JP3581593B2 - Laminated biaxially oriented polyester film - Google Patents

Description

【００２７】
ここで、Ａは芳香族基又は脂肪族基、Ｘ_１ 及びＸ_２ はそれぞれ同一若しくは異なるエステル形成性官能基又は水素原子、Ｒ_１ 、Ｒ_２ 、Ｒ_３ 及びＲ_４ はそれぞれアルキル基及びアリール基よりなる群から選ばれた同一又は異なる基、ｎは正の整数である。
【００２８】
上記スルホン酸４級ホスホニウム塩の好ましい具体例としては、３，５―ジカルボキシベンゼンスルホン酸テトラブチルホスホニウム塩、３，５―ジカルボキシベンゼンスルホン酸テトラフェニルホスホニウム塩、３，５―ジカルボメトキシベンゼンスルホン酸テトラブチルホスホニウム塩、３，５―ジカルボメトキシベンゼンスルホン酸テトラフェニルホスホニウム塩、３―カルボキシベンゼンスルホン酸テトラブチルホスホニウム塩、３，５―ジ（β―ヒドロキシエトキシカルボニル）ベンゼンスルホン酸テトラブチルホスホニウム塩、４―ヒドロキシエトキシベンゼンスルホン酸テトラブチルホスホニウム塩、ビスフェノールＡ―３，３′―ジ（スルホン酸テトラブチルホスホニウム塩）、２，６―ジカルボキシナフタレン―４―スルホン酸テトラブチルホスホニウム等をあげることができる。一種のみを単独で用いても二種以上併用してもよい。また上記スルホン酸４級ホスホニウム塩はベースポリマーのポリエステル鎖に結合しているか遊離しているかは限定されない。従ってポリエステルを重合する際スルホン酸４級ホスホニウム塩化合物を共存させて、ポリエステルの重合体鎖中に含有せしめたり、ポリエステルを押出機に投入して溶融押出しする際に、スルホン酸４級ホスホニウム塩化合物も同時に投入して溶融混練して製造するなど上記スルホン酸４級ホスホニウム塩の含有方法は特に限定されない。
【００２９】
上記ポリエステルは、それ自体公知であり、かつそれ自体公知の方法で製造することができる。
【００３０】
上記ポリエステルとしては、ｏ―クロロフェノール中の溶液として３５℃で測定して求めた固有粘度が０．４〜０．９のものが好ましく、０．５〜０．７のものがさらに好ましく、０．５１〜０．６５のものが特に好ましい。
【００３１】
本発明の積層二軸配向ポリエステルフィルムは、ポリエステル層Ａとポリエステル層Ｂの２層より構成される。２層のポリエステルは同じものでも違ったものでもよいが、同じものが好ましい。
【００３２】
本発明における積層二軸配向ポリエステルフィルムは、自身の屑フィルムを自己回収できる自己循環回収可能な、両面の表面粗さに差のある積層ポリエステルフィルムであって、回収ポリマーをポリエステルＢ層を構成するポリマーの一部に使用することができる。
【００３３】
本発明における積層二軸配向ポリエステルフィルムは、ポリエステルＡ層の上にポリエステルＢ層を積層になる積層二軸配向ポリエステルフィルムであって、次式（１）〜（３）の関係を満足している必要がある。
【００３４】
【数４】
ＷＲａ（Ｂ）＞ＷＲａ（Ａ） ……（１）
（ｔ_Ｂ ／ｔ）×１００＝１５〜５０（％） ……（２）
１０＜ｔ_Ｂ ／ｄ_Ｂ ≦４５ ……（３）
ここで、ＷＲａ（Ａ）：ポリエステルＡ層の表面粗さ（ｎｍ）
ＷＲａ（Ｂ）：ポリエステルＢ層の表面粗さ（ｎｍ）
ｔ_Ａ ：ポリエステルＡ層の厚み（μｍ）
ｔ_Ｂ ：ポリエステルＢ層の厚み（μｍ）
ｔ ：フィルムの全厚み （μｍ）
ｄ_Ｂ ：ポリエステルＢ層に含有された滑剤全粒子の平均粒径（μｍ）
である。
【００３５】
さらに、前記ポリエステルＢ層のポリマーは、回収した積層ポリエステルフィルムによるポリマー、好ましくは積層ポリエステルフィルムの製造時に副生した要回収フィルムのポリマー（自己回収したポリマー）を含んでいる必要がある。
【００３６】
積層二軸配向ポリエステルフィルムの製造において、自己回収したポリマーをポリエステルＡ層、すなわち平坦層に使用すると、巻取性付与のため粗面層（ポリエステルＢ層）に含有させた大きな滑剤がポリエステルＡ層に入ることになり、このため平坦層（ポリエステルＡ層）に高突起が形成され、電磁変換特性が悪化し、高密度磁気記録媒体のベースフィルムとしては適さなくなる。
【００３７】
本発明において、ｔ_Ｂ ／ｔ×１００の値が１５％未満であると、積層ポリエステルフィルムを自己回収したポリマーをポリエステルＢ層に回収できる比率が小さくなり（回収ポリマーの滑剤組成はポリエステルＢ層の滑剤組成より、平坦層の分、うすまっているため、滑剤添加量の濃度の濃い新しいポリマー（バージンポリマー）を補い、組成補正する必要があり、結果として回収比率は１５％未満よりさらに小さくなる）、積層二軸配向ポリエステルフィルムとしてのコストが高くなり、市場参入への適用範囲が狭くなり、好ましくない。
【００３８】
一方、（ｔ_Ｂ ／ｔ）×１００の値が５０％を超えると、平坦層（ポリエステルＡ層）が薄くなるため粗面層（ポリエステルＢ層）に含有される滑剤の影響が平坦層（ポリエステルＡ層）に及ぼし、平坦面が粗くなり、磁性面を粗す結果となり、電磁変換特性が悪くなる。特に磁性層の厚みが薄い、より高密度磁気記録媒体では、この平坦面の粗面化の影響が電磁変換特性を悪くし、該高密度磁気記録媒体のベースフィルムとして適さなくなる。
【００３９】
本発明において、ｔ_Ｂ ／ｄ_Ｂ の比は１０〜４５である必要がある。この比（ｔ_Ｂ ／ｄ_Ｂ ）が１０未満、すなわち粗面層の厚みを薄くしすぎた場合、あるいは粗面層に含有される滑剤粒子の平均粒径を大きくしすぎた場合、前者については粗面層に回収できる回収ポリマー量が少なくなり、フィルムの製造コストアップとなり、市場投入への適用範囲が狭くなり、好ましくない。また、後者の場合、粗面層に含まれる大きな滑剤粒子が平坦層に影響し、平坦面が粗面化となり、電磁変換特性が悪化し、高密度磁気記録媒体のベースフィルムとしては好ましくない。
【００４０】
一方、ｔ_Ｂ ／ｄ_Ｂ の比が４５を超えると、すなわち粗面層の厚みに対し、粗面層に含まれる滑剤粒子の平均粒径が小さすぎると、粗面層に形成される突起が低くなりすぎ、充分な巻取性が得られなくなる。
【００４１】
本発明における粗面層（ポリエステルＢ層）に含まれる滑剤は単成分系でも多成分系でも良いが、好ましくは少なくとも平均粒径の異なる２種の滑剤を含有している多成分系が好ましい。さらに好ましくは電磁変換特性を悪化させない範囲で、中粒子を少量添加し、すべり性を付与するため小粒子を中粒子より多く添加させた多成分系である。単成分系では小粒子を用いた場合、十分なエアースクイズ性が得られず、巻取性、ハンドリング性が不足し、また中〜大粒子を用いた場合は添加量を多くした場合、電磁変換特性が低下し、また少ないとフィルムの滑り性が不足し、単成分系では両者の特性を両立させることが難しくなる。
【００４２】
上記積層二軸配向ポリエステルフィルムに含有される滑剤は耐熱性高分子粒子および／または球状シリカ粒子が好ましい。中粒子が耐熱性高分子粒子、小粒子が球状シリカ粒子からなることがさらに好ましい。この耐熱性高分子粒子としては、例えば架橋ポリスチレン樹脂粒子、架橋シリコーン樹脂粒子、架橋アクリル樹脂粒子、架橋スチレン―アクリル樹脂粒子、架橋ポリエステル粒子、ポリイミド粒子、メラミン樹脂粒子等が挙げられる。この中でも架橋ポリスチレン樹脂粒子や架橋シリコーン樹脂粒子を含有させると、本発明の効果が一層顕著となるので好ましい。
【００４３】
上記した耐熱性高分子粒子や球状シリカ粒子を用いることにより、ポリエステルとの親和性の良い、また比較的そろった大きさの突起が形成され、フィルムの滑り性、耐削れ性が良くなり、また電磁変換特性も良くなる。
【００４４】
本発明における積層二軸配向ポリエステルフィルムは、少なくとも粗面層（ポリエステルＢ層）に滑剤を含有するが、該粗面層には該積層二軸配向ポリエステルフィルムの製造時に副生する要回収フィルムのポリマー（回収したポリマー）を一部含有することが好ましい。この回収ポリマーの使用、すなわち自己循環回収ポリマーの使用は、例えば図１に示すとおりである。図１で、ポリエステルＢ層は、積層フィルムを自己回収したポリマー（回収ポリマー：回収チップ）とバージンポリマー（バージンチップ）からなり、ポリエステルＡ（平坦面層）はバージンポリマー（バージンチップ）からなる。
【００４５】
このとき、ポリエステルＢ層の滑剤ｉの最終組成は、ポリエステルＡ層の厚みｔ_Ａ 、ポリエステルＢ層の厚みｔ_Ｂ 、ポリエステルＡ層に用いるバージンチップ中の滑剤ｉの組成Ｃ_Ａｉ、ポリエステルＢ層に用いるバージンチップ中の滑剤ｉの組成Ｃ_Ｖｉ、および回収ポリマーの比率Ｒに関係し、次式より計算される組成であることが好ましい。すなわち、ポリエステルＢ層の滑剤ｉの最終組成がこの式から計算される組成であれば、自己循環回収は可能であり、異なる場合には自己循環回収はできなくなる。
【００４６】
【数５】
Ｃ_Ｂｉ＝（Ｃ_Ａｉ× ｔ_Ａ ×Ｒ ＋１００× Ｃ_ｖｉ×（ｔ_Ｂ −（ｔ_Ａ ＋ｔ_Ｂ ） ×Ｒ／１００））／（ｔ_Ｂ ×（１００−Ｒ））
ここで、ｔ_Ａ ：ポリエステルＡ層の厚み（μｍ）
ｔ_Ｂ ：ポリエステルＢ層の厚み（μｍ）
Ｃ_Ａｉ：ポリエステルＡ層に用いる滑剤ｉのバージンチップ中の滑剤ｉの組成（ｗｔ％）
Ｃ_Ｂｉ：ポリエステルＢ層中の滑剤ｉの最終組成（ｗｔ％）
Ｃ_Ｖｉ：ポリエステルＢ層に用いるバージンチップ中の、滑剤ｉの組成（ｗｔ％）
Ｒ ：回収ポリマーの比率（％）
である。
【００４７】
図１における回収ポリマー（回収チップ）には、また、滑剤ｉの組成、ポリエステルＡ層とポリエステルＢ層の厚み構成比が同じで、全体厚みが製品ポリエステルフィルムと異なる回収積層ポリエステルフィルムを用いることもできる。また、図１における粗面層（ポリエステルＢ層）のポリマー固有粘度は、平坦面層（ポリエステルＡ層）のポリマー固有粘度より小さいことが製造コストの点から好ましいが、場合によってはポリエステルＢ層に用いるバージンポリマーの固有粘度をポリエステルＡ層の固有粘度より高目にし、回収ポリマーの比率、固有粘度等と調整して同じ値にもっていくこともできる。
【００４８】
上記積層二軸配向ポリエステルフィルムは、ポリエステルＡ層には１種以上の滑剤を、またポリエステルＢ層には２種以上の滑剤を添加した系が好ましいが、本発明はこれに限定されず、ポリエステルＡ層に滑剤を添加しない系、またポリエステルＢ層が１種の滑剤系からなり、上記式を満たす積層二軸配向ポリエステルフィルムであるなら、特に限定されない。
【００４９】
本発明におけるポリエステルとしては、ポリエチレンテレフタレート又はポリエチレン―２，６―ナフタレートが好ましい。特に、厚みが６μｍ以下で高いヤング率が求められる二軸配向フィルムを得るには、ポリエチレン―２，６―ナフタレートがより好ましい。
【００５０】
