JP2004107836A - Method for producing carbon fiber - Google Patents
Method for producing carbon fiber Download PDFInfo
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- JP2004107836A JP2004107836A JP2002274019A JP2002274019A JP2004107836A JP 2004107836 A JP2004107836 A JP 2004107836A JP 2002274019 A JP2002274019 A JP 2002274019A JP 2002274019 A JP2002274019 A JP 2002274019A JP 2004107836 A JP2004107836 A JP 2004107836A
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- 229920000049 Carbon (fiber) Polymers 0.000 title claims abstract description 60
- 239000004917 carbon fiber Substances 0.000 title claims abstract description 60
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 45
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 16
- 239000000835 fiber Substances 0.000 claims abstract description 180
- 238000003763 carbonization Methods 0.000 claims abstract description 82
- 230000005484 gravity Effects 0.000 claims abstract description 76
- 229920002239 polyacrylonitrile Polymers 0.000 claims abstract description 24
- 238000005259 measurement Methods 0.000 claims abstract description 16
- 238000010000 carbonizing Methods 0.000 claims abstract description 5
- 238000000034 method Methods 0.000 claims description 32
- 230000007423 decrease Effects 0.000 claims description 11
- 229920006240 drawn fiber Polymers 0.000 abstract 3
- 230000001105 regulatory effect Effects 0.000 abstract 2
- 230000000052 comparative effect Effects 0.000 description 10
- 239000002243 precursor Substances 0.000 description 8
- 238000004513 sizing Methods 0.000 description 6
- BAPJBEWLBFYGME-UHFFFAOYSA-N Methyl acrylate Chemical compound COC(=O)C=C BAPJBEWLBFYGME-UHFFFAOYSA-N 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 230000000704 physical effect Effects 0.000 description 4
- 238000009987 spinning Methods 0.000 description 4
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- JAHNSTQSQJOJLO-UHFFFAOYSA-N 2-(3-fluorophenyl)-1h-imidazole Chemical compound FC1=CC=CC(C=2NC=CN=2)=C1 JAHNSTQSQJOJLO-UHFFFAOYSA-N 0.000 description 2
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 229920001577 copolymer Polymers 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- LVHBHZANLOWSRM-UHFFFAOYSA-N methylenebutanedioic acid Natural products OC(=O)CC(=C)C(O)=O LVHBHZANLOWSRM-UHFFFAOYSA-N 0.000 description 2
- 239000011550 stock solution Substances 0.000 description 2
- 238000004381 surface treatment Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 238000007088 Archimedes method Methods 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
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- 238000011161 development Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000001891 gel spinning Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
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- 230000000379 polymerizing effect Effects 0.000 description 1
- 238000012805 post-processing Methods 0.000 description 1
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は高強度炭素繊維の製造法に関する。
【０００２】
【従来の技術】
従来、ポリアクリロニトリル（ＰＡＮ）系繊維を原料として高性能の炭素繊維が製造されることは知られており、航空機を始めスポーツ用品まで広い範囲で使用されている。
【０００３】
とりわけ、高強度・高弾性の炭素繊維は宇宙航空用途に使用されており、これらは更なる高性能化が求められている。
【０００４】
ＰＡＮ系前駆体繊維を用いて炭素繊維を製造する方法としては、前駆体繊維を２００〜３００℃の酸化性雰囲気下で延伸又は収縮を行いながら酸化処理（耐炎化処理）を行った後、３００〜１０００℃以上の不活性ガス雰囲気中で炭素化を行う方法が知られている。
【０００５】
とりわけ３００〜９００℃付近での炭素化工程の繊維処理方法は、炭素繊維の強度発現に大きく影響を及ぼし、これまでに多くの検討が行われてきた。
【０００６】
特許文献１では、耐炎化繊維を３００〜８００℃において、不活性雰囲気中２５％までの範囲で伸長を加えながら炭素化し、耐炎化繊維の原長に対し負とならないように処理することによって、高配向度を保ち、高強度の炭素繊維を得ることが開示されている。
【０００７】
また、特許文献２、特許文献３では、５００℃付近での繊維長さの急激な変化をコントロールするため、３００〜５００℃、５００〜８００℃と、工程を２つに分けることで緻密な高強度炭素繊維が得られることが開示されている。
【０００８】
さらに、特許文献４では、耐炎化繊維を不活性雰囲気中、比重が１．４５に達するまでの昇温速度を５０〜３００℃／分、さらに比重が１．６０〜１．７５に達するまでの昇温速度を１００〜８００℃／分とする２段炭素化を行うことにより、ボイドの少ない炭素繊維が得られることが開示されている。
【０００９】
特許文献５でも特許文献４と同様に、３００〜８００℃において昇温勾配をコントロールする事により緻密な炭素繊維が得られることが開示されている。
【００１０】
しかしながら、緻密、高配向度且つ高強度を有する炭素繊維を得るためには、最適な繊維物性での緊縮を行う事が必要であり、これらの方法に記載されている温度範囲や、昇温勾配だけでは繊維の緻密さをコントロールする事は難しく、またパラメーターとして比重だけでは、緻密、高配向度且つ高強度を有する炭素繊維を得ることは困難で、従来、より緻密、高配向度且つ高強度の炭素繊維を得るための方法が求められている。
【００１１】
さらに、このような従来の低温での炭素化工程（第一炭素化工程）において得られる処理糸（第一炭素化処理糸）は、次工程の高温での炭素化工程（第二炭素化工程）において高張力処理すると、比重が低下する、並びに、糸切れが多くなるなどの問題がある。
【００１２】
【特許文献１】
特開昭５４−１４７２２２号公報（第１〜３頁）
【特許文献２】
特開昭５９−１５０１１６号公報（第１〜２頁）
【特許文献３】
特公平３−２３６５１号公報（第１〜３頁）
【特許文献４】
特公平３−１７９２５号公報（第１〜３頁）
【特許文献５】
特開昭６２−２３１０２８号公報（第１〜３頁）
【００１３】
【発明が解決しようとする課題】
本発明者は、長年にわたり鋭意検討を重ねた結果、炭素化工程における、耐炎化繊維の各物性と、温度と、延伸倍率との間に重要な関連があり、これらを制御することにより高強度炭素繊維を製造できることを知得した。即ち、第一炭素化工程と第二炭素化工程とからなり、ＰＡＮ系耐炎化繊維を炭素化する炭素化工程の第一炭素化工程を、一次延伸処理と二次延伸処理とに分け、それぞれ所定の温度及び延伸倍率で延伸処理すると共に、一次延伸処理を、耐炎化繊維の、弾性率、比重、及び広角Ｘ線測定における結晶子サイズが所定の範囲を満たす範囲で行い、且つ二次延伸処理を、一次延伸処理後の繊維の、比重、及び広角Ｘ線測定における結晶子サイズが所定の範囲を満たす範囲で行うことにより、高強度の炭素繊維を製造することが可能となる第一炭素化処理糸が得られることを知得した。
【００１４】
このようにして得られる第一炭素化処理糸は、第二炭素化工程において高張力処理しても、比重の低下や糸切れを起こすことなく、高強度の炭素繊維が得られることを知得し、本発明を完成するに至った。
