JP3547986B2 - Biaxially oriented polyester film - Google Patents

Description

【０００６】
ここで、
α_ｔ （ＭＤ）；フィルム長手方向の熱膨張係数
α_ｔ （ＴＤ）；フィルム幅方向の熱膨張係数
α_ｈ （ＭＤ）；フィルム長手方向の湿度膨張係数
α_ｈ （ＴＤ）；フィルム幅方向の湿度膨張係数
Ｓ（ＭＤ）；フィルム長手方向の熱収縮率
Ｓ（ＴＤ）；フィルム幅方向の熱収縮率
である。
【０００７】
【発明の実施の形態】
本発明に用いられるポリエステルとしては、ポリエチレンテレフタレート、ポリエチレンイソフタレート、ポリブチレンテレフタレート、ポリエチレン−２，６−ナフタレート、ポリエチレン−α，β−ビス（２−クロルフェノキシ）エタン−４，４′−ジカルボキシレートなどが挙げられるが、これらのポリエステルのなかでも、ポリエチレンテレフタレート、ポリエチレン−２，６−ナフタレート、ポリエチレン−α，β−ビス（２−クロルフェノキシ）エタン−４，４′−ジカルボキシレートが好ましく、特にポリエチレン−２，６−ナフタレートが好ましい。また、本発明に用いられるポリエステルは、上記ポリエステルの１種類の単独でも、２種以上のポリエステルの共重合体や、２種以上のポリエステルの混合物であってもよい。さらに、本発明の効果を阻害しない範囲であれば、各種添加剤が添加されていても構わない。
【０００８】
本発明における二軸配向ポリエステルフィルムは、公知の方法に準じて製造することができる。例えば、ポリエチレン−２，６−ナフタレートを溶融押し出しし、好ましくは融点（Ｔｍ；℃）ないし（Ｔｍ＋７０）℃の温度で溶融押し出しし、急冷却固化して未延伸フィルムとし、さらにこの未延伸フィルムを一軸方向（縦方向または横方向）に（Ｔｇ−１０）〜（Ｔｇ＋７０）℃の温度（ただし、Ｔｇ；ポリエチレン−２，６−ナフタレートのガラス転移温度）で所定の倍率に延伸し、次いで上記延伸方向と直角方向（一段目が縦方向の場合には二段目は横方向となる）にＴｇ〜（Ｔｇ＋７０）℃の温度で所定の倍率に延伸し、さらに熱処理する方法を用いて製造することができる。その際、延伸倍率、延伸温度、熱処理条件などは、上記フィルムの特性から選択、決定される。延伸面積倍率は、好ましくは９〜２６倍、さらに好ましくは１２〜２６倍である。熱固定温度は１９０〜２５０℃、熱処理時間は１〜６０秒の範囲である。
【０００９】
以上の逐次二軸延伸法のほか、同時二軸延伸法を用いることができる。また、逐次二軸延伸法において、縦方向、横方向の延伸回数は１回に限られるものではなく、縦−横延伸を数回の延伸処理により行うことができ、その回数に限定されるものではない。例えば、さらに機械的特性を上げたい場合には、熱固定処理前の上記二軸延伸フィルムについて、（Ｔｇ＋２０）〜（Ｔｇ＋７０）℃の温度で熱処理し、さらにこの熱処理温度より１０〜４０℃高い温度で縦方向または横方向に延伸し、次いでさらに、この延伸温度より２０〜５０℃高い温度で横方向または縦方向に延伸し、縦方向の場合、総合延伸倍率を３．０〜６．０倍、横方向の場合、総合延伸倍率を３．０〜５．５倍とするのが好ましい。
【００１０】
本発明の二軸配向ポリエステルフィルムは、フィルムの長手方向の熱膨張係数αt （ＭＤ）（×１０^-6／℃）、幅方向の熱膨張係数αt （ＴＤ）（×１０^-6／℃）、長手方向の湿度膨張係数αh （ＭＤ）（×１０^-6／％ＲＨ）、幅方向の湿度膨張係数αh （ＴＤ）（×１０^-6／％ＲＨ）、６５℃で９日間保持したときの熱収縮率Ｓ（ＭＤ）（％）、同幅方向の熱収縮率Ｓ（ＴＤ）（％）が、下記式（ II ）の範囲にある必要があり、
【００１３】
【数６】

