JP4435560B2 - Ion exchange membrane and method for producing the same - Google Patents

Description

The present invention relates to a septum membrane contact and their preparation for direct methanol fuel cells.

  Ion exchange membranes are widely used as membranes for batteries such as polymer electrolyte fuel cells, redox flow cells, zinc-bromine cells, and dialysis membranes. Among these, a polymer electrolyte fuel cell using an ion exchange membrane as an electrolyte is a clean and highly efficient power generation system that continuously supplies fuel and an oxidant, and extracts chemical energy as electricity when they react. In recent years, it has become increasingly important for automobile use, home use and portable use from the viewpoint of low temperature operation and miniaturization. A polymer electrolyte fuel cell generally has a gas diffusion electrode having a catalyst supported on both sides of a solid polymer diaphragm acting as an electrolyte, and a chamber (fuel chamber) on the side where one gas diffusion electrode exists. ) Is supplied with a fuel comprising hydrogen gas or methanol, etc., and an oxygen-containing gas such as oxygen or air as an oxidant is supplied to the chamber on the other gas diffusion electrode side, and an external load circuit is provided between the gas diffusion electrodes. By connecting these, the fuel cell is operated. In particular, direct methanol fuel cells that use methanol as a direct fuel are expected to be a relatively small output power source, especially for portable devices, because the fuel is liquid and is easy to handle. Has been.

  The basic structure of such a direct methanol fuel cell is shown in FIG. In the figure, (1) is a battery partition, (2) is a fuel flow hole, (3) is an oxidant gas flow hole, (4) is a fuel chamber side diffusion electrode, (5) is an oxidant chamber side gas diffusion electrode, (6) shows a solid polymer electrolyte membrane. In this direct methanol fuel cell, protons (hydrogen ions) and electrons are generated in the fuel chamber side diffusion electrode (4) from methanol supplied to the fuel chamber (7), and the protons are contained in the solid polymer electrolyte (6). Is transferred to the other oxidant chamber (8) and reacts with oxygen in the air or oxygen gas to produce water. At this time, the electrons generated in the fuel chamber side diffusion electrode (4) move to the oxidant chamber side gas diffusion electrode (5) through the external load circuit to obtain electric energy.

  In the direct methanol fuel cell having such a structure, a cation exchange membrane is usually used for the diaphragm. However, the cation exchange membrane has a low electrical resistance and a high physical strength. In addition, characteristics such as low permeability of methanol used as fuel are required. For example, when an ion exchange membrane having high methanol permeability is used as a fuel cell membrane, it is difficult to sufficiently suppress the diffusion of methanol in the fuel chamber to the oxidation chamber side, and it is difficult to obtain a large battery output. Become.

  Conventionally, a perfluorocarbon sulfonic acid membrane is mainly used as a cation exchange membrane used as a diaphragm for a direct methanol fuel cell. However, although this film is excellent in chemical stability, it has been difficult to reduce electric resistance by thinning because of insufficient physical strength. In addition, when methanol is used as the fuel, there are problems that the perfluorocarbon sulfonic acid membrane is significantly swollen and deformed, and the diffusion of methanol to the oxidation chamber cannot be sufficiently suppressed. Furthermore, the perfluorocarbon sulfonic acid membrane was expensive.

  Also, as a polymer electrolyte fuel cell membrane, a polyolefin or fluororesin porous membrane is used, and this is impregnated with a monomer having a functional group capable of introducing a cation exchange group by a specific method. It has been proposed to obtain a cation exchange membrane having a low electrical resistance and a very low gas permeability by a polymerization method (for example, Patent Documents 1 and 2). However, these cation exchange membranes are effective when used as membranes for polymer electrolyte fuel cells using hydrogen gas as the fuel, but when used as membranes for direct methanol fuel cells. However, the permeability of methanol was not sufficiently suppressed, so that there was a problem that methanol diffused to the oxidation chamber side and the battery performance was lowered.

  On the other hand, in order to improve the water retention and ion conductivity of the ion exchange membrane, a membrane in which silica or silica fibers are uniformly dispersed in the ion exchange membrane has been proposed (for example, Patent Document 3). Although the water retention and ionic conductivity are certainly improved by such a method, according to the study by the present inventors, it is clear that the methanol permeability does not change or is deteriorated in some cases. It was.

JP 2001-135328 A Japanese Patent Laid-Open No. 11-310649 JP-A-6-1111827

  As described above, no cation exchange membrane conventionally used as a diaphragm for a direct methanol fuel cell has low methanol permeability and low electrical resistance (high ionic conductivity). Currently. Accordingly, the present invention provides an ion exchange membrane that can stably obtain a high battery output when used as a direct methanol fuel cell diaphragm, having low liquid permeability, particularly methanol permeability and low membrane resistance. With the goal.

The present inventors have continued intensive studies in view of the above problems. As a result, as a method for producing an ion exchange membrane, an inorganic filler having a porous membrane as a base material and having an average primary particle major axis in a specific range with respect to the average pore size of the porous membrane is ionized. The ion exchange membrane produced by impregnating the porous membrane with the suspension added to the monomer that is the precursor of the exchange resin was found to have low methanol permeability and low electrical resistance. As a result, the present invention has been completed.

That is, the present invention has a pore having an average pore diameter in the range of 0.01 to 2 μm and a porous membrane made of a polyolefin resin as a base material, and a hydrocarbon ion exchange resin exists in the pore. An inorganic filler and a hydrocarbon ion, wherein the average value of the major axis of primary particles is not less than the average pore size of the pores of the porous membrane and not more than 50 μm on at least one side of the porous membrane A membrane for a direct methanol fuel cell comprising an ion exchange membrane having a layer containing an exchange resin.

Further another aspect of the present invention are those according to the manufacturing method of the ion exchange membrane, still another invention is a direct methanol fuel cell using the above SL direct methanol fuel cell septum membrane.

The ion exchange membrane used in the present invention has a low electric resistance and a very low permeability of a liquid, particularly methanol. Furthermore, if a porous stretched film made of polyolefin resin is used as a substrate, it can be excellent in dimensional stability, heat resistance, and chemical resistance. For this reason, the direct methanol fuel cell using this ion exchange membrane as a diaphragm can suppress the crossover of the fuel and the oxygen-containing gas and stably obtain a high cell output for a long period of time. Moreover, according to the manufacturing method of the present invention, it is possible to easily and efficiently manufacture an ion exchange membrane having the excellent features as described above.

The ion exchange membrane used as a diaphragm for a direct methanol fuel cell of the present invention (hereinafter simply referred to as “the ion exchange membrane of the present invention”) has pores having an average pore diameter in the range of 0.01 to 2 μm, and An ion exchange membrane in which a porous membrane made of a polyolefin resin is used as a base material (sometimes referred to as a support material or a reinforcing material), and a hydrocarbon ion exchange resin is present in the pores. At least one surface is characterized in that there is a layer containing an inorganic filler and a hydrocarbon ion exchange resin, wherein the average value of the major axis of primary particles is not less than the average pore size of the pores of the porous membrane and not more than 50 μm. Have In other words, this ion exchange membrane has a pore having an average pore diameter in the range of 0.01 to 2 μm and includes a porous membrane made of a polyolefin resin , and at least one of the porous membrane layers It consists of an inorganic filler-containing layer present on one side, the pores of the porous membrane are filled with a hydrocarbon-based ion exchange resin, and the inorganic filler-containing layer has an average value of the major axis of the primary particles, It is an ion exchange membrane comprising an inorganic filler and a hydrocarbon ion exchange resin that are not less than the average pore diameter of the pores of the porous membrane and not more than 50 μm.

  As the porous membrane serving as the base material, a porous membrane having pores having an average pore diameter in the range of 0.01 to 2 μm, and an ion exchange membrane using the porous membrane as a base material can be formed. As described above, any known porous membrane may be used as long as at least a part of the pores communicate with each other. On the other hand, when the average pore size is 0.01 μm or less, the pores (inside the pores) of the porous substrate are insufficiently filled with the ion exchange resin, resulting in a film having high electrical resistance. On the other hand, when it is 2 μm or more, high methanol impermeability cannot be obtained. More preferably, it has pores having an average pore diameter of 0.01 to 1 μm. In addition, the average pore diameter of the porous membrane is a value measured by a bubble point method based on JISK3832.

  In order to reduce the electrical resistance of the ion exchange membrane and to maintain high physical strength, the porosity (also referred to as porosity) is preferably 20 to 95%, particularly preferably 30 to 90%. The degree (JIS P-8117) is preferably 1000 seconds or less, particularly preferably 500 seconds or less. The thickness is preferably 5 to 150 μm, more preferably 10 to 120 μm, and particularly preferably 10 to 70 μm.

The form of the said porous film is not specifically limited, Porous films, such as a porous stretched film and a porous non-stretched film, a woven fabric, a nonwoven fabric, etc. can be used without a restriction | limiting . As the material , polyolefin resin is used because it is excellent in mechanical strength , chemical stability, and chemical resistance, and is particularly well-suited with hydrocarbon ion exchange resins . Examples of the polyolefin resin include 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. A homopolymer, a copolymer, etc. can be mentioned, Among these, polyethylene or polypropylene resin is particularly preferable, and polyethylene resin is most preferable.

  Further, a porous film made of a polyolefin resin is preferable, and a porous film made of a polyethylene resin, particularly a stretched film is particularly preferable in that it is easy to obtain a material having the average pore diameter and is excellent in strength.

  Such a porous film can be obtained by, for example, a method described in JP-A No. 2002-338721, or a commercially available product (for example, Asahi Kasei “Hypore”, Ube Industries “Eupor”, Tonen Tapils “Setera” ”, Nitto Denko“ Exepor ”, Mitsui Chemicals“ Hilet ”, etc.).

The pores of the porous membrane are filled with a hydrocarbon ion exchange resin. The hydrocarbon ion exchange resin may be any known ion exchange resin made of a resin having a group having cation exchange ability and / or anion exchange ability (hereinafter simply referred to as ion exchange group). Not only is the manufacturing cost cheaper than sulfonic acid, etc., but when the substrate made of a porous membrane is a polyolefin-based porous (stretched) film having high strength, the thin film has a good compatibility with the substrate. The portion other than the ion exchange group is a resin having a structure mainly composed of carbon and hydrogen in that the resistance can be reduced by the conversion . There may be a small amount of other atoms such as fluorine, chlorine, bromine, oxygen, nitrogen, silicon, sulfur, boron, and phosphorus in the portion other than the ion exchange group. It is 40 mol% or less, particularly 10 mol% or less, based on the total number of constituent atoms . ( Such an ion exchange resin is referred to as a hydrocarbon-based ion exchange resin, and hereinafter also simply referred to as an ion exchange resin. ) Particularly preferred are polystyrene-based monomers obtained by copolymerizing a styrene-based polymerizable monomer and a cross-linkable monomer copolymerizable with the styrene-based monomer.

  Examples of the ion exchange group include cation exchange groups such as sulfonic acid groups, carboxylic acid groups, phosphonic acid groups, and salts corresponding to these acids. Generally, sulfonic acid groups that are strongly acidic groups are used. Is particularly preferred. Examples of the anion exchange group include primary to tertiary amino groups, quaternary ammonium groups, pyridyl groups, imidazole groups, quaternary pyridinium groups, and quaternary imidazolium groups. A quaternary ammonium group or a quaternary pyridinium group is preferably used.

