JP2001184624A - Glass ceramic substrate for information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass ceramic substrate for an information memory medium in which decrease in the magnetic characteristics of a recording medium due to alkali elution or defects due to alkali corrosion are significantly decreased, which has a ultrasmooth surface so as to respond an increase in the memory capacity of the information memory medium and the lower floating height or the contact state of a magnetic head, and moreover, which realizes faster rotation of the information transmission rate and higher mechanical strength for mobile use, and to provide a magnetic information memory medium produced by forming a magnetic medium film on that glass ceramic substrate. SOLUTION: The glass ceramic substrate for an information memory medium contains lithium disilicate (Li2O.2SiO2) as the main crystal phase and has 4 to 8% content of Li2O calculated as the mass of oxides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate used in an information storage device, and more particularly to a substrate having an ultra-smooth substrate surface suitable for near-contact recording and contact recording, and having a high Young's modulus and a low A glass ceramic substrate for an information storage medium, a method for manufacturing the same, and a film formation process for the information storage medium substrate, which have specific gravity characteristics, good mechanical characteristics, and also have a thermal expansion characteristic matching a drive component. It relates to an information storage medium to be formed.

[0002]

2. Description of the Related Art In recent years, with the use of multimedia in personal computers and the spread of digital video cameras, digital cameras, and the like, data such as moving images and audio have been handled, and the demand for information storage devices with high storage density has increased. It is growing. Therefore, in order to increase the recording density of the information storage medium, it is necessary to increase the bit and track densities and to reduce the size of the bit cells. The head operates in a state closer to the surface of the information storage medium as the bit cells are reduced in size. As described above, when the head operates in a low flying state (near contact) or a contact state (contact) with respect to the information storage medium substrate, super smoothness of the substrate surface is important. Furthermore, in contrast to the conventional landing zone technology, a ramp load technology has been developed in which the magnetic head is brought into complete contact and the start and stop of the head is removed from the information magnetic storage medium substrate. Is moving toward a smoother direction.

[0003] Furthermore, with the increase in information capacity, technology has been developed to increase the information transfer speed by increasing the speed of the information magnetic storage medium substrate of the magnetic storage device today. As the number increases, deflection and deformation occur, so that the substrate material is required to have a high Young's modulus and a low specific gravity. Further, with the miniaturization and higher precision of the magnetic film, further reduction of the alkali components (Li, Na, K) eluted from the substrate material is required. In addition, information magnetic storage devices such as a removable type and a card type are now being studied and put into practical use with respect to the current fixed type information magnetic storage device, and applications to digital video cameras, digital cameras and the like are beginning to be developed. For this reason, especially in mobile applications, the mechanical strength of the substrate itself is also an important factor.

[0004] Further, regarding these information storage media, mobile information (APS cameras, mobile phones, digital cameras,
Applications such as digital video cameras, card drives), desktop PCs (hard disk drives), servers (hard disk drives), new high-density media (perpendicular magnetic storage media, island magnetic storage media, storage media for semiconductor memory), etc. The characteristics required for the substrate, including the development for these new applications, are becoming more diverse and sophisticated.

In addition, in these information storage media, in addition to the surface smoothness in high density, the elution of alkali from the substrate causes (a) a decrease in the magnetic properties of the storage medium (the alkali component is diffused into the storage medium. (B) Deterioration of the magnetic properties of the medium), (b) Attachment of defects to the substrate surface (the eluted alkali component diffuses to the surface of the recording medium and becomes a compound, which is attached to the surface as foreign matter), (c) ) Basic problems such as recording skipping problems must be cleared.

The above phenomenon will be described in more detail. First, regarding the alkali elution phenomenon, when producing glass ceramics requiring an alkali component as a component of the crystal phase, the concentration of the alkali component of the raw glass is
These alkali components are required in a larger amount than the stoichiometric amount required for the crystal phase, and after crystallization, these alkali components which are not consumed in the glass matrix phase remain. This causes (i) thermal diffusion into the recording medium during film formation to generate a component of the recording medium and a compound (for example, a compound with Cr), thereby deteriorating the magnetic properties of the recording medium, or (ii) recording. The compound diffuses over time to the surface of the medium and combines with water or carbon dioxide gas to form a hydroxide or a carbonate. This compound becomes a foreign substance on the surface and causes surface defects and recording skip.

