JP3752397B2 - Laminated biaxially oriented polyester film - Google Patents

Description

【００２７】
ここで、Ａは芳香族基又は脂肪族基、Ｘ₁ 及びＸ₂ 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、Ｒ₁ 、Ｒ₂ 、Ｒ₃ 及びＲ₄ 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、自身のフィルムで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＝５０〜９０（％） ……（２）
１０＜ｔ_B ／ｄ_B ≦６０ ……（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】
さらに好ましくは、ポリエステルＢ層のポリマーが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）を含んでいる積層二軸配向ポリエステルフィルムである。
【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の値は５０〜９０（％）である必要がある。この値が５０％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粗面層（ポリエステルＢ層）に回収使用できる比率が少なくなり（本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、滑剤含有濃度の濃いバージンポリマー（新しいポリマー）を補い、組成補正する必要があり、結果として回収比率は５０％未満よりさらに少なくなる）、積層二軸配向ポリエステルフィルムとしての製造コストが高くなり、市場投入への適用範囲が狭くなく、好ましくない。
【００３８】
一方、（ｔ_B ／ｔ）×１００の値が９０％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、平坦面が粗くなってしまい、このため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。
【００３９】
本発明において、ｔ_B ／ｄ_B の比は１０〜６０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６０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３〜８ｎｍが好ましく、さらに好ましくは４〜８ｎｍ、特に好ましくは５〜７ｎｍである。ＷＲａ（Ａ）が８ｎｍ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３ｎｍ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６〜１８ｎｍ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６ｎｍ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１８ｎｍ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／ｍｍ² 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／ｍｍ² であり、さらに好ましくはそれぞれ６００〜９００ｋｇ／ｍｍ² 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／ｍｍ² 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／ｍｍ² 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／ｍｍ² 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１×１０⁶ Ω・ｃｍ〜９×１０⁸ 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 ：Ｏ₂ ⁺
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１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（０．０４６ｍｍ² ）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１００ｃｍ² 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９１μｍ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４×１０⁸ 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５．２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３．９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９００ｋｇ／ｍｍ² 、横方向６００ｋｇ／ｍｍ² 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０．５μｍ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。
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。
【００８８】
［比較例１〜３］
添加する滑剤粒子、層厚み構成、および回収ポリマーの比率を表１に示すように変更するほかは実施例１と同様にして積層二軸配向ポリエステルフィルムを得た。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。
【００８９】
［実施例２〜７］
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、４〜６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倍に、また実施例７では縦方向の延伸倍率を４．０倍、横方向の延伸倍率を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]
BACKGROUND OF THE INVENTION
The present invention relates to a laminated biaxially oriented polyester film. More specifically, it is a laminated film capable of self-recovery, a laminated biaxially oriented polyester film that has excellent electromagnetic conversion characteristics as a base film for high-density magnetic recording media, and excellent winding and handling properties as a base film. About.
[0002]
[Prior art]
A biaxially oriented polyester film represented by a polyethylene terephthalate film is widely used because of its excellent physical and chemical properties, particularly as a base film of a magnetic recording medium.
[0003]
In recent years, magnetic recording media have been increased in density and capacity, and accordingly, flatness of the base film and reduction in thickness have been demanded. However, if the surface of the base film is flattened in order to maintain excellent electromagnetic conversion characteristics, the slipping property is insufficient, and for example, when rolled up into a roll, wrinkles or blocking occurs, and the surface of the film roll becomes uneven. As a result, the appropriate range of tension, contact pressure, and speed when reducing product yield or winding is narrowed, making winding very difficult. In addition, if the sliding property is poor even in the film processing step, the friction with the metal roll that comes into contact increases, and scraping powder is generated, which causes a missing magnetic recording signal, that is, a dropout.
[0004]
In general, to improve the slipperiness of polyester film, the surface of the film is uneven by (i) a method in which inert particles are precipitated from catalyst residues in the production process, or (ii) a method in which inert particles are added. The method of giving is used. In general, the larger the size and the greater the content of the particles in these films, the greater the improvement in 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 electromagnetic conversion characteristics. If the surface roughness of the base surface is rough, when processing into a magnetic recording medium, the surface unevenness of the base film protrudes to the surface of the magnetic layer even after the magnetic layer is applied, thereby degrading electromagnetic conversion characteristics. In this case, the larger the size of the particles in the base film and the greater the content thereof, the rougher the surface and the worse the electromagnetic conversion characteristics.
