JP4621344B2 - Proton conducting membrane or film and fuel cell using them - Google Patents

Description

【００２６】
（式中、Ｒは水素原子又はメチル基を示し、Ｘは基の両末端が炭素原子である２価の有機基を示す。）
で表わされる化合物を挙げることができる。
【００２７】
特に、本発明においては、上記基Ｘは、好ましくは、一般式（Ａ）
【００２８】
【化２】

【００２９】
（式中、Ｒ’はエチレン基又はプロピレン基を示し、Ｒ”は炭素原子数１〜１０、好ましくは、２〜６の直鎖状又は分岐鎖状アルキレン基を示し、ｐは１〜１０の整数であり、ｑは０、１又は２である。）
で表わされる２価基か、又は一般式（Ｂ）
【００３０】
【化３】

【００３１】
（式中、Ａｒ及びＡｒ’はそれぞれ独立に２価の芳香族炭化水素基、好ましくは、フェニレン基を示し、Ｒ'"は炭素原子数１〜１０、好ましくは、２〜６の直鎖状又は分岐鎖状アルキレン基を示し、ｒは０又は１であり、ｒが１のとき、ｓは０又は１である。）
で表わされる２価基を示す。
【００３２】
従って、上記一般式（Ｉ）で表わされるＰ−モノマーの好ましい具体例としては、例えば、２−メタクリロイルオキシエチルホスフェート、メタクリロイルテトラ（オキシエチレン）ホスフェート、メタクリロイルペンタ（オキシプロピレン）ホスフェートや、４−スチリルメトキシブチルホスフェート等を挙げることができる。
【００３３】
ホスホン酸基を有するモノマーの好ましい例としては、一般式（II）
【００３４】
【化４】

【００３５】
（式中、Ｒは水素原子又はメチル基を示し、Ｙは基の両末端が炭素原子である２価の有機基を示す。）
で表わされる化合物を挙げることができる。
【００３６】
特に、本発明においては、上記基Ｙは、好ましくは、一般式（Ｂ）
【００３７】
【化５】

【００３８】
（式中、Ａｒ及びＡｒ’はそれぞれ独立に２価の芳香族炭化水素基、好ましくは、フェニレン基を示し、Ｒ'"は炭素原子数１〜１０、好ましくは、２〜６の直鎖状又は分岐鎖状アルキレン基を示し、ｒは０又は１であり、ｒが１のとき、ｓは０又は１である。）
で表わされる２価基を示す。
【００３９】
従って、上記一般式（II）で表わされるホスホン酸基を有するモノマーの好ましい具体例としては、例えば、４−（２−スチリルメトキシエチル）フェニルホスホン酸、４−（スチリルメトキシ）ブチルホスホン酸、スチリルメチルホスホン酸等の化合物を挙げることができる。
【００４０】
また、ホスフィン酸基を有するモノマーの好ましい例としては、一般式（III)
【００４１】
【化６】

【００４２】
（式中、Ｒは水素原子又はメチル基を示し、Ｚは基の両末端が炭素原子である２価の有機基を示す。）
で表わされる化合物を挙げることができる。
【００４３】
特に、本発明においては、上記基Ｚは、好ましくは、一般式（Ｂ）
【００４４】
【化７】

【００４５】
（式中、Ａｒ及びＡｒ’はそれぞれ独立に２価の芳香族炭化水素基、好ましくは、フェニレン基を示し、Ｒ'"は炭素原子数１〜１０、好ましくは、２〜６の直鎖状又は分岐鎖状アルキレン基を示し、ｒは０又は１であり、ｒが１のとき、ｓは０又は１である。）
で表わされる２価基を示す。
【００４６】
従って、上記一般式（III)で表わされるホスフィン酸基を有するモノマーの具体例としては、例えば、４−（２−スチリルメトキシエチル）フェニルホスフィン酸、４−（スチリルメトキシ）ブチルホスフィン酸、スチリルメチルホスフィン酸等の化合物を挙げることができる。
【００４７】
本発明によれば、Ｐ−モノマーと共に、リン酸基、ホスホン酸基又はホスフィン酸基を有する多官能性モノマー（以下、多官能性Ｐ−モノマーということがある。）を用いることができる。
【００４８】
このような多官能性Ｐ−モノマーの好ましい例として、例えば、一般式（IV）
【００４９】
【化８】

