JP5158309B2 - ELECTROLYTE MEMBRANE FOR SOLID POLYMER FUEL CELL AND METHOD FOR PRODUCING THE SAME - Google Patents

ELECTROLYTE MEMBRANE FOR SOLID POLYMER FUEL CELL AND METHOD FOR PRODUCING THE SAME Download PDF

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JP5158309B2
JP5158309B2 JP2006275100A JP2006275100A JP5158309B2 JP 5158309 B2 JP5158309 B2 JP 5158309B2 JP 2006275100 A JP2006275100 A JP 2006275100A JP 2006275100 A JP2006275100 A JP 2006275100A JP 5158309 B2 JP5158309 B2 JP 5158309B2
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electrolyte membrane
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fluororesin
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光人 高橋
敏夫 大庭
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Shin Etsu Chemical Co Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Description

本発明は、高いプロトン伝導性を有し、かつ、メタノールクロスオーバー量が抑制された固体高分子型燃料電池用電解質膜、特にメタノールを燃料とする直接メタノール型燃料電池用電解質膜及びその製造方法に関する。   The present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell having high proton conductivity and a reduced amount of methanol crossover, particularly an electrolyte membrane for a direct methanol fuel cell using methanol as a fuel, and a method for producing the same. About.

固体高分子電解質型イオン交換膜を用いた燃料電池は、作動温度が１００℃以下と低く、そのエネルギー密度が高いことから、電気自動車の電源や簡易補助電源として広く実用化が期待されている。この燃料電池においては、固体高分子電解質膜、白金系の触媒、ガス拡散電極、及び高分子電解質膜と電極の接合体などに関する重要な要素技術がある。しかし、この中でも燃料電池としての良好な特性を有する固体高分子電解質膜の開発は最も重要な技術の一つである。   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.

固体高分子電解質膜型燃料電池においては、電解質膜の両面にガス拡散電極が複合されており、膜と電極とは実質的に一体構造になっている。このため、電解質膜はプロトンを伝導するための電解質として作用し、また、加圧下においても燃料である水素やメタノールと酸化剤とを直接混合させないための隔膜としての役割も有する。このような電解質膜としては、電解質としてプロトンの移動速度が大きく、イオン交換容量が高いこと、電気抵抗を低く保持するために保水性が一定かつ高いことが要求される。一方、隔膜としての役割から、膜の力学的な強度が大きいこと、及び寸法安定性が優れていること、長期の使用に対する化学的な安定性に優れていること、燃料である水素ガスやメタノール、酸化剤である酸素ガスに対して過剰な透過性を有しないことなどが要求される。   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.

初期の固体高分子電解質膜型燃料電池では、スチレンとジビニルベンゼンの共重合で製造した炭化水素系樹脂のイオン交換膜が電解質膜として使用されていた。しかし、この電解質膜は、耐久性が非常に低いため実用性に乏しく、そのため、その後はデュポン社によって開発されたフッ素樹脂系のパーフルオロスルホン酸膜「ナフィオン」（デュポン社登録商標）等が一般に用いられてきた。   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, the fluororesin-based perfluorosulfonic acid membrane “Nafion” (registered trademark of DuPont) developed by DuPont is generally used thereafter. Has been used.

しかしながら、「ナフィオン」等の従来のフッ素樹脂系電解質膜は、化学的な耐久性や安定性には優れているが、メタノールを燃料とする直接メタノール型燃料電池（ＤＭＦＣ）ではメタノールが電解質膜を通過するクロスオーバー現象が生じ、出力が低下する問題があった。更に、フッ素樹脂系電解質膜は、モノマーの合成から出発するために製造工程が多く、コストが高くなる問題があり、実用化する場合の大きな障害になっている。   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.

そのため、前記「ナフィオン」等に替わる低コストの電解質膜を開発する努力が行われてきた。放射線グラフト重合法により、フッ素樹脂系の膜にスルホン基を導入して固体高分子電解質膜を作製する方法が、特許文献１（特開２００１−３４８４３９号公報）、特許文献２（特開２００２−３１３３６４号公報）、特許文献３（特開２００３−８２１２９号公報）に提案されている。   For this reason, efforts have been made to develop low-cost electrolyte membranes that replace the “Nafion” and the like. A method of producing a solid polymer electrolyte membrane by introducing a sulfone group into a fluororesin-based membrane by radiation graft polymerization is disclosed in Patent Document 1 (JP 2001-348439 A) and Patent Document 2 (JP 2002-2002). 3133364) and Patent Document 3 (Japanese Patent Laid-Open No. 2003-82129).

しかし、これらの放射線グラフト重合において、スチレンなどのグラフト材原料であるラジカル反応性モノマーのグラフト重合では、高いプロトン伝導性を得るにはスチレンのグラフト率を上げることが求められるが、プロトン伝導性の向上に比例してメタノールクロスオーバー量も増加してしまう問題があり、現状、放射線グラフト膜において高プロトン伝導性と低メタノールクロスオーバー量はトレードオフの関係になっていた。   However, in these radiation graft polymerizations, in the graft polymerization of radical reactive monomers that are raw materials for graft materials such as styrene, it is required to increase the graft ratio of styrene in order to obtain high proton conductivity. There is a problem that the amount of methanol crossover increases in proportion to the improvement, and at present, high proton conductivity and low methanol crossover amount have a trade-off relationship in the radiation graft membrane.

これに対し、特許文献４（特開２００４−５９７５２号公報）では、架橋したフッ素系フィルムに放射線グラフト重合法により作製した固体高分子電解質膜によるメタノールクロスオーバー量の抑制が提案されているが、メタノールクロスオーバー量の抑制は十分でなく、更にメタノールクロスオーバー量の少ない固体高分子電解質膜が求められている。   On the other hand, Patent Document 4 (Japanese Patent Application Laid-Open No. 2004-59752) proposes suppression of the amount of methanol crossover by a solid polymer electrolyte membrane produced by a radiation graft polymerization method on a crosslinked fluorine-based film. The suppression of the amount of methanol crossover is not sufficient, and there is a need for a solid polymer electrolyte membrane with a smaller amount of methanol crossover.

特開２００１−３４８４３９号公報JP 2001-348439 A 特開２００２−３１３３６４号公報JP 2002-313364 A 特開２００３−８２１２９号公報JP 2003-82129 A 特開２００４−５９７５２号公報JP 2004-59752 A

本発明は、上記事情に鑑みなされたもので、放射線グラフト重合法により得られる固体高分子電解質膜であって、高いプロトン伝導性を有し、かつ、メタノールクロスオーバー量が抑制された固体高分子型燃料電池用電解質膜、特にメタノールを燃料とする直接メタノール型燃料電池用電解質膜並びにその製造方法を提供することを目的とする。   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, having a high proton conductivity and a reduced amount of methanol crossover It is an object of the present invention to provide an electrolyte membrane for a fuel cell, particularly an electrolyte membrane for a direct methanol fuel cell using methanol as a fuel, and a method for producing the membrane.

本発明者らは、上記目的を達成するために鋭意検討を行った結果、予め吸収線量が８００ｋＧｙ〜１２００ｋＧｙの放射線を４０℃以下の温度で照射したフッ素樹脂系フィルムを１００℃以上で加熱処理し、そのフッ素樹脂系フィルムにラジカル反応性モノマーをグラフト重合させて得られる固体高分子電解質膜が、高いプロトン伝導度においてもメタノールクロスオーバー量が抑えられることを見出し、本発明をなすに至った。 As a result of diligent studies to achieve the above object, the present inventors heat-treated a fluororesin film previously irradiated with radiation having an absorbed dose of 800 kGy to 1200 kGy at a temperature of 40 ° C. or lower at 100 ° C. or higher. The present inventors have found that a solid polymer electrolyte membrane obtained by graft polymerization of a radical-reactive monomer to the fluororesin film can suppress the amount of methanol crossover even at high proton conductivity.

従って、本発明は、下記固体高分子型燃料電池用電解質膜及びその製造方法を提供する。
請求項１：
予め吸収線量が８００ｋＧｙ〜１２００ｋＧｙの放射線を４０℃以下の温度で照射することにより架橋を導入したフッ素樹脂系フィルムを１００℃以上で加熱処理した後、更に放射線を照射してイオン伝導性基を含有する又はイオン伝導性基を導入可能な重合性モノマーを前記フッ素樹脂系フィルムにグラフト重合し、イオン伝導性基を導入可能な重合性モノマーをグラフト重合させた場合は引き続きイオン伝導性基を導入することを特徴とする固体高分子型燃料電池用電解質膜の製造方法。
請求項２：
フッ素樹脂系フィルムに吸収線量が８００ｋＧｙ〜１２００ｋＧｙの電子線を照射してこのフッ素樹脂系フィルムに架橋を導入した請求項１記載の製造方法。
請求項３：
フッ素樹脂系フィルムがエチレン−テトラフルオロエチレン共重合フィルムである請求項１又は２記載の製造方法。
請求項４：
請求項１，２又は３記載の製造方法によって得られた固体高分子型燃料電池用電解質膜。
Accordingly, the present invention provides the following electrolyte membrane for a polymer electrolyte fuel cell and a method for producing the same.
Claim 1:
A fluororesin film introduced with crosslinking by irradiation with radiation of 800 kGy to 1200 kGy in advance at a temperature of 40 ° C. or lower is heat-treated at 100 ° C. or higher and further irradiated with radiation to contain an ion conductive group. Or when a polymerizable monomer capable of introducing an ion conductive group is graft-polymerized onto the fluororesin film and a polymerizable monomer capable of introducing an ion conductive group is graft-polymerized, the ion conductive group is subsequently introduced. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell.
Claim 2:
The production method according to claim 1, wherein the fluororesin-based film is irradiated with an electron beam having an absorbed dose of 800 kGy to 1200 kGy to introduce crosslinking into the fluororesin-based film.
Claim 3:
The method according to claim 1 or 2, wherein the fluororesin film is an ethylene-tetrafluoroethylene copolymer film.
Claim 4:
An electrolyte membrane for a polymer electrolyte fuel cell obtained by the production method according to claim 1, 2 or 3.

本発明の固体高分子電解質膜は、高いプロトン伝導度と低メタノールクロスオーバー性を有し、燃料電池用の電解質膜、特にダイレクトメタノール型燃料電池用の電解質膜として好適であり、この固体高分子電解質膜を用いることで、メタノールのクロスオーバー量が抑制でき、非常に高性能の燃料電池を得ることができる。   The solid polymer electrolyte membrane of the present invention has high proton conductivity and low methanol crossover properties, and is suitable as an electrolyte membrane for fuel cells, particularly as an electrolyte membrane for direct methanol fuel cells. By using the electrolyte membrane, the amount of methanol crossover can be suppressed, and a very high performance fuel cell can be obtained.

本発明の固体高分子電解質膜は、予め放射線を照射したフッ素樹脂系フィルムを、１００℃以上で加熱処理した後に、再度電子線を照射し反応性モノマーをグラフト重合させることにより得られるものである。ここで、使用されるフッ素樹脂系フィルムとしては、室温で架橋構造を導入しやすいエチレン−テトラフルオロエチレン共重合樹脂（ＥＴＦＥ）が望ましく使用できる。
上記フッ素樹脂系フィルムに放射線を８００ｋＧｙから１２００ｋＧｙ照射することにより架橋構造を導入することが望ましい。照射線量が８００ｋＧｙ未満では架橋の効果が出現し難く、また、１２００ｋＧｙを超えると、主鎖の切断も多くなり、グラフト後の膜の機械的強度が低下するおそれがある。
放射線を照射する温度は、室温（２０〜４０℃）付近乃至それ以下でよいが、フッ素樹脂系フィルムの融点以下であれば構わない。 The solid polymer electrolyte membrane of the present invention is obtained by subjecting a fluororesin film previously irradiated with radiation to a heat treatment at 100 ° C. or higher, and then irradiating an electron beam again to graft polymerize the reactive monomer. . Here, as the fluororesin film to be used, an ethylene-tetrafluoroethylene copolymer resin (ETFE) which can easily introduce a crosslinked structure at room temperature can be desirably used.
It is desirable to introduce a crosslinked structure by irradiating the fluororesin-based film with radiation from 800 kGy to 1200 kGy. When the irradiation dose is less than 800 kGy, the effect of crosslinking hardly appears, and when it exceeds 1200 kGy, the main chain is frequently cut, and the mechanical strength of the film after grafting may be lowered.
The temperature at which the radiation is applied may be around room temperature (20 to 40 ° C.) or lower, but may be lower than the melting point of the fluororesin film.

本発明においては、上記架橋したフッ素樹脂系フィルムを更に加熱処理することにより、得られる固体高分子電解質膜の特性が向上する。加熱温度は１００℃〜２６０℃が好ましく、特に１００℃〜２００℃が好ましい。加熱温度が１００℃未満であると加熱処理の効果が得られない場合があり、また、２６０℃を超えると基材の融点を超えるためフィルムが変形するおそれがある。なお、加熱時間は適宜選定されるが、通常１〜１０時間特に３〜６時間である。   In the present invention, the properties of the obtained solid polymer electrolyte membrane are improved by further heat-treating the crosslinked fluororesin film. The heating temperature is preferably 100 ° C to 260 ° C, particularly preferably 100 ° C to 200 ° C. If the heating temperature is less than 100 ° C., the effect of the heat treatment may not be obtained. If the heating temperature exceeds 260 ° C., the melting point of the substrate may be exceeded, and the film may be deformed. The heating time is appropriately selected, but is usually 1 to 10 hours, particularly 3 to 6 hours.

上記放射線を照射し加熱処理したフッ素樹脂系フィルムに、イオン交換基（イオン伝導性基）、もしくはイオン交換基が導入可能なラジカル反応性モノマー（重合性モノマー）を放射線の照射によりグラフト重合させることにより、固体高分子電解質膜を得ることができる。放射線グラフト重合は、フッ素樹脂系フィルムに放射線を照射することでラジカルを生成し、そこをグラフト点としてラジカル反応性モノマーをグラフトする方法であるが、この場合、放射線を用いるグラフト法には、フッ素樹脂系フィルムの主鎖に予め放射線を照射して、グラフトの起点となるラジカルを生成させた後、フッ素樹脂系フィルムをモノマーと接触させてグラフト反応を行う前照射法と、モノマーとフッ素樹脂系フィルムの共存下に放射線を照射する同時照射法とがあるが、本発明においては、いずれの方法をも採用できる。   Graft-polymerizing an ion-exchange group (ion-conductive group) or a radical-reactive monomer (polymerizable monomer) into which an ion-exchange group can be introduced into the fluororesin-based film that has been irradiated with radiation and heat-treated. Thus, a solid polymer electrolyte membrane can be obtained. Radiation graft polymerization is a method in which a radical is generated by irradiating a fluororesin film with radiation, and a radical reactive monomer is grafted using this as a grafting point. In this case, the grafting method using radiation includes fluorine. Radiation is applied to the main chain of the resin-based film in advance to generate radicals that will be the starting point of grafting, and then the pre-irradiation method in which the fluororesin-based film is brought into contact with the monomer to perform the graft reaction, and the monomer and fluororesin system Although there is a simultaneous irradiation method in which radiation is irradiated in the presence of a film, any method can be adopted in the present invention.

なお、この場合、フッ素樹脂系フィルムの膜厚は特に限定されないが、１０〜１００μｍ、特に１０〜５０μｍであることが好ましい。   In this case, the film thickness of the fluororesin film is not particularly limited, but is preferably 10 to 100 μm, particularly preferably 10 to 50 μm.

本発明でフッ素樹脂系フィルムにラジカル反応性モノマーをグラフト重合させるために照射する放射線としては、γ線、Ｘ線、電子線、イオンビーム、紫外線などが例示されるが、ラジカル生成の容易さからγ線、電子線が好ましい。
放射線の吸収線量としては、１ｋＧｙ以上、特に１〜１００ｋＧｙ、とりわけ１〜５０ｋＧｙとすることが好ましく、１ｋＧｙ未満ではラジカル生成量が少なく、グラフトし難くなる場合があり、１００ｋＧｙを超えるとグラフト率が大きくなりすぎて得られる電解質膜の機械的強度が低下する場合がある。
更に、放射線の照射は、ヘリウム、窒素、アルゴンガスなどの不活性ガス雰囲気中で行うのが好ましく、該ガス中の酸素濃度は１００ｐｐｍ以下、より好ましくは５０ｐｐｍ以下が好ましいが、必ずしも酸素不在下で行う必要はない。 Examples of the radiation to be irradiated for graft polymerization of the radical reactive monomer on the fluororesin film in the present invention include γ-rays, X-rays, electron beams, ion beams, ultraviolet rays and the like. Gamma rays and electron beams are preferred.
The absorbed dose of radiation is preferably 1 kGy or more, particularly preferably 1 to 100 kGy, particularly preferably 1 to 50 kGy, and if it is less than 1 kGy, the amount of radical generation may be small and grafting may be difficult, and if it exceeds 100 kGy, the graft rate increases. The mechanical strength of the electrolyte membrane obtained by becoming too small may be reduced.
Further, the irradiation with radiation is preferably performed in an inert gas atmosphere such as helium, nitrogen, and argon gas, and the oxygen concentration in the gas is preferably 100 ppm or less, more preferably 50 ppm or less, but it is not necessarily in the absence of oxygen. There is no need to do it.

本発明の固体高分子電解質膜においては、架橋フッ素樹脂系フィルムに放射線を照射してグラフト重合させるラジカル反応性モノマーとして、スチレン又はその誘導体があげられる。
スチレン又はその誘導体としては、スチレン、α−メチルスチレン、スチレンスルホン酸ナトリウム、トリフルオロスチレン等の置換されたスチレン誘導体などをあげることができる。
更に、耐酸化性向上を目的として、上記スチレン等のラジカル反応性モノマーと、１分子中にラジカル重合性基を２個以上有する架橋剤を、上記スチレン等のラジカル反応性モノマー量に対し０．１〜５ｍｏｌ％の架橋剤と共グラフト重合させることによりグラフト鎖中に架橋構造を導入することができる。
ここで、放射線を照射し加熱処理したフッ素樹脂系フィルムにグラフトするラジカル反応性モノマーの使用量は、フッ素樹脂系フィルム１００質量部に対してラジカル反応性モノマーを１００〜１０，０００質量部、特に４００〜２，０００質量部使用することが好ましい。ラジカル反応性モノマーが少なすぎるとフッ素樹脂系フィルムとの接触が不十分となる場合があり、多すぎるとラジカル反応性モノマーが効率的に使用できなくなるおそれがある。また、フッ素樹脂系フィルムにラジカル反応性モノマーをグラフト重合するに際しては、アゾビスイソブチロニトリル等の開始剤を本発明の目的を損なわない範囲で適宜用いてもよい。 In the solid polymer electrolyte membrane of the present invention, styrene or a derivative thereof can be cited as a radical reactive monomer that undergoes graft polymerization by irradiating a crosslinked fluororesin film with radiation.
Examples of styrene or derivatives thereof include substituted styrene derivatives such as styrene, α-methylstyrene, sodium styrenesulfonate, and trifluorostyrene.
Furthermore, for the purpose of improving oxidation resistance, a radical reactive monomer such as styrene and a cross-linking agent having two or more radical polymerizable groups in one molecule are added to the amount of the radical reactive monomer such as styrene. A cross-linked structure can be introduced into the graft chain by co-grafting with 1 to 5 mol% of a cross-linking agent.
Here, the amount of the radical reactive monomer grafted onto the fluororesin film that has been irradiated with radiation and heat-treated is 100 to 10,000 parts by mass of the radical reactive monomer with respect to 100 parts by mass of the fluororesin film. It is preferable to use 400 to 2,000 parts by mass. If the amount of the radical reactive monomer is too small, the contact with the fluororesin film 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 film, an initiator such as azobisisobutyronitrile may be appropriately used as long as the object of the present invention is not impaired.

更に、本発明においては、グラフト反応時に溶媒を用いることができる。溶媒としては、反応性モノマーを均一に溶解するものが好ましく、例えばアセトン、メチルエチルケトン等のケトン類、酢酸エチル、酢酸ブチル等のエステル類、メチルアルコール、エチルアルコール、プロピルアルコール、ブチルアルコール等のアルコール類、テトラヒドロフラン、ジオキサン等のエーテル類、Ｎ，Ｎ−ジメチルホルムアミド、Ｎ，Ｎ−ジメチルアセトアミド、ベンゼン、トルエン等の芳香族炭化水素、ｎ−ヘプタン、ｎ−へキサン、シクロヘキサン等の脂肪族又は脂環族炭化水素、あるいはこれらの混合溶媒を用いることができる。
また、本発明においてグラフト重合を行う際は、窒素、アルゴンなどの不活性ガス雰囲気中が望ましく、酸素濃度は５ｖｏｌ％以下が好ましい。
上記グラフト重合の反応条件としては、０〜１００℃、特に４０〜８０℃の温度で、１〜４０時間、特に４〜２０時間反応させることが好ましい。 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, the graft polymerization is preferably performed in an inert gas atmosphere such as nitrogen or argon, and the oxygen concentration is preferably 5 vol% or less.
The reaction conditions for the graft polymerization are preferably 0 to 100 ° C., particularly 40 to 80 ° C., for 1 to 40 hours, particularly 4 to 20 hours.

上述したように、放射線を照射した架橋フッ素樹脂系フィルムにラジカル反応性モノマーをグラフト重合させた後、該ラジカル反応性モノマーがイオン伝導性基を導入可能な重合性モノマーである場合、イオン伝導性基を導入する。イオン伝導性基としては、スルホン酸基等が挙げられ、スルホン酸基を導入するためのスルホン化は公知の方法によって行うことができ、例えばクロロスルホン酸−ジクロロエタン中に浸漬することによってクロロスルホン酸基を導入し、その後純水中に浸漬させ加水分解することによりスルホン化させる等の方法を採用し得る。   As described above, when a radical-reactive monomer is graft-polymerized on a cross-linked fluororesin film irradiated with radiation, and the radical-reactive monomer is a polymerizable monomer capable of introducing an ion-conductive group, Introduce a group. Examples of the ion conductive group include a sulfonic acid group and the like. Sulfonation for introducing the sulfonic acid group can be performed by a known method. For example, chlorosulfonic acid is immersed in chlorosulfonic acid-dichloroethane. A method of introducing a group and then sulfonating it by immersion in pure water and hydrolysis can be employed.

このようにして得られた固体高分子電解質膜は、燃料電池用として用いられる。
本発明の燃料電池は、燃料極と空気極の間に上記固体高分子電解質膜が設けられているものであり、固体高分子電解質膜の両面に触媒層・燃料拡散層およびセパレータを配置することでメタノールのクロスオーバーが少ない燃料電池を製造することが可能になったものである。なお、燃料極、空気極の構成、材質、燃料電池の構成は公知のものとすることができる。 The solid polymer electrolyte membrane thus obtained is used for a fuel cell.
In the fuel cell of the present invention, the solid polymer electrolyte membrane is provided between a fuel electrode and an air electrode, and a catalyst layer, a fuel diffusion layer, and a separator are disposed on both sides of the solid polymer electrolyte membrane. Thus, it is possible to manufacture a fuel cell with less methanol crossover. Note that the configurations and materials of the fuel electrode and the air electrode and the configuration of the fuel cell can be known.

以下、実施例及び比較例を示して本発明を具体的に説明するが、本発明は下記実施例に制限されるものではない。なお、以下の例において配合量はいずれも質量部である。また、各測定値は以下の測定により求めた。   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 addition, in the following examples, all compounding amounts are parts by mass. Moreover, each measured value was calculated | required by the following measurements.

（１）グラフト率
グラフト前後の膜の質量変化から、次式よりグラフト率を求めた。
グラフト率 ＝｛（グラフト後フィルム質量−グラフト前フィルム質量）／グラフト前フ
ィルム質量｝×１００（％）
（２）プロトン伝導度
インピーダンスアナライザ（ソーラトロン社製１２６０）を使用し、４端子交流インピーダンス法により室温で短冊状サンプル（幅１ｃｍ）の長手方向の膜抵抗を測定して求めた。
（３）メタノール透過係数
１０ｍｏｌ／Ｌメタノール水と純水を電解質膜で隔離し、室温でメタノール水側から電解質膜を透過して純水側に出てきたメタノール量をガスクロマトグラフィーで定量して求めた。 (1) Graft rate From the mass change of the membrane before and after grafting, the graft rate was determined from the following formula.
Graft ratio = {(film weight after grafting−film weight before grafting) / film before grafting
Film mass} × 100 (%)
(2) Proton conductivity Using an impedance analyzer (Solartron 1260), the membrane resistance in the longitudinal direction of the strip-shaped sample (width 1 cm) was measured at room temperature by a four-terminal AC impedance method.
(3) Methanol Permeability Coefficient 10 mol / L Methanol water and pure water are separated by an electrolyte membrane, and the amount of methanol that permeates the electrolyte membrane from the methanol water side at room temperature and exits to the pure water side is determined by gas chromatography. Asked.

［実施例１］
ＥＴＦＥフィルム（厚さ２５μｍ、６×５ｃｍ角、質量０．１３ｇ）に、低電圧電子線（ＥＢ）照射装置（岩崎電気社製ライトビームＬ）により窒素雰囲気中室温で電子線を１０００ｋＧｙ照射した。そのＥＴＦＥフィルムを１５０℃にて６時間真空加熱処理を行い、その後室温まで冷却した。再度窒素雰囲気中室温で電子線を１０ｋＧｙ照射してラジカルを生成させた後、予め窒素によるバブリングにより酸素を除去したスチレン１０部、トルエン１０部、アゾビスイソブチロニトリル０．００１部が仕込んである溶液中にフィルムを浸漬させ、６０℃で１６時間加熱し、グラフト重合した結果、グラフト率は４３．７％であった。
上記グラフト重合したフィルムを０．２ｍｏｌ％クロロスルホン酸／ジクロロエタン混合液に浸漬し、５０℃で６時間加熱後、純水中に６０℃一晩浸漬し、加水分解することで、スルホン酸基を含有する固体高分子電解質膜を得た。得られた固体高分子電解質膜の室温におけるプロトン伝導度を測定した結果、０．１０Ｓ／ｃｍであった。また、メタノール透過係数は０．８７×１０-7ｍ2／ｈであった。得られた固体高分子電解質膜の特性結果を表１に示す。 [Example 1]
An ETFE film (thickness 25 μm, 6 × 5 cm square, mass 0.13 g) was irradiated with an electron beam of 1000 kGy at room temperature in a nitrogen atmosphere with a low voltage electron beam (EB) irradiation device (Light Beam L manufactured by Iwasaki Electric Co., Ltd.). The ETFE film was vacuum-heated at 150 ° C. for 6 hours, and then cooled to room temperature. After irradiation of 10 kGy with an electron beam at room temperature in a nitrogen atmosphere again to generate radicals, 10 parts of styrene, 10 parts of toluene, and 0.001 part of azobisisobutyronitrile, from which oxygen was previously removed by bubbling with nitrogen, were charged. The film was immersed in a solution, heated at 60 ° C. for 16 hours, and subjected to graft polymerization. As a result, the graft ratio was 43.7%.
The graft-polymerized film is immersed in a 0.2 mol% chlorosulfonic acid / dichloroethane mixed solution, heated at 50 ° C. for 6 hours, then immersed in pure water at 60 ° C. overnight, and hydrolyzed to remove sulfonic acid groups. The contained solid polymer electrolyte membrane was obtained. The proton conductivity at room temperature of the obtained solid polymer electrolyte membrane was measured and found to be 0.10 S / cm. The methanol permeability coefficient was 0.87 × 10 −7 m 2 / h. The characteristic results of the obtained solid polymer electrolyte membrane are shown in Table 1.

［比較例１］
ＥＴＦＥフィルムに電子線を１０００ｋＧｙ照射した後、室温で７日間放置したＥＴＦＥフィルムにグラフト重合した以外は実施例１と同様の操作を行った。グラフト率は３７．９％、プロトン伝導度は０．１０Ｓ／ｃｍ、メタノール透過係数は１．６６×１０-7ｍ2／ｈであった。 [Comparative Example 1]
The same operation as in Example 1 was performed except that the ETFE film was irradiated with an electron beam of 1000 kGy and then grafted onto an ETFE film which had been left at room temperature for 7 days. The graft ratio was 37.9%, the proton conductivity was 0.10 S / cm, and the methanol permeability coefficient was 1.66 × 10 −7 m 2 / h.

［比較例２］
電子線を照射せずに１５０℃にて６時間加熱処理を行ったＥＴＦＥフィルムにグラフト重合した以外は実施例１と同様の操作を行った。グラフト率は４３．０％、プロトン伝導度は０．１４Ｓ／ｃｍ、メタノール透過係数は２．２９×１０-7ｍ2／ｈであった。 [Comparative Example 2]
The same operation as in Example 1 was performed except that graft polymerization was performed on an ETFE film that had been heat-treated at 150 ° C. for 6 hours without irradiation with an electron beam. The graft ratio was 43.0%, the proton conductivity was 0.14 S / cm, and the methanol permeability coefficient was 2.29 × 10 −7 m 2 / h.

［比較例３］
電子線照射及び加熱処理をしていないＥＴＦＥフィルムを使用した以外は実施例１と同様の操作を行った。グラフト率は４２．９％、プロトン伝導度は０．１６Ｓ／ｃｍ、メタノール透過係数は２．３５×１０-7ｍ2／ｈであった。 [Comparative Example 3]
The same operation as in Example 1 was performed except that an ETFE film not subjected to electron beam irradiation and heat treatment was used. The graft ratio was 42.9%, the proton conductivity was 0.16 S / cm, and the methanol permeability coefficient was 2.35 × 10 −7 m 2 / h.

［比較例４］
市販のＮａｆｉｏｎ１１２（デュポン社登録商標）膜のプロトン伝導度とメタノール透過係数を測定した。プロトン伝導度は０．０９Ｓ／ｃｍ、メタノール透過係数は４．９８×１０-7ｍ2／ｈであった。
以上の結果を表１に示す。 [Comparative Example 4]
The proton conductivity and methanol permeability coefficient of a commercially available Nafion 112 (DuPont registered trademark) membrane were measured. The proton conductivity was 0.09 S / cm, and the methanol permeability coefficient was 4.98 × 10 −7 m 2 / h.
The results are shown in Table 1.

Figure 0005158309
Figure 0005158309

Claims (4)

予め吸収線量が８００ｋＧｙ〜１２００ｋＧｙの放射線を４０℃以下の温度で照射することにより架橋を導入したフッ素樹脂系フィルムを１００℃以上で加熱処理した後、更に放射線を照射してイオン伝導性基を含有する又はイオン伝導性基を導入可能な重合性モノマーを前記フッ素樹脂系フィルムにグラフト重合し、イオン伝導性基を導入可能な重合性モノマーをグラフト重合させた場合は引き続きイオン伝導性基を導入することを特徴とする固体高分子型燃料電池用電解質膜の製造方法。 A fluororesin film introduced with crosslinking by irradiation with radiation of 800 kGy to 1200 kGy in advance at a temperature of 40 ° C. or lower is heat-treated at 100 ° C. or higher and further irradiated with radiation to contain an ion conductive group. Or when a polymerizable monomer capable of introducing an ion conductive group is graft-polymerized onto the fluororesin film and a polymerizable monomer capable of introducing an ion conductive group is graft-polymerized, the ion conductive group is subsequently introduced. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell. フッ素樹脂系フィルムに吸収線量が８００ｋＧｙ〜１２００ｋＧｙの電子線を照射してこのフッ素樹脂系フィルムに架橋を導入した請求項１記載の製造方法。   The production method according to claim 1, wherein the fluororesin-based film is irradiated with an electron beam having an absorbed dose of 800 kGy to 1200 kGy to introduce crosslinking into the fluororesin-based film. フッ素樹脂系フィルムがエチレン−テトラフルオロエチレン共重合フィルムである請求項１又は２記載の製造方法。   The method according to claim 1 or 2, wherein the fluororesin film is an ethylene-tetrafluoroethylene copolymer film. 請求項１，２又は３記載の製造方法によって得られた固体高分子型燃料電池用電解質膜。   An electrolyte membrane for a polymer electrolyte fuel cell obtained by the production method according to claim 1, 2 or 3.
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