JP2008243419A - Manufacturing method for fluorine-based nonwoven fabric, fluorine-based nonwoven fabric, solid polymer electrolyte membrane for solid polymer fuel cell, and membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a fluorine-based nonwoven fabric, capable of manufacturing fluorine-based nonwoven fabric by an electric field spinning method using undiluted spinning liquid containing polymer containing fluorine with aliphatic ring structure in a principal chain and solvent without using water soluble resin or electrolyte, to provide a solid polymer electrolyte membrane for the solid polymer fuel cell using the fluorine-based nonwoven fabric, and to provide the membrane electrode assembly for the solid polymer fuel cell. <P>SOLUTION: The solvent with a boiling point of 110°C or more is used as the solvent in the manufacturing method for the fluorine-based unwoven fabric manufacturing by the electric field spinning method using the undiluted spinning liquid containing the fluorine containing solid polymer with the aliphatic ring structure in the principal chain and the solvent. The fluorine-based unwoven fabric has fiber density of 7.5 cm<SP>3</SP>/m<SP>2</SP>or less and thickness of 23 μm or less. The solid polymer electrolyte membrane 25 contains the fluorine-based unwoven fabric. In addition, the polymer electrolyte membrane 25 is installed between an anode 23 and a cathode 24 in the membrane electrode assembly 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a fluorine-based nonwoven fabric, a fluorine-based nonwoven fabric, a solid polymer electrolyte membrane for a polymer electrolyte fuel cell, and a membrane electrode assembly.

  In the polymer electrolyte fuel cell, for example, a cell is formed by sandwiching a membrane electrode assembly between two separators, and a plurality of cells are stacked. The membrane electrode assembly includes an anode and a cathode having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode. For the solid polymer electrolyte membrane, a fluorine-based proton conductive polymer such as a perfluorocarbon polymer having a sulfonic acid group (hereinafter referred to as a sulfonic acid type perfluorocarbon polymer) is usually used. The solid polymer electrolyte membrane is required to have low electrical resistance.

  In order to reduce the electrical resistance of the solid polymer electrolyte membrane, the solid polymer electrolyte membrane may be thinned. However, when the solid polymer electrolyte membrane is thinned, the mechanical strength of the membrane is lowered, and it becomes difficult to process or handle when manufacturing a membrane electrode assembly.

  In addition, the solid polymer electrolyte membrane is likely to increase in size in the length direction of the membrane when it contains water, and various problems are likely to occur. For example, when the solid polymer electrolyte membrane swells due to water generated by the reaction, water vapor supplied with the fuel gas, etc., and the size increases, the electrode follows the dimensional change of the solid polymer electrolyte membrane. However, since the membrane electrode assembly is constrained by a separator or the like, the dimension increase of the solid polymer electrolyte membrane becomes “wrinkles”. And this wrinkle may fill the groove | channel of a separator and may inhibit the flow of gas.

The following solid polymer electrolyte membranes have been proposed as solid polymer electrolyte membranes that are thin but have high mechanical strength and excellent dimensional stability when containing water.
(1) A solid polymer electrolyte membrane reinforced with a fluorine-based nonwoven fabric produced by a melt blown method (Patent Document 1).
The fluorine-based nonwoven fabric is required to be as thin as possible in order to reduce the electric resistance of the solid polymer electrolyte membrane. For this purpose, it is necessary to further reduce the diameter of the continuous fibers constituting the fluorine-based nonwoven fabric.

  An electrospinning method is known as a method for producing a nonwoven fabric composed of ultrafine continuous fibers. However, using a spinning stock solution in which a fluoropolymer is dissolved in a perfluoro solvent and trying to produce a fluorine-based nonwoven fabric by electrospinning, the spinning stock solution has a low polarity, so that a continuous fiber cannot be formed and a nonwoven fabric is obtained. It is said that it cannot be done.

Then, the following method is proposed as a method of manufacturing a fluorine-type nonwoven fabric by an electrospinning method.
(2) A method for producing a fluorine-based nonwoven fabric by an electrospinning method using a spinning stock solution containing an amorphous fluorine-containing polymer, a water-soluble resin or an electrolyte, and a perfluoro solvent (Patent Document 2).

  In the method (2), Cytop (produced by Asahi Glass Co., Ltd., fluorine-containing polymer having an aliphatic ring structure in the main chain) as an amorphous fluorine-containing polymer, polyvinyl alcohol as a water-soluble resin, and fluorine-based proton conductivity as an electrolyte. As a polymer and a perfluoro solvent, CT-solv. (Asahi Glass Co., Ltd., boiling point 100 ° C.) is actually used.

However, since the fluorine-based nonwoven fabric produced by the method (2) contains a water-soluble resin or an electrolyte, the fluorine-based nonwoven fabric itself easily swells and has poor dimensional stability. Moreover, when non-fluorine-type compounds, such as polyvinyl alcohol, are included, chemical durability becomes inadequate.
Therefore, the fluorine-based nonwoven fabric produced by the method (2) is not suitable as a fluorine-based nonwoven fabric for reinforcing the solid polymer electrolyte membrane for a polymer electrolyte fuel cell.
US Patent Application Publication No. 2006/0159973 JP 2006-144138 A

  The present invention relates to a fluorine-based nonwoven fabric capable of producing a fluorine-based nonwoven fabric by an electrospinning method using a spinning solution containing a fluorine-containing polymer having an aliphatic ring structure in the main chain and a solvent without using a water-soluble resin or an electrolyte. A fluorine-based non-woven fabric having a low electrical resistance, high mechanical strength, excellent dimensional stability when containing water, and excellent chemical durability; A solid polymer electrolyte membrane for a polymer electrolyte fuel cell with high mechanical strength and excellent dimensional stability when containing water; and a membrane electrode assembly for a polymer electrolyte fuel cell with high output and excellent durability provide.

