JP4266567B2 - Laminated polyethylene-2,6-naphthalate film - Google Patents

Description

【００１７】
（ここで、式（１）〜（３）中の、Ｔｉはポリエチレン-2,6-ナフタレートに可溶なチタン化合物のチタン元素としてのモル数を、組成物中のエチレン-2,6-ナフタレート成分のモル数で割った値（ミリモル％）であり、Ｐはリン化合物のリン元素としてのモル数を組成物中のエチレン-2,6-ナフタレート成分のモル数で割った値（ミリモル％）である。）の範囲で含有し、リン化合物が、以下の式（Ｉ）
【化４】

（ここで、式中の、Ｒ 1 およびＲ 2 はそれぞれ炭素数原子数１〜４のアルキル基、Ｘは−ＣＨ ₂ −または―ＣＨ ( Ｙ ) −を示す（Ｙは、ベンゼン環を示す。）。）で表されるホスホネート化合物であり、かつ平均粒径が１００ｎｍ以上の不活性粒子を含有していない、そして、
第一の層側の表面は、高さが１ｎｍ以上１００ｎｍ以下でかつ幅が５μｍ以上１００μｍ以下のうねり状突起を１００個／ｍｍ²以上２万個／ｍｍ²以下の頻度で有し、かつ第二の層側の表面よりも中心面平均粗さ（ＷＲａ）が小さいデジタル記録方式の磁気記録媒体のベースフィルムに用いる積層ポリエチレン-2,6-ナフタレートフィルムによって達成される。
【００１８】
本発明によれば、本発明の好ましい態様として、第一の層を構成するポリエチレン-2,6-ナフタレート組成物に含まれる、（ロ）チタン化合物が、下記一般式（ＩＩ）
【００２１】
【化５】

【００２２】
（上記式（II）中、Ｒ³ _,Ｒ⁴ _,Ｒ⁵ _,Ｒ⁶は、２〜10個の炭素原子を有するアルキル基または炭素数６〜８のフェニル基であり、ｍは１〜３の整数である。）
で表わされる化合物または上記一般式（ＩＩ）で表わされる化合物と下記一般式（ＩＩＩ）
【００２３】
【化６】

【００２４】
（上記式中、ｎは２〜４の整数を表わす）
で表わされる芳香族多価カルボン酸との反応生成物であること、または（ハ）不活性粒子が実質的にないことのいずれかを具備する積層ポリエチレン-2,6-ナフタレートフィルムも提供される。
【００２５】
また、本発明によれば、本発明の好ましい態様として、第二の層に含まれる不活性粒子の平均粒径と、第一の層の厚みが下記式（４）
【００２６】
【数４】