As described above, in recent years where the recording density has been dramatically improved, the above problem is becoming one of the factors which hinder the improvement of the recording density. It has been demanded.

As a substrate for a magnetic recording medium, an aluminum alloy or the like has been conventionally used. However, in the case of an aluminum alloy substrate, projections or spot-like irregularities are formed on the substrate surface in the polishing step due to various material defects. In terms of properties, it is not sufficient as the substrate for the high-density storage medium.
In addition, aluminum alloy is a soft material and has low Young's modulus and low surface hardness, so it has the drawback that it is easily vibrated and deformed at high speed rotation of the drive, and it is difficult to cope with thinning. . Furthermore, it cannot sufficiently meet today's demands for high-density recording, such as deformation due to contact of the head, causing damage to the medium and deformation due to high-speed rotation.

With the rapid trend toward higher densification, recently, aluminosilicate glass which has been subjected to chemical strengthening treatment has been used instead of aluminum alloy as a magnetic disk substrate material which is advantageous in strength and suitable for high density. (SiO ₂ —Al ₂
O ₃ -Na ₂ O) various glass ceramics is used. In the case of aluminosilicate glass, (A) polishing is performed after chemical strengthening, and the unstable element of the strengthening layer in thinning the disk is high. (B) Since the chemical strengthening is performed, the alkali content as the composition of the substrate itself is reduced. And the problem of alkali corrosion is likely to occur. That is, since a large amount of Na ₂ O component is contained as an essential component in the glass surface layer, the film forming characteristics are deteriorated, and an etching process or a barrier coating process for preventing Na ₂ O elution is required.
There is a disadvantage that it is difficult to stably produce a product at low cost, such as a problem such as minute undulation of a substrate.

On the other hand, a substrate material with less alkali elution
Glass ceramics may be used as a material. For example,
SiO described in JP-A-6-329440_Two−Li_TwoO-
MgO-P_TwoO_FiveSeries glass ceramics
Lithium disilicate (Li_TwoO.2SiO_Two) And α-q
Quartz (α-SiO_Two) And α-quartz (α-S
iO_Two) By controlling the spherical particle size
No need for conventional mechanical or chemical textures
And the surface roughness (Ra) obtained by polishing is 15 to 50 °.
With a texture material on the entire surface of the substrate that enables control in a range
And a very excellent material.
No. 6 publication SiO_Two−Li_TwoOK_TwoO-MgO-Z
nO-P_TwoO_Five―Al_TwoO_ThreeSystem or SiO_Two−Li_TwoO-
K_TwoO-MgO-ZnO-P_TwoO_Five―Al_TwoO_Three―ZrO_Twosystem
Glass ceramics use lithium disilicate as the main crystal phase.
(Li_TwoO.2SiO_Two), Lithium disilicate and α-quo
Arts (α-SiO_Two) Mixed crystal or lithium disilicate and
And α-cristobalite (α-SiO_Two) Low mixed crystal
Laser technology characterized by at least one kind
Glass ceramics for sture, as disclosed in JP-A-9-35
No. 234, the glass ceramic substrate is made of SiO.
_Two-Al_TwoO_Three−Li_TwoIn O-based glass, the main crystal phase
Lithium silicate (Li_TwoO.2SiO_Two) And β-spodjoux
Men (Li _TwoO ・ Al_TwoO_Three・ 4SiO_Two)
A disc substrate, which has the international publication number WO97 / 0116.
The glass ceramic substrate described in Japanese Patent Application Laid-Open No.
Patent No. 35234, and new crystallization of the above composition system
Lower the heat treatment (680-770 ° C)
Putite (Li_TwoO ・ Al_TwoO_Three・ 2SiO_Two) Is deposited
Things.

However, although these glass-ceramic substrates have less alkali elution than the chemically strengthened amorphous glass, alkali elution still occurs. Even with glass ceramic substrates, problems such as "deterioration of magnetic properties of the storage medium", "attachment of defects to the substrate surface", and "problem of skipping over recording" due to alkali elution are becoming problems. However, with respect to these glass-ceramic substrates, no mention is made of any improvement with respect to alkali elution, and no discussion is made on mechanical strength such as crystal particle diameter, crystallinity, Young's modulus and specific gravity described below. . In particular, JP-A-9-
No. 35234 and International Publication No. WO 97/011
The glass-ceramic substrate described in Japanese Patent Publication No. 64 has a negative thermal expansion characteristic in the main crystal phase (the substrate has low expansion characteristics).
Β-spodumene (Li ₂ O.Al ₂ O ₃ .4
An SiO _2), crystals with α- quartz (alpha-SiO ₂₎ and α- cristobalite (alpha-SiO ₂₎ crystals or the like positive thermal expansion properties of the SiO ₂ system (resulting substrate becomes high expansion characteristic) It is clear that the material in which a crystal having a negative thermal expansion characteristic is precipitated as a main crystal has a negative effect on the difference in thermal expansion coefficient with the components of the information storage medium device. . Japanese Unexamined Patent Publication No. 9-35234 discloses a magnetic disk having a polished surface roughness Ra.
(Arithmetic average roughness) is 20 ° or less, but the surface roughness Ra (arithmetic average roughness) disclosed in Examples is 12 to 17 °.
However, the above requirements are still rough, and it is not possible to sufficiently cope with the low flying height of the magnetic head accompanying the improvement of the storage capacity.
In addition, the crystallization heat treatment temperature requires a high temperature of 820 to 920 ° C., which hinders low cost and mass productivity.

[0012]

SUMMARY OF THE INVENTION The object of the present invention is, as described above, "It is necessary to reduce the size of the bit cell with the increase in storage density. When the head operates in a low flying state (near contact) or a contact state (contact) with respect to the information storage medium substrate in this manner, the head is operated closer to the information storage medium surface. For the smoothness, the surface roughness Ra (arithmetic average roughness) is required to be 5.0 ° or less, more preferably 3.0 ° or less, and further preferably 2.0 ° or less.
"With the ultra-smoothness, the crystal grains inside the substrate can withstand the precision polishing at the atomic level, so the type and size of crystals that can withstand the chemical durability and physical properties derived from ultra-precision polishing , Crystal grain shape and crystallinity are required. "
"With the increase in storage density, it is necessary to increase the rotation speed of the substrate. For such a high-speed rotation, high Young's modulus and low specific gravity are important for the substrate material." The mechanical strength of the substrate material is important for mobile applications, especially for mobile applications. "" Because the positioning of the head and the media requires high precision, high dimensional accuracy is required for each component of the media substrate and disk. Therefore, the difference between the average linear expansion coefficients of these components must be reduced as much as possible in the operating environment temperature range. "
The elution of the alkali component in the glass needs to be further reduced since the orientation of the magnetic film is reduced and the generation of the defect due to the generation of the compound of the alkali component diffused to the surface occurs. Particularly, elution of an alkali component from glass ceramics occurs from an amorphous portion in a matrix. Therefore, it is necessary to reduce as much as possible other than an alkali component in a crystal. In order to solve the problems that cannot be solved by the above-mentioned conventional technology, the characteristics required at present are eliminated, and the magnetic storage of the recording medium due to the alkali elution and the defect due to the alkali elution are eliminated. Increases the storage capacity of the medium, lowers the flying height of the magnetic head or super-smooths the substrate due to the contact state, further increases the rotation speed of the information transfer speed, increases the mechanical strength for mobile applications, and configures other storage media It is an object of the present invention to provide a glass ceramic substrate for an information storage medium having compatibility with a component material and a magnetic information storage medium in which a coating of a magnetic medium is formed on the glass ceramic substrate.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive tests and researches to achieve the above object, and have found that a glass ceramic substrate for an information storage medium having lithium disilicate in a main crystal phase has a high density. Good surface and physical properties (various strength, average linear expansion coefficient (Avera
The present inventors have found that a glass ceramic suitable for a substrate for an information storage medium can be obtained which has a composition capable of remarkably reducing alkali elution and has a composition capable of remarkably reducing alkali elution.