【００１５】
よって、本発明の目的とするところは、上記問題を解決した、高強度の炭素繊維の製造法を提供することにある。
【００１６】
【課題を解決するための手段】
上記目的を達成する本発明は、以下に記載のものである。
【００１７】
〔１〕 不活性雰囲気中で、第一炭素化工程において、比重１．３〜１．４のポリアクリロニトリル系耐炎化繊維を３００〜９００℃の温度範囲内で、１．０３〜１．０６の延伸倍率で一次延伸処理し、次いで０．９〜１．０１の延伸倍率で二次延伸処理した後、第二炭素化工程において８００〜１７００℃の温度範囲内で炭素化する炭素繊維の製造法において、第一炭素化工程における一次延伸処理を下記条件（１）乃至（３）のいずれをも満たす範囲で行い、二次延伸処理を下記条件（４）、（５）の両方を満たす範囲で行い、さらに第二炭素化工程で（６）を満たす範囲で行う炭素繊維の製造法。
第一炭素化工程条件
一次延伸条件
（１） ポリアクリロニトリル系耐炎化繊維の弾性率が極小値まで低下した時点から１．０ｔｆ／ｍｍ２に増加するまでの範囲
（２） ポリアクリロニトリル系耐炎化繊維の比重が１．５に達するまでの範囲
（３） ポリアクリロニトリル系耐炎化繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズが１．４５ｎｍに達するまでの範囲
二次延伸条件
（４） 一次延伸処理後の繊維の比重が二次延伸処理中に上昇し続ける範囲
（５） 一次延伸処理後の繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズが１．４５ｎｍより大きくならない範囲
第二炭素化工程条件
（６） 第二炭素化工程での繊維張力（Ｆ ｇｆ／ｍｍ２）と第一炭素化工程後の繊維断面積（Ｓ ｍｍ２）とで算出される繊維応力（Ｄ ｇｆ）が下式
０．１８ ＞ Ｄ ＞ ０．０８
〔但し、Ｄ ＝ Ｆ × Ｓ〕
を満たす範囲
〔２〕 第一炭素化工程後における繊維の広角Ｘ線測定（回折角２６°）における配向度が７６．０％以上である〔１〕に記載の炭素繊維の製造法。
【００１８】
〔３〕 第二炭素化工程終了後に得られる炭素繊維の単繊維径が３〜８μｍである〔１〕又は〔２〕に記載の炭素繊維の製造法。
【００１９】
【発明の実施の形態】
以下、本発明を詳細に説明する。
【００２０】
本発明の炭素繊維の製造法に用いるＰＡＮ系前駆体繊維は、アクリロニトリルを９０質量％以上、好ましくは９５質量％以上含有する単量体を重合した紡糸溶液を湿式又は乾湿式紡糸法において紡糸した後、水洗・乾燥・延伸して得られる繊維を用いることが好ましい。これらの前駆体繊維は、従来公知のものが何ら制限なく使用できる。
【００２１】
得られた前駆体繊維は、引き続き加熱空気中２００〜２８０℃で耐炎化処理される。この時の処理は、一般的に、延伸倍率０．８５〜１．３の範囲で処理され、繊維比重１．３〜１．４のＰＡＮ系耐炎化繊維とするものであり、耐炎化時の張力（延伸配分）は特に限定されるものでは無い。
【００２２】
本発明の炭素繊維の製造法においては、上記耐炎化繊維を、不活性雰囲気中で、第一炭素化工程において、３００〜９００℃の温度範囲内で、１．０３〜１．０６の延伸倍率で一次延伸処理し、次いで０．９〜１．０１の延伸倍率で二次延伸処理した後、第二炭素化工程において８００〜１７００℃の温度範囲内で炭素化する。
【００２３】
上記第一炭素化工程において、一次延伸処理では、ＰＡＮ系耐炎化繊維の弾性率が極小値まで低下した時点から１．０ｔｆ／ｍｍ２に増加するまでの範囲、同繊維の比重が１．５に達するまでの範囲、且つ同繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズが１．４５ｎｍに達するまでの範囲で、１．０３〜１．０６の延伸倍率で、延伸処理を行う。
【００２４】
上記のＰＡＮ系耐炎化繊維弾性率が極小値まで低下した時点から１．０ｔｆ／ｍｍ２に増加するまでの範囲は、図１に示すＢの範囲である。
【００２５】
耐炎化繊維の弾性率が極小値まで低下した時点から１．０ｔｆ／ｍｍ２に増加するまでの範囲で延伸（１．０３〜１．０６倍）を行うことにより、糸切れを抑制し、低弾性率部が効率的に延伸され高配向化が可能となり、緻密な一次延伸処理糸を得ることができる。
【００２６】
これに対し、弾性率が極小値に低下する前（Ａの範囲）での１．０３倍以上の延伸は、糸切れを増加させ、著しい強度低下を招くので好ましくない。
【００２７】
また、弾性率が極小値まで低下し、次いで１．０ｔｆ／ｍｍ２に増加した後（Ｃの範囲）での１．０３倍以上の延伸は、糸の弾性率が高く、無理な延伸を強いるので、繊維欠陥・ボイドを増加させ、延伸の効果を損なうので好ましくない。よって、上記弾性率の範囲内で一次延伸処理を行う。
【００２８】
耐炎化繊維の比重が１．５に達するまでの範囲で延伸（１．０３〜１．０６倍）を行うことにより、ボイドの生成を抑制しながら、配向度の向上が出来、高品位の一次延伸処理糸を得ることができる。
【００２９】
これに対し、比重が１．５より高い範囲での１．０３倍以上の一次延伸は、無理な延伸によりボイドの生成を増長し、最終的な炭素繊維の構造欠陥、比重低下を招くため好ましくない。よって、上記比重の範囲内で一次延伸処理を行う。
【００３０】
ＰＡＮ系耐炎化繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズは、一次延伸処理時の温度上昇につれて増加し続ける。その増加状態は、図２に示されるように結晶子サイズ０．９ｎｍ付近と１．４５ｎｍ付近に変曲点を持つ曲線である。よって前述の、結晶子サイズが１．４５ｎｍに達するまでの範囲は、後の変曲点に達するまでの範囲である。
【００３１】
耐炎化繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズが１．４５ｎｍに達するまでの範囲で延伸（１．０３〜１．０６倍）を行うことにより、より緻密でボイドの少ない、一次延伸処理糸を得ることができる。
【００３２】
これに対し、結晶子サイズが１．４５ｎｍに達した後での１．０３倍以上の一次延伸は、無理な延伸により糸切れを発生させるだけではなく、ボイドの発生を招くため、好ましくない。
【００３３】
また、一次延伸における延伸倍率が１．０３倍未満では、延伸の効果が少なく、高強度の炭素繊維を得ることができないので好ましくない。延伸倍率が１．０６倍より高いと、糸切れを招き、高品位及び高強度の炭素繊維を得ることはできないので好ましくない。
【００３４】
上記方法により得られた一次延伸処理糸は、引き続いて以下の二次延伸処理を施す。
【００３５】
一次延伸処理後の繊維の比重が二次延伸処理中に上昇し続ける範囲、及び一次延伸処理後の繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズが１．４５ｎｍより大きくならない範囲で０．９〜１．０１倍の延伸倍率で延伸処理を行う。
【００３６】
二次延伸処理中における一次延伸処理後の繊維の比重は、図３に示されるように温度上昇につれて、変化しない（上昇しない）条件と、上昇し続ける条件と、上昇後下降する条件（二次延伸処理中に繊維比重が低下する条件）とがある。
【００３７】
これらの条件のうち、一次延伸処理後の繊維の比重が二次延伸処理中に上昇し続ける条件で０．９〜１．０１倍の延伸倍率で延伸処理を行うことにより、即ち変化しない区間を含むことなく又は低下することなく上昇し続ける条件で延伸処理を行うことにより、ボイド生成を抑制し、最終的に緻密な炭素繊維を得ることができる。
【００３８】
これに対し、二次延伸処理中に繊維比重が低下すると、ボイドの生成を増長し、緻密な炭素繊維を得ることができず、好ましくない。また、二次延伸処理中に繊維比重が変化しない区間を含むと、二次延伸処理の効果が見られないので、好ましくない。よって、二次延伸処理は繊維比重が上昇し続ける範囲である。
【００３９】
また、一次延伸処理後の繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズが１．４５ｎｍより大きくならない範囲で０．９〜１．０１倍の延伸倍率で延伸処理を行うことにより、結晶が成長することなく、緻密化され、ボイドの生成も抑制でき、最終的に高い緻密性を有した炭素繊維を得ることができる。
【００４０】
これに対し、結晶子サイズが１．４５ｎｍより大きくなる範囲での二次延伸処理は、ボイドの生成を増長すると共に、糸切れによる品位低下を招き、高強度の炭素繊維を得ることができず、好ましくない。よって、二次延伸処理は上記結晶子サイズの範囲内で行う。
【００４１】
なお、二次延伸処理における延伸倍率が０．９倍未満では、配向度の低下が著しく、高強度の炭素繊維を得ることができないので好ましくない。延伸倍率が１．０１倍より高いと、糸切れを招き、高品位及び高強度の炭素繊維を得ることはできないので好ましくない。よって、二次延伸処理における延伸倍率は０．９〜１．０１の範囲内が好ましい。
【００４２】
また、高強度の炭素繊維を得るためには、第一炭素化処理糸の広角Ｘ線測定（回折角２６°）における配向度が７６．０％以上あることが好ましい。
【００４３】
７６．０％未満では最終的に高強度の炭素繊維を得ることができないので好ましくない。
【００４４】
上記のごとくして、第一炭素化工程における耐炎化繊維の一次延伸処理、二次延伸処理は行われ、第一炭素化処理糸となる。また、上記第一炭素化工程は、一つの炉若しくは二つ以上の炉で、連続的若しくは別々に処理しても差し支えなく、前述の処理条件範囲内での処理によるところであれば何ら問題はない。
【００４５】
上記第一炭素化処理糸は引き続き、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、しかも高張力下で炭素化処理される。
【００４６】
なお、第二炭素化工程での繊維張力（Ｆ ｇｆ／ｍｍ２）は、第一炭素化工程後の繊維直径、即ち繊維断面積（Ｓ ｍｍ２）により変わるため、本発明においては張力ファクターとして繊維応力（Ｄ ｇｆ）を用い、この繊維応力の範囲は下式
０．１８ ＞ Ｄ ＞ ０．０８
〔但し、Ｄ ＝ Ｆ × Ｓ〕
を満たす範囲としている。
【００４７】
ここで繊維断面積は、繊維直径をｎ＝２０で測定し、その平均値を用い、真円として算出した値を使用している。
【００４８】
従来の第一炭素化工程で得られる第一炭素化処理糸を、８００〜１７００℃の温度範囲で高張力下において第二炭素化処理する場合は、比重が低下し、比重が１．８１以上のものを得る事は困難であると共に、糸切れが多くなるなどの問題がある。また、従来の方法では高配向の炭素繊維を得る事は困難である。
【００４９】
これに対し、本発明の方法で得られる上記第一炭素化処理糸は、８００〜１７００℃の温度範囲で第二炭素化処理する場合、高張力下でも比重の低下や糸切れを起こすことなく、比重が１．８２以上のものも得ることができ、また、本発明の方法で得られる第二炭素化処理糸は、高張力下で処理するため高配向のものを容易に得る事ができる。
