JP4168627B2 - Polyester film for magnetic recording medium, method for producing the same, and magnetic recording medium - Google Patents

Description

ただし、式中のＲ₁は、
【００２１】
【化２】

【００２２】
【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、
【００２３】
また、式中のＲ₂ は、
【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。
【００２４】
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。
【００２５】
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。
【００２６】
【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。）
【００２７】
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】

（図中のｎは１〜５の整数）
を挙げることができる。
【００２８】
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。
【００２９】
【化７】

または
【化８】

（ｎは２以上の整数、好ましくは２０〜５０の整数）
【００３０】
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。
【００３１】
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。
【００３２】
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。また、ペレタイズの際に、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。
【００３３】
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エーテル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。
【００３４】
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。
【００３５】
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を良化させる目的で、不活性粒子を含有させることが好ましい。なお、本発明で言う不活性粒子とは、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。
【００３６】
本発明の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、磁気ヘッドを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、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。
【００３７】
本発明の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。
【００３８】
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添加することが好ましい。この際、Ｂ層に添加す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。不活性粒子の平均粒径ｄは、磁気記録媒体用に用いる場合には、０．０１〜２μｍが好ましく、より好ましくは０．０１〜１μｍである。含有量は０．００１〜３重量％、好ましくは０．００５〜１重量％である。この場合、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。
【００３９】
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、積層フィルムとして用いる際の、Ｂ層の厚みは０．０１〜５μｍであると、製膜性がより一層良好となり好ましい。Ｂ層の厚みは、好ましくは０．０３〜２μｍ、より好ましくは０．０５〜１μｍである。
【００４０】
本発明の積層ポリエステルフィルムは、Ａ層／Ｂ層の２層積層構成であっても、十分に発明の効果を発揮するが、基層部（Ａ層）の両側に異なるフィルムを積層したＣ層／Ａ層／Ｂ層の３層積層構成であってもよいし、また４層以上の積層構成としてもよい。３層積層構成とする場合にも、Ｂ層は磁気テープの走行性を担う必要があるため、上述の通り、比較的粒径の大きな不活性粒子を含有する必要がある。ただし、この場合、磁気テープとしたときの電磁変換特性や磁気ヘッドとの走行性を担う表面はＣ層が担うため、基層部であるＡ層は実質的に不活性粒子を含有しない平滑な層とすることができる。
【００４１】
３層積層とする場合、Ｃ層に添加する不活性粒子の平均粒径は、０．００１〜０．５μｍが好ましく、含有量は０．０１〜１重量％が好ましい。また、Ｃ層の厚みは、０．０１μｍ〜１μｍが好ましく、より好ましくは０．０３μｍ〜０．５μｍ、さらに好ましくは０．０５〜０．３μｍである。
【００４２】
本発明の積層ポリエステルフィルムのＢ層側の表面の表面粗さＲａ_(B)は３〜１５ｎｍであり、好ましくは５〜１２ｎｍ、さらに好ましくは７〜１０ｎｍである。Ｒａ_(B)が３ｎｍ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１５ｎｍより大きい場合には、磁気テープとして用いる際、走行面側の粒子が脱落し易くなり、走行特性を悪化させたり、ドロップアウトなどの原因となるため好ましくない。
【００４３】
本発明の積層ポリエステルフィルムのＢ層と反対側の表面の表面粗さＲａ_(NB)は０．５〜１０ｎｍであり、好ましくは１〜８ｎｍ、さらに好ましくは１．５〜６．５ｎｍである。Ｒａ_(B)が０．５ｎｍより小さい場合には、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ため好ましくない。Ｒａ_(NB)が１０ｎｍより大きい場合には、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。
【００４４】
本発明の積層ポリエステルフィルムの表裏の表面粗さの差Ｒａ_(B)−Ｒａ_(NB)は１〜７ｎｍであり、Ｂ層側の表面粗さの方が大きい。好ましくは２〜５ｎｍである。Ｒａ_(B)−Ｒａ_(NB)が７ｎｍより大きい場合、比較的粗いＢ層側の表面が、平滑なＢ層と反対側の表面に転写し、磁気テープとした際の磁性面側が粗くなって、電磁変換特性を低下させるため好ましくない。また、Ｒａ_(B)−Ｒａ_(NB)が１ｎｍより小さい場合には、製膜、加工工程において、ハンドリング性が低下し、ロールとして巻き取ることが困難となり、生産性が低下するため好ましくない。
【００４５】
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／ｃｍ²以下であり、好ましくは５０個／ｃｍ²以下、より好ましくは１０個／ｃｍ²以下である。同様に粗大突起数Ｈ２は１０個／ｃｍ²以下であり、好ましくは５個／ｃｍ²以下、より好ましくは２個／ｃｍ²以下である。なお、本発明においてフィルム表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。
【００４６】
本発明の積層ポリエステルフィルムのＡ層中の粒子の実体平均粒径Ｄｖと不活性粒子の粒径Ｄの比Ｄｖ／Ｄは１〜３が好ましく、より好ましくは１〜２、最も好ましくは１〜１．５である。粒子の実体平均粒径Ｄｖは、フィルム中の粒子の粒子周りのボイドの大きさをも含めた大きさであるので、Ｄｖ／Ｄの値は粒子周りのポイドの大きさの尺度となる。本発明のＡ層に用いるポリマーアロイはポリエチレンテレフタレートなどのポリエステルと比較して溶融粘度が大きいためや粒子との親和性が低いことが理由と考えられるが、粒子周りにボイドができやすい特徴がある。粒子周りにできるボイドが大きいと製膜、加工工程中や磁気テープとした場合の走行中に粒子が脱落しやすくなり、磁気テープ特性を低下させるほか、突起が扁平となって、磁気ヘッドとの接触面積が増え、磁気ヘッドの走行性が低下することがある。このように、粒子周りのボイドが大きくてＤｖ／Ｄが３より大きい場合には粒子脱落や磁気ヘッド走行性が低下することがあるため、好ましくない。
【００４７】
本発明の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ったり、粒子の周りに生成するボイドが大きくなり、本発明の範囲内に制御できない場合がある。
【００４８】
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。
【００４９】
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、１０〜２５ＧＰａの範囲であることが好ましく、より好ましくは１２〜２２ＧＰａ、さらに好ましくは１４〜２０ＧＰａである。該ヤング率の和が１０ＧＰａ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２５ＧＰａ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。
【００５０】
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５．５ＧＰａ以上が好ましい、より好ましくは６ＧＰａ以上である。長手方向のヤング率が５．５ＧＰａに満たない場合には、磁気テープとして用いる際、磁気ヘッドとのヘッド当たりが悪くなり、電磁変換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。
【００５１】
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。
【００５２】
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。
【００５３】
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。
【００５４】
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。
【００５５】
本発明の積層ポリエステルフィルムの６０℃、８０％ＲＨの条件下、長手方向に２６ＭＰａの荷重をかけた状態で、７２時間放置した場合における幅方向の寸法変化率は、テープの伸び変形性の観点から−０．４〜０％の範囲であることが好ましい。より好ましくは、−０．３〜０％である。この寸法変化率が上記範囲から外れた場合、磁気テープとして使用する際、トラックずれを起こしやすくなることがある。
【００５６】
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９０〜１５０℃であることが好ましく、より好ましくは９５〜１３０℃、さらに好ましくは９８〜１２０℃の範囲内である。
【００５７】
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。
【００５８】
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ータストレージ用などの磁気記録媒体である。中でも好ましくは、高密度磁気記録用テープ、例えば、データストレージ用のベースフィルムに適したものである。該データストレージのデータ記録容量は、好ましくは３０ＧＢ（ギガバイト）以上、より好ましくは７０ＧＢ以上、さらに好ましくは１００ＧＢ以上である。
【００５９】
本発明の積層ポリエステルフィルムの厚みは、３〜８μｍが好ましく、より好ましくは４〜７μｍ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ことがあり、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場合がある。
【００６０】
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。
【００６１】
本発明の積層ポリエステルフィルムは、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。
【００６２】
また、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。
【００６３】
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。
【００６４】
磁性層の形成法としては、磁性粉を、熱硬化性樹脂、熱可塑性樹脂あるいは放射線硬化性組成物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。
【００６５】
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。
【００６６】
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。
【００６７】
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。
【００６８】
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。
【００６９】
本発明の積層ポリエステルフィルムの製造方法について述べるが、特にこれに限定されない。
【００７０】
まず、ポリエステルとポリイミドのポリマーアロイを押出機を用いた溶融押出により、積層部用ポリマと積層させて口金から吐出し、溶融ポリマーを冷却固化させてシート状に成形し、その後２軸延伸、熱固定することが好ましい。
【００７１】
上記、ポリマーアロイの製造方法はポリエステルのペレットとポリエステルおよびポリイミドからなるマスターペレットを混合する方法が好ましい。ポリエステルのペレットとポリイミドの単体のペレット同士は、一般的に溶融粘度が大きく異なるため、押出機にて直接混合した場合、混練不良によって、分散不良物を生じやすく、最終フィルムにおいて粗大突起物の原因となることがある。
【００７２】
上記、ポリエステルおよびポリイミドからなるマスターペレットの製造方法は、ポリエステルとポリイミドのペレットを押出機にて溶融混練する手法と、ポリエステルの重合段階でポリイミドを共重合する手法が好ましく例示される。この場合、共重合の方が分散不良が生じにくいが、最終フィルムの結晶化度が低下し、フィルム強度が低下する場合がある。
【００７３】
ポリエステルとポリイミドのペレットを押出機にて溶融混練して、マスターペレットを作成する場合、ポリイミドの濃度は３５〜６５重量％が好ましく、より好ましくは４０〜６０重量％である。ポリイミドの濃度がこの範囲を外れた場合、相分離または分散不良によって、ポリマー中に粗大ドメインが生成することがある。溶融混練に用いる押出機は、混練性の観点からベント式の２軸混練押出機が好ましく例示される。このときの滞留時間は３０〜６００秒であることが好ましく、より好ましくは６０〜３００秒、最も好ましくは１８０〜３００秒である。滞留時間が３０秒以下の場合、十分に混練が行われず粗大分散物が生成することがあり、滞留時間が６００秒を超える場合、長い時間溶融温度にさらされるため、熱劣化物が生成し、フィルムにした際、粗大突起となることがある。
【００７４】
また、このようにポリマーアロイからなるペレットを作成する場合、通常のポリエステル単体フィルムの製造工程などと比較して、分散不良物の生成や、コンタミの混入の可能性が高いため、溶融混練時に濾過を行うことによって粗大分散物やコンタミを除いておく方法が最終フィルムの粗大突起の低減に有効である。この場合にフィルターとしては、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。中でも、サンドフィルター、５〜２０μｍカットの繊維焼結ステンレス金属フィルターがより好ましく例示される。溶融混練の段階で５μｍカット以下のフィルターを用いると、フィルターの目詰まりのため、生産性が著しく低下することがあり、２０μｍカット以上のフィルターでは、後の押出製膜工程に粗大異物が混入し、製膜前の濾過工程でフィルター寿命が短く生産性が低下することがある。
【００７５】
