JP3600688B2 - Magnetic recording media - Google Patents

Description

【００１２】
で表される潤滑層が設けられていることを特徴とする磁気記録媒体。
【００１３】
このようにして得られる磁気記録媒体は、上記の構成を有することにより低温から高温多湿雰囲気においても低い摩擦係数と高い耐久性さらに高い耐候性を有する。
【００１４】
（２）保護層がプラズマＣＶＤ法により成膜された硬質炭素膜からなる上記（１）記載の磁気記録媒体。
【００１５】
（３）金属薄膜型磁性層の磁性材料がＣｏ（コバルト）である（１）又は（２）のいずれかに記載の磁気記録媒体。
【００１６】
（４）上記化２で示されるカルボン酸エステルのＲが炭素数１４〜２３の直鎖のアルキル基である（１）ないし（３）のいずれかに記載の磁気記録媒体。
【００１７】
（５）上記化２で示されるカルボン酸エステルのＲｆが炭素数８〜２１のパーフルオロアルキル基である（１）ないし（４）のいずれかに記載の磁気記録媒体。
【００１８】
（６）上記化２で示されるカルボン酸エステルのｎが２〜４である（１）ないし（５）のいずれかに記載の磁気記録媒体。
【００１９】
ここで、金属薄膜型磁性層とは、真空薄膜形成技術でＣｏ、Ｃｏ−Ｎｉ等の強磁性金属材料を被着した層のことである。また、保護層とは、金属薄膜型磁性層の上に設けられる、硬質炭素膜、ＳｉＯ膜、ＳｉＯ_Ｘ膜等を指し、磁性層の腐食防止の目的で設けられる。上記、硬質炭素膜は、真空蒸着法、スパッタリング法、プラズマＣＶＤ法等により、ＳｉＯ膜は真空蒸着法により、ＳｉＯ_Ｘ膜はプラズマＣＶＤ法によりそれぞれ成膜することができる。
【００２０】
硬質炭素膜は前記の方法により成膜できるが、プラズマＣＶＤ法により成膜した保護層をもつ磁気記録媒体は、特に耐磨耗性に優れている。
【００２１】
金属薄膜型磁性層の磁性材料は、前記のような金属又は合金からなるものであるが、Ｃｏを使用したものは、特に電磁変換特性が良く高密度記録媒体に有利である。
【００２２】
（４）ないし（６）の構成のような特定のカルボン酸パーフルオロアルキルエステルは、原料の工業的入手が容易であるため生産性の向上をはかることが可能となる。
【００２３】
【発明の実施の形態】
本発明に係る磁気記録媒体について、具体的に以下に説明する。
【００２４】
（潤滑層）
本発明に係る磁気記録媒体の潤滑層は、一般式ＲＣＯＯ（ＣＨ_２）_ｎＲｆでかつＲは炭素数１４以上の直鎖状のアルキル基、Ｒｆは炭素数８以上のパーフルオロアルキル基、ｎは２以上であるカルボン酸エステルからなるものである。
【００２５】
上記一般式ＲＣＯＯ（ＣＨ_２）_ｎＲｆにおけるアルキル基Ｒの炭素数が１４以上では、優れた耐久性を有するが、とくに炭素数が１４〜２３のものが好ましい。炭素数が２３より大きいものは、効果において差異はないが（飽和するため）工業的に入手しにくくなるので、産業上のメリットがない。これらの中でも媒体の耐久性等の特性が特に向上するため炭素数が１５、１６のものはもっとも好ましい。このアルキル基Ｒの炭素数が１４未満では、常温での摩擦が上昇する不具合がある。これは、アルキル基の炭素数が少ないと潤滑剤の分子内凝集が起こりやすくなるために塗布面（磁性面）全体をカバーしにくく、まだら（海島状のムラ）状態になり、摩擦係数が不均一となり、結果として摩擦が上昇すると考えられる。この対策として凝集により塗布面をカバーできなくなった分をあらかじめ過剰に塗布してもよいが、単位面積当たりの潤滑剤の量が多くなりすぎるためにスティックスリップを起こして摩擦が上昇してしまい好ましくない。
【００２６】
さらに、上記一般式のＲはアルキル基、すなわち直鎖状の飽和炭化水素基である。Ｒが直鎖状であっても不飽和型の炭化水素基、すなわち分子内に二重結合または三重結合を有する炭化水素基の場合では、長期保存すると酸化等が進行するために摩擦が上昇してしまう。また、Ｒが飽和であっても枝分かれしたいわゆる分枝状炭化水素基では、枝分かれによるかさ高さのために配向しにくく、摩擦が上昇して好ましくない。
【００２７】
一方、上記一般式のＲｆ、すなわちパーフルオロアルキル基の炭素数は、８〜２１のものが好ましい。これより炭素数の大きいものは、効果が飽和するので差異はないが原料の工業的入手が困難であるため産業上のメリットがない。また、溶解性等の問題から保護層形成が困難になる可能性もある。これらの中でも炭素数が８〜１４のものは特に好ましい。このようなパーフルオロアルキル基が配向することにより、疎水性の原子として働くフッ素がほぼ均一に配列されることとなり塗布面（磁性面）全体が潤滑剤でカバーされた状態となるため、水分が近づきにくくなって撥水性を得ることができ、結果的に優れた耐候性を備えるものとなる。一方、炭素数が８未満ではパーフルオロアルキル基は十分に配向せず、塗布面のカバーが十分でなく、必要なだけの撥水性が得られない。
【００２８】
また、上記一般式のＲｆはパーフルオロアルキル基、すなわち飽和型のものである。これは上記したように分子内に二重結合、三重結合等の不飽和結合を有する場合では、長期保存すると酸化等が進行するために摩擦が上昇してしまうためである。ここで、上記パーフルオロアルキル基は直鎖状、枝分かれ状のどちらでもよい。
【００２９】
このような上記カルボン酸エステルを得るには、アルキル基が直鎖で飽和型の炭素数Ｒ＋１である高級モノカルボン酸とフッ化アルキル基が飽和の一般式でＲｆ（ＣＨ_２）_ｎＯＨなる構造のフッ素アルコールを用いて合成すればよい。このとき、ｎは２以上であるアルコールを使用する。すなわち、前記カルボン酸エステルの一般式のｎも２以上となる。ｎ＝０のアルコールはアルコール合成後分解するため存在しないことと、詳しい理由は不明であるがｎ＝１の場合においては保存後の摩擦が劣化する問題がある。また、ｎが４を超えるものは効果が飽和するので差異は生じにくいが、工業的に入手が困難で、産業上のメリットがないため、実質上ｎは２〜４、実際に使用できるものとしては、
