JP4975217B2 - Carbon fiber and method for producing the same, method for producing carbon fiber precursor fiber, and prepreg - Google Patents

Carbon fiber and method for producing the same, method for producing carbon fiber precursor fiber, and prepreg Download PDF

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JP4975217B2
JP4975217B2 JP2001061775A JP2001061775A JP4975217B2 JP 4975217 B2 JP4975217 B2 JP 4975217B2 JP 2001061775 A JP2001061775 A JP 2001061775A JP 2001061775 A JP2001061775 A JP 2001061775A JP 4975217 B2 JP4975217 B2 JP 4975217B2
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carbon fiber
fiber
gpa
precursor
shear strength
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JP2002266172A (en
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和也 後藤
一城 古賀
稔之 伊藤
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Mitsubishi Chemical Corp
Mitsubishi Rayon Co Ltd
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Mitsubishi Chemical Corp
Mitsubishi Rayon Co Ltd
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Description

【0001】
【発明の属する技術分野】
本発明は、炭素繊維、炭素繊維用前駆体繊維、及び炭素繊維強化複合材料成形用の中間基材であるプリプレグに関する。
【0002】
【従来の技術】
炭素繊維強化複合材料(以下CFRPと記す)は、スポーツレジャー関連から産業用途、航空機用途まで広く用いられており、航空機や鉄道車両等の床材としても用いられている。
【0003】
床材としては軽量かつ高剛性、高強度のため、CFRPをスキン材とし、ハニカム構造体や発泡体のコア材に接着、乃至一体成形したサンドイッチパネルが使用されることが多い。
【0004】
このような、床材としてのサンドイッチパネルに要求される性能のひとつとして、貫通衝撃に強いことがある。これはスキン材の面方向からの、すなわち補強繊維に対して横方向のスキン材を貫通するような衝撃に対しての強度が要求されるということであり、傘や杖で突いた時のことを想定している。
【0005】
このような貫通衝撃強度を高めたい場合には、CFRPスキンの厚みを厚くしたりコア材の密度を上げたりすればよいが、いずれも重量的には増加する方向である。
【0006】
【発明が解決しようとする課題】
本発明の目的は、繊維に対して横方向の貫通衝撃強度に優れた炭素繊維、またその炭素繊維を得るための炭素繊維用前駆体繊維、およびこれらの製造方法を提供することであり、この炭素繊維を用いた貫通衝撃強度に優れる炭素繊維強化複合材料用プリプレグを提供することである。このような炭素繊維は、CFRPをスキン材とするサンドイッチ構造体において、重量を増加させることなく、そのスキン材の面方向、すなわち補強繊維に対して横方向に対する貫通衝撃強度を向上させることができる
【0007】
【課題を解決するための手段】
本発明は、せん断強度が1.4GPa以上、引張弾性率が270GPa以下であることを特徴とする炭素繊維である。本発明の炭素繊維においては、湿式紡糸法によって製造された炭素繊維用前駆体繊維が焼成されてなる炭素繊維であることが好ましい。
【0009】
さらに本発明は、上記炭素繊維を製造するための炭素繊維前駆体繊維を湿式紡糸法によって製造する炭素繊維前駆体繊維の製造方法であって
乾燥前の凝固糸の膨潤度を100%以下とし、乾燥前の延伸倍率を1.1倍以上、1.2倍以下とすることを特徴とする炭素繊維前駆体繊維の製造方法である。この方法においては、凝固浴の温度を50℃以下とすることが好ましい。
【0010】
また本発明は、上記製造方法により製造された炭素繊維用前駆体繊維を40分以上耐炎化処理した後、炭化して、引張弾性率が270GPa以下かつせん断強度が1.4GPa以上である炭素繊維を得ることを特徴とする炭素繊維の製造方法である。
【0011】
本発明は、せん断強度が1.4GPa以上、引張弾性率が270GPa以下である炭素繊維にマトリックス樹脂が含浸されてなる炭素繊維強化複合材料用プリプレグも含む。
【0012】
【発明の実施の形態】
本発明の炭素繊維は、そのせん断強度が1.4GPa以上でなければならない。ここでいうせん断強度とはいわゆる通常炭素繊維の強度として象徴的に用いられる引張強度ではなく、図1に模式図を示すように、繊維10の周方向に加わるせん断変形に対する強度のことである。
【0013】
本発明者らはCFRPの繊維方向に対して横方向からの荷重、特に衝撃的な荷重が与えられたときの現象について鋭意検討した結果、横方向からの荷重に対しては炭素繊維のせん断強度が効いていることを見出した。
【0014】
CFRPの横方向からの荷重に関する研究はこれまでも若干なされてきた。例えば特開昭57−42934号公報には炭素繊維の結節強度が高いとCFRPのシャルピー衝撃強度が高くなるとの報告があるが、本発明者らの検討によれば、CFRPの横方向からの荷重には炭素繊維のせん断強度が支配的に効いており、その炭素繊維のせん断強度は引張方向の強度、例えば通常炭素繊維の引張強度としてカタログなどに記載のある、ストランド引張強度とは相関のないことを見出した。
【0015】
また更に本発明者らは、炭素繊維のせん断強度が1.0GPa以上であるとき、その炭素繊維を用いて成形したCFRPは、その繊維方向に対して横方向からの荷重に非常に強いことを見出した。炭素繊維のせん断強度が1.2GPa以上であれば、そのCFRPは繊維方向に対した横方向からの荷重により強くなるためにより好ましく、炭素繊維のせん断強度が1.4GPa以上であるときは更に好ましい。本発明では特に炭素繊維のせん断強度を1.4GPa以上とする。
【0016】
せん断強度の測定方法としては次の方法によって測定する。すなわち、厚み0.5mm以下、体積繊維含有率(以下Vfと略記する)が60〜70%の厚みが一定な一方向CFRPを成形する。マトリックス樹脂としては特に限定はないが、エポキシ樹脂組成物が好ましい。このCFRPを繊維方向に対して幅を5mm程度にカットし、試験片とする。このCFRP中の炭素繊維の横方向からせん断変形を与えるように、例えば図2に示すような鉄製の治具にセットし、CFRPのせん断強度を測定する。次にマトリックス樹脂のみで硬化、成形し、同様にしてマトリックス樹脂硬化物のせん断強度を測定する。そしてマトリックス樹脂硬化物のせん断強度、CFRPのせん断強度と試験片CFRPのVfから換算し、炭素繊維のせん断強度を算出する。
【0017】
図2に示す治具は、試験片支持部上側押さえ1a、1bと試験片支持部下側台3a、3bの間に試験片6を挟み、上側押さえ1a、1bと下側台3a、3bとをネジによりそれぞれ固定できるようになっている。下側台3a、3bはスペーサー5を介して相互に固定されている。試験片せん断破壊刃部の上側押さえ2と下側台4とは、その間に試験片6を挟み、相互にネジで固定できるようになっており、1aおよび3aで構成される図面左側の支持部と1bおよび3bで構成される図面右側の支持部との間に、可動に配されている。せん断を測定する隙間、すなわち、図面左側の支持部と試験片せん断破壊刃部(2および4)との隙間ならびに試験片せん断破壊刃部と図面右側の支持部との隙間dは0とし、隙間壁面には潤滑油等を塗布し、滑りを良くしておく。1aと3a、2と4、1bと3bの間に試験片を図2のように挟み、試験片せん断破壊刃部の上側押さえ2の上部から荷重をかけてゆき、試験片が破壊した時点の荷重を測る。図3はせん断破壊後の状態を示す模式図である。
【0018】
このとき、試験片のない状態で測定したときの荷重はこの隙間壁面での摩擦力であるが、この荷重が測定する最低荷重に対して、その3%以下になるように摩擦力を調節する。
【0019】
次に、炭素繊維用前駆体繊維、炭素繊維の製造方法につき、湿式紡糸法により製造する方法の例について説明する。まずアクリロニトリルを主成分とし、アクリロニトリルと共重合可能な重合性不飽和モノマーを溶液重合、懸濁重合等により重合し、この重合体を溶剤に溶解して紡糸原液とする。重合性不飽和単量体の具体例としては、アクリル酸、メタクリル酸、イタコン酸、及びそれらのアルカリ金属塩、アンモニウム塩、またはアルキルエステル類、並びにアクリルアミド、メタクリルアミド及びそれらの誘導体、並びにアリルスルホン酸、メタリルスルホン酸及びそれらの塩類、並びにアルキルエステル類などが挙げられる。また、重合体を溶解する溶剤としては、ジメチルスルホキシド、ジメチルホルムアミド、ジメチルアセトアミドなどが挙げられる。次に紡糸原液をノズル孔より凝固浴中に吐出して凝固糸とし、これを洗浄および必要に応じ延伸する。続いて乾燥して緻密化するが、乾燥工程の前に油剤を付与するのが好ましい。そして乾燥緻密化した糸条を高温の加熱ローラー等による乾熱延伸あるいは加圧スチームによるスチーム延伸等を行い、炭素繊維用前駆体繊維を得る。
【0020】
炭素繊維を得るには、炭素繊維用前駆体繊維を焼成する。すなわち、空気雰囲気中で加熱する耐炎化工程とこれに引き続く不活性雰囲気中で加熱する炭素化工程との二つの工程に付す。
【0021】
本発明の炭素繊維の製造方法においては、ポリアクリロニトリルを主成分とする炭素繊維前駆体繊維を焼成してなるPAN系の炭素繊維が好ましいが、特にこれに限定されるものではない。
【0022】
また、炭素繊維前駆体繊維を焼成して本発明の炭素繊維を得る場合の本発明に用いられる炭素繊維前駆体繊維としてはコスト面から、あるいはマトリックスとの接着性の面から湿式紡糸されたものが好ましい。
【0023】
素繊維用前駆体繊維は湿式紡糸法により紡糸された炭素繊維用前駆体繊維であって、凝固糸の膨潤度が100%以下であるものが好ましい。凝固糸の膨潤度が100%以下である場合、ボイド構造を少なく抑えることができ、炭素繊維前駆体繊維が緻密な構造となり、焼成後の炭素繊維のせん断強度が向上する。凝固糸の膨潤度が90%以下の場合は、より緻密な炭素繊維用前駆体繊維が得られるのでより好ましい。膨潤度が80%以下の場合は更に好ましい。
【0024】
膨潤度は次の方法で求める。すなわち、サンプリングした乾燥前の凝固糸に付着した水分を完全に拭き取って質量を測定しW1とする。続いて該サンプルを110℃で2時間熱風乾燥機で乾燥させて質量を測定しW2とする。膨潤度は下記(1)式で求められる。
【0025】
【数1】

Figure 0004975217
【0026】
膨潤度を低く抑えるためには凝固速度を遅くすることが効果的であり、凝固浴の温度を低くする方法が例示できる。凝固浴の温度は50℃以下が好ましく、40℃以下は更に好ましく、35℃以下は特に好ましい。ただし湿式紡糸法の場合は、束切れや毛羽の発生を防止するという観点から、凝固浴の温度を20℃とするのが好ましい。
【0027】
また、乾燥工程前であまり延伸させないことも膨潤度を低く抑える上で効果的である。具体的には乾燥工程前での延伸倍率は3.5倍以下が好ましく、2.5倍以下は更に好ましい。1.5倍以下は特に好ましい。乾燥工程前で延伸させないほど膨潤度は低く抑えられるため下限としては1.0倍以上が好ましいが、乾燥工程前の延伸が1.0倍の場合、毛羽や束切れが発生する傾向があるので、工程安定のためには1.1倍以上が好ましい。ただし、本発明では特に、乾燥前の延伸倍率を1.1倍以上、1.2倍以下とする。
【0028】
素繊維用前駆体繊維の径については細い方が、焼成後の炭素繊維のせん断強度が向上するので好ましく、単繊維の平均のデニール数で、1.2デニール以下が好ましい。1.0デニール以下は炭素繊維のせん断強度がより向上するのでより好ましく、0.7デニール以下は更に好ましい。
【0029】
次に炭素繊維用前駆体繊維を耐炎化する工程について説明する。
【0030】
耐炎化条件は、単繊維表層部と単繊維中心部との構造差を決定づけるため重要である。特に耐炎化温度は、かかる構造差への影響が大きいので重要である。耐炎化温度としては200〜300℃の範囲が好ましい。
【0031】
耐炎化時間を長くすることによっても高せん断強度の炭素繊維を得ることができる。具体的には耐炎化時間は40分以上とすることが好ましい。ここで耐炎化時間とは、繊維束が耐炎化炉内に滞留している全時間をいう。耐炎化時間が40分未満であると、単糸表層部と単糸中心部との構造差が顕著になり、単糸中心部の耐炎化が不十分で、次の炭化の工程で中心部が焼失し、得られる炭素繊維のせん断強度が低下することがあるという点で不利である。耐炎化時間が60分以上の場合はより好ましい。しかしながら、耐炎化時間が長くなりすぎると生産性が低下するという点で不利であるため、耐炎化時間は180分以下が好ましい。
【0032】
炭素繊維の引張弾性率については、引張弾性率が高くなるにつれてせん断強度は低くなる傾向があるため、炭素繊維の引張弾性率は350GPa以下が好ましい。炭素繊維の引張弾性率が270GPa以下の場合にはその炭素繊維のせん断強度が高くなるので更に好ましい。しかしながら、引張弾性率が低すぎるとCFRPの特に引張に関する特性が低下するという点で不利であるので、炭素繊維の引張弾性率は100GPa以上が好ましい。尚、引張弾性率はJIS R 7601に則ったストランド状態で測定する。ただし、本発明では特に、炭素繊維の引張弾性率を270GPa以下とする。
【0033】
本発明の炭素繊維を補強材とするプリプレグもまた本発明とするところのものである。
【0034】
本発明のプリプレグに使用されるマトリックス樹脂としては特に限定はないが、熱硬化性樹脂がプリプレグの取り扱い性に優れるために好ましい。熱硬化性樹脂の中でもエポキシ樹脂、ビスマレイミド樹脂、不飽和ポリエステル樹脂、ビニルエステル樹脂、フェノール樹脂、ベンゾキサジン樹脂、シアネートエステル樹脂の各樹脂組成物が好ましく用いられる。また、マトリックス樹脂の含浸方法も特に制限はなく、マトリックス樹脂を加温し、粘度を下げて補強材に含浸させるホットメルト方式でも良いし、マトリックス樹脂を溶剤や水に溶かしたり、または適当な乳化剤等を使用して水に分散させたりして低粘度化したものを補強材に含浸させ、その後溶剤、または水を乾燥させるラッカー方式や水分散方式でも良い。
【0035】
本発明のプリプレグに使用される炭素繊維の形態としては特に制限はなく、炭素繊維糸条を数本から数百本並べて引き揃え、マトリックス樹脂を含浸する一方向材のような形態でも良いし、炭素繊維糸条1本から数本にマトリックス樹脂を含浸したヤーンプリプレグのような形態でも良い。また、炭素繊維糸条の平織りや綾織り、朱子織り等の織物とし、マトリックス樹脂を含浸したものでも良い。あるいは補強材をマット状に加工し、マトリックス樹脂を含浸させたマットプリプレグの形態でも良い。
【0036】
本発明の炭素繊維、並びにプリプレグの用途としては特に制限はないが、本発明の炭素繊維、あるいはプリプレグから得られるCFRPは、横方向から加えられる荷重、特に衝撃荷重に強いので、フロアパネル構造体、特にハニカムや発泡体をコア材とするスキン材の用途が好適である。また、本発明の炭素繊維、あるいはプリプレグから得られるCFRPは、横方向からの衝撃荷重に強いので、シャルピーやアイゾット衝撃強度が高く、ゴルフシャフトや釣り竿、テニス、バドミントンのラケットなどのスポーツレジャー用途にも好適に用いられる。
【0037】
【実施例】
以下、本発明を実施例に基づき詳細に説明するが、もちろん本発明はこれらの実施例に限定されるものではない。ただし、実施例1〜4および7〜9は参考用である。
【0038】
(実施例1)
アクリロニトリル/メタクリル酸=98/2の共重合体をジメチルホルムアミドに溶解、湿式紡糸を行い、トータルの延伸倍率を10.0倍として単繊維の平均デニール数が1.0デニールであるフィラメント数24,000の炭素繊維用前駆体繊維を得た。凝固浴の温度は45℃で凝固糸を得、凝固浴を通過後80℃の温水浴中で延伸した。乾燥工程前での延伸倍率は3.00倍とした。凝固糸をサンプリングし膨潤度を測定したところ98%であった。次いで、凝固糸を油剤処理し、乾燥して緻密化し、スチーム延伸により3.33倍に延伸し、炭素繊維用前駆体繊維を得た。
【0039】
この炭素繊維用前駆体繊維を250℃、50分で耐炎化処理後、炭素化し、炭素繊維を得た。ストランド引張弾性率は240GPa、ストランド引張強度は5.2GPaであった。
【0040】
こうして得られた炭素繊維を一方向に引き揃えマトリックス樹脂を含浸させてプリプレグを得た。マトリックス樹脂の組成はジャパンエポキシレジン社製液状ビスフェノールA型エポキシレジン、エピコート828:40質量部、ジャパンエポキシレジン社製固形ビスフェノールA型エポキシレジン、エピコート1002:30質量部、大日本インキ化学社製フェノールノボラック型エポキシレジン、エピクロンN740:30質量部に硬化剤としてジャパンエポキシレジン社製ジシアンジアミド、Dicy−7:4質量部、保土谷化学社製ジクロロジメチルウレア、DCMU99:4質量部を均一混合したものを用い、ホットメルト方式で含浸し、プリプレグ化した。プリプレグの炭素繊維目付は150g/m2であった。
【0041】
このプリプレグを一方向に積層して130℃×1時間で硬化させ、厚み0.25mm、Vf65%のCFRPを成形した。このCFRPを繊維方向に対して5mmの幅にカットし、せん断試験用の試験片とした。
【0042】
得られた試験片を図1に示した治具にセットし、せん断強度を測定した。測定時のクロスヘッドスピード(試験片せん断破壊刃部の移動速度)は2mm/分とした。測定は5点実施した。CFRPのせん断強度の平均値は0.76GPaであった。
【0043】
次にマトリックス樹脂のみを硬化させ、厚み0.5mmの樹脂板を成形した。この樹脂板を5mm幅にカットし、上記と同様にしてせん断強度を測定したところ0.16GPaであった。各要素のせん断強度の関係は下記式で与えられる。従って炭素繊維のせん断強度は1.08GPaであった。
【0044】
【数2】
Figure 0004975217
【0045】
該プリプレグ2枚を各繊維方向が直行するように積層して130℃×1時間で成形したCFRPをスキン材とし、コア材にヘクセル社製ノーメックスハニカム(セルサイズ:1/8インチ、密度:3.0ポンド/キュービックフィート)を用いてハニカムサンドイッチパネルを成形し、直径3mmの先端が平らな質量1kgの鉄製の円柱をスキン材表面に対して垂直に自由落下させてスキン材を貫通したときのエネルギーを求めたところ、0.82Jと高い値を示した。数値を表1にまとめた。
【0046】
(比較例1)
実施例1と同様にして炭素繊維用前駆体繊維を紡糸した。ただし乾燥工程前の延伸倍率を5.00倍とした。実施例1と同様にして膨潤度を測定したところ、112%であった。該炭素繊維用前駆体繊維を実施例1と同様にして焼成し、炭素繊維を得た。ストランド特性を測定したところ、弾性率は240GPa、強度は5.2GPaと実施例1の炭素繊維と同等であった。
【0047】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ0.82GPaであった。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、0.52Jと非常に低い値であった。
【0048】
(実施例2)
実施例1と同様にして炭素繊維用前駆体繊維を紡糸した。ただし凝固浴の温度は37℃とした。実施例1と同様にして膨潤度を測定したところ、94%であった。該炭素繊維用前駆体繊維を実施例1と同様にして焼成し、炭素繊維を得た。ストランド特性を測定したところ、弾性率は240GPa、強度は5.3GPaであった。
【0049】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ1.15GPaと高い値を示した。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、0.94Jと非常に高い値であった。
【0050】
(実施例3)
実施例1と同様にして炭素繊維用前駆体繊維を紡糸した。ただし凝固浴の温度を30℃とした。実施例1と同様にして膨潤度を測定したところ、88%であった。該炭素繊維用前駆体繊維を実施例1と同様にして焼成し、炭素繊維を得た。ストランド特性を測定したところ、弾性率は240GPa、強度は5.3GPaであった。
【0051】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ1.22GPaと高い値を示した。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、1.02Jと非常に高い値であった。
【0052】
(実施例4)
実施例3と同様にして炭素繊維用前駆体繊維を紡糸した。ただし乾燥工程前の延伸倍率を2.0倍とした。実施例1と同様にして膨潤度を測定したところ、82%であった。該炭素繊維用前駆体繊維を実施例1と同様にして焼成し、炭素繊維を得た。ストランド特性を測定したところ、弾性率は240GPa、強度は5.4GPaであった。
【0053】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ1.31GPaと高い値を示した。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、1.24Jと非常に高い値であった。
【0054】
(実施例5)
実施例3と同様にして炭素繊維用前駆体繊維を紡糸した。ただし乾燥工程前の延伸倍率を1.2倍とした。実施例1と同様にして膨潤度を測定したところ、72%であった。該炭素繊維用前駆体繊維を実施例1と同様にして焼成し、炭素繊維を得た。ストランド特性を測定したところ、弾性率は240GPa、強度は5.5GPaであった。
【0055】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ1.45GPaと高い値を示した。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、1.42Jと非常に高い値であった。
【0056】
(実施例6)
実施例5で紡糸した炭素繊維用前駆体繊維を実施例1と同様にして焼成した。ただし耐炎化の処理時間を80分とした。得られた炭素繊維のストランド特性を測定したところ、弾性率は240GPa、強度は5.5GPaであった。
【0057】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ1.51GPaと高い値を示した。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、1.60Jと非常に高い値であった。
【0058】
(実施例7)
実施例4で紡糸した炭素繊維用前駆体繊維を焼成した。耐炎化の処理時間を50分と実施例1と同じとしたが、炭素化の温度を上げてストランド引張弾性率を300GPaに調整した。ストランド引張強度は6.1GPaであった。
【0059】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ1.18GPaと高い値を示した。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、1.11Jと高い値であった。
【0060】
(実施例8)
実施例1と同様にして炭素繊維用前駆体繊維を紡糸した。ただし、乾燥緻密化後のスチーム延伸での倍率を4.17倍とし、トータルの延伸倍率を12.5倍とした。また、凝固糸の膨潤度を測定したところ98%であった。得られた炭素繊維用前駆体繊維の単繊維の平均デニールは0.8デニールであった。
【0061】
この炭素繊維用前駆体繊維を実施例1と同様にして焼成し炭素繊維を得た。ストランド引張弾性率は240GPa、ストランド引張強度は5.7GPaであった。
【0062】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ1.24GPaと高い値を示した。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、1.02Jと高い値であった。
【0063】
(実施例9)
実施例1と同様にして炭素繊維用前駆体繊維を紡糸した。ただし、乾燥緻密化後のスチーム延伸での倍率を5.56倍とし、トータルの延伸倍率を16.7倍とした。また、凝固糸の膨潤度を測定したところ98%であった。得られた炭素繊維用前駆体繊維の単繊維の平均デニールは0.6デニールであった。
【0064】
この炭素繊維用前駆体繊維を実施例7と同様にして焼成し炭素繊維を得た。ストランド引張弾性率は300GPa、ストランド引張強度は6.9GPaであった。
【0065】
該炭素繊維について実施例1と同様にして炭素繊維のせん断強度を求めたところ1.31GPaと高い値を示した。また、該炭素繊維を用いたプリプレグを用い、実施例1と同様にしてハニカムサンドイッチパネルを成形し、貫通エネルギーを求めたところ、1.33Jと高い値であった。
【0066】
【表1】
Figure 0004975217
【0067】
【発明の効果】
本発明の炭素繊維はそのせん断強度が1.4GPa以上であるので、CFRPとしたときの面方向、すなわち補強繊維に対して横方向からの荷重、特に衝撃荷重に強い。また本発明により得られる炭素繊維用前駆体繊維は湿式紡糸法により紡糸された炭素繊維用前駆体繊維であって、凝固糸の膨潤度が100%以下で、乾燥前の延伸倍率が1.1倍以上、1.2倍以下であるので、該炭素繊維用前駆体繊維を焼成して得られる炭素繊維はせん断強度が高い。また本発明のプリプレグは補強材としてせん断強度が1.4GPa以上の炭素繊維を用いているため、本発明のプリプレグを成形して得られるCFRPは横方向からの荷重、特に衝撃荷重に強い。また上記炭素繊維、炭素繊維用前駆体繊維の製造方法が提供された。
【図面の簡単な説明】
【図1】せん断破壊を説明するための模式図である。
【図2】せん断強度測定用の治具に試験片をセットした直後、試験を実施する前の状態を示す模式図である。
【図3】せん断強度測定用の治具に試験片をセットし、試験片にせん断荷重を与えて破壊させた後の状態を示す模式図である。
【符号の説明】
1a,1b:試験片支持部上側押さえ
2:試験片せん断破壊刃部上側押さえ
3a,3b:試験片支持部下側台
4:試験片せん断破壊刃部の下側台
5:試験片支持部間のギャップを調節するスペーサー
6:試験片
10:炭素繊維
L:試験片が一方向CFRPである時の炭素繊維の方向
d:せん断変形を与える隙間[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a prepreg which is a carbon fiber, a precursor fiber for carbon fiber, and an intermediate substrate for forming a carbon fiber reinforced composite material.
[0002]
[Prior art]
Carbon fiber reinforced composite materials (hereinafter referred to as CFRP) are widely used from sports and leisure related to industrial uses and aircraft uses, and are also used as flooring materials for aircraft and railway vehicles.
[0003]
As a flooring material, a sandwich panel in which CFRP is used as a skin material and bonded or integrally formed with a honeycomb structure or a foam core material is often used because of its light weight, high rigidity, and high strength.
[0004]
One of the performance required for such a sandwich panel as a flooring material is that it is resistant to penetration impact. This means that the strength against the impact from the skin material surface direction, that is, through the skin material in the direction transverse to the reinforcing fiber, is required, when it was struck with an umbrella or a cane Is assumed.
[0005]
In order to increase such penetration impact strength, the thickness of the CFRP skin may be increased or the density of the core material may be increased, both of which increase in weight.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a carbon fiber excellent in penetrating impact strength in a transverse direction to the fiber, a precursor fiber for carbon fiber for obtaining the carbon fiber, and a production method thereof. An object of the present invention is to provide a prepreg for a carbon fiber reinforced composite material having excellent penetration impact strength using carbon fiber. Such a carbon fiber can improve the penetration impact strength in the surface direction of the skin material, that is, in the lateral direction with respect to the reinforcing fiber, without increasing the weight in the sandwich structure using CFRP as the skin material.
[0007]
[Means for Solving the Problems]
  The present invention has a shear strength of 1.4 GPa or moreThe tensile elastic modulus is 270 GPa or lessIt is the carbon fiber characterized by being. The carbon fiber of the present invention is a carbon fiber obtained by firing a precursor fiber for carbon fiber produced by a wet spinning method.Togapreferable.
[0009]
  Furthermore, the present invention providesCarbon fiber precursor fiber for producing the carbon fiberBy wet spinningManufactureCarbon fiber precursor fiber manufacturing methodBecause,
A method for producing a carbon fiber precursor fiber, wherein the degree of swelling of the coagulated yarn before drying is 100% or less, and the draw ratio before drying is 1.1 times or more and 1.2 times or less. In this method, the temperature of the coagulation bath is preferably 50 ° C. or lower.
[0010]
  The present invention also provides,UpAfter carbon fiber precursor fiber produced by the production method is flameproofed for 40 minutes or more, carbonized,TensionElastic modulus270A carbon fiber manufacturing method characterized by obtaining a carbon fiber having a GPa or less and a shear strength of 1.4 GPa or more.
[0011]
  The present invention has a shear strength of 1.4 GPa or moreThe tensile elastic modulus is 270 GPa or lessCarbon fiberIn timeA carbon fiber reinforced composite prepreg impregnated with a matrix resin is also included.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
  The carbon fiber of the present invention has a shear strength of1.4Must be greater than or equal to GPa. The shear strength here is not the tensile strength symbolically used as the strength of the so-called normal carbon fiber but the strength against the shear deformation applied in the circumferential direction of the fiber 10 as shown in the schematic diagram of FIG.
[0013]
As a result of intensive studies on the phenomenon when a load from the transverse direction, particularly an impact load, is given to the fiber direction of CFRP, the present inventors have found that the shear strength of the carbon fiber against the load from the transverse direction. I found that is effective.
[0014]
There have been some studies on the lateral loading of CFRP. For example, Japanese Patent Application Laid-Open No. 57-42934 reports that when the knot strength of carbon fiber is high, the Charpy impact strength of CFRP increases, but according to the study by the present inventors, the load from the lateral direction of CFRP The shear strength of the carbon fiber is dominantly applied to the carbon fiber, and the shear strength of the carbon fiber has no correlation with the tensile strength in the tensile direction, for example, as described in the catalog as the tensile strength of the normal carbon fiber. I found out.
[0015]
  Furthermore, the present inventors have shown that when the shear strength of the carbon fiber is 1.0 GPa or more, the CFRP molded using the carbon fiber is very resistant to a load from the lateral direction with respect to the fiber direction. I found it. If the shear strength of the carbon fiber is 1.2 GPa or more, the CFRP is more preferable because it becomes stronger due to the load from the lateral direction with respect to the fiber direction, and more preferable if the shear strength of the carbon fiber is 1.4 GPa or more. .In the present invention, the shear strength of the carbon fiber is particularly set to 1.4 GPa or more.
[0016]
The shear strength is measured by the following method. That is, a unidirectional CFRP having a constant thickness of 0.5 mm or less and a volume fiber content (hereinafter abbreviated as Vf) of 60 to 70% is formed. The matrix resin is not particularly limited, but an epoxy resin composition is preferable. The CFRP is cut to a width of about 5 mm with respect to the fiber direction to obtain a test piece. In order to apply shear deformation from the lateral direction of the carbon fiber in the CFRP, for example, it is set in an iron jig as shown in FIG. 2, and the shear strength of the CFRP is measured. Next, it is cured and molded only with the matrix resin, and the shear strength of the cured matrix resin is measured in the same manner. Then, the shear strength of the carbon fiber is calculated by converting from the shear strength of the cured matrix resin, the shear strength of CFRP, and Vf of the test piece CFRP.
[0017]
The jig shown in FIG. 2 sandwiches the test piece 6 between the test piece support portion upper pressers 1a and 1b and the test piece support portion lower bases 3a and 3b, and connects the upper pressers 1a and 1b and the lower bases 3a and 3b. Each can be fixed with screws. The lower bases 3 a and 3 b are fixed to each other via a spacer 5. The upper presser 2 and the lower base 4 of the test piece shear breaking blade portion are configured such that the test piece 6 is sandwiched therebetween and can be fixed to each other with screws, and the support portion on the left side of the drawing composed of 1a and 3a And a support portion on the right side of the drawing composed of 1b and 3b. The gap for measuring shear, that is, the gap between the support portion on the left side of the drawing and the test piece shear fracture blade portion (2 and 4) and the gap d between the test piece shear fracture blade portion and the support portion on the right side of the drawing is 0. Apply lubricating oil etc. to the wall surface to keep it slippery. A test piece is sandwiched between 1a and 3a, 2 and 4, 1b and 3b as shown in FIG. 2, and a load is applied from the upper part of the upper press 2 of the test piece shear breaking blade portion. Measure the load. FIG. 3 is a schematic diagram showing a state after shear fracture.
[0018]
At this time, the load when measured without a test piece is the frictional force at the wall surface of the gap, but the frictional force is adjusted so that this load is 3% or less of the minimum load to be measured. .
[0019]
Next, an example of a method for producing the carbon fiber precursor fiber and the carbon fiber by a wet spinning method will be described. First, a polymerizable unsaturated monomer that is mainly composed of acrylonitrile and copolymerizable with acrylonitrile is polymerized by solution polymerization, suspension polymerization, or the like, and this polymer is dissolved in a solvent to obtain a spinning dope. Specific examples of the polymerizable unsaturated monomer include acrylic acid, methacrylic acid, itaconic acid, and alkali metal salts, ammonium salts, or alkyl esters thereof, and acrylamide, methacrylamide and derivatives thereof, and allyl sulfone. Examples include acids, methallylsulfonic acids and their salts, and alkyl esters. Examples of the solvent for dissolving the polymer include dimethyl sulfoxide, dimethylformamide, dimethylacetamide and the like. Next, the spinning solution is discharged into the coagulation bath from the nozzle hole to obtain a coagulated yarn, which is washed and stretched as necessary. Subsequently, it is dried and densified, but it is preferable to apply an oil before the drying step. Then, the dried and densified yarn is subjected to dry heat stretching using a high-temperature heating roller or the like, or steam stretching using pressurized steam, and the like, to obtain a carbon fiber precursor fiber.
[0020]
In order to obtain carbon fiber, the precursor fiber for carbon fibers is baked. That is, it is subjected to two steps of a flameproofing step of heating in an air atmosphere and a subsequent carbonization step of heating in an inert atmosphere.
[0021]
In the carbon fiber production method of the present invention, PAN-based carbon fibers obtained by firing a carbon fiber precursor fiber mainly composed of polyacrylonitrile are preferable, but the present invention is not particularly limited thereto.
[0022]
The carbon fiber precursor fiber used in the present invention when the carbon fiber precursor fiber is fired to obtain the carbon fiber of the present invention is wet-spun from the viewpoint of cost or adhesiveness to the matrix. Is preferred.
[0023]
CharcoalThe raw fiber precursor fiber is a carbon fiber precursor fiber spun by a wet spinning method, and preferably has a coagulated yarn swelling degree of 100% or less. When the degree of swelling of the coagulated yarn is 100% or less, the void structure can be suppressed to a small level, the carbon fiber precursor fiber becomes a dense structure, and the shear strength of the carbon fiber after firing is improved. A swelling degree of the coagulated yarn of 90% or less is more preferable because a denser precursor fiber for carbon fiber can be obtained. More preferably, the degree of swelling is 80% or less.
[0024]
The degree of swelling is determined by the following method. That is, the moisture adhering to the sampled coagulated yarn before drying is completely wiped off and the mass is measured to obtain W1. Subsequently, the sample is dried with a hot air dryer at 110 ° C. for 2 hours, and its mass is measured to obtain W2. The degree of swelling is determined by the following formula (1).
[0025]
[Expression 1]
Figure 0004975217
[0026]
In order to keep the degree of swelling low, it is effective to slow the coagulation rate, and a method for lowering the temperature of the coagulation bath can be exemplified. The temperature of the coagulation bath is preferably 50 ° C. or lower, more preferably 40 ° C. or lower, and particularly preferably 35 ° C. or lower. However, in the case of the wet spinning method, it is preferable to set the temperature of the coagulation bath to 20 ° C. from the viewpoint of preventing bundle breakage and fluff generation.
[0027]
  In addition, it is effective to keep the degree of swelling low so that the film is not stretched so much before the drying step. Specifically, the draw ratio before the drying step is preferably 3.5 times or less, and more preferably 2.5 times or less. 1.5 times or less is particularly preferable. Since the degree of swelling is kept low enough that the film is not stretched before the drying process, the lower limit is preferably 1.0 times or more. However, when the stretching before the drying process is 1.0 times, fluff and bundle breakage tend to occur. In order to stabilize the process, 1.1 times or more is preferable.However, particularly in the present invention, the stretching ratio before drying is 1.1 times or more and 1.2 times or less.
[0028]
CharcoalAs for the diameter of the precursor fiber for elementary fibers, the thinner one is preferable because the shear strength of the carbon fiber after firing is improved, and the average denier number of single fibers is preferably 1.2 denier or less. 1.0 denier or less is more preferable because the shear strength of the carbon fiber is further improved, and 0.7 denier or less is more preferable.
[0029]
Next, the process of making the carbon fiber precursor fiber flame resistant will be described.
[0030]
The flameproofing condition is important because it determines the structural difference between the single fiber surface layer and the single fiber center. In particular, the flameproofing temperature is important because it greatly affects such a structural difference. The flameproofing temperature is preferably in the range of 200 to 300 ° C.
[0031]
A carbon fiber with high shear strength can also be obtained by increasing the flameproofing time. Specifically, the flameproofing time is preferably 40 minutes or longer. Here, the flameproofing time means the total time that the fiber bundle stays in the flameproofing furnace. When the flameproofing time is less than 40 minutes, the structural difference between the single yarn surface layer portion and the single yarn central portion becomes remarkable, the flameproofing of the single yarn central portion is insufficient, and the central portion is in the next carbonization step. This is disadvantageous in that it can be burned down and the shear strength of the resulting carbon fiber can be reduced. It is more preferable when the flameproofing time is 60 minutes or more. However, if the flameproofing time is too long, it is disadvantageous in that the productivity is lowered. Therefore, the flameproofing time is preferably 180 minutes or less.
[0032]
  On the tensile modulus of carbon fiberIsSince the shear strength tends to decrease as the tensile modulus increases, the tensile modulus of carbon fiber is preferably 350 GPa or less. When the tensile elastic modulus of the carbon fiber is 270 GPa or less, the shear strength of the carbon fiber is increased, which is more preferable. However, if the tensile modulus is too low, it is disadvantageous in that the properties related to tension of CFRP, in particular, are lowered. The tensile elastic modulus is measured in a strand state according to JIS R7601.However, in the present invention, in particular, the tensile elastic modulus of the carbon fiber is set to 270 GPa or less.
[0033]
The prepreg using the carbon fiber of the present invention as a reinforcing material is also the present invention.
[0034]
The matrix resin used in the prepreg of the present invention is not particularly limited, but a thermosetting resin is preferable because it is excellent in handleability of the prepreg. Among the thermosetting resins, epoxy resin, bismaleimide resin, unsaturated polyester resin, vinyl ester resin, phenol resin, benzoxazine resin, and cyanate ester resin are preferably used. Also, the method of impregnating the matrix resin is not particularly limited, and it may be a hot melt method in which the matrix resin is heated and the viscosity is lowered to impregnate the reinforcing material, or the matrix resin is dissolved in a solvent or water, or an appropriate emulsifier. For example, a lacquer method or a water dispersion method may be used in which a reinforcing material is impregnated with a material whose viscosity has been reduced by dispersing in water using a lacquer method or water dispersion method.
[0035]
The form of the carbon fiber used in the prepreg of the present invention is not particularly limited, and may be a form such as a unidirectional material impregnated with a matrix resin by arranging several to hundreds of carbon fiber yarns. A form such as a yarn prepreg in which one to several carbon fiber yarns are impregnated with a matrix resin may be used. Moreover, it may be a woven fabric such as a plain weave, twill weave, satin weave of carbon fiber yarn, and may be impregnated with a matrix resin. Alternatively, it may be in the form of a mat prepreg in which a reinforcing material is processed into a mat shape and impregnated with a matrix resin.
[0036]
There is no particular limitation on the use of the carbon fiber and prepreg of the present invention, but the CFRP obtained from the carbon fiber or prepreg of the present invention is strong against a load applied from the lateral direction, particularly an impact load. In particular, a skin material having a honeycomb or foam as a core material is suitable. In addition, CFRP obtained from the carbon fiber or prepreg of the present invention is strong against impact load from the lateral direction, so it has high Charpy and Izod impact strength, and is suitable for sports leisure applications such as golf shafts, fishing rods, tennis, and badminton rackets. Are also preferably used.
[0037]
【Example】
  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, of course, this invention is not limited to these Examples.However, Examples 1-4 and 7-9 are for reference.
[0038]
Example 1
A copolymer of acrylonitrile / methacrylic acid = 98/2 is dissolved in dimethylformamide, wet spinning is performed, the total draw ratio is 10.0 times, and the average denier number of single fibers is 24. 000 carbon fiber precursor fibers were obtained. The temperature of the coagulation bath was 45 ° C to obtain coagulated yarn, and after passing through the coagulation bath, it was drawn in a hot water bath at 80 ° C. The draw ratio before the drying step was 3.00 times. The coagulated yarn was sampled and the degree of swelling was measured and found to be 98%. Next, the coagulated yarn was treated with an oil agent, dried and densified, and stretched 3.33 times by steam stretching to obtain a precursor fiber for carbon fiber.
[0039]
  This carbon fiber precursor fiber is subjected to a flame resistance treatment at 250 ° C. for 50 minutes and then carbonized., CharcoalA raw fiber was obtained. The strand tensile modulus was 240 GPa and the strand tensile strength was 5.2 GPa.
[0040]
  The carbon fibers thus obtained are aligned in one direction and impregnated with a matrix resin.TepI got a repreg. The composition of the matrix resin is a liquid bisphenol A type epoxy resin manufactured by Japan Epoxy Resin, Epicoat 828: 40 parts by mass, a solid bisphenol A type epoxy resin manufactured by Japan Epoxy Resin, Epicoat 1002: 30 parts by mass, phenol manufactured by Dainippon Ink and Chemicals, Inc. Novolac type epoxy resin, Epicron N740: 30 parts by mass of dicyandiamide manufactured by Japan Epoxy Resin Co., Dicy-7: 4 parts by mass, dichlorodimethylurea manufactured by Hodogaya Chemical Co., DCMU99: 4 parts by mass are uniformly mixed. Used and impregnated by a hot melt method to form a prepreg. Carbon fiber basis weight of prepreg is 150g / m2Met.
[0041]
This prepreg was laminated in one direction and cured at 130 ° C. for 1 hour to form CFRP having a thickness of 0.25 mm and Vf of 65%. This CFRP was cut into a width of 5 mm with respect to the fiber direction to obtain a test piece for a shear test.
[0042]
The obtained test piece was set on the jig shown in FIG. 1 and the shear strength was measured. The crosshead speed at the time of measurement (the moving speed of the test piece shear fracture blade) was 2 mm / min. The measurement was performed at 5 points. The average value of the shear strength of CFRP was 0.76 GPa.
[0043]
Next, only the matrix resin was cured to form a resin plate having a thickness of 0.5 mm. This resin plate was cut into a width of 5 mm, and the shear strength was measured in the same manner as described above, which was 0.16 GPa. The relationship of the shear strength of each element is given by the following formula. Therefore, the shear strength of the carbon fiber was 1.08 GPa.
[0044]
[Expression 2]
Figure 0004975217
[0045]
CFRP formed by laminating the two prepregs so that each fiber direction is orthogonal and molding at 130 ° C. × 1 hour is used as a skin material, and the core material is Nomex honeycomb manufactured by Hexel (cell size: 1/8 inch, density: 3 0.0 lb / cubic foot) was used to form a honeycomb sandwich panel, and an iron cylinder with a flat 3 kg diameter tip and a mass of 1 kg was allowed to fall freely perpendicular to the skin material surface and penetrate the skin material. When energy was calculated, it showed a high value of 0.82J. The numerical values are summarized in Table 1.
[0046]
(Comparative Example 1)
A precursor fiber for carbon fiber was spun in the same manner as in Example 1. However, the draw ratio before the drying step was 5.00 times. When the degree of swelling was measured in the same manner as in Example 1, it was 112%. The carbon fiber precursor fiber was fired in the same manner as in Example 1 to obtain carbon fiber. When the strand properties were measured, the elastic modulus was 240 GPa and the strength was 5.2 GPa, which was the same as that of the carbon fiber of Example 1.
[0047]
The shear strength of the carbon fiber was determined in the same manner as in Example 1 and found to be 0.82 GPa. Further, a honeycomb sandwich panel was formed using the prepreg using the carbon fiber in the same manner as in Example 1, and the penetration energy was obtained. As a result, the value was as low as 0.52 J.
[0048]
(Example 2)
A precursor fiber for carbon fiber was spun in the same manner as in Example 1. However, the temperature of the coagulation bath was 37 ° C. When the degree of swelling was measured in the same manner as in Example 1, it was 94%. The carbon fiber precursor fiber was fired in the same manner as in Example 1 to obtain carbon fiber. When the strand characteristics were measured, the elastic modulus was 240 GPa and the strength was 5.3 GPa.
[0049]
With respect to the carbon fiber, when the shear strength of the carbon fiber was determined in the same manner as in Example 1, it showed a high value of 1.15 GPa. Further, when a honeycomb sandwich panel was formed using the prepreg using the carbon fiber in the same manner as in Example 1 and the penetration energy was determined, it was as high as 0.94 J.
[0050]
(Example 3)
A precursor fiber for carbon fiber was spun in the same manner as in Example 1. However, the temperature of the coagulation bath was 30 ° C. When the degree of swelling was measured in the same manner as in Example 1, it was 88%. The carbon fiber precursor fiber was fired in the same manner as in Example 1 to obtain carbon fiber. When the strand characteristics were measured, the elastic modulus was 240 GPa and the strength was 5.3 GPa.
[0051]
With respect to the carbon fiber, the shear strength of the carbon fiber was determined in the same manner as in Example 1, and a high value of 1.22 GPa was shown. Further, when a honeycomb sandwich panel was formed using the prepreg using the carbon fiber in the same manner as in Example 1 and the penetration energy was obtained, it was a very high value of 1.02J.
[0052]
Example 4
In the same manner as in Example 3, a precursor fiber for carbon fiber was spun. However, the draw ratio before the drying step was 2.0 times. When the degree of swelling was measured in the same manner as in Example 1, it was 82%. The carbon fiber precursor fiber was fired in the same manner as in Example 1 to obtain carbon fiber. When the strand characteristics were measured, the elastic modulus was 240 GPa and the strength was 5.4 GPa.
[0053]
With respect to the carbon fiber, when the shear strength of the carbon fiber was determined in the same manner as in Example 1, it showed a high value of 1.31 GPa. Further, when a honeycomb sandwich panel was formed using the prepreg using the carbon fiber in the same manner as in Example 1 and the penetration energy was determined, it was a very high value of 1.24 J.
[0054]
(Example 5)
In the same manner as in Example 3, a precursor fiber for carbon fiber was spun. However, the draw ratio before the drying step was 1.2 times. When the degree of swelling was measured in the same manner as in Example 1, it was 72%. The carbon fiber precursor fiber was fired in the same manner as in Example 1 to obtain carbon fiber. When the strand characteristics were measured, the elastic modulus was 240 GPa and the strength was 5.5 GPa.
[0055]
With respect to the carbon fiber, when the shear strength of the carbon fiber was determined in the same manner as in Example 1, it showed a high value of 1.45 GPa. Further, when a honeycomb sandwich panel was formed using the prepreg using the carbon fiber in the same manner as in Example 1 and the penetration energy was determined, it was a very high value of 1.42J.
[0056]
(Example 6)
The precursor fiber for carbon fiber spun in Example 5 was fired in the same manner as in Example 1. However, the flameproofing treatment time was 80 minutes. When the strand characteristics of the obtained carbon fiber were measured, the elastic modulus was 240 GPa and the strength was 5.5 GPa.
[0057]
With respect to the carbon fiber, the shear strength of the carbon fiber was determined in the same manner as in Example 1, and a high value of 1.51 GPa was shown. Further, when a honeycomb sandwich panel was formed in the same manner as in Example 1 using the prepreg using the carbon fiber and the penetration energy was obtained, it was a very high value of 1.60 J.
[0058]
(Example 7)
The precursor fiber for carbon fiber spun in Example 4 was fired. Although the flameproofing treatment time was 50 minutes and the same as in Example 1, the carbonization temperature was raised and the strand tensile modulus was adjusted to 300 GPa. The strand tensile strength was 6.1 GPa.
[0059]
With respect to the carbon fiber, the shear strength of the carbon fiber was determined in the same manner as in Example 1, and a high value of 1.18 GPa was shown. Further, when a honey prepreg using the carbon fiber was used to form a honeycomb sandwich panel in the same manner as in Example 1 and the penetration energy was determined, it was as high as 1.11 J.
[0060]
(Example 8)
A precursor fiber for carbon fiber was spun in the same manner as in Example 1. However, the ratio of steam stretching after drying and densification was 4.17 times, and the total stretching ratio was 12.5 times. Further, the degree of swelling of the coagulated yarn was measured and found to be 98%. The average denier of the single fiber of the obtained precursor fiber for carbon fiber was 0.8 denier.
[0061]
  This carbon fiber precursor fiber was fired in the same manner as in Example 1.CharcoalA raw fiber was obtained. The strand tensile modulus was 240 GPa and the strand tensile strength was 5.7 GPa.
[0062]
When the shear strength of the carbon fiber was determined in the same manner as in Example 1, it was as high as 1.24 GPa. Further, a honeycomb sandwich panel was formed using the prepreg using the carbon fiber in the same manner as in Example 1, and the penetration energy was obtained. As a result, the value was as high as 1.02 J.
[0063]
Example 9
A precursor fiber for carbon fiber was spun in the same manner as in Example 1. However, the ratio of steam stretching after drying and densification was 5.56 times, and the total stretching ratio was 16.7 times. Further, the degree of swelling of the coagulated yarn was measured and found to be 98%. The average denier of the single fiber of the obtained precursor fiber for carbon fiber was 0.6 denier.
[0064]
  This carbon fiber precursor fiber was fired in the same manner as in Example 7.CharcoalA raw fiber was obtained. The strand tensile modulus was 300 GPa and the strand tensile strength was 6.9 GPa.
[0065]
With respect to the carbon fiber, when the shear strength of the carbon fiber was determined in the same manner as in Example 1, it showed a high value of 1.31 GPa. Further, a honeycomb sandwich panel was formed using the prepreg using the carbon fiber in the same manner as in Example 1, and the penetration energy was obtained. As a result, the value was as high as 1.33 J.
[0066]
[Table 1]
Figure 0004975217
[0067]
【The invention's effect】
  The carbon fiber of the present invention has shear strength.1.4Since it is GPa or more, it is strong against a load in the plane direction when CFRP is used, that is, a load from the lateral direction with respect to the reinforcing fiber, particularly an impact load. The present inventionObtained byThe precursor fiber for carbon fiber is a precursor fiber for carbon fiber spun by a wet spinning method, and the degree of swelling of the coagulated yarn is 100% or less.And the draw ratio before drying is 1.1 times or more and 1.2 times or lessTherefore, the carbon fiber obtained by firing the precursor fiber for carbon fiber has high shear strength. The prepreg of the present invention has a shear strength as a reinforcing material.1.4Since carbon fiber of GPa or higher is used, CFRP obtained by molding the prepreg of the present invention is resistant to lateral loads, particularly impact loads. Moreover, the manufacturing method of the said carbon fiber and the precursor fiber for carbon fibers was provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining shear fracture.
FIG. 2 is a schematic diagram showing a state immediately after a test piece is set immediately after setting a test piece on a jig for measuring shear strength.
FIG. 3 is a schematic view showing a state after a test piece is set on a jig for measuring shear strength, and a shear load is applied to the test piece to break it.
[Explanation of symbols]
1a, 1b: Upper side holding part of test piece support
2: Test piece shear fracture blade upper side presser
3a, 3b: Test piece support part lower base
4: Lower base of test piece shear fracture blade
5: Spacer for adjusting the gap between the test piece support parts
6: Test piece
10: Carbon fiber
L: Direction of carbon fiber when the test piece is unidirectional CFRP
d: Gap giving shear deformation

Claims (6)

せん断強度が1.4GPa以上、引張弾性率が270GPa以下であることを特徴とする炭素繊維。A carbon fiber having a shear strength of 1.4 GPa or more and a tensile elastic modulus of 270 GPa or less . 湿式紡糸法によって製造された炭素繊維用前駆体繊維が焼成されてなる請求項1記載の炭素繊維。  The carbon fiber according to claim 1, wherein the carbon fiber precursor fiber produced by a wet spinning method is fired. 請求項1または2記載の炭素繊維を製造するための炭素繊維前駆体繊維を湿式紡糸法によって製造する炭素繊維前駆体繊維の製造方法であって
乾燥前の凝固糸の膨潤度を100%以下とし、乾燥前の延伸倍率を1.1倍以上、1.2倍以下とすることを特徴とする炭素繊維用前駆体繊維の製造方法。
A according to claim 1, wherein the method of producing a carbon fiber precursor fiber you prepared me by the wet spinning method carbon fiber precursor fiber for the production of carbon fibers,
A method for producing a precursor fiber for carbon fiber, wherein the degree of swelling of the coagulated yarn before drying is 100% or less, and the draw ratio before drying is 1.1 times or more and 1.2 times or less.
凝固浴の温度を50℃以下とする請求項記載の炭素繊維用前駆体繊維の製造方法。The method for producing a precursor fiber for carbon fiber according to claim 3 , wherein the temperature of the coagulation bath is 50 ° C or lower. 請求項または記載の製造方法により製造された炭素繊維用前駆体繊維を40分以上耐炎化処理した後、炭化して、引張弾性率が270GPa以下かつせん断強度が1.4GPa以上である炭素繊維を得ることを特徴とする炭素繊維の製造方法。The precursor fiber for carbon fiber produced by the production method according to claim 3 or 4 is subjected to a flameproofing treatment for 40 minutes or more and then carbonized to have a tensile elastic modulus of 270 GPa or less and a shear strength of 1.4 GPa or more. A method for producing carbon fiber, comprising obtaining carbon fiber. 請求項1記載の炭素繊維にマトリックス樹脂が含浸されてなる炭素繊維強化複合材料用プリプレグ。  A prepreg for a carbon fiber reinforced composite material, wherein the carbon fiber according to claim 1 is impregnated with a matrix resin.
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