JP3829964B2

JP3829964B2 - Method for producing carbon fiber reinforced carbon composite

Info

Publication number: JP3829964B2
Application number: JP27455698A
Authority: JP
Inventors: 朝明山田
Original assignee: Tokai Carbon Co Ltd
Current assignee: Tokai Carbon Co Ltd
Priority date: 1998-09-29
Filing date: 1998-09-29
Publication date: 2006-10-04
Anticipated expiration: 2018-09-29
Also published as: JP2000103686A

Description

【０００１】
【発明の属する技術分野】
本発明は、緻密な材質組織を有し、高密度、高強度の材質性状を備え、とくに高純度が要求される半導体製造用のルツボ、ヒータ、炉材などの各種部材として有用な炭素繊維強化炭素複合材（以下「Ｃ／Ｃ材」ともいう）の製造方法に関する。
【０００２】
【従来の技術】
Ｃ／Ｃ材は、炭素繊維の複合化による卓越した比強度、比弾性率を有するうえに炭素材特有の軽量性と優れた耐熱性および化学的安定性を備えているため、航空・宇宙機用の構造材料や高温炉用部材をはじめ半導体製造用の各種部材、例えばＣＺ法による単結晶引き上げ用のルツボ、ヒータ、炉材など、高温苛酷な条件下で使用される用途分野で有用されている。
【０００３】
このＣ／Ｃ材を製造する代表的な技術としては、 (1)マトリックスとなる熱硬化性樹脂液を含浸した炭素繊維の織布を積層し、プレス等で所定形状に圧縮成形したのちプリプレグ成形体を非酸化性雰囲気下で焼成炭化処理する方法、 (2)熱硬化性樹脂液に浸した炭素繊維のトウをフィラメントワインディング法で所定形状に成形し、このプリプレグ成形体を同様に焼成炭化処理する方法、 (3)炭素繊維のプリフォーム組織中にＣＶＤ（化学的気相蒸着法）により熱分解炭素を沈着させる方法などが知られている。
【０００４】
このうち、大型のＣ／Ｃ材を得るためには (1)の方法が工業的手段として最も実用性に優れている。しかしながら、 (1)の方法を採る場合には圧縮成形時に相当量の熱硬化性樹脂液が外部に圧出したり、プリプレグ成形体を焼成炭化する過程で熱硬化性樹脂に含まれる揮発性成分が揮散するなどの現象が起こるために、得られるＣ／Ｃ材の材質組織には微細な空孔が生じ、低密度、低強度なものとなり易い難点がある。そこで、Ｃ／Ｃ材の材質組織の空孔中に炭化性のフェノール樹脂やフラン樹脂などのバインダー樹脂あるいは石炭系や石油系のピッチを強制含浸したのち焼成する二次的な緻密化処理が一般に行われている。
【０００５】
例えば、特開平２−２８３６６６号公報には二次元乃至三次元に配向させたピッチ系の炭素繊維にコールタールピッチ及び／又は石油系ピッチを含浸させ、次いで含浸させた状態で炭化処理を施し、次いでこの処理材に２０００〜３０００℃で黒鉛化処理を施し、次いで緻密化処理として、黒鉛化されたものに軟化点が１５０〜２５０℃で実質的にキノリン不溶分を含まないコールタールピッチ及び／又は石油系ピッチを含浸させ、続いて炭化−黒鉛化処理を施す工程を所望の密度になるまで繰り返すＣ／Ｃ材の製造方法が、また特開平５−１３９８３２号公報には軟化点が２００〜３００℃の光学的等方性コールタールピッチを１０〜６０重量％含む熱硬化性樹脂との混合物を炭素繊維に含浸させプリプレグをつくり、これを成形し次いで炭化処理を行って得られた一次焼成体に、実質的にキノリン不溶分を含まず軟化点が１５０〜２５０℃の高軟化点ピッチを含浸させ、引き続き空気中で２００〜３５０℃で不融化した後、不活性雰囲気下で炭化−黒鉛化処理を行う工程を、嵩密度が１．６g/cc以上になるまで繰り返す炭素材料の製造方法が提案されている。
【０００６】
また、本出願人も高密度で強度特性に優れたＣ／Ｃ材の製造方法として、炭素繊維にマトリックス結合材を含浸して複合成形したのち非酸化性雰囲気下で焼成炭化して得られたＣ／Ｃ複合体を基材とし、該Ｃ／Ｃ基材にピッチを含浸し非酸化性雰囲気下８００〜１２００℃で焼成炭化する処理を複数回反復して材質の嵩密度を１．１〜１．５g/ccにする第１緻密化工程と、次いで熱硬化性樹脂液を含浸硬化し非酸化性雰囲気下８００〜１２００℃で焼成炭化する処理を複数回反復して材質の嵩密度を１．６g/cc以上にする第２緻密化工程を、順次に施すＣ／Ｃ材の製造方法（特開平８−245273号公報）を提案した。
【０００７】
しかしながら、熱硬化性樹脂やピッチを含浸して二次的に緻密化する方法は、これら液状の熱硬化性樹脂やピッチをＣ／Ｃ材の微細な空孔の最深部にまで充分に含浸することが難しく、更に空孔に含浸した熱硬化性樹脂やピッチが焼成炭化する際にも低揮発性成分などの放出により新たな気孔が発生するなどのために、繰り返し行っても緻密化には限界がある。
【０００８】
