JP3568888B2 - Glass substrate for information recording medium, information recording medium, and method for producing them - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、高密度記録再生を可能にする情報記録媒体用ガラス基板、情報記録媒体、及びそれらの製造方法等に関するものである。
【０００２】
【従来の技術】
情報記憶装置に搭載される情報記録媒体の一つとして、ハードディスク（ＨＤＤ）に搭載される磁気ディスクが知られている。磁気ディスクにおいては近年、記録容量の向上に対する要請が強く、記録エリアの拡大や、高密度記録化が急務となっている。
【０００３】
記録エリアの拡大のためには、主表面の平滑な領域をできるだけ広く確保する必要がある。しかし、ガラス基板の研磨条件によって、基板外周端部において、ガラス基板の主表面に対して面が下がる面弛れ（面だれ）や、主表面に対する面の盛り上がり（以下***という）が生じ、このような形状をもつ磁気ディスクに対して磁気ヘッドを浮上走行させると、面弛れや***の箇所でヘッドが傾き、ヘッドの飛行が不安定になるのでクラッシュを起こすことがあり、また、面弛れや***の箇所は記録エリアの拡大の障害となっていた。これらの問題を解消するため、本願出願人は、ガラス基板の研磨条件（研磨加工圧力と研磨加工時間）を所定範囲とすることによって、***等を小さく抑える技術を開発し、先に出願を行っている（特開平５−８９４５９号公報）。また、ヘッドの飛行を安定させるため、面弛れを表す曲率を規定した技術が提案されている（特開平５−２９０３６５号公報）。
【０００４】
一方、高密度の記録を可能にする要因として、磁気ディスクに対する磁気ヘッドの浮上高さをできるだけ低くすることが必要であり、そのためには磁気ディスク表面をより平滑にする必要がある。
【０００５】
近年では磁気ディスクが平滑になった場合であっても磁気ヘッドの吸着を防止するために、磁気ヘッドにパッドを取り付けた磁気ヘッドや、より低浮上高さが実現可能となるＬＵＬ（Ｌｏａｄ／Ｕｎｌｏａｄ）方式の開発が盛んに行われている。このＬＵＬ方式の場合、通常、磁気ディスク表面は平滑であって、磁気ヘッドは磁気ディスクが停止しているときは、磁気ディスクの外側に待機しており、磁気ディスクが回転した後、ガイド機構を使って磁気ヘッドがディスクの外側からディスク面上に移動してきて記録再生を行うので、一般にＣＳＳ方式と比較して低浮上走行となる。ＬＵＬ方式の場合、磁気ヘッドの浮上安定性を確保するため基板の外周端部形状をＣＳＳ方式に比べ厳密に制御する必要がある。ＬＵＬ方式の場合、ヘッドの低浮上走行が可能であるので、ＣＳＳ方式に比べより高密度記録が可能となる。
【０００６】
ＬＵＬ方式による磁気ヘッドの低浮上化を実現するために、磁気ディスク用基板として、平坦性、平滑性に優れているガラス基板が注目されている。通常、ガラス基板の機械的耐久性を向上させるため、ガラス基板表層に含まれる一部のイオンを、そのイオンより大きなイオン半径を有する化学強化処理液中のイオンで置換することにより、ガラス基板を強化する化学強化処理が行われる。
【０００７】
【発明が解決しようとする課題】
しかしながら、従来においては化学強化処理の影響が考慮されていないか、あるいは、化学強化処理を施すことを前提としていないため、化学強化処理の施されたガラス基板を使用して磁気記録媒体を作製すると、基板の外周端部形状が原因で、磁気ヘッドの浮上走行が不安定となり、ヘッドクラッシュが発生するためヘッドの低浮上化が図れず、また、記録エリアの拡大も困難であることが判明した。
このため、特にＬＵＬ方式の磁気記録媒体の実現が困難であるという問題があった。なお、ＣＳＳ方式の場合も、磁気ヘッドの浮上安定性と、記録エリアの拡大のため、基板の外周端部形状を制御することが好ましい。
また、基板の内周端部においても、***等があると、磁気ディスクを固定するクランプ当たり、磁気ディスクが傾いたり、ゆがんで固定されるという問題があり、基板の機械的強度が弱い場合は、割れが発生する問題があり、基板の内周端部形状も制御することが望まれる。
【０００８】
本発明は上述の背景のもとでなされたものであり、所望の外周端部形状及び／又は内周端部形状を有する化学強化処理後のガラス基板を得ることが可能な情報記録媒体用ガラス基板の製造方法等の提供を第一の目的とする。
また、化学強化による機械的耐久性を有しつつ、高密度記録が可能な程度に十分な平滑度を有し、かつ、記録エリアを周縁にまで拡大することが可能な情報記録媒体等の提供を第二の目的とする。
【０００９】
【課題を解決するための手段】
本発明者らは鋭意研究の結果、ガラス基板に化学強化処理を施すと、ガラス表層のイオンがより大きなイオン半径を有するイオンと交換されることによって、ガラス基板に伸びが若干量発生し、基板の外周端部及び／又は内周端部の形状（エッジプロファイル：Ｅｄｇｅ Ｐｒｏｆｉｌｅ）が変化することを突き止め、特にこの化学強化処理によって発生した外周端部の形状変化が原因で、磁気ヘッドの浮上走行が不安定となり、ヘッドクラッシュが発生するためヘッドの低浮上化が図れず、また、記録エリアの拡大が困難となっていることを突き止めた。具体的には、図６（ａ）に示すように、ガラス基板１の外周端部及び／又は内周端部において、化学強化処理によって矢印の方向に伸びが発生するので、主表面２と面取部３との境界付近に図６（ｂ）に示すような***５を生じる。なお、面取部３と側壁部４との境界付近にも同様に***が生じるが、この***はヘッドや主表面との関係では通常問題とならない。
【００１０】
そして、さらに研究を重ねた結果、化学強化処理によって引き起こされるガラス基板の外周端部及び／又は内周端部の形状変化を、化学強化処理条件によって制御しうることを第一に見出した。また、化学強化処理前のガラス基板の外周端部形状及び／又は内周端部形状を、面取り加工の施されたガラス基板の主表面の研磨条件によって制御しうることを第二に見出した。そして、これらを利用することで、所望の外周端部形状及び／又は内周端部形状を有する化学強化処理後のガラス基板が得られることを見出し本第一発明を完成するに至った。
また、化学強化処理後のガラス基板の外周端部形状を、所定の数値範囲を満たす形状とすることによって、磁気ヘッドの浮上走行が安定し、ヘッドクラッシュを起こすことなくヘッドの低浮上化が図れ、また、記録エリアの拡大が図れること、及びこれらのことが特にＬＵＬ方式の磁気記録媒体について極めて有効であることを見出し本第二発明を完成するに至った。
【００１１】
本発明は以下の構成を有する。
【００１２】
（構成１）化学強化処理によって引き起こされるガラス基板の少なくとも外周端部及び／又は内周端部の形状変化と、化学強化処理条件との関係を予め把握する工程と、前記関係に基づいてガラス基板に化学強化処理を施す工程と、を有することを特徴とする情報記録媒体用ガラス基板の製造方法。
【００１３】
（構成２）化学強化処理によって引き起こされるガラス基板の少なくとも外周端部及び／又は内周端部の形状変化と、化学強化処理条件との関係を予め把握する工程と、前記化学強化処理によるガラス基板の外周端部及び／又は内周端部の形状変化を見込んで、化学強化処理前のガラス基板の外周端部及び／又は内周端部の形状を決定し、この決定した外周端部及び／又は内周端部の形状を有する化学強化処理前のガラス基板を得る工程と、上記で得られた化学強化処理前のガラス基板に化学強化処理を施して、所望の外周端部及び／又は内周端部形状を有する化学強化処理後のガラス基板を得る工程と、を有することを特徴とする情報記録媒体用ガラス基板の製造方法。
【００１４】
（構成３）前記化学強化処理によって引き起こされるガラス基板の外周端部及び／又は内周端部の形状変化が少ない化学強化処理条件で、前記化学強化処理を行うことを特徴とする構成１又は２に記載の情報記録媒体用ガラス基板の製造方法。
【００１５】
（構成４）前記化学強化処理は、化学強化によりガラス基板表層に生ずる圧縮応力層の深さが３〜１００μｍとなり、化学強化によりガラス基板表層に生ずる圧縮応力の値が１〜１５ｋｇ／ｍｍ２となり、かつ、化学強化によりガラス基板内部に生ずる引張応力の値が４．５ｋｇ／ｍｍ２以下となる化学強化処理条件で行うことを特徴とする構成１乃至３の何れか一に記載の情報記録媒体用ガラス基板の製造方法。
【００１６】
（構成５）前記化学強化処理条件が、化学強化処理における処理温度及び処理時間であることを特徴とする構成１乃至４の何れか一に記載の情報記録媒体用ガラス基板の製造方法。
【００１７】
（構成６）前記処理温度は２８０〜４００℃の範囲、処理時間は０．５〜５時間の範囲であることを特徴とする構成５記載の情報記録媒体用ガラス基板の製造方法。
【００１８】
（構成７）面取り加工の施されたガラス基板の主表面の研磨条件と、この主表面研磨によって得られるガラス基板の外周端部及び／又は内周端部形状との関係を予め把握しておき、この関係に基づいてガラス基板の主表面の研磨条件を制御して、前記化学強化処理前のガラス基板を得ることを特徴とする構成２乃至６の何れか一に記載の情報記録媒体用ガラス基板の製造方法。
【００１９】
（構成８）前記ガラス基板の主表面の研磨条件を、研磨後のガラス基板の外周端部及び／又は内周端部形状が、ガラス基板の主表面に対して面下がりの状態になる研磨条件とすることを特徴とする構成７記載の情報記録媒体用ガラス基板の製造方法。
【００２０】
（構成９）ガラス基板の主表面に対して面下がりの状態になる前記研磨条件が、硬度６０〜８０（Ａｓｋｅｒ−Ｃ）の軟質ポリシャを用い、研磨時のガラス基板に対する加工面圧を４０〜１５０ｇ／ｃｍ２とする条件であることを特徴とする構成８記載の情報記録媒体用ガラス基板の製造方法。
【００２１】
（構成１０）化学強化処理を施された情報記録媒体用ガラス基板であって、化学強化処理後のガラス基板の外周端部及び／又は内周端部形状が、外周端部及び／又は内周端部の所定領域において、前記ガラス基板の主表面の平坦面を基準面（ゼロ）として、±０．３５μｍの範囲内に収まる形状であることを特徴とする情報記録媒体用ガラス基板。
【００２２】
（構成１１）化学強化処理を施された情報記録媒体用ガラス基板であって、化学強化処理後の外周端部形状が、グライド領域の外周端から一定間隔離れた記録エリア内の点までの領域において、前記ガラス基板主表面の平坦面を基準面（ゼロ）とした場合、最も高点（Ｓｋｉ−ｊｕｍｐ（スキージャンプ）点）の値（Ｓｋｉ−ｊｕｍｐ（スキージャンプ）値）が±０．３５μｍ以内で、かつ、前記平坦面を基準面とした場合のグライド領域の外周端位置（Ｒｏｌｌ−Ｏｆｆ（ロールオフ）点）の値（Ｒｏｌｌ−Ｏｆｆ（ロールオフ）値）が±０．３５μｍ以内であることを特徴とする構成１０に記載の情報記録媒体用ガラス基板。
【００２３】
（構成１２）化学強化によってガラス基板表層に生じた圧縮応力層の深さが３〜１００μｍであり、化学強化によってガラス基板表層に生じた圧縮応力の値が１〜１５ｋｇ／ｍｍ２であり、かつ、化学強化によってガラス基板内部に生じた引張応力の値が４．５ｋｇ／ｍｍ２以下であることを特徴とする構成１０又１１に記載の情報記録媒体用ガラス基板。
【００２４】
（構成１３）構成１乃至９のいずれかに記載の方法によって得られる情報記録媒体用ガラス基板の表面に、少なくとも記録層を形成する工程を有することを特徴とする情報記録媒体の製造方法。
【００２５】
（構成１４）構成１０乃至１２のいずれかに記載の情報記録媒体用ガラス基板の表面に、少なくとも磁性層を形成したことを特徴とする情報記録媒体。
【００２６】
（構成１５）ＬＵＬ（ロード・アンロード）方式の磁気記録媒体であることを特徴とする構成１４記載の情報記録媒体。
【００２７】
【作用】
構成１によれば、化学強化処理によって引き起こされるガラス基板の外周端部の形状変化（特にガラス基板の厚み方向の変化量）と化学強化処理条件との関係を予め把握しておき、この関係に基づいてガラス基板の化学強化処理を行うことによって、化学強化処理によって引き起こされるガラス基板の外周端部の形状変化を、化学強化処理条件によって制御することが可能となる。
