JP2002352819A - Fluorine ion exchange resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorine ion exchange resin film of low dry weight (EW) per one equivalent weight, being excellent in durability, which is used for a fuel cell. SOLUTION: The dry weight (EW) per one equivalent weight of ion exchange group is 250-940, while decrease in weight after boiling process for eight hours under water is 5 wt.% or less according to a dry weight reference before boiling process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorine-based ion exchange resin membrane used for a fuel cell.

[0002]

2. Description of the Related Art A fluorinated ion exchange resin is a polymer material having a strong acid group such as a sulfonic acid group or a carboxylic acid group in a polymer chain and having a property of selectively transmitting specific ions. Therefore, it is used in various applications such as polymer electrolyte fuel cells, chloralkali, water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrators, humidity sensors, gas sensors, and the like. Among them, fuel cells convert the chemical energy of fuel into electric energy by electrochemically oxidizing hydrogen, methanol, etc.
It is drawing attention as a clean source of electrical energy. As such a fluorine-based ion exchange resin, for example, a perfluoro-based solid polymer electrolyte represented by Nafion (registered trademark, manufactured by DuPont) is known. Perfluoro-based solid polymer electrolytes are characterized by high ionic conductivity and extremely high chemical stability.

When a fluorine-based ion exchange resin membrane is used as a solid polymer electrolyte membrane for a fuel cell, an electrolyte membrane having a high ion conductivity is desired in order to minimize the electric resistance during power generation. The ionic conductivity of a membrane greatly depends on the number of ion-exchange groups and is usually a dry weight per equivalent (E
A fluorine-based ion exchange resin membrane having a W) of about 950 to 1200 is used. Although the fluorinated ion exchange resin membrane having an EW of less than 950 shows a higher ionic conductivity,
There is a major problem that the composition is easily dissolved in water or hot water and has poor durability when used for fuel cell applications. JP 6
JP-A-322034 discloses a method for producing a high molecular weight fluorine-based ion exchange resin precursor. Among them, it has been suggested that in order for the fluorine-based ion-exchange resin membrane to have good physical properties, it is desirable to prepare it using the high molecular weight precursor. However, no specific solution is given as to what EW and molecular weight the precursor should have in order to improve the water solubility. Japanese Patent Application Laid-Open No. 4-366137 discloses that EW is 700 to
A fluorinated ion exchange resin membrane having a water absorption of 1000 or less by weight at 1000 is disclosed. When such a fluorine-based ion-exchange resin membrane is used for a fuel cell, a high output is obtained, but no solution is shown with respect to water solubility, and the durability when the fuel cell is operated for a long time is not shown. There was a problem. Therefore, it was necessary to find a specific solution for improving water solubility even at low EW.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low EW fluorine ion exchange resin membrane which can be used for a fuel cell.

[0005]

Means for Solving the Problems The present inventor has conducted intensive studies to solve the above-mentioned problems, and as a result, based on JIS K-7210, a melt index (MI (g) measured at a temperature of 270 ° C. under a load of 2.16 kg. / 10 min)) is low,
That is, it was found that the solubility in water can be improved by preparing a low EW fluorine-based ion exchange resin membrane using a fluorine-based ion-exchange resin precursor having a high molecular weight. Surprisingly, no matter how low the EW is, even if the precursor satisfies the following formula (1), even if the fluorine-based ion exchange resin membrane is subjected to boiling treatment, it is found that the precursor is not critically dissolved in water. Was. log ₁₀ MI ≦ [(EW-850) / 90] +3 (1) Further, the weight loss due to boiling treatment in water for 8 hours is 5 wt% or less, preferably 1 wt%, based on the dry weight before boiling treatment.
The following low EW fluorine-based ion exchange resin membrane was found to be useful for polymer electrolyte fuel cell applications. That is, the present invention provides: The dry weight (EW) per equivalent of ion exchange group is 2
1. a fluorine-based ion-exchange resin membrane characterized in that it has a weight loss of 50 to 940 and a weight loss by boiling for 8 hours in water of 5 wt% or less based on a dry weight before the boiling. The weight loss is 1 wt% or less. 2. The fluorinated ion exchange resin membrane according to the above. The EW is 250 or more and 700 or less. Or 2. 4.1. The fluorinated ion exchange resin membrane described in 4.1. ~ 3. 5. A membrane electrode assembly comprising the fluorine-based ion exchange resin membrane according to any one of the above, 5.1. ~ 3. A polymer electrolyte fuel cell, comprising the fluorine-based ion exchange resin membrane according to any one of the above,
About.