ｎ−Ｃ_１４Ｈ_２９ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、ｎ−Ｃ_１５Ｈ_３１ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、
ｎ−Ｃ_１６Ｈ_３３ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、ｎ−Ｃ_１７Ｈ_３５ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、
ｎ−Ｃ_１８Ｈ_３７ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、ｎ−Ｃ_１９Ｈ_３９ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、
ｎ−Ｃ_２０Ｈ_４１ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、ｎ−Ｃ_２１Ｈ_４３ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、
ｎ−Ｃ_２２Ｈ_４５ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７、ｎ−Ｃ_１５Ｈ_３１ＣＯＯＣ_２Ｈ_４Ｃ_１０Ｆ_２１、
ｎ−Ｃ_１５Ｈ_３１ＣＯＯＣ_２Ｈ_４Ｃ_１１Ｆ_２３、ｎ−Ｃ_１５Ｈ_３１ＣＯＯＣ_２Ｈ_４Ｃ_１２Ｆ_２５、
ｎ−Ｃ_１５Ｈ_３１ＣＯＯＣ_２Ｈ_４Ｃ_１３Ｆ_２７、ｎ−Ｃ_１５Ｈ_３１ＣＯＯＣ_３Ｈ_６Ｃ_８Ｆ_１７、
ｎ−Ｃ_１５Ｈ_３１ＣＯＯＣ_４Ｈ_８Ｃ_８Ｆ_１７、ｎ−Ｃ_１８Ｈ_３７ＣＯＯＣ_２Ｈ_４Ｃ_１０Ｆ_２１、
ｎ−Ｃ_２０Ｈ_４１ＣＯＯＣ_２Ｈ_４Ｃ_１０Ｆ_２１
等が挙げられる。
【００３０】
またこのようなカルボン酸エステルは、Ｒの数において５０％以上の主成分の炭素数の±２のアルキル基を混合して含んでいてもよく、Ｒｆにおいても５０％以上の主成分の炭素数の±２のパーフルオロアルキル基を混合して含んでいてもよい。これらの混合比は５０／５０〜１００／０の範囲が潤滑性のバランスがとれているため好ましい。
【００３１】
このような潤滑層の形成方法は、上記カルボン酸エステルからなる潤滑剤を例えば、メタノール、エタノール、ブタノール、イソプロピルアルコール（ＩＰＡ）、アセトン、メチルエチルケトン（ＭＥＫ）、メチルイソブチルケトン（ＭＩＢＫ）、シクロヘキサノン、シクロヘキサン、テトラヒドロフラン（ＴＨＦ）、ジメチルホルムアミド（ＤＭＦ）、酢酸エチル、酢酸ブチル、ジオキサン、ヘキサン、ヘプタン、オクタン、トルエン、キシレン、リグロイン、石油エーテルなどの溶媒に溶解して得られた溶液を保護層の表面に塗布あるいは噴霧するかして、後に乾燥すればよい。
【００３２】
その磁性層面への塗布量は、潤滑剤量として０．５〜１０ｍｇ／ｍ^２であるのが好ましい。特に３〜８ｍｇ／ｍ^２が好ましい。上記塗布量とすることにより、走行性、耐久性、耐候性が向上する。
【００３３】
また塗布量０．５ｍｇ／ｍ^２を割ると潤滑剤が少ないことよりムラになり摩擦係数の変動と上昇を引き起こすとともに耐候性の低下を招き、１０ｍｇ／ｍ^２を越えると潤滑剤が過剰となるためスティックスリップを生じる。という不具合がある。
【００３４】
（非磁性基体）
非磁性基体は蒸着工程に耐えられるものであれば何でもよく、特に限定されなが例えば、ポリエチレンテレフタレート（ＰＥＴ）、ポリエチレンナフタレート（ＰＥＮ）、ポリイミド、アラミド、ポリエーテルエーテルケトン（ＰＥＥＫ）、ポリサルフォン等のフィルムが挙げられる。その厚さは、磁気記録媒体が使用される用途により適宜選択されるが、例えば磁気記録媒体がビデオテープとして使用される場合、録画時間やシステム要求値にあわせて選択され、通常は５〜４０μｍである。
【００３５】
また、磁性層の表面粗さ、ひいては媒体の記録面側の表面粗さを制御するために上記基体上に微粒子層を設けてもよい。微粒子層は、ジルコニア、シリカ、アルミナなど無機粒子を樹脂と共に水又は溶剤に分散させ塗布することによって得られる。これら無機粒子の粒子径は、５〜４０ｎｍより選択され、塗布後の密度は１×１０^４〜１００×１０^４個／ｍｍ^２程度とすればよい。
【００３６】
さらに、基体の磁性層が設けられる面とは反対側の面にバックコート層を設けてもよい。
【００３７】
バックコート層は、結合剤樹脂と無機化合物及び／又はカーボンブラックとを有機溶媒に混合分散させたバックコート用塗料を磁性層とは反対側の基体表面に塗布することにより形成される。また、バックコート層の塗料組成はこの種の磁気記録媒体に用いられるものであればいずれのものも使用できる。例えば、結着剤樹脂は塩化ビニル系共重合体、ポリウレタン樹脂、アクリル樹脂、エポキシ樹脂、フェノキシ樹脂、ポリエステル樹脂等であり、単独又は混合して使用しても良く、媒体の特性、工程条件により適宜選択される。カーボンブラックとしてはファーネスカーボンブラック、サーマルカーボンブラック等を挙げることができ、無機化合物としては、例えば炭酸カルシウム、アルミナ、α−酸化鉄等を挙げることができる。これら粒子は媒体に要求される電気抵抗、摩擦特性等から粒子サイズを適宜選択すればよい。有機溶剤は、例えばケトン類、芳香族炭化水素類等であり、使用する結合材樹脂の溶解性を考慮し適宜選択すればよい。
【００３８】
（金属薄膜型磁性層）
金属薄膜型磁性層を形成する磁性金属はＣｏ、Ｃｏ−Ｎｉ、Ｃｏ−Ｃｕ、Ｃｏ−Ｐｔ、Ｃｏ−Ｆｅ、Ｃｏ−Ｃｒ、Ｃｏ−Ｎｉ−Ｃｒ、Ｃｏ−Ｎｉ−Ｆｅ、Ｃｏ−Ｐｔ−Ｃｒ、Ｃｏ−Ｃｒ−Ｔａ、Ｃｏ−Ｎｉ−Ｂ、Ｃｏ−Ｆｅ−Ｂ、Ｃｏ−Ｎｉ−Ｆｅ−Ｂ等が使用される。これらの中でも特にＣｏは保磁力、磁束密度が大きいために、高密度記録に適している。また、磁性金属にＣｏ−Ｎｉ等のＮｉ含有合金を使用した場合、Ｎｉの延性により、スチル寿命が延びるようになる。
【００３９】
上記磁性層の形成方法は、均一な薄膜が形成できれば問題なく、非磁性基体上に一般的な真空薄膜成形技術により形成することが可能であり、例えば、真空蒸着法、スパッタリング法等を用いることができるが、生産性から真空蒸着法が多用される。
【００４０】
このような磁性層の形成に真空蒸着法を用いる場合、蒸着用チャンバー内を１０^−６Ｔｏｒｒ程度まで排気した後、電子銃にて磁性層の原料の溶解を行い、その原料全体が溶解した時点で蒸着を始める。また、磁性層の磁気特性を制御するために、磁性層中に酸素を導入するには酸素、オゾン、亜酸化窒素から選ばれた酸化性ガスを蒸着チャンバー内に導入し蒸着部位にて放出すればよい。このように形成される磁性層の膜厚は、１００〜３００ｎｍ程度である。
【００４１】
上記金属又はこれらの合金は非磁性基体に直接被着するだけでなく、下地層を介して被着してもよい。ここでいう下地層とは、前記したような微粒子層の他に、場合によっては、基体上に直接又は表面に微粒子層を有する基体上に設けた、Ａｌ、Ｔｉ、Ｎｉ、Ｂｉ、Ｓｂ、Ｐｂ、Ｓｎ、Ｇａ、Ｉｎ、Ｃｄ、Ｇｅ、Ｓｉ、Ｔｌ等の金属を主体とする層をさす。この金属を主体とする層を用いることによって磁性層の耐食性、付着性及び電磁変換特性等を向上させることが可能である。
【００４２】
（保護層）
上述した磁性層への水分の進入を防ぎ、磁性層の腐食を防止することならびに潤滑性を付与することを目的に磁性層に保護層が設けられる。このような保護層には硬質炭素膜、ＳｉＯ膜、ＳｉＯ_Ｘ膜等が用いられ、このような材料の中でも、特に硬質炭素膜は、硬くヘッドによる磨耗が少ないために、好ましい。ここで、硬質炭素膜とは高次に炭素が結合した合成炭素膜のことをさし、具体的には、屈折率の値が１．９以上を有するのものである。このような屈折率を有するものは、その屈折率から硬度を近似することができ、例えば屈折率が１．９のときのビッカース硬度は６５０ｋｇ／ｍｍ^２である。
【００４３】
このような、屈折率１．９以上を有する硬質炭素膜の形成方法は、一般的な真空薄膜成形技術（プラズマＣＶＤ法、スパッタリング法、真空蒸着法等）により可能であるが、特にプラズマＣＶＤ法を用いることにより、膜質や組成のコントロールが容易で保護層をより緻密に成膜することが可能で磁性層が温度や湿度に影響されにくくなるため好ましい。
【００４４】
硬質炭素膜の形成方法について、プラズマＣＶＤ法を用いる場合を例に説明する。原反（磁性金属を蒸着した基体）を搬送させるチャンバー内を１０^−５Ｔｏｒｒ以下に排気した後、炭化水素ガスと必要に応じて添加ガスを、反応圧力として、１〜１０^−２Ｔｏｒｒになるように所定量を導入する。その導入量はチャンバーの容積とポンプの排気能力に依存するので必要に応じて適宜決定する。
【００４５】
炭化水素ガスとしては、特に制限はないが、取り扱い上常温常圧でガス状のものがよく、例えばメタン、エタン、プロパン、ブタン、ペンタン、エチレン、プロピレン、アセチレン、メチルアセチレンの少なくとも一種から選択される。シラン系や窒素系のガスは毒性を有していたり、腐食性のガスもありまた重合しても硬質炭素膜とはならないので望ましくない。
【００４６】
必要に応じて用いる添加ガスとしては、水素、ネオン、ヘリウム、アルゴンの少なくとも一種から選択される。その添加比率は炭化水素量に対し、添加ガス／炭化水素ガス（モル比）で１〜０．０１程度とすればよい。上記比率が大きすぎる、すなわち炭化水素ガスに対し添加ガス量が多すぎると成膜速度が低下するおそれがある。
【００４７】
放電電源は、１０ｋＨｚ〜４５０ｋＨｚの周波数が好ましく、更に５０ｋＨｚ〜２００ｋＨｚの周波数が好ましい。１０ｋＨｚより周波数が低いと長時間の運転が困難になる。一方、４５０ｋＨｚより周波数が高いと膜が緻密にならないおそれがある。特に直流に近い周波数では異常放電が発生した場合、イオンエネルギーが大きくなるためにテープに穴が空く等の不具合がある。
【００４８】
また、成膜中に原反を搬送させる場合にはテープがアース電位に接地されている冷却ドラムに沿って走行することが好ましい。放電空間を空中に浮いたままテープが走行した場合には、ベースフィルムの熱による変形を生じると共に付着したイオンがチャージアップして次のイオンが成膜できず、膜質としても柔らかく結果としてテープ特性も向上しない。
【００４９】
このように形成される保護層の膜厚は、４〜１５ｎｍ程度であることが好ましい。膜厚が厚すぎるとスペーシング損失が大きくなり、高密度記録媒体として適さない。一方、薄すぎると信頼性に問題を生じる場合がある。
【００５０】
【実施例】
以下、本発明の具体的実施例を示す。
【００５１】
試料
磁気記録媒体の試料の作成方法を、表２試料Ｎｏ１を例に挙げて説明する。
【００５２】
厚さが６μｍのポリエチレンテレフタレートのフィルムにＳｉＯ_２微粒子（平均粒子径１２ｎｍ）を１００×１０^４個／ｍｍ^２となるように樹脂と共に塗布した基体に、真空蒸着法により、１００ｎｍの膜厚となるように、Ｃｏ（コバルト）の蒸着を行い、これを繰り返して２００ｎｍの膜厚の磁性層を成形した。更にその上にプラズマＣＶＤ法により硬質炭素膜を成膜した。このときの反応ガスは、エチレンとＡｒ（流量比２：１）を用いて１００ｋＨｚの電源にて１０ｎｍの厚さに成膜した。別途後述する方法によって測定したこの硬質炭素膜の屈折率の値は２．１であった。また、成膜した硬質炭素膜の水素／炭素比をＥＲＤＡ（Ｅｌａｓｔｉｃ Ｒｅｃｏｉｌ Ｄｅｔｅｃｔｉｏｎ Ａｎａｌｙｓｉｓ）により測定した結果０．３であった。ついで表１に示す潤滑剤（試料Ｎｏ１の場合はＣ_１４Ｈ_２９ＣＯＯＣ_２Ｈ_４Ｃ_８Ｆ_１７）をＭＩＢＫ、ヘプタンの混合溶媒に溶解し、磁性面上に５ｍｇ／ｍ^２となるように塗布乾燥した。さらに基体の裏面にバックコート層を設けた後に、８ｍｍ幅に裁断することにより試料を作製した。
【００５３】
他の試料も同様にして作成した。ここで、試料Ｎｏ１４の磁性層の材料はＣｏ：Ｎｉ＝８：２（重量比）の合金である。また、試料Ｎｏ２２〜２４は硬質炭素膜を設けなかった。
【００５４】
なお、バックコート層の組成は以下の通りとした。
【００５５】
カーボンブラック（粒径 ８０ｎｍ） ７５重量部
カーボンブラック（粒径 ２０ｎｍ） ２０重量部
α−Ｆｅ_２Ｏ_３ ３重量部
塩化ビニル−酢酸ビニル−ビニルアルコール重合体 ４０重量部
ポリウレタン樹脂 ６０重量部
メチルエチルケトン ８００重量部
シクロヘキサノン ４８０重量部
トルエン ３２０重量部
ポリイソシアネート（固形分５０％） ４０重量部
【００５６】
【表１】

【００５７】
評価方法
このようにして得た８ｍｍビデオテープサンプルを温湿度の条件を変えた環境にて摩擦係数、スチル、シャトルテストの測定を行い、さらに、保存テスト、電磁変換特性を確認した。また、硬質炭素膜の硬度を測定するために屈折率を測定し、さらにその膜厚も測定した。
【００５８】
（摩擦係数）
摩擦係数の測定は、抱き角９０度のピン摩擦試験器にてオイラーの式により繰り返し摩擦係数を測定することにより評価した。ピンは２ｍｍφで表面性０．２ＳのＳＵＳ３０４を使用した。負荷荷重は１０ｇ、繰り返し回数は１００往復とした。また測定は−５℃、２０℃１０％ＲＨ、２０℃６０％ＲＨ、４０℃９０％ＲＨの４つの環境にて行った。
【００５９】
（スチル特性）
スチル特性は、ソニー社製Ｓ１５００デッキを使用し、８ＭＨｚの信号を記録した後、スチルモードにて出力が初期より−３ｄＢまで低下する時間を測定した。ここで測定は２０℃１０％ＲＨ、２０℃６０％ＲＨ、４０℃９０％ＲＨの３つの環境にて行った。
【００６０】
（シャトルテスト）
ソニー社製Ｓ１５００デッキを使用し、８ＭＨｚの信号を記録し、出力が初期より−３ｄＢまで低下するまでの繰り返しパス回数を測定した。ここで測定はスチル特性と同様の環境にて行った。
【００６１】
（保存テスト）
保存テストは、リール状態で試料を６０℃９０％ＲＨにて７日間保存した後に２０℃６０％ＲＨにて６時間放置後、摩擦係数を測定した。測定は上記摩擦の測定方法と同様に行った。但し、測定環境は２０℃６０％ＲＨである。
【００６２】
また、８ｍｍ幅、長さ１ｍの試料を同様に６０℃９０％ＲＨにて７日間保存し、保存前後の飽和磁化Ｂｍの変化率をＶＳＭ（Ｖｉｂｒａｔｉｎｇ Ｓａｍｐｌｅ Ｍａｇｎｅｔｍｅｔｅｒ）により測定し求めた。計算式は以下の通りである。
【００６３】
ΔＢｍ（％）＝（Ｂｍ（保存前）−Ｂｍ（保存後））／Ｂｍ（保存前）×１００
（電磁変換特性）
電磁変換特性（表２では電特と記載）は、ソニー社製Ｓ１５００デッキを使用し、８ＭＨｚの信号を記録再生して測定し評価した。ここで標準テープはＴＤＫ社製Ｈｉ８ビデオテープ（Ｐ６−１２０）を用いた。
【００６４】
（屈折率、膜厚）
Ｓｉウエハ上に表２と同一条件で成膜された硬質炭素膜の屈折率及び膜厚をエリプソメーター（溝尻光学工業所製）により測定した。前記したように、硬質炭素膜の屈折率を測定することによりその硬度を知ることができる。その方法としては、硬質炭素膜について、エリプソメーターにて屈折率を測定し、一方で微小硬度計（ＮＥＣ（株）社製）によりビッカース硬度を測定し、予め検量線を作成しておくことで屈折率から硬度を知ることができる。ここでは屈折率及び膜厚の値を記載した。
【００６５】
評価結果
表２に各試料について各評価項目に対する結果を示す。
【００６６】
【表２】

【００６７】
表２より磁性層上に保護層（硬質炭素膜）を有し、さらに一般式ＲＣＯＯ（ＣＨ_２）_ｎＲｆでかつＲは炭素数１４以上の直鎖のアルキル基、Ｒｆは炭素数８以上のパーフルオロアルキル基、ｎは２以上で表されるカルボン酸エステルを潤滑層に使用したものは高温高湿度の範囲での摩擦係数、スチル、シャトルの各特性、保存特性、電磁変換特性において良好な結果が得られた。また、低温、常温での結果も良好なことから、本発明に係る磁気記録媒体は、低温から高温多湿雰囲気での使用や保存においても高い耐久性や走行性を維持できることがわかる。磁性層にＣｏ−Ｎｉ合金を使用したもの（Ｎｏ．１４）については電磁変換特性が＋３．５ｄＢ未満と他のものより低いが、これは磁性層に依存するものであり、＋５．０ｄＢ以上のＤＶＣ規格を満たすものではないが、Ｈｉ８規格は十分に満たしている。
【００６８】
【発明の効果】
以上説明したように、本発明に係る金属薄膜型磁気記録媒体は、低温から高温高湿度の範囲で高い耐久性と耐候性、特に被コーティング面の耐久摩擦、シャトル特性、保存特性がよく、高密度記録媒体として優れている。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a metal thin-film magnetic recording medium, and more particularly, to a metal thin-film magnetic recording medium in which a lubricating layer having high durability in a range from low temperature to high temperature and high humidity is provided on a protective layer.
[0002]
[Prior art]
Conventional magnetic recording media in which a magnetic layer is formed by coating are generally widely used. These are generally produced by applying and drying a magnetic paint in which a magnetic material and other additives are dispersed in an organic binder such as a vinyl chloride-vinyl acetate copolymer, a polyester resin, and a polyurethane resin.
[0003]
On the other hand, a ferromagnetic metal material such as a Co-Ni alloy is formed on a film-like substrate such as polyethylene terephthalate (PET) by a vacuum thin film forming technique (a vacuum deposition method, a sputtering method, an ion plating method, etc.). Also, a so-called metal thin film type magnetic recording medium has been proposed. Such a metal thin film type magnetic recording medium can make the thickness of the magnetic layer extremely thin as compared with the conventional coating type magnetic recording medium, and is excellent in coercive force, squareness ratio, etc. Since the magnetic layer has excellent conversion characteristics and no magnetic binder such as an organic binder is present in the magnetic layer, the packing density of the magnetic material is high and the recording density can be improved, so that it has been put to practical use.
[0004]
However, since the metal thin-film magnetic recording medium is formed by depositing the magnetic metal directly on the substrate, the magnetic layer surface has a good smoothness and therefore has a substantial contact area and a lubricating property. Due to the absence, there is a problem in durability, including weather resistance, running performance, etc., such as an increase in friction coefficient. For this purpose, attempts have been made to improve durability and running properties by providing a carboxylic acid or its ester as a lubricating layer on the surface of the magnetic layer, but the carboxylic acid is ionized in a high-temperature and high-humidity atmosphere. However, there is a problem that the friction increases when stored in a high-temperature and high-humidity atmosphere because the carboxylic acid ester also has no water repellency.
[0005]
On the other hand, in order to improve such a defect, Japanese Patent Application Laid-Open No. 62-256218 discloses that a ferromagnetic metal thin film is formed on a nonmagnetic support, and a carboxylic acid perfluoroalkyl ester is formed on the ferromagnetic metal thin film. On a magnetic recording medium. " This application proposes a magnetic recording medium using a perfluoroalkyl carboxylate capable of maintaining a lubricating effect even at low to normal temperatures.
[0006]
[Problems to be solved by the invention]
However, although the above-mentioned publication improves the durability from room temperature to low temperature of 25 ° C. and −5 ° C., it does not discuss the durability in a high-temperature and high-humidity atmosphere. A lubricating layer that can be maintained has not been proposed.
[0007]
Therefore, the present invention has a protective layer on a magnetic layer that can maintain a low coefficient of friction and high durability even when used or stored in a low-temperature to high-temperature and high-humidity atmosphere and can also have high weather resistance. An object of the present invention is to provide a metal thin film magnetic recording medium having a novel lubricating layer thereon.
[0008]
[Means for Solving the Problems]
The present inventor has conducted intensive studies on lubricants in order to achieve the above object, and as a result, it has been found that a straight-chain saturated carboxylic acid ester having a specified number of carbon atoms is physically and chemically stable even in a high-temperature and high-humidity atmosphere. The present invention has been made based on the viewpoint.
[0009]
Specifically, this is achieved by the following configurations (1) to (6).
[0010]
(1) A metal thin film type magnetic layer and a protective layer are sequentially formed on a non-magnetic substrate, and a general formula
[0011]
Embedded image

[0012]
A magnetic recording medium comprising a lubricating layer represented by the formula:
[0013]
The magnetic recording medium obtained in this manner has a low friction coefficient, high durability and high weather resistance even in a low-temperature to high-temperature and high-humidity atmosphere by having the above configuration.
[0014]
(2) The magnetic recording medium according to the above (1), wherein the protective layer comprises a hard carbon film formed by a plasma CVD method.
[0015]
(3) The magnetic recording medium according to (1) or (2), wherein the magnetic material of the metal thin film type magnetic layer is Co (cobalt).
[0016]
(4) The magnetic recording medium according to any one of (1) to (3), wherein R of the carboxylic acid ester represented by Chemical Formula 2 is a linear alkyl group having 14 to 23 carbon atoms.
[0017]
(5) The magnetic recording medium according to any one of (1) to (4), wherein Rf of the carboxylic acid ester represented by Chemical Formula 2 is a perfluoroalkyl group having 8 to 21 carbon atoms.
[0018]
(6) The magnetic recording medium according to any one of (1) to (5), wherein n of the carboxylic acid ester represented by Chemical Formula 2 is 2 to 4.
[0019]
Here, the metal thin film type magnetic layer is a layer on which a ferromagnetic metal material such as Co or Co-Ni is applied by a vacuum thin film forming technique. The protective layer refers to a hard carbon film, a SiO film, a SiO _X film or the like provided on the metal thin film type magnetic layer, and is provided for the purpose of preventing corrosion of the magnetic layer. The hard carbon film can be formed by a vacuum deposition method, a sputtering method, a plasma CVD method, or the like, the SiO film can be formed by a vacuum deposition method, and the SiO _X film can be formed by a plasma CVD method.
[0020]
The hard carbon film can be formed by the method described above, but a magnetic recording medium having a protective layer formed by a plasma CVD method is particularly excellent in abrasion resistance.
[0021]
The magnetic material of the metal thin-film type magnetic layer is made of the above-mentioned metals or alloys, but those using Co have particularly good electromagnetic conversion characteristics and are advantageous for high-density recording media.
[0022]
The specific perfluoroalkyl carboxylate as in the constitutions (4) to (6) can improve the productivity because the raw material is easily industrially available.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
The magnetic recording medium according to the present invention will be specifically described below.
[0024]
(Lubricant layer)
The lubricating layer of the magnetic recording medium according to the present invention has a general formula RCOO (CH ₂ ) _n Rf, where R is a linear alkyl group having 14 or more carbon atoms, Rf is a perfluoroalkyl group having 8 or more carbon atoms, n Is composed of two or more carboxylic acid esters.
[0025]
When the alkyl group R in the general formula RCOO (CH ₂ ) _n Rf has 14 or more carbon atoms, the alkyl group R has excellent durability, but particularly preferably has 14 to 23 carbon atoms. If the number of carbon atoms is larger than 23, there is no difference in the effect (saturation), but it is difficult to obtain industrially, and therefore there is no industrial merit. Among them, those having 15 or 16 carbon atoms are most preferable because characteristics such as durability of the medium are particularly improved. If the alkyl group R has less than 14 carbon atoms, there is a problem that friction at normal temperature increases. This is because if the number of carbon atoms in the alkyl group is small, it is difficult for the lubricant to cover the entire coated surface (magnetic surface) because intramolecular aggregation of the lubricant is likely to occur, resulting in a mottled (sea-island-like unevenness) state and a low friction coefficient. It is believed that this will be uniform, resulting in increased friction. As a countermeasure, an excess of the coating surface that cannot be covered due to aggregation may be applied in advance, but the amount of the lubricant per unit area becomes too large, causing stick-slip and increasing friction, which is preferable. Absent.
[0026]
Further, R in the above general formula is an alkyl group, that is, a linear saturated hydrocarbon group. Even if R is a straight-chain, in the case of an unsaturated hydrocarbon group, that is, a hydrocarbon group having a double bond or triple bond in the molecule, if stored for a long period of time, oxidation and the like will proceed, and friction will increase. Would. Further, even when R is saturated, a branched so-called branched hydrocarbon group is difficult to be oriented due to the bulkiness due to the branching, and undesirably increases friction.
[0027]
On the other hand, Rf in the above general formula, that is, a perfluoroalkyl group preferably has 8 to 21 carbon atoms. If the number of carbon atoms is larger than this, there is no difference because the effect is saturated, but there is no industrial merit because the raw material is difficult to obtain industrially. Further, formation of the protective layer may be difficult due to problems such as solubility. Among them, those having 8 to 14 carbon atoms are particularly preferred. By such orientation of the perfluoroalkyl group, fluorine acting as a hydrophobic atom is arranged almost uniformly, and the entire application surface (magnetic surface) is covered with the lubricant, so that water is not removed. It becomes difficult to approach and water repellency can be obtained, resulting in excellent weather resistance. On the other hand, if the number of carbon atoms is less than 8, the perfluoroalkyl group is not sufficiently oriented, the cover of the coated surface is not sufficient, and the necessary water repellency cannot be obtained.
[0028]
Rf in the above general formula is a perfluoroalkyl group, that is, a saturated type. This is because, as described above, in the case where the molecule has an unsaturated bond such as a double bond or a triple bond in the molecule, if stored for a long period of time, oxidation and the like proceed, so that friction increases. Here, the perfluoroalkyl group may be linear or branched.
[0029]
In order to obtain such a carboxylic acid ester, a structure in which the alkyl group is a straight-chain, higher monocarboxylic acid having a saturated carbon number of R + 1 and a general formula in which the alkyl fluoride group is saturated is Rf (CH ₂ ) _n OH. May be synthesized using the above-mentioned fluorine alcohol. At this time, alcohol in which n is 2 or more is used. That is, n in the general formula of the carboxylic acid ester is 2 or more. The alcohol of n = 0 is decomposed after the synthesis of the alcohol, and therefore does not exist. The detailed reason is unknown, but when n = 1, there is a problem that the friction after storage deteriorates. In addition, when n exceeds 4, the effect is saturated and the difference hardly occurs, but it is difficult to obtain industrially and there is no industrial merit. Is
_{n-C 14 H 29 COOC 2} H 4 C 8 F 17, n-C 15 H 31 COOC 2 H 4 C 8 F 17,
_{n-C 16 H 33 COOC 2} H 4 C 8 F 17, n-C 17 H 35 COOC 2 H 4 C 8 F 17,
_{n-C 18 H 37 COOC 2} H 4 C 8 F 17, n-C 19 H 39 COOC 2 H 4 C 8 F 17,
_{n-C 20 H 41 COOC 2} H 4 C 8 F 17, n-C 21 H 43 COOC 2 H 4 C 8 F 17,
_{n-C 22 H 45 COOC 2} H 4 C 8 F 17, n-C 15 H 31 COOC 2 H 4 C 10 F 21,
_{n-C 15 H 31 COOC 2} H 4 C 11 F 23, n-C 15 H 31 COOC 2 H 4 C 12 F 25,
_{n-C 15 H 31 COOC 2} H 4 C 13 F 27, n-C 15 H 31 COOC 3 H 6 C 8 F 17,
_{n-C 15 H 31 COOC 4} H 8 C 8 F 17, n-C 18 H 37 COOC 2 H 4 C 10 F 21,
_{n-C 20 H 41 COOC 2} H 4 C 10 F 21
And the like.
[0030]
Further, such a carboxylic acid ester may contain a mixture of an alkyl group of ± 2 of the carbon number of the main component of 50% or more in the number of R, and also in Rf, the carbon number of the main component of 50% or more. Of ± 2 perfluoroalkyl groups. These mixing ratios are preferably in the range of 50/50 to 100/0 because the lubricity is balanced.
[0031]
The method for forming such a lubricating layer is as follows. For example, methanol, ethanol, butanol, isopropyl alcohol (IPA), acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclohexanone, cyclohexane , Tetrahydrofuran (THF), dimethylformamide (DMF), ethyl acetate, butyl acetate, dioxane, hexane, heptane, octane, toluene, xylene, ligroin, petroleum ether, and the like, and the resulting solution is dissolved on a surface of the protective layer. It may be applied or sprayed on and then dried later.
[0032]
The coating amount on the magnetic layer surface is preferably 0.5 to 10 mg / m ² as a lubricant amount. Particularly, 3 to 8 mg / m ² is preferable. By setting the above-mentioned application amount, running property, durability, and weather resistance are improved.
[0033]
When the applied amount is less than 0.5 mg / m ² , the amount of the lubricant is small, so that the unevenness is caused, and the friction coefficient fluctuates and increases, and the weather resistance is reduced. When the applied amount exceeds 10 mg / m ² , the lubricant becomes excessive. This causes stick-slip. There is a problem.
[0034]
(Non-magnetic substrate)
The non-magnetic substrate is not particularly limited as long as it can withstand the vapor deposition step, and is not particularly limited. Examples thereof include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, aramid, polyetheretherketone (PEEK), and polysulfone. Film. The thickness is appropriately selected depending on the application in which the magnetic recording medium is used. For example, when the magnetic recording medium is used as a video tape, the thickness is selected according to a recording time or a system required value, and is usually 5 to 40 μm. It is.
[0035]
Further, a fine particle layer may be provided on the substrate in order to control the surface roughness of the magnetic layer and, consequently, the surface roughness on the recording surface side of the medium. The fine particle layer is obtained by dispersing inorganic particles such as zirconia, silica, and alumina together with a resin in water or a solvent and coating the dispersion. The particle diameter of these inorganic particles is selected from 5 to 40 nm, and the density after coating may be about 1 × 10 ^{4 to} 100 × 10 ⁴ particles / mm ² .
[0036]
Further, a back coat layer may be provided on the surface of the substrate opposite to the surface on which the magnetic layer is provided.
[0037]
The back coat layer is formed by applying a back coat paint in which a binder resin and an inorganic compound and / or carbon black are mixed and dispersed in an organic solvent to the surface of the substrate opposite to the magnetic layer. The backcoat layer may have any paint composition as long as it is used for this type of magnetic recording medium. For example, the binder resin is a vinyl chloride copolymer, a polyurethane resin, an acrylic resin, an epoxy resin, a phenoxy resin, a polyester resin, or the like, and may be used alone or as a mixture, depending on the characteristics of the medium and the process conditions. It is appropriately selected. Examples of the carbon black include furnace carbon black and thermal carbon black, and examples of the inorganic compound include calcium carbonate, alumina, and α-iron oxide. The size of these particles may be appropriately selected based on the electric resistance, friction characteristics, and the like required for the medium. The organic solvent is, for example, a ketone or an aromatic hydrocarbon, and may be appropriately selected in consideration of the solubility of the binder resin used.
[0038]
(Metal thin film type magnetic layer)
The magnetic metal forming the metal thin film type magnetic layer is Co, Co-Ni, Co-Cu, Co-Pt, Co-Fe, Co-Cr, Co-Ni-Cr, Co-Ni-Fe, Co-Pt-Cr. , Co-Cr-Ta, Co-Ni-B, Co-Fe-B, Co-Ni-Fe-B and the like are used. Of these, Co is particularly suitable for high-density recording because of its large coercive force and magnetic flux density. When a Ni-containing alloy such as Co-Ni is used as the magnetic metal, the still life is extended due to the ductility of Ni.
[0039]
The method for forming the magnetic layer is not problematic as long as a uniform thin film can be formed, and can be formed on a non-magnetic substrate by a general vacuum thin film forming technique. For example, a vacuum evaporation method, a sputtering method, or the like is used. However, a vacuum deposition method is frequently used from the viewpoint of productivity.
[0040]
When a vacuum evaporation method is used to form such a magnetic layer, the inside of the evaporation chamber is evacuated to about 10 ⁻⁶ Torr, and then the raw material of the magnetic layer is dissolved with an electron gun. Start deposition with. In order to introduce oxygen into the magnetic layer to control the magnetic properties of the magnetic layer, an oxidizing gas selected from oxygen, ozone, and nitrous oxide is introduced into the deposition chamber and released at the deposition site. Just fine. The thickness of the magnetic layer thus formed is about 100 to 300 nm.
[0041]
The above metals or alloys thereof may be deposited not only directly on the non-magnetic substrate but also via an underlayer. The term “underlayer” as used herein means, in addition to the above-described fine particle layer, in some cases, Al, Ti, Ni, Bi, Sb, Pb provided directly on the substrate or on a substrate having a fine particle layer on the surface. , Sn, Ga, In, Cd, Ge, Si, Tl and the like. By using a layer mainly composed of this metal, it is possible to improve the corrosion resistance, adhesion, electromagnetic conversion characteristics, and the like of the magnetic layer.
[0042]
(Protective layer)
A protective layer is provided on the magnetic layer for the purpose of preventing the entry of moisture into the magnetic layer, preventing corrosion of the magnetic layer, and imparting lubricity. A hard carbon film, a SiO film, a SiO _X film, or the like is used for such a protective layer. Among such materials, a hard carbon film is particularly preferable because it is hard and has little wear by a head. Here, the hard carbon film refers to a synthetic carbon film in which carbon is bonded to a higher order carbon, and specifically, has a refractive index of 1.9 or more. Those having such a refractive index can approximate the hardness from the refractive index. For example, when the refractive index is 1.9, the Vickers hardness is 650 kg / mm ² .
[0043]
Such a method of forming a hard carbon film having a refractive index of 1.9 or more can be performed by a general vacuum thin film forming technique (plasma CVD method, sputtering method, vacuum deposition method, etc.). Is preferred because the film quality and composition can be easily controlled, the protective layer can be formed more densely, and the magnetic layer is less affected by temperature and humidity.
[0044]
A method for forming a hard carbon film will be described using a case where a plasma CVD method is used as an example. After evacuating the inside of the chamber for transferring the raw material (the substrate on which the magnetic metal is deposited) to 10 ⁻⁵ Torr or less, the reaction pressure of the hydrocarbon gas and, if necessary, the added gas becomes 1 to 10 ⁻² Torr. So as to introduce a predetermined amount. The introduction amount depends on the volume of the chamber and the pumping capacity of the pump, and is appropriately determined as necessary.
[0045]
The hydrocarbon gas is not particularly limited, but is preferably a gaseous gas at normal temperature and normal pressure in handling, and is, for example, selected from at least one of methane, ethane, propane, butane, pentane, ethylene, propylene, acetylene, and methylacetylene. You. Silane-based and nitrogen-based gases are not desirable because they are toxic, corrosive, and do not form a hard carbon film when polymerized.
[0046]
The additional gas used as necessary is selected from at least one of hydrogen, neon, helium, and argon. The addition ratio may be about 1 to 0.01 in terms of added gas / hydrocarbon gas (molar ratio) with respect to the amount of hydrocarbons. If the above ratio is too large, that is, if the amount of the added gas is too large relative to the hydrocarbon gas, the film formation rate may be reduced.
[0047]
The discharge power source preferably has a frequency of 10 kHz to 450 kHz, and more preferably has a frequency of 50 kHz to 200 kHz. If the frequency is lower than 10 kHz, long-time operation becomes difficult. On the other hand, if the frequency is higher than 450 kHz, the film may not be dense. In particular, when abnormal discharge occurs at a frequency close to DC, there is a problem that a hole is formed in the tape due to an increase in ion energy.
[0048]
In the case where the raw material is transported during the film formation, it is preferable that the tape runs along a cooling drum that is grounded to the ground potential. If the tape runs while floating in the air in the discharge space, the base film is deformed by heat and the attached ions are charged up and the next ion cannot be formed. Also does not improve.
[0049]
The thickness of the protective layer thus formed is preferably about 4 to 15 nm. If the film thickness is too large, the spacing loss increases, which is not suitable as a high-density recording medium. On the other hand, if it is too thin, a problem may occur in reliability.
[0050]
【Example】
Hereinafter, specific examples of the present invention will be described.
[0051]
Sample A method for preparing a sample of the magnetic recording medium will be described with reference to Sample No. 1 in Table 2 as an example.
[0052]
In thickness was coated with 6μm polyethylene terephthalate film to SiO ₂ fine particles (average particle size 12 nm) to 100 × 10 ⁴ cells / mm ² and comprising as a resin substrate by a vacuum deposition method, a thickness of 100nm Thus, Co (cobalt) was deposited, and this was repeated to form a magnetic layer having a thickness of 200 nm. Further, a hard carbon film was formed thereon by a plasma CVD method. As a reaction gas at this time, a film was formed to a thickness of 10 nm using a power supply of 100 kHz using ethylene and Ar (flow ratio: 2: 1). The value of the refractive index of this hard carbon film measured by a method described later separately was 2.1. Further, the hydrogen / carbon ratio of the formed hard carbon film was measured by ERDA (Elastic Recoil Detection Analysis), and as a result, was 0.3. Next, the lubricant shown in Table 1 (C ₁₄ H ₂₉ COOC ₂ H ₄ C ₈ F _{17 in} the case of sample No. 1) was dissolved in a mixed solvent of MIBK and heptane, and applied on the magnetic surface so as to be 5 mg / m ^2. Dried. Further, after providing a back coat layer on the back surface of the substrate, a sample was prepared by cutting to a width of 8 mm.
[0053]
Other samples were prepared in the same manner. Here, the material of the magnetic layer of Sample No. 14 is an alloy of Co: Ni = 8: 2 (weight ratio). Samples 22 to 24 were not provided with a hard carbon film.
[0054]
The composition of the back coat layer was as follows.
[0055]
Carbon black (particle size 80 nm) 75 parts by weight Carbon black (particle size 20 nm) 20 parts by weight α-Fe ₂ O ₃ parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol polymer 40 parts by weight Polyurethane resin 60 parts by weight Methyl ethyl ketone 800 parts by weight Parts by weight Cyclohexanone 480 parts by weight Toluene 320 parts by weight Polyisocyanate (solid content 50%) 40 parts by weight
[Table 1]

[0057]
Evaluation method The friction coefficient, still, and shuttle test of the 8 mm video tape sample thus obtained were measured in an environment where the temperature and humidity conditions were changed, and a storage test and electromagnetic conversion characteristics were further confirmed. . Further, the refractive index was measured to measure the hardness of the hard carbon film, and the film thickness was also measured.
[0058]
(Coefficient of friction)
The measurement of the coefficient of friction was evaluated by repeatedly measuring the coefficient of friction according to Euler's equation using a pin friction tester with a 90 ° embracing angle. The pin used was SUS304 having a diameter of 2 mm and a surface property of 0.2S. The applied load was 10 g, and the number of repetitions was 100 reciprocations. The measurement was performed in four environments of -5 ° C, 20 ° C 10% RH, 20 ° C 60% RH, and 40 ° C 90% RH.
[0059]
(Still characteristics)
The still characteristics were measured using an S1500 deck manufactured by Sony Corporation, recording a signal of 8 MHz, and measuring the time during which the output was reduced from the initial state to −3 dB in the still mode. Here, the measurement was performed in three environments of 20 ° C. 10% RH, 20 ° C. 60% RH, and 40 ° C. 90% RH.
[0060]
(Shuttle test)
Using an S1500 deck manufactured by Sony Corporation, an 8 MHz signal was recorded, and the number of repetitive passes until the output dropped from the initial stage to -3 dB was measured. Here, the measurement was performed in the same environment as the still characteristic.
[0061]
(Save test)
In the storage test, the sample was stored in a reel state at 60 ° C. and 90% RH for 7 days, then left at 20 ° C. and 60% RH for 6 hours, and then the friction coefficient was measured. The measurement was performed in the same manner as the above-mentioned method of measuring friction. However, the measurement environment is 20 ° C. and 60% RH.
[0062]
Similarly, a sample having a width of 8 mm and a length of 1 m was similarly stored at 60 ° C. and 90% RH for 7 days, and the change rate of the saturation magnetization Bm before and after the storage was measured by a VSM (Vibrating Sample Magnetmeter). The calculation formula is as follows.
[0063]
ΔBm (%) = (Bm (before storage) −Bm (after storage)) / Bm (before storage) × 100
(Electromagnetic conversion characteristics)
The electromagnetic conversion characteristics (described in Table 2 as "Denoku") were evaluated by recording and reproducing an 8 MHz signal using a Sony S1500 deck. Here, a Hi8 video tape (P6-120) manufactured by TDK was used as a standard tape.
[0064]
(Refractive index, film thickness)
The refractive index and the film thickness of the hard carbon film formed on the Si wafer under the same conditions as in Table 2 were measured by an ellipsometer (manufactured by Mizojiri Optical Industrial Co., Ltd.). As described above, the hardness can be known by measuring the refractive index of the hard carbon film. The method is to measure the refractive index of the hard carbon film with an ellipsometer and measure the Vickers hardness with a micro hardness meter (manufactured by NEC Corporation), and prepare a calibration curve in advance. The hardness can be known from the refractive index. Here, the values of the refractive index and the film thickness are described.
[0065]
Evaluation results Table 2 shows the results for each evaluation item for each sample.
[0066]
[Table 2]

[0067]
As shown in Table 2, a protective layer (hard carbon film) is provided on the magnetic layer, and furthermore, a general formula RCOO (CH ₂ ) _n Rf, R is a linear alkyl group having 14 or more carbon atoms, and Rf is a linear alkyl group having 8 or more carbon atoms. Those using a perfluoroalkyl group, where n is a carboxylic acid ester represented by 2 or more, in the lubricating layer have a good friction coefficient in the range of high temperature and high humidity, still and shuttle properties, storage properties and electromagnetic conversion properties. The result was obtained. In addition, the results obtained at low temperature and normal temperature show good results, indicating that the magnetic recording medium according to the present invention can maintain high durability and running properties even when used and stored in a low to high temperature and high humidity atmosphere. In the case of using a Co—Ni alloy for the magnetic layer (No. 14), the electromagnetic conversion characteristics are lower than +3.5 dB and lower than those of other magnetic layers, but this depends on the magnetic layer and is higher than +5.0 dB. Although it does not meet the DVC standard, the Hi8 standard does.
[0068]
【The invention's effect】
As described above, the metal thin-film magnetic recording medium according to the present invention has high durability and weather resistance in a range from low temperature to high temperature and high humidity, and particularly has good durability friction, shuttle property, and storage property of the coated surface, and high performance. Excellent as a density recording medium.

Claims (6)

A metal thin film type magnetic layer and a protective layer are sequentially formed on a non-magnetic substrate, and a general formula

A magnetic recording medium comprising a lubricating layer represented by the formula: 2. The magnetic recording medium according to claim 1, wherein the protective layer comprises a hard carbon film formed by a plasma CVD method. 3. The magnetic recording medium according to claim 1, wherein the magnetic material of the metal thin film type magnetic layer is Co (cobalt). 4. The magnetic recording medium according to claim 1, wherein R of the carboxylic acid ester represented by Chemical Formula 1 is a linear alkyl group having 14 to 23 carbon atoms. The magnetic recording medium according to any one of claims 1 to 4, wherein Rf of the carboxylic acid ester represented by Chemical Formula 1 is a perfluoroalkyl group having 8 to 21 carbon atoms. 6. The magnetic recording medium according to claim 1, wherein n of the carboxylic acid ester represented by Chemical Formula 1 is 2 to 4.