JP2005302289A - Glass substrate for information recording medium and magnetic information recording medium using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for an information recording medium having excellent abrasion resistance, being lightweight and having high fracture toughness and to provide a magnetic information recording medium using the same. <P>SOLUTION: The glass substrate for the information recording medium has ≤12 μm<SP>-1/2</SP>brittleness index in water and/or ≤7 μm<SP>-1/2</SP>brittleness index in an atmosphere of ≤-5°C dew point, or the glass substrate for the information recording medium comprises glass containing 40 to 75% SiO<SB>2</SB>, 2 to 45% B<SB>2</SB>O<SB>3</SB>and/or Al<SB>2</SB>O<SB>3</SB>and 0 to 40% R'<SB>2</SB>O (R' denotes at least one selected from Li, Na and K) by mole % and having ≥90% sum total content of SiO<SB>2</SB>, B<SB>2</SB>O<SB>3</SB>, Al<SB>2</SB>O<SB>3</SB>and R'<SB>2</SB>O. The magnetic information recording medium has at least a magnetic recording layer on the glass substrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glass substrate for an information recording medium and a magnetic information recording medium using the same. More specifically, the present invention relates to a glass substrate for information recording media that has excellent scratch resistance, is lightweight, and has high fracture toughness, and a magnetic information recording medium represented by a hard disk using the glass substrate for information recording media. It is about.

Conventionally, aluminum, glass, ceramics, and the like have been used as a substrate material for a magnetic information recording medium. Currently, aluminum and glass are mainly put into practical use according to size and application. Among them, the glass substrate has few surface defects and is excellent in smoothness and surface hardness. As glass used as a substrate for a magnetic information recording medium, chemically strengthened glass, crystallized glass, and the like by an ion exchange method are known. As the chemically strengthened glass, for example, in Patent Document 1, in terms of weight%, SiO ₂ : 50 to 65%, Al ₂ O ₃ : 0.5 to 14%, R ₂ O (where R is an alkali metal ion) : 10 to 32%, ZnO: 1 to 15%, B ₂ O ₃ : 1.1 to 14% was chemically strengthened by forming a compressive stress layer on the surface of the glass substrate by an ion exchange method using alkali ions. A glass substrate for a magnetic disk is disclosed. Moreover, as crystallized glass, for example, in Patent Document 2, in terms of weight%, SiO ₂ : 65 to 83%, Li ₂ O: 8 to 13%, K ₂ O: 0 to 7%, MgO: 0 .5~5%, ZnO: 0~5%, PbO: 0~5%, however, MgO + ZnO + PbO: 0.5~5 %, P 2 O 5: 1~4%, Al 2 O 3: 0~7% As ₂ O ₃ + Sb ₂ O ₃ : 0 to 2%, a crystallized glass substrate for a magnetic disk containing fine Li ₂ O.2SiO ₂ crystal particles as a main crystal is disclosed.

  However, in recent years, an information recording apparatus such as a magnetic disk represented by a hard disk is required to have a high recording density and a high speed of data writing and reading. . Although the current disk rotation speed is about 7200 rpm, it is expected to increase to 15000 rpm or more in the future. This requirement is expected to become even stronger especially for server hard disk drives that process large amounts of data. However, when the number of rotations of the recording medium is increased, the recording medium is deflected and resonance is increased, and the risk that the surface of the recording medium collides with the magnetic head and the reading error or the magnetic head crashes increases. Therefore, in the current recording medium, the distance (flying distance) between the magnetic head and the recording medium cannot be reduced to a certain extent, which is becoming an obstacle to increasing the recording density of the magnetic recording apparatus. This problem of deflection and resonance of the recording medium is solved by the use of a high modulus substrate material.

However, the aluminum substrate that has been generally used so far has an elastic modulus of about 72 GPa, and the glass substrate is about 80 to 100 GPa and cannot yet cope with high-speed rotation. There is a movement to respond. The increase in the thickness of the substrate is accompanied by an increase in weight, so that the power consumption for high speed rotation increases. Accordingly, a substrate material that is lighter than a dense aluminum alloy (2.76 g / cm ³ ) is required from the market. In addition, since the aluminum substrate has a surface hardness much lower than that of glass and easily undergoes plastic deformation, the surface of the recording medium may be dented due to a collision between the high-speed rotating substrate and the magnetic head. On the other hand, a glass substrate is superior to an aluminum substrate in terms of elastic modulus, surface hardness, and surface smoothness, but is more fragile because it is more brittle than an aluminum substrate, and the presence of slight scratches formed in the manufacturing process leads to breakage. For example, when glass is used as the magnetic disk substrate, many processing processes such as circular processing, centering, and inner and outer circumferential surface processing are required. During these processings, many scratches that can become breakage points also occur in the glass edge portion and the like, and slight scratches that are formed not only in the manufacturing process but also in mounting on the spindle and other handling lead to substrate damage. In particular, this problem becomes more important as the rotation speed of the magnetic disk increases. In order to solve these problems, it is necessary to provide a substrate glass having a low density and not easily damaged, or a substrate glass having high resistance to breakage of glass, that is, high fracture toughness.
JP-A-1-239036 US Pat. No. 5,391,522

  Under such circumstances, the present invention can cope with the trend toward higher speed rotation and higher recording density, has a low density, excellent scratch resistance, is hardly scratched, and is resistant to breakage progression. An object of the present invention is to provide a glass substrate for an information recording medium having high strength, that is, fracture toughness, and a magnetic information recording medium using the same.

  As a result of intensive studies to achieve the above object, the inventors of the present invention are made of a glass substrate having a brittleness index value measured in water and / or a dry atmosphere, or a glass having a specific composition. The present inventors have found that a glass substrate can be adapted to the purpose as a glass substrate for an information recording medium, and have completed the present invention based on this finding.

That is, the present invention
(1) A glass substrate for information recording medium (hereinafter referred to as glass substrate I for information recording medium), wherein the brittleness index value in water is 12 μm ^−1/2 or less,
(2) A glass substrate for an information recording medium having a brittleness index value in an atmosphere having a dew point of −5 ° C. or less of 7 μm ^−1/2 or less (hereinafter referred to as an information recording medium glass substrate II). ,
(3) An information recording medium having a brittleness index value in water of 12 μm ^−1/2 or less and an brittleness index value in an atmosphere having a dew point of −5 ° C. or less of 7 μm ^−1/2 or less. Glass substrate (hereinafter referred to as glass substrate III for information recording medium),
(4) In a mol%, SiO ₂ and B ₂ O ₃ and / or Al ₂ O ₃ are included in a total amount of more than 65%, and RO (R is selected from Mg, Ca, Zn, Sr and Ba). At least one selected) 0-20%, R ′ ₂ O (R ′ is at least one selected from Li, Na and K) 0-28%, TiO ₂ 0-10% and ZrO ₂ 0-10 %, And the glass substrate for an information recording medium according to the above (1), (2) or (3), comprising a glass having a total content of 95% or more,
(5) mol%, SiO ₂ 40-75%, B ₂ O ₃ and / or Al ₂ O ₃ 2-45% and R ′ ₂ O (R ′ is at least one selected from Li, Na and K) Species) For an information recording medium comprising 0 to 40% of glass and comprising a glass having a total content of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ and R ′ ₂ O of 90% or more Glass substrate (hereinafter referred to as glass substrate IV for information recording medium),
(6) The glass substrate for information recording media according to (5), wherein the brittleness index value in water is 12 μm ^−1/2 or less,
(7) The glass substrate for information recording media according to the above (5) or (6), wherein the brittleness index value in an atmosphere having a dew point of −5 ° C. or less is 7 μm ^−1/2 or less,
(8) The glass substrate for information recording media according to any one of (1) to (7), wherein the Young's modulus is 70 GPa or more,
(9) The glass substrate for an information recording medium according to any one of (1) to (8), wherein the rigidity is 20 GPa or more,
(10) The glass substrate for an information recording medium according to any one of the above (1) to (9), which is made of glass having a region having a viscosity of 1 Pa · s or more in a temperature region above the liquidus temperature,
(11) The glass for an information recording medium according to any one of the above (1) to (10), comprising a glass having a thermal expansion coefficient of 60 × 10 ⁻⁷ / ° C. or higher at a temperature of 100 to 300 ° C. substrate,
(12) The glass substrate for information recording media according to any one of (1) to (11) above, which does not have a chemical strengthening layer,
(13) The glass substrate for an information recording medium according to any one of (1) to (11) above, which has a chemical strengthening layer, and (14) any one of (1) to (13) above. A magnetic information recording medium comprising at least a magnetic recording layer on the glass substrate for the information recording medium,
Is to provide.

  The glass substrate for information recording media of the present invention is excellent in scratch resistance, is lightweight and has a high resistance to fracture progression, that is, fracture toughness, and is being produced and processed such as a magnetic disk as compared with a conventional glass substrate for information recording media. Damage during use as an information recording medium can be greatly reduced. Furthermore, since glass can be mass-produced at the same or lower cost as a commercially available glass substrate, it can be greatly expected as a glass substrate for a next-generation magnetic recording medium that is inexpensive.

  The glass substrate for information recording medium of the present invention has four embodiments, that is, glass substrates I to IV for information recording medium.

The glass substrate I for information recording medium of the present invention is a glass substrate having a brittleness index value in water of 12 μm ^−1/2 or less. As the brittleness index value in water becomes lower, the glass substrate becomes less brittle. Fragility index value in the water is preferably 10.5 [mu] m ^-1/2 or less, more preferably 9 .mu.m ^-1/2 or less, more preferably 8 [mu] m ^-1/2 or less. Due to the brittleness index value in water being such a value, it is possible to destroy glass substrates when they are immersed in a polishing liquid or when handling glass substrates that are wet with a polishing liquid or a cleaning liquid. Is less likely to occur.

The glass substrate II for information recording medium of the present invention is a glass substrate having a brittleness index value of 7 μm ^−1/2 or less in an atmosphere having a dew point of −5 ° C. or less. The index value is preferably 6 μm ^−1/2 or less, more preferably 5 μm ^−1/2 or less, and further preferably 4 μm ^−1/2 or less. When the dew point is −5 ° C. or lower, that is, the brittleness index value in the dry atmosphere is such a value, when handling the glass substrate for information recording medium in the dry atmosphere, information using the glass substrate is used. Destruction is unlikely to occur when using a recording medium.

The glass substrate III for information recording media of the present invention has a brittleness index value in water of 12 μm ^−1/2 or less and a brittleness index value in an atmosphere having a dew point of −5 ° C. or less of 7 μm ^−1/2 or less. It is a glass substrate. Fragility index value in the water is preferably 10.5 [mu] m ^-1/2 or less, more preferably 9 .mu.m ^-1/2 or less, more preferably not more 8 [mu] m ^-1/2 or less, following the atmosphere above the dew point -5 ° C. The brittleness index value in is preferably 6 μm ^−1/2 or less, more preferably 5 μm ^−1/2 or less, and further preferably 4 μm ^−1/2 or less. The glass substrate III has both the properties of the glass substrates I and II, and is less likely to break even if used or handled in any environment.

In the present invention, the brittleness index value B proposed by BR Lawn et al. Is adopted as the brittleness index value of the glass substrate [“Journal of the American Chemical Society (J. Am. Chem. Soc.) 62, 347-350 (1979)]. Here, the brittleness index value B is calculated from the formula V = Hv / Kc from the Vickers hardness value Hv and the fracture toughness value Kc of the glass.
Defined by

  The Vickers hardness value Hv and the fracture toughness value Kc of the glass can be measured by a method in which a sharp diamond indenter of a Vickers hardness tester is pushed into the glass. That is, the hardness of the glass can be obtained by the following equation from the size of the indentation of the indenter remaining on the glass surface when the Vickers indenter is pushed.

ここで、Ｐはビッカース圧子の押しこみ荷重であり、ａはビッカース圧痕の対角線長である。一方、ガラスの破壊靭性Ｋｃはビッカース圧子を押しこんだときにガラスの表面に残る圧子の圧痕の大きさと圧痕の隅から発生するクラックの長さより次式で求められる。

Here, P is the indentation load of the Vickers indenter, and a is the diagonal length of the Vickers indentation. On the other hand, the fracture toughness Kc of the glass is obtained by the following equation from the size of the indentation of the indenter remaining on the glass surface when the Vickers indenter is pushed in and the length of the crack generated from the corner of the indentation.

ここで、Ｅはガラスのヤング率、Ｃは圧痕の隅から発生するクラックの長さである。Ｋｃを正しく求めるための必要条件はＣ／ａ比が２．５以上に大きくなることである。

Here, E is the Young's modulus of the glass, and C is the length of the crack generated from the corner of the indentation. A necessary condition for correctly obtaining Kc is that the C / a ratio is increased to 2.5 or more.

  The brittleness index value B of the glass is calculated from Hv and Kc obtained above by B = Hv / Kc. In the present invention, the comparative example is described for comparison with the comparative example described later. The method shown in JP-A-10-158028, that is,

により算出した値を採用する。

The value calculated by is adopted.

  The difference between the brittleness value using the calculation formula shown in Japanese Patent Laid-Open No. 10-158028 and the brittleness value evaluated by the Hv / Kc formula is almost 5% or less. It can also be evaluated correctly using the formula shown in. Actually, the calculation formula shown in Japanese Patent Laid-Open No. 10-158028 is derived on the basis of Lawn et al.'S Hv / Kc calculation formula and has the same basic concept.

  For the brittleness index value in water, a drop of pure water is dropped on the surface of the sample, and after 30 seconds, a Vickers indenter is pushed in from the water drop to introduce indentations and cracks. Immediately after that, the sample was immersed in pure water, taken out after 24 hours, wiped off with water, and immediately measured by measuring the size of indentations and cracks. The brittleness index value in an atmosphere with a dew point of −5 ° C. or lower is measured by measuring the dew point around the sample in a dry nitrogen atmosphere and pushing in the Vickers indenter while confirming that the dew point is −5 ° C. or lower. It is a value calculated by introducing indentations and cracks and measuring their sizes.

  Since the glass substrates I, II and III for the information recording medium of the present invention have the brittleness index values as described above, they are difficult to be scratched and can be chemically strengthened equivalent to conventional glass. Breakage in the process and breakage during use as a product can be greatly reduced.

As such glass substrates I to III, the glass composition contains SiO ₂ and B ₂ O ₃ and / or Al ₂ O ₃ in a total amount of more than 65% in mol%, and RO (R is At least one selected from Mg, Ca, Zn, Sr and Ba) 0-20%, R ′ ₂ O (R ′ is at least one selected from Li, Na and K) 0-28%, Mention may be made of glass comprising TiO ₂ 0 to 10% and ZrO ₂ 0 to 10% and having a total content of the above components of 95% or more.

In this glass composition, the total content of SiO ₂ and B ₂ O ₃ and / or Al ₂ O ₃ is preferably more than 65 mol% and not more than 90 mol%, more preferably 70 to 90 mol%, still more preferably Is in the range of 70 to 85 mol%. Further, the content of SiO ₂ is preferably 40 to 75 mol%, more preferably 50 to 70 mol%, and the content of Al ₂ O ₃ is preferably 0 to 25 mol%, more preferably 1 to 1. It is 20 mol%, More preferably, it is 2-15 mol%. The content of B ₂ O ₃ is preferably 0 to 25 mol%, more preferably 1 to 25 mol%, and still more preferably 2 to 20 mol%. The RO content is preferably 15 mol% or less, more preferably 12 mol% or less. The MgO content is preferably 15 mol% or less, more preferably 12 mol% or less, and the CaO content is preferably 10 mol% or less, more preferably 8 mol% or less. The content of ZnO is preferably 10 mol% or less, more preferably 8 mol% or less, and the content of SrO is preferably 10 mol% or less, more preferably 8 mol% or less. The content of BaO is preferably 10 mol% or less, more preferably 5 mol% or less. As this RO, MgO is preferable.

The content of R ′ ₂ O is preferably 25 mol% or less, more preferably 10 to 25 mol%. The content of Li ₂ O is preferably 20 mol% or less, 18 mole% and more preferably less, more preferably 5 to 15 mol%, content of Na ₂ O is preferably not more than 20 mol% More preferably, it is 15 mol% or less, More preferably, it is 1-10 mol%. The content of K ₂ O is preferably 15 mol% or less, more preferably 10 mol% or less, and still more preferably 0 to 8 mol%. The total content of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , RO and R ′ ₂ O is preferably 85 mol% or more, more preferably 90 mol% or more, and still more preferably 95 mol% or more. It is.

Further, the content of TiO ₂ is preferably 0 to 7 mol%, more preferably 0 to 5 mol%, and the content of ZrO ₂ is preferably 0 to 8 mol%, more preferably 0 to 6 mol%. %. The total content of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , RO, R ′ ₂ O, TiO ₂ and ZrO ₂ is preferably 95 mol% or more, more preferably 98 mol% or more. . Further, the molar ratio of B ₂ O ₃ to Al ₂ O ₃ (B ₂ O ₃ / Al ₂ O ₃ ) is preferably in the range of 0.5 to 1.5, more preferably in the range of 0.8 to 1.2. It is.

As a combination of the above components, for example, mol%, SiO ₂ 40 to 75%, B ₂ O ₃ 1 to 25%, Al ₂ O ₃ 1 to 20% (however, SiO ₂ , B ₂ O ₃ and Al ₂ The total content with O ₃ exceeds 65%.), MgO 0-15%, ZnO 0-10%, CaO 0-10%, SrO 0-10%, BaO 0-10% (however, MgO and CaO) And ZnO, SrO and BaO are less than 20% in total.), Li ₂ O 0-20%, Na ₂ O 0-20%, K ₂ O 0-15% (however, Li ₂ O and Na The total content of ₂ O and K ₂ O is less than 28%.), Glass containing TiO ₂ 0-10% and ZrO ₂ 0-10%, and the total content of the above components being 95% or more Can be mentioned.

SiO ₂ is a main component that forms a network structure of glass. If the content is less than 40 mol%, the durability of the glass deteriorates and the glass tends to devitrify. On the other hand, when it exceeds 75 mol%, the high-temperature viscosity becomes high and the glass becomes difficult to melt. Accordingly, the content of SiO ₂ is preferably in the range of 40 to 75 mol%, particularly preferably in the range of 50 to 70 mol%.

B ₂ O ₃ is an important component of the present invention. When B ₂ O ₃ is introduced instead of SiO ₂ , the brittleness of the glass is greatly reduced, the specific gravity is lowered, and the high-temperature viscosity is also lowered, so that the solubility of the glass is greatly improved. However, if the amount introduced exceeds 25 mol%, the durability of the glass deteriorates, and phase separation tends to occur, so that a high-quality glass may not be produced. On the other hand, if the amount introduced is less than 1 mol%, the brittleness deteriorates and the high-temperature viscosity also increases, so there is a possibility that low-cost mass production cannot be achieved. Therefore, the content of B ₂ O ₃ is preferably 1 to 25 mol%, particularly preferably 2 to 20 mol%.

Al ₂ O ₃ is very important not only as a component that contributes to heat resistance, durability and low brittleness to glass, but also as a component that stabilizes the glass structure and increases its rigidity together with SiO ₂ . However, if the content is less than 1 mol%, the effect of suppressing the elution of alkali from the glass is small, and it is difficult to make a glass having good durability. If the content exceeds 20 mol%, the high-temperature meltability of the glass deteriorates. Therefore, the content is preferably in the range of 1 to 20 mol%, more preferably in the range of 2 to 15 mol%.

  MgO, CaO, ZnO, SrO and BaO are components introduced in order to lower the viscosity at the time of melting the glass and to increase the meltability and mass productivity. When the total content is 20 mol% or more, the brittleness increases, so that the glass tends to be damaged, and the specific gravity and devitrification temperature tend to increase. The content of MgO, CaO, ZnO, SrO and BaO in consideration of both the solubility and low brittleness of the glass is 0-15 mol% for MgO, preferably 0-12 mol%, and 0-10 mol% for ZnO. Preferably 0 to 8 mol%, CaO 0 to 10 mol%, preferably 0 to 8 mol%, SrO 0 to 10 mol%, preferably 0 to 8 mol%, BaO 0 to 10 mol%, preferably Is in the range of 0 to 5 mol%, and their total content is preferably less than 20 mol%, more preferably 15 mol% or less.

Li ₂ O, Na ₂ O, and K ₂ O are very useful components that lower the viscosity at the time of melting the glass, promote the melting, and reduce the brittleness of the glass. However, when the content thereof is more than 28%, not only the chemical durability is deteriorated, because the alkali comes to many deposition on the glass surface, there is a fear that attack the magnetic film, Li ₂ The content of O, Na ₂ O, and K ₂ O is such that Li ₂ O is 0 to 20 mol%, preferably 0 to 18 mol%, Na ₂ O is 0 to 20 mol%, preferably 0 to 15 mol%, K ₂ O is 0 to 15 mol%, preferably with 0 to 10 mol%, preferably the total content thereof less than 28 mol%, more preferably kept below 25 mole%.

The total content of SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ is preferably in the range of 70 to 90 mol%, more preferably 80 to 90 mol%, and the total content of RO and R ′ ₂ O The amount is preferably 5 to 35 mol%, more preferably 10 to 30 mol%, still more preferably 10 to 25 mol%, and particularly preferably 10 to 22 mol%.

ZrO ₂ and TiO ₂ are components introduced to improve the chemical durability of the glass and increase the rigidity. When small amounts of ZrO ₂ and TiO ₂ are added to the glass, the durability, elastic modulus, and brittleness of the glass are improved, but the specific gravity increases rapidly, and when it is introduced more, the tendency of devitrification of the glass becomes stronger. Therefore, the contents of ZrO ₂ and TiO ₂ are respectively limited to 0 to 10 mol%, preferably 0 to 7 mol% and 0 to 10 mol%, preferably 0 to 8 mol%.

  The total content of the above components is 95 mol% or more.

In addition to the above components, this glass has a total of 2 mol% or less of As ₂ O ₃ , Sb ₂ O ₃ , F, Cl, SO ₃ in order to improve the solubility, clarity, moldability, etc. of the glass. It is possible to introduce. In order to improve the durability and elastic modulus of the glass, other oxides such as rare earth metal oxides such as Y ₂ O ₃ and La ₂ O ₃ can be added at a ratio of 5 mol% or less.

Furthermore, in _{mol%, SiO 2 55~75%, B} 2 O 3 0~20%, Al 2 O 3 1~20% ( provided that the total content of SiO ₂ and B ₂ O ₃ and Al ₂ O ₃ 65% or more), MgO 0-15%, ZnO 0-10%, CaO 0-10%, SrO 0-10%, BaO 0-10% (however, the total content of MgO, CaO, ZnO, SrO and BaO) (Content of RO is 20% or less), Li ₂ O 0-20%, Na ₂ O 0-20%, K ₂ O 0-6% (however, Li ₂ O, Na ₂ O and K ₂ O) And the total content (R ′ ₂ O content) is 28% or less), TiO ₂ 0-10% and ZrO ₂ 0-10%, and the total content of the above components is 95% or more. be able to.

The glass substrate IV for information recording medium of the present invention comprises SiO ₂ 40 to 75%, B ₂ O ₃ and / or Al ₂ O _{3 2 to} 45% and R ′ ₂ O (R ′ is Li, Na and A glass comprising at least one selected from K) 0 to 40% and having a total content of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ and R ′ ₂ O of 90% or more It is.

In this glass composition, the content of SiO ₂ is preferably 50 to 70 mol%, and the content of B ₂ O ₃ is preferably 0 to 25 mol%, more preferably 1 to 25 mol%, and still more preferably 2 to 2 mol%. The content of Al ₂ O ₃ is preferably 0 to 25 mol%, more preferably 1 to 20 mol%, and still more preferably 2 to 15 mol%. The total content of SiO ₂ , B ₂ O ₃ and Al ₂ O ₃ is preferably 65 to 90 mol%, more preferably 70 to 90 mol%, still more preferably 70 to 85 mol%. The R ′ ₂ O content is preferably 0 to 28 mol% (provided that 0 is excluded when RO is 0 mol%), more preferably 25 mol% or less, and still more preferably 10 to 25 mol%. The content of Li ₂ O is preferably 20 mol% or less, more preferably 18 mol% or less, still more preferably 5 to 15 mol%, and the content of Na ₂ O is preferably 20 mol% or less, more preferably 15 mol% or less, more preferably 1 to 10 mol%, the content of K ₂ O is preferably 15 mol% or less, more preferably 10 mol% or less, more preferably 0 to 8 mole% is there. Furthermore, the content of RO is preferably 15 mol% or less, more preferably 12 mol% or less. The MgO content is preferably 15 mol% or less, more preferably 12 mol% or less, and the CaO content is preferably 10 mol% or less, more preferably 8 mol% or less. The content of ZnO is preferably 10 mol% or less, more preferably 8 mol% or less, and the content of SrO is preferably 10 mol% or less, more preferably 8 mol% or less. The content of BaO is preferably 10 mol% or less, more preferably 5 mol% or less. As RO, MgO is particularly preferable.

The total content of RO and R ′ ₂ O is preferably 5 to 35 mol%, more preferably 10 to 30 mol%, still more preferably 10 to 25 mol%, and particularly preferably 10 to 22 mol%. Furthermore, can include TiO ₂ 0 mol%, the content of the preferred TiO ₂ is 0 to 7 mol%. The can include ZrO ₂ 0 mol%, preferably ZrO ₂ content is 0 to 7 mol%.

The glass substrate IV is, 12 [mu] m ^-1/2 or less brittleness index value in water, preferably 10.5 [mu] m ^-1/2 or less, more preferably 9 .mu.m ^-1/2 or less, more preferably 8 [mu] m ^-1/2 or less It can be. Further, the brittleness index value in an atmosphere having a dew point of −5 ° C. or less is 7 μm ^−1/2 or less, preferably 6 μm ^−1/2 or less, more preferably 5 μm ^−1/2 or less, and further preferably 4 μm ^−1/2. It can be as follows.

  In the glass substrates I to IV for information recording media of the present invention, the Young's modulus can be set to 70 GPa or more, preferably 75 GPa or more, more preferably 85 GPa or more.

  In order to prevent the glass substrate from being deformed by resonance or the like when the information recording medium including the thin glass substrate is rotated at high speed, it is preferable to increase the Young's modulus of the glass substrate. For example, when a magnetic disk made of a glass substrate having a Young's modulus of 70 GPa or more and having a diameter of 3.5 inches and a thickness of 0.635 mm is rotated at 10,000 rpm, the magnetic disk and the recording / reproducing head The flying height can be secured stably at about 1 μm or less.

  Further, in a glass substrate having a low brittleness index value in water, the Young's modulus is 70 GPa or more, so that the glass substrate is cracked when it is ground and polished in a polishing solution, and wetted with a polishing solution or a cleaning solution. Breaking when handling a glass substrate in a damaged state is much less likely to occur.

  Further, in a glass substrate having a low brittleness index value in water and / or in a dry atmosphere, since the Young's modulus is 70 GPa or more, the glass substrate is difficult to bend due to rotation or load. When the recording medium is used, destruction particularly when the information recording medium rotates at a high speed is further less likely to occur.

  In the glass substrates I to IV of the present invention, the rigidity can be set to 20 GPa or more, preferably 25 GPa or more, more preferably 30 GPa or more.

  In order to prevent the glass substrate from being deformed by resonance or the like when an information recording medium including a thin glass substrate is rotated at high speed, it is preferable to increase the rigidity of the glass substrate. For example, when a magnetic disk made of a glass substrate made of glass having a rigidity of 20 GPa or more and having a diameter of 3.5 inches and a thickness of 0.635 mm is rotated at 10,000 rpm, the magnetic disk and the recording / reproducing head The flying height can be secured stably at about 1 μm or less.

  In addition, in a glass substrate having a low brittleness index value in water, the rigidity is 20 GPa or more, so that the glass substrate is cracked when it is ground and polished in a state where it is immersed in a polishing liquid, or wet with a polishing liquid or a cleaning liquid. Breaking when handling a glass substrate in a damaged state is much less likely to occur.

  Further, in a glass substrate having a low brittleness index value in water and / or in a dry atmosphere, since the rigidity of the glass substrate is more than 20 GPa, the glass substrate is difficult to bend due to rotation or load. When the recording medium is used, destruction particularly when the information recording medium rotates at a high speed is further less likely to occur.

Further, in the glass substrates I to IV of the present invention, the specific elastic modulus (value obtained by dividing Young's modulus by its density) can be 27 × 10 ⁶ N · m / kg or more.

When the specific elastic modulus is 27 × 10 ⁶ N · m / kg or more, the deflection at the time of high-speed rotation of the information recording medium can be 2 μm or less, and as a result, the flying height can be stably secured at 1 μm or less. it can. In addition, since the deflection at the time of high-speed rotation is small, the glass substrate having a small brittleness index value is less likely to break. The specific elastic modulus is more preferably 30 × 10 ⁶ N · m / kg or more.

In the glass substrates I to IV of the present invention, the density can be 2.65 g / cm ³ or less, preferably 2.50 g / cm ³ or less.

Furthermore, in the glass substrates I to IV of the present invention, the fracture toughness value is 0.75 MPa / m ^1/2 or more, preferably 0.80 MPa / m ^1/2 or more, more preferably 0.83 MPa / m ^1/2. That's it. When the fracture toughness value is 0.75 MPa / m ^1/2 or more, breakage is less likely to occur when processing a glass substrate or when using an information recording medium.

  In the glass substrates I to IV for information recording media of the present invention, those made of glass having a region having a viscosity of 1 Pa · s or more in the temperature region above the liquidus temperature are preferable.

  In order to obtain a glass substrate for an information recording medium, it is necessary to prevent the glass substrate from being substantially devitrified in the production process. For this purpose, at least the melting of the raw material and the supply of the molten glass to the mold are performed at the liquidus temperature. It is necessary to do it above.

  For this reason, in the glass substrates I to IV of the present invention, the liquidus temperature of the material glass is preferably 1350 ° C. or less, more preferably 1250 ° C. or less, and particularly preferably 1150 ° C. or less.

  Here, if the viscosity at the time of supplying the molten glass to the mold is less than 1 Pa · s, not only is it difficult to control the flow rate of the molten glass, but a thin and flat glass substrate for an information recording medium is formed by press molding. It becomes difficult to obtain.

  The glass substrates I to IV of the present invention are more preferably made of glass having a region having a viscosity of 3 Pa · s or more in a temperature region above the liquidus temperature.

  In the glass substrates I to IV of the present invention, the transition point of the material glass can be set to 470 to 640 ° C. If the glass transition point is too high, the temperature range in which press molding can be performed becomes narrow, making it difficult to press form a thin glass substrate. On the other hand, if the glass transition point is too low, a magnetic film such as a recording layer is formed on the glass substrate. Alternatively, after the formation, the range of the heat treatment temperature performed for the purpose of improving the magnetic characteristics is narrowed. A preferred transition point is in the range of 470-620 ° C.

In the glass substrates I to IV for information recording media of the present invention, those made of glass having a thermal expansion coefficient of 60 × 10 ⁻⁷ / ° C. or more at a temperature of 100 to 300 ° C. are preferable.

  When information is recorded on an information recording medium such as a magnetic disk, an optical disk, or a magneto-optical disk, or when information recorded on the information recording medium is reproduced, the information recording medium is provided in the information processing apparatus. The drive motor is rotated while being fixed to the spindle of the drive motor by a clamp. At this time, if the thermal expansion coefficient of the information recording medium and the thermal expansion coefficient of the clamp are significantly different, the following problem occurs. Occurs.

  That is, when the information recording medium is rotated, the temperature of the information recording medium, the spindle, the clamp, and the like is rapidly increased to, for example, about 90 ° C. due to heat generated by the drive motor. If the thermal expansion coefficient of the clamp is significantly different, loosening occurs between the information recording medium and the clamp due to the temperature rise, and distortion or deflection occurs in the information recording medium. As a result, information recording The position of a data recording location (track) on the medium changes, and an error is likely to occur in information recording or reproduction. Such a problem is particularly a problem with large substrates such as 3.5 inches.

Therefore, it is preferable that the thermal expansion coefficient of the glass substrates I to IV of the present invention is as close as possible to the thermal expansion coefficient of the clamp. Since the clamp is generally made of a stainless alloy, the thermal expansion coefficient at 100 to 300 ° C. of the glass substrates I to IV of the present invention is preferably 60 × 10 ⁻⁷ / ° C. or more, more preferably. It is 70 × 10 ⁻⁷ / ° C. or more, more preferably 70 × 10 ⁻⁷ / ° C. to 120 × 10 ⁻⁷ / ° C., particularly preferably 80 × 10 ⁻⁷ / ° C. to 100 × 10 ⁻⁷ / ° C.

  The glass substrates I to IV for information recording media of the present invention may not have a chemical strengthening layer, or may be provided with a chemical strengthening layer by performing a known chemical strengthening treatment if desired. May be. When the chemical strengthening treatment is performed, it is preferable to select a composition suitable for the chemical strengthening treatment from the above glass composition range.

  The chemical strengthening treatment can be performed by an ion exchange method. This ion exchange method is performed using a molten salt containing Na ions and K ions to obtain chemically strengthened glass. As the treated molten salt containing Na ions and K ions, sodium nitrate, potassium nitrate and mixed molten salts thereof are preferably used, but are not limited to nitrates, and sulfates, bisulfates, carbonates, halides are not limited. Etc. may be used. As described above, the glass used in the present invention has low brittleness and high fracture toughness, and the bending strength is increased by ion exchange. Therefore, the obtained chemically strengthened glass has excellent fracture resistance.

  There is no restriction | limiting in particular as a manufacturing method of the glass substrate for information recording media of this invention, Various methods can be used. For example, a high-temperature melting method, that is, a predetermined proportion of glass raw material is melted in air or in an inert gas atmosphere, homogenized by bubbling or stirring, etc., and made into plate glass by a well-known press method, down-draw method and float method. Thereafter, circular processing, centering, inner and outer circumferential processing, grinding, polishing, and the like are performed to obtain an information recording medium substrate having a desired size and shape. In polishing, lapping and polishing with an abrasive such as cerium oxide are performed with an abrasive or diamond pellets, so that the surface accuracy can be in the range of 0.1 to 0.6 nm, for example.

  The magnetic information recording medium of the present invention has at least a magnetic recording layer on the above-described glass substrates I to IV for the information recording medium of the present invention. The configuration of the magnetic information recording medium includes, for example, the glass substrate A configuration in which an underlayer, a magnetic recording layer, a protective layer, and a lubricating layer are sequentially provided above can be given.

  Here, examples of the magnetic recording layer include Co—Cr, Co—Cr—Pt, Co—Ni—Cr, Co—Ni—Pt, Co—Ni—Cr—Pt, and Co—Cr—Ta. A system or the like can be used. As the underlayer, for example, a Ni layer, a Ni-P layer, a Cr layer, or the like can be used. As the protective layer, for example, a carbon film or the like can be used. The lubricant can be used.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

In addition, the physical property of the glass obtained by each example was measured in accordance with the method shown below.
(1) A Young's modulus 20 × 20 × 100 mm sample is prepared, and a longitudinal wave velocity (Vl) and a transverse wave velocity (Vs) when a 5 MHz ultrasonic wave propagates through the sample are measured around. After measurement using (UVM-2 manufactured by Ultrasonic Industry Co., Ltd.), it was obtained by the following formula.

Young's modulus = (4G ² -3G · Vl ² · ρ) / (G−Vl ² · ρ)
G = Vs ²・ ρ
ρ: Sample density (g / cm ³ )
(2) Rigidity The rigidity can be obtained as G when measuring the Young's modulus in (1) above.
(3) Liquid phase temperature The sample was placed in a platinum container and allowed to stand in a gradient temperature furnace for 30 minutes, and then the presence or absence of crystals on the surface and inside of the sample was observed using an optical microscope. The lowest temperature at which no crystals were precipitated was taken as the liquidus temperature.
(4) Glass transition point (Tg), yield point (Td)
A sample of 5 mmφ × 20 mm was measured at a temperature increase rate of + 4 ° C./min using a thermomechanical analyzer (TMA8140) manufactured by Rigaku Corporation. As the standard sample using SiO _2.
(5) Coefficient of thermal expansion Means the coefficient of thermal expansion at 100 to 300 ° C., and was measured together when measuring the glass transition point.
(6) Brittleness index value Vickers with the indentation load shown in Table 1 to Table 15 for a sample processed into a 2 mm thick plate using a micro hardness tester (MVK-E) manufactured by Akashi Manufacturing Co., Ltd. An indenter was pushed in to introduce indentations and cracks into the sample.

The indentation load is preferably set to a value with a probability of 60 or more in order to accurately measure the brittleness index value, Vickers hardness, fracture toughness, etc., and more preferably a value of 70 or more. , 80 or more is more preferable.
The measured diagonal length a of the Vickers indentation a and the length C of the crack generated from the corner of the Vickers indentation generated on the sample surface when the Vickers indenter was pushed in were measured.

From the above measured values, the Vickers hardness Hv, the fracture toughness Kc, and the brittleness index value B were determined using the mathematical formulas (1) to (3).
In order to obtain the brittleness index value B, Vickers hardness Hv, fracture toughness Kc, etc. in water, a pure water droplet is dropped on the sample surface, and after 30 seconds, a Vickers indenter is pushed into the sample from above the water droplet and indentations and cracks. Is introduced.

In order to obtain the brittleness index value B, Vickers hardness Hv, fracture toughness Kc, etc. in an atmosphere with a dew point of −5 ° C. or lower, the dew point around the sample must be −5 ° C. or lower in a dry nitrogen atmosphere. While checking, a Vickers indenter is pushed into the sample to introduce indentations and cracks.
The probabilities in Tables 1 to 14 are occurrence probabilities per vertex of cracks generated from the four vertexes of the indentation.

Examples 1-81
As a starting material, SiO ₂ , Al ₂ O ₃ , Al (OH) ₃ , B ₂ O ₃ , HBO ₃ , MgO, Mg (OH) ₂ , MgCO are used so as to obtain glasses having the compositions shown in Tables 1 to 14. ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , ZnO, Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , TiO ₂ , ZrO _2, etc. are weighed 300 to 1500 g and mixed thoroughly to prepare A batch was formed, which was put into a platinum crucible, and the glass was melted in air at a temperature of 1400 to 1600 ° C. for about 3 to 8 hours. After melting, the glass melt was poured into a 40 × 40 × 20 mm carbon mold, allowed to cool to the glass transition temperature, immediately placed in an annealing furnace, held for 1 hour, and then allowed to cool to room temperature in the furnace. The obtained glass did not precipitate crystals that could be observed with a microscope.

  The glass thus obtained was processed to prepare samples for evaluating physical properties, and physical properties were evaluated. The results are shown in Tables 1-14.

比較例１〜３
特開平１０−１５８０２８号公報に記載されているガラスについて、その物性を表１５に示した。

Comparative Examples 1-3
Table 15 shows the physical properties of the glass described in JP-A-10-158028.

Example 82
Using the glass obtained in Examples 1 to 81, (1) rough lapping step (rough grinding step), (2) shape processing step, (3) fine lapping step (fine grinding step), (4) end mirror processing A glass substrate for an information recording medium is manufactured by sequentially performing a process, (5) a first polishing process, (6) a second polishing process, (7) an inspection process, and (8) a magnetic disk manufacturing process. Manufactured.
In addition, the water of the polishing liquid used for the polishing apparatus from the above (4) end mirror processing step to (6) second polishing step was pure water.

(1) Coarse lapping process First, a disk-shaped glass substrate having a diameter of 96 mmφ and a thickness of 1.5 mm was obtained from molten glass by direct pressing using an upper mold, a lower mold, and a trunk mold. In this case, in addition to the direct press, a disk-shaped glass substrate may be obtained by cutting out with a grinding wheel from a sheet glass formed by a downdraw method or a float method.
Next, a lapping process was performed on the glass substrate to improve dimensional accuracy and shape accuracy. This lapping process was performed using a double-sided lapping machine and using abrasive grains having a particle size of # 400. Specifically, first, using alumina abrasive grains of grain size # 400, setting the load to about 980 N, and rotating the sun gear and the internal gear, both surfaces of the glass substrate housed in the carrier have a surface accuracy of 0 to 1 μm. And lapping to a surface roughness (Rmax) of about 6 μm.

(2) Shape processing step Next, a cylindrical grindstone is used to make a hole in the central portion of the glass substrate, and the outer peripheral end surface is ground to a diameter of 95 mmφ. Chamfered. At this time, the surface roughness of the end face of the glass substrate was about 4 μm in Rmax.

(3) Fine lapping step Next, the grain size of the abrasive grains was changed to # 1000 and the surface of the glass substrate was lapped so that the surface roughness was about 2 μm in Rmax and about 0.2 μm in Ra. The glass substrate after the lapping process was immersed in each washing tank (applied with ultrasonic waves) in a neutral detergent and water in order to perform ultrasonic cleaning.

(4) End mirror processing step Next, the surface roughness of the end surface (inner periphery, outer periphery) of the glass substrate was polished to about 1 μm at Rmax and about 0.3 μm at Ra while rotating the glass substrate by brush polishing. And the surface of the glass substrate which finished the said end surface mirror surface process was washed with water.

(5) 1st grinding | polishing process Next, in order to remove the damage | wound and distortion which remained in the lapping process mentioned above, the 1st grinding | polishing process was performed using the double-side polish apparatus. In a double-side polishing apparatus, a glass substrate held by a carrier is brought into close contact with an upper and lower surface plate to which a polishing pad is attached, the carrier is engaged with a sun gear and an internal gear, and the glass substrate is sandwiched between upper and lower surface plates. Press. Thereafter, a polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass substrate, whereby the glass substrate revolves while rotating on the surface plate to simultaneously polish both surfaces. Hereinafter, the same apparatus was used as the double-side polishing apparatus used in the examples.
Specifically, a polishing process was performed using a hard polisher (hard urethane foam) as a polisher. The polishing conditions were cerium oxide (average particle size 1.3 μm) + pure water as a polishing liquid, load: 9.8 mN / mm ² , and polishing time: 15 minutes. The glass substrate after the first polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, isopropyl alcohol (IPA), and IPA (steam drying), ultrasonically cleaned, and dried. .

(6) Second Polishing Step Next, a second polishing step was performed using a double-side polishing apparatus of the same type as that used in the first polishing step and changing the polisher to a soft polisher (suede pad). This second polishing step is intended to reduce, for example, the surface roughness Ra to about 1.0 to 0.3 μm or less while maintaining the flat surface obtained in the first polishing step. is there. The polishing conditions were cerium oxide (average particle size 0.8 μm) + pure water as the polishing liquid, load: 9.8 mN / mm ² , and polishing time 5 minutes. The glass substrate after the second polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.
Although the glass substrate of the present Example did not have a chemical strengthening layer, the glass substrate was not broken during the polishing step or during handling of the steps.

(7) Inspection Step Next, a visual inspection of the glass substrate surface after the drying and a precise inspection using light reflection / scattering / transmission were performed. As a result, no defects such as scratches were found on the glass substrate surface.
Further, when the surface roughness of the main surface of the glass substrate obtained through the above steps was measured with an atomic force microscope (AFM), it had an ultra-smooth surface with Rmax = 2.13 nm and Ra = 0.20 nm. A glass substrate for a magnetic disk was obtained.

(8) Magnetic disk manufacturing process A NiAl seed layer, a CrV underlayer, a CoPtCrB magnetic layer, and a hydrogenated carbon protective layer are formed on both main surfaces of the glass substrate for a magnetic disk obtained through the above processes using an in-line sputtering apparatus. Were sequentially formed, and a perfluoropolyether lubricating layer was formed by a dip method to obtain a magnetic disk. When the obtained magnetic disk was subjected to a touchdown height test, the touchdown height showed a good value of 5 nm. Further, the head did not crash even when the load / unload test (100,000 times) was performed.

Example 83
A magnetic disk was manufactured in the same manner as in Example 82 except that the following chemical strengthening step was performed between the (6) second polishing step and the inspection step (7) in Example 82.
In the chemical strengthening step, a chemical strengthening solution containing a mixture of potassium nitrate and sodium nitrate is prepared, the chemical strengthening solution is heated to 380 ° C., and the cleaned and dried glass substrate is immersed for about 4 hours to perform the chemical strengthening treatment. Then, the glass substrate after chemical strengthening was sequentially immersed in each washing tank of sulfuric acid, neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.
About the obtained glass substrate, when a 0.4 mm thin piece was cut out and measured using the polarization microscope, it was confirmed that the chemical strengthening layer is formed. In the glass substrate of this example, the glass substrate was not broken during the polishing step or during handling of the steps.
When the obtained magnetic disk was subjected to a touchdown height test, the touchdown height showed a good value of 5 nm. Further, the head did not crash even when the load / unload test (100,000 times) was performed.

  The glass substrate for information recording medium of the present invention is suitable for use as a magnetic information recording medium because of its low density, excellent scratch resistance, resistance to scratching, and high resistance to breakage, that is, fracture toughness. Can do.

Claims (14)

A glass substrate for an information recording medium, wherein a brittleness index value in water is 12 μm ^−1/2 or less. A glass substrate for an information recording medium, wherein a brittleness index value in an atmosphere having a dew point of -5 ° C or lower is 7 µm ^-1/2 or lower. A glass substrate for information recording media, wherein the brittleness index value in water is 12 μm ^−1/2 or less and the brittleness index value in an atmosphere having a dew point of −5 ° C. or less is 7 μm ^−1/2 or less. . In a mol%, the total amount of SiO ₂ and B ₂ O ₃ and / or Al ₂ O ₃ is more than 65%, and RO (R is at least selected from Mg, Ca, Zn, Sr and Ba) 1 type) 0-20%, R ′ ₂ O (R ′ is at least one selected from Li, Na and K) 0-28%, TiO ₂ 0-10% and ZrO ₂ 0-10% The glass substrate for an information recording medium according to claim 1, 2 or 3, comprising a glass having a total content of 95% or more. In _{mol%, SiO 2 40~75%, B} 2 O 3 and / or Al ₂ O ₃ 2~45% and R _'2 O (R' is at least one member selected from the group consisting of Li, Na and K) 0 A glass substrate for an information recording medium, characterized by comprising glass having a content of ˜40% and a total content of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ and R ′ ₂ O of 90% or more. ^{6. The} glass substrate for information recording media according to claim 5, wherein the brittleness index value in water is 12 μm ^−1/2 or less. The glass substrate for an information recording medium according to claim 5 or 6, wherein a brittleness index value in an atmosphere having a dew point of -5 ° C or lower is 7 µm ^-1/2 or lower. The glass substrate for an information recording medium according to any one of claims 1 to 7, wherein the Young's modulus is 70 GPa or more. The glass substrate for an information recording medium according to any one of claims 1 to 8, wherein the rigidity is 20 GPa or more. The glass substrate for an information recording medium according to any one of claims 1 to 9, wherein the glass substrate is made of glass having a region having a viscosity of 1 Pa · s or more in a temperature region equal to or higher than a liquidus temperature. 11. The glass substrate for an information recording medium according to claim 1, comprising a glass having a thermal expansion coefficient of 60 × 10 ⁻⁷ / ° C. or higher at a temperature of 100 to 300 ° C. 11. The glass substrate for information recording media according to any one of claims 1 to 11, which does not have a chemical strengthening layer. The glass substrate for information recording media according to any one of claims 1 to 11, which has a chemically strengthened layer. A magnetic information recording medium comprising at least a magnetic recording layer on the glass substrate for an information recording medium according to any one of claims 1 to 13.