Ion-exchange membrane of the present invention, on at least one surface of the ion exchange resin in the pores described above is filled porous membrane (porous membrane layer), Yusuke average value of the long diameter of the primary particles of said multi Anashitsumaku There is a layer (inorganic filler-containing layer) containing an inorganic filler (hereinafter also simply referred to as “inorganic filler”) having an average pore diameter of 50 μm or less and an ion exchange resin. If the major axis of the inorganic filler (the length of the longest part in the filler particles) is less than the average pore diameter of the pores of the porous membrane , the methanol permeability cannot be reduced, or the membrane Since the resistance becomes high, the ion exchange membrane having low methanol permeability and low electrical resistance, which is the object of the present invention, cannot be obtained. On the other hand, if it exceeds 50 μm, it is extremely difficult to produce an ion exchange membrane, and even if it can be produced, suppression of methanol permeability is insufficient. Preferably, it is an inorganic filler whose major axis is not less than the average pore diameter of the pores of the porous membrane and not more than 10 μm.

  The shape of the inorganic filler is not particularly limited, and may be any shape such as a spherical shape, a fiber shape, a layer shape (film shape), or an irregular pulverized shape, but it is a layer shape in that sufficient methanol impermeability can be exhibited. It is preferable that Furthermore, among the layered particles, particles having an aspect ratio in the range of 50 to 2000, particularly 200 to 1000 are most preferable. The aspect ratio of the layered particle is a ratio between the thickness of the layered particle and the length (long diameter) of the longest diameter portion of the particle, and can be generally determined by observation with an electron microscope.

  The material of the inorganic filler is not particularly limited as long as it is an inorganic material. However, in view of high ion conductivity, durability of the ion exchange membrane, etc., it has hydrophilicity and ions such as sulfonic acid and amino group. It is preferable that it exhibits corrosion resistance even in the presence of an exchange group. For example, at least one metal oxide selected from the group consisting of Group IIA, Group IVA, Group IIIB, and Group IVB of the periodic table, composite oxide, hydroxide, carbonate, sulfate, Powders such as silicates or mixtures thereof can be used. The Group IIA metal of the periodic table is preferably calcium or magnesium, the Group IVA metal is titanium or zirconium, the Group IIB metal is aluminum, and the Group IVB metal is silicon. It is. Specific examples of inorganic fillers that can be suitably used in the present invention include various silicates such as montmorillonite and talc, oxides such as silicon oxide (silica), aluminum oxide (alumina), and titanium oxide; calcium carbonate, carbonate Examples thereof include carbonates such as magnesium and barium carbonate; hydroxides such as magnesium hydroxide, calcium hydroxide and aluminum hydroxide; sulfates such as calcium sulfate, barium sulfate and aluminum sulfate. Among these, it is particularly preferable to use at least one inorganic filler selected from the group consisting of silicate, silica, alumina, and titanium oxide.

  Examples of the layered particles of such materials include natural or artificial minerals such as montmorillonite, bentonite, smectite, hectorite, beidellite, soconite, perovskite, saponite, kaolin, sericite, mica, talc, layered silicate.

  The thickness of the inorganic filler-containing layer is not particularly limited, and may be appropriately changed and adjusted according to the use, etc. In order to obtain sufficient methanol non-permeability and high ionic conductivity, 0.05 to 5 μm It is preferable that it exists in the range, and it is more preferable that it exists in the range of 0.1-3 micrometers. Further, the ratio of the inorganic filler to the ion exchange resin in the layer is not particularly limited. However, in order to obtain easy methanol and sufficient methanol impermeability and high ionic conductivity, the inorganic filler: The weight ratio of the ion exchange resin is preferably in the range of 1: 100 to 70: 100, and more preferably in the range of 1: 100 to 45: 100. As the proportion of the inorganic filler is larger, the methanol permeability is suppressed, but when it is extremely increased, the ionic conductivity tends to be lowered. Further, when no ion exchange resin is present, ionic conductivity cannot be obtained.

  In the ion exchange membrane of the present invention, the ion exchange resin in the porous membrane layer (present in the pores of the porous membrane) and the ion exchange resin in the inorganic filler-containing layer are preferably the same type of ion exchange resin. . Further, the ion exchange resin in the porous membrane layer (inside the pores of the porous membrane) and the ion exchange resin in the inorganic filler-containing layer are preferably a continuous phase (integrated polymer) having no interface. In the case of such an ion exchange membrane, an ion exchange membrane having particularly high ion conductivity (low membrane resistance) can be obtained.

  A schematic diagram of the structure of the ion exchange membrane of the present invention including such a porous membrane, an inorganic filler, and an ion exchange resin is shown in FIG. 2 (in the figure, the size ratio of each part is arbitrary, and It does not accurately indicate the size of the ion exchange membrane). That is, the layer 12 containing the ion exchange resin 10 and the inorganic filler 11 is formed on at least one surface of the substrate made of the porous film 9. Many pores of the porous membrane communicate with each other, and the ion exchange resin 10 is also present in the pores. In FIG. 2, the layer 12 containing the ion exchange resin 10 and the inorganic filler 11 exists only on one surface of the porous membrane 9, and the layer composed only of the ion exchange resin 10 exists on the opposite surface. A layer containing an ion exchange resin and an inorganic filler may be present on the surface, or conversely, nothing may be present (the surface of the porous membrane is exposed as it is). If there is a layer containing an ion exchange resin and an inorganic filler on at least one side, sufficient methanol impermeability can be obtained, but an ion exchange membrane having a layer containing an ion exchange resin and an inorganic filler on both sides. Some are easier to manufacture. In addition, the ion exchange resin does not have to be completely present in the pores of the porous membrane, and some of the pores may not be filled with the ion exchange resin, but a high ion exchange capacity is obtained. Therefore, it is preferable that as many ion exchange resins as possible exist in the pores.

  Further, in FIG. 2, the portion where the ion exchange resin 10 is present may contain other components, and various known additives as additives for the ion exchange resin, resins other than the ion exchange resin, and the like. It is done. The ion exchange resin in the pores of the porous membrane 9 may contain a small amount of an inorganic filler, particularly an inorganic filler whose major axis is less than or equal to the pore size of the porous membrane. Usually, the abundance ratio of the inorganic filler in the pores is smaller than the abundance ratio of the inorganic filler in the layer containing the ion exchange resin and the inorganic filler, generally 1/5 or less, preferably 1/10 by mass ratio. Hereinafter, it is particularly preferably 1/100 or less.

  Although the manufacturing method of the ion exchange membrane of the said invention is not specifically limited, From the viewpoint that a high performance membrane can be manufactured efficiently, it can manufacture suitably with the following manufacturing methods 1 or 2.

Manufacturing method 1. Method of polymerizing monomer (monomer) after infiltrating into pores of porous membrane In this method, first, the average value of the major axis of the primary particles is greater than the average pore size of the pores of the porous membrane. And a polymerizable monomer selected from the group consisting of an inorganic filler that is 50 μm or less and a polymerizable monomer that polymerizes to give an ion exchange resin or a polymerizable monomer that gives an ion exchange resin precursor resin. A suspension (hereinafter referred to as suspension 1) is obtained. The inorganic filler used here may be the one described above. At this time, it is preferable to use a surface-treated inorganic filler in order to improve dispersibility. Generally, when using a polymerizable monomer that gives an ion exchange resin by polymerization, using an inorganic filler that has been subjected to a hydrophilic treatment, when using a polymerizable monomer that gives an ion exchange resin precursor, It is preferable to use a hydrophobic inorganic filler.

  The polymerizable monomer that gives an ion exchange resin by polymerization means a polymerizable monomer that is used in the production of conventionally known ion exchange resins and becomes an ion exchange resin by polymerization. Specifically, sulfonic acid diameter monomers such as styrene sulfonic acid, vinyl sulfonic acid and α-halogenated vinyl sulfonic acid, carboxylic acid diameter monomers such as methacrylic acid, acrylic acid and maleic anhydride, vinyl phosphoric acid and the like Examples thereof include phosphonic acid diameter monomers, salts and esters thereof. Examples of the monomer having an anion exchange group include amine diameter monomers such as vinylbenzyltrimethylamine and vinylbenzyltriethylamine, nitrogen-containing heterocyclic diameter monomers such as vinylpyridine and vinylimidazole, salts and esters thereof. Kind.

  The polymerizable monomer that gives an ion exchange resin precursor resin by polymerization is a resin that can be introduced with ion exchange groups by polymerization, which is used in the production of conventionally known ion exchange resins, that is, ion exchange. Means a polymerizable monomer that yields a resin having a functional group capable of introducing a group; specifically, styrene, α-methylstyrene, vinyltoluene, having a functional group into which a cation exchange group can be introduced, Aromatic vinyl compounds such as 2,4-dimethylstyrene, p-tert-butylstyrene, α-halogenated styrene, vinylnaphthalene and the like, and as a monomer having a functional group capable of introducing an anion exchange group, Examples include styrene, vinyl toluene, chloromethyl styrene, vinyl pyridine, vinyl imidazole, α-methyl styrene, vinyl naphthalene, etc. .

  In the production method of the present invention, either a polymerizable monomer that polymerizes to give an ion exchange resin or a polymerizable monomer that gives an ion exchange resin precursor resin may be used. When the porous film is a porous film, it has good permeability, so a polymerizable monomer that polymerizes to give an ion exchange resin precursor resin can be used, and then an ion exchange group can be introduced as described later. preferable.

The above polymerizable monomers may be used in combination of a plurality of types, and further may be used in combination with other monomers such as a crosslinkable monomer. By blending a crosslinkable monomer, the resulting ion exchange resin becomes insoluble, which is preferable because stability is improved. The crosslinkable monomer is not particularly limited, and examples thereof include polyfunctional vinyl compounds such as divinylbenzenes, divinylsulfone, butadiene, chloroprene, divinylbiphenyl, trivinylbenzene, and trimethylolmethanetrimethacrylic acid. Polyfunctional methacrylic acid derivatives such as esters, methylenebisacrylamide, hexamethylene dimethacrylamide and the like are used. (In the following description, a polymerizable monomer that polymerizes to give an ion exchange resin, a polymerizable monomer that polymerizes to give an ion exchange resin precursor resin, a crosslinkable monomer, and other optional components are included. All the monomers are collectively referred to as polymerizable monomers.)
Furthermore, the suspension 1 preferably contains a polymerization initiator for polymerization described later. The polymerization initiator is not particularly limited as long as it is a polymerization initiator capable of polymerizing the polymerizable monomer as described above, and specifically, octanoyl peroxide, lauroyl peroxide. , T-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-hexylperoxybenzoate, di-t-butylperoxide, etc. Of organic peroxides.

  Furthermore, the suspension 1 may contain, as necessary, known additives for producing an ion exchange resin by polymerization of monomers, such as a solvent and a plasticizer.

  The method for preparing the suspension 1 is not particularly limited, and in general, the polymerizable monomer to be used, the inorganic filler, the polymerization initiator, and other various added components blended as necessary are weighed. And stirring and mixing with a general mixer. Further, the ratio of the inorganic filler and the polymerizable monomer is not particularly limited, but in order to make the ratio of the inorganic filler in the inorganic filler-containing layer as described above, 100 parts by weight of the polymerizable monomer The inorganic filler is preferably 1 to 70 parts by weight, and more preferably 1 to 45 parts by weight. In addition, although a detailed reason is unknown, as a general tendency, the ratio of the inorganic filler in the obtained inorganic filler-containing layer tends to be larger than the ratio of the inorganic filler in the used suspension. As the polymerizable monomer, a crosslinkable monomer of 0.1 to 100 parts by weight of a polymerizable monomer that gives an ion exchange resin by polymerization or an ion exchange resin precursor is given. 50 parts by weight, particularly 1 to 40 parts by weight; it is preferred that the polymerizable monomer other than these is 0 to 100 parts by weight. The polymerization initiator is preferably 0.1 to 20 parts by weight, particularly 0.5 to 10 parts by weight, based on 100 parts by weight of the polymerizable monomer. When a plasticizer is blended, the plasticizer may be 0 to 50 parts by weight with respect to 100 parts by weight of the polymerizable monomer.

Suspension 1 as described above is brought into contact with a porous membrane such as a porous stretched film to allow the polymerizable monomer to penetrate into the pores of the porous membrane. As the porous membrane, one having pores having an average pore diameter in the range of 0.01 to 2 μm as described above is used. The contact method is not particularly limited, and examples thereof include a method in which the suspension 1 is applied or sprayed onto the porous membrane, or the porous membrane is immersed in the suspension 1. By this contact, the polymerizable monomer and the component dissolved in the polymerizable monomer among the optional components blended as necessary penetrate into the pores of the porous membrane. At this time, by using an inorganic filler having an average value of the major axis of primary particles not less than the average pore diameter of the pores of the porous membrane and not more than 50 μm as the inorganic filler, the inorganic filler is contained in the pores of the porous membrane. Hardly penetrates, and a layer made of an inorganic filler, a polymerizable monomer, and other optional components is formed on the surface of the porous membrane. In addition, it is estimated that even if the filler has a diameter smaller than the pore diameter, it does not penetrate into the pores because these particles are aggregated into larger secondary particles. When dipping, the polymerizable monomer remaining on the surface of the porous membrane will continue to penetrate into the pores after being pulled up, so it is necessary to continue soaking until it completely penetrates into the pores. There is no. In the case of dipping, the dipping time is generally 0.1 seconds to a few dozen minutes, although it depends on the type of the porous membrane and the composition of the suspension.

  Subsequently, the polymerizable monomer is polymerized. The polymerization method is not particularly limited, and a known method may be adopted as a polymerization method of the blended polymerizable monomer.In general, a polymerization initiator composed of the peroxide is used, A method of polymerizing by heating is preferable because the operation is easy and relatively uniform polymerization is possible. In polymerization, in order to prevent polymerization inhibition by oxygen and to obtain surface smoothness, it is more preferable to perform polymerization after covering with a film of polyester or the like. Further, by covering with such a film, excess suspension is removed, and a thin and uniform ion exchange membrane can be obtained. In addition, the polymerization temperature in the case of polymerization by thermal polymerization is not particularly limited, and may be appropriately selected and applied from known conditions, but is generally about 50 to 150 ° C, preferably about 60 to 120 ° C. . In addition, when the solvent is contained in the suspension 1, it is preferable to remove this solvent prior to the polymerization.

  The membrane obtained by polymerization in this way, when a polymerizable monomer that polymerizes to give an ion exchange resin is used, becomes the ion exchange membrane of the present invention as it is, but is polymerized to give an ion exchange resin. When a polymerizable monomer that gives a precursor is used, an ion exchange group is further introduced into a resin comprising the polymer of the polymerizable monomer, that is, an ion exchange resin precursor resin, and the ion exchange resin is introduced into the ion exchange resin. Need to be converted. The method for introducing the ion exchange group is not particularly limited, and a known method may be adopted. The type of ion exchange group to be introduced may be appropriately selected according to the purpose. Specifically, when obtaining a cation exchange resin, treatment such as sulfonation, chlorosulfonation, phosphoniumation, hydrolysis, anion exchange, etc. When a resin is obtained, a desired ion exchange group can be introduced by performing amination, alkylation or the like. By introducing the ion exchange group, the ion exchange membrane of the present invention can be obtained.

Manufacturing method 2. Method of dissolving resin (polymer) in solvent and penetrating into pores of porous membrane As a second method for producing the ion exchange membrane of the present invention, in the production method 1 described above, a polymerizable monomer Instead of this, a method using an ion exchange resin or a precursor resin thereof and a solvent may be used. In other words, the polymerization monomer is polymerized before contacting the porous membrane. In this method, generally, the ion exchange resin or its precursor resin does not permeate into the porous pores as it is, so it is necessary to make a solution dissolved in a solvent. The inorganic filler is as described above.

  The ion exchange resin to be used is not particularly limited as long as it can be dissolved in a solvent, and any known one may be used, but the hydrocarbon ion exchange resin as described above is preferable. The ion exchange resin precursor resin can be made into an ion exchange resin by a known ion exchange group introduction method, and is not particularly limited as long as it is a resin that is soluble in the solvent to be used. Examples include so-called engineering plastics such as polystyrene, polyaryl ether, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene oxide, and polyimide, and elastomers such as polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer. .

  The solvent is not particularly limited as long as it dissolves the ion exchange resin or its precursor resin, and is appropriately selected from known solvents. Examples of such solvents include water, acetone, dichloroethane, chloroform, methanol, ethanol, 1-propanol, 2-propanol, methyl ethyl ketone, acetonitrile, nitromethane, tetrahydrofuran, dioxane, N, N-dimethylformamide, toluene and the like. It is done. Further, these solvents may be a single solvent or a mixed solvent of two or more kinds. Considering the ease of removing the solvent, it is preferable to use an organic solvent.

In the suspension (suspension 2) containing the inorganic filler, the ion exchange resin or its precursor resin, and the solvent as described above, the mixing ratio thereof is not particularly limited. When even considered in conjunction sex and finally obtained ion-exchange membrane performance than methanol barrier property, such as, ion exchange resin or major axis average porous membrane of the primary particles relative to the precursor resin 100 parts by weight The inorganic filler which is 1 to 20 times the average pore diameter is 1 to 70 parts by weight, particularly 1 to 45 parts by weight, and the organic solvent is 10 to 500 parts by weight, particularly 20 to 200 parts by weight. Further, the suspension 2 may contain other components as necessary, and specifically, various polymerizable monomers and plasticizers exemplified in the production method 1 may be mentioned. As the plasticizers, dibutyl phthalate, dioctyl phthalate, dimethyl isophthalate, dibutyl adipate, triethyl citrate, acetyl tributyl citrate, dibutyl sebacate and the like are generally used.

  Such a suspension 2 is brought into contact with the porous membrane in the same manner as in the production method 1, and an ion exchange resin or a precursor resin thereof, an organic solvent and, if necessary, in the pores of the porous membrane. Among the components to be blended, a component soluble in an organic solvent penetrates.

  In production method 2, it is necessary to subsequently remove the solvent used. The removal method is not particularly limited, and a known solvent removal method such as natural drying, vacuum drying, heat drying, and reduced pressure drying may be used.

  When an ion exchange resin is used, the ion exchange membrane of the present invention is obtained by removing the solvent. However, when an ion exchange resin precursor resin is used, an ion exchange group is subsequently added to the precursor resin. Must be converted to an ion exchange resin. The conversion method to the ion exchange resin is the same as described in Production Method 1. The ion exchange membrane of this invention is obtained by conversion to this ion exchange resin.

  The ion exchange resin in the ion exchange membrane obtained by the above production methods (1 and 2) has an ion exchange capacity of 0.2 to 5.5 from the viewpoint of lowering the electric resistance value of the obtained ion exchange membrane. It is preferable to adjust the amount of ion-exchange groups so that it is 0 mmol / g, particularly 0.5 to 3.0 mmol / g. Further, the water content is preferably 5% or more, and more preferably 10% or more so that the proton conductivity is not easily lowered by drying. Generally, the moisture content is maintained at about 5 to 90%. In order to obtain a moisture content in such a range, it can be controlled by a known method such as adjustment of the type of ion exchange group, ion exchange capacity, and degree of crosslinking.

Since the ion exchange membrane of the present invention obtained by such a manufacturing method can use a high-strength and thin porous film as described above, the ion exchange capacity of the hydrocarbon ion exchange resin is adjusted. By doing so, the electric resistance value can be expressed as an electric resistance in a 3 mol / L-sulfuric acid aqueous solution of 0.30 Ω · cm ² or less, and further 0.15 Ω · cm ² or less. In addition, even when the inner layer is a porous film, the ion exchange resin in the voids is satisfactorily filled, so that the methanol permeability can be made extremely small, for example, the methanol per 50% methanol solution at 25 ° C. Transmittance is 1.0 × 10 ³ g · m ⁻² · 24 hr ⁻¹ · atm ⁻¹ or less, especially 0.2 to 0.8 × 10 ³ g · m ⁻² · 24 hr ⁻¹ · atm ⁻¹ You can also get what is. Since the methanol permeability of the ion exchange membrane of the present invention is small in this way, when it is directly used as a diaphragm for a methanol type fuel cell, the methanol supplied to the fuel chamber and the oxidant chamber permeates the diaphragm and the opposite chamber. Can be prevented, and a battery with high output can be obtained. In this case, if a layer having a layer containing an inorganic filler and an ion exchange resin only on one side is used, it is more preferable to install the layer so that the layer is on the fuel chamber side. A direct methanol fuel cell in which the ion exchange membrane of the present invention manufactured by the manufacturing method of the present invention is applied as a direct methanol fuel cell diaphragm generally has a structure as shown in FIG. However, the ion exchange membrane of the present invention can of course be applied to a direct methanol fuel cell having another known structure.

  In order to describe the present invention more specifically, examples and comparative examples will be described below, but the present invention is not limited to these examples. In addition, the characteristic of the cation exchange membrane shown in an Example and a comparative example shows the value measured with the following method.

(1) cation exchange capacity and moisture content;
A cation exchange membrane is immersed in a 1 (mol / l) HCl aqueous solution for 10 hours or more to obtain a hydrogen ion type, and then replaced with a sodium ion type with a 1 (mol / l) NaCl aqueous solution to separate the released hydrogen ions with a potentiometric titrator. It was quantified by (COMTITE-900, manufactured by Hiranuma Sangyo Co., Ltd.) (Amol). Next, the same cation exchange membrane is immersed in 1 (mol / l) HCl aqueous solution for 4 hours or more, washed thoroughly with ion exchange water, and then the membrane is taken out and wiped with a tissue paper or the like to wipe off the moisture on the surface. Wg) was measured. Next, the membrane was dried under reduced pressure at 60 ° C. for 5 hours, and its weight was measured (Dg). Based on the measured value, the cation exchange capacity was determined by the following equation.

Cation exchange capacity = A × 1000 / D [mmol / g-dry weight]
Moisture content = 100 × (WD) / D [%]
(2) Electric resistance A cation exchange membrane was placed in the center of a two-chamber cell equipped with a platinum electrode, and the cell was filled with a 3 (mol / l) sulfuric acid aqueous solution at 25 ° C. Lugin tubes were provided on both sides of the cation exchange membrane, and were connected to the reference electrode by salt bridges. A potential (aV) when a current of 100 (mA / cm ² ) was passed through the membrane and a potential (bV) when a current of 100 (mA / cm ² ) was passed without sandwiching the membrane were measured. The electrical resistance of the cation exchange membrane was obtained from the following equation.

Electrical resistance = 1000 × (ab) / 100 [Ω · cm ² ].
(3) Heat resistance (shrinkage rate)
The sample membrane for measurement preliminarily dried in a dryer at 50 ° C. for 1 hour is immersed in 90 ° C. ion exchange water for 4 hours, then taken out from the ion exchange water and measured for dimensions, and the shrinkage rate is obtained by the following equation. It was.

S = 100 × (La−Lb) / La
S: Shrinkage rate (%)
La: Length of the membrane dried in a dryer at 50 ° C. (cm)
Lb: Length (cm) of a film immersed in ion exchange water at 90 ° C. for 4 hours.

(4) Methanol permeability As a method for measuring the methanol permeability, a liquid permeation tester by a differential pressure method based on JIS K 7126A was used. The cation exchange membrane used for the measurement was impregnated with 50% methanol at 25 ° C. for 30 minutes and then mounted on a liquid permeation tester. The amount of methanol that permeated the cation exchange membrane was measured by gas chromatogram. The liquid used for the measurement was 50% methanol kept at 25 ° C. Methanol permeability was determined by the following formula.

Q = q × 76 / (a × t × Pa)
Q: Methanol permeability (g / m ² · 24 hr · atm)
q: methanol permeation amount t; measurement time a: methanol permeation area Pa: methanol partial pressure.

(5) Fuel cell output voltage First, on the cation exchange membrane to be measured, carbon black supported by 30% by weight of platinum having an average particle diameter of 2 nm as a catalyst, and sulfonated polystyrene-poly (ethylene-butylene) -Polystyrene triblock copolymer (cation exchange capacity 0.9) mixed with a 5% solution of alcohol and dichloroethane, and dried under reduced pressure at 80 ° C for 4 hours. Thermocompression bonding is performed for 100 seconds under a pressure of 5 MPa, and the mixture is allowed to stand at room temperature for 2 minutes to obtain a cation exchange membrane / gas diffusion electrode assembly. Next, the obtained cation exchange membrane / gas diffusion electrode assembly was sandwiched from both sides by carbon paper electrodes having a thickness of 200 μm and a porosity of 80%, and assembled into a fuel cell having the structure shown in FIG. Then, a fuel cell temperature was set to 25 ° C., a 10% methanol aqueous solution was supplied to the fuel electrode side, and atmospheric pressure oxygen was supplied to the oxidation electrode side at 200 (ml / min.), And a power generation test was performed. The cell terminal voltage was measured at (A / cm ² ), 0.1 (A / cm ² ), and 0.3 (A / cm ² ).

(6) Durability evaluation After measurement of the output voltage, a continuous power generation test was performed under the conditions of 25 ° C. and current density of 0.1 (A / cm ² ), and the output voltage after 250 hours was measured. The durability of the membrane was evaluated.

(7) Measurement of thickness of inorganic filler and ion-exchange resin layer and inorganic filler content The thickness of the inorganic filler and ion-exchange resin layer (inorganic filler-containing layer) is measured by scanning electron microscope and electron probe microanalyzer. Was measured by cross-sectional observation and elemental analysis of the ion exchange membrane. Furthermore, the inorganic filler content of the layer was calculated by elemental analysis.

Examples 1-7
In accordance with the composition table shown in Table 1, each monomer composition is mixed with silicate as an inorganic filler whose average primary particle length is not less than 0.1 times the average pore size of the porous stretched film and not more than 50 μm. After obtaining a mixture (suspension), 400 g of the obtained mixture was put into a 500 ml glass container, and a porous membrane (membrane of 20 cm × 20 cm) made of polyethylene (PE, weight average molecular weight 250,000) each. The thickness of 25 μm, the porosity of 40%, and the average pore size of 0.02 μm) were immersed at 25 ° C. for 10 minutes under atmospheric pressure, and these porous membranes were impregnated with the monomer composition. The inorganic filler A is montmorillonite, which is a layered silicate, and is composed of particles having an average particle diameter of 2.0 μm and an aspect ratio in the range of 200 to 1000 (“Esben”, tetraalkyl manufactured by Nippon Organoclay Co., Ltd.). Ammonium treated product). Inorganic filler B is hectorite which is a layered silicate, and is composed of particles having an average particle diameter of 2.0 μm and an aspect ratio in the range of 200 to 1000 (“SAN” manufactured by Coop Chemical Co., a tetraalkylammonium treated product) ). The inorganic filler C is mica which is a layered silicate, and is composed of particles having an average particle diameter of 4.2 μm and an aspect ratio in the range of 200 to 1000 (“4CD-Ts” manufactured by Topy Industries, Ltd., tetraalkylammonium treatment). Product). The inorganic filler D is spherical silica having an average particle size of 0.02 μm (“HM-20L” manufactured by Tokuyama Corporation, hexamethyldisilazane-treated product).

Subsequently, the porous film is taken out from the monomer composition, and coated on both sides of the porous film using a 100 μm polyester film as a release agent, and then heated at 80 ° C. for 5 hours under nitrogen pressure of 3 kg / cm ^2. Polymerized. Next, the obtained membrane was immersed in a 1: 1 mixture of 98% concentrated sulfuric acid and chlorosulfonic acid having a purity of 90% or more at 40 ° C. for 45 minutes to obtain a sulfonic acid type cation exchange membrane. The film thickness, cation exchange capacity, moisture content, electrical resistance, heat resistance, methanol permeability coefficient, fuel cell output voltage and durability of each sulfonic acid type cation exchange membrane thus obtained were measured. These results are shown in Table 2. Note that these ion exchange membranes had a layer made of an inorganic filler and an ion exchange resin formed on both sides of the porous film according to the electron microscope observation (shown in Table 2 is the thickness on one side). In this observation, the presence of the inorganic filler was not observed in the pores of the porous film used as the substrate, and it was confirmed that the content was at most 0.01%.

Comparative Example 1
According to the composition table shown in Table 1, the same monomers as in Example 1 were mixed to obtain a monomer composition containing no silicate. 400 g of the obtained monomer composition is put into a 500 ml glass container, and the same polyethylene porous membrane as described above is immersed at 25 ° C. for 10 minutes under atmospheric pressure, and the monomer composition is placed in the void of the porous membrane. Filled. Subsequently, the same operation as in Example 1 was performed to obtain a sulfonic acid type cation exchange membrane, and the same evaluation as in Example 1 was performed. The results are shown in Table 2.

Comparative Example 2
According to the composition table shown in Table 1, the same monomer as in Example 1 was used, and 5 parts by weight of silica having an average particle size of 0.02 μm was mixed with this to obtain a mixture (suspension). 400 g of the obtained mixture was put in a 500 ml glass container, and instead of the polyethylene porous membrane used in Example 1, a polyethylene porous membrane having a thickness of 25 μm, a porosity of 50%, and an average pore diameter of 0.6 μm was placed under atmospheric pressure. Then, it was immersed at 25 ° C. for 10 minutes to fill the voids of the porous membrane with the monomer composition. Next, the same operation as in Example 1 was performed to obtain a sulfonic acid type cation exchange membrane. The film thickness, cation exchange capacity, water content, electrical resistance, heat resistance, methanol permeability, and fuel cell output voltage of the obtained sulfonic acid type cation exchange membrane were measured. These results are shown together in Table 2. According to the electron microscopic observation of the cross section of the ion exchange membrane, it was confirmed that the inorganic filler and the ion exchange resin were present in the same ratio not only on both sides of the porous film but also on the void portion of the porous film. It was done.