Hereinafter, the fluorine-based ion exchange resin membrane of the present invention will be described in detail. The fluorine-based ion exchange resin membrane of the present invention is a fluorocarbon polymer having a sulfonic acid type or carboxylic acid type ion exchange group represented by the following formula (2).

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The equivalent weight (EW) of the fluorinated ion exchange resin membrane of the present invention, that is, the dry weight per equivalent of the ion exchange group is from 250 to 940, preferably from 250 to 940.
It is from 800 to 700, more preferably from 250 to 700, even more preferably from 250 to 600.
A smaller EW is preferable because the ionic conductivity becomes higher. When the EW is small, the solubility in water increases, so that the smaller the melt index described later, the better. The weight reduction ratio when the fluorine-based ion exchange resin membrane of the present invention is subjected to boiling treatment in water for 8 hours is 5 wt% or less based on the dry weight before the boiling treatment, and preferably 1 watt.
t% or less. When the weight loss is 5 wt% or less,
This is preferable because durability when used in a fuel cell is improved.

The thickness of the fluorine-based ion exchange resin membrane of the present invention is preferably 1 μm or more and 500 μm or less. The thickness is preferably 1 μm or more because the gas permeability can be reduced and the power generation characteristics during fuel cell operation can be improved, and the thickness is preferably 500 μm or less because the DC resistance during power generation can be reduced. Further, as described in JP-A-8-162132, a porous membrane obtained by stretching a PTFE membrane,
In some cases, it has fibrillated fibers disclosed in JP-A-1499881 and JP-B-63-61337. The low EW fluorine-based ion exchange resin membrane of the present invention is difficult to dissolve in water or hot water for a long period of time, and thus can be used for a polymer electrolyte fuel cell.

The fluorinated ion exchange resin membrane of the present invention is produced from a fluorinated ion exchange resin precursor represented by the following formula (3).

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The fluorine-based ion exchange resin precursor used at this time has a temperature of 27 based on JIS K-7210.
The melt index (MI (g / 10 minutes)) measured at 0 ° C. and a load of 2.16 kg is 2,000 or less and 0.0
It is characterized by being 1 or more, preferably 1000 or less and 0.01 or more, more preferably 100 or less and 0.01 or more, and still more preferably 10 or less and 0.01 or more. Further, the optimum MI satisfies the following equation (1) and depends on the EW.
It is preferable that the lower the value, the lower the MI. log ₁₀ MI ≦ [(EW-850) / 90] +3 (1)

Hereinafter, a method for producing the fluorine-based ion exchange resin membrane of the present invention will be described. The fluorinated ion exchange resin membrane of the present invention comprises a step of polymerizing a fluorinated ion exchange resin precursor, a molding step, and a step of forming an ion exchange group by a hydrolysis treatment. (Polymerization) The fluorocarbon ion exchange resin precursor refers to a fluorocarbon polymer having an ion exchange group precursor such as a sulfonic acid group or a carboxylic acid group. Such fluorocarbon polymers include CF ₂ = CX ¹ X ² (X
And ¹ and X ² are fluorinated olefin represented by the halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms) _{independently, CF 2 = CF (-O- (} CF 2 -CF (CF
^{_{2 X 3)) b -O c}} - (CFR 1) d - (CFR 2) e
— (CF ₂ ) _f —X ⁵ ) (X ³ is a halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms, b is an integer of 0 to 8, c is 0 or 1, d, e and f are each independently an integer of 0 to 6 (however, d + e + f is not equal to 0); R ¹ and R ² are each independently a halogen element or a perfluoroalkyl group or a fluorochloroalkyl group having 1 to 10 carbon atoms; X ⁵ is CO ₂ R ³ , COR ⁴ ,
Alternatively, a fluorocarbon copolymer with SO ₂ R ⁴ (R ³ is a hydrocarbon alkyl group having 1 to ³ carbon atoms, and R ⁴ is a halogen element) is preferable.

Typical fluorinated olefins include CF
_Two= CF_Two, CF_Two= CFCl, CF_Two= CCl_TwoIs raised
I can do it. As the vinyl fluoride compound, specifically,
CF _Two= CFO (CF_Two)_Z-SO_TwoF, CF_Two= CF
OCF_TwoCF (CF_Three) O (CF_Two)_Z-SO_TwoF, C
F_Two= CF (CF_Two)_Z-SO_TwoF, CF_Two= CF (O
CF_TwoCF (CF_Three))_Z-1− (CF_Two)_Two-SO
_TwoF, CF_Two= CFO (CF_Two)_Z-CO_TwoR, CF_Two
= CFOCF_TwoCF (CF_Three) O (CF_Two)_Z-CO_Two
R, CF_Two= CF (CF_Two)_Z-CO_TwoR, CF_Two= C
F (OCF_TwoCF (CF_Three))_Z− (CF_Two)_Two-CO
_TwoR (z is an integer of 1 to 8, R is a hydrocarbon of 1 to 3 carbon atoms)
Represents an alkyl group). The above-mentioned Fluo
Hydrocarbon copolymers are hexafluoropropylene,
Perfluoroolefin such as lorotrifluoroethylene
Tertiary or perfluoroalkyl vinyl ether
It may be a copolymer containing components.

As a polymerization method of such a fluorine-based ion exchange resin precursor, a solution polymerization method in which the above vinyl fluoride compound is dissolved in a solvent such as Freon and then reacted with a gas of fluorinated olefin to carry out polymerization, And a emulsion polymerization method in which a vinyl fluoride compound is charged and emulsified in water together with a surfactant and then reacted with a fluorinated olefin gas for polymerization. In order to obtain a fluorine-based ion-exchange resin precursor having particularly low EW and low MI, for example, JP-A-7-252322
The method disclosed in Japanese Patent Application Laid-Open Publication No. H10-205,837 is preferably used. In the present invention, MI is not more than 2000 and not less than 0.01, preferably 10
0.01 or less, more preferably 100 or less.
A fluorinated ion exchange resin precursor of 01 or more, still more preferably 10 or less and 0.01 or more is used.

(Molding) In order to form such a fluorine-based ion exchange resin precursor into a film, a general melt extrusion molding method (T-die method, inflation method, calendering method, etc.)
Is used. As another method, there is a solvent casting method in which the solvent of the solution or dispersion of the above-mentioned fluorine-based ion exchange resin precursor is evaporated to form a cast film. At this time, a porous membrane obtained by stretching a PTFE membrane described in JP-A-8-162132 or JP-A-53-149881 can be used.
The above dispersion may be cast on fibrillated fibers disclosed in JP-B-63-61337 and JP-B-63-61337. In some cases, the fluorine-based ion exchange resin precursor is melt-extruded with a pelletizer or the like to form a pellet.

(Hydrolysis treatment) The fluorinated ion-exchange resin precursor is hydrolyzed by contacting the thus formed fluorinated ion-exchange resin precursor with a reaction liquid to produce a fluorinated ion-exchange resin membrane. In this case, the hydrolysis of the ion exchange group precursor can be carried out in an aqueous alkali hydroxide solution, and it is advantageous to use a relatively high temperature solution in order to further increase the hydrolysis reaction rate. For example, Japanese Patent Application Laid-Open No. 61-19638 discloses a method in which an aqueous solution containing 20 to 25% of sodium hydroxide is used and subjected to a hydrolysis treatment at 70 to 90 ° C. for 16 hours. Also, an aqueous solution of an alkali hydroxide and methyl alcohol, ethyl alcohol, an alcohol solvent such as propyl alcohol, to swell the film and accelerate the hydrolysis reaction rate,
Alternatively, a method of hydrolyzing with a mixture with a water-soluble organic solvent such as dimethyl sulfoxide has been used. For example, 11 to 13% of potassium hydroxide and 30% of dimethyl sulfoxide described in JP-A-57-139127 are disclosed.
Hydrolyzing at 90 ° C. for 1 hour using an aqueous solution containing the aqueous solution, 15 to 50% by weight of an alkali hydroxide and 0.1 to 30% of a water-soluble organic compound described in JP-A-3-6240.
20% at 60-130 ° C using an aqueous solution containing wt%
This is the method of performing the hydrolysis treatment for 24 hours. Further, the hydrolysis treatment may be performed in a state where the fluorine-based ion exchange resin precursor is in the form of a pellet, a solution or a dispersion.

After the ion exchange group is formed by the hydrolysis treatment, the membrane is washed with water, whereby the fluorinated ion exchange resin membrane of the present invention having an alkali metal type ion exchange group or an alkaline earth metal type ion exchange group is obtained. Can be obtained. Further, by performing an acid treatment with an inorganic acid such as hydrochloric acid, it is possible to produce the fluorinated ion exchange resin membrane of the present invention having an acid type ion exchange group. A solution prepared by dissolving the hydrofluoric ion-exchange resin in an alcohol solvent or the like after the hydrolysis treatment, and performing an acid treatment as necessary after casting to form a film, or a solution in which the acid treatment is dissolved in an alcohol solvent or the like. Alternatively, the fluorine-based ion-exchange resin membrane of the present invention can be obtained by forming a dispersion into a cast film. In some cases, it is preferable to heat and fix the film obtained by the cast film formation at a temperature of 100 ° C. or higher in order to reduce the solubility in water. In the case of these cast films, PTFE described in JP-A-8-162132 is also used.
A porous membrane obtained by stretching a membrane;
Fibrillated fibers disclosed in JP-A-1 and JP-B-63-61337 may be used.

(Membrane Electrode Assembly) When the fluorine-based ion exchange resin membrane of the present invention is used in a polymer electrolyte fuel cell, a membrane electrode assembly (MEA) in which two kinds of electrodes, an anode and a cathode, are joined on both sides. used. The electrode is composed of fine particles of catalytic metal and a conductive agent carrying the fine particles, and optionally contains a water repellent. The catalyst used for the electrode is not particularly limited as long as it promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen.Platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium , Tungsten, manganese, vanadium or alloys thereof. Among them, platinum is mainly used. MEA from the electrode and ion exchange membrane
For example, the following method is performed. Platinum-supporting carbon serving as an electrode substance is dispersed in a solution in which a fluorine-based ion exchange resin is dissolved in a mixed solution of alcohol and water to form a paste. A predetermined amount of this is applied to a PTFE sheet and dried. Next, the application surfaces of the PTFE sheet are faced to each other, and an ion exchange membrane is interposed therebetween, and transfer bonding is performed by hot pressing. The hot pressing temperature depends on the type of ion exchange membrane, but is usually 100 ° C. or higher,
It is preferably at least 130 ° C, more preferably at least 150 ° C.