The method for producing a fluorine-based nonwoven fabric of the present invention is a method for producing a fluorine-based nonwoven fabric by an electrospinning method using a spinning solution containing a fluorine-containing polymer having an aliphatic ring structure in the main chain and a solvent. In addition, a solvent containing a solvent having a boiling point of 110 ° C. or higher is used.
The fluorine-based nonwoven fabric of the present invention comprises continuous fibers of a fluorine-containing polymer having an aliphatic ring structure in the main chain, has a basis weight of 7.5 cm ³ / m ² or less, and a thickness of 23 μm or less. And

The solid polymer electrolyte membrane for a polymer electrolyte fuel cell of the present invention comprises the fluorine-based nonwoven fabric of the present invention.
The membrane / electrode assembly for a polymer electrolyte fuel cell of the present invention is obtained by arranging the polymer electrolyte membrane for a polymer electrolyte fuel cell of the present invention between an anode and a cathode.

According to the method for producing a fluorine-based nonwoven fabric of the present invention, without using a water-soluble resin or an electrolyte, an electrospinning method using a spinning stock solution containing a fluorine-containing polymer having an aliphatic ring structure in the main chain and a solvent is used. Fluorine-based nonwoven fabric can be manufactured.
According to the fluorine-based nonwoven fabric of the present invention, it is possible to obtain a solid polymer electrolyte membrane having low electric resistance, high mechanical strength, and excellent dimensional stability when containing water. Moreover, the fluorine-type nonwoven fabric of this invention is excellent in chemical durability.

The solid polymer electrolyte membrane for a polymer electrolyte fuel cell of the present invention has low electrical resistance, high mechanical strength, and excellent dimensional stability when containing water.
The membrane / electrode assembly for a polymer electrolyte fuel cell of the present invention has high output and excellent durability.

  In this specification, the repeating unit represented by the formula (α) is referred to as a repeating unit (α). Groups represented by other formulas are also described in the same manner. Moreover, the compound represented by Formula (1) is described as a compound (1). The same applies to compounds represented by other formulas.

<Fluorine-based nonwoven fabric>
The fluorine-based nonwoven fabric of the present invention is composed of continuous fibers of a fluorine-containing polymer having an aliphatic ring structure in the main chain, has a basis weight of 7.5 cm ³ / m ² or less, and a thickness of 23 μm or less.

The fluorine-containing polymer having an aliphatic ring structure in the main chain refers to a polymer in which one or more carbon atoms constituting the aliphatic ring structure are carbon atoms constituting the main chain of the fluorine-containing polymer. The carbon atom of the main chain is derived from two carbon atoms of the polymerizable double bond of the monomer constituting the fluorine-containing polymer, or the monomer having two polymerizable double bonds is subjected to cyclopolymerization. In the case of the fluorine-containing polymer obtained in this way, it is derived from 4 carbon atoms of 2 polymerizable double bonds. As atoms constituting the aliphatic ring structure, oxygen atoms, nitrogen atoms, and the like may be included in addition to carbon atoms. As the aliphatic ring structure, a perfluoroaliphatic ring structure having 1 to 2 oxygen atoms is preferable. The number of atoms constituting the aliphatic ring structure is preferably 4-7. As the polymerizable double bond, a vinyl group, an allyl group, an acryloyl group, and a methacryloyl group are preferable.
The fluorine-containing polymer having an aliphatic ring structure in the main chain is hardly crystallized due to the twist caused by the structure and is soluble in a solvent. Examples of the fluorine-containing polymer having an aliphatic ring structure in the main chain include polymers having repeating units (α) to (ζ).

Here, k is an integer from 1 to 4, ^{R f} is perfluoroalkoxy groups perfluoroalkyl group or C1-8 1 to 8 carbon ^atoms, X 1, ^{X 2} are each fluorine An atom or a trifluoromethyl group. In (CX ¹ X ² ) _k , when k is 2 or more, the combination of X ¹ and X ² may be different for each carbon atom.
As the fluorine-containing polymer having an aliphatic ring structure in the main chain, a polymer having a repeating unit (β1) or (ε1) is preferable.

  The fluorine-containing polymer having an aliphatic ring structure in the main chain preferably has substantially no ionic group from the viewpoint of dimensional stability. Having substantially no ionic group means that the molecule does not contain an ionic functional group such as a sulfonic acid group, a phosphoric acid group, a carboxyl group, a sulfoimide group, or an ammonia group.

The continuous fiber means a fiber having an aspect ratio of 10,000 or more. The fiber length is preferably 20 mm or more.
The fiber diameter (diameter) of the continuous fiber is preferably 0.01 to 5 μm, and more preferably 0.01 to 0.5 μm. If the fiber diameter is 0.01 μm or more, the tensile strength per fiber is sufficient, and the handling properties are good. If the fiber diameter is 5 μm or less, proton transfer is performed smoothly, so that an increase in electrical resistance due to the fluorine-based nonwoven fabric can be suppressed. Moreover, since the number of intersections between fibers per thickness increases, the mechanical strength and dimensional stability of the solid polymer electrolyte membrane are improved.
The fiber diameter of the continuous fiber is measured from a cross-sectional micrograph.

The thickness of the fluorine-based nonwoven fabric is 23 μm or less, preferably 19 μm or less, more preferably 14 μm or less, and even more preferably 9 μm or less, from the viewpoint of the electric resistance of the solid polymer electrolyte membrane.
From the viewpoint of the mechanical strength of the solid polymer electrolyte membrane, the thickness of the fluorine-based nonwoven fabric is preferably at least twice the diameter of the constituted fiber, more preferably at least three times. That there is not enough thickness with respect to the fiber diameter means that in the obtained nonwoven fabric, the constituent fibers do not have sufficient intersections, and as a result, good mechanical strength is achieved. It cannot be expressed.
The thickness of the fluorine-based nonwoven fabric is measured from a micrograph of the cross section, and is the maximum value.

The opening ratio of the fluorine-based nonwoven fabric is preferably 66 to 80%. If the aperture ratio of the fluorine-based nonwoven fabric is within this range, a reinforced polymer electrolyte membrane can be obtained without significantly increasing the increase in electrical resistance in the thickness direction due to the insertion of the reinforcing body into the electrolyte membrane. .
The aperture ratio of the fluorine-based nonwoven fabric is calculated from the following formula.
Opening ratio (%) = 100−A × 100 / (B × C).
However, A is the basis weight (g / m ² ) of the fluorine-containing polymer that is the material of the fluorine-based nonwoven fabric, B is the density (g / m ³ ) of the fluorine-containing polymer that is the material of the nonwoven fabric, and C Is the thickness (m) of the nonwoven fabric.

