Ion exchange membrane, polyolefin-based porous membrane, membrane electrode conjugate, water electrolysis apparatus, and method of producing polyolefin-based porous membrane

Abstract

To provide a polyolefin-based porous membrane capable of making an ion exchange membrane hard to generate break of a membrane when mounted on a water electrolysis apparatus, having strong toughness and low membrane resistance, and a support body of the ion exchange membrane, and a method of producing the polyolefin-based porous membrane.SOLUTION: An ion exchange membrane includes: a porous support body including a polyolefin resin; and an ion exchange resin which is a hydrocarbon-based polymer filled in voids of the porous support body, wherein each elastic modulus in an MD direction and a TD direction is 500 MPa or more, and each tear strength in the MD direction and the TD direction is 3.5 N or more.SELECTED DRAWING: None

Description

[Technical field]

[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. [Background technology]

[0002] Porous membranes formed from thermoplastic resins are widely used as substance separation membranes, selective permeation membranes, support membranes, isolation membranes, 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 having a porous membrane as a support and pores filled with an ion exchange resin 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 produce hydrogen gas and oxygen gas. Hydrogen produced using energy obtained by a method that suppresses the generation of carbon dioxide as electricity does not contain CO 2 Also known as free hydrogen or green hydrogen, it is expected to be the next generation of clean energy that will replace fossil fuels.

[0004] Among water electrolysis methods, the anion exchange membrane (AEM) water electrolysis method is attracting attention because it does not require the use of expensive precious metals as catalysts. In the AEM water electrolysis method, an alkaline aqueous solution may be used in the operating environment. For the anion exchange membrane used in the AEM water electrolysis method, 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 (Hipore (registered trademark) manufactured by Asahi Kasei Chemicals Corporation, Ceteera (registered trademark) manufactured by Tonen Chemical Nasu Corporation, etc.) as the substrate. Anion exchange membranes using such supports have characteristics such as low membrane resistance and excellent mechanical strength due to the presence of the support. In addition to polyethylene porous membranes, other olefin porous membranes disclosed include 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 a separator for lithium ion batteries.

[0005] However, since the olefin resin has low affinity with the anion exchange resin 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 that is a porous membrane using silane-modified polyolefin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2009-215500 [Patent Document 2] Patent Publication No. 2010-215901 [Patent Document 3] International Publication No. 2016-104792 [Patent Document 4] Patent No. 7020654 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the anion exchange membrane described in Patent Document 4 has high membrane resistance and is expected to lose its toughness during use, so there is a demand for a membrane that functions adequately as an anion exchange membrane and has sufficient toughness. The present invention solves the problems of the conventional techniques described above, and provides an ion exchange membrane that has high toughness and is unlikely to be damaged 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. [Means for solving the problem]

[0008] The present inventors have found that by setting the tear characteristics of an ion exchange membrane of a predetermined structure to be 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 apparatus when the ion exchange membrane is mounted in the water electrolysis apparatus 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 apparatus when the ion exchange membrane is mounted in the water electrolysis apparatus 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 (F40-F30) value equal to or greater than 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 apparatus when the ion exchange membrane is mounted in the water electrolysis apparatus and used repeatedly.

[0011] Furthermore, the present inventors have found that by constructing an ion exchange membrane using as a support a polyolefin-based porous membrane produced by a method including predetermined steps, 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 apparatus when the ion exchange membrane is installed in the water electrolysis apparatus and used repeatedly.

[0012] Since ion exchange resins have ion exchange groups, they tend to swell when water is present. In contrast, when water is reduced (water is no longer present), the ion exchange resins shrink. Therefore, when the ion exchange membrane is fixed with a gasket or the like, a local load may be applied at the boundary between the part fixed with the gasket and the part not fixed, due to the dimensional change caused by the swelling and shrinkage of the ion exchange membrane. The ion exchange membrane of the present invention using the polyolefin porous membrane of the present invention as a support is unlikely to break even if it is repeatedly swollen and dried over a long period of time, which is thought to contribute to improving the life of the water electrolysis device. The above problems become more pronounced in anion exchange membranes, and therefore 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 exhibits its effects more effectively, particularly when used as anion exchange membranes in AEM water electrolysis devices. Specifically, the present invention comprises the following:

[0013] [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] 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 in the pores of the porous support, the toughness in each of the MD and TD directions being 0.25 J or more.

[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] Film resistance of 0.5 Ω cm per 20 μm 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 contains 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 (F40 - F30) in each of the MD and TD directions is 2.0 MPa or more, 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 the stress-strain curve obtained in a tensile test.

[0017]

[13] The polyolefin-based porous membrane according to

[12] , which contains 60 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] , having 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] , 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.

[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] and

[18] and an electrode.

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

[11] and

[18] .

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

[19] .

[0020]

[22] 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 and an olefin-based elastomer, the content of the olefin-based elastomer in the resin composition being 5% by mass or more and less than 50% by mass 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.

[0021]

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

[22] , wherein the polyolefin resin contains polypropylene.

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

[22] or

[23] , wherein the amount of the 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 membrane according to any one of

[22] to

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

[0022]

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

[22] to

[25] , wherein the melting point of the olefin-based elastomer measured by DSC (differential scanning calorimetry) based on JIS K7121 (1987) is not less than (melting point of the polyolefin resin - 15) ° C. and not more than (melting point of the polyolefin resin + 5) ° C. Effect of the Invention

[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, that is, an ion exchange membrane having high toughness that is unlikely to break even when incorporated into a water electrolysis device. By using this ion exchange membrane, particularly when used in a water electrolysis device, the ion exchange membrane is unlikely to break even when repeatedly swollen and dried during repeated use, so that the life of the water electrolysis device can be extended. [Brief description of the drawings]

[0024] [Figure 1] FIG. 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 anion exchange membrane which is one embodiment of an ion exchange membrane having the ion exchange membrane of the present invention or a porous membrane produced by the method of the present invention as a support. [Diagram 2]1 is a graph showing stress-strain curves of the porous films obtained in Example 13 and Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present invention will be described in detail. [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-based porous membrane of the present invention can be used as a porous support that serves as the base material of the ion exchange membrane.