なお、ここでいう５μｍカットのフィルターとは、濾過精度５μｍ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。
【００７６】
上記、溶融混練によって作成したマスターペレットを、透過型電子顕微鏡で３万〜５０万倍の倍率で観察した場合、外部添加粒子などの添加物に起因しない構造（例えば、ポリマードメインなど）が直径５００ｎｍ以下に制御されていると、その後の希釈工程でポリマー同士が分散されやすく好ましい。５００ｎｍ以上の構造が存在する場合、希釈工程で十分に分散せず、フィルムにおいて粗大突起となることがある。
【００７７】
本発明のフィルムの製造方法において、ポリエステルとポリイミドのポリマーアロイを押出機にて溶融押出し、口金から吐出する際には、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ため、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濾過することが好ましい。特に、積層の際のＡ層および３層積層構成の際はＢ層と反対側の最外層のポリマーは、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。本発明のポリマーアロイの製造工程では、通常ポリエステル単体に比べ、混練工程などによるコンタミや分散不良物に起因して、粗大突起が生成しやすいため、上記の手法により、濾過を強化することが粗大突起を少なくする方法として有効である。
【００７８】
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。
【００７９】
本発明の積層ポリエステルフィルムは該シート状成形物を長手方向と幅方向の２軸に延伸した後、熱処理することにより製造される。この際、長手方向、および、幅方向の延伸は１段階ずつで行っても良いが、少なくとも２段階以上に分けて延伸する場合、本発明の効果を得られやすいため好ましい。また、再縦、再横延伸を行う場合、本発明の効果を得られやすく、特に好ましい。
【００８０】
本発明の積層ポリエステルフィルムを製造する際の長手方向の総延伸倍率は、特に限定されないが、３〜８倍が好ましく、より好ましくは４．５〜６倍である。長手方向の総延伸倍率が３倍より小さな場合は、長手方向の弾性率が低下するため、電磁変換特性が低下することがあり、長手方向の総延伸倍率が８倍より大きな場合には、粒子周りのボイドが大きくなり、表面粗さや粗大突起数が本発明の範囲から外れることがある。このうち、再縦延伸倍率を総縦延伸倍率の２５％以下にする場合、本発明の効果が得られやすく好ましい。再縦延伸を行う場合、１度目の縦延伸の延伸倍率は２．５〜４．０倍、再縦延伸倍率は１．２〜１．８倍が好ましい。
【００８１】
本発明の積層ポリエステルフィルムを製造する際の幅方向の総延伸倍率は、特に限定されないが、３〜８倍が好ましく、より好ましくは３．５〜６倍である。幅方向の総延伸倍率が３倍より小さな場合は、粒子周りのボイドが長手方向に大きくなり、表面粗さや粗大突起数が本発明の範囲から外れたり、磁気テープとした際のトラックずれが起こりやすくなったりする。幅方向の総延伸倍率が６倍以上である場合、フィルム破れによって生産性が低下することがある。なお、再横延伸倍率を総横延伸倍率の２０％以上にする場合、本発明の効果が得られやすく好ましい。再横延伸を行う場合、１度目の横延伸の延伸倍率は３．０〜４．５倍、再縦延伸倍率は１．２〜２倍が好ましい。
【００８２】
本発明の積層ポリエステルフィルムを製造する際の長手方向の延伸温度は、特に限定されないが、Ｔｇ＋１０℃〜Ｔｇ＋３０℃の範囲（ここで、ＴｇはＡ層のポリマーアロイのガラス転移温度である。以下同様。）で行う場合、ポリマーアロイの延伸性が良好となり、表面粗さや粗大突起数が本発明の範囲内に制御しやすいため好ましい。再縦延伸を行う場合、再縦延伸温度はＴｇ＋３０℃〜Ｔｇ＋５０℃が好ましい。
【００８３】
本発明の積層ポリエステルフィルムを製造する際の幅方向の延伸温度は、特に限定されないが、Ｔｇ＋１０℃〜Ｔｇ＋５０℃の範囲で行う場合、縦延伸によって長手方向にボイドが生成することを抑制し、表面粗さや粗大突起数を本発明の範囲内に制御しやすいため好ましい。再横延伸を行う場合、再横延伸温度はＴｇ＋８０℃〜Ｔｇ＋１１０℃が好ましい。
【００８４】
本発明の積層ポリエステルフィルムを製造する際の長手方向の延伸速度は、特に限定されないが、５万〜２０万％／分の範囲で行う場合、ポリマーアロイの延伸性が良好となり、表面粗さや粗大突起数が本発明の範囲内に制御しやすいため好ましい。再縦延伸速度は７万〜２０万％／分の範囲が好ましい。
【００８５】
本発明の積層ポリエステルフィルムを製造する際の幅方向の延伸速度は、特に限定されないが、２０００〜１００００％／分の範囲で行う場合、ポリマーアロイの延伸性が良好となり、表面粗さや粗大突起数が本発明の範囲内に制御しやすいため好ましい。再横延伸速度は５０００〜２００００％／分が好ましい。
【００８６】
本発明の積層ポリエステルフィルムを製造する際の熱処理は、Ｔｇ＋１００℃〜Ｔｇ＋１２５℃の範囲で０．２〜１０秒行うことが本発明の効果を得るため好ましい方法である。
【００８７】
本発明の積層ポリエステルフィルムの延伸形式としては、長手方向に延伸した後に幅方向に延伸を行うなどの逐次二軸延伸法や、同時二軸テンター等を用いて長手方向と幅方向を同時に延伸する同時二軸延伸法、さらに、逐次二軸延伸法と同時二軸延伸法を組み合わせた方法などが包含される。特に、最終の延伸を幅方向に行うことが、表面粗さや粗大突起数を本発明の範囲内に制御するため好ましい方法として例示される。
【００８８】
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Ａ／Ｂ２層積層ポリエステルフィルムの例を示す。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。
【００８９】
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。
【００９０】
次に、該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、所定の割合で混合して、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。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。
【００９１】
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を、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、積層部用ポリマと積層させて、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。この際、異物や変質ポリマーを除去するために各種のフィルター、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である。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てもよい。また、積層フイルムとするために、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。
【００９２】
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、２層構造でＡ層、Ｂ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７０〜１７０℃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２．５〜４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５００００〜２０００００％／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３〜４．５倍）、延伸速度は２０００〜１００００％／分、温度は９５〜１６０℃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８０〜１８０℃の加熱ロール群で、延伸倍率１．２〜１．８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１１０〜２２５℃、延伸倍率１．２〜２．０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、２１５〜２４０℃で、時間は０．２〜１０秒の範囲で行うのが好ましい。
【００９３】
（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。
【００９４】
（１）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
【００９５】
（２）粒子の実体平均粒径Ｄｖ
スライドグラス上に長方形に切断したフィルムを１枚のせて、流動パラフィンをその上に落下させた後、カバーグラスを置き、フィルム表面を透過型光学顕微鏡を用いて暗視視野法で観察するとフィルム内部に存在する粒子が星点状に観察される。この時、フィルム表面近傍に位置する粒子に焦点を合わせた画像を、画像解析装置のハイビジョンモニターに取り込み、入力した異物像を二値化し、粒子の数と面積を求める。面積は等面積の円とし、円相当径を求め、これを粒子の実体平均粒径Ｄｖとした。この観察を場所を変えて、１０回繰り返す。
フィルム中に２種類以上の異なる粒径を有する粒子が存在する場合、円相当径の分布が２つ以上のピークを持つ分布となって現れる。この場合は、それぞれの分布に対する実体平均粒径Ｄｖを測定する。
【００９６】
（３）不活性粒子の平均粒径Ｄ
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不活性粒子を観察する。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。
【００９７】
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。
【００９８】
（４）実体平均粒径／平均粒径（Ｄｖ／Ｄ）
前記（２）の測定より得られた実体平均粒径Ｄｖと（３）の測定より得られた不活性粒子の平均粒径Ｄより算出する。
【００９９】
フィルム中に２種類以上の粒径の異なる粒子が存在する場合、実体平均粒径、平均粒径ともに２種類以上算出されるので、まず、それぞれの粒径の粒子に対するＤｖ／Ｄを別個に算出したのち、粒子の含有量で重みづけして平均した値を求める。
【０１００】
（５）ポリエステル、ポリイミド、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。
【０１０１】
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
【０１０２】
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。
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る。
【０１０３】
（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。
【０１０４】
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（あるいはＰＥＩ）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（あるいはＰＥＩ）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（あるいはＰＥＩ）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（あるいはＰＥＩ）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（あるいはＰＥＩ）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。
【０１０５】
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
【０１０６】
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。
【０１０７】
（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
【０１０８】
（８）熱収縮率
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８０℃、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
【０１０９】
（９）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。
【０１１０】
また、上記手法での測定が困難である場合は、３次元粗さ計（小坂研究所製ＳＥ−３ＡＫ：下記条件で、フィルム幅方向に走査して５０回測定を行う。触針先端半径２μｍ、触針荷重０．０７ｇ、測定面積幅０．５ｍｍ×長さ１５ｍｍ（ピッチ０．１ｍｍ）、カットオフ値０．０８ｍｍ）を用いて、高さ０．２８μｍ以上の突起個数と高さ０．５６μｍ以上の突起個数を測定し、１００ｃｍ²に換算することによって、Ｈ１、Ｈ２を求めても良い。さらに、必要に応じて、原子間力顕微鏡（ＡＦＭ）や４検出式ＳＥＭなど公知のフィルム表面の突起個数測定手法を併用しても良い。
【０１１１】
（１０）幅方向の寸法変化率（％）
サンプルサイズ：長手方向 １００ｍｍ、幅方向 ３０ｍｍ
上記サンプルを、２３℃、６５％ＲＨ、無荷重の条件下にて、２４時間調湿調温した後、大日本印刷（株）製クロムマスク上に、サンプルを静電気により貼り付け、光学顕微鏡を用いて、幅方向の長さ（Ｌ０_W）を測定する。その後、６０℃、８０％ＲＨの条件下、長手方向に３２ＭＰａの荷重をかけた状態で、７２時間放置した。７２時間後、荷重を解放し、２３℃、６５％ＲＨ、無荷重の条件下にて２４時間調湿調温後、幅方向の長さ（Ｌ１_W）を測定した。寸法変化率は下記式により求めた。
寸法変化率（％）＝［（Ｌ１_W−Ｌ０_W）／Ｌ０_W］×１００
【０１１２】
（１１）磁気テープの電磁変換特性（Ｓ／Ｎ）
フィルム表面に、下記組成の磁性塗料および非磁性塗料をエクストルージョンコーターにより重層塗布（上層は磁性塗料で、塗布厚０．１μｍ、非磁性下層の厚みは適宜変化させた。）し、磁気配向させ、乾燥させる。次いで反対面に下記組成のバックコートを塗布した後、小型テストカレンダー装置（スチール／ナイロンロール、５段）で、温度８５℃、線圧２００ｋｇ／ｃｍでカレンダー処理した後、６０℃で、４８時間キュアリングする。上記テープ原反を８ｍｍ幅にスリットし、パンケーキを作成した。次いで、このパンケーキから長さ２００ｍ分をカセットに組み込んで、カセットテープとした。
【０１１３】
（磁性塗料の組成）
・強磁性金属粉末 ： １００重量部
・変成塩化ビニル共重合体 ： １０重量部
・変成ポリウレタン ： １０重量部
・ポリイソシアネート ： ５重量部
・ステアリン酸 ： １．５重量部
・オレイン酸 ： １重量部
・カーボンブラック ： １重量部
・アルミナ ： １０重量部
・メチルエチルケトン ： ７５重量部
・シクロヘキサノン ： ７５重量部
・トルエン ： ７５重量部
【０１１４】
（バックコートの組成）
・カーボンブラック（平均粒径２０ｎｍ） ： ９５重量部
・カーボンブラック（平均粒径２８０ｎｍ）： １０重量部
・αアルミナ ： ０．１重量部
・変成ポリウレタン ： ２０重量部
・変成塩化ビニル共重合体 ： ３０重量部
・シクロヘキサノン ： ２００重量部
・メチルエチルケトン ： ３００重量部
・トルエン ： １００重量部
【０１１５】
市販のＨｉ８用ＶＴＲを用いてビデオ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より作成したテープを０デシベル（ｄＢ）として比較測定した。なお、走行条件は２５℃、６０％ＲＨである。
電磁変換特性が比較例１と比較して、次の基準で評価した。
＋０．５ｄＢ以上：◎（高密度記録磁気テープ用途として、優れたレベルである。）
−０．５ｄＢ以上、＋０．５ｄＢ未満：○（高密度記録磁気テープ用途として、使用可能なレベルである。）
−０．５ｄＢ未満：×（高密度記録磁気テープ用途として、不十分なレベルである。）
