JP2004197062A - Porous film, composite ion exchange film, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a porous film comprising a polybenzazole-based polymer having excellent heat resistance, mechanical strengths, smoothness, interlayer separation resistance and penetrability of a functional agent, and a composite ion exchange film composited with an ion exchange resin. <P>SOLUTION: The porous film is produced by preparing a thin film by passing a polymer dope comprising the polybenzazole-based polymer sandwitched between at least two sheets of a film-like support through rolls, a slit or a press, introducing the thin film into a coagulation bath and coagulating the thin film by separating the support in the coagulation bath. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２０】
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。
【００２１】
【化２】

【００２２】
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。
【００２３】
【化３】

【００２４】
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。
【００２５】
【化４】

【００２６】
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。
【００２７】
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。
【００２８】
【化５】

【００２９】
【化６】

【００３０】
【化７】

【００３１】
【化８】

【００３２】
【化９】

【００３３】
【化１０】

【００３４】
【化１１】

【００３５】
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。
【００３６】
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。
【００３７】
【化１２】

【００３８】
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。
【００３９】
【化１３】

【００４０】
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。
【００４１】
【化１４】

【００４２】
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。
【００４３】
【化１５】

【００４４】
【化１６】

【００４５】
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。
【００４６】
【化１７】

【００４７】
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。
【００４８】
【化１８】

【００４９】
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。
【００５０】
【化１９】

【００５１】
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。
【００５２】
【化２０】

【００５３】
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。
【００５４】
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。
【００５５】
【化２１】

【００５６】
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。
【００５７】
【化２２】

【００５８】
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。
【００５９】
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。
【００６０】
【化２３】

【００６１】
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。
【００６２】
【化２４】

【００６３】
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。
【００６４】
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。
【００６５】
【化２５】

【００６６】
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。
【００６７】
【化２６】

【００６８】
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。
【００６９】
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。
【００７０】
【化２７】

【００７１】
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。
【００７２】
【化２８】

【００７３】
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。
【００７４】
【化２９】

【００７５】
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。
【００７６】
【化３０】

【００７７】
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。
【００７８】
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、溶液の粘度が高く加工困難であり、また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。これらの溶液を、ポリリン酸、メタンスルホン酸等の溶媒で希釈して、ポリマードープとして用いる。
【００７９】
本発明のポリベンザゾールの多孔膜は、押出しおよび薄膜化、凝固、洗浄および乾燥等の工程により製膜される。均一な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、多孔性支持体膜の表面開孔率や空隙率が小さくなったり、多孔性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。
【００８０】
本発明におけるポリベンザゾール系ポリマードープの製膜方法は、２枚のフィルム状シートの間に挟んだポリマードープをロールやスリットまたはプレスを介して薄膜化したものを凝固浴に導き、凝固浴中でフィルム状シートを剥離、凝固させる手法が最も好ましい。ここでいう薄膜化とは、上記の手段等を用いて凝固前のポリマードープの状態で、一般的には厚みが１０μｍから５００μｍ程度にすることを言うが、限定なく市場要求に従って任意に設定できる。ロールやスリットまたはプレスの構成、配置はさまざまな組合わせをとることができる。望ましくは、少なくとも二枚のフィルム状シートの間に挟んだポリマードープを、少なくとも二本のロールの間にはさみ、向かい合ったロールを反対方向に回転させ、薄膜化したポリマードープを送り出す方式である。
【００８１】
圧延されたポリマードープを挟んだフィルム状シートは、ガイドロールを介して凝固浴に導かれ、凝固浴中でフィルム状シートを剥離することにより、ポリマードープは凝固し、多孔膜となる。凝固浴中でフィルム状シートを剥離することによりポリマー溶液を完全に凝固する前に、フィルム状シートを透過した貧溶媒またはその蒸気で該ポリベンザゾール系ポリマーの凝固の少なくとも一部を行うことにより、支持体膜表面および内部の構造、空隙率を制御することが可能となる。
【００８２】
ここで、最外層のフィルム状シートとポリマードープとの間に多孔質支持体や布帛、不織布等を挟んで複合化膜としてもよい。また、フィルム状シートとして多孔質支持体や布帛、不織布をそのまま用いて複合化膜として用いることもできる。多孔質支持体や布帛、不織布は通気性や液透過性があることが望ましい。該ポリベンザゾール系ポリマーの貧溶媒またはその蒸気を透過させるフィルム状シートとしては、ポリプロピレンからなる多孔質状のフィルム状シートが好ましく、その他ポリエチレン，ポリテトラフルオロエチレン等の各種材質の多孔質状のフィルム状シートが使用可能である。特に、凝固液として水または水とその他の溶媒との混合溶媒や水溶液を用いる場合、水蒸気のみを透過させ液体の水を透過させない、多孔質支持体を用いることが好ましい。これらは、公称孔径が０．０３μｍから１０μｍ程度の市販のメンブランフィルターや、電池用セパレーター膜を利用できる。
【００８３】
ここでいう凝固浴とは、凝固液が入った槽だけでなく、凝固性を有する気体、ミスト、蒸気が存在するゾーンも含む。凝固液としては、水、金属塩水溶液、多価アルコール、非プロトン性極性溶媒、プロトン極性溶媒等さらにはドープ希釈溶媒である、ポリリン酸、メタンスルホン酸の水溶液等が挙げられる。またこれらのミスト、蒸気も挙げられる。凝固液の温度は１０℃以上７０℃以下が好ましい。さらに好ましくは３０℃以上６０℃以下である。一般的に膜構造は、ポリマードープフィルムへの凝固液滲入と、ポリマードープ薄膜からのポリマー溶媒の流出のバランスにより、構造が決まる。凝固液温度が低すぎると、凝固液とポリマー溶媒の液液交換が不十分となり、所望の膜構造が得られない。凝固液温度が高すぎると、構造的には望ましいものが得られるが、強度的に非常に弱いものになりやすい。本発明においては、凝固液温度が１０℃以上７０℃以下が好ましい。さらに好ましくは３０℃以上６０℃以下で構造および強度的に満足な多孔膜が得られる。
【００８４】
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多孔性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、成形加工が困難となり、また経済的にも好ましくないほか、得られる多孔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。また、この範囲よりも濃度が高いと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。光学異方性を示すポリベンザゾール系ポリマー溶液から製膜した多孔膜ではイオン交換樹脂を大量に含浸できるような空隙率の大きな連続した空隙を有する多孔性のポリベンザゾール系ポリマー膜が得られないため好ましくない。
【００８５】
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。
【００８６】
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。
【００８７】
上記のようにして凝固されたポリベンザゾール系ポリマーからなる多孔性支持体膜は、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。洗浄は多孔性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、多孔性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。
【００８８】
押出しおよび薄膜化工程、凝固工程、洗浄工程および乾燥工程等は連続的に行ってもよく、また、バッチ式で行ってもよい。さらに各工程の間に、含浸やコート、ラミネート処理による複合化、延伸、紫外線や電子線、コロナ照射等の表面処理、アニール処理等、目的に応じてその他の特別な工程を加えてもよい。
【００８９】
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該多孔性支持体膜にイオン交換樹脂を複合化させ、複合イオン交換膜を得る方法について説明する。即ち、該多孔性支持体膜を乾燥させずに、イオン交換樹脂溶液に浸漬し、該多孔性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複合イオン交換膜を得る方法である。多孔性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。
【００９０】
本発明の多孔性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。該多孔性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、該多孔性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。
【００９１】
該多孔性支持体膜のこのような特徴により、該多孔性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多孔性支持体膜も収縮するので、該多孔膜性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、本発明の複合イオン交換膜は優れた燃料透過抑止性を示す。本発明の多孔性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多孔性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、それに伴う多孔性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ばかりでなく、多孔性支持体膜の両面に支持体を含まないイオン交換樹脂の表面層が形成されないため好ましくない。
【００９２】
該複合イオン交換膜はまた、該多孔性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、該多孔性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多孔性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多孔性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多孔性支持体膜内部から排出されたイオン交換樹脂溶液が該多孔性支持体膜の表面外部で乾燥して該多孔膜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多孔性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。
【００９３】
本発明の多孔性支持体膜以外の膜、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性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多孔性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り、また多孔性支持体膜複合層を挟む形のイオン交換樹脂層も形成されない。イオン交換樹脂溶液の含浸、乾燥を複数回繰り返すことで、この状態を低減可能であるが、工程が複雑になるため好ましくない。
【００９４】
本発明の複合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。
【００９５】
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多孔性支持体膜を溶解、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多孔性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多孔性支持体膜を用いる複合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複合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。
【００９６】
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複合イオン交換膜の膜厚などに応じて適宜選択される。
【００９７】
上記のようにして得られる複合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。
【００９８】
また、本発明の複合イオン交換膜は、上記で記述したように複合層を挟む形で複合層の両面に支持体を含まないイオン交換樹脂からなる表面層を有することを特徴とする。複合イオン交換膜が該複合層と該表面層を有することにより、該複合イオン交換膜は高い機械的強度を有し、かつ、表面に電極層を形成させた場合の電極層との密着性に優れるという特長を有する。該表面層の厚みはそれぞれ１μｍ以上５０μｍ以下であり、かつ、それぞれが該複合イオン交換膜の全厚みの半分を超えない範囲であることが好ましい。該表面層の厚みが上記範囲よりも小さいと電極層との密着性が悪くなり、イオン伝導性が低下するなどするため好ましくない。また該表面層の厚みが上記範囲よりも大きいと、複合層による補強の効果が複合イオン交換膜の最外表面まで及ばず、複合イオン交換膜が吸湿した場合に表面層のみが大きく膨潤して表面層が複合層から剥離するなどするため好ましくない。該表面層の厚みのさらに好ましい範囲は２μｍ以上３０μｍ以下である。
【００９９】
複合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、複合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、該複合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、該複合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多孔性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。
【０１００】
本発明の複合イオン交換膜は高いイオン伝導性を有しながら、機械的強度に優れる。また、その特性を生かして、複合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。
【０１０１】
（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。実施例中で示される特性は、以下の方法で測定・評価したものである。
（評価法・測定法）
１、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、水洗後の多孔性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。
【０１０２】
２、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多孔性支持体膜の表面構造を観察した。
【０１０３】
３、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。
【０１０４】
４、多孔性支持体膜厚み
未乾燥の多孔性支持体膜の厚みは次に示す方法により測定した。測定荷重を変更可能なマイクロメータを用い、各荷重における水中での支持体膜の厚みを測定した。測定した厚みを荷重に対してプロットし、直線部分を荷重０に外挿したときの切片の値を厚みとし、一つの試料について５ヶ所で測定した厚みの平均値を支持体膜の厚みとした。
【０１０５】
５、複合イオン交換膜の厚さおよび、それを構成する層の厚さ
該複合イオン交換膜を構成する複合層および該複合層を挟む形で複合層の両面に形成された多孔性支持体膜を含まないイオン交換樹脂からなる表面層の厚さは、多孔質状のフィルム状幅３００μｍ×長さ５ｍｍに切り出した複合膜片を、ルベアック８１２（ナカライテスク製）／ルベアックＮＭＡ（ナカライテスク製）／ＤＭＰ３０（ＴＡＡＢ製）＝１００／８９／４の組成とした樹脂で包埋し、６０℃で１２時間硬化させて試料ブロックを作製した。ウルトラミクロトーム（ＬＫＢ製２０８８ＵＬＴＲＯＴＯＭＥ ５）を用いて平滑な断面が露出するようブロックの先端をダイヤモンドナイフ（住友電工製ＳＫ２０４５）で切削した。このようにして露出させた複合膜の断面を光学顕微鏡で写真撮影し、既知の長さのスケールを同倍率で撮影したものと比較することで測定した。多孔膜支持体の空隙率が大きい場合等で、少なくとも一方の面の表面層とその内側の複合層とが明確な界面を形成せずに界面付近の構造が連続的に変化している場合があるが、その場合は光学顕微鏡で連続的な構造の変化が確認できる部分のうち、複合イオン交換膜の外表面に最も近い部分を複合層の最外表面として、そこから複合イオン交換膜の外表面までの距離を該表面層の厚みとした。
【０１０６】
６、複合イオン交換膜のイオン交換樹脂（ＩＣＰ）含有率
複合イオン交換膜のイオン交換樹脂含有率は以下の方法により測定した。１１０℃で６時間真空乾燥させた複合イオン交換膜の目付けＤｃ［ｇ／ｍ２］を測定し、複合イオン交換膜の作製に用いたのと同じ製造条件の多孔性支持体膜をイオン交換樹脂を複合化させずに乾燥させて測定した乾燥多孔性支持体膜の目付けＤｓ［ｇ／ｍ２］とから、以下の計算によりイオン交換樹脂含有率を求めた。
イオン交換樹脂含有率［重量％］＝（Ｄｃ−Ｄｓ）／Ｄｃ×１００
また、複合イオン交換膜のイオン交換樹脂含有率は以下の方法によって測定することもできる。すなわち、複合イオン交換膜を複合イオン交換膜中の多孔性支持体膜成分あるいは、イオン交換樹脂成分のいずれかのみを溶解可能な溶剤に浸漬して一方の成分を抽出、除去した後、元の複合イオン交換膜との重量変化を測定することでイオン交換樹脂の含有率を求めることができる。
【０１０７】
７、強度・引張弾性率
イオン交換膜の強度特性は、気温２５℃、相対湿度５０％の雰囲気で、オリエンテック社製テンシロンを用いて測定した。試料は幅１０ｍｍの短冊状とし、支間長４０ｍｍ、引っ張り速度２０ｍｍ／ｓｅｃで測定した応力歪み曲線から算出した。
【０１０８】
８、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（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）
【０１０９】
９、ガス透過率
イオン交換膜のガス透過率は以下の方法で測定した。イオン交換膜をメッシュ状のステンレス製サポート上に置き、ホルダーに固定した後、イオン交換膜の一方の面に室温にて水蒸気で飽和したヘリウムガスをゲージ圧が０．０９ＭＰａとなるようにして流通させ、イオン交換膜の他方の面に透過してくるヘリウムガスの量を石鹸膜流量計を用いて測定し算出した。
【０１１０】
１０、発電特性
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、東レ製カーボンペーパーＴＧＰＨ−０６０に白金の付着量が１ｍｇ／ｃｍ２になるように塗布、乾燥して、電極触媒層付きガス拡散層を作成した。２枚の電極触媒層付きガス拡散層の間に、膜試料を、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、膜−電極接合体とした。この接合体をＥｌｅｃｔｒｏｃｈｅｍ社製評価用燃料電池セルＦＣ２５−０２ＳＰに組み込んでセル温度８０℃、ガス加湿温度８０℃、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特性評価を行った。
【０１１１】
１１．乾燥膜物性
（表面粗さ）
乾燥後の膜を、マイクロマップ社製三次元非接触表面形状計測システムをもちいて、二乗平均粗さの測定をおこなった。
【０１１２】
１２．引張弾性率
乾燥後の膜を縦方向（ＭＤ方向）および横方向（ＴＤ方向）にそれぞれ長さ１００ｍｍ、幅１０ｍｍの短冊状に切り出して試験片とし、引張測定器（島津製作所製オートグラフ 機種名ＡＧ−５０００Ａ）を用い、引張速度５０ｍｍ／分、チャック間距離４０ｍｍで引張試験をおこない、引張弾性率を測定した。
【０１１３】
１３．弾性率温度依存性、弾性率保持率
乾燥後の膜を縦方向（ＭＤ）および横方向（ＴＤ）にそれぞれ長さ４０ｍｍ、幅５ｍｍの短冊状に切り出して試験片とし、動的粘弾性測定装置（アイティ計測製 機種名ＤＶＡ−２２５）を用い、室温から４００℃まで、昇温速度５℃／分、１０Ｈｚで測定をおこなった。弾性率保持率として３００℃／３０℃の弾性率比を用いた。
【０１１４】
１４．層間剥離試験
乾燥後の膜を縦方向（ＭＤ方向）および横方向（ＴＤ方向）にそれぞれ長さ２０ｍｍ、幅１０ｍｍの短冊状に切り出して試験片とし、膜の表裏面に、粘着テープの接着面を張り合わせた。
引張測定器（島津製作所製オートグラフ 機種名ＡＧ−５０００Ａ）を用い、引張速度５０ｍｍ／分、チャック間距離４０ｍｍで、テープをゆっくりとはがし、両方の粘着テープの粘着面にフィルムが移行する層間剥離現象の有無を調べた。（図３参照）
【０１１５】
（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２．５重量％の等方性溶液を調製した。この溶液を、公称目開き２０μｍフィルターを通してから、二本の対向ロールの間にある二枚のポリプロピレンからなる多孔質状のフィルム状シートの間に挟み、二本のロールにおいて、向かい合ったロールを反対方向に回転させ、ドープを圧延しながらポリプロピレンからなる多孔質状フィルム状シートをごと送り出し、２５℃、相対湿度８０％の恒温恒湿槽雰囲気において３０分間凝固させた後に凝固浴に導いた。凝固液は６０℃の水をもちいた。このとき、対向ロール間のギャップを調整し、ドープ厚みで２００μｍになるようにした。凝固浴中でポリプロピレンからなる多孔質状のフィルム状シートを剥離し、ドープを凝固液に接触させてさらに凝固させた。図２に、製造法の模式図を示した。その後、生成した膜を洗液がｐＨ７±０．５を示すまで水洗を行ってポリベンザゾール系ポリマーからなる多孔性支持体膜を作成した。作成したポリベンザゾール系ポリマーからなる多孔性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。乾燥膜については、上記凝固させた膜を水洗した後にテンターで両端を把持しつつ１５０℃で２０秒間熱固定して厚み５．２μｍのポリベンザゾール膜を得た。乾燥後の膜を、マイクロマップ社製三次元非接触表面形状計測システムをもちいて、二乗平均粗さの測定をおこなった。層間剥離性、引張弾性率、弾性率温度依存性測定結果を表２に示した。
【０１１６】
（比較例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２．５重量％の等方性溶液を調製した。この溶液を、７０℃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。この条件においては、ポリベンザゾール系ポリマー溶液は高粘度となってしまい、スキージ方向に筋斑が発生し、平滑なフィルムを得ることができなかった。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％の恒温恒湿槽中に置いて１時間凝固し、生成した膜を洗液がｐＨ７±０．５を示すまで水洗を行ってポリベンザゾール系ポリマーからなる多孔性支持体膜を作成した。作成した多孔性支持体膜は、基盤に接している側の表面は緻密構造を形成しているのに対して、基盤に接していない側の表面は多孔構造を形成してい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、両面に開口部を持たない膜であることを確認した。
【０１１７】
（比較例２）
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２．５重量％の等方性溶液を調製した。この溶液を、公称目開き２０μｍフィルターを通してから、二本の対向ロールの間にある二枚のポリエチレンテレフタレートからなるフィルム状シートの間に挟み、二本のロールにおいて、向かい合ったロールを反対方向に回転させ、ドープを圧延しながらポリエチレンテレフタレートからなるフィルム状シートごと送り出し凝固浴に導いた。凝固液は６０℃の水をもちいた。このとき、対向ロール間のギャップを調整し、ドープ厚みで２００μｍになるようにした。凝固浴中でポリエチレンテレフタレートからなるフィルム状シートを剥離し、ドープを凝固液に接触させてさらに凝固させた。その後、生成した膜を洗液がｐＨ７±０．５を示すまで水洗を行ってポリベンザゾール系ポリマーからなる多孔性支持体膜を作成した。作成したポリベンザゾール系ポリマーからなる多孔性支持体膜は両面に開口部を持たない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。乾燥膜については、上記凝固させた膜を水洗した後にテンターで両端を把持しつつ１５０℃で２０秒間熱固定して厚み５．４μｍのポリベンザゾール膜を得た。 乾燥後の膜を、マイクロマップ社製三次元非接触表面形状計測システムをもちいて、二乗平均粗さの測定をおこなった。層間剥離性、引張弾性率、弾性率温度依存性測定結果を表１に示した。
【０１１８】
【表１】

【０１１９】
比較例１から、流延法による製造方法ではポリベンザゾール系ポリマー溶液は高粘度となってしまうためにスキージ方向に筋斑が発生し、平滑な膜フィルムを得ることができない。また、基盤に接している側の表面は緻密構造を形成してしまう。一方、実施例１である本発明による製造方法においてはポリベンザゾール系ポリマー溶液が高粘度であっても平滑な膜フィルムを得ることができ、また両面に開口部を持つ連続した空孔を有する多孔膜を製造することができる。比較例２から、フィルム状シートがポリベンザゾール系ポリマーの貧溶媒またはその蒸気を透過させないフィルム状シートを用いて成形加工後に直ぐに水のように凝固力の強い貧溶媒である凝固液の凝固浴に導き、フィルム状シートを剥離し直接凝固液に接触させて凝固させた場合では、膜の表面構造は緻密化してしまい多孔質状の構造形成を実現させることはできない。
【０１２０】
（実施例２）
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２．５重量％の等方性溶液を調製した。この溶液を、公称目開き２０μｍフィルターを通してから、二本の対向ロールの間にある二枚のポリプロピレンからなる多孔質状のフィルム状シートの間に挟み、二本のロールにおいて、向かい合ったロールを反対方向に回転させ、ドープを圧延しながらポリプロピレンからなる多孔質状のフィルム状シートごと送り出し、２５℃、相対湿度８０％の恒温恒湿槽雰囲気において３０分間凝固させた後に凝固浴に導いた。凝固液は６０℃の水をもちいた。このとき、対向ロール間のギャップを調整し、ドープ厚みで２００μｍになるようにした。凝固浴中でポリプロピレンからなる多孔質状のフィルム状シートを剥離し、ドープを凝固液に接触させてさらに凝固させた。その後、生成した膜を洗液がｐＨ７±０．５を示すまで水洗を行ってポリベンザゾール系ポリマーからなる支持体多孔膜を作成した。この多孔性支持体膜を水中でステンレス製のフレームに固定し、多孔性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。この多孔性支持体膜を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２の複合イオン交換膜を調製した。
【０１２１】
（比較例３）
比較例３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％ナフィオン溶液や実施例２で用いた１０％ナフィオン水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。
【０１２２】
（比較例４）
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８重量％の光学異方性溶液を調製した。この溶液を、公称目開き２０μｍフィルターを通してから、二本の対向ロールの間にある二枚のポリプロピレンからなる多孔質状のフィルム状シートの間に挟み、二本のロールにおいて、向かい合ったロールを反対方向に回転させ、ドープを圧延しながらポリプロピレンからなる多孔質状のフィルム状シートごと送り出し、２５℃、相対湿度８０％の恒温恒湿槽雰囲気において３０分間凝固させた後に凝固浴に導いた。凝固液は６０℃の水をもちいた。このとき、対向ロール間のギャップを調整し、ドープ厚みで２００μｍになるようにした。凝固浴中でポリプロピレンからなる多孔質状のフィルム状シートを剥離し、ドープを凝固液に接触させてさらに凝固させた。その後、生成した膜を洗液がｐＨ７±０．５を示すまで水洗を行って多孔性支持体膜を作成した。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、多孔性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。この多孔性支持体膜を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比較例４の複合イオン交換膜を調製した。
【０１２３】
（比較例５）
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２．５重量％の等方性溶液を調製した。この溶液を、７０℃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。この条件においては、ポリベンザゾール系ポリマー溶液は高粘度となってしまい、スキージ方向に筋斑が発生し、平滑なフィルムを得ることができなかった。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％の恒温恒湿槽中に置いて１時間凝固し、生成した膜を洗液がｐＨ７±０．５を示すまで水洗を行って多孔性支持体膜を作成した。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、多孔性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。この多孔性支持体膜を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比較例５の複合イオン交換膜を調製した。
【０１２４】
実施例２、比較例３、４、５の物性値を表１に示す。
【０１２５】
【表２】

【０１２６】
実施例２の複合イオン交換膜は比較例３である市販のナフィオン１１２膜と対比して破断強度ならびに引張弾性率の大きなイオン交換膜であることがわかる。また実施例２の複合イオン交換膜は内部に多孔膜支持体を有するにもかかわらず、多孔膜支持体を含まない比較例３に比べてイオン導電率、発電性能ともに大幅な低下を起こすことなく、ガス透過率は半分以下の小さい値に抑えられており、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。比較例４の光学異方性溶液より得られたポリベンザゾール系ポリマーからなる支持体膜を用いた場合では、イオン導電率、発電性能ともに低下してしまい、燃料電池の高分子固体電解質膜としては優れた特性を備えることはできなかった。比較例５の流延法により製造された多孔性支持体膜を用いた複合イオン交換膜においては、平滑な膜（フィルム）を得ることができないという問題があり、またイオン導電率、発電性能ともに低下してしまい、燃料電池の高分子固体電解質膜としては優れた特性を備えることはできなかった。
【０１２７】
【発明の効果】
以上のとおり、本発明は特許請求項範囲に記載のとおりの構成を採用することにより、優れた耐熱性、機械的強度、平滑性、耐層間剥離性および機能性剤の含浸性を兼ね備えたポリベンゾアゾール系ポリマーよりなる多孔膜および機械的強度が高く、イオン伝導性、発電特性、ガスバリヤー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。
【図面の簡単な説明】
【図１】複合イオン交換膜の断面構造の模式図である。
【図２】本発明における製造方法の模式図である。
【図３】層間剥離試験の模式図である。
【符号の説明】１ 表面層Ａ、 ２ 複合層、 ３ 表面層Ｂ、 ４ フィルム状シート、 ５ ポリベンザゾール系ポリマー溶液、 ６ プレスロール、７ 凝固浴、 ８ 凝固液、 ９ ガイドロール、 １０ ポリベンザゾール系ポリマーからなる多孔膜、 １１ 試験膜、 １２ 粘着テープ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a porous film made of a polybenzoazole-based polymer having excellent heat resistance, mechanical strength, smoothness, and delamination resistance, and a method for producing the same. Further, the present invention relates to a composite ion exchange membrane having excellent mechanical strength and ion conductivity, particularly to a solid polymer electrolyte membrane.
[0002]
[Prior art]
With the development of electronics and other technologies, there is a strong demand for flexible films and films that have both excellent heat resistance and mechanical properties. Examples of the heat-resistant organic polymer include aramid, aromatic polyimide, aromatic polyether ketone, and the like. However, these films are insufficient in heat resistance (aramid, aromatic polyether ketone), have relatively high moisture absorption, and are unsatisfactory in electrical insulation and moisture absorption dimensional stability (aramid). ) And the molding process is complicated (aromatic polyimide), and each has its own drawbacks.
[0003]
Patent Literature 1 discloses a polybenzoazole. Polybenzoazole is more excellent in heat resistance than aromatic polyimide and also excellent in strength. However, polybenzoazole has a high rigidity, so that it tends to have a liquid crystal structure, and when the film is formed, it is excessively oriented in the discharge direction. Therefore, the formed film is easily fibrillated, and the film is formed in the film forming direction (MD direction). Although the mechanical strength is strong, the mechanical strength in the direction perpendicular to the MD direction (TD direction) is weak, and it has a disadvantage that it is easily torn.
[0004]
Patent Literature 2 discloses a method for producing an oriented polybenzoazole film. However, the polybenzoazole film obtained by this method has a problem that film formation is very complicated and delamination tends to occur in the film thickness direction.
[0005]
Film formation by the casting method using an applicator is also a well-known technique, but with a high-viscosity dope solution such as polybenzoazole, streaks appear in the squeegee direction and a smooth film or film can be obtained. Can not.
[0006]
On the other hand, in recent years, new power generation technologies with excellent energy efficiency and environmental friendliness have been attracting attention. Among them, polymer electrolyte fuel cells using polymer solid electrolyte membranes have features such as high energy density, and low operating temperature compared to other types of fuel cells, so they can be easily started and stopped. In addition, development as power supply devices for electric vehicles, distributed power generation, and the like has been progressing. In addition, a direct methanol fuel cell, which also uses a solid polymer electrolyte membrane and directly supplies methanol as a fuel, is being developed for use as a power source for portable devices. A proton conductive ion exchange resin membrane is usually used for the polymer solid electrolyte membrane. In addition to proton conductivity, the polymer solid electrolyte membrane is required to have properties such as fuel permeation suppression properties for preventing permeation of hydrogen and the like of fuel and mechanical strength. As such a polymer solid electrolyte membrane, for example, a perfluorocarbon sulfonic acid polymer membrane into which a sulfonic acid group is introduced, such as Nafion (trade name) manufactured by DuPont, USA, is known.
[0007]
In order to increase the output and efficiency of a polymer electrolyte fuel cell, it is effective to reduce the ionic conduction resistance of the polymer electrolyte membrane. One of the measures is to reduce the film thickness. Attempts have been made to reduce the film thickness of a solid polymer electrolyte membrane such as Nafion. However, when the film thickness is reduced, the mechanical strength is reduced, and the polymer solid electrolyte membrane and the electrode are apt to be damaged when hot-pressed, for example, when the polymer solid electrolyte membrane is joined to the electrode, and the polymer solid electrolyte membrane is changed due to a change in the dimensions of the membrane. There has been such a problem that the electrode bonded to the membrane is peeled off and the power generation characteristics are deteriorated. In addition, the reduction of the film thickness has a problem that the fuel permeation deterrence is reduced, which causes a reduction in electromotive force and a reduction in fuel use efficiency.
[0008]
Further, the polymer solid electrolyte membrane is used not only as the ion exchange resin membrane of the fuel cell as described above, but also as an electrolysis application such as alkali electrolysis and hydrogen production from water, and various batteries such as lithium batteries and nickel hydrogen batteries. Applications in a wide range of applications such as electrolyte applications in the electrochemical field, mechanical functional materials such as micro-actuators and artificial muscles, ion / molecule recognition / response functional materials, separation / purification functional materials, etc. It is considered that a superior function can be provided by achieving higher strength and thinner polymer solid electrolyte membrane in each application.
[0009]
As a method for improving the mechanical strength of the polymer solid electrolyte membrane and suppressing the dimensional change, a composite polymer solid electrolyte membrane in which various reinforcing materials are combined with the polymer solid electrolyte membrane has been proposed. Patent Literature 3 discloses a composite solid polymer electrolyte membrane in which voids of an expanded porous polytetrafluoroethylene membrane are impregnated with a perfluorocarbon sulfonic acid polymer as an ion exchange resin and integrated. However, in these composite polymer solid electrolyte membranes, since the reinforcing material is made of polytetrafluoroethylene, the reinforcing material is softened by heat during power generation, and dimensional changes due to creep are likely to occur. When the acid polymer solution is impregnated and dried, the volume of the void portion of the reinforcing material hardly changes, so that the perfluorocarbon sulfonic acid polymer precipitated inside the void of the reinforcing material tends to be unevenly distributed, and the void is formed by the polymer. Complete filling requires a complicated process, such as repeating the process of impregnation and drying of the ion exchange resin solution several times, and a membrane with excellent fuel permeation suppression properties is obtained because voids are likely to remain. It had a problem that it was difficult to be performed. Patent Literature 4 discloses a composite polymer solid electrolyte membrane in which fibrillated polytetrafluoroethylene is dispersed as a reinforcing material in a perfluorocarbon sulfonic acid polymer membrane. However, such composite polymer solid electrolyte membranes have problems that the reinforcing material has a discontinuous structure, does not provide sufficient mechanical strength, and the deformation of the membrane cannot be suppressed. Had.
[0010]
Polybenzazole-based polymers such as polybenzoxazole (PBO) and polybenzimidazole (PBI) are excellent in high heat resistance, high strength, and high elastic modulus, and thus are suitable as a reinforcing material for a solid polymer electrolyte membrane. Is expected.
[0011]
Patent Document 5 discloses a method of forming a film of an optically anisotropic polybenzazole-based polymer solution and then coagulating it through an isotropic process by moisture absorption to obtain a polybenzazole film. The polybenzazole film obtained by such a method is a transparent and dense film, and is not suitable for the purpose of impregnating an ion exchange resin into an ion exchange membrane.
[0012]
In forming a polybenzazole-based polymer solution, film formation by a casting method using an applicator is also a well-known technique. However, when a polybenzazole-based polymer solution having a polymer concentration of 1% by weight or more is used, the viscosity of the polybenzazole-based polymer solution becomes high, streaks appear in the squeegee direction, and a smooth film cannot be obtained. A practically usable polymer concentration is at most 0.5% by weight. For this reason, not only is the economy inferior, but also the strength and elastic modulus of the obtained film are insufficient. In the film made of the polybenzazole-based polymer obtained by the casting method, the surface structure on the side in contact with the base and the surface structure on the side not in contact with the base are different and form an asymmetric structure. The surface on the side in contact with the base forms a dense structure, whereas the surface on the side not in contact with the base forms a porous structure. When the ion exchange resin is impregnated into the support membrane made of the polybenzazole-based polymer having such an asymmetric structure, the ion exchange resin cannot be sufficiently impregnated at the portion where the dense structure is formed. In addition, there is a problem that the power generation performance of the obtained ion exchange membrane becomes insufficient.
[0013]
[Patent Document 1]
Japanese Patent Publication No. 61-501452
[Patent Document 2]
Japanese Patent Publication No. 6-503521
[Patent Document 3]
JP-A-8-162132
[Patent Document 4]
JP 2001-35508 A
[Patent Document 5]
JP-A-2000-273214
[0014]
[Problems to be solved by the invention]
The present invention solves the above-described problems of the prior art, and has excellent heat resistance, mechanical strength, smoothness, a porous membrane made of a polybenzoazole-based polymer having both the delamination resistance and the impregnation of a functional agent, and An object of the present invention is to provide a manufacturing method thereof. Further, the present invention provides a composite ion exchange membrane suitable for use as a polymer solid electrolyte membrane having high heat resistance, mechanical strength, smoothness and delamination resistance, and excellent ion conductivity, and a method for producing the same. Is provided.
[0015]
[Means for Solving the Problems]
The present inventors have conducted intensive studies, and as a result, have succeeded in developing an excellent composite ion-exchange membrane by enabling the production of a good support membrane composed of a polybenzazole-based polymer.
[0016]
That is, the porous membrane made of the polybenzoazole-based polymer of the present invention is obtained by thinning a polymer dope made of a polybenzazole-based polymer sandwiched between at least two supports through a roll, a slit or a press. It is characterized by being produced by leading to a coagulation bath, peeling and coagulating the film-like sheet in the coagulation bath. Further, the composite ion-exchange membrane of the present invention is formed on both surfaces of the composite layer in which a porous layer made of the above-mentioned polybenzazole-based polymer is impregnated with an ion-exchange resin, and the composite layer is sandwiched therebetween. The method is characterized in that a surface layer made of an ion exchange resin that does not include a porous membrane is formed.
(1) An isotropic solution of a polybenzazole-based polymer was manufactured by guiding a sandwich between at least two film-like sheets into a coagulation bath, and peeling and coagulating the film-like sheets in the coagulation bath. , A porous membrane made of a polybenzazole-based polymer.
(2) An isotropic solution of a polybenzazole-based polymer of 0.5% by weight or more and 3% by weight or less is thinned while being sandwiched between at least two film-like sheets. A porous membrane comprising a polybenzazole-based polymer.
(3) a porous film made of a polybenzazole-based polymer, wherein the coagulation bath is a poor solvent of a polybenzazole-based polymer, or a mixture of a poor solvent and a good solvent, or a solution containing salts in a poor solvent. .
(4) The film-like sheet is a film-like sheet through which the poor solvent of the polybenzazole-based polymer or the vapor thereof permeates, and the coagulation of the polybenzazole-based polymer with the poor solvent or the vapor thereof permeating the film-like sheet A porous membrane comprising a polybenzazole-based polymer, wherein at least a part of the porous membrane is performed.
(5) An isotropic solution of a polybenzazole-based polymer in an amount of 0.5% by weight or more and 3% by weight or less sandwiched between at least two film-like sheets is guided to a coagulation bath, and a film is formed in the coagulation bath. A method for producing a porous membrane comprising a polybenzazole-based polymer, comprising peeling and coagulating a sheet-like sheet.
(6) A composite layer comprising a porous membrane made of a polybenzazole-based polymer impregnated with an ion-exchange resin, and an ion-exchange resin not containing a porous membrane formed on both sides of the composite layer so as to sandwich the composite layer Is a composite ion exchange membrane having a surface layer.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the porous membrane and the composite ion exchange membrane made of the polybenzazole-based polymer of the present invention will be described in detail.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
The polybenzazole-based polymer used as the support membrane of the present invention refers to a polymer having a structure including an oxazole ring, a thiazole ring, and an imidazole ring in a polymer chain, and a repeating unit represented by the following general formula. What is included in it.
[0019]
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[0020]
Here, Ar1, Ar2, and Ar3 represent aromatic units, and may have a substituent such as various aliphatic groups, aromatic groups, halogen groups, hydroxyl groups, nitro groups, cyano groups, and trifluoromethyl groups. good. These aromatic units include a monocyclic system unit such as a benzene ring, a condensed ring system unit such as naphthalene, anthracene, and pyrene, and a polycyclic aromatic unit in which two or more aromatic units are connected via an arbitrary bond. But it's fine. In addition, the positions of N and X in the aromatic unit are not particularly limited as long as the positions are such that a benzazole ring can be formed. Further, these may be not only hydrocarbon-based aromatic units, but also heterocyclic-based aromatic units containing N, O, S, etc. in the aromatic ring. X represents O, S, NH.
Ar1 is preferably represented by the following general formula.
[0021]
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[0022]
Here, Y1 and Y2 represent CH or N, and Z represents a direct bond, -O-, -S-, -SO2-, -C (CH3) 2-, -C (CF3) 2-, -CO-. Show.
Ar2 is preferably represented by the following general formula.
[0023]
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[0024]
Here, W represents -O-, -S-, -SO2-, -C (CH3) 2-, -C (CH3) 2-, -CO-.
Ar3 is preferably represented by the following general formula.
[0025]
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[0026]
These polybenzazole-based polymers may be homopolymers having the above-described repeating units, or may be random, alternating or block copolymers obtained by combining the above-described structural units. For example, US Pat. Examples described in U.S. Pat. No. 4,533,692, U.S. Pat. No. 4,533,724, U.S. Pat. No. 4,533,693, U.S. Pat. No. 4,539,567, and U.S. Pat. No. 4,578,432 are also exemplified.
[0027]
Specific examples of these polybenzazole-based structural units include those represented by the following structural formula.
[0028]
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[0029]
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[0030]
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[0031]
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[0032]
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[0033]
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[0034]
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[0035]
Furthermore, not only these polybenzazole-based constituent units but also random, alternating or block copolymers with other polymer constituent units may be used. At this time, it is preferable that the other polymer constituent units are selected from aromatic polymer constituent units having excellent heat resistance. Specifically, a polyimide-based structural unit, a polyamide-based structural unit, a polyamide-imide-based structural unit, a polyoxydiazole-based structural unit, a polyazomethine-based structural unit, a polybenzazole-imide-based structural unit, a polyetherketone-based structural unit, Examples thereof include polyethersulfone-based structural units.
[0036]
Examples of the polyimide structural unit include those represented by the following general formula.
[0037]
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[0038]
Here, Ar4 is represented by a tetravalent aromatic unit, but is preferably represented by the following structure.
[0039]
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[0040]
Ar5 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.
[0041]
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[0042]
Specific examples of these polyimide structural units include those represented by the following structural formula.
[0043]
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[0044]
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[0045]
Examples of the polyamide structural unit include those represented by the following structural formula.
[0046]
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[0047]
Here, Ar6, Ar7 and Ar8 are preferably 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.
[0048]
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[0049]
Specific examples of these polyamide structural units include those represented by the following structural formula.
[0050]
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[0051]
Examples of the polyamideimide-based structural unit include those represented by the following structure.
[0052]
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[0053]
Here, Ar9 is preferably selected from the structures shown as specific examples of the above Ar5.
[0054]
Specific examples of these polyamideimide structural units include those represented by the following structural formula.
[0055]
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[0056]
Examples of the polyoxydiazole-based structural unit include those represented by the following structural formula.
[0057]
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[0058]
Here, Ar10 is preferably selected from the structures shown as specific examples of Ar5.
[0059]
Specific examples of these polyoxydiazole-based constitutional units include those represented by the following structural formula.
[0060]
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[0061]
Examples of the polyazomethine-based structural unit include those represented by the following structure.
[0062]
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[0063]
Here, Ar11 and Ar12 are preferably selected from the structures shown as specific examples of Ar6.
[0064]
Specific examples of these polyazomethine-based structural units include those represented by the following structural formula.
[0065]
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[0066]
Examples of the polybenzazole imide-based structural unit include those represented by the following structural formula.
[0067]
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[0068]
Here, Ar13 and Ar14 are preferably selected from the structures shown as specific examples of Ar4.
[0069]
Specific examples of the polybenzazole imide-based structural unit include those represented by the following structural formula.
[0070]
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[0071]
The polyetherketone-based structural unit and the polyethersulfone-based structural unit generally have a structure in which an aromatic unit is connected with a ketone bond or a sulfone bond together with an ether bond, and include a structural component selected from the following structural formula.
[0072]
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[0073]
Here, Ar15 to Ar23 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.
[0074]
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[0075]
Specific examples of these polyetherketone-based constitutional units include those represented by the following structural formulas.
[0076]
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[0077]
The aromatic polymer constituent units that can be copolymerized with these polybenzazole-based polymer constituent units do not strictly refer to the repeating units in the polymer chain, but can be present together with the polybenzazole-based constituent units in the polymer main chain. It shows the unit. Not only one kind of these aromatic polymer constituent units that can be copolymerized but also two or more kinds can be used in combination for copolymerization. In order to synthesize such a copolymer, an amino group, a carboxyl group, a hydroxyl group, a halogen group, or the like is introduced into the terminal of a polybenzazole-based polymer constituent unit, and the reaction in the synthesis of these aromatic polymers is performed. Polymerization may be carried out as a component, or a carboxyl group may be introduced into a terminal of the unit containing these aromatic polymer constituent units, and then polymerized as a reaction component in the synthesis of a polybenzazole polymer.
[0078]
The polybenzazole-based polymer is subjected to condensation polymerization in a polyphosphoric acid solvent to obtain a polymer. The polymerization degree of the polymer is represented by the intrinsic viscosity, and is preferably 15 dL / g or more, more preferably 20 dL / g or more. If it is below this range, the strength of the resulting support membrane is undesirably low. The intrinsic viscosity is preferably 35 dL / g or less, more preferably 26 dL / g or less. If it exceeds this range, the viscosity of the solution is high and processing is difficult, and the concentration range of the polybenzazole-based polymer solution from which an isotropic solution is obtained is limited, and it is difficult to form a film under isotropic conditions. Is not preferred. These solutions are diluted with a solvent such as polyphosphoric acid and methanesulfonic acid, and used as a polymer dope.
[0079]
The porous film of polybenzazole of the present invention is formed by processes such as extrusion and thinning, coagulation, washing and drying. As a means for realizing a uniform porous structure, a method is used in which a film-formed isotropic polybenzazole-based polymer solution is brought into contact with a poor solvent to coagulate. The poor solvent is a solvent that is miscible with the solvent of the polymer solution, and may be in a liquid phase or a gas phase. Further, a combination of solidification with a poor solvent in a gas phase and solidification with a poor solvent in a liquid phase can also be preferably used. As the poor solvent used for coagulation, in addition to water, an aqueous acid solution and an aqueous inorganic salt solution, organic solvents such as alcohols, glycols, and glycerin can be used. In combination with the polybenzazole-based polymer solution used, In some cases, problems such as a decrease in the surface porosity and porosity of the porous support membrane and the formation of discontinuous cavities inside the porous support membrane occur. Special care must be taken in the selection. In the coagulation of the isotropic polybenzazole-based polymer solution in the present invention, in addition to water vapor, methanesulfonic acid aqueous solution, phosphoric acid aqueous solution, glycerin aqueous solution, and inorganic salt aqueous solution such as magnesium chloride aqueous solution, coagulation with poor solvent By selecting the conditions, the structure and porosity of the surface and the inside of the support membrane were controlled. Particularly preferred coagulation means are a method of coagulation by contact with water vapor, a method of coagulation by contact with water after a short period of contact with water vapor in the early stage of coagulation, a method of coagulation by contact with an aqueous methanesulfonic acid solution, and the like. is there.
[0080]
In the method for forming a polybenzazole-based polymer dope in the present invention, a thin film obtained by thinning a polymer dope sandwiched between two film-like sheets through a roll, a slit, or a press is guided to a coagulation bath. The method of peeling and solidifying the film-like sheet by using the above method is most preferable. The term “thinning” as used herein means that the thickness of the polymer dope before coagulation is generally adjusted to about 10 μm to 500 μm using the above-described means, but can be arbitrarily set according to market requirements without limitation. . The configuration and arrangement of the roll, slit or press can take various combinations. Desirably, the polymer dope sandwiched between at least two film-like sheets is sandwiched between at least two rolls, and the opposing rolls are rotated in opposite directions to send out the thinned polymer dope.
[0081]
The film-like sheet sandwiching the rolled polymer dope is guided to a coagulation bath via a guide roll, and the polymer dope is coagulated by peeling the film-like sheet in the coagulation bath to form a porous film. Before completely coagulating the polymer solution by peeling the film-like sheet in a coagulation bath, by performing at least a part of coagulation of the polybenzazole-based polymer with a poor solvent or vapor thereof permeating the film-like sheet. In addition, it is possible to control the structure and porosity of the surface and the inside of the support membrane.
[0082]
Here, a composite film may be formed by sandwiching a porous support, a fabric, a nonwoven fabric, or the like between the outermost film sheet and the polymer dope. Alternatively, a porous support, a cloth, or a nonwoven fabric can be used as it is as a film-like sheet and used as a composite film. It is desirable that the porous support, the cloth and the nonwoven fabric have air permeability and liquid permeability. As the film-like sheet that allows the poor solvent of the polybenzazole-based polymer or its vapor to permeate, a porous film-like sheet made of polypropylene is preferable, and porous films made of various materials such as polyethylene and polytetrafluoroethylene are also preferable. Film-like sheets can be used. In particular, when water or a mixed solvent of water and another solvent or an aqueous solution is used as the coagulating liquid, it is preferable to use a porous support that allows only water vapor to pass and does not allow liquid water to pass. These can use a commercially available membrane filter having a nominal pore size of about 0.03 μm to 10 μm, or a battery separator membrane.
[0083]
The coagulation bath referred to here includes not only a tank containing a coagulation liquid but also a zone in which a gas, a mist, and a vapor having coagulability exist. Examples of the coagulating liquid include water, an aqueous solution of a metal salt, a polyhydric alcohol, an aprotic polar solvent, a proton polar solvent, and the like, and an aqueous solution of polyphosphoric acid and methanesulfonic acid, which are dope diluting solvents. In addition, these mist and steam are also included. The temperature of the coagulating liquid is preferably from 10 ° C to 70 ° C. More preferably, it is 30 ° C. or more and 60 ° C. or less. In general, the structure of the membrane is determined by the balance between the infiltration of the coagulating liquid into the polymer-doped film and the outflow of the polymer solvent from the polymer-doped thin film. If the temperature of the coagulating liquid is too low, liquid-liquid exchange between the coagulating liquid and the polymer solvent becomes insufficient, and a desired membrane structure cannot be obtained. If the temperature of the coagulating liquid is too high, a desirable structure is obtained, but the strength tends to be very weak. In the present invention, the coagulation liquid temperature is preferably from 10 ° C to 70 ° C. More preferably, at 30 ° C. or more and 60 ° C. or less, a porous film having satisfactory structure and strength can be obtained.
[0084]
It is important that the polybenzazole-based polymer solution used in the present invention is formed under a composition under isotropic conditions in order to obtain a uniform and large porosity porous support membrane. Is preferably 0.3% or more, more preferably 0.5% or more, and still more preferably 0.8% or more. If the concentration is lower than this range, the viscosity of the polymer solution becomes small, making the molding process difficult, and it is not economically 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, the solution shows anisotropy depending on the polymer composition and the degree of polymerization of the polybenzazole-based polymer, which is not preferable. A porous membrane made from a polybenzazole polymer solution exhibiting optical anisotropy can provide a porous polybenzazole polymer film with continuous voids with a large porosity that can impregnate a large amount of ion exchange resin. Not preferred
[0085]
The following method can be used to adjust the concentration of the polybenzazole-based polymer solution to the above range. That is, a method of once separating a polymer solid from a polymerized polybenzazole-based polymer solution, adjusting the concentration by adding a solvent again and dissolving the polymer solid, and further, from a polymer solution that is still condensation-polymerized in polyphosphoric acid. A method of adjusting the concentration by adding a solvent to the polymer solution and diluting it without separating the polymer solid, and a method of directly obtaining a polymer solution having the above concentration range by adjusting the polymerization composition of the polymer.
[0086]
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 obtained by combining these solvents. Among them, methanesulfonic acid and polyphosphoric acid are particularly preferred.
[0087]
The porous support membrane made of the polybenzazole-based polymer solidified as described above has problems such as promotion of decomposition of the polymer by the remaining solvent, and outflow of the residual solvent when using the composite electrolyte membrane. Thorough cleaning is desirable for avoidance purposes. Washing can be performed by immersing the porous support membrane in a washing solution. A particularly preferred cleaning solution is water. Washing with water is preferably performed until the pH of the washing solution when the porous 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. is there.
[0088]
The extrusion and thinning step, the coagulation step, the washing step, the drying step, and the like may be performed continuously, or may be performed in a batch system. Further, between the respective steps, other special steps may be added according to the purpose, such as compounding by impregnation, coating, laminating, stretching, surface treatment such as irradiation of ultraviolet rays, electron beams, and corona, and annealing.
[0089]
A method for obtaining a composite ion exchange membrane by combining an ion exchange resin with the porous support membrane made of the polybenzazole-based polymer obtained by the above method will be described. That is, without drying the porous support membrane, the composite ion exchange membrane is immersed in an ion exchange resin solution, the liquid inside the porous support membrane is replaced with the ion exchange resin solution, and then dried. How to get. When the liquid inside the porous support membrane is different from the solvent composition of the ion exchange resin solution, a method of preliminarily replacing the liquid inside according to the solvent composition may be adopted.
[0090]
The porous 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 porous support membrane is fixed to a metal frame or the like without impregnating the ion exchange resin into the inside of the porous support membrane and dried while limiting shrinkage in the plane direction, the shrinkage occurs in the film thickness direction, The apparent film thickness of the porous support film after drying is in the range of 0.5% to 10% of the film thickness before drying.
[0091]
Due to such characteristics of the porous support membrane, when the liquid inside the pores of the porous support membrane is replaced with an ion exchange resin solution and then dried, the ion exchange resin solution impregnated in the pores is dried. As the solvent evaporates and the volume of the ion exchange resin solution decreases, the porous support membrane also shrinks, so that the voids inside the porous membrane support membrane are filled with the precipitated ion exchange resin. A simple composite membrane structure can be easily obtained. Due to this composite membrane structure, the composite ion exchange membrane of the present invention exhibits excellent fuel permeation suppression properties. In the case of a porous support membrane other than the porous support membrane of the present invention, for example, a porous support membrane composed of an expanded polytetrafluoroethylene polymer porous membrane, the solvent of the ion exchange resin solution impregnated inside the voids evaporates. Even if the volume of the ion-exchange resin solution is reduced, the porous support membrane shrinks less with it, so that not only a large number of voids not filled with the ion-exchange resin are formed inside the composite membrane after drying, but also On the other hand, the surface layer of the ion exchange resin containing no support is not formed on both surfaces of the porous support membrane, which is not preferable.
[0092]
The composite ion-exchange membrane also has properties such as the concentration and viscosity of the ion-exchange resin solution, the volatility of a solvent, and the thickness and the like of the porous support membrane, because the porous support membrane significantly shrinks. By adjusting the combination of the porosity and the like, the ion-exchange resin adheres to both surfaces of the porous support membrane in parallel with the formation of the composite layer filling the internal voids of the porous support membrane. The excess ion exchange resin solution or the ion exchange resin solution discharged from the inside of the porous support membrane due to the shrinkage of the support membrane is dried outside the surface of the porous support membrane to form the porous membrane. By forming the ion-exchange resin layer without the support, it is possible to easily form a structure in which the surface layer of the ion-exchange resin without the porous support membrane is formed on both surfaces of the composite layer with the composite layer interposed therebetween. Can be realized.
[0093]
As described above, since a membrane other than the porous support membrane of the present invention, for example, a porous support membrane made of polytetrafluoroethylene polymer does not undergo significant shrinkage, it is impregnated with an ion exchange resin solution and dried. Even when the ion exchange resin precipitates inside the porous support membrane during this process, voids remain, and no ion exchange resin layer sandwiching the porous support membrane composite layer is formed. This state can be reduced by repeating the impregnation and drying of the ion exchange resin solution a plurality of times, but this is not preferable because the process becomes complicated.
[0094]
The ion exchange resin used in the composite ion exchange membrane of the present invention is not particularly limited. In addition to the above-mentioned perfluorocarbon sulfonic acid polymer, for example, polystyrene sulfonic acid, poly (trifluorostyrene) sulfonic acid, polyvinyl phosphone Acid, polyvinyl carboxylic acid, at least one ionomer of polyvinyl sulfonic acid polymer, polysulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyphenylquinoxaline, polyaryl ketone, polyether ketone, polybenzazole And ionomers in which at least one of aromatic polymers such as polyaramid polymer is sulfonated, phosphonated or carboxylated Kill. As used herein, the polysulfone polymer includes at least one of a polyether sulfone, a polyaryl sulfone, a polyaryl ether sulfone, a polyphenyl sulfone, and a polyphenylene sulfone polymer. Further, the polyetherketone polymer referred to here includes at least one of polyetheretherketone, polyetherketone-ketone, polyetheretherketone-ketone, and polyetherketoneether-ketone polymer.
[0095]
The solvent of the ion exchange resin solution described above can be selected from solvents that do not dissolve, decompose or extremely swell the polybenzazole-based polymer porous support membrane and can dissolve the ion exchange resin. However, in order to precipitate the ion exchange resin by removing the solvent after impregnating the support membrane with the ion exchange resin solution, the solvent can be removed by evaporating using a means such as heating or decompression. It is preferable that Here, since the polybenzazole polymer porous support membrane of the present invention has high heat resistance, a composite ion exchange using a polytetrafluoroethylene porous support membrane that causes creep from a temperature of about 100 ° C. The fact that a composite ion exchange membrane can be produced using an ion exchange resin solution containing a high boiling point solvent that cannot be used in the production of a membrane is also an excellent feature from the viewpoint that many types of ion exchange resins can be selected.
[0096]
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 depending on the type of the ion exchange resin, the thickness of the composite ion exchange membrane to be obtained, and the like. Is done.
[0097]
The content of the ion exchange resin in the composite ion exchange membrane obtained as described above is preferably 50% by weight or more. More preferably, it is at least 80% by weight. If the content is less than this range, the conductive resistance of the film becomes large, or the water retention of the film is reduced, so that sufficient power generation performance cannot be obtained.
[0098]
Further, the composite ion exchange membrane of the present invention is characterized in that it has a surface layer made of an ion exchange resin containing no support on both surfaces of the composite layer with the composite layer interposed therebetween as described above. Since the composite ion-exchange membrane has the composite layer and the surface layer, the composite ion-exchange membrane has high mechanical strength and, when the electrode layer is formed on the surface, improves the adhesion to the electrode layer. It has the feature of being excellent. It is preferable that the thickness of each of the surface layers is 1 μm or more and 50 μm or less, and that each does not exceed half of the total thickness of the composite ion exchange membrane. If the thickness of the surface layer is smaller than the above range, the adhesion to the electrode layer is deteriorated, and the ionic conductivity is undesirably reduced. When the thickness of the surface layer is larger than the above range, the effect of reinforcement by the composite layer does not extend to the outermost surface of the composite ion exchange membrane, and only the surface layer swells greatly when the composite ion exchange membrane absorbs moisture. It is not preferable because the surface layer is separated from the composite layer. A more preferable range of the thickness of the surface layer is 2 μm or more and 30 μm or less.
[0099]
For the purpose of further improving properties such as mechanical strength, ion conductivity, and peeling resistance of the ion-exchange resin layer formed on the surface of the composite ion-exchange membrane, it is also preferable to heat-treat the composite ion-exchange membrane under appropriate conditions. Can be used. Further, in order to adjust the thickness of the surface layer of the ion exchange resin formed on the surface, the composite ion exchange membrane is further immersed in an ion exchange resin solution or the ion exchange resin solution is applied to the composite ion exchange membrane. Or to increase the amount of the ion-exchange resin layer by drying, or to scrape a part of the ion-exchange resin solution adhered to the surface of the porous support membrane after immersion in the ion-exchange resin solution, A method of reducing the amount of the ion-exchange resin layer deposited by scraping off with an air knife, a roller, or the like, or absorbing with a solution-absorbing material such as filter paper or sponge can also be used. Alternatively, a method of further improving the adhesion of the ion-exchange resin layer by applying a heat press can be used together.
[0100]
The composite ion exchange membrane of the present invention has excellent mechanical strength while having high ion conductivity. Further, by utilizing its characteristics, it can be used as a composite ion exchange membrane, particularly as a polymer solid electrolyte membrane of a polymer electrolyte fuel cell.
[0101]
(Example)
Examples of the present invention will be described below, but the present invention is not limited to these examples. The characteristics shown in the examples were measured and evaluated by the following methods.
(Evaluation and measurement methods)
1. Structure observation by transmission electron microscope
The cross-sectional structure of the film was observed by a transmission electron microscope (TEM) by the following method. First, a sample section for observation was prepared as follows. That is, the water inside the porous support membrane sample after water washing was replaced with ethanol, and further sufficiently replaced with an epoxy monomer. The sample was kept in an epoxy monomer at 45 ° C. for 6 hours, and then heat-treated at 60 ° C. for 20 hours to cure the epoxy (epoxy embedding). Using a microtome equipped with a diamond knife, the sample embedded in epoxy in this way is prepared into ultrathin sections whose thickness is such that the interference color changes from silver to gold, and treated with a KOH-saturated ethanol solution for 15 minutes. The epoxy was removed with (de-epoxy). Further, the sample was washed with ethanol and subsequently with water, and carbon-deposited on a sample stained with RuO4, and observed using a TEM (JEM-2010) manufactured by JEOL at an acceleration voltage of 200 kV.
[0102]
2. Structural observation by atomic force microscope
Structure observation by an atomic force microscope (AFM) was performed by the following method. That is, using an AFM (SPA300 [observation mode: DFM mode, cantilever: SI-DF3, scanner: FS-100A]) manufactured by Seiko Instruments Inc., an undried porous support membrane held on a sample stage in water was used. The surface structure was observed.
[0103]
3. 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 using an Ubbelohde viscometer in a thermostat at 25 ° C. and calculated.
[0104]
4. Thickness of porous support membrane
The thickness of the undried porous support membrane was measured by the following method. Using a micrometer capable of changing the measurement load, the thickness of the support film in water at each load was measured. The measured thickness was plotted against the load, the value of the intercept when the linear portion was extrapolated to a load of 0 was defined as the thickness, and the average value of the thickness measured at five locations for one sample was defined as the thickness of the support membrane. .
[0105]
5. The thickness of the composite ion exchange membrane and the thickness of the layers constituting it
The thickness of the surface layer made of the ion exchange resin which does not include the composite layer constituting the composite ion exchange membrane and the porous support membrane formed on both surfaces of the composite layer so as to sandwich the composite layer is porous. A composite film piece cut into a film-like width of 300 μm × length 5 mm is wrapped with a resin having a composition of Lubeac 812 (manufactured by Nacalai Tesque) / Lubeac NMA (manufactured by Nacalai Tesque) / DMP30 (manufactured by TAAB) = 100/89/4. The sample was buried and cured at 60 ° C. for 12 hours to prepare a sample block. The tip of the block was cut with a diamond knife (SK2045 manufactured by Sumitomo Electric Industries) so that a smooth cross section was exposed using an ultramicrotome (2088 ULTROTOME 5 manufactured by LKB). The cross section of the composite membrane thus exposed was photographed with an optical microscope, and measured by comparing a scale of known length with that photographed at the same magnification. For example, when the porosity of the porous membrane support is large, at least one surface layer and the inner composite layer do not form a clear interface, and the structure near the interface is continuously changing. However, in that case, of the portions where the continuous structural change can be confirmed with an optical microscope, the portion closest to the outer surface of the composite ion exchange membrane is taken as the outermost surface of the composite layer, and The distance to the surface was defined as the thickness of the surface layer.
[0106]
6. Content of ion exchange resin (ICP) in composite ion exchange membrane
The ion exchange resin content of the composite ion exchange membrane was measured by the following method. The basis weight Dc [g / m2] of the composite ion exchange membrane which was vacuum-dried at 110 ° C. for 6 hours was measured, and the porous support membrane under the same production conditions as those used for producing the composite ion exchange membrane was used. From the basis weight Ds [g / m2] of the dried porous support membrane measured by drying without forming a composite, the ion exchange resin content was determined by the following calculation.
Ion exchange resin content [% by weight] = (Dc−Ds) / Dc × 100
Further, the ion exchange resin content of the composite ion exchange membrane can also be measured by the following method. That is, the composite ion-exchange membrane is immersed in a solvent capable of dissolving only one of the porous support membrane component or the ion-exchange resin component in the composite ion-exchange membrane to extract and remove one of the components. By measuring the weight change with the composite ion exchange membrane, the content of the ion exchange resin can be determined.
[0107]
7. Strength and tensile modulus
The strength characteristics of the ion exchange membrane were measured in an atmosphere at a temperature of 25 ° C. and a relative humidity of 50% using Tensilon manufactured by Orientec. The sample was formed into a strip having a width of 10 mm, and the length was calculated from a stress-strain curve measured at a span length of 40 mm and a pulling speed of 20 mm / sec.
[0108]
8. Ionic conductivity
The ionic conductivity σ was measured as follows. A platinum wire (diameter: 0.2 mm) is pressed against the surface of a 10 mm-wide strip-shaped film sample on a self-made measurement probe (made of tetrafluoroethylene), and the sample is placed in a thermo-hygrostat at 80 ° C. and 95% relative humidity. , And the AC impedance at 10 kHz between the platinum wires was measured by a SOLARTRON 1250FREQNCY RESPONSE ANALYSER. The contact resistance between the membrane and the platinum wire was determined by the following equation from the linear gradient Dr [Ω / cm] in which the distance between the electrodes was changed from 10 mm to 40 mm at 10 mm intervals, and the measured distance between the electrodes was plotted against the measured resistance. Canceled and calculated.
σ [S / cm] = 1 / (film width × film thickness [cm] × Dr)
[0109]
9. Gas permeability
The gas permeability of the ion exchange membrane was measured by the following method. After placing the ion-exchange membrane on a mesh-shaped stainless steel support and fixing it to a holder, helium gas saturated with water vapor at room temperature is flowed to one side of the ion-exchange membrane at a gauge pressure of 0.09 MPa. Then, the amount of helium gas permeating the other surface of the ion exchange membrane was measured and calculated using a soap membrane flow meter.
[0110]
10. Power generation characteristics
A 20% Nafion (trade name) solution (product number: SE-2092) manufactured by DuPont was charged with platinum-supported carbon (carbon: Valcan XC-72 manufactured by Cabot, platinum supported amount: 40% by weight), and the weight ratio of platinum to Nafion was changed. The mixture was added at a ratio of 2.7: 1 and stirred to prepare a catalyst paste. This catalyst paste was applied to Toray carbon paper TGPH-060 so that the amount of platinum deposited was 1 mg / cm 2, and dried to form a gas diffusion layer with an electrode catalyst layer. By sandwiching the membrane sample between the two gas diffusion layers with an electrode catalyst layer such that the electrode catalyst layer is in contact with the membrane sample, and by pressing and heating at 120 ° C. and 2 MPa for 3 minutes by a hot press method, A membrane-electrode assembly was obtained. This assembly was assembled into an evaluation fuel cell FC25-02SP manufactured by Electrochem, and power generation characteristics were obtained at a cell temperature of 80 ° C., a gas humidification temperature of 80 ° C., a gas flow rate of 300 mL / min of hydrogen as a fuel gas, and a flow rate of 1000 mL / min of air as an oxidizing gas. An evaluation was performed.
[0111]
11. Dry film properties
(Surface roughness)
The dried film was measured for its root-mean-square roughness using a three-dimensional non-contact surface shape measurement system manufactured by Micromap.
[0112]
12. Tensile modulus
The dried film is cut into strips each having a length of 100 mm and a width of 10 mm in the longitudinal direction (MD direction) and the transverse direction (TD direction) to form test pieces, and a tensile tester (Autograph model name: AG-5000A manufactured by Shimadzu Corporation) ), A tensile test was performed at a tensile speed of 50 mm / min and a distance between chucks of 40 mm, and the tensile elastic modulus was measured.
[0113]
13. Elastic modulus temperature dependence, elastic modulus retention
The dried film is cut into strips each having a length of 40 mm and a width of 5 mm in the machine direction (MD) and the cross direction (TD) to obtain test pieces, and a dynamic viscoelasticity measuring device (Model name DVA-225 manufactured by IT Measurement Co., Ltd.) Was measured from room temperature to 400 ° C. at a rate of temperature increase of 5 ° C./min and 10 Hz. The elastic modulus ratio of 300 ° C./30° C. was used as the elastic modulus retention.
[0114]
14． Delamination test
The dried film was cut into strips each having a length of 20 mm and a width of 10 mm in the longitudinal direction (MD direction) and the lateral direction (TD direction) to form test pieces, and the adhesive surfaces of the adhesive tape were adhered to the front and back surfaces of the film. .
Using a tensile tester (Autograph made by Shimadzu Corporation, model name: AG-5000A), peel off the tape slowly at a tensile speed of 50 mm / min and a distance between chucks of 40 mm, and delaminate the film to the adhesive surface of both adhesive tapes. The phenomenon was examined. (See Fig. 3)
[0115]
(Example 1)
Methanolsulfonic acid was added to a dope containing 14% by weight of a polyparaphenylene cis benzobisoxazole polymer having an IV of 24 dL / g in polyphosphoric acid, and diluted to obtain a polyparaphenylene cis benzobisoxazole having a concentration of 2.5% by weight. An isotropic solution was prepared. The solution is passed through a 20 μm filter with a nominal opening and sandwiched between two porous film sheets of polypropylene between two opposing rolls. Then, while rolling the dope, the porous film-like sheet made of polypropylene was sent out while rolling the dope, and was coagulated for 30 minutes in a constant temperature / humidity bath atmosphere at 25 ° C. and a relative humidity of 80%, and then led to a coagulation bath. The coagulation liquid used water of 60 degreeC. At this time, the gap between the opposing rolls was adjusted so that the thickness of the dope was 200 μm. The porous film-like sheet made of polypropylene was peeled off in a coagulation bath, and the dope was brought into contact with a coagulation liquid to further coagulate. FIG. 2 shows a schematic diagram of the manufacturing method. Thereafter, the resulting membrane was washed with water until the washing liquid showed a pH of 7 ± 0.5 to prepare a porous support membrane made of a polybenzazole-based polymer. Observation of the surface morphology by atomic force microscopy and transmission electron microscopy show that the prepared porous support membrane made of polybenzazole-based polymer is a porous membrane having continuous pores with openings on both sides. It was confirmed by cross-sectional morphology observation. The dried film was washed with water and then heat-set at 150 ° C. for 20 seconds while holding both ends with a tenter to obtain a 5.2 μm-thick polybenzazole film. The dried film was measured for its root-mean-square roughness using a three-dimensional non-contact surface shape measurement system manufactured by Micromap. Table 2 shows the measurement results of the delamination property, tensile elastic modulus, and elastic modulus temperature dependency.
[0116]
(Comparative Example 1)
Methanolsulfonic acid was added to a dope containing 14% by weight of a polyparaphenylene cis benzobisoxazole polymer having an IV of 24 dL / g in polyphosphoric acid, and diluted to obtain a polyparaphenylene cis benzobisoxazole having a concentration of 2.5% by weight. An isotropic solution was prepared. This solution was formed on a glass plate heated to 70 ° C. using a 300 μm clearance applicator at a film formation rate of 5 mm / sec. Under these conditions, the polybenzazole-based polymer solution had a high viscosity, streaks occurred in the squeegee direction, and a smooth film could not be obtained. The dope film thus formed on the glass plate is coagulated for 1 hour in a constant temperature / humidity bath at 25 ° C. and a relative humidity of 80%, and the resulting film shows a pH of 7 ± 0.5. The substrate was washed with water until a porous support membrane composed of a polybenzazole-based polymer was prepared. In the prepared porous support membrane, the surface on the side in contact with the substrate has a dense structure, whereas the surface on the side not in contact with the substrate has a porous structure. It was confirmed by surface morphology observation with a force microscope and cross-sectional morphology observation with a transmission electron microscope, and it was confirmed that the film had no openings on both sides.
[0117]
(Comparative Example 2)
Methanolsulfonic acid was added to a dope containing 14% by weight of a polyparaphenylene cis benzobisoxazole polymer having an IV of 24 dL / g in polyphosphoric acid, and diluted to obtain a polyparaphenylene cis benzobisoxazole having a concentration of 2.5% by weight. An isotropic solution was prepared. This solution is passed through a nominal aperture of 20 μm filter, and then sandwiched between two film-like sheets made of polyethylene terephthalate between two opposing rolls. In the two rolls, the opposing rolls are rotated in opposite directions. Then, the dope was rolled and sent out together with a film-like sheet made of polyethylene terephthalate to be led to a coagulation bath. The coagulation liquid used water of 60 degreeC. At this time, the gap between the opposing rolls was adjusted so that the thickness of the dope was 200 μm. The film-like sheet made of polyethylene terephthalate was peeled off in a coagulation bath, and the dope was brought into contact with a coagulation liquid to further coagulate. Thereafter, the resulting membrane was washed with water until the washing liquid showed a pH of 7 ± 0.5 to prepare a porous support membrane made of a polybenzazole-based polymer. It was confirmed by observation of surface morphology with an atomic force microscope and observation of cross-sectional morphology with a transmission electron microscope that the prepared porous support membrane composed of a polybenzazole-based polymer had no openings on both sides. The dried film was washed with water and then heat-set at 150 ° C. for 20 seconds while holding both ends with a tenter to obtain a 5.4 μm thick polybenzazole film. The dried film was measured for its root-mean-square roughness using a three-dimensional non-contact surface shape measurement system manufactured by Micromap. Table 1 shows the measurement results of the delamination property, tensile elastic modulus, and elastic modulus temperature dependency.
[0118]
[Table 1]

[0119]
From Comparative Example 1, in the production method by the casting method, the polybenzazole-based polymer solution has a high viscosity, so that streaks occur in the squeegee direction, and a smooth film film cannot be obtained. In addition, the surface in contact with the base forms a dense structure. On the other hand, in the production method according to the present invention which is Example 1, even if the polybenzazole-based polymer solution has a high viscosity, a smooth membrane film can be obtained, and continuous pores having openings on both sides are provided. A porous membrane can be manufactured. From Comparative Example 2, a coagulation bath for a coagulation liquid, which is a poor solvent having a strong coagulation force like water immediately after molding using a film-like sheet in which a poor solvent of a polybenzazole-based polymer or a film-like sheet impervious to the vapor thereof is used. When the film-like sheet is peeled off and solidified by direct contact with a coagulating liquid, the surface structure of the film becomes dense and a porous structure cannot be formed.
[0120]
(Example 2)
Methanolsulfonic acid was added to a dope containing 14% by weight of a polyparaphenylene cis benzobisoxazole polymer having an IV of 24 dL / g in polyphosphoric acid, and diluted to obtain a polyparaphenylene cis benzobisoxazole having a concentration of 2.5% by weight. An isotropic solution was prepared. The solution is passed through a 20 μm filter with a nominal opening and sandwiched between two porous film sheets of polypropylene between two opposing rolls. The dope was rolled, and the dope was rolled and sent out together with a porous film sheet made of polypropylene. After being solidified for 30 minutes in a constant temperature and constant humidity atmosphere at 25 ° C. and a relative humidity of 80%, the dope was guided to a coagulation bath. The coagulation liquid used water of 60 degreeC. At this time, the gap between the opposing rolls was adjusted so that the thickness of the dope was 200 μm. The porous film-like sheet made of polypropylene was peeled off in a coagulation bath, and the dope was brought into contact with a coagulation liquid to further coagulate. Thereafter, the resulting membrane was washed with water until the washing liquid showed a pH of 7 ± 0.5 to prepare a support porous membrane made of a polybenzazole-based polymer. This porous support membrane was fixed to a stainless steel frame in water, and the water inside the porous support membrane was replaced with a 20% Nafion (trade name) solution (product number: SE-20192, manufactured by DuPont) which is an ion exchange resin solution. ) Was replaced with a mixed solvent of water: ethanol: 1-propanol = 26: 26: 48 (weight ratio) which is almost the same as the solvent composition of the above). This porous support membrane was immersed in a 20% Nafion (trade name) solution at 25 ° C. for 15 hours, taken out of the solution, and the solvent of the Nafion (trade name) solution impregnated inside the membrane and adhered to the membrane surface was air-dried. Evaporate and dry. The dried membrane was preliminarily heat-treated in an oven at 60 ° C. for 1 hour to remove residual solvent, and then heat-treated at 150 ° C. for 1 hour in a nitrogen atmosphere to prepare a composite ion exchange membrane of Example 2. .
[0121]
(Comparative Example 3)
As Comparative Example 3, 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 the 10% Nafion aqueous solution used in Example 2, and is a polymer electrolyte fuel cell. Is widely used as a proton exchange membrane for use.
[0122]
(Comparative Example 4)
An optical anisotropic material having a polyparaphenylene cis benzobisoxazole concentration of 8% by weight was diluted by adding methanesulfonic acid to a dope containing 14% by weight of a polyparaphenylene cis benzobisoxazole polymer having an IV of 24 dL / g in polyphosphoric acid. A neutral solution was prepared. The solution is passed through a 20 μm filter with a nominal opening and sandwiched between two porous film sheets of polypropylene between two opposing rolls. The dope was rolled, and the dope was rolled and sent out together with a porous film sheet made of polypropylene. After being solidified for 30 minutes in a constant temperature and constant humidity atmosphere at 25 ° C. and a relative humidity of 80%, the dope was guided to a coagulation bath. The coagulation liquid used water of 60 degreeC. At this time, the gap between the opposing rolls was adjusted so that the thickness of the dope was 200 μm. The porous film-like sheet made of polypropylene was peeled off in a coagulation bath, and the dope was brought into contact with a coagulation liquid to further coagulate. Thereafter, the resulting membrane was washed with water until the washing liquid showed a pH of 7 ± 0.5 to form a porous support membrane. This support membrane was fixed to a stainless steel frame in water, and the water inside the porous support membrane was replaced with a 20% Nafion (trade name) solution (product number: SE-20192) manufactured by DuPont, which is an ion exchange resin solution. Substitution was carried out with a mixed solvent of water: ethanol: 1-propanol = 26: 26: 48 (weight ratio) substantially the same as the solvent composition. This porous support membrane was immersed in a 20% Nafion (trade name) solution at 25 ° C. for 15 hours, taken out of the solution, and the solvent of the Nafion (trade name) solution impregnated inside the membrane and adhered to the membrane surface was air-dried. Evaporate and dry. The dried membrane was preliminarily heat-treated in an oven at 60 ° C. for 1 hour to remove the residual solvent, and then heat-treated at 150 ° C. for 1 hour in a nitrogen atmosphere to prepare a composite ion exchange membrane of Comparative Example 4. .
[0123]
(Comparative Example 5)
Methanolsulfonic acid was added to a dope containing 14% by weight of a polyparaphenylene cis benzobisoxazole polymer having an IV of 24 dL / g in polyphosphoric acid, and diluted to obtain a polyparaphenylene cis benzobisoxazole having a concentration of 2.5% by weight. An isotropic solution was prepared. This solution was formed on a glass plate heated to 70 ° C. using a 300 μm clearance applicator at a film formation rate of 5 mm / sec. Under these conditions, the polybenzazole-based polymer solution had a high viscosity, streaks occurred in the squeegee direction, and a smooth film could not be obtained. The dope film thus formed on the glass plate is coagulated for 1 hour in a constant temperature / humidity bath at 25 ° C. and a relative humidity of 80%, and the resulting film shows a pH of 7 ± 0.5. The substrate was washed with water until a porous support membrane was formed. This support membrane was fixed to a stainless steel frame in water, and the water inside the porous support membrane was replaced with a 20% Nafion (trade name) solution (product number: SE-20192) manufactured by DuPont, which is an ion exchange resin solution. Substitution was carried out with a mixed solvent of water: ethanol: 1-propanol = 26: 26: 48 (weight ratio) substantially the same as the solvent composition. This porous support membrane was immersed in a 20% Nafion (trade name) solution at 25 ° C. for 15 hours, taken out of the solution, and the solvent of the Nafion (trade name) solution impregnated inside the membrane and adhered to the membrane surface was air-dried. Evaporate and dry. The dried membrane was preliminarily heat-treated 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 a composite ion exchange membrane of Comparative Example 5. .
[0124]
Table 1 shows the physical property values of Example 2 and Comparative Examples 3, 4, and 5.
[0125]
[Table 2]

[0126]
It can be seen that the composite ion exchange membrane of Example 2 is an ion exchange membrane having a higher breaking strength and a higher tensile modulus than the commercially available Nafion 112 membrane of Comparative Example 3. In addition, despite the fact that the composite ion exchange membrane of Example 2 has a porous membrane support inside, the ion conductivity and the power generation performance are not significantly reduced as compared with Comparative Example 3 which does not include the porous membrane support. In addition, the gas permeability is suppressed to a small value of half or less, which indicates that the fuel cell has excellent characteristics as a polymer solid electrolyte membrane. In the case of using a support membrane made of a polybenzazole-based polymer obtained from the optically anisotropic solution of Comparative Example 4, both the ionic conductivity and the power generation performance were reduced, and as a polymer solid electrolyte membrane for a fuel cell, Could not have excellent properties. The composite ion exchange membrane using the porous support membrane produced by the casting method of Comparative Example 5 has a problem that a smooth membrane (film) cannot be obtained, and both the ionic conductivity and the power generation performance are poor. Thus, the polymer solid electrolyte membrane of the fuel cell could not have excellent characteristics.
[0127]
【The invention's effect】
As described above, the present invention adopts a configuration as described in the claims to obtain a polymer having excellent heat resistance, mechanical strength, smoothness, resistance to delamination and impregnation of a functional agent. A porous solid membrane composed of a benzoazole-based polymer and a solid polymer electrolyte membrane having high mechanical strength and excellent ion conductivity, power generation properties and gas barrier properties can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic view of a cross-sectional structure of a composite ion exchange membrane.
FIG. 2 is a schematic view of a manufacturing method according to the present invention.
FIG. 3 is a schematic diagram of a delamination test.
[Description of Signs] 1 surface layer A, 2 composite layer, 3 surface layer B, 4 film-like sheet, 5 polybenzazole-based polymer solution, 6 press roll, 7 coagulation bath, 8 coagulation liquid, 9 guide roll, 10 poly Porous membrane composed of benzazole polymer, 11 test membrane, 12 adhesive tape

Claims (6)

A polybenzazole produced by introducing an isotropic solution of a polybenzazole-based polymer between at least two film-like sheets into a coagulation bath and peeling and coagulating the film-like sheets in the coagulation bath. A porous membrane made of a sol-based polymer. 0.5 to 3% by weight of an isotropic solution of a polybenzazole-based polymer is thinned while being sandwiched between at least two film-like sheets. A porous membrane comprising the polybenzazole-based polymer according to claim 1. The polybenza according to any one of claims 1 to 2, wherein the coagulation bath is a poor solvent of a polybenzazole-based polymer, a mixture of a poor solvent and a good solvent, or a solution containing salts in the poor solvent. A porous membrane made of a sol-based polymer. The film-like sheet is a film-like sheet that allows the poor solvent of the polybenzazole-based polymer or its vapor to permeate, and the poor solvent or its vapor that permeates the film-like sheet causes at least the coagulation of the polybenzazole-based polymer. A porous membrane comprising the polybenzazole-based polymer according to any one of claims 1 to 3, wherein the porous membrane is partially formed. An isotropic solution of a polybenzazole-based polymer of 0.5% by weight or more and 3% by weight or less sandwiched between at least two film-like sheets is guided to a coagulation bath, and the film-like sheets are coagulated in the coagulation bath. A method for producing a porous membrane comprising a polybenzazole-based polymer, characterized in that the membrane is exfoliated and solidified. A composite layer formed by impregnating a porous membrane made of a polybenzazole-based polymer with an ion-exchange resin, and a surface layer made of an ion-exchange resin not containing a porous membrane formed on both sides of the composite layer so as to sandwich the composite layer 5. A composite ion exchange membrane comprising: a porous membrane comprising the polybenzazole-based polymer according to claim 1;

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