By taking into account the above-described restrictions on the thickness of the nonwoven fabric and the restrictions on the aperture ratio, it is obvious that there is substantially a preferable range in the characteristic value of the basis weight of the nonwoven fabric. From these, the basis weight of the fluorine-based nonwoven fabric, from the viewpoint of the electrical resistance of the solid polymer electrolyte membrane, and a 7.5 cm ³ / ^{m 2} or less, preferably 6.3 cm ³ / ^{m 2} or less, 4.7 cm ³ / m ² or less is more preferable. Moreover, 1 cm < ³ > / m < ² > or more is preferable from the handling point of a fluorine-type nonwoven fabric.
The basis weight of the fluorine-based nonwoven fabric was 25 ° C. A polyethylene terephthalate (hereinafter referred to as PET) film with an adhesive was pressed against the fluorine-based nonwoven fabric, and the fluorine-based nonwoven fabric was transferred to the film. The basis weight (g / m ² ) of the fluorine-based nonwoven fabric is obtained from the area of the nonwoven fabric and the mass increase of the PET film, and the density of the fluorine-containing polymer having an aliphatic ring structure in the main chain at 25 ° C. (g / cm ³ ) From the weight per unit area (cm ³ / m ² ) is obtained.

<Method for producing fluorine-based nonwoven fabric>
In the present invention, a fluorine-based nonwoven fabric is produced by an electrospinning method.
The electrospinning method is a method of spinning fibers electrically by applying a high voltage to the spinning dope.

The electrospinning method has the following characteristics.
(I) Compared with other methods, it can be manufactured with a simple apparatus.
Known methods for producing nonwoven fabrics include meltblown, spunbond, and papermaking methods, all of which require large-scale nonwoven fabric production equipment, and separate fiber production equipment is required to prepare the raw material fibers. The device cost is high.
(Ii) An ultrafine continuous fiber aggregate is obtained.
Manufacturing a non-woven fabric composed of ultrafine fibers using a normal non-woven fabric facility is severe in terms of conditions and has many limitations such as the viscosity of the raw material and stretchability. On the other hand, since the electrospinning method is a spinning method using a solution, volume shrinkage occurs in the drying process, and since the raw material itself has a low viscosity, molding with an ultrafine nozzle is possible. Easy to obtain continuous fiber.
(Iii) The fiber assembly is usually obtained as a nonwoven fabric in which fibers are combined.
In the electrospinning method, since solidification from a solution and spinning by stretching occur simultaneously or sequentially, the fiber assembly is obtained as a nonwoven fabric in which fibers are bonded to each other.

  FIG. 1 is a schematic configuration diagram illustrating an example of a nonwoven fabric manufacturing apparatus using an electrospinning method. The nonwoven fabric manufacturing apparatus 10 applies a high voltage between the syringe 12 filled with the spinning dope, the rotatable drum 16 disposed so as to face the needle 14 of the syringe 12, and the needle 14 and the drum 16. And a syringe pump (not shown) for discharging the spinning solution from the syringe at a constant flow rate by moving the plunger portion of the syringe 12 at a constant speed in the discharge direction.

  First, the spinning solution is filled into the syringe 12. While rotating the drum 16, a high voltage is applied between the needle 14 and the drum 16 by the high voltage power source 18. The syringe pump is operated, and the spinning solution is discharged from the needle 14 at the tip of the syringe 12 at a constant speed. When a voltage is applied to the tip of the needle 14 and the electrostatic attractive force exceeds the surface tension of the spinning stock solution, the spinning stock solution is deformed into a conical shape called Taylor cone at the tip of the needle 14, and the tip of the cone Stretched. The stretched spinning dope is refined by electrostatic repulsion of the positively charged spinning dope. The solvent instantly evaporates from the refined spinning dope, and ultrafine fibers are formed. Positively charged fibers adhere to the negatively charged drum 16. As the fibers gradually accumulate on the rotating drum 16, a fluorine-based nonwoven fabric is formed on the drum 16.

  The spinning dope is a solution containing a fluorine-containing polymer having an aliphatic ring structure in the main chain and a solvent. The solvent is a solvent containing a solvent having a boiling point of 110 ° C. or higher. The boiling point is preferably 130 ° C. or higher, and more preferably 160 ° C. or higher. The boiling point is not preferably too high and is preferably 220 ° C. or lower because the electric field drawing process requires solidification and drying of the polymer component from the solution during solution spinning. The boiling point of the solvent is a value at atmospheric pressure.

The solvent having a boiling point of 110 ° C. or higher is preferably a perfluoro solvent from the viewpoint of the solubility of the fluorine-containing polymer.
Examples of commercially available solvents having a boiling point of 110 ° C. or higher include CT-solv. 180 (Asahi Glass Co., Ltd., perfluoro solvent, boiling point: 180 ° C.). The following solvents are also available.
Fluorine-containing alicyclic hydrocarbons: perfluorodecalin (bp 142 ° C.), perfluoro (1,3,5-trimethylcyclohexane) (bp 125 ° C.), perfluorotetradecahydrophenanthrene (bp 215 ° C.) and the like.
Fluorine-containing alkylamines: perfluorotripropylamine (bp 130 ° C.), perfluorotributylamine (bp 178 ° C.), perfluorotripentylamine (normal pressure conversion bp of reduced pressure distillation boiling point about 200 ° C., expected bp 230-240 ° C. from calculation), etc. .
Fluorinated aliphatic hydrocarbons: perfluorononane (bp 123 ° C.), perfluorodecane (bp 144 ° C.), perfluorododecane (bp 178 ° C.), 1H-perfluorodecane (bp 160-170 ° C.), 1H-perfluorooctane (bp 120-130 ° C.) ) 1H, 1H, 1H, 2H, 2H-perfluorooctane (bp 150-160 ° C.) and the like.
Fluorinated ethers: methyl perfluorooctyl ether (normal pressure conversion bp 150-160 ° C.), methyl perfluorononyl ether (normal pressure conversion bp 175 ° C.), and the like.

