more preferably in the range from the melting point (Tm) - 7°C to the melting point (Tm) of the porous membrane (i.e., Tm - 7°C to Tm), and even more preferably in the range from the melting point (Tm) - 6°C to the melting point (Tm) - 2°C of the porous membrane (i.e., Tm - 6°C to Tm - 2°C). When the temperature in the relaxation operation is within the above range, not only can residual stress due to the stretching step be removed but also the orientation of molecular chains can be firmly fixed, which is preferable from the viewpoints of preventing a decrease in ion permeability near the melting point of the porous membrane and improving the performance of the electrochemical device.

[0082] (Alkaline water electrolysis cell) The alkaline water electrolysis cell of this embodiment is an electrolytic cell comprising the diaphragm for alkaline water electrolysis of this embodiment described above, an anode, and a cathode, with the diaphragm for alkaline water electrolysis disposed between the anode and the cathode. Hereinafter, an example of an alkaline water electrolysis cell of this embodiment comprising the cathode, anode, and diaphragm described above will be described with reference to the drawings. The alkaline water electrolysis cell of this embodiment is not limited to the one described below. Furthermore, components included in the alkaline water electrolysis cell other than the anode, cathode, and diaphragm are not limited to those listed below, and known components can be appropriately selected, designed, etc.

[0083] The alkaline water electrolysis cell of this embodiment is a bipolar electrolysis cell formed by stacking the diaphragm for alkaline water electrolysis of this embodiment described above and a bipolar element holding an anode and a cathode. In other words, the alkaline water electrolysis cell of this embodiment is a bipolar electrolysis cell including a plurality of combinations (also referred to as "electrolytic cells") of an anode, a cathode, and the diaphragm for alkaline water electrolysis of this embodiment disposed between the anode and the cathode. The diaphragm for alkaline water electrolysis of this embodiment is characterized by including a porous membrane containing 50 mass% or more of a polyethylene resin and having a tortuosity of 3.00 or less, and can provide a diaphragm that ensures good airtightness of the electrolytic cell even when a sheet-like gasket is used, while enabling water electrolysis at a low cell voltage.

[0084] As described above, the bipolar electrolytic cell for alkaline water electrolysis of the present embodiment is characterized by including the diaphragm for alkaline water electrolysis of the present embodiment described above, and other configurations are not particularly limited. Hereinafter, the configuration of one example of a bipolar electrolytic cell for alkaline water electrolysis of the present embodiment will be described with reference to the drawings.

[0085] Fig. 1 shows a side view of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. Fig. 2 shows a side view of the zero gap structure of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment, focusing on the portion enclosed by the dashed square frame in Fig. 1. Fig. 3 shows a plan view of an electrode chamber portion of an example of a bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment. As shown in Fig. 1, the bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment is a bipolar electrolytic cell 50 in which a plurality of electrolytic cells 65, each including an anode 2a, a cathode 2c, a partition wall 1 separating the anode 2a and the cathode 2c, and an outer frame 3 bordering the partition wall 1, are stacked one on top of the other with a diaphragm 4 sandwiched between them.

[0086] Although not particularly limited, the bipolar electrolytic cell for alkaline water electrolysis of this embodiment preferably has a zero-gap structure Z in which the diaphragm 4 is in contact with the anode 2 a and the cathode 2 c (see FIG. 2 ).

[0087] In the bipolar electrolytic cell 50 of the present embodiment, the partition wall 1, the outer frame 3, and the diaphragm 4 define an electrode chamber 5 through which the electrolytic solution passes, and the electrode chamber 5 is provided with a plurality of current plates 6 arranged parallel to a given direction D1 along the partition wall 1 (see FIGS. 2 and 3 ).

[0088] 2 and 3 , a bipolar element 60 used in an example bipolar electrolytic cell for alkaline water electrolysis includes a partition wall 1 that separates an anode 2a from a cathode 2c, and an outer frame 3 that borders the partition wall. More specifically, the partition wall 1 is conductive, and the outer frame 3 is provided along the outer edge of the partition wall 1 so as to surround the partition wall 1.

[0089] In this embodiment, the bipolar element 60 may be used so that the given direction D1 along the partition wall 1 is normally the vertical direction. Specifically, when the partition wall 1 has a rectangular shape in a plan view as shown in Figures 2 and 3, the bipolar element 60 may be used so that the given direction D1 along the partition wall 1 is the same direction as the direction of one of two pairs of opposing sides (see Figures 1 to 3). In this specification, the vertical direction is also referred to as the electrolyte passage direction.

[0090] In this embodiment, as shown in Fig. 1 , the bipolar electrolytic cell 50 is configured by stacking the required number of bipolar elements 60. In the example shown in Fig. 1 , the bipolar electrolytic cell 50 includes a fast head 51g, an insulating plate 51i, and an anode terminal element 51a arranged in this order from one end, and further includes an anode side gasket portion 7, a diaphragm 4, a cathode side gasket portion 7, and a bipolar element 60 arranged in this order. At this time, the bipolar element 60 is arranged so that the cathode 2c faces the anode terminal element 51a. The anode side gasket portion 7 to the bipolar element 60 are arranged repeatedly the number of times required for the designed production volume. After the required number of arrangements of the anode side gasket portion 7 to the bipolar element 60 are repeated, the anode side gasket portion 7, the diaphragm 4, and the cathode side gasket portion 7 are again arranged in a row, and finally the cathode terminal element 51c, the insulating plate 51i, and the loose head 51g are arranged in this order. The bipolar electrolytic cell 50 is integrated by clamping the entire cell together using a clamping mechanism such as a tie rod 51r (see FIG. 1) or a hydraulic cylinder, to form the bipolar electrolytic cell 50. The arrangement of the bipolar electrolytic cell 50 can be selected arbitrarily, either from the anode 2a side or the cathode 2c side, and is not limited to the above-mentioned order.

[0091] As shown in FIG. 1 , in a bipolar electrolytic cell 50, a bipolar element 60 is disposed between an anode terminal element 51 a and a cathode terminal element 51 c, and diaphragms 4 are disposed between the anode terminal element 51 a and the bipolar element 60, between adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51 c.

[0092] In the bipolar electrolytic cell 50 of this embodiment, as shown in FIGS. 2 and 3, the partition wall 1, the outer frame 3, and the diaphragm 4 define an electrode chamber 5 through which the electrolyte passes.

[0093] Specifically, the electrode chambers 5 have, at the boundary with the outer frame 3, an electrolyte inlet for introducing the electrolyte into the electrode chambers 5 and an electrolyte outlet for discharging the electrolyte from the electrode chambers 5. More specifically, the anode chamber 5a is provided with an anolyte inlet for introducing the electrolyte into the anode chamber 5a and an anolyte outlet for discharging the electrolyte discharged from the anode chamber 5a, and the cathode chamber 5c is provided with a catholyte inlet for introducing the electrolyte into the cathode chamber 5c and a catholyte outlet for discharging the electrolyte discharged from the cathode chamber 5c.

[0094] In the example shown in FIGS. 1 to 3 , the rectangular partition wall 1 and the rectangular diaphragm 4 are arranged in parallel to each other, and the inner surface of the rectangular parallelepiped outer frame 3 provided on an edge of the partition wall 1, facing the partition wall 1, is perpendicular to the partition wall 1, and therefore the electrode chamber 5 has a rectangular parallelepiped shape.

