JP4543546B2 - Polyester film for magnetic recording media - Google Patents

Description

ただし、式中のＲ₁は、
【００２２】
【化２】

【００２３】
【化３】

などの脂肪族炭化水素基、脂環族炭化水素基、芳香族炭化水素基から選ばれた一種もしくは二種以上の基を表して、
また、式中のＲ₂ は、
【００２４】
【化４】

などの脂肪族炭化水素基、脂環族炭化水素基、芳香族炭化水素基から選ばれた一種もしくは二種以上の基を表す。
【００２５】
かかるポリイミドは、テトラカルボン酸および／またはその酸無水物と、脂肪族一級モノアミン、芳香族一級モノアミン、脂肪族一級ジアミンおよび芳香族一級ジアミンよりなる群から選ばれる一種もしくは二種以上の化合物を脱水縮合することにより得ることができる。
【００２６】
ポリエステルとの溶融成形性や取り扱い性、表面突起の形成性などの点から、下記一般式で示されるような、ポリイミド構成成分にエーテル結合を含有するポリエーテルイミドが特に好ましい。
【００２７】
【化５】

（ただし、上記式中Ｒ₃は、６〜３０個の炭素原子を有する２価の芳香族または脂肪族残基、Ｒ₄は６〜３０個の炭素原子を有する２価の芳香族残基、２〜２０個の炭素原子を有するアルキレン基、２〜２０個の炭素原子を有するシクロアルキレン基、および２〜８個の炭素原子を有するアルキレン基で連鎖停止されたポリジオルガノシロキサン基からなる群より選択された２価の有機基である。）
【００２８】
上記Ｒ₃、Ｒ₄ としては、例えば、下記式群に示される芳香族残基
【化６】

を挙げることができる。
【００２９】
本発明では、ポリエステルとの親和性、コスト、溶融成形性等の観点から、２，２−ビス［４−（２，３−ジカルボキシフェノキシ）フェニル］プロパン二無水物とｍ−フェニレンジアミン、またはｐ−フェニレンジアミンとの縮合物である、下記式で示される繰り返し単位を有するポリマーが好ましい。
【００３０】
【化７】

