JPH11116267A - Glass having high modulus of specific elasticity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a glass material having high strength, high shock resistance, a high modulus of specific elasticity, high heat resistance and high surface smoothness. SOLUTION: The glass has >=36×10<6> Nm/kg modulus of specific elasticity G, <=9 Å surface roughness Ra and >700 deg.C transition temp. or >=110 GPa Young's modulus, <=9 Å surface roughness Ra and >700 deg.C transition temp. It may have a compsn. contg., by mol, 25-52% SiO2 , 5-35% Al2 O3 , 15-45% MgO, 0-17% Y2 O3 0-25% TiO2 , 0-8% ZrO2 , 1-30% CaO (5%<=Y2 O3 +TiO2 +ZrO2 + CaO<=30%) and 0-5% B2 O3 +P2 O5 as glass forming oxides. The glass is useful as glass for the substrate of a magnetic disk.

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. It relates to the glass used. In particular, the present invention relates to a glass which has a high specific elastic modulus and / or a Young's modulus, a high heat resistance, and has a high surface smoothness when used as a substrate and is suitable for a substrate for an information recording medium or the like.

[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.

Accordingly, 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, a chemically strengthened glass substrate is disclosed in
The 39,036 No. (hereinafter referred to as prior art 1), a SiO ₂ 60 to 70% by weight, the _{Al 2 O 3 0.5~14%, R} 2
O (wherein R is an alkali metal) from 10 to 32% of the ZnO 1~15%, B ₂ O ₃ glass substrate disclosed a magnetic recording medium was enhanced by ion exchange glass containing 1.1 to 14% Have been.

As crystallized glass, Japanese Patent Application Laid-Open No. 7-1877
No. 11 (hereinafter referred to as prior art 2) discloses that Si
O ₂ 50 to 65% of CaO 18 to 25% of Na ₂ O 6 to 1
1% 6-12% of K ₂ O, the Al ₂ O ₃ 0 to 2.5% include F 5 to 9% glass substrate for a magnetic recording medium comprising a canasite is disclosed as the predominant crystal . In addition, US patents
No. 5,391,522 (hereinafter referred to as Prior Art 3) discloses SiO ₂
The 65 to 83%, the Li ₂ O 8 to 13 percent, K ₂ O 0 to 7%
0.5 to 5.5% MgO, 0 to 5% ZnO, 0 to PbO
5% (provided that 0.5 to 5% of MgO + ZnO + PbO), P 2
O ₅ is 1 to 4%, Al ₂ O ₃ is 0 to 7%, and As ₂ O ₃ + Sb ₂ O ₃ is 0.
A glass substrate for crystallization of a magnetic disk, which contains fine Li ₂ O.2SiO ₂ crystal particles as a main crystal, is disclosed. As an alkali-free glass substrate, JP-A-8-1697
No. 24 (hereinafter referred to as Prior Art 4) discloses that Si
The _{O 2 + Al 2 O 3 35~55} %, B 2 O 3 of 0%, CaO +
BaO is 40-60%, but CaO ≧ 5%, ZnO + SrO +
The MgO 0%, the TiO ₂ 0 to 5%, a ZrO ₂ 0 to 5%,
A glass substrate for a magnetic disk having a composition containing 0 to 1% of As ₂ O ₃ and / or Sb ₂ O ₃ is disclosed.

[0005]

By the way, recent HD
D (Hard disk driver) is required to increase the recording capacity in response to the high performance of personal computers.
In accordance with the miniaturization and high performance of personal computers, miniaturization and thinning of a disk substrate, low flying of a magnetic head, and high-speed rotation of a disk have been proposed. Future 2.5 inch diameter disk substrate thickness will be 0.43m from the current 0.631mm
m, and even thinner to 0.381mm. Recently, the demand for rigidity of board material has become more severe due to the higher density of 3.5 inch hard disk recording for servers and the higher speed of data processing.
The limits of conventional aluminum substrates are beginning to appear. It is expected that the capacity and size of hard disks will be further advanced in the future. Therefore, magnetic recording medium substrate materials are required to be thinner, have higher strength, have higher surface flatness, and have higher impact resistance.

However, the thinner the disk substrate, the more easily it bends and warps. On the other hand, with the increase in the recording density, the flying height of the magnetic head and the rotation of the magnetic disk have been increasing, and the above-described bending or warping of the substrate causes damage to the magnetic disk. However, when a substrate made of glass used for a hard disk is made thinner than it is now, the problems due to the above-described bending and warping become apparent, and it is impossible to cope with the thinning. The degree of deflection or warpage of the disk substrate can be evaluated from the specific elastic modulus (= Young's modulus / specific gravity) or Young's modulus of the substrate material. Even if the thickness is reduced, a material having a higher specific elastic modulus is required to suppress the deflection and warpage of the substrate to such an extent that no problem occurs. In addition, a material having a higher Young's modulus is required in order to suppress the problem of bending of the substrate when the substrate is rotated at high speed.

[0007] This can be explained based on the following facts. That is, with the recent miniaturization, high capacity, and high speed of HDDs, the thickness of future magnetic recording medium substrates is currently increasing from 0.8 mm at 3.5 inches to 0.635 mm, and from 0.635 mm at 2.5 inches to 0.43 mm. It is predicted to be as thin as 0.38mm. In addition, the rotation speed of the substrate is
It is predicted that the rotation speed will increase from 00 rpm to 10,000 rpm and further to 14000 rpm. The thinner the substrate for such a magnetic recording medium, the more easily the substrate bends, swells and warps, and the higher the speed of the rotation, the higher the stress applied to the substrate (the force acting on the disk based on the wind pressure generated by the rotation). Can be expected to increase. Based on the theory of mechanics, the deflection W of a disc receiving a load of P per unit area is expressed by the following equation.

[0008]

(Equation 1) Here, a is the outer diameter of the disk, h is the thickness of the substrate, and E is the Young's modulus of the disk material. In the stationary state, the force applied to the disk is only gravity, and the deflection W is expressed by the following equation, where d is the specific gravity of the disk material.

[0009]

(Equation 2) Here, G is the specific elastic modulus (= Young's modulus / specific gravity) of the disc material. On the other hand, in the rotating state of the disk, when it is considered that the gravitational component balances the centrifugal force component and can be ignored, the force applied to the disk may be a wind pressure based on the rotation. Wind pressure is a function of the disk rotation speed and is generally said to be proportional to its square. Therefore, the deflection W when the disk rotates at high speed is expressed by the following equation.

[0010]

(Equation 3) Therefore, a substrate material having a high Young's modulus E is required to suppress the deflection of the high-speed rotating substrate. According to the calculations of the present inventors, the thickness of the 2.5-inch substrate is changed from 0.635 mm to 0.43 mm.
In addition, when the thickness of the 3.5-inch substrate is reduced from 0.8 mm to 0.635 mm, a substrate material having a higher specific elastic modulus than conventional materials is required. Also, if the rotation speed of the 3.5-inch high-end board is increased from the current 7200 rpm to 10,000 rpm in the future,
An aluminum substrate having a Young's modulus of about 0 Gpa cannot be used, and a new substrate material having a higher Young's modulus is required. The higher the specific elastic modulus or Young's modulus of the substrate material, the higher the rigidity of the substrate as well as the greater the impact resistance and strength of the substrate. Are strongly demanded from the HDD market.

In addition to the specific elastic modulus and Young's modulus, there are other physical properties required for a glass substrate for a magnetic recording medium in order to increase the recording density. One is high heat resistance and one is high surface smoothness. In order to increase the recording density of a magnetic recording medium, it is necessary to enhance magnetic properties such as the coercive force of a magnetic layer (magnetic recording layer). The coercive force of the magnetic layer varies depending on the magnetic material used, but the same material can be increased by heat treatment. Therefore, apart from the development of a new magnetic material, it is desired to heat-treat the magnetic layer formed on the substrate at a higher temperature in order to obtain a higher coercive force using an existing material. In addition, high recording density can be achieved by lowering the flying height of the magnetic head.
Therefore, the flying height of the magnetic head will be further reduced in the future. In order to enable the magnetic head to have a low flying height, it is necessary that the surface of the disk has high smoothness. For that purpose, the surface of the substrate needs to have smoothness.

However, the chemically strengthened glass disclosed in Prior Art 1 has a glass transition point of about 500 ° C. On the other hand, in order to improve the magnetic properties such as the coercive force of the magnetic layer, heat treatment at a temperature higher than 500 ° C. is effective. Therefore, the chemically strengthened glass described in the prior art 1 has insufficient heat resistance of the glass itself. Further, the chemically strengthened glass generally has a glass surface provided with an ion exchange layer of alkali metal ions. However, when a magnetic layer is formed on the surface of chemically strengthened glass and subjected to a heat treatment, there is a problem that ions in the ion exchange layer move to the magnetic layer and exert a bad influence. The movement of alkali metal ions to the magnetic layer becomes more active as the temperature increases. In order to suppress such movement of alkali metal ions, heat treatment at a lower temperature is preferable. It is difficult to improve magnetic properties by heat treatment at a high temperature using a chemically strengthened glass substrate, and it is difficult to obtain a magnetic recording medium having a high coercive force. The above chemically strengthened glass has a specific elastic modulus of about 30 × 10
^Since it is about ⁶ Nm / kg, the Young's modulus is about 80 GPa, and the rigidity is low, it has a drawback that it cannot be used for a 3.5-inch high-end disk substrate or a thin disk substrate. In addition, the chemically strengthened glass substrate has a stress layer formed on both the front and back surfaces, but if this stress layer is not given uniform and equal stress, warpage will occur, resulting in low flying height and high speed rotation of the magnetic head. It is difficult to respond.

The conventional crystallized glass disclosed in prior arts 2 and 3 is excellent in heat resistance because it does not cause a transition. However, glass substrates for magnetic recording media are required to have higher surface smoothness as the recording density becomes higher. This is because it is necessary to reduce the flying height of the magnetic head in order to increase the recording density of the magnetic recording medium. However, since crystallized glass contains many fine particles, it is difficult to obtain a substrate having a surface roughness (Ra) of 10 Å or less. As a result, the flatness of the surface is poor, and the surface shape of the magnetic disk deteriorates. For the purpose of preventing the magnetic head from being attracted to the magnetic disk, for example, an unevenness control layer formed on a substrate is formed. However, a substrate using crystallized glass has a problem that it is difficult to control the surface morphology of the unevenness control layer.

The alkali-free glass described in Prior Art 4 is
It has a high transition temperature of at most 730 ° C. However, the specific elastic modulus of glass is about 27 to 34 × 10 ⁶ Nm / kg, and the Young's modulus is about 70 to 90 GPa.

As a substrate having excellent heat resistance, there is, for example, a carbon substrate for a magnetic recording medium as disclosed in Japanese Patent Application Laid-Open No. 3-273525 (hereinafter referred to as Prior Art 5). However, the carbon substrate has a specific elastic modulus of 15-19.
As low as about × 10 ⁶ Nm / kg, the mechanical strength is inferior to that of glass, and it is difficult to cope with the demand for thinner substrates required for the downsizing of magnetic disks. Further, the carbon substrate has many surface defects, and it is difficult to increase the recording density.