That is, the invention according to claim 1 contains lithium disilicate (Li ₂ O · 2SiO ₂ ) as a main crystal phase, and the content of Li ₂ O is 4% by mass or less in terms of oxide mass. A glass ceramic substrate for an information storage medium, wherein the crystallinity of the crystal phase of lithium disilicate is 15 to 40% by mass. The glass ceramic substrate for an information storage medium according to claim 1, wherein the average linear expansion coefficient at −50 to + 70 ° C. is +65 to + 130 × 10 ⁻⁷ / ° C. The glass ceramic substrate for an information storage medium according to claim 1 or 2, wherein the Young's modulus (GPa) / specific gravity is 37 or more. To claim 1 The glass ceramic substrate for an information storage medium according to any one of claims 1 to 4, wherein the invention according to claim 5 has a bending strength of 400 MPa or more. The glass-ceramic substrate for an information storage medium according to any one of claims 1 to 3, wherein the invention according to claim 6 is characterized in that (1) lithium disilicate (Li ₂
O.2SiO ₂ ) and (2) α-quartz (α-Si
O ₂ ) or α-quartz solid solution (α-SiO ₂ solid solution)
Wherein the crystal grain size (average) of the entire main crystal phase is 0.05 μm or less.
5. The glass-ceramic substrate for an information storage medium according to any one of (5) and (7), wherein the main crystal phase is (1) lithium disilicate (Li ₂ O · 2SiO ₂ ).
And (2) α-quartz (α-SiO ₂ ) or α-quartz
It contains a quartz solid solution (α-SiO ₂ solid solution), the crystallinity of the α-quartz or α-quartz solid solution crystal phase is 3 to 35% by mass, and the crystal particle diameter (average) is 0.
The glass ceramic substrate for an information storage medium according to any one of claims 1 to 6, characterized in that the crystal grain is not more than 10 µm. The glass-ceramic substrate for an information storage medium according to any one of claims 1 to 7, wherein the glass-ceramic substrate has a spherical shape.
9. O-free material.
The glass ceramics substrate for an information storage medium according to any one of the above, wherein the surface roughness Ra (arithmetic mean roughness) after polishing is 5.0 ° or less. The glass ceramic substrate for an information storage medium according to any one of claims 1 to 9, wherein the composition of the glass ceramic is SiO 2 in terms of mass percentage (in terms of oxide). _{2 70 ~77% Li 2 O 4} ~ 8% K 2 O 0.5 ~ 5% MgO + ZnO + SrO + BaO + CaO 1 ~ 7% Y 2 O 3 + WO 3 + La 2 O 3 + Bi 2 O 3 + SnO 2 0 ~ 3% P 2 O 5 1.0 to 2.5% ZrO ₂ 2.0 to 7% Al ₂ O ₃ 5 to 10% Na ₂ O 0.5 to 3% Sb ₂ O ₃ + As ₂ O ₃₀ 0 to 2% Claims, characterized by containing
The glass ceramics substrate for an information storage medium according to any one of claims 10 to 10, wherein the composition of the glass ceramics is SiO ₂ 70 to 77% Li _{2 in} terms of mass percentage (in terms of oxide). O 4 to 8% K ₂ O 0.5 to 5% MgO + ZnO + SrO + BaO + CaO 1 to 7% Y ₂ O ₃ + WO ₃ + La ₂ O ₃ + Bi ₂ O ₃ + SnO ₂₀ 0 to 3% P ₂ O ₅ 1.0 to 2.5 % ZrO ₂ 2.0 to 7% Al ₂ O ₃ 5 to 10% Na ₂ O 0 to 1% Sb ₂ O ₃ + As ₂ O ₃ 0 to 2% Claim 1
The glass ceramics substrate for an information storage medium according to any one of claims 10 to 10, wherein the invention according to claim 13 forms a nucleus by heat-treating the raw glass at 400 ° C to 600 ° C for 1 to 7 hours. The crystal growth is performed by heat treatment at 700 ° C. to 760 ° C. for 1 to 7 hours, and the surface roughness Ra (arithmetic mean roughness) after polishing is set to 5 ° or less.
Or a method for manufacturing a glass-ceramic substrate for an information storage medium according to claim 12, wherein the invention according to claim 14 is a method for manufacturing a glass-ceramic substrate for information storage medium according to any one of claims 1 to 13, Membrane and optionally N
This is an information storage medium disk formed by i-P plating or forming an underlayer, a protective layer, a lubricating film, and the like.

The main crystal phase and the crystal grain size (average), crystallinity, Young's modulus, specific gravity, mechanical strength, average linear expansion coefficient, surface characteristics, composition, heat treatment of the glass-ceramic substrate for an information storage medium of the present invention. The reasons for limiting the conditions are described below. The composition is expressed in terms of mass percentage on an oxide basis as in the raw glass.