[0006]
In this way, as a means of making the contradictory properties of improving winding properties and electromagnetic conversion characteristics compatible, by making 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 on which the magnetic layer is applied is flattened by using a lubricant with small particles or by reducing the amount added, while the rough surface on the opposite surface (traveling surface side) on which the magnetic layer is not applied. The face layer is roughened by using a lubricant having a large particle size or increasing the amount of addition.
[0008]
That is, the characteristics of the lubricant used, such as the type of lubricant, the particle size, the amount of addition, etc., differ greatly between the flat layer on the application surface side and the rough surface layer on the running surface side.
[0009]
In the case of a single-layer film, the film waste generated in the film production process can be recovered and rechiped, and the film can be manufactured again, but in the case of the laminated film, the recovered chip of the laminated film itself has a lubricant composition. Since it differs from the lubricant composition of a rough surface layer and a flat layer, if it re-enters in manufacture of a laminated | multilayer film, the lubricant composition of the re-introduced layer will change and will interfere with a film characteristic.
[0010]
On the other hand, recently, it has been proposed that such a laminated film recovery chip is put into an intermediate layer portion (core layer portion) of a three-layer laminated film and reused.
[0011]
However, in this method, in addition to the recovery chip of the three-layer laminated film itself, the thickness of the intermediate layer portion must be thick enough to recover the recovery chip of the laminated film. As a result, it is necessary to use a fairly thick film. In addition, those containing a lubricant having a large particle diameter and those containing a large amount of lubricant have a limited use because they affect the formation of protrusions on the surface layer even when used in the intermediate part.
[0012]
In addition, as described above, recent magnetic recording media are required to have higher density and higher capacity, and the base film is required to have a thinner thickness. Therefore, the thickness of the three-layer laminated film is also reduced. It is substantially difficult to re-inject the recovered polymer (chip) of the laminated film into the intermediate layer of the three-layer laminated film.
[0013]
Therefore, the present situation is that the collected polymer of such a laminated film is unavoidably discarded, which leads to an increase in the cost of the film. These waste films are treated as industrial waste, but it will become more difficult in the future.
[0014]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a laminated biaxially oriented polyester film that can be a base film for a high-density magnetic recording medium that can be self-circulated and is excellent in winding and handling properties and has excellent electromagnetic conversion characteristics. .
[0015]
[Means for Solving the Problems]
As a result of earnest research to achieve the above object, the present inventor is a laminated film having a rough surface layer and a flat layer, the thickness of the rough surface layer is larger than that of the flat layer, and the thickness of the rough surface layer is By making the ratio of the average particle size of the lubricant contained in the rough surface layer within a specific range, it is used for a part of the film that needs to be recovered during production of the laminated film, in other words, the recovered polymer is used for the production of its own film. Even if it is self-circulated, the surface properties of the product laminated film are hardly changed, and the obtained laminated film has excellent electromagnetic conversion characteristics as a base film for high-density magnetic recording media, and is wound as a base film. The present inventors have found that it is excellent in handleability, and have reached the present invention.
[0016]
  That is, the present invention is a laminated biaxially oriented polyester film in which a polyester B layer is laminated on a polyester A layer,The polyester B layer contains a polymer that self-collects the laminated polyester film,It is a laminated biaxially oriented polyester film characterized in that the polyester A layer and the polyester B layer satisfy the relationships of the following formulas (1) to (3).
[0017]
[Equation 3]
WRa (B)> WRa (A) (1)
(T_B/ T) × 100 = 50 to 90 (%) (2)
10 <t_B/ D_B≦ 60 …… (3)
Here, WRa (A): Surface roughness of polyester A layer (nm)
WRa (B): Surface roughness of polyester B layer (nm)
t_A: Polyester A layer thickness (μm)
t_B: Polyester B layer thickness (μm)
t: Total thickness of film (μm)
d_B: Average particle diameter (μm) of all lubricant particles contained in the polyester B layer
It is.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The polyester in the present invention is an aromatic polyester having 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, particularly film-forming properties by melt molding.
[0020]
Examples of aromatic dicarboxylic acids include terephthalic acid, naphthalene dicarboxylic 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 do. Examples of the aliphatic glycol include alicyclic groups such as polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, and cyclohexanedimethanol. A diol etc. can be mentioned.
[0021]
As such a polyester, those having alkylene terephthalate or alkylene naphthalate as a main constituent are preferably used. Among them, not only polyethylene terephthalate and polyethylene-2,6-naphthalate, 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. A copolymer in which is ethylene glycol is particularly preferred. In this case, 20 mol% or less of the total acid component can be the above-mentioned aromatic dicarboxylic acid other than terephthalic acid or 2,6-naphthalenedicarboxylic acid, and alicyclic dicarboxylic acids such as adipic acid and sebacic acid, for example. An alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid; Further, 20 mol% or less of the total glycol component may be the above-mentioned glycol other than ethylene glycol, and aromatic diols such as hydroquinone, resorcin, 2,2-bis (4-hydroxyphenyl) propane, etc .; 1,4 -An aliphatic diol having an aromatic ring such as dihydroxydimethylbenzene; polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like.
[0022]
The polyester in the present invention includes, for example, a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid and an aliphatic oxyacid such as ω-hydroxycaproic acid, a dicarboxylic acid component and an oxycarboxylic acid component. Those which are copolymerized or bonded in an amount of 20 mol% or less based on the total amount of the above are also included.
[0023]
Furthermore, the polyester in the present invention contains a tri- or higher functional polycarboxylic acid or polyhydroxy compound such as trimellitic acid in an amount in a substantially linear range, for example, 2 mol% or less based on the total acid component. And those obtained by copolymerizing pentaerythritol and the like.
[0024]
Furthermore, it is preferable to contain 0.02-45 mmol% (based on the acid component of the polyester) of a sulfonic acid quaternary phosphonium salt compound in the polyester of the present invention. 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 decreases over time. There is, and is not preferable. With this content, the AC volume resistivity of the molten film is reduced to 1 × 10⁶Ω · cm ～ 9 × 10⁸It can be set to Ω · cm. This AC volume resistivity is 9 × 10⁸When it exceeds Ω · cm, the effect of increasing the casting speed is small, while 1 × 10⁶If it is less than Ω · cm, the film may break down during electrostatic adhesion in the casting process, which is not preferable.
[0025]
The sulfonic acid quaternary phosphonium salt is a compound represented by the following formula.
[0026]
[Chemical 1]

[0027]
Here, A is an aromatic group or an aliphatic group, X₁And X₂Are the same or different ester-forming functional groups or hydrogen atoms, R₁, R₂, R_ThreeAnd R_FourAre the same or different groups each selected from the group consisting of alkyl groups and aryl groups, and n is a positive integer.
[0028]
Preferred examples of the sulfonic acid quaternary phosphonium salt include 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid tetraphenylphosphonium salt, 3,5-dicarbomethoxybenzene. Tetrabutylphosphonium sulfonate, tetraphenylphosphonium 3,5-dicarbomethoxybenzenesulfonate, tetrabutylphosphonium 3, carboxybenzenesulfonate, tetrabutyl 3,5-di (β-hydroxyethoxycarbonyl) benzenesulfonate Phosphonium salt, 4-hydroxyethoxybenzenesulfonic acid tetrabutylphosphonium salt, bisphenol A-3,3'-di (sulfonic acid tetrabutylphosphonium salt), 2,6-dicarboxynaphthalene-4-sulfur Phosphate tetrabutylphosphonium like. Only one kind may be used alone, or two or more kinds may be used in combination. Moreover, it is not limited whether the said sulfonic acid quaternary phosphonium salt is couple | bonded with the polyester chain of the base polymer, or is free. Therefore, when the polyester is polymerized, the sulfonic acid quaternary phosphonium salt compound is allowed to coexist in the polymer chain of the polyester, or when the polyester is put into an extruder and melt extruded, the sulfonic acid quaternary phosphonium salt compound is used. The method for containing the sulfonic acid quaternary phosphonium salt is not particularly limited.
[0029]
The polyester is known per se and can be produced by a method known per se.
[0030]
The polyester preferably has an intrinsic viscosity of 0.4 to 0.9 as measured in a solution in o-chlorophenol at 35 ° C., more preferably 0.5 to 0.7. Those of .51 to 0.65 are particularly preferred.
[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 that can be self-recovered and can be self-recovered with its own film, and has a difference in surface roughness on both sides. Can be used for some.
[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 relationships of the following formulas (1) to (3). There is a need.
[0034]
[Expression 4]
WRa (B)> WRa (A) (1)
(T_B/ T) × 100 = 50 to 90 (%) (2)
10 <t_B/ D_B≦ 60 …… (3)
Here, WRa (A): Surface roughness of polyester A layer (nm)
WRa (B): Surface roughness of polyester B layer (nm)
t_A: Polyester A layer thickness (μm)
t_B: Polyester B layer thickness (μm)
t: Total thickness of film (μm)
d_B: Average particle diameter (μm) of all lubricant particles contained in the polyester B layer
It is.
[0035]
More preferably, it is a laminated biaxially oriented polyester film in which the polymer of the polyester B layer contains the polymer of the film to be recovered (by self-recovered polymer) produced as a by-product during the production of the laminated polyester film.
[0036]
In the production of a laminated biaxially oriented polyester film, when the self-recovered polymer is used in the polyester A layer, that is, the flat layer, a large lubricant contained in the rough surface layer (polyester B layer) for imparting winding properties is used in the polyester A layer. Therefore, high protrusions are formed on the flat layer (polyester A layer), the electromagnetic conversion characteristics are deteriorated, and it is not suitable as a base film for a high-density magnetic recording medium.
[0037]
In the present invention, (t_B/ T) × 100 needs to be 50 to 90 (%). If this value is less than 50%, the ratio at which the polymer obtained by self-recovering the laminated polyester film can be recovered and used in the rough surface layer (polyester B layer) decreases (the lubricant composition of this recovered polymer is more than the lubricant composition of the polyester B layer). Since the flat layer is thin, it is necessary to compensate for the virgin polymer (new polymer) with a high concentration of lubricant and to correct the composition, resulting in a recovery ratio of less than 50%). The production cost as an oriented polyester film is increased, and the application range to market is not narrow, which is not preferable.
[0038]
On the other hand, (t_BWhen the value of / t) × 100 exceeds 90%, the flat layer (polyester A layer) becomes thin, so the influence 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, which deteriorates the electromagnetic conversion characteristics and is not preferable as a base film for a high-density magnetic recording medium.
[0039]
In the present invention, t_B/ D_BThe ratio needs to be 10-60. This ratio (t_B/ D_B) Is less than 10, that is, when the thickness of the rough surface layer is made too thin, or when the average particle diameter of the lubricant particles contained in the rough surface layer is made too large, the former is a recovered polymer that can be recovered in the rough surface layer. The amount is reduced, the film production cost is increased, and the application range to the market is narrowed. In the latter case, large lubricant particles contained in the rough surface layer affect the flat layer, the flat surface becomes rough, electromagnetic conversion characteristics deteriorate, and it is not preferable as a base film for a high-density magnetic recording medium.
[0040]
On the other hand, t_B/ D_BIf the ratio exceeds 60, 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 protrusions formed on the rough surface layer become too low, and sufficient winding It is not possible to obtain the takeability.
[0041]
The lubricant contained in the rough surface layer (polyester B layer) in the present invention may be a single-component system or a multi-component system, but preferably a multi-component system containing at least two kinds of lubricants having different average particle diameters. More preferably, it is a multi-component system in which a small amount of medium particles are added within a range not deteriorating the electromagnetic conversion characteristics and more small particles are added than the medium particles in order to impart slipperiness. In the single component system, when small particles are used, sufficient air squeeze property cannot be obtained, winding properties and handling properties are insufficient, and when medium to large particles are used, if the addition amount is increased, electromagnetic conversion When the properties are lowered and the amount is too small, the slipping property of the film is 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 middle particles are heat-resistant polymer particles and the small particles are spherical silica particles. Examples of the heat-resistant polymer particles include crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, and melamine resin particles. Among these, the inclusion of crosslinked polystyrene resin particles or crosslinked silicone resin particles is preferable because the effect of the present invention becomes more remarkable.
[0043]
By using the heat-resistant polymer particles and spherical silica particles described above, protrusions having a good affinity with polyester and relatively uniform sizes are formed, and the slipperiness and abrasion resistance of the film are improved. Electromagnetic conversion characteristics are also improved.
[0044]
The laminated biaxially oriented polyester film in the present invention contains a lubricant in at least the rough surface layer (polyester B layer), and the rough surface layer contains a recovery-required film produced as a by-product during the production of the laminated biaxially oriented polyester film. It is preferable that a part of the polymer (recovered polymer) is contained. The use of the recovered polymer, that is, the use of the self-circulating recovered polymer is as shown in FIG. 1, for example. In FIG. 1, the polyester B layer is composed of a polymer (collected polymer: collected chip) and a virgin polymer (virgin chip) obtained by self-collecting the laminated film, 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 the thickness t of the polyester A layer._APolyester B layer thickness t_B, Composition C of lubricant i in virgin chip used for polyester A layer_Ai, Composition C of lubricant i in virgin chip used for polyester B layer_Vi, And the ratio R of the recovered polymer, and a composition calculated from the following formula is preferable. That is, if the final composition of the lubricant i of the polyester B layer is a composition calculated from this equation, self-circulating recovery is possible, and if different, self-circulating 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: Polyester A layer thickness (μm)
t_B: Polyester B layer thickness (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 of lubricant i in virgin chip used for polyester B layer (wt%)
R: Ratio of recovered polymer (%)
It is.
[0047]
For the recovered polymer (recovered chip) in FIG. 1, it is also possible to use a recovered laminated polyester film in which the composition of the lubricant i, the thickness composition ratio of the polyester A layer and the polyester B layer are the same, and the total thickness is different from the product polyester film. it can. Moreover, it is preferable from the point of manufacturing cost that the polymer intrinsic viscosity of the rough surface layer (polyester B layer) in FIG. 1 is smaller than the polymer intrinsic viscosity of the flat surface layer (polyester A layer). The intrinsic viscosity of the virgin polymer used can be made higher than the intrinsic viscosity of the polyester A layer, and adjusted to the same value by adjusting the ratio of recovered polymer, 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, but the present invention is not limited to this. There is no particular limitation as long as it is a system in which no lubricant is added to the A layer, and the polyester B layer is a laminated biaxially oriented polyester film satisfying the above formula, comprising a single lubricant system.
[0049]
The polyester in the present invention is preferably polyethylene terephthalate or polyethylene-2,6-naphthalate. In particular, polyethylene-2,6-naphthalate is more preferable in order to obtain a biaxially oriented film having a thickness of 6 μm or less and a high Young's modulus.
[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 surface roughness (WRa (A)) is preferably 3 to 8 nm, more preferably 4 to 8 nm, and particularly preferably 5 to 7 nm. When WRa (A) exceeds 8 nm, sufficient electromagnetic conversion characteristics cannot be obtained. On the other hand, when WRa (A) is less than 3 nm, the slipperiness of the film is deteriorated and a sufficient slit yield cannot be obtained. In addition, the slippage between the flat surface and the pass roll system in the film or tape manufacturing process is deteriorated, the process wrinkles are generated due to poor transportability, and the yield of the product is greatly reduced.
[0051]
Further, WRa (B) of the rough surface layer is preferably 6 to 18 nm, more preferably 7 to 17 nm, and particularly preferably 9 to 15 nm. If WRa (B) is less than 6 nm, the slipperiness of the film is poor and sufficient slit yield cannot be obtained. On the other hand, when WRa (B) exceeds 18 nm, the influence of the protrusion of the protrusion toward the flat surface becomes large, the flat surface becomes rough, and sufficient electromagnetic conversion characteristics cannot be obtained.
[0052]
The laminated biaxially oriented polyester film in the present invention has a Young's modulus in the longitudinal direction and the transverse direction of 450 to 2000 kg / mm, respectively.²And it is preferable that ratio (vertical / horizontal) of both is 0.3-2.5. More preferably, the Young's modulus in the longitudinal direction and the transverse direction is 500 to 1200 kg / mm, respectively.²More preferably, each is 600 to 900 kg / mm²It is. The ratio (horizontal / vertical) of both is preferably 0.4 to 2.0, and particularly preferably 0.6 to 1.6.
[0053]
Young's modulus in the vertical direction of the film is 450 kg / mm²If it is less than 1, the strength in the longitudinal direction of the magnetic tape becomes weak, and if it is applied to the magnetic recording apparatus, it will be easily broken if a strong force is applied in the longitudinal direction. The lateral Young's modulus is 450 kg / mm²If it is less than 1, the transverse strength of the magnetic tape becomes weak, the contact between the tape and the magnetic head becomes weak, 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 / mm²If it exceeds 1, the draw ratio becomes high during film formation, the film breaks frequently, and the product yield is remarkably deteriorated.
[0054]
Also, if the ratio between the longitudinal Young's modulus and the lateral Young's modulus is less than 0.3, sufficient magnetic tape longitudinal strength cannot be obtained, and when applied to a magnetic recording device, a strong force is applied in the longitudinal direction. Cutting frequently occurs. On the other hand, if the ratio of the longitudinal Young's modulus and the lateral Young's modulus exceeds 2.5, sufficient transverse strength of the magnetic tape cannot be obtained, and when the tape is run, the tape edge is damaged, which is satisfactory. Durability is not obtained.
[0055]
The ratio of the longitudinal Young's modulus to the lateral 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 4-9 micrometers, Most preferably, it is 4-7 micrometers. If this thickness exceeds 10 μm, the length of the magnetic tape put in the cassette becomes short, and a sufficient recording capacity cannot be obtained. On the other hand, when the thickness is less than 3 μm, film breakage frequently occurs during film formation, and 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 non-oriented laminated film can be produced by a conventionally produced method for producing laminated films. 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 polyester can be used. More specifically, it can be produced by a method such as coextrusion or extrusion lamination.
[0058]
The unoriented laminated film obtained by the above method can be made into a laminated biaxially oriented film according to the production method of the biaxially oriented film accumulated conventionally. For example, polyester is melted and coextruded 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. (where Tg is the glass transition temperature of the polyester) and is stretched at a magnification of 2.5 times or more, preferably 3 times or more, and then Tg to (Tg + 70) in the direction perpendicular to the stretching direction. ) It is preferable that the film is stretched at a magnification of 2.5 times or more, preferably 3 times or more at a temperature of ° C. Further, if necessary, the film may be stretched again in the machine direction and / or the transverse direction. Thus, the total draw ratio is preferably 9 times or more, more preferably 12 to 35 times, and particularly preferably 15 to 30 times as the area draw ratio. Furthermore, the biaxially oriented film can be heat-set at a temperature of (Tg + 70) ° C. to (Tm−10) ° C., for example, preferably heat-set at 180 to 250 ° C. The heat setting time is preferably 1 to 60 seconds.
[0059]
The laminated biaxially oriented polyester film in the present invention contains 0.02-45 mmol% of sulfonic acid quaternary phosphonium salt, and the film has an AC volume resistivity of 1 × 10.⁶Ω · cm ～ 9 × 10⁸More preferably, it is Ω · cm. That is, by containing the sulfonic acid quaternary phosphonium salt within the above range, the pinning property is improved at the time of film formation, and high-speed film formation becomes possible.
[0060]
The laminated biaxially oriented polyester film of the present invention is preferably used as a base film for a high-density magnetic recording medium or a high-density digital recording medium (data cartridge, digital video tape, etc.).
[0061]
Note that various physical property values 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 ashing method (for example, P3-3 type manufactured by Yamato Kagaku) to expose the particles. The treatment conditions are such that the polyester is ashed but the particles are not damaged. This is observed with an SRM (scanning electron microscope), and the image of the particle (light density produced by the particle) is connected to an image analyzer, and the following numerical processing is performed on the number of particles of 5000 or more by changing the observation location and formula ( The number average particle diameter d obtained by 4) is defined as the average particle diameter.
[0063]
[Formula 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 in which the polyester is dissolved but the particles are not dissolved, and the particles are centrifuged from the solution to obtain the particle content in a ratio (% by weight) to the total amount of the particles.
[0064]
(2) Layer thickness
Using a secondary ion mass spectrometer (SIMS), the concentration ratio between the element caused by the highest concentration of particles in the film ranging from the surface layer to a depth of 3000 nm and the carbon element of the polyester (M⁺/ C⁺) Is 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. And the particle concentration 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 ½ of the maximum value (this depth is deeper than the depth at which the maximum value is reached) 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: 12KV
Primary ion current: 200 nA
Raster area: 400 μm
Analysis area: 30% gate
Measurement vacuum: 6.0 × 10^-3Torr
E-GUN: 0.5KV-3.0A
In addition, when the most contained particles in the range from the surface layer to a depth of 3000 nm are organic polymer particles, it is difficult to measure by SIMS. Therefore, XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy) is performed while etching from the surface. The surface depth may be obtained by measuring a depth profile similar to the above by the method.
[0066]
(3) Total film thickness
10 films are stacked so that no dust enters, the thickness is measured with a dot-type electronic micrometer, and the film thickness per sheet is calculated.
[0067]
(4) Young's modulus
The film is cut into a sample width of 10 mm and a length of 15 cm, the chuck is set to 100 mm, and the film is pulled with an Instron type universal tensile tester under the conditions of a tensile speed of 10 mm / min and a chart speed of 500 mm / min. The Young's modulus is calculated from the tangent of the rising part of the obtained load-elongation curve.
[0068]
(5) Electromagnetic conversion characteristics
Using the following commercially available equipment, a signal with a frequency of 7.4 MHz is recorded, and the ratio of the 6.4 MHz and 7.4 MHz values of the reproduced signal is defined as the C / N of the tape. OdB was expressed as a relative value and judged as follows.
A: +3 dB or more
○: +1 to +3 dB
X: Less than +1 dB
Equipment used
8mm video recorder: Sony Corporation EDV-6000
C / N measurement: Noise meter manufactured by Shiba Soku Co., Ltd.
[0069]
(6) Slit yield
The slit yield when slitting the film and winding 20 or more rolls on a roll with a width of 700 mm and a length of 7000 m is determined by the following.
Slit yield
A: 90% or more
○: 70 to less than 90%
X: Less than 70%
[0070]
(7) Surface roughness (WRa)
Using a non-contact type three-dimensional roughness meter (NT-2000) manufactured by WYCO, measurement magnification is 25 times, measurement area is 247 μm × 188 μm (0.046 mm)²), The number of measurements (n) is 10 or more, 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 the value calculated and calculated by the following formula.
[0071]
[Expression 7]

[0072]
Z_jkIs the X-axis direction (247 μm) and the Y-axis direction (188 μm) perpendicular to the M-axis and N-division, respectively, and the Z-axis direction orthogonal to the X and Y planes at the j-th and k-th positions in each direction. Of height.
[0073]
(8) Film cost
Based on the ratio of the recovered polymer, the determination was made as follows.
A: Recovery ratio (R) is 50% or more
○: Recovery ratio (R) is 30% to less than 50%
Δ: Recovery ratio (R) of 10% to less than 30%
X: Recovery ratio (R) is less than 10%
[0074]
(9) Coefficient of friction of film
Place a fixed glass plate on the lower side of the two superimposed films, take the film on the lower side of the superimposed film (film in contact with the glass plate) with a low-speed roll (about 10 cm / min), A detector is fixed to one end of the upper film (opposite to the take-off direction of the lower film), and the starting tensile force between the films is detected. The thread used at that time weighs 1 kg and lower area is 100 cm.²Use one.
The friction coefficient (μs) was obtained from the following equation.
[0075]
[Equation 8]

[0076]
(10) Measurement of volume resistivity
The volume resistivity of the molten film is measured using the apparatus shown in FIG. The measurement sample 1 uses a film having a thickness of about 150 μm. 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 disposed on the upper surface of the cylindrical lower electrode 2 having a diameter of 20 cm, and the measurement sample is in close contact with the electrode in the meantime. insert.
[0077]
The lower electrode 2 has a built-in charging device 4 and a temperature detection end 5, the variation in the surface temperature measurement of the lower electrode is within 1 ° C, and the temperature difference from the detection end portion is 2 ° C at a heating rate of 8 ° C / min. Configure to be within. The detected temperature is measured with a reading thermometer 7. The entire electrode is placed in the heat insulating box 11.
[0078]
The power source 18 applies the generated voltage between the two electrodes via the standard resistor 9, which is a power source that generates a direct current of 100V when measuring the DC volume resistivity of the film, and the AC volume of the film. When measuring the resistivity, the power source generates 100 V and 50 Hz. The current flowing in this circuit is read by the eletron meter 10 having an internal impedance of 100 MΩ or more as a voltage generated across the standard resistor.
[0079]
The AC volume resistivity of the film-like polymer is measured at the temperature rise rate of the lower electrode of 8 ° C./min with the above-mentioned device, and the electrode is melted by DSC of the polymer + 30 ° C. Is obtained from the applied voltage E, current I, electrode area S, and electrode interval d by the following equation.
[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 additive particles shown in Table 1 as a lubricant are usually added. Polymerization was performed by the above method to obtain a virgin chip for a flat layer (A layer) having an intrinsic viscosity (o-chlorophenol, 35 ° C.) of 0.61. On the other hand, the rough surface layer (B layer) chip was supplemented with the recovery 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 rough surface layer (A layer) chip. Further, the virgin chip for the A layer and the B layer contained 2 mmol% of a sulfonic acid quaternary phosphonium salt compound.
[0083]
These polymers for the A layer and B layer were each dried at 170 ° C. for 6 hours. Thus, the dried chips were supplied to the two extruder hoppers at a ratio so as to have the layer thickness configuration shown in Table 1, and melted at a melting temperature of 280 to 300 ° C., using a multi-manifold coextrusion die. The B layer was laminated on one side of the A layer and extruded onto a rotary 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 91 μm.
[0084]
The AC volume resistivity of this laminated unstretched film is 4 × 10⁸It was Ω · cm.
[0085]
The laminated unstretched film thus obtained is preheated to 120 ° C., further heated by an IR heater with a surface temperature of 900 ° C. from above 15 mm between low-speed and high-speed rolls, and stretched 5.2 times. It was rapidly cooled, then supplied to a stenter, and stretched 3.9 times in the transverse direction at 145 ° C. The obtained biaxially stretched film was heat-fixed 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 900 kg / mm in the longitudinal direction.², Horizontal direction 600kg / mm²Met.
[0086]
In addition, the following magnetic paint is applied to one side (layer A) of this laminated biaxially oriented polyester film so as to have a coating thickness of 0.5 μm, and then subjected to orientation treatment in a 2500 gauss DC magnetic field, followed by heat drying at 100 ° C. Thereafter, a super calendar process (linear pressure 300 kg / cm, temperature 80 ° C.) was performed and wound up. The wound roll was held in an oven at 55 ° C. for 3 days and then cut to 8 mm width to obtain a magnetic tape.
[0087]
Magnetic paint preparation:
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) was added, and high-speed shear dispersion was performed for 1 hour to obtain a magnetic paint.
Magnetic paint composition:
100 parts by weight of acicular Fe particles
15 parts by weight of vinyl chloride-vinyl acetate copolymer
(Sekisui Chemical's ESREC 7A)
5 parts by weight of thermoplastic polyurethane resin
5 parts by weight of chromium oxide
5 parts by weight of carbon black
2 parts by weight of lecithin
Fatty acid ester 1 part by weight
50 parts by weight of toluene
50 parts by weight of methyl ethyl ketone
50 parts by weight of cyclohexanone
About the obtained magnetic tape, the electromagnetic conversion characteristic was measured with the said measuring method. The results are shown in Table 1.
[0088]
[Comparative Examples 1-3]
A laminated biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the lubricant particles to be added, the layer thickness configuration, and the ratio of the recovered polymer were changed as shown in Table 1. 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 are as shown in Table 1.
[0089]
[Examples 2 to 7]
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 order to obtain the Young's modulus, in Examples 2 and 4 to 6, the longitudinal draw ratio was 5.1 times, the transverse draw ratio was 4.9 times, and in Example 3, the longitudinal draw ratio was 4 times. 8 times, the stretching ratio in the transverse direction was 5.2 times, and in Example 7, 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 are as shown in Table 1.
[0091]
As is clear from Table 1, the present invention is a laminated biaxially oriented polyester film having 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, it is possible to provide a laminated biaxially oriented polyester film having excellent electromagnetic conversion characteristics as a high-density magnetic recording medium, excellent winding properties, and excellent cost merit. Can do. 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 self-circulating recovery method.
FIG. 2 is a schematic view of an apparatus for measuring the volume resistivity of a molten polymer.
[Explanation of symbols]
1: Polymer
2: Lower electrode
3: Upper electrode
4: Charger
5: Temperature detection end
6: Ammeter
7: Reading thermometer
8: Power supply
9: Standard resistance
10: Electron meter
11: Thermal insulation box

Claims (11)

A laminated biaxially oriented polyester film in which a polyester B layer is laminated on a polyester A layer, the polyester B layer contains a polymer by self-recovery of the laminated polyester film, and the polyester A layer and the polyester B layer are A laminated biaxially oriented polyester film characterized by satisfying the relationships of formulas (1) to (3):

Here, WRa (A): Surface roughness of polyester A layer (nm)
WRa (B): Surface roughness of polyester B layer (nm)
t _A : Polyester A layer thickness (μm)
t _B : Polyester B layer thickness (μm)
t: Total thickness of film (μm)
d _B : Average particle diameter (μm) of all lubricant particles contained in the 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 3 to 8 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 3 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 that of the polyester A layer. Polyester B layer is made from the recovered polymer and virgin polymer, laminated biaxially oriented polyester film of claim 1 Symbol placement final composition of lubricants i CBi (wt%) satisfies the following formula B layer.

Here, t _A : thickness of the polyester A layer (μm)
t _B : Polyester B layer thickness (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 the lubricant i in the virgin polymer in the 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 or 5, wherein the polyester B layer contains at least two kinds of lubricants having different average particle diameters. 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 B layer is polyethylene-2,6-naphthalate. The polymer of the polyester A layer and / or the B layer contains 0.02 to 45 mmol% of a sulfonic acid quaternary phosphonium salt compound, and the AC 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 5, which is cm. The laminated biaxially oriented polyester film according to claim 1 or 5, which is used for a digital recording magnetic recording tape. The laminated biaxially oriented polyester film according to claim 10, which is used for a magnetic recording tape for data storage.

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