【００１４】
の範囲である。上記の値が、０．０５未満では、テープの幅方向の寸法変化が悪くなり、一方、１．０を超えると、テープの長手方向の寸法変化が悪くなり、エラーが発生し易くなるので好ましくない。
【００１５】
ポリエステルとして、ポリエチレン−２，６−ナフタレートを用いると、本発明の骨子である温度膨張係数、湿度膨張係数、６５℃で９日間保持したときの熱収縮率の関係を特定範囲にし易いという面から、本発明の効果がより一層顕著となるので好ましい。
【００１６】
本発明の二軸配向ポリエステルフィルムにおいては、フィルムの長手方向のヤング率Ｙ（ＭＤ）とフィルム幅方向のヤング率Ｙ（ＴＤ）の比、Ｙ（ＭＤ）／Ｙ（ＴＤ）が好ましくは１．４〜２．０、さらに好ましくは１．４〜１．９である。Ｙ（ＭＤ）／Ｙ（ＴＤ）の値が１．４未満では、テープの長手方向の強度が不足するためテープが伸びたりして好ましくなく、一方、２．０を超えると、一方向にかなり延伸されるため製膜性が悪く、生産性が低下し好ましくない。なお、ヤング率は、長手方向のヤング率と幅方向のヤング率の和が１，２００ｋｇ／ｍｍ^２ 以上が好ましく、さらに好ましくは１，４００ｋｇ／ｍｍ^２ 以上である。ヤング率の和が１，２００ｋｇ／ｍｍ^２ 以上であると、出力特性が向上し、ヘッドとの当たりが良くなるので好ましい。
【００１７】
また、本発明の二軸配向ポリエステルフィルムは、Ａ層およびＢ層の２層からなり、Ａ層厚みｔとＡ層中に含有される粒子の平均粒径ｄとの比ｔ／ｄが次式の範囲にあることが好ましい。
【００１８】
【数７】
１０＜ｔ／ｄ≦３０
【００１９】
ｔ／ｄの値が１０以下の場合、Ａ層中の粒子がＢ層表面を粗し、出力特性が低下し、一方、３０を超えると、Ａ層表面の粗さが著しく低下し、巻き取り性が悪化し、または粒子がフィルムから脱落しやすくなり、加工工程で削られるので好ましくない。
【００２０】
さらに、本発明の二軸配向ポリエステルフィルムは、磁気記録媒体用であって、磁性層を塗布する層の表面粗さＷＲａが好ましくは０．５〜７ｎｍ、さらに好ましくは１．０〜５．０ｎｍである。この表面粗さＷＲａが０．５ｎｍ未満では、フィルム−フィルム間の滑り性が悪化し、フィルムの巻き取り性が悪化するので好ましくなく、一方、７ｎｍを超えると、テープとしたときに、磁性面が粗化し、出力特性が低下するので好ましくない。
【００２１】
この表面粗さＷＲａは、フィルム中の不活性微粒子、例えば周期律表第ＩＩＡ，第ＩＩＢ、第ＩＶＡ、第ＩＶＢの元素を含有する無機微粒子（例えば、カオリン、アルミナ、酸化チタン、炭酸カルシウム、二酸化ケイ素など）、シリコン樹脂、架橋ポリスチレンなどの耐熱性の高い高分子よりなる微粒子などを含有させることで、あるいは、微細凹凸を形成する表面処理剤、例えば易滑塗剤のコーティング処理によって調整することができる。不活性微粒子を含有させる場合、微粒子の平均粒径は、０．０５〜０．８μｍ、さらには０．０８〜０．７μｍであることが好ましく、またこの量は、０．０５〜１．０重量％（対ポリマー）、さらには０．２〜０．６重量％（対ポリマー）であることが好ましい。
【００２２】
本発明の二軸配向ポリエステルフィルムは、全厚みが７μｍ未満、好ましくは３．０〜６．０μｍである必要がある。フィルムの全厚みが７μｍ以上となると、テープの長時間化およびカセットサイズのコンパクト化ができなくなるので好ましくない。
【００２３】
以上のような本発明の二軸配向ポリエステルフィルムは、特にデジタル記録型磁気媒体用ベースフィルムや、デジタル記録型データストレージ用途として好適である。
【００２４】
【実施例】
以下、実施例を挙げて本発明をさらに具体的に説明するが、本発明は、これらに実施例に限定されるものではない。なお、実施例中の各特性値は、下記の方法で測定した。
【００２５】
１．ヤング率
フィルムを試料幅１０ｍｍ、長さ１５ｃｍに切り、チャック間１００ｍｍにして引張速度１０ｍｍ／分、チャート速度５００ｍｍ／分でインストロンタイプの万能引張試験装置で引っ張り、得られた荷重−伸び曲線の立ち上がり部の接線より、ヤング率を計算した。
【００２６】
２．フィルム表面粗さ（ＷＲａ）
ＷＹＫＯ社製、非接触三次元粗さ計（ＴＯＰＯ−３Ｄ）を用いて、測定倍率４０倍、測定面積２４２μｍ×２３９μｍ（０．０５８ｍｍ^２ ）の条件にて測定を行い、同粗さ計の内蔵ソフトによる表面解析により、ＷＲａは以下の式により計算されたアウトプットされた値を用いた。
【００２７】
【数８】

