JP2004206741A

JP2004206741A - Glass substrate for magnetic disk, and magnetic disk using the same

Info

Publication number: JP2004206741A
Application number: JP2002371271A
Authority: JP
Inventors: Motoyuki Miyata; 素之宮田; Takashi Naito; 孝内藤; Hirotaka Yamamoto; 浩貴山本; Hiroyuki Akata; 広幸赤田
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2002-12-24
Filing date: 2002-12-24
Publication date: 2004-07-22
Anticipated expiration: 2022-12-24
Also published as: JP4193489B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic disk adaptive to high density recording, appropriate in thermal expanding coefficient, high in mechanical strength and excellent in mass-producibility, and to provide a magnetic disk using the substrate. <P>SOLUTION: The glass substrate contains rare-earth oxides of Pr, Nd, Sm and Eu. The thermal expanding coefficient of the substrate in the temperature range of 30 to 100°C is equal to or greater than 65x10<SP>-7</SP>/°C and equal to or less than 90x10<SP>-7</SP>/°C. Transmissivity of the substrate having thickness of 0.635mm in visible light beams having wavelengths of 300nm to 700nm is equal to or greater than 50% and equal to or less than 90%. When 1kOe magnetic field is applied to the substrate, the magnetization is made equal to or less than 3x10<SP>-3</SP>emu/cc. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、磁気ディスク用ガラス基板に係わり、特に熱膨脹係数及び機械的特性が適正で、さらに、量産性が良好な高密度記録に適した磁気ディスク用ガラス基板及びそれを用いた磁気ディスクに関する。
【０００２】
【従来の技術】
現在、汎用大型コンピューターやパーソナルコンピューター用の記録媒体として、さらにはデジタル信号で配信される映像を一時的に保管する家庭用のサーバーとして、磁気ディスク装置が用いられている。従来はこの磁気ディスク用の基板として汎用向けやデスクトップ型のパーソナルコンピューター用途には3.5″ サイズのアルミニウム基板が、また持ち運び可能なノート型のパーソナルコンピューター用には主に２.５″ のガラス基板が用いられてきた。
【０００３】
このガラス基板はアルミニウム基板に比べ硬くて変形し難く、かつ、表面平滑度が優れているため、前記汎用型の３.５″ あるいは３″サイズの基板にも適用されるようになってきている。さらには１.８″ ，１″といった小型携帯端末用の記録装置にもこのガラス基板が適用されようとしている。
【０００４】
こうした小型化の他、磁気ディスク装置に対する大容量化の要請が強まっており、近年では年率１００％の割合でその記憶容量が増大している。これに対応するには記録部の磁気ヘッドの浮上量をより低減させる必要があるため、より平滑な記録面を持つ磁気ディスクの開発が必要である。
【０００５】
現在では、化学強化ガラス基板や、結晶化ガラス基板を用いることにより、ガラス本来の持つ割れの問題を克服している。しかしながら、化学強化された非晶質のガラス基板では、化学強化の工程の際、アルカリイオンの置換によって強化するために表面が荒れ、将来のヘッド低浮上化に対応することが難しい。さらに上記のような使用環境下では、化学強化ガラスの表面は、置換されたイオン半径の大きいアルカリイオンが化学的に不安定であるため、生産工程中の洗浄工程や成膜工程における加熱過程の際、あるいは長期間の使用や高温多湿といった環境のもとでこのアルカリイオンが基板表面に移動，析出し、磁性膜の磁気特性の劣化，膜の剥がれや粘着などの不良を生ずることが懸念される。
【０００６】
一方、結晶化ガラス基板は、非晶質なガラスの中に結晶質の微粒子が生成しているが、この非晶質部分と結晶部分の硬度差により研磨速度が異なり、磁気ディスクに求められている更なる高密度化に対応できる十分な平滑性を持った記録面が作り難いという問題があった。
【０００７】
上記のような問題を克服するため、発明者らは、特開平１０−０８３５３１号公報に記載のように、ガラス基板に希土類イオンを含有させることにより機械的強度を高め、この問題を解決している。
【０００８】
【特許文献１】
特開平１０−０８３５３１号公報
【０００９】
【発明が解決しようとする課題】
上記特開平１０−０８３５３１号公報では、基板の機械的強度は高いガラス基板は得られるものの、磁気ディスク用ガラス基板として必要な特性である熱膨張係数の適正化や量産性が十分に考慮されているとは言いがたかった。そのため、熱衝撃などの熱的環境試験においてガラス基板とそれを支持する磁気ディスクドライブ装置部材との熱膨張特性の不整合によるクラックの発生による上記ドライブ装置の高速回転時に生じるトラックずれが発生することが考えられる。これは、今後の大容量化に伴い、より厳しい課題となるものと思われる。
【００１０】
そこで本発明では、特に熱膨張係数および機械的特性が適正で、さらに、量産性が良好な高密度記録に適した磁気ディスク用ガラス基板及びそれを用いた磁気ディスクを得ることを目的とした。
【００１１】
【課題を解決するための手段】
上記課題を解決するため、本発明の磁気ディスク用ガラス基板は、重量百分率で
ＳｉＯ₂：５５％〜７０％、
Ａｌ₂Ｏ₃：１０％〜２０％、
Ｂ₂Ｏ₃：０％〜８％、
Ｒ₂Ｏ：１３％〜１７％（Ｒはアルカリ金属元素を表す）、
ＺｎＯ：０％〜１０％、
の酸化物換算で示される酸化物を含有し、さらに下記の酸化物換算の重量百分率でＰｒ₂Ｏ₃またはＮｄ₂Ｏ₃を１％〜７％、またはＳｍ₂Ｏ₃を２.５％〜９％、またはＥｕ₂Ｏ₃を２.５％〜８％を含有し、前記Ｒ₂Ｏ（Ｒはアルカリ金属元素を表す）が、Ｌｉ₂Ｏ，Ｎａ₂Ｏ，Ｋ₂Ｏからなり、かつＬｉ₂ＯとＮａ₂Ｏの割合がＬｉ₂Ｏ／Ｎａ₂Ｏの比で０.６１以上，６.００以下であり、３０℃〜１００℃の温度範囲における熱膨張係数が６５×１０^-7／℃以上，９０×１０^-7／℃以下である。
【００１２】
さらに本発明の磁気ディスク用ガラス基板は、厚さ０.６３５mm において、波長３００ｎｍ〜７００ｎｍの可視光における透過率が５０％以上９０％以下であり、かつ１ｋＯｅの磁界を印加したときの磁化が３×１０^-3ｅｍｕ／cc以下である。