【００５０】
（式中、ＲとＸは前記と同じであり、ｍは２又は３である。）
で表わされるリン酸ジエステル又はトリエステルを挙げることができる。
【００５１】
本発明においては、このような多官能性Ｐ−モノマーのうち、特に、基Ｘが前記一般式（Ａ）で表わされる基であるものが好ましい。
【００５２】
従って、このような多官能性Ｐ−モノマーの具体例として、例えば、ビス（メタクリロイルオキシエチル）ホスフェート、ビス｛５−（メタクリロイルオキシエチルオキシカルボニル）ペンチル｝ホスフェート等のリン酸ジエステルを挙げることができる。
【００５３】
Ｐ−モノマーがこのような多官能性Ｐ−モノマーを含むとき、この多官能性Ｐ−モノマーの割合は５０モル％以下であり、好ましくは、４５モル％以下である。
【００５４】
このように、Ｐ−モノマーと共に多官能性Ｐ−モノマーを用いることによって、得られるＰ−ポリマーは、上記多官能性Ｐ−モノマーの架橋反応によって、三次元構造、即ち、架橋構造を有し、かくして、Ｐ−ポリマーの耐水性や耐溶剤性等の物性を更に改善することができる。
【００５５】
また、本発明によれば、Ｐ−モノマーと共に、リン酸基、ホスホン酸基及びホスフィン酸基のいずれも有しない多官能性モノマー（以下、多官能性非Ｐ−モノマーということがある。）を用いることができる。このように、Ｐ−モノマーが多官能性非Ｐ−モノマーを含むとき、この多官能性非Ｐ−モノマーの割合は５０モル％以下であり、好ましくは、４５モル％以下である。
【００５６】
このように、Ｐ−モノマーと共に多官能性非Ｐ−モノマーを用いることによって、得られるＰ−ポリマーの種々の物性、例えば、ガラス転移温度、親水性の程度、柔軟性、機械的強度等を調整することもできる。
【００５７】
しかし、本発明によるプロトン伝導性膜において、Ｐ−ポリマーに架橋構造をもたせるための手段は、上記に限定されるものではなく、例えば、官能基間の反応、過酸化物による架橋、電子線等の照射、オゾンの作用等、従来より知られている適宜の手段を利用することができる。
【００５８】
更に、本発明によれば、Ｐ−モノマーと共に、リン酸基、ホスホン酸基及びホスフィン酸基のいずれも有しない単官能性モノマー（以下、単官能性非Ｐ−モノマーということがある。）をも用いてもよい。
【００５９】
このような単官能性非Ｐ−モノマーとしては、例えば、スチレン、ビニルスルホン酸、スチレンスルホン酸ナトリウム等のビニルモノマー類、エチルビニルエーテル等のビニルエーテル類、アクリル酸ブチル、メトキシエチルアクリレート、２−エチルヘキシルメタクリレート、アクリル酸等のアクリルモノマー類、Ｎ，Ｎ−ジメチルアミノプロピルアクリルアミド、２−アクリルアミド−２−メチルプロパンスルホン酸等のアクリルアミド類を挙げることができる。
【００６０】
本発明において、Ｐ−モノマー（多官能性Ｐ−モノマーを含む。）と共に単官能性非Ｐ−モノマーを用いる場合、その単官能性非Ｐ−モノマーの割合は、用いる基材多孔質膜の空孔率にもよるが、通常、Ｐ−モノマーに対して、９０モル％以下の範囲であり、好ましくは、８０モル％以下の範囲である。単官能性非Ｐ−モノマーの割合がＰ−モノマー（多官能性Ｐ−モノマーを含む。）に対して９０モル％よりも多いときは、高プロトン伝導性膜を得ることができない。
【００６１】
このように、Ｐ−モノマーと、必要に応じて、これ以外の種々のモノマーとを用いて、多孔質膜の空孔内に、それらのモノマーから得られるＰ−ポリマーを担持させて、本発明によるプロトン伝導性膜を得るには、基材多孔質膜に上記Ｐ−モノマーと、必要に応じて、これ以外の種々のモノマーを担持させ、熱重合や光重合等、従来より知られている適宜の方法によって、上記モノマーを重合させればよい。しかし、重合法としては、なかでも、光重合法が簡便で安全あり、しかも、短時間でＰ−ポリマーを得ることができる。また、必要に応じて、光重合を行なった後、残余のＰ−モノマーを重合させるために、より高温で更に光重合や熱重合を行なってもよい。
【００６２】
このように、Ｐ−モノマーの光重合を行なうためには、前記Ｐ−モノマーに光重合開始剤を混合、溶解し、これを多孔質膜に含浸させた後、光照射すればよい。
【００６３】
上記光重合開始剤は、従来より知られているものを適宜に用いればよい。例えば、２−ベンジル−２−ジメチルアミノ−１−（４−モルホリノフェニル）ブタノン−１（チバガイギー社製イルガキュア３６９）、２−メチル−１−｛４−（メチルチオ）フェニル｝−２−モルホリノプロパノン−１（チバガイギー社製イルガキュア９０７）、１−ヒドロキシシクロヘキシルフェニルケトン（チバガイギー社製イルガキュア１８４）、ベンジルジメチルケタール（チバガイギー社製イルガキュア６５１）等を用いることができる。３００ｎｍ以上の波長の光を用いても重合が可能であるものが特に好ましい。このような光重合開始剤は、通常、Ｐ−モノマーに対して0.０１〜５重量％程度加えられる。
【００６４】
Ｐ−モノマーや、場合によっては、Ｐ−モノマーと共に他の共重合性モノマー、多官能性モノマー、光重合開始剤等を含む混合物を多孔質膜の空孔内に担持させるためには、例えば、Ｐ−モノマーや上記混合物に多孔質膜を浸漬したり、また、Ｐ−モノマーや上記混合物を基材多孔質膜に塗布すればよい。
【００６５】
このように、Ｐ−モノマーや上記混合物を多孔質膜に担持させるに際して、これらＰ−モノマーや上記混合物の粘度を適宜に調整してもよい。即ち、粘度を高めるためにモノマーの一部を予備重合させたり、また、適宜のポリマーを少量、添加し、溶解させてもよい。反対に、粘度を下げるために、適当な溶剤を加えて、希釈してもよい。
【００６６】
このようにして、多孔質膜にＰ−モノマーを担持させた後、例えば、ポリエステル樹脂製離型フィルムで多孔質膜を挟み、この交換膜を酸素（従って、例えば、空気）から遮断して、高圧水銀ランプ等を用いてＰ−モノマーに光照射し、光重合させることによって、Ｐ−ポリマーを多孔質膜の空孔内に担持させてなるプロトン伝導性膜を得ることができる。
【００６７】
上記光重合に必要な光照射量は、系により異なるが、通常は、0.１〜５Ｊ／ｃｍ² 程度で十分である。光重合は、得られるＰ−ポリマーの分子量を高くするために、通常、室温付近で行なうが、重合率を高めるために、より高い温度で光重合を行なってもよく、また、最初は低温で、次いで、高温で光重合してもよい。
【００６８】
本発明によれば、上記Ｐ−モノマーを多孔質膜に含浸させる際、多孔質膜の空孔をＰ−モノマーが充填する比率（充填率）が低いときは、このＰ−モノマーの重合後も、基材多孔質膜は、通気性を有する多孔質構造を有しており、かくして、通気性を有するプロトン伝導性多孔質膜を得ることができる。他方、上記充填率が高いときは、Ｐ−モノマーの重合後、基材多孔質膜は、その空孔が実質的に閉塞されて、通気性のないプロトン伝導性無孔膜を得ることができる。一応の目安として、Ｐ−モノマーの充填率が８０％以上であれば、基材多孔質膜の空孔が実質的に閉塞されてなる通気性のないプロトン伝導性無孔膜を得ることができる。
【００６９】
本発明においては、Ｐ−モノマーは、基材多孔質膜の空孔を充填するのみならず、基材多孔質膜の少なくとも一方の表面の少なくとも一部を被覆していてもよい。この場合、Ｐ−モノマーの充填率は１００％を越える。このように、基材多孔質膜にＰ−モノマーを１００％を越える充填率で担持させ、これに光照射すれば、多孔質膜は，その空孔がＰ−ポリマーで充填されているのみならず、少なくとも一方の表面の少なくとも一部がＰ−ポリマーで被覆されたプロトン伝導性膜を得ることができる。
【００７０】
更に、本発明によれば、このようにして得られたプロトン伝導性膜の有する空孔の残余の空隙、即ち、このようにして得られたプロトン伝導性膜に残存する空隙を加熱、収縮させ、又は加熱、溶融させる等の適宜手段によって、プロトン伝導性膜に残存する上記空隙の少なくとも一部を閉塞して、プロトン伝導性フィルムとすることができ、特に、好ましくは、プロトン伝導性膜に残存する空隙をすべて閉塞して、通気性のないプロトン伝導性無孔フィルムを得ることができる。また、必要に応じて、プロトン伝導性膜に残存する空隙を一部閉塞して、通気性のあるプロトン伝導性有孔フィルムを得ることができる。
【００７１】
このように、リン酸基、ホスホン酸基又はホスフィン酸基を側鎖に有するＰ−ポリマーを基材多孔質膜の空孔内に担持させてなるプロトン伝導性膜やプロトン伝導性フィルムは、高いプロトン伝導性を有する。本発明によれば、多孔質膜へのＰ−モノマーの充填率を高くして、多孔質膜の有する空孔へのＰ−ポリマーの充填率を高くするほど、高いプロトン伝導性を有する膜やフィルムを得ることができる。
【００７２】
本発明によれば、このように、多孔質構造を有し、通気性を有するプロトン伝導性膜や、反対に、無孔構造のプロトン伝導性膜を得ることができ、また、多孔質構造を有し、通気性を有するプロトン伝導性フィルムや、反対に、無孔構造のプロトン伝導性フィルムを得ることができる。多孔質構造を有し、通気性を有するプロトン伝導性膜やフィルムは、例えば、選択透過性荷電膜等、その空隙を活かした用途に好ましく用いることができる。
【００７３】
しかし、多孔質構造を有し、通気性を有するプロトン伝導性膜やフィルムは、燃料電池用セパレーターとして用いれば、ガスのクロスリークが起こりやすい等の問題がある。従って、このような用途には、上述したように、多孔質膜の空孔を実質的にすべてＰ−ポリマーで充填したプロトン伝導性無孔膜を用いたり、また、プロトン伝導性多孔質膜を前述したように加熱、溶融させる等の適宜の手段によって、プロトン伝導性膜に残存する空隙をすべて閉塞してなるプロトン伝導性無孔フィルムを用いることが好ましい。
【００７４】
本発明によれば、Ｐ−ポリマーからなるプロトン伝導性ポリマーを多孔質膜に複合化して、プロトン伝導性膜又はフィルムとしたものであり、好ましくは、Ｍ−モノマーを多孔質膜に含浸させ、この多孔質膜の空孔内で重合させて、Ｐ−ポリマを生成させると共に、このＰ−ポリマーを上記多孔質膜の空孔内に担持させて、多孔質膜とＰ−ポリマーとの一体化を実現したものである。
【００７５】
従って、本発明によれば、基材多孔質膜とプロトン伝導性ポリマーとの複合化に由来して、種々の点ですぐれたプロトン伝導性膜又はフィルムを得ることができる。例えば、超高分子量ポリエチレン等からなる強靱な多孔質膜を基材として用いることによって、Ｐ−ポリマーに由来する高いプロトン伝導性に加えて、高い機械的強度とすぐれたハンドリング性を有するプロトン伝導性膜又はフィルムを得ることができる。
【００７６】
特に、本発明に従って、Ｐ−モノマーを多孔質膜の空孔内に担持させ、重合させて、Ｐ−ポリマーを基材多孔質膜と一体化することによって、Ｐ−ポリマー鎖を多孔質膜の網目に高度に絡みつかせることができ、更には、Ｐ−モノマーと共に多官能性モノマーとを共重合させれば、架橋したＰ−ポリマーと多孔質膜を構成するポリマー鎖とが相互貫通したポリマーネットワークによって物理的な結合が生じ、かくして、プロトン伝導性ポリマーと多孔質膜との密着性を一層強めたプロトン伝導性膜やフィルムを得ることができる。
【００７７】
【実施例】
以下に実施例を挙げて本発明を説明するが、本発明はこれら実施例により何ら限定されるものではない。また、以下において、用いた多孔質膜の特性や、得られたプロトン伝導性膜又はフィルムの特性は、次のようにして評価した。
【００７８】
（膜又はフィルムの厚み）
１／１００００シックネスゲージで測定した。
（多孔質膜の空孔率）
多孔質膜の単位面積Ｓ（ｃｍ² ）あたりの重量Ｗ（ｇ）、平均厚みｔ（μｍ）及び密度ｄ（ｇ／ｃｍ³ ）から下式にて算出した。
空孔率（％）＝（１−（１０⁴ ・Ｗ／(Ｓ・ｔ・ｄ））×１００
【００７９】
（プロトン伝導度）
プロトン伝導性膜又はフィルムを温度２５℃、相対湿度５０％に調整した環境下に４時間放置した後、ヒューレットパッカード社ＬＣＲメーターＨＰ４２８４Ａを用いて、白金電極間に所定厚みの１ｃｍ角の試料を挟み、温度２５℃、相対湿度５０％の条件下で複素インピーダンス法にて測定し、虚数部の抵抗値ゼロに外挿したときの実数部の抵抗値を用いてプロトン伝導度を算出した。
【００８０】
（基材多孔質膜の空孔へのＰ−ポリマーの体積充填率）
基材多孔質膜の体積Ｖ（ｃｍ³ ）、基材多孔質膜の空孔率Φ（％）、Ｐ−ポリマーの重量Ｍ（ｇ）及びＰ−ポリマーの密度ｄ（ｇ／ｃｍ³ ）から下式にて算出した。
充填率（％) ＝10⁴ ・Ｍ／（Ｖ・Φ・ｄ）
（引張強度）
ダンベル型に打ち抜いた試験片（ＪＩＳ Ｋ ７１１３、プラスチックの引張試験方法における１号形試験片に準拠）について、引張試験機（（株）島津製作所製オートグラフＡＧＳ−５０Ｄ）を用いて測定した。
【００８１】
実施例１
（プロトン伝導性膜の製造）
２−メタクリロイルオキシエチルホスフェート／ビス（メタクリロイルオキシエチル）ジホスフェート（６５／３５モル比）からなるＰ−モノマー（共栄社化学（株）製ライトエステルＰ−１Ｍ）５０重量％とブチルアクリレート５０重量％とからなるモノマー混合物１００重量部にベンジルジメチルケタール（チバガイギー社製イルガキュア６５１）0.５重量部を溶解させた。
【００８２】
これを希釈することなく、そのまま、重量平均分子量1.０×１０⁶ の超高分子量ポリエチレン樹脂からなる多孔質膜Ｔ１（膜厚２５μｍ、空孔率４０％、平均孔径0.１０μｍ）の両面に塗布して、多孔質膜の空孔に含浸させた。
【００８３】
このように処理した多孔質膜をポリエステル樹脂製離型フィルムで挟んで、多孔質膜を空気から遮断した後、高圧水銀ランプを備えた光照射装置（アイグラフィック（株）製ＵＢ０２１−１Ｂ−１３）を用いて、上記多孔質膜にエネルギー1.５Ｊ／ｃｍ² にて光照射して、その空孔内で上記モノマー混合物を光重合させ、Ｐ−ポリマーを生成させると共に、これを上記多孔質膜の空孔内に担持させて、厚み３５μｍのプロトン伝導性膜Ｆ１を得た。このプロトン伝導性膜においては、多孔質膜の空孔は上記Ｐ−ポリマーにて完全に充填されており、また、多孔質膜の両表面も、上記Ｐ−ポリマー層で被覆されていた。
【００８４】
上記プロトン伝導性膜Ｆ１のプロトン伝導度は2.１×１０^-3Ｓ／ｃｍであり、引張強度は８７ＭＰａであった。
【００８５】
（燃料電池）
白金触媒を0.６ｍｇ／ｃｍ² の割合で表面に担持させたカーボンペーパー２枚の間に上記プロトン伝導性膜Ｆ１を挟み、ホットプレスを用いて接合して、膜−電極接合体（ＭＥＡ）を製作した。
【００８６】
（株）東陽テクニカ製燃料電池評価装置を用いて、上記ＭＥＡの燃料電池特性を評価した。背圧弁は絞らず、圧力は常圧にて行なった。加湿器温度は水素側８０℃、酸素側７０℃とし、燃料電池セル温度は７０℃とした。Ｔａｆｅｌ法にて電流−電圧（Ｉ−Ｖ）曲線を得たところ、結果を図１に示すように、プロトン交換膜として、ナフィオン（登録商標）１１７膜を用いた場合とほぼ同等の電流−電圧（Ｉ−Ｖ）曲線を得た。即ち、本発明によるプロトン伝導性膜は、ナフィオン１１７膜と同等の燃料電池特性を有する。
【００８７】
実施例２
実施例１と同じ２−メタクリロイルオキシエチルホスフェートとビス（メタクリロイルオキシエチル）ジホスフェートとからなるＰ−モノマー１００重量部に１−ヒドロキシシクロヘキシルフェニルケトン（チバガイギー社製イルガキュア１８４）0.５重量部を溶解させた。
【００８８】
実施例１と同じ超高分子量ポリエチレン樹脂からなる多孔質膜Ｔ１をポリエステル樹脂製離型フィルム上に載せ、多孔質膜の露出表面に、上記Ｐ−モノマーを希釈することなく、そのまま、塗布し、バーでしごいて余剰のモノマーを多孔質膜の表面から除去して、多孔質膜の空孔中にのみ、上記モノマーを含浸させた。
【００８９】
このように処理した多孔質膜の露出表面にもポリエステル樹脂製離型フィルムを被せて、多孔質膜を空気から遮断し、実施例１と同じ光照射装置を用いて、エネルギー1.５Ｊ／ｃｍ² にて多孔質膜に光照射して、その空孔内で上記モノマーを光重合させ、Ｐ−ポリマーを生成させると共に、このＰ−ポリマーを上記空孔内に担持させて、厚み２５μｍのプロトン伝導性膜Ｆ２を得た。このプロトン伝導性膜においては、多孔質膜の空孔はポリマーにて完全に充填されていた。このプロトン伝導性膜Ｆ２のプロトン伝導度は8.５×１０^-4Ｓ／ｃｍであった。
【００９０】
実施例３
実施例１と同じ２−メタクリロイルオキシエチルホスフェートとビス（メタクリロイルオキシエチル）ジホスフェートとからなるＰ−モノマー１００重量部に１−ヒドロキシシクロヘキシルフェニルケトン（チバガイギー社製イルガキュア１８４）0.５重量部を溶解させ、これをメタノールでモノマー濃度３０重量％に希釈した。
【００９１】
重量平均分子量2.４×１０⁶ の超高分子量ポリエチレン樹脂からなる多孔質膜Ｔ２（膜厚４０μｍ、空孔率４４％、平均孔径0.１５μｍ）をポリエステル樹脂製離型フィルム上に載せ、この多孔質膜の露出表面に、上記モノマー混合物の希釈溶液を塗布し、バーでしごいて余剰のモノマー混合物を多孔質膜の表面から除去して、風乾して、多孔質膜の空孔中にのみ、上記モノマー混合物を含浸させた。
【００９２】
このように処理した多孔質膜の露出表面にもポリエステル樹脂製離型フィルムを被せて、多孔質膜を空気から遮断し、実施例１と同じ光照射装置を用いて、エネルギー1.５Ｊ／ｃｍ² にて多孔質膜に光照射して、その空孔内で上記モノマー混合物を光重合させ、Ｐ−ポリマーを生成させると共に、このＰ−ポリマーを上記空孔内に担持させて、厚み４０μｍのプロトン伝導性膜Ｆ３を得た。このプロトン伝導性膜においては、多孔質膜の空孔はポリマーにて部分的に充填されていた。このプロトン伝導性膜Ｆ２のプロトン伝導度は4.０×１０^-5Ｓ／ｃｍであった。
【００９３】
比較例１
実施例１において、基材多孔質膜を用いることなく、ポリエステル樹脂製離型フィルム上に実施例１と同じ２−メタクリロイルオキシエチルホスフェートとビス（メタクリロイルオキシエチル）ジホスフェートとからなるＰ−モノマー５０重量％とブチルアクリレート５０重量％とからなるモノマー混合物を厚み３５μｍの層に塗布した。
【００９４】
この塗布層の上にもポリエステル樹脂製離型フィルムを載せて、上記モノマー混合物の塗布層を空気から遮断し、実施例１と同じ光照射装置を用いて、エネルギー1.５Ｊ／ｃｍ² にて光照射して、上記モノマー混合物からＰ−ポリマーを生成させて、このＰ−ポリマーのみからなる厚み３５μｍのプロトン伝導性膜Ｒ１を得た。このプロトン伝導性膜のプロトン電導度は2.３×１０^-3Ｓ／ｃｍであり、また、引張強度は、８ＭＰａであった。
【００９５】
比較例２
東ソー（株）製ポリナスＰＳ−５を強酸性カチオン交換樹脂を用いてイオン交換し、ナトリウム塩を遊離酸に変換し、これを濃縮した後、メタノールに溶解させて、２０％濃度のポリスチレンスルホン酸のメタノール溶液を調製した。
【００９６】
実施例３と同じ超高分子量ポリエチレン樹脂からなる多孔質膜Ｔ２をポリエステル樹脂製離型フィルムに載せ、その露出表面に上記ポリスチレンスルホン酸のメタノール溶液を塗布し、乾燥させて、厚み５８μｍのプロトン伝導性膜Ｒ２を得た。
【００９７】
このプロトン伝導性膜においては、多孔質膜の空孔は上記ポリスチレンスルホン酸にて完全に充填されており、また、多孔質膜の上記ポリスチレンスルホン酸の塗布側の表面も、ポリスチレンスルホン酸の層で被覆されていた。このプロトン伝導性膜Ｒ２のプロトン伝導度は2.０×１０^-5Ｓ／ｃｍであった。
【００９８】
このプロトン伝導性膜を２４時間水に浸漬したところ、ポリスチレンスルホン酸が一部、水中に溶出した結果、この水への浸漬後に再び温度２５℃、相対湿度５０％に調湿してプロトン伝導度を測定したところ、3.７×１０^-6Ｓ／ｃｍであった。
【００９９】
【発明の効果】
以上のように、本発明によるプロトン伝導性膜は、リン酸基、ホスホン酸基又はホスフィン酸基を側鎖に有するＰ−ポリマーを多孔質膜の空孔内に担持させてなるものであり、高いプロトン伝導性を有するのみならず、高い強度を有し、更に、上記ポリマーは水不溶性である。特に、本発明に従って、リン酸基、ホスホン酸基又はホスフィン酸基を有するＰ−モノマーを多孔質膜の空孔内で重合させて、リン酸基、ホスホン酸基又はホスフィン酸基を側鎖に有するＰ−ポリマーを生成させると共に、このＰ−ポリマーを上記多孔質膜の空孔内に担持させてなるプロトン伝導性膜によれば、Ｐ−ポリマーと多孔質膜が一体化され、Ｐ−ポリマーは多孔質膜に対して高度の密着性を有する。しかも、本発明によるプロトン伝導性膜は、従来のスルホン酸基含有フッ素樹脂膜からなるプロトン伝導性膜に比べて格段に低廉に得ることができる。
【０１００】
かくして、本発明によるプロトン伝導性膜は、燃料電池におけるイオン交換膜として好適に用いることができ、ここに、低廉であることから、燃料電池システムのコストを大幅に低減せしめて、その実用化を速めることができる。
【図面の簡単な説明】
【図１】は、本発明によるプロトン伝導性膜を用いて調製した膜−電極接合体（ＭＥＡ）の燃料電池特性を示すＴａｆｅｌ法による電流−電圧（Ｉ−Ｖ）曲線である。[0001]
[Industrial application fields]
The present invention relates to a proton conductive membrane having proton conductivity, a proton conductive film obtained therefrom, and a method for producing them, and further to a fuel cell using the proton conductive membrane or film as a proton exchange membrane.
[0002]
[Prior art]
Conventionally, proton conductive membranes have been used for applications such as ion exchange membranes and humidity sensors, but in recent years, they have also attracted attention for their use as solid electrolyte membranes in polymer electrolyte fuel cells. For example, a sulfonic acid group-containing fluororesin film represented by DuPont's Nafion (registered trademark) has been studied for use as a solid electrolyte in electric vehicles and fuel cells for distributed power sources. These fluororesin-based proton conductive membranes have the disadvantage that they are very expensive. In order to put the proton conductive membrane into practical use in new applications such as fuel cells, it is indispensable to have high proton conductivity and low price.
[0003]
Thus, various methods for obtaining a proton conductive membrane by incorporating an electrolyte polymer into a porous membrane having pores have been proposed. For example, in JP-A-9-194609, the pores of a porous film made of a hydrophobic resin such as a fluororesin, a polyethylene resin, or a polypropylene resin are impregnated with a solution of the same hydrophobic polymer and dried. A method has been proposed in which after a polymer is supported on a porous membrane, ion exchange groups such as sulfonic acid groups, protonated amino groups, and carboxyl groups are introduced into the polymer, thus producing an ion exchange membrane. However, according to such a method, it is difficult to uniformly distribute the ion exchange groups in the porous membrane, and the proton conductivity is not sufficient.
[0004]
Therefore, recently, a polymer having a phosphate ester group as an ion exchange group, that is, a polymer derived from a methacrylic acid derivative having a phosphate group in the side chain has been used as a proton exchange membrane for a polymer electrolyte fuel cell. Proceedings of the Society of Polymer Science, Japan, Vol. 48, No. 3, page 414 (1999), “Proceedings of the Society of Polymer Science, Japan” Vol. 48, No. 10, page 2393 (1999), No. 4, page 751 (2000), etc.
[0005]
According to these documents, a polymer derived from a methacrylic acid derivative having a phosphate ester group in the side chain has a high proton conductivity because the proton dissociation degree of the phosphate ester group is large and exhibits strong acidity. In addition, although the main chain is a hydrocarbon, it has heat resistance and hardly dissolves in water. As described above, the polymer having a phosphate group as a substituent in the side chain is water-insoluble because a strong network is formed between the polymer chains due to hydrogen bonds formed between the phosphate groups. It seems to be because.
[0006]
However, the polymer itself derived from a methacrylic acid derivative having a phosphate group in the side chain is difficult to use as a proton exchange membrane for a fuel cell because it has low mechanical strength and is brittle. In addition, the above-mentioned polymer often gels at the time of its production, and the obtained polymer has poor solubility. For practical use, there are still many problems in terms of production and moldability.
[0007]
In general, in order to impart proton conductivity to a porous membrane, it is necessary to have a proton generation source or transport site in the membrane, and the sulfonic acid group mentioned above has such a proton generation source or transport site. This is a representative example. However, the polymer having a sulfonic acid group is typically polystyrene sulfonic acid or polyvinyl sulfonic acid, which are all water-soluble. Therefore, it is difficult to use these polymers as they are as a proton exchange membrane of a fuel cell using hydrogen gas or oxygen gas with steam humidification. That is, in order to use as a proton exchange membrane of a fuel cell, it is necessary to subject the polymer to some water insolubilization treatment.
[0008]
In order to insolubilize the water-soluble polymer, it is necessary to carry out a crosslinking treatment or copolymerize with a monomer that gives a water-insoluble polymer together with a monomer having a sulfonic acid group to form a copolymer.
[0009]
