JP3379621B2 - Material used for information recording medium substrate, substrate using the same, and magnetic disk using the substrate - Google Patents

Description

Detailed Description of the Invention TECHNICAL FIELD OF THE INVENTION

The present invention relates to a material used for a substrate for an information recording medium such as a magnetic disk or an optical disk, and particularly to a substrate material for an information recording medium made of glass, a substrate made of this material, and an information recording using this substrate. Regarding the medium.

[0002]

2. Description of the Related Art Conventionally, for example, as substrates for magnetic disks (hard disks), there are aluminum substrates, glass substrates, ceramic substrates, carbon substrates, etc., and aluminum substrates and glass substrates are mainly used according to size and use. And are in practical use. Among them, the glass substrate is attracting attention as a present and future substrate because of its excellent surface smoothness and mechanical strength. As such a glass substrate, a chemically strengthened glass substrate in which the surface of the glass substrate is strengthened by ion exchange and a non-alkali glass substrate containing substantially no alkali are known. For example, as a chemically strengthened glass substrate, Japanese Patent Laid-Open No. 1-239036 discloses:
By weight%, SiO ₂ is 60 to 70% and Al ₂ O ₃ is 0.5 to 14
%, R ₂ O (where R is an alkali metal) 10 to 32%,
A glass substrate for a magnetic recording medium is disclosed, which is reinforced by ion exchange of a glass containing 1 to 15% of ZnO and 1.1 to 14% of B ₂ O ₃ . In addition, as a non-alkali glass substrate, in JP-A-8-169724, the weight percentage is
SiO ₂ + Al ₂ O ₃ 35-55%, B ₂ O ₃ 0-10%, CaO
+ BaO 40 to 60%, CaO ≥5%, ZnO + SrO
+ MgO 0-10%, TiO ₂ 0-5%, ZrO ₂ 0-5
%, As ₂ O ₃ and / or Sb ₂ O ₃ in a composition of 0 to 1% is disclosed.

[0003]

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.
It has been proposed to reduce the size and thickness of the disk substrate in response to the downsizing and performance of personal computers. Future 2.5 inch disk substrate thickness will be 0.631 mm to 0.43 mm,
Furthermore, it is expected to be reduced to 0.381 mm.
By the way, the thinner the disk substrate, the more likely it is to bend or warp. On the other hand, for the purpose of increasing the recording density, the distance between the disk and the magnetic head is becoming narrower, and the above-mentioned bending and warpage of the substrate causes damage to the magnetic disk. However, if the glass substrate currently used for hard disks is made thinner than it is now, the problems due to the above-mentioned bending and warping become apparent, and it is not possible to reduce the thickness. The degree of bending and warpage of the disk substrate can be evaluated from the specific elastic modulus (= Young's modulus / specific gravity) of the substrate material. A material having a higher specific elastic modulus is required in order to suppress the bending and warpage of the substrate to the extent that problems do not occur even when the substrate is made thin. However,
In the glass composition of a particular system, it is not always clearly known what component affects the specific elastic modulus.

Therefore, the present invention establishes a theoretical relationship between the specific elastic modulus of glass and the composition, and based on the calculation based on the theoretical relationship, it is preferable to use SiO ₂ as a substrate for information recording media such as a magnetic disk substrate.
-Al ₂ O ₃ -RO system glass (where R is a divalent metal) is focused on, and in this glass, the influence of the glass component on the specific elastic modulus was investigated, and the materials currently known. It is an object of the present invention to provide a new glass material having a higher specific elastic modulus. It is another object of the present invention to provide an information recording medium substrate using the above material, and an information recording medium using this substrate.

[0005]

To achieve the above object, the present invention is as follows. A material used for a substrate for an information recording medium, which is made of glass of SiO ₂ —Al ₂ O ₃ —RO system (where R is a divalent metal), wherein the glass is 20
Information recording comprising a material characterized by containing mol% or more of Al ₂ O ₃ [Claim 1], a glass of SiO ₂ —Al ₂ O ₃ —RO system (where R is a divalent metal). A material used for a medium substrate, characterized in that the glass contains 20 mol% or more of MgO as RO [claim 2] SiO ₂ -Al ₂ O ₃ -RO system (where R is two A material used for a substrate for an information recording medium made of glass (which is a valent metal), wherein the glass further contains Y ₂ O ₃ (claim 3), Y ₂ O ₃ is 0. .5 to 17 mol% of the above-mentioned material (claim 4), any one of the above-mentioned materials containing either or both of TiO ₂ and ZrO ₂ (claim 5), and the material of the present invention An information recording medium substrate [claim 6], wherein the information recording medium is a magnetic disk. [7] and a magnetic disk having at least a magnetic layer on the substrate of the present invention [claim 8].