[0027] (Polyolefin resin) The polyolefin-based porous membrane of the present invention is mainly composed of polyolefin resin. The polyolefin resin constituting the polyolefin-based porous membrane includes 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 it has excellent heat resistance and moldability.

[0028] In addition, the above-mentioned main component means that the resin composition containing the above-mentioned polyolefin resin and a polyolefin-based elastomer described later is taken as the standard (100 mass%) and contains the above-mentioned polyolefin resin in an amount of 50 mass% or more, more preferably 60 mass% or more, and even more preferably 70 mass% or more.

[0029] In the AEM water electrolysis device, from the viewpoint of enhancing the water electrolysis performance, the operating temperature is preferably about 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 because the physical properties of the support do not change during long-term use. From such a 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 as a support for an ion exchange membrane, but on the other hand, if it is too high, the moldability deteriorates, so the upper limit is preferably 280°C or lower, more preferably 270°C or lower, and even more preferably 200°C or lower.

[0030] The melting point herein refers to a value measured by DSC (differential scanning calorimetry) based on 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, it is preferable that the polypropylene is a homopolymer, which is a single polymer of propylene. Examples of comonomers contained in the copolymer with other olefins include ethylene and α-olefins such as 1-butene, 1-pentene, 4-methylpentene-1, and 1-octene. The content of these comonomers in 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 1×10 5 5×10 or more 6 Preferably, it is 5×10 or less. 5 More than 2.5 x 10 6 It is more preferable that it is 9×10 or less. 5 More than 2×10 6 More preferably, the weight average molecular weight is 1×10 or less. 5If the weight average molecular weight is less than 5×10, the entanglement between the molecules cannot be sufficiently ensured, and therefore, the membrane may be torn during film formation or the strength of the porous membrane may be insufficient. 6 In the above cases, the viscosity becomes too high, which may cause the thickness uniformity to deteriorate or the moldability to deteriorate. In particular, when forming a thick film suitable as a support for an ion exchange membrane, if the weight average molecular weight becomes too high, the internal pressure of the extruder is likely to increase during melt kneading, so the size of the extruder must be excessively large relative to the discharge amount, which is not preferable because it leads to increased costs. The molecular weight distribution of the polypropylene resin is preferably about 5 to 10. If the molecular weight distribution is within the above range, the workability is good when melt kneading with a plasticizer and extruding in the wet method of producing a porous membrane 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 the above range, the workability when melt-kneading with a plasticizer and extruding the mixture is improved, as is the molecular weight distribution.

[0033] (Olefin 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 as a substrate. Examples of the olefin-based elastomer include ethylene-α-olefin copolymer, propylene-α-olefin copolymer, 1-butene-α-olefin copolymer, etc. 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 resin is plasticized by the plasticizer, so that the molecular diffusion of the polyolefin resin is accelerated, and in the case of a polyolefin resin with high crystallinity, a coarse high-order structure crystal may be formed. If the high-order structure of the crystal becomes coarse, unevenness occurs between a portion that is sufficiently oriented and a portion that is not, in the subsequent stretching process, which may result in embrittlement when filled with an ion exchange resin. In the present invention, the inventors have found that by adding a certain amount of olefin-based elastomer to a polyolefin resin, not only the toughness of the porous film is improved, but also the crystal structure of the polyolefin resin, which is the main component, is refined, and the coarse high-order structure that is likely to occur in wet porous film formation can be suppressed. Although the detailed mechanism is unclear, it is believed that when an olefin-based elastomer is added to a polyolefin resin in a preferred range, the presence of the elastomer component in the molecular diffusion path of the polyolefin resin suppresses the molecular chain of the polyolefin resin from diffusing over a long distance, and promotes crystallization on the spot, thereby refines the crystal structure.

[0035] With respect to the resin composition containing the polyolefin resin and the olefin-based elastomer as the standard (100% by mass), the lower limit of 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 the upper limit 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 in the mechanical property evaluation of the ion exchange membrane using the produced porous membrane as a substrate. If the content exceeds 50% by mass, the elastomeric properties become too strong, and the pores of the porous membrane may be blocked. If the pores are blocked, the porosity of the porous membrane will be low and the air resistance will be too high, so that the ion exchange capacity will decrease and the membrane resistance will be high when the membrane is finally made into an ion exchange membrane. By setting the content of the olefin-based elastomer within the above preferred range, a porous membrane with excellent toughness and tenacity can be obtained by combining with the membrane production method described later.

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

[0037] (Other additives) Various additives can be blended into the resin composition as necessary. Examples of such additives include antioxidants such as phenol-based, phosphorus-based, and sulfur-based, nucleating agents such as aromatic phosphate metal salt-based, benzoic acid metal salt-based, and sorbitol-based, light stabilizers, and antistatic agents. These additives may be blended directly into the resin composition, or may be blended as a master batch in which the additives are mixed in advance with the polyolefin resin. The blending amount of each additive is not particularly limited, but is usually 0.01% by mass or more and 5.00% by mass or less with respect to the resin composition. Here, 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. When a β-crystal nucleating agent is used, needle-shaped crystals are formed, which may cause strong anisotropy in the initial high-order structure. Therefore, when polypropylene is used, it is better to use an α-crystal nucleating agent as the crystal nucleating agent. When purchasing a commercially available polypropylene resin, whether or not β crystals are blended can be determined by, for example, checking the crystalline fusion heat peak of DSC. Since the β crystals of polypropylene have a lower melting point than the α crystals, the crystalline fusion heat peak derived from the β crystals appears at a lower temperature than the crystalline fusion heat peak derived from the α crystals. Specifically, in the case of homopolypropylene, it is observed in the range of 120°C to 150°C.