As described above, at present, an oxide having a high specific elastic modulus or a Young's modulus, high heat resistance, excellent surface smoothness (surface roughness <5 angstroms), and which can be mass-produced at low cost. Glass is not yet found on the market. The Young's modulus of SiO ₂ -Al ₂ O ₃ -MgO based glass, which is well known as a commercially available high Young's modulus oxide glass,
At most, it is about 80-90 Gpa. Therefore, we have a specific elastic modulus G of 36 × 10 ⁶ Nm / kg or more, or 11
With the aim of providing a glass material having a Young's modulus of 0 Gpa or more, a novel glass composition was designed based on theoretical calculations proposed by the present inventors and various tests and studies were repeated. As a result, by introducing a large amount of components such as Al ₂ O ₃ , Y ₂ O ₃ , MgO, TiO ₂ , and rare earth metal oxides that greatly contribute to the improvement of the Young's modulus of glass, an unprecedented high Young's modulus can be achieved. The present invention was completed by finding a glass which has excellent surface smoothness, high heat resistance and can be mass-produced at low cost.

That is, the present invention provides a high strength and high impact resistance, a high specific elastic modulus, a high heat resistance, which are required in accordance with the future miniaturization, thinning, and high recording density of information recording medium substrates. An object is to provide a new glass material that satisfies high surface smoothness. More specifically, the purpose of the present invention is to
To provide a glass substrate which has a glass transition temperature of not less than 36 × 10 ⁶ Nm / kg, a glass transition temperature of not less than 700 ° C., and a high surface smoothness (surface roughness Ra of not more than 9 angstroms) without containing microcrystalline particles. It is in. Furthermore, an object of the present invention is to have a Young's modulus of 110 GPa or more and high surface smoothness without containing fine crystal grains (surface roughness Ra is 9 Å or less).
The object of the present invention is to provide a glass substrate showing the following.

[0018]

Means for Solving the Problems To achieve the above object, the present invention is as follows. [Claim 1] A glass for a substrate, wherein the specific elastic modulus G is 36 × 10 ⁶ Nm / kg or more. [Claim 2] The glass according to claim 1, wherein the surface roughness (Ra) can be 9 angstrom or less. [Claim 3] The transition point temperature is higher than 700 ° C.
Or the glass according to 2. [Claim 4] As an oxide constituting glass, mol%
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
A glass characterized by being at least ⁶ Nm / kg. [Claim 5] As ₂ O ₃ + Sb ₂ O ₃ : 0-3%, and ZnO + SrO + NiO + C
_{oO + FeO + CuO + Fe 2} O 3 + Cr 2 O 3 + B 2 O 3 + P 2 O 5 + V 2 O 5: glass according to claim 4, further containing 0-5%. [Claim 6] As an oxide constituting glass, mol%
Expressed as: SiO ₂ : 25-50%, Al ₂ O ₃ : 10-37%, MgO: 5-
It has a composition of 40%, TiO ₂ : 1-25% and a specific elastic modulus of 36
× 10 ⁶ Nm / kg or more. [Claim _{7] 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 + C
_{uO + Fe 2 O 3 + Cr} 2 O 3 + B 2 O 3 + P 2 O 5 + V 2 O 5: glass according to claim 6, further comprising 0-5%. [Claim 8] As an oxide constituting glass, mol%
Expressed as: SiO ₂ : 25-50%, Al ₂ O ₃ : 20-40%, CaO: 8-
It has a composition of 30%, Y ₂ O ₃ : 2-15%, and a specific elastic modulus of 36%.
× 10 ⁶ Nm / kg or more. [Claim 9] MgO: 0-20%, TiO 2: 0-25%, Li 2 O: 0-1
2%, As ₂ O ₃ + Sb ₂ O ₃ : 0-3%, and ZnO + SrO + NiO + CoO + FeO + C
_{uO + Fe 2 O 3 + Cr} 2 O 3 + B 2 O 3 + P 2 O 5 + V 2 O 5: glass according to claim 8, further comprising 0-5%. [Claim 10] The glass according to any one of claims 1 to 9, having a Young's modulus of 110 GPa or more. [Claim 11] A glass for a substrate having a Young's modulus of 110 GPa or more. [Claim 12] The glass according to claim 11, which can have a surface roughness (Ra) of 9 ° or less. [Claim 13] The glass according to claim 11 or 12, having a transition point temperature higher than 700 ° C. By mol% as oxides constituting the claim 14 of _{glass, SiO 2: 30-60%, Al} 2 O 3: 0-35%, MgO: 0
_{-40%, Li 2 O: 0-20} %, 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 + D
_{y 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 to do. [Claim _{15] TiO 2: 0-20%,} ZrO 2: 0-8%, provided _{that, TiO 2 + ZrO 2: 0-20} %, CaO: 0-15%, ZnO: 0
-15%, NiO: 0-15%, Fe 2 O 3: 0-15%, however, C
_{aO + ZnO + NiO + Fe 2} O 3: 0-15%, further including the claims 1
The glass according to 4. [Claim _{16] As 2 O 3 + Sb} 2 O 3: 0-2%, B 2 O 3 + P 2 O 5 + N
b ₂ O ₅ + V ₂ O ₅ + Cr ₂ O ₃ + Ga ₂ O ₃ + CoO + SrO + BaO + SrO + FeO + CuO +
_{MnO + Na 2 O + K 2} O: 0-8% further including the claims 14 or 1
The glass according to 5. [17] The glass according to any one of [14] to [16], wherein the specific elastic modulus G is 36 × 10 ⁶ Nm / kg or more. [Claim 18] Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,
Ga, Ge, Y, Zr, Nb, Mo, La, Ce, Pr, Nd, Pm, Sm, E
u, Gd, Tb, Dy, Ho, Er, Tm, Yb, Hf, Ta and W are oxides of one or more metals selected from the group consisting of 3 to
A glass for an information recording medium, comprising 30 mol%. [Claim 19] The glass according to claim 18, having a Young's modulus of 90 GPa or more. [Claim 20] The glass according to any one of claims 1 to 19, which is a glass for a substrate of a magnetic disk. [Claim 21] A magnetic disk comprising at least a magnetic layer on the substrate made of glass according to claim 20.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the present invention, glass is glass substantially containing no crystal particles, and does not include crystallized glass containing at least 20% or more of crystal particles and what is called glass ceramics.

The glass according to the first to third aspects of the present invention has a specific elastic modulus G of 36 ×.
It is a glass for substrates characterized by having a density of 10 ⁶ Nm / kg or more. When the specific elastic modulus G is less than 36 × 10 ⁶ Nm / kg, the deflection becomes large when the substrate is used. For example, when the substrate is 0.43 mm or less in thickness required for a next-generation magnetic recording medium disk, , The maximum deflection is greater than 1.4 μm. As a result, there is a problem that the flying stability of the head cannot be obtained, and recording and reproduction cannot be performed stably. Further, in order to obtain a substrate having a maximum deflection of 1.25 μm or less, glass having a specific elastic modulus G of 37 × 10 ⁶ Nm / kg or more is preferable. Also,
The specific elastic modulus is 42 × 10 ⁶ Nm / kg from the viewpoint that a substrate with a maximum deflection of 1.4 μm or less can be obtained even when the thickness is reduced and the substrate is 0.381 mm or less in thickness.
The above glass is more preferable. Incidentally, the higher the specific elastic modulus, the better, but practically, about 45 × 10 ⁶ Nm / kg
It is as follows.

The glass according to claim 2 has a specific elastic modulus G.
In addition to being 36 × 10 ⁶ Nm / kg or more, the glass can have a surface roughness (Ra) of 9 Å or less. Higher surface smoothness enables lower flying height of the head for higher density of the magnetic disk, and the surface roughness (R
By setting a) to 9 angstroms or less, it is possible to achieve a lower flying height than the conventional one. In order to further increase the density of the magnetic disk, it is preferable that the glass is made of glass that can have a surface roughness (Ra) of 6 Å or less. The glass according to claim 3 has a specific elastic modulus G of 36 × 10 ⁶ Nm / kg or more and / or a surface roughness (Ra) of 9 Å or less, and a transition point temperature of 700 ° C. Higher glass. With a transition point temperature higher than 700 ° C,
In addition to the reduction in deflection, a substrate having higher heat resistance than a conventional substrate can be provided, and a magnetic disk with improved magnetic properties such as coercive force can be provided.

Specific examples of the glass having the characteristics described in claims 1 to 3 include the glasses described in claims 4 to 9. These glasses have a configuration using an oxide glass made of a cation having a small ionic radius, a strong chemical bonding force, and a high packing density in the glass structure, in order to satisfy the characteristics described in claims 1 to 3. Has become.

Glass according to claims 4 and 5 The glass composition according to claim 4 is a composition mainly designed to increase the specific elastic modulus, and the specific elastic modulus G is 36 × 10
⁶ Nm / kg or more. When the specific elastic modulus G is 36 × 10 ⁶ Nm / kg or more, a substrate with small deflection can be obtained. For example, the thickness required for next-generation magnetic recording media disks
Even with a substrate of 0.43 mm or less, a substrate with a maximum deflection of less than 1.4 μm can be obtained. As a result, the flying stability of the head is excellent, and recording and reproduction can be performed stably. Further, in order to obtain a substrate having a maximum deflection of 1.25 μm or less, the specific elastic modulus G is preferably 37 × 10 ⁶ Nm / kg or more. In addition, the thickness has been reduced and the thickness is 0.381m
The maximum deflection is 1.
Glass having a specific elastic modulus of 42 × 10 ⁶ Nm / kg or more is more preferable, from the viewpoint that a substrate suppressed to 4 μm or less can be obtained. Incidentally, the higher the specific elastic modulus is, the more preferable,
Practically, it is about 45 × 10 ⁶ Nm / kg or less.

Further, the glass according to the fourth and fifth aspects can have a surface roughness (Ra) of 9 angstrom or less. Higher surface smoothness allows lower flying height of the head for higher density magnetic disks, and lowering the surface roughness (Ra) to less than 9 angstroms enables lower flying height than conventional ones. Become. In order to further increase the density of the magnetic disk, the surface roughness (Ra) is preferably set to 6 Å or less. Further, the glass according to claims 4 and 5 is a glass having a transition point temperature higher than 700 ° C. When the transition point temperature is higher than 700 ° C., it is possible to provide a substrate having higher heat resistance than conventional substrates in addition to reduction in deflection, and to provide a magnetic disk having improved magnetic properties such as coercive force. be able to.

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 the substrate for magnetic recording media such as the strength and rigidity of the glass can be increased, and the heat resistance of the glass is improved It can also be done. However, as a main component of glass, more than 52%
Since the oxide glass into which SiO ₂ has been introduced shows almost no specific elastic modulus exceeding 36 × 10 ⁶ Nm / kg, the content of SiO ₂ is 5%.
Suitably, it is less than 2. On the other hand, when the content of SiO ₂ is less than 25%, the crystallization stability of the glass is considerably deteriorated,
Glass cannot be made stable enough to be mass-produced. Therefore,
The lower limit of SiO ₂ is 25%. Therefore, the content of SiO ₂ is
Suitably, it is in the range of 25-52%, preferably in the range of 30-50%.

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 increases the rigidity thereof 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 the 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 both as a glass skeleton-forming component and a modifying component, lowering the high-temperature viscosity of the 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 introduced together with MgO to improve the rigidity and strength of the glass and 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 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 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 the content of 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 melting property 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 of B ₂ O ₃ + P ₂ O ₅ should be 5% or less, preferably 3.5% or less from the viewpoint of improving the solubility of glass and adjusting the crystallization stability and physical properties of glass. Is appropriate. 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 added as a defoaming agent 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, the content is suitably 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. .