[0095] The bipolar electrolytic cell 50 is usually fitted with headers, which are pipes for distributing or collecting the electrolyte, and is provided with an anode inlet header for introducing the electrolyte into the anode chamber 5a and a cathode inlet header for introducing the electrolyte into the cathode chamber 5c, located at the lower part of the outer frame 3 at the edge of the partition wall 1. Similarly, an anode outlet header for discharging the electrode solution from the anode chamber 5a and a cathode outlet header for discharging the electrolyte from the cathode chamber 5c are provided at the upper part of the outer frame 3 at the edge of the partition wall 1. Representative arrangements of headers fitted to the bipolar electrolytic cell 50 shown in Figures 1 to 3 are an internal header type and an external header type, but either type may be adopted in the present invention, and are not particularly limited.

[0096] In the bipolar electrolytic cell 50 of this embodiment, the electrolyte distributed in the anode inlet header is introduced into the anode chamber 5a through the anolyte inlet, passes through the anode chamber 5a, is discharged from the anode chamber 5a through the anolyte outlet, and is collected in the anode outlet header.

[0097] As shown in FIGS. 2 and 3, the electrode chamber in this embodiment includes a plurality of current plates 6 arranged parallel to a given direction D1 along the partition wall 1.

[0098] The current plate 6 reduces convection that occurs in the electrode chamber 5 due to turbulence in the gas-liquid flow within the electrode chamber 5, thereby suppressing a local increase in the temperature of the electrolyte.

[0099] In particular, in the example shown in FIGS. 1 to 3 , a plurality of rectifying plates 6 are provided at a constant interval (pitch) in a direction perpendicular to a given direction D1 along the partition wall 1 (in the illustrated example, the electrolyte solution passing direction).

[0100] In addition, in one example of a bipolar electrolytic cell 50, the current plate 6 has substantially the same length as the height of the electrode chamber 5, is provided perpendicular to the partition wall 1, and has through-holes at a predetermined pitch in a given direction D1 along the partition wall 1 (in the illustrated example, the direction of passage of the electrolyte). In the present invention, the shape of the electrode chamber 5 is not limited to the rectangular parallelepiped of the example shown in Figs. 1 to 3 , and may be modified appropriately depending on the planar shapes of the partition wall 1 and the diaphragm 4, the angle between the partition wall 2 and the inner surface of the outer frame 3 on the partition wall 2 side, and the like, and any shape may be used as long as the effects of the present invention are obtained.

[0101] In the present invention, the arrangement of the current plate 6 in the electrode chamber 5 is not limited to the examples shown in FIGS.

[0102] In the present invention, the number of rectifying plates 6 and the constant intervals (pitch) of the rectifying plates 6 in the direction perpendicular to the given direction D1 along the partition wall 1 may be determined as appropriate, as long as the effects of the present invention are obtained. Here, the intervals between the rectifying plates 6 do not have to be constant. In the present invention, the length of the rectifying plates 6, the angle between the rectifying plates 6 and the partition wall 1, the number of through holes, and the constant intervals (pitch) of the through holes in the given direction D1 along the partition wall 1 may be determined as appropriate, as long as the effects of the present invention are obtained. Here, the intervals between the through holes do not have to be constant.

[0103] In the examples shown in FIGS. 1 to 3 , the partition wall 1, the anode 2 a, and the cathode 2 c all have a plate-like shape with a predetermined thickness; however, the present invention is not limited thereto, and they may all or partly have a zigzag or wavy shape in cross section, or may have a shape with rounded edges.

[0104] [Diaphragm for alkaline water electrolysis] The diaphragm 4 used in the electrolytic cell for alkaline water electrolysis of this embodiment is the diaphragm for alkaline water electrolysis of the present invention described above, and therefore further description thereof will be omitted.

[0105] [Electrodes (anode, cathode)] In the alkaline water electrolysis reaction, alkaline water is electrolyzed in an electrolytic cell equipped with an electrode pair (i.e., an anode and a cathode) connected to a power source, generating oxygen gas at the anode and hydrogen gas at the cathode. The electrode 2 included in the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment will be described in detail below. In this specification, the term "electrode" refers to either or both of the anode 2a and the cathode 2c.

[0106] In the case of a zero gap electrolytic cell described below, it is necessary to degas the gas generated from the back side of the surface in contact with the diaphragm 4, and therefore the porous electrode is preferably perforated on the surface opposite to the surface in contact with the diaphragm 4.

[0107] The porous electrode in this embodiment is not particularly limited, but examples thereof include electrodes having a mesh structure such as a plain weave mesh type, a punched type, and an expanded type, and metal foams, from the viewpoint of controlling the average pore size. Among these, from the viewpoint of controlling the size and shape of the pores, it is preferable to have a mesh structure selected from the group consisting of a plain weave mesh type, a punched type, and an expanded type.

[0108] The porous electrode in this embodiment may be the substrate itself, or may have a highly reactive catalyst layer on the surface of the substrate, but it is preferable that the porous electrode has a highly reactive catalyst layer on the surface of the substrate.

[0109] The material of the substrate is not particularly limited, and examples thereof include conductive substrates made of at least one selected from the group consisting of nickel, iron, mild steel, stainless steel, vanadium, molybdenum, copper, silver, manganese, platinum group metals, graphite, and chromium. A conductive substrate made of an alloy of two or more metals or a mixture of two or more conductive materials may also be used. Among these, nickel and nickel-based alloys are preferred from the viewpoints of the conductivity of the substrate and durability to the usage environment.

[0110] Examples of methods for forming a catalyst layer on a substrate include plating methods, thermal spraying methods such as plasma spraying, thermal decomposition methods in which a precursor layer solution is applied to a substrate and then heat is applied, methods in which a catalyst substance is mixed with a binder component and then fixed to the substrate, and vacuum film formation methods such as sputtering.

[0111] In the zero-gap configuration described below, the diaphragm 4 is pressed against the electrode more strongly than in conventional electrolytic cells. For example, in an electrode using an expanded base material, the diaphragm 4 may be damaged at the edge of the opening, or may be embedded in the opening, creating a gap between the cathode 2c and the diaphragm 4 and resulting in an increase in voltage.

[0112] In order to solve the above problems, it is preferable to make the electrode shape as flat as possible. For example, a method can be applied in which an expanded substrate (e.g., an expanded substrate) is pressed with a roller to form a flat shape. In this case, it is desirable to press the expanded substrate to 95% to 110% of the original thickness of the metal plate before the expanding process to flatten it.

[0113] The electrode 2 manufactured by the above-mentioned treatment not only prevents damage to the diaphragm 4 but also, unexpectedly, reduces the voltage. The reason for this is not clear, but it is thought to be because the surface of the diaphragm 4 and the electrode surface come into uniform contact, resulting in a more uniform current density.

[0114] The size of the electrode 2 is not particularly limited and can be determined according to the shape and size of the bipolar electrolytic cell for alkaline water electrolysis, the electrolytic cell, the bipolar element, the partition wall, etc., and also according to the desired electrolysis capacity, etc. For example, when the partition wall has a plate shape, the size of the electrode 2 may be determined according to the size of the partition wall.

[0115] [Gasket] In the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment, the sealing region (edge) of the diaphragm 4 and the bipolar element 60 are preferably stacked together with a gasket 7 interposed therebetween. The gasket 7 is used to seal the space between the bipolar element 60 and the diaphragm 4 and the space between the bipolar elements 60 against the electrolytic solution and the generated gas, and can prevent leakage of the electrolytic solution or the generated gas to the outside of the cell and mixing of gases between the two electrode chambers.

