JP2002025583A - Electrolyte film for solid high polymer molecule fuel cell and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid high polymer molecule fuel cell excellent in stability of initial performance and long-term performance, having a positive ion exchange film which has low resistance, high hardness, and hydrogen gas leakage as an electrolyte. SOLUTION: The solid high polymer molecule fuel cell consists of a film laminated with two or more layers of perfluorocarbon polymer containing a sulfonic group. One or more of the above layers are reinforced with a fibril-like fluorocarbon polymer, and one or more of the layers consists of the positive ion exchange film as an electrolyte which are not substantially reinforced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A hydrogen / oxygen fuel cell has attracted attention as a power generation system whose reaction product is only water in principle and has almost no adverse effect on the global environment. Solid polymer fuel cells were once mounted on spacecraft in the Gemini and Biosatellite programs, but the power density at that time was low. Since then, higher performance alkaline fuel cells have been developed, and up to the present space shuttle, alkaline fuel cells have been adopted for space applications.

However, in recent years, polymer electrolyte fuel cells have attracted attention again due to technological advances. The reasons are as follows. (1) A highly conductive film was developed as a solid polymer electrolyte. (2) By supporting a catalyst used for the gas diffusion electrode layer on carbon and coating the same with an ion exchange resin, high activity can be obtained.

In order to further improve the performance, it is conceivable to reduce the electric resistance by increasing the sulfonic acid group concentration and reducing the thickness of the solid polymer electrolyte membrane. However, a remarkable increase in the sulfonic acid group concentration decreases the mechanical strength and tear strength of the electrolyte membrane, causes dimensional changes during handling, and reduces the durability of the electrolyte membrane due to long-term operation due to easy creep of the electrolyte membrane. And the like. On the other hand, a reduction in thickness causes problems such as a decrease in mechanical strength and tear strength of the electrolyte membrane, and a decrease in workability and handleability when the membrane is bonded to a gas diffusion electrode.

[0005]

As a method for solving the above problem, polytetrafluoroethylene (hereinafter, referred to as PT) is used.
It is called FE. ) A method of impregnating a porous membrane with a fluorinated ion exchange polymer having a sulfonic acid group has been proposed (Japanese Patent Publication No. 5-75835). However, although the thickness can be reduced, the electrical resistance of the porous PTFE membrane is sufficient. There was a problem that did not decrease. Also, in this method, since the interface between the porous PTFE membrane and the ion exchange polymer is not completely adhered, when used as an electrolyte membrane of a polymer electrolyte fuel cell, hydrogen gas leaks due to poor adhesion when used for a long time due to poor adhesion. There is a problem that the battery performance increases and the battery performance decreases.

As a method of solving the high electric resistance of the membrane, a cation exchange membrane reinforced with a fibril-like, woven-like or non-woven-like perfluorocarbon polymer has been proposed (JP-A-6-231779). . This membrane has low resistance, and the power generation characteristics of a fuel cell produced using this membrane were relatively good, but the thickness was at most 100 to 200 μm.
However, since the thickness was not sufficiently thin and the thickness was uneven, the power generation characteristics and mass productivity were insufficient. Further, the adhesion between the perfluorocarbon polymer and the fluorinated ion exchange polymer having a sulfonic acid group was not sufficient, and the hydrogen gas permeability was relatively high, so that the output when a fuel cell was constructed was not sufficient.

Accordingly, the present invention provides a cation exchange membrane which is a thin, uniform and low hydrogen gas-permeable reinforcing thin film which can be mass-produced, as an electrolyte membrane for a polymer electrolyte fuel cell. It is another object of the present invention to provide a polymer electrolyte fuel cell having excellent power generation characteristics by including the electrolyte membrane.

[0008]

According to the present invention, there is provided a laminate comprising at least two layers of a cation exchange layer composed of a perfluorocarbon polymer having a sulfonic acid group, wherein at least one of the cation exchange layers has a fibril shape. An electrolyte membrane for a polymer electrolyte fuel cell, wherein the electrolyte membrane is reinforced with a reinforcing material composed of a fluorocarbon polymer, and at least one of the cation exchange layers is not substantially reinforced with a reinforcing material. A manufacturing method and a polymer electrolyte fuel cell having the electrolyte membrane are provided.

[0009]

DETAILED DESCRIPTION OF THE INVENTION In the present specification, the term "precursor group of sulfonic acid group" refers to a group which can be converted to a sulfonic acid group (--SO ₃ H group) by performing hydrolysis, acidification treatment and the like. Say. Specifically, a —SO ₂ F group, a —SO ₂ Cl group, and the like can be given.

In the present invention, when a reinforcing material comprising a fibril-like fluorocarbon polymer (hereinafter referred to as a fibril-like reinforcing material) is contained in a cation exchange membrane,
Even if the amount contained in the film is small, a reinforcing effect such as increasing the tear strength and reducing the dimensional change can be exhibited. Also,
Since the increase in the resistance of the membrane due to the inclusion of the fibril-like reinforcing material can be reduced, it is an effective reinforcing material.

A perfluorocarbon polymer having a sulfonic acid group reinforced by the fibril-like reinforcing material (hereinafter referred to as a perfluorocarbon polymer)
It is called a sulfonic acid type perfluorocarbon polymer. ) Is a useful film because of its low electric resistance and high mechanical strength. However, as compared with a membrane made of a sulfonic acid type perfluorocarbon polymer containing no fibril-like reinforcing material, hydrogen gas permeability is higher. Therefore, when used as an electrolyte membrane for a fuel cell, the hydrogen supplied to the anode permeates the cathode and directly reacts with the oxygen supplied to the cathode on the cathode catalyst. And the output of the fuel cell decreases.