【００２７】
（ここで、式（４）中の、ｔAは第一の層の厚み（μｍ）であり、ｄBは第二の層に含まれる不活性粒子の平均粒径（μｍ）である。）
を満足すること、第二の層に含まれる不活性粒子は、その平均粒径（ｄB）が０．１μｍ以上１μｍ以下で、第二の層の重量を基準としたときのその含有量が０．０１重量％以上１．０重量％以下であること、第一の層側の表面の中心面平均粗さ（ＷＲａA）が０．５ｎｍ以上１０ｎｍ以下であること、第二の層側の表面の中心面平均粗さ（ＷＲａB）が３ｎｍ以上２０ｎｍ以下であること、第一の層は０．８μｍ以上の厚みを有し、第二の層は含有する不活性粒子の平均粒径（ｄB）の０．５倍以上の厚みを有し、かつ両者の厚みの合計が２μｍ以上７μｍ以下であることのいずれかを具備する積層ポリエチレン-2,6-ナフタレートフィルムも提供される。
【００２８】
さらに本発明によれば、本発明の積層ポリエチレン-2,6-ナフタレートフィルムと、該積層ポリエチレン-2,6-ナフタレートフィルムの第一の層側の表面に設けられた磁性層と、該積層ポリエチレン-2,6-ナフタレートフィルムの第二の層側の表面に設けられたバックコート層とからなることを特徴とする磁気記録媒体、特にその好ましい態様として磁性層が強磁性金属薄膜層である磁気記録媒体も提供される。
【００２９】
【発明の実施の形態】
本発明の積層ポリエチレン-2,6-ナフタレートフィルムは、第一の層の片面に第二の層を積層したものであり、以下に説明する。
【００３０】
［第一の層のポリエチレン-2,6-ナフタレート組成物］
本発明において、第一の層を構成するポリエチレン-2,6-ナフタレート組成物は、８０重量％以上、好ましくは８５重量％以上がポリエチレン-2,6-ナフタレート樹脂からなるものであり、ポリエチレン-2,6-ナフタレート樹脂以外の他の樹脂を、混合したものであっても良い。また、ここでいうポリエチレン-2,6-ナフタレート樹脂とは、エチレン-2,6-ナフタレート成分を主たる繰返し単位とするポリエステルである。なおここでいう主たる繰り返し単位とは、全繰り返し単位の８０モル％以上、好ましくは８５モル％以上が、エチレン-2,6-ナフタレート成分からなるものである。ポリエチレン-2,6-ナフタレート樹脂を構成するエチレン-2,6-ナフタレート成分以外の共重合成分、すなわち第３成分としては、テレフタル酸、イソフタル酸、フタル酸等の如き２，６−ナフタレンジカルボン酸以外の芳香族ジカルボン酸、アジピン酸、アゼライン酸、セバシン酸、デカンジカルボン酸等の如き脂肪族ジカルボン酸、シクロヘキサンジカルボン酸等の如き脂環族ジカルボン酸、トリメチレングリコール、ジエチレングリコール、テトラメチレングリコール、シクロヘキサンジメタノール等のグリコールが例示でき、これらは単独で使用しても二種以上を併用してもよい。
【００３１】
本発明において、第一の層を構成するポリエチレン-2,6-ナフタレート組成物は、ポリマーの製造時に安定剤としてリン化合物が添加されている。リン化合物としては、リン酸、亜リン酸、ホスホン酸、ホスホネート化合物及びそれらの誘導体等があげられ、これらは単独で使用してもよく、また二種以上併用してもよい。これらの中でも、特に前記一般式（Ｉ）で表されるホスホネート化合物が好ましい。特に好ましいホスホネート化合物は、カルボメトキシメタンホスホン酸、カルボエトキシメタンホスホン酸、カルボプロポキシメタンホスホン酸、カルボプトキシメタンホスホン酸のジメチルエステル、ジエチルエステル、ジプロピルエステルおよびジブチルエステルである。上記のホスホネート化合物は、通常安定剤として使用されるリン化合物に比べ、チタン化合物との反応が比較的緩やかに進行する。すなわち、チタン化合物の触媒活性が重縮合反応中に長時間持続することから、ポリエチレン-2,6-ナフタレートヘのチタン化合物の添加量が少なくでき、また、触媒に対して、多量の安定剤を添加しても、ポリエチレン-2,6-ナフタレートの熱安定性を損ないにくい特性を有しているからである。
【００３２】
リン化合物の添加時期は、エステル交換反応またはエステル化反応が実質的に終了した後であればいつでもよく、例えば、重縮合反応を開始する以前の大気圧下でも、重縮合反応を開始した後の減圧下でも、重縮合反応の末期でもまた、重縮合反応の終了後、すなわちポリマーを得た後に添加してもよい。
【００３３】
第一の層を構成するポリエチレン-2,6-ナフタレート組成物は、触媒に起因する異物が少ないことが必要である。そのため、本発明において、第一の層を構成するポリエチレン-2,6-ナフタレート組成物の製造に用いる触媒は、実質的にポリマー中に可溶なチタン化合物である。なお、ここでいう実質的にとは、ポリエチレン-2,6-ナフタレートポリマー中のアンチモン元素およびゲルマニウム元素の含有量は高々５ミリモル％以下であることを意味する。アンチモン元素およびゲルマニウム元素の含有量が５ミリモル％以下を超えると、これらの触媒に起因する異物が析出し、第一の層の表面が粗いものとなる。
【００３４】
本発明で触媒として用いられるチタン化合物は、ポリマー中に可溶なものであれば特に限定されず、ポリエチレン-2,6-ナフタレートの重縮合触媒として一般的なチタン化合物、例えば、酢酸チタンやテトラ−ｎ−ブトキシチタンなどが挙げられる。それらの中でも、特に望ましいのは、前記一般式（ＩＩ）で表わされる化合物または前記一般式（ＩＩ）で表わされる化合物と前記一般式（ＩＩＩ）で表わされる芳香族多価カルボン酸との反応生成物である。
【００３５】
前記一般式（ＩＩ）で表わされるテトラアルコキサイドチタンとしては、式中のＲ³、Ｒ⁴、Ｒ⁵およびＲ⁶がそれぞれ２〜10個の炭素原子を有するアルキル基または炭素数６〜８のフェニル基で、ｍが１〜３の整数であれば特に限定されない。特に前記一般式（ＩＩ）で表わされるテトラアルコキサイドチタンのなかでも、テトライソプロポキシチタン、テトラプロポキシチタン、テトラ−ｎ−ブトキシチタン、テトラエトキシチタン、テトラフェノキシチタンなどが好ましい。また、かかるチタン化合物として反応させる一般式（ＩＩＩ）で表される芳香族多価カルボン酸としては、フタル酸、トリメリット酸、ヘミメリット酸、ピロメリット酸が好ましく用いられる。なお、一般式（ＩＩＩ）で表される芳香族多価カルボン酸は、無水物であってもよい。上記チタン化合物と芳香族多価カルボン酸またはその無水物とを反応させる場合には、溶媒に芳香族多価カルボン酸またはその無水物の一部とを溶解し、これにチタン化合物を滴下し、０〜２００℃の温度で３０分以上反応させれば良い。
【００３６】
本発明において、第１の層は、ポリマー中に可溶なチタン金属元素として４ミリモル％以上１５ミリモル％以下含有することが必要である。特に好ましいポリマー中に可溶なチタン金属元素の含有量は、第１の層の重量を基準として、６ミリモル％以上１２ミリモル％以下の範囲である。該チタン金属元素の含有量が下限未満ではポリエチレン-2,6-ナフタレートの生産性が低下し、目標の分子量のポリエチレン-2,6-ナフタレートが得られない。一方、該チタン金属元素の含有量が上限を超えると、ポリマーの熱安定性が低下し、フィルム製造時の分子量低下が大きくなり目的のポリエチレン-2,6-ナフタレートが得られない。なお、ここで言うチタン金属元素量は、エステル交換反応による第一段階反応をする場合は、エステル交換反応触媒として使用されたチタン化合物と重縮合反応触媒として使用されたチタン化合物の合計を示す。
【００３７】
また、本発明において、第１の層を構成するポリエチレン-2,6-ナフタレート組成物は、前述のチタン化合物を触媒としかつ前述のリン化合物を安定剤として製造されたものであり、両者の含有量は、前記式（２）および（３）を満足すること必要である。
【００３８】
上記（Ｐ／Ｔｉ）が下限未満の場合、熱安定性が低下し好ましくない。また、上記（Ｐ／Ｔｉ）が上限を超えるとポリエチレン-2,6-ナフタレートの重合反応性が大幅に低下し、目的のポリエチレン-2,6-ナフタレートを得ることができない。本発明で用いるポリエチレン-2,6-ナフタレートにおいて、（Ｐ／Ｔｉ）の適正範囲は通常の金属触媒よりも極めて狭く、この適正範囲にある場合、本発明のごとく従来にない効果を得ることができる。上記（２）式中の（Ｐ／Ｔｉ）の好ましい範囲は４以上１０以下である。また、上記（Ｔｉ＋Ｐ）が下限に満たない場合は、静電印加法によるフィルム製膜プロセスにおける生産性が大きく低下し、またフィルム厚みの均一性も低下することに起因する成形加工性、特に製膜性の低下や耐衝撃性の低下が生じ、満足な性能が得られなくなる。一方、上記（Ｔｉ＋Ｐ）が上限を超える場合は、触媒に起因する異物が少量ではあるが発生し、磁気記録媒体とした場合にドロップアウトが発生し、電磁変換特性が低下してしまい、満足な性能が得られなくなる。好ましい上記（３）式中の（Ｔｉ＋Ｐ）は２５ミリモル％以上１００ミリモル％以下の範囲である。
【００３９】
本発明において、第一の層を構成するポリエチレン−２，６−ナフタレート組成物は、２，６−ナフタレンジカルボン酸とエチレングリコールを原料として用いたものでも、２，６−ナフタレンジカルボン酸ジメチルに代表される２，６−ナフタレンジカルボン酸のエステル形成性誘導体とエチレングリコールを原料として用いたものでもよい。これらのなかでも、原料として用いる全ジカルボン酸成分の８０モル％以上が２，６−ナフタレンジカルボン酸ジメチルである、エステル交換反応を経由して製造されたものが好ましい。２，６−ナフタレンジカルボン酸ジメチルを原料物質に使用すると、２，６−ナフタレンジカルボン酸を原料とする製造方法に比較し、重縮合反応中に安定剤として添加したリン化合物の飛散が少ないという利点がある。また、２，６−ナフタレンジカルボン酸ジメチルを原料物質とする製造方法の中でも、触媒の添加量を低減できることから、チタン化合物の少なくとも一部をエステル交換反応開始前に添加し、エステル交換反応触媒と重縮合反応触媒の二つ触媒を兼用させる製造方法が好ましく、特にエステル交換反応を０．０５ＭＰａ以上０．２０ＭＰａ以下の加圧下にて実施するのが、よりエステル交換反応触媒として使用するチタン化合物量を低減できることから好ましい。エステル交換反応時の圧力が、０．０５ＭＰａ以下では、チタン化合物の触媒作用による反応の促進が十分では無く、一方０．２０ＭＰａ以上では、副生成物として発生するジエチレングリコールのポリマー中の含有量が著しく増加し、ポリマーの熱安定性等の特性が劣ってしまう。
【００４０】
このようにして得られた第一の層を構成するポリエチレン-2,6-ナフタレート組成物は、従来用いられている三酸化アンチモンに代表されるアンチモン触媒を使用したときのような異物を含まない。しかも、ゲルマニウム触媒を使用したときのようなコストの上昇はなく、また、従来型のチタン触媒使用時のような溶融時熱安定性が劣ることが無く、磁気記録媒体のベースフィルムに極めて好適である。
【００４１】
第一の層を構成するポリエチレン-2,6-ナフタレート樹脂組成物の固有粘度は、０．５０以上０．８０以下の範囲にあることが好ましく、さらに０．５５以上０．７５以下、特に０．６０以上〜０．７０以下の範囲が好ましい。固有粘度が下限未満であると、フィルムの耐衝撃性が不足するため好ましくない。他方、固有粘度が上限を超えると、原料ポリマーの固有粘度を過剰に引き上げる必要があり不経済である。
【００４２】
［第二の層のポリエチレン-2,6-ナフタレート組成物］
本発明において、第二の層を構成するポリエチレン-2,6-ナフタレート組成物は、８０重量％以上、好ましくは８５重量％以上がポリエチレン-2,6-ナフタレート樹脂からなるものであり、ポリエチレン-2,6-ナフタレート樹脂以外の他の樹脂を、混合したものであっても良い。また、ここでいうポリエチレン-2,6-ナフタレート樹脂とは、エチレン-2,6-ナフタレート成分を主たる繰返し単位とするポリエステルである。なおここでいう主たる繰り返し単位とは、全繰り返し単位の８０モル％以上、好ましくは８５モル％以上が、エチレン-2,6-ナフタレート成分からなるものである。ポリエチレン-2,6-ナフタレート樹脂を構成するエチレン-2,6-ナフタレート成分以外の共重合される第３成分（共重合成分）としては、前記第一の層を構成するポリエチレン-2,6-ナフタレート組成物で説明したのと同じものが使用できる。
【００４３】
また、第二の層を構成するポリエチレン-2,6-ナフタレート組成物は、上記のものであれば、特に制限されず、それ自体公知のものを好適に使用でき、かつそれ自体公知の方法によって製造することができる。特に好ましいのは、触媒に起因する粗大粒子の発生を抑制できることから、前述の第一の層を構成するポリエチレン-2,6-ナフタレート組成物で説明したのと同じポリエチレン-2,6-ナフタレート組成物である。
【００４４】
［積層ポリエチレン-2,6-ナフタレートフィルム］
本発明の積層ポリエチレン-2,6-ナフタレートフィルムは、前述のポリエチレン-2,6-ナフタレート組成物からなる第一の層と第二の層とが積層されたものである。第１の層と第２の層とを構成するポリエチレン-2,6-ナフタレートは、同じ組成のものでも、異なる組成のものでもあっても良い。特に好ましいのは、第１の層と第２の層とを構成するポリエチレン-2,6-ナフタレートが同じ組成のものである。
【００４５】
また、本発明の積層ポリエチレン−２，６−ナフタレートフィルムは、第一の層が平坦な電磁変換特性等に優れた表面を形成し、第２の層が粗い走行性に優れた表面を形成する。そして、第二の層の第一の層と接していない表面には、必要に応じ被覆層を設けてもよい、また、第一の層の第二の層と接していない表面にも、本発明の効果を阻害しない範囲で、薄い被覆層を設けてもよい。これらの皮膜層は、それ自体公知の皮膜層を好適に使用できる。これらの中でも、第一の側の表面に微細粒子を含む被膜層が形成された積層ポリエチレン−２，６−ナフタレートフィルムが好ましい。微細粒子としてはシリカ、炭酸カルシウム、アルミナ、ポリアクリル、ポリスチレン、内外部のそれぞれの性質が異なる物質で構成される多層構造のコアシェル型粒子が例示でき、電磁変換特性から平均粒径は５ｎｍ以上５０ｎｍ以下であることが好ましい。また、バインダー樹脂としては、ポリエステル、アクリル、ポリビニルアルコール、トラガントゴム、カゼイン、ゼラチン、セルロース誘導体、ポリウレタン等の有極性高分子およびこれらの共重合体、ブレンド体が使用できる。特に好ましいバインダー樹脂は、ポリエステルフィルムとの接着性、平坦性、微粒子の保持力、耐ブロッキング性の観点から、ポリエステル、アクリル及びこれらの共重合体が好ましい。被膜層の厚みは１ｎｍ以上２０ｎｍ以下が好ましい。本発明で用いられる被膜層は、水溶性、水分散性、或いは乳化液等の水性塗液の形態で使用されることが好ましい。被膜を形成するために、必要に応じて、上記組成物以外の他の樹脂や化合物、例えば帯電防止剤、着色剤、界面活性剤、ワックス、架橋剤、紫外線吸収剤などを添加することができる。
【００４６】
本発明において、第１の層は、平坦な電磁変換特性等に優れた表面を形成することから、平均粒径が１００ｎｍ以上、好ましくは６０ｎｍ以上、更に好ましくは１０ｎｍ以上の不活性粒子を実質的に含有しないことが好ましい。ここでいう実質的にとは、触媒を析出させて不活性粒子を形成したり、外部から不活性粒子を添加したりしていないことを意味する。
【００４７】