[0116] The material of the gasket 7 is not particularly limited, and may be selected from known insulating rubber materials, resin materials, etc. Specific examples of the rubber material or resin material include natural rubber (NR), styrene butadiene rubber (SBR), chloroprene rubber (CR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), silicone rubber (SR), ethylene-propylene rubber (EPT), ethylene-propylene-diene rubber (EPDM), fluororubber (FR), isobutylene-isoprene rubber (IIR), urethane rubber (UR), and chlorosulfonated PE rubber (CSM); fluororesin materials such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE); and resin materials such as polyphenylene sulfide (PPS), PE, polyimide, and polyacetal. Among these, ethylene-propylene-diene rubber (EPDM) and fluororubber (FR) are particularly suitable from the viewpoint of elastic modulus and alkali resistance.

[0117] The gasket 7 may have a reinforcing material embedded therein. This prevents the gasket 7 from being crushed when sandwiched and pressed by the frame during stacking, making it easier to prevent breakage. Known metal materials, resin materials, and carbon materials can be used for such reinforcing materials. Specific examples include metals such as nickel and stainless steel; resins such as nylon, polypropylene, PVDF, PTFE, and PPS; and carbon materials such as carbon particles and carbon fibers. Suitable shapes of the reinforcing material include woven fabric, nonwoven fabric, short fiber, and porous film. Furthermore, a protective layer may be provided on the surface of the gasket 7. This can improve adhesion between the gasket 7 and the element and can also improve the alkali resistance of the gasket 7. The material for such a protective layer can be selected from the materials used for the gasket 7.

[0118] The size of the gasket 7 is not particularly limited and may be designed to match the dimensions of the electrode chamber 5 and the membrane, but it is preferable that the width be 10 mm to 40 mm.

[0119] The thickness of the gasket 7 is not particularly limited and is designed depending on the material, elastic modulus, and cell area of ​​the gasket 7. A preferable range of the thickness is 1 mm to 10 mm, and more preferably 1.5 mm to 10 mm.

[0120] Furthermore, the shape of the gasket 7 is not particularly limited, but is preferably designed to match the shape of the bipolar element 60. From the viewpoint of good operability when assembling the electrolytic cell 50, a sheet shape is preferred, and in particular a frame-shaped sheet shape that contacts the outer periphery (outer frame 3) of the bipolar element 60 is more preferred. By using a structure in which the diaphragm 4 is sandwiched between two gaskets 7 at the outer periphery (outer frame 3) of the bipolar element 60 (a structure in which the diaphragm 4 sandwiched between the two gaskets 7 is sandwiched by the outer periphery (outer frame 3) of the bipolar element 60), it is possible to achieve both easy assembly of the electrolytic cell 50 and airtightness. That is, the electrolytic cell for alkaline water electrolysis of this embodiment is preferably an electrolytic cell comprising the above-described diaphragm for alkaline water electrolysis of this embodiment, a sheet-like gasket, an anode, and a cathode, with the diaphragm for alkaline water electrolysis disposed between the anode and the cathode. Furthermore, the electrolytic cell for alkaline water electrolysis according to this embodiment is preferably an electrolytic cell comprising the diaphragm for alkaline water electrolysis according to the embodiment described above, two sheet-like gaskets, an anode, and a cathode, the diaphragm for alkaline water electrolysis being disposed between the anode and the cathode, and the two sheet-like gaskets being disposed to sandwich the diaphragm for alkaline water electrolysis. Furthermore, when the gasket 7 has a rectangular slit structure (a structure having a U-shaped cross section) capable of accommodating the diaphragm 4, the spacing of the slit portions sandwiching the diaphragm 4 is preferably 0.2 mm to 1.2 mm, more preferably 0.25 mm to 1.1 mm, more preferably 0.3 mm to 1.0 mm, and even more preferably 0.35 mm to 0.8 mm. Furthermore, the depth of the slit portions of the slit structure into which the diaphragm 4 is inserted is preferably 4.0 mm to 90 mm, more preferably 4.5 mm to 85 mm, and even more preferably 5.0 mm to 80 mm.

[0121] Furthermore, the height of the protrusions when provided is not particularly limited, but is preferably 0.5 mm to 5 mm in order to exert a sufficient pressing force.

[0122] The elastic modulus of the gasket 7 is not particularly limited and is designed depending on the material of the electrode 2 and the cell area. A preferred range of the elastic modulus is a tensile stress at 100% deformation of 0.20 MPa to 20 MPa, more preferably 1.0 MPa to 10 MPa from the viewpoint of sealing characteristics and cell strength when stacked. The tensile stress can be measured in accordance with JIS K6251. For example, an Autograph AG manufactured by Shimadzu Corporation may be used.

[0123] An adhesive may be used when attaching the gasket 7 to the bipolar element 60. The adhesive may be applied to one side of the gasket 7 and then attached to the outer frame 3 on one side of the element. After the adhesive has dried, it is preferable to spray water on the electrode surfaces of the bipolar alkaline water bipolar element 60 to moisten the electrodes 2. In the case of a gasket 7 having a slit that accommodates the edge of the diaphragm 4 so that it can hold the diaphragm 4, the gasket 7 may be attached while holding the diaphragm 4, or the diaphragm 4 may be held after being attached.

[0124] [Zero gap structure] The bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment is preferably, but not particularly limited to, a so-called "zero gap structure" Z in which the diaphragm 4 is in contact with the anode 2a and the cathode 2c, as shown in Fig. 2 . The "zero gap structure" Z is a structure that can maintain a state in which the anode 2a and the diaphragm 4 are in contact with each other and the cathode 2c and the diaphragm 4 are in contact with each other over the entire electrode surfaces, or a state in which the inter-electrode distance is substantially the same as the thickness of the diaphragm 4 and there is almost no gap between the anode 2a and the diaphragm 4 and between the cathode 2c and the diaphragm 4 over the entire electrode surfaces. During alkaline water electrolysis, if there is a gap between the diaphragm 4 and the anode 2a or the cathode 2c, in addition to the electrolytic solution, a large amount of gas bubbles generated during electrolysis will remain in this portion, resulting in a very high electrical resistance. On the other hand, when the zero gap structure Z is formed, the generated gas is quickly released to the side of the electrode 2 opposite to the diaphragm 4 side through the pores in the electrode 2, thereby reducing the distance between the anode 2 a and the cathode 2 c (hereinafter also referred to as the "inter-electrode distance"), minimizing voltage loss due to the electrolytic solution and the occurrence of gas accumulation near the electrodes, and keeping the electrolysis voltage low.

[0125] Several means for constructing the zero gap structure Z have already been proposed, including a method in which the anode 2a and cathode 2c are processed to be completely smooth and then pressed together so as to sandwich the diaphragm 4, and a method in which an elastic body such as a spring is disposed between the electrode 2 and the partition wall 4 and the electrode 2 is supported by this elastic body. Note that preferred embodiments of the means for constructing the zero gap structure Z in the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment will be described later.

[0126] In the bipolar element 60 of the zero-gap cell, a means for reducing the inter-electrode distance is preferably provided by disposing an elastic spring between the electrode 2 and the partition wall 1, and supporting the electrode 2 with this spring. For example, in a first example, a spring made of a conductive material may be attached to the partition wall 1, and the electrode 2 may be attached to this spring. In a second example, a spring may be attached to the electrode rib 6 attached to the partition wall 1, and the electrode 2 may be attached to this spring. When adopting such a configuration using an elastic body, the strength, number, shape, etc. of the spring must be appropriately adjusted as necessary to prevent uneven contact pressure between the electrode 2 and the diaphragm 4.

