JPH11232627A - Substrate for information record medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate, for an information recording medium, which can deal with the high-speed rotation of a drive and with the thin shape and the high recording density of the record medium and whose reliability is high, to provide a glass, for chemical reinforcement, which is used for the substrate and to provide a magnetic disk which uses the substrate. SOLUTION: A substrate for an information record medium is composed of a chemically reinforced glass obtained from a glass, for chemical reinforcement in which the total content of SiO2 , Al2 O3 and R2 O (where R represents an alkaline metal) exceeds 98 wt. % and whose specific mudulus of elasticity is at 30×10<2> or higher. In a magnetic disk, at least a magnetic layer is formed on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate for an information recording medium, a chemically strengthened glass and a chemically strengthened glass used for the substrate, and a magnetic disk using the substrate. More specifically, the present invention relates to a highly reliable information recording medium substrate capable of coping with high-speed rotation of a driving device and thinning and high recording density of a recording medium, glass for chemical strengthening used in the production of this substrate, and The present invention relates to a chemically strengthened glass constituting the substrate obtained by chemically strengthening the glass, and a highly reliable magnetic disk using the information recording medium substrate.

[0002]

2. Description of the Related Art In recent years, demand for information recording media such as a magnetic disk, an optical disk, and a magneto-optical disk has been rapidly increasing with the development of electronics technology, particularly information-related technology represented by a computer. Plastic and inorganic glass are known as the material of the substrate used for such an information recording medium. However, the plastic substrate is likely to be warped or run out with changes in the environment such as temperature and humidity. Inorganic glass, particularly chemically strengthened glass, has recently attracted attention because of its drawback of poor dimensional stability, and its application to substrates for information recording media has been attempted.

[0003] The chemically strengthened glass is generally prepared by immersing the glass to be treated in a molten salt containing monovalent ions having a larger ionic radius than the alkali metal contained in the glass to be treated. The alkali metal ions in the molten salt are exchanged for monovalent ions in the molten salt, and are chemically strengthened.

Various glass has been disclosed as the glass to be treated, that is, the glass for chemical strengthening, used for a substrate for an information recording medium or the like. For example, (1) Si
O ₂ 60.0-70.0 wt%, Al ₂ O ₃ 0.5.0
14.0 wt%, R ₂ O (wherein, R is an alkali metal) 10.0 to 32.0 wt%, ZnO 1.0 to 1
5.0 wt% and B ₂ O ₃ from 1.1 to 14.0 those containing by weight% (KOKOKU 4-70262 JP) (2)
One containing 58 to 70% by weight of SiO _2, 13 to 22% by weight of Al ₂ O ₃ , 6 to 10% by weight of Li ₂ O, 5 to 12% by weight of Na ₂ O and _{2 to} 5% by weight of ZrO ₂ 8-48537 JP), (3) SiO ₂ 55~
62 wt%, Al ₂ O ₃ 10~18 wt%, ZrO ₂
2 to 10% by weight, MgO 2 to 5% by weight, BaO 0.
1 to 3 wt%, Na ₂ O 12~15 wt%, K ₂ O ₂
5 wt%, P ₂ O ₅ 0~7 wt% and TiO ₂
0.5 to 5% by weight, and the total amount of Al ₂ O ₃ and TiO ₂ is 13 to 20% by weight (Japanese Patent Publication No. 1-1)
67245 JP), (4) SiO ₂ 64~70 wt%, Al ₂ O ₃ 14~20 wt%, Li ₂ O 4 to 6 wt%, Na ₂ O 7 to 10% by weight, MgO 0 to 4 wt% And ZrO ₂ containing 0 to 1.5% by weight (Japanese Patent Publication No. 6-76224). However, these glasses for chemical strengthening have some drawbacks as shown below for substrates of information recording media, and are not always satisfactory.

[0005] In addition to flatness and chemical durability, a substrate for an information recording medium has high reliability especially capable of coping with high-speed rotation of a driving device and thinning and high recording density of a recording medium. There is a need for a substrate, that is, a substrate that is not cracked or deformed even if it is thin.

However, in general, as the rotation speed increases, the amount of deflection during rotation increases, and this tendency becomes more pronounced as the specific gravity becomes higher if the Young's modulus is the same. The glass for chemical strengthening of the above (1) contains a high specific gravity component such as ZnO or BaO as an essential component. Particularly, in the examples in the publication, a glass composition containing a relatively large amount of such a high specific gravity is used. For this reason, it is difficult to form a reliable substrate using the chemically strengthened glass obtained therefrom.

Further, the flying height of the head tends to be further reduced in order to achieve a higher recording density. In particular, a magnetoresistive head expected as a next-generation head of an inductive head (MR head) has a very low flying height. For this reason, not only bending, deformation, and resonance during rotation, but also a large surface roughness of the disk may lead to undesired situations such as damage due to contact between the disk substrate and the head and defective data writing / reading in the future. is there. In this regard, the glass for chemical strengthening of the above (2) has a Z component of 2% by weight or more
Since rO ₂ is contained, it is difficult to obtain chemically strengthened glass having a smooth surface.