なお、これらのことは、ガラス基板の内周端部についても同様である。
化学強化処理としては、ガラス基板表層に含まれる一部のイオンを、そのイオンより大きなイオン半径を有する化学強化処理液中のイオンで置換することにより化学強化を行うイオン交換による化学強化処理法や、ガラス基板表層に含まれるアルカリイオンを除去することにより化学強化を行う脱アルカリ処理による化学強化処理法等が挙げられる。イオン交換による化学強化処理法の場合、ガラス基板の面内方向に伸びが発生するので主表面に対する形状変化量は正の値（***する方向）になり、脱アルカリ処理による化学強化処理法の場合は、ガラス基板が面内方向に縮むので主表面に対する形状変化量は負の値（面弛れの方向）になる。ガラス基板の内周端部の形状変化量は、外周端部の形状変化量に比べ１割〜２割程度小さい。
【００２８】
構成２によれば、構成１の効果に加え、化学強化処理によるガラス基板の外周端部の形状変化を見込んで、この化学強化処理による外周端部の形状変化を相殺しうる外周端部の形状変化を有する化学強化処理前のガラス基板を用いることによって、化学強化処理後のガラス基板の外周端部の形状をより厳密かつ所望の形状に制御することが可能となる。
なお、これらのことは、ガラス基板の内周端部についても同様である。
【００２９】
構成３によれば、化学強化処理によって引き起こされるガラス基板の外周端部の形状変化が少ない化学強化処理条件で化学強化処理を行うことによって、例えば、化学強化処理前のガラス基板の外周端部が平坦であれば、化学強化処理によって引き起こされるガラス基板の外周端部の形状変化を少なく抑えることが可能である。また、例えば、構成２に記載のように、化学強化処理によるガラス基板の外周端部の形状変化を相殺しうる外周端部の形状変化を有する化学強化処理前のガラス基板を用いる場合であっても、化学強化処理前後におけるガラス基板の外周端部の形状変化が小さいので、大きな形状変化を伴う場合に比べ、外周端部形状が制御しやすく、形状変化のバラツキが少なく処理の安定性の面で優れる。
なお、これらのことは、ガラス基板の内周端部についても同様である。
【００３０】
構成４によれば、第一に、化学強化によりガラス基板表層に生ずる圧縮応力層深さを３〜１００μｍとすることによって、好ましいガラス基板の機械的強度を有しつつ、しかも化学強化処理を施したときの外周端部の形状変化量を低く抑えることができる。
圧縮応力層の深さが３μｍ未満の場合、ガラス基板の強度が弱くなる（傷に対する耐久性や、耐破壊特性が劣化する）ので好ましくなく、１００μｍを超える場合、化学強化処処理を施したときの外周端部の形状変化量が大きくなるので、外周端部形状を制御しにくくなるため好ましくない。好ましい圧縮応力層の深さは４０〜８０μｍであり、より好ましくは５０〜７０μｍである。
第二に、化学強化によりガラス基板表層に生ずる圧縮応力の値を１〜１５ｋｇ／ｍｍ２とし、化学強化によりガラス基板内部に生ずる引張応力の値を４．５ｋｇ／ｍｍ２以下とすることによって、ガラス基板の強度及び経時破損に対する耐久性を向上させることができる。
圧縮応力の値が１ｋｇ／ｍｍ２未満の場合、ガラス基板の強度が弱くなるく（傷に対する耐久性や、耐破壊特性が劣化する）ので好ましくなく、１５ｋｇ／ｍｍ２を超えた場合、化学強化処理を施したときの外周端部の形状変化量が大きくなるので、外周端部形状を制御しにくくなるため好ましくない。
また、引張応力の値が、４．５ｋｇ／ｍｍ２を超えた場合、化学強化処理を施したときの外周端部の形状変化量が大きくなるので、外周端部形状を制御しにくくなるため好ましくない。
より好ましくは、化学強化によってガラス基板表層に生ずる圧縮応力層の深さが４０〜８０μｍ、化学強化によってガラス基板表層に生ずる圧縮応力の値が３〜１４ｋｇ／ｍｍ２、かつ、化学強化によってガラス基板内部に生ずる引張応力の値が２．５ｋｇ／ｍｍ２以下となる化学強化処理条件が、ガラス基板の機械的強度、端部形状の制御の点で好ましい。
なお、圧縮応力層の深さ、圧縮応力値、張応応力値を最適なバランスにすることで、上記効果はさらに顕著になる。
なお、これらのことは、ガラス基板の内周端部についても同様である。
【００３１】
構成５によれば、化学強化処理条件である処理温度及び処理時間を所定の範囲内とすることによって、化学強化処理によるガラス基板の外周端部及び／又は内周端部の形状変化量を所定の範囲内に抑えることが容易に可能となる。
なお、化学強化処理条件としては、処理温度、処理時間の他に、溶融塩の種類やその混合比などの条件があるが、これらのうち、処理温度、処理時間は、溶融塩の種類や混合比に比べて、簡単に調整でき、したがって、量産性や作業性の観点から有効な条件である。
【００３２】
構成６に示すように、具体的な化学強化処理条件は、処理温度を２８０〜４００℃の範囲とし、処理時間を０．５〜５時間の範囲とすることが好ましい。
処理温度が２８０℃未満の場合、溶融塩の融点以下となるので好ましくなく、４００℃を超える場合、処理時間が短くなり作業性が悪くなるので好ましくない。 また、処理時間は、０．５時間未満の場合、作業性が悪くなるので好ましくなく、５時間を超える場合、生産性が悪くなるので好ましくない。
なお、化学強化処理によるガラス基板の外周端部及び／又は内周端部の形状変化量を低く抑える観点から好ましい処理温度及び処理時間は、ガラス基板の組成や化学強化処理液の組成等によって異なるので一概に言えないが、例えば、処理温度を３２０〜３８０℃、好ましくは処理温度を３４０〜３６０℃の範囲とし、処理時間を１〜４時間の範囲とすることが好ましい。
【００３３】
構成７によれば、面取り加工の施されたガラス基板の主表面の研磨条件と、主表面研磨によって得られるガラス基板の外周端部形状及び／又は内周端部形状との関係を予め把握しておき、この関係に基づいてガラス基板の主表面の研磨条件を制御することによって、所望の外周端部形状及び／又は内周端部形状を有する化学強化処理前のガラス基板を容易かつ高精度で得ることが可能となる。
【００３４】
構成８によれば、ガラス基板の主表面の研磨条件を、研磨後のガラス基板の外周端部形状が、図１に示すようなガラス基板１の主表面２に対して面下がりの状態になる研磨条件とすることによって、化学強化処理による外周端部の形状変化を相殺しうる外周端部形状を有する化学強化処理前のガラス基板を容易かつ高精度で得ることが可能となる。
なお、これらのことは、ガラス基板の内周端部についても同様である。
【００３５】
構成９によれば、硬度６０〜８０（Ａｓｋｅｒ−Ｃ）の軟質ポリシャを用い、研磨時のガラス基板に対する加工面圧を４０〜１５０ｇ／ｃｍ２とすることによって、ガラス基板の主表面に対して面下がりの状態である外周端部形状を有する化学強化処理前のガラス基板を容易かつ高精度で得ることが可能となる。また、外周端部形状の制御が容易である。
なお、他の研磨条件が同じであれば、ポリシャ（研磨パッド）の硬度を硬くするに従い外周端部形状が面下がり形状になる傾向がある。また、加工面圧が高くなるに従い外周端部形状が***形状になる傾向がある。さらに、周速が早い程外周端部形状が面下がり形状になる傾向がある。
なお、研磨装置の構造、大きさや、研磨剤の量などの研磨条件によっても外周端部形状は変化するが、ポリシャの硬度による外周端部形状の制御は制御性が良く、制御が容易で、制御できる幅も大きい。したがって、ポリシャの硬度による外周端部形状の制御を主とし、加工面圧や周速による外周端部形状の制御を副とすることが好ましい。
これらのことはガラス基板の内周端部についても同様である。
【００３６】
構成１０によれば、化学強化処理後のガラス基板の外周端部形状を、外周端部の所定領域において、前記ガラス基板の主表面の平坦面を基準面（ゼロ）として、±０．３５μｍの範囲内（−０．３５μｍ〜＋０．３５μｍ）に収まる形状とすることによって、磁気ヘッドの浮上走行が安定し、ヘッドクラッシュを起こすことなくヘッドの低浮上化（高密度記録再生）が図れ、また、記録エリアの拡大が図れる。つまり、化学強化処理後のガラス基板の外周端部形状について、記録エリアの拡大や高密度記録化に支障をきたさない程度の平坦性が得られる。このため、特にＬＵＬ方式の磁気記録媒体に対して極めて有効である。
なお、外周端部の所定領域は任意に定めることができるが、外周端部において平坦性が損なわれる領域、すなわち、ガラス基板の主表面の平坦面を基準面とした場合基準面からのずれが大きい領域を所定領域とすることが好ましい。
具体的には、例えば、記録エリア（通常主表面の平坦性が確保させるエリア）の外周端から、グライド領域の外周端までの領域を、所定領域と定めることができる。また、例えば、基板の側壁部から記録エリアの外周端よりも内側までの領域を、所定領域と定めることもできる。
外周端部形状は、より好ましくは基準面に対し±０．２０μｍ以内（−０．２０〜０．２０μｍ）、さらに好ましくは基準面に対し±０．１０μｍ以内（−０．１０〜０．１０μｍ）の範囲内に収まる形状とすることが望ましい。
なお、これらのことは、ガラス基板の内周端部についても同様である。
【００３７】
構成１１によれば、化学強化処理後の外周端部形状が、グライド領域の外周端から一定間隔離れた記録エリア内の点までの領域において、ガラス基板主表面の平坦面を基準面（ゼロ）とした場合、最も高点（Ｓｋｉ−ｊｕｍｐ点）の値（Ｓｋｉ−ｊｕｍｐ値）が±０．３５μｍ以内で、かつ、前記平坦面を基準面とした場合のグライド領域の外周端位置（Ｒｏｌｌ−Ｏｆｆ点）の値（Ｒｏｌｌ−Ｏｆｆ値）が±０．３５μｍ以内である形状とするとすることによって、構成１０の効果が得られるとともに、Ｓｋｉ−ｊｕｍｐ点、Ｒｏｌｌ−Ｏｆｆ点といった基準点に着目して数値管理を行うことで、製造工程における製品管理が容易となる。
ここで、Ｓｋｉ−ｊｕｍｐ値とは、基板の外周端部形状が、ガラス基板の主表面の平坦面を基準とした場合の最も高い点（Ｓｋｉ−ｊｕｍｐ点）の値をいい、Ｒｏｌｌ−Ｏｆｆ値とは、前記平坦面を基準面とした場合のグライド領域の外周端位置における輪郭線上点（Ｒｏｌ１−Ｏｆｆ点）の値をいう。詳しくは、以下のように測定されるものである。
図２に示すように、円板状のガラス基板の中心を通り、主表面に垂直な面でガラス基板を切断した断面を考える。この断面において、主表面の輪郭線上の記録エリア内に２点の基準点を設定し、中心から近い順にＲｌ、Ｒ２とする。また、記録エリアの外周端部からさらに外周方向に一定の距離のマージンをとった点Ｒ３（グライド領域の外周端位置）を設定する。次に、点Ｒｌと点Ｒ２とを結び、その延長線を描く。そうしたときに、点Ｒ２から点Ｒ３までの領域において、基板の輪郭線上の点と、直線Ｒ１Ｒ２（又はその延長線）との距離を測る。その距離が正の方向に最も高いところの基板の輪郭線上の点ＳがＳｋｉ−ｊｕｍｐ（スキージャンプ）点であり、その距離ｓの値がＳｋｉ−ｊｕｍｐ値である。また、点Ｒ３の位置における輪郭線上点ＲがＲｏｌｌ−Ｏｆｆ（ロールオフ）点であり、点Ｒと直線Ｒ１Ｒ２（又はその延長線）との距離ｒがＲｏｌｌ−Ｏｆｆ値である。
なお、図３に示すように、Ｓｋｉ−ｊｕｍｐ値は若干マイナスとなることがありこの場合Ｓｋｉ−ｊｕｍｐは面の下がりを示す。また、図４に示すように、Ｒｏｌｌ−Ｏｆｆ値はプラスとなることがありこの場合Ｒｏｌｌ−Ｏｆｆは面の***を示す。なお、図４は、Ｓｋｉ−ｊｕｍｐ値とＲｏｌｌ−Ｏｆｆ値が一致する場合である。
【００３８】
なお、基板のサイズに応じて、上記点Ｒｌ、Ｒ２、Ｒ３を適宜選択する。例えば、外径サイズが２．５インチ、３．０インチ、３．５インチの基板の場合、Ｒ３点は、基板の側壁面（側壁部）から内側に１ｍｍの位置に定める。また、外径サイズが２．５インチ（外径６５ｍｍφ）の基板の場合、例えば、基板の中心からの距離が、それぞれ、２３ｍｍの点（Ｒ１）、２７ｍｍの点（Ｒ２）、３１．５ｍｍの点（Ｒ３）、３２．５ｍｍの点（側壁面）のように定めることができる。
【００３９】
Ｓｋｉ−ｊｕｍｐ値が−０．３５μｍ〜＋０．３５μｍの範囲を超える場合、磁気ヘッドの浮上安定性が悪くなり、ひどい場合はヘッドクラッシュが発生し磁気ディスクドライブに搭載できなくなるので好ましくない。
また、Ｒｏｌｌ−Ｏｆｆ値が−０．３５μｍ〜０．３５μｍの範囲を超える場合、上述と同様、磁気ヘッドの浮上安定性が悪くなり、ひどい場合はヘッドクラッシュが発生し、磁気ディスクドライブに搭載できなくなるので好ましくない。
【００４０】
より好ましいＳｋｉ−ｊｕｍｐ値、Ｒｏｌｌ−Ｏｆｆ値は、それぞれ、±０．２０μｍ以内（−０．２０〜０．２０μｍ）、さらに好ましくは、±０．１０μｍ以内（−０．１０〜０．１０μｍ）である。
【００４１】
構成１２によれば、第一に、化学強化によりガラス基板表層に生ずる圧縮応力層深さを３〜１００μｍとすることによって、好ましいガラス基板の機械的強度を有する情報記録媒体用ガラス基板が得られる。
圧縮応力層の深さが３μｍ未満の場合、ガラス基板の強度が弱くなる（傷に対する耐久性や、耐破壊特性が劣化する）ので好ましくなく、１００μｍを超える場合、化学強化処処理を施す際の形状変化量が大きくなり、良好な外周端部形状を有する基板が得られないので好ましくない。好ましい圧縮応力層の深さは４０〜８０μｍであり、より好ましくは５０〜７０μｍである。
第二に、化学強化によりガラス基板表層に生ずる圧縮応力の値が１〜１５ｋｇ／ｍｍ２とし、化学強化によりガラス基板内部に生ずる引張応力の値が４．５ｋｇ／ｍｍ２以下とすることによって、ガラス基板の強度及び経時破損に対する耐久性が向上するので好ましい。
圧縮応力の値が１ｋｇ／ｍｍ２未満の場合、ガラス基板の強度が弱くなるく（傷に対する耐久性や、耐破壊特性が劣化する）ので好ましくなく、１５ｋｇ／ｍｍ２を超えた場合、化学強化処理を施す際の形状変化量が大きくなり、良好な外周端部形状を有する基板が得られないので好ましくない。
また、引張応力の値が、４．５ｋｇ／ｍｍ２を超えた場合、化学強化処理を施す際の形状変化量が大きくなり、良好な外周端部形状を有する基板が得られないので好ましくない。
より好ましくは、化学強化によってガラス基板表層に生ずる圧縮応力層の深さが４０〜８０μｍ、化学強化によってガラス基板表層に生ずる圧縮応力の値が３〜１４ｋｇ／ｍｍ２、かつ、化学強化によってガラス基板内部に生ずる引張応力の値が２．５ｋｇ／ｍｍ２以下となる化学強化処理条件が、ガラス基板の機械的強度、端部形状の制御の点で好ましい。
なお、圧縮応力層の深さ、圧縮応力値、張応応力値を最適なバランスにすることで、上記効果はさらに顕著になる。
【００４２】
構成１３によれば、ガラス基板の外周端面形状が平坦で、記録エリアを拡大できる情報記録媒体が得られる。また、内周端面形状が平坦で、基板の割れを防止し、情報記録媒体を磁気記憶装置に正しく装着することができる。
【００４３】
構成１４によれば、ガラス基板の外周端面形状が平坦で、記録エリアを拡大でき、かつ、高密度記録が可能な磁気記録媒体が得られる。また、内周端面形状が平坦で、基板の割れを防止し、情報記録媒体を磁気記憶装置に正しく装着することができる。
【００４４】
構成１５のように、本発明は、磁気ヘッドの超低浮上化が可能なＬＵＬ（ロード・アンロード）方式の磁気記録媒体に適用することによって、最もその効果が発揮される。
【００４５】
【発明の実施の形態】
（実施例１）
実施例１では、化学強化処理条件と、基板の外周端部形状の変化量、基板の外径・内径の変化量等、圧縮応力層の厚さ、圧縮応力値、引張応力値、及び基板の抗折強度との関係を求めた。
【００４６】
端面鏡面研磨後に、主表面を精密研磨（ポリッシング）された３．５インチ径（９５ｍｍφ）及び２．５インチ径（６５ｍｍφ）のガラス基板を複数枚用意し、化学強化処理条件（強化温度、強化時間）を変化させたときの、基板の内径・外径変化量及び、Ｓｋｉ−ｊｕｍｐ値を測定した。
なお、化学強化処理前の基板外周端部がほぼ平坦である（したがって、Ｓｋｉ−ｊｕｍｐ値及びＲｏｌｌ−Ｏｆｆ値もともにほぼゼロである）基板を使用した。また、２．５インチ径の場合、Ｒ３点は側壁面４から内側に１ｍｍの位置（基板の中心からの距離が３１．５ｍｍの位置）に定め、Ｒ２点は側壁面４から内側に５．５ｍｍの位置（基板の中心からの距離が２７ｍｍの位置）に定めた。３．５インチ径の場合は、Ｒ３点は側壁面４から内側に１ｍｍの位置（基板の中心からの距離が４６．５ｍｍの位置）に定め、Ｒ２点は側壁面４から内側に５．５ｍｍの位置（基板の中心からの距離が４２ｍｍの位置）に定めた（図２）。そして、Ｓｋｉ−ｊｕｍｐ値は点Ｒ２Ｒ３間の領域において最も高点となる測定値とし、Ｓｋｉ−ｊｕｍｐ変化量は化学強化処理前後のＳｋｉ−ｊｕｍｐ値の差から求めた。Ｓｋｉ−ｊｕｍｐ値は表面粗さ測定器（サ−フテストＳＶ−６２４：ミットヨ社製）で測定した。
また、基板の内径・外径変化量は、化学強化処理前後の基板の内径及び外径寸法差を計算した値で、基板の内外径はマイクロメーターで測定した。
化学強化溶液は、硝酸カリウム（６０ｗｔ％）と硝酸ナトリウム（４０ｗｔ％）とを混合したものを使用した。
表１に３．５インチ径の基板についての結果を示し、表２に２．５インチ径の基板についての結果を示す。
【００４７】
【表１】
上記結果が示すように化学強化条件が強くなる（温度が高くなる、強化時間が長くなる、応力が大きくなる）に従い、基板の外径・内径変化量が大きくなり、Ｓｋｉ−ｊｕｍｐ変化量も大きくなることがわかった。
従って、磁気ディスク用ガラス基板に要求される機械的・化学的耐久性を満足する範囲内で化学強化処理条件を決定し、上記で求めた強化条件と、Ｓｋｉ−ｊｕｍｐ変化量との相関関係から、化学強化処理条件によって引き起こされるＳｋｉ−ｊｕｍｐ量を見込んで、化学強化処理前の端部形状をラッピング工程、およびポリッシング工程の合わせ込みによって所定の端部形状にすることによって、厳密な端部形状の制御が可能になる。
なお、磁気ディスク用ガラス基板として使用するために必要な抗折強度は、３．５インチ径の場合、１５〜２０ｋｇｆ程度である（したがって試料１−１〜１−７はいずれも十分な抗折強度を有する）ことから、Ｓｋｉ−ｊｕｍｐ変化量が少ない（０〜０．０１０μｍ）化学強化条件（３４０〜３６０℃、１．５〜２ｈｒ）で、化学強化処理することがガラス基板の外周端部形状の変化を小さく抑える上で良好であることがわかり、Ｓｋｉ−ｊｕｍｐ変化量がより少ない（０〜０．００４μｍ）化学強化条件（３４０℃、１．５〜２ｈｒ）がより好ましいことがわかる。
また、２．５インチ径の場合も同様で、磁気ディスク用ガラス基板として使用するために必要な抗折強度は、１０〜１５ｋｇｆ程度である（したがって試料２−１〜２−８はいずれも十分な抗折強度を有する）ことから、Ｓｋｉ−ｊｕｍｐ変化量が少ない（０〜０．００４μｍ）化学強化条件（３４０〜３６０℃、０．６〜２ｈｒ）がより好ましいことがわかる。
以上の結果から、端部形状変化量（Ｓｋｉ−ｊｕｍｐ変化量）が少なく、機械的強度を満足するためのより好ましい化学強化処理条件は、化学強化によりガラス基板表層に生ずる圧縮応力層の深さが４０〜８０μｍ、化学強化によりガラス基板表層に生ずる圧縮応力の値が３〜１４ｋｇ／ｍｍ２、かつ、化学強化によりガラス基板内部に生ずる引張応力の値が２．５ｋｇ／ｍｍ２以下であることが上記結果から言える。
【００４９】
（実施例２）
実施例２では、ガラス基板の主表面を研磨する際に使用する研磨パッドのポリシャの硬度と外周端部形状との関係を調べた。
図５及び表３にポリシャの硬度とＲｏｌｌ−Ｏｆｆ値との関係を示す。なお、３．５インチ径の基板を使用し、Ｒ３点は側壁面４から内側に１ｍｍの位置に定め、Ｒ３点における基準面からのずれ量ｒをＲｏｌｌ−Ｏｆｆ値とした（図２）。また、研磨剤供給量及び加圧面圧は一定とし、試料数は１００枚とした。
図５及び表３から、硬度６０未満では、研磨後のガラス基板の外周端部形状を、ガラス基板の主表面に対して面下がりの状態にできないことがわかる。また、硬度を硬くするに従い面下がり形状になる傾向があることがわかる。
したがって、ガラス基板を化学強化する場合、化学強化処理することによりＳｋｉ−ｊｕｍｐ変化量がプラスの方向に変化することから、ガラス基板の端部形状を良好なものにするためには、化学強化処理前、すなわち研磨工程後のガラス基板の端部形状をガラス基板の主表面に対して面下がりの状態にしなければならず、研磨工程で使用するポリシャの硬度は、６０以上（Ａｓｋｅｒ−Ｃ）としなければならないことがわかる。研磨工程で使用するポリシャの硬度としては、硬度６０〜８０（Ａｓｋｅｒ−Ｃ）、好ましくは、平均してＲｏｌｌ−Ｏｆｆ傾向となる硬度６６〜８０（Ａｓｋｅｒ−Ｃ）とすることが望ましい。
【００５０】
【表３】
（実施例３）
実施例３では、磁気ディスク用ガラス基板、及び磁気ディスクを作製した。
（１）粗ラッピング工程
まず、溶融ガラスを、上型、下型、胴型を用いてダイレクトプレスして、直径９６．０ｍｍφ、厚さ１．８ｍｍの円板状のアルミノシリケートガラスからなるガラス基板を得た。
なお、この場合、ダイレクトプレス以外に、ダウンドロー法やフロート法で形成したシートガラスから研削砥石で切り出して円板状のガラス基板を得てもよい。 なお、アルミノシリケートガラスとしては、ＳｉＯ２：５８〜７５重量％、Ａｌ２Ｏ３：５〜２３重量％、Ｌｉ２Ｏ：３〜１０重量％、Ｎａ２Ｏ：４〜１３重量％を主成分として含有する化学強化用ガラス（例えば、ＳｉＯ２：６３．５重量％、Ａｌ２Ｏ３：１４．２重量％、Ｎａ２Ｏ：１０．４重量％、Ｌｉ２Ｏ：５．４重量％、ＺｒＯ２：６．０重量％、Ｓｂ２Ｏ３：０．４重量％、Ａｓ２Ｏ３：０．１重量％含有するアルミノシリケートガラス）を使用した。
次いで、ガラス基板にラッピング工程を施した。このラッピング工程は、寸法精度及び形状精度の向上を目的としている。ラッピング工程は、ラッピング装置を用いて行い、砥粒の粒度を＃４００で行った。
詳しくは、はじめに粒度♯４００のアルミナ砥粒を用い、荷重Ｌを１００ｋｇ程度に設定して、内転ギアと外転ギアを回転させることによって、キャリア内に収納したガラス基板の両面を面精度０〜１μｍ、表面粗さ（Ｒｍａｘ）６μｍ（ＪＩＳＢ０６０１で測定）程度にラッピングした。
【００５２】
（２）形状加工工程
次に、円筒状の砥石を用いてガラス基板の中央部分に孔を開けるとともに、外周端面も研削して直径を９５ｍｍφとした後、外周端面及び内周端面に所定の面取り加工を施した。このときのガラス基板端面の表面粗さは、Ｒｍａｘで４μｍ程度であった。
【００５３】
（３）端面鏡面加工工程
次いで、スラリー（酸化セリウム砥粒）を用いたブラシ研磨により、ガラス基板を回転させながらガラス基板の外周端面及び内周端面の表面粗さを外周端面（側壁面）がＲｍａｘ＝０．１７μｍ、Ｒａ＝０．０２μｍ、外周端面（面取面）がＲｍａｘ＝０．７７μｍ、Ｒａ＝０．１０μｍ、内周端面（側壁面）がＲｍａｘ＝０．１７μｍ、Ｒａ＝０．０２μｍ、内周端面（面取面）がＲｍａｘ＝０．６０μｍ、Ｒａ＝０．０８μｍに研磨した。なお、Ｒｍａｘ、Ｒａは、ＴｅｎｃｏｒＰ２：ＫＬＡ−Ｔｅｎｋｏｒ社製で測定した。
上記端面鏡面加工工程を終えたガラス基板を水洗浄した。
【００５４】
（４）ラッピング工程
次に、砥粒の粒度を＃１０００に変え、ガラス基板表面をラッピングすることにより、平坦度３μｍ、表面粗さをＲｍａｘで２μｍ程度、Ｒａが０．２μｍ程度とした。なお、Ｒｍａｘ、ＲａはＡＦＭ（原子間力顕微鏡）で測定した。
上記ラッピング工程を終えたガラス基板を、中性洗剤、水の各洗浄槽に順次浸漬して、洗浄した。
【００５５】
（５）ポリッシング工程
次に、ポリッシング工程を施した。このポリッシング工程は、上述したラッピング工程で残留した傷や歪みの除去を目的とするもので、研磨装置を用いて行った。
ここで、基板の端部形状の変化は、ポリッシング工程で使用するポリシャ（研磨パッド）、加工面圧等の条件に大きく依存しており、先の実施例１によって得られた化学強化条件（３４０℃×２ｈｒ）で外周端部形状が変化する量（Ｓｋｉ−ｊｕｍｐ変化量：０．００４μｍ）を見込んで、ポリッシング工程後の基板端部形状が、Ｓｋｉ−ｊｕｍｐ値＝０μｍ程度、Ｒｏｌｌ−Ｏｆｆ値＝約−０．００４μｍ程度になるポリッシング条件を選定して研磨を行った。なお、Ｓｋｉ−ｊｕｍｐ値、Ｒｏｌｌ−Ｏｆｆ値は実施例１及び２と同じ条件で測定した。
研磨条件は以下の通りである。
研磨液：酸化セリウム（平均粒径１．０μｍ）（遊離砥粒＋水）
ポリシャ：軟質ポリシャ（硬度６８（Ａｓｋｅｒ−Ｃ）
加工圧：２００ｋｇ（面圧：６６ｇ／ｃｍ２）
研磨時間：８０ｍｉｎ
除去量：５０μｍ
上定盤回転教：２０ｒｐｍ
下定盤回転数：２６ｒｐｍ
キャリアの回転教（公転）：３ｒｐｍ
キャリアの回転数（自転）：３ｒｐｍ
上記ポリッシング工程を終えたガラス基板を、中性洗剤、純水、純水、ＩＰＡ（イソプロピルアルコール）、ＩＰＡ（蒸気乾燥）の各洗浄槽に順次浸漬して行った。
得られた基板の外周端部形状を表面粗さ測定器（サーフテストＳＶ−６２４：ミットヨ社製）で測定したところ、Ｓｋｉ−ｊｕｍｐ値＝＋０．００２μｍ、Ｒｏｌｌ−Ｏｆｆ値＝−０．００５μｍであり、主表面に対し若干面下がり気味の外周端部形状が得られた。
【００５６】
（６）化学強化工程
次に、洗浄工程を終えたガラス基板に化学強化を施した。化学強化は、化学強化処理槽に硝酸カリウム（６０％）と硝酸ナトリウム（４０％）を混合した化学強化溶液を用意し、この化学強化溶液を３４０℃に加熱し、３００℃に予熱された洗浄済みのガラス基板を２時間浸漬して行った。
上記化学強化を終えたガラス基板を、２０℃の水槽に浸漬して急冷し、約１０分間維持した。これにより、微小クラックが入った不良品を除去することができる。
上記化学強化工程を終えたガラス基板を、濃度１０重量％の硫酸、中性洗剤、純水、純水、ＩＰＡの各洗浄槽に順次浸漬して洗浄した。
【００５７】
上記の工程を経て得られたガラス基板の外周端部形状を測定したところ、Ｓｋｉ−ｊｕｍｐ値＝＋０．００２μｍ、Ｒｏｌｌ−Ｏｆｆ値＝＋０．００５μｍとなり、さらに、点Ｒ２からＲ３までの領域で主表面を基準面として、±０．００５μｍの範囲内（−０．００５μｍ〜＋０．００５μｍ）に収まる良好な値を示し、ほぼ平坦な基板外周端部を有する化学強化処理後のガラス基板が得られた。
なお、この化学強化処理後に得られたガラス基板の圧縮応力層の深さは７９．８μｍ、圧縮応力の値は１３．８ｋｇ／ｍｍ２、引張応力の値は２．０ｋｇ／ｍｍ２となり、表１の試料１−２で示した値と同じであった。
また、ガラス基板主表面の表面粗さ（Ｒａ、Ｒｍａｘ）、表面うねりＷａ、及び基板外周端部における微小領域での表面うねり（微小うねり）Ｗａ（Ｒａ）を測定したところ、Ｒａ＝０．５１ｎｍ、Ｒｍａｘ＝５．２０ｎｍ、Ｗａ（Ｒａ）＝０．５０ｎｍ、Ｗａ＝０．４３ｎｍであった。
なお、表面粗さＲａ、Ｒｍａｘは、ＡＦＭ（原子間力顕微鏡）で、微小領域での表面うねり（微小うねり）Ｗａ（Ｒａ）は、多機能表面解析装置（ＭｉｃｒｏＸＡＭ：ＰＨＡＳＥ ＳＨＩＦＴ ＴＥＣＨＮＯＬＯＧＹ社製）による測定で、表面うねりＷａは、多機能ディスク干渉計（ＯＰＴＩＦＬＡＴ：ＰＨＡＳＥ ＳＨＩＦＴ ＴＥＣＨＮＯＬＯＧＹ社製）でそれぞれ測定した。
微小領域での表面うねり（微小うねり）Ｗａ（Ｒａ）と、表面うねりＷａの測定条件、定義は以下の通りである。
微小領域での表面うねり（微小うねり）Ｗａ（Ｒａ）、表面うねりＷａは、白色光などを用いて、基板面の所定領域を走査し、基板面からの反射光と基準面からの反射光とを合成し、合成点に生じた干渉縞により表面うねりが計算される。
微小領域での表面うねり（微小うねり）Ｗａ（Ｒａ）は、うねりの周期が２μｍ〜４μｍ程度のもので、中心線から測定曲線までの偏差の絶対値の平均を指す。ここで、中心線とは、測定曲線の平均線と平行な直線を引いたとき、この直線と測定曲線で囲まれる面積が、この直線の両側で等しくなる直線をいう。
微小領域での表面うねり（微小うねり）Ｗａ（Ｒａ）は、以下の式（１）で表される値である。
【００５８】
【数１】
なお、上記微小領域での表面うねり（微小うねり）Ｗａ（Ｒａ）は、約５００μｍ×約６００μｍの矩形領域（約２５００００ピクセル）で測定された値である。
表面うねりＷａは、うねりの周期が３００μｍ〜５μｍ程度と、上記微小領域での表面うねりＷａ（Ｒａ）の周期と比べ、比較的大きな山（谷）のもので、中心線から測定曲線までの偏差の絶対値の平均を指す。中心線の定義は上記と同じである。
表面うねりＷａは、以下の式（２）で表される値である。
【００６０】
【数２】
なお、上記表面うねりＷａの値は、基板の中心から半径ｒ＝２０．３〜４５．０ｍｍの範囲（約１１５４００ピクセル）で測定された値である。
【００６２】
（７）磁気ディスク製造工程
上述した工程を経て得られた磁気ディスク用ガラス基板の両面に、インライン型スパッタリング装置を用いて、ＮｉＡｌシード層、ＣｒＭｏ下地層、ＣｏＣｒＰｔＴａ磁性層、水素化カーボン保護層を順次成膜し、ディップ法によってパーフルオロポリエーテル液体潤滑層を成膜してＬＵＬ（ロード・アンロード）方式用磁気ディスクを得た。
この得られた磁気ディスクをＬＵＬ方式のＨＤＤ（ハードディスクドライブ）に搭載したが、外周端部形状（***や面下がり）によるヘッドクラッシュは発生せず、磁気ヘッドの浮上安定性は良好であった。また、表面粗さ（Ｒａ、Ｒｍａｘ）、表面うねりＷａ、微小領域での表面うねり（微小うねり）Ｗａ（Ｒａ）はいずれも良好（値が小さい）であることから、タッチダウンハイトも１０ｎｍ以下と良好な値を示し、ヘッドクラッシュを起こすこともなかった。また、記録エリアの拡大を図ることができた。
【００６３】
（比較例１）
上記のポリッシング工程において特に外周端部形状のあわせ込みを行わず（面下がり気味にしない）、化学強化処理条件を３８０℃×４ｈｒとしたこと以外は、実施例３と同様にして磁気ディスク用ガラス基板及び磁気ディスクを作製した。
その結果、ガラス基板主表面の表面粗さは、実施例３と同程度であったが、Ｓｋｉ−ｊｕｍｐ＝＋０．４２１μｍ、Ｒｏｌｌ−Ｏｆｆ＝＋０．４２０μｍとなって、端部形状によるヘッドクラッシュが発生した。
なお、化学強化処理後に得られたガラス基板の圧縮応力層の深さは１４０．８μｍ、圧縮応力の値は２０．５ｋｇ／ｍｍ２、引張応力の値は２．７ｋｇ／ｍｍ２となり、表１の試料１−７に示した値と同じであった。
なお、基板外周端部における微小領域での表面うねりＷａ（Ｒａ）及び表面うねりＷａを測定したところ、Ｗａ（Ｒａ）＝０．９３ｎｍ、Ｗａ＝１．８５ｎｍであった。
【００６４】
実施例３と比較例１の結果から、実施例３では、磁気ディスク用ガラス基板に要求される機械的耐久性を満足する範囲内で化学強化処理条件を決定し、上記で求めた化学強化処理条件と、ガラス基板の端部形状変化量との相関関係から、化学強化処理条件によって引き起こされる端部形状の変化量を見込んで、化学強化処理前の端部形状を研磨工程等の合わせ込みによって所定の端部形状に仕上げることで、ＬＵＬ方式のＨＤＤ（ハードディスクドライブ）に搭載しても、外周端部形状（***や面下がり）によるヘッドクラッシュは発生せず、磁気ヘッドの浮上安定性が良好となる磁気ディスク用ガラス基板及び磁気ディスクが得られるが、比較例２のように合わせ込みを行わない場合は、ＬＵＬ方式に適用可能な磁気ディスク用ガラス基板及び磁気ディスクが得られないことがわかる。
実施例３と比較例１の結果から、化学強化処理による外周端面の形状変化が大きくなるにつれて（化学強化処理条件が強くなるにつれて）、Ｓｋｉ−ｊｕｍｐ値、表面うねりＷａ、Ｗａ（Ｒａ）が大きくなることがわかる。
【００６５】
（実施例４）
上記実施例３においてポリッシング工程後の洗浄処理工程に、ケイフッ酸処理を加えたこと以外は実施例３と同様にしてＣＳＳ方式用の磁気ディスク用ガラス基板及び磁気ディスクを作製した。
その結果、外周端部形状（Ｓｋｉ−ｊｕｍｐ値、Ｒｏｌｌ−Ｏｆｆ値）は同程度で、ケイフッ酸処理によりガラス基板主表面の表面粗さがＲｍａｘ＝７．８ｎｍ、Ｒａ＝０．８３ｎｍとなり、外周端部形状によるヘッドクラッシュは発生せず、磁気ヘッドの浮上安定性は良好であった。また、記録エリアの拡大を図ることができた。
【００６６】
（実施例５）
上記実施例３において、化学強化工程で３８０℃×４時間の化学強化処理条件を適用するために、先の実施例１によって得られた化学強化処理条件（３８０℃×４時間）で外周端部形状が変化する量（Ｓｋｉ−ｊｕｍｐ変化量：０．０３５μｍ）を見込んで、ポリッシング工程後の基板の端部形状が、Ｓｋｉ−ｊｕｍｐ値＝０μｍ程度、Ｒｏｌｌ−Ｏｆｆ値＝約−０．０３５μｍ程度になるポリッシング条件を選定して研磨を行ったこと以外は実施例３と同様にして磁気ディスク用ガラス基板及び磁気ディスクを作製した。
なお、研磨条件としては、ポリシャの硬度が８０（Ａｓｋｅｒ−Ｃ）のものを使用し、加工圧、研磨時間等、他の研磨条件は適宜調整して研磨を行った。
その結果、得られた基板の外周端部形状を測定したところ、Ｓｋｉ−ｊｕｍｐ値＝＋０．０３μｍ、Ｒｏｌｌ−Ｏｆｆ値＝−０．０４μｍであり、実施例３と比較して外周端部形状が悪化した。この得られた磁気ディスクをＬＵＬ方式のＨＤＤ（ハードディスクドライブ）に搭載したが、外周端部形状（***や面下がり）によるヘッドクラッシュは発生せず、磁気ヘッドの浮上安定性は良好であった。また、記録エリアの拡大を図ることができた。これは、化学強化処理による外周端部形状の変化量が大きすぎて、的確な端部形状の制御が行えなかったものと考えられる。なお、実施例３と実施例５の条件で複数枚のガラス基板を作製し、端部形状の測定を行ったところ、実施例３の方が端部形状のばらつきが少なく、安定して端部形状が良好なガラス基板が得られることが確認できた。
【００６７】
なお、本発明は上述した実施例に限定されるものではない。
【００６８】
例えば、本発明は、ガラス基板の外周端部に限らず内周端部の形状の制御にも同様に適用できる。
【００６９】
また、外周端部形状及び／又は内周端部形状を制御するための化学強化条件としては、加熱温度、浸漬時間だけでなく、化学強化処理溶液の種類（例えば、硝酸カリウムと硝酸ナトリウムの混合比など）によっても調整することができる。また、化学強化処理溶液の種類としては、硝酸カリウムと硝酸ナトリウムとの混合塩に限らず、硝酸カリウム単独の塩、硝酸ナトリウム単独の塩や、Ｎａ２ＳＯ４、Ｋ２ＳＯ４、ＮａＢｒ、ＫＢｒ、ＫＮＯ２、ＮａＮＯ２などの溶融塩を使用することができる。
【００７０】
さらに、外周端部形状及び／又は内周端部形状を制御するための手段として、化学強化処理を挙げたがこれに限らず、ポリッシング工程後の基板端部形状を若干***気味にしておき、このガラス基板に面下がり傾向の処理（例えば、脱アルカリ処理）することにより、外周端部形状及び／又は内周端部形状を制御することも可能である。
【００７１】
本発明は、化学強化処理後に主表面研磨処理を施す場合にも適用できる。この場合、各処理における外周端部形状及び／又は内周端部形状の変化を考慮し、所望の外周端部形状及び／又は内周端部形状が得られるように各処理条件を選択すればよい。
【００７２】
本発明の情報記録媒体用ガラス基板は、磁気ディスク用ガラス基板に限らず、光ディスク用ガラス基板、光磁気ディスク用ガラス基板などにも適用できることは言うまでもない。
【００７３】
【発明の効果】
本発明の情報記録媒体用ガラス基板の製造方法等によれば、所望の外周端部形状及び内周端部形状を有する化学強化処理後のガラス基板を得ることができる。また、本発明の情報記録媒体等によれば、化学強化による機械的耐久性を有しつつ、高密度記録が可能な程度に十分な平滑度を有し、かつ、記録エリアを周縁にまで拡大することが可能である。
【図面の簡単な説明】
【図１】基板の外周端部における面下がりの状態を説明するための部分断面図である。
【図２】基板の外周端部におけるＳｋｉ−ｊｕｍｐ値及びＲｏｌｌ−Ｏｆｆ値を説明するための部分断面図である。
【図３】基板の外周端部におけるＳｋｉ−ｊｕｍｐ値及びＲｏｌｌ−Ｏｆｆ値を説明するための部分断面図である。
【図４】基板の外周端部におけるＳｋｉ−ｊｕｍｐ値及びＲｏｌｌ−Ｏｆｆ値を説明するための部分断面図である。
【図５】ポリシャの硬度とＲｏｌｌ−Ｏｆｆ変化量との関係を示す図である。
【図６】基板の外周端部における***の様子を説明するための部分断面図である。
【符号の説明】
１ ガラス基板
２ 主表面
３ 面取部
４ 側壁部
５ ***
ｓ Ｓｋｉ−ｊｕｍｐ値
ｒ Ｒｏｌｌ−Ｏｆｆ値[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a glass substrate for an information recording medium that enables high-density recording and reproduction, an information recording medium, a method for manufacturing the same, and the like.
[0002]
[Prior art]
A magnetic disk mounted on a hard disk (HDD) is known as one of information recording media mounted on an information storage device. In recent years, there has been a strong demand for improving the recording capacity of magnetic disks, and there is an urgent need to increase the recording area and increase the recording density.
[0003]
In order to enlarge the recording area, it is necessary to secure a smooth area on the main surface as large as possible. However, depending on the polishing conditions of the glass substrate, at the outer peripheral edge of the substrate, surface slackening (surface drooping) in which the surface is lowered with respect to the main surface of the glass substrate and swelling of the surface with respect to the main surface (hereinafter referred to as bulge) occur. If the magnetic head is levitated and run on a magnetic disk having such a shape, the head may tilt at a place where the surface is loose or bumpy, and the flight of the head may become unstable, causing a crash. The ridges and bumps hindered the expansion of the recording area. In order to solve these problems, the applicant of the present application has developed a technique for suppressing protrusions and the like by reducing the polishing conditions (polishing pressure and polishing time) of a glass substrate within a predetermined range, and filed an application first. (JP-A-5-89459). Further, in order to stabilize the flight of the head, there has been proposed a technique in which a curvature representing surface slack is defined (Japanese Patent Laid-Open No. 5-290365).
[0004]
On the other hand, as a factor enabling high-density recording, it is necessary to reduce the flying height of the magnetic head with respect to the magnetic disk as much as possible, and for that purpose, it is necessary to make the surface of the magnetic disk smoother.
[0005]
In recent years, in order to prevent the magnetic head from being attracted even when the magnetic disk becomes smooth, a magnetic head having a pad attached to the magnetic head or an LUL (Load / Unload) capable of realizing a lower flying height is realized. ) The development of the method is actively underway. In the case of this LUL system, the surface of the magnetic disk is usually smooth, and the magnetic head is on standby outside the magnetic disk when the magnetic disk is stopped. Since the magnetic head moves from the outside of the disk onto the disk surface to perform recording and reproduction, the flying head generally runs lower than the CSS system. In the case of the LUL method, it is necessary to control the shape of the outer peripheral end of the substrate more strictly than in the CSS method in order to ensure the flying stability of the magnetic head. In the case of the LUL system, since the head can travel at a low flying height, higher density recording can be performed as compared with the CSS system.
[0006]
In order to realize a low flying height of the magnetic head by the LUL method, a glass substrate having excellent flatness and smoothness has been attracting attention as a magnetic disk substrate. Usually, in order to improve the mechanical durability of the glass substrate, a part of the ions contained in the surface layer of the glass substrate is replaced with ions in a chemical strengthening treatment solution having a larger ion radius than the ions, thereby replacing the glass substrate. A chemical strengthening process for strengthening is performed.
[0007]
[Problems to be solved by the invention]
However, conventionally, the influence of the chemical strengthening treatment is not considered, or it is not assumed that the chemical strengthening treatment is performed. Therefore, when a magnetic recording medium is manufactured using a glass substrate subjected to the chemical strengthening treatment, It has been found that the floating movement of the magnetic head becomes unstable due to the shape of the outer peripheral end of the substrate, and a head crash occurs, so that the flying height of the head cannot be reduced, and it is also difficult to enlarge the recording area. .
Therefore, there is a problem that it is particularly difficult to realize a magnetic recording medium of the LUL system. Also in the case of the CSS method, it is preferable to control the shape of the outer peripheral end of the substrate in order to increase the flying stability of the magnetic head and the recording area.
Also, at the inner peripheral end of the substrate, if there is a bulge or the like, there is a problem that the magnetic disk is tilted or warped and fixed in a clamp for fixing the magnetic disk, and when the mechanical strength of the substrate is weak, There is a problem that cracks occur, and it is desired to control the shape of the inner peripheral end portion of the substrate.
[0008]
The present invention has been made under the above-mentioned background, and is a glass for an information recording medium capable of obtaining a chemically strengthened glass substrate having a desired outer peripheral end shape and / or inner peripheral end shape. A first object is to provide a method of manufacturing a substrate and the like.
Also, to provide an information recording medium or the like which has sufficient durability to enable high-density recording while having mechanical durability due to chemical strengthening, and is capable of expanding a recording area to the periphery. For the second purpose.
[0009]
[Means for Solving the Problems]
The present inventors have conducted intensive studies and found that when a glass substrate is subjected to a chemical strengthening treatment, ions in the glass surface layer are exchanged for ions having a larger ion radius, so that a slight amount of elongation occurs in the glass substrate, Of the outer peripheral end and / or inner peripheral end of the magnetic head (edge profile: Edge Profile), and in particular, due to the change in the shape of the outer peripheral end caused by this chemical strengthening treatment, the magnetic head levitates. Was unstable, and a head crash occurred, so that the flying height of the head could not be reduced, and it was found that it was difficult to enlarge the recording area. Specifically, as shown in FIG. 6A, the outer periphery and / or the inner periphery of the glass substrate 1 is elongated in the direction of the arrow by the chemical strengthening treatment, so that the
[0010]
Further, as a result of further studies, it was first found that the shape change of the outer peripheral end and / or the inner peripheral end of the glass substrate caused by the chemical strengthening treatment can be controlled by the chemical strengthening treatment conditions. Secondly, the inventors have found that the shape of the outer peripheral end and / or the inner peripheral end of the glass substrate before the chemical strengthening treatment can be controlled by the polishing condition of the main surface of the chamfered glass substrate. Then, they have found that a glass substrate having a desired outer peripheral end shape and / or inner peripheral end shape after chemical strengthening treatment can be obtained by utilizing these, and the present invention has been completed.
In addition, by forming the outer peripheral end of the glass substrate after the chemical strengthening treatment into a shape that satisfies a predetermined numerical range, the flying and running of the magnetic head is stabilized, and the flying of the head can be reduced without causing a head crash. Further, the present inventors have found that the recording area can be enlarged and that these are extremely effective especially for the LUL type magnetic recording medium, and have completed the second invention.
[0011]
The present invention has the following configuration.
[0012]
(Configuration 1) A step of previously grasping the relationship between the shape change of at least the outer peripheral end and / or the inner peripheral end of the glass substrate caused by the chemical strengthening treatment and the chemical strengthening treatment condition, and the glass substrate based on the relationship Performing a chemical strengthening process on the glass substrate for an information recording medium.
[0013]
(Structure 2) a step of previously grasping the relationship between the shape change of at least the outer peripheral end and / or the inner peripheral end of the glass substrate caused by the chemical strengthening treatment and the chemical strengthening treatment condition; The shape of the outer peripheral end and / or the inner peripheral end of the glass substrate before the chemical strengthening treatment is determined in consideration of the change in the shape of the outer peripheral end and / or the inner peripheral end of the glass substrate. Alternatively, a step of obtaining a glass substrate before the chemical strengthening process having the shape of the inner peripheral end portion, and subjecting the glass substrate before the chemical strengthening process obtained above to a chemical strengthening process to obtain a desired outer peripheral end portion and / or inner portion. Obtaining a glass substrate having a peripheral end shape after the chemical strengthening treatment, the method comprising the steps of:
[0014]
(Structure 3) The
[0015]
(Structure 4) In the chemical strengthening treatment, the depth of the compressive stress layer generated in the surface layer of the glass substrate by the chemical strengthening is 3 to 100 μm, and the value of the compressive stress generated in the surface layer of the glass substrate by the chemical strengthening is 1 to 15 kg / mm. 2 And the value of the tensile stress generated inside the glass substrate due to chemical strengthening is 4.5 kg / mm. 2 4. The method for producing a glass substrate for an information recording medium according to any one of Configurations 1 to 3, wherein the method is performed under the following chemical strengthening treatment conditions.
[0016]
(Structure 5) The method for manufacturing a glass substrate for an information recording medium according to any one of structures 1 to 4, wherein the chemical strengthening treatment conditions are a treatment temperature and a treatment time in the chemical strengthening treatment.
[0017]
(Structure 6) The method for manufacturing a glass substrate for an information recording medium according to
[0018]
(Configuration 7) The relationship between the polishing conditions of the main surface of the glass substrate subjected to the chamfering process and the outer peripheral end and / or inner peripheral end shape of the glass substrate obtained by the main surface polishing is grasped in advance. The glass for an information recording medium according to any one of
[0019]
(Structure 8) The polishing conditions for the main surface of the glass substrate are such that the shape of the outer peripheral end and / or the inner peripheral end of the polished glass substrate is lower than the main surface of the glass substrate. The method for producing a glass substrate for an information recording medium according to Configuration 7, wherein:
[0020]
(Structure 9) The polishing conditions for lowering the surface with respect to the main surface of the glass substrate are as follows: a soft polisher having a hardness of 60 to 80 (Asker-C) is used, and the processing surface pressure on the glass substrate during polishing is 40 to 80. 150g / cm 2 9. The method for manufacturing a glass substrate for an information recording medium according to Configuration 8, wherein:
[0021]
(Structure 10) A glass substrate for an information recording medium which has been subjected to a chemical strengthening treatment, wherein the outer peripheral end and / or the inner peripheral end of the glass substrate after the chemical strengthening treatment have an outer peripheral end and / or an inner periphery. A glass substrate for an information recording medium, wherein a shape of a flat surface of a main surface of the glass substrate falls within a range of ± 0.35 μm with a flat surface of a main surface of the glass substrate as a reference plane (zero) in a predetermined region at an end.
[0022]
(Structure 11) A glass substrate for an information recording medium that has been subjected to a chemical strengthening treatment, wherein the outer peripheral end shape after the chemical strengthening treatment is a region up to a point in a recording area separated from the outer peripheral end of the glide region by a predetermined distance. In the above, when the flat surface of the glass substrate main surface is defined as a reference plane (zero), the value of the highest point (Ski-jump (ski jump) point) (Ski-jump (ski jump) value) is ± 0.35 μm. And the value (Roll-Off (roll-off) value) of the outer peripheral end position (Roll-Off (roll-off) point) of the glide region when the flat surface is set as the reference surface is within ± 0.35 μm. 13. The glass substrate for an information recording medium according to Configuration 10, wherein:
[0023]
(Configuration 12) The depth of the compressive stress layer generated on the surface of the glass substrate by chemical strengthening is 3 to 100 μm, and the value of the compressive stress generated on the surface of the glass substrate by chemical strengthening is 1 to 15 kg / mm. 2 And the value of the tensile stress generated inside the glass substrate by the chemical strengthening is 4.5 kg / mm. 2 12. The glass substrate for an information recording medium according to configuration 10 or 11, wherein:
[0024]
(Structure 13) A method for manufacturing an information recording medium, comprising a step of forming at least a recording layer on a surface of a glass substrate for an information recording medium obtained by the method according to any one of Structures 1 to 9.
[0025]
(Arrangement 14) An information recording medium, characterized in that at least a magnetic layer is formed on the surface of the glass substrate for an information recording medium according to any of Arrangements 10 to 12.
[0026]
(Structure 15) The information recording medium according to Structure 14, wherein the information recording medium is a magnetic recording medium of a LUL (load / unload) system.
[0027]
[Action]
According to Configuration 1, the relationship between the shape change (particularly, the amount of change in the thickness direction of the glass substrate) of the outer peripheral end portion of the glass substrate caused by the chemical strengthening process and the chemical strengthening process conditions are grasped in advance, and this relationship is determined. By performing the chemical strengthening process on the glass substrate based on the chemical strengthening process, it becomes possible to control the shape change of the outer peripheral end portion of the glass substrate caused by the chemical strengthening process, by the chemical strengthening process conditions.
The same applies to the inner peripheral end of the glass substrate.
As the chemical strengthening treatment, a method of chemically strengthening treatment by ion exchange in which a part of ions contained in the surface layer of the glass substrate is replaced with ions in a chemical strengthening treatment solution having a larger ion radius than the ions to perform chemical strengthening, And a chemical strengthening method by a dealkalization treatment for performing chemical strengthening by removing alkali ions contained in the surface layer of the glass substrate. In the case of chemical strengthening by ion exchange, elongation occurs in the in-plane direction of the glass substrate, so the amount of shape change with respect to the main surface becomes a positive value (the direction in which the glass substrate protrudes). Since the glass substrate shrinks in the in-plane direction, the shape change amount with respect to the main surface becomes a negative value (the direction of surface sag). The shape change amount of the inner peripheral end of the glass substrate is smaller by about 10% to 20% than the shape change amount of the outer peripheral end.
[0028]
According to the
The same applies to the inner peripheral end of the glass substrate.
[0029]
According to the
The same applies to the inner peripheral end of the glass substrate.
[0030]
According to the fourth aspect, first, by setting the depth of the compressive stress layer generated in the surface layer of the glass substrate by chemical strengthening to 3 to 100 μm, it is possible to perform the chemical strengthening treatment while maintaining the preferable mechanical strength of the glass substrate. In this case, the amount of change in the shape of the outer peripheral end can be reduced.
When the depth of the compressive stress layer is less than 3 μm, the strength of the glass substrate is weakened (the durability against scratches and the destruction resistance are deteriorated), which is not preferable. When the depth exceeds 100 μm, chemical strengthening treatment is performed. Since the shape change amount of the outer peripheral end becomes large, it becomes difficult to control the outer peripheral end shape, which is not preferable. The preferred depth of the compressive stress layer is 40 to 80 μm, more preferably 50 to 70 μm.
Second, the value of the compressive stress generated in the surface layer of the glass substrate due to chemical strengthening is set to 1 to 15 kg / mm. 2 And the value of the tensile stress generated inside the glass substrate by chemical strengthening is 4.5 kg / mm. 2 By the following, the strength of the glass substrate and the durability against breakage with time can be improved.
Compressive stress value is 1kg / mm 2 If it is less than 15 kg / mm, the strength of the glass substrate is weakened (the durability to scratches and the fracture resistance deteriorate). 2 When the value exceeds, the amount of change in the shape of the outer peripheral end when the chemical strengthening treatment is performed becomes large, and it is difficult to control the shape of the outer peripheral end.
Further, the value of the tensile stress is 4.5 kg / mm 2 When the value exceeds, the amount of change in the shape of the outer peripheral end when the chemical strengthening treatment is performed becomes large, and it is difficult to control the shape of the outer peripheral end.
More preferably, the depth of the compressive stress layer generated in the surface layer of the glass substrate by the chemical strengthening is 40 to 80 μm, and the value of the compressive stress generated in the surface layer of the glass substrate by the chemical strengthening is 3 to 14 kg / mm. 2 And the value of the tensile stress generated inside the glass substrate by chemical strengthening is 2.5 kg / mm 2 The following chemical strengthening treatment conditions are preferable in terms of controlling the mechanical strength and the shape of the end portion of the glass substrate.
The above-mentioned effect becomes more remarkable by setting the depth, the compressive stress value, and the tension stress value of the compressive stress layer in an optimal balance.
The same applies to the inner peripheral end of the glass substrate.
[0031]
According to the fifth aspect, by setting the processing temperature and the processing time, which are the chemical strengthening processing conditions, within a predetermined range, the shape change amount of the outer peripheral edge and / or the inner peripheral edge of the glass substrate due to the chemical strengthening processing is predetermined. Can easily be suppressed within the range.
The chemical strengthening treatment conditions include, in addition to the treatment temperature and treatment time, conditions such as the type of the molten salt and the mixing ratio thereof. It is easier to adjust than the ratio, and therefore is an effective condition from the viewpoint of mass productivity and workability.
[0032]
As shown in Configuration 6, specific chemical strengthening treatment conditions preferably include a treatment temperature in a range of 280 to 400 ° C. and a treatment time in a range of 0.5 to 5 hours.
If the treatment temperature is lower than 280 ° C., it is not preferable because the melting temperature is lower than the melting point of the molten salt, and if it is higher than 400 ° C., the processing time is shortened and the workability is deteriorated. If the processing time is less than 0.5 hour, the workability is deteriorated, and if it is more than 5 hours, the productivity is deteriorated, which is not preferable.
From the viewpoint of suppressing the amount of shape change of the outer peripheral end and / or inner peripheral end of the glass substrate due to the chemical strengthening treatment, the preferred treatment temperature and treatment time vary depending on the composition of the glass substrate, the composition of the chemical strengthening treatment liquid, and the like. Therefore, for example, the processing temperature is preferably in the range of 320 to 380 ° C., preferably the processing temperature is in the range of 340 to 360 ° C., and the processing time is preferably in the range of 1 to 4 hours.
[0033]
According to the configuration 7, the relationship between the polishing conditions of the main surface of the glass substrate subjected to the chamfering process and the outer peripheral end shape and / or the inner peripheral end shape of the glass substrate obtained by the main surface polishing is grasped in advance. In addition, by controlling the polishing conditions of the main surface of the glass substrate based on this relationship, the glass substrate having the desired outer peripheral end shape and / or inner peripheral end shape before the chemical strengthening treatment can be easily and highly accurately formed. It is possible to obtain at.
[0034]
According to the configuration 8, the polishing conditions of the main surface of the glass substrate are set such that the outer peripheral end shape of the polished glass substrate is lower than the
The same applies to the inner peripheral end of the glass substrate.
[0035]
According to Configuration 9, a soft polisher having a hardness of 60 to 80 (Asker-C) is used, and the processing surface pressure on the glass substrate during polishing is 40 to 150 g / cm. 2 By doing so, it is possible to easily and accurately obtain a glass substrate before the chemical strengthening treatment having an outer peripheral end shape that is in a state of being lowered with respect to the main surface of the glass substrate. Further, the control of the outer peripheral end shape is easy.
If the other polishing conditions are the same, as the hardness of the polisher (polishing pad) increases, the shape of the outer peripheral end portion tends to be lowered. Further, as the processing surface pressure increases, the outer peripheral end portion tends to have a raised shape. Further, the higher the peripheral speed is, the more the outer peripheral end portion tends to have a lower surface.
The outer peripheral end shape changes depending on the polishing conditions such as the structure, size, and amount of the polishing agent of the polishing apparatus, but the control of the outer peripheral end shape by the hardness of the polisher has good controllability and is easy to control. The controllable width is also large. Therefore, it is preferable that the control of the outer peripheral end shape based on the hardness of the polisher be the main, and the control of the outer peripheral end shape by the processing surface pressure and the peripheral speed be the secondary.
The same applies to the inner peripheral end of the glass substrate.
[0036]
According to Configuration 10, the shape of the outer peripheral end of the glass substrate after the chemical strengthening treatment is set to ± 0.35 μm in a predetermined region of the outer peripheral end, with the flat surface of the main surface of the glass substrate as a reference plane (zero). By making the shape fall within the range (−0.35 μm to +0.35 μm), the flying and running of the magnetic head is stabilized, and the flying of the head can be reduced without causing a head crash (high-density recording / reproducing). Thus, the recording area can be enlarged. In other words, the flatness of the outer peripheral end portion of the glass substrate after the chemical strengthening treatment can be obtained to such an extent that it does not hinder the enlargement of the recording area and the high-density recording. For this reason, it is extremely effective especially for a LUL type magnetic recording medium.
Note that the predetermined region of the outer peripheral end can be arbitrarily determined, but a region where flatness is impaired at the outer peripheral end, that is, a deviation from the reference surface when the flat surface of the main surface of the glass substrate is used as the reference surface. It is preferable that a large area be a predetermined area.
Specifically, for example, an area from the outer peripheral edge of the recording area (an area where the flatness of the main surface is normally ensured) to the outer peripheral edge of the glide area can be defined as the predetermined area. Further, for example, a region from the side wall of the substrate to the inside of the outer peripheral edge of the recording area can be defined as a predetermined region.
The outer peripheral end shape is more preferably within ± 0.20 μm (−0.20 to 0.20 μm) with respect to the reference plane, and still more preferably within ± 0.10 μm (−0.10 to 0.10 μm) with respect to the reference plane. It is desirable that the shape be within the range of (2).
The same applies to the inner peripheral end of the glass substrate.
[0037]
According to the eleventh configuration, the outer peripheral end shape after the chemical strengthening processing is such that the flat surface of the glass substrate main surface is the reference plane (zero) in a region from the outer peripheral end of the glide region to a point in the recording area separated by a predetermined distance. , The value of the highest point (Ski-jump point) (Ski-jump value) is within ± 0.35 μm and the outer peripheral end position (Roll−) of the glide region when the flat surface is used as the reference surface. The effect of Configuration 10 can be obtained by forming the shape such that the value (Roll-Off value) of the (Off point) is within ± 0.35 μm, and attention is paid to reference points such as the Ski-jump point and the Roll-Off point. By performing the numerical control by using the digital camera, the product control in the manufacturing process becomes easy.
Here, the Ski-jump value refers to the value of the highest point (Ski-jump point) when the outer peripheral end shape of the substrate is based on the flat surface of the main surface of the glass substrate, and the Roll-Off value Means a value of a point on a contour line (Rol1-Off point) at an outer peripheral end position of the glide region when the flat surface is used as a reference surface. Specifically, it is measured as follows.
As shown in FIG. 2, a cross section of the glass substrate cut along a plane passing through the center of the disk-shaped glass substrate and perpendicular to the main surface is considered. In this cross-section, two reference points are set in the recording area on the contour line of the main surface, and R1 and R2 are set in order from the center. In addition, a point R3 (the outer peripheral end position of the glide area) is set at a margin of a certain distance in the outer peripheral direction from the outer peripheral end of the recording area. Next, the point R1 and the point R2 are connected, and an extension line is drawn. In such a case, the distance between the point on the contour of the substrate and the straight line R1R2 (or an extension thereof) is measured in the region from the point R2 to the point R3. The point S on the contour line of the substrate where the distance is the highest in the positive direction is the Ski-jump (ski jump) point, and the value of the distance s is the Ski-jump value. A point R on the contour at the position of the point R3 is a Roll-Off (roll-off) point, and a distance r between the point R and the straight line R1R2 (or an extension thereof) is a Roll-Off value.
In addition, as shown in FIG. 3, the Ski-jump value may be slightly negative, and in this case, the Ski-jump indicates a lowering of the surface. In addition, as shown in FIG. 4, the Roll-Off value may be positive, and in this case, the Roll-Off indicates a bump on the surface. FIG. 4 shows a case where the Ski-jump value matches the Roll-Off value.
[0038]
The points R1, R2, and R3 are appropriately selected according to the size of the substrate. For example, in the case of a substrate having an outer diameter of 2.5 inches, 3.0 inches, or 3.5 inches, the point R3 is set at a position 1 mm inward from the side wall surface (side wall portion) of the substrate. In the case of a substrate having an outer diameter of 2.5 inches (outer diameter of 65 mmφ), for example, the distance from the center of the substrate is 23 mm (R1), 27 mm (R2), and 31.5 mm, respectively. The point (R3) can be determined as a 32.5 mm point (side wall surface).
[0039]
If the Ski-jump value exceeds the range of −0.35 μm to +0.35 μm, the flying stability of the magnetic head deteriorates, and if it is severe, a head crash occurs and it becomes impossible to mount the magnetic head on a magnetic disk drive.
If the Roll-Off value exceeds the range of −0.35 μm to 0.35 μm, the flying stability of the magnetic head is deteriorated as described above, and if it is severe, a head crash occurs and the magnetic head can be mounted on a magnetic disk drive. It is not preferable because it disappears.
[0040]
More preferably, the Ski-jump value and the Roll-Off value are respectively within ± 0.20 μm (−0.20 to 0.20 μm), and still more preferably within ± 0.10 μm (−0.10 to 0.10 μm). It is.
[0041]
According to the twelfth aspect, first, by setting the depth of the compressive stress layer generated in the surface layer of the glass substrate by chemical strengthening to 3 to 100 μm, a glass substrate for an information recording medium having a preferable mechanical strength of the glass substrate can be obtained. .
When the depth of the compressive stress layer is less than 3 μm, the strength of the glass substrate is weakened (the durability against scratches and the destruction resistance are deteriorated). The amount of shape change is large, and a substrate having a favorable outer peripheral end shape cannot be obtained, which is not preferable. The preferred depth of the compressive stress layer is 40 to 80 μm, more preferably 50 to 70 μm.
Second, the value of the compressive stress generated in the surface layer of the glass substrate due to chemical strengthening is 1 to 15 kg / mm. 2 And the value of the tensile stress generated inside the glass substrate by chemical strengthening is 4.5 kg / mm. 2 The following is preferable because the strength of the glass substrate and the durability against breakage with time are improved.
Compressive stress value is 1kg / mm 2 If it is less than 15 kg / mm, the strength of the glass substrate is weakened (the durability to scratches and the fracture resistance deteriorate). 2 When the ratio exceeds, the amount of change in shape during the chemical strengthening treatment becomes large, and a substrate having a favorable outer peripheral end shape cannot be obtained, which is not preferable.
Further, the value of the tensile stress is 4.5 kg / mm 2 When the ratio exceeds, the amount of change in shape during the chemical strengthening treatment becomes large, and a substrate having a favorable outer peripheral end shape cannot be obtained, which is not preferable.
More preferably, the depth of the compressive stress layer generated in the surface layer of the glass substrate by the chemical strengthening is 40 to 80 μm, and the value of the compressive stress generated in the surface layer of the glass substrate by the chemical strengthening is 3 to 14 kg / mm. 2 And the value of the tensile stress generated inside the glass substrate by chemical strengthening is 2.5 kg / mm 2 The following chemical strengthening treatment conditions are preferable in terms of controlling the mechanical strength and the shape of the end portion of the glass substrate.
The above-mentioned effect becomes more remarkable by setting the depth, the compressive stress value, and the tension stress value of the compressive stress layer in an optimal balance.
[0042]
According to the thirteenth aspect, it is possible to obtain an information recording medium in which the outer peripheral end surface shape of the glass substrate is flat and the recording area can be enlarged. In addition, the inner peripheral end surface shape is flat, the substrate is prevented from cracking, and the information recording medium can be correctly mounted on the magnetic storage device.
[0043]
According to the configuration 14, it is possible to obtain a magnetic recording medium in which the outer peripheral end surface shape of the glass substrate is flat, the recording area can be enlarged, and high-density recording can be performed. In addition, the inner peripheral end surface shape is flat, the substrate is prevented from cracking, and the information recording medium can be correctly mounted on the magnetic storage device.
[0044]
As in Configuration 15, the present invention is most effective when applied to a magnetic recording medium of the LUL (load / unload) type capable of ultra-low flying height of the magnetic head.
[0045]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
In Example 1, the thickness of the compressive stress layer, the compressive stress value, the tensile stress value, and the amount of change in the shape of the outer peripheral end of the substrate, the amount of change in the outer diameter / inner diameter of the substrate, etc. The relationship with bending strength was determined.
[0046]
After mirror polishing of the end face, a plurality of 3.5 inch (95 mmφ) and 2.5 inch diameter (65 mmφ) glass substrates whose main surfaces are precisely polished (polished) are prepared. Time) was measured for the amount of change in the inner and outer diameters of the substrate and the Ski-jump value.
A substrate having a substantially flat outer peripheral end portion before the chemical strengthening treatment (therefore, both the Ski-jump value and the Roll-Off value were substantially zero) was used. In the case of a 2.5-inch diameter, the point R3 is set at a position 1 mm inward from the side wall surface 4 (a position at a distance of 31.5 mm from the center of the substrate). It was set at a position of 5 mm (a position at a distance of 27 mm from the center of the substrate). In the case of a 3.5-inch diameter, the point R3 is set at a position 1 mm inward from the side wall surface 4 (a position at a distance of 46.5 mm from the center of the substrate), and the point R2 is set 5.5 mm inward from the
The amount of change in the inner and outer diameters of the substrate is a value obtained by calculating the difference between the inner and outer diameters of the substrate before and after the chemical strengthening treatment, and the inner and outer diameters of the substrate were measured with a micrometer.
The chemical strengthening solution used was a mixture of potassium nitrate (60 wt%) and sodium nitrate (40 wt%).
Table 1 shows the results for a 3.5 inch diameter substrate, and Table 2 shows the results for a 2.5 inch diameter substrate.
[0047]
[Table 1]
As shown in the above results, as the chemical strengthening condition becomes stronger (the temperature becomes higher, the strengthening time becomes longer, and the stress becomes larger), the change in the outer diameter and the inner diameter of the substrate increases, and the change in Ski-jump also increases. It turned out to be.
Therefore, the chemical strengthening treatment conditions are determined within a range that satisfies the mechanical and chemical durability required for the magnetic disk glass substrate, and the correlation between the strengthening conditions obtained above and the Ski-jump change amount is determined. In consideration of the amount of Ski-jump caused by the chemical strengthening process conditions, the end shape before the chemical strengthening process is set to a predetermined end shape by combining the lapping step and the polishing step, thereby obtaining a precise end shape. Can be controlled.
The bending strength required for use as a glass substrate for a magnetic disk is about 15 to 20 kgf in the case of a 3.5-inch diameter (thus, samples 1-1 to 1-7 have sufficient bending strengths). Therefore, it is possible to perform the chemical strengthening treatment under the chemical strengthening condition (340 to 360 ° C., 1.5 to 2 hours) in which the Ski-jump change amount is small (0 to 0.010 μm) because of the strength of the glass substrate. It can be seen that this is good in suppressing the change in shape, and that the chemical strengthening condition (340 ° C., 1.5 to 2 hr) with a smaller Ski-jump change amount (0 to 0.004 μm) is more preferable.
The same applies to the case of a 2.5-inch diameter, and the bending strength required for use as a glass substrate for a magnetic disk is about 10 to 15 kgf (therefore, all of the samples 2-1 to 2-8 have a sufficient bending strength). It can be seen that the chemical strengthening condition (340 to 360 ° C, 0.6 to 2 hr) with a small Ski-jump change (0 to 0.004 µm) is more preferable.
From the above results, a more preferable chemical strengthening treatment condition for satisfying the mechanical strength with a small end shape change amount (Ski-jump change amount) is the depth of the compressive stress layer generated in the surface layer of the glass substrate by the chemical strengthening. Is 40 to 80 μm, and the value of compressive stress generated in the surface layer of the glass substrate by chemical strengthening is 3 to 14 kg / mm. 2 And the value of the tensile stress generated inside the glass substrate by chemical strengthening is 2.5 kg / mm 2 The following can be said from the above results.
[0049]
(Example 2)
In Example 2, the relationship between the hardness of the polisher of the polishing pad used when polishing the main surface of the glass substrate and the outer peripheral end shape was examined.
FIG. 5 and Table 3 show the relationship between the polisher hardness and the Roll-Off value. A substrate having a diameter of 3.5 inches was used, the point R3 was set at a position 1 mm inward from the
From FIG. 5 and Table 3, it can be seen that, when the hardness is less than 60, the outer peripheral end shape of the polished glass substrate cannot be lowered to the main surface of the glass substrate. Further, it can be seen that as the hardness is increased, the surface tends to be lowered.
Therefore, when the glass substrate is chemically strengthened, the amount of change in Ski-jump changes in a positive direction due to the chemical strengthening process. Therefore, in order to improve the shape of the end portion of the glass substrate, the chemical strengthening process is performed. Before, that is, the end portion shape of the glass substrate after the polishing process must be in a state of being lowered with respect to the main surface of the glass substrate, and the hardness of the polisher used in the polishing process is 60 or more (Asker-C). We know that we have to. The polisher used in the polishing step preferably has a hardness of 60 to 80 (Asker-C), and preferably has a hardness of 66 to 80 (Asker-C), which has a Roll-Off tendency on average.
[0050]
[Table 3]
(Example 3)
In Example 3, a glass substrate for a magnetic disk and a magnetic disk were manufactured.
(1) Rough lapping process
First, the molten glass was directly pressed using an upper mold, a lower mold and a body mold to obtain a disk-shaped glass substrate made of aluminosilicate glass having a diameter of 96.0 mmφ and a thickness of 1.8 mm.
In this case, in addition to the direct press, a disk-shaped glass substrate may be obtained by cutting out a sheet glass formed by a down-draw method or a float method with a grinding wheel. The aluminosilicate glass is SiO 2 2 : 58-75% by weight, Al 2 O 3 : 5 to 23% by weight, Li 2 O: 3 to 10% by weight, Na 2 O: glass for chemical strengthening containing 4 to 13% by weight as a main component (for example, SiO 2 : 63.5% by weight, Al 2 O 3 : 14.2% by weight, Na 2 O: 10.4% by weight, Li 2 O: 5.4% by weight, ZrO 2 : 6.0% by weight, Sb 2 O 3 : 0.4% by weight, As 2 O 3 : Aluminosilicate glass containing 0.1% by weight).
Next, a lapping step was performed on the glass substrate. This lapping step aims at improving dimensional accuracy and shape accuracy. The lapping step was performed using a lapping apparatus, and the grain size of the abrasive grains was # 400.
Specifically, first, using alumina abrasive grains with a grain size of # 400, setting the load L to about 100 kg, and rotating the internal rotation gear and the external rotation gear, both surfaces of the glass substrate housed in the carrier have a surface accuracy of 0. Lapping was performed to about 1 μm and a surface roughness (Rmax) of about 6 μm (measured by JIS B0601).
[0052]
(2) Shape processing process
Next, a hole was made in the center of the glass substrate using a cylindrical grindstone, and the outer peripheral end surface was also ground to a diameter of 95 mmφ. Then, the outer peripheral end surface and the inner peripheral end surface were subjected to predetermined chamfering. At this time, the surface roughness of the end face of the glass substrate was about 4 μm in Rmax.
[0053]
(3) Mirror finish process
Next, the surface roughness of the outer peripheral end surface and the inner peripheral end surface of the glass substrate is changed to Rmax = 0.17 μm, Ra by rotating the glass substrate by brush polishing using a slurry (cerium oxide abrasive grains). = 0.02 μm, outer peripheral end surface (chamfered surface) Rmax = 0.77 μm, Ra = 0.10 μm, inner peripheral end surface (sidewall surface) Rmax = 0.17 μm, Ra = 0.02 μm, inner peripheral end surface (surface) The ground surface was polished to Rmax = 0.60 μm and Ra = 0.08 μm. In addition, Rmax and Ra were measured by TencorP2: manufactured by KLA-Tencor.
The glass substrate after the end mirror processing step was washed with water.
[0054]
(4) Wrapping process
Next, the particle size of the abrasive grains was changed to # 1000, and the surface of the glass substrate was wrapped so that the flatness was 3 μm, the surface roughness was about 2 μm in Rmax, and Ra was about 0.2 μm. Note that Rmax and Ra were measured by AFM (atomic force microscope).
The glass substrate after the lapping step was washed by sequentially immersing the glass substrate in a neutral detergent and water washing tank.
[0055]
(5) Polishing process
Next, a polishing step was performed. This polishing step is for the purpose of removing scratches and distortion remaining in the above-described lapping step, and was performed using a polishing apparatus.
Here, the change in the shape of the end portion of the substrate greatly depends on the conditions such as the polisher (polishing pad) used in the polishing step, the processing surface pressure, etc., and the chemical strengthening condition (340) obtained in the first embodiment is used. In view of the amount by which the outer peripheral edge shape changes at (° C. × 2 hr) (Ski-jump change amount: 0.004 μm), the substrate edge shape after the polishing step is approximately Ski-jump value = 0 μm and Roll-Off value. = Polishing was performed under the conditions of about −0.004 μm. The Ski-jump value and the Roll-Off value were measured under the same conditions as in Examples 1 and 2.
The polishing conditions are as follows.
Polishing liquid: cerium oxide (average particle size 1.0 μm) (free abrasive + water)
Polisher: Soft polisher (hardness 68 (Asker-C)
Processing pressure: 200 kg (surface pressure: 66 g / cm 2 )
Polishing time: 80min
Removal amount: 50 μm
Upper surface plate rotation teaching: 20 rpm
Lower platen rotation speed: 26 rpm
Revolutionary teaching of career (revolution): 3 rpm
Carrier rotation (rotation): 3 rpm
The glass substrate after the polishing step was sequentially immersed in each of cleaning tanks of a neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying).
The outer peripheral end shape of the obtained substrate was measured with a surface roughness measuring device (Surftest SV-624: manufactured by Mityo Corporation). The Ski-jump value = + 0.002 μm and the Roll-Off value = −0.005 μm. There was obtained an outer peripheral end shape slightly inclined to the main surface.
[0056]
(6) Chemical strengthening process
Next, the glass substrate after the cleaning step was chemically strengthened. For chemical strengthening, prepare a chemical strengthening solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed in a chemical strengthening treatment tank, heat this chemical strengthening solution to 340 ° C, and wash it preheated to 300 ° C. The glass substrate was immersed for 2 hours.
The glass substrate that had been chemically strengthened was immersed in a water bath at 20 ° C., rapidly cooled, and maintained for about 10 minutes. This makes it possible to remove defective products having minute cracks.
The glass substrate after the chemical strengthening step was washed by sequentially immersing it in each of 10% by weight sulfuric acid, a neutral detergent, pure water, pure water and IPA.
[0057]
When the shape of the outer peripheral edge of the glass substrate obtained through the above steps was measured, the Ski-jump value = + 0.002 μm and the Roll-Off value = + 0.005 μm. Using the surface as a reference surface, a good value within the range of ± 0.005 μm (−0.005 μm to +0.005 μm) is obtained, and a glass substrate having a substantially flat substrate outer peripheral edge after the chemical strengthening treatment is obtained. Was.
The depth of the compressive stress layer of the glass substrate obtained after the chemical strengthening treatment was 79.8 μm, and the value of the compressive stress was 13.8 kg / mm. 2 , The value of tensile stress is 2.0 kg / mm 2 And was the same as the value shown for Sample 1-2 in Table 1.
The surface roughness (Ra, Rmax) of the main surface of the glass substrate, the surface undulation Wa, and the surface undulation (small undulation) Wa (Ra) in a minute region at the outer peripheral edge of the substrate were measured, and Ra = 0.51 nm. , Rmax = 5.20 nm, Wa (Ra) = 0.50 nm, and Wa = 0.43 nm.
The surface roughnesses Ra and Rmax are measured by an AFM (atomic force microscope), and the surface undulations (micro undulations) Wa (Ra) in a minute area are measured by a multifunctional surface analyzer (MicroXAM: manufactured by PHASE SHIFT TECHNOLOGY). In the measurement, the surface waviness Wa was measured by a multifunctional disk interferometer (OPTIFLAT: manufactured by PHASE SHIFT TECHNOLOGY).
The surface undulation (micro undulation) Wa (Ra) in the minute region and the measurement conditions and definition of the surface undulation Wa are as follows.
Surface undulation (micro undulation) Wa (Ra) in a minute area, surface undulation Wa scans a predetermined area of a substrate surface using white light or the like, and reflects reflected light from the substrate surface and reflected light from the reference surface. Are synthesized, and the surface undulation is calculated by the interference fringes generated at the synthesis point.
The surface undulation (small undulation) Wa (Ra) in the minute region has a swell period of about 2 μm to 4 μm and indicates an average of absolute values of deviations from the center line to the measurement curve. Here, the center line refers to a straight line in which, when a straight line parallel to the average line of the measurement curve is drawn, the area surrounded by the straight line and the measurement curve is equal on both sides of the straight line.
The surface undulation (small undulation) Wa (Ra) in the minute region is a value represented by the following equation (1).
[0058]
(Equation 1)
The surface undulation (small undulation) Wa (Ra) in the small area is a value measured in a rectangular area (about 250,000 pixels) of about 500 μm × about 600 μm.
The surface undulation Wa is a relatively large peak (valley) compared to the period of the surface undulation Wa (Ra) in the above-mentioned minute region, where the period of the undulation is about 300 μm to 5 μm, and the deviation from the center line to the measurement curve. Mean the absolute value of The definition of the center line is the same as above.
The surface undulation Wa is a value represented by the following equation (2).
[0060]
(Equation 2)
The value of the surface waviness Wa is a value measured in a range of a radius r = 20.3 to 45.0 mm (about 115400 pixels) from the center of the substrate.
[0062]
(7) Magnetic disk manufacturing process
A NiAl seed layer, a CrMo underlayer, a CoCrPtTa magnetic layer, and a hydrogenated carbon protective layer were sequentially formed on both sides of the glass substrate for a magnetic disk obtained through the above-described steps using an in-line type sputtering apparatus, and a dipping method was performed. Thus, a perfluoropolyether liquid lubricating layer was formed to obtain a magnetic disk for LUL (load / unload) system.
The obtained magnetic disk was mounted on a LUL type HDD (hard disk drive), but no head crash occurred due to the outer peripheral end shape (raised or lowered), and the flying stability of the magnetic head was good. Further, the surface roughness (Ra, Rmax), the surface undulation Wa, and the surface undulation (small undulation) Wa (Ra) in a minute area are all good (small values), so that the touchdown height is also 10 nm or less. It showed good values and did not cause head crash. In addition, the recording area could be expanded.
[0063]
(Comparative Example 1)
In the above polishing step, the glass for a magnetic disk was manufactured in the same manner as in Example 3 except that the shape of the outer peripheral end portion was not particularly adjusted (the surface was not slightly lowered) and the chemical strengthening treatment conditions were set to 380 ° C. × 4 hours. A substrate and a magnetic disk were produced.
As a result, the surface roughness of the main surface of the glass substrate was almost the same as that of Example 3, but Ski-jump = + 0.421 μm and Roll-Off = + 0.420 μm. Occurred.
The depth of the compressive stress layer of the glass substrate obtained after the chemical strengthening treatment was 140.8 μm, and the value of the compressive stress was 20.5 kg / mm. 2 The value of the tensile stress is 2.7 kg / mm 2 Which was the same as the value shown in Sample 1-7 in Table 1.
When the surface waviness Wa (Ra) and the surface waviness Wa in the minute region at the outer peripheral edge of the substrate were measured, Wa (Ra) = 0.93 nm and Wa = 1.85 nm.
[0064]
From the results of Example 3 and Comparative Example 1, in Example 3, the chemical strengthening treatment conditions were determined within a range satisfying the mechanical durability required for the glass substrate for a magnetic disk, and the chemical strengthening treatment determined above was determined. From the correlation between the condition and the amount of change in the end shape of the glass substrate, the amount of change in the end shape caused by the chemical strengthening treatment conditions is anticipated, and the end shape before the chemical strengthening treatment is adjusted by a polishing process or the like. By finishing to a predetermined end shape, even when mounted on a LUL type HDD (hard disk drive), no head crash occurs due to the outer end shape (raised or lowered), and the flying stability of the magnetic head is good. A magnetic disk glass substrate and a magnetic disk can be obtained, but if alignment is not performed as in Comparative Example 2, a magnetic disk glass substrate applicable to the LUL system It can be seen that the fine magnetic disk can not be obtained.
From the results of Example 3 and Comparative Example 1, as the shape change of the outer peripheral end face due to the chemical strengthening treatment increases (as the chemical strengthening treatment conditions increase), the Ski-jump value, the surface waviness Wa, and Wa (Ra) increase. It turns out that it becomes.
[0065]
(Example 4)
A glass substrate for a CSS-type magnetic disk and a magnetic disk were manufactured in the same manner as in Example 3 except that the hydrofluoric acid treatment was added to the cleaning process after the polishing process in Example 3 described above.
As a result, the outer peripheral end shapes (Ski-jump value, Roll-Off value) are almost the same, and the surface roughness of the glass substrate main surface becomes Rmax = 7.8 nm and Ra = 0.83 nm by the hydrofluoric acid treatment. No head crash occurred due to the end shape, and the flying stability of the magnetic head was good. In addition, the recording area could be expanded.
[0066]
(Example 5)
In the above-mentioned Example 3, in order to apply the chemical strengthening treatment conditions of 380 ° C. × 4 hours in the chemical strengthening step, the outer peripheral end portion was obtained under the chemical strengthening treatment conditions (380 ° C. × 4 hours) obtained in the previous Example 1. In anticipation of the amount of change in the shape (Ski-jump change amount: 0.035 μm), the edge shape of the substrate after the polishing step is such that the Ski-jump value is about 0 μm and the Roll-Off value is about −0.035 μm. A glass substrate for a magnetic disk and a magnetic disk were produced in the same manner as in Example 3 except that polishing was performed by selecting the polishing conditions that resulted in:
Polishing conditions were such that the polisher had a hardness of 80 (Asker-C), and other polishing conditions such as processing pressure and polishing time were appropriately adjusted for polishing.
As a result, when the outer peripheral edge shape of the obtained substrate was measured, the Ski-jump value = + 0.03 μm and the Roll-Off value = −0.04 μm. Got worse. The obtained magnetic disk was mounted on a LUL type HDD (hard disk drive), but no head crash occurred due to the outer peripheral end shape (raised or lowered), and the flying stability of the magnetic head was good. In addition, the recording area could be expanded. It is considered that this is because the amount of change in the outer peripheral end shape due to the chemical strengthening treatment was too large, and accurate control of the end shape could not be performed. In addition, when a plurality of glass substrates were manufactured under the conditions of Example 3 and Example 5, and the shape of the end portion was measured, the variation in the shape of the end portion was smaller in Example 3, and the end portion was more stable. It was confirmed that a glass substrate having a good shape was obtained.
[0067]
Note that the present invention is not limited to the above-described embodiment.
[0068]
For example, the present invention can be similarly applied to control of the shape of the inner peripheral end as well as the outer peripheral end of the glass substrate.
[0069]
The chemical strengthening conditions for controlling the outer peripheral end shape and / or the inner peripheral end shape include not only the heating temperature and the immersion time, but also the type of the chemical strengthening treatment solution (for example, the mixing ratio of potassium nitrate and sodium nitrate). Etc.) can also be adjusted. Further, the type of the chemical strengthening treatment solution is not limited to a mixed salt of potassium nitrate and sodium nitrate, but may be a salt of potassium nitrate alone, a salt of sodium nitrate alone, or a sodium salt. 2 SO 4 , K 2 SO 4 , NaBr, KBr, KNO 2 , NaNO 2 And the like.
[0070]
Furthermore, as a means for controlling the outer peripheral end shape and / or the inner peripheral end shape, a chemical strengthening treatment is mentioned, but the present invention is not limited to this, and the substrate end shape after the polishing step is slightly raised. By subjecting the glass substrate to a process of lowering the surface (for example, dealkalization treatment), it is possible to control the shape of the outer peripheral end and / or the inner peripheral end.
[0071]
The present invention is also applicable to a case where a main surface polishing treatment is performed after a chemical strengthening treatment. In this case, considering the change of the outer peripheral end shape and / or the inner peripheral end shape in each processing, each processing condition is selected so that a desired outer peripheral end shape and / or inner peripheral end shape is obtained. Good.
[0072]
It goes without saying that the glass substrate for an information recording medium of the present invention is not limited to a glass substrate for a magnetic disk, but can be applied to a glass substrate for an optical disk, a glass substrate for a magneto-optical disk, and the like.
[0073]
【The invention's effect】
According to the method for manufacturing a glass substrate for an information recording medium of the present invention, it is possible to obtain a glass substrate after a chemical strengthening treatment having a desired outer peripheral end shape and inner peripheral end shape. According to the information recording medium of the present invention, etc., it has mechanical durability due to chemical strengthening, has sufficient smoothness to enable high-density recording, and extends the recording area to the periphery. It is possible to do.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view for explaining a state in which an outer peripheral end of a substrate is lowered.
FIG. 2 is a partial cross-sectional view for explaining a Ski-jump value and a Roll-Off value at an outer peripheral end of a substrate.
FIG. 3 is a partial cross-sectional view for explaining a Ski-jump value and a Roll-Off value at an outer peripheral end of a substrate.
FIG. 4 is a partial cross-sectional view for explaining a Ski-jump value and a Roll-Off value at an outer peripheral end of a substrate.
FIG. 5 is a diagram illustrating a relationship between hardness of a polisher and a Roll-Off change amount.
FIG. 6 is a partial cross-sectional view for explaining a state of a protrusion at an outer peripheral end of the substrate.
[Explanation of symbols]
1 Glass substrate
2 Main surface
3 chamfer
4 Side wall
5 Uplift
s Ski-jump value
r Roll-Off value
Claims (11)
前記化学強化処理によるガラス基板の外周端部及び／又は内周端部の形状変化を見込んで、化学強化処理前のガラス基板の外周端部及び／又は内周端部の形状を決定し、この決定した外周端部及び／又は内周端部の形状を有する化学強化処理前のガラス基板を得る工程と、
上記で得られた化学強化処理前のガラス基板に化学強化処理を施して、所望の外周端部及び／又は内周端部形状を有する化学強化処理後のガラス基板を得る工程と、
を有することを特徴とする情報記録媒体用ガラス基板の製造方法。A step of previously grasping a relationship between a shape change of at least an outer peripheral end and / or an inner peripheral end of the glass substrate caused by the chemical strengthening treatment and a chemical strengthening treatment condition;
In consideration of the change in the shape of the outer peripheral end and / or the inner peripheral end of the glass substrate due to the chemical strengthening treatment, the shape of the outer peripheral end and / or the inner peripheral end of the glass substrate before the chemical strengthening treatment is determined. A step of obtaining a glass substrate before the chemical strengthening treatment having a shape of the determined outer peripheral end and / or inner peripheral end;
Performing a chemical strengthening treatment on the glass substrate before the chemical strengthening treatment obtained above to obtain a glass substrate after the chemical strengthening treatment having a desired outer peripheral end portion and / or inner peripheral end shape;
A method for producing a glass substrate for an information recording medium, comprising:
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000294516A JP3568888B2 (en) | 1999-09-30 | 2000-09-27 | Glass substrate for information recording medium, information recording medium, and method for producing them |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
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| JP11-280779 | 1999-09-30 | ||
| JP28077999 | 1999-09-30 | ||
| JP2000294516A JP3568888B2 (en) | 1999-09-30 | 2000-09-27 | Glass substrate for information recording medium, information recording medium, and method for producing them |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2004126672A Division JP2004265582A (en) | 1999-09-30 | 2004-04-22 | Glass substrate for magnetic disk, and magnetic disk |
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| Publication Number | Publication Date |
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| JP2001167427A JP2001167427A (en) | 2001-06-22 |
| JP3568888B2 true JP3568888B2 (en) | 2004-09-22 |
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| WO2006075609A1 (en) * | 2005-01-12 | 2006-07-20 | Nippon Sheet Glass Co., Ltd. | Grooved glass substrate, micro chemical chip and process for producing them |
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