また、ＣＶＤ（Chemical Vapor Deposition : 化学的気相蒸着法）やＣＶＩ（Chemical Vapor Infiltration : 化学的気相浸透法）などにより、炭化水素を気相熱分解して微細な空孔中に熱分解炭素を沈着させて緻密化を図る方法も開発されている。例えば、特開平１−２１２２７７号公報には炭素繊維成形体１０〜７０ Vol％および炭素質マトリックス５〜８０ Vol％から構成され、かつ空隙率が１０〜５５％であるＣ／Ｃ材料の空隙部に気相熱分解により炭素を沈積充填し、続いてこの充填物の表面に気相熱分解により炭素を沈積被覆するＣ／Ｃ材の製造法が開示されている。
【０００９】
更に、炭素繊維と炭素質マトリックスの形成原料からなる成形体を炭化し、得られた炭化物にピッチ類または樹脂類の含浸、炭化処理を施し、気孔率が８〜１５％であるＣ／Ｃ材とした後、さらに前記Ｃ／Ｃ材料の空孔に炭化水素を９５０〜１２００℃の温度、１０〜２００Torrの圧力で熱分解して得られる熱分解炭素を堆積する緻密化処理を行い、気孔率を６％以下とするＣ／Ｃ材料の製造方法（特開平２−145477号公報）、炭素繊維で作られた成形体に、メタンと水素の混合ガスを、温度を１２００〜１３００℃、メタンと水素の混合ガスの全圧を２０〜８０Torr、メタンの分圧を１０〜３２．５Torrとして気相浸透法による熱分解炭素を沈積させるようにしたＣ／Ｃ材の製造方法（特開平８−2976号公報）などが提案されている。
【００１０】
【発明が解決しようとする課題】
気相法により熱分解炭素をＣ／Ｃ材の空孔に充填して緻密化する場合、原料ガスを空孔内に充満させて熱分解するものであるから、Ｃ／Ｃ材の表面部である空孔入口部に熱分解炭素が析出堆積することはできるだけ避けねばならない。空孔入口部に熱分解炭素が析出堆積すると、空孔内に原料ガスが流通充満し難くなるために空孔内、特に空孔深部には熱分解炭素の堆積が相対的に少なくなり、それ以上の緻密化が困難となる。これは、原料ガスの濃度を高め、熱分解炭素の析出速度を高めるとより顕著になる。一方、原料ガス濃度を極めて低く設定すればこの難点は解消できるが、処理時間が長くなり、非能率となる欠点がある。
【００１１】
本発明は上記問題点を解消するために鋭意研究した結果完成に至ったもので、その目的は、Ｃ／Ｃ材の空孔に気相法による熱分解炭素を効率よく充填することができ、緻密なＣ／Ｃ材とくに高純度で半導体製造用の各種部材として好適に用いられる炭素繊維強化炭素複合材の製造方法を提供することにある。
【００１２】
【課題を解決するための手段】
上記の目的を達成するための本発明による炭素繊維強化炭素複合材の製造方法は、炭素繊維に熱硬化性樹脂液を含浸して硬化成形し、非酸化性雰囲気中で焼成炭化して得られたＣ／Ｃ複合体を高純度化処理したのち、反応温度１２００〜１３００℃、反応装置内の全圧１０〜１００Torr、反応前期の原料ガス濃度を１０〜２０ Vol％、反応後期の原料ガス濃度を１０ Vol％未満、のＣＶＤ反応条件に設定して、Ｃ／Ｃ複合体の空孔中に熱分解炭素を沈着して緻密化することを構成上の特徴とする。
【００１３】
上記の製造方法において、高純度化処理は、不活性ガス、真空中あるいはハロゲン含有ガス雰囲気中で１５００〜２５００℃の温度で熱処理するものであることが好ましく、またＣＶＤ反応条件として反応前期のＣＶＤ反応時間は全ＣＶＤ反応時間の２０〜７０％であることが好ましく、２０〜４０％がより好ましい。
【００１４】
【発明の実施の形態】
本発明において強化材となる炭素繊維としては、ポリアクリロニトリル系、レーヨン系、ピッチ系などの各種原料から製造された平織、朱子織、綾織などの織布を一次元または多次元方向に配向した繊維体、フエルト、トウなどが使用される。また、含浸する熱硬化性樹脂液には、例えば、フェノール系、フラン系などの残炭率が５０重量％以上の熱硬化性樹脂液が好適に用いられる。
【００１５】
これらの炭素繊維は熱硬化性樹脂液に浸漬または塗布することにより熱硬化性樹脂液を含浸し、例えば炭素繊維織布の表面を熱硬化性樹脂液で充分に濡らしたのち半硬化してプリプレグを形成し、ついで積層加圧成形して複合成形体を作製する。なお、この複合時に、炭素繊維量がＣ／Ｃ複合体とした場合の繊維体積含有率(Vf)として５０〜７０％になるように予め設定することが強度確保の面から望ましい。
【００１６】
複合成形体は樹脂成分などを加熱硬化したのち、常法により非酸化性雰囲気に保持された加熱炉中で焼成炭化することによりＣ／Ｃ複合体が得られる。加熱炉としては、コークス粉のような炭素質パッキング材で被包しながら焼成炭化する形式のリードハンマー炉や系内を窒素、アルゴン等の非酸化性ガスで保持された電気炉などが用いられ、焼成炭化は通常８００℃以上の温度で行われる。
【００１７】
本発明は、このようにして得られたＣ／Ｃ複合体を先ず高純度化処理する。高純度化処理は、例えば不活性ガス、真空中あるいはハロゲン含有ガス雰囲気中で１５００〜２５００℃の温度で熱処理することにより行われる。高純度化処理はＣ／Ｃ複合体中に含まれる金属成分等の灰分を加熱して揮散除去するために行うものであるから、不純物金属を蒸気圧の高いハロゲン化物に転化して揮散除去するハロゲン含有ガス雰囲気中で熱処理する方法が最も好ましい。高純度化処理は緻密化前の空孔が相対的に多く存在する状態で行うことが必要で、その結果、空孔内部の不純物金属を効果的に除去することが可能となる。なお、この高純度化処理は、Ｃ／Ｃ複合体を作製する工程である焼成炭化工程に引き続き連続的に行うことが熱エネルギーの経済性から望ましい。