【００５０】
このように、本発明の方法は、第二炭素化工程における高張力下での炭素化処理が比重の低下や糸切れを起こすことなく可能であり、配向度アップが可能であり、高強度の第二炭素化処理糸が得られる。
【００５１】
得られた第二炭素化処理糸、即ち第二炭素化工程終了後に得られる炭素繊維は、引き続き公知の方法により、表面処理を施した炭素繊維となり得る。さらに、炭素繊維の後加工をしやすくし、取扱性を向上させる目的で、サイジング処理することが好ましい。サイジング方法は、従来の公知の方法で行うことができ、サイジング剤は、用途に即して適宜組成を変更して使用し、均一付着させた後に、乾燥することが好ましい。
【００５２】
なお、第二炭素化処理糸の単繊維径は３〜８μｍであることが好ましい。
【００５３】
このようにして得られた炭素繊維は、高強度であり、本発明の製造法によりなし得るものである。
【００５４】
【実施例】
以下、本発明を実施例及び比較例により更に具体的に説明する。また、各実施例及び比較例における延伸条件、延伸後、及び炭素繊維物性についての評価方法は以下の方法により実施した。
【００５５】
＜結晶子サイズ、配向度＞
Ｘ線回折装置：リガク製ＲＩＮＴ１２００Ｌ、コンピュータ：日立２０５０／３２を使用し、回折角２６°における結晶子サイズを回折パターンより、配向度を半価幅より求めた。
【００５６】
＜比重＞
アルキメデス法により測定した。試料繊維はアセトン中にて脱気処理し測定した。
【００５７】
＜炭素繊維ストランド強度、弾性率＞
ＪＩＳ Ｒ ７６０１に規定された方法により測定した。
【００５８】
＜単糸繊維弾性率＞
ＪＩＳ Ｒ ７６０６（２０００）に規定された方法により測定した。
【００５９】
実施例１
アクリロニトリル９５質量％／アクリル酸メチル４質量％／イタコン酸１質量％よりなる共重合体紡糸原液を湿式又は乾湿式紡糸し、水洗・乾燥・延伸・オイリングして繊維直径１１．７μｍの前駆体繊維を得た。この繊維を加熱空気中２００〜２５０℃の熱風循環式耐炎化炉で耐炎化処理し、繊維比重１．３３のポリアクリロニトリル系耐炎化糸を得た。
【００６０】
次いで、この耐炎化糸を不活性雰囲気中３００〜９００℃の温度範囲内の第一炭素化工程において、一次延伸・二次延伸処理を以下に示す条件で実施した。
【００６１】
一次延伸は図１のＢの範囲内で、延伸倍率１．０４倍で処理した。この一次延伸処理後の糸、即ち一次延伸処理糸は、弾性率０．８ｔｆ／ｍｍ２、比重１．３６、結晶子サイズ ０．９０ｎｍの、糸切れのない糸であった。
【００６２】
その後この一次延伸処理糸を、引き続き第一炭素化工程において、二次延伸が終了するまで比重が上昇し続ける範囲、且つ結晶子サイズが１．４５ｎｍより大きくならない範囲で、延伸倍率１．０１倍で二次延伸処理したところ、比重１．８、配向度８０．２％、繊維直径７．８μｍ、繊維断面積０．００００４７７８２２ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００６３】
さらに、上記処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力３５１９ｇｆ／ｍｍ２（０．２１７ｇｆ／ｄ）、繊維応力０．１６８ｇｆで処理し、引き続き公知の方法にて表面処理、サイジングを施し、乾燥して比重１．８４０、配向度８１．３％、繊維直径６．９μｍ、単繊維強度５７０ｋｇｆ／ｍｍ２、ストランド強度５６５ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００６４】
実施例２
表１に示すように、実施例１で得られた第一炭素化処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力２６２７ｇｆ／ｍｍ２（０．１６２ｇｆ／ｄ）、繊維応力０．１２６ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例１と同様の処理を行い、比重１．８４０、配向度８１．２％、繊維直径７．０μｍ、単繊維強度５９０ｋｇｆ／ｍｍ２、ストランド強度５７５ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００６５】
実施例３
表１に示すように、実施例１で得られた第一炭素化処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力１７５２ｇｆ／ｍｍ２（０．１０８ｇｆ／ｄ）、繊維応力０．０８４ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例１と同様の処理を行い、比重１．８３５、配向度８０．９％、繊維直径７．１μｍ、単繊維強度５６５ｋｇｆ／ｍｍ２、ストランド強度５５０ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００６６】
比較例１
表１に示すように、実施例１で得られた第一炭素化処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力４３７９ｇｆ／ｍｍ２（０．２７ｇｆ／ｄ）、繊維応力０．２０９ｇｆで処理し、糸切れの多い第二炭素化処理糸を得、引き続き実施例１と同様の処理を行った。
【００６７】
また、得られた炭素繊維は、比重１．８３５、配向度８１．３％、繊維直径６．８μｍ、単繊維強度５２０ｋｇｆ／ｍｍ２、ストランド強度５２５ｋｇｆ／ｍｍ２と低強度であった。
【００６８】
比較例２
表１に示すように、実施例１で得られた第一炭素化処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力１３１４ｇｆ／ｍｍ２（０．０８１ｇｆ／ｄ）、繊維応力０．０６３ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例１と同様の処理を行った。
【００６９】
しかし、得られた炭素繊維は、比重１．８３０、配向度８０．５％、繊維直径７．２μｍ、単繊維強度５４０ｋｇｆ／ｍｍ２、ストランド強度５３５ｋｇｆ／ｍｍ２と低強度であった。
【００７０】
比較例３
実施例１で得られた第一炭素化工程における一次延伸処理糸の二次延伸処理を、二次延伸が終了するまでにおいて比重が上昇した後下降する範囲、且つ結晶子サイズが１．４７ｎｍとなる範囲で、延伸倍率１．００倍で行い、比重１．８、配向度８０．１％、繊維直径７．８μｍ、繊維断面積０．００００４７７８２２ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００７１】
次いで、この処理糸を表１に示すように、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力２６２７ｇｆ／ｍｍ２（０．１６２ｇｆ／ｄ）、繊維応力０．１２６ｇｆで処理し、糸切れの多い第二炭素化処理糸を得、引き続き実施例１と同様の処理を行った。
【００７２】
また、得られた炭素繊維は、比重１．８１０、配向度８１．０％、繊維直径６．９μｍ、単繊維強度５１０ｋｇｆ／ｍｍ２、ストランド強度５１０ｋｇｆ／ｍｍ２と低強度であった。
【００７３】
実施例４
実施例１で得られた第一炭素化工程における一次延伸処理糸の二次延伸処理を、二次延伸が終了するまで比重が上昇し続ける範囲、且つ結晶子サイズが１．４５ｎｍより大きくならない範囲で、延伸倍率１．００倍で行い、比重１．７、配向度７９．４％、繊維直径８．２μｍ、繊維断面積０．００００５２８０８６ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００７４】
次いで、この処理糸を表１に示すように、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力２３２８ｇｆ／ｍｍ２（０．１５２ｇｆ／ｄ）、繊維応力０．１２３ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例１と同様の処理を行い、比重１．８３５、配向度８１．１％、繊維直径７．０μｍ、単繊維強度６２０ｋｇｆ／ｍｍ２、ストランド強度５９０ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００７５】
実施例５
実施例１で得られた第一炭素化工程における一次延伸処理糸の二次延伸処理を、二次延伸が終了するまで比重が上昇し続ける範囲、且つ結晶子サイズが１．４５ｎｍより大きくならない範囲で、延伸倍率１．０１倍で行い、比重１．６、配向度７７．６％、繊維直径８．４μｍ、繊維断面積０．００００５５４１６１ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００７６】
次いで、この処理糸を表１に示すように、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力２２３４ｇｆ／ｍｍ２（０．１５５ｇｆ／ｄ）、繊維応力０．１２４ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例１と同様の処理を行い、比重１．８３０、配向度８１．０％、繊維直径６．９μｍ、単繊維強度５６０ｋｇｆ／ｍｍ２、ストランド強度５５５ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００７７】
比較例４
実施例１で得られた第一炭素化工程における一次延伸処理糸の二次延伸処理を、二次延伸が終了するまでにおいて比重が変化しない（上昇しない）範囲、且つ結晶子サイズが１．４５ｎｍとなる範囲で、延伸倍率１．００倍で行い、比重１．５、配向度７７．０％、繊維直径９．０μｍ、繊維断面積０．００００６３６１５４ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００７８】
次いで、この処理糸を表１に示すように、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力２１８９ｇｆ／ｍｍ２（０．１６２ｇｆ／ｄ）、繊維応力０．１３９ｇｆで処理し、糸切れの多い第二炭素化処理糸を得、引き続き実施例１と同様の処理を行った。
【００７９】
また、得られた炭素繊維は、比重１．７９５、配向度８０．４％、繊維直径６．９μｍ、単繊維強度５００ｋｇｆ／ｍｍ２、ストランド強度４９０ｋｇｆ／ｍｍ２と低強度であった。
【００８０】
実施例６
アクリロニトリル９５質量％／アクリル酸メチル４質量％／イタコン酸１質量％よりなる共重合体紡糸原液を湿式又は乾湿式紡糸し、水洗・乾燥・延伸・オイリングして繊維直径８．４μｍの前駆体繊維を得た。この繊維を加熱空気中２００〜２５０℃の熱風循環式耐炎化炉で耐炎化処理し、繊維比重１．３３のポリアクリロニトリル系耐炎化糸を得た。