However, even though it is possible to avoid complete dissolution in water by applying a crosslinking treatment to the water-soluble polymer, it is inevitable that the polymer swells when contacted with water. Thus, water insolubilization due to cross-linking of the water-soluble polymer results in a decrease in the mechanical strength of the polymer, so that it is difficult to use a water-insoluble polymer water-insoluble polymer as a proton exchange membrane for a fuel cell. It is.
[0010]
On the other hand, in order to obtain a water-insoluble polymer by copolymerization with a monomer that gives a water-insoluble polymer, the proportion of the sulfonic acid group-containing monomer in the monomer to be polymerized must be relatively low, Originally, the proton conductivity required as a proton exchange membrane is impaired, and therefore a polymer having high proton conductivity cannot be obtained.
[0011]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems in proton conductive membranes or films, and has a durability and mechanical strength, a proton conductive membrane or film, a production method thereof, and further, An object of the present invention is to provide a fuel cell using as a proton exchange membrane.
[0012]
[Means for solving problems]
According to the present invention, a polymer having a phosphoric acid group, a phosphonic acid group or a phosphinic acid group in its side chain (hereinafter sometimes referred to as “P-polymer”) is supported in the pores of the porous membrane. A proton conductive membrane is provided.
[0013]
In particular, according to the present invention, a monomer having a phosphoric acid group, a phosphonic acid group or a phosphinic acid group (hereinafter sometimes referred to as “P-monomer”) is polymerized in the pores of the porous membrane, There is provided a proton conductive membrane characterized in that a P-polymer is produced and the P-polymer is supported in the pores of the porous membrane.
[0014]
Furthermore, according to the present invention, the P-monomer is impregnated into the porous membrane and polymerized in the pores of the porous membrane to form the P-polymer, and the P-polymer is added to the porous membrane. A method for producing a proton conductive membrane is provided, which is supported in the pores of the membrane.
[0015]
In addition, according to the present invention, there is provided a proton conductive film obtained by closing at least a part of a void when a void remains in the pores of the proton conductive membrane, and such a manufacturing method.
[0016]
In addition to the above, according to the present invention, there is provided a fuel cell using the proton conductive film as a proton exchange membrane.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The proton conductive membrane according to the present invention is one in which P-polymer is supported in the pores of the porous membrane, and preferably the P-monomer is polymerized in the pores of the porous membrane to obtain the above P -A polymer is produced and this P-polymer is supported in the pores of the porous membrane.
[0018]
In the proton conductive membrane according to the present invention, the porous membrane used as the substrate is not particularly limited, and those made of various resins can be used. Examples of such resins include fluorine resins such as polytetrafluoroethylene, 6,6-nylon, various polyamide resins, polyester resins such as polyethylene terephthalate, polyether resins such as dimethylphenylene oxide and polyether ether ketone, Α-olefins such as ethylene and propylene, alicyclic unsaturated hydrocarbons such as norbornene, (co) polymers such as conjugated dienes such as butadiene and isoprene, such as polyethylene resins, polypropylene resins, and ethylene-propylene rubbers And aliphatic hydrocarbon resins such as elastomers such as butadiene rubber, isoprene rubber, butyl rubber and norbornene rubber, and hydrogenated products thereof. These resins may be used alone or in combination of two or more to form the porous film.
[0019]
According to the present invention, among the porous membranes made of the various resins described above, a polyolefin resin, particularly a weight average molecular weight of 5.0 × 10 ^Five Above, preferably 1.0 × 10 ⁶ A porous film made of the above high molecular weight polyethylene resin is preferably used because it is excellent in strength and heat resistance. In addition, a porous film made of a fluororesin such as polytetrafluoroethylene or polyvinylidene fluoride is also preferably used in the present invention because of its excellent chemical resistance and heat resistance.
[0020]
According to the present invention, the substrate porous membrane may be hydrophilized by an appropriate means conventionally known. Such a hydrophilicized porous membrane is produced using, for example, a polymer having a hydrophilic group such as a sulfonic acid group, a phosphoric acid group, a carboxyl group, an amino group, an amide group, or a hydroxyl group or a blend thereof as a raw material. It can be obtained by filming. In addition, after the polymer having no hydrophilic group is formed into a porous film, the porous film is subjected to, for example, sulfonation treatment, or a surfactant is supported. Can be obtained by:
[0021]
In the present invention, the substrate porous membrane usually has a porosity in the range of 20 to 90%, preferably 30 to 85%. When the porosity of the porous membrane is smaller than 20%, such a porous membrane may be impregnated with P-monomer and polymerized to carry P-polymer in the pores of the porous membrane. A membrane having high proton conductivity cannot be obtained. However, when the porosity of the porous membrane is greater than 90%, the proton conductive membrane obtained by supporting P-polymer in the pores of such a porous membrane is not sufficient in strength and handled. And difficult to use in various applications.
[0022]
The substrate porous membrane is not particularly limited as long as the P-monomer can be held in the porous membrane, but the average pore diameter is usually in the range of 0.001 to 100 μm. And preferably in the range of 0.005 to 10 μm. Similarly, the thickness of the porous membrane is not particularly limited, but is usually 1 mm or less, and preferably in the range of 5 to 500 μm.
[0023]
In the proton conductive membrane according to the present invention, the P-monomer is impregnated into a porous membrane and polymerized in the pores of the porous membrane to form the P-polymer, and the P-polymer is added to the porous membrane. It can be obtained by supporting it in the pores of the membrane.
[0024]
According to the present invention, among the P-monomers, preferred examples of the monomer having a phosphate group include those represented by the general formula (I)
[0025]
[Chemical 1]

[0026]
(In the formula, R represents a hydrogen atom or a methyl group, and X represents a divalent organic group in which both ends of the group are carbon atoms.)
The compound represented by these can be mentioned.
[0027]
In particular, in the present invention, the group X is preferably represented by the general formula (A)
[0028]
[Chemical 2]

[0029]
(In the formula, R ′ represents an ethylene group or a propylene group, R ″ represents a linear or branched alkylene group having 1 to 10 carbon atoms, preferably 2 to 6 carbon atoms, and p is 1 to 10). An integer, q is 0, 1 or 2.)
Or a general formula (B)
[0030]
[Chemical 3]

[0031]
(In the formula, Ar and Ar ′ each independently represent a divalent aromatic hydrocarbon group, preferably a phenylene group, and R ′ ″ is a straight chain having 1 to 10 carbon atoms, preferably 2 to 6 carbon atoms. Or a branched alkylene group, r is 0 or 1, and when r is 1, s is 0 or 1.)
The bivalent group represented by these is shown.
[0032]
Accordingly, preferred specific examples of the P-monomer represented by the general formula (I) include, for example, 2-methacryloyloxyethyl phosphate, methacryloyl tetra (oxyethylene) phosphate, methacryloyl penta (oxypropylene) phosphate, and 4-styryl. And methoxybutyl phosphate.
[0033]
Preferred examples of the monomer having a phosphonic acid group include those represented by the general formula (II)
[0034]
[Formula 4]

[0035]
(In the formula, R represents a hydrogen atom or a methyl group, and Y represents a divalent organic group in which both ends of the group are carbon atoms.)
The compound represented by these can be mentioned.
[0036]
In particular, in the present invention, the group Y is preferably represented by the general formula (B)
[0037]
[Chemical formula 5]

[0038]
(In the formula, Ar and Ar ′ each independently represent a divalent aromatic hydrocarbon group, preferably a phenylene group, and R ′ ″ is a straight chain having 1 to 10 carbon atoms, preferably 2 to 6 carbon atoms. Or a branched alkylene group, r is 0 or 1, and when r is 1, s is 0 or 1.)
The bivalent group represented by these is shown.
[0039]
Accordingly, preferred specific examples of the monomer having a phosphonic acid group represented by the general formula (II) include 4- (2-styrylmethoxyethyl) phenylphosphonic acid, 4- (styrylmethoxy) butylphosphonic acid, and styryl. Mention may be made of compounds such as methylphosphonic acid.
[0040]
Preferred examples of the monomer having a phosphinic acid group include those represented by the general formula (III)
[0041]
[Chemical 6]

[0042]
(In the formula, R represents a hydrogen atom or a methyl group, and Z represents a divalent organic group in which both ends of the group are carbon atoms.)
The compound represented by these can be mentioned.
[0043]
In particular, in the present invention, the group Z is preferably represented by the general formula (B)
[0044]
[Chemical 7]

[0045]
(In the formula, Ar and Ar ′ each independently represent a divalent aromatic hydrocarbon group, preferably a phenylene group, and R ′ ″ is a straight chain having 1 to 10 carbon atoms, preferably 2 to 6 carbon atoms. Or a branched alkylene group, r is 0 or 1, and when r is 1, s is 0 or 1.)
The bivalent group represented by these is shown.
[0046]
Therefore, specific examples of the monomer having a phosphinic acid group represented by the general formula (III) include, for example, 4- (2-styrylmethoxyethyl) phenylphosphinic acid, 4- (styrylmethoxy) butylphosphinic acid, styrylmethyl. Mention may be made of compounds such as phosphinic acid.
[0047]
According to the present invention, a polyfunctional monomer having a phosphoric acid group, a phosphonic acid group or a phosphinic acid group (hereinafter sometimes referred to as a polyfunctional P-monomer) can be used together with the P-monomer.
[0048]
Preferred examples of such polyfunctional P-monomer include, for example, the general formula (IV)
[0049]
[Chemical 8]

[0050]
(In the formula, R and X are the same as described above, and m is 2 or 3.)
The phosphoric acid diester or triester represented by these can be mentioned.
[0051]
In the present invention, among such polyfunctional P-monomers, the group X is preferably a group represented by the general formula (A).
[0052]
Accordingly, specific examples of such polyfunctional P-monomers include phosphoric acid diesters such as bis (methacryloyloxyethyl) phosphate and bis {5- (methacryloyloxyethyloxycarbonyl) pentyl} phosphate. .
[0053]
When the P-monomer contains such a multifunctional P-monomer, the proportion of this multifunctional P-monomer is 50 mol% or less, preferably 45 mol% or less.
[0054]
Thus, by using a polyfunctional P-monomer together with a P-monomer, the resulting P-polymer has a three-dimensional structure, that is, a crosslinked structure, by the crosslinking reaction of the polyfunctional P-monomer. Thus, physical properties such as water resistance and solvent resistance of the P-polymer can be further improved.
[0055]
Moreover, according to this invention, the polyfunctional monomer (henceforth a polyfunctional non-P-monomer) which does not have any of a phosphoric acid group, a phosphonic acid group, and a phosphinic acid group with a P-monomer. Can be used. Thus, when the P-monomer contains a polyfunctional non-P-monomer, the proportion of this polyfunctional non-P-monomer is 50 mol% or less, and preferably 45 mol% or less.
[0056]
In this way, by using a polyfunctional non-P-monomer together with a P-monomer, various physical properties of the obtained P-polymer, such as glass transition temperature, degree of hydrophilicity, flexibility, mechanical strength, etc., are adjusted. You can also
[0057]
However, in the proton conducting membrane according to the present invention, the means for giving the P-polymer a crosslinked structure is not limited to the above, and examples thereof include reaction between functional groups, crosslinking by peroxide, and electron beam. Appropriate means known in the art such as irradiation of ozone and action of ozone can be used.
[0058]
Furthermore, according to the present invention, a monofunctional monomer having no phosphoric acid group, phosphonic acid group or phosphinic acid group together with the P-monomer (hereinafter, sometimes referred to as monofunctional non-P-monomer). May also be used.
[0059]
Examples of such monofunctional non-P-monomers include vinyl monomers such as styrene, vinyl sulfonic acid and sodium styrene sulfonate, vinyl ethers such as ethyl vinyl ether, butyl acrylate, methoxyethyl acrylate, and 2-ethylhexyl methacrylate. And acrylic monomers such as acrylic acid, and acrylamides such as N, N-dimethylaminopropylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid.
[0060]
In the present invention, when a monofunctional non-P-monomer is used together with a P-monomer (including a polyfunctional P-monomer), the ratio of the monofunctional non-P-monomer is determined based on the empty space of the substrate porous membrane to be used. Although it depends on the porosity, it is usually in the range of 90 mol% or less, preferably 80 mol% or less with respect to the P-monomer. When the proportion of the monofunctional non-P-monomer is more than 90 mol% with respect to the P-monomer (including the polyfunctional P-monomer), a high proton conductive membrane cannot be obtained.
[0061]
In this way, the P-monomer and, if necessary, various other monomers are used to support the P-polymer obtained from these monomers in the pores of the porous membrane, and the present invention. In order to obtain a proton conductive membrane by the above-mentioned method, the above-mentioned P-monomer and, if necessary, various other monomers are supported on a porous substrate membrane, and heat polymerization, photopolymerization, etc. are conventionally known. The monomer may be polymerized by an appropriate method. However, among these polymerization methods, the photopolymerization method is simple and safe, and a P-polymer can be obtained in a short time. If necessary, after photopolymerization, photopolymerization or thermal polymerization may be further performed at a higher temperature in order to polymerize the remaining P-monomer.
[0062]
Thus, in order to carry out photopolymerization of the P-monomer, a photopolymerization initiator is mixed and dissolved in the P-monomer, impregnated in a porous film, and then irradiated with light.
[0063]
What is necessary is just to use what is conventionally known for the said photoinitiator suitably. For example, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) butanone-1 (Irgacure 369 manufactured by Ciba Geigy), 2-methyl-1- {4- (methylthio) phenyl} -2-morpholinopropanone -1 (Irgacure 907 manufactured by Ciba Geigy), 1-hydroxycyclohexyl phenyl ketone (Irgacure 184 manufactured by Ciba Geigy), benzyldimethyl ketal (Irgacure 651 manufactured by Ciba Geigy) and the like can be used. Those that can be polymerized even when using light having a wavelength of 300 nm or more are particularly preferred. Such a photopolymerization initiator is usually added in an amount of about 0.01 to 5% by weight based on the P-monomer.
[0064]
In order to support a P-monomer or a mixture containing another copolymerizable monomer, a polyfunctional monomer, a photopolymerization initiator and the like together with a P-monomer in some cases in the pores of the porous film, for example, What is necessary is just to immerse a porous membrane in P-monomer or the said mixture, and just apply | coat P-monomer or the said mixture to a base-material porous membrane.
[0065]
As described above, when the P-monomer or the mixture is supported on the porous membrane, the viscosity of the P-monomer or the mixture may be appropriately adjusted. That is, a part of the monomer may be prepolymerized to increase the viscosity, or a small amount of an appropriate polymer may be added and dissolved. Conversely, in order to lower the viscosity, a suitable solvent may be added for dilution.
[0066]
In this way, after the P-monomer is supported on the porous membrane, for example, the porous membrane is sandwiched with a release film made of polyester resin, and this exchange membrane is shielded from oxygen (and thus, for example, air), A proton conductive membrane in which the P-polymer is supported in the pores of the porous membrane can be obtained by irradiating the P-monomer with light using a high-pressure mercury lamp or the like and photopolymerizing it.
[0067]
The amount of light irradiation required for the photopolymerization varies depending on the system, but is usually 0.1 to 5 J / cm. ² The degree is sufficient. In order to increase the molecular weight of the resulting P-polymer, the photopolymerization is usually carried out at around room temperature. However, in order to increase the polymerization rate, the photopolymerization may be carried out at a higher temperature. Then, photopolymerization may be performed at a high temperature.
[0068]
According to the present invention, when the porous membrane is impregnated with the P-monomer, if the ratio of filling the pores of the porous membrane with the P-monomer (filling rate) is low, even after the polymerization of the P-monomer. The base porous membrane has a porous structure having air permeability, and thus a proton-conductive porous membrane having air permeability can be obtained. On the other hand, when the filling ratio is high, after the polymerization of the P-monomer, the pores of the substrate porous membrane are substantially blocked, and a proton-conductive nonporous membrane without air permeability can be obtained. . As a temporary guide, if the P-monomer filling rate is 80% or more, a non-breathable proton-conductive nonporous membrane in which the pores of the porous substrate membrane are substantially blocked can be obtained. .
[0069]
In the present invention, the P-monomer not only fills the pores of the substrate porous membrane, but may cover at least a part of at least one surface of the substrate porous membrane. In this case, the filling rate of P-monomer exceeds 100%. Thus, if the porous film is loaded with P-monomer at a filling rate exceeding 100% and irradiated with light, the porous film can only be filled with P-polymer. However, it is possible to obtain a proton conductive membrane in which at least a part of at least one surface is coated with P-polymer.
[0070]
Furthermore, according to the present invention, the voids remaining in the vacancies of the proton conductive membrane thus obtained, that is, the voids remaining in the proton conductive membrane thus obtained are heated and contracted. Or, by appropriate means such as heating or melting, at least a part of the voids remaining in the proton conductive membrane can be closed to form a proton conductive film, and particularly preferably the proton conductive membrane. All remaining voids can be blocked to obtain a non-breathable proton conductive nonporous film. Further, if necessary, a part of voids remaining in the proton conductive membrane can be blocked to obtain a proton conductive porous film having air permeability.
[0071]
As described above, a proton conductive membrane or a proton conductive film in which a P-polymer having a phosphoric acid group, a phosphonic acid group or a phosphinic acid group in the side chain is supported in the pores of the base porous membrane is high. Proton conductivity. According to the present invention, the higher the filling rate of P-monomer in the porous membrane and the higher the filling rate of P-polymer in the pores of the porous membrane, A film can be obtained.
[0072]
According to the present invention, it is possible to obtain a proton-conductive membrane having a porous structure and air permeability, and on the contrary, a non-porous proton-conductive membrane. Thus, a proton conductive film having air permeability and a non-porous proton conductive film can be obtained. Proton conductive membranes and films having a porous structure and air permeability can be preferably used for applications utilizing the voids such as a selectively permeable charged membrane.
[0073]
However, proton-conductive membranes and films having a porous structure and air permeability have problems such that gas cross-leak is likely to occur when used as a fuel cell separator. Therefore, for such an application, as described above, a proton conductive nonporous membrane in which substantially all pores of the porous membrane are filled with P-polymer is used, or a proton conductive porous membrane is used. As described above, it is preferable to use a proton conductive non-porous film in which all voids remaining in the proton conductive membrane are closed by appropriate means such as heating and melting.
[0074]
According to the present invention, a proton conductive polymer composed of P-polymer is combined with a porous membrane to form a proton conductive membrane or film, preferably, the porous membrane is impregnated with M-monomer, Polymerization is performed in the pores of the porous membrane to form P-polymer, and the P-polymer is supported in the pores of the porous membrane to integrate the porous membrane and the P-polymer. Is realized.
[0075]
Therefore, according to the present invention, it is possible to obtain a proton conductive membrane or film that is excellent in various respects due to the composite of the base porous membrane and the proton conductive polymer. For example, by using a tough porous membrane made of ultrahigh molecular weight polyethylene or the like as a base material, in addition to high proton conductivity derived from P-polymer, proton conductivity having high mechanical strength and excellent handling properties A membrane or film can be obtained.
[0076]
In particular, according to the present invention, the P-monomer is supported in the pores of the porous membrane, polymerized, and the P-polymer is integrated with the substrate porous membrane to thereby integrate the P-polymer chain into the porous membrane. A polymer that can be highly entangled in a network, and further, if a polyfunctional monomer is copolymerized with a P-monomer, a cross-linked P-polymer and a polymer chain constituting a porous membrane are interpenetrated. A physical bond is generated by the network, and thus a proton conductive membrane or film having a further enhanced adhesion between the proton conductive polymer and the porous membrane can be obtained.
[0077]
【Example】
EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the following, the characteristics of the porous membrane used and the characteristics of the obtained proton conductive membrane or film were evaluated as follows.
[0078]
(Membrane or film thickness)
It was measured with a 1/10000 thickness gauge.
(Porosity of porous membrane)
Unit area S (cm of porous membrane) ² ) Weight W (g), average thickness t (μm) and density d (g / cm) ^Three ) From the following formula.
Porosity (%) = (1− (10 ^Four ・ W / (S ・ t ・ d)) × 100
[0079]
(Proton conductivity)
After leaving the proton conductive membrane or film for 4 hours in an environment adjusted to a temperature of 25 ° C. and a relative humidity of 50%, a 1 cm square sample of a predetermined thickness is sandwiched between platinum electrodes using a Hewlett Packard LCR meter HP4284A. The proton conductivity was calculated using the complex impedance method under conditions of a temperature of 25 ° C. and a relative humidity of 50%, and using the resistance value of the real part when extrapolated to zero resistance value of the imaginary part.
[0080]
(Volume filling rate of P-polymer into pores of substrate porous membrane)
Volume V (cm of substrate porous membrane) ^Three ), Porosity Φ (%) of the porous substrate membrane, weight M (g) of P-polymer and density d (g / cm of P-polymer) ^Three ) From the following formula.
Filling rate (%) = 10 ^Four ・ M / (V ・ Φ ・ d)
(Tensile strength)
A test piece punched into a dumbbell shape (JIS K 7113, based on No. 1 type test piece in the plastic tensile test method) was measured using a tensile tester (Autograph AGS-50D manufactured by Shimadzu Corporation).
[0081]
Example 1
(Manufacture of proton conducting membrane)
2-methacryloyloxyethyl phosphate / bis (methacryloyloxyethyl) diphosphate (65/35 mole ratio) P-monomer (Kyoeisha Chemical Co., Ltd. light ester P-1M) 50% by weight and butyl acrylate 50% by weight 0.5 parts by weight of benzyldimethyl ketal (Irgacure 651 manufactured by Ciba Geigy Co., Ltd.) was dissolved in 100 parts by weight of the monomer mixture.
[0082]
Without dilution, the weight average molecular weight is 1.0 × 10 ⁶ The porous membrane T1 (thickness 25 μm, porosity 40%, average pore diameter 0.10 μm) was coated on both surfaces of the porous membrane T1 to impregnate the pores of the porous membrane.
[0083]
The porous membrane thus treated is sandwiched between release films made of polyester resin, the porous membrane is cut off from the air, and then a light irradiation device equipped with a high-pressure mercury lamp (UB021-1B-13 manufactured by Igraphic Co., Ltd. ) With an energy of 1.5 J / cm ² Is irradiated with light to photopolymerize the monomer mixture in the pores to form a P-polymer, and this is supported in the pores of the porous membrane, and the proton conductive membrane has a thickness of 35 μm. F1 was obtained. In this proton conductive membrane, the pores of the porous membrane were completely filled with the P-polymer, and both surfaces of the porous membrane were covered with the P-polymer layer.
[0084]
The proton conductivity of the proton conductive membrane F1 is 2.1 × 10. ^-3 S / cm, and the tensile strength was 87 MPa.
[0085]
(Fuel cell)
0.6 mg / cm of platinum catalyst ² A membrane-electrode assembly (MEA) was manufactured by sandwiching the proton conductive membrane F1 between two pieces of carbon paper supported on the surface at a ratio of, and bonding using a hot press.
[0086]
The fuel cell characteristics of the MEA were evaluated using a fuel cell evaluation device manufactured by Toyo Corporation. The back pressure valve was not throttled, and the pressure was normal pressure. The humidifier temperature was 80 ° C. on the hydrogen side and 70 ° C. on the oxygen side, and the fuel cell temperature was 70 ° C. When a current-voltage (IV) curve was obtained by the Tafel method, the result was as shown in FIG. 1. As shown in FIG. An (IV) curve was obtained. That is, the proton conducting membrane according to the present invention has the same fuel cell characteristics as the Nafion 117 membrane.
[0087]
Example 2
0.5 parts by weight of 1-hydroxycyclohexyl phenyl ketone (Irgacure 184 manufactured by Ciba Geigy Co.) was dissolved in 100 parts by weight of P-monomer composed of 2-methacryloyloxyethyl phosphate and bis (methacryloyloxyethyl) diphosphate as in Example 1. I let you.
[0088]
A porous film T1 made of the same ultrahigh molecular weight polyethylene resin as in Example 1 was placed on a release film made of a polyester resin, and applied to the exposed surface of the porous film as it was without diluting the P-monomer. Excess monomer was removed from the surface of the porous membrane by squeezing with a bar, and the monomer was impregnated only in the pores of the porous membrane.
[0089]
The exposed surface of the porous membrane thus treated is covered with a release film made of a polyester resin so that the porous membrane is shielded from the air, and using the same light irradiation apparatus as in Example 1, the energy is 1.5 J / cm. ² The porous film is irradiated with light to photopolymerize the monomer in the pores to form a P-polymer, and the P-polymer is supported in the pores to conduct proton conduction with a thickness of 25 μm. The characteristic film F2 was obtained. In this proton conductive membrane, the pores of the porous membrane were completely filled with the polymer. The proton conductivity of the proton conductive membrane F2 is 8.5 × 10. ^-Four S / cm.
[0090]
Example 3
0.5 parts by weight of 1-hydroxycyclohexyl phenyl ketone (Irgacure 184 manufactured by Ciba Geigy Co.) was dissolved in 100 parts by weight of P-monomer composed of 2-methacryloyloxyethyl phosphate and bis (methacryloyloxyethyl) diphosphate as in Example 1. This was diluted with methanol to a monomer concentration of 30% by weight.
[0091]
Weight average molecular weight 2.4 × 10 ⁶ A porous membrane T2 (film thickness 40 μm, porosity 44%, average pore diameter 0.15 μm) made of an ultrahigh molecular weight polyethylene resin was placed on a polyester resin release film, and the porous membrane T2 A diluted solution of the monomer mixture was applied, and the excess monomer mixture was removed from the surface of the porous membrane by squeezing with a bar, and air-dried to impregnate the monomer mixture only in the pores of the porous membrane. .
[0092]
The exposed surface of the porous membrane thus treated is covered with a release film made of a polyester resin so that the porous membrane is shielded from the air, and using the same light irradiation apparatus as in Example 1, the energy is 1.5 J / cm. ² The porous film is irradiated with light to photopolymerize the monomer mixture in the pores to form a P-polymer, and the P-polymer is supported in the pores to form protons having a thickness of 40 μm. A conductive film F3 was obtained. In this proton conductive membrane, the pores of the porous membrane were partially filled with polymer. The proton conductivity of this proton conductive membrane F2 is 4.0 × 10 ^-Five S / cm.
[0093]
Comparative Example 1
In Example 1, a P-monomer 50 comprising 2-methacryloyloxyethyl phosphate and bis (methacryloyloxyethyl) diphosphate, the same as in Example 1, on a polyester resin release film without using a base porous membrane. A monomer mixture consisting of 50% by weight and 50% by weight of butyl acrylate was applied to a layer having a thickness of 35 μm.
[0094]
A polyester resin release film is also placed on this coating layer, the coating layer of the monomer mixture is shielded from air, and using the same light irradiation apparatus as in Example 1, an energy of 1.5 J / cm. ² Was irradiated with light to produce a P-polymer from the monomer mixture, and a proton conductive membrane R1 having a thickness of 35 μm made of only this P-polymer was obtained. The proton conductivity of this proton conducting membrane is 2.3 × 10 ^-3 S / cm, and the tensile strength was 8 MPa.
[0095]
Comparative Example 2
Polyester PS-5 manufactured by Tosoh Corporation was ion-exchanged using a strongly acidic cation exchange resin to convert the sodium salt into a free acid, which was concentrated and then dissolved in methanol to give 20% polystyrene sulfonic acid. A methanol solution was prepared.
[0096]
A porous membrane T2 made of the same ultrahigh molecular weight polyethylene resin as in Example 3 was placed on a release film made of polyester resin, a methanol solution of polystyrene sulfonic acid was applied to the exposed surface and dried, and proton conduction with a thickness of 58 μm was applied. The characteristic film R2 was obtained.
[0097]
In this proton conductive membrane, the pores of the porous membrane are completely filled with the polystyrene sulfonic acid, and the surface of the porous membrane on the side where the polystyrene sulfonic acid is applied is also a layer of polystyrene sulfonic acid. It was covered with. The proton conductivity of this proton conductive membrane R2 is 2.0 × 10 ^-Five S / cm.
[0098]
When this proton conductive membrane was immersed in water for 24 hours, part of the polystyrene sulfonic acid was eluted in the water. As a result, after being immersed in this water, the temperature was adjusted to 25 ° C. and the relative humidity was 50%, and the proton conductivity was adjusted. Measured 3.7 × 10 ^-6 S / cm.
[0099]
【The invention's effect】
As described above, the proton conductive membrane according to the present invention is formed by supporting a P-polymer having a phosphoric acid group, a phosphonic acid group or a phosphinic acid group in the side chain in the pores of the porous membrane, Not only has high proton conductivity, but also high strength, and the polymer is water insoluble. In particular, according to the present invention, a P-monomer having a phosphoric acid group, a phosphonic acid group or a phosphinic acid group is polymerized in the pores of the porous membrane, and the phosphoric acid group, the phosphonic acid group or the phosphinic acid group is used as a side chain. According to the proton conductive membrane in which the P-polymer is produced and the P-polymer is supported in the pores of the porous membrane, the P-polymer and the porous membrane are integrated. Has a high degree of adhesion to the porous membrane. Moreover, the proton conductive membrane according to the present invention can be obtained at a much lower cost than a proton conductive membrane made of a conventional sulfonic acid group-containing fluororesin membrane.
[0100]
Thus, the proton conductive membrane according to the present invention can be suitably used as an ion exchange membrane in a fuel cell, and since it is inexpensive, the cost of the fuel cell system can be greatly reduced, and its practical use can be realized. You can speed up.
[Brief description of the drawings]
FIG. 1 is a current-voltage (IV) curve by Tafel method showing fuel cell characteristics of a membrane-electrode assembly (MEA) prepared using a proton conducting membrane according to the present invention.

Claims (14)

Formula (I)

(In the formula, R represents a hydrogen atom or a methyl group, and X represents a divalent organic group in which both ends of the group are carbon atoms.)
A monomer having a phosphoric acid group represented by the formula is polymerized in the pores of the porous membrane to form a polymer having a phosphate group in the side chain, and this polymer is supported in the pores of the porous membrane. Proton-conducting membrane characterized by being made.   The proton conductive membrane according to claim 1, wherein the porous membrane is made of an ultrahigh molecular weight polyolefin resin or a fluororesin.   The proton conductive membrane according to claim 1, wherein the polymer has a crosslinked structure. Proton conducting film comprising closed at least part of the voids of the remaining pores of the proton conducting membrane according to any one of claims 1 to 3. Formula (I)

(In the formula, R represents a hydrogen atom or a methyl group, and X represents a divalent organic group in which both ends of the group are carbon atoms.)
The porous membrane is impregnated with a monomer having a phosphoric acid group represented by the following formula , and polymerized in the pores of the porous membrane to form a polymer having a phosphoric acid group in the side chain. A method for producing a proton conductive membrane, wherein the proton conductive membrane is supported in pores of a porous membrane. 6. The method according to claim 5 , wherein the polymer is crosslinked with a monomer having a phosphate group and a polyfunctional monomer having a phosphate group and / or a polyfunctional monomer having no phosphate group. A method for producing a proton conductive film. 6. The method for producing a proton conductive film according to claim 5 , wherein the porous membrane is made of an ultrahigh molecular weight polyolefin resin or a fluororesin. A polyfunctional monomer having a phosphate group is represented by the general formula (IV)

(Wherein, R represents a hydrogen atom or a methyl group, X is both ends of the group indicates a divalent organic group is a carbon atom, m is 2 or 3.)
The method for producing a proton conductive film according to claim 6, wherein the phosphoric acid diester is represented by the formula: Formula (I)

(In the formula, R represents a hydrogen atom or a methyl group, and X represents a divalent organic group in which both ends of the group are carbon atoms.)
The porous membrane is impregnated with a monomer having a phosphoric acid group represented by the following formula , and polymerized in the pores of the porous membrane to form a polymer having a phosphoric acid group in the side chain. Proton-conductive film produced by supporting in a pore of a porous membrane to obtain a proton-conductive membrane, and then closing at least a part of the remaining voids of the pores of the proton-conductive membrane Method. The method according to claim 9 , wherein the polymer is crosslinked with a monomer having a phosphate group and a polyfunctional monomer having a phosphate group and / or a polyfunctional monomer having no phosphate group. A method for producing a proton conductive film. A polyfunctional monomer having a phosphate group is represented by the general formula (IV)

(Wherein, R represents a hydrogen atom or a methyl group, X is both ends of the group indicates a divalent organic group is a carbon atom, m is 2 or 3.)
The method for producing a proton conductive film according to claim 10, wherein the phosphoric acid diester is represented by the formula: The method for producing a proton conductive film according to claim 9 , wherein the porous membrane is made of an ultrahigh molecular weight polyolefin resin or a fluororesin. A fuel cell using the proton conductive membrane according to any one of claims 1 to 3 as a proton exchange membrane. A fuel cell using the proton conductive film according to claim 4 as a proton exchange membrane.

Images