JPH1160283A - Chemically reinforced glass substrate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate comprising low alkali glass (including alkali-free glass) having a high specific elastic modulus and a high Young's modulus enabling to correspond to the low flotation of a magnetic head and the high speed rotation of a disk, chemically reinforced by the exchange of ions, and having a high flexural strength, and to provide a method for producing the same. SOLUTION: This chemically reinforced glass substrate has an ion-exchanged layer on at least the surface of the substrate and a flexural strength of >=24 kg/mm<2> . Therein, portions except the ion-exchanged layer do not contain an alkali metal oxide or contains <=5 mol.% of Na2 O and/or <=10 mol.% of Li2 O, and further contains at least one kind of divalent metal oxide. The method for producing the glass substrate comprises immersing a glass substrate not containing an alkali metal oxide or containing <=5 mol.% of Na2 O and/or <=10 mol.% of Li2 O and further containing at least one kind of divalent metal oxide in a solution containing an alkali metal ion or divalent metal ion having a larger ion radius than that of a divalent metal ion constituting the divalent metal oxide to form an ion-exchanged layer on at least the surface of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION

The present invention is suitable for a substrate for an information recording medium such as a magnetic disk and an optical disk, a heat-resistant substrate for a low-temperature polycrystalline silicon liquid crystal display expected as a next-generation LCD, or a substrate for electric and electronic parts. The present invention relates to a glass substrate used, a method for manufacturing the same, and an information recording medium using the glass substrate. In particular, glass having high specific elastic modulus and / or Young's modulus and high heat resistance, having high surface smoothness when used as a substrate, and having high bending strength and suitable for information recording medium substrates and the like. The present invention relates to a substrate, a method for manufacturing the same, and an information recording medium using the glass substrate.

[0002]

2. Description of the Related Art The main components of a magnetic storage device such as a computer are a magnetic recording medium and a magnetic head for magnetic recording and reproduction. Flexible disks and hard disks are known as magnetic recording media. Among these, as a substrate material for a hard disk (magnetic disk), for example, an aluminum substrate, a glass substrate, a ceramic substrate,
There is a carbon substrate and the like. However, practically, an aluminum substrate and a glass substrate are mainly used depending on the size and use. Recently, the flying height of a magnetic head has been remarkably reduced with the miniaturization of hard disk drives for notebook personal computers and the densification of magnetic recording. Accordingly, extremely high accuracy has been required for the surface smoothness of the magnetic disk substrate. However, in the case of aluminum alloy, since the hardness is low, even if polishing is performed using a high-precision abrasive and a machine tool, the polished surface is plastically deformed. Is difficult to manufacture. Even if nickel-phosphorus plating is applied to the surface of aluminum alloy, surface roughness
Ra cannot be less than 20 angstroms.
Further, as hard disk drives have become smaller and thinner, there is a strong demand for reducing the thickness of the magnetic disk substrate. However, since aluminum alloy has low strength and rigidity, it is difficult to make the disk thin while maintaining a predetermined strength required by the specifications of the hard disk drive.

Therefore, a glass substrate for a magnetic disk having high strength, high rigidity, high impact resistance and high surface smoothness has appeared. Glass substrates are attracting attention as current and future substrates because of their excellent surface smoothness and mechanical strength. As the glass substrate, for example, a chemically strengthened glass substrate whose substrate surface is strengthened by an ion exchange method, a crystallized glass substrate that has been subjected to a crystallization treatment, and an alkali-free glass substrate substantially free of alkali are well known. I have.

For example, as a chemically strengthened glass substrate, Japanese Patent Application Laid-Open No. 1-239036 (hereinafter referred to as prior art 1) discloses that SiO ₂ is 60-70% by weight and Al ₂ O ₃ is 0.5-1% by weight.
4%, R ₂ O (R is an alkali metal) 10 to 32
%, ZnO 1 to 15% and B ₂ O ₃ 1.1 to 14% are ion-exchanged to form a compressive stress layer on the surface of the glass substrate by ion exchange. I have.

However, glass that has been chemically strengthened by ion exchange contains a large amount of alkali components. Therefore, when used for a long time in a high-temperature, high-humidity environment, alkali ions are precipitated from a thin portion of the magnetic film, such as a pinhole portion of the magnetic film or a peripheral portion of the magnetic film, or a portion where the glass is exposed, and this triggers the magnetic film. Have been found to have disadvantages such as corrosion or deterioration of the steel. So recently,
In order to solve this problem, a glass substrate for a magnetic disk made of non-alkali glass has been disclosed (for example,
See JP-A-8-169724 and JP-A-9-12333.

[0006]

However, it has been considered that such an alkali-free glass cannot be chemically strengthened because it does not contain an alkali metal. as a result,
Sufficient strength could not be obtained, or reinforcement had to be performed by a method other than chemical reinforcement. In addition, with the recent miniaturization and thinning of hard disks and high-density recording, the flying height of magnetic heads and the speed of disk rotation are rapidly increasing. Therefore, there is a more stringent demand to reduce the influence of the deflection of the disk substrate material. However, most of the conventional ion exchange strengthened substrate glass introduces a large amount of alkali ions into the glass for ion exchange. Therefore, most of the tempered glass has a low specific elastic modulus and a low Young's modulus. Cannot cope with The inventors of the present invention have studied over a long period of time a glass having a high specific elastic modulus and a high Young's modulus, and have found that a low alkali glass containing no large amount of alkali is preferable. And it is necessary to strengthen such glass. Therefore, an object of the present invention is to provide a glass substrate made of a low alkali glass (including an alkali-free glass) having a high specific elastic modulus or a high Young's modulus capable of coping with a low flying height of a magnetic head and a high speed of disk rotation. Another object of the present invention is to provide a glass substrate having high bending strength, which is chemically strengthened by ion exchange, and a method for manufacturing the same. Still another object of the present invention is to provide an information recording medium using a glass substrate having a high specific elastic modulus or a high Young's modulus capable of coping with a low flying height of a magnetic head and a high speed of disk rotation, and having a high bending strength. To provide.

[0007]

SUMMARY OF THE INVENTION The present invention is as follows. [Claim 1] A glass substrate having an ion-exchange layer on at least the surface of the substrate, wherein a portion other than the ion-exchange layer does not contain an alkali metal oxide, or 5 mol% or less of Na ₂ O and / or 10 mol% or less of Li ₂ O (however,
The total content of Na ₂ O and Li ₂ O is 10 mol% or less), the portion other than the ion-exchange layer contains at least one type of divalent metal oxide, and has a flexural strength of 25 kg / m
substrate which is characterized in that m ² or more. [2] The substrate according to [1], wherein portions other than the ion exchange layer do not contain an alkali metal oxide. [Claim 3] The substrate according to claim 1 or 2, wherein the ion exchange layer contains an alkali metal ion or a divalent metal ion having an ion radius larger than that of the divalent metal ion constituting the divalent metal oxide. [Claim 4] In the ion exchange layer, at least a part of the divalent metal ion constituting the divalent metal oxide is replaced with an alkali metal ion or a divalent metal ion having an ion radius larger than the divalent metal ion. The substrate according to claim 3, wherein the substrate is formed by performing. [Claim 5] The divalent metal oxide is MgO, CaO, S
The substrate according to any one of claims 1 to 4, wherein the substrate is at least one selected from rO and ZnO. [Claim 6] The divalent metal oxide is MgO.
The substrate according to claim 1. [7] The substrate according to any one of [1] to [6], wherein the content of the divalent metal oxide in a portion other than the ion exchange layer is in the range of 5 to 45 mol%. [Claim 8] An alkali metal ion and a divalent metal ion having an ion radius larger than the divalent metal ion constituting the divalent metal oxide are Li ion, Na ion, K ion, Zn ion, Ca ion, and Sr ion. And at least one selected from the group consisting of Ba ions and Ba ions.
The substrate according to any one of claims 1 to 7. [Claim 9] Specific elastic modulus G or 11 of 36 × 10 ⁶ Nm / kg or more
The substrate according to claim 1, having a Young's modulus of 0 GPa or more. [Claim 10] Na ₂ O containing no alkali metal oxide or 5 mol% or less and / or 10 mol% or less of Li
A glass substrate containing ₂ O (the total content of Na ₂ O and Li ₂ O is 10 mol% or less) and containing at least one type of divalent metal oxide; A method for producing a glass substrate, comprising: immersing the substrate in a solution containing an alkali metal ion or a divalent metal ion having an ionic radius larger than that of the divalent metal ion to form an ion-exchange layer on at least the surface of the substrate. [Claim 11] The substrate on which the ion exchange layer is formed is 25 kg.
The method according to claim 10 for selecting the ion exchange conditions to have / mm ² or more flexural strength. [Claim 12] The divalent metal oxide is MgO, CaO,
The method according to claim 10, wherein the method is one or more selected from SrO and ZnO. [13] The method according to any one of [10] to [12], wherein the glass before forming the ion-exchange layer contains 5 to 45 mol% of a divalent metal oxide. [Claim 14] An alkali metal ion or a divalent metal having an ionic radius larger than the divalent metal ion constituting the divalent metal oxide is Li ion, Na ion, K ion,
It is at least one selected from the group consisting of Zn ions, Ca ions, Sr ions, and Ba ions.
14. The method according to any one of items 13 to 13. [15] The method according to any one of claims 10 to 14, wherein the immersion in the solution is performed at a temperature of 400 ° C or higher. [Claim 16] A specific elastic modulus G or 1 of 36 × 10 ⁶ Nm / kg or more.
The method according to claim 10, having a Young's modulus of 10 GPa or more. [17] A chemically strengthened glass substrate manufactured by the manufacturing method according to any one of [10] to [16]. [18] An information recording medium substrate comprising the glass substrate according to any one of [1] to [9] and [17]. [19] An information recording medium comprising at least a substrate and an information recording section, wherein the substrate is the substrate according to [18]. [20] The information recording medium according to [19], wherein the information recording medium is a magnetic recording medium.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Glass Substrate The glass substrate of the present invention is a glass substrate having an ion exchange layer on at least the surface of the substrate. Further, in this glass substrate, the portion other than the ion exchange layer does not contain an alkali metal oxide, or 5 mol% or less of Na ₂ O and / or 10 mol% or less of Li ₂ O (however, Na ₂ O And the total content of Li ₂ O is 10 mol% or less) and at least one divalent metal oxide. That is, it is non-alkali glass or low alkali glass. Examples of the divalent metal oxide include MgO, CaO, SrO, and Z.
One or more oxides selected from nO can be mentioned. Also, the content of these divalent metal oxides,
For example, the content is preferably 5 mol% or more in forming the ion exchange layer. However, the upper limit of the content of the divalent metal oxide is preferably set to 45 mol% for forming glass. Further, the content of the divalent metal oxide is preferably in the range of 10 to 40 mol%. The shape and dimensions of the glass substrate are not particularly limited, and can be appropriately determined according to the use of the glass substrate. Further, the glass substrate of the present invention has a specific elastic modulus of 36 × 10 ⁶ Nm / kg or more from the viewpoint of a high specific elastic modulus or a high Young's modulus capable of coping with a low flying height of the magnetic head and a high speed of disk rotation. G or 110 GPa
It is preferable to have the above Young's modulus.

