JP4362276B2 - Fine carbon fiber, its production method and its use - Google Patents

Fine carbon fiber, its production method and its use Download PDF

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JP4362276B2
JP4362276B2 JP2002315420A JP2002315420A JP4362276B2 JP 4362276 B2 JP4362276 B2 JP 4362276B2 JP 2002315420 A JP2002315420 A JP 2002315420A JP 2002315420 A JP2002315420 A JP 2002315420A JP 4362276 B2 JP4362276 B2 JP 4362276B2
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carbon fiber
fine carbon
fiber
mill
fine
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JP2003227039A (en
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竜之 山本
利夫 森田
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Resonac Holdings Corp
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Showa Denko KK
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    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

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  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
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  • Compositions Of Macromolecular Compounds (AREA)
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Description

【0001】
【発明の属する技術分野】
本発明は、樹脂、セラミックスや金属などの母材との接着性に優れ、さらに母材中に均一に分散することができる低アスペクト比(繊維の長さ/繊維の直径)微細炭素繊維およびその製造方法に関する。
【0002】
更に詳しくは、気相法により得られた炭素繊維を湿式により処理を行い、繊維表面に母材との濡れ性を改善することができる官能基で修飾した低アスペクト比微細炭素繊維およびその製造方法に関する。
【0003】
また、本発明は導電性や熱伝導性を改善するために使用するフィラー材として、あるいはFED(フィールドエミッションディスプレー)用の電子放出素材として、更には水素やメタン、もしくは各種気体を吸蔵する媒体として、透明電極、電磁遮蔽、二次電池などに有用な低アスペクト比微細炭素繊維およびその製造方法に関する。
【0004】
また、乾電池、鉛蓄電池、キャパシタや最近のLiイオン二次電池をはじめとする各種二次電池の正極または負極にこの微細な炭素繊維を添加して充放電容量の改善、極板の強度を改善した電池用電極に関する。
【0005】
【従来の技術】
炭素繊維は、その高強度、高弾性率、高導電性等の優れた特性から各種の複合材料に使用されている。近年のエレクトロニクス技術の発展に伴ない、電磁波遮蔽材、静電防止材用の導電性フィラーとして、あるいは、樹脂への静電塗装のためのフィラーや透明導電性樹脂用のフィラーとしての用途が期待されている。また、摺動性、耐磨耗性が高い材料として電気ブラシ、可変抵抗器などヘの応用も期待されている。さらに、高導電性、耐熱伝導性、耐エレクトロマイグレーションを有するため、LSI等のデバイスの配線材料としても注目を浴びている。
【0006】
有機繊維を不活性雰囲気中で熱処理して、炭化することにより製造されている従来のポリアクリロニトリル(PAN)系炭素繊維、ピッチ系炭素繊維、セルロース炭素繊維などは繊維径が5〜10μmと比較的太く、導電性があまりよくないため、主に樹脂やセラミックス等の補強材料として広く用いられてきた。
【0007】
1980年代に遷移金属触媒下で炭化水素等のガスを熱分解する気相法炭素繊維の製造方法の研究がされるようになり、これらの方法により、繊維径が0.1〜0.2μm(100〜200nm)程度で、アスペクト比10〜500程度のものが得られるようになった。例えば、ベンゼン等の有機化合物を原料とし、触媒としてフェロセン等の有機遷移金属化合物をキャリアガスとともに高温の反応炉に導入し、基盤上に生成させる方法(例えば、特許文献1参照。)、浮遊状態で生成させる方法(例えば、特許文献2参照。)、あるいは反応炉壁に成長させる方法(例えば、特許文献3参照。)等が開示されている。
【0008】
さらに、この炭素繊維の炭素は易黒鉛化性であり、2000℃以上で熱処理を行うと、結晶性が非常に発達し、電気伝導性を向上することができるため、この炭素繊維は導電性フィラー材として樹脂用フィラーや二次電池の添加材等に使用されるようになった。
【0009】
これらの炭素繊維は、形状や結晶構造に特徴があり、炭素六角網面の結晶が年輪状に円筒形に巻かれ積層した構造を示し、その中心部には極めて細い中空構造を有する繊維である。また、2000℃以上で熱処理した炭素繊維は、繊維断面が多角化し、その内部に間隙が生成する場合もある。
【0010】
また、これらの炭素繊維は直径が小さいので比較的大きなアスペクト比を有し、通常これら繊維は互いに絡まりあって毛玉のような凝集体を形成している。
【0011】
さらに、気相法により製造された炭素繊維は熱分解炭素層を含むため滑らかな表面を有している。不活性雰囲気中で2000℃以上で熱処理した炭素繊維は結晶性が向上するため、より平滑な表面を有している。また、高温で熱処理しているため、炭素繊維の表面に官能基はほとんど存在しない。
【0012】
上述の炭素繊維を樹脂などの母材と混合した場合、繊維が毛玉のように絡まりあった凝集体を形成しているため、樹脂やセラミックス等の母材中に均一に炭素繊維を分散させることができず、所望の電気的、熱的、機械的特性を得ることができない。
【0013】
また、これらアスペクト比の大きな繊維を樹脂に混ぜた複合体の表面を走査型電子顕微鏡で観察すると、その複合体表面は平滑ではなく、樹脂で覆われてない繊維が毛羽立っているように見える。例えば、これを静電防止材として集積回路(IC)用トレーなどに用いた場合、トレーとの接触箇所で微小な傷の発生や繊維の脱落による異物の付着によりディスクまたはウェハの品質、歩留まりの低下の原因となり得る。
【0014】
また、樹脂などの母材と炭素繊維との濡れ性、親和性が不十分だと密着性が低下し、得られた複合体の機械的強度の低下や炭素繊維の脱落の原因となり、複合体の品質の低下を招いてしまう。
【0015】
そこで、フィラーとして、分散性の向上、複合体表面の平面性を得るために長繊維を粉砕する試みが行われてきた。これまでは、短繊維を得るために炭素繊維をボールミルなど乾式粉砕によって炭素繊維の粉砕を行っていた(例えば、特許文献4参照。)。しかし、ボールミルやロールミルなど衝撃による炭素繊維の粉砕は、互いに絡まり合う炭素繊維を解砕する程度で、粉砕がある程度進行するとミル内部で粉体が凝集したり、固結して、それ以上粉砕による微細化が進行せず、得られる繊維は長さが数μm程度であるという問題があった。
【0016】
【特許文献1】
特開昭60−27700号公報
【特許文献2】
特開昭60−54998号公報
【特許文献3】
特許第2778434号公報
【特許文献4】
特開平1−65144号公報
【0017】