または
【００３１】
【化８】

（ｎは２以上の整数、好ましくは２０〜５０の整数）
このポリエーテルイミドは、“ウルテム”（登録商標）の商品名で、ジーイープラスチックス社より入手可能である。
【００３２】
本発明のＡ層を構成するポリマーアロイには、分散径を制御するために、必要に応じて、相溶化剤を併用してもよい。この場合、相溶化剤の種類は、ポリマーの種類によって異なるが、添加量は０．０１〜１０重量％が好ましい。
【００３３】
本発明において、ポリイミドをポリエステルに添加する時期は、ポリエステルの重合前、例えば、エステル化反応前に添加してもよいし、重合後に添加してもよい。また、溶融押出前に、ポリエステルとポリイミドを混合してペレタイズしてもよい。
【００３４】
また本発明のＡ層を構成するポリマーアロイをより好ましい分散状態に調整する他の方法としては、例えば、タンデム押出機を用いて混合する方法、２種類以上のポリエステルを用いてポリイミドを微分散させる方法、粉砕器でポリイミドを粉末状に粉砕した後に混合する方法、両者を溶媒に溶解し共沈させることにより混合する方法、一方を溶媒に溶かした溶液状とした後に他方に混合する方法なども挙げられるが、この限りではない。特に好ましくは、２種以上のポリエステルを用い、まず、高分子量ポリエステルとポリイミドをペレタイズによって、一旦、ポリイミドを高濃度（例えば、３５〜６５重量％、より好ましくは４０〜６０重量％）含有するマスターペレットを作成してから、さらに溶融押出前に比較的低分子量のポリエステルで希釈して、所定の濃度に調整する方法を用いると、ポリマー同士の分散性が向上し、本発明のポリマーアロイとしてより好ましい分散状態を示すことがある。また、この手法では、ポリマーアロイ全体としての溶融粘度は低く抑えられるため、溶融成型性が向上し、生産性が向上することがあり好ましい。
【００３５】
本発明のＡ層以外のフィルム層に用いるポリマー種は特に限定されないが、Ａ層に用いたものと同じポリエステル、またはＡ層に用いたものと同じポリエステルとポリイミドからなるポリマーアロイを用いた場合、基層部と積層部に溶融粘度の差が生じにくいため、積層斑や口金すじなど生産工程でのトラブルが生じにくいため好ましい。最も好ましくは、Ａ層に用いたものと同じポリエステルとポリイミドをＡ層と同じ重量比で含むポリマーアロイを用いる場合がよい。
【００３６】
本発明の積層ポリエステルフィルムのＡ層には、実質的に不活性粒子を含有しない場合、Ａ層中の粒子の凝集による粗大突起の生成や、フィルター詰まりの問題が低減するため好ましい。ここでいう「実質的に不活性粒子を含有しない」とは、Ａ層中の不活性粒子が全く含まれないか、あるいは含まれたとしても、平均粒径が１０ｎｍより小さい場合、もしくは、不活性粒子の含有量が０．００１重量％より少ない場合をいう。
【００３７】
ただし、本発明の積層ポリエステルフィルムのＡ層には、特に限定されないが、磁気記録媒体としたときの、磁気テープの走行耐久性や、磁気ヘッドとの走行性の良化、あるいは、巻き取り性などハンドリング性の向上のため、不活性粒子を含有させてもよい。なお、本発明でいう不活性粒子とは、平均粒径１０ｎｍ〜１μｍ程度の無機または有機の粒子で、本発明のポリマー中で化学反応を起こしたり、電磁気的影響により磁気記録に悪影響を与えないものを言う。不活性粒子としては、酸化チタン、炭酸カルシウム、カオリン、タルク、湿式または乾式シリカ、コロイド状シリカ、リン酸カルシウム、硫酸バリウム、アルミナおよびジルコニア等の無機粒子、アクリル酸類、スチレン、シリコーン、イミド等を構成成分とする有機粒子、ポリエステル重合反応時に添加する触媒等によって析出する粒子（いわゆる内部粒子）や、界面活性剤などがある。
【００３８】
本発明の積層ポリエステルフィルムのＡ層に不活性粒子を含有させる場合、平均粒径は０．００１〜０．５μｍが好ましく、より好ましくは０．０１〜０．３μｍである。不活性粒子の平均粒径が０．５μｍより大きい場合には、磁気記録媒体として用いた場合、電磁変換特性が悪化したり、磁気ヘッドと傷つけやすくなる場合がある。不活性粒子の平均粒径が０．００１μｍより小さい場合には、粒子凝集が起こりやすく、またポリマー中に良好に分散させることが困難であり表面突起個数等を制御しにくいため、好ましくない。
【００３９】
本発明の積層ポリエステルフィルムのＡ層に不活性粒子を含有させる場合、含有量は０．０１〜１重量％が好ましく、より好ましくは０．０２〜０．０５重量％である。不活性粒子の含有量が１重量％より大きい場合、粒子凝集により突起が粗大となって、電磁変換特性を悪化させたり、突起が削れやすくなることがある。不活性粒子の含有量が０．０１重量％より小さい場合には、磁気ヘッドとの走行性の良化の効果が小さいため、好ましくない。
【００４０】
本発明の積層ポリエステルフィルムのＢ層には、製膜および加工時のハンドリング性向上や磁気記録媒体とした際の走行性、走行耐久性の付与の目的から不活性粒子を含有させる。この際、Ｂ層に含有させる不活性粒子としては、前述のような不活性粒子を用いることができる。不活性粒子は１種類でも良いが、２種類以上併用しても構わない。Ｂ層の不活性粒子の平均粒径ｄは、０．０５〜１μｍが好ましく、より好ましくは０．１〜０．５μｍである。平均粒径が１μｍを越える場合、フィルムを巻き取った状態で保存しておく際に、突起が平滑な磁性面側（ｆ面側）に転写し、ｆ面側を粗くし、電磁変換特性を低下させることがある。また、平均粒径が０．０５μｍより小さい場合には、ハンドリング性や磁気テープの走行性に十分な効果を及ぼさないことがある。Ｂ層の不活性粒子の含有量は０．０５〜１．５重量％、好ましくは０．１〜１重量％である。不活性粒子の含有量が１重量％を越える場合には、蒸着加工工程での冷却効率が低下し、「しわ」やオリゴマー析出の原因となったり、転写により電磁変換特性を低下させることがある。
【００４１】
本発明の積層ポリエステルフィルムのＢ層の厚みはフィルム全体の厚みの２０％以下であると、製膜性が良好であり好ましい。Ｂ層の厚みは、より好ましくはフィルム全体の厚みの１５％以下、特に好ましくは１０％以下である。また、厚みは０．０１〜１．５μｍであると、製膜性がより一層良好となり好ましい。好ましくは０．０３〜１μｍ、より好ましくは０．０５〜０．７５μｍである。また、Ｂ層の厚みｔは不活性粒子の平均粒径ｄの０．１〜１０倍が好ましく、より好ましくは０．２〜５倍である。ｔ／ｄが０．１より小さい場合は、不活性粒子が脱落しやすくなることがあり、１０を越える場合には、Ｂ層側の突起高さが不揃いとなって、走行性やハンドリング性に十分な効果を及ぼさないことがある。
【００４２】
本発明の積層ポリエステルフィルムは、Ａ層／Ｂ層の２層積層構成の基材フィルムの少なくともＢ層と反対側の表面に易滑平滑層（Ｃ層）が設けられたフィルム構成、または、Ｂ層のＡ層と反対側にポリエステルまたはポリエステルとポリイミド、および、不活性粒子を必須成分としてなる積層部（Ｄ層）が設けられたＤ層／Ａ層／Ｂ層の３層積層構成である場合に、本発明の効果を十分に発揮できるので好ましいが、これに限定されるものではない。
【００４３】
本発明の積層ポリエステルフィルムは、易滑平滑層（Ｃ層）を設ける場合、Ｃ層はコーティングにより形成される。Ｃ層は、特に限定されないが、水溶性高分子と不活性粒子を主たる成分にしたものから形成されることが好ましい。Ｃ層は、磁気ヘッドとの走行性、走行耐久性の観点から、少なくともＢ層と反対側の表面に設けられなければならない。Ｃ層を設けることにより、テープの保存工程や蒸着加工工程において、フィルム中から表面に析出する低分子量体を効果的に抑止することができるため好ましい。また、特に限定されないが、磁気テープに加工する工程や、保存中のオリゴマー析出の抑止の観点から、Ｂ層側の表面にも易滑平滑層（Ｃ’層）を設けたＣ層／Ａ層／Ｂ層／Ｃ’層の構成をとってもよい。
ただし、この場合はＣ’層を設けない場合と比較して、生産効率が低下する。
【００４４】
本発明の積層ポリエステルフィルムにＣ層を設ける場合、Ｃ層を構成する水溶性高分子としては、水酸基、エーテル基、エステル基、スルホン基、アミド基、メトキシ基、ヒドロキシプロポキシ基等の極性基を持ち、分子量が１万〜２００万、好ましくは１０万〜１００万のものが使用でき、具体例としては、ポリビニルアルコール、トラガントゴム、アラビアゴム、カゼイン、ゼラチン、メチルセルロース、ヒドロキシエチルセルロース、カルボキシメチルセルロース、テレフタル酸、イソフタル酸、トリメリット酸などの多価カルボン酸とエチレングリコールなどからなる水溶性ポリエステル、水溶性ポリエステルエーテル共重合体等が適用でき、これらのブレンド体も適用できる。中でも、メチルセルロースと水溶性ポリエステルのブレンド体がＡ層とのぬれ性の点から特に好ましく例示される。
【００４５】
本発明の積層ポリエステルフィルムにＣ層を設ける場合、Ｃ層を構成する不活性粒子の種類としては、前述のような粒子が例示されるが、中でも、アクリル酸類、スチレン、シリコーン、イミド等を構成成分とする有機粒子、特にアクリル酸類またはイミド類を構成成分とする有機粒子である場合、ポリエステルとポリイミドを主成分とするＡ層との親和性が高いためと考えられるが、コーティングの塗布斑が起こりにくく、製膜、加工工程における粒子の脱落や表面の傷付きが著しく低減するため好ましい。
【００４６】
本発明の積層ポリエステルフィルムにＣ層を設ける場合、Ｃ層を構成する不活性粒子の平均粒径ｄ_cは５〜５０ｎｍが好ましく、より好ましくは６〜２５ｎｍ、最も好ましくは７〜２０ｎｍである。Ｃ層はコーティングにより形成される層であるため、平均粒径が５０ｎｍを越える場合は、製膜、加工工程で粒子が著しく脱落しやすくなる場合がある。また、平均粒径が５ｎｍより小さい場合には、塗液を調合する際に不活性粒子が凝集し易くなり、粗大突起の原因となったり、製膜、加工工程で脱落しやすくなる場合がある。
【００４７】
本発明の積層ポリエステルフィルムにＣ層を設ける場合、Ｃ層を構成する不活性粒子の含有量は３００万〜７０００万個／ｍｍ²である。なお、Ｃ層の粒子含有量を面積当たりの個数で表しているのは、Ｃ層は粒子の平均粒径に対して、極めて薄いため、Ｃ層に含有する粒子は、ほぼすべてＣ層側の表層に露出するためである。含有量を水溶性高分子との比率で表す場合、水溶性高分子１００重量部（Ｃ層中にシランカップリング剤またはチタンカップリング剤を含有させるときは、水溶性高分子と該カップリング剤の合計量１００重量部）に対して５〜５０重量部が好ましく、より好ましくは１０〜４０重量部である。粒子の含有量がこの範囲であると粒子のＣ層からの脱落がなく、また電磁変換特性も向上する。
【００４８】
本発明の積層ポリエステルフィルムにＣ層を設ける場合、Ｃ層の被覆厚みは、特に限定されないが、好ましくは１ｎｍ〜５０ｎｍ、より好ましくは、５ｎｍ〜２５ｎｍの範囲であることが、本発明のフィルムを得るのに有効である。Ｃ層の厚みが１ｎｍより小さい場合、コーティングの際の単位面積当たりの塗布量が非常に少なくなるため、安定塗布が困難となり、５０ｎｍより大きい場合は、インラインにおける塗液の乾燥が不十分となったり、Ｃ層が延伸の際に割れて、剥がれやすくなったりする。
【００４９】
本発明の積層ポリエステルフィルムは、Ｄ層／Ａ層／Ｂ層の３層積層とする場合、Ｄ層に用いるポリマーはＡ層を構成するポリエステルと同一のポリエステル、または、Ａ層を構成するポリマーアロイと同一のポリエステルとポリイミドからなるポリマーアロイである場合、積層斑や口金すじ等の製膜工程における問題を抑制しやすいため好ましい。なかでも、Ｄ層にポリエステルのみを用いる場合は、Ａ層を構成するポリエステルより高分子量のポリエステルを用いること、また、ポリエステルとポリイミドからなるポリマーアロイを用いる場合は、それぞれＡ層を構成するポリエステル、ポリイミドと同一分子量のものを用い、ポリイミドの含有量も等しくすることが、製膜の際の問題を低減するために特に好ましい手法である。
【００５０】
本発明の積層ポリエステルフィルムのＤ層に用いるポリエステルがエチレンテレフタレートを主要構成成分とするポリエステルである場合、ポリエステルは直重法およびＤＭＴ法のいずれによるものでもよいが、ＤＭＴ法の時はエステル交換触媒として酢酸カルシウムを用いることが好ましい。また重合段階では、特に限定されないが、ゲルマニウム化合物を重合触媒として用いることが異物による粗大突起を低減させるため好ましい。ゲルマニウム触媒としては、公知のとおり、(1)無定形酸化ゲルマニウム、(2)５μｍ以下の結晶性酸化ゲルマニウム、(3)酸化ゲルマニウムをアルカリ金属またはアルカリ土類金属もしくはそれらの化合物の存在下にグリコールに溶解した溶液、および、(4)酸化ゲルマニウムを水に溶解し、これにグリコールを加え水を留去して調整した酸化ゲルマニウムのグリコール溶液等が用いられる。
【００５１】
本発明の積層ポリエステルフィルムは、Ｄ層／Ａ層／Ｂ層の３層積層とする場合、Ｄ層に含有させる不活性粒子の種類としては、前述のような粒子が例示される。中でも、コロイド状シリカや微分散アルミナやスチレン、シリコーン、イミド等を構成成分とする有機粒子が好ましく例示される。
【００５２】
本発明の積層ポリエステルフィルムをＤ層／Ａ層／Ｂ層の３層積層とする場合、Ｄ層に含有させる不活性粒子の平均粒径ｄ_Dは、１０〜５０ｎｍが好ましく、より好ましくは１５〜５０ｎｍ、最も好ましくは２０〜４０ｎｍである。平均粒径が５０ｎｍを越える場合には、蒸着型磁性層を有する磁気テープとしては、磁性面側の突起が粗大であり、電磁変換特性の低下や、磁気ヘッドを傷付けてしまい、走行耐久性の低下を招く場合がある。平均粒径が２０ｎｍより小さい場合には、磁性面側の突起高さが低いため、磁気ヘッドとの摩擦が高くなりすぎて、ヘッドの走行性が悪化したり、製膜、加工の際にロールとの摩擦のために傷が付きやすくなったりする。
【００５３】
本発明の積層ポリエステルフィルムをＤ層／Ａ層／Ｂ層の３層積層とする場合、Ｄ層に含有させる不活性粒子の含有量は０．１〜３重量％が好ましく、より好ましくは０．３〜１．５重量％、最も好ましくは０．５〜１重量％である。含有量が３重量％を越える場合には、溶融成形の工程で粒子の凝集が起こり突起が粗大となって、電磁変換特性が低下したり、突起が削れやすくなったりする。含有量が０．１重量％より少ない場合、磁性面が平坦となりすぎて、ヘッドの走行性が悪化したり、製膜、加工の際にロールとの摩擦のために傷が付きやすくなったりする。
【００５４】
本発明の積層ポリエステルフィルムをＤ層／Ａ層／Ｂ層の３層積層とする場合、Ｄ層の厚みｔ_Dは０．０１μｍ〜０．８μｍが好ましく、より好ましくは０．０３μｍ〜０．５μｍ、さらに好ましくは０．０５〜０．１μｍである。Ｄ層の厚みが０．０１μｍより薄い場合、Ｄ層の粒子が脱落し易くなり、走行耐久性の悪化などを招くことがあり、また厚みが０．５μｍより厚い場合には、突起の高さが不揃いとなるため、ヘッドの走行性の低下を招くことがある。また、Ｄ層厚みｔ_Dは平均粒径ｄ_Dの０．１〜１０倍が好ましく、より好ましくは０．５〜５倍である場合、電磁変換特性とヘッド走行性がともに良好となる。
【００５５】
本発明の積層ポリエステルフィルムをＤ層／Ａ層／Ｂ層の３層積層とする場合、特に限定されないが、各フィルム層中に、脂肪酸エステルのようなワックスや界面活性剤を含有させる場合、フィルム中から表面に析出する低分子量体を効果的に抑止することができるため好ましい。より好ましくは、Ｂ層、Ｄ層に比較的高濃度に含有させ、Ａ層には低濃度に含有させるか、または、実質的に含有させない場合、弾性率の低下などを引き起こす懸念が少ない。ワックスとしては、カルナウバワックスのような天然ワックス、または、ステアリルステアレート、ベヘニルベヘネートのような脂肪酸エステルが挙げられ、特にカルナウバワックスが好ましく例示される。界面活性剤としては、ウンデシルスルホン酸ナトリウム、ドデシルスルホン酸カリウムなどのアルキルスルホン酸のアルカリ金属塩もしくはアルカリ土類金属塩や、ドデシルベンゼンスルホン酸ナトリウム、ドデシルベンゼンスルホン酸リチウムなどのアルキルベンゼンスルホン酸のアルカリ金属塩もしくはアルカリ土類金属塩が挙げられ、特にドデシルベンゼンスルホン酸ナトリウムが好ましく例示される。含有量としては、０．１〜２重量％が好ましく、より好ましくは、０．２〜０．８重量％である。
【００５６】
本発明の積層ポリエステルフィルムのＢ層側の表面（ｂ面）の表面粗さＲａ_bは５〜２０ｎｍであり、好ましくは６〜１７ｎｍ、さらに好ましくは７〜１５ｎｍである。Ｒａ_bが５ｎｍより小さい場合には、製膜および加工工程において十分なハンドリング性が得られず生産性が低下したり、磁気テープに加工した際の走行性や耐摩耗性が低下して、十分な磁気テープ特性が得られないため好ましくない。Ｒａ_bが２０ｎｍより大きい場合には、磁気テープとして用いる際、走行面側の形態が磁性面側に転写して、電磁変換特性を悪化させたり、走行面側の粒子が脱落し易くなり、走行特性の悪化やドロップアウトなどの原因となるため好ましくない。また、蒸着型磁性層を有する磁気テープの場合、蒸着工程における冷却効率が低下するため、「しわ」等の熱負けの原因となったり、オリゴマーが析出しやすくなる。
【００５７】
本発明の積層ポリエステルフィルムのＢ層と反対側の表面（ｆ面）の表面粗さＲａ_fは０．１〜５ｎｍであり、好ましくは１〜４ｎｍ、さらに好ましくは１．５〜３ｎｍである。Ｒａ_bが０．１ｎｍより小さい場合は、工業的に製造が困難であったり、磁気テープに加工した際の磁気ヘッドとの走行性が低下して十分な磁気テープ特性が得られない場合がある。Ｒａ_fが５ｎｍより大きい場合には、蒸着型磁性層を有する磁気テープとして用いる際、電磁変換特性が低下したり、磁気ヘッドを傷つけやすくなるため好ましくない。
【００５８】
本発明の積層ポリエステルフィルムのｆ面の粗大突起数Ｈ１は、電磁変換特性、走行耐久性の観点から、１００個／１００ｃｍ²以下であり、好ましくは５０個／１００ｃｍ²以下、より好ましくは１０個／１００ｃｍ²以下である。同様に粗大突起数Ｈ２は１０個／１００ｃｍ²以下であり、好ましくは５個／１００ｃｍ²以下、より好ましくは２個／１００ｃｍ²以下である。粗大突起数Ｈ１が１００個／１００ｃｍ²を越えると、電磁変換特性が悪化するため好ましくなく、Ｈ２が１０個／１００ｃｍ²を越えると、磁気ヘッドが傷付きやすくなって、走行耐久性が悪化する。なお、本発明でｆ面の粗大突起数を表すＨ１、Ｈ２は、後述の測定法によって定義される値である。
【００５９】
本発明の積層ポリエステルフィルムのＡ層中のポリイミドの含有量は、ポリマーアロイ中の５〜３０重量％の範囲にあることが好ましい。さらに好ましくは、８〜１５重量％である。一般的にポリエステルとポリイミドの溶融粘度は大きく異なるため、ポリイミドの含有量が５重量％未満であると、押出機にて十分に微分散することが困難な場合があり、ポリイミドのドメインが粗大となることによって、表面突起が粗大となる場合がある。また、ポリイミドの含有量が３０重量％を超える量であると、押出成形加工や延伸加工を施すことが困難となり、フィルム破れや押出時の口金すじなどの製膜、加工上のトラブルの原因となる場合がある。
【００６０】
本発明の積層ポリエステルフィルムは、本発明の効果を阻害しない範囲内で、熱安定剤、酸化防止剤、紫外線吸収剤、帯電防止剤、難燃剤、顔料、染料、脂肪酸エステル、ワックスなどの有機滑剤などが添加されてもよい。
【００６１】
本発明の積層ポリエステルフィルムの長手方向のヤング率と幅方向のヤング率の和は、９〜２０ＧＰａの範囲であることが好ましく、より好ましくは１０〜１８ＧＰａ、さらに好ましくは１１〜１５ＧＰａである。該ヤング率の和が９ＧＰａ未満であれば、例えば、磁気記録媒体用などに用いる場合、走行時の磁気記録ヘッドやガイドピンから受ける張力のため、磁気テープに伸び変形が生じやすくなり、さらに電磁変換特性（出力特性）に悪影響を与えたりして、実用上使用に耐えない場合がある。また、該ヤング率の和が２０ＧＰａを越えるフィルムは工業的に製造が困難であったり、フィルムの耐引裂性や寸法安定性が著しく低下したりする場合がある。
【００６２】
本発明の積層ポリエステルフィルムの長手方向のヤング率は、磁気ヘッドとのヘッド当たりの観点から、４．３ＧＰａ以上であることが好ましい。より好ましくは４．５ＧＰａ以上、最も好ましくは５ＧＰａ以上である。
【００６３】
本発明の積層ポリエステルフィルムの幅方向のヤング率はテープエッジダメージや、長手方向の伸びを抑える観点から、４．７ＧＰａ以上であることが好ましい。より好ましくは５ＧＰａ以上、最も好ましくは５．５ＧＰａ以上である。
【００６４】
本発明の積層ポリエステルフィルムの長手方向の温度１００℃、３０分における熱収縮率は、テープの伸び変形性および保存性の観点から、１．２％以下であることが好ましい。より好ましくは、１％以下である。該熱収縮率が１．２％を越える場合は、寸法安定性が損なわれやすくなる場合がある。例えば磁気記録媒体用においては、ベースフィルムの磁気層を塗布するなどのフィルム加工工程における熱履歴や走行時の磁気テープと磁気記録ヘッドとの摩擦熱による磁気テープの昇温時にテープの熱変形が起こりやすくなったり、フィルム表面の耐久性が劣下したり、テープの保存性が悪化する場合がある。
【００６５】
本発明の積層ポリエステルフィルムの長手方向の温度８０℃、３０分における熱収縮率は、テープの伸び変形性および保存性の観点から、０．３％以下であることが好ましい。より好ましくは、０．２５％以下である。
【００６６】
本発明の積層ポリエステルフィルムの幅方向の温度１００℃、３０分における熱収縮率は、テープの伸び変形性および保存性の観点から、０．５％以下であることが好ましい。より好ましくは、０．３％以下である。該熱収縮率が０．５％を越える場合は、寸法安定性が損なわれやすくなる場合がある。例えば磁気記録媒体用においては、ベースフィルムの磁気層を塗布するなどのフィルム加工工程における熱履歴や走行時の磁気テープと磁気記録ヘッドとの摩擦熱による磁気テープの昇温時にテープの熱変形が起こりやすくなったり、フィルム表面の耐久性が劣下したり、テープの保存性が悪化する場合がある。
【００６７】
本発明の積層ポリエステルフィルムの幅方向の温度８０℃、３０分における熱収縮率は、テープの伸び変形性および保存性の観点から、０．１％以下であることが好ましい。より好ましくは、０．０５％以下である。
【００６８】
