JP2005135681A - Solid polymer electrolyte film and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte film, obtained by a radiation graft polymerization method, with high proton conductivity and excellent oxidation resistance and a fuel cell using the same. <P>SOLUTION: The solid polymer electrolyte film, obtained by graft polymerizing reactive monomers on fluorochemical resin irradiated, is so structured to have front and rear surfaces of the electrolyte film in different composition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid polymer electrolyte membrane having a high proton transfer speed, high ion exchange capacity, excellent oxidation resistance, and suitable for a fuel cell, and a fuel cell using the same.

  A fuel cell using a solid polymer electrolyte type ion exchange membrane is expected to be widely put into practical use as a power source for electric vehicles or a simple auxiliary power source because its operating temperature is as low as 100 ° C. or less and its energy density is high. In this fuel cell, there are important elemental technologies related to a solid polymer electrolyte membrane, a platinum-based catalyst, a gas diffusion electrode, and a polymer electrolyte membrane-electrode assembly. However, among these, development of a solid polymer electrolyte membrane having good characteristics as a fuel cell is one of the most important technologies.

  In a solid polymer electrolyte membrane fuel cell, gas diffusion electrodes are combined on both sides of the electrolyte membrane, and the membrane and the electrode have a substantially integrated structure. For this reason, the electrolyte membrane acts as an electrolyte for conducting protons, and also has a role as a diaphragm for preventing direct mixing of hydrogen or methanol as a fuel with an oxidizing agent even under pressure. Such an electrolyte membrane is required to have a high proton transfer rate as an electrolyte, a high ion exchange capacity, and a constant and high water retention in order to keep the electric resistance low. On the other hand, because of its role as a diaphragm, the mechanical strength of the membrane is large, its dimensional stability is excellent, its chemical stability with respect to long-term use is excellent, and hydrogen gas or methanol as fuel Further, it is required that the gas does not have excessive permeability with respect to oxygen gas which is an oxidizing agent.

  In early polymer electrolyte membrane fuel cells, ion exchange membranes of hydrocarbon resins produced by copolymerization of styrene and divinylbenzene were used as electrolyte membranes. However, this electrolyte membrane has poor durability because of its very low durability. Therefore, after that, fluororesin-based perfluorosulfonic acid membrane “Nafion” (registered trademark of DuPont) developed by DuPont is generally used. Has been used.

However, conventional fluororesin-based electrolyte membranes such as “Nafion” are excellent in chemical durability and stability. However, in direct methanol fuel cells (DMFC) using methanol as fuel, methanol is used as an electrolyte membrane. There is a problem that the crossover phenomenon occurs and the output decreases.
Furthermore, since the fluororesin-based electrolyte membrane starts from the synthesis of the monomer, there are many manufacturing processes, and there is a problem that the cost becomes high, which is a big obstacle when put into practical use.

  For this reason, efforts have been made to develop low-cost electrolyte membranes that replace the “Nafion” and the like. In addition, in the radiation graft polymerization method, a method of producing a solid polymer electrolyte membrane by grafting a fluorocarbon reactive monomer to a fluororesin membrane and sulfonating is disclosed in JP-A-2002-313364 ( Patent Document 1) and Japanese Patent Laid-Open No. 2003-82129 (Patent Document 2). These describe that a solid electrolyte membrane having a strong membrane strength after grafting and excellent oxidation resistance can be produced by imparting a crosslinked structure to the PTFE film.

  However, in the radiation graft polymerization of fluorocarbon-based reactive monomers, reactive monomers such as perfluorovinyl ether sulfonic acid have low polymerizability alone, so that an electrolyte membrane having a high graft rate can be stably obtained in the production process. It is difficult.

  Therefore, Japanese Patent Laid-Open No. 2003-082129 (Patent Document 3) proposes a method by co-grafting with tetrafluoroethylene (TFE) using a highly polymerizable monomer.

  However, since TFE is a gas, it is difficult to handle, and there is a problem that restrictions on graft polymerization conditions are increased.

  As described above, a solid electrolyte membrane obtained by graft polymerization of a fluorocarbon-based reactive monomer by a radiation graft polymerization method has excellent oxidation resistance, but has a low graft conductivity and a low proton conductivity. There is a problem, and a film obtained by graft polymerization of a hydrocarbon-based reactive monomer by a radiation graft polymerization method has a problem that it has a high proton conductivity due to a high graft ratio, but has a poor oxidation resistance. In addition, it has been difficult to obtain a film having both of the above characteristics. Therefore, it has been desired to develop a solid electrolyte membrane having these characteristics without any problems.

JP 2002-313364 A JP 2003-82129 A Japanese Patent Laid-Open No. 2003-082129

  The present invention has been made in view of the above circumstances, and is a solid polymer electrolyte membrane obtained by a radiation graft polymerization method, which has high proton conductivity and excellent oxidation resistance And it aims at providing the fuel cell using this electrolyte membrane.

  As a result of intensive studies to achieve the above object, the present inventor is a solid polymer electrolyte membrane obtained by graft polymerization of a reactive monomer to a fluorine-based resin irradiated with radiation, the electrolyte membrane The front and back surfaces of each are composed of different compositions, preferably one surface is composed of a composition obtained by graft polymerization of a hydrocarbon compound, and the other surface is graft polymerized with a fluorine-containing hydrocarbon compound. What is composed of the obtained composition is a solid polymer electrolyte membrane having high proton conductivity and excellent oxidation resistance, and this solid polymer electrolyte membrane is used as a fuel electrode and an air electrode. It has been found that a high-performance fuel cell can be obtained by providing it in between, and the present invention has been made.

  In this case, in the present invention, by irradiating the fluororesin with an electron beam as radiation, the range in which the electron beam reaches in the film thickness direction is regulated by adjusting the acceleration voltage, and radicals are formed only on one side of the film. It is possible to create reactive sites and easily create a difference in radical reaction site distribution on both sides of the membrane, which allows different reactive monomers to be graft polymerized on the front and back surfaces of the membrane. Thus, an electrolyte membrane can be obtained in which the front and back surfaces of the electrolyte membrane of the present invention are composed of different compositions. Preferably, a hydrocarbon-based reactive monomer having high radical polymerization reactivity is grafted on one side of the membrane and sulfonated to have high proton conductivity. By grafting a fluorocarbon-based reactive monomer on the surface, it was possible to produce a solid polymer electrolyte membrane having both high proton conductivity and excellent oxidation resistance.

Accordingly, the present invention provides the following matters.
[Claim 1]
A solid polymer electrolyte membrane obtained by graft polymerization of a reactive monomer to a fluororesin irradiated with radiation, wherein the solid and the back surfaces of the electrolyte membrane are composed of different compositions Polymer electrolyte membrane.
[Claim 2]
2. The electrolyte membrane according to claim 1, wherein one surface of the electrolyte membrane is composed of a composition obtained by graft polymerization of a hydrocarbon compound, and the other surface is composed of a composition obtained by graft polymerization of a fluorine-containing hydrocarbon compound. Solid polymer electrolyte membrane.
[Claim 3]
Fluorine resin is tetrafluoroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, tetrafluoroethylene-ethylene copolymer resin, vinylidene fluoride The solid polymer electrolyte membrane according to claim 1 or 2, which is at least one selected from resins.
[Claim 4]
4. The radiation-irradiated fluororesin is obtained by previously irradiating radiation at an absorbed dose of 5 kGy or more at a temperature higher than the melting point and further irradiating an electron beam at a temperature of 20 to 40 ° C. Solid polymer electrolyte membrane.
[Claim 5]
A fuel cell comprising the solid polymer electrolyte membrane according to any one of claims 1 to 4 between a fuel electrode and an air electrode.
[Claim 6]
6. The fuel cell according to claim 5, wherein a surface composed of a composition obtained by graft polymerization of a fluorine-containing hydrocarbon compound of the solid polymer electrolyte membrane is disposed on the air electrode side.
[Claim 7]
A method for producing a solid polymer electrolyte membrane in which a reactive monomer is graft-polymerized onto a fluorine-based resin irradiated with radiation. The first radical-reactive monomer is graft-polymerized by irradiating one side of the fluorine-based resin with an electron beam. After that, the other surface of the fluororesin is irradiated with an electron beam to graft polymerize the second other radical-reactive monomer, and a solid polymer electrolyte membrane having different compositions on the front and back surfaces of the electrolyte membrane is obtained. A method for producing a solid polymer electrolyte membrane, comprising:

  The solid polymer electrolyte membrane of the present invention is a solid polymer electrolyte membrane obtained by a radiation graft polymerization method, which combines high proton conductivity and excellent oxidation resistance. By using this electrolyte membrane, It can be a direct methanol fuel cell with very high performance.

  Hereinafter, the present invention will be described in more detail. The solid polymer electrolyte membrane of the present invention is obtained by graft polymerization of a reactive monomer to a fluorine resin irradiated with radiation. Here, as the fluororesin used, tetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin ( PFA), ethylene tetrafluoride-ethylene copolymer resin (ETFE), vinylidene fluoride resin (PVDF) and the like are exemplified, and one of these can be used alone or in combination of two or more. The shape can be a sheet, film, or plate.

  In the present invention, a solid polymer electrolyte membrane can be obtained by graft-polymerizing an ion exchange group or a radical reactive monomer capable of introducing an ion exchange group onto the surface of the fluororesin by radiation irradiation. In this case, in the grafting method using radiation, the main chain of the fluororesin is irradiated with radiation in advance to generate radicals that are the starting points of grafting, and then before the grafting reaction is performed by bringing the fluororesin into contact with the monomer. There are an irradiation method and a simultaneous irradiation method in which radiation is irradiated in the coexistence of a monomer and a fluorine-based resin, and any method can be adopted in the present invention.

  In the present invention, an electron beam is preferably used as the radiation to be irradiated for graft polymerization of the radical reactive monomer onto the fluororesin. The acceleration voltage of the electron beam can be defined according to the film thickness of the fluororesin, and is preferably regulated to an acceleration voltage in a range where the electron beam does not pass through the fluororesin, and is preferably 50 to 200 kV, particularly 80 to 130 kV. . In this case, the film thickness of the fluororesin is preferably 25 to 100 μm, particularly 50 to 80 μm. In the present invention, a radical reaction active site can be created only on one side of the film by irradiating the fluorine resin with an electron beam as radiation, thereby irradiating each of the front and back surfaces of the fluorine resin with an electron beam. This makes it possible to easily create the difference in active site distribution necessary for the grafting reaction, and to graft polymerize different reactive monomers on the front and back surfaces of the membrane, which will penetrate the fluororesin such as gamma rays. When radiation is used, different reactive monomers cannot be graft-polymerized on the front and back surfaces of the film, and the object of the present invention cannot be achieved.

Further, the irradiation dose of the electron beam is preferably 5 to 100 kGy, particularly preferably 5 to 50 kGy, and if it is less than 5 kGy, the graft ratio to the extent that the functional group properties can be effectively obtained may not be obtained. If it exceeds, the strength of the fluororesin may be significantly reduced.
Note that, when the temperature at which the electron beam is irradiated becomes high, the radical disappears easily. Therefore, the temperature at the irradiation is preferably room temperature or lower.

  Further, the electron beam irradiation is preferably performed in an inert gas atmosphere such as helium, nitrogen, or argon gas, and the oxygen concentration in the gas is preferably 100 ppm or less, particularly preferably 50 ppm or less, but is always performed in the absence of oxygen. There is no need.

  If the irradiation dose of the electron beam is less than 1 kGy, the graft ratio to such an extent that the functional group properties effectively act cannot be obtained, and if it exceeds 1 MGy, the strength of the fluororesin tends to decrease significantly. On the other hand, in Japanese Patent Application Laid-Open No. 2001-348439, a fluororesin having a crosslinked structure can be obtained by previously irradiating the fluororesin with radiation at a temperature equal to or higher than the melting point, thereby improving the film strength against radiation. Has been proposed. Also in the solid polymer electrolyte membrane of the present invention, the fluororesin is irradiated with radiation at a temperature equal to or higher than the melting point in advance to form a fluororesin having a cross-linked structure, which is used as the fluororesin. As described above, it is preferable to generate a radical by irradiating an electron beam at room temperature (20 to 40 ° C.) or lower, preferably 20 to 40 ° C. to graft polymerize the reactive monomer.

  Here, examples of the radiation irradiated to the fluororesin in advance at a temperature equal to or higher than the melting point include electron beams, γ rays, X rays, ion beams, and ultraviolet rays. preferable.

  The absorbed dose of radiation previously irradiated to the fluororesin at a temperature equal to or higher than the melting point is preferably 5 kGy or more, and particularly preferably 10 to 100 kGy. If it is less than 5 kGy, a sufficient crosslinking effect may not be achieved, and if it exceeds 100 kGy, mechanical properties such as elongation and strength of the fluororesin may be deteriorated.

  Furthermore, the irradiation with radiation above the melting point of the fluororesin is preferably carried out in an inert gas atmosphere such as helium, nitrogen or argon gas, and the oxygen concentration in the gas is preferably 500 ppm or less, particularly preferably 200 ppm or less. .

  In the solid polymer electrolyte membrane of the present invention, as a radical reactive monomer that is graft polymerized by irradiating an electron beam to a fluorine-based resin, any ion-exchange group or a monomer into which an ion-exchange group can be introduced can be used without particular limitation. However, in order to configure the front and back surfaces of the electrolyte membrane with different compositions, it is necessary to use at least two different reactive monomers. In particular, in the present invention, one surface of the electrolyte membrane is composed of a composition obtained by graft polymerization of a hydrocarbon compound, and the other surface is composed of a composition obtained by graft polymerization of a fluorine-containing hydrocarbon compound. Therefore, it is preferable to use a hydrocarbon-based reactive monomer and a fluorine-containing hydrocarbon-based monomer as the radical-reactive monomer.

  Here, the hydrocarbon-based reactive monomer to be grafted is homopolymerizable and has an ion-exchange functional group or does not have an ion-exchange functional group, but uses a chemical reaction. Thus, a hydrocarbon-based reactive monomer capable of imparting an ion-exchange functional group is preferable.

  In this case, examples of ion-exchangeable functional groups include phenolic hydroxyl groups, carboxylic acid groups, amine groups, and sulfonic acid groups. In addition, acyloxy groups, ester groups, acid imide groups, and the like can be quantitatively converted to ion-exchangeable functional groups such as phenolic hydroxyl groups and sulfonic acid groups by hydrolysis, and monomers having these groups are also used. can do.

  Specific examples of the hydrocarbon-based reactive monomer having an ion-exchange functional group include acrylic acid ester, methacrylic acid ester, maleic acid ester, fumaric acid ester, hydroxyoxystyrene, acyloxystyrene, vinyl ester, and vinyl sulfonic acid. Examples thereof include esters, styrene carboxylic acids, styrene alkyl sulfonates, and vinyl sulfonic acids. In addition, as said esters, a C1-C10 alkylester is preferable.

  In addition, when using a monomer that does not have an ion-exchangeable functional group but can impart an ion-exchangeable functional group using a chemical reaction, the reactivity without an ion-exchangeable functional group After performing graft polymerization with a monomer, an ion-exchangeable functional group can be imparted by sulfonation using a chemical reaction. The hydrocarbon-based reactive monomer that does not have an ion-exchange functional group but can impart an ion-exchange functional group using a chemical reaction includes styrene, α-methylstyrene, vinyl toluene, Hydroxystyrene or the like can be used. The sulfone group can be introduced into the reactive monomer by reacting with a sulfonating agent such as sulfuric acid or fuming sulfuric acid.

  Furthermore, if necessary, a crosslinkable monomer such as a monomer having a plurality of vinyl groups such as divinylbenzene can be mixed in an amount of 0.1 to 15 mol 1% with respect to the reactive monomer.

In addition, the fluorine-containing hydrocarbon-based reactive monomer has the same ion-exchange functional group as the above-mentioned hydrocarbon-based reactive monomer, or has no ion-exchange functional group, but the chemical reaction A fluorine-containing hydrocarbon-based monomer capable of imparting an ion-exchangeable functional group using is preferably used. In this fluorine-containing reactive monomer, functional groups that can be converted into ion-exchangeable functional groups by hydrolysis include —SO ₂ F, —SO ₂ NH ₂ , —SO ₂ NH ₄ , —COOH, — CN, -COF, -COOR (R is an alkyl group having 1 to 10 carbon atoms) and the like, and these functional groups are suitable because they can easily give a sulfone group or a carboxylic acid group by hydrolysis. .

Specific examples of the fluorine-containing hydrocarbon-based reactive monomer include the following compounds.
Trifluoroethylenesulfonyl halide CF ₂ ═CFSO ₂ X (X: —F or —Cl)
Trifluorovinyl ether sulfonyl halide CF ₂ ═CF—O—SO ₂ X (X: —F or —Cl)
Perfluoroallylfluorosulfide CF ₂ ═CFCF ₂ —O—SO ₂ F
Perfluorovinyl ether sulfonyl fluoride CF ₂ ═CF—O—CF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F
Trifluorostyrene CF ₂ = CFC ₆ H ₅
Trifluoroacrylate CF ₂ ═CFCOOR (R: —CH ₃ or —C (CH ₃ ) ₃ )

  In the present invention, as a method of graft polymerization of the reactive monomer to the fluororesin, the first radical reactive monomer is graft polymerized by irradiating one side of the fluororesin with an electron beam, It can be carried out by irradiating the other surface with an electron beam and graft polymerizing a second other radical-reactive monomer. In addition, the irradiation conditions of an electron beam should just irradiate both surfaces on conditions, such as the said acceleration voltage and irradiation amount.

  Here, the amount of the radical reactive monomer grafted on each surface of the fluororesin irradiated with radiation is 1,000 to 100,000 parts by mass of the radical reactive monomer with respect to 100 parts by mass of the fluororesin, In particular, it is preferable to use 4,000 to 20,000 parts by mass. If the amount of the radical reactive monomer is too small, the contact may be insufficient. If the amount is too large, the radical reactive monomer may not be used efficiently.

  Moreover, when graft-polymerizing a radical-reactive monomer to a fluororesin, an initiator such as azobisisobutyronitrile may be appropriately used as long as the object of the present invention is not impaired.

  Furthermore, in the present invention, a solvent can be used during the graft reaction. As the solvent, those that uniformly dissolve the reactive monomer are preferable. For example, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate and butyl acetate, alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol , Ethers such as tetrahydrofuran and dioxane, aromatic hydrocarbons such as N, N-dimethylformamide, N, N-dimethylacetamide, benzene and toluene, aliphatic or alicyclic rings such as n-heptane, n-hexane and cyclohexane A group hydrocarbon or a mixed solvent thereof can be used.

  In the present invention, it is preferable to adjust the oxygen concentration in the reaction atmosphere during graft polymerization to 0.05 to 5% (volume%, the same applies hereinafter). It is considered that oxygen in the reaction atmosphere reacts with radicals in the system to become carbonyl radicals or peroxy radicals, and acts to suppress further reactions. When the oxygen concentration is less than 0.05%, the radically polymerizable monomer is homopolymerized and a gel insoluble in the solvent is generated. Therefore, the raw material is wasted and it takes time to remove the gel. If it exceeds%, the graft ratio may decrease. A desirable oxygen concentration is 0.1 to 3%, and a more desirable oxygen concentration is 0.1 to 1%. In addition, as gas other than oxygen, inert gas, such as nitrogen and argon, is used.

  In addition, as reaction conditions of the said graft polymerization, it is preferable to set it as the reaction time of 1 to 40 hours, especially 4 to 20 hours at the temperature of 0-100 degreeC, especially 40-80 degreeC.

  As described above, a solid polymer electrolyte membrane can be obtained by graft polymerization of a radical reactive monomer to a fluorine-based resin irradiated with radiation, and further sulfonated as necessary.

  In the fuel cell of the present invention, the solid polymer electrolyte membrane is provided between a fuel electrode and an air electrode. In this case, it is preferable from the viewpoint of oxidation resistance that the surface of the solid polymer electrolyte membrane obtained by graft polymerization of the fluorine-containing hydrocarbon compound is disposed on the air electrode side. Note that the configurations and materials of the fuel electrode and the air electrode and the configuration of the fuel cell can be known.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In the following examples, the blending amount is mass%.

[Example 1]
The depth dose distribution of an electron beam (100 keV) with respect to a PTFE film having a thickness of 50 μm when the electron beam acceleration voltage was set to 130 kV was determined by EGS program calculation. The results are shown in FIG. 1 (graph of relative absorbed dose against PTFE film depth). The program calculation conditions by EGS are as shown in FIG. 2. In a vacuum atmosphere, a nitrogen gas layer 3 (15 mm), a PTFE film 2 (thickness 50 μm) laminated on aluminum 1 (thickness 1 mm), The relative absorbed dose (%) with respect to the depth when the electron beam (100 keV) was irradiated at a specific acceleration voltage through the titanium foil 4 (thickness 10 μm) was determined.
According to this calculation result, when a single-sided PTFE film having a thickness of 50 μm was irradiated with an electron beam at an acceleration voltage of 130 kV, a relative absorbed dose of 50% was obtained at a depth of about 45 μm.

  An electron beam was irradiated with an acceleration voltage of 130 kV and an irradiation dose of 30 kGy at room temperature in a nitrogen gas atmosphere with an oxygen concentration of 30 ppm or less on one side of a PTFE film (5 cm square, mass 0.25 g) having a thickness of 50 μm.

  Subsequently, oxygen is removed by five times of degassing / nitrogen replacement, and the styrene solution containing hydrocarbon reactive monomer (40 parts by mass of styrene, 2 parts by mass of divinylbenzene, azobisisobutyro is substituted with nitrogen gas). Nitrile 0.01 parts by mass, n-hexane 40 parts by mass) was introduced into the glass separable flask containing the irradiated PTFE film until the membrane was immersed. The reaction was performed at 60 ° C. for 15 hours, and then the membrane was taken out, washed with toluene and acetone, and then dried. The graft ratio determined by the following formula was 35%.

Formula for calculating graft ratio:
X = 100 × (W ₁ −W _o ) / W _o
X: Graft ratio (%)
W ₀ : Weight of PTFE film before grafting (g)
W ₁ : Weight of PTFE film after grafting (g)

  Subsequently, the membrane grafted as described above was reacted with chlorosulfonic acid at 50 ° C. for 2 hours in a 1,2-dichloroethane solvent. The obtained membrane was washed with 1,2-dichloroethane and ion-exchanged water and dried.

Subsequently, the other surface of the PTFE film was again irradiated with an electron beam at an acceleration voltage of 80 kV. In addition, the depth dose distribution (calculated by the program calculation by ECG similarly to the above) with respect to the PTFE film having a thickness of 50 μm at the acceleration voltage of 80 kV is as shown in FIG.
After irradiation, oxygen is removed by a deaeration operation, nitrogen substitution is performed, and a solution containing fluorine-containing reactive monomer CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F (fluorine-carbon-based) The film was immersed in 30 parts by mass of a monomer, 30 parts by mass of hexafluorometaxylene, and 0.01 parts by mass of azobisisobutyronitrile, and reacted at 60 ° C. for 24 hours. Then, the solid electrolyte membrane was obtained by sulfonation by a conventional method.

Table 1 shows the ion exchange capacity, proton conductivity, and oxidation resistance of the electrolyte membranes obtained in the above examples. The ion exchange capacity (I _EC (meq / g)) of the membrane was determined by neutralization titration, and the proton conductivity was determined by performing normal membrane resistance measurement. For the evaluation of oxidation resistance, the prepared electrolyte membrane was incorporated into a battery, and the voltage drop after 200 hours in the durability test operation was determined. The durability test conditions are as shown in Table 2.

[Example 2]
An experiment similar to Example 1 was performed except that a PTFE film irradiated with 100 kGy of γ rays at 340 ° C. was used in advance.

[Comparative Example 1]
An electron beam was irradiated with an acceleration voltage of 130 kV and an irradiation dose of 30 kGy at room temperature in a nitrogen gas atmosphere with an oxygen concentration of 30 ppm or less on a PTFE film (5 cm square, mass 0.25 g) having a thickness of 50 μm. Subsequently, oxygen is removed by five times of degassing / nitrogen replacement, and the solution is replaced with nitrogen gas, and contains a fluorine-containing monomer CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F The film was immersed in the same composition as in the example, and reacted at 60 ° C. for 24 hours. Thereafter, sulfonation was performed by a conventional method, and the characteristics were evaluated in the same manner as in the Examples.

[Comparative Example 2]
An electron beam was irradiated with an acceleration voltage of 130 kV and an irradiation dose of 30 kGy at room temperature in a nitrogen gas atmosphere with an oxygen concentration of 30 ppm or less on a PTFE film (5 cm square, mass 0.25 g) having a thickness of 50 μm. Subsequently, oxygen was removed by five times of degassing / nitrogen replacement, the gas was replaced with nitrogen gas, and the membrane was immersed in a styrene solution (composition is the same as in the example), which is a hydrocarbon monomer, at 60 ° C. for 15 hours. Reacted. Thereafter, sulfonation was performed by a conventional method, and the characteristics were evaluated in the same manner as in the Examples.

In Example 1, it is a graph which shows the result of having calculated | required the depth dose distribution with respect to the PTFE film of thickness 50 micrometers of the electron (100 keV) when irradiating an electron beam with the acceleration voltage of an electron beam being 130 kV by the program calculation by EGS. is there. It is the schematic which shows the program calculation conditions by EGS used in Example 1. FIG. In Example 1, it is a graph which shows the result which calculated | required the depth dose distribution with respect to the PTFE film of thickness 50 micrometers of the electron (100 keV) when irradiating an electron beam with the acceleration voltage of an electron beam being 80 kV by the program calculation by EGS. is there.

Explanation of symbols

1 Aluminum 2 PTFE film 3 Nitrogen gas layer 4 Titanium foil

Claims (7)

  A solid polymer electrolyte membrane obtained by graft polymerization of a reactive monomer to a fluororesin irradiated with radiation, wherein the solid and the back surfaces of the electrolyte membrane are composed of different compositions Polymer electrolyte membrane.   2. The electrolyte membrane according to claim 1, wherein one surface of the electrolyte membrane is composed of a composition obtained by graft polymerization of a hydrocarbon compound, and the other surface is composed of a composition obtained by graft polymerization of a fluorine-containing hydrocarbon compound. Solid polymer electrolyte membrane.   Fluorine resin is tetrafluoroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, tetrafluoroethylene-ethylene copolymer resin, vinylidene fluoride The solid polymer electrolyte membrane according to claim 1 or 2, which is at least one selected from resins.   4. The radiation-irradiated fluororesin is obtained by previously irradiating radiation at an absorbed dose of 5 kGy or more at a temperature higher than the melting point and further irradiating an electron beam at a temperature of 20 to 40 ° C. Solid polymer electrolyte membrane.   A fuel cell comprising the solid polymer electrolyte membrane according to any one of claims 1 to 4 between a fuel electrode and an air electrode.   6. The fuel cell according to claim 5, wherein a surface composed of a composition obtained by graft polymerization of a fluorine-containing hydrocarbon compound of the solid polymer electrolyte membrane is disposed on the air electrode side. A method for producing a solid polymer electrolyte membrane in which a reactive monomer is graft-polymerized onto a fluorine-based resin irradiated with radiation. The first radical-reactive monomer is graft-polymerized by irradiating one side of the fluorine-based resin with an electron beam. After that, the other surface of the fluororesin is irradiated with an electron beam to graft polymerize the second other radical-reactive monomer, and a solid polymer electrolyte membrane having different compositions on the front and back surfaces of the electrolyte membrane is obtained. A method for producing a solid polymer electrolyte membrane, comprising: