WO2023140330A1

WO2023140330A1 - Porous membrane, ion exchange membrane, water electrolysis device, and production method for porous membrane

Info

Publication number: WO2023140330A1
Application number: PCT/JP2023/001560
Authority: WO
Inventors: 祐三嶋; 武範磯村; まさみ菅田
Original assignee: 株式会社トクヤマ
Priority date: 2022-01-20
Filing date: 2023-01-19
Publication date: 2023-07-27

Abstract

Provided are: a porous membrane that has excellent durability, and is suitable as a support for an ion exchange resin; and a porous membrane and an anion exchange membrane that are capable of inhibiting a change in hydrogen gas permeability over time during repetitive use thereof in water electrolysis.　The porous membrane contains a polyolefin resin, and has a porosity of 20-80% and a BET specific surface area of at least 40 m²/g as calculated by a nitrogen adsorption method. This ion exchange membrane is obtained by filling pores of the porous membrane with an ion exchange resin.

Description

Porous membrane, ion exchange membrane, water electrolysis device, and method for producing porous membrane

The present invention relates to a porous membrane, an ion exchange membrane, a water electrolysis device, and a method for producing a porous membrane.

　Porous membranes are used in a variety of applications. For example, it is used in various applications such as filtration membranes, air-permeable films, separators for capacitors, separators for lithium ion batteries and the like, and supports (base materials) for fuel cells.

Among the above applications, an ion-exchange membrane in which a porous membrane is used as a support and the pores (voids) of the porous membrane are filled with an ion-exchange resin can be used as a membrane for a solid fuel cell, or a membrane for water electrolysis or alkaline water electrolysis depending on the ion-exchange resin to be filled.

As described above, porous membranes are used in a wide range of applications, from filtration and separation purposes to separator applications and even fuel cell applications.

　As a porous membrane with high heat resistance and durability, development is being carried out to use an olefin resin with a high melting point as a porous membrane. For example, development of a porous film made of polymethylpentene resin having a melting point of 200° C. or higher is underway (see Patent Document 1). The porous membrane described in Patent Document 1 has excellent durability and can be suitably used as a separator for capacitors. Since the porous membrane made of this polymethylpentene resin is excellent in durability and heat resistance, it is thought that it can be used for applications other than separators for capacitors.

JP 2004-224915 A

As mentioned above, porous membranes are used in various applications. Among them, the following applications are attracting attention. In recent years, it is strongly desired to use hydrogen as an alternative to petroleum energy. Therefore, as a method for producing hydrogen, development of water electrolysis technology is being actively studied. Above all, the water electrolysis technology using an anion exchange membrane has the following merits.

In water electrolysis technology using anion exchange membranes, the reaction field becomes alkaline. Therefore, in the water electrolysis technology, inexpensive non-precious metal catalysts can be used. In addition, inexpensive metals such as stainless steel can be used for the members to be used. In such technology, the specifications are such that hydrogen is taken out while consuming water on the cathode side.

The anion exchange membrane used in the water electrolysis technology may use a porous membrane as a support because of its good handling. Specifically, at least the pores (voids) of the porous membrane are filled with an anion exchange resin to form an anion exchange membrane.

It is assumed that the porous membrane made of polymethylpentene resin described in Patent Document 1 can be sufficiently used as a support for such an ion-exchange resin (a support for forming an ion-exchange membrane by filling the pores of the ion-exchange resin with the ion-exchange resin).

However, according to the studies of the present inventors, it was found that there is room for improvement in the following points when the conventional porous membrane made of polymethylpentene resin is simply used as an anion exchange membrane as a support for an ion exchange resin, particularly as a support for an anion exchange resin. In other words, when an anion exchange membrane made of polymethylpentene resin with good durability and heat resistance and using a conventional porous membrane as a support is used for applications such as water electrolysis, it was found that there is room for improvement during repeated use. Specifically, during repeated use, the gas permeability (specifically, the hydrogen permeability) tends to increase, and the hydrogen extraction efficiency on the cathode side tends to decrease, leaving room for improvement.

Therefore, an object of the present invention is to provide a porous membrane with excellent durability. Another object of the present invention is to provide a porous membrane that can be used repeatedly as a support for ion-exchange resins, particularly as a support for anion-exchange resins, even when used in techniques such as water electrolysis.

The present inventors have diligently studied in order to solve the above problems. As a result, the present inventors have found that a porous membrane made of a polyolefin resin having a specific porosity and having pores with a large BET specific surface area, that is, having relatively small pores can solve the above problems, and have completed the present invention below.

[1] A porous film containing a polyolefin resin, having a BET specific surface area of 40 m ² /g or more as measured by a nitrogen adsorption method, and a porosity of 20% or more and 80% or less.
[2] The porous membrane according to [1], wherein the pore diameter having the maximum peak is present at 100 nm or less in the pore size distribution curve obtained by the nitrogen adsorption method.

[3] The porous membrane according to [1] or [2], wherein the total pore volume of pores having a diameter of 100 nm or less accounts for 80% or more of the total pore volume in the pore size distribution curve obtained by the nitrogen adsorption method.
[4] The porous membrane according to any one of [1] to [3], which has an average pore diameter of 80 nm or less as determined by a nitrogen adsorption method.

[5] The porous membrane according to any one of [1] to [4], wherein the polyolefin resin contains at least one resin selected from the group consisting of polymethylpentene resin and polypropylene resin.
[6] The porous membrane according to any one of [1] to [5], which has a thickness of 10 to 200 μm.

[7] The porous membrane according to [5], wherein the polymethylpentene resin accounts for 95% by mass or more in the porous membrane.
[8] An ion-exchange membrane comprising the porous membrane according to any one of [1] to [7] and an ion-exchange resin filled in the pores of the porous membrane.

[9] The ion exchange membrane according to [8], wherein the ion exchange resin is an anion exchange resin.
[10] A water electrolysis device comprising the ion exchange membrane according to [8] or [9].

[11] A method for producing a porous membrane comprising, in this order, the steps of heating a composition containing a polyolefin resin and a plasticizer to obtain a sheet-like first molded body, stretching the first molded body at a temperature lower than the melting point of the polyolefin resin in the range of 70° C. or more and 178° C. or less to obtain a second molded body, and removing the plasticizer from the second molded body.
[12] The method for producing a porous membrane according to [11], wherein the step of obtaining the second molded body is a step of biaxially stretching the first molded body at a longitudinal draw ratio of 2 or more and a lateral draw ratio of 2 or more to obtain the second molded body.

According to the present invention, a porous membrane with excellent durability can be obtained. In addition, the porous membrane of the present invention can be suitably used as an ion exchange membrane in which the pores are filled with an ion exchange resin. In particular, since it has specially controlled pores, when it is used as a support for ion-exchange resins in electrolysis applications, it can be used repeatedly. Among them, when an anion exchange resin membrane (a porous membrane in which pores are filled with an anion exchange resin) is used for water electrolysis, the gas leakage rate (hydrogen permeability) can be suppressed even when used repeatedly.