【００２８】
ここで、Ｚ_ｊｋは、測定方向（２４２μｍ）、それと直交する方向（２３９μｍ）をそれぞれＭ分割、Ｎ分割したときのｊ番目、ｋ番目の位置における２次元粗さチャート上の高さである。
【００２９】
３．粒子の平均粒径
フィルム断面を、透過型電子顕微鏡（ＴＥＭ）を用い、１０万倍以上の倍率で観察した。ＴＥＭの切片厚さは約１００ｎｍとし、場所を変えて１００視野以上測定した。粒子の平均粒径は、重量平均径（等価円相当径）から求めた。
【００３０】
４．熱膨張係数（α_ｔ ）
フィルムのサンプルをフィルム横方向長さ１５ｍｍに切り出し、真空理工（株）製、ＴＭ−３０００にセットし、窒素雰囲気下、６０℃で３０分間、前処理し、その後、室温まで降温させ、その後、２５℃から７０℃まで２℃／分で昇温し、各温度でのサンプル長を測定し、次式より熱膨張係数（α_ｔ ）を算出した。
【００３１】
【数９】
α_ｔ ＝｛〔（Ｌ_２ −Ｌ_１ ）×１０^６ 〕／（Ｌ_１ ×△Ｔ）｝
ここで、
Ｌ_１ ；４５℃時のサンプル長（ｍｍ）
Ｌ_２ ；５５℃時のサンプル長（ｍｍ）
△Ｔ；１０（＝５５−４５℃）
である。
【００３２】
５．湿度膨張係数（α_ｈ ）
フィルムのサンプルをフィルム横方向に、長さ１５ｍｍ、幅５ｍｍに切り出し、真空理工（株）製、ＴＭ−３０００にセットし、窒素雰囲気下から、湿度２０％ＲＨ、および湿度８０％ＲＨ一定に保ち、そのときのサンプルの長さを測定し、次式より湿度膨張係数（α_ｈ ）を算出した。
【００３３】
【数１０】
α_ｈ ＝｛〔（Ｌ_２ −Ｌ_１ ）×１０^６ 〕／（Ｌ_１ ×△Ｈ）｝
ここで、
Ｌ_１ ；湿度２０％ＲＨ時のサンプル長（ｍｍ）
Ｌ_２ ；湿度８０％ＲＨ時のサンプル長（ｍｍ）
△Ｈ；６０（＝８０−２０％ＲＨ）
である。
【００３４】
６．フィルムの熱収縮率
６５℃に設定されたオーブン中の中に、あらかじめ正確な長さを測定した長さ約３０ｃｍ、幅１ｃｍのフィルムを無荷重で入れ、９日間熱処理し、その後、オーブンよりサンプルを取り出し、室温に戻してからその寸法の変化を読み取った。熱処理前の長さ（Ｌ_０ ）と熱処理による寸法変化量（ΔＬ）より、次式で熱収縮率（％）を求めた。
【００３５】
【数１１】
熱収縮率＝（ΔＬ／Ｌ_０ ）×１００
【００３６】
７．フィルム積層厚み
２次イオン質量分析装置（ＳＩＭＳ）を用いて、表層から深さ３，０００ｎｍの範囲のフィルム中の粒子のうち、最も高濃度の粒子に起因する元素とポリエステルの炭素元素の濃度比（Ｍ^＊ ／Ｃ^＊ ）を粒子濃度とし、表面から深さ３，０００ｎｍまで厚さ方向の分析を行う。表層では表面という界面のために粒子濃度は低く、表面から遠ざかるにつれて粒子濃度は高くなる。本発明のフィルムの場合は、いったん極大値となった粒子濃度がまた減少し始める。この濃度分布曲線をもとに、表面粒子濃度の極大値の１／２となる深さ（この深さは、極大値となる深さよりも深い）を求め、これを積層厚さとした。条件は、次のとおり。
【００３７】
▲１▼測定装置
２次イオン質量分析装置（ＳＩＭＳ）
ドイツ、ＡＴＯＭＩＫＡ社製、Ａ−ＤＩＤＡ３０００
▲２▼測定条件
１次イオン種；Ｏ_２ ^＋
１次イオン加速電圧；１２ＫＶ
１次イオン電流；２００ｎＡ
ラスター領域；４００μｍ□
分析領域；ゲート３０％
測定真空度；５．０×１０^−９ Ｔｏｒｒ
Ｅ−ＧＵＮ；０．５ＫＶ−３．０Ａ
【００３８】
なお、表層から深さ３，０００ｎｍの範囲に最も多く含有する粒子が有機高分子粒子の場合はＳＩＭＳでは測定が難しいので、表面からエッチングしながらＸＰＳ（Ｘ線光電子分光法）、ＩＲ（赤外分光法）などで、上記と同様のデプスプロファイルを測定し、積層厚さを求めてもよいし、電子顕微鏡などによる断面観察で、粒子濃度の変化状態やポリマーの違いによるコントラストの差から界面を認識し、積層厚さを求めることもできる。さらには、積層ポリマーを剥離後、薄膜段差測定機を用いて、積層厚さを求めることもできる。
【００３９】
８．エラーレート
メディアロジック社製、ＭＬ４５００Ｂ、ＱＩＣ用システムを用いて、下記条件でエラーレートを測定した。
Ｃｕｒｒｅｎｔ；１５．４２ｍＡ
Ｆｒｅｑｕｅｎｃｙ；０．２５ｍＨｚ
Ｌｏｃａｔｉｏｎ；０
Ｔｈｒｅｓｈｏｌｄ；４０．０
Ｂａｄ／Ｇｏｏｄ／Ｍａｘ＝１：１：１
Ｔｒａｃｋｓ；２８
なお、エラーレート数は、測定したトラック数（＝２８）の平均値で表した。
９．電磁変換特性
メディアロジック社製、ＭＬ４５００Ｂ、ＱＩＣ用システムを用いて測定した。
【００４０】
１０．削れ性（走行耐久性）
ソニー（株）製、ＥＶ−Ｓ７００を用い、走行開始、停止を繰り返しながら１００時間走行させ、走行状態を調べるとともに、出力測定を行った。このときの磁気テープの走行耐久性を下記のように判定した。
＜３段階測定＞
○；テープの端が折れたり、ワカメ状にならない。また、削れがなく白粉付着がない。
△；若干、テープの端の折れやワカメが発生したり、少量の白粉付着が見られる。
×；テープの折れやワカメの発生が著しい。また、テープ削れが著しく白粉が多量に発生する。
【００４１】
１１．巻き取り性（巻き上がり良品率）
フィルムを５００ｍｍ幅で４，０００ｍ、ロール状に１００本巻き取ったときに得られる良品数を百分率で示した。このときの良品とは、▲１▼フィルムが円筒状に巻き上げられており、角張ったり、垂れ下がったりしておらず、▲２▼フィルムロールにしわの発生がないものをいう。
【００４２】
〔実施例１〕
平均粒径０．１μｍの単分散シリカ粒子を０．２５重量％および平均粒径０．６μｍの炭酸カルシウム粒子を０．０１６重量％含有する固有粘度０．６３ｄｌ／ｇ（ｏ−クロロフェノールを溶媒として用い、２５℃で測定した値）のポリエチレン−２，６−ナフタレートを１８０℃で５時間乾燥したのち、３００℃で溶融押し出しし、６０℃に保持したキャスティングドラム上で急冷固化させて、未延伸フィルムを得た。この未延伸フィルムを速度差を持った２つのロール間で長手方向に１２０℃の温度で５．２倍延伸し、さらにテンターによって横方向に４．０倍延伸し、その後、２２０℃で１５秒間熱処理をした。このようにして、厚さ６μｍのフィルムを得て、巻き取った。
【００４３】
一方、下記に示す組成物をボールミルに入れ、１６時間混練り、分散したのち、イソシアナート化合物（バイエル社製のデスモジュールＬ）５重量部を加え、１時間高速剪断分散して磁性塗料とした。

【００４４】
この磁性塗料を、上述のポリエチレン−２，６−ナフタレートフィルムの片面に塗布厚２μｍになるように塗布し、次いで２，５００ガウスの直流磁場で配向処理を行い、１００℃で加熱乾燥後、スーパーカレンダー処理（線圧；２００ｋｇ／ｃｍ、温度；８０℃）を行い、巻き取った。この巻き取ったロールを５５℃のオーブン中に３日間放置した。さらに、下記組成のバックコート層塗料を厚さ１μｍに塗布し、乾燥させ、さらに６．３５ｍｍ（＝１／４インチ）に裁断し、磁気テープを得た。