本発明において積層二軸配向ポリエステルフィルムの粗面層および平坦層の表面粗さは特に限定されないが、高密度磁気記録媒体、特に高密度デジタル記録媒体用のベースフィルムとして用いる場合、ポリエステルＡ層面の表面粗さ（ＷＲａ（Ａ））は１〜５ｎｍが好ましく、さらに好ましくは１〜４ｎｍ、特に好ましくは２〜４ｎｍである。ＷＲａ（Ａ）が５ｎｍを超えると、十分な電磁変換特性が得られなくなる。一方、ＷＲａ（Ａ）が１ｎｍ未満では、フィルムの滑り性が悪くなり、十分なスリット歩留りが得られなくなる。また、フィルムあるいはテープ製造工程での平坦面とパスロール系での滑り性が悪くなり、搬送性不良により工程シワが発生し、製品の歩留りを大きく低下させるようになる。
【００５１】
また、粗面層のＷＲａ（Ｂ）は５〜２０ｎｍが好ましく、さらに好ましくは７〜１７ｎｍ、特に好ましくは９〜１５ｎｍである。ＷＲａ（Ｂ）が５ｎｍ未満ではフィルムの滑り性が悪く、十分なスリット歩留りが得られない。一方、ＷＲａ（Ｂ）が２０ｎｍを超えると、平坦面側への突起の突出しの影響が大きくなり、平坦面が粗面化し、十分な電磁変換特性が得られなくなる。
【００５２】
本発明における積層二軸配向ポリエステルフィルムは、縦方向および横方向のヤング率がそれぞれ４５０〜２０００ｋｇ／ｍｍ^２ で、両者の比（縦／横）が０．３〜２．５であることが好ましい。さらに好ましくは、縦方向および横方向のヤング率はそれぞれ５００〜１２００ｋｇ／ｍｍ^２ であり、さらに好ましくはそれぞれ６００〜９００ｋｇ／ｍｍ^２ である。また、両者の比（横／縦）は好ましくは０．４〜２．０であり、特に好ましくは０．６〜１．６である。
【００５３】
フィルムの縦方向のヤング率が４５０ｋｇ／ｍｍ^２ 未満であると、磁気テープの縦方向の強度が弱くなり、磁気記録装置にかけられたとき縦方向に強い力がかかると容易に破断してしまう。また横方向のヤング率が４５０ｋｇ／ｍｍ^２ 未満であると、磁気テープの横方向の強度が弱くなり、テープと磁気ヘッドとの当たりが弱くなり、満足し得る電磁変換特性が得られない。一方、縦方向あるいは横方向のヤング率が２０００ｋｇ／ｍｍ^２ を超えると、フィルム製膜時、延伸倍率が高くなり、フィルム破断が多発し、製品歩留りが著しく悪くなる。
【００５４】
また、縦ヤング率と横ヤング率の比が０．３未満であると、十分な磁気テープの縦方向の強度が得られなくなり、磁気記録装置にかけたとき、縦方向に強い力がかかるとテープ切断が多発する。一方、縦ヤング率と横ヤング率の比が２．５を超えると、十分な磁気テープの横方向の強度が得られず、テープを走行させた場合、テープエッジに損傷が発生し、満足し得る耐久性が得られない。
【００５５】
なお、上記縦ヤング率と横ヤング率の比は、リニアー方式の磁気記録媒体用ベースとして用いる場合は０．９〜２．５、またヘリカル方式の磁気記録媒体用ベースとして用いる場合は０．３〜１．０であることがより好ましい。
【００５６】
また、本発明における積層二軸配向ポリエステルフィルムの全体の厚みは特に限定されないが、高密度磁気記録媒体ベースフィルムとして用いる場合、全体の厚みは３〜１０μｍが好ましい。さらに好ましくは４〜９μｍ、特に好ましくは４〜７μｍである。この厚みが１０μｍを超えると、カセットにいれられる磁気テープの長さが短くなり、十分な記録容量が得られない。一方、３μｍ未満ではフィルム製膜時にフィルム破断が多発し、またフィルムの巻取性が悪くなり、歩留りが大きく低下する。
【００５７】
本発明における積層二軸配向ポリエステルフィルムは、従来から知られている、あるいは当業界に蓄積されている方法に準じて製造することができる。例えば、先ず未配向積層フィルムを製造し、次いで該フィルムを二軸配向させることで得ることができる。この未配向積層フィルムは、従来から蓄積された積層フィルムの製造法で製造することができる。例えば、粗面を形成するポリエステル層と、反対面（平坦面）を形成するポリエステル層とを、ポリエステルの溶融状態または冷却固化された状態で積層する方法を用いることができる。さらに具体的には、例えば共押し出し、エクストルージョンラミネート等の方法で製造できる。
【００５８】
上記の方法で得られる未配向積層フィルムは、さらに従来から蓄積された二軸配向フィルムの製造法に準じて、積層二軸配向フィルムとすることができる。例えば、融点（Ｔｍ：℃）乃至（Ｔｍ＋７０）℃の温度でポリエステルを溶融・共押出しして未延伸積層フィルムを得、該未延伸積層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（但し、Ｔｇ：ポリエステルのガラス転移温度）で２．５倍以上、好ましくは３倍以上の倍率で延伸し、次いで上記延伸方向と直角方向にＴｇ〜（Ｔｇ＋７０）℃の温度で２．５倍以上、好ましくは３倍以上の倍率で延伸するのが好ましい。さらに必要に応じて縦方向および／または横方向に再度延伸してもよい。このようにして、全延伸倍率は、面積延伸倍率として９倍以上が好ましく、１２〜３５倍がさらに好ましく、１５〜３０倍が特に好ましい。さらにまた、二軸配向フィルムは（Ｔｇ＋７０）℃〜（Ｔｍ−１０）℃の温度で熱固定することができ、例えば１８０〜２５０℃で熱固定するのが好ましい。熱固定時間は１〜６０秒が好ましい。
【００５９】
本発明における積層二軸配向ポリエステルフィルムは、スルホン酸４級ホスホニウム塩を０．０２〜４５ｍｍｏｌ％含有し、かつフィルムの交流体積抵抗率が１×１０^６ Ω・ｃｍ〜９×１０^８ Ω・ｃｍであることが、より好ましい。すなわち、スルホン酸４級ホスホニウム塩を上記範囲内で含有させることにより、製膜時、ピニング性が良くなり、高速化製膜が可能となる。
【００６０】
本発明の積層二軸配向ポリエステルフィルムは、高密度磁気記録媒体または高密度デジタル記録媒体（データカートリッジ、デジタル方式のビデオテープ等）用のベースフィルムとして好ましく用いられる。
【００６１】
なお、本発明における種々の物性値および特性は、以下の如く測定されたものであり、かつ定義される。
【００６２】
（１）粒子の平均粒径（ＤＰ）
フィルム表面からポリエステルをプラズマ低温灰化処理法（例えばヤマト科学製Ｐ３−３型）で除去し、粒子を露出させる。処理条件はポリエステルは灰化されるが粒子はダメージを受けない条件を選択する。これをＳＲＭ（走査型電子顕微鏡）で観察し、粒子の画像（粒子によってできる光の濃淡）をイメージアナライザーに結び付け、観察箇所を変えて粒子数５０００個以上で次の数値処理を行いそれに式（４）によって求めた数平均粒径ｄを平均粒径とする。
【００６３】
【数６】
ｄ＝Σｄｉ／ｎ ……（４）
ここで、ｄｉは粒子の円相当径（μｍ）、ｎは個数である。
サンプルをポリエステルは溶解するが粒子は溶解しない溶媒を用いて溶解し、溶液から粒子を遠心分離し、粒子の全体量に対する比率（重量％）をもって粒子含有量とする。
【００６４】
（２）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３０００ｎｍまでの範囲のフィルム中の粒子の内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３０００ｎｍ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。そして一旦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層粒子濃度が極大値の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、これを表層厚さとする。
【００６５】
条件は次の通りである。
▲１▼測定装置
２次イオン質量分析装置（ＳＩＭＳ）
▲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 ：６．０×１０^−３Ｔｏｒｒ
Ｅ―ＧＵＮ ：０．５ＫＶ―３．０Ａ
なお、表層から深さ３０００ｎｍ迄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）などで上記同様のデブスプロファイルを測定し表層厚さを求めてもよい。
【００６６】
（３）フィルム全体の厚み
ゴミの入らないようにしてフィルムを１０枚重ね、打点式電子マイクロメータにて厚みを測定し、１枚当たりのフィルム厚みを計算する。
【００６７】
（４）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／分の条件でインストロンタイプの万能引張試験装置にて引っ張る。得られる荷重―伸び曲線の立ち上がり部の接線よりヤング率を計算する。
【００６８】
（５）電磁変換特性
下記市販の機器を用いて、周波数７．４ＭＨＺの信号を記録し、その再生信号の６．４ＭＨＺと７．４ＭＨＺの値の比をそのテープのＣ／Ｎとし、実施例３のＣ／ＮをＯｄＢとし、相対値で表し、次のように判定した。
◎：＋３ｄＢ以上
○：＋１〜＋３ｄＢ
×：＋１ｄＢ未満
使用した機器
８ｍｍビデオレコーダー：ソニー（株）製ＥＤＶ―６０００
Ｃ／Ｎ測定：シバソク（株）製ノイズメータ
【００６９】
（６）スリット歩留り
フィルムをスリットし、幅７００ｍｍ、長さ７０００ｍでロールに２０本以上巻いた時のスリット歩留りを求め、下記により判定する。
スリット歩留り
◎：９０％以上
○：７０〜９０％未満
×：７０％未満
【００７０】
（７）表面粗さ（ＷＲａ）
ＷＹＣＯ社製、非接触式三次元粗さ計（ＮＴ−２０００）を用いて、測定倍率２５倍、測定面積２４７μｍ×１８８μｍ（０．０４６ｍｍ^２ ）の条件にて、測定数（ｎ）１０以上で測定を行い、該粗さ計に内蔵され表面解析ソフトにより、中心面平均粗さ（ＷＲａ）を求める。
（Ａ）中心面平均粗さ（ＷＲａ）
下記式により計算され、アウトプットされた値である。
【００７１】
【数７】

【００７２】
Ｚ_ｊｋはＸ軸方向（２４７μｍ）、それと直行するＹ軸方向（１８８μｍ）をそれぞれＭ分割、Ｎ分割したときの各方向のｊ番目、ｋ番目の位置に於けるＸ、Ｙ平面における直行するＺ軸方向の高さである。
【００７３】
（８）フィルムコスト
回収ポリマーの比率より、次のように判定した。
◎：回収比率（Ｒ）が５０％以上
○：回収比率（Ｒ）が３０％以上〜５０％未満
△：回収比率（Ｒ）が１０％以上〜３０％未満
×：回収比率（Ｒ）が１０％未満
【００７４】
（９）フィルムの摩擦係数
重ね合わせた２枚のフィルムの下側に固定したガラス板を置き、重ね合わせたフィルムの下側（ガラス板と接しているフィルム）のフィルムを低速ロールにて引取り（約１０ｃｍ／分）、上側のフィルムの一端（下側フィルムの引取り方向と逆端）に検出器を固定してフィルム／フィルム間のスタート時の引張力を検出する。尚、そのときに用いるスレッドは重さ１ｋｇ、下側面積１００ｃｍ^２ のものを使用する。
なお摩擦係数（μｓ）は次式より求めた。
【００７５】
【数８】

【００７６】
（１０）体積抵抗率の測定
溶融フィルムの体積抵抗率の測定は、図２に示す装置を用いて測定する。測定サンプル１は厚さ約１５０μｍのフィルムを用いる。直径２０ｃｍの円柱状下部電極２の上面に、１５０μｍの平行な隙間が保持できる直径５．６ｃｍ、厚さ０．２ｃｍの上部電極３を配し、この間に測定サンプルが電極と密着するようにして挿入する。
