JP4612207B2 - Carbon fiber fabric and prepreg using the same - Google Patents

Description

炭素繊維束のＳｉ量は５００ｐｐｍ以下が好ましい。
また、ＪＩＳ−Ｌ１０１３に準拠して測定される炭素繊維束の引掛強さにおいて、断面積１ｍｍ^２として換算した強さが４５０Ｎ以上であることが好ましい。
また、炭素繊維束のフィラメント数は１０００〜１２０００本であることが好ましい。
また、開口率は１０％以下であることが好ましい。
本発明のプリプレグは、上記の炭素繊維織物に対して、３０〜６０重量％の樹脂が含浸されていることを特徴とする。
【０００７】
【発明の実施の形態】
以下、本発明を詳細に説明する。
本発明の炭素繊維織物は、炭素繊維束からなる縦糸と横糸が製織された、平織、朱子織、綾織等の織物である。炭素繊維束は複数の炭素繊維の単繊維が集束したものであり、通常、アクリロニトリル系重合体、ピッチ等の単繊維を束ねた前駆体繊維束（トウ）を焼成して製造される。
そして、本発明の炭素繊維織物においては、下記式（１）で表される縦糸および横糸の糸幅変動率ＣＶ（％）が、いずれも１０％以下である。
【０００８】
【数３】

【０００９】
糸幅変動率ＣＶ（％）は、縦糸および横糸それぞれについて、任意のｎ箇所で糸幅を測定し、得られた糸幅の測定値ａ₁、…、ａ_nと、これら測定値の平均値ｘとから上記式（１）を用いて算出した値であり、縦糸および横糸それぞれについて求められる。
ここで、糸幅を測定する場合、通常、織物の中央部の縦糸および横糸を１００本ずつ選択し、１本の糸について１箇所の糸幅を測定する。つまり、縦糸および横糸それぞれについて１００箇所の糸幅を測定し、得られたａ₁〜ａ₁₀₀の１００個のデータから平均値ｘを求め、縦糸および横糸それぞれの糸幅変動率ＣＶ（％）を算出する。
【００１０】
このように縦糸および横糸についてそれぞれ算出された糸幅変動率ＣＶ（％）の少なくとも一方が１０％を超えると、開口率が増加し、炭素繊維織物の外観が劣るとともに、プリプレグ製造時の樹脂含浸性が低下し、繊維強化複合材料の強化材として適さない。糸幅変動率ＣＶ（％）のより好ましい範囲は７％以下である。
【００１１】
炭素繊維織物の縦糸および横糸である炭素繊維束は、複数の炭素繊維の単繊維が集束したものである。この単繊維の繊維断面の形状には特に制限はないが、繊維断面の長径と短径との比（長径／短径）が、１．０５〜１．６であることが好ましく、さらに好ましくは、１．１０〜１．４であり、より好ましくは１．１５〜１．３０である。長径／短径比がこの範囲内にあれば、炭素繊維束の集束性が優れ、炭素繊維織物の外観も優れるとともに樹脂含浸性がさらに向上し、かつ強度も高くなる。長径／短径比が１．０５未満では、単繊維間の空隙が減少し、炭素繊維織物の樹脂含浸性が低下する場合がある。長径／短径比が１．６を超えると、繊維束の集束性が低下し、炭素繊維束を製造する際の焼成工程通過性が悪化し、炭素繊維束が安定に得られない場合がある、また、繊維断面が不均一化するため、炭素繊維束のストランド強度および引掛強さが低下し、炭素繊維織物の強度が不十分となる場合がある。さらに、毛羽などが多発し、その結果炭素繊維織物の外観も劣る場合がある。
【００１２】
ここで、単繊維の繊維断面の長径と短径との比（長径／短径）は、以下のようにして決定される。
内径１ｍｍの塩化ビニル樹脂製のチューブ内に測定用の炭素繊維束を通した後、これをナイフで輪切りにして試料を準備する。ついで、該試料を繊維断面が上を向くようにしてＳＥＭ試料台に接着し、さらにＡｕを約１０ｎｍの厚さにスパッタリングしてから、ＰＨＩＬＩＰＳ社製ＸＬ２０走査型電子顕微鏡により、加速電圧７．００ｋＶ、作動距離３１ｍｍの条件で繊維断面を観察し、単繊維の繊維断面の長径および短径を測定し、長径÷短径で長径／短径比率が決定される。
【００１３】
また、使用する炭素繊維束のＳｉ量は、５００ｐｐｍ以下であることが好ましく、さらに好ましくは３００ｐｐｍ以下であり、より好ましくは２００ｐｐｍ以下である。Ｓｉ量がこの範囲内にあれば、炭素繊維織物の樹脂含浸性がさらに優れ、かつ外観品位が高い炭素繊維織物となる。Ｓｉ量が５００ｐｐｍより多くなりすぎると、得られる炭素繊維束がばらけにくくなり、炭素繊維織物のドレープ性等の織物品位が悪くなる傾向にある。また、炭素繊維束製造工程における焼成時にシリカが多く飛散して焼成安定性が悪くなり、炭素繊維束を安定して得ることができなくなるおそれがある。
【００１４】
このＳｉ量は、前駆体繊維束を製造する際に使用されるシリコン系油剤に由来するものである。ここで、Ｓｉ量は、ＩＣＰ発光分析装置によって測定することができる。測定は以下のように実施される。
試料を風袋既知の白金るつぼに入れ６００〜７００℃マッフル炉で灰化し、その重量を測定して灰分を求める。次に炭酸ナトリウムを規定量加え、バーナーで溶融し、ＤＩ水で溶解しながら５０ｍｌポリメスフラスコに定容する。本試料をＩＣＰ発光分析法によりＳｉの定量を行う。
【００１５】
また、本発明の炭素繊維織物に使用する炭素繊維束を構成している単繊維は、その表面に単繊維の長手方向に延びる複数の皺を有していることが好ましい。このような皺の存在により、炭素繊維束の集束性が優れるとともに炭素繊維織物の樹脂含浸性がさらに向上する。
このような皺の深さは、単繊維の円周長さ２μｍの範囲で最高部と最低部の高低差によって規定される。高低差は、走査型原子間力顕微鏡（ＡＦＭ）や走査型トンネル顕微鏡（ＳＴＭ）を用いて単繊維の表面を走査して表面形状を測定することができる。具体的には以下の通りである。
【００１６】
炭素繊維の単繊維を数本試料台上にのせ、両端を固定し、さらに周囲にドータイトを塗り測定サンプルとする。原子間力顕微鏡（セイコーインスツルメンツ製、ＳＰＩ３７００／ＳＰＡ−３００）によりシリコンナイトライド製のカンチレバーを使用してＡＦＭモードにて測定を行う。単繊維の２〜７μｍの範囲を走査して得られた測定画像を二次元フーリエ変換にて低周波成分をカットしたのち逆変換を行い繊維の曲率を除去する。このようにして得られた平面画像の断面より、皺の深さを定量する。
【００１７】
本発明の炭素繊維束における単繊維の表面の皺の深さは、好ましくは８０ｎｍ以上であり、より好ましくは１００ｎｍ以上であり、さらに好ましくは１５０ｎｍ以上である。皺の深さが８０ｎｍ未満では、単繊維間の空隙が減少し、樹脂含浸性が悪くなる。また、単繊維が均一にばらけにくくなり、織布の外観品位が悪化する。一方、皺の深さが深くなりすぎると繊維束の集束性が低下し、炭素繊維束を製造する際の焼成工程通過性が悪化し、炭素繊維束を安定して得ることができなくなる。また、炭素繊維束の表面欠陥が増え、ストランド強度が低下する。さらに、単繊維間の摩擦が増加して、引掛強さが低下する傾向にある。
【００１８】
本発明の炭素繊維束の引掛強さは、断面積１ｍｍ² として換算した強さが４５０Ｎ以上であることが望ましい。より好ましくは５００Ｎ以上であり、さらに好ましくは５５０Ｎ以上である。引掛強さが４５０Ｎ未満では、糸切れしやすくなるため、炭素繊維束を製造する際の焼成工程通過性が悪化し、炭素繊維束を安定して得ることができなくなる。
【００１９】
ここで、引掛強さは、ＪＩＳ−Ｌ １０１３に記載された試験法に準拠して測定される。以下の測定方法について詳しく説明する。
図１のように、Ｕ字状の炭素繊維束１に、炭素繊維束２を引っ掛け、これをＵ字状にし、これら炭素繊維束１，２の交差部分から１００ｍｍの位置に、長さ２５ｍｍの掴み部３，４を取り付けて、試験体とする。試験体の作製の際、０．１×１０^-3Ｎ／デニールの荷重を掛けて炭素繊維束の引き揃えを行う。引張時のクロスヘッド速度は１００ｍｍ／ｍｉｎで実施する。
【００２０】
本発明の炭素繊維織物に使用する炭素繊維束は、フィラメント数が１０００〜１２０００本であることが好ましい。フィラメント数が１０００本未満では、織布にする際に必要な炭素繊維本数が多くになりコスト高となる。また，フィラメント数１２０００本以上では開口率１０％以下の炭素繊維織物を得るには開繊処理が必須となり、しかも取扱い性が極めて悪い織物となる場合がある。好ましくは、１０００〜９０００本である。
【００２１】
また、本発明で使用される炭素繊維束のストランド強度は、好ましくは３８０ｋｇｆ／ｍｍ² 以上であり、より好ましくは４００ｋｇｆ／ｍｍ² 以上であり、さらに好ましくは４２０ｋｇｆ／ｍｍ² 以上である。ストランド強度が３８０ｋｇｆ／ｍｍ² 未満では、糸切れしやすくなるため、炭素繊維束を製造する際の焼成工程通過性が悪化し、炭素繊維束を安定して得られない場合がある。また、この炭素繊維束からなる炭素繊維織物を用いた繊維強化複合材料のコンポジット特性、例えば、繊維の直角方向の曲げ強度（ＦＳ０゜）などが低下する場合がある。
ここで、ストランド強度強度は、ＪＩＳ Ｒ ７６０１に記載された試験法に準拠して測定される。
【００２２】
炭素繊維織物の開口率は１０％以下であることが好ましい。開口率が１０％を超えると織物外観が劣るとともに、樹脂含浸性が低下したり、強化材として使用した場合に炭素繊維の有する強度等の機械的特性が十分に発現しない場合がある。
ここでいう開口率とは、織物において、１００ｍｍ×１００ｍｍの単位面積における、縦糸または横糸のいずれもが存在しない開口部の合計面積の比率である。開口部の面積測定は、（株）キーエンス製、ＣＶ−１００等の市販の画像処理センサーを使用し、下記の計算式により求めることができる。
開口率（％）＝開口部の面積の和（ｍｍ²）×１００／１００００（ｍｍ²）
また、本発明の炭素繊維織物は、織物密度（１インチあたりの炭素繊維束の本数）が５〜４０本/吋であることが好ましい。５本/吋未満では、織物密度が粗すぎて開口率が増大し、繊維強化複合材料としての機能が薄れ、４０本／吋を超えると高密度になりすぎて製織性不良となり、樹脂含浸性が悪く，強度発現性が低下する場合がある。
【００２３】
次に、本発明の炭素繊維織物の製造方法について説明する。
本発明の炭素繊維束は、例えば前駆体繊維束としてアクリロニトリル系重合体の繊維束を用いた場合、以下のようにして製造することができる。
まず、湿式紡糸などによってアクリロニトリル系重合体の単繊維からなる前駆体繊維束を紡糸する。
ついで、複数の前駆体繊維束を平行に揃えた状態で耐炎化炉に導入し、２００〜３００℃に加熱された空気などの酸化性気体を前駆体繊維束に吹き付けることによって、前駆体繊維束を耐炎化して耐炎繊維束を得る。
ついで、この耐炎繊維束を炭素化炉に導入し、不活性雰囲気中、１２００〜２０００℃の温度で炭素化して炭素繊維束を得る。さらに、２０００〜２８００℃の温度で黒鉛化して高弾性炭素繊維束を得る。
【００２４】
得られた炭素繊維束に、マトリックス樹脂との親和性を向上させる目的で表面酸化処理を施す。表面酸化処理法は、特に制限はなく気相酸化処理、溶剤酸化処理、あるいは電解酸化処理などにより実施される。
続いて、繊維の保護およびマトリックス樹脂との親和性向上の目的でサイジング処理を施す。サイジング処理は、ローラー浸漬法、ローラー接触法など一般に工業的に用いられている方法などによって行われる。
サイジング剤を付着した炭素繊維は、続いて乾燥処理され、サイジング剤を付着させる際に同時に付着したサイジング剤溶液に含まれていた水、あるいは有機溶媒などの除去が行われる。ここでの乾燥処理は、熱風、熱板、ローラー、各種赤外線ヒーターなどを熱媒として利用した方法などによって行われる。
【００２５】
そして得られた炭素繊維束を縦糸および横糸として、レピア織機、シャトル織機、グリッパ織機、ジェット織機等の織機を用いて、平織、朱子織、綾織等の炭素繊維織物を製織する。
【００２６】
このようにして製造された炭素繊維織物は、樹脂が溶解している樹脂溶液に浸漬されるラッカー法（溶剤法）や、樹脂フィルムを熱圧着させるホットメルト法等の公知の方法でプリプレグとされ、繊維強化複合材料の強化材として使用される。この場合、必要に応じて、炭素繊維織物の開繊処理を行ってもよい。
プリプレグに使用される樹脂としては、例えば、エポキシ樹脂、不飽和ポリエステル樹脂、フェノール樹脂等の熱硬化性樹脂の他、ナイロン樹脂、ポリエステル樹脂、ポリブチレンテレフタレート樹脂等の熱可塑性樹脂が挙げられる。
プリプレグ中においては炭素繊維織物の重量を１００重量％とした場合、この炭素繊維織物に対して３０〜６０重量％の樹脂が含浸されていることが好ましい。含浸量が３０重量％未満では、ボイドが発生しやすく、強度低下を招く場合があり、６０重量％を超えると樹脂フローが起こり所定の厚みが得られない場合がある。
【００２７】
このような炭素繊維織物は、複数の炭素繊維の単繊維が集束した炭素繊維束からなる縦糸と横糸が製織された炭素繊維織物であり、縦糸および横糸それぞれの任意のｎ箇所で糸幅を測定し、得られた糸幅の測定値ａ₁、…、ａ_nと、これら測定値の平均値ｘとから上記式（１）を用いて算出した縦糸および横糸の糸幅変動率（％）が、いずれも１０％以下であるので、縦糸および横糸の糸幅にむらがなく均一で、低開口率で、樹脂含浸性に優れ、織物の外観品位も良好である。このような炭素繊維織物はプリプレグとして、繊維強化複合材料とするのに最適である。
【００２８】
【実施例】
以下、本発明を実施例を示して詳しく説明する。
炭素繊維前駆体繊維束は、アクリルニトリル系重合体をジメチルアセトアミドに溶解し紡糸原液を調製し、湿式紡糸にて作製した。紡糸原液は、濃度５０〜７０重量％、温度３０〜５０℃のジメチルアセトアミド水溶液からなる第一凝固浴中に吐出させて凝固糸とした。次いで該凝固糸を濃度５０〜７０重量％、温度３０〜５０℃のジメチルアセトアミド水溶液からなる第２凝固浴中にて所定量の延伸を施し、さらに４倍以上の湿熱延伸を行い、炭素繊維前駆体繊維束を得た。炭素繊維前駆体繊維束の断面の長径と短径との比、皺の深さは、凝固浴濃度および温度、さらに延伸条件を変更することにより調整した。
【００２９】
［実施例１］
フィラメント数３０００本（繊度１９８０ｄｔｅｘ）の炭素繊維を縦糸および横糸として使用して、レピア織機で平織し、織物目付けが２００ｇ／ｍ^２の炭素繊維織物を製造した。
なお、使用した炭素繊維束は、単繊維の繊維断面の長径と短径との比（長径／短径）が１．２０で、皺の深さが２１０ｎｍで、Ｓｉ量は１６０ｐｐｍ、ストランド強度は４６８０ＭＰａ、引掛強さは７６０Ｎであった。
得られた織物の縦糸および横糸の糸幅変動率（％）、開口率（％）を測定し、織物外観品位を下記の方法で評価した結果を表１に示す。
また、得られた炭素繊維織物にホットメルト法でエポキシ樹脂を含浸させたところ、樹脂含浸性が優れていた。
【００３０】
（１）糸幅変動率ＣＶ（％）
得られた織物の中央部の縦糸および横糸を１００本ずつ選択し、１本の糸について１箇所の糸幅を測定した。そして得られた測定値ａ₁〜ａ₁₀₀から平均値ｘを求め、上記式（１）を使用して糸幅変動率ＣＶ（％）を算出した。
（２）開口率（％）
１００ｍｍ×１００ｍｍの単位面積における、縦糸または横糸のいずれもが存在しない開口部の合計面積の比率である。開口部の面積測定は、（株）キーエンス製、ＣＶ−１００等の市販の画像処理センサーを使用し、下記の計算式により求めた。
開口率（％）＝開口部の面積の和（ｍｍ²）×１００／１００００（ｍｍ²）
（３）織物外観品位
目視で評価した。
【００３１】
［比較例１］
フィラメント数３０００本（繊度１９８０ｄｔｅｘ）の炭素繊維を縦糸および横糸として使用して、レピア織機で平織し、織物目付けが２００ｇ／ｍ^２の炭素繊維織物を製造した。
なお、使用した炭素繊維束は、単繊維の繊維断面の長径と短径との比（長径／短径）が１．０で、皺の深さが５０ｎｍで、Ｓｉ量は２５０ｐｐｍ、ストランド強度は４８００ＭＰａ、引掛強さは９５０Ｎであった。
実施例１と同様にして、得られた織物の糸幅変動率（％）、開口率（％）を測定し、織物外観品位を評価した結果を表１に示す。
また、得られた炭素繊維織物にホットメルト法でエポキシ樹脂を含浸させたところ、ピンホールが多発し樹脂含浸性が劣っていた
【００３２】
【表１】

【００３３】
【発明の効果】
以上説明したように本発明の炭素繊維織物は、縦糸および横糸の糸幅にむらがなく均一で、低開口率で、樹脂含浸性に優れ、織物の外観品位も良好である。このような炭素繊維織物は、プリプレグとして繊維強化複合材料を製造するのに最適であり、炭素繊維の有する強度等の機械的特性が発現した繊維強化複合材料を製造できる。
【図面の簡単な説明】
【図１】引掛強さの測定方法を説明する説明図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbon fiber fabric used as a reinforcing material for a fiber-reinforced composite material.
[0002]
[Prior art]
Carbon fibers, glass fibers, aramid fibers, and the like are used as reinforcing materials for fiber reinforced composite materials. Among these, carbon fibers are excellent in specific strength, specific elastic modulus, heat resistance, chemical resistance, and the like, and are used in fiber reinforced composite materials for aircraft applications, sports applications such as golf shafts and fishing rods, and general industrial applications.
Moreover, when carbon fiber is used as a reinforcing material, it is often used in the form of a woven fabric using carbon fiber for warp and weft. A fiber reinforced composite material using a carbon fiber fabric is manufactured as follows, for example.
[0003]
First, a precursor fiber bundle obtained by bundling thousands to tens of thousands of single fibers of a polyacrylonitrile-based polymer is fired at a temperature of 200 to 300 ° C. in an oxidizing gas such as air in a flameproofing process (firing process). Thus, a flame resistant fiber bundle is obtained. Next, in the carbonization step (firing step), the flame resistant fiber bundle is carbonized at a temperature of 300 to 2000 ° C. in an inert atmosphere to obtain a carbon fiber bundle. And after weaving this carbon fiber bundle as warp and weft to make a woven fabric, it is impregnated with a synthetic resin and molded into a predetermined shape to obtain a fiber-reinforced composite material.
[0004]
[Problems to be solved by the invention]
Precursor fiber bundles used in the production of carbon fiber bundles are high so that the fiber bundles are scattered in the firing process and the single fibers constituting the fiber bundles are not entangled with adjacent fiber bundles or wound around rollers. Convergence is required.
However, the carbon fiber bundle obtained from the precursor fiber bundle having high convergence is similarly high in convergence. Therefore, in the carbon fiber woven fabric obtained by weaving such a carbon fiber bundle, the single fiber is difficult to be uniformly dispersed due to the high convergence of the carbon fiber bundle, and the width of the carbon fiber bundle that is the warp and weft is reduced. Unevenness was likely to occur. If the width of the carbon fiber bundle is uneven, the appearance of the fabric is inferior and the aperture ratio is increased, and there is a problem that the resin is not uniformly impregnated and voids are easily generated, that is, the resin impregnation property is inferior.
[0005]
Accordingly, an object of the present invention is to provide a carbon fiber woven fabric having uniform width of carbon fiber bundles which are warp and weft, a low opening ratio, excellent resin impregnation property and good appearance quality of the woven fabric. .
[0006]
[Means for Solving the Problems]
The carbon fiber woven fabric of the present invention is a carbon fiber woven fabric in which warp and weft are woven from a bundle of carbon fibers in which a plurality of carbon fibers are bundled, and the yarn width is measured at any n locations of the warp and weft. Then, the obtained yarn width measured values a ₁ ,..., _An and the average value x of these measured values, and using the following formula (1), the warp and weft yarn width variation rate CV (%) but both Ri der than 10%, the ratio of the major axis to the minor axis of the fiber cross section of the single fiber (major axis / minor axis) of 1.05 to 1.6, the carbon fiber bundle, the single fiber surface And a plurality of wrinkles extending in the longitudinal direction of the single fiber, and the difference in height between the highest part and the lowest part is 80 nm or more in the range of the circumferential length of the single fiber of 2 μm .
[Expression 2]

Si content of coal Moto繊維束is preferably 500ppm or less.
Moreover, in the hook strength of the carbon fiber bundle measured based on JIS-L1013, it is preferable that the strength converted into a cross-sectional area of 1 mm ² is 450 N or more.
Moreover, it is preferable that the number of filaments of a carbon fiber bundle is 1000-12000.
The aperture ratio is preferably 10% or less.
The prepreg of the present invention is characterized in that the carbon fiber fabric is impregnated with 30 to 60% by weight of resin.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The carbon fiber woven fabric of the present invention is a woven fabric such as plain weave, satin weave, twill weave, etc., in which warp and weft made of carbon fiber bundles are woven. The carbon fiber bundle is a bundle of a plurality of single fibers of carbon fibers, and is usually manufactured by firing a precursor fiber bundle (tow) in which single fibers such as acrylonitrile polymer and pitch are bundled.
In the carbon fiber fabric of the present invention, the warp yarn and weft yarn width variation rate CV (%) represented by the following formula (1) are both 10% or less.
[0008]
[Equation 3]

[0009]
The yarn width variation rate CV (%) is measured with respect to each of the warp and weft yarns at arbitrary n locations. The obtained yarn width measured values a ₁ ,..., _An and the average value of these measured values This is a value calculated from x and using the above formula (1), and is obtained for each of the warp and the weft.
Here, when measuring the yarn width, 100 warp yarns and weft yarns in the center of the woven fabric are usually selected one by one, and one yarn width is measured for one yarn. That is, 100 yarn widths are measured for each of the warp and weft yarns, the average value x is obtained from the 100 data obtained from a _{1 to} a ₁₀₀ , and the yarn width variation rate CV (%) of each of the warp and weft yarns is obtained. calculate.
[0010]
As described above, when at least one of the yarn width variation rates CV (%) calculated for the warp and weft exceeds 10%, the opening ratio increases, the appearance of the carbon fiber fabric is inferior, and the resin impregnation during prepreg production is performed. It is not suitable as a reinforcing material for fiber-reinforced composite materials. A more preferable range of the yarn width variation rate CV (%) is 7% or less.
[0011]
A carbon fiber bundle that is a warp and a weft of a carbon fiber fabric is a collection of a plurality of carbon fibers. The shape of the fiber cross section of this single fiber is not particularly limited, but the ratio of the major axis to the minor axis (major axis / minor axis) of the fiber section is preferably 1.05 to 1.6, and more preferably. 1.10 to 1.4, more preferably 1.15 to 1.30. If the ratio of major axis / minor axis is within this range, the convergence property of the carbon fiber bundle is excellent, the appearance of the carbon fiber fabric is excellent, the resin impregnation property is further improved, and the strength is increased. When the major axis / minor axis ratio is less than 1.05, the voids between the single fibers may decrease, and the resin impregnation property of the carbon fiber woven fabric may deteriorate. When the ratio of the long diameter / short diameter exceeds 1.6, the fiber bundle is less converged, the carbon fiber bundle may be deteriorated, and the carbon fiber bundle may not be stably obtained. Moreover, since the fiber cross section becomes non-uniform, the strand strength and hook strength of the carbon fiber bundle may be lowered, and the strength of the carbon fiber fabric may be insufficient. Furthermore, fuzz etc. occur frequently, and as a result, the appearance of the carbon fiber fabric may be inferior.
[0012]
Here, the ratio of the major axis to the minor axis (major axis / minor axis) of the fiber cross section of the single fiber is determined as follows.
After passing a carbon fiber bundle for measurement through a tube made of vinyl chloride resin having an inner diameter of 1 mm, the sample is prepared by cutting it with a knife. Next, the sample was adhered to the SEM sample stage with the fiber cross-section facing upward, and Au was sputtered to a thickness of about 10 nm, and then an acceleration voltage of 7.00 kV was measured using a PHILIPS XL20 scanning electron microscope. The fiber cross section is observed under the condition of a working distance of 31 mm, the major axis and minor axis of the fiber section of the single fiber are measured, and the major axis / minor axis ratio is determined by the major axis / minor axis.
[0013]
Moreover, it is preferable that the amount of Si of the carbon fiber bundle to be used is 500 ppm or less, More preferably, it is 300 ppm or less, More preferably, it is 200 ppm or less. If the amount of Si is within this range, the carbon fiber woven fabric is more excellent in resin impregnation and has a high appearance quality. When the amount of Si is more than 500 ppm, the obtained carbon fiber bundles are not easily scattered, and the quality of the fabric such as the drapeability of the carbon fiber fabric tends to deteriorate. In addition, a large amount of silica is scattered during firing in the carbon fiber bundle manufacturing process, resulting in poor firing stability, and the carbon fiber bundle may not be stably obtained.
[0014]
This amount of Si is derived from the silicon-based oil used when the precursor fiber bundle is manufactured. Here, the amount of Si can be measured by an ICP emission spectrometer. The measurement is performed as follows.
A sample is put into a platinum crucible known as a tare and ashed in a muffle furnace at 600 to 700 ° C., and its weight is measured to obtain an ash content. Next, a prescribed amount of sodium carbonate is added, melted with a burner, and fixed in a 50 ml volumetric flask while dissolving in DI water. This sample is quantified by Si by ICP emission analysis.
[0015]
Moreover, it is preferable that the single fiber which comprises the carbon fiber bundle used for the carbon fiber fabric of this invention has several wrinkles extended in the longitudinal direction of a single fiber on the surface. Due to the presence of such wrinkles, the convergence of the carbon fiber bundle is excellent and the resin impregnation of the carbon fiber fabric is further improved.
The depth of such wrinkles is defined by the difference in height between the highest part and the lowest part in the range of the circumferential length of the single fiber of 2 μm. The height difference can be measured by scanning the surface of a single fiber using a scanning atomic force microscope (AFM) or a scanning tunneling microscope (STM). Specifically, it is as follows.
[0016]
Place several single carbon fibers on a sample stage, fix both ends, and apply dotite around to make a measurement sample. Measurement is performed in an AFM mode using an atomic force microscope (Seiko Instruments, SPI3700 / SPA-300) using a silicon nitride cantilever. The measurement image obtained by scanning the range of 2 to 7 μm of the single fiber is subjected to inverse transformation after cutting the low frequency component by two-dimensional Fourier transformation to remove the curvature of the fiber. The depth of the wrinkles is quantified from the cross section of the planar image thus obtained.
[0017]
The wrinkle depth on the surface of the single fiber in the carbon fiber bundle of the present invention is preferably 80 nm or more, more preferably 100 nm or more, and further preferably 150 nm or more. When the depth of the wrinkles is less than 80 nm, voids between the single fibers are reduced and the resin impregnation property is deteriorated. Moreover, it becomes difficult to disperse | distribute a single fiber uniformly, and the external appearance quality of a woven fabric deteriorates. On the other hand, when the depth of the wrinkles becomes too deep, the fiber bundles are less converged, the carbon fiber bundles are not easily passed through during the firing process, and the carbon fiber bundles cannot be obtained stably. Moreover, the surface defect of a carbon fiber bundle increases and strand strength falls. Furthermore, the friction between single fibers increases and the hook strength tends to decrease.
[0018]
The hook strength of the carbon fiber bundle of the present invention is preferably 450 N or more in terms of the cross-sectional area of 1 mm ² . More preferably, it is 500N or more, More preferably, it is 550N or more. If the catching strength is less than 450 N, yarn breakage is likely to occur, so that the carbon fiber bundle cannot be stably obtained because the carbon fiber bundle passing property is deteriorated.
[0019]
Here, the hook strength is measured in accordance with a test method described in JIS-L 1013. The following measurement method will be described in detail.
As shown in FIG. 1, a carbon fiber bundle 2 is hooked on a U-shaped carbon fiber bundle 1 to form a U-shape, and a length of 25 mm is formed at a position 100 mm from the intersection of the carbon fiber bundles 1 and 2. Grip parts 3 and 4 are attached to form a test specimen. When producing the test specimen, the carbon fiber bundle is aligned by applying a load of 0.1 × 10 ⁻³ N / denier. The crosshead speed during tension is 100 mm / min.
[0020]
The carbon fiber bundle used in the carbon fiber fabric of the present invention preferably has 1000 to 12000 filaments. If the number of filaments is less than 1000, the number of carbon fibers necessary for making a woven fabric increases, resulting in an increase in cost. In addition, when the number of filaments is 12,000 or more, the opening process is essential to obtain a carbon fiber woven fabric having an opening ratio of 10% or less, and the woven fabric may be extremely poor in handleability. Preferably, it is 1000-9000.
[0021]
The strand strength of the carbon fiber bundle used in the present invention is preferably 380 kgf / mm ² or more, more preferably 400 kgf / mm ² or more, and further preferably 420 kgf / mm ² or more. If the strand strength is less than 380 kgf / mm ² , yarn breakage is likely to occur, so that the carbon fiber bundle may not be stably obtained due to deterioration in the passability of the firing process when producing the carbon fiber bundle. Further, the composite characteristics of the fiber reinforced composite material using the carbon fiber fabric made of the carbon fiber bundle, for example, the bending strength (FS 0 °) in the direction perpendicular to the fiber may be lowered.
Here, the strand strength strength is measured in accordance with a test method described in JIS R7601.
[0022]
The opening ratio of the carbon fiber fabric is preferably 10% or less. When the open area ratio exceeds 10%, the appearance of the fabric is inferior, the resin impregnation property is lowered, and the mechanical properties such as the strength of the carbon fiber may not be sufficiently exhibited when used as a reinforcing material.
Here, the opening ratio is a ratio of the total area of openings in which no warp or weft is present in a unit area of 100 mm × 100 mm in a woven fabric. The area measurement of the opening can be obtained by the following calculation formula using a commercially available image processing sensor such as CV-100 manufactured by Keyence Corporation.
Opening ratio (%) = sum of area of opening (mm ² ) × 100/10000 (mm ² )
In addition, the carbon fiber fabric of the present invention preferably has a fabric density (number of carbon fiber bundles per inch) of 5 to 40 / 吋. If the number is less than 5 / cm, the fabric density is too coarse and the opening ratio increases, and the function as a fiber reinforced composite material is thinned. The strength development may be reduced.
[0023]
Next, the manufacturing method of the carbon fiber fabric of this invention is demonstrated.
The carbon fiber bundle of the present invention can be produced as follows, for example, when an acrylonitrile polymer fiber bundle is used as the precursor fiber bundle.
First, a precursor fiber bundle composed of single fibers of acrylonitrile-based polymer is spun by wet spinning or the like.
Next, the precursor fiber bundle is introduced into a flameproofing furnace in a state where a plurality of precursor fiber bundles are aligned in parallel, and an oxidizing gas such as air heated to 200 to 300 ° C. is blown onto the precursor fiber bundle. To obtain a flame-resistant fiber bundle.
Next, this flame resistant fiber bundle is introduced into a carbonization furnace and carbonized at a temperature of 1200 to 2000 ° C. in an inert atmosphere to obtain a carbon fiber bundle. Furthermore, graphitization is performed at a temperature of 2000 to 2800 ° C. to obtain a highly elastic carbon fiber bundle.
[0024]
The obtained carbon fiber bundle is subjected to a surface oxidation treatment for the purpose of improving the affinity with the matrix resin. The surface oxidation treatment method is not particularly limited, and is performed by gas phase oxidation treatment, solvent oxidation treatment, electrolytic oxidation treatment, or the like.
Subsequently, sizing is performed for the purpose of protecting the fibers and improving the affinity with the matrix resin. The sizing treatment is performed by a generally used method such as a roller dipping method or a roller contact method.
The carbon fiber to which the sizing agent is attached is subsequently dried, and water or an organic solvent contained in the sizing agent solution attached at the time of attaching the sizing agent is removed. The drying process here is performed by a method using hot air, a hot plate, a roller, various infrared heaters or the like as a heat medium.
[0025]
Then, using the obtained carbon fiber bundle as warp and weft, weaving carbon fiber fabrics such as plain weaving, satin weaving, twill weaving using looms such as rapier looms, shuttle looms, gripper looms and jet looms.
[0026]
The carbon fiber fabric thus produced is made into a prepreg by a known method such as a lacquer method (solvent method) in which a resin solution is dissolved or a hot melt method in which a resin film is thermocompression bonded. Used as a reinforcement for fiber reinforced composite materials. In this case, you may perform the fiber-opening process of a carbon fiber fabric as needed.
Examples of the resin used for the prepreg include thermoplastic resins such as nylon resins, polyester resins, and polybutylene terephthalate resins, in addition to thermosetting resins such as epoxy resins, unsaturated polyester resins, and phenol resins.
In the prepreg, when the weight of the carbon fiber fabric is 100% by weight, it is preferable that 30 to 60% by weight of the resin is impregnated with respect to the carbon fiber fabric. If the impregnation amount is less than 30% by weight, voids are likely to be generated and the strength may be reduced. If it exceeds 60% by weight, a resin flow may occur and a predetermined thickness may not be obtained.
[0027]
Such a carbon fiber woven fabric is a carbon fiber woven fabric in which warp and weft are woven from a bundle of carbon fibers in which a plurality of carbon fibers are bundled, and the yarn width is measured at any n locations of the warp and weft. Then, the obtained yarn width measured values a ₁ ,..., _An and the average value x of these measured values are used to calculate the yarn width variation rate (%) of the warp and weft yarns calculated using the above formula (1). Since both are 10% or less, the warp and weft yarn widths are uniform and uniform, the opening ratio is low, the resin impregnation property is excellent, and the appearance quality of the fabric is also good. Such a carbon fiber fabric is most suitable as a prepreg for a fiber-reinforced composite material.
[0028]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples.
The carbon fiber precursor fiber bundle was produced by dissolving an acrylonitrile-based polymer in dimethylacetamide to prepare a spinning stock solution and wet spinning. The spinning dope was discharged into a first coagulation bath composed of an aqueous dimethylacetamide solution having a concentration of 50 to 70% by weight and a temperature of 30 to 50 ° C. to obtain a coagulated yarn. Next, the coagulated yarn is subjected to a predetermined amount of stretching in a second coagulation bath made of a dimethylacetamide aqueous solution having a concentration of 50 to 70% by weight and a temperature of 30 to 50 ° C., and further subjected to wet heat stretching of 4 times or more to obtain a carbon fiber precursor. A body fiber bundle was obtained. The ratio of the major axis to the minor axis in the cross section of the carbon fiber precursor fiber bundle and the depth of the wrinkles were adjusted by changing the coagulation bath concentration and temperature, and the stretching conditions.
[0029]
[Example 1]
Carbon fibers having a filament number of 3000 (fineness: 1980 dtex) were used as warp and weft yarns and plain woven with a rapier loom to produce a carbon fiber fabric having a fabric weight of 200 g / m ² .
The carbon fiber bundle used has a ratio of major axis to minor axis (major axis / minor axis) of the fiber cross section of the single fiber of 1.20, the wrinkle depth is 210 nm, the Si amount is 160 ppm, and the strand strength is It was 4680 MPa, and the catching strength was 760N.
Table 1 shows the results of measuring the yarn width variation rate (%) and opening rate (%) of the obtained warp and weft yarns, and evaluating the fabric appearance quality by the following method.
Moreover, when the obtained carbon fiber fabric was impregnated with an epoxy resin by a hot melt method, the resin impregnation property was excellent.
[0030]
(1) Yarn width variation rate CV (%)
100 warp yarns and weft yarns in the center of the obtained woven fabric were selected one by one, and the width of one yarn was measured for one yarn. Then an average value x from the obtained measured values a ₁ ~a _100, was calculated yarn width variation rate CV (%) using the above equation (1).
(2) Opening ratio (%)
It is the ratio of the total area of the openings where neither warp nor weft is present in a unit area of 100 mm × 100 mm. The area of the opening was measured using a commercially available image processing sensor such as CV-100 manufactured by Keyence Corporation, using the following calculation formula.
Opening ratio (%) = sum of area of opening (mm ² ) × 100/10000 (mm ² )
(3) The appearance of the fabric was evaluated visually.
[0031]
[Comparative Example 1]
Carbon fibers having a filament number of 3000 (fineness: 1980 dtex) were used as warp and weft yarns and plain woven with a rapier loom to produce a carbon fiber fabric having a fabric weight of 200 g / m ² .
In addition, the carbon fiber bundle used has a ratio of the major axis to the minor axis (major axis / minor axis) of the fiber cross section of a single fiber of 1.0, the wrinkle depth is 50 nm, the Si amount is 250 ppm, and the strand strength is It was 4800 MPa and the hook strength was 950N.
Table 1 shows the results of measuring the yarn width variation rate (%) and the opening rate (%) of the obtained woven fabric in the same manner as in Example 1 and evaluating the woven fabric appearance quality.
Further, when the obtained carbon fiber fabric was impregnated with an epoxy resin by a hot melt method, pinholes were frequently generated and the resin impregnation property was inferior.
[Table 1]

[0033]
【The invention's effect】
As described above, the carbon fiber woven fabric of the present invention is uniform in warp and weft yarn widths, has a low opening ratio, excellent resin impregnation properties, and good appearance quality of the fabric. Such a carbon fiber woven fabric is most suitable for producing a fiber reinforced composite material as a prepreg, and a fiber reinforced composite material exhibiting mechanical properties such as strength of the carbon fiber can be produced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining a method of measuring hook strength.

Claims (6)

A carbon fiber woven fabric in which warps and wefts composed of a bundle of carbon fibers in which single fibers of a plurality of carbon fibers are bundled are woven,
Using the following formula (1), the yarn width is measured at arbitrary n locations of the warp and weft yarns, and the obtained yarn width measured values a ₁ ,..., _An and the average value x of these measured values are used. calculated warp and weft yarn width variation rate CV (%) are both Ri der 10% or less,
The ratio (major axis / minor axis) of the major axis to the minor axis of the fiber cross section of the single fiber is 1.05 to 1.6,
The carbon fiber bundle has a plurality of wrinkles extending in the longitudinal direction of the single fiber on the surface of the single fiber, and the height difference between the highest part and the lowest part is 80 nm or more in the range of the circumferential length of the single fiber of 2 μm. Characteristic carbon fiber fabric.

The carbon fiber fabric according to claim 1, wherein the Si amount of the carbon fiber bundle measured by ICP emission analysis is 500 ppm or less. In hooking strength of the carbon fiber bundle to be measured in accordance with JIS L 1013, the carbon fiber fabric according to claim 1 or 2 intensity was calculated as the cross-sectional area 1 mm ² is equal to or not less than 450 N. The carbon fiber fabric according to any one of claims 1 to 3 , wherein the number of filaments of the carbon fiber bundle is 1000 to 12000. The carbon fiber woven fabric according to any one of claims 1 to 4, wherein an opening ratio is 10% or less. A prepreg characterized in that the carbon fiber fabric according to any one of claims 1 to 5 is impregnated with 30 to 60% by weight of a resin.

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