Description of the Glass Composition The glass forming the glass substrate having a high specific elastic modulus or a high Young's modulus includes the glass having the following composition. These glasses include alkali-free and low alkali. Glass (1): mol% as oxide constituting glass
Expressed as: SiO ₂ : 25-52%, Al ₂ O ₃ : 5-35%, MgO: 15-
_{45%, Y 2 O 3:} 0-17%, TiO 2: 0-25%, ZrO 2: 0-8%, Ca
O: 1-30%, provided that Y ₂ O ₃ + TiO ₂ + ZrO ₂ + CaO: 5-30%, B ₂ O ₃
+ P ₂ O ₅ : having a composition of 0-5% and a specific elastic modulus of 36 × 1
0 ⁶ Nm / kg or more in the glass is. This glass also
As ₂ O ₃ + Sb ₂ O ₃ : 0-3%, and ZnO + SrO + NiO + CoO + FeO + CuO + Fe
_It may contain ₂ O ₃ + Cr ₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ + V ₂ O ₅ : 0-5%. Glass (2): mol% as oxide constituting glass
Expressed as: SiO ₂ : 25-50%, Al ₂ O ₃ : 10-37%, MgO: 5
-40%, TiO ₂ : 1-25%, with specific modulus of 36
× 10 ⁶ Nm / kg or more glass. This glass further contains Y ₂ O ₃ : 0-17%, ZrO ₂ : 0-8%, CaO: 0-25%, As ₂ O ₃ +
Sb ₂ O ₃ : 0-3%, and ZnO + SrO + NiO + CoO + FeO + CuO + Fe ₂ O ₃ + Cr
₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ + V ₂ O ₅ : 0-5%. Glass (3): mol% as oxide constituting glass
Expressed as: SiO ₂ : 25-50%, Al ₂ O ₃ : 20-40%, CaO: 8
-30%, Y ₂ O ₃ : 2-15%, with specific modulus of 36
× 10 ⁶ Nm / kg or more glass. This glass is further _{MgO: 0-20%, TiO 2:} 0-25%, Li 2 O: 0-10%, As 2 O 3 +
Sb ₂ O ₃ : 0-3%, and ZnO + SrO + NiO + CoO + FeO + CuO + Fe ₂ O ₃ + Cr
₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ + V ₂ O ₅ : 0-5%.

Glass (4): SiO ₂ : 30-60%, Al ₂ O ₃ : 2-3 in terms of mol% as an oxide constituting glass.
5%, MgO: 0-40%, Li 2 O: 0-10%, Y 2 O 3: 0-
_{27%, La 2 O 3:} 0-27%, CeO 2: 0-27%, Pr 2 O 3:
_{0-27%, Nd 2 O 3:} 0-27%, Sm 2 O 3: 0-27%, Eu 2
O ₃ : 0-27%, Gd ₂ O ₃ : 0-27%, Tb ₂ O ₃ : 0-27
_{%, Dy 2 O 3: 0-27} %, Ho 2 O 3: 0-27%, Er 2 O 3: 0-
_{27%, Tm 2 O 3:} 0-27%, Yb 2 O 3: 0-27%, however,
Y ₂ O ₃ + La ₂ O ₃ + CeO ₂ + Pr ₂ O ₃ + Nd ₂ O ₃ + Sm ₂ O ₃ + Eu ₂ O ₃ + Gd ₂ O ₃ + Tb ₂
O ₃ + Dy ₂ O ₃ + Ho ₂ O ₃ + Er ₂ O ₃ + Tm ₂ O ₃ + Yb ₂ O ₃ : 1-27%, Li ₂ O
+ MgO + Y ₂ O ₃ + La ₂ O ₃ + CeO ₂ + Pr ₂ O ₃ + Nd ₂ O ₃ + Sm ₂ O ₃ + Eu ₂ O ₃ + Gd ₂
O ₃ + Tb ₂ O ₃ + Dy ₂ O ₃ + Ho ₂ O ₃ + Er ₂ O ₃ + Tm ₂ O ₃ + Yb ₂ O ₃ > 25% and Young's modulus is 110 GPa or more Glass. This glass also has a TiO ₂ : 0-20%, Zr
O ₂ : 0 to 8%, provided that TiO ₂ + ZrO ₂ : 0 to 20% and CaO: 0
-15%, ZnO: 0-15%, NiO: 0-15%, Fe 2 O 3:
0-15%, however, CaO + ZnO + NiO + Fe 2 O 3: can contain 0-15%. Further, As ₂ O ₃ + Sb ₂ O ₃ : 0-2%, B ₂ O
_{3 + P 2 O 5 + Nb} 2 O 5 + V 2 O 5 + Cr 2 O 3 + Ga 2 O 3 + CoO + SrO + BaO + FeO
+ CuO + MnO + Na ₂ O: 0-8%. Glass (5): TiO ₂ : 5 to 30%, Al ₂ O ₃ : 0 to 10%, expressed as mol% as oxide constituting glass, Si
O ₂ : 35-60%, (MgO + CaO): 10-45%, provided
CaO is _{1-45%, (Li 2 O +} Na 2 O): glass having a composition which is 3-30%.

[0011] Glass composition of the glass (1) Glass (1) is mainly a composition that is configured to increase the specific elastic modulus, specific modulus G is 36 × 10 ⁶ N
m / kg or more. SiO ₂ is a component that functions as an oxide for forming a network structure of glass and increases the stability of the glass structure, that is, the crystallization stability against devitrification. In addition, by combining SiO _{2 with} an intermediate oxide such as Al ₂ O 3, the mechanical properties required for a substrate for a magnetic recording medium such as the strength and rigidity of the glass can be increased, and the heat resistance of the glass is improved. You can also. However, oxide glass introduced many SiO ₂ from 52% as the main component of the glass, since almost no specific elastic modulus greater than 36 × 10 ⁶ Nm / kg, the content of SiO ₂ is less 52% Something is appropriate. On the other hand, when the content of SiO ₂ is less than 25%, the crystallization stability of the glass is considerably deteriorated, and a glass which is stable enough to be mass-produced cannot be produced. Therefore, the lower limit of SiO ₂ is 25%. Therefore, the content of SiO ₂ is suitably in the range of 25 to 52%, preferably in the range of 30 to 50%.

Al ₂ O ₃ is very important not only as a component that contributes to the high heat resistance and high durability of the glass, but also as a component that stabilizes the glass structure and enhances its rigidity together with SiO ₂ .
Especially when Al ₂ O ₃ is replaced with SiO ₂ and introduced into glass, Al
₂ O ₃ enters the skeleton of the glass and has a great effect of increasing the Young's modulus and heat resistance of the glass as a skeleton forming component. That is,
Al ₂ O ₃ is an essential component for increasing the Young's modulus of the glass and improving the heat resistance. However, Al ₂ O
_If the content of ₃ is less than 5%, the Young's modulus of the glass cannot be sufficiently improved. In addition, the content of Al ₂ O ₃
If it exceeds 35%, it becomes impossible to introduce a large amount of MgO, which is a component contributing to the improvement of the specific elastic modulus of the glass, and the high-temperature melting property of the glass also deteriorates. Therefore, the content of Al ₂ O ₃ is suitably in the range of 5 to 35%, preferably in the range of 7 to 32%.

MgO improves the rigidity and strength of glass,
It is a component introduced to improve high-temperature solubility. It also contributes to the improvement of the crystallization stability and the homogeneity of the glass. Particularly, when the content of Al ₂ O ₃ is less than 20%, a large amount of MgO is required to maintain a high specific modulus of glass.
Is preferably introduced. However, when the content of MgO is 4
If it exceeds 5%, a glass having crystallization stability sufficient for mass production cannot be produced. If the content of MgO is less than 15%, the Young's modulus of the glass tends to decrease. Therefore, the content of MgO is suitably in the range of 15 to 45%, preferably in the range of 22 to 40%.

Y ₂ O ₃ is a component added to enhance the crystallization stability of glass, and to improve durability and high-temperature melting property. In particular, the introduction of a small amount of Y ₂ O ₃ greatly contributes to the improvement of the glass specific modulus and the improvement of the glass homogeneity. However, when too much Y ₂ O ₃ is added, the Young's modulus of the glass increases, but the specific gravity also increases sharply, and conversely, the specific elastic modulus of the glass tends to decrease. Therefore, the content of Y ₂ O ₃ is 1
It is suitable that the content is 7% or less, preferably 15% or less. In order to obtain distinct effects of the addition of Y ₂ O ₃ is, Y ₂ O ₃
Is preferably 0.5% or more.

TiO ₂ acts as both a glass skeleton-forming component and a modifying component, lowering the high-temperature viscosity of glass, improving the meltability, stabilizing the structure and increasing its durability. In addition, when TiO ₂ is introduced into glass as a component, the specific gravity of glass does not increase so much, but the Young's modulus of glass can be greatly improved. Especially for the glass to introduce a large amount of MgO and Al ₂ O _3, TiO ₂ improves the high-temperature solubility and crystallization stability of the glass, the glass in combination with the oxides such as MgO and Al ₂ O ₃ It can be greatly expected to increase the specific elastic modulus of. However, if too much TiO ₂ is introduced, the tendency of phase separation of the glass becomes stronger, and the crystallization stability of the glass and its homogeneity tend to deteriorate. Therefore, it is appropriate that the content of TiO ₂ is 25% or less, preferably 20% or less. In order to obtain distinct effects of the addition of TiO ₂ is preferably in a content of TiO ₂ 1% or more.

CaO is a component that is introduced together with MgO to improve the rigidity and strength of the glass and to improve the high-temperature solubility. In addition, CaO contributes to improvement of crystallization stability and glass homogeneity of glass, similarly to MgO. As described above, when the content of Al ₂ O ₃ is less than 20%, it is preferable to introduce a large amount of MgO in order to maintain a high specific elastic modulus of the glass. It is a component that is introduced to improve the meltability and crystallization stability. However, if the content of CaO exceeds 30%, a glass having crystallization stability sufficient for mass production cannot be produced.
Therefore, the content of CaO is 30% or less, preferably 27%.
The following is appropriate. In order to obtain a clear effect of adding CaO, the content of CaO is preferably set to 2% or more.

ZrO ₂ is a component added mainly to increase the durability and rigidity of the glass. When a small amount of ZrO ₂ is added, it has the effect of improving the glass heat resistance, and also improves the crystallization stability against devitrification of the glass. However, when ZrO ₂ exceeds 8%, the high-temperature melting property of the glass is remarkably deteriorated, the surface smoothness of the glass is also deteriorated, and the specific gravity is increased. Therefore, the content of ZrO ₂ is suitably at most 8%, preferably at most 6%. In order to obtain distinct effects of the addition of ZrO _2, when a content of ZrO ₂ is preferably 0.5% or more.

It is appropriate that Y ₂ O ₃ + TiO ₂ + ZrO ₂ + CaO is in the range of 1 to 30%. These components are components that contribute to improving the Young's modulus of the glass and improving the crystallization stability. If the total of these components is less than 1%, the Young's modulus of the glass tends to decrease, and the crystallization stability of the glass tends to decrease. On the other hand, all of these components increase the specific gravity of the glass, and when introduced in a large amount, the specific elastic modulus of the glass decreases. Therefore, the content of Y ₂ O ₃ + TiO ₂ + ZrO ₂ + CaO is suitably in the range of 1 to 30%, preferably in the range of 5.5 to 27%.

P ₂ O ₅ and B ₂ O ₃ are both components added to adjust the high-temperature solubility of glass. For example, when a small amount of P ₂ O ₅ or B ₂ O ₃ is introduced into glass, the specific elastic modulus of the glass does not change significantly, whereas the high-temperature viscosity of the glass is considerably reduced, so that the effect of facilitating melting of the glass is improved. large. The total amount of B ₂ O ₃ + P ₂ O ₅ is preferably 5% or less, and more preferably 3.5% or less, from the viewpoint of improving the solubility of glass and adjusting the crystallization stability and physical properties of glass. It is. In order to obtain a clear addition effect of B ₂ O ₃ and P ₂ O ₅ , the total content is preferably 0.5% or more.

As ₂ O ₃ and Sb ₂ O ₃ are components to be added as defoaming agents in order to homogenize the glass. An appropriate amount of As ₂ O ₃ , Sb ₂ O ₃ or As ₂ O ₃ + depending on the high temperature viscosity of each glass
Adding Sb ₂ O ₃ to the glass results in a more homogeneous glass. However, if the amount of the defoaming agent is too large, the specific gravity of the glass tends to increase and the specific elasticity tends to decrease, and the glass tends to react with the melting platinum crucible to damage the crucible. Therefore, it is appropriate that the addition amount is 3% or less, preferably 2% or less. Incidentally, in order to obtain a clear addition effect of these defoaming agents, the content should be 0.2%.
% Is preferable.

Further, V ₂ O ₅ , Cr ₂ O ₃ , ZnO, SrO, NiO
, CoO, Fe ₂ O ₃ , CuO and other components are all added when adjusting the high-temperature melting property and physical properties of the glass. For example, a small amount of _{V 2 O 5, Cr 2 O} 3, CuO,
When a colorant such as CoO is added to the glass, the glass has infrared absorption characteristics, and the heat treatment of the magnetic film by irradiation with a heating lamp can be effectively performed. ZnO + SrO + NiO + CoO +
The sum of FeO + CuO + Fe ₂ O ₃ + Cr ₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ + V ₂ O ₅ is the improvement in the solubility of the glass and the crystallization stability and physical properties of the glass. From the viewpoint of adjustment, it is appropriate that the content is 5% or less, preferably 4% or less.

In addition to the above components, impurities in the raw material, for example,
Even if Fe ₂ O _{3 and the} like and Cl, F, SO _{3 and the} like, which are glass fining agents, are contained up to 1%, the desired physical properties of the glass of the present invention are not substantially impaired. In addition, since this glass is an alkali-free glass containing substantially no alkali component, when a thin film is formed on a substrate made of this glass, the alkali component does not diffuse into the thin film on the substrate and does not adversely affect the glass. .

The glass composition of the glass (2) Glass (2) is mainly a composition that is configured to increase the specific elastic modulus, specific modulus G is 36 × 10 ⁶ N
m / kg or more. SiO ₂ is a component that functions as an oxide for forming a network structure of glass and increases the stability of the glass structure, that is, the crystallization stability against devitrification. In addition, SiO ₂ has the strength of glass by combining with an intermediate oxide such as Al ₂ O ₃ ,
The mechanical properties required for the magnetic recording medium substrate, such as the rigidity, can be increased, and the heat resistance of the glass can also be improved. However, Al ₂ O ₃ , which is a component that contributes to the improvement of impact resistance and mechanical strength of glass, cannot be introduced into glass containing SiO ₂ in an amount exceeding 50% as a main component of glass. Therefore, from the viewpoint of obtaining a glass having a larger specific elastic modulus, the upper limit of the content is suitably set to 50%. On the other hand, when the content of SiO ₂ is less than 25%, the crystallization stability of the glass is considerably deteriorated, and a glass which is stable enough to be mass-produced cannot be produced. Therefore, SiO ₂
Is appropriately set to 25%. Suitably, the content of SiO ₂ is in the range of 25 to 50%, preferably 30 to 49%.

Al ₂ O ₃ is very important not only as a component that contributes to the high heat resistance and high durability of the glass, but also as a component that stabilizes the glass structure and increases its rigidity together with SiO ₂ .
Especially when Al ₂ O ₃ is replaced with SiO ₂ and introduced into glass, Al
₂ O ₃ enters the skeleton of the glass and has a great effect of increasing the Young's modulus and heat resistance of the glass as a skeleton forming component. That is,
Al ₂ O ₃ is an essential component for increasing the Young's modulus of the glass and improving the heat resistance. However, when the content of MgO is 25% or less in order to further increase the bending strength and impact resistance of the glass, the content of Al ₂ O ₃ is reduced to 10%.
%, The Young's modulus of the glass cannot be sufficiently improved, and a desired specific elastic modulus cannot be obtained. If the Al ₂ O ₃ content exceeds 37%, the high-temperature melting property of the glass deteriorates,
A homogeneous glass cannot be produced, and the crystallization stability of the glass also decreases. Therefore, the upper limit of the content of Al ₂ O ₃ is suitably set to 37%. The content of Al ₂ O ₃ is suitably in the range of 10 to 37%, preferably in the range of 11 to 35%.

MgO improves the rigidity and strength of the glass,
It is a component introduced to improve high-temperature solubility. Mg
O also contributes to the improvement of the crystallization stability and the homogeneity of the glass. In particular, when a large amount of Al ₂ O ₃ is introduced as a component that greatly contributes to the improvement of the Young's modulus of the glass, in order to improve the stabilization of the glass structure and to reduce the viscosity at high temperatures to facilitate melting. MgO is a preferred component. However, when the content of MgO exceeds 40%, a glass composition having a large amount of Al ₂ O ₃ introduced to enhance the impact resistance and strength of the glass can produce a glass having crystallization stability sufficient for mass production. Absent. On the other hand, if the content of MgO is less than 5%,
Glass having sufficient stability and high specific modulus cannot be produced. Therefore, the content of MgO is suitably in the range of 5 to 40%, preferably in the range of 7 to 35%.

TiO ₂ functions as a glass skeleton-forming component and also as a modifying component, and is a component that lowers the high-temperature viscosity of glass, improves the melting property, stabilizes the structure, and increases its durability. In addition, when TiO ₂ is introduced into glass as a component, the specific gravity of glass does not increase so much, but the Young's modulus of glass can be greatly improved. Especially for glass that introduces a large amount of Al ₂ O ₃ , TiO ₂ improves the high-temperature melting property and crystallization stability of the glass, and it is greatly likely that the combination with Al ₂ O ₃ increases the specific elastic modulus of the glass. Can be expected. However, when the content of TiO ₂ exceeds 25%, the tendency of phase separation of the glass increases, and the crystallization stability of the glass and the homogeneity thereof tend to deteriorate. In addition, the addition of 1% or more of TiO ₂ greatly improves the high-temperature solubility of glass. Therefore, the content of TiO ₂ is suitably in the range of 1 to 25%, preferably in the range of 2 to 20%.

Y ₂ O ₃ is a component that improves the Young's modulus of glass, enhances crystallization stability, and improves durability and high-temperature melting property. In particular, when a large amount of Al ₂ O ₃ is introduced into glass in order to increase the bending strength and impact resistance of the glass, the effect of Y ₂ O ₃ as an auxiliary flux of Al ₂ O ₃ is excellent. For example, 25%
When the above Al ₂ O ₃ is introduced into glass, a homogeneous glass can be produced by adding Y ₂ O ₃ . Where Y ₂
Since O ₃ is relatively expensive, it is preferable that the addition amount is small in terms of cost. Also, the addition of an appropriate amount of Y ₂ O ₃
It greatly contributes to the improvement of the glass specific modulus, but when the content of Y ₂ O ₃ exceeds 17%, the specific gravity increases more than the glass's Young's modulus, contributing to the improvement of the glass specific modulus. No longer. Therefore, the content of Y ₂ O ₃ is suitably in the range of 0 to 17%, preferably 1 to 15%, depending on the amount of Al ₂ O ₃ introduced.

CaO, together with MgO, is a component that can improve the rigidity and strength of the glass and improve the high-temperature solubility. It also contributes to improving the crystallization stability of the glass and the glass homogeneity. When a large amount of Al ₂ O ₃ is introduced as a component that greatly contributes to the improvement of the Young's modulus of glass, CaO is used not only to improve the stabilization of the glass structure, but also to lower the viscosity at high temperatures and facilitate melting. Is preferred. If the content of CaO exceeds 25%, a composition having a large amount of Al ₂ O ₃ introduced in order to increase the impact resistance and strength of the glass cannot produce a glass having crystallization stability that can be mass-produced. Therefore, the upper limit of the content of CaO is suitably 25%. In order to obtain a clear addition effect of CaO, its content is preferably 2% or more.

ZrO ₂ is a component mainly added to increase the durability and rigidity of the glass. When a small amount of ZrO ₂ is added, it has the effect of improving the glass heat resistance, and also improves the crystallization stability against devitrification of the glass. However, when the content of ZrO ₂ exceeds 8%, the high-temperature melting property of the glass is remarkably deteriorated, the surface smoothness of the glass is deteriorated, and the specific gravity increases. Therefore, the content of ZrO ₂ is 8% or less, preferably 6%.
The following is appropriate. In order to obtain distinct effects of the addition of ZrO _2, when a content of ZrO ₂ is preferably 0.5% or more.

As ₂ O ₃ and Sb ₂ O ₃ are components added as a defoaming agent in order to homogenize the glass. Appropriate amount of As ₂ O ₃ , Sb ₂ O ₃ or As ₂ O ₃ + Sb according to high temperature viscosity of each glass
Adding ₂ O ₃ to the glass results in a more homogeneous glass. However, when the addition amount of these defoaming agents is too large, the specific gravity of the glass tends to increase and decrease the specific elastic modulus,
There is also a tendency for the crucible to react with the melting platinum crucible and damage the crucible. Therefore, it is appropriate that the addition amount is 3% or less, preferably 2% or less. In order to obtain a clear addition effect of these defoaming agents, it is preferable that the content is 0.2% or more.

P ₂ O ₅ , V ₂ O ₅ , B ₂ O ₃ , Cr ₂ O ₃ , ZnO, SrO,
Other components such as NiO, CoO, Fe ₂ O ₃ , and CuO can be added when adjusting the high-temperature solubility and physical properties of the glass. For example, when a small amount of P ₂ O ₅ is introduced into glass, the specific elastic modulus of the glass does not greatly change, but the high-temperature viscosity of the glass is considerably reduced, so that the effect of facilitating melting of the glass is great. Also, a small amount of V ₂ O ₅ , Cr ₂ O
₃ , When adding coloring agents such as CuO and CoO to glass,
By imparting infrared absorption properties to the glass, heat treatment of the magnetic film by irradiation with a heating lamp can be effectively performed. ZnO +
SrO + NiO + CoO + FeO + CuO + Fe ₂ O ₃ + Cr ₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ + V ₂ O ₅・
From the viewpoint of adjusting the thermal properties, the content is suitably 5% or less.

In addition to the above components, impurities in the raw material, for example,
Even if Fe ₂ O _{3 and the} like and Cl, F, SO _{3 and the} like which are glass fining agents are contained up to 1%, the desired physical properties of the glass of the present invention are not substantially impaired. In the case of non-alkali glass containing no Li ₂ O, when a thin film is formed on a substrate made of this glass, the alkali component does not diffuse into the thin film on the substrate and does not have any adverse effect.

The glass composition of the glass (3) Glass (3) is mainly a composition that is configured to increase the specific elastic modulus, specific modulus G is 36 × 10 ⁶ N
m / kg or more. SiO ₂ is a component that functions as an oxide for forming a network structure of glass and increases the stability of the glass structure, that is, the crystallization stability against devitrification. In addition, by combining with an intermediate oxide such as Al ₂ O ₃ , the mechanical properties required for a substrate for a magnetic recording medium such as the strength and rigidity of the glass can be increased, and the heat resistance of the glass can be improved. it can. However, however, since the CaO -Al ₂ O ₃ -SiO ₂ based oxide glass obtained by introducing SiO ₂ of greater than 50% as the main component of the glass is almost no specific elastic modulus greater than 36 × 10 ⁶ Nm / kg , the content of SiO ₂ is suitably 50% or less. On the other hand, when the content of SiO ₂ is 25% or less, the crystallization stability of the glass is considerably deteriorated, and a glass which is stable enough to be mass-produced cannot be produced. Therefore, the lower limit of SiO ₂ is 25%
It is. Therefore, the content of SiO ₂ is suitably in the range of 25 to 50%, preferably in the range of 30 to 50%.

Al ₂ O ₃ is very important not only as a component that contributes to the high heat resistance and high durability of the glass, but also as a component that stabilizes the glass structure and enhances its rigidity together with SiO ₂ .
Especially when Al ₂ O ₃ is replaced with SiO ₂ and introduced into glass, Al
₂ O ₃ enters the skeleton of the glass and has a great effect of increasing the Young's modulus and heat resistance of the glass as a skeleton forming component. That is,
Al ₂ O ₃ is an essential component for increasing the Young's modulus of the glass and improving the heat resistance. However, Al ₂ O
_If the content of ₃ is less than 20%, the Young's modulus of the glass cannot be sufficiently improved. On the other hand, when the content of Al ₂ O ₃ exceeds 40%, the high-temperature melting property of the glass also deteriorates, so that a homogeneous glass cannot be produced and the crystallization stability of the glass also decreases. Therefore, the content of Al ₂ O ₃ is in the range of 20 to 40%,
Preferably is suitably in the range of ₂ from 1 to 37%.

CaO improves the rigidity and strength of the glass,
A component that improves high-temperature solubility. Of course, it also contributes to the improvement of the crystallization stability and the homogeneity of the glass. Especially as a component that greatly contributes to the improvement of Young's modulus in glass
When a large amount of Al ₂ O ₃ is introduced, it is necessary to add CaO to improve the stabilization of the glass structure and to reduce the high-temperature viscosity to facilitate melting. However, if the content is less than 8%, the crystallization stability of the glass is significantly reduced, whereas if it exceeds 30%, the Young's modulus of the glass tends to be low. Therefore, the content of CaO is suitably in the range of 8 to 30%, preferably in the range of 10 to 27%.

Y ₂ O ₃ is a component added to improve the Young's modulus of the glass, enhance crystallization stability, and improve durability and high-temperature melting property. In particular, when introducing a large amount of Al ₂ O ₃ into the glass to increase the Young's modulus of the glass, the Al
Y ₂ O ₃ as a co熔剤of ₂ O ₃ is effective. For example, when 25% or more of Al ₂ O ₃ is introduced into glass, a homogeneous glass can be produced by adding Y ₂ O ₃ as an auxiliary flux. However, since Y ₂ O ₃ is relatively expensive, the content of Y ₂ O ₃ is preferably a relatively small amount, up to 15%, depending on the physical properties of the glass required. However, when the content of Y ₂ O ₃ is too small, the high-temperature melting property of the glass also deteriorates, and the specific elastic modulus also decreases. Therefore, it is appropriate that the lower limit of the content of Y ₂ O ₃ is 2%. The content of Y ₂ O ₃ is suitably in the range of 2 to 15%, preferably in the range of 3 to 12%.

MgO has the effect of improving the rigidity and strength of the glass and improving the high-temperature melting property, and also contributes to the improvement of the crystallization stability and the homogeneity of the glass, and the effect of increasing the specific elastic modulus. Since it is also a component, it can be added as desired. However, if the content of MgO exceeds 20%, it is impossible to add a large amount of CaO, which is an essential component, and the crystallization stability of the glass tends to decrease. Therefore, the upper limit of the content of MgO is suitably set to 20%. In order to obtain a clear addition effect of MgO, its content is preferably 5% or more.

TiO ₂ functions as a glass skeleton-forming component and a modifying component, and is a component that lowers the high-temperature viscosity of glass, improves the melting property, stabilizes the structure, and increases its durability. In addition, when TiO ₂ is introduced into glass as a component, the specific gravity of glass does not increase so much, but the Young's modulus of glass can be greatly improved. However, for CaO -Al ₂ O ₃ -SiO ₂ based oxide glass, the introduction of many TiO ₂ too, intensified phase separation tendency of glass, rather crystallization stability and homogeneity of the glass Tends to worsen. Therefore, the content is suitably at most 25%, preferably at most 20%. In order to obtain distinct effects of TiO _2, it is suitable that the content of TiO ₂ is more than 1%.

Li ₂ O is a component that mainly lowers the high-temperature viscosity of glass to facilitate melting. In particular, when the content of Al ₂ O ₃ is large, introducing a small amount of Li ₂ O is very effective in homogenizing the glass. However, if the content is too large, the durability of the glass tends to deteriorate, and the Young's modulus tends to decrease. Therefore, the content of Li ₂ O is 15% or less, preferably 1%.
It is appropriate that the content be 2% or less. In order to obtain a clear effect of adding Li ₂ O, its content is preferably set to 1.5% or more.

As ₂ O ₃ and Sb ₂ O ₃ are components to be added as defoaming agents in order to homogenize the glass. An appropriate amount of As ₂ O ₃ , Sb ₂ O ₃ or As ₂ O ₃ + depending on the high temperature viscosity of each glass
Adding Sb ₂ O ₃ to the glass results in a more homogeneous glass. However, if the amount of the defoaming agent is too large, the specific gravity of the glass tends to increase and the specific elasticity tends to decrease, and the glass tends to react with the melting platinum crucible to damage the crucible. Therefore, it is appropriate that the addition amount is 3% or less, preferably 2% or less. Incidentally, in order to obtain a clear addition effect of these defoaming agents, the content should be 0.2%.
% Is preferable.

P ₂ O ₅ , V ₂ O ₅ , B ₂ O ₃ , Cr ₂ O ₃ , ZnO, SrO,
Other components such as NiO, CoO, Fe ₂ O ₃ , and CuO are components added when adjusting the high-temperature melting property and physical properties of the glass. For example, when a small amount of P ₂ O ₅ is introduced into glass, the specific elastic modulus of the glass does not change significantly,
Since the high-temperature viscosity of the glass is considerably reduced, the effect of facilitating melting of the glass is great. Also, a small amount of V ₂ O ₅ , Cr ₂ O ₃ ,
When a coloring agent such as CuO 2 or CoO is added to the glass, the glass has infrared absorption characteristics, and the magnetic film can be effectively heated by irradiation with a heating lamp. ZnO + SrO + Ni
The sum of O + CoO + FeO + CuO + Fe ₂ O ₃ + Cr ₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ + V ₂ O ₅ is the viewpoint that the mechanical and thermal properties of the glass are adjusted Therefore, it is appropriate that the content is 5% or less. In addition to the above components, impurities in the raw material, for example, Fe ₂ O _{3 and the} like and Cl, F 2, SO _{3 and the} like which are fining agents for the glass may be contained up to 1%, respectively. Physical properties are not substantially impaired.

The glass composition of the glass (4) glass (4) is mainly a composition that is configured to increase the Young's modulus, the Young's modulus 110GP
a or more. SiO ₂ acts as an oxide for forming a glass network structure, and stabilizes the glass structure, that is, increases the crystallization stability against devitrification. In addition, by combining with an intermediate oxide such as Al ₂ O ₃ , the mechanical properties required for a substrate for a magnetic recording medium such as the strength and rigidity of the glass can be increased, and the heat resistance of the glass can be improved. it can. However, in a glass composition in which more than 60% of SiO ₂ is introduced as a main component of glass, a large amount of Al ₂ O ₃ , which is a component contributing to the improvement of impact resistance and mechanical strength of glass, cannot be introduced. Therefore, in order to develop a glass having a larger Young's modulus, it is necessary to suppress the content of SiO ₂ to 60% or less. On the other hand, if the content of SiO ₂ is suppressed too low,
For example, if it is less than 30%, the crystallization stability of the glass is considerably deteriorated, and a glass which is stable enough to be mass-produced cannot be produced. Therefore, the content of SiO ₂ is in the range of 30-60%. In particular, it is preferably in the range of 32-55%.

Al ₂ O ₃ is very important not only as a component that contributes to the high heat resistance and high durability of the glass, but also as a component that stabilizes the glass structure and enhances its rigidity together with SiO ₂ .
In particular, when Al ₂ O ₃ is substituted for SiO ₂ and introduced into glass, the effect of entering the skeleton of the glass and increasing the Young's modulus and heat resistance of the glass as a skeleton forming component is great. That is, Al ₂ O ₃
Is an essential component for increasing the Young's modulus of the glass and for improving the heat resistance. However, if the content of Y ₂ O ₃ is 5% or less in order to further increase the bending strength and impact resistance of the glass, if the content of Al ₂ O ₃ is less than 2%, the Young's modulus of the glass will be insufficient. Can't improve. Also,
When Al ₂ O ₃ is added in excess of 35%, the high-temperature melting property of the glass deteriorates, so that a homogeneous glass cannot be produced and the crystallization stability of the glass also decreases. Therefore, its content is in the range of 2-35%. In particular, the range is preferably 3 to 30%.

MgO improves the rigidity and strength of the glass,
It is a component introduced to improve high-temperature solubility. Furthermore, MgO also contributes to improving the crystallization stability of the glass and the glass homogeneity. In particular, when a large amount of Al ₂ O ₃ is introduced into glass as a component that greatly contributes to the improvement of Young's modulus, in order to improve the stabilization of the glass structure, it is necessary to lower the viscosity at high temperature and facilitate melting. Even MgO is a very important component. However, if more than 40% of MgO is introduced into the glass, the glass with a large amount of Y ₂ O ₃ or Al ₂ O ₃ introduced in order to increase the impact resistance and strength of the glass, has a crystallization stability sufficient for mass production. Can not be obtained. Therefore, the content of MgO is suitably in the range of 0-40%. In particular, the content of MgO is preferably in the range of 5-35%.

Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₂ O ₃ , Nd ₂ O ₃ , Sm
₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂
Rare earth metal oxides such as O ₃ and Yb ₂ O ₃ are components added to improve the Young's modulus of the glass, increase crystallization stability, and improve durability and high-temperature melting property. In particular, when a large amount of Al ₂ O ₃ is introduced into glass in order to increase the bending strength and impact resistance of the glass, the role of the rare earth metal oxide as an auxiliary flux of Al ₂ O ₃ cannot be ignored. For example, 20%
When introducing the above Al ₂ O ₃ into glass, Y ₂ O ₃ is an essential component for producing a homogeneous glass. However, since rare earth metal oxides are relatively expensive, it is preferable to introduce as little rare earth metal oxide as possible according to the desired Young's modulus. Also, if the amount of the rare earth metal oxide is too large, the Young's modulus of the glass increases,
The specific gravity also increases greatly. On the other hand, when an appropriate amount of rare earth metal oxide is introduced into glass, it greatly contributes to improvement of the glass Young's modulus. Therefore, the total content of the rare earth metal oxide is suitably in the range of 1-27% in accordance with the Young's modulus required for the glass used as the magnetic disk substrate. In particular, the total content of the rare earth metal oxide is preferably in the range of 2 to 20%.

Li ₂ O is a very useful component for improving the high-temperature melting property of glass. Furthermore, when a small amount of Li ₂ O is introduced, the Young's modulus of the glass does not change much, but there is an advantage that the specific gravity can be greatly reduced. Also, even in small quantities
Glass into which Li ₂ O has been introduced can be chemically strengthened by ion exchange, which is advantageous when producing high-strength glass.
However, when the amount of Li ₂ O introduced is too large, the crystallization stability of the glass tends to decrease. Therefore, the amount of Li ₂ O introduced is preferably 15% or less. In order to obtain distinct effects of the addition of Li ₂ O, it is suitable that the content of Li ₂ O is at least 2%.

TiO ₂ functions as both a glass skeleton forming component and a modifying component, lowers the high-temperature viscosity of glass, improves the melting property, stabilizes the structure and increases its durability. In addition, when TiO ₂ is introduced into glass as a component, the specific gravity of glass does not increase so much, but the Young's modulus of glass can be greatly improved. Especially for glass with a high content of MgO or Al ₂ O ₃ , TiO ₂ improves the high-temperature solubility and crystallization stability of the glass, and can increase the Young's modulus of the glass in combination with Al ₂ O _3. We can expect much. However, when too much TiO ₂ is introduced, the tendency of phase separation of the glass is increased, and the crystallization stability of the glass and its homogeneity may be deteriorated. Therefore, it is appropriate that the content of TiO ₂ is 20% or less. In particular, it is preferably at most 15%. In order to obtain distinct effects of the addition of TiO _2, it is suitable that the content of TiO ₂ is more than 2%.

ZrO ₂ is a component added mainly to increase the durability and rigidity of the glass. Addition of a small amount of ZrO ₂ has the effect of improving the glass heat resistance, and also improves the crystallization stability against devitrification of the glass. However, when ZrO ₂ is introduced in an amount exceeding 8%, the high-temperature melting property of the glass is significantly deteriorated, the surface smoothness of the glass is also deteriorated, and the specific gravity is increased. Therefore, the content of ZrO ₂ is preferably set to 8% or less, more preferably 6% or less. In addition, ZrO
From the viewpoint of obtaining the effect of adding _2, ZrO ₂ content is suitably not less than 0.5%.

CaO, ZnO, NiO and Fe ₂ O ₃ are components mainly introduced for improving the high-temperature melting property and crystallization stability of glass. These components have a large cation radius,
When mixed with O and introduced into glass, there is an effect of improving crystallization stability. However, when the introduction amount is too large, the specific gravity of the glass tends to increase, and the Young's modulus tends to decrease.
Therefore, the total content of CaO, ZnO, NiO and Fe ₂ O ₃ is 1
It is preferably at most 5%, more preferably at most 12%. From the viewpoint of obtaining the effect of adding these components, it is appropriate that the total content is 1% or more.

As ₂ O ₃ and Sb ₂ O ₃ are components added as defoaming agents in order to homogenize the glass. Appropriate amount of As ₂ O ₃ or Sb ₂ O ₃ or As ₂ O ₃ + Sb ₂ O ₃ according to high temperature viscosity of each glass
Is added to the glass to obtain a more homogeneous glass.
However, if the added amount of these defoamers is too large, the specific gravity of the glass tends to increase and the Young's modulus tends to decrease, and the glass may react with the melting platinum crucible and damage the crucible. Therefore, the addition amount of As ₂ O ₃ + Sb ₂ O ₃ is preferably 2% or less, and more preferably 1.5% or less.

SrO, CoO, Fe ₂ O ₃ , CuO, Cr ₂ O ₃ , B ₂ O ₃ , P ₂
Components such as O ₅ and V ₂ O ₅ are components added when adjusting the high-temperature solubility and physical properties of glass. For example, when a small amount of P ₂ O ₅ is introduced into glass, there is no significant change in the Young's modulus of the glass, but the high-temperature viscosity of the glass is considerably reduced, so that the effect of facilitating melting of the glass is great. Also, when a small amount of coloring agent such as V ₂ O ₅ , Cr ₂ O ₃ , CuO, CoO is added to the glass, the glass has infrared absorption properties, and the heat treatment of the magnetic film by irradiation with a heating lamp is performed effectively. Can be ZnO + SrO + NiO + CoO + FeO + CuO + Cr ₂ O ₃ + B ₂ O ₃
The sum of + P ₂ O ₅ + V ₂ O ₅ is suitably 5% or less from the viewpoint of improving the high-temperature melting property of the glass and adjusting the mechanical and thermal properties of the glass.

In addition to the above basic components, impurities in the raw materials, for example, Cl, F, SO _{3 and the} like, which are clarifiers for glass, each containing up to 1% may impair the gist of the glass composition of the present invention. Absent.

The glass composition of the glass (5) Glass (5) are mainly large Young's modulus, which is configured to reduce and lower the liquidus temperature composition, for example, in Young's modulus than 100GPa And the liquidus temperature is 1250 ° C. or less. TiO ₂ is an essential component capable of improving the Young's modulus without significantly increasing the specific gravity, and such an effect can be obtained by adding 5 mol% or more. But 3
If it exceeds 0 mol%, the devitrification resistance of the postcard deteriorates, and a liquidus temperature of 1250 ° C. or lower, which can be easily produced, tends not to be obtained. Therefore, TiO ₂ is suitably in the range of 5-30 mol%. Preferably, it is in the range of 6-25 mol%.

Al ₂ O ₃ does not contribute to the improvement of the Young's modulus, but is effective in lowering the liquidus temperature of the glass, suppressing the tendency of phase separation, improving the viscosity in the working temperature range, and improving the chemical strengthening characteristics. . However, if it is added in excess of 10 mol%, on the contrary, there is a tendency that a remarkable rise in liquidus temperature and formation of undissolved matter due to deterioration of solubility are caused. Therefore, Al ₂ O ₃ is 0-10
Suitably, it is in the mole% range. SiO ₂ is an essential component for forming a glass structure. To obtain a liquidus temperature of 1250 ° C. or less, the content is suitably 35 mol% or more. However, if it exceeds 60 mol%, the Young's modulus decreases to 100 GPa or less. Therefore, SiO ₂ is 35-
Suitably, it is in the range of 60 mol%. Preferably, it is in the range of 35-50 mol%.

MgO and CaO are both components that increase the Young's modulus. Furthermore, comparing MgO and CaO, MgO has the function of raising the liquidus temperature and the function of lowering the specific gravity.
Has a function of lowering the liquidus temperature and a function of increasing the specific gravity. From the viewpoint of obtaining a liquidus temperature of 1250 ° C. or lower, it is preferable to reduce the content of CaO to 1 to 45 mol%. Furthermore, to obtain a Young's modulus of 110 GPa or more,
It is appropriate that the total content of MgO and CaO is 10 mol% or more. However, when it exceeds 45 mol%, vitrification tends to be difficult. Therefore, MgO + CaO is 10−45
It is suitable to be in the range of mol%.

Na ₂ O is a component that has an effect of lowering the liquidus temperature while lowering the Young's modulus, and is particularly effective when TiO ₂ is present. Even in the case of glass containing a large amount of TiO ₂ , the liquidus temperature can be increased by 1250 by adding Na ₂ O.
° C or lower. Further, since there is also an effect of increasing the coefficient of thermal expansion, by adjusting the amount of Na ₂ O,
It can also be approximated to a stainless steel alloy used for a clamp fixed to a drive motor spindle. On the other hand, Li ₂ O is a component that lowers the high-temperature viscosity of glass and facilitates melting without lowering the Young's modulus. But,
Li ₂ O has a smaller effect of lowering the liquidus temperature and a larger effect of increasing the coefficient of thermal expansion than Na ₂ O. So Li ₂ O
And the total content of Na ₂ O in the range of 3-30%,
The Young's modulus, liquidus temperature and coefficient of thermal expansion can be adjusted.

Description of Ion Exchange Layer The glass substrate of the present invention has an ion exchange layer on at least the surface of the substrate. The surface of the substrate means a surface that forms two opposing flat surfaces of a flat glass substrate. The ion exchange layer contains an alkali metal ion or a divalent metal ion having an ion radius larger than that of the divalent metal ion constituting the divalent metal oxide originally contained in the glass constituting the glass substrate. That is, in the ion exchange layer, at least a part of the divalent metal ion constituting the divalent metal oxide is replaced by an alkali metal ion or a divalent metal ion having an ion radius larger than the divalent metal ion. Is formed.

The alkali metal ion and the divalent metal ion having an ion radius larger than that of the divalent metal ion constituting the divalent metal oxide include, for example, Na ion, K ion, Zn ion, Ca ion, Sr ion and At least one type of ion selected from the group consisting of Ba ions can be used. The magnitude relation of these ions is as follows.

[0059]

Embedded image Li ⁺ <Na ⁺ <K ⁺ Mg ²⁺ <Zn ²⁺ <Ca ²⁺ <Sr ²⁺ <Ba ²⁺ Mg ²⁺ <Li ⁺ <Zn ²⁺ <Ca ²⁺ <Na ⁺ <Sr ²⁺ <K ⁺ <Ba ²⁺

As described above, Mg ions have the smallest ionic radius, and by introducing a large amount of MgO into glass, the ion exchange rate can be promoted and the effect of chemical strengthening of the glass can be greatly amplified. But more than 45%
When MgO is introduced into glass, there is a tendency that a glass having crystallization stability sufficient for mass production cannot be produced. When the content of MgO is less than 5%, ion exchange becomes insufficient,
A desired bending strength may not be obtained. There, MgO
Is suitably in the range of 5-45%.
It is particularly preferable in the range of 10 to 40%.

The method of forming the ion-exchange layer will be described later, but the ion-exchange layer is formed so as to have a bending strength of 25 kg / mm ² or more. The bending strength of the glass substrate before forming the ion exchange layer depends on the type of glass, but it is usually
It is about 10 to 14 kg / mm ² . The bending strength due to the formation of the ion exchange layer depends on the type of the divalent metal oxide to be ion-exchanged, the alkali metal ion and the divalent metal ion introduced by the ion exchange, and the degree of ion exchange (concentration and thickness of the layer). Can be selected as appropriate.
The bending strength by forming the ion exchange layer is preferably 30 kg /
mm ² or more.

[0062] In the process for producing a glass substrate having an ion exchange layer of the production method the present invention the glass substrate, or not containing alkali metal oxides, or 5 mol% or less of Na ₂ O and / or 10 mole% or less of Li ₂ O (however,
The total content of Na ₂ O and Li ₂ O is 10 mol% or less), and a glass substrate containing at least one kind of divalent metal oxide is used. This glass substrate can be formed using the glass mentioned in the description of the glass substrate of the present invention.
It can be formed using (5). Further, the glass substrate has a specific elastic modulus G of 36 × 10 ⁶ Nm / kg or more from the viewpoint of a high specific elastic modulus or a high Young's modulus that can cope with a low flying height of the magnetic head and a high speed of disk rotation. It preferably has a Young's modulus of 110 GPa or more.

In the production method of the present invention, the glass substrate is treated with a solution containing an alkali metal ion or a divalent metal ion having an ion radius larger than that of the divalent metal ion constituting the divalent metal oxide contained in the substrate. To form an ion exchange layer on at least the surface of the substrate. The ions introduced into the glass by ion exchange are metal ions having a larger ion radius than the divalent metal ions constituting the divalent metal oxide contained in the substrate, such as Li ions, Na ions, K ions, and Zn ions. At least one selected from the group consisting of ions, Ca ions, Sr ions, and Ba ions can be given. As described above, the magnitude relation of these ions is as follows.

[0064]

Embedded image Li ⁺ <Na ⁺ <K ⁺ Mg ²⁺ <Zn ²⁺ <Ca ²⁺ <Sr ²⁺ <Ba ²⁺ Mg ²⁺ <Li ⁺ <Zn ²⁺ <Ca ²⁺ <Na ⁺ <Sr ²⁺ <K ⁺ <Ba ²⁺

Mg ions have the smallest ionic radius, and Zn ions and Ca ions have the smallest ionic radii. Therefore, the divalent metal oxide contained in the glass is Mg
One or two selected from O, CaO, SrO and ZnO
Preferably, it is at least one species. In particular, by introducing a large amount of MgO into the glass, the ion exchange rate can be promoted and the effect of chemical strengthening of the glass can be greatly amplified.

In the case of a glass containing MgO, Li ion, Na ion, K ion, Zn ion, Ca ion, Sr ion, or B ion
Ion exchange can be performed by immersion in a solution containing a ions. In the case of glass containing CaO, Na
Ion exchange can be performed by immersion in a solution containing ions, Sr ions, or Ba ions. Furthermore, Zn
In the case of glass containing O, ion exchange can be performed by immersion in a solution containing Na ions, Ca ions, Sr ions, or Ba ions.

The immersion in the solution can be carried out, for example, at a temperature of 400 ° C. or higher, preferably in the range of 500 to 750 ° C. When the alkali component contained in the glass is reduced, the glass transition point is high (500 to 900).
° C). For glass having a high glass transition temperature, the ion exchange treatment temperature can be increased, and ion exchange can be effectively promoted. The immersion time can be appropriately selected depending on the desired bending strength, and is, for example, about 60 to 360 minutes.