Further, when chemically strengthening glass for chemical strengthening in order to obtain a substrate for an information recording medium, conventionally, at a temperature lower than the strain point, in order to improve the strength without deforming the glass, In order to avoid decomposition of a molten salt in an ion exchange treatment bath for chemical strengthening, ion exchange is performed at a temperature lower than the strain point. However, the glass for chemical strengthening of (3) is
As shown in the examples in the gazette, the ion exchange temperature is required to be 480 ° C. or higher, so that the deformation of the disk-shaped substrate and the decomposition of the molten salt are inevitable.

On the other hand, in the glass for chemical strengthening of (4), ion exchange is performed at 370 ° C.
According to the examples in the gazette, in order to obtain an ion exchange layer of about 300 μm, it is necessary to immerse in a molten salt for as long as 22 hours, and the ion exchange efficiency is extremely poor. As described above, when the ion exchange treatment is performed at a relatively low temperature, the treatment generally takes a long time, and the chemical strengthening treatment cannot be performed efficiently.

[0010]

SUMMARY OF THE INVENTION Under such circumstances, a first object of the present invention is to provide a chemical strengthening method capable of performing efficient ion exchange, easily having a deep strain layer and a high bending strength. Provided is a highly reliable information recording medium substrate that can be used for high-speed rotation of a drive device, thinning of a recording medium, high recording density, and the like, which is obtained by using glass for chemical strengthening that can provide glass. It is in.

A second object of the present invention is to provide a substrate for an information recording medium having the above-mentioned excellent performance, capable of performing efficient ion exchange, easily providing a deep strain layer and high bending strength. It is an object of the present invention to provide a glass for chemical strengthening that provides a chemically strengthened glass having the same.

Further, a third object of the present invention is to provide a magnetic disk using the information recording medium substrate.

[0013]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, by using a glass having a specific composition and properties as a glass for chemical strengthening, Have been achieved, and the present invention has been completed based on this finding.

That is, a first object of the present invention is to use
_A substrate for an information recording medium comprising a chemically strengthened glass obtained from a _2- Al ₂ O ₃ —R ₂ O-based (where R is an alkali metal) chemically strengthened glass, wherein the chemically strengthened glass is A substrate for an information recording medium (hereinafter referred to as an information recording medium) having a total content of SiO ₂ , Al ₂ O ₃ and R ₂ O of more than 98% by weight and a specific elastic modulus of 30 × 10 ² or more; referred to as a use substrate I. Incidentally may be simply referred to as substrate I.), as well as composition, substantially SiO ₂ 61.0 to 7
5.0 wt%, Al ₂ O ₃ from 10.0 to 22.0 wt%,
Li ₂ O 4.0 to 8.0 wt% and Na ₂ O 10.
A substrate for an information recording medium (hereinafter, referred to as a substrate) made of chemically strengthened glass obtained from 1 to 15.0% by weight.
This is referred to as an information recording medium substrate II. It may be simply referred to as substrate II. ).

[0015] A second object of the present invention is to provide a SiO _2-
Al ₂ O ₃ -R ₂ O system (wherein, R represents an alkali metal) a chemically strengthened glass for, SiO ₂ and Al ₂ O ₃
And R ₂ O total content exceeds 98% by weight of, and the glass for chemical strengthening, wherein the specific elastic modulus is 30 × 10 ² or more (hereinafter referred to as chemically strengthened glass I.), The composition Is substantially 61.0 to 75.0% by weight of SiO ₂ and Al ₂
O ₃ 10.0-22.0 wt%, Li ₂ O 4.0~
8.0 wt% and Na ₂ O from 10.1 to 15.0 glass for chemical strengthening, characterized in that the weight% (hereinafter, referred to as chemically strengthened glass II.), As well as the chemically strengthened glass I , And II are chemically strengthened (hereinafter, referred to as chemically strengthened glasses I and II, respectively).

Further, a third object of the present invention is achieved by a magnetic disk having at least a magnetic layer provided on the information recording medium substrates I and II.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a glass for chemical strengthening I used for a substrate I for an information recording medium according to the present invention will be described. This glass I for chemical strengthening is SiO ₂ —Al ₂ O ₃ —
R ₂ O-based (where R is an alkali metal) glass having a total content of SiO ₂ , Al ₂ O ₃ and R ₂ O of 98
It is necessary to exceed by weight. In the glass for chemical strengthening, SiO ₂ is a main component for forming a glass skeleton, and Al ₂ O ₃ is a component for improving chemical durability and promoting ion exchange. In addition, R ₂ O
Preferred are Li ₂ O and / or Na ₂ O, and in particular, Li ₂ O is the most preferred component as an alkali ion to be subjected to ion exchange. In the glass for chemical strengthening I of the present invention, the above SiO ₂ , Al ₂ O ₃ and R ₂
When the total content with O exceeds 98% by weight, a glass having a specific gravity of less than 2.45 is obtained, and as a result, a glass having a high specific elastic modulus is obtained. Li ₂ O and / or N
the total amount of a ₂ O is preferably 15.0 to 20.0 wt%.
The reason is that the total amount of Li ₂ O and / or Na ₂ O is 2
If it exceeds 0% by weight, the chemical durability may deteriorate, and the long-term reliability of the glass may be deteriorated. Conversely, if the total amount of Na ₂ O and / or Li ₂ O is less than 15%, the chemical durability may decrease. The ion exchange performance in strengthening is reduced, and a sufficiently thick compressive stress layer may not be obtained by low-temperature, short-time chemical strengthening treatment.