First, regarding the average linear expansion coefficient,
With the increase in recording density, high precision is required for positioning the magnetic head and the medium. Therefore, high dimensional accuracy is required for each component of the medium substrate and the disk. Therefore, the influence of the difference in the average coefficient of linear expansion on these components cannot be ignored. Therefore, the difference in the coefficient of thermal expansion must be minimized. More precisely, it may be preferred that the average linear expansion coefficient of the media substrate is very slightly greater than the average linear expansion coefficient of these components. In particular, the thermal expansion coefficient of components used for a small magnetic information storage medium is +9.
A substrate having a coefficient of thermal expansion of about 0 to + 100 × 10 ⁻⁷ / ° C. is often used.
Depending on the drive maker, a material having a thermal expansion coefficient (around +70 to + 125 × 10 ⁻⁷ / ° C.) out of this range may be used as a component. For the above reasons, the crystal system of the present invention, while aiming at the balance with the strength, so that it can widely correspond to the material of the component used,
The average linear expansion coefficient range must be determined, and the range is +65 to + 130 × in the range of −50 to + 70 ° C.
It is preferably 10 ⁻⁷ / ° C. Further, the average linear expansion coefficient is more preferably + 95 × 10 ⁻⁷ / ° C. or more, and +1
It is more preferably at most 10 × 10 ⁻⁷ / ° C.

Next, the Young's modulus, specific gravity, and mechanical strength will be described. Regarding the Young's modulus and specific gravity, the glass ceramic substrate for an information storage medium of the present invention is required to prevent deformation and static vibration of the substrate against a high-speed rotation of 10,000 rpm or more corresponding to a high information transfer speed. High rigidity,
Must have low specific gravity. Further, when used in a portable storage device such as a head contact or a removable storage device, it is necessary to have a mechanical strength, a high Young's modulus, and a surface hardness that can sufficiently withstand it.

However, if the specific gravity is large even if the rigidity is merely high, the weight is large at the time of high-speed rotation, causing deflection and vibration. Conversely, if the rigidity is small even at a low specific gravity, vibration is similarly generated. Therefore, it is necessary to balance seemingly contradictory characteristics of high rigidity and low specific gravity, and the preferable range is Young's modulus (GPa) / specific gravity of 37 or more. A more preferred range is 39 or more, a still more preferred range is 41 or more, and a most preferred range is 43 or more. Note that there is a preferable range for the rigidity. Even if the above range is satisfied at a low specific gravity, it is preferable that at least the Young's modulus of the substrate is 95 GPa or more from the viewpoint of the problem of vibration generation. In the example of the present invention, the glass ceramic substrate had a Young's modulus in a range of 95 GPa or more and 120 GPa or less. The same applies to the specific gravity. From the viewpoint of the problem of the occurrence of vibration, the specific gravity is 2.60 even if the rigidity is high.
Or less, more preferably 2.57 or less. In Examples of the present invention, the specific gravity was in the range of 2.40 or more and 2.60 or less.

In addition, information storage media for mobile use and the like are required to have shock resistance (100 G to 500 G) and high mechanical strength enough to withstand head slap. Therefore, the bending strength of the substrate is 400 MPa. It is preferably at least 500 MPa, more preferably at least 500 MPa. In the examples of the present invention, the glass ceramic substrate had a bending strength in the range of 400 MPa or more and 800 MPa or less.

Next, regarding the main crystal phase, the glass-ceramic substrate containing lithium disilicate has high crystal anisotropy, defects such as few impurities, and a dense, uniform and fine structure as an information magnetic storage medium. This is because it is very useful because it can realize mechanical strength, ease of processing, controllability of thermal expansion characteristics, high chemical durability, and the like. Further, by including α-quartz or α-quartz solid solution as the main crystal phase, the bending strength can be made harder,
At the same time, the average linear expansion coefficient at −50 to + 70 ° C. can be set higher, so that the glass ceramic substrate containing (1) lithium disilicate and (2) α-quartz or α-quartz solid solution has a high mechanical strength, It is very excellent in controllability of average linear expansion coefficient and chemical stability, and is preferable.