【００８１】
次いで、この耐炎化糸を不活性雰囲気中３００〜９００℃の温度範囲内の第一炭素化工程において、一次延伸・二次延伸処理を以下に示す条件で実施した。
【００８２】
一次延伸は図１のＢの範囲内で、延伸倍率１．０５５倍で処理した。この一次延伸処理後の糸、即ち一次延伸処理糸は、弾性率０．８５ｔｆ／ｍｍ２、比重１．３７、結晶子サイズ ０．９０ｎｍの、糸切れのない糸であった。
【００８３】
その後この一次延伸処理糸を、引き続き第一炭素化工程において、二次延伸が終了するまで比重が上昇し続ける範囲、且つ結晶子サイズが１．４５ｎｍより大きくならない範囲で、延伸倍率１．０１倍で二次延伸処理したところ、比重１．８、配向度８０．０％、繊維直径５．５μｍ、繊維断面積０．００００２３７５７６ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００８４】
さらに、上記処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力５２５５ｇｆ／ｍｍ２（０．３２４ｇｆ／ｄ）、繊維応力０．１２５ｇｆで処理し、引き続き公知の方法にて表面処理、サイジングを施し、乾燥して比重１．８３５、配向度８２．２％、繊維直径４．９μｍ、単繊維強度７２０ｋｇｆ／ｍｍ２、ストランド強度６９０ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００８５】
なお、本例の処理条件は、前駆体繊維の繊維直径８．４μｍと小さいため、実施例２と比較し、得られた炭素繊維の強度は１００ｋｇｆ／ｍｍ２余り高い。このことは、得られた炭素繊維の繊維直径の差のよるものと考えられる。
【００８６】
実施例７
表１に示すように、実施例６で得られた第一炭素化処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力３４８７ｇｆ／ｍｍ２（０．２１５ｇｆ／ｄ）、繊維応力０．０８３ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例６と同様の処理を行い、比重１．８３０、配向度８１．９％、繊維直径５．０μｍ、単繊維強度６９０ｋｇｆ／ｍｍ２、ストランド強度６７５ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００８７】
比較例５
表１に示すように、実施例６で得られた第一炭素化処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力７７０７ｇｆ／ｍｍ２（０．４７５２ｇｆ／ｄ）、繊維応力０．１８３ｇｆで処理し、糸切れの多い第二炭素化処理糸を得、引き続き実施例６と同様の処理を行った。
【００８８】
また、得られた炭素繊維は、比重１．８３０、配向度８２．０％、繊維直径４．８μｍ、単繊維強度６２０ｋｇｆ／ｍｍ２、ストランド強度６３５ｋｇｆ／ｍｍ２と繊維直径の小さいことを考慮に入れると低強度であった。
【００８９】
比較例６
表１に示すように、実施例６で得られた第一炭素化処理糸を第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力２４３３ｇｆ／ｍｍ２（０．１５ｇｆ／ｄ）、繊維応力０．０５８ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例６と同様の処理を行った。
【００９０】
しかし、得られた炭素繊維は、比重１．８２０、配向度８１．６％、繊維直径５．１μｍ、単繊維強度５４０ｋｇｆ／ｍｍ２、ストランド強度５３５ｋｇｆ／ｍｍ２と繊維直径の小さいことを考慮に入れると低強度であった。
【００９１】
比較例７
実施例６で得られた第一炭素化工程における一次延伸処理糸の二次延伸処理を、二次延伸が終了するまでにおいて比重が上昇した後下降する範囲、且つ結晶子サイズが１．４７ｎｍとなる範囲で、延伸倍率１．０１倍で行い、比重１．８、配向度８０．０％、繊維直径５．５μｍ、繊維断面積０．００００２３７５７６ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００９２】
次いで、この処理糸を表１に示すように、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力５２５５ｇｆ／ｍｍ２（０．３２４ｇｆ／ｄ）、繊維応力０．１２５ｇｆで処理し、糸切れの多い第二炭素化処理糸を得、引き続き実施例６と同様の処理を行った。
【００９３】
また、得られた炭素繊維は、比重１．８１０、配向度８１．８％、繊維直径５．０μｍ、単繊維強度５８０ｋｇｆ／ｍｍ２、ストランド強度６３０ｋｇｆ／ｍｍ２と繊維直径の小さいことを考慮に入れると低強度であった。
【００９４】
実施例８
実施例６で得られた第一炭素化工程における一次延伸処理糸の二次延伸処理を、二次延伸が終了するまで比重が上昇し続ける範囲、且つ結晶子サイズが１．４５ｎｍより大きくならない範囲で、延伸倍率１．０１倍で行い、比重１．７、配向度７９．５％、繊維直径５．８μｍ、繊維断面積０．００００２６４２００ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００９５】
次いで、この処理糸を表１に示すように、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力４５６４ｇｆ／ｍｍ２（０．２９８ｇｆ／ｄ）、繊維応力０．１２１ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例６と同様の処理を行い、比重１．８３０、配向度８２．１％、繊維直径４．９μｍ、単繊維強度６７０ｋｇｆ／ｍｍ２、ストランド強度６７５ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００９６】
実施例９
実施例６で得られた第一炭素化工程における一次延伸処理糸の二次延伸処理を、二次延伸が終了するまで比重が上昇し続ける範囲、且つ結晶子サイズが１．４５ｎｍより大きくならない範囲で、延伸倍率１．０１倍で行い、比重１．６、配向度７８．０％、繊維直径６．３μｍ、繊維断面積０．００００３１１７１５ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００９７】
次いで、この処理糸を表１に示すように、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力３４３１ｇｆ／ｍｍ２（０．２３８ｇｆ／ｄ）、繊維応力０．１０７ｇｆで処理し、糸切れのない第二炭素化処理糸を得、引き続き実施例６と同様の処理を行い、比重１．８３５、配向度８２．０％、繊維直径４．９μｍ、単繊維強度７３０ｋｇｆ／ｍｍ２、ストランド強度７００ｋｇｆ／ｍｍ２の炭素繊維を得た。
【００９８】
比較例８
実施例６で得られた第一炭素化工程における一次延伸処理糸の二次延伸処理を、二次延伸が終了するまでにおいて比重が変化しない（上昇しない）範囲、且つ結晶子サイズが１．４５ｎｍとなる範囲で、延伸倍率１．０１倍で行い、比重１．５、配向度７７．３％、繊維直径６．８μｍ、繊維断面積０．００００３６３１５７ｍｍ２の、糸切れのない二次延伸処理糸が得られた。
【００９９】
次いで、この処理糸を表１に示すように、第二炭素化工程において、不活性雰囲気中８００〜１７００℃の温度範囲内で、繊維張力４３７９ｇｆ／ｍｍ２（０．３２４ｇｆ／ｄ）、繊維応力０．１５９ｇｆで処理し、糸切れの多い第二炭素化処理糸を得、引き続き実施例６と同様の処理を行った。
【０１００】
また、得られた炭素繊維は、比重１．８０５、配向度８１．４％、繊維直径４．８μｍ、単繊維強度５００ｋｇｆ／ｍｍ２、ストランド強度６１０ｋｇｆ／ｍｍ２と繊維直径の小さいことを考慮に入れると低強度であった。
【０１０１】
【表１】
【発明の効果】
本発明の製造法によれば、第一炭素化工程、及び第一炭素化工程において、繊維の各種物性を参照して炭素化処理を行うことにより、高配向且つボイドレスな緻密な構造を有する高強度炭素繊維を得ることができる。
【図面の簡単な説明】
【図１】第一炭素化工程における一次延伸時の温度上昇に対するＰＡＮ系耐炎化繊維の弾性率の推移を示すグラフである。
【図２】第一炭素化工程における一次延伸時の温度上昇に対するＰＡＮ系耐炎化繊維の結晶子サイズの推移を示すグラフである。
【図３】第一炭素化工程における二次延伸時の温度上昇に対する一次延伸処理糸の比重の推移を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing high-strength carbon fiber.
[0002]
[Prior art]
BACKGROUND ART Conventionally, it has been known that high-performance carbon fibers are produced from polyacrylonitrile (PAN) fibers as raw materials, and are used in a wide range of fields from aircraft to sports equipment.
[0003]
In particular, high-strength and high-elasticity carbon fibers are used for aerospace applications, and these are required to have higher performance.
[0004]
As a method for producing a carbon fiber using a PAN-based precursor fiber, the precursor fiber is subjected to an oxidation treatment (flame-resistance treatment) while being stretched or shrunk in an oxidizing atmosphere at 200 to 300 ° C. There is known a method of performing carbonization in an inert gas atmosphere at a temperature of １０００1000 ° C. or higher.
[0005]
In particular, the fiber treatment method in the carbonization step at around 300 to 900 ° C. greatly affects the strength development of carbon fibers, and many studies have been made so far.