[0038] <Method of manufacturing polyolefin-based porous membrane> Next, the method for producing the polyolefin-based porous membrane of the present invention will be described. There are two known methods for producing the polyolefin-based porous membrane: a dry method (a method for making the resin porous by adding a crystal nucleating agent or inorganic particles) and a wet method (a phase separation method using a plasticizer). In the dry method, a crystal nucleating agent or inorganic particles is mixed into a molten resin, and the resulting mixture is extruded from a die and cooled. Then, the resulting sheet is stretched under specific conditions to cleave the crystal parts and the periphery of the added particles to obtain a porous membrane. This method is also called a stretch-cleavage method because pores are formed by stretching.

[0039] In the wet method, first, the resin is heated, melted, and 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 film. In the dry method, the crystals are torn to open the holes, resulting in coarse holes and inferior strength, but the dry method is characterized by excellent manufacturing costs because no cleaning process is required.

[0040] In the wet method, uniform micropores are obtained by phase separation with the plasticizer, and the film has the characteristics of excellent flatness and strength. Generally, porous films made of commercialized polypropylene resins are produced by a dry method, but the porous film of the present invention is preferably produced by a wet method. The method for producing the polyolefin porous film of the present invention includes the following steps (a) to (d). (a) a step of 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 solution to obtain a gel 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. After the step (d), steps such as heat treatment, aging, corona treatment, and hydrophilization treatment may be carried out as necessary.

[0041] Each step will now be described in more detail. (a) Step of obtaining a gel-like solution The process for obtaining a gel-like solution is preferably a method in which a resin composition containing a polyolefin resin and an olefin-based elastomer, and various additives as necessary, are introduced into a kneader, and while heating and melting, a plasticizer is added up to a predetermined amount, and then the mixture is further kneaded to mix uniformly. Here, the plasticizer is not particularly limited as long as it has sufficient compatibility with the resin composition. Specific examples include aliphatic carboxylates such as methyl stearate and butyl stearate, aromatic carboxylates such as diisononyl phthalate and bis-2-ethylhexyl phthalate, and aliphatic hydrocarbons such as liquid paraffin. In order 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 is sufficiently higher than the melting point of the resin composition. In addition, 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, and are easy to mold with little bleeding out during the manufacturing process. When liquid paraffin or paraffin wax is used, holes are less likely to be formed compared to when aromatic carboxylic acid esters are used, so a large amount of them is required, which may increase costs. These plasticizers can be used alone or in combination.

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

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

[0044] In the extruder, the resin composition is mixed with the plasticizer and various additives added as required 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 about 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 and kneading temperature, the better; however, if the melting and kneading temperature is too low, unmelted resin will occur, and in the subsequent stretching process, process defects such as film breakage and uneven stretching may occur.In addition, in the final porous film, the unmelted material may cause poor appearance and uneven thickness.If the melting and kneading temperature is too high, the mechanical strength of the final porous film may decrease due to the deterioration of resin.

[0046] When using a twin-screw extruder, 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 in the above range, the residence time of the mixture is not too long, and each raw material 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 shear of the screw, so a low rotation speed is preferable, but 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 step (b) of obtaining a gel-like sheet, the gel-like solution is formed into a sheet shape and then cooled to obtain a gel-like sheet. The sheet can be obtained by cooling the gel liquid once at room temperature and then press-molding it again at a temperature equal to or higher than the melting point of the gel liquid, or by supplying the gel liquid from an extruder to a die and extruding the gel solution from the die. In this case, the extrusion method may be either the T-die method or the inflation method, but from the viewpoint of achieving a uniform thickness, the T-die method is preferred.

[0048] Here, the gel-like sheet may be a single layer membrane or may have a multi-layer structure of two or more layers. Methods for producing a multi-layer gel-like sheet include a method of producing separate gel-like sheets and then heat fusing them, and a co-extrusion method in which the resins of each layer are fed from separate extruders to one die and extruded while being integrated. As a substrate for an ion exchange membrane, it is preferable to use the co-extrusion method from the viewpoints that the adhesive strength between each layer is high and that it is easy to form a through hole between the layers.

[0049] The cooling method for forming the sheet can be a known cooling method such as direct contact with cooling air, cooling water, or other cooling medium, or contact with a roll cooled with a refrigerant. By quenching at the lowest possible temperature during cooling, the crystal structure of the polyolefin resin becomes dense, and the stretchability in the subsequent process and the toughness of the final ion exchange membrane can be improved. The lower the cooling temperature, the better, but from the standpoint of compatibility with workability, such as preventing condensation, it is preferable to set the cooling temperature to about 0°C to 25°C. It is necessary to cool both sides until the temperature falls below the crystallization end temperature. Here, the crystallization end temperature refers to the extrapolated crystallization end temperature measured according to JIS K7121 (1987).

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

[0051] (c) Step of obtaining a biaxially stretched gel film Next, the obtained gel-like sheet is biaxially stretched. 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. In addition, the stretching may be one-stage stretching or multi-stage stretching. In the case of only uniaxial stretching, the molecular chains are excessively oriented in only one direction, so that when an ion exchange membrane is produced using the obtained porous membrane as a substrate, the unstretched direction may become significantly embrittled, and therefore, biaxial stretching is required. In addition, tenter stretching may be performed in a batch manner.

[0052] The lower limit of the area stretching ratio (longitudinal ratio x lateral ratio) which is the sum of the longitudinal and lateral 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 crystal structure generated in the gel-like sheet can be sufficiently refined to improve the mechanical strength. If the lower limit is less than 10 times, the higher-order structure of the crystals that remain unrefined 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. In addition, since the structure is not sufficiently subdivided, the pore size becomes coarse, and the gas barrier property when made into an ion exchange membrane may be poor. The upper limit of the area 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 area stretching ratio, the higher the strength of the porous membrane, but the excessive orientation progresses and the entanglement of the molecular chains becomes weak, so that the elongation decreases when made into an ion exchange membrane, and as a result, the toughness may decrease. Whether the area magnification is sufficient or not can be judged by the (F40-F30) value described later.

