Ion exchange membrane, polyolefin-based porous membrane, membrane electrode assembly, water electrolysis device, and method for producing polyolefin-based porous membrane

Abstract

The present invention provides: an ion exchange membrane that has high toughness, does not easily break when incorporated in a water electrolysis device, and has low membrane resistance; a polyolefin-based porous membrane that can be used as a support of the ion exchange membrane; and a method for producing the polyolefin-based porous membrane.　The ion exchange membrane includes a porous support and an ion exchange resin filled in voids of the porous support. The tear strength of the ion exchange membrane in both the machine direction and the transverse direction is 3.5 N or more.

Description

Ion exchange membrane, polyolefin-based porous membrane, membrane electrode assembly, water electrolysis device, and method for manufacturing polyolefin-based porous membrane

[0001] The present invention relates to an ion exchange membrane, a polyolefin-based porous membrane, a membrane electrode assembly, a water electrolysis device, and a method for producing a polyolefin-based porous membrane.

[0002] Porous membranes formed from thermoplastic resins are widely used as substance separation membranes, selective permeable membranes, support membranes, separators, etc. Examples of applications include battery separators used in lithium ion secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, and polymer batteries, separators for electric double layer capacitors, various filters such as reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes, moisture-permeable waterproof clothing, medical materials, and supports for ion exchange membranes.

[0003] Among the above-mentioned uses, an ion exchange membrane, which uses a porous membrane as a support and has ion exchange resins filled into its pores, can be used as a membrane for a polymer electrolyte fuel cell or a membrane for water electrolysis. Water electrolysis is a method for producing hydrogen, in which water is electrolyzed to generate hydrogen gas and oxygen gas. Hydrogen produced using the energy obtained by a method that suppresses the generation of carbon dioxide as electricity can be used to produce hydrogen without CO ２ It is called free hydrogen or green hydrogen and is expected to be the next generation of clean energy that will replace fossil fuels.

[0004] Among water electrolysis methods, AEM water electrolysis using an anion exchange membrane (AEM) has attracted attention because it does not require the use of expensive precious metals as catalysts. AEM water electrolysis may use an alkaline aqueous solution in the operating environment. For the anion exchange membrane used in AEM water electrolysis, it has been disclosed that a highly chemically resistant olefin-based porous membrane or nonwoven fabric is used as the support. For example, Patent Document 1 discloses an anion exchange membrane using an ultra-high molecular weight polyethylene porous membrane (such as Hipore (registered trademark) manufactured by Asahi Kasei Chemicals Corporation or Setira (registered trademark) manufactured by Tonen Chemical Nasu Corporation) as the substrate. Anion exchange membranes using such supports have characteristics such as low membrane resistance and excellent mechanical strength due to the support. In addition to polyethylene porous membranes, other olefin porous membranes have also been disclosed, such as a dry-process polypropylene porous film (Patent Document 2) and a wet-process polypropylene microporous membrane (Patent Document 3), which can be suitably used as separators for lithium-ion batteries.

[0005] However, since olefin resins have low affinity with the anion exchange resins filled therein, there is a problem that the toughness of the anion exchange membrane tends to decrease when the membrane is made into an anion exchange membrane. To address this problem, for example, Patent Document 4 discloses an anion exchange membrane made of a porous membrane using a silane-modified polyolefin.

[0006] Japanese Patent Application Laid-Open No. 2009-215500 Japanese Patent Application Laid-Open No. 2010-215901 International Publication No. 2016-104792 Japanese Patent No. 7020654

[0007] However, the anion exchange membrane described in Patent Document 4 has high membrane resistance and is expected to lose toughness during use, so a membrane that functions adequately as an anion exchange membrane and has sufficient toughness has been desired. The present invention solves the problems of the prior art described above, and provides an ion exchange membrane that has high toughness that makes it difficult for the membrane to be broken even when incorporated into a water electrolysis device and has low membrane resistance, a polyolefin porous membrane that can be used as a support for the ion exchange membrane, and a method for producing the polyolefin porous membrane.

[0008] The present inventors have found that by setting the tear characteristics of an ion exchange membrane having a predetermined structure within a specific range, it is possible to improve the toughness of the ion exchange membrane while reducing the membrane resistance of the ion exchange membrane, thereby improving the life of the water electrolysis device when the ion exchange membrane is installed in the water electrolysis device and used repeatedly.

[0009] Furthermore, the present inventors have found that by setting the toughness of an ion exchange membrane having a predetermined structure within a specific range, it is possible to improve the toughness of the ion exchange membrane while reducing the membrane resistance of the ion exchange membrane, thereby improving the life of the water electrolysis device when the ion exchange membrane is installed in the water electrolysis device and used repeatedly.

[0010] Furthermore, the present inventors have found that by constructing an ion exchange membrane using as a support a polyolefin porous membrane having a toughness and an (F40-F30) value of at least a predetermined value, it is possible to improve the toughness of the ion exchange membrane while reducing the membrane resistance of the ion exchange membrane, thereby improving the life of the water electrolysis device when the ion exchange membrane is installed in the device and used repeatedly.

[0011] Furthermore, the present inventors have found that by constructing an ion exchange membrane using a polyolefin porous membrane produced by a method including predetermined steps as a support, it is possible to reduce the membrane resistance of the ion exchange membrane and improve the toughness of the ion exchange membrane, thereby improving the life of the water electrolysis device when the ion exchange membrane is installed in the device and used repeatedly.

[0012] Because ion exchange resins have ion exchange groups, they tend to swell in the presence of water. In contrast, when water is reduced (water is no longer present), the ion exchange resin shrinks. Therefore, when the ion exchange membrane is fixed with a gasket or the like, dimensional changes due to swelling and shrinkage can cause localized loads at the boundary between the portion fixed with the gasket and the portion not fixed. The ion exchange membrane of the present invention, which uses the polyolefin porous membrane of the present invention as a support, is less likely to break even after repeated swelling and drying over a long period of time, which is thought to contribute to improving the life of the water electrolysis device. The above problem is more pronounced in anion exchange membranes. Therefore, the ion exchange membrane using the polyolefin porous membrane of the present invention as a support, the ion exchange membrane of the present invention, or the ion exchange membrane using the porous membrane produced by the method of the present invention as a support, is particularly effective when used as an anion exchange membrane in an AEM water electrolysis device. Specifically, the present invention has the following configurations.

[0013] [1] An ion exchange membrane comprising a porous support and an ion exchange resin filled into the pores of the porous support, and having a tear strength of 3.5 N or more in each of the MD and TD directions. [2] The ion exchange membrane according to [1], having a tear strength of 3.5 N or more and 15 N or less in each of the MD and TD directions. [3] An ion exchange membrane comprising a porous support and an ion exchange resin filled into the pores of the porous support, and having a toughness of 0.25 J or more in each of the MD and TD directions.

[0014] [4] The ion exchange membrane according to [3], wherein the toughness in each of the MD direction and the TD direction is 0.25 J or more and 1.00 J or less. [5] The ion exchange membrane according to any one of [1] to [4], wherein the elastic modulus in each of the MD direction and the TD direction is 500 MPa or more and 1800 MPa or less. [6] The membrane resistance per 20 μm is 0.5 Ω cm ２ The ion exchange membrane according to any one of [1] to [5] below.

[0015] [7] The ion exchange membrane according to any one of [1] to [6], which has a thickness of 10 μm or more and 200 μm or less. [8] The ion exchange membrane according to any one of [1] to [7], wherein the ion exchange resin is a hydrocarbon polymer. [9] The anion exchange membrane according to any one of [1] to [8], wherein the ion exchange resin includes an anion exchange resin.

[0016]

[10] The ion exchange membrane according to any one of [1] to [9], wherein the porous support is a porous membrane containing a polyolefin resin.

[11] The ion exchange membrane according to

[10] , wherein the polyolefin resin contains a polypropylene resin.

[12] A polyolefin-based porous membrane having a toughness of 0.35 J or more in each of the MD and TD directions, and having (F40 - F30) of 2.0 MPa or more in each of the MD and TD directions, where F40 (MPa) is the stress at a strain of 0.4 and F30 is the stress at a strain of 0.3 on the horizontal axis of a stress-strain curve obtained in a tensile test.

[0017]

[13] The polyolefin-based porous membrane according to

[12] , which contains 60% by mass or more of polypropylene based on the resin composition constituting the polyolefin-based porous membrane.

[14] The polyolefin-based porous membrane according to

[12] or

[13] , which contains 5% by mass or more and 40% by mass or less of an olefin-based elastomer based on the resin composition constituting the polyolefin-based porous membrane.

[15] The polyolefin-based porous membrane according to any one of

[12] to

[14] , which has a thickness of 10 μm or more and 150 μm or less.

[0018]

[16] The polyolefin-based porous membrane according to any one of

[12] to

[15] , which has an air permeability resistance of 100 cc of air per 20 μm of thickness of 300 seconds or more and 7000 seconds or less according to Japanese Industrial Standards P8117:2009.

[17] The polyolefin-based porous membrane according to any one of

[12] to

[16] , which is used as a support for an ion exchange resin.

[18] An ion exchange membrane comprising the polyolefin-based porous membrane according to any one of

[12] to

[17] as a support, and an ion exchange resin filled in the pores of the support.

[0019]

[19] A membrane electrode assembly comprising the ion exchange membrane according to any one of [1] to

[11] or

[18] and an electrode.

[20] A water electrolysis device comprising the ion exchange membrane according to any one of [1] to

[11] or

[18] .

[21] A water electrolysis device comprising the membrane electrode assembly according to

[19] .

[0020]

[22] A method for producing a polyolefin-based porous film, comprising the following steps (a) to (d): (a) a resin composition comprising a polyolefin resin and an olefin-based elastomer, wherein the content of the olefin-based elastomer in the resin composition is 5% by mass or more and less than 50% by mass based on the resin composition, and a plasticizer are melted and kneaded to obtain a gel-like solution; (b) the gel-like solution is cooled to obtain a gel-like sheet; (c) the gel-like sheet is biaxially stretched with an areal stretching ratio of 10 times or more and 35 times or less in MD and TD to obtain a biaxially stretched gel-like film; and (d) the gel-like film is washed with a solvent, and the film after washing is dried to obtain a polyolefin-based porous film.

[0021]

[23] The method for producing a polyolefin-based porous film according to

[22] , wherein the polyolefin resin comprises polypropylene.

[24] The method for producing a polyolefin-based porous film according to

[22] or

[23] , wherein the amount of plasticizer added is 40 mass% or more and 70 mass% or less based on the gel solution.

[25] The method for producing a polyolefin-based porous film according to any one of

[22] to

[24] , wherein the olefin-based elastomer is a propylene-based copolymer.

[0022]

[26] The method for producing polyolefin-based porous membrane according to any one of

[22] to

[25] , the melting point of described olefin-based elastomer measured by DSC (differential scanning calorimetry) according to JIS K7121 (1987) is (the melting point of described polyolefin resin-15) ℃ or more (the melting point of described polyolefin resin+5) ℃ or less.

[0023] The ion exchange membrane having the polyolefin porous membrane of the present invention as a support, the ion exchange membrane of the present invention, or the ion exchange membrane having the porous membrane produced by the method of the present invention as a support can provide an ion exchange membrane having excellent toughness while maintaining low membrane resistance, i.e., an ion exchange membrane having high toughness that is less likely to break even when incorporated into a water electrolysis device. The use of this ion exchange membrane, particularly when used in a water electrolysis device, can extend the life of the water electrolysis device because the ion exchange membrane is less likely to break even when repeatedly swollen and dried during repeated use.

[0024] 1 is a schematic diagram of a water electrolysis device using an ion exchange membrane having the polyolefin porous membrane of the present invention as a support, an ion exchange membrane of the present invention, or an anion exchange membrane which is one embodiment of an ion exchange membrane having the porous membrane produced by the method of the present invention as a support. FIG. 2 is a graph showing stress-strain curves of the porous membranes obtained in Example 13 and Comparative Example 3.

[0025] DETAILED DESCRIPTION OF THE INVENTION [Ion Exchange Membrane] The ion exchange membrane of the present invention comprises a porous support and an ion exchange resin filled in the pores of the porous support.

[0026] <Porous Support> The polyolefin porous membrane of the present invention can be used as the porous support that serves as the base material of the ion exchange membrane.

[0027] (Polyolefin Resin) The polyolefin porous membrane of the present invention is mainly composed of a polyolefin resin. Examples of the polyolefin resin constituting the polyolefin porous membrane include polymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl-1-heptene. These polymers can be used alone or in combination of two or more. Among these, polypropylene is preferably used as the main component because of its excellent heat resistance and moldability.

[0028] Furthermore, the above-mentioned main component means that the resin composition containing the above-mentioned polyolefin resin and a polyolefin-based elastomer described later is used as the basis (100 mass%), and the polyolefin resin accounts for 50 mass% or more, more preferably 60 mass% or more, and even more preferably 70 mass% or more.

[0029] In an AEM water electrolysis device, from the viewpoint of improving water electrolysis performance, the operating temperature is preferably a temperature environment of approximately 60°C to 80°C. Therefore, when used as a support for an ion exchange membrane, it is preferable that crystal relaxation does not occur at that temperature, since this prevents changes in the physical properties of the support from occurring over long-term use. From this viewpoint, the melting point of the polyolefin resin is preferably 140°C or higher and 290°C or lower. The lower limit is more preferably 145°C or higher, more preferably 150°C or higher, and even more preferably 160°C or higher. The higher the melting point, the more preferable it is for a support for an ion exchange membrane. However, if the melting point is too high, moldability deteriorates. Therefore, the upper limit is preferably 280°C or lower, more preferably 270°C or lower, and even more preferably 200°C or lower.

[0030] Here, the melting point refers to a value measured by DSC (differential scanning calorimetry) in accordance with JIS K7121 (1987), and all subsequent descriptions refer to values ​​obtained by the above measurement. When polypropylene is used as the main component, the polypropylene may be a copolymer with other olefins, but from the viewpoint of mechanical strength, a homopolymer, which is a single polymer of propylene, is preferable. Examples of comonomers contained in copolymers with other olefins include ethylene and α-olefins such as 1-butene, 1-pentene, and 4-methylpentene-1, 1-octene. The content of these comonomers in the polypropylene is preferably 10% by mass or less, more preferably 5% by mass or less.

[0031] The weight average molecular weight of polypropylene resin is 1 x 10 ５ 5x10 or more ６ Preferably, it is 5×10 or less. ５ 2.5 x 10 or more ６More preferably, it is 9×10 or less. ５ 2x10 or more ６ It is more preferable that the weight average molecular weight is 1×10 or less. ５ If the weight average molecular weight is less than 5×10, the entanglement between the molecules cannot be sufficiently ensured, which may cause breakage during film formation or may result in insufficient strength of the porous film. ６ In the above cases, viscosity becomes too high, so that thickness uniformity may be deteriorated or moldability may be deteriorated.In particular, when forming a thick film suitable as a support for ion exchange membrane, if weight-average molecular weight becomes too high, the internal pressure of the extruder is likely to be high during melt-kneading, so the size of the extruder must be excessively large relative to the discharge amount, which is undesirable because it leads to increased costs.The molecular weight distribution of polypropylene resin is preferably about 5 or more and 10 or less.When molecular weight distribution is within the above range, the workability is good when melt-kneading with plasticizer and extruding in the wet method of porous membrane production described later.

[0032] The polypropylene resin preferably has a melt flow rate (MFR) of 0.3 g / 10 min or more and less than 1.0 g / 10 min. When the MFR is within this range, the workability when melt-kneading with a plasticizer and extruding the resulting mixture is improved, as is the molecular weight distribution.

[0033] (Olefin-Based Elastomer) The resin composition constituting the polyolefin-based porous membrane of the present invention preferably contains an olefin-based elastomer in order to improve the toughness of the substrate. Examples of olefin-based elastomers include ethylene-α-olefin copolymers, propylene-α-olefin copolymers, and 1-butene-α-olefin copolymers. When the polyolefin resin is polypropylene, it is preferable to use a propylene-α-olefin copolymer from the viewpoint of compatibility. The propylene-α-olefin copolymer may be a binary copolymer such as a propylene-ethylene copolymer, or a ternary copolymer such as a propylene-ethylene-butene copolymer. The arrangement of the monomers may be a random copolymer or a block copolymer.

[0034] In the presence of a plasticizer, the plasticizer plasticizes the resin, accelerating molecular diffusion of the polyolefin resin. This can lead to the formation of coarse, high-order crystals in highly crystalline polyolefin resins. If the high-order crystal structure becomes coarse, unevenness between sufficiently oriented and insufficient portions can occur during the subsequent stretching process, resulting in embrittlement when filled with ion exchange resin. In the present invention, the inventors have discovered that adding a certain amount of olefin-based elastomer to a polyolefin resin not only improves the toughness of the porous membrane, but also refines the crystalline structure of the polyolefin resin, which is the main component, thereby suppressing the formation of coarse, high-order structures that tend to occur during wet porous membrane production. While the detailed mechanism is unclear, it is believed that adding a preferred amount of olefin-based elastomer to a polyolefin resin inhibits long-distance diffusion of the polyolefin resin's molecular chains by providing an elastomer component in the molecular diffusion pathway of the polyolefin resin, thereby promoting in-situ crystallization and thereby refines the crystalline structure.

[0035] With respect to the resin composition containing the polyolefin resin and the olefin-based elastomer (100% by mass), the proportion of the olefin-based elastomer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less. If the content of the olefin-based elastomer is less than 5% by mass, the effect of improving the toughness of the substrate cannot be sufficiently obtained, and the membrane may become brittle when the mechanical properties of the ion exchange membrane produced using the porous membrane as a substrate are evaluated. If the content exceeds 50% by mass, the elastomeric properties become too strong, which may result in clogging of the pores of the porous membrane. If the pores are clogged, the porosity of the porous membrane will be low and the air resistance will be too high, which may result in a reduced ion exchange capacity and increased membrane resistance when the ion exchange membrane is finally produced. By adjusting the content of the olefin-based elastomer to the above-mentioned preferred range, and by combining it with the film-forming method described below, a porous film having excellent toughness and tenacity can be obtained.

[0036] Here, the melting point of the olefin-based elastomer is not particularly limited, but from the viewpoint of preventing clogging of pores during film formation, it is preferably (melting point of polyolefin resin - 15) ° C or more and (melting point of polyolefin resin + 5) ° C or less relative to the melting point of the polyolefin resin which is the main component.

[0037] (Other Additives) Various additives can be blended into the resin composition as needed. Examples of such additives include antioxidants such as phenolic, phosphorus, and sulfur-based ones; nucleating agents such as aromatic phosphate ester metal salts, benzoic acid metal salts, and sorbitol-based ones; light stabilizers; and antistatic agents. These additives can be blended directly into the resin composition or as a masterbatch premixed with the polyolefin resin. The amount of each additive is not particularly limited, but is typically 0.01% by mass or more and 5.00% by mass or less relative to the resin composition. When polypropylene is used as the polyolefin resin, examples of nucleating agents for polypropylene include α-crystal nucleating agents and β-crystal nucleating agents, but it is preferable not to include a β-crystal nucleating agent. If a β-crystal nucleating agent is used, needle-shaped crystals may be formed, which may result in strong anisotropy in the initial higher-order structure. Therefore, when using polypropylene, it is better to use an α-crystal nucleating agent as the nucleating agent. When purchasing a commercially available polypropylene resin, whether or not it contains β-crystals can be determined, for example, by checking the crystalline heat of fusion peak in DSC. Since the melting point of β-crystal polypropylene is lower than that of α-crystal polypropylene, the peak of the heat of fusion of β-crystal polypropylene appears at a lower temperature than the peak of the heat of fusion of α-crystal polypropylene. Specifically, in the case of homopolypropylene, the peak appears in the range of 120°C to 150°C.

[0038] <The method for producing polyolefin porous membrane> Next, the method for producing polyolefin porous membrane of the present invention will be explained.There are two known methods for producing polyolefin porous membrane: dry method (the method of adding nucleating agent or inorganic particles etc. to resin to make it porous) and wet method (the phase separation method using plasticizer).In dry method, nucleating agent or inorganic particles is mixed with molten resin, and then the obtained mixture is extruded from a die and cooled.Then, the obtained sheet is stretched under specific conditions, so that the periphery of crystalline part or added particles is split, and thus a porous membrane is obtained.Because pores are formed by stretching, it is also called stretch splitting method.

[0039] In the wet process, a resin is first melt-mixed with a plasticizer. The resulting resin solution is then extruded through a die and cooled to form a gel-like sheet. The resulting gel-like sheet is stretched in at least one direction, after which the plasticizer is removed with a solvent and the sheet is dried to obtain a porous membrane. In the dry process, the crystals are torn open to form holes, resulting in coarse pores and poor strength. However, the dry process has the advantage of being cost-effective because no cleaning process is required.

[0040] The wet method is characterized by uniform micropores due to phase separation with the plasticizer, resulting in excellent flatness and strength. While commercially available porous membranes made of polypropylene resins are generally produced by dry methods, the porous membrane of the present invention is preferably produced by wet methods. The method for producing the polyolefin porous membrane of the present invention includes the following steps (a) to (d): (a) melt-kneading a resin composition containing a polyolefin resin and an olefin-based elastomer with a plasticizer to obtain a gel-like solution; (b) cooling the gel-like solution to obtain a gel-like sheet; (c) biaxially stretching the gel-like sheet to obtain a biaxially stretched gel-like film; and (d) washing the gel-like film with a solvent and drying the washed film to obtain a porous membrane. Furthermore, after step (d), steps such as heat treatment, aging, corona treatment, and hydrophilization treatment may be performed as necessary.

[0041] Each step will be described in more detail below. (a) Step of Obtaining a Gel-Like Solution: The preferred step of obtaining a gel-like solution involves introducing a resin composition containing a polyolefin resin and an olefin-based elastomer, along with various additives as needed, into a kneader, adding a plasticizer to a predetermined amount while heating and melting, and then further kneading to achieve a uniform mixture. The plasticizer is not particularly limited as long as it has sufficient compatibility with the resin composition. Specific examples include aliphatic carboxylic acid esters such as methyl stearate and butyl stearate, aromatic carboxylic acid esters such as diisononyl phthalate and bis-2-ethylhexyl phthalate, and aliphatic hydrocarbons such as liquid paraffin. To obtain a stable gel-like sheet without changing the plasticizer content after kneading with the resin composition, it is preferable that the boiling point of the plasticizer be sufficiently higher than the melting point of the resin composition. Furthermore, the plasticizer may be solid at room temperature as long as it has a melting point below the melt-kneading temperature of the resin composition and is liquid during kneading. Examples of such solid plasticizers include stearyl alcohol, ceryl alcohol, paraffin wax, and polyethylene oxide. Among these plasticizers, aromatic carboxylic acid esters are preferably used because they are easy to form holes in the porous membrane, have little bleed-out during the manufacturing process, and are easy to mold.When liquid paraffin or paraffin wax is used, it is difficult to form holes compared to when aromatic carboxylic acid esters are used, so a large amount must be added, which may increase costs.These plasticizers can be used alone or in combination.

[0042] The amount of plasticizer added is preferably 40% by mass or more and 70% by mass or less, based on the gel solution (100% by mass) which is the sum of the resin composition and the plasticizer. The lower limit is more preferably 50% by mass or more, and even more preferably 55% by mass or more. If the amount of plasticizer added is less than 40% by mass, a sufficient number of pores will not be formed, which may result in a decrease in the ion exchange capacity of the final ion exchange membrane and an increase in membrane resistance. The upper limit is more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less. If the amount of plasticizer added exceeds 70% by mass, the viscosity may be too low, which may deteriorate the workability during membrane formation, or the entanglement of molecular chains may become weak, which may result in a decrease in the strength of the resulting porous membrane. By setting the amount of plasticizer added within the above preferred range, a membrane that combines sufficient strength and pore formation for use as a substrate for AEM can be obtained using the membrane formation method described below without causing a decrease in stretchability during membrane formation.

[0043] The method and apparatus for kneading the resin composition, plasticizer, and various optional additives are not particularly limited as long as they can be melt-kneaded uniformly. The raw materials may be directly fed into the extruder, but for uniform kneading, the solids of the polyolefin resin, olefin-based elastomer, and various additives may be premixed using a Henschel mixer or the like and then fed into the kneader. The kneader may be a small batch kneader, such as the Labo Plastomill manufactured by Toyo Seiki Seisakusho Co., Ltd., or a continuous kneader such as a twin-screw extruder. Methods using a twin-screw extruder, such as those described in JP-B 06-104736 and Japanese Patent No. 3347835, may be used.

[0044] In the extruder, the resin composition, plasticizer, and various additives added as needed are mixed at a temperature at which the resin composition is completely melted. The melt-kneading temperature varies depending on the polyolefin resin used, but the lower limit is preferably (melting point of polyolefin resin + 5°C), more preferably (melting point of polyolefin resin + 10°C). The upper limit is preferably (melting point of polyolefin resin + 70°C), more preferably (melting point of polyolefin resin + 60°C). Since the melting point of polypropylene in the present invention is approximately 160°C to 180°C, the melt-kneading temperature is preferably 165°C to 250°C.

[0045] From the viewpoint of suppressing the deterioration of resin, the lower the melting kneading temperature, the better.But if the melting kneading temperature is too low, the unmelted matter of resin will occur, and in the subsequent stretching process, the process failure such as film breakage or uneven stretching may occur.In addition, in the final porous film, the unmelted matter may cause the appearance failure or thickness unevenness etc. of the final porous film.If the melting kneading temperature is too high, the mechanical strength of the final porous film may be reduced due to the deterioration of resin.

[0046] When a twin-screw extruder is used, the ratio (L / D) of the screw length (D) to the diameter (L) is preferably 25 or more and 80 or less. The lower limit is preferably 30 or more, more preferably 35 or more. The upper limit is preferably 70 or less, more preferably 60 or less. When L / D is within the above range, the residence time of the mixture does not become too long, and the raw materials can be uniformly dispersed well while preventing deterioration of the resin. In addition, the rotation speed (N) of the extruder is preferably 100 rpm or more and 400 rpm or less. If the rotation speed is too high, the resin may be deteriorated due to shearing of the screw, so a low rotation speed is preferable. However, if the rotation speed is too low, unmelted material may be generated due to poor kneading, so it may be adjusted appropriately while checking the properties of the extruded resin.

[0047] (b) Step of Obtaining a Gel-Like Sheet In the (b) step of obtaining a gel-like sheet, the gel-like solution is formed into a sheet and then cooled to obtain a gel-like sheet. This sheet can be obtained by once cooling the gel-like liquid at room temperature and then press-molding it again at a temperature above the melting point of the gel-like liquid, or by supplying the gel-like liquid from an extruder to a die and extruding the gel-like solution from the die. In this case, either the T-die method or the inflation method may be used as the extrusion method, but the T-die method is preferred from the viewpoint of achieving a uniform thickness.

[0048] Here, the gel-like sheet may be a single-layer membrane or may have a multilayer structure of two or more layers. Known methods for producing a multilayer gel-like sheet include a method in which separate gel-like sheets are produced and then heat-sealed, and a co-extrusion method in which the resins of each layer are fed from separate extruders to a single die and extruded while being integrated. For the substrate of an ion-exchange membrane, the co-extrusion method is preferred from the viewpoints of high adhesive strength between the layers and ease of forming interconnecting pores between the layers.

[0049] As for the cooling method during sheeting, known cooling methods can be used, such as direct contact with cooling air, cooling water, or other cooling medium, or contact with a roll cooled with a refrigerant. Rapid cooling at as low a temperature as possible during cooling densifies the crystalline structure of the polyolefin resin, improving the stretchability in subsequent processes and the toughness of the final ion exchange membrane. The lower the cooling temperature, the better, but from the standpoint of preventing condensation and achieving both workability, a temperature of approximately 0°C to 25°C is preferred. Cooling must be carried out until both sides reach the crystallization end temperature or below. Here, the crystallization end temperature refers to the extrapolated crystallization end temperature measured in accordance with JIS K7121 (1987).

[0050] The thickness of the gel-like sheet is not particularly limited, but is set appropriately depending on the thickness of the desired porous membrane, and is preferably approximately 0.2 mm or more and 5 mm or less, and more preferably 0.5 mm or more and 3 mm or less.

[0051] (c) Step of Obtaining Biaxially Stretched Gel-State Film Next, the obtained gel-state sheet is stretched biaxially. The stretching method is performed by a tenter method, a roll method, or a combination of these. In the case of biaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, or a combination of these may be used. Furthermore, stretching may be performed in one stage or multiple stages. If only uniaxial stretching is performed, the molecular chains will be excessively oriented in only one direction, and when an ion exchange membrane is produced using the obtained porous membrane as a substrate, the unstretched direction may become significantly embrittled, so biaxial stretching is necessary. Furthermore, tenter stretching may be performed in a batch system.

[0052] The lower limit of the areal stretching ratio (longitudinal ratio × transverse ratio), which is the sum of the longitudinal and transverse ratios in the stretching process, is preferably 10 times or more, more preferably 12 times or more, and even more preferably 16 times or more. If the lower limit is within the above preferred range, the initial crystalline structure formed in the gel-like sheet can be sufficiently refined, thereby improving mechanical strength. If the lower limit is less than 10 times, the high-order structure of the remaining crystals that have not been refined becomes the starting point, and when an ion exchange membrane is produced using the obtained porous membrane as a substrate, embrittlement is likely to occur. Furthermore, since the structure is not sufficiently refined, the pore size becomes coarse, which may result in poor gas barrier properties when formed into an ion exchange membrane. The upper limit of the areal stretching ratio is preferably 40 times or less, more preferably 35 times or less, even more preferably 30 times or less, and particularly preferably less than 25 times. The higher the areal stretching ratio, the higher the strength of the porous membrane, but excessive orientation will occur, weakening the entanglement of molecular chains, resulting in a decrease in elongation when formed into an ion exchange membrane, and as a result, a decrease in toughness. Whether the area magnification is sufficient or not can be determined by the (F40-F30) value described later.

[0053] The stretching temperature is preferably set to a temperature below the melting point of the polyolefin resin, which is the main component. More preferably, it is in the range of (the crystal dispersion temperature Tcd of the polyolefin resin) to (the melting point of the polyolefin resin - 5°C), where Tcd is the crystal dispersion temperature of the polyolefin resin. A temperature below (the melting point of the polyolefin resin - 5°C) can prevent the resin from fusing to the clips and stretching rolls that grip the sheet during stretching. Here, the crystal dispersion temperature Tcd of the polyolefin resin can be determined from the temperature characteristics of dynamic viscoelasticity measured according to ASTM D4065 using a sheet that has been melt-pressed at the melting point + 50°C and then ice-cooled to 0°C. Specifically, in the case of polypropylene resin in the present invention, since it has a crystal dispersion temperature between 110°C and 130°C and a melting point between 160°C and 180°C, the stretching temperature is preferably 110°C or higher and 175°C or lower, more preferably higher than 115°C and lower than 160°C, and even more preferably 120°C or higher and 155°C or lower. When sequential drawing or multi-stage drawing is performed, the drawing temperatures may be the same or different.

[0054] Here, in the present invention, it is important that the stretching is performed while the gel-like sheet contains a plasticizer. By performing stretching before the plasticizer is removed, the crystalline structure can be uniformly crushed, thereby improving the toughness of the porous film. Furthermore, by uniformly crushing the crystalline structure, uniform and dense pores are formed, making it less likely that the ion exchange resin will become embrittled due to its coarse and dense structure.

[0055] (d) Step of washing and drying the gel film to obtain a porous membrane. Subsequently, the gel film obtained in step (c) is washed with a solvent to extract the plasticizer. The solvent used to extract the plasticizer is not particularly limited, as long as it is a poor solvent for the resin composition and a good solvent for the plasticizer. Examples of solvents include hydrocarbons such as n-hexane and cyclohexane, fluorocarbons in which some or all of the hydrogen atoms in hydrocarbons have been replaced with fluorine, alcohols such as ethanol and isopropanol, and ketones such as acetone and 2-butanone. Known methods for washing the gel film can be used, such as immersing the gel film in a solvent, showering, or a combination of these. The washing solvent after washing can be removed by air drying, heat drying, or the like. Drying is preferably performed at a low temperature of less than 50°C to prevent pore blockage due to heating or destruction of the pore structure due to rapid evaporation of the washing solvent.

[0056] After removing the plasticizer, a heat treatment may be performed to stabilize the porous membrane. Heat treatment stabilizes the crystal structure and relieves residual strain, thereby stabilizing the dimensions and the crystal structure within the membrane. The higher the heat treatment temperature, the faster the stabilization can be achieved. However, a high temperature can cause rapid shrinkage or pore blockage due to melting of the crystals. Therefore, the temperature should be adjusted appropriately according to the desired porosity.

[0057] <Characteristics of polyolefin-based porous membrane> The polyolefin-based porous membrane of the present invention has high mechanical properties, so when used as the support of ion-exchange membrane, it can have excellent effect of suppressing embrittlement, and can obtain the excellent ion-exchange membrane with high toughness.Below, the characteristics of the polyolefin-based porous membrane of the present invention will be described.In addition, the measuring method of each characteristic will be described in detail in Example.

[0058] (1) Thickness The thickness of the polyolefin-based porous membrane of the present invention is not particularly limited. However, in order to exhibit suitable performance as a support for an ion exchange membrane, it is preferably 10 μm or more and 150 μm or less. From the viewpoint of reducing the membrane resistance when used as an ion exchange membrane, a thinner thickness is preferable, but on the other hand, a thinner thickness reduces the gas barrier property and mechanical strength. In particular, in AEM water electrolysis using an anion exchange membrane, a high pressure is applied to the membrane, so a certain thickness is preferable from the viewpoint of mechanical strength and gas barrier property. Therefore, the thickness of the porous membrane is more preferably 15 μm or more and 120 μm or less, and even more preferably 25 μm or more and 100 μm or less.

[0059] (2) Porosity The porosity of the polyolefin porous membrane of the present invention is preferably 10% or more and less than 50%.The lower limit of the porosity is more preferably 15% or more, even more preferably 20% or more, and particularly preferably 30% or more.If the porosity is less than 10%, when used as a support for ion exchange membrane, the amount of ion exchange resin filled is reduced, so that ion conductivity is deteriorated and membrane resistance is likely to increase.In addition, if the porosity is more than 50%, when used as an ion exchange membrane, the expansion due to water absorption of ion exchange resin in a wet state cannot be suppressed, and the shape of the ion exchange membrane may not be maintained.The upper limit of the porosity is more preferably 45% or less.

[0060] (3) Air resistance The air resistance per 20 μ m of polyolefin porous membrane of the present invention is preferably 300s / 100ccAir or more and 7000s / 100ccAir.The lower limit of the air resistance per 20 μ m is preferably 400s / 100ccAir or more, more preferably 500s / 100ccAir.If the air resistance per 20 μ m is lower than 300s / 100ccAir, when used as the support of ion exchange membrane, it may have poor gas barrier properties.The upper limit of the air resistance per 20 μ m of polyolefin porous membrane is preferably 5000s / 100ccAir or less, more preferably 2500s / 100ccAir or less, and even more preferably 1350s / 100ccAir or less. If the air resistance is too high, when the membrane is used as a support for an ion exchange resin, the impregnation of the ion exchange resin may be slow, which may result in a decrease in productivity, and the membrane resistance of the resulting ion exchange membrane may be high.

[0061] (4) Elastic modulus The lower limit of the tensile modulus of the MD direction (the length direction of the membrane surface, machine direction) and TD direction (the direction perpendicular to the MD direction, the width direction of the membrane surface) of the polyolefin porous membrane of the present invention is preferably 200 MPa or more, more preferably 300 MPa or more, and even more preferably 400 MPa or more.The higher the elastic modulus, the more preferable it is; however, when an olefin elastomer is added as in the present invention, the elastic modulus tends to be low, so the practical upper limit is about 1500 MPa.In addition, if excessive orientation is applied to increase the elastic modulus, the elongation decreases, and as a result, the toughness may decrease.Therefore, the upper limit of the elastic modulus is preferably 1200 MPa or less, more preferably 1000 MPa or less.When the elastic modulus is within a preferred range, when used as a support for ion exchange membrane, it is less likely to wrinkle and has excellent handling properties.In addition, when used as a support for ion exchange membrane, the elastic modulus of the ion exchange membrane finally obtained can also be increased.

[0062] Furthermore, the ratio of the elastic modulus in the MD direction to the elastic modulus in the TD direction (MD elastic modulus / TD elastic modulus) is preferably 0.5 to 1.5. If the elastic modulus ratio is outside this range, the anisotropy is so strong that when used as a support for an ion exchange membrane, anisotropy occurs in the dimensional change when the ion exchange membrane swells, and when the membrane is incorporated into a water electrolysis device and used, wrinkles and other defects may occur due to the difference in dimensional change.

[0063] (5) Toughness (J) The toughness of the polyolefin porous film of the present invention in MD and TD is preferably 0.35 J or more.Here, toughness is one of the parameters that indicate the tenacity of a material, and refers to the amount of energy required to cause breakage when pulling a material.Specifically, as described in L. E. Nielsen (Onogi Shigeharu); "Mechanical Properties of Polymers" 98-100, Kagaku Dojin (1965), it can be calculated from the area of ​​the stress-strain curve obtained in tensile test.

[0064] If the toughness of polyolefin porous membrane is 0.35J or more, when it is used as the support of ion exchange membrane, it can exhibit excellent brittleness suppression effect, and can obtain the ion exchange membrane that is strong and difficult to break.The lower limit of toughness is more preferably 0.40J or more.The higher the toughness, the better, but the practical upper limit is about 1.5J.

[0065] (6) F30 (stress at 30% strain), F40 (stress at 40% strain) The (F40-F30) in the MD and TD directions of the polyolefin porous membrane of the present invention is preferably 2.0 MPa or more.When polyolefin porous membrane is used as the support of ion exchange membrane, it is preferable that the crystalline structure in the porous membrane is sufficiently subdivided and oriented.If the refinement and orientation of the structure are insufficient, even if the porous membrane has high mechanical properties, it may become significantly embrittled when filled with ion exchange resin.(F40-F30) is used as the parameter for determining this refinement and orientation.

[0066] When a film is stretched at a constant speed, the stress changes according to the change in the internal structure. In the low strain region of less than 10%, the stress increases linearly with the strain, but then the increase in stress becomes gradual. Here, if there is a coarse structure that is not oriented inside the porous film, the stress is released in the process of the internal structure being crushed or oriented when deformation is applied, so the increase in stress with respect to the strain becomes even smaller. Therefore, the degree of orientation can be evaluated by evaluating the value of (F40 - F30).

[0067] The present inventors have found that when the value of (F40 - F30) is less than 2.0 MPa, even if the porous membrane has sufficient toughness, it tends to become embrittled when used as a support for an ion exchange membrane. The lower limit of (F40 - F30) is preferably 2.0 MPa or more, more preferably 2.5 MPa or more, and even more preferably 3.0 MPa or more.

[0068] The higher the (F40-F30), the stronger the orientation. Therefore, the upper limit of (F40-F30) is preferably 10.0 MPa or less, more preferably 9.0 MPa or less, and even more preferably 8.0 MPa or less. If (F40-F30) exceeds 10.0 MPa, the orientation will be too strong, resulting in a decrease in toughness, and as a result, the ion exchange membrane may become easily embrittled when formed into an ion exchange membrane.

[0069] The polyolefin porous membrane of the present invention preferably has the above-mentioned (F40-F30) properties in both the MD and TD directions.

[0070] [Method for manufacturing an ion exchange membrane using a polyolefin-based porous membrane as a support] The porous membrane of the present invention obtained by the above method can be suitably used as a support for an ion exchange resin. The ion exchange resin (type of ion exchange group) to be supported may be appropriately determined depending on the intended application. The ion exchange resin may be either an anion exchange resin or a cation exchange resin. In particular, when used as a support for an anion exchange resin, it is preferable because it can be used in anion exchange membrane (AEM)-type water electrolysis, which is water electrolysis for producing hydrogen. When supporting an ion exchange resin, it is preferable to use a single support without overlapping. When two or more supports are stacked, peeling may occur at the stacked interface. Furthermore, if thermocompression bonding or the like is performed to sufficiently bond the stacked interface, the pores may be crushed, increasing the membrane resistance. The method for supporting the ion exchange resin is not particularly limited, but the following four methods may be mentioned, for example.

[0071] (1) A polymerizable composition containing an ion-exchange group-containing monomer (or a solution of the polymerizable composition, if necessary) is brought into contact with a porous membrane to fill the pores of the porous membrane with the polymerizable composition. The polymerizable composition filled in the pores is then polymerized. To obtain the desired ion-exchange membrane, a polymerizable composition consisting solely of the ion-exchange group-containing monomer may be used, or a polymerizable composition containing the ion-exchange group-containing monomer and, if necessary, other monomers may be used. The other monomers may include a polyfunctional crosslinker, such as divinylbenzene.

[0072] (2) A polymerizable composition (or a solution of the polymerizable composition, if necessary) containing a monomer capable of introducing ion-exchange groups is contacted with a porous membrane, and the pores of the porous membrane are filled with the polymerizable composition. The polymerizable composition is then polymerized. Ion-exchange groups are then introduced into the resulting precursor polymer, in which the monomer capable of introducing ion-exchange groups has been polymerized. This process is described in more detail below. First, a polymerizable composition containing a polymerizable monomer having a halogenoalkyl group (e.g., chloromethylstyrene, bromomethylstyrene, iodomethylstyrene, etc.), optionally a crosslinkable polymerizable monomer (e.g., a divinylbenzene compound), and an effective amount of polymerization initiator (e.g., an organic peroxide) is contacted with the polyolefin-based porous membrane. The voids of the porous membrane are then filled with the polymerizable composition, which is then polymerized and cured to prepare a precursor ion-exchange membrane filled with a resin having a halogenoalkyl group. The halogenoalkyl group is then converted into an ion-exchange membrane, forming the ion-exchange membrane. In this method, a polymerizable monomer having a halogenoalkyl group is exemplified, but it is also possible to prepare a precursor of the precursor before introducing the halogenoalkyl group using, for example, styrene, and then introduce the halogenoalkyl group into the precursor. After the introduction of the halogenoalkyl group, the same operations as described above can be carried out.

[0073] (3) Polymerizing a polymerizable composition containing an ion-exchange group-containing monomer. The resulting solution containing the ion-exchange group-containing polymer is brought into contact with the polyolefin-based porous membrane to form an ion-exchange membrane in which the ion-exchange resin (the polymer) fills at least the pores. The polymerizable composition can also contain other monomers containing crosslinking agents, but care must be taken because excessive crosslinking tends to reduce the solubility of the ion-exchange group-containing polymer.

[0074] (4) A polymerizable composition containing a monomer capable of introducing ion-exchange groups is polymerized. A solution of the resulting polymer is brought into contact with a porous membrane, and the pores of the porous membrane are filled with the polymer (a precursor polymer formed by polymerizing a monomer capable of introducing ion-exchange groups). Then, ion-exchange groups are introduced into the precursor polymer formed by polymerizing the monomer capable of introducing ion-exchange groups. Even in this method, other monomers, including crosslinkers, can be blended into the polymerizable composition; however, care must be taken because excessive crosslinking tends to reduce the solubility of the precursor polymer.

[0075] Among the above methods, it is preferable to adopt the method (1) or (2) in consideration of productivity, the amount of ion exchange groups introduced, the insolubility of the ion exchange resin, etc. In other words, it is preferable to adopt a method in which a monomer composition of polymerizable monomers is once impregnated into a porous membrane, followed by polymerization, and then, if necessary, introduction of ion exchange groups.

[0076] The ion exchange resin is not particularly limited, but considering compatibility with and adhesion to the porous membrane, it is preferable that the resin portion excluding the ion exchange groups be composed of a crosslinked hydrocarbon polymer. Here, a hydrocarbon polymer refers to a polymer that is substantially free of carbon-fluorine bonds and in which the majority of the bonds in the main chain and side chains constituting the polymer are carbon-carbon bonds. This hydrocarbon polymer may contain small amounts of other atoms, such as oxygen, nitrogen, silicon, sulfur, boron, and phosphorus, between the carbon-carbon bonds via ether bonds, ester bonds, amide bonds, siloxane bonds, and the like. Furthermore, the atoms bonded to the main chain and side chains do not all need to be hydrogen atoms; they may be substituted with small amounts of other atoms, such as chlorine, bromine, fluorine, and iodine, or with substituents containing other atoms. The amount of these elements other than carbon and hydrogen is preferably 40 mol % or less, and more preferably 10 mol % or less, of all elements constituting the resin (polymer) excluding the ion exchange groups.

[0077] The anion exchange groups in the anion exchange membrane (AEM) (the anion exchange groups of the anion exchange resin filled in the pores of the porous membrane) are not particularly limited, but are preferably quaternary ammonium bases or pyridinium bases, taking into consideration ease of production and availability. When an anion exchange membrane is produced by the above-described production method, the counter ions of the anion exchange groups are often obtained as halogen ions. In this case, the anion exchange membrane having halogen ions as counter ions is preferably ion-exchanged to the OH- type counter ions by, for example, immersing the anion exchange membrane having halogen ions as counter ions in an excess amount of an alkaline aqueous solution. The ion exchange method is not particularly limited, and may be performed by a known method, for example, by immersing an anion exchange electrolyte membrane having halogen ions as counter ions in an aqueous solution of sodium hydroxide or potassium hydroxide for 2 to 10 hours. The cation exchange groups in the cation exchange membrane (cation exchange groups possessed by the cation exchange resin filled in the voids of the porous membrane) are not particularly limited, but are preferably sulfonic acid or carboxylic acid types in consideration of ease of production, availability, etc.

[0078] [Characteristics of the ion exchange membrane] The ion exchange membrane of the present invention uses a polyolefin-based porous membrane as a support, which has high toughness and a high (F40-F30) value. Therefore, when incorporated into a water electrolysis device, the membrane is less likely to break even during long-term use, contributing to a longer life of the water electrolysis device. The characteristics of the ion exchange membrane of the present invention are described below.

[0079] (1) Ion Exchange Capacity (meq. / g) The ion exchange capacity of the ion exchange membrane of the present invention is not particularly limited. However, in order to exhibit suitable performance as an ion exchange membrane, it is preferably 1.0 meq. / g or more, more preferably 1.2 meq. / g, and even more preferably 1.4 meq. / g. The higher the ion exchange capacity, the better the ionic conductivity, so a higher ion exchange capacity is preferable. On the other hand, there is a risk that the swelling rate when hydrated may become too high, resulting in gelation or a significant decrease in strength, so in order to balance ionic conductivity and strength, the upper limit is preferably 6.0 meq. / g or less.

[0080] (2) Membrane resistance (Ω・cm２ The membrane resistance of the ion exchange membrane of the present invention is not particularly limited. However, in order to exhibit suitable performance as an ion exchange membrane, the membrane resistance per 20 μm is 0.5 Ω cm ２ It is preferable that the film resistance per 20 μm is 0.5 Ω cm or less. ２ If the fuel cell has a voltage of 0.1 V or less, when it is incorporated into a hydrogen production device or the like, the device can be operated at a low voltage, resulting in an excellent energy consumption rate.

[0081] (3) Tear Strength (N) The tear strength (N) in the MD and TD directions of the ion exchange membrane of the present invention is preferably 3.5 N or more. The lower limit of the tear strength is more preferably 4.0 N or more, and even more preferably 5.0 N or more. The higher the tear strength, the more resistant the ion exchange membrane is to tearing. Because the ion exchange membrane of the present invention has high tear strength, it is less likely to tear, even if it is damaged, for example, when it is installed in a water electrolysis device. Furthermore, in a water electrolysis device, when the ion exchange membrane is fixed to a cell with a gasket or the like, stress due to swelling and shrinkage of the film is concentrated at the boundary between the fixed and unfixed portions, which can cause the boundary to tear over long periods of use. Because the ion exchange membrane of the present invention has high tear strength, it is less likely to tear even over long periods of use and has an excellent lifespan. While a higher tear strength is preferable, the practical upper limit is about 15 N.

[0082] (4) Toughness (J) The toughness in the MD direction and TD direction of the ion exchange membrane of the present invention is preferably 0.25 J or more. As mentioned above, toughness is a parameter indicating the tenacity of a material. Because the ion exchange membrane of the present invention has high toughness, it is strong as a material, is less likely to break when handled, and has excellent handleability. Furthermore, like the tear strength, it is strong and therefore less likely to break, and has an excellent lifespan. The lower limit of the toughness is more preferably 0.30 J or more. The higher the toughness, the better, but the practical upper limit is 1.00 J or less.

[0083] (5) Elastic Modulus (MPa) The elastic modulus in the MD and TD directions of the ion exchange membrane of the present invention is not particularly limited, but is preferably 500 MPa or more. The lower limit of the elastic modulus is more preferably 600 MPa or more, and even more preferably 1000 MPa or more. If the elastic modulus is high, for example, when the obtained ion exchange membrane is transported in the next step, it is less likely to wrinkle and has excellent handling properties. The higher the elastic modulus, the more preferable it is, but the substantial upper limit is 1800 MPa or less.

[0084] (6) Thickness The thickness of the ion exchange membrane of the present invention is not particularly limited. However, in order to exhibit suitable performance as an ion exchange membrane, it is preferably 10 μm or more and 200 μm or less. From the viewpoint of reducing the membrane resistance of the ion exchange membrane, a thinner thickness is preferable, but on the other hand, a thinner thickness reduces the gas barrier property and mechanical strength. In particular, in AEM water electrolysis using an anion exchange membrane, high pressure is applied to the membrane, so a certain thickness is preferable from the viewpoint of handleability and gas barrier property. Therefore, the thickness of the ion exchange membrane is more preferably 15 μm or more and 170 μm or less, and even more preferably 25 μm or more and 150 μm or less.

[0085] [Method for manufacturing a membrane electrode assembly using an ion exchange membrane] A membrane electrode assembly (MEA) can be manufactured using the ion exchange membrane of the present invention. The MEA is a composite membrane in which an ion exchange membrane and an electrode are integrated. Here, the integrated electrodes may include a first electrode that is a cathode and a second electrode that is an anode. Furthermore, the membrane electrode assembly may include only a catalyst electrode layer, or may also include a gas diffusion layer. The membrane electrode assembly may have an ion exchange membrane interposed between the first electrode and the second electrode.

[0086] The electrode may contain a metal catalyst and, optionally, an ion conductive agent, a conductive agent, and a binder. The proportions of the metal catalyst, the ion conductive agent, the conductive agent, and the binder in the electrode may be appropriately adjusted depending on the materials used.

[0087] The metal catalyst promotes the oxidation or reduction reaction. The metal catalyst is typically in the form of particles. Examples of the metal catalyst that can be used include platinum, gold, silver, palladium, iridium, rhodium, ruthenium, tin, iron, cobalt, nickel, manganese, molybdenum, tungsten, vanadium, chromium, tantalum, zirconium, aluminum, zinc, oxides or hydroxides thereof, and alloys thereof. The metal catalyst for the anode preferably contains nickel. The metal catalyst for the cathode preferably contains platinum, gold, silver, palladium, iridium, rhodium, ruthenium, tin, iron, cobalt, nickel, manganese, or alloys thereof.

[0088] The ion conductive agent increases the ionic conductivity of the electrode. Examples of the ion conductive agent include perfluorocarbon polymers, aromatic polyether ether ketones, and polysulfones having acidic functional groups. Ion exchange resins may also be used as the ion conductive agent. The conductive agent increases the electronic conductivity of the electrode. The conductive agent may also be used as a carrier for a metal catalyst. Examples of the conductive agent that can be used include carbon black, activated carbon, graphite, fullerene, carbon nanotubes, and mixtures thereof.

[0089] The binder increases the rigidity of the electrode, and examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, polyacrylic acid compounds, imide compounds, and mixtures thereof.

[0090] The method for producing the membrane-electrode assembly is not particularly limited, and any known method may be used. For example, the following method may be used. First, an ion exchange membrane is prepared. The ion exchange membrane may be in a wet state, but is preferably in a dry state. Next, a metal catalyst is mixed with, optionally, an ion conductor, a conductive agent, a binder, and an organic solvent to prepare a first electrode-forming composition and a second electrode-forming composition, respectively. These electrode-forming compositions are applied, for example, to a release paper to obtain a coating film. This coating film is dried. The dried coating film is peeled off from the release paper and laminated on one main surface and the other main surface of the ion exchange membrane, respectively. Note that an ion conductor may be applied to each main surface of the ion exchange membrane in advance. Alternatively, the first electrode-forming composition and / or the second electrode-forming composition may be directly applied to each main surface of the ion exchange membrane to form a coating film.

[0091] The resulting laminate is then subjected to heating, pressure, or both to integrate the first and second coating films with the ion exchange membrane. In this manner, a membrane electrode assembly is obtained in which the first electrode, the ion exchange membrane, and the second electrode are laminated in this order. Note that either the first electrode or the second electrode may be omitted, or an electrode may be provided on only one side of the ion exchange membrane.

[0092] [Water electrolysis device including ion exchange membrane or MEA and manufacturing method thereof] A water electrolysis device can be formed using the ion exchange membrane or membrane electrode assembly (MEA) of the present invention described above. In particular, when it is made into an anion exchange membrane (AEM), it can be used as a membrane or membrane electrode assembly for water electrolysis that can produce hydrogen. The configuration of the water electrolysis device is as shown in Figure 1. The water electrolysis device may be a water electrolysis device that uses water or a low-concentration alkaline aqueous solution, or may be a device that uses a high-concentration alkaline aqueous solution of 5 mass % or more.

[0093] Specifically, a catalyst layer (anode 2 and cathode 3) composed of an anion exchange resin with a catalyst dispersed therein is disposed on the anion exchange membrane 1, and a gas diffusion layer 4 is provided on each. The configuration of the gas diffusion layer 4 is not particularly limited, and a porous material, such as graphite fiber, commonly used in AEM-type water electrolysis devices can be used. The anion exchange membrane 1, anode 2, and cathode 3 may be replaced with the MEA described above. In the metal housing 10, the anode chamber 5 on the anode 2 side is provided with a water inlet 6 for supplying water and an oxygen outlet 7 for discharging oxygen. Furthermore, the cathode chamber 8 on the cathode 3 side is provided with a hydrogen outlet 9 for discharging hydrogen. This configuration enables hydrogen to be produced by water electrolysis. In the water electrolysis cell described above, the anion exchange membrane functions as a solid electrolyte membrane that transfers ions between the anode and cathode. Furthermore, it serves to suppress mixing of oxygen gas generated at the anode and hydrogen gas generated at the cathode.

[0094] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The properties of the porous membranes used in the examples and comparative examples of the present invention, and the properties of the ion exchange membranes using these porous membranes, were evaluated by the following methods. Unless temperature is specified, measurements were carried out at room temperature (25°C).

[0095] <Weight-average molecular weight, molecular weight distribution> The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polyolefin resin and olefin-based elastomer were determined by gel permeation chromatography (GPC) under the following conditions. Note that each molecular weight is a relative value based on polystyrene and dibenzyl. From Mw and Mn, the molecular weight distribution was calculated as Mw / Mn. Apparatus: High-temperature GPC apparatus (HLC-8321GPC / HT, manufactured by Tosoh) Detector: Differential refractive index detector RI Column: Shodex HT-G, Shodex HT-806M (manufactured by Showa Denko) Solvent: 1,2,4-trichlorobenzene Flow rate: 1.0 mL / min Column temperature: 145°C Injection volume: 0.200 mL Standard samples: Monodisperse polystyrene manufactured by Tosoh, dibenzyl manufactured by Tokyo Chemical Industry Co., Ltd.

[0096] <MFR, Melting Point> The MFR of the polyolefin resin and the olefin-based elastomer was measured in accordance with JIS K 7210-1: 2014. The melting points of the polyolefin resin and the olefin-based elastomer were measured by DSC in accordance with JIS K 7121 (1987).

[0097] <Thickness (μm)> A porous membrane was cut into a size of 120 mm × 120 mm, and the thickness was measured at a total of nine points at 30 mm intervals in both the width and length directions using a contact thickness meter (Digimatic Indicator ID-H0530, manufactured by Mitutoyo Corporation), and the measured thickness was defined as the thickness of the membrane.

[0098] <Porosity (%)> The volume V (cm ３ ) and mass M (g) were measured, and the porosity P was calculated using the following formula: where ρ is the density (g / cm ) of the resin composition forming the porous film. ３ ) P = 100 × (1 - M / (ρ × V)) Here, the density of crystalline polyolefin changes depending on the difference in crystallinity caused by the molding method, so the density of the resin composition was determined by melting the resin composition at a temperature above the melting point of 50°C, pressing it to a thickness of about 0.1 mm using a compression molding machine, and quenching it in ice water at 0°C.

[0099] <Air Resistance (sec / 100 cc Air)> Based on JIS P8117: 2009, the air resistance of the porous membrane was measured using an Oken type air permeability tester (EGO1-7-1MR) manufactured by Asahi Seiko Co., Ltd. The obtained air resistance was divided by the membrane thickness (μm) and then multiplied by 20 to calculate the air resistance per 20 μm.

[0100] <Tensile properties> A tensile test was carried out using an autograph AGS-X manufactured by Shimadzu under the following conditions: Test speed: 5 mm / min; Test piece dimensions: rectangular shape with a width of 10 mm and a length of 50 mm; Distance between grippers (initial length) L ０: 30 mm Thickness: Three points in the center of each test piece were measured using a contact type thickness gauge (Digimatic Indicator ID-H0530, manufactured by Mitutoyo Corporation), and the average value was taken as the thickness of the test piece. From the obtained test force F (N) and the displacement ΔL of the gripper, the stress σ and strain ε were calculated based on the following formula. The obtained stress σ was plotted on the vertical axis and the strain ε on the horizontal axis to obtain a stress-strain curve. From this stress-strain curve, the following tensile properties (1) to (4) were determined. Note that each value was measured in both the MD direction and the TD direction. σ (MPa) = F (N) / S (mm ２ ) ε=ΔL(mm) / L ０ (mm) Here, when evaluating the ion exchange membrane, a dried chloride ion type membrane was used, which was obtained by immersing the ion exchange membrane in a 0.5 mol / L NaCl aqueous solution for 10 hours or more, rinsing it with ion exchange water, and air-drying it at room temperature (25°C) for 12 hours or more.

[0101] (1) Tensile modulus (MPa) The modulus was calculated from the slope of the linear region of the stress-strain curve. Specifically, the slope in the linear region at the beginning of the tensile test was determined using the following formula to calculate the tensile modulus E (MPa): E (MPa) = Δσ (MPa) / Δε

[0102] (2) F30 (MPa) On the horizontal axis of the stress-strain curve, the stress (MPa) was read at a strain of 0.3, and this value was taken as F30 (MPa).

[0103] (3) F40 (MPa) On the horizontal axis of the stress-strain curve, the stress (MPa) was read at a strain of 0.4, and this value was taken as F40 (MPa).

[0104] (4) Toughness (J) The integral value of the test force F [N]-displacement ΔL [m] curve from the initial stage to fracture was calculated as toughness (J), which is the fracture energy.

[0105] <Tear Strength (N)> A tear test was performed at a test speed of 200 mm / min based on JIS K7128-3 (1998), and the obtained maximum tear load (N) was taken as the tear strength (N). Measurements were made in both the MD and TD directions. Here, when evaluating an ion exchange membrane, a chloride ion-type dried membrane was used, which was obtained by immersing the ion exchange membrane in a 0.5 mol / L NaCl aqueous solution for 10 hours or more, rinsing with ion exchange water, and air-drying at room temperature (25°C) for 12 hours or more.

[0106] <Ion exchange capacity (IEC) (meq. / g)> The ion exchange membrane was immersed in a 0.5 mol / L NaCl aqueous solution for 10 hours or more to convert it to a chloride ion type. Then, the chloride ion type membrane was immersed in a 0.2 mol / L NaNO3 aqueous solution to convert it to a chloride ion type. ３ The chloride ions liberated during this process were quantified using a potentiometric titrator (COMTITE-900, manufactured by Hiranuma Sangyo Co., Ltd.) with an aqueous silver nitrate solution, and the resulting value was designated as A (mol).

[0107] Next, the same ion exchange membrane was immersed in a 0.5 mol / L NaCl aqueous solution for 4 hours or more to convert it to the chloride ion type again. After immersion, the ion exchange membrane was thoroughly washed with ion exchange water, the moisture on the surface was wiped off, and the weight W (g) of the ion exchange membrane when wet was measured. This ion exchange membrane was dried under reduced pressure at 60°C for 5 hours, and the weight D (g) after drying was measured. From each measurement value, the ion exchange capacity was calculated using the following formula: Ion exchange capacity (meq. / g) = A x 1000 / D

[0108] <Membrane resistance (Ω・cm ２ The ion exchange membrane was immersed in a 0.5 mol / L aqueous solution of NaCl for 10 hours or more to convert it to a chloride ion type. The ion exchange membrane after the above treatment was placed in the center of a two-compartment cell equipped with platinum electrodes, and 0.5 mol / L aqueous solution of NaCl was applied to both sides of the ion exchange membrane. －１ Then, the resistance a (Ω cm) between the electrodes at 25°C was measured using an AC bridge (frequency 1000 cycles / sec). ２ Similarly, the resistance b (Ω cm) between the electrodes was measured without the ion exchange membrane. ２The membrane resistance (Ω cm) was calculated from the measured values ​​using the following formula: ２ )=(a−b) The obtained membrane resistance was divided by the membrane thickness (μm) and then multiplied by 20 to calculate the membrane resistance per 20 μm.

[0109] <Cycle Evaluation (Toughness Evaluation)> An ion exchange membrane cut to a size of 20 mm x 20 mm was sandwiched between two stainless steel frames measuring 40 mm wide x 40 mm long x 1.5 mm thick and having a 15 mm diameter hole in the center, and the four corners were screwed together to secure the membrane. The ion exchange membrane sandwiched between the frames was then immersed in ion exchange water heated to 60°C and allowed to stand for 30 minutes. The ion exchange membrane was then removed, the surface moisture was wiped off, and the membrane was dried in an oven at 60°C for 1 hour. After repeating the above procedure 100 times, the ion exchange membrane was removed from the frame, and the appearance of the ion exchange membrane was confirmed. Those with cracks confirmed by visual inspection of the appearance were deemed defective. Ten test pieces were cut out from one ion exchange membrane, and the test was evaluated based on the percentage of those with defects confirmed by visual inspection. The evaluation results were expressed as follows: ○: 0 to 1 defective sheet out of 10 sheets △: 2 to 3 defective sheets out of 10 sheets ×: 4 or more defective sheets out of 10 sheets

[0110] Example 1 (Production of Porous Membrane) 75% by mass of homopolypropylene (MFR = 0.5 g / 10 min, weight average molecular weight 1,050,000, molecular weight distribution 6, melting point 170 ° C.) as a polyolefin resin, and 25% by mass of propylene-based propylene-ethylene-butene random copolymer (MFR = 6.0 g / 10 min, melting point 160 ° C., weight average molecular weight 340,000, molecular weight distribution 2.2) as an olefin-based elastomer were mixed in a Henschel mixer and the resulting resin composition was then fed into a twin-screw extruder. Next, 60% by mass of diisononyl phthalate (total of 100% by mass of the resin composition and plasticizer) was added through the side feeder of the twin-screw extruder as a plasticizer, and the mixture was melt-kneaded at 180 ° C. and 100 rpm to obtain a gel-like solution. The resulting gel-like solution was extruded through a T-die installed at the tip of the twin-screw extruder and taken up by a 25 ° C. cooling roll to form a gel-like sheet with a thickness of approximately 1 mm. The obtained gel-like sheet was biaxially stretched at 130 ° C. by a tenter-type simultaneous biaxial stretching machine to 4 times the longitudinal and 4 times the transverse stretching ratio, to obtain a biaxially stretched gel-like film. The obtained biaxially stretched gel-like film was immersed in acetone to extract and remove diisononyl phthalate, and then the adhering acetone was dried and removed to obtain a porous film. The obtained porous film was evaluated as described above. The results are shown in Table 1.

[0111] (Production of Ion Exchange Membrane) A polymerizable monomer composition was obtained by mixing chloromethylstyrene (95 parts by mass), a 57% by mass styrene solution of divinylbenzene (5 parts by mass), a polymerization initiator (trade name: Perbutyl O, 5 parts by mass), and an epoxy compound (trade name: Epolite 40E, 5 parts by mass). 400 g of the obtained polymerizable monomer composition was placed in a 500 ml glass container, and the porous membrane (20 cm x 20 cm) formed above was immersed in the polymerizable monomer composition. The porous membrane was then removed from the polymerizable monomer composition, and 100 μm polyester films were laminated on both sides of the removed porous membrane as release agents. The resulting laminate was heated at 80°C for 5 hours under a nitrogen pressure of 0.3 MPa, polymerizing the polymerizable monomer composition in the porous membrane. The obtained membrane was immersed in an aqueous solution containing 6% by mass of trimethylamine and 25% by mass of acetone at room temperature for 16 hours to aminated the chloromethylstyrene polymerized portion, washed with pure water, and then air-dried for 16 hours or more to obtain an ion exchange membrane. The obtained ion exchange membrane was evaluated as described above. The results are shown in Table 2.

[0112] Examples 2 to 9, 20, Comparative Examples 1 to 9 Porous membranes and ion exchange membranes were prepared in the same manner as in Example 1, except that the mixing ratio of the polyolefin resin, olefin-based elastomer, and plasticizer, as well as the stretching temperature and stretching ratio, were changed as shown in Table 1. The obtained porous membranes and ion exchange membranes were evaluated as described above. The results are shown in Tables 1 and 2.

[0113] Example 10 The polyolefin resin, olefin-based elastomer, and plasticizer were the same as those used in Example 1. A resin composition containing 90% by weight of polyolefin resin and 10% by weight of olefin-based elastomer, to which 60% by weight of plasticizer was added, was placed in a Toyo Seiki Seisaku-sho Laboplastomill and melt-kneaded at 180°C and 50 rpm to obtain a gel-like solution. The resulting gel-like solution was solidified at room temperature to obtain a gel-like solid. A certain amount was cut out from the resulting gel-like solid and pressed into a sheet using a compression molding machine heated to 180°C. The sheet was then introduced into ice water at 0°C to cool and solidify, obtaining a gel-like sheet approximately 0.5 mm thick. The resulting gel-like sheet was biaxially stretched at 145°C using a small tenter-type batch stretching machine to a length of 4 times and a width of 4 times, obtaining a gel-like film. The resulting gel-like film was immersed in acetone to extract and remove diisononyl phthalate, and the adhering acetone was then dried and removed to obtain a porous film. The obtained porous membrane was used to obtain an ion exchange membrane in the same manner as in Example 1. The obtained porous membrane and ion exchange membrane were evaluated as described above. The results are shown in Tables 1 and 2.

[0114] Examples 11 to 18, Comparative Example 10 Porous membranes and ion exchange membranes were prepared in the same manner as in Example 10, except that the mixing ratios of the polyolefin resin, olefin-based elastomer, and plasticizer were changed as shown in Table 1. The obtained porous membranes and ion exchange membranes were evaluated as described above. The results are shown in Tables 1 and 2.

[0115] Example 19 A porous membrane and an ion exchange membrane were produced in the same manner as in Example 10, except that a homopolypropylene having an MFR of 0.5 g / 10 min, a weight average molecular weight of 1,020,000, a molecular weight distribution of 8.8, and a melting point of 162°C was used as the polyolefin resin. The obtained porous membrane and ion exchange membrane were evaluated as described above. The results are shown in Tables 1 and 2.

[0116] Comparative Example 11 Production of a porous membrane was attempted in the same manner as in Example 1, except that the compounding ratios of the polyolefin resin, olefin-based elastomer, and plasticizer were as shown in Table 1. Because the amount of plasticizer was high and the gel composition was soft, the gel composition was torn when extruded from the T-die and taken up with rolls, and a gel sheet could not be obtained.

[0117] Comparative Example 12 An attempt was made to produce a porous membrane in the same manner as in Example 1, except that the compounding ratios of the polyolefin resin, the olefin-based elastomer, and the plasticizer, and the stretching temperature and magnification were as shown in Table 1. During stretching, the gel film frequently broke due to coming off the stretching machine clips, and a porous membrane could not be obtained.

[0118] Comparative Example 13 An attempt was made to produce a porous film in the same manner as in Example 1, except that the compounding ratios of the polyolefin resin, the olefin-based elastomer, and the plasticizer, and the stretching temperature and ratio were as shown in Table 1. The film broke during stretching, and a porous film could not be obtained.

[0119] Example 21 A porous membrane and an ion exchange membrane were produced in the same manner as in Example 10, except that Vistamaxx 3000, a propylene-based elastomer manufactured by ExxonMobil, was used as the olefin-based elastomer, the initial gel-like sheet was molded to a thickness of approximately 1.0 mm, and the mixing ratio of the polyolefin resin, olefin-based elastomer, and plasticizer was changed as shown in Table 1. The obtained porous membrane and ion exchange membrane were evaluated as described above. The results are shown in Tables 1 and 2.

[0120] Example 22 A porous membrane and an ion exchange membrane were prepared in the same manner as in Example 21, except that Vistamaxx 3980FL, a propylene elastomer manufactured by ExxonMobil, was used as the olefin elastomer. The obtained porous membrane and ion exchange membrane were evaluated as described above. The results are shown in Tables 1 and 2.

[0121] Example 23 A porous membrane and an ion exchange membrane were prepared in the same manner as in Example 21, except that Vistamaxx 3588FL, a propylene elastomer manufactured by ExxonMobil, was used as the olefin elastomer. The obtained porous membrane and ion exchange membrane were evaluated as described above. The results are shown in Tables 1 and 2.

[0122] Examples 24 to 26 When producing a porous membrane, a roll-type longitudinal stretching machine and a tenter-type transverse stretching machine were used, and stretching was performed by a sequential stretching method in which stretching was performed in the MD direction and then in the TD direction, and the stretching ratio and stretching temperature were as shown in Table 1. Porous membranes and ion exchange membranes were produced in the same manner as in Example 1, except that the obtained porous membranes and ion exchange membranes were evaluated as described above. The results are shown in Tables 1 and 2.

[0123]

[0124]

[0125] As can be seen from Table 2, the ion exchange membranes of the present invention (Examples 1 to 26) had a tear strength of 3.5 N or more in both the MD and TD directions, and the toughness ratings were △ or ◯, indicating good results. In contrast, the ion exchange membrane of Comparative Example 10 had an excessively small porosity of the polyolefin-based porous membrane, making it impossible to measure the membrane resistance and ion exchange capacity of the resulting ion exchange membrane. Furthermore, the ion exchange membranes of Comparative Examples 1 to 9 had a tear strength of less than 3.5 N in at least either the MD or TD direction, resulting in a poor toughness rating of ×. Furthermore, in Comparative Example 11, the amount of plasticizer added was outside the preferred range of the present invention, and in Comparative Examples 12 and 13, the stretching temperature was outside the preferred range of the present invention, indicating that a porous membrane could not be obtained.

[0126] Furthermore, as can be seen from Table 1, the polyolefin-based porous membranes of the present invention (Examples 1 to 26) had a toughness of 0.35 J or more in both the MD and TD directions, and (F40 - F30) was 2.0 MPa or more. As a result, the toughness of the obtained ion exchange membranes was evaluated as △ or ◯, as shown in Table 2, and was good. In contrast, the porous membranes of Comparative Examples 1, 2, and 5 to 9 had a toughness of less than 0.35 J, and the porous membranes of Comparative Examples 3 and 4 had a (F40 - F30) of less than 2.0 MPa in either the MD or TD direction, and the toughness of the obtained ion exchange membranes was evaluated as ×, which was poor. Furthermore, in Comparative Example 10, the content of the polyolefin-based elastomer in the resin composition constituting the gel solution was outside the preferred range of the present invention, and therefore the obtained membrane had a porosity of 0%, no pores were formed, and was poor as a porous membrane, as shown in Table 1. Since no pores were formed, the ion exchange resin could not be filled inside. As shown in Table 2, the membrane resistance of the obtained ion exchange membrane was extremely high, and the ion exchange capacity could not be measured, making it a defective ion exchange membrane.

[0127] As can be seen from Table 1, in the polyolefin porous membrane manufacturing methods of the present invention (Examples 1 to 20), the toughness evaluation of the ion exchange membranes obtained was △ or ◯, as shown in Table 2, which was good. In contrast, in the methods of Comparative Examples 1 to 4, the stretching ratio was outside the preferred range of the present invention, and therefore, as shown in Table 2, the toughness evaluation of the ion exchange membranes obtained was ×, which was poor. In addition, in the methods of Comparative Examples 5 to 9, the resin composition constituting the gel solution did not contain a polyolefin elastomer, and therefore, as shown in Table 2, the toughness evaluation of the ion exchange membranes obtained was ×, which was poor. In addition, in the method of Comparative Example 10, the content of the polyolefin elastomer in the resin composition constituting the gel solution was outside the preferred range of the present invention, and therefore, as shown in Table 1, the porosity of the obtained membrane was 0% and no pores were formed, and it was a poor porous membrane. Because pores were not formed, the ion exchange resin could not be filled inside, and as shown in Table 2, the membrane resistance of the obtained ion exchange membranes was extremely high and the ion exchange capacity could not be measured, and it was a poor ion exchange membrane.

[0128] REFERENCE SIGNS LIST 1 anion exchange membrane 2 anode 3 cathode 4 gas diffusion layer 5 anode chamber 6 water supply port 7 oxygen outlet 8 cathode chamber 9 hydrogen outlet

Claims

1. An ion exchange membrane comprising a porous support and an ion exchange resin filled in the pores of the porous support, the ion exchange membrane having a tear strength of 3.5 N or more in each of the MD and TD directions.

2. 2. The ion exchange membrane according to claim 1, having a tear strength in each of the MD and TD directions of 3.5 N or more and 15 N or less.

3. An ion exchange membrane comprising a porous support and an ion exchange resin filled in the pores of the porous support, the toughness in each of the MD direction and the TD direction being 0.25 J or more.

4. The ion exchange membrane according to claim 3 , wherein the toughness in each of the MD direction and the TD direction is 0.25 J or more and 1.00 J or less.

5. 4. The ion exchange membrane according to claim 1, wherein the elastic modulus in each of the MD direction and the TD direction is 500 MPa or more and 1800 MPa or less.

6. Film resistance per 20 μm is 0.5 Ω cm ２ The ion exchange membrane according to claim 1 or 3, wherein:

7. The ion exchange membrane according to claim 1 or 3, having a thickness of 10 μm or more and 200 μm or less.

8. The ion exchange membrane according to claim 1 or 3, wherein the ion exchange resin is a hydrocarbon polymer.

9. The anion exchange membrane of claim 1 or 3, wherein the ion exchange resin comprises an anion exchange resin.

10. The ion exchange membrane according to claim 1 or 3, wherein the porous support is a porous membrane containing a polyolefin resin.

11. The ion exchange membrane of claim 10 , wherein the polyolefin resin comprises a polypropylene resin.

12. A polyolefin-based porous membrane having a toughness of 0.35 J or more in each of the MD and TD directions, and (F40-F30) in each of the MD and TD directions is 2.0 MPa or more, where F40 (MPa) is the stress at strain 0.4 and F30 is the stress at strain 0.3 on the horizontal axis of a stress-strain curve obtained in a tensile test, The polyolefin-based porous film described above contains 60 mass% or more of polypropylene based on the resin composition constituting the polyolefin-based porous film.

13. The polyolefin-based porous film according to claim 12, comprising 5% by mass or more and 40% by mass or less of an olefin-based elastomer based on the resin composition constituting the polyolefin-based porous film.

14. The polyolefin-based porous membrane according to claim 12 or 13, having a thickness of 10 μm or more and 150 μm or less.

15. The polyolefin-based porous membrane according to claim 12 or 13, having an air permeability resistance of 100 cc of air per 20 μm thickness according to Japanese Industrial Standards P8117: 2009 of 300 seconds or more and 7000 seconds or less.

16. The polyolefin-based porous membrane according to claim 12 or 13, which is used as a support for an ion exchange resin.

17. An ion exchange membrane comprising the polyolefin-based porous membrane according to claim 12 or 13 as a support and an ion exchange resin filled in the pores of the support.

18. A membrane electrode assembly comprising the ion exchange membrane according to claim 1, 3 or 17 and an electrode.

19. A water electrolysis device comprising the ion exchange membrane according to claim 1, 3 or 17.

20. A water electrolysis device comprising the membrane electrode assembly according to claim 18.

21. A method for producing a polyolefin-based porous membrane, comprising the following steps (a) to (d): (a) a step of melt-kneading a resin composition containing a polyolefin resin including polypropylene and an olefin-based elastomer, the content of the olefin-based elastomer in the resin composition being 5% by mass or more and 40% by mass or less based on the resin composition, and the content of the polypropylene in the resin composition being 60% by mass or more based on the resin composition, with a plasticizer to obtain a gel-like solution; (b) cooling the gel-like solution to obtain a gel-like sheet; (c) biaxially stretching the gel-like sheet at area stretch ratios in MD and TD of 10 to 35 times to obtain a biaxially stretched gel-like film; and (d) A step of washing the gel film with a solvent and drying the washed film to obtain a polyolefin-based porous membrane.