JP2014110232A - Fluorine-based polymer electrolyte film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorine-based polymer electrolyte film having excellent mechanical strength and proton conductivity.SOLUTION: The fluorine-based polymer electrolyte film is formed by impregnating a fluorine-based polymer electrolyte into a polyolefin microporous film having voids of 0.05 to 0.5 μm in pore size, wherein conductivity is 0.1 S/cm or more.

Description

  The present invention relates to a fluorine-based polymer electrolyte membrane.

  A fuel cell is one that converts the chemical energy of fuel directly into electrical energy by electrochemically oxidizing fuel such as hydrogen and methanol in the battery, and is attracting attention as a clean electrical energy supply source. Has been. 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.

  In such a polymer electrolyte fuel cell, a polymer electrolyte membrane having a thickness of about 20 to 120 μm is generally used, and a proton made of a perfluorocarbon polymer having a chemically stable sulfonic acid group. Exchange membranes are often used. When power generation is performed, a catalyst layer containing a metal catalyst is joined to the outer surface of the solid polymer electrolyte membrane to produce a membrane catalyst layer assembly, and a gas diffusion layer made of carbon paper, carbon cloth, or the like on the outer surface. A membrane electrode assembly is produced by arranging each of the above. Further, conductive separators are disposed on both outer surfaces of the gas diffusion layer, and a gas flow path is formed between the membrane electrode assembly and the separator to form a minimum unit of power generation called a single cell. Since the voltage generated in a single cell during normal power generation is 1 V or less, a plurality of single cells are stacked and used in order to obtain a practical voltage. In this case, the joining of the catalyst layer to the solid polymer electrolyte membrane described above is performed by using a liquid in which carbon carrying a metal catalyst and a solid polymer electrolyte resin (ion exchange resin) are dispersed in a dispersion medium as main solid components. It is carried out by applying directly to the solid polymer electrolyte membrane or by applying it onto a separately prepared substrate and then transferring it to the solid polymer electrolyte membrane by a hot press method or the like.

Fuel cell membranes must have long-term thermal, mechanical and chemical stability under harsh conditions. Since the life of a fuel cell membrane is directly proportional to the physical properties of the membrane, development of a membrane with excellent mechanical strength is desired.
One method for developing a fuel cell membrane with excellent mechanical strength is to prepare the membrane with a more mechanically stable porous support. As a result, excessive shrinkage and swelling of the polymer electrolyte membrane used as a material for the fuel cell membrane caused by water generated during fuel cell operation can be prevented, and a more durable membrane can be provided. It becomes.
Patent Document 1 discloses a proton exchange membrane, and Patent Document 2 discloses a proton exchange membrane using various microporous membranes.

International Publication 2010/101195 Pamphlet JP 2005-216769 A

The proton exchange membranes disclosed in Patent Documents 1 and 2 have insufficient mechanical strength, and there is still room for improvement.
Further, when a hydrophobic polymer material is used as the microporous membrane material of the fuel cell membrane, it can exhibit minimum swelling in water and can be mechanically and chemically stabilized. Further, by selecting a microporous membrane having a small pore diameter, the mechanical strength tends to be excellent. However, when an inert hydrophobic polymer material such as polyolefin is selected as the microporous membrane, it has a low affinity with ion exchange materials with high hydrophilicity such as commonly used sulfonic acid-containing polymers. In the case of a hydrophobic microporous membrane having a small pore size, there is a possibility that the microporous membrane is not sufficiently impregnated with an ion exchange material, causing a membrane defect such as a hole in the microporous membrane or not exhibiting proton conductivity. .
In view of the above circumstances, an object of the present invention is to provide a fluorine-based polymer electrolyte membrane having excellent mechanical strength and proton conductivity.

  As a result of intensive studies to solve the above problems, the present inventors have combined a fluorine-based polymer electrolyte and a microporous membrane made of polyolefin with a small pore diameter to obtain a fluorine-based material having excellent mechanical strength and proton conductivity. The present inventors have found that a polymer electrolyte membrane can be realized, and have completed the present invention.

That is, the present invention is as follows.
[1]
A fluoropolymer electrolyte membrane obtained by impregnating a fluoropolymer electrolyte with a polyolefin microporous membrane having pores having a pore size of 0.05 to 0.5 μm,
A fluorine-based polymer electrolyte membrane having a conductivity of 0.1 S / cm or more.
[2]
The fluorine-based polymer electrolyte membrane according to [1] above, wherein the ion-exchange capacity of the fluorine-based polymer electrolyte is 0.5 to 5.0 meq / g.
[3]
The fluorine-based polymer electrolyte membrane according to the above [1] or [2], further comprising a polyazole compound.
[4]
The fluorine-based polymer electrolyte membrane according to any one of the above [1] to [3], further containing a thioether compound.
[5]
The fluorine-based polymer electrolyte is a copolymer containing a repeating unit represented by the following general formula (1) and a repeating unit represented by the following general formula (2): [4] The fluorine-based polymer electrolyte membrane according to any one of [4].
_{- (CF 2 CF 2) -} (1)
_{- (CF 2 -CF (-O- (} CF 2 CFX) n -O p - (CF 2) m -SO 3 H)) - (2)
(In formula (2), X represents a fluorine atom or —CF ₃ group, n represents an integer of 0 to 1, m represents an integer of 0 to 12, and p represents 0 or 1. However, n and m are simultaneously It will not be 0.)
[6]
A step of impregnating a polyolefin microporous membrane having a void having a pore diameter of 0.05 to 0.5 μm with a fluorine-based polymer electrolyte solution containing a solvent represented by the following general formula (4):
Volatilizing the solvent of the impregnated fluoropolymer electrolyte solution,
A method for producing a fluorine-based polymer electrolyte membrane comprising:
C _q H _r (OH) _s (4)
(In formula (4), q represents an integer of 3 or more, r represents an integer of 2q + 2-s, and s represents an integer of 1 or more.)
[7]
A membrane electrode assembly (MEA) comprising the fluorine-based polymer electrolyte membrane according to any one of [1] to [5] above.
[8]
A fuel cell comprising the fluorine-based polymer electrolyte membrane according to any one of [1] to [5].

  According to the present invention, a fluorine-based polymer electrolyte membrane having excellent mechanical strength and proton conductivity can be provided.

  Hereinafter, a 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.

  The polymer electrolyte membrane in the present embodiment is obtained by impregnating a fluoropolymer electrolyte into a polyolefin microporous membrane (hereinafter, also simply referred to as “microporous membrane”) having pores having a pore diameter of 0.05 to 0.5 μm. And its conductivity is 0.1 S / cm or more.

[Fluoropolymer electrolyte]
The fluorine-based polymer electrolyte (hereinafter also simply referred to as “polymer electrolyte”) in the present embodiment is not particularly limited, but is represented by the following general formula (1) from the viewpoint of mechanical strength and ion exchange capacity. It is preferable that it is a copolymer containing the repeating unit and the repeating unit represented by the following general formula (2).
_{- (CF 2 CF 2) -} (1)
_{- (CF 2 -CF (-O- (} CF 2 CFX) n -O p - (CF 2) m -SO 3 H)) - (2)
(In formula (2), X represents a fluorine atom or a —CF ₃ group, n represents an integer of 0 to 5, m represents an integer of 0 to 12, and p represents 0 or 1. However, n and m are simultaneously It will not be 0.)

The fluorine-based polymer electrolyte in the present embodiment can be obtained, for example, by synthesizing a precursor polymer and then subjecting the precursor polymer to alkali hydrolysis, acid decomposition, or the like. For example, the copolymer having a repeating unit represented by the general formulas (1) and (2) is obtained by polymerizing a precursor polymer having a repeating unit represented by the following general formula (3). The precursor polymer can be obtained by alkali hydrolysis, acid treatment or the like.
_{- [CF 2 CF 2] a-} [CF 2 -CF (-O- (CF 2 CFX) n-Op- (CF 2) m-A)] g- (3)
(In the formula (3), X represents a fluorine atom or —CF ₃ group, n represents an integer of 0 to 5, m represents an integer of 0 to 12, and p represents 0 or 1. However, n and m does not simultaneously become 0. A represents COOR ¹ , COR ² or SO ₂ R ² , R ¹ represents an alkyl group having 1 to 3 carbon atoms, and R ² represents a halogen atom.)

  The precursor polymer is produced, for example, by copolymerizing a fluorinated olefin compound and a vinyl fluoride compound.

Here, the fluorinated olefin compound is not particularly limited. For example, tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, monochlorotrifluoroethylene, perfluorobutylethylene (C ₄ F ₉ CH═CH ₂ ), Examples include perfluorohexaethylene (C ₆ F ₁₃ CH═CH ₂ ), perfluorooctaethylene (C ₆ F _I7 CH═CH ₂ ), and the like. These are used singly or in combination of two or more.

Moreover, it does not specifically limit as a vinyl fluoride compound, For example, the general formula enumerated 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 those represented by ₂ R ⁹ and the like. 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 a known copolymerization method. Such a copolymerization 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 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. Here, examples of the fluorinated hydrocarbon include trichlorotrifluoroethane, 1, 1, 1, 2, 3, 4, 4, 5, 5, 5-decafluoropentane, etc. Those selected from the group consisting of compounds are preferably used.
(Ii) A method of performing polymerization by reacting a vinyl fluoride compound and a gas of a fluorinated olefin compound by using a vinyl fluoride compound itself as a polymerization solvent without using a solvent such as fluorine-containing hydrocarbon (bulk polymerization).
(Iii) A method 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 (emulsion polymerization).
(Iv) A method in which an aqueous solution of a surfactant and a co-emulsifier such as alcohol is used, and a 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 (miniemulsion polymerization, Microemulsion polymerization)
(V) A method in which an aqueous solution of a suspension stabilizer is used and polymerization is performed by reacting a vinyl fluoride compound and a gas of a fluorinated olefin compound in a state filled and suspended in the 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 g / 10 minutes or more, more preferably 0.1 g / 10 minutes or more, still more preferably 0.3 g / 10 minutes or more, and 1 g / 10 minutes or more. Particularly preferred. Although it does not specifically limit as an upper limit of MFR, 100 g / 10min or less is preferable, 50 g / 10min or less is more preferable, 10 g / 10min or less is further more preferable, 5 g / 10 or less is especially preferable. By adjusting the MFR of the precursor polymer to a range of 0.01 to 100 g / 10 min, molding processing such as film formation tends to be performed favorably. In addition, MFR of a precursor polymer is measured based on JISK-7210. Specifically, the melt flow rate of the fluorinated 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 measured using the MFR ( g / 10 minutes).

  The precursor polymer prepared according to the above may be hydrolyzed in a basic reaction liquid, sufficiently washed with warm water or the like, and then 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.

  The fluorine-based polymer electrolyte in the present embodiment is preferably 100% by mass with respect to the entire polymer used as the polymer electrolyte from the viewpoint of chemical durability. For example, a hydrocarbon-based polymer electrolyte or the like can be arbitrarily selected. May be included in proportions. Examples of such hydrocarbon polymer electrolytes include polyphenylene sulfide, polyphenylene ether, polysulfone, polyethersulfone, polyetherethersulfone, polyetherketone, polyetheretherketone, polythioetherethersulfone, polythioetherketone, polythiol Thioetheretherketone, polybenzimidazole, polybenzoxazole, polyoxadiazole, polybenzoxazinone, polyxylylene, polyphenylene, polythiophene, polypyrrole, polyaniline, polyacene, polycyanogen, polynaphthyridine, polyphenylene sulfide sulfone, polyphenylene sulfone, Polyimide, polyetherimide, polyesterimide, polyamideimide, polyarylate, Family polyamides, polystyrenes, polyesters, polycarbonates, and the like. The content of the hydrocarbon-based polymer electrolyte is preferably 50% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less with respect to the entire polymer electrolyte.

  The fluorinated polymer electrolyte in this embodiment preferably has an ion exchange capacity of 0.5 to 5.0 meq / g. By setting the ion exchange capacity to 5.0 meq / g or less, swelling of the polymer electrolyte membrane containing the polymer electrolyte under fuel cell operating conditions (high temperature, high humidity, etc.) tends to be reduced. is there. Reduction of swelling of the polymer electrolyte membrane means that the strength of the polymer electrolyte membrane is reduced, or that the durability of the polymer electrolyte membrane such as wrinkles is peeled off from the electrode, and further the gas barrier property is reduced. This leads to improvement of problems. 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 has a good power generation capability even under high temperature and low humidity. Tend to be maintained. From the above viewpoint, the ion exchange capacity of the fluoropolymer electrolyte is preferably 0.5 to 5.0 meq / g, more preferably 0.8 to 4.0 meq / g, and still more preferably 1.0. -3.5 meq / g.

In addition, the ion exchange capacity of the fluorine-based polymer electrolyte in the present 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.

  The ion exchange capacity of the fluorine-based polymer electrolyte is adjusted to be within the above numerical range by adjusting the number of ion-exchange groups present in 1 g of the fluorine-based polymer electrolyte.

  The fluoropolymer electrolyte membrane in 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, from the viewpoint of heat resistance during fuel cell operation. Especially preferably, it is 130 degreeC or more.

  Here, the glass transition temperature of the fluorine-based polymer electrolyte membrane is measured according to JIS-C-6481. Specifically, the fluoropolymer electrolyte membrane is cut into a width of 5 mm, the test piece is heated from room temperature at a rate of 20 ° C./minute using a dynamic viscoelasticity measuring device, and the test piece is measured using the viscoelasticity measuring device. The dynamic viscoelasticity and loss tangent are measured, and the peak temperature of the measured 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 fluorine-based polymer electrolyte.

  The moisture content at 80 ° C. of the fluorine-based polymer electrolyte in the present embodiment is preferably 30% by mass to 330% by mass, more preferably 70% by mass to 280% by mass, and still more preferably 120% by mass to It is 255 mass%, Most preferably, it is 160 mass%-220 mass%. By adjusting the water content of the fluorine-based polymer electrolyte to the above range, there is a tendency to exhibit effects such as long-term dimensional change stability and high battery performance under high temperature and low humidification conditions. When the water content at 80 ° C. is 30% by mass or more, there is a sufficient amount of water for proton transfer, so that excellent cell performance tends to be exhibited when used in a fuel cell. On the other hand, when the water content at 80 ° C. is 330% by mass or less, the fluorine-based polymer electrolyte is less likely to become a gel and tends to be easily formed as a film.

[Polyolefin microporous membrane]
As polyolefin resin used as the raw material of the polyolefin microporous film in this embodiment, the polymer which contains propylene or ethylene as a main monomer component is preferable. Although this polyolefin resin may consist only of said main monomer components, it may contain monomer components, such as butene, pentene, hexene, 4-methylpentene, in addition to that.

Specific examples of polyolefin resins include ultra-high molecular weight polyethylene (UHMWPE), high density polyethylene (HDPE), medium density polyethylene, low density polyethylene (LDPE), and linear low density obtained using Ziegler multi-site catalysts. Polyethylene such as polyethylene and ultra-low density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-based polymer obtained using a single site catalyst, and a copolymer with other single scene copolymerizable with propylene Examples thereof include simple substances such as (propylene-ethylene copolymer, propylene-ethylene-α-olefin copolymer) and mixtures thereof. Among these, polyethylene is preferable from the viewpoint of moldability of the microporous membrane, more preferably ultrahigh molecular weight polyethylene and high density polyethylene, and still more preferably ultrahigh molecular weight polyethylene. From the viewpoint of moldability and physical properties (mechanical strength, porosity, film thickness) of the microporous membrane, the weight average molecular weight of the ultrahigh molecular weight polyethylene is preferably 1 × 10 ⁵ or more, more preferably 3 × 10 ⁵ or more, More preferably, it is 5 × 10 ⁵ or more, and 5 × 10 ⁵ to 15 × 10 ⁶ is particularly preferable. From the viewpoint of heat resistance, polypropylene is preferable.

  In addition, the polyolefin microporous film in the present embodiment is optionally made of metal soaps such as potassium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. You may contain a well-known additive in the range which does not impair the subject achievement and effect of this invention.

  The polyolefin microporous membrane in this embodiment preferably has a porosity of 10% to 90%, more preferably 20% to 90%, still more preferably 30% to 85%, 35 % To 85% is particularly preferable. When the porosity is in the range of 10% to 90%, the effects of improving the proton conductivity of the polymer electrolyte membrane, improving the strength, and suppressing the dimensional change tend to become more prominent.

  The porosity of the polyolefin microporous membrane can be adjusted to the above range by changing the number of pores, pore diameter, pore shape, draw ratio, gelling agent addition amount and type of gelling agent in the microporous membrane. Can do. As a means for increasing the porosity of the polyolefin microporous membrane, for example, a method of adjusting the addition amount of the gelling agent to 30 to 80% by mass can be mentioned. By adjusting the addition amount of the gelling agent within this range, the moldability of the polyolefin resin is maintained and the plasticizing effect is sufficient, so that the lamellar crystals of the polyolefin resin are efficiently stretched and the draw ratio is increased. be able to. On the other hand, examples of means for lowering the porosity of the polyolefin microporous membrane include reducing the amount of gelling agent and reducing the draw ratio.

  The polyolefin microporous membrane in 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. It is particularly preferable that the thickness is 0.0 μm to 20 μm. When the film thickness is in the range of 0.1 μm to 50 μm, the polymer electrolyte can be easily filled into the microporous membrane, and the dimensional change of the polymer electrolyte membrane tends to be further suppressed. Here, the film thickness of the microporous membrane is determined by sufficiently allowing the membrane to stand in a constant temperature and humidity room of 50% RH, and then using a known film thickness meter (for example, trade name “B-1 manufactured by Toyo Seiki Seisakusho”). ") Means the value measured using.

  The film thickness of the polyolefin microporous membrane can be adjusted to the above range by changing the solid content of the cast solution, the amount of extruded resin, the extrusion speed, and the stretching ratio of the microporous membrane.

  In the microporous polyolefin membrane in the present embodiment, the pore diameter of the voids is adjusted in the range of 0.05 μm to 0.5 μm. By setting the pore diameter to 0.5 μm or less, the mechanical strength of the polymer electrolyte membrane in which the microporous membrane is impregnated with the polymer electrolyte is improved. On the other hand, by setting the pore size of the microporous membrane to 0.05 μm or more, the voids of the microporous membrane are easily impregnated with the polymer electrolyte, have excellent mechanical strength, and exhibit good ion conductivity. There is a tendency. From the above viewpoint, the pore diameter of the voids of the polyolefin microporous membrane is preferably 0.05 μm to 0.48 μm, more preferably 0.05 μm to 0.45 μm, and 0.05 μm to 0.4 μm. It is particularly preferred. Here, the pore diameter of the voids of the polyolefin microporous membrane refers to the average pore diameter measured using a palm porometer (for example, product name: Porometer 3G manufactured by Xonics) by the bubble point method.

  The pore diameter of the voids of the polyolefin microporous membrane can be determined by changing the plasticizer dispersibility, the draw ratio of the polyolefin microporous membrane, the irradiation dose and irradiation time of the electron beam or plasma, the plasticizer extraction solvent and the extraction time. It can adjust to the said range.

  The polyolefin microporous membrane in the present embodiment is 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 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. A method for producing a polyolefin microporous membrane includes a step (i) of melt-kneading a polyolefin composition, a plasticizer and an antioxidant in a nitrogen atmosphere, and extruding the melt-kneaded product obtained through the step (i) to form a sheet. Step (ii) for forming into a sheet and cooling and solidifying; Step (iii) for obtaining a film-like formed product by stretching at least uniaxially the sheet-like cooling and solidified material obtained through Step (ii); And (iv) extracting a plasticizer from the molded product obtained through (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. Phosphorus antioxidants such as tris (2,4-di-t-butylphenyl) phosphite, tetrakis (2,4-di-t-butylphenyl) -4,4-biphenylene-diphosphonite, A secondary antioxidant such as a sulfur-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 plasticizers include hydrocarbons such as liquid paraffin and paraffin wax, di-2-ethylhexyl phthalate, diisodecyl phthalate, and diheptyl phthalate. Of these, hydrocarbons are preferred.

  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 in the present embodiment preferably has a draw ratio of 7 times or more in terms of area magnification from the viewpoint of the balance between porosity and mechanical strength. Moreover, it is preferable that extending | stretching temperature is 100-135 degreeC, and it is more preferable that it is 110-130 degreeC.

  In step (iv), the solvent used for extracting the plasticizer (extraction solvent) is a poor solvent for polyethylene and polypropylene, and a good solvent for the plasticizer, and has a boiling point of polyolefin. Those lower than the melting point of the composition are preferred. Examples of such an extraction solvent 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, Examples thereof include organic solvents represented by halogenated hydrocarbons such as 1,1-trichloroethane. These extraction solvents are used alone or in combination of two or more.

  In 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 to obtain polyolefin. A microporous membrane can be 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.

  The polyolefin microporous membrane in the present embodiment is preferably further subjected to heat setting treatment from the viewpoint of reducing shrinkage. By performing this heat setting treatment, the shrinkage of the microporous membrane under a high temperature atmosphere can be reduced, and the dimensional change of the polymer electrolyte membrane can be further reduced. The heat setting is performed, for example, by 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 in the present embodiment is 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. It may be given. By performing the surface treatment, the surface of the microporous membrane can be hydrophilized, and in addition to the effect of high filling of the polymer electrolyte solution, the water content of the polymer electrolyte membrane can be adjusted.

[Fluoropolymer electrolyte membrane]
The fluorine-based polymer electrolyte membrane in the present embodiment is obtained by impregnating a fluorine-based polymer electrolyte into the voids of a polyolefin microporous membrane.

The polymer electrolyte membrane in the present embodiment is excellent in mechanical strength by combining a polyolefin microporous membrane including voids having a specific pore size and a fluorine-based polymer electrolyte, and has a high proton conductivity (hereinafter, Simply referred to as “conductivity”). The proton conductivity of the polymer electrolyte membrane in the present embodiment is 0.1 S / cm or more, preferably 0.11 S / cm, from the viewpoint of maintaining the performance as a solid polymer electrolyte membrane. More preferably, it is 12 S / cm or more.
The conductivity of the polymer electrolyte membrane can be adjusted by controlling the ion exchange capacity of the fluorine-based polymer electrolyte, the pore diameter, porosity, film thickness, and solvent type of the polymer electrolyte solution of the polyolefin microporous membrane.

The conductivity of the fluorine-based polymer electrolyte membrane in the present embodiment is measured as follows using a polymer membrane water content test apparatus (manufactured by Nippon Bell, model number: MSB-AD-V-FC).
First, a polymer electrolyte membrane is cut into a width of 1 cm and a length of 3 cm and attached to a conductivity measuring cell. Next, the conductivity measuring cell is mounted in the chamber of the test apparatus, the inside of the chamber is adjusted to an atmosphere of 90 ° C. and less than 1% RH, and the influence of moisture on the polymer electrolyte membrane is once removed. Thereafter, water vapor generated using ion-exchanged water is introduced to humidify the inside of the chamber, and the atmosphere is adjusted to 90 ° C. and 50% RH. After confirming that the atmosphere in the chamber is stable, the conductivity (S / cm) of the polymer electrolyte membrane is measured.

  In addition to the polymer electrolyte and the polyolefin microporous membrane, the polymer electrolyte membrane 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)
The polyazole compound in the present embodiment is not particularly limited. For example, a polyimidazole compound, a polybenzimidazole compound, a polybenzobisimidazole compound, a polybenzoxazole compound, a polyoxazole compound, a polythiazole compound, Examples thereof include a polymer of a compound having a hetero five-membered ring containing one or more nitrogen atoms in the ring, such as a polybenzothiazole compound. The hetero five-membered ring may contain an oxygen atom, a sulfur atom or the like in addition to the nitrogen atom.

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

  Moreover, it is preferable that the molecular weight of a polyazole compound is 300-500,000 (polystyrene conversion) as a weight average molecular weight by a gel permeation chromatography (GPC) measurement. When the molecular weight of the polyazole compound is within the above range, durability tends to be improved.

  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 can be increased, and as a result, a higher output can be obtained during operation of the fuel cell. The ion exchange capacity of the modified polyazole compound is preferably 0.1 to 3.5 meq / g.

  The method for modifying 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-promotoluenesulfonic acid, chloroalkylsulfonic acid and the like are used. And a method of introducing an ion exchange group into the polyazole compound, a method of polymerizing by containing 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 from the viewpoint of durability. Here, “dispersed in the shape of islands” means that a phase containing a polyazole compound in the phase of the polymer electrolyte is a particle when observed with a transmission electron microscope (TEM) without performing a staining treatment. It means a state dispersed in a shape. Dispersing 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.

  Furthermore, the polymer electrolyte and the polyazole compound may be, for example, in a state of being ionically bonded to form an acid-base ion complex or in a covalently bonded state. 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 The nitrogen atom of the group may be bonded to each other by ionic bond or 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 a 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, When measured by FT-IR, the shifted absorption peaks derived from the chemical bond between the sulfonic acid group in the polymer electrolyte and the imidazole group in PBI are 1458 cm ⁻¹ , 1567 cm ⁻¹ , 1634 cm ^−1. It is recognized in the vicinity.

  In addition, 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 (Tanδ) obtained in the temperature rising process from room temperature to 200 ° C. , It becomes higher than that of a polymer electrolyte membrane to which PBI is not added. Such an increase in Tg is preferable from the viewpoint of improving the heat resistance of the polymer electrolyte membrane and improving the mechanical strength.

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

(Thioether compound)
The thioether compound in this 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 dimethyl thioether, diethyl thioether, dipropyl thioether, methyl ethyl thioether, and methyl butyl thioether; tetrahydrothiophene and tetrahydroapiran. And cyclic thioethers; aromatic thioethers such as 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, the polymer obtained by using what was illustrated above as a monomer like a polyphenylene sulfide (PPS) is used as a thioether compound. May be.

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

  The polyphenylene sulfide suitably 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 in a polar solvent; A method of polymerizing a compound in the presence of sodium sulfide or sodium hydrogen sulfide and sodium hydroxide; a method of polymerizing a halogen-substituted aromatic compound in a polar solvent in the presence of hydrogen sulfide and sodium hydroxide or sodium aminoalkanoate; or And a method by self-condensation of p-chlorothiophenol. Among these, a method of reacting sodium sulfide with 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 10 μmol / g to 10,000 μmol / g, more preferably 15 μmol. / 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 having a content of -SX group satisfying the above range, the dispersibility is improved as the miscibility with the polymer electrolyte in the present embodiment is improved. Molecular electrolyte membranes tend to exhibit higher durability under high temperature and low humidification conditions.

  Moreover, as the thioether compound, those having an acidic functional group introduced at the terminal can be suitably used. 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. Group is preferred, and sulfonic acid group is particularly preferred among them.

  In addition, it does not specifically limit as an introduction method of an acidic functional group, A general method can be used. For example, when a sulfonic acid group is introduced 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, JournalI of AppIied Polymer Science, VoI. 91, E.I. Montoneri, JournalI of Polymer Science: PartA: PoImer Chemistry, VoI. 27, 3043-3051 (1989).

  Moreover, what substituted the said acidic functional group introduce | transduced into the metal salt or amine salt can also be used suitably as a thioether compound. As the metal salt, alkali metal salts such as sodium salt and potassium salt, and alkaline earth metal salts such as calcium salt are preferable.

  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. 2.0 μm is preferable, 0.01 μm to 1.0 μm is more preferable, 0.01 μm to 0.5 μm is further preferable, and 0.01 μm to 0.1 μm is particularly preferable. . The average particle size of the thioether compound is a value measured by a laser diffraction / scattering particle size distribution measuring apparatus (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 during melt kneading with the polymer electrolyte or the like; Examples thereof include a method of filtering the solution to remove coarse thioether compound particles and using the solution after filtration. The melt viscosity of the thioether compound used for melt kneading is preferably 1 to 10,000 poise, more preferably 100 to 10,000 poise, from the viewpoint of moldability. The melt viscosity is a value obtained by holding for 6 minutes using a flow tester at 300 ° C., a load of 196 N, L / D (L: orifice length, D: orifice inner diameter) = 10/1.

  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 / It is more preferably 0.05, more preferably 80/20 to 99.9 / 0.1, and particularly preferably 90/10 to 99.5 / 0.5. By setting the mass ratio of the polymer electrolyte to 60 or more, the ion conductivity is improved, and more excellent battery characteristics can be realized. On the other hand, by setting the mass ratio of the thioether compound to 40 or less, the durability of the molded polymer electrolyte in battery operation under high temperature and low humidification conditions can be improved.

  Moreover, when using a thioether compound and a polyazole compound together, it is preferable that ratio (Wc / Wd) of the mass (Wc) of the polyazole compound with respect to the mass (Wd) of the thioether compound is 1/99 to 99/1. From the viewpoint of the balance between chemical stability and durability (dispersibility), Wc / Wd is more preferably 5/95 to 95/5, still more preferably 10/90 to 90/10, Particularly preferred is 20/80 to 80/20.

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

  In the present embodiment, the thickness of the polymer electrolyte membrane is preferably 1 μm to 500 μm, more preferably 1 μm to 250 μm, still more preferably 1 μm to 100 μm, and particularly preferably 1 μm to 50 μm. Adjusting the film thickness to the above range can reduce inconveniences such as direct reaction between hydrogen and oxygen, resulting in differential pressure and distortion during handling during fuel cell production and during fuel cell operation. However, it is preferable in that the film is hardly damaged. Furthermore, adjusting the film thickness to the above range is preferable from the viewpoint of maintaining the ion permeability of the polymer electrolyte membrane and maintaining the performance as a solid polymer electrolyte membrane.

[Production method of polymer electrolyte membrane]
Next, although the manufacturing method of the fluorine-type polymer electrolyte membrane in this embodiment is demonstrated, the following manufacturing methods are examples and are not specifically limited.
The fluorine-based polymer electrolyte membrane in the present embodiment is, for example,
A step of impregnating a polyolefin microporous membrane having a void having a pore diameter of 0.05 to 0.5 μm with a fluorine-based polymer electrolyte solution containing a solvent represented by the following general formula (4):
Volatilizing the solvent of the impregnated fluoropolymer electrolyte solution,
A method for producing a fluorine-based polymer electrolyte membrane comprising:
C _q H _r (OH) _s (4)
(In formula (4), q represents an integer of 3 or more, r represents an integer of 2q + 2-s, and s represents an integer of 1 or more.)
Can be obtained.
By the production method including the above-described steps, a fluorine-based polymer electrolyte membrane in which a minute gap of the polyolefin microporous membrane is impregnated with a fluorine-based polymer electrolyte can be obtained.

  The method of impregnating the polymer electrolyte in the voids of the polyolefin microporous membrane is not particularly limited. For example, a method of applying a polymer electrolyte solution described later to the microporous membrane, or a method of applying the polymer electrolyte solution to the microporous membrane. Examples of the method include a method of drying after impregnation. For example, a polyelectrolyte solution film is formed on a moving or stationary elongated casting substrate (sheet), an elongated microporous membrane is contacted on the solution, and an unfinished composite structure is formed. Make it. The incomplete composite structure is dried in a hot air circulation tank. Next, a method of forming a polymer electrolyte membrane by further forming a film of a polymer electrolyte solution on the dried incomplete composite structure can be mentioned. The contact between the polymer electrolyte solution and the microporous membrane may be performed in a dry state, in an undried state or in a wet state. Moreover, when making it contact, you may carry out pressure bonding with a rubber roller, or controlling the tension | tensile_strength of a microporous film. Further, a sheet containing a polymer electrolyte may be preliminarily formed by extrusion molding, cast molding, or the like, and this sheet may be filled by hot pressing with a microporous film.

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

  The polymer electrolyte membrane in the present embodiment is preferably further subjected to heat treatment. By this heat treatment, the polyolefin microporous membrane and the polymer electrolyte portion in the polymer electrolyte membrane are firmly bonded, and as a result, the mechanical strength tends to be further improved. The temperature of this heat treatment is preferably 90 ° C to 230 ° C, more preferably 100 ° C to 210 ° C, still more preferably 110 ° C to 200 ° C, and particularly preferably 120 ° C to 180 ° C. By adjusting the temperature of the heat treatment to the above range, the adhesion between the microporous membrane and the electrolyte portion tends to be improved. Moreover, the said temperature range is suitable also from a viewpoint of maintaining the high moisture content and mechanical strength of a polymer electrolyte membrane. Although the heat treatment time depends on the heat treatment temperature, it is preferably 1 minute to 3 hours, more preferably 5 minutes to 3 hours, and even more preferably 10 minutes to obtain a highly durable polymer electrolyte membrane. 2 hours, particularly preferably 10 minutes to 30 minutes.

(Polymer electrolyte solution)
The fluorine-based polymer electrolyte solution used for filling the voids of the polyolefin microporous membrane with a polymer electrolyte contains a specific solvent, the polymer electrolyte, and other additives as required. This polymer electrolyte solution is used as it is or after passing through steps such as filtration and concentration, and then used as a filling liquid for a polyolefin microporous membrane.

The polymer electrolyte solution in this embodiment contains at least one solvent represented by the following general formula (4).
_{C q H r (OH) s} - (4)
(In formula (4), q represents an integer of 3 or more, r represents an integer of 2q + 2-s, and s represents an integer of 1 or more.)

Examples of the solvent include 1-propanol, 2-propanol, 1-butanol, 2-butanol, 3-butanol, propanediol, and butanediol. Of these, butanol and 1,3-propanediol are particularly preferable.
By using a solvent having 3 or more carbon atoms, the molecular chain of the polymer electrolyte is loosened, and the dispersibility of the polymer electrolyte in the solution is increased. Further, by using a hydrophilic alcohol having 3 or more carbon atoms, the affinity between the water in the solution and the swollen polymer electrolyte is maintained.

  Moreover, the ratio (Wf / We) of the mass (Wf) of water to the mass (We) of the solvent represented by the general formula (4) contained in the polymer electrolyte solution is 10/90 to 90/10. Is preferred. From the viewpoint of the chemical stability of the polymer electrolyte, Wf / We is more preferably 20/80 to 80/20, further preferably 30/70 to 70/30, and 40/60 to 60 / 40 is particularly preferred.

  Further, when a monohydric alcohol and a polyhydric alcohol are used in combination as the solvent represented by the general formula (4), the ratio (Wh / Wg) of the mass (Wh) of the polyhydric alcohol to the mass (Wg) of the monohydric alcohol is 1/99 to 99/1 is preferable. From the viewpoint of the chemical stability of the polymer electrolyte, Wh / Wg is more preferably 5/95 to 95/5, further preferably 10/90 to 90/10, and 20/80 to 80 /. 20 is particularly preferred.

  The manufacturing method of the polymer electrolyte solution in this embodiment is demonstrated. The method for producing the polymer electrolyte solution is not particularly limited except that the solvent to be contained is defined. For example, after obtaining a solution in which the polymer electrolyte is dissolved or dispersed in the solvent, the solution is added to the solution as necessary. It can be obtained by dispersing the additive. Alternatively, it can be obtained by first mixing a polymer electrolyte and an additive through steps such as melt extrusion and stretching, and dissolving or dispersing the mixture in a solvent. Although the solvent represented by the general formula (4) may be added in any step, it is preferably added after the polymer electrolyte is dissolved or dispersed and before coating.

  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 or the like, 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, for example, 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 a solvent (a solvent having a good affinity with a resin) that can dissolve or suspend the polymer electrolyte, and has a general formula ( The solvent may not be the solvent represented by 4). 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 in the solvent as it is, but the polymer electrolyte is sealed under atmospheric pressure or autoclaving. It is preferable to dissolve or disperse the polymer electrolyte in a solvent in a temperature range of 0 to 250 ° C. under a pressed condition. 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 with respect to water is preferably 0.1 to 10 with respect to water 1, and more preferably with respect to water 1. 0.1-1.

  Polyelectrolyte solutions include emulsions (in which liquid particles are dispersed as colloidal particles or coarser particles to form a milky state), suspensions (solid particles in a liquid are colloidal particles) Or dispersed as particles that can be seen with a microscope), colloidal liquid (macromolecule dispersed state), micellar liquid (a lyophilic colloidal dispersion system formed by associating many small molecules with intermolecular force), etc. 1 type (s) or 2 or more types are included.

  Further, the polymer electrolyte solution may be concentrated or filtered according to the molding method and use of the polymer electrolyte membrane. 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 tends to increase and it becomes difficult to handle, whereas if it is too low, the productivity tends to decrease. Therefore, it is preferable to adjust to the range of 0.5% by mass to 50% by mass.

  Although it does not specifically limit as a method of concentration, For example, the method of heating a polymer electrolyte solution and evaporating a solvent, the method of concentrate | evaporating under reduced pressure, etc. are mentioned. A method for filtering the polymer electrolyte solution is not particularly limited, and a typical method is, for example, 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. In the case of using a metal filter, it is preferable that the 90% collection particle size is 50 to 100 times the average particle size 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 fluorine-based polymer electrolyte membrane in the present 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 in the present embodiment only needs to have the same configuration as a known MEA except that the polymer electrolyte membrane in the present embodiment is adopted as the polymer electrolyte membrane.

  The electrode catalyst layer is composed of fine particles of a catalyst metal and a conductive agent supporting the catalyst metal, and a water repellent is included as necessary. The catalyst metal 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, 1 type or more chosen from the group which consists of vanadium and these alloys is mentioned. Among the above, platinum is particularly preferable.

  As a manufacturing method of MEA, a well-known manufacturing method can be employ | adopted using the fluorine-type polymer electrolyte membrane of this embodiment, For example, the following methods are mentioned. 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 polytetrafluoroethylene (PTFE) sheet and dried. Next, the application surface of PTFE sheet faces each other, a polymer electrolyte membrane is sandwiched between them, and heat-pressed at 100 ° C. to 200 ° C. to obtain a MEA by transfer bonding. As the electrode binder, generally, an ion exchange resin dissolved in a solvent (alcohol, water, etc.) is used. From the viewpoint of durability, the polymer electrolyte solution of the present embodiment may be used as the electrode binder. 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 packing 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 that of the known one except that the above MEA is employed 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.

  The fluorine-based polymer electrolyte membrane in the present embodiment described above is excellent in mechanical strength and electrical conductivity, and is suitable as an electrolyte material for a solid polymer electrolyte fuel cell.

  Unless otherwise specified, the various parameters described above are measured according to the measurement methods in the following examples.

  Hereinafter, the present embodiment will be described more specifically by way of examples. However, the present embodiment is not limited to only 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 200 m ² ) in a proton state of the counter ion of the ion exchange group is placed in 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 room of constant temperature and humidity of 23 ° C. and 50% RH, the film thickness was measured using a film thickness meter (product name: B-1 manufactured by Toyo Seiki Seisakusho). Was measured.

(3) Pore size The average pore size was measured by a bubble point method using a palm porometer (product of Xonics, product name: Porometer 3G).

(4) Porosity A 20 cm square sample was taken and calculated from its volume and mass using the following equation.
Porosity (%) = (volume (cm ³ ) −mass (g) / density of polyethylene) / volume (cm ³ )

(5) Tensile strength at break The membrane sample was cut into a rectangular film of 70 mm × 10 mm, and the tensile strength at break (kgf / cm ² ) in the machine direction (MD) and the width direction (TD) was measured according to JISK-7127.

(6) Conductivity Conductivity measurement of the polymer electrolyte membrane in high-temperature water (80 ° C., 100% RH) was performed using a circuit element measuring machine (manufactured by HIOKI, model number: 3522-50). The polymer electrolyte membrane was cut into a width of 1 cm and a length of 6 cm and immersed in ion-exchanged water in a thermostatic bath adjusted to 80 ° C. for 60 minutes. Thereafter, six electrode wires having a diameter of 0.5 mm were arranged in parallel at equal intervals of 1 cm on the membrane, sandwiched between acrylic plates, and immersed in ion-exchanged water in a thermostatic chamber adjusted to 80 ° C. In this state, resistance was measured by the AC impedance method (10 kHz), and the resistance values at the interelectrode distances of 1 cm, 2 cm, 3 cm, 4 cm, and 5 cm were measured. A regression line was drawn for the resistance value at the distance between the electrodes, and the slope was defined as the resistance value per unit length (Ω / cm). From this value, the conductivity Z (S / cm) at 80 ° C. was determined using the following formula.
Z = 1 / film thickness (cm) / film width (cm) / resistance per unit length (Ω / cm)

[Example 1]
(Preparation of polymer electrolyte solution)
First, a precursor of perfluorosulfonic acid resin obtained from tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₂ —SO ₂ F, which is a polymer polymer precursor polymer (EW after hydrolysis and acid treatment) : 730 g / equivalent, ion exchange capacity 1.3 meq / g) 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. Then, the pellet was immersed in 60 degreeC 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 perfluorocarbon sulfonic acid resin solution having a solid content concentration of 5% by mass. This solution was designated as Solution 1.

  After concentrating the solution 1 on a rotary evaporator at a hot water bath temperature of 80 ° C. until the solid content concentration becomes 20% by mass, the mass of water contained in the solution 1 after concentration of 1,3-propanediol and butanol is The mixture was mixed so that 1,3-propanediol / butanol / water = 4/1/5. This solution after mixing was designated as Solution 2.

(Production of polyolefin microporous membrane)
19.2% by mass of ultra high molecular weight polyethylene with a viscosity average molecular weight of 1 million, 12.8% by mass of high density polyethylene with a viscosity average molecular weight of 250,000, 48% by mass of dioctyl phthalate (DOP), and 20% by mass of fine silica After granulation, the mixture was melt-kneaded by a twin-screw extruder equipped with a T-die at the tip, extruded, rolled with rolls heated from both sides, and formed into a sheet having a thickness of 80 μm. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. The microporous membrane was stretched 4.5 times in the longitudinal direction at 110 ° C., then stretched 1.7 times in the transverse direction at 120 ° C., and finally heat treated at 129 ° C.

(Production of polymer electrolyte membrane)
The obtained polyolefin microporous membrane (film thickness: 9 μm, void pore size: 0.16 μm) was fixed with an 11 cm × 11 cm SUS frame, and the polyolefin microporous membrane was immersed in the solution 2 to obtain a polyolefin microporous membrane. The solution 2 was impregnated in the voids. Next, the polyolefin microporous membrane sufficiently impregnated with the solution 2 was heat-treated in an oven at 120 ° C. for 1 hour to evaporate the solvent, thereby obtaining a polymer electrolyte membrane. Table 1 shows the evaluation results of the polymer electrolyte membrane.

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

(Production of polymer electrolyte membrane)
A polyolefin microporous membrane (manufactured by DSM Soltech, grade: Solupor 3P07A, film thickness: 18 μm, pore diameter of the gap: 0.6 μm) was fixed with an 11 cm × 11 cm SUS frame, and the polyolefin microporous membrane was immersed in the solution 1 Then, the solution 1 was impregnated into the voids of the polyolefin microporous membrane. Next, the polyolefin microporous membrane sufficiently impregnated with the solution 1 was heat-treated in an oven at 120 ° C. for 1 hour to volatilize the solvent, thereby obtaining a polymer electrolyte membrane. Table 1 shows the evaluation results of the polymer electrolyte membrane.

[Comparative Example 2]
A polymer electrolyte membrane was obtained in the same manner as in Example 1 except that the solution 2 was changed to the solution 1. Table 1 shows the evaluation results of the polymer electrolyte membrane.

  From the results in Table 1, it can be seen that the fluorine-based polymer electrolyte membrane in the present embodiment is excellent in mechanical strength and proton conductivity.

  The fluorine-based polymer electrolyte membrane of the present invention has industrial applicability as an electrolyte material for a polymer electrolyte fuel cell.

Claims (8)

A fluoropolymer electrolyte membrane obtained by impregnating a fluoropolymer electrolyte with a polyolefin microporous membrane having pores having a pore size of 0.05 to 0.5 μm,
A fluorine-based polymer electrolyte membrane having a conductivity of 0.1 S / cm or more.   The fluorine polymer electrolyte membrane according to claim 1, wherein the ion exchange capacity of the fluorine polymer electrolyte is 0.5 to 5.0 meq / g.   The fluorine-based polymer electrolyte membrane according to claim 1 or 2, further comprising a polyazole compound.   The fluorine-based polymer electrolyte membrane according to any one of claims 1 to 3, further comprising a thioether compound. The fluoropolymer electrolyte is a copolymer containing a repeating unit represented by the following general formula (1) and a repeating unit represented by the following general formula (2). The fluorine-based polymer electrolyte membrane according to any one of the above.
_{- (CF 2 CF 2) -} (1)
_{- (CF 2 -CF (-O- (} CF 2 CFX) n -O p - (CF 2) m -SO 3 H)) - (2)
(In formula (2), X represents a fluorine atom or —CF ₃ group, n represents an integer of 0 to 1, m represents an integer of 0 to 12, and p represents 0 or 1. However, n and m are simultaneously It will not be 0.) A step of impregnating a polyolefin microporous membrane having a void having a pore diameter of 0.05 to 0.5 μm with a fluorine-based polymer electrolyte solution containing a solvent represented by the following general formula (4):
Volatilizing the solvent of the impregnated fluoropolymer electrolyte solution,
A method for producing a fluorine-based polymer electrolyte membrane comprising:
C _q H _r (OH) _s (4)
(In formula (4), q represents an integer of 3 or more, r represents an integer of 2q + 2-s, and s represents an integer of 1 or more.)   The membrane electrode assembly (MEA) containing the fluorine-type polymer electrolyte membrane of any one of Claims 1-5.   A fuel cell comprising the fluorine-based polymer electrolyte membrane according to any one of claims 1 to 5.