【０１１６】
（１２）ドロップアウト
上記のカセットテープと装置を用いて、ドロップアウト（ＤＯ）個数を求めた。
ＤＯ個数の測定は、作成したテープを市販のカメラ一体型Ｈｉ８テープレコーダーで録画後、１分間再生して画面に現れたブロック状のモザイク個数を数えることによって行った。なお、走行条件は２５℃、６０％ＲＨである。
３０個以下：○（高密度記録磁気テープ用途として、使用可能なレベルである。）
３０個以上：×（高密度記録磁気テープ用途として、不十分なレベルである。）
【０１１７】
（１３）トラックずれ
上記テープ原反を１／２インチ幅にスリットし、磁気テープとして、長さ６７０ｍ分を、カセットに組み込んでカセットテープとした。
上記で作成したカセットテープを、２５℃、６５％ＲＨの雰囲気中に２４時間保存した後、テープ走行試験機を用いて、下記の１〜５の条件で順番に走行させた時の幅方向の寸法変化をレーザ寸法測定器で常時読みとり、下記のとおり走行前後でのテープ幅変化を求め、「トラックずれ」とした。条件１の温度、湿度、張力下で走行前のテープ幅の初期値をＬ０（μｍ）、下記条件５で走行させた後のテープ幅をＬ１（μｍ）として、以下の式より「トラックずれ」を算出した。
【０１１８】
条件１：２０℃、５０％ＲＨ、張力 ８５ｇ 走行回数 ３回
条件２：２０℃、５０％ＲＨ、張力１４０ｇ 走行回数 ３回
条件３：４０℃、６０％ＲＨ、張力１４０ｇ 走行回数 １００回
条件４：２０℃、５０％ＲＨ、張力１４０ｇ 走行回数 ３回
条件５：２０℃、５０％ＲＨ、張力 ８５ｇ 走行回数 ３回
【０１１９】
トラックずれ（μｍ）＝｜Ｌ０−Ｌ１｜
このトラックずれが０．５μｍ以下である場合、高密度記録磁気テープ用途として、使用可能なレベルである（○）と判断し、０．５μｍより大きい場合、高密度記録磁気テープ用途として、不十分なレベルである（×）と判断した。
【０１２０】
（１４）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。
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。
【０１２１】
（１５）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。
【０１２２】
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。
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
【０１２３】
（１６）総合評価
上記評価の電磁変換特性、ドロップアウト、および、トラックずれの特性のうち、いずれもが高密度記録磁気テープ用途として、優れたレベルである（◎）または、使用可能なレベルである（○）ものを、総合的に高密度記録磁気テープ用途として使用可能（○）と評価し、上記の特性のうち、高密度記録磁気テープ用途として、不十分なレベルである（×）ものが１項目以上あるものについては、総合的に密度記録磁気テープ用途として不十分（×）と評価した。
【０１２４】
【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。
【０１２５】
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％とを、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（滞留時間２５０秒）に供給して、１０μｍカットの繊維焼結ステンレス金属フィルターで濾過した後、ＰＥＩを５０重量％含有したブレンドチップを作成した。該ブレンドチップを透過型電子顕微鏡で３万倍の倍率で観察したところ、直径約２００ｎｍの相分離構造が観察された。
【０１２６】
次いで、押出機２台を用い、製膜を行った。２９５℃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５８重量部と平均粒径０．１７μｍ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）ペレット３重量部と平均粒径０．０２５μｍのγ−アルミナ粒子を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（Ａ１）を１８０℃で３時間真空乾燥した後に供給した。
【０１２７】
また、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６７重量部と平均粒径０．１７μｍ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）ペレット１２重量部と平均粒径０．７５μｍの球状シリカ粒子を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１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。
【０１２８】
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、Ｔダイ中で合流させ、表面温度２５℃のキャストドラムに静電荷を印加させながら密着冷却固化し、２層積層未延伸フィルム（積層厚み比Ａ１／Ｂ１＝１１／１）を作成した。
【０１２９】
この未延伸フィルムをロール式延伸機にて長手方向に２段で、速度６００００％／分、温度１２５℃で３．０倍延伸し、さらに、テンターを用いて、幅方向に速度３０００％／分、温度１２８℃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１４０℃で１．４倍に再延伸し、テンターを用いて幅方向に温度２０５℃で１．９倍再延伸した。定長下で温度２２０℃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６ＧＰａ、幅方向のヤング率は４．７ＧＰａであった。また、該フィルムを透過型電子顕微鏡で３万倍の倍率で観察したところ、直径１０ｎｍ以上の相分離構造は観察されなかった。
【０１３０】
この積層ポリエステルフィルムは、表２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】
参考例２
実施例１と同様にして、表１のように、Ａ層のポリマーのジビニルベンゼン架橋粒子の含有量を０．１重量％に変更し、Ｂ層のポリマーをポリエチレンテレフタレート（平均粒径０．３μｍのジビニルベンゼン架橋粒子を０．５重量％と平均粒径０．８μｍのシリカ粒子０．０６重量％を含有する）に変更し、２層積層未延伸フィルム（積層厚み比Ａ２／Ｂ２＝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２段で、速度６２０００％／分、温度１２５℃で３．１倍延伸し、さらに、テンターを用いて、幅方向に速度３３００％／分、温度１３０℃で３．６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１４５℃で１．５倍に再延伸し、テンターを用いて幅方向に温度２００℃で１．９倍再延伸した。定長下で温度２２０℃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６．２ＧＰａ、幅方向のヤング率は５．１ＧＰａであった。
【０１３３】
この２軸配向フィルムは、表２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】
参考例３
表１のように、Ａ層ポリマーのＰＥＴとＰＥＩの重量比を８５：１５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Ａ１／Ｂ１＝１１／１）を作成した。
【０１３５】
この未延伸フィルムをロール式延伸機にて長手方向に２段で、速度５００００％／分、温度１４０℃で３．０５倍延伸し、さらに、テンターを用いて、幅方向に速度２５００％／分、温度１３８℃で３．５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２０５℃で１．９５倍再延伸した。定長下で温度２２５℃で９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５．８ＧＰａ、幅方向のヤング率は４．８ＧＰａであった。
【０１３６】
この積層ポリエステルフィルムは、表２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４
表１のように、Ａ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、平均粒径０．２５μｍのシリカ粒子を０．０５％含有）に変更し、Ｂ層ポリマーＰＥＮ／ＰＥＩ（重量比９０：１０、平均粒径０．２５μｍの架橋ジビニルベンゼン粒子を０．５％含有と平均粒径０．７μｍのシリカ粒子を０．０３％含有）を実施例１と同様にして、２層積層未延伸フィルム（積層厚み比Ａ１／Ｂ１＝５／１）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２段で、速度８００００％／分、温度１６０℃で３．１倍延伸し、さらに、テンターを用いて、幅方向に速度５０００％／分、温度１６０℃で４．２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１８５℃で１．０５倍に再延伸し、テンターを用いて幅方向に温度２４０℃で１．７５倍再延伸した。定長下で温度２６０℃で６秒間熱処理後、幅方向に２％の弛緩処理を行い、厚さ約４．２μｍ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３．５μｍ、Ｂ層０．７μｍであった。長手方向のヤング率は７．９ＧＰａ、幅方向のヤング率は７．１ＧＰａであった。
【０１３９】
この積層ポリエステルフィルムは、表２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】
比較例１
Ａ層ポリマーとして、ＰＥＴとＰＥＩのブレンドチップを用いる代わりに、実質的に粒子を含有しないＰＥＴチップを用いた以外は、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。
【０１４１】
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２段で、速度６００００％／分、温度１０５℃で３．０倍延伸し、さらに、テンターを用いて、幅方向に速度３０００％／分、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１３０℃で１．４倍に再延伸し、テンターを用いて幅方向に温度１５０℃で１．９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６．５ＧＰａ、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２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。
【０１４３】
比較例２
実施例１と全く同様にして、２層積層構成の未延伸フィルムを作成した。
【０１４４】
次いで、この未延伸フィルムをロール式延伸機にて長手方向に２段で、速度７００００％／分、温度９５℃で３．５倍延伸し、さらに、テンターを用いて、幅方向に速度３０００％／分、温度１２０℃で３．０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１３０℃で１．７倍に再延伸し、テンターを用いて幅方向に温度１８０℃で１．２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６．８ＧＰａ、幅方向のヤング率は４．５ＧＰａであった。
【０１４５】
この積層ポリエステルフィルムは、表２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。
【０１４６】
比較例３
実施例１と全く同じ原料を用い、ただし、Ａ層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、２層積層構成の未延伸フィルムを作成した。その後の延伸と熱処理は実施例１と全く同様に行い、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６ＧＰａ、幅方向のヤング率は４．７ＧＰａであった。
【０１４７】
この積層ポリエステルフィルムは、表２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。
【０１４８】
比較例４
Ｂ層ポリマーとして平均粒径０．３μｍのジビニルベンゼン架橋粒子を３重量％と平均粒径１．２μｍの球状シリカ粒子を０．１重量％含有するＰＥＴ／ＰＥＩのブレンドポリマー（重量比９０：１０）を用いた以外は実施例１と同様にして、２層積層構成の未延伸フィルムを作成した。その後の延伸と熱処理は実施例１と全く同様に行い、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６ＧＰａ、幅方向のヤング率は４．７ＧＰａであった。
【０１４９】
この積層ポリエステルフィルムは、表２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。
【０１５０】
比較例５
Ａ層ポリマーとして、ＰＥＴ／ＰＥＩの混合ポリマー（重量比９０：１０、平均粒径０．１７μｍのジビニルベンゼン架橋粒子を０．２４重量％と平均粒径０．７５の球状シリカ粒子を０．０１重量％含有）を用い、積層を行わなかった以外は実施例１と同様にして、単層の未延伸フィルムを作成した。その後の延伸と熱処理は実施例１と全く同様に行い、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６ＧＰａ、幅方向のヤング率は４．７ＧＰａであった。
【０１５１】
この積層ポリエステルフィルムは、表２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６
Ａ層ポリマーとして、ＰＥＴ／ＰＥＩのブレンドポリマー（重量比６０：４０、粒子添加量は、実施例１と同様）を用いた。ただし、Ａ層ポリマーの濾過方法は、１．２μｍカットの繊維焼結ステンレス金属フィルターは押出が不良となるため使用できなかったため、サンドフィルターおよび３μｍカットの繊維焼結ステンレス金属フィルターを用いる方法に変更し、２層積層構成の未延伸フィルムを作成した。その後、長手方向に２段で、速度５００００％／分、温度１８０℃で３．５倍延伸し、さらに、テンターを用いて、幅方向に速度３５００％／分、温度１８０℃で４．５倍延伸した。定長下で温度２５０℃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。（未延伸フィルムの延伸性が不良であったため、実施例１と同様の再縦、再横延伸を施す延伸方法は不可能であった。）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４ＧＰａ、幅方向のヤング率は４．４ＧＰａであった。
【０１５３】
この積層ポリエステルフィルムは、表２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。
【０１５４】
比較例７
ポリイミドを用いず、３００℃に加熱された押出機に、実質的に不活性粒子を含有しない固有粘度０．６５のポリエチレン（２．６−ナフタレンジカルボキシレート）（ＰＥＮ）ペレット９８重量部と重量平均粒径０．５μｍ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０．６５のポリエチレン（２．６−ナフタレンジカルボキシレート）（ＰＥＮ）ペレット２重量部の混合原料を１８０℃で３時間真空乾燥した後に供給し、その他の条件は、実施例１と同じ条件で未延伸フィルムを作成した。
【０１５５】
この未延伸フィルムをロール式延伸機にて長手方向に２段で、速度６００００％／分、温度１３５℃で４．２倍延伸し、さらに、テンターを用いて、幅方向に速度３０００％／分、温度１４０℃で３．０倍延伸した。定長下で温度２２０℃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のポリエステルフィルムを得た。長手方向のヤング率は７．０ＧＰａ、幅方向のヤング率は５．７ＧＰａであった。
【０１５６】
このポリエステルフィルムは、表２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】
【表１】