【００１８】
本発明は、高純度化処理されたＣ／Ｃ複合体をＣＶＤ反応装置にセットして、特定の反応条件下にＣＶＤ反応させることにより熱分解炭素を析出させ、Ｃ／Ｃ複合体の空孔中に沈着させることにより緻密化を図るものである。ＣＶＤ反応はメタン、プロパン、プロピレン、ベンゼンなどの易熱分解性の炭化水素ガスを原料ガスとして、アルゴンなどの不活性ガスや水素ガスなどのキャリアガスとともにＣＶＤ反応装置に導入し、原料ガスを熱分解して熱分解炭素を析出させるものである。
【００１９】
本発明は、この原料ガスを熱分解させる際のＣＶＤ反応条件として、反応温度１２００〜１３００℃、反応装置内の全圧１０〜１００Torr、反応前期の原料ガス濃度を１０〜２０ Vol％、反応後期の原料ガス濃度を１０ Vol％未満、に設定制御してＣ／Ｃ複合体の空孔に熱分解炭素を沈着させるものである。
【００２０】
反応温度を１２００〜１３００℃の範囲に設定するのは、反応温度が１２００℃を下回ると熱分解速度が遅く緻密化に長時間を要し、能率が低下するためである。一方１３００℃を越えると熱分解速度が速いためにＣ／Ｃ複合体の表面部における炭素の析出が多くなり、空孔入口部での熱分解炭素の堆積が増大して空孔内部への炭素の沈着が阻害され、充分に緻密化することができなくなるためである。
【００２１】
また、原料ガスの熱分解時の反応装置内の全圧は１０〜１００Torrの範囲に設定される。全圧が１０Torr未満では原料ガス分子相互の衝突機会が少なくなるので熱分解炭素の生成速度が遅くなり、効率よく熱分解炭素を析出し空孔内に沈着させることが困難となる。しかしながら、全圧が１００Torrを上回る場合には気相中においてすす状の炭素の発生が著しくなるために効果的に熱分解炭素を析出させることが難しく、空孔内を熱分解炭素で充填し、緻密化することが困難になるためである。
【００２２】
更に、本発明ではＣＶＤ反応を前期と後期に分け、ＣＶＤ反応前期における原料ガス濃度を１０〜２０ Vol％に設定制御し、反応後期における原料ガス濃度を１０ Vol％未満に設定制御することが必要である。反応前期における原料ガス濃度を高く設定するのは、反応前期においては比較的大きな空孔に熱分解炭素を析出沈着する必要があり、一方反応後期には残った比較的に小さな空孔に熱分解炭素を析出沈着することが効果的であるからである。
【００２３】
そのため、反応前期では原料ガス濃度は１０〜２０ Vol％に設定される。原料ガス濃度が１０ Vol％未満では大きな空孔に熱分解炭素を析出充填するのに長時間を要し、一方、２０ Vol％を越える高濃度では気相反応時にすす状の熱分解炭素の生成を伴うために、熱分解炭素を効果的に析出し、空孔内に沈着、緻密化することが困難となる。
【００２４】
なお、反応前期の反応時間は全ＣＶＤ反応時間の２０〜７０％であることが好ましく、２０〜４０％がより好ましい。反応前期の反応時間が２０％未満であると、熱分解炭素の析出に多くの時間が必要となり、空孔内への沈着、緻密化が充分に行えないためである。しかしながら、反応時間が全ＣＶＤ反応時間の７０％を越えると、Ｃ／Ｃ材表面に熱分解炭素の皮膜が形成されるようになり、ＣＶＤ反応後期における熱分解炭素の空孔内への沈着、充填が阻害されることとなるためである。
【００２５】
このようにして比較的に大きな空孔に熱分解炭素を充填したのち、残された比較的に小さな空孔や微細な空隙部には原料ガス濃度を小さく設定し、すなわち反応後期においては原料ガス濃度１０ Vol％未満に設定制御することにより、相対的に小さな空孔や微細な空隙部に効果的に熱分解炭素を析出沈着することが可能となる。反応後期における原料ガス濃度を１０ Vol％以上とすると表面皮膜が生成し易くなって、緻密化が阻害されることとなるためである。なお、原料ガス濃度が小さ過ぎると緻密化に時間がかかり非能率となるので、反応後期における原料ガス濃度は３ Vol％以上であることが好ましい。
【００２６】
これらの反応条件下にＣＶＤ反応を行うことにより、Ｃ／Ｃ複合体の空孔部が熱分解炭素によって充填されて材質組織が緻密化し、高純度で高密度、高強度の材質性状を備えたＣ／Ｃ材を製造することが可能となる。なお、このようにして製造されたＣ／Ｃ材は、必要に応じて表面に耐酸化コーティングを施すこともできる。
【００２７】
【実施例】
以下、本発明の実施例を比較例と対比して説明する。
【００２８】
実施例１〜５、比較例１〜６
(1)Ｃ／Ｃ複合体の作製
ポリアクリロニトリル系高強度高弾性タイプの平織炭素繊維織布に、フェノール樹脂初期縮合物（残炭率50％）を塗布して十分に含浸させ、４８時間風乾してプリプレグシートを作成した。このプリプレグシート３０枚を積層してモールドに入れ、温度７０℃、圧力２０kg/cm²の熱圧条件で５時間プレスして硬化成形したのち、窒素ガス雰囲気中で５℃／hrの昇温速度で１０００℃に加熱し、５時間保持して焼成炭化した。このようにして、１００×１００×７mmのＣ／Ｃ複合体を作製した。次いで、Ｃ／Ｃ複合体を塩素ガス気流中１０℃／min の昇温速度で１８００℃に加熱し、５時間保持して高純度化処理した。このようにして作製した高純度化処理を施したＣ／Ｃ複合体の炭素繊維体積含有率(Vf)は６５％、嵩密度は１．３８g/cc、気孔率は１４．２％、灰分は３ ppm（高純度化処理を行わない場合は１１００ppm ）であった。
【００２９】
(2)ＣＶＤによる緻密化処理
高周波誘導加熱方式のＣＶＤ装置の反応炉内に上記Ｃ／Ｃ複合体をセットし、異なるＣＶＤ反応条件に設定してＣ／Ｃ複合体の空孔中に熱分解炭素を析出沈着させた。なお、原料ガスにはプロパンガス、キャリアガスには水素を用い、総ガス流量を１．０リットル／分に設定した。ＣＶＤ反応は、反応炉内を真空中で所定の温度に加熱したのち水素ガスを導入し、再び炉内の温度が所定の温度に達した時点で原料ガスを導入して、設定した条件でＣＶＤ反応させた。なお、ガス流量はマスフローコントローラーで、炉内圧力は圧力コントローラーで設定値に制御した。
【００３０】
比較例７、８
オートクレーブによりＣ／Ｃ複合体にフェノール樹脂初期縮合物を含浸し、窒素ガス雰囲気下、温度２０００℃で５時間焼成した。なお、オートクレーブ含浸は温度２５℃、圧力８kg/cm²で４時間処理した。このような緻密化処理を２回（比較例８）、５回（比較例９）繰り返し行った。
【００３１】
このようにして緻密化したＣ／Ｃ材について、下記の方法により嵩密度、気孔率、層間強度、及びＳｉＯガスとの反応性を測定した。得られた結果を、ＣＶＤ反応条件と対比して表１に示した。
▲１▼嵩密度；外寸法と重量から算出。
▲２▼気孔率；水銀圧入法により径 0.001〜 300μm の気孔率を測定。
▲３▼層間強度；試料を幅 5mmに切断し、クロスヘッドスピード 1mm/min、スパン30mmで、Ｘ-P直線が低下する時の荷重から算出。
▲４▼ＳｉＯガスとの反応性；シリカ粉末とフェノール樹脂とをＳｉＯ₂：Ｃ（フェノール樹脂の残炭素）＝１：１の割合で混合し、加熱硬化して厚さ 3mmの板状成形体とし、この成形体を板状のＣ／Ｃ材の上に乗せ不活性ガス雰囲気中、常圧、1850℃の温度で１時間熱処理した際のＣ／Ｃ材の重量増加率から測定。
【００３２】
【表１】

【００３３】
表１の結果から、本発明の製造方法により製造した実施例のＣ／Ｃ材は、嵩密度１．６４〜１．６７(g/cc)、気孔率４．０〜６．０％と緻密化され、また層間強度も安定しており、ＳｉＯガスとの反応性も低位にあることが判る。これに対して、ＣＶＤ反応温度が低い比較例２、炉内圧力が低い比較例３ではＣＶＤ反応を長時間行っても緻密化の効率が低く、嵩密度の増加や気孔率の低下が少ない。また、反応温度が高い比較例１、炉内圧力が高い比較例４ではすす状の熱分解炭素が生成するために緻密化の効果が殆ど認められなかった。更に、原料ガス濃度を一定とした比較例５、あるいは原料ガス濃度を反応前期で低く（10Vol%未満）反応後期で高く（10〜20Vol%）設定した比較例６では表面の気孔が閉塞したために嵩密度の上昇効果が小さく、緻密化され難いことが認められた。
【００３４】
また、オートクレーブにより樹脂を含浸し、焼成炭化して緻密化した比較例７及び比較例８では、繰り返し処理する操作の煩雑さに比べて緻密化の効果が少なく、非能率、非効率であることが判る。なお、実施例１において、高純度化処理を施さないＣ／Ｃ複合体を用いて実施例１と同一条件のＣＶＤ反応により緻密化したのち、同じ条件で高純度化した場合の灰分は６ppm であり、空孔内を熱分解炭素で緻密化する前に高純度化する方が効果的であることが判る。
【００３５】
【発明の効果】
以上のとおり、本発明によれば、特定のＣＶＤ反応条件に設定制御してＣ／Ｃ複合体の空孔中に熱分解炭素を沈着することにより、効率よく緻密化され、高密度、高強度のＣ／Ｃ材を製造することが可能となる。また、緻密化前に高純度化処理することにより空孔内部まで効果的に不純物除去ができ、例えば、半導体製造用のルツボ、ヒータ、炉材などの各種部材に用いるＣ／Ｃ材の製造方法として有用性が高い。[0001]
BACKGROUND OF THE INVENTION
The present invention has a dense material structure, high density and high strength material properties, and carbon fiber reinforcement useful as various members such as crucibles, heaters, and furnace materials for semiconductor manufacturing that require particularly high purity. The present invention relates to a method for producing a carbon composite material (hereinafter also referred to as “C / C material”).