本発明のＡ層のポリマーの補外ガラス転移開始温度（Ｔｇ_onset）は、特に限定されないが９２〜１５０℃であることが好ましく、より好ましくは９６〜１３０℃、さらに好ましくは９８〜１２０℃の範囲内である。また、Ａ層のポリマーのガラス転移温度（Ｔｇ）は、特に限定されないが、１０５〜１７０℃であることが好ましく、より好ましくは、１１０〜１４０℃である。Ｔｇ_onsetおよびＴｇが本範囲に満たない場合、磁気テープ走行時の寸法安定性が低下したり、テープ保存時に熱収縮によるしわが入りやすくなるほか、蒸着用磁気記録媒体として用いる際には、蒸着工程においてフィルムが熱収縮することによる「しわ」が発生する場合がある。また、Ｔｇ_onsetおよびＴｇが本範囲を越える場合には、延伸等に要する温度が高くなり過ぎるため、生産性が低下したり、延伸ロール等の設備の耐久性が低下することがある。
【００６９】
本発明のＡ層を構成するポリマーアロイの固有粘度は、フィルム成形加工の安定性や熱可塑性樹脂との混合性の観点から、０．５５〜３．０（ｄｌ／ｇ）の範囲であることが好ましく、さらに好ましくは、０．６０〜２．０（ｄｌ／ｇ）である。また、製膜後のフィルムの固有粘度は、フィルム成形加工の安定性や寸法安定性などの観点から、０．５０〜２．０（ｄｌ／ｇ）の範囲であることが好ましく、さらに好ましくは０．５５〜１．０（ｄｌ／ｇ）である。
【００７０】
本発明の積層ポリエステルフィルムの全厚みは、３〜８μｍである。好ましくは４〜７μｍであり、より好ましくは４．５〜６．５μｍである。厚みが３μｍより小さい場合は、テープに腰がなくなるため、電磁変換特性が低下する。厚みが８μｍより大きい場合は、テープ１巻あたりのテープ長さが短くなるため、磁気テープの小型化、高容量化が困難になるため好ましくない。
【００７１】
本発明の積層ポリエステルフィルムは、さらに他のポリマー層、例えば、ポリオレフィン、ポリアミド、ポリ塩化ビニリデンおよびアクリル系ポリマーを直接、あるいは接着剤などの層を介して積層してもよい。
【００７２】
本発明の２軸延伸フィルムは、必要に応じて、熱処理、成形、表面処理、ラミネート、コーティング、印刷、エンボス加工、エッチングなどの任意の加工を行ってもよい。
【００７３】
本発明の積層ポリエステルフィルムの少なくとも片面に磁性層を設けることにより、磁気記録媒体として用いることができる。磁性層を設ける面は、フィルムのいずれの面でも、あるいは、両方の面でも良いが、前記積層構造のフィルムを用いる場合は、Ａ層側に磁性層を設けることが好ましい。
【００７４】
磁性層としては、強磁性金属薄膜や強磁性金属微粉末を結合剤中に分散してなる磁性層や金属酸化物塗布による磁性層などが好適な例として挙げられる。前記強磁性金属薄膜に用いる金属としては、鉄、コバルト、ニッケルやその合金等が好ましい。また、前記強磁性金属微粉末を結合剤中に分散してなる磁性層に用いる強磁性金属微粉末としては、強磁性六方晶フェライト微粉末や、鉄、コバルト、ニッケルやその合金からなる粉末が好ましい。前記結合剤としては熱可塑性樹脂、熱硬化性樹脂、反応型樹脂やこれらの混合物などが好ましい。
【００７５】
磁性層の形成法としては、磁性粉を熱硬化性、熱可塑性あるいは放射線硬化性などの結合剤と混練し、塗布、乾燥を行う塗布法、金属または合金を蒸着、スパッタリング、イオンプレーティング法などにより、基材フィルム上に直接磁性金属薄膜層を形成する乾式法のいずれの方式も採用できる。
【００７６】
本発明の磁気記録媒体においては、磁性層上に保護膜が設けられていてもよい。この保護膜によってさらに走行耐久性、耐食性を改善することができる。保護膜としては、シリカ、アルミナ、チタニア、ジルコニア、酸化コバルト、酸化ニッケルなどの酸化物保護膜、窒化チタン、窒化ケイ素、窒化ホウ素などの窒化物保護膜、炭化ケイ素、炭化クロム、炭化ホウ素等の炭化物保護膜、グラファイト、無定型カーボンなどの炭素からなる炭素保護膜があげられる。
【００７７】
前記炭素保護膜は、プラズマＣＶＤ法、スパッタリング法等で作成したアモルファス、グラファイト、ダイヤモンド構造、もしくはこれらの混合物からなるカーボン膜であり、特に好ましくは一般にダイヤモンドライクカーボンと呼ばれる硬質カーボン膜である。
【００７８】
また、この硬質炭素保護膜上に付与する潤滑剤との密着をさらに向上させる目的で、硬質炭素保護膜表面を酸化性もしくは不活性気体のプラズマによって表面処理しても良い。
【００７９】
本発明では、磁気記録媒体の走行耐久性および耐食性を改善するため、上記磁性層もしくは保護膜上に、潤滑剤や防錆剤を付与することが好ましい。
【００８０】
本発明の積層ポリエステルフィルムの用途は、均一で微細な表面形態と高い寸法安定性を必要とするデジタル記録方式の磁気記録媒体である。中でも、蒸着型の磁性層を有する磁気記録媒体に特に好ましく用いることができる。具体的には、データストレージ用高密度磁気記録用テープやデジタルビデオテープなどのベースフィルムに適したものである。
【００８１】
以下、本発明の積層ポリエステルフィルムの製造方法の例について説明するが、これに限定されるものではない。ここでは、Ａ層ポリマーのポリエステルとして、ポリエチレンテレフタレートを用い、ポリイミドとして、ポリエーテルイミド“ウルテム”を用いたＤ／Ａ／Ｂ３層積層ポリエステルフィルムの例を示す。また、Ａ／Ｂ２層積層構成の基材フィルムに易滑平滑層（Ｃ層）を設ける場合には、基材フィルムの製造方法は、Ｄ層部を用いない以外は、本例と同様にすればよい。製造条件は、用いるポリエステルおよびポリイミド、または積層構成によって異なる。
【００８２】
まず、常法に従い、テレフタル酸とエチレングリコールをエステル化することにより、または、テレフタル酸ジメチルとエチレングリコールをエステル交換反応することにより、ビス−β−ヒドロキシエチルテレフタレート（ＢＨＴ）を得る。次にこのＢＨＴを重合槽に移行しながら、真空下で２８０℃に加熱して重合反応を進める。ここで、固有粘度が０．５程度のポリエステルを得る。得られたポリエステルをペレット状にして減圧下におき、固相重合する。固相重合する場合は、ペレット状ポリエステルをあらかじめ１８０℃以下の温度で予備結晶化させた後、１９０〜２５０℃で１ｍｍＨｇ程度の減圧下、１０〜５０時間固相重合させる。また、フィルムを構成するポリエステルに不活性粒子を含有させる場合には、エチレングリコールに不活性粒子を所定割合にてスラリーの形で分散させ、このエチレングリコールを重合時に添加する方法が好ましい。不活性粒子を添加する際には、例えば、不活性粒子を合成時に得られる水ゾルやアルコールゾルを一旦乾燥させることなく添加すると粒子の分散性がよい。また、不活性粒子の水スラリーを直接ポリエステルペレットと混合し、ベント式２軸混練押出機を用いて、ポリエステルに練り込む方法も有効である。不活性粒子の含有量を調節する方法としては、上記方法で高濃度の不活性粒子のマスターを作っておき、それを製膜時に不活性粒子を実質的に含有しないポリエステルで希釈して不活性粒子の含有量を調節する方法が有効である。
【００８３】
次に、ポリエチレンテレフタレートのペレットとポリエーテルイミドのペレットを混合して、２７０〜３００℃に加熱されたベント式の２軸混練押出機に供給して、溶融押出する。このときの剪断速度は５０〜３００ｓｅｃ^-1が好ましく、より好ましくは１００〜２００ｓｅｃ^-1、滞留時間は０．５〜１０分が好ましく、より好ましくは１〜５分の条件である。混合比率は、２０〜８０％が好ましく、より好ましくは４０〜６０％である。ポリエーテルイミドの混合比率が高すぎたり、低すぎたりすると、混練にて両者が十分に相溶しない場合がある。さらに、上記条件にて両者が相溶しない場合は、得られたチップを再び２軸押出機に投入し相溶するまで押出を繰り返してもよい。
【００８４】
得られたポリエーテルイミド含有のポリエステルのペレットと不活性粒子のマスターペレット、および、ポリエステルのペレットを所定の割合になるように混合して、１８０℃で３時間以上真空乾燥した後、固有粘度が低下しないように窒素気流下あるいは真空下で、２８０〜３２０℃に加熱された押出機に供給し、スリット状のダイから押出し、キャスティングロール上で冷却して未延伸フィルムを得る。
【００８５】
その際、ポリマー中の異物や変質ポリマー、未溶融物などを除去する方法としては、各種のフィルター、例えば、焼結金属、多孔性セラミック、サンド、金網などの素材からなるフィルターを用いることが好ましい。特に、Ａ層および３層積層構成の際はＤ層のポリマーは、１．２μｍカット以下の繊維焼結ステンレス金属フィルターによりポリマーを濾過すること好ましく例示される。より好ましくは、０．８μｍ以下のフィルターである。また、必要に応じて、２つ以上のフィルター部分を通過させ、２段階以上で濾過するとより効果的に未溶融物を除去できるため好ましい。最も好ましくは、サンドフィルター、１．２μｍカットの繊維焼結ステンレス金属フィルターおよび０．８μｍカットの繊維焼結ステンレス金属フィルターを順に用いて、３段階に濾過する方法が挙げられる。
【００８６】
なお、ここでいう１．２μｍカットのフィルターとは、濾過精度１．２μｍのことをいい、濾過精度とはＪＩＳ−Ｂ８３５６の方法によりフィルターメディアを透過した最大グラスビーズ粒径を意味する。
【００８７】
また、必要に応じて、定量供給性を向上させるためにギアポンプを設けることが好ましい。
【００８８】
フィルムを積層する方法としては、２台以上の押出機およびマニホールドまたは合流ブロックを用いて、複数の異なるポリマーを溶融積層する方法が好ましい。
【００８９】
次に、この未延伸フィルムを２軸延伸し、２軸配向させる。延伸方法としては、逐次２軸延伸法または同時２軸延伸法を用いることができる。ここでは、最初に長手方向、次に幅方向の延伸を行う逐次２軸延伸法を用いる。延伸温度については、積層の構成成分により異なるが、例えば、３層構造でＡ層、Ｂ層、Ｄ層ともにポリエチレンテレフタレートとポリエーテルイミドの混合ポリマー（混合重量比９：１）からなる場合を例示して説明する。未延伸フィルムを７０〜１３０℃の加熱ロール群で加熱し、長手方向に３〜８倍に１段もしくは多段で延伸（再縦延伸を行う場合は１段目の延伸は２〜４倍）し、２０〜５０℃の冷却ロール群で冷却する。長手方向延伸速度は１０００〜５００００％／分の範囲で行うのが好ましい。続いて、幅方向の延伸を行う。幅方向の延伸方法としては、例えば、テンターを用いる方法が一般的である。幅方向の延伸倍率は３〜８倍（再横延伸を行う場合は１段目の延伸は２〜４倍）、延伸速度は１０００〜２００００％／分、温度は８０〜１５０℃の範囲で行うのが好ましい。さらに必要に応じて、再縦延伸および／または再横延伸を行う。その場合の延伸条件としては、長手方向の延伸は、温度８０〜１７０℃の加熱ロール群で、延伸倍率１．１〜２．５倍、幅方向の延伸方法としてはテンターを用いる方法が好ましく、温度８０〜１８０℃、延伸倍率１．１〜２．５倍で行うのが好ましい。続いて、この延伸フィルムを緊張下または幅方向に弛緩しながら熱処理する。この場合の熱処理温度は、２００℃〜２３０℃、好ましくは、２１０〜２２０℃で、時間は０．２〜１０秒の範囲で行うのが好ましい。
【００９０】
２層積層フィルムに易滑平滑層（Ｃ層）を被覆する場合、被覆する時期は上記フィルム製造過程において、理論上、長手方向延伸前、幅方向延伸前、幅方向延伸後、さらにはフィルム製膜後オフラインにてコーティング可能であるが、Ｃ層が極薄層であることから上記幅方向延伸前あるいは後のいずれかで被覆し、被覆後Ｃ層が固定されるまではロール等に接触しないようにするのが好ましい。従って、例えば、長手方向延伸、続いて幅方向延伸を行う逐次二軸延伸における幅方向延伸前、あるいは同時二軸延伸における延伸前等においてＣ層を被覆することが好ましい。被覆はフィルム連続製造工程中でコーティングする、いわゆるインラインコーティング等が工業的に好ましい。オフライン専用の別工程にて行っても良い。
【００９１】
（物性の測定方法ならびに効果の評価方法）
本発明における特性値の測定方法並びに効果の評価方法は次の通りである。
【００９２】
（１）表面の突起高さと突起個数
原子間力顕微鏡（ＡＦＭ）を用いて、以下の条件で、場所を変えて測定を１０回行う。
装置：NanoScopeIII AFM (Digital Instruments社製）
カンチレバー：シリコン単結晶
走査モード ：タッピングモード
走査範囲 ：５μｍ×５μｍ
走査速度 ：０．５Ｈｚ
測定環境 ：温度 ２５℃、相対湿度 ５５％
平坦面より、２〜５０ｎｍの範囲にある突起個数を測定し、その平均をとって、１ｍｍ²当たりの数に換算する。
【００９３】
（２）表面粗さＲａ
小坂研究所製の高精度薄膜段差測定器ＥＴ−１０を用いて中心線平均粗さＲａを測定した。条件は下記のとおりであり、フィルム幅方向に走査して２０回測定を行った平均値をもって値とした。
・触針先端半径：０．５μｍ
・触針荷重 ：５ｍｇ
・測定長 ：１ｍｍ
・カットオフ値：０．０８ｍｍ
【００９４】
（３）不活性粒子の平均粒径
フィルム断面を透過型電子顕微鏡（ＴＥＭ）を用い、１万倍以上の倍率で観察する。ＴＥＭの切片厚さは約１００ｎｍとし、場所を変えて１００視野以上測定する。測定した等価円相当径の重量平均を不活性粒子の平均粒径ｄとした。
フィルム中に粒径の異なる２種類以上の粒子が存在する場合、上記の等価円相当径の個数分布が２種類以上のピークを有する分布となるため、そのそれぞれについて、別個に平均粒径を算出する。
【００９５】
（４）ポリエステル、ポリイミド、フィルム層中の不活性粒子の含有量
ポリエステルとポリイミドとの両者を溶解する適切な溶媒に溶解し、¹Ｈ核のＮＭＲ（核磁気共鳴）スペクトルを測定する。適切な溶媒は、ポリマーの種類によって異なるが、例えば、ヘキサフルオロイソプロパノール（ＨＦＩＰ）／重クロロホルムが用いられる。得られたスペクトルにおいて、ポリエステル、ポリイミドに特有の吸収（例えばＰＥＴであればテレフタル酸の芳香族プロトンの吸収、ＰＥＩであればビスフェノールＡの芳香族のプロトンの吸収）のピーク面積強度をもとめ、その比率とプロトン数よりポリエステルとポリイミドのモル比を算出する。さらに各々のポリマーの単位ユニットに相当する式量より重量比を算出する。測定条件は、例えば、以下のような条件であるが、ポリマーの種類によって異なるため、この限りではない。
【００９６】
装置 ：BRUKER DRX-500（ブルカー社）
溶媒 ：ＨＦＩＰ／重クロロホルム
観測周波数：４９９．８ＭＨｚ
基準 ：ＴＭＳ（テトラメチルシラン）（０ｐｐｍ）
測定温度 ：３０℃
観測幅 ：１０ＫＨｚ
データ点 ：６４Ｋ
acquisiton time ：４．９５２秒
pulse delay time：３．０４８秒
積算回数 ：２５６回
また、必要に応じて、顕微ＦＴ−ＩＲ法（フーリエ変換顕微赤外分光法）で組成分析を行ってもよい。その場合、ポリエステルのカルボニル基に起因するピークとそれ以外の物質に起因するピークの比から求める。なお、ピーク高さ比を重量比に換算するために、あらかじめ重量比既知のサンプルで検量線を作成してポリエステルとそれ以外の物質の合計量に対するポリエステル比率を求める。これと、不活性粒子含有量よりＰＥＩ比率を求める。また、必要に応じてＸ線マイクロアナライザーを併用してもよい。
【００９７】
また、不活性粒子の含有量については、ポリエステル、ポリイミドは溶解するが不活性粒子は溶解させない溶媒を選んで、ポリエステル、ポリイミドを溶解し、不活性粒子を遠心分離して重量百分率を求めた。
【００９８】
（５）易滑平滑層（Ｃ層）中の不活性粒子の含有量
Ｃ層側のフィルム表面を走査型電子顕微鏡（ＳＥＭ）を用いて、３万倍程度の拡大倍率でフィルム表面を１０視野以上観察し、突起状に見える突起が１ｍｍ²当たり何個あるかを求めることにより測定した。
【００９９】
（６）積層厚さ
透過型電子顕微鏡（日立製Ｈ−６００型）を用いて、加速電圧１００ｋＶで、フィルム断面を、超薄切片法（ＲｕＯ₄染色）で観察する。その界面の観察結果から、各層の厚さを求める。倍率は、判定したい積層厚さによって適切な倍率を選ぶが、１万〜１０万倍が適当である。
【０１００】
また、２次イオン質量分析装置（ＳＩＭＳ）を用いて測定することもできる。
表層から深さ３０００ｎｍの範囲のフィルム中の不活性粒子の内もっとも高濃度の粒子（積層部と基層部でポリイミドの含有量が異なる場合には、ポリイミドでも可）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、表面から深さ３０００ｎｍまで厚さ方向にＳＩＭＳで分析する。表層では不活性粒子に起因する元素濃度は低く、表面から遠ざかるにつれて不活性粒子に起因する元素濃度は高くなる。本発明フィルムの場合は一旦極大値となった不活性粒子に起因する元素濃度がまた減少し始める。この濃度分布曲線において、不活性粒子に起因する元素濃度が極大値の１／２まで減少した深さを積層厚さとする。条件は次の通りである。
【０１０１】
ｉ）測定装置
２次イオン質量分析装置（ＳＩＭＳ）
西独、ＡＴＯＭＩＫＡ社製 Ａ−ＤＩＤＡ３０００
ii）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 ：５．０×１０^-9Ｔｏｒｒ
Ｅ−ＧＵＮ ：０．５ＫＶ−３．０Ａ
なお、表層から深さ３０００ｎｍの範囲に最も多く含有する不活性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プスプロファイルを測定し積層厚みを求めることもできる。
【０１０２】
（７）ヤング率
ＡＳＴＭ−Ｄ８８２に規定された方法に従って、インストロンタイプの引張試験機を用いて測定した。測定は下記の条件とした。
測定装置：オリエンテック（株）製フイルム強伸度自動測定装置“テンシロン”ＡＭＦ／ＲＴＡ−１００
試料サイズ：幅１０ｍｍ×試長間１００ｍｍ、
引張り速度：２００ｍｍ／分
測定環境：温度２３℃、湿度６５％ＲＨ
【０１０３】
（８）粗大突起数Ｈ１、Ｈ２
測定面（１００ｃｍ²）同士を２枚重ね合わせて静電気力（印加電圧５．４ｋｖ）で密着させた後、２枚のフィルム間で粗大突起の光の干渉によって生じるニュートン環から粗大突起の高さを判定し、１重環以上の粗大突起数をＨ１、２重環以上の粗大突起数をＨ２とした。なお、光源はハロゲンランプに５６４ｎｍのバンドパスフィルタをかけて用いた。
【０１０４】
（９）熱収縮率（加工時および保存時の寸法安定性）
ＪＩＳ Ｃ２３１８に従って、測定した。
試料サイズ：幅１０ｍｍ、標線間隔２００ｍｍ
測定条件：温度１００℃、処理時間３０分、無荷重状態
熱収縮率を次式より求めた。
熱収縮率（％）＝［（Ｌ₀−Ｌ）／Ｌ₀］×１００
Ｌ₀：加熱処理前の標線間隔
Ｌ：加熱処理後の標線間隔
この結果、長手方向の熱収縮率が１％以下であり、幅方向の熱収縮率が０．５％以下である場合、加工時および保存時の寸法安定性が良好である（○）とし、長手方向、幅方向のいずれか一方でもこの範囲から外れる場合、加工時および保存時の寸法安定性が不良である（×）と判定した。
【０１０５】
（１０）磁気テープの電磁変換特性（Ｓ／Ｎ）
本発明のフィルムのＢ層と反対側の表面に連続真空蒸着装置を用いて、微量の酸素の存在下において、コバルト−酸素薄膜を１５０ｎｍの膜厚で形成した。次にコバルト−酸素薄膜上にスパッタリング法により、ダイアモンド状カーボン保護膜を１０ｎｍの厚みで常法で形成させ、フッ素含有脂肪酸エステル系潤滑剤を３ｎｍの厚みで塗布した。続いて、Ｂ層側の表面に、カーボンブラック、ポリウレタン、シリコーンからなるバックコート層を５００ｎｍの厚みで設け、スリッターにより幅６．３５ｍｍにスリットしリールに巻き取り磁気記録テープ（ＤＶＣビデオテープ）を作成した。
【０１０６】
上記、磁気記録テープの特性評価は、市販のカメラ一体型デジタルビデオテープレコーダーを改造したもの用いてビデオＳ／Ｎ比を求めた。Ｓ／Ｎ比の測定には、ＴＶ試験信号発生器から信号を供給し、ビデオノイズメーターを用い、比較例１のフィルムより作成したテープを０デシベル（ｄＢ）として比較測定し、次の基準で評価した。。なお、走行条件は２５℃、６０％ＲＨである。
【０１０７】
○：＋０．５ｄＢ以上
△：−０．５ｄＢ以上、＋０．５ｄＢ未満
×：−０．５ｄＢ未満
ここでいう、○は蒸着型の高密度記録磁気テープ用途として、優れたレベルであることをいい、△は使用可能であり、×は不十分なレベルであることをいう。
【０１０８】
（１１）蒸着安定性
本発明のフィルム３０００ｍ、１０本に対して、上記（１０）の連続真空蒸着を行い、該蒸着工程における工程安定性を以下の基準で評価した。
【０１０９】
○：オリゴマー付着などによるフィルム切れが起こったり、または、幅方向の収縮などに起因する「しわ」が発生した本数が２本以下であった。
【０１１０】
△：３本または４本で、オリゴマー付着などによるフィルム切れが起こったり、または、幅方向の収縮などに起因する「しわ」が発生した。
【０１１１】
×：５本以上、でオリゴマー付着などによるフィルム切れが起こったり、または、幅方向の収縮などに起因する「しわ」が発生した。
【０１１２】
ここでいう、○は蒸着工程における工程安定性が優れていることをいい、△は使用可能であり、×は不十分なレベルであることをいう。
【０１１３】
（１２）オリゴマー抑止性
本発明のフィルムを、１５０℃で３０分、オーブン中に放置し、低分子量体を強制的にフィルム表面に析出させ、ｆ面側の表面をアルミ蒸着して微分干渉顕微鏡で総合倍率１０００倍で、２５視野観察する。各視野での低分子量体の大きさが、表面写真上で０．５ｍｍ以上のものの個数を数え、その総数１ｍｍ²あたりに換算して、を表面オリゴマ析出個数（個／ｍｍ²）とした。
【０１１４】
（１３）固有粘度
オルトクロロフェノール中、２５℃で測定した溶液粘度から下式から計算する。
【０１１５】
η_sp／Ｃ＝[η]＋Ｋ[η]²・Ｃ
ここで、η_sp＝（溶液粘度／溶媒粘度）−１、Ｃは溶媒１００ｍｌあたりの溶解ポリマー重量（ｇ／１００ｍｌ、通常１．２）、Ｋはハギンス定数（０．３４３とする）である。また、溶液粘度、溶媒粘度はオストワルド粘度計を用いて測定した。
【０１１６】
（１４）補外ガラス転移開始温度（Ｔｇ_onset）、ガラス転移温度（Ｔｇ）
下記装置および条件で比熱測定を行い、ＪＩＳ Ｋ７１２１に従って決定した。
【０１１７】
装置 ：ＴＡ Ｉｎｓｔｒｕｍｅｎｔ社製温度変調ＤＳＣ
測定条件：
加熱温度 ：２７０〜５７０Ｋ（ＲＣＳ冷却法）
温度校正 ：高純度インジウムおよびスズの融点
温度変調振幅：±１Ｋ
温度変調周期：６０秒
昇温ステップ：５Ｋ
試料重量 ：５ｍｇ
試料容器 ：アルミニウム製開放型容器（２２ｍｇ）
参照容器 ：アルミニウム製開放型容器（１８ｍｇ）
