JP4434666B2 - Method for producing solid polymer electrolyte membrane and fuel cell - Google Patents

Method for producing solid polymer electrolyte membrane and fuel cell Download PDF

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JP4434666B2
JP4434666B2 JP2003305837A JP2003305837A JP4434666B2 JP 4434666 B2 JP4434666 B2 JP 4434666B2 JP 2003305837 A JP2003305837 A JP 2003305837A JP 2003305837 A JP2003305837 A JP 2003305837A JP 4434666 B2 JP4434666 B2 JP 4434666B2
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electrolyte membrane
polymer electrolyte
solid polymer
fluororesin
fuel cell
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JP2005078871A (en
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敏夫 大庭
敦雄 川田
紀文 高橋
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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
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Description

本発明は、固体高分子電解質膜の製造方法、及びこれにより得られる電解質膜を用いた燃料電池に関する。   The present invention relates to a method for producing a solid polymer electrolyte membrane, and a fuel cell using the electrolyte membrane obtained thereby.

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 is not very practical 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.

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 the electrolyte membrane. There is a problem that the crossover phenomenon occurs and the output decreases.
Further, since the fluororesin-based electrolyte membrane starts from the synthesis of the monomer, there are problems in that the number of manufacturing steps is increased and the cost is increased, which is a great obstacle when put to 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、特開２００１−３４８４３９号公報（特許文献１）、特開２００２−３１３３６４号公報（特許文献２）、特開２００３−８２１２９号公報（特許文献３）で提案されている。   For this reason, efforts have been made to develop low-cost electrolyte membranes that replace the “Nafion” and the like. JP-A-2001-348439 (Patent Document 1), JP-A-2002-313364 discloses a method of producing a solid polymer electrolyte membrane by introducing a sulfone group into a fluororesin-based membrane by a radiation graft polymerization method. (Patent Document 2) and JP-A-2003-82129 (Patent Document 3).

しかし、これらの放射線グラフト重合において、高グラフト率のものを得るには、スチレンなどのグラフト原料であるラジカル反応性モノマーの単独重合と見られるゲル状物がフッ素系樹脂表面や反応容器に付着するため、生産性が著しく低いという問題があった。ゲル状物の生成を防止する目的で、安定剤やラジカル禁止剤、連鎖移動剤などを併用した場合、ゲル化は抑制できるものの、グラフト率が低く、所望のイオン交換容量を有する固体高分子電解質膜を得ることが困難であった。すなわち、生産性と固体高分子電解質膜の特性を同時に満足する製造方法は確立できていなかった。   However, in these radiation graft polymerizations, in order to obtain a high graft ratio, a gel-like material that appears to be a homopolymerization of a radical reactive monomer that is a graft material such as styrene adheres to the surface of the fluororesin or the reaction vessel Therefore, there is a problem that productivity is remarkably low. When a stabilizer, radical inhibitor, chain transfer agent or the like is used in combination for the purpose of preventing the formation of a gel, gelation can be suppressed, but the graft ratio is low and the solid polymer electrolyte has a desired ion exchange capacity It was difficult to obtain a film. That is, a production method that satisfies the productivity and the characteristics of the solid polymer electrolyte membrane at the same time has not been established.

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

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る生産性と特性を同時に満足する固体高分子電解質膜の製造方法、及びその電解質膜を用いた燃料電池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 an object thereof is to provide a method for producing a solid polymer electrolyte membrane that simultaneously satisfies the productivity and characteristics of the radiation graft polymerization method, and a fuel cell using the electrolyte membrane. And

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、放射線グラフト重合法による固体高分子電解質膜の製造において、放射線を照射したフッ素系樹脂にラジカル反応性モノマーをグラフト重合する際、雰囲気ガス中の酸素濃度を特定の濃度にコントロールすることで、グラフト原料がゲル化せず、グラフト率が高くなり、生産性と特性を同時に満足し得ることを見出し、本発明をなすに至った。   As a result of intensive studies to achieve the above object, the present inventors grafted a radical-reactive monomer onto a fluorine-based resin irradiated with radiation in the production of a solid polymer electrolyte membrane by a radiation graft polymerization method. In this case, by controlling the oxygen concentration in the atmospheric gas to a specific concentration, the graft raw material is not gelled, the graft rate is increased, and the productivity and characteristics can be satisfied at the same time, and the present invention is made. It came.

従って、本発明は、下記の固体高分子電解質膜の製造方法、及び燃料電池を提供する。
〔請求項１〕 放射線を照射したフッ素系樹脂に、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、ジビニルベンゼンから選ばれるラジカル反応性モノマーをグラフト重合させ、更にスチレン、α−メチルスチレン、トリフルオロスチレン、ジビニルベンゼンから選ばれるラジカル反応性モノマーをグラフト重合させた場合はスルホン化させて固体高分子電解質膜を製造する方法であって、前記グラフト重合を酸素濃度０．０５〜５体積％の酸素を含む不活性ガス雰囲気下で行うことを特徴とする固体高分子電解質膜の製造方法。
〔請求項２〕 前記フッ素系樹脂が、テトラフルオロエチレン系重合体、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル系共重合体、及びテトラフルオロエチレン−ヘキサフルオロプロピレン系共重合体から選ばれる少なくとも１種である請求項１記載の固体高分子電解質膜の製造方法。
〔請求項３〕 請求項１又は２記載の製造方法で製造された固体高分子電解質膜が、燃料極と空気極の間に設けられていることを特徴とする燃料電池。
Accordingly, the present invention provides the following method for producing a solid polymer electrolyte membrane and a fuel cell.
[Claim 1] Radiation-reactive monomers selected from styrene, α-methylstyrene, sodium styrenesulfonate, trifluorostyrene, and divinylbenzene are graft-polymerized to a fluororesin irradiated with radiation, and further styrene, α-methyl When a radical reactive monomer selected from styrene, trifluorostyrene, and divinylbenzene is graft-polymerized, the polymer is sulfonated to produce a solid polymer electrolyte membrane, and the graft polymerization is performed at an oxygen concentration of 0.05 to 5 A method for producing a solid polymer electrolyte membrane, which is performed in an inert gas atmosphere containing volume% oxygen.
[Claim 2] The fluororesin is at least one selected from a tetrafluoroethylene polymer, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and a tetrafluoroethylene-hexafluoropropylene copolymer. The method for producing a solid polymer electrolyte membrane according to claim 1.
[Claim 3] A fuel cell, characterized in that the solid polymer electrolyte membrane produced by the production method according to claim 1 or 2 is provided between a fuel electrode and an air electrode.

本発明の製造方法によれば、グラフト原料がゲル化せず、グラフト率の高い固体高分子電解質膜が得られる。本発明の方法により製造された固体高分子電解質膜は、高いイオン伝導度を示し、かつメタノールに対する膨潤が少ないため、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適している。   According to the production method of the present invention, a solid polymer electrolyte membrane having a high graft rate can be obtained without the graft raw material being gelled. The solid polymer electrolyte membrane produced by the method of the present invention exhibits high ionic conductivity and is less swelled with methanol. Therefore, it is suitable as an electrolyte membrane for fuel cells, particularly as an electrolyte membrane for direct methanol fuel cells. Yes.

本発明の固体電解質膜の製造方法は、フッ素系樹脂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り、該グラフト重合時の雰囲気ガス中に酸素を０．０５〜５体積％の濃度で含有することを特徴とするものである。   The method for producing a solid electrolyte membrane of the present invention is a method in which a radical is generated by irradiating a fluororesin with radiation, and a radical-reactive monomer is grafted using the radical as a grafting point. In the atmosphere gas during the graft polymerization, In which oxygen is contained at a concentration of 0.05 to 5% by volume.

本発明で使用されるフッ素系樹脂としては、ポリテトラフルオロエチレン（ＰＴＦＥ）、４フッ化エチレン−６フッ化プロピレン共重合体（ＦＥＰ）、４フッ化エチレン−パーフロロアルキルビニルエーテル共重合体（ＰＦＡ）、エチレン−４フッ化エチレン共重合体（ＥＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）などが例示されるが、耐熱性からＰＴＦＥ、ＦＥＰ、ＰＦＡが望ましい。これらは、１種を単独で又は２種以上を併用することができる。   Examples of the fluororesin used in the present invention include polytetrafluoroethylene (PTFE), tetrafluoroethylene-6 fluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). ), Ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), etc., but PTFE, FEP, and PFA are desirable from the viewpoint of heat resistance. These can be used alone or in combination of two or more.

フッ素系樹脂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。ラジカル生成の容易さからγ線、電子線が好ましい。   Examples of the radiation applied to the fluororesin include γ rays, X rays, electron beams, ion beams, and ultraviolet rays. Gamma rays and electron beams are preferred because of the ease of radical generation.

フッ素系樹脂に照射する放射線の吸収線量は、５ｋＧｙ以上であることが望ましい。５ｋＧｙ未満であると、ラジカル生成量が少なく、グラフトし難くなるおそれがある。また、１００ｋＧｙを超えるとフッ素系樹脂の伸び、強度などの機械特性が低下するおそれがあるため、より望ましい吸収線量は５〜１００ｋＧｙ、更に望ましい吸収線量は１０〜５０ｋＧｙである。   The absorbed dose of radiation applied to the fluororesin is preferably 5 kGy or more. If it is less than 5 kGy, the amount of radical generation is small, and grafting may be difficult. Moreover, since there exists a possibility that mechanical characteristics, such as elongation and intensity | strength of fluororesin, may fall when it exceeds 100 kGy, a more desirable absorbed dose is 5-100 kGy, and a more desirable absorbed dose is 10-50 kGy.

放射線を照射する際の温度は室温付近でよいが、予めフッ素系樹脂の融点以上の温度で放射線を照射した後に、室温付近、好ましくは２０〜４０℃で放射線を再度照射することが、フッ素系樹脂の放射線照射による機械特性低下を防止するために望ましい。
なお、この場合の放射線の吸収線量としては、フッ素系樹脂の融点以上での照射を５ｋＧｙ以上、特に１０〜１００ｋＧｙとすることが好ましく、また室温付近での照射を５ｋＧｙ以上、特に１０〜５０ｋＧｙとすることが好ましい。 Although the temperature at the time of irradiation may be near room temperature, after irradiation with radiation at a temperature higher than the melting point of the fluororesin in advance, irradiation with radiation again at about room temperature, preferably 20 to 40 ° C. It is desirable to prevent deterioration of mechanical properties due to irradiation of resin.
In this case, the absorbed dose of radiation is preferably 5 kGy or more, particularly 10 to 100 kGy for irradiation at the melting point or more of the fluororesin, and 5 kGy or more, particularly 10 to 50 kGy for irradiation near room temperature. It is preferable to do.

また、この放射線の照射雰囲気としては、窒素、ヘリウム、アルゴンなどの不活性ガス雰囲気が好ましく、該ガス中の酸素濃度は５００ｐｐｍ以下が好ましく、２００ｐｐｍ以下が更に好ましい。   The irradiation atmosphere is preferably an inert gas atmosphere such as nitrogen, helium, or argon, and the oxygen concentration in the gas is preferably 500 ppm or less, and more preferably 200 ppm or less.

上記放射線を照射したフッ素系樹脂にグラフトするラジカル反応性モノマーとしては、例えば、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、ジビニルベンゼンなどが例示される。   Examples of the radical reactive monomer that is grafted onto the fluororesin irradiated with the radiation include styrene, α-methylstyrene, sodium styrenesulfonate, trifluorostyrene, divinylbenzene, and the like.

放射線を照射したフッ素系樹脂にグラフトするラジカル反応性モノマーの使用量は、フッ素系樹脂１００質量部に対してラジカル反応性モノマーを１，０００〜１００，０００質量部、特に４，０００〜２０，０００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。   The amount of the radical reactive monomer grafted onto the fluororesin irradiated with radiation is 1,000 to 100,000 parts by mass, particularly 4,000 to 20,000 parts of the radical reactive monomer with respect to 100 parts by mass of the fluororesin. It is preferable to use 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.

上記フッ素系樹脂に上記ラジカル反応性モノマーをグラフト重合するに際し、アゾビスイソブチルニトリルなどの開始剤、トルエン、キシレン、ヘキサン、ヘプタンなどの有機溶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。   When the radical reactive monomer is graft-polymerized to the fluororesin, an initiator such as azobisisobutylnitrile, or an organic solvent such as toluene, xylene, hexane, or heptane may be appropriately used as long as the object of the present invention is not impaired. Good.

ここで、本発明においては、グラフト重合を行う際の反応雰囲気中の酸素濃度を０．０５〜５％（体積％、以下同様。）に調整することが必要である。反応雰囲気中の酸素は、系内のラジカルと反応し、カルボニルラジカルやパーオキシラジカルとなり、それ以上の反応を抑制する作用を果たしていると考えられる。酸素濃度が０．０５％未満であるとラジカル重合性モノマーが単独重合し、溶剤に不溶のゲルが生成するため、原料が無駄になるとともに、ゲルの除去にも時間がかかり、酸素濃度が５％を超えるとグラフト率が低下する。望ましい酸素濃度は０．１〜３％であり、更に望ましい酸素濃度は０．１〜１％である。なお、酸素以外のガスとしては、窒素、アルゴンなどの不活性ガスが使用される。   Here, in the present invention, it is necessary 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 radical polymerizable monomer is homopolymerized and a gel insoluble in the solvent is generated. Therefore, the raw materials are wasted and it takes time to remove the gel. If it exceeds%, the graft ratio decreases. 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.

なお、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時間の反応時間とすることが好ましい。   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.

上述したように、放射線を照射したフッ素系樹脂にラジカル反応性モノマーをグラフト重合させ、更に必要に応じてスルホン化させることにより、固体高分子電解質膜を得ることができる。   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.

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、この固体高分子電解質膜の両面に触媒層・燃料拡散層及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ない燃料電池を製造することができる。   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, a fuel cell free from methanol crossover can be produced.

以下、実施例及び比較例を示し、本発明を具体的に説明するが、本発明は下記の実施例に制限されるものではない。   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.

［実施例１］
ポリテトラフルオロエチレンフイルム（５ｃｍ角、厚さ５０μｍ、質量０．２５ｇ）に、３４０℃の窒素雰囲気下、60Ｃｏ−γ線を線量率７ｋＧｙ／ｈで、吸収線量３０ｋＧｙ照射した。このγ線を照射したフイルムに、更に２５℃の窒素雰囲気下、電子線を吸収線量３０ｋＧｙで照射した。このフイルムを、スチレン４０質量部、ジビニルベンゼン２質量部、ｎ−ヘキサン４０質量部、アゾビスイソブチルニトリル０．０１質量部が仕込まれた５００ｃｃのセパラブルフラスコに入れ、酸素を０．１体積％含む窒素を１００ｃｃ／分通気しながら６０℃で１６時間加熱し、グラフト重合したところ、フラスコ内にゲルの生成は認められなかった。また、下記の式より算出したグラフト率は３５％であった。
グラフト率＝（グラフト後フイルム重量−グラフト前フイルム重量）／グラフト前
フイルム重量×１００（％）
なお、グラフト後フイルム重量は、グラフト後のフイルムをアセトンで３回洗浄し、６０℃で２時間真空乾燥させた後の重量とした。 [Example 1]
Polytetrafluoroethylene film (5 cm square, thickness 50 μm, mass 0.25 g) was irradiated with 60 Co-γ rays at a dose rate of 7 kGy / h and an absorbed dose of 30 kGy in a nitrogen atmosphere at 340 ° C. The film irradiated with γ rays was further irradiated with an electron beam at an absorbed dose of 30 kGy in a nitrogen atmosphere at 25 ° C. This film was put into a 500 cc separable flask charged with 40 parts by mass of styrene, 2 parts by mass of divinylbenzene, 40 parts by mass of n-hexane and 0.01 parts by mass of azobisisobutylnitrile, and 0.1% by volume of oxygen. When the nitrogen containing was heated at 60 ° C. for 16 hours while venting 100 cc / min and graft polymerization was carried out, no gel was formed in the flask. The graft ratio calculated from the following formula was 35%.
Graft rate = (film weight after grafting−film weight before grafting) / before grafting
Film weight x 100 (%)
The weight of the film after grafting was the weight after the film after grafting was washed three times with acetone and vacuum-dried at 60 ° C. for 2 hours.

上記フイルムをクロロスルホン酸３０質量部と１，２−ジクロロエタン７０質量部の混合液に浸漬し、５０℃で２時間加熱後、９０℃の１Ｎ苛性カリ水溶液中に１時間浸漬することで加水分解し、続いて９０℃の２Ｎ塩酸に１時間浸漬後、純水で３回洗浄し、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純水中に１時間浸漬後の表面のイオン伝導度は０．１Ｓ／ｃｍであり、固体高分子電解質膜をメタノールに２５℃、１６時間浸漬後の膨潤度は４％であった。 The above film is immersed in a mixed solution of 30 parts by mass of chlorosulfonic acid and 70 parts by mass of 1,2-dichloroethane, heated at 50 ° C. for 2 hours, and then hydrolyzed by being immersed in a 1N caustic potash aqueous solution at 90 ° C. for 1 hour. Subsequently, after being immersed in 2N hydrochloric acid at 90 ° C. for 1 hour, it was washed with pure water three times to obtain a solid polymer electrolyte membrane containing sulfonic acid groups.
The ionic conductivity of the surface of the obtained solid polymer electrolyte membrane after immersion in pure water for 1 hour is 0.1 S / cm, and the degree of swelling after immersion of the solid polymer electrolyte membrane in methanol at 25 ° C. for 16 hours Was 4%.

［比較例１］
グラフト重合時に、酸素を実質的に含まない窒素（酸素濃度０．０１体積％以下）を通気した以外は実施例１と同様にした結果、液の粘度上昇が著しく、ＰＴＦＥフイルム表面、及びセパラブルフラスコ表面に水あめ状のゲルが付着していた。 [Comparative Example 1]
As in Example 1, except that nitrogen (oxygen concentration 0.01 vol% or less) containing substantially no oxygen was passed during graft polymerization, the viscosity of the liquid was remarkably increased, and the PTFE film surface and separable A starchy gel was attached to the flask surface.

［比較例２］
グラフト重合時に、空気と窒素を１／１の比率で混合したものを通気した以外は実施例１と同様にした結果、ゲルの発生はなかったが、グラフト率は６％と低かった。 [Comparative Example 2]
At the time of graft polymerization, the same procedure as in Example 1 was conducted except that a mixture of air and nitrogen at a ratio of 1/1 was aerated. As a result, no gel was generated, but the graft ratio was as low as 6%.

［比較例３］
ナフィオン１１２（デュポン社製商品名）について、実施例１と同様にイオン伝導度及びメタノール膨潤度を測定したところ、イオン伝導度は０．１Ｓ／ｃｍ、メタノール膨潤度は６０％であった。 [Comparative Example 3]
For Nafion 112 (trade name, manufactured by DuPont), the ionic conductivity and the methanol swelling degree were measured in the same manner as in Example 1. The ionic conductivity was 0.1 S / cm, and the methanol swelling degree was 60%.

Claims (3)

放射線を照射したフッ素系樹脂に、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、ジビニルベンゼンから選ばれるラジカル反応性モノマーをグラフト重合させ、更にスチレン、α−メチルスチレン、トリフルオロスチレン、ジビニルベンゼンから選ばれるラジカル反応性モノマーをグラフト重合させた場合はスルホン化させて固体高分子電解質膜を製造する方法であって、前記グラフト重合を酸素濃度０．０５〜５体積％の酸素を含む不活性ガス雰囲気下で行うことを特徴とする固体高分子電解質膜の製造方法。 Radiation-reactive monomers selected from styrene, α-methylstyrene, sodium styrenesulfonate, trifluorostyrene, and divinylbenzene are grafted onto the fluororesin irradiated with radiation, and styrene, α-methylstyrene, trifluorostyrene , A method of producing a solid polymer electrolyte membrane by sulfonation when a radical reactive monomer selected from divinylbenzene is graft-polymerized , wherein the graft polymerization is performed using oxygen having an oxygen concentration of 0.05 to 5% by volume. A method for producing a solid polymer electrolyte membrane, which is performed in an inert gas atmosphere. 前記フッ素系樹脂が、テトラフルオロエチレン系重合体、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル系共重合体、及びテトラフルオロエチレン−ヘキサフルオロプロピレン系共重合体から選ばれる少なくとも１種である請求項１記載の固体高分子電解質膜の製造方法。   2. The fluororesin is at least one selected from a tetrafluoroethylene polymer, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and a tetrafluoroethylene-hexafluoropropylene copolymer. A method for producing a solid polymer electrolyte membrane. 請求項１又は２記載の製造方法で製造された固体高分子電解質膜が、燃料極と空気極の間に設けられていることを特徴とする燃料電池。   3. A fuel cell, wherein the solid polymer electrolyte membrane produced by the production method according to claim 1 or 2 is provided between a fuel electrode and an air electrode.
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