JP5189394B2 - Polymer electrolyte membrane - Google Patents

Description

  The present invention relates to a polymer electrolyte membrane.

  A fuel cell is one that converts the chemical energy of the fuel directly into electrical energy by electrochemically oxidizing fuel such as hydrogen and methanol in the battery, and is a clean electrical energy supply source. Attention has been paid. In particular, solid polymer electrolyte fuel cells are expected to be used as alternative power sources for automobiles, home cogeneration systems, portable generators, and the like because they operate at a lower temperature than other fuel cells.

  Such a solid polymer electrolyte fuel cell has a membrane electrode in which gas diffusion electrodes having a structure in which an electrode catalyst layer (anode catalyst layer, cathode catalyst layer) and a gas diffusion layer are laminated are bonded to both surfaces of a proton exchange membrane. At least a joined body is provided. The proton exchange membrane here is a polymer electrolyte membrane made of a composition having a strongly acidic group such as a sulfonic acid group or a carboxylic acid group in a polymer chain and a property of selectively transmitting protons. Examples of the composition used for such a proton exchange membrane include a perfluoro proton composition typified by Nafion (registered trademark, manufactured by DuPont) having high chemical stability, and a proton exchange membrane using the same. Are preferably used.

  During operation of the fuel cell, fuel (eg, hydrogen) is supplied to the gas diffusion electrode on the anode side, and oxidant (eg, oxygen or air) is supplied to the gas diffusion electrode on the cathode side. The operation of the fuel cell is realized by connecting both electrodes with an external circuit. Specifically, when hydrogen is used as fuel, hydrogen is oxidized on the anode catalyst in the anode catalyst layer to generate protons. After passing through the proton conductive polymer in the anode catalyst layer, the proton moves in the proton exchange membrane and reaches the cathode catalyst in the same layer through the proton conductive polymer in the cathode catalyst layer. On the other hand, electrons generated simultaneously with protons due to oxidation of hydrogen reach the gas diffusion electrode on the cathode side through an external circuit. On the cathode catalyst in the cathode electrode layer, the proton and oxygen in the oxidant react to generate water. At this time, electric energy is extracted.

  At this time, the proton exchange membrane must also serve as a gas barrier partition by lowering the gas permeability. When the gas permeability of the proton exchange membrane is high, leakage of anode-side hydrogen to the cathode and leakage of cathode-side oxygen to the anode, that is, cross-leakage occurs. When a cross leak occurs, a so-called chemical short circuit occurs and a good voltage cannot be taken out. There is also a problem that the hydrogen on the anode side reacts with the oxygen on the cathode side to generate hydrogen peroxide and deteriorate the proton exchange membrane.

  On the other hand, from the viewpoint of reducing the internal resistance of the battery and increasing the output, it has been studied to reduce the thickness of the proton exchange membrane that is an electrolyte. However, if this proton exchange membrane is thinned, the effect as a gas barrier partition is reduced, and the problem of cross leak becomes more serious. Furthermore, since the mechanical strength of the membrane itself is reduced by reducing the thickness of the proton exchange membrane, it becomes difficult to handle the membrane during fabrication of the membrane electrode assembly and cell assembly, and water generated on the cathode side. There is a problem that the film is torn by changing the dimensions including the.

In order to solve such problems, a proton exchange membrane in which a polytetrafluoroethylene porous membrane is impregnated with a fluorine ion exchange resin having a sulfonic acid group has been proposed (see Patent Document 1). A proton exchange membrane in which a polyethylene porous membrane is impregnated with an ion exchange resin has been proposed (see Patent Document 2).
Japanese Patent Publication No. 5-75835 Japanese Examined Patent Publication No. 7-68377

  However, the proton exchange membrane disclosed in Patent Document 1 is insufficient from the viewpoint of mechanical strength because polytetrafluoroethylene is a material with poor elasticity. In addition, since the proton exchange membrane disclosed in Patent Document 2 has insufficient heat resistance of polyethylene, the membrane melts when the proton exchange membrane is heat-treated or a membrane electrode assembly is produced. There is a problem of being torn.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polymer electrolyte membrane having superior dimensional stability, mechanical strength, and heat resistance as compared with the prior art.

The present invention for solving the above-mentioned problems includes a polyolefin composition containing 5% by mass or more of polypropylene and ultrahigh molecular weight polyethylene having a weight average molecular weight of 5 × 10 ⁵ or more, and has a porosity of 10% to 90%, a membrane A polyolefin microporous membrane having a thickness of 0.1 μm to 50 μm and a pore diameter of 0.03 μm to 5 μm, and the pores of the polyolefin microporous membrane are filled with an ion exchange capacity of 1.3 to 3.0 meq. / G polymer electrolyte , wherein the polymer electrolyte is a perfluorocarbon sulfonic acid resin, and the perfluorocarbon sulfonic acid resin is a repeating unit represented by the following formula (1) And a polymer electrolyte membrane selected from the group consisting of a copolymer having a repeating unit represented by the following general formula (2) and a metal salt thereof.
-(CF ₂ CF ₂ )-(1)
_{- (CF 2 -CF (-O- (} CF 2 CFXO) n - (CF 2) m -SO 3 H)) - (2)
(In the formula, X represents a fluorine atom or —CF ₃ group, n represents an integer of 0 to 5, and m represents an integer of 0 to 12. However, n and m are not 0 at the same time.)
Here, from the viewpoint of durability, the polymer electrolyte membrane further contains a polyazole compound mixed with the polymer electrolyte and filled in the pores, and the thioether compound is preferably polyphenylene sulfide, and the polymer electrolyte And further containing a thioether compound filled in the pores, and the thioether compound is preferably polyphenylene sulfide , or mixed with a polymer electrolyte and filled in the pores, a polyazole compound and a thioether compound It is preferable that the polyazole compound is a polyimidazole compound, and the thioether compound is polyphenylene sulfide .

  According to the present invention, it is possible to provide a polymer electrolyte membrane that is more excellent in dimensional stability, mechanical strength, and heat resistance than before.

  Hereinafter, the best mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist.

  This embodiment includes a polyolefin composition containing 1% by mass or more of polypropylene, a polyolefin microporous material having a porosity of 10% to 90%, a film thickness of 0.1 μm to 50 μm, and a pore diameter of 0.03 μm to 5 μm. A polymer electrolyte membrane comprising a membrane and a polymer electrolyte having an ion exchange capacity of 0.5 to 3.0 meq / g filled in the pores of the polyolefin microporous membrane.

(Polymer electrolyte)
The polymer electrolyte according to this embodiment has a ion exchange capacity of 0.5 to 3.0 meq / g, and is a polymer compound having an ion exchange group so as to satisfy this condition. By setting the ion exchange capacity to 3.0 meq / g or less, a polymer electrolyte membrane containing this polymer electrolyte is preferable because swelling under high temperature and high humidity during fuel cell operation is reduced. Reduction of the swelling of the polymer electrolyte membrane causes problems such as a decrease in strength of the polymer electrolyte membrane, generation of wrinkles and separation from the electrode, and a problem of reduced gas barrier properties. Can improve. On the other hand, by setting the ion exchange capacity to 0.5 meq / g or more, the fuel cell equipped with the polymer electrolyte membrane satisfying such conditions can maintain its power generation capability well. From these viewpoints, the ion exchange capacity of the polymer electrolyte is more preferably 0.65 to 2.0 meq / g, and still more preferably 0.8 to 1.5 meq / g.

In addition, the ion exchange capacity of the polymer electrolyte in this embodiment is measured as follows. First, a membrane made of a polymer electrolyte in which the counter ion of the ion exchange group is in a proton state is immersed in a saturated NaCl aqueous solution at 25 ° C., and the aqueous solution is stirred for a sufficient time. Subsequently, the proton in the saturated NaCl aqueous solution is neutralized and titrated with a 0.01N sodium hydroxide aqueous solution. A membrane made of a polymer electrolyte in which the counter ion of the ion exchange group obtained by filtration after neutralization is in the form of sodium ions is rinsed with pure water, further vacuum-dried, and weighed. The amount of sodium hydroxide required for neutralization is M (mmol), the mass of a membrane made of a polymer electrolyte in which the counter ion of the ion exchange group is sodium ion is W (mg), and the equivalent mass EW ( g / equivalent).
EW = (W / M) −22
Furthermore, the ion exchange capacity (milli equivalent / g) is calculated by taking the reciprocal of the obtained EW value and multiplying it by 1000.