Next, regarding the content of Li ₂ O, this component is a very important essential component for facilitating production and melting of the raw glass and for precipitating lithium disilicate. Heretofore, since this component has incorporated a Li ₂ O component more than the stoichiometric amount necessary for constituting lithium disilicate, extra Li ₂ O which does not contribute to the constitution of this crystal phase is used. Is present in the glass phase. This becomes an alkali-eluting component and increases the possibility of causing the above-described problem.

More specifically, from the viewpoint of the alkali elution amount, the crystallized glass has a smaller alkali elution amount than the chemically strengthened amorphous glass as described above. Must be reduced. As a result of a detailed test study on these, the amount of alkali elution from the substrate surface in a predetermined alkali elution test was 2.5 inch disk substrate (external dimensions: outer diameter 65 mmφ, inner diameter 20 mmφ, thickness 0.635 mm, chamfer processing: 0.1m at 45 °
m), when the elution amount per unit area is equal to or greater than 0.016 μg / cm ² , if the elution amount per unit area is equal to or greater than 0.016 μg / cm ^{2, the} magnetic properties decrease due to alkali diffusion at the time of film formation of the recording medium or the alkali diffuses to the surface of the recording medium. The production of the alkali compound by the components, for example, 10,000 rpm
It has been clarified that a read error or a head crash occurs on a magnetic disk substrate requiring the above high-speed rotation. The alkali elution amount was 0.0
More preferably from (0.7 [mu] g / disc below 2.5 inch disk substrate) 11μg / cm ² or less, with 0.008 / cm ² or less (0.5 [mu] g / disc below 2.5 inch disk substrate) Most preferably.

Therefore, lithium disilicate is contained as a main crystal phase in order to have the Li ₂ O content necessary for constituting lithium disilicate and to reduce extra Li ₂ O which causes alkali elution as much as possible. The content must be controlled to be lower than the upper limit of the Li ₂ O content of the conventional glass ceramic substrate. That is, if the amount is less than 4% by mass, it becomes difficult to precipitate the crystals in a fine state, and at the same time, it becomes difficult to melt the original glass. If the amount exceeds 8% by mass, the surplus exceeding the stoichiometric amount constituting the crystals is obtained. Since a large amount of the Li ₂ O component remains in the glass matrix, a problem of Li ion elution occurs. In addition, a better glass-ceramic substrate, particularly, an alkali elution amount of 0.011 μg / cm ²
In order to obtain the following glass-ceramic substrate, the Li ₂ O content is preferably 4% by mass or more and less than 8% by mass, more preferably 4.5% by mass or more and less than 8% by mass. Most preferably, it is 5% by mass or more and less than 8% by mass.

Further, Li as a component constituting the main crystal phase
Other crystalline phases requiring ₂ O (eg, Spodumen)
e, Eucryptite, Petalite, etc.), it is effective to limit the range of the Li ₂ O content, but β- having a negative thermal expansion characteristic is effective.
With respect to spodumene, β-eucryptite, and β-cristobalite (β-SiO ₂ ), it is more likely that it is difficult to obtain a desired average linear expansion coefficient. Is preferably not contained.

Next, regarding the crystallinity of lithium disilicate, as described above, desired mechanical strength, workability, thermal expansion characteristics, chemical durability, etc. were obtained as glass ceramic substrates for information recording media. In addition, in order to reduce the excess Li ₂ O in the glass matrix at the Li ₂ O content and eliminate the problem of alkali elution, the content is preferably 15% by mass or more and 40% by mass or less. The content is more preferably more than 20% by mass and up to 40% by mass, and most preferably more than 20% by mass and up to 38% by mass.

The α-quartz or α-quartz solid solution crystal has a crystallinity of 3% by mass or more and 35% by mass in order to obtain desired physical properties in controlling mechanical strength (particularly bending strength) and thermal expansion characteristics. % Is preferable. A more preferred range is from 5 to 35% by mass.