また、本発明の積層ポリエチレン-2,6-ナフタレートフィルムは、第１の層側の表面に、後述の３次元表面粗さ計によって測定された高さが１ｎｍ以上１００ｎｍ以下で、幅が５ｎｍ以上１００μｍ以下のうねり状突起を１００個／ｍｍ²以上２万個／ｍｍ² 以下の頻度で有することが必要である。なお、うねり状突起の幅は、フィルム長手方向に対し０±１０度の方向で測定された値である。該幅の測定方向は、積層ポリエチレン-2,6-ナフタレートフィルムを磁気記録媒体としたときの、磁気記録システムの磁気ヘッドが磁気テープのスキャンするトラックの方向に相当する。うねり状突起の頻度が下限未満だと、製膜工程での搬送性に劣ったり、フィルム−フィルム間のブロッキング現象が発生したり、また金属薄膜型磁気記録用として用いられたときに、高温高湿条件下のテープの走行性が乏しくなる。一方、うねり状突起の頻度が上限を超えると、電磁変換特性に支障をきたし、高密度磁気記録媒体用のベースフィルムとしては適さない。好ましいうねり状突起の頻度は、１５０個／ｍｍ²以上１万個／ｍｍ²以下、更に好ましくは２００個／ｍｍ²以上５０００個／ｍｍ²以下の範囲である。
【００４８】
また、本発明において、該うねり状突起の高さの平均は、２ｎｍ以上５０ｎｍ以下、更に２ｎｍ以上３０ｎｍ以下であることが好ましい。該うねり状突起の平均高さが下限未満であると、製膜工程での搬送性が乏しくなったり、フィルム−フィルム間のブロッキング現象が発生したり、また金属薄膜型磁気記録用として用いられた場合、高温高湿条件下のテープの走行性といった点で不十分になることがある。一方、うねり状突起の平均高さが上限を超えると、電磁変換特性に支障をきたしたりすることがある。また、本発明において、該うねり状突起の幅の平均は、８μｍ以上８０μｍ以下、更には１０μｍ以上６０μｍ以下であることが好ましい。該うねり状突起の平均幅が上限を超えると、製膜工程での搬送性が乏しくなったり、フィルム−フィルム間のブロッキング現象が発生したり、また金属薄膜型磁気記録用として用いられた場合、高温高湿条件下のテープの走行性といった点で不十分になることがある。一方、うねり状突起の平均幅が下限未満だと、うねり状突起の高さが２５ｎｍ以下の領域で、製膜工程での搬送性、テープの走行性の点が不十分となる。
【００４９】
第１の層側の表面にあるうねり状突起は、その形成方法によって制約を受けるものでないが、第２の層に含有せしめた不活性粒子の延伸に伴う第１の層の突き上げ作用によって形成されたものが好ましい。この突き上げ作用をより効率よく発現させるには、第２の層に含有せしめた不活性粒子の平均粒径と第１の層の厚さとが特定の関係を満たすようにするのが好ましい。具体的には、第２の層は、不活性粒子を１種類または種類や粒径の異なる不活性粒子を２種以上含有する。そして、不活性粒子が１種類の場合は、その平均粒径を、また、不活性粒子が２種類以上の場合は、粒子のうち最も平均粒径の大きな不活性粒子の平均粒径を、ｄ_B（μｍ）とし、第一の層の厚さをｔ_A（μｍ）としたときに、前記式（４）を満足させるのが好ましい。上記ｔ_A／ｄ_Bは、さらに４以上３０以下であることが好ましい。
【００５０】
本発明において、第一の層側の表面は、表面粗さが、中心面平均粗さ（ＷＲａ_A）で０．５ｎｍ以上１０ｎｍ以下、更には０．５ｎｍ以上５ｎｍ以下であることが好ましい。該表面粗さが上限を超えると、電磁変換特性等が低下しやすい。一方、該表面粗さが下限未満だと、フィルムの耐ブロッキング性が悪化することがある。
【００５１】
本発明において、第二の層は、前述のとおり、不活性粒子を含有する。そして、第二の層側の表面は、第一の層側の表面よりも中心面平均粗さ（ＷＲａ）が粗い。さらに、積層ポリエチレン-2,6-ナフタレートフィルムの第二の層側の表面は、上記の表面粗さの関係を維持しつつ、中心面平均粗さ（ＷＲａ_B）が３ｎｍ以上２０ｎｍ以下、更には３ｎｍ以上１７ｍ以下であることが好ましい。なお、第二の層側の表面粗さ（ＷＲａ_B）が上限を超えると、第一の層側の表面に形成されるうねり状突起の高さや幅を、前述の範囲にすることが難しくなる。一方、該ＷＲａ_Bが、下限未満では、搬送等におけるフィルムのブロッキング性やテープにしたときの走行性などが低下しやすい。さらにＷＲａ_BがＷＲａ_A以下では、その平坦性の故に、ベースフィルムの製膜工程での搬送、傷付き、巻取り、巻出しといったハンドリング性の悪化をきたし、またロールに巻いたときの形状（ロールフォーメーション）が悪化し、生産性の悪化、製品歩留りの低下、ひいては製品の製造コストの上昇をきたす。
【００５２】
第２の層側の表面に、上記の表面粗さを付与し、かつ第１の層側の表面に上記のうねり状突起を発現させるには、第２の層に含有される不活性粒子の平均粒径（ｄ_B）は０．１μｍ以上１μｍ以下であることが好ましく、更に０．２μｍ以上０．８μｍ以下、特に０．２μｍ以上０．６μｍ以下であることが好ましい。
【００５３】
この平均粒径ｄ_Bを有する不活性粒子としては、架橋シリコーン樹脂、架橋ポリスチレン、架橋スチレン−ジビニルベンゼン共重合体、ポリメチルメタクリレート、メチルメタクリレート共重合体、架橋メチルメタクリレート共重合体、ポリテトラフルオロエチレン、ポリビニリデンフルオライド、ポリアクリロニトリル、ベンゾグアナミン樹脂等の如き耐熱性有機高分子からなる微粒子、シリカ、アルミナ、二酸化チタン、カオリン、タルク、グラファイト、炭酸カルシウム、長石、二硫化モリブデン等の如き無機化合物からなる微粒子のいずれを用いてもよい。
【００５４】
第二の層は、上記平均粒径ｄ_Bを有する不活性粒子のほかに、該不活性粒子よりも平均粒径の小さい不活性粒子を１種以上含有させることができる。そしてこの場合、第２、第３の小さい粒子としては、平均粒径が０．０１μｍ以上０．１μｍ以下の微細粒子、例えばコロイダルシリカ、α、γ、δ、θ等の結晶形態を有するアルミナ等の微細粒子を好ましく用いることができる。また平均粒径ｄ_Bを有する不活性粒子として例示したもののうち平均粒径が０．０１μｍ以上０．１μｍ以下の微細粒子も用いることもできる。これら不活性粒子の含有量は、第二の層の重量を基準として、０．０１重量％以上１重量％以下、更には０．０５重量％以上０．８重量％以下、特に０．１重量％以上０．６重量％であることが好ましい。
【００５５】
本発明において、積層ポリエチレン-2,6-ナフタレートフィルムの全厚みは、通常２μｍ以上２０μｍ以下であり、好ましくは２．５μｍ以上１０μｍ以下、更に好ましくは３μｍ以上７μｍ以下である。平坦面を形成する第一の層と走行面を形成する第二の層との層厚構成は、第一の層の表面に前記うねり状突起が生じるように、第二の層に添加する不活性粒子の平均粒径ｄ_Bと第一の層の厚さとが、前述の関係を満足するように構成されるのが好ましい。また、第一の層の厚さは、０．８μｍ以上であることが好ましく、第二の層の厚さは、前記平均粒径ｄ_Bの１／２倍以上（μｍ）であることが好ましい。
【００５６】
本発明において、磁気記録媒体としてのヘッドタッチ、走行耐久性を初めとする各種性能を向上させつつ、磁気記録媒体の薄膜化を達成するには、積層ポリエチレン-2,6-ナフタレートフィルムのヤング率は、縦方向（フィルムの製膜方向）が４．５ＧＰa以上、さらに４．９ＧＰａ以上、特に５．２ＧＰａ以上であることが好ましく、横方向（フィルムの幅方向）が８ＧＰa以上、さらに９．５ＧＰa以上、特に１１ＧＰａ以上であることが好ましい。また積層ポリエチレン-2,6-ナフタレートフィルムの結晶化度は、２８％以上３８％以下であることが望ましい。結晶化度が下限を下回ると、熱収縮率が大きくなるし、一方、上限を上回るとフィルムの耐磨耗性が悪化し、ロールやガイドピン表面と摺動した場合に白粉が生じやすくなる。
【００５７】
［積層ポリエチレン-2,6-ナフタレートフィルムの製造方法］
本発明の積層ポリエチレン-2,6-ナフタレートフィルムは、従来から知られている或いは当業界に蓄積されている方法で製造することができる。そのうち、共押出し法により製造するのが好ましい。例えば、二軸配向ポリエチレン-2,6-ナフタレートフィルムで説明すると、押出し口金内または口金以前（一般に前者はマルチマニホールド方式、後者はフィードブロック方式と呼ぶ）で、前述の第一の層を構成するポリエチレン-2,6-ナフタレートと不活性粒子を含有する第二の層を構成するポリエチレン-2,6-ナフタレートとを、溶融状態にて積層複合し、前述の好適な厚み比の積層構造と成し、次いで口金より融点２８０℃〜３３０℃の温度でフィルム状に共押出した後、１０〜３０℃で急冷固化し未延伸積層ポリエチレン-2,6-ナフタレートフィルムを得る。しかる後に、該未延伸積層フィルムを常法に従って一軸方向（縦方向または横方向）に１２０〜１６０℃の温度で２．５〜８．０倍の倍率で、好ましくは３．０〜７．５倍の倍率で延伸し、次いで前記方向とは直交する方向に１２０〜１６０℃の温度で２．５〜８．０倍の倍率で、好ましくは３．０〜７．５倍の倍率で延伸する。更に必要に応じて縦方向及び／または横方向に再度延伸しても良い。即ち、２段、３段、４段、或いは多段の延伸を行うと良い。全延伸倍率は、面積延伸倍率として通常９倍以上、好ましくは１２〜３５倍、更に好ましくは１５〜２６倍である。更に引き続いて、二軸配向フィルムを１８０〜２５０℃で熱固定結晶化することによって優れた寸法安定性が付与される。なお、熱固定時間は１〜６０秒が好ましい。このようにして、層間の密着性が高い二軸配向積層ポリエチレン-2,6-ナフタレートフィルムが得られる。
【００５８】
なお、積層ポリエチレン-2,6-ナフタレートフィルムの製造に際し、ポリエチレン-2,6-ナフタレート樹脂に、所望により上述の不活性粒子以外の添加剤例えば安定剤、着色剤、溶融ポリマーの固有抵抗調整剤等を添加・含有させてもよい。なお、前述の皮膜層は、延伸工程が完了するまでの段階で、フィルム表面に皮膜層を形成するための塗液を塗布し、延伸工程やその後の熱固定工程で乾燥することで、形成するのが好ましい。
【００５９】
［磁気記録媒体の製造方法］
本発明の積層ポリエチレン-2,6-ナフタレートフィルムをベースフィルムに用いた磁気記録媒体は、第一の層側の表面、すなわち平坦面側の表面に、真空蒸着、スパッタリング、イオンプレーティング等の方法により、鉄、コバルト、クロムまたはこれらを主成分とする合金もしくは酸化物より成る強磁性金属薄膜層を形成し、またその表面に、目的や用途などの必要に応じてダイアモンドライクカーボン（ＤＬＣ）等の保護層やフッ素カルボン酸系潤滑層を順次設け、更に第二の層側の表面に公知のバックコート層を設けることにより、特に短波長領域の出力、Ｓ／Ｎ、Ｃ／Ｎ等の電磁変換特性に優れ、ドロップアウト、エラーレートの少ない高密度記録用蒸着型磁気記録媒体とすることができる。この蒸着型磁気記録媒体は、アナログ信号記録用Ｈｉ８、デジタル信号記録用デジタルビデオカセットレコーダ（ＤＶＣ）、データ８ミリ、マンモス、ＡＩＴ用テープ媒体として極めて有用である。
【００６０】
また、本発明の積層ポリエチレン-2,6-ナフタレートフィルムは、第一の層側の表面、すなわち平坦面側表面に、鉄または鉄を主成分とする針状微細磁性粉を塩化ビニル、塩化ビニル・酢酸ビニル共重合体等のバインダーに均一分散し、磁性層厚みが１μｍ以下、好ましくは０．１〜１μｍとなるように塗布し、更に第２の層側の表面に公知の方法でバックコート層を設けることにより、特に短波長領域での出力、Ｓ／Ｎ、Ｃ／Ｎ等の電磁変換特性に優れ、ドロップアウト、エラーレートの少ない高密度記録用メタル塗布型磁気記録媒体とすることができる。また、必要に応じて第一の層側の表面に、該メタル粉含有磁性層の下地層として微細な酸化チタン粒子等を含有する非磁性層を磁性層と同様の有機バインダー中に分散、塗設することもできる。このメタル塗布型磁気記録媒体は、アナログ信号記録用８ミリビデオ、Ｈｉ８、βカムＳＰ、Ｗ−ＶＨＳ、データ８ミリ、ＤＤＳＩＶ、デジタルβカム、Ｄ２，Ｄ３，ＳＸ、ＬＴＯ、ＤＬＴ等用テープ媒体として極めて有用である。
【００６１】
【実施例】
以下、本発明を実施例により具体的に説明する。なお、本発明における各特性は、以下の方法によって測定または評価される。また、実施例中の「部」および「％」は、特に断らない限り、「重量部」および「重量％」である。
（１）固有粘度
ｏ−クロロフェノール溶媒中３５℃で測定した値から求める。
（２）粒子の平均粒径１（平均粒径：０．０６μｍ以上）
島津製作所製ＣＰ−５０型セントリフューグル パーティクルサイズ アナライザー（Ｃeｎｔｒｉｆuｇａｌ Ｐａｒｔｉｃｌｅ Ｓｉｚｅ Ａｎａｌｙｚｅｒ）を用いて測定する。得られる遠心沈降曲線を基に算出した各粒径の粒子とその存在量との積算曲線から、５０マスパーセントに相当する粒径「等価球直径」を読み取り、この値を上記平均粒径とする（Ｂｏｏｋ「粒度測定技術」日刊工業新聞発行、１９７５年、頁２４２〜２４７参照）。
（３）粒子の平均粒径２（平均粒径：０．０６μｍ未満）
小突起を形成する平均粒径０．０６μｍ未満の粒子は、光散乱法を用いて測定する。即ち、Ｎｉｃｏｍｐ Ｉｎｓｔｒｕｍｅｎｔｓ Ｉｎｃ.社製のＮＩＣＯＭＰ ＭＯＤＥＬ ２７０ ＳＵＢＭＩＣＲＯＮ ＰＡＲＴＩＣＬＥ ＳＩＺＥＲにより求められる全粒子の５０重量％の点にある粒子の「等価球直径」をもって表示する。
（４）層厚
フィルムの全厚はマイクロメーターにてランダムに１０点測定し、その平均値を用いる。層厚は、薄い側の層厚を以下に述べる方法にて測定し、また厚い側の層厚は全厚より薄い側の層厚に引き算して求める。即ち、二次イオン質量分析装置（ＳＩＭＳ）を用いて、表層から深さ５０００ｎｍの範囲のフィルム中の粒子の内最も高濃度の粒子に起因する元素とポリエチレン-2,6-ナフタレートの炭素元素の濃度比（Ｍ⁺／Ｃ⁺）を粒子濃度とし、表面から深さ５０００ｎｍまで厚さ方向の分析を行う。表層では表面という界面の為に粒子濃度は低く、表面から遠ざかるにつれて粒子濃度は高くなる。本発明の場合、粒子濃度は一旦安定値１になった後、上昇或いは減少して安定値２になる場合と、単調に減少する場合とがある。この分布曲線をもとに、前者の場合は（安定値１＋安定値２）／２の粒子濃度を与える深さをもって、また後者の場合は粒子濃度が安定値１の１／２になる深さ（この深さは安定値１を与える深さよりも深い）をもって、当該層の層厚とする。
測定条件は以下の通りである。
▲１▼測定装置
二次イオン質量分析装置（ＳＩＭＳ）：ＰＥＲＫＩＮ ＥＬＭＥＲ社製 ６３００
▲２▼測定条件一次イオン種：Ｏ２＋
一次イオン加速電圧：１２ｋＶ
一次イオン電流：２００ｎＡ
ラスター領域：４００μｍ□
分析領域：ゲート３０％
測定真空度：６．０×１０^-9Ｔｏｒｒ
Ｅ−ＧＵＮＮ：０．５ｋＶ−３．０Ａ
なお、表層から５０００ｎｍの範囲に最も多く含有する粒子がシリコーン樹脂以外の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ＦＴ−ＩＲ（フーリエトランスフォーム赤外分光法）、粒子によってはＸＰＳ（Ｘ線高電子分光法）等で上記同様の濃度分布曲線を測定し、層厚を求める。
（５）フィルム表面のうねり状突起
非接触式三次元表面粗さ計（ＷＹＫＯ社製：ＮＴ−２０００）を用いて、うねり状突起の大きさ、高さに応じ、測定倍率２５倍、測定面積２４６．６μｍ×１８７．５μｍ（＝０．０４６２ｍｍ²）、または測定倍率２．５倍、測定面積２．５ｍｍ×１．９ｍｍ（＝４．７５ｍｍ²）の条件にて測定し、得られた三次元粗さチャートより、うねりの高さ、幅を読み取る。なお、測定はフィルムの長手方向に対し５〜１０度の方向に切り出したサンプルにて行った。また、うねり状突起の平均高さおよび平均幅は、ランダムに測定した５０点の突起の平均値から算出した。
（６）中心面平均粗さ（ＷＲａ）
非接触式三次元表面粗さ計（ＷＹＫＯ社製：ＮＴ−２０００）を用いて測定倍率２５倍、測定面積２４６．６μｍ×１８７．５μｍ（＝０．０４６２ｍｍ²）の条件にて測定し、該粗さ計に内臓された表面解析ソフトにより中心面平均粗さＷＲａを以下の式より求める。
【００６２】
【数５】

【００６３】
Ｚ_jkは測定方法（２４６．６μｍ）、それと直行する方法（１８７．５μｍ）をそれぞれｍ分割、ｎ分割したときの各方向のｊ番目、ｋ番目の位置における２次元粗さチャート上の高さである。
（７）ヤング率
フィルムを試料巾１０ｍｍ、長さ１５ｃｍに切り、チャック間１００ｍｍ、引張速度１０ｍｍ／分、チャート速度５００ｍｍ／分の条件下で万能引張試験装置（東洋ボールドウィン製、商品名：テンシロン）にて引っ張る。得られた荷重―伸び曲線の立ち上がり部の接線よりヤング率を計算する。
（８）耐ブロッキング性
２枚のフィルムを用意し、一方のフィルムの第一の層側の表面と、他方のフィルムの第二の層側の表面とを重ね合せ、まず５０℃×７０％ＲＨの雰囲気下にて、無荷重下で２４時間処理し、次に１５Ｎ／ｍｍ²の荷重下で１００時間処理した。処理後の貼り合わされたフィルム積層体を、５ｃｍ幅の短冊状に切り取り、引張り試験機にて荷重を加えた箇所の剥離強度（ｍＮ／５ｃｍ）で評価する。なお、評価は剥離強度の値から下記の基準で評価する。
【００６４】
○：０〜５０ｍＮ／５ｃｍ
△：５０ｍＮ／５ｃｍを超え、１００ｍＮ／５ｃｍ未満
×：１００ｍＮ／５ｃｍ〜破断発生
（９）第１の層中の不活性粒子
試料フィルム小片を走査型電子顕微鏡用試料台に固定し、日本電子（株）製スパッターリング装置（ＪＦＣ−１１００型イオンエッチング装置）を用いてフィルム表面に下記条件にてイオンエッチング処理を施す。条件は、ベルジャー内に試料を設置し、約１０^-3Ｔｏｒｒの真空状態まで真空度を上げ、電圧０.２５ｋＶ、電流１２.５ｍＡにて約１０分間イオンエッチングを実施する。更に同装置にて、フィルム表面に金スパッターを施し、走査型電子顕微鏡にて５,０００〜１０,０００倍で観察し、日本レギュレーター（株）製ルーゼックス５００にて各不活性粒粒子の等価球径分布を求める。得られら等価球形分布から、粒径が１００ｎｍを超える不活性粒子を抜き出し、その重量積算５０％の点から、粒径１００ｎｍを超える不活性粒子の平均粒径を算出する。
（１０）磁気テープの製造及び特性評価
積層ポリエチレンテレフタレートフィルムの第一の層側の表面に、真空蒸着によりコバルト−酸素薄膜を１１０ｎｍの厚みで形成し、次にコバルト−酸素薄膜層上に、スパッタリング法によりダイヤモンド状カーボンを１０ｎｍの厚みで形成させ、更に含フッ素カルボン酸系潤滑剤を順次設ける。続いて、コバルト−酸素薄膜を形成したのとは反対側の表面に、カーボンブラック、ポリウレタン、シリコーンからなるバックコート層を厚みが５００ｎｍとなるように設け、スリッターにより幅８ｍｍ及び６．３５ｍｍにスリットし、市販のリールに巻き取り、磁気テープを作成した。市販のＨｉ８方式８ｍｍビデオテープレコーダーを用いてビデオＳ／Ｎ比を、市販のカメラ一体型デジタルビデオテープレコーダーを用いてドロップアウト（ＤＯ）個数を求める。
【００６５】
ＤＯ個数の測定は、作成した６．３５ｍｍテープを市販のカメラ一体型デジタルビデオテープレコーダーで録画後、１分間の再生をして画面に現れたブロック状のモザイクの個数をカウントすることによって行う。
【００６６】
Ｃ／Ｎは、市販のＨｉ８用ＶＴＲ（ＳＯＮＹ株式会社製、ＥＶ−ＢＳ３０００）を用いて、７ＭＨｚ±１ＭＨｚのＣ／Ｎの測定を行った。このＣ／Ｎを市販のＨｉ８用ビデオテープ（ＳＯＮＹ株式会社製、蒸着型テープ Ｅ６−１２０ＨＭＥ４）と比較して、＋３ｄＢ以上のフィルムを優、＋１〜＋３ｄＢのフィルムを良、＋１ｄＢ未満を不良として、評価した。
【００６７】
高温恒湿下の走行耐久性は４０℃、８０％ＲＨで記録再生を７００回繰り返した後のＣ／Ｎを測定し、初期値からのずれで判定する。
【００６８】
○：初期値に対して＋０．０ｄＢ以上
△：初期値に対して−１．０ｄＢ以上〜＋０．０ｄＢ未満
×：初期値に対して−１．０ｄＢ未満
（１１）フィルムの熱安定性
フィルムを固定枠に均一に張り、熱風乾燥機にて、大気中の雰囲気で、温度２４０℃で５分間処理した。処理前後のフィルムを、それぞれ試料巾１０ｍｍ、長さ１５ｃｍに切り、チャック間１００ｍｍにして引張速度１０ｍｍ／分にて、引張試験機（東洋ボールドウィン製、商品名：テンシロン）で引っ張る。得られた荷重―伸び曲線の破断時の応力を算出する。そして、処理後の破断強度が、処理前の破断強度に対して６０％を超えるフィルムを熱安定性良好（表中の記号：○）、処理後の破断強度が、処理前の破断強度に対して３０〜６０％であるフィルムをやや熱安定性に劣る（表中の記号：△）、処理後の破断強度が、処理前の破断強度に対して３０未満であるフィルムを熱安定性が極めて劣悪（表中の記号：×）として、評価した。
（１２）チタン、リンおよび金属元素の含有量
チタン、リン原子濃度は、乾燥したサンプルを走査電子顕微鏡（ＳＥＭ、日立計測機器サービスＳ５７０型）にセットし、それに連結したエネルギー分散型Ｘ線マイクローアナライザー（ＸＭＡ、堀場ＥＭＡＸ−７０００）にて定量分析を実施した。
【００６９】
ポリエチレンテレフタレート中の触媒金属濃度は、粒状のサンプルをアルミ板上で加熱溶融した後、圧縮プレス機で平面を有する成形体を作成し、蛍光Ｘ線装置（理学電機工業３２７０Ｅ型）にて、定量分析した。
【００７０】
［実施例１］
２，６−ジメチルナフタレート１００部とエチレングリコール５６部の混合物に、テトラ−ｎ−ブチルチタネート０．０１１部を加圧反応が可能なＳＵＳ(ステンレス)製容器に仕込み、０．０７ＭＰａの加圧を行い１４０℃から２４０℃に昇温しながらエステル交換反応させた後、トリエチルホスホノアセテート０．０４２部を添加し、エステル交換反応を終了させた。
【００７１】
その後反応生成物を重合容器に移し、２９０℃まで昇温して１００Ｐａの高真空にて重縮合反応を行い、固有粘度０．６２、ジエチレングリコール量１．５モル％（２，６−エチレンナフタレート成分対比）の第一の層用ポリエチレン−２，６−ナフタレート樹脂（ＰＥＮ）組成物を得た。また該ＰＥＮ組成物に、更に滑剤として表１に示す不活性粒子を添加し、分散させて、固有粘度０．６２の第２の層用のＰＥＮ組成物を得た。
【００７２】
これらの第一の層用および第二の層用ＰＥＮ組成物をそれぞれ１７０℃で６時間乾燥後、２台の押出し機に供給し、溶融温度３０５℃にて溶融し、マルチマニホールド型共押出しダイを用いて、第一の層用ＰＥＮ組成物の片面に第二の層用ＰＥＮ組成物を積層させ、６０℃に急冷して厚さ９０μｍの未延伸積層フィルムを得た。得られた未延伸フィルムを予熱し、更に低速・高速のロール間でフィルム温度１３０℃にて３．７倍に延伸し、急冷し、続いて下記に示す組成の水溶液を第一の層側の表面に塗布した。
塗布液の組成：
（１）アクリル―ポリエステル樹脂 ８０重量％
・ポリエステル成分：−２，６−ナフタル酸（７０モル％）、イソフタル酸（１８モル％）、５―ナトリウムスルホイソフタル酸（１２モル％）／エチレングリコール（９２モル％）、ジエチレングリコール（８モル％）
・アクリル樹脂成分：メチルメタクリレート（８０モル％）、グルシジルメタクリレート（１５モル％）、ｎ―ブチルアクリレート（５モル％）
・ポリエステル成分／アクリル樹脂成分のモル比＝３／７
（２）アクリル樹脂微粒子（平均粒径３０ｎｍ） ５重量％
（３）界面活性剤
・三洋化成（株）社製 エマルミン１１０ １５重量％
被膜層厚み（乾燥後）：５．２ｎｍ
続いてステンターに供給し、１５０℃にて横方向に５．０倍に延伸した。得られた二軸延伸積層フィルムを２０８℃の熱風で４秒間熱固定し、厚み４．７μｍの積層二軸配向ポリエチレン−２，６−ナフタレートフィルムを得た。各層の厚みについては、２台の押出し機の吐出量により調整した。この積層ポリエチレン−２，６−ナフタレートフィルムのヤング率は縦方向５．６ＧＰａ、横方向１１．２ＧＰａであった。
【００７３】
得られた積層ポリエチレン-2,6-ナフタレートフィルムおよびそれを磁気テープにしたときの特性を表２に示す。
【００７４】
［実施例２］
第一の層用ＰＥＮ組成物の製造で用いるチタン化合物を、トリメリット酸チタン０．０２部に変更する以外は、実施例１と同様にして、第一の層用ＰＥＮ組成物を得た。なお、トリメリット酸チタンは、無水トリメリット酸２重量部をエチレングリコール９８重量部に混ぜたエチレングリコール溶液にテトラブトキシチタンを無水トリメリット酸に対してモル比が０．５となるように添加し、空気中常圧下で８０℃に保持して６０分間反応せしめ、その後、常温に冷却し、１０倍量のアセトンによって生成触媒を再結晶化させ、析出物をろ紙によって濾過し、１００℃で２時間乾燥せしめることで製造した。
【００７５】
得られた第一の層用ＰＥＮ組成物と不活性粒子を表１に示すとおり変更した以外は実施例１と同様にして製造した第２の層用ＰＥＮ組成物とを用意し、表１に示すとおり、第１の層および第２の層の厚みを変更した以外は、実施例１と同様にして、積層ポリエチレン-2,6-ナフタレートフィルムを得た。
【００７６】
得られた積層ポリエチレン-2,6-ナフタレートフィルムおよびそれを磁気テープにしたときの特性を表２に示す。
【００７７】
［実施例５〜６、比較例１〜１２］
表１に示すとおり変更した以外は、実施例１と同様にして、積層ポリエチレン-2,6-ナフタレートフィルムを得た。
【００７８】
得られた積層ポリエチレン-2,6-ナフタレートフィルムおよびそれを磁気テープにしたときの特性を表２に示す。
【００７９】
［比較例１３］
第１の層を構成するのに用いたＰＥＮに、平均粒径１２０ｎｍの真球状シリカを０．０３重量％になるように添加した以外は、実施例１と同様な操作を繰り返した。
【００８０】
得られた積層ポリエチレン−２，６−ナフタレートフィルムおよびそれをベースフィルムに用いた磁気テープの特性を表２に示す。
【００８１】
【表１】

【００８２】
【表２】

【００８３】
表１中の、ＴＢＴはテトラ−ｎ−ブトキシチタン、ＴＭＴはトリメリット酸チタン、ＴＥＰＡはトリエチルホスホノアセテート、ＰＥＥはカルボエトキシメタン−ホスホン酸ジエチルエステル、ＨＰＥはヒドロキシメチレン−ホスホン酸ジエチルエステルを意味する。また、比較例２および比較例４は、第１の層および第２の層を構成するポリマーのＩＶが低すぎて製膜できず、その後の評価を行っていない。さらにまた、比較例６は、製膜時のピニング性が悪く、その後の評価に耐え得るフィルムが得られなかった。
【００８４】
【発明の効果】
本発明の積層ポリエチレン−２，６−ナフタレートフィルムは、耐ブロッキング性に優れながら、さらに触媒に起因する異物も抑制されており、高密度磁気記録媒体のベースフィルムとして用いると、得られる磁気記録媒体に、ドロップアウトが少なく、電磁変換特性に優れ、しかも走行耐久性に優れるという特性を同時に具備させることができ、その工業的価値は極めて高い。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laminated polyethylene-2,6-naphthalate film. More specifically, when the base film of the magnetic recording medium has few coarse protrusions and is excellent in blocking resistance, the obtained magnetic recording medium can have excellent electromagnetic conversion characteristics and running durability, and can have a low dropout. The present invention relates to a -2,6-naphthalate film and a magnetic recording medium using it as a base film.
[0002]
[Prior art]
In recent years, the progress of high-density magnetic recording media has been remarkable, for example, a metal thin film type magnetic recording medium in which a ferromagnetic metal thin film is formed on a nonmagnetic support by a physical deposition method such as vacuum deposition or sputtering or a plating method, Development and commercialization of thin-layer coating type magnetic recording media in which acicular magnetic powder such as metal powder or iron oxide powder is applied to 2 μm or less are underway. As the former example, for example, a Co vapor deposition tape (Japanese Patent Laid-Open No. 54-147010) and a perpendicular magnetic recording medium made of a Co—Cr alloy (Japanese Patent Laid-Open No. 52-134706) are known. Further, as the latter example, for example, high-density magnetic recording using an ultrathin layer coating type magnetic recording medium (Electrotechnical Society Technical Report MR94-78 (1995-02)) is known. Furthermore, it is also known to use a polyethylene-2,6-naphthalate film, which can be made thinner than a polyethylene terephthalate film, as a base film of the magnetic recording medium in order to achieve high-density recording of the obtained magnetic recording medium.
[0003]
Conventional coating type magnetic recording media (magnetic recording media in which magnetic powder is mixed with an organic polymer binder and coated on a nonmagnetic support) have a magnetic layer thickness of about 2 μm or more, so that the recording wavelength In addition, only a long and low recording density was obtained. Therefore, it has been studied to improve the recording density by reducing the thickness of the magnetic layer, and a ferromagnetic metal thin film formed by thin film forming means such as vacuum deposition, sputtering or ion plating is used as the magnetic layer ( The thickness of the magnetic layer is 0.2 μm or less), or a magnetic layer thinner than the conventional coating type by providing a nonmagnetic underlayer when applying the magnetic layer (the thickness of the magnetic layer) Is about 0.13 μm).
[0004]
By the way, in a high-density magnetic recording medium in which the recording density is increased by thinning the magnetic layer in this way, the surface state of the nonmagnetic support (base film) tends to have a great influence on the surface properties of the magnetic layer. In a thin-film magnetic recording medium, the surface state of the nonmagnetic support is directly expressed as irregularities on the surface of the magnetic layer (magnetic recording layer), which causes noise in recording / reproducing signals. Therefore, it is desirable that the surface of the nonmagnetic support is as flat as possible, and that there is no foreign matter due to the catalyst.
[0005]
On the other hand, the surface of the nonmagnetic support (base film) is as rough as possible from the viewpoint of handling such as film formation of the nonmagnetic support (base film), transport in the film forming process, scratching, winding and unwinding. It is desirable. This is because if the film surface is too flat, the slipping property between the film and the film deteriorates, blocking phenomenon occurs, and the shape (roll formation) when wound on a roll deteriorates, resulting in a decrease in product yield. This increases the manufacturing cost of the product.
[0006]
As described above, the surface of the nonmagnetic support is required to be flat from the viewpoint of electromagnetic conversion characteristics, and is required to be rough from the viewpoint of handling properties and film manufacturing costs.
[0007]
Further, the metal thin film type magnetic recording medium has a traveling property on the surface of the metal thin film as a serious problem when actually used. In a coating type magnetic recording medium in which a conventional magnetic powder is mixed in an organic polymer binder and applied to a base film, a lubricant can be dispersed in the binder to improve the runnability of the magnetic layer surface. It was. However, the metal thin film type magnetic recording medium cannot take such a measure, and has a drawback such as inferior running property, particularly running property under high temperature and high humidity conditions.
[0008]
Therefore, in order to produce an excellent quality high density magnetic recording medium, it is necessary for the handling of the film and the traveling property of the magnetic recording medium while having the above-mentioned contradictory properties, that is, the flatness required for electromagnetic conversion characteristics and the like. It is necessary to give a rough surface to the surface.
[0009]
As a specific method for this purpose, (1) a method of applying a specific coating agent on the film surface to form a discontinuous film (Japanese Patent Publication No. 3-80410, Japanese Patent Laid-Open No. 60-180839, Japanese Patent Laid-Open No. 60-180838, JP-A-60-180837, JP-A-56-16937, JP-A-58-68223, etc.), (2) A method of coating and forming a continuous film having fine irregularities on the film surface (special (Kaihei 5-194472, JP-A-5-210833), (3) A method of making the front and back surfaces different by a technique such as a co-extrusion method (JP-A-2-214657, JP-B-7-80282), (1) or A method based on a combination of (2) and (3) (Japanese Patent Laid-Open No. 3-73409) has been proposed.
[0010]
However, the above-mentioned method of coating and forming a discontinuous film or a continuous film having fine irregularities can solve problems such as film-to-film sliding and blocking, but it can be used to form a base film, transport it in the film forming process, From the viewpoint of product yield and product cost, there is a problem in application to a base film for a high-density and large-capacity magnetic recording medium in terms of handling such as sticking, winding and unwinding. The conventional coextrusion technique or the method of combining the coextrusion technique with a discontinuous film or a continuous film also has the same problem. Further, in the case of a metal thin film type magnetic recording medium, the problem of running property under high temperature and high humidity conditions still remains.
[0011]
Polyethylene-2,6-naphthalate uses a polymerization catalyst in the production thereof in order to allow the polymerization reaction to proceed smoothly. Various metal compounds are known as the polymerization catalyst. Among them, antimony (Sb) compounds such as antimony trioxide are widely used because they are inexpensive and have high polymerization activity. However, a part of the Sb compound is reduced during the reaction to generate metal Sb and other foreign matters to generate coarse protrusions, thereby causing deterioration in electromagnetic conversion characteristics and dropout. Or destabilizing the manufacturing process and deteriorating the quality of the molded product.
[0012]
As polycondensation catalysts other than antimony compounds, titanium compounds such as germanium compounds and tetra-n-butoxy titanium have been proposed. Since germanium compounds are quite expensive, there is a problem that the production cost of polyethylene-2,6-naphthalate increases. On the other hand, when a titanium compound is used as a polymerization catalyst, the generation of the metal Sb and other foreign matters as described above is suppressed, and the problems caused by the foreign matters are improved. There is a problem that the film is cut during film formation or the film becomes brittle.
[0013]
Therefore, a laminated polyethylene-2,6-naphthalate film with few coarse protrusions, excellent blocking resistance, excellent electromagnetic conversion characteristics when used as a metal thin film type magnetic recording medium, and excellent running properties under high temperature and high humidity conditions is still available. It is currently not provided.
[0014]
[Problems to be solved by the invention]
The object of the present invention is to eliminate the disadvantages of the prior art, have few coarse protrusions, have excellent blocking resistance, and have excellent running properties and electromagnetic conversion characteristics under high-temperature and high-humidity conditions when used as a metal thin film type magnetic recording medium. It is an object of the present invention to provide a laminated polyethylene-2,6-naphthalate film and a magnetic recording medium using it as a base film, particularly a ferromagnetic metal thin film type magnetic recording medium.
[0015]
[Means for Solving the Problems]
  Thus, according to the present invention, an object of the present invention is to provide a polyethylene-2,6-naphthalate composition containing inert particles on one side of the first layer comprising a polyethylene-2,6-naphthalate composition. A laminated polyethylene-2,6-naphthalate film in which two layers are laminated,
  The first layer isThe transesterification reaction catalyst and the polycondensation reaction catalyst are titanium compounds soluble in polyethylene-2,6-naphthalate,Phosphorus compounds andTheThe titanium compound is converted into the following formulas (1) to (3):
[0016]
[Equation 3]

[0017]
(Here, Ti in formulas (1) to (3) is the number of moles of titanium compound soluble in polyethylene-2,6-naphthalate as the titanium element, and ethylene-2,6-naphthalate in the composition. The value divided by the number of moles of the component (mmol%), and P is the value obtained by dividing the number of moles of the phosphorus compound as the phosphorus element by the number of moles of the ethylene-2,6-naphthalate component in the composition (mmol%) In the range ofThe phosphorus compound has the following formula (I)
[Formula 4]

(Where R in the formula 1 And R 2 Are each an alkyl group having 1 to 4 carbon atoms, and X is —CH ₂ -Or-CH ( Y ) -(Y represents a benzene ring). ) Phosphonate compound represented byAnd does not contain inert particles having an average particle size of 100 nm or more, and
  The surface on the first layer side has 100 wavy projections / mm having a height of 1 nm to 100 nm and a width of 5 μm to 100 μm.²More than 20,000 pieces / mm²It has the following frequency, and the center plane average roughness (WRa) is smaller than the surface on the second layer sideUsed as a base film for digital recording magnetic recording mediaAchieved by laminated polyethylene-2,6-naphthalate film.
[0018]
  According to the present invention, as a preferred embodiment of the present invention, included in the polyethylene-2,6-naphthalate composition constituting the first layer,(B) The titanium compound has the following general formula (II)
[0021]
[Chemical formula 5]

[0022]
(In the above formula (II), R^Three _,R^Four _,R^Five _,R⁶Is an alkyl group having 2 to 10 carbon atoms or a phenyl group having 6 to 8 carbon atoms, and m is an integer of 1 to 3. )
Or a compound represented by the above general formula (II) and the following general formula (III)
[0023]
[Chemical 6]

[0024]
(In the above formula, n represents an integer of 2 to 4)
There is also provided a laminated polyethylene-2,6-naphthalate film which is either a reaction product with an aromatic polycarboxylic acid represented by (III) or (c) substantially free of inert particles. The
[0025]
According to the present invention, as a preferred embodiment of the present invention, the average particle diameter of the inert particles contained in the second layer and the thickness of the first layer are represented by the following formula (4).
[0026]
[Expression 4]

[0027]
(Here, tA in the formula (4) is the thickness (μm) of the first layer, and dB is the average particle size (μm) of the inert particles contained in the second layer.)
The inert particles contained in the second layer have an average particle size (dB) of 0.1 μm or more and 1 μm or less, and the content of the inert particles based on the weight of the second layer is 0. 0.01% by weight or more and 1.0% by weight or less, the center surface average roughness (WRaA) of the surface on the first layer side is 0.5 nm or more and 10 nm or less, and the surface on the second layer side The center surface average roughness (WRaB) is 3 nm or more and 20 nm or less, the first layer has a thickness of 0.8 μm or more, and the second layer has an average particle diameter (dB) of inert particles contained therein. The thickness is 0.5 times or more and the total thickness of both is 2 μm or more and 7 μm or less.WithA laminated polyethylene-2,6-naphthalate film comprising either is also provided.
[0028]
Furthermore, according to the present invention, the laminated polyethylene-2,6-naphthalate film of the present invention, a magnetic layer provided on the first layer side surface of the laminated polyethylene-2,6-naphthalate film, A magnetic recording medium comprising a laminated polyethylene-2,6-naphthalate film and a backcoat layer provided on the surface on the second layer side. In particular, as a preferred embodiment, the magnetic layer is a ferromagnetic metal thin film layer. A magnetic recording medium is also provided.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
The laminated polyethylene-2,6-naphthalate film of the present invention is obtained by laminating the second layer on one side of the first layer, and will be described below.
[0030]
[Polyethylene-2,6-naphthalate composition of first layer]
In the present invention, the polyethylene-2,6-naphthalate composition constituting the first layer comprises 80% by weight or more, preferably 85% by weight or more of a polyethylene-2,6-naphthalate resin. A resin other than 2,6-naphthalate resin may be mixed. The polyethylene-2,6-naphthalate resin here is a polyester having an ethylene-2,6-naphthalate component as a main repeating unit. Here, the main repeating unit means that 80 mol% or more, preferably 85 mol% or more of all repeating units are composed of an ethylene-2,6-naphthalate component. Copolymerization component other than the ethylene-2,6-naphthalate component constituting the polyethylene-2,6-naphthalate resin, that is, the third component is 2,6-naphthalenedicarboxylic acid such as terephthalic acid, isophthalic acid, phthalic acid, etc. Aromatic dicarboxylic acids such as aromatic dicarboxylic acids, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, etc., cycloaliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid, trimethylene glycol, diethylene glycol, tetramethylene glycol, cyclohexane Glycols such as dimethanol can be exemplified, and these may be used alone or in combination of two or more.
[0031]
  In the present invention, the polyethylene-2,6-naphthalate composition constituting the first layer is added with a phosphorus compound as a stabilizer during the production of the polymer. Examples of phosphorus compounds include phosphoric acid, phosphorous acid, phosphonic acid, phosphonate compounds, and derivatives thereof, and these may be used alone or in combination of two or more. Among these, the phosphonate compound represented by the general formula (I) is particularly preferable. Particularly preferred phosphonate compounds are carbomethoxymethanephosphonic acid, carboethoxymethanephosphonic acid, carbopropoxymethanephosphonic acid, carboptoxymethanephosphonic acid.AcidDimethyl ester, diethyl ester, dipropyl ester and dibutyl ester. The phosphonate compound proceeds relatively slowly with the titanium compound as compared with the phosphorus compound usually used as a stabilizer. That is, since the catalytic activity of the titanium compound lasts for a long time during the polycondensation reaction, the amount of titanium compound added to polyethylene-2,6-naphthalate can be reduced, and a large amount of stabilizer can be added to the catalyst. Even so, it is because the polyethylene-2,6-naphthalate has a characteristic that it is difficult to impair the thermal stability.
[0032]
The phosphorus compound may be added at any time after the transesterification or esterification reaction is substantially completed. For example, the phosphorus compound may be added after the start of the polycondensation reaction even under atmospheric pressure before the start of the polycondensation reaction. It may be added under reduced pressure, at the end of the polycondensation reaction, or after completion of the polycondensation reaction, that is, after the polymer is obtained.
[0033]
The polyethylene-2,6-naphthalate composition constituting the first layer needs to have a small amount of foreign matters due to the catalyst. Therefore, in the present invention, the catalyst used for producing the polyethylene-2,6-naphthalate composition constituting the first layer is a titanium compound that is substantially soluble in the polymer. The term “substantially” as used herein means that the content of antimony element and germanium element in the polyethylene-2,6-naphthalate polymer is at most 5 mmol%. When the content of the antimony element and the germanium element exceeds 5 mmol% or less, foreign matters resulting from these catalysts are precipitated, and the surface of the first layer becomes rough.
[0034]
The titanium compound used as a catalyst in the present invention is not particularly limited as long as it is soluble in the polymer, and is a titanium compound commonly used as a polycondensation catalyst for polyethylene-2,6-naphthalate, such as titanium acetate and tetra -N-butoxy titanium etc. are mentioned. Among them, particularly preferable is a reaction product of the compound represented by the general formula (II) or the compound represented by the general formula (II) and the aromatic polyvalent carboxylic acid represented by the general formula (III). It is a thing.
[0035]
As tetraalkoxide titanium represented by the general formula (II), R in the formula^Three, R^Four, R^FiveAnd R⁶Is an alkyl group having 2 to 10 carbon atoms or a phenyl group having 6 to 8 carbon atoms and m is an integer of 1 to 3, and is not particularly limited. Among the tetraalkoxide titaniums represented by the general formula (II), tetraisopropoxy titanium, tetrapropoxy titanium, tetra-n-butoxy titanium, tetraethoxy titanium, tetraphenoxy titanium and the like are preferable. As the aromatic polyvalent carboxylic acid represented by the general formula (III) to be reacted as the titanium compound, phthalic acid, trimellitic acid, hemimellitic acid, and pyromellitic acid are preferably used. The aromatic polyvalent carboxylic acid represented by the general formula (III) may be an anhydride. When the titanium compound and the aromatic polyvalent carboxylic acid or its anhydride are reacted, the aromatic polyvalent carboxylic acid or a part of its anhydride is dissolved in a solvent, and the titanium compound is dropped into this, What is necessary is just to make it react for 30 minutes or more at the temperature of 0-200 degreeC.
[0036]
In the present invention, the first layer needs to contain 4 mmol% to 15 mmol% as a titanium metal element soluble in the polymer. The content of the titanium metal element soluble in a particularly preferred polymer is in the range of 6 to 12 mmol% based on the weight of the first layer. When the content of the titanium metal element is less than the lower limit, the productivity of polyethylene-2,6-naphthalate is lowered and polyethylene-2,6-naphthalate having a target molecular weight cannot be obtained. On the other hand, if the content of the titanium metal element exceeds the upper limit, the thermal stability of the polymer is lowered, and the molecular weight reduction during film production is increased, so that the intended polyethylene-2,6-naphthalate cannot be obtained. In addition, the amount of titanium metal elements referred to here indicates the total of the titanium compound used as the transesterification reaction catalyst and the titanium compound used as the polycondensation reaction catalyst when performing the first stage reaction by the transesterification reaction.
[0037]
In the present invention, the polyethylene-2,6-naphthalate composition constituting the first layer is produced using the above-described titanium compound as a catalyst and the above-described phosphorus compound as a stabilizer. The amount needs to satisfy the above formulas (2) and (3).
[0038]
When the above (P / Ti) is less than the lower limit, the thermal stability is lowered, which is not preferable. On the other hand, when the above (P / Ti) exceeds the upper limit, the polymerization reactivity of polyethylene-2,6-naphthalate is greatly lowered, and the desired polyethylene-2,6-naphthalate cannot be obtained. In the polyethylene-2,6-naphthalate used in the present invention, the appropriate range of (P / Ti) is much narrower than that of a normal metal catalyst, and when it is within this proper range, an unprecedented effect can be obtained as in the present invention. it can. A preferable range of (P / Ti) in the formula (2) is 4 or more and 10 or less. Further, when the above (Ti + P) is less than the lower limit, the productivity in the film forming process by the electrostatic application method is greatly reduced, and the moldability due to the decrease in the uniformity of the film thickness, particularly the production The film properties and impact resistance are reduced, and satisfactory performance cannot be obtained. On the other hand, when the above (Ti + P) exceeds the upper limit, a small amount of foreign matter is generated due to the catalyst, and when a magnetic recording medium is used, dropout occurs and electromagnetic conversion characteristics deteriorate, which is satisfactory. Performance cannot be obtained. Preferable (Ti + P) in the above formula (3) is in the range of 25 mmol% to 100 mmol%.
[0039]
  In the present invention, the polyethylene-2,6-naphthalate composition constituting the first layer is2,6-Naphthalenedicarboxylic acidAnd ethylene glycol as raw materials,Dimethyl 2,6-naphthalenedicarboxylateRepresented by2,6-Naphthalenedicarboxylic acidThese may also be used as raw materials of an ester-forming derivative and ethylene glycol. Among these, 80 mol% or more of all dicarboxylic acid components used as raw materials areDimethyl 2,6-naphthalenedicarboxylateThose produced via transesterification are preferred.Dimethyl 2,6-naphthalenedicarboxylateIs used as a raw material,2,6-Naphthalenedicarboxylic acidThere is an advantage that the phosphorus compound added as a stabilizer during the polycondensation reaction is less scattered than the production method using as a raw material. Also,Dimethyl 2,6-naphthalenedicarboxylateIn addition, the amount of catalyst added can be reduced among the production methods that use as a raw material, so at least a portion of the titanium compound is added before the start of the transesterification reaction, and both the transesterification reaction catalyst and the polycondensation reaction catalyst are combined. In particular, the transesterification reaction is preferably carried out under a pressure of 0.05 MPa or more and 0.20 MPa or less because the amount of the titanium compound used as the transesterification reaction catalyst can be further reduced. When the pressure during the transesterification reaction is 0.05 MPa or less, the promotion of the reaction by the catalytic action of the titanium compound is not sufficient. On the other hand, when the pressure is 0.20 MPa or more, the content of diethylene glycol generated as a by-product in the polymer is remarkably high. This increases the polymer's thermal stability and other properties.
[0040]
The polyethylene-2,6-naphthalate composition constituting the first layer thus obtained does not contain foreign substances as in the case of using a conventionally used antimony catalyst typified by antimony trioxide. . In addition, there is no increase in cost as in the case of using a germanium catalyst, and there is no deterioration in thermal stability at the time of melting as in the case of using a conventional titanium catalyst, which is extremely suitable for a base film of a magnetic recording medium. is there.
[0041]
The intrinsic viscosity of the polyethylene-2,6-naphthalate resin composition constituting the first layer is preferably in the range of 0.50 to 0.80, more preferably 0.55 to 0.75, especially 0. The range of .60 or more and 0.70 or less is preferable. If the intrinsic viscosity is less than the lower limit, the impact resistance of the film is insufficient. On the other hand, if the intrinsic viscosity exceeds the upper limit, it is necessary to raise the intrinsic viscosity of the raw polymer excessively, which is uneconomical.
[0042]
[Second layer polyethylene-2,6-naphthalate composition]
In the present invention, the polyethylene-2,6-naphthalate composition constituting the second layer comprises 80% by weight or more, preferably 85% by weight or more of a polyethylene-2,6-naphthalate resin. A resin other than 2,6-naphthalate resin may be mixed. The polyethylene-2,6-naphthalate resin here is a polyester having an ethylene-2,6-naphthalate component as a main repeating unit. Here, the main repeating unit means that 80 mol% or more, preferably 85 mol% or more of all repeating units are composed of an ethylene-2,6-naphthalate component. As the third component (copolymerization component) to be copolymerized other than the ethylene-2,6-naphthalate component constituting the polyethylene-2,6-naphthalate resin, the polyethylene-2,6- The same as described for the naphthalate composition can be used.
[0043]
Further, the polyethylene-2,6-naphthalate composition constituting the second layer is not particularly limited as long as it is as described above, and those known per se can be suitably used, and by a method known per se. Can be manufactured. Particularly preferably, since the generation of coarse particles due to the catalyst can be suppressed, the same polyethylene-2,6-naphthalate composition as described in the polyethylene-2,6-naphthalate composition constituting the first layer described above is used. It is a thing.
[0044]
[Laminated polyethylene-2,6-naphthalate film]
The laminated polyethylene-2,6-naphthalate film of the present invention is obtained by laminating a first layer and a second layer made of the above-described polyethylene-2,6-naphthalate composition. The polyethylene-2,6-naphthalate constituting the first layer and the second layer may have the same composition or different compositions. Particularly preferred is polyethylene-2,6-naphthalate having the same composition constituting the first layer and the second layer.
[0045]
  In the laminated polyethylene-2,6-naphthalate film of the present invention, the first layer forms a flat surface excellent in electromagnetic conversion characteristics and the like, and the second layer forms a rough surface excellent in running properties. To do. The surface of the second layer that is not in contact with the first layer may be provided with a coating layer as necessary, and the surface of the first layer that is not in contact with the second layer may also be You may provide a thin coating layer in the range which does not inhibit the effect of invention. As these coating layers, known coating layers can be suitably used. Among these, a laminate in which a coating layer containing fine particles is formed on the surface of the first sidePolyethylene-2,6-naA phthalate film is preferred. Examples of the fine particles include silica, calcium carbonate, alumina, polyacryl, polystyrene, and core-shell type particles having a multilayer structure composed of substances having different internal and external properties, and the average particle size is 5 nm to 50 nm from electromagnetic conversion characteristics. The following is preferable. In addition, as the binder resin, polar polymers such as polyester, acrylic, polyvinyl alcohol, tragacanth rubber, casein, gelatin, cellulose derivatives, polyurethane, and copolymers and blends thereof can be used. Particularly preferred binder resins are polyester, acrylic, and copolymers thereof from the viewpoints of adhesion to a polyester film, flatness, fine particle retention, and blocking resistance. The thickness of the coating layer is preferably 1 nm or more and 20 nm or less. The coating layer used in the present invention is preferably used in the form of an aqueous coating solution such as water-soluble, water-dispersible, or emulsion. In order to form a film, other resins and compounds other than the above-described composition, for example, an antistatic agent, a coloring agent, a surfactant, a wax, a crosslinking agent, an ultraviolet absorber and the like can be added as necessary. .
[0046]
In the present invention, since the first layer forms a surface excellent in flat electromagnetic conversion characteristics and the like, the inert particles having an average particle diameter of 100 nm or more, preferably 60 nm or more, more preferably 10 nm or more are substantially formed. It is preferable not to contain. The term “substantially” as used herein means that no catalyst is deposited to form inert particles, or no inert particles are added from the outside.
[0047]
In addition, the laminated polyethylene-2,6-naphthalate film of the present invention has a height of 1 nm to 100 nm and a width of 5 nm as measured by a three-dimensional surface roughness meter described later on the surface on the first layer side. 100 wavinesses of 100 μm or less / mm²More than 20,000 pieces / mm² It is necessary to have the following frequency. The width of the wavy projection is a value measured in a direction of 0 ± 10 degrees with respect to the film longitudinal direction. The measurement direction of the width corresponds to the direction of the track scanned by the magnetic tape of the magnetic recording system when a laminated polyethylene-2,6-naphthalate film is used as the magnetic recording medium. If the frequency of the wavy projection is less than the lower limit, the transportability in the film-forming process is poor, the film-film blocking phenomenon occurs, and when the film is used for metal thin film type magnetic recording, the temperature is high. The running performance of the tape under wet conditions becomes poor. On the other hand, if the frequency of the wavy projections exceeds the upper limit, electromagnetic conversion characteristics are hindered, and it is not suitable as a base film for a high-density magnetic recording medium. The preferred frequency of the wavy projection is 150 / mm²More than 10,000 pieces / mm²Or less, more preferably 200 / mm²More than 5000 pieces / mm²The range is as follows.
[0048]
In the present invention, the average height of the wavy projections is preferably 2 nm to 50 nm, and more preferably 2 nm to 30 nm. When the average height of the wavy projections is less than the lower limit, the transportability in the film-forming process is poor, the film-film blocking phenomenon occurs, and it is used for metal thin film type magnetic recording. In this case, the tape may be insufficient in terms of running properties under high temperature and high humidity conditions. On the other hand, when the average height of the undulating protrusions exceeds the upper limit, the electromagnetic conversion characteristics may be hindered. In the present invention, the average width of the wavy projections is preferably 8 μm or more and 80 μm or less, more preferably 10 μm or more and 60 μm or less. When the average width of the wavy projections exceeds the upper limit, the transportability in the film forming process becomes poor, the blocking phenomenon between the film and the film occurs, or when used for metal thin film type magnetic recording, It may be insufficient in terms of running properties of the tape under high temperature and high humidity conditions. On the other hand, when the average width of the wavy projections is less than the lower limit, the transportability in the film forming process and the running property of the tape are insufficient in the region where the height of the wavy projections is 25 nm or less.
[0049]
The wavy projections on the surface on the first layer side are not restricted by the formation method, but are formed by the push-up action of the first layer accompanying the stretching of the inert particles contained in the second layer. Are preferred. In order to express this push-up action more efficiently, it is preferable that the average particle diameter of the inert particles contained in the second layer and the thickness of the first layer satisfy a specific relationship. Specifically, the second layer contains one kind of inert particles or two or more kinds of inert particles having different kinds and particle sizes. If the number of the inert particles is one, the average particle size is determined. If the number of the inert particles is two or more, the average particle size of the inert particles having the largest average particle size is defined as d._B(Μm) and the thickness of the first layer is t_A(Μm), it is preferable to satisfy the formula (4). T_A/ D_BIs preferably 4 or more and 30 or less.
[0050]
In the present invention, the surface on the first layer side has a surface roughness of center surface average roughness (WRa)._A) In the range of 0.5 nm to 10 nm, preferably 0.5 nm to 5 nm. When the surface roughness exceeds the upper limit, electromagnetic conversion characteristics and the like are likely to be deteriorated. On the other hand, if the surface roughness is less than the lower limit, the blocking resistance of the film may deteriorate.
[0051]
In the present invention, the second layer contains inert particles as described above. The surface on the second layer side has a larger center plane average roughness (WRa) than the surface on the first layer side. Furthermore, the surface on the second layer side of the laminated polyethylene-2,6-naphthalate film has a center plane average roughness (WRa) while maintaining the above-described surface roughness relationship._B) Is preferably 3 nm to 20 nm, more preferably 3 nm to 17 m. The surface roughness on the second layer side (WRa_B) Exceeds the upper limit, it becomes difficult to make the height and width of the wavy projections formed on the surface on the first layer side within the above-mentioned range. On the other hand, the WRa_BHowever, if it is less than the lower limit, the blocking property of the film during conveyance or the like, and the running property when used as a tape are likely to deteriorate. WRa_BIs WRa_AIn the following, due to its flatness, handling properties such as transport, scratching, winding and unwinding in the film forming process of the base film are deteriorated, and the shape (roll formation) when wound on a roll is deteriorated. Deteriorating productivity, reducing product yield, and increasing product manufacturing costs.
[0052]
In order to impart the above surface roughness to the surface on the second layer side and to express the above-mentioned wavy projections on the surface on the first layer side, the inert particles contained in the second layer Average particle size (d_B) Is preferably 0.1 μm or more and 1 μm or less, more preferably 0.2 μm or more and 0.8 μm or less, and particularly preferably 0.2 μm or more and 0.6 μm or less.
[0053]
This average particle diameter d_BExamples of the inert particles include: crosslinked silicone resin, crosslinked polystyrene, crosslinked styrene-divinylbenzene copolymer, polymethyl methacrylate, methyl methacrylate copolymer, crosslinked methyl methacrylate copolymer, polytetrafluoroethylene, polyvinylidene fluoride. Fine particles made of heat-resistant organic polymers such as polyacrylonitrile and benzoguanamine resin, and fine particles made of inorganic compounds such as silica, alumina, titanium dioxide, kaolin, talc, graphite, calcium carbonate, feldspar, molybdenum disulfide It may be used.
[0054]
The second layer has the average particle diameter d_BIn addition to the inert particles having the above, one or more inert particles having an average particle size smaller than that of the inert particles can be contained. In this case, the second and third small particles include fine particles having an average particle diameter of 0.01 μm or more and 0.1 μm or less, such as colloidal silica, alumina having a crystal form such as α, γ, δ, θ, or the like. These fine particles can be preferably used. The average particle diameter d_BFine particles having an average particle diameter of 0.01 μm or more and 0.1 μm or less can be used among those exemplified as the inert particles having the above. The content of these inert particles is 0.01% by weight or more and 1% by weight or less, more preferably 0.05% by weight or more and 0.8% by weight or less, particularly 0.1% by weight, based on the weight of the second layer. % To 0.6% by weight is preferable.
[0055]
In the present invention, the total thickness of the laminated polyethylene-2,6-naphthalate film is usually 2 μm or more and 20 μm or less, preferably 2.5 μm or more and 10 μm or less, more preferably 3 μm or more and 7 μm or less. The thickness of the first layer forming the flat surface and the second layer forming the running surface is such that the wavy projections are formed on the surface of the first layer. Average particle diameter d of active particles_BAnd the thickness of the first layer are preferably configured to satisfy the aforementioned relationship. The thickness of the first layer is preferably 0.8 μm or more, and the thickness of the second layer is the average particle diameter d._BIt is preferable that it is 1/2 times or more (μm).
[0056]
In the present invention, in order to achieve thinning of a magnetic recording medium while improving various performances such as head touch and running durability as a magnetic recording medium, Young of a laminated polyethylene-2,6-naphthalate film is used. The rate is 4.5 GPa or more in the longitudinal direction (film forming direction), more preferably 4.9 GPa or more, and particularly preferably 5.2 GPa or more, and the lateral direction (film width direction) is 8 GPa or more, and further 9. It is preferably 5 GPa or more, particularly 11 GPa or more. The crystallinity of the laminated polyethylene-2,6-naphthalate film is desirably 28% or more and 38% or less. When the crystallinity is below the lower limit, the thermal shrinkage rate is increased. On the other hand, when the crystallinity is higher than the upper limit, the abrasion resistance of the film is deteriorated, and white powder tends to be generated when sliding on the roll or guide pin surface.
[0057]
[Method for producing laminated polyethylene-2,6-naphthalate film]
The laminated polyethylene-2,6-naphthalate film of the present invention can be produced by a method conventionally known or accumulated in the art. Among these, it is preferable to manufacture by a coextrusion method. For example, in the case of a biaxially oriented polyethylene-2,6-naphthalate film, the first layer is formed in the extrusion die or before the die (generally the former is called the multi-manifold method and the latter is called the feed block method). Polyethylene-2,6-naphthalate and polyethylene-2,6-naphthalate constituting the second layer containing inert particles are laminated and composited in a molten state, And then coextruded from the die at a melting point of 280 ° C. to 330 ° C. into a film and then rapidly cooled and solidified at 10 to 30 ° C. to obtain an unstretched laminated polyethylene-2,6-naphthalate film. Thereafter, the unstretched laminated film is uniaxially (longitudinal or transverse) in a conventional manner at a temperature of 120 to 160 ° C. and a magnification of 2.5 to 8.0 times, preferably 3.0 to 7.5. The film is stretched at a magnification of twice, and then stretched at a temperature of 120 to 160 ° C. at a magnification of 2.5 to 8.0 times, preferably at a magnification of 3.0 to 7.5 times, in a direction orthogonal to the above direction. . Further, it may be stretched again in the longitudinal direction and / or the transverse direction as necessary. That is, it is good to perform 2 steps, 3 steps, 4 steps, or multi-stage stretching. The total draw ratio is usually 9 times or more, preferably 12 to 35 times, more preferably 15 to 26 times as the area draw ratio. Subsequently, excellent dimensional stability is imparted by heat-fixing crystallization of the biaxially oriented film at 180 to 250 ° C. The heat setting time is preferably 1 to 60 seconds. In this way, a biaxially oriented laminated polyethylene-2,6-naphthalate film with high interlayer adhesion is obtained.
[0058]
In the production of a laminated polyethylene-2,6-naphthalate film, the polyethylene-2,6-naphthalate resin may be optionally adjusted to additives other than the above-mentioned inert particles, such as stabilizers, colorants, and specific resistance of the molten polymer. An agent or the like may be added and contained. In addition, the above-mentioned film layer is formed by applying a coating liquid for forming a film layer on the film surface and drying in the stretching process and the subsequent heat setting process until the stretching process is completed. Is preferred.
[0059]
[Method of manufacturing magnetic recording medium]
The magnetic recording medium using the laminated polyethylene-2,6-naphthalate film of the present invention as a base film is formed by vacuum deposition, sputtering, ion plating, etc. on the surface on the first layer side, that is, the surface on the flat surface side. According to the method, a ferromagnetic metal thin film layer made of iron, cobalt, chromium, or an alloy or oxide containing these as a main component is formed, and diamond-like carbon (DLC) is formed on the surface as required for the purpose or application. By sequentially providing a protective layer such as a protective layer and a fluorocarboxylic acid-based lubricating layer, and further providing a known backcoat layer on the surface on the second layer side, output in the short wavelength region, S / N, C / N, etc. A vapor-deposited magnetic recording medium for high-density recording that has excellent electromagnetic conversion characteristics, low dropout, and low error rate can be obtained. This vapor deposition type magnetic recording medium is extremely useful as an analog signal recording Hi8, digital signal recording digital video cassette recorder (DVC), data 8 mm, mammoth, and AIT tape medium.
[0060]
Further, the laminated polyethylene-2,6-naphthalate film of the present invention is made of iron chloride or acicular fine magnetic powder mainly composed of iron chloride on the surface on the first layer side, that is, the flat surface side surface. Uniformly disperse in a binder such as vinyl / vinyl acetate copolymer, apply so that the thickness of the magnetic layer is 1 μm or less, preferably 0.1 to 1 μm, and then back the surface of the second layer by a known method. By providing a coat layer, a metal-coated magnetic recording medium for high-density recording that has excellent output characteristics in the short wavelength region, electromagnetic conversion characteristics such as S / N, C / N, and low dropout and error rate. Can do. Further, if necessary, a nonmagnetic layer containing fine titanium oxide particles or the like as an underlayer of the metal powder-containing magnetic layer is dispersed and coated in the same organic binder as the magnetic layer on the surface on the first layer side. It can also be set up. This metal-coated magnetic recording medium is a tape medium for analog signal recording 8 mm video, Hi8, β cam SP, W-VHS, data 8 mm, DDSIV, digital β cam, D2, D3, SX, LTO, DLT, etc. As extremely useful.
[0061]
【Example】
Hereinafter, the present invention will be specifically described by way of examples. Each characteristic in the present invention is measured or evaluated by the following method. In the examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified.
(1) Intrinsic viscosity
Obtained from a value measured at 35 ° C. in an o-chlorophenol solvent.
(2) Average particle diameter 1 (average particle diameter: 0.06 μm or more)
Measurement is performed using a CP-50 type centrifuggle particle size analyzer (Shimadzu Seisakusho). The particle size “equivalent sphere diameter” corresponding to 50 mass percent is read from the integrated curve of the particles of each particle size calculated based on the obtained centrifugal sedimentation curve and the abundance thereof, and this value is used as the average particle size. (See Book “Particle Size Measurement Technology” published by Nikkan Kogyo Shimbun, 1975, pages 242-247).
(3) Average particle diameter 2 (average particle diameter: less than 0.06 μm)
Particles having an average particle size of less than 0.06 μm that form small protrusions are measured using a light scattering method. That is, the “equivalent sphere diameter” of the particle at the point of 50% by weight of the total particle determined by NICOM MODEL 270 SUBMICRON PARTICLE SIZER manufactured by Nicomp Instruments Inc. is displayed.
(4) Layer thickness
The total thickness of the film is measured at 10 points randomly with a micrometer, and the average value is used. The layer thickness is obtained by measuring the layer thickness on the thin side by the method described below, and subtracting the layer thickness on the thick side from the layer thickness on the side thinner than the total thickness. That is, using a secondary ion mass spectrometer (SIMS), an element derived from the highest concentration of particles in a film having a depth of 5000 nm from the surface layer and a carbon element of polyethylene-2,6-naphthalate Concentration ratio (M⁺/ C⁺) Is the particle concentration, and analysis in the thickness direction is performed from the surface to a depth of 5000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the present invention, the particle concentration may once increase to a stable value 1 and then increase or decrease to a stable value 2 and may decrease monotonously. Based on this distribution curve, in the former case, the depth gives a particle concentration of (stable value 1 + stable value 2) / 2, and in the latter case, the depth at which the particle concentration is ½ of the stable value 1. (This depth is deeper than the depth that gives a stable value of 1), which is the layer thickness of the layer.
The measurement conditions are as follows.
(1) Measuring device
Secondary ion mass spectrometer (SIMS): 6300 manufactured by PERKIN ELMER
(2) Measurement conditions Primary ion species: O2 +
Primary ion acceleration voltage: 12 kV
Primary ion current: 200 nA
Raster area: 400 μm
Analysis area: 30% gate
Measuring vacuum: 6.0 × 10^-9Torr
E-GUNN: 0.5kV-3.0A
In the case where the most contained particles in the range of 5000 nm from the surface layer are organic polymer particles other than silicone resin, it is difficult to measure with SIMS, so FT-IR (Fourier transform infrared spectroscopy) while etching from the surface, Depending on the particle, a concentration distribution curve similar to the above is measured by XPS (X-ray high electron spectroscopy) or the like to determine the layer thickness.
(5) Wavy projections on the film surface
Using a non-contact type three-dimensional surface roughness meter (manufactured by WYKO: NT-2000), the measurement magnification is 25 times and the measurement area is 246.6 μm × 187.5 μm (= 0.0462mm²), Or a measurement magnification of 2.5 times, a measurement area of 2.5 mm × 1.9 mm (= 4.75 mm)²) And the height and width of the swell are read from the obtained three-dimensional roughness chart. In addition, the measurement was performed with the sample cut out in the direction of 5 to 10 degrees with respect to the longitudinal direction of the film. Further, the average height and average width of the undulating protrusions were calculated from the average value of 50 protrusions measured at random.
(6) Center plane average roughness (WRa)
Using a non-contact type three-dimensional surface roughness meter (manufactured by WYKO: NT-2000), measurement magnification is 25 times, measurement area is 246.6 μm × 187.5 μm (= 0.0462 mm)²), And the center plane average roughness WRa is obtained from the following formula using surface analysis software built in the roughness meter.
[0062]
[Equation 5]

[0063]
Z_jkIs the height on the two-dimensional roughness chart at the j-th and k-th positions in each direction when the measurement method (246.6 μm) and the direct method (187.5 μm) are divided into m and n, respectively. .
(7) Young's modulus
The film is cut into a sample width of 10 mm and a length of 15 cm, and pulled with a universal tensile tester (product name: Tensilon, manufactured by Toyo Baldwin) under the conditions of 100 mm between chucks, a tensile speed of 10 mm / min, and a chart speed of 500 mm / min. The Young's modulus is calculated from the tangent of the rising portion of the obtained load-elongation curve.
(8) Blocking resistance
Two films are prepared, and the surface on the first layer side of one film and the surface on the second layer side of the other film are overlapped. First, in an atmosphere of 50 ° C. × 70% RH, Treated under no load for 24 hours, then 15 N / mm²For 100 hours. The laminated film laminate after the treatment is cut into a strip shape having a width of 5 cm, and evaluated by the peel strength (mN / 5 cm) at a location where a load is applied by a tensile tester. In addition, evaluation is evaluated according to the following criteria from the value of peel strength.
[0064]
○: 0 to 50 mN / 5 cm
Δ: Over 50 mN / 5 cm and less than 100 mN / 5 cm
X: 100 mN / 5 cm to fracture occurrence
(9) Inactive particles in the first layer
The sample film piece is fixed on a sample stage for a scanning electron microscope, and an ion etching process is performed on the film surface under the following conditions using a sputtering apparatus (JFC-1100 type ion etching apparatus) manufactured by JEOL. The condition is that a sample is placed in a bell jar and about 10^-3The degree of vacuum is increased to a vacuum state of Torr, and ion etching is performed at a voltage of 0.25 kV and a current of 12.5 mA for about 10 minutes. Further, using the same apparatus, the film surface was sputtered with gold, observed with a scanning electron microscope at a magnification of 5,000 to 10,000 times, and an equivalent sphere of each inert particle with a Luzex 500 manufactured by Japan Regulator Co., Ltd. Find the diameter distribution. From the obtained equivalent spherical distribution, inert particles having a particle size exceeding 100 nm are extracted, and the average particle size of the inert particles exceeding 100 nm is calculated from the point of 50% by weight.
(10) Manufacture and characteristic evaluation of magnetic tape
A cobalt-oxygen thin film is formed with a thickness of 110 nm by vacuum deposition on the surface of the first layer side of the laminated polyethylene terephthalate film, and then diamond-like carbon is formed with a thickness of 10 nm on the cobalt-oxygen thin film layer by sputtering. Then, a fluorine-containing carboxylic acid-based lubricant is sequentially provided. Subsequently, a back coat layer made of carbon black, polyurethane and silicone is provided on the surface opposite to the surface on which the cobalt-oxygen thin film is formed so as to have a thickness of 500 nm, and slitted to a width of 8 mm and 6.35 mm by a slitter. Then, it was wound up on a commercially available reel to produce a magnetic tape. A commercially available Hi8 8 mm video tape recorder is used to determine the video S / N ratio, and a commercially available camera-integrated digital video tape recorder is used to determine the number of dropouts (DO).
[0065]
The number of DOs is measured by recording the produced 6.35 mm tape with a commercially available camera-integrated digital video tape recorder, playing it for 1 minute, and counting the number of block mosaics that appear on the screen.
[0066]
C / N measured C / N of 7 MHz ± 1 MHz using a commercially available VTR for Hi8 (manufactured by Sony Corporation, EV-BS3000). Compare this C / N with a commercially available video tape for Hi8 (manufactured by Sony Corporation, vapor deposition type tape E6-120HME4), a film of +3 dB or more is excellent, a film of +1 to +3 dB is good, and a film less than +1 dB is bad, evaluated.
[0067]
The running durability under high temperature and humidity is determined by measuring the C / N after repeating recording and reproduction 700 times at 40 ° C. and 80% RH and deviating from the initial value.
[0068]
○: +0.0 dB or more with respect to the initial value
Δ: From −1.0 dB to less than +0.0 dB with respect to the initial value
X: Less than -1.0 dB with respect to the initial value
(11) Thermal stability of the film
The film was evenly stretched on a fixed frame and treated with a hot air dryer at a temperature of 240 ° C. for 5 minutes in an atmosphere of the atmosphere. The film before and after the treatment is cut into a sample width of 10 mm and a length of 15 cm, respectively, and pulled by a tensile tester (manufactured by Toyo Baldwin, trade name: Tensilon) at a tensile speed of 10 mm / min with a chuck distance of 100 mm. The stress at break of the obtained load-elongation curve is calculated. A film having a fracture strength after treatment exceeding 60% with respect to the fracture strength before treatment has good thermal stability (symbol in the table: ◯), and the fracture strength after treatment is relative to the fracture strength before treatment. 30% to 60% of the film is slightly inferior in thermal stability (symbol in the table: Δ), and the film having a breaking strength after treatment of less than 30 with respect to the breaking strength before treatment has extremely high thermal stability. Evaluation was made as inferior (symbol in table: x).
(12) Content of titanium, phosphorus and metal elements
Titanium and phosphorus atom concentrations are determined with an energy dispersive X-ray microanalyzer (XMA, Horiba EMAX-7000) connected to the dried sample set in a scanning electron microscope (SEM, Hitachi Instrument Service S570). Analysis was performed.
[0069]
The catalyst metal concentration in polyethylene terephthalate is determined by heating and melting a granular sample on an aluminum plate, creating a molded body having a flat surface with a compression press, and using a fluorescent X-ray apparatus (Rigaku Corporation 3270E type). analyzed.
[0070]
[Example 1]
A mixture of 100 parts of 2,6-dimethylnaphthalate and 56 parts of ethylene glycol is charged with 0.011 part of tetra-n-butyl titanate in a SUS (stainless steel) container capable of pressure reaction, and pressurized to 0.07 MPa. Then, the ester exchange reaction was carried out while raising the temperature from 140 ° C. to 240 ° C., and then 0.042 part of triethylphosphonoacetate was added to complete the ester exchange reaction.
[0071]
Thereafter, the reaction product is transferred to a polymerization vessel, heated to 290 ° C. and subjected to a polycondensation reaction at a high vacuum of 100 Pa, and has an intrinsic viscosity of 0.62 and an amount of diethylene glycol of 1.5 mol% (2,6-ethylene naphthalate). Component-2) polyethylene-2,6-naphthalate resin (PEN) composition for the first layer was obtained. Further, inert particles shown in Table 1 as a lubricant were further added and dispersed in the PEN composition to obtain a PEN composition for the second layer having an intrinsic viscosity of 0.62.
[0072]
These PEN compositions for the first layer and the second layer were each dried at 170 ° C. for 6 hours, then supplied to two extruders, melted at a melting temperature of 305 ° C., and a multi-manifold coextrusion die Was used to laminate the PEN composition for the second layer on one side of the PEN composition for the first layer, and rapidly cooled to 60 ° C. to obtain an unstretched laminated film having a thickness of 90 μm. The obtained unstretched film is preheated, further stretched 3.7 times at a film temperature of 130 ° C. between low-speed and high-speed rolls, quenched, and subsequently an aqueous solution having the composition shown below is applied to the first layer side. Applied to the surface.
Composition of coating solution:
(1) Acrylic-polyester resin 80% by weight
Polyester component: -2,6-naphthalic acid (70 mol%), isophthalic acid (18 mol%), 5-sodium sulfoisophthalic acid (12 mol%) / ethylene glycol (92 mol%), diethylene glycol (8 mol%) )
Acrylic resin component: methyl methacrylate (80 mol%), glycidyl methacrylate (15 mol%), n-butyl acrylate (5 mol%)
-Mole ratio of polyester component / acrylic resin component = 3/7
(2) Acrylic resin fine particles (average particle size 30 nm) 5% by weight
(3) Surfactant
-Sanyo Chemical Co., Ltd. Emarumin 110 15% by weight
Film layer thickness (after drying): 5.2 nm
Then, it supplied to the stenter and extended | stretched 5.0 times in the horizontal direction at 150 degreeC. The obtained biaxially stretched laminated film was heat-fixed with hot air at 208 ° C. for 4 seconds to obtain a laminated biaxially oriented polyethylene-2,6-naphthalate film having a thickness of 4.7 μm. About the thickness of each layer, it adjusted with the discharge amount of two extruders. The Young's modulus of this laminated polyethylene-2,6-naphthalate film was 5.6 GPa in the vertical direction and 11.2 GPa in the horizontal direction.
[0073]
Table 2 shows the properties of the obtained laminated polyethylene-2,6-naphthalate film and its magnetic tape.
[0074]
[Example 2]
A PEN composition for the first layer was obtained in the same manner as in Example 1 except that the titanium compound used in the production of the PEN composition for the first layer was changed to 0.02 part of titanium trimellitic acid. Note that titanium trimellitic acid is added to an ethylene glycol solution in which 2 parts by weight of trimellitic anhydride is mixed with 98 parts by weight of ethylene glycol so that the molar ratio of tetrabutoxy titanium to trimellitic anhydride is 0.5. The reaction is carried out for 60 minutes while maintaining at 80 ° C. under atmospheric pressure in the air, and then cooled to room temperature, the produced catalyst is recrystallized with 10 times the amount of acetone, and the precipitate is filtered through filter paper. It was manufactured by drying for hours.
[0075]
A PEN composition for the second layer produced in the same manner as in Example 1 except that the obtained PEN composition for the first layer and the inert particles were changed as shown in Table 1 were prepared. As shown, a laminated polyethylene-2,6-naphthalate film was obtained in the same manner as in Example 1 except that the thicknesses of the first layer and the second layer were changed.
[0076]
Table 2 shows the properties of the obtained laminated polyethylene-2,6-naphthalate film and its magnetic tape.
[0077]
    [Example5To 6, Comparative Examples 1 to 12]
  A laminated polyethylene-2,6-naphthalate film was obtained in the same manner as in Example 1 except that the changes were made as shown in Table 1.
[0078]
Table 2 shows the properties of the obtained laminated polyethylene-2,6-naphthalate film and its magnetic tape.
[0079]
    [Comparative Example 13]
  Used to construct the first layerPENIn addition, the same operation as in Example 1 was repeated except that spherical silica having an average particle diameter of 120 nm was added to 0.03% by weight.
[0080]
  Obtained laminated polyethylene-2,6-NaTable 2 shows the characteristics of the phthalate film and the magnetic tape using it as a base film.
[0081]
[Table 1]

[0082]
[Table 2]

[0083]
In Table 1, TBT means tetra-n-butoxy titanium, TMT means trimellitic acid titanium, TEPA means triethylphosphonoacetate, PEE means carboethoxymethane-phosphonic acid diethyl ester, HPE means hydroxymethylene-phosphonic acid diethyl ester To do. Moreover, in Comparative Example 2 and Comparative Example 4, the polymer IV constituting the first layer and the second layer was too low to form a film, and subsequent evaluation was not performed. Furthermore, in Comparative Example 6, the pinning property during film formation was poor, and a film that could withstand subsequent evaluation was not obtained.
[0084]
【The invention's effect】
  Laminated polyethylene of the present invention-2,6-NaThe phthalate film has excellent anti-blocking properties, and further suppresses foreign substances caused by the catalyst. When used as a base film for high-density magnetic recording media, the resulting magnetic recording media have few dropouts and electromagnetic conversion characteristics. In addition, it can be provided with the characteristics of excellent durability and running durability, and its industrial value is extremely high.

Claims (11)

Laminated polyethylene-2,6- in which a second layer composed of a polyethylene-2,6-naphthalate composition containing inert particles is laminated on one side of a first layer composed of a polyethylene-2,6-naphthalate composition. A naphthalate film,
The first layer is a titanium compound in which the transesterification reaction catalyst and the polycondensation reaction catalyst are soluble in polyethylene-2,6-naphthalate, and the phosphorus compound and the titanium compound are represented by the following formulas (1) to (3).

(Here, Ti in formulas (1) to (3) is the number of moles of titanium compound soluble in polyethylene-2,6-naphthalate as the titanium element, ethylene-2,6-naphthalate component in the composition. P is a value obtained by dividing the number of moles of the phosphorus compound as the phosphorus element by the number of moles of the ethylene-2,6-naphthalate component in the composition (mmol%). is there.)
The phosphorus compound is contained in the following formula (I)
[Chemical 1]
R < ¹ > O-C (O) -X-P (O)-(OR < ² > ) ₂ ... (I)
(Here, R ¹ and R ² in the formula are each an alkyl group having 1 to 4 carbon atoms, X represents —CH ₂ — or —CH (Y) — (Y represents a benzene ring). ).)
In a phosphonate compound represented, and the average particle size does not contain more inert particles 100 nm, and,
Surface of the first layer side has a height of less wavy protrusions 100μm or 100nm or less and a width of 5μm or 1 nm 100 pieces / mm ² or more 20,000 / mm ² or less frequently, and the A laminated polyethylene-2,6-naphthalate film, characterized in that it is used as a base film of a digital recording magnetic recording medium having a center plane average roughness (WRa) smaller than the surface on the second layer side. The titanium compound soluble in polyethylene-2,6-naphthalate is a compound represented by the following general formula (II) or a compound represented by the following general formula (II) and an aromatic polyvalent represented by the following general formula (III): The laminated polyethylene-2,6-naphthalate film according to claim 1, which is a reaction product with carboxylic acid.

(In the above formula, n represents an integer of 2 to 4) The laminated polyethylene-2,6-naphthalate film according to claim 1, wherein the average particle diameter of the inert particles contained in the second layer and the thickness of the first layer satisfy the following formula (4).

(Here, tA in Formula (4) is the thickness (μm) of the first layer, and dB is the average particle size (μm) of the inert particles contained in the second layer.)   The inert particles contained in the second layer have an average particle size (dB) of 0.1 μm or more and 1 μm or less and a content of 0.01% by weight or more based on the weight of the second layer. The laminated polyethylene-2,6-naphthalate film according to claim 1, which is 1.0% by weight or less.   The laminated polyethylene-2,6-naphthalate film according to claim 1, wherein a film layer is provided on at least one surface of the laminated polyethylene-2,6-naphthalate film.   The laminated polyethylene-2,6-naphthalate film according to claim 1, wherein the center plane average roughness (WRaA) of the surface on the first layer side is 0.5 nm or more and 10 nm or less.   The laminated polyethylene-2,6-naphthalate film according to claim 1, wherein the center plane average roughness (WRaB) of the surface on the second layer side is 3 nm or more and 20 nm or less.   The first layer has a thickness of 0.8 μm or more, the second layer has a thickness of 0.5 times or more the average particle diameter (dB) of the inert particles contained, The laminated polyethylene-2,6-naphthalate film according to claim 1, wherein the total thickness of the two layers is 2 μm or more and 7 μm or less. The laminated polyethylene-2,6-naphthalate film according to any one of claims 1 to 8 , which is used for a base film of a digital recording magnetic recording medium. The laminated polyethylene-2,6-naphthalate film according to any one of claims 1 to 8 , and a magnetic layer provided on the first layer side surface of the laminated polyethylene-2,6-naphthalate film, A magnetic recording medium comprising a back coat layer provided on the surface on the second layer side of the laminated polyethylene-2,6-naphthalate film. The magnetic recording medium according to claim 10 , wherein the magnetic layer is a ferromagnetic metal thin film layer.