  This ion exchange capacity is adjusted to fall within the above numerical range by adjusting the number of ion exchange groups present in 1 g of the polymer electrolyte membrane.

  In addition, the polymer electrolyte according to the present embodiment has a glass transition temperature of preferably 80 ° C. or higher, more preferably 100 ° C. or higher, more preferably 120 ° C. or higher, particularly from the viewpoint of heat resistance during fuel cell operation. Preferably it is 130 degreeC or more. Here, the glass transition temperature of the polymer electrolyte is measured according to JIS-C-6481. Specifically, the polymer electrolyte molded into a film shape is cut into a width of 5 mm, and the test piece is heated from room temperature at a rate of 2 ° C./minute using a dynamic viscoelasticity measuring device. The dynamic viscoelasticity and loss tangent of the specimen are measured. The measured peak temperature of loss tangent is defined as the glass transition temperature. The glass transition temperature is adjusted by controlling the structural formula, molecular weight, ion exchange capacity, etc. of the polymer electrolyte.

  Examples of the polymer electrolyte include perfluorocarbon polymer compounds having an ion exchange group in the molecule, those obtained by introducing an ion exchange group into a hydrocarbon polymer compound having an aromatic ring in the molecule, and metal salts thereof. One or more selected from the group consisting of Among these, from the viewpoint of chemical stability, one or more selected from the group consisting of perfluorocarbon polymer compounds having an ion exchange group in the molecule and metal salts thereof are particularly preferable. Examples of the hydrocarbon polymer compound having an aromatic ring in the molecule include polyphenylene sulfide, polyphenylene ether, polysulfone, polyethersulfone, polyetherethersulfone, polyetherketone, polyetheretherketone, polythioetherethersulfone, polythiol. Thioetherketone, polythioetheretherketone, polybenzimidazole, polybenzoxazole, polyoxadiazole, polybenzoxazinone, polyxylylene, polyphenylene, polythiophene, polypyrrole, polyaniline, polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide sulfone, polyphenylene sulfone, Polyimide, polyether imide, polyester imide, polyamide imide, poly Rate, aromatic polyamide, polystyrene, polyesters, polycarbonates. These are used singly or in combination of two or more.

  Among these hydrocarbon polymer compounds having an aromatic ring in the molecule, from the viewpoint of heat resistance, oxidation resistance and hydrolysis resistance, polyphenylene sulfide, polyphenylene ether, polysulfone, polyethersulfone, polyetherethersulfone, Polyetherketone, Polyetheretherketone, Polythioetherethersulfone, Polythioetherketone, Polythioetheretherketone, Polybenzimidazole, Polybenzoxazole, Polyoxadiazole, Polybenzoxazinone, Polyxylylene, Polyphenylene, Polythiophene, Polypyrrole, Polyaniline , Polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide sulfone, polyphenylene sulfone, polyimide, polyetherimide, poly One or more members selected from the group consisting of esters imide are preferable. In addition, the ion exchange group introduced into these is, for example, preferably a sulfonic acid group, a sulfonimide group, a sulfonamide group, a carboxylic acid group, and a phosphoric acid group, and particularly preferably a sulfonic acid group. This ion exchange group is introduced into the hydrocarbon polymer compound by a conventional method.

In addition, perfluorocarbon polymer compounds having an ion exchange group in the molecule are represented by the following general formula (I)
_{- (CF 2) p - (} I)
Is a polymer compound having a perfluoroalkylene group and an ion exchange group. In the above formula (I), p represents an integer. Examples of such a polymer compound include perfluorocarbon sulfonic acid resin, perfluorocarbon carboxylic acid resin, perfluorocarbon sulfonimide resin, perfluorocarbon sulfonamide resin, and perfluorocarbon phosphoric acid resin. Or the amine salt and metal salt of these resin are mentioned. These are used singly or in combination of two or more.

More specifically, the perfluorocarbon polymer compound includes a polymer having a structural unit represented by the following general formula (II).
^{_{- (CF 2 CX 1 X 2}} ) a - [CF 2 -CF (-O- (CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - ( ^{_{CF 2) f -X 4)]}} g - (II)
Here, in the formula ^{(II), X 1, X} 2 and ^{X 3} represents a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms independently. a and g each independently represent a number of 0 or more and less than 1, and a + g = 1. b shows the integer of 0-8. c represents 0 or 1; d, e, and f each independently represent an integer of 0 to 10, but d + e + f is an integer larger than 0. R ¹ and R ² each independently represent a halogen atom other than a fluorine atom, a C 1-10 perfluoroalkyl group or a C 1-10 fluorochloroalkyl group. X ⁴ represents COOZ, SO ₃ Z, PO ₃ Z ₂ or PO ₃ HZ. Z represents a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or a substituted or unsubstituted ammonium group (NH ₄ , NH ₃ R ³ , NH ₂ R ³ R ⁴ , NHR ³ R ⁴ R ^5, or NR ³ R ⁴ R ⁵ R ⁶ ). R ³ , R ⁴ , R ⁵ and R ⁶ each independently represents an alkyl group or an aryl group.

Among these, the perfluorocarbon polymer compound is preferably selected from the group consisting of perfluorocarbon sulfonic acid resins and metal salts thereof. As the perfluorocarbon sulfonic acid resin, a copolymer having a repeating unit represented by the above formula (1) and a repeating unit represented by the above general formula (2) is more preferable. Furthermore, the perfluorocarbon sulfonic acid resin and the metal salt thereof are at least one selected from the group consisting of perfluorocarbon sulfonic acid resins having structural units represented by the following general formulas (III) and (IV) Is particularly preferred.
_{- (CF 2 CF 2) a} - [CF 2 -CF (-O-CF 2 -CF (CF 3)) b -O- (CF 2) f -SO 3 Z)] g - (III)
Here, in formula (III), a and g each independently represent a number of 0 or more and less than 1, and a + g = 1. b shows the integer of 1-8. f shows the integer of 0-10. Z represents a hydrogen atom or an alkali metal atom.
_{- (CF 2 CF 2) a} - [CF 2 -CF (-O- (CF 2) f -SO 3 Z)] g - (IV)
Here, in formula (IV), a and g each independently represent a number of 0 or more and less than 1, and a + g = 1. b shows the integer of 1-8. f shows the integer of 0-10. Z represents a hydrogen atom or an alkali metal atom.

After synthesizing a perfluorocarbon polymer compound having an ion exchange group according to this embodiment, for example, a precursor polymer, the precursor polymer is obtained by alkali hydrolysis, acid decomposition, or the like. For example, the polymer having the structural unit represented by the general formula (II) is obtained by polymerizing a precursor polymer having the structural unit represented by the following general formula (V), and then the alkali of the precursor polymer. Obtained by hydrolysis, acid treatment and the like.
^{_{- [CF 2 CX 1 X 2}} ] a - [CF 2 -CF (-O- (CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - ( ^{_{CF 2) f -X 5)]}} g - (V)
Here, in formula (V), X ¹ , X ² , X ³ , R ¹ and R ² , and a, b, c, d, e, f and g are the same as those in formula (II) above. It is synonymous. X ⁵ is COOR ⁷ , COR ⁸ or SO ₂ R ⁸ . R ⁷ represents an alkyl group having 1 to 3 carbon atoms, and R ⁴ represents a halogen atom. )

The precursor polymer is produced, for example, by copolymerizing a fluorinated olefin compound and a vinyl fluoride compound. Here, examples of the fluorinated olefin compound include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, monochlorotrifluoroethylene, perfluorobutylethylene (C ₄ F ₉ CH═CH ₂ ), perfluorohexaethylene ( C ₆ F ₁₃ CH═CH ₂ ), perfluorooctaethylene (C ₆ F ₁₇ CH═CH ₂ ) and the like. These are used singly or in combination of two or more.