【０１５８】
【表２】

【０１５９】
【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裏の表面粗さと粗大突起数を規定することにより、特に磁気記録媒体用ベースフィルムして使用したときにトラックずれやドロップアウトが少なく良好な電磁変換特性を示す高密度磁気記録テープを製造でき、磁気記録媒体用ベースフィルム用として好適な２軸配向ポリエステルフィルムとすることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biaxially oriented polyester film for a magnetic recording medium in which the quality of the polyester film, in particular, thermal dimensional stability and surface characteristics 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. However, if 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. Therefore, there is an increasing demand for improvement of characteristics such as thermal dimensional stability and storage stability in a tape usage environment.
[0003]
Further, in order to reduce the size of the recording signal, it is necessary to make the thickness of the magnetic layer very thin, and accordingly, the influence of the surface of the base film on the surface shape of the magnetic tape is increasing. For this reason, as the base film, there is an increasing need to lower the protrusion height, smooth the surface, and precisely control the surface roughness, and the development of a film having a surface that satisfies these requirements has been developed. Longed for.
[0004]
Conventionally, an aramid film has been used from the viewpoint of strength and dimensional stability as a base film capable of meeting the above dimensional stability requirements. Aramid film is disadvantageous in terms of cost because of its high price, and it is also disadvantageous in that production efficiency is low because it cannot be molded by melt extrusion like conventional polyethylene terephthalate film, but it is a substitute. It is currently used because there is no.
[0005]
On the other hand, as a technique for improving the dimensional stability of a biaxially oriented polyester film having high productivity, a biaxially oriented polyester film composed of polyethylene terephthalate and polyetherimide (for example, JP-A-2000-141475) is known. ing.
[0006]
However, the above-mentioned biaxially oriented polyester film also has voids around the added particles when the conventional film forming technique is used due to factors such as greatly different melt viscosity from conventional polyesters such as polyethylene terephthalate. At present, there is a problem that it is easy to form, and it is difficult to precisely control the surface form preferable as a high-density magnetic recording medium.
[0007]
[Problems to be solved by the invention]
The object of the present invention is to provide excellent dimensional stability, small voids around the particles, and precise control of the surface morphology such as surface roughness. Especially when used as a base film for magnetic recording media, An object of the present invention is to provide a biaxially oriented polyester film suitable for use as a base film for a magnetic recording medium, capable of producing a high-density magnetic recording tape exhibiting good electromagnetic conversion characteristics with little dropout.
[0008]
[Means for Solving the Problems]
The present invention is a laminated polyester film having at least two film layers in which a laminated part (B layer) is laminated on at least one of a base layer part (A layer) made of polyester and polyimide, on the B layer side Surface roughness Ra_(B), Surface roughness Ra on the side opposite to the B layer_(NB), Surface roughness difference Ra between the front and back film surfaces_(B)-Ra_(NB)The number of coarse protrusions H1 on the film surface opposite to the B layer and the number of coarse protrusions H2 on the film surface opposite to the B layer satisfy the following relationship.
[0009]
      3 ≦ Ra_(B)(Nm) ≦9
  0.5 ≦ Ra_(NB)(Nm) ≦6.5
      2.1 ≦ Ra_(B)-Ra_(NB)(Nm) ≦ 5
      0 ≦ H1 (pieces / 100cm²) ≦ 100
      0 ≦ H2 (pieces / 100cm²) ≦ 10
[0010]
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. 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.
[0011]
In the laminated polyester film of the present invention, it is necessary that at least one of the A layer and the B layer constituting this is biaxially oriented. If all the layers are not oriented or uniaxially oriented, the characteristics of the present invention cannot be satisfied.
[0012]
The A layer of the present invention is composed of a polymer alloy containing polyester and polyimide as essential components. The term “essential component” as used herein means that the component occupies 80% or more of the whole. For example, in the above case, the total amount of polyester and polyimide is 80% by weight or more of the film of the present invention. Occupation.
[0013]
The polymer alloy referred to in the present invention is a polymer multi-component system, and may be a block copolymer by copolymerization or a polymer blend by mixing or the like. However, the case where polymer particles such as polystyrene particles and polymethyl methacrylate particles are externally added is excluded.
[0014]
The polyester used in the present invention is a polymer comprising a polyester unit composed of an acid component such as an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol component.
[0015]
As the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and the like can be used. As alicyclic dicarboxylic acid, cyclohexane dicarboxylic acid etc. can be used, for example. As the aliphatic dicarboxylic acid, for example, adipic acid, sebacic acid, dodecanedioic acid and the like can be used. Of these, terephthalic acid, 2,6-naphthalenedicarboxylic acid and the like can be preferably used, and terephthalic acid can be particularly preferably used. These acid components may be used alone or in combination of two or more.
[0016]
Examples of the diol component include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, Triethylene glycol, 2,2′-bis (4′-β-hydroxyethoxyphenyl) propane and the like can be used, and ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol are particularly preferable. Diethylene glycol or the like can be used, and ethylene glycol can be used particularly preferably. These diol components may be used alone or in combination of two or more.
[0017]
Examples of the polyester used in the present invention include polyethylene terephthalate (PET) and poly (ethylene-2,6-naphthalenedicarboxylate) (PEN), and from the viewpoint of melt moldability, most preferably polyethylene terephthalate ( PET).
[0018]
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.
[0019]
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) means that, for example, a polymer alloy made of polyester and polyimide is used to create an unstretched or biaxially stretched film, and the cross section of the film is observed with a transmission electron microscope. When observed at a magnification of 30,000 to 500,000, it means that a structure having a diameter of 200 nm or more (for example, a polymer domain with poor dispersion) not observed due to additives such as externally added particles is not observed. However, the method for determining the affinity between polyester and polyimide is not particularly limited to this, and if necessary, by observing a single glass transition point by temperature modulation type DSC (MDSC). It may be determined that there is good affinity.
[0020]
[Chemical 1]

However, R in the formula₁Is
[0021]
[Chemical 2]

[0022]
[Chemical 3]

Represents one or more groups selected from an aliphatic hydrocarbon group such as, an alicyclic hydrocarbon group, an aromatic hydrocarbon group,
[0023]
R in the formula₂Is
[Formula 4]

Represents one or two or more groups selected from an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group.
[0024]
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.
[0025]
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.
[0026]
[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 A divalent organic group selected from the group consisting of polydiorganosiloxane groups chain-terminated with alkylene groups having carbon atoms. )
[0027]
R above_Three, R_FourAs, for example, an aromatic residue represented by the following formula group
[Chemical 6]

(N in the figure is an integer of 1 to 5)
Can be mentioned.
[0028]
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.
[0029]
[Chemical 7]

Or
[Chemical 8]