得られたフィルムおよびテープの特性を、表１に示す。表１から明らかなように、エラーレートがなく、出力特性も良好であった。
【００４５】
〔実施例２〕
平均粒径０．３μｍのシリカ粒子を０．０１重量％および平均粒径０．０９μｍのシリカ粒子を０．３０重量％含有する固有粘度０．６２ｄｌ／ｇ（ｏ−クロロフェノールを溶媒として用い、２５℃で測定した値）のポリエチレン−２，６−ナフタレートをＡ層とし、平均粒径０．０９μｍのシリカ粒子を０．０１重量％含有する固有粘度０．６３ｄｌ／ｇ（ｏ−クロロフェノールを溶媒として用い、２５℃で測定した値）のポリエチレン−２，６−ナフタレートをＢ層として、共押し出し法により、未延伸積層フィルムを得た。得られた未延伸積層フィルムを、低速・高速のロール間で長手方向に１２０℃の温度で５．２倍延伸し、さらにテンターによって１２５℃で横方向に４．０倍延伸し、さらにステンターに供給して、２２０℃で１５秒間熱処理をし、厚さ４．５μｍ（Ａ層厚み１．１μｍ）のフィルムを得た。このフィルムに、実施例１と同様にして、Ｂ層表面に磁性塗料を、Ａ層側にバックコート層塗料を施し、裁断して、磁気テープを得た。得られたテープの特性を表１に示す。実施例１と同様に、良好な結果が得られた。
【００４６】
〔実施例３〕
平均粒径０．５μｍの架橋シリコン樹脂粒子を０．０２重量％および平均粒径０．０９μｍのアルミナ粒子を０．３重量％含有する固有粘度０．６２ｄｌ／ｇ（ｏ−クロロフェノールを溶媒として用い、２５℃で測定した値）のポリエチレンテレフタレートを、１７０℃で３時間乾燥したのち、３００℃で溶融押し出しし、２５℃に保持したキャスティングドラム上で急冷固化させて、未延伸フィルムを得た。得られた未延伸積層フィルムを、７５℃に予熱し、さらに低速・高速のロール間で１４ｍｍ上方より８３０℃の表面温度のＩＲヒーターを用いて加熱して２．２５倍に延伸し、急冷し、続いてステンターに供給し、１１０℃で幅方向に３．６倍延伸した。さらに、引き続いて１１０℃で予熱し、低速・高速のロール間で２．５倍に長手方向に延伸し、さらにステンターに供給し、２４０℃で２秒間熱固定し、厚み６．０μｍのフィルムを得た。このフィルムを用いて、実施例１と同様にして磁気テープを得た。得られたテープの特性を表１に示す。実施例１と同様に良好な結果が得られた。
【００４７】
〔実施例４〕
表１に示す架橋シリコン樹脂粒子とアルミナ粒子を含有する固有粘度０．６２ｄｌ／ｇ（ｏ−クロロフェノールを溶媒として用い、２５℃で測定した値）のポリエチレンテレフタレートをＡ層とし、表１に示すシリカ粒子を含む固有粘度０．６３ｌ／ｇのポリエチレンテレフタレートをＢ層として、共押し出し法により、未延伸積層フィルムを得た。得られた未延伸フィルムを、実施例３と同様にしてフィルムおよび磁気テープを得た。このとき、磁性層はＢ層表面に、バックコート層はＡ層表面に施した。このフィルムおよび磁気テープの特性を表１に示す。実施例１と同様に良好な結果が得られた。
【００４８】
〔比較例１〕
実施例１と同様にして、ポリエチレン−２，６−ナフタレートの未延伸フィルムを得て、得られた未延伸フィルムを、７５℃に予熱し、さらに低速・高速のロール間で１４ｍｍ上方より８３０℃の表面温度のＩＲヒーターにて加熱し、３．８倍に延伸し、急冷後、ステンターに供給し、１２０℃にて幅方向に５．２倍に延伸し、その後、２００℃で１０秒間熱固定し、厚み６μｍのフィルムを得た。また、このフィルムを用い、実施例１と同様にして磁気テープを得た。結果を表２に示す。本比較例は、上記式（１）の範囲を外れる場合であり、トラックずれによると思われるエラーレートが高い。
【００４９】
〔比較例２〕
表２に示す架橋シリコン樹脂粒子とアルミナ粒子を含有する固有粘度０．６３ｄｌ／ｇ（ｏ−クロロフェノールを溶媒として用い、２５℃で測定した値）のポリエチレン−２，６−ナフタレートを１７０℃で３時間乾燥したのち、３００℃で溶融押し出しし、２５℃に保持したキャスティングドラム上で急冷固化させて、未延伸フィルムを得た。得られた未延伸フィルムを、速度差を持った２つのロール間で長手方向に９０℃の温度で３．６倍延伸し、さらにテンターによって横方向に３．９倍延伸し、その後、２２０℃で１５秒間熱処理をし、厚さ６μｍのフィルムを得た。また、実施例１と同様にして、磁気テープを得た。このフィルムおよび磁気テープの特性を、表２に示す。上記式（Ｉ）の範囲を外れ、トラックずれによると思われるエラーレートが高く、またフィルムのヤング率が低いため、テープにしたときの耐久性およびヘッドのあたり不足によって、出力特性が悪化する結果となった。
【００５０】
〔比較例３〕
平均粒径０．３μｍのシリカ粒子を２．０重量％含有する固有粘度０．６１ｄｌ／ｇ（ｏ−クロロフェノールを溶媒として用い、２５℃で測定した値）のポリエチレンテレフタレートをＡ層とし、同様のシリカ粒子を０．１重量％含有する固有粘度０．６２ｄｌ／ｇ（ｏ−クロロフェノールを溶媒として用い、２５℃で測定した値）のポリエチレンテレフタレートをＢ層とし、比較例２と同様にして、厚さ６μｍの積層延伸フィルム（Ａ層厚み０．４μｍ）、および磁気テープを得た。得られた二軸配向積層フィルムと磁気テープの特性を、表２に示す。本比較例は、上記式（Ｉ）の範囲を外れ、トラックずれによると思われるエラーレートが高く、またｔ／ｄの値が１０以下のため、巻き取り性および走行耐久性が悪く、削れによってエラーレートが高かった。
【００５１】
【表１】