Examples of the vinyl fluoride compound include the general formulas listed below;
_{CF 2 = CFO (CF 2)} q -SO 2 F, CF 2 = CFOCF 2 CF (CF 3) O (CF 3) q -SO 2 F, CF 2 = CF (CF 2) q -SO 2 F, CF _{2 = CF (OCF 2 CF (} CF 3)) q - (CF 2) q - 1 -SO 2 F, CF 2 = CFO (CF 2) q -CO 2 R 9, CF 2 = CFOCF 2 CF (CF 3 ^{_{) O (CF 2) q -CO}} 2 R 9, CF 2 = CF (CF 2) q -CO 2 R 9, CF 2 = CF (OCF 2 CF (CF 3)) q - (CF 2) 2 -CO ₂ R ⁹
The thing represented by is mentioned. In the above formulas, q is an integer of 1 to 8, ^{R 9} represents an alkyl group having 1 to 3 carbon atoms.

  The precursor polymer can be synthesized by known copolymerization. Such a synthesis method is not particularly limited, and examples thereof include the following methods.

(I) A method (solution polymerization) in which a polymerization solvent such as a fluorinated hydrocarbon is used and a vinyl fluoride compound and a gas of a fluorinated olefin compound are reacted while being charged and dissolved in the polymerization solvent. As the fluorine-containing hydrocarbon, for example, a group consisting of compounds collectively called “Freon” such as trichlorotrifluoroethane, 1, 1, 1, 2, 3, 4, 4, 5, 5, 5-decafluoropentane and the like. Those selected are preferably used.
(Ii) A method in which polymerization is carried out by reacting a vinyl fluoride compound and a gas of a fluorinated olefin compound using a vinyl fluoride compound itself as a polymerization solvent without using a solvent such as fluorine-containing hydrocarbon (bulk polymerization). .
(Iii) A method (emulsion polymerization) in which an aqueous solution of a surfactant is used as a polymerization solvent, and polymerization is performed by reacting a vinyl fluoride compound and a gas of a fluorinated olefin compound in a state of being charged and dissolved in the polymerization solvent.
(Iv) A method in which an aqueous solution of a surfactant and an auxiliary emulsifier such as alcohol is used, and polymerization is performed by reacting a vinyl fluoride compound and a gas of a fluorinated olefin compound in a state where the aqueous solution is filled and emulsified (mini-emulsion polymerization). , Microemulsion polymerization).
(V) A method in which an aqueous solution of a suspension stabilizer is used and polymerization is carried out by reacting a vinyl fluoride compound and a gas of a fluorinated olefin compound in a state of being filled and suspended in this aqueous solution (suspension polymerization).

In the present embodiment, melt mass flow rate (hereinafter abbreviated as “MFR”) can be used as an index of the polymerization degree of the precursor polymer. In the present embodiment, the MFR of the precursor polymer is preferably 0.01 or more, more preferably 0.1 or more, and still more preferably 0.3 or more. Although the upper limit of MFR is not limited, 100 or less are preferable, 10 or less are more preferable, and 5 or less are still more preferable. By adjusting the MFR to a range of 0.01 to 100, molding processing such as film formation can be favorably performed. The MFR of the precursor polymer is measured according to JIS K-7210. Specifically, the melt flow rate of the fluorine-containing ion exchange resin precursor measured at a temperature of 270 ° C. and a load of 2.16 kg using an apparatus having an inner diameter of 2.09 mm and a length of 8 mm was MFR (g / 10 min). And
Measured by.

  The precursor polymer prepared as described above may be hydrolyzed in a basic reaction liquid, sufficiently washed with warm water or the like, and acid-treated. By this acid treatment, the precursor polymer is protonated to obtain a perfluorocarbon polymer compound. For example, a perfluorocarbon sulfonic acid resin precursor polymer is protonated to obtain a perfluorocarbon sulfonic acid resin.

(Polyolefin microporous membrane)
The polyolefin microporous membrane according to this embodiment includes a polyolefin composition having fine pores and containing 1% by mass or more of polypropylene. Although this polyolefin composition consists of polyolefin, in addition to polypropylene, other polyolefin may be contained in it. Such polyolefin is preferably a polymer having propylene or ethylene as a main monomer component. This polyolefin may be composed of only the main monomer component, but may have other monomer components such as butene, pentene, hexene, 4-methylpentene. Specific examples of the other polyolefin include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene and ultra-low-density polyethylene obtained using a Ziegler-based multisite catalyst, and ethylene-vinyl acetate copolymer. Copolymers, ethylene polymers obtained using a single site catalyst, and copolymers with other monomers copolymerizable with propylene (propylene-ethylene copolymers, propylene-ethylene-α-olefin copolymers) Etc.).

  The polyolefin composition according to the present embodiment preferably contains 1% by mass or more of polypropylene from the viewpoint of heat resistance, more preferably contains 5% by mass or more, more preferably contains 20% by mass or more, and 50 Those containing at least mass% are particularly preferred, and those containing at least 90 mass% are very particularly preferred.

  A polyolefin microporous membrane containing polypropylene in the polyolefin composition can dramatically improve heat resistance as compared to a microporous membrane made of polyethylene alone. That is, the polyolefin microporous membrane according to the present embodiment can operate the fuel cell at a high temperature of 100 ° C. or higher, and can be heat-treated at 150 ° C. or higher after forming the polymer electrolyte membrane. The polymer electrolyte membrane of this embodiment can have its mechanical strength stabilized by heat treatment. From this viewpoint, in particular, when the glass transition temperature of the polymer electrolyte is 130 ° C. or higher, the content of polypropylene in the polyolefin composition is more preferably 5% by mass or more, and more preferably 20% by mass or more. More preferably, it is particularly preferably 50% by mass or more, and particularly preferably 90% by mass or more.

  The polypropylene according to this embodiment includes a propylene homopolymer (homopolypropylene), and an ethylene propylene random copolymer and an ethylene propylene block copolymer containing 1.0% by mass or less of ethylene as a monomer component in addition to propylene.

The polypropylene according to this embodiment may be a crystalline polymer composed of propylene polymer units. The weight average molecular weight of the polypropylene according to this embodiment is preferably 3.0 × 10 ⁵ or more, and more preferably 3.5 × 10 ^{5 to} 7.5 × 10 ⁵ from the viewpoint of heat resistance. In the present embodiment, the weight average molecular weight is measured by a gel-permeation chromatography method (GPC method) in terms of polystyrene.
Moreover, the polypropylene which concerns on this embodiment may be terminal-modified in order to improve the filling property of the above-mentioned polymer electrolyte. The ion exchange group used for terminal modification is preferably, for example, one selected from the group consisting of a sulfonic acid group (sulfo group), a sulfonimide group, a sulfonamide group, a carboxylic acid group (carboxyl group), and a phosphoric acid group. Sulfonic acid groups are preferred.

  Polyethylene other than polypropylene contained in the polyolefin composition is preferably polyethylene.

The polyethylene according to this embodiment is an ultrahigh molecular weight polyethylene having a weight average molecular weight of preferably 5 × 10 ⁵ or more, more preferably 1 × 10 ⁶ to 15 × 10 ⁶ from the viewpoint of heat resistance. The polyethylene content in the polyolefin composition is preferably 95% by mass or less, more preferably 80% by mass or less, still more preferably 50% by mass or less, and particularly preferably 10% by mass or less from the viewpoint of heat resistance. In this embodiment, in order to increase the concentration of the polyolefin solution described later and improve the strength of the polyolefin microporous membrane, the ultrahigh molecular weight polyethylene having a weight average molecular weight of 1 × 10 ⁶ or more and the weight average molecular weight of 1 × A composition (polyethylene composition) with 10 ⁵ or more and less than 5 × 10 ⁵ high-density polyethylene can be used. The content of the ultrahigh molecular weight polyethylene in the polyethylene composition is preferably 1% by mass or more, more preferably 10 to 70% by mass, based on 100% by mass of the entire polyethylene composition.

  In addition, the polyolefin microporous membrane according to the present embodiment, if necessary, metal soaps such as potassium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, coloring pigments, etc. The known additives may be contained within a range that does not impair the achievement and effects of the present invention.

  The polyolefin microporous membrane according to this embodiment preferably has a porosity of 10% to 90%, more preferably 20% to 90%, still more preferably 30% to 90%, and 50%. It is especially preferable that it is -85%. Here, the porosity of the polyolefin microporous membrane is measured by a mercury porosimeter (for example, manufactured by Shimadzu Corporation, trade name: Autopore IV 9520, initial pressure of about 20 kPa) by a mercury intrusion method. When the porosity is in the range of 10% to 90%, there is an effect that it is possible to achieve both improvement in ion conductivity of the polymer electrolyte membrane, improvement in strength of the polymer electrolyte membrane, and suppression of dimensional change. Played. The porosity of the polyolefin microporous membrane is adjusted by the number of pores, pore diameter, pore shape, draw ratio, plasticizer addition amount and type of plasticizer in the polyolefin microporous membrane.

  The polyolefin microporous membrane according to this embodiment preferably has a thickness of 0.1 μm to 50 μm, more preferably 0.5 μm to 30 μm, still more preferably 1.0 μm to 20 μm, and 2.0 μm. It is particularly preferable that it is ˜20 μm. Here, the film thickness of the polyolefin microporous film is determined by sufficiently placing the film in a room with a constant temperature and humidity of 50% RH and then using a known film thickness meter (for example, trade name “B-” manufactured by Toyo Seiki Seisakusho Co., Ltd.). 1 "). When the film thickness is in the range of 0.1 μm to 50 μm, the polymer electrolyte can fill the polyolefin microporous film with pores, and the dimensional change of the polymer electrolyte is suppressed. The film thickness of the polyolefin microporous film is adjusted by the solid content of the cast solution, the amount of the extruded resin, the extrusion speed, and the draw ratio of the polyolefin microporous film.

  The polyolefin microporous membrane according to this embodiment preferably has a pore diameter of 0.03 μm to 5 μm, more preferably 0.03 μm to 3 μm, still more preferably 0.05 μm to 3 μm, and 0 It is particularly preferable that the thickness is 0.05 μm to 1 μm. Here, the pore diameter of the polyolefin microporous membrane is an average pore diameter, and is measured by a mercury porosimeter (for example, trade name: Autopore IV 9520, manufactured by Shimadzu Corporation) by a mercury intrusion method. When the pore diameter is in the range of 0.03 μm to 5 μm, the polymer electrolyte can be easily filled in the voids of the polyolefin microporous membrane, and the effect that it is difficult to escape is produced. The numerical value of the pore diameter of the polyolefin microporous membrane is adjusted by the dispersibility of the plasticizer, the draw ratio of the polyolefin microporous membrane, the irradiation dose and the irradiation time, the plasticizer extraction solvent and the extraction time.

  The polyolefin microporous membrane can be obtained, for example, by the following production method. First, a mixture obtained by adding a plasticizer, an antioxidant and the like to a polyolefin composition containing 1% by mass or more of polypropylene is melt-kneaded. Thereafter, the obtained mixture is extruded, extracted, stretched, etc., and formed into a film, whereby a polyolefin microporous film is obtained. Moreover, you may add inorganic fine powder etc. further to the said mixture which consists of a polyolefin composition and an additive. The method for producing a polyolefin microporous membrane used in the present embodiment includes a step (i) of melt-kneading a polyolefin composition containing 1% by mass or more of polypropylene, a plasticizer and an antioxidant in a nitrogen atmosphere, and a step (i The melt-kneaded product obtained through the step (ii) is extruded, formed into a sheet and cooled and solidified (ii), and the sheet-like cooled and solidified product obtained through the step (ii) is stretched at least in a uniaxial direction. It is preferable to have a step (iii) of obtaining a film-like molded product and a step (iv) of extracting a plasticizer from the molded product obtained through the step (iii).

  As said antioxidant, the phenolic antioxidant which is a primary antioxidant is preferable. Furthermore, 2,6-di-t-butyl-4-methylphenol, pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and the like. In addition, tris (2,4-di-t-butylphenyl) phosphite, tetrakis (2,4-di-t-butylphenyl) -4,4-biphenylene-diphosphonite, which are secondary antioxidants A phosphorus-based antioxidant such as dilauryl-thio-dipropionate may be used in combination with a phenol-based antioxidant as necessary.

  Moreover, the said plasticizer points out the non-volatile solvent which can form a uniform solution above the melting | fusing point, when it mixes with a polyolefin composition. Examples of such a plasticizer include hydrocarbons such as liquid paraffin and paraffin wax, di-2-ethylhexyl phthalate, diisodecyl phthalate, and diheptyl phthalate. Of these, hydrocarbons are preferred as the plasticizer.

  In step (iv), the solvent (extraction solvent) used when extracting the plasticizer is a poor solvent for polyethylene and polypropylene, and a good solvent for the plasticizer, and has a boiling point. Is preferably lower than the melting point of the polyolefin composition. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane, alcohols such as methanol, ethanol and isopropanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran, methylene chloride, 1,1, Examples thereof include organic solvents represented by halogenated hydrocarbons such as 1-trichloroethane. These extraction solvents are used alone or in combination of two or more.

  In the step (iii), for example, a film-like molded product can be obtained by stretching by a uniaxial stretching machine, stretching by a simultaneous biaxial stretching machine, sequential biaxial stretching, or the like. The polyolefin microporous membrane according to the present embodiment is preferably 20 times or more in terms of the area magnification and 40 times or more in terms of the area magnification from the viewpoint of improving the porosity and mechanical strength in a good balance. Further preferred. The stretching temperature is preferably 100 to 135 ° C, and more preferably 110 to 130 ° C.

  In the step (iv), most of the plasticizer contained in the molded product is extracted by immersing the film-shaped molded product in the extraction solvent described above, and then the molded product is sufficiently dried. A polyolefin microporous membrane is obtained. By this extraction, it is preferable that the residual amount of plasticizer in the polyolefin microporous membrane be less than 1% by mass from the viewpoint of reducing impurities eluted from the polymer electrolyte during fuel cell operation.

  It is preferable that the polyolefin microporous film obtained through each of the above steps is further subjected to a heat setting treatment to reduce shrinkage. By performing this heat setting treatment, the shrinkage of the polyolefin microporous membrane under a high temperature atmosphere can be reduced, and the dimensional change of the polymer electrolyte membrane can be reduced. The heat setting is performed on the polyolefin microporous film by, for example, relaxing the stress in the TD direction in a temperature range of about 100 to 135 ° C. with a TD tenter.

  In addition, the polyolefin microporous membrane according to the present embodiment may be subjected to surface treatment such as electron beam irradiation, plasma irradiation, surfactant coating, chemical modification, etc., as long as the problems and effects of the present invention are not impaired. May be applied. Since the surface of the polyolefin microporous membrane can be hydrophilized by applying the surface treatment, it is preferable from the viewpoint of the filling property of the polymer electrolyte solution.

(Additive)
In addition to the polymer electrolyte and the polyolefin microporous membrane, the polymer electrolyte membrane of the present embodiment may contain an additive such as a polyazole compound or a thioether compound) for the purpose of improving durability. These additives are used singly or in combination of two or more.

(Polyazole compound)
Examples of the polyazole compound according to this embodiment include a polyimidazole compound, a polybenzimidazole compound, a polybenzobisimidazole compound, a polybenzoxazole compound, a polyoxazole compound, a polythiazole compound, and a polybenzothiazole compound. Examples thereof include a polymer of a compound having a hetero five-membered ring containing one or more nitrogen atoms in the ring of the compound as a constituent element. The hetero five-membered ring may contain an oxygen atom, a sulfur atom or the like in addition to the nitrogen atom.

  Moreover, it is preferable that the molecular weight of a polyazole compound is 300-500,000 (polystyrene conversion) as a weight average molecular weight at the time of GPC measurement.

  Examples of the compound having the five-membered ring as a constituent element include p-phenylene group, m-phenylene group, naphthalene group, diphenylene ether group, diphenylene sulfone group, biphenylene group, terphenyl group, and 2,2-bis. From the viewpoint of obtaining heat resistance, it is preferable to use a compound in which a divalent aromatic group represented by (4-carboxyphenylene) hexafluoropropane group is bonded to a hetero five-membered ring. Specifically, polybenzimidazole is preferably used as the polyazole compound.

  In addition, the polyazole compound may be a compound in which an ion exchange group is introduced (modified polyazole compound) using the following general modification method. Examples of such modified polyazole compounds include those obtained by introducing one or more groups selected from the group consisting of amino groups, quaternary ammonium groups, carboxyl groups, sulfonic acid groups, and phosphonic acid groups into the polyazole compounds. In addition, by introducing an anionic ion exchange group into the polyazole compound, the ion exchange capacity of the entire polymer electrolyte membrane of the present embodiment can be increased, resulting in high output during fuel cell operation. This is useful. The ion exchange capacity of the modified polyazole compound is preferably 0.1 to 3.5 meq / g.

  The modification method of the polyazole compound is not particularly limited. For example, fuming sulfuric acid, concentrated sulfuric acid, sulfuric anhydride and its complex, sultone such as propane sultone, α-bromotoluenesulfonic acid, chloroalkylsulfonic acid, etc. Examples thereof include a method of introducing an ion exchange group into the polyazole compound, a method of polymerizing by adding an ion exchange group at the time of monomer synthesis of the polyazole compound, and the like.

  The polyazole compound is preferably dispersed in islands in the polymer electrolyte phase. Here, “is dispersed in the form of islands” means a state in which a phase containing a polyazole compound is dispersed in the form of particles in a polymer electrolyte phase when TEM observation is performed without performing a staining treatment. means. Dispersion in such a state indicates that the portion mainly composed of the polyazole compound is uniformly finely dispersed in the portion mainly composed of the polymer electrolyte, which is preferable from the viewpoint of durability.

  Further, the polymer electrolyte and the polyazole compound may form, for example, an ion-bonded ion-base complex or a covalent bond. That is, for example, when the polymer electrolyte has a sulfonic acid group and the polyazole compound has a reactive group such as an imidazole group, an oxazole group, or a thiazole group, the sulfonic acid group in the polymer electrolyte and each reaction in the polyazole compound A nitrogen atom of the group may be bonded to each other by an ionic bond or a covalent bond.

Whether or not the ionic bond or the covalent bond exists can be confirmed using a Fourier-Transform Infrared Spectrometer (hereinafter referred to as FT-IR). For example, when perfluorocarbon sulfonic acid resin is used as the polymer electrolyte and poly [2,2 ′ (m-phenylene) -5,5′-benzimidazole] (hereinafter referred to as PBI) is used as the polyazole compound, it is determined by FT-IR. When performing the measurement, the absorption peak was shifted from chemical bond with the imidazole group of sulfonic acid groups and in PBI of the polymer electrolyte is observed 1458cm around ^-1, 1567Cm around ^-1, around 1634 cm ^-1 .

Further, when a polymer electrolyte membrane to which PBI was added was prepared and a dynamic viscoelasticity test was performed on the membrane, the peak temperature (Tg) of the loss tangent (Tan δ) obtained in the temperature rising process from room temperature to 200 ° C. Higher than that of a polymer electrolyte membrane to which PBI is not added. Such an increase in Tg is preferable because the heat resistance and mechanical strength of the polymer electrolyte membrane can be improved.
(Thioether compound)

The thioether compound according to the present embodiment is a compound having a chemical structure of — (R—S) _r — (S is a sulfur atom, R is a hydrocarbon group, and r is an integer of 1 or more). Specific examples of the compound having such a chemical structure include dialkyl thioethers such as dimethylthioether, diethylthioether, dipropylthioether, methylethylthioether, and methylbutylthioether, tetrahydrothiophene, and tetrahydroapiran. Examples thereof include aromatic thioethers such as cyclic thioether, methylphenyl sulfide, ethylphenyl sulfide, diphenyl sulfide, and dibenzyl sulfide. In addition, you may use what was illustrated here as a thioether compound as it is, for example, you may use the polymer obtained by using what was illustrated for a monomer like a polyphenylene sulfide (PPS) as a thioether compound.

  From the viewpoint of durability, the thioether compound is preferably a polymer (oligomer or polymer) having r of 10 or more, more preferably a polymer having r of 1,000 or more. A particularly preferred thioether compound is polyphenylene sulfide (PPS).

  Here, polyphenylene sulfide will be described. The polyphenylene sulfide used in the present embodiment is a polyphenylene sulfide having a paraphenylene sulfide skeleton of preferably 70 mol% or more, more preferably 90 mol% or more.

  The method for producing the polyphenylene sulfide is not particularly limited. For example, a method in which a halogen-substituted aromatic compound (p-dichlorobenzene or the like) is polymerized in the presence of sulfur and sodium carbonate, a halogen-substituted aromatic compound in a polar solvent. Is polymerized in the presence of sodium sulfide or sodium hydrogen sulfide and sodium hydroxide, a method of polymerizing a halogen-substituted aromatic compound in the presence of hydrogen sulfide and sodium hydroxide or sodium aminoalkanoate in a polar solvent, or Examples include a method by self-condensation of p-chlorothiophenol. Among these, a method of reacting sodium sulfide and p-dichlorobenzene in an amide solvent such as N-methylpyrrolidone or dimethylacetamide or a sulfone solvent such as sulfolane is preferably used.

  Further, the content of -SX group (S is a sulfur atom, X is an alkali metal atom or a hydrogen atom) in polyphenylene sulfide is preferably usually 10 μmol / g to 10,000 μmol / g, more preferably 15 μmol / g. g to 10,000 μmol / g, more preferably 20 μmol / g to 10,000 μmol / g.

  That the content of the —SX group is in the above range means that there are many reaction active sites. By using polyphenylene sulfide in which the content concentration of -SX group satisfies the above range, the miscibility with the polymer electrolyte according to the present embodiment is improved, the dispersibility is improved, and it is higher under high temperature and low humidification conditions. It is thought that durability is obtained.

  Moreover, what introduce | transduced the acidic functional group into the terminal can also be used suitably for a thioether compound. The acidic functional group to be introduced is selected from the group consisting of sulfonic acid group, phosphoric acid group, carboxylic acid group, maleic acid group, maleic anhydride group, fumaric acid group, itaconic acid group, acrylic acid group, and methacrylic acid group. Are preferred, and sulfonic acid groups are most preferred.

  In addition, the introduction method of an acidic functional group is not specifically limited, A general method is used. For example, when introducing a sulfonic acid group into a thioether compound, it can be introduced under known conditions using a sulfonating agent such as sulfuric anhydride or fuming sulfuric acid. More specifically, for example, K.K. Hu, T .; Xu, W .; Yang, Y. et al. Fu, Journal of Applied Polymer Science, Vol. 91, E.E. Montoneri, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 27, 3043-3051 (1989).

  Further, those in which the introduced acidic functional group is further substituted with a metal salt or an amine salt are also suitably used as the thioether compound. The metal salt is preferably an alkali metal salt such as sodium salt or potassium salt, or an alkaline earth metal salt such as calcium salt.

  Furthermore, when the thioether compound is used in a powder form, the average particle diameter of the thioether compound is 0.01 μm to from the viewpoint of favorably realizing an effect such as a long life by improving dispersibility in the polymer electrolyte. It is preferably 2.0 μm, more preferably 0.01 μm to 1.0 μm, further preferably 0.01 μm to 0.5 μm, and most preferably 0.01 μm to 0.1 μm. This average particle size is a value measured by a laser diffraction / scattering particle size distribution measuring device (for example, model number: LA-950, manufactured by Horiba, Ltd.).

  As a method of finely dispersing the thioether compound in the polymer electrolyte, for example, a method of pulverizing and finely dispersing by applying high shear at the time of melt kneading with the polymer electrolyte, etc., after obtaining a polymer electrolyte solution described later, Examples thereof include a method of filtering the solution to remove coarse thioether compound particles and using the solution after filtration. From the viewpoint of molding processability, the melt viscosity of polyphenylene sulfide suitably used for melt kneading is preferably 1 to 10,000 poise, and more preferably 100 to 10,000 poise. The melt viscosity is a value obtained by holding for 6 minutes at 300 ° C., a load of 196 N, L / D (L: orifice length, D: orifice inner diameter) = 10/1 using a flow tester.

  The ratio (Wa / Wd) of the mass (Wa) of the polymer electrolyte to the mass (Wd) of the thioether compound is preferably 60/40 to 99.99 / 0.01, and 70/30 to 99.95 / 0.05 is more preferable, 80/20 to 99.9 / 0.1 is still more preferable, and 90/10 to 99.5 / 0.5 is particularly preferable. By setting the mass ratio of the polymer electrolyte to 60 or more, better ion conductivity can be realized, and better battery characteristics can be realized. On the other hand, by setting the mass ratio of the thioether compound to 40 or less, durability in battery operation under high temperature and low humidity conditions can be improved.

  The ratio (Wc / Wd) of the mass (Wc) of the polyazole compound to the mass (Wd) of the thioether compound is preferably 1/99 to 99/1. Further, from the viewpoint of the balance between chemical stability and durability (dispersibility), Wc / Wd is more preferably 5/95 to 95/5, further preferably 10/90 to 90/10, and 20/80 to 80/20 is particularly preferred.

  Furthermore, the proportion of the total mass of the polyazole compound and the thioether compound in the polymer electrolyte membrane is preferably 0.01% by mass to 50% by mass. From the viewpoint of balance between ion conductivity and durability (dispersibility), the total mass is more preferably 0.05% by mass to 45% by mass, and further preferably 0.1% by mass to 40% by mass. 0.2 mass% to 35 mass% is particularly preferable, and 0.3 mass% to 30 mass% is extremely preferable.

(Polymer electrolyte membrane)
In the present embodiment, the thickness of the polymer electrolyte membrane is preferably 1 μm to 500 μm, more preferably 2 μm to 100 μm, and still more preferably 5 μm to 50 μm. Adjusting the film thickness within this range can reduce inconveniences such as direct reaction between hydrogen and oxygen, and may cause differential pressure, strain, etc. during handling of the fuel cell and during fuel cell operation. However, it is preferable in that the film is hardly damaged. Furthermore, it is preferable to adjust the film thickness within this range from the viewpoint of maintaining the ion permeability of the polymer electrolyte membrane and maintaining the performance as a solid polymer electrolyte membrane.

  Next, the manufacturing method of the polymer electrolyte membrane of this embodiment is demonstrated. The polymer electrolyte membrane of the present embodiment can be obtained by filling the polymer electrolyte in the fine pores of the polyolefin microporous membrane.

  The method of filling the pores of the polyolefin microporous membrane with the polymer electrolyte is not particularly limited. For example, a method of applying a polymer electrolyte solution described later to the polyolefin microporous membrane, For example, a method of drying after impregnating the porous film may be used. Alternatively, a sheet containing a polymer electrolyte may be preliminarily molded by extrusion molding, cast molding, or the like, and this sheet may be filled with a polyolefin microporous film by hot pressing.

  Further, for the purpose of improving the conductivity and mechanical strength of the polymer electrolyte membrane, one or more layers containing the polymer electrolyte are laminated on at least one main surface of the polymer electrolyte membrane thus produced. May be. Moreover, the polymer electrolyte membrane of this embodiment may bridge | crosslink the compounds contained there, using a crosslinking agent, an ultraviolet-ray, an electron beam, a radiation.

  The polymer electrolyte membrane of the present embodiment is preferably subjected to heat treatment after being obtained by molding as described above. By this heat treatment, the crystal part and the polymer solid electrolyte part in the polymer electrolyte membrane are firmly bonded, and as a result, the mechanical strength can be stabilized. The temperature of this heat treatment is preferably 120 ° C to 230 ° C, more preferably 130 ° C to 210 ° C, and further preferably 150 ° C to 200 ° C. By adjusting the temperature of the heat treatment within this range, the adhesion between the crystal part and the electrolyte composition part is improved. The temperature for the heat treatment is also suitable from the viewpoint of maintaining the characteristics of the polymer electrolyte membrane. Although depending on the temperature of the heat treatment, the heat treatment time is preferably 5 minutes to 3 hours, more preferably 10 minutes to 2 hours, from the viewpoint of obtaining a polymer electrolyte membrane having high durability.

(Polymer electrolyte solution)
The polymer electrolyte solution according to the present embodiment contains the polymer electrolyte, a solvent, and other additives as necessary. This polymer electrolyte solution is used as it is, or after passing through processes such as filtration and concentration, as a filling liquid for the polyolefin microporous membrane. Alternatively, this solution can be used alone or in combination with another electrolyte solution and used as a material such as a polymer electrolyte membrane or an electrode binder.

  A method for producing a polymer electrolyte solution according to this embodiment will be described. The method for producing the polymer electrolyte solution is not particularly limited. For example, after obtaining a solution in which the polymer electrolyte is dissolved or dispersed in a solvent, the additive is dispersed in the solution as necessary. Alternatively, first, the polymer electrolyte and the additive are mixed through steps such as melt extrusion and stretching, and the mixture is dissolved or dispersed in a solvent. In this way, a polymer electrolyte solution is obtained.

More specifically, first, a molded product made of a polymer electrolyte precursor polymer is immersed in a basic reaction liquid and hydrolyzed. By this hydrolysis treatment, the precursor polymer of the polymer electrolyte is converted into a polymer electrolyte.
Next, the hydrolyzed molded product is sufficiently washed with warm water, and then the molded product is subjected to an acid treatment. The acid used for the acid treatment is not particularly limited, but mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid and trifluoroacetic acid are preferred. By this acid treatment, the precursor polymer of the polymer electrolyte is protonated, and a polymer electrolyte such as a perfluorocarbon sulfonic acid resin is obtained.

  The above-mentioned molded product (molded product containing a polymer electrolyte) treated with an acid as described above is dissolved or suspended in a solvent (solvent having good affinity with the resin) that can dissolve or suspend the polymer electrolyte. It is. Examples of such solvents include protic organic solvents such as water, ethanol, methanol, n-propanol, isopropyl alcohol, butanol, and glycerin, N, N-dimethylformamide, N, N-dimethylacetamide, and N-methyl. And aprotic organic solvents such as pyrrolidone. These are used singly or in combination of two or more. In particular, when one kind of solvent is used, the solvent is preferably water. Moreover, when using 2 or more types in combination, the mixed solvent of water and a protic organic solvent is especially preferable.

  The method for dissolving or suspending the polymer electrolyte in the solvent is not particularly limited. For example, the polymer electrolyte may be dissolved or dispersed as it is in the above solvent, but the polymer electrolyte may be dissolved in a temperature range of 0 to 250 ° C. under atmospheric pressure or under conditions of airtight pressure in an autoclave or the like. It is preferable to dissolve or disperse in. In particular, when water and a protic organic solvent are used as the solvent, the mixing ratio of water and the protic organic solvent depends on the dissolution method, dissolution conditions, type of polymer electrolyte, total solid content concentration, dissolution temperature, stirring speed, etc. The ratio of the mass of the protic organic solvent to water is preferably 0.1 to 10 protic organic solvent relative to water 1, and more preferably 0 to 1 relative to water 1. .1-5.

  The polyelectrolyte solution is an emulsion (a liquid particle in which liquid particles are dispersed as colloidal particles or coarser particles to form a milky state), a suspension (solid particles in a liquid are colloidal particles or Such as those dispersed as particles that can be seen with a microscope), colloidal liquid (macromolecules dispersed), micellar liquid (a lyophilic colloidal dispersion system formed by a large number of intermolecular forces) 1 type or 2 types or more are included.

  In addition, the polymer electrolyte solution can be concentrated or filtered according to the molding method and application of the polymer electrolyte membrane. The concentration method is not particularly limited, and examples thereof include a method of heating a polymer electrolyte solution to evaporate a solvent and a method of concentrating under reduced pressure. When the polymer electrolyte solution is used as a coating solution, if the solid content of the polymer electrolyte solution is too high, the viscosity increases and it becomes difficult to handle. It is preferable in it being 5 mass%-50 mass%. A method for filtering the polymer electrolyte solution is not particularly limited, but a typical example is a method of pressure filtration using a filter. It is preferable to use a filter medium having a 90% collection particle size of 10 to 100 times the average particle size of solid particles contained in the polymer electrolyte solution. Examples of the material of the filter medium include paper and metal. In particular, when the filter medium is paper, the 90% collection particle diameter is preferably 10 to 50 times the average particle diameter of the solid particles. When using a metal filter, it is preferable that the 90% collection particle diameter is 50 to 100 times the average particle diameter of the solid particles. Setting the 90% collection particle size to 10 times or more of the average particle size suppresses that the pressure required for liquid feeding becomes too high or that the filter is blocked in a short period of time. Can be suppressed. On the other hand, setting the 90% collection particle size to 100 times or less of the average particle size is preferable from the viewpoint of satisfactorily removing particle agglomerates and resin undissolved materials that cause foreign matters on the film.

(Membrane electrode assembly)
The polymer electrolyte membrane of this embodiment can be used as a constituent member of a membrane electrode assembly and a solid polymer electrolyte fuel cell. A unit in which two types of electrode catalyst layers of an anode and a cathode are bonded to both surfaces of a polymer electrolyte membrane is called a membrane electrode assembly (hereinafter sometimes abbreviated as “MEA”). A material in which a pair of gas diffusion layers are bonded to the outer side of the electrode catalyst layer so as to face each other may be referred to as MEA. The MEA according to this embodiment may have the same configuration as that of a known MEA except that the polymer electrolyte membrane according to this embodiment is adopted.

  The electrode catalyst layer is composed of fine particles of a catalytic metal and a conductive agent supporting the catalyst metal, and a water repellent is included as necessary. The catalyst may be any metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen. Platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium And one or more selected from the group consisting of these alloys. Of these, platinum is mainly preferred.

  The MEA production method may be any known production method except that the polymer electrolyte membrane of the present embodiment is used, and examples thereof include the following methods. First, platinum-supported carbon serving as an electrode material is dispersed in a solution obtained by dissolving an electrode binder ion exchange resin in a mixed solution of alcohol and water to obtain a paste. A certain amount of this is applied to a PTFE sheet and dried. Next, the application surface of the PTFE sheet is faced to each other, and a polymer electrolyte membrane is sandwiched therebetween, and transfer joining is performed by hot pressing at 100 ° C. to 200 ° C. to obtain an MEA. The electrode binder is generally prepared by dissolving an ion exchange resin in a solvent (alcohol, water, etc.). However, the polymer electrolyte solution of this embodiment can also be used, and this polymer electrolyte solution is used from the viewpoint of durability. preferable.

(Solid polymer electrolyte fuel cell)
The MEA obtained as described above, and in some cases, a MEA having a structure in which a pair of gas diffusion electrodes are further opposed to the outer side of the electrode catalyst layer, is a common solid polymer electrolyte such as a bipolar plate or a backing plate. A solid polymer electrolyte fuel cell is configured in combination with components used in the fuel cell. Such a solid polymer electrolyte fuel cell may have the same configuration as a known one except that the above MEA is adopted as the MEA.

  The bipolar plate means a composite material of graphite and resin having a groove for flowing a gas such as fuel or oxidant on its surface, or a metal plate. In addition to the function of transmitting electrons to an external load circuit, the bipolar plate has a function of a flow path for supplying fuel and oxidant to the vicinity of the electrode catalyst. A solid polymer electrolyte fuel cell according to this embodiment is manufactured by inserting a plurality of the MEAs between the bipolar plates and stacking them.

  According to the present embodiment described above, it is possible to provide a polymer electrolyte membrane that has excellent heat resistance, is easy to handle, and can exhibit high reliability and high performance. This polymer electrolyte membrane is suitable as an electrolyte material for a solid polymer electrolyte fuel cell. Moreover, the polymer electrolyte membrane of this embodiment has high dimensional stability and mechanical strength. Therefore, there is an effect of suppressing breakage of the membrane at the time of MEA production and cell assembly in the solid polymer electrolyte fuel cell, and suppressing dimensional change depending on the moisture content. Moreover, since this polymer electrolyte membrane has high heat resistance, it can be subjected to heat treatment in order to enhance the chemical durability of the proton exchange membrane itself.

  Although the best mode for carrying out the present invention has been described above, the present invention is not limited to the present embodiment. The present invention can be variously modified without departing from the gist thereof.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited only to these Examples. Measurement methods and evaluation methods for various physical properties in Examples and the like are as follows.

(1) Ion exchange capacity A polymer electrolyte membrane (with one main surface area of approximately ² to 20 cm ² ) in which protons of ion exchange group counter ions are in a proton state is added to 30 mL of a saturated NaCl aqueous solution at 25 ° C. It was immersed and left for 30 minutes with stirring. Subsequently, the proton in the saturated NaCl aqueous solution was neutralized and titrated as a 0.01N sodium hydroxide aqueous solution using phenolphthalein as an indicator. The polymer electrolyte membrane in which the counter ion of the ion exchange group obtained by filtration after neutralization was in the state of sodium ion was rinsed with pure water, further vacuum dried and weighed. The amount of sodium hydroxide required for neutralization is M (mmol), the mass of the polymer electrolyte membrane whose sodium ion is the counter ion of the ion exchange group is W (mg), and the equivalent mass EW (g / equivalent) )
EW = (W / M) −22
Furthermore, the ion exchange capacity (milli equivalent / g) was calculated by taking the inverse of the obtained EW value and multiplying it by 1000.

(2) Film thickness After the film sample was allowed to stand for 1 hour or more in a constant temperature and humidity room at 23 ° C. and 50% RH, the film was measured using a film thickness meter (trade name “B-1” manufactured by Toyo Seiki Seisakusho). The thickness was measured.

(3) Tensile strength A membrane sample was cut into a rectangular membrane of 70 mm x 10 mm, and its tensile strength was measured according to JIS K-7127.

(4) Puncture strength Using a compression tester (trade name “KES-G5” manufactured by Kato Tech Co., Ltd.), a needle puncture test of the membrane sample was performed. The maximum load of the obtained load displacement curve was defined as the puncture strength (gf / 25μ). A needle having a diameter of 0.5 mm and a tip curvature radius of 0.25 mm was used, and the piercing speed of the needle into the membrane sample was 2 cm / second.

(5) Dimensional change The film sample was cut into a rectangular film of 4 cm × 3 cm, left in a constant temperature and humidity room (23 ° C., 50% RH) for 1 hour or longer, and then each of the dried rectangular film samples in the planar direction Dimensions were measured.
Next, the rectangular membrane sample whose dimensions were measured was boiled in hot water at 80 ° C. for 1 hour, and water was sufficiently absorbed so that the amount of mass change due to moisture in the electrolyte membrane was 5% or less. At this time, the film was taken out from the hot water, and it was confirmed that the amount of change in mass was 5% or less with an electronic balance in a state where water on the surface was sufficiently removed. The wet membrane sample that was swollen by absorbing this water was taken out of the hot water, and each dimension in the planar direction was measured. Based on the respective dimensions in the plane direction in the dry state, the average of the increments of the respective dimensions in the plane direction in the wet state from the respective dimensions in the dry state was taken as the dimensional change amount (%).

(6) Glass transition temperature The glass transition temperature of the polymer electrolyte was measured based on JIS-C-6481. First, the polymer electrolyte was cut into a width of 5 mm, and the viscoelasticity was raised from the room temperature at a rate of 2 ° C./minute using a dynamic viscoelasticity measuring device (made by IT Measurement Control, model number: DVA-225). The dynamic viscoelasticity and loss tangent of the test piece were measured with a measuring device. The measured peak temperature of loss tangent was defined as the glass transition temperature.

[Example 1]
(Preparation of polymer electrolyte solution)
First, a precursor of a perfluorosulfonic acid resin obtained from tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₂ —SO ₂ F, which is a polymer polymer precursor polymer (after hydrolysis and acid treatment) EW: 730 g / equivalent) pellets were prepared. Next, the precursor pellet was contacted with an aqueous solution in which potassium hydroxide (15% by mass) and methyl alcohol (50% by mass) were dissolved at 80 ° C. for 20 hours to perform a hydrolysis treatment. The subsequent pellets were immersed in 60 ° C. water for 5 hours. Next, the treatment of immersing the pellets immersed in water in a 2N aqueous hydrochloric acid solution at 60 ° C. for 1 hour was repeated 5 times, each time replacing the aqueous hydrochloric acid solution with a new one. And the pellet after having been repeatedly immersed in hydrochloric acid aqueous solution was washed with ion-exchange water and dried. As a result, pellets of perfluorocarbon sulfonic acid resin (PFSA), which is a polymer electrolyte, were obtained.

  The pellet was placed in a 5 L autoclave together with an aqueous ethanol solution (water: ethanol = 50.0: 50.0 (mass ratio)), sealed, heated to 160 ° C. with stirring with a blade, and held for 5 hours. Thereafter, the autoclave was naturally cooled to obtain a uniform perfluorosulfonic acid resin solution having a solid content concentration of 5% by mass. This was designated as Solution 1.

(Production of polyolefin microporous membrane)
20% by mass of ultrahigh molecular weight polyethylene having a weight average molecular weight of 2.5 × 10 ⁶ , 70% by mass of high density polyethylene having a weight average molecular weight of 3.3 × 10 ⁵ and 10% by mass of polypropylene having a weight average molecular weight of 4 × 10 ⁵ A polyolefin composition was obtained by adding 0.375 parts by mass of an antioxidant to 100 parts by mass of a polyolefin composition containing. 30 parts by mass of this polyolefin composition was put into a twin screw extruder (58 mmφ, L / D = 42, strong kneading type). Moreover, 70 mass parts of liquid paraffin was supplied from the side feeder of this twin-screw extruder, and it melt-kneaded at 200 rpm, and prepared the polyolefin solution in an extruder.
Subsequently, the melt-kneaded product was extruded at 190 ° C. from a T die installed at the tip of the extruder, and a sheet was formed while being taken up by a cooling roll. Next, the molded sheet was sequentially biaxially stretched 5 × 5 at 110 ° C. to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, followed by drying and heat treatment to obtain a polyolefin microporous membrane.

(Production of polymer electrolyte membrane)
The obtained polyolefin microporous membrane (film thickness: 8 μm, pore diameter: 0.06 μm, porosity: 35%) was fixed on the polyolefin microporous membrane with an 11 cm × 11 cm SUS frame, and then the above The polyolefin microporous membrane was immersed in the solution 1, and the pores of the polyolefin microporous membrane were impregnated with the solution 1. The polyolefin microporous membrane impregnated with the solution 1 was dried in an oven at 90 ° C. for 5 minutes. This series of impregnation and drying processes was repeated a plurality of times until the solution 1 was sufficiently impregnated in the pores of the polyolefin microporous membrane. Next, the polyolefin microporous membrane sufficiently impregnated with the solution 1 was heat-treated in an oven at 150 ° C. for 30 minutes to obtain a polymer electrolyte membrane. Table 1 shows the evaluation results of the polymer electrolyte membrane.
[Example 2]

(Preparation of polymer electrolyte solution)
In the same manner as in Example 1, Solution 1 was prepared.

(Production of polyolefin microporous membrane)
0.375 parts by mass of an antioxidant was added to 100 parts by mass of a polyolefin composition consisting only of polypropylene having a weight average molecular weight of 4 × 10 ⁵ to obtain a polyolefin composition. 30 parts by mass of this polyolefin composition was put into a twin screw extruder (58 mmφ, L / D = 42, strong kneading type). Moreover, 70 mass parts of liquid paraffin was supplied from the side feeder of this twin-screw extruder, and it melt-kneaded at 200 rpm, and prepared the polyolefin solution in an extruder.
Subsequently, the melt-kneaded product was extruded at 220 ° C. from a T die installed at the tip of the extruder, and a sheet was formed while being taken up by a cooling roll. Subsequently, the molded sheet was sequentially biaxially stretched 7 × 5 at 110 ° C. to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, followed by drying and heat treatment to obtain a polyolefin microporous membrane.

(Production of polymer electrolyte membrane)
A polymer electrolyte membrane was obtained in the same manner as in Example 1 from the obtained polyolefin microporous membrane (film thickness: 12 μm, pore diameter: 0.1 μm, porosity: 50%). Table 1 shows the evaluation results of the polymer electrolyte membrane.

[Comparative Example 1]
(Preparation of polymer electrolyte solution)
In the same manner as in Example 1, Solution 1 was prepared.

(Production of polymer electrolyte membrane)
The solution 1 was sufficiently stirred using a stirrer and then concentrated under reduced pressure at 80 ° C. to obtain a cast solution having a solid content of 20%.
21 g of the cast solution was poured into a petri dish having a diameter of 15.4 cm, and dried on a hot plate at 90 ° C. for 1 hour. Next, the petri dish was placed in an oven and heat treated at 160 ° C. for 1 hour. Thereafter, the petri dish in which the membrane was formed was taken out of the oven and cooled, and then ion-exchanged water was poured into the petri dish to peel off the membrane to obtain a polymer electrolyte membrane having a thickness of about 30 μm. Table 1 shows the evaluation results of the polymer electrolyte membrane.

  From the above results, the polymer electrolyte membrane of Example 1 according to the present invention has heat resistance that can withstand heat treatment at 150 ° C. or higher, and also has dimensional stability and mechanical strength (tensile strength, puncture strength). It was confirmed to be excellent.

Claims (4)

Including a polyolefin composition containing 5% by mass or more of polypropylene and ultrahigh molecular weight polyethylene having a weight average molecular weight of 5 × 10 ⁵ or more , porosity of 10% to 90%, film thickness of 0.1 μm to 50 μm, pores A polyolefin microporous membrane having a pore diameter of 0.03 μm to 5 μm,
A polymer electrolyte membrane filled with the pores of the polyolefin microporous membrane and having an ion exchange capacity of 1.3 to 3.0 meq / g ,
The polymer electrolyte is a perfluorocarbon sulfonic acid resin, and the perfluorocarbon sulfonic acid resin has a repeating unit represented by the following formula (1) and a repeating unit represented by the following general formula (2). A polymer electrolyte membrane selected from the group consisting of a copolymer and a metal salt thereof.
-(CF ₂ CF ₂ )-(1)
_{- (CF 2 -CF (-O- (} CF 2 CFXO) n - (CF 2) m -SO 3 H)) - (2)
(In the formula, X represents a fluorine atom or —CF ₃ group, n represents an integer of 0 to 5, and m represents an integer of 0 to 12. However, n and m are not 0 at the same time.) 2. The polymer electrolyte membrane according to claim 1, further comprising a polyazole compound mixed with the polymer electrolyte and filled in the pores , wherein the polyazole compound is a polyimidazole compound . The polymer electrolyte membrane according to claim 1, further comprising a thioether compound mixed with the polymer electrolyte and filled in the pores , wherein the thioether compound is polyphenylene sulfide . The polyazole compound and the thioether compound, which are mixed with the polymer electrolyte and filled in the pores, further contain the polyazole compound is a polyimidazole compound, and the thioether compound is polyphenylene sulfide. The polymer electrolyte membrane described in 1.