JP2004197278A

JP2004197278A - Method for producing carbon fiber

Info

Publication number: JP2004197278A
Application number: JP2002368810A
Authority: JP
Inventors: Hidekazu Yoshikawa; 秀和吉川; Toshitsugu Matsuki; 寿嗣松木; Taro Oyama; 太郎尾山; Koichi Sakajiri; 浩一坂尻; Hiroyuki Sato; 弘幸佐藤
Original assignee: Toho Tenax Co Ltd
Current assignee: Teijin Ltd
Priority date: 2002-12-19
Filing date: 2002-12-19
Publication date: 2004-07-15

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polyacrylonitrile(PAN)-based carbon fiber of good strand form having high specific gravity, high strength and high elongation and free from fluff. <P>SOLUTION: The method for the production of the carbon fiber comprises the 1st carbonization step to heat-treat a PAN-based flame-resistant fiber having a specific gravity of 1.3-1.5 in an inert atmosphere to obtain a primary carbonized fiber having a specific gravity of 1.50-1.70, the primary treatment of the 2nd carbonization step to carry out the primary treatment of the fiber obtained by the 1st carbonization step under a condition to give a specific resistance, specific gravity, nitrogen content, orientation and crystallite size satisfying respective specific ranges while keeping the fiber stress within a prescribed range during the primary treatment, and the secondary treatment of the primary treated fiber under a condition to give a specific resistance, specific gravity and crystallite size satisfying respective specific ranges while keeping the fiber stress within a prescribed range during the secondary treatment. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は高強度・高伸度の炭素繊維の製造方法に関する。
【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、高比重、高強度且つ高伸度(強度／弾性率)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、高比重、高強度且つ高伸度を有する炭素繊維を得ることは困難で、従来より高比重、高強度且つ高伸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、従来の炭素化工程においては、毛羽が多くなったり、ストランド形態についてストランドの引揃え性が乱れ、その結果として品位が悪くなったりす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】
本発明者等は、長年にわたり鋭意検討を重ねた結果、ＰＡＮ系耐炎化繊維を炭素化する炭素化工程であって、第一炭素化工程と第二炭素化工程とからなる炭素化工程の第二炭素化工程を、一次処理と二次処理とに分ける場合、それぞれの処理における繊維の各物性と、温度と、繊維の延伸張力との間に重要な関連があることを知得した。更に、これらを制御することにより、高比重、高強度且つ高伸度を有し、毛羽の無い、良好なストランド形態の炭素繊維を製造できることを知得し、本発明を完成するに到った。
【００１４】
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炭素繊維の製造方法を提供することにある。
【００１５】
【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。
【００１６】
〔１〕第一炭素化工程において比重１．３〜１．５のポリアクリロニトリル系耐炎化繊維を不活性雰囲気中、熱処理して得られた比重１．５０〜１．７０の第一炭素化処理繊維を、第二炭素化工程において不活性雰囲気中で８００〜１８００℃の温度範囲内で炭素化する炭素繊維の製造方法であって、第二炭素化工程における一次処理として下記条件(１)乃至(５)のいずれをも満たす範囲で(６)の延伸処理を行い、次いで二次処理として下記条件(７)乃至(９)のいずれをも満たす範囲で(１０)の延伸処理を行う炭素繊維の製造方法。
第二炭素化工程条件
一次処理条件
(１) 第一炭素化処理繊維の比抵抗値が４００Ω・ｇ／ｍ²以上の範囲
(２) 第一炭素化処理繊維の比重が一次処理中上昇し続ける範囲
(３) 第一炭素化処理繊維の窒素含有量が１０質量％以上の範囲
(４) 第一炭素化処理繊維の広角Ｘ線測定(回折角２６°)における配向度が８０．８％以下で、一次処理中上昇し続ける範囲
(５) 第一炭素化処理繊維の広角Ｘ線測定(回折角２６°)における結晶子サイズが１．４７ｎｍより大きくならない範囲
(６) 第二炭素化工程一次処理での繊維張力(Ｆｇｆ／ｍｍ²)と第一炭素化処理繊維の断面積(Ｓｍｍ²)とで算出される繊維応力(ＤＮ)が下式
１．２４ × １０^-3 ＞Ｄ＞０．４６ × １０^-3
〔但し、Ｄ＝Ｆ × Ｓ × ９．８／１０００
Ｓ＝ πＡ² ／４
Ａは第一炭素化処理繊維の直径(ｍｍ)〕
を満たす範囲で繊維張力を与える延伸処理
二次処理条件
(７) 一次処理繊維の比抵抗値が４００Ω・ｇ／ｍ²未満の範囲
(８) 一次処理繊維の比重が変化しない又は低下する低下するまでの範囲
(９) 一次処理繊維の広角Ｘ線測定(回折角２６°)における結晶子サイズが１．４７ｎｍより大きく、且つ二次処理中上昇し続ける又は変化しない範囲
(１０) 第二炭素化工程二次処理での繊維張力(Ｇｇｆ／ｍｍ²)と第一炭素化処理繊維の断面積(Ｓｍｍ²)とで算出される繊維応力(ＥＮ)が下式
０．６０ × １０^-3 ＞Ｅ＞０．２３ × １０^-3
〔但し、Ｅ＝Ｇ × Ｓ × ９．８／１０００
Ｓ＝ πＡ² ／４
Ａは第一炭素化処理繊維の直径(ｍｍ)〕
を満たす範囲で繊維張力を与える延伸処理
〔２〕得られる炭素繊維の伸度が２．２０％以上である請求項１に記載の炭素繊維の製造方法。
【００１７】
〔３〕得られる炭素繊維の単繊維径が３〜８μｍである〔１〕に記載の炭素繊維の製造方法。
【００１８】
【発明の実施の形態】
以下、本発明を詳細に説明する。
【００１９】
本発明の炭素繊維の製造方法に用いる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。
【００２０】
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０．８５〜１．３０の範囲で処理され、繊維比重１．３〜１．５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。
【００２１】
本発明の炭素繊維の製造方法においては、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、３００〜８００℃の温度範囲内で前処理(第一炭素化処理)して繊維比重１．５０〜１．７０の第一炭素化処理繊維を得、この第一炭素化処理繊維を第二炭素化工程において８００〜１８００℃の温度範囲内で、同工程を一次処理と二次処理とに分けて炭素化処理する。
【００２２】
上記第二炭素化工程の一次処理では、第一炭素化処理繊維の比抵抗値が４００Ω・ｇ／ｍ²以上の範囲、同繊維の比重が一次処理中上昇し続ける範囲、同繊維の窒素含有量が１０質量％以上の範囲、同繊維の広角Ｘ線測定(回折角２６°)における配向度が８０．８％以下で、一次処理中上昇し続ける範囲、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１．４７ｎｍより大きくならない範囲で同繊維を延伸処理する。
【００２３】
上記第一炭素化処理繊維の第二炭素化工程一次処理における、比抵抗値、比重、窒素含有量、並びに、広角Ｘ線測定(回折角２６°)での配向度及び結晶子サイズの、変化及び条件範囲の一例を、それぞれ図１、２、３、４及び５に示す。
【００２４】
なお、第二炭素化工程一次処理での繊維張力(Ｆｇｆ／ｍｍ²)は、第一炭素化工程後の繊維直径、即ち繊維断面積(Ｓｍｍ²)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(ＤＮ)を用い、この繊維応力の範囲は下式１．２４ × １０^-3 ＞Ｄ＞０．４６ × １０^-3
〔但し、Ｄ＝Ｆ × Ｓ × ９．８／１０００
Ｓ＝ πＡ² ／４
Ａは第一炭素化処理繊維の直径(ｍｍ)〕
を満たす範囲としている。
【００２５】
ここで繊維断面積は、ＪＩＳ−Ｒ−７６０１に規定する測微顕微鏡による方法において繊維直径を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。
【００２６】
上記方法により得られた一次処理繊維は、引き続いて以下の二次処理を施す。
【００２７】
この二次処理においては、一次処理繊維の比抵抗値が４００Ω・ｇ／ｍ²未満の範囲、同繊維の比重が変化しない又は低下する範囲、更に、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１．４７ｎｍより大きく且つ二次処理中上昇し続ける又は変化しない範囲で同繊維を延伸処理する。
【００２８】
上記一次処理繊維の二次処理における、比抵抗値、比重、及び広角Ｘ線測定(回折角２６°)での結晶子サイズの、変化及び条件範囲の一例を、それぞれ図６、７及び８に示す。
【００２９】
なお、第二炭素化工程二次処理での繊維張力(Ｇｇｆ／ｍｍ²)も、一次処理時と同様に第一炭素化工程後の繊維直径、即ち繊維断面積(Ｓｍｍ²)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(ＥＮ)を用い、この繊維応力の範囲は下式
０．６０ × １０^-3 ＞Ｅ＞０．２３ × １０^-3
〔但し、Ｅ＝Ｇ × Ｓ × ９．８／１０００
Ｓ＝ πＡ² ／４
Ａは第一炭素化処理繊維の直径(ｍｍ)〕
を満たす範囲としている。
【００３０】
得られた第二炭素化処理繊維、即ち第二炭素化工程二次処理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。
【００３１】
また、第二炭素化処理繊維の伸度は２．２０％以上であることが好ましい。更に、第二炭素化処理繊維の単繊維径(繊維直径)は３〜８μｍであることが好ましい。
【００３２】
このようにして得られた炭素繊維は、高比重、高強度且つ高伸度を有し、毛羽の無い、良好なストランド形態の炭素繊維であり、本発明の製造方法によりなし得るものである。
【００３３】
【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処理条件、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。
【００３４】
＜比抵抗値＞
比抵抗値の測定に関しては、ＪＩＳ−Ｒ−７６０１に規定する体積抵抗率のストランドの試験Ａ法を参考に行うことができる。ただし、ＪＩＳ−Ｒ−７６０１では、電気抵抗値に、炭素繊維の比重を掛け合わせた体積抵抗率を求めており、比抵抗値〔Ｘ（Ω・ｇ／ｍ²）〕を求めるには、下式
Ｘ＝Ｒｂ×ｔ／Ｌ
Ｒｂ：試験片長Ｌのときの電気抵抗（Ω）、ｔ：試験片の繊度（ｔｅｘ）、Ｌ：抵抗測定時の試験片長（ｍ）
を用いて行った。なお、抵抗測定時の試験片長については、１ｍ程度で測定することが好ましい。
【００３５】
＜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。
【００３６】
＜窒素含有量＞
元素分析装置(ＦＩＳＯＮＳＩＮＳＴＲＵＭＥＮＴＳ社製)により測定した元素分析値から求めた。
【００３７】
＜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。
【００３８】
＜ストランド強度、弾性率、伸度＞
ＪＩＳＲ７６０１に規定された方法によりストランド強度、弾性率を測定し、得られた強度を弾性率で割ることで伸度を求めた。
【００３９】
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１２．０μｍの前駆体繊維を得た。この繊維を加熱空気中、入口温度(最低温度)２００℃、出口温度(最高温度)２６０℃の熱風循環式耐炎化炉で耐炎化処理し、繊維比重１．３４のＰＡＮ系耐炎化繊維を得た。
【００４０】
この耐炎化繊維を不活性雰囲気中、入口温度(最低温度)３００℃、出口温度(最高温度)５００℃の第一炭素化炉において熱処理し、比重１．５０、繊維直径９．０μｍ、繊維断面積６．３６×１０^-5ｍｍ²の第一炭素化処理繊維を得た。
【００４１】
次いで、この第一炭素化処理繊維を不活性雰囲気中、入口温度(最低温度)８００℃、出口温度(最高温度)１８００℃の第二炭素化炉において、一次処理・二次処理を以下に示す条件で実施した。
【００４２】
先ず、上記第一炭素化処理繊維を、比抵抗値、比重、窒素含有量、配向度、及び結晶子サイズについて、図１、２、３、４及び５に示す範囲内に調節すると共に、繊維張力１６７９ｇｆ／ｍｍ²、繊維応力１．０４６×１０^-3Ｎで延伸処理し、一次処理繊維を得た。
【００４３】
その後この一次処理繊維を、引き続き第二炭素化工程において二次処理が終了するまで、比抵抗値、比重、及び結晶子サイズについて、図６、７及び８に示す範囲内に調節すると共に、繊維張力６７１ｇｆ／ｍｍ²、繊維応力０．４１８×１０^-3Ｎで延伸処理し、二次処理繊維を得た。
【００４４】
さらに、上記二次処理繊維を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１．８０４、繊維直径６．８μｍ、ストランド強度５３９０ＭＰａ、ストランド弾性率２４３ＧＰａ、ストランド伸度２．２２％の、毛羽の無い、良好なストランド形態の炭素繊維を得た。
【００４５】
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繊維を、第二炭素化工程一次処理において、繊維張力１３３８ｇｆ／ｍｍ²、繊維応力０．８３４×１０^-3Ｎで処理した以外は実施例１と同様の処理を行い、比重１．８０３、繊維直径６．９μｍ、ストランド強度５３４０ＭＰａ、ストランド弾性率２４２ＧＰａ、ストランド伸度２．２１％の、毛羽の無い、良好なストランド形態の炭素繊維を得た。
【００４６】
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繊維を、第二炭素化工程一次処理において、繊維張力１０００ｇｆ／ｍｍ²、繊維応力０．６２３×１０^-3Ｎで処理した以外は実施例１と同様の処理を行い、比重１．８０２、繊維直径７．０μｍ、ストランド強度５２９０ＭＰａ、ストランド弾性率２４１ＧＰａ、ストランド伸度２．２０％の、毛羽の無い、良好なストランド形態の炭素繊維を得た。
【００４７】
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繊維を、第二炭素化工程一次処理において、繊維張力２０１４ｇｆ／ｍｍ²、繊維応力１．２５５×１０^-3Ｎで処理した以外は実施例１と同様の処理を行った。
【００４８】
しかし、得られた炭素繊維は、比重１．８０２、繊維直径６．８μｍ、ストランド強度５２９０ＭＰａ、ストランド弾性率２４４ＧＰａの良好なストランド形態のものであったが、ストランド伸度２．１８％と低伸度で、毛羽の多いものであった。
【００４９】
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繊維を、第二炭素化工程一次処理において、繊維張力６７１ｇｆ／ｍｍ²、繊維応力０．４１８×１０^-3Ｎで処理した以外は実施例１と同様の処理を行った。
【００５０】
しかし、得られた炭素繊維は、毛羽の無い、良好なストランド形態のものであったが、比重１．７９７、繊維直径７．０μｍ、ストランド強度５１４５ＭＰａ、ストランド弾性率２３９ＧＰａ、ストランド伸度２．１５％と低強度、低伸度であった。
【００５１】
比較例３
表１に示すように、実施例２で得られた第二炭素化工程一次処理繊維を、第二炭素化工程二次処理において、繊維張力３３５ｇｆ／ｍｍ²、繊維応力０．２０９×１０^-3Ｎで処理した以外は実施例２と同様の処理を行った。
【００５２】
しかし、得られた炭素繊維は、比重１．８０３、繊維直径７．０μｍ、ストランド強度５２９０ＭＰａ、ストランド弾性率２４０ＧＰａ、ストランド伸度２．２０％の、毛羽の無いものであったが、ストランド形態はストランドの引揃え性が乱れており纏りの無い悪い形態であった。
【００５３】
実施例４
表１に示すように、実施例２で得られた第二炭素化工程一次処理繊維を、第二炭素化工程二次処理において、繊維張力８６６ｇｆ／ｍｍ²、繊維応力０．５４０×１０^-3Ｎで処理した以外は実施例２と同様の処理を行い、比重１．８０２、繊維直径６．９μｍ、ストランド強度５３４０ＭＰａ、ストランド弾性率２４４ＧＰａ、ストランド伸度２．２０％の、毛羽の無い、良好なストランド形態の炭素繊維を得た。
【００５４】
比較例４
表１に示すように、実施例２で得られた第二炭素化工程一次処理繊維を、第二炭素化工程二次処理において、繊維張力１０００ｇｆ／ｍｍ²、繊維応力０．６２３×１０^-3Ｎで処理した以外は実施例２と同様の処理を行った。
【００５５】
しかし、得られた炭素繊維は、比重１．７９８、繊維直径６．８μｍ、ストランド強度５２９０ＭＰａの、毛羽の無い、良好なストランド形態のものであったが、ストランド弾性率２４５ＧＰａ、ストランド伸度２．１６％と低伸度であった。
【００５６】
実施例５
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９．０μｍの前駆体繊維を得た。この繊維を加熱空気中、入口温度(最低温度)２００℃、出口温度(最高温度)２６０℃の熱風循環式耐炎化炉で耐炎化処理し、繊維比重１．３４のＰＡＮ系耐炎化繊維を得た。
【００５７】
この耐炎化繊維を不活性雰囲気中、入口温度(最低温度)３００℃、出口温度(最高温度)５００℃の第一炭素化炉において熱処理し、比重１．５０、繊維直径６．８μｍ、繊維断面積３．６３×１０^-5ｍｍ²の第一炭素化処理繊維を得た。
【００５８】
次いで、この第一炭素化処理繊維を不活性雰囲気中、入口温度(最低温度)８００℃、出口温度(最高温度)１８００℃の第二炭素化炉において、一次処理・二次処理を以下に示す条件で実施した。
【００５９】
先ず、上記第一炭素化処理繊維を、比抵抗値、比重、窒素含有量、配向度、及び結晶子サイズについて、図１、２、３、４及び５に示す範囲内に調節すると共に、繊維張力３１９８ｇｆ／ｍｍ²、繊維応力１．１３８×１０^-3Ｎで処理し、一次処理繊維を得た。
【００６０】
その後この一次処理繊維を、引き続き第二炭素化工程において二次処理が終了するまで、比抵抗値、比重、及び結晶子サイズについて、図６、７及び８に示す範囲内に調節すると共に、繊維張力１２４３ｇｆ／ｍｍ²、繊維応力０．４４３×１０^-3Ｎで処理し、二次処理繊維を得た。
【００６１】
さらに、上記二次処理繊維を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１．８０６、繊維直径４．９μｍ、ストランド強度６４２０ＭＰａ、ストランド弾性率２８６ＧＰａ、ストランド伸度２．２４％の、毛羽の無い、良好なストランド形態の炭素繊維を得た。
【００６２】
なお、本例の処理条件は、前駆体繊維の繊維直径９．０μｍと小さいため、実施例１と比較し、得られた炭素繊維の強度は１０００ＭＰａほど高い。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。また、弾性率の差については最高温度域の差によるものと考えられる。
【００６３】
実施例６
表１に示すように、実施例５で得られた第一炭素化処理繊維を、第二炭素化工程一次処理において、繊維張力２４６０ｇｆ／ｍｍ²、繊維応力０．８７５×１０^-3Ｎで処理した以外は実施例５と同様の処理を行い、比重１．８０５、繊維直径５．０μｍ、ストランド強度６３２０ＭＰａ、ストランド弾性率２８４ＧＰａ、ストランド伸度２．２２％の、毛羽の無い、良好なストランド形態の炭素繊維を得た。
【００６４】
実施例７
表１に示すように、実施例５で得られた第一炭素化処理繊維を、第二炭素化工程一次処理において、繊維張力１７１６ｇｆ／ｍｍ²、繊維応力０．６１１×１０^-3Ｎで処理した以外は実施例５と同様の処理を行い、比重１．８０４、繊維直径５．０μｍ、ストランド強度６２７０ＭＰａ、ストランド弾性率２８３ＧＰａ、ストランド伸度２．２１％の、毛羽の無い、良好なストランド形態の炭素繊維を得た。
【００６５】
比較例５
表１に示すように、実施例５で得られた第一炭素化処理繊維を、第二炭素化工程一次処理において、繊維張力３７０３ｇｆ／ｍｍ²、繊維応力１．３１８×１０^-3Ｎで処理した以外は実施例５と同様の処理を行った。
【００６６】
しかし、得られた炭素繊維は、比重１．８０４、繊維直径４．８μｍ、ストランド強度６２７０ＭＰａ、ストランド弾性率２８６ＧＰａの良好なストランド形態のものであったが、ストランド伸度２．１９％と低伸度で、毛羽の多いものであった。
【００６７】
比較例６
表１に示すように、実施例５で得られた第一炭素化処理繊維を、第二炭素化工程一次処理において、繊維張力１２４３ｇｆ／ｍｍ²、繊維応力０．４４３×１０^-3Ｎで処理した以外は実施例５と同様の処理を行った。
【００６８】
しかし、得られた炭素繊維は、毛羽の無い、良好なストランド形態のものであったが、比重１．８０３、繊維直径５．１μｍ、ストランド強度６１２５ＭＰａ、ストランド弾性率２８３ＧＰａ、ストランド伸度２．１６％と繊維直径の小さいことを考慮に入れると低強度、低伸度であった。
【００６９】
比較例７
表１に示すように、実施例６で得られた第二炭素化工程一次処理繊維を、第二炭素化工程二次処理において、繊維張力６２２ｇｆ／ｍｍ²、繊維応力０．２２１×１０^-3Ｎで処理した以外は実施例６と同様の処理を行った。
【００７０】
しかし、得られた炭素繊維は、比重１．８０５、繊維直径５．１μｍ、ストランド強度６３２０ＭＰａ、ストランド弾性率２８１ＧＰａ、ストランド伸度２．２５％の、毛羽の無いものであったが、ストランド形態はストランドの引揃え性が乱れており纏りの無い悪い形態であった。
【００７１】
実施例８
表１に示すように、実施例６で得られた第二炭素化工程一次処理繊維を、第二炭素化工程二次処理において、繊維張力１４９２ｇｆ／ｍｍ²、繊維応力０．５３１×１０^-3Ｎで処理した以外は実施例６と同様の処理を行い、比重１．８０４、繊維直径４．９μｍ、ストランド強度６３７０ＭＰａ、ストランド弾性率２８７ＧＰａ、ストランド伸度２．２２％の、毛羽の無い、良好なストランド形態の炭素繊維を得た。
【００７２】
比較例８
表１に示すように、実施例６で得られた第二炭素化工程一次処理繊維を、第二炭素化工程二次処理において、繊維張力２４６０ｇｆ／ｍｍ²、繊維応力０．８７５×１０^-3Ｎで処理した以外は実施例６と同様の処理を行った。
【００７３】
しかし、得られた炭素繊維は、比重１．８００、繊維直径４．８μｍ、ストランド強度６２７０ＭＰａの、毛羽の無い、良好なストランド形態のものであったが、ストランド弾性率２８９ＧＰａ、ストランド伸度２．１７％と低伸度であった。
【００７４】
【表１】

【００７５】
【発明の効果】
本発明の製造方法によれば、第一炭素化工程、並びに、第一炭素化工程一次処理及び二次処理において、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、高比重、高強度且つ高伸度を有し、毛羽の無い、良好なストランド形態の炭素繊維を得ることができる。
【図面の簡単な説明】
【図１】第二炭素化工程における一次処理時の温度上昇に対する第一炭素化処理繊維の比抵抗値の推移を示すグラフである。
【図２】第二炭素化工程における一次処理時の温度上昇に対する第一炭素化処理繊維の比重の推移を示すグラフである。
【図３】第二炭素化工程における一次処理時の温度上昇に対する第一炭素化処理繊維の窒素含有量の推移を示すグラフである。
【図４】第二炭素化工程における一次処理時の温度上昇に対する第一炭素化処理繊維の配向度の推移を示すグラフである。
【図５】第二炭素化工程における一次処理時の温度上昇に対する第一炭素化処理繊維の結晶子サイズの推移を示すグラフである。
【図６】第二炭素化工程における二次処理時の温度上昇に対する一次処理繊維の比抵抗値の推移を示すグラフである。
【図７】第二炭素化工程における二次処理時の温度上昇に対する一次処理繊維の比重の推移を示すグラフである。
【図８】第二炭素化工程における二次処理時の温度上昇に対する一次処理繊維の結晶子サイズ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, high-elongation carbon fiber.
[0002]
[Prior art]
BACKGROUND ART Conventionally, it has been known that high-performance carbon fibers are produced using polyacrylonitrile (PAN) fibers as raw materials, and they are used in a wide range 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 Patent Literature 1, the oxidized fiber is carbonized at 300 to 800 ° C. in an inert atmosphere while being extended up to 25% in an inert atmosphere, and is treated so as not to be negative with respect to the original length of the oxidized fiber. It is disclosed to obtain high strength carbon fibers.
[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 a high specific gravity, a high strength and a high elongation (strength / elastic modulus), it is necessary to perform contraction with optimal fiber properties, and these methods are described. It is difficult to control the fineness of the fiber only by the temperature range and the temperature rise gradient, and it is difficult to obtain carbon fiber with high specific gravity, high strength and high elongation by using only specific gravity as a parameter. There is a need for a method for obtaining carbon fibers having specific gravity, high strength and high elongation.
[0011]
Furthermore, in the conventional carbonization process, there are problems such as an increase in fluff and an irregularity in strand alignment with respect to the strand form, resulting in poor quality.
[0012]
[Patent Document 1]
JP-A-54-147222 (pages 1 to 3)
[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 (pages 1 to 3)
[0013]
[Problems to be solved by the invention]
The present inventors have conducted intensive studies for many years, and as a result, the carbonization step for carbonizing the PAN-based oxidized fiber, which is the first carbonization step and the second carbonization step, When the carbonization step is divided into a primary treatment and a secondary treatment, it has been found that there is an important relationship between each physical property of the fiber in each treatment, the temperature, and the drawing tension of the fiber. Furthermore, by controlling these, it was found that carbon fibers having a high specific gravity, a high strength and a high elongation, having no fluff, and having a good strand shape could be produced, and the present invention was completed. .
[0014]
Accordingly, it is an object of the present invention to provide a method for producing carbon fiber that solves the above-mentioned problems.
[0015]
[Means for Solving the Problems]
The present invention that achieves the above object is as described below.
[0016]
[1] First carbonization treatment with a specific gravity of 1.50 to 1.70 obtained by heat-treating polyacrylonitrile-based oxidized fibers having a specific gravity of 1.3 to 1.5 in an inert atmosphere in the first carbonization step. A method for producing a carbon fiber in which a fiber is carbonized in an inert atmosphere in a temperature range of 800 to 1800 ° C. in a second carbonization step, wherein the primary treatment in the second carbonization step is as follows: A carbon fiber which is subjected to the stretching treatment of (6) within a range satisfying any of (5) and then subjected to a stretching treatment of (10) as a secondary treatment within a range satisfying any of the following conditions (7) to (9). Manufacturing method.
Secondary carbonization process conditions Primary treatment conditions
(1) The specific resistance value of the first carbonized fiber is in the range of 400 Ω · g / m ² or more.
(2) Range in which the specific gravity of the first carbonized fiber continues to increase during the primary treatment
(3) The range in which the nitrogen content of the first carbonized fiber is 10% by mass or more.
(4) A range in which the degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °) of the first carbonized fiber is 80.8% or less and continues to increase during the primary treatment.
(5) Range in which the crystallite size of the first carbonized fiber is not larger than 1.47 nm in wide-angle X-ray measurement (diffraction angle 26 °).
(6) The fiber stress (DN) calculated from the fiber tension (F gf / mm ² ) in the second carbonization step primary treatment and the cross-sectional area (S mm ² ) of the first carbonization treated fiber is as follows: 1.24 × 10 ⁻³ >D> 0.46 × 10 ⁻³
[However, D = F × S × 9.8 / 1000
S = πA ^2/4
A is the diameter (mm) of the first carbonized fiber]
Drawing treatment secondary treatment conditions that give fiber tension within the range that satisfies
(7) The range where the specific resistance value of the primary treated fiber is less than 400 Ω · g / m ²
(8) The specific gravity of the primary treated fiber does not change or decreases.
(9) The range where the crystallite size in the wide-angle X-ray measurement (diffraction angle 26 °) of the primary-treated fiber is larger than 1.47 nm and continues to increase or does not change during the secondary treatment
(10) The fiber stress (EN) calculated from the fiber tension (G gf / mm ² ) and the cross-sectional area (S mm ² ) of the first carbonized fiber in the second carbonization step secondary treatment is lower. Formula 0.60 × 10 ⁻³ >E> 0.23 × 10 ⁻³
[However, E = G × S × 9.8 / 1000
S = πA ^2/4
A is the diameter (mm) of the first carbonized fiber]
A stretching process for giving a fiber tension within a range satisfying the above [2]. The method for producing a carbon fiber according to claim 1, wherein the elongation of the obtained carbon fiber is 2.20% or more.
[0017]
[3] The method for producing a carbon fiber according to [1], wherein the obtained carbon fiber has a single fiber diameter of 3 to 8 μm.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
[0019]
The PAN-based precursor fiber used in the method for producing a carbon fiber of the present invention was obtained 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.
[0020]
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 1.30 to obtain a PAN-based flame-resistant fiber having a fiber specific gravity of 1.3 to 1.5. The tension (stretch distribution) is not particularly limited.
[0021]
In the method for producing carbon fiber of the present invention, the oxidized fiber is pretreated (first carbonization treatment) in an inert atmosphere in a first carbonization step within a temperature range of 300 to 800 ° C. A first carbonized fiber having a fiber specific gravity of 1.50 to 1.70 is obtained, and the first carbonized fiber is subjected to a first carbonization process in a second carbonization process within a temperature range of 800 to 1800 ° C. Carbonization treatment is performed separately from the next treatment.
[0022]
In the primary treatment of the second carbonization step, the specific resistance value of the first carbonized fiber is in the range of 400 Ω · g / m ² or more, the specific gravity of the fiber is continuously increasing during the primary treatment, and the nitrogen content of the fiber is high. In the range of 10% by mass or more, the degree of orientation in the wide-angle X-ray measurement (diffraction angle 26 °) of the fiber is 80.8% or less, the range which continues to increase during the primary treatment, and the wide-angle X-ray measurement The fiber is stretched within a range where the crystallite size at a diffraction angle of 26 ° does not become larger than 1.47 nm.
[0023]
In the first treatment of the second carbonization step of the first carbonized fiber, the specific resistance, specific gravity, nitrogen content, and the degree of orientation and crystallite size in wide-angle X-ray measurement (diffraction angle 26 °), change Examples of conditions and condition ranges are shown in FIGS.
[0024]
The fiber tension (F gf / mm ² ) in the first treatment of the second carbonization step varies depending on the fiber diameter after the first carbonization step, that is, the fiber cross-sectional area (S mm ² ). The fiber stress (DN) is used as a factor, and the range of the fiber stress is as follows: 1.24 × 10 ⁻³ >D> 0.46 × 10 ⁻³
[However, D = F × S × 9.8 / 1000
S = πA ^2/4
A is the diameter (mm) of the first carbonized fiber]
Range.
[0025]
Here, the fiber cross-sectional area is obtained by measuring a fiber diameter at n = 20 by a method using a microscopic microscope defined in JIS-R-7601, using an average value thereof, and using a value calculated as a perfect circle.
[0026]
The primary treatment fiber obtained by the above method is subsequently subjected to the following secondary treatment.
[0027]
In this secondary treatment, the specific resistance of the primary treated fiber is in a range of less than 400 Ω · g / m ^2, a range in which the specific gravity of the fiber does not change or decreases, and a wide-angle X-ray measurement (diffraction angle 26 The fiber is drawn to the extent that the crystallite size in (°) is greater than 1.47 nm and continues to rise or does not change during the secondary treatment.
[0028]
FIGS. 6, 7 and 8 show examples of the change and the condition range of the specific resistance value, the specific gravity, and the crystallite size in wide-angle X-ray measurement (diffraction angle 26 °) in the secondary treatment of the primary-treated fiber, respectively. Show.
[0029]
The fiber tension (G gf / mm ² ) in the secondary treatment of the second carbonization step also varies depending on the fiber diameter after the first carbonization step, ie, the fiber cross-sectional area (S mm ² ), as in the primary treatment. Therefore, in the present invention, fiber stress (EN) is used as a tension factor, and the range of the fiber stress is as follows: 0.60 × 10 ⁻³ >E> 0.23 × 10 ⁻³
[However, E = G × S × 9.8 / 1000
S = πA ^2/4
A is the diameter (mm) of the first carbonized fiber]
Range.
[0030]
The obtained second carbonized fiber, that is, the carbon fiber obtained after the completion of the secondary treatment in the second carbonization step, can be subsequently subjected to a surface treatment 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.
[0031]
The elongation of the second carbonized fiber is preferably 2.20% or more. Furthermore, the single fiber diameter (fiber diameter) of the second carbonized fiber is preferably 3 to 8 μm.
[0032]
The carbon fiber thus obtained is a carbon fiber having a high specific gravity, a high strength and a high elongation, having no fluff and having a good strand shape, and can be produced by the production method of the present invention.
[0033]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The processing conditions in each of the examples and the comparative examples, and the methods for evaluating the physical properties of carbon fibers were implemented by the following methods.
[0034]
<Specific resistance value>
The measurement of the specific resistance value can be performed with reference to a test A method for a strand having a volume resistivity specified in JIS-R-7601. However, according to JIS-R-7601, the volume resistivity obtained by multiplying the electric resistance value by the specific gravity of the carbon fiber is obtained. To obtain the specific resistance value [X (Ω · g / m ² )], Formula X = Rb × t / L
Rb: electrical resistance (Ω) when the test piece length is L, t: fineness (tex) of the test piece, L: test piece length (m) when measuring the resistance
This was performed using In addition, it is preferable to measure about 1 m about the test piece length at the time of resistance measurement.
[0035]
<Specific gravity>
It was measured by the Archimedes method. The sample fiber was degassed in acetone and measured.
[0036]
<Nitrogen content>
It was determined from an elemental analysis value measured by an elemental analyzer (manufactured by FISONS INSTRUMENTS).
[0037]
<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.
[0038]
<Strand strength, elastic modulus, elongation>
The strand strength and elastic modulus were measured by the method specified in JIS R 7601, and the obtained strength was divided by the elastic modulus to obtain elongation.
[0039]
Example 1
Wet or dry-wet spinning of a copolymer spinning stock solution consisting of 95% by mass of acrylonitrile / 4% by mass of methyl acrylate / 1% by mass of itaconic acid, followed by washing, drying, stretching and oiling, and precursor fibers having a fiber diameter of 12.0 μm Got. This fiber is subjected to a flame-resistant treatment in a heated air in a hot-air circulation type flame-proof furnace having an inlet temperature (minimum temperature) of 200 ° C. and an outlet temperature (maximum temperature) of 260 ° C. to obtain a PAN-based flame-resistant fiber having a specific gravity of 1.34. Was.
[0040]
This oxidized fiber is heat-treated in an inert atmosphere in a first carbonization furnace having an inlet temperature (minimum temperature) of 300 ° C. and an outlet temperature (maximum temperature) of 500 ° C., a specific gravity of 1.50, a fiber diameter of 9.0 μm, and a fiber breakage. A first carbonized fiber having an area of 6.36 × 10 ⁻⁵ mm ² was obtained.
[0041]
Next, primary treatment and secondary treatment of the first carbonized fiber in an inert atmosphere in a second carbonization furnace having an inlet temperature (minimum temperature) of 800 ° C. and an outlet temperature (maximum temperature) of 1800 ° C. are shown below. It was carried out under the conditions.
[0042]
First, the first carbonized fiber was adjusted for specific resistance, specific gravity, nitrogen content, degree of orientation, and crystallite size within the ranges shown in FIGS. Drawing treatment was performed at a tension of 1679 gf / mm ² and a fiber stress of 1.046 × 10 ⁻³ N to obtain a primary treated fiber.
[0043]
After that, the primary-treated fiber is adjusted to the specific resistance value, specific gravity, and crystallite size within the ranges shown in FIGS. 6, 7 and 8 until the secondary treatment in the second carbonization step is completed. Drawing was performed at a tension of 671 gf / mm ² and a fiber stress of 0.418 × 10 ⁻³ N to obtain a secondary-treated fiber.
[0044]
Furthermore, the above-mentioned secondary-treated fiber is subjected to surface treatment and sizing by a known method, dried, and dried to a specific gravity of 1.804, a fiber diameter of 6.8 μm, a strand strength of 5390 MPa, a strand elastic modulus of 243 GPa, and a strand elongation of 2.22. % Fluff-free, good strand morphology carbon fiber was obtained.
[0045]
Example 2
As shown in Table 1, the first carbonized fiber obtained in Example 1 was treated in the first treatment of the second carbonization step with a fiber tension of 1338 gf / mm ² and a fiber stress of 0.834 × 10 ⁻³ N. The same treatment as in Example 1 was performed except that the specific gravity was 1.803, the fiber diameter was 6.9 μm, the strand strength was 5340 MPa, the strand elastic modulus was 242 GPa, and the strand elongation was 2.21%. Was obtained.
[0046]
Example 3
As shown in Table 1, the first carbonized fiber obtained in Example 1 was treated in the first treatment of the second carbonization step with a fiber tension of 1000 gf / mm ² and a fiber stress of 0.623 × 10 ⁻³ N. The same treatment as in Example 1 was carried out except that the specific gravity was 1.802, the fiber diameter was 7.0 μm, the strand strength was 5290 MPa, the strand elastic modulus was 241 GPa, and the strand elongation was 2.20%. Was obtained.
[0047]
Comparative Example 1
As shown in Table 1, the first carbonized fiber obtained in Example 1 was treated in the first treatment of the second carbonization step with a fiber tension of 2014 gf / mm ² and a fiber stress of 1.255 × 10 ⁻³ N. The same processing as in Example 1 was performed except for the above.
[0048]
However, the obtained carbon fiber had a specific gravity of 1.802, a fiber diameter of 6.8 μm, a strand strength of 5290 MPa, and a good strand shape with a strand elastic modulus of 244 GPa. The degree was fluffy.
[0049]
Comparative Example 2
As shown in Table 1, the first carbonized fiber obtained in Example 1 was treated in the second carbonization step primary treatment with a fiber tension of 671 gf / mm ² and a fiber stress of 0.418 × 10 ⁻³ N. The same processing as in Example 1 was performed except for the above.
[0050]
However, the obtained carbon fiber had a good strand form without fluff, but had a specific gravity of 1.797, a fiber diameter of 7.0 μm, a strand strength of 5145 MPa, a strand elastic modulus of 239 GPa, and a strand elongation of 2.15. %, Low strength and low elongation.
[0051]
Comparative Example 3
As shown in Table 1, in the second carbonization step secondary treatment, the second carbonization step primary treatment fiber obtained in Example 2 was subjected to a fiber tension of 335 gf / mm ² and a fiber stress of 0.209 × 10 ^−3. The same processing as in Example 2 was performed except that the processing was performed with N.
[0052]
However, the obtained carbon fiber had a specific gravity of 1.803, a fiber diameter of 7.0 μm, a strand strength of 5290 MPa, a strand elastic modulus of 240 GPa, and a strand elongation of 2.20%. The alignment of the strands was disturbed, and it was a bad form without a uniform.
[0053]
Example 4
As shown in Table 1, in the second carbonization step secondary treatment, the second carbonization step primary treatment fiber obtained in Example 2 was subjected to a fiber tension of 866 gf / mm ² and a fiber stress of 0.540 × 10 ^−3. Except for treating with N, the same treatment as in Example 2 was performed, and the specific gravity was 1.802, the fiber diameter was 6.9 μm, the strand strength was 5340 MPa, the strand elastic modulus was 244 GPa, and the strand elongation was 2.20%. Thus, a carbon fiber having a simple strand form was obtained.
[0054]
Comparative Example 4
As shown in Table 1, in the second treatment in the second carbonization step, the fiber subjected to the first treatment in the second carbonization step obtained in Example 2 was subjected to a fiber tension of 1000 gf / mm ² and a fiber stress of 0.623 × 10 ^−3. The same processing as in Example 2 was performed except that the processing was performed with N.
[0055]
However, the obtained carbon fiber had a specific gravity of 1.798, a fiber diameter of 6.8 μm, a strand strength of 5290 MPa, and was in a good strand form without fluff, but had a strand elastic modulus of 245 GPa and a strand elongation of 2. The elongation was as low as 16%.
[0056]
Example 5
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 9.0 μm. Got. This fiber is subjected to a flame-resistant treatment in a heated air in a hot-air circulation type flame-proof furnace having an inlet temperature (minimum temperature) of 200 ° C. and an outlet temperature (maximum temperature) of 260 ° C. to obtain a PAN-based flame-resistant fiber having a specific gravity of 1.34. Was.
[0057]
This oxidized fiber is heat-treated in an inert atmosphere in a first carbonization furnace having an inlet temperature (minimum temperature) of 300 ° C. and an outlet temperature (maximum temperature) of 500 ° C., a specific gravity of 1.50, a fiber diameter of 6.8 μm, and a fiber breakage. A first carbonized fiber having an area of 3.63 × 10 ⁻⁵ mm ² was obtained.
[0058]
Next, primary treatment and secondary treatment of the first carbonized fiber in an inert atmosphere in a second carbonization furnace having an inlet temperature (minimum temperature) of 800 ° C. and an outlet temperature (maximum temperature) of 1800 ° C. are shown below. It was carried out under the conditions.
[0059]
First, the first carbonized fiber was adjusted for specific resistance, specific gravity, nitrogen content, degree of orientation, and crystallite size within the ranges shown in FIGS. The fiber was treated at a tension of 3198 gf / mm ² and a fiber stress of 1.138 × 10 ⁻³ N to obtain a primary treated fiber.
[0060]
After that, the primary-treated fiber is adjusted to the specific resistance value, specific gravity, and crystallite size within the ranges shown in FIGS. 6, 7 and 8 until the secondary treatment in the second carbonization step is completed. The fiber was treated at a tension of 1243 gf / mm ² and a fiber stress of 0.443 × 10 ⁻³ N to obtain a secondary-treated fiber.
[0061]
Further, the above-mentioned secondary-treated fiber is subjected to surface treatment and sizing by a known method, dried, and dried to a specific gravity of 1.806, a fiber diameter of 4.9 μm, a strand strength of 6420 MPa, a strand elastic modulus of 286 GPa, and a strand elongation of 2.24. % Fluff-free, good strand morphology carbon fiber was obtained.
[0062]
In addition, since the processing conditions of this example are as small as 9.0 μm in the fiber diameter of the precursor fiber, the strength of the obtained carbon fiber is higher than that of Example 1 by about 1000 MPa. This is considered to be due to the difference in the fiber diameter of the obtained carbon fibers. The difference in elastic modulus is considered to be due to the difference in the maximum temperature range.
[0063]
Example 6
As shown in Table 1, the first carbonized fiber obtained in Example 5 was treated in the first treatment of the second carbonization step with a fiber tension of 2460 gf / mm ² and a fiber stress of 0.875 × 10 ⁻³ N. The same treatment as in Example 5 was carried out except that the specific gravity was 1.805, the fiber diameter was 5.0 μm, the strand strength was 6320 MPa, the strand elastic modulus was 284 GPa, and the strand elongation was 2.22%. Was obtained.
[0064]
Example 7
As shown in Table 1, the first carbonized fiber obtained in Example 5 was treated with a fiber tension of 1716 gf / mm ² and a fiber stress of 0.611 × 10 ⁻³ N in the first treatment of the second carbonization step. The same treatment as in Example 5 was carried out except that the specific gravity was 1.804, the fiber diameter was 5.0 μm, the strand strength was 6270 MPa, the strand elastic modulus was 283 GPa, and the strand elongation was 2.21%. Was obtained.
[0065]
Comparative Example 5
As shown in Table 1, the first carbonized fiber obtained in Example 5 was treated with a fiber tension of 3703 gf / mm ² and a fiber stress of 1.318 × 10 ⁻³ N in the first treatment of the second carbonization step. The same processing as in Example 5 was performed except for the above.
[0066]
However, the obtained carbon fiber was in a good strand form with a specific gravity of 1.804, a fiber diameter of 4.8 μm, a strand strength of 6270 MPa, and a strand elasticity of 286 GPa. The degree was fluffy.
[0067]
Comparative Example 6
As shown in Table 1, the first carbonized fiber obtained in Example 5 was treated with a fiber tension of 1243 gf / mm ² and a fiber stress of 0.443 × 10 ⁻³ N in the first treatment of the second carbonization step. The same processing as in Example 5 was performed except for the above.
[0068]
However, the obtained carbon fiber had a good strand shape without fluff, but had a specific gravity of 1.803, a fiber diameter of 5.1 μm, a strand strength of 6125 MPa, a strand elastic modulus of 283 GPa, and a strand elongation of 2.16. % And low elongation, taking into account the small fiber diameter.
[0069]
Comparative Example 7
As shown in Table 1, in the second carbonization step secondary treatment, the second carbonization step primary treatment fiber obtained in Example 6 was subjected to a fiber tension of 622 gf / mm ² and a fiber stress of 0.221 × 10 ^−3. The same processing as in Example 6 was performed except that the processing was performed with N.
[0070]
However, the obtained carbon fiber had a specific gravity of 1.805, a fiber diameter of 5.1 μm, a strand strength of 6320 MPa, a strand elasticity of 281 GPa, and a strand elongation of 2.25%. The alignment of the strands was disturbed, and it was a bad form without a uniform.
[0071]
Example 8
As shown in Table 1, in the second treatment in the second carbonization step, the fiber subjected to the first treatment in the second carbonization step obtained in Example 6 was subjected to a fiber tension of 1492 gf / mm ² and a fiber stress of 0.531 × 10 ^−3. Except for treating with N, the same treatment as in Example 6 was performed, and the specific gravity was 1.804, the fiber diameter was 4.9 μm, the strand strength was 6370 MPa, the strand elastic modulus was 287 GPa, and the strand elongation was 2.22%. Thus, a carbon fiber having a simple strand form was obtained.
[0072]
Comparative Example 8
As shown in Table 1, in the second carbonization step secondary treatment, the second carbonization step primary treatment fiber obtained in Example 6 was subjected to a fiber tension of 2460 gf / mm ² and a fiber stress of 0.875 × 10 ^−3. The same processing as in Example 6 was performed except that the processing was performed with N.
[0073]
However, the obtained carbon fiber had a specific gravity of 1.800, a fiber diameter of 4.8 μm, a strand strength of 6270 MPa, and was in a good strand form without fluff, but had a strand elastic modulus of 289 GPa and a strand elongation of 2. The elongation was as low as 17%.
[0074]
[Table 1]

[0075]
【The invention's effect】
According to the production method of the present invention, in the first carbonization step, and in the first treatment and the second treatment in the first carbonization step, by performing the carbonization treatment with reference to various physical properties of the fiber, high specific gravity, high specific gravity It is possible to obtain a good strand-shaped carbon fiber having strength and high elongation and having no fluff.
[Brief description of the drawings]
FIG. 1 is a graph showing a change in a specific resistance value of a first carbonized fiber with respect to a temperature rise during a primary treatment in a second carbonization step.
FIG. 2 is a graph showing a change in specific gravity of a first carbonized fiber with respect to a temperature increase during a primary treatment in a second carbonization step.
FIG. 3 is a graph showing a change in the nitrogen content of the first carbonized fiber with respect to a temperature increase during the primary treatment in the second carbonization step.
FIG. 4 is a graph showing a change in the degree of orientation of the first carbonized fiber with respect to a temperature rise during the primary treatment in the second carbonization step.
FIG. 5 is a graph showing a change in crystallite size of a first carbonized fiber with respect to a temperature rise during a primary treatment in a second carbonization step.
FIG. 6 is a graph showing a transition of a specific resistance value of a primary-treated fiber with respect to a temperature rise during a secondary treatment in a second carbonization step.
FIG. 7 is a graph showing a change in specific gravity of a primary treatment fiber with respect to a temperature rise during a secondary treatment in a second carbonization step.
FIG. 8 is a graph showing the transition of the crystallite size of the primary treated fiber with respect to the temperature rise during the secondary treatment in the second carbonization step.

Claims

第一炭素化工程において比重１．３〜１．５のポリアクリロニトリル系耐炎化繊維を不活性雰囲気中、熱処理して得られた比重１．５０〜１．７０の第一炭素化処理繊維を、第二炭素化工程において不活性雰囲気中で８００〜１８００℃の温度範囲内で炭素化する炭素繊維の製造方法であって、第二炭素化工程における一次処理として下記条件(１)乃至(５)のいずれをも満たす範囲で(６)の延伸処理を行い、次いで二次処理として下記条件(７)乃至(９)のいずれをも満たす範囲で(１０)の延伸処理を行う炭素繊維の製造方法。
第二炭素化工程条件
一次処理条件
(１) 第一炭素化処理繊維の比抵抗値が４００Ω・ｇ／ｍ²以上の範囲
(２) 第一炭素化処理繊維の比重が一次処理中上昇し続ける範囲
(３) 第一炭素化処理繊維の窒素含有量が１０質量％以上の範囲
(４) 第一炭素化処理繊維の広角Ｘ線測定(回折角２６°)における配向度が８０．８％以下で、一次処理中上昇し続ける範囲
(５) 第一炭素化処理繊維の広角Ｘ線測定(回折角２６°)における結晶子サイズが１．４７ｎｍより大きくならない範囲
(６) 第二炭素化工程一次処理での繊維張力(Ｆｇｆ／ｍｍ²)と第一炭素化処理繊維の断面積(Ｓｍｍ²)とで算出される繊維応力(ＤＮ)が下式
１．２４ × １０^-3 ＞Ｄ＞０．４６ × １０^-3
〔但し、Ｄ＝Ｆ × Ｓ × ９．８／１０００
Ｓ＝ πＡ² ／４
Ａは第一炭素化処理繊維の直径(ｍｍ)〕
を満たす範囲で繊維張力を与える延伸処理
二次処理条件
(７) 一次処理繊維の比抵抗値が４００Ω・ｇ／ｍ²未満の範囲
(８) 一次処理繊維の比重が変化しない又は低下する範囲
(９) 一次処理繊維の広角Ｘ線測定(回折角２６°)における結晶子サイズが１．４７ｎｍより大きく、且つ二次処理中上昇し続ける又は変化しない範囲
(１０) 第二炭素化工程二次処理での繊維張力(Ｇｇｆ／ｍｍ²)と第一炭素化処理繊維の断面積(Ｓｍｍ²)とで算出される繊維応力(ＥＮ)が下式
０．６０ × １０^-3 ＞Ｅ＞０．２３ × １０^-3
〔但し、Ｅ＝Ｇ × Ｓ × ９．８／１０００
Ｓ＝ πＡ² ／４
Ａは第一炭素化処理繊維の直径(ｍｍ)〕
を満たす範囲で繊維張力を与える延伸処理In the first carbonization step, a polyacrylonitrile-based oxidized fiber having a specific gravity of 1.3 to 1.5 is heat-treated in an inert atmosphere in a first carbonization-processed fiber having a specific gravity of 1.50 to 1.70. A method for producing carbon fiber in which carbonization is performed in an inert atmosphere within a temperature range of 800 to 1800 ° C. in a second carbonization step, wherein the primary treatment in the second carbonization step includes the following conditions (1) to (5) The method for producing a carbon fiber in which the stretching treatment of (6) is performed within a range satisfying any of the following conditions, and then the stretching treatment of (10) is performed as a secondary treatment within a range satisfying any of the following conditions (7) to (9): .
Secondary carbonization process conditions Primary treatment conditions
(1) The specific resistance value of the first carbonized fiber is in the range of 400 Ω · g / m ² or more.
(2) Range in which the specific gravity of the first carbonized fiber continues to increase during the primary treatment
(3) The range in which the nitrogen content of the first carbonized fiber is 10% by mass or more.
(4) A range in which the degree of orientation in wide-angle X-ray measurement (diffraction angle 26 °) of the first carbonized fiber is 80.8% or less and continues to increase during the primary treatment.
(5) Range in which the crystallite size of the first carbonized fiber is not larger than 1.47 nm in wide-angle X-ray measurement (diffraction angle 26 °).
(6) The fiber stress (DN) calculated from the fiber tension (F gf / mm ² ) in the second carbonization step primary treatment and the cross-sectional area (S mm ² ) of the first carbonization treated fiber is as follows: 1.24 × 10 ⁻³ >D> 0.46 × 10 ⁻³
[However, D = F × S × 9.8 / 1000
S = πA ^2/4
A is the diameter (mm) of the first carbonized fiber]
Drawing treatment secondary treatment conditions that give fiber tension within the range that satisfies
(7) The range where the specific resistance value of the primary treated fiber is less than 400 Ω · g / m ²
(8) Range in which the specific gravity of the primary treated fiber does not change or decreases
(9) The range where the crystallite size in the wide-angle X-ray measurement (diffraction angle 26 °) of the primary-treated fiber is larger than 1.47 nm and continues to increase or does not change during the secondary treatment
(10) The fiber stress (EN) calculated from the fiber tension (G gf / mm ² ) and the cross-sectional area (S mm ² ) of the first carbonized fiber in the second carbonization step secondary treatment is lower. Formula 0.60 × 10 ⁻³ >E> 0.23 × 10 ⁻³
[However, E = G × S × 9.8 / 1000
S = πA ^2/4
A is the diameter (mm) of the first carbonized fiber]
Drawing process that gives fiber tension within the range that satisfies

得られる炭素繊維の伸度が２．２０％以上である請求項１に記載の炭素繊維の製造方法。The method for producing a carbon fiber according to claim 1, wherein the elongation of the obtained carbon fiber is 2.20% or more.

得られる炭素繊維の単繊維径が３〜８μmである請求項１に記載の炭素繊維の製造方法。The method for producing carbon fibers according to claim 1, wherein the obtained carbon fibers have a single fiber diameter of 3 to 8 µm.