(N is an integer of 2 or more, preferably an integer of 20 to 50)
[0030]
This polyetherimide is available from GE Plastics under the trade name “Ultem” (registered trademark).
[0031]
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.
[0032]
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. Further, during pelletization, once a master pellet containing a high concentration of polyimide (for example, 35 to 65% by weight, more preferably 40 to 60% by weight) is prepared, it is further diluted with polyester, When the method of adjusting the concentration is used, the dispersibility between the polymers is improved, and a more preferable dispersion state may be exhibited as the polymer alloy of the present invention.
[0033]
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 method of mixing polyetherimide using two or more types of polyester, A method of dispersing, a method of mixing after pulverizing polyimide with a pulverizer, a method of mixing by dissolving both in a solvent and coprecipitation, a method of mixing one into a solution after dissolving one in a solvent However, this is not the case.
[0034]
The polymer species used for the film layer other than the A layer of the present invention is not particularly limited, but when using the same polyester as that used for the A layer, or the polymer alloy composed of the same polyester and polyimide as used for the A layer, 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.
[0035]
The layer A of the laminated polyester film of the present invention is not particularly limited, but for the purpose of improving the running durability of the magnetic tape and the running property with the magnetic head when used as a magnetic recording medium, inert particles are used. It is preferable to contain. 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.
[0036]
When the inert particles are contained in the A layer 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. If the average particle size of the inert particles is smaller than 0.001 μm, the effect of improving the running property with the magnetic head is small, which is not preferable.
[0037]
When the inert particles are contained in the A layer 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 greater than 1% by weight, the projections may become coarse due to particle aggregation, and the electromagnetic conversion characteristics may be deteriorated or the projections 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.
[0038]
In the layer B of the laminated polyester film of the present invention, it is preferable to add inert particles 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 added to 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 is preferably 0.01 to 2 μm, more preferably 0.01 to 1 μm, when used for a magnetic recording medium. The content is 0.001 to 3% by weight, preferably 0.005 to 1% by weight. In this case, the thickness t of the B layer is preferably 0.1 to 10 times, more preferably 0.2 to 5 times the average particle diameter d of the inert particles.
[0039]
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 using as a laminated | multilayer film, the thickness of B layer is 0.01-5 micrometers, and film forming property becomes further favorable and is preferable. The thickness of the B layer is preferably 0.03 to 2 μm, more preferably 0.05 to 1 μm.
[0040]
Even if the laminated polyester film of the present invention has a two-layer laminated structure of A layer / B layer, the effect of the invention is sufficiently exerted, but the C layer / layer in which different films are laminated on both sides of the base layer portion (A layer) A three-layer structure of layer A / B may be used, or a structure of four or more layers may be used. Even in the case of a three-layer structure, the B layer needs to bear the running property of the magnetic tape, and therefore needs to contain inert particles having a relatively large particle size as described above. However, in this case, since the C layer is responsible for the electromagnetic conversion characteristics when used as a magnetic tape and the surface responsible for running performance with the magnetic head, the A layer which is the base layer is a smooth layer substantially containing no inert particles. It can be.
[0041]
In the case of a three-layer laminate, the average particle size of the inert particles added to the C layer is preferably 0.001 to 0.5 μm, and the content is preferably 0.01 to 1% by weight. The thickness of the C layer is preferably 0.01 μm to 1 μm, more preferably 0.03 μm to 0.5 μm, and still more preferably 0.05 to 0.3 μm.
[0042]
Surface roughness Ra of the layer B side surface of the laminated polyester film of the present invention_(B)Is 3 to 15 nm, preferably 5 to 12 nm, more preferably 7 to 10 nm. Ra_(B)If the thickness is smaller than 3 nm, sufficient handleability cannot be obtained in the film forming and processing steps, and the productivity is lowered, and the running property and wear resistance when processed into a magnetic tape are lowered. This is not preferable because the tape characteristics cannot be obtained. Ra_(B)When the diameter is larger than 15 nm, particles on the running surface side easily fall off when used as a magnetic tape, which is not preferable because it deteriorates running characteristics or causes dropout.
[0043]
Surface roughness Ra of the surface opposite to the B layer of the laminated polyester film of the present invention_(NB)Is 0.5 to 10 nm, preferably 1 to 8 nm, and more preferably 1.5 to 6.5 nm. Ra_(B)Is less than 0.5 nm, it is not preferable because the running property with the magnetic head when processed into a magnetic tape is lowered and sufficient magnetic tape characteristics cannot be obtained. Ra_(NB)When the thickness is larger than 10 nm, it is not preferable because the electromagnetic conversion characteristics are deteriorated or the magnetic head is easily damaged when used as a magnetic tape.
[0044]
Difference Ra between the front and back surface roughness of the laminated polyester film of the present invention Ra_(B)-Ra_(NB)Is 1 to 7 nm, and the surface roughness on the B layer side is larger. Preferably it is 2-5 nm. Ra_(B)-Ra_(NB)Is larger than 7 nm, the surface on the side of the relatively rough B layer is transferred to the surface on the opposite side of the smooth B layer, and the magnetic surface becomes rough when used as a magnetic tape, which is preferable because the electromagnetic conversion characteristics are deteriorated. Absent. Ra_(B)-Ra_(NB)When the thickness is smaller than 1 nm, the handling property is lowered in the film forming and processing steps, and it becomes difficult to wind up as a roll, which is not preferable because the productivity is lowered.
[0045]
The number of coarse protrusions H1 on the surface opposite to the B layer of the laminated polyester film of the present invention is 100 / cm from the viewpoint of electromagnetic conversion characteristics and running durability.²Or less, preferably 50 / cm²Or less, more preferably 10 pieces / cm²It is as follows. Similarly, the number of coarse protrusions H2 is 10 / cm.²Or less, preferably 5 / cm²Or less, more preferably 2 pieces / cm²It is as follows. In the present invention, H1 and H2 representing the number of coarse protrusions on the film surface are values defined by the measurement method described later.
[0046]
The ratio Dv / D of the actual average particle diameter Dv of the particles in the layer A of the laminated polyester film of the present invention to the particle diameter D of the inert particles is preferably 1 to 3, more preferably 1 to 2, and most preferably 1 to 2. 1.5. Since the actual average particle diameter Dv of the particle is a size including the size of the void around the particle of the particle in the film, the value of Dv / D is a measure of the size of the void around the particle. The polymer alloy used in the A layer of the present invention is considered to be because the melt viscosity is higher than that of polyester such as polyethylene terephthalate and the reason is that the affinity with the particles is low, but there is a characteristic that voids are easily formed around the particles. . If the voids around the particles are large, the particles can easily fall off during film formation, processing, and when running as a magnetic tape, degrading the magnetic tape characteristics, and the protrusions are flattened. The contact area increases, and the traveling performance of the magnetic head may decrease. Thus, when the void around the particle is large and Dv / D is larger than 3, it is not preferable because the particle dropout and the traveling performance of the magnetic head may be deteriorated.
[0047]
It is preferable that content of the polyimide in A layer 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. Moreover, if the content of the polyimide exceeds 30% by weight, it becomes difficult to perform extrusion molding and stretching, which causes troubles in film formation such as film tearing and die lines during extrusion, and processing. Or the voids generated around the particles become large and cannot be controlled within the scope of the present invention.
[0048]
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.
[0049]
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 10 to 25 GPa, more preferably 12 to 22 GPa, and even more preferably 14 to 20 GPa. If the sum of the Young's moduli is less than 10 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 may be adversely affected and may not be practically usable. Further, a film having a sum of Young's moduli exceeding 25 GPa may be difficult to produce industrially, and the tear resistance and dimensional stability of the film may be significantly reduced.
[0050]
The Young's modulus in the longitudinal direction of the laminated polyester film of the present invention is preferably 5.5 GPa or more, more preferably 6 GPa or more. When the Young's modulus in the longitudinal direction is less than 5.5 GPa, when used as a magnetic tape, the head contact with the magnetic head deteriorates, and the electromagnetic conversion characteristics are adversely affected, so that it cannot be used practically. There is.
[0051]
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.
[0052]
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.
[0053]
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.
[0054]
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.
[0055]
The dimensional change rate in the width direction when the laminated polyester film of the present invention is allowed to stand for 72 hours under a load of 26 MPa in the longitudinal direction under the conditions of 60 ° C. and 80% RH is the viewpoint of the stretch deformability of the tape. Is preferably in the range of -0.4 to 0%. More preferably, it is -0.3 to 0%. If this dimensional change rate is out of the above range, track deviation may easily occur when used as a magnetic tape.
[0056]
Extrapolated glass transition onset temperature (Tg) of the polymer of layer A of the present invention_onset) Is not particularly limited, but is preferably 90 to 150 ° C, more preferably 95 to 130 ° C, still more preferably 98 to 120 ° C.
[0057]
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).
[0058]
The use of the laminated polyester film of the present invention is a magnetic recording medium for data storage or the like that requires a uniform and fine surface form and high dimensional stability. Among these, a tape suitable for high-density magnetic recording, for example, a base film for data storage is preferable. The data storage capacity of the data storage is preferably 30 GB (gigabytes) or more, more preferably 70 GB or more, and even more preferably 100 GB or more.
[0059]
The thickness of the laminated polyester film of the present invention is preferably 3 to 8 μm, more preferably 4 to 7 μm. When the thickness is less than 3 μm, the tape becomes stiff and electromagnetic conversion characteristics may deteriorate. When the thickness is greater than 8 μm, the tape length per one tape is shortened, so the magnetic tape can be downsized. It may be difficult to increase the capacity.
[0060]
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.
[0061]
The laminated polyester 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.
[0062]
Further, 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.
[0063]
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.
[0064]
As a method for forming the magnetic layer, magnetic powder is kneaded with a binder such as a thermosetting resin, a thermoplastic resin, or a radiation curable composition, and a coating method in which coating and drying are performed, a metal or alloy is deposited, sputtered, Any method of a dry method in which a magnetic metal thin film layer is directly formed on a substrate film by an ion plating method or the like can be adopted.
[0065]
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.
[0066]
The carbon protective film is a carbon film made of amorphous, graphite, diamond structure, or a mixture thereof prepared by plasma CVD, sputtering, or the like, and particularly preferably a hard carbon film generally called diamond-like carbon.
[0067]
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.
[0068]
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.
[0069]
Although the manufacturing method of the laminated polyester film of this invention is described, it does not specifically limit to this.
[0070]
First, a polymer alloy of polyester and polyimide is melt-extruded using an extruder and laminated with a polymer for a laminated portion and discharged from a die. The molten polymer is cooled and solidified to form a sheet, and then biaxially stretched, heat It is preferable to fix.
[0071]
The polymer alloy is preferably produced by mixing polyester pellets and master pellets made of polyester and polyimide. Polyester pellets and polyimide single pellets generally differ greatly in melt viscosity, so when mixed directly with an extruder, poor kneading tends to cause poor dispersion, causing coarse protrusions in the final film It may become.
[0072]
Preferred examples of the above method for producing master pellets made of polyester and polyimide include a method of melt-kneading polyester and polyimide pellets with an extruder and a method of copolymerizing polyimide at the polyester polymerization stage. In this case, copolymerization is less likely to cause poor dispersion, but the crystallinity of the final film may be reduced, and film strength may be reduced.
[0073]
When a master pellet is prepared by melting and kneading polyester and polyimide pellets in an extruder, the concentration of polyimide is preferably 35 to 65% by weight, more preferably 40 to 60% by weight. If the polyimide concentration is outside this range, coarse domains may be generated in the polymer due to phase separation or poor dispersion. The extruder used for melt-kneading is preferably exemplified by a vent type twin-screw kneading extruder from the viewpoint of kneadability. The residence time at this time is preferably 30 to 600 seconds, more preferably 60 to 300 seconds, and most preferably 180 to 300 seconds. When the residence time is 30 seconds or less, kneading is not sufficiently performed and a coarse dispersion may be generated. When the residence time exceeds 600 seconds, the material is exposed to the melting temperature for a long time. When formed into a film, it may become a coarse protrusion.
[0074]
In addition, when preparing pellets made of polymer alloy in this way, there is a high possibility of generation of defective dispersion and contamination contamination compared to the production process of a normal polyester single film. The method of removing coarse dispersion and contamination by performing is effective in reducing coarse protrusions of the final film. In this case, it is preferable to use a filter made of a material such as sintered metal, porous ceramic, sand, or wire mesh. Among these, a sand filter and a 5-20 μm cut fiber sintered stainless steel metal filter are more preferred. If a filter with a 5 μm cut or less is used in the melt-kneading stage, the productivity may be significantly reduced due to clogging of the filter. If the filter has a 20 μm cut or more, coarse foreign substances are mixed in the subsequent extrusion film forming process. In the filtration step before film formation, the filter life may be short and productivity may be reduced.
[0075]
The filter of 5 μm cut here means a filtration accuracy of 5 μm, and the filtration accuracy means the maximum glass bead particle size that has passed through the filter media by the method of JIS-B8356.
[0076]
When the above-described master pellets prepared by melt-kneading are observed with a transmission electron microscope at a magnification of 30,000 to 500,000, the structure (for example, polymer domain) that does not originate from additives such as externally added particles has a diameter of 500 nm. Controlled below, it is preferable that the polymers are easily dispersed in the subsequent dilution step. When a structure having a thickness of 500 nm or more exists, it may not be sufficiently dispersed in the dilution step, resulting in coarse protrusions in the film.
[0077]