An integral curve (ΣV vs. D) of the pore volume due to nitrogen adsorption of the porous membrane obtained in Example 2. Pore size distribution curve (dV/dlogD) by nitrogen adsorption of the porous membrane obtained in Example 2. Schematic diagram of a water electrolysis device using an anion exchange membrane in which the pores of the porous membrane are filled with an anion exchange resin.

The porous membrane of the present invention contains a polyolefin resin, has a BET specific surface area of 40 m ² /g or more as measured by a nitrogen adsorption method, and has a porosity of 20% or more and 80% or less. Since the BET specific surface area is relatively large and voids are present, the porous membrane of the present invention has many pores with small pore diameters. Therefore, it is considered that particularly excellent effects are exhibited when the ion exchange resin is filled. Although it is only an estimate, it can be considered as follows.

In other words, the porous membrane of the present invention has many relatively small pores (pores). Therefore, when the ion-exchange resin is filled in the pores (voids), it is considered that the expansion and contraction of the ion-exchange resin can be easily followed. Then, it is considered that gaps are less likely to occur between the pores and the ion exchange resin. As a result, it is considered that the increase in gas permeability can be suppressed during repeated use.

Next, an example of filling an anion exchange resin and using the resulting anion exchange membrane for water electrolysis will be described. In water electrolysis using an anion exchange membrane, the structure is such that hydrogen is extracted while consuming water on the cathode side. The anion exchange resin packed in the porous membrane is usually easily swollen with water. Therefore, it is considered that when sufficient water is supplied to the membrane, the anion exchange resin swells and sufficiently adheres to the pores of the porous membrane. However, during repeated use, if the amount of water becomes insufficient or if the resin becomes dry, the swollen anion exchange resin will shrink. At this time, if the pores (diameter) of the porous membrane are relatively large, it is considered that the shrinkage of the anion exchange resin cannot be followed. As a result, it is presumed that separation occurs at the interface between the anion exchange resin and the membrane, increasing the gas permeability. In particular, in water electrolysis using an anion exchange membrane, hydrogen is taken out of the system. Therefore, it is preferable that the gas permeability of the anion exchange membrane does not change (even if it changes, it is suppressed) even after repeated use. Since the porous membrane of the present invention has a large number of relatively small pores, it can follow the expansion and contraction of the anion exchange resin. And it is thought that it can suppress that a gas permeability (hydrogen permeability) becomes high. Therefore, the porous membrane of the present invention can be suitably used as a support for ion-exchange resins, particularly as a support for anion-exchange resins used in water electrolysis.

The porous membrane of the present invention will be described in detail below.

In this specification, unless otherwise specified, the notation "x to y" using numerical values x and y means "x or more and y or less". In such notation, when only the numerical value y is given a unit, the unit is also applied to the numerical value x.

<Olefin resin>
The porous membrane of the present invention contains an olefinic resin. Moreover, the porous membrane of the present invention preferably contains an olefinic resin as a main component. Furthermore, it is preferable that the porous membrane consists only of an olefin resin.
Here, "containing as a main component" means that the polyolefin resin is preferably 50% by mass, more preferably 70% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 99% by mass or more, based on the entire porous membrane (100% by mass).
Olefin resins are excellent in mechanical strength, chemical stability, and chemical resistance. Specific resins include homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl-1-heptene. These olefinic resins can be used without any limitation on the commercially available ones. A single species can be used, or a mixture of multiple species can be used. Among these, from the viewpoint of high heat resistance, polypropylene resins selected from propylene homopolymers and copolymers of propylene and ethylene containing propylene as a main component, or poly4-methylpentene-1 resins, and polymethylpentene resins selected from poly3-methylpentane-1 resins are preferable.
From the viewpoint of heat resistance, the porous membrane preferably contains polymethylpentene resin as the polyolefin resin. The proportion of the polyolefin resin in the porous membrane can be measured by Fourier transform infrared spectroscopy (FT-IR).

Although the melting point of the polyolefin-based resin is not particularly limited, it is preferably within the following ranges in consideration of the heat resistance of the resulting porous membrane. Specifically, the temperature is preferably 100° C. or higher and 250° C. or lower, more preferably 110° C. or higher and 250° C. or lower, even more preferably 140° C. or higher and 250° C. or lower, and particularly preferably 180° C. or higher and 250° C. or lower.

If the melting point of the polyolefin resin is one, the melting point of the resin itself should be checked. When a mixture of multiple types of resins is used, the melting point of the polyolefin resin determined by a measurement method according to JIS K 7121 using a differential scanning calorimeter (DSC) may be adopted. When the melting point of the porous membrane itself is analyzed, the measurement should be performed after the porous membrane is once dissolved in order to eliminate the influence of orientation and the like. The melting point referred to in the present invention refers to the peak top temperature of the heat of fusion measured under the above conditions. When multiple types of resins are used and multiple peaks are present, the melting point of the crystalline polyolefin-based resin that is the main component (the one with the highest compounding ratio) may be used as a reference.

<Characteristics of porous membrane>
The porous membrane of the present invention satisfies the following physical properties. The BET specific surface area determined by the nitrogen adsorption method is 40 m ² /g or more, and the porosity is 20% or more and 80% or less. The measurement was performed by the method described in Examples.

When the BET specific surface area is 40 m ² /g or more, a large number of small pores are present, and excellent effects are exhibited. In particular, even when it is used as a support for an ion-exchange resin and is repeatedly used for water electrolysis, an increase in gas permeability can be suppressed. In order to exhibit this effect more and consider industrial productivity of the porous membrane, use as an ion-exchange membrane (use as a support), etc., the BET specific surface area is preferably within the following range. Specifically, the BET specific surface area is preferably 40 to 200 m ² /g, more preferably 60 to 150 m ² /g, even more preferably 60 to 90 m ² /g. The BET specific surface area is a value measured by the method described in the examples below.

In the present invention, the porosity of the porous membrane is 20% or more and 80% or less. If it is less than 20%, the amount of resin that fills the voids is reduced, and the ionic conductivity is deteriorated when used for water electrolysis, which is not preferable. If it exceeds 80%, the volume change due to expansion/contraction of the ion-exchange resin is large, and the shape of the anion-exchange membrane cannot be maintained, which is not preferable. Considering the ionic conductivity, the mechanical strength of the anion exchange membrane, etc., the porosity is preferably 20% or more and 70% or less, more preferably 20% or more and 50% or less, even more preferably 20% or more and 40% or less, and particularly preferably 20% or more and 35% or less. In particular, the porosity is preferably 20 to 35% in order to reduce the rate of change in hydrogen permeability (hydrogen permeability due to humidity cycles) repeatedly measured by changing the humidity while maintaining the ion conductivity and mechanical strength of the anion exchange membrane. In addition, this porosity is the value measured by the method described in the following examples.

In the present invention, other physical properties are not particularly limited as long as the porous membrane has a BET specific surface area of 40 m ² /g or more and a porosity of 20% or more and 80% or less. However, in order for the porous membrane of the present invention to exhibit particularly excellent effects, it preferably satisfies the following physical properties.