[0006]
In
[0007]
Further, in Patent Documents 2 and 3, in order to control a sudden change in fiber length near 500 ° C., a fine high-density process is performed by dividing the process into 300 to 500 ° C. and 500 to 800 ° C. It is disclosed that a high strength carbon fiber can be obtained.
[0008]
Further, in Patent Document 4, the flame-resistant fiber is heated in an inert atmosphere at a heating rate of 50 to 300 ° C./min until the specific gravity reaches 1.45, and further until the specific gravity reaches 1.60 to 1.75. It is disclosed that carbon fibers with few voids can be obtained by performing two-stage carbonization at a heating rate of 100 to 800 ° C./min.
[0009]
Patent Literature 5 also discloses that, similarly to Patent Literature 4, a dense carbon fiber can be obtained by controlling the temperature rising gradient at 300 to 800 ° C.
[0010]
However, in order to obtain a carbon fiber having high density, high degree of orientation and high strength, it is necessary to perform contraction with optimal fiber physical properties, and the temperature range and temperature gradient described in these methods are required. It is difficult to control the fineness of the fiber alone, and it is difficult to obtain a carbon fiber with high density, high degree of orientation and high strength by using only the specific gravity as a parameter. There is a demand for a method for obtaining carbon fibers.
[0011]
Further, the treated yarn (first carbonized treated yarn) obtained in such a conventional low-temperature carbonizing step (first carbonized step) is subjected to the subsequent high-temperature carbonizing step (second carbonized step). When the high tension treatment is performed in (1), there are problems such as a decrease in specific gravity and an increase in thread breakage.
[0012]
[Patent Document 1]
JP-A-54-147222 (
[Patent Document 2]
JP-A-59-150116 (pages 1-2)
[Patent Document 3]
Japanese Patent Publication No. 3-23651 (pages 1-3)
[Patent Document 4]
Japanese Patent Publication No. 3-17925 (pages 1-3)
[Patent Document 5]
JP-A-62-231028 (
[0013]
[Problems to be solved by the invention]
The present inventor has conducted extensive studies over the years, and as a result, in the carbonization process, there is an important relationship between each physical property of the oxidized fiber, the temperature, and the draw ratio, and by controlling these, high strength is obtained. It has been found that carbon fibers can be produced. That is, the first carbonization step of the carbonization step of carbonizing the PAN-based oxidized fiber comprises a first carbonization step and a second carbonization step, and is divided into a primary stretching treatment and a secondary stretching treatment. Along with stretching at a predetermined temperature and stretching ratio, primary stretching is performed within a range where the modulus of elasticity, specific gravity, and crystallite size in wide-angle X-ray measurement of the oxidized fiber satisfy a predetermined range, and secondary stretching is performed. By performing the treatment in a range in which the specific gravity of the fiber after the primary drawing treatment and the crystallite size in wide-angle X-ray measurement satisfy a predetermined range, it is possible to produce a high-strength carbon fiber. It was found that a chemically treated yarn was obtained.
[0014]
It is known that the first carbonized yarn obtained in this way can provide a high-strength carbon fiber without causing a decrease in specific gravity or yarn breakage even when subjected to a high tension treatment in the second carbonization step. Thus, the present invention has been completed.
[0015]
Accordingly, it is an object of the present invention to provide a method for producing high-strength carbon fiber which solves the above-mentioned problems.
[0016]
[Means for Solving the Problems]
The present invention that achieves the above object is as described below.
[0017]
[1] In an inert atmosphere, in a first carbonization step, a polyacrylonitrile-based oxidized fiber having a specific gravity of 1.3 to 1.4 is heated in a temperature range of 300 to 900 ° C. to a temperature of 1.03 to 1.06. A method for producing a carbon fiber in which a primary stretching process is performed at a stretching ratio and then a second stretching process is performed at a stretching ratio of 0.9 to 1.01, and then carbonized in a temperature range of 800 to 1700 ° C. in a second carbonization step. In the first step, the primary stretching in the first carbonization step is performed within a range satisfying any of the following conditions (1) to (3), and the secondary stretching is performed within a range satisfying both the following conditions (4) and (5). And a method of producing a carbon fiber in the second carbonization step in a range satisfying (6).
First carbonization process conditions
Primary stretching conditions
(1) 1.0 tf / mm from the time when the modulus of elasticity of the polyacrylonitrile-based oxidized fiber decreases to a minimum value. 2 Range to increase to
(2) Range until the specific gravity of the polyacrylonitrile-based oxidized fiber reaches 1.5
(3) Range until crystallite size reaches 1.45 nm in wide angle X-ray measurement (diffraction angle 26 °) of polyacrylonitrile-based oxidized fiber
Secondary stretching conditions
(4) The range in which the specific gravity of the fiber after the primary drawing continues to increase during the secondary drawing
(5) The range where the crystallite size in the wide-angle X-ray measurement (diffraction angle 26 °) of the fiber after the primary drawing treatment does not become larger than 1.45 nm.
Second carbonization process conditions
(6) Fiber tension (F gf / mm) in the second carbonization step 2 ) And the fiber cross-sectional area after the first carbonization step (S mm 2 ) Is calculated by the following equation.
0.18>D> 0.08
[However, D = F × S]
Range to satisfy
[2] The method for producing a carbon fiber according to [1], wherein the degree of orientation of the fiber after the first carbonization step is 76.0% or more in wide-angle X-ray measurement (diffraction angle 26 °).
[0018]
[3] The method of producing a carbon fiber according to [1] or [2], wherein the carbon fiber obtained after the second carbonization step has a single fiber diameter of 3 to 8 μm.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
[0020]
The PAN-based precursor fiber used in the method for producing a carbon fiber of the present invention was prepared by spinning a spinning solution obtained by polymerizing a monomer containing acrylonitrile at 90% by mass or more, preferably 95% by mass or more, by a wet or dry-wet spinning method. Thereafter, it is preferable to use fibers obtained by washing, drying and stretching. As these precursor fibers, conventionally known ones can be used without any limitation.
[0021]
The obtained precursor fiber is subsequently subjected to a flameproofing treatment at 200 to 280 ° C in heated air. The treatment at this time is generally performed at a draw ratio of 0.85 to 1.3 to obtain a PAN-based oxidized fiber having a fiber specific gravity of 1.3 to 1.4. The tension (stretch distribution) is not particularly limited.
[0022]
In the method for producing carbon fiber of the present invention, the oxidized fiber is subjected to a draw ratio of 1.03 to 1.06 in an inert atmosphere in a first carbonization step within a temperature range of 300 to 900 ° C. And then secondarily stretched at a stretching ratio of 0.9 to 1.01, and then carbonized in a temperature range of 800 to 1700 ° C. in the second carbonization step.
[0023]
In the above-mentioned first carbonization step, in the primary drawing treatment, 1.0 tf / mm from the point in time when the elastic modulus of the PAN-based oxidized fiber decreased to the minimum value. 2 , A range in which the specific gravity of the fiber reaches 1.5, and a range in which the crystallite size in the wide-angle X-ray measurement (diffraction angle 26 °) of the fiber reaches 1.45 nm. The stretching treatment is performed at a stretching ratio of 1.03 to 1.06.
[0024]
1.0 tf / mm from the time when the elastic modulus of the PAN-based oxidized fiber decreased to the minimum value 2 Is the range of B shown in FIG.
[0025]
1.0 tf / mm from the time when the modulus of elasticity of the oxidized fiber is reduced to the minimum value 2 By performing stretching (1.03 to 1.06 times) in the range up to increase, the yarn breakage is suppressed, the low elastic modulus portion is efficiently stretched, and high orientation can be performed, and dense primary stretching is performed. A treated yarn can be obtained.
[0026]
On the other hand, stretching of 1.03 times or more before the elastic modulus decreases to the minimum value (range A) is not preferable because it increases yarn breakage and causes a significant decrease in strength.
[0027]
Further, the elastic modulus decreases to a minimum value, and then 1.0 tf / mm 2 Stretching of 1.03 times or more after the increase in the range (C range) is not preferable because the elastic modulus of the yarn is high and forced stretching is performed, thereby increasing fiber defects and voids and impairing the effect of drawing. . Therefore, the primary stretching treatment is performed within the range of the elastic modulus.
[0028]
By performing stretching (1.03 to 1.06 times) in the range until the specific gravity of the flame-resistant fiber reaches 1.5, the degree of orientation can be improved while suppressing the generation of voids, and the primary quality is high. A drawn yarn can be obtained.
[0029]
On the other hand, the primary stretching of 1.03 times or more in the range where the specific gravity is higher than 1.5 is preferable because it increases the generation of voids by unreasonable stretching and eventually causes structural defects of the carbon fiber and a decrease in specific gravity. Absent. Therefore, the primary stretching treatment is performed within the range of the above specific gravity.
[0030]
The crystallite size of the PAN-based oxidized fiber in wide-angle X-ray measurement (diffraction angle: 26 °) continues to increase as the temperature increases during the primary stretching treatment. The increasing state is a curve having inflection points near the crystallite size of 0.9 nm and 1.45 nm as shown in FIG. Therefore, the range until the crystallite size reaches 1.45 nm described above is a range until the inflection point is reached later.
[0031]
Stretching (1.03 to 1.06 times) in the range until the crystallite size in the wide-angle X-ray measurement (diffraction angle 26 °) of the oxidized fiber reaches 1.45 nm increases the density and the number of voids. Thus, a primary drawn yarn can be obtained.
[0032]
On the other hand, the primary stretching of 1.03 times or more after the crystallite size reaches 1.45 nm is not preferable because not only yarn stretching is caused by excessive stretching but also voids are generated.
[0033]
On the other hand, if the stretching ratio in the primary stretching is less than 1.03, the effect of stretching is small, and high-strength carbon fibers cannot be obtained. If the draw ratio is higher than 1.06, yarn breakage is caused, and high-quality and high-strength carbon fibers cannot be obtained.
[0034]
The primary drawn yarn obtained by the above method is subsequently subjected to the following secondary drawing treatment.
[0035]
The range in which the specific gravity of the fiber after the primary drawing continues to increase during the secondary drawing, and the range in which the crystallite size in the wide-angle X-ray measurement (diffraction angle 26 °) of the fiber after the primary drawing does not become larger than 1.45 nm. At a stretching ratio of 0.9 to 1.01 times.
[0036]
As shown in FIG. 3, the specific gravity of the fiber after the primary stretching during the secondary stretching is not changed (not increased), continuously increased, and decreased after the temperature (secondary). A condition under which the specific gravity of the fiber is reduced during the stretching treatment).
[0037]
Of these conditions, by performing the stretching treatment at a stretching ratio of 0.9 to 1.01 times under the condition that the specific gravity of the fiber after the primary stretching process continues to increase during the secondary stretching process, By performing the stretching treatment under the condition of continuing to rise without containing or lowering, the generation of voids can be suppressed, and finally a dense carbon fiber can be obtained.
[0038]
On the other hand, if the specific gravity of the fiber decreases during the secondary stretching, the generation of voids increases, and a dense carbon fiber cannot be obtained, which is not preferable. In addition, it is not preferable to include a section where the specific gravity of the fiber does not change during the secondary stretching, because the effect of the secondary stretching is not seen. Therefore, the secondary drawing treatment is in a range where the fiber specific gravity continues to increase.
[0039]
Further, by performing stretching at a stretching ratio of 0.9 to 1.01 times within a range in which the crystallite size in the wide-angle X-ray measurement (diffraction angle 26 °) of the fiber after the primary stretching is not larger than 1.45 nm. Thus, the crystal is densified without growing the crystal, the generation of voids can be suppressed, and finally a carbon fiber having high densities can be obtained.
[0040]
On the other hand, the second stretching treatment in a range where the crystallite size is larger than 1.45 nm increases void generation and lowers the quality due to thread breakage, and cannot obtain high-strength carbon fibers. Is not preferred. Therefore, the secondary stretching is performed within the range of the crystallite size.
[0041]
If the stretching ratio in the secondary stretching treatment is less than 0.9, the degree of orientation is remarkably reduced and a high-strength carbon fiber cannot be obtained, which is not preferable. When the draw ratio is higher than 1.01, the yarn breakage is caused, and high-quality and high-strength carbon fibers cannot be obtained. Therefore, the stretching ratio in the secondary stretching is preferably in the range of 0.9 to 1.01.
[0042]
In order to obtain a high-strength carbon fiber, it is preferable that the degree of orientation of the first carbonized yarn is 76.0% or more in wide-angle X-ray measurement (diffraction angle 26 °).
[0043]
If it is less than 76.0%, a high-strength carbon fiber cannot be finally obtained, which is not preferable.
[0044]
As described above, the primary drawing process and the secondary drawing process of the oxidized fiber in the first carbonization step are performed to obtain the first carbonized yarn. In addition, the first carbonization step may be performed continuously or separately in one furnace or two or more furnaces, and there is no problem as long as the processing is performed within the above-described processing conditions. .
[0045]
Subsequently, in the second carbonization step, the first carbonized yarn is carbonized in an inert atmosphere within a temperature range of 800 to 1700 ° C. and under high tension.
[0046]
The fiber tension in the second carbonization step (F gf / mm 2 ) Is the fiber diameter after the first carbonization step, that is, the fiber cross-sectional area (S mm 2 ), The fiber stress (D gf) is used as a tension factor in the present invention.
0.18>D> 0.08
[However, D = F × S]
Range.
[0047]
Here, the fiber cross-sectional area is a value obtained by measuring the fiber diameter at n = 20, using the average value thereof, and calculating as a perfect circle.
[0048]
When the first carbonization yarn obtained in the conventional first carbonization step is subjected to the second carbonization treatment under a high tension in a temperature range of 800 to 1700 ° C., the specific gravity decreases and the specific gravity is 1.81 or more. It is difficult to obtain such a material, and there are problems such as increased yarn breakage. Moreover, it is difficult to obtain highly oriented carbon fibers by the conventional method.
[0049]
On the other hand, when the first carbonized yarn obtained by the method of the present invention is subjected to the second carbonization treatment in a temperature range of 800 to 1700 ° C, the specific gravity does not decrease and the yarn does not break even under high tension. , Specific gravity of 1.82 or more can be obtained, and the second carbonized yarn obtained by the method of the present invention can be easily obtained in a high orientation since it is treated under high tension. .
[0050]
Thus, the method of the present invention is capable of performing carbonization treatment under high tension in the second carbonization step without lowering the specific gravity or causing yarn breakage, increasing the degree of orientation, and achieving high strength. A second carbonized yarn is obtained.
[0051]
The obtained second carbonized yarn, that is, the carbon fiber obtained after the completion of the second carbonization step, can be subsequently converted into a surface-treated carbon fiber by a known method. Furthermore, it is preferable to perform a sizing treatment for the purpose of facilitating post-processing of the carbon fiber and improving the handleability. The sizing method can be performed by a conventionally known method, and it is preferable that the sizing agent is used after changing the composition as appropriate according to the application, and that the sizing agent is uniformly adhered and then dried.
[0052]
In addition, the single fiber diameter of the second carbonized yarn is preferably 3 to 8 μm.
[0053]
The carbon fiber thus obtained has high strength and can be produced by the production method of the present invention.
[0054]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The stretching conditions, after stretching, and the methods for evaluating the physical properties of carbon fibers in the respective examples and comparative examples were implemented by the following methods.
[0055]
<Crystallite size, degree of orientation>
Using an X-ray diffractometer: RINT1200L manufactured by Rigaku and a computer: Hitachi 2050/32, the crystallite size at a diffraction angle of 26 ° was determined from the diffraction pattern, and the degree of orientation was determined from the half width.
[0056]
<Specific gravity>
It was measured by the Archimedes method. The sample fiber was degassed in acetone and measured.
[0057]
<Strength and elastic modulus of carbon fiber strand>
It was measured by the method specified in JIS R 7601.
[0058]
<Single fiber elastic modulus>
It was measured by the method specified in JIS R 7606 (2000).
[0059]
Example 1
A copolymer spinning stock solution consisting of 95% by mass of acrylonitrile / 4% by mass of methyl acrylate / 1% by mass of itaconic acid is wet- or dry-wet spun, washed with water, dried, stretched and oiled, and precursor fiber having a fiber diameter of 11.7 μm. Got. The fiber was subjected to a flame-proof treatment in a hot-air circulation type flame-proof furnace at 200 to 250 ° C. in heated air to obtain a polyacrylonitrile-based flame-resistant yarn having a fiber specific gravity of 1.33.
[0060]
Next, in the first carbonization step of the flame-resistant yarn in a temperature range of 300 to 900 ° C. in an inert atmosphere, primary stretching and secondary stretching were performed under the following conditions.
[0061]
The primary stretching was performed at a stretching ratio of 1.04 within the range of B in FIG. The yarn after the primary drawing, that is, the primary drawn yarn has an elastic modulus of 0.8 tf / mm. 2 The yarn had a specific gravity of 1.36 and a crystallite size of 0.90 nm and had no breakage.
[0062]
Thereafter, in the first carbonization step, the primary drawn yarn is stretched to 1.01 times in a range where the specific gravity continues to increase until the secondary drawing is completed and the crystallite size does not become larger than 1.45 nm. , A specific gravity of 1.8, a degree of orientation of 80.2%, a fiber diameter of 7.8 μm, and a fiber cross-sectional area of 0.0000477822 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0063]
Further, in the second carbonization step, the treated yarn is subjected to a fiber tension of 3519 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.217 gf / d) and a fiber stress of 0.168 gf, followed by surface treatment and sizing by a known method, and dried to a specific gravity of 1.840, a degree of orientation of 81.3%, and a fiber diameter of 6.9 μm. , Single fiber strength 570kgf / mm 2 , Strand strength 565kgf / mm 2 Was obtained.
[0064]
Example 2
As shown in Table 1, in the second carbonization step, the first carbonized yarn obtained in Example 1 was subjected to a fiber tension of 2627 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.162 gf / d) and a fiber stress of 0.126 gf to obtain a second carbonized yarn without breakage. Subsequently, the same treatment as in Example 1 is performed to obtain a specific gravity of 1.840 and a degree of orientation of 81. 2%, fiber diameter 7.0 μm, single fiber strength 590 kgf / mm 2 , Strand strength 575kgf / mm 2 Was obtained.