That is, as a result of the study by the present inventors, Al ₂ O
₃ , MgO, and Y ₂ O ₃ contribute to the improvement of the specific elastic modulus and Young's modulus, and contain Al ₂ O ₃ or MgO in a relatively large amount,
It was also found that glass having a high specific elastic modulus can be obtained by adding Y ₂ O ₃ . Based on this fact, a glass having a desired specific elastic modulus and Young's modulus can be obtained by appropriately determining the composition of the glass.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. In SiO ₂ -Al ₂ O ₃ -RO based glass used in information (description of items common to the glass of the present invention) recording medium substrate material and description of the substrate present invention, SiO ₂ is one of the fundamental components of the glass Acts as a network structure-forming oxide and has the effect of improving the crystallization stability of the glass structure. The content of SiO ₂ is preferably 25 to 55 mol%. If it is 25 mol% or less, the crystallization stability of the glass deteriorates, and it is difficult to produce a stable glass that can be mass-produced. On the other hand, if it exceeds 55 mol%, the specific elastic modulus and Young's modulus of the glass suddenly decrease. More preferably, it is 30 to 50 mol%. It is a divalent metal oxide
As RO, MgO, CaO, ZnO, NiO or the like can be used. However, there is no intention to limit to these.

Further, the specific elastic modulus and Young's modulus of glass are improved.
In order to further₂And ZrO₂ A kind selected from
It is preferable to add. In that case, TiO₂And / or ZrO₂
Is 5 mol% or more in total, so that the specific elastic modulus and
The effect of improving the Young's modulus can be obtained. TiO
₂Young without significantly increasing the specific gravity of the glass
The rate can be improved. However, too many
If it is contained in a large amount, the phase separation tendency of the glass is strengthened, rather
It may deteriorate the crystallization stability and homogeneity of the glass.
Therefore, it is preferable to set the amount to 25 mol% or less.
It is even more preferable that the content be less than 1%. ZrO₂The content of
It is preferable to suppress it to 8 mol% or less. Over 8 mol%
Then, the high temperature solubility of the glass deteriorates significantly, and the glass surface
This is because the surface flatness also deteriorates and the specific gravity also increases.
It Further, it is preferably 6 mol% or less.

Further, in order to improve the melting property of glass, Li
₂ O can also be added. However, adding too much tends to reduce the Young's modulus, so a small amount (for example, 2
Mol% or less) is preferable. Further, when Li ₂ O is contained, it is possible to carry out a chemical strengthening treatment by ion exchange in order to enhance the strength of the glass. On the other hand, Li ₂ O
In the case of a non-alkali glass containing no glass, when a thin film is formed on a substrate made of this glass, it is possible to prevent the alkaline component from diffusing into the thin film on the substrate and adversely affecting it. Further, in order to improve the crystallization stability of the glass,
_{B 2 O 3, P 2 O} 5, V 2 O 5, GeO 2, Ga 2 O 3, may be added such as HfO _2. As a desulfurizing agent for homogenizing glass, a small amount of As ₂ O ₃ , Sb ₂ O _3, etc. (eg 3 mol% or less)
May be added. In addition, ZnO, SrO, NiO, CoO, Fe ₂ O
₃ , CuO, Cr ₂ O ₃ , B ₂ O ₃ , P ₂ O ₅ , V ₂ O _{5 and the} like may be added in order to adjust the high temperature solubility and physical properties of the glass. When adding a small amount of coloring agents such as V ₂ O ₅ , Cr ₂ O ₃ , CuO, and CoO to glass, make the glass have infrared absorption properties and effectively heat-treat the magnetic layer by irradiation with a heating lamp. You can

The method for producing the glass and glass substrate of the present invention is not particularly limited, and various glass production methods can be used. For example, a high-temperature melting method, that is, a glass raw material in a predetermined ratio is melted in air or an inert gas atmosphere, and the glass is homogenized by bubbling, adding a defoaming agent, stirring, etc. Plate glass is formed by a method such as dolo forming, and thereafter, processing such as grinding and polishing is performed to obtain a substrate having a desired size and shape.
In the polishing, lapping and polishing with polishing powder such as cerium oxide can be performed to bring the surface accuracy to a range of 3 to 5 angstroms, for example.

Description of glass according to claim 1 The glass according to claim 1 contains Al ₂ O _{3 in an amount} of 20 mol% or more. In the SiO ₂ —Al ₂ O ₃ —RO glass, the higher the Al ₂ O ₃ content, the higher the specific elastic modulus. When the Al ₂ O ₃ content is 20 mol% or more, a glass having a specific elastic modulus larger than that of the glass conventionally known as a substrate for information recording medium, for example, 38 × 10 ⁶ Nm / kg or more. Can be obtained. The upper limit of the Al ₂ O ₃ content is preferably 40 mol%. When Al ₂ O ₃ is more than 40 mol%, the high temperature meltability of glass may be deteriorated and the crystallization stability may not be obtained. The Al ₂ O ₃ content is preferably in the range of 21 to 35 mol%, more preferably 25 to 35 mol%. When Al ₂ O ₃ is contained by 20 mol% or more, as RO,
It is preferable to use at least one selected from MgO and CaO. When a large amount of Al ₂ O ₃ is contained, these components effectively act as components such as stabilizing the glass structure and lowering the high temperature viscosity to facilitate melting. However, if these components are contained too much, the crystallization stability of the glass may be impaired. Therefore, MgO + CaO is 15-40
It is suitable to set it in the range of mol%.

Description of glass according to claim 2 The glass according to claim 2 contains 20 mol% of MgO as RO.
Contains more than In SiO ₂ -Al ₂ O ₃ -RO based glass, Mg
The higher the O 2 content, the higher the specific elastic modulus. When the MgO content is 20 mol% or more, it is possible to obtain a glass having a specific elastic modulus higher than that of the glass conventionally known as a substrate for information recording medium, for example, 38 × 10 ⁶ Nm / kg or more. You can The upper limit of the MgO content is 45 mol%
Is preferred. If the MgO content is more than 45 mol%, the crystallization stability of the glass may not be obtained. Mg
The O 2 content is preferably in the range of 20-40 mol%. Further, when the content of MgO is 20 mol% or more, Al ₂ O ₃
Is preferably 5 to 40 mol%. When Al ₂ O ₃ is less than 5 mol%, the stabilization of the glass structure may be impaired, and when it exceeds 40 mol%, the high temperature meltability of the glass may be deteriorated and the crystallization stability may not be obtained. CaO may be contained as RO in addition to MgO. CaO is
It mainly functions to improve the high temperature meltability and crystallization stability of glass. However, if the CaO content is too high, the specific elastic modulus of the glass may be reduced. Therefore, the CaO content is preferably 27 mol% or less.

Description of Glasses According to Claims 3 and 4 The glass according to claims 3 and 4 contains Y ₂ O ₃ . SiO ₂
In the -Al ₂ O ₃ -RO glass, the specific elastic modulus can be increased by incorporating Y ₂ O ₃ . The Y ₂ O ₃ content is preferably 0.5 to 17 mol%. Y ₂ O ₃ improves the Young's modulus and, as a result, the specific elastic modulus,
If it is 0.5 mol%, the effect is difficult to appear. On the other hand, Y ₂ O ₃ increases Young's modulus as well as specific gravity, so that if the content exceeds a certain amount, the effect of increasing the specific elastic modulus reaches a ceiling. That is, when the Y ₂ O ₃ content exceeds 17 mol%, it does not contribute to the improvement of the specific elastic modulus. Furthermore, Y ₂
From the viewpoint that O ₃ is expensive, it is preferable to add a small amount. Y ₂ O ₃ additive effect, SiO ₂ -Al ₂ O ₃ -RO
It can be obtained irrespective of the content of Al ₂ O ₃ or MgO as RO in the system glass, but Y in the glass containing 20 mol% or more of Al ₂ O ₃ of the present invention and the glass containing 20 mol% or more of MgO ₂ O ₃ can also be added. Especially Al ₂ O ₃ is 2
In the case of glass containing 0 mol% or more, the addition of Y ₂ O ₃ is effective in improving the specific elastic modulus and the high temperature meltability of the glass.

