JP3412804B2 - Information recording medium substrate - Google Patents

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 used for the substrate, a chemically strengthened glass, 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, a glass for chemical strengthening used for manufacturing the substrate, The present invention relates to a chemically strengthened glass constituting the substrate obtained by chemically strengthening the same, and a highly reliable magnetic disk using the substrate for an information recording medium.

[0002]

2. Description of the Related Art In recent years, the demand for information recording media such as magnetic disks, optical disks, and magneto-optical disks has been rapidly increasing with the progress of electronics technology, particularly information-related technology represented by computers. Plastic and inorganic glass are known as materials for the substrate used in such an information recording medium, but the substrate made of plastic causes warping and surface wobbling with changes in the environment such as temperature and humidity. However, since it has a drawback that it is inferior in dimensional stability, recently, inorganic glass, particularly chemically strengthened glass, has attracted attention, and its application to substrates for information recording media has been attempted.

This 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 therein and the monovalent ions in the molten salt are exchanged and chemically strengthened.

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

The information recording medium substrate has not only flatness and chemical durability, but also in recent years, particularly in recent years, it has high reliability that can cope with high-speed rotation of the driving device and thinning and high recording density of the recording medium. There is a demand for a substrate, that is, a substrate that is thin and does not crack or deform.

However, generally, as the rotation speed increases, the amount of deflection during rotation increases, and this tendency becomes more remarkable as the specific gravity increases, 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 and BaO as an essential component. Particularly, in the examples of the publication, a glass composition having a high specific gravity containing these in relatively large amounts. Therefore, it is difficult to construct a reliable substrate using the chemically strengthened glass obtained from it.

Further, in order to achieve higher recording density, the flying height of the head tends to become lower, and in particular, the magnetoresistive head which is expected as the next-generation head of the induction type head. The flying height of the (MR head) is extremely low. Therefore, in addition to bending, deformation, and resonance during rotation, if the surface of the disk is rough, damage due to contact between the disk substrate and the head, data write / read failures, and other undesirable situations may occur. is there. In this regard, the glass for chemical strengthening of (2) above contains 2% by weight or more of Z as an essential component.
Since it contains rO ₂ , it is difficult to obtain a chemically strengthened glass having a smooth surface.

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

On the other hand, in the chemical strengthening glass of (4) above, ion exchange is performed at 370 ° C.,
According to the examples in the publication, in order to obtain an ion exchange layer having a thickness of about 300 μm, it is necessary to soak the molten salt for 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 requires a long time, and the chemical strengthening treatment cannot be efficiently performed.

[0010]

Under these circumstances, the first object of the present invention is to carry out efficient ion exchange, to facilitate chemical strengthening having a deep strained layer and a high bending strength. To provide a highly reliable substrate for an information recording medium, which is obtained by using a glass for chemical strengthening capable of giving a glass and which can respond to a high-speed rotation of a driving device, a thin recording medium and a high recording density. Especially.

A second object of the present invention is to use the above-mentioned substrate for an information recording medium having excellent performance, to enable efficient ion exchange, to easily provide a deep strained layer and a high bending strength. Another object of the present invention is to provide a glass for chemical strengthening which gives the chemically strengthened glass.

A third object of the present invention is to provide a magnetic disk using the above-mentioned information recording medium substrate.

[0013]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that the glass for chemical strengthening has a specific composition and properties, Based on this finding, the present invention has been completed.

That is, the first object of the present invention is SiO.
_A substrate for an information recording medium comprising chemically strengthened glass obtained from _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 information recording medium, characterized in that the total content of SiO ₂ , Al ₂ O ₃ and R ₂ O exceeds 98% by weight, and the specific elastic modulus is 30 × 10 ² or more (hereinafter referred to as information recording medium. Substrate I. It may be simply referred to as substrate I.), and the composition is substantially SiO ₂ 61.0 to 7.
5.0% by weight, Al ₂ O ₃ 10.0 to 22.0% by weight,
Li ₂ O 4.0 to 8.0 wt% and Na ₂ O 10.
A substrate for an information recording medium made of a chemically strengthened glass obtained from a chemically strengthened glass of 1 to 15.0% by weight (hereinafter,
This is referred to as the information recording medium substrate II. It may be simply referred to as the substrate II. ) Is achieved.