[0065]
Example 3
As shown in Table 1, in the second carbonization step, the first carbonized yarn obtained in Example 1 was subjected to a fiber tension of 1752 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.108 gf / d) and a fiber stress of 0.084 gf to obtain a second carbonized yarn without breakage. Subsequently, the same treatment as in Example 1 was performed, with a specific gravity of 1.835 and a degree of orientation of 80. 9%, fiber diameter 7.1 μm, single fiber strength 565 kgf / mm 2 , Strand strength 550kgf / mm 2 Was obtained.
[0066]
Comparative Example 1
As shown in Table 1, the first carbonized yarn obtained in Example 1 was subjected to a fiber tension of 4379 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. in the second carbonization step. 2 (0.27 gf / d) and a fiber stress of 0.209 gf to obtain a second carbonized yarn having many yarn breaks. The same treatment as in Example 1 was subsequently performed.
[0067]
The obtained carbon fiber had a specific gravity of 1.835, a degree of orientation of 81.3%, a fiber diameter of 6.8 μm, and a single fiber strength of 520 kgf / mm. 2 , Strand strength 525kgf / mm 2 And low strength.
[0068]
Comparative Example 2
As shown in Table 1, the first carbonized yarn obtained in Example 1 was subjected to a fiber tension of 1314 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. in the second carbonization step. 2 (0.081 gf / d) and a fiber stress of 0.063 gf to obtain a second carbonized yarn without breakage, and the same treatment as in Example 1 was successively performed.
[0069]
However, the obtained carbon fiber had a specific gravity of 1.830, a degree of orientation of 80.5%, a fiber diameter of 7.2 μm, and a single fiber strength of 540 kgf / mm. 2 , Strand strength 535kgf / mm 2 And low strength.
[0070]
Comparative Example 3
The secondary drawing of the primary drawn yarn in the first carbonization step obtained in Example 1 is performed until the specific gravity increases and then falls until the secondary drawing is completed, and the crystallite size is 1.47 nm. In a certain range, the stretching is performed at a draw ratio of 1.00, specific gravity 1.8, orientation degree 80.1%, fiber diameter 7.8 μm, fiber cross-sectional area 0.0000477822 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0071]
Next, as shown in Table 1, in the second carbonization step, the treated yarn was subjected to a fiber tension of 2627 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.162 gf / d) and a fiber stress of 0.126 gf to obtain a second carbonized yarn having many yarn breaks, and subsequently the same treatment as in Example 1 was performed.
[0072]
The obtained carbon fiber had a specific gravity of 1.810, a degree of orientation of 81.0%, a fiber diameter of 6.9 μm, and a single fiber strength of 510 kgf / mm. 2 , Strand strength 510kgf / mm 2 And low strength.
[0073]
Example 4
The secondary drawing of the primary drawn yarn in the first carbonization step obtained in Example 1 is performed in a range where the specific gravity continues to increase until the secondary drawing is completed, and a range where the crystallite size does not become larger than 1.45 nm. The stretching ratio was 1.00, the specific gravity was 1.7, the degree of orientation was 79.4%, the fiber diameter was 8.2 μm, and the fiber cross-sectional area was 0.0000528086 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0074]
Next, as shown in Table 1, in the second carbonization step, the treated yarn was subjected to a fiber tension of 2328 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.152 gf / d) and a fiber stress of 0.123 gf to obtain a second carbonized yarn without breakage. Subsequently, the same treatment as in Example 1 was performed to obtain a specific gravity of 1.835 and a degree of orientation of 81. 1%, fiber diameter 7.0 μm, single fiber strength 620 kgf / mm 2 , Strand strength 590kgf / mm 2 Was obtained.
[0075]
Example 5
The secondary drawing of the primary drawn yarn in the first carbonization step obtained in Example 1 is performed in a range where the specific gravity continues to increase until the secondary drawing is completed, and a range where the crystallite size does not become larger than 1.45 nm. At a draw ratio of 1.01, and a specific gravity of 1.6, a degree of orientation of 77.6%, a fiber diameter of 8.4 μm, and a fiber cross-sectional area of 0.0000554161 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0076]
Next, as shown in Table 1, in the second carbonization step, the treated yarn was subjected to a fiber tension of 2234 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.155 gf / d) and a fiber stress of 0.124 gf to obtain a second carbonized yarn without breakage. Subsequently, the same treatment as in Example 1 is performed, and the specific gravity is 1.830 and the degree of orientation is 81. 0%, fiber diameter 6.9 μm, single fiber strength 560 kgf / mm 2 , Strand strength 555kgf / mm 2 Was obtained.
[0077]
Comparative Example 4
In the secondary drawing of the primary drawn yarn in the first carbonization step obtained in Example 1, the specific gravity does not change (do not rise) until the secondary drawing is completed, and the crystallite size is 1.45 nm. The stretching is performed at a draw ratio of 1.00, the specific gravity is 1.5, the degree of orientation is 77.0%, the fiber diameter is 9.0 μm, and the fiber cross section is 0.0000636154 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0078]
Next, as shown in Table 1, this treated yarn was subjected to a fiber tension of 2189 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. in the second carbonization step. 2 (0.162 gf / d) and a fiber stress of 0.139 gf to obtain a second carbonized yarn having many yarn breaks, and subsequently the same treatment as in Example 1 was performed.
[0079]
The obtained carbon fiber had a specific gravity of 1.795, a degree of orientation of 80.4%, a fiber diameter of 6.9 μm, and a single fiber strength of 500 kgf / mm. 2 , Strand strength 490kgf / mm 2 And low strength.
[0080]
Example 6
A copolymer spinning stock solution consisting of 95% by mass of acrylonitrile / 4% by mass of methyl acrylate / 1% by mass of itaconic acid is wet- or dry-wet spun, washed with water, dried, stretched and oiled, and precursor fibers having a fiber diameter of 8.4 μm. Got. The fiber was subjected to a flame-proof treatment in a hot-air circulation type flame-proof furnace at 200 to 250 ° C. in heated air to obtain a polyacrylonitrile-based flame-resistant yarn having a fiber specific gravity of 1.33.
[0081]
Next, in the first carbonization step of the flame-resistant yarn in a temperature range of 300 to 900 ° C. in an inert atmosphere, primary stretching and secondary stretching were performed under the following conditions.
[0082]
The primary stretching was performed at a stretching ratio of 1.055 within the range of B in FIG. The yarn after the primary drawing, that is, the primary drawn yarn has an elastic modulus of 0.85 tf / mm. 2 The yarn had a specific gravity of 1.37 and a crystallite size of 0.90 nm and had no breakage.
[0083]
Thereafter, in the first carbonization step, the primary drawn yarn is stretched to 1.01 times in a range where the specific gravity continues to increase until the secondary drawing is completed and the crystallite size does not become larger than 1.45 nm. , The specific gravity is 1.8, the degree of orientation is 80.0%, the fiber diameter is 5.5 μm, and the fiber cross section is 0.0000237576 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0084]
Further, in the second carbonization step, the treated yarn is subjected to a fiber tension of 5255 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.324 gf / d), treated with a fiber stress of 0.125 gf, subsequently subjected to surface treatment and sizing by a known method, and dried to obtain a specific gravity of 1.835, a degree of orientation of 82.2%, and a fiber diameter of 4.9 μm. , Single fiber strength 720 kgf / mm 2 , Strand strength 690kgf / mm 2 Was obtained.
[0085]
The processing conditions of this example are as follows: the fiber diameter of the precursor fiber is as small as 8.4 μm, so that the strength of the obtained carbon fiber is 100 kgf / mm as compared with Example 2. 2 Too expensive. This is considered to be due to the difference in the fiber diameter of the obtained carbon fibers.
[0086]
Example 7
As shown in Table 1, the first carbonized yarn obtained in Example 6 was subjected to a fiber tension of 3487 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. in the second carbonization step. 2 (0.215 gf / d) and a fiber stress of 0.083 gf to obtain a second carbonized yarn without breakage. Subsequently, the same treatment as in Example 6 was performed to obtain a specific gravity of 1.830 and a degree of orientation of 81. 9%, fiber diameter 5.0 μm, single fiber strength 690 kgf / mm 2 , Strand strength 675kgf / mm 2 Was obtained.
[0087]
Comparative Example 5
As shown in Table 1, the first carbonized yarn obtained in Example 6 was subjected to a fiber tension of 7707 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. in the second carbonization step. 2 (0.4752 gf / d) and a fiber stress of 0.183 gf to obtain a second carbonized yarn having many yarn breaks. The same treatment as in Example 6 was subsequently performed.
[0088]
The obtained carbon fiber had a specific gravity of 1.830, a degree of orientation of 82.0%, a fiber diameter of 4.8 μm, and a single fiber strength of 620 kgf / mm. 2 , Strand strength 635 kgf / mm 2 When the fiber diameter was small, the strength was low.
[0089]
Comparative Example 6
As shown in Table 1, in the second carbonization step, the first carbonized yarn obtained in Example 6 was subjected to a fiber tension of 2433 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.15 gf / d) and a fiber stress of 0.058 gf to obtain a second carbonized yarn without breakage. The same treatment as in Example 6 was subsequently performed.
[0090]
However, the obtained carbon fiber had a specific gravity of 1.820, a degree of orientation of 81.6%, a fiber diameter of 5.1 μm, and a single fiber strength of 540 kgf / mm. 2 , Strand strength 535kgf / mm 2 When the fiber diameter was small, the strength was low.
[0091]
Comparative Example 7
The secondary drawing of the primary drawn yarn in the first carbonization step obtained in Example 6 was performed until the specific gravity increased and then decreased until the secondary drawing was completed, and the crystallite size was 1.47 nm. In a certain range, the stretching was performed at a draw ratio of 1.01, and the specific gravity was 1.8, the degree of orientation was 80.0%, the fiber diameter was 5.5 μm, and the fiber cross-sectional area was 0.0000237576 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0092]
Next, as shown in Table 1, this treated yarn was subjected to a fiber tension of 5255 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. in the second carbonization step. 2 (0.324 gf / d) and a fiber stress of 0.125 gf to obtain a second carbonized yarn having many yarn breaks, and the same treatment as in Example 6 was performed.
[0093]
The obtained carbon fiber had a specific gravity of 1.810, a degree of orientation of 81.8%, a fiber diameter of 5.0 μm, and a single fiber strength of 580 kgf / mm. 2 , Strand strength 630kgf / mm 2 When the fiber diameter was small, the strength was low.
[0094]
Example 8
In the secondary drawing of the primary drawn yarn in the first carbonization step obtained in Example 6, the specific gravity is continuously increased until the secondary drawing is completed, and the crystallite size is not larger than 1.45 nm. At a draw ratio of 1.01, a specific gravity of 1.7, a degree of orientation of 79.5%, a fiber diameter of 5.8 μm, and a fiber cross-sectional area of 0.0000264200 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0095]
Next, as shown in Table 1, this treated yarn was subjected to a fiber tension of 4564 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. in the second carbonization step. 2 (0.298 gf / d) and a fiber stress of 0.121 gf to obtain a second carbonized yarn without breakage. Subsequently, the same treatment as in Example 6 was performed to obtain a specific gravity of 1.830 and a degree of orientation of 82. 1%, fiber diameter 4.9 μm, single fiber strength 670 kgf / mm 2 , Strand strength 675kgf / mm 2 Was obtained.
[0096]
Example 9
In the secondary drawing of the primary drawn yarn in the first carbonization step obtained in Example 6, the specific gravity is continuously increased until the secondary drawing is completed, and the crystallite size is not larger than 1.45 nm. At a draw ratio of 1.01, a specific gravity of 1.6, a degree of orientation of 78.0%, a fiber diameter of 6.3 μm, and a fiber cross-sectional area of 0.00003111715 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0097]
Next, as shown in Table 1, in the second carbonization step, the treated yarn was subjected to a fiber tension of 3431 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. 2 (0.238 gf / d) and a fiber stress of 0.107 gf to obtain a second carbonized yarn without breakage. Subsequently, the same treatment as in Example 6 was performed to obtain a specific gravity of 1.835 and a degree of orientation of 82. 0%, fiber diameter 4.9 μm, single fiber strength 730 kgf / mm 2 , Strand strength 700kgf / mm 2 Was obtained.
[0098]
Comparative Example 8
In the secondary drawing of the primary drawn yarn in the first carbonization step obtained in Example 6, the specific gravity does not change (do not increase) until the secondary drawing is completed, and the crystallite size is 1.45 nm. In this range, the stretching is performed at a draw ratio of 1.01, and the specific gravity is 1.5, the degree of orientation is 77.3%, the fiber diameter is 6.8 μm, and the fiber cross section is 0.0000363157 mm. 2 Thus, a secondary drawn yarn without breakage was obtained.
[0099]
Next, as shown in Table 1, this treated yarn was subjected to a fiber tension of 4379 gf / mm in an inert atmosphere within a temperature range of 800 to 1700 ° C. in the second carbonization step. 2 (0.324 gf / d) and a fiber stress of 0.159 gf to obtain a second carbonized yarn having many yarn breaks. The same treatment as in Example 6 was subsequently performed.
[0100]
The obtained carbon fiber had a specific gravity of 1.805, a degree of orientation of 81.4%, a fiber diameter of 4.8 μm, and a single fiber strength of 500 kgf / mm. 2 , Strand strength 610kgf / mm 2 When the fiber diameter was small, the strength was low.
[0101]
[Table 1]
【The invention's effect】
According to the production method of the present invention, in the first carbonization step, and in the first carbonization step, the carbonization treatment is performed with reference to various physical properties of the fiber, whereby a highly oriented and voidless dense structure having a dense structure is obtained. A strong carbon fiber can be obtained.
[Brief description of the drawings]
FIG. 1 is a graph showing a change in the elastic modulus of a PAN-based oxidized fiber with respect to a rise in temperature during primary stretching in a first carbonization step.
FIG. 2 is a graph showing a change in crystallite size of a PAN-based oxidized fiber with respect to a temperature rise during primary stretching in a first carbonization step.
FIG. 3 is a graph showing a change in specific gravity of a first drawn yarn with respect to a temperature rise during a second drawing in a first carbonization step.
Claims (3)
第一炭素化工程条件
一次延伸条件
（１） ポリアクリロニトリル系耐炎化繊維の弾性率が極小値まで低下した時点から１．０ｔｆ／ｍｍ２に増加するまでの範囲
（２） ポリアクリロニトリル系耐炎化繊維の比重が１．５に達するまでの範囲
（３） ポリアクリロニトリル系耐炎化繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズが１．４５ｎｍに達するまでの範囲
二次延伸条件
（４） 一次延伸処理後の繊維の比重が二次延伸処理中に上昇し続ける範囲
（５） 一次延伸処理後の繊維の広角Ｘ線測定（回折角２６°）における結晶子サイズが１．４５ｎｍより大きくならない範囲
第二炭素化工程条件
（６） 第二炭素化工程での繊維張力（Ｆ ｇｆ／ｍｍ２）と第一炭素化工程後の繊維断面積（Ｓ ｍｍ２）とで算出される繊維応力（Ｄ ｇｆ）が下式
０．１８ ＞ Ｄ ＞ ０．０８
〔但し、Ｄ ＝ Ｆ × Ｓ〕
を満たす範囲In an inert atmosphere, in the first carbonization step, a polyacrylonitrile-based oxidized fiber having a specific gravity of 1.3 to 1.4 is drawn at a draw ratio of 1.03 to 1.06 within a temperature range of 300 to 900 ° C. In the method for producing carbon fibers, a primary stretching treatment is performed, followed by a secondary stretching treatment at a stretching ratio of 0.9 to 1.01, and then carbonizing in a temperature range of 800 to 1700 ° C. in a second carbonization step. The primary stretching in the one carbonization step is performed in a range that satisfies all of the following conditions (1) to (3), and the secondary stretching is performed in a range that satisfies both of the following conditions (4) and (5). A method for producing carbon fibers in the second carbonization step in a range satisfying (6).
First carbonization step conditions Primary stretching conditions (1) Range from the point at which the elastic modulus of the polyacrylonitrile-based oxidized fiber decreases to a minimum value until it increases to 1.0 tf / mm 2 (2) Polyacrylonitrile-based oxidized fiber (3) Range until the crystallite size of the polyacrylonitrile-based oxidized fiber reaches 1.45 nm in wide-angle X-ray measurement (diffraction angle 26 °). The range where the specific gravity of the fiber after the primary drawing continues to increase during the secondary drawing (5) The crystallite size of the fiber after the primary drawing in wide-angle X-ray measurement (diffraction angle 26 °) is larger than 1.45 nm. not without the scope second carbonization process conditions (6) fiber stress is calculated out with fiber tension (F gf / mm 2) and the fiber cross-sectional area after the first carbonization step in the second carbonization step (S mm 2) D gf) is the following formula 0.18>D> 0.08
[However, D = F × S]
Range to satisfy
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| JP2002274019A JP2004107836A (en) | 2002-09-19 | 2002-09-19 | Method for producing carbon fiber |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009060793A1 (en) * | 2007-11-06 | 2009-05-14 | Toho Tenax Co., Ltd. | Carbon fiber strand and process for producing the same |
| WO2009060653A1 (en) * | 2007-11-06 | 2009-05-14 | Toho Tenax Co., Ltd. | Carbon fiber strand and process for producing the same |
-
2002
- 2002-09-19 JP JP2002274019A patent/JP2004107836A/en active Pending
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009060793A1 (en) * | 2007-11-06 | 2009-05-14 | Toho Tenax Co., Ltd. | Carbon fiber strand and process for producing the same |
| WO2009060653A1 (en) * | 2007-11-06 | 2009-05-14 | Toho Tenax Co., Ltd. | Carbon fiber strand and process for producing the same |
| JP2009114578A (en) * | 2007-11-06 | 2009-05-28 | Toho Tenax Co Ltd | Carbon fiber strand and process for producing the same |
| US8124228B2 (en) | 2007-11-06 | 2012-02-28 | Toho Tenax Co., Ltd. | Carbon fiber strand and process for producing the same |
| US8129017B2 (en) | 2007-11-06 | 2012-03-06 | Toho Tenax Co., Ltd. | Carbon fiber strand and process for producing the same |
| JP5100758B2 (en) * | 2007-11-06 | 2012-12-19 | 東邦テナックス株式会社 | Carbon fiber strand and method for producing the same |
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