【００１３】
また本発明の磁気ディスクは、磁気ディスク用ガラス基板と、この基板上に直接又は他の層を介して形成された磁性層を有する磁気ディスクであって、上記ガラス基板は重量百分率で
ＳｉＯ₂：５５％〜７０％、
Ａｌ₂Ｏ₃：１０％〜２０％、
Ｂ₂Ｏ₃：０％〜８％、
Ｒ₂Ｏ：１３％〜１７％（Ｒはアルカリ金属元素を表す）、
ＺｎＯ：０％〜１０％
の酸化物換算で示される酸化物を含有し、さらに下記の酸化物換算の重量百分率でＰｒ₂Ｏ₃またはＮｄ₂Ｏ₃を１％〜７％、またはＳｍ₂Ｏ₃を２.５％〜９％、またはＥｕ₂Ｏ₃を２.５％〜８％を含有し、前記Ｒ₂Ｏ（Ｒはアルカリ金属元素を表す）が、Ｌｉ₂Ｏ，Ｎａ₂Ｏ，Ｋ₂Ｏからなり、かつＬｉ₂ＯとＮａ₂Ｏの割合がＬｉ₂Ｏ／Ｎａ₂Ｏの比で０.６１以上，６.００以下であり、３０℃〜１００℃の温度範囲における熱膨張係数が６５×１０^-7／℃以上，９０×１０^-7／℃以下である。
【００１４】
また本発明の磁気ディスクは、少なくともガラス基板と、その表面上に直接または他の層を介して形成される磁性膜とを有する磁気ディスクであって、厚さ０.６３５mm のガラス基板の波長３００ｎｍ〜７００ｎｍの可視光における透過率が５０％以上９０％以下であり、かつこのガラス基板に１ｋＯｅの磁界を印加したときの磁化が３×１０^-3ｅｍｕ／cc以下である。
【００１５】
【発明の実施の形態】
次に、本発明の実施の形態を詳細に説明する。
【００１６】
【実施例１】
図１に、本発明による磁気ディスク基板の平面図を示す。本発明では磁気ディスク用ガラス基板１として直径６５mmφ，厚さ０.６３５mmの２.５″型ガラス基板を作製した。なお、この基板は内周チャックのための直径２０mmφの丸穴２が形成されている。また、この内周，外周部は、チャンファー部３が形成されている。このチャンファーは、基板エッジ部に両面４５°の面取りがなされている。
【００１７】
この磁気ディスク用ガラス基板の作製は、以下のようにして行った。まず、目的のガラス組成になるように定められた量の原料粉末を秤量して混合し、白金製の坩堝に入れて、電気炉中で１６００℃で溶解した。原料が十分に溶解した後、攪拌羽をガラス融液に挿入し、約４時間攪拌した。その後、攪拌羽を取り出し、３０分間静置した後、鋳型に融液を流し込むことによって直径約７０mmφ，厚さ約１mmのガラスブロックを得た。その後、このガラスのガラス転移点付近までガラスブロックを再加熱し、徐冷して歪み取りを行った。
【００１８】
次いで、歪み取りされたガラスブロックを内周，外周を同心円としてコアドリルを用いて切り出した。さらに、内外周をダイヤモンド砥石を用いてチャンファー部の面取り加工を行った。その後、両面を粗研磨し、次いでポリッシングを行い、さらに洗浄剤，純水で基板を洗浄し、磁気ディスク用ガラス基板とした。以上のように本発明の磁気ディスク用ガラス基板では、化学強化処理のような特別な強化処理を施していない。
【００１９】
本基板上に磁性膜を成膜し、磁気ディスクを作製した。図２に、本発明で作製した磁気記録媒体の断面構造の概略図を示す。図２において１は本発明で作製したガラス基板、４は磁性膜の粒径を制御するための粒径制御層、５は磁性膜の配向を制御するための配向制御層、６は磁性膜、７は保護膜、８は潤滑膜である。本発明では４の粒径制御層としてＮｉＡｌ系の合金膜を２０ｎｍ成膜した。また５の配向制御層としてＣｒＭｏ系合金薄膜を１０ｎｍ、さらに６の磁性膜としてＣｏＣｒＰｒＢ系磁性膜を２０ｎｍ成膜した。また保護膜にはＣを４ｎｍ成膜した。これらの薄膜はすべてスパッタリング法を用いて成膜した。また潤滑膜はスパッタ終了後、塗布法によって形成した。
【００２０】
以上のようにして作製した磁気ディスク用ガラス基板、及びそれに磁性膜を形成した磁気ディスクの特性，量産性を評価し、ガラス組成の検討を行った。
【００２１】
まず、添加する希土類元素の種類に着目し、色々な組成のガラスを作製した。表１に、本発明で作製したガラスの組成、及びそれらのガラス基板及び磁気ディスクの特性を示す。
【００２２】
【表１】

【００２３】
表１において、希土類元素以外の母ガラス組成は、同一組成のアルミノホウケイ酸ガラスとした。含有させる希土類酸化物の量はいずれも３重量％と一定にした。ガラス基板の特性として、マイクロビッカース硬さ，可視光の透過率、及び着色性及びガラス基板の歩留まりを評価した。マイクロビッカース硬さは荷重５００ｇ，荷重印加時間１５秒の条件で荷重を印加し、１０点の平均値として求めた。可視光の透過率は、分光光度計を用いて３００ｎｍから７００ｎｍまでの波長の分光透過率曲線より透過率スペクトルを測定し、この波長範囲の光の全透過率の積分値として求めた。着色性は目視により着色の程度を評価し、無色のものは×、着色しているものは○とした。歩留まりの評価は、ガラス基板をレーザー光照射による散乱光により異物数を検査する装置により評価し、気泡，研磨傷，かけ，表面異物等の不良がディスク片面当たり２０個以上のものを不良としてカウントし、不良でないものの割合を評価した。
【００２４】
また磁気ディスクの特性として磁化、及び磁化の標準偏差，記録再生特性及び磁気ディスクの歩留まりを評価した。また基板加工前のブロック作製から磁気ディスク作製にいたるまでの総合歩留まりを評価した。磁化及び磁化の標準偏差は、Ｂ−Ｈ曲線を振動試料型磁力計（ＶＳＭ）によって測定し、磁性膜のヒステリシスループのバックグラウンド成分を基板からの磁性とし、そのバックグラウンド成分の大きさを評価した。表には磁界として１ｋＯｅ印加したときのバックグラウンドの磁化の大きさを掲載した。
【００２５】
またこの磁気ディスクの記録再生特性を評価した。図３に、本発明で作製した記録再生特性評価用の磁気ディスクドライブを示す。図３において、９は磁気ディスク、１０はスピンドル、１１は磁気ヘッド、１２は磁気ヘッドのアーム、１３はヘッドを駆動するためのボイスコイルモーター、１４は全体を支える筐体である。なお、この図では記されていないが、磁気ディスク９の下部にはスピンドルモーターが設置されており、ディスク全体を回転させる。図３の磁気ディスクドライブに各磁気ディスクを搭載し、２０Ｇｂ／ｉｎ² に相当する磁気信号を記録し、磁気記録再生特性を評価した。この評価を１５０枚のディスクに対して行い、十分な記録再生特性が得られたものの割合を磁気ディスク歩留まりとして表記した。
【００２６】
さらに上記のガラス基板歩留まりと磁気ディスク歩留まりより総合歩留まりを評価した。総合での歩留まりが８０％未満のものを×、８０％以上９０％未満のものを○、９０％以上のものを◎とした。
【００２７】
表１の基板特性のマイクロビッカース硬さはいずれの基板でも６４０以上が得られており、良好であることが分かった。また可視光の透過率は、いずれの基板でも８０％以上であった。これらのうちＮｄ，Ｐｒ，Ｓｍ，Ｅｕ，Ｈｏ，Ｅｒは可視光域に希土類のｆ−ｆ遷移に起因するシャープな吸収が見られた。このため、他の元素に比べて透過率は若干低下しており、８５％以下であった。しかしながらこの鋭い吸収のため、ガラス基板に明確な着色が見られた。白熱灯下での目視観察による評価では、Ｐｒは黄緑、Ｎｄは紫色、Ｓｍ，Ｅｕは非常に淡いがそれぞれ黄色と桃色に着色しているのが見られた。また、Ｅｒ，Ｈｏも桃色に着色していた。
【００２８】
そのほかの希土類元素を含有させた基板は無色であり、透過率はいずれも８５％を超え、着色は見られなかった。
【００２９】
これらの基板に対するガラス基板の歩留まりを評価すると、明瞭な着色の見られたＰｒ，Ｎｄ，Ｓｍ，Ｅｕ，Ｈｏ，Ｅｒでは加工による不良、特に傷不良が着色していないものに比べて少なく、歩留まりが９５％以上となった。これは、基板加工工程，洗浄工程において基板が可視であるため、取扱いが容易なことから歩留まりが向上したと考えられる。
【００３０】
また比較例として酸化ニッケル（ＮｉＯ）を含有する着色性の高いガラス基板について評価した。この基板は透過率が４７％と低く、ガラス中に存在する気泡、あるいは熔融時のるつぼを構成する成分のガラス中への溶損を発見することが難しく、基板表面にこれらが残存することから歩留まりが低下していた。また若干ＮｉＯ含有量を低下させ、透過率を５０％以下としたガラス基板では、基板を光が透過して、基板内部を観察可能であることが分かった。このため、気泡などによる不良が減少し、歩留まりが向上した。
【００３１】
以上のことから、透過率と磁気ディスクの歩留まりとの間に明瞭な相関関係が見られた。ガラス基板の透過率が５０％以上９０％以下のとき着色性が良好で、歩留まりが良好なガラス基板が得られた。透過率が５０％未満となると基板中に残存する気泡，炉材混入が発見し難く、歩留まり低下の要因となった。また基板の透過率が９０％をこえると、基板取扱いが難しくなり、傷などの加工不良が増加していたため、好ましいといえなかった。
【００３２】
また上記の光学的な特性を達成するため、添加する元素はＰｒ，Ｎｄ，Ｓｍ，Ｅｕ，Ｅｒ又はＨｏが良好であることが分かった。このうち、Ｐｒ，Ｎｄ，Ｅｒ又はＨｏであれば着色が顕著であり、より好ましかった。
【００３３】
次に、磁気ディスクの磁気特性について評価した。Ｓｃ，Ｙ，Ｌａを含有した磁気ディスクでは、基板の磁化の大きさが１０^-4ｅｍｕ／ccのオーダーであり、きわめて小さい磁化量であった。Ｓｍを用いたときは、磁化は反磁性的な挙動を示しており、−４×１０^-4ｅｍｕ／ccとなった。またＰｒ，Ｎｄ，Ｅｕでは１〜３×１０^-3ｅｍｕ／ccのオーダーであったが、Ｇｄ，Ｔｂ，Ｄｙ，Ｈｏ，Ｅｒ，Ｔｍ，Ｙｂでは５×１０^-3〜２×１０^-2ｅｍｕ／ccと、磁化の値が大きくなっていた。
【００３４】
磁化の固体差を示す磁化の標準偏差を評価したところ、磁化の大きさの大きいものほど大きくなっており、基板によるばらつきが大きくなっていた。特に磁化の大きさが３×１０^-3を超えるＧｄ，Ｔｂ，Ｄｙ，Ｈｏ，Ｅｒ，Ｔｍ，Ｙｂでは、磁化の標準偏差が１×１０^-3ｅｍｕ／cc以上となり、基板による磁気特性のばらつきが大きくなった。
【００３５】
磁気記録再生特性による磁気ディスク歩留まりを見ると、磁化が３×１０^-3ｅｍｕ／cc以下で、磁化の標準偏差が１×１０^-3ｅｍｕ／cc未満の試料では、良好な磁気特性の得られる磁気ディスクが９０％以上と良好であったが、磁化が３×１０^-3ｅｍｕ／ccを超え、かつ磁化の標準偏差が１×１０^-3ｅｍｕ／cc以上となる試料では、歩留まりが８０％以下と急激に低下していることが分かった。これは、基板に含有される希土類元素の若干の固体差により基板の磁気特性が変化し、そのために標準偏差が大きくなるため、記録する際の磁界を一定にした場合の記録にばらつきが生じたためと考えられる。
【００３６】
以上より、基板の磁化に与える影響が小さい希土類元素としてＳｃ，Ｙ，Ｌａ，Ｐｒ，Ｎｄ，Ｓｍ，Ｅｕが良好であった。また、磁化の大きさが３×１０^-3ｅｍｕ／cc以下であれば磁気記録再生のばらつきが小さい磁気記録媒体が得られた。磁化の大きさが３×１０^-3ｅｍｕ／ccを超えると磁気記録再生特性に基板ごとのばらつきが大きくなるため、好ましいとはいえなかった。
【００３７】
上記の光学的な特性が及ぼすガラス基板の歩留まりに与える影響、及び磁気的な特性が記録再生特性に及ぼす影響を考慮して総合歩留まりを評価した。その結果、両者とも良好なＰｒ，Ｎｄ，Ｓｍ，Ｅｕを用いたガラス基板の場合、総合歩留まりが８０％以上となり、良好であった。これに対してその他の希土類を添加した場合には、総合歩留まりが８０％以下となるため、良好といえなかった。
【００３８】
また、特に希土類元素としてＰｒを用いると、総合歩留まりが９０％となり、さらに良好な結果が得られた。
【００３９】
次に、希土類酸化物の種類と添加量の関係について詳細に調べた。着色については、表１で透明であったものについては含有量を増減させても透過率に変化は見られなかった。このため、着色した元素のうち、Ｐｒ，Ｅｒ，Ｓｍについて、その含有量を変化させたガラス基板を作製し、表１と同様の検討を行った。表２に、検討した結果を示す。
【００４０】
【表２】

【００４１】
Ｐｒの含有量を変化させていったところ、試料Ｎo.１７のＰｒ₂Ｏ₃を０.７重量％含有するガラス基板では、マイクロビッカース硬さが低く、そのためガラスの機械的強度が低いためにガラス基板歩留まりが８２％と低かった。１％の試料Ｎo.１６、及び１.５％〜７％の実施例１８〜２１では、マイクロビッカース硬さも高い値を示しており、着色，磁気特性とも良好であった。この事から総合歩留まりも８０％を超えており、良好な結果となった。
【００４２】
一方、試料Ｎo.２２のようにＰｒ₂Ｏ₃含有量が７％を超えるものでは着色に関しては問題無かったものの、磁気ディスクの磁化が３×１０^-3ｅｍｕ／ccを超える値となった。このため、磁化のばらつきが大きくなり、磁気ディスク歩留まりが８０％を下回り、好ましい結果とは言えなかった。さらに実施例２３のガラス基板ではガラス中の希土類元素が均一にガラス中に溶解せず、不良品数が多く、歩留まりが１５％と低かった。このため、ガラス基板材料としては好ましくなかった。
【００４３】
さらに希土類元素をＥｒに変えた場合の実施例をみると、Ｅｒ含有量が０.５％の試料Ｎo.２５では含有量が少なく、マイクロビッカース硬さが小さいため、歩留まりが悪かった。またこのとき磁気ディスクの磁化の値が３.１ ×１０^-3ｅｍｕ／ccと高く、磁気ディスクとしての歩留まりも低下していた。またＥｒ含有量が１％からＥｒ含有量を増加させていくと、マイクロビッカース硬さも高くなり、透過率は低くなって基板歩留まりは上昇するものの、磁化が依然として３×１０^-3ｅｍｕ／ccを超えるため、基板としての歩留まりが低下していた。以上より、希土類元素としてＥｒを用いた場合では、基板の硬さ，光学特性，磁気特性の両者を同時に満たす組成範囲が存在しないことが分かった。
【００４４】
Ｓｍについてみると、光学的特性については２.５重量％以上であると透過率が８５％以下で適正な範囲となった。磁気特性は１０重量％含有させても適正であったが、１０重量％を超えるとＰｒの時と同様にガラス中に残存原料が残り、好ましくなかった。
【００４５】
同様にＮｄ，Ｅｕ，Ｈｏについて検討を行ったところ、Ｎｄ，Ｅｕについては、８重量％を超える場合に磁気特性が良好でなかったものの、Ｓｍと同様の結果が得られた。ＨｏについてはＥｒと同じく、光学的特性と磁気特性の両者を同時に満たす組成範囲が存在しなかったたため、好ましい結果が得られなかった。
【００４６】
以上より、光学的特性，磁気特性の双方で好ましい組成範囲をとる希土類元素としてＰｒ，Ｎｄ，Ｓｍ，Ｅｕが良好であると判断できた。その中でもＰｒ，
Ｎｄを用いれば１重量％〜７重量％の組成範囲で良好な組成範囲をとることができた。またＳｍの場合では２.５〜９重量％、Ｅｕの場合では２.５〜８重量％で良好な特性を得ることができた。またＰｒを１.５重量％〜５.２重量％含有させた場合については、総合歩留まりが９０％以上となり、非常に良好な結果が得られた。
【００４７】
これらの希土類の含有量が少ないと、マイクロビッカース硬さなどの機械的強度が低かったり、透過率が高かったりし、ガラス基板の歩留まりが低下するため好ましくなかった。また希土類含有量が多いと、基板の磁化の値が大きくなるため、磁気特性が良好でなくなった。また、さらに多量に添加するとガラス中に原料が残存するため、好ましくなかった。
【００４８】
【実施例２】
次に、磁気ディスク用ガラス基板として適切なガラス組成範囲について検討した。表３に、本発明で作製したガラス基板の実施例を示す。添加する希土類としては実施例１で良好な結果が得られたＰｒを用いた。表のガラス組成の中で、Ｒ₂ＯとはＬｉ₂Ｏ，Ｎａ₂Ｏ，Ｋ₂Ｏのトータルのアルカリ金属酸化物含有量を示す。
【００４９】
【表３】

【００５０】
各試料について、磁気ディスク用ガラス基板作製の際のガラスの安定性，ガラス材の熱膨張係数，ガラス基板表面のマイクロビッカース硬さ，円環強度を示した。
【００５１】
ここで、熱膨張係数は各ガラスのブロックを作製し、１５mm×４mm×４mmの熱膨張測定用試験片を切り出し、熱膨張測定装置を用いて測定した。測定温度範囲は、３０℃〜１００℃とした。
【００５２】
マイクロビッカース硬さは、ダイヤモンド圧子をガラス基板の表面に荷重500ｇ，荷重印加時間１５秒の条件で印加し、１０点の平均値として求めた。
【００５３】
また得られた基板より実施例１と同様に磁気ディスクを作製し、これを図３に示した磁気ディスクドライブに搭載してドライブの熱衝撃試験を実施した。熱衝撃試験によりガラスにクラックや割れ，トラックずれによる読み取りエラーなどの問題が生じなかった場合は○を、生じた場合を×とした。熱衝撃試験は−４０℃で２時間保持後、８０℃まで急速加熱させ、８０℃で２時間保持後、−４０℃まで急冷する。これを５回繰り返し、その間で上記した問題が生じるか否かを判定した。
【００５４】
ガラスの安定性では、ガラス溶解後ガラス基板中に見られる気泡，脈理，異物などが顕著に見られたものは×とし、そのような物が見られず、清澄なガラスが得られた場合は○とした。
【００５５】
また、円環強度は以下のようにして求めた。２.５″ 基板の内周部の上部に、外径２２mmφの円環を載せ、また内径６３mmφ，外径６５mmφの円環の基板の下部に設置した後、円環に荷重をかけて破壊強度を測定した。
【００５６】
まず、Ｌｉ₂Ｏ，Ｎａ₂Ｏ，Ｋ₂Ｏのトータルのアルカリ酸化物量（表中のＲ₂Ｏ）を変化させた試料を表３のＮo.４２〜４９に示す。
【００５７】
Ｎo.４３，Ｎo.４４のようにアルカリ金属酸化物含有量が１３％未満のガラスを用いた場合、熱衝撃試験でガラスにクラックが生じた。また、逆にＮo.４９のようにアルカリ金属酸化物の含有量が１７重量％を超えるような場合には、熱衝撃試験ではトラックずれによるエラーが生じ、また高速回転試験では回転歪が生じやすくなるため、トラックずれによるエラーが生じるため好ましくなかった。Ｎo.４２，４５〜４８のガラスのようにアルカリ金属酸化物の合計の含有量が
１３重量％〜１７重量％の場合、熱衝撃試験で良好な結果が得られ、好ましい結果となった。
【００５８】
これらのガラスの熱膨張係数に着目すると、表３よりＮo.４３，Ｎo.４４のガラスはそれぞれ５９×１０^-7／℃，６１×１０^-7／℃とドライブ装置部材の熱膨張係数である７０×１０^-7／℃〜８０×１０^-7／℃よりもかなり小さくなっていた。これらのガラスでは、他の装置部材との熱膨張の差異により熱衝撃試験においてクラックが発生したりトラックずれが生じたりしたため、好ましいとは言えなかった。
【００５９】
Ｎo.４２，４５〜４８のガラスに示すように、熱膨張係数が６５×１０^-7／℃以上，９０×１０^-7／℃以下であれば熱衝撃試験で良好な結果が得られた。以上より、適正な熱膨張係数は６５×１０^-7／℃以上，９０×１０^-7／℃以下であった。
【００６０】
つぎに、Ｎo.５０〜５５においてＳｉＯ₂ 含有量について検討した。ＳｉＯ₂ 含有量が５４重量％のＮo.５２のガラスでは、円環強度が十分でなく、磁気ディスク用ガラス基板として適切ではなかった。またＮo.５５のようにＳｉＯ₂ 量が７０重量％を超えると、ガラス溶解時に気泡などの発生が顕著になり、好ましくなかった。以上より、ＳｉＯ₂ 含有量は５５重量％以上７０重量％以下であると磁気ディスク用ガラス基板として良好な結果が得られた。
【００６１】
次にＡｌ₂Ｏ₃含有量について検討した。Ｎo.５７のＡｌ₂Ｏ₃含有量が２１重量％であるガラスでは、ガラスの熔融温度が高くなりすぎ、１６００℃の熔融ではガラスの原料が残存したため、好ましくなかった。Ａｌ₂Ｏ₃含有量が１０重量％のＮo.５８に記載のガラスでは、安定したガラスが得られ、磁気ディスク用ガラス基板としても良好な結果が得られたが、Ａｌ₂Ｏ₃含有量が９.５重量％のＮo.５９ガラスでは、ガラス中に脈理等の不均一が生じた。以上より、Ａｌ₂Ｏ₃の含有量が１０重量％以上，２０重量％以下のとき良好なガラスが得られた。
【００６２】
さらにＢ₂Ｏ₃含有量について検討した。Ｂ₂Ｏ₃含有量が増加するに伴い、円環強度は向上したが、Ｎo.６０に示すように、９重量％であるガラスでは熱衝撃試験でガラスにクラックが生じた。以上より、Ｂ₂Ｏ₃含有量が８重量％以下であれば良好なガラスが得られた。
【００６３】
ＺｎＯに関しては、Ｎo.７２に示すように、添加量が１０重量％を超えるとガラス中に結晶の析出が著しくなり、安定なガラスを得ることが難しかった。１０重量％ではこのような結晶の析出は認められなかった。従って、ＺｎＯ含有量は、１０重量％以下であることが好ましかった。
【００６４】
次に、アルカリ金属酸化物のうち、Ｌｉ₂Ｏ含有量とＮａ₂Ｏ含有量に着目して、組成比について検討した。Ｌｉ₂Ｏ／Ｎａ₂Ｏ比が０.６０のＮo.６５のガラスおよび６.１５のＮo.６７のガラスでは熱衝撃試験においてガラスにクラックが発生し、また円環強度も低下しており、Ｌｉ₂Ｏ／Ｎａ₂Ｏ比としては、0.61以上，６.００以下であることが好ましかった。
【００６５】
【発明の効果】
本発明の磁気ディスク用ガラス基板は、基板が着色しており、磁界印加時の磁化が小さいため、量産性に優れた磁気ディスク用ガラス基板、及びそれを用いた磁気ディスクが作製できる。さらに本発明の磁気ディスク用ガラス基板は熱膨張係数が６５〜９０×１０^-7／℃であるため磁気ディスクドライブ装置部材の熱膨張係数と整合性が良好なため、熱衝撃試験等によるガラスのクラック発生やトラックずれなどの問題が少ないため、高記録密度，高信頼性が要求される磁気ディスクの基板材料として最適である。
【図面の簡単な説明】
【図１】本発明の磁気ディスク用ガラス基板の平面図。
【図２】本発明の磁気ディスク用ガラス基板を用いた磁気ディスクの断面図。
【図３】本発明で作製した磁気ディスク装置の概略図。
【符号の説明】
１…磁気ディスク用ガラス基板、２…内周チャック用穴、３…チャンファー部、４…粒径制御層、５…配向制御層、６…磁性膜、７…保護膜、８…潤滑膜、９…磁気ディスク、１０…スピンドル、１１…磁気ヘッド、１２…磁気ヘッドのアーム、１３…ボイスコイルモーター、１４…筐体。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a glass substrate for a magnetic disk, and more particularly to a glass substrate for a magnetic disk which has a proper thermal expansion coefficient and mechanical properties and is suitable for high-density recording with good mass productivity and a magnetic disk using the same.
[0002]
[Prior art]
At present, a magnetic disk device is used as a recording medium for a general-purpose large-sized computer or a personal computer, and also as a home server for temporarily storing video distributed by digital signals. Conventionally, a 3.5 "aluminum substrate has been used as a substrate for magnetic disks for general-purpose or desktop personal computers, and a 2.5" glass substrate has been mainly used for portable notebook personal computers. Has been used.
[0003]
Since this glass substrate is harder and harder to deform than an aluminum substrate, and has an excellent surface smoothness, it is also being applied to the general-purpose 3.5 "or 3" size substrate. . Furthermore, this glass substrate is about to be applied to recording devices for small portable terminals such as 1.8 "and 1".
[0004]
In addition to such miniaturization, there is an increasing demand for a magnetic disk device to have a large capacity, and in recent years, its storage capacity has been increasing at an annual rate of 100%. To cope with this, it is necessary to further reduce the flying height of the magnetic head of the recording unit, and therefore, it is necessary to develop a magnetic disk having a smoother recording surface.
[0005]
At present, the problem of cracks inherent in glass has been overcome by using a chemically strengthened glass substrate or a crystallized glass substrate. However, in the case of a chemically strengthened amorphous glass substrate, the surface is roughened due to replacement by alkali ions during the chemical strengthening process, and it is difficult to cope with a future low flying height of the head. Further, under the use environment as described above, the surface of the chemically strengthened glass is chemically unstable with the substituted alkali ions having a large ionic radius. It is feared that these alkali ions migrate and deposit on the substrate surface during use, or under long-term use or high-temperature, high-humidity environments, resulting in the deterioration of the magnetic properties of the magnetic film, and the occurrence of defects such as film peeling and adhesion. You.
[0006]
On the other hand, in the crystallized glass substrate, crystalline fine particles are generated in the amorphous glass, but the polishing rate is different due to the difference in hardness between the amorphous portion and the crystal portion, which is required for a magnetic disk. However, there is a problem that it is difficult to create a recording surface having sufficient smoothness to cope with further higher density.
[0007]
In order to overcome the above-described problems, the inventors have increased the mechanical strength by incorporating rare earth ions into a glass substrate as described in JP-A-10-083531, and solved this problem. I have.
[0008]
[Patent Document 1]
JP-A-10-083531
[0009]
[Problems to be solved by the invention]
In Japanese Patent Application Laid-Open No. 10-083531, although a glass substrate having a high mechanical strength can be obtained, optimization of the thermal expansion coefficient and mass productivity, which are characteristics required for a glass substrate for a magnetic disk, are sufficiently considered. It was hard to say that there was. Therefore, in a thermal environment test such as a thermal shock, a track shift occurs at the time of high-speed rotation of the drive device due to a crack due to a mismatch in thermal expansion characteristics between the glass substrate and a magnetic disk drive device member supporting the glass substrate. Can be considered. This seems to be a more severe issue as the capacity increases in the future.
[0010]
Therefore, an object of the present invention is to provide a glass substrate for a magnetic disk, which has a suitable thermal expansion coefficient and mechanical characteristics and is suitable for high-density recording with good mass productivity, and a magnetic disk using the same.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the glass substrate for a magnetic disk of the present invention has a weight percentage of
SiO _Two : 55% to 70%,
Al _Two O _Three : 10% to 20%,
B _Two O _Three : 0% to 8%,
R _Two O: 13% to 17% (R represents an alkali metal element),
ZnO: 0% to 10%,
Containing an oxide expressed in terms of oxide, and further containing Pr in the following weight percentage in terms of oxide: _Two O _Three Or Nd _Two O _Three From 1% to 7%, or Sm _Two O _Three From 2.5% to 9%, or Eu _Two O _Three From 2.5% to 8%, _Two O (R represents an alkali metal element) is converted to Li _Two O, Na _Two O, K _Two Consisting of O 2 and Li _Two O and Na _Two The proportion of O 2 is Li _Two O / Na _Two The ratio of O is 0.61 or more and 6.00 or less, and the coefficient of thermal expansion in the temperature range of 30 ° C. to 100 ° C. is 65 × 10 ^-7 / ℃ or more, 90 × 10 ^-7 / ° C or lower.
[0012]
Furthermore, the glass substrate for a magnetic disk of the present invention has a transmittance of 50% or more and 90% or less for visible light having a wavelength of 300 nm to 700 nm and a magnetization of 3 kPa when a magnetic field of 1 kOe is applied at a thickness of 0.635 mm. × 10 ^-3 emu / cc or less.
[0013]
Further, the magnetic disk of the present invention is a magnetic disk having a glass substrate for a magnetic disk and a magnetic layer formed directly or via another layer on the substrate, wherein the glass substrate is expressed in weight percentage.
SiO _Two : 55% to 70%,
Al _Two O _Three : 10% to 20%,
B _Two O _Three : 0% to 8%,
R _Two O: 13% to 17% (R represents an alkali metal element),
ZnO: 0% to 10%
Containing the oxide represented by the oxide conversion of _Two O _Three Or Nd _Two O _Three From 1% to 7%, or Sm _Two O _Three From 2.5% to 9%, or Eu _Two O _Three From 2.5% to 8%, _Two O (R represents an alkali metal element) is converted to Li _Two O, Na _Two O, K _Two Consisting of O 2 and Li _Two O and Na _Two The proportion of O 2 is Li _Two O / Na _Two The ratio of O is 0.61 or more and 6.00 or less, and the coefficient of thermal expansion in the temperature range of 30 ° C. to 100 ° C. is 65 × 10 ^-7 / ℃ or more, 90 × 10 ^-7 / ° C or lower.
[0014]
Further, the magnetic disk of the present invention is a magnetic disk having at least a glass substrate and a magnetic film formed directly or via another layer on the surface thereof, wherein the glass substrate having a thickness of 0.635 mm has a wavelength of 300 nm. Has a transmittance of 50% or more and 90% or less for visible light of up to 700 nm, and has a magnetization of 3 × 10 3 when a magnetic field of 1 kOe is applied to the glass substrate. ^-3 emu / cc or less.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail.
[0016]
Embodiment 1
FIG. 1 shows a plan view of a magnetic disk substrate according to the present invention. In the present invention, a 2.5 ″ glass substrate having a diameter of 65 mm and a thickness of 0.635 mm was manufactured as a glass substrate 1 for a magnetic disk. In this substrate, a round hole 2 having a diameter of 20 mm for an inner peripheral chuck was formed. A chamfer portion 3 is formed on the inner and outer peripheries of the chamfer, and the chamfer is chamfered at 45 ° on both sides of a substrate edge portion.
[0017]
The production of the glass substrate for a magnetic disk was performed as follows. First, raw material powders in an amount determined to have a desired glass composition were weighed and mixed, put in a platinum crucible, and melted at 1600 ° C. in an electric furnace. After the raw materials were sufficiently dissolved, the stirring blade was inserted into the glass melt and stirred for about 4 hours. Thereafter, the stirring blade was taken out and allowed to stand for 30 minutes, and then a melt was poured into a mold to obtain a glass block having a diameter of about 70 mmφ and a thickness of about 1 mm. Thereafter, the glass block was reheated to near the glass transition point of the glass, and gradually cooled to remove strain.
[0018]
Next, the glass block from which the distortion was removed was cut out using a core drill with the inner circumference and the outer circumference being concentric circles. Furthermore, chamfering of the chamfer portion was performed on the inner and outer circumferences using a diamond grindstone. Thereafter, both surfaces were roughly polished, then polished, and the substrate was further washed with a detergent and pure water to obtain a glass substrate for a magnetic disk. As described above, the glass substrate for a magnetic disk of the present invention is not subjected to a special strengthening treatment such as a chemical strengthening treatment.
[0019]
A magnetic film was formed on this substrate to produce a magnetic disk. FIG. 2 shows a schematic diagram of a cross-sectional structure of a magnetic recording medium manufactured according to the present invention. In FIG. 2, 1 is a glass substrate produced by the present invention, 4 is a particle size control layer for controlling the particle size of the magnetic film, 5 is an orientation control layer for controlling the orientation of the magnetic film, 6 is a magnetic film, 7 is a protective film and 8 is a lubricating film. In the present invention, a NiAl-based alloy film having a thickness of 20 nm was formed as the grain size control layer 4. Further, a CrMo-based alloy thin film was formed as an orientation control layer of 5 nm by 10 nm, and a CoCrPrB-based magnetic film of 20 nm was formed as 6 magnetic films. C was deposited to a thickness of 4 nm on the protective film. All of these thin films were formed by a sputtering method. After the sputtering, the lubricating film was formed by a coating method.
[0020]
The characteristics and mass productivity of the magnetic disk glass substrate manufactured as described above and the magnetic disk on which the magnetic film was formed were evaluated, and the glass composition was examined.
[0021]
First, attention was paid to the types of rare earth elements to be added, and glasses having various compositions were produced. Table 1 shows the compositions of the glasses produced according to the present invention and the properties of the glass substrates and magnetic disks.
[0022]
[Table 1]

[0023]
In Table 1, the mother glass composition other than the rare earth element was aluminoborosilicate glass having the same composition. The amount of the rare earth oxide to be contained was kept constant at 3% by weight. As characteristics of the glass substrate, micro Vickers hardness, transmittance of visible light, coloring property, and yield of the glass substrate were evaluated. The micro Vickers hardness was determined as an average value of 10 points by applying a load under the conditions of a load of 500 g and a load application time of 15 seconds. The transmittance of visible light was obtained by measuring a transmittance spectrum from a spectral transmittance curve of a wavelength from 300 nm to 700 nm using a spectrophotometer, and calculating the integrated value of the total transmittance of light in this wavelength range. The degree of coloring was visually evaluated to evaluate the degree of coloring. A colorless substance was evaluated as x, and a colored substance was evaluated as ○. Yield is evaluated by using a device that inspects the glass substrate for the number of foreign substances using scattered light from laser light irradiation, and counts defects with more than 20 defects on one side of the disc, such as bubbles, polishing scratches, chips, and surface foreign substances. Then, the ratio of non-defective products was evaluated.
[0024]
In addition, magnetization, standard deviation of magnetization, recording / reproduction characteristics, and yield of the magnetic disk were evaluated as characteristics of the magnetic disk. In addition, the overall yield from block fabrication before substrate processing to magnetic disk fabrication was evaluated. The magnetization and the standard deviation of the magnetization were measured by measuring the BH curve with a vibrating sample magnetometer (VSM), the background component of the hysteresis loop of the magnetic film was taken as the magnetism from the substrate, and the magnitude of the background component was evaluated. did. The table shows the magnitude of background magnetization when 1 kOe is applied as a magnetic field.
[0025]
The recording / reproducing characteristics of the magnetic disk were evaluated. FIG. 3 shows a magnetic disk drive for evaluation of recording and reproduction characteristics manufactured according to the present invention. In FIG. 3, 9 is a magnetic disk, 10 is a spindle, 11 is a magnetic head, 12 is an arm of the magnetic head, 13 is a voice coil motor for driving the head, and 14 is a housing for supporting the whole. Although not shown in this figure, a spindle motor is provided below the magnetic disk 9 to rotate the entire disk. Each magnetic disk is mounted on the magnetic disk drive of FIG. ^Two Was recorded, and the magnetic recording / reproducing characteristics were evaluated. This evaluation was performed for 150 disks, and the ratio of those having sufficient recording / reproducing characteristics was expressed as the magnetic disk yield.
[0026]
Further, the overall yield was evaluated from the above glass substrate yield and magnetic disk yield. When the overall yield was less than 80%, the result was x, when the yield was 80% or more and less than 90%, and the result was 90% or more.
[0027]
The micro Vickers hardness of the substrate characteristics shown in Table 1 was 640 or more for any of the substrates, which proved to be good. In addition, the transmittance of visible light was 80% or more for each of the substrates. Of these, Nd, Pr, Sm, Eu, Ho, and Er showed sharp absorption in the visible light region due to the ff transition of the rare earth. Therefore, the transmittance was slightly lower than that of the other elements, and was 85% or less. However, due to this sharp absorption, clear coloring was observed on the glass substrate. In the evaluation by visual observation under an incandescent lamp, it was found that Pr was yellowish-green, Nd was purple, and Sm and Eu were very pale but yellow and pink, respectively. Er and Ho were also colored pink.
[0028]
The substrates containing other rare earth elements were colorless, the transmittance exceeded 85%, and no coloring was observed.
[0029]
When the yield of the glass substrate with respect to these substrates was evaluated, Pr, Nd, Sm, Eu, Ho, and Er in which clear coloring was observed had fewer defects due to processing, particularly scratch defects, as compared with the non-colored substrate. Was 95% or more. It is considered that the yield was improved because the substrate was visible in the substrate processing step and the cleaning step, and the handling was easy.
[0030]
As a comparative example, a glass substrate containing nickel oxide (NiO) and having high coloring properties was evaluated. This substrate has a low transmittance of 47%, and it is difficult to find bubbles existing in the glass or erosion of the components constituting the crucible during melting in the glass, and these remain on the substrate surface. Yield was decreasing. In addition, it was found that in the case of a glass substrate having a slightly reduced NiO content and a transmittance of 50% or less, light was transmitted through the substrate and the inside of the substrate could be observed. For this reason, defects due to bubbles and the like were reduced, and the yield was improved.
[0031]
From the above, a clear correlation was found between the transmittance and the yield of the magnetic disk. When the transmittance of the glass substrate was 50% or more and 90% or less, a glass substrate having good colorability and a good yield was obtained. If the transmittance is less than 50%, bubbles remaining in the substrate and the mixture of furnace materials are hardly found, which causes a decrease in yield. On the other hand, if the transmittance of the substrate exceeds 90%, handling of the substrate becomes difficult and processing defects such as scratches increase, which is not preferable.
[0032]
In addition, it was found that Pr, Nd, Sm, Eu, Er or Ho was good as an element to be added in order to achieve the above optical characteristics. Among them, Pr, Nd, Er or Ho was more remarkable in coloring and was more preferable.
[0033]
Next, the magnetic characteristics of the magnetic disk were evaluated. In a magnetic disk containing Sc, Y, and La, the magnitude of magnetization of the substrate is 10 ^-Four It was of the order of emu / cc and had a very small magnetization. When Sm was used, the magnetization showed a diamagnetic behavior, and -4 × 10 ^-Four emu / cc. For Pr, Nd and Eu, 1-3 × 10 ^-3 The order of emu / cc was 5 × 10 for Gd, Tb, Dy, Ho, Er, Tm, and Yb. ^-3 ~ 2 × 10 ^-2 The value of magnetization was large, emu / cc.
[0034]
When the standard deviation of the magnetization indicating the individual difference of the magnetization was evaluated, the larger the magnitude of the magnetization, the larger the standard deviation and the larger the variation depending on the substrate. In particular, the magnitude of magnetization is 3 × 10 ^-3 For Gd, Tb, Dy, Ho, Er, Tm, and Yb, the standard deviation of magnetization is 1 × 10 ^-3 emu / cc or more, and variations in magnetic characteristics depending on the substrate increased.
[0035]
Looking at the magnetic disk yield due to the magnetic recording / reproducing characteristics, the magnetization is ^-3 At emu / cc or less, the standard deviation of magnetization is 1 × 10 ^-3 In the sample of less than emu / cc, the magnetic disk having good magnetic properties was as good as 90% or more, but the magnetization was 3 × 10 ^-3 emu / cc and the standard deviation of magnetization is 1 × 10 ^-3 It was found that in the sample having emu / cc or more, the yield sharply decreased to 80% or less. This is because the magnetic characteristics of the substrate change due to a slight difference in the solid content of the rare earth element contained in the substrate, and therefore the standard deviation increases. it is conceivable that.
[0036]
As described above, Sc, Y, La, Pr, Nd, Sm, and Eu were favorable as rare earth elements having a small effect on the magnetization of the substrate. In addition, the magnitude of magnetization is 3 × 10 ^-3 If it is less than emu / cc, a magnetic recording medium with small variations in magnetic recording and reproduction was obtained. Magnetization of 3 × 10 ^-3 If it exceeds emu / cc, the variation in magnetic recording / reproducing characteristics among the substrates increases, so that it is not preferable.
[0037]
The total yield was evaluated in consideration of the effects of the above optical characteristics on the yield of the glass substrate and the effects of the magnetic characteristics on the recording / reproducing characteristics. As a result, in the case of a glass substrate using Pr, Nd, Sm, and Eu, both of which were favorable, the total yield was 80% or more, which was favorable. On the other hand, when other rare earth elements were added, the total yield was not more than 80%, which was not good.
[0038]
In particular, when Pr was used as the rare earth element, the overall yield was 90%, and more favorable results were obtained.
[0039]
Next, the relationship between the type of rare earth oxide and the amount added was examined in detail. Regarding the coloring, those which were transparent in Table 1 showed no change in transmittance even when the content was increased or decreased. For this reason, among the colored elements, Pr, Er, and Sm were manufactured for glass substrates in which the contents were changed, and the same examination as in Table 1 was performed. Table 2 shows the results of the study.
[0040]
[Table 2]

[0041]
When the content of Pr was changed, Pr of sample No. 17 was changed. _Two O _Three The glass substrate containing 0.7% by weight had a low micro Vickers hardness and a low mechanical strength of the glass, resulting in a low glass substrate yield of 82%. In the sample No. 16 of 1% and the examples 18 to 21 of 1.5% to 7%, the micro Vickers hardness also showed a high value, and both the coloring and the magnetic properties were good. As a result, the overall yield exceeded 80%, which was a good result.
[0042]
On the other hand, as shown in sample No. 22, Pr _Two O _Three When the content exceeded 7%, there was no problem with coloring, but the magnetization of the magnetic disk was 3 × 10 ^-3 The value exceeded emu / cc. For this reason, the variation in magnetization was large, and the yield of the magnetic disk was less than 80%, which was not a favorable result. Further, in the glass substrate of Example 23, the rare earth elements in the glass were not uniformly dissolved in the glass, the number of defective products was large, and the yield was as low as 15%. For this reason, it was not preferable as a glass substrate material.
[0043]
Further, in an example in which the rare earth element was changed to Er, the sample No. 25 having an Er content of 0.5% had a low content and a low micro Vickers hardness, so that the yield was poor. At this time, the value of the magnetization of the magnetic disk is 3.1 × 10 ^-3 It was as high as emu / cc, and the yield as a magnetic disk was also low. When the Er content is increased from 1% to 1%, the Vickers hardness increases, the transmittance decreases, and the substrate yield increases, but the magnetization is still 3 × 10 5 ^-3 Since it exceeds emu / cc, the yield as a substrate has been reduced. From the above, it has been found that when Er is used as the rare earth element, there is no composition range that simultaneously satisfies both the hardness, the optical characteristics, and the magnetic characteristics of the substrate.
[0044]
As for Sm, when the optical property was 2.5% by weight or more, the transmittance was in an appropriate range at 85% or less. The magnetic properties were appropriate even when the content was 10% by weight, but when the content exceeded 10% by weight, the remaining raw materials remained in the glass as in the case of Pr, which was not preferable.
[0045]
Similarly, when Nd, Eu, and Ho were examined, the same results as those of Sm were obtained for Nd and Eu although the magnetic properties were not good when the content exceeded 8% by weight. As for Ho, there was no composition range satisfying both the optical characteristics and the magnetic characteristics at the same time as Er, and therefore, a favorable result was not obtained.
[0046]
From the above, it was determined that Pr, Nd, Sm, and Eu were favorable as rare earth elements having a preferable composition range in both optical characteristics and magnetic characteristics. Among them, Pr,
When Nd was used, a favorable composition range could be obtained in the composition range of 1% by weight to 7% by weight. In the case of Sm, 2.5 to 9% by weight, and in the case of Eu, 2.5 to 8% by weight, good characteristics could be obtained. When Pr was contained in an amount of 1.5 wt% to 5.2 wt%, the overall yield was 90% or more, and very good results were obtained.
[0047]
If the content of these rare earths is small, the mechanical strength such as micro Vickers hardness is low, the transmittance is high, and the yield of the glass substrate is unfavorably reduced. Also, when the rare earth content is large, the value of the magnetization of the substrate becomes large, so that the magnetic properties are not good. Further, if added in a larger amount, the raw materials remain in the glass, which is not preferable.
[0048]
Embodiment 2
Next, a glass composition range suitable for a glass substrate for a magnetic disk was examined. Table 3 shows examples of the glass substrate manufactured according to the present invention. As the rare earth to be added, Pr which obtained a good result in Example 1 was used. Among the glass compositions in the table, R _Two O is Li _Two O, Na _Two O, K _Two Shows the total alkali metal oxide content of O 2.
[0049]
[Table 3]

[0050]
For each sample, the stability of the glass when preparing the glass substrate for a magnetic disk, the coefficient of thermal expansion of the glass material, the micro-Vickers hardness of the glass substrate surface, and the ring strength were shown.
[0051]
Here, the coefficient of thermal expansion was measured by preparing a block of each glass, cutting out a test piece for measuring thermal expansion of 15 mm × 4 mm × 4 mm, and using a thermal expansion measuring device. The measurement temperature range was 30 ° C to 100 ° C.
[0052]
The micro Vickers hardness was determined as an average value of 10 points by applying a diamond indenter to the surface of the glass substrate under the conditions of a load of 500 g and a load application time of 15 seconds.
[0053]
Further, a magnetic disk was prepared from the obtained substrate in the same manner as in Example 1, and was mounted on the magnetic disk drive shown in FIG. 3, and a thermal shock test of the drive was performed. When no problem such as a crack, a crack, or a reading error due to track deviation occurred in the glass by the thermal shock test, ○ was given, and when it occurred, X was given. In the thermal shock test, after heating at −40 ° C. for 2 hours, the material is rapidly heated to 80 ° C., kept at 80 ° C. for 2 hours, and rapidly cooled to −40 ° C. This was repeated five times, during which time it was determined whether or not the above-described problem occurred.
[0054]
Regarding the stability of the glass, if the bubbles, striae, foreign matter, etc., which are seen in the glass substrate after melting the glass, are marked as ×, and no such things are seen, and clear glass is obtained Is ○.
[0055]
The ring strength was determined as follows. A ring with an outer diameter of 22 mmφ is placed on the upper part of the inner peripheral part of the 2.5 ″ substrate, and the ring is mounted on the lower part of the ring with an inner diameter of 63 mmφ and an outer diameter of 65 mmφ. Was measured.
[0056]
First, Li _Two O, Na _Two O, K _Two O 2 total alkali oxide amount (R in the table _Two Samples with different O 2) are shown in Table 3 Nos. 42 to 49.
[0057]
When a glass having an alkali metal oxide content of less than 13%, such as No. 43 and No. 44, was used, cracks occurred in the glass in the thermal shock test. Conversely, when the content of the alkali metal oxide exceeds 17% by weight as in No. 49, an error due to track deviation occurs in the thermal shock test, and rotational distortion easily occurs in the high-speed rotation test. Therefore, an error due to track deviation occurs, which is not preferable. No. 42, 45-48, the total content of alkali metal oxides
In the case of 13% by weight to 17% by weight, good results were obtained in the thermal shock test, and preferable results were obtained.
[0058]
Focusing on the thermal expansion coefficients of these glasses, Table 3 shows that the glasses of No. 43 and No. ^-7 / ° C, 61 × 10 ^-7 / ° C and the thermal expansion coefficient of the drive device member, 70 × 10 ^-7 / ℃ ～ 80 × 10 ^-7 / ° C. These glasses were not preferable because cracks and track deviations occurred in a thermal shock test due to differences in thermal expansion from other device members.
[0059]
No. 42, 45 to 48, the coefficient of thermal expansion is 65 × 10 ^-7 / ℃ or more, 90 × 10 ^-7 / ° C or lower, good results were obtained in the thermal shock test. From the above, the proper coefficient of thermal expansion is 65 × 10 ^-7 / ℃ or more, 90 × 10 ^-7 / ° C or lower.
[0060]
Next, in Nos. 50 to 55, SiO _Two The content was examined. SiO _Two The glass of No. 52 having a content of 54% by weight had insufficient ring strength and was not suitable as a glass substrate for magnetic disks. Also, as in No. 55, SiO _Two If the amount exceeds 70% by weight, bubbles and the like are remarkably generated during melting of the glass, which is not preferable. From the above, SiO _Two When the content was 55% by weight or more and 70% by weight or less, good results were obtained as a glass substrate for a magnetic disk.
[0061]
Next, Al _Two O _Three The content was examined. No.57 Al _Two O _Three In the case of glass having a content of 21% by weight, the melting temperature of the glass was too high, and melting at 1600 ° C. was not preferable because the glass raw material remained. Al _Two O _Three In the glass described in No. 58 having a content of 10% by weight, a stable glass was obtained and a good result was obtained as a glass substrate for a magnetic disk. _Two O _Three In the case of No. 59 glass having a content of 9.5% by weight, non-uniformity such as striae occurred in the glass. From the above, Al _Two O _Three When the content of is not less than 10% by weight and not more than 20% by weight, good glass was obtained.
[0062]
Further B _Two O _Three The content was examined. B _Two O _Three As the content increased, the ring strength was improved, but as shown in No. 60, cracks occurred in the glass of 9% by weight in the thermal shock test. From the above, B _Two O _Three When the content was 8% by weight or less, good glass was obtained.
[0063]
As for ZnO, as shown in No. 72, when the addition amount exceeds 10% by weight, precipitation of crystals becomes remarkable in the glass, and it is difficult to obtain a stable glass. At 10% by weight, no such crystals were precipitated. Therefore, the ZnO content was preferably 10% by weight or less.
[0064]
Next, among the alkali metal oxides, Li _Two O content and Na _Two Focusing on the O 2 content, the composition ratio was examined. Li _Two O / Na _Two In the case of glass No. 65 having an O ratio of 0.60 and glass having a No. 67 of 6.15, cracks were generated in the glass in the thermal shock test, and the ring strength was also reduced. _Two O / Na _Two The O 2 ratio was preferably 0.61 or more and 6.00 or less.
[0065]
【The invention's effect】
Since the glass substrate for a magnetic disk of the present invention is colored and has low magnetization when a magnetic field is applied, a glass substrate for a magnetic disk excellent in mass productivity and a magnetic disk using the same can be manufactured. Further, the glass substrate for a magnetic disk of the present invention has a coefficient of thermal expansion of 65 to 90 × 10 ^-7 / ° C, which has good matching with the coefficient of thermal expansion of the magnetic disk drive device members, and has few problems such as cracks in the glass and track deviation due to thermal shock tests. Therefore, high recording density and high reliability are required. It is most suitable as a substrate material of a magnetic disk to be used.
[Brief description of the drawings]
FIG. 1 is a plan view of a glass substrate for a magnetic disk of the present invention.
FIG. 2 is a sectional view of a magnetic disk using the magnetic disk glass substrate of the present invention.
FIG. 3 is a schematic diagram of a magnetic disk drive manufactured by the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Glass substrate for magnetic disks, 2 ... Hole for inner peripheral chuck, 3 ... Chamfer part, 4 ... Particle size control layer, 5 ... Orientation control layer, 6 ... Magnetic film, 7 ... Protective film, 8 ... Lubricating film, 9 magnetic disk, 10 spindle, 11 magnetic head, 12 arm of magnetic head, 13 voice coil motor, 14 housing.

Claims

55% ~70%,: SiO ₂ in% by weight
Al ₂ O ₃ : 10 to 20%,
_{_{B 2 O 3: 0% ~8}} %,
R ₂ O: 13% to 17% (R represents an alkali metal element),
ZnO: 0% to 10%,
By weight of oxide represented in terms of oxide, further Pr ₂ O ₃ or Nd ₂ O ₃ 1% to 7% in weight percentage of oxides in terms of the following, or Sm ₂ O ₃ 2.5% 9%, or Eu ₂ O ₃ and containing 2.5% to 8%, the R ₂ O (R represents an alkali metal element) is composed of _{_{Li 2 O, Na 2 O,}} K 2 O, and Li ₂ O and Na ₂ O ratio of Li _₂ O / Na ₂ O ratio in the 0.61 or more and 6.00 or less, 30 ° C. to 100 ° C. thermal expansion coefficient of 65 × 10 ^-7 at a temperature range of A glass substrate for a magnetic disk, wherein the glass substrate has a temperature of not less than 90 ° C. and not more than 90 × 10 ⁻⁷ / ° C.

At a thickness of 0.635 mm, the transmittance for visible light with a wavelength of 300 nm to 700 nm is 50% or more and 90% or less, and the magnetization when a magnetic field of 1 kOe is applied is 3 × 10 ⁻³ emu / cc or less. A glass substrate for a magnetic disk, comprising:

What is claimed is: 1. A magnetic disk comprising: a glass substrate for a magnetic disk; and a magnetic layer formed directly or via another layer on the substrate, wherein the glass substrate has a weight percentage of SiO ₂ : 55% to 70%;
Al ₂ O ₃ : 10% to 20%,
_{_{B 2 O 3: 0% ~8}} %,
R ₂ O: 13% to 17% (R represents an alkali metal element),
ZnO: 0% to 10%,
By weight of oxide represented in terms of oxide, further Pr ₂ O ₃ or Nd ₂ O ₃ 1% to 7% in weight percentage of oxides in terms of the following, or Sm ₂ O ₃ 2.5% 9%, or Eu ₂ O ₃ and containing 2.5% to 8%, the R ₂ O (R represents an alkali metal element) is composed of _{_{Li 2 O, Na 2 O,}} K 2 O, and Li ₂ O and Na ₂ O ratio of Li _₂ O / Na ₂ O ratio in the 0.61 or more and 6.00 or less, 30 ° C. to 100 ° C. thermal expansion coefficient of 65 × 10 ^-7 at a temperature range of A magnetic disk characterized by being at least 90 ° ^C./° C. and at most 90 × 10 ⁻⁷ / ° C.

A magnetic disk having at least a glass substrate and a magnetic film formed directly or via another layer on the surface thereof, wherein the glass substrate having a thickness of 0.635 mm has a transmittance of visible light having a wavelength of 300 nm to 700 nm. Is 50% or more and 90% or less, and the magnetization when a magnetic field of 1 kOe is applied to the glass substrate is 3 × 10 ⁻³ emu / cc or less.