Example 8
A mixture (suspension) was obtained by mixing 100 parts by weight of a polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer, 3 parts by weight of silicate A as an inorganic filler, and 100 parts by weight of dichloroethane as a solvent. 400 g of the obtained monomer composition is put in a 500 ml glass container, and the same polyethylene porous membrane as described above is immersed at 25 ° C. for 10 minutes under atmospheric pressure, and the polymer solution is filled into the voids of the porous membrane. did. The impregnation property of these polymer solutions was 30 seconds. Subsequently, the porous membrane was taken out from the suspension and heated at 25 ° C. for 6 hours to obtain a membrane-like product. Next, the same operation as in Example 1 was performed to obtain a sulfonic acid type cation exchange membrane, and the same evaluation as in Example 1 was performed. The results are shown in Table 3.

As described above, the ion exchange membrane of the present invention has low electrical resistance and extremely low methanol permeability. The reason why the above-described effects in the present invention are manifested is not clear, but the inorganic filler is uniformly deposited on the substrate made of the porous film to form a layer and block the opening of the pores of the porous film. Therefore, not only can the liquid such as methanol be effectively prevented from passing through, but also the ion exchange resin layer containing the inorganic filler is sufficiently thin so that the electrical resistance is not increased, and particularly used as a fuel cell. In this case, it is considered that the output characteristics are not deteriorated. In the case of using the sheet or film of a porous formed of a polyolefin resin as the base material may familiar with the hydrocarbon-based cation-exchange resin and said substrate further hydrocarbon void portion of the substrate Due to the anchor effect caused by the ion-exchange resin being buried, the adhesion between the two becomes strong. For example, when the membrane is used directly as a diaphragm for a methanol type fuel cell, the membrane is thermocompression bonded to the fuel and oxidant gas diffusion electrode, or to the fuel cell. Even after being mounted and used for a long period of time, the above-described excellent characteristics are maintained well, and the obtained direct methanol fuel cell seems to stably exhibit a high cell output.
more than

FIG. 1 is a conceptual diagram showing the basic structure of a direct methanol fuel cell. FIG. 2 is a schematic view showing the structure of the ion exchange membrane of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Battery partition 2; Fuel flow hole 3; Oxidant gas flow hole 4; Fuel chamber side diffusion electrode 5; Oxidant chamber side gas diffusion electrode 6; Solid polymer electrolyte 7; Fuel chamber 8; Oxidant chamber 9; Material membrane 10; ion exchange resin 11; inorganic filler 12; layer made of inorganic filler and ion exchange resin

Claims (5)

An ion exchange membrane having pores with an average pore size in the range of 0.01 to 2 μm, a porous membrane made of a polyolefin resin as a base material, and a hydrocarbon ion exchange resin in the pores. And a layer containing an inorganic filler and a hydrocarbon ion exchange resin having an average value of the major axis of primary particles not less than the average pore size of the porous membrane and not more than 50 μm on at least one surface of the porous membrane. A membrane for a direct methanol fuel cell comprising an ion-exchange membrane in which there is a gas. 2. The direct methanol fuel according to claim 1, wherein the inorganic filler in which the average value of the major axis of the primary particles is not less than the average pore size of the pores of the porous membrane and not more than 50 μm is layered particles having an aspect ratio in the range of 50 to 2,000. Battery diaphragm. (1) A porous membrane having pores with an average pore diameter in the range of 0.01 to 2 μm and a polyolefin resin , wherein the average primary particle major axis is greater than or equal to the pore average pore diameter of the porous membrane And a suspension containing an inorganic filler that is 50 μm or less, and a polymerizable monomer that polymerizes to give a hydrocarbon ion exchange resin or a polymerizable monomer that gives a hydrocarbon ion exchange resin precursor resin ; Making the polymerizable monomer permeate into the pores of the porous membrane by contact, and then (2) the polymerizable monomer contained in the suspension in the pores and on the surface of the porous membrane. (3) When a suspension containing a polymerizable monomer that polymerizes to give a hydrocarbon ion exchange resin precursor resin is used, the resulting polymer is converted into a hydrocarbon ion exchange. Hydrocarbon on the surface of the porous membrane by converting to resin 2. A layer comprising a system ion exchange resin and the inorganic filler is formed, and a layer consisting essentially of a hydrocarbon ion exchange resin is formed in the pores of the porous membrane. Or the manufacturing method of the diaphragm for direct methanol type fuel cells of 2. (1) A porous membrane having pores having an average pore diameter in the range of 0.01 to 2 μm and made of a polyolefin resin . (I) An average value of primary particles' long diameter is a pore of the porous membrane. An inorganic filler having an average pore size of 50 μm or less, (ii) a hydrocarbon ion exchange resin or a hydrocarbon ion exchange resin precursor resin, and (iii) a porous membrane in contact with a suspension containing a solvent And (2) removing the solvent contained in the suspension in the pores and on the surface of the porous membrane, and (3) hydrocarbon ions. by converting the resin to the hydrocarbon-based ion-exchange resin in the case of using a suspension containing exchange resin precursor resin, the porous surface to a hydrocarbon-based ion-exchange resin and the inorganic filler film Forming a layer containing Said porous manufacturing method of a direct methanol fuel cell membrane as claimed in claim 1 or 2 in the pores and forming a layer made of substantially only hydrocarbon-based ion exchange resin membrane.   A direct methanol fuel cell using the direct methanol fuel cell membrane according to claim 1 or 2.

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