JP3573444B2 - Carbonaceous separator member for polymer electrolyte fuel cell and method of manufacturing the same - Google Patents
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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Description
【０００１】
【発明の属する技術分野】
本発明は、固体高分子型（ＳＰＥ型）燃料電池用の炭素質セパレータ部材及びその製造方法に関する。
【０００２】
【従来の技術】
固体高分子型燃料電池はパーフルオロカーボンスルフォン酸等のイオン交換膜からなる固体高分子の電解質膜と、その両側に設けた２つの電極とそれぞれの電極に水素等の燃料ガスあるいは酸素等の酸化剤ガスを供給するガス供給溝を設けたセパレータ、及びその外側に設けた２つの集電体等から構成されている。
【０００３】
このセパレータには、例えば燃料ガスと酸化剤ガスとを完全に分離した状態で電極に供給するために高度のガス不透過性が要求され、また発電効率を高くするために電池の内部抵抗を小さくすることが必要である。更に、電池反応に伴う発熱を効率よく放散させるために高い熱伝導性や耐蝕性に優れている等の材質特性が必要とされている。
【０００４】
このような材質特性が要求されるセパレータとして、例えば特開平４−２６７０６２号公報にはセパレータの材質を純銅やステンレス鋼などで構成する例が開示されている。しかしながら、これらの金属系の材質では燃料ガスとして用いる水素ガスと長時間に亘って接触するために、水素脆性による材質劣化が生じ、電池性能が低下する欠点がある。
【０００５】
また、リン酸型燃料電池ではセパレータに炭素質系の材料、特にガス不透過性に優れているガラス状カーボン材が使用されている。ガラス状カーボン材はフェノール系樹脂やフラン系樹脂などの熱硬化性樹脂液を成形し加熱硬化後、非酸化性雰囲気中８００℃以上の温度で焼成炭化して得られるガラス質の性状を呈する特異な炭素材である。
【０００６】
しかしながら、ガラス状カーボン材は緻密な組織構造を有し、高いガス不透過性を示す反面、硬度が高く脆性であるので加工性が悪いという欠点がある。更に金属系の材質に比べて熱伝導率が低く電気比抵抗も大きいという難点があり、リン酸型燃料電池に比較して高電流密度で運転される固体高分子型燃料電池のセパレータとして使用するには適当でない。
【０００７】
これに対して黒鉛材は、ガラス状カーボン材に比べて熱伝導率が高く、電気比抵抗も低いという特徴があるが、組織中に微細な気孔空隙が多数存在するためにガス不透過性が低く、黒鉛材をそのまま固体高分子型燃料電池のセパレータとして使用することはできない。また、この気孔空隙に熱硬化性樹脂液を含浸し、加熱硬化して気孔空隙を閉塞することによりガス不透過性にする試みは従来から種々の方法が提案されている。
【０００８】
例えば、含浸する樹脂を特定するものとして特開昭５２−１２５４８８号公報には炭素材料にフリーデルクラフツ樹脂を含浸硬化する不浸透性炭素製品の製造方法が、特開昭５９−５７９７５号公報には炭素基材にフェノール樹脂とピッチとの相溶物を含浸し、該含浸物を炭化あるいは黒鉛化処理する不浸透性炭素材料の製造法が、また特公平６−３１１８４号公報にはカーボン材にクレゾール樹脂を４０〜９５重量％の割合で含有するクレゾール樹脂とフェノール樹脂の混合樹脂液を含浸硬化する不浸透性カーボン材の製造方法等が提案されている。
【０００９】
また、含浸硬化条件を特定するものとして特公平５−６７５９５号公報には炭素質素材を含浸槽に入れ、減圧下で液状の熱硬化性樹脂に浸漬し、ついで系内を加圧状態に切り換えて液状樹脂が初期硬化するまで３０℃以上の温度で加熱処理する不浸透性炭素材の製造方法が提案されている。
【００１０】
しかしながら、これらの方法で得られる不浸透性炭素材を固体高分子型燃料電池のセパレータとして用いるには、ガス不透過性、熱伝導性、導電性等の特性をバランスよく付与する点で充分なものではなく、特に黒鉛材には物理的性状、例えば電気抵抗等の特性に異方性が生じ易い難点がある。
【００１１】
そこで本出願人はガス不透過性、熱伝導性、導電性、耐蝕性等に優れ、これらの性能をバランスよく備え、固体高分子型燃料電池のセパレータ等として好適な黒鉛部材の製法として、最大粒径１２５μｍ 以下の炭素質粉末に結合材を加えて加熱混練後ＣＩＰ成形し、次いで焼成、黒鉛化して得られた平均気孔径１０μｍ 以下、気孔率２０％以下の等方性黒鉛材に熱硬化性樹脂液を含浸、硬化処理する固体高分子型燃料電池用黒鉛部材の製造方法（特開平８−２２２２４１号公報）を開発提案した。
【００１２】
【発明が解決しようとする課題】
本発明者らは、上記特開平８−２２２２４１号公報の技術を基に更に研究を進めた結果、導電性に優れた天然黒鉛を人造黒鉛と併用し、それらの粒子性状や混合比等を特定して、結合材である熱硬化性樹脂と混練、一体化することにより特性の方向性が少なく、特に電気比抵抗の異方性が小さく、また成形性が良好で、ガス不透過性も高く、固体高分子型燃料電池用のセパレータ部材として好適な炭素質材となし得ることを見出した。
【００１３】
本発明は上記の知見に基づいて開発されたものであり、その目的は材質性状の等方性が高く、特に電気比抵抗の異方性を低減化し、ガス不透過性に優れた固体高分子型燃料電池用の炭素質セパレータ部材及びその製造方法を提供することにある。
【００１４】
【課題を解決するための手段】
上記目的を達成するための本発明による固体高分子型燃料電池用炭素質セパレータ部材は、人造黒鉛粉と天然黒鉛粉とが重量比で８０：２０〜６０：４０の割合で混合された黒鉛粉末１００重量部と熱硬化性樹脂１０〜２５重量部とからなり、人造黒鉛粉の平均粒子径Ａが５０μｍ 以下、天然黒鉛粉の平均粒子径ＢがＡ×（１／５〜１／１０）であり、面方向の電気比抵抗が０．０２Ωｃｍ以下、電気比抵抗の異方比（厚さ方向／面方向）が２以下、ガス透過率が１０−６ｃｃ／ｃｍ２・ｍｉｎ 以下の特性を有する板状成形体から形成したことを構成上の特徴とする。
【００１５】
また、その製造方法は、平均粒子径Ａが５０μｍ 以下の人造黒鉛粉と平均粒子径ＢがＡ×（１／５〜１／１０）の天然黒鉛粉とを、重量比で８０：２０〜６０：４０の割合で混合し、混合した黒鉛粉末１００重量部に熱硬化性樹脂を１０〜２５重量部の重量比で配合、混練したのち、解砕し、篩い分けして粒径２ｍｍ以下の解砕粒を１５０〜２８０℃の温度で熱圧モールド法により板状体に成形、加熱硬化することを構成上の特徴とする。
【００１６】
更に、他の製造方法は、平均粒子径Ａが５０μｍ 以下の人造黒鉛粉と平均粒子径ＢがＡ×（１／５〜１／１０）の天然黒鉛粉とを、重量比で８０：２０〜６０：４０の割合で混合し、混合した黒鉛粉末１００重量部に熱硬化性樹脂を１０〜２５重量部の重量比で配合、混練したのち、解砕し、篩い分けして粒径２ｍｍ以下の解砕粒を熱圧モールド法により板状体に成形し、更に１５０〜２８０℃の温度で樹脂成分を加熱硬化することを構成上の特徴とする。
【００１７】
【発明の実施の形態】
本発明の固体高分子型燃料電池用の炭素質セパレータ部材は、黒鉛粉末を熱硬化性樹脂を結合材として一体化した樹脂結合炭素質材から形成され、黒鉛粉末は人造黒鉛粉と天然黒鉛粉とを混合した混合粉末であり、人造黒鉛粉と天然黒鉛粉との混合割合は、重量比で８０：２０〜６０：４０の範囲に設定される。天然黒鉛は人造黒鉛に比べて黒鉛結晶の発達度が高く、導電性や熱伝導性に優れているが、鱗状を呈して特性の方向性が著しく大きいという特徴がある。例えば導電性は面方向（Ｘ−Ｙ方向）では大きく、厚さ方向（Ｚ方向）では小さく、異方性が高くなる。したがって、天然黒鉛粉のみを熱硬化性樹脂により結合し、一体化しても導電性等の異方性が著しく大きくセパレータ部材として使用することは困難である。
【００１８】
そこで、本発明は人造黒鉛粉と併用し、人造黒鉛粉と天然黒鉛粉とを重量比で８０：２０〜６０：４０の割合で混合し、かつ人造黒鉛粉の平均粒子径Ａが５０μｍ 以下で、天然黒鉛粉の平均粒子径ＢがＡ×（１／５〜１／１０）に規制した点に特徴がある。人造黒鉛粉と天然黒鉛粉との混合粉末を熱硬化性樹脂と混練すると、天然黒鉛粉は人造黒鉛粉に比べて樹脂との濡れ性が低いので、主に人造黒鉛粉の粒子同志が接合してその粒子間に空隙が形成され、天然黒鉛粉はこの空隙部に補足され固定化される。すなわち、本発明は人造黒鉛粉が相互に接合形成した空隙部に天然黒鉛粉を補足し、固定するために両者を重量比で８０：２０〜６０：４０の割合で混合し、かつ人造黒鉛粉の平均粒子径Ａが５０μｍ 以下で、天然黒鉛粉の平均粒子径ＢがＡ×（１／５〜１／１０）に設定するのである。
【００１９】
人造黒鉛粉の混合割合が重量比で８０を越えると、天然黒鉛の優れた導電性の効果が小さく、一方６０を下回ると天然黒鉛粉を補足し、充分に固定化することができなくなるためである。人造黒鉛粉の平均粒子径Ａを５０μｍ 以下に設定するのは、炭素質セパレータ部材に加工する際に粒子径が大きいと人造黒鉛粉の脱落等により空孔が形成されガス不透過性が低下したり、電池内を汚染し、電池性能の低下が起こるためである。また、人造黒鉛粉相互の接合により形成された空隙部に天然黒鉛粉を補足し、ランダム方向に固定化するために天然黒鉛粉の平均粒子径Ｂは人造黒鉛粉の平均粒子径Ａの（１／５〜１／１０）の範囲に設定される。その結果、天然黒鉛粉の優れた導電性のメリットを生かしつつ異方性のデメリットを排除することが可能となる。
【００２０】
本発明の炭素質セパレータ部材は、この黒鉛粉末と熱硬化性樹脂とを炭素質粉末１００重量部、熱硬化性樹脂１０〜２５重量部との割合で構成される。バインダーとなる熱硬化性樹脂が１０重量部未満では成形性が悪くなりガス不透過性が低下する。一方、熱硬化性樹脂が２５重量部を越えると導電性が低下してセパレータ部材として十分な性能を保持出来なくなるためである。
【００２１】
なお、熱硬化性樹脂は黒鉛粉末の結合材として機能するもので、固体高分子型燃料電池の発電稼働時の温度である８０〜１２０℃に耐える耐熱性、及びｐＨ２〜３程度のスルフォン酸や硫酸酸性に耐え得る耐酸性があれば特に制限はなく、例えばフェノール樹脂、フラン樹脂、エポキシ樹脂等の樹脂が用いられる。
【００２２】
更に、本発明の固体高分子型燃料電池用炭素質セパレータ部材は、上記の組織構造において面方向（すなわちＸ−Ｙ方向）の電気比抵抗が０．０２Ωｃｍ以下であり、厚さ方向（すなわちＺ方向）／面方向の電気比抵抗の比が２以下であることが必要である。黒鉛粉末を熱硬化性樹脂を結合材として一体化した樹脂結合炭素質材は、加圧成形時に加圧方向と、それに直角方向との間に材質性状に方向性が生じ易く、面方向と厚さ方向の電気比抵抗の値が大きく異なるために電気比抵抗が増大する難点がある。
【００２３】
すなわち、面方向と厚さ方向とで電気比抵抗に異方性があると、内部における電流の流れが不均一となり電池の内部抵抗の増大を招き、発電効率が低下する。そのため、本発明は面方向の電気比抵抗を０．０２Ωｃｍ以下、厚さ方向／面方向の電気比抵抗の比を２以下に設定するものである。なお、このような電気的特性は、上述した人造黒鉛粉と天然黒鉛粉との混合比、及び人造黒鉛粉の平均粒子径Ａならびに天然黒鉛粉の平均粒子径Ｂ等を特定範囲に設定することにより付与することが可能となる。
【００２４】
この炭素質セパレータ部材は、熱硬化性樹脂量を１０〜２５重量部に設定するとともに、自己成形性を有する天然黒鉛粉を用いることによって不通気性の組織構造が形成され、ガス透過率が１０−６ｃｃ／ｃｍ２・ｍｉｎ 以下のガス不透過性を備えることができる。
【００２５】
本発明の固体高分子型燃料電池用炭素質セパレータ部材は、上記の組織構造を備え、電気的特性の等方性に優れ、またガス不透過性にも優れた炭素質の板状成形体から形成したものであるから、これら特性がバランスよく機能して、固体高分子型燃料電池用のセパレータ部材として優れた性能を発揮することが可能となる。
【００２６】
本発明の固体高分子型燃料電池用炭素質セパレータ部材の製造方法は、先ず適宜な手段で粉砕、篩い分けして、平均粒子径Ａが５０μｍ 以下の人造黒鉛粉と、平均粒子径ＢがＡ×（１／５〜１／１０）の天然黒鉛粉とを、作成し、人造黒鉛粉と天然黒鉛粉とを重量比で８０：２０〜６０：４０の割合で均一に混合して、黒鉛粉末を調製する。
【００２７】
次いで、混合した黒鉛粉末１００重量部に熱硬化性樹脂を１０〜２５重量部の重量比で配合し、混練する。なお、熱硬化性樹脂は不揮発分が６０％以上のものを用いることが好ましく、また熱硬化性樹脂液（初期縮合物）あるいは熱硬化性樹脂液をアルコールなどの揮発性の有機溶媒に溶解した溶液として黒鉛粉末に配合し、充分に混練する。
【００２８】
得られた混練物は、必要に応じて乾燥して揮発性成分や用いた有機溶媒等を揮散除去したのち、粉砕機により解砕し、篩い分けして、粒径２ｍｍ以下の解砕粒を調製する。解砕処理は、非導電性の樹脂被膜で覆われた黒鉛粉末の集合体である混練物を解砕して黒鉛面を露出させて導電性を向上させ、更に、混練時における黒鉛粉末の方向性、すなわち電気比抵抗等の材質性状の異方性を是正するために行うものである。したがって、解砕粒の粒度が大きいとこれらの効果が充分に果たされなくなるので、粒径２ｍｍ以下の解砕粒が用いられる。
【００２９】
炭素質セパレータを成形する方法は、樹脂成分が耐食性に優れる特性となるように、適宜な温度及び圧力で熱圧成形時に十分な熱硬化を行う方法、あるいは熱圧成形し成形体を得たのち適宜な温度にて十分な熱硬化を行う方法を用いることができる。
【００３０】
前者の場合、解砕粒を所望形状の成形型に充填し、バインダー樹脂として用いる熱硬化性樹脂の種類により熱圧成形時の温度及び圧力を温度４０〜２８０℃、圧力１００〜５００ｋｇ／ｃｍ２の熱圧モールド法により適宜調整する。例えばフェノール樹脂を使用する場合には、温度１５０〜２８０℃、圧力１００〜５００ｋｇ／ｃｍ２の熱圧モールド法により所望形状に成形、熱硬化することにより、炭素質セパレータ部材である板状成形体が製造される。また、得られた成形体をさらに１５０〜２８０℃の温度に保持して熱硬化反応を進行させると耐食性が向上する。
【００３１】
後者の場合、解砕粒を所望形状の成形型に充填し、バインダー樹脂として用いる熱硬化性樹脂の種類により熱圧成形時の温度及び圧力を適宜調整するが、温度４０〜２８０℃、圧力１００〜５００ｋｇ／ｃｍ２の熱圧モールド法により所望形状に成形し、さらに得られた成形体を１００〜２８０℃の温度に保持して成形体の熱硬化反応を進行させると耐食性が向上した炭素質セパレータ部材である板状成形体が製造される。
【００３２】
なお、炭素質セパレータ部材の平面形状、溝形状は熱圧成形により形成することもできるが、機械加工により形成する場合には加工した後に１００〜２８０℃の温度に保持すると加工歪みを除去でき寸法精度が良好となる。
【００３３】
【実施例】
以下、本発明の実施例を比較例と対比して説明する。
【００３４】
実施例１〜４、比較例１〜８
平均粒子径Ａが３０μｍ の人造黒鉛粉と、平均粒子径Ｂが５μｍ 及び３０μｍ の天然黒鉛粉とを用いて異なる重量比で人造黒鉛粉と天然黒鉛粉とを均一に混合して、黒鉛粉末を作成した。熱硬化性樹脂には不揮発分７０％のフェノール樹脂を用い、メタノールに溶解して樹脂濃度を７５重量％に調整した。これらの黒鉛粉末及びフェノール樹脂溶液を異なる量比で配合し、室温で充分に混練したのち真空乾燥して、メタノールをはじめ揮発性成分を揮散除去した。次いで、解砕し篩い分けして、粒径の異なる解砕粒を調製した。この解砕粒を成形粉として、成形型に充填して温度１８０℃、圧力２４０Ｋｇ／ｃｍ２の熱圧条件で１０分間処理し、縦横２１０ｍｍ、厚さ４ｍｍの片溝付き平板を各条件で２０枚づつ製造した。このようにして製造した製造条件を対比して、表１に示した。
【００３５】
【表１】
これらの平板の各種特性を下記の方法により測定して、その結果を表２に示した。
▲１▼電気比抵抗（Ωｃｍ）；ＪＩＳ Ｒ７２０２「人造黒鉛電極の試験方法」の電圧降下法による。
▲２▼嵩密度（ｇ／ｃｍ３）；アルキメデス法による。
▲３▼曲げ強度（ Ｋｇｆ／ｃｍ２ ）；ＪＩＳ Ｋ６９１１により測定。
▲４▼ガス不透過性；窒素ガスにより１Ｋｇ／ｃｍ２の圧力をかけた際のガス透過量を測定して、透過率が１０−６（ｃｃ／ｃｍ２ ｍｉｎ）以下のものを合格とした。
【００３７】
【表２】
表１、２の結果から、本発明の製造方法により製造され、本発明の特性要件を充足する実施例の炭素質平板は、比較例に比べて面方向（Ｘ−Ｙ方向）の電気比抵抗が小さく、また厚さ方向（Ｚ方向）の電気比抵抗との異方性も小さいことが認められる。更に、ガス不透過性にも優れており、固体高分子型燃料電池用炭素質セパレータ部材として優れた性能を備えていることが判る。これに対し、天然黒鉛粉を併用しない比較例１〜３では電気比抵抗の異方性は小さいが、ガス不透過性に劣り、特に熱硬化性樹脂の配合量が少ない場合には一層著しくなる。一方天然黒鉛粉のみを用いた比較例４、７では電気比抵抗の異方性が顕著で、また天然黒鉛粉の平均粒子径Ｂが人造黒鉛粉の平均粒子径Ａと、Ｂ＝Ａ×（１／５〜１／１０）の関係を満たさない比較例５、６では電気比抵抗の異方性が高くなることが判明する。
【００３９】
【発明の効果】
以上のとおり、本発明の固体高分子型燃料電池用炭素質セパレータ部材によれば、電気比抵抗及びその異方比が小さいので電池の内部抵抗の増大化による発電効率の低下を抑制することができ、またガス不透過性も高く、優れた電池性能を備えたセパレータ部材の提供が可能となる。また、本発明の製造方法によれば、人造黒鉛粉と天然黒鉛粉とを併用し、その平均粒子径及び混合比、熱硬化性樹脂の配合量等を特定範囲に設定することにより、優れた性能を備えた本発明の固体高分子型燃料電池用炭素質セパレータ部材の製造が可能となる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a carbonaceous separator member for a polymer electrolyte fuel cell (SPE type) fuel cell and a method for producing the same.
[0002]
[Prior art]
A polymer electrolyte fuel cell is a solid polymer electrolyte membrane composed of an ion exchange membrane such as perfluorocarbon sulfonic acid, two electrodes provided on both sides thereof, and a fuel gas such as hydrogen or an oxidant such as oxygen applied to each electrode. It comprises a separator provided with a gas supply groove for supplying gas, and two current collectors provided outside the separator.
[0003]
The separator is required to have a high degree of gas impermeability, for example, to supply the fuel gas and the oxidizing gas to the electrode in a completely separated state, and to reduce the internal resistance of the battery in order to increase the power generation efficiency. It is necessary to. Furthermore, in order to efficiently dissipate the heat generated by the battery reaction, there is a need for material properties such as high thermal conductivity and excellent corrosion resistance.
[0004]
As a separator requiring such material properties, for example, Japanese Patent Application Laid-Open No. 4-267062 discloses an example in which the separator is made of pure copper, stainless steel, or the like. However, since these metal materials are in contact with hydrogen gas used as a fuel gas for a long period of time, there is a disadvantage that material deterioration due to hydrogen embrittlement occurs and battery performance is reduced.
[0005]
In the phosphoric acid fuel cell, a carbonaceous material, particularly a glassy carbon material having excellent gas impermeability, is used for the separator. The glassy carbon material exhibits a glassy property obtained by molding a thermosetting resin liquid such as a phenolic resin or a furan resin, heating and curing, and then calcining and carbonizing at a temperature of 800 ° C or more in a non-oxidizing atmosphere. Carbon material.
[0006]
However, the glassy carbon material has a dense texture structure and shows high gas impermeability, but has a drawback of poor workability due to high hardness and brittleness. Furthermore, it has the disadvantage that the thermal conductivity is low and the electric resistivity is large as compared with metal-based materials, and it is used as a separator of a polymer electrolyte fuel cell operated at a higher current density than a phosphoric acid fuel cell. Not suitable for
[0007]
Graphite materials, on the other hand, are characterized by higher thermal conductivity and lower electrical resistivity than glassy carbon materials, but have a high gas impermeability due to the presence of many fine pores in the structure. It is too low to use graphite material as it is as a separator for polymer electrolyte fuel cells. In addition, various methods have been proposed for impregnating the pores with a thermosetting resin liquid, heating and hardening the pores to close the pores, thereby making the pores impermeable.
[0008]
For example, Japanese Unexamined Patent Publication (Kokai) No. 52-125488 discloses a method for producing an impervious carbon product by impregnating and curing a Friedel Crafts resin in a carbon material. Discloses a method for producing an impervious carbon material by impregnating a carbon base material with a phenol resin-pitch compatible material and carbonizing or graphitizing the impregnated material. Japanese Patent Publication No. 6-31184 discloses a carbon material. A method for producing an impervious carbon material which impregnates and cures a mixed resin solution of a cresol resin and a phenol resin containing a cresol resin at a ratio of 40 to 95% by weight has been proposed.
[0009]
Japanese Patent Publication No. Hei 5-67595 discloses a method of specifying impregnation hardening conditions in which a carbonaceous material is placed in an impregnation tank, immersed in a liquid thermosetting resin under reduced pressure, and then the system is switched to a pressurized state. There has been proposed a method for producing an impermeable carbon material in which a heat treatment is performed at a temperature of 30 ° C. or more until the liquid resin is initially cured.
[0010]
However, in order to use the impervious carbon material obtained by these methods as a separator of a polymer electrolyte fuel cell, it is sufficient to impart well-balanced properties such as gas impermeability, thermal conductivity, and conductivity. In particular, graphite materials have a drawback that physical properties such as electrical resistance tend to be anisotropic.
[0011]
Therefore, the present applicant has excellent gas impermeability, thermal conductivity, electrical conductivity, corrosion resistance, etc., and has these performances in a well-balanced manner. A binder is added to a carbonaceous powder having a particle size of 125 μm or less, and the mixture is heated and kneaded, then CIP-molded, and then calcined and graphitized, and is thermoset to an isotropic graphite material having an average pore diameter of 10 μm or less and a porosity of 20% or less. A method for producing a graphite member for a polymer electrolyte fuel cell, which is impregnated with a conductive resin liquid and cured, has been developed and proposed (JP-A-8-222241).
[0012]
[Problems to be solved by the invention]
The present inventors have further researched based on the technology of JP-A-8-222241, and as a result, used natural graphite having excellent conductivity in combination with artificial graphite, and specified the particle properties and mixing ratio thereof. By kneading and integrating with the thermosetting resin as the binder, the directionality of the characteristics is small, especially the anisotropy of the electric resistivity is small, and the moldability is good and the gas impermeability is high. It has been found that a carbonaceous material suitable as a separator member for a polymer electrolyte fuel cell can be obtained.
[0013]
The present invention has been developed based on the above findings, and its object is a solid polymer having high isotropy of material properties, particularly reducing anisotropy of electric resistivity, and having excellent gas impermeability. It is an object of the present invention to provide a carbonaceous separator member for a fuel cell and a method for manufacturing the same.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, a carbonaceous separator member for a polymer electrolyte fuel cell according to the present invention is a graphite powder in which artificial graphite powder and natural graphite powder are mixed at a weight ratio of 80:20 to 60:40. 100 parts by weight and 10 to 25 parts by weight of the thermosetting resin, the average particle size A of the artificial graphite powder is 50 μm or less, and the average particle size B of the natural graphite powder is A × (1/5 to 1/10). Yes, the electrical resistivity in the surface direction is 0.02 Ωcm or less, the anisotropic ratio of electrical resistivity (thickness direction / surface direction) is 2 or less, and the gas permeability is 10 −6 cc / cm 2 · min or less. It is characterized by being formed from a plate-shaped molded body having the same.
[0015]
In addition, the production method is a method in which artificial graphite powder having an average particle diameter A of 50 μm or less and natural graphite powder having an average particle diameter B of A × (１ ／ to 1/10) are used in a weight ratio of 80:20 to 60. : 100 parts by weight of the mixed graphite powder was mixed with a thermosetting resin in a weight ratio of 10 to 25 parts by weight, kneaded, crushed, and sieved to obtain a powder having a particle size of 2 mm or less. The constitution is characterized in that the crushed granules are formed into a plate-like body by a hot-press molding method at a temperature of 150 to 280 ° C. and are cured by heating.
[0016]
Further, another production method is to mix artificial graphite powder having an average particle diameter A of 50 μm or less and natural graphite powder having an average particle diameter B of A × (１ ／ to 1/10) in a weight ratio of 80:20 to The mixture was mixed at a ratio of 60:40, and 100 parts by weight of the mixed graphite powder was blended with a thermosetting resin at a weight ratio of 10 to 25 parts by weight, kneaded, crushed, and sieved to obtain a particle size of 2 mm or less. The crushed granules are formed into a plate by a hot-press molding method, and the resin component is further heated and cured at a temperature of 150 to 280 ° C.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The carbonaceous separator member for a polymer electrolyte fuel cell of the present invention is formed from a resin-bonded carbonaceous material obtained by integrating graphite powder with a thermosetting resin as a binder, and the graphite powder is made of artificial graphite powder and natural graphite powder. And the mixing ratio of artificial graphite powder and natural graphite powder is set in the range of 80:20 to 60:40 by weight. Natural graphite has a higher degree of development of graphite crystals and is superior in electrical conductivity and thermal conductivity as compared with artificial graphite, but has the characteristic that it exhibits a scale-like shape and the directionality of its characteristics is extremely large. For example, the conductivity is large in the plane direction (XY direction), small in the thickness direction (Z direction), and high in anisotropy. Therefore, even if only natural graphite powder is bonded with a thermosetting resin and integrated, it is difficult to use as a separator member because the anisotropy such as conductivity is extremely large.
[0018]
Thus, the present invention uses artificial graphite powder in combination with artificial graphite powder and natural graphite powder in a weight ratio of 80:20 to 60:40, and the artificial graphite powder has an average particle size A of 50 μm or less. It is characterized in that the average particle size B of the natural graphite powder is restricted to A × (1/5 to 1/10). When a mixture of artificial graphite powder and natural graphite powder is kneaded with a thermosetting resin, natural graphite powder has a lower wettability with resin than artificial graphite powder. Thus, voids are formed between the particles, and the natural graphite powder is captured and fixed in the voids. That is, in the present invention, the artificial graphite powder is mixed with the artificial graphite powder at a weight ratio of 80:20 to 60:40 in order to supplement and fix the natural graphite powder in the voids formed by joining the artificial graphite powder. Is 50 μm or less, and the average particle size B of the natural graphite powder is set to A × (1/5 to 1/10).
[0019]
When the mixing ratio of the artificial graphite powder exceeds 80 by weight, the excellent conductivity effect of natural graphite is small. On the other hand, when the mixing ratio is less than 60, the natural graphite powder is supplemented and cannot be sufficiently fixed. is there. The reason for setting the average particle size A of the artificial graphite powder to 50 μm or less is that if the particle size is large during processing into a carbonaceous separator member, pores are formed due to falling off of the artificial graphite powder and the gas impermeability is reduced. Or the inside of the battery is contaminated, and the battery performance is deteriorated. In addition, in order to supplement natural graphite powder into voids formed by joining artificial graphite powder with each other and to fix the natural graphite powder in a random direction, the average particle size B of the natural graphite powder is (1) of the average particle size A of the artificial graphite powder. / 5/10). As a result, it is possible to eliminate the disadvantage of anisotropy while taking advantage of the excellent conductivity of natural graphite powder.
[0020]
The carbonaceous separator member of the present invention comprises the graphite powder and the thermosetting resin in a ratio of 100 parts by weight of the carbonaceous powder and 10 to 25 parts by weight of the thermosetting resin. If the amount of the thermosetting resin serving as a binder is less than 10 parts by weight, the moldability is deteriorated and the gas impermeability is reduced. On the other hand, if the amount of the thermosetting resin exceeds 25 parts by weight, the conductivity is lowered, and it becomes impossible to maintain sufficient performance as a separator member.
[0021]
The thermosetting resin functions as a binder for the graphite powder, and has heat resistance to withstand a temperature of 80 to 120 ° C., which is the temperature at the time of power generation operation of the polymer electrolyte fuel cell, and sulfonic acid having a pH of about 2 to 3 There is no particular limitation as long as it has acid resistance that can withstand sulfuric acid, and for example, a resin such as a phenol resin, a furan resin, and an epoxy resin is used.
[0022]
Further, the carbonaceous separator member for a polymer electrolyte fuel cell of the present invention has an electrical resistivity of 0.02 Ωcm or less in a plane direction (that is, XY direction) and a thickness direction (that is, Z It is necessary that the ratio of electrical resistivity in the direction) / plane direction is 2 or less. A resin-bonded carbonaceous material obtained by integrating graphite powder with a thermosetting resin as a binder is likely to have directionality in the material properties between the pressing direction and the direction perpendicular to the pressing direction during pressing, and has a thickness in the plane direction. However, there is a problem that the electrical resistivity increases because the electrical resistivity in the vertical direction greatly differs.
[0023]
That is, if the electrical resistivity has anisotropy in the plane direction and the thickness direction, the current flow in the inside becomes uneven and the internal resistance of the battery increases, and the power generation efficiency decreases. Therefore, in the present invention, the electrical resistivity in the surface direction is set to 0.02 Ωcm or less, and the ratio of the electrical resistivity in the thickness direction to the electrical resistivity in the surface direction is set to 2 or less. In addition, such electric characteristics are set in a specific range such as the mixing ratio between the artificial graphite powder and the natural graphite powder, and the average particle diameter A of the artificial graphite powder and the average particle diameter B of the natural graphite powder. It becomes possible to give.
[0024]
The carbonaceous separator member has a thermosetting resin content of 10 to 25 parts by weight, and has an air-impermeable structure formed by using natural graphite powder having self-molding property, and has a gas permeability of 10%. Gas impermeability of −6 cc / cm 2 · min or less can be provided.
[0025]
The carbonaceous separator member for a polymer electrolyte fuel cell of the present invention has the above-described structure, is excellent in isotropy of electrical characteristics, and is also made of a carbonaceous plate-like molded body excellent in gas impermeability. Since it is formed, these characteristics function in a well-balanced manner, and it is possible to exhibit excellent performance as a separator member for a polymer electrolyte fuel cell.
[0026]
In the method for producing a carbonaceous separator member for a polymer electrolyte fuel cell according to the present invention, first, artificial graphite powder having an average particle diameter A of 50 μm or less and pulverized and sieved by appropriate means, and an average particle diameter B of A × (1/5 to 1/10) of natural graphite powder is prepared, and artificial graphite powder and natural graphite powder are uniformly mixed at a weight ratio of 80:20 to 60:40 to obtain a graphite powder. Is prepared.
[0027]
Next, a thermosetting resin is blended with 100 parts by weight of the mixed graphite powder in a weight ratio of 10 to 25 parts by weight and kneaded. The thermosetting resin preferably has a nonvolatile content of 60% or more. The thermosetting resin liquid (initial condensate) or the thermosetting resin liquid is dissolved in a volatile organic solvent such as alcohol. It is mixed with the graphite powder as a solution and kneaded well.
[0028]
The obtained kneaded material is dried as necessary to remove volatile components and the used organic solvent, and then crushed by a crusher and sieved to prepare crushed particles having a particle size of 2 mm or less. I do. The crushing treatment is performed by crushing a kneaded material, which is an aggregate of graphite powder covered with a non-conductive resin film, to expose the graphite surface to improve conductivity, and further, to improve the direction of the graphite powder during kneading. This is performed in order to correct the anisotropy of the material properties such as electrical properties, that is, electrical resistivity. Therefore, if the particle size of the crushed particles is large, these effects cannot be sufficiently achieved, so that crushed particles having a particle size of 2 mm or less are used.
[0029]
The method of forming the carbonaceous separator is a method of performing sufficient thermosetting at the appropriate temperature and pressure at the time of hot pressing so that the resin component has excellent corrosion resistance, or after obtaining a molded product by hot pressing. A method of performing sufficient thermal curing at an appropriate temperature can be used.
[0030]
In the former case, the crushed granules are filled in a mold having a desired shape, and the temperature and pressure during the hot pressing are set to a temperature of 40 to 280 ° C. and a pressure of 100 to 500 kg / cm 2 depending on the type of the thermosetting resin used as the binder resin. It is appropriately adjusted by a hot-press molding method. For example, when a phenolic resin is used, a plate-like molded body that is a carbonaceous separator member is formed by molding into a desired shape by a hot-press molding method at a temperature of 150 to 280 ° C. and a pressure of 100 to 500 kg / cm 2 and thermosetting. Is manufactured. Further, when the obtained molded body is further kept at a temperature of 150 to 280 ° C. to advance the thermosetting reaction, the corrosion resistance is improved.
[0031]
In the latter case, the crushed granules are filled in a mold having a desired shape, and the temperature and pressure during hot pressing are appropriately adjusted depending on the type of the thermosetting resin used as the binder resin. A carbon separator having improved corrosion resistance when formed into a desired shape by a hot-press molding method of 500 kg / cm 2 , and when the obtained molded body is kept at a temperature of 100 to 280 ° C. and a thermosetting reaction of the molded body is advanced. A plate-shaped molded body as a member is manufactured.
[0032]
The planar shape and the groove shape of the carbonaceous separator member can be formed by hot pressing. However, in the case of forming by machining, if the temperature is kept at 100 to 280 ° C. after processing, the processing distortion can be removed. The accuracy is improved.
[0033]
【Example】
Hereinafter, examples of the present invention will be described in comparison with comparative examples.
[0034]
Examples 1-4, Comparative Examples 1-8
Using artificial graphite powder having an average particle diameter A of 30 μm and natural graphite powder having an average particle diameter B of 5 μm and 30 μm, artificial graphite powder and natural graphite powder are uniformly mixed at different weight ratios to obtain graphite powder. Created. A phenol resin having a nonvolatile content of 70% was used as the thermosetting resin, and dissolved in methanol to adjust the resin concentration to 75% by weight. The graphite powder and the phenol resin solution were mixed at different ratios, sufficiently kneaded at room temperature, and then dried under vacuum to volatilize and remove volatile components including methanol. Next, it was crushed and sieved to prepare crushed granules having different particle diameters. The crushed granules are used as molding powder, filled in a molding die, and treated at a temperature of 180 ° C. under a pressure of 240 Kg / cm 2 for 10 minutes, and 20 flat plates with a single groove of 210 mm in length and 4 mm in thickness under each condition are prepared. Manufactured one by one. Table 1 compares the manufacturing conditions thus manufactured.
[0035]
[Table 1]
Various properties of these flat plates were measured by the following methods, and the results are shown in Table 2.
{Circle around (1)} Electric resistivity (Ωcm): Measured according to the voltage drop method of JIS R7202 “Test method for artificial graphite electrode”.
{Circle around (2)} Bulk density (g / cm 3 ); by Archimedes method.
(3) Flexural strength (Kgf / cm 2 ); measured according to JIS K6911.
{Circle around (4)} Gas impermeability: The gas permeability when a pressure of 1 kg / cm 2 was applied with nitrogen gas was measured, and those having a transmittance of 10 −6 (cc / cm 2 min) or less were accepted. .
[0037]
[Table 2]
From the results of Tables 1 and 2, the carbonaceous flat plate of the example manufactured by the manufacturing method of the present invention and satisfying the characteristic requirements of the present invention has a higher electrical resistivity in the plane direction (X-Y direction) than the comparative example. Is small, and the anisotropy with respect to the electrical resistivity in the thickness direction (Z direction) is also small. Furthermore, it is also excellent in gas impermeability, and it turns out that it has excellent performance as a carbonaceous separator member for a polymer electrolyte fuel cell. On the other hand, in Comparative Examples 1 to 3 in which natural graphite powder was not used in combination, the anisotropy of electric resistivity was small, but the gas impermeability was inferior, and it became more remarkable especially when the blending amount of the thermosetting resin was small. . On the other hand, in Comparative Examples 4 and 7 using only natural graphite powder, the anisotropy of the electrical resistivity was remarkable, and the average particle size B of the natural graphite powder was the same as the average particle size A of the artificial graphite powder, and B = A × ( In Comparative Examples 5 and 6, which do not satisfy the relationship of (1/5 to 1/10), it is found that the anisotropy of the electrical resistivity increases.
[0039]
【The invention's effect】
As described above, according to the carbonaceous separator member for a polymer electrolyte fuel cell of the present invention, since the electrical resistivity and the anisotropic ratio thereof are small, it is possible to suppress a decrease in power generation efficiency due to an increase in the internal resistance of the battery. It is possible to provide a separator member which has high gas impermeability and excellent battery performance. According to the production method of the present invention, artificial graphite powder and natural graphite powder are used in combination, and the average particle diameter and the mixing ratio thereof, and the amount of the thermosetting resin are set in a specific range. It is possible to produce a carbonaceous separator member for a polymer electrolyte fuel cell having high performance according to the present invention.
Claims (3)
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| NL1014403C1 (en) * | 2000-02-17 | 2001-08-20 | Nedstack Holding B V | Method for manufacturing a plate-shaped semi-finished product that is suitable for use in, among others, Polymer Electrolyte Fuel Cells. |
| JP4743356B2 (en) * | 2000-05-15 | 2011-08-10 | 日清紡ホールディングス株式会社 | Manufacturing method of fuel cell separator, fuel cell separator, and polymer electrolyte fuel cell |
| US7049021B2 (en) | 2000-06-29 | 2006-05-23 | Osaka Gas Company Limited | Conductive composition for solid polymer type fuel cell separator, solid polymer type fuel cell separator, solid polymer type fuel cell and solid polymer type fuel cell system using the separator |
| FR2812119B1 (en) * | 2000-07-24 | 2002-12-13 | Commissariat Energie Atomique | CONDUCTIVE COMPOSITE MATERIAL AND ELECTRODE FOR FUEL CELL USING THE THERMO-COMPRESSED MATERIAL |
| US7063914B2 (en) | 2000-09-04 | 2006-06-20 | Nippon Steel Chemical Co., Ltd. | Fuel cell separator, process for producing the same and material therefor |
| EP1351329B1 (en) | 2001-02-15 | 2009-11-25 | Panasonic Corporation | Polymer electrolyte type fuel cell |
| JP2004192878A (en) * | 2002-12-10 | 2004-07-08 | Tokai Carbon Co Ltd | Method for producing separator material for polymer electrolyte fuel cell |
| JP2004303453A (en) * | 2003-03-28 | 2004-10-28 | Nichias Corp | Manufacturing method of fuel cell separator |
| JP2005122974A (en) * | 2003-10-15 | 2005-05-12 | Dainippon Ink & Chem Inc | Fuel cell separator and fuel cell |
| JP2005174821A (en) * | 2003-12-12 | 2005-06-30 | Nissan Motor Co Ltd | Manufacturing method of separator for fuel cell and separator for fuel cell |
| JP4918984B2 (en) * | 2005-11-15 | 2012-04-18 | 日清紡ホールディングス株式会社 | Conductive resin composition for porous fuel cell separator and method for producing the same |
| JP5057263B2 (en) * | 2005-12-21 | 2012-10-24 | 東海カーボン株式会社 | Separator material for polymer electrolyte fuel cell and method for producing the same |
| JP5392973B2 (en) | 2006-02-20 | 2014-01-22 | 日産自動車株式会社 | Fuel cell system |
| JP2009093991A (en) * | 2007-10-11 | 2009-04-30 | Nichias Corp | Resin composition for fuel cell separator and fuel cell separator |
| DE112009005392B4 (en) * | 2009-11-23 | 2021-05-06 | Audi Ag | Method of making a porous article |
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