The glass for chemical strengthening I is (Li
₂ O + Na ₂ O) / (SiO ₂ + Al ₂ O ₃ ) weight ratio 0.1
Those in the range of 45 to 0.33 are preferred. If the weight ratio is less than 0.145, the viscosity of the glass becomes extremely high, so that melting may be difficult. If the weight ratio exceeds 0.33, the Young's modulus of the glass tends to decrease and the degree of crystallinity tends to increase. Can be A particularly preferable weight ratio is in the range of 0.15 to 0.25 from the viewpoint of the balance of glass viscosity, glass Young's modulus, crystallinity, and the like.

In particular, (Li ₂ O + Na ₂ O) / (SiO ₂ +
Al ₂ O ₃ ) is 0.18 or more, and Na ₂ O / (Na ₂ O
When (+ Li ₂ O) is 0.67 or more, a glass having better chemical durability and alkali elution resistance can be obtained.

Further, in the glass I for chemical strengthening, it is necessary that the specific elastic modulus is 30 × 10 ² or more. If the specific elastic modulus is less than 30 × 10 ^2, it is difficult to obtain a highly reliable information recording medium substrate. From the viewpoint of the reliability of the substrate, a preferable specific elastic modulus is 32 × 10 ² or more. In addition, this specific elastic modulus is Young's modulus / specific gravity, and the Young's modulus is a value measured by a method described later.

The glass for chemical strengthening I may have the above-mentioned properties, and the content of each component is not particularly limited.
Is the same as

Next, the glass for chemical strengthening II used for the substrate II for information recording media of the present invention will be described. In the glass for chemical strengthening II, the composition is substantially SiO ₂
61.0 to 75.0 wt%, Al ₂ O ₃ 10.0~2
2.0% by weight, Li ₂ O 4.0 to 8.0 wt% and Na ₂ O 10.1 to 15.0 wt%. SiO ₂ is a main component forming a glass skeleton as described above,
If the content is less than 61.0% by weight, the devitrification resistance is reduced, and a glass that can be manufactured stably cannot be obtained. In addition, the viscosity is reduced and molding is difficult. Melting becomes difficult. From the viewpoints of devitrification resistance, viscosity, moldability and the like, the preferable content of SiO ₂ is 62.0 to 7
The range is 2.0% by weight.

Al ₂ O ₃ is a component that enhances chemical durability and promotes ion exchange as described above. If its content is less than 10.0% by weight, the above effects are not sufficiently exhibited. However, if it exceeds 22.0% by weight, the melting property and the devitrification resistance of the glass decrease. From the viewpoints of balance of chemical durability, ion exchangeability, glass melting property, and devitrification resistance, the preferable content of Al ₂ O ₃ is 13.0.
２20.0% by weight.

Li ₂ O is the most preferred component as an alkali ion to be subjected to ion exchange. If its content is less than 4.0% by weight, chemically strengthened glass having a thick strained layer and strength when subjected to chemical strengthening treatment. Is difficult to obtain,
If it exceeds 8.0% by weight, chemical durability and devitrification resistance decrease. The performance and chemical durability of chemically strengthened glass,
From the viewpoint of devitrification resistance and the like, the preferred Li ₂ O content is in the range of 4.5 to 6.5% by weight.

Na ₂ O is a component for obtaining chemically strengthened glass similarly to the above Li ₂ O, and its content is 10.
If it is less than 1% by weight, it is difficult to obtain a chemically strengthened glass having a sufficiently thick strained layer, and if it exceeds 15.0% by weight, the chemical durability is reduced. From the viewpoint of the performance and chemical durability of the chemically strengthened glass, the preferable content of Na ₂ O is in the range of 10.1 to 12.0% by weight.

If desired, K ₂ may be used as an alkaline component.
O may be used, but since it does not participate in ion exchange, its content is about 0 to 1.0% by weight.

As the glass for chemical strengthening II, the above S
When the total content of iO ₂ , Al ₂ O ₃ , Li ₂ O and Na ₂ O is 9
Those exceeding 8% by weight are preferred. When the total content exceeds 98% by weight, the specific gravity falls below 2.45, and a glass having a high specific elastic modulus can be obtained. Glass for chemical strengthening
In II, the specific elastic modulus is usually 30 × 10 ² or more, preferably 32 × 10 ² or more.