【００７７】
下部電極２は加電装置４と温度検出端５を内蔵し、下部電極の表面温度の測定面におけるバラツキが１℃以内、検出端部分との温度差が昇温速度８℃／分において２℃以内となるように構成する。なお、検出温度は読取温度計７で測定する。電極の全体は保温箱１１中に配置する。
【００７８】
電源１８はその発生電圧を標準抵抗９を介して両電極間に印加するが、該電源はフィルムの直流体積抵抗率を測定する場合は１００Ｖの直流を発生する電源であって、フィルムの交流体積抵抗率を測定する場合は１００Ｖ、５０Ｈｚを発生する電源である。この回路に流れる電流は標準抵抗の両端に発生する電圧を、内部インピーダンスが１００ＭΩ以上のエレトロンメーター１０で読取る。
【００７９】
フィルム状ポリマーの交流体積抵抗率の測定は、上記装置により、下部電極の昇温測速度が８℃／分、該電極はポリマーのＤＳＣによる融点＋３０℃の温度にて行ない、交流体積抵抗率Ｚは、印加電圧Ｅ、電流Ｉ、電極面積Ｓ、電極間隔ｄより次式で求められる。
【００８０】
【数９】

【００８１】
【実施例】
以下、実施例を挙げて本発明をさらに説明する。
【００８２】
［実施例１］
ジメチル―２，６―ナフタレートとエチレングリコールとを、エステル交換触媒として酢酸マンガンを、重合触媒として三酸化アンチモンを、安定剤として亜燐酸を、さらに滑剤として表１に示す添加粒子を添加して常法により重合し、固有粘度（ｏ―クロロフェノール、３５℃）０．６１の平坦層（Ａ層）用のバージンチップを得た。一方、粗面層（Ｂ層）用チップは表１に示す回収率で自身の積層フィルムの回収チップと表１に示すバージンチップで補い、粗面層（Ａ層）用チップとした。またＡ層、Ｂ層用バージンチップにはスルホン酸４級ホスホニウム塩化合物を２ｍｍｏｌ％含有させた。
【００８３】
これらＡ層用およびＢ層用のポリマーをそれぞれ、１７０℃で６時間乾燥させた。こうして、乾燥チップを表１に示した層厚み構成になるような比率にて、２台の押出機ホッパーに供給し、溶融温度２８０〜３００℃で溶融し、マルチマニホールド型共押出ダイを用いてＡ層の片側にＢ層を積層させ、表面仕上げ０．３Ｓ程度、表面温度６０℃の回転冷却ドラム上に押出し、厚み２１２μｍの積層未延伸フィルムを得た。
【００８４】
この積層未延伸フィルムの交流体積抵抗率は４×１０^８ Ω・ｃｍであった。
【００８５】
このようにして得られた積層未延伸フィルムを１２０℃に予熱し、さらに低速、高速のロール間で１５ｍｍ上方より９００℃の表面温度のＩＲヒーターにて加熱して５．１倍に延伸し、急冷し、続いてステンターに供給し、１４５℃にて横方向に４．９倍に延伸した。得られた二軸延伸フィルムを２１０℃の熱風で４秒間熱固定し、厚み４．５μｍの積層二軸配向ポリエステルフィルムを得た。これらのフィルムのヤング率は縦方向８００ｋｇ／ｍｍ^２ 、横方向６５０ｋｇ／ｍｍ^２ であった。
【００８６】
また、この積層二軸配向ポリエステルフィルムの片面（Ａ層）に下記磁気塗料を塗布厚０．２μｍとなるように塗布し、次いで２５００ガウスの直流磁場中で配向処理を行い、１００℃で加熱乾燥後、スーパーカレンダー処理（線圧３００ｋｇ／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日間保持した後、８ｍｍ幅に裁断して磁気テープを得た。
【００８７】
磁気塗料の調製：
下記に示す組成物をボールミルに入れ、１６時間混練、分散させた後、イソシアネート化合物（バイエル社製のデスモジュール）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。
【００８８】
磁性塗料の組成：
針状Ｆｅ粒子 １００重量部
塩化ビニル―酢酸ビニル共重合体 １５重量部
（積水化学製エスレック７Ａ）
熱可塑性ポリウレタン樹脂 ５重量部
酸化クロム ５重量部
カーボンブラック ５重量部
レシチン ２重量部
脂肪酸エステル １重量部
トルエン ５０重量部
メチルエチルケトン ５０重量部
シクロヘキサノン ５０重量部
得られた磁気テープについて、上記測定方法により電磁変換特性を測定した。結果は表１に示す。
【００８９】
［実施例２〜８、比較例１〜４］
添加する滑剤粒子、層厚み構成、回収ポリマー比率およびヤング率を表１に示すように変更するほかは実施例１と同様にして積層フィルムを得た。なおヤング率を得るため実施例２については、縦方向の延伸倍率を５．１倍、横方向の延伸倍率を４．９倍に、実施例４〜６、比較例１〜４では縦方向の延伸倍率を５．２倍、横方向の延伸倍率を３．９倍に、実施例３では縦方向の延伸倍率を４．８倍、横方向の延伸倍率を５．２倍、実施例７では縦方向の延伸倍率３．５倍、横方向の延伸倍率５．８倍に、また実施例８では縦方向の延伸倍率４．０倍、横方向の延伸倍率５．４倍にした。
【００９０】
次に、得られた積層二軸配向ポリエステル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。各特性の測定結果は表１に示すとおりであった。
【００９１】
表１から明らかなように本発明によるものは優れた電磁変換特性、優れた巻取性を有し、かつコストメリットに優れた高密度磁気記録媒体として優れた特性を有する積層二軸配向ポリエステルフィルムであった。
【００９２】
【表１】

【００９３】
【発明の効果】
本発明によれば、高密度磁気記録媒体として優れた電磁変換特性を有し、巻取性にも優れ、またコストメリット的にも優れた特性を兼ね備えた積層二軸配向ポリエステルフィルムを提供することができる。このフィルムは高密度磁気記録媒体用ベースフィルムとして、特にデジタル記録方式のビデオテープあるいはデータストレージ用テープとして有用である。
【図面の簡単な説明】
【図１】自己循環回収の方法を示す説明図である。
【図２】溶融ポリマーの体積抵抗率を測定する装置の模式図である。
【符号の説明】
１：ポリマー
２：下部電極
３：上部電極
４：加電装置
５：温度検出端
６：電流計
７：読取温度計
８：電源
９：標準抵抗
１０：エレクトロンメーター
１１：保温箱[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laminated biaxially oriented polyester film. More specifically, the laminated biaxially oriented polyester film is a laminated film that is capable of self-circulation recovery, has excellent electromagnetic characteristics as a base film for high-density magnetic recording media, and also has excellent winding and handling properties as a base film. About.
[0002]
[Prior art]
A biaxially oriented polyester film represented by a polyethylene terephthalate film has been used for a wide range of applications, particularly as a base film for magnetic recording media, because of its excellent physical and chemical properties.
[0003]
In recent years, higher density and higher capacity of magnetic recording media have been promoted, and accordingly, flatness and thinner thickness of a base film have been demanded. However, when the surface of the base film is flattened to maintain excellent electromagnetic conversion characteristics, slipperiness is insufficient, for example, when rolled up in a roll form, wrinkles or blocking occurs, and the surface of the film roll becomes uneven. Therefore, the appropriate range of tension, contact pressure, and speed at the time of lowering the product yield or winding up becomes narrow, and it becomes very difficult to wind up. Also, in the film processing step, if the slipperiness is poor, the friction between the metal roll and the metal roll in contact increases, and shavings are generated, which causes a loss of the magnetic recording signal, that is, a dropout.
[0004]
Generally, to improve the slipperiness of a polyester film, (i) a method of precipitating inactive particles from a catalyst residue in a raw material polymer in a production process, and (ii) a method of adding inert particles to a film surface, etc. Has been adopted. Generally, the larger the size and the greater the content of the particles in these films, the greater the improvement in the slipperiness.
[0005]
On the other hand, as described above, the surface of the base film is required to be as flat as possible from the viewpoint of improving the electromagnetic conversion characteristics. If the surface roughness of the base surface is rough, when the magnetic recording medium is processed, surface irregularities of the base film protrude from the surface of the magnetic layer even after the application of the magnetic layer, thereby deteriorating the electromagnetic conversion characteristics. In this case, as the size and the content of the particles in the base film are larger, the surface roughness becomes coarser, and the electromagnetic conversion characteristics are deteriorated.
[0006]
As described above, as means for achieving both contradictory characteristics of improvement in winding property and improvement in electromagnetic conversion characteristics, by forming a laminated film, the surface on which the magnetic layer is applied is flattened to improve the electromagnetic conversion characteristics, Means for improving the slipperiness by roughening the opposite surface are widely known.
[0007]
In this case, the flat layer on the surface to be coated with the magnetic layer is flattened by using a lubricant with small particles or by reducing the amount of addition, while the rough surface on the opposite side (running surface side) where the magnetic layer is not coated is used. The surface layer is roughened by using a lubricant having a large particle size or increasing the amount of the lubricant added.
[0008]
That is, the flat layer on the application surface side and the rough surface layer on the running surface side differ greatly in the characteristics of the lubricant used, for example, the type of lubricant, the particle size, the amount added, and the like.
[0009]
In the case of a single-layer film, the film waste generated in the film manufacturing process is collected and re-chipped, and the film can be manufactured again, especially in the case of the laminated film. However, in the case of the laminated film, the collected chip of the laminated film itself has a lubricant composition. Since the lubricant composition of the rough surface layer and the flat layer is also different, when re-inputted into the production of the laminated film, the lubricant composition of the re-inputted layer changes, and the film properties are disturbed.
[0010]
On the other hand, recently, it has been proposed that such a collected chip of a laminated film is put into an intermediate layer (core layer) of a three-layer laminated film and reused.
[0011]
However, in this method, in addition to the collected chips of the three-layer laminated film itself, the thickness of the intermediate layer part must be large enough to collect the collected chips of the laminated film. Need to be a fairly thick film. Further, those containing a lubricant having a large particle size or containing a large amount of a lubricant affect the formation of projections on the surface layer even when used in the intermediate portion, so that the use thereof is limited.
[0012]
Also, as described above, recent magnetic recording media are required to have higher density and higher capacity, and the base film is required to be thinner and thinner. It is substantially difficult to re-inject the collected chips of the laminated film into the intermediate layer of the three-layer laminated film.
[0013]
Therefore, it is the present situation that such collected chips of the laminated film are forced to be discarded, which leads to an increase in the cost of the film. Although such waste films are treated as industrial waste, it is becoming more difficult in the future.
[0014]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a laminated biaxially oriented polyester film which can be used as a base film for a high-density magnetic recording medium having self-recycling recovery, excellent winding properties, excellent handling properties, and excellent electromagnetic characteristics. .
[0015]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve such a problem, and as a result, used a recovered polymer for a part of the polymer forming the rough layer of the laminated film, and made the thickness of the rough layer smaller than the thickness of the flat layer. By setting the ratio of the average particle size of the lubricant contained in the thickness of the rough surface layer and the rough surface layer to a specific range, a polymer obtained by collecting a waste film generated during the production of the laminated film is used as the recovered polymer, That is, they were able to be recovered by self-circulation, and found that the laminated film had excellent electromagnetic conversion characteristics as a base film for a high-density magnetic recording medium, and was also excellent in winding property, leading to the present invention. .
[0016]
That is, the present invention relates to a laminated biaxially oriented polyester film in which a polyester B layer is laminated on a polyester A layer, wherein the film satisfies the following formulas (1) to (3), and A laminated biaxially oriented polyester film, characterized in that the polymer of the layer contains the polymer of the recovered laminated polyester film.
[0017]
(Equation 3)
WRa (B)> WRa (A) (1)
(T_B/ T) × 100 = 15 to 50 (%) (2)
10 <t_B/ D_B≤45 ... (3)
Here, WRa (A): surface roughness of the polyester A layer (nm)
WRa (B): Surface roughness of the polyester B layer (nm)
t_A: Thickness of polyester A layer (μm)
t_B: Thickness of polyester B layer (μm)
t: Total thickness of the film (μm)
d_B: Average particle size (μm) of all particles of lubricant contained in polyester B layer
It is.
[0018]
More preferably, the laminated biaxially oriented polyester film described above, wherein the polymer of the polyester B layer contains a polymer obtained by self-recovering the laminated polyester film.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
The polyester in the present invention is an aromatic polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyesters are substantially linear and have film-forming properties, especially film-forming properties by melt molding.
[0020]
Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, and anthracene dicarboxylic acid. Can be. Examples of the aliphatic glycol include a polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, and decamethylene glycol, and an alicyclic group such as cyclohexanedimethanol. Diols and the like can be mentioned.
[0021]
As such a polyester, a polyester containing alkylene terephthalate or alkylene naphthalate as a main component is preferably used. Among them, not only polyethylene terephthalate and polyethylene-2,6-naphthalate, but also, for example, 80 mol% or more of all dicarboxylic acid components are terephthalic acid or 2,6-naphthalenedicarboxylic acid, and 80 mol% or more of all glycol components. Is particularly preferred. At that time, not more than 20 mol% of the total acid component can be the above-mentioned aromatic dicarboxylic acids other than terephthalic acid or 2,6-naphthalenedicarboxylic acid, and alicyclic dicarboxylic acids such as adipic acid and sebacic acid. An alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid; Further, 20 mol% or less of the total glycol component can be the above-mentioned glycol other than ethylene glycol. For example, aromatic diols such as hydroquinone, resorcin, and 2,2-bis (4-hydroxyphenyl) propane; Aliphatic diols having an aromatic ring such as dihydroxydimethylbenzene; polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like.
[0022]
In the polyester of the present invention, for example, a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid or an aliphatic oxyacid such as ω-hydroxycaproic acid, a dicarboxylic acid component and an oxycarboxylic acid component. And those which are copolymerized or bonded at 20 mol% or less based on the total amount of
[0023]
Further, the polyester in the present invention may contain a tricarboxylic or polyfunctional polycarboxylic acid or a polyhydroxy compound such as trimellitic acid in an amount in a substantially linear range, for example, an amount of 2 mol% or less based on the total acid components. And pentaerythritol and the like.
[0024]
Further, the polyester in the present invention preferably contains a quaternary phosphonium salt compound of sulfonic acid in an amount of 0.02 to 45 mmol% (based on the acid component of the polyester). When the content is less than 0.02 mmol%, the effect of increasing the casting speed is small, and when the content exceeds 45 mmol%, the discharge function of the discharge electrode when the film is electrostatically adhered is deteriorated with time. Is not preferred. According to this content, the AC volume resistivity of the molten film is 1 × 10⁶Ω · cm ~ 9 × 10⁸Ω · cm. This AC volume resistivity is 9 × 10⁸When it exceeds Ω · cm, the effect of increasing the casting speed is small.⁶If it is less than Ω · cm, it is not preferable because dielectric breakdown of the film may occur during electrostatic adhesion in the casting process.
[0025]
The sulfonic acid quaternary phosphonium salt is a compound represented by the following formula.
[0026]
Embedded image

[0027]
Here, A is an aromatic group or an aliphatic group, X₁And X₂Are the same or different ester-forming functional groups or hydrogen atoms,₁, R₂, R₃And R₄Are the same or different groups selected from the group consisting of an alkyl group and an aryl group, respectively, and n is a positive integer.
[0028]
Preferred specific examples of the quaternary phosphonium salt of sulfonic acid include tetrabutylphosphonium salt of 3,5-dicarboxybenzenesulfonic acid, tetraphenylphosphonium salt of 3,5-dicarboxybenzenesulfonic acid, and 3,5-dicarbomethoxybenzene. Tetrabutylphosphonium sulfonic acid salt, Tetraphenylphosphonium 3,5-dicarbomethoxybenzenesulfonic acid salt, Tetrabutylphosphonium salt of 3-carboxybenzenesulfonic acid, Tetrabutyl 3,5-di (β-hydroxyethoxycarbonyl) benzenesulfonate Phosphonium salt, 4-hydroxyethoxybenzenesulfonate tetrabutylphosphonium salt, bisphenol A-3,3'-di (tetrabutylphosphonium sulfonate), 2,6-dicarboxynaphthalene-4-sulfate Phosphate tetrabutylphosphonium like. One kind may be used alone, or two or more kinds may be used in combination. The quaternary phosphonium salt of sulfonic acid is not limited whether it is bonded to or free from the polyester chain of the base polymer. Therefore, when polymerizing a polyester, a quaternary phosphonium salt compound of sulfonic acid is allowed to coexist and be contained in a polymer chain of the polyester, or when a polyester is injected into an extruder and melt-extruded, a quaternary phosphonium salt compound of sulfonic acid is used. The method for containing the above quaternary phosphonium sulfonic acid salt is not particularly limited, for example, the quaternary phosphonium salt of the sulfonic acid is added at the same time and melt-kneaded.
[0029]
The polyesters are known per se and can be produced by a method known per se.
[0030]
The above-mentioned polyester preferably has an intrinsic viscosity of 0.4 to 0.9, more preferably 0.5 to 0.7, measured at 35 ° C. as a solution in o-chlorophenol, and more preferably 0.5 to 0.7. Particularly preferred are those having a diameter of .51 to 0.65.
[0031]
The laminated biaxially oriented polyester film of the present invention is composed of two layers, a polyester layer A and a polyester layer B. The two layers of polyester may be the same or different, but the same is preferred.
[0032]
The laminated biaxially oriented polyester film in the present invention is a laminated polyester film having a difference in surface roughness on both sides, which is capable of self-recycling and recovering its own waste film, and the recovered polymer constitutes a polyester B layer. Can be used for some of the polymers.
[0033]
The laminated biaxially oriented polyester film in the present invention is a laminated biaxially oriented polyester film in which a polyester B layer is laminated on a polyester A layer, and satisfies the following expressions (1) to (3). There is a need.
[0034]
(Equation 4)
WRa (B)> WRa (A) (1)
(T_B/ T) × 100 = 15 to 50 (%) (2)
10 <t_B/ D_B≤45 ... (3)
Here, WRa (A): surface roughness of the polyester A layer (nm)
WRa (B): Surface roughness of the polyester B layer (nm)
t_A: Thickness of polyester A layer (μm)
t_B: Thickness of polyester B layer (μm)
t: Total thickness of the film (μm)
d_B: Average particle size (μm) of all particles of lubricant contained in polyester B layer
It is.
[0035]
Further, the polymer of the polyester B layer needs to include a polymer of the recovered laminated polyester film, preferably a polymer of a film to be recovered which is by-produced during the production of the laminated polyester film (self-recovered polymer).
[0036]
In the production of the laminated biaxially oriented polyester film, when the self-recovered polymer is used for the polyester A layer, that is, the flat layer, the large lubricant contained in the rough surface layer (polyester B layer) for imparting the winding property is changed to the polyester A layer. As a result, high protrusions are formed on the flat layer (polyester A layer), and the electromagnetic conversion characteristics are deteriorated, so that it is not suitable as a base film of a high-density magnetic recording medium.
[0037]
In the present invention, t_BIf the value of / t × 100 is less than 15%, the ratio of the polymer that self-collected the laminated polyester film to the polyester B layer becomes small (the lubricant composition of the recovered polymer is smaller than that of the polyester B layer, Therefore, it is necessary to supplement a new polymer (virgin polymer) with a high concentration of a lubricant additive amount and correct the composition, resulting in a recovery ratio of less than 15%.) The cost as a polyester film is increased, and the range of application to market entry is reduced, which is not preferable.
[0038]
On the other hand, (t_BIf the value of (/ t) × 100 exceeds 50%, the flat layer (polyester A layer) becomes thin, so the effect of the lubricant contained in the rough surface layer (polyester B layer) affects the flat layer (polyester A layer). As a result, the flat surface becomes rough and the magnetic surface becomes rough, resulting in poor electromagnetic conversion characteristics. In particular, in the case of a higher density magnetic recording medium having a thin magnetic layer, the effect of the roughening of the flat surface deteriorates the electromagnetic conversion characteristics and is not suitable as a base film of the higher density magnetic recording medium.
[0039]
In the present invention, t_B/ D_BShould be 10-45. This ratio (t_B/ D_B) Is less than 10, that is, when the thickness of the rough surface layer is too thin, or when the average particle size of the lubricant particles contained in the rough surface layer is too large, the former can be recovered in the rough surface layer. The amount is small, the production cost of the film is increased, and the range of application to the market is narrowed, which is not preferable. In the latter case, large lubricant particles contained in the rough layer affect the flat layer, the flat surface becomes rough, and the electromagnetic conversion characteristics deteriorate, which is not preferable as a base film of a high-density magnetic recording medium.
[0040]
On the other hand, t_B/ D_BIf the ratio exceeds 45, that is, if the average particle size of the lubricant particles contained in the rough surface layer is too small relative to the thickness of the rough surface layer, the projections formed in the rough surface layer will be too low, and sufficient winding It is no longer possible to obtain ease.
[0041]
The lubricant contained in the rough surface layer (polyester B layer) in the present invention may be a single component system or a multicomponent system, but is preferably a multicomponent system containing at least two lubricants having different average particle diameters. More preferably, it is a multi-component system in which a small amount of medium particles is added in a range that does not deteriorate the electromagnetic conversion characteristics and small particles are added more than the medium particles in order to impart slipperiness. In a single component system, when small particles are used, sufficient air squeezing property cannot be obtained, winding property and handling property are insufficient, and when medium to large particles are used, the amount of addition is increased, electromagnetic conversion If the properties are deteriorated, and if the content is too small, the slipperiness of the film becomes insufficient, and it is difficult to achieve both properties in a single component system.
[0042]
The lubricant contained in the laminated biaxially oriented polyester film is preferably heat-resistant polymer particles and / or spherical silica particles. More preferably, the medium particles are made of heat-resistant polymer particles and the small particles are made of spherical silica particles. Examples of the heat-resistant polymer particles include cross-linked polystyrene resin particles, cross-linked silicone resin particles, cross-linked acrylic resin particles, cross-linked styrene-acryl resin particles, cross-linked polyester particles, polyimide particles, melamine resin particles, and the like. Among these, it is preferable to include crosslinked polystyrene resin particles or crosslinked silicone resin particles, since the effects of the present invention become more remarkable.
[0043]
By using the above-mentioned heat-resistant polymer particles or spherical silica particles, projections having a good affinity for polyester and a relatively uniform size are formed, and the slipperiness and abrasion resistance of the film are improved, and Electromagnetic conversion characteristics are also improved.
[0044]
The laminated biaxially oriented polyester film of the present invention contains a lubricant in at least the roughened layer (polyester B layer). It is preferable to partially contain a polymer (recovered polymer). The use of the recovered polymer, that is, the use of the self-circulating recovered polymer is, for example, as shown in FIG. In FIG. 1, the polyester B layer is composed of a polymer obtained by self-recovering the laminated film (recovered polymer: recovered chip) and a virgin polymer (virgin chip), and the polyester A (flat surface layer) is composed of a virgin polymer (virgin chip).
[0045]
At this time, the final composition of the lubricant i of the polyester B layer is determined by the thickness t of the polyester A layer._A, Polyester B layer thickness t_B, Composition C of lubricant i in virgin tip used for polyester A layer_AiComposition of lubricant i in virgin chips used for polyester B layer_Vi, And the ratio R of the recovered polymer, and is preferably a composition calculated by the following equation. That is, if the final composition of the lubricant i of the polyester B layer is a composition calculated from this formula, self-circulation recovery is possible, and if different, self-circulation recovery is not possible.
[0046]
(Equation 5)
C_Bi= (C_Ai× t_A× R + 100 × C_vi× (t_B− (T_A+ T_B) × R / 100)) / (t_B× (100-R))
Where t_A: Thickness of polyester A layer (μm)
t_B: Thickness of polyester B layer (μm)
C_Ai: Composition of lubricant i in virgin chip of lubricant i used for polyester A layer (wt%)
C_Bi: Final composition of lubricant i in polyester B layer (wt%)
C_Vi: Composition (wt%) of lubricant i in virgin chip used for polyester B layer
R: ratio of recovered polymer (%)
It is.
[0047]
For the recovered polymer (recovered chip) in FIG. 1, a recovered laminated polyester film having the same composition of the lubricant i and the same thickness composition ratio of the polyester A layer and the polyester B layer but having a different overall thickness from the product polyester film may be used. it can. The polymer intrinsic viscosity of the rough surface layer (polyester B layer) in FIG. 1 is preferably smaller than the polymer intrinsic viscosity of the flat surface layer (polyester A layer) from the viewpoint of manufacturing cost. The intrinsic viscosity of the virgin polymer used may be higher than the intrinsic viscosity of the polyester A layer, and adjusted to the same value by adjusting the ratio of the recovered polymer, the intrinsic viscosity, and the like.
[0048]
The laminated biaxially oriented polyester film is preferably a system in which one or more lubricants are added to the polyester A layer and two or more lubricants are added to the polyester B layer. However, the present invention is not limited to this. The system is not particularly limited as long as it is a system in which a lubricant is not added to the layer A, and the polyester bilayer is a laminated biaxially oriented polyester film which satisfies the above formula, which is composed of one type of lubricant system.
[0049]
As the polyester in the present invention, polyethylene terephthalate or polyethylene-2,6-naphthalate is preferable. In particular, to obtain a biaxially oriented film having a thickness of 6 μm or less and requiring a high Young's modulus, polyethylene-2,6-naphthalate is more preferable.
[0050]
In the present invention, the surface roughness of the rough surface layer and the flat layer of the laminated biaxially oriented polyester film is not particularly limited, but when used as a base film for a high-density magnetic recording medium, particularly a high-density digital recording medium, the polyester A layer surface The surface roughness (WRa (A)) is preferably from 1 to 5 nm, more preferably from 1 to 4 nm, particularly preferably from 2 to 4 nm. If WRa (A) exceeds 5 nm, sufficient electromagnetic conversion characteristics cannot be obtained. On the other hand, if WRa (A) is less than 1 nm, the film has poor slipperiness, and a sufficient slit yield cannot be obtained. In addition, the smoothness between the flat surface and the pass roll system in the film or tape manufacturing process is deteriorated, and wrinkles are caused due to poor transportability, thereby greatly reducing the product yield.
[0051]
Further, WRa (B) of the rough surface layer is preferably 5 to 20 nm, more preferably 7 to 17 nm, and particularly preferably 9 to 15 nm. If WRa (B) is less than 5 nm, the film has poor slipperiness, and a sufficient slit yield cannot be obtained. On the other hand, when WRa (B) exceeds 20 nm, the influence of the protrusion of the protrusion on the flat surface side becomes large, the flat surface becomes rough, and sufficient electromagnetic conversion characteristics cannot be obtained.
[0052]
The laminated biaxially oriented polyester film of the present invention has a Young's modulus in the longitudinal direction and the transverse direction of 450 to 2000 kg / mm, respectively.²It is preferable that the ratio (length / width) of both is 0.3 to 2.5. More preferably, the Young's modulus in the longitudinal direction and the transverse direction are each 500 to 1200 kg / mm.²And more preferably 600 to 900 kg / mm, respectively.²It is. The ratio (horizontal / vertical) is preferably 0.4 to 2.0, and particularly preferably 0.6 to 1.6.
[0053]
The Young's modulus of the film in the longitudinal direction is 450 kg / mm²If it is less than 7, the strength of the magnetic tape in the longitudinal direction is weakened, and the magnetic tape is easily broken when a strong force is applied in the longitudinal direction when applied to a magnetic recording device. The Young's modulus in the lateral direction is 450 kg / mm²If it is less than 1, the strength of the magnetic tape in the lateral direction is weakened, the contact between the tape and the magnetic head is weakened, and satisfactory electromagnetic conversion characteristics cannot be obtained. On the other hand, the Young's modulus in the vertical or horizontal direction is 2000 kg / mm²Exceeding the film thickness, the draw ratio becomes high during film formation, the film breaks frequently, and the product yield is remarkably deteriorated.
[0054]
If the ratio of the longitudinal Young's modulus to the transverse Young's modulus is less than 0.3, sufficient strength in the longitudinal direction of the magnetic tape cannot be obtained. Frequent disconnection. On the other hand, if the ratio of the longitudinal Young's modulus to the transverse Young's modulus exceeds 2.5, sufficient strength in the transverse direction of the magnetic tape cannot be obtained, and when the tape is run, the tape edge is damaged, and the tape is not satisfactory. The obtained durability cannot be obtained.
[0055]
The ratio of the vertical Young's modulus to the horizontal Young's modulus is 0.9 to 2.5 when used as a base for a linear magnetic recording medium, and 0.3 when used as a base for a helical magnetic recording medium. More preferably, it is 1.0.
[0056]
The total thickness of the laminated biaxially oriented polyester film in the present invention is not particularly limited, but when used as a high-density magnetic recording medium base film, the total thickness is preferably 3 to 10 μm. More preferably, it is 4 to 9 μm, particularly preferably 4 to 7 μm. If the thickness exceeds 10 μm, the length of the magnetic tape to be inserted into the cassette becomes short, and a sufficient recording capacity cannot be obtained. On the other hand, if the thickness is less than 3 μm, the film is frequently broken during film formation, the winding property of the film is deteriorated, and the yield is greatly reduced.
[0057]
The laminated biaxially oriented polyester film in the present invention can be produced according to a conventionally known method or a method accumulated in the art. For example, it can be obtained by first producing an unoriented laminated film and then biaxially orienting the film. This unoriented laminated film can be produced by a conventionally accumulated method for producing a laminated film. For example, a method of laminating a polyester layer forming a rough surface and a polyester layer forming an opposite surface (flat surface) in a molten state or a cooled and solidified state of the polyester can be used. More specifically, it can be manufactured by a method such as co-extrusion or extrusion lamination.
[0058]
The unoriented laminated film obtained by the above method can be further made into a laminated biaxially oriented film according to a conventionally accumulated method for producing a biaxially oriented film. For example, polyester is melted and co-extruded at a temperature of melting point (Tm: ° C) to (Tm + 70) ° C to obtain an unstretched laminated film, and the unstretched laminated film is uniaxially (longitudinal or transverse) (Tg- 10) to (Tg + 70) ° C. (however, Tg: glass transition temperature of polyester) at a stretching ratio of 2.5 times or more, preferably 3 times or more, and then Tg to (Tg + 70) in a direction perpendicular to the stretching direction. It is preferred that the film is stretched at a temperature of at least 2.5 times, preferably at least 3 times. Further, if necessary, the film may be stretched again in the machine direction and / or the cross direction. As described above, the total stretching ratio is preferably 9 times or more, more preferably 12 to 35 times, particularly preferably 15 to 30 times as the area stretching ratio. Furthermore, the biaxially oriented film can be heat-set at a temperature of (Tg + 70) ° C. to (Tm−10) ° C., and is preferably heat-set at, for example, 180 to 250 ° C. The heat setting time is preferably 1 to 60 seconds.
[0059]
The laminated biaxially oriented polyester film of the present invention contains 0.02 to 45 mmol% of a quaternary phosphonium salt of sulfonic acid and has an AC volume resistivity of 1 × 10 4.⁶Ω · cm ~ 9 × 10⁸More preferably, it is Ω · cm. That is, by containing the quaternary phosphonium salt of sulfonic acid in the above range, the pinning property is improved during film formation, and high-speed film formation is possible.
[0060]
The laminated biaxially oriented polyester film of the present invention is preferably used as a base film for high-density magnetic recording media or high-density digital recording media (such as data cartridges and digital video tapes).
[0061]
The various physical properties and characteristics in the present invention are measured and defined as follows.
[0062]
(1) Average particle diameter (DP)
The polyester is removed from the film surface by a plasma low-temperature incineration method (for example, Model P3-3 manufactured by Yamato Kagaku) to expose the particles. Processing conditions are selected such that the polyester is ashed but the particles are not damaged. This is observed with an SRM (scanning electron microscope), the image of the particles (shading of light generated by the particles) is linked to an image analyzer, and the number of particles to be observed is changed, and the following numerical processing is performed for 5000 or more particles. The number average particle diameter d obtained in 4) is defined as the average particle diameter.
[0063]
(Equation 6)
d = Σdi / n (4)
Here, di is the equivalent circle diameter (μm) of the particles, and n is the number.
The sample is dissolved using a solvent that dissolves the polyester but does not dissolve the particles, and the particles are centrifuged from the solution. The ratio (% by weight) to the total amount of the particles is defined as the particle content.
[0064]
(2) Layer thickness
Using a secondary ion mass spectrometer (SIMS), the concentration ratio (M) of the element resulting from the highest concentration of particles in the film from the surface layer to the depth of 3000 nm and the carbon element of the polyester (M⁺/ C⁺) Is taken as the particle concentration, and analysis in the thickness direction is performed from the surface to a depth of 3000 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. Then, the particle concentration that has once reached the maximum value starts to decrease again. Based on this concentration distribution curve, a depth at which the surface layer particle concentration is の of the local maximum value (this depth is deeper than the local maximum value) is determined, and this is defined as the surface layer thickness.
[0065]
The conditions are as follows.
(1) Measuring device
Secondary ion mass spectrometer (SIMS)
(2) Measurement conditions
Primary ion species: O₂ ⁺
Primary ion acceleration voltage: 12 KV
Primary ion current: 200 nA
Raster area: 400 μm □
Analysis area: Gate 30%
Measurement vacuum degree: 6.0 × 10^-3Torr
E-GUN: 0.5KV-3.0A
In addition, when the particles most contained in the range from the surface layer to the depth of 3000 nm are organic polymer particles, it is difficult to measure by SIMS. Therefore, XPS (X-ray photoelectron spectroscopy) and IR (infrared spectroscopy) are performed while etching from the surface. Method) or the like, the same depth profile may be measured to determine the surface layer thickness.
[0066]
(3) Overall film thickness
Ten films are stacked so that dust does not enter, the thickness is measured with a dot-type electronic micrometer, and the film thickness per one film is calculated.
[0067]
(4) Young's modulus
The film is cut into a sample having a width of 10 mm and a length of 15 cm. The distance between the chucks is set to 100 mm. The film is pulled by an Instron type universal tensile tester under the conditions of a pulling speed of 10 mm / min and a chart speed of 500 mm / min. The Young's modulus is calculated from the tangent at the rising portion of the obtained load-elongation curve.
[0068]
(5) Electromagnetic conversion characteristics
Using the following commercially available equipment, a signal having a frequency of 7.4 MHZ was recorded, and the ratio of the 6.4 MHZ and 7.4 MHZ values of the reproduced signal was set as the C / N of the tape. It was OdB, expressed as a relative value, and determined as follows.
◎: +3 dB or more
：: +1 to +3 dB
×: less than +1 dB
Equipment used
8mm video recorder: Sony Corporation's EDV-6000
C / N measurement: Noise meter manufactured by Shibasoku Co., Ltd.
[0069]
(6) Slit yield
The film is slit, and the slit yield is determined when 20 or more rolls are wound on a roll at a width of 700 mm and a length of 7000 m, and is determined as follows.
Slit yield
◎: 90% or more
：: 70 to less than 90%
×: less than 70%
[0070]
(7) Surface roughness (WRa)
Using a non-contact type three-dimensional roughness meter (NT-2000) manufactured by WYCO, a measurement magnification is 25 times, and a measurement area is 247 μm × 188 μm (0.046 mm²The measurement is performed with the number of measurements (n) of 10 or more under the condition of (1), and the center plane average roughness (WRa) is obtained by surface analysis software built in the roughness meter.
(A) Center plane average roughness (WRa)
It is calculated and output by the following formula.
[0071]
(Equation 7)

[0072]
Z_jkIs the Z-axis direction orthogonal to the X and Y planes at the j-th and k-th positions in each direction when the X-axis direction (247 μm) and the Y-axis direction (188 μm) orthogonal thereto are divided into M and N, respectively. Height.
[0073]
(8) Film cost
It was determined as follows from the ratio of the recovered polymer.
：: Recovery rate (R) is 50% or more
：: Recovery ratio (R) is 30% or more to less than 50%
Δ: Recovery ratio (R) is 10% or more and less than 30%
×: Recovery ratio (R) is less than 10%
[0074]
(9) Coefficient of friction of film
The fixed glass plate is placed under the two superposed films, and the film on the lower side of the superposed film (the film in contact with the glass plate) is taken up by a low-speed roll (about 10 cm / min), A detector is fixed to one end of the upper film (the end opposite to the direction in which the lower film is pulled out), and the tensile force at the start between the films is detected. The thread used at that time weighs 1 kg and the lower area is 100 cm.²Use those.
The coefficient of friction (μs) was determined by the following equation.
[0075]
(Equation 8)

[0076]
(10) Measurement of volume resistivity
The measurement of the volume resistivity of the molten film is performed using the apparatus shown in FIG. As the measurement sample 1, a film having a thickness of about 150 μm is used. On the upper surface of the cylindrical lower electrode 2 having a diameter of 20 cm, an upper electrode 3 having a diameter of 5.6 cm and a thickness of 0.2 cm capable of holding a parallel gap of 150 μm is arranged. insert.
[0077]
The lower electrode 2 has a built-in power supply device 4 and a temperature detection end 5, and the variation in the surface temperature of the lower electrode on the measurement surface is within 1 ° C., and the temperature difference with the detection end is 2 ° C. at a heating rate of 8 ° C./min. It is configured to be within. The detected temperature is measured by the reading thermometer 7. The whole of the electrode is placed in the heat insulation box 11.
[0078]
The power supply 18 applies the generated voltage between the two electrodes via the standard resistor 9. When the DC volume resistivity of the film is measured, the power supply is a power supply that generates a DC of 100 V. When measuring the resistivity, it is a power supply generating 100 V and 50 Hz. As for the current flowing through this circuit, the voltage generated across the standard resistor is read by an eletron meter 10 having an internal impedance of 100 MΩ or more.
[0079]
The measurement of the AC volume resistivity of the film-like polymer is performed by the above-mentioned apparatus at a temperature rise rate of the lower electrode of 8 ° C./min. Is obtained from the following equation from the applied voltage E, the current I, the electrode area S, and the electrode interval d.
[0080]
(Equation 9)

[0081]
【Example】
Hereinafter, the present invention will be further described with reference to examples.
[0082]
[Example 1]
Dimethyl-2,6-naphthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and the additive particles shown in Table 1 as a lubricant were added. A virgin chip for a flat layer (layer A) having an intrinsic viscosity (o-chlorophenol, 35 ° C.) of 0.61 was obtained by polymerization by a method. On the other hand, the chip for the rough surface layer (B layer) was supplemented with the recovered chip of its own laminated film and the virgin chip shown in Table 1 at the recovery rate shown in Table 1 to obtain a chip for the rough surface layer (A layer). The virgin chips for the A layer and the B layer contained a quaternary phosphonium salt sulfonic acid compound at 2 mmol%.
[0083]
Each of the polymers for the layer A and the layer B was dried at 170 ° C. for 6 hours. Thus, the dried chips are supplied to two extruder hoppers at a ratio such that the layer thickness is as shown in Table 1, and melted at a melting temperature of 280 to 300 ° C., using a multi-manifold type coextrusion die. The layer B was laminated on one side of the layer A and extruded on a rotating cooling drum having a surface finish of about 0.3 S and a surface temperature of 60 ° C. to obtain a laminated unstretched film having a thickness of 212 μm.
[0084]
The alternating volume resistivity of this laminated unstretched film is 4 × 10⁸Ω · cm.
[0085]
The laminated unstretched film thus obtained was preheated to 120 ° C., further heated by an IR heater having a surface temperature of 900 ° C. from 15 mm above between low-speed and high-speed rolls, and stretched 5.1 times. After quenching, it was supplied to a stenter and stretched 145 times in the transverse direction at 145 ° C. The obtained biaxially stretched film was heat-set with hot air at 210 ° C. for 4 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 4.5 μm. The Young's modulus of these films is 800 kg / mm in the longitudinal direction.²650 kg / mm in horizontal direction²Met.
[0086]
On one side (layer A) of this laminated biaxially oriented polyester film, the following magnetic paint was applied so as to have a coating thickness of 0.2 μm, then subjected to an orientation treatment in a DC magnetic field of 2500 gauss, and dried by heating at 100 ° C. Thereafter, a super calender treatment (linear pressure: 300 kg / cm, temperature: 80 ° C.) was performed and the film was wound. The wound roll was kept in an oven at 55 ° C. for 3 days, and then cut into a width of 8 mm to obtain a magnetic tape.
[0087]
Preparation of magnetic paint:
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 (Desmodule manufactured by Bayer AG) was added, followed by high-speed shearing dispersion for 1 hour to obtain a magnetic paint.
[0088]
Composition of magnetic paint:
Acicular Fe particles 100 parts by weight
15 parts by weight of vinyl chloride-vinyl acetate copolymer
(Eslec 7A manufactured by Sekisui Chemical)
5 parts by weight of thermoplastic polyurethane resin
Chromium oxide 5 parts by weight
5 parts by weight carbon black
Lecithin 2 parts by weight
1 part by weight of fatty acid ester
50 parts by weight of toluene
50 parts by weight of methyl ethyl ketone
Cyclohexanone 50 parts by weight
The electromagnetic conversion characteristics of the obtained magnetic tape were measured by the above measurement method. The results are shown in Table 1.
[0089]
[Examples 2 to 8, Comparative Examples 1 to 4]
A laminated film was obtained in the same manner as in Example 1 except that the lubricant particles to be added, the layer thickness constitution, the recovered polymer ratio and the Young's modulus were changed as shown in Table 1. In Example 2, in order to obtain a Young's modulus, the stretching ratio in the longitudinal direction was 5.1 times, and the stretching ratio in the transverse direction was 4.9 times. In Examples 4 to 6 and Comparative Examples 1 to 4, The stretching ratio was 5.2 times, the stretching ratio in the horizontal direction was 3.9 times, and in Example 3, the stretching ratio in the longitudinal direction was 4.8 times, and the stretching ratio in the horizontal direction was 5.2 times. The stretching ratio in the longitudinal direction was 3.5 times and the stretching ratio in the transverse direction was 5.8 times. In Example 8, the stretching ratio in the longitudinal direction was 4.0 times and the stretching ratio in the transverse direction was 5.4 times.
[0090]
Next, a magnetic tape was obtained in the same manner as in Example 1 using the obtained laminated biaxially oriented polyester film. The measurement results of each characteristic were as shown in Table 1.
[0091]
As is clear from Table 1, the laminated biaxially oriented polyester film according to the present invention has excellent electromagnetic conversion characteristics, excellent winding properties, and excellent characteristics as a high-density magnetic recording medium excellent in cost merit. Met.
[0092]
[Table 1]

[0093]
【The invention's effect】
According to the present invention, there is provided a laminated biaxially oriented polyester film having excellent electromagnetic conversion properties as a high-density magnetic recording medium, excellent winding properties, and also excellent properties in terms of cost merit. Can be. This film is useful as a base film for high-density magnetic recording media, particularly as a digital recording video tape or data storage tape.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a method of self-circulation recovery.
FIG. 2 is a schematic diagram of an apparatus for measuring the volume resistivity of a molten polymer.
[Explanation of symbols]
1: Polymer
2: Lower electrode
3: Upper electrode
4: Power supply device
5: Temperature detection end
6: Ammeter
7: Reading thermometer
8: Power supply
9: Standard resistance
10: Electron meter
11: Heat insulation box

Claims (13)

A laminated biaxially oriented polyester film in which a polyester B layer is laminated on a polyester A layer, wherein the film satisfies the following formulas (1) to (3), and the polymer of the polyester B layer is A laminated biaxially oriented polyester film comprising a polymer of the recovered laminated polyester film.
(Equation 1)
WRa (B)> WRa (A) (1)
(T _B / t) × 100 = 15 to 50 (%) (2)
10 <t _B / d _B ≦ 45 (3)
Here, WRa (A): surface roughness of the polyester A layer (nm)
WRa (B): Surface roughness of the polyester B layer (nm)
t _A : thickness of polyester A layer (μm)
t _B : thickness of polyester B layer (μm)
t: Total thickness of the film (μm)
d _B : average particle size (μm) of all lubricant particles contained in polyester B layer
It is. The laminated biaxially oriented polyester film according to claim 1, wherein the polyester A layer has a surface roughness WRa (A) of 1 to 5 nm, and the polyester B layer has a surface roughness WRa (B) of 6 to 18 nm. The laminated biaxially oriented polyester film according to claim 1, wherein the total thickness of the film is 4 to 10 µm. The laminated biaxially oriented polyester film according to claim 1, wherein the polymer intrinsic viscosity of the polyester B layer is smaller than the polymer intrinsic viscosity of the polyester A layer. The laminated biaxially oriented polyester film according to claim 1, wherein the layer thickness constitutional ratio of the collected laminated polyester film is the same as the layer thickness constitutional ratio of the laminated biaxially oriented polyester film of the product. The laminated biaxially oriented polyester film according to claim 1 or 5, wherein the polyester B layer comprises a recovered polymer and a virgin polymer, and the final composition C _Bi (wt%) of the lubricant i in the B layer satisfies the following formula.
(Equation 2)
C _Bi = (C _Ai × t _A × R + 100 × C _vi × (t _B − (t _A + t _B ) × R / 100)) / (t _B × (100−R))
Here, t _A : thickness of polyester A layer (μm)
t _B : thickness of polyester B layer (μm)
C _Ai : Composition of lubricant i in polyester A layer (wt%)
C _Bi : Final composition of lubricant i in polyester B layer (wt%)
C _Vi : Composition of lubricant i in virgin polymer in polyester B layer (wt%)
R: ratio of recovered polymer in polyester B layer (%)
It is. The laminated biaxially oriented polyester film according to claim 1, 5 or 6, wherein the recovered polymer is a polymer obtained by self-recovery of the laminated polyester film. 7. The laminated biaxially oriented polyester film according to claim 1, wherein the polyester B layer contains at least two or more lubricants having different average particle sizes. Longitudinal and transverse Young's modulus, respectively 450~2000kg / mm ^2, the laminated biaxially oriented polyester film of both the ratio (vertical / horizontal) of claim 1, wherein a 0.3 to 2.5 of the film . The laminated biaxially oriented polyester film according to claim 1, wherein the polymer of the polyester A layer and the polyester layer B comprises polyethylene-2,6-naphthalate. The polymer of the polyester A layer and / or the B layer contains a quaternary phosphonium salt sulfonic acid compound in an amount of 0.02 to 45 mmol%, and the alternating current volume resistivity of the film is 1 × 10 ⁶ Ω · cm to 9 × 10 ⁸ Ω. The laminated biaxially oriented polyester film according to claim 1 or 6. 7. The laminated biaxially oriented polyester film according to claim 1, which is used for a digital recording type magnetic recording tape. The laminated biaxially oriented polyester film according to claim 12, which is used for a magnetic recording tape for data storage.

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