Glass according to claims 6 and 7 The glass composition according to claims 6 and 7 is a composition mainly designed to increase the specific elastic modulus, and the specific elastic modulus G is
36 × 10 ⁶ Nm / kg or more. When the specific elastic modulus G is 36 × 10 ⁶ Nm / kg or more, a substrate with small deflection can be obtained. For example, even when a substrate having a thickness of 0.43 mm or less required for a next-generation magnetic recording medium disk is used, a substrate having a maximum deflection of less than 1.4 μm can be obtained. As a result, the flying stability of the head is excellent, and recording and reproduction can be performed stably. In addition, the maximum deflection is 1.25
μm or less, specific elastic modulus G is 37 × 10 ⁶ Nm / kg
It is preferable that it is above. In addition, the specific elastic modulus is 42 × 10 ⁶ Nm / kg from the viewpoint that a substrate whose maximum deflection is suppressed to 1.4 μm or less can be obtained even when the thickness is reduced and the substrate is 0.381 mm or less in thickness. The above glass is more preferable. The specific elastic modulus is preferably as high as possible, but practically it is about 45 × 10 ⁶ Nm / kg or less.

Further, the glass according to claims 6 and 7 can have a surface roughness (Ra) of 9 angstrom or less. Higher surface smoothness allows lower flying height of the head for higher density magnetic disks, and lowering the surface roughness (Ra) to less than 9 angstroms enables lower flying height than conventional ones. Become. In order to further increase the density of the magnetic disk, the surface roughness (Ra) is preferably set to 6 Å or less. Further, the glass according to claims 6 and 7 is a glass having a transition point temperature higher than 700 ° C. When the transition point temperature is higher than 700 ° C., it is possible to provide a substrate having higher heat resistance than conventional substrates in addition to reduction in deflection, and to provide a magnetic disk having improved magnetic properties such as coercive force. be able to.

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 can enhance the mechanical properties required for a substrate for a magnetic recording medium, such as strength and rigidity of glass, by combining with an intermediate oxide such as Al ₂ O _3, and improve the heat resistance of glass. It 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, it is appropriate that the lower limit of SiO ₂ be 25%. SiO ₂ content is 2
Suitably, it is in the range of 5 to 50%, preferably in the range of 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 set to 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 acts as a glass skeleton-forming component and also as a modifying component, 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 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 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. Also, Li ₂ O
In the case of containing, it is possible to perform chemical strengthening treatment by ion exchange in order to increase the strength of the glass. On the other hand, 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 adversely affect it.

Glass according to claims 8 and 9 The glass composition according to claims 8 and 9 is a composition mainly designed to increase the specific elastic modulus, and the specific elastic modulus G is
36 × 10 ⁶ Nm / kg or more. When the specific elastic modulus G is 36 × 10 ⁶ Nm / kg or more, a substrate with small deflection can be obtained. For example, even when a substrate having a thickness of 0.43 mm or less required for a next-generation magnetic recording medium disk is used, a substrate having a maximum deflection of less than 1.4 μm can be obtained. As a result, the flying stability of the head is excellent, and recording and reproduction can be performed stably. In addition, the maximum deflection is 1.25
μm or less, specific elastic modulus G is 37 × 10 ⁶ Nm / kg
It is preferable that it is above. In addition, the specific elastic modulus is 42 × 10 ⁶ Nm / kg from the viewpoint that a substrate whose maximum deflection is suppressed to 1.4 μm or less can be obtained even when the thickness is reduced and the substrate is 0.381 mm or less in thickness. The above glass is more preferable. The specific elastic modulus is preferably as high as possible, but practically it is about 45 × 10 ⁶ Nm / kg or less.

Further, the glass according to the eighth and ninth aspects can have a surface roughness (Ra) of 9 angstrom or less. Higher surface smoothness allows lower flying height of the head for higher density magnetic disks, and lowering the surface roughness (Ra) to less than 9 angstroms enables lower flying height than conventional ones. Become. In order to further increase the density of the magnetic disk, the surface roughness (Ra) is preferably set to 6 Å or less. Further, the glass according to claims 8 and 9 is a glass having a transition point temperature higher than 700 ° C. When the transition point temperature is higher than 700 ° C., it is possible to provide a substrate having higher heat resistance than conventional substrates in addition to reduction in deflection, and to provide a magnetic disk having improved magnetic properties such as coercive force. be able to.

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, more than 50% as the main component of glass
CaO -Al ₂ O ₃ -SiO ₂ based oxide glass obtained by introducing SiO ₂ is
Since it hardly shows a specific elastic modulus exceeding 36 × 10 ⁶ Nm / kg, the content of SiO ₂ is suitably at most 50%. 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%. Therefore, the content of SiO ₂ is in the range of 25 to 50%,
Preferably, the range is 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, the range is 21 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 glass and improving the high-temperature melting property, and also contributes to the improvement of the crystallization stability and the homogeneity of glass, and the effect of increasing the specific elastic modulus. Since it is also a component, it can be added as desired. However, when the content of MgO exceeds 20%, it is not possible to add a large amount of CaO, which is an essential component, and the crystallization stability of 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 serves as a glass skeleton-forming component and also as a modifying component, and is a component that reduces 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 addition effect of Li ₂ O, its content is preferably 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.

Glass according to claims 11 to 13 The glass according to claim 11 of the present invention has a Young's modulus of 11
It is a glass for substrates characterized by being at least 0 GPa. When the Young's modulus is less than 110 GPa,
In the case of rotation at the above speed, the influence of the deflection of the substrate due to the wind force increases, causing a problem that the flying stability of the head cannot be obtained, and a problem that recording and reproduction cannot be performed stably. Young's modulus is preferably 120G
It is preferably at least Pa, more preferably at least 130 GPa, from the viewpoint that the flying stability of the head can be obtained. The higher the Young's modulus, the better, but practically, it is about 150 GPa or less.

The glass according to claim 12 is a glass having a Young's modulus of 110 GPa or more and a surface roughness (Ra) of 9 Å or less. Higher surface smoothness enables lower flying height of the head for higher density of the magnetic disk, and the surface roughness (R
By setting a) to 9 angstroms or less, it is possible to achieve a lower flying height than the conventional one. In order to further increase the density of the magnetic disk, it is preferable that the glass is made of glass that can have a surface roughness (Ra) of 6 Å or less.

The glass of claim 13 has a Young's modulus of 110.
In addition to being not less than GPa and / or having a surface roughness (Ra) of not more than 9 Å, the glass has a transition point temperature higher than 700 ° C. Transition point temperature 700 ℃
By being higher, it is possible to provide a substrate having higher heat resistance than the conventional substrate in addition to the reduction of the deflection, and it is possible to provide a magnetic disk having improved magnetic properties such as coercive force. Specific examples of the glass having the characteristics described in claims 11 to 13 include the glasses described in claims 14 to 16. These glasses are claimed in claim 11
In order to satisfy the characteristics described in Nos. 1 to 13, an oxide glass composed of a cation having a small ionic radius, a strong chemical bonding force, and a high packing density in a glass structure is used.

The glass SiO _{2 according to the present invention} functions as an oxide for forming a network structure of the glass, and stabilizes the glass structure, that is, increases 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 too small, for example, if it is less than 30%, the crystallization stability of the glass will be 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. 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, the content is set to 35% or less. In particular, 1
It is preferably in the range of -30%.

MgO improves the rigidity and strength of glass,
It is a component introduced to improve high-temperature solubility. Furthermore, MgO also contributes to improving the crystallization stability of the glass and improving the glass homogeneity. In particular, when a large amount of Al ₂ O ₃ is introduced as a component that greatly contributes to the improvement of Young's modulus in glass, 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, Li ₂ O content is 2%
It is appropriate that the above is true. Incidentally, from the viewpoint of increasing the crystallization stability of the glass and improving the homogeneity, durability and high-temperature melting property of the glass, 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 + E
Suitably, r ₂ O ₃ + Tm ₂ O ₃ + Yb ₂ O ₃ > 25%.

TiO ₂ acts both as a glass skeleton forming component and a modifying component, lowering the high-temperature viscosity of glass, improving the melting property, 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 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, the total content is suitably 1% or more.

As ₂ O ₃ and Sb ₂ O ₃ are components added as a defoaming agent 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, CuO, Cr ₂ O ₃ , B ₂ O ₃ , P ₂ O ₅ , V ₂ O
Components such as 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. 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 + P ₂ O ₅ +
The total amount of 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.

Glass according to claims 18 to 19 This glass is made of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, G
a, Ge, Y, Zr, Nb, Mo, La, Ce, Pr, Nd, Pm, Sm, Eu,
Oxides of one or more metals selected from the group consisting of Gd, Tb, Dy, Ho, Er, Tm, Yb, Hf, Ta, and W;
An information recording medium glass containing 0 mol%. As described above, the oxides of Y and Ti contribute to the improvement of the Young's modulus.However, the use of these materials has a high dielectric constant and a material that, when introduced into glass, increases the packing density of glass. This is based on the inventors' theoretical thinking of increasing the Young's modulus of the glass. Similarly, a relatively high Young's modulus (for example, 90 Gpa or more) can be obtained by appropriately introducing a metal oxide listed above that can improve the packing density of glass when introduced in a range of 3 to 30 mol%. Glass can be obtained. Such a glass is very suitable for a substrate for an information recording medium such as a magnetic disk. If the amount of the metal oxide introduced is less than 3 mol%, the Young's modulus of the glass is insufficiently improved, which is not preferable. When the amount of the metal oxide introduced exceeds 30 mol%, the crystal stability of glass and its homogeneity are deteriorated, or the specific gravity is greatly increased, and the specific elastic modulus is increased depending on the type of metal. It is not preferred because it lowers it. The lower limit of the amount of the metal oxide to be introduced is preferably 5 mol%, more preferably 10 mol%, from the viewpoint of improving the Young's modulus. In addition, the upper limit of the amount of the metal oxide to be introduced is preferably 25 mol%, more preferably 20 mol%, from the viewpoints of crystal stability of glass, homogeneity thereof, and specific elastic modulus.

Glass and Substrate Production Method The glass of the present invention can be produced by a known production method. For example, a high-temperature melting method, that is, a glass material of a predetermined ratio is melted in the air or in an inert gas atmosphere, and the glass is homogenized by bubbling, addition of a defoaming agent, stirring, etc. Sheet glass can be obtained by such a method. Thereafter, processing such as grinding and polishing is performed to obtain a magnetic recording medium substrate having a desired size and shape. In the polishing, the surface roughness (Ra) can be set, for example, in a range of 3 to 5 Å by performing lapping and polishing with a polishing powder such as cerium oxide.

The glass of the present invention has heat resistance, surface smoothness,
It has excellent chemical durability, optical properties and mechanical strength. It can be suitably used as a heat-resistant substrate for a low-temperature polycrystalline silicon liquid crystal display device or a glass substrate for electric or electronic components.

Description of the Magnetic Disk The magnetic disk of the present invention is characterized by having at least a magnetic layer on the substrate made of the glass of the present invention. The magnetic disk (hard disk) of the present invention is a magnetic disk (hard disk) in which at least a magnetic layer is formed on the main surface of the glass substrate of the present invention, and will be described below. As layers other than the magnetic layer,
Underlayer, protective layer, lubricating layer, unevenness control layer and the like,
It is formed as needed. 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 may be any of horizontal magnetic recording and perpendicular magnetic recording. Specifically, the magnetic layer mainly contains Co, for example.
CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr and CoNiCrP
t, CoNiCrTa, CoCrPtTa, CoCrPtSiO and the like. 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 being attracted 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.

[0082]

The present invention will be further described below with reference to examples. Tables 1 to 5 show the glass compositions of Examples 1 to 61 by mol%.
In Tables 6 to 13, the glass compositions of Examples 100 to 190 are shown in mol%. As the starting material to be used in dissolving the glass _{Korara, SiO 2, Al 2 O 3} , Al (OH) 3, MgO, Ca
Using CO ₃ , Y ₂ O ₃ , TiO ₂ , ZrO ₂ , Li ₂ CO ₃ etc., Table 1
250 to 300 g were weighed to a predetermined ratio shown in 12, and mixed well to form a blended batch, which was placed in a platinum crucible and melted in air at 1550 ° C for 3 to 5 hours. After melting, the glass melt is size 180 × 15 × 25mm
Alternatively, it was poured into a carbon mold of φ67 mm × 5 mm, allowed to cool to the glass transition point temperature, immediately put into an annealing furnace, annealed for about 1 hour in the glass transition temperature range, and allowed to cool to room temperature in the furnace. The obtained glass did not precipitate crystals that could be observed with a microscope.

A glass of 180 × 15 × 25 mm size is
After being polished to 00 × 10 × 10 mm and 10 × 10 × 20 mm, it was used as a sample for measurement of Young's modulus, specific gravity, and DSC. φ
67mm x 5mm thick disk glass φ65 x 0.5mm thick
To obtain a surface roughness measurement sample. For the DSC measurement, a 10 × 1 × 20 mm plate glass was polished to 150 mesh powder, 50 mg was weighed and placed in a platinum pan,
This was performed using a C-3300 type DSC apparatus. The measurement of the Young's modulus was performed by an ultrasonic method using a sample of 100 × 10 × 10 mm. For the glasses of Examples 1 to 61, data of the surface roughness, specific gravity, Young's modulus, specific elastic modulus, and transition point temperature obtained by the measurement are shown in Tables 1 to 5 together with the glass composition. In addition, the obtained glass was cut into a disk shape, and the main surface was polished with cerium oxide to obtain a magnetic disk substrate having an outer circle radius of 32.5 mm, an inner circle radius of 10.0 mm, and a thickness of 0.43 mm. . Tables 1 to 5 also show the measurement results of the deflection of the obtained substrate. In addition, for the glasses of Examples 100 to 190, the surface roughness, the Young's modulus obtained by the measurement,
And data of the transition point temperature together with the glass composition in Tables 6-1.
3 is shown. For comparison, the ion-exchange glass substrate disclosed in JP-A-1-239036 and the ion-exchanged glass substrate disclosed in JP-A-7-1877 were used.
Table 5 shows the compositions and properties of the glass substrates described in Japanese Patent Publication No. 11 as Comparative Examples 1 and 2, respectively.

[0084]

[Table 1]

[0085]

[Table 2]

[0086]

[Table 3]

[0087]

[Table 4]

[0088]

[Table 5]

[0089]

[Table 6]

[0090]

[Table 7]

[0091]

[Table 8]

[0092]

[Table 9]

[0093]

[Table 10]

[0094]

[Table 11]

[0095]

[Table 12]

[0096]

[Table 13]

As apparent from Tables 1 to 13, Example 1
It can be seen that glasses 61 to 61 and 100 to 190 have a high glass transition point, and thus have sufficient heat resistance to perform a desired heat treatment (generally at 700 ° C. or lower).
In particular, since the strength properties of glass such as Young's modulus and / or specific elastic modulus are large, when used as a substrate for a magnetic recording medium, even if the glass substrate rotates at high speed, the substrate is less likely to warp or shake. It can be seen that the substrate can be made thinner. Furthermore, the surface roughness (R) of these glasses
a) can be polished to less than 5 angstroms,
Since the flatness is excellent, the flying height of the magnetic head can be reduced. Further, the glasses of Examples 1 to 61 also have a small deflection. Therefore, the glass of the present invention is useful as a glass substrate for a magnetic recording medium.

On the other hand, the chemically strengthened glass substrate of Comparative Example 1 is excellent in surface smoothness and flatness, but is considerably inferior to the glass substrate of the present invention in strength characteristics such as heat resistance and specific elastic modulus. Therefore, when manufacturing a magnetic recording medium, the heat treatment on the magnetic layer for obtaining a high coercive force cannot be performed sufficiently, and a magnetic recording medium having a high coercive force cannot be obtained.
Further, glass having a small specific elastic modulus of about 30 × 10 ⁶ Nm / kg cannot cope with thinning because the substrate warp or bend is large. The crystallized glass substrate of Comparative Example 2 is inferior to the glass of the present invention in specific elastic modulus and smoothness. In particular, high-density recording cannot be achieved because the smoothness of the substrate is impaired by the presence of large crystal grains. The glass of the present invention has a Young's modulus, a high specific modulus and a high heat resistance, and is extremely useful as a magnetic disk substrate.

Manufacturing Method of Hard Disk As shown in FIG. 1, a magnetic disk 1 is provided on a glass substrate 2 formed by using the glass of the above-described first embodiment, in this order, a concavo-convex control layer 3, a base layer 4, and a magnetic layer 5 , A protective layer 6 and a lubricating layer 7. Explaining each layer specifically, the substrate 1 has an outer circle radius of 32.5 mm, an inner circle radius of 10.0 mm, and a thickness of
It was machined on a 0.43 mm disk, and its main surfaces were precisely polished so that the surface roughness was Ra = 4 Å and Rmax = 40 Å. The roughness control layer has an average roughness of 50 Å and a surface roughness of
Rmax 150 Å, nitrogen content 5-3
5% AlN thin film. The underlayer is a CrV thin film having a thickness of about 600 Å, and the composition ratio is Cr: 83 at.
%, V: 17 at%. The magnetic layer is a thin film of CoPtCr having a thickness of about 300 Å, and the composition ratio is Co: 76a.
t%, 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 onto the carbon protective layer by spin coating to a thickness of 8 Å.

Next, a method for manufacturing a magnetic disk will be described. First, the glass produced in Example 1 was radiated to the outer circle radius.
32.5mm, inner circle radius 10.0mm, thickness 0.5mm on a disk, grinding both surfaces, precision polishing so that the surface roughness Ra = 4 angstrom, Rmax = 40 angstrom magnetic disk Obtain a glass substrate for use. Next, the glass substrate is set on a substrate holder, and then sent into a charging chamber of an in-line sputtering apparatus. Subsequently, the holder on which the glass substrate is set is fed into the first chamber where the Al target is etched, and is sputtered in an atmosphere of Ar + N ₂ gas (N ₂ = 4%) at a pressure of 4 mtorr, a substrate temperature of 350 ° C. As a result, the surface roughness Rmax =
150 angstroms and 50 angstroms
An AlN thin film (irregularity forming layer) was obtained. Next, the holder on which the glass substrate on which AlN was formed was set was placed in a CrV (C
r: 83 at%, V: 17 at%) a second chamber in which a target is installed, CoPtCr (Co: 76 at%, Pt:
(6.6 at%, Cr: 17.4 at%) are sequentially and sequentially fed into a third chamber in which a target is installed, and a film is formed on a substrate. These films have a pressure of 2 mtorr and a substrate temperature of 3 mtorr.
Sputtering in Ar atmosphere at 50 ° C.
A CrV underlayer of 0 Å and a CoPtCr magnetic layer of about 300 Å in thickness are obtained.

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, heat treatment is performed in an atmosphere of Ar gas (pressure 2 mtorr) in the fourth chamber. The above substrate is sent to the fifth chamber where the carbon target is installed, and Ar + H ₂ gas (H ₂ = 6%)
Except that the film was formed in an atmosphere, the above CrV underlayer and CoPt
Under the same film forming conditions as the Cr magnetic layer, a carbon protective layer having a thickness of about 100 Å is obtained. Finally, the substrate up to the formation of the carbon protective layer is taken out of the inline sputtering apparatus, and a perfluoropolyether is applied on 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.

[0102]

According to the glass of the present invention, 36 × 10
Has a high specific elastic modulus of ⁶ Nm / kg or more or a Young's modulus of 110 GPa or more, a high transition temperature (high heat resistance) of 700 ° C or more, and excellent surface smoothness (surface roughness Ra <9 Å). In addition, a glass substrate having high strength can be provided. 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.
Further, according to the present invention, it is possible to provide a magnetic disk capable of high-density recording capable of coping with a low flying height of the magnetic head and a magnetic disk capable of avoiding breakage even if the magnetic head is reduced in thickness.

[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.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 5/84 G11B 5/84 A 7/24 526 7/24 526V

Claims (21)

[Claims] 1. A glass for a substrate, wherein the specific elastic modulus G is 36 × 10 ⁶ Nm / kg or more. 2. The glass according to claim 1, wherein the surface roughness (Ra) can be set to 9 ° or less. 3. The method according to claim 1, wherein the transition point temperature is higher than 700 ° C.
Or the glass according to 2. 4. An oxide constituting the glass, which is represented by mol%
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 : Glass having a composition of 0-5% and a specific elastic modulus of 36 × 10 ⁶ Nm / kg or more. 5. As ₂ O ₃ + Sb ₂ O ₃ : 0-3%, and ZnO + SrO
+ NiO + CoO + FeO + CuO + Cr ₂ O ₃ + Fe ₂ O ₃ + B ₂ O ₃ + P
_{2 O 5 + V 2 O 5} : glass according to claim 4, further containing 0-5%. 6. An oxide constituting the glass, which is represented by mol%
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. 7. Y ₂ O ₃ : 0-17%, ZrO ₂ : 0-8%, CaO: 0-2
_{5%, 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: glass according to claim 6, further comprising 0-5%. 8. An oxide constituting the glass, which is represented by mol%
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. 9. MgO: 0-20%, TiO ₂ : 0-25%, Li ₂ O: 0-
_{12%, 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: glass according to claim 8, further comprising 0-5%. 10. The glass according to claim 1, having a Young's modulus of 110 GPa or more. 11. A glass for a substrate having a Young's modulus of 110 GPa or more. 12. The glass according to claim 11, wherein the glass can have a surface roughness (Ra) of 9 ° or less. 13. The glass according to claim 11, having a transition point temperature higher than 700 ° C. 14. An oxide constituting glass, expressed as mol%, SiO ₂ : 30-60%, Al ₂ O ₃ : 0-35%, MgO: 0
_{-40%, Li 2 O: 0-20} %, 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 + Ce
O 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%
The glass which has the composition which is below, and Young's modulus is 110 GPa or more. 15. TiO ₂ : 0-20%, ZrO ₂ : 0-8%,
However, TiO ₂ + ZrO ₂ : 0-20%, CaO: 0-15%, Zn
O: 0-15%, NiO: 0-15 %, Fe 2 O 3: 0-15%, however, CaO + ZnO + NiO + Fe 2 O 3: 0-15% more glass according to claim 14 comprising a. 16. 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 + Sr
O + FeO + CuO + MnO + Na 2 O + K 2 O: 0-8% more glass according to claim 14 or 15 including. 17. The glass according to claim 14, wherein the specific elastic modulus G is 36 × 10 ⁶ Nm / kg or more. 18. Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Z
n, Ga, Ge, Y, Zr, Nb, Mo, La, Ce, Pr, Nd, Pm, Sm,
Oxides of one or more metals selected from the group consisting of Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Hf, Ta and W
A glass for an information recording medium characterized by containing about 30 mol%. 19. The glass according to claim 18, having a Young's modulus of 90 GPa or more. 20. The glass according to claim 1, which is a glass for a substrate of a magnetic disk. 21. A magnetic disk having at least a magnetic layer on a substrate made of the glass according to claim 20.