【発明が解決しようとする課題】
本発明の目的は、500nm以下の径と100以下のアスペクト比を有し、摺動性、導電性、熱伝導性等の特性に優れ、また樹脂などの母材との分散性、濡れ性、密着性に優れた微細な炭素繊維を提供することにある。
【0018】
【課題を解決するための手段】
母材との密着性を改善する方法としては、母材との接触面積を大きくするために、径の細い炭素繊維を用いたり、母材樹脂との濡れ性や密着性を改善するために、炭素繊維を酸化処理したり、表面に官能基を導入する方法が行なわれているが、本発明者らは、上記問題点に鑑み鋭意研究を行った結果、アスペクト比が大きく、互いに絡まりあった微細炭素繊維を湿式粉砕することにより、短時間で凝集体が破壊され、所望のアスペクト比の微細炭素繊維が得られることを見出した。また、粉砕後の微細炭素繊維表面、破断面(破断部分)に官能基が導入されていることを見出し、これが樹脂などの母材との密着性を改善することができることを確認した。さらに、微細炭素繊維をスラリー化する際に用いる界面活性剤の種類や有機溶剤の種類によって表面官能基の分布量、種類を制御できることも見出した。
【0019】
本発明によれば、樹脂、セラミックスまたは金属などの母材中に均一に分散し、複合体表面平滑性を改善することができ、短繊維と母材との密着性に優れた表面官能基を有する、低アスペクト比微細炭素を、粉砕操作で容易に製造することができる。
【0020】
すなわち、本発明は以下の微細炭素繊維、その製造方法及びその用途に関する。
1.内部に中空構造を有し、多層構造からなる気相法炭素繊維であって、外径が2〜500nm、アスペクト比が1〜100であり、繊維の中空構造に沿った繊維表面に破断面を有する微細炭素繊維。
2.破断面が微細な凹みを有している前記1に記載の微細炭素繊維。
3.微細な凹みが、繊維内部の中空構造と連通している前記2に記載の微細炭素繊維。
4.繊維表面に官能基を有している前記1乃至3のいずれかひとつに記載の微細炭素繊維。
5.官能基が、水酸基、フェノール性水酸基、カルボキシル基、アミノ基、キノン基及びラクトン基からなる群から選択される少なくともひとつである前記4に記載の微細炭素繊維。
6.中空構造が、一部閉じている前記1乃至5のいずれかひとつに記載の微細炭素繊維。
7.X線回折法による(002)面の平均面間隔d002が0.342nm以下の炭素からなる前記1乃至6のいずれかひとつに記載の微細炭素繊維。
8.ホウ素またはホウ素化合物を含有する前記1乃至6のいずれかひとつに記載の微細炭素繊維。
9.ホウ素を炭素繊維の結晶内に0.01〜5質量%含有する前記8に記載の微細炭素繊維。
10.炭素繊維全量に対して、前記1乃至9のいずれかひとつに記載の微細炭素繊維を5〜80質量%含有する微細炭素繊維混合物。
11.内部に中空構造を有し、多層構造からなり、外径が2〜500nm、アスペクト比が10以上の分岐状気相法炭素繊維を含む気相法炭素繊維を水及び/または有機溶媒の存在下で湿式粉砕する工程を有することを特徴とする微細炭素繊維の製造方法。
12.粉砕工程が、界面活性剤の存在下で行なわれる前記11に記載の微細炭素繊維の製造方法。
13.前記気相法炭素繊維に、所望によりホウ素またはホウ素化合物を加え、2000〜3500℃で熱処理した後、湿式粉砕を行なう前記11に記載の微細炭素繊維の製造方法。
14.湿式粉砕された微細炭素繊維に、所望によりホウ素またはホウ素化合物を加え、2000〜3500℃で熱処理する工程を含む前記11に記載の微細炭素繊維の製造方法。
15.前記11乃至14のいずれかひとつに記載の方法によって得られた微細炭素繊維。
16.前記1乃至9及び15のいずれかひとつに記載の微細炭素繊維を含む微細炭素繊維組成物。
17.樹脂を含む前記16に記載の微細炭素繊維組成物。
18.前記1乃至9及び15のいずれかひとつに記載の微細炭素繊維を含む導電性材料。
19.前記1乃至9及び15のいずれかひとつに記載の微細炭素繊維を電極材料に含む二次電池。
20.前記1乃至9及び15のいずれかひとつに記載の微細炭素繊維を含むガス吸蔵材料。
【0021】
本発明の低アスペクト比微細炭素繊維は、樹脂との密着性、親和性及び分散性の優れた炭素繊維を得るために、気相法で製造した微細炭素繊維の粉砕条件の検討を進める中で見出された従来知られていない微細な凹みと表面官能基を有する低アスペクト比炭素繊維である。
【0022】
本発明の低アスペクト比微細炭素繊維は透明電極用のフィラー、水素、メタン等のガス貯蔵用材料として用いることが好ましいが、これに限定されるものではなく、電磁遮蔽、二次電池などの導電付与材や熱伝導性フィラーとしても用いることができる。また、OPCドラム、プリント回路基板などの表面に導電性を付与させる材料としても用いることができる。
【0023】
【発明の実施の形態】
以下、本発明の微細炭素繊維について説明する。
【0024】
本発明の微細炭素繊維は、気相法で製造された微細炭素繊維であって、繊維表面の少なくとも一部に破断面を有し、内部に中空構造を持つ多層構造(年輪構造)を有する外径2〜500nm、好ましくは2〜200nm、アスペクト比1〜100、好ましくは3〜20の微細炭素繊維である。破断面は、粉砕などによって生成した部分の表面を示し、表面化学構造(主に表面に存在する官能基)が反応性に富んでいる基底面内の欠損部のエッジ炭素原子、結晶子の境界部のエッジ炭素原子などが現れている。
【0025】
本発明の微細炭素繊維は、気相法で製造された分岐状気相法炭素繊維を含む炭素繊維を例えば水及び/または有機溶剤中に分散させた後、必要に応じて界面活性剤を添加して湿式により粉砕することで得られる。
【0026】
粉砕後、乾燥して得られた微細炭素繊維は、その繊維表面に破断面あるいは破断面及び微細な凹みを有し、水酸基、フェノール性水酸基、カルボキシル基、キノン基、ラクトン基などの酸素を含む官能基、アミノ基、アミド基が導入されている。これらの官能基は酸素または窒素を持っているので樹脂などとの親和性が向上する。
【0027】
本発明で使用する分岐状気相法炭素繊維は中空構造を有し、分岐部分の中空構造が連通しているが、その中空部分が一部閉じているものも混在している。分岐部分を含めて繊維全体が互いに連通した中空構造を有する炭素繊維の場合、これを粉砕することで、分岐部分の分岐部付近で破断が起きる。その結果、微細な凹みが生じて中空構造の連通箇所が繊維表面に現われ、樹脂などとの濡れ性、接着性を改善することができる。
【0028】
また、混在する中空構造の一部が閉じた分岐状気相法炭素繊維炭素を粉砕することにより、粉砕後の繊維の表面積が大きくなり樹脂との濡れ性が向上する。また、粉砕により折れた分岐部の表面には微小の凹凸ができて樹脂との密着性が改善する。
【0029】
本発明の微細炭素繊維は、湿式粉砕の際に使用する界面活性剤の種類、有機溶剤の種類、乾燥温度(官能基の脱離温度)を変えることにより、炭素繊維表面を修飾する官能基の分布量、種類を変えることができ、樹脂との濡れ性、接着性を改善することができる。
【0030】
以下に本発明の微細炭素繊維を製造するために好適な方法について説明する。
【0031】
本発明の微細炭素繊維は、内部に中空構造を有し、多層構造からなり、外径が2〜500nm、アスペクト比が10以上の分岐状気相法炭素繊維を含む気相法炭素繊維を水及び/または有機溶媒の存在下で湿式粉砕することにより製造することができる。
【0032】
用いる気相法炭素繊維は、一般的には、有機遷移金属化合物を用いて有機化合物を熱分解することにより得ることができる。
【0033】
炭素繊維の原料となる有機化合物は、トルエン、ベンゼン、ナフタレン、エチレン、アセチレン、エタン、天然ガス、一酸化炭素等のガス及びそれらの混合物も可能である。中でもトルエン、ベンゼン等の芳香族炭化水素が好ましい。
【0034】
有機遷移金属化合物は、触媒となる遷移金属を含むものである。遷移金属としては、周期律表第IVa 、Va、VIa 、VIIa、VIII族(第4〜10族)の金属を含む有機化合物である。中でもフェロセン、ニッケロセン等の化合物が好ましい。
【0035】
上記有機化合物と有機遷移金属化合物を気化して、予め500〜1300℃に加熱した水素などの還元性ガスと混合し、800〜1300℃に加熱した反応炉へ供給し反応させて、炭素繊維を得る。
【0036】
粉砕に際しては、熱分解により得られる原料微細炭素繊維の表面に付着したタールなどの有機物を除くために予め900〜1300℃で熱処理することが好ましい。
【0037】
湿式粉砕するために、界面活性剤を含有する水及び/または有機溶剤に微細炭素繊維を分散させる。微細炭素繊維の濃度は1〜30質量%、好ましくは3〜20質量%、より好ましくは5〜15質量%がよい。1質量%以下では粉砕効率が悪く、30質量%以上では溶媒に炭素繊維を分散させることが難しく、またスラリーの粘度が高くなり流動性が悪く、粉砕効率が低下する。
【0038】
界面活性剤は、陰イオン性界面活性剤、陽イオン性界面活性剤、非イオン性界面活性剤、両性界面活性剤の炭素材料に用いられる界面活性剤を適用することができるが、非イオン性界面活性剤、陰イオン性界面活性剤、陽イオン性界面活性剤が好ましい。例えば、トリトン(Triton;商品名)などのポリエチレングリコールアルキルフェニルエーテル、ポリエチレングリコールアルキルフェニルエーテルの硫酸エステル塩、塩化ベンザルコニウムを挙げられる。界面活性剤の添加量は炭素繊維に対して0.01〜50質量%、好ましくは0.1〜30質量%がよい。
【0039】
有機溶媒としては、メタノール、エタノール、n−ブタノール、n−プロパノール、n−ヘキサノールなどのアルコール類、n−デカン、n−ペンタン、n−ヘキサン、n−ヘプタンなどの鎖状炭化水素、ベンゼン、トルエン、キシレンなどの芳香族炭化水素、アセトン、メチルエチルケトンなどのケトン類、ジエチルエーテル、ジブチルエーテルなどのエーテル類、酢酸エチル、酢酸ブチルなどのエステル類を用いることができる。
【0040】
粉砕機としては、剪断、圧縮、摩擦力を利用した回転円筒式ミル、振動ボールミル、遊星ボールミル、媒体撹拌式ミルもしくはコロイドミルなど公知の装置を用いることができる。
【0041】
粉砕した後の炭素繊維を含む組成液は、ろ過洗浄操作により溶媒や界面活性剤を除いた後、風熱乾燥、真空乾燥、凍結乾燥などにより繊維に付着した溶媒を除去する。溶媒を除去する処理温度を調整することにより、官能基の脱離温度差を利用して繊維表面上の官能基の種類を制御することができる。
【0042】
また、塩酸、硝酸や硫酸等による処理や水蒸気、炭酸ガスあるいはKOH、NaOHなどのアルカリによる賦活処理を行って、導入する表面官能基の種類や分布量を調整することもできる。
【0043】
本発明の粉砕処理により得られる炭素繊維は、外径が2〜500nm、アスペクト比が1〜100の微細炭素繊維であり、その5〜80質量%が繊維の中空構造に沿った繊維表面に破断面を有する微細炭素繊維となっている。
【0044】
このようにして得られた本発明の微細炭素繊維は、その繊維長さの標準偏差(μm)が2.0以下、好ましくは1.0以下、さらに好ましくは0.5以下であり、分布が狭くバラツキが少ないので、導電性フィラー、熱伝導性フィラーとして用いたときその複合材料の品質を良好に保つことができる。
【0045】
微細炭素繊維の導電性を向上させるために、原料の気相法炭素繊維あるいは粉砕・乾燥後の微細炭素繊維を不活性雰囲気下で2000〜3500℃の熱処理して黒鉛化度を上げることができる。さらに導電性を一層向上させるために、微細炭素繊維に炭化ホウ素(B4C)、酸化ホウ素(B23)、元素状ホウ素、ホウ酸(H3BO3)、ホウ酸塩等のホウ素化合物と混合して不活性雰囲気下で2000〜3500℃で熱処理を行なってもよい。
【0046】
なお、黒鉛化した炭素繊維は結晶性が発達し機械的強度が向上するため、粉砕前に気相法炭素繊維を黒鉛化処理すると所望の繊維長さに粉砕するのに多くのエネルギー及び時間を要する。
【0047】
ホウ素化合物の添加量は、用いるホウ素化合物の化学的特性、物理的特性に依存するために限定されないが、例えば炭化ホウ素(B4C)を使用した場合には、炭素繊維に対して0.05〜10質量%、好ましくは0.1〜5質量%の範囲がよい。本ホウ素化合物との熱処理により、微細炭素繊維の導電性が向上し、炭素の結晶性(平均面間隔d002)が向上する。具体的には、ホウ素またはホウ素化合物を添加しなかった場合、X線回折法による(002)面の平均面間隔d002は0.342nm以下であるが、添加した場合には平均面間隔はd002は0.338nm以下とできる。
【0048】
使用する熱処理炉は2000℃以上、好ましくは2300℃以上の目的とする温度が保持できる炉であればよく、通常の、アチソン炉、抵抗炉、高周波炉他の何れの装置でもよい。また、場合によっては、粉体または成形体に直接通電して加熱する方法も採用できる。
【0049】
熱処理の雰囲気は非酸化性の雰囲気、好ましくはアルゴン、ヘリウム、ネオン等の1種もしくは2種以上の希ガス雰囲気がよい。熱処理の時間は、生産性の面からは出来るだけ、短い方が好ましい。長時間加熱していると、燒結し固まってくるので、製品収率も悪化する。熱処理温度は成形体等の中心部の温度が目標温度に達した後、1時間以下その温度に保持すれば十分である。
【0050】
繊維は熱処理すると一部分が燒結し、通常品と同様にブロック状になっている。従って、そのままでは電極等に添加したり、電子放出能材に使用することは出来ないので成形体を解砕してフィラー材として適する形態にしなければならない。
【0051】
そのため、このブロックを、解砕、粉砕、分級してフィラー材として適するように処理をすると同時に、非繊維物を分離する。粉砕が不十分だと電極材との混合がうまくいかず、添加効果が出ない。
【0052】
フィラーとして望ましい形態にするためには、熱処理後のブロック状のものを先ず、2mm以下の大きさに解砕し、更に粉砕機で粉砕する。解砕機としては通常使用されるアイスクラッシャーやロートプレックス等の解砕機が使用できる。
【0053】
粉砕機としては、衝撃型の粉砕機のパルペライザーやボールミル、自生粉砕機、また、ミクロジェット等の粉砕機が使用出来る。非繊維物を分離する分級は気流分級等で行うことが出来る。
【0054】
本発明の微細炭素繊維は、電池用電極に添加すると充放電容量や電極板強度等の電池の性能を向上することができる。電池としては、リチウム電池、鉛蓄電池、ポリマー電池、乾電池等の電極板の導電性を向上したり、インターカレーション能力を必要とする電池を挙げることができる。
【0055】
本発明の微細炭素繊維は、導電性が良いので、これらの電池の導電性を高めることができるばかりでなく、リチウム電池では負極用炭素材料としてのインターカレーション能力が大きいので充放電容量を増加することができる。
【0056】
電極中への微細炭素繊維の添加量は、上記製法により製造された炭素繊維として0.1〜20質量%の範囲が好ましい。添加量が20質量%より大きくなると電極中の炭素の充填密度が小さくなり、電池にしたときの充放電容量が低下する。また、0.1質量%より少なくなると添加効果が小さい。
【0057】
本発明の微細炭素繊維を添加して電極とするには、例えばリチウム電池の負極は、黒鉛粉末やメソフューズカーボンマイクロビーズ(MCMB)等が用いられるが、これに微細炭素繊維及びバインダーを添加し、充分に混練して繊維ができるだけ均一に分散するようにする。
【0058】
本発明の微細炭素繊維は、そのままの状態で、あるいは他の炭素繊維と混合した炭素繊維混合物の状態で、あるいは樹脂、セラミックスや金属などの母材と混合した組成物の状態で、各種の用途に供することができる。母材として樹脂を用いる用途には、本発明の微細炭素繊維を樹脂混合物に対して5〜50質量%含有するように調製する。樹脂としては、例えばフェノール樹脂、エポキシ樹脂、ポリウレタン樹脂、ポリイミド樹脂、不飽和ポリエステル樹脂などの熱硬化性樹脂やポリアミド樹脂、ポリウレタン樹脂、塩化ビニル樹脂、アクリル樹脂、セルロース樹脂などの熱可塑性樹脂、あるいはシリコーンゴム、ポリウレタンゴム、スチレンブタジエンゴム、天然ゴムなどのゴムを挙げることができる。
【0059】
【実施例】
以下、本発明について代表的な例を示し、さらに具体的に説明する。なお、これらは説明のための単なる例示であって、本発明はこれらに何等制限されるものでない。
【0060】
なお、以下の例において、分岐状炭素繊維含有量(質量%)は、透過電子顕微鏡(TEM)による炭素繊維の断面写真において、炭素繊維の断面合計に対する分岐状炭素繊維の断面積の割合を求め、比重を同じとして質量%とした。
【0061】
ホウ素含有量(質量%)は、炭素繊維の粉末試料に炭酸カルシウムを加え、酸素気流中で灰化した後、この灰に炭酸カルシウムを加え、加熱して溶融させ、溶融物を水に溶解し、水溶液をICP発光分析法(Inductively coupled plasma atomic emission spectroscopy method)により定量分析した。
【0062】
実施例1
平均直径が25nm、平均長さが10,000nm、アスペクト比が400で分岐状気相法炭素繊維が30質量%含まれる気相法炭素繊維2gとエタノール50gを内容積300cm3のメノウ製遊星ミルに投入し、直径1.0mmのジルコニア製ビーズを200g入れて4時間粉砕処理を行った。処理後、150℃で3時間乾燥を行った。その後、この気相法炭素繊維を走査型電子顕微鏡で観察し、繊維長さを測定した。また、同試料の赤外線分析を行った。
【0063】
結果として、この粉砕により平均直径が25nm、平均長さ250nm、アスペクト比が10、d002が0.340nmである微細炭素繊維を得ることができた。このとき粉砕した炭素繊維を走査型電子顕微鏡により観察、写真を撮影した後、炭素繊維の長さをノギスで100本分測定し、長さ分布を求めた。その結果を図1に示す。このときの標準偏差は0.10μm(100nm)であった。赤外線分析の結果、水酸基の伸縮振動3600cm-1による光の吸収が観察された。
【0064】
実施例2
平均直径が33nm、平均長さが16,500nm、アスペクト比が500で分岐状気相法炭素繊維が30質量%含まれた、ホウ素化合物を用いて黒鉛化処理を行った気相法炭素繊維2gとエタノール50gを内容積300cm3のメノウ製遊星ミルに投入し、直径1.0mmのジルコニア製ビーズを200g入れて4時間粉砕処理を行った。処理後、150℃で3時間乾燥を行った。その後、この気相法炭素繊維を走査型電子顕微鏡で観察し、繊維長さを測定した。また、同試料の赤外線分析を行った。なお、本試料のホウ素含有量は0.7質量%であった。
【0065】
結果として、この粉砕により平均直径が33nm、平均長さ420nm、アスペクト比が13、d002が0.337nmである微細炭素繊維を得ることができた。このとき粉砕した炭素繊維を走査型電子顕微鏡により観察、写真を撮影した後、炭素繊維の長さをノギスで50本分測定し、長さ分布を求めた。その結果を図2に示す。このときの標準偏差は0.22μm(220nm)であった。また、赤外線分析の結果、水酸基の伸縮振動3600cm-1による光の吸収が観察された。
【0066】
比較例1
平均直径が33nm、平均長さが16,500nm、アスペクト比が500で分岐状気相法炭素繊維30質量%含まれた黒鉛化処理を行った気相法炭素繊維90gを内容積2000cm3のアルミナ製ボールミルに投入し、回転数75rpmで18時間粉砕処理を行った。なお、このとき前記ボールミルには、繊維の粉砕のため直径30mmのアルミナ製ボールを30個入れておいた。処理後、この気相法炭素繊維を走査型電子顕微鏡を用いて観察し、繊維長さを測定した。また、同試料の赤外線分析を行った。
【0067】
結果として、平均直径が33nm、平均長さ4,980nm、アスペクト比が150までしか粉砕することができなかった。粉砕した炭素繊維を走査型電子顕微鏡により観察、写真を撮影した後、炭素繊維の長さをノギスで50本分測定し、長さ分布を求めた。このときの繊維長さ分布を図3に示す。標準偏差は3.07μm(3070nm)であった。赤外線分析の結果、ほとんど水酸基の伸縮振動による光の吸収は見られなかった。
【0068】
実施例3
実施例1の湿式粉砕した焼成微細炭素繊維、実施例2の湿式粉砕した黒鉛化微細炭素繊維、比較例1の乾式粉砕した黒鉛化炭素繊維をそれぞれフェーノール樹脂に40質量%混合したときの粘度(25℃;センチポアズ(cP)またはmPa・s)を粘度計でJIS K 7117に準拠して測定した。その結果を表1に示す。
【0069】
【表1】

Figure 0004362276
【0070】
湿式粉砕した微細炭素繊維を混合した樹脂(実施例1、2)は、乾式粉砕した微細炭素繊維を混合した樹脂(比較例1)に比べ、コンパウンドの粘度は1/3以下に低下し、取り扱い性の改善が認められた。
【0071】
【発明の効果】
(1)本発明の炭素繊維は、樹脂などの母材と混合する際の加工性に優れ、樹脂中によく分散し、得られる複合体の表面平滑性も改善される。
(2)本発明の炭素繊維は、微小な凹みや中空構造を有し水素やメタンとの付加反応性が高いため、ガス貯蔵に適している。
(3)本発明の方法で得られる微細炭素繊維は、その繊維長さの分布が狭く、バラツキが少ないので、導電性フィラー、熱伝導性フィラーとして用いたときその複合材料の品質を良好に保つことができる。
【0072】
【図面の簡単な説明】
【図1】 実施例1の微細炭素繊維の繊維長さ分布図である。
【図2】 実施例2の微細炭素繊維の繊維長さ分布図である。
【図3】 比較例1の微細炭素繊維の繊維長さ分布図である。[0001]
BACKGROUND OF THE INVENTION
The present invention is excellent in adhesion to a base material such as resin, ceramics or metal, and further has a low aspect ratio (fiber length / fiber diameter) fine carbon fiber that can be uniformly dispersed in the base material and its It relates to a manufacturing method.
[0002]
More specifically, the low-aspect-ratio fine carbon fiber modified with a functional group capable of improving the wettability with a base material on the fiber surface by wet-treating the carbon fiber obtained by the vapor phase method and a method for producing the same About.
[0003]
In addition, the present invention is used as a filler material used to improve electrical conductivity and thermal conductivity, as an electron emission material for FED (field emission display), and as a medium for storing hydrogen, methane, or various gases. The present invention relates to a low aspect ratio fine carbon fiber useful for transparent electrodes, electromagnetic shielding, secondary batteries, and the like, and a method for producing the same.
[0004]
In addition, this fine carbon fiber is added to the positive electrode or negative electrode of various secondary batteries including dry batteries, lead-acid batteries, capacitors and recent Li-ion secondary batteries to improve the charge / discharge capacity and the strength of the electrode plate. The present invention relates to a battery electrode.
[0005]
[Prior art]
Carbon fiber is used in various composite materials because of its excellent properties such as high strength, high elastic modulus, and high conductivity. With the development of electronics technology in recent years, it is expected to be used as a conductive filler for electromagnetic shielding materials and antistatic materials, or as a filler for electrostatic coating on resins and fillers for transparent conductive resins. Has been. In addition, application to electric brushes, variable resistors and the like is also expected as a material having high slidability and wear resistance. Furthermore, since it has high conductivity, heat resistance, and electromigration resistance, it has attracted attention as a wiring material for devices such as LSI.
[0006]
Conventional polyacrylonitrile (PAN) -based carbon fibers, pitch-based carbon fibers, and cellulose carbon fibers that are manufactured by heat-treating and carbonizing organic fibers in an inert atmosphere have a fiber diameter of 5 to 10 μm. Since it is thick and has poor conductivity, it has been widely used mainly as a reinforcing material for resins and ceramics.
[0007]
In the 1980's, research on methods for producing vapor-grown carbon fibers in which gases such as hydrocarbons are pyrolyzed under a transition metal catalyst has been conducted. 100 to 200 nm) and an aspect ratio of about 10 to 500 can be obtained. For example, an organic compound such as benzene is used as a raw material, and an organic transition metal compound such as ferrocene as a catalyst is introduced into a high-temperature reactor together with a carrier gas, and generated on a substrate (for example, see Patent Document 1), floating state. (For example, refer to Patent Document 2) or a method for growing on a reaction furnace wall (for example, refer to Patent Document 3).
[0008]
Furthermore, the carbon of this carbon fiber is graphitizable, and when heat-treated at 2000 ° C. or higher, the crystallinity is greatly developed and the electrical conductivity can be improved. As a material, it has come to be used for fillers for resins, additives for secondary batteries, and the like.
[0009]
These carbon fibers are characterized by their shape and crystal structure, and show a structure in which crystals of carbon hexagonal mesh surfaces are wound in a cylindrical shape in an annual ring shape, and have a very thin hollow structure at the center. . Moreover, the carbon fiber heat-processed above 2000 degreeC may diversify a fiber cross section, and a gap | interval may produce | generate in the inside.
[0010]
Moreover, since these carbon fibers have a small diameter, they have a relatively large aspect ratio. Usually, these fibers are entangled with each other to form a flocculent aggregate.
[0011]
Furthermore, since the carbon fiber manufactured by the vapor phase method includes a pyrolytic carbon layer, it has a smooth surface. Since the carbon fiber heat-treated in an inert atmosphere at 2000 ° C. or higher has improved crystallinity, it has a smoother surface. Moreover, since it heat-processes at high temperature, there is almost no functional group on the surface of carbon fiber.
[0012]
When the above-mentioned carbon fiber is mixed with a base material such as a resin, an aggregate in which the fibers are entangled like a pill is formed, so that the carbon fiber is uniformly dispersed in the base material such as resin or ceramics. And the desired electrical, thermal, and mechanical properties cannot be obtained.
[0013]
Further, when the surface of the composite obtained by mixing these fibers having a large aspect ratio with the resin is observed with a scanning electron microscope, the surface of the composite is not smooth, and the fibers not covered with the resin appear to be fluffy. For example, when this is used as an antistatic material in an integrated circuit (IC) tray or the like, the quality of the disk or wafer is reduced due to the occurrence of minute scratches at the contact point with the tray or the attachment of foreign matter due to fiber dropping. It can cause a decline.
[0014]
In addition, if the wettability and affinity between the base material such as resin and the carbon fiber are insufficient, the adhesion will be reduced, resulting in a decrease in the mechanical strength of the resulting composite and the loss of the carbon fiber. The quality of the product will be degraded.
[0015]
Therefore, attempts have been made to pulverize long fibers as fillers in order to improve dispersibility and to obtain the planarity of the composite surface. In the past, carbon fibers were pulverized by dry pulverization such as a ball mill in order to obtain short fibers (see, for example, Patent Document 4). However, the pulverization of carbon fibers by impact such as ball mill and roll mill is to the extent that the entangled carbon fibers are crushed. There was a problem that miniaturization did not proceed and the resulting fiber had a length of about several μm.
[0016]
[Patent Document 1]
JP-A-60-27700
[Patent Document 2]
JP-A-60-54998
[Patent Document 3]
Japanese Patent No. 2778434
[Patent Document 4]
JP-A-1-65144
[0017]
[Problems to be solved by the invention]
An object of the present invention has a diameter of 500 nm or less and an aspect ratio of 100 or less, and is excellent in properties such as slidability, conductivity, thermal conductivity, and dispersibility with a base material such as a resin, wettability, The object is to provide fine carbon fibers having excellent adhesion.
[0018]
[Means for Solving the Problems]
As a method of improving the adhesion with the base material, in order to increase the contact area with the base material, to use a carbon fiber with a small diameter, to improve the wettability and adhesion with the base material resin, Although methods for oxidizing carbon fibers and introducing functional groups on the surface have been carried out, the present inventors conducted extensive research in view of the above problems, and as a result, the aspect ratio was large and they were entangled with each other. It has been found that by finely grinding fine carbon fibers, aggregates are destroyed in a short time, and fine carbon fibers having a desired aspect ratio can be obtained. Moreover, it discovered that the functional group was introduce | transduced into the fine carbon fiber surface after a grinding | pulverization, and a torn surface (breaking part), and confirmed that this could improve adhesiveness with base materials, such as resin. Furthermore, the present inventors have also found that the distribution amount and type of surface functional groups can be controlled by the type of surfactant used when slurrying fine carbon fibers and the type of organic solvent.
[0019]
According to the present invention, a surface functional group that is uniformly dispersed in a base material such as resin, ceramics, or metal, can improve the surface smoothness of the composite, and has excellent adhesion between short fibers and the base material. The low-aspect-ratio fine carbon can be easily produced by a pulverization operation.
[0020]
That is, the present invention relates to the following fine carbon fibers, a production method thereof and uses thereof.
1. Vapor-grown carbon fiber having a hollow structure inside and having a multilayer structure, an outer diameter of 2 to 500 nm, an aspect ratio of 1 to 100, and a fracture surface on the fiber surface along the fiber hollow structure Having fine carbon fiber.
2. 2. The fine carbon fiber according to 1 above, wherein the fracture surface has a fine dent.
3. 3. The fine carbon fiber according to 2 above, wherein the fine recess communicates with the hollow structure inside the fiber.
4). 4. The fine carbon fiber according to any one of 1 to 3, which has a functional group on the fiber surface.
5. 5. The fine carbon fiber according to 4 above, wherein the functional group is at least one selected from the group consisting of a hydroxyl group, a phenolic hydroxyl group, a carboxyl group, an amino group, a quinone group, and a lactone group.
6). 6. The fine carbon fiber according to any one of 1 to 5, wherein a hollow structure is partially closed.
7). Average spacing d of (002) planes by X-ray diffraction method 002 7. The fine carbon fiber according to any one of 1 to 6 above, wherein the carbon fiber is 0.342 nm or less.
8). The fine carbon fiber according to any one of 1 to 6 above, containing boron or a boron compound.
9. 9. The fine carbon fiber according to 8, wherein boron is contained in an amount of 0.01 to 5% by mass in the crystal of the carbon fiber.
10. The fine carbon fiber mixture which contains 5-80 mass% of fine carbon fibers as described in any one of said 1 thru | or 9 with respect to carbon fiber whole quantity.
11. Vapor grown carbon fiber including branched vapor grown carbon fiber having a hollow structure inside, having a multilayer structure, outer diameter of 2 to 500 nm and aspect ratio of 10 or more in the presence of water and / or organic solvent A method for producing fine carbon fibers, characterized by comprising a step of wet pulverizing with a glass.
12 12. The method for producing fine carbon fibers according to 11 above, wherein the pulverizing step is performed in the presence of a surfactant.
13. 12. The method for producing fine carbon fiber according to 11 above, wherein boron or a boron compound is added to the vapor grown carbon fiber as desired, heat treated at 2000 to 3500 ° C., and then wet pulverized.
14 12. The method for producing fine carbon fiber according to 11 above, comprising a step of adding boron or a boron compound to the finely pulverized fine carbon fiber as required, and heat-treating at 2000 to 3500 ° C.
15. 15. Fine carbon fiber obtained by the method according to any one of 11 to 14 above.
16. A fine carbon fiber composition comprising the fine carbon fiber according to any one of 1 to 9 and 15.
17. 17. The fine carbon fiber composition as described in 16 above, which contains a resin.
18. A conductive material comprising the fine carbon fiber according to any one of 1 to 9 and 15.
19. A secondary battery comprising the fine carbon fiber according to any one of 1 to 9 and 15 as an electrode material.
20. A gas storage material comprising the fine carbon fiber according to any one of 1 to 9 and 15.
[0021]
The low aspect ratio fine carbon fiber of the present invention is in the process of studying the pulverization conditions of fine carbon fiber produced by a gas phase method in order to obtain carbon fiber excellent in adhesion, affinity and dispersibility with resin. It is a low-aspect ratio carbon fiber having a fine dent and a surface functional group that has not been known so far.
[0022]
The low aspect ratio fine carbon fiber of the present invention is preferably used as a gas storage material such as a filler for transparent electrodes, hydrogen, methane, etc., but is not limited thereto, and is not limited to such materials as electromagnetic shielding and secondary batteries. It can also be used as an imparting material or a thermally conductive filler. It can also be used as a material for imparting conductivity to the surface of an OPC drum, a printed circuit board or the like.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the fine carbon fiber of the present invention will be described.
[0024]
The fine carbon fiber of the present invention is a fine carbon fiber produced by a gas phase method, and has an outer surface having a multilayer structure (annular ring structure) having a fracture surface at least part of the fiber surface and a hollow structure inside. It is a fine carbon fiber having a diameter of 2 to 500 nm, preferably 2 to 200 nm, and an aspect ratio of 1 to 100, preferably 3 to 20. The fracture surface shows the surface of the part generated by crushing, etc., and the edge carbon atoms and crystallite boundaries in the defect in the basal plane where the surface chemical structure (mainly functional groups present on the surface) is highly reactive Some edge carbon atoms appear.
[0025]
The fine carbon fiber of the present invention is obtained by dispersing a carbon fiber containing a branched vapor-grown carbon fiber produced by a vapor-phase method in, for example, water and / or an organic solvent, and then adding a surfactant as necessary. And obtained by pulverization by a wet method.
[0026]
The fine carbon fiber obtained by pulverization and drying has a fracture surface or fracture surface and fine dents on the fiber surface, and contains oxygen such as hydroxyl group, phenolic hydroxyl group, carboxyl group, quinone group, and lactone group. Functional groups, amino groups, and amide groups are introduced. Since these functional groups have oxygen or nitrogen, the affinity with a resin or the like is improved.
[0027]
The branched vapor grown carbon fiber used in the present invention has a hollow structure in which the hollow structure of the branched portion is communicated, but some of the hollow portions are partially closed. In the case of a carbon fiber having a hollow structure in which the entire fiber including the branch part is in communication with each other, the pulverization causes breakage in the vicinity of the branch part of the branch part. As a result, a fine dent is generated, and a communicating portion of the hollow structure appears on the fiber surface, so that wettability with resin or the like and adhesion can be improved.
[0028]
In addition, the surface area of the fiber after pulverization can be reduced by pulverizing the branched vapor grown carbon fiber carbon in which a part of the mixed hollow structure is closed. big Improved wettability with the resin. In addition, minute irregularities are formed on the surface of the branch portion broken by pulverization, and the adhesion to the resin is improved.
[0029]
The fine carbon fiber of the present invention has a functional group that modifies the surface of the carbon fiber by changing the type of surfactant used during wet grinding, the type of organic solvent, and the drying temperature (functional group desorption temperature). The distribution amount and type can be changed, and the wettability and adhesiveness with the resin can be improved.
[0030]
A method suitable for producing the fine carbon fiber of the present invention will be described below.
[0031]
The fine carbon fiber of the present invention has a hollow structure inside, has a multi-layer structure, has an outer diameter of 2 to 500 nm, and includes a branched vapor grown carbon fiber having an aspect ratio of 10 or more. And / or wet milling in the presence of an organic solvent.
[0032]
The vapor grown carbon fiber to be used can be generally obtained by thermally decomposing an organic compound using an organic transition metal compound.
[0033]
The organic compound used as the raw material of the carbon fiber can be a gas such as toluene, benzene, naphthalene, ethylene, acetylene, ethane, natural gas, carbon monoxide, or a mixture thereof. Of these, aromatic hydrocarbons such as toluene and benzene are preferred.
[0034]
The organic transition metal compound contains a transition metal serving as a catalyst. The transition metal is an organic compound containing a metal of groups IVa, Va, VIa, VIIa, and VIII (groups 4 to 10) of the periodic table. Of these, compounds such as ferrocene and nickelocene are preferred.
[0035]
The organic compound and the organic transition metal compound are vaporized, mixed with a reducing gas such as hydrogen previously heated to 500 to 1300 ° C., supplied to a reaction furnace heated to 800 to 1300 ° C., and reacted to produce carbon fiber. obtain.
[0036]
In pulverization, it is preferable to perform heat treatment at 900 to 1300 ° C. in advance in order to remove organic substances such as tar adhering to the surface of the raw material fine carbon fiber obtained by thermal decomposition.
[0037]
In order to wet-grind, fine carbon fibers are dispersed in water and / or an organic solvent containing a surfactant. The concentration of the fine carbon fiber is 1 to 30% by mass, preferably 3 to 20% by mass, and more preferably 5 to 15% by mass. If it is 1% by mass or less, the pulverization efficiency is poor, and if it is 30% by mass or more, it is difficult to disperse the carbon fibers in the solvent.
[0038]
As the surfactant, an anionic surfactant, a cationic surfactant, a nonionic surfactant, and a surfactant used for a carbon material of an amphoteric surfactant can be applied. Surfactants, anionic surfactants, and cationic surfactants are preferred. Examples thereof include polyethylene glycol alkyl phenyl ether such as Triton (trade name), sulfate ester salt of polyethylene glycol alkyl phenyl ether, and benzalkonium chloride. The addition amount of the surfactant is 0.01 to 50% by mass, preferably 0.1 to 30% by mass with respect to the carbon fiber.
[0039]
Examples of organic solvents include alcohols such as methanol, ethanol, n-butanol, n-propanol, and n-hexanol, chain hydrocarbons such as n-decane, n-pentane, n-hexane, and n-heptane, benzene, and toluene. Aromatic hydrocarbons such as xylene, ketones such as acetone and methyl ethyl ketone, ethers such as diethyl ether and dibutyl ether, and esters such as ethyl acetate and butyl acetate can be used.
[0040]
As the pulverizer, a known apparatus such as a rotating cylindrical mill, a vibrating ball mill, a planetary ball mill, a medium stirring mill, or a colloid mill using shearing, compression, and frictional force can be used.
[0041]
The composition liquid containing the carbon fiber after pulverization removes the solvent and the surfactant by filtration and washing operation, and then removes the solvent adhering to the fiber by wind-heat drying, vacuum drying, freeze drying or the like. By adjusting the treatment temperature for removing the solvent, the type of functional group on the fiber surface can be controlled using the difference in the desorption temperature of the functional group.
[0042]
Further, the type and distribution amount of the surface functional groups to be introduced can be adjusted by treatment with hydrochloric acid, nitric acid, sulfuric acid or the like or activation treatment with water vapor, carbon dioxide gas or alkali such as KOH or NaOH.
[0043]
The carbon fiber obtained by the pulverization treatment of the present invention is a fine carbon fiber having an outer diameter of 2 to 500 nm and an aspect ratio of 1 to 100, and 5 to 80% by mass breaks on the fiber surface along the hollow structure of the fiber. It is a fine carbon fiber having a cross section.
[0044]
The fine carbon fiber of the present invention thus obtained has a standard deviation (μm) of the fiber length of 2.0 or less, preferably 1.0 or less, more preferably 0.5 or less, and a distribution. Since it is narrow and has little variation, the quality of the composite material can be kept good when used as a conductive filler or a heat conductive filler.
[0045]
In order to improve the conductivity of the fine carbon fiber, the raw material vapor-grown carbon fiber or the fine carbon fiber after pulverization / drying can be heat-treated at 2000 to 3500 ° C. in an inert atmosphere to increase the degree of graphitization. . In order to further improve conductivity, boron carbide (B Four C), boron oxide (B 2 O Three ), Elemental boron, boric acid (H Three BO Three ), And a boron compound such as borate may be mixed and heat-treated at 2000 to 3500 ° C. in an inert atmosphere.
[0046]
Since graphitized carbon fiber develops crystallinity and mechanical strength is improved, if the vapor-grown carbon fiber is graphitized before pulverization, much energy and time are required for pulverization to a desired fiber length. Cost.
[0047]
The amount of boron compound added is not limited because it depends on the chemical and physical properties of the boron compound used. For example, boron carbide (B Four When C) is used, the range is from 0.05 to 10% by mass, preferably from 0.1 to 5% by mass, based on the carbon fiber. By heat treatment with the boron compound, the conductivity of the fine carbon fiber is improved, and the crystallinity of carbon (average interplanar spacing d) 002 ) Will improve. Specifically, when no boron or boron compound is added, the average spacing d of (002) planes by X-ray diffraction method. 002 Is 0.342 nm or less, but when added, the average spacing is d 002 Can be 0.338 nm or less.
[0048]
The heat treatment furnace to be used may be a furnace capable of maintaining a target temperature of 2000 ° C. or higher, preferably 2300 ° C. or higher, and may be any ordinary apparatus such as an Atchison furnace, a resistance furnace, or a high frequency furnace. Moreover, depending on the case, the method of heating by energizing powder or a molded object directly is also employable.
[0049]
The atmosphere for the heat treatment is a non-oxidizing atmosphere, preferably an atmosphere of one or more rare gases such as argon, helium and neon. The heat treatment time is preferably as short as possible from the viewpoint of productivity. When heated for a long time, the product yield deteriorates because it sets and solidifies. It is sufficient for the heat treatment temperature to be maintained for 1 hour or less after the temperature of the central part of the molded body or the like reaches the target temperature.
[0050]
When heat-treated, a part of the fiber is sintered and formed into a block shape like a normal product. Therefore, since it cannot be added to an electrode or the like as it is or used as an electron emission ability material, the molded body must be crushed into a form suitable as a filler material.
[0051]
Therefore, this block is crushed, pulverized and classified so as to be suitable as a filler material, and at the same time, the non-fibrous material is separated. If the pulverization is insufficient, mixing with the electrode material will not work and the additive effect will not be achieved.
[0052]
In order to obtain a desirable form as the filler, the heat-treated block-like material is first pulverized to a size of 2 mm or less and further pulverized by a pulverizer. As a crusher, a crusher such as a commonly used ice crusher or a rotoplex can be used.
[0053]
As a pulverizer, a pulverizer such as an impact type pulverizer, a ball mill, an autogenous pulverizer, or a pulverizer such as a microjet can be used. Classification that separates non-fibrous materials can be performed by airflow classification or the like.
[0054]
When the fine carbon fiber of the present invention is added to a battery electrode, battery performance such as charge / discharge capacity and electrode plate strength can be improved. Examples of the battery include a battery that improves the conductivity of an electrode plate such as a lithium battery, a lead storage battery, a polymer battery, and a dry battery, and that requires intercalation ability.
[0055]
Since the fine carbon fiber of the present invention has good conductivity, not only can the conductivity of these batteries be improved, but also the lithium battery has a large intercalation capability as a carbon material for negative electrodes, thus increasing the charge / discharge capacity. can do.
[0056]
The amount of fine carbon fiber added to the electrode is preferably in the range of 0.1 to 20% by mass as the carbon fiber produced by the above production method. When the addition amount is larger than 20% by mass, the packing density of carbon in the electrode is reduced, and the charge / discharge capacity when the battery is formed is lowered. Moreover, when it becomes less than 0.1 mass%, an addition effect is small.
[0057]
In order to make the electrode by adding the fine carbon fiber of the present invention, for example, graphite powder, mesofuse carbon microbeads (MCMB), etc. are used for the negative electrode of the lithium battery. And kneading sufficiently to disperse the fibers as uniformly as possible.
[0058]
The fine carbon fiber of the present invention can be used for various applications in the state as it is, in the state of a carbon fiber mixture mixed with other carbon fibers, or in the state of a composition mixed with a base material such as resin, ceramics or metal. Can be used. For applications using a resin as a base material, the fine carbon fiber of the present invention is prepared so as to contain 5 to 50% by mass with respect to the resin mixture. Examples of the resin include a thermosetting resin such as a phenol resin, an epoxy resin, a polyurethane resin, a polyimide resin, and an unsaturated polyester resin, a polyamide resin, a thermoplastic resin such as a polyurethane resin, a vinyl chloride resin, an acrylic resin, and a cellulose resin, or Examples thereof include silicone rubber, polyurethane rubber, styrene butadiene rubber, and natural rubber.
[0059]
【Example】
Hereinafter, the present invention will be described in more detail with representative examples. Note that these are merely illustrative examples, and the present invention is not limited thereto.
[0060]
In the following examples, the content (mass%) of the branched carbon fiber is the ratio of the cross-sectional area of the branched carbon fiber to the total cross-section of the carbon fiber in the cross-sectional photograph of the carbon fiber by a transmission electron microscope (TEM). The specific gravity is the same, and the mass% is set.
[0061]
The boron content (mass%) is obtained by adding calcium carbonate to a carbon fiber powder sample and ashing in an oxygen stream, adding calcium carbonate to the ash, heating and melting, and dissolving the melt in water. The aqueous solution was quantitatively analyzed by ICP emission spectrometry (Inductively coupled plasma atomic emission spectroscopy).
[0062]
Example 1
An average volume of 25 nm, an average length of 10,000 nm, an aspect ratio of 400, and 30 g of vapor-grown vapor-grown carbon fiber and 30 g of vapor-grown carbon fiber and 50 g of ethanol have an internal volume of 300 cm. Three Were put into an agate mill made of Ano and 200 g of zirconia beads having a diameter of 1.0 mm were added and pulverized for 4 hours. After the treatment, drying was performed at 150 ° C. for 3 hours. Thereafter, the vapor grown carbon fiber was observed with a scanning electron microscope, and the fiber length was measured. In addition, infrared analysis of the sample was performed.