Description of Information Recording Medium Substrate The information recording medium substrate of the present invention is characterized by being made of the above-mentioned glass material of the present invention. Examples of the information recording medium include a magnetic recording medium,
Examples of magnetic recording media include magnetic disks such as hard disks. The size and shape of the substrate can be appropriately determined according to the application. Furthermore, the substrate of the present invention is characterized by having high surface smoothness. The high surface smoothness specifically means that the surface roughness (Ra) is 5 Å or less. The smoothness of the substrate surface has an advantage that when a magnetic disk is used, the distance between the magnetic head and the magnetic disk can be reduced and the recording density can be increased.

Description of Magnetic Disk The magnetic disk (hard disk) of the present invention is characterized in that at least a magnetic layer is formed on the main surface of the above-mentioned substrate. As the layers other than the magnetic layer, various known layers can be appropriately provided as necessary. Such layers are
From the viewpoint of function, examples include a base layer, a protective layer, a lubricating layer, and an unevenness control layer. Various thin film forming techniques are used to form each of these layers. The material of the magnetic layer is not particularly limited. Examples of the magnetic layer include Co-based, ferrite-based, iron-
Examples include rare earth materials. The magnetic layer is a horizontal magnetic recording,
Any magnetic layer for perpendicular magnetic recording may be used. Specific examples of the magnetic layer include CoPt and CoC containing Co as a main component.
r, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiCrPt, CoNiCrT
Magnetic thin films such as a, CoCrPtTa, and CoCrPtSiO can be used. Alternatively, the magnetic layer may be divided into non-magnetic layers to form a multilayer structure in which noise is reduced. The underlayer in the magnetic layer is
It is selected according to the magnetic layer. As the underlayer, for example,
At least one or more materials selected from non-magnetic metals such as Cr, Mo, Ta, Ti, W, V, B, and Al, or an underlayer made of oxides, nitrides, and carbides of these metals can be used. . In the case of the magnetic layer containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving the magnetic characteristics. The base layer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are laminated. For example, Al / Cr / CrMo,
Examples include a multi-layer underlayer such as Al / Cr / Cr.

Further, an unevenness control layer may be provided between the substrate and the magnetic layer or on the magnetic layer to prevent the magnetic head and the magnetic disk from being attracted to each other. By providing this unevenness control layer, the surface roughness of the magnetic disk is adjusted appropriately, so that the magnetic head and the magnetic disk do not stick to each other, and a highly reliable magnetic disk can be obtained. Various materials and forming methods for the unevenness control layer are known and are not particularly limited. For example, as the material of the unevenness control layer, Al, Ag, Ti, Nb, Ta, Bi, Si, Zr, Cr, Cu, Au,
At least one metal selected from Sn, Pd, Sb, Ge, Mg, or the like, an alloy thereof, or an underlayer made of an oxide, a nitride, a carbide thereof, or the like can be given.
From the viewpoint of easy formation, Al simple substance or Al alloy,
A metal containing Al as a main component such as Al oxide or Al nitride is desirable. Further, considering the head stiction, the surface roughness of the unevenness forming layer is preferably Rmax = 50 to 300 angstrom. A more preferable range is Rmax = 100 to 200 angstrom. 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, the magnetic head and the magnetic disk are damaged, and the head crashes due to the attraction. It is not preferable because it causes Also, Rmax is 3
When it exceeds 00 angstrom, the glide height (glide height) becomes large and the recording density is lowered, which is not preferable. It should be noted that, without providing the unevenness control layer, the glass substrate surface may be provided with unevenness by means such as etching treatment or laser light irradiation and then subjected to texturing treatment.

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 device or the like. Further, these protective films may be a single layer, or may be a multi-layer structure composed of the same or different types of films. Another protective layer may be formed on the protective layer or instead of the protective film. For example, colloidal silica fine particles may be dispersed and applied in a solution of tetraalkoxylane diluted with an alcohol-based solvent on the protective layer, and further baked to form a silicon oxide (SiO ₂ ) film. In this case, it functions as both a protective film and an unevenness control layer. Although various proposals have been made for the lubricating layer, in general, a liquid lubricant such as perfluoropolyether is diluted with a solvent such as Freon, and the surface of the medium is dipping, spin-coated, or sprayed. It is applied by, and heat-treated as necessary to form.

[0018]

EXAMPLES The present invention will be described in more detail based on the following examples. Method for Manufacturing Glass Substrate for Magnetic Disk Hereinafter, the present invention will be described in more detail with reference to Examples. As Examples 1 to 10 starting _{material, SiO 2, Al 2 O 3} , Al (OH) 3, MgO, Ca
Using CO _3, Y ₂ O _3, and _{TiO 2, ZrO 2, Li 2} O, and 250~300g weighed in a predetermined ratio, thoroughly mixed to form a formulation batch, placed in a platinum crucible, Glass was melted at 1550 ° C. in air for 3 to 5 hours. After melting, the glass melt is poured into a predetermined carbon mold, allowed to cool to the glass transition temperature, immediately placed in an annealing furnace, and annealed within the glass transition temperature range for about 1 hour to room temperature in the furnace. Chilled The obtained glass is a glass containing substantially no crystal particles in which crystals that can be observed with a microscope do not precipitate. The obtained glass sample was cut into a disk shape, and the main surface was polished with cerium oxide to obtain a glass substrate for a magnetic disk. Table 1 shows the measurement results of the composition, surface roughness (Ra), specific gravity, Young's modulus and specific elastic modulus of the obtained glass substrate for magnetic disk. Comparative Example 1 For comparison, Table 2 shows the composition and characteristics of the chemically strengthened glass substrate by ion exchange (Comparative Example 1) described in JP-A-1-239036.

[0019]

[Table 1]

[0020]

[Table 2]

[0021] Table 1 of Example 1, comparing Example 2 and 3, the Young's modulus and the specific main components are believed to contribute to the elastic modulus Al ₂ O _3, MgO, of Y ₂ O _3, Al ₂ O _When only ₃ is changed, the Young's modulus is increased and the specific gravity is decreased by containing a large amount of Al ₂ O ₃ , and as a result, the specific elastic modulus is increased. Example 1 and Example 5,
And comparing Example 3 and Example 4, the main components Al ₂ O ₃ , MgO, which are considered to contribute to Young's modulus and specific elastic modulus,
It can be seen that when only MgO of Y ₂ O ₃ is changed, the Young's modulus and the specific elastic modulus are increased by containing a large amount of MgO. Comparing Example 6 and Example 7, Y ₂
It can be seen that inclusion of O ₃ increases Young's modulus and specific elastic modulus. From the results of Examples 1 to 10,
Further, it can be seen that the materials to which TiO ₂ and ZrO ₂ are added can obtain high Young's modulus and high specific elastic modulus. Thus, Al ₂ O ₃
Of 20 mol% or more, MgO of 20 mol% or more, or Y ₂ O ₃ contained, the Young's modulus and the specific elastic modulus can be effectively improved. On the other hand, since the chemically strengthened glass substrate of Comparative Example 1 has a small content of Al ₂ O ₃ and contains neither MgO ₂ nor Y ₂ O ₃ , the Young's modulus and the specific elastic modulus are significantly inferior to those of the present invention. .

Method of Manufacturing Magnetic Disk As shown in FIG. 1, the magnetic disk 1 of the present invention comprises an unevenness control layer 3, an underlayer 4,
The magnetic layer 5, the protective layer 6, and the lubricating layer 7 are formed.
Explaining each layer in detail, the substrate 1 has an outer diameter of 65.
mmφ, central hole diameter 20 mmφ, thickness 0.381 mm
Of the disk, and both of its main surfaces were precision-polished so that the surface roughness was Ra = 4 angstroms and Rmax = 40 angstroms. The roughness control layer has an average roughness of 50 Å and a surface roughness Rmax.
Is 150 Å, nitrogen content is 5 to 35%
Is a thin film of AlN. The underlayer is a CrV thin film with 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 with a thickness of about 300 Å, and the composition ratio is Co: 76 at.
%, Pt: 6.6 at% and Cr: 17.4 at%. The protective layer is a carbon thin film having a thickness of about 100 Å. The lubricating layer is formed by coating a lubricating layer made of perfluoropolyether on the carbon protective layer by a spin coating method to have a thickness of 8 angstrom.

Next, a method of manufacturing a magnetic disk according to an embodiment of the present invention will be described. First, the glass manufactured in this example was manufactured to have an outer diameter of 65 mmφ and a central hole diameter of 20 mm.
Φ, 0.381 mm thick disk is ground, and both main surfaces have surface roughness Ra = 4 Å, Rmax =
A glass substrate for a magnetic disk is obtained by precision polishing to a thickness of 40 Å. Next, after setting the glass substrate in the substrate holder, it is sent to the preparation chamber of the in-line sputtering device. Then, the holder on which the glass substrate was set was sent into the first chamber where the Al target was etched, the pressure was 4 mtorr, the substrate temperature was 350 ° C.,
Sputtering is performed in an Ar + N ₂ gas (N ₂ = 4%) atmosphere.
As a result, an AlN thin film (unevenness forming layer) having a surface roughness Rmax of 150 Å and a film thickness of 50 Å was obtained on the glass substrate. Next, the holder on which the glass substrate on which the AlN film is formed is set is set to CrV (Cr: 83a).
t%, V: 17 at%) The second chamber in which the target is installed, CoPtCr (Co: 76 at%, Pt: 6.6 at)
%, Cr: 17.4 at%) continuously and sequentially sends the film to the third chamber in which the target is installed to form a film on the substrate. These films have a pressure of 2 mtorr, a substrate temperature of 350 ° C,
Sputtering is performed in an Ar atmosphere to obtain a CrV underlayer having a film thickness of about 600 Å and a CoPtCr magnetic layer having a film thickness of about 300 Å. Then, the unevenness control layer, the underlayer,
The laminated body on which the magnetic layer is formed is sent to a fourth chamber provided with a heater for heat treatment. At this time, the inside of the fourth chamber is set to an Ar gas (pressure of 2 mtorr) atmosphere, and as shown in Table 2, the heat treatment is performed while changing the heat treatment temperature. The above-mentioned CrV underlayer and CoPtCr were prepared except that the above-mentioned substrate was sent to the fifth chamber in which a carbon target was installed and the film was formed in an atmosphere of Ar + H ₂ gas (H ₂ = 6%).
Under the same film forming conditions as the magnetic layer, a carbon protective layer having a film thickness of about 100 Å is obtained. Finally, the substrate on which the carbon protective layer has been formed is taken out of the in-line sputtering device, and perfluoropolyether is applied to the surface of the carbon protective layer by a dipping method to form a lubricating layer having a thickness of 8 Å. I got a magnetic disk. The present invention has been described above with reference to the preferred embodiments, but the present invention is not limited to the above embodiments.

According to the present invention, the SiO ₂ -Al ₂ O ₃ -RO system glass (where R is a divalent metal) preferable as a substrate for an information recording medium such as a magnetic disk substrate is currently known. It is possible to provide a glass material exhibiting a higher specific elastic modulus (= Young's modulus / specific gravity) than the existing materials. Further, it is possible to provide an information recording medium substrate and an information recording medium which can be thinned using this material.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a magnetic disk 1 of the present invention in which an unevenness control layer 3, an underlayer 4, a magnetic layer 5, a protective layer 6, and a lubricating layer 7 are sequentially formed on a glass substrate 2.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-100137 (JP, A) European patent application publication 710627 (EP, A 1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C03C 1/00-14/00

Claims (8)

(57) [Claims] 1. A SiO ₂ -containing Al ₂ O ₃ of 20 mol% or more.
Al ₂ O ₃ -RO based (wherein, R is a divalent metal) Ri Do of glass, for an information recording medium that is substantially free of crystal grain
Glass substrate. 2. Si containing 20 mol% or more of MgO as RO
O ₂ -Al ₂ O ₃ -RO based (wherein, R is a divalent metal) Ri Do of glass, the information recording medium is substantially free of crystal grain
Glass substrate for body. 3. A SiO ₂ -Al ₂ O ₃ -RO based further contains Y ₂ O ₃ (wherein, R is a divalent metal) Ri Do of glass, the actual
A glass substrate for an information recording medium that does not qualitatively contain crystal particles. 4. The substrate according to claim _3, which contains Y ₂ O ₃ in an amount of 0.5 to 17 mol%. 5. The substrate according to claim 1, which contains one or both of TiO ₂ and ZrO ₂ . 6. The contract wherein the information recording medium is a magnetic disk.
The substrate according to any one of claims 1 to 5. 7. A group according to any one of claims 1 to 5.
An information recording medium provided with a plate. 8. A group according to any one of claims 1 to 5.
A magnet characterized by having at least a magnetic layer on the plate.
Damn disc.