【００５２】
【表２】

【００５３】
【発明の効果】
本発明の二軸配向ポリエステルフィルムは、磁気テープなどの磁気記録媒体としたときのトラックずれなどの寸法変化によるエラーレートの発生がなく、出力特性が良く、特にデジタルデータストレージ用テープとして有用である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film useful for magnetic recording media, particularly for digital data storage.
[0002]
[Prior art]
Polyester films have excellent thermal and mechanical properties and are therefore used in a wide variety of fields such as for magnetic recording media and electrical insulation. Above all, in magnetic recording media, especially in data storage applications, tape capacity and density have been considerably increasing, and accordingly, demands on base films have become strict. In data storage applications that use the linear track method, such as QIC and DLT, the track pitch is made very narrow in order to achieve high tape capacity. There is a problem of causing a track shift and causing an error. These dimensional changes are presumed to be due to changes in temperature and humidity during tape use, and to changes in tape width and longitudinal direction caused by fluctuations in tape running tension caused by recent drive miniaturization. Is done. However, the extent to which these dimensional changes are affected by individual factors has not yet been elucidated, and is a problem in increasing the capacity of tapes.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to solve the problem of dimensional change in the longitudinal direction and the width direction, and in particular, in a digital data storage application of a linear track system, an error rate due to a track shift hardly occurs and output characteristics can be improved. It is to provide a biaxially oriented polyester film.
[0004]
[Means for Solving the Problems]
The present invention comprises a biaxially oriented polyester film having a total thickness of less than 7 μm, wherein the polyester is polyethylene-2,6-naphthalate or polyethylene terephthalate, the coefficient of thermal expansion αt (× 10 ⁻⁶ / ° C.), A biaxially oriented polyester film characterized by having a coefficient αh (× 10 ⁻⁶ /% RH) and a heat shrinkage S (%) when held at 65 ° C. for 9 days is in the range of the following formula ( II ). .
[0005]
(Equation 4)

[0006]
here,
α _t (MD); coefficient of thermal expansion in the film longitudinal direction α _t (TD); coefficient of thermal expansion in the film width direction α _h (MD); coefficient of humidity expansion in the film longitudinal direction α _h (TD); humidity in the film width direction Expansion coefficient S (MD); Heat shrinkage rate S (TD) in the longitudinal direction of the film; Heat shrinkage rate in the film width direction.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Examples of the polyester used in the present invention include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polyethylene-α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxy. And the like. Among these polyesters, polyethylene terephthalate, polyethylene-2,6-naphthalate, polyethylene-α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate are preferred. Particularly, polyethylene-2,6-naphthalate is preferred. The polyester used in the present invention may be one of the above-mentioned polyesters alone, a copolymer of two or more polyesters, or a mixture of two or more polyesters. Further, various additives may be added as long as the effects of the present invention are not impaired.
[0008]
The biaxially oriented polyester film in the present invention can be manufactured according to a known method. For example, polyethylene-2,6-naphthalate is melt-extruded, preferably melt-extruded at a temperature of melting point (Tm; ° C) to (Tm + 70) ° C, quenched and solidified to form an unstretched film. The film is stretched in a uniaxial direction (longitudinal direction or transverse direction) at a temperature of (Tg-10) to (Tg + 70) ° C. (Tg; glass transition temperature of polyethylene-2,6-naphthalate) at a predetermined magnification, and then stretched as described above. In a direction perpendicular to the direction (when the first stage is a vertical direction, the second stage is a horizontal direction), it is stretched at a predetermined magnification at a temperature of Tg to (Tg + 70) ° C., and further subjected to a heat treatment. Can be. At that time, the stretching ratio, the stretching temperature, the heat treatment conditions and the like are selected and determined from the characteristics of the film. The stretching area magnification is preferably 9 to 26 times, and more preferably 12 to 26 times. The heat setting temperature ranges from 190 to 250 ° C, and the heat treatment time ranges from 1 to 60 seconds.
[0009]
In addition to the sequential biaxial stretching method described above, a simultaneous biaxial stretching method can be used. Further, in the sequential biaxial stretching method, the number of stretching in the longitudinal direction and the transverse direction is not limited to one, and the longitudinal-lateral stretching can be performed by several stretching processes, and is limited to the number of times. is not. For example, when it is desired to further improve the mechanical properties, the biaxially stretched film before the heat-setting treatment is heat-treated at a temperature of (Tg + 20) to (Tg + 70) ° C, and is further heated at a temperature higher by 10 to 40 ° C than this heat-treating temperature. In the longitudinal or transverse direction, and then further in the transverse or longitudinal direction at a temperature 20 to 50 ° C. higher than the stretching temperature. In the case of the longitudinal direction, the total stretching ratio is 3.0 to 6.0 times. In the case of the transverse direction, the total stretching ratio is preferably 3.0 to 5.5 times.
[0010]
The biaxially oriented polyester film of the present invention has a coefficient of thermal expansion in the longitudinal direction of the film αt (MD) (× 10 ⁻⁶ / ° C.), a coefficient of thermal expansion in the width direction αt (TD) (× 10 ⁻⁶ / ° C.), Longitudinal humidity expansion coefficient αh (MD) (× 10 ⁻⁶ /% RH), width direction humidity expansion coefficient αh (TD) (× 10 ⁻⁶ /% RH), heat when held at 65 ° C. for 9 days The shrinkage ratio S (MD) (%) and the heat shrinkage ratio S (TD) (%) in the same width direction must be within the range of the following formula ( II ) ,
[0013]
(Equation 6)