A second object of the present invention is SiO ₂ −.
A glass for chemical strengthening of Al ₂ O ₃ —R ₂ O system (where R is an alkali metal), which comprises SiO ₂ and Al ₂ O _3.
And R ₂ O have a total content of more than 98% by weight and a specific elastic modulus of 30 × 10 ² or more, a glass for chemical strengthening (hereinafter referred to as glass for chemical strengthening I), composition. Is substantially SiO ₂ 61.0 to 75.0% by weight, Al ₂
O ₃ 10.0-22.0 wt%, Li ₂ O 4.0~
Glass for chemical strengthening (hereinafter referred to as glass II for chemical strengthening), characterized by being 8.0% by weight and 10.1-15.0% by weight of Na ₂ O, and the above glass I for chemical strengthening. , II are chemically strengthened and chemically strengthened glass (hereinafter referred to as chemically strengthened glasses I and II, respectively).

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

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION First, a glass for chemical strengthening I used in a substrate I for an information recording medium of the present invention will be described. The chemically strengthened glass I 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 the weight percentage. In this glass for chemical strengthening, SiO ₂ is a main component that forms the glass skeleton, and Al ₂ O ₃ is a component that improves chemical durability and promotes ion exchange. Also, R ₂ O
Of these, Li ₂ O and / or Na ₂ O are preferable, and Li ₂ O is the most preferable component as an alkali ion to be subjected to ion exchange. In the glass I for chemical strengthening of the present invention, the above-mentioned SiO ₂ , Al ₂ O ₃ and R _{2 are used.}
When the total content with O exceeds 98% by weight, a glass having a specific gravity of less than 2.45 can be obtained, and as a result, a glass having a high specific elastic modulus can be obtained. Also Li ₂ O and / or N
The total amount of a ₂ O is preferably 15.0 to 20.0% by weight.
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 credibility of the glass may be deteriorated. Conversely, if the total content of Na ₂ O and / or Li ₂ O is less than 15%, the chemical resistance may be reduced. The ion exchange performance in strengthening may deteriorate, and a sufficiently thick compressive stress layer may not be obtained by low temperature and short time chemical strengthening treatment.

The glass I for chemical strengthening 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 preferable. If this weight ratio is less than 0.145, the viscosity of the glass becomes extremely high, which may make it difficult to melt. If it exceeds 0.33, the Young's modulus of the glass tends to decrease and the crystallinity tends to increase. To be From the viewpoints of glass viscosity, Young's modulus of glass, balance of crystallinity and the like, a particularly preferable weight ratio is in the range of 0.15 to 0.25.

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

The chemical strengthening glass I may be any one having the above-mentioned properties, and the content of each component is not particularly limited, but usually the chemical strengthening glass II described below.
It is similar to the case of.

Next, the chemically strengthening glass II used in the substrate II for the information recording medium of the present invention will be described. In this glass for chemical strengthening II, the composition is substantially SiO ₂
61.0 to 75.0% by weight, Al ₂ O ₃ 10.0 to 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 the main component forming the glass skeleton as described above,
If the content is less than 61.0% by weight, the devitrification resistance is lowered, a glass that can be stably produced cannot be obtained, and the viscosity is lowered, which makes molding difficult. Melting becomes difficult. From the viewpoint of devitrification resistance, viscosity, moldability, etc., the preferable SiO ₂ content is 62.0 to 7
It is in the range of 2.0% by weight.

Al ₂ O ₃ is a component that improves chemical durability and promotes ion exchange as described above, and if the content is less than 10.0% by weight, the above effect is not sufficiently exhibited. However, if it exceeds 22.0% by weight, the melting property and devitrification resistance of glass deteriorate. From the standpoint of balance between chemical durability, ion exchangeability, glass meltability and devitrification resistance, the preferred Al ₂ O ₃ content is 13.0.
˜20.0% by weight.

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

Na ₂ O is a component for obtaining a chemically strengthened glass like 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 strained layer having a sufficient thickness, and if it exceeds 15.0% by weight, the chemical durability is lowered. From the viewpoint of the performance and chemical durability of the chemically strengthened glass, the preferable Na ₂ O content 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
The total content of iO ₂ , Al ₂ O ₃ , Li ₂ O and Na ₂ O is 9
A content of more than 8% by weight is suitable. If this total content exceeds 98% by weight, the specific gravity falls below 2.45, and 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 this glass II for chemical strengthening, the essential components SiO ₂ , Al ₂ O ₃ , Li ₂ O and Na ₂ O are used.
Together with MgO 0-1.5 wt%, CaO 0-1.
5% by weight, ZnO 0-1.5% by weight, ZrO ₂ 0-
1.5% by weight, TiO ₂ 0 to 1.5% by weight, B ₂ O ₃
It may contain 0 to 1.0 wt%, Sb ₂ O ₃ 0 to 1.0 wt% 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, but when they exceed 1.5% by weight, ion exchange is inhibited and the strained layer of the chemically strengthened glass obtained is obtained. Is not preferable because it reduces the thickness. Further, B ₂ O ₃ has an effect of improving the meltability of glass by adding a small amount, but if it exceeds 1.0% by weight, ion exchange is hindered, and the thickness of the strain layer of the chemically strengthened glass obtained is 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 property, but if it exceeds 1.5% by weight, the specific gravity increases and the melting property decreases, so Is not preferable because the surface smoothness of is deteriorated. TiO ₂ has the effect of improving the glass meltability by adding a small amount, but if it exceeds 1.5% by weight, ion exchange is hindered and the thickness of the strain layer of the chemically strengthened glass obtained becomes small. Not preferable.

Further, Sb ₂ O ₃ and As ₂ O ₃ are refining agents, and if both exceed 1.0% by weight, the chemical strengthening property is deteriorated and the specific gravity is increased, which is not preferable. In particular, S
The total content of b ₂ O ₃ and As ₂ O ₃ is preferably in the range of 0 to 1.0% by weight.

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

Therefore, the alkali non-elution property is one of the properties required for the information recording medium substrate. The alkali non-elution property is considered to have a correlation with the content of Al ₂ O ₃ and the value of the surface compressive stress after chemical strengthening. Al ₂ O
₃ is a component that improves the exchangeability between alkali ions during chemical strengthening, while suppressing the elution of alkali ions.

The surface compressive stress is a stress generated when the alkali metal ions in the glass surface layer are replaced with alkali metal ions having a larger ionic radius in the chemical strengthening step, and the movement of the alkali metal ions in the glass surface layer is caused. If the stress is large, the elution of alkali metal ions to the outside of the glass is suppressed because it acts to hinder it.

In this respect, 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 the alkali elution is extremely low, and when the substrate for an information recording medium is constructed, it is contained in the magnetic layer. The risk of alkali metal diffusion is extremely low.

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

The chemically strengthened glasses I and II are obtained by chemically strengthening the above-mentioned chemically strengthened glasses I and II of the present invention. This chemical strengthening treatment is not particularly limited, and a conventionally known method, for example, a glass for chemical strengthening in a treatment bath containing Na ions and / or K ions is used.
It can be carried out by subjecting I and II to an ion exchange treatment. It is essential that this treatment be carried out at a temperature below the strain point of 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, but the treatment bath is not limited to nitrate, and sulfate, bisulfate, carbonate , Bicarbonate or halide may be used. When the treatment bath contains Na ions, the Na ions exchange ions with Li ions in the glass, and when the treatment bath contains K ions, the K ions exchange with Li and Na ions in the glass. If ion-exchanged and the treatment bath further 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, alkali metal ions in the glass surface layer part are replaced with alkali metal ions having a larger ionic radius, a strained layer is formed in the glass surface layer part, a compressive stress is formed on the glass surface, and a tensile stress is formed inside the glass. By doing so, the glass is chemically strengthened. As described above, the glass for chemical strengthening I, 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,
The chemically strengthened glasses I and II have excellent fracture resistance.

Thus, in the chemically strengthened glasses I and II obtained by chemically strengthening the chemically strengthened glasses I and II of the present invention, in order to obtain a reliable and excellent performance substrate for information recording media. The strained layer has a 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, g / mm ² or more, preferably 49 kg / mm ² or more.