Therefore, in the present invention, a cation exchange layer comprising a sulfonic acid type perfluorocarbon polymer reinforced with a fibril-like reinforcing material (hereinafter referred to as a fibril reinforcing layer).
A cation exchange layer made of a sulfonic acid-type perfluorocarbon polymer that is not reinforced with a fibril-like reinforcing material (hereinafter referred to as a non-reinforced layer) is used as an electrolyte membrane for a fuel cell. As a result, hydrogen gas permeability can be lowered.

The electrolyte membrane of the present invention has at least one fibril reinforcing layer and one non-reinforcing layer laminated on each layer, and is not a laminate of only fibril reinforcing layers or a laminate of only non-reinforcing layers. The electrolyte membrane is preferably laminated so as to have a symmetrical structure in the thickness direction in consideration of the handleability of the membrane, the dimensional change of the membrane with respect to changes in temperature and humidity, and the like. For example, in the case of three layers, fibril reinforcement layer / non-reinforcement layer / fibril reinforcement layer, and in the case of five layers, fibril reinforcement layer / non-reinforcement layer / fibril reinforcement layer / Examples of the configuration include a non-reinforced layer / fibril reinforcing layer, a non-reinforced layer / fibril reinforcing layer / non-reinforced layer / fibril reinforcing layer / non-reinforced layer, and the like.

In the case of five or more layers, a fibril reinforcing layer having a different composition may be used, or an unreinforced layer having a different composition may be used. For example, the configuration of fibril reinforcing layer 1 / no reinforcing layer / fibril reinforcing layer 2 / no reinforcing layer / fibril reinforcing layer 1, no reinforcing layer 1 / fibril reinforcing layer / no reinforcing layer 2 / fibril reinforcing layer / no reinforcing layer 1, etc. And can be.

The total thickness of the electrolyte membrane used in the present invention is preferably 3 to 70 μm. If the thickness is less than 3 μm, defects are likely to occur when joining the electrodes,
If the thickness is larger than m, the film resistance increases. Especially the thickness is 10-30
When the thickness is μm, the film resistance is low, no defects are generated, and the power generation characteristics are favorable and stable when incorporated in a fuel cell and evaluated.

The thickness of each of the fibril reinforcing layer and the non-reinforcing layer constituting the electrolyte membrane is 0.5
It is preferably from 50 to 50 μm and from 0.3 to 50 μm, particularly preferably from 3 to 30 μm and from 1 to 30 μm. If the thickness per layer of the fibril reinforcing layer is less than 0.5 μm, large defects are likely to be generated when producing the fibril reinforcing layer, and the reinforcing effect of the fibril reinforcing material tends to be reduced. When the thickness per fibril reinforcing layer is greater than 50 μm, the resistance of the obtained film increases. No reinforcement layer 1
If the thickness per layer is less than 0.3 μm, defects are likely to occur when laminated with the fibril reinforcing layer,
The thicker the film, the greater the resistance of the resulting film.

In the fibril reinforcing layer of the present invention, the fibril-like reinforcing material of the fluorocarbon polymer is preferably contained in an amount of 0.5 to 15% based on the total mass of the fibril reinforcing layer. If it is less than 0.5%, the reinforcing effect is not sufficiently exhibited, and if it is more than 15%, the resistance tends to increase. 2
The case of 8% is particularly preferable because the resistance does not increase, the reinforcing effect is sufficiently exhibited, and the moldability is also good.

Examples of the fluorocarbon polymer used as a reinforcing material in the present invention include a copolymer of PTFE and tetrafluoroethylene with a small amount of a fluorine-based monomer. Specific examples thereof include PTFE, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-chlorotrifluoroethylene copolymer, tetrafluoroethylene-perfluoro (2,2-dimethyl-1,3-dioxole) Examples include a copolymer, a tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer such as a tetrafluoroethylene-perfluoro (butenyl vinyl ether) copolymer, and PTFE is particularly preferred. In the case of a copolymer, the amount of polymerized units other than the polymerized unit based on tetrafluoroethylene is preferably 5 mol% or less, particularly preferably 1 mol% or less.

Known polymers are widely used as the sulfonic acid type perfluorocarbon polymer in the present invention. Preferred polymers include those of the general formula CF ₂ ＣＦCF (O
_{CF 2 CFX) m -O p -} (CF 2) n SO 3 H ( wherein X is a fluorine atom or a trifluoromethyl group, m is 0
3 is an integer, n is an integer of 0 to 12, p is 0 or 1, and when n = 0, p = 0. )) And a copolymer of a perfluorovinyl compound represented by the formula (1) with a perfluoroolefin or a perfluoroalkylvinyl ether. Specific examples of the perfluorovinyl compound include compounds represented by Formulas 1 to 4. However, in the formulas 1 to 4, q is an integer of 1 to 9;
Is an integer of 1 to 8, s is an integer of 0 to 8, and z is 2 or 3.

[0020]

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A polymer containing a polymerized unit based on a perfluorovinyl compound having a sulfonic acid group is usually -SO ₂
It is polymerized using a perfluorovinyl compound having an F group. The perfluorovinyl compound having a —SO ₂ F group can be homopolymerized, but has low radical polymerization reactivity. Therefore, it is usually used together with a comonomer such as perfluoroolefin or perfluoro (alkyl vinyl ether) as described above. Used after polymerization. Examples of the perfluoroolefin to be a comonomer include tetrafluoroethylene, hexafluoropropylene, and the like, but usually tetrafluoroethylene is preferably employed.

As the perfluoro (alkyl vinyl ether) serving as a comonomer, CF ₂ ＣＦCF— (OCF ₂ C
FY) a compound represented by _t -O-R ^f are preferred. Here, in the formula, Y is a fluorine atom or a trifluoromethyl group, and t is an integer of 0 to 3. R ^f is a straight or C _u F _{2u + 1} perfluoroalkyl group (1 ≦ represented branched
u ≦ 12).

CF ₂ ＣＦCF— (OCF ₂ CFY) _t —O—
Preferred examples of the compound represented by R ^f include compounds of formulas 5 to 7. Here, in Formulas 5 to 7, v is an integer of 1 to 8, w is an integer of 1 to 8, and x is 1
-3.

[0024]

Embedded image

In addition to perfluoroolefins and perfluoro (alkyl vinyl ethers), fluorine-containing monomers such as perfluoro (3-oxahepta-1,6-diene) are also perfluorovinyl compounds having -SO ₂ F groups as comonomers. May be copolymerized.

In the present invention, the concentration of the sulfonic acid group in the sulfonic acid type perfluorocarbon polymer constituting the electrolyte membrane, that is, the ion exchange capacity is 0.5 to 0.5.
It is preferably 2.0 meq / g dry resin, especially 0.7 to 1.6 meq / g dry resin. When the ion exchange capacity is lower than this range, the resistance of the obtained electrolyte membrane increases, while when it is high, the mechanical strength of the electrolyte membrane tends to be insufficient.

The electrolyte membrane of the present invention preferably has a tear strength of 1 N / mm or more in any direction. The ratio of the tear strength in the direction with the highest tear strength to the tear strength in the lowest direction is preferably 1: 1 to 10: 1. For example, when the electrolyte membrane is formed into a film by single-screw extrusion, the direction through a single-screw extruder (hereinafter MD
It is called direction. ) Has the lowest tear strength, and the direction perpendicular to the MD direction (hereinafter referred to as the TD direction) has the highest tear strength.

In the present invention, the tear strength is measured by the method according to JIS-K7128 as follows. After immersing the film in 90 ° C. pure water for 16 hours, a strip sample having a width of 5 cm and a length of 15 cm is cut out, and the direction in which the tear strength is to be measured is defined as the length direction. Each sample has a length of 15c from the center of the short side so as to be bisected along the length direction.
Make a cut to 7.5 cm, half of m. Next, one of the cut ends is attached to the upper chuck of the tensile tester and the other is attached to the lower chuck so as to be torn from the cut portion, and the distance between the chucks is increased at a speed of 200 mm / min at 25 ° C., and the tear load is measured. The tear strength is calculated as a value (N / mm) obtained by dividing the tear load by the thickness of the sample. About 5 to 10 samples are measured in each direction, and the average value is defined as the tear strength.

The method for producing an electrolyte membrane according to the present invention is a method for producing a perfluorocarbon polymer having a sulfonic acid group precursor group (hereinafter referred to as a sulfonic acid group precursor type perfluorocarbon polymer) and a fibrillable fluorocarbon polymer. It is characterized in that the fibril reinforcing layer is constituted by a film (hereinafter, referred to as a fibril reinforcing film) obtained by forming the mixture into a film and stretching the obtained film (hereinafter, referred to as film A). In the film A, the fibrillable fluorocarbon polymer may be at least partially fibrillated.However, in the description of the production method in the present specification, the film after the stretching treatment is referred to as a fibril-reinforced film. The film before processing is referred to as film A.

The above-mentioned stretching step is preferably carried out under heating after laminating the stretching auxiliary film on at least one side of the film A. The stretching may be uniaxial stretching in which stretching is performed only in the MD direction or TD direction, or biaxial stretching in which stretching is performed in both the MD direction and TD direction, but biaxial stretching is preferably performed. In the case of uniaxial stretching, it is preferable to stretch in the TD direction in order to make the mechanical properties (tear strength) of the obtained film almost uniform in the MD and TD directions. In the case of biaxial stretching, the stretching may be performed simultaneously in the MD and TD directions, or may be performed sequentially.

In the stretching operation, the film A is a film constituting a non-reinforced layer (hereinafter referred to as a non-reinforced film).
May be performed before or after lamination. When performing after lamination, the film A and the stretching auxiliary film may not be laminated adjacent to each other.

When the film A or a laminated film of the film A and the non-reinforced film is stretched, if only these films are stretched, it is difficult to make them thin evenly. A film having a uniform thickness can be obtained. That is, the stretching auxiliary film in the present invention is a film laminated to assist the stretching of the fibril reinforcing film.

Specifically, it is preferable that the electrolyte membrane of the present invention is prepared by the following procedure. (1) Mixing of a fibrillable fluorocarbon polymer and a sulfonic acid group precursor type perfluorocarbon polymer. (2) Kneading and pelletizing the mixture obtained in (1) by twin-screw extrusion. (3) Using the pellets obtained in (2), forming a film by uniaxial extrusion and producing a film A by smoothing the film. (4) After laminating the stretching auxiliary film on film A, stretching,
Heat treated to produce fibril reinforced film. (5) Preparation of a non-reinforced film by uniaxial extrusion of a sulfonic acid group precursor type perfluorocarbon polymer. (6) Lamination of film A or fibril reinforced film and non-reinforced film. (7) Hydrolysis, acidification treatment, washing and drying.

The steps (1) to (7) will be described more specifically. Since the fibril-like reinforcing material is obtained by applying a shearing force to the fibrillable fluorocarbon polymer powder, first, only the fibril-like reinforcing material is prepared using the above fluorocarbon polymer, and the sulfonic acid group precursor type perfluorocarbon is prepared. It is also possible to prepare a reinforced film by mixing with a polymer or dispersing a fibril-like reinforcing material in a solution of a sulfonic acid group precursor-type perfluorocarbon polymer, and forming a cast film.

However, in order to uniformly disperse the fibril-like reinforcing material in the film, the above-mentioned fluorocarbon polymer powder and sulfonic acid group precursor type perfluorocarbon polymer powder are mixed (step (1)), and then kneaded. Then, the method of fibrillating the fluorocarbon polymer powder (step (2)) is preferable, and this method is employed in the method of the present invention. The step (1) is performed by mixing and dispersing the fluorocarbon polymer powder in a polymerization solution obtained by polymerizing the sulfonic acid group precursor type perfluorocarbon polymer, and thereafter, aggregating, washing, drying, and kneading ( (Step (2)).

At this time, the mixture of the sulfonic acid group precursor type perfluorocarbon polymer and the fluorocarbon polymer powder is kneaded by twin-screw extrusion molding and pelletizing. Alternatively, the mixture may be kneaded first and then subjected to twin-screw extrusion.

Next, the obtained pellets are uniaxially extruded and formed into a film in step (3), preferably under heating. Also, without going through the pelletizing step (2),
The mixture may be directly uniaxially extruded and formed into a film in the uniaxial extrusion molding step, and the fluorocarbon polymer may be fibrillated at the same time. In the case of uniaxial extrusion molding under heating, the temperature of the film is 200 to 270 ° C.
It is preferable to mold to such an extent. If the film temperature is less than 200 ° C., the discharge pressure becomes too high,
Productivity may be reduced. Film temperature is 270
If the temperature exceeds ℃, the surface of the obtained film becomes rough and the thickness becomes non-uniform, which is not preferable.

The thickness of the film obtained after completing the step (3) is about 80 to 500 μm.
Since the surface smoothness of the film A obtained in the step (3) decreases as the amount of the fibril-like reinforcing material increases, the film A is smoothed by a hot press if necessary.

Next, a stretching aid film is laminated on at least one side of the film A, and if necessary, stretched several times, preferably biaxially, to obtain a fibril reinforcing film having a thickness of 0.5 to 50 μm. (Step (4)).
Specifically, for example, a film A is
The laminate is heated and laminated using a roll press heated to about 0 to 100 ° C., biaxially stretched under heating, and the stretching auxiliary film is peeled to obtain a fibril reinforcing film having a thickness of 0.5 to 50 μm. If the amount of the fibril reinforcing material increases, a defect may occur due to biaxial stretching. Therefore, it is preferable to perform a heat treatment by a hot press after the step (4).

On the other hand, a film is formed by uniaxial extrusion using only the sulfonic acid group precursor type perfluorocarbon polymer, and a non-reinforced film of preferably 3 to 50 μm is separately prepared (step (5)). The unreinforced film and the fibril-reinforced film are, for example, 100 to 2
Heat lamination using a roll press heated to about 50 ° C. to produce a laminated film of about 3 to 70 μm (step (6)). Next, the precursor film of the sulfonic acid group is converted into a sulfonic acid group by hydrolysis, acidification treatment and drying (step (7)) of the laminated film, and the fibril reinforcing layer and the non-reinforcing layer are formed. A thin film is obtained.

In the stretching step (4), the stretching ratio in one stretching operation varies depending on the type of the sulfonic acid type perfluorocarbon polymer used, but is preferably 30 times or less in area ratio. The above stretching is
It may be repeated any number of times.
Thin films of less than can also be obtained.

The laminating step (6) may be performed before the stretching step (4). In this case, the film A, which is a precursor of the fibril reinforcing film, and the non-reinforced film are laminated. However, when the laminating step (6) is performed before the stretching step (4), if the fibril content increases, a defect may occur in the unreinforced layer in the stretching step.
The laminating step (6) is preferably performed after the stretching step (4). In addition, the above hydrolysis and acidification treatment (7)
May be performed before the laminating step (6). That is, the fibril reinforced film and the non-reinforced film may be laminated after the sulfonic acid group precursor of each of the fibril reinforced film and the non-reinforced film is converted into a sulfonic acid group.

Usually, the electrolyte membrane of the present invention is obtained through the above steps, but the electrolyte membrane of the present invention can also be obtained by casting a non-reinforced layer. That is, (1)-
After performing the step (3), a stretching auxiliary film is laminated on the obtained film by heating and stretched under heating (step (4)).
After that, the step (7) is performed to obtain an acidified fibril reinforcing film, and the solution of the sulfonic acid type perfluorocarbon polymer is formed on the fibril reinforcing film without performing the steps (5) and (6). Cast film is formed using Here, the step (7) may be performed before performing the biaxial stretching operation.

Further, a cast film is formed on a separately prepared base material using a solution of a sulfonic acid type perfluorocarbon polymer to form a non-reinforcing layer, and then a non-reinforcing layer is laminated on the fibril reinforcing film. Thus, an electrolyte membrane comprising a fibril reinforcing layer and a non-reinforcing layer is obtained. That is, at least one surface of the acid-converted fibril reinforcing film obtained in the same manner as described above, the base material on which the non-reinforcement layer is formed by casting is formed, and the surface on which the non-reinforcement layer is formed is fibril-reinforced. Laminated in contact with the film, after transferring the non-reinforcement layer onto the fibril reinforcement film by hot pressing, for example, an electrolyte membrane comprising a fibril reinforcement layer and a non-reinforcement layer is obtained by peeling the substrate. .

Here, the substrate to be formed into a film by casting with a solution of the sulfonic acid type perfluorocarbon polymer is not particularly limited as long as it can be easily peeled off from the non-reinforced layer after hot pressing. For example, a polyester film can be used.

The stretching auxiliary film used in the step (4) is not particularly limited as long as it can be stretched. For example, a polyethylene terephthalate film, a polybutylene terephthalate film, a polyethylene film,
Ethylene-α-olefin copolymer film, ethylene-vinyl alcohol copolymer film, ethylene-vinyl acetate copolymer film, ethylene-vinyl acetate-vinyl chloride copolymer film, ethylene-vinyl chloride copolymer film, polypropylene Film, polyvinyl chloride film, polyamide film, polyvinyl alcohol film and the like. Among them, a polyethylene terephthalate film or a polypropylene film is preferable.

Particularly, an amorphous polyethylene terephthalate film and a cast polypropylene film are preferred because they can be stretched at a relatively low temperature and have good stretchability. The temperature at the time of biaxial stretching varies depending on the type of the stretching auxiliary film, but a temperature range of 40 to 150 ° C. is preferable from the viewpoint of stretchability.

The polymer electrolyte fuel cell of the present invention can be obtained according to a usual method, for example, as follows. First,
A solution of a conductive carbon black powder carrying platinum catalyst fine particles and a solution of a sulfonic acid type perfluorocarbon polymer are mixed to obtain a uniform dispersion, and a gas diffusion electrode is formed by any of the following methods to form a membrane electrode junction. Get the body. As the membrane, a cation exchange membrane made of a sulfonic acid type perfluorocarbon polymer reinforced with a fibril-like reinforcing material is used.

The first method is a method in which the uniform dispersion is applied to both surfaces of the cation exchange membrane, dried, and then adhered to both surfaces with two carbon cloths or carbon papers.
In the second method, the uniform dispersion is applied to two carbon cloths or carbon papers and dried, and then the cation exchange membrane is applied so that the surface coated with the uniform dispersion adheres to the cation exchange membrane. It is a method of sandwiching from both sides.

The obtained membrane / electrode assembly is provided with a groove serving as a passage for a fuel gas or an oxidizing gas, sandwiched between separators made of a conductive carbon plate, and incorporated in a cell to be incorporated into a cell. Is obtained.

In the polymer electrolyte fuel cell obtained as described above, hydrogen gas is supplied to the anode side, and oxygen or air is supplied to the cathode side. At the anode, a reaction of H ₂ → 2H ⁺ + 2e ⁻ occurs, and at the cathode, a reaction of 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O occurs, whereby chemical energy is converted into electric energy.

[0052]

EXAMPLES Example 1 Weight Based on Tetrafluoroethylene
Combined unit and CF_Two= CF-OCF_TwoCF (CF _Three) O (C
F_Two)_TwoSO_TwoCopolymer powder comprising polymer units based on F
Powder (ion exchange capacity when converted to acid form and measured)
1 meq / g dry resin, hereinafter referred to as copolymer A
U. ) 9600 g and PTFE powder (trade name: Fluon C)
D-1, manufactured by Asahi Glass Co., Ltd.) and extruded
9500 g of pellets were obtained by molding. The obtained peret
Into a film with a single-screw extruder and a thickness of 150 μm
Was obtained. Once the obtained film is
After smoothing the surface with a hot roll press at temperature,
200μm thick amorphous film
Sandwiched between both sides by two ethylene terephthalate films
, And hot roll press at 80 ° C.
A laminated film was obtained.

The laminated film was biaxially stretched at 85 ° C. by 1.4 times in the direction (MD direction) through a single screw extruder and 7 times in the direction perpendicular to the MD direction (TD direction) ( (Area stretch ratio 10 times) and further subjected to a hot roll press at 200 ° C. to obtain a stretched film having a thickness of 15 μm. On the other hand, pellets were formed by twin-screw extrusion using only the copolymer A, and then uniaxially extruded to obtain a film having a thickness of 5 μm.

A 5 μm thick non-reinforced film is laminated on both sides of the 15 μm thick stretched film by a hot roll press at 180 ° C., and a fibril reinforcing layer and a non-reinforcing layer are laminated to form a 25 μm thick three-layer film. I got The resulting three-layer film was hydrolyzed using an aqueous solution containing dimethyl sulfoxide and potassium hydroxide, acidified with hydrochloric acid, washed and dried to form a 25 μm-thick film (laminated film). The thickness of the obtained film was measured at 10 points at intervals of 5 cm, and the thickness variation was in a range of ± 3 μm.

[Measurement of tear strength of laminated film]
After being immersed in pure water at 90 ° C. for 16 hours, a strip sample having a width of 5 cm and a length of 15 cm was cut out. As for this sample, a sample whose length direction coincides with the MD direction and a sample whose length direction coincides with the TD direction were each 5 samples. Each sample was cut from the center of the short side to 7.5 cm, which is half the length of 15 cm, so as to be bisected along the length direction. One of the cut pieces was attached to the upper chuck of the tensile tester and the other was attached to the lower chuck so that the cut piece was torn from the cut portion.
The space between the chucks was spread at a speed of one minute, and the tear load was measured. The tear strength is calculated by dividing the tear load by the sample thickness.
The average value of the sample was taken. The tear strength of the obtained laminated film was 2.0 N / mm in the MD direction and 7.5 N / m in the TD direction.
m.

[Measurement of Resistance of Laminated Film] 5 m from the above laminated film
A strip-shaped membrane sample having a width of m was prepared, and a platinum wire (diameter: 0.2 mm) was formed on the surface of the strip-shaped film sample for 5 m in parallel with the width direction.
Five samples were pressed at m intervals, the sample was held in a constant temperature and humidity apparatus at 80 ° C. and a relative humidity of 95%, and the AC impedance between the platinum wires at an AC of 10 kHz was measured to determine the AC specific resistance. Since five platinum wires are pressed at 5 mm intervals, the distance between the electrodes is 5, 10, 15, 20 mm
The effect of contact resistance between the platinum wire and the film is excluded by measuring the AC resistance at each distance between the electrodes and calculating the specific resistance of the film from the gradient of the distance and the resistance. did. A good linear relationship was obtained between the distance between the electrodes and the measured resistance, and the specific resistance was calculated from the gradient and the thickness by the following equation. Specific resistance ρ (Ω · cm) = sample width (cm) × sample thickness (cm) × resistance electrode gradient (Ω / cm) The specific resistance of the obtained laminated film was 6 Ω · cm.

[Measurement of Hydrogen Gas Permeability of Laminated Film] The obtained laminated film was incorporated into a cell for a gas permeation device at 70 ° C., and humidified hydrogen was supplied to one side and humidified argon gas was supplied to the other side. 3.3 cm ² , gas flow 30 cm ³ /
The hydrogen gas permeating in min was detected by gas chromatography and the hydrogen gas permeability of the membrane was calculated. The hydrogen gas permeability was determined by measuring the flow rate of gas permeating per 1 Pa of pressure of the permeated gas per 1 cm ² per 1 cm ² of the membrane area under a standard condition (0 ° C., 1 atm) and converting it to a 1 cm thick membrane. It was a numerical value. The hydrogen gas permeability of the laminated film at 70 ° C. and 95% relative humidity was 6.9 × 10 ⁻¹² cm ³ (STP) ·
cm · cm ⁻² · s ⁻¹ · Pa ⁻¹ .

[Production and Evaluation of Fuel Cell] A fuel cell was assembled as follows. Polymerized units based on tetrafluoroethylene and CF ₂ ＣＦCF—OCF ₂ CF (CF
₃ ) A copolymer powder composed of polymerized units based on O (CF ₂ ) ₂ SO ₃ H (ion exchange capacity: 1.1 meq / g dry resin) and platinum-supported carbon in a mass ratio of 1: 3. A coating liquid containing ethanol as a dispersion medium was applied on a carbon cloth by a die coating method, and dried to form a gas diffusion electrode layer having a thickness of 10 μm and a platinum carrying amount of 0.5 mg / cm ² .

The two carbon cloths were opposed to each other so that the respective gas diffusion electrode layers faced inward, the laminated film was sandwiched between them, and pressed using a flat plate press to produce a membrane electrode assembly. A fuel cell having an effective membrane area of 25 cm ² was assembled by disposing a separator made of a carbon plate in which narrow grooves for gas passages were cut in a zigzag shape on both outer sides of the membrane electrode assembly and a heater on the outside thereof.

The temperature of the fuel cell was maintained at 80 ° C., and air was supplied to the cathode and hydrogen was supplied to the anode at 1.5 atm. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.63 V. Further, the above fuel cell was continuously operated at 80 ° C. and a current density of 1 A / cm ² . The terminal voltage after 1000 hours was 0.63 V, and there was no change.

[Example 2] A pellet was obtained after forming a film in the same manner as in Example 1 except that the copolymer A powder was changed to 9730 g and the PTFE powder was changed to 270 g.
A 0 μm film was obtained. A stretch assisting film was laminated on this film in the same manner as in Example 4 to obtain a laminated film. At 85 ° C., each axial direction (MD
(Direction and TD direction), each of which was biaxially stretched 2.5 times (area stretching ratio: 6.3 times), and the stretching auxiliary film was peeled off to obtain a fibril reinforcing film having a thickness of 40 μm.

On the other hand, a non-reinforced film consisting of the copolymer A alone was obtained in the same manner as in Example 1 except that the thickness was 40 μm. The fibril reinforced film having a thickness of 40 μm was laminated on both sides of the non-reinforced film by a heated roll press to obtain a three-layer film. The obtained three-layer film was hydrolyzed using an aqueous solution containing dimethyl sulfoxide and potassium hydroxide, acidified with hydrochloric acid, washed and dried to form a film having a thickness of 120 μm.

This film was again sandwiched from both sides with an amorphous polyethylene terephthalate film having a thickness of 200 μm as a stretching auxiliary film, and heated and laminated in the same manner as described above.
Biaxial stretching was performed twice in the MD and TD directions at a temperature of 4 ° C. (area stretching ratio: 4), and the stretching auxiliary film was peeled off to obtain a 30 μm-thick laminated film. The thickness of the obtained film is 5c
The measurement was performed at 10 points at m intervals, and the thickness variation was ± 3 μm.
Was in the range.

When the obtained laminated film was evaluated in the same manner as in Example 1, the tear strength was 1.4 N / mm in the MD direction and TD.
Direction is 9.5N / mm, AC specific resistance is 5Ω · cm
And the hydrogen gas permeability is 6.4 × 10 ⁻¹² cm ³ (S
TP) .cm.cm ^-2 .s ^-1 .Pa ^-1 .

A fuel cell was assembled in the same manner as in Example 1 using the above laminated film, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.65 V. Also, 10
The terminal voltage after 00 hours was 0.65 V, and there was no change.

[Example 3] A pellet was obtained and then formed into a film in the same manner as in Example 2, except that the copolymer powder was changed to 9600 g and the PTFE powder was changed to 400 g.
A μm film was obtained. Using this film as a film for producing a fibril reinforcing layer, processing such as lamination and stretching was performed in the same manner as in Example 2 to obtain a laminated film having a thickness of 30 μm. When the thickness variation of the obtained film was measured in the same manner as in Example 1, it was in the range of ± 3 μm.

When the obtained laminated film was evaluated in the same manner as in Example 1, the tear strength was 8.8 N / mm in the MD direction and T
D direction is 13 N / mm, AC specific resistance is 6 Ω · cm
Met. The hydrogen gas permeability of this laminated film at 70 ° C. and 95% relative humidity was 6.2 × 10 ⁻¹² cm ³ (S
TP) .cm.cm ^-2 .s ^-1 .Pa ^-1 .

A fuel cell was assembled in the same manner as in Example 1 using the above laminated film, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.64 V. Also, 10
The terminal voltage after 00 hours was 0.64 V, and there was no change.

[Example 4] A pellet was obtained in the same manner as in Example 1 except that the amount of the copolymer A was changed to 9400 g and the amount of the PTFE powder was changed to 600 g.
A 0 μm film was obtained. Using this film, a stretching auxiliary film was laminated in the same manner as in Example 1, and the thickness was 20 μm in the same manner as in Example 1 except that the stretching ratio was 3.3 times in each axial direction (area stretching ratio was 10 times). Was obtained.

On the other hand, the polymer obtained by hydrolyzing the copolymer A and converting it into an acid form is dissolved in ethanol under heating,
A solution having a solid content of 9% of the total mass was obtained. Using this solution, cast films were formed on both sides of the stretched film to form layers each having a thickness of 5 μm, and a laminated film having a thickness of 30 μm was obtained. When the thickness variation of the obtained film was measured in the same manner as in Example 1, it was in the range of ± 3 μm.

When the obtained laminated film was evaluated in the same manner as in Example 1, the tear strength was 10 N / mm in the MD direction and TD.
The direction was 17 N / mm, and the AC specific resistance was 7 Ω · cm. The hydrogen gas permeability of this laminated film at 70 ° C. and 95% relative humidity was 6.8 × 10 ⁻¹² cm ³ (ST
P) · cm · cm ⁻² · s ⁻¹ · Pa ⁻¹ .

A fuel cell was assembled in the same manner as in Example 1 using the above laminated film, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.62 V. Also, 10
The terminal voltage after 00 hours was 0.62 V, and there was no change.

Example 5 (Comparative Example) The unstretched thickness 25 obtained during the preparation of the fibril reinforcing layer in Example 2
Using a 0 μm film, the film was roll-rolled at 180 ° C. using a heated roll press to reduce the thickness of the film to obtain a 100 μm thick fibril reinforced film. This film was hydrolyzed, acidified, washed and dried in the same manner as in Example 1 to obtain a fibril-reinforced film having a thickness of 100 μm. When the variation in the thickness of the obtained film was measured in the same manner as in Example 1, there was a variation of ± 15 μm.

When the fibril reinforcing film was evaluated in the same manner as in Example 1 without performing operations such as lamination, the tear strength was as follows:
The MD direction was 1.6 N / mm, the TD direction was 10 N / mm, and the AC specific resistance was 5 Ω · cm. The hydrogen gas ^{permeability, 12.6 × 10 -1 2 cm 3} (STP) · cm ·
cm ^-2 · s ^-1 · Pa ^-1 .

Using the fibril reinforcing film, a fuel cell was assembled in the same manner as in Example 1, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.54 V.
The terminal voltage after 1000 hours was 0.52V.

Example 6 (Comparative Example) A film was formed in the same manner as in Example 1 except that only the copolymer A was used.
A membrane containing no fibril-like reinforcement was produced. This film was hydrolyzed, acidified, washed and dried in the same manner as in Example 1 to obtain a film having a thickness of 50 μm. When the thickness variation of the obtained film was measured in the same manner as in Example 1, it was in the range of ± 5 μm.

Example 1 without performing operations such as laminating the above films
When the tear strength was evaluated in the same manner as in the above, the tear strength was 0.
4 N / mm, the TD direction was 0.6 N / mm, and the AC specific resistance was 5 Ω · cm. The hydrogen gas permeability is
6.0 × 10 ⁻¹² cm ³ (STP) · cm · cm ⁻² · s ⁻¹
-It was Pa- ¹ . A fuel cell was assembled using the above membrane in the same manner as in Example 1, and the power generation characteristics were evaluated in the same manner as in Example 1. When the terminal voltage at a current density of 1 A / cm ² was measured, the terminal voltage was 0.53 V. Also, 1
The terminal voltage after 000 hours was 0.50V.

[0078]

According to the present invention, a cation exchange membrane having a low electric resistance and a high mechanical strength which are not present in conventional membranes, a small variation in thickness, and a low hydrogen gas permeability is provided by a solid polymer electrolyte. Thus, a polymer electrolyte fuel cell having excellent initial performance and excellent long-term performance stability can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B29C 55/02 B29C 55/02 4J100 C08F 214/26 C08F 214/26 5H026 C08J 5/04 C08J 5/04 5 / 22 101 5/22 101 CEW CEW C08L 27/12 C08L 27/12 H01M 8/10 H01M 8/10 // B29K 23:00 B29K 23:00 27:12 27:12 67:00 67:00 B29L 7: 00 B29L 7:00 9:00 9:00 31:34 31:34 F term (reference) 4D006 GA47 JA02 MA03 MA06 MA31 MB06 MC23 MC28 MC30 MC48 MC74 NA36 NA48 PC80 4F071 AA26 AA26X AA27 AA27C AA27X AH15 BA01 BB06 BB07 BC01 FA02 FA05 FB01 FC02 FC03 FC06 FD02 4F072 AA04 AA08 AB04 AD07 AK05 AK16 AK20 AL11 4F210 AA11 AA16 AA24 AG01 AG03 AH33 AR06 QC05 QG01 QG15 QG18 4J002 BD12W BD15W BD15X FA04X FD01X GQ00 GQ02 4 AC26P AE38Q BA56Q CA04 DA56 JA45 5H026 AA06 BB01 BB02 CC03 CX05 EE19 HH00 HH03 HH05 HH08

Claims (10)

[Claims] 1. A reinforcing material comprising a laminate of two or more cation exchange layers comprising a perfluorocarbon polymer having a sulfonic acid group, wherein at least one of said cation exchange layers comprises a fibril-like fluorocarbon polymer. And wherein at least one of the cation exchange layers is not substantially reinforced with a reinforcing material. 2. The electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, which has a thickness of 3 to 70 μm. 3. The solid polymer type according to claim 1, wherein the fluorocarbon polymer serving as the reinforcing material is contained in the total mass of the cation exchange layer reinforced with the reinforcing material in an amount of 0.5 to 15%. Electrolyte membrane for fuel cells. 4. A perfluorocarbon polymer having a sulfonic acid group, CF ₂ = polymerized units based on CF ₂ and CF ₂ =
_{CF (OCF 2 CFX) m -O} p - a (CF _{2) n} SO ₃ X polymerized units (here based on H fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is 0-1
Is an integer of 2, p is 0 or 1, and when n = 0, p = 0. 4. The electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, which is a copolymer comprising: 5. The method for producing an electrolyte membrane according to claim 1, wherein the cation exchange layer reinforced with the reinforcing material has a sulfonic acid group precursor group. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, comprising: forming a mixture of a polymer and a fibrillable fluorocarbon polymer into a film and stretching the resulting film. 6. A film obtained by molding a mixture of a perfluorocarbon polymer having a precursor group of a sulfonic acid group and a fluorocarbon polymer capable of fibrillation into a film, and a film having a precursor group of a sulfonic acid group. The solid according to claim 5, wherein after laminating a film obtained by molding the perfluorocarbon polymer into a film, a stretching auxiliary film is laminated on at least one surface of the obtained laminated film, and biaxially stretched under heating. A method for producing an electrolyte membrane for a polymer fuel cell. 7. A film obtained by molding a mixture of a perfluorocarbon polymer having a precursor group of a sulfonic acid group and a fluorocarbon polymer capable of fibrillation into a film, and a stretching auxiliary film is laminated on at least one surface of the film. The solid according to claim 5, wherein after biaxial stretching under heating, a film obtained by forming a perfluorocarbon polymer having a sulfonic acid group precursor group into a film shape is laminated on the obtained film. A method for producing an electrolyte membrane for a polymer fuel cell. 8. A film obtained by molding a mixture of a perfluorocarbon polymer having a precursor group of a sulfonic acid group and a fibrilable fluorocarbon polymer into a film shape, and laminating a stretching auxiliary film on at least one surface of the film. After biaxially stretching under heating, a precursor group of a sulfonic acid group is converted into a sulfonic acid group, and then a film made of a perfluorocarbon polymer having a sulfonic acid group is laminated on the obtained film. 3. The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to item 1. 9. The method according to claim 6, wherein the stretching auxiliary film is made of a polyethylene terephthalate film or a polypropylene film, and the stretching is performed at a temperature of 40 to 200 ° C. Method. 10. A polymer electrolyte fuel cell, wherein gas diffusion electrodes are arranged on both surfaces of the electrolyte membrane according to claim 1, 2, 3 or 4.