[0053] The stretching temperature is preferably set to a temperature lower than the melting point of the polyolefin resin, which is the main component, and more preferably, is in the range of (polyolefin resin crystal dispersion temperature Tcd) to (polyolefin resin melting point -5°C), where Tcd is the crystal dispersion temperature of the polyolefin resin. If the temperature is lower than (polyolefin resin melting point -5°C), the resin can be prevented from fusing to the clips that hold the sheet during stretching and the stretching rolls. Here, the polyolefin resin crystal dispersion temperature Tcd can be determined from the temperature characteristics of dynamic viscoelasticity measured according to ASTM D4065 using a sheet that is melt-pressed at melting point +50°C of the resin composition and then ice-cooled at 0°C. Specifically, since the polypropylene resin in the present invention has a crystal dispersion temperature of 110° C. to 130° C. and a melting point of 160° C. to 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 stretching or multistage stretching is performed, the respective stretching temperatures may be the same or different.

[0054] Here, in the present invention, it is important that the stretching is performed in a state in which the gel-like sheet contains a plasticizer. By performing the stretching before the plasticizer is removed, the crystal structure can be uniformly crushed, and the toughness of the porous film can be improved. In addition, by uniformly crushing the crystal structure, the pores are formed uniformly and densely, so that embrittlement due to the coarseness and density of the ion exchange resin is unlikely to occur.

[0055] (d) A process 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. Here, the solvent for extracting 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 the solvent include hydrocarbons such as n-hexane and cyclohexane, fluorocarbons in which some or all of the hydrogen in hydrocarbons are replaced with fluorine, alcohols such as ethanol and isopropanol, and ketones such as acetone and 2-butanone. As a washing method, a method of immersing the gel film in a solvent, a shower method, or a combination of these, or other known methods can be used. The washing solvent after washing can be removed by air drying, heat drying, or the like. From the viewpoint of suppressing the blocking of pores due to heating and the destruction of the pore structure due to the rapid evaporation of the washing solvent, it is preferable to dry at a low temperature of less than 50°C.

[0056] After removing the plasticizer, a heat treatment may be performed to stabilize the porous film. Heat treatment stabilizes the crystal structure and relieves residual strain, thereby stabilizing the dimensions and the crystal structure within the film. The higher the heat treatment temperature, the faster the stabilization can be achieved, but if the temperature is too high, there is a risk of sudden shrinkage or pore blockage due to melting of the crystals, so the temperature should be adjusted appropriately according to the desired porosity.

[0057] <Characteristics of polyolefin-based porous membranes> The polyolefin-based porous membrane of the present invention has high mechanical properties, so when it is used as the support of ion-exchange membrane, it can obtain the excellent ion-exchange membrane with excellent toughness and excellent effect of suppressing embrittlement.The properties of the polyolefin-based porous membrane of the present invention are described below.The measurement method of each property will be described in detail in the embodiment.

[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, the thinner the thickness, the lower the gas barrier property and mechanical strength. In particular, in the AEM water electrolysis using an anion exchange membrane, a high pressure is applied to the membrane, so it is preferable that the membrane has a certain thickness 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-based 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, further preferably 20% or more, and particularly preferably 30% or more. If the porosity is less than 10%, when used as a support for an ion exchange membrane, the amount of ion exchange resin filled is reduced, so that the ion conductivity may deteriorate and the membrane resistance may increase. In addition, if the porosity is more than 50%, the expansion of the ion exchange resin due to water absorption in a wet state cannot be suppressed when used as an ion exchange membrane, 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 μm of the polyolefin-based porous membrane of the present invention is preferably 300s / 100ccAir or more and 7000s / 100ccAir. The lower limit of the air resistance per 20 μm is preferably 400s / 100ccAir or more, more preferably 500s / 100ccAir. If the air resistance per 20 μm is lower than 300s / 100ccAir, the gas barrier property may be poor when used as a support for an ion exchange membrane. The upper limit of the air resistance per 20 μm of the polyolefin-based 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 used as a support for an ion exchange resin, the impregnation of the ion exchange resin may be slow, which may deteriorate productivity. In addition, the membrane resistance of the obtained ion exchange membrane is high.

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

[0062] 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, the dimensional change when the ion exchange membrane swells is anisotropic, and thus when incorporated into a water electrolysis device and used, wrinkles and the like may occur due to the difference in dimensional change, causing problems.

[0063] (5) Toughness (J) The toughness in the MD and TD directions of the polyolefin-based porous membrane of the present invention 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 break a material when it is pulled. Specifically, as described in LE Nielsen (Onogi Shigeji); "Kinematic Properties of Polymers" 98-100, Kagaku Dojin (1965), it can be calculated from the area of ​​the stress-strain curve obtained in a tensile test.

[0064] If the toughness of the polyolefin-based porous membrane is 0.35 J or more, when it is used as a support for an ion exchange membrane, it exhibits excellent embrittlement suppression effect, and can obtain a strong and tear-resistant ion exchange membrane. The lower limit of the toughness is more preferably 0.40 J or more. The higher the toughness, the better, but the practical upper limit is about 1.5 J.

[0065] (6) F30 (stress at 30% strain), F40 (stress at 40% strain) The (F40-F30) in the MD and TD directions of the polyolefin-based porous membrane of the present invention is preferably 2.0 MPa or more. When the polyolefin-based porous membrane is used as a support for an ion-exchange membrane, it is preferable that the crystal structure in the porous membrane is sufficiently finely divided and oriented. If the structure is not finely oriented or oriented enough, 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 a parameter to determine this fineness 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 respect to the strain, but thereafter the increase in stress becomes more gradual. If there is a coarse structure without orientation inside the porous film, the stress is released in the process of the internal structure breaking and orienting 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 brittle 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 (F40-F30) is, the stronger the orientation is. The upper limit of (F40-F30) is preferably 10.0 MPa or less, more preferably 9.0 MPa or less, and further preferably 8.0 MPa or less. If (F40-F30) exceeds 10.0 MPa, the orientation is too strong, so that the toughness decreases, and as a result, the ion exchange membrane may become easily embrittled when it is made into the membrane.