That is, in the porous membrane, it is preferable that the pore diameter having the maximum peak exists at 100 nm or less in the pore size distribution curve obtained by the nitrogen adsorption method. In this case, since it has relatively small pores, an excellent effect is exhibited. In particular, when used as a support for an ion-exchange membrane, the pores are more likely to follow shrinkage, swelling, etc. of the ion-exchange resin during repeated use, and it is thought that detachment of the ion-exchange resin from the pores can be reduced. And it is thought that diffusion of gas can be suppressed. Therefore, considering the industrial productivity of the porous membrane itself, the maximum peak of the pore diameter is preferably 1 nm or more and 100 nm or less, more preferably 10 nm or more and 90 nm or less, further preferably 20 nm or more and 90 nm or less, and particularly preferably 20 nm or more and 75 nm or less. As for the pore diameter having this maximum peak, the pore volume (V) and the pore diameter (D) are determined by the BJH method described below. Then, the value (dV/dlogD) obtained by differentiating the pore volume (V) with the logarithm (logD) of the pore diameter (D) is plotted against the pore diameter (D) (pore diameter distribution curve). It can be obtained from (see FIG. 2).

In addition, it is more preferable that the pores in the porous membrane satisfy the following requirements. Specifically, the total ratio of the pore volume of pores having a pore diameter of 100 nm or less is preferably 80% or more of the total pore volume. Satisfying such requirements means that there are many voids and small pores. Therefore, especially when used as a support for an ion-exchange membrane, it is thought that diffusion of gas during repeated use can be suppressed. In particular, it is possible to reduce the change in hydrogen permeability during repeated use with changing humidity. Therefore, considering the above effect and the mechanical properties of the porous membrane itself, the total pore volume ratio of pores having a pore diameter of 100 nm or less is more preferably 82% or more and 100% or less, more preferably 85% or more and 100% or less, and particularly preferably 90% or more and 100% or less. In addition, this total ratio can be obtained from the integral curve of the pore volume (see FIG. 1). Furthermore, the total percentage may be 80% or more, or 95% or more. The total percentage may be 100% or less, 99% or less, or 98% or less.

Furthermore, in order for the porous membrane to exhibit more excellent effects, it is preferable that the average pore diameter is 80 nm or less. This average pore diameter is more preferably 5 nm or more and 50 nm or less, further preferably 10 nm or more and 40 nm or less, in consideration of excellent effects and mechanical properties of the porous membrane itself. The average pore diameter may be 15 nm or more and may be 30 nm or less.

In the porous membrane of the present invention, the pore diameter having the maximum peak and the total ratio of the pore volume of the pores preferably satisfy the above ranges. If these requirements are satisfied, pore diameter peaks (protrusions on the graph) in the pore diameter distribution curve may exist other than the maximum peak. In this case, peaks other than the maximum peak are preferably present at pore diameters of 100 nm or less. (See Figure 2).

The pores as described above can be achieved by adjusting the manufacturing conditions of the porous membrane, which will be detailed below. Specifically, the type and molecular weight of the polyolefin resin to be used, and when a plasticizer is used, the amount and type of the plasticizer, film forming conditions for the film, specifically, magnification during stretching, temperature, etc. may be adjusted.

In the present invention, the film thickness of the porous membrane is not particularly limited. However, in order to exhibit suitable performance as a support for an ion-exchange membrane, the film thickness is preferably within the following range. Specifically, the film thickness is preferably 10 to 200 μm. Also, from the viewpoint of obtaining a film with a smaller film resistance, the thickness is preferably 15 to 170 μm. In particular, when used as a support for an ion exchange resin, a sufficient thickness is required in order to sufficiently secure the ion exchange capacity and the like. Therefore, considering the balance between strength and mechanical properties, the thickness of the porous membrane is more preferably 20 to 150 μm, particularly preferably 30 to 100 μm.

In addition, the porous membrane of the present invention preferably has the pores and the following mechanical strength. Specifically, the tensile modulus in the machine direction (machine direction (flow direction) MD in the case of extrusion molding) and the transverse direction (the width direction (TD) in the case of extrusion molding) is preferably 200 MPa or more, more preferably 300 MPa or more, and even more preferably 400 MPa or more. It is considered that the higher the tensile modulus, the better. However, considering the industrial production of the porous membrane, it is preferably 1500 MPa or less, more preferably 1400 MPa. In addition, the lower limit of the tensile strength in both MD and TD is preferably 5 MPa or more, more preferably 8 MPa or more, and the upper limit is not particularly limited, but is preferably 100 MPa or less, more preferably 80 MPa or less, and still more preferably 70 MPa or less. In addition, the lower limit of the elongation at break of the porous membrane is preferably 5% or more, more preferably 10% or more, and the upper limit is not particularly limited, but is preferably 400% or less, more preferably 150% or less.

As with pores, these mechanical properties can be adjusted by adjusting the materials used, the mixing ratio of each material, and the film-forming conditions.

<Method for producing porous membrane>
In the present invention, the porous membrane can be produced by a known method. Specifically, it is preferably produced by performing the following steps (i) to (iii).

(i) Step; First, an olefin resin and a plasticizer are kneaded to produce a composition containing them.

(ii) step; forming the obtained composition into a sheet by a known method.

(iii) Step; Remove the plasticizer from the sheet.

In the (i) step, the composition is produced by a known method. Specifically, the olefin resin and the plasticizer may be melt-kneaded at a temperature equal to or higher than the melting points of the olefin resin and the plasticizer. If the kneading temperature is too high, the resin may be deteriorated. Therefore, the kneading temperature can be, for example, in the range of +10° C. to +50° C. of the melting point of the olefin resin. The amount of the plasticizer to be used may be appropriately determined according to the properties of the intended porous membrane, but it is preferable to use 50 to 200 parts by mass, more preferably 60 to 140 parts by mass, more preferably 70 to 130 parts by mass, and particularly preferably 80 to 120 parts by mass, based on 100 parts by mass of the olefin resin. The composition may also contain a crystal nucleating agent and the like.

In the present invention, when using a plasticizer, the plasticizer is not particularly limited as long as it can be sufficiently mixed with the polyolefin resin described above. Specific examples include aliphatic carboxylic acid esters such as methyl stearate and butyl stearate, aromatic carboxylic acid esters such as diisononyl phthalate and bis-2-ethylhexyl phthalate, and aliphatic hydrocarbons such as liquid paraffin. Among them, aromatic carboxylic acid esters are preferred. These can be used alone or in combination of multiple types.

In the (ii) step, the composition obtained in the (i) step is formed into a sheet by a known method. The method of forming a sheet is not particularly limited, but film forming using an extruder equipped with a T-die, film forming using an inflation machine, sheet forming using press molding, or the like can be employed.

In the step (iii), a film containing a plasticizer is impregnated in a solvent that is a poor solvent for the olefin resin and a good solvent for the plasticizer, and the plasticizer is removed to form a porous film. It is also possible to prepare an unstretched sheet in step (ii), remove the plasticizer in step (iii), and then biaxially stretch the sheet.

After the (iv) (iii) step, the obtained porous membrane can be heat-treated (the porous membrane is left under a certain temperature range).