Further, Li ion, Na ion, K ion, Zn
As a solution containing ions, Ca ions, Sr ions, or Ba ions, it is preferable to use a treatment bath containing sodium nitrate, potassium nitrate, calcium nitrate, strontium nitrate, barium nitrate and a mixed nitrate thereof,
Not limited to nitrates, sulfates, bisulfates,
Carbonates, bicarbonate halides and the like may be used. When the ion exchange solution contains Li ion, Na ion, K ion, Zn ion, Ca ion, Sr ion, and Ba ion, Na ion, K ion, Ca ion, Sr ion, and Ba ion
The ions exchange with Li ions or Mg ions in the glass as follows.

[0069]

Embedded image Li ⁺ (glass) LiNa ⁺ or K ⁺ (treatment bath) Mg ⁺² (glass) ⇔2Na ⁺ (treatment bath) Mg ⁺² (glass) ⇔2K ⁺ (treatment bath) Mg ⁺² (glass) ) ⇔Ca ⁺² (treatment bath) Mg ⁺² (glass) ⇔Sr ⁺² (treatment bath) Mg ⁺² (glass) ⇔Ba ⁺² (treatment bath) Mg ⁺² (glass) ⇔Zn ⁺² (treatment bath )

By this ion exchange, the alkali metal ion or divalent metal ion in the glass surface layer is replaced by an alkali metal ion or divalent metal ion having a larger ionic radius, and a compressive stress layer is formed on the glass surface layer. Glass is chemically strengthened. As described above, the chemically strengthened glass used in the present invention has a high Young's modulus or a high specific elastic modulus, has excellent ion exchange performance, and has a high bending strength. Have.
Therefore, the magnetic recording substrate of the present invention made of this chemically strengthened glass also has excellent destruction resistance.

The glass substrate of the present invention is preferably formed by processing into a substrate for a magnetic recording medium such as the above-mentioned glass disk for chemical strengthening and then chemically strengthening by the method of the present invention. The glass substrate of the present invention has a high Young's modulus or a high specific elastic modulus, and is excellent in heat resistance, surface smoothness, chemical durability, optical properties, and mechanical strength. Therefore, for example, it is suitable as a substrate for an information recording medium such as a magnetic recording medium. Furthermore, glass substrates for magneto-optical disks and glass substrates for electro-optics such as optical disks,
It can be suitably used as a heat-resistant substrate for a low-temperature polycrystalline silicon liquid crystal display device expected as an LCD or a glass substrate for electric / electronic parts.

Description of the Magnetic Disk The magnetic recording medium of the present invention is a magnetic disk (hard disk) having at least a magnetic layer formed on the main surface of the above-described glass substrate of the present invention. This magnetic disk will be described below. The layers other than the magnetic layer include an underlayer, a protective layer, a lubricating layer, an unevenness control layer, and the like from the functional aspect, and are formed as necessary. Various thin film forming techniques are used to form these layers. The material of the magnetic layer is not particularly limited. Examples of the magnetic layer include, in addition to Co-based, ferrite-based and iron-rare-earth-based. The magnetic layer
Any of horizontal magnetic recording and perpendicular magnetic recording may be used. As the magnetic layer, specifically, for example, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr or Co
Magnetic thin films such as NiCrPt, CoNiCrTa, CoCrPtTa, and CoCrPtSiO can be used. Further, the magnetic layer may be divided by a non-magnetic layer to have a multilayer structure in which noise is reduced.

The underlayer in the magnetic layer is selected according to the magnetic layer. As the underlayer, for example, Cr, Mo, Ta, T
Examples include at least one or more materials selected from nonmagnetic metals such as i, W, V, B, and Al, and an underlayer made of an oxide, nitride, carbide, or the like of those metals. In the case of a magnetic layer containing Co as a main component, from the viewpoint of improving the magnetic properties,
Preferably, it is Cr alone or a Cr alloy. 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 multilayer base layer of Al / Cr / CrMo, Al / Cr / Cr, or the like can be given.

An unevenness control layer may be provided between the substrate and the magnetic layer or above the magnetic layer to prevent the magnetic head and the magnetic disk from sticking to each other. By providing the unevenness control layer, the surface roughness of the magnetic disk is appropriately adjusted, so that the magnetic head and the magnetic disk do not stick to each other, and a highly reliable magnetic disk can be obtained. There are various known materials and methods for forming the unevenness control layer, and there is no particular limitation. For example, as the material of the unevenness control layer, Al, Ag, Ti, Nb, Ta, Bi, Si, Zr, Cr, Cu, Au,
At least one or more metals selected from Sn, Pd, Sb, Ge, Mg, and the like, or alloys thereof, or an underlayer made of oxides, nitrides, carbides, and the like thereof, and the like are given.
From the viewpoint of easy formation, Al alone, Al alloy,
It is desirable to use a metal containing Al as a main component, such as Al oxide or Al nitride.

In consideration of head stiction, the surface roughness of the unevenness forming layer is preferably Rmax = 50 to 300 Å. A more preferred range is Rmax = 100-200 Å. Rm
When ax is less than 50 angstroms, the magnetic disk surface is almost flat, so the magnetic head and the magnetic disk are attracted, the magnetic head and the magnetic disk are attracted, and the magnetic head and the magnetic disk are damaged or the head is crashed due to the attracting. It is not preferable because it causes Also, Rmax is 3
If the thickness exceeds 00 angstroms, the glide height (glide height) is increased, and the recording density is undesirably reduced. Note that, without providing the unevenness control layer, the surface of the glass substrate may be subjected to texturing by providing an unevenness by means of etching treatment, laser light irradiation, or the like.

Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film.
These protective films can be continuously formed with an underlayer, a magnetic layer, and the like by an in-line type sputtering apparatus or the like. Further, these protective films may have a single-layer structure or a multi-layer structure composed of the same or different films. Another protective layer may be formed on the protective layer or in place of the protective film. For example, colloidal silica fine particles may be dispersed and applied in a state where tetraalkoxylan is diluted with an alcohol-based solvent on the protective layer, followed by firing to form a silicon oxide (SiO ₂ ) film. In this case, it functions as both the protective film and the unevenness control layer. A wide variety of lubrication layers have been proposed, but generally, a liquid lubricant, perfluoropolyether, is diluted with a solvent such as Freon, and the medium surface is dipped, spin-coated, or sprayed. And heat-treating as necessary.

[0077]

The present invention will be further described below with reference to examples. Examples 1 to 9 Examples 1 to 9 are production examples of chemically strengthened glass and chemically strengthened glass used for producing the glass substrate of the present invention. Starting materials for melting these glasses include SiO ₂ ,
Al ₂ O ₃ , Al (OH) ₃ , MgO, CaCO ₃ , Y ₂ O ₃ , TiO ₂ , ZrO ₂ ,
Commonly used oxides, carbonates, nitrates, hydroxides and the like such as Li ₂ CO ₃ were used. These raw materials are weighed in a predetermined ratio shown in Tables 1 and 2 in a ratio of 0.3 to 18.0 kg, and mixed well to form a blended batch, which is put into a platinum crucible and heated at 1550 to 1600 ° C. The glass was melted in air for 5 hours. After melting, melt the glass melt to a size of 180 × 1
Pour into a 5 × 25 mm or 300 × 250 × 60 carbon mold, allow to cool to the glass transition temperature, immediately put into an annealing furnace, anneal for about 1 hour in the glass transition temperature range, and room temperature in the furnace Allowed to cool to room temperature. The obtained glass did not precipitate crystals that could be observed with a microscope.

Glass having a size of 300 × 250 × 60 mm and a size of 50 × 15 × 1 mm and a diameter of 95 mm × a thickness of 0.8 m
The resultant was polished into a disk-shaped glass to obtain a glass for chemical strengthening. These glasses were kept at a temperature of 550-650 ° C.
KNO ₃ nitrate, 60% KNO ₃ and 40% NaNO ₃ , 85% KNO ₃ and 15% Ca (NO ₃ )
₂ and 85% KNO ₃ and 15% Sr (NO ₃ ) ₂ for 4 to 16 hours in a mixed nitrate treatment bath to remove alkali ions such as Li or Na or alkaline earth ions such as Mg on the glass surface layer. ,
Na, K, Ca, Zn and Sr ions in the pretreatment bath were respectively ion-exchanged and chemically strengthened. Thus, nine types of chemically strengthened glass of Examples 1 to 9 were obtained. The bending strengths of these chemically strengthened glasses are shown in the properties column of Tables 1 and 2 together with the bending strength before chemical strengthening.

A glass of 180 × 15 × 25 mm size is
00 × 10 × 10mm, 10 × 10 × 20mm, 10 × 1 ×
After polishing to 20 mm, the sample was measured for Young's modulus, specific gravity, and DSC. The DSC measurement was performed by polishing a 10 × 1 × 20 mm plate glass into a 150 mesh powder, weighing 50 mg into a platinum pan, and using a MAC-3300 DSC device. The measurement of the Young's modulus was performed by an ultrasonic method using a sample of 100 × 10 × 10 mm. The data obtained by the measurement are shown in Tables 1 and 2 together with the composition of the glass. For comparison, Table 2 shows the characteristics of a commercially available TS10 crystallized glass substrate disclosed in Patent Publication No. 2516553 as Comparative Example 1.

[0080]

【table 1】

[0081]

[Table 2]

As is clear from Tables 1 and 2, Example 1
The chemically strengthened glass substrates of Nos. 9 to 9 have large strength characteristics such as Young's modulus and specific elastic modulus. Therefore, when used as a substrate for a magnetic recording medium, even if the glass substrate rotates at a high speed, the substrate is warped or blurred. It can be seen that it hardly occurs, and it is possible to cope with a thinner substrate. Further, the surface roughness (Ra) of these glasses can be polished to 5 ° or less, and the flatness is excellent, so that the magnetic head can be reduced in flying height and is useful as a glass substrate for a magnetic recording medium. It is. On the other hand, the crystallized glass substrate of Comparative Example 1 has almost the same excellent bending strength as the glass of the present invention,
Because the Young's modulus is considerably inferior to the glass substrate of the present invention,
Inability to cope with thinning and high-speed rotation of substrates. In particular, high-density recording cannot be achieved because the smoothness of the substrate is impaired by the presence of large crystal grains.

For the chemically strengthened glass obtained in Example 1-9, the shape of the 3.5 magnetic disk substrate (φ95 m
m, center hole diameter φ 25 mm, thickness 0.8 mm), and then chemically strengthened by the method described in the above-mentioned Example 1-9 to obtain a magnetic disk substrate made of chemically strengthened glass. These chemically strengthened glass substrates are set in a disk drive and
Even when the substrate was rotated at 5000 rpm, it was not broken. 35,000 rpm for a disk with a magnetic film on this substrate
Did not destroy it.

Embodiment 10 (Method of Manufacturing Magnetic Disk) As for the method of manufacturing a magnetic disk, as shown in FIG. 1, the disk 1 of the present invention is In this example, the unevenness control layer 3, the underlayer 4, the magnetic layer 5, the protective layer 6, and the lubricating layer 7 are formed. Explaining each layer specifically, the substrate 1 has an outer diameter of 47.5 mm,
It was processed on a disk having an inner diameter of 22.5 mm and a thickness of 0.8 mm, and both main surfaces were precisely polished so that the surface roughness was Ra = 4 Å and Rmax = 35 Å. The unevenness control layer is an AlN thin film having an average roughness of 50 Å, a surface roughness Rmax of 150 Å, and a nitrogen content of 5-35%. The underlayer is a thin film of CrV having a thickness of about 600 angstroms, and has a composition ratio of Cr: 83 at% and V: 17 at%. The magnetic layer is a thin film of CoPtCr having a thickness of about 300 Å, and the composition ratio is C
o: 76 at%, Pt: 6.6 at%, Cr: 17.4 at%. The protective layer is a carbon thin film having a thickness of about 100 angstroms. The lubricating layer is formed by applying a lubricating layer made of perfluoropolyether to the carbon protective layer by spin coating to a thickness of 8 angstroms.

Next, a method of manufacturing a magnetic disk according to one embodiment of the present invention will be described. First, the chemically strengthened glass manufactured in Example 5 was used for an outer diameter of 47.5 mm, an inner diameter of 22.5 mm,
A disk having a thickness of 0.8 mm is ground, and both main surfaces are precisely polished so that the roughness becomes Ra = 4 Å and Rmax = 35 Å, and chemically strengthened to obtain a glass substrate for a magnetic disk. Next, after setting the chemically strengthened glass substrate in the substrate holder, the glass substrate is fed into a charging chamber of an inline sputtering apparatus. Subsequently, the holder on which the chemically strengthened glass substrate is set is fed into the first chamber in which the Al target is etched, and is sputtered at a pressure of 4 mtorr, a substrate temperature of 350 ° C., and an Ar + N 2 gas atmosphere. As a result, the surface roughness Rmax 150
Angstrom, thin film thickness of 50 Angstrom Al
An N thin film (an uneven layer) was obtained.

Next, the holder on which the chemically strengthened glass substrate on which AlN was formed was set to CrV (Cr: 83 at%, V: 17 at).
%) CoPtCr (second chamber with target installed)
(Co: 76 at%, Pt: 6.6 at%, Cr: 17.4 at%) The film is continuously and sequentially fed into a third chamber in which a target is installed, and a film is formed on a substrate. These films were sputtered at a pressure of 2 mtorr, a substrate temperature of 350 ° C. and an Ar atmosphere, and a CrV underlayer having a thin film thickness of about 600 Å and a thin film thickness of about 300 Å.
Obtain an Angstrom CoPtCr magnetic layer. Next, the laminate on which the unevenness control layer, the underlayer, and the magnetic layer are formed is sent to a fourth chamber provided with a heater for performing a heat treatment. At this time, Ar gas mtor
r) Heat treatment is performed by changing the heat treatment temperature to an atmosphere.

The same film forming conditions as those of the CrV underlayer and the CoPtCr magnetic layer were used except that the above substrate was fed into a fifth chamber in which a carbon target was installed, and was formed in an atmosphere of Ar + H ₂ (H ₂ = 6%). Thus, a carbon protective layer having a thin film thickness of about 100 Å is obtained. Finally, the substrate up to the formation of the carbon protective layer is taken out of the in-line sense sputtering apparatus, and a perfluoropolyether is applied to the surface of the carbon protective layer by dipping to form a lubricating layer having a thickness of 8 Å. To obtain a magnetic disk.
As described above, the present invention has been described with reference to the preferred embodiments, but the present invention is not limited to the above embodiments.

[0088]

By using the glass of the present invention, an ion exchange layer can be formed to provide a glass substrate having a bending strength of 25 kg / mm ² or more, even if the glass is non-alkali glass or low alkali glass. . According to the present invention, 36
Even if it is an alkali-free glass or a low alkali glass having a high specific elastic modulus of × 10 ⁶ Nm / kg or more or a large Young's modulus of 110 GPa or more, a glass having an ion exchange layer and a bending strength of 25 kg / mm ² or more. A substrate can be provided. Furthermore, it has a high transition temperature (high heat resistance) of 700 ° C. or more, and excellent surface smoothness (surface roughness Ra <
It is also possible to provide a glass substrate having a thickness of 9 angstrom) and having a bending strength of 25 kg / mm ² or more. Further, since the glass of the present invention has excellent heat resistance, the heat treatment required for improving the properties of the magnetic film can be performed without deforming the substrate. Since recording can be achieved and the specific elastic modulus and strength are large, the magnetic disk can be made thinner and the magnetic disk can be prevented from being damaged. Further, since it can be obtained relatively stably as glass and is easy to produce on an industrial scale, it can be greatly expected as an inexpensive substrate glass for next-generation magnetic recording media.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a magnetic disk 1 in which a concavo-convex control layer 3, a base layer 4, a magnetic layer 5, a protective layer 6, and a lubricating layer 7 are sequentially formed on a glass substrate 2.

Claims (20)

[Claims] 1. A glass substrate having an ion exchange layer on at least the surface of the substrate, wherein a portion other than the ion exchange layer does not contain an alkali metal oxide, or 5 mol% or less of Na ₂ O and / or 10
Mol% or less of Li ₂ O (however, the total content of Na ₂ O and Li ₂ O is 1
0 mol% or less), a portion other than the ion-exchange layer contains at least one kind of divalent metal oxide, and a flexural strength of 25 kg / mm ² or more. 2. The substrate according to claim 1, wherein portions other than the ion exchange layer do not contain an alkali metal oxide. 3. The substrate according to claim 1, wherein the ion exchange layer contains an alkali metal ion or a divalent metal ion having an ionic radius larger than that of the divalent metal ion constituting the divalent metal oxide. 4. The ion exchange layer according to claim 1, wherein at least a part of the divalent metal ion constituting the divalent metal oxide is replaced with an alkali metal ion or a divalent metal ion having an ion radius larger than the divalent metal ion. The substrate according to claim 3, wherein the substrate is formed by performing. 5. The method according to claim 1, wherein the divalent metal oxide is MgO, CaO, S
The substrate according to any one of claims 1 to 4, wherein the substrate is at least one selected from rO and ZnO. 6. The method according to claim 5, wherein the divalent metal oxide is MgO.
The substrate according to claim 1. 7. The substrate according to claim 1, wherein the content of the divalent metal oxide in a portion other than the ion exchange layer is in the range of 5 to 45 mol%. 8. An alkali metal ion and a divalent metal ion having an ion radius larger than that of the divalent metal ion constituting the divalent metal oxide are Li, Na, K, Zn, Ca, and Sr ions. And at least one selected from the group consisting of Ba ions and Ba ions.
The substrate according to any one of claims 1 to 7. 9. A specific elastic modulus G or 11 of 36 × 10 ⁶ Nm / kg or more.
The substrate according to claim 1, having a Young's modulus of 0 GPa or more. 10. An alkali metal oxide-free or less than 5 mol% Na ₂ O and / or less than 10 mol% Li
A glass substrate containing ₂ O (the total content of Na ₂ O and Li ₂ O is 10 mol% or less) and containing at least one type of divalent metal oxide; A method for producing a glass substrate, comprising: immersing the substrate in a solution containing an alkali metal ion or a divalent metal ion having an ionic radius larger than that of the divalent metal ion to form an ion-exchange layer on at least the surface of the substrate. 11. A substrate on which an ion exchange layer is formed has a weight of 25 kg.
The method according to claim 10 for selecting the ion exchange conditions to have / mm ² or more flexural strength. 12. The divalent metal oxide may be MgO, CaO,
The method according to claim 10, wherein the method is one or more selected from SrO and ZnO. 13. The production method according to claim 10, wherein the glass before forming the ion exchange layer contains 5 to 45 mol% of a divalent metal oxide. 14. An alkali metal ion or a divalent metal having an ionic radius larger than that of the divalent metal ion constituting the divalent metal oxide is a Li ion, a Na ion, a K ion,
It is at least one selected from the group consisting of Zn ions, Ca ions, Sr ions, and Ba ions.
14. The method according to any one of items 13 to 13. 15. The production method according to claim 10, wherein the immersion in the solution is performed at a temperature of 400 ° C. or higher. 16. A specific elastic modulus G or 1 of 36 × 10 ⁶ Nm / kg or more.
The method according to claim 10, having a Young's modulus of 10 GPa or more. 17. A chemically strengthened glass substrate produced by the production method according to claim 10. Description: 18. A substrate for an information recording medium, comprising the glass substrate according to claim 1. Description: 19. An information recording medium comprising at least a substrate and an information recording section, wherein the substrate is the substrate according to claim 18. 20. The information recording medium according to claim 19, wherein the information recording medium is a magnetic recording medium.