JP2004352571A - Glass composition and glass substrate - Google Patents
Glass composition and glass substrate Download PDFInfo
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- JP2004352571A JP2004352571A JP2003153238A JP2003153238A JP2004352571A JP 2004352571 A JP2004352571 A JP 2004352571A JP 2003153238 A JP2003153238 A JP 2003153238A JP 2003153238 A JP2003153238 A JP 2003153238A JP 2004352571 A JP2004352571 A JP 2004352571A
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- glass substrate
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- 239000011521 glass Substances 0.000 title claims abstract description 134
- 239000000758 substrate Substances 0.000 title claims abstract description 111
- 239000000203 mixture Substances 0.000 title claims abstract description 16
- 230000035939 shock Effects 0.000 claims abstract description 23
- 229910052708 sodium Inorganic materials 0.000 claims abstract description 7
- -1 lanthanoid metal oxides Chemical class 0.000 claims abstract description 6
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 6
- 229910044991 metal oxide Inorganic materials 0.000 claims abstract description 6
- 229910052700 potassium Inorganic materials 0.000 claims abstract description 6
- 229910052747 lanthanoid Inorganic materials 0.000 claims abstract description 5
- 229910052712 strontium Inorganic materials 0.000 claims abstract description 5
- 229910052788 barium Inorganic materials 0.000 claims abstract description 4
- 229910052791 calcium Inorganic materials 0.000 claims abstract description 4
- 150000001875 compounds Chemical class 0.000 claims abstract description 4
- 229910052749 magnesium Inorganic materials 0.000 claims abstract description 4
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 4
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 12
- 230000009477 glass transition Effects 0.000 claims description 9
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 8
- 238000005728 strengthening Methods 0.000 claims description 8
- 229910010413 TiO 2 Inorganic materials 0.000 claims description 7
- 238000005496 tempering Methods 0.000 claims description 2
- 230000007704 transition Effects 0.000 claims 1
- 229910052796 boron Inorganic materials 0.000 abstract description 3
- 229910052782 aluminium Inorganic materials 0.000 abstract description 2
- 239000010408 film Substances 0.000 description 32
- 239000010410 layer Substances 0.000 description 22
- 238000000034 method Methods 0.000 description 18
- 230000000694 effects Effects 0.000 description 16
- 230000003287 optical effect Effects 0.000 description 15
- 239000003513 alkali Substances 0.000 description 12
- 230000007423 decrease Effects 0.000 description 12
- 239000000126 substance Substances 0.000 description 12
- 230000003746 surface roughness Effects 0.000 description 9
- 238000004891 communication Methods 0.000 description 8
- 239000011241 protective layer Substances 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 238000012360 testing method Methods 0.000 description 6
- 229910001149 41xx steel Inorganic materials 0.000 description 5
- 229910000272 alkali metal oxide Inorganic materials 0.000 description 5
- 238000004140 cleaning Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 239000000155 melt Substances 0.000 description 5
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 230000000704 physical effect Effects 0.000 description 5
- 238000005498 polishing Methods 0.000 description 5
- 238000004544 sputter deposition Methods 0.000 description 5
- 230000000087 stabilizing effect Effects 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000007373 indentation Methods 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 238000001771 vacuum deposition Methods 0.000 description 4
- 229910000943 NiAl Inorganic materials 0.000 description 3
- NPXOKRUENSOPAO-UHFFFAOYSA-N Raney nickel Chemical compound [Al].[Ni] NPXOKRUENSOPAO-UHFFFAOYSA-N 0.000 description 3
- 229910052804 chromium Inorganic materials 0.000 description 3
- 238000000151 deposition Methods 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 238000007772 electroless plating Methods 0.000 description 3
- 239000000696 magnetic material Substances 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- 229910000599 Cr alloy Inorganic materials 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 239000005345 chemically strengthened glass Substances 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000010828 elution Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 230000005484 gravity Effects 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- 239000000314 lubricant Substances 0.000 description 2
- 239000006249 magnetic particle Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000010702 perfluoropolyether Substances 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 239000002356 single layer Substances 0.000 description 2
- HUAUNKAZQWMVFY-UHFFFAOYSA-M sodium;oxocalcium;hydroxide Chemical compound [OH-].[Na+].[Ca]=O HUAUNKAZQWMVFY-UHFFFAOYSA-M 0.000 description 2
- 238000004528 spin coating Methods 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 238000007740 vapor deposition Methods 0.000 description 2
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 238000007088 Archimedes method Methods 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- 229910002441 CoNi Inorganic materials 0.000 description 1
- 229910018979 CoPt Inorganic materials 0.000 description 1
- 229910000684 Cobalt-chrome Inorganic materials 0.000 description 1
- 229910052692 Dysprosium Inorganic materials 0.000 description 1
- 229910052693 Europium Inorganic materials 0.000 description 1
- 229910002546 FeCo Inorganic materials 0.000 description 1
- 229910052688 Gadolinium Inorganic materials 0.000 description 1
- 229910052689 Holmium Inorganic materials 0.000 description 1
- 229910018068 Li 2 O Inorganic materials 0.000 description 1
- 229910052765 Lutetium Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- 229910052772 Samarium Inorganic materials 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 229910052771 Terbium Inorganic materials 0.000 description 1
- 229910052775 Thulium Inorganic materials 0.000 description 1
- 229910052769 Ytterbium Inorganic materials 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 239000005456 alcohol based solvent Substances 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001721 carbon Chemical class 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000003426 chemical strengthening reaction Methods 0.000 description 1
- 239000010952 cobalt-chrome Substances 0.000 description 1
- 239000008119 colloidal silica Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000004031 devitrification Methods 0.000 description 1
- 238000007865 diluting Methods 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000006025 fining agent Substances 0.000 description 1
- 239000000156 glass melt Substances 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 238000007733 ion plating Methods 0.000 description 1
- 238000010884 ion-beam technique Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 239000010687 lubricating oil Substances 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000006060 molten glass Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 239000012788 optical film Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 239000006058 strengthened glass Substances 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- 229920001187 thermosetting polymer Polymers 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 238000005019 vapor deposition process Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C3/00—Glass compositions
- C03C3/04—Glass compositions containing silica
- C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
- C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
- C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C3/00—Glass compositions
- C03C3/04—Glass compositions containing silica
- C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
- C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C3/00—Glass compositions
- C03C3/04—Glass compositions containing silica
- C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
- C03C3/095—Glass compositions containing silica with 40% to 90% silica, by weight containing rare earths
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C3/00—Glass compositions
- C03C3/04—Glass compositions containing silica
- C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
- C03C3/097—Glass compositions containing silica with 40% to 90% silica, by weight containing phosphorus, niobium or tantalum
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明はガラス基板及びこれに用いるガラス組成物に関し、より詳細には磁気ディスク、光磁気ディスク、ＤＶＤ、ＭＤなどの情報記録用媒体や光通信用素子などの基板として用いるガラス基板及びこれに用いるガラス組成物に関するものである。
【０００２】
【従来の技術】
従来、磁気ディスク用基板としては、デスクトップ用コンピュータやサーバなどの据え置き型にはアルミニウム合金が、他方ノート型コンピュータやモバイル型コンピュータなどの携帯型にはガラス基板が一般に使用されていたが、アルミニウム合金は変形しやすく、また硬さが不十分であるため研磨後の基板表面の平滑性が十分とは言えなかった。さらに、ヘッドが機械的に磁気ディスクに接触する際、磁性膜が基板から剥離しやすいという問題もあった。そこで、変形が少なく、平滑性が良好で、かつ機械的強度の大きいガラス基板が携帯型のみならず据え置き型の機器やその他の家庭用情報機器にも今後広く使用されていくものと予測されている。
【０００３】
ガラス基板としては、基板表面のアルカリ元素を他のアルカリ元素と置換することにより圧縮歪みを発生させ、機械的強度を向上させた化学強化ガラスが知られている。しかし化学強化ガラスでは煩雑なイオン交換工程が必要であり、またイオン交換後の再加工が不可能であるため製造歩留を上げることが難しかった。また、ガラス基板にイオン交換性を持たせるために、アルカリイオンの基板中での移動が容易となるようにしていたので、基板表面のアルカリイオンが、磁性膜を成膜する際の加熱工程時に表面に移動して溶出したり、あるいは磁性膜を侵食したり、磁性膜の付着強度を劣化させたりする問題があった。
【０００４】
一方、化学強化処理を行わない一般的なガラス基板としてはソーダライム基板があるが、このソーダライム基板を情報記録用基板として用いるには機械的強度、化学的耐久性が不十分であった。また、液晶基板などに使用されているガラス材料では、高温での熱安定性を維持するため無アルカリあるいは低アルカリ化によって線熱膨張係数を低く抑えているので、ＳＵＳ鋼などでできたクランプやスピンドルモータ部材の線熱膨張係数との差が大きく、記録媒体の記録装置への取付け時や情報記録時に不具合が生じることがあった。また機械的強度が不十分であるため情報記録用基板へ適用は困難であった。
【０００５】
また光フィルタや光スイッチなどの光通信用素子でも基板としてガラス基板が用いられているが、ガラス基板から溶出したアルカリ成分によって前記素子が劣化することがあった。また、ガラス基板上に形成される膜の密度が大きくなるほど、温度・湿度の変化による波長シフトが抑制されるところ、従来広く用いられている真空蒸着法では形成できる膜の密度に限界があった。
【０００６】
さらには、ガラス基板を情報記録用として用いる場合に、情報記録用膜をガラス基板上に形成する際、表面に加わえられる圧力や加熱、衝撃によりガラス基板にクラックが入り、製品の歩留まりが低下することがあった。
【０００７】
【特許文献１】
特開２００１−１９４６６号公報（特許請求の範囲の欄、表１〜表５）
【０００８】
【発明が解決しようとする課題】
本発明はこのような従来の問題に鑑みてなされたものであり、その目的とするところは、強化処理を行うことなく熱衝撃に強いガラス基板及びガラス組成物を提供することにあり、さらには高い機械的強度を有し、また線熱膨張係数がモータ部材のそれに近く、さらには高い破壊靭性を有するガラス基板及びガラス組成物を提供することにある。
【０００９】
【課題を解決するための手段】
本発明によれば、重量％で、ＳｉＯ２：４５〜７５％、Ａｌ２Ｏ３：１〜２０％、Ｂ２Ｏ３：０〜８％（ただし、ゼロを含む）、ＳｉＯ２＋Ａｌ２Ｏ３＋Ｂ２Ｏ３：６０〜９０％、Ｒ２Ｏ（Ｒ＝Ｌｉ，Ｎａ，Ｋ）の総量：０〜２０％（ただし、ゼロを含む）、Ｒ’Ｏ（Ｒ’＝Ｍｇ，Ｃａ，Ｓｒ，Ｂａ，Ｚｎ）の総量：０〜２０％（ただし、ゼロを含む）、ＴｉＯ２＋ＺｒＯ２＋ＬｎｘＯｙ：０〜１２％（ただしゼロを含む、またＬｎｘＯｙはランタノイド金属酸化物及びＹ２Ｏ３，Ｎｂ２Ｏ５，Ｔａ２Ｏ５からなる群より選ばれた少なくとも１つの化合物を意味する）の各ガラス成分を有することを特徴とするガラス組成物が提供される。なお、以下「％」は特に断りのない限り「重量％」を意味するものとする。
【００１０】
また本発明によれば、前記ガラス組成物から作製したことを特徴とするガラス基板が提供される。
【００１１】
ここで耐熱衝撃性の観点から、強化処理を行うことなく、前記式（１）から算出される熱衝撃度数を４０より大きくすることが望ましい。
【００１２】
強化処理を行うことなく、比弾性率Ｅ／ρを３０以上、破壊靭性値Ｋｃを１．００以上、線熱膨張係数αを４０×１０−７〜９０×１０−７／℃、ガラス転移温度Ｔｇを５００℃以上とするのが好ましい。
【００１３】
また、表面積／体積（以下、「比表面積」と記すことがある）を１〜５０／ｍｍの範囲とし、最も薄い部分の厚みを２ｍｍ以下とするのが好ましい。
【００１４】
なお、比弾性率（Ｅ／ρ）はヤング率Ｅを比重ρで割った値であって、ヤング率はＪＩＳ Ｒ １６０２ファインセラミックスの弾性試験方法の動的弾性率試験方法に準じて測定し、比重ρはアルキメデス法により２５℃の蒸留水中で測定したものである。また破壊靭性値Ｋｃは、ビッカース硬度試験機を用いて、荷重５００ｇ、負荷時間１５ｓｅｃの条件下にてビッカース圧子にて圧痕をつけ下記式から算出した（図２を参照）。
【００１５】
線熱膨張係数Ａは、示差膨張測定装置を用いて、荷重：５ｇ、温度範囲：２５〜１００℃、昇温速度：５℃／ｍｉｎの条件で測定した値である。ガラス転移点Ｔｇは、粉末状に調整したガラス試料を示差熱測定装置を用いて、荷重５ｇで、２５〜７００℃の温度範囲を５℃／ｍｉｎの昇温率で加熱し測定した値である。また、比表面積Ｓ／Ｖは、ガラス基板が円盤状の場合には例えば図３に示すようにして算出する。
【００１６】
【発明の実施の形態】
本発明者等は、強化処理を行うことなく耐熱衝撃性を高めるべく鋭意検討を重ねた。その結果、ガラスのマトリックス成分としてＳｉＯ２を用い、そこに所定量のＡｌ２Ｏ３及びＢ２Ｏ３を含有させてガラスの骨格を形成することにより所定の剛性が得られ、またＲ２Ｏ（Ｒ：Ｌｉ，Ｎａ，Ｋ）及びＲ’Ｏ（Ｒ’：Ｍｇ，Ｃａ，Ｓｒ，Ｂａ，Ｚｎ）の総量、さらには（ＴｉＯ２＋ＺｒＯ２＋ＬｎｘＯｙ）の総量を所定範囲とすることにより高い耐熱衝撃性を得られることを見出し本発明をなすに至った。
【００１７】
以下、本発明に係るガラス組成物の成分についてその限定した理由について説明する。まずＳｉＯ２はガラスのマトリックスを形成する成分である。その含有量が４５％未満では、ガラスの構造が不安定となり化学的耐久性が劣化すると共に、溶融時粘性特性が悪くなり成形性に支障を来す。一方含有量が７５％を超えると、溶融性が悪くなり生産性が低下すると共に、十分な剛性が得られなくなる。そこで含有量を４５〜７５％の範囲と定めた。より好ましい範囲は４８〜７４％の範囲である。
【００１８】
Ａｌ２Ｏ３はガラスのマトリックス中に入り、ガラス構造を安定化させ、化学的耐久性を向上させる効果を奏する。含有量が１％未満では十分な安定化効果が得られない。他方２０％を超えると溶融性が悪くなり、生産性に支障を来す。そこで含有量を１〜２０％の範囲と定めた。より好ましい範囲は３〜１８％の範囲である。
【００１９】
Ｂ２Ｏ３は溶融性を改善し生産性を向上させると共に、ガラスのマトリックス中に入りガラス構造を安定化させ、化学的耐久性を向上させる効果を奏する。含有量が８％を超えると、溶融時粘性特性が悪くなり、成形性に支障を来すと共に、ガラスが不安定になる。そこで含有量を８％以下（ただしゼロを含む）の範囲と定めた。より好ましい上限値は６％であり、好ましい下限値は１％である。
【００２０】
ガラスの骨格成分であるこれら３つのガラス成分の総量が６０％より少ないと、ガラスの構造が脆弱となる一方、前記総量が９０％を超えると、溶融性が低下し生産性が落ちる。そこで前記総量を６０〜９０％の範囲と定めた。より好ましい範囲は６５〜８８％の範囲である。
【００２１】
アルカリ金属酸化物Ｒ２Ｏ（Ｒ＝Ｌｉ，Ｎａ，Ｋ）は、溶融性を改善し、線熱膨張係数を増大させる効果を奏する。その総量が２０％超えるとガラス骨格間に分散されるアルカリ量が過剰となりアルカリ溶出量が増大する。そこでアルカリ金属酸化物の総量を２０％以下（ただしゼロを含む）の範囲と定めた。一方、アルカリ金属酸化物の総量が２％未満であると溶融性の改善および線熱膨張係数の増大という効果が充分には得られないことがある。したがって、好ましい下限値は２％である。アルカリ金属酸化物の総量のより好ましい上限値は１８％である。また、アルカリ溶出量を低減する、いわゆるアルカリ混合効果を得るためには、前記アルカリ金属酸化物の各成分の下限含有量をそれぞれ０．１％とするのが望ましい。一方、化学的耐久性および溶融安定性の観点から、上限含有量をＬｉ２ＯとＮａ２Ｏとは１５％、Ｋ２Ｏは１０％とするのが望ましい。
【００２２】
また２価の金属酸化物Ｒ’Ｏ（Ｒ’：Ｍｇ，Ｃａ，Ｓｒ，Ｂａ，Ｚｎ）は、剛性を上げると共に溶融性を改善し、ガラス構造を安定化させる効果を奏する。Ｒ’Ｏの総量が２０％を超えると、ガラス構造が不安定となり溶融生産性が低下すると共に化学的耐久性が低下する。そこでＲ’Ｏの含有量を２０％以下と定めた。Ｒ’Ｏの総量のより好ましい上限値は１８％である。Ｒ’Ｏの各成分の好適含有量は次の通りである。
【００２３】
ＭｇＯは剛性を上げると共に溶融性を改善する効果を奏する。含有量が２０％を超えるとガラス構造が不安定となり、溶融生産性が低下すると共に化学的耐久性が低下するおそれがある。したがって含有量は０〜１９％の範囲が好ましい。より好ましい上限値は１８％である。
【００２４】
またＣａＯは線熱膨張係数及び剛性を上げると共に溶融性を改善する効果を奏する。含有量が１０％を超えると、ガラス構造が不安定となり溶融生産性が低下すると共に化学的耐久性が低下するおそれがある。したがって含有量は０〜１０％の範囲が好ましい。より好ましい上限値は９％である。
【００２５】
ＳｒＯは線熱膨張係数を上げ、ガラス構造を安定化すると共に、溶融性を改善する効果を奏する。含有量が８％を超えるとガラス構造が不安定となるおそれがある。したがって含有量は０〜８％の範囲が好ましい。より好ましい上限値は６％である。
【００２６】
ＢａＯはＳｒＯを同じ効果を奏し、その含有量が８％を超えるとガラス構造が不安定となるおそれがある。したがって含有量は０〜８％の範囲が好ましい。より好ましい上限値は６％である。
【００２７】
ＺｎＯは化学的耐久性及び剛性を上げると共に溶融性を改善する効果を奏する。含有量が６％を超えると、ガラス構造が不安定となり溶融生産性が低下すると共に化学的耐久性が低下するおそれがある。したがって含有量は０〜６％の範囲が好ましい。より好ましい上限値は５％である。
【００２８】
ＴｉＯ２はガラスの構造を強固にし、剛性を向上させると共に溶融性を改善する効果を奏する。またＺｒＯ２もガラスの構造を強固にし剛性を向上させると共に化学的耐久性を向上させる効果を奏する。そしてＬｎｘＯｙはガラスの構造を堅固にし剛性および靭性を向上させる効果を奏する。なお、このＬｎｘＯｙはランタノイド金属酸化物及びＹ２Ｏ３，Ｎｂ２Ｏ５，Ｔａ２Ｏ５からなる群より選ばれた少なくとも１つの化合物を意味し、ランタノイド金属酸化物としては、Ｌｎ２Ｏ３やＬｎＯなどが種類があり、ＬｎとしてはＬａ、Ｃｅ、Ｅｒ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｔｍ、Ｙｂ、Ｌｕなどが挙げられる。ここで（ＴｉＯ２＋ＺｒＯ２＋ＬｎｘＯｙ）が１２％を超えるとガラスが不安定となり、靭性が大幅に低下すると共に失透傾向が高まり生産性が著しく低下する。そこでこれらの総量を１２％以下と定めた。より好ましい総量は０〜１１．５％の範囲である。
【００２９】
本発明のガラス組成物には、Ｓｂ２Ｏ３などの清澄剤を２％以下の範囲でさらに添加してもよい。その他必要により従来公知のガラス成分及び添加剤を本発明の効果を害しない範囲で添加しても構わない。
【００３０】
次に本発明のガラス基板について説明する。本発明のガラス基板の大きな特徴は前記ガラス組成物を用いて製造したことにある。ガラス基板の製造方法に特に限定はなく、これまで公知の製造方法を用いることができる。例えば、各成分の原料として各々相当する酸化物、炭酸塩、硝酸塩、水酸化物等を使用し、所望の割合に秤量し、粉末で十分に混合して調合原料とする。これを例えば１，３００〜１，５５０℃に加熱された電気炉中の白金坩堝などに投入し、溶融清澄後、撹拌均質化して予め加熱された鋳型に鋳込み、徐冷してガラスブロックにする。次に、ガラス転移点付近まで再加熱し、徐冷して歪み取りを行う。そして得られたガラスブロックを円盤形状にスライスして、内周および外周を同心円としてコアドリルを用いて切り出す。あるいは溶融ガラスをプレス成形して円盤状に成形する。そして、このようにして得られた円盤状のガラス基板は、さらにその両面を粗研磨および研磨された後、水、酸、アルカリの少なくとも１つの液で洗浄されて最終的なガラス基板とされる。
【００３１】
ここで、本発明のガラス基板を例えば情報記録用媒体の基板として用いる場合に、ヘッドの浮上量や記録媒体の膜厚を小さくする観点などから、研磨工程後のガラス基板の表面粗度Ｒａを１ｎｍ以下とし、且つ洗浄工程後の表面粗度Ｒａ’を表面粗度Ｒａの１．５倍以下とするのが好ましい。アルカリ成分を多く含む、強化処理を行ったガラス基板の場合には、研磨により表面粗度Ｒａを１ｎｍ以下にすることは可能であるが、次の洗浄工程において、水や酸、アルカリで基板表面を表面洗浄したときに、化学的耐久性が低いため表面が激しく浸食される結果、洗浄工程後の表面粗度Ｒａ’が大きくなってしまう。一方、強化処理しないガラス基板では一般に、基板の表面および内部の組成が均質であるので、洗浄工程においても基板の表面粗度Ｒａ’は大きくは変化しない。このため、ガラス成分を最適化することにより洗浄工程後の表面粗度Ｒａ’を研磨工程後の表面粗度Ｒａの１．５倍以下とすることも可能となる。
【００３２】
本発明に係るガラス基板ではつぎの諸物性を満足しているのが好ましい。まず、前記式（１）から算出される熱衝撃度数が４０より大きいことが好ましい。この熱衝撃度数が４０以下であると、急激な熱衝撃が加わった際基板が割れることがあるからである。より好ましい熱衝撃度数は４５以上である。
【００３３】
比弾性率（Ｅ／ρ）が３０以上であるのが好ましい。強化処理を行っていないガラス基板では機械的強度は基板の剛性に依存するため、比弾性率が３０よりも小さいと、基板の機械的強度が不十分となり、ＨＤＤ搭載時に外部から衝撃を受けた際、ＨＤＤ部材との締結部分から破損しやすくなるからである。より好ましい比弾性率（Ｅ／ρ）は３２以上である。
【００３４】
破壊靭性値Ｋｃは１．００以上が好ましい。ガラス基板を情報記録用媒体として用いる場合、破壊靭性値Ｋｃが１．００未満であると、ガラス基板表面に磁性膜などの記録膜を形成する工程において加わえられる圧力などによりガラス基板にひび割れが生じることがあるからである。また、破壊靭性値Ｋｃが１．００未満であると、基板の機械加工において基板が損傷を受けやすくなり、加工歩留まりが大きく低下する。破壊靭性値Ｋｃのより好ましい下限値は１．０２である。
【００３５】
線熱膨張係数αは４０×１０−７〜９０×１０−７／℃の範囲が好ましい。線熱膨張係数αがこの範囲から外れると、ガラス基板を用いた情報記録用媒体を取り付ける駆動部の材料の線熱膨張係数との差が大きくなって、情報記録用媒体の固定部に応力が発生し、基板の破損や基板の変形による記録位置のズレが発生し、記録の読み書きができなくなるからである。線熱膨張係数のより好ましい下限値は４２×１０−７／℃であり、より好ましい上限値は８５×１０−７／℃である。
【００３６】
ガラス転移温度Ｔｇは５００℃以上が好ましい。ガラス転移温度をこのような範囲とするには、例えば骨格成分であるＳｉＯ２，Ｂ２Ｏ３，Ａｌ２Ｏ３の総量及びそれら比率、そしてガラス転移温度を大幅に低下させる成分であるアルカリ金属酸化物の添加量を、目的とする主物性を劣化させない範囲で調整すればよい。
【００３７】
比表面積Ｓ／Ｖは１〜５０の範囲が好ましい。比表面積Ｓ／Ｖが１より小さいと、板厚が厚くなり実用化が困難となることがあり、一方比表面積Ｓ／Ｖが５０より大きいと、板厚が薄くなり加工の際割れやすくなることがあるからである。比表面積Ｓ／Ｖのより好ましい範囲は１．０２〜４５である。
【００３８】
またガラス基板の最も薄い部分の厚みは２ｍｍ以下であるのが好ましい。ハードディスクドライブ装置などは小型薄型化が近年急速に進んでいるため、前記厚みが２ｍｍより厚いと、現在及び将来におけるハードディスクドライブ装置などへの搭載に適さなくなり汎用性が低下するからである。より好ましい厚みは１．５ｍｍ以下である。
【００３９】
本発明のガラス基板は、その大きさに限定はなく３．５，２．５，１．８インチ、あるいはそれ以下の小径ディスクとすることもでき、またその厚さは２ｍｍや１ｍｍ、０．６３ｍｍ、あるいはそれ以下といった薄型とすることもできる。
【００４０】
次に、本発明のガラス基板を用いた情報記録用媒体について説明する。情報記録用媒体の基板として本発明のガラス基板を用いると、耐久性および高記録密度が実現される。以下、図面に基づき情報記録用媒体について説明する。
【００４１】
図１は磁気ディスクの斜視図である。この磁気ディスクＤは、円形のガラス基板１の表面に磁性膜２を直接形成したものである。磁性膜２の形成方法としては従来公知の方法を用いることができ、例えば磁性粒子を分散させた熱硬化性樹脂を基板上にスピンコートして形成する方法や、スパッタリング、無電解めっきにより形成する方法が挙げられる。スピンコート法での膜厚は約０．３〜１．２μｍ程度、スパッタリング法での膜厚は０．０４〜０．０８μｍ程度、無電解めっき法での膜厚は０．０５〜０．１μｍ程度であり、薄膜化および高密度化の観点からはスパッタリング法および無電解めっき法による膜形成が好ましい。
【００４２】
磁性膜に用いる磁性材料としては、特に限定はなく従来公知のものが使用できるが、高い保持力を得るために結晶異方性の高いＣｏを基本とし、残留磁束密度を調整する目的でＮｉやＣｒを加えたＣｏ系合金などが好適である。具体的には、Ｃｏを主成分とするＣｏＰｔ、ＣｏＣｒ、ＣｏＮｉ、ＣｏＮｉＣｒ、ＣｏＣｒＴａ、ＣｏＰｔＣｒ、ＣｏＮｉＰｔや、ＣｏＮｉＣｒＰｔ、ＣｏＮｉＣｒＴａ、ＣｏＣｒＰｔＴａ、ＣｏＣｒＰｔＢ、ＣｏＣｒＰｔＳｉＯなどが挙げられる。磁性膜は、非磁性膜（例えば、Ｃｒ、ＣｒＭｏ、ＣｒＶなど）で分割しノイズの低減を図った多層構成（例えば、ＣｏＰｔＣｒ／ＣｒＭｏ／ＣｏＰｔＣｒ、ＣｏＣｒＰｔＴａ／ＣｒＭｏ／ＣｏＣｒＰｔＴａなど）としてもよい。上記の磁性材料の他、フェライト系、鉄−希土類系や、ＳｉＯ２、ＢＮなどからなる非磁性膜中にＦｅ、Ｃｏ、ＦｅＣｏ、ＣｏＮｉＰｔ等の磁性粒子を分散された構造のグラニュラーなどであってもよい。また、磁性膜は、内面型および垂直型のいずれの記録形式であってもよい。
【００４３】
また、磁気ヘッドの滑りをよくするために磁性膜の表面に潤滑剤を薄くコーティングしてもよい。潤滑剤としては、例えば液体潤滑剤であるパーフロロポリエーテル（ＰＦＰＥ）をフレオン系などの溶媒で希釈したものが挙げられる。
【００４４】
さらに必要により下地層や保護層を設けてもよい。磁気ディスクにおける下地層は磁性膜に応じて選択される。下地層の材料としては、例えば、Ｃｒ、Ｍｏ、Ｔａ、Ｔｉ、Ｗ、Ｖ、Ｂ、Ａｌ、Ｎｉなどの非磁性金属から選ばれる少なくとも一種以上の材料が挙げられる。Ｃｏを主成分とする磁性膜の場合には、磁気特性向上等の観点からＣｒ単体やＣｒ合金であることが好ましい。また、下地層は単層とは限らず、同一又は異種の層を積層した複数層構造としても構わない。例えば、Ｃｒ／Ｃｒ、Ｃｒ／ＣｒＭｏ、Ｃｒ／ＣｒＶ、ＮｉＡｌ／Ｃｒ、ＮｉＡｌ／ＣｒＭｏ、ＮｉＡｌ／ＣｒＶ等の多層下地層としてもよい。
【００４５】
磁性膜の摩耗や腐食を防止する保護層としては、例えば、Ｃｒ層、Ｃｒ合金層、カーボン層、水素化カーボン層、ジルコニア層、シリカ層などが挙げられる。これらの保護層は、下地層、磁性膜など共にインライン型スパッタ装置で連続して形成できる。また、これらの保護層は、単層としてもよく、あるいは、同一又は異種の層からなる多層構成としてもよい。なお、上記保護層上に、あるいは上記保護層に替えて、他の保護層を形成してもよい。例えば、上記保護層に替えて、Ｃｒ層の上にテトラアルコキシランをアルコール系の溶媒で希釈した中に、コロイダルシリカ微粒子を分散して塗布し、さらに焼成して酸化ケイ素（ＳｉＯ２）層を形成してもよい。
【００４６】
以上、情報記録用媒体の一実施態様として磁気ディスクについて説明したが、情報記録用媒体はこれに限定されるものではなく、光磁気ディスクや光ディスクなどにも本発明のガラス基板を用いることができる。
【００４７】
また、本発明のガラス基板は光通信用素子にも好適に使用できる。従来のガラス基板に比べて線熱膨張係数が４０×１０−７〜９０×１０−７／℃の範囲と大きいので、蒸着工程で加熱されたガラス基板が冷却されて縮む量が大きくなり、このガラス基板の収縮により基板表面に形成された膜が圧縮されてその密度が大きくなる。この結果、温度・湿度の変化による波長シフトが抑制される。
【００４８】
以下、波長多重分割（「ＤＷＤＭ」；Ｄｅｎｓｅ Ｗａｖｅｌｅｎｇｔｈ Ｄｉｖｉｓｉｏｎ Ｍｕｌｔｉｐｌｅｘｉｎｇ）用の光フィルタを例に本発明のガラス基板を用いた光通信用素子について説明する。誘電体多層膜を用いた光フィルタは高屈折率層と低屈折率層とを有し、これらの層を積層した構造を有している。これらの層を形成する方法としては、特に限定はなく従来公知の方法、例えば真空蒸着法、スパッタリング法、イオンプレーティング法、イオンビームアシスト法などを用いることができる。この中でも生産性が高いことから真空蒸着法が推奨される。真空蒸着は、真空中で蒸着材料を加熱し、発生した蒸気を基体上に凝縮・付着させて薄膜を形成する方法である。蒸着材料の加熱方法には、抵抗加熱、外熱ルツボ、電子ビーム、高周波、レーザーなどの各種方法がある。具体的な蒸着条件として、真空度は１×１０−３〜５×１０−３Ｐａ程度である。蒸着中は真空度が一定となるように電磁弁を制御して導入酸素量を調整する。そして層厚モニターにより所定層厚となったところでシャターを閉じて蒸着を終了する。
【００４９】
各膜厚としては特に限定はないが、光学的膜厚が波長の１／４とするのが基本であって、一般的に１μｍ程度までである。また、総層数は一般的に１００層を超える。用いる膜材料としては例えば、誘電体や半導体、金属であって、この中でも誘電体が特に好ましい。
【００５０】
以上、本発明のガラス基板を用いた光通信用素子の一実施態様としてＤＷＤＭ用の光フィルタについて説明したが、光通信用素子はこれに限定されるものではなく、本発明のガラス基板は光スイッチ、合分波素子などの光通信用素子にも使用できる。
【００５１】
【実施例】
実施例１〜４８，比較例１〜５
定められた量の原料粉末を白金るつぼに秤量して入れ、混合したのち、電気炉中で１，５５０℃で溶解した。原料が充分に溶解したのち、撹拌羽をガラス融液に挿入し、約１時間撹拌した。その後、撹拌羽を取り出し、３０分間静置したのち、治具に融液を流しこむことによってガラスブロックを得た。その後各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、徐冷して歪取りを行った。得られたガラスブロックを約１．５ｍｍの厚さ、２．５インチの円盤形状にスライスし、内周，外周を同心円としてカッターを用いて切り出した。そして、両面を粗研磨及び研磨、洗浄を行って実施例及び比較例のガラス基板を作製した。作製したガラス基板について各種物性評価を行った。なお、物性評価方法は前記の通りである。また、熱衝撃性試験Ａ及び熱衝撃性試験Ｂについては下記試験方法および判定基準で行った。結果を合わせて表１〜表４に示す。
【００５２】
（熱衝撃性試験Ａ）
外径６５ｍｍ、内径２０ｍｍ、厚さ０．６３５ｍｍの円盤形状のガラス基板を、３００℃の電気炉内に３０分間放置した後、２０℃の冷水中に投入し、ガラス基板が割れなかった場合を「○」、割れた場合を「×」とした。
【００５３】
（熱衝撃性試験Ｂ）
外径４８ｍｍ、内径１２ｍｍ、厚さ０．５０８ｍｍの円盤形状のガラス基板を、３００℃の電気炉内に３０分間放置した後、２０℃の冷水中に投入し、ガラス基板が割れなかった場合を「○」、割れた場合を「×」とした。
【００５４】
【表１】
【表２】
【表３】
【表４】
表１〜表３から明らかなように、実施例１〜４８のガラス基板では、線熱膨張係数αは４３．２×１０−７〜７４．６×１０−７／℃の範囲とＨＤＤの部材と近い値であった。また破壊靭性値Ｋｃは１．０２以上であり、比弾性率Ｅ／ρは３２．４以上と従来のガラス基板に比べ大きい値であった。そしてまたガラス転移温度Ｔｇは５０４℃以上であった。このようなガラス基板の物性値から算出した実施例１〜４８のガラス基板の熱衝撃度数Ｈは４０よりいずれも大きく、熱衝撃性試験Ａ及びＢにおいてガラス基板が割れることはなかった。
【００５９】
一方、表４によれば、比較例１のガラス基板では、（ＴｉＯ２＋ＺｒＯ２＋ＬｎｘＯｙ）の含有量が１２．５％と多かったため、破壊靭性値が低くなると共に熱衝撃度数Ｈが小さくなり、熱衝撃性試験Ａ及びＢにおいてガラス基板が割れてしまった。また比較例２のガラス基板では、ＳｉＯ２の含有量が４３．６％と少なく、そしてＲ’Ｏの含有量が２２．２％と多く、さらに（ＴｉＯ２＋ＺｒＯ２＋ＬｎｘＯｙ）の含有量が１９．７％と多かったため、ガラスの構造が軟弱となり線熱膨張係数α、破壊靭性値Ｋｃ、熱衝撃度数Ｈにおいて所望値が得られなかった。一方、ＳｉＯ２の含有量が７７．１％と多かった比較例３のガラス基板では、破壊靭性値Ｋｃ及び比弾性率が低下すると共に、熱衝撃度数Ｈが小さくなった。比較例４のガラス基板では、Ａｌ２Ｏ３及びＲ２Ｏ（Ｒ：Ｌｉ，Ｎａ，Ｋ）の含有量が多く、また比較例５のガラス基板では、Ｂ２Ｏ３および骨格成分（ＳｉＯ２＋Ａｌ２Ｏ３＋Ｂ２Ｏ３）の含有量が多かったため、破壊靭性値Ｋｃ及び熱衝撃度数Ｈにおいて所望値が得られなかった。
【００６０】
【発明の効果】
本発明に係るガラス組成物及びガラス基板は、強化処理を行うことなく高い耐熱衝撃性を有するので、ガラス基板表面に記録膜などを形成する工程において生じる急激な熱変化によっても破損することがない。また高い剛性を有し、さらには適度な表面硬度を有し基板表面の傷を防止すると共に研磨などの表面加工が容易である。そしてまた従来に比べ線熱膨張係数が高くＨＤＤの部材のそれに近くなったので、記録装置への取付け時や情報記録時に不具合が生じることがない。また破壊靭性値が高いので情報記録用基板の製造時などに基板が破損することがない。高い比弾性率を有するので、ガラス基板の高速回転時における回転安定性が向上する。
【００６１】
本発明に係るガラス基板を情報記録用媒体に使用すると、表面処理が容易で、製造工程中において破損することがなく、耐久性に優れ、高い記録密度が得られる。
【００６２】
また本発明に係るガラス基板を光通信用素子に使用すると、経時変化が少なく、温度・湿度の変化による波長シフトを抑制できる。
【図面の簡単な説明】
【図１】本発明のガラス基板を用いた情報記録用媒体の一例を示す斜視図である。
【図２】ビッカース圧子で押圧したときにできるガラス基板表面の圧痕とクラックの模式図である。
【図３】比表面積（＝表面積／体積）の算出例を示す図である。
【符号の説明】
１ ガラス基板
２ 磁性膜
Ｄ 磁気ディスク[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a glass substrate and a glass composition used for the same, and more particularly, to a glass substrate used as a substrate for an information recording medium such as a magnetic disk, a magneto-optical disk, a DVD, an MD, or an optical communication element, and a glass substrate used for the same. It relates to a glass composition.
[0002]
[Prior art]
Conventionally, as a substrate for a magnetic disk, an aluminum alloy is generally used for a stationary type such as a desktop computer or a server, and a glass substrate is generally used for a portable type such as a notebook computer or a mobile computer. Was easily deformed and had insufficient hardness, so that the smoothness of the substrate surface after polishing could not be said to be sufficient. Further, when the head mechanically contacts the magnetic disk, there is a problem that the magnetic film is easily peeled off from the substrate. Therefore, glass substrates with little deformation, good smoothness, and high mechanical strength are expected to be widely used not only for portable devices but also for stationary devices and other household information devices in the future. I have.
[0003]
As a glass substrate, a chemically strengthened glass in which a compressive strain is generated by replacing an alkali element on the substrate surface with another alkali element to improve mechanical strength is known. However, chemically strengthened glass requires a complicated ion exchange process, and it is difficult to rework after ion exchange, so that it has been difficult to increase the production yield. Also, in order to make the glass substrate ion-exchangeable, the alkali ions on the substrate surface are easily moved in the substrate. There is a problem that it migrates to the surface and elutes, erodes the magnetic film, or deteriorates the adhesion strength of the magnetic film.
[0004]
On the other hand, a soda-lime substrate is a general glass substrate not subjected to the chemical strengthening treatment, but the mechanical strength and the chemical durability were insufficient for using the soda-lime substrate as an information recording substrate. In addition, glass materials used for liquid crystal substrates, etc., have low linear thermal expansion coefficients due to no alkali or low alkalinity in order to maintain thermal stability at high temperatures, so clamps made of SUS steel etc. The difference between the linear thermal expansion coefficient of the spindle motor member and the linear thermal expansion coefficient is large, and a problem may occur when a recording medium is attached to a recording device or when information is recorded. In addition, application to an information recording substrate was difficult due to insufficient mechanical strength.
[0005]
Glass substrates are also used as substrates for optical communication elements such as optical filters and optical switches, but the elements may be deteriorated by alkali components eluted from the glass substrates. In addition, as the density of a film formed on a glass substrate increases, the wavelength shift due to changes in temperature and humidity is suppressed. However, there is a limit to the density of a film that can be formed by a conventionally widely used vacuum deposition method. .
[0006]
Furthermore, when a glass substrate is used for information recording, when the information recording film is formed on the glass substrate, cracks occur in the glass substrate due to pressure, heating, and impact applied to the surface, and the product yield is reduced. There was something to do.
[0007]
[Patent Document 1]
JP 2001-19466 A (Claims, Tables 1 to 5)
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of such a conventional problem, and has as its object to provide a glass substrate and a glass composition that are resistant to thermal shock without performing a strengthening treatment. It is an object of the present invention to provide a glass substrate and a glass composition having a high mechanical strength, a linear thermal expansion coefficient close to that of a motor member, and a high fracture toughness.
[0009]
[Means for Solving the Problems]
According to the present invention, SiO 2 : 45 to 75%, Al 2 O 3 : 1 to 20%, B 2 O 3 : 0 to 8% (including zero), SiO 2 + Al 2 O by weight%. 3 + B 2 O 3: 60~90 %, the total amount of R 2 O (R = Li, Na, K): 0~20% ( however, including zero), R'O (R '= Mg , Ca, Sr , Ba, the total amount of Zn): 0~20% (however, including zero), TiO 2 + ZrO 2 + Ln x O y: 0~12% ( but including zero, also Ln x O y of the lanthanoid metal oxide and Y 2 O 3 , Nb 2 O 5 , and Ta 2 O 5 (which means at least one compound selected from the group consisting of glass components). Hereinafter, “%” means “% by weight” unless otherwise specified.
[0010]
Further, according to the present invention, there is provided a glass substrate produced from the glass composition.
[0011]
Here, from the viewpoint of thermal shock resistance, it is desirable to make the thermal shock frequency calculated from the above equation (1) larger than 40 without performing the strengthening treatment.
[0012]
Without the strengthening treatment, the specific elastic modulus E / ρ is 30 or more, the fracture toughness value Kc is 1.00 or more, the linear thermal expansion coefficient α is 40 × 10 −7 to 90 × 10 −7 / ° C., and the glass transition temperature. The Tg is preferably set to 500 ° C. or higher.
[0013]
Further, it is preferable that the surface area / volume (hereinafter, sometimes referred to as “specific surface area”) is in the range of 1 to 50 / mm, and the thickness of the thinnest portion is 2 mm or less.
[0014]
The specific elastic modulus (E / ρ) is a value obtained by dividing the Young's modulus E by the specific gravity ρ, and the Young's modulus is measured according to the dynamic elastic modulus test method of JIS R 1602 Fine Ceramics Elasticity Test Method, The specific gravity ρ is measured in distilled water at 25 ° C. by the Archimedes method. In addition, the fracture toughness value Kc was calculated from the following equation using a Vickers hardness tester by applying an indentation with a Vickers indenter under the conditions of a load of 500 g and a load time of 15 sec (see FIG. 2).
[0015]
The linear thermal expansion coefficient A is a value measured using a differential expansion measuring device under the conditions of a load of 5 g, a temperature range of 25 to 100 ° C., and a temperature rising rate of 5 ° C./min. The glass transition point Tg is a value obtained by heating a powdery glass sample at a load of 5 g in a temperature range of 25 to 700 ° C. at a rate of 5 ° C./min using a differential calorimeter. . The specific surface area S / V is calculated, for example, as shown in FIG. 3 when the glass substrate has a disk shape.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have intensively studied to increase the thermal shock resistance without performing the strengthening treatment. As a result, the SiO 2 used as the matrix component of the glass, there predetermined rigidity is obtained by forming a skeleton of glass by incorporating Al 2 O 3 and B 2 O 3 in a predetermined amount, also R 2 O (R: Li, Na, K ) and R'O (R ': Mg, Ca , Sr, Ba, Zn) total, more to a total volume of a predetermined range of (TiO 2 + ZrO 2 + Ln x O y) The present inventors have found that a higher thermal shock resistance can be obtained, and have accomplished the present invention.
[0017]
Hereinafter, the reasons for limiting the components of the glass composition according to the present invention will be described. First, SiO 2 is a component that forms a glass matrix. If the content is less than 45%, the structure of the glass becomes unstable and the chemical durability is deteriorated, and at the same time, the viscous property at the time of melting is deteriorated and the formability is hindered. On the other hand, if the content exceeds 75%, the meltability deteriorates, the productivity decreases, and sufficient rigidity cannot be obtained. Therefore, the content is set in the range of 45 to 75%. A more preferred range is from 48 to 74%.
[0018]
Al 2 O 3 enters the glass matrix, has the effect of stabilizing the glass structure and improving the chemical durability. If the content is less than 1%, a sufficient stabilizing effect cannot be obtained. On the other hand, if it exceeds 20%, the meltability deteriorates and the productivity is hindered. Therefore, the content is set in the range of 1 to 20%. A more preferred range is from 3 to 18%.
[0019]
B 2 O 3 has the effect of improving the meltability and improving the productivity, as well as stabilizing the glass structure by entering the glass matrix and improving the chemical durability. If the content exceeds 8%, the viscosity property at the time of melting is deteriorated, which impairs the moldability and makes the glass unstable. Therefore, the content was determined to be within a range of 8% or less (including zero). A more preferred upper limit is 6%, and a preferred lower limit is 1%.
[0020]
When the total amount of these three glass components, which are the skeleton components of the glass, is less than 60%, the structure of the glass becomes brittle. On the other hand, when the total amount exceeds 90%, the meltability decreases and the productivity decreases. Therefore, the total amount is set in the range of 60 to 90%. A more preferred range is from 65 to 88%.
[0021]
The alkali metal oxide R 2 O (R = Li, Na, K) has an effect of improving the melting property and increasing the linear thermal expansion coefficient. If the total amount exceeds 20%, the amount of alkali dispersed between the glass skeletons becomes excessive, and the amount of alkali elution increases. Therefore, the total amount of the alkali metal oxides is set to a range of 20% or less (including zero). On the other hand, if the total amount of the alkali metal oxides is less than 2%, the effects of improving the melting property and increasing the linear thermal expansion coefficient may not be sufficiently obtained. Therefore, a preferred lower limit is 2%. A more preferred upper limit of the total amount of the alkali metal oxides is 18%. In order to reduce the alkali elution amount, that is, to obtain a so-called alkali mixing effect, it is preferable that the lower limit contents of the respective components of the alkali metal oxide are each 0.1%. On the other hand, from the viewpoints of chemical durability and melt stability, it is desirable that the upper limit contents are 15% for Li 2 O and Na 2 O and 10% for K 2 O.
[0022]
The divalent metal oxide R'O (R ': Mg, Ca, Sr, Ba, Zn) has the effect of increasing rigidity, improving meltability, and stabilizing the glass structure. When the total amount of R'O exceeds 20%, the glass structure becomes unstable, the melt productivity decreases, and the chemical durability decreases. Therefore, the content of R'O is determined to be 20% or less. A more preferred upper limit of the total amount of R'O is 18%. The preferred content of each component of R'O is as follows.
[0023]
MgO has the effect of increasing rigidity and improving meltability. If the content exceeds 20%, the glass structure becomes unstable, and the melt productivity may decrease, and the chemical durability may decrease. Therefore, the content is preferably in the range of 0 to 19%. A more preferred upper limit is 18%.
[0024]
In addition, CaO has the effect of increasing the coefficient of linear thermal expansion and rigidity and improving the meltability. If the content exceeds 10%, the glass structure becomes unstable, the melt productivity may decrease, and the chemical durability may decrease. Therefore, the content is preferably in the range of 0 to 10%. A more preferred upper limit is 9%.
[0025]
SrO has the effect of increasing the linear thermal expansion coefficient, stabilizing the glass structure, and improving the meltability. If the content exceeds 8%, the glass structure may be unstable. Therefore, the content is preferably in the range of 0 to 8%. A more preferred upper limit is 6%.
[0026]
BaO has the same effect as SrO, and if its content exceeds 8%, the glass structure may become unstable. Therefore, the content is preferably in the range of 0 to 8%. A more preferred upper limit is 6%.
[0027]
ZnO has the effect of increasing the chemical durability and rigidity and improving the meltability. If the content exceeds 6%, the glass structure becomes unstable, the melt productivity may decrease, and the chemical durability may decrease. Therefore, the content is preferably in the range of 0 to 6%. A more preferred upper limit is 5%.
[0028]
TiO 2 has the effect of strengthening the structure of the glass, improving the rigidity, and improving the melting property. ZrO 2 also has the effect of strengthening the glass structure, improving rigidity, and improving chemical durability. The Ln x O y is an effect of improving a firm to rigidly and toughness structural glass. Incidentally, the Ln x O y means lanthanoid metal oxides and Y 2 O 3, Nb 2 O 5, Ta least one compound selected from the group consisting of 2 O 5, as the lanthanoid metal oxide, Ln There are types such as 2 O 3 and LnO, and examples of Ln include La, Ce, Er, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu. Here (TiO 2 + ZrO 2 + Ln x O y) becomes unstable glass exceeds 12%, productivity increases devitrification tendency with toughness is greatly reduced significantly decreases. Therefore, the total amount of these is determined to be 12% or less. A more preferred total is in the range of 0-11.5%.
[0029]
A fining agent such as Sb 2 O 3 may be further added to the glass composition of the present invention in a range of 2% or less. In addition, if necessary, conventionally known glass components and additives may be added as long as the effects of the present invention are not impaired.
[0030]
Next, the glass substrate of the present invention will be described. A major feature of the glass substrate of the present invention is that the glass substrate is manufactured using the glass composition. The method for manufacturing the glass substrate is not particularly limited, and a known manufacturing method can be used. For example, oxides, carbonates, nitrates, hydroxides and the like corresponding to the respective components are used as raw materials, weighed to a desired ratio, and sufficiently mixed with powder to prepare a prepared raw material. This is put into, for example, a platinum crucible in an electric furnace heated to 1,300 to 1,550 ° C., melted and clarified, stirred and homogenized, poured into a pre-heated mold, and gradually cooled to form a glass block. . Next, it is reheated to the vicinity of the glass transition point, gradually cooled, and the strain is removed. Then, the obtained glass block is sliced into a disk shape, and the inner and outer peripheries are cut into concentric circles using a core drill. Alternatively, the molten glass is press-formed and formed into a disk shape. The disc-shaped glass substrate thus obtained is further roughly polished and polished on both sides, and then washed with at least one of water, acid, and alkali to form a final glass substrate. .
[0031]
Here, when the glass substrate of the present invention is used, for example, as a substrate of an information recording medium, the surface roughness Ra of the glass substrate after the polishing step is determined from the viewpoint of reducing the flying height of the head and the film thickness of the recording medium. It is preferable to set the surface roughness Ra ′ to 1 nm or less and the surface roughness Ra ′ after the cleaning step to 1.5 times or less the surface roughness Ra. In the case of a strengthened glass substrate containing a large amount of alkali components, the surface roughness Ra can be reduced to 1 nm or less by polishing. However, in the next cleaning step, the surface of the substrate is washed with water, acid, or alkali. When the surface is cleaned, the surface is severely eroded due to low chemical durability, and as a result, the surface roughness Ra ′ after the cleaning step is increased. On the other hand, in a glass substrate that has not been strengthened, the composition of the surface and the inside of the substrate is generally uniform, so that the surface roughness Ra ′ of the substrate does not change significantly even in the cleaning step. Therefore, by optimizing the glass component, the surface roughness Ra ′ after the cleaning step can be made 1.5 times or less the surface roughness Ra after the polishing step.
[0032]
The glass substrate according to the present invention preferably satisfies the following various physical properties. First, it is preferable that the thermal shock frequency calculated from the equation (1) is larger than 40. If the thermal shock frequency is 40 or less, the substrate may be broken when a sudden thermal shock is applied. A more preferable thermal shock frequency is 45 or more.
[0033]
The specific elastic modulus (E / ρ) is preferably 30 or more. Since the mechanical strength of a glass substrate not subjected to the tempering treatment depends on the rigidity of the substrate, if the specific elastic modulus is less than 30, the mechanical strength of the substrate becomes insufficient and an external impact is applied when the HDD is mounted. In this case, it is easy to be damaged from the fastening portion with the HDD member. A more preferable specific elastic modulus (E / ρ) is 32 or more.
[0034]
The fracture toughness value Kc is preferably 1.00 or more. When a glass substrate is used as an information recording medium, if the fracture toughness value Kc is less than 1.00, cracks may occur in the glass substrate due to pressure applied in a step of forming a recording film such as a magnetic film on the surface of the glass substrate. This is because it may occur. When the fracture toughness value Kc is less than 1.00, the substrate is easily damaged in the machining of the substrate, and the processing yield is greatly reduced. A more preferred lower limit of the fracture toughness value Kc is 1.02.
[0035]
The linear thermal expansion coefficient α is preferably in the range of 40 × 10 −7 to 90 × 10 −7 / ° C. If the coefficient of linear thermal expansion α is out of this range, the difference from the coefficient of linear thermal expansion of the material of the drive unit to which the information recording medium using the glass substrate is attached increases, and stress is applied to the fixed part of the information recording medium. This is because the recording position shifts due to breakage of the substrate or deformation of the substrate, and reading and writing of the recording cannot be performed. A more preferred lower limit of the linear thermal expansion coefficient is 42 × 10 −7 / ° C., and a more preferred upper limit is 85 × 10 −7 / ° C.
[0036]
The glass transition temperature Tg is preferably 500 ° C. or higher. In order to set the glass transition temperature in such a range, for example, the total amount and ratio of SiO 2 , B 2 O 3 , and Al 2 O 3 as skeletal components, and alkali metal, a component that significantly lowers the glass transition temperature, are used. What is necessary is just to adjust the addition amount of an oxide in the range which does not deteriorate the target main physical property.
[0037]
The specific surface area S / V is preferably in the range of 1 to 50. If the specific surface area S / V is less than 1, the sheet thickness may be large and practical use may be difficult. On the other hand, if the specific surface area S / V is more than 50, the sheet thickness may be small and the sheet may be easily cracked during processing. Because there is. A more preferable range of the specific surface area S / V is 1.02 to 45.
[0038]
The thickness of the thinnest portion of the glass substrate is preferably 2 mm or less. This is because hard disk drive devices and the like have been rapidly becoming smaller and thinner in recent years, and if the thickness is more than 2 mm, they will not be suitable for mounting on current and future hard disk drive devices and the like, and their versatility will be reduced. A more preferred thickness is 1.5 mm or less.
[0039]
The size of the glass substrate of the present invention is not limited, and may be a small disk of 3.5, 2.5, 1.8 inches or smaller, and the thickness may be 2 mm, 1 mm, 0.1 mm or less. It can be as thin as 63 mm or less.
[0040]
Next, an information recording medium using the glass substrate of the present invention will be described. When the glass substrate of the present invention is used as a substrate of an information recording medium, durability and high recording density are realized. Hereinafter, the information recording medium will be described with reference to the drawings.
[0041]
FIG. 1 is a perspective view of a magnetic disk. The magnetic disk D is obtained by directly forming a
[0042]
The magnetic material used for the magnetic film is not particularly limited, and a conventionally known magnetic material can be used. A Co-based alloy to which Cr is added is preferable. Specific examples include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, and CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, and CoCrPtSiO. The magnetic film may have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa) in which noise is reduced by dividing the magnetic film with a nonmagnetic film (for example, Cr, CrMo, CrV, or the like). In addition to the above-described magnetic materials, ferrite, iron-rare earth, and granular having a structure in which magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a nonmagnetic film made of SiO 2 , BN, or the like. Is also good. Further, the magnetic film may be of any of an internal surface type and a vertical type.
[0043]
Further, the surface of the magnetic film may be thinly coated with a lubricant in order to improve the slip of the magnetic head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.
[0044]
If necessary, a base layer or a protective layer may be provided. The underlayer in the magnetic disk is selected according to the magnetic film. Examples of the material of the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving magnetic properties. The underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. For example, a multi-layer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, and NiAl / CrV may be used.
[0045]
Examples of the protective layer for preventing abrasion and corrosion of the magnetic film include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an underlayer, a magnetic film and the like by an in-line type sputtering apparatus. In addition, these protective layers may be a single layer, or may be a multi-layer structure including the same or different layers. Note that another protective layer may be formed on the protective layer or in place of the protective layer. For example, instead of the above-mentioned protective layer, colloidal silica fine particles are dispersed and applied in a state where tetraalkoxylan is diluted with an alcohol-based solvent on a Cr layer, and further baked to form a silicon oxide (SiO 2 ) layer. It may be formed.
[0046]
As described above, the magnetic disk has been described as one embodiment of the information recording medium. However, the information recording medium is not limited to this, and the glass substrate of the present invention can be used for a magneto-optical disk or an optical disk. .
[0047]
Further, the glass substrate of the present invention can be suitably used for an optical communication element. Since the coefficient of linear thermal expansion is as large as 40 × 10 −7 to 90 × 10 −7 / ° C. as compared with the conventional glass substrate, the amount of shrinkage due to cooling of the glass substrate heated in the vapor deposition process is increased. Due to the shrinkage of the glass substrate, the film formed on the substrate surface is compressed and its density increases. As a result, wavelength shift due to changes in temperature and humidity is suppressed.
[0048]
Hereinafter, an optical communication device using a glass substrate of the present invention will be described using an optical filter for wavelength multiplexing division (“DWDM”; Dense Wavelength Division Multiplexing) as an example. An optical filter using a dielectric multilayer film has a high refractive index layer and a low refractive index layer, and has a structure in which these layers are stacked. The method for forming these layers is not particularly limited, and a conventionally known method, for example, a vacuum deposition method, a sputtering method, an ion plating method, an ion beam assist method, or the like can be used. Among them, the vacuum evaporation method is recommended because of high productivity. Vacuum deposition is a method in which a deposition material is heated in a vacuum, and the generated vapor is condensed and adhered on a substrate to form a thin film. Various methods such as resistance heating, external heat crucible, electron beam, high frequency, and laser can be used as a method for heating the deposition material. As a specific deposition condition, the degree of vacuum is about 1 × 10 −3 to 5 × 10 −3 Pa. During vapor deposition, the amount of oxygen introduced is adjusted by controlling the solenoid valve so that the degree of vacuum is constant. Then, when the layer thickness becomes a predetermined layer thickness by the layer thickness monitor, the shutter is closed to terminate the vapor deposition.
[0049]
Although there is no particular limitation on each film thickness, it is fundamental that the optical film thickness is １ ／ of the wavelength, and is generally up to about 1 μm. Also, the total number of layers generally exceeds 100 layers. The film material used is, for example, a dielectric, a semiconductor, or a metal. Among them, the dielectric is particularly preferable.
[0050]
As described above, the optical filter for DWDM has been described as one embodiment of the optical communication device using the glass substrate of the present invention. However, the optical communication device is not limited to this, and the glass substrate of the present invention may be an optical filter. It can also be used for optical communication devices such as switches and multiplexing / demultiplexing devices.
[0051]
【Example】
Examples 1 to 48, Comparative Examples 1 to 5
A specified amount of raw material powder was weighed and placed in a platinum crucible, mixed, and then melted at 1,550 ° 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 1 hour. Thereafter, the stirring blade was taken out, and allowed to stand for 30 minutes, and then a melt was poured into a jig to obtain a glass block. Thereafter, the glass block was reheated to near the glass transition point of each glass, and gradually cooled to remove strain. The obtained glass block was sliced into a disk shape of about 1.5 mm thickness and 2.5 inches, and the inner and outer circumferences were cut into concentric circles using a cutter. Then, both surfaces were roughly polished, polished, and cleaned to produce glass substrates of Examples and Comparative Examples. Various physical properties evaluation was performed about the produced glass substrate. The physical property evaluation method is as described above. The thermal shock test A and the thermal shock test B were performed according to the following test methods and criteria. The results are shown in Tables 1 to 4.
[0052]
(Thermal shock test A)
A disk-shaped glass substrate having an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm was left in an electric furnace at 300 ° C. for 30 minutes, and then poured into cold water at 20 ° C., where the glass substrate was not broken. “○”, and the case of cracking was “×”.
[0053]
(Thermal shock test B)
A disc-shaped glass substrate having an outer diameter of 48 mm, an inner diameter of 12 mm, and a thickness of 0.508 mm was left in an electric furnace at 300 ° C. for 30 minutes, and then poured into cold water at 20 ° C., where the glass substrate was not broken. “○”, and the case of cracking was “×”.
[0054]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
As is clear from Tables 1 to 3, in the glass substrates of Examples 1 to 48, the linear thermal expansion coefficient α is in the range of 43.2 × 10 −7 to 74.6 × 10 −7 / ° C. Was close to the value. Further, the fracture toughness value Kc was 1.02 or more, and the specific elastic modulus E / ρ was 32.4 or more, which was larger than that of the conventional glass substrate. The glass transition temperature Tg was 504 ° C. or higher. The thermal shock frequency H of each of the glass substrates of Examples 1 to 48 calculated from the physical property values of such a glass substrate was larger than 40, and the glass substrates did not crack in the thermal shock tests A and B.
[0059]
On the other hand, according to Table 4, the glass substrate of Comparative Example 1, since the content of (TiO 2 + ZrO 2 + Ln x O y) there were many and 12.5%, thermal shock frequency H along with fracture toughness is low The glass substrate was broken in the thermal shock tests A and B. The glass substrate of Comparative Example 2, the content of SiO 2 is less 43.6% and contained many R'O content is 22.2%, more (TiO 2 + ZrO 2 + Ln x O y) Since the amount was as large as 19.7%, the structure of the glass became soft, and desired values could not be obtained in the linear thermal expansion coefficient α, the fracture toughness value Kc, and the thermal shock frequency H. On the other hand, in the glass substrate of Comparative Example 3 in which the content of SiO 2 was as large as 77.1%, the fracture toughness value Kc and the specific elastic modulus decreased, and the thermal shock frequency H decreased. In the glass substrate of Comparative Example 4, the contents of Al 2 O 3 and R 2 O (R: Li, Na, K) are large, and in the glass substrate of Comparative Example 5, B 2 O 3 and the skeleton component (SiO 2 + Al 2 O 3 + B 2 O 3 ), the desired values could not be obtained in the fracture toughness value Kc and the thermal shock frequency H.
[0060]
【The invention's effect】
Since the glass composition and the glass substrate according to the present invention have high thermal shock resistance without performing a strengthening treatment, the glass composition and the glass substrate are not damaged even by a rapid thermal change generated in a process of forming a recording film on the surface of the glass substrate. . In addition, it has high rigidity, has a suitable surface hardness, prevents scratches on the substrate surface, and is easy to perform surface processing such as polishing. Further, since the coefficient of linear thermal expansion is higher than that of a member of the HDD as compared with the related art, no trouble occurs at the time of attaching to a recording device or at the time of recording information. Further, since the fracture toughness value is high, the substrate is not damaged at the time of manufacturing the information recording substrate. Since the glass substrate has a high specific elastic modulus, rotational stability during high-speed rotation of the glass substrate is improved.
[0061]
When the glass substrate according to the present invention is used for an information recording medium, the surface treatment is easy, there is no breakage during the manufacturing process, the durability is excellent, and a high recording density is obtained.
[0062]
Further, when the glass substrate according to the present invention is used for an element for optical communication, a change with time is small, and a wavelength shift due to a change in temperature and humidity can be suppressed.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of an information recording medium using a glass substrate of the present invention.
FIG. 2 is a schematic diagram of indentations and cracks formed on a glass substrate surface when pressed with a Vickers indenter.
FIG. 3 is a diagram showing a calculation example of a specific surface area (= surface area / volume).
[Explanation of symbols]
DESCRIPTION OF
Claims (5)
ＳｉＯ２：４５〜７５％、
Ａｌ２Ｏ３：１〜２０％、
Ｂ２Ｏ３：０〜８％（ただし、ゼロを含む）、
ＳｉＯ２＋Ａｌ２Ｏ３＋Ｂ２Ｏ３：６０〜９０％、
Ｒ２Ｏ（Ｒ＝Ｌｉ，Ｎａ，Ｋ）の総量：０〜２０％（ただし、ゼロを含む）、
Ｒ’Ｏ（Ｒ’＝Ｍｇ，Ｃａ，Ｓｒ，Ｂａ，Ｚｎ）の総量：０〜２０％（ただし、ゼロを含む）、
ＴｉＯ２＋ＺｒＯ２＋ＬｎｘＯｙ：０〜１２％（ただしゼロを含む、またＬｎｘＯｙはランタノイド金属酸化物及びＹ２Ｏ３，Ｎｂ２Ｏ５，Ｔａ２Ｏ５からなる群より選ばれた少なくとも１つの化合物を意味する）
の各ガラス成分を有することを特徴とするガラス組成物。In weight percent,
SiO 2 : 45 to 75%,
Al 2 O 3 : 1 to 20%,
B 2 O 3: 0~8% (however, including zero),
SiO 2 + Al 2 O 3 + B 2 O 3 : 60 to 90%,
R 2 O (R = Li, Na, K) total amount: 0 to 20% (including zero),
R′O (R ′ = Mg, Ca, Sr, Ba, Zn) total amount: 0 to 20% (including zero),
TiO 2 + ZrO 2 + Ln x O y: 0~12% ( but including zero, also Ln x O y is selected from the group consisting of lanthanoid metal oxides and Y 2 O 3, Nb 2 O 5, Ta 2 O 5 Or at least one compound)
A glass composition comprising the following glass components:
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