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 a chemical that is unlikely to self-destruct. 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.
m ² or more, and in some cases, 49 kg / mm ² or more. The methods for measuring the tensile stress, compressive stress and bending strength will be described later.

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

The steps of grinding and polishing are generally roughly divided into (1) roughing (rough grinding), (2) sanding (fine grinding and lapping), (3) first polishing (polishing), (4) Each step of the second polishing (final polishing, polishing). By the synergistic effect of these precision polishing steps and 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, information recording 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 treatment of a mixed solution of hydrofluoric acid and nitric acid or a concavo-convex film of aluminum or the like is formed on the surface of the substrate.
Alternatively, texturing may be performed by making unevenness by means of irradiation with laser light or ultraviolet light.

Further, as the information recording medium substrate,
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 change amount with respect to a full flat is 3.0 μm or less. Is preferable, and further, even if the thickness h is 0.7 mm or less, the flatness is preferably 2.0 μm or less.

The information recording medium substrate of the present invention is used as a substrate for an information recording medium such as a magnetic disk, a magneto-optical disk, an optical disk, etc., and is particularly suitable as a magnetic disk substrate. As the magnetic disk substrate,
Although not particularly limited, 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 preferable. .

The magnetic disk of the present invention comprises at least a magnetic layer provided on the above-mentioned magnetic disk substrate, and is for a magnetic disk made of the chemically strengthened glass of the present invention having a predetermined flatness and surface roughness. On the substrate, usually 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 is
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 of Cr alone or a Cr alloy from the viewpoint of improving the magnetic characteristics.

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

In the present invention, an unevenness control layer may be provided between the glass substrate and the magnetic layer or on the magnetic layer to prevent the magnetic head and the magnetic recording medium from being attracted to each other. 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.

Various materials and methods for forming the unevenness control layer are known and are not particularly limited, but a non-magnetic metal material having a melting point higher than that of the glass substrate for an information recording medium of the present invention described above is used. It is preferable. Examples of the material for the unevenness control layer include Al, Ag, and T.
i, Nb, Ta, Bi, Si, Zr, Cr, Cu, A
At least one metal selected from u, Sn, Pd, Sb, Ge, Mg, or the like, an alloy thereof, or an oxide, a nitride, or a carbide thereof can be used.

From the viewpoint of easy formation and effect, the material of the unevenness control layer is preferably a simple substance of Al, an Al alloy, a metal compound containing aluminum as a main component such as aluminum oxide or aluminum nitride. Further, in consideration of head stiction, the surface roughness of the unevenness control layer is preferably Rmax = 50 to 300 angstrom. A more preferable range is Rmax = 1
It is from 00 to 200 angstroms. If Rmax is less than 50 angstroms, the surface of the magnetic recording medium is almost flat, so that the magnetic head and the magnetic recording medium are attracted to each other, the magnetic head and the magnetic recording medium are damaged, or the head is crashed due to the attraction. Also, R
When max exceeds 300 angstroms, the glide height (glide height) becomes large and the recording density is lowered, 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 and used 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,
Examples of the magnetic thin film include CoCrTaPt and CoCrPtSiO. The magnetic layer includes a magnetic film and a nonmagnetic film (for example,
A multilayer structure (for example, CoPtCr / CrMo) that is divided by Cr, CrMo, CrV, etc. to reduce noise.
/ CoPtCr, CoCrTaPt / CrMo / CoC
rTaPt).

As a magnetic layer for a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), a Co-based alloy containing Y, Si, a rare earth element, Hf, and G is used.
Also included are impurity elements selected from e, Sn, and Zn, or those containing oxide films of these impurity elements.

In addition to the above, as the magnetic layer, 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 be in either an inner surface type or a vertical 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 device. Also,
These protective layers may be a single layer or may have a multi-layer 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 on a Cr film diluted with an alcohol solvent on a Cr film, and further baked to form a silicon oxide (SiO ₂ ) film. You may form.

Further, the lubricating layer in the magnetic disk of the present invention is not particularly limited, and for example, perfluoropolyether (PEPE), which is a liquid lubricant, is diluted with a solvent such as Freon, and the surface of the medium is subjected to a dipping method. It is applied by a spin coating method, a spray method, or the like, and is subjected to heat treatment as necessary to form it.

[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 by the following methods. <Glass for chemical strengthening> (1) Young's modulus sufficiently annealed 20 mm × 20 mm × 100 mm
The longitudinal wave velocity of 5MHz ultrasonic wave was measured using the sample of
It was calculated by the following formula.

[0059]

[Chemical 1] (2) Specific elastic modulus The specific elastic modulus was calculated from Young's modulus / specific gravity. (3) Alkali elution amount It was measured according to the method described in the specification text (method for measuring increase in alkali metal concentration in treatment bath). (4) 50 cc of liquidus temperature glass was placed in a platinum crucible, covered with a lid, and held 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 × microscope. The temperature shown in the table is the lowest temperature at which crystals do not precipitate.

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

(Examples 1 to 14, Comparative Examples 1 to 3) Tables 1 to 1
Silica powder, aluminum hydroxide, alumina, lithium carbonate, sodium carbonate, sodium nitrate, magnesium carbonate, calcium carbonate, zinc oxide, zirconium oxide, titanium oxide, boric acid, oxidation so that the oxide film composition shown in Table 3 is obtained. After preparing a mixture of about 2 kg using antimony, arsenous acid, etc., 1450 to 1 in a platinum crucible.
After melting and refining at 550 ° C., a glass for chemical strengthening was produced by casting in an iron mold and annealing. The physical properties are shown in Tables 1 to 3.

Next, from this glass, 25 × 85 × 1.5
An optically polished flat plate of mm was prepared and used as a sample for chemical strengthening. Then, the weight ratio of NaNO ₃ and KNO ₃ is 4:
Using the mixed salt of No. 6, the sample for chemical strengthening above
Chemically strengthened glass was produced by treating at 0 ° C. for the time shown in Tables 1 to 3. 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, each of the glasses for chemical strengthening of the present invention of Examples has a specific gravity of 2.54 or less,
Young's modulus is 7500 kg / mm ² or more, specific elastic modulus is 30
It is × 10 ² . Further, considering the above Tables 1 to 3 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 bending 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, the chemically strengthened glass 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 has high reliability such that deformation or resonance does not easily occur at high speed rotation. It turns out that

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

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. As a measurement sample, the stress distribution of this sample was measured with a strain gauge. Example 6
1 is a stress distribution chart of Comparative Example 1, and FIG. 2 is a stress distribution chart of Comparative Example 1.
3 shows a stress distribution chart of Comparative Example 2.

From this figure, it is understood that in the glass for chemical strengthening of the present invention of Example 6, strong stress and a deep strained layer can be obtained by the chemical strengthening treatment at low temperature for a short time. Further, since the tensile stress inside the glass is not too large, the risk of breakage due to slight scratches on the surface is small.

On the other hand, in the glass for chemical strengthening of Comparative Example 1,
Since the amount of the alkali metal oxide film component is small, the amount of ion exchange is small and the thickness of the strained layer is small. In addition, since a large amount of alkaline earth metal oxide film having an action of hindering ion exchange is contained, extremely strong tensile stress is generated inside the glass.
As a result, the higher the strength of the glass, the higher the risk of natural destruction.

Further, the glass for chemical strengthening of Comparative Example 2 is A
Since the content of l ₂ O ₃ is small and is out of the range of the present invention, ion exchange is extremely difficult. Therefore, in the obtained chemically strengthened glass, the compressive stress on the surface is weak and the thickness of the strained layer is small.

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

When a glide test was performed on the obtained magnetic disk, no hits (the head scratched the projections on the magnetic disk surface) or crashes (the head collided with the projections on the magnetic disk surface) were not observed. . The surface roughness (Ra) of the information recording medium substrate is 5
It was angstrom, and the flatness was 1 μm.

(Embodiment 16) Al (film thickness 50 angstrom) / Cr (1,000 angstrom) on both sides of the same information recording medium substrate as used in the embodiment 15.
/ CrMo (100 Å) underlayer, CoPtCr (120 Å) / CrM
A magnetic layer of o (50 angstrom) / CoPtCr (120 angstrom) and a Cr (50 angstrom) protective layer were formed by an in-line type sputtering apparatus.

Organosilicon compound solution (mixture of water, isopropanol and tetraethoxysilane) in which SiO ₂ particles (particle size 100 angstrom) are dispersed in the above substrate.
The protective layer made of SiO ₂ and having a texture function is formed by immersing it in a solvent, and then the protective layer is dipped 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 observed. It was also confirmed that no defect was generated in the film such as the magnetic layer.

Example 17 In Example 16, the underlayer was Al / Cr / Cr and the magnetic layer was CoNiCrTa.
A magnetic disk was obtained in the same manner as in Example 16 except that the above was adopted. It was confirmed that this magnetic disk was the same as in Example 16.

[0077]

INDUSTRIAL APPLICABILITY According to the present invention, a glass for chemical strengthening is used, which enables efficient ion exchange and can easily give a chemically strengthened glass having a deep strained layer and a high bending strength. By using the chemically strengthened glass as the substrate material, it is possible to obtain a highly reliable substrate for an information recording medium which can cope with high-speed rotation of the driving device, thinning of the recording medium and high recording density. 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 drawings]

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

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

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

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B 5/62-5/82 C03C 3/083

Claims (9)

(57) [Claims] 1. SiO ₂ 61.0 to 75.0% by weight,
Al ₂ O ₃ 10.0~22.0 wt%, _Li 2 O
4.0 to 8.0 _wt%, Na 2 O _10.1~15.0
% By weight, MgO 0-1.5% by weight, CaO 0-1.
5 wt%, ZnO 0 to 1.5 wt%, _ZrO 2 0 to
Contains 1.5% by weight of SiO ₂ , Al ₂ O ₃ and Li ₂ O
And a Na ₂ O content of more than 98% by weight, and a liquidus temperature of 980 ° C. or less. A chemically strengthened glass obtained from the glass for chemical strengthening, having a specific elastic modulus of 30 × 10 ^2.
A substrate for an information recording medium having the above. 2. The substrate for information recording medium according to claim 1, which is a chemically strengthened glass obtained by an ion exchange treatment using a treatment bath containing Na ions and K ions. 3. Li ₂ O + N in glass for chemical strengthening
a total amount of ₂ O is, the information recording medium substrate according to claim 1 or 2, characterized in that it is from 15.0 to 20.0 wt%. 4. The glass for chemical strengthening comprises (Li ₂ O + Na
₂ O) / (SiO ₂ + Al ₂ O ₃ ) weight ratio 0.145 to
Substrate for an information recording medium according to any one of claims Koko 1-3 is of 0.33. 5. The composition of the glass for chemical strengthening is SiO ₂
62.0 to 72.0% by weight, Al ₂ O ₃ 13.0 to ₂
0.0% by weight, Li ₂ O 4.5 to 6.5% by weight and Na ₂ O 10.1 to 12.0% by weight.
4. The information recording medium substrate according to any one of 4 above. 6. The glass for chemical strengthening comprises pulverizing twice its specific gravity (g) into an average particle size of 425 to 600 μm,
When immersed in 2 kg of a mixed salt of potassium nitrate and sodium nitrate in a weight ratio of 6: 4 at 380 ° C. for 4 hours for ion exchange treatment, and then immersed in a treatment bath of 100 ml of pure water at 80 ° C. for 24 hours The amount of increase in alkali metal concentration of the treatment bath is 7.0 mg / liter or less.
An information recording medium substrate according to claim 5 . 7. A strained layer having a thickness of 80 μm or more is obtained within 8 hours when the glass for chemical strengthening is chemically strengthened by ion exchange treatment in a treatment bath containing Na ions and / or K ions. substrate for information recording medium according to any one of claims 1 to 6 intended. 8. A surface roughness (Ra) of the information recording medium substrate according to any one of claims 1 to 7 comprising chemically tempered glass is less than 10 angstroms. 9. The substrate for information recording medium according to any one of claims 1-8, a magnetic disk formed by providing at least a magnetic layer.