[0002]
[Prior art]
C / C materials have excellent specific strength and specific elastic modulus due to the combination of carbon fibers, as well as light weight, excellent heat resistance and chemical stability that are unique to carbon materials. It is useful in various application fields that are used under severe conditions such as structural materials and high temperature furnace components for semiconductor manufacturing, such as crucibles for single crystal pulling by CZ method, heaters, furnace materials, etc. Yes.
[0003]
Typical techniques for producing this C / C material include: (1) Laminating carbon fiber woven fabric impregnated with a thermosetting resin liquid as a matrix, compression molding to a predetermined shape with a press, etc., and then prepreg molding (2) A carbon fiber tow dipped in a thermosetting resin liquid is formed into a predetermined shape by the filament winding method, and this prepreg molded body is similarly fired and carbonized. (3) A method in which pyrolytic carbon is deposited in a carbon fiber preform structure by CVD (chemical vapor deposition) is known.
[0004]
Among these, the method (1) is most practical as an industrial means for obtaining a large C / C material. However, when the method of (1) is adopted, a volatile component contained in the thermosetting resin in the process of compressing a considerable amount of thermosetting resin liquid to the outside during compression molding or firing and carbonizing the prepreg molded body. Since a phenomenon such as volatilization occurs, fine pores are generated in the material structure of the obtained C / C material, and there is a difficulty that it tends to be low density and low strength. Therefore, secondary densification is generally performed by forcibly impregnating the pores of the material structure of the C / C material with a binder resin such as carbonizable phenolic resin or furan resin, or a pitch of coal or petroleum, followed by firing. Has been done.
[0005]
For example, in JP-A-2-283666, pitch-based carbon fibers oriented two-dimensionally or three-dimensionally are impregnated with coal tar pitch and / or petroleum-based pitch, and then carbonized in the impregnated state. Next, this treated material is subjected to graphitization at 2000 to 3000 ° C., and then as a densification treatment, a coal tar pitch having a softening point of 150 to 250 ° C. and substantially free of quinoline-insoluble components as graphitized and / or Alternatively, a method for producing a C / C material in which a step of impregnating petroleum pitch and subsequent carbonization-graphitization treatment is repeated until a desired density is achieved, and Japanese Patent Application Laid-Open No. 5-139932 discloses a softening point of 200 to A carbon fiber is impregnated with a mixture of a thermosetting resin containing 10 to 60% by weight of an optically isotropic coal tar pitch at 300 ° C. to produce a prepreg, which is then molded The primary fired body obtained by performing the heat treatment was impregnated with a high softening point pitch having substantially no quinoline insoluble content and a softening point of 150 to 250 ° C., and subsequently infusible at 200 to 350 ° C. in air. Thereafter, a method for producing a carbon material has been proposed in which the step of carbonizing and graphitizing in an inert atmosphere is repeated until the bulk density reaches 1.6 g / cc or more.
[0006]
In addition, the present applicant, as a method for producing a C / C material having high density and excellent strength characteristics, was obtained by impregnating a carbon fiber with a matrix binder and performing composite molding, followed by firing and carbonization in a non-oxidizing atmosphere. Using a C / C composite as a base material, a process of impregnating the C / C base material with pitch and firing and carbonizing at 800 to 1200 ° C. in a non-oxidizing atmosphere is repeated a plurality of times to obtain a bulk density of the material of 1.1 to 1.1. The bulk density of the material is set to 1 by repeating the first densification step to 1.5 g / cc and then impregnating and curing the thermosetting resin liquid and baking and carbonizing at 800 to 1200 ° C. in a non-oxidizing atmosphere several times. A method for producing a C / C material (Japanese Patent Laid-Open No. 8-245273) was proposed in which the second densification step of 6 g / cc or higher is sequentially performed.
[0007]
However, the method of secondary densification by impregnating a thermosetting resin or pitch sufficiently impregnates the liquid thermosetting resin or pitch into the deepest part of the fine pores of the C / C material. In addition, even when repeated, it is difficult to densify because new pores are generated due to the release of low volatility components when the thermosetting resin or pitch impregnated in the pores is burnt and carbonized. There is a limit.
[0008]
In addition, hydrocarbons are vapor-phase pyrolyzed into fine pores by CVD (Chemical Vapor Deposition) and CVI (Chemical Vapor Infiltration). A method has also been developed for depositing and densifying. For example, Japanese Patent Laid-Open No. 1-212277 discloses a void portion of a C / C material composed of a carbon fiber molded body 10 to 70 Vol% and a carbonaceous matrix 5 to 80 Vol% and having a porosity of 10 to 55%. Discloses a method for producing a C / C material in which carbon is deposited and filled by vapor-phase pyrolysis, and subsequently carbon is deposited and coated on the surface of the filling by vapor-phase pyrolysis.
[0009]
Further, a molded body made of carbon fiber and a carbonaceous matrix forming material is carbonized, and the obtained carbide is impregnated with a pitch or a resin and carbonized, and a C / C material having a porosity of 8 to 15%. Then, a densification treatment is performed to deposit pyrolytic carbon obtained by pyrolyzing hydrocarbons in the pores of the C / C material at a temperature of 950 to 1200 ° C. and a pressure of 10 to 200 Torr. A method for producing a C / C material with a content of 6% or less (JP-A-2-145477), a molded body made of carbon fiber, a mixed gas of methane and hydrogen, a temperature of 1200 to 1300 ° C., and methane A method for producing a C / C material in which pyrolytic carbon is deposited by a vapor infiltration method with a total pressure of a mixed gas of hydrogen of 20 to 80 Torr and a partial pressure of methane of 10 to 32.5 Torr (Japanese Patent Laid-Open No. 8-2976) Etc.) have been proposed.
[0010]
[Problems to be solved by the invention]
When the pyrolytic carbon is filled in the pores of the C / C material by the vapor phase method and densified, the raw material gas is filled in the pores and pyrolyzed, so the surface portion of the C / C material It should be avoided as much as possible that pyrolytic carbon deposits and accumulates at a hole entrance. If pyrolytic carbon deposits and accumulates at the inlet of the pores, it is difficult for the raw material gas to flow and fill in the pores, so that the deposition of pyrolytic carbon is relatively small in the pores, particularly in the deep portions of the pores. The above densification becomes difficult. This becomes more remarkable when the concentration of the raw material gas is increased and the deposition rate of pyrolytic carbon is increased. On the other hand, if the raw material gas concentration is set to be extremely low, this difficulty can be solved, but there is a disadvantage that the processing time becomes long and inefficiency occurs.
[0011]
The present invention has been completed as a result of diligent research to solve the above problems, and its purpose is to efficiently fill the pores of the C / C material with pyrolytic carbon by a vapor phase method, An object of the present invention is to provide a method for producing a dense C / C material, particularly a carbon fiber reinforced carbon composite material that is highly purified and is suitably used as various members for semiconductor production.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a carbon fiber reinforced carbon composite material according to the present invention is obtained by impregnating a carbon fiber with a thermosetting resin liquid, curing and molding, and firing and carbonizing in a non-oxidizing atmosphere. After purifying the C / C composite, the reaction temperature is 1200 to 1300 ° C., the total pressure in the reactor is 10 to 100 Torr, the raw material gas concentration in the first reaction is 10 to 20 Vol%, the raw material gas concentration in the second reaction. Is set to the CVD reaction condition of less than 10% by volume, and pyrolytic carbon is deposited and densified in the pores of the C / C composite.
[0013]
In the production method described above, the high-purity treatment is preferably a heat treatment at a temperature of 1500 to 2500 ° C. in an inert gas, vacuum or halogen-containing gas atmosphere. The reaction time is preferably 20 to 70% of the total CVD reaction time, and more preferably 20 to 40%.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The carbon fiber used as the reinforcing material in the present invention is a fiber in which woven fabrics such as plain weave, satin weave, twill weave, etc., manufactured from various raw materials such as polyacrylonitrile, rayon, and pitch are oriented in one or more dimensions. Body, felt, toe, etc. are used. Moreover, as the thermosetting resin liquid to be impregnated, for example, a thermosetting resin liquid having a residual carbon ratio of 50% by weight or more such as phenol-based or furan-based is suitably used.
[0015]
These carbon fibers are impregnated with a thermosetting resin solution by dipping or coating in a thermosetting resin solution. For example, the surface of a carbon fiber woven fabric is sufficiently wetted with a thermosetting resin solution and then semi-cured to prepare a prepreg. Is formed, and then laminated and pressure-molded to produce a composite molded body. In addition, it is desirable from the viewpoint of securing strength that the fiber volume content (Vf) when the amount of carbon fiber is a C / C composite is set to 50 to 70% at the time of this composite.
[0016]
The composite molded body is obtained by heat-curing a resin component or the like, and then calcining and carbonizing in a heating furnace maintained in a non-oxidizing atmosphere by a conventional method to obtain a C / C composite. As the heating furnace, a lead hammer furnace that burns and carbonizes while being encased in a carbonaceous packing material such as coke powder, or an electric furnace in which the system is held with a non-oxidizing gas such as nitrogen or argon is used. Calcination carbonization is usually performed at a temperature of 800 ° C. or higher.
[0017]
In the present invention, the C / C composite thus obtained is first subjected to a purification treatment. The purification treatment is performed by heat treatment at a temperature of 1500 to 2500 ° C., for example, in an inert gas, vacuum, or halogen-containing gas atmosphere. Since the high-purification treatment is performed to volatilize and remove the ash such as metal components contained in the C / C composite, the impurity metal is converted to a halide having a high vapor pressure and volatilized and removed. The most preferable method is a heat treatment in a halogen-containing gas atmosphere. The high-purification treatment needs to be performed in a state where there are relatively many vacancies before densification, and as a result, the impurity metal inside the vacancies can be effectively removed. In addition, it is desirable from the economical viewpoint of thermal energy that this high-purification process is performed continuously following the calcination carbonization process which is a process for producing a C / C composite.
[0018]
In the present invention, a highly purified C / C composite is set in a CVD reactor, and a pyrolytic carbon is deposited by subjecting the C / C composite to a CVD reaction under specific reaction conditions. It is densified by depositing inside. In the CVD reaction, an easily pyrolytic hydrocarbon gas such as methane, propane, propylene, and benzene is used as a raw material gas and introduced into a CVD reactor together with an inert gas such as argon or a carrier gas such as hydrogen gas, and the raw material gas is heated. It decomposes to deposit pyrolytic carbon.
[0019]
In the present invention, the CVD reaction conditions for thermally decomposing the raw material gas include a reaction temperature of 1200 to 1300 ° C., a total pressure of 10 to 100 Torr in the reactor, a raw material gas concentration of 10 to 20 Vol% in the first reaction period, and a late reaction time. The raw material gas concentration is controlled to be less than 10 Vol%, and pyrolytic carbon is deposited in the pores of the C / C composite.
[0020]
The reason why the reaction temperature is set in the range of 1200 to 1300 ° C. is that when the reaction temperature is lower than 1200 ° C., the thermal decomposition rate is slow and a long time is required for densification, and the efficiency is lowered. On the other hand, when the temperature exceeds 1300 ° C., the pyrolysis rate is high, so that the carbon deposits on the surface of the C / C composite increases, and the deposition of pyrolytic carbon at the vacancy inlet increases and the carbon inside the vacancies increases. This is because the deposition of hindered is hindered and cannot be sufficiently densified.
[0021]
Further, the total pressure in the reaction apparatus during the thermal decomposition of the raw material gas is set in the range of 10 to 100 Torr. If the total pressure is less than 10 Torr, the chances of collision between the raw material gas molecules are reduced, so the generation rate of pyrolytic carbon is slow, and it becomes difficult to deposit pyrolytic carbon efficiently and deposit it in the pores. However, when the total pressure exceeds 100 Torr, the generation of soot-like carbon in the gas phase becomes significant, so it is difficult to effectively deposit pyrolytic carbon, and the pores are filled with pyrolytic carbon, This is because densification becomes difficult.
[0022]
Furthermore, in the present invention, it is necessary to divide the CVD reaction into the first half and the second half, set the source gas concentration in the first half of the CVD reaction to 10-20 Vol%, and set the source gas concentration in the second half of the reaction to less than 10 Vol%. It is. Setting the raw material gas concentration in the early reaction period requires the deposition of pyrolytic carbon in relatively large vacancies in the early reaction period, while pyrolysis into the relatively small vacancies remaining in the late reaction period. This is because it is effective to deposit and deposit carbon.
[0023]
Therefore, the source gas concentration is set to 10 to 20 Vol% in the first reaction period. If the raw material gas concentration is less than 10 Vol%, it takes a long time to deposit and fill pyrolytic carbon in large pores, while if it exceeds 20 Vol%, soot-like pyrolytic carbon is produced during the gas phase reaction. Therefore, it becomes difficult to effectively deposit pyrolytic carbon and deposit and densify it in the pores.
[0024]
In addition, it is preferable that the reaction time of the first reaction period is 20 to 70% of the total CVD reaction time, and more preferably 20 to 40%. This is because if the reaction time in the first reaction period is less than 20%, a large amount of time is required for the deposition of pyrolytic carbon, and the deposition and densification in the pores cannot be performed sufficiently. However, when the reaction time exceeds 70% of the total CVD reaction time, a film of pyrolytic carbon is formed on the surface of the C / C material, and deposition of pyrolytic carbon into vacancies in the late stage of the CVD reaction, It is because filling will be inhibited.
[0025]
After filling the relatively large vacancies with pyrolytic carbon in this way, the raw material gas concentration is set small in the remaining relatively small vacancies and fine voids, that is, in the latter stage of the reaction By controlling the concentration to be less than 10 Vol%, it becomes possible to effectively deposit pyrolytic carbon in relatively small pores and fine voids. This is because if the concentration of the raw material gas in the latter stage of the reaction is 10 Vol% or more, a surface film is easily generated and densification is hindered. Note that if the source gas concentration is too small, densification takes time and inefficiency occurs. Therefore, the source gas concentration in the latter stage of the reaction is preferably 3 Vol% or more.
[0026]
By performing the CVD reaction under these reaction conditions, the pores of the C / C composite are filled with pyrolytic carbon, the material structure becomes dense, and the material properties of high purity, high density, and high strength are provided. It becomes possible to produce a C / C material. In addition, the C / C material manufactured in this way can also be provided with an oxidation resistant coating on the surface as necessary.
[0027]
【Example】
Examples of the present invention will be described below in comparison with comparative examples.
[0028]
Examples 1-5, Comparative Examples 1-6
(1) Preparation of C / C composite Polyacrylonitrile-based high-strength high-elasticity plain woven carbon fiber woven fabric is coated with a phenol resin initial condensate (residual carbon ratio of 50%) and thoroughly impregnated, and then air-dried for 48 hours. Thus, a prepreg sheet was created. 30 sheets of this prepreg sheet are laminated and put in a mold, and after 5 hours pressing under hot pressure conditions of a temperature of 70 ° C. and a pressure of 20 kg / cm ^2, a temperature rise rate of 5 ° C./hr in a nitrogen gas atmosphere is performed. And heated to 1000 ° C., held for 5 hours and calcined. In this way, a 100 × 100 × 7 mm C / C composite was produced. Next, the C / C composite was heated to 1800 ° C. at a rate of temperature increase of 10 ° C./min in a chlorine gas stream and maintained for 5 hours for high purification treatment. The carbon fiber volume content (Vf) of the C / C composite subjected to the purification treatment thus prepared is 65%, the bulk density is 1.38 g / cc, the porosity is 14.2%, the ash content is It was 3 ppm (1100 ppm when no high-purification treatment was performed).
[0029]
(2) Densification treatment by CVD The above C / C composite is set in a reaction furnace of a high frequency induction heating type CVD apparatus, set to different CVD reaction conditions, and pyrolyzed in the pores of the C / C composite. Carbon was deposited. Note that propane gas was used as the source gas, hydrogen was used as the carrier gas, and the total gas flow rate was set to 1.0 liter / min. In the CVD reaction, the inside of the reaction furnace is heated to a predetermined temperature in a vacuum and then hydrogen gas is introduced. When the temperature in the furnace reaches the predetermined temperature again, the raw material gas is introduced and CVD is performed under the set conditions. Reacted. The gas flow rate was controlled to a set value by a mass flow controller and the furnace pressure was controlled by a pressure controller.
[0030]
Comparative Examples 7 and 8
The C / C composite was impregnated with the phenol resin initial condensate by an autoclave and calcined at a temperature of 2000 ° C. for 5 hours in a nitrogen gas atmosphere. The autoclave impregnation was performed at a temperature of 25 ° C. and a pressure of 8 kg / cm ² for 4 hours. Such densification treatment was repeated twice (Comparative Example 8) and 5 times (Comparative Example 9).
[0031]
The C / C material thus densified was measured for bulk density, porosity, interlayer strength, and reactivity with SiO gas by the following methods. The obtained results are shown in Table 1 in comparison with the CVD reaction conditions.
(1) Bulk density: Calculated from external dimensions and weight.
(2) Porosity: The porosity of 0.001 to 300 μm in diameter was measured by mercury porosimetry.
(3) Interlaminar strength: Calculated from the load when the X-P straight line drops when the sample is cut to a width of 5 mm, the crosshead speed is 1 mm / min, and the span is 30 mm.
(4) Reactivity with SiO gas: Silica powder and phenol resin are mixed at a ratio of SiO ₂ : C (residual carbon of phenol resin) = 1: 1, and heated and cured to form a plate-like molded product having a thickness of 3 mm. Measured from the weight increase rate of the C / C material when the molded body was placed on a plate-like C / C material and heat-treated in an inert gas atmosphere at normal pressure and a temperature of 1850 ° C. for 1 hour.
[0032]
[Table 1]

[0033]
From the results shown in Table 1, the C / C materials of Examples produced by the production method of the present invention are dense with a bulk density of 1.64 to 1.67 (g / cc) and a porosity of 4.0 to 6.0%. In addition, the interlayer strength is stable and the reactivity with SiO gas is low. In contrast, in Comparative Example 2 where the CVD reaction temperature is low and Comparative Example 3 where the furnace pressure is low, the efficiency of densification is low even when the CVD reaction is performed for a long time, and the increase in bulk density and the decrease in porosity are small. In Comparative Example 1 where the reaction temperature was high and Comparative Example 4 where the pressure inside the furnace was high, soot-like pyrolytic carbon was produced, so that the densification effect was hardly recognized. Further, in Comparative Example 5 in which the raw material gas concentration was constant, or in Comparative Example 6 in which the raw material gas concentration was set low in the first reaction (less than 10 Vol%) and higher in the second reaction (10 to 20 Vol%), the surface pores were blocked. It was recognized that the effect of increasing the bulk density was small and difficult to be densified.
[0034]
Moreover, in Comparative Example 7 and Comparative Example 8 in which the resin is impregnated with an autoclave and calcined and carbonized to be densified, the effect of densification is small compared to the complexity of the operation for repeated treatment, and it is inefficient and inefficient. I understand. In Example 1, the C / C composite not subjected to the purification treatment was densified by the CVD reaction under the same conditions as in Example 1, and then the ash content in the case of being purified under the same conditions was 6 ppm. It can be seen that it is more effective to purify the pores before they are densified with pyrolytic carbon.
[0035]
【The invention's effect】
As described above, according to the present invention, by setting and controlling to specific CVD reaction conditions and depositing pyrolytic carbon in the pores of the C / C composite, it is efficiently densified, high density and high strength. It becomes possible to produce the C / C material. Also, impurities can be effectively removed to the inside of the pores by high-purification treatment before densification. For example, a method for producing C / C materials used for various members such as crucibles, heaters, furnace materials for semiconductor production As useful as.

Claims

Carbon fiber is impregnated with a thermosetting resin solution, cured and molded, and the C / C composite obtained by firing and carbonizing in a non-oxidizing atmosphere is subjected to high-purity treatment, and then reaction temperature is 1200 to 1300 ° C. The C / C composite is emptied by setting the CVD reaction conditions such that the total pressure in the apparatus is 10 to 100 Torr, the source gas concentration in the first reaction is 10 to 20 Vol%, and the source gas concentration in the latter reaction is less than 10 Vol%. A method for producing a carbon fiber-reinforced carbon composite material, characterized in that pyrolytic carbon is deposited in the pores and densified.

The method for producing a carbon fiber-reinforced carbon composite material according to claim 1, wherein the purification treatment is a heat treatment at a temperature of 1500 to 2500 ° C in an inert gas, vacuum or halogen-containing gas atmosphere.

The method for producing a carbon fiber-reinforced carbon composite material according to claim 1, wherein the CVD reaction time in the first reaction period is 20 to 70% of the total CVD reaction time.