In the method for producing a film of the present invention, when a polymer alloy of polyester and polyimide is melt-extruded with an extruder and discharged from a die, in order to remove foreign matters, denatured polymer, unmelted material, etc. in the polymer, It is preferable to filter using a filter, for example, a filter made of a material such as sintered metal, porous ceramic, sand, or wire mesh. In particular, the outermost layer polymer on the side opposite to the B layer is preferably exemplified by filtering the polymer with a fiber sintered stainless steel filter having a cut of 1.2 μm or less in the case of the layer A and the three-layer structure. . 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. In the production process of the polymer alloy of the present invention, it is easy to generate coarse protrusions due to contamination and poor dispersion due to the kneading process, etc., as compared with normal polyester alone. This is effective as a method of reducing protrusions.
[0078]
Moreover, it is preferable to provide a gear pump in order to improve the quantitative supply as required.
[0079]
The laminated polyester film of the present invention is produced by stretching the sheet-like molded product in two directions, ie, the longitudinal direction and the width direction, followed by heat treatment. At this time, the stretching in the longitudinal direction and the width direction may be performed in one step, but stretching in at least two steps is preferable because the effect of the present invention can be easily obtained. Moreover, when performing re-longitudinal and re-lateral stretching, it is easy to obtain the effects of the present invention, which is particularly preferable.
[0080]
The total draw ratio in the longitudinal direction when the laminated polyester film of the present invention is produced is not particularly limited, but is preferably 3 to 8 times, more preferably 4.5 to 6 times. When the total stretching ratio in the longitudinal direction is smaller than 3 times, the elastic modulus in the longitudinal direction is lowered, so that the electromagnetic conversion characteristics may be deteriorated. When the total stretching ratio in the longitudinal direction is larger than 8 times, the particles The surrounding voids become large, and the surface roughness and the number of coarse protrusions may be out of the scope of the present invention. Among these, when the re-longitudinal stretch ratio is set to 25% or less of the total longitudinal stretch ratio, the effect of the present invention is easily obtained, which is preferable. When performing re-longitudinal stretching, the stretching ratio of the first longitudinal stretching is preferably 2.5 to 4.0 times, and the re-longitudinal stretching ratio is preferably 1.2 to 1.8 times.
[0081]
Although the total draw ratio of the width direction at the time of manufacturing the laminated polyester film of this invention is not specifically limited, 3-8 times are preferable, More preferably, it is 3.5-6 times. When the total stretching ratio in the width direction is smaller than 3 times, voids around the particles are increased in the longitudinal direction, the surface roughness and the number of coarse protrusions are out of the scope of the present invention, and track deviation occurs when the magnetic tape is used. It becomes easy. When the total draw ratio in the width direction is 6 times or more, productivity may be reduced due to film breakage. In addition, when the re-lateral stretching ratio is 20% or more of the total lateral stretching ratio, the effect of the present invention is easily obtained, which is preferable. When performing re-lateral stretching, the stretching ratio of the first lateral stretching is preferably 3.0 to 4.5 times, and the re-longitudinal stretching ratio is preferably 1.2 to 2 times.
[0082]
The stretching temperature in the longitudinal direction when producing the laminated polyester film of the present invention is not particularly limited, but is in the range of Tg + 10 ° C. to Tg + 30 ° C. (where Tg is the glass transition temperature of the polymer alloy of the A layer. The same applies hereinafter). .) Is preferable because the polymer alloy has good stretchability and the surface roughness and the number of coarse protrusions can be easily controlled within the scope of the present invention. When performing re-longitudinal stretching, the re-longitudinal stretching temperature is preferably Tg + 30 ° C. to Tg + 50 ° C.
[0083]
The stretching temperature in the width direction at the time of producing the laminated polyester film of the present invention is not particularly limited, but when it is performed in the range of Tg + 10 ° C. to Tg + 50 ° C., it suppresses the formation of voids in the longitudinal direction by longitudinal stretching, and the surface This is preferable because the roughness and the number of coarse protrusions can be easily controlled within the scope of the present invention. When performing relateral stretching, the relateral stretching temperature is preferably Tg + 80 ° C. to Tg + 110 ° C.
[0084]
The stretching speed in the longitudinal direction when producing the laminated polyester film of the present invention is not particularly limited, but when it is carried out in the range of 50,000 to 200,000% / min, the polymer alloy has good stretchability, and the surface roughness and coarseness. The number of protrusions is preferable because it is easy to control within the scope of the present invention. The re-longitudinal stretching speed is preferably in the range of 70,000 to 200,000% / min.
[0085]
The stretching speed in the width direction when producing the laminated polyester film of the present invention is not particularly limited, but when it is performed in the range of 2000 to 10,000% / min, the stretchability of the polymer alloy becomes good, and the surface roughness and the number of coarse protrusions are increased. Is preferable because it is easily controlled within the scope of the present invention. The re-lateral stretching speed is preferably 5000 to 20000% / min.
[0086]
The heat treatment for producing the laminated polyester film of the present invention is preferably performed in the range of Tg + 100 ° C. to Tg + 125 ° C. for 0.2 to 10 seconds in order to obtain the effects of the present invention.
[0087]
As the stretching method of the laminated polyester film of the present invention, the longitudinal direction and the width direction are simultaneously stretched using a sequential biaxial stretching method such as stretching in the width direction after stretching in the longitudinal direction, or a simultaneous biaxial tenter. A simultaneous biaxial stretching method and a method combining a sequential biaxial stretching method and a simultaneous biaxial stretching method are included. In particular, the final stretching in the width direction is exemplified as a preferable method for controlling the surface roughness and the number of coarse protrusions within the scope of the present invention.
[0088]
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 an A / B two-layer laminated polyester film using polyethylene terephthalate as the polyester of the A layer polymer and polyetherimide “Ultem” as the polyimide is shown. The manufacturing conditions vary depending on the polyester and polyimide used, or the laminated structure.
[0089]
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 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 during film formation. A method of adjusting the content of the particles is effective.
[0090]
Next, the pellets of polyethylene terephthalate and the pellets of polyetherimide are mixed at a predetermined ratio, supplied to a vent type twin-screw kneading extruder heated to 270 to 300 ° C., and melt extruded. The residence time at this time is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes. 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.
[0091]
The obtained polyetherimide-containing polyester pellets were vacuum dried at 180 ° C. for 3 hours or more, and then placed in an extruder heated to 280 to 320 ° C. in a nitrogen stream or under vacuum so as not to lower the intrinsic viscosity. The unstretched film is obtained by feeding and laminating with the polymer for the laminated portion, extruding from a slit-shaped die, and cooling on a casting roll. At this time, it is preferable to use various types of filters, for example, filters made of materials such as sintered metal, porous ceramics, sand, and wire mesh, in order to remove foreign substances and altered polymers. Particularly preferred is a method in which a sand filter, a 1.2 μm cut fiber sintered stainless steel filter and a 0.8 μm cut fiber sintered stainless steel metal filter are used in this order to perform filtration in three stages. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property. Further, in order to obtain a laminated film, a plurality of different polymers are melt-laminated using two or more extruders and manifolds or merging blocks.
[0092]
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 layer A and the layer B are made of a mixed polymer of polyethylene terephthalate and polyetherimide (mixing weight ratio 9: 1) will be described as an example. To do. The unstretched film is heated with a heating roll group at 70 to 170 ° C., and stretched in one or more stages 3 to 8 times in the longitudinal direction (when re-stretching is performed, the first stage stretching is 2.5 to 4 times) ) And cooling with a cooling roll group of 20 to 50 ° C. The longitudinal stretching speed is preferably 50,000 to 200,000% / 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 performing re-lateral stretching, the first stage stretching is 3 to 4.5 times), the stretching speed is 2000 to 10000% / min, and the temperature is in the range of 95 to 160 ° C. It is preferable to carry out. 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 at a temperature of 80 to 180 ° C., a stretching ratio of 1.2 to 1.8 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 110 to 225 ° C. and a draw ratio of 1.2 to 2.0 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 ° C. to 230 ° C., preferably 215 to 240 ° C., and the time is preferably 0.2 to 10 seconds.
[0093]
(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.
[0094]
(1) 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
[0095]
(2) The actual average particle diameter Dv of the particles
Place a piece of rectangular cut film on a slide glass, drop liquid paraffin on it, place a cover glass, and observe the film surface with a transmission optical microscope by night vision method. Particles present in are observed as star points. At this time, an image focused on the particles located in the vicinity of the film surface is taken into a high-definition monitor of the image analyzer, and the inputted foreign object image is binarized to obtain the number and area of the particles. The area was a circle of equal area, the equivalent circle diameter was determined, and this was defined as the actual average particle diameter Dv of the particles. Repeat this observation 10 times at different locations.
When particles having two or more different particle sizes are present in the film, the equivalent circle diameter distribution appears as a distribution having two or more peaks. In this case, the actual average particle diameter Dv for each distribution is measured.
[0096]
(3) Average particle diameter D of inert particles
The cross section of the film is observed using a transmission electron microscope (TEM), and the inert particles are observed at a magnification of 10,000 times or more. The section thickness of TEM is about 100 nm, and the measurement is performed at 100 fields or more at different locations. The measured average weight of equivalent circle diameter was defined as the average particle diameter D of the inert particles.
[0097]
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.
[0098]
(4) Actual average particle diameter / average particle diameter (Dv / D)
It is calculated from the actual average particle diameter Dv obtained by the measurement of (2) and the average particle diameter D of the inert particles obtained by the measurement of (3).
[0099]
When two or more types of particles having different particle sizes are present in the film, both the actual average particle size and the average particle size are calculated. Therefore, first, Dv / D for each particle size is calculated separately. After that, an average value is obtained by weighting with the content of particles.
[0100]
(5) Content of polyester, polyimide, inert particles
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.
[0101]
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
[0102]
Moreover, you may perform a composition analysis by microscopic FT-IR method (Fourier transform microinfrared 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 than that substance. 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.
As for the content of inert particles, a solvent that dissolves polyester and polyimide but does not dissolve inert particles is selected. Polyester and polyimide are dissolved, and the inert particles are centrifuged to obtain a weight percentage.
[0103]
(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.
[0104]
In addition, an element caused by the highest concentration of particles (or PEI) among the inert particles in the film having a depth in the range of 3000 nm from the surface layer, which can also be measured using a secondary ion mass spectrometer (SIMS), 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 (or PEI) is low, and the element concentration caused by the inert particles (or PEI) 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 (or PEI) once having reached the maximum value starts to decrease again. In this concentration distribution curve, the depth at which the element concentration due to the inert particles (or PEI) is reduced to ½ of the maximum value is defined as the stacking thickness. The conditions are as follows.
[0105]
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
[0106]
In addition, when 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.
[0107]
(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
[0108]
(8) Thermal shrinkage
It measured according to JIS C2318.
Sample size: width 10 mm, marked line interval 200 mm
Measurement conditions: Temperature 80 ° C, 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
[0109]
(9) 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.
[0110]
In addition, when measurement by the above method is difficult, a three-dimensional roughness meter (SE-3AK manufactured by Kosaka Laboratory: scans in the film width direction under the following conditions and performs measurement 50 times. Radius of tip of stylus is 2 μm. Using a stylus load of 0.07 g, a measurement area width of 0.5 mm × length of 15 mm (pitch of 0.1 mm), and a cutoff value of 0.08 mm), the number of protrusions having a height of 0.28 μm or more and a height of 0. Measure the number of protrusions of 56μm or more, 100cm²H1 and H2 may be obtained by converting to. Furthermore, if necessary, a known method for measuring the number of protrusions on the film surface such as an atomic force microscope (AFM) or a 4-detection SEM may be used in combination.
[0111]
(10) Dimensional change rate in the width direction (%)
Sample size: 100 mm in the longitudinal direction, 30 mm in the width direction
After the above sample was conditioned at 23 ° C., 65% RH and no load for 24 hours, the sample was affixed statically on a chrome mask manufactured by Dai Nippon Printing Co., Ltd. Use the length in the width direction (L0_W). Then, it was left for 72 hours under a condition of 60 ° C. and 80% RH with a load of 32 MPa applied in the longitudinal direction. 72 hours later, the load was released, and after adjusting the humidity for 24 hours under the conditions of 23 ° C., 65% RH and no load, the length in the width direction (L1_W) Was measured. The dimensional change rate was determined by the following formula.
Dimensional change rate (%) = [(L1_W-L0_W) / L0_W] × 100
[0112]
(11) Electromagnetic conversion characteristics of magnetic tape (S / N)
On the film surface, a magnetic paint and a non-magnetic paint having the following composition are applied by an extrusion coater (the upper layer is a magnetic paint, the coating thickness is 0.1 μm, and the thickness of the non-magnetic lower layer is appropriately changed) and magnetically oriented. ,dry. Next, a back coat having the following composition was applied to the opposite surface, and then calendered with a small test calender (steel / nylon roll, 5 steps) at a temperature of 85 ° C. and a linear pressure of 200 kg / cm, and then at 60 ° C. for 48 hours. Cure. The original tape was slit to 8 mm width to prepare a pancake. Subsequently, a length of 200 m from this pancake was incorporated into a cassette to obtain a cassette tape.
[0113]
(Composition of magnetic paint)
・ Ferromagnetic metal powder: 100 parts by weight
-Modified vinyl chloride copolymer: 10 parts by weight
・ Modified polyurethane: 10 parts by weight
・ Polyisocyanate: 5 parts by weight
・ Stearic acid: 1.5 parts by weight
・ Oleic acid: 1 part by weight
・ Carbon black: 1 part by weight
・ Alumina: 10 parts by weight
・ Methyl ethyl ketone: 75 parts by weight
・ Cyclohexanone: 75 parts by weight
・ Toluene: 75 parts by weight
[0114]
(Backcoat composition)
Carbon black (average particle size 20 nm): 95 parts by weight
Carbon black (average particle size 280 nm): 10 parts by weight
・ Α alumina: 0.1 parts by weight
・ Modified polyurethane: 20 parts by weight
-Modified vinyl chloride copolymer: 30 parts by weight
・ Cyclohexanone: 200 parts by weight
・ Methyl ethyl ketone: 300 parts by weight
・ Toluene: 100 parts by weight
[0115]
The video S / N ratio was determined using a commercially available Hi8 VTR. 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 produced from Comparative Example 1 at 0 decibel (dB). The traveling conditions are 25 ° C. and 60% RH.
In comparison with Comparative Example 1, the electromagnetic conversion characteristics were evaluated according to the following criteria.