(Fuel Cell) A solid polymer electrolyte fuel cell comprises an MEA, a current collector, a fuel cell frame, a gas supply device, and the like. Among these, the current collector (bipolar plate) is a graphite or metal flange having a gas flow path on the surface and the like, and supplies hydrogen and oxygen to the MEA surface in addition to transmitting electrons to an external load circuit. It has a function as a flow path. M between these current collectors
A fuel cell is manufactured by inserting EAs and stacking a plurality of them. The operation of the fuel cell is performed by supplying hydrogen to one electrode and oxygen or air to the other electrode. The operating temperature of the fuel cell is preferably 50 ° C. or higher, since the higher the temperature, the higher the catalytic activity.
Although it is often operated at 100 ° C., it may be operated at 100 ° C. to 150 ° C. The higher the supply pressure of oxygen or hydrogen, the higher the output of the fuel cell is, which is preferable. However, it is preferable to adjust the pressure to an appropriate pressure range so that the membrane is not damaged. The fluorinated ion exchange resin membrane of the present invention can be used for chloralkali, water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrator, humidity sensor, gas sensor and the like.

[0019]

EXAMPLES Hereinafter, the present invention will be described in more detail based on Examples.
Although described, the present invention is not limited to the embodiments.
No. (Example 1) First, fluorine ion exchange was performed as follows.
A resin precursor, CF2 = CF2 (hereinafter referred to as TFE)
U. ) And CF_Two= CFOCF_TwoCF (CF_Three) O (CF
_Two) _Two-SO_TwoF (hereinafter referred to as S monomer).
A fluorocarbon copolymer was polymerized. One liter
CF in stainless steel autoclave_TwoClCFCl_Two
580 g of S monomer (hereinafter referred to as CFC 113)
, After purging with nitrogen,
Purged with FE. The temperature was 35 ° C and the pressure of TFE was
After adjusting to 0.157 MPa-G (gauge pressure), (n-
C_ThreeF₇COO-)_Two113 solution containing 5wt%
Was added, and polymerization was carried out for about three and a half hours. this
During this time, TFE is supplied from outside the system so that the TFE pressure is constant.
Feeded. TFE was purged from the obtained polymerization solution.
Thereafter, CFC113 was distilled off at 90 ° C. and normal pressure.
The remaining S monomer was distilled off at 0 ° C. under reduced pressure. Furthermore,
Dry at 150 ° C. for 2 days under reduced pressure and dry 10.5 g of fluorine
An ion exchange resin precursor was obtained.

EW of this fluorine-based ion exchange resin precursor
Was 796 and MI was 18. About 1 g of a film formed by extruding this fluorine-based ion exchange resin precursor into a 500 μm-thick film is mixed with 15 wt% of potassium hydroxide and 30 wt.
A hydrolysis treatment was performed by contacting a reaction liquid containing wt% dimethylsulfoxide and 55 wt% water at 60 ° C. for 4 hours. Thereafter, the film is immersed in water at 60 ° C. for 4 hours, and then immersed in a 2N hydrochloric acid aqueous solution at 60 ° C. for 3 hours, and then the acid is washed out with ion exchanged water to obtain a fluorinated ion exchange resin membrane having a sulfonic acid group. Was. This fluorine-based ion exchange resin membrane was vacuum dried at 30 ° C. for 8 hours, and the film weight W ₁ (g) was measured. After weighing, the film was put again in ion-exchanged water and the water was boiled for 8 hours. After cooling, the film was taken out of the water and washed with ion-exchanged water. Then, the film was vacuum dried again at 30 ° C. for 8 hours, and the film weight W ₂ (g) was measured. Weight reduction ratio Y (%) due to boiling on a dry weight basis before boiling
Was calculated by the following equation. Y = (W ₁ −W ₂ ) / W ₁ × 100 The results are shown in Table 1.

Example 2 First, a copolymer of TFE and S monomer, which is a precursor of a fluorinated ion exchange resin, was polymerized as follows. A 1-liter stainless steel autoclave was charged with 850 g of the S monomer, and then purged with nitrogen and subsequently with TFE. After setting the temperature to 35 ° C. and the pressure of TFE to 0.392 MPa-G, C containing 5 wt% of (n-C ₃ F ₇ COO—) ₂ was used.
1.70 g of FC113 solution was added, and polymerization was carried out for about one and a half hours. During this time, TFE was fed from outside the system so that the TFE pressure was constant. From the obtained polymerization solution, TF
After purging E, the remaining S monomer was distilled off at 90 ° C. under reduced pressure. Furthermore, it was dried under reduced pressure at 150 ° C. for 2 days,
18.2 g of a fluorine-based ion exchange resin precursor was obtained. The EW of this fluorine-based ion exchange resin precursor is 706, MI
Was 23. Using this fluorine-based ion-exchange resin precursor, a fluorine-based ion-exchange resin membrane was prepared in the same manner as in Example 1, and the weight reduction ratio due to the boiling treatment was determined.
Table 1 shows the results.

(Comparative Example 1) EW was 673 and MI was 2
A fluorine-based ion-exchange resin membrane was prepared in the same manner as in Example 1 using the same fluorine-based ion-exchange resin precursor as in Example 1 except that the value was 061, and the weight reduction ratio due to the boiling treatment was determined. Table 1 shows the results. (Comparative Example 2) Approximately 1 g of a 500 μm thick film of the same fluorinated ion exchange resin precursor as in Example 1 except that EW was 614 and MI was 44230,
A reaction liquid containing wt% of potassium hydroxide, 30 wt% of dimethylsulfoxide and 55 wt% of water was added at 60 ° C.
For 4 hours to carry out a hydrolysis treatment. Thereafter, when the film was immersed in water at 60 ° C. for 4 hours, all of the film was dissolved in water. Table 1 shows the results.

[0023]

[Table 1]

Example 3 TFE and CF ₂ ＣＦCFO (CF ₂ ) ₂ —SO as precursors of a fluorine ion exchange resin
A fluorocarbon copolymer of ₂ F was polymerized product. The EW of this fluorine-based ion exchange resin precursor is 698, MI
Was 3.0 (satisfies the relationship of the above formula (1)). A film formed by melt-extruding the fluorine-based ion exchange resin precursor to a thickness of 100 μm was mixed with a reaction liquid containing 15 wt% of potassium hydroxide, 30 wt% of dimethyl sulfoxide and 55 wt% of water at 60 ° C. The contact was carried out for a time to carry out a hydrolysis treatment. Thereafter, the film is immersed in water at 60 ° C. for 4 hours, and then immersed in a 2N hydrochloric acid aqueous solution at 60 ° C. for 3 hours, and then the acid is washed out with ion exchanged water to obtain a fluorinated ion exchange resin membrane having a sulfonic acid group. Was. This fluorinated ion exchange resin membrane is heated at 110 ° C. for 8 hours.
After vacuum drying for a time, the film weight W ₁ (g) was measured.
After weighing, place the film in ion-exchanged water again,
Boil for hours. After cooling, the film was taken out of the water and washed with ion-exchanged water. And again, the film
After vacuum drying at 10 ° C. for 8 hours, the film weight W ₂ (g) was measured. The weight loss ratio Y (%) due to the boiling treatment on a dry weight basis before the boiling treatment was calculated by the following equation. Y = (W ₁ −W ₂ ) / W ₁ × 100 The weight reduction ratio at this time was −1.1%, and the compound was not dissolved in water.

Further, the proton conductivity of the fluorine-based ion exchange resin membrane was measured as follows. First, a film is cut out in a wet state, and the thickness T is measured. And width 1c
m, a two-terminal conductivity measurement cell for measuring conductivity in the length direction of the membrane having a length of 5 cm. This cell was placed in ion-exchanged water at 80 ° C., and the resistance R of a real component at a frequency of 10 kHz was measured by the AC impedance method, and the proton conductivity σ was derived from the following equation. σ = L / (R × T × W) σ: proton conductivity (S / cm) T: thickness (cm) R: resistance value (Ω) L (= 5): film length (cm) W (= 1) : Membrane width (cm) The proton conductivity at this time was 0.27 S / cm.
Table 2 shows the above results.

Example 4 TFE and CF ₂ ＣＦCFO (CF ₂ ) ₂ —SO as precursors of a fluorine-based ion exchange resin
A fluorocarbon copolymer of ₂ F was polymerized product. The EW of this fluorine-based ion exchange resin precursor is 805, MI
Was 3.8 (satisfies the relationship of the above formula (1)). Using this fluorine-based ion exchange resin precursor,
A fluorine-based ion-exchange resin membrane was produced in the same manner as in Example 3, and the weight loss ratio and the proton conductivity due to the boiling treatment were measured. At this time, the weight reduction ratio was 0.5%, and it was not dissolved in water. The proton conductivity is 0.23
S / cm. Table 2 shows the results. Example 5 As a fluorine-based ion exchange resin precursor, T
A fluorocarbon copolymer of FE and CF ₂ ＣＦCFO (CF ₂ ) ₂ —SO ₂ F was polymerized. The EW of the fluorine-based ion exchange resin precursor was 861 and the MI was 2.4 (satisfies the relationship of the above formula (1)). Using this fluorine-based ion-exchange resin precursor, a fluorine-based ion-exchange resin membrane was prepared in the same manner as in Example 3, and the weight loss ratio due to boiling treatment and the proton conductivity were measured. At this time, the weight reduction ratio was -1.1%, which was not dissolved in water. The proton conductivity was 0.22 S / cm. Table 2 shows the results.

Comparative Example 3 TFE and CF ₂ ＣＦCFO (CF ₂ ) ₂ —SO
A fluorocarbon copolymer of ₂ F was polymerized product. The EW of this fluorine-based ion exchange resin precursor is 670, MI
Was 16.4 (not satisfying the relationship of the above formula (1)). Using this fluorine-based ion-exchange resin precursor, a fluorine-based ion-exchange resin membrane was prepared in the same manner as in Example 3, and the weight loss ratio due to boiling treatment and the proton conductivity were measured. At this time, the weight reduction ratio was 7.6%, and dissolution in water was observed. The proton conductivity is 0.30 S /
cm. Table 2 shows the results.

[0028]

[Table 2]

[0029]

According to the present invention, an EW of 250 to 9 produced from a fluorine-based ion exchange resin precursor having an MI of 2000 or less is used.
For a fluorine-based ion exchange resin membrane of 40 or less, the weight loss due to the boiling treatment in water for 8 hours is 5% based on the dry weight before the boiling treatment.
wt% or less, and high durability can be realized when used for fuel cell applications. In particular, a fluorine-based ion exchange resin membrane having an EW of 700 or less, produced from the precursor satisfying the following formula (1), has no weight loss due to boiling treatment in water for 8 hours, shows high proton conductivity, and has a high fuel conductivity. Effective for battery applications. log ₁₀ MI ≦ [(EW-850) / 90] +3 (1)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 8/10 H01M 8/10 // C08L 27:12 C08L 27:12 F term (Reference) 4F071 AA07C AF36C AF42C AH15 FA02 FA05 FA06 FB01 FB07 FC01 5H026 AA06 BB01 CX05 HH05 HH08 HH10

Claims (5)

[Claims] 1. A fluorine-based ion having an equivalent weight (EW) of 250 or more and 940 or less, and a weight loss by boiling for 8 hours in water of 5 wt% or less on a dry weight basis before the boiling. Exchange resin membrane. 2. The fluorine-based ion exchange resin membrane according to claim 1, wherein the weight loss is 1 wt% or less. 3. The fluorine-based ion exchange resin membrane according to claim 1, wherein the EW is 250 or more and 700 or less. 4. A membrane-electrode assembly comprising the fluorine-based ion-exchange resin membrane according to claim 1. 5. A polymer electrolyte fuel cell comprising the fluorinated ion exchange resin membrane according to claim 1.