[0127] Furthermore, by increasing the rigidity of the other electrode 2 that is paired with the electrode 2 supported via the elastic body (for example, by making the rigidity of the anode stronger than that of the cathode), a structure is achieved in which deformation is small even when pressed. Meanwhile, the electrode 2 supported via the elastic body has a flexible structure that deforms when the diaphragm 4 is pressed against it, which makes it possible to absorb unevenness due to tolerances in the manufacturing precision of the electrolytic cell 50 and deformation of the electrode 2, thereby maintaining the zero gap structure Z.

[0128] In the bipolar electrolytic cell 50 for alkaline water electrolysis of this embodiment, as shown in FIG. 2 , a conductive elastic body 2 e and a current collector 2 r are provided between the cathode 2 c or the anode 2 a and the partition wall 1, such that the conductive elastic body 2 e is sandwiched between the cathode 2 c or the anode 2 a and the current collector 2 r.

[0129] (Alkaline water electrolysis apparatus) An example of an alkaline water electrolysis apparatus in which the bipolar electrolytic cell for alkaline water electrolysis of the present embodiment can be used is shown in Fig. 4. In addition to the bipolar electrolytic cell 50 for alkaline water electrolysis of the present embodiment, the alkaline water electrolysis apparatus 70 may include a liquid feed pump 71, a gas-liquid separation tank 72, a water supply device 73, a rectifier 74, an oxygen concentration meter 75, a hydrogen concentration meter 76, a flow meter 77, a pressure meter 78, a heat exchanger 79, a pressure control valve 80, etc.

[0130] (Alkaline water electrolysis) By performing electrolysis by circulating the electrolytic solution in an alkaline water electrolysis device including the bipolar electrolytic cell for alkaline water electrolysis according to the present embodiment, excellent electrolysis efficiency and high purity of the generated gas can be maintained even after high density current operation or variable power supply operation, and highly efficient alkaline water electrolysis can be performed.

[0131] The electrolyte solution that can be used for the alkaline water electrolysis of this embodiment may be an alkaline aqueous solution in which an alkali salt is dissolved, such as an aqueous NaOH solution or an aqueous KOH solution. The concentration of the alkali salt is not particularly limited, but is preferably 20% by mass to 50% by mass, and more preferably 25% by mass to 40% by mass. Among these, a 25% by mass to 40% by mass aqueous KOH solution is particularly preferred from the viewpoints of ionic conductivity, kinetic viscosity, and freezing at low temperatures.

[0132] The temperature of the electrolytic solution in the electrolytic cell is not particularly limited, but is preferably 60°C to 100°C. Within this temperature range, it is possible to effectively prevent thermal deterioration of electrolytic device components such as gaskets and diaphragms while maintaining high electrolysis efficiency. The temperature of the electrolytic solution is more preferably 65°C to 95°C, and particularly preferably 70°C to 90°C.

[0133] In the alkaline water electrolysis of this embodiment, the current density applied to the electrolytic cell is not particularly limited, but is preferably 3 kA / m ２ ~20 kA / m ２ Preferably, it is 6 kA / m ２ ~15kA / m ２ In particular, when a variable power supply is used, it is preferable that the upper limit of the current density be within the above range.

[0134] In alkaline water electrolysis of this embodiment, the pressure inside the electrolytic cell is not particularly limited, but is preferably 3 kPa to 1000 kPa, and more preferably 3 kPa to 300 kPa.

[0135] The flow rate of the electrolyte per electrode chamber and other conditions may be appropriately controlled depending on the configuration of the bipolar electrolytic layer for alkaline water electrolysis.

[0136] The bipolar electrolytic cell for alkaline water electrolysis according to the embodiment of the present invention has been described above with reference to the drawings. However, the bipolar electrolytic cell for alkaline water electrolysis according to the present invention is not limited to the above example, and appropriate modifications can be made to the above embodiment.

[0137] Examples of the present invention will be described below, but these examples are merely illustrative examples for suitably explaining the present invention and do not limit the present invention in any way.

[0138] [Methods for measuring and evaluating physical properties] The analytical and evaluation methods used in the examples and comparative examples are as follows: (1) to (3) and (6) were all measured in a state where the pores of the porous membrane were not filled with water.

[0139] (1) Thickness (μm) A porous membrane was cut into a size of 10 cm in MD × 10 cm in TD, and 9 points (3 points × 3 points) were selected in a grid pattern, and the thickness was measured at room temperature of 23°C using a Digimatic Indicator (manufactured by Mitutoyo Corporation, Code No. 543-390B), and the average value of the measurements at the 9 points was taken as the thickness of the diaphragm.

[0140] (2) Porosity (%) A 10 cm x 10 cm square sample was cut out from the porous membrane, and its volume (cm ３ ) and mass (g), and compare them with the film density (g / cm ３ ), the porosity was calculated using the following formula: ３ ) = 10 (cm) x 10 (cm) x film thickness (cm) Porosity (%) = (volume - mass / film density) x 100 / volume Note that the film density was calculated by heating the porous film or raw material resin used to a melting point or higher in a heat press, press-molding it into a sheet, cutting it into a certain size (for example, 10 cm x 10 cm), measuring the film thickness to calculate the sheet volume, and then measuring the sheet mass, and then calculating from the following formula: Film density (g / cm ３ ) = sheet mass (g) / sheet volume (cm ３ )

[0141] (3) Air permeability (seconds) and 100 μm thickness equivalent air permeability (seconds) JIS P-8117: 2009 compliant digital Oken type air permeability tester (EG01 type, measurement nozzle measurement diameter 12.82φ mm, manufactured by Asahi Seiko Co., Ltd.) was used to measure the time (seconds) for 100 mL of air to pass through, and this was taken as the air permeability (seconds) of the porous membrane. From the obtained air permeability, the air permeability equivalent to 100 μm thickness was obtained using the following formula. 100 μm thickness equivalent air permeability (seconds) = (air permeability (seconds) / membrane (μm)) × 100 Samples were cut into 10 cm × 10 cm from the porous membranes of the examples or comparative examples, and measurements were taken at four approximately equal locations, and the average value was used.

[0142] (4) Water permeation rate (g / 2 min) Measurement samples were cut into 10 cm x 10 cm squares from the porous membrane. A porous membrane that had been pre-soaked in ethanol for 1 minute was set in a 41 mm diameter stainless steel liquid permeation cell (Advantec Co., Ltd., Stirring Type Ultra Holder UHP-43K), and the ethanol on the membrane was washed with distilled water. After that, distilled water was passed through the cell for 2 minutes at a differential pressure of about 50,000 Pa (inside and outside the liquid permeation cell). After 2 minutes, the mass of the water that had permeated was taken as the water permeation rate (g / 2 min). The differential pressure was measured by connecting a handy manometer (Nidek Components Co., Ltd., PG-100-102GP) to the pressurized side of the liquid permeation cell.

