JP3972674B2 - Carbon fiber manufacturing method and carbon fiber reinforced resin composition - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、例えば導電性の優れた成形品、シート、プリプレグ等を得るために有用な炭素繊維およびその製造方法、該炭素繊維を含んでなる炭素繊維強化樹脂組成物等に関するものである。
【０００２】
【従来の技術】
近年、コンピュータやＯＡ機器の分野の発展により、高い電磁波シールド性や、高い制電性が求められるようになった。電磁波シールド性や制電性を高めるには、成形品の導電性を十分に高めることが必要となる。
【０００３】
炭素繊維強化複合材料は、強度、剛性、寸法安定性、導電性等に優れることから、有用であり、事務機器用途、自動車用途、コンピュータ用途（ＩＣトレイ、ノートパソコンの筐体（ハウジング）など）等の一般産業分野に広く展開され、その需要は年々増加しつつある。
【０００４】
成形品の導電性を高めるには、炭素繊維の含有量を増してやればよいが、炭素繊維の量を増やすと材料の成形が著しく困難になり、かつ経済性が低下したり、成形品外観が悪化することが多い。
【０００５】
そこで、炭素繊維の含有量を増加させることなく、成形品の導電性を高める手法として、炭素繊維自体の導電性を高める方法が提案されている。例えば、特開昭５７−５６５８６号公報には、ポリビニルピロリドンを付着した炭素繊維が開示されている。また、米国特許第6,231,788号明細書および米国特許第6,248,262号明細書には、熱可塑性樹脂を付着させた炭素繊維が開示されているが、発明者らが追試した結果では、確かにエポキシ樹脂をサイジング剤としたものより導電性が優れるが、最近の電子機器に適用するには十分ではなく、また付着した熱可塑性樹脂の影響により、成形品の強度、剛性や熱安定性などを低下させる場合があり、その使用には制限があった。
【０００６】
【発明が解決しようとする課題】
本発明は、かかる従来技術の問題点に鑑み、導電性が極めて優れる成形品を与える炭素繊維およびその製造方法、炭素繊維を用いてなる繊維強化樹脂組成物等を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、かかる課題を解決するために、気相成長炭素繊維および／またはカーボンナノチューブが表面に付着されてなる炭素繊維であって、前記気相成長炭素繊維および／またはカーボンナノチューブは８０％以上の繊維状物質と２０％以下の粒子状物質で構成されており、付着されている気相成長炭素繊維および／またはカーボンナノチューブが、前記炭素繊維１００重量部に対し０．０１〜２０重量部の範囲内である炭素繊維、その炭素繊維からなる炭素繊維ロービング、チョップド炭素繊維、ミルド炭素繊維を見出した。また、本発明の炭素繊維強化樹脂組成物は、かかる炭素繊維等とマトリックス樹脂とを含んでなることを特徴とするものである。
【０００８】
【発明の実施の形態】
以下、本発明の樹脂組成物における好ましい実施形態について具体的に説明する。
【０００９】
本発明における気相成長炭素繊維およびカーボンナノチューブ（以下、両者を総してカーボンナノチューブ）とは、気相で結晶を成長させる製造方法（気相成長法）により得られるカーボンナノチューブを指す。これらカーボンナノチューブは、グラファイトの１枚面を巻いて筒状にした形状を有しており、そのグラファイト層が一層で巻いた構造を持つものが単層カーボンナノチューブ、２層以上で巻いたものが多層カーボンナノチューブであり、本発明においてはそのいずれでも使用できるが、好ましくは多層カーボンナノチューブである。また、これらは、針状、コイル状、チューブ、カップ状の形態など任意の形態をとることができ、また、これらを２種類以上ブレンドしたものでもよい。
【００１０】
カーボンナノチューブの特徴である円筒状のグラファイト構造は高分解能透過型電子顕微鏡で調べることができる。グラファイトの層は、透過型電子顕微鏡でまっすぐにはっきりと見えるほど好ましいが、グラファイト層は乱れていても構わない。グラファイト層が乱れたものは、カーボンナノファイバーと定義することがあるが、このようなカーボンナノファイバーも本発明においてはカーボンナノチューブに含むものとする。
【００１１】
本発明のカーボンナノチューブは、一般にレーザーアブレーション法、アーク放電法、熱ＣＶＤ法、プラズマＣＶＤ法、燃焼法などで製造できるが、どのような方法で製造したカーボンナノチューブでも構わない。篠原らが報告しているようにゼオライトを触媒の担体としてアセチレンを原料に熱ＣＶＤ法で作る方法は、特に精製することなく、多少の熱分解炭素等の炭素被覆はあるものの、純度が高く、良くグラファイト化された多層カーボンナノチューブが得られる点で特に好ましい方法である(Chemical Physics Letters 303(1999) 117-124)。
【００１２】
かかるカーボンナノチューブの単糸の繊維径としては、より本発明の効果を明確にするものとして、１〜３０ｎｍが好ましく、さらに好ましくは３〜２０ｎｍである。
【００１３】
本発明におけるカーボンナノチューブは親水性であることが、本発明の効果を効率よく発現させる上で好ましい。ここでの親水性は、水（イオン交換水）に対する分散性を目安とすることができる。例えば、カーボンナノチューブ１０ｍｇに、イオン交換水５０ｍｌを加えて、超音波洗浄機（ＹＡＭＡＴＯ化学製、ＢＲＡＮＳＯＮ３２１０、発信周波数４７ＫＨｚ、出力１３０Ｗ）にて１時間処理後、４８時間静置して得られた試料溶液にて確認することができる。すなわち、溶液全体が均一な黒色透明な溶液であれば親水性と判断できる。
【００１４】
さらに本発明は、下記式で定義されるカーボンナノチューブ外表面の炭素に対する酸含有率が２％以上、さらに４％以上、とりわけ８％以上であることが好ましい。
【００１５】
【数２】
上式に示す分子のＡｃは、外表面に酸を有するカーボンナノチューブ１ｇに含まれる酸のモル数である。純度１００％のカーボンナノチューブを得ることは困難であり、それを同定することも困難であるため、ここで言うカーボンナノチューブとは５万倍の倍率で走査型電子顕微鏡で見たときに繊維状の物質がその電子顕微鏡の視野の中に８０％以上であるカーボン質材料であればカーボンナノチューブと言って差し支えない。従って、厳密に定義すればカーボンナノチューブ外表面だけに酸性基を有するのではなく、カーボンナノチューブに付着した炭素、カーボンナノチューブに混在する炭素粒子も含んだ状態で酸量を測定し、すべてカーボンナノチューブの表面に酸性基があるとして計算したものである。外表面に酸を有するカーボンナノチューブとは、図１の模式図に示されるように、カーボンナノチューブ外表面に少なくとも１種類以上の官能基を有するカーボンナノチューブのことである。官能基の種類は特に限定されないが、例えば、水酸基、カルボニル基、カルボキシル基、ニトロ基、スルホン基、エーテル基、などを挙げることができる。外表面に酸を有するカーボンナノチューブに含まれる酸のモル数の測定には、例えば、アルカリ水溶液を用いた中和滴定の測定から計算によって求める。
【００１７】
上式に示す分母は、カーボンナノチューブ１ｇに含まれるカーボンナノチューブ外表面の炭素のモル数である。カーボンナノチューブ平均外周を、カーボンナノチューブ平均層数とカーボンナノチューブ平均円周の乗算結果を用いて除算することで、カーボンナノチューブ全体に対するカーボンナノチューブ外表面の炭素率を求める。これに、カーボンナノチューブ１ｇを炭素原子の原子量（１２ｇ／ｍｏｌ）で除算した結果（つまり、カーボンナノチューブ１ｇ中に含まれる炭素原子のモル数）を乗算することで、カーボンナノチューブ１ｇに含まれるカーボンナノチューブ外表面の炭素のモル数を求める。カーボンナノチューブ平均外半径Ｒａ、カーボンナノチューブ平均内半径Ｒｂは図１に示すように定義され、例えば、透過型電子顕微鏡（ＴＥＭ）観察結果から、ひとつのカーボンナノチューブを重複して用いないルール適用して、任意に少なくとも１０点以上、好ましくは２０点以上のカーボンナノチューブの外半径、内半径を計測し、それぞれ平均値を計算することで求める。カーボンナノチューブ層間距離Ｒｋは、公知の値である０．３４ｎｍを用いる。
【００１８】
かかる、親水性を有するカーボンナノチューブまたは前記式で示されるカーボンナノチューブ外表面の炭素に対する酸含有率が２％以上であるカーボンナノチューブを得る方法については特に制限はないが、多層カーボンナノチューブをプラズマ処理する方法が好ましく用いられる。酸含有量を高めるためには、酸化剤を用いて酸化する方法、酸素ガス存在下で焼成する方法が知られているが、これらを用いると層数の少ないカーボンナノチューブは分解してしまう場合がある。それに比較してプラズマ処理は、表面層のみをマイルドに処理できる処理であり、カーボンナノチューブの分解を抑え、上記特徴を有するカーボンナノチューブを効率良く製造する上で好ましい。
【００１９】
本発明において、プラズマ処理とは、特に制限されないが、例えば公知の低温プラズマ処理のことをいい、処理空間内にカーボンナノチューブと処理するガスを供給した状態で高電圧を印可して発生するプラズマにより、カーボンナノチューブを処理する方法である。プラズマ発生ガスとしては、特に限定されないが、有機、無機ガスが目的に応じ単独あるいは混合されて用いられる。たとえば、酸素、窒素、水素、アンモニア、メタン、エチレン、４フッ化炭素などが挙げられる。処理装置としては、特に限定されるものではなく、公知の内部電極方式または外部電極方式が使用されるが、電極の汚染のない点から外部電極方式が好ましい。処理圧力、電源周波数、処理出力などの処理条件は特に限定されるものではなく目的に応じ好ましく選定すればよい。
【００２０】
プラズマ処理には、種々の処理があるが具体例として、酸素ガスプラズマ処理が好ましい。その理由は、通常カーボンナノチューブは、アモルファスカーボンなどが表面に付着しており、そのアモルファスカーボン成分を酸化して二酸化炭素にして除去することができ、カーボンナノチューブの親水化などの修飾だけでなく、同時に精製もできるからである。酸素ガスプラズマ処理の条件は、装置、放電形態によって異なるが外部電極方式の場合、圧力は５〜１００Ｐａが好ましい。プラズマ処理の条件によって、アモルファスカーボンのような熱分解炭素被覆物は、取り除くことも出来れば適度に残すことも出来る。適度に残した方が、カーボンナノチューブ全体の外表面積が大きくなり、樹脂への親和性が高くなり好ましい。
【００２１】
また別の具体的な処理方法として、細いカーボンナノチューブの処理には、窒素プラズマが好ましい。酸素プラズマよりもマイルドに処理が出来るため、カーボンナノチューブ自体が燃え尽きて無くなることはない。窒素プラズマ処理でも、処理後空気中にさらすことにより、窒素プラズマにより、切られた結合は、空気中の酸素と反応して、カルボキシル基やカルボニル基、ヒドロキシル基等になる。
【００２２】
かかるカーボンナノチューブの本発明に係る炭素繊維への付着量は、該炭素繊維１００重量部に対して０．０１〜２０重量部の範囲内であり、好ましくは０．１〜１０重量部の範囲内であり、さらに好ましくは０．５〜５重量部の範囲内である。付着量が０．０１重量部未満では得られる成形品の導電性が十分に発現できない場合があり、２０重量部を越えると成形性が低下する場合がある。
【００２３】
本発明の気相成長炭素繊維および／またはカーボンナノチューブを付着させる前の炭素繊維（以下、「付着前炭素繊維」と称する。）は、炭素の含有率が８５〜１００重量％の範囲内にあり、少なくとも部分的にはグラファイト構造を有するものである。これらの具体例としては、ポリアクリロニトリル系炭素繊維、レーヨン系炭素繊維、リグニン系炭素繊維、ピッチ系炭素繊維等繊維状のものであれば特に制限はないが、本発明の炭素繊維から得られる成形体の良好な導電性を満足し、かつ安価なコストを実現できる点でポリアクリロニトリル系炭素繊維が好適に用いられる。
【００２４】
また、本発明に係る炭素繊維の特性は特に限定はないが、本発明の効果をより向上させるためには、炭素繊維の引張強度が３ＧＰａ以上であり、引張弾性率が３５０ＧＰａ以下であり、かつ該炭素繊維の電気抵抗が４０Ω・ｇ／ｍ２未満であるものを用いることが好ましい。
【００２５】
ここで言う「炭素繊維の引張強度」および「炭素繊維の引張弾性率」とは、ＪＩＳ Ｒ ７６０１に基づいた樹脂含浸ストランド法で測定した強度および弾性率である。また「炭素繊維の電気抵抗」とは、１ｍ長の炭素繊維の両端に測定端子を接続する２線式測定法で測定した長さ当たりの電気抵抗値に、炭素繊維の同長さ当たりの重量を乗じたものを意味し、この際、通常の製造法において得られる繊維束の形態で測定しても良く、この場合も同様に得られた長さ当たりの電気抵抗値に繊維束の同長さ当たりの重量を乗じて求める。
【００２６】
さらに、導電性の観点から、付着前炭素繊維としては、広角Ｘ線回折法により測定された結晶サイズ（Ｌｃ）が、１〜６ｎｍの範囲内であるものが好ましい。Ｌｃが１ｎｍ以上であることは、付着前炭素繊維の炭化もしくは黒鉛化が十分であり、付着前炭素繊維自体の導電性および弾性率が良好になる。また、このような付着前炭素繊維を用いた樹脂組成物、およびそれからつくられる成形品は導電性の向上が期待できる。一方、Ｌｃが６ｎｍ以内であるということは、付着前炭素繊維の過剰な炭化もしくは黒鉛化を抑えることになり、付着前炭素繊維自体の導電性が優れ、かつ、付着前炭素繊維の折損を防ぐことが期待できる。そのため、樹脂組成物中の繊維長さは長くなり、優れた導電性が得られるだけでなく機械的特性の中でとくに機械的強度の点で良好となり好ましい。より好ましくは１．３〜４．５ｎｍ、特に好ましくは１．６〜３．６ｎｍの範囲であることが、樹脂組成物およびそれからつくられる成形品の高い導電性および機械的特性を得るのに好ましい。なお、広角Ｘ線回折法によるＬｃの測定は、日本学術振興会第１１７委員会、炭素、３６、ｐ２５（１９６３）に記載された方法に基づいて測定した。
【００２７】
本発明における炭素繊維は、その形状に特に限定は無く、連続長繊維束（炭素繊維ロービング）をはじめ、この連続長繊維束をカットしたチョップド糸、粉砕されてなるミルド糸などの原料、織物（クロス）、フェルトなどの中間基材、また用途や必要特性に応じて様々な形態をとることが出来る。特にプリプレグやシート等の用途には炭素繊維ロービングが使用され、とりわけ生産性に有利な炭素繊維強化熱可塑性樹脂成形品を製造する際には、カットしたチョップド糸、あるいは粉砕したミルド炭素繊維が好ましく用いられる。中でもほぼ所定の長さにカットしたチョップド炭素繊維は、熱可塑性樹脂と容易にコンパウンドでき、その取扱い性や得られる成形品の導電性の観点からより好ましい。また、このチョップド炭素繊維における繊維長さは、取扱性の観点から１〜２６ｍｍの範囲内が好ましく、２〜１５ｍｍの範囲内が特に好ましい。同様に本発明の炭素繊維を粉砕したミルド炭素繊維の長さも特に限定はないが、取扱性の観点から１０〜１５００μｍの範囲内が好ましく、３０〜１０００μｍの範囲内が特に好ましい。
【００２８】
本発明におけるカーボンナノチューブを付着前炭素繊維に付着させる方法には特に制限はなく、例えば、カーボンナノチューブを水または有機溶媒に分散させ、得られた溶液中に付着前炭素繊維を浸漬させた後、溶媒のみを除去する含浸法、あるいは、付着前炭素繊維に溶液を滴下、散布して付着せしめた後、その溶媒を除去する方法などが挙げられる。とりわけ生産性の観点から、含浸法が本発明の効果を向上させるために好ましい。また、含浸法における溶媒は、水またはアルコールが取扱い性、環境負荷の観点から好ましく使用できる。
【００２９】
また、本発明による炭素繊維強化樹脂組成物（以下、樹脂組成物という）は、上記したような炭素繊維とマトリックス樹脂とを含んでなるものである。ここで使用しうるマトリックス樹脂としては、特に制限はなく熱硬化性樹脂、熱可塑性樹脂のいずれでもよい。
【００３０】
かかる熱可塑性樹脂としては、例えば、ポリエチレンテレフタレート（ＰＥＴ）、ポリブチレンテレフタレート（ＰＢＴ）、ポリトリメチレンテレフタレート（ＰＴＴ）、ポリエチレンナフタレート（ＰＥＮ）、液晶ポリエステル等のポリエステルや、ポリエチレン（ＰＥ）、ポリプロピレン（ＰＰ）、ポリブチレン等のポリオレフィンや、スチレン系樹脂の他や、ポリオキシメチレン（ＰＯＭ）、ポリアミド（ＰＡ）、ポリカーボネート（ＰＣ）、ポリメチレンメタクリレート（ＰＭＭＡ）、ポリ塩化ビニル（ＰＶＣ）、ポリフェニレンスルフィド（ＰＰＳ）、ポリフェニレンエーテル（ＰＰＥ）、ポリイミド（ＰＩ）、ポリアミドイミド（ＰＡＩ）、ポリエーテルイミド（ＰＥＩ）、ポリスルホン（ＰＳＵ）、ポリエーテルスルホン、ポリケトン（ＰＫ）、ポリエーテルケトン（ＰＥＫ）、ポリエーテルエーテルケトン（ＰＥＥＫ）、ポリアリレート（ＰＡＲ）、ポリエーテルニトリル（ＰＥＮ）、フェノール（ノボラック型など）フェノキシ樹脂、フッ素樹脂、更にポリスチレン系、ポリオレフィン系、ポリウレタン系、飽和ポリエステル系、ポリアミド系、ポリブタジエン系、ポリイソプレン系、フッ素系等の熱可塑エラストマー等や、これらの共重合体、変性体、および２種類以上ブレンドした樹脂などであってもよい。また、更に機械的特性向上のために、上記熱可塑性樹脂にその他のエラストマーもしくはゴム成分を添加した樹脂であってもよい。また、これら熱可塑性樹脂は２種以上を併用して用いることができる。
【００３１】
熱硬化性樹脂とは、加熱または放射線や触媒などの手段によって硬化される際に実質的に不溶かつ不融性に変化し得る特性を持った樹脂である。その具体例としては、フェノール樹脂、ユリア樹脂、メラミン樹脂、ベンゾグアナミン樹脂、アルキド樹脂、不飽和ポリエステル樹脂、ビニルエステル樹脂、ジアリルテレフタレート樹脂、エポキシ樹脂、シリコーン樹脂、ウレタン樹脂、フラン樹脂、ケトン樹脂、キシレン樹脂、熱硬化性ポリイミド樹脂などが挙げられる。これらの樹脂は１種または２種以上を併用して用いることができる。
【００３２】
上記樹脂組成物は、本発明の炭素繊維を樹脂組成物全量に対して１〜７０重量％が好ましく、５〜５０重量％配合してなるものがさらに好ましい。
【００３３】
本発明の樹脂組成物は、例えば射出成形、ブロー成形、回転成形、押出成形、プレス成形、トランスファー成形、フィラメントワインディング成形などの成形方法によって成形されるが、最も望ましい成形法は、生産性の高い射出成形により成形するのがより好ましい。
【００３４】
なお、本発明の樹脂組成物には必要に応じて他の公知の添加剤を併用することも可能である。添加剤の具体例としては、酸化防止剤や耐熱安定剤、耐候剤、離型剤及び滑剤、顔料、染料、可塑剤、帯電防止剤、難燃剤、強化材などが挙げられる。
【００３５】
【実施例】
以下、実施例により本発明をさらに詳細に説明する。
（１）カーボンナノチューブ付着量の測定方法カーボンナノチューブを付着した炭素繊維を約５ｇを採取し、ガラス製の容器に投入する。 次にこの容器を１２０℃で３時間乾燥し、吸湿しないように注意しながら室温まで冷却後、秤量した値をＷ１（ｇ）とする。この炭素繊維入り容器に水を約１５ｇ加え、超音波洗浄機（ＴＡＭＡＴＯ化学製、ＢＲＡＮＳＯＮ３２１０、発信周波数４７ＫＨｚ、出力１３０Ｗ）にて１時間処理しカーボンナノチューブを洗い流した。次に濾紙（Ｔｏｙｏ Ｒｏｓｈｉ Ｋａｉｓｈａ、Ｆｉｌｔｅｒ Ｐａｐｅｒ２号 １２５ｍｍ）を用いて洗浄液を濾過させ、カーボンナノチューブを除去した炭素繊維のみを取り出した。かかるカーボンナノチューブを除去した後の炭素繊維を１２０℃で３時間乾燥し、吸湿しないように注意しながら室温まで冷却後、秤量した値をＷ２（ｇ）とする。
【００３６】
以上の処理を経て、カーボンナノチューブの付着量を、次式により求める。
【００３７】
カーボンナノチューブの付着量＝（Ｗ1−Ｗ2）／Ｗ2（単位：Ｗｔ％）
（２）成形品の導電性評価方法（表面抵抗率）
炭素繊維を採取し、ＡＳＴＭ Ｄ２５７−９９に従い、炭素繊維量を１０％として繊維強化複合材料の試験片を作成し、その表面抵抗を求める。
【００３８】
試験片は、図２に示すように、長さ８０ｍｍ×幅８０ｍｍ×厚さ３ｍｍの板状成形品に、導電性ペースト（藤倉化成（株）製ドータイト）を図のＡ〜Ｄの４箇所に塗布した。なお、Ａ〜Ｄの相互間隔は２０ｍｍとし、外周片からの距離はいずれも１０ｍｍの位置とした。そして、ＡＢ間、ＡＣ間、ＢＤ間、ＣＤ間の抵抗を測定し、その４種の測定値の平均値をもって表面抵抗率（単位はＬｏｇΩ/ｃｍ２）として求めた。測定には、アドバンテスト社製デジタルマルチメーターＲ６５８１を用いた。さらに導電性に加え、製造上の容易さ、成形品の外観品位、環境負荷の少なさを判断し、○○：より優れる、○：優れる、△：劣る、×：著しく劣る、の４段階の総合評価とした。
本発明の実施例および比較例に用いた成分は以下の通りである。
（１）カーボンナノチューブの調整方法
ＣＮＴ−１：カーボンナノチューブ
Ｋ．Ｈｅｒｎａｄｉ、Ａ．Ｆｏｎｓｅｃａらによる報告を参照（Ｚｅｏｌｉｔｅｓ １７：４１６−４２３、１９９６）し、酢酸鉄（２ｇ）、酢酸コバルト（２ｇ）、Ｙ型ゼオライト（１０ｇ）を秤量し、メタノール（１００ｍｌ）を加えて、振とう器にて１時間攪拌後、メタノール分を乾燥除去し、触媒を得た。次に、ＣＶＤ反応装置を用いて、反応管内の石英ウール上に触媒１ｇをあらかじめセットし、窒素（３０ｃｃ／分）雰囲気下で６００℃まで昇温後、アセチレン（６ｃｃ／分）、窒素（３０ｃｃ／分）雰囲気下で６００℃×５時間保持しカーボンナノチューブを合成した。その後、窒素（３０ｃｃ／分）雰囲気下で室温まで冷却し、反応混合物を取り出した。
【００３９】
前記の反応混合物を、フッ化水素酸１０％水溶液中で３時間攪拌後、ろ紙（Ｔｏｙｏ Ｒｏｓｈｉ Ｋａｉｓｈａ、Ｆｉｌｔｅｒ Ｐａｐｅｒ ２号 １２５ｍｍ）を用いてろ過し、ろ紙上の固形物を、イオン交換水、アセトン溶液にて洗浄後、乾燥し、カーボンナノチューブ（ＣＮＴ−１）を得た。ＣＮＴ−１の透過型電子顕微鏡（ＴＥＭ）観察結果から、多層カーボンナノチューブを多く含むことがわかった。また、ＳＥＭのＥＤＸを用いて元素分析を行ったところ、Ｙ型ゼオライトの存在率はＥＤＸの測定限界以下（ほぼ０％）である結果を得た。
【００４０】
前記カーボンナノチューブ（ＣＮＴ−１）１０ｍｇに、イオン交換水５０ｍｌを加えて、超音波洗浄機（ＹＡＭＡＴＯ化学製、ＢＲＡＮＳＯＮ３２１０、発信周波数４７ＫＨｚ、出力１３０Ｗ）にて１時間処理後、４８時間静置して得られた試料のｐＨをガラス電極式水素イオン濃度計（東亜電波工業、ＨＭ−３０Ｖ）を用いて測定したところ、ｐＨ＝７．０でり、この結果からＣＮＴ−１の酸のモル数は１０ｍｇあたり、ほぼ０ｍｏｌであり、前記式を用いてカーボンナノチューブ外表面の炭素に対する酸含有率（％）を計算すれば、０％と算出される。なお、ＣＮＴ−１の水溶液には黒い沈殿物が多く確認され、親水性を示さなかったた。
【００４１】
ＣＮＴ−２：プラズマ処理したカーボンナノチューブ
前記で得たカーボンナノチューブ（ＣＮＴ−１）０．５ｇを、ガラス製シャーレー上にうすく広げて、ＹＡＭＡＴＯ化学製ＰＬＡＳＭＡ ＣＨＡＭＢＥＲ ＭＯＤＥＬ ＰＣ−１０１Ａを用いて、酸素ガス、圧力２０Ｐａ、ＰＯＷＥＲ３００Ｗの条件で、５分間プラズマ処理を行い、一度取り出して、シャーレー上のプラズマ処理カーボンナノチューブを、かき混ぜ（ひっくり返す、転がす等の動作）、シャーレー上にうすく広げ、再び同様のプラズマ処理を行う作業を繰り返し、合計１５分（計３回）のプラズマ処理を行いプラズマ処理したカーボンナノチューブ（ＣＮＴ−２）を得た。前記プラズマ処理カーボンナノチューブ（ＣＮＴ−２）の透過型電子顕微鏡（ＴＥＭ）観察結果から、多層カーボンナノチューブを多く含むことが確認できた。
【００４２】
前記プラズマ処理後のカーボンナノチューブ（ＣＮＴ−２）１０ｍｇに、イオン交換水５０ｍｌを加えて、超音波洗浄機（ＹＡＭＡＴＯ化学製、ＢＲＡＮＳＯＮ３２１０、発信周波数４７ＫＨｚ、出力１３０Ｗ）にて１時間処理後、４８時間静置して得られた分散液のｐＨを、ガラス電極式水素イオン濃度計（東亜電波工業、ＨＭ−３０Ｖ）を用いて測定したところ、ｐＨ＝５．５であった。一般によく知られた中和滴定を、４２．５×１０-6（ｍｏｌ／ｌ）の水酸化ナトリウム水溶液を用いて、ｐＨ＝７．０を終点として行った結果、水酸化ナトリウム水溶液１４５ｍｌを要した。つまり、０．２５ｍｇの水酸化ナトリウム（ＮａＯＨ、４０ｇ／ｍｏｌ）を要した。この結果から、プラズマ処理後のカーボンナノチューブ１０ｍｇ中の酸のモル数は６．３×１０-6（ｍｏｌ）と計算できる。透過型電子顕微鏡（ＴＥＭ）を用いて、ひとつのカーボンナノチューブを重複して用いないルールを適用して、任意に２０点のカーボンナノチューブの外半径、内半径を計測し、それぞれ平均値を計算した結果、Ｒａ：カーボンナノチューブ平均外半径１１．５ｎｍ、Ｒｂ：カーボンナノチューブ平均内半径３．３ｎｍの結果を得た。また、Ｒｋ：カーボンナノチューブ層間距離０．３４ｎｍを用いた。
【００４３】
これらの結果から、前記式を用いてカーボンナノチューブ外表面の炭素に対する酸含有率（％）を計算した結果、１２％の結果を得た。
【００４４】
なお、ＣＮＴ−２の水溶液は均一な黒色透明であり、十分な親水性を有した。
【００４５】
ＣＮＴ−３：プラズマ処理したカーボンナノチューブ
J.L.Hutchisonらの方法（Carbon 39 (2001) 761-770)に従って、アーク放電法でカーボンナノチューブを生成した。アノードは直径3.2mm長さ140mmの穴に触媒が埋め込まれた直径8.2mmのグラファイトロッド、カソードは直径10mm,長さ25mmのグラファイトロッドとした。触媒は、次のように調製した。粒子径2-5μmのNi,Co,Fe粉末の混合物と硫黄原子を良く粉砕した後、アルゴンガス下で５００℃１時間焼成した。ボールミルでμサイズまで粉砕した後すぐにカーボン粉末と混ぜた。3.2mmの穴をドリルであけたグラファイトロッドにぎっしりつめた。アノードの組成は、カーボンに対して、Ni 2.6at%,Co 0.7at%,Fe 1.45at%,S 0.75at%であった。アルゴン：水素体積比１：１で３５０torrで７５−８０Aのアーク電流でＣＮＴ合成を行った。両電極は2mmの距離で電圧差は２６〜２８Ｖとした。
【００４６】
得られたカーボンナノチューブを含むカーボン０．５ｇを、ガラス製シャーレー上にうすく広げて、ＹＡＭＡＴＯ化学製ＰＬＡＳＭＡ ＣＨＡＭＢＥＲ ＭＯＤＥＬ ＰＣ−１０１Ａを用いて、窒素ガス、圧力２０Ｐａ、ＰＯＷＥＲ３００Ｗの条件で、５分間プラズマ処理を行い、一度取り出して、シャーレー上のプラズマ処理カーボンナノチューブを、かき混ぜ（ひっくり返す、転がす等の動作）、シャーレー上にうすく広げ、再び同様のプラズマ処理を行う作業を繰り返し、合計１０分（計２回）のプラズマ処理を行った。
【００４７】
プラズマ処理後のカーボン材料１０ｍｇに、イオン交換水５０ｍｌを加えて、超音波洗浄機（ＹＡＭＡＴＯ化学製、ＢＲＡＮＳＯＮ３２１０、発信周波数４７ＫＨｚ、出力１３０Ｗ）にて１時間処理後、４８時間静置して得られた試料を観察したところ、カーボンナノチューブ分散液と黒い沈殿物が確認できた。分散液を、遠心分離器（装置：ＫＵＢＯＴＡ ＫＲ−２００００Ｔ、ローター：ＲＡ−３ ５０ｍｌ×８本）を用いて、回転数１２０００ｒｐｍ（約１７０００（×ｇ））×１時間、遠心分離したところ、上澄み液として、透明感のある黒色の溶液を得た。スポイトで溶液部分を回収し、高分解能透過型電子顕微鏡で観察した結果、炭素不純物の付着したカーボンナノチューブが多く見られた。５万倍の走査型電子顕微鏡で見たところ、８０％は、繊維状物質で、２０％は粒子状物質であった。
【００４８】
上澄み液を乾燥させ、プラズマ処理したカーボンナノチューブ（ＣＮＴ−３）を得た。ＣＮＴ−３を再度水に分散させて、ＣＮＴ−２と同様に酸量を量り、酸含有率を求めたところ８．５％であった。
【００４９】
なお、ＣＮＴ−３の親水性もＣＮＴ−２同様に十分であった。
（２） 炭素繊維の調整方法
ポリアクリロニトリルを主成分とする共重合体から紡糸、焼成処理を行い、総フィラメント数４８、０００本の炭素繊維連続トウを得た。
【００５０】
この連続トウの特性を下記に示す。
【００５１】
単位長さ当たり質量 ３．３ｇ／ｍ
比重 １．８引張強度 ３．０ＧＰａ
引張弾性率 ２２５ＧＰａ
電気抵抗 ３６．０Ω・ｇ／ｍ２
ＣＦ−１：炭素繊維連続トウにカーボンナノチューブを付着させずにカートリッジカッターを用いて上記炭素繊維連続トウを６ｍｍ長にカットしてチョップド炭素繊維を得た。
【００５２】
ＣＦ−２：ＣＮＴ−１をＮ−メチルピロリドン（ＮＭＰ）溶媒中に分散させて４重量％の濃度の溶液を調製し、この液を上記した炭素繊維連続トウに含浸法により繊維基材に対し２重量％となるように付与した後、２８０℃で１５分間乾燥した後、カートリッジカッターを用いて上記炭素繊維連続トウを６ｍｍ長にカットしてチョップド糸を得た。上述の方法よりカーボンナノチューブの付着量を求めたところ、１．９重量％であった。
【００５３】
ＣＦ−３：ＣＮＴ−２をイオン交換水に分散させて４重量％の濃度の溶液を調製し、この液を上記した炭素繊維連続トウに含浸法により繊維基材に対し２重量％となるように付与した後、２１０℃で５分間乾燥した後、カートリッジカッターを用いて上記炭素繊維連続トウを６ｍｍ長にカットしてチョップド糸を得た。上述の方法よりカーボンナノチューブの付着量を求めたところ、２．２重量％であった。
【００５４】
ＣＦ−４：ＣＮＴ−３をイオン交換水に分散させて４重量％の濃度の溶液を調製し、この液を上記した炭素繊維連続トウに含浸法により繊維基材に対し２重量％となるように付与した後、熱風乾燥機で２１０℃で５分間乾燥した後、カートリッジカッターを用いて上記炭素繊維連続トウを６ｍｍ長にカットしてチョップド糸を得た。上述の方法よりカーボンナノチューブの付着量を求めたところ、２．０重量％であった。
【００５５】
（実施例１、２、３および比較例１）
ＪＳＷ製ＴＥＸ−３０α型２軸押出機を用い、バレル温度３００℃、回転数１５０ｒｐｍの条件で、ポリカーボネート樹脂（ＧＥプラスチックス社製レキサン１４１Ｒ−１１１）をメインホッパーから投入し、またサイドホッパーからは、水分率０．０５％以下になるように十分乾燥した各チョップド炭素繊維を、炭素繊維量１０％なるよう混練し、不連続の炭素繊維を含有するガットを連続的に押出した。これを冷却後、カッターで５ｍｍ長に切断して、炭素繊維強化樹脂ペレットを得た。
【００５６】
上記したペレットを８０℃にて５時間以上真空中で乾燥させた後、住友プロマット社製小型射出成形機にてバレル温度３２０℃、金型温度８０℃で成形し、この成形品を導電性の評価に供した。
【００５７】
実施例１〜３および比較例１の結果を表１にまとめて示す。
【００５８】
【表１】
表１より、実施例１〜３の成形品は、比較例１に対して極めて優れた導電性（表面抵抗率）を示すことが明らかである。また、実施例１，２の分散溶媒に水を使用したものは、実施例３よりも導電性が高く、かつ経済性、作業性、環境負荷の面でも有利である。
【００６０】
【発明の効果】
本発明によれば、導電性が極めて優れる成形品が製造できる炭素繊維およびその製造方法、その炭素繊維を用いてなる繊維強化樹脂組成物等を得ることができる。
【図面の簡単な説明】
【図１】多層カーボンナノチューブの模式図である。
【図２】表面抵抗率を測定するための試験片の平面図である。
【符号の説明】
１：導電性ペースト塗布範囲Ａ
２：導電性ペースト塗布範囲Ｂ
３：導電性ペースト塗布範囲Ｃ
４：導電性ペースト塗布範囲Ｄ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbon fiber useful for obtaining, for example, a molded article, sheet, prepreg and the like having excellent electrical conductivity, a method for producing the same, a carbon fiber reinforced resin composition containing the carbon fiber, and the like.
[0002]
[Prior art]
In recent years, with the development of the field of computers and OA equipment, high electromagnetic shielding properties and high antistatic properties have been demanded. In order to improve the electromagnetic shielding property and the antistatic property, it is necessary to sufficiently enhance the conductivity of the molded product.
[0003]
Carbon fiber reinforced composite materials are useful because they are excellent in strength, rigidity, dimensional stability, electrical conductivity, etc., and are useful for office equipment, automobiles, and computers (IC trays, notebook PC housings, etc.) It is widely deployed in general industrial fields such as, and its demand is increasing year by year.
[0004]
In order to increase the conductivity of the molded product, it is sufficient to increase the carbon fiber content. However, if the amount of carbon fiber is increased, the molding of the material becomes extremely difficult, the economic efficiency is lowered, and the appearance of the molded product is reduced. Often worse.
[0005]
Therefore, as a method for increasing the conductivity of a molded product without increasing the carbon fiber content, a method for increasing the conductivity of the carbon fiber itself has been proposed. For example, Japanese Patent Application Laid-Open No. 57-56586 discloses carbon fibers to which polyvinyl pyrrolidone is attached. Further, in US Pat.Nos. 6,231,788 and 6,248,262, carbon fibers to which a thermoplastic resin is attached are disclosed. It has better electrical conductivity than the sizing agent, but it is not enough to be applied to recent electronic devices, and the strength, rigidity, thermal stability, etc. of the molded product are reduced due to the influence of the attached thermoplastic resin. And its use was limited.
[0006]
[Problems to be solved by the invention]
An object of this invention is to provide the carbon fiber which gives the molded article which is extremely excellent in electroconductivity, its manufacturing method, the fiber reinforced resin composition using carbon fiber, etc. in view of the problem of this prior art.
[0007]
[Means for Solving the Problems]
In order to solve such a problem, the present invention is a carbon fiber formed by vapor-grown carbon fiber and / or carbon nanotubes attached to the surface.The vapor-grown carbon fiber and / or carbon nanotube is composed of 80% or more fibrous material and 20% or less particulate material,A carbon fiber in which the vapor-grown carbon fiber and / or carbon nanotube attached is within a range of 0.01 to 20 parts by weight with respect to 100 parts by weight of the carbon fiber, a carbon fiber roving comprising the carbon fiber, and chopped carbon Fiber, milled carbon fiber was found. The carbon fiber reinforced resin composition of the present invention is characterized by comprising such carbon fibers and a matrix resin.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the resin composition of the present invention will be specifically described.
[0009]
In the present invention, the vapor-grown carbon fiber and the carbon nanotube (hereinafter collectively referred to as carbon nanotube) refer to a carbon nanotube obtained by a production method (vapor-phase growth method) in which crystals are grown in the vapor phase. These carbon nanotubes have a shape in which one surface of graphite is wound into a cylindrical shape, and those having a structure in which the graphite layer is wound in one layer are those in which single-walled carbon nanotubes are wound in two or more layers. Multi-walled carbon nanotubes can be used in the present invention, but multi-walled carbon nanotubes are preferred. Moreover, these can take arbitrary forms, such as a needle shape, a coil shape, a tube shape, and a cup shape, and what blended these 2 or more types may be used.
[0010]
The cylindrical graphite structure that is characteristic of carbon nanotubes can be examined with a high-resolution transmission electron microscope. The graphite layer is preferred so that it can be seen straight and clearly in a transmission electron microscope, but the graphite layer may be disordered. What disturbs the graphite layer may be defined as carbon nanofiber, and such carbon nanofiber is also included in the carbon nanotube in the present invention.
[0011]
The carbon nanotube of the present invention can be generally produced by a laser ablation method, an arc discharge method, a thermal CVD method, a plasma CVD method, a combustion method or the like, but may be a carbon nanotube produced by any method. As reported by Shinohara et al., The method of making acetylene as a raw material by a thermal CVD method using zeolite as a catalyst support has a high purity, although there is some carbon coating such as pyrolytic carbon without any particular purification. This is a particularly preferable method in that a well graphitized multi-walled carbon nanotube can be obtained (Chemical Physics Letters 303 (1999) 117-124).
[0012]
The fiber diameter of the single yarn of the carbon nanotube is preferably 1 to 30 nm, and more preferably 3 to 20 nm, for further clarifying the effect of the present invention.
[0013]
The carbon nanotubes in the present invention are preferably hydrophilic in order to efficiently express the effects of the present invention. The hydrophilicity here can be based on dispersibility in water (ion exchange water). For example, a sample obtained by adding 50 ml of ion-exchanged water to 10 mg of carbon nanotubes, treating for 1 hour with an ultrasonic washing machine (manufactured by Yamato Chemical, BRANSON 3210, transmission frequency 47 KHz, output 130 W), and allowing to stand for 48 hours It can be confirmed with a solution. That is, if the whole solution is a uniform black transparent solution, it can be determined to be hydrophilic.
[0014]
Furthermore, in the present invention, the acid content with respect to carbon on the outer surface of the carbon nanotube defined by the following formula is preferably 2% or more, more preferably 4% or more, and particularly preferably 8% or more.
[0015]
[Expression 2]
Ac of the molecule shown in the above formula is the number of moles of acid contained in 1 g of carbon nanotubes having an acid on the outer surface. It is difficult to obtain carbon nanotubes with a purity of 100%, and it is difficult to identify them, so the carbon nanotubes referred to here are fibrous when viewed with a scanning electron microscope at a magnification of 50,000 times. If the material is a carbonaceous material with 80% or more in the field of view of the electron microscope, it can be called a carbon nanotube. Therefore, strictly speaking, the acid amount is measured not only having an acidic group only on the outer surface of the carbon nanotube but also including carbon adhering to the carbon nanotube and carbon particles mixed in the carbon nanotube. It is calculated assuming that there are acidic groups on the surface. The carbon nanotube having an acid on the outer surface is a carbon nanotube having at least one kind of functional group on the outer surface of the carbon nanotube, as shown in the schematic diagram of FIG. The type of the functional group is not particularly limited, and examples thereof include a hydroxyl group, a carbonyl group, a carboxyl group, a nitro group, a sulfone group, and an ether group. For the measurement of the number of moles of acid contained in the carbon nanotube having acid on the outer surface, for example, it is obtained by calculation from the measurement of neutralization titration using an alkaline aqueous solution.
[0017]
The denominator shown in the above formula is the number of moles of carbon on the outer surface of the carbon nanotube contained in 1 g of the carbon nanotube. By dividing the average outer circumference of the carbon nanotube by using the multiplication result of the average number of carbon nanotube layers and the average circumference of the carbon nanotube, the carbon ratio of the outer surface of the carbon nanotube relative to the entire carbon nanotube is obtained. Carbon nanotubes contained in 1 g of carbon nanotubes are multiplied by the result obtained by dividing 1 g of carbon nanotubes by the atomic weight of carbon atoms (12 g / mol) (that is, the number of moles of carbon atoms contained in 1 g of carbon nanotubes). Obtain the number of moles of carbon on the outer surface. The carbon nanotube average outer radius Ra and the carbon nanotube average inner radius Rb are defined as shown in FIG. 1. For example, from the observation result of a transmission electron microscope (TEM), a rule that does not use one carbon nanotube repeatedly is applied. The outer and inner radii of the carbon nanotubes are arbitrarily measured at least 10 points, preferably 20 points or more, and the average value is calculated for each. The carbon nanotube interlayer distance Rk uses a known value of 0.34 nm.
[0018]
There is no particular limitation on the method of obtaining the carbon nanotube having hydrophilicity or the carbon nanotube having an acid content of 2% or more with respect to the carbon on the outer surface of the carbon nanotube represented by the above formula, but the multi-wall carbon nanotube is plasma-treated. The method is preferably used. In order to increase the acid content, a method of oxidizing using an oxidant and a method of firing in the presence of oxygen gas are known, but if these are used, carbon nanotubes with a small number of layers may be decomposed. is there. In comparison, the plasma treatment is a treatment that can mildly treat only the surface layer, and is preferable for efficiently producing the carbon nanotubes having the above characteristics by suppressing the decomposition of the carbon nanotubes.
[0019]
In the present invention, the plasma treatment is not particularly limited, but it refers to, for example, a known low-temperature plasma treatment, which is caused by plasma generated by applying a high voltage in a state where carbon nanotubes and a gas to be treated are supplied into the treatment space. This is a method for treating carbon nanotubes. Although it does not specifically limit as plasma generation gas, Organic and inorganic gas are used individually or in mixture according to the objective. For example, oxygen, nitrogen, hydrogen, ammonia, methane, ethylene, carbon tetrafluoride and the like can be mentioned. The processing apparatus is not particularly limited, and a known internal electrode system or external electrode system is used, but the external electrode system is preferable from the viewpoint of no contamination of the electrodes. Processing conditions such as processing pressure, power supply frequency, processing output and the like are not particularly limited and may be preferably selected according to the purpose.
[0020]
There are various types of plasma treatment, but oxygen gas plasma treatment is preferable as a specific example. The reason for this is that usually carbon nanotubes have amorphous carbon or the like attached to the surface, and the amorphous carbon component can be oxidized and removed to carbon dioxide, not only modifications such as hydrophilicity of carbon nanotubes, This is because it can be purified at the same time. The conditions for the oxygen gas plasma treatment vary depending on the apparatus and discharge mode, but in the case of the external electrode system, the pressure is preferably 5 to 100 Pa. Depending on the conditions of the plasma treatment, the pyrolytic carbon coating such as amorphous carbon can be removed or left moderately. It is preferable to leave it in an appropriate amount because the outer surface area of the entire carbon nanotube is increased and the affinity for the resin is increased.
[0021]
As another specific processing method, nitrogen plasma is preferable for processing thin carbon nanotubes. Since it can be processed milder than oxygen plasma, the carbon nanotubes themselves will not burn out and disappear. Even in the nitrogen plasma treatment, the bond cut by the nitrogen plasma reacts with oxygen in the air by being exposed to air after the treatment, and becomes a carboxyl group, a carbonyl group, a hydroxyl group, or the like.
[0022]
Such carbon nanotubesCharcoal according to the present inventionAmount of adhesion to fiberThe charcoalIt is in the range of 0.01 to 20 parts by weight, preferably in the range of 0.1 to 10 parts by weight, more preferably in the range of 0.5 to 5 parts by weight with respect to 100 parts by weight of the raw fibers. is there. If the adhesion amount is less than 0.01 parts by weight, the resulting molded product may not be sufficiently conductive, and if it exceeds 20 parts by weight, the moldability may be reduced.
[0023]
The present inventionThe carbon fiber before adhering the vapor-grown carbon fiber and / or the carbon nanotube (hereinafter referred to as “carbon fiber before adhesion”)The carbon content is in the range of 85 to 100% by weight, and at least partially has a graphite structure. Specific examples of these are not particularly limited as long as they are fibrous, such as polyacrylonitrile-based carbon fiber, rayon-based carbon fiber, lignin-based carbon fiber, and pitch-based carbon fiber, but are obtained from the carbon fiber of the present invention. A polyacrylonitrile-based carbon fiber is preferably used in that it satisfies the good electrical conductivity of the body and can realize an inexpensive cost.
[0024]
Also, Charcoal according to the present inventionThe properties of the raw fibers are not particularly limited, but in order to further improve the effects of the present invention, carbon fibersMaintenanceThe tensile strength is 3 GPa or more, the tensile elastic modulus is 350 GPa or less, and the electric resistance of the carbon fiber is 40 Ω · g / m.2It is preferable to use those that are less than.
[0025]
The “tensile strength of carbon fiber” and “tensile modulus of carbon fiber” referred to here are strength and elastic modulus measured by a resin impregnated strand method based on JIS R7601. The “electric resistance of carbon fiber” means the electric resistance value per length measured by a two-wire measurement method in which measurement terminals are connected to both ends of a 1 m long carbon fiber, and the weight per length of the carbon fiber. In this case, it may be measured in the form of a fiber bundle obtained in a normal production method. In this case, the electrical resistance value per length obtained in the same manner is also used. Calculate by multiplying the weight per hit.
[0026]
Furthermore, from the viewpoint of conductivityEt al.As the raw fibers, those having a crystal size (Lc) measured by a wide-angle X-ray diffraction method within a range of 1 to 6 nm are preferable. Lc is 1 nm or more, Charcoal before adhesionCarbonization or graphitization of the fiber is sufficient, Charcoal before adhesionThe conductivity and elastic modulus of the elemental fiber itself are improved. Also like thisCharcoal before adhesionThe resin composition using the raw fibers and the molded product made therefrom can be expected to have improved conductivity. On the other hand, Lc is within 6 nm, Charcoal before adhesionWill suppress excessive carbonization or graphitization of the fiber., Charcoal before adhesionThe fiber itself has excellent conductivity, and, Charcoal before adhesionIt can be expected to prevent breakage of the fiber. For this reason, the fiber length in the resin composition is increased, and not only excellent electrical conductivity can be obtained, but also mechanical properties are particularly favorable in terms of mechanical strength, which is preferable. A range of 1.3 to 4.5 nm is more preferable, and a range of 1.6 to 3.6 nm is particularly preferable in order to obtain high conductivity and mechanical properties of the resin composition and a molded product made therefrom. . In addition, the measurement of Lc by a wide angle X-ray diffraction method was measured based on the method described in Japan Society for the Promotion of Science 117th Committee, carbon, 36, p25 (1963).
[0027]
The carbon fiber in the present invention is not particularly limited in shape, and includes a continuous long fiber bundle (carbon fiber roving), a raw material such as a chopped yarn obtained by cutting this continuous long fiber bundle, a milled yarn obtained by pulverization, a woven fabric ( Cloth), felt, and other intermediate base materials, and various forms can be taken according to the application and required characteristics. In particular, carbon fiber roving is used for applications such as prepregs and sheets, and cut chopped yarns or crushed milled carbon fibers are preferred, especially when producing carbon fiber reinforced thermoplastic resin molded articles advantageous to productivity. Used. Among them, chopped carbon fiber cut to a substantially predetermined length can be easily compounded with a thermoplastic resin, and is more preferable from the viewpoints of handleability and conductivity of a molded product to be obtained. In addition, the fiber length in the chopped carbon fiber is preferably in the range of 1 to 26 mm, particularly preferably in the range of 2 to 15 mm, from the viewpoint of handleability. Similarly, the length of the milled carbon fiber obtained by pulverizing the carbon fiber of the present invention is not particularly limited, but is preferably in the range of 10 to 1500 μm and particularly preferably in the range of 30 to 1000 μm from the viewpoint of handleability.
[0028]
Carbon nanotube in the present inventionAdhere before charcoalThere is no particular limitation on the method for adhering to the fiber, for example, the carbon nanotube is dispersed in water or an organic solvent,Adhering to charcoalImmerse the fiberAfter soakingAn impregnation method to remove only the solvent, or, Charcoal before adhesionFor example, a method of removing the solvent after dropping the solution onto the fiber and applying it to the fiber may be used. In particular, from the viewpoint of productivity, the impregnation method is preferable in order to improve the effect of the present invention. In addition, water or alcohol can be preferably used as the solvent in the impregnation method from the viewpoints of handleability and environmental load.
[0029]
Moreover, the carbon fiber reinforced resin composition (hereinafter referred to as a resin composition) according to the present invention comprises the carbon fiber and the matrix resin as described above. The matrix resin that can be used here is not particularly limited and may be either a thermosetting resin or a thermoplastic resin.
[0030]
Examples of such thermoplastic resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyester such as liquid crystal polyester, polyethylene (PE), and polypropylene. (PP), polyolefins such as polybutylene, styrene resins, polyoxymethylene (POM), polyamide (PA), polycarbonate (PC), polymethylene methacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), polyphenylene ether (PPE), polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone, Ketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyarylate (PAR), polyethernitrile (PEN), phenol (novolak type, etc.) phenoxy resin, fluorine resin, polystyrene, polyolefin Thermoplastic elastomers such as polyurethane, saturated polyester, polyamide, polybutadiene, polyisoprene, and fluorine, copolymers thereof, modified products, and resins blended in two or more types Good. Further, in order to further improve mechanical properties, a resin obtained by adding another elastomer or a rubber component to the thermoplastic resin may be used. These thermoplastic resins can be used in combination of two or more.
[0031]
The thermosetting resin is a resin having characteristics that can be substantially insoluble and infusible when cured by heating or means such as radiation or a catalyst. Specific examples include phenol resin, urea resin, melamine resin, benzoguanamine resin, alkyd resin, unsaturated polyester resin, vinyl ester resin, diallyl terephthalate resin, epoxy resin, silicone resin, urethane resin, furan resin, ketone resin, xylene. Examples thereof include resins and thermosetting polyimide resins. These resins can be used alone or in combination of two or more.
[0032]
The resin composition is preferably 1 to 70% by weight, more preferably 5 to 50% by weight of the carbon fiber of the present invention based on the total amount of the resin composition.
[0033]
The resin composition of the present invention is molded by a molding method such as injection molding, blow molding, rotational molding, extrusion molding, press molding, transfer molding, filament winding molding, etc. The most desirable molding method is high productivity. More preferably, it is formed by injection molding.
[0034]
The resin composition of the present invention can be used in combination with other known additives as necessary. Specific examples of the additive include an antioxidant, a heat stabilizer, a weathering agent, a release agent and a lubricant, a pigment, a dye, a plasticizer, an antistatic agent, a flame retardant, and a reinforcing material.
[0035]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
(1) Measuring method of carbon nanotube adhesion amount About 5 g of carbon fibers to which carbon nanotubes are adhered are collected and put into a glass container. Next, this container was dried at 120 ° C. for 3 hours, cooled to room temperature while taking care not to absorb moisture, and the weighed value was1(G). About 15 g of water was added to the carbon fiber-containing container, and the carbon nanotubes were washed away by treatment with an ultrasonic cleaner (TAMATO Chemical Co., BRANSON 3210, transmission frequency 47 KHz, output 130 W) for 1 hour. Next, the cleaning liquid was filtered using a filter paper (Toyo Roshi Kaisha, Filter Paper No. 125 mm)., Charcoal with carbon nanotubes removedOnly the fiber was taken out.Charcoal after removing such carbon nanotubesThe fiber was dried at 120 ° C for 3 hours, cooled to room temperature while taking care not to absorb moisture, and the weighed value was2(G).
[0036]
Through the above processing, the adhesion amount of the carbon nanotube is obtained by the following equation.
[0037]
Carbon nanotube adhesion amount = (W1-W2) / W2(Unit: Wt%)
(2) Conductivity evaluation method for molded products (surface resistivity)
A carbon fiber is collected, a test piece of a fiber reinforced composite material is prepared according to ASTM D257-99 with a carbon fiber content of 10%, and the surface resistance is obtained.
[0038]
As shown in FIG. 2, the test piece is a plate-shaped molded product having a length of 80 mm × width of 80 mm × thickness of 3 mm, and conductive paste (Dotite manufactured by Fujikura Kasei Co., Ltd.) at four locations A to D in the figure. Applied. The distance between A to D was 20 mm, and the distance from the outer peripheral piece was 10 mm. And resistance between AB, between AC, between BD, and between CD was measured, and it calculated | required as surface resistivity (a unit is Log (ohm) / cm2) with the average value of the 4 types of measured values. For the measurement, a digital multimeter R6581 manufactured by Advantest Corporation was used. Furthermore, in addition to conductivity, the ease of manufacturing, the appearance quality of the molded product, and the low environmental load are judged, and ◯: Excellent, ○: Excellent, △: Inferior, ×: Significantly inferior Overall evaluation was made.
The components used in Examples and Comparative Examples of the present invention are as follows.
(1) Carbon nanotube adjustment method
CNT-1: Carbon nanotube
K. Hernadi, A.M. See the report by Fonseca et al. (Zeolites 17: 416-423, 1996), weigh iron acetate (2 g), cobalt acetate (2 g), Y-type zeolite (10 g), add methanol (100 ml) and shake. After stirring in a vessel for 1 hour, the methanol content was removed by drying to obtain a catalyst. Next, using a CVD reactor, 1 g of catalyst was set in advance on quartz wool in the reaction tube, heated to 600 ° C. in a nitrogen (30 cc / min) atmosphere, acetylene (6 cc / min), nitrogen (30 cc) / Min) Carbon nanotubes were synthesized by holding at 600 ° C. for 5 hours in an atmosphere. Then, it cooled to room temperature under nitrogen (30cc / min) atmosphere, and took out the reaction mixture.
[0039]
The reaction mixture was stirred in a 10% aqueous solution of hydrofluoric acid for 3 hours, and then filtered using a filter paper (Toyo Roshi Kaisha, Filter Paper No. 125 mm). The solid on the filter paper was subjected to ion exchange water, acetone. After washing with a solution and drying, carbon nanotubes (CNT-1) were obtained. From the observation result of transmission electron microscope (TEM) of CNT-1, it was found that many CNTs were included. Further, when elemental analysis was performed using EDX of SEM, the result was that the abundance of the Y-type zeolite was below the EDX measurement limit (approximately 0%).
[0040]
Add 50 ml of ion-exchanged water to 10 mg of the carbon nanotube (CNT-1), treat it for 1 hour with an ultrasonic cleaner (YAMATO Chemical, BRANSON 3210, transmission frequency 47 KHz, output 130 W), and leave it for 48 hours. When the pH of the obtained sample was measured using a glass electrode type hydrogen ion concentration meter (Toa Denpa Kogyo, HM-30V), pH = 7.0. From this result, the number of moles of acid of CNT-1 was It is approximately 0 mol per 10 mg, and when the acid content (%) with respect to carbon on the outer surface of the carbon nanotube is calculated using the above formula, it is calculated as 0%. In addition, many black deposits were confirmed in the aqueous solution of CNT-1, and it did not show hydrophilicity.
[0041]
CNT-2: Plasma-treated carbon nanotube
The carbon nanotube (CNT-1) obtained above (0.5 g) was thinly spread on a glass petri dish, and YAMATO Chemical's PLASMA CHAMBER MODEL PC-101A was used under the conditions of oxygen gas, pressure 20 Pa, POWER 300 W, 5 Perform plasma treatment for 1 minute, take out once, stir the plasma treated carbon nanotubes on the petri dish (turn over, roll etc.), spread it thinly on the petri dish, repeat the same plasma treatment again, total 15 minutes ( A total of three times of plasma treatment was performed to obtain a plasma-treated carbon nanotube (CNT-2). From the result of transmission electron microscope (TEM) observation of the plasma-treated carbon nanotube (CNT-2), it was confirmed that it contained a lot of multi-walled carbon nanotubes.
[0042]
After adding 50 ml of ion-exchange water to 10 mg of the carbon nanotube (CNT-2) after the plasma treatment, the treatment is performed for 48 hours after being treated with an ultrasonic cleaner (YAMATO Chemical, BRANSON 3210, transmission frequency 47 KHz, output 130 W) for 48 hours. When the pH of the dispersion obtained by standing was measured using a glass electrode type hydrogen ion concentration meter (Toa Denki Kogyo, HM-30V), the pH was 5.5. A well-known neutralization titration is performed at 42.5 × 10-6As a result of using (mol / l) aqueous sodium hydroxide solution with pH = 7.0 as the end point, 145 ml of aqueous sodium hydroxide solution was required. That is, 0.25 mg of sodium hydroxide (NaOH, 40 g / mol) was required. From this result, the number of moles of acid in 10 mg of carbon nanotubes after plasma treatment was 6.3 × 10.-6(Mol). Using a transmission electron microscope (TEM), applying the rule of not using one carbon nanotube redundantly, arbitrarily measured the outer radius and inner radius of 20 carbon nanotubes, and calculated the average value respectively. As a result, Ra: carbon nanotube average inner radius 11.5 nm, Rb: carbon nanotube average inner radius 3.3 nm were obtained. Further, Rk: a carbon nanotube interlayer distance of 0.34 nm was used.
[0043]
From these results, the acid content (%) with respect to carbon on the outer surface of the carbon nanotube was calculated using the above formula, and as a result, a result of 12% was obtained.
[0044]
In addition, the aqueous solution of CNT-2 was uniform black transparent, and had sufficient hydrophilicity.
[0045]
CNT-3: Plasma-treated carbon nanotube
Carbon nanotubes were produced by the arc discharge method according to the method of J.L. Hutchison et al. (Carbon 39 (2001) 761-770). The anode was a graphite rod with a diameter of 3.2 mm and a catalyst embedded in a hole with a diameter of 3.2 mm and a length of 140 mm, and the cathode was a graphite rod with a diameter of 10 mm and a length of 25 mm. The catalyst was prepared as follows. A mixture of Ni, Co, and Fe powder having a particle size of 2-5 μm and sulfur atoms were pulverized well, and then calcined at 500 ° C. for 1 hour under argon gas. Immediately after being pulverized to μ size with a ball mill, it was mixed with carbon powder. It was tightly packed in a graphite rod with a 3.2mm hole drilled. The composition of the anode was 2.6 at% for Ni, 0.7 at% for Co, 1.45 at% for Fe, and 0.75 at% for S. CNT synthesis was performed at an arc current of 75-80 A at 350 torr with an argon: hydrogen volume ratio of 1: 1. Both electrodes were 2 mm in distance and the voltage difference was 26-28V.
[0046]
0.5 g of the carbon containing the obtained carbon nanotubes was thinly spread on a glass petri dish, and plasma treatment was performed for 5 minutes under the conditions of nitrogen gas, pressure 20 Pa, and POWER300W using PLASMA CHAMBER MODEL PC-101A manufactured by YAMATO CHEMICAL. Once removed, the plasma-treated carbon nanotubes on the petri dish are stirred (turned over, rolled, etc.), spread slightly on the petri dish, and repeated the same plasma treatment for a total of 10 minutes (two times in total) ) Plasma treatment was performed.
[0047]
It is obtained by adding 50 ml of ion exchange water to 10 mg of the carbon material after the plasma treatment, treating it for 1 hour with an ultrasonic cleaning machine (manufactured by Yamato Chemical, BRANSON 3210, transmission frequency 47 KHz, output 130 W), and then allowing it to stand for 48 hours. When the sample was observed, a carbon nanotube dispersion and a black precipitate were confirmed. The dispersion was centrifuged at 12000 rpm (about 17000 (× g)) × 1 hour using a centrifuge (apparatus: KUBOTA KR-20000T, rotor: RA-3 50 ml × 8). As a liquid, a transparent black solution was obtained. The solution portion was collected with a dropper and observed with a high-resolution transmission electron microscope. As a result, many carbon nanotubes with carbon impurities attached were observed. When viewed with a scanning electron microscope of 50,000 times, 80% were fibrous substances and 20% were particulate substances.
[0048]
The supernatant liquid was dried to obtain plasma-treated carbon nanotubes (CNT-3). CNT-3 was dispersed again in water, the amount of acid was measured in the same manner as in CNT-2, and the acid content was determined to be 8.5%.
[0049]
In addition, the hydrophilicity of CNT-3 was sufficient like CNT-2.
(2) Carbon fiber adjustment method
Spinning and firing were performed from a copolymer containing polyacrylonitrile as a main component to obtain a carbon fiber continuous tow having a total filament number of 48,000.
[0050]
The characteristics of this continuous tow are shown below.
[0051]
Mass per unit length 3.3g / m
Specific gravity 1.8 Tensile strength 3.0 GPa
Tensile modulus 225 GPa
Electrical resistance 36.0Ω ・ g / m2
CF-1: Carbon fiber is not attached to the carbon fiber continuous tow, and the carbon fiber is used with a cartridge cutter.Continuation toeCut to 6 mm length to obtain chopped carbon fiber.
[0052]
CF-2: CNT-1 is dispersed in an N-methylpyrrolidone (NMP) solvent to prepare a solution having a concentration of 4% by weight, and this solution is impregnated into the above-described carbon fiber continuous tow with respect to the fiber substrate. 2% by weight, dried at 280 ° C. for 15 minutes, and then carbon fiber using a cartridge cutter.Continuation toeCut to 6 mm length to obtain chopped yarn. The amount of carbon nanotubes deposited was determined by the above method and found to be 1.9% by weight.
[0053]
CF-3: CNT-2 is dispersed in ion-exchanged water to prepare a solution having a concentration of 4% by weight. This solution is impregnated into the above-described carbon fiber continuous tow so as to be 2% by weight with respect to the fiber base material. And then dried at 210 ° C. for 5 minutes, and then the above-mentioned carbon fiber using a cartridge cutter.Continuation toeCut to 6 mm length to obtain chopped yarn. When the adhesion amount of the carbon nanotube was determined by the above method, it was 2.2% by weight.
[0054]
CF-4: CNT-3 is dispersed in ion-exchanged water to prepare a solution having a concentration of 4% by weight. This solution is impregnated into the above-described carbon fiber continuous tow so as to be 2% by weight with respect to the fiber substrate. And then dried with a hot air dryer at 210 ° C. for 5 minutes, and then the above carbon fiber using a cartridge cutter.Continuation toeCut to 6 mm length to obtain chopped yarn. When the adhesion amount of the carbon nanotube was determined by the above method, it was 2.0% by weight.
[0055]
(Examples 1, 2, 3 and Comparative Example 1)
Using a JSW TEX-30α type twin screw extruder, polycarbonate resin (GE Plastics Lexan 141R-111) was charged from the main hopper under conditions of a barrel temperature of 300 ° C. and a rotation speed of 150 rpm. Each chopped carbon fiber sufficiently dried so as to have a moisture content of 0.05% or less was kneaded so that the amount of carbon fiber was 10%, and a gut containing discontinuous carbon fibers was continuously extruded. After cooling this, cut it into 5 mm long with a cutter,StrengthResin pellets were obtained.
[0056]
After drying the above pellets at 80 ° C. in a vacuum for 5 hours or more, the pellets are molded at a barrel temperature of 320 ° C. and a mold temperature of 80 ° C. with a small injection molding machine manufactured by Sumitomo Promat Co., Ltd. We used for evaluation.
[0057]
The results of Examples 1 to 3 and Comparative Example 1 are summarized in Table 1.
[0058]
[Table 1]
From Table 1, it is clear that the molded articles of Examples 1 to 3 exhibit extremely excellent conductivity (surface resistivity) relative to Comparative Example 1. Moreover, what used water for the dispersion solvent of Example 1, 2 has higher electroconductivity than Example 3, and is advantageous also in terms of economical efficiency, workability | operativity, and environmental load.
[0060]
【The invention's effect】
According to the present invention, it is possible to obtain a carbon fiber capable of producing a molded article having extremely excellent conductivity, a method for producing the same, a fiber reinforced resin composition using the carbon fiber, and the like.
[Brief description of the drawings]
FIG. 1 is a schematic view of a multi-walled carbon nanotube.
FIG. 2 is a plan view of a test piece for measuring surface resistivity.
[Explanation of symbols]
1: Conductive paste application range A
2: Conductive paste application range B
3: Conductive paste application range C
4: Conductive paste application range D
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