なお、ガラス転移温度は下記式により算出した。
【０１１８】
ガラス転移温度＝（補外ガラス転移開始温度＋補外ガラス転移終了温度）／２
（１５）総合評価
上記の（９）、（１０）、（１１）の評価項目のうち、以下の判定基準で判断した。
【０１１９】
○：すべての特性が優れているレベル（○）であるか、または、２つの項目が優れている（○）で１つの項目が使用可能（△）である。
【０１２０】
×：どれか１つの項目でも不十分なレベル（×）があるか、または、２つが使用可能（△）である。
【０１２１】
ここでいう、○は蒸着型磁性層を有する磁気記録媒体用途として適していることをいい、×は蒸着型磁性層を有する磁気記録媒体用途として適さないことをいう。
【０１２２】
【実施例】
次の実施例に基づき、本発明の実施形態を説明する。
【０１２３】
実施例１
常法により得られた固有粘度０．８５のポリエチレンテレフタレート（ＰＥＴ）のペレット（Ｔｇ８０℃）５０重量％と、Ｇｅｎｅｒａｌ Ｅｌｅｃｔｒｉｃ（ＧＥ）社製の固有粘度０．６８の“ウルテム”１０１０（Ｔｇ２１６℃）５０重量％を、２９０℃に加熱された同方向回転タイプのベント式２軸混練押出機に供給して、ＰＥＩを５０重量％含有したブレンドチップ（II）を作成した。
【０１２４】
次いで、押出機２台を用い、製膜を行った。２９０℃に加熱された押出機Ａには、上記ペレタイズ操作により得たブレンドチップ２０重量部と実質的に不活性粒子を含有しない固有粘度０．６２のポリエチレンテレフタレート（ＰＥＴ）ペレット８０重量部の混合原料（Ａ１）を１８０℃で３時間真空乾燥した後に供給した。２９５℃に加熱された押出機Ｂには、上記ペレタイズ操作により得たブレンドチップ２０重量部と実質的に不活性粒子を含有しない固有粘度０．６２のポリエチレンテレフタレート（ＰＥＴ）ペレット６０重量部と平均粒径０．２５μｍの架橋ジビニルベンゼン粒子を２重量％含有する固有粘度０．６２のポリエチレンテレフタレート（ＰＥＴ）のペレット２０重量部の混合原料（Ｂ１）を１８０℃で３時間真空乾燥した後に供給した。続いて、Ａ１をサンドフィルター、１．２μｍカットの繊維焼結ステンレス金属フィルターおよび０．８μｍカットの繊維焼結ステンレス金属フィルターの順に３段階に濾過し、Ｂ１をサンドフィルター、３μｍカットの繊維焼結ステンレス金属フィルターの順に２段階で濾過した後、２層用の矩形の合流ブロック（フィードブロック）にて、Ａ／Ｂの積層した。また各層の厚みはそれぞれのラインに設置されたギヤポンプの回転数を調節して押出量を制御することによって調節した。これを静電印加キャスト法を用いて、表面温度２５℃のキャスティングドラム上に巻き付けて冷却固化し、２層積層未延伸フィルム（積層厚み比Ａ１／Ｂ１＝１０／１）を作成した。
【０１２５】
この未延伸フィルムをロール式延伸機にて、１１０℃で長手方向に３．１倍延伸した。この延伸は２組ずつのロールの周速差を利用して行った。この一軸延伸フィルムのＡ層上に次の水溶液を塗布した。
【０１２６】
メチルセルロース ０．１０重量部
水溶性ポリエステル ０．３重量％
アミノエチルシランカップリング剤 ０．０１重量％
カルナウバワックス ０．２重量％
平均粒径２０ｎｍのアクリル粒子 ０．０２重量％
固形分塗布濃度 ２０ｍｇ／ｍ²
さらに、テンターを用いて、幅方向に温度１００℃で３．４倍延伸した。続いて、ロール式延伸機で長手方向に１段で、温度１５０℃で１．５５倍に再延伸し、テンターを用いて幅方向に温度１９５℃で１．６倍再延伸した。定長下で温度２０５℃で８秒間熱処理後、幅方向に５％の弛緩処理を行い、厚さ約６．０μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は５．２ＧＰａ、幅方向のヤング率は６．１ＧＰａであった。
【０１２７】
この積層ポリエステルフィルムは、表３に示したとおり、ドロップアウトが少なく、電磁変換特性、走行耐久性など磁気記録媒体用ベースフィルムとして優れた特性を有していた。
【０１２８】
実施例２
表１のように、Ａ層、Ｂ層ポリマーは実施例１と全く同様にして、２層積層未延伸フィルム（積層厚み比Ａ／Ｂ＝１１／１）を作成した。
【０１２９】
この未延伸フィルムを、実施例１と全く同様の延伸方法、延伸温度、延伸倍率で延伸し、厚さ約６μｍの積層ポリエステルフィルムを得た。ただし、塗布した水溶液のアミノエチルシランカップリング剤を０．０１重量％から、０．１５重量％に組成変更し、不活性粒子を平均粒径１２ｎｍの極微細シリカ（０．０３重量％）に組成変更した。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は５．１ＧＰａ、幅方向のヤング率は６．２ＧＰａであった。
【０１３０】
この積層ポリエステルフィルムは、表３に示したとおり、ドロップアウトが少なく、電磁変換特性、走行耐久性など磁気記録媒体用ベースフィルムとして優れた特性を有していた。
【０１３１】
実施例３
表１のように、Ａ層、Ｂ層ポリマーのＰＥＴとＰＥＩの重量比を８５：１５に変更し、Ｂ層の不活性粒子を平均粒径０．１８μｍのケイ酸アルミニウム粒子（０．９５重量％含有）に変更した以外は、実施例１と同様にして、２層積層未延伸フィルム（積層厚み比Ａ／Ｂ＝１１／１）を作成した。
【０１３２】
この未延伸フィルムをロール式延伸機にて長手方向に、温度１２０℃で３．０５倍延伸し、不活性粒子を平均粒径１８ｎｍの極微細シリカ（０．１６重量％）に変更した以外は実施例１と同様の水溶液を塗布した後、テンターを用いて、幅方向に温度１０５℃で３．４倍延伸した。続いて、ロール式延伸機で長手方向に、温度１５０℃で１．７倍に再延伸し、テンターを用いて幅方向に温度２００℃で１．７倍再延伸した。定長下で温度２００℃で８秒間熱処理後、幅方向に３％の弛緩処理を行い、厚さ約６μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は５．０ＧＰａ、幅方向のヤング率は５．７ＧＰａであった。
【０１３３】
この積層ポリエステルフィルムは、表３に示したとおり、ドロップアウトが少なく、電磁変換特性、走行耐久性など磁気記録媒体用ベースフィルムとして優れた特性を有していた。
【０１３４】
実施例４
押出機を３台用いて、製膜を行った。表１のように、Ａ層、Ｂ層のポリマー組成、粒子含有量は実施例１と全く同様にし、Ｄ層ポリマーとして、ＰＥＩを５０重量％含有したブレンドチップ２０重量部と実質的に不活性粒子を含有しない固有粘度０．６２のポリエチレンテレフタレート（ＰＥＴ）ペレット５重量部と平均粒径２５ｎｍの架橋ジビニルベンゼン粒子を１重量％含有する固有粘度０．６２のポリエチレンテレフタレート（ＰＥＴ）のペレット７５重量部の混合原料を用いた。なお、Ｂ層、Ｄ層にはドデシルベンゼンスルホン酸ナトリウムを０．３重量％、Ａ層には０．１重量％含有させた。また、Ａ、Ｂ層ポリマーの濾過方法も、実施例１と同様にし、Ｄ層ポリマーはサンドフィルター、１．２μｍカットの繊維焼結ステンレス金属フィルターおよび０．８μｍカットの繊維焼結ステンレス金属フィルターの順に３段階に濾過した。３層積層未延伸フィルム（積層厚み比Ｄ／Ａ／Ｂ＝０．１５／１１／１）を作成した。
【０１３５】
この未延伸フィルムの延伸方式、延伸温度、延伸倍率等は実施例１と全く同様にして、厚さ約６．１μｍの積層ポリエステルフィルムを得た。ただし、実施例１のような水溶液の塗布は行わなかった。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍ、Ｄ層０．０７５μｍであった。長手方向のヤング率は５．２ＧＰａ、幅方向のヤング率は６．１ＧＰａであった。
【０１３６】
この積層ポリエステルフィルムは、表３に示したとおり、ドロップアウトが少なく、電磁変換特性、走行耐久性など磁気記録媒体用ベースフィルムとして優れた特性を有していた。
【０１３７】
実施例５
表１のように、Ａ層、Ｂ層、Ｄ層ポリマーをポリ（エチレン−２，６−ナフタレンジカルボキシレート）（ＰＥＮ）とＰＥＩの混合ポリマー（重量比９０：１０）に変更し、Ｄ層の不活性粒子を平均粒径３０ｎｍの極微細シリカ粒子（１．２％含有）に変更し、Ｂ層の不活性粒子を平均粒径０．１８μｍのケイ酸アルミニウム粒子（０．５％含有）に変更し、押出機の温度を３台ともに３２０℃に変更して、実施例４と同様に、３層積層未延伸フィルム（積層厚み比Ｄ／Ａ／Ｂ＝０．２／１０／１）を作成した。
【０１３８】
この未延伸フィルムをロール式延伸機にて長手方向に温度１３５℃で４．５倍延伸し、さらに、テンターを用いて、幅方向に温度１３０℃で５．５倍延伸した。その後、定長下で温度２４０℃で６秒間熱処理後、幅方向に２％の弛緩処理を行い、厚さ約４．５μｍの積層ポリエステルフィルムを得た。なお、再縦、再横延伸は行わなかった。各層のフィルム厚みは、Ａ層４μｍ、Ｂ層０．４μｍ、０．０８μｍであった。長手方向のヤング率は７．２ＧＰａ、幅方向のヤング率は７．５ＧＰａであった。
【０１３９】
この積層ポリエステルフィルムは、表３に示したとおり、ドロップアウトが少なく、電磁変換特性、走行耐久性など磁気記録媒体用ベースフィルムとして優れた特性を有していた。
【０１４０】
実施例６
表１のように、Ａ層、Ｂ層、Ｄ層ポリマーをＰＥＴとＰＥＩの混合ポリマー（重量比８０：２０）に変更し、Ｂ層の不活性粒子を平均粒径０．２μｍの架橋ジビニルベンゼン粒子（０．２重量％含有）、Ｄ層の不活性粒子を平均粒径２０ｎｍの極微細シリカ粒子（１．５重量％含有）に変更した以外は実施例４と同様にして、３層積層未延伸フィルム（積層厚み比Ｄ／Ａ／Ｂ＝０．１／１５／１）を作成した。
【０１４１】
この未延伸フィルムをロール式延伸機にて長手方向に、温度１２５℃で３倍延伸し、さらに、テンターを用いて、幅方向に温度１１５℃で３．３倍延伸した。続いて、ロール式延伸機で長手方向に、温度１５５℃で１．８倍に再延伸し、テンターを用いて幅方向に温度２００℃で１．７倍再延伸した。定長下で温度２００℃で８秒間熱処理後、幅方向に３％の弛緩処理を行い、厚さ約８μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層７．５μｍ、Ｂ層０．５μｍ、０．０５μｍであった。長手方向のヤング率は４．９ＧＰａ、幅方向のヤング率は５．４ＧＰａであった。
【０１４２】
この積層ポリエステルフィルムは、表３に示したとおり、ドロップアウトが少なく、電磁変換特性、走行耐久性など磁気記録媒体用ベースフィルムとして優れた特性を有していた。
【０１４３】
実施例７
表１のように、Ａ層、Ｂ層ポリマーを、ＰＥＴとＰＥＩの混合ポリマー（重量比７０：３０）に変更し、Ｂ層の不活性粒子を平均粒径０．１８μｍのケイ酸アルミニウム粒子（０．３５重量％含有）に変更して、実施例１と同様に２層積層未延伸フィルム（積層厚み比Ａ／Ｂ＝１１／１）を作成した。
【０１４４】
この未延伸フィルムを、この未延伸フィルムをロール式延伸機にて長手方向に、温度１３０℃で３．０５倍延伸し、不活性粒子を平均粒径１２ｎｍの極微細シリカ（０．０３５重量％）に変更した以外は実施例１と同様の水溶液を塗布した後、テンターを用いて、幅方向に温度１１０℃で３．５倍延伸した。続いて、ロール式延伸機で長手方向に、温度１５５℃で１．７５倍に再延伸し、テンターを用いて幅方向に温度２００℃で１．８倍再延伸した。定長下で温度２０５℃で８秒間熱処理後、幅方向に２％の弛緩処理を行い、厚さ約６μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は４．８ＧＰａ、幅方向のヤング率は５．２ＧＰａであった。
【０１４５】
この積層ポリエステルフィルムは、表３に示したとおり、ドロップアウトが少なく、電磁変換特性、走行耐久性など磁気記録媒体用ベースフィルムとして優れた特性を有していた。
【０１４６】
実施例８
表１のように、Ａ層ポリマーをＰＥＮとＰＥＩの混合ポリマー（重量比９２：８）に変更し、Ｂ層、Ｃ層ポリマーをＰＥＮに変更した。Ｂ層の不活性粒子を平均粒径０．２μｍの架橋ジビニルベンゼン粒子（０．１７重量％含有）、Ｄ層の不活性粒子を平均粒径４５ｎｍの極微細シリカ粒子（０．５重量％含有）に変更し、実施例５と同様にして、３層積層未延伸フィルム（積層厚み比Ｄ／Ａ／Ｂ＝０．２／７．５／１）を作成した。
【０１４７】
この未延伸フィルムの延伸条件などは実施例５と同様にして、厚さ３．５μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層３μｍ、Ｂ層０．４μｍ、０．０８μｍであった。長手方向のヤング率は７．１ＧＰａ、幅方向のヤング率は７．４ＧＰａであった。
【０１４８】
この積層ポリエステルフィルムは、表３に示したとおり、ドロップアウトが少なく、電磁変換特性、走行耐久性など磁気記録媒体用ベースフィルムとして優れた特性を有していた。
【０１４９】
比較例１
Ａ層、Ｂ層ポリマーとして、ＰＥＴとＰＥＩのブレンドポリマーを用いる代わりにＰＥＴを用いた以外は、粒子含有量等は実施例１と同様にして、Ａ／Ｂ２層積層構成の未延伸フィルムを作成した。なお、押出機の温度は２台とも２８０℃とした。
【０１５０】
次いで、実施例１と同様にして、この未延伸フィルムをロール式延伸機にて長手方向に温度１０５℃で３．１倍延伸し、実施例１と同様の水溶液を塗布した後、テンターを用いて、幅方向に温度９５℃で３．４倍延伸した。続いて、ロール式延伸機で長手方向に温度１５０℃で１．５５倍に再延伸し、テンターを用いて幅方向に温度１９０℃で１．６倍再延伸した。定長下で温度２１０℃で８秒間熱処理後、幅方向に５％の弛緩処理を行い、厚さ約６μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は５．３ＧＰａ、幅方向のヤング率は６．７ＧＰａであった。
【０１５１】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１５２】
比較例２
Ａ層ポリマーをＰＥＴ、Ｂ層、Ｄ層ポリマーをＰＥＴ／ＰＥＩ（重量比９０：１０）として、粒子含有量等は実施例１と全く同様にして、３層積層構成の未延伸フィルムを作成した。
【０１５３】
次いで、この未延伸フィルムを比較例１と同様の延伸条件で延伸し、厚さ約６．１μｍの積層ポリエステルフィルムを得た。ただし、水溶液の塗布は行わなかった。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は５．２ＧＰａ、幅方向のヤング率は６．５ＧＰａであった。
【０１５４】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１５５】
比較例３
表２のように、Ｂ層の不活性粒子を平均粒径１．１μｍの球状シリカ粒子（０．１重量％含有）に変更した以外は、実施例１と全く同様にして、厚さ約６μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は５．２ＧＰａ、幅方向のヤング率は６．１ＧＰａであった。
【０１５６】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１５７】
比較例４
表２のように、塗布する水溶液の不活性粒子の含有量を０．０１重量％に変更した以外は、実施例１と全く同様にして、厚さ約６μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は５．２ＧＰａ、幅方向のヤング率は６．１ＧＰａであった。
【０１５８】
比較例５
表２のように、Ｄ層の不活性粒子を平均粒径６０ｎｍの球状シリカ粒子（２重量％含有）とする以外は、実施例４と全く同様にして、厚さ約６．１μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍ、Ｄ層０．０７５μｍであった。長手方向のヤング率は５．２ＧＰａ、幅方向のヤング率は６．１ＧＰａであった。
【０１５９】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１６０】
比較例６
Ａ層の組成を実施例１のＢ層と同じ（ＰＥＴ／ＰＥＩ＝９０：１０、平均粒径０．２７μｍのジビニルベンゼン架橋粒子を０．３重量％含有する。）に変更し、積層を行わずに、単層の未延伸フィルムを作製した。
【０１６１】
水溶液の組成、延伸方式、延伸条件等は実施例１と全く同様にして、厚さ約６μｍのポリエステルフィルムを得た。長手方向のヤング率は５．２ＧＰａ、幅方向のヤング率は６．１ＧＰａであった。
【０１６２】
比較例７
表２のように、Ａ層、Ｂ層、Ｄ層ポリマーのＰＥＴ／ＰＥＩの重量比６０：４０に変更し、Ｄ層の不活性粒子を平均粒径３０ｎｍの極微細球状シリカ粒子（３．１重量％含有）に変更し、また、各層のポリマーの濾過方法を３μｍカットの繊維焼結ステンレス金属フィルターのみを用いる方法に変更して、３層積層構成の未延伸フィルムを作成した。実施例４と同様の延伸条件では、再縦、再横延伸性は不良であり、破れが多発した。このため、未延伸フィルムをロール式延伸機にて長手方向に温度１１０℃で３．５倍延伸し、さらに、テンターを用いて、幅方向に温度１００℃で４．５倍延伸した。その後、定長下で温度２０５℃で７秒間熱処理後、幅方向に５％の弛緩処理を行い、厚さ約６．１μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍ、Ｄ層０．０７５μｍであった。長手方向のヤング率は４．１ＧＰａ、幅方向のヤング率は４．９ＧＰａであった。
【０１６３】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１６４】
比較例８
表２のように、実施例４と全く同様にして、３層積層未延伸フィルムを作製した。
【０１６５】
この未延伸フィルムをロール式延伸機にて長手方向に温度１１０℃で３．５倍延伸し、さらに、テンターを用いて、幅方向に温度１００℃で４．５倍延伸した。その後、定長下で温度２０５℃で７秒間熱処理後、幅方向に５％の弛緩処理を行い、厚さ約２．４μｍの積層ポリエステルフィルムを得た。なお、再縦、再横延伸は行わなかった。長手方向のヤング率は５．１ＧＰａ、幅方向のヤング率は５．５ＧＰａであった。
【０１６６】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１６７】
比較例９
表２のように、Ａ層ポリマーとして、平均粒径６０ｎｍのシリカを０．０３重量％含有するＰＥＴ／ＰＥＩのブレンドポリマー（重量比９０：１０）を用い、Ｂ層ポリマーとして、平均粒径０．２５μｍのケイ酸アルミニウム粒子を０．４重量％含有するＰＥＴを用い、Ａ層の濾過手法は公知の手法（３μｍカットの繊維焼結ステンレス金属フィルター、１段）を用い、２層積層未延伸フィルム（積層厚み比Ａ／Ｂ＝４／１）を作成した。
【０１６８】
この未延伸フィルムを、９５℃で長手方向に３．２倍延伸した。この延伸は２組ずつのロールの周速差を利用して行った。この一軸延伸フィルムのＡ層上に次の水溶液を塗布した。
【０１６９】
メチルセルロース ０．１０重量部
水溶性ポリエステル ０．３重量％
アミノエチルシランカップリング剤 ０．０１重量％
平均粒径１２ｎｍの極微細シリカ ０．０３重量％
固形分濃度 ２０ｍｇ／ｍ²
その後、テンターを用いて１１５℃で幅方向に３．４倍延伸した。さらに長手方向に１４０℃で１．５倍延伸し、続いてこのフィルムを定長下で２２０℃、５秒間熱処理した後、幅方向に５％の弛緩処理を行い、厚さ５μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層４μｍ、Ｂ層１μｍであった。長手方向のヤング率は５．３ＧＰａ、幅方向のヤング率は５．４ＧＰａであった。
【０１７０】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１７１】
比較例１０
表２のように、Ａ層ポリマーとして実質的に粒子を含有しないＰＥＴを用い、Ｂ層ポリマーとして平均粒径０．２μｍの架橋ジビニルベンゼン粒子を０．３重量％含有するＰＥＴを用い、Ｄ層ポリマーとして平均粒径３０ｎｍの球状シリカ粒子を０．３重量％含有するＰＥＴ／ＰＥＩブレンドポリマー（重量比９０：１０）を用い、３層積層未延伸フィルムを得た。Ｄ層の濾過手法は公知の手法（１．２μｍカットの繊維焼結ステンレス金属フィルター、１段）を用い、２層積層未延伸フィルム（積層厚み比Ｄ／Ａ／Ｂ＝０．０５／３．９５／１）を作成した。
【０１７２】
この未延伸フィルムを、９５℃で長手方向に３．２倍延伸した。この延伸は２組ずつのロールの周速差を利用して行った。その後、テンターを用いて１００℃で幅方向に４．５倍延伸した。さらに長手方向に１４０℃で１．５倍延伸し、続いてこのフィルムを定長下で２２０℃、５秒間熱処理した後、幅方向に７％の弛緩処理を行い、厚さ５μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層３．９５μｍ、Ｂ層１μｍ、Ｄ層０．０５μｍであった。長手方向のヤング率は５．５ＧＰａ、幅方向のヤング率は５．６ＧＰａであった。
【０１７３】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１７４】
比較例１１
表２のように、Ｄ層の不活性粒子を平均粒径３０ｎｍの球状シリカ（３．１重量％含有）に変更し、Ｂ層の不活性粒子を平均粒径０．１８μｍのケイ酸アルミニウム粒子（０．５重量％含有）に変更する以外は、実施例４と全く同様にして、厚さ約９．９μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層９μｍ、Ｂ層０．８μｍ、Ｄ層０．１μｍであった。長手方向のヤング率は５．１ＧＰａ、幅方向のヤング率は６．２ＧＰａであった。
【０１７５】
この積層ポリエステルフィルムは、表３に示したとおり、磁気記録媒体用途のフィルムとして劣るものであった。
【０１７６】
比較例１２
表２のように、Ｂ層の不活性粒子を平均粒径２０ｎｍの極微細球状シリカ粒子（２．５重量％含有）に変更して、積層構成をＢ／Ａ／Ｂ型３層積層（積層厚み比Ｂ／Ａ／Ｂ＝１／１１／１）に変更する以外は、実施例４と全く同様にして、厚さ約６．５μｍの積層ポリエステルフィルムを得た。各層のフィルム厚みは、Ａ層５．５μｍ、Ｂ層０．５μｍであった。長手方向のヤング率は５．１ＧＰａ、幅方向のヤング率は６．２ＧＰａであった。
【０１７７】
この積層ポリエステルフィルムは、表３に示したとおり、磁気テープとして使用した場合、テープ走行不良を生じ、磁気記録媒体用途のフィルムとして劣るものであった。
【０１７８】
【表１】

【０１７９】
【表２】

【０１８０】
【表３】

【０１８１】
【発明の効果】
本発明によれば、ポリエステルにポリイミドを含有させ、良好な寸法安定性を有するフィルムの表面の突起高さと突起個数、および、表面粗さを規定する、または、積層構成と各層に含有させる不活性粒子の平均粒径と粒子含有量を規定することにより、保存安定性と電磁変換特性を高いレベルで両立させた磁気記録媒体用ポリエステルフィルムを得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biaxially oriented polyester film in which the quality of the polyester film, in particular, thermal dimensional stability and surface properties are greatly improved.
[0002]
[Prior art]
Biaxially oriented polyester films are used for various applications because of their excellent thermal properties, dimensional stability, mechanical properties, and ease of control of surface morphology, and their usefulness as base films especially for magnetic tapes is well known. is there. In recent years, magnetic tapes have been required to have high density recording in order to reduce the weight, size, and recording time of equipment. For high density recording, it is effective to shorten the recording wavelength and reduce the recording signal.
[0003]
With high density recording and downsizing of recording signal, the form of magnetic layer is shifting from iron oxide coating type to metal coating type and metal deposition type, especially for applications that require high density recording such as digital video tape In general, an evaporation type magnetic recording medium in which a ferromagnetic metal thin film layer (hereinafter referred to as an evaporation layer) is provided on one surface of a base film has been widely used. The thickness of this vapor deposition layer is usually about 0.04 to 0.5 μm, and is very thin as compared with other types of magnetic layers. Therefore, the surface of the base film becomes the surface shape of the magnetic tape as it is. For this reason, it is necessary to control the surface properties of the base film such as the protrusion height, the number of protrusions, and the surface roughness very precisely.
[0004]
Further, when the recording signal is reduced in size, there is a problem that the recording track is liable to be shifted due to heat during running of the magnetic tape and thermal deformation during storage of the tape. In addition, due to the heat in the vapor deposition process of providing a ferromagnetic metal thin film layer to form a magnetic recording medium, problems such as deterioration of film flatness and deterioration of electromagnetic conversion characteristics due to generation of oligomers, and use of a magnetic recording medium Therefore, it has been demanded that the film has high thermal dimensional stability and does not deteriorate in quality even under a high temperature environment.
[0005]
Therefore, in the high density recording, particularly, the base film for a vapor deposition type magnetic recording medium, the present situation is that the control of the fine surface form, the dimensional stability against heat and the quality stability are particularly required. Needless to say, high productivity is required to supply these products to the market at low cost.
[0006]
In terms of controlling surface properties, conventionally, a laminated polyester film containing particles for forming surface protrusions (for example, JP-A-7-272249) or a method of coating a discontinuous film containing fine particles (for example, JP-A-3-208639) is known. However, due to the low heat resistance of polyester, there are still problems relating to stability of the vapor deposition process, such as generation of “wrinkles” due to heat applied in the vapor deposition process and oligomer precipitation.
[0007]
Conventionally, an aramid film (for example, Japanese Patent Application Laid-Open No. 10-114038) is known as a base film that can meet the above-described requirements for heat resistance and dimensional stability.
Aramid film is disadvantageous in terms of cost because of its high price, and also disadvantageous in that production efficiency is low because it cannot be molded by melt extrusion like conventional polyethylene terephthalate film. Development of a base film with high productivity is eagerly desired.
[0008]
On the other hand, as a technique for improving the dimensional stability of a biaxially oriented polyester film having high productivity, as a result of intensive studies, a biaxially oriented polyester film composed of polyethylene terephthalate and polyetherimide (Japanese Patent Laid-Open No. 12-141475). ) Was developed.
[0009]
However, when this biaxially oriented polyester film having high productivity is used as a base film for a vapor deposition type magnetic recording medium, there is no known method for controlling the preferred surface form as a vapor deposition type base film. At present, no knowledge has been obtained regarding techniques for solving the problem of deposition stability, such as the precipitation of oligomers and the suppression of generation of “wrinkles” in the deposition process. Even when the above-mentioned surface control method is applied to the above film, the problem of coating spots based on the difference in wettability between the surface of polyester and polyimide and the difference in affinity between the polymer and coating liquid, Various difficult problems remain such as deterioration of the lamination state due to the difference in melt viscosity, and the application method is not known at all.
[0010]
[Problems to be solved by the invention]
The object of the present invention is to improve the characteristics of a biaxially oriented polyester film composed of polyester and polyimide having high productivity and dimensional stability, and the surface morphology such as surface roughness is controlled precisely, and in particular, vapor deposition type magnetic recording. A high-density magnetic recording tape showing good electromagnetic conversion characteristics when used as a base film for a medium can be produced, and a biaxially oriented polyester film suitable as a base film for a magnetic recording medium is provided.
[0011]
[Means for Solving the Problems]
  The above-mentioned purpose is a laminated polyester film having a base layer part (A layer) containing polyester and polyimide as essential components and having a total thickness of 3 to 8 μm composed of at least two film layers, 5 to 70 million protrusions / mm with a protrusion height of 5 nm to 25 nm on the surface (f-plane)²Polyester for magnetic recording media that exists and satisfies the following relationship: surface roughness Ra on the f-plane side, surface roughness Rab on the opposite surface (b-plane), and the number of coarse protrusions H1 and H2 on the film surface on the f-plane side This can be achieved by forming a film.
  0.1 ≦ Raf (nm) ≦ 5
      5 ≦ Rab (nm) ≦ 20
  0 ≦ H1 (pieces / 100cm²) ≦ 100
  0 ≦ H2 (pieces / 100cm²) ≦ 10
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The film of the present invention is a laminated polyester film having at least two film layers in which a laminated part (referred to as B layer) is laminated on at least one of a base layer part (referred to as A layer). When the film is composed of only one layer, the characteristics of the present invention cannot be satisfied. When used for a magnetic recording medium, the A layer is generally the thickest layer in the film, and mainly serves to maintain strength and dimensional stability. Furthermore, it is also a layer that generally has the greatest influence on film forming properties. The layer B, which is a laminated part, is a layer having a thinner film layer than the layer A, and is a layer that mainly serves to obtain tape running performance and running durability when used as a magnetic tape, and has a relatively rough surface. As a result, good running performance can be obtained.
[0013]
In the laminated polyester film of the present invention, at least the A layer constituting it needs to be biaxially oriented. If all the layers are not oriented or uniaxially oriented, the characteristics of the present invention cannot be satisfied.
[0014]
The layer A of the present invention comprises a polymer alloy having polyester and polyimide as essential components as essential components. The polymer alloy here refers to a polymer multi-component system, which may be a block copolymer by copolymerization or a polymer blend by mixing or the like. However, the case where the thing marketed as a particle is added externally is excluded. The term “becomes as an essential component” herein refers to a case where the component occupies 80% by weight or more of the whole. For example, in the above case, the total amount of polyester and polyimide occupies 80% by weight of the A layer. That means.
[0015]
The polyester used in the present invention is a polymer containing 70% by weight or more of a polyester unit composed of an acid component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid and a diol component.
[0016]
Particularly preferred examples of the acid component include terephthalic acid and 2,6-naphthalenedicarboxylic acid. These acid components may be used alone or in combination of two or more.
[0017]
Examples of the diol component include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and diethylene glycol. These diol components may be used alone or in combination of two or more.
[0018]
The polyester used in the present invention is particularly preferably exemplified by polyethylene terephthalate (PET) and poly (ethylene-2,6-naphthalenedicarboxylate) (PEN), which have melt moldability and biaxial stretchability (film forming property). From the viewpoint, polyethylene terephthalate (PET) is most preferable.
[0019]
Polyester includes trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, polyfunctional compounds such as 2,4-dioxybenzoic acid, monofunctional compounds such as lauryl alcohol and phenyl isocyanate, p-hydroxybenzoic acid, Copolymerization of aromatic hydroxycarboxylic acid such as m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, p-aminophenol, p-aminobenzoic acid, etc., in an amount that does not impair the effects of the present invention. May be.
[0020]
Another polymer polyimide used in the present invention is not particularly limited as long as it has a good affinity with polyester and is melt moldable. For example, one containing a structural unit represented by the following general formula: preferable. Here, having good affinity (compatibility) refers to, for example, using a polymer alloy composed of polymer 1 and polymer 2 to create an unstretched or biaxially stretched film, When observed at a magnification of 30,000 to 500,000 times with a microscope, it means that a structure having a diameter of 200 nm or more (for example, a polymer domain having poor dispersion) that is not caused by additives such as externally added particles is not observed. However, the method for determining the affinity between polymer 1 and polymer 2 is not particularly limited to this, and a single glass transition point is observed by temperature-modulated DSC (MDSC) as necessary. It may be determined that there is good affinity.
[0021]
[Chemical 1]

However, R in the formula₁Is
[0022]
[Chemical 2]

[0023]
[Chemical Formula 3]

Represents one or more groups selected from an aliphatic hydrocarbon group such as, an alicyclic hydrocarbon group, an aromatic hydrocarbon group,
R in the formula₂Is
[0024]
[Formula 4]

Represents one or two or more groups selected from an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group.
[0025]
Such polyimide dehydrates one or more compounds selected from the group consisting of tetracarboxylic acid and / or its anhydride and an aliphatic primary monoamine, aromatic primary monoamine, aliphatic primary diamine and aromatic primary diamine. It can be obtained by condensation.
[0026]
From the viewpoints of melt moldability with polyester, handleability, and formation of surface protrusions, a polyetherimide containing an ether bond in the polyimide component as shown by the following general formula is particularly preferred.
[0027]
[Chemical formula 5]

(However, in the above formula, R_ThreeIs a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms, R_FourIs a divalent aromatic residue having 6 to 30 carbon atoms, an alkylene group having 2 to 20 carbon atoms, a cycloalkylene group having 2 to 20 carbon atoms, and 2 to 8 carbons A divalent organic group selected from the group consisting of polydiorganosiloxane groups chain-terminated with alkylene groups having atoms. )
[0028]
R above_Three, R_FourAs, for example, an aromatic residue represented by the following formula group
[Chemical 6]

Can be mentioned.
[0029]
In the present invention, 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride and m-phenylenediamine from the viewpoint of affinity with polyester, cost, melt moldability, and the like, or A polymer having a repeating unit represented by the following formula, which is a condensate with p-phenylenediamine, is preferred.
[0030]
[Chemical 7]

Or
[0031]
[Chemical 8]

(N is an integer of 2 or more, preferably an integer of 20 to 50)
This polyetherimide is available from GE Plastics under the trade name “Ultem” (registered trademark).
[0032]
In order to control the dispersion diameter, the polymer alloy constituting the A layer of the present invention may be used in combination with a compatibilizing agent as necessary. In this case, although the kind of compatibilizer varies depending on the kind of polymer, the addition amount is preferably 0.01 to 10% by weight.
[0033]
In the present invention, the time when the polyimide is added to the polyester may be added before the polymerization of the polyester, for example, before the esterification reaction, or after the polymerization. Further, before melt extrusion, polyester and polyimide may be mixed and pelletized.
[0034]
In addition, as another method for adjusting the polymer alloy constituting the A layer of the present invention to a more preferable dispersion state, for example, a method of mixing using a tandem extruder, a fine dispersion of polyimide using two or more kinds of polyesters Method, method of mixing after pulverizing polyimide with a pulverizer, method of mixing by dissolving both in a solvent and coprecipitation, method of mixing one into a solution after dissolving one in a solvent, etc. This is not the case. Particularly preferably, a master containing two or more kinds of polyesters and first containing a high molecular weight polyester and polyimide by pelletizing and once containing a high concentration of polyimide (for example, 35 to 65% by weight, more preferably 40 to 60% by weight). Using a method of preparing pellets and then diluting with a relatively low molecular weight polyester before melt extrusion and adjusting to a predetermined concentration improves the dispersibility between the polymers, and makes the polymer alloy of the present invention more A preferred dispersion state may be exhibited. In addition, this method is preferable because the melt viscosity of the polymer alloy as a whole can be kept low, so that melt moldability is improved and productivity is improved.
[0035]
The polymer species used for the film layer other than the A layer of the present invention is not particularly limited, but when the same polyester as that used for the A layer or the same polymer and polyimide as the one used for the A layer is used, Since the difference in melt viscosity is unlikely to occur between the base layer portion and the laminated portion, it is preferable because troubles in the production process such as laminated spots and die lines are less likely to occur. Most preferably, a polymer alloy containing the same polyester and polyimide as used for the A layer in the same weight ratio as that of the A layer may be used.
[0036]
When the layer A of the laminated polyester film of the present invention contains substantially no inert particles, it is preferable because generation of coarse protrusions due to aggregation of particles in the layer A and problems of filter clogging are reduced. As used herein, “substantially no inert particles” means that the inert particles in the A layer are not included at all, or even if included, the average particle diameter is smaller than 10 nm, or The case where the content of active particles is less than 0.001% by weight.
[0037]
However, the layer A of the laminated polyester film of the present invention is not particularly limited. However, when the magnetic recording medium is used, the running durability of the magnetic tape, the running property with the magnetic head is improved, or the winding property is improved. In order to improve handling properties, inert particles may be included. The inert particles referred to in the present invention are inorganic or organic particles having an average particle diameter of about 10 nm to 1 μm and do not cause a chemical reaction in the polymer of the present invention or adversely affect magnetic recording due to electromagnetic influence. Say things. Inactive particles include titanium oxide, calcium carbonate, kaolin, talc, wet or dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, and other inorganic particles, acrylic acids, styrene, silicone, imide, etc. Organic particles, particles precipitated by a catalyst added during the polyester polymerization reaction (so-called internal particles), surfactants, and the like.
[0038]
When the inert particles are contained in the layer A of the laminated polyester film of the present invention, the average particle size is preferably 0.001 to 0.5 μm, more preferably 0.01 to 0.3 μm. When the average particle diameter of the inert particles is larger than 0.5 μm, when used as a magnetic recording medium, electromagnetic conversion characteristics may be deteriorated or the magnetic head may be easily damaged. When the average particle diameter of the inert particles is smaller than 0.001 μm, it is not preferable because particle aggregation is likely to occur, and it is difficult to disperse well in the polymer and the number of surface protrusions is difficult to control.
[0039]
When the inert particles are contained in the layer A of the laminated polyester film of the present invention, the content is preferably 0.01 to 1% by weight, more preferably 0.02 to 0.05% by weight. When the content of the inert particles is larger than 1% by weight, the protrusions may become coarse due to particle aggregation, and the electromagnetic conversion characteristics may be deteriorated or the protrusions may be easily scraped. When the content of the inert particles is smaller than 0.01% by weight, the effect of improving the running performance with the magnetic head is small, which is not preferable.
[0040]
In the layer B of the laminated polyester film of the present invention, inert particles are contained for the purpose of improving handling properties during film formation and processing, and imparting running properties and running durability when used as a magnetic recording medium. At this time, the inert particles as described above can be used as the inert particles contained in the B layer. One type of inert particles may be used, but two or more types may be used in combination. The average particle diameter d of the inert particles of the B layer is preferably 0.05 to 1 μm, more preferably 0.1 to 0.5 μm. When the average particle diameter exceeds 1 μm, when the film is stored in a wound state, the protrusions are transferred to the smooth magnetic surface side (f surface side), the f surface side is roughened, and the electromagnetic conversion characteristics are improved. May decrease. On the other hand, when the average particle size is smaller than 0.05 μm, the handling property and the running property of the magnetic tape may not be sufficiently affected. The content of inert particles in the B layer is 0.05 to 1.5% by weight, preferably 0.1 to 1% by weight. When the content of the inert particles exceeds 1% by weight, the cooling efficiency in the vapor deposition process is lowered, which may cause “wrinkles” and oligomer precipitation, and may deteriorate the electromagnetic conversion characteristics by transfer. .
[0041]
When the thickness of the B layer of the laminated polyester film of the present invention is 20% or less of the thickness of the entire film, the film forming property is favorable and preferable. The thickness of the B layer is more preferably 15% or less, particularly preferably 10% or less, of the thickness of the entire film. Moreover, when the thickness is 0.01 to 1.5 μm, the film forming property is further improved, which is preferable. Preferably it is 0.03-1 micrometer, More preferably, it is 0.05-0.75 micrometer. The thickness t of the B layer is preferably 0.1 to 10 times, more preferably 0.2 to 5 times the average particle size d of the inert particles. When t / d is smaller than 0.1, the inert particles may easily fall off. When t / d is greater than 10, the height of the protrusion on the B layer side is uneven, which improves running performance and handling properties. May not have sufficient effect.
[0042]
The laminated polyester film of the present invention has a film configuration in which an easy-sliding smooth layer (C layer) is provided on the surface opposite to the B layer of a base film having a two-layer laminate configuration of A layer / B layer, or B In the case of a three-layer laminated structure of D layer / A layer / B layer in which a laminated part (D layer) containing polyester or polyester and polyimide and inert particles as essential components is provided on the side opposite to the A layer Moreover, it is preferable because the effects of the present invention can be sufficiently exhibited, but the present invention is not limited to this.
[0043]
In the laminated polyester film of the present invention, when an easy-smoothing smooth layer (C layer) is provided, the C layer is formed by coating. The C layer is not particularly limited, but is preferably formed from a water-soluble polymer and inert particles as main components. The C layer must be provided at least on the surface opposite to the B layer from the viewpoint of running performance with the magnetic head and running durability. Providing the C layer is preferable because it can effectively inhibit low molecular weight substances deposited on the surface from the film in the tape storage step and vapor deposition step. Although not particularly limited, C layer / A layer in which a slippery smooth layer (C ′ layer) is provided on the surface on the B layer side from the viewpoint of suppressing the oligomer precipitation during storage and processing into a magnetic tape. A / B layer / C ′ layer may be employed.
However, in this case, the production efficiency is lowered as compared with the case where the C ′ layer is not provided.
[0044]
When the layer C is provided on the laminated polyester film of the present invention, the water-soluble polymer constituting the layer C includes polar groups such as a hydroxyl group, an ether group, an ester group, a sulfone group, an amide group, a methoxy group, and a hydroxypropoxy group. Having a molecular weight of 10,000 to 2,000,000, preferably 100,000 to 1,000,000. Specific examples include polyvinyl alcohol, tragacanth gum, gum arabic, casein, gelatin, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, terephthalic acid In addition, water-soluble polyesters, water-soluble polyester ether copolymers, etc. composed of polyvalent carboxylic acids such as isophthalic acid and trimellitic acid and ethylene glycol can be applied, and blends thereof can also be applied. Among these, a blend of methyl cellulose and water-soluble polyester is particularly preferably exemplified from the viewpoint of wettability with the A layer.
[0045]
When the laminated polyester film of the present invention is provided with the C layer, examples of the inert particles constituting the C layer include the particles as described above. Among them, acrylic acids, styrene, silicone, imide and the like are included. In the case of organic particles as components, especially organic particles having acrylic acid or imide as a constituent component, it is considered that the affinity between the polyester and the A layer mainly composed of polyimide is high, but the coating spots of the coating are It is preferable because it is difficult to occur and particle dropping and surface scratches are significantly reduced during film formation and processing.
[0046]
When providing the C layer in the laminated polyester film of the present invention, the average particle diameter d of the inert particles constituting the C layer_cIs preferably 5 to 50 nm, more preferably 6 to 25 nm, and most preferably 7 to 20 nm. Since the C layer is a layer formed by coating, if the average particle diameter exceeds 50 nm, the particles may be remarkably easily dropped during film formation and processing. In addition, when the average particle size is smaller than 5 nm, the inert particles are likely to aggregate when the coating liquid is prepared, which may cause coarse protrusions and may be easily dropped during film formation and processing. .
[0047]
When the C layer is provided on the laminated polyester film of the present invention, the content of the inert particles constituting the C layer is 3 million to 70 million pieces / mm.²It is. The particle content of the C layer is expressed by the number per area because the C layer is extremely thin with respect to the average particle diameter of the particles, so that almost all the particles contained in the C layer are on the C layer side. This is because it is exposed to the surface layer. When the content is expressed as a ratio to the water-soluble polymer, 100 parts by weight of the water-soluble polymer (when the silane coupling agent or titanium coupling agent is contained in the layer C, the water-soluble polymer and the coupling agent are used). Is preferably 5 to 50 parts by weight, more preferably 10 to 40 parts by weight. When the content of the particles is within this range, the particles do not fall off from the C layer, and the electromagnetic conversion characteristics are improved.
[0048]
When the C layer is provided on the laminated polyester film of the present invention, the coating thickness of the C layer is not particularly limited, but is preferably 1 nm to 50 nm, more preferably 5 nm to 25 nm. It is effective to get. When the thickness of the C layer is smaller than 1 nm, the coating amount per unit area during coating becomes very small, so that stable coating becomes difficult. When the thickness is larger than 50 nm, the in-line coating liquid is insufficiently dried. Or the C layer breaks during stretching and becomes easy to peel off.
[0049]
When the laminated polyester film of the present invention is a three-layer laminate of D layer / A layer / B layer, the polymer used for the D layer is the same polyester as the polyester constituting the A layer, or the polymer alloy constituting the A layer In the case of a polymer alloy composed of the same polyester and polyimide, it is preferable because problems in the film forming process such as lamination spots and die lines are easily suppressed. Among them, when only polyester is used for the D layer, a polyester having a higher molecular weight than the polyester constituting the A layer is used, and when a polymer alloy composed of polyester and polyimide is used, the polyester constituting the A layer, Using the same molecular weight as that of polyimide and making the content of polyimide equal is a particularly preferable method for reducing problems during film formation.
[0050]
When the polyester used for the D layer of the laminated polyester film of the present invention is a polyester having ethylene terephthalate as a main constituent, the polyester may be either a direct weight method or a DMT method. As calcium acetate, it is preferable to use. In the polymerization stage, although not particularly limited, it is preferable to use a germanium compound as a polymerization catalyst in order to reduce coarse protrusions due to foreign matters. As known germanium catalysts, (1) amorphous germanium oxide, (2) crystalline germanium oxide of 5 μm or less, and (3) germanium oxide in the presence of an alkali metal, an alkaline earth metal, or a compound thereof are known. And a solution of germanium oxide prepared by dissolving (4) germanium oxide in water and adding glycol to the solution to distill off the water.
[0051]
When the laminated polyester film of the present invention is a three-layer laminate of D layer / A layer / B layer, examples of the inert particles contained in the D layer include the particles described above. Among these, organic particles containing colloidal silica, finely dispersed alumina, styrene, silicone, imide and the like as constituent components are preferably exemplified.
[0052]
When the laminated polyester film of the present invention is a three-layer laminate of D layer / A layer / B layer, the average particle diameter d of the inert particles contained in the D layer_DIs preferably 10 to 50 nm, more preferably 15 to 50 nm, and most preferably 20 to 40 nm. When the average particle diameter exceeds 50 nm, the magnetic tape having the vapor deposition type magnetic layer has a large projection on the magnetic surface side, which deteriorates the electromagnetic conversion characteristics and damages the magnetic head. It may cause a decrease. When the average particle size is smaller than 20 nm, the height of the projection on the magnetic surface side is low, so the friction with the magnetic head becomes too high, and the running performance of the head deteriorates or rolls are formed during film formation and processing. It is easy to get scratched due to friction.
[0053]
When the laminated polyester film of the present invention is a three-layer laminate of D layer / A layer / B layer, the content of the inert particles contained in the D layer is preferably 0.1 to 3% by weight, more preferably 0.00. It is 3 to 1.5% by weight, most preferably 0.5 to 1% by weight. When the content exceeds 3% by weight, the particles are aggregated in the melt molding step, and the protrusions become coarse, so that the electromagnetic conversion characteristics are deteriorated or the protrusions are easily scraped. When the content is less than 0.1% by weight, the magnetic surface becomes too flat and the running performance of the head is deteriorated, or the film is easily scratched due to friction with the roll during film formation and processing. .
[0054]
When the laminated polyester film of the present invention is a three-layer laminate of D layer / A layer / B layer, the thickness t of the D layer_DIs preferably 0.01 μm to 0.8 μm, more preferably 0.03 μm to 0.5 μm, and still more preferably 0.05 to 0.1 μm. When the thickness of the D layer is less than 0.01 μm, the particles of the D layer are likely to fall off, which may cause deterioration in running durability. When the thickness is greater than 0.5 μm, the height of the protrusions May be inconsistent, which may lead to a reduction in head running performance. D layer thickness t_DIs the average particle size d_DIs preferably 0.1 to 10 times, more preferably 0.5 to 5 times, both electromagnetic conversion characteristics and head running properties are good.
[0055]
When the laminated polyester film of the present invention is a three-layer laminate of D layer / A layer / B layer, it is not particularly limited, but when each film layer contains a wax such as a fatty acid ester or a surfactant, the film It is preferable because low molecular weight substances deposited on the surface from inside can be effectively suppressed. More preferably, when the B layer and the D layer are contained at a relatively high concentration and the A layer is contained at a low concentration or is not substantially contained, there is little concern that the elastic modulus is lowered. Examples of the wax include natural waxes such as carnauba wax, and fatty acid esters such as stearyl stearate and behenyl behenate, and carnauba wax is particularly preferred. Surfactants include alkali metal salts or alkaline earth metal salts of alkyl sulfonic acids such as sodium undecyl sulfonate and potassium dodecyl sulfonate, and alkyl benzene sulfonic acids such as sodium dodecyl benzene sulfonate and lithium dodecyl benzene sulfonate. Examples thereof include alkali metal salts and alkaline earth metal salts, and sodium dodecylbenzenesulfonate is particularly preferred. As content, 0.1 to 2 weight% is preferable, More preferably, it is 0.2 to 0.8 weight%.
[0056]
Surface roughness Ra of the surface (b surface) on the B layer side of the laminated polyester film of the present invention_bIs 5 to 20 nm, preferably 6 to 17 nm, and more preferably 7 to 15 nm. Ra_bIf the thickness is smaller than 5 nm, sufficient handling is not obtained in the film forming and processing steps, resulting in a decrease in productivity and a decrease in running performance and wear resistance when processed into a magnetic tape. This is not preferable because the tape characteristics cannot be obtained. Ra_bIs larger than 20 nm, when used as a magnetic tape, the shape on the traveling surface side is transferred to the magnetic surface side, the electromagnetic conversion characteristics are deteriorated, and particles on the traveling surface side easily fall off. This is not preferable because it causes deterioration and dropout. Further, in the case of a magnetic tape having a vapor deposition type magnetic layer, the cooling efficiency in the vapor deposition process is lowered, so that heat loss such as “wrinkles” or oligomers are likely to precipitate.
[0057]
Surface roughness Ra of the surface (f surface) opposite to the B layer of the laminated polyester film of the present invention_fIs 0.1 to 5 nm, preferably 1 to 4 nm, more preferably 1.5 to 3 nm. Ra_bIs smaller than 0.1 nm, it may be difficult to produce industrially, or the running property with a magnetic head when processed into a magnetic tape may be reduced, and sufficient magnetic tape characteristics may not be obtained. Ra_fIs larger than 5 nm, it is not preferable because the electromagnetic conversion characteristics are deteriorated and the magnetic head is easily damaged when used as a magnetic tape having a vapor deposition type magnetic layer.
[0058]
The number H1 of coarse protrusions on the f-side of the laminated polyester film of the present invention is 100/100 cm from the viewpoint of electromagnetic conversion characteristics and running durability.²Or less, preferably 50/100 cm²Or less, more preferably 10/100 cm²It is as follows. Similarly, the number of coarse protrusions H2 is 10/100 cm.²Or less, preferably 5/100 cm²Or less, more preferably 2/100 cm²It is as follows. The number of coarse protrusions H1 is 100/100 cm.²Exceeding 10 is not preferable because electromagnetic conversion characteristics deteriorate, and H2 is 10/100 cm.²If it exceeds, the magnetic head is easily damaged, and the running durability deteriorates. In the present invention, H1 and H2 representing the number of coarse protrusions on the f-plane are values defined by a measurement method described later.
[0059]
It is preferable that content of the polyimide in A layer of the laminated polyester film of this invention exists in the range of 5-30 weight% in a polymer alloy. More preferably, it is 8 to 15% by weight. Generally, since the melt viscosity of polyester and polyimide is greatly different, if the polyimide content is less than 5% by weight, it may be difficult to sufficiently finely disperse in the extruder, and the polyimide domain is coarse. As a result, the surface protrusions may become coarse. In addition, if the polyimide content exceeds 30% by weight, it is difficult to perform extrusion molding and stretching, causing film formation such as film breakage and die lines during extrusion, and troubles in processing. There is a case.
[0060]
The laminated polyester film of the present invention is an organic lubricant such as a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a pigment, a dye, a fatty acid ester, and a wax, as long as the effects of the present invention are not impaired. Etc. may be added.
[0061]
The sum of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the laminated polyester film of the present invention is preferably in the range of 9 to 20 GPa, more preferably 10 to 18 GPa, and still more preferably 11 to 15 GPa. If the sum of the Young's moduli is less than 9 GPa, for example, when used for a magnetic recording medium, the magnetic tape is easily stretched and deformed due to the tension received from the magnetic recording head and guide pins during running, and the electromagnetic The conversion characteristics (output characteristics) may be adversely affected and may not be practically used. In addition, a film having a sum of Young's modulus exceeding 20 GPa may be difficult to produce industrially, and the tear resistance and dimensional stability of the film may be significantly reduced.
[0062]
The Young's modulus in the longitudinal direction of the laminated polyester film of the present invention is preferably 4.3 GPa or more from the viewpoint of per head with the magnetic head. More preferably, it is 4.5 GPa or more, and most preferably 5 GPa or more.
[0063]
The Young's modulus in the width direction of the laminated polyester film of the present invention is preferably 4.7 GPa or more from the viewpoint of suppressing tape edge damage and elongation in the longitudinal direction. More preferably, it is 5 GPa or more, and most preferably 5.5 GPa or more.
[0064]
The heat shrinkage rate at 30 ° C. for 30 minutes in the longitudinal direction of the laminated polyester film of the present invention is preferably 1.2% or less from the viewpoint of the stretch deformability and storage stability of the tape. More preferably, it is 1% or less. When the heat shrinkage rate exceeds 1.2%, the dimensional stability may be easily lost. For example, in the case of magnetic recording media, thermal deformation of the tape occurs when the temperature of the magnetic tape rises due to heat history in the film processing process such as applying a magnetic layer of the base film or frictional heat between the magnetic tape and the magnetic recording head during running. It may occur easily, the durability of the film surface may deteriorate, or the storage stability of the tape may deteriorate.
[0065]
The heat shrinkage rate at 30 ° C. for 30 minutes in the longitudinal direction of the laminated polyester film of the present invention is preferably 0.3% or less from the viewpoints of tape stretch deformability and storage stability. More preferably, it is 0.25% or less.
[0066]
The heat shrinkage rate at 30 ° C. for 30 minutes in the width direction of the laminated polyester film of the present invention is preferably 0.5% or less from the viewpoints of tape stretch deformability and storage stability. More preferably, it is 0.3% or less. When the thermal shrinkage rate exceeds 0.5%, the dimensional stability may be easily lost. For example, in the case of magnetic recording media, thermal deformation of the tape occurs when the temperature of the magnetic tape rises due to heat history in the film processing process such as applying a magnetic layer of the base film or frictional heat between the magnetic tape and the magnetic recording head during running. It may occur easily, the durability of the film surface may deteriorate, or the storage stability of the tape may deteriorate.
[0067]
The heat shrinkage rate at 80 ° C. for 30 minutes in the width direction of the laminated polyester film of the present invention is preferably 0.1% or less from the viewpoint of stretch deformability and storage stability of the tape. More preferably, it is 0.05% or less.
[0068]
Extrapolated glass transition onset temperature (Tg) of the polymer of layer A of the present invention_onset) Is not particularly limited, but is preferably 92 to 150 ° C, more preferably 96 to 130 ° C, and still more preferably 98 to 120 ° C. Further, the glass transition temperature (Tg) of the polymer of the A layer is not particularly limited, but is preferably 105 to 170 ° C, more preferably 110 to 140 ° C. Tg_onsetWhen Tg and Tg are less than this range, the dimensional stability during running of the magnetic tape is reduced, wrinkles due to thermal shrinkage tend to occur during tape storage, and when used as a magnetic recording medium for vapor deposition, “Wrinkles” may occur due to heat shrinkage of the film. Tg_onsetWhen Tg exceeds this range, the temperature required for stretching and the like becomes too high, so that productivity may be lowered and durability of equipment such as stretching rolls may be lowered.
[0069]
The intrinsic viscosity of the polymer alloy constituting the A layer of the present invention is in the range of 0.55 to 3.0 (dl / g) from the viewpoint of film forming stability and miscibility with a thermoplastic resin. Is more preferable, and 0.60 to 2.0 (dl / g) is more preferable. In addition, the intrinsic viscosity of the film after film formation is preferably in the range of 0.50 to 2.0 (dl / g), more preferably from the viewpoint of film forming stability and dimensional stability. 0.55 to 1.0 (dl / g).
[0070]
The total thickness of the laminated polyester film of the present invention is 3 to 8 μm. Preferably it is 4-7 micrometers, More preferably, it is 4.5-6.5 micrometers. When the thickness is smaller than 3 μm, the tape becomes dull and electromagnetic conversion characteristics deteriorate. When the thickness is larger than 8 μm, the tape length per tape is shortened, which makes it difficult to reduce the size and increase the capacity of the magnetic tape.
[0071]
In the laminated polyester film of the present invention, other polymer layers such as polyolefin, polyamide, polyvinylidene chloride and acrylic polymer may be laminated directly or via a layer such as an adhesive.
[0072]
The biaxially stretched film of the present invention may be subjected to any processing such as heat treatment, molding, surface treatment, laminating, coating, printing, embossing, etching, etc. as necessary.
[0073]
By providing a magnetic layer on at least one side of the laminated polyester film of the present invention, it can be used as a magnetic recording medium. The surface on which the magnetic layer is provided may be any surface of the film or both surfaces. However, when the film having the laminated structure is used, it is preferable to provide the magnetic layer on the A layer side.
[0074]
Suitable examples of the magnetic layer include a magnetic layer formed by dispersing a ferromagnetic metal thin film or fine powder of ferromagnetic metal in a binder, a magnetic layer coated with a metal oxide, and the like. As the metal used for the ferromagnetic metal thin film, iron, cobalt, nickel, alloys thereof, and the like are preferable. The ferromagnetic metal fine powder used in the magnetic layer in which the ferromagnetic metal fine powder is dispersed in a binder includes ferromagnetic hexagonal ferrite fine powder, powder made of iron, cobalt, nickel and alloys thereof. preferable. The binder is preferably a thermoplastic resin, a thermosetting resin, a reactive resin, or a mixture thereof.
[0075]
As a method for forming the magnetic layer, magnetic powder is kneaded with a binder such as thermosetting, thermoplastic or radiation curable, and coating and drying are performed. Metal or alloy is deposited, sputtering, ion plating, etc. Thus, any of dry methods in which a magnetic metal thin film layer is directly formed on a substrate film can be employed.
[0076]
In the magnetic recording medium of the present invention, a protective film may be provided on the magnetic layer. This protective film can further improve running durability and corrosion resistance. As protective films, oxide protective films such as silica, alumina, titania, zirconia, cobalt oxide, nickel oxide, nitride protective films such as titanium nitride, silicon nitride, boron nitride, silicon carbide, chromium carbide, boron carbide, etc. Examples thereof include a carbon protective film made of carbon such as a carbide protective film, graphite, and amorphous carbon.
[0077]
The carbon protective film is a carbon film made of amorphous, graphite, a diamond structure, or a mixture thereof prepared by a plasma CVD method, a sputtering method, or the like, and particularly preferably a hard carbon film generally called diamond-like carbon.
[0078]
Further, the surface of the hard carbon protective film may be surface-treated with plasma of oxidizing or inert gas for the purpose of further improving the adhesion with the lubricant applied on the hard carbon protective film.
[0079]
In the present invention, in order to improve running durability and corrosion resistance of the magnetic recording medium, it is preferable to apply a lubricant or a rust preventive agent on the magnetic layer or the protective film.
[0080]
The use of the laminated polyester film of the present invention is a magnetic recording medium of a digital recording system that requires a uniform and fine surface form and high dimensional stability. Among them, it can be particularly preferably used for a magnetic recording medium having an evaporation type magnetic layer. Specifically, it is suitable for a base film such as a high density magnetic recording tape for data storage or a digital video tape.
[0081]
Hereinafter, although the example of the manufacturing method of the lamination | stacking polyester film of this invention is demonstrated, it is not limited to this. Here, an example of a D / A / B three-layer laminated polyester film in which polyethylene terephthalate is used as the polyester of the layer A polymer and polyetherimide “Ultem” is used as the polyimide is shown. Moreover, when providing a slippery smooth layer (C layer) in the base film of A / B two-layer lamination structure, the manufacturing method of a base film is the same as this example except not using D layer part. That's fine. The manufacturing conditions vary depending on the polyester and polyimide used, or the laminated structure.
[0082]
First, bis-β-hydroxyethyl terephthalate (BHT) is obtained by esterifying terephthalic acid and ethylene glycol or by transesterifying dimethyl terephthalate and ethylene glycol according to a conventional method. Next, while transferring this BHT to the polymerization tank, the polymerization reaction is advanced by heating to 280 ° C. under vacuum. Here, a polyester having an intrinsic viscosity of about 0.5 is obtained. The obtained polyester is pelletized and placed under reduced pressure to undergo solid phase polymerization. In the case of solid-phase polymerization, the pelletized polyester is preliminarily crystallized at a temperature of 180 ° C. or lower, and then solid-phase polymerized at 190 to 250 ° C. under a reduced pressure of about 1 mmHg for 10 to 50 hours. Moreover, when making the polyester which comprises a film contain an inert particle, the method to which an inert particle is disperse | distributed in the form of a slurry in ethylene glycol in a predetermined ratio, and adding this ethylene glycol at the time of superposition | polymerization is preferable. When the inert particles are added, for example, when the water sol or alcohol sol obtained at the time of synthesis is added without drying, the particles have good dispersibility. Also effective is a method in which a water slurry of inert particles is directly mixed with polyester pellets and kneaded into polyester using a vented twin-screw kneading extruder. As a method for adjusting the content of the inert particles, a master of a high concentration of inert particles is prepared by the above method, and this is diluted with a polyester that does not substantially contain inert particles at the time of film formation. A method of adjusting the content of the particles is effective.
[0083]
Next, the pellets of polyethylene terephthalate and the pellets of polyetherimide are mixed, supplied to a vent type twin-screw kneading extruder heated to 270 to 300 ° C., and melt extruded. The shear rate at this time is 50 to 300 sec.^-1Is preferable, more preferably 100 to 200 sec.^-1The residence time is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes. The mixing ratio is preferably 20 to 80%, more preferably 40 to 60%. If the mixing ratio of the polyetherimide is too high or too low, the two may not be sufficiently compatible by kneading. Furthermore, when both are not compatible on the said conditions, the obtained chip | tip may be thrown into a biaxial extruder again, and extrusion may be repeated until it is compatible.
[0084]
The obtained polyetherimide-containing polyester pellets, inert particle master pellets, and polyester pellets were mixed at a predetermined ratio and vacuum-dried at 180 ° C. for 3 hours or more. An unstretched film is obtained by supplying to an extruder heated to 280 to 320 ° C. under a nitrogen stream or under vacuum so as not to decrease, extruding from a slit die, and cooling on a casting roll.
[0085]
At that time, it is preferable to use various filters, for example, a filter made of a material such as sintered metal, porous ceramic, sand, and wire mesh, as a method for removing foreign substances, altered polymer, unmelted material, etc. in the polymer. . In particular, in the case of the A layer and the three-layer laminated structure, the polymer of the D layer is preferably exemplified by filtering the polymer with a fiber sintered stainless metal filter having a cut of 1.2 μm or less. More preferably, the filter is 0.8 μm or less. Moreover, it is preferable to pass through two or more filter parts and filter in two or more stages, if necessary, because the unmelted material can be more effectively removed. Most preferably, a method is used in which a sand filter, a 1.2 μm cut fiber sintered stainless metal filter, and a 0.8 μm cut fiber sintered stainless metal filter are used in this order to perform filtration in three stages.
[0086]
In addition, the filter of 1.2 micrometer cut here means the filtration precision of 1.2 micrometers, and the filtration precision means the largest glass bead particle size which permeate | transmitted the filter media by the method of JIS-B8356.
[0087]
Moreover, it is preferable to provide a gear pump in order to improve the quantitative supply as required.
[0088]
As a method of laminating the film, a method of melt laminating a plurality of different polymers using two or more extruders and a manifold or a merge block is preferable.
[0089]
Next, this unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. Here, a sequential biaxial stretching method in which stretching in the longitudinal direction first and then in the width direction is used. The stretching temperature varies depending on the constituent components of the laminate. For example, a case where the A layer, the B layer, and the D layer are made of a mixed polymer of polyethylene terephthalate and polyetherimide (mixing weight ratio 9: 1) in a three-layer structure is illustrated. To explain. The unstretched film is heated with a heating roll group at 70 to 130 ° C., and stretched in one or more stages 3 to 8 times in the longitudinal direction (when re-longitudinal stretching is performed, the first stage stretching is 2 to 4 times). It cools with the cooling roll group of 20-50 degreeC. The longitudinal stretching speed is preferably in the range of 1000 to 50000% / min. Subsequently, stretching in the width direction is performed. As a stretching method in the width direction, for example, a method using a tenter is common. The stretching ratio in the width direction is 3 to 8 times (in the case of re-lateral stretching, the first stage stretching is 2 to 4 times), the stretching speed is 1000 to 20000% / min, and the temperature is in the range of 80 to 150 ° C. Is preferred. Further, if necessary, re-longitudinal stretching and / or re-lateral stretching is performed. As stretching conditions in that case, stretching in the longitudinal direction is preferably a heating roll group having a temperature of 80 to 170 ° C., and a stretching ratio of 1.1 to 2.5 times, and a stretching method in the width direction is preferably a method using a tenter. It is preferable to carry out at a temperature of 80 to 180 ° C. and a draw ratio of 1.1 to 2.5 times. Subsequently, this stretched film is heat-treated under tension or while relaxing in the width direction. In this case, the heat treatment temperature is 200 to 230 ° C., preferably 210 to 220 ° C., and the time is preferably 0.2 to 10 seconds.
[0090]
