JP4389143B2

JP4389143B2 - Method for producing high-strength polyolefin fiber

Info

Publication number: JP4389143B2
Application number: JP2001292219A
Authority: JP
Inventors: 勝二小田; 悟堂阪本; 康雄大田; 浩貴村瀬
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 2001-09-25
Filing date: 2001-09-25
Publication date: 2009-12-24
Anticipated expiration: 2021-09-25
Also published as: JP2003096617A

Description

【０００１】
【発明の属する技術分野】
本発明は、各種スポーツ衣料や防弾・防護衣料・防護手袋や各種安全用品などの高性能テキスタイル、タグロープ・係留ロープ、ヨットロープ、建築用ロープなどの各種ロープ製品、釣り糸、ブラインドケーブルなどの各種組み紐製品、漁網・防球ネットなどの網製品さらには化学フィルター・電池セパレーター・コンデンサーセパレーターや各種不織布の補強材あるいはテントなどの幕材、又はヘルメットやスキー板などのスポーツ用やスピーカーコーン用やプリプレグなどのコンポジット用の補強繊維など、産業上広範囲に応用可能な新規な高強度ポリオレフィン繊維の製造方法に関する。
【０００２】
【従来の技術】
高強度ポリオレフィン繊維に関しては例えば、特公昭６０―４７９２２号公報、特公昭６２−２５７４１４号公報に開示されるごとく、超高分子量のポリエチレンを原料にし、いわゆる“ゲル紡糸法・溶液紡糸”により従来に無い高強度・高弾性率繊維が得られることが知られており、既に産業上広く利用されている。
【０００３】
しかしながら、上記の方法では溶媒・重合体との混合物を使用する事から、工業的に見るとコストが非常に高くなる。つまり、該特許に開示されている方法では、原料ポリエチレンの濃度は高々５０％以下であり生産性に乏しい。又、溶媒を使用すると回収・精製設備などの付帯設備が必ず必要になりコストがかかる。さらに、環境面でも好ましく無い。
【０００４】
溶融紡糸によって得られる高強度ポリオレフィン繊維に関しては例えば、ＵＳＰ４２２８１１８に開示されている。同特許によれば、少なくとも２０，０００の数平均分子量および１２５，０００より小さい重量平均分子量を有するポリエチレンを２２０〜３３５℃に保たれた紡糸口金から押し出し少なくとも３０ｍ／ｍｉｎの速度で引き取り１１５〜１３２℃で２０倍以上延伸することにより少なくとも強度１０．６ｃＮ／ｄｔｅｘ以上の高強度ポリエチレン繊維の製造方法が開示されている。
【０００５】
また、溶融紡糸においては、低コストで且つ生産性の高い、紡糸から延伸まで連続して行う直接紡糸・延伸法による製造方法が一般的であり、ポリオレフィン繊維も例外ではない。例えば、特開平５−１８６９０８号公報および特開平５−２１４６０９号公報によれば、ポリオレフィンを溶融紡出し、冷却ダクトにより冷却後、表面温度５〜３０℃の冷却ロールあるいは０〜１０℃に冷却された収束剤付与ローラ−により急冷した後、連続的にインラインで表面温度８０〜１５０℃の加熱ロールにより加熱後、高倍率延伸する製造方法が開示されている。
【０００６】
しかしながら、上記の様な直接紡糸・延伸法で繊維を製造した場合、別工程で製造して得られた繊維に比べると延伸速度の違いからか、物性が低下する傾向が見られ、本来の性能を十分に引き出すことができなかった。
【０００７】
【発明が解決しようとする課題】
本発明は、溶融紡糸における直接紡糸・延伸法により得られる高強度ポリオレフィン繊維の製造方法を提供することにある。
【０００８】
即ち本発明は以下の構成からなる。
１．重量平均分子量が６０，０００〜６００，０００であり、重量平均分子量と数平均分子量の比（Ｍｗ／Ｍｎ）が４．５以下であるポリオレフィン重合体を下記の条件で溶融紡糸・直接延伸することを特徴とする高強度ポリオレフィン繊維の製造方法。
（１）複屈折率（Δｎ）が０．００８以上となる引取り速度と吐出線速度の比（ドラフト比）で冷却固化しながら繊維を引き取った後、（２）連続して表面温度が当該未延伸繊維の結晶分散温度以下の温度で複屈折率が０．０２〜０．０４となる倍率で一段目の延伸を行い、（３）更に当該延伸繊維の結晶分散温度以上で延伸を行う。
２．ポリオレフィン重合体が５個以上の炭素を有するアルキル基の分岐鎖が炭素１，０００個あたり０．０１〜３．０存在するポリエチレンであることを特徴とする１記載の高強度ポリオレフィン繊維の製造方法。
３．一段目の延伸倍率が１．２倍以上であり、総延伸倍率が１０倍以上であることを特徴とする１又は２記載の高強度ポリオレフィン繊維の製造方法。
【０００９】
本発明の最大の特徴は、重量平均分子量が６０，０００〜６００，０００であり、重量平均分子量と数平均分子量の比（Ｍｗ／Ｍｎ）が４．５以下である重合体を、溶融押出しによる直接紡糸・延伸法で下記条件を満たして行うことである。
（１）複屈折率（Δｎ）が少なくとも０．００８以上となる引取り速度と吐出線速度の比（ドラフト比）で冷却固化しながら繊維を引き取った後、
（２）連続して表面温度が該未延伸繊維の結晶分散温度以下の延伸ロールにより複屈折率が０．０２〜０．０４となる倍率で一段目の延伸を行い、
（３）更に連続して該延伸繊維の結晶分散温度以上で延伸を行う
【００１０】
即ち本繊維の製造に当たっては、重合体の重量平均分子量が６０，０００〜６００，０００であることが重要であり、重量平均分子量と数平均分子量の比（Ｍｗ／Ｍｎ）が４．５以下となることが重要である。好ましくは、重合体の重量平均分子量が６０，０００〜３００，０００であることが重要であり、重量平均分子量と数平均分子量の比（Ｍｗ／Ｍｎ）が４．０以下となることが重要である。さらに好ましくは、重合体の重量平均分子量が６０，０００〜２００，０００であることが重要であり、重量平均分子量と数平均分子量の比（Ｍｗ／Ｍｎ）が３．０以下となることが極めて重要である。
【００１１】
本発明における重合体とは、その繰り返し単位が実質的にエチレンであることを特徴とし、少量の他のモノマーはα−オレフィンが共重合される。α−オレフィンと共重合体を用いることによって長鎖の分岐をある程度含有させることは本繊維を製造する上で、特に紡糸に於いての製糸上の安定を与えることとなり、より好ましい。つまり、特許２９６３１９９号に開示されるように、ポリエチレンに長鎖分岐を含有させることにより、紡糸時のメルトフラクチャーの発生を低減させることが可能となる。しかしながらエチレン以外の含有量が増えすぎると反って延伸の阻害要因となる為、高強度・高弾性率繊維を得るという観点からは、５個以上の炭素を有するアルキル基からなる分岐鎖が炭素１，０００個あたり０．０１〜３個以下であることが好ましい、より好ましくは炭素１，０００個あたり０．０１〜１個であり、さらに好ましくは０．０５〜１．０個である。このようなポリエチレンポリマーは例えば、特許２９６３１９９に開示されるように、メタロセン触媒を用いて重合することが可能であるが、それにより限定されるものでは無い。
【００１２】
重合体の重量平均分子量が６０，０００未満となると溶融成形加工をし易いものの分子量が低い為に実際に得られる糸の強度は小さいものとなる。又、重合体の重量平均分子量が６００，０００を越えるような高分子量では溶融粘度が極めて高くなり、溶融成型加工が極めて困難となる。又、繊維状態の重量平均分子量と数平均分子量の比が４．５以上となると、同じ重量平均分子量の重合体を用いた場合と比較し最高延伸倍率が低く又、得られた糸の強度は低いものとなる。これは、緩和時間の長い分子鎖が延伸を行う際に延びきることが出来ずに破断が生じてしまうことと、分子量分布が広くなることによって低分子量成分が増加する為に分子末端が増加する事により強度低下が起こると推測している。
【００１３】
本発明では、鋭意検討することにより上記の様な重合体から、直接紡糸・延伸法で高強度ポリオレフィン繊維を得る手法を考案した。つまり、このような重合体を押出し機で溶融し、ギアポンプにて定量的に紡糸口金を介して吐出させる。その後、先ず、複屈折率（Δｎ）が０．００８以上、好ましくは０．０１以上、更に好ましくは０．０１２以上となる引取り速度と吐出線速度の比（ドラフト比）で冷風にて該糸状を冷却固化しながら引き取る。この時、複屈折率を０．００８以上とする為には、紡糸速度と吐出線速度の比を１００以上、好ましくは２００以上、更に好ましくは３００以上であることが重要である。紡糸速度と吐出線速度の比は、紡糸口金孔径、単孔吐出量、重合体密度、引取り速度から計算することが出来る。
【００１４】
引き続き該未延伸繊維を以下に示す様な方法で延伸することが最も重要である。即ち該繊維を、該繊維の結晶分散温度以下の温度で、具体的には６５℃以下で複屈折率（Δｎ）が０．０２〜０．０４、より好ましくは０．０２７〜０．０３３となる倍率で一段目の延伸を行い、該延伸繊維の結晶分散温度以上の温度で、具体的には９０℃以上でさらに多段延伸を行うことが重要である。上記の様な手法を採用することにより驚く程、繊維の物性が向上することを見いだした。延伸方法は特にこだわらない。これまでに公知な手法、例えばローラー延伸、スリット延伸などが推奨されるがこれに限定されるものでは無い。
【００１５】
通常、ポリエチレン配向物の最も高温側に観察される吸収は、結晶分散と呼ばれており、結晶相内の分子鎖熱運動に直接関与していると考えられている。この結晶分散温度は、動的粘弾性測定を行うことで測定することが出来る。即ち、測定で得られた貯蔵弾性率、損失弾性率から、損失正接を計算し、各温度で得られたこれらの三つの値を対数で縦軸に取り、横軸を温度でプロットし最も高温側に現れる吸収が結晶分散である。
【００１６】
ＵＳＰ４２２８１１８、特表平８−５０４８９１号公報、特開平５−１８６９０８号公報等、多数の文献に開示されるように、ポリオレフィン繊維を延伸する場合、該繊維を加熱し少なくとも５０℃以上で延伸することが、物性面・生産性面でも好ましいことが開示されている。しかしながら、本発明では驚くべきことに、これまでの技術と相反して該繊維の結晶分散温度以下の温度条件で複屈折率（Δｎ）を制御しながら該繊維を延伸すると飛躍的に繊維物性が向上することを見い出し、本発明に到達した。
【００１７】
即ち、好ましくは該繊維の結晶分散温度より１０℃以上低い温度、好ましくは２０℃以上低い温度で複屈折率（Δｎ）が０．０２〜０．０４、より好ましくは０．０２７〜０．０３３となる倍率で一段目の延伸を行うことが極めて重要である。又、２段目の延伸以降は、該繊維の結晶分散温度より好ましくは２０℃以上高い温度、さらに好ましくは３０℃以上高い温度で延伸を行うことが重要である。
【００１８】
複屈折率（Δｎ）を制御しながら、連続的に該繊維の結晶分散温度散以下の温度で一段目の延伸を行うことで繊維物性が向上する理由は定かでは無いが、以下の様に推測している。つまり、紡糸である程度分子配向を進めることにより、一段目の延伸がスムーズに行われる。更に該繊維の結晶分散温度以下の温度で延伸を行うことにより、繊維により延伸張力がかかる。又、該繊維の結晶分散温度以下で延伸を行っているが為に、結晶自体は延伸によって動きにくく、主に非晶部分のみの延伸が行われる。と推測しているが、詳細は定かで無い。
【００１９】
以下に本発明における特性値に関する測定法および測定条件を説明する。
【００２０】
（強度・弾性率）
本発明における強度，弾性率は、オリエンティック社製「テンシロン」を用い、試料長２００ｍｍ（チャック間長さ）、伸長速度１００％／分の条件で歪ー応力曲線を雰囲気温度２０℃、相対湿度６５％条件下で測定し、破断点での応力を強度（ｃＮ／ｄｔｅｘ）、曲線の原点付近の最大勾配を与える接線より弾性率（ｃＮ／ｄｔｅｘ）を計算して求めた。なお、各値は１０回の測定値の平均値を使用した。
【００２１】
（重量平均分子量Ｍｗ、数平均分子量ＭｎおよびＭｗ／Ｍｎ）
重量平均分子量Ｍｗ、数平均分子量ＭｎおよびＭｗ／Ｍｎは、ゲル・パーミエーション・クロマトグラフィー（ＧＰＣ）によって測定した。ＧＰＣ装置としては、Ｗａｔｅｒｓ製ＧＰＣ１５０ＣＡＬＣ／ＧＰＣを持ち、カラムとしてはＳＨＯＤＥＸ製ＧＰＣＵＴ８０２．５を一本ＵＴ８０６Ｍを２本用いて測定した。測定溶媒は、ｏ−ジクロロベンゼンを使用しカラム温度を１４５℃した。試料濃度は１．０ｍｇ／ｍｌとし、２００マイクロリットル注入し測定した。分子量の検量線は、ユニバーサルキャリブレーション法により分子量既知のポリスチレン試料を用いて構成されている。
【００２２】
（分岐の測定）
重合体の分岐の測定は、１３Ｃ−ＮＭＲ（１２５ＭＨｚ）を用いて決定される。ランダル（Ｒａｎｄａｌｌ）の方法（Ｒｅｖ．Ｍａｃｒｏｍｏｌ．Ｃｈｅｍ．Ｐｈｙｓ．，Ｃ２９（２＆３），Ｐ．２８５−２９７）の記載されている方法を用いて測定を行った。
【００２３】
（動的粘弾弾性測定）
本発明における動的粘度測定は、オリエンテック社製「レオバイブロンＤＤＶ−０１ＦＰ型」を用いて行った。繊維は全体として１００デニール±１０デニールとなるように分繊あるいは合糸し、各単繊維ができる限り均一に配列するように配慮して、測定長（鋏金具間距離）が２０ｍｍとなるように繊維の両末端をアルミ箔で包みセルロース系接着剤で接着する。その際の糊代ろ長さは、鋏金具との固定を考慮して５ｍｍ程度とする。各試験片は、２０ｍｍの初期幅に設定された鋏金具（チャック）に糸が弛んだり捩じれたりしないように慎重に設置され、予め６０℃の温度、１１０Ｈｚの周波数にて数秒、予備変形を与えてから本実験を実施した。本実験では−１５０℃から１５０℃の温度範囲で約１℃／分の昇温速度において１１０Ｈｚの周波数での温度分散を低温側より求めた。測定においては静的な荷重を５ｇｆに設定し、繊維が弛まない様に試料長を自動調整させた。動的な変形の振幅は１５μｍに設定した。
【００２４】
（複屈折率）
本発明における複屈折率測定は、ニコン製「ＯＰＴＩＰＨＯＴ−ＰＯＬ」を用いて行った。スライドグラス上に封入液（ツェーデル油または流動パラフィン）を滴下し、５〜６ｍｍ長の繊維軸に対し４５°の角度に切断した試料を切断面を上にして液中に浸漬する。試料スライドグラスを回転ステージに載せて、スケールと繊維が平行になるように調整してアナライザーを挿入し暗視界にした後、コンペセーターを３０にして縞数ｎを数える。次に、コンペセーターを３０〜４０の方向に廻して試料が最初に最も暗くなる点のコンペセーターの目盛ａと、反対方向に廻して試料が最初に最も暗くなるコンペセーターの目盛ｂを測定して、その後、コンペセーターを３０に戻してアナライザーを外し、試料の直径ｄを測定する。以上の測定を数回繰り返した後、以下の式に基づいて複屈折率（Δｎ）を算出する。
Δｎ＝Γ／ｄ
Γ（レターデーション）＝ｎλο＋ε
λο＝５８９ｎｍ
ε：Ｃ／１００００（装置定数＝０．８１６）とｉより求める。
ｉ＝（ａ−ｂ）
【００２５】
（紡糸速度と吐出線速度の比）
紡糸速度と吐出線速度の比（ドラフト比）は、以下の式で与えられる
ドラフト比（Ψ）＝紡糸速度（Ｖｓ）／吐出線速度（Ｖ）
【００２６】
【実施例】
以下、実施例をもって本発明を説明する。
【００２７】
（実施例１）
重量平均分子量１１５，０００、重量平均分子量と数平均分子量の比が２．３、５個以上の炭素を有する長さの分岐鎖が炭素１，０００個あたり０．４個である高密度ポリエチレンをφ０．８ｍｍ、３０Ｈからなる紡糸口金から２９０℃で単孔吐出量０．５ｇ／ｍｉｎの速度で押し出す。押し出された繊維を５ｃｍの保温区間を通過させ、その後２０℃、０．５ｍ／ｓのクエンチで冷却後、紡糸速度３５０ｍ／ｍｉｎで引き取り、連続して表面温度２０℃の延伸ローラー１上で１段目の２．５倍延伸を行った後、更に連続して表面温度１１５℃の延伸ローラー２上で２段目の５．３倍延伸を行い、延伸糸を得た。この時、延伸前の繊維の複屈折率は０．０１２、１段延伸後の繊維の複屈折率は０．０３０であった。得られた繊維の物性を表１に示した。
【００２８】
（実施例２）
実施例１の高密度ポリエチレンを同様の条件で押し出し冷却された繊維を、紡糸速度２５０ｍ／ｍｉｎで引き取り、連続して表面温度２０℃の延伸ローラー１上で１段目の３．５倍延伸を行った後、更に連続して表面温度１１５℃の延伸ローラー２上で２段目の４．０倍延伸を行い、延伸糸を得た。この時、延伸前の繊維の複屈折率は０．００９、１段延伸後の繊維の複屈折率は０．０３３であった。得られた繊維の物性を表１に示した。
【００２９】
（実施例３）
実施例１の高密度ポリエチレンを同様の条件で押し出し冷却された繊維を、紡糸速度４５０ｍ／ｍｉｎで引き取り、連続して表面温度２０℃の延伸ローラー１上で１段目の１．７５倍延伸を行った後、更に連続して表面温度１１５℃の延伸ローラー２上で２段目の６．０倍延伸を行い、延伸糸を得た。この時、延伸前の繊維の複屈折率は０．０１６、１段延伸後の繊維の複屈折率は０．０２８であった。得られた繊維の物性を表１に示した。
【００３０】
（実施例４）
１段目の延伸温度を５０℃、１段目の延伸倍率を３．０倍、２段目の延伸倍率を４．３倍とした以外は、実施例１と同様の条件で延伸糸を作成した。この時、延伸前の繊維の複屈折率は０．０１２、１段延伸後の繊維の複屈折率は０．０３２であった。得られた繊維の物性を表１に示した。
【００３１】
（実施例５）
１段目の延伸温度を１０℃、１段目の延伸倍率を２．０倍、２段目の延伸倍率を６．８倍とした以外は、実施例１と同様の条件で延伸糸を作成した。この時、延伸前の繊維の複屈折率は０．０１２、１段延伸後の繊維の複屈折率は０．０２９であった。得られた繊維の物性を表１に示した。
【００３２】
（実施例６）
重量平均分子量１５２，０００、重量平均分子量と数平均分子量の比が２．４、５個以上の炭素を有する長さの分岐鎖が炭素１，０００個あたり０．８個である高密度ポリエチレンをφ１．２ｍｍ、３０Ｈからなる紡糸口金から同様の条件で押し出し冷却された繊維を、紡糸速度３００ｍ／ｍｉｎで引き取り、連続して表面温度２０℃の延伸ローラー１上で１段目の２．０倍延伸を行った後、更に連続して表面温度１１５℃の延伸ローラー２上で２段目の５．５倍延伸を行い、延伸糸を得た。この時、延伸前の繊維の複屈折率は０．０１０、１段延伸後の繊維の複屈折率は０．０３０であった。得られた繊維の物性を表１に示した。
【００３３】
（比較例１）
実施例１の高密度ポリエチレンを同様の条件で押し出し冷却された繊維を、紡糸速度３５０ｍ／ｍｉｎで引き取り、連続して表面温度１００℃の延伸ローラー１上で１段目の２．５倍延伸を行った後、更に連続して表面温度１１５℃の延伸ローラー２上で２段目の５．１倍延伸を行い、延伸糸を得た。この時、延伸前の繊維の複屈折率は０．０１２、１段延伸後の繊維の複屈折率は０．０３３であった。得られた繊維の物性を表２に示した。
【００３４】
（比較例２）
実施例１と同じ高密度ポリエチレンを同様の条件で紡糸口金から押し出し冷却された繊維を、紡糸速度１００ｍ／ｍｉｎで引き取り、連続して表面温度２０℃の延伸ローラー１上で１段目の４．０倍延伸を行った後、更に連続して表面温度１１５℃の延伸ローラー２上で２段目の３．５倍延伸を行い、延伸糸を得た。この時、延伸前の繊維の複屈折率は０．００４、１段延伸後の繊維の複屈折率は０．０１８であった。得られた繊維の物性を表２に示した。
【００３５】
（比較例３）
実施例１と同じ高密度ポリエチレンを同様の条件で紡糸口金から押し出し冷却された繊維を、紡糸速度６００ｍ／ｍｉｎで引き取り、連続して表面温度２０℃の延伸ローラー１上で１段目の延伸を行おうとしたところ、１．２倍以上の延伸が不可能であった為、１段目で１．１倍延伸し、更に連続して表面温度１１５℃の延伸ローラー２上で２段目の５．８倍延伸を行い、延伸糸を得た。この時、延伸前の繊維の複屈折率は０．０２２、１段延伸後の繊維の複屈折率は０．０２３であった。得られた繊維の物性を表２に示した。
【００３６】
（比較例４）
実施例１と同じ高密度ポリエチレンを同様の条件で紡糸口金から押し出し冷却された繊維を、表面温度２０℃、速度３５０ｍ／ｍｉｎの紡糸ローラーで引き取り、連続して表面温度１１５℃の延伸ローラー１上で１２．０倍延伸を行い、延伸糸を得た。得られた繊維の物性を表２に示した。
【００３７】
（比較例５）
重量平均分子量１２１，５００、重量平均分子量と数平均分子量の比が５．１、５個以上の炭素を有する長さの分岐鎖が炭素１，０００個あたり０．４個である高密度ポリエチレンをφ０．８ｍｍ、３０Ｈからなる紡糸口金から２７０℃で単孔吐出量０．５ｇ／ｍｉｎの速度で押し出す。押し出された繊維を、５ｃｍの保温区間を通過させ、その後２０℃、０．５ｍ／ｓのクエンチで冷却後、紡糸速度３５０ｍ／ｍｉｎで引き取り、連続して表面温度２０℃の延伸ローラー１上で１段目の２．５倍の延伸を行った後、更に連続して表面温度１１５℃の延伸ローラー２上で２段目の３．１倍の延伸を行い、延伸糸を得た。この時、延伸前の繊維の複屈折率は０．０１２、１段延伸後の繊維の複屈折率は０．０３４であった。得られた繊維の物性を表２に示した。
【００３８】
【表１】

【００３９】
【表２】

【００４０】
【発明の効果】
本発明によると新規な高強度ポリオレフィン繊維を環境不可が少なく、生産性良く製造することを可能とした。
【図面の簡単な説明】
【図１】本発明の製造方法にかかる製造装置の一例を示す模式図。
【符号の説明】
１：紡糸ノズル、２：保温筒、３：クエンチ、４：オイリングローラー、５：紡糸ローラー、６：延伸ローラー１、７：引取ローラー１、８：延伸ローラ−２、９：引取ローラー２、１０：巻取り機[0001]
BACKGROUND OF THE INVENTION
The present invention relates to various sports clothing, high-performance textiles such as bulletproof / protective clothing / protective gloves and various safety goods, various rope products such as tag ropes, mooring ropes, yacht ropes, construction ropes, various braids such as fishing lines and blind cables. Products, net products such as fishing nets and ball-proof nets, chemical filters, battery separators, condenser separators, various non-woven reinforcing materials or curtains such as tents, sports such as helmets and skis, speaker cones, prepregs, etc. The present invention relates to a method for producing a novel high-strength polyolefin fiber that can be applied to a wide range of industries, such as composite reinforcing fibers.
[0002]
[Prior art]
As for high-strength polyolefin fibers, for example, as disclosed in Japanese Patent Publication Nos. 60-47922 and 62-257414, ultrahigh molecular weight polyethylene is used as a raw material, so-called “gel spinning method / solution spinning”. It is known that high-strength and high-modulus fibers can be obtained and are already widely used in industry.
[0003]
However, since the above method uses a mixture of a solvent and a polymer, the cost is very high from an industrial viewpoint. That is, in the method disclosed in the patent, the concentration of the raw material polyethylene is at most 50%, and the productivity is poor. In addition, if a solvent is used, ancillary facilities such as recovery / purification facilities are necessarily required, which is costly. Furthermore, it is not preferable in terms of environment.
[0004]
US Pat. No. 4,228,118 discloses a high-strength polyolefin fiber obtained by melt spinning. According to the patent, polyethylene having a number average molecular weight of at least 20,000 and a weight average molecular weight of less than 125,000 is extruded from a spinneret maintained at 220-335 ° C. and taken at a speed of at least 30 m / min. A method for producing a high-strength polyethylene fiber having a strength of at least 10.6 cN / dtex by stretching 20 times or more at a temperature is disclosed.
[0005]
In melt spinning, a low-cost and high-productivity production method based on a direct spinning / stretching method that is continuously performed from spinning to stretching is common, and polyolefin fibers are no exception. For example, according to JP-A-5-186908 and JP-A-5-214609, a polyolefin is melt-spun and cooled by a cooling duct, and then cooled to a cooling roll having a surface temperature of 5 to 30 ° C. or 0 to 10 ° C. A manufacturing method is disclosed in which the film is rapidly cooled by a sizing agent application roller, continuously heated in-line by a heating roll having a surface temperature of 80 to 150 ° C., and then stretched at a high magnification.
[0006]
However, when the fiber is produced by the direct spinning / drawing method as described above, the physical properties tend to be reduced due to the difference in the drawing speed compared to the fiber obtained by a separate process, and the original performance Could not be fully extracted.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing a high-strength polyolefin fiber obtained by a direct spinning / drawing method in melt spinning.
[0008]
That is, this invention consists of the following structures.
1. A polyolefin polymer having a weight average molecular weight of 60,000 to 600,000 and a ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) of 4.5 or less is melt-spun and directly stretched under the following conditions: A process for producing a high-strength polyolefin fiber characterized by
(1) After taking up the fiber while cooling and solidifying at a ratio (draft ratio) between the take-off speed and the discharge linear speed at which the birefringence index (Δn) is 0.008 or more, (2) the surface temperature is continuously First-stage stretching is performed at a magnification at which the birefringence is 0.02 to 0.04 at a temperature equal to or lower than the crystal dispersion temperature of the unstretched fiber.
2. 2. The method for producing a high-strength polyolefin fiber according to 1, wherein the polyolefin polymer is polyethylene having 0.01 to 3.0 branched chains of an alkyl group having 5 or more carbon atoms per 1,000 carbon atoms. .
3. The method for producing high-strength polyolefin fibers according to 1 or 2, wherein the first stage draw ratio is 1.2 times or more and the total draw ratio is 10 times or more.
[0009]
The greatest feature of the present invention is that a polymer having a weight average molecular weight of 60,000 to 600,000 and a ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) of 4.5 or less is obtained by melt extrusion. The direct spinning / drawing method satisfies the following conditions.
(1) After taking up the fiber while cooling and solidifying at a ratio (draft ratio) between the take-off speed and the discharge linear speed at which the birefringence (Δn) is at least 0.008,
(2) The first stage is stretched at a magnification such that the birefringence is 0.02 to 0.04 by a stretching roll whose surface temperature is continuously below the crystal dispersion temperature of the unstretched fiber,
(3) Further, the drawing is continuously performed at a temperature higher than the crystal dispersion temperature of the drawn fiber.
That is, in the production of this fiber, it is important that the polymer has a weight average molecular weight of 60,000 to 600,000, and the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) is 4.5 or less. It is important to be. Preferably, it is important that the weight average molecular weight of the polymer is 60,000 to 300,000, and it is important that the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) is 4.0 or less. is there. More preferably, it is important that the weight average molecular weight of the polymer is 60,000 to 200,000, and the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) is 3.0 or less. is important.
[0011]
The polymer in the present invention is characterized in that the repeating unit is substantially ethylene, and a small amount of other monomers are copolymerized with α-olefin. Inclusion of a long chain branch to some extent by using an α-olefin and a copolymer is more preferable in terms of producing the fiber, particularly in terms of spinning stability in spinning. That is, as disclosed in Japanese Patent No. 2963199, it is possible to reduce the occurrence of melt fracture at the time of spinning by incorporating polyethylene into long-chain branches. However, if the content other than ethylene is excessively increased, it becomes a hindrance to stretching, and therefore, from the viewpoint of obtaining a high-strength and high-modulus fiber, a branched chain composed of an alkyl group having 5 or more carbons is carbon 1 It is preferable that it is 0.01-3 or less per 1,000, More preferably, it is 0.01-1 per 1,000 carbons, More preferably, it is 0.05-1.0. Such a polyethylene polymer can be polymerized using a metallocene catalyst as disclosed in, for example, Japanese Patent No. 2963199, but is not limited thereto.
[0012]
When the weight average molecular weight of the polymer is less than 60,000, although it is easy to be melt-molded, the actually obtained yarn has a low strength because the molecular weight is low. On the other hand, if the polymer has a high molecular weight exceeding 600,000, the melt viscosity becomes extremely high and melt molding becomes very difficult. In addition, when the ratio of the weight average molecular weight and the number average molecular weight in the fiber state is 4.5 or more, the maximum draw ratio is lower than when a polymer having the same weight average molecular weight is used, and the strength of the obtained yarn is It will be low. This is because a molecular chain with a long relaxation time cannot be extended during stretching and breakage occurs, and the molecular weight increases due to an increase in low molecular weight components due to a broad molecular weight distribution. It is speculated that the strength will decrease due to this.
[0013]
In the present invention, a method for obtaining a high-strength polyolefin fiber from the above-mentioned polymer by direct spinning / drawing method has been devised by intensive studies. That is, such a polymer is melted by an extruder and discharged quantitatively by a gear pump through a spinneret. After that, first, the birefringence index (Δn) is 0.008 or more, preferably 0.01 or more, and more preferably 0.012 or more. Take the filament while cooling and solidifying. At this time, in order to set the birefringence to 0.008 or more, it is important that the ratio between the spinning speed and the discharge linear speed is 100 or more, preferably 200 or more, more preferably 300 or more. The ratio of the spinning speed and the discharge linear speed can be calculated from the spinneret hole diameter, the single hole discharge amount, the polymer density, and the take-up speed.
[0014]
Subsequently, it is most important to draw the undrawn fiber by the following method. That is, when the fiber is at a temperature not higher than the crystal dispersion temperature of the fiber, specifically 65 ° C. or lower, the birefringence (Δn) is 0.02 to 0.04, more preferably 0.027 to 0.033. It is important that the first stage of stretching is performed at such a magnification, and that further multistage stretching is performed at a temperature equal to or higher than the crystal dispersion temperature of the stretched fiber, specifically at 90 ° C. or higher. It has been found that the physical properties of the fibers are surprisingly improved by adopting the above-described method. The stretching method is not particularly particular. Conventionally known methods such as roller stretching and slit stretching are recommended, but are not limited thereto.
[0015]
Usually, the absorption observed on the highest temperature side of the polyethylene alignment product is called crystal dispersion and is considered to be directly related to the molecular chain thermal motion in the crystal phase. This crystal dispersion temperature can be measured by performing dynamic viscoelasticity measurement. That is, the loss tangent is calculated from the storage elastic modulus and loss elastic modulus obtained by measurement, and these three values obtained at each temperature are plotted on the vertical axis, and the horizontal axis is plotted on the horizontal axis to plot the highest temperature. Absorption appearing on the side is crystal dispersion.
[0016]
US Pat. No. 4,228,118, JP-A-8-504891, JP-A-5-186908, and the like, when drawing a polyolefin fiber, the fiber is heated and drawn at least at 50 ° C. or more. However, it is disclosed that it is preferable in terms of physical properties and productivity. However, surprisingly, in the present invention, when the fiber is stretched while controlling the birefringence index (Δn) under a temperature condition below the crystal dispersion temperature of the fiber, contrary to the conventional techniques, the fiber properties are dramatically improved. It has been found that it has improved and has reached the present invention.
[0017]
That is, the birefringence (Δn) is preferably 0.02 to 0.04, more preferably 0.027 to 0.033 at a temperature lower than the crystal dispersion temperature of the fiber by 10 ° C. or more, preferably 20 ° C. or more. It is extremely important to perform the first-stage stretching at a magnification of Further, after the second stage drawing, it is important to carry out the drawing at a temperature that is preferably 20 ° C. or higher, more preferably 30 ° C. or higher than the crystal dispersion temperature of the fiber.
[0018]
While controlling the birefringence index (Δn), the reason why the fiber physical properties are improved by continuously stretching the first stage at a temperature equal to or lower than the crystal dispersion temperature of the fiber is not clear, but is estimated as follows. is doing. That is, the first-stage stretching is smoothly performed by advancing molecular orientation to some extent by spinning. Further, the stretching tension is applied by the fiber by stretching at a temperature lower than the crystal dispersion temperature of the fiber. In addition, since the drawing is performed at a temperature lower than the crystal dispersion temperature of the fiber, the crystal itself is difficult to move by drawing, and only the amorphous part is drawn. The details are not clear.
[0019]
Hereinafter, measurement methods and measurement conditions relating to characteristic values in the present invention will be described.
[0020]
(Strength / elastic modulus)
For the strength and elastic modulus of the present invention, “Tensilon” manufactured by Orientic Co., Ltd. was used, and the strain-stress curve was measured at an ambient temperature of 20 ° C. and relative humidity under the conditions of a sample length of 200 mm (length between chucks) and an elongation rate of 100% / min Measured under the conditions of 65%, the stress at the breaking point was obtained by calculating the strength (cN / dtex) and the elastic modulus (cN / dtex) from the tangent that gives the maximum gradient near the origin of the curve. In addition, each value used the average value of 10 times of measured values.
[0021]
(Weight average molecular weight Mw, number average molecular weight Mn and Mw / Mn)
The weight average molecular weight Mw, the number average molecular weight Mn, and Mw / Mn were measured by gel permeation chromatography (GPC). A GPC 150C ALC / GPC manufactured by Waters was used as a GPC apparatus, and a single GPC UT802.5 manufactured by SHODEX was used as a column, and two UT806M were used. The measurement solvent used was o-dichlorobenzene and the column temperature was 145 ° C. The sample concentration was 1.0 mg / ml, and 200 microliters were injected and measured. The molecular weight calibration curve is constructed using a polystyrene sample with a known molecular weight by the universal calibration method.
[0022]
(Branch measurement)
Measurement of polymer branching is determined using 13 C-NMR (125 MHz). Measurements were made using the method described by Randall's method (Rev. Macromol. Chem. Phys., C29 (2 & 3), P.285-297).
[0023]
(Dynamic viscoelasticity measurement)
The dynamic viscosity measurement in the present invention was performed using “Leovibron DDV-01FP type” manufactured by Orientec. The fibers are split or combined so that the entire fiber is 100 denier ± 10 denier, and the measurement length (distance between the brace) is 20 mm in consideration of arranging the single fibers as uniformly as possible. Wrap both ends of the fiber in aluminum foil and bond with cellulosic adhesive. In this case, the glue allowance length is set to about 5 mm in consideration of fixing with the metal fitting. Each test piece was carefully placed on a brace (chuck) set to an initial width of 20 mm so that the yarn would not loosen or twist and was preliminarily deformed for several seconds at a temperature of 60 ° C. and a frequency of 110 Hz. This experiment was conducted after that. In this experiment, temperature dispersion at a frequency of 110 Hz was obtained from the low temperature side at a temperature increase rate of about 1 ° C./min in the temperature range of −150 ° C. to 150 ° C. In the measurement, the static load was set to 5 gf, and the sample length was automatically adjusted so that the fibers did not loosen. The amplitude of dynamic deformation was set to 15 μm.
[0024]
(Birefringence)
The birefringence measurement in the present invention was performed using “OPTIPHOT-POL” manufactured by Nikon. An encapsulating liquid (Zedel oil or liquid paraffin) is dropped on a slide glass, and a sample cut at an angle of 45 ° with respect to a fiber axis having a length of 5 to 6 mm is immersed in the liquid with the cut surface facing upward. A sample slide glass is placed on a rotating stage, adjusted so that the scale and the fiber are parallel, and an analyzer is inserted to make a dark field of view. Then, the competition sweater is set to 30, and the number of fringes n is counted. Next, turn the competition sweater in the direction of 30 to 40, and measure the scale a of the competition sweater where the sample is darkest first and the scale b of the competition sweater where the sample is darkest first when turning in the opposite direction. Thereafter, the competer is returned to 30, the analyzer is removed, and the diameter d of the sample is measured. After repeating the above measurement several times, the birefringence (Δn) is calculated based on the following equation.
Δn = Γ / d
Γ (retardation) = nλο + ε
λο = 589nm
ε: C / 10000 (equipment constant = 0.816) and i are obtained.
i = (ab)
[0025]
(Ratio of spinning speed and discharge linear speed)
The ratio between the spinning speed and the discharge linear speed (draft ratio) is given by the following formula: draft ratio (Ψ) = spinning speed (Vs) / discharge linear speed (V)
[0026]
【Example】
Hereinafter, the present invention will be described with reference to examples.
[0027]
Example 1
A high-density polyethylene having a weight-average molecular weight of 115,000, a ratio of the weight-average molecular weight to the number-average molecular weight of 2.3, 0.4 branched chains having a length of 5 or more carbons per 0.4 carbons It extrudes from the spinneret which consists of (phi) 0.8mm and 30H at a speed | rate of 290 degreeC and the discharge rate of a single hole 0.5g / min. The extruded fiber is passed through a 5 cm heat insulation section, then cooled at a quenching rate of 20 ° C. and 0.5 m / s, taken up at a spinning speed of 350 m / min, and continuously 1 on a stretching roller 1 having a surface temperature of 20 ° C. After the 2.5-fold drawing of the second stage, the second-stage 5.3-fold drawing was continuously performed on the drawing roller 2 having a surface temperature of 115 ° C. to obtain a drawn yarn. At this time, the birefringence of the fiber before stretching was 0.012, and the birefringence of the fiber after one-stage stretching was 0.030. Table 1 shows the physical properties of the obtained fiber.
[0028]
(Example 2)
The fiber obtained by extruding and cooling the high-density polyethylene of Example 1 under the same conditions is taken out at a spinning speed of 250 m / min, and continuously stretched 3.5 times on a drawing roller 1 having a surface temperature of 20 ° C. Then, the second stage 4.0-fold stretching was performed continuously on the stretching roller 2 having a surface temperature of 115 ° C. to obtain a stretched yarn. At this time, the birefringence of the fiber before stretching was 0.009, and the birefringence of the fiber after one-stage stretching was 0.033. Table 1 shows the physical properties of the obtained fiber.
[0029]
(Example 3)
The fiber obtained by extruding and cooling the high-density polyethylene of Example 1 under the same conditions is taken out at a spinning speed of 450 m / min, and continuously stretched 1.75 times on a stretching roller 1 having a surface temperature of 20 ° C. After this, the second-stage 6.0-fold drawing was performed continuously on the drawing roller 2 having a surface temperature of 115 ° C. to obtain a drawn yarn. At this time, the birefringence of the fiber before stretching was 0.016, and the birefringence of the fiber after one-stage stretching was 0.028. Table 1 shows the physical properties of the obtained fiber.
[0030]
(Example 4)
A drawn yarn was prepared under the same conditions as in Example 1 except that the first stage draw temperature was 50 ° C., the first stage draw ratio was 3.0 times, and the second stage draw ratio was 4.3 times. did. At this time, the birefringence of the fiber before stretching was 0.012, and the birefringence of the fiber after one-stage stretching was 0.032. Table 1 shows the physical properties of the obtained fiber.
[0031]
(Example 5)
A drawn yarn was prepared under the same conditions as in Example 1 except that the first stage drawing temperature was 10 ° C., the first stage drawing ratio was 2.0 times, and the second stage drawing ratio was 6.8 times. did. At this time, the birefringence of the fiber before drawing was 0.012, and the birefringence of the fiber after one-stage drawing was 0.029. Table 1 shows the physical properties of the obtained fiber.
[0032]
(Example 6)
A high-density polyethylene having a weight average molecular weight of 152,000, a ratio of the weight average molecular weight to the number average molecular weight of 2.4, and 5 branched chains having a length of at least 5 carbons per 0.8 carbons. Fibers extruded and cooled from a spinneret consisting of φ1.2 mm and 30 H under the same conditions are drawn at a spinning speed of 300 m / min, and continuously 2.0 times the first stage on a drawing roller 1 having a surface temperature of 20 ° C. After the stretching, the second stage 5.5-fold stretching was performed continuously on the stretching roller 2 having a surface temperature of 115 ° C. to obtain a stretched yarn. At this time, the birefringence of the fiber before stretching was 0.010, and the birefringence of the fiber after one-stage stretching was 0.030. Table 1 shows the physical properties of the obtained fiber.
[0033]
(Comparative Example 1)
The fiber obtained by extruding and cooling the high-density polyethylene of Example 1 under the same conditions is taken up at a spinning speed of 350 m / min, and continuously stretched 2.5 times in the first stage on a stretching roller 1 having a surface temperature of 100 ° C. Then, the yarn was stretched 5.1 times at the second stage on the drawing roller 2 having a surface temperature of 115 ° C. to obtain a drawn yarn. At this time, the birefringence of the fiber before stretching was 0.012, and the birefringence of the fiber after one-stage stretching was 0.033. The physical properties of the obtained fiber are shown in Table 2.
[0034]
(Comparative Example 2)
3. The same high-density polyethylene as in Example 1 was extruded from the spinneret under the same conditions, and the cooled fiber was taken up at a spinning speed of 100 m / min and continuously on the drawing roller 1 having a surface temperature of 20 ° C. After the 0-fold stretching, the second-stage 3.5-fold stretching was performed continuously on the stretching roller 2 having a surface temperature of 115 ° C. to obtain a stretched yarn. At this time, the birefringence of the fiber before stretching was 0.004, and the birefringence of the fiber after one-stage stretching was 0.018. The physical properties of the obtained fiber are shown in Table 2.
[0035]
(Comparative Example 3)
The same high-density polyethylene as in Example 1 was extruded and cooled from the spinneret under the same conditions, and the fiber was taken out at a spinning speed of 600 m / min and continuously drawn on the drawing roller 1 having a surface temperature of 20 ° C. Since it was impossible to stretch 1.2 times or more, it was stretched 1.1 times in the first stage, and then continuously in the second stage 5 on the stretching roller 2 having a surface temperature of 115 ° C. The film was drawn 8 times to obtain a drawn yarn. At this time, the birefringence of the fiber before drawing was 0.022, and the birefringence of the fiber after one-stage drawing was 0.023. The physical properties of the obtained fiber are shown in Table 2.
[0036]
(Comparative Example 4)
The same high-density polyethylene as in Example 1 was extruded from the spinneret under the same conditions and cooled, and the fiber was taken up by a spinning roller having a surface temperature of 20 ° C. and a speed of 350 m / min, and continuously on the stretching roller 1 having a surface temperature of 115 ° C. Was stretched 12.0 times to obtain a stretched yarn. The physical properties of the obtained fiber are shown in Table 2.
[0037]
(Comparative Example 5)
A high-density polyethylene having a weight average molecular weight of 121,500, a ratio of the weight average molecular weight to the number average molecular weight of 5.1, and 0.4 branched chains having a length of 5 or more carbons per 1,000 carbons. It extrudes from the spinneret which consists of (phi) 0.8mm and 30H at 270 degreeC with the speed | rate of the single hole discharge amount 0.5g / min. The extruded fiber is allowed to pass through a 5 cm heat insulation section, and then cooled by quenching at 20 ° C. and 0.5 m / s, then taken up at a spinning speed of 350 m / min, and continuously on a drawing roller 1 having a surface temperature of 20 ° C. After the first stage of 2.5-fold stretching, the second-stage 3.1-fold stretching was performed continuously on the stretching roller 2 having a surface temperature of 115 ° C. to obtain a stretched yarn. At this time, the birefringence of the fiber before stretching was 0.012, and the birefringence of the fiber after one-stage stretching was 0.034. The physical properties of the obtained fiber are shown in Table 2.
[0038]
[Table 1]

[0039]
[Table 2]

[0040]
【The invention's effect】
According to the present invention, it has become possible to produce new high-strength polyolefin fibers with high environmental productivity and with low productivity.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a manufacturing apparatus according to a manufacturing method of the present invention.
[Explanation of symbols]
1: Spinning nozzle, 2: Thermal insulation cylinder, 3: Quenching, 4: Oiling roller, 5: Spinning roller, 6: Stretching roller 1, 7: Pulling roller 1, 8: Stretching roller-2, 9: Pulling roller 2, 10 : Winding machine

Claims

A polyolefin polymer having a weight average molecular weight of 60,000 to 600,000 and a ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) of 4.5 or less is melt-spun and directly stretched under the following conditions: A process for producing a high-strength polyolefin fiber characterized by
(1) After taking up the fiber while cooling and solidifying at a ratio (draft ratio) between the take-off speed and the discharge linear speed at which the birefringence index (Δn) is 0.008 or more, (2) the surface temperature is continuously First-stage stretching is performed at a magnification at which the birefringence is 0.02 to 0.04 at a temperature equal to or lower than the crystal dispersion temperature of the unstretched fiber, and (3) the stretching is further performed at a temperature equal to or higher than the crystal dispersion temperature of the stretched fiber.

2. The high-strength polyolefin fiber according to claim 1, wherein the polyolefin polymer is polyethylene having 0.01 to 3.0 branched chains of alkyl groups having 5 or more carbon atoms per 1,000 carbon atoms. Production method.

The method for producing high-strength polyolefin fibers according to claim 1 or 2, wherein the first stage draw ratio is 1.2 times or more and the total draw ratio is 10 times or more .