In the glass for chemical strengthening II, the essential components SiO ₂ , Al ₂ O ₃ , Li ₂ O and Na ₂ O
Together with 0 to 1.5% by weight of MgO and 0 to 1% of CaO.
5% by weight, ZnO 0-1.5% by weight, ZrO ₂ 0-0
1.5 wt%, TiO ₂ 0 to 1.5 wt%, B ₂ O ₃
0-1.0 wt%, may contain Sb ₂ O ₃ 0-1.0% by weight and As ₂ O ₃ 0 to 1.0 wt%. Here, MgO, CaO and ZnO have the effect of improving the meltability of the glass by adding a small amount thereof, but if any of them exceeds 1.5% by weight, the ion exchange is inhibited, and the strained layer of the obtained chemically strengthened glass is obtained. Is undesirably small. Further, B ₂ O ₃ has an effect of improving the melting property of glass when added in a small amount. However, when it exceeds 1.0% by weight, ion exchange is inhibited, and the thickness of the strained layer of the chemically strengthened glass obtained is reduced. It is not preferable because it becomes smaller.

On the other hand, ZrO ₂ has the effect of lowering the melt viscosity of the glass without impairing the chemical strengthening properties. Is not preferred, because the surface smoothness of the sample becomes poor. TiO ₂ has the effect of improving the meltability of the glass when added in a small amount. However, when it exceeds 1.5% by weight, ion exchange is inhibited and the thickness of the strained layer of the chemically strengthened glass obtained becomes small. Not preferred.

Further, Sb ₂ O ₃ and As ₂ O ₃ are fining agents, and if both exceed 1.0% by weight, it is not preferable because it causes deterioration of chemical strengthening properties and an increase in specific gravity. In particular, S
b ₂ a total content of O ₃ and As ₂ O ₃ is good in the range of 0 to 1.0 wt%.

In the glass I and II for chemical strengthening of the present invention, the specific gravity is preferably 2.45 or less, particularly preferably 2.43 or less, from the viewpoint that a glass having a high specific elastic modulus can be obtained. The liquidus temperature is preferably 980 ° C. or lower from the viewpoint of moldability, and particularly preferably 930 ° C. or lower. The method for measuring the liquidus temperature will be described later. Further, a powder having twice the specific gravity (g) having an average particle size of 425 to 600 μm was immersed in 2 kg of a mixed salt of potassium nitrate and sodium nitrate at a weight ratio of 6: 4 at 380 ° C. for 4 hours, and ionized. After the exchange treatment, this was added to 100 m of pure water at 80 ° C.
1 when immersed in a treatment bath for 24 hours, the increase in alkali metal concentration in the treatment bath is preferably 7.0 mg / L or less, particularly preferably 5.3 mg / L or less. If the increase in alkali metal concentration exceeds 7.0 mg / liter, for example, when a magnetic disk is manufactured, alkali metal ions in the glass substrate may diffuse into the magnetic film and cause corrosion.

Therefore, the alkali non-eluting property is one of the characteristics required for the information recording medium substrate. It is considered that alkali non-elution has a correlation with the content of Al ₂ O ₃ and the value of surface compressive stress after chemical strengthening. Al ₂ O
Reference numeral ₃ is a component that improves the exchangeability between alkali ions during chemical strengthening, but suppresses elution of alkali ions.

The surface compressive stress is a stress generated when alkali metal ions in the glass surface layer are replaced by alkali metal ions having a larger ionic radius in the chemical strengthening step, and causes the movement of the alkali metal ions in the glass surface layer. If the stress is large, the elution of the alkali metal ion out of the glass is suppressed.

In this regard, the chemically strengthened glass of the present invention is made of Al
_In addition to containing a relatively large amount of ₂ O ₃ , the surface compressive stress is also relatively large due to the interaction of each component, so that the elution of alkali is extremely low. Extremely low risk of alkali metal diffusion.

The glass for chemical strengthening I and I of the present invention
As I, when chemically strengthened by ion exchange treatment in a treatment bath containing Na ions and / or K ions,
It is preferable that a strained layer having a thickness of 80 μm or more can be obtained within 8 hours from the viewpoint of excellent chemical strengthening property. In particular, a strained layer having a thickness of 80 μm or more can be obtained within 4 hours. The method for measuring the thickness of the strained layer will be described later.

The chemically strengthened glasses I and II are obtained by chemically strengthening the aforementioned chemically strengthened glasses I and II, respectively. The chemical strengthening treatment is not particularly limited, and may be performed by a conventionally known method, for example, in a treatment bath containing Na ions and / or K ions.
It can be carried out by subjecting I and II to ion exchange treatment. It is important to perform this treatment at a temperature below the strain point of the lath and at a temperature at which the molten salt does not decompose. Na
As the treatment bath containing ions and / or K ions, it is preferable to use a treatment bath containing sodium nitrate and / or potassium nitrate. However, the treatment bath is not limited to nitrate, and may be sulfate, bisulfate, or carbonate. , Bicarbonates and halides may be used. When the treatment bath contains Na ions, the Na ions ion-exchange with Li ions in the glass. When the treatment bath contains K ions, the K ions exchange with Li ions and Na ions in the glass. When the treatment bath contains Na ions and K ions, these Na ions and K ions are ion-exchanged with Li ions and Na ions in the glass, respectively. By this ion exchange, the alkali metal ions on the glass surface layer are replaced by alkali metal ions with a larger ionic radius, a strained layer is formed on the glass surface layer, and a compressive stress is formed on the glass surface and a tensile stress is formed inside the glass. This chemically strengthens the glass. As described above, the chemically strengthened glasses I and II of the present invention
Has excellent ion exchange performance, so the strained layer formed by ion exchange is deep and has high bending strength,
Chemically strengthened glasses I and II have excellent fracture resistance.

As described above, in the chemically strengthened glasses I and II obtained by chemically strengthening the chemically strengthened glasses I and II of the present invention, a reliable and excellent substrate for an information recording medium can be obtained. Has a strain layer thickness of 100 μm or more, a tensile stress of 7.0 kg / mm ² or less, a compressive stress of 5.0 kg / mm ² or more, and a bending strength of 45 k
Advantageously, it is at least g / mm ² , preferably at least 49 kg / mm ² .

That is, when the compressive stress and the tensile stress are within the above ranges and the thickness of the strained layer is 100 μm or more, an ideal stress distribution is formed in the cross section of the chemically strengthened glass, and the chemical breakdown hardly occurs. It becomes tempered glass.

The chemically strengthened glass and the information recording medium substrate made of this glass have a bending strength of 45 kg / m 2.
m ² or more, and in some cases, 49 kg / mm ² or more. The methods for measuring the tensile stress, the compressive stress and the bending strength will be described later.

The information recording medium substrate of the present invention comprises the above-mentioned chemically strengthened glass. The method for manufacturing the substrate is not particularly limited, and a conventionally known method can be used. For example, by molding directly into a disk shape by direct press method, or by down draw molding method, fusion method, after forming into a plate shape by a float method, etc., then processing into a disk shape, further grinding and polishing treatment, An information recording medium substrate having a desired size and shape is obtained.

The steps of grinding and polishing are usually roughly divided into (1) roughing (rough grinding), (2) sanding (fine grinding, lapping), (3) first polishing (polishing), (4) It consists of each step of second polishing (final polishing, polishing). By the synergistic effect of the precision polishing step and the chemically strengthened glass, it is possible to obtain a substrate for an information recording medium having a surface roughness (Ra) of 10 Å or less, and further, to record an information recording medium of 7 Å or less. It is also possible to obtain a medium substrate.

As a substrate for an information recording medium, if necessary, a wet etching process using a mixed solution of hydrofluoric acid and nitric acid or a concavo-convex film of aluminum or the like is formed on the substrate surface.
Alternatively, irregularities may be formed by means such as irradiation with laser light or ultraviolet light, and texturing may be performed.

Further, as the substrate for the information recording medium,
A substrate used for an information recording medium having a diameter of 2.5 inches or less and having a thickness h of 1.0 mm or less, a flatness which is a maximum value of a change amount with respect to a full flat is 3.0 μm or less. Is preferable, and even when the thickness h is 0.7 mm or less, the flatness is preferably 2.0 μm or less.

The substrate for an information recording medium of the present invention is used as a substrate for an information recording medium such as a magnetic disk, a magneto-optical disk, and an optical disk, and is particularly suitable as a substrate for a magnetic disk. As a substrate for this magnetic disk,
Although there is no particular limitation, for example, a magnetic disk substrate corresponding to a low flying head, a magnetic disk substrate corresponding to a magnetoresistive (MR) head or a large magnetoresistive (GMR) head, and the like are preferably exemplified. .

The magnetic disk of the present invention comprises at least a magnetic layer provided on the above-mentioned magnetic disk substrate, and has a predetermined flatness and surface roughness. On the substrate, usually an underlayer,
It can be manufactured by sequentially laminating a magnetic layer (recording layer), a protective layer and a lubricating layer.

The underlayer in the magnetic disk of the present invention comprises:
It is appropriately selected according to the magnetic layer provided thereon. For example, in the case of a magnetic layer containing Co as a main component, it is preferable to use an underlayer made of Cr alone or a Cr alloy from the viewpoint of improving magnetic properties.

As the underlayer, for example, Cr, Mo, T
a, a material made of at least one material selected from nonmagnetic metals such as Ti, W, V, B, and Al. 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, Cr / C
r, Cr / CrMo, Cr / CrV, CrV / CrV,
Al / Cr / CrMo, Al / Cr / Cr, Al / Cr
/ CrV, Al / CrV / CrV, etc.

In the present invention, an unevenness control layer may be provided between the glass substrate and the magnetic layer or above the magnetic layer to prevent the magnetic head and the magnetic recording medium from adsorbing. By providing this unevenness control layer, the surface roughness of the magnetic recording medium is appropriately adjusted, so that the magnetic head and the magnetic recording medium do not stick to each other, and a highly reliable magnetic recording medium can be obtained.

There are various known materials and methods for forming the concavo-convex control layer, and there is no particular limitation. For example, a non-magnetic metal material having a melting point higher than the melting point of the above-mentioned glass substrate for an information recording medium of the present invention is used. Is preferred. Examples of the material of such an unevenness control layer include Al, Ag, and T.
i, Nb, Ta, Bi, Si, Zr, Cr, Cu, A
At least one or more metals selected from u, Sn, Pd, Sb, Ge, Mg and the like, or alloys thereof, or oxides, nitrides, carbides, and the like thereof are exemplified.

The material of the unevenness control layer is preferably a metal compound containing aluminum as a main component, such as Al alone, an Al alloy, aluminum oxide, and aluminum nitride, from the viewpoint of easy formation and effectiveness. Further, in consideration of head stiction, the surface roughness of the unevenness control layer is desirably Rmax = 50 to 300 Å. A more preferred range is Rmax = 1
00 to 200 angstroms. When Rmax is less than 50 angstroms, the surface of the magnetic recording medium is nearly flat, so that the magnetic head and the magnetic recording medium are attracted, and the magnetic head and the magnetic recording medium may be damaged, or a head crash may occur due to the attracting. Also, R
If max exceeds 300 angstroms, the glide height (glide height) becomes large, which causes a decrease in recording density, which is not preferable.

The material of the magnetic layer in the magnetic disk of the present invention is not particularly limited, and can be appropriately selected from conventionally known materials. As this magnetic layer,
For example, CoPt, CoCr, Co containing Co as a main component
Ni, CoNiCr, CoCrTa, CoPtCr, C
oNiPt, CoNiCrPt, CoNiCrTa,
Magnetic thin films such as CoCrTaPt and CoCrPtSiO can be used. The magnetic layer is formed by converting the magnetic film to a non-magnetic film (for example,
Multi-layer structure (for example, CoPtCr / CrMo) in which noise is reduced by dividing by Cr, CrMo, CrV, etc.
/ CoPtCr, CoCrTaPt / CrMo / CoC
rTaPt).

As a magnetic layer corresponding to a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), Y, Si, rare earth elements, Hf, G
An impurity element selected from e, Sn, and Zn, or an element containing an oxide film of these impurity elements is also included.

As the magnetic layer, in addition to the above, magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a non-magnetic film made of ferrite, iron-rare earth, SiO ₂ , BN, or the like. It may be a granular structure or the like. Further, the magnetic layer may have any of an inner surface type and a perpendicular type recording format.

Next, the protective layer in the magnetic disk of the present invention is not particularly limited, and examples thereof include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective layers can be continuously formed with an underlayer, a magnetic layer, and the like by an in-line type sputtering apparatus. Also,
These protective layers may be a single layer or a multilayer structure composed of the same or different films.

In the present invention, another protective layer may be formed on the protective layer or in place of the protective layer. For example, instead of the above-mentioned protective layer, colloidal silica fine particles are dispersed and applied to a Cr film after diluting tetraalkoxylan with an alcohol-based solvent, and then fired to form a silicon oxide (SiO ₂ ) film. It may be formed.

The lubricating layer in the magnetic disk of the present invention is not particularly limited. For example, perfluoropolyether (PEPE), which is a liquid lubricant, is diluted with a solvent such as Freon, and the surface of the medium is dipped. It is applied by spin coating, spraying, or the like, and is formed by performing heat treatment as necessary.

[0057]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

The physical properties of the chemically strengthened glass and the chemically strengthened glass were determined according to the following methods. <Chemical strengthening glass> (1) Young's modulus 20 mm x 20 mm x 100 mm sufficiently annealed
The longitudinal wave velocity of the 5 MHz ultrasonic wave was measured using
It was calculated by the following equation.

[0059]

Embedded image (2) Specific elastic modulus The specific elastic modulus was determined from Young's modulus / specific gravity. (3) Alkali elution amount Measured according to the method described in the specification (method of measuring increase in alkali metal concentration in treatment bath). (4) Liquidus temperature 50 cc of glass was placed in a platinum crucible, covered, and kept in a muffle furnace at a predetermined temperature for 24 hours, and then the presence or absence of crystals on the glass surface and inside was observed using a 100-times microscope. The temperature shown in the table is the lowest temperature at which no crystals are precipitated.

<Chemically Tempered Glass> (1) Strain Layer Thickness The depth of the strain layer from the surface was measured by a Babinet correction method using a precision strain gauge manufactured by Toshiba Corporation. (2) Flexural strength A sample having a thickness of 1.5 mm and a width of 25 mm (end surface # 1000 finish) was measured by a three-point bending test with a span of 50 mm, and the average value of 10 samples was shown in the table. (3) Tensile stress Measured together with the strain layer thickness. (4) Compressive stress Measured together with the strain layer thickness.

(Examples 1 to 14, Comparative Examples 1 to 3)
In order to obtain the oxide film composition shown in Table 3, silica stone powder, aluminum hydroxide, alumina, lithium carbonate, sodium carbonate, sodium nitrate, magnesium carbonate, calcium carbonate, zinc oxide, zirconium oxide, titanium oxide, boric acid, oxide About 2 kg of a mixture was prepared using antimony, arsenic acid, etc., and then placed in a platinum crucible at 1450-1.
After melting and fining at 550 ° C., it was cast into an iron mold and annealed to produce a glass for chemical strengthening. The physical properties are shown in Tables 1 to 3.

Next, 25 × 85 × 1.5
An optically polished flat plate having a thickness of 2 mm was prepared and used as a sample for chemical strengthening. Then, the weight ratio of NaNO ₃ to KNO ₃ was 4:
Using the mixed salt of No. 6, the sample for chemical strengthening was 380
It processed at the temperature for 1 hour shown in Tables 1-3, and produced the chemically strengthened glass. The physical properties of this product are shown in Tables 1 to 3.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

As is clear from the table, the glasses for chemical strengthening of the present invention of the examples all have specific gravities of 2.54 or less.
Young's modulus is more than 7500 kg / mm ² , specific elastic modulus is 30
× 10 ² . Further, considering Tables 1 to 3 above and FIGS. 1 to 3 below, the chemically strengthened glass of the present invention has a strain layer thickness of 100 μm or more and a transverse rupture strength of 45 kg /.
mm ² or more, tensile stress is 7.0 kg / mm ² or less, and compressive stress is 5.0 kg / mm ² or more. Therefore, any glass for chemical strengthening obtained from the chemically strengthened glass of the present invention is suitable as a substrate material for an information recording medium, which is highly resistant to scratches and highly resistant to deformation and resonance during high-speed rotation. It turns out that it is.

Further, in the glass for chemical strengthening of the present invention of Example, although the amount of alkali elution is small, as in Comparative Example, A
It can be seen that when the content of l ₂ O ₃ is small and out of the range of the present invention, and when the content of the alkali metal oxide film is larger than the range of the present invention, the alkali elution amount is large. As described above, when the alkali elution amount is large, for example, when a magnetic disk is manufactured, alkali metal ions in the glass substrate may diffuse into the magnetic film and cause corrosion or the like.

Further, a plate having a polished surface of 25 mm × 85 mm × 1.0 mm was prepared from the glass for chemical strengthening of Example 6 and Comparative Examples 1 and 2 and subjected to chemical strengthening treatment, and then sliced in the cross-sectional direction. This was used as a measurement sample, and the stress distribution of this sample was measured with a strain gauge. Example 6
FIG. 1 shows a stress distribution diagram of FIG. 1, and FIG. 2 shows a stress distribution diagram of Comparative Example 1.
FIG. 3 shows a stress distribution diagram of Comparative Example 2.

From this figure, it can be seen that in the glass for chemical strengthening of the present invention of Example 6, a strong stress and a deep strain layer can be obtained by low-temperature and short-time chemical strengthening treatment. In addition, since the tensile stress inside the glass is not too large, there is little risk of breakage due to a slight surface scratch.

On the other hand, in the glass for chemical strengthening of Comparative Example 1,
Since the alkali metal oxide film component is small, the amount of ion exchange is small, and the thickness of the strained layer is small. Further, since a large amount of an alkaline earth metal oxide film having an action of preventing ion exchange is contained, a very strong tensile stress is generated inside the glass.
As a result, a glass that has a higher risk of spontaneous destruction as it seeks to obtain a higher strength is obtained.

The glass for chemical strengthening of Comparative Example 2 was A
Since the content of l ₂ O ₃ is small and out of the range of the present invention, ion exchange is extremely difficult. For this reason, the obtained chemically strengthened glass has low surface compressive stress and a small thickness of the strained layer.

(Example 15) Using the chemically strengthened glass obtained in Example 1, an in-line type was formed on both sides of an information recording medium substrate having a diameter of 2.5 inches and a thickness of 0.8 mm by a direct press method. Using a sputtering apparatus of
A texture layer, a CrMo underlayer, a CoPtCrTa magnetic layer, and a carbon protective layer were sequentially formed by sputtering with 1N to obtain a magnetic disk.

A glide test was performed on the obtained magnetic disk. As a result, no hit (the head touches a protrusion on the surface of the magnetic disk) or crash (the head collides with the protrusion on the surface of the magnetic disk) was not recognized. . The surface roughness (Ra) of the information recording medium substrate is 5
Angstrom, and the flatness was 1 μm.

(Example 16) Al (50 angstrom film thickness) / Cr (1,000 angstrom) film was formed on both surfaces of the same information recording medium substrate as used in the fifteenth embodiment.
/ CrMo (100 Å) underlayer, CoPtCr (120 Å) / CrM
A magnetic layer composed of o (50 angstroms) / CoPtCr (120 angstroms) and a protective layer of Cr (50 angstroms) were formed by an in-line type sputtering apparatus.

An organic silicon compound solution (a mixture of water, isopropanol, and tetraethoxysilane) in which SiO ₂ particles (particle diameter: 100 Å) are dispersed on the above substrate
To form a protective layer made of SiO ₂ having a texture function by baking and further dip-treating the protective layer with a lubricant made of perfluoropolyether to form a lubricating layer. A magnetic disk for head was obtained. When a glide test was performed on the obtained magnetic disk, no hit or crash was recognized. It was also confirmed that no defect occurred in the film such as the magnetic layer.

(Example 17) In Example 16, the underlayer was made of Al / Cr / Cr, and the magnetic layer was made of CoNiCrTa.
A magnetic disk was obtained in the same manner as in Example 16 except for the above. This magnetic disk was confirmed to be the same as in Example 16.

[0077]

According to the present invention, there is provided a glass for chemical strengthening, which enables efficient ion exchange and can easily provide a chemically strengthened glass having a deep strain layer and high bending strength. By using the chemically strengthened glass as the substrate material, a highly reliable information recording medium substrate that can cope with high-speed rotation of the driving device, thinning of the recording medium, and high recording density can be obtained. This information recording medium substrate is suitable, for example, as a magnetic disk substrate, a magneto-optical disk substrate, or an optical disk substrate.

[Brief description of the drawings]

FIG. 1 is a stress distribution diagram of one example of chemically strengthened glass obtained from the glass for chemical strengthening of Example 6.

FIG. 2 is a stress distribution diagram of one example of chemically strengthened glass obtained from the glass for chemical strengthening of Comparative Example 1.

FIG. 3 is a stress distribution diagram of one example of chemically strengthened glass obtained from the glass for chemical strengthening of Comparative Example 2.

Claims (13)

[Claims] 1. An SiO ₂ —Al ₂ O ₃ —R ₂ O system (provided that
R is an alkali metal) is a substrate for an information recording medium comprising a chemically strengthened glass obtained from the glass for chemical strengthening, wherein the glass for chemical strengthening is SiO ₂ , Al ₂ O _3, and R ₂ O.
Is more than 98% by weight and the specific elastic modulus is 30
× 10 ² or more, a substrate for an information recording medium. 2. In the glass for chemical strengthening, R ₂ O is Li ₂
O and / or Na ₂ O a substrate for information recording medium according to claim 1. 3. The total amount of Li ₂ O + Na ₂ O is 15.0.
3. The substrate for an information recording medium according to claim 2, wherein the amount is from 2 to 20.0% by weight. 4. The glass for chemical strengthening is (Li ₂ O + Na ₂
O) / (SiO ₂ + Al ₂ O ₃ ) weight ratio 0.145-0.
33. The information recording medium substrate according to claim 2, wherein the substrate is 33. 5. The composition according to claim 5, wherein the composition is substantially SiO ₂ 61.0-7.
5.0 wt%, Al ₂ O ₃ from 10.0 to 22.0 wt%,
Li ₂ O 4.0 to 8.0 wt% and Na ₂ O 10.
An information recording medium substrate comprising a chemically strengthened glass obtained from a glass for chemical strengthening of 1 to 15.0% by weight. 6. The chemical strengthening glass composition is substantially Si
O ₂ 62.0-72.0 wt%, Al ₂ O ₃ 13.0
6. The information recording medium substrate according to claim 5, wherein the content of Li ₂ O is 4.5 to 6.5 wt% and Na ₂ O is 10.1 to 12.0 wt%. 7. The glass for chemical strengthening has a liquidus temperature of 980 ° C.
The information recording medium substrate according to claim 1, wherein the substrate is: 8. The glass for chemical strengthening is pulverized to a weight twice as large as its specific gravity (g) to an average particle size of 425 to 600 μm,
After immersing in 2 kg of a mixed salt of potassium nitrate and sodium nitrate at a weight ratio of 6: 4 for 4 hours at 380 ° C. for 4 hours, and then immersing it in a treatment bath of 100 ml of pure water at 80 ° C. for 24 hours. 2. The treatment bath according to claim 1, wherein the amount of increase in alkali metal concentration is 7.0 mg / liter or less.
8. The information recording medium substrate according to any one of items 7 to 7. 9. When the glass for chemical strengthening is chemically strengthened by ion exchange in a treatment bath containing Na ions and / or K ions, a strained layer having a thickness of 80 μm or more can be obtained within 8 hours. The information recording medium substrate according to any one of claims 1 to 8, wherein 10. The information recording medium substrate according to claim 1, comprising a chemically strengthened glass having a surface roughness (Ra) of 10 Å or less. 11. A glass for chemical strengthening of the SiO ₂ —Al ₂ O ₃ —R ₂ O system (where R is an alkali metal), wherein a total content of SiO ₂ , Al ₂ O ₃ and R ₂ O is contained. Glass for chemical strengthening characterized in that the amount exceeds 98% by weight and the specific elastic modulus is 30 × 10 ² or more. 12. The composition according to claim 5, wherein the composition is substantially SiO ₂
75.0 wt%, Al ₂ O ₃ 10.0~22.0 wt%, Li ₂ O 4.0 to 8.0 wt% and Na ₂ O 1
Glass for chemical strengthening characterized by being 0.1 to 15.0% by weight. 13. A magnetic disk comprising at least a magnetic layer provided on the information recording medium substrate according to claim 1. Description: