JP3978668B2 - Ion exchange membrane and method for producing the same - Google Patents

Description

【００１５】
ここで、Ａｒ₁，Ａｒ₂，Ａｒ₃は、芳香族単位を示し、各種脂肪族基、芳香族基、ハロゲン基、水酸基、ニトロ基、シアノ基、トリフルオロメチル基等の置換基を有していても良い。これら芳香族単位は、ベンゼン環などの単環系単位、ナフタレン、アントラセン、ピレンなどの縮合環系単位、それらの芳香族単位が２個以上任意の結合を介してつながった多環系芳香族単位でも良い。また、芳香族単位におけるＮおよびＸの位置はベンザゾール環を形成できる配置であれば特に限定されるものではない。さらに、これらは炭化水素系芳香族単位だけでなく、芳香環内にＮ，Ｏ，Ｓ等を含んだヘテロ環系芳香族単位でも良い。ＸはＯ，Ｓ，ＮＨを示す。
上記Ａｒ₁は、下記一般式で表されるものが好ましい。
【００１６】
【化２】

【００１７】
ここで、Ｙ₁、Ｙ₂はＣＨまたはＮを示し、Ｚは直接結合、−Ｏ−，−Ｓ−，−ＳＯ₂−，−Ｃ（ＣＨ₃）₂−，−Ｃ（ＣＦ₃）₂−，−ＣＯ−を示す。
Ａｒ₂は、下記一般式で表されるものが好ましい。
【００１８】
【化３】

【００１９】
ここで、Ｗは−Ｏ−，−Ｓ−，−ＳＯ₂−，−Ｃ（ＣＨ₃）₂−，−Ｃ（ＣＨ₃）₂−，−ＣＯ−を示す。
Ａｒ₃は、下記一般式で表されるものが好ましい。
【００２０】
【化４】

【００２１】
これらポリベンザゾール系ポリマーは、上述の繰り返し単位を有するホモポリマーであっても良いが、上記構造単位を組み合わせたランダム、交互あるいはブロック共重合体であっても良く、例えば米国特許第４７０３１０３号、米国特許第４５３３６９２号、米国特許第４５３３７２４号、米国特許第４５３３６９３号、米国特許第４５３９５６７号、米国特許第４５７８４３２号等に記載されたものなども例示される。
【００２２】
これらポリベンザゾール系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００２３】
【化５】

【００２４】
【化６】

【００２５】
【化７】

【００２６】
【化８】

【００２７】
【化９】

【００２８】
【化１０】

【００２９】
【化１１】

【００３０】
さらに、これらポリベンザゾール系構成単位だけでなく、他のポリマー構成単位とのランダム、交互あるいはブロック共重合体であっても良い。この時、他のポリマー構成単位としては耐熱性に優れた芳香族系ポリマー構成単位から選ばれることが好ましい。具体的には、ポリイミド系構成単位、ポリアミド系構成単位、ポリアミドイミド系構成単位、ポリオキシジアゾール系構成単位、ポリアゾメチン系構成単位、ポリベンザゾールイミド系構成単位、ポリエーテルケトン系構成単位、ポリエーテルスルホン系構成単位などを挙げることができる。
【００３１】
ポリイミド系構成単位の例としては、下記一般式で表されるものが挙げられる。
【００３２】
【化１２】

【００３３】
ここで、Ａｒ₄は４価の芳香族単位で表されるが、下記構造で表されるものが好ましい。
【００３４】
【化１３】

【００３５】
また、Ａｒ₅は二価の芳香族単位であり、下記構造で表されるものが好ましい。ここで示される芳香環上には、メチル基、メトキシ基、ハロゲン基、トリフルオロメチル基、水酸基、ニトロ基、シアノ基等の各種置換基が存在していても良い。
【００３６】
【化１４】

【００３７】
これらポリイミド系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００３８】
【化１５】

【００３９】
【化１６】

【００４０】
ポリアミド系構成単位の例としては、下記構造式で表されるのもが挙げられる。
【００４１】
【化１７】

【００４２】
ここで、Ａｒ₆，Ａｒ₇，Ａｒ₈はそれぞれ独立に下記構造から選ばれるものが好ましい。ここで示される芳香環上には、メチル基、メトキシ基、ハロゲン基、トリフルオロメチル基、水酸基、ニトロ基、シアノ基等の各種置換基が存在していても良い。
【００４３】
【化１８】

【００４４】
これらポリアミド系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００４５】
【化１９】

【００４６】
ポリアミドイミド系構成単位の例としては、下記構造で表されるものが挙げられる。
【００４７】
【化２０】

【００４８】
ここで、Ａｒ₉は上記Ａｒ₅の具体例として示される構造から選ばれるものが好ましい。
【００４９】
これらポリアミドイミド構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００５０】
【化２１】

【００５１】
ポリオキシジアゾール系構成単位の例としては、下記構造式で表されるものが挙げられる。
【００５２】
【化２２】

【００５３】
ここで、Ａｒ₁₀は上記Ａｒ₅の具体例として示される構造から選ばれるものが好ましい。
【００５４】
これらポリオキシジアゾール系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００５５】
【化２３】

【００５６】
ポリアゾメチン系構成単位の例としては、下記構造で表されるものが挙げられる。
【００５７】
【化２４】

【００５８】
ここで、Ａｒ₁₁，Ａｒ₁₂は、上記Ａｒ₆の具体例として示される構造から選ばれるものが好ましい。
【００５９】
これらポリアゾメチン系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００６０】
【化２５】

【００６１】
ポリベンザゾールイミド系構成単位の例としては、下記構造式で表されるものが挙げられる。
【００６２】
【化２６】

【００６３】
ここで、Ａｒ₁₃、Ａｒ₁₄は上記Ａｒ₄の具体例として示される構造から選ばれるものが好ましい。
【００６４】
これらポリベンザゾールイミド系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００６５】
【化２７】

【００６６】
ポリエーテルケトン系構成単位、ポリエーテルスルホン系構成単位は、一般に芳香族ユニットをエーテル結合とともにケトン結合やスルホン結合で連結した構造を有するものであり、下記構造式から選択される構造成分を含む。
【００６７】
【化２８】

【００６８】
ここで、Ａｒ₁₅〜Ａｒ₂₃はそれぞれ独立に下記構造で表されるものが好ましい。ここで示される芳香環上には、メチル基、メトキシ基、ハロゲン基、トリフルオロメチル基、水酸基、ニトロ基、シアノ基等の各種置換基が存在していても良い。
【００６９】
【化２９】

【００７０】
これらポリエーテルケトン系構成単位の具体例としては、下記構造式で表すものを例示することができる。
【００７１】
【化３０】

【００７２】
これらポリベンザゾール系ポリマー構成単位と共に共重合できる芳香族ポリマー構成単位は、厳密にポリマー鎖内の繰り返し単位を指しているのではなく、ポリマー主鎖中にポリベンザゾール系構成単位と共に存在できる構成単位を示しているものである。これら共重合できる芳香族ポリマー構成単位は一種だけでなく二種以上を組み合わせて共重合することもできる。このような共重合体を合成するには、ポリベンザゾール系ポリマー構成単位からなるユニット末端にアミノ基、カルボキシル基、水酸基、ハロゲン基等を導入して、これらの芳香族系ポリマーの合成における反応成分として重合しても良いし、これらの芳香族系ポリマー構成単位を含むユニット末端にカルボキシル基を導入してポリベンザゾール系ポリマーの合成における反応成分として重合しても良い。
【００７３】
前記ポリベンザゾール系ポリマーは、ポリ燐酸溶媒中で縮合重合されポリマーが得られる。ポリマーの重合度は極限粘度で表され、１５ｄＬ／ｇ以上が好ましく、より好ましくは２０ｄＬ／ｇ以上である。この範囲を下回った場合、得られる支持体膜の強度が低く好ましくない。また極限粘度は、３５ｄＬ／ｇ以下が好ましく、２６ｄＬ／ｇ以下がより好ましい。この範囲を上回った場合、等方性の溶液が得られるポリベンザゾール系ポリマー溶液の濃度範囲が限られ、等方性の条件での製膜が困難となるため好ましくない。
【００７４】
ポリベンザゾール系ポリマー溶液の製膜方法としては、ドクターブレード等を用いてポリマー溶液を基体上にキャスティングする流延法と呼ばれる製膜方法のほかにも、直線状スリットダイから押し出す方法や円周状スリットダイからブロー押し出しする方法、二枚の基体に挟んだポリマー溶液をローラーでプレスするサンドイッチ法、スピンコート法など、溶液を膜状に成型するあらゆる方法が使用できる。本発明の目的に適した好ましい製膜方法は流延法、サンドイッチ法である。流延法の基板やサンドイッチ法の基体にはガラス板や金属板、樹脂フィルム等の他、凝固時の支持体膜の空隙構造を制御する等の目的で種々の多孔質材料を基板、基体として好ましく用いることができる。
【００７５】
本発明で用いるポリベンザゾール系ポリマー溶液は、均一でかつ空隙率の大きな支持体膜を得るために等方性条件の組成で製膜することが重要であり、ポリベンザゾール系ポリマー溶液の好ましい濃度範囲は、０．３％以上であり、より好ましくは０．５％以上、さらに好ましくは０．８％以上である。この範囲よりも濃度が低いとポリマー溶液の粘度が小さくなり、適用できる製膜方法が限られるほか、得られる支持体膜の強度が小さくなるため好ましくない。またさらに、濃度範囲は、３％以下が好ましく、より好ましくは２％以下、さらに好ましくは１．５％以下である。この範囲よりも濃度が高いと空隙率の大きな支持体膜が得られないばかりか、ポリベンザゾール系ポリマーのポリマー組成や重合度によっては溶液が異方性を示すため好ましくない。
【００７６】
ポリベンザゾール系ポリマー溶液の濃度を上記で示したような範囲に調整するには次に示すような方法をとる事ができる。すなわち、重合されたポリベンザゾール系ポリマー溶液から一旦ポリマー固体を分離し、再度溶媒を加えて溶解することで濃度調整を行なう方法。さらには、ポリ燐酸中で縮合重合されたままのポリマー溶液からポリマー固体を分離することなく、そのポリマー溶液に溶媒を加えて希釈し、濃度調整を行なう方法。さらにはポリマーの重合組成を調整することで上記濃度範囲のポリマー溶液を直接得る方法などである。
【００７７】
ポリマー溶液の濃度調整に用いるのに好ましい溶媒としては、メタンスルホン酸、ジメチル硫酸、ポリ燐酸、硫酸、トリフルオロ酢酸などがあげられ、あるいはこれらの溶媒を組み合わせた混合溶媒を用いることもできる。中でも特にメタンスルホン酸、ポリリン酸が好ましい。
【００７８】
支持体膜の多孔質構造を実現する手段としては、製膜された等方性のポリベンザゾール系ポリマー溶液を、貧溶媒と接触させて凝固する方法を用いる。貧溶媒はポリマー溶液の溶媒と混和できる溶媒であって、液相状態であっても気相状態であっても良い。さらに、気相状態の貧溶媒による凝固と液相状態の貧溶媒による凝固を組み合わせることも好ましく用いることができる。凝固に用いる貧溶媒としては、水、酸水溶液や無機塩水溶液の他、アルコール類、グリコール類、グリセリンなどの有機溶媒等を利用することができるが、使用するポリベンザゾール系ポリマー溶液との組み合わせによっては、支持体膜の表面開孔率や空隙率が小さくなったり、支持体膜の内部に不連続な空洞ができたりするなどの問題が生じるため、凝固に用いる貧溶媒の選択には特に注意が必要である。本発明における等方性のポリベンザゾール系ポリマー溶液の凝固においては、水蒸気、メタンスルホン酸水溶液、リン酸水溶液、グリセリン水溶液の他、塩化マグネシウム水溶液などの無機塩水溶液などの中から貧溶媒と凝固条件を選択することにより支持体膜表面および内部の構造、空隙率を制御するに至った。特に好ましい凝固の手段は水蒸気と接触させて凝固する方法や、凝固の初期において水蒸気に短時間接触させた後に水に接触させて凝固する方法、メタンスルホン酸水溶液に接触させて凝固する方法などである。
【００７９】
ポリマーの凝固が進むと、支持体膜は収縮しようとする。凝固が進行する間は支持体膜の不均一な収縮によるシワの発生などを抑制する目的でテンターや固定枠を用いる場合もある。また、ガラス板などの基板上に成型したポリマー溶液を凝固する場合には、基板面の粗さを制御することで基板上での収縮を制御する場合もある。
【００８０】
上記のようにして凝固された支持体膜は、残留する溶媒によるポリマーの分解の促進や、複合電解質膜を使用する際に残留溶媒が流出するなどの問題を避ける目的で、十分に洗浄することが望ましい。洗浄は支持体膜を洗浄液に浸漬することで行なうことができる。特に好ましい洗浄液は水である。水による洗浄は、支持体膜を水中に浸漬したときの洗液のｐＨが５〜８の範囲になるまで行なうことが好ましく、さらに好ましくはｐＨが６．５〜７．５の範囲である。
【００８１】
上記に述べた特定の濃度範囲のポリベンザゾール系ポリマー等方性溶液を用い、上記に述べたような方法から選ばれた適当な凝固手段を用いることにより本発明の目的に適した構造を有するポリベンザゾール系ポリマーよりなる支持体膜が得られる。すなわち、支持体膜の少なくとも一方の表面に開口部を持つ連続した空隙を有する多孔質の支持体膜である。支持体膜はポリベンザゾール系ポリマーのフィブリル状繊維から形成される立体網目構造からなり、三次元的に連続した空隙を有することを、実施例に示したような原子間力顕微鏡を用いる水中での支持体膜表面の観察、および、エポキシ包埋−脱エポキシにより水中の構造を保持した支持体膜の透過型電子顕微鏡観察による断面観察から確認した。特開２００２−２０３５７６には膜の厚さ方向に貫通する連通孔を有する膜支持体にイオン伝導性物質が導入された電解質膜が記載されているが、これに記載されているような連通孔の方向性が主に膜の厚さ方向に限定されている支持体を燃料電池の電解質膜に用いた場合、膜の面方向のイオン伝導性物質の連続性が小さいために燃料電池のイオン交換膜に用いた場合に燃料ガスの濃度分布や電極触媒の付着量など面方向に不均一な状態が生じるとイオン交換膜の局所的な劣化が生じやすいなどの問題があるため好ましくない。
【００８２】
本発明の支持体膜の空隙率は９０体積％以上であることが好ましく、さらに好ましくは９５体積％以上である。空隙率がこの範囲よりも小さいと、イオン交換樹脂を複合化させた場合のイオン交換樹脂の含有率が小さく、イオン導電性が低下するため好ましくない。
【００８３】
本発明の支持体膜は、少なくとも一方の面の開孔率が４０％以上であることが好ましく、さらに好ましくは５０％以上、特に好ましくは６０％以上である。少なくとも一方の面の開孔率がこの範囲よりも小さいと、支持体膜とイオン交換樹脂を複合化させる際に支持体膜の空隙内部にイオン交換樹脂が含浸されにくくなるため好ましくない。
【００８４】
上述のような方法で得られたポリベンザゾール系ポリマーよりなる多孔質の該支持体膜にイオン交換樹脂を複合化させ、イオン交換膜を得る方法について説明する。即ち、該支持体膜を乾燥させずに、イオン交換樹脂溶液に浸漬し、該支持体膜内部の液をイオン交換樹脂溶液に置換してから乾燥させる方法によりイオン交換膜を得る方法である。支持体膜内部の液がイオン交換樹脂溶液の溶媒組成と異なる場合には、その溶媒組成にあわせてあらかじめ内部の液を置換しておく方法も採られる。
【００８５】
本発明の支持体膜は乾燥により空隙内部の液体の体積が減少するのにしたがって空隙構造が収縮し、支持体膜の見かけの体積が大幅に減少するという特徴を有する。該支持体膜の内部にイオン交換樹脂を含浸することなく金属の枠などに固定して面方向の収縮を制限して乾燥させた場合には、収縮は膜厚方向に起こり、該支持体膜の乾燥後の見かけの膜厚は、乾燥前の膜厚の０．５％から１０％の範囲である。本発明の支持体膜以外の多孔質支持体膜、例えば、延伸ポリテトラフルオロエチレンポリマー多孔質膜からなる支持体膜ではこのような大幅な収縮は起こらない。
【００８６】
該支持体膜のこのような特徴により、該支持体膜の空隙内部の液をイオン交換樹脂溶液に置換してから乾燥させた場合、空隙内部に含浸された該イオン交換樹脂溶液の溶媒が蒸発して、該イオン交換樹脂溶液の体積が減少するにつれて該支持体膜も収縮するので、該支持体膜内部の空隙が析出したイオン交換樹脂によって満たされた緻密な複合膜構造を容易に得ることができる。この複合膜構造により、本発明のイオン交換膜は優れた燃料透過抑止性を示す。本発明の支持体膜以外の多孔質支持体膜、例えば、延伸ポリテトラフルオロエチレンポリマー多孔質膜からなる支持体膜では空隙内部に含浸されたイオン交換樹脂溶液の溶媒が蒸発して該イオン交換樹脂溶液の体積が減少しても、それに伴う支持体膜の収縮が少ないため、乾燥後の複合膜内部にはイオン交換樹脂で満たされていない空隙が多数できるため好ましくない。
【００８７】
該イオン交換膜はまた、該支持体膜が大幅に収縮するため、該イオン交換樹脂溶液の濃度や粘度、溶媒の揮発性などの物性と、該支持体膜の膜厚や空隙率等の組み合わせを調整することで、該イオン交換樹脂が該支持体膜の内部空隙を満たした複合層を形成するのと並行して該支持体膜の両面に付着していた過剰なイオン交換樹脂溶液や、該支持体膜の収縮に伴って該支持体膜内部から排出されたイオン交換樹脂溶液が該支持体膜の表面外部で乾燥して該支持体を含まないイオン交換樹脂層を形成することにより、結果として該複合層を挟む形で該複合層の両面に支持体膜を含まないイオン交換樹脂の表面層を形成した構造を容易に実現することができる。
【００８８】
本発明の支持体膜以外の膜、例えばポリテトラフルオロエチレンポリマーからなる多孔質支持体膜は上記で述べたように、大幅な収縮が起こらないため、イオン交換樹脂溶液を含浸して乾燥する際に支持体膜内部にイオン交換樹脂が析出しても空隙が残ったままの状態となる。この状態を解消するためにはイオン交換樹脂溶液の含浸、乾燥を複数回繰り返す必要があり、工程が複雑になるため好ましくない。
【００８９】
本発明のイオン交換膜に使用されるイオン交換樹脂は特に限定されるものではなく、前述のパーフルオロカーボンスルホン酸ポリマー以外にも、例えばポリスチレンスルホン酸、ポリ（トリフルオロスチレン）スルホン酸、ポリビニルホスホン酸、ポリビニルカルボン酸、ポリビニルスルホン酸ポリマーの少なくとも一つのアイオノマー、ポリスルホン、ポリフェニレンオキシド、ポリフェニレンスルホキシド、ポリフェニレンスルフィド、ポリフェニレンスルフィドスルホン、ポリパラフェニレン、ポリフェニルキノキサリン、ポリアリールケトン、ポリエーテルケトン、ポリベンザゾール及びポリアラミドポリマーなどの芳香族ポリマーの少なくとも一つがスルホン化、ホスホン化またはカルボキシル化されたアイオノマー等が適用できる。ここでいうポリスルホンポリマーにはポリエーテルスルホン、ポリアリールスルホン、ポリアリールエーテルスルホン、ポリフェニルスルホン及びポリフェニレンスルホンポリマーの少なくとも一つが含まれる。また、ここでいうポリエーテルケトンポリマーにはポリエーテルエーテルケトン、ポリエーテルケトン−ケトン、ポリエーテルエーテルケトン−ケトンおよびポリエーテルケトンエーテル−ケトンポリマーの少なくとも一つが含まれる。
【００９０】
上記に記述したイオン交換樹脂溶液の溶媒はポリベンザゾール系ポリマー支持体膜を溶解、分解あるいは極端に膨潤させず、かつイオン交換樹脂を溶解できる溶媒の中から選ぶことができる。ただし、イオン交換樹脂溶液を支持体膜に含浸させた後に溶媒を除去してイオン交換樹脂を析出させる為、溶媒は加熱や減圧などの手段を用いて蒸発させるなどして除去することができるものであることが好ましい。ここで、本発明のポリベンザゾール系ポリマー支持体膜は高い耐熱性を有することから、１００℃程度の温度からクリープを生じるポリテトラフルオロエチレン製の支持体膜を用いるイオン交換膜の作製では使用できない高沸点の溶媒を含むイオン交換樹脂溶液を使用してイオン交換膜を作製できることも、多くの種類のイオン交換樹脂が選択できるという観点から優れた特徴である。
【００９１】
上記に記述したイオン交換樹脂溶液の濃度および、イオン交換樹脂の分子量は特に限定されるものではないが、イオン交換樹脂の種類や得ようとするイオン交換膜の膜厚などに応じて適宜選択される。
【００９２】
上記のようにして得られるイオン交換膜に占めるイオン交換樹脂の含有率は５０重量％以上であることが好ましい。さらに好ましくは８０重量％以上である。この範囲より小さい含有率の場合、膜の導電抵抗が大きくなったり、膜の保水性が低下したりして、十分な発電性能が得られないため好ましくない。
【００９３】
イオン交換膜は機械的強度やイオン伝導性、表面に形成されるイオン交換樹脂層の耐剥離性などの特性をさらに向上させる目的で、イオン交換膜を適当な条件で熱処理する方法も好ましく用いることができる。また、表面に形成されるイオン交換樹脂の表面層の厚みを調整するために、該イオン交換膜をさらにイオン交換樹脂溶液に浸漬したり、該イオン交換膜にイオン交換樹脂溶液を塗布したりしてから乾燥することによりイオン交換樹脂層の付着量を増加させたり、あるいは、イオン交換樹脂溶液に浸漬した後に支持体膜の表面に付着したイオン交換樹脂溶液の一部をスクレーパー、エアナイフ、ローラーなどで掻き落としたり、ろ紙やスポンジのような溶液吸収性のある材料で吸収したりすることにより、イオン交換樹脂層の付着量を減少させたりする方法も用いることができる。あるいは、熱プレスをかけることによりイオン交換樹脂層の密着性をさらに向上させるなどの方法を併せて用いることもできる。
【００９４】
さらに本発明は、上記イオン交換膜を利用したことを特徴とする電解質膜・電極接合体である。本発明の貯蔵弾性率が大きく、高温での貯蔵弾性率の低下の少ないイオン交換膜と電極触媒層を接合させることで、高温や加湿の条件においても従来のイオン交換膜に比べてイオン交換膜の変形が少ないため、電極の剥離が起こりにくい電解質膜・電極接合体とすることができる。ここで、電解質膜・電極接合体の作製方法としては、イオン交換膜上にスキージやスクリーン印刷、スプレーなどを用いて直接電極ペーストを塗布する方法、イオン交換膜上に別途調整した電極層シートをヒートプレス等を用いて密着させる方法、その他、イオン交換膜上に電極を接合させるあらゆる方法をとることができる。
【００９５】
さらに本発明は、上記電解質膜・電極接合体を使用したことを特徴とする燃料電池である。該電解質膜・電極接合体を使用した燃料電池は、高温、高圧、加湿の条件で運転した場合においても、従来の電解質膜・電極接合体を用いた燃料電池に比べて電解質膜の破損や電極の剥離が起こりにくいため優れた耐久性を有する。
【００９６】
本発明のイオン交換膜は高いイオン伝導性を有しながら、耐熱性に優れる。また、その特性を生かして、イオン交換膜特に固体高分子形燃料電池の高分子固体電解質膜として利用することができる。
【００９７】
実施例
以下に本発明の実施例を示すが本発明はこれらの実施例に限定されるものではない。
評価法・測定法
＜透過型電子顕微鏡による構造観察＞
透過型電子顕微鏡（ＴＥＭ）による膜の断面構造の観察は以下の方法で行った。まず、観察用試料切片を次のようにして作成した。すなわち、水洗後の支持体膜試料内部の水をエタノールに置換、さらにエポキシモノマーに十分置換した。
試料はそのままエポキシモノマー中で４５℃、６時間保持した後、さらに６０℃、２０時間熱処理することでエポキシを硬化させた（エポキシ包埋）。このようにしてエポキシ包埋された試料はダイヤモンドナイフを備えたミクロトームを用いて、干渉色が銀から金色を示す程度の厚みの超薄切片に調製し、ＫＯＨ飽和エタノール溶液で１５分処理することでエポキシを除去した（脱エポキシ）。さらにエタノール、続いて水で洗浄し、ＲｕＯ₄で染色した試料にカーボン蒸着し、ＪＥＯＬ製ＴＥＭ（ＪＥＭ−２０１０）を用いて加速電圧２００ｋＶで観察した。
【００９８】
＜原子間力顕微鏡による構造観察＞
原子間力顕微鏡（ＡＦＭ）による構造観察は以下の方法で行った。すなわち、Ｓｅｉｋｏ Ｉｎｓｔｒｕｍｅｎｔｓ社製のＡＦＭ（ＳＰＡ３００［観察モード：ＤＦＭモード、カンチレバー：ＳＩ−ＤＦ３、スキャナー：ＦＳ−１００Ａ］）を使用し、水中の試料ステージに保持した未乾燥の支持体膜の表面構造を観察した。
【００９９】
＜走査型電子顕微鏡による構造観察＞
走査型電子顕微鏡（ＳＥＭ）による構造観察は以下の方法で行った。まず、水洗した支持体膜内部の水をエタノールに置換、さらに酢酸イソアミルに十分置換した後、日立製臨界点乾燥装置（ＨＣＰ−１）を用いて、ＣＯ₂臨界点乾燥を施した。このようにして臨界点乾燥した支持体膜に厚さ１５０オングストロームの白金コートを施し、日立製ＳＥＭ（Ｓ−８００）を用いて加速電圧１０ｋＶ、試料傾斜角度３０度で観察を行った。
【０１００】
＜極限粘度＞
メタンスルホン酸を溶媒として、０．５ｇ／Ｌの濃度に調整したポリマー溶液の粘度をウベローデ型粘度計を用いて２５℃恒温槽中で測定し、算出した。
【０１０１】
＜動的粘弾性測定＞
イオン交換膜の動的粘弾性は次のようにして測定した。幅５ｍｍの短冊状の試料をユービーエム社製動的粘弾性測定装置（型式名：Ｒｈｅｏｇｅｌ−Ｅ４０００）にチャック間距離１４ｍｍとなるようにセットし、引っ張りモードで周波数１０Ｈｚ、歪み０．７％、窒素気流中、２５℃〜２００℃の温度範囲で測定した。
【０１０２】
＜イオン導電率＞
イオン導電率σは次のようにして測定した。自作測定用プローブ（ポリテトラフルオロエチレン製）上で幅１０ｍｍの短冊状膜試料の表面に白金線（直径：０．２ｍｍ）を押しあて、８０℃、相対湿度９５％の恒温恒湿槽中に試料を保持し、白金線間の１０ｋＨｚにおける交流インピーダンスをＳＯＬＡＲＴＲＯＮ社１２５０ＦＲＥＱＵＥＮＣＹ ＲＥＳＰＯＮＳＥ ＡＮＡＬＹＳＥＲにより測定した。極間距離を１０ｍｍから４０ｍｍまで１０ｍｍ間隔で変化させて測定し、極間距離と抵抗測定値をプロットした直線の勾配Ｄｒ［Ω／ｃｍ］から下記の式により膜と白金線間の接触抵抗をキャンセルして算出した。
σ［Ｓ／ｃｍ］＝１／（膜幅×膜厚［ｃｍ］×Ｄｒ）
【０１０３】
＜電解質膜・電極接合体の作製および発電試験＞
デュポン社製２０％ナフィオン（商品名）溶液（品番：ＳＥ−２０１９２）に、白金担持カーボン（カーボン：Ｃａｂｏｔ社製ＶａｌｃａｎＸＣ−７２、白金担持量：４０重量％）を、白金とナフィオンの重量比が２．７：１になるように加え、撹拌して触媒ペーストを調製した。この触媒ペーストをイオン交換膜に白金の付着量が１ｍｇ／ｃｍ２になるように塗布、乾燥して、電極触媒層付きイオン交換膜を作成した。２枚の東レ製カーボンペーパーＴＧＰＨ−０６０の間に、イオン交換膜を、電極触媒層が膜試料に接するように挟み、ホットプレス法により１２０℃、２ＭＰａにて３分間加圧、加熱することにより電解質膜・電極接合体を作製した。作製した電解質膜・電極接合体を耐圧性の評価用燃料電池セルに組み込んでセル温度１３０℃、ガス加湿温度１２０℃、ガス圧力０．３ＭＰａ、燃料ガスとして水素３００ｍL／ｍｉｎ、酸化ガスとして空気１０００ｍL／ｍｉｎのガス流量において発電試験を行った。
【０１０４】
実施例１
ポリ燐酸中にＩＶ＝２４ｄＬ／ｇのポリパラフェニレンシスベンゾビスオキサゾールポリマーを１４重量％含んだドープにメタンスルホン酸を加えて希釈し、ポリパラフェニレンシスベンゾビスオキサゾール濃度１重量％の等方性溶液を調製した。この溶液を、９０℃に加熱したガラス板上にクリアランス３００μｍのアプリケータを用いて製膜速度５ｍｍ／秒で製膜した。このようにしてガラス板上に製膜したドープ膜をそのまま２５℃、相対湿度８０％の恒温恒湿槽中において１０分間凝固したのち、さらに２５℃の純水中にて１５分間凝固を行い、生成した膜を洗液がｐＨ７±０．５を示すまで水洗を行って支持体膜を作成した。作成した支持体膜は両面に開口部を持つ連続した空孔を有する多孔質の膜であることを原子間力顕微鏡による表面形態観察および、透過型電子顕微鏡による断面形態観察により確認した。この支持体膜を水中でステンレス製のフレームに固定し、支持体膜の内部の水をイオン交換樹脂溶液であるデュポン社製２０％ナフィオン（商品名）溶液（品番：ＳＥ−２０１９２）の溶媒組成とほぼ同じ水：エタノール：１−プロパノール＝２６：２６：４８（重量比）の混合溶媒で置換した。
この支持体膜を２０％ナフィオン（商品名）溶液に２５℃で１５時間浸漬した後溶液から取り出し、膜の内部に含浸および膜表面に付着したナフィオン（商品名）溶液の溶媒を風乾により揮発させ乾燥させた。乾燥させた膜は６０℃のオーブン中で１時間予備熱処理して残留した溶媒を除いた後、窒素雰囲気下、１５０℃で１時間熱処理を行なうことにより実施例１のイオン交換膜を調製した。
【０１０５】
比較例１
比較例１として、市販されているデュポン社製ナフィオン１１２（商品名）膜を用いた。この膜は実施例１で用いた２０％ナフィオン溶液に含まれるナフィオンポリマーと同じパーフルオロカーボンスルホン酸ポリマーからなるプロトン交換膜であり、固体高分子形燃料電池用のプロトン交換膜として広く用いられているものである。
【０１０６】
比較例２
膜厚２０μｍ、空隙率８９％の延伸多孔質ＰＴＦＥ（ポリテトラフルオロエチレン）シートをステンレス製のフレームに固定し、２０％ナフィオン（商品名）溶液に２５℃で１５時間浸漬した後溶液から取り出し、膜の内部に含浸および膜表面に付着したナフィオン（商品名）溶液の溶媒を風乾により揮発させ乾燥させた。この含浸−風乾を５回繰り返して、延伸多孔質ＰＴＦＥ膜の空隙部及び表面にナフィオン（商品名）樹脂が充填された膜を形成した。乾燥させた膜は６０℃のオーブン中で１時間予備熱処理して残留した溶媒を除いた後、窒素雰囲気下、１５０℃で１時間熱処理を行なうことにより比較例２のイオン交換膜を調製した。
【０１０７】
実施例１および比較例２のイオン交換膜について、電解質膜・電極接合体を作製し、上記に示した高温の発電試験条件において、セル電圧０．５Ｖで１００時間の発電を行った後、電解質膜・電極接合体を取り出して、電極の接合状態を調べたところ、実施例１のイオン交換膜の接合状態は良好であったのに対して、比較例２のイオン交換膜については電極の一部がイオン交換膜から剥離していた。
【０１０８】
実施例１比較例１の物性値を表１に示す。
【０１０９】
【表１】

【０１１０】
実施例１のイオン交換膜は比較例１である市販のナフィオン１１２膜、および比較例２のイオン交換膜と対比して３０℃での貯蔵弾性率Ｇ’₃₀の値が１．３５×１０⁹Ｐａと大きいイオン交換膜であることがわかる。また実施例１のイオン交換膜は内部に支持体を有するにもかかわらず、支持体を含まない比較例１に比べてイオン導電率の大幅な低下を起こすことがないことがわかる。
【０１１１】
さらに、実施例１のイオン交換膜は比較例２のイオン交換膜に比して高温発電時の電極の密着性が良好であった。実施例１のイオン交換膜は貯蔵弾性率が大きく、かつ高温での貯蔵弾性率の低下も少ないため、高温での発電時に膜の寸法変化が小さく、電極の剥離が起こらなかったものと推定される。このように本発明のイオン交換膜は高温での燃料電池の高分子固体電解質膜として優れた特性を備えていることがわかる。
【０１１２】
【発明の効果】
耐熱性が高く、イオン伝導性に優れた高分子固体電解質膜を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ion exchange membrane excellent in mechanical strength and ion conductivity, and more particularly to a polymer solid electrolyte membrane.
[0002]
[Prior art]
In recent years, new power generation technologies with excellent energy efficiency and environmental friendliness have attracted attention.
Among them, polymer electrolyte fuel cells using polymer electrolyte membranes have high energy density, and have features such as easy startup and shutdown because of lower operating temperatures than other types of fuel cells. Developments as power supply devices for electric vehicles and distributed power generation are advancing. In addition, direct methanol fuel cells that use a solid polymer electrolyte membrane and directly supply methanol as a fuel are also being developed for applications such as power sources for portable devices. As the polymer solid electrolyte membrane, a proton conductive ion exchange resin membrane is usually used. In addition to proton conductivity, the polymer solid electrolyte membrane must have characteristics such as fuel permeation deterrence and mechanical strength to prevent the permeation of fuel hydrogen and the like. As such a polymer solid electrolyte membrane, for example, a perfluorocarbon sulfonic acid polymer membrane into which a sulfonic acid group is introduced as represented by Nafion (trade name) manufactured by DuPont, USA is known.
[0003]
In order to increase the output and efficiency of the polymer electrolyte fuel cell, it is effective to reduce the ionic conduction resistance of the polymer solid electrolyte membrane, and one of the measures is to reduce the film thickness. Attempts have also been made to reduce the film thickness of solid polymer electrolyte membranes such as Nafion. However, when the film thickness is reduced, the mechanical strength is reduced, and the polymer solid electrolyte is liable to break when the polymer solid electrolyte membrane and the electrode are joined by hot pressing, or due to fluctuations in the dimensions of the membrane. There have been problems such as the electrode bonded to the film being peeled off and the power generation characteristics being deteriorated. Furthermore, the fuel permeation deterrence is lowered by reducing the film thickness, which causes problems such as a reduction in electromotive force and a decrease in fuel utilization efficiency. Furthermore, attempts have been made to operate the polymer electrolyte fuel cells at higher temperatures for the purpose of increasing the output of the polymer electrolyte fuel cells, improving the catalytic activity, simplifying the cooling system, and utilizing exhaust heat. However, perfluorocarbon sulfonic acid polymer membranes such as those represented by Nafion have a significant decrease in the mechanical strength of the membrane, especially at high temperatures, and the membrane tends to deform, causing electrode peeling, and controlling the moisture content of the membrane. There are problems such as difficulty and reduced power generation characteristics.
[0004]
The polymer solid electrolyte membrane is not only used as an ion exchange resin membrane for a fuel cell as described above, but also in electrolysis applications such as alkaline electrolysis and hydrogen production from water, and various batteries such as lithium batteries and nickel metal hydride batteries. It can also be used in a wide range of applications such as applications in the electrochemical field such as electrolyte applications, mechanical functional materials such as micro actuators and artificial muscles, recognition / response functional materials such as ions and molecules, and separation / purification functional materials. It is possible to provide unprecedented functions by achieving high strength, thinning, and high heat resistance of the solid polymer electrolyte membrane in each application.
[0005]
As a method for improving the mechanical strength of the polymer solid electrolyte membrane and suppressing dimensional changes, a composite polymer solid electrolyte membrane in which various reinforcing materials are combined with the polymer solid electrolyte membrane has been proposed. Patent Document 1 describes a composite polymer solid electrolyte membrane in which a void portion of a stretched porous polytetrafluoroethylene membrane is impregnated with a perfluorocarbon sulfonic acid polymer that is an ion exchange resin and integrated. However, because these composite polymer solid electrolyte membranes are made of polytetrafluoroethylene, the reinforcement material is softened by the heat generated during power generation, and the elastic modulus of the electrolyte membrane is greatly reduced, resulting in dimensional changes. In particular, the dimensional change is remarkable at a high temperature exceeding 100 ° C. In addition, when the reinforcing material is impregnated with a perfluorocarbon sulfonic acid polymer solution and dried, the volume of the void portion of the reinforcing material hardly changes, so that the perfluorocarbon sulfonic acid polymer precipitated inside the reinforcing material voids is unevenly distributed. In order for the air gap to be completely filled with the polymer, a complicated process such as impregnation and drying of the ion exchange resin solution is required several times, and fuel permeation is suppressed because the air gap tends to remain. There was a problem that it was difficult to obtain a film having excellent properties. Patent Document 2 describes a composite polymer solid electrolyte membrane in which polytetrafluoroethylene fibrillated as a reinforcing material is dispersed in a perfluorocarbon sulfonic acid polymer membrane. However, such a composite polymer solid electrolyte membrane has problems such as electrode peeling due to insufficient mechanical strength due to the discontinuous structure of the reinforcing material, and deformation of the membrane cannot be suppressed. Had.
[0006]
Polybenzazole polymers such as polybenzoxazole (PBO) and polybenzimidazole (PBI) are excellent in terms of high heat resistance, high strength, and high elastic modulus, and are therefore suitable for reinforcing materials for polymer solid electrolyte membranes. Expected to be. Patent Document 3 describes a polymer solid electrolyte membrane in which a PBO porous membrane and various ion exchange resins are combined. However, the surface of the PBO porous film obtained by the method of directly solidifying a PBO solution film formed from a dope exhibiting liquid crystallinity described in this in a water bath has a dense layer with few openings on both sides. When the ion exchange resin is compounded, the ion exchange resin solution is not easily impregnated inside the membrane, the content of the ion exchange resin in the composite membrane is reduced, and the ion conductivity inherent in the ion exchange resin is reduced. There was a problem that the characteristics were greatly deteriorated.
[0007]
Patent Document 4 describes a method for producing a polymer film for a fuel cell in which an acid is trapped in the voids of a PBI porous membrane. However, the film trapped with a free acid obtained by the method described in this document has low ion conductivity in a low temperature region such as 100 ° C. or lower as compared with the above-described ion exchange membrane such as Nafion, There were problems such as easy acid leakage. Furthermore, Patent Document 5 discloses a method for forming a polybenzazole film by forming a polybenzazole polymer solution having optical anisotropy and then coagulating through an isotropic process by moisture absorption. The polybenzazole film obtained by the method described in 1) is a transparent and highly dense film, and is not suitable for the purpose of impregnating an ion exchange resin to form an ion exchange membrane.
[0008]
Furthermore, by introducing an ion exchange group such as a sulfonic acid group into a polymer having excellent strength and heat resistance, or by polymerizing a monomer having an ion exchange group to prepare a polymer having excellent strength and heat resistance, it is reinforced. Non-Patent Document 1 and Patent Documents 6 and 7 describe a method for obtaining a high-strength, high-heat-resistant ion exchange membrane without using a material. If the amount of ion exchange groups introduced is increased in order to obtain ion conductivity, the strength and heat resistance are reduced, and swelling at the time of moisture absorption increases.
[0009]
[Patent Document 1]
JP-A-8-162132 [Patent Document 2]
JP 2001-35508 A [Patent Document 3]
International Publication No. WO00 / 22684 Pamphlet [Patent Document 4]
International Publication No. WO 98/14505 Pamphlet [Patent Document 5]
JP 2000-273214 A [Patent Document 6]
Japanese Patent Laid-Open No. 5-1149 [Patent Document 7]
US Patent Application Publication No. 2002/0091225 [Non-patent Document 1]
F. Lufrano, 3 others, “Sulfonated Polysulfone as Promising Membranes for Polymer Electrolyte Fuel Cells”, Journal of Applied Polymer Science (Journal of Applied Polymer Science) Polymer Science), (USA), John Wiley & Sons, Inc., 2000, 77, p. 1250-1257
[0010]
[Problems to be solved by the invention]
The present invention provides an ion exchange membrane suitable for use as a polymer solid electrolyte membrane having high mechanical strength and excellent ion conductivity.
[0011]
[Means for Solving the Problems]
That is, the present invention relates to an ion exchange membrane having a support membrane having voids and a composite layer made of an ion exchange resin impregnated in the voids, wherein the support membrane is a polysiloxane having a weight of 0.3 wt% to 3 wt%. It consists of a three-dimensional network structure formed from fibrillar fibers of polybenzazole polymer produced by solidifying an isotropic solution containing a benzazole polymer into a film and then having three-dimensional continuous voids. It is a porous membrane made of a polybenzazole-based polymer, and has a storage elastic modulus G ′ _{30 at} 30 ° C. of 8 × 10 ⁸ Pa or more and storage at 200 ° C. in the dynamic viscoelasticity measurement of the ion exchange membrane. The ion exchange membrane is characterized in that the ratio of the elastic modulus G ′ ₂₀₀ to G ′ ₃₀ is 30 % or more. An electrolyte membrane / electrode assembly using the ion exchange membrane, and a fuel cell using the same.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The ion exchange membrane of the present invention has a storage elastic modulus G ′ _{30 at} 30 ° C. of 6 × 10 ⁸ Pa or more obtained by dynamic viscoelasticity measurement of the tensile force of the ion exchange membrane, and a storage elastic modulus at 200 ° C. The ratio of G ′ ₂₀₀ to G ′ ₃₀ is 1% or more. Such an ion exchange membrane not only has excellent dimensional stability near room temperature, but also has a small change in dimensional stability at high temperatures compared to near room temperature. When it is used as a solid polymer electrolyte membrane for a fuel cell, problems such as electrode peeling are less likely to occur, when it is used under conditions with severe temperature changes such as repeated shutdown, or at high temperatures exceeding 100 ° C. Excellent durability even in such cases. When G ′ ₃₀ is smaller than 6 × 10 ⁸ Pa, the dimensional stability of the ion exchange membrane is decreased, which is not preferable. Further, when the ratio of G ′ ₂₀₀ to G ′ ₃₀ is less than 1%, it is not preferable because a dimensional change is likely to occur under a condition where the temperature change is severe or a high temperature operation condition and durability is lowered. A more preferable range of G ′ ₃₀ is 8 × 10 ⁸ Pa or more, and particularly preferably 1 × 10 ⁹ Pa or more. A more preferable range of the ratio of G ′ ₂₀₀ to G ′ ₃₀ is 10% or more, and particularly preferably 30% or more.
[0013]
Furthermore, the ion exchange membrane of the present invention has a support membrane having voids and a composite layer made of an ion exchange resin impregnated in the voids. By having the composite layer in the ion exchange membrane, the elastic modulus of the ion exchange membrane can be improved and stabilized even when the heat resistance and dimensional stability of the ion exchange resin itself used in the ion exchange membrane are low. . Further, in the present invention, the support membrane is a porous membrane made of a polybenzazole polymer having voids. In addition to polyolefin polymers such as polyethylene and polypropylene having low heat resistance, fluorine polymers such as polytetrafluoroethylene having a low elastic modulus at a high temperature exceeding 100 ° C. and large creep deformation are preferred as the support membrane of the present invention. Absent. The polybenzazole-based polymer used as the support membrane of the present invention refers to a polymer having a structure containing an oxazole ring, a thiazole ring, and an imidazole ring in the polymer chain, and the repeating unit represented by the following general formula is a polymer chain. This is what is contained inside.
[0014]
[Chemical 1]

[0015]
Here, Ar ₁ , Ar ₂ , Ar ₃ represent aromatic units and have various aliphatic groups, aromatic groups, halogen groups, hydroxyl groups, nitro groups, cyano groups, trifluoromethyl groups and other substituents. May be. These aromatic units are monocyclic units such as benzene rings, condensed ring units such as naphthalene, anthracene, and pyrene, and polycyclic aromatic units in which two or more of these aromatic units are connected via an arbitrary bond. But it ’s okay. Moreover, the position of N and X in an aromatic unit will not be specifically limited if it is the arrangement | positioning which can form a benzazole ring. Furthermore, these may be not only hydrocarbon aromatic units but also heterocyclic aromatic units containing N, O, S, etc. in the aromatic ring. X represents O, S, NH.
The Ar ₁ is preferably represented by the following general formula.
[0016]
[Chemical formula 2]

[0017]
Here, Y ₁ and Y ₂ represent CH or N, Z represents a direct bond, —O—, —S—, —SO ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —. , -CO-.
Ar ₂ is preferably represented by the following general formula.
[0018]
[Chemical 3]

[0019]
Here, W is -O -, - S -, - SO 2 -, - C (CH 3) 2 -, - C (CH 3) 2 -, - shows a CO-.
Ar ₃ is preferably represented by the following general formula.
[0020]
[Formula 4]

[0021]
These polybenzazole-based polymers may be homopolymers having the above-mentioned repeating units, but may be random, alternating or block copolymers in which the above structural units are combined. For example, US Pat. No. 4,703,103, Examples thereof include those described in US Pat. No. 4,533,692, US Pat. No. 4,533,724, US Pat. No. 4,533,693, US Pat. No. 4,359,567, US Pat. No. 4,578,432, and the like.
[0022]
Specific examples of these polybenzazole-based structural units include those represented by the following structural formulas.
[0023]
[Chemical formula 5]

[0024]
[Chemical 6]

[0025]
[Chemical 7]

[0026]
[Chemical 8]

[0027]
[Chemical 9]

[0028]
[Chemical Formula 10]

[0029]
Embedded image

[0030]
Furthermore, not only these polybenzazole-based structural units, but also random, alternating or block copolymers with other polymer structural units may be used. At this time, the other polymer constituent unit is preferably selected from aromatic polymer constituent units having excellent heat resistance. Specifically, polyimide structural unit, polyamide structural unit, polyamideimide structural unit, polyoxydiazole structural unit, polyazomethine structural unit, polybenzazoleimide structural unit, polyether ketone structural unit, Examples thereof include polyethersulfone structural units.
[0031]
As an example of a polyimide-type structural unit, what is represented by the following general formula is mentioned.
[0032]
Embedded image

[0033]
Here, Ar ₄ is represented by a tetravalent aromatic unit, but is preferably represented by the following structure.
[0034]
Embedded image

[0035]
Ar ₅ is a divalent aromatic unit and is preferably represented by the following structure. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.
[0036]
Embedded image

[0037]
Specific examples of these polyimide-based structural units include those represented by the following structural formulas.
[0038]
Embedded image

[0039]
Embedded image

[0040]
Examples of the polyamide-based structural unit include those represented by the following structural formula.
[0041]
Embedded image

[0042]
Here, it is preferable that Ar ₆ , Ar ₇ and Ar ₈ are each independently selected from the following structures. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.
[0043]
Embedded image

[0044]
Specific examples of these polyamide-based structural units include those represented by the following structural formulas.
[0045]
Embedded image

[0046]
Examples of the polyamideimide-based structural unit include those represented by the following structure.
[0047]
Embedded image

[0048]
Here, Ar ₉ is preferably selected from the structures shown as specific examples of Ar ₅ .
[0049]
Specific examples of these polyamideimide structural units include those represented by the following structural formulas.
[0050]
Embedded image

[0051]
Examples of the polyoxydiazole-based structural unit include those represented by the following structural formula.
[0052]
Embedded image

[0053]
Here, Ar ₁₀ is preferably selected from the structures shown as specific examples of Ar ₅ .
[0054]
Specific examples of these polyoxydiazole structural units include those represented by the following structural formulas.
[0055]
Embedded image

[0056]
Examples of polyazomethine structural units include those represented by the following structure.
[0057]
Embedded image

[0058]
Here, Ar ₁₁ and Ar ₁₂ are preferably selected from structures shown as specific examples of Ar ₆ .
[0059]
Specific examples of these polyazomethine structural units include those represented by the following structural formulas.
[0060]
Embedded image

[0061]
Examples of the polybenzazole imide-based structural unit include those represented by the following structural formula.
[0062]
Embedded image

[0063]
Here, Ar ₁₃ and Ar ₁₄ are preferably selected from the structures shown as specific examples of Ar ₄ .
[0064]
Specific examples of these polybenzazole imide-based structural units include those represented by the following structural formulas.
[0065]
Embedded image

[0066]
The polyether ketone structural unit and the polyether sulfone structural unit generally have a structure in which an aromatic unit is connected with an ether bond by a ketone bond or a sulfone bond, and includes a structural component selected from the following structural formula.
[0067]
Embedded image

[0068]
Here, Ar _{15 to} Ar ₂₃ are preferably each independently represented by the following structure. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.
[0069]
Embedded image

[0070]
Specific examples of these polyetherketone structural units include those represented by the following structural formula.
[0071]
Embedded image

[0072]
The aromatic polymer structural unit that can be copolymerized with these polybenzazole-based polymer structural units does not strictly indicate a repeating unit in the polymer chain, but can be present together with the polybenzazole-based structural units in the polymer main chain. Indicates the unit. These copolymerizable aromatic polymer structural units can be copolymerized not only alone but also in combination of two or more. In order to synthesize such a copolymer, an amino group, a carboxyl group, a hydroxyl group, a halogen group, etc. are introduced at the end of a unit consisting of a polybenzazole polymer constituent unit, and the reaction in the synthesis of these aromatic polymers. It may be polymerized as a component, or may be polymerized as a reaction component in the synthesis of a polybenzazole-based polymer by introducing a carboxyl group into the terminal of a unit containing these aromatic polymer constituent units.
[0073]
The polybenzazole-based polymer is subjected to condensation polymerization in a polyphosphoric acid solvent to obtain a polymer. The degree of polymerization of the polymer is expressed by intrinsic viscosity, preferably 15 dL / g or more, and more preferably 20 dL / g or more. If it falls below this range, the strength of the resulting support membrane is low, which is not preferred. The intrinsic viscosity is preferably 35 dL / g or less, and more preferably 26 dL / g or less. Exceeding this range is not preferable because the concentration range of the polybenzazole polymer solution from which an isotropic solution is obtained is limited, and film formation under isotropic conditions becomes difficult.
[0074]
As a method for forming a polybenzazole polymer solution, in addition to a casting method called casting method in which a polymer solution is cast on a substrate using a doctor blade or the like, a method of extruding from a linear slit die or a circumference Any method for forming a solution into a film, such as a method of blow-extrusion from a slit slit die, a sandwich method in which a polymer solution sandwiched between two substrates is pressed with a roller, or a spin coating method can be used. Preferred film forming methods suitable for the purpose of the present invention are the casting method and the sandwich method. As a substrate for casting and a substrate for sandwich method, various porous materials are used as substrates and substrates for the purpose of controlling the void structure of the support film during solidification in addition to glass plates, metal plates, resin films, etc. It can be preferably used.
[0075]
It is important that the polybenzazole-based polymer solution used in the present invention is formed in a composition under isotropic conditions in order to obtain a support film having a uniform and high porosity, which is preferable for the polybenzazole-based polymer solution. The concentration range is 0.3% or more, more preferably 0.5% or more, and further preferably 0.8% or more. If the concentration is lower than this range, the viscosity of the polymer solution becomes small, and the applicable film forming method is limited, and the strength of the obtained support film is small, which is not preferable. Furthermore, the concentration range is preferably 3% or less, more preferably 2% or less, and still more preferably 1.5% or less. If the concentration is higher than this range, a support film having a large porosity cannot be obtained, and the solution exhibits anisotropy depending on the polymer composition and degree of polymerization of the polybenzazole polymer, which is not preferable.
[0076]
In order to adjust the concentration of the polybenzazole polymer solution to the range shown above, the following method can be used. That is, a method in which a polymer solid is once separated from a polymerized polybenzazole-based polymer solution, and the concentration is adjusted by adding a solvent again and dissolving. Furthermore, a method of adjusting the concentration by adding a solvent to the polymer solution and diluting the polymer solution without separating the polymer solid from the polymer solution that has been subjected to condensation polymerization in polyphosphoric acid. Furthermore, there is a method of directly obtaining a polymer solution in the above concentration range by adjusting the polymerization composition of the polymer.
[0077]
Preferred solvents for use in adjusting the concentration of the polymer solution include methanesulfonic acid, dimethylsulfuric acid, polyphosphoric acid, sulfuric acid, trifluoroacetic acid, and the like, or a mixed solvent combining these solvents can also be used. Of these, methanesulfonic acid and polyphosphoric acid are particularly preferable.
[0078]
As a means for realizing the porous structure of the support membrane, a method of coagulating the formed isotropic polybenzazole polymer solution in contact with a poor solvent is used. The poor solvent is a solvent miscible with the solvent of the polymer solution, and may be in a liquid phase state or a gas phase state. Further, a combination of coagulation with a poor solvent in a gas phase and coagulation with a poor solvent in a liquid phase can be preferably used. As a poor solvent used for coagulation, water, acid aqueous solution, inorganic salt aqueous solution, alcohols, glycols, organic solvents such as glycerin, etc. can be used, but the combination with polybenzazole polymer solution to be used Depending on the problem, the surface porosity and porosity of the support membrane may be reduced, or discontinuous cavities may be formed inside the support membrane. Caution must be taken. In the coagulation of the isotropic polybenzazole-based polymer solution in the present invention, coagulation with a poor solvent from among water vapor, methanesulfonic acid aqueous solution, phosphoric acid aqueous solution, glycerin aqueous solution and inorganic salt aqueous solution such as magnesium chloride aqueous solution. By selecting the conditions, the surface and internal structure of the support film and the porosity were controlled. Particularly preferred solidification means are a method of solidifying by contacting with water vapor, a method of solidifying by contacting water vapor for a short time in the initial stage of solidification, then a method of solidifying by contacting with water, a method of solidifying by contacting with an aqueous methanesulfonic acid solution, etc. is there.
[0079]
As the polymer solidifies, the support membrane tends to shrink. While solidification proceeds, a tenter or a fixed frame may be used for the purpose of suppressing generation of wrinkles due to uneven shrinkage of the support film. Further, when solidifying a polymer solution molded on a substrate such as a glass plate, the shrinkage on the substrate may be controlled by controlling the roughness of the substrate surface.
[0080]
The support membrane solidified as described above should be thoroughly washed for the purpose of avoiding problems such as acceleration of polymer degradation by the residual solvent and outflow of residual solvent when using the composite electrolyte membrane. Is desirable. Cleaning can be performed by immersing the support membrane in a cleaning solution. A particularly preferred cleaning solution is water. Washing with water is preferably carried out until the pH of the washing solution when the support membrane is immersed in water is in the range of 5 to 8, more preferably in the range of 6.5 to 7.5.
[0081]
Using a polybenzazole-based polymer isotropic solution having a specific concentration range as described above, and having a structure suitable for the purpose of the present invention by using an appropriate coagulation means selected from the methods as described above. A support film made of a polybenzazole-based polymer is obtained. That is, it is a porous support film having continuous voids having openings on at least one surface of the support film. The support membrane consists of a three-dimensional network formed from fibrillar fibers of a polybenzazole-based polymer and has three-dimensional continuous voids in water using an atomic force microscope as shown in the examples. This was confirmed by observation of the surface of the support film and cross-sectional observation of the support film that retained the structure in water by epoxy embedding-deepoxidation by transmission electron microscope observation. Japanese Patent Application Laid-Open No. 2002-203576 describes an electrolyte membrane in which an ion conductive material is introduced into a membrane support having a communication hole penetrating in the thickness direction of the membrane. When a support whose orientation is mainly limited to the thickness direction of the membrane is used for the electrolyte membrane of a fuel cell, the continuity of the ion conductive material in the surface direction of the membrane is small, so the ion exchange of the fuel cell When used in a membrane, if a non-uniform state occurs in the surface direction, such as the concentration distribution of fuel gas or the amount of electrode catalyst attached, there is a problem that local deterioration of the ion exchange membrane tends to occur, which is not preferable.
[0082]
The porosity of the support film of the present invention is preferably 90% by volume or more, and more preferably 95% by volume or more. When the porosity is smaller than this range, the content of the ion exchange resin when the ion exchange resin is combined is small, and the ionic conductivity is lowered, which is not preferable.
[0083]
The support membrane of the present invention preferably has a porosity of at least one surface of 40% or more, more preferably 50% or more, and particularly preferably 60% or more. If the open area ratio of at least one surface is smaller than this range, it is not preferable because the ion exchange resin is hardly impregnated in the voids of the support membrane when the support membrane and the ion exchange resin are combined.
[0084]
A method for obtaining an ion exchange membrane by combining an ion exchange resin with a porous support membrane made of a polybenzazole-based polymer obtained by the above method will be described. That is, it is a method of obtaining an ion exchange membrane by a method in which the support membrane is immersed in an ion exchange resin solution without drying, and the solution inside the support membrane is replaced with an ion exchange resin solution and then dried. When the liquid inside the support membrane is different from the solvent composition of the ion exchange resin solution, a method in which the liquid inside is replaced in advance according to the solvent composition is also employed.
[0085]
The support membrane of the present invention is characterized in that the void structure shrinks as the volume of the liquid inside the void decreases due to drying, and the apparent volume of the support membrane is greatly reduced. When the inside of the support film is fixed to a metal frame without impregnating the ion exchange resin and dried by limiting the shrinkage in the surface direction, the shrinkage occurs in the film thickness direction. The apparent film thickness after drying ranges from 0.5% to 10% of the film thickness before drying. Such a significant shrinkage does not occur in a porous support film other than the support film of the present invention, for example, a support film made of a stretched polytetrafluoroethylene polymer porous film.
[0086]
Due to such characteristics of the support membrane, when the liquid inside the voids of the support membrane is replaced with an ion exchange resin solution and then dried, the solvent of the ion exchange resin solution impregnated inside the voids evaporates. As the volume of the ion exchange resin solution decreases, the support membrane also shrinks, so that a dense composite membrane structure filled with the ion exchange resin in which voids inside the support membrane are deposited can be easily obtained. Can do. Due to this composite membrane structure, the ion exchange membrane of the present invention exhibits excellent fuel permeation deterrence. In a porous support film other than the support film of the present invention, for example, a support film made of a stretched polytetrafluoroethylene polymer porous film, the solvent of the ion exchange resin solution impregnated in the voids is evaporated and the ion exchange is performed. Even if the volume of the resin solution is reduced, the support membrane accompanying the shrinkage is small, and therefore there are many voids not filled with the ion exchange resin inside the composite membrane after drying.
[0087]
The ion exchange membrane is also a combination of the physical properties such as the concentration and viscosity of the ion exchange resin solution, the volatility of the solvent, the film thickness and the porosity of the support membrane, etc. By adjusting the excess ion exchange resin solution adhered to both surfaces of the support film in parallel with the formation of a composite layer in which the ion exchange resin filled the internal voids of the support film, The ion exchange resin solution discharged from the inside of the support membrane with the shrinkage of the support membrane is dried outside the surface of the support membrane to form an ion exchange resin layer not containing the support, As a result, it is possible to easily realize a structure in which a surface layer of an ion exchange resin not including a support film is formed on both sides of the composite layer so as to sandwich the composite layer.
[0088]
Since the membrane other than the support membrane of the present invention, for example, the porous support membrane made of polytetrafluoroethylene polymer does not cause significant shrinkage as described above, when impregnated with an ion exchange resin solution and dried. Even if the ion exchange resin is deposited inside the support film, the voids remain. In order to eliminate this state, it is necessary to repeat the impregnation and drying of the ion exchange resin solution a plurality of times, which is not preferable because the process becomes complicated.
[0089]
The ion exchange resin used for the ion exchange membrane of the present invention is not particularly limited, and other than the above-mentioned perfluorocarbon sulfonic acid polymer, for example, polystyrene sulfonic acid, poly (trifluorostyrene) sulfonic acid, polyvinyl phosphonic acid. , Polyvinyl carboxylic acid, at least one ionomer of a polyvinyl sulfonic acid polymer, polysulfone, polyphenylene oxide, polyphenylene sulfoxide, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyphenyl quinoxaline, polyaryl ketone, polyether ketone, polybenzazole and Ionomer in which at least one of aromatic polymers such as polyaramid polymer is sulfonated, phosphonated or carboxylated can be applied. . The polysulfone polymer here includes at least one of polyethersulfone, polyarylsulfone, polyarylethersulfone, polyphenylsulfone, and polyphenylenesulfone polymer. The polyether ketone polymer referred to here includes at least one of polyether ether ketone, polyether ketone-ketone, polyether ether ketone-ketone and polyether ketone ether-ketone polymer.
[0090]
The solvent for the ion exchange resin solution described above can be selected from solvents that do not dissolve, decompose or swell the polybenzazole polymer support membrane and can dissolve the ion exchange resin. However, since the solvent is removed after the support membrane is impregnated with the ion exchange resin solution to deposit the ion exchange resin, the solvent can be removed by evaporating using means such as heating or decompression. It is preferable that Here, since the polybenzazole-based polymer support membrane of the present invention has high heat resistance, it is used in the production of an ion exchange membrane using a support membrane made of polytetrafluoroethylene that generates creep from a temperature of about 100 ° C. The ability to produce an ion exchange membrane using an ion exchange resin solution containing a solvent having a high boiling point that cannot be produced is also an excellent feature from the viewpoint that many types of ion exchange resins can be selected.
[0091]
The concentration of the ion exchange resin solution described above and the molecular weight of the ion exchange resin are not particularly limited, but are appropriately selected according to the type of ion exchange resin and the thickness of the ion exchange membrane to be obtained. The
[0092]
The content of the ion exchange resin in the ion exchange membrane obtained as described above is preferably 50% by weight or more. More preferably, it is 80 weight% or more. When the content is smaller than this range, the conductive resistance of the film increases or the water retention of the film decreases, so that sufficient power generation performance cannot be obtained.
[0093]
For the purpose of further improving characteristics such as mechanical strength, ion conductivity, and peeling resistance of the ion exchange resin layer formed on the surface of the ion exchange membrane, a method of heat-treating the ion exchange membrane under appropriate conditions is also preferably used. Can do. Further, in order to adjust the thickness of the surface layer of the ion exchange resin formed on the surface, the ion exchange membrane is further immersed in the ion exchange resin solution, or the ion exchange resin solution is applied to the ion exchange membrane. The amount of the ion exchange resin layer attached is increased by drying, or a part of the ion exchange resin solution adhering to the surface of the support film after being immersed in the ion exchange resin solution is scraper, air knife, roller, etc. It is also possible to use a method of reducing the amount of the ion-exchange resin layer deposited by scraping off or absorbing with a solution-absorbing material such as filter paper or sponge. Alternatively, a method of further improving the adhesion of the ion exchange resin layer by applying a hot press can be used together.
[0094]
Furthermore, the present invention provides an electrolyte membrane / electrode assembly using the ion exchange membrane. The ion exchange membrane of the present invention having a large storage elastic modulus and little decrease in the storage elastic modulus at high temperature is joined to the electrode catalyst layer, so that the ion exchange membrane can be compared with the conventional ion exchange membrane even under high temperature and humidification conditions. Therefore, it is possible to obtain an electrolyte membrane / electrode assembly in which peeling of the electrode hardly occurs. Here, as a manufacturing method of the electrolyte membrane / electrode assembly, a method of directly applying an electrode paste on the ion exchange membrane using a squeegee, screen printing, spraying, or the like, an electrode layer sheet prepared separately on the ion exchange membrane is used. Any method of adhering an electrode on an ion exchange membrane can be employed, such as a method of closely attaching using a heat press or the like.
[0095]
Furthermore, the present invention is a fuel cell using the above-mentioned electrolyte membrane / electrode assembly. Even when the fuel cell using the electrolyte membrane / electrode assembly is operated under the conditions of high temperature, high pressure, and humidification, the electrolyte membrane is damaged or the electrode is damaged as compared with the fuel cell using the conventional electrolyte membrane / electrode assembly. It has excellent durability because it is difficult to peel off.
[0096]
The ion exchange membrane of the present invention is excellent in heat resistance while having high ion conductivity. Moreover, it can be utilized as an ion exchange membrane, particularly as a polymer solid electrolyte membrane of a polymer electrolyte fuel cell, taking advantage of its characteristics.
[0097]
EXAMPLES Examples of the present invention are shown below, but the present invention is not limited to these examples.
Evaluation Method / Measurement Method <Structural Observation with Transmission Electron Microscope>
Observation of the cross-sectional structure of the film with a transmission electron microscope (TEM) was performed by the following method. First, an observation sample section was prepared as follows. That is, the water inside the support membrane sample after washing with water was substituted with ethanol, and further sufficiently substituted with an epoxy monomer.
The sample was kept in the epoxy monomer as it was at 45 ° C. for 6 hours, and then the epoxy was cured by further heat treatment at 60 ° C. for 20 hours (epoxy embedding). The epoxy-embedded sample is prepared into an ultrathin slice with a thickness that shows the interference color from silver to gold using a microtome equipped with a diamond knife, and treated with a KOH saturated ethanol solution for 15 minutes. The epoxy was removed with (de-epoxy). Further, carbon was vapor-deposited on a sample washed with ethanol and subsequently with water and stained with RuO ₄ , and observed with a JEOL TEM (JEM-2010) at an acceleration voltage of 200 kV.
[0098]
<Structural observation with atomic force microscope>
Structure observation with an atomic force microscope (AFM) was performed by the following method. That is, the surface structure of an undried support film held on an underwater sample stage using AFM (SPA 300 [observation mode: DFM mode, cantilever: SI-DF3, scanner: FS-100A]) manufactured by Seiko Instruments Inc. Was observed.
[0099]
<Structural observation by scanning electron microscope>
Structure observation by a scanning electron microscope (SEM) was performed by the following method. First, the water inside the washed support membrane was replaced with ethanol and further sufficiently replaced with isoamyl acetate, and then CO ₂ critical point drying was performed using a Hitachi critical point dryer (HCP-1). The support film thus dried at the critical point was coated with a platinum coating having a thickness of 150 angstroms, and observed using an SEM (S-800) manufactured by Hitachi at an acceleration voltage of 10 kV and a sample tilt angle of 30 degrees.
[0100]
<Intrinsic viscosity>
Using methanesulfonic acid as a solvent, the viscosity of the polymer solution adjusted to a concentration of 0.5 g / L was measured and calculated using a Ubbelohde viscometer in a 25 ° C. constant temperature bath.
[0101]
<Dynamic viscoelasticity measurement>
The dynamic viscoelasticity of the ion exchange membrane was measured as follows. A strip-shaped sample with a width of 5 mm was set on a dynamic viscoelasticity measuring apparatus (model name: Rheogel-E4000) manufactured by UBM Co., Ltd. so that the distance between chucks was 14 mm, and the frequency was 10 Hz and the strain was 0.7% in the tensile mode. It measured in the temperature range of 25 degreeC-200 degreeC in nitrogen stream.
[0102]
<Ionic conductivity>
The ionic conductivity σ was measured as follows. A platinum wire (diameter: 0.2 mm) is pressed against the surface of a strip-shaped film sample having a width of 10 mm on a self-made measuring probe (made of polytetrafluoroethylene) and placed in a constant temperature and humidity chamber at 80 ° C. and a relative humidity of 95%. The sample was held, and the AC impedance at 10 kHz between the platinum wires was measured by SOLARTRON 1250 FREQUENCY RESPONSE ANALYSER. The contact distance between the membrane and the platinum wire is measured by the following formula from the slope Dr [Ω / cm] of the straight line in which the distance between the electrodes is changed from 10 mm to 40 mm at intervals of 10 mm and the distance between the electrodes and the measured resistance value are plotted. Canceled and calculated.
σ [S / cm] = 1 / (film width × film thickness [cm] × Dr)
[0103]
<Preparation of electrolyte membrane / electrode assembly and power generation test>
DuPont 20% Nafion (trade name) solution (product number: SE-20192), platinum-supported carbon (carbon: Valbot XC-72, Cabot Co., platinum supported amount: 40 wt%), platinum and Nafion weight ratio The catalyst paste was prepared by adding 2.7: 1 and stirring. This catalyst paste was applied to the ion exchange membrane so that the amount of platinum deposited was 1 mg / cm 2 and dried to prepare an ion exchange membrane with an electrode catalyst layer. By sandwiching an ion exchange membrane between two Toray carbon papers TGPH-060 so that the electrode catalyst layer is in contact with the membrane sample, by pressurizing and heating at 120 ° C. and 2 MPa for 3 minutes by a hot press method An electrolyte membrane / electrode assembly was prepared. The produced electrolyte membrane / electrode assembly is assembled into a fuel cell for pressure resistance evaluation, and the cell temperature is 130 ° C., the gas humidification temperature is 120 ° C., the gas pressure is 0.3 MPa, the fuel gas is 300 mL / min, and the oxidizing gas is 1000 mL of air. A power generation test was conducted at a gas flow rate of / min.
[0104]
Example 1
Isotropic with polyparaphenylene cis bisbisoxazole concentration of 1% by weight by adding methane sulfonic acid to a dope containing 14% by weight of polyparaphenylene cis benzobisoxazole polymer with IV = 24 dL / g in polyphosphoric acid A solution was prepared. This solution was formed on a glass plate heated to 90 ° C. using an applicator having a clearance of 300 μm at a film forming rate of 5 mm / second. The dope film thus formed on the glass plate was solidified for 10 minutes in a constant temperature and humidity chamber at 25 ° C. and 80% relative humidity, and then solidified in pure water at 25 ° C. for 15 minutes, The produced membrane was washed with water until the washing solution showed pH 7 ± 0.5 to prepare a support membrane. The prepared support film was confirmed to be a porous film having continuous pores having openings on both sides by observation of a surface form using an atomic force microscope and a cross-sectional form using a transmission electron microscope. This support membrane is fixed to a stainless steel frame in water, and the water composition inside the support membrane is a solvent composition of a DuPont 20% Nafion (trade name) solution (product number: SE-20192) which is an ion exchange resin solution. And a mixed solvent of water: ethanol: 1-propanol = 26: 26: 48 (weight ratio).
This support membrane was immersed in a 20% Nafion (trade name) solution at 25 ° C. for 15 hours and then removed from the solution. The solvent of the Nafion (trade name) solution impregnated inside the membrane and adhered to the membrane surface was volatilized by air drying. Dried. The dried membrane was preheated in an oven at 60 ° C. for 1 hour to remove the remaining solvent, and then heat treated at 150 ° C. for 1 hour in a nitrogen atmosphere to prepare the ion exchange membrane of Example 1.
[0105]
Comparative Example 1
As Comparative Example 1, a commercially available Nafion 112 (trade name) membrane manufactured by DuPont was used. This membrane is a proton exchange membrane made of the same perfluorocarbon sulfonic acid polymer as the Nafion polymer contained in the 20% Nafion solution used in Example 1, and is widely used as a proton exchange membrane for polymer electrolyte fuel cells. Is.
[0106]
Comparative Example 2
A stretched porous PTFE (polytetrafluoroethylene) sheet having a thickness of 20 μm and a porosity of 89% was fixed to a stainless steel frame, immersed in a 20% Nafion (trade name) solution at 25 ° C. for 15 hours, and then taken out from the solution. The solvent of Nafion (trade name) solution impregnated inside the membrane and adhered to the membrane surface was volatilized by air drying and dried. This impregnation-air drying was repeated 5 times to form a membrane filled with Nafion (trade name) resin in the voids and the surface of the stretched porous PTFE membrane. The dried membrane was preheated in an oven at 60 ° C. for 1 hour to remove the remaining solvent, and then heat treated at 150 ° C. for 1 hour in a nitrogen atmosphere to prepare an ion exchange membrane of Comparative Example 2.
[0107]
For the ion exchange membranes of Example 1 and Comparative Example 2, an electrolyte membrane / electrode assembly was prepared, and after generating power for 100 hours at a cell voltage of 0.5 V under the high-temperature power generation test conditions described above, the electrolyte The membrane / electrode assembly was taken out and the state of electrode bonding was examined. The ion exchange membrane of Example 1 was in good condition, whereas the ion exchange membrane of Comparative Example 2 was one of the electrodes. The part was peeled off from the ion exchange membrane.
[0108]
Example 1 The physical properties of Comparative Example 1 are shown in Table 1.
[0109]
[Table 1]

[0110]
Compared with the commercially available Nafion 112 membrane of Comparative Example 1 and the ion exchange membrane of Comparative Example 2, the ion exchange membrane of Example 1 has a storage elastic modulus G ′ ₃₀ value of 1.35 × 10 ⁹ at 30 ° C. It can be seen that this is an ion exchange membrane having a large Pa. Further, it can be seen that the ion exchange membrane of Example 1 does not cause a significant decrease in ionic conductivity as compared with Comparative Example 1 which does not include a support, although it has a support inside.
[0111]
Furthermore, the ion exchange membrane of Example 1 had better electrode adhesion during high-temperature power generation than the ion exchange membrane of Comparative Example 2. Since the ion exchange membrane of Example 1 has a large storage elastic modulus and a small decrease in the storage elastic modulus at high temperatures, it is estimated that the dimensional change of the membrane was small during power generation at high temperatures, and no electrode peeling occurred. The Thus, it can be seen that the ion exchange membrane of the present invention has excellent characteristics as a polymer solid electrolyte membrane of a fuel cell at high temperatures.
[0112]
【The invention's effect】
A polymer solid electrolyte membrane having high heat resistance and excellent ion conductivity can be provided.

Claims (3)

An ion exchange membrane having a support membrane having voids and a composite layer made of an ion exchange resin impregnated in the voids, the support membrane comprising a polybenzazole-based polymer having a weight of 0.3 wt% to 3 wt% A polybenzazole-based polymer having a three-dimensional continuous void formed of a three-dimensional network structure formed from fibrillar fibers of a polybenzazole-based polymer produced by forming an isotropic solution into a film and then coagulating it In the dynamic viscoelasticity measurement of the ion exchange membrane, the storage elastic modulus G ′ _{30 at} 30 ° C. is 8 × 10 ⁸ Pa or more and the storage elastic modulus G ′ _{200 at} 200 ° C. An ion exchange membrane characterized in that the ratio of to G ′ ₃₀ is 30 % or more. An electrolyte membrane / electrode assembly using the ion exchange membrane according to claim 1. A fuel cell comprising the electrolyte membrane / electrode assembly according to claim 2.