[0014]
Range. If the above value is less than 0.05, the dimensional change in the width direction of the tape becomes worse, while if it exceeds 1.0, the dimensional change in the longitudinal direction of the tape becomes worse and an error easily occurs. Absent.
[0015]
When polyethylene-2,6-naphthalate is used as the polyester, the relationship between the temperature expansion coefficient, the humidity expansion coefficient, and the heat shrinkage rate when held at 65 ° C. for 9 days, which are the essence of the present invention, can be easily set to a specific range. It is preferable because the effect of the present invention becomes more remarkable.
[0016]
In the biaxially oriented polyester film of the present invention, the ratio of the Young's modulus Y (MD) in the longitudinal direction of the film to the Young's modulus Y (TD) in the film width direction, Y (MD) / Y (TD), is preferably 1. It is 4-2.0, more preferably 1.4-1.9. If the value of Y (MD) / Y (TD) is less than 1.4, the strength of the tape in the longitudinal direction is insufficient, so that the tape may be undesirably stretched. Since the film is stretched, the film forming property is poor, and the productivity is undesirably reduced. The sum of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction is preferably 1,200 kg / mm ² or more, more preferably 1,400 kg / mm ² or more. It is preferable that the sum of the Young's modulus is 1,200 kg / mm ² or more, because the output characteristics are improved and the contact with the head is improved.
[0017]
The biaxially oriented polyester film of the present invention is composed of two layers, A layer and B layer, and the ratio t / d of the thickness t of the A layer to the average particle diameter d of the particles contained in the A layer is represented by the following formula. Is preferably within the range.
[0018]
(Equation 7)
10 <t / d ≦ 30
[0019]
When the value of t / d is 10 or less, the particles in the layer A roughen the surface of the layer B, and the output characteristics are deteriorated. This is not preferable because the properties are deteriorated or the particles easily fall off the film and are cut off in the processing step.
[0020]
Furthermore, the biaxially oriented polyester film of the present invention is for a magnetic recording medium, and the surface roughness WRa of the layer on which the magnetic layer is applied is preferably 0.5 to 7 nm, more preferably 1.0 to 5.0 nm. It is. If the surface roughness WRa is less than 0.5 nm, the slipperiness between the film and the film deteriorates, and the winding property of the film deteriorates, which is not preferable. Is undesirably roughened and output characteristics deteriorate.
[0021]
This surface roughness WRa can be determined by using inert fine particles in the film, for example, inorganic fine particles containing elements of Periodic Tables IIA, IIB, IVA, and IVB (for example, kaolin, alumina, titanium oxide, calcium carbonate, and carbon dioxide). Adjustment by incorporating fine particles of high heat-resistant polymer such as silicon), silicon resin, cross-linked polystyrene, etc., or by coating with a surface treatment agent that forms fine irregularities, for example, a lubricating agent. Can be. When containing inert fine particles, the average particle size of the fine particles is preferably 0.05 to 0.8 μm, more preferably 0.08 to 0.7 μm, and the amount is 0.05 to 1.0 μm. % By weight (based on polymer), and more preferably from 0.2 to 0.6% by weight (based on polymer).
[0022]
The biaxially oriented polyester film of the present invention needs to have a total thickness of less than 7 μm, preferably 3.0 to 6.0 μm. If the total thickness of the film is 7 μm or more, it is not preferable because the length of the tape and the size of the cassette cannot be reduced.
[0023]
The biaxially oriented polyester film of the present invention as described above is particularly suitable as a base film for a digital recording type magnetic medium or as a digital recording type data storage use.
[0024]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, each characteristic value in an Example was measured by the following method.
[0025]
1. The Young's modulus film was cut into a sample having a width of 10 mm and a length of 15 cm, and pulled with an Instron-type universal tensile tester at a tensile speed of 10 mm / min and a chart speed of 500 mm / min with a chuck of 100 mm. The Young's modulus was calculated from the tangent at the rising portion.
[0026]
2. Film surface roughness (WRa)
Using a non-contact three-dimensional roughness meter (TOPO-3D) manufactured by WYKO, measurement is performed under the conditions of a measurement magnification of 40 times and a measurement area of 242 μm × 239 μm (0.058 mm ² ), and the built-in roughness meter is used. The output value calculated by the following formula was used for WRa by the surface analysis using software.
[0027]
(Equation 8)

[0028]
Here, Z _jk is the height on the two-dimensional roughness chart at the j-th and k-th positions when the measurement direction (242 μm) and the direction (239 μm) orthogonal thereto are divided into M and N, respectively.
[0029]
3. The cross section of the film having an average particle size of the particles was observed at a magnification of 100,000 or more using a transmission electron microscope (TEM). The thickness of the section of the TEM was about 100 nm, and the measurement was carried out for 100 or more visual fields at different locations. The average particle diameter of the particles was determined from the weight average diameter (equivalent circle equivalent diameter).
[0030]
4. Thermal expansion coefficient (α _t )
A film sample was cut out to a film lateral length of 15 mm, set in TM-3000 manufactured by Vacuum Riko Co., Ltd., pretreated at 60 ° C. for 30 minutes in a nitrogen atmosphere, and then cooled to room temperature. The temperature was raised from 25 ° C. to 70 ° C. at 2 ° C./min, the sample length at each temperature was measured, and the coefficient of thermal expansion (α _t ) was calculated from the following equation.
[0031]
(Equation 9)
α _t = {[(L ₂ −L ₁ ) × 10 ⁶ ] / (L ₁ × {T)}
here,
L ₁ ; sample length at 45 ° C. (mm)
L ₂ ; sample length at 55 ° C (mm)
ΔT; 10 (= 55-45 ° C.)
It is.
[0032]
5. Humidity expansion coefficient (α _h )
A film sample was cut out in the lateral direction of the film into a length of 15 mm and a width of 5 mm, and set on a TM-3000 manufactured by Vacuum Riko Co., Ltd., and kept at a constant humidity of 20% RH and 80% RH under a nitrogen atmosphere. The length of the sample at that time was measured, and the humidity expansion coefficient (α _h ) was calculated from the following equation.
[0033]
(Equation 10)
α _h = {[(L ₂ −L ₁ ) × 10 ⁶ ] / (L ₁ × {H)}
here,
L ₁ : Sample length at 20% RH (mm)
L ₂ : sample length at 80% RH (mm)
ΔH; 60 (= 80-20% RH)
It is.
[0034]
6. A film with a length of about 30 cm and a width of 1 cm, whose exact length was measured in advance, was placed in an oven set at a heat shrinkage of 65 ° C without any load, heat-treated for 9 days, and then sampled from the oven Was taken out and returned to room temperature, and the change in its dimensions was read. From the length (L ₀ ) before the heat treatment and the dimensional change (ΔL) due to the heat treatment, the heat shrinkage (%) was determined by the following equation.
[0035]
(Equation 11)
Heat shrinkage = (ΔL / L ₀ ) × 100
[0036]
7. Using a film lamination thickness secondary ion mass spectrometer (SIMS), the concentration ratio of the element attributable to the highest concentration particle to the carbon element of the polyester among the particles in the film having a depth of 3,000 nm from the surface layer. (M ^* / C ^* ) is defined as the particle concentration, and the analysis is performed in the thickness direction from the surface to a depth of 3,000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film according to the invention, the particle concentration, which once reached a maximum, starts to decrease again. Based on this concentration distribution curve, a depth at which the maximum value of the surface particle concentration was 1/2 (this depth was deeper than the depth at which the maximum value was reached) was obtained, and this was defined as the lamination thickness. The conditions are as follows.
[0037]
(1) Measuring device Secondary ion mass spectrometer (SIMS)
A-DIDA3000, manufactured by ATOMIKA, Germany
(2) Measurement conditions Primary ion species; O ₂ ⁺
Primary ion acceleration voltage; 12 KV
Primary ion current; 200 nA
Raster area: 400 μm □
Analysis area; gate 30%
Measurement vacuum degree: 5.0 × 10 ⁻⁹ Torr
E-GUN; 0.5KV-3.0A
[0038]
In addition, when the particles most contained in the range of 3,000 nm in depth from the surface layer are organic polymer particles, it is difficult to measure by SIMS. Therefore, XPS (X-ray photoelectron spectroscopy) and IR (infrared Spectroscopy) may be used to measure the same depth profile as above to determine the lamination thickness, or to observe the cross-section using an electron microscope or the like to determine the interface from the change in particle concentration or the difference in contrast due to the difference in polymer. It is also possible to recognize and determine the lamination thickness. Furthermore, after the laminated polymer is peeled off, the laminated thickness can be determined by using a thin film step measuring device.
[0039]
8. Error Rate The error rate was measured under the following conditions using a ML4500B, QIC system manufactured by Medialogic.
Current; 15.42 mA
Frequency; 0.25 mHz
Location; 0
Threshold; 40.0
Bad / Good / Max = 1: 1: 1
Tracks; 28
The number of error rates was represented by an average value of the measured number of tracks (= 28).
9. Electromagnetic conversion characteristics Measured using a system for QIC, ML4500B, manufactured by MediaLogic.
[0040]
10. Sharpness (running durability)
Using an EV-S700 manufactured by Sony Corporation, the vehicle was run for 100 hours while repeatedly starting and stopping the running, and the running state was examined and the output was measured. The running durability of the magnetic tape at this time was determined as follows.
<Three-step measurement>
；: The end of the tape is not broken or wakame. Also, there is no scraping and no white powder adhesion.
Δ: Slight breakage of the tape end or wakame occurs, and a small amount of white powder adhered.
X: Tape breakage and wakame generation are remarkable. In addition, tape scraping is remarkable and a large amount of white powder is generated.
[0041]
11. Rewindability (Rolling up good product rate)
The number of non-defective products obtained when 100 films were wound in a roll shape at 4,000 m in a width of 500 mm was shown in percentage. The non-defective product at this time means that (1) the film is wound up in a cylindrical shape, is not angular or hanging, and (2) has no wrinkles on the film roll.
[0042]
[Example 1]
0.25% by weight of monodisperse silica particles having an average particle diameter of 0.1 μm and 0.016% by weight of calcium carbonate particles having an average particle diameter of 0.6 μm, and an intrinsic viscosity of 0.63 dl / g (o-chlorophenol is dissolved in a solvent) Polyethylene-2,6-naphthalate) was dried at 180 ° C for 5 hours, melt-extruded at 300 ° C, and quenched and solidified on a casting drum kept at 60 ° C. A stretched film was obtained. This unstretched film is stretched 5.2 times in the longitudinal direction at a temperature of 120 ° C. between two rolls having a speed difference, further stretched 4.0 times in a transverse direction by a tenter, and then at 220 ° C. for 15 seconds. Heat treatment was performed. Thus, a film having a thickness of 6 μm was obtained and wound up.
[0043]
On the other hand, the composition shown below was placed in a ball mill, kneaded and dispersed for 16 hours, and then 5 parts by weight of an isocyanate compound (Desmodur L, manufactured by Bayer AG) was added. .

[0044]
This magnetic paint is applied to one side of the above-mentioned polyethylene-2,6-naphthalate film so as to have a coating thickness of 2 μm, then subjected to an orientation treatment in a DC magnetic field of 2,500 gauss, and dried by heating at 100 ° C. A super calender treatment (linear pressure; 200 kg / cm, temperature; 80 ° C.) was performed, and the film was wound. The wound roll was left in an oven at 55 ° C. for 3 days. Further, a backcoat layer paint having the following composition was applied to a thickness of 1 μm, dried, and further cut to 6.35 mm (= 1/4 inch) to obtain a magnetic tape.

Table 1 shows the properties of the obtained film and tape. As is clear from Table 1, there was no error rate and the output characteristics were good.
[0045]
[Example 2]
An intrinsic viscosity of 0.62 dl / g containing 0.01% by weight of silica particles having an average particle diameter of 0.3 μm and 0.30% by weight of silica particles having an average particle diameter of 0.09 μm (using o-chlorophenol as a solvent, Layer A of polyethylene-2,6-naphthalate (measured at 25 ° C.) having an intrinsic viscosity of 0.63 dl / g (o-chlorophenol containing 0.01% by weight of silica particles having an average particle size of 0.09 μm). An unstretched laminated film was obtained by a co-extrusion method using polyethylene-2,6-naphthalate (value measured at 25 ° C. as a solvent) as a layer B. The obtained unstretched laminated film is stretched 5.2 times at a temperature of 120 ° C. in the longitudinal direction between low-speed and high-speed rolls, and further stretched 4.0 times in the transverse direction at 125 ° C. by a tenter. The film was supplied and heat-treated at 220 ° C. for 15 seconds to obtain a film having a thickness of 4.5 μm (A layer thickness: 1.1 μm). In the same manner as in Example 1, this film was coated with a magnetic paint on the layer B surface and a backcoat layer paint on the layer A side, and cut to obtain a magnetic tape. Table 1 shows the properties of the obtained tape. As in Example 1, good results were obtained.
[0046]
[Example 3]
An intrinsic viscosity of 0.62 dl / g (containing o-chlorophenol as a solvent) containing 0.02% by weight of crosslinked silicone resin particles having an average particle diameter of 0.5 μm and 0.3% by weight of alumina particles having an average particle diameter of 0.09 μm Polyethylene terephthalate (measured at 25 ° C.) was dried at 170 ° C. for 3 hours, melt-extruded at 300 ° C., and quenched and solidified on a casting drum maintained at 25 ° C. to obtain an unstretched film. . The obtained unstretched laminated film is preheated to 75 ° C., further stretched 2.25 times by heating using an IR heater having a surface temperature of 830 ° C. from 14 mm above between low-speed and high-speed rolls, and quenched. Subsequently, it was supplied to a stenter and stretched 3.6 times in the width direction at 110 ° C. Further, the film is subsequently preheated at 110 ° C., stretched 2.5 times in the longitudinal direction between low-speed and high-speed rolls, further supplied to a stenter, and heat-set at 240 ° C. for 2 seconds to form a film having a thickness of 6.0 μm. Obtained. Using this film, a magnetic tape was obtained in the same manner as in Example 1. Table 1 shows the properties of the obtained tape. Good results were obtained as in Example 1.
[0047]
[Example 4]
A layer of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g (measured at 25 ° C. using o-chlorophenol as a solvent) containing the crosslinked silicon resin particles and alumina particles shown in Table 1 is shown in Table 1. An unstretched laminated film was obtained by co-extrusion using polyethylene terephthalate having an intrinsic viscosity of 0.63 l / g containing silica particles as a layer B. A film and a magnetic tape were obtained from the obtained unstretched film in the same manner as in Example 3. At this time, the magnetic layer was applied to the surface of the layer B, and the back coat layer was applied to the surface of the layer A. Table 1 shows the characteristics of the film and the magnetic tape. Good results were obtained as in Example 1.
[0048]
[Comparative Example 1]
In the same manner as in Example 1, an unstretched film of polyethylene-2,6-naphthalate was obtained, and the obtained unstretched film was preheated to 75 ° C., and further 830 ° C. between the low-speed and high-speed rolls by 14 mm above. Is heated by an IR heater having a surface temperature of 3.8, stretched 3.8 times, quenched, supplied to a stenter, stretched 5.2 times in the width direction at 120 ° C, and then heated at 200 ° C for 10 seconds. It was fixed to obtain a film having a thickness of 6 μm. Using this film, a magnetic tape was obtained in the same manner as in Example 1. Table 2 shows the results. In this comparative example, the value is out of the range of the above equation (1), and the error rate considered to be due to track deviation is high.
[0049]
[Comparative Example 2]
Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.63 dl / g (measured at 25 ° C. using o-chlorophenol as a solvent) containing cross-linked silicon resin particles and alumina particles shown in Table 2 at 170 ° C. After drying for 3 hours, the mixture was melt-extruded at 300 ° C. and rapidly cooled and solidified on a casting drum maintained at 25 ° C. to obtain an unstretched film. The obtained unstretched film is stretched 3.6 times in the longitudinal direction at a temperature of 90 ° C. between two rolls having a speed difference, further stretched 3.9 times in a transverse direction by a tenter, and then 220 ° C. For 15 seconds to obtain a film having a thickness of 6 μm. Further, a magnetic tape was obtained in the same manner as in Example 1. Table 2 shows the characteristics of the film and the magnetic tape. As a result of deviating from the range of the above formula (I), the error rate considered to be due to the track deviation is high, and the Young's modulus of the film is low. It became.
[0050]
[Comparative Example 3]
A layer made of polyethylene terephthalate having an intrinsic viscosity of 0.61 dl / g (measured at 25 ° C. using o-chlorophenol as a solvent) containing 2.0% by weight of silica particles having an average particle diameter of 0.3 μm, and In the same manner as in Comparative Example 2, polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g (a value measured at 25 ° C. using o-chlorophenol as a solvent) containing 0.1% by weight of silica particles was used as the B layer. Then, a laminated stretched film having a thickness of 6 μm (layer A thickness 0.4 μm) and a magnetic tape were obtained. Table 2 shows the properties of the obtained biaxially oriented laminated film and the magnetic tape. This comparative example is out of the range of the above formula (I), has a high error rate which is considered to be due to track deviation, and has a value of t / d of 10 or less. Error rate was high.
[0051]
[Table 1]

[0052]
[Table 2]

[0053]
【The invention's effect】
The biaxially oriented polyester film of the present invention has no error rate due to dimensional change such as track deviation when used as a magnetic recording medium such as a magnetic tape, has good output characteristics, and is particularly useful as a tape for digital data storage. .

Claims (6)

It consists of a biaxially oriented polyester film having a total thickness of less than 7 μm, wherein the polyester is polyethylene-2,6-naphthalate or polyethylene terephthalate, and has a coefficient of thermal expansion α _t (× 10 ⁻⁶ / ° C.) and a coefficient of humidity expansion α _h (× 10 ⁻⁶ /% RH), a biaxially oriented polyester film having a heat shrinkage S (% ) in the range of the following formula ( II ) when held at 65 ° C. for 9 days.

here,
α _t (MD); coefficient of thermal expansion in the film longitudinal direction α _t (TD); coefficient of thermal expansion in the film width direction α _h (MD); coefficient of humidity expansion in the film longitudinal direction α _h (TD); humidity in the film width direction Expansion coefficient S (MD); Thermal shrinkage rate S (TD) in the film longitudinal direction; Thermal shrinkage rate in the film width direction. The ratio of the longitudinal Young's modulus of the film Y (MD) and width direction of the film a Young's modulus Y (TD) Y (MD) / Y (TD) is in the range of 1.4 to 2.0 according to claim 1 Symbol placement Biaxially oriented polyester film. The film according to claim 1 or 2, wherein the film is composed of two layers, an A layer and a B layer, and the ratio t / d between the thickness t of the A layer and the average particle diameter d of the particles contained in the A layer is in the range of the following formula . The biaxially oriented polyester film according to claim 1.
[Equation 3]
10 <t / d ≦ 30 The biaxially oriented polyester film according to any one of claims 1 to 4, which is for a magnetic recording medium and has a surface roughness WRa of 0.5 to 7 nm on a layer on which a magnetic layer is applied. The biaxially oriented polyester film according to any one of claims 1 to 4, which is used for a digital recording type magnetic medium. The biaxially oriented polyester film according to claim 5 , which is used for data storage.