+0.5 dB or more: A (excellent level for high-density recording magnetic tape applications)
−0.5 dB or more and less than +0.5 dB: ○ (at a level that can be used for high-density recording magnetic tape applications)
Less than −0.5 dB: × (Insufficient level for high-density recording magnetic tape applications)
[0116]
(12) Dropout
The number of dropouts (DO) was determined using the above cassette tape and apparatus.
The number of DO was measured by recording the created tape with a commercially available camera-integrated Hi8 tape recorder, playing it for 1 minute, and counting the number of block mosaics that appeared on the screen. The traveling conditions are 25 ° C. and 60% RH.
30 or less: ○ (at a level that can be used for high-density recording magnetic tape applications)
30 or more: × (Insufficient level for high-density recording magnetic tape applications)
[0117]
(13) Track deviation
The original tape was slit into a 1/2 inch width, and a 670 m length of magnetic tape was incorporated into the cassette to form a cassette tape.
After the cassette tape prepared above was stored in an atmosphere of 25 ° C. and 65% RH for 24 hours, it was measured in the width direction when it was sequentially run under the conditions 1 to 5 below using a tape running tester. The dimensional change was constantly read with a laser dimensional measuring instrument, and the tape width change before and after running was obtained as described below, and was defined as “track deviation”. The initial value of the tape width before running under the temperature, humidity and tension of condition 1 is L0 (μm), and the tape width after running under condition 5 is L1 (μm). Was calculated.
[0118]
Condition 1: 20 ° C, 50% RH, tension 85g Number of travels 3 times
Condition 2: 20 ° C., 50% RH, tension 140 g, travel count 3 times
Condition 3: 40 ° C., 60% RH, tension 140 g, travel count 100 times
Condition 4: 20 ° C., 50% RH, tension 140 g, travel count 3 times
Condition 5: 20 ° C., 50% RH, tension 85 g, travel count 3 times
[0119]
Track deviation (μm) = | L0−L1 |
When this track deviation is 0.5 μm or less, it is judged that it is a level that can be used as a high density recording magnetic tape application (◯), and when it is larger than 0.5 μm, it is insufficient as a high density recording magnetic tape application. (×).
[0120]
(14) Intrinsic viscosity
Calculate from the following formula from the solution viscosity measured at 25 ° C. in orthochlorophenol.
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.
[0121]
(15) 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.
[0122]
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.
Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
[0123]
(16) Comprehensive evaluation
Any of the above-evaluated electromagnetic conversion characteristics, dropout characteristics, and track deviation characteristics are excellent (◎) or usable (○) for high density recording magnetic tape applications. Is comprehensively usable as a high-density recording magnetic tape application (◯), and among the above characteristics, there is one or more items that are at an insufficient level (x) as a high-density recording magnetic tape application. About thing, it evaluated that it was inadequate (x) as a density recording magnetic tape use comprehensively.
[0124]
【Example】
Based on the following examples, embodiments of the present invention will be described.
[0125]
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% by weight is supplied to a co-rotating bent type twin-screw kneading extruder (residence time: 250 seconds) heated to 290 ° C., filtered through a 10 μm cut fiber sintered stainless metal filter, and then subjected to PEI. A blend chip containing 50 wt% was prepared. When the blend chip was observed with a transmission electron microscope at a magnification of 30,000 times, a phase separation structure having a diameter of about 200 nm was observed.
[0126]
Next, film formation was performed using two extruders. In Extruder A heated to 295 ° C., 20 parts by weight of the blend chips obtained by the above pelletizing operation and 58 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 substantially containing no inert particles were obtained. Inherently containing 3 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 containing 2% by weight of crosslinked divinylbenzene particles having a particle diameter of 0.17 μm and 2% by weight of γ-alumina particles having an average particle diameter of 0.025 μm A mixed raw material (A1) of 20 parts by weight of polyethylene terephthalate (PET) pellets having a viscosity of 0.62 was vacuum-dried at 180 ° C. for 3 hours and then supplied.
[0127]
Further, the extruder B heated to 295 ° C. has 20 parts by weight of the blend chip obtained by the pelletizing operation and 67 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 substantially containing no inert particles. And 12 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 containing 2% by weight of crosslinked divinylbenzene particles having an average particle diameter of 0.17 μm and 1% by weight of spherical silica particles having an average particle diameter of 0.75 μm. A mixed raw material (B1) of 1 part by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 was vacuum-dried at 180 ° C. for 3 hours and then supplied.
[0128]
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 filtering in two steps in the order of a stainless steel metal filter, they are merged in a T-die, closely cooled and solidified while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., and a two-layer laminated unstretched film (laminate thickness ratio A1 / B1 = 11/1).
[0129]
This unstretched film was stretched 3.0 times at a speed of 60000% / min and at a temperature of 125 ° C. in two stages in a longitudinal direction using a roll-type stretching machine, and further, a speed of 3000% / min in the width direction using a tenter. The film was stretched 3.4 times at a temperature of 128 ° C. Subsequently, the film was re-stretched 1.4 times at a temperature of 140 ° C. in one step with a roll-type stretching machine, and re-stretched 1.9 times at a temperature of 205 ° C. with a tenter. After heat treatment at a constant length of 220 ° C. for 8 seconds, 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 6 GPa, and the Young's modulus in the width direction was 4.7 GPa. Further, when the film was observed with a transmission electron microscope at a magnification of 30,000, a phase separation structure having a diameter of 10 nm or more was not observed.
[0130]
As shown in Table 2, 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]
  referenceExample 2
  In the same manner as in Example 1, as shown in Table 1, the content of divinylbenzene crosslinked particles in the polymer of the A layer was changed to 0.1% by weight, and the polymer of the B layer was changed to polyethylene terephthalate (average particle size of 0.3 μm). The divinylbenzene crosslinked particles were changed to 0.5% by weight and containing 0.06% by weight of silica particles having an average particle diameter of 0.8 μm), and a two-layer laminated unstretched film (lamination thickness ratio A2 / B2 = 11 / 1) was created.
[0132]
This unstretched film was stretched 3.1 times at a speed of 62000% / min and at a temperature of 125 ° C. in two stages in the longitudinal direction using a roll-type stretching machine, and further, a speed of 3300% / min in the width direction using a tenter. The film was stretched 3.6 times at a temperature of 130 ° C. Subsequently, the film was re-stretched 1.5 times at a temperature of 145 ° C. in a single step in a longitudinal direction using a roll-type stretching machine, and re-stretched 1.9 times at a temperature of 200 ° C. using a tenter. After heat treatment at a constant length of 220 ° C. for 8 seconds, 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 6.2 GPa, and the Young's modulus in the width direction was 5.1 GPa.
[0133]
As shown in Table 2, the biaxially oriented film had excellent properties as a base film for a magnetic recording medium, such as low dropout and electromagnetic conversion characteristics and running durability.
[0134]
  referenceExample 3
  As shown in Table 1, a two-layer laminated unstretched film (laminate thickness ratio A1 / B1 = 11 /) was obtained in the same manner as in Example 1 except that the weight ratio of PET and PEI of the A layer polymer was changed to 85:15. 1) was created.
[0135]
This unstretched film was stretched 3.05 times at a speed of 50000% / min and at a temperature of 140 ° C. in two stages in the longitudinal direction using a roll-type stretching machine, and further, a speed of 2500% / min in the width direction using a tenter. The film was stretched 3.5 times at a temperature of 138 ° C. Subsequently, the film was re-stretched 1.55 times at a temperature of 150 ° C. in a single step with a roll-type stretching machine and re-stretched 1.95 times at a temperature of 205 ° C. in the width direction using a tenter. After heat treatment at a temperature of 225 ° C. for 9 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 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 5.8 GPa, and the Young's modulus in the width direction was 4.8 GPa.
[0136]
As shown in Table 2, 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 4
As shown in Table 1, the layer A polymer is a mixed polymer of poly (ethylene-2,6-naphthalenedicarboxylate) (PEN) and PEI (weight ratio 90:10, silica particles having an average particle size of 0.25 μm is 0). .05% content), and B layer polymer PEN / PEI (weight ratio 90:10, 0.5% cross-linked divinylbenzene particles having an average particle size of 0.25 μm and silica particles having an average particle size of 0.7 μm) 0.03% content) was made in the same manner as in Example 1 to prepare a two-layer laminated unstretched film (lamination thickness ratio A1 / B1 = 5/1).
[0138]
This unstretched film was stretched 3.1 times at a speed of 80000% / min and at a temperature of 160 ° C. in two stages in a longitudinal direction using a roll-type stretching machine, and further, a speed of 5000% / min in the width direction using a tenter. The film was stretched 4.2 times at a temperature of 160 ° C. Subsequently, the film was re-stretched 1.05 times at a temperature of 185 ° C. in a single step in a longitudinal direction using a roll-type stretching machine, and re-stretched 1.75 times at a temperature of 240 ° C. in a width direction using a tenter. After heat treatment at a temperature of 260 ° 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 4.2 μm. The film thickness of each layer was A layer 3.5 μm and B layer 0.7 μm. The Young's modulus in the longitudinal direction was 7.9 GPa, and the Young's modulus in the width direction was 7.1 GPa.
[0139]
As shown in Table 2, 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]
Comparative Example 1
An unstretched film having an A / B two-layer laminate structure was prepared in the same manner as in Example 1 except that a PET chip containing substantially no particles was used instead of a blend chip of PET and PEI as the A layer polymer. Created.
[0141]
Next, in the same manner as in Example 1, this unstretched film was stretched 3.0 times at a speed of 60000% / min and at a temperature of 105 ° C. in two stages in the longitudinal direction using a roll-type stretching machine, and further using a tenter. The film was stretched 3.4 times in the width direction at a speed of 3000% / min and a temperature of 100 ° C. Subsequently, the film was re-stretched 1.4 times at a temperature of 130 ° C. in a single step in a longitudinal direction using a roll-type stretching machine, and re-stretched 1.9 times at a temperature of 150 ° C. in a width direction using a tenter. After heat treatment at a temperature of 210 ° 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 6.5 GPa, and the Young's modulus in the width direction was 5.4 GPa.
[0142]
As shown in Table 2, this laminated polyester film was inferior as a film for magnetic recording media.
[0143]
Comparative Example 2
An unstretched film having a two-layer laminated structure was prepared in exactly the same manner as in Example 1.
[0144]
Subsequently, this unstretched film was stretched 3.5 times at a speed of 70000% / min and at a temperature of 95 ° C. in two stages in a longitudinal direction using a roll-type stretching machine, and further, a speed of 3000% in the width direction using a tenter. / Min, stretched 3.0 times at a temperature of 120 ° C. Subsequently, the film was re-stretched 1.7 times at a temperature of 130 ° C. in a single stage in the longitudinal direction using a roll-type stretching machine, and re-stretched 1.2 times at a temperature of 180 ° C. in the width direction using a tenter. After heat treatment at a temperature of 210 ° 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 6.8 GPa, and the Young's modulus in the width direction was 4.5 GPa.
[0145]
As shown in Table 2, this laminated polyester film was inferior as a film for magnetic recording media.
[0146]
Comparative Example 3
Exactly the same raw materials as in Example 1 were used, except that the filtration method of the A layer polymer was changed to a method using only a 3 μm cut fiber sintered stainless metal filter to prepare an unstretched film having a two-layer laminated structure. Subsequent stretching and heat treatment were performed in exactly the same manner as in Example 1 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 6 GPa, and the Young's modulus in the width direction was 4.7 GPa.
[0147]
As shown in Table 2, this laminated polyester film was inferior as a film for magnetic recording media.
[0148]
Comparative Example 4
PET / PEI blend polymer containing 3% by weight of divinylbenzene crosslinked particles having an average particle size of 0.3 μm and 0.1% by weight of spherical silica particles having an average particle size of 1.2 μm as a B layer polymer (weight ratio 90:10) ) Was used in the same manner as in Example 1 to prepare an unstretched film having a two-layer laminated structure. Subsequent stretching and heat treatment were performed in exactly the same manner as in Example 1 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 6 GPa, and the Young's modulus in the width direction was 4.7 GPa.
[0149]
As shown in Table 2, this laminated polyester film was inferior as a film for magnetic recording media.
[0150]
Comparative Example 5
As the A layer polymer, a mixed polymer of PET / PEI (weight ratio 90:10, 0.24% by weight of divinylbenzene crosslinked particles having an average particle size of 0.17 μm, and 0.01% spherical silica particles having an average particle size of 0.75) A single-layer unstretched film was prepared in the same manner as in Example 1 except that no lamination was performed. Subsequent stretching and heat treatment were performed in exactly the same manner as in Example 1 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 6 GPa, and the Young's modulus in the width direction was 4.7 GPa.
[0151]
As shown in Table 2, this laminated polyester film was inferior as a film for magnetic recording media.
[0152]
Comparative Example 6
As the A layer polymer, a blend polymer of PET / PEI (weight ratio 60:40, particle addition amount is the same as in Example 1) was used. However, the filtration method of the layer A polymer was changed to a method using a sand filter and a 3 μm cut fiber sintered stainless metal filter because the 1.2 μm cut fiber sintered stainless metal filter could not be used due to poor extrusion. And the unstretched film of 2 layer laminated structure was created. Then, it is stretched 3.5 times at a speed of 50000% / min and at a temperature of 180 ° C. in two stages in the longitudinal direction, and further using a tenter, the speed is 3500% / min in the width direction and 4.5 times at a temperature of 180 ° C. Stretched. After heat treatment at a temperature of 250 ° 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. (Because the stretchability of the unstretched film was poor, it was impossible to perform restretching and retransverse stretching as in Example 1.) The film thickness of each layer was A layer 5.5 μm, B The layer was 0.5 μm. The Young's modulus in the longitudinal direction was 4 GPa, and the Young's modulus in the width direction was 4.4 GPa.
[0153]
As shown in Table 2, this laminated polyester film was inferior as a film for magnetic recording media.
[0154]
Comparative Example 7
An extruder heated to 300 ° C. without using polyimide, and 98 parts by weight of polyethylene (2.6-naphthalenedicarboxylate) (PEN) pellets having an intrinsic viscosity of 0.65 substantially containing no inert particles A mixed raw material of 2 parts by weight of polyethylene (2.6-naphthalenedicarboxylate) (PEN) pellets containing 0.6% intrinsic viscosity containing 2% by weight of crosslinked divinylbenzene particles having an average particle diameter of 0.5 μm is obtained at 180 ° C. for 3 hours. An unstretched film was prepared under the same conditions as in Example 1 except for supplying after vacuum drying.
[0155]
This unstretched film was stretched 4.2 times in the longitudinal direction at a speed of 60000% / min and at a temperature of 135 ° C. by a roll-type stretching machine, and further stretched by a speed of 3000% / min in the width direction using a tenter. The film was stretched 3.0 times at a temperature of 140 ° C. After heat treatment at a constant length of 220 ° C. for 8 seconds, a relaxation treatment of 2% in the width direction was performed to obtain a polyester film having a thickness of about 6 μm. The Young's modulus in the longitudinal direction was 7.0 GPa, and the Young's modulus in the width direction was 5.7 GPa.
[0156]
As shown in Table 2, this polyester film was inferior as a film for magnetic recording media.
[0157]
[Table 1]