The solvent may contain other solvents except for a solvent having a boiling point of 110 ° C. or higher.
Examples of the other solvent include perfluorobenzene, trifluoroethane, perfluoro (2-butyltetrahydrofuran) and the like.
Other commercially available solvents include Fluorinert FC-77 (manufactured by 3M, perfluoro solvent, boiling point: 100 ° C.), CT-solv. 100 (Asahi Glass Co., Ltd., perfluoro solvent, boiling point: 100 ° C., substitute chlorofluorocarbons such as AK-225, etc.).

  The proportion of the solvent having a boiling point of 110 ° C. or higher is preferably 10 to 100% by mass, more preferably 25 to 100% by mass, and particularly preferably 50 to 100% by mass in the solvent (100% by mass). If the proportion of the solvent having a boiling point of 110 ° C. or higher is 10% by mass or more, continuous fibers can be reliably formed.

The ratio of the fluorine-containing polymer having an aliphatic ring structure in the main chain is preferably 2.0 to 15.0% by mass in the spinning dope (100% by mass).
The discharge amount of the spinning dope is preferably 0.1 to 50 mL / hour.
The inner diameter of the tip of the needle 14 is preferably 0.1 to 2 mm.
The distance from the tip of the needle 14 to the drum 16 is preferably 5 to 40 cm.
The voltage applied between the needle 14 and the drum 16 is preferably 1 to 40 kV.

<Solid polymer electrolyte membrane>
The solid polymer electrolyte membrane for a polymer electrolyte fuel cell of the present invention (hereinafter referred to as a solid polymer electrolyte) is a membrane containing a proton conductive polymer and a fluorine-based nonwoven fabric.

  The thickness of the solid polymer electrolyte membrane is preferably 25 μm or less, more preferably 20 μm or less, and particularly preferably 15 μm or less. Further, the thickness of the solid polymer electrolyte membrane is preferably 10 μm or more, and more preferably 12 μm or more. When the thickness of the solid polymer electrolyte membrane is 25 μm or less, the electric resistance of the solid polymer electrolyte membrane can be sufficiently lowered. In addition, it tends to cause reverse diffusion of generated water generated on the cathode side. If the thickness of the solid polymer electrolyte membrane is 10 μm or more, the mechanical strength becomes high and troubles such as gas leakage hardly occur.

  The solid polymer electrolyte membrane has a fluorine-based material on at least one surface of a layer reinforced with a fluorine-based nonwoven fabric (hereinafter referred to as a reinforcing layer) from the viewpoint that electric resistance at the joint between the solid polymer electrolyte membrane and the electrode can be reduced. It is preferable to have a layer that is not reinforced with a nonwoven fabric (hereinafter referred to as a non-reinforcing layer), and it is more preferable to have a non-reinforcing layer on both sides of the reinforcing layer.

The proton conductive polymer of the non-reinforcing layer may be the same as or different from the proton conductive polymer of the reinforcing layer.
The non-reinforcing layer may contain other components excluding the fluorine-based nonwoven fabric as long as the electrical resistance is not increased.

The thickness of the non-reinforcing layer is preferably 1 to 5 μm and more preferably 1 to 3 μm on one side from the viewpoint that the fuel gas barrier property is excellent and electric resistance can be suppressed.
The thickness of the non-reinforcing layer is the shortest distance from the surface of the solid polymer electrolyte membrane to the fluorine-based nonwoven fabric, and can be measured by cross-sectional observation using an optical microscope, laser microscope, SEM or the like.

(Proton conducting polymer)
Examples of the proton conductive polymer include a fluorine-based proton conductive polymer, a hydrocarbon-based proton conductive polymer, and the like. From the viewpoint of durability, a fluorine-based proton conductive polymer is preferable.

Examples of the fluorine-based proton conductive polymer include sulfonic acid type perfluorocarbon polymers.
The sulfonic acid type perfluorocarbon polymer is selected from the group consisting of perfluoroolefins (tetrafluoroethylene (hereinafter referred to as TFE), hexafluoropropylene, etc.), chlorotrifluoroethylene, and perfluoro (alkyl vinyl ether). A copolymer having a repeating unit based on one or more types and a repeating unit having a sulfonic acid group is preferable, and a copolymer H having a repeating unit based on TFE and a repeating unit having a sulfonic acid group is particularly preferable. As the repeating unit having a sulfonic acid group, a repeating unit represented by the following formula (A) is more preferable.

  However, X is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, and p is 0 or 1.

Copolymer H after obtaining a precursor polymer F by polymerizing a monomer mixture containing a compound having a TFE and -SO 2 _F group, a sulfonic acid group -SO 2 _F groups in the precursor polymer F Can be obtained by converting to Conversion of the —SO ₂ F group into a sulfonic acid group is performed by hydrolysis and acidification treatment.

As the compound having a —SO ₂ F group, the compound (1) is preferable.
_{CF 2 = CF- (OCF 2 CFX} ) m -O p - (CF 2) n -SO 2 F ··· (1).
However, X is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, and p is 0 or 1.

As the compound (1), compounds (11) to (14) are preferable.
CF ₂ = CFO (CF ₂ ) _q SO ₂ F (11),
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _r SO ₂ F (12),
CF ₂ = CF (CF ₂ ) _s SO ₂ F (13),
_{CF 2 = CF (OCF 2 CF} (CF 3)) t O (CF 2) 2 SO 2 F ··· (14).
However, q is an integer of 1-8, r is an integer of 1-8, s is an integer of 1-8, and t is an integer of 1-5.

  Hydrocarbon proton conductive polymers include sulfonated polyarylene, sulfonated polybenzoxazole, sulfonated polybenzothiazole, sulfonated polybenzimidazole, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, Sulfonated polyphenylene sulfone, sulfonated polyphenylene oxide, sulfonated polyphenylene sulfoxide, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfide sulfone, sulfonated polyether ketone, sulfonated polyether ether ketone, sulfonated polyether ketone ketone, sulfonated polyimide, etc. Is mentioned.

