JP2004316052A - Oil formulation for producing carbon fiber and method for producing the carbon fiber - Google Patents
Oil formulation for producing carbon fiber and method for producing the carbon fiber Download PDFInfo
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【０００１】
【発明の属する技術分野】
本発明は、強度の優れた炭素繊維を提供するための炭素繊維製造用油剤及びそれを用いた炭素繊維用前駆体繊維束及び炭素繊維の製造方法に関する。
【０００２】
【従来の技術】
炭素繊維は他の繊維に比べて優れた比強度及び比弾性率を有するため、その優れた機械的特性を利用して樹脂との複合材料用の補強繊維として工業的に広く利用されている。近年、炭素繊維複合材料の優位性はますます高まり、特にゴルフ、釣竿等のスポーツ用途や航空宇宙用途においては、この炭素繊維複合材料に対する高性能化要求が強い。複合材料としての特性、中でも剛性や圧縮強度といった特性は炭素繊維そのものの特性に起因するところが大きく、この要求はとりもなおさず炭素繊維自身への高性能化要求であり、例えば弾性率の向上や高い圧縮強度の発現といった特性が求められている。
【０００３】
最も広く利用されているポリアクリロニトリル系炭素繊維は、アクリル系前駆体繊維束を２００〜４００℃の酸化性雰囲気下で耐炎化繊維へ転換する耐炎化工程、少なくとも１０００℃の不活性雰囲気下で炭素化する炭化工程を経て、工業的に製造される。これら焼成工程においては、単繊維同士の接着が発生し、得られる炭素繊維の品質、品位を低下させるという問題があった。
【０００４】
この問題に対し、耐熱性の高いシリコーン油剤をアクリル系前駆体繊維束に付与する技術が多数提案され、工業的に広く適用されている。例えば、特定のアミノ変成シリコーン、エポキシ変性シリコーン、アルキレンオキサイド変性シリコーンを混合した油剤は、空気中及び窒素中での加熱時の減量が少なく、接着防止効果が高いことが開示されている（例えば、特許文献１）。しかしながら、このような従来のシリコーン油剤を用いて高性能な炭素繊維を得るために高張力で焼成を行うと、低粘度のため、耐炎化工程において単繊維間に薄く広く介在して単繊維間距離を縮め、またあるいは単繊維同士を実質的に接触させてしまうため、耐炎化反応に必須となる酸素の供給を妨げ、その結果、耐炎化反応の進行度ムラ、いわゆる焼成ムラの発生が誘起され、更にはこれが原因となって、続く炭化工程において糸切れや毛羽発生等の問題を引き起こしやすく、生産性向上の大きな障害となる。高性能な炭素繊維を生産性良く製造するためには、高張力に加えて、より表面が平滑なプリカーサーを高糸条密度で焼成することが有利であるが、このような条件においては、上記焼成ムラの悪影響がよりいっそう顕著となり、糸条密度、張力、処理速度を低下させざるを得ないのが現状である。この問題に対し、シリコーン油剤の硬化挙動を特定することにより、油剤を単繊維間に固まるようにして介在させることによって酸素が供給されるようにして焼成ムラを改善する技術（例えば、特許文献２）が開示されているが、更なる炭素繊維の高性能化については限界があった。
【０００５】
【特許文献１】特公平３−４０１５２号公報（全体）
【０００６】
【特許文献２】特開２００１−１７２８８０号公報（全体）
【０００７】
【発明が解決しようとする課題】
本発明は、上記問題点を解決し、耐炎化工程での単繊維間接着を防ぎ、単繊維間への酸素の供給を円滑に行うことができる炭素繊維製造用油剤を提供せんとするものである。特に高糸条密度、高張力の条件下においても、耐炎化のムラを減少し、優れた性能を有する炭素繊維を製造するための炭素繊維製造用油剤及びそれを用いた炭素繊維用前駆体繊維束及び炭素繊維の製造方法を提供せんとするものである。
【０００８】
【課題を解決するための手段】
本発明は、鋭意検討した結果、反応性界面活性剤を用いることによって、更に炭素繊維が高性能化するという発見に基づいてなされたもので、下記骨子によって上記課題を解決するものである。
【０００９】
即ち、本発明は、少なくとも反応性界面活性剤を含む炭素繊維製造用油剤であり、また、それが付与されてなる炭素繊維用前駆体繊維束であり、また、かかる炭素繊維用前駆体繊維束を焼成せしめる炭素繊維の製造方法である。さらに、広角Ｘ線により測定される炭素網面の（００２）面の結晶サイズＬｃと配向度（π００２）が式（１）を満たす炭素繊維である。
（１）ｙ≧３＊Ｌｃ＋７８
ｙ：配向度（π００２）（％）
Ｌｃ：炭素網面の（００２）面の結晶サイズ（ｎｍ）
【００１０】
【発明の実施の形態】
以下、本発明をより詳細に説明する。
【００１１】
本発明の炭素繊維製造用油剤の必須成分である反応性界面活性剤とは、疎水部と親水部からなる界面活性剤に、反応性基が結合したものである。ここでいう界面活性剤とはいわゆる乳化剤や分散剤と呼ばれるものも含むものである。ここで反応性基とは、反応性の不飽和結合等であれば特に限定されない。また、かかる反応性基は界面活性剤の構造の何れに含まれていてもよい。つまり、反応性界面活性剤の界面活性剤たる主骨格に対して付加した基として含まれていてもよいし、主骨格と反応性基との間になんらかの連結基を有していてもよいし、主骨格中に反応性の不飽和結合等が含まれていてもよい。反応性界面活性剤の界面活性剤たる主骨格に対してペンダント的に付加した基としては、不飽和結合を含む基、例えば、ビニル基やアリル基（２−プロペニル基）、１−プロペニル基等や、エポキシ基等を適用しうるが、末端が不飽和結合になるビニル基もしくはアリル基が特に好ましい。また、主骨格と反応性基との間になんらかの連結基を有する例としては、連結基として、エチレンオキサイド等のアルキレンオキサイドやメチレン基等のアルキレン等が一つ以上含まれていても構わない。具体的には、例えば、α−［１−［（アリルオキシ）メチル］−２−（ノニルフェノキシ）エチル］−ω−ヒドロキシポリオキシエチレン等のノニルフェノールのエチレンオキサイド付加物にビニル基やアリル基、１−プロペニル基が連結基を通して結合したり、直接結合した反応性界面活性剤（例えば、旭電化工業（株）製アデカリアソープ（登録商標）のＮＥシリーズや第一工業製薬（株）製アクアロン（登録商標）のＲＮシリーズ等）、アルキルエーテルを主骨格とする化合物にビニル基やアリル基、１−プロペニル基等が連結基を通して結合したり直接結合した反応性界面活性剤（例えば、旭電化工業（株）製アクアロンのＥＲシリーズ、同ＳＲシリーズ、同ＫＨシリーズ、Ｃｌａｒｉａｎｔ社Ｅｍｕｌｓｏｇｅｎ Ｒシリーズ、花王（株）製ラムテル（登録商標）シリーズ等）、アクリル酸またはメタクリル酸と、ポリエチレングリコール、またはポリエチレングリコールとポリプロピレングリコールの共重合体とのエステル物やその誘導体（例えば、日本油脂（株）製ブレンマー（登録商標）シリーズ）、イソプレンスルホン酸塩（例えば、ＪＳＲ（株）製）、等が挙げられる。
【００１２】
主骨格中に反応性の不飽和結合等が含まれている例としては、具体的には、ポリオキシエチレンひまし油（日本エマルジョン（株）製エマレックスＣ−シリーズ）、オレイン酸のような不飽和脂肪酸とポリエチレンオキサイド等とのエステル物等が挙げられる。
【００１３】
なお、反応性界面活性剤として、通常の界面活性剤と同様に、反応性界面活性剤の界面活性剤たる主骨格がノニオン性、アニオン性、カチオン性、両性のいずれのタイプも使用できるが、付着量のコントロールが容易という点でカチオン性やノニオン性は好ましく、アミノ基等がもたらす弱カチオン性やノニオン性はなお好ましく、付着量のコントロールが最も容易であるという点でノニオン性は特に好ましい。
【００１４】
本発明の炭素繊維用油剤は、かかる反応性界面活性剤を後述する主成分（油分）と混合したものであるが、反応性界面活性剤と主成分を混合した、いわゆるストレートオイル状であってもよいし、主成分および反応性界面活性剤を水等の親水性媒体に混合した、いわゆる乳化状態または分散状態であってもよい。また、いずれの場合にも反応性界面活性剤以外の通常の界面活性剤を併用してもよい。ここでいう通常の界面活性剤とは前述の反応性基を有さない界面活性剤をいう。反応性基を有さない界面活性剤としては、例えばポリエチレングリコールのアルキルエーテルやアルキルフェニルエーテル、アルキルアミンエーテルなどを挙げることができる。これら通常の界面活性剤を加えることにより、油剤全体としての反応性を制御することができる。例えば、上記具体例に挙げた日本油脂（株）製ブレンマーシリーズの反応性界面活性剤等を用いた場合には、反応性が高すぎて油剤が反応した時、繊維同士の束縛や擬似的な接着を起こしたり、繊維を痛めるまでに硬化する傾向にあるので、そのような場合に有効である。また、後述するように、主成分を親水性媒体に乳化または分散させる場合、通常の界面活性剤を乳化または分散の助剤として併用できる。
【００１５】
反応性界面活性剤に通常の界面活性剤を併用する場合は、反応性界面活性剤の重量が、通常の界面活性剤と同量もしくはそれ以上であるのが好ましい。反応性界面活性剤の量が、通常の界面活性剤よりも少ないと本発明の効果が得られにくい場合がある。
【００１６】
また、油剤を水等の親水性媒体に乳化または分散せしめる場合は、反応性界面活性剤の配合量は、油剤の乳化系または分散系の安定性によって適宜決められるが、主成分１００重量部に対して、１０〜１００重量部が好ましく、１０〜５０重量部が更に好ましく、２０〜４０重量部がなかんずく好ましい。反応性界面活性剤の配合量が主成分１００重量部に対して、１０重量部よりも少ないと本発明の効果が得られにくかったり、あるいは乳化または分散安定性が確保できない場合があり、１００重量部より多いと効果が飽和したり、もしくは後述する反応性界面活性剤の推定する作用において、反応しきれない反応性界面活性剤量が増加し、それらが前駆体繊維束の単繊維内部に浸透し、欠陥の元になって本発明の効果が損なわれる場合がある。また、反応性界面活性剤と通常の界面活性剤を併用する場合は、油剤の乳化系または分散系の安定性によって適宜決められるが、反応性界面活性剤と通常の界面活性剤との総量が主成分１００重量部に対して、１０〜１００重量部が好ましく、１０〜５０重量部が更に好ましく、２０〜４０重量部がなかんずく好ましい。これら界面活性剤の総量が主成分１００重量部に対して１０重量部よりも少ないと本発明の効果が得られにくかったり、あるいは乳化または分散安定性が確保できない場合があり、１００重量部より多いと効果が飽和したり、もしくは後述する反応性界面活性剤の推定する作用において、反応しきれない反応性界面活性剤量の単繊維内部に浸透し、欠陥の元になって本発明の効果が損なわれる場合がある。
【００１７】
上記のごとき反応性界面活性剤を用いると、炭素繊維が高性能化する理由については、必ずしも定かではないが、次のように考えている。即ち、従来の油剤中の乳化剤または分散剤として用いられてきた界面活性剤は、界面活性剤同士あるいは後述する油剤主成分との反応性がないため、油剤を前駆体繊維束に付与した後、界面活性剤の１つ１つの分子が独立で前駆体繊維束の単繊維内部に浸透する。この単繊維内部に侵入した界面活性剤は炭素繊維の欠陥の核となり、強度低下を引き起こす原因であった。一方、界面活性剤に反応性を与えると、界面活性剤同士あるいは後述する油剤の主成分に反応して結合し、反応性界面活性剤はもはや１つ１つの分子が独立して挙動することができず、大きな分子となり、前駆体繊維束の単繊維内部に浸透することができなくなる。
【００１８】
また更に、この単繊維内部への拡散による欠陥の核生成については、油剤の主成分についても同様のことが言え、反応性界面活性剤を用いると、主成分は更に巨大分子となり、単繊維内部に拡散しにくくなり、ボイド等の欠陥生成を抑制することになる。また更に、主成分が更に巨大分子化することによって油剤の水分揮発後の粘度も上昇し、繊維間にゴム的な固まり状で残りやすくなり、高糸条密度、高張力の条件下においても、単繊維間接着を防ぎ、耐炎化工程での酸素の供給が円滑に行うことができる、と考えている。
【００１９】
本発明の炭素繊維製造用油剤は、上記反応性界面活性剤を必須成分とするが、油剤の役割を果たす主成分が必要である。主成分としては、２４０℃で２時間、空気中で熱処理した時に、その減量率が７０％以下、好ましくは５０％以下に抑えられるような耐熱性があるものが好ましく、芳香族系有機化合物やシリコーン類は好ましい一例である。特に、シリコーン類は、離型性も高く、好ましく用いられる。また、シリコーン類は、ジメチルポリシロキサン等のジオルガノポリシロキサンや、それを基本にしたアミノ変性やエポキシ変性やポリエーテル変性等の各種変性物が知られており、本発明にも用いられるが、少なくとも本発明の炭素繊維製造用油剤の主成分の一部にはアミノ変性シリコーンが含まれているのは好ましく、アミノ変性シリコーンとポリエーテル変性シリコーンを併用するのは更に好ましく、アミノ変性シリコーンとエポキシ変性シリコーンとポリエーテル変性シリコーンを併用するのが特に好ましい。ここでエポキシ変性シリコーンは耐熱性に、ポリエーテル変性シリコーンは乳化安定性に寄与する効果がある。また、アミノ変性シリコーンの含有量は、主成分中２０〜１００重量％が好ましく、３０〜１００重量％がより好ましく、４０〜１００重量％がなお好ましい。アミノ変性シリコーンの含有量が主成分中２０重量％に満たない場合には、前駆体繊維同士の束縛や擬似的な接着が起こって、前駆体繊維を延伸しながら焼成する際に毛羽が立ったり、糸切れを起こすという場合がある。
【００２０】
本発明の炭素繊維製造用油剤を前駆体繊維束に付与することにより炭素繊維用前駆体繊維束を得ることができる。前駆体繊維束としては、ピッチ系とポリアクリロニトリル系が挙げられるが、ポリアクリロニトリル系繊維は特に好ましい。
【００２１】
本発明の炭素繊維製造用油剤は前駆体繊維束の製糸工程のいずれの段階で付与してもよい。例えば紡糸後、延伸前付与してもよいし、延伸後に付与してもよいし、あるいは製糸工程の最後の段階、すなわち巻取り直前に付与してもよい。延伸における単繊維間接着を防ぐという点で延伸前に付与するのがより好ましい。
【００２２】
付与する様態は、上記のように必須成分としての反応性界面活性剤と主成分のみからなる、いわばストレートオイル状で付与しても構わないし、必須成分に水等の親水性媒体を加えて乳化状態もしくは分散状態として、付与しても構わない。これらは、油剤の付与量対比効果で適宜決められるが、炭素繊維製造用油剤中に固形分が１〜５重量％、より好ましくは２〜４重量％含まれた乳化または分散状態として、付与するのが好ましい。なお、固形分の含有量は、水分が蒸発しやすいように、広い底を持った容器中に少量の油剤を入れて薄く拡げた状態で、４０℃で１２時間オーブン処理し、その前後の重量変化から求められる。乳化または分散した時の主成分の平均粒子径は、０．００１〜１μｍが好ましく、０．００１〜０．５μｍがより好ましく、０．０５〜０．２μｍがなかんずく好ましい。かかる平均粒子径は光散乱等を原理とする粒度分布計で確認することができる。
【００２３】
油剤を前駆体繊維束に付与した後は、かかる前駆体繊維束を加熱するのが好ましい。加熱することにより、上述した反応性界面活性剤と主成分との反応がより進行しやすくなる。加熱温度は、１２０〜２２０℃が好ましく、１４０〜２１０℃がより好ましく、１６０〜２００℃が更に好ましい。２２０℃を超えると単繊維間接着を起こしやすく、１２０℃以下では反応に時間が掛かり、効率的ではない場合がある。加熱時間は、油剤がストレートオイルの場合は、５〜１２０秒が好ましく、１０〜９０秒がより好ましく、１５〜６０秒が更に好ましい。加熱時間が５秒に満たないと反応が不十分になり、本発明の効果が十分に発現しない場合があり、１２０秒を超えても、効果は飽和していることが多い。油剤が水等の親水性媒体を含んでいる場合は、前記の加熱時間に好ましくは５〜３０秒、より好ましくは１０〜２０秒を加えると好ましい加熱時間となる。この時間は、水等の親水性媒体の乾燥に要する時間であるので、加熱温度や加熱の方式、例えば、接触加熱か非接触加熱か等、によって適宜決められる。加熱する形態は、電気ヒーターやスチーム等で加熱した空気の中に前駆体繊維束を通過させるテンターや赤外線加熱装置のような非接触式と、プレート式ヒーターやドラム式ヒーター等のような接触式のいずれもが用いられるが、接触式の方が熱伝達効率の点でより好ましい。
【００２４】
このようにして得られた本発明の炭素繊維用前駆体繊維束は、前述のごとく油剤が単繊維間にとどまる傾向が高くなり、繊維内部の欠陥が減少するという効果を有するだけでなく、以下に述べるとおり張力や温度を従来に比べ高めに設定し焼成せしめることが可能となる。従って、本発明の前駆体繊維束を用いることで例えば高い圧縮強度や弾性率を発現する高性能な炭素繊維を得ることができる。尚、本発明でいう炭素繊維とは、黒鉛構造を有する黒鉛化繊維も含むものである。
【００２５】
かかる焼成工程は、炭素繊維用前駆体繊維束を例えば２００〜４００℃の酸化性雰囲気下で耐炎化繊維へ転換する耐炎化工程と、５００〜８００℃の不活性雰囲気下で処理する前炭化工程と１０００〜２０００℃の不活性雰囲気下で炭素化する炭化工程を有することができる。耐炎化工程は、２２０〜２７０℃で行うのがより好ましい。
【００２６】
かかる耐炎化工程を経た、いわゆる耐炎化繊維束は、従来の耐炎化繊維束に比べ、酸化ムラが減少し、酸化進行度が高い傾向にある。具体的には、かかる酸化進行度をギ酸への溶出度から求めることができる。これは、ギ酸に浸漬すると酸化不足の部分が選択的に溶出することを利用して得た指標であり、浸漬前後の耐炎化繊維束の重量差を浸漬前の重量で除すことで求められる。かかる溶出度は０〜２％が好ましく、０〜１．５％がより好ましく、０〜１．１％がなかんずく好ましい。かかる溶出度が２％を超えると酸化ムラが増加し酸化進行度が低下し、焼成ムラの発生が誘起され、前炭化工程での延伸が困難になるという場合がある。
【００２７】
前炭化工程においては優れた炭素繊維の機械特性を得るために延伸比を０．９〜１．４とすることができるが、特に複合材料において優れた圧縮強度を得るためには、高張力で処理することが好ましく、そのための延伸比としては１〜１．３が好ましい。延伸比が１未満であると、所定の束状の炭素繊維のストランド弾性率を有するのに、炭化工程において高温で行わなければならなく、高温により後述する結晶サイズを成長させ、後述の式（１）を満たさず、優れた圧縮強度を得られない場合があり、１．３を超えると糸切れや毛羽等の発生が起こりやすく、品位の優れた炭素繊維が得られない場合がある。
【００２８】
炭化工程においては、得ようとする炭素繊維に求める性能によって変わるが、処理温度を１０００〜３０００℃とすることが好ましい。特に束状の炭素繊維のストランド引張強度が６．５ＧＰａを超えるような高強度炭素繊維を得ることを目的とする場合には、処理温度１２００〜１５００℃がより好ましい。一方、束状の炭素繊維のストランド弾性率が３４０ＧＰａを超えるような高弾性率炭素繊維を得ることを目的とする場合は、処理温度１５００〜３０００℃が好ましく、１８００〜３０００℃がより好ましい。尚、処理温度が１０００℃未満であると油剤に用いてシリコーン類が糸束に付着したままとなり炭素繊維の特性を損なう場合があり、処理温度が３０００℃を超えると糸切れや毛羽等の発生が起こりやすく、品位の優れた炭素繊維が得られないという場合がある。
【００２９】
前述のごとく本発明の油剤を用いることによって、前炭化工程での優れた高張力化が行えるため、高性能な炭素繊維を得ることが可能となる。すなわち、本発明の炭素繊維は広角Ｘ線回析より測定される炭素網面の（００２）面の結晶サイズＬｃと配向度（π００２）が式（１）を満たすことが好ましい。
（１）ｙ≧３＊Ｌｃ＋７８
ｙ：配向度（π００２）（％）
Ｌｃ：炭素網面の（００２）面の結晶サイズ（ｎｍ）
より好ましくは式（２）を満たすものである。
（２）ｙ≧３＊Ｌｃ＋８０
ｙ：配向度（π００２）（％）
Ｌｃ：炭素網面の（００２）面の結晶サイズ（ｎｍ）
ここで配向度ｙは炭素繊維の弾性率と相関があり、弾性率が高くなるほど配向度ｙも高くなる傾向にある。一方、結晶サイズは圧縮強度の発現と逆相関があり結晶サイズが小さくなるほど圧縮強度が高まる傾向にある。すなわち、配向度ｙと結晶サイズＬｃとの関係が式（１）を満たすことにより、高弾性率と高圧縮強度の発現の両立が可能となり、高性能な繊維強化複合材料の提供が可能となるものである。ここで結晶サイズＬｃは２５（ｎｍ）が好ましく、２．４〜４．８（ｎｍ）がより好ましく、２．５〜４．５（ｎｍ）が更に好ましい。結晶サイズが２未満であると弾性率が低下するという場合があり、５を超えると圧縮強度が低下するという場合がある。ここでいう配向度ｙおよび結晶サイズＬｃはＸ線源としてＣｕＫα（Ｎｉフィルター使用）を用いたＸ線回折法により求められるものである。結晶サイズＬｃは面指数（００２）回折線のピークの半値幅から、次のＳｃｈｅｒｒｅｒの式を用いて計算して求められる。
【００３０】
Ｌｃ（ｈｋｌ）＝Ｋλ／β０ｃｏｓθＢ
但し、
Ｌｃ（ｈｋｌ）：微結晶（ｈｋｌ）面に垂直な方向の平均の大きさ
Ｋ：１．０、λ：０．１５４１８ｎｍ（Ｘ線の波長）
β０：（βＥ ２−β１ ２）１／２
βＥ：見かけの半値幅（測定値）、β１：１．０４６×１０−２ｒａｄ
θＢ：Ｂｒａｇｇの回析角
また、配向度ｙは面指数（００２）回析線の結晶ピークを円周方向にスキャンして得られる強度分布の半値幅から次式により求めた。
【００３１】
ｙ＝（１８０−Ｈ）／１８０
但し、
Ｈ：見かけの半値幅（ｄｅｇ）
但し、回折強度はローレンツ因子による補正後の値を使用するものである。なかでも、これまで圧縮強度の向上が困難であった束状の炭素繊維のストランド引張弾性率が３４０ＧＰａを超えるような高弾性率炭素繊維であっても、上記式（１）を満たすことが可能となり、高い弾性率と高い圧縮強度の両立が可能となるものである。
【００３２】
本発明の繊維強化複合材料は上記炭素繊維と樹脂硬化物からなるものである。本発明の炭素繊維を用いることによって例えばＡＳＴＭ Ｄ６９５に準拠して測定される圧縮強度が１２５０ＭＰａ以上である繊維強化複合材料を得ることが可能となる。また、ＪＩＳ Ｒ７６０１による引張弾性率が３４０ＧＰａ以上でかつ圧縮強度が１２５０ＭＰａ以上である繊維強化複合材料を得ることが可能となり、ゴルフクラブ用シャフトや釣竿に好適に用いられる。
【００３３】
【実施例】
以下、実施例によって、本発明を更に詳細に説明する。なお、実施例によって本発明が制限されることはない。
【００３４】
本実施例において、耐炎化繊維の特性、炭素繊維の各種特性および繊維強化複合材料の圧縮強度は下記方法により測定した。
（１）ギ酸への溶出度
１２０℃に設定したオーブンで十分に乾燥させた耐炎化繊維束の重量を測定した後、該耐炎化繊維束２．５重量部を１００重量部のギ酸に浸漬し、２５℃で１００分間震盪した。その後、耐炎化繊維束を取り出して十分に水洗及び９０℃で２時間湯洗し、１２０℃に設定したオーブンで十分に乾燥させた。得られたギ酸処理された耐炎化繊維束の重量を量り、ギ酸処理前後の耐炎化繊維束の重量差をギ酸処理前の重量で除すことでギ酸溶出度を求めた。
（２）炭素繊維束のストランド引張強度およびストランド弾性率
ＪＩＳ Ｒ７６０１に記載の方法に準じて、次の組成の樹脂を炭素繊維束に含浸し、１３０℃、３５分の条件で加熱硬化させ、引張試験片を作製し、引張強度、引張弾性率を測定した。
＜樹脂組成＞
・３，４−エポキシシクロヘキシルメチル−３，４−エポキシ−シクロヘキシル−カルボキシレート（ＥＲＬ−４２２１、ユニオンカーバイド社製）１００重量部
・３フッ化ホウ素モノエチルアミン（ステラケミファ株式会社製） ３重量部
・アセトン（和光純薬工業株式会社製） ４重量部
（３）炭素網面（００２）面の結晶サイズＬｃおよび結晶配向度
Ｘ線回折法にて下記条件にて測定する面指数（００２）の回折線より求めた。本実施例ではＸ線回折装置として（株）理学電機社製、４０３６Ａ型（管球）を使用して、透過法により測定した。
Ａ．測定試料の作製
被測定炭素繊維から、長さ４ｃｍの試験片を切り出し、金型とコロジオン・アルコール溶液を用いて固め、角柱形状とし測定試料とした。
Ｂ．測定条件
Ｘ線源：ＣｕＫα（Ｎｉフィルター使用）
出力 ：４０ｋＶ、２０ｍＡ
Ｃ．結晶サイズＬｃの測定
上述した透過法の２θ／θスキャンで得られた面指数（００２）のピークの半値幅から、次のＳｃｈｅｒｒｅｒの式を用いて計算して求めた。
【００３５】
Ｌｃ（ｈｋｌ）＝Ｋλ／β０ｃｏｓθＢ
但し、
Ｌｃ（ｈｋｌ）：微結晶（ｈｋｌ）面に垂直な方向の平均の大きさ
Ｋ：１．０、λ：０．１５４１８ｎｍ（Ｘ線の波長）
β０：（βＥ ２−β１ ２）１／２
βＥ：見かけの半値幅（測定値）、β１：１．０４６×１０−２ｒａｄ
θＢ：Ｂｒａｇｇの回析角
Ｄ．結晶配向度（π００２）ｙの測定
上述した透過法を用い面指数（００２）回析線の結晶ピークを円周方向にスキャンして得られる強度分布の半値幅から次式を用いて計算して求めた。
【００３６】
ｙ＝（１８０−Ｈ）／１８０
但し、
Ｈ：見かけの半値幅（ｄｅｇ）
（４）プリプレグの作製
次に示す原料樹脂を混合し、３０分攪拌して樹脂組成物を得た。
【００３７】
【００３８】
この上に炭素繊維をクリールから巻きだしトラバースを介して配列する。更にその上から、前期樹脂フィルムで再度覆い、ロールで回転しながら、加圧し樹脂を繊維束内に含浸せしめ、幅３００ｍｍ、長さ２．７ｍの一方向プリプレグを作製した。ここで、プリプレグの繊維目付はドラムの回転数とトラバースの送り速度を変化させた。
（５）繊維強化複合材料の圧縮強度
上記プリプレグを繊維方向を一方向に引き揃えて積層し、温度１３０℃、加圧０．３ＭＰａで、２時間硬化させ、厚さが１ｍｍの積層板（繊維強化複合材料）を成形した。
【００３９】
かかる積層板から、被破壊部分が中心になるように、厚さ１±０．１ｍｍ、幅１２．７±０．１３ｍｍ、長さ８０±０．０１３ｍｍ、ゲージ部の長さ５±０．１３ｍｍの試験片を切り出した。尚、試験片の両端（各３７．５ｍｍづつ）は補強板を接着剤等で固着させてゲージ部長さ５±０．１３ｍｍとした。
【００４０】
ＡＳＴＭ Ｄ６９５に準拠し、歪み速度１．２７ｍｍ／分の条件で、試験数ｎ＝６について測定し、得られた圧縮強度を繊維体積分率６０％に換算して、その平均値を繊維強化複合材料の圧縮強度とした。
実施例１
下記処方の炭素繊維製造用油剤を調製した。
【００４１】
アミノ変成シリコーン ５０重量部
エポキシ変性シリコーン ２５重量部
ポリエーテル変性シリコーン ２５重量部
反応性界面活性剤 ３０重量部
水 ４０００重量部
反応性界面活性剤としては、ノニルフェノールのエチレンオキサイド付加物にビニル基を連結基を通して結合した化合物（旭電化工業（株）製、アデカリアソープＮＥ−１０）を使用した。３種のシリコーンが混合したシリコーン主成分の平均粒子径は、粒度分布計で測定した結果、０．１μｍであった。
【００４２】
この油剤を、アクリル系繊維（０．７ｄｔｅｘ、３０００フィラメント）に付着させ、次いで１７０℃×３０秒で乾燥させた。その後、延伸倍率５のスチーム延伸を経て、炭素繊維用前駆体繊維束を得た。
【００４３】
かかる炭素繊維用前駆体繊維束を８本合糸して単繊維数２４０００本とした後、２５０℃で延伸倍率１．０５の耐炎化工程、６５０℃の前炭化工程、１４００℃の炭化工程を経て、炭素繊維を得た。
実施例２
反応性界面活性剤としてメタクリル酸ポリエチレングリコール１０ｍｏｌ−ポリプロピレングリコール４ｍｏｌのブロック共重合体を用いた以外は実施例１と同様に炭素繊維製造用油剤、炭素繊維用前駆体繊維束及び炭素繊維を製造した。
実施例３
反応性界面活性剤として、ポリオキシエチレンひまし油（日本エマルジョン（株）製エマレックスＣ−５０）を用いた以外は実施例１と同様に炭素繊維製造用油剤、炭素繊維用前駆体繊維束及び炭素繊維を製造した。
比較例１
ノニルフェノールのエチレンオキサイド付加物にビニル基を連結基を通して結合した化合物をノニルフェノールのエチレンオキサイド１０ｍｏｌ付加物に変更した以外は実施例１と同様に炭素繊維製造用油剤、炭素繊維用前駆体繊維束及び炭素繊維を製造した。
比較例２
ノニルフェノールのエチレンオキサイド付加物にビニル基を連結基を通して結合した化合物をポリエチレングリコール１０ｍｏｌ−ポリプロピレングリコール４ｍｏｌのブロック共重合体とアクリル酸のエステル物に変更した以外は実施例１と同様に炭素繊維製造用油剤、炭素繊維用前駆体繊維束及び炭素繊維を製造した。
比較例３
ノニルフェノールのエチレンオキサイド付加物にビニル基を連結基を通して結合した化合物をポリオキシエチレン硬化ひまし油（日本エマルジョン（株）製エマレックスＨＣ−５０；ポリオキシエチレンひまし油に水素付加して不飽和結合をなくした化合物）に変更した以外は実施例１と同様に炭素繊維用油剤、炭素繊維用前駆体繊維束及び炭素繊維を製造した。
実施例４
実施例１と同様な方法で炭素繊維用前駆体繊維束を作製し、かかる前駆体繊維束を４本合糸して単繊維数１２０００本とした後、延伸倍率１．００、温度２３０〜２６０℃で耐炎化処理した。
【００４４】
この耐炎化処理した繊維束を最高温度７００℃の前炭化炉で延伸倍率１．２０で前炭化処理し、最高温度２０００℃の炭化炉で延伸比０．９６で炭化処理した後、最高温度２５００℃の黒鉛化炉で延伸比１．０５で黒鉛化処理した。続いて濃度０．１モル／ｌの硫酸水溶液を電解液として電解表面処理し、水洗、１５０℃で乾燥処理したのち、サイジング剤を付与し、毛羽の少ない良好な品位の炭素繊維を得た。
【００４５】
この炭素繊維を用い、前述した方法によりプリプレグ及び繊維強化複合材料を作製し、ＡＳＴＭ Ｄ６９５の評価方法に従って、繊維強化複合材料の圧縮強度を測定した。また、得られたプリプレグの繊維目付は１９０ｇ／ｍ２、樹脂含有量は３５重量％であった。
比較例４
比較例１と同じ油剤組成の炭素繊維用前駆体繊維束を用い、実施例４と同様の方法で炭素繊維を得ようとしたが、前炭化延伸率を１．１０とすると糸切れが多発するため、前炭化延伸比を０．９５にして通過させた。また、前炭化延伸比低下により弾性率が低下するため、最高温度を２７００℃にあげ、黒鉛化処理した。
【００４６】
前炭化から黒鉛化までの工程で毛羽発生、部分的な糸切れが発生しており、工程通過性は不良であった。得られた炭素繊維は、毛羽が非常に多かった。
【００４７】
この炭素繊維を用い、前述した方法によりプリプレグ及び繊維強化複合材料を作製し、ＡＳＴＭ Ｄ６９５の評価方法に従って、繊維強化複合材料の圧縮強度を測定した。また、得られたプリプレグの繊維目付は１９０ｇ／ｍ２、樹脂含有量は３５重量％であった。
【００４８】
上記実施例１〜４、比較例１〜４における各結果を表１に示した。実施例はいずれも、比較例に対して酸化が進行しており、高い炭素繊維の強度を示した。
【００４９】
【表１】
なお、表１において、耐炎化行程での酸化不足度は、耐炎化繊維束をギ酸に浸漬すると、酸化不足の部分が選択的に溶出することを利用して得た指標であり、比較例１を基準とした相対比である。その値が大きい程、酸化不足であることを示す。また、比較例１のギ酸溶出度は、１．２％であった。
実施例５
実施例１と同様の炭素繊維製造用油剤、炭素繊維用前駆体繊維束を用い、かかる炭素繊維用前駆体繊維束を４本合糸して単繊維数１２０００本とした後、実質的に撚りのない状態で２３０〜２６０℃の空気中で、延伸比１．０で耐炎化処理し、この耐炎化処理した繊維束を最高温度７００℃の前炭化炉で延伸倍率１．２０で前炭化処理し、最高温度２０００℃の炭化炉で延伸比０．９６で炭化処理した後、最高温度２２００℃の黒鉛化炉で延伸比１．０５で黒鉛化処理した。続いて濃度０．１モル／ｌの硫酸水溶液を電解液として電解表面処理し、水洗、１５０℃で乾燥処理したのち、サイジング剤を付与し、毛羽の少ない良好な品位の炭素繊維を得た。
【００５１】
この炭素繊維を用い、前述した方法によりプリプレグ及び繊維強化複合材料を作製し、ＡＳＴＭ Ｄ６９５の評価方法に従って、繊維強化複合材料の圧縮強度を測定した。また、得られたプリプレグの繊維目付は１２５ｇ／ｍ２、樹脂含有量は２４重量％であった。
実施例６
最高温度２５００℃の黒鉛化炉で処理した以外は、実施例５と同様に製造し、毛羽の少ない良好な品位の炭素繊維を得た。
実施例７
最高温度２７００℃の黒鉛化炉で処理した以外は、実施例５と同様に製造し、毛羽の少ない良好な品位の炭素繊維を得た。
比較例５
比較例１同様の炭素繊維製造用油剤、炭素繊維用前駆体繊維束を用いた以外は実施例５と同様の方法で炭素繊維を得ようとしたが、前炭化延伸率を１．１０とすると糸切れが多発するため、前炭化延伸比を０．９５にして通過させた。また、前炭化延伸比低下により弾性率が低下するため、最高温度を２５００℃にあげ、黒鉛化処理した。前炭化から黒鉛化までの工程で毛羽が発生し、得られた炭素繊維は、毛羽が多いものであった。
比較例６
比較例１同様の炭素繊維製造用油剤、炭素繊維用前駆体繊維束を用いた以外は実施例５と同様の方法で炭素繊維を得ようとしたが、前炭化延伸率を１．１０とすると糸切れが多発するため、前炭化延伸比を０．９５にして通過させた。また、前炭化延伸比低下により弾性率が低下するため、最高温度を２７００℃にあげ、黒鉛化処理した。
【００５２】
前炭化から黒鉛化までの工程で毛羽発生、部分的な糸切れが発生しており、工程通過性は不良であった。得られた炭素繊維は、毛羽が非常に多かった。
比較例７
比較例１同様の炭素繊維製造用油剤、炭素繊維用前駆体繊維束を用いた以外は実施例５と同様の方法で炭素繊維を得ようとしたが、前炭化延伸率を１．１０とすると糸切れが多発するため、前炭化延伸比を０．９５にして通過させた。また、前炭化延伸比低下により弾性率が低下するため、最高温度を３０００℃にあげ、黒鉛化処理した。
【００５３】
前炭化から黒鉛化までの工程で毛羽発生、部分的な糸切れが発生しており、工程通過性は不良であった。得られた炭素繊維は、毛羽が非常に多かった。
【００５４】
上記実施例５〜７、比較例５〜７における各結果を表２に示した。実施例はいずれも、前記式（１）を満たし、実施例５〜７の炭素繊維を用いた繊維強化複合材料の圧縮強度は、比較例対比高い強度を示した。
【００５５】
【表２】
なお、表２において、耐炎化行程での酸化不足度は、耐炎化繊維束をギ酸に浸漬すると、酸化不足の部分が選択的に溶出することを利用して得た指標であり、比較例１を基準とした相対比である。その値が大きい程、酸化不足であることを示す。また、比較例１のギ酸溶出度は、１．２％であった。
【００５７】
【発明の効果】
本発明の炭素繊維製造用油剤によって、耐炎化工程において単繊維間への酸素の供給が円滑になり、耐炎化処理時の焼成ムラが減少する。さらには、耐炎化工程において、高糸条密度、高張力の条件下であっても、単繊維間接着を防ぎ、単繊維間への酸素の供給が円滑であり、前炭化工程での高張力条件が容易なため優れた強度を有する炭素繊維を製造することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to an oil agent for producing carbon fibers for providing carbon fibers having excellent strength, a precursor fiber bundle for carbon fibers using the same, and a method for producing carbon fibers.
[0002]
[Prior art]
Since carbon fibers have superior specific strength and specific elastic modulus as compared with other fibers, carbon fibers are industrially widely used as reinforcing fibers for composite materials with resins by utilizing their excellent mechanical properties. In recent years, the superiority of the carbon fiber composite material has been increasing more and more, and especially in sports applications such as golf and fishing rods and aerospace applications, there is a strong demand for higher performance of the carbon fiber composite material. The properties of the composite material, especially the properties such as rigidity and compressive strength, are largely due to the properties of the carbon fiber itself, and this requirement is a demand for high performance of the carbon fiber itself, for example, improvement of elastic modulus and Characteristics such as high compressive strength are required.
[0003]
The most widely used polyacrylonitrile-based carbon fiber is an oxidization-resistant fiber in an oxidizing atmosphere at a temperature of 200 to 400 ° C. It is industrially manufactured through a carbonizing process. In these baking processes, there was a problem that adhesion between the single fibers occurred, and the quality and quality of the obtained carbon fibers were reduced.
[0004]
To address this problem, many techniques for applying a silicone oil agent having high heat resistance to an acrylic precursor fiber bundle have been proposed and widely applied industrially. For example, it is disclosed that an oil agent in which a specific amino-modified silicone, epoxy-modified silicone, or alkylene oxide-modified silicone is mixed has a small weight loss upon heating in air or nitrogen and has a high anti-adhesion effect (for example, Patent Document 1). However, when firing is performed under high tension to obtain high-performance carbon fibers using such a conventional silicone oil agent, due to low viscosity, thin and widely interposed between the single fibers in the flame-proofing step, the Since the distance is shortened or the single fibers are brought into substantial contact with each other, the supply of oxygen, which is indispensable for the flame-proofing reaction, is hindered. This further causes problems such as yarn breakage and fluffing in the subsequent carbonization step, which is a major obstacle to improving productivity. In order to produce a high-performance carbon fiber with high productivity, it is advantageous to bake a precursor having a smoother surface at a high yarn density in addition to a high tension. At present, the adverse effect of firing unevenness becomes even more remarkable, and the yarn density, tension, and processing speed must be reduced. In order to solve this problem, a technology for improving the unevenness in firing by specifying the curing behavior of the silicone oil agent so that the oil agent is interposed between the single fibers so as to be hardened so that oxygen is supplied (for example, Patent Document 2) ) Is disclosed, but there is a limit to further improving the performance of carbon fibers.
[0005]
[Patent Document 1] Japanese Patent Publication No. 3-40152 (whole)
[0006]
[Patent Document 2] JP-A-2001-172880 (whole)
[0007]
[Problems to be solved by the invention]
The present invention solves the above problems, prevents adhesion between single fibers in the flame-proofing step, and provides an oil agent for carbon fiber production that can smoothly supply oxygen between single fibers. is there. Oil agent for producing carbon fiber for reducing carbonization unevenness even under conditions of high yarn density and high tension and producing carbon fiber having excellent performance, and precursor fiber for carbon fiber using the same It is intended to provide a method for producing bundles and carbon fibers.
[0008]
[Means for Solving the Problems]
The present invention has been made based on the finding that carbon fibers have higher performance by using a reactive surfactant as a result of intensive studies, and solves the above problems by the following gist.
[0009]
That is, the present invention relates to an oil agent for carbon fiber production containing at least a reactive surfactant, a carbon fiber precursor fiber bundle to which the oil agent is applied, and such a carbon fiber precursor fiber bundle. Is a method for producing carbon fibers. Further, the carbon fiber has a crystal size Lc of the (002) plane of the carbon network plane measured by wide-angle X-rays and a degree of orientation (π002) satisfying the expression (1).
(1) y ≧ 3 * Lc + 78
y: degree of orientation (π002) (%)
Lc: crystal size (nm) of the (002) plane of the carbon network plane
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail.
[0011]
The reactive surfactant, which is an essential component of the oil agent for producing carbon fiber of the present invention, is one in which a reactive group is bonded to a surfactant comprising a hydrophobic part and a hydrophilic part. The term "surfactant" as used herein includes those so-called emulsifiers and dispersants. Here, the reactive group is not particularly limited as long as it is a reactive unsaturated bond or the like. Further, such a reactive group may be contained in any of the structures of the surfactant. That is, it may be included as a group added to the main skeleton as a surfactant of the reactive surfactant, or may have any linking group between the main skeleton and the reactive group. The main skeleton may contain a reactive unsaturated bond or the like. As the group pendantly added to the main skeleton of the surfactant, which is a surfactant, a group containing an unsaturated bond, for example, a vinyl group, an allyl group (2-propenyl group), a 1-propenyl group, or the like. Alternatively, an epoxy group or the like can be used, but a vinyl group or an allyl group at which the terminal becomes an unsaturated bond is particularly preferable. Further, as an example having a certain linking group between the main skeleton and the reactive group, one or more linking groups such as an alkylene oxide such as ethylene oxide and an alkylene such as a methylene group may be included. Specifically, for example, a vinyl group or an allyl group may be added to an ethylene oxide adduct of nonylphenol such as α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene. A reactive surfactant in which a propenyl group is bonded through a linking group or directly bonded thereto (for example, NE series of Adekalyap Soap (registered trademark) manufactured by Asahi Denka Kogyo Co., Ltd. and Aqualon manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (Registered trademark) RN series), a reactive surfactant in which a vinyl group, an allyl group, a 1-propenyl group, or the like is bonded or directly bonded to a compound having an alkyl ether as a main skeleton through a linking group (for example, Asahi Denka Kogyo Co., Ltd.) Aqualon ER series, SR series, KH series, Clariant Emulsogen R series, Kao Ramtel (registered trademark) series, etc.), esters of acrylic acid or methacrylic acid with polyethylene glycol or a copolymer of polyethylene glycol and polypropylene glycol and derivatives thereof (for example, Blenmer (manufactured by NOF Corporation) (Registered trademark) series), isoprene sulfonate (for example, manufactured by JSR Corporation), and the like.
[0012]
Specific examples of the main skeleton containing a reactive unsaturated bond or the like include polyoxyethylene castor oil (Emalex C-series manufactured by Nippon Emulsion Co., Ltd.) and unsaturated oleic acid such as oleic acid. Examples include esters of fatty acids with polyethylene oxide and the like.
[0013]
In addition, as a reactive surfactant, as in the case of a normal surfactant, the main skeleton serving as the surfactant of the reactive surfactant is nonionic, anionic, cationic, and any of amphoteric types can be used. Cationicity and nonionicity are preferable in that the control of the amount of adhesion is easy, weak cationicity and nonionicity provided by an amino group and the like are still more preferable, and nonionicity is particularly preferable in terms of easy control of the amount of adhesion.
[0014]
The oil agent for carbon fiber of the present invention is obtained by mixing such a reactive surfactant with a main component (oil component) described later, and is in the form of a so-called straight oil in which the reactive surfactant and the main component are mixed. It may be a so-called emulsified state or a dispersed state in which a main component and a reactive surfactant are mixed in a hydrophilic medium such as water. In each case, a normal surfactant other than the reactive surfactant may be used in combination. Here, the ordinary surfactant refers to the above-mentioned surfactant having no reactive group. Examples of the surfactant having no reactive group include alkyl ether, alkyl phenyl ether, and alkyl amine ether of polyethylene glycol. By adding these ordinary surfactants, the reactivity of the entire oil agent can be controlled. For example, in the case of using the reactive surfactant of the Blemmer Series manufactured by NOF CORPORATION listed in the above specific examples, when the reactivity is too high and the oil reacts, binding of fibers to each other or pseudo This is effective in such a case because the adhesive tends to be hardened before the fiber is damaged or the fiber is damaged. Further, as described later, when emulsifying or dispersing the main component in a hydrophilic medium, a general surfactant can be used in combination as an emulsifying or dispersing aid.
[0015]
When a general surfactant is used in combination with the reactive surfactant, the weight of the reactive surfactant is preferably equal to or more than that of the general surfactant. If the amount of the reactive surfactant is smaller than that of a normal surfactant, the effect of the present invention may not be easily obtained.
[0016]
When the oil is emulsified or dispersed in a hydrophilic medium such as water, the amount of the reactive surfactant is appropriately determined depending on the stability of the emulsified or dispersed system of the oil, but the amount is preferably 100 parts by weight of the main component. On the other hand, 10 to 100 parts by weight is preferable, 10 to 50 parts by weight is more preferable, and 20 to 40 parts by weight is particularly preferable. If the amount of the reactive surfactant is less than 10 parts by weight with respect to 100 parts by weight of the main component, the effect of the present invention may not be easily obtained, or emulsification or dispersion stability may not be ensured. If the number of the reactive surfactants exceeds the limit, the effect saturates, or the amount of the reactive surfactant that cannot be completely reacted increases in the estimated action of the reactive surfactant described later, and the amount of the reactive surfactant permeates into the single fiber of the precursor fiber bundle. However, the effects of the present invention may be impaired due to defects. When a reactive surfactant and an ordinary surfactant are used in combination, the amount is appropriately determined depending on the stability of the emulsified or dispersed system of the oil agent, but the total amount of the reactive surfactant and the ordinary surfactant is determined. 10 to 100 parts by weight, preferably 10 to 50 parts by weight, more preferably 20 to 40 parts by weight, based on 100 parts by weight of the main component. If the total amount of these surfactants is less than 10 parts by weight with respect to 100 parts by weight of the main component, the effect of the present invention may be difficult to obtain, or emulsification or dispersion stability may not be secured, and more than 100 parts by weight. And the effect is saturated, or in the presumed action of the reactive surfactant described below, penetrates into the inside of the single fiber of the amount of the reactive surfactant that cannot be completely reacted, and the effect of the present invention becomes May be impaired.
[0017]
The reason why the use of the above-mentioned reactive surfactant enhances the performance of the carbon fiber is not necessarily clear, but is considered as follows. That is, since surfactants that have been used as emulsifiers or dispersants in conventional oils have no reactivity with each other or with oil components as described below, after applying the oil to the precursor fiber bundle, Each molecule of the surfactant independently penetrates into the single fiber of the precursor fiber bundle. The surfactant that has penetrated into the inside of the single fiber became a nucleus of a defect of the carbon fiber and caused a reduction in strength. On the other hand, if the surfactant is given reactivity, it reacts with and binds to each other or to the main component of the oil agent described later, and the reactive surfactant can behave independently of each other molecule. As a result, it becomes a large molecule and cannot penetrate into the single fiber of the precursor fiber bundle.
[0018]
Further, regarding the nucleation of defects due to the diffusion into the inside of the single fiber, the same can be said for the main component of the oil agent. When the reactive surfactant is used, the main component becomes a macromolecule, and the inside of the single fiber becomes large. And the generation of defects such as voids is suppressed. Furthermore, the viscosity of the oil agent after water vaporization increases due to the macromolecularization of the main component, and the oil agent tends to remain in the form of a rubber-like mass between fibers, and even under conditions of high yarn density and high tension, It is considered that adhesion between single fibers can be prevented, and the supply of oxygen in the flameproofing step can be performed smoothly.
[0019]
The oil agent for producing carbon fiber of the present invention contains the above-mentioned reactive surfactant as an essential component, but requires a main component that plays a role of the oil agent. As the main component, those having heat resistance such that the weight loss rate is suppressed to 70% or less, preferably 50% or less when heat-treated in air at 240 ° C. for 2 hours are preferable. Silicones are a preferred example. In particular, silicones have high releasability and are preferably used. In addition, silicones are known to include diorganopolysiloxanes such as dimethylpolysiloxane, and various modified products based on the same, such as amino-modified, epoxy-modified, and polyether-modified silicones. Preferably, at least a part of the main component of the oil agent for producing carbon fiber of the present invention contains an amino-modified silicone, more preferably, a combination of an amino-modified silicone and a polyether-modified silicone, It is particularly preferable to use a modified silicone and a polyether-modified silicone in combination. Here, the epoxy-modified silicone has an effect of contributing to heat resistance, and the polyether-modified silicone has an effect of contributing to emulsion stability. In addition, the content of the amino-modified silicone is preferably 20 to 100% by weight, more preferably 30 to 100% by weight, and still more preferably 40 to 100% by weight of the main component. When the content of the amino-modified silicone is less than 20% by weight in the main component, binding or pseudo-adhesion of the precursor fibers occurs, and fluffing occurs when the precursor fiber is fired while being stretched. In some cases, thread breakage may occur.
[0020]
A precursor fiber bundle for carbon fiber can be obtained by applying the oil agent for producing carbon fiber of the present invention to the precursor fiber bundle. Examples of the precursor fiber bundle include a pitch-based fiber and a polyacrylonitrile-based fiber, and a polyacrylonitrile-based fiber is particularly preferable.
[0021]
The oil agent for producing carbon fibers of the present invention may be applied at any stage of the process of producing the precursor fiber bundle. For example, it may be applied after spinning, before stretching, after stretching, or may be applied at the last stage of the spinning process, ie, immediately before winding. It is more preferable to apply it before stretching from the viewpoint of preventing adhesion between single fibers in stretching.
[0022]
The mode of application may consist of only a reactive surfactant as an essential component and a main component as described above, and may be applied in a so-called straight oil form, or may be emulsified by adding a hydrophilic medium such as water to the essential component. It may be provided as a state or a dispersed state. These are appropriately determined depending on the effect of the applied amount of the oil agent, but are applied as an emulsified or dispersed state in which the solid content is 1 to 5% by weight, more preferably 2 to 4% by weight, in the oil agent for carbon fiber production. Is preferred. The solid content was determined by placing a small amount of oil in a container with a wide bottom and spreading it thinly in a container with a wide bottom so that water could easily evaporate. Sought from change. The average particle diameter of the main component when emulsified or dispersed is preferably 0.001 to 1 μm, more preferably 0.001 to 0.5 μm, and particularly preferably 0.05 to 0.2 μm. Such an average particle diameter can be confirmed by a particle size distribution meter based on light scattering or the like.
[0023]
After applying the oil agent to the precursor fiber bundle, it is preferable to heat the precursor fiber bundle. By heating, the reaction between the above-mentioned reactive surfactant and the main component becomes easier to proceed. The heating temperature is preferably from 120 to 220C, more preferably from 140 to 210C, and still more preferably from 160 to 200C. If the temperature exceeds 220 ° C., adhesion between single fibers is likely to occur. If the temperature is lower than 120 ° C., the reaction takes a long time and the reaction may not be efficient. When the oil agent is straight oil, the heating time is preferably from 5 to 120 seconds, more preferably from 10 to 90 seconds, even more preferably from 15 to 60 seconds. If the heating time is less than 5 seconds, the reaction becomes insufficient, and the effect of the present invention may not be sufficiently exhibited. Even if the heating time exceeds 120 seconds, the effect is often saturated. When the oil agent contains a hydrophilic medium such as water, the heating time is preferably 5 to 30 seconds, more preferably 10 to 20 seconds, when added to the above heating time. Since this time is the time required for drying the hydrophilic medium such as water, it is appropriately determined according to the heating temperature and heating method, for example, contact heating or non-contact heating. The heating method is a non-contact type such as a tenter or an infrared heating device that allows the precursor fiber bundle to pass through air heated by an electric heater or steam, and a contact type such as a plate type heater or a drum type heater. Are used, but the contact type is more preferable in terms of heat transfer efficiency.
[0024]
The precursor fiber bundle for carbon fiber of the present invention obtained in this way has a high tendency that the oil agent stays between the single fibers as described above, and has the effect of reducing defects inside the fiber, as well as the following. As described above, it is possible to set the tension and temperature to be higher than those in the related art and to perform firing. Therefore, by using the precursor fiber bundle of the present invention, for example, a high-performance carbon fiber exhibiting high compressive strength and elastic modulus can be obtained. The carbon fibers referred to in the present invention also include graphitized fibers having a graphite structure.
[0025]
The sintering step includes a oxidizing step of converting the precursor fiber bundle for carbon fiber into oxidized fiber under an oxidizing atmosphere of, for example, 200 to 400 ° C, and a pre-carbonizing step of performing treatment in an inert atmosphere of 500 to 800 ° C. And a carbonization step of carbonizing under an inert atmosphere at 1000 to 2000 ° C. It is more preferable to perform the flame-proofing step at 220 to 270 ° C.
[0026]
The so-called flame-resistant fiber bundle that has undergone such a flame-proofing process tends to have less oxidation unevenness and a higher degree of oxidation progress than the conventional flame-resistant fiber bundle. Specifically, the degree of oxidation progress can be determined from the degree of elution into formic acid. This is an index obtained by utilizing the fact that the insufficiently oxidized portion is selectively eluted when immersed in formic acid, and is obtained by dividing the weight difference between the oxidized fiber bundles before and after immersion by the weight before immersion. . The elution degree is preferably 0 to 2%, more preferably 0 to 1.5%, particularly preferably 0 to 1.1%. If the elution degree exceeds 2%, the unevenness of oxidation increases, the degree of progress of oxidation decreases, and the occurrence of unevenness in firing is induced, which may make stretching in the pre-carbonization step difficult.
[0027]
In the pre-carbonization step, the draw ratio can be set to 0.9 to 1.4 in order to obtain excellent mechanical properties of the carbon fiber. It is preferable to carry out the treatment, and the stretching ratio therefor is preferably from 1 to 1.3. When the draw ratio is less than 1, the carbonization step must be performed at a high temperature in order to have a predetermined strand elastic modulus of the bundle of carbon fibers. If 1) is not satisfied, excellent compressive strength may not be obtained, and if it exceeds 1.3, yarn breakage or fluff is likely to occur, and high-quality carbon fiber may not be obtained.
[0028]
In the carbonization step, the treatment temperature is preferably set to 1000 to 3000 ° C., although it depends on the performance required for the carbon fiber to be obtained. In particular, when it is intended to obtain a high-strength carbon fiber in which the strand tensile strength of the bundle-shaped carbon fiber exceeds 6.5 GPa, the processing temperature is more preferably from 1200 to 1500 ° C. On the other hand, when it is intended to obtain a high elastic modulus carbon fiber in which the strand elastic modulus of the bundle of carbon fibers exceeds 340 GPa, the processing temperature is preferably 1500 to 3000 ° C, more preferably 1800 to 3000 ° C. If the treatment temperature is lower than 1000 ° C., silicones may remain on the yarn bundles as an oil agent and the properties of the carbon fiber may be impaired. If the treatment temperature exceeds 3000 ° C., yarn breakage or fluff may occur. Is likely to occur, and a high-quality carbon fiber cannot be obtained.
[0029]
As described above, by using the oil agent of the present invention, excellent high tension can be achieved in the pre-carbonization step, and thus it is possible to obtain high-performance carbon fibers. That is, in the carbon fiber of the present invention, it is preferable that the crystal size Lc and the degree of orientation (π002) of the (002) plane of the carbon network plane measured by wide-angle X-ray diffraction satisfy Expression (1).
(1) y ≧ 3 * Lc + 78
y: degree of orientation (π002) (%)
Lc: crystal size (nm) of the (002) plane of the carbon network plane
More preferably, it satisfies the expression (2).
(2) y ≧ 3 * Lc + 80
y: degree of orientation (π002) (%)
Lc: crystal size (nm) of the (002) plane of the carbon network plane
Here, the degree of orientation y has a correlation with the elastic modulus of the carbon fiber, and the degree of orientation y tends to increase as the elastic modulus increases. On the other hand, the crystal size has an inverse correlation with the development of the compressive strength, and the compressive strength tends to increase as the crystal size decreases. That is, when the relationship between the degree of orientation y and the crystal size Lc satisfies the expression (1), it is possible to achieve both high elastic modulus and high compressive strength, and to provide a high-performance fiber-reinforced composite material. Things. Here, the crystal size Lc is preferably 25 (nm), more preferably 2.4 to 4.8 (nm), and still more preferably 2.5 to 4.5 (nm). If the crystal size is less than 2, the elastic modulus may decrease, and if it exceeds 5, the compressive strength may decrease. Here, the degree of orientation y and the crystal size Lc are determined by an X-ray diffraction method using CuKα (using a Ni filter) as an X-ray source. The crystal size Lc is calculated from the half width of the peak of the plane index (002) diffraction line using the following Scherrer equation.
[0030]
Lc (hkl) = Kλ / β0cos θB
However,
Lc (hkl): average size in the direction perpendicular to the microcrystal (hkl) plane
K: 1.0, λ: 0.15418 nm (wavelength of X-ray)
β0: (ΒE 2−β1 2)1/2
βE: Apparent half width (measured value), β1: 1.046 × 10-2rad
θB: Diffraction angle of Bragg
The degree of orientation y was determined by the following formula from the half width of the intensity distribution obtained by scanning the crystal peak of the plane index (002) diffraction line in the circumferential direction.
[0031]
y = (180−H) / 180
However,
H: Apparent half width (deg)
However, the diffraction intensity uses a value corrected by the Lorentz factor. Above all, it is possible to satisfy the above equation (1) even with a high elastic modulus carbon fiber in which the strand tensile elastic modulus of the bundle-like carbon fiber, which has been difficult to improve the compressive strength, exceeds 340 GPa. Thus, it is possible to achieve both high elastic modulus and high compressive strength.
[0032]
The fiber-reinforced composite material of the present invention comprises the above-mentioned carbon fiber and a cured resin. By using the carbon fiber of the present invention, it is possible to obtain a fiber-reinforced composite material having a compressive strength of 1250 MPa or more measured according to, for example, ASTM D695. Further, it is possible to obtain a fiber-reinforced composite material having a tensile elastic modulus of 340 GPa or more according to JIS R7601 and a compressive strength of 1250 MPa or more, and is suitably used for a golf club shaft and a fishing rod.
[0033]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited by the embodiments.
[0034]
In this example, the properties of the oxidized fiber, the various properties of the carbon fiber, and the compressive strength of the fiber-reinforced composite material were measured by the following methods.
(1) Degree of elution into formic acid
After measuring the weight of the oxidized fiber bundle sufficiently dried in an oven set at 120 ° C., 2.5 parts by weight of the oxidized fiber bundle was immersed in 100 parts by weight of formic acid, and shaken at 25 ° C. for 100 minutes. . Thereafter, the oxidized fiber bundle was taken out, washed sufficiently with water and washed with hot water at 90 ° C. for 2 hours, and sufficiently dried in an oven set at 120 ° C. The formic acid-treated oxidized fiber bundle was weighed, and the weight difference between the oxidized fiber bundle before and after the formic acid treatment was divided by the weight before the formic acid treatment to determine the degree of formic acid elution.
(2) Strand tensile strength and strand modulus of carbon fiber bundle
In accordance with the method described in JIS R7601, a carbon fiber bundle is impregnated with a resin having the following composition, heat-cured at 130 ° C. for 35 minutes to prepare a tensile test specimen, and measure tensile strength and tensile modulus. did.
<Resin composition>
-100 parts by weight of 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate (ERL-4221, manufactured by Union Carbide)
・ 3 parts by weight of boron trifluoride monoethylamine (manufactured by Stella Chemifa KK)
・ Acetone (Wako Pure Chemical Industries, Ltd.) 4 parts by weight
(3) Crystal size Lc and degree of crystal orientation on carbon network plane (002) plane
It was determined from the diffraction line of plane index (002) measured under the following conditions by X-ray diffraction. In this example, measurement was performed by a transmission method using a 4036A type (tube) manufactured by Rigaku Corporation as an X-ray diffractometer.
A. Preparation of measurement sample
A test piece having a length of 4 cm was cut out from the carbon fiber to be measured, solidified using a mold and a collodion-alcohol solution, and formed into a prism shape to obtain a measurement sample.
B. Measurement condition
X-ray source: CuKα (using Ni filter)
Output: 40kV, 20mA
C. Measurement of crystal size Lc
From the half width of the peak of the plane index (002) obtained by the 2θ / θ scan of the transmission method described above, it was calculated using the following Scherrer equation.
[0035]
Lc (hkl) = Kλ / β0cos θB
However,
Lc (hkl): average size in the direction perpendicular to the microcrystal (hkl) plane
K: 1.0, λ: 0.15418 nm (wavelength of X-ray)
β0: (ΒE 2−β1 2)1/2
βE: Apparent half width (measured value), β1: 1.046 × 10-2rad
θB: Diffraction angle of Bragg
D. Measurement of crystal orientation degree (π002) y
Using the transmission method described above, the crystal peak of the plane index (002) diffraction line was scanned in the circumferential direction, and was calculated from the half width of the intensity distribution obtained by the following equation.
[0036]
y = (180−H) / 180
However,
H: Apparent half width (deg)
(4) Preparation of prepreg
The following raw resin was mixed and stirred for 30 minutes to obtain a resin composition.
[0037]
[0038]
On top of this, the carbon fibers are unwound from the creel and arranged via a traverse. Further, the resin bundle was covered again with the resin film, and the resin was impregnated into the fiber bundle while being rotated by a roll to produce a unidirectional prepreg having a width of 300 mm and a length of 2.7 m. Here, the basis weight of the prepreg was changed by changing the rotation speed of the drum and the feed speed of the traverse.
(5) Compressive strength of fiber reinforced composite material
The prepreg was laminated with the fiber direction aligned in one direction and cured at 130 ° C. under a pressure of 0.3 MPa for 2 hours to form a laminate (fiber reinforced composite material) having a thickness of 1 mm.
[0039]
From such a laminated plate, the thickness is 1 ± 0.1 mm, the width is 12.7 ± 0.13 mm, the length is 80 ± 0.013 mm, and the length of the gauge is 5 ± 0.13 mm so that the portion to be destroyed becomes the center. Was cut out. In addition, the reinforcing plate was fixed to both ends (each 37.5 mm each) of the test piece with an adhesive or the like to have a gauge portion length of 5 ± 0.13 mm.
[0040]
According to ASTM D695, the number of tests n = 6 was measured under the condition of a strain rate of 1.27 mm / min, the obtained compressive strength was converted to a fiber volume fraction of 60%, and the average value was used as the fiber reinforced composite. The compressive strength of the material was used.
Example 1
An oil agent for carbon fiber production having the following formulation was prepared.
[0041]
Amino-modified silicone 50 parts by weight
25 parts by weight of epoxy-modified silicone
25 parts by weight of polyether-modified silicone
30 parts by weight of reactive surfactant
4000 parts by weight of water
As the reactive surfactant, a compound (Adekaria Soap NE-10, manufactured by Asahi Denka Kogyo KK) in which a vinyl group was bonded to an ethylene oxide adduct of nonylphenol through a linking group was used. The average particle size of the silicone main component in which the three types of silicones were mixed was 0.1 μm as measured by a particle size distribution analyzer.
[0042]
This oil agent was attached to an acrylic fiber (0.7 dtex, 3000 filaments), and then dried at 170 ° C. for 30 seconds. Thereafter, a precursor fiber bundle for carbon fiber was obtained through steam drawing at a draw ratio of 5.
[0043]
After eight such carbon fiber precursor fiber bundles are combined into a single fiber number of 24,000, a flame resistance process at 250 ° C. and a draw ratio of 1.05, a pre-carbonizing process at 650 ° C., and a carbonizing process at 1400 ° C. Through the process, a carbon fiber was obtained.
Example 2
An oil agent for producing carbon fibers, a precursor fiber bundle for carbon fibers, and carbon fibers were produced in the same manner as in Example 1 except that a block copolymer of polyethylene glycol methacrylate 10 mol-polypropylene glycol 4 mol was used as a reactive surfactant. .
Example 3
Except for using polyoxyethylene castor oil (Emarex C-50, manufactured by Nippon Emulsion Co., Ltd.) as the reactive surfactant, the same procedure as in Example 1 was carried out for producing an oil agent for producing carbon fibers, a precursor fiber bundle for carbon fibers, and a carbon fiber. Fiber was produced.
Comparative Example 1
An oil agent for carbon fiber production, a precursor fiber bundle for carbon fiber, and a carbon fiber in the same manner as in Example 1 except that the compound in which a vinyl group was bonded to the ethylene oxide adduct of nonylphenol through a linking group was changed to a 10 mol adduct of nonylphenol ethylene oxide. Fiber was produced.
Comparative Example 2
For producing carbon fibers in the same manner as in Example 1, except that the compound in which a vinyl group was bonded to the ethylene oxide adduct of nonylphenol through a linking group was changed to a block copolymer of polyethylene glycol 10 mol-polypropylene glycol 4 mol and an acrylic acid ester. An oil agent, a precursor fiber bundle for carbon fibers, and carbon fibers were produced.
Comparative Example 3
A compound in which a vinyl group is bonded to an ethylene oxide adduct of nonylphenol through a linking group is used as a polyoxyethylene hardened castor oil (Nippon Emulsion Co., Ltd., Emarex HC-50; hydrogenated polyoxyethylene castor oil to eliminate unsaturated bonds) Except that the compound was changed to (Compound), an oil agent for carbon fiber, a precursor fiber bundle for carbon fiber, and carbon fiber were produced in the same manner as in Example 1.
Example 4
A precursor fiber bundle for carbon fiber was prepared in the same manner as in Example 1, and four such precursor fiber bundles were plied to 12,000 single fibers, followed by a draw ratio of 1.00 and a temperature of 230 to 260. The sample was subjected to a flame-resistant treatment at ℃.
[0044]
The flame-resistant fiber bundle is pre-carbonized at a draw ratio of 1.20 in a pre-carbonization furnace at a maximum temperature of 700 ° C., carbonized at a draw ratio of 0.96 in a carbonization furnace at a maximum temperature of 2000 ° C., and then heated to a maximum temperature of 2500. It was graphitized in a graphitization furnace at a stretching ratio of 1.05. Subsequently, an electrolytic surface treatment was performed using an aqueous solution of sulfuric acid having a concentration of 0.1 mol / l as an electrolytic solution, followed by washing with water and drying at 150 ° C., and then applying a sizing agent to obtain good quality carbon fibers with less fluff.
[0045]
Using this carbon fiber, a prepreg and a fiber-reinforced composite material were produced by the method described above, and the compressive strength of the fiber-reinforced composite material was measured according to the evaluation method of ASTM D695. The fiber weight of the obtained prepreg was 190 g / m.2The resin content was 35% by weight.
Comparative Example 4
A carbon fiber precursor fiber bundle having the same oil composition as in Comparative Example 1 was used to obtain a carbon fiber in the same manner as in Example 4. However, when the pre-carbonization draw ratio was 1.10, thread breakage frequently occurred. For this reason, the pre-carbonized stretching ratio was set to 0.95 and passed. Further, since the modulus of elasticity decreases due to a decrease in the pre-carbonization stretching ratio, the maximum temperature was raised to 2700 ° C. and graphitization was performed.
[0046]
In the process from pre-carbonization to graphitization, fluff was generated and partial yarn breakage occurred, and the process passability was poor. The obtained carbon fiber had very much fluff.
[0047]
Using this carbon fiber, a prepreg and a fiber-reinforced composite material were produced by the method described above, and the compressive strength of the fiber-reinforced composite material was measured according to the evaluation method of ASTM D695. The fiber weight of the obtained prepreg was 190 g / m.2The resin content was 35% by weight.
[0048]
Table 1 shows the results of Examples 1 to 4 and Comparative Examples 1 to 4. In each of the examples, oxidation progressed with respect to the comparative example, and high carbon fiber strength was exhibited.
[0049]
[Table 1]
In Table 1, the degree of oxidation deficiency in the oxidation-resistant process is an index obtained by utilizing that the oxidation-deficient portion selectively elutes when the oxidized fiber bundle is immersed in formic acid. It is a relative ratio based on. The larger the value, the more insufficient the oxidation. Further, the elution degree of formic acid in Comparative Example 1 was 1.2%.
Example 5
Using the same oil agent for carbon fiber production and the precursor fiber bundle for carbon fiber as in Example 1, four such precursor fiber bundles for carbon fiber were plied into 12,000 single fibers and then substantially twisted. In a temperature of 230 to 260 ° C. in an air-free state at a draw ratio of 1.0, and the oxidized fiber bundle is pre-carbonized at a draw ratio of 1.20 in a pre-carbonizing furnace having a maximum temperature of 700 ° C. Then, carbonization was performed at a stretching ratio of 0.96 in a carbonization furnace having a maximum temperature of 2000 ° C., and then graphitization was performed at a stretching ratio of 1.05 in a graphitization furnace having a maximum temperature of 2200 ° C. Subsequently, an electrolytic surface treatment was performed using an aqueous solution of sulfuric acid having a concentration of 0.1 mol / l as an electrolytic solution, followed by washing with water and drying at 150 ° C., and then applying a sizing agent to obtain good quality carbon fibers with less fluff.
[0051]
Using this carbon fiber, a prepreg and a fiber-reinforced composite material were produced by the method described above, and the compressive strength of the fiber-reinforced composite material was measured according to the evaluation method of ASTM D695. The fiber weight of the obtained prepreg was 125 g / m.2The resin content was 24% by weight.
Example 6
Except that the treatment was performed in a graphitization furnace having a maximum temperature of 2500 ° C., it was manufactured in the same manner as in Example 5 to obtain a good quality carbon fiber with less fluff.
Example 7
Except that the treatment was performed in a graphitization furnace having a maximum temperature of 2700 ° C., it was manufactured in the same manner as in Example 5 to obtain good quality carbon fibers with less fluff.
Comparative Example 5
Comparative Example 1 An attempt was made to obtain carbon fibers in the same manner as in Example 5, except that the same oil agent for carbon fiber production and the precursor fiber bundle for carbon fibers were used. Since the yarn breakage frequently occurs, the pre-carbonized draw ratio was set to 0.95 and the yarn was passed. Further, since the modulus of elasticity decreases due to a decrease in the pre-carbonization stretching ratio, the maximum temperature was raised to 2500 ° C., and graphitization was performed. Fuzz was generated in the process from pre-carbonization to graphitization, and the obtained carbon fiber had many fuzz.
Comparative Example 6
Comparative Example 1 An attempt was made to obtain carbon fibers in the same manner as in Example 5, except that the same oil agent for producing carbon fibers and the same precursor fiber bundle for carbon fibers were used. Since the yarn breakage frequently occurs, the pre-carbonized draw ratio was set to 0.95 and the yarn was passed. Further, since the modulus of elasticity decreases due to a decrease in the pre-carbonization stretching ratio, the maximum temperature was raised to 2700 ° C., and graphitization was performed.
[0052]
In the process from pre-carbonization to graphitization, fluff was generated and partial yarn breakage occurred, and the process passability was poor. The obtained carbon fiber had very much fluff.
Comparative Example 7
Comparative Example 1 An attempt was made to obtain carbon fibers in the same manner as in Example 5, except that the same oil agent for producing carbon fibers and the same precursor fiber bundle for carbon fibers were used. Since the yarn breakage frequently occurs, the pre-carbonized draw ratio was set to 0.95 and the yarn was passed. Further, since the modulus of elasticity decreases due to a decrease in the pre-carbonization stretching ratio, the maximum temperature was raised to 3000 ° C. and graphitization was performed.
[0053]
In the process from pre-carbonization to graphitization, fluff was generated and partial yarn breakage occurred, and the process passability was poor. The obtained carbon fibers had very much fluff.
[0054]
Table 2 shows the results of Examples 5 to 7 and Comparative Examples 5 to 7. In each of the examples, the formula (1) was satisfied, and the compressive strength of the fiber-reinforced composite material using the carbon fibers of Examples 5 to 7 was higher than that of the comparative example.
[0055]
[Table 2]
In Table 2, the degree of oxidation deficiency in the oxidation-resistant process is an index obtained by utilizing that the oxidation-deficient portion is selectively eluted when the oxidized fiber bundle is immersed in formic acid. Is a relative ratio based on The larger the value, the more insufficient the oxidation. Further, the elution degree of formic acid in Comparative Example 1 was 1.2%.
[0057]
【The invention's effect】
By the oil agent for carbon fiber production of the present invention, the supply of oxygen between the single fibers in the flame-proofing step becomes smooth, and uneven firing during the flame-proofing treatment is reduced. Furthermore, in the flame-proofing step, even under conditions of high yarn density and high tension, adhesion between the single fibers is prevented, the supply of oxygen between the single fibers is smooth, and high tension in the pre-carbonization step is achieved. Since the conditions are easy, a carbon fiber having excellent strength can be manufactured.
Claims (13)
（１）ｙ≧３＊Ｌｃ＋７８
ｙ：配向度（π００２）（％）
Ｌｃ：炭素網面の（００２）面の結晶サイズ（ｎｍ）A carbon fiber in which the crystal size Lc of the (002) plane of the carbon network plane measured by wide-angle X-ray diffraction and the degree of orientation (π002) y satisfy the formula (1).
(1) y ≧ 3 * Lc + 78
y: degree of orientation (π002) (%)
Lc: crystal size (nm) of (002) plane of carbon network plane
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