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

[0070] [Method for producing 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 ion exchange resin. The ion exchange resin (type of ion exchange group) to be supported may be appropriately determined depending on the intended use. 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 for anion exchange membrane (AEM) type water electrolysis, which is water electrolysis for producing hydrogen. When supporting the ion exchange resin, it is preferable that the support is a single layer without overlapping. When two or more supports are laminated, peeling may occur at the laminated interface. In addition, when performing thermocompression bonding or the like to sufficiently bond the laminated interface, the pores may be crushed and the membrane resistance may increase. The method for supporting the ion exchange resin is not particularly limited, but for example, the following four methods can be mentioned.

[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. At this time, in order to obtain the desired ion-exchange membrane, a polymerizable composition consisting of only an ion-exchange group-containing monomer may be used, or a polymerizable composition containing an ion-exchange group-containing monomer and other monomers that are blended as necessary may be used. The other monomers may include a crosslinking agent that is multifunctional, such as divinylbenzene.

[0072] (2) A polymerizable composition containing a monomer capable of introducing an ion exchange group (or a solution of the polymerizable composition, if necessary) is brought into contact with a porous membrane, and the pores of the porous membrane are filled with the polymerizable composition. The polymerizable composition is then polymerized. Thereafter, an ion exchange group is introduced into the resulting precursor polymer in which the monomer capable of introducing an ion exchange group is polymerized. More detailed explanation is as follows. First, a polymerizable composition containing a polymerizable monomer having a halogenoalkyl group (e.g., chloromethylstyrene, bromomethylstyrene, iodomethylstyrene, etc.), if necessary, a crosslinkable polymerizable monomer (e.g., a divinylbenzene compound), and an effective amount of a polymerization initiator (e.g., an organic peroxide) is contacted with the polyolefin-based porous membrane. Then, the polymerizable composition is filled into the voids of the porous membrane, and then polymerized and cured to prepare a precursor of an ion exchange membrane filled with a resin having a halogenoalkyl group. Next, the halogenoalkyl group is converted into an ion exchange group to form an 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, etc., and then introduce the halogenoalkyl group into the precursor. After the introduction of the halogenoalkyl group, the same operations as described above may be carried out.

[0073] (3) Polymerize a polymerizable composition containing an ion-exchange group-containing monomer. By contacting the obtained solution containing the ion-exchange group-containing polymer with the above-mentioned polyolefin-based porous membrane, an ion-exchange membrane is obtained in which the ion-exchange resin (the polymer) is filled at least in the pores. The polymerizable composition can also contain other monomers containing a crosslinking agent, but care must be taken because if the degree of crosslinking becomes too high, the solubility of the ion-exchange group-containing polymer tends to decrease.

[0074] (4) A polymerizable composition containing a monomer capable of introducing an ion exchange group is polymerized. The resulting polymer solution is brought into contact with a porous membrane, and the pores of the porous membrane are filled with the polymer (a precursor polymer obtained by polymerizing a monomer capable of introducing an ion exchange group). Then, an ion exchange group is introduced into a precursor polymer obtained by polymerizing a monomer capable of introducing an ion exchange group. In this method, the polymerizable composition can also contain other monomers including a crosslinking agent, but care must be taken because if the degree of crosslinking becomes too high, the solubility of the precursor polymer tends to decrease.

[0075] Among the above methods, it is preferable to adopt the method (1) or (2) in consideration of the productivity, the amount of ion exchange group 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 a polymerizable monomer is once impregnated into a porous membrane, then polymerized, and an ion exchange group is introduced as necessary.

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

[0077] The anion exchange group in the anion exchange membrane (AEM) (the anion exchange group of the anion exchange resin filled in the voids of the porous membrane) is not particularly limited, but is preferably a quaternary ammonium base or a pyridinium base in consideration of ease of production, availability, etc. In addition, when the anion exchange membrane is produced by the above-mentioned production method, the counter ion of the anion exchange group is often obtained as a halogen ion. In this case, it is preferable to ion-exchange the counter ion to OH- type by immersing the anion exchange membrane having the halogen ion as the counter ion in an excess amount of an alkaline aqueous solution. There is no particular limitation on the ion exchange method, and it is possible to carry out the ion exchange by a known method, for example, by immersing the anion exchange electrolyte membrane having the halogen ion as the counter ion in an aqueous solution of sodium hydroxide or potassium hydroxide for 2 to 10 hours. The cation exchange groups in the cation exchange membrane (the cation exchange groups of 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 ion exchange membranes] The ion exchange membrane of the present invention uses a polyolefin-based porous membrane having high toughness and high (F40-F30) as a support, and therefore, when incorporated in a water electrolysis device, the membrane is unlikely to be damaged even after long-term use, which contributes to extending the 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 ion conductivity, so the higher the ion exchange capacity is, the more preferable it is. On the other hand, there is a risk that the swelling rate when hydrated becomes too high, causing gelation or a significant decrease in strength, so in order to balance ion conductivity and strength, the upper limit is preferably 6.0 meq. / g or less.

[0080] (2) Membrane resistance (Ω cm 2 ) The membrane resistance of the ion exchange membrane of the present invention is not particularly limited. However, in order for the ion exchange membrane to exhibit suitable performance, the membrane resistance per 20 μm is preferably 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 the fuel cell is incorporated into a hydrogen production device, for example, 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 3.5N or more. The lower limit of the tear strength is more preferably 4.0N or more, and even more preferably 5.0N or more. The higher the tear strength, the more difficult the ion exchange membrane is to tear. The ion exchange membrane of the present invention has a high tear strength, so that it is difficult to tear even if it is scratched when it is incorporated into a water electrolysis device. In addition, 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 part and the unfixed part, and the boundary may be torn during long-term use. Since the ion exchange membrane of the present invention has a high tear strength, the membrane is difficult to tear even during long-term use and has a long life. The higher the tear strength, the more preferable it is, but the practical upper limit is about 15N.

[0082] (4) Toughness (J) The toughness in the MD direction and the TD direction of the ion exchange membrane of the present invention is preferably 0.25 J or more. As described above, toughness is a parameter indicating the tenacity of a material. Since the ion exchange membrane of the present invention has high toughness, it is strong as a material, is not easily broken when handled, and has excellent handling properties. In addition, like the tear strength, it is not easily broken because of its toughness, and has an excellent lifespan. The lower limit of the toughness is more preferably 0.30 J or more. The higher the toughness, the more preferable it is, 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 process, 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, a high pressure is applied to the membrane, so it is preferable that the membrane has a certain thickness from the viewpoint of handling property 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 of 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 which is a cathode and a second electrode which is an anode. Furthermore, the membrane electrode assembly may include only a catalyst electrode layer, or may 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. For example, platinum, gold, silver, palladium, iridium, rhodium, ruthenium, tin, iron, cobalt, nickel, manganese, molybdenum, tungsten, vanadium, chromium, tantalum, zirconium, aluminum, zinc, oxides or hydroxides thereof, or alloys thereof can be used as the metal catalyst. The metal catalyst for the anode preferably includes nickel. The metal catalyst for the cathode preferably includes platinum, gold, silver, palladium, iridium, rhodium, ruthenium, tin, iron, cobalt, nickel, manganese, or alloys thereof.

[0088] The ion conductive agent enhances the ion conductivity of the electrode. Examples of the ion conductive agent include perfluorocarbon polymers, aromatic polyether ether ketones, polysulfones, etc., each of which has an acidic functional group. Ion exchange resins may also be used as the ion conductive agent. The conductive agent enhances the electronic conductivity of the electrode. The conductive agent may be used as a support for a metal catalyst. Examples of the conductive agent include carbon black, activated carbon, graphite, fullerene, carbon nanotubes, and mixtures thereof.

[0089] The binder increases the rigidity of the electrode. Examples of the binder that can be used include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based 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, the metal catalyst is mixed with, optionally, an ion conductive agent, 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, for example, applied onto a release paper to obtain a coating film. The 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 conductive agent may be applied in advance onto each main surface of the ion exchange membrane. Alternatively, the first electrode-forming composition and / or the second electrode-forming composition may be directly applied onto each main surface of the ion exchange membrane to form a coating film.

[0091] The obtained laminate is subjected to heating, pressure, or both to integrate the first coating film and the second coating film 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, and an electrode may be provided on only one side of the ion exchange membrane.

[0092] [Water electrolysis device equipped with ion exchange membrane or MEA and its manufacturing method] 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 capable of producing hydrogen. The configuration of the water electrolysis device is as shown in FIG. 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, catalyst layers (anode 2 and cathode 3) in which a catalyst is dispersed in anion exchange resin are arranged on anion exchange membrane 1, and each is provided with a gas diffusion layer 4. The configuration of the gas diffusion layer 4 is not particularly limited, and a porous material such as graphite fiber that is generally used in AEM type water electrolysis devices can be used. Here, the above-mentioned MEA may be used instead of the anion exchange membrane 1, anode 2, and cathode 3. In the metal housing 10, the anode chamber 5 on the anode 2 side is provided with a water supply port 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. With the above-mentioned configuration, hydrogen can be produced by water electrolysis. In the above-mentioned water electrolysis cell, the anion exchange membrane functions as a solid electrolyte membrane that transfers ions between the anode and the cathode, and also plays a role in suppressing the mixing of oxygen gas generated at the anode and hydrogen gas generated at the cathode. EXAMPLES

[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 those porous membranes, were evaluated by the following methods. Unless temperature is mentioned, the measurements were performed 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 polyolefin resin and olefin 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. The molecular weight distribution was calculated as Mw / Mn from Mw and Mn. Equipment: High-temperature GPC equipment (Tosoh, HLC-8321GPC / HT) Detector: RI refractive index detector Column: Shodex HT-G, Shodex HT-806M (Showa Denko) Solvent: 1,2,4-trichlorobenzene ·Flow rate: 1.0mL / min Column temperature: 145℃ ·Injection volume: 0.200mL ·Standard sample: Monodisperse polystyrene manufactured by Tosoh Corporation, 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 based on JIS K 7210-1:2014. Further, the melting point of the polyolefin resin and the olefin-based elastomer was measured by DSC based on JIS K 7121 (1987).

[0097] <Thickness (μm)> From the porous membrane cut into 120 mm × 120 mm, a total of 9 thicknesses were measured at intervals of 30 mm in the width direction and the length direction using a contact thickness gauge (Mitutoyo Corporation's Digimatic Indicator ID-H0530), and the thickness was taken as the membrane thickness.

[0098] <Porosity (%)> The volume V (cm 3 ) and mass M (g) of the porous membrane were measured, and the porosity P was calculated using the following formula. In the formula, ρ is the density (g / cm 3 ) of the resin composition forming the porous membrane. P = 100 × (1 - M / (ρ × V)) Here, since the density of the crystalline polyolefin changes due to the difference in crystallinity depending on the molding, as the density of the resin composition, after melting the resin composition at the melting point + 50°C, it was pressed to a thickness of about 0.1 mm using a compression molding machine and quenched with ice water at 0°C, and the density of the obtained sheet was used.

[0099] <Air permeability resistance (sec / 100ccAir)> Based on JIS P8117:2009, the air permeability resistance of the porous membrane was measured using a King Research air permeability tester (EGO1-7-1MR) manufactured by Asahi Seiko Co., Ltd. After dividing the obtained air permeability resistance by the film thickness (μm) and then multiplying by 20, the air permeability resistance per 20 μm was calculated.

[0100] <Tensile properties> A tensile test was carried out under the following conditions using a Shimadzu Autograph AGS-X. Test speed: 5mm / min - Test piece dimensions: 10mm wide x 50mm long strip Grip distance (initial length) L 0 :30mm Thickness: Three points in the center of each test piece were measured using a contact thickness gauge (Digital Indicator ID-H0530, manufactured by Mitutoyo Corporation), and the average value was regarded as the thickness of the test piece. From the obtained test force F (N) and the gripper displacement ΔL, 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 obtained. Note that each value was measured in both the MD and TD directions. 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 elastic 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 obtained from the following formula, and the tensile elastic modulus E (MPa) was calculated. E(MPa)=Δσ(MPa) / Δε

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

[0103] (3) F40 (MPa) On the horizontal axis of the stress-strain curve, the stress (MPa) at a strain of 0.4 was read, and this value was designated 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 carried out 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 performed in both the MD and TD directions. 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.

[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 was immersed in a 0.2 mol / L NaNO 3 The chloride ions liberated during this process were quantified using a potentiometric titrator (COMTITE-900, manufactured by Hiranuma Sangyo Co., Ltd.) with a silver nitrate aqueous 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 the 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. The ion exchange capacity was calculated from each measurement value 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 NaCl aqueous solution for 10 hours or more to convert it to a chloride ion type. The ion exchange membrane was placed in the center of a two-chamber cell equipped with platinum electrodes, and 0.5 mol / L NaCl was added to both sides of the ion exchange membrane. -1 -NaCl solution was filled. Then, the resistance between the electrodes at 25°C, a (Ω cm 2 ) was measured. Similarly, the resistance b (Ω cm) between the electrodes was measured without the ion exchange membrane. 2 From the measured values, the membrane resistance was calculated according to the following formula. Membrane resistance (Ω cm 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 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 with a hole of 15 mm diameter in the center, and the four corners were screwed in place. The ion exchange membrane sandwiched between the frames was then immersed in ion exchange water heated to 60°C and left to stand for 30 minutes. The ion exchange membrane was then pulled out, the moisture on the surface was wiped off, and the membrane was dried in an oven at 60°C for 1 hour. After repeating the above operation 100 times, the ion exchange membrane was removed from the frame and the appearance of the ion exchange membrane was confirmed. The membrane was deemed defective if cracks were found in the visual inspection of the appearance. The test was carried out by cutting out 10 test pieces from one ion exchange membrane, and the percentage of those found to be defective in appearance was evaluated. The evaluation results are shown as follows: ○: 0 to 1 defective out of 10 △: 2-3 out of 10 were defective ×: 4 or more defective sheets out of 10

[0110] <Example 1> (Production of porous membranes) As a polyolefin resin, 75% by mass of homopolypropylene with MFR=0.5g / 10min, weight average molecular weight of 1,050,000, molecular weight distribution of 6, and melting point of 170°C, and as an olefin-based elastomer, 25% by mass of propylene-ethylene-butene random copolymer (MFR=6.0g / 10min, melting point 160°C, weight average molecular weight of 340,000, molecular weight distribution of 2.2) with propylene as the main component were charged into a Henschel mixer and mixed to form a resin composition, which was then charged into a twin-screw extruder. Next, as a plasticizer, 60% by mass of diisononyl phthalate was added from the side feeder of the twin-screw extruder, with the total of the resin composition and the plasticizer being 100% by mass, and the mixture was melt-kneaded at 180°C and 100 rpm to obtain a gel-like solution. The obtained gel-like solution was extruded from a T-die attached to the tip of a twin-screw extruder and taken up with a cooling roll at 25° C. to form a gel-like sheet having a thickness of about 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 length and 4 times the width 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 attached 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] (Ion exchange membrane manufacturing) Chloromethylstyrene (95 parts by mass), styrene solution of 57% by mass-divinylbenzene (5 parts by mass), polymerization initiator (trade name: Perbutyl O, 5 parts by mass), and epoxy compound (trade name: Epolite 40E, 5 parts by mass) were mixed to obtain a polymerizable monomer composition. 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. Then, the porous membrane was taken out of the polymerizable monomer composition, and 100 μm polyester films were laminated on both sides of the porous membrane as release materials. The laminate was heated at 80° C. for 5 hours under nitrogen pressure of 0.3 MPa to polymerize 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> A porous membrane and an ion exchange membrane were produced in the same manner as in Example 1, except that the mixing ratio of the polyolefin resin, the olefin-based elastomer, and the plasticizer, as well as the stretching temperature and the stretching ratio were 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.

[0113] <Example 10> The polyolefin resin, olefin-based elastomer, and plasticizer were the same as those used in Example 1. A resin composition of 90% by mass of polyolefin resin and 10% by mass of olefin-based elastomer was mixed with 60% by mass of plasticizer and placed in a Labo Plastomill manufactured by Toyo Seiki Seisakusho, melt-kneaded at 180°C and 50 rpm to obtain a gel-like solution. The obtained gel-like solution was solidified at room temperature to obtain a gel-like solid. A certain amount was cut out from the obtained gel-like solid, pressed into a sheet using a compression molding machine heated to 180°C, and then introduced into ice water at 0°C to cool and solidify, obtaining a gel-like sheet with a thickness of about 0.5 mm. The obtained gel-like sheet was biaxially stretched to 4 times the length and 4 times the width at 145°C using a small tenter-type batch stretching machine to obtain a gel-like film. The obtained gel-like film was immersed in acetone to extract and remove diisononyl phthalate, and then the attached acetone was dried and removed to obtain a porous membrane. 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> A porous membrane and an ion exchange membrane were produced in the same manner as in Example 10, except that the mixing ratio of the polyolefin resin, the olefin-based elastomer, and the plasticizer was changed as shown in Table 1. The obtained porous membrane and the ion exchange membrane 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 MFR=0.5g / 10min, weight average molecular weight of 1,020,000, molecular weight distribution of 8.8, and melting point of 162°C was used as the polyolefin resin. The porous membrane and the ion exchange membrane obtained were evaluated as described above. The results are shown in Tables 1 and 2.