In the present invention, the method for producing the porous membrane is not particularly limited. Specifically, the porous membrane of the present invention that satisfies specific requirements may be produced by adjusting the types of materials to be used, their compounding ratios, their film-forming methods, and the like. That is, for example, when trying to produce a porous film having the same characteristics from sheets obtained using different film-forming machines, the characteristics (molecular weight, molecular weight distribution, etc.) of the olefin resin used, the blending amount of the plasticizer, the draw ratio, the draw temperature, etc. may be adjusted. Among such differences in conditions, it is preferable to stretch the sheet at a relatively low temperature in order to produce a porous membrane with a relatively small pore diameter, which is one of the characteristic features of the porous membrane of the present invention. In this case, a plasticizer that is highly compatible with the olefin resin to be used is selected, and further, when stretching is performed, it is preferable to perform the step (ii). Basically, the porous membrane can be produced by the above method. Next, an example of using polymethylpentene resin, particularly 4-methylpentene-1 resin, which is a suitable olefinic resin, will be described.

Among them, when forming a sheet in step (ii), it is preferable to produce a sheet containing a plasticizer, stretch the obtained sheet to obtain a stretched film, and finally remove the plasticizer in step (iii). In this case, the stretching conditions in step (ii) are preferably such that the temperature during stretching (the ambient temperature during stretching of the sheet) is lower than the melting point of the olefin resin by 70°C or more. The stretching temperature is preferably 90° C. or more lower than the melting point of the olefin resin, further preferably 110° C. or more, and most preferably 140° C. or more.
The draw ratio is preferably 1.1 to 5 times in the longitudinal direction and 1.1 to 5 times in the transverse direction, more preferably 2 to 5 times in the longitudinal direction and 2 to 5 times in the transverse direction. When a sheet is formed by press molding, there is no vertical or horizontal direction, but it is preferable to stretch 1.1 to 5 times, preferably 2 to 5 times in a uniaxial direction (considered as stretching in the longitudinal direction), and 1.1 to 5 times, preferably 2 to 5 times in a direction perpendicular to the uniaxial direction (considered as stretching in the horizontal direction). It is considered that the stretching in the step (ii) can suppress the decrease in the BET specific surface area, that is, the expansion of the pore diameter can be suppressed. As a result, a porous membrane satisfying the requirements of the present invention in terms of BET specific surface area and porosity can be easily produced. In addition, when stretching a polyolefin resin, it is common to stretch in a temperature range from the crystal dispersion temperature to the melting point, but by stretching at a lower temperature, the orientation of the resin molecular chain can be controlled and the mechanical properties can be improved. That is, in order to produce a porous membrane having a large number of relatively small pores, it is preferable to stretch the plasticizer-containing film at a relatively low stretching temperature. On the other hand, if the stretching temperature is excessively low, the sheet may have low flexibility and may not be sufficiently stretched. The stretching temperature is preferably no lower than 178°C below the melting point of the olefin resin. In other words, it is preferable to set the stretching temperature to “the melting point of the olefin resin −178° C.” or higher. Further, it is more preferable that the stretching temperature is set to “the melting point of the olefinic resin −168° C.” or higher.

<Preferred production example when using 4-methylpentene-1 resin>
In the step (i), it is preferable to use a composition containing 50 to 200 parts by mass of a plasticizer (preferably an aromatic carboxylic acid ester, specifically diisononyl phthalate, etc.) per 100 parts by mass of a 4-methylpentene-1 resin (for example, a resin having a melting point of 239°C). In order to stretch at a relatively low temperature and easily produce a porous membrane (a porous membrane having relatively small pores) that satisfies the requirements of the present invention, it is more preferable to use a composition containing 60 to 140 parts by mass of a plasticizer, more preferably to use a composition containing 70 to 130 parts by mass, and particularly preferably to use a composition containing 80 to 120 parts by mass, based on 100 parts by mass of 4-methylpentene-1 resin. The composition is preferably melt-kneaded at a temperature equal to or higher than the melting point of the 4-methylpentene-1 resin to obtain a composition in which the plasticizer is uniformly dispersed. A crystal nucleating agent or the like may be added to this composition, if necessary.

In the (ii) step, first, the composition obtained in the (i) step is formed into a sheet (to form a membrane/film) by a known method. The thickness of the sheet is not particularly limited, but a sheet with a thickness of 30 to 500 μm is preferable. Although the physical properties of this sheet are not particularly limited, it is preferable to adjust the diameter of the spherulites to 5 μm or less. The above adjustment can be achieved by using a crystal nucleating agent or by adjusting film forming conditions. For example, in the case of press molding, it is preferred that the composition melted by heating to 220 to 250° C. is pressed at a pressure of 1 to 3 MPa and cooled at a temperature of 0 to 25° C. for 1 to 5 minutes.

The obtained sheet is preferably biaxially stretched within the above temperature range. It is preferable to draw in an atmosphere at a temperature lower than the melting point of the olefin resin by 70°C or more, and when 4-methylpentene-1 resin is used, it is preferably in an atmosphere at a temperature lower than the melting point of the olefin resin by 90°C or more, preferably 110°C or more. The lower limit of the temperature during stretching is preferably 61° C. or higher, more preferably 71° C. or higher, and even more preferably 80° C. or higher.
In addition, the draw ratio may be appropriately determined so that the BET specific surface area and porosity of the obtained porous membrane satisfy the requirements of the present invention. In particular, the press-molded material is preferably stretched under the above conditions.

When 4-methylpentene-1 resin is used as the olefin resin, the stretching temperature is preferably 169°C or lower, more preferably 149°C or lower, and even more preferably 129°C or lower. A low stretching temperature tends to increase the mechanical strength of the porous membrane. On the other hand, if the stretching temperature is too low, sufficient stretching may not be performed, and the molded body may break during stretching. The stretching temperature is preferably 61° C. or higher, more preferably 71° C. or higher, still more preferably 80° C. or higher, particularly preferably 90° C. or higher, and most preferably 100° C. or higher.

The obtained sheet is preferably biaxially stretched within the above temperature range. In particular, it is preferable to biaxially stretch the film in a temperature range of 80 to 120°C. In addition, the draw ratio may be appropriately determined so that the BET specific surface area and porosity of the obtained porous membrane satisfy the requirements of the present invention. In particular, the press-molded material is preferably stretched under the above conditions.

The stretching method may be any of biaxial stretching (simultaneous biaxial stretching, sequential biaxial stretching), but in order to create more fine pores, biaxial stretching at the above stretching ratio is preferred.

In the present invention, it is preferable to stretch under the above conditions before removing the plasticizer in the following step (iii). It is considered that pores having a small pore size can be efficiently formed because the film is stretched before the plasticizer is removed. That is, by stretching under the above conditions before removing the plasticizer, a porous film having a BET specific surface area of 40 m ² /g or more and a porosity of 20% or more and 80% or less as determined by the nitrogen adsorption method can be effectively produced.

In step (iii), the plasticizer is removed from the sheet obtained in step (ii). The resulting membrane is contacted with a solvent, preferably impregnated with the solvent, to remove the plasticizer. A solvent that is a poor solvent for the 4-methylpentene-1 resin and a good solvent for the plasticizer is not particularly limited, and known solvents such as those described in Patent Document 1 can be used. Preferred solvents among them are
Hydrocarbons such as n-hexane and cyclohexane,
Fluorocarbons in which some or all of the hydrogens in hydrocarbons are substituted with fluorine,
alcohols such as ethanol and isopropanol,
Examples include ketones such as acetone and 2-butanone.

