JP3539577B2

JP3539577B2 - Fiber reinforced composite material

Info

Publication number: JP3539577B2
Application number: JP15601494A
Authority: JP
Inventors: 勝也谷
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 1994-07-07
Filing date: 1994-07-07
Publication date: 2004-07-07
Anticipated expiration: 2019-07-07
Also published as: JPH0820651A

Description

【０００１】
【産業上の利用分野】
本発明は繊維強化複合材料に関する。さらに詳しくは軽量にして且つ高強度、高剛性、耐クリープ性を有し、また落雷等の危険性のある場所で用いて安全な物品、特にゴルフシャフト、釣竿、テニス用ラケット等に適した繊維強化複合材料に関する。
【０００２】
【従来の技術】
炭素繊維はガラス繊維に比較して高強力、高剛性、且つ軽量であるため高性能複合材料として多くの分野で用いられている。特に航空機、自動車等の運搬装置やゴルフシャフト、釣竿、テニス用ラケット等のスポーツ用品分野で一次あるいは二次構造体に広く利用されてきた。一方、スーパー繊維と称される全芳香族ポリアミド繊維、全芳香族ポリエステル繊維、超高分子量ポリエチレン繊維等が出現したことでこれら補強材に用いた高性能複合材料の開発が行われてきた。またハイブリッド型複合材料例えば炭素繊維と全芳香族ポリアミド繊維併用した高性能複合材料の検討も行われている。スーパー繊維の中でもポリベンザゾール繊維（ＰＢＺ繊維）は引張強度４．０ＧＰａ以上、初期引張弾性率１４０ＧＰａ以上、分解開始温度６７０Ｃ、限界酸素指数５６と優れた力学特性と高い耐熱性・難燃性を有し、且つ性能面でバランスのとれた高性能繊維であることから複合材料の補強材として注目されてきた。最近、ポリベンザゾール繊維の工業的な生産技術が開発されるに至り該繊維を補強材にした高性能複合材料の開発が本格化してきた。
【０００３】
【発明が解決しようとする課題】
従来、炭素繊維は複合材料の補強材として優れた性能を有しているが、(1) 耐衝撃性が低い、(2) 導電性で落雷等の危険がある等の欠点のために用途展開に制約を受けている。一方、全芳香族ポリアミド繊維又は全芳香族ポリエステル繊維を補強材とした複合材料は、(1) 耐加水分解性に欠ける、(2) 強力並びに弾性率は炭素繊維を補強材にしたものに及ばない、(3) 耐衝撃性は炭素繊維補強材にしたものより高いが未だ十分とはいえない等の欠点がある。なお、炭素繊維と全芳香族ポリアミド繊維を補強材に併用したハイブリッド型複合材料は互いの繊維の有する欠点はある程度補えるが、反面、素材固有の特徴が半減されることもある。前記素材の欠点を解消すべく特開昭６０−１７４６４６号公報は補強材に超高分子量ポリエチレン繊維を用いた複合材料を提案している。しかし、超高分子量ポリエチレン繊維は従来の素材に比較して、(1) 剛性が劣る、(2) 接着性に欠ける、(2) 融点が１４０℃以下であり耐熱性に欠ける等の欠点があり複合材の用途は自ずと制限される。高引張強度、高初期引張弾性率、難燃性、耐変形性に優れるポリベンザゾール繊維を補強材に用いれば従来素材の持つ欠点は解消でき、広い要求特性を満たす本格的な繊維強化複合材料が期待できる。しかし、開発の進行と共にポリベンザゾール繊維は耐衝撃強度や耐加水分解性に難点があり補強材用にはさらに改良を要することが分かってきた。本発明は耐衝撃強度に優れた繊維強化複合材料の提供を目的とすることである。
【０００４】
【課題を解決するための手段】
本発明者は前記目的を達成すべく鋭意検討した結果、ポリベンザゾール繊維の耐衝撃性該繊維のボイド直径と密接に関係しており、平均ボイド直径を極力抑えたポリベンザゾール繊維を補強材に用いれば高性能複合材料が得られることを見出して本発明に至った。即ち、４．０ＧＰａ以上の引張強度と１４０ＧＰａ以上の初期引張弾性率を有し且つボイド直径が３５Å以下のポリベンザゾール繊維とマトリックス樹脂からなることを特徴とする繊維強化複合材料を趣旨とするものである。
【０００５】
本発明を詳細に説明する。本発明でいうポリベンゾオキサゾール繊維（ＰＢＯ）ホモポリマー、ポリベンゾチアゾール（ＰＢＴ）ホモポリマー及びそれらＰＢＯ、ＰＢＴのランダム、シーケンシャルあるいはブロック共重合体をいう。ここでポリベンゾオキサゾール、ポリベンゾチアゾール及びそれらのランダム、シーケンシャルあるいはブロック共重合ポリマーは、例えば Wolfeらの「Liquid Crystalline Polymer Compositions, Process and Products」U.S. Patent 4,703,103 (October 27,1987) 、「 Liquid Crystalline Polymer Compositions, Process and Products 」U.S. Patent 4,533,692(August 6,1985)、「Liquid CrystallinePoly(2,6-Benzothiazole) Composition, Process and Products 」 U.S. Patent 4,533,724 (August 6,1985)、「Liquid Crystalline Polymer Compositions, Process and Products 」U.S. Patent 4,533,693(August 6,1985)、 Eversの「Thermooxidatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole Polymres」U.S. Patent 4,359,567(November 16,1982）; Tsaiらの「Method for Making Heterocyclic Block Copolymer」U.S. Patent 4,578,432 (March 25, 1986)、などに記載されている。
ＰＢＺポリマーに含まれる構造単位としては、好ましくはライオトロピック液晶ポリマーから選択される。
この繊維は少なくとも４．０ＧＰａの引張強度と少なくとも１４０ＧＰａの初期引張弾性率を満たす強伸度特性が必要である。該繊維の引張強度が４．０ＧＰａ未満又は初期引張弾性率が１４０ＧＰａ未満の場合にあっては繊維強化複合材料としての強力及び剛性が低くガラス繊維や全芳香族ポリアミド繊維、全芳香族ポリエステル繊維及び超高分子量ポリエチレン繊維と競合できなくなる。また、複合材中に占める繊維含有比率を高めて強力及び剛性の向上に対処する該繊維の特徴である高引張強度と高初期引張弾性率に基づく軽量化の効果が失われる。
【０００６】
モノマー単位は構造式（ａ）〜（ｈ）に記載されている。そのポリマーは好ましくは、本質的に構造式（ａ）〜（ｈ）から選択されるモノマー単位からなり、更に好ましくは本質的に構造式（ａ）〜（ｃ）から選択されたモノマー単位からなる。
ＰＢＺポリマーのドープを形成するための好適な溶媒としては、クレゾールやそのポリマーを溶解しうる非酸化性の酸が含まれる。好適な酸溶媒の例としては、ポリリン酸、メタンスルフォン酸及び高濃度の硫酸あるいはそれらの混合物が挙げられる。更に適する溶媒はポリリン酸及びメタンスルフォン酸である。また最も適する溶媒はポリリン酸である。
【０００７】
【化１】

【０００８】
【化２】

【０００９】
本発明の繊維強化複合材料の補強材として使用するポリベンザゾール繊維はボイド直径が３５Å以下であることが重要である。これまでポリベンザゾール繊維はスーパー繊維の中でも特に高い引張強度と高い初期引張弾性率を有することは知られている。しかし、最近、水分が存在すると引張特性は低下していくことが分かり、本発明者はポリベンザゾール繊維の引張強度が水分により低下する原因につき検討を続けてきた。その過程において、(1) 引張強度の低下が水分によるポリベンザゾール分子鎖の加水分解によるによること、(2) 比較的大きなボイドからの水分子の侵入が加水分解を加速していることをを見い出すと共にさらに驚くべきことにポリベンザゾール繊維の衝撃特性は平均ボイド直径に関係していることを知見した。このとは繊維のボイド直径を小さくすれば加水分解性のみならず耐衝撃性も改善されることを意味している。本発明者はボイド直径と衝撃特性の関係につき詳細な検討を行った結果、平均ボイド直径が３５Å以下であるポリベンザゾール繊維を補強材に用いた複合材は従来品に比べて耐衝撃性は著しく向上することが改善されるも明かとなった。さらに繊維のボイド直径を決定する製糸要因を詳細に検討した結果、紡糸口金から吐出された紡出糸中のポリリン酸を抽出する非溶媒性の液体（例えばリン酸水溶液）の濃度が極めて大きな影響力を持つことを見い出した。具体的にはポリベンザゾール重合体を主成分とするポリマーとポリリン酸からなるドープから紡糸して繊維を製造するに際し、濃度５重量％以上のリン酸水溶液を用いることで平均ボイド直径３５Å以下を達成することが出来る。なお、紡出糸は抽出・洗浄処理により繊維中のポリリン酸を所望の水準まで低減させた後で乾燥処理を施される。この乾燥処理をオンラインで行う場合、平均ボイド直径を小さくする観点からは糸条の進行方向に順次温度を高めて加熱する所謂温度勾配型の乾燥方式が推奨される。
【００１０】
ポリベンザゾール繊維の単糸繊度に特に制限はないが通常０．３〜１０デニールの範囲が好ましい。単糸繊度を下げて繊維本数を多くすると複合材にした時に外力が分散して衝撃強度は向上する。しかし、単糸繊度の小さい繊維を得ようとすると一般に紡糸ドラフト（＝糸条引取速度／吐出線速度）は高くなる方向となり紡糸に際して糸切れを生じ易くなる。現在の技術水準では繊度０．３デニール未満では安定した紡糸調子が得にくくなり紡糸生産性は低下する。他方、単糸繊度が太くすると紡出糸中のポリリン酸の除去に要する時間が長くなり糸条洗浄装置の長大化と糸掛け操作性の低下につながる。また同一ヤーン繊度の場合、単糸繊度を太くすれば繊維本数は減ることになり複合材にした時に外力は分散しにくくなり衝撃強度が低下する。したがって実用的な単糸繊度の上限は１０デニールが好ましい。
【００１１】
後述するようにポリベンザゾール繊維とマトリックス樹脂との接着性は繊維強化複合材の特性及びコスト的に重要な因子である。接着性を向上させる手段として種々の方法が考えられるが比較的簡便で顕著な効果が得られるのは繊維断面を非円形、所謂異形断面とすることである。この異形断面繊維は非円形断面を有する吐出孔からポリベンザゾールのドープを紡糸することで比較的容易に得ることができる。
【００１２】
本発明の繊維強化複合材料の補強材として使用するポリベンザゾール繊維は長繊維として使用してもよく、また適当長さに切断された短繊維あるいはパルプ状繊維として使用することもできる。長繊維として使用する場合、単に引き揃えるだけでもよいし、平織、朱子織、綾織等の各種構造の織物として使用することが出来る。また目的によっては他の繊維、例えば炭素繊維、ガラス繊維、全芳香族ポリアミド繊維、全芳香族ポリエステル繊維及び超高分子量ポリエチレン繊維と混合使用する事も可能である。本発明に使用するポリベンザゾール繊維はマトリックス樹脂との接着性を向上させるため製糸工程上必要な油剤などの処理剤、仕上げ剤等を抽出等により予め除去してもよいし、さらに、該繊維上に予めカップリング剤や表面改質剤で処理を行ってもよい。また、ポリベンザゾール繊維の表面にコロナ放電処理を行うことも推奨される。
【００１３】
本発明の繊維強化複合材料は前記ポリベンザゾール繊維に熱硬化性ポリマー材料例えば不飽和ポリエステル樹脂、エポキシ樹脂、ポリウレタン樹脂、フェノール樹脂、または熱可塑性ポリマー材料例えばナイロン樹脂、ポリプロピレン樹脂、ポリフェニレンサルファイド樹脂、ＡＢＳ樹脂、さらには弾性ポリマー材料、ゴム等をマトリックス樹脂に用いて成形される。後者の場合、補強繊維とマトリックス繊維とを編成してシート状物とし、これを溶融変形して熱可塑性複合材料とすることができる。ここで重要なことはポリベンザゾール繊維は分解開始温度が６７０℃、限界酸素指数５６と既存有機合成繊維の中では極めて高い耐熱性・難燃性を有しており他のスーパー繊維を補強材にする場合に比して熱的な面で熱硬化性又は熱可塑性の何れの場合もマトリックス樹脂の選択の自由度は大きいことである。
【００１４】
次に繊維強化複合材料の製造方法について簡単に説明する。本発明の繊維強化複合材の補強用繊維として用いるポリベンザゾール料繊維は、ポリリン酸を溶媒に用いたポリベンザゾール重合体のドープを軟化点以上で熱分解点未満の温度に保つて紡糸部に供給し、複数個の吐出細孔が配設された紡糸口金を通して横吹き気流帯域中に吐出され、該横吹き気流帯域中を通過した後、該紡出糸を引き続いて非溶媒性の液体からなる抽出媒帯と接触させる。ここで非溶媒性の液体としては濃度５重量％以上のリン酸水溶液を用いることが肝要である。次いで該糸条は洗浄装置例えばスプレー又はシャワーが配設された複数個のローラー群に巻掛けて繊維中のリン酸の低減・除去を行う。該洗浄ローラー群を通過させた糸条は必要に応じて表面に付着する水分を例えばエアナイフ等の手段で低減せしめた後、直ちにパッケージに巻き上げてバッチで乾燥を行ってもよいが一旦パッケージに巻き上げた後に行ってもよいが生産性の面からは一旦巻き上げることなくオンライン処理することが好ましい。この場合、糸条の乾燥手段に特に制限はなく例えば加熱ローラーに接触させる、高温加熱気体中を走行させる、高周波による内部加熱等の手段が利用できる。なお、必要に応じて乾燥処理後の糸条に仕上げ剤を付与してもよい。
【００１５】
次に繊維強化複合体の成形について述べる。ポリベンザゾール長繊維をマトリックス樹脂と組合せる方法には例えば一方向に引き揃えた該繊維束にマトリックス樹脂又はその溶液をスプレーあるいは含浸させたり、また予め該繊維を平織、朱子織等の織物とした後に上記マトリックス樹脂又はその溶液をスプレーあるいは含浸させることも可能である。あるいは、ポリベンザゾール短繊維をマトリックス樹脂又はその溶液中に含浸させ、混練することもできる。さらに上述のような複合材料の成形に際しては、補強材用繊維とマトリックス樹脂との混合物を加熱（必要に応じて加圧）することにより直接成形することもできるが、特にマトリックス樹脂がエポキシ樹脂、不飽和ポリエステル樹脂等の熱硬化性樹脂である場合には、所謂プリプレグあるいはプリミックスと称されるように、予めポリベンザゾール繊維あるいはその織物に含浸させたマトリックス樹脂を［Ｂ−ステージ］と称されている中間段階まで硬化反応を進めさせた後、所定の加熱及び加圧条件を用いて成形し、複合材料とする方法も可能である。このように本発明の繊維強化複合材料は種々の成形方法により有用な成形物を提供することができるが代表的な成形方法は圧縮成形である。つまり所定の形式の金型を用いて機械的に圧縮あるいはオートクレーブ中で気体による圧力をかける等によって成形することができる。その他に通常用いられるような注型成形方、スプレー法、パンドレイアップ法、インジェクション成形法、プルトロージョン法等、補強用繊維の形状及び／又はマトリックス樹脂の特性に合わせて選択することができる。
【００１６】
以下に本発明に置ける評価尺度は下記の方法で求めた。
＜繊度＞
試料を標準状態（温度２２＋２度、相対湿度６５＋２％の状態）の試験室で２４時間静置した後、ラップリールを用いて試料９０ｍを採取し、その重量を測定して９０００ｍの重量に換算して繊度とした。
＜繊維のボイド直径＞
小角Ｘ線散乱強度の測定はクラツキカメラを用いて測定した。試料は長さ約６ｍの繊維を測定ホルダーに巻き付けて用いた。Ｘ線の出力は４５Ｋｖ・１５０ｍＡで、ＣｕＫα線をニッケルフィルターで単色化して用いた。クラツキカメラの縦制限スリットは４２ｍｍ、巾制限スリットは０．０７ｍｍ、受光部スリットの縦制限１０ｍｍ、巾制限は０．１４ｍｍで行った。測定した範囲（２θ）は０．１度〜３．０度である。ステップ幅は０．０２５度刻みで、３０秒若しくはそれ以上を積算した。バックグラウンド散乱の補正は、試料及び空気散乱の測定結果から次式を用いて行った。
Ｉ＝μＩsample−Ｉair
μ＝Ｉair(0)／Ｉsample(0)
ここでＩは真の散乱強度、Ｉsampleは試料を入れた状態での実測散乱強度、Ｉair は試料を入れない状態で測定した散乱強度をそれぞれ示す。試料を測定した後、散乱角が０度で強度測定を行い、試料の吸収強度を決定した。ボイドサイズの測定はギニエプロットを用いて行った。散乱角度（Ｉ）の対数と散乱ベクトル（ｋ）の自乗をプロットし、ｋの自乗の値が０から０．０１Å^1/2 の範囲のデーターについて直線近似し、直線の傾き（Ｓ）から次式を用いて計算した。
Ｄ＝２（ｓ）^1/2
＜繊維の引張強度、初期引張弾性率および衝撃強度の測定法＞
ＪＩＳＬ１０１３（１９８１）に規定された方法と条件によって測定した。
＜複合材料の曲げ強度、衝撃強度の測定法＞
ＪＩＳＫ６９１１（１９７９）に規定された方法と条件に準じた方法と条件出測定した。但し、成形物の試験試料の大きさは、厚さ３ｍｍ、幅２５ｍｍ、長さ６３．５ｍｍとした。
【００１７】
【実施例】
以下に本発明を実施例により詳述するが本発明はもとより、これらの実施例に限定されるものではない。
＜実施例１＞
ポリベンズオキサゾール重合体とポリリン酸からなる濃度１４重量％のドープを断面形状が楕円で孔径０．１７μｍ（円形断面相当径に換算した）を有する紡糸口金から吐出して該紡糸口金の下方で７５℃に加熱された空気を流速０．５ｍ／秒で吹き当てた後、濃度２４重量％のリン酸水溶液浴に導入して溶媒の抽出を行い、次いで駆動ローラーで糸条速度を２５０ｍ／分に規定した後、ネルソン型のローラー群に巻き掛け、該ローラー上でスプレー状にイオン交換水を吹き付けて糸条に残留するリン酸を抽出・除去した。さらに該糸条を１８０〜２４０℃の温度に加熱されたネルソン型のローラー群に巻き掛けて乾燥処理を行い、次いでエチレンオキサイドとプロピレンオキサイドのランダム共重合体を主成分とするポリエーテル系の仕上げ油剤を付与して繊度５００Ｄ／３３２Ｆ、平均ボイド直径２１Å、引張強度５．８ＧＰａ、初期引張弾性率２７１ＧＰａ、衝撃強度４５２ジュール／ｄのポリベンズオキサゾールマルチフィラメント繊維を得た。該マルチフィラメントをエチレンとグリシジルメタクリレート（重量比９５対５）の共重合体の２０％２分散液に、該共重合体の付着率３％owfとなるように浸漬処理した。浸漬処理後のマルチフイラメントをフィラメントワインデング法により引き揃え、エポキシ樹脂系溶液［アラルダイトＬＹ５６４（チバギイギー社製）］に埋め込んだ。次いでこれらを８０℃で４時間硬化させて表１の実施例１に示す特性の繊維強化複合材料を得た。
【００１８】
＜実施例２＞
実施例１において抽出浴のリン酸水溶液の濃度１６重量％に変えた以外は実施例１の条件を用いて紡糸・洗浄・乾燥・油剤処理を行って、繊度５００Ｄ／３３２Ｆ、平均ボイド直径２９Å、引張強度５．８ＧＰａ、初期引張弾性率２６９ＧＰａ、衝撃強度４２７ジュール／ｄの特性を有するポリベンズオキサゾールマルチフィラメント繊維を得た。該繊維を用いて実施例１に記載したと同様の方法・条件で繊維強化複合材に加工した。
【００１９】
＜実施例３＞
実施例１において紡出糸に接触させるリン酸水溶液の濃度７重量％に変えた以外は実施例１の条件を用いて紡糸・洗浄・乾燥・油剤処理を行って、繊度５００Ｄ／３３２Ｆ、平均ボイド直径３４Å、引張強度５．８ＧＰａ、初期引張弾性率２６６ＧＰａ、衝撃強度４１４ジュール／ｄの特性を有するポリベンズオキサゾールマルチフィラメント繊維を得た。該繊維を用いて実施例１に記載したと同様の方法・条件で繊維強化複合材に加工した。
【００２０】
＜比較例１＞
実施例１において紡出糸に接触させるリン酸水溶液の濃度３．５重量％に変えた以外は実施例１の条件を用いて紡糸・洗浄・乾燥・油剤処理を行って、繊度５００Ｄ／３３２Ｆ、平均ボイド直径３９Å、引張強度５．７ＧＰａ、初期引張弾性率２６６ＧＰａ、衝撃強度３８９ジュール／ｄの特性を有するポリベンズオキサゾールマルチフィラメント繊維を得た。該繊維を用いて実施例１に記載したと同様の方法・条件で繊維強化複合材に加工し、これを比較例１とした。
【００２１】
＜比較例２＞
実施例１において紡出糸にポリベンザゾールの固有粘度を１５ｄｌ／ｇに変えた以外は実施例１の条件を用いて紡糸・洗浄・乾燥・油剤処理を行って、繊度５００Ｄ／３３２Ｆ、平均ボイド直径２３Å、引張強度３．９ＧＰａ、初期引張弾性率１３８ＧＰａ、衝撃強度３３９ジュール／ｄの特性を有するポリベンズオキサゾールマルチフィラメント繊維を得た。該繊維を用いて実施例１に記載したと同様の方法・条件で繊維強化複合材に加工した。
【００２２】
＜比較例３〜５＞
実施例１において補強繊維に繊度１０００Ｄ／２００Ｆの超高分子量ポリエチレン繊維、繊度１５００Ｄ／１０００Ｆのポリパラフェニレンテレフタルアミド繊維（ケブラー２９デュポン社商品名）及び繊度１２００Ｄ／１０００Ｆの炭素繊維をそれぞれ用いて繊維強化複合材に成形し、比較例３、４、５とした。上記実施例１〜３及び比較例１〜５の評価結果をまとめて表１に示した。
【００２３】
【表１】

【００２４】
表１より本発明に属する実施例１〜３の繊維強化複合材は曲げ特性、衝撃特性ともにバランスがとれて高水準にあり、特に衝撃特性は平均ボイド直径が大きなポリベンズオキサゾール繊維を補強材に用いた比較例１や低い引張強度・初期引張弾性率のポリベンズオキサゾール繊維を用いた比較例２及び補強繊維が超高分子量ポリエチレン繊維やポリパラフェニレンテレフタルアミド繊維である比較例３〜５の繊維強化複合材に比べて衝撃性の著しく改善されていることが分かる。
【００２５】
【発明の効果】
本発明の繊維強化複合材料は従来の繊維強化複合材料に比べて高強力、高剛性、高衝撃強度である利点を有している。したがって本発明の繊維強化複合材料を用いると従来にない高機能を備えたスポーツ用品、例えばゴルフシャフト、テニス用ラケット等また運搬装置・設備、例えば航空機、自動車、自転車、船舶等の製造が可能になる。中でも繊維強化複合材料の主流である炭素繊維可強化複合材料に比べて落雷の危険性がないことも利点である。[0001]
[Industrial applications]
The present invention relates to a fiber reinforced composite material. More specifically, a fiber that is lightweight and has high strength, high rigidity, and creep resistance, and is suitable for use in places where there is a risk of lightning, such as golf shafts, fishing rods, and tennis rackets. Related to reinforced composite materials.
[0002]
[Prior art]
Carbon fibers are used in many fields as high-performance composite materials because they have higher strength, higher rigidity, and lighter weight than glass fibers. In particular, it has been widely used as a primary or secondary structure in the field of sports equipment such as a transportation device such as an aircraft or an automobile, a golf shaft, a fishing rod, a tennis racket and the like. On the other hand, with the advent of wholly aromatic polyamide fibers, wholly aromatic polyester fibers, ultrahigh molecular weight polyethylene fibers, and the like, which are called super fibers, high-performance composite materials used for these reinforcing materials have been developed. In addition, a hybrid type composite material, for example, a high-performance composite material using carbon fibers and wholly aromatic polyamide fibers in combination has been studied. Among super fibers, polybenzazole fiber (PBZ fiber) has excellent mechanical properties such as a tensile strength of 4.0 GPa or more, an initial tensile modulus of 140 GPa or more, a decomposition start temperature of 670 C, a limiting oxygen index of 56, and high heat resistance and flame retardancy. Since it is a high-performance fiber having a good balance in performance, it has attracted attention as a reinforcing material for composite materials. Recently, the industrial production technology of polybenzazole fiber has been developed, and the development of a high-performance composite material using the fiber as a reinforcing material has been in full swing.
[0003]
[Problems to be solved by the invention]
Conventionally, carbon fiber has excellent performance as a reinforcing material for composite materials.However, its application has been expanded due to drawbacks such as (1) low impact resistance, (2) electrical conductivity and danger of lightning, etc. Is constrained. On the other hand, a composite material using a wholly aromatic polyamide fiber or a wholly aromatic polyester fiber as a reinforcing material has (1) a lack of hydrolysis resistance, and (2) a strength and an elastic modulus that are as high as those using carbon fiber as a reinforcing material. (3) Impact resistance is higher than that of carbon fiber reinforced material, but it is not sufficient yet. Although a hybrid composite material in which carbon fibers and wholly aromatic polyamide fibers are used in combination as a reinforcing material can compensate for the disadvantages of each other to some extent, the characteristics inherent to the material may be reduced by half. In order to solve the disadvantages of the above-mentioned materials, Japanese Patent Application Laid-Open No. Sho 60-174646 proposes a composite material using ultrahigh molecular weight polyethylene fibers as a reinforcing material. However, ultra high molecular weight polyethylene fibers have disadvantages compared to conventional materials, such as (1) poor rigidity, (2) lacking adhesiveness, and (2) lacking in heat resistance with a melting point of 140 ° C or less. The use of composites is naturally limited. A full-fledged fiber-reinforced composite material that meets the wide range of required characteristics by using polybenzazole fiber, which has excellent tensile strength, high initial tensile modulus, flame retardancy, and deformation resistance, as a reinforcing material, can overcome the disadvantages of conventional materials. Can be expected. However, with the progress of development, it has been found that polybenzazole fibers have problems in impact strength and hydrolysis resistance, and further improvement is required for reinforcing materials. An object of the present invention is to provide a fiber-reinforced composite material having excellent impact resistance.
[0004]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object, and found that the impact resistance of the polybenzazole fiber is closely related to the void diameter of the fiber, and the reinforcing material is a polybenzazole fiber having an average void diameter as small as possible. The present inventors have found that a high-performance composite material can be obtained by using the compound of the present invention. That is, a fiber-reinforced composite material having a tensile strength of 4.0 GPa or more and an initial tensile modulus of elasticity of 140 GPa or more and comprising a polybenzazole fiber having a void diameter of 35 ° or less and a matrix resin. It is.
[0005]
The present invention will be described in detail. The term "polybenzoxazole fiber (PBO) homopolymer" or "polybenzothiazole (PBT) homopolymer" as used in the present invention and a random, sequential or block copolymer of PBO and PBT. Here, polybenzoxazole, polybenzothiazole and their random, sequential or block copolymers are described, for example, in Wolfe et al., "Liquid Crystalline Polymer Compositions, Process and Products" US Patent 4,703,103 (October 27,1987), "Liquid Crystalline Polymer" Compositions, Process and Products `` US Patent 4,533,692 (August 6,1985), `` Liquid CrystallinePoly (2,6-Benzothiazole) Composition, Process and Products '' US Patent 4,533,724 (August 6,1985), `` Liquid Crystalline Polymer Compositions, Process and Process Products `` US Patent 4,533,693 (August 6,1985), Evers `` Thermooxidatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole Polymres '' US Patent 4,359,567 (November 16,1982); Tsai et al., `` Method for Making Heterocyclic Block Copolymer '' US Patent 4,578,432 (March 25, 1986).
The structural unit contained in the PBZ polymer is preferably selected from a lyotropic liquid crystal polymer.
The fibers must have high elongation properties that satisfy a tensile strength of at least 4.0 GPa and an initial tensile modulus of at least 140 GPa. When the fiber has a tensile strength of less than 4.0 GPa or an initial tensile modulus of less than 140 GPa, the fiber reinforced composite material has low strength and low rigidity, such as glass fiber, wholly aromatic polyamide fiber, wholly aromatic polyester fiber and Cannot compete with ultra high molecular weight polyethylene fibers. In addition, the weight reduction effect based on the high tensile strength and the high initial tensile modulus, which are the characteristics of the fiber, which increases the fiber content ratio in the composite material and copes with the improvement in the strength and rigidity, is lost.
[0006]
The monomer units are described in structural formulas (a) to (h). The polymer preferably consists essentially of monomer units selected from structural formulas (a)-(h), and more preferably consists essentially of monomer units selected from structural formulas (a)-(c) .
Suitable solvents for forming the PBZ polymer dope include cresol and non-oxidizing acids that can dissolve the polymer. Examples of suitable acid solvents include polyphosphoric acid, methanesulfonic acid and concentrated sulfuric acid or mixtures thereof. Further suitable solvents are polyphosphoric acid and methanesulfonic acid. The most suitable solvent is polyphosphoric acid.
[0007]
Embedded image

[0008]
Embedded image

[0009]
It is important that the polybenzazole fiber used as a reinforcing material of the fiber-reinforced composite material of the present invention has a void diameter of 35 ° or less. It has been known that polybenzazole fibers have particularly high tensile strength and high initial tensile modulus among super fibers. However, recently, it has been found that the tensile properties decrease in the presence of moisture, and the present inventors have continued to study the cause of the decrease in the tensile strength of polybenzazole fibers due to moisture. In the process, it was confirmed that (1) the decrease in tensile strength was due to hydrolysis of the polybenzazole molecular chain due to moisture, and (2) the penetration of water molecules from relatively large voids accelerated the hydrolysis. We have found and more surprisingly found that the impact properties of polybenzazole fibers are related to the average void diameter. This means that reducing the void diameter of the fiber improves not only the hydrolyzability but also the impact resistance. The present inventor has conducted a detailed study on the relationship between the void diameter and the impact characteristics. As a result, the composite material using a polybenzazole fiber having an average void diameter of 35 ° or less as a reinforcing material has a higher impact resistance than a conventional product. It is also clear that the remarkable improvement has been improved. Furthermore, a detailed study of the thread-making factor that determines the void diameter of the fiber revealed that the concentration of the non-solvent liquid (for example, aqueous phosphoric acid) that extracts polyphosphoric acid in the spun yarn discharged from the spinneret has a very large effect. I found to have power. Specifically, in producing a fiber by spinning from a dope composed of a polybenzazole polymer-based polymer and polyphosphoric acid, the average void diameter is reduced to 35 ° or less by using a phosphoric acid aqueous solution having a concentration of 5% by weight or more. Can be achieved. The spun yarn is subjected to a drying treatment after the polyphosphoric acid in the fiber is reduced to a desired level by an extraction / washing treatment. When this drying process is performed online, a so-called temperature gradient type drying method in which the temperature is sequentially increased and heated in the traveling direction of the yarn is recommended from the viewpoint of reducing the average void diameter.
[0010]
The fineness of the single fiber of the polybenzazole fiber is not particularly limited, but is usually preferably in the range of 0.3 to 10 denier. When the single fiber fineness is reduced and the number of fibers is increased, the external force is dispersed when a composite material is formed, and the impact strength is improved. However, in order to obtain a fiber having a small single-filament fineness, the spinning draft (= the yarn take-up speed / the discharge linear speed) generally becomes higher, and the yarn is likely to break during spinning. In the current state of the art, if the fineness is less than 0.3 denier, it is difficult to obtain a stable spinning condition, and the spinning productivity is reduced. On the other hand, when the fineness of the single yarn is large, the time required for removing polyphosphoric acid from the spun yarn becomes long, which leads to an increase in the length of the yarn cleaning device and a decrease in yarn hooking operability. In addition, in the case of the same yarn fineness, if the single yarn fineness is increased, the number of fibers is reduced, and when a composite material is formed, the external force is hardly dispersed and the impact strength is reduced. Therefore, the upper limit of the practical single yarn fineness is preferably 10 denier.
[0011]
As described below, the adhesion between the polybenzazole fiber and the matrix resin is an important factor in terms of the properties and cost of the fiber-reinforced composite material. Although various methods are conceivable as means for improving the adhesiveness, a relatively simple and remarkable effect is obtained by making the fiber cross section a non-circular, so-called irregular cross section. The irregular cross section fiber can be obtained relatively easily by spinning a dope of polybenzazole from a discharge hole having a non-circular cross section.
[0012]
The polybenzazole fiber used as a reinforcing material of the fiber-reinforced composite material of the present invention may be used as a long fiber, or may be used as a short fiber or pulp-like fiber cut to an appropriate length. When used as long fibers, they may be simply drawn together or used as woven fabrics of various structures such as plain weave, satin weave and twill weave. Depending on the purpose, it is also possible to use a mixture with other fibers such as carbon fiber, glass fiber, wholly aromatic polyamide fiber, wholly aromatic polyester fiber and ultrahigh molecular weight polyethylene fiber. The polybenzazole fiber used in the present invention may be preliminarily removed by extraction or the like of a treating agent such as an oil agent necessary for the spinning process, a finishing agent, or the like in order to improve the adhesiveness with the matrix resin. The surface may be previously treated with a coupling agent or a surface modifier. It is also recommended that corona discharge treatment be performed on the surface of the polybenzazole fiber.
[0013]
The fiber-reinforced composite material of the present invention is a thermosetting polymer material such as an unsaturated polyester resin, an epoxy resin, a polyurethane resin, a phenolic resin, or a thermoplastic polymer material such as a nylon resin, a polypropylene resin, a polyphenylene sulfide resin. It is molded using an ABS resin, furthermore, an elastic polymer material, rubber or the like as a matrix resin. In the latter case, a reinforcing fiber and a matrix fiber are knitted to form a sheet, which is melt-deformed to obtain a thermoplastic composite material. What is important here is that polybenzazole fiber has a decomposition start temperature of 670 ° C and a limiting oxygen index of 56, which is extremely high heat resistance and flame retardancy among existing organic synthetic fibers. In this case, the degree of freedom in selecting the matrix resin is greater in both cases of thermosetting and thermoplastic in terms of thermal aspect.
[0014]
Next, a method for producing a fiber-reinforced composite material will be briefly described. The polybenzazole-based fiber used as a reinforcing fiber of the fiber-reinforced composite material of the present invention is a spinning section in which a dope of a polybenzazole polymer using polyphosphoric acid as a solvent is kept at a temperature equal to or higher than a softening point and lower than a thermal decomposition point. Is supplied to the horizontal blown airflow zone through a spinneret provided with a plurality of discharge pores, and after passing through the horizontal blown airflow zone, the spun yarn is subsequently subjected to a non-solvent liquid. In contact with an extraction medium zone consisting of Here, it is important to use a phosphoric acid aqueous solution having a concentration of 5% by weight or more as the non-solvent liquid. Next, the yarn is wound around a plurality of rollers provided with a cleaning device such as a spray or a shower to reduce and remove phosphoric acid in the fiber. The yarn that has passed through the washing roller group may be dried as a batch by immediately winding it into a package after reducing the moisture adhering to the surface with an air knife, for example, if necessary, but once winding into a package. May be performed afterwards, but from the viewpoint of productivity, it is preferable to perform online processing without winding up once. In this case, the means for drying the yarn is not particularly limited, and for example, means such as contact with a heating roller, running in a high-temperature heated gas, and internal heating by high frequency can be used. In addition, you may provide a finishing agent to the yarn after a drying process as needed.
[0015]
Next, molding of the fiber reinforced composite will be described. The method of combining polybenzazole long fibers with a matrix resin is, for example, spraying or impregnating a matrix resin or a solution thereof into the fiber bundle aligned in one direction, or pre-treating the fibers with a woven fabric such as plain weave or satin weave. After that, it is also possible to spray or impregnate the matrix resin or a solution thereof. Alternatively, polybenzazole short fibers can be impregnated in a matrix resin or a solution thereof and kneaded. Further, when molding the above-described composite material, the mixture of the reinforcing material fiber and the matrix resin can be directly molded by heating (pressing if necessary). In the case of a thermosetting resin such as an unsaturated polyester resin, a matrix resin previously impregnated in polybenzazole fiber or its woven fabric is referred to as [B-stage], so-called prepreg or premix. After the curing reaction is advanced to the intermediate stage, a method of forming a composite material by using predetermined heating and pressurizing conditions is also possible. As described above, the fiber-reinforced composite material of the present invention can provide useful molded articles by various molding methods, but a typical molding method is compression molding. That is, it can be formed by mechanical compression or application of gas pressure in an autoclave using a mold of a predetermined type. In addition, it can be selected according to the shape of the reinforcing fiber and / or the characteristics of the matrix resin, such as a casting method, a spray method, a pan lay-up method, an injection molding method, a pultrusion method, and the like, which are usually used.
[0016]
Hereinafter, the evaluation scale in the present invention was determined by the following method.
<Fineness>
After the sample was allowed to stand for 24 hours in a test room in a standard condition (temperature of 22 + 2 degrees, relative humidity of 65 + 2%), a sample of 90 m was collected using a wrap reel, and the weight was measured and converted to a weight of 9000 m. And fineness.
<Void diameter of fiber>
The measurement of the small-angle X-ray scattering intensity was measured using a crack camera. As a sample, a fiber having a length of about 6 m was wound around a measurement holder. The output of the X-ray was 45 Kv and 150 mA, and the CuKα ray was monochromated with a nickel filter and used. The length limit slit of the cracking camera was 42 mm, the width limit slit was 0.07 mm, the length limit of the light receiving section slit was 10 mm, and the width limit was 0.14 mm. The measured range (2θ) is from 0.1 to 3.0 degrees. The step width was 0.025 degrees, and 30 seconds or more were integrated. The correction of the background scattering was performed using the following formula based on the measurement results of the sample and the air scattering.
I = μIsample−Iair
μ = Iair (0) / Isample (0)
Here, I is the true scattering intensity, Isample is the measured scattering intensity with the sample inserted, and Iair is the scattering intensity measured without the sample. After measuring the sample, the intensity was measured at a scattering angle of 0 degree to determine the absorption intensity of the sample. The measurement of the void size was performed using a Guinier plot. The logarithm of the scattering angle (I) and the square of the scattering vector (k) are plotted, data of which the square of k is in the range of 0 to 0.01Å1 ^{/ 2} are linearly approximated, and the slope of the straight line (S) is It was calculated using the formula.
D = 2 (s) ^1/2
<Measurement method of fiber tensile strength, initial tensile modulus and impact strength>
It was measured by the method and conditions specified in JIS L1013 (1981).
<Measuring method of bending strength and impact strength of composite material>
The measurement was carried out under the method and conditions specified in JIS K6911 (1979). However, the size of the test sample of the molded product was 3 mm in thickness, 25 mm in width, and 63.5 mm in length.
[0017]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.
<Example 1>
A dope consisting of a polybenzoxazole polymer and polyphosphoric acid at a concentration of 14% by weight is discharged from a spinneret having an elliptical cross-sectional shape and a pore diameter of 0.17 μm (converted to a circular cross-section equivalent diameter), and is discharged under the spinneret by 75%. After blowing air heated to a temperature of 0.5 ° C. at a flow rate of 0.5 m / sec, the solvent was extracted by introducing the solution into a 24% by weight phosphoric acid aqueous solution bath, and then the yarn speed was increased to 250 m / min by a driving roller. After stipulating, it was wound around a Nelson-type roller group, and ion-exchanged water was sprayed on the roller in a spray form to extract and remove phosphoric acid remaining on the yarn. Further, the yarn is wound around a group of Nelson-type rollers heated to a temperature of 180 to 240 ° C. to perform a drying treatment, and then a polyether-based finishing mainly composed of a random copolymer of ethylene oxide and propylene oxide is performed. The oil agent was applied to obtain a polybenzoxazole multifilament fiber having a fineness of 500D / 332F, an average void diameter of 21 °, a tensile strength of 5.8 GPa, an initial tensile modulus of elasticity of 271 GPa, and an impact strength of 452 joules / d. The multifilament was immersed in a 20% dispersion of a copolymer of ethylene and glycidyl methacrylate (weight ratio 95: 5) so that the adhesion of the copolymer was 3% owf. The multifilaments after the immersion treatment were aligned by a filament winding method, and embedded in an epoxy resin-based solution [Araldite LY564 (manufactured by Cibagiigy)]. Next, these were cured at 80 ° C. for 4 hours to obtain a fiber-reinforced composite material having the characteristics shown in Example 1 of Table 1.
[0018]
<Example 2>
Spinning / washing / drying / oil treatment was performed under the same conditions as in Example 1 except that the concentration of the aqueous solution of phosphoric acid in the extraction bath was changed to 16% by weight in Example 1, and the fineness was 500D / 332F, the average void diameter was 29 °, A polybenzoxazole multifilament fiber having characteristics of a tensile strength of 5.8 GPa, an initial tensile modulus of elasticity of 269 GPa and an impact strength of 427 Joules / d was obtained. Using the fiber, a fiber-reinforced composite material was processed in the same manner and under the same conditions as described in Example 1.
[0019]
<Example 3>
Spinning / washing / drying / oil treatment was performed under the same conditions as in Example 1 except that the concentration of the phosphoric acid aqueous solution to be brought into contact with the spun yarn was changed to 7% by weight, and the fineness was 500D / 332F, average void. A polybenzoxazole multifilament fiber having a diameter of 34 °, a tensile strength of 5.8 GPa, an initial tensile elastic modulus of 266 GPa and an impact strength of 414 joules / d was obtained. Using the fibers, a fiber-reinforced composite material was processed in the same manner and under the same conditions as described in Example 1.
[0020]
<Comparative Example 1>
Spinning / washing / drying / oil treatment was performed using the conditions of Example 1 except that the concentration of the phosphoric acid aqueous solution to be brought into contact with the spun yarn was changed to 3.5% by weight in Example 1, and the fineness was 500D / 332F. A polybenzoxazole multifilament fiber having the following properties: average void diameter: 39 °, tensile strength: 5.7 GPa, initial tensile modulus: 266 GPa, impact strength: 389 joules / d. The fiber was used to process into a fiber-reinforced composite material in the same manner and under the same conditions as described in Example 1, and this was used as Comparative Example 1.
[0021]
<Comparative Example 2>
Spinning, washing, drying, and oil treatment were performed under the same conditions as in Example 1 except that the intrinsic viscosity of polybenzazole was changed to 15 dl / g in the spun yarn, and the fineness was 500D / 332F, and the average void was changed. A polybenzoxazole multifilament fiber having characteristics of a diameter of 23 °, a tensile strength of 3.9 GPa, an initial tensile modulus of 138 GPa, and an impact strength of 339 joules / d was obtained. Using the fiber, a fiber-reinforced composite material was processed in the same manner and under the same conditions as described in Example 1.
[0022]
<Comparative Examples 3 to 5>
In Example 1, the fibers were prepared by using ultrahigh molecular weight polyethylene fibers having a fineness of 1000D / 200F, polyparaphenylene terephthalamide fibers having a fineness of 1500D / 1000F (trade name of Kevlar 29 Dupont), and carbon fibers having a fineness of 1200D / 1000F as the reinforcing fibers. It was molded into a reinforced composite material to make Comparative Examples 3, 4, and 5. Table 1 shows the evaluation results of Examples 1 to 3 and Comparative Examples 1 to 5 collectively.
[0023]
[Table 1]

[0024]
Table 1 shows that the fiber-reinforced composite materials of Examples 1 to 3 belonging to the present invention have a high level of balance in both bending properties and impact properties. Particularly, the impact properties are based on polybenzoxazole fibers having a large average void diameter as a reinforcing material. Fibers of Comparative Example 1 used, Comparative Example 2 using polybenzoxazole fibers having low tensile strength and initial tensile modulus, and Comparative Examples 3 to 5 in which the reinforcing fibers are ultrahigh molecular weight polyethylene fibers or polyparaphenylene terephthalamide fibers. It can be seen that the impact strength is significantly improved as compared with the reinforced composite material.
[0025]
【The invention's effect】
The fiber-reinforced composite material of the present invention has the advantages of high strength, high rigidity, and high impact strength as compared with conventional fiber-reinforced composite materials. Therefore, the use of the fiber-reinforced composite material of the present invention makes it possible to produce sports equipment with unprecedented high performance, such as golf shafts, tennis rackets, etc., as well as transportation equipment and facilities, such as aircraft, automobiles, bicycles, ships, and the like. Become. Above all, there is an advantage that there is no danger of lightning as compared with a carbon fiber reinforced composite material which is a mainstream of fiber reinforced composite materials.

Claims

A fiber-reinforced composite material having a tensile strength of 4.0 GPa or more, an initial tensile modulus of 140 GPa or more , and a polybenzazole fiber having a void diameter of 35 ° or less and a matrix resin .