  The ion exchange capacity of the proton conducting polymer is preferably 0.5 to 2.0 meq / g dry resin, and more preferably 0.7 to 1.6 meq / g dry resin. If the ion exchange capacity is 0.5 meq / g dry resin or more, the electric resistance of the solid polymer electrolyte membrane can be sufficiently lowered. When the ion exchange capacity is 2.0 meq / g dry resin or less, the hydrophilicity of the polymer is suppressed, and the solid polymer electrolyte membrane does not dissolve during power generation.

(Method for producing solid polymer electrolyte membrane)
As a manufacturing method of a solid polymer electrolyte membrane, the following method is mentioned, for example.
(A-1) A casting method in which a fluorine-based nonwoven fabric is coated or impregnated with a solution or dispersion containing a proton conductive polymer, and then dried to form a film.
(A-2) A method of laminating and integrating a film-like material containing a proton-conductive polymer previously formed on a fluorine-based nonwoven fabric.
If necessary, the solid polymer electrolyte membrane may be reinforced by stretching or the like.

When the non-reinforcing layer is provided on at least one side of the reinforcing layer, examples of the method for producing the solid polymer electrolyte membrane include the following methods.
(B-1) A method in which a non-reinforcing layer is simultaneously formed when a solid polymer electrolyte membrane is formed by the method of (a-1) or (a-2).
(B-2) A method of applying a solution or dispersion containing a proton conductive polymer to the surface of the solid polymer electrolyte membrane (reinforcing layer) obtained by the method of (a-1) or (a-2) .
(B-3) A membrane-like material containing a proton-conducting polymer previously formed on the surface of the solid polymer electrolyte membrane (reinforcing layer) obtained by the method (a-1) or (a-2) (Reinforcement layer) is laminated and integrated.

<Membrane electrode assembly>
FIG. 2 is a cross-sectional view showing an example of a membrane electrode assembly for a polymer electrolyte fuel cell of the present invention (hereinafter referred to as a membrane electrode assembly). The membrane electrode assembly 20 is in contact with the catalyst layer 21 between the anode 23 having the catalyst layer 21 and the gas diffusion layer 22, the cathode 24 having the catalyst layer 21 and the gas diffusion layer 22, and the anode 23 and the cathode 24. And a solid polymer electrolyte membrane 25 arranged in the above state.

(Solid polymer electrolyte membrane)
The solid polymer electrolyte membrane 25 is a membrane containing the proton conductive polymer and the fluorine-based nonwoven fabric described above.

(Catalyst layer)
The catalyst layer 21 is a layer containing a catalyst and a proton conductive polymer.
Examples of the catalyst include a supported catalyst in which platinum or a platinum alloy is supported on a carbon support. The catalyst for the cathode 24 is preferably a supported catalyst in which a platinum-cobalt alloy is supported on a carbon support from the viewpoint of durability.
Examples of the carbon carrier include carbon black powder. From the viewpoint of durability, carbon black powder graphitized by heat treatment or the like is preferable.
Examples of the proton conductive polymer include a fluorine-based proton conductive polymer and a hydrocarbon polymer. From the viewpoint of durability, a fluorine-based proton conductive polymer is preferable.

  The catalyst layer 21 may contain a water repellent agent from the viewpoint of increasing the effect of suppressing flooding. As a water repellent, a copolymer of TFE and hexafluoropropylene, a copolymer of TFE and perfluoro (alkyl vinyl ether) (hereinafter referred to as PFA), polytetrafluoroethylene (hereinafter referred to as PTFE). Etc.). As the water repellent, a fluorine-containing polymer that can be dissolved in a solvent is preferable because the catalyst layer 21 can be easily subjected to water repellent treatment. The ratio of the water repellent agent is preferably 0.01 to 30% by mass in the catalyst layer 21 (100% by mass).

(Gas diffusion layer)
Examples of the gas diffusion layer 22 include carbon paper, carbon cloth, and carbon felt.
The gas diffusion layer 22 is preferably subjected to a water repellent treatment with PTFE or the like.

(Carbon layer)
The membrane electrode assembly 20 may have a carbon layer 26 between the catalyst layer 21 and the gas diffusion layer 22 as shown in FIG. By disposing the carbon layer 26, the gas diffusibility on the surface of the catalyst layer 21 is improved, and the power generation performance of the polymer electrolyte fuel cell is greatly improved.

The carbon layer 26 is a layer containing carbon and a nonionic fluorine-containing polymer.
As carbon, carbon nanofibers having a fiber diameter of 1 to 1000 nm and a fiber length of 1000 μm or less are preferable.
Examples of the nonionic fluorine-containing polymer include PTFE.

(Method for producing membrane electrode assembly)
The membrane electrode assembly 20 is manufactured by the following method, for example.
(X-1) A method in which the catalyst layer 21 is formed on the solid polymer electrolyte membrane 25 to form a membrane catalyst layer assembly, and the membrane catalyst layer assembly is sandwiched between the gas diffusion layers 22.
(X-2) A method in which the catalyst layer 21 is formed on the gas diffusion layer 22 to form electrodes (anode 23, cathode 24), and the solid polymer electrolyte membrane 25 is sandwiched between the electrodes.

When membrane electrode assembly 20 has carbon layer 26, membrane electrode assembly 20 is manufactured by the following method, for example.
(Y-1) A dispersion containing carbon and a nonionic fluorine-containing polymer is applied on a base film and dried to form a carbon layer 26, and a catalyst layer 21 is formed on the carbon layer 26. A method in which the layer 21 and the solid polymer electrolyte membrane 25 are bonded together, the base film is peeled off to form a membrane catalyst layer assembly having a carbon layer 26, and the membrane catalyst layer assembly is sandwiched between the gas diffusion layers 22.
(Y-2) A dispersion containing carbon and a nonionic fluoropolymer is applied on the gas diffusion layer 22 and dried to form a carbon layer 26. The membrane catalyst layer in the method (x-1) A method in which a joined body is sandwiched between gas diffusion layers 22 each having a carbon layer 26.

Examples of the method for forming the catalyst layer 21 include the following methods.
(Z-1) A method of applying the catalyst layer forming liquid on the solid polymer electrolyte membrane 25, the gas diffusion layer 22, or the carbon layer 26 and drying it.
(Z-2) A method in which a catalyst layer forming solution is applied onto a substrate film, dried to form a catalyst layer 21, and the catalyst layer 21 is transferred onto a solid polymer electrolyte membrane 25.

The catalyst layer forming liquid is a liquid in which a proton conductive polymer and a catalyst are dispersed in a dispersion medium. The liquid for forming a catalyst layer can be prepared, for example, by mixing a liquid composition described later and a catalyst dispersion.
Since the viscosity of the catalyst layer forming liquid varies depending on the method of forming the catalyst layer 21, it may be a dispersion of about several tens of cP or a paste of about 20,000 cP.
The catalyst layer forming liquid may contain a thickener in order to adjust the viscosity. Examples of the thickener include ethyl cellulose, methyl cellulose, cellosolve thickener, and fluorinated solvents (pentafluoropropanol, chlorofluorocarbon, etc.).

The liquid composition is a dispersion in which a proton conductive polymer is dispersed in a dispersion medium containing an organic solvent having a hydroxyl group and water.
The organic solvent having a hydroxyl group is preferably an organic solvent having 1 to 4 carbon atoms in the main chain, and examples thereof include methanol, ethanol, n-propanol, isopropanol, tert-butanol, and n-butanol. The organic solvent which has a hydroxyl group may be used individually by 1 type, and 2 or more types may be mixed and used for it.

The proportion of water is preferably 10 to 99% by mass and more preferably 40 to 99% by mass in the dispersion medium (100% by mass). By increasing the proportion of water, the dispersibility of the proton conductive polymer in the dispersion medium can be improved.
The proportion of the organic solvent having a hydroxyl group is preferably from 1 to 90 mass%, more preferably from 1 to 60 mass%, in the dispersion medium (100 mass%).
The dispersion medium may contain a fluorine-containing solvent. Examples of the fluorine-containing solvent include hydrofluorocarbon, fluorocarbon, hydrochlorofluorocarbon, fluoroether, fluorine-containing alcohol, and the like.
The proportion of the proton conductive polymer is preferably 1 to 50% by mass and more preferably 3 to 30% by mass in the liquid composition (100% by mass).

<Solid polymer fuel cell>
The membrane electrode assembly of the present invention is used for a polymer electrolyte fuel cell. A polymer electrolyte fuel cell is manufactured, for example, by forming a cell by sandwiching a membrane electrode assembly between two separators and stacking a plurality of cells.
Examples of the separator include a conductive carbon plate in which a groove serving as a passage for a fuel gas or an oxidizing gas containing oxygen (air, oxygen, etc.) is formed.
Examples of the polymer electrolyte fuel cell include a hydrogen / oxygen fuel cell and a direct methanol fuel cell (DMFC).

  In the method for producing a fluorine-based nonwoven fabric of the present invention described above, the fluorine-based nonwoven fabric is produced by an electrospinning method using a spinning solution containing a fluorine-containing polymer having an aliphatic ring structure in the main chain and a solvent. In the method, since a solvent containing a solvent having a boiling point of 110 ° C. or higher is used as the solvent, a stock solution for spinning containing a fluorine-containing polymer having an aliphatic ring structure in the main chain and a solvent without using a water-soluble resin or an electrolyte. A fluorine-based nonwoven fabric can be produced by an electrospinning method using

The fluorine-based nonwoven fabric of the present invention described above is composed of continuous fibers of a fluorine-containing polymer having an aliphatic ring structure in the main chain, and has a basis weight of 7.5 cm ³ / m ² or less, and has a thickness of Since the thickness is 23 μm or less, a solid polymer electrolyte membrane having low electrical resistance, high mechanical strength, and excellent dimensional stability when containing water can be obtained. Moreover, since the fluorine-type nonwoven fabric of this invention does not contain water-soluble resin or electrolyte, it is excellent in chemical durability, and is excellent in the dimensional stability of fluorine-type nonwoven fabric itself.

Further, in the solid polymer electrolyte membrane of the present invention described above, since it includes the fluorine-based nonwoven fabric of the present invention, in order to reduce the electrical resistance, even if the thickness is reduced, the mechanical strength is high, Excellent dimensional stability when containing water.
Further, in the membrane electrode assembly of the present invention described above, the solid polymer electrolyte membrane has a high mechanical strength even when the thickness is reduced in order to reduce the electric resistance, and the dimensions when containing water. Since the solid polymer electrolyte membrane of the present invention having excellent stability is provided, the output is high and the durability is excellent.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
Example 1 is an example, and Examples 2 to 4 are comparative examples.

(Fiber diameter of continuous fiber)
The cross section of the fluorine-based nonwoven fabric was observed with a laser microscope, and the fiber diameter of the continuous fibers that appeared on the section of the fluorine-based nonwoven fabric was measured.

(Thickness of fluorine-based nonwoven fabric)
The cross section of the fluorine-based nonwoven fabric was observed with a laser microscope, and the thickness of the thickest part was measured.

(Amount of fluorine-based non-woven fabric)
The weight per unit area of the fluorine-based nonwoven fabric is 25 ° C. The pressure-sensitive PET film with an adhesive is pressed against the fluorine-based nonwoven fabric, the fluorine-based nonwoven fabric is transferred to the film, the area of the transferred fluorine-based nonwoven fabric, and the mass of the PET film From the increase, the basis weight (g / m ² ) of the fluorine-based nonwoven fabric is obtained, and further, the basis weight (cm ³ / m ³ ) is calculated from the density (g / cm ³ ) at 25 ° C. of the fluoropolymer that is the material of the fluorine-based nonwoven fabric. ² ) was obtained.

(Opening ratio of fluorine-based nonwoven fabric)
The opening ratio of the fluorine-based nonwoven fabric was calculated from the following formula.
Opening ratio (%) = 100−A × 100 / (B × C).
However, A is the basis weight (g / m ² ) of the fluorine-containing polymer that is the material of the fluorine-based nonwoven fabric, B is the density (g / m ³ ) of the fluorine-containing polymer that is the material of the nonwoven fabric, and C Is the thickness (cm) of the nonwoven fabric.

(Non-reinforcing layer thickness)
The cross section of the solid polymer electrolyte membrane was observed with a laser microscope, and the shortest distance from the surface of the solid polymer electrolyte membrane to the fluorine-based nonwoven fabric was measured.

(Dimensional change rate when containing water)
A 200 mm square sample was cut out from the solid polymer electrolyte membrane. The sample was exposed to an atmosphere at a temperature of 25 ° C. and a relative humidity of 50% for 16 hours, and the length and width of the sample were measured. Then, after immersing the sample in ion exchange water at 25 ° C. for 1 hour, the length was measured in the same manner. The average value of the elongation in the vertical direction and the horizontal direction of the sample was determined and used as the dimensional change rate.

(Initial cell voltage)
As a separator, a carbon plate (groove width 1 mm, land portion 1 mm) in which narrow grooves for gas passage were cut into a zigzag shape was prepared.
A separator was disposed on both outer sides of the membrane electrode assembly, and a heater was further disposed on the outer side of the separator to assemble a polymer electrolyte fuel cell having an effective membrane area of 25 cm ² .

The temperature of the polymer electrolyte fuel cell was maintained at 80 ° C., and air was supplied to the cathode and hydrogen was supplied to the anode at 0.15 MPa, respectively. Each gas was supplied to each electrode while being humidified to a relative humidity of 50% using a humidifier. The cell voltage at a current density of 0.1 A / cm ² and 1A / cm ² were measured.

In addition, in order to clarify the difference in Ω loss of the electrolyte membrane in the thickness direction, the cell voltage of the polymer electrolyte fuel cell when the reinforced solid polymer electrolyte membrane of Examples 1 and 2 was used, and an example The difference from the cell voltage of the polymer electrolyte fuel cell in the case of using 3 unreinforced solid polymer electrolyte membrane was calculated from the following equation.
Voltage difference = cell voltage of a solid polymer fuel cell when a reinforced solid polymer electrolyte membrane is used−cell voltage of a solid polymer fuel cell when an unreinforced solid polymer electrolyte membrane is used.
In the two types of polymer electrolyte fuel cells, if only the polymer electrolyte membrane is different and the electrodes (catalyst layer and gas diffusion layer) and separator are the same, the difference in cell voltage is the thickness of the polymer electrolyte membrane. It can be considered that the voltage loss is derived from the difference in proton conductivity in the vertical direction. The voltage difference is considered to be an extra proton conduction resistance caused by inserting the reinforcing body, and is preferably close to zero.

[Example 1]
Production of fluorine-based nonwoven fabric:
To a solution of a fluorine-containing polymer having a repeating unit (ε1) (Asahi Glass Co., Ltd., Cytop CTL-107S, solvent: Fluorinert FC-77 (manufactured by 3M, boiling point: 100 ° C., solid content: 7% by mass)) sol.180 (Asahi Glass Co., Ltd., boiling point: 180 ° C.) was added to prepare a spinning dope.
The proportion of the fluorine-containing polymer having an aliphatic ring structure in the main chain is 7% by mass in the spinning solution (100% by mass), and the proportion of the solvent having a boiling point of 110 ° C. or higher is that of the solvent (100% by mass). Of these, it was 15% by mass.

A non-woven fabric production apparatus (manufactured by Iuchi Seisakusho Co., Ltd.) was prepared by electrospinning. A stainless syringe needle of 25 G (inner diameter: 0.25 mm, outer diameter: 0.5 mm, length 5 cm) was attached to the tip of a disposable syringe with a capacity of 10 mL.
Using the nonwoven fabric manufacturing apparatus and the spinning solution, electrospinning was performed under the conditions of the distance from the tip of the needle to the drum: 7.5 cm, the applied voltage: 20 kV, and the discharge rate: 0.20 mL / hour. A fluorine-based nonwoven fabric A composed of continuous fibers having a fiber diameter of 0.4 to 5.0 μm was obtained on a drum. The aspect ratios of continuous fibers were all 10,000 or more. When an area of 2.6 cm × 2.6 cm of the fluorine-based nonwoven fabric A was observed with a microscope, fibers having a fiber length of 13 mm or less were not observed.
The thickness, basis weight, and aperture ratio of the fluorinated nonwoven fabric A were measured. The results are shown in Table 1. The density of the fluoropolymer having an aliphatic ring structure in the main chain at 25 ° C. was 2.0 g / cm ³ .

Production of solid polymer electrolyte membrane:
Solution A (solvent: ethanol, solid) of copolymer H1 (ion exchange capacity: 1.1 meq / g dry resin) composed of a repeating unit based on TFE and a repeating unit represented by the following formula (A-1) Min: 5% by mass).

  With the edge of the fluorine-based nonwoven fabric A restrained, the fluorine-based nonwoven fabric A was immersed in the solution A, pulled up at a rate of 100 mm per minute, and the solution A was impregnated with the fluorine-based nonwoven fabric A. After the impregnation operation was repeated three times, the film was dried at 55 ° C. for 1 hour in a state where the fluorine-based nonwoven fabric A was constrained to obtain a reinforcing layer film.

Solution A was applied on PET by a die coating method and dried at 140 ° C. for 1 hour to obtain a film for a non-reinforcing layer having a thickness of 3 μm.
A non-reinforcing layer film was disposed on both sides of the reinforcing layer film, and a solid polymer electrolyte membrane A having a thickness of 21 μm was obtained by a hot press method (180 ° C., 5 Pa, 15 minutes). The thickness of the non-reinforcing layer was 3 μm per side.
The dimensional change rate of the solid polymer electrolyte membrane A was measured. The results are shown in Table 2.

Manufacture of membrane electrode assembly:
Copolymer A was placed in a mixed solvent of ethanol and water (ethanol / water = 1/1 mass ratio) and dissolved by stirring in a flask equipped with a reflux function at 60 ° C. for 16 hours. (Solid content: 9% by mass) was obtained.
Separately, water and ethanol were added to platinum-supported carbon in this order, and a catalyst dispersion (solid content: 9% by mass) dispersed in a mixed dispersion medium of ethanol and water (ethanol / water = 1/1 mass ratio). )

The liquid composition and the catalyst dispersion were mixed at a liquid composition / catalyst dispersion = 11/3 (mass ratio) to prepare a catalyst layer forming liquid.
The catalyst layer forming solution was applied to both surfaces of the solid polymer electrolyte membrane A by a die coating method and dried to form a catalyst layer having a thickness of 10 μm and a platinum loading of 0.5 mg / cm ² . Membrane electrode assembly A was obtained by disposing carbon cloth as a gas diffusion layer on both outer sides of the catalyst layer.
Using the membrane electrode assembly A, a polymer electrolyte fuel cell was produced, and the initial cell voltage was measured. The results are shown in Table 3.

[Example 2]
Production of fluorine-based nonwoven fabric:
Using a melt blown nonwoven fabric manufacturing apparatus (manufactured by Nippon Nozzle Co., Ltd.), using PFA (manufactured by Asahi Glass Co., Ltd., full-on PFA P-61XP, melt flow rate: 40 g / 10 min), spinning nozzle temperature: 380 ° C., hot air temperature for stretching: Under the condition of 400 ° C., a fluorine-based nonwoven fabric B was formed on a conveyor having suction capability.

The fluorine-based nonwoven fabric B was consolidated by a hot press method (290 ° C., 10 MPa). The PFA constituting the fluorine-based nonwoven fabric B was a continuous fiber having a fiber diameter of 0.5 μm, and all the aspect ratios were 10,000 or more. When an area of 2.6 cm × 2.6 cm of the fluorine-based nonwoven fabric B was observed with a microscope, fibers having a fiber length of 13 mm or less were not observed.
The thickness, basis weight, and aperture ratio of the fluorinated nonwoven fabric B were measured. The results are shown in Table 1. The density of PFA at 25 ° C. was 2.0 g / cm ³ .

Production of solid polymer electrolyte membrane:
A solid polymer electrolyte membrane B was obtained in the same manner as in Example 1 except that the fluorine-based nonwoven fabric B was used instead of the fluorine-based nonwoven fabric A.
The dimensional change rate of the solid polymer electrolyte membrane B was measured. The results are shown in Table 2.

Manufacture of membrane electrode assembly:
A membrane / electrode assembly B was obtained in the same manner as in Example 1 except that the solid polymer electrolyte membrane B was used instead of the solid polymer electrolyte membrane A.
Using the membrane electrode assembly B, a polymer electrolyte fuel cell was produced, and the initial cell voltage was measured. The results are shown in Table 3. From Tables 2 and 3, it can be seen that the dimensional change rate of Example 2 is higher than that of Example 1, and the initial cell characteristics are also low.

[Example 3]
Production of unreinforced solid polymer electrolyte membrane:
A film was obtained by a casting method using a solution (solid content: 20% by mass) of a commercially available fluorine-based proton conductive polymer (manufactured by Dupont, Nafion R). The film was used as an unreinforced solid polymer electrolyte membrane C.
The fluorine-based proton conductive polymer constituting Nafion R has a repeating unit represented by the formula (A-1).
The dimensional change rate of the solid polymer electrolyte membrane C was measured. The results are shown in Table 2. From Table 2, it was found that the dimensional change rate was extremely large as compared with Example 1.

Manufacture of membrane electrode assembly:
A membrane / electrode assembly C was obtained in the same manner as in Example 1 except that the solid polymer electrolyte membrane C was used instead of the solid polymer electrolyte membrane A.
Using the membrane / electrode assembly C, a polymer electrolyte fuel cell was prepared, and the initial cell voltage was measured. The results are shown in Table 3.

[Example 4]
Production of fluorine-based nonwoven fabric:
A fluorine-containing polymer solution having a repeating unit (ε1) (Asahi Glass Co., Cytop CTL-107S, solvent: Fluorinert FC-77 (manufactured by 3M, boiling point: 100 ° C.), solid content: 7% by mass) is spun as it is. Electrospinning was attempted in the same manner as in Example 1 using as a stock solution. One minute after the start, the tip of the needle was clogged, and the spinning solution could not be discharged, and no nonwoven fabric was obtained.

  By using the fluorine-based nonwoven fabric, the solid polymer electrolyte membrane and the membrane electrode assembly of the present invention, a high output and long life solid molecular fuel cell can be obtained.

It is a schematic block diagram which shows an example of the nonwoven fabric manufacturing apparatus by an electrospinning method. It is sectional drawing which shows an example of the membrane electrode assembly of this invention. It is sectional drawing which shows the other example of the membrane electrode assembly of this invention.

Explanation of symbols

20 Membrane / Electrode Assembly 21 Catalyst Layer 23 Anode 24 Cathode 25 Solid Polymer Electrolyte Membrane

Claims (4)

In a method for producing a fluorine-based nonwoven fabric by electrospinning using a spinning dope containing a fluorine-containing polymer having an aliphatic ring structure in the main chain and a solvent,
A method for producing a fluorine-based nonwoven fabric, comprising using a solvent having a boiling point of 110 ° C. or higher as the solvent. Consisting of continuous fibers of a fluoropolymer having an aliphatic ring structure in the main chain,
A fluorine-based nonwoven fabric having a basis weight of 7.5 cm ³ / m ² or less and a thickness of 23 μm or less.   A solid polymer electrolyte membrane for a polymer electrolyte fuel cell, comprising the fluorine-based nonwoven fabric according to claim 2.   A membrane electrode assembly for a polymer electrolyte fuel cell, wherein the polymer electrolyte membrane comprising the fluorine-based nonwoven fabric according to claim 2 is disposed between an anode and a cathode.

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