[0158]
[Table 2]

[0159]
【The invention's effect】
According to the present invention, when a polyimide is contained in polyester and the surface roughness and the number of coarse protrusions on the front and back sides of a film having good dimensional stability are defined, the track is particularly used as a base film for a magnetic recording medium. A high-density magnetic recording tape showing good electromagnetic conversion characteristics with little deviation and dropout can be produced, and a biaxially oriented polyester film suitable for a base film for a magnetic recording medium can be obtained.

Claims (14)

A laminated polyester film having at least two film layers in which a laminated part (B layer) is laminated on at least one of a base layer part (A layer) made of polyester and polyimide, and having a surface roughness on the B layer side Ra _(B) , surface roughness Ra _(NB) on the opposite side to the B layer, difference in surface roughness Ra _(B) -Ra _(NB) , surface roughness on the opposite side to the B layer A polyester film for magnetic recording media, wherein the number of protrusions H1 and the number of coarse protrusions H2 on the film surface opposite to the B layer satisfy the following relationship:
3 ≦ Ra _(B) (nm) ≦ 9
0.5 ≦ Ra _(NB) (nm) ≦ 6.5
2.1 ≦ Ra _(B) −Ra _(NB) (nm) ≦ 5
0 ≦ H1 (pieces / 100 cm ² ) ≦ 100
0 ≦ H2 (pieces / 100 cm ² ) ≦ 10  The polyester film for magnetic recording media according to claim 1, wherein the ratio Dv / D of the actual average particle diameter Dv to the particle diameter D of the particles in the A layer is 1 to 3.  Layer A contains 0.001 to 1% by weight of inert particles having an average particle size of 0.001 to 0.5 μm, and Layer B contains 0.001 to 0.001 of inert particles having an average particle size of 0.01 to 1.0 μm. The polyester film for magnetic recording media according to claim 1 or 2, comprising 3% by weight.  The polyester film for magnetic recording media according to any one of claims 1 to 3, wherein the polyimide of layer A is polyetherimide.  The polyester film for magnetic recording media 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 the extrapolated glass transition start temperature (Tg _onset ) of the polymer of the A layer is 90 to 150 ° C.  The polyester film for magnetic recording media according to any one of claims 1 to 6, wherein 5 to 30% by weight of polyimide is contained in the A layer.  The heat shrinkage rate at 100 ° C for 30 minutes in the longitudinal direction of the film is 1.2% or less, the heat shrinkage rate at 80 ° C for 30 minutes is 0.3% or less, and the heat shrinkage rate at 100 ° C for 30 minutes in the width direction. Is 0.5% or less, the thermal shrinkage rate at 80 ° C. for 30 minutes is 0.1% or less, and under the conditions of 60 ° C. and 80% RH, with a load of 26 MPa in the longitudinal direction, The polyester film for a magnetic recording medium according to any one of claims 1 to 7, wherein the dimensional change rate in the width direction when left for 72 hours is in the range of -0.4 to 0%.  The total film thickness is 3 to 8 µm, the elastic modulus in the longitudinal direction is 5.5 GPa or more, and the sum of the elastic modulus in the longitudinal direction and the width direction is 10 to 25 GPa. Polyester film for magnetic recording media.  The polymer alloy of polyester and polyimide is filtered through a fiber sintered stainless metal filter having a thickness of 1.2 μm or less, then laminated with a polymer for a laminated portion, melt-extruded from a die and an unstretched film is formed, and then Tg + 10 in the film longitudinal direction. The film is stretched in two or more stages at a stretching ratio of 2.5 to 4.0 times at a stretching temperature of ℃ to Tg + 30 ° C and at a stretching speed of 50,000 to 200,000% / min, and then in the width direction, Tg + 10 ° C to Tg + 50 ° C. The film was stretched at a stretching speed of 3.0 to 4.5 times at a stretching speed of 2000 to 10,000% / min, and further at a temperature Tg + 30 ° C. to Tg + 50 ° C. and a magnification of 1.2 to 1.8 times. After re-longitudinal stretching and re-lateral stretching at a temperature of Tg + 80 ° C. to Tg + 110 ° C. and a magnification of 1.2 to 2.0 times, heat treatment is performed at Tg + 100 ° C. to Tg + 125 ° C. for 0.2 to 10 seconds. Method for producing a polyester film for magnetic recording medium characterized and.  A magnetic recording medium comprising a magnetic layer on at least one surface of the polyester film for magnetic recording medium according to claim 1.  The magnetic recording medium according to claim 11, wherein a ferromagnetic metal thin film is formed on at least one surface of the polyester film for magnetic recording medium.  12. The magnetic recording medium according to claim 11, wherein a magnetic layer is formed by dispersing ferromagnetic metal fine powder or ferromagnetic hexagonal ferrite fine powder in a binder on at least one surface of the polyester film for magnetic recording medium. .  14. A digital recording cassette magnetic tape comprising the magnetic recording medium according to claim 11.