The temperature at which the solvent and the sheet are brought into contact is preferably 20 to 50°C.

After removing the plasticizer, a heat treatment can be performed to stabilize the porous membrane. The temperature is preferably higher than the crystal dispersion temperature and lower than the melting point. Below the crystal dispersion temperature, crystal growth does not progress and does not lead to stabilization. Moreover, at high temperatures above the melting point, the pores are closed due to melting of the resin. However, in order to achieve stabilization, it is desirable to perform heat treatment at a temperature as high as possible.
As described above, the porous membrane is obtained by removing the plasticizer from the molded article formed in the form of a sheet to make the cast sheet porous. The porous membrane can be a porous cast sheet. This porous membrane is superior in planar smoothness as compared with a porous membrane using a nonwoven fabric or the like obtained by a spinning method. Therefore, in a membrane-electrode assembly in which an electrode catalyst is laminated on a porous membrane, which will be described later, the contact with the electrode catalyst is excellent.

Because the porous membrane of the present invention has excellent effects and porosity, it can be suitably used for conventional applications. Among these, it can be used particularly preferably as a support for ion exchange resins. Next, the use of the ion exchange resin as a support will be described.

<Support for ion exchange resin>
The porous membrane obtained by the above method can be suitably used as a support for ion exchange resins. The supported ion-exchange resin (type of ion-exchange group) may be appropriately determined according to the intended use. The ion exchange resin may be either an anion exchange resin or a cation exchange resin. Among them, when it is used as a support for an anion exchange resin, it is preferable because it can be used for water electrolysis for producing hydrogen and anion exchange membrane type water electrolysis.

The method for supporting the ion-exchange resin is not particularly limited, but the following four methods can be mentioned.

(1) A polymerizable composition containing an ion-exchange group-containing monomer (a solution of the polymerizable composition as necessary) is brought into contact with a porous membrane to fill the pores of the porous membrane with the polymerizable composition. After that, the polymerizable composition filled in the pores is polymerized. At this time, a polymerizable composition comprising only ion-exchange group-containing monomers can be used so as to obtain the desired ion-exchange membrane. Polymerizable compositions containing ion-exchange group-containing monomers and optionally other monomers can also be used. Other monomers may include crosslinkers that are multifunctional such as divinylbenzene.

(2) A polymerizable composition containing a monomer capable of introducing an ion-exchange group (a solution of the polymerizable composition if necessary) is brought into contact with the porous membrane, and the pores of the porous membrane are filled with the polymerizable composition. The polymerizable composition is then polymerized. Thereafter, ion exchange groups are introduced into the resulting precursor polymer obtained by polymerizing a monomer into which ion exchange groups can be introduced.

A more detailed explanation is as follows. First, a polymerizable composition containing a polymerizable monomer having a halogenoalkyl group (e.g., chloromethylstyrene, bromomethylstyrene, iodomethylstyrene, chloroethylstyrene, bromoethylstyrene, bromobutylstyrene, etc.), optionally a crosslinkable polymerizable monomer (e.g., divinylbenzene, divinylbiphenyl, divinylnaphthalene, etc.), and an effective amount of a polymerization initiator (e.g., an organic peroxide such as benzoyl peroxide) is brought into contact with the porous membrane containing the polyolefin resin. Then, after filling the pores of the porous membrane with the polymerizable composition, the composition is polymerized and cured to prepare an ion-exchange membrane precursor filled with a resin having a halogenoalkyl group. Then, an ion-exchange membrane is formed by converting the halogenoalkyl groups into ion-exchange groups.

In this method, a polymerizable monomer having a halogenoalkyl group was exemplified, but for example, a precursor may be prepared using styrene or the like before the halogenoalkyl group is introduced, and the halogenoalkyl group may be introduced into it. After introducing the halogenoalkyl group, the same operations as described above may be carried out.

(3) polymerizing a polymerizable composition containing an ion-exchange group-containing monomer; An ion-exchange membrane in which at least the pores are filled with the ion-exchange resin (the polymer) is obtained by contacting the solution of the ion-exchange group-containing polymer containing the obtained polymer with the porous membrane. Other monomers containing a cross-linking agent can be added to the polymerizable composition, but if the degree of cross-linking is too high, the solubility of the ion-exchange group-containing polymer tends to decrease, so caution is required.

(4) polymerizing a polymerizable composition containing a monomer capable of introducing an ion exchange group; A solution of the obtained polymer is brought into contact with the porous membrane, and the pores of the porous membrane are filled with the polymer (precursor polymer obtained by polymerizing a monomer capable of introducing an ion-exchange group). After that, ion exchange groups are introduced into the precursor polymer. Also in this method, other monomers containing a cross-linking agent can be added to the polymerizable composition, but if the degree of cross-linking is too high, the solubility of the precursor polymer tends to decrease, so caution is required.

Among the above methods, it is preferable to adopt the method (1) or (2) in consideration of the productivity, the amount of ion exchange groups introduced, the insolubility of the ion exchange resin, and the like. In other words, it is preferable to adopt a method of once impregnating a porous membrane with a monomer composition of polymerizable monomers, polymerizing it, and introducing ion-exchange groups as necessary. Among these methods, the solubility in water of the ion exchange resin is also a factor, but from the viewpoint of productivity, it is most preferable to adopt the method (2).

The ion-exchange resin to be introduced into the pores of the support is not particularly limited, but considering compatibility with the porous membrane, adhesion, etc., the resin portion excluding the ion-exchange groups is preferably composed of a crosslinked hydrocarbon-based polymer. Here, the hydrocarbon-based polymer refers to a polymer in which substantially no carbon-fluorine bonds are included and most of the bonds in the main chain and side chains constituting the polymer are composed of carbon-carbon bonds. This hydrocarbon-based polymer may contain a small amount of other atoms such as oxygen, nitrogen, silicon, sulfur, boron and phosphorus between carbon-carbon bonds due to ether bonds, ester bonds, amide bonds, siloxane bonds and the like. In addition, all the atoms bonded to the main chain and side chains do not need to be hydrogen atoms, and in small amounts may be substituted with other atoms such as chlorine, bromine, fluorine, and iodine, or substituents containing other atoms. 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 ion exchange groups.

The anion-exchange group in the anion-exchange ion-exchange membrane (the anion-exchange group possessed by the anion-exchange resin filled in the pores 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 and availability.

When the anion exchange resin membrane is produced by the above production method, the counter ion of the anion exchange group is often obtained as a halide ion. In this case, the anion-exchange membrane having halide ions as counter ions is preferably immersed in an excessive amount of alkaline aqueous solution to exchange the counter ions in OH ⁻ type or HCO ₃ ⁻ type ion exchange. The ion exchange method is not particularly limited, and for example, in the case of ion exchange to the OH ⁻ type, an anion exchange type ion exchange membrane having the halogen ion as a counter ion is immersed in an aqueous solution of sodium hydroxide or potassium hydroxide for 2 to 10 hours. Similarly, in the case of ion-exchanging to HCO ₃ ^- type, it may be performed by immersing in an aqueous solution of sodium hydrogencarbonate or potassium hydrogencarbonate.

The cation exchange group in the cation exchange type ion exchange membrane (the cation exchange group possessed by the cation exchange resin filled in the pores of the porous membrane) is not particularly limited, but considering the ease of production, availability, etc., the sulfonic acid type or carboxylic acid type is preferred.

<Water electrolysis using anion exchange membrane>
The ion exchange membrane of the present invention can be produced by the above method. Among them, when it is made into an anion exchange type ion exchange membrane, it can be used as a membrane for water electrolysis capable of producing hydrogen. The configuration of the water electrolysis device is as shown in FIG. The water electrolysis device may be a water electrolysis device using water or a low-concentration alkaline aqueous solution, or an alkaline water electrolysis device using a high-concentration alkaline aqueous solution of 5% by mass or more.

Specifically, a catalyst layer (anode 2 and cathode 3) in which a catalyst is dispersed in an anion exchange resin is arranged on the anion exchange membrane 1, and a gas diffusion layer 4 is provided on each. A water supply port 6 for supplying water and an oxygen discharge port 7 for discharging oxygen are provided in the anode chamber 5 on the anode 2 side. Furthermore, the cathode chamber 8 on the cathode 3 side is provided with a hydrogen discharge port 9 for discharging hydrogen. Anion exchange membrane 1 , anode 2 , cathode 3 , gas diffusion layer 4 , anode chamber 5 and cathode chamber 8 are housed in, for example, housing 10 . With the configuration as described above, hydrogen can be produced by water electrolysis. Such a water electrolysis cell comprises, for example, a housing 10 , an anion exchange membrane 1 housed within the housing 10 , and an anode chamber 5 and a cathode chamber 8 separated by the anion exchange membrane 1 .

In the water electrolysis cell as described above, the anion exchange membrane functions as a solid electrolyte membrane that transfers ions between the anode and cathode. Furthermore, it plays a role in suppressing mixing of oxygen gas generated at the anode and hydrogen gas generated at the cathode. In the technique of water electrolysis, when a large amount of hydrogen gas permeates from the cathode to the anode, there is a risk of explosion due to rapid reaction with oxygen gas in the anode. Therefore, it is preferable that the gas permeability of the anion exchange membrane, which is a diaphragm, is low. Furthermore, it is very important that the gas permeability does not increase due to deterioration or the like even in long-term use that involves starting and stopping in actual use.

The anion exchange membrane using the porous membrane of the present invention can suppress an increase in gas permeability (diffusion of gas) even during repeated use. Specifically, it is possible to suppress an increase in gas permeability even under conditions of repeated use as in the following examples. The reason for this effect is considered to be that the porous membrane of the present invention has many relatively small pores. In other words, even when the amount of water in the water electrolysis device decreases or the water disappears in repeated use, the pores of the porous membrane are relatively small, so it is considered that the pores of the porous membrane easily follow the contraction of the anion exchange resin. Since the anion exchange resin has ion exchange groups, it tends to swell in the presence of water. On the other hand, it is thought that the anion exchange resin shrinks when the water is reduced (there is no more water). Therefore, it is considered that the shape conformability to the anion exchange resin is important during repeated use, and the porous membrane of the present invention has a large number of relatively small pores, so it is considered that the above effects are exhibited.

The present invention will be described in detail below with reference to examples, but the present invention is not limited by these examples.

The following methods were used to evaluate the properties of the porous membranes used in Examples and Comparative Examples, and the properties of anion exchange membranes using these porous membranes.

<Evaluation of porous membrane>
1. BET specific surface area, pore diameter having the maximum peak in the porous membrane, total ratio of pore volume of pores having a pore diameter of 100 nm or less, average pore diameter Using BelSorp Mini II manufactured by Microtrack Bell, a nitrogen adsorption isotherm was obtained from a nitrogen partial pressure of 1 × 10 ^-3 to 0.999. The adsorption isotherm was analyzed by the BET method to determine the specific surface area (m ² /g) and average pore diameter (nm). Also, the adsorption isotherm was analyzed by the BJH method to obtain an integral curve of pore volume (cm ³ /g) versus pore diameter D (nm). This curve was normalized by the total pore volume to calculate the total percentage of pore volume with pore diameters of 100 nm or less. Further, by differentiating the integrated curve of the pore volume V with the natural logarithm LogD of the pore diameter D, a pore diameter distribution curve (dV/dlogD) with respect to the pore diameter D was obtained.

2. 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.
Note that ρ in the formula is the density of the resin (g/cm ³ ).
P=100×(1−M/(ρ×V)).

3. Confirmation of Melting Point of Olefin Resin Using a differential scanning calorimeter (DSC) ThermoPlus EVO manufactured by Rigaku Corporation, the temperature was raised from room temperature to 330° C. at 10° C./min in a nitrogen atmosphere. The peak top temperature of the endothermic peak was read from the obtained DSC curve and taken as the melting point of the olefin resin.

4. Measurement of Mechanical Properties of Porous Membrane After cutting the porous membrane into strips of 1 cm×5 cm, a tensile test was performed at room temperature at a tensile speed of 5 mm/min using Autograph AGS-X manufactured by SHIMADZU. The distance between chucks was set to 3 cm. From the obtained stress-strain curve, the tensile modulus was calculated from the slope of the linear region appearing immediately after the start of the test.
Specifically, from the test force F and the initial cross-sectional area S of the test piece, the tensile stress σ was determined by the following formula.
σ = F/S
Further, the tensile strain ε was obtained from the following equation from the initial length _L0 of the parallel portion of the test piece and the increment ΔL of the length of the parallel portion.
ε = ΔL/L ₀
A stress-strain curve was drawn from the tensile stress σ and the tensile strain ε, and the slope of the linear region appearing immediately after the start of the test was obtained from the following formula to calculate the tensile elastic modulus E.
E = Δσ/Δε
Further, the tensile strength was taken as the maximum value of the tensile stress in the process from the start of the test to the fracture, and the value was read from the stress-strain curve. The elongation at break was determined by the following formula using the initial length _L0 of the test piece and the increment ΔL _Max of the length of the parallel portion until breakage.
Elongation at break = 100 x (ΔL _Max /L ₀ )

<Production of anion exchange membrane>
A polymerizable monomer composition was obtained by mixing 95 parts by mass of chloromethylstyrene, 5 parts by mass of a styrene solution of 57% by mass-divinylbenzene, 5 parts by mass of a polymerization initiator (trade name: Perbutyl O), and 5 parts by mass of an epoxy compound (trade name: Epolite 40E). 400 g of the obtained polymerizable monomer composition was placed in a 500 ml glass container, and the porous membrane (20 cm×20 cm) formed in Examples and Comparative Examples was immersed in the polymerizable monomer composition.

Subsequently, the porous membrane was taken out from the polymerizable monomer composition, and a 100 μm polyester film was laminated on both sides of the taken-out porous membrane as a release material. The resulting laminate was heated at 80° C. for 5 hours under a nitrogen pressure of 0.3 MPa to polymerize the polymerizable monomer composition.