[0063]
As a result, this grinding gives an average diameter of 25 nm, an average length of 250 nm, an aspect ratio of 10, d 002 It was possible to obtain fine carbon fibers having a thickness of 0.340 nm. At this time, the pulverized carbon fiber was observed with a scanning electron microscope and photographed, and then the length of the carbon fiber was measured for 100 pieces with calipers to obtain a length distribution. The result is shown in FIG. The standard deviation at this time was 0.10 μm (100 nm). As a result of infrared analysis, stretching vibration of hydroxyl group 3600cm -1 Absorption of light by was observed.
[0064]
Example 2
2g of vapor grown carbon fiber graphitized using a boron compound, having an average diameter of 33nm, an average length of 16,500nm, an aspect ratio of 500 and 30% by mass of branched vapor grown carbon fiber. And ethanol 50g, internal volume 300cm Three Were put into an agate mill made of Ano and 200 g of zirconia beads having a diameter of 1.0 mm were added and pulverized for 4 hours. After the treatment, drying was performed at 150 ° C. for 3 hours. Thereafter, the vapor grown carbon fiber was observed with a scanning electron microscope, and the fiber length was measured. In addition, infrared analysis of the sample was performed. In addition, the boron content of this sample was 0.7 mass%.
[0065]
As a result, this grinding gives an average diameter of 33 nm, an average length of 420 nm, an aspect ratio of 13, d 002 It was possible to obtain fine carbon fibers having a thickness of 0.337 nm. At this time, the pulverized carbon fiber was observed with a scanning electron microscope and photographed, and then the length of the carbon fiber was measured with 50 calipers to obtain a length distribution. The result is shown in FIG. The standard deviation at this time was 0.22 μm (220 nm). As a result of infrared analysis, the stretching vibration of hydroxyl group was 3600 cm. -1 Absorption of light by was observed.
[0066]
Comparative Example 1
90 g of vapor-grown carbon fiber having an average diameter of 33 nm, an average length of 16,500 nm, an aspect ratio of 500 and 30% by mass of branched vapor-grown carbon fiber and having a content of 2000 cm Three Were put into an alumina ball mill and pulverized at a rotational speed of 75 rpm for 18 hours. At this time, 30 balls made of alumina having a diameter of 30 mm were placed in the ball mill for fiber grinding. After the treatment, the vapor grown carbon fiber was observed using a scanning electron microscope, and the fiber length was measured. In addition, infrared analysis of the sample was performed.
[0067]
As a result, it was possible to grind only to an average diameter of 33 nm, an average length of 4,980 nm, and an aspect ratio of 150. The pulverized carbon fiber was observed with a scanning electron microscope and photographed, and then the length of the carbon fiber was measured with 50 calipers to determine the length distribution. The fiber length distribution at this time is shown in FIG. The standard deviation was 3.07 μm (3070 nm). As a result of infrared analysis, light absorption due to the stretching vibration of the hydroxyl group was hardly observed.
[0068]
Example 3
Viscosity when 40% by mass of each of the wet-pulverized calcined fine carbon fiber of Example 1, the wet-pulverized graphitized fine carbon fiber of Example 2, and the dry-pulverized graphitized carbon fiber of Comparative Example 1 in phenol resin ( 25 ° C .; centipoise (cP) or mPa · s) was measured according to JIS K 7117 with a viscometer. The results are shown in Table 1.
[0069]
[Table 1]
Figure 0004362276
[0070]
Resin mixed with wet-pulverized fine carbon fibers (Examples 1 and 2) has a compound viscosity reduced to 1/3 or less compared with resin mixed with dry-pulverized fine carbon fibers (Comparative Example 1). Sex improvement was observed.
[0071]
【The invention's effect】
(1) The carbon fiber of the present invention has excellent processability when mixed with a base material such as a resin, is well dispersed in the resin, and improves the surface smoothness of the resulting composite.
(2) The carbon fiber of the present invention is suitable for gas storage because it has a minute dent and a hollow structure and has high addition reactivity with hydrogen and methane.
(3) The fine carbon fiber obtained by the method of the present invention has a narrow fiber length distribution and little variation. Therefore, when used as a conductive filler or a heat conductive filler, the quality of the composite material is kept good. be able to.
[0072]
[Brief description of the drawings]
1 is a fiber length distribution diagram of fine carbon fibers of Example 1. FIG.
2 is a fiber length distribution diagram of fine carbon fibers of Example 2. FIG.
3 is a fiber length distribution diagram of fine carbon fibers of Comparative Example 1. FIG.

Claims (6)

内部に中空構造を有し、多層構造からなり、外径が2〜500nm、アスペクト比が10以上の分岐状気相法炭素繊維を含む気相法炭素繊維を900〜1300℃で加熱処理し、次いで水及び/または有機溶媒の存在下で回転円筒式ミル、振動ボールミル、遊星ボールミル、媒体攪拌式ミル、コロイドミルのいずれかにより湿式粉砕する工程を有することを特徴とする微細炭素繊維の製造方法。A vapor grown carbon fiber including a branched vapor grown carbon fiber having a hollow structure inside, having a multilayer structure, an outer diameter of 2 to 500 nm, and an aspect ratio of 10 or more is heated at 900 to 1300 ° C., Next, a method for producing fine carbon fibers, comprising a step of wet-grinding in the presence of water and / or an organic solvent by any one of a rotating cylindrical mill, a vibrating ball mill, a planetary ball mill, a medium stirring mill, and a colloid mill . 粉砕工程が、界面活性剤の存在下で行なわれる請求項1に記載の微細炭素繊維の製造方法。The method for producing fine carbon fibers according to claim 1, wherein the pulverization step is performed in the presence of a surfactant. 気相法炭素繊維を水及び/または有機溶媒中に1〜30質量%含む請求項1または2に記載の微細炭素繊維の製造方法。The manufacturing method of the fine carbon fiber of Claim 1 or 2 which contains 1-30 mass% of vapor grown carbon fiber in water and / or an organic solvent. 請求項1〜3のいずれかひとつの製造方法によって微細炭素繊維を得、該微細炭素繊維に、所望によりホウ素またはホウ素化合物を加え、2000〜3500℃で熱処理する工程を含む微細炭素繊維の製造方法。A method for producing fine carbon fiber, comprising the steps of obtaining fine carbon fiber by the production method according to any one of claims 1 to 3, adding boron or a boron compound to the fine carbon fiber as desired, and heat-treating at 2000 to 3500 ° C. . 内部に中空構造を有し、多層構造からなり、外径が2〜500nm、アスペクト比が10以上の分岐状気相法炭素繊維を含む気相法炭素繊維に所望によりホウ素またはホウ素化合物を加え、2000〜3500℃で熱処理し、次いで水及び/または有機溶媒の存在下で回転円筒式ミル、振動ボールミル、遊星ボールミル、媒体攪拌式ミル、コロイドミルのいずれかにより湿式粉砕する工程を有することを特徴とする微細炭素繊維の製造方法。Boron or a boron compound is optionally added to a vapor grown carbon fiber including a branched vapor grown carbon fiber having a hollow structure inside, a multilayer structure, an outer diameter of 2 to 500 nm, and an aspect ratio of 10 or more, It has a step of heat-treating at 2000 to 3500 ° C. and then wet-grinding in the presence of water and / or an organic solvent by any of a rotating cylindrical mill, a vibrating ball mill, a planetary ball mill, a medium stirring mill, and a colloid mill. A method for producing fine carbon fibers. 2000〜3500℃で熱処理した炭素繊維を水及び/または有機溶媒中に1〜30質量%含む請求項5に記載の微細炭素繊維の製造方法。The manufacturing method of the fine carbon fiber of Claim 5 which contains 1-30 mass% of carbon fibers heat-processed at 2000-3500 degreeC in water and / or an organic solvent.
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