The surface roughness R having such excellent smoothness
a, It is difficult to realize unless the crystal grain size is regulated in order to realize polishing workability and remarkably excellent mechanical strength, especially bending strength, and the crystal grain size of the entire main crystal phase including lithium disilicate Must be 0.05 μm or less. Therefore, even when the main crystal phase contains (1) lithium disilicate and (2) α-quartz or α-quartz solid solution, the average of the crystal grain diameter of the entire main crystal phase must be 0.05 μm or less. still,
(2) With respect to α-quartz or α-quartz solid solution, the average crystal grain size can be 0.10 μm or less depending on the shape and other characteristics of the crystal grains. Also,
Regarding a preferable range, the average of the crystal particle diameter of the entire main crystal phase is 0.05 μm or less, (1) the average of the crystal particle diameter of lithium disilicate crystal is 0.04 μm or less, and (2) α-quartz or α-quartz. The average of the crystal particle diameters of the solid solution crystals is 0.07 μm or less, and a more preferable range is that the average of the crystal particle diameters of the entire main crystal phase is 0.03 μm or less,
(1) The average of the crystal particle diameters of lithium disilicate crystals is 0.0
3 μm or less, (2) the average of the crystal particle diameters of α-quartz or α-quartz solid solution crystals is 0.05 μm or less.

Regarding the particle shape of the precipitated crystal phase,
In the case of an irregular shape, it is difficult to obtain good smoothness, and the precipitated crystals are liable to fall off, causing particles to damage the magnetic head and the medium. It is preferable in terms of the surface characteristics of the medium substrate, and it is preferable that the medium substrate be substantially spherical.

Next, in the composition range of the raw glass, Li
_The reasons for limiting each component other than the 2O component as described above will be described below. That is, the SiO ₂ component is composed of lithium disilicate (Li ₂ O · 2SiO ₂ ) and α-quartz (α-SiO) which are precipitated as a main crystal phase by heat treatment of the raw glass.
₂ ), which is a very important component for producing α-quartz solid solution (α-SiO ₂ solid solution) crystals. If the amount is less than 70% by mass, precipitated crystals of the obtained glass ceramic are unstable and the structure is coarse. When the content exceeds 77% by mass, melting and forming of the raw glass becomes difficult.

MgO, ZnO, SrO, BaO, CaO
The components are components that improve the melting property of glass and prevent coarsening of precipitated crystals, and at the same time, lithium disilicate (Li ₂ O.2SiO ₂ ) and α-quartz (α- SiO ₂ ), α-quartz solid solution (α-S
It is an effective component for precipitating each crystal particle of iO ₂ solid solution) into a sphere. Therefore, the total amount of each component is 1.
The content is preferably 0% by mass or more, but if it exceeds 7% by mass, the obtained crystals are unstable and the structure tends to be coarse. In the case of MgO + ZnO + SrO + BaO, 1
It is preferably from 2% by mass to 2% by mass.

In the present invention, the P ₂ O ₅ component is indispensable as a crystal nucleating agent for glass. However, in order to promote the formation of crystal nuclei and prevent coarsening of the precipitated crystal phase, the amount of P ₂ O ₅ is 1.0 mass. % Or more is preferable. In addition, we prevent milk glass devitrification of original glass,
In order to maintain mass production stability, the content is preferably 2.5% by mass or less.

Like the P ₂ O ₅ component, the ZrO ₂ component not only functions as a crystal nucleating agent for glass, but also has a remarkable effect on refining precipitated crystals, improving the mechanical strength of the material, and improving the chemical durability. Is a very important component that has been found to have The amount is preferably 2.0% by mass or more, provided that
Excessive addition makes it difficult to melt the raw glass and
Since the tendency of rSiO ₄ etc. to remain undissolved increases,
The amount of the ZrO ₂ component is preferably 7% by mass or less.

The Al ₂ O ₃ component is a component for improving the chemical durability and mechanical strength, particularly the hardness, of the glass ceramic, and its amount is preferably at least 5% by mass. However, when the Al ₂ O ₃ component is excessive, the melting and devitrification tend to deteriorate, and the precipitated crystalline phase is a β-spodumene (Li ₂ O.Al ₂ O _3.
4SiO ₂ ). As described above, β-spodumene (Li ₂ O.Al ₂ O _3.
Since the precipitation of 4SiO ₂ ) significantly lowers the average linear expansion coefficient of the material, the precipitation of these crystals must be avoided. Therefore, the content of the Al ₂ O ₃ component is preferably 10% by mass or less. More preferably, the content is 5% by mass or more and 8% by mass or less.

