JPH10226532A - Glass composition for magnetic disk substrate and magnetic disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a glass composition for magnetic disk substrate and a magnetic disk substrate capable of easily molding, easily grinding after the crystallization by heating and chemically strengthening by ion exchange after molding and grinding and excellent in chemical durability, mechanical strength, heat resistance, surface smoothness, surface flatness and small in the deterioration of magnetic film property. SOLUTION: The glass composition for magnetic disk substrate has a composition of by wt.%, 66-80 SiO2 , 5-15 Al2 O3 , 3-8.5 Li2 O, 0-3 Na2 O, 0-3 K2 O, 0.5-8 TiO2 , 3.5-8 ZrO2 , 0.5-3 P2 O5 , 0-2 Sb2 O3 and 0-2 Sb2 O3 as oxides and has a theoretical optical basicity of <=0.548. The magnetic disk substrate is strengthened by ion-exchanging after molding and grinding the composition. A main crystal phase formed by molding, heat-treating and grinding the composition in the magnetic disk substrate is Li2 O.2SiO2 or spodumene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a glass composition for a magnetic disk substrate and a magnetic disk substrate. More specifically, the present invention can be easily formed and easily polished even after depositing at least one of Li ₂ O.2SiO ₂ and spodumene as a main crystal phase by glass heat treatment. Or can be chemically strengthened by ion exchange of glass after molding and polishing, suitable for computer hard disk etc. which has excellent chemical durability, mechanical strength, heat resistance, surface flatness, surface smoothness The present invention relates to a glass composition for a magnetic disk substrate for producing a magnetic disk substrate, and a magnetic disk substrate obtained from the composition.

[0002]

2. Description of the Related Art Magnetic disks are mainly used as recording media for computers and the like. Conventionally, aluminum alloys have been used as magnetic disk substrate materials. In recent years, with the trend toward smaller, thinner, and higher recording densities of magnetic disks, there has been an increasing demand for high flatness and high smoothness. Since aluminum alloys cannot be used,
An alternative magnetic disk substrate material is needed. The characteristics required for a magnetic disk substrate include the flatness and smoothness of the disk surface and the high strength, high hardness, chemical durability, migration resistance, and heat resistance of the disk substrate. Therefore, it is necessary to increase the thickness of the disk and harden the surface. When the thickness of the disk is reduced, undulation occurs and the flatness deteriorates, so that the number of times the magnetic head collides with the disk increases, causing plastic deformation of the disk and data destruction.
Therefore, since the flying height (the gap between the magnetic head and the magnetic disk) cannot be reduced, there arises a problem that the recording density does not increase. Further, when the magnetic film is made of platinum, a potential is generated between the aluminum alloy substrate and the magnetic film to cause electric field corrosion, which causes a phenomenon that the magnetic film is attacked. Glass substrates for magnetic disks have been developed as substrate materials for solving the problems of these aluminum alloys. Glass substrates for magnetic disks are roughly classified into two types: an ion exchange type and a crystallized glass type. An ion exchange type glass substrate for a magnetic disk generally has a large amount of an alkali component in the glass, and the alkali component often migrates to the substrate surface, often causing a phenomenon of deteriorating the magnetic film characteristics.
Crystallized glass type glass substrates for magnetic disks have been developed to compensate for the disadvantages of aluminum alloy substrates and ion exchange type glass substrates, and various glass compositions have been proposed so far. JP-A-62-725
No. 47, JP-A-4-144938, JP-A-6
Li ₂ O—SiO ₂ -based crystallized glass proposed in JP-A-329440 and JP-A-7-157331 is a glass composition containing a large amount of an alkali component. Such a glass composition suppresses the movement of alkali ions by incorporating a certain amount of alkali components into the precipitated crystals, but since a considerable amount of alkali components remains even in the matrix glass that is not a crystal, the ion exchange type is used. Similarly, the properties of the magnetic film may be degraded by alkali migration, and it is difficult to cope with future thinning. In particular, Li ₂ O · SiO ₂ as proposed in JP-A-62-72547 (the lithium metasilicate) crystals, the chemical durability is very poor, which may worsen the magnetic film characteristics by the alkali migration . Li ₂ O—Al ₂ O ₃ —SiO ₂ -based crystallized glass proposed in JP-A-6-329439 is
Melting at a high temperature of 1550 ° C. or higher is required, and melting and molding are not easy. Further, the Li ₂ O—Al ₂ O ₃ —SiO ₂ -based crystallized glass proposed in Japanese Patent Application Laid-Open No. 7-247138 has the disadvantage that the chemical durability is inferior because the SiO ₂ component in the glass composition is small. There is.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to easily form a glass, and to easily polish the glass after crystallization by heat treatment, or to ion-exchange the glass after forming and polishing. Magnetic disk for producing magnetic disk substrates that can be chemically strengthened, have excellent chemical durability, mechanical strength, heat resistance, surface smoothness, surface flatness, and have less deterioration of magnetic film characteristics due to alkali migration An object of the present invention is to provide a glass composition for a substrate and a magnetic disk substrate.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the glass has a theoretical optical basicity of 0.548 or less, and is strengthened by ion exchange. When heat-treated, a glass composition having a specific composition in which Li ₂ O.2SiO ₂ and at least one crystal of spodumene are precipitated as main crystal phases can be easily formed and polished. In addition, they have found that they have excellent chemical and physical characteristics when used as a magnetic disk substrate, and have completed the present invention based on this finding. That is, the present invention provides:
SiO _2: 66 to 80 wt%, Al ₂ O _3: 5~15 wt%, Li ₂ O: 3~8.5 wt%, Na ₂ O: 0~3 wt%, K ₂ O: 0~3 by weight %, Provided that Li ₂ O + Na ₂ O +
K ₂ O: 3 to 10 wt%, TiO _2: 0.5 to 8 wt%,
ZrO _2: 3.5 to 8 wt%, P ₂ O _5: 0.5~3 wt%, Sb ₂ O _3: 0~2 wt%, As ₂ O _3: 0~2 wt%
And a glass composition for a magnetic disk substrate having a theoretical optical basicity of 0.548 or less. (2) As an oxide, SiO ₂ : 66 to 75% by weight, Al ₂ O ₃ : 5.5 to 10% by weight, Li ₂ O: 4 to 8.
5 wt%, Na ₂ O: 0 to 2 wt%, K ₂ O: 0 to 2 wt%, _{however, Li 2 O + Na 2 O} + K 2 O: 4~9 wt%,
TiO _2: 2 to 6 wt%, ZrO _2: 3.8~6.5 wt%, P ₂ O _5: 1~2.5 wt%, Sb ₂ O _3: 0~2 wt%, As ₂ O ₃ : A glass composition for a magnetic disk substrate having a composition of 0 to 2% by weight and a theoretical optical basicity of 0.548 or less;
SiO ₂ : 66 to 75% by weight, Al ₂ O ₃ : 5.5 to 7.5
Wt%, Li ₂ O: 5~8.5 wt%, Na ₂ O: 0~2
% By weight, K ₂ O: 0 to 2% by weight, provided that Li ₂ O + Na ₂
O + K ₂ O: 5~9 wt%, TiO _2: 2~4 wt%, Z
rO ₂ : 4.1 to 6% by weight, P ₂ O ₅ : 1 to 2.5% by weight,
Sb ₂ O _3: 0 to 1 wt%, As ₂ O _3: has the composition 0-1% by weight, for a magnetic disk substrate theoretical optical basicity is equal to or is 0.548 or less Glass composition,
(4) After molding and polishing the glass composition for a magnetic disk substrate according to any one of (1) to (3),
(5) Item (1): a magnetic disk substrate characterized in that the alkali metal ions in the glass surface layer are ion-exchanged with alkali metal ions having a larger ionic radius at a temperature between 550 ° C. and 550 ° C. to strengthen the magnetic disk. The glass composition for a magnetic disk substrate according to any one of (1) to (3), formed by molding, heat-treating and polishing, wherein the main crystal phase is Li ₂ O · 2Si.
A magnetic disk substrate characterized by being at least one of O ₂ and spodumene; (6) as an oxide:
SiO _2: 66 to 80 wt%, Al ₂ O _3: 5.5~10 wt%, Li ₂ O: 3~8.5 wt%, Na ₂ O: 0~3 wt%, K ₂ O: 0~ 3% by weight, provided that Li ₂ O + Na ₂ O
+ K ₂ O: 3~10 wt%, TiO _2: 0.5~8 wt%, ZrO _2: 3.5~8 wt%, P ₂ O _5: 0.5~3 wt%, Sb ₂ O _3: 0-2 wt%, As ₂ O _3: a glass composition having a composition of 0-2 weight%, molding, heat treatment, and polished was prepared, the main crystal phase of Li ₂ O · 2SiO ₂ and spodumene (7) The magnetic disk substrate according to (5) or (6), wherein the total crystallinity is 20% by volume or more, (8) The glass composition for a magnetic disk substrate according to any one of items (1) to (3), wherein the glass composition has a weight loss of 6 × 10 ⁻⁷ g / cm ² · h or less in a water elution test of glass by a powder method. (9) In a water dissolution test of glass or crystallized glass by the powder method, the weight loss was 6 × 10 ⁻⁷ g / cm ^2.
h. The magnetic disk substrate according to any one of (4) to (7), wherein h is equal to or less than h.

[0005]

DETAILED DESCRIPTION OF THE INVENTION Magnetic disk glass composition for substrates of the present invention, as the oxide, SiO _2: 66 to 80 wt%, Al ₂ O _3: 5~15 wt%, Li ₂ O: 3~8 .5 wt%, Na ₂ O: 0 to 3 wt%, K ₂ O: 0 to 3 wt%,
However, Li ₂ O + Na ₂ O + K ₂ O: 3 to 10% by weight, T
iO ₂ : 0.5 to 8% by weight, ZrO ₂ : 3.5 to 8% by weight,
P ₂ O ₅ : 0.5 to 3% by weight, Sb ₂ O ₃ : 0 to 2% by weight,
As ₂ O ₃ : having a composition of 0 to 2% by weight and a theoretical optical basicity of 0.548 or less. The glass composition for a magnetic disk substrate of the present invention may contain B ₂ O ₃ : 0 to 5 if necessary.
% By weight, MgO: 0 to 8% by weight, CaO: 0 to 5% by weight, SrO: 0 to 5% by weight, BaO: 0 to 5% by weight, Z
An oxide such as nO: 0 to 5% by weight and PbO: 0 to 3% by weight can be contained. In the composition of the present invention, SiO ₂ is a glass-forming oxide, and when the glass is subjected to heat treatment, the main crystal phases of Li ₂ O · 2SiO ₂ and spodumene (Li ₂ O · Al ₂ O ₃ .4SiO ₂ ) are formed. It is a component. When the content of SiO ₂ is less than 66% by weight, it is difficult to reduce the theoretical optical basicity of the glass to 0.548 or less, and the chemical durability deteriorates.
In the case of crystallization, the above crystals may not be easily precipitated. If the content of SiO ₂ exceeds 80% by weight, the melting temperature may be too high and the production may be difficult. S
The content of iO ₂ is more preferably 66 to 75% by weight in consideration of productivity. In the composition of the present invention, Al ₂ O ₃ is a glass intermediate oxide, and is a constituent component of spodumene which is a main crystal phase when glass is subjected to heat treatment. When the content of Al ₂ O ₃ is less than 5% by weight, the chemical durability deteriorates. Al ₂ O ₃ content of 15% by weight
If the melting point exceeds the above range, the melting temperature may increase, and production may be difficult. In consideration of chemical durability and productivity, the content of Al ₂ O ₃ is more preferably 5.5 to 10% by weight, and still more preferably 5.5 to 7.5% by weight.

In the composition of the present invention, Li ₂ O functions as a flux, and when the glass is ion-exchanged and strengthened, it is the smallest ion among alkali metal ions. A component that can strengthen the glass by ion exchange with a larger alkali metal ion with a larger radius, and when heat-treating the glass,
It is a constituent component of Li ₂ O · 2SiO _{2 as} a main crystal phase and spodumene. When the content of Li ₂ O is less than 3% by weight, the melting temperature becomes too high and ion exchange is performed.
When strengthening, ion exchange is difficult, and there is a possibility that characteristics may not be improved. When the glass is heat-treated, Li
There is a possibility that ₂ O · 2SiO ₂ and spodumene crystal are hardly precipitated. When the content of Li ₂ O exceeds 8.5% by weight, the theoretical optical basicity of the glass is hardly reduced to 0.548 or less, and the chemical durability and migration resistance are deteriorated, and the properties of the magnetic film are adversely affected. May be given. Li
The content of ₂ O is preferably 4 to 8.5% by weight, more preferably 5 to 8.5% by weight in consideration of productivity, ion exchange amount, chemical durability and migration resistance. Is more preferred. In the composition of the present invention, Na ₂
O and K ₂ O are fluxes, and improve the meltability of the composition, and Na ₂ O is a component capable of strengthening the glass by ion exchange with alkali metal ions having a larger ionic radius than sodium such as potassium. is there. Considering the chemical durability and migration resistance of the magnetic disk substrate,
Rather than using Li ₂ O alone, it is preferable to use these alkali components in combination with Li ₂ O and to prevent a decrease in chemical durability and alkali migration by using a plurality of types of alkali components. The content of Na ₂ O or K ₂ O exceeds 3% by weight, or Li ₂ O + N
When the total content of a ₂ O + K ₂ O exceeds 10% by weight,
It is difficult to keep the theoretical optical basicity of the glass at 0.548 or less, and the chemical durability of the magnetic disk substrate may be reduced and the migration resistance may be reduced. The content of each of Na ₂ O and K ₂ O is more preferably 2% by weight or less in consideration of chemical durability, migration resistance, and theoretical optical basicity of glass. Further, more preferably the total amount of _{Li 2 O + Na 2 O +} K 2 O is from 4 to 9 wt%, and yet more preferably 5-9 wt%.

In the composition of the present invention, TiO ₂ , ZrO ₂
And P ₂ O ₅ serve as a crystallization promoter. Further, TiO ₂ also plays a role as a flux, or as an important component that induces a structural change on the surface of the magnetic disk substrate by reacting sensitively with laser light when performing laser texturing. When the content of TiO ₂ is less than 0.5% by weight, the effect as a crystallization accelerator, the effect as a flux, and the effect as a laser reaction component are poor, and the content of TiO ₂ is 8% by weight. If it exceeds 300, the glass may be easily devitrified during molding. The content of TiO ₂ is determined as an effect as a crystallization accelerator, an effect as a flux,
In consideration of the effect as a laser reaction component and devitrification, the content is more preferably 2 to 6% by weight, and still more preferably 2 to 4% by weight. ZrO ₂ also has a function of significantly improving the chemical durability, but if the content of ZrO ₂ is less than 3.5% by weight, there is a possibility that the improvement of the chemical durability may not be recognized. If the content of ZrO ₂ exceeds 8% by weight, it may not be completely melted in glass and may be unmelted. Considering the effect as a crystallization accelerator, chemical durability and meltability, the content of ZrO ₂ is 3.
More preferably, the content is 8 to 6.5% by weight.
More preferably, it is% by weight. P ₂ O ₅ has a function as a flux, and particularly has a function to remarkably improve the refractory property of ZrO _2. However, if the content of P ₂ O ₅ is less than 0.5% by weight, it may act as a crystallization accelerator. And the effect of improving the refractory property of ZrO ₂ are poor, and the content of P ₂ O ₅ is 3% by weight.
If it exceeds 300, the amount of corrosion of the molten crucible may increase. The content of P ₂ O ₅ is from 1 to 2.5% by weight in consideration of the effect as a crystallization accelerator and the effect as a flux, particularly the effect of improving the hard-melting property of ZrO ₂ and the corrosiveness of a crucible. More preferably, there is. In the composition of the present invention, Sb ₂
O ₃ and As ₂ O ₃ serve as fining agents when the glass is melted. If the content of Sb ₂ O ₃ or As ₂ O ₃ alone or in combination is less than 0.1% by weight, the effect as a fining agent may be poor, but 2% by weight or less. With sufficient clarification effect. As ₂ O ₃
Can be used in combination with Sb ₂ O ₃ as a fining agent or alone, but it is preferable not to use it from an environmental point of view.
The total amount of Sb ₂ O ₃ + As ₂ O ₃ is more preferably 0.2 to 1% by weight in consideration of the fining effect.

[0008] B ₂ O ₃ , ZnO and PbO, which can be added to the composition of the present invention as required, have a function as a flux. If the content of B ₂ O ₃ exceeds 5% by weight, chemical durability may be deteriorated, and crystallization may be suppressed when heat treatment is performed. More preferably, the content of B ₂ O ₃ is 3.5% by weight or less. ZnO has a function of improving chemical durability, but the content of ZnO is 5%.
If the amount is more than 10% by weight, the amount of precipitated crystals may be reduced when heat treatment is performed. The content of ZnO is 4.5% by weight
It is more preferred that: Although PbO has a remarkable function as a flux, it is preferable not to use it from an environmental point of view. When PbO is used, if its content exceeds 3% by weight, chemical durability may be deteriorated, and if heat treatment is performed, the amount of precipitated crystals may be reduced. Pb
The content of O is more preferably 1.5% by weight or less. MgO, CaO, SrO, and BaO, which can be added to the composition of the present invention as required, are glass-modified oxides and have a function of widening the working temperature range. In particular, MgO has a function of improving chemical durability.
MgO content of more than 8% by weight or CaO, S
If the content of rO or BaO exceeds 5% by weight, the glass may become too stable and the amount of precipitated crystals may decrease. Considering the amount of precipitated crystals, the content of MgO is 5
% By weight or less, and CaO, Sr
More preferably, the contents of O and BaO are each 3% by weight or less. In some cases, laser light or the like is used as a method for texture of the magnetic disk substrate. In that case, Co, Mn, V, Cr, Cu, Au, Ag, P having absorption at the wavelength of the light to be used.
t, Mo, Ni, Fe, Te, Ce, Se, Nd, P
Elements such as r, Sm, Er, and S or compounds containing these elements can be contained in the glass composition as long as the properties of the magnetic disk are not adversely affected.

The glass composition for a magnetic disk substrate of the present invention has a theoretical optical basicity of 0.548 or less. With such a low theoretical optical basicity of the glass composition, even if a small amount of alkali is contained in the glass, the magnetic disk substrate has excellent chemical durability, which is a necessary and important property, A highly reliable magnetic disk substrate can be obtained. In the present invention, the theoretical optical basicity of the glass composition for a magnetic disk substrate is more preferably 0.544 or less, further preferably 0.540 or less. Theoretical optical basicity of glass (The The
oretical OpticalBasicity)
And J. A. Duffy and M.E. D. Ingram,
In 1975, the Journal of Inorgan
ic and Nuclear Chemistry,
Vol. 37, p. 1203, and Physics and
Chemistry of Glasses, Volume 16,
No. 6, page 119, and the theoretical optical basicity ガ ラ ス of glass is calculated by the following equation. Lambda = sigma oxidation number of _{{(z i × r i)} / 2γ i} ... (1) z i in equation cation i in each oxide component,
r _i represents the number of cations i present in each oxide component relative to the total oxygen number in the glass, that is, γ _i represents the basicity adjustment parameter of the cation i. Here, γ _i is L. From Pauling's electronegativity χ _i , it can be obtained by the following equation. γ _i = 1.36 ×
(Χ _i −0.26) Therefore, the theoretical optical basicity ガ ラ ス of glass is represented by the following equation. Lambda = sigma as _{{(z i × r i)} / (2.72 × χ i -0.707)} ... (2) Example, SiO _2: 72.0 mol%, Al ₂ O _3: 3.6
Mol%, Li ₂ O: 10.3 mol%, K ₂ O: 1.0 mol%, TiO _2: 3.4 mol%, ZrO _2: 2.1 mol%, P
₂ O ₅ : 1.0 mol%, MgO: 3.0 mol%, CaO:
ガ ラ ス is calculated for a glass having a composition of 2.1 mol% and ZnO: 1.5 mol%. χ For _i , “Basic Chemical Handbook, Revised 3rd Edition” (Maruzen, 1984) II-5
The Pauling electronegativity value described on page 89 is used. The value of z _i depends on the oxide structure, and the value of χ _i is P
The electronegativity of the auling is determined as shown in Table 1.

[0010]

[Table 1]

Next, the value of r _i is determined. To determine the value of r _i , first calculate the total oxygen number in the glass. The total oxygen number is determined as follows as the sum of the oxygen numbers of the respective oxides constituting the glass. R _i of each cation, can be determined all the oxygen number obtained as the number of the cation when the 1. For example,
SiO ₂ can be obtained from the following equation. SiO ₂ : (0.720 × 1) /1.887=0.316 Table 2 shows the results of the above-described calculations for r _i of each cation.

[0012]

[Table 2]

By substituting the values of z _i and χ _i shown in Table 1 and the values of r _i shown in Table 2 into the equation (2) for the theoretical optical basicity, the above glass is obtained. The theoretical optical basicity of the composition will be 0.5337. The glass composition for a magnetic disk substrate of the present invention is obtained by melting, shaping, polishing, and then subjecting the glass to ion exchange and strengthening by a known method such as immersing the glass in a molten salt such as NaNO ₃ or KNO _3. It can be performed. The processing temperature is NaNO ₃ or KN
The process is performed at a temperature between about 350 ° C., which is higher than the melting point of O _3, and about 550 ° C., which is lower than the glass transition temperature of the glass composition. Further, the ion exchange treatment time is preferably set to 10 hours or more. By the ion exchange treatment, lithium ions in the glass surface layer are exchanged for sodium ions or potassium ions having a larger ionic radius, and when Na ₂ O is contained in the glass, the sodium ions are changed to an ionic radius. It is exchanged for potassium ion etc. which is larger than. By these ion exchanges, a compressive stress layer is formed on the glass surface, so that a tempered glass magnetic disk substrate with high strength can be obtained. In the glass composition for a magnetic disk substrate of the present invention, at least one of Li ₂ O.2SiO ₂ and spodumene is precipitated as a main crystal phase by heat treatment. The Li ₂ O.2SiO ₂ crystal is rod-shaped and has high mechanical strength. However, when the crystal size exceeds 1 μm, polishing workability deteriorates.
By using an appropriate crystallization accelerator such as iO ₂ , ZrO ₂ , P ₂ O ₅ and an appropriate crystallization treatment, the crystal size is preferably 1 μm or less, more preferably 0.5 μm or less. Spodumene crystals are granular crystals, and T
By using a crystallization accelerator such as iO ₂ , ZrO ₂ , P ₂ O ₅ and an appropriate crystallization treatment, fine crystals of the same degree as Li ₂ O · 2SiO ₂ crystals can be uniformly obtained. In order to achieve the higher recording density required for magnetic disks in the future, it is necessary to provide a disk substrate with extremely high smoothness and surface accuracy. In this case, it is preferable that the Li ₂ O.2SiO ₂ crystal is the main crystal phase and no spodumene crystal is precipitated.
When the Li ₂ O · 2SiO ₂ crystal is the main crystal phase and no spodumene crystal is precipitated, the Al ₂ O ₃ component ratio in the residual glass matrix becomes higher than before the crystallization treatment.
The chemical durability of the glass phase increases. As a result, the difference in chemical durability between the crystal phase and the matrix glass phase is reduced, so that the difference in polishing speed between the two phases is small, and Li ₂ O ·
From the crystallized glass on which fine crystals of 2SiO ₂ are precipitated, a disk substrate with extremely high surface smoothness can be obtained. On the other hand, when spodumene crystals precipitate in large quantities,
Al ₂ in the residual glass matrix compared to before the crystallization treatment
Since the O ₃ component ratio is reduced, the chemical durability of the glass phase is slightly inferior, and the chemical durability of the spodumene crystal is higher than that of the Li ₂ O · 2SiO ₂ crystal. The difference in durability increases. As a result, the difference in polishing speed between the two phases is slightly increased, and texture formation can be performed simultaneously with polishing. Therefore, the amount and size of the spodumene crystal, the spodumene crystal and L
By controlling the ratio of i ₂ O.2SiO ₂ crystals, it is possible to obtain freely from a very smooth substrate surface to a substrate surface on which a desired texture according to the application is formed.
Further, by controlling the ratio of the spodumene crystal to the Li ₂ O.2SiO ₂ crystal, the thermal expansion coefficient of the magnetic disk substrate can be controlled between 80 × 10 ⁻⁷ / ° C. and 110 × 10 ⁻⁷ / ° C. It is possible. The maximum amount of the Li ₂ O · 2SiO ₂ crystal becomes the crystal phase because the final crystallization temperature is about 72 ° C.
When the temperature is set to 0 ° C. or lower, the spodumene crystal has the maximum amount of crystal phase because the final crystallization temperature is about 730.
C. or higher. In the magnetic disk substrate of the present invention, the total crystallinity of the main crystal phase, Li ₂ O.2SiO _{2, the} spodumene crystal and the other crystals, is represented by powder X
It is preferably 20% by volume or more by a calibration curve method using linear diffraction. When the total crystallinity is less than 20% by volume,
There is a possibility that satisfactory mechanical strength cannot be obtained as a magnetic disk substrate.

[0014] The magnetic disk glass composition for substrates of the present invention, when heated, lithium feldspar besides the main crystal phase as a secondary crystalline phase _{(Li 2 O · Al 2 O} 3 · 6SiO 2), α- quartz, beta- Cristobalite (SiO ₂ ) and the like may precipitate, but by the precipitation of these sub-crystal phases,
The properties of the composition according to the invention are not impaired. α-quartz is
It starts to precipitate at about 650 ° C., and when spodumene crystals start to precipitate, the amount of the crystals decreases. The glass composition for a magnetic disk substrate of the present invention preferably has a weight loss of 6 × 10 ⁻⁷ g / cm ² · h or less in a water elution test of glass by a powder method. In a water elution test of glass by a powder method, if the weight loss is 6 × 10 ⁻⁷ g / cm ² · h or less,
Even if a small amount of alkali is contained in the glass, a highly reliable magnetic disk substrate having excellent chemical durability, which is a necessary and important characteristic of the magnetic disk substrate, can be obtained. Weight loss in water elution test of glass by the powder method,
It is more preferably 4 × 10 ⁻⁷ g / cm ² · h or less, and further preferably 2 × 10 ⁻⁷ g / cm ² · h or less. The magnetic disk substrate of the present invention has a weight loss of 6 × 10 ⁻⁷ g / cm ^{2 in} a water elution test of glass or crystallized glass (hereinafter collectively referred to as “glass”) by a powder method.
H is preferably equal to or less than h. In a water elution test of glass by a powder method, if the weight loss is 6 × 10 ⁻⁷ g / cm ² · h or less, even if a small amount of alkali is contained in the glass, it is necessary and important for the magnetic disk substrate. A magnetic disk substrate with excellent chemical durability, which is a characteristic, and high reliability. Weight loss in water elution test of glass by the powder method,
It is more preferably 4 × 10 ⁻⁷ g / cm ² · h or less, and further preferably 2 × 10 ⁻⁷ g / cm ² · h.

A method for testing water elution of glass or crystallized glass (hereinafter collectively referred to as "glass") by the powder method according to the present invention will be described. First, the glass is ground in a mortar or the like. The opening of the crushed glass powder is 1.70m
m and sieve with a standard sieve of 0.85 mm, pass through 1.70 mm and 0.8
The glass powder remaining on 5 mm is used as a sample. This glass powder is placed in a beaker containing diethyl ether, subjected to ultrasonic cleaning for 2 to 3 minutes, and the cloudy liquid is discarded. After repeating the ultrasonic cleaning using diethyl ether once more, the ultrasonic cleaning is performed for 2 to 3 minutes using methanol, and the liquid is discarded. Thereafter, the glass powder is dried in a beaker at 120 ° C. for 1 hour and allowed to cool in a desiccator. The washed glass powder is weighed by the same number of grams as the specific gravity measured in advance so that the surface area is the same,
Place in a 70 mesh (0.21 mm) platinum basket. Soak it in a beaker containing methanol while keeping it in a platinum basket, apply ultrasonic cleaning for 2 to 3 minutes, pull out the platinum basket from the beaker, dry at 120 ° C for 1 hour, and let cool in a desiccator I do. The cooled platinum basket containing glass powder is weighed to the unit of 10 ^-5 g. Next, a weighed platinum basket containing glass powder is put in a Teflon container, and then 100 ml of ion-exchanged water is put in, and the container is sealed with a Teflon lid. This is placed in a thermostat that has been previously heated to 80 ° C., and left for 66 hours to perform a water resistance test. 66 hours later,
The basket made of platinum containing the glass powder is taken out of the container made of Teflon and ultrasonically washed in methanol for 2-3 minutes. After the ultrasonic cleaning, the substrate is dried at 120 ° C. for 1 hour and allowed to cool in a desiccator. The cooled basket made of platinum containing glass powder is weighed to the unit of 10 ^-5 g, and the weight loss is determined from the weight before and after the water resistance test. From the weight loss and the surface area value previously measured using a specific surface area meter, the weight loss per 1 cm ² per hour is calculated. The test is repeated three times for one type of glass, and the average value is regarded as the weight loss in the water elution test of the glass.

The magnetic disk substrate of the present invention is prepared by molding the glass composition for a magnetic disk substrate of the present invention, polishing it for ion exchange and strengthening it by ion exchange, and crystallizing it for heat treatment after heat treatment. This is a magnetic disk substrate manufactured by polishing. The method for molding the glass composition is not particularly limited. For example, the raw material can be heated and melted in a tank kiln, or melted by directly energizing, and then molded by press molding or cast-slice molding. There is no particular limitation on the processing method of the molded article.For example, in the case of heat treatment, after heat treatment at a relatively low temperature to generate a large number of crystal nuclei and then increasing the temperature to grow the crystal, It is preferable for obtaining crystals. There is no particular limitation on the method of polishing the molded article after the treatment. For example, synthetic abrasive grains such as synthetic diamond, silicon oxide, silicon carbide, aluminum oxide, zirconium oxide, boron carbide, c-BN, natural diamond, and oxidized Polishing can be performed by a known method using natural abrasive grains such as cerium. By using the glass composition for a magnetic disk substrate of the present invention, even when ion-exchanged or heat-treated, a magnetic disk substrate having high strength, high hardness, chemical durability, and excellent heat resistance can be obtained. be able to. Since the composition of the present invention has a low theoretical optical basicity of 0.548 or less, it can achieve high chemical durability, and has excellent migration resistance. Can be kept.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. The raw materials used in Examples and Comparative Examples were SiO ₂ , Al (OH) ₃ , Li ₂ C
O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , TiO ₂ , ZrO ₂ , Al
PO ₄ , Sb ₂ O ₃ , As ₂ O ₃ , H ₃ BO ₃ , Mg (OH) ₂ ,
CaCO ₃ , SrCO ₃ , BaCO ₃ , ZnO and PbO
It is. In Examples and Comparative Examples, the crystal phase, crystallinity, bending strength, and arithmetic average roughness Ra were measured by the following methods. (1) Crystal phase The obtained polished compact was measured using an X-ray diffractometer. (2) Crystallinity First, a calibration curve of the crystal phase to be obtained was prepared.
For example, in the case of a spodumene crystal, Li ₂ CO ₃ , Al (OH) ₃ and SiO ₂ are weighed so that the composition of the spodumene is Li ₂ O: Al ₂ O ₃ : SiO ₂ = 1: 1: 4. Then, isopropyl alcohol was added and wet-mixed for 24 hours. Thereafter, isopropyl alcohol was removed, and sintering was performed until the increase in the X-ray diffraction peak intensity disappeared to produce a spodumene crystal. Crush this spodumene crystal,
The powder was mixed with mother glass powder in which no crystal was precipitated at various ratios, peak intensities were measured for four main peaks in X-ray diffraction, and a calibration curve was prepared. Melting and forming glass,
After heat treatment and polishing, a crystallinity measurement sample was obtained. The measurement sample was measured by X-ray diffraction, and the crystallinity was determined from a calibration curve created in advance. (3) Bending strength The glass molded body was heat-treated and processed according to JIS R 1601, or processed according to JIS R 1601, followed by ion exchange treatment, and the bending strength was measured by three-point bending. (4) Arithmetic Mean Roughness Ra The obtained polished molded body was subjected to an atomic force microscope (Digita).
1 Instruments (manufactured by Instruments). Randomly select 5 locations on the sample surface
4 randomly in a 10 μm × 10 μm field of view
This line was drawn and each Ra was calculated. The average of the total 20 locations was defined as the arithmetic average roughness Ra. Example 1 Glass composition: SiO ₂ : 70.0% by weight, Al ₂ O ₃ :
6.0 wt%, Li ₂ O: 8.0 wt%, TiO _2: 2.5
Wt%, ZrO _2: 4.0 wt%, P ₂ O _5: 1.8 wt%, Sb ₂ O _3: 0.2 wt%, B ₂ O _3: 2.0 wt%, C
aO: 2.0% by weight, BaO: 1.5% by weight and ZnO:
Each component raw material was weighed and mixed so as to be 2.0% by weight.
When the composition of this glass is represented by mol%, SiO ₂ : 69.
87 mol%, Al ₂ O ₃ : 3.53 mol%, Li ₂ O: 1
6.05 mol%, TiO _2: 1.88 mol%, ZrO _2:
1.95 mol%, P ₂ O _5: 0.76 mole%, Sb ₂ O _3:
0.04 mol%, B ₂ O _3: 1.72 mol%, CaO: 2.
14 mol%, BaO: 0.59 mol% and ZnO: 1.4
The glass composition has a theoretical optical basicity of 0.5395. The mixed raw materials are put into a platinum crucible in an electric furnace and melted at 1,450 ° C. for 5 hours,
After stirring to homogeneity, the mixture was formed into a plate of 50 × 50 × 5 mm, strain-reduced and cooled to obtain a glass molded body. This glass compact is heated at 600 ° C. for 3 hours, and then at 800 ° C. for 2 hours.
Heat treatment was performed for a time to precipitate crystals in the glass. Further, the surface of the molded body was wrapped for 30 minutes using silicon carbide abrasive grains having an average particle size of 10 μm, and further, an average particle size of 1 μm
Polished with cerium oxide abrasive grains for 15 minutes to obtain a polished molded body. In this polished compact, the crystal phase 1 was spodumene, the crystal phase 2 was Li ₂ O.2SiO ₂ , and the crystal phase 3 was α-quartz. The crystallinity was as follows: 21% by volume of spodumene, 16% by volume of Li ₂ O · 2SiO ₂ , α-
Quartz was 14% by volume. The weight loss in the water elution test of the crystallized glass by the powder method was 4.1 × 1.
It was 0 ^-7 g / cm ² · h, the transverse rupture strength was 270 MPa, and the arithmetic average roughness Ra was 18.0 °. Examples 2 to 7 In the same manner as in Example 1, depending on the composition, 1,400 to 1,5
A glass composition obtained by melting at 30 ° C. for 3 to 24 hours was molded, and a crystallized glass molded body obtained by heat treatment under the conditions shown in Table 3 was polished in the same manner as in Example 1. With respect to the obtained polished molded body, the crystal phase, the degree of crystallinity, the weight loss, the bending strength and the arithmetic average roughness Ra in the water elution test of the crystallized glass by a powder method were measured. The results are shown in Table 3. Example 8 The glass composition was SiO ₂ : 70.0% by weight, Al ₂ O ₃ :
6.0 wt%, Li ₂ O: 8.0 wt%, TiO _2: 2.5
Wt%, ZrO _2: 4.0 wt%, P ₂ O _5: 1.8 wt%, Sb ₂ O _3: 0.2 wt%, B ₂ O _3: 2.0 wt%, C
aO: 2.0% by weight, BaO: 1.5% by weight and ZnO:
Each component raw material was weighed and mixed so as to be 2.0% by weight.
When the composition of this glass is represented by mol%, SiO ₂ : 69.
87 mol%, Al ₂ O ₃ : 3.53 mol%, Li ₂ O: 1
6.05 mol%, TiO _2: 1.88 mol%, ZrO _2:
1.95 mol%, P ₂ O _5: 0.76 mole%, Sb ₂ O _3:
0.04 mol%, B ₂ O _3: 1.72 mol%, CaO: 2.
14 mol%, BaO: 0.59 mol% and ZnO: 1.4
The glass composition has a theoretical optical basicity of 0.5395. The mixed raw materials are put into a platinum crucible in an electric furnace and melted at 1,450 ° C. for 5 hours,
After stirring to homogeneity, the mixture was formed into a plate of 50 × 50 × 5 mm, strain-reduced and cooled to obtain a glass molded body. The glass compact is kept at 570 ° C. for 3 hours, and then at 670 ° C. for 2 hours.
Heat treatment was performed for a time to precipitate crystals in the glass. Further, the surface of the molded body was wrapped for 30 minutes using silicon carbide abrasive grains having an average particle size of 10 μm, and further, an average particle size of 1 μm
Polished with cerium oxide abrasive grains for 15 minutes to obtain a polished molded body. In this polished compact, the crystal phase 1 was Li ₂ O · 2
SiO ₂ , and the crystal phase 2 was α-quartz. The crystallinity was 20% by volume of Li ₂ O.2SiO _{2 and} 19% by volume of α-quartz. The weight loss in the water elution test of the crystallized glass by the powder method was 3.8 × 10 ^−7.
g / cm ² · h, the transverse rupture strength is 230 MPa,
The arithmetic average roughness Ra was 7.0 °. Examples 9 to 15 As in Example 8, 1,400 to 1,5 depending on the composition.
A glass composition obtained by melting at 30 ° C. for 3 to 24 hours was molded, and a crystallized glass molded body obtained by heat treatment under the conditions shown in Table 3 was polished in the same manner as in Example 8. With respect to the obtained polished molded body, the crystal phase, the degree of crystallinity, the weight loss, the bending strength and the arithmetic average roughness Ra in the water elution test of the crystallized glass by a powder method were measured. The results are shown in Table 3. Example 16 Glass composition: SiO ₂ : 70.0% by weight, Al ₂ O ₃ :
6.0 wt%, Li ₂ O: 8.0 wt%, TiO _2: 2.5
Wt%, ZrO _2: 4.0 wt%, P ₂ O _5: 1.8 wt%, Sb ₂ O _3: 0.2 wt%, B ₂ O _3: 2.0 wt%, C
aO: 2.0% by weight, BaO: 1.5% by weight and ZnO:
Each component raw material was weighed and mixed so as to be 2.0% by weight.
When the composition of this glass is represented by mol%, SiO ₂ : 69.
87 mol%, Al ₂ O ₃ : 3.53 mol%, Li ₂ O: 1
6.05 mol%, TiO _2: 1.88 mol%, ZrO _2:
1.95 mol%, P ₂ O _5: 0.76 mole%, Sb ₂ O _3:
0.04 mol%, B ₂ O _3: 1.72 mol%, CaO: 2.
14 mol%, BaO: 0.59 mol% and ZnO: 1.4
The glass composition has a theoretical optical basicity of 0.5395. The mixed raw materials are put into a platinum crucible in an electric furnace and melted at 1,450 ° C. for 5 hours,
After stirring to homogeneity, the mixture was formed into a plate of 50 × 50 × 5 mm, strain-reduced and cooled to obtain a glass molded body. The surface of this glass molded body was wrapped for 30 minutes using silicon carbide abrasive grains having an average particle size of 10 μm, and further, an average particle size of 1 μm
Polished with cerium oxide abrasive grains for 15 minutes to obtain a polished molded body. The polished molded body was immersed in a molten sodium nitrate bath kept at 450 ° C. for 48 hours to exchange lithium ions in the glass surface layer with sodium ions, thereby chemically strengthening the polished molded body. This polished molded article had a weight loss of 4.0 × 10 in a water elution test of glass by a powder method.
^-7 g / cm ² · h, transverse rupture strength was 280 MPa, and arithmetic mean roughness Ra was 6.5 °. Examples 17 to 18 In the same manner as in Example 16, the polished molded body obtained by molding and polishing the glass composition was subjected to ion exchange under the conditions shown in Table 3 to chemically strengthen it. With respect to the obtained polished molded body, weight loss, bending strength and arithmetic average roughness Ra in a water elution test of glass by a powder method were measured. The results are shown in Table 3.

[0018]

[Table 3]

[0019]

[Table 4]

[0020]

[Table 5]

[0021]

[Table 6]

[0022]

[Table 7]

[0023]

[Table 8]

The glass compositions of the present invention of Examples 1 to 7
Molded body produced by molding, heat treatment and polishing
All have a spodumene crystal phase of 20% by volume or more,
Weight loss in water dissolution test of crystallized glass by powder method
Small is 4.6 × 10^-7g / cm^Two・ Below h, the bending strength is
200 MPa or more, and arithmetic average roughness Ra is 23.0 ..
The following are preferable characteristics for the magnetic disk substrate.
Have. Glass compositions of the present invention of Examples 8 to 14
, Polishing, molding, heat treatment, polishing
The body is all Li_TwoO.2SiO_Two13% by volume or less of crystal phase
In the water dissolution test of crystallized glass by the powder method
Weight loss is 3.8 × 10^-7g / cm^TwoH or less,
The bending strength is 210 MPa or more, and the arithmetic average roughness Ra is
Less than 10.5
It has new characteristics. Further, in Example 15 of the present invention,
Made from glass composition by molding, heat treatment and polishing
The obtained polished molded product has a theoretical optical basicity of 0.548.
, But Li_TwoO.2SiO_Two23 phases of crystal phase
% In water dissolution test of crystallized glass by powder method
Weight loss is 5.3 × 10^-7g / cm^Two・ H is strong
The degree is 210 MPa and the arithmetic average roughness Ra is 7.3Å
And have the desirable characteristics as a magnetic disk substrate
I have. Furthermore, the glass set of the present invention of Examples 16 to 18
Manufactured by molding, polishing and ion exchange strengthening
All of the polished compacts are leached out of glass by the powder method.
Weight loss in test was 4.0 × 10^-7g / cm^Two・ H or less
The transverse rupture strength is 240 MPa or more, and the arithmetic mean
The roughness Ra is 6.5 mm or less, and is used as a magnetic disk substrate.
And favorable characteristics. Comparative Example 1 The glass composition was SiO_Two: 82.0% by weight, Al_TwoO_Three:
5.5% by weight, Li_TwoO: 6.5% by weight, TiO_Two: 0.5
Wt%, ZrO_Two: 4.0% by weight, P_TwoO_Five: 0.5 weight
%, Sb_TwoO_Three: 0.2% by weight and MgO: 0.8% by weight
Raw materials of the respective components were weighed and mixed so as to be as possible. This glass pair
When the composition is expressed in mol%, SiO_Two: 80.32 mol%, A
l_TwoO_Three: 3.18 mol%, Li_TwoO: 12.80 mol%,
TiO_Two: 0.37 mol%, ZrO_Two1.91 mol%, P
_TwoO_Five: 0.21 mol%, Sb_TwoO_Three: 0.04 mol% and M
gO: 1.17 mol%, which is the theoretical value of this glass composition
The optical basicity is 0.5233. Mixed raw
Was charged into a platinum crucible in an electric furnace and heated.
O_TwoDo not melt even when the temperature reaches 1,550 ° C.
won. Comparative Example 2 When the glass composition was SiO_Two: 72.0% by weight, Al_TwoO_Three:
3.0% by weight, Li_TwoO: 10.5% by weight, K_TwoO: 2.0
Wt%, ZrO_Two: 3.0% by weight, P_TwoO_Five： 1.8 weight
%, Sb_TwoO_Three: 0.2% by weight, B_TwoO_Three: 3.5% by weight, M
gO: 2.0% by weight and BaO: 2.0% by weight.
Each component material was weighed and mixed. The composition of this glass
%, SiO_Two: 68.44 mol%, Al_TwoO_Three:
1.68 mol%, Li_TwoO: 20.08 mol%, K_TwoO:
1.21 mol%, ZrO_Two1.39 mol%, P_TwoO_Five: 0.
72 mol%, Sb_TwoO_Three: 0.04 mol%, B_TwoO_Three: 2.8
7 mol%, MgO: 2.83 mol%, and BaO: 0.74
Mol%, the theoretical optical basicity of this glass composition
The degree is 0.5494. Mix the raw materials in an electric furnace
Pour into a platinum crucible and melt at 1,450 ° C for 5 hours.
After stirring to make it quality, it becomes 50 × 50 × 5mm plate
It was molded, strain-reduced, and cooled to obtain a glass molded body. This gala
Molded body at 570 ° C for 3 hours, then at 780 ° C for 2 hours
During the heat treatment, crystals were precipitated in the glass. further,
Use silicon carbide abrasive grains with an average particle size of 10 μm for the surface of the compact
And wrap it for 30 minutes.
Polished with cerium fluoride abrasive for 15 minutes
Obtained. This polished molded body is made of Li_TwoAl with large amount of O_TwoO_Three
Is small, the theoretical optical basicity is large,
Weight loss in water dissolution test of crystallized glass by powder method
Small is 6.5 × 10^-7g / cm^Two・ It was a little big with h. Comparative Example 3 The glass composition was SiO_Two: 58.0% by weight, Al_TwoO_Three:
7.0% by weight, Li_TwoO: 7.0% by weight, K_TwoO: 2.0 weight
%, TiO_Two: 2.0% by weight, ZrO_Two: 4.0% by weight,
P_TwoO_Five1.8% by weight, Sb_TwoO_Three: 0.2% by weight, B
_TwoO_Three: 4.0% by weight, MgO: 5.0% by weight, BaO:
Each component to be 6.0% by weight and ZnO: 3.0% by weight.
The raw materials were weighed and mixed. Shows the composition of this glass in mol%
Then, SiO_Two: 59.67 mol%, Al_TwoO_Three: 4.2
4 mol%, Li_TwoO: 14.48 mol%, K_TwoO: 1.31
Mol%, TiO_Two1.55 mol%, ZrO_Two: 2.01 m
%, P _TwoO_Five: 0.78 mol%, Sb_TwoO_Three: 0.04 mol
%, B_TwoO_Three: 3.55 mol%, MgO: 7.67 mol%,
BaO: 2.42 mol% and ZnO: 2.28 mol%
Thus, the theoretical optical basicity of the glass composition is 0.1.
5564. Platinum crucible in electric furnace
And melt at 1,450 ° C for 5 hours to make it homogeneous
After shaking, form into a 50 x 50 x 5 mm plate and remove
The glass molded body was obtained by straining and cooling. Of this glass compact
The surface was formed using silicon carbide abrasive grains having an average particle size of 10 μm.
Lapping for more than 1 minute
Polishing was carried out for 15 minutes with abrasive grains to obtain a polished molded body. This
Melted sodium nitrate kept at 360 ° C
Immersed in a bath for 72 hours to remove lithium ions from the glass surface layer
Is ion-exchanged with sodium ions, and the abrasive compact is chemically
Strengthened. This polished molded body is made of glass water by a powder method.
Weight loss in dissolution test is 17.5 × 10^-7g / cm^Two・
h was big. Comparative Example 4 The glass composition was SiO_Two: 66.0% by weight, Al_TwoO_Three: 1
0.0% by weight, Li_TwoO: 8.0% by weight, TiO_Two: 3.0
Wt%, ZrO_Two: 3.5% by weight, P_TwoO_Five: 0.8 weight
%, Sb_TwoO_Three: 0.2% by weight, B_TwoO_Three1.0% by weight and
MgO: Weigh and mix each ingredient material to 7.5 wt%.
I combined. When the composition of this glass is represented by mol%, SiO 2
_Two: 63.23 mol%, Al_TwoO_Three: 5.65 mol%, Li_Two
O: 15.42 mol%, TiO_Two: 2.16 mol%, Zr
O_Two: 1.64 mol%, P_TwoO_Five: 0.32 mol%, Sb_TwoO
_Three: 0.04 mol%, B_TwoO_Three: 0.83 mol% and Mg
O: 10.71 mol%, which is the theory of this glass composition
Optical basicity is 0.5544. Mixed raw
Into a platinum crucible in an electric furnace,
After melting for a time and stirring to make it homogeneous, 50 × 50
It is molded into a × 5 mm plate, strain-reduced and cooled to form a glass molded body.
Obtained. The surface of the glass molded body is made of
Lapping for 30 minutes using silicon carbide abrasive grains
Polished for 15 minutes with cerium oxide abrasive grains of uniform particle size 1μm
Thus, a polished molded body was obtained. This abrasive compact is heated to 400 ° C.
Immerse in the molten sodium nitrate bath for 72 hours
Lithium ions on the surface layer
It was replaced and the abrasive compact was chemically strengthened. This abrasive compact
Means weight loss in water dissolution test of glass by powder method
Is 9.9 × 10^-7g / cm^Two・ It was big with h. Comparative Examples 1 to
The results of No. 4 are summarized in Table 4.

[0025]

[Table 9]

[0026]

[Table 10]

From the results shown in Table 4, in Comparative Examples 1 to 3 in which a glass composition different from the glass composition for a magnetic disk substrate of the present invention was used, melting of the glass was impossible, or Even if a magnetic disk substrate can be manufactured, the weight loss in the water elution test cannot be reduced sufficiently even after crystallization by heat treatment, and the magnetic weight in the water elution test is small due to ion exchange. Cannot be a disk substrate. Also,
Although the glass composition for a magnetic disk substrate of Comparative Example 4 was within the composition range of the composition of the present invention, since the theoretical optical basicity was large, the magnetic disk substrate strengthened by ion exchange showed water elution. Large weight loss in test.

[0028]

The glass composition of the present invention can be easily formed, and after polishing, the alkali metal ions in the glass surface layer are exchanged with alkali metal ions having a larger ionic radius to chemically strengthen the glass. In addition, or by crystallizing the main crystal phase as Li ₂ O.2SiO ₂ and / or spodumene by heat treatment, and then polishing it, excellent chemical durability, mechanical strength, surface smoothness, surface flatness A magnetic disk substrate having heat resistance, heat resistance, and less deterioration of magnetic film characteristics due to alkali migration can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ikuo Kuriyama 2-21 Hamamatsubara-cho, Nishinomiya-shi, Hyogo Yamamura Glass Co., Ltd. (72) Inventor Hajime Wakabayashi 2-21 Hamamatsubara-cho, Nishinomiya-shi, Hyogo Yamamura Glass Inside

Claims (9)

[Claims] 1. A as oxide, SiO _2: 66 to 80 wt% Al ₂ O _3: 5~15 wt% Li ₂ O: 3~8.5 wt% Na ₂ O: 0~3 wt% K ₂ O : 0-3% by weight, _{however, Li 2 O + Na 2 O} + K 2 O: 3~10 wt% TiO _2: 0.5 to 8 wt% ZrO _2: 3.5 to 8 wt% P ₂ O _5: 0.5 to 3 wt% Sb ₂ O _3: 0-2 wt% as ₂ O _3: has the composition 0-2% by weight, a magnetic disk theoretical optical basicity is equal to or is 0.548 or less Glass composition for substrates. Wherein as the oxide, SiO _2: 66-75 wt% Al ₂ O _3: 5.5~10 wt% Li ₂ O: 4 to 8.5 wt% Na ₂ O: 0 to 2 wt% K ₂ O: 0 to 2 wt%, _{however, Li 2 O + Na 2 O} + K 2 O: 4~9 wt% TiO _2: 2 to 6 wt% ZrO _2: 3.8 to 6.5 wt% P ₂ O _5: 1~ 2.5 wt% Sb ₂ O _3: 0-2 wt% as ₂ O _3: has the composition 0-2% by weight, the theoretical optical basicity is equal to or is 0.548 or less Glass composition for magnetic disk substrates. 3. As oxides, SiO ₂ : 66 to 75% by weight Al ₂ O ₃ : 5.5 to 7.5% by weight Li ₂ O: 5 to 8.5% by weight Na ₂ O: 0 to ₂ % by weight % K ₂ O: 0 to 2 wt%, _{however, Li 2 O + Na 2 O} + K 2 O: 5~9 wt% TiO _2: 2 to 4 wt% ZrO _2: 4.1 to 6 wt% P ₂ O _5: 1~ 2.5 wt% Sb ₂ O _3: 0 to 1 wt% as ₂ O _3: has the composition 0-1% by weight, the theoretical optical basicity is equal to or is 0.548 or less Glass composition for magnetic disk substrates. 4. The glass composition for a magnetic disk substrate according to claim 1, which is molded and polished,
A magnetic disk substrate characterized in that alkali metal ions in a glass surface layer are ion-exchanged with alkali metal ions having a larger ionic radius at a temperature between 50 ° C. and 550 ° C. to strengthen the magnetic disk substrate. 5. A glass composition for a magnetic disk substrate according to any one of claims 1 to 3, wherein the glass composition is formed, heat-treated, and polished, and has a main crystal phase of Li ₂ O.2SiO ₂ and spodumene. A magnetic disk substrate, which is at least one of the following. 6. As oxides, SiO ₂ : 66 to 80% by weight Al ₂ O ₃ : 5.5 to 10% by weight Li ₂ O: _{3 to} 8.5% by weight Na ₂ O: 0 to 3% by weight K ₂ O: 0 to 3 wt%, _{however, Li 2 O + Na 2 O} + K 2 O: 3~10 wt% TiO _2: 0.5 to 8 wt% ZrO _2: 3.5 to 8 wt% P ₂ O _5: 0. 5-3 wt% Sb ₂ O _3: 0-2 wt% As ₂ O _3: a glass composition having a composition of 0-2 weight%, molding, heat treatment, and polished was prepared, the main crystal phase Li magnetic disk substrate characterized in that at least one of the ₂ O · 2SiO ₂ and spodumene. 7. The magnetic disk substrate according to claim 5, wherein the total crystallinity is 20% by volume or more. 8. The glass for a magnetic disk substrate according to claim 1, wherein a weight loss of the glass in a water elution test by a powder method is not more than 6 × 10 ⁻⁷ g / cm ² · h. Composition. 9. The magnetic material according to claim 4, wherein a weight loss is 6 × 10 ⁻⁷ g / cm ² · h or less in a water elution test of glass or crystallized glass by a powder method. Disk substrate.