When a two-layer laminated film is coated with an easy-smooth smooth layer (C layer), the coating period is theoretically before the longitudinal stretching, before the stretching in the width direction, after the stretching in the width direction, and further in the film production process. Although coating can be performed off-line after film formation, since the C layer is an extremely thin layer, it is coated either before or after stretching in the width direction, and does not contact a roll or the like until the C layer is fixed after coating. It is preferable to do so. Accordingly, for example, it is preferable to coat the C layer before the stretching in the width direction in the sequential biaxial stretching in which the stretching in the longitudinal direction is followed by the stretching in the width direction, or before the stretching in the simultaneous biaxial stretching. The coating is industrially preferred, so-called inline coating, in which coating is performed during the continuous film production process. It may be performed in a separate process dedicated for offline use.
[0091]
(Methods for measuring physical properties and methods for evaluating effects)
The characteristic value measurement method and effect evaluation method in the present invention are as follows.
[0092]
(1) Surface protrusion height and number of protrusions
Using an atomic force microscope (AFM), measurement is performed 10 times at different locations under the following conditions.
Equipment: NanoScopeIII AFM (manufactured by Digital Instruments)
Cantilever: Silicon single crystal
Scanning mode: Tapping mode
Scanning range: 5 μm × 5 μm
Scanning speed: 0.5Hz
Measurement environment: Temperature 25 ° C, relative humidity 55%
From the flat surface, measure the number of protrusions in the range of 2 to 50 nm, take the average, 1 mm²Convert to per number.
[0093]
(2) Surface roughness Ra
The center line average roughness Ra was measured using a high precision thin film level difference measuring device ET-10 manufactured by Kosaka Laboratory. The conditions were as follows, and the value was defined as an average value obtained by scanning 20 times in the film width direction.
・ Tip tip radius: 0.5μm
-Stylus load: 5mg
・ Measurement length: 1mm
・ Cutoff value: 0.08mm
[0094]
(3) Average particle size of inert particles
The cross section of the film is observed at a magnification of 10,000 times or more using a transmission electron microscope (TEM). The section thickness of TEM is about 100 nm, and the measurement is performed at 100 fields or more at different locations. The measured weight average of equivalent circle equivalent diameters was defined as the average particle diameter d of the inert particles.
When two or more kinds of particles having different particle diameters exist in the film, the number distribution of equivalent circle equivalent diameters is a distribution having two or more peaks, and the average particle diameter is calculated separately for each of them. To do.
[0095]
(4) Polyester, polyimide, content of inert particles in the film layer
Dissolved in a suitable solvent that dissolves both polyester and polyimide,¹The NMR (nuclear magnetic resonance) spectrum of the H nucleus is measured. A suitable solvent varies depending on the type of polymer, for example, hexafluoroisopropanol (HFIP) / deuterated chloroform is used. In the obtained spectrum, the peak area intensity of absorption peculiar to polyester and polyimide (for example, absorption of aromatic protons of terephthalic acid in the case of PET, absorption of aromatic protons of bisphenol A in the case of PEI) is obtained. The molar ratio of polyester and polyimide is calculated from the ratio and the number of protons. Further, the weight ratio is calculated from the formula amount corresponding to the unit unit of each polymer. The measurement conditions are, for example, the following conditions, but are not limited to this because they differ depending on the type of polymer.
[0096]
Equipment: BRUKER DRX-500 (Bruker)
Solvent: HFIP / deuterated chloroform
Observation frequency: 499.8 MHz
Standard: TMS (tetramethylsilane) (0 ppm)
Measurement temperature: 30 ° C
Observation width: 10 KHz
Data point: 64K
acquisiton time: 4.952 seconds
pulse delay time: 3.048 seconds
Integration count: 256 times
Moreover, you may perform a composition analysis by the microscopic FT-IR method (Fourier transform microscopic infrared spectroscopy) as needed. In that case, it calculates | requires from ratio of the peak resulting from the carbonyl group of polyester, and the peak resulting from other substances. In order to convert the peak height ratio to the weight ratio, a calibration curve is prepared with a sample whose weight ratio is known in advance, and the polyester ratio relative to the total amount of polyester and other substances is determined. The PEI ratio is determined from this and the inert particle content. Moreover, you may use together an X-ray microanalyzer as needed.
[0097]
Moreover, about content of an inert particle, the polyester and polyimide melt | dissolve, but the solvent which does not melt | dissolve an inert particle was selected, polyester and polyimide were melt | dissolved, the inert particle was centrifuged, and the weight percentage was calculated | required.
[0098]
(5) Content of inert particles in the easy-smooth smooth layer (C layer)
Using a scanning electron microscope (SEM), the film surface on the C layer side is observed at 10 magnifications or more at an enlargement ratio of about 30,000 times.²It was measured by determining how many hits there were.
[0099]
(6) Lamination thickness
Using a transmission electron microscope (H-600 type manufactured by Hitachi), the film cross section was measured with an ultrathin section method (RuO) at an acceleration voltage of 100 kV_FourObserve by staining). The thickness of each layer is obtained from the observation result of the interface. As the magnification, an appropriate magnification is selected depending on the laminated thickness to be determined, but 10,000 to 100,000 is appropriate.
[0100]
Moreover, it can also measure using a secondary ion mass spectrometer (SIMS).
Among the inert particles in the film having a depth of 3000 nm from the surface layer, the highest concentration of particles (if the content of polyimide is different between the laminated part and the base part, polyimide may be used) and the polyester Carbon element concentration ratio (M⁺/ C⁺) Is analyzed by SIMS in the thickness direction from the surface to a depth of 3000 nm. In the surface layer, the element concentration caused by the inert particles is low, and the element concentration caused by the inert particles increases as the distance from the surface increases. In the case of the film of the present invention, the element concentration due to the inert particles once having reached the maximum value starts to decrease again. In this concentration distribution curve, the depth at which the element concentration caused by the inert particles is reduced to ½ of the maximum value is defined as the stack thickness. The conditions are as follows.
[0101]
i) Measuring device
Secondary ion mass spectrometer (SIMS)
West Germany, A-DIDA3000 manufactured by ATOMICA
ii) 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: 5.0 × 10^-9Torr
E-GUN: 0.5KV-3.0A
If the inert particles contained most in the range of 3000 nm in depth from the surface layer are organic polymer particles, it is difficult to measure by SIMS. Therefore, XPS (X-ray photoelectron spectroscopy), IR (infrared) is used while etching from the surface. It is also possible to determine the stack thickness by measuring a depth profile similar to that described above using a spectroscopic method.
[0102]
(7) Young's modulus
According to the method prescribed | regulated to ASTM-D882, it measured using the Instron type tensile tester. The measurement was performed under the following conditions.
Measuring device: Orientec Co., Ltd. film strong elongation automatic measuring device “Tensilon” AMF / RTA-100
Sample size: width 10 mm x test length 100 mm,
Tensile speed: 200 mm / min
Measurement environment: Temperature 23 ° C, humidity 65% RH
[0103]
(8) Number of coarse protrusions H1, H2
Measuring surface (100cm²) Are superposed on each other and brought into close contact with each other by an electrostatic force (applied voltage 5.4 kv), and the height of the coarse protrusion is determined from the Newton ring generated by the interference of the light of the coarse protrusion between the two films. The number of coarse protrusions of a heavy ring or more was H1, and the number of coarse protrusions of a double ring or more was H2. The light source used was a halogen lamp with a 564 nm bandpass filter.
[0104]
(9) Thermal shrinkage (dimensional stability during processing and storage)
It measured according to JIS C2318.
Sample size: width 10 mm, marked line interval 200 mm
Measurement conditions: temperature 100 ° C, treatment time 30 minutes, no load
The thermal shrinkage rate was obtained from the following formula.
Thermal contraction rate (%) = [(L₀-L) / L₀] × 100
L₀: Mark interval before heat treatment
L: Mark interval after heat treatment
As a result, when the heat shrinkage rate in the longitudinal direction is 1% or less and the heat shrinkage rate in the width direction is 0.5% or less, the dimensional stability during processing and storage is good (O), When either one of the longitudinal direction and the width direction deviated from this range, it was determined that the dimensional stability during processing and storage was poor (x).
[0105]
(10) Electromagnetic conversion characteristics of magnetic tape (S / N)
A cobalt-oxygen thin film having a thickness of 150 nm was formed on the surface opposite to the B layer of the film of the present invention using a continuous vacuum deposition apparatus in the presence of a small amount of oxygen. Next, a diamond-like carbon protective film was formed with a thickness of 10 nm on the cobalt-oxygen thin film by a sputtering method, and a fluorine-containing fatty acid ester lubricant was applied with a thickness of 3 nm. Subsequently, a back coat layer made of carbon black, polyurethane, and silicone is provided on the surface on the B layer side with a thickness of 500 nm, slit to a width of 6.35 mm by a slitter, and wound on a reel to form a magnetic recording tape (DVC video tape). Created.
[0106]
The characteristics evaluation of the magnetic recording tape described above was performed by obtaining a video S / N ratio using a commercially available camera-integrated digital video tape recorder. For the measurement of the S / N ratio, a signal was supplied from a TV test signal generator, and a video noise meter was used to compare and measure the tape made from the film of Comparative Example 1 at 0 decibel (dB). evaluated. . The traveling conditions are 25 ° C. and 60% RH.
[0107]
○: +0.5 dB or more
Δ: -0.5 dB or more and less than +0.5 dB
X: Less than -0.5 dB
Here, ◯ means that it is an excellent level as a vapor deposition type high density recording magnetic tape application, Δ means that it can be used, and X means that it is an insufficient level.
[0108]
(11) Vapor deposition stability
The continuous vacuum deposition of the above (10) was performed on 10 films of 3000 m of the present invention, and the process stability in the deposition process was evaluated according to the following criteria.
[0109]
◯: The number of film wrinkles due to adhesion of oligomers or the like, or “wrinkles” due to shrinkage in the width direction was 2 or less.
[0110]
Δ: With 3 or 4, the film was cut due to oligomer adhesion or “wrinkles” due to shrinkage in the width direction or the like occurred.
[0111]
X: 5 or more, film breakage due to adhesion of oligomer or the like, or “wrinkle” due to shrinkage in the width direction occurred.
[0112]
Here, ◯ means that the process stability in the vapor deposition process is excellent, Δ means that it can be used, and x means an insufficient level.
[0113]
(12) Oligomer deterrence
The film of the present invention is allowed to stand in an oven at 150 ° C. for 30 minutes to forcibly deposit low molecular weight substances on the film surface, and the surface on the f-plane side is vapor-deposited with aluminum to obtain a total magnification of 1000 times with a differential interference microscope. , Observe 25 visual fields. The number of low molecular weight bodies in each field of view is 0.5 mm or more on the surface photograph, and the total number is 1 mm.²In terms of per unit, the number of surface oligomer deposition (pieces / mm²).
[0114]
(13) Intrinsic viscosity
Calculate from the following formula from the solution viscosity measured at 25 ° C. in orthochlorophenol.
[0115]
η_sp/ C = [η] + K [η]²・ C
Where η_sp= (Solution viscosity / solvent viscosity) -1, C is the weight of dissolved polymer per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (assuming 0.343). The solution viscosity and solvent viscosity were measured using an Ostwald viscometer.
[0116]
(14) Extrapolated glass transition start temperature (Tg_onset), Glass transition temperature (Tg)
Specific heat was measured with the following equipment and conditions, and determined according to JIS K7121.
[0117]
Apparatus: Temperature modulation DSC manufactured by TA Instrument
Measurement condition:
Heating temperature: 270-570K (RCS cooling method)
Temperature calibration: Melting point of high purity indium and tin
Temperature modulation amplitude: ± 1K
Temperature modulation period: 60 seconds
Temperature rising step: 5K
Sample weight: 5mg
Sample container: Aluminum open container (22 mg)
Reference container: Aluminum open container (18mg)
The glass transition temperature was calculated by the following formula.
[0118]
Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
(15) Comprehensive evaluation
Of the evaluation items (9), (10), and (11) above, the following criteria were used.
[0119]
○: All characteristics are excellent (◯), or two items are excellent (◯) and one item can be used (Δ).
[0120]
X: Either one of the items has an insufficient level (x), or two are usable (Δ).
[0121]
Here, ◯ means that it is suitable for a magnetic recording medium having a vapor deposition type magnetic layer, and x means that it is not suitable for a magnetic recording medium having a vapor deposition type magnetic layer.
[0122]
【Example】
Based on the following examples, embodiments of the present invention will be described.
[0123]
Example 1
50 wt% of polyethylene terephthalate (PET) pellets (Tg 80 ° C.) having an intrinsic viscosity of 0.85 obtained by a conventional method, and “Ultem” 1010 (Tg 216 ° C.) having an intrinsic viscosity of 0.68 manufactured by General Electric (GE) 50 wt% was supplied to a co-rotating bent type twin-screw kneader / extruder heated to 290 ° C. to prepare a blend chip (II) containing 50 wt% PEI.
[0124]
Next, film formation was performed using two extruders. In the extruder A heated to 290 ° C., 20 parts by weight of the blend chip obtained by the above pelletizing operation and 80 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 substantially containing no inert particles are mixed. The raw material (A1) was supplied after vacuum drying at 180 ° C. for 3 hours. In Extruder B heated to 295 ° C., 20 parts by weight of blend chips obtained by the above pelletizing operation, 60 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 substantially containing no inert particles, and an average A mixed raw material (B1) of 20 parts by weight of pellets of polyethylene terephthalate (PET) having an intrinsic viscosity of 0.62 containing 2% by weight of crosslinked divinylbenzene particles having a particle diameter of 0.25 μm was supplied after being vacuum-dried at 180 ° C. for 3 hours. . Subsequently, A1 is filtered in three stages in the order of a sand filter, a 1.2 μm cut fiber sintered stainless metal filter and a 0.8 μm cut fiber sintered stainless metal filter, and B1 is a sand filter, 3 μm cut fiber sintered. After filtration in two stages in the order of the stainless steel metal filter, A / B was laminated in a rectangular merge block (feed block) for two layers. The thickness of each layer was adjusted by adjusting the number of revolutions of a gear pump installed in each line to control the amount of extrusion. This was wound on a casting drum having a surface temperature of 25 ° C. using an electrostatic application casting method, and cooled and solidified to prepare a two-layer laminated unstretched film (lamination thickness ratio A1 / B1 = 10/1).
[0125]
This unstretched film was stretched 3.1 times in the longitudinal direction at 110 ° C. by a roll-type stretching machine. This stretching was performed using the difference in peripheral speed between two sets of rolls. The following aqueous solution was apply | coated on the A layer of this uniaxially stretched film.
[0126]
0.10 parts by weight of methylcellulose
Water-soluble polyester 0.3% by weight
Aminoethylsilane coupling agent 0.01% by weight
Carnauba wax 0.2% by weight
Acrylic particles with an average particle size of 20 nm 0.02% by weight
Solid content coating concentration 20mg / m²
Further, using a tenter, the film was stretched 3.4 times in the width direction at a temperature of 100 ° C. Subsequently, the film was re-stretched 1.55 times at a temperature of 150 ° C. in a single stage in the longitudinal direction with a roll-type stretching machine, and re-stretched 1.6 times at a temperature of 195 ° C. in the width direction using a tenter. After heat treatment at a temperature of 205 ° C. for 8 seconds under a constant length, 5% relaxation treatment was performed in the width direction to obtain a laminated polyester film having a thickness of about 6.0 μm. The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 5.2 GPa, and the Young's modulus in the width direction was 6.1 GPa.
[0127]
As shown in Table 3, this laminated polyester film had excellent properties as a base film for a magnetic recording medium, such as low dropout, electromagnetic conversion characteristics and running durability.
[0128]
Example 2
As shown in Table 1, the A-layer and B-layer polymers were prepared in the same manner as in Example 1 to prepare a two-layer laminated unstretched film (laminate thickness ratio A / B = 11/1).
[0129]
This unstretched film was stretched by the same stretching method, stretching temperature and stretching ratio as in Example 1 to obtain a laminated polyester film having a thickness of about 6 μm. However, the composition of the aminoethylsilane coupling agent in the applied aqueous solution was changed from 0.01% by weight to 0.15% by weight, and the inert particles were changed to ultrafine silica (0.03% by weight) having an average particle diameter of 12 nm. The composition was changed. The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 5.1 GPa, and the Young's modulus in the width direction was 6.2 GPa.
[0130]
As shown in Table 3, this laminated polyester film had excellent properties as a base film for a magnetic recording medium, such as low dropout, electromagnetic conversion characteristics and running durability.
[0131]
Example 3
As shown in Table 1, the weight ratio of PET and PEI of the A layer and B layer polymers was changed to 85:15, and the inert particles of the B layer were aluminum silicate particles having an average particle size of 0.18 μm (0.95 wt. A two-layer laminated unstretched film (lamination thickness ratio A / B = 11/1) was prepared in the same manner as in Example 1 except that the content was changed to “% content”.
[0132]
Except that this unstretched film was stretched 3.05 times in a longitudinal direction at a temperature of 120 ° C. by a roll-type stretching machine, and the inert particles were changed to ultrafine silica (0.16 wt%) having an average particle diameter of 18 nm. After applying the same aqueous solution as in Example 1, the film was stretched 3.4 times in the width direction at a temperature of 105 ° C. using a tenter. Subsequently, the film was re-stretched 1.7 times at a temperature of 150 ° C. in the longitudinal direction using a roll-type stretching machine, and re-stretched 1.7 times at a temperature of 200 ° C. in the width direction using a tenter. After a heat treatment at a temperature of 200 ° C. for 8 seconds under a constant length, a relaxation treatment of 3% in the width direction was performed to obtain a laminated polyester film having a thickness of about 6 μm. The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 5.0 GPa, and the Young's modulus in the width direction was 5.7 GPa.
[0133]
As shown in Table 3, this laminated polyester film had excellent properties as a base film for a magnetic recording medium, such as low dropout, electromagnetic conversion characteristics and running durability.
[0134]
Example 4
Film formation was performed using three extruders. As shown in Table 1, the polymer composition and particle content of the A layer and the B layer were exactly the same as in Example 1, and the D layer polymer was substantially inactive with 20 parts by weight of blend chips containing 50% by weight of PEI. 75 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 containing 5 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 and 1% by weight of crosslinked divinylbenzene particles having an average particle diameter of 25 nm. Part of the mixed raw material was used. The B layer and D layer contained 0.3% by weight of sodium dodecylbenzenesulfonate, and the A layer contained 0.1% by weight. The filtration method for the A and B layer polymers was the same as in Example 1. The D layer polymer was a sand filter, a 1.2 μm cut fiber sintered stainless metal filter, and a 0.8 μm cut fiber sintered stainless metal filter. It filtered in three steps in order. A three-layer laminated unstretched film (lamination thickness ratio D / A / B = 0.15 / 11/1) was prepared.
[0135]
A stretched polyester film having a thickness of about 6.1 μm was obtained in the same manner as in Example 1 except for the stretching method, stretching temperature, stretching ratio, and the like of this unstretched film. However, the application of the aqueous solution as in Example 1 was not performed. The film thickness of each layer was A layer 5.5 μm, B layer 0.5 μm, and D layer 0.075 μm. The Young's modulus in the longitudinal direction was 5.2 GPa, and the Young's modulus in the width direction was 6.1 GPa.
[0136]
As shown in Table 3, this laminated polyester film had excellent properties as a base film for a magnetic recording medium, such as low dropout, electromagnetic conversion characteristics and running durability.
[0137]
Example 5
As shown in Table 1, the A layer, B layer, and D layer polymers were changed to poly (ethylene-2,6-naphthalenedicarboxylate) (PEN) and PEI mixed polymer (weight ratio 90:10), and D layer The inert particles in the B layer were changed to ultrafine silica particles having an average particle size of 30 nm (containing 1.2%), and the inert particles in the B layer were aluminum silicate particles having an average particle size of 0.18 μm (containing 0.5%). And the temperature of all three extruders was changed to 320 ° C., and similarly to Example 4, a three-layer laminated unstretched film (lamination thickness ratio D / A / B = 0.2 / 10/1) It was created.
[0138]
This unstretched film was stretched 4.5 times at a temperature of 135 ° C. in the longitudinal direction using a roll stretching machine, and further stretched 5.5 times at a temperature of 130 ° C. in the width direction using a tenter. Thereafter, after heat treatment at a temperature of 240 ° C. for 6 seconds under a constant length, a relaxation treatment of 2% in the width direction was performed to obtain a laminated polyester film having a thickness of about 4.5 μm. In addition, re-longitudinal and re-lateral stretching were not performed. The film thickness of each layer was A layer 4 μm, B layer 0.4 μm, and 0.08 μm. The Young's modulus in the longitudinal direction was 7.2 GPa, and the Young's modulus in the width direction was 7.5 GPa.
[0139]
As shown in Table 3, this laminated polyester film had excellent properties as a base film for a magnetic recording medium, such as low dropout, electromagnetic conversion characteristics and running durability.
[0140]
Example 6
As shown in Table 1, the A-layer, B-layer and D-layer polymers were changed to a mixed polymer of PET and PEI (weight ratio 80:20), and the inert particles in the B-layer were crosslinked divinylbenzene having an average particle size of 0.2 μm. Three-layer lamination in the same manner as in Example 4 except that the particles (containing 0.2% by weight) and the inert particles in layer D were changed to ultrafine silica particles (containing 1.5% by weight) having an average particle diameter of 20 nm. An unstretched film (lamination thickness ratio D / A / B = 0.1 / 15/1) was prepared.
[0141]
This unstretched film was stretched 3 times in the longitudinal direction at a temperature of 125 ° C. by a roll stretching machine, and further stretched 3.3 times in the width direction at a temperature of 115 ° C. using a tenter. Subsequently, the film was re-stretched 1.8 times at a temperature of 155 ° C. in the longitudinal direction with a roll-type stretching machine, and re-stretched 1.7 times at 200 ° C. in the width direction using a tenter. After heat treatment at a temperature of 200 ° C. for 8 seconds under a constant length, 3% relaxation treatment was performed in the width direction to obtain a laminated polyester film having a thickness of about 8 μm. The film thickness of each layer was A layer 7.5 μm, B layer 0.5 μm, and 0.05 μm. The Young's modulus in the longitudinal direction was 4.9 GPa, and the Young's modulus in the width direction was 5.4 GPa.
[0142]
As shown in Table 3, this laminated polyester film had excellent properties as a base film for a magnetic recording medium, such as low dropout, electromagnetic conversion characteristics and running durability.
[0143]
Example 7
As shown in Table 1, the polymer of layer A and layer B was changed to a mixed polymer of PET and PEI (weight ratio 70:30), and the inert particles of layer B were aluminum silicate particles having an average particle size of 0.18 μm ( In the same manner as in Example 1, a two-layer laminated unstretched film (lamination thickness ratio A / B = 11/1) was prepared.
[0144]
This unstretched film was stretched 3.05 times at a temperature of 130 ° C. in the longitudinal direction with a roll-type stretcher, and the inert particles were ultrafine silica (0.035 wt%) having an average particle diameter of 12 nm. The same aqueous solution as in Example 1 was applied except that it was changed to), and then stretched 3.5 times at a temperature of 110 ° C. in the width direction using a tenter. Subsequently, the film was re-stretched 1.75 times at a temperature of 155 ° C. in the longitudinal direction using a roll-type stretching machine, and re-stretched 1.8 times at 200 ° C. in the width direction using a tenter. After heat treatment at a temperature of 205 ° C. for 8 seconds under a constant length, a relaxation treatment of 2% in the width direction was performed to obtain a laminated polyester film having a thickness of about 6 μm. The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 4.8 GPa, and the Young's modulus in the width direction was 5.2 GPa.
[0145]
As shown in Table 3, this laminated polyester film had excellent properties as a base film for a magnetic recording medium, such as low dropout, electromagnetic conversion characteristics and running durability.
[0146]
Example 8
As shown in Table 1, the A layer polymer was changed to a mixed polymer of PEN and PEI (weight ratio 92: 8), and the B layer and C layer polymers were changed to PEN. Cross-linked divinylbenzene particles having an average particle size of 0.2 μm (containing 0.17% by weight) as inert particles in the B layer, and ultrafine silica particles having an average particle size of 45 nm (containing 0.5% by weight) as the inert particles in the D layer In the same manner as in Example 5, a three-layer laminated unstretched film (lamination thickness ratio D / A / B = 0.2 / 7.5 / 1) was produced.
[0147]
The unstretched film was stretched under the same conditions as in Example 5 to obtain a laminated polyester film having a thickness of 3.5 μm. The film thickness of each layer was A layer 3 μm, B layer 0.4 μm, and 0.08 μm. The Young's modulus in the longitudinal direction was 7.1 GPa, and the Young's modulus in the width direction was 7.4 GPa.
[0148]
As shown in Table 3, this laminated polyester film had excellent properties as a base film for a magnetic recording medium, such as low dropout, electromagnetic conversion characteristics and running durability.
[0149]
Comparative Example 1
Create an unstretched film with an A / B two-layer structure in the same manner as in Example 1 except that PET is used as the A layer and B layer polymer instead of using a blend polymer of PET and PEI. did. The temperature of both extruders was 280 ° C.
[0150]
Next, in the same manner as in Example 1, this unstretched film was stretched 3.1 times in the longitudinal direction at a temperature of 105 ° C. using a roll-type stretching machine, and after applying the same aqueous solution as in Example 1, a tenter was used. The film was stretched 3.4 times at a temperature of 95 ° C. in the width direction. Subsequently, the film was re-stretched 1.55 times in the longitudinal direction at a temperature of 150 ° C. using a roll-type stretching machine, and re-stretched 1.6 times in the width direction at a temperature of 190 ° C. using a tenter. After heat treatment at a temperature of 210 ° C. for 8 seconds under a constant length, a relaxation treatment of 5% in the width direction was performed to obtain a laminated polyester film having a thickness of about 6 μm. The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 5.3 GPa, and the Young's modulus in the width direction was 6.7 GPa.
[0151]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0152]
Comparative Example 2
An unstretched film having a three-layer laminated structure was prepared in the same manner as in Example 1 except that the A layer polymer was PET, the B layer, and the D layer polymer was PET / PEI (weight ratio 90:10). .
[0153]
Next, this unstretched film was stretched under the same stretching conditions as in Comparative Example 1 to obtain a laminated polyester film having a thickness of about 6.1 μm. However, the aqueous solution was not applied. The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 5.2 GPa, and the Young's modulus in the width direction was 6.5 GPa.
[0154]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0155]
Comparative Example 3
As shown in Table 2, a thickness of about 6 μm was obtained in exactly the same manner as in Example 1 except that the inert particles in the B layer were changed to spherical silica particles (containing 0.1 wt%) having an average particle size of 1.1 μm. A laminated polyester film was obtained. The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 5.2 GPa, and the Young's modulus in the width direction was 6.1 GPa.
[0156]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0157]
Comparative Example 4
As shown in Table 2, a laminated polyester film having a thickness of about 6 μm was obtained in the same manner as in Example 1 except that the content of the inert particles in the aqueous solution to be applied was changed to 0.01% by weight. The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 5.2 GPa, and the Young's modulus in the width direction was 6.1 GPa.
[0158]
Comparative Example 5
As shown in Table 2, a laminated polyester having a thickness of about 6.1 μm was used in the same manner as in Example 4 except that the inert particles of layer D were spherical silica particles having an average particle size of 60 nm (containing 2% by weight). A film was obtained. The film thickness of each layer was A layer 5.5 μm, B layer 0.5 μm, and D layer 0.075 μm. The Young's modulus in the longitudinal direction was 5.2 GPa, and the Young's modulus in the width direction was 6.1 GPa.
[0159]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0160]
Comparative Example 6
The composition of layer A was changed to the same as layer B of Example 1 (PET / PEI = 90: 10, containing 0.3% by weight of divinylbenzene crosslinked particles having an average particle size of 0.27 μm), and lamination was performed. Without producing a single-layer unstretched film.
[0161]
The composition of the aqueous solution, the stretching method, the stretching conditions, etc. were exactly the same as in Example 1 to obtain a polyester film having a thickness of about 6 μm. The Young's modulus in the longitudinal direction was 5.2 GPa, and the Young's modulus in the width direction was 6.1 GPa.
[0162]
Comparative Example 7
As shown in Table 2, the weight ratio of PET / PEI of the A layer, B layer, and D layer polymer was changed to 60:40, and the inert particles in the D layer were changed to ultrafine spherical silica particles having an average particle diameter of 30 nm (3.1). In addition, the polymer filtration method of each layer was changed to a method using only a 3 μm cut fiber sintered stainless metal filter to prepare an unstretched film having a three-layer laminated structure. Under the same stretching conditions as in Example 4, the re-longitudinal and re-lateral stretching properties were poor, and tearing occurred frequently. For this reason, the unstretched film was stretched 3.5 times at a temperature of 110 ° C. in the longitudinal direction with a roll stretching machine, and further stretched 4.5 times at a temperature of 100 ° C. in the width direction using a tenter. Thereafter, after heat treatment at a constant length of 205 ° C. for 7 seconds, a relaxation treatment of 5% in the width direction was performed to obtain a laminated polyester film having a thickness of about 6.1 μm. The film thickness of each layer was A layer 5.5 μm, B layer 0.5 μm, and D layer 0.075 μm. The Young's modulus in the longitudinal direction was 4.1 GPa, and the Young's modulus in the width direction was 4.9 GPa.
[0163]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0164]
Comparative Example 8
As shown in Table 2, a three-layer laminated unstretched film was produced in exactly the same manner as in Example 4.
[0165]
This unstretched film was stretched 3.5 times at a temperature of 110 ° C. in the longitudinal direction using a roll stretching machine, and further stretched 4.5 times at a temperature of 100 ° C. using a tenter. Thereafter, after heat treatment at a constant length of 205 ° C. for 7 seconds, a relaxation treatment of 5% in the width direction was performed to obtain a laminated polyester film having a thickness of about 2.4 μm. In addition, re-longitudinal and re-lateral stretching were not performed. The Young's modulus in the longitudinal direction was 5.1 GPa, and the Young's modulus in the width direction was 5.5 GPa.
[0166]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0167]
Comparative Example 9
As shown in Table 2, a PET / PEI blend polymer (weight ratio 90:10) containing 0.03% by weight of silica having an average particle size of 60 nm was used as the A layer polymer, and an average particle size of 0 was used as the B layer polymer. A PET containing 0.4% by weight of 25 μm aluminum silicate particles is used, and the filtration method for the A layer is a known method (3-μm cut fiber sintered stainless steel filter, one stage). A film (lamination thickness ratio A / B = 4/1) was prepared.
[0168]
This unstretched film was stretched 3.2 times in the longitudinal direction at 95 ° C. This stretching was performed using the difference in peripheral speed between two sets of rolls. The following aqueous solution was apply | coated on the A layer of this uniaxially stretched film.
[0169]
0.10 parts by weight of methylcellulose
Water-soluble polyester 0.3% by weight
Aminoethylsilane coupling agent 0.01% by weight
Ultrafine silica with an average particle size of 12 nm 0.03% by weight
Solid concentration 20mg / m²
Thereafter, the film was stretched 3.4 times in the width direction at 115 ° C. using a tenter. Further, the film was stretched 1.5 times at 140 ° C. in the longitudinal direction, and then this film was heat-treated at 220 ° C. for 5 seconds under a constant length, and then 5% relaxation treatment was performed in the width direction to obtain a laminated polyester film having a thickness of 5 μm. Got. The film thickness of each layer was A layer 4 μm and B layer 1 μm. The Young's modulus in the longitudinal direction was 5.3 GPa, and the Young's modulus in the width direction was 5.4 GPa.
[0170]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0171]
Comparative Example 10
As shown in Table 2, PET containing substantially no particles was used as the A layer polymer, and PET containing 0.3% by weight of crosslinked divinylbenzene particles having an average particle size of 0.2 μm was used as the B layer polymer. A PET / PEI blend polymer (weight ratio 90:10) containing 0.3% by weight of spherical silica particles having an average particle size of 30 nm was used as a polymer to obtain a three-layer laminated unstretched film. The filtration method of D layer uses a well-known method (1.2 micrometer cut fiber sintered stainless metal filter, one step), and a two-layer laminated unstretched film (lamination thickness ratio D / A / B = 0.05 / 3. 95/1).
[0172]
This unstretched film was stretched 3.2 times in the longitudinal direction at 95 ° C. This stretching was performed using the difference in peripheral speed between two sets of rolls. Then, it extended | stretched 4.5 times in the width direction at 100 degreeC using the tenter. Further, the film was stretched 1.5 times at 140 ° C. in the longitudinal direction, and then this film was heat-treated at 220 ° C. for 5 seconds under a constant length, followed by 7% relaxation treatment in the width direction, and a laminated polyester film having a thickness of 5 μm. Got. The film thickness of each layer was A layer 3.95 μm, B layer 1 μm, D layer 0.05 μm. The Young's modulus in the longitudinal direction was 5.5 GPa, and the Young's modulus in the width direction was 5.6 GPa.
[0173]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0174]
Comparative Example 11
As shown in Table 2, the inert particles of layer D were changed to spherical silica (containing 3.1 wt%) having an average particle size of 30 nm, and the inert particles of layer B were aluminum silicate particles having an average particle size of 0.18 μm A laminated polyester film having a thickness of about 9.9 μm was obtained in the same manner as in Example 4 except that the content was changed to (containing 0.5% by weight). The film thickness of each layer was A layer 9 μm, B layer 0.8 μm, and D layer 0.1 μm. The Young's modulus in the longitudinal direction was 5.1 GPa, and the Young's modulus in the width direction was 6.2 GPa.
[0175]
As shown in Table 3, this laminated polyester film was inferior as a film for magnetic recording media.
[0176]
Comparative Example 12
As shown in Table 2, the inert particles of layer B were changed to ultrafine spherical silica particles (containing 2.5% by weight) having an average particle size of 20 nm, and the layered structure was a B / A / B type three layered layer (laminated layer) A laminated polyester film having a thickness of about 6.5 μm was obtained in the same manner as in Example 4 except that the thickness ratio was changed to B / A / B = 1/1/1/1). The film thickness of each layer was A layer 5.5 μm and B layer 0.5 μm. The Young's modulus in the longitudinal direction was 5.1 GPa, and the Young's modulus in the width direction was 6.2 GPa.
[0177]
As shown in Table 3, when this laminated polyester film was used as a magnetic tape, it caused poor running of the tape and was inferior as a film for magnetic recording media.
[0178]
[Table 1]

[0179]
[Table 2]

[0180]
[Table 3]

[0181]
【The invention's effect】
According to the present invention, polyimide is contained in polyester, the projection height and the number of projections on the surface of the film having good dimensional stability, and the surface roughness are specified, or the inertness contained in the laminated structure and each layer By defining the average particle size and particle content of the particles, it is possible to obtain a polyester film for a magnetic recording medium that achieves both storage stability and electromagnetic conversion characteristics at a high level.

Claims (10)

A laminated polyester film having a base layer part (A layer) comprising polyester and polyimide as essential components and having a total thickness of 3 to 8 μm composed of at least two film layers, one surface (f surface) There are 5 to 70 million projections with a projection height of 5 to 25 nm / mm ² , the surface roughness Raf on the f-plane side, the surface roughness Rab on the opposite surface (b-plane), and the film on the f-plane side A polyester film for a magnetic recording medium, wherein the number of coarse protrusions H1 and H2 on the surface satisfies the following relationship:
0.1 ≦ Raf (nm) ≦ 5
5 ≦ Rab (nm) ≦ 20
0 ≦ H1 (pieces / 100 cm ² ) ≦ 100
0 ≦ H2 (pieces / 100 cm ² ) ≦ 10 Laminated part (B layer) containing polyester or polyester and polyimide as essential components on one side of the base layer part (A layer) and 0.05 to 1.5% by weight of inert particles having an average particle size of 0.05 to 1 μm 3 to 70 million particles / mm ² and water-soluble particles having an average particle diameter of 7 to 25 nm provided on the surface opposite to the B layer of at least the B layer. The polyester film for magnetic recording media according to claim 1, which is a laminated polyester film comprising an easy-slip smooth layer (C layer) containing a conductive polymer.  Laminated part (B layer) containing polyester or polyester and polyimide as essential components on one side of the base layer part (A layer) and 0.05 to 1.5% by weight of inert particles having an average particle size of 0.05 to 1 μm Is laminated, and on the side opposite to the B layer, a laminated part (D layer) containing polyester or polyester and polyimide as essential components and containing 0.1 to 3% by weight of inert particles having an average particle diameter of 10 to 50 nm is laminated. The polyester film for a magnetic recording medium according to claim 1, wherein the polyester film is a laminated polyester film having a laminated structure of at least three layers of D layer / A layer / B layer. The polyester film for magnetic recording media according to any one of claims 1 to 3 , wherein the polyimide of the A layer is a polyetherimide. The polyester film for a magnetic recording medium according to any one of claims 1 to 4 , wherein the polyester of the A layer contains an ethylene terephthalate unit as a main component. The polyester film for magnetic recording media according to any one of claims 1 to 5 , wherein polyimide is contained in the A layer in an amount of 5 to 30% by weight. The sum of the elastic modulus in the film longitudinal direction and the width direction is 9 to 20 GPa, the elastic modulus in the film longitudinal direction is 4.3 GPa or more, and the elastic modulus in the film width direction is 4.7 GPa or more. polyester film for magnetic recording medium according to any one of 1 to 6. The magnetic recording medium formed by providing at least one surface in the magnetic layer of the polyester film for magnetic recording medium according to any one of claims 1-7. A magnetic recording medium comprising a ferromagnetic metal thin film formed on at least one surface of the polyester film for a magnetic recording medium according to claim 7 . Cassettes digital recording system comprising a magnetic recording medium according to claim 8 or 9.