Y ₂ O ₃ , WO ₃ , La ₂ O ₃ , Bi ₂ O ₃ , S
The nO ₂ component is an important component that improves the lowered meltability in the low-content Li ₂ O component composition and also increases the Young's modulus of the glass. When the total amount exceeds 3% by mass, the nO ₂ component becomes stable. Precipitation of crystals becomes difficult. In addition, Bi ₂ O ₃
With respect to the components, coexistence with As ₂ O ₃ causes a coloring action after crystallization, which has the effect of facilitating detection of the presence or absence of flaws and increasing the efficiency of laser energy absorption in laser texture. In addition, Y ₂ O ₃ + WO ₃
In + La ₂ O ₃ + Bi ₂ O ₃ , the content is preferably 1% by mass or more and less than 3% by mass.

The K ₂ O component not only improves the melting property of the glass but also prevents coarsening of precipitated crystals, and in the present invention, particularly, in the present invention, other alkali components (Li ₂ O component and / or Na ₂ O component) By coexisting with (mixing with), there is an important effect of suppressing elution or diffusion of alkali ions.
The above is preferred. However, if it is contained excessively, the precipitated crystals become coarse, the crystal phase changes, and the chemical durability deteriorates, so the amount is preferably 5% by mass or less.

As with the K ₂ O component, the Na ₂ O component has the effect of improving the melting property of the glass and at the same time preventing the deposited crystals from becoming coarse, and in the present invention, in particular, in the present invention, other alkali components (Li ₂ O Component and K ₂ O component), there is an important effect of suppressing the diffusion of alkali ions.
_When the three components of ₂ O, Na ₂ O, and K ₂ O are mixed in an appropriate range, the effect of preventing elution with respect to the total amount of alkali is most exhibited. To achieve this effect, Na ₂ O
The content of the component is preferably 0.5% by mass or more, but its effect is not so remarkable as that of the K ₂ O component. Therefore, when the content is more than necessary, the alkali elution tends to increase. Therefore, the content is preferably 3% by mass or less.

However, when the content is less than 1% by mass, the elution prevention due to the mixing effect of the three alkalis is slightly lowered, but the mixing effect of the two alkalis of the Li ₂ O component and the K ₂ O component exists. Since the Na ₂ O component content itself is low, it is possible to obtain a glass-ceramic substrate with an extremely low alkali elution amount even in this case.

Here, the alkali mixing effect will be described.
Originally, the amount of alkali eluted is due to the alkali ions in the glass matrix. It is thought that if the total amount of these alkali components is large, the amount of alkali eluted will also increase, but coexistence (mixing) of two or more types of alkalis Thus, the amount of alkali elution can be significantly reduced as compared with the case where only one alkali component is used. This is because the diffusion coefficient of each alkali component can be reduced by mixing these alkali components. In particular and two combinations of Li ₂ O component and K ₂ O component, in which ,, the effect was very good in 3 principal components of the combination of Li ₂ O component, Na ₂ O component and K ₂ O ingredients there were. However, even if the diffusion coefficient is lowered, if the original content of each alkali component is large, the alkali elution amount increases in proportion to this. The present application is directed to a glass having a low alkali elution amount and optimizing the alkali content.

The Sb ₂ O ₃ and As ₂ O ₃ components can be added as a fining agent at the time of glass melting, but the sum of these components is preferably 2% by mass or less, more preferably 1% by mass or less.

Next, for the reason that PbO is not substantially contained, it is an unfavorable component in improving the precision and miniaturization of the magnetic film and also in the environment because it is easily diffused into the magnetic medium film. Therefore, use should be avoided as much as possible.

In addition to the above composition, Cu, Co, Fe,
One or more elements selected from Mn, Cr, Sn, and V can be contained up to 2% by mass in terms of oxide. Further, one or more elements selected from Ge, Gd, Ti, Ta and Nb can be contained up to 5% by mass in terms of oxide.

Next, in order to manufacture the glass-ceramic substrate for a magnetic information storage medium according to the present invention, the glass having the above composition is melted, hot-formed and / or cold-worked, and then 400-600. 1-7 at a temperature in the range of ° C
Heat treatment for hours to form crystal nuclei, followed by 700-760
The crystallization is performed by heat treatment at a temperature in the range of 1 to 7 hours. Under these heat treatment conditions, a glass-ceramic substrate having a desired crystal phase, crystal grain size and crