Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/10—Supported membranes; Membrane supports
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/26—Polyalkenes
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
  • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/36—After-treatment
  • C08J9/40—Impregnation
  • C08J9/42—Impregnation with macromolecular compounds
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features

Definitions

• 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.
• 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.
• porous membranes are used in a wide range of applications, from filtration and separation purposes to separator applications and even fuel cell applications.
• 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.
• 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.
• 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.
• 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.
• 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).
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the porous membrane of the present invention 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.
• an anion exchange resin membrane a porous membrane in which pores are filled with an anion exchange resin
• the gas leakage rate hydrogen permeability
• 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.
• 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.
• 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.
• porous membrane of the present invention will be described in detail below.
• 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.
• "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 ⁇ -olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl-1-heptene.
• ⁇ -olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl-1-heptene.
• 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.
• 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).
• 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.
• 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.
• the melting point of the polyolefin resin is one, the melting point of the resin itself should be checked.
• 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.
• 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.
• the melting point of the crystalline polyolefin-based resin that is the main component may be used as a reference.
• 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.
• 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.
• 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.
• 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.
• 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.
• this porosity is the value measured by the method described in the following examples.
• 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.
• it preferably satisfies the following physical properties.
• 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 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.
• 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.
• 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).
• the pores in the porous membrane satisfy the following requirements.
• 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.
• 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.
• this total ratio can be obtained from the integral curve of the pore volume (see FIG. 1).
• 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.
• 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.
• 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.
• the film thickness of the porous membrane is not particularly limited.
• the film thickness is preferably within the following range.
• the film thickness is preferably 10 to 200 ⁇ m.
• the thickness is preferably 15 to 170 ⁇ m.
• the thickness of the porous membrane is more preferably 20 to 150 ⁇ m, particularly preferably 30 to 100 ⁇ m.
• the porous membrane of the present invention preferably has the pores and the following mechanical strength.
• 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.
• 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.
• 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.
• these mechanical properties can be adjusted by adjusting the materials used, the mixing ratio of each material, and the film-forming conditions.
• the porous membrane can be produced by a known method. Specifically, it is preferably produced by performing the following steps (i) to (iii).
• Step First, an olefin resin and a plasticizer are kneaded to produce a composition containing them.
• step forming the obtained composition into a sheet by a known method.
• the composition is produced by a known method.
• 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.
• the plasticizer when using a 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.
• aromatic carboxylic acid esters are preferred. These can be used alone or in combination of multiple types.
• 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.
• 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.
• the obtained porous membrane can be heat-treated (the porous membrane is left under a certain temperature range).
• the method for producing the porous membrane is not particularly limited.
• 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.
• the sheet 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.
• 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).
• the porous membrane can be produced by the above method.
• 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.
• 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.
• a porous membrane satisfying the requirements of the present invention in terms of BET specific surface area and porosity can be easily produced.
• 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.
• a plasticizer preferably an aromatic carboxylic acid ester, specifically diisononyl phthalate, etc.
• 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.
• 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 ⁇ m is preferable.
• the physical properties of this sheet are not particularly limited, it is preferable to adjust the diameter of the spherulites to 5 ⁇ m or less.
• the above adjustment can be achieved by using a crystal nucleating agent or by adjusting film forming conditions.
• 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.
• 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.
• the press-molded material is preferably stretched under the above conditions.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 polymerizable composition containing a polymerizable monomer having a halogenoalkyl group e.g., chloromethylstyrene, bromomethylstyrene, iodomethylstyrene, chloroethylstyrene, bromoethylstyrene, bromobutylstyrene, etc.
• a crosslinkable polymerizable monomer e.g., divinylbenzene, divinylbiphenyl, divinylnaphthalene, etc.
• a polymerization initiator e.g., an organic peroxide such as benzoyl peroxide
• 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.
• 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.
• the method (1) or (2) 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.
• 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.
• 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.
• 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.
• the counter ion of the anion exchange group is often obtained as a halide ion.
• 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.
• 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.
• 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.
• 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.
• 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 .
• 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 .
• 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.
• 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.
• 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.
• 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.
• ⁇ F/S
• the tensile strain ⁇ was obtained from the following equation from the initial length L0 of the parallel portion of the test piece and the increment ⁇ L of the length of the parallel portion.
• ⁇ ⁇ L/L 0
• a stress-strain curve was drawn from the tensile stress ⁇ and the tensile strain ⁇ , 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 ⁇ / ⁇
• 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.
• 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.
• the porous membrane was taken out from the polymerizable monomer composition, and a 100 ⁇ m 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.
• 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.
• 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.
• 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)").
• 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.
• GTR Tech Co., Ltd., GTR-200XFTS gas permeability measuring device
• 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.).
• a carrier gas argon gas
• 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%.
• Example 1 Manufacturing and evaluation of porous membrane> A porous membrane was produced according to the following method.
• 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).
• TPX poly-4-methylpentene-1 resin
• DX845 diisononyl phthalate
• 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.
• 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.
• 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 ( ⁇ V vs. D) of the pore volume due to nitrogen adsorption of the obtained porous membrane.
• 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.
• 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.

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