[0143] (5) Tortuosity The pore diameter d (μm) and the tortuosity τ (dimensionless) are calculated as the air permeation rate constant R ｇａｓ (m ３ / (m ２ sec Pa), water permeation rate constant R ｌｉｑ (m ３ / (m ２ sec Pa), air molecular velocity ν (m / sec), water viscosity η (Pa sec), standard pressure P ｓ (=101325 Pa), porosity ε (%), and film thickness L (μm) were calculated using the following formula: d=2ν×(R ｌｉｑ / R ｇａｓ ) × (16η / 3P ｓ ) x 10 ６ τ=(d×(ε / 100)×ν / (3L×P ｓ ×R ｇａｓ )) １／２ Here, R ｇａｓwas calculated from the air permeability (sec) using the following formula: ｇａｓ = 0.0001 / (air permeability × (6.424 × 10 －４ )×(0.01276×101325)) R ｌｉｑ is the ratio of the measured water permeation rate (g / 2 min) to the area S (cm ２ ), measurement time (120 sec), differential pressure P ｇａｐ The specific gravity of the distilled water used was 1 g / cm ３ and S was calculated from the diameter of the liquid permeation cell used to measure the water permeation rate, which was 4.1 cm. ｌｉｑ = Water permeability / (S x 120 x P ｇａｐ ) / 100 Also, ν is the gas constant R (=8.314), absolute temperature T (K), pi (π), and the average molecular weight of air M (=2.896×10 －２ The σ was calculated from the σ (kg / mol) using the following formula: ν = ((8R × T) / (π × M)) １／２

[0144] (6) Puncture Strength (gf) Using a puncture tester "NDG5" (manufactured by Kato Tech Co., Ltd.), a porous membrane was fixed with a sample holder having an opening diameter of 11.3 mm. A puncture test was performed on the center of the fixed porous membrane under the conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / sec in an atmosphere of 25°C, thereby measuring the puncture strength (gf) as the maximum puncture load, and determining the puncture strength per 100 μm of membrane thickness (gf / 100 μm).

[0145] The measurements of water permeability and pin puncture strength involve deformation of the porous membrane, so the test specimens were used only for those measurements. The same test specimens were used for the measurements of membrane thickness, porosity, and air permeability, as well as for the evaluation of water electrolysis described below.

[0146] [Evaluation of Water Electrolysis] The monoelectrode electrolytic cell and electrolysis system used in the evaluation of water electrolysis will be described below.

[0147] [Monopolar electrolytic cell] A bipolar electrolytic cell is an electrolytic cell with a bipolar zero-gap structure, as shown in Figure 1, which is composed of an anode terminal element, a cathode terminal element, and multiple bipolar elements. In this evaluation, a monopolar electrolytic cell composed of an anode terminal element and a cathode terminal element was prepared and used. Each electrolytic cell was similarly equipped with the anode, cathode, and diaphragm of each example and comparative example. The header pipe of the electrolytic cell was an external header type.

[0148] The electrodes (anode, cathode) used in the water electrolysis evaluation were prepared as follows. The diaphragms used were those produced in the Examples and Comparative Examples. <Anode> A nickel expand-type substrate was used as the anode, with a mesh center-to-center distance in the long direction (LW) of 4.6 mm, a mesh center-to-center distance in the short direction (SW) of 3.1 mm, and a substrate thickness of 1.3 mm. <Cathode> An electrode prepared by the following procedure was used as the cathode. The conductive substrate was a plain-woven mesh-type substrate in which nickel fine wires with a diameter of 0.15 mm were woven into 40 meshes. The substrate was blasted with alumina powder with a weight-average particle size of 100 μm or less, then acid-treated in 6 N hydrochloric acid at room temperature for 5 minutes, washed with water, and dried. <Conductive Elastic Body> The conductive elastic body was prepared by woven nickel wires with a wire diameter of 0.15 mm and corrugated to a wave height of 5 mm. The thickness was 5 mm, and the repulsive force at 50% compression deformation was 150 g / cm. ２ The mesh count was approximately 5. <Element> The element was a rectangle measuring 70 mm x 90 mm, with the anode and cathode areas being 48 mm x 58 mm. The anode chamber depth (anode chamber depth) was 10 mm, the cathode chamber depth (cathode chamber depth) was 10 mm, and the material was nickel. A nickel anode receiver measuring 9 mm in height and 10 mm in diameter was attached to the anode terminal element by welding, and a nickel current collector receiver measuring 6 mm in height and 10 mm in diameter was attached to the cathode terminal element by welding.

[0149] A nickel expand metal with a thickness of 1.3 mm, an opening width of 4.6 mm, and a vertical length of 3.1 mm was used as the current collector. This current collector was fixed to the current collector holder of the cathode terminal element with nickel screws. The conductive elastic body described above was placed on the current collector, and the cathode described above was placed on the conductive elastic body. Next, the anode described above was fixed to the anode holder of the anode terminal element with nickel screws. The cathode side element and the anode side element were stacked via a 70 mm × 90 mm diaphragm and two EPDM sheet-shaped gaskets with outer dimensions of 90 mm × 70 mm and inner dimensions of 70 mm × 50 mm, each with a square-shaped (frame-shaped) structure, which was positioned so as to sandwich the diaphragm. This formed a zero-gap structure in which the cathode and anode were pressed against the diaphragm.

[0150] [Electrolysis System] The monopolar electrolytic cell was incorporated into an electrolysis device 70 shown in FIG. 4 and used for alkaline water electrolysis. The electrolysis system will now be outlined with reference to FIG. 4. A 30% KOH aqueous solution was sealed as the electrolyte in the gas-liquid separation tank 72 and the external header-type monopolar electrolytic cell 50. This electrolyte was circulated between the anode chamber and the anode gas-liquid separation tank (oxygen separation tank 72o) and between the cathode chamber and the cathode gas-liquid separation tank (hydrogen separation tank 72h) by a liquid feed pump 71. The flow rate of the electrolyte was measured with a flow meter 77 and adjusted to 0.3 L / min, and the temperature was adjusted to 80°C with a ribbon heater 79. SUS316 10AA piping was used for the electrolyte-contacting parts of the circulation flow path. The gas-liquid separation tanks 72 (72h and 72o) had a height of 240 mm and a volume of 2.3 L. The liquid volume in each of the gas-liquid separation tanks 72h and 72o was set to about 50% of the design volume. A current was applied from the rectifier 74 to the cathode and anode of each electrolysis cell at a predetermined electrode density.

[0151] The rectifier 74 used was a ZX-S-800LAN manufactured by Takasago Machinery Works, Ltd. The hydrogen concentration meter 76 used was an SD-1D manufactured by Riken Keiki Co., Ltd. The pressure gauge 78 used was a KP15-17G manufactured by Nagano Keiki Co., Ltd. The flow meter 77, ribbon heater 79, liquid feed pump 71, gas-liquid separation tank 72 (72h and 72o), water supply unit 73, etc. were all devices commonly used in the relevant technical field.

[0152] (External Leak Test) The diaphragm was immersed in ethanol for 1 minute, and then in distilled water for 4 minutes, and the inside of the diaphragm (inside the holes) was replaced with distilled water. This operation was carried out at room temperature, and after immersion in distilled water, it was quickly assembled into a monopolar electrolytic cell. The monopolar electrolytic cell was assembled into an electrolysis device, and a handy manometer (PG-100-102GP, manufactured by Nidek Components) was connected, and an airtightness test was carried out inside the monopolar electrolytic cell. Air pressure of approximately 3 kPa was sent into the electrolytic cell, and the pressure was measured immediately after the electrolytic cell was sealed and after 1 minute had passed, and evaluated according to the following evaluation criteria. A (Excellent): Pressure was maintained, and the pressure fluctuation was 3% or less. B (Poor): Pressure was maintained, but the pressure fluctuation was more than 3%. C (Poor): Pressure was not maintained, and the pressure dropped quickly.

[0153] (Initial Short Circuit Test) For the diaphragms that were evaluated as A in the external leak test, the electrolyte was subsequently sent to the same electrolysis device, and the electrolytic cell was filled with the electrolyte at room temperature. The resistance between the anode and cathode was measured using a digital multimeter (CDM-2000D, manufactured by Custom Co., Ltd.), and evaluated according to the following evaluation criteria. A (Excellent): The resistance between the anode and cathode was 1 kΩ cm ２ Above B (inferior): Resistance between anode and cathode is 1 kΩ cm ２ less than

[0154] (Initial characteristic measurement) For the membranes that were evaluated as A in the initial short circuit test, the same electrolysis device was used to measure the initial characteristics at an electrolyte temperature of 80°C and 6 kA / m ２ After one hour of energization, the current density was reduced to 1 kA / m ２ Changed to 15kA / m ２ Up to 1 kA / m ２The current density was increased stepwise, and the voltage (V) of the electrolytic cell was measured each time. When the current density reached 2.4 V during the current density increase, the electrolysis was stopped. The initial characteristics at this time were evaluated according to the following evaluation criteria. ２ The results are shown in Table 2, where the voltage of the electrolytic cell at 15 kA / m is the cell voltage (V). A (Excellent): 15 kA / m ２ 2.35V or less at 5kA / m ２ 15kA / m or more ２ Less than 2.35V C (inferior): 5kA / m ２ Less than or equal to 2.35V

[0155] Example 1: 20 parts by mass of PE with a viscosity average molecular weight of 4,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Liquid paraffin with a kinematic viscosity of 82 cSt at 38°C was added as a pore-forming material to the cylinder of the twin-screw extruder via side feed in two batches so that the liquid paraffin content was 80 parts by mass in the total mixture (100 parts by mass) melt-kneaded and extruded. The addition ratio of the two batches was 3 / 1, and the temperature of the liquid paraffin at the time of addition was 120°C. The melt-kneading conditions were a screw rotation speed of 250 rpm and an extrusion rate of 15 kg / h. The set temperatures were 200°C for the kneading section and 200°C for the slit nozzle. The molten mixture emerging from the 7 mm slit nozzle was then air-cooled on a mesh conveyor to obtain a kneaded mixture. Next, the kneaded material was pressed and molded at 225 ° C. under a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Co., Ltd.), and then cooled to 20 ° C. to produce a 3 mm thick raw sheet. The raw sheet was set in a simultaneous biaxial stretching machine and simultaneously biaxially stretched in a 125 ° C. environment so that the stretch ratio after relaxation was 4.0 × 4.0 times, followed by a relaxation operation at a relaxation rate of 5.4%. Next, the stretched raw sheet was taken out and, while its four sides were fixed with clips in a stainless steel frame, immersed in methylene chloride to extract the pore-forming material, dried at room temperature to remove the methylene chloride, and then placed in an oven at 133 ° C. for 0.5 hours to perform heat setting to obtain a porous membrane. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane are shown in Table 2. This porous membrane was immersed in ethanol for 1 minute, then immersed in distilled water for 4 minutes to form a membrane with the pores filled with distilled water, which was then used as a diaphragm. The evaluation results of the diaphragm are shown in Table 2.

[0156] (Example 2) A porous membrane and a diaphragm were obtained in the same manner as in Example 1, except that the temperature during stretching was changed to 126° C. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2.

[0157] (Example 3) A porous membrane and a diaphragm were obtained in the same manner as in Example 1, except that the temperature during stretching was changed to 128° C. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2.

[0158] Example 4 A porous membrane and a diaphragm were obtained in the same manner as in Example 1, except that the parts by mass of PE during melt-kneading were changed to 25 parts by mass, the parts by mass of liquid paraffin were changed to 75 parts by mass, and the temperature during stretching was changed to 126° C. Table 1 shows the production conditions for the porous membrane, and Table 2 shows the evaluation results of the obtained porous membrane and diaphragm.

[0159] Example 5 A porous membrane and a diaphragm were obtained in the same manner as in Example 1, except that PE having a viscosity average molecular weight of 7,500,000 was used, the parts by mass of PE during melt kneading were 22.2 parts by mass, the parts by mass of liquid paraffin were 77.8 parts by mass, the liquid paraffin addition ratio for the first / second addition was 1 / 1, the extrusion rate was 10 kg / h, the temperatures set for the kneading section were 205°C, and the slit nozzle was 205°C, and the stretching conditions were a stretching temperature of 120°C, a stretch ratio of 3.5 x 3.5, and a heat setting temperature of 130°C. The production conditions for the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2.

[0160] (Example 6) PE having a viscosity average molecular weight of 2 million, and tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant at 0.3% by mass relative to PE, and liquid paraffin having a kinematic viscosity of 82 cSt at 38 ° C. as a pore-forming material were mixed at a ratio of 18 / 82 (mass ratio) and kneaded at 200 ° C. using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.). Next, the kneaded product was pressed and molded at 200 ° C. using a Mini Test Press (manufactured by Toyo Seiki Co., Ltd.) at a pressure of 15 MPa, and then cooled at 20 ° C. to produce a raw sheet having a thickness of 3 mm. The raw sheet was set in a biaxial stretching machine and sequentially biaxially stretched so that the stretch ratio after relaxation was 5.0 × 5.0 times in a 120 ° C. environment, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched raw sheet was then removed and, while secured to a stainless steel frame with clips on all four sides, immersed in methylene chloride to extract the pore-forming material, and then dried at room temperature to remove the methylene chloride, thereby obtaining a porous membrane. The manufacturing conditions for the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane are shown in Table 2. This porous membrane was immersed in ethanol for 1 minute, and then immersed in distilled water for 4 minutes to form a membrane with the pores filled with distilled water, which was then used as a diaphragm. The evaluation results of the diaphragm are shown in Table 2.

[0161] (Example 7) PE with a viscosity average molecular weight of 900,000, and tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant at 0.3% by mass relative to PE, and liquid paraffin with a kinematic viscosity of 82 cSt at 38 ° C. as a pore-forming material were mixed at a ratio of PE / pore-forming material = 30 / 70 (mass ratio), and kneaded at 200 ° C. using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.). Next, the kneaded product was pressed and molded at 200 ° C. using a Mini Test Press (manufactured by Toyo Seiki Co., Ltd.) at a pressure of 15 MPa, and then cooled at 20 ° C. to produce a raw sheet with a thickness of 3 mm. The raw sheet was set in a biaxial stretching machine and simultaneously biaxially stretched to a stretch ratio of 4.0 × 4.0 times after relaxation in a 125 ° C. environment, followed by a relaxation operation at a relaxation rate of 5.4%. The stretched raw sheet was then removed and, while secured to a stainless steel frame on all four sides with clips, immersed in methylene chloride to extract the pore-forming material, then dried at room temperature to remove the methylene chloride, and then placed in an oven at 130°C for 0.5 hours to perform heat setting to obtain a porous membrane. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane are shown in Table 2. This porous membrane was immersed in ethanol for 1 minute, and then immersed in distilled water for 4 minutes to form a membrane with the pores filled with distilled water, which was then used as a diaphragm. The evaluation results of the diaphragm are shown in Table 2.

[0162] (Example 8) A porous membrane and a diaphragm were obtained in the same manner as in Example 7, except that PE having a viscosity average molecular weight of 2,000,000 was used, the PE / pore-forming material ratio was 25 / 75 (mass ratio), the stretching temperature was 120°C, the stretching ratio was 3.5x3.5, and the heat setting temperature was 125°C. The production conditions for the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2.

[0163] (Example 9) A porous membrane and a diaphragm were obtained in the same manner as in Example 1, except that the PE / pore-forming material ratio was 25 / 75 (mass ratio), the stretching temperature was 120°C, the stretching ratio was 6.0 x 6.0, and the heat setting temperature was 125°C. The production conditions for the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2.

[0164] (Example 10) PE having a viscosity average molecular weight of 2 million and high molecular weight PE having a viscosity average molecular weight of 300,000 were mixed in a mass ratio of 1 / 1 (contact angle of the mixture with water 94 °), tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionate]methane as an antioxidant was used in an amount of 0.3% by mass relative to the total amount of PE, and liquid paraffin having a kinematic viscosity of 82 cSt at 38 ° C. as a pore-forming material was mixed at a mass ratio of 25 / 75 and kneaded at 200 ° C. using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.). Next, the kneaded product was pressed and molded at 200 ° C. using a mini test press (manufactured by Toyo Seiki Co., Ltd.) at a pressure of 15 MPa, and then cooled at 20 ° C. to produce a 3 mm thick raw sheet. The raw sheet was set in a biaxial stretching machine and simultaneously biaxially stretched in an environment of 125 ° C so that the stretch ratio after relaxation was 4.0 × 4.0, followed by a relaxation operation at a relaxation rate of 5.4%. Next, the stretched raw sheet was taken out and, while its four sides were fixed with clips in a stainless steel frame, immersed in methylene chloride to extract the pore-forming material, dried at room temperature to remove the methylene chloride, and then placed in an oven at 130 ° C for 0.5 h to perform heat setting to obtain a porous membrane. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane are shown in Table 2. This porous membrane was immersed in ethanol for 1 minute, then immersed in distilled water for 4 minutes to form a membrane with the pores filled with distilled water, which was then used as a diaphragm. The evaluation results of the diaphragm are shown in Table 2.

[0165] Example 11: 25 parts by mass of PE with a viscosity-average molecular weight of 2,000,000 was fed via a feeder to the feed port of a twin-screw co-rotating screw extruder. Liquid paraffin with a kinematic viscosity of 82 cSt at 38°C was added as a pore-forming material to the cylinder of the twin-screw extruder via side feed in two batches so that the liquid paraffin content was 75 parts by mass in the total mixture (100 parts by mass) melt-kneaded and extruded. The addition ratio of the two batches was 4 / 1, and the temperature of the liquid paraffin at the time of addition was 120°C. The melt-kneading conditions were a screw rotation speed of 250 rpm and an extrusion rate of 20 kg / h. The set temperatures were 200°C for the kneading section and 200°C for the slit nozzle. The molten mixture emerging from the 7 mm slit nozzle was then air-cooled on a mesh conveyor to obtain a kneaded mixture. Next, the kneaded mixture was pressed and molded at 225°C under a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Co., Ltd.), and then cooled to 20°C to produce a 3 mm thick raw sheet. The raw sheet was fixed on all four sides with clips in a stainless steel frame and immersed in methylene chloride to extract the pore-forming material, and then dried at room temperature to remove the methylene chloride. This raw sheet was placed in a simultaneous biaxial stretching machine and simultaneously biaxially stretched in a 125°C environment so that the stretch ratio after relaxation was 4.0 x 4.0 times. After performing a relaxation operation at a relaxation rate of 5.4%, the sheet was placed in an oven at 130°C for 0.5 hours and heat-set to obtain a porous membrane. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane are shown in Table 2. This porous membrane was immersed in ethanol for 1 minute and then in distilled water for 4 minutes to form a membrane with the pores filled with distilled water, which was then used as a diaphragm. The evaluation results of the diaphragm are shown in Table 2.

[0166] (Example 12) High molecular weight PE with a viscosity average molecular weight of 300,000, and tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant with respect to the high molecular weight PE at 0.3% by mass, and liquid paraffin with a kinematic viscosity of 82 cSt at 38 ° C. as a pore-forming material was mixed at a ratio of PE / pore-forming material = 25 / 75 (mass ratio), and kneaded at 200 ° C. using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.). Next, the kneaded product was pressed and molded at 200 ° C. at a pressure of 15 MPa using a Mini Test Press (manufactured by Toyo Seiki Co., Ltd.), and then cooled at 20 ° C. to produce a raw sheet with a thickness of 3 mm. The raw sheet was fixed on all four sides with clips in a stainless steel frame, immersed in methylene chloride to extract the pore-forming material, and then dried at room temperature to remove the methylene chloride. This raw sheet was set in a biaxial stretching machine and simultaneously biaxially stretched in a 125°C environment so that the stretch ratio after relaxation was 2.5 x 2.5 times, followed by a relaxation operation at a relaxation rate of 5.4%, and then placed in a 130°C oven for 0.5 hours to perform heat setting, thereby obtaining a porous membrane. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane are shown in Table 2. This porous membrane was immersed in ethanol for 1 minute and then in distilled water for 4 minutes to obtain a membrane in a state where the pores were filled with distilled water, and used as a diaphragm. The evaluation results of the diaphragm are shown in Table 2.

[0167] (Example 13) 25 parts by mass of PE having a viscosity average molecular weight of 2,000,000, and 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionate]methane as an antioxidant, 50 parts by mass of dioctyl phthalate as a pore-forming material, and 25 parts by mass of finely divided silica (Nipsil LP manufactured by Tosoh Silica Corporation) were mixed and kneaded at 200 ° C. using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.). Next, the kneaded product was pressed and molded at 200 ° C. at a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Co., Ltd.), and then cooled at 20 ° C. to produce a raw sheet having a thickness of 2.5 mm. The raw sheet, secured on all four sides with clips in a stainless steel frame, was immersed in methylene chloride to extract the pore-forming material, then immersed in ethanol, and then immersed in a 30% aqueous potassium hydroxide solution heated to 90°C to extract and remove the finely divided silica in the raw sheet. The sheet was then washed to remove the alkali and dried in an oven to remove moisture, yielding a raw sheet for stretching. The raw sheet for stretching was placed in a biaxial stretching machine and simultaneously biaxially stretched in a 125°C environment to a stretch ratio of 6.0 x 4.0 after relaxation. A relaxation operation was then performed at a relaxation rate of 3.2%, and the sheet was then placed in a 130°C oven for 0.5 hours to perform heat setting, yielding a porous membrane. The manufacturing conditions for the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane are shown in Table 2. This porous membrane was immersed in ethanol for 1 minute, then in distilled water for 4 minutes to form a membrane with the pores filled with distilled water, which was then used as a diaphragm. The evaluation results of the diaphragm are shown in Table 2.

[0168] (Example 14) A porous membrane and a diaphragm were produced in the same manner as in Example 13, except that a high-molecular-weight PE having a viscosity-average molecular weight of 300,000 was used and the stretching ratio was changed to 2.5 × 2.5. The production conditions for the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2.

[0169] (Example 15) A porous membrane and a diaphragm were produced in the same manner as in Example 13, except that a high-molecular-weight PE having a viscosity-average molecular weight of 700,000 was used and the stretching temperature was changed to 130° C. The production conditions for the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2.

[0170] (Example 16) 20 parts by mass of zirconium oxide (SPZ manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) having an average primary particle size of 300 nm as an inorganic compound and 20 parts by mass of polyethylene having a viscosity average molecular weight of 4,000,000 were fed to separate feed ports of a twin-screw co-rotating extruder using separate feeders. Furthermore, liquid paraffin having a kinematic viscosity of 82 cSt at 38 ° C. as a pore-forming material was added to the cylinder of the twin-screw extruder via side feed in two batches so that the liquid paraffin amount ratio in the total mixture (100 parts by mass) melt-kneaded and extruded was 60 parts by mass. The addition ratio of the two batches was 1st / 2nd = 2 / 1, and the temperature of the liquid paraffin at the time of addition was 115 ° C. The melt-kneading conditions were a screw rotation speed of 250 rpm and an extrusion rate of 10 kg / h. The set temperatures were 210 ° C. for the kneading section and 205 ° C. for the slit nozzle. Subsequently, the molten kneaded material coming out of the 7 mm slit nozzle was air-cooled on a mesh conveyor to obtain a kneaded material. Next, the kneaded material was pressed and molded at 225 ° C. under a pressure of 15 MPa using a mini test press (manufactured by Toyo Seiki Co., Ltd.), and then cooled at 20 ° C. to produce a 3 mm thick raw sheet. The raw sheet was set in a simultaneous biaxial stretching machine, and after simultaneous biaxial stretching in a 120 ° C. environment so that the stretching ratio after relaxation was 3.5 × 3.5 times, a relaxation operation was performed at a relaxation rate of 5.4%. Next, the stretched raw sheet was taken out and, with its four sides fixed with clips in a stainless steel frame, immersed in methylene chloride to extract the pore-forming material, dried at room temperature to remove the methylene chloride, and then placed in a 125 ° C. oven for 0.5 h to perform heat setting to obtain a porous membrane. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane are shown in Table 2. This porous membrane was immersed in ethanol for 1 minute and then in distilled water for 4 minutes to fill the pores with distilled water, and used as a diaphragm. The evaluation results of the diaphragm are shown in Table 2.

[0171] (Comparative Example 1) A porous membrane and a diaphragm were produced in the same manner as in Example 5, except that the parts by mass of PE during melt-kneading were 25 parts by mass, the parts by mass of liquid paraffin were 75 parts by mass, and heat setting was not performed. The production conditions of the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2. When the initial properties were measured, a current density of 13 kA / m ２exceeds 2.35V and 14kA / m ２ The electrolysis was stopped because the voltage reached 2.4 V at 1000 kJ / s. In other words, this diaphragm was unable to achieve both airtightness and a low cell voltage.

[0172] (Comparative Example 2) A porous membrane and a diaphragm were produced in the same manner as in Example 1, except that the parts by mass of PE during melt-kneading were 27.3 parts by mass, the parts by mass of liquid paraffin were 72.7 parts by mass, the stretching temperature was 128°C, and the heat setting temperature was 136°C. The production conditions for the porous membrane are shown in Table 1, and the evaluation results of the obtained porous membrane and diaphragm are shown in Table 2. When the initial properties were measured, ２ The electrolysis was stopped because the voltage exceeded 2.35 V and reached 2.4 V. In other words, this diaphragm was unable to achieve both airtightness and a low cell voltage.

[0173]

[0174]

[0175] The diaphragm for alkaline water electrolysis of the present invention exhibits good airtightness even when a sheet-like gasket is used, enables water electrolysis at a low cell voltage, and can be suitably used for hydrogen production by water electrolysis.

[0176] 1 Partition wall 2a Anode 2c Cathode 2e Conductive elastic body 2r Current collector 3 Outer frame 4 Diaphragm 5 Electrode chamber 5a Anode chamber 5c Cathode chamber 50 Electrolytic cell 51a Anode terminal element 51c Cathode terminal element 51g Fast head, loose head 51i Insulating plate 51r Tie rod 6 Rectifier plate 60 Element 65 Electrolytic cell 7 Gasket part 70 Alkaline water electrolysis device 71 Liquid feed pump 72h Cathode side gas-liquid separation tank (hydrogen separation tank) 72o Anode side gas-liquid separation tank (oxygen separation tank) 73 Water supply device 74 Rectifier 75 Oxygen concentration meter 76 Hydrogen concentration meter 77 Flow meter 78 Pressure gauge 79 Heat exchanger 80 Pressure control valve Z Zero gap structure D1 Given Direction

Claims

1. A method of use characterized by using a porous membrane containing polyethylene, wherein the polyethylene content in the resin component is 50% by mass or more, the curvature ratio is 3.00 or less, and the water permeability is 0.1 g / 2 min or more and 500 g / 2 min or less as a diaphragm for alkaline water electrolysis.

2. The method of use according to claim 1, wherein the thickness of the porous membrane is 40 μm or more and 1000 μm or less.

3. The method of use according to claim 1 or 2, wherein the curvature ratio of the porous membrane is 0.30 or more and 2.50 or less.

4. The method of use according to claim 1 or 2, wherein the curvature ratio of the porous membrane is 1.00 or more and 2.50 or less.

5. The method of use according to claim 1 or 2, wherein the porosity of the porous membrane is 20% or more and 95% or less.

6. The method of use according to claim 1 or 2, wherein the air permeability of the porous membrane is 10 seconds or more and 4000 seconds or less when calculated on a 100 μm basis.

7. The method of use according to claim 1 or 2, wherein the viscosity-average molecular weight of the polyethylene is 300,000 or more and 7,500,000 or less.

8. A diaphragm for alkaline water electrolysis, comprising a porous membrane containing polyethylene, wherein the polyethylene content in the resin component of the porous membrane is 50% by mass or more, the curvature ratio of the porous membrane is 3.00 or less, and the water permeability of the porous membrane is 0.1 g / 2 min or more and 500 g / 2 min or less.

9. The alkaline water electrolysis diaphragm according to claim 8, wherein the film thickness is 40 μm or more and 1000 μm or less.

10. The alkaline water electrolysis diaphragm according to claim 8 or 9, wherein the curvature ratio of the porous membrane is 0.30 or more and 2.50 or less.

11. The alkaline water electrolysis diaphragm according to claim 8 or 9, wherein the curvature ratio of the porous membrane is 1.00 or more and 2.50 or less.

12. The alkaline water electrolysis diaphragm according to claim 8 or 9, wherein the porosity of the porous membrane is 20% or more and 95% or less.

13. The alkaline water electrolysis diaphragm according to claim 8 or 9, wherein the permeability of the porous membrane is 10 seconds or more and 4000 seconds or less when calculated on a 100 μm basis.

14. The alkaline water electrolysis diaphragm according to claim 8 or 9, wherein the viscosity-average molecular weight of the polyethylene is 300,000 or more and 7,500,000 or less.

15. A diaphragm for alkaline water electrolysis according to claim 8 or 9, Anode and, Equipped with a cathode, An electrolytic cell for alkaline water electrolysis, wherein the diaphragm for alkaline water electrolysis is positioned between the anode and the cathode.

16. A diaphragm for alkaline water electrolysis according to claim 8 or 9, Sheet-type gasket and Anode and, Equipped with a cathode, An electrolytic cell for alkaline water electrolysis, wherein the diaphragm for alkaline water electrolysis is positioned between the anode and the cathode.

17. A diaphragm for alkaline water electrolysis according to claim 8 or 9, Two sheet-like gaskets, Anode and, Equipped with a cathode, An electrolytic cell for alkaline water electrolysis, wherein the alkaline water electrolysis diaphragm is placed between the anode and the cathode, and the two sheet-like gaskets are installed so as to sandwich the alkaline water electrolysis diaphragm.