[0116] <Comparative Example 11> A porous membrane was produced in the same manner as in Example 1, except that the compounding ratio of the polyolefin resin, the olefin-based elastomer, and the plasticizer was as shown in Table 1. Since the amount of plasticizer was large and the composition was soft, the gel composition was torn when it was extruded from the T-die and taken up by a roll, and a gel sheet could not be obtained.

[0117] <Comparative Example 12> A porous membrane was produced 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. During stretching, the gelled film was frequently torn due to coming off the stretching machine clip, and a porous membrane could not be obtained.

[0118] <Comparative Example 13> 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 ratio were as shown in Table 1. The film broke during stretching, and a porous membrane could not be obtained.

[0119] <Example 21> As the olefin-based elastomer, Vistamaxx3000, a propylene-based elastomer manufactured by ExxonMobil, was used, the initial gel-like sheet was molded to a thickness of about 1.0 mm, and the mixing ratio of the polyolefin resin, the olefin-based elastomer, and the plasticizer was changed as shown in Table 1. A porous membrane and an ion exchange membrane were produced in the same manner as in Example 10. 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 Vistamaxx3980FL, a propylene elastomer manufactured by ExxonMobil, was used as the olefin elastomer. The porous membrane and the ion exchange membrane obtained 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 Vistamaxx3588FL, a propylene elastomer manufactured by ExxonMobil, was used as the olefin elastomer. The porous membrane and the ion exchange membrane obtained 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 are used, A porous membrane and an ion exchange membrane were produced in the same manner as in Example 1, except that the 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. The obtained porous membrane and ion exchange membrane were evaluated as described above. The results are shown in Tables 1 and 2.

[0123] [Table 1]

[0124] [Table 2]

[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 was evaluated as △ or ◯, which was good. In contrast, the ion exchange membrane of Comparative Example 10 had an excessively small porosity of the polyolefin-based porous membrane, so that the membrane resistance and ion exchange capacity of the obtained ion exchange membrane could not be measured. 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, and were evaluated as poor in toughness, i.e., X. 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, so 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 toughness of 0.35 J or more in both MD and TD, and (F40-F30) was 2.0 MPa or more. As a result, the toughness evaluation of the obtained ion exchange membranes was △ or ◯, which was good, as shown in Table 2. 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 (F40-F30) of less than 2.0 MP in either the MD or TD direction, and the toughness evaluation of the obtained ion exchange membrane was poor, i.e., ×. 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, so that the obtained membrane had a porosity of 0% as shown in Table 1, and no pores were formed, and the membrane was poor as a porous membrane. Since no pores were formed, the ion exchange resin could not be filled inside, and the membrane resistance of the obtained ion exchange membrane was extremely high as shown in Table 2, and the ion exchange capacity could not be measured, and the membrane was poor as an ion exchange membrane.

[0127] As can be seen from Table 1, in the polyolefin-based porous membrane production method of the present invention (Examples 1 to 20), the toughness of the ion exchange membranes obtained was evaluated as △ 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 of the obtained ion exchange membranes was evaluated as x, 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-based elastomer, and therefore, as shown in Table 2, the toughness of the obtained ion exchange membrane was evaluated as ×, which was poor. In the method of 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, as shown in Table 1, the obtained membrane had a porosity of 0% and no pores were formed, and was a poor porous membrane. Since no pores were formed, the ion exchange resin could not be filled inside, and as shown in Table 2, the membrane resistance of the obtained ion exchange membrane was extremely high, the ion exchange capacity could not be measured, and it was a poor ion exchange membrane. [Explanation of symbols]

[0128] 1. Anion exchange membrane 2 Anode 3. Cathode 4 Gas diffusion layer 5 Anode chamber 6 Water supply inlet 7 Oxygen outlet 8 Cathode Chamber 9 Hydrogen outlet

Claims

1. An ion exchange membrane comprising a porous support containing a polyolefin resin and an ion exchange resin which is a hydrocarbon polymer filled into the pores of the porous support, the ion exchange membrane having an elastic modulus of 500 MPa or more in each of the MD direction and the TD direction, and a tear strength of 3.5 N or more in each of the MD direction and the TD direction.

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 containing a polyolefin resin and an ion exchange resin which is a hydrocarbon polymer filled in the pores of the porous support, the ion exchange membrane having an elastic modulus of 500 MPa or more in each of the MD direction and the TD direction, and a toughness of 0.25 J or more in each of the MD direction and the TD direction.

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

9. The ion exchange membrane according to claim 1 or 3, wherein the porous support is a polyolefin-based porous membrane in which, when the stress at strain 0.4 is F40 (MPa) and the stress at strain 0.3 is F30 on the horizontal axis of a stress-strain curve obtained in a tensile test, (F40-F30) in each of the MD and TD directions is 2.0 MPa or more.

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

11. The ion exchange membrane according to claim 1 or 3, wherein the porous support is a polyolefin-based porous membrane obtained by a production method including the following steps (a) to (d): (a) a step of melt-kneading a resin composition containing a polyolefin resin and an olefin-based elastomer, the resin composition having a content of the olefin-based elastomer of 5% by mass or more and 40% by mass or less, based on the resin composition, and a content of the polyolefin resin of 60% by mass or more, based on the resin composition, with a plasticizer at a temperature of (melting point of the polyolefin resin + 5°C) to (melting point of the polyolefin resin + 70°C) to obtain a gel-like solution; (b) cooling the gel-like solution at 0° C. to 25° C. until both sides are below the crystallization end temperature to obtain a gel-like sheet; (c) biaxially stretching the gel-like sheet at a temperature between (the crystal dispersion temperature Tcd of the polyolefin resin) and (the melting point of the polyolefin resin - 5°C) with an areal stretching ratio in MD and TD of 10 times or more and 35 times or less 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.

12. The ion exchange membrane according to claim 1 or 3, wherein the polyolefin resin comprises a polypropylene resin.

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

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

15. A water electrolysis device comprising the membrane electrode assembly according to claim 13.

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