A film-like product obtained by polymerizing the polymerizable monomer composition 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 aminate the polymerized portion of chloromethylstyrene and washed with pure water to obtain an anion exchange membrane.

<Evaluation of anion exchange membrane>
The produced anion exchange membrane was evaluated according to the following method. Methods for measuring various physical properties of anion exchange membranes will be described below in Examples and Comparative Examples.

i) Anion Exchange Capacity and Moisture Content First, the anion exchange membrane was immersed in a 0.5 mol·L ^-1 -NaCl aqueous solution for 10 hours or more to convert it to a chloride ion type. Then, the chloride ion-type anion exchange membrane was brought into contact with a 0.2 mol·L ^-1 -NaNO ₃ aqueous solution to replace it with a nitrate ion-type. At this time, liberated chloride ions were quantified by a potentiometric titrator (COMTITE-900, manufactured by Hiranuma Sangyo Co., Ltd.) using an aqueous solution of silver nitrate (the measured number of moles of chloride ions is defined as "A (mol)").

Next, the same anion exchange membrane was immersed in a 0.5 mol·L ⁻¹ -NaCl aqueous solution at 25° C. for 4 hours or longer, and thoroughly washed with ion-exchanged water. Thereafter, the film was taken out and wiped off with tissue paper or the like, and the wet weight ("W (g)") was measured. Furthermore, the membrane was dried under reduced pressure at 60° C. for 5 hours and its weight was measured (“D (g)”). Based on the above measured values, the anion exchange capacity and water content were determined by the following equations.
Ion exchange capacity ([mmol g ^-1 - dry weight]) = A x 1000/D
Moisture content ([%]) = 100 × (WD) / D

ii) Measurement of Membrane Resistance The anion exchange membrane was immersed in a 0.5 mol/L-KHCO ₃ aqueous solution for 10 hours or longer to change the counter ion to the bicarbonate type, then washed with pure water and dried at room temperature for 24 hours or longer.

The treated anion exchange membrane was placed in the center of a two-compartment cell with platinum electrodes. Both sides of the anion exchange membrane were filled with 0.5 mol·L ^-1 -KHCO ₃ aqueous solution. Then, the resistance between the electrodes at 25° C. was measured using an AC bridge (frequency: 1000 cycles/second) (the measured resistance is defined as “a (Ω·cm ² )”). Similarly, the resistance between the electrodes was measured without installing the anion exchange membrane (the measured resistance value is defined as "b (Ω·cm ² )"). Based on the above measurements, the membrane resistance was determined by the following equation.
Membrane resistance ([Ω·cm ² ]) = (ab)

iii) Hydrogen Gas Permeability The anion exchange membrane was immersed in a 0.5 mol/L-KHCO ₃ aqueous solution for 10 hours or more to convert the counter ion to a bicarbonate type. Then, it was washed with pure water and dried at room temperature for 24 hours or more.

A 5 cm x 5 cm piece of the anion exchange membrane subjected to the above treatment was cut out and attached to a gas permeability measuring device (GTR Tech Co., Ltd., GTR-200XFTS) to measure the amount of hydrogen permeation. Basically, the measurement was carried out according to JIS K7126-2 (Plastic-Film and Sheet Gas Permeability Test Method-Part 2: Isobaric Method).

The specific measurement method is as follows. First, the anion exchange membrane was sandwiched between the cells of the device and installed in the device. A carrier gas (argon gas) was passed through one of the spaces partitioned by the anion exchange membrane under conditions of a temperature of 40° C., a relative humidity of 90% RH, and a flow rate of 30 mL/min. In the other space, hydrogen gas was passed as a test gas under conditions of a temperature of 40° C., a relative humidity of 90% RH, and a flow rate of 30 mL/min. This state was maintained for 1 hour so that the temperature of the entire cell was kept constant (40° C.).

After that, at the sampling time (“t(s)”), the amount of hydrogen permeated to the carrier gas side was detected with a gas chromatograph. Based on the results, the hydrogen permeability per test area of 9.62 cm ² was calculated as the hydrogen permeability of the anion exchange membrane at 40°C and relative humidity of 90%.

After that, the carrier gas and the test gas were each switched to a flow rate of 30 mL/min, 40° C., and a relative humidity of 20%, and the temperature of the entire cell was kept constant (40° C.) for 1 hour. Then, the same measurement was performed, and the hydrogen permeability under the conditions of 40° C. and a relative humidity of 20% was obtained.
The hydrogen permeability is a value calculated based on the following formula.
Hydrogen permeability [cc/m ² · 24hr · atm] = (273/T) x (1/A) x B x (1/t)
T: Measured temperature (K)
A: Transmission area (cm ² )
B: Amount of permeated gas (μL)
t: Sampling time (s)

iv) Changes in Hydrogen Permeability with Humidity Cycling According to the method described in iii), hydrogen gas permeability measurements were repeated at 40° C. and relative humidity of 90% and 20%. Changes in hydrogen permeability were evaluated under conditions of humidity cycling between 90% and 20% relative humidity (repeated humidity changes). In the table, the change rate (%) of the 30th value to the 1st value of the hydrogen permeability at 40° C. and 20% relative humidity is shown (the closer to 100%, the lower the hydrogen permeability).

Example 1
<Manufacturing and evaluation of porous membrane>
A porous membrane was produced according to the following method.

(i) Step; 50% by mass of poly-4-methylpentene-1 resin (TPX (registered trademark)-DX845 manufactured by Mitsui Chemicals, Inc., melting point 239°C) and 50% by mass of diisononyl phthalate (100 parts by mass of plasticizer per 100 parts by mass of olefin resin) were melt-kneaded at 250°C for 10 minutes using a twin-screw kneader to obtain a kneaded product (composition).

(ii) Step: The resulting kneaded material (composition) was pressed into a sheet using a compression molding machine heated to 240°C, and then introduced into ice water at 0°C to cool and solidify to obtain a sheet-like molded body with a thickness of 0.21 mm (210 µm).

(iii) Step; Subsequently, the obtained sheet-like molding was subjected to simultaneous biaxial stretching by a tenter method at a stretching temperature of 80°C and a stretching ratio of 3 times in the longitudinal direction and 3 times in the lateral direction.
(iv) Step: The obtained stretched film was immersed in acetone to extract and remove diisononyl phthalate, and then the adhering acetone was removed by drying to obtain a porous membrane.

The resulting porous membrane was evaluated for porosity, BET specific surface area by nitrogen gas adsorption measurement, total pore volume ratio of pores with a pore diameter of 100 nm or less, average pore diameter, maximum peak of pore diameter in the porous membrane, and tensile modulus, tensile strength, and elongation at break by tensile test. evaluated. Table 1 shows the results.
In addition, the thickness of the obtained porous film was measured with a Mitutoyo Digimatic Indicator ID-H0530, and the results are also shown in Table 1.

<Production and evaluation of anion exchange membrane>
Next, an anion-exchange membrane was produced using the obtained porous membrane as a support by the method described above. The prepared anion exchange membrane was measured for anion exchange capacity, membrane resistance, hydrogen gas permeability at 40° C. relative humidity of 90% and 40° C. relative humidity of 20%, and the rate of change in hydrogen gas permeability due to humidity cycles. Table 1 shows the results.

Example 2
A porous membrane was produced and evaluated, and an anion exchange membrane using the same was produced and evaluated in the same manner as in Example 1, except that the stretching temperature was changed to 100°C. Table 1 shows the results.
FIG. 1 shows the integral curve (ΣV vs. D) of the pore volume due to nitrogen adsorption of the obtained porous membrane. In addition, FIG. 2 shows the pore size distribution curve (dV/dlogD) of the obtained porous membrane by nitrogen adsorption.

Example 3
A porous membrane was produced and evaluated, and an anion exchange membrane using the same was produced and evaluated in the same manner as in Example 1, except that the stretching temperature was changed to 120°C. Table 1 shows the results.

Example 4
A porous membrane was produced and evaluated, and an anion exchange membrane using the same was produced and evaluated in the same manner as in Example 1, except that the stretching temperature was changed to 140°C. Table 1 shows the results.

Example 5
A porous membrane was produced and evaluated in the same manner as in Example 1, except that the stretching temperature was changed to 90° C. and the stretching ratio was changed to 2 times in the vertical direction and 2 times in the horizontal direction. Table 1 shows the results.

Example 6
A porous membrane was produced and evaluated in the same manner as in Example 5, except that sequential biaxial stretching was performed by a tenter method at a draw ratio of 1.5 times in the longitudinal direction and 1.5 times in the lateral direction. Table 1 shows the results.

Example 7
A porous membrane was produced and evaluated in the same manner as in Example 6, except that the draw ratio was changed to 3.5 times in the vertical direction and 3.5 times in the horizontal direction. Table 1 shows the results.

Example 8
A porous membrane was produced and evaluated in the same manner as in Example 3, except that biaxial rolling was performed with heated rolls at a draw ratio of 2.2 times in the vertical direction and 2.2 times in the horizontal direction. Table 1 shows the results.

Example 9
A porous membrane was produced and evaluated in the same manner as in Example 8, and an anion exchange membrane was produced and evaluated using the same, except that the draw ratio was changed to 3 times in the vertical direction and 3 times in the horizontal direction. Table 1 shows the results.

Example 10
A porous membrane was produced and evaluated, and an anion exchange membrane was produced and evaluated using the same method as in Example 8, except that the draw ratio was changed to 4 times in the vertical direction and 4 times in the horizontal direction. Table 1 shows the results.

Example 11
The composition was melt-kneaded using a twin-screw kneader, extruded from a T-die onto a water-cooled cast drum to obtain a cast sheet, the stretching temperature was changed to 130 ° C., and the stretching ratio was 4.5 times in length and 4.5 times in width. Table 1 shows the results.

Example 12
A porous membrane was produced and evaluated in the same manner as in Example 11, except that the draw ratio was changed to 5.2 times in the vertical direction and 5.2 times in the horizontal direction. Table 1 shows the results.

Example 13
Poly 4-methylpentene-1 resin (TPX (registered trademark)-DX845 manufactured by Mitsui Chemicals, Inc., melting point 239° C.) 50% by mass, diisononyl phthalate 50% by mass (100 parts by mass of plasticizer per 100 parts by mass of olefin resin), 0.5% by mass of nucleating agent (NA-11 by ADEKA) added to the resin, and the stretching temperature was changed to 120° C., and the longitudinal stretching ratio was 4.5 times. , the width of 4.5 times, the preparation and evaluation of the porous membrane, and the preparation and evaluation of the anion exchange membrane using the same. Table 1 shows the results.

Example 14
A porous membrane was produced and evaluated, and an anion exchange membrane using the same was produced and evaluated in the same manner as in Example 13, except that the stretching temperature was changed to 130°C. Table 1 shows the results.

Comparative example 1
A porous membrane was formed in the same manner as in Example 1, except that the stretching temperature was changed to 60°C. However, the molding broke during stretching.
Comparative example 2
A porous membrane was formed in the same manner as in Example 1, except that the stretching temperature was changed to 170°C. However, the molding broke during stretching.
Comparative example 3
The sheet-shaped molding produced in the step (ii) of Example 1 was immersed in acetone to extract and remove diisononyl phthalate as a plasticizer. Subsequently, the sheet obtained by removing the plasticizer was subjected to simultaneous biaxial stretching at a temperature of 160° C. at a draw ratio of 2 times in the longitudinal direction and 2 times in the transverse direction to produce a porous membrane. The obtained porous membrane was evaluated in the same manner as in Example 1, and an anion exchange membrane was prepared and evaluated using the porous membrane.
The pore size was increased by stretching after the pore formation, and the BET specific surface area was greatly reduced. Moreover, the elongation at break deteriorated to 4%, and the porous membrane was easily broken.
In addition, the anion exchange membrane produced using the porous membrane was measured for the anion exchange capacity, the membrane resistance, the hydrogen gas permeability at 40 ° C. relative humidity of 90% and 40 ° C. relative humidity of 20%, and the rate of change in hydrogen gas permeability due to humidity cycles. Table 1 shows the results.

Reference Signs List 1 Anion exchange membrane 2 Anode 3 Cathode 4 Gas diffusion layer 5 Anode chamber 6 Water supply port 7 Oxygen outlet 8 Cathode chamber 9 Hydrogen outlet 10 Housing

Claims

A porous film containing a polyolefin resin, having a BET specific surface area of 40 m 2 /g or more as determined by a nitrogen adsorption method, and a porosity of 20% or more and 80% or less.
The porous membrane according to claim 1, wherein the pore diameter having the maximum peak exists at 100 nm or less in the pore size distribution curve obtained by the nitrogen adsorption method.
The porous membrane according to claim 1 or 2, wherein the total pore volume of pores having a diameter of 100 nm or less accounts for 80% or more of the total pore volume in the pore size distribution curve obtained by the nitrogen adsorption method.
The porous membrane according to claim 1 or 2, having an average pore diameter of 80 nm or less by a nitrogen adsorption method.
The porous membrane according to claim 1 or 2, wherein the polyolefin resin contains at least one resin selected from the group consisting of polymethylpentene resin and polypropylene resin.
The porous membrane according to claim 1 or 2, which has a thickness of 10 to 200 μm.
The porous membrane according to claim 5, wherein the polymethylpentene resin accounts for 95% by mass or more in the porous membrane.
A porous membrane according to claim 1 or 2;
and an ion exchange resin filled in the pores of the porous membrane.
The ion exchange membrane according to claim 8, wherein the ion exchange resin is an anion exchange resin.
A water electrolysis device comprising the ion exchange membrane according to claim 8.
a step of heating a composition containing a polyolefin resin and a plasticizer to obtain a sheet-like first molded body;
obtaining a second molded body by stretching the first molded body at a temperature lower than the melting point of the polyolefin resin in the range of 70° C. or more and 178° C. or less;
removing the plasticizer from the second compact;
in this order.
The method for producing a porous membrane according to claim 11, wherein the step of obtaining the second molded body is a step of biaxially stretching the first molded body at a longitudinal draw ratio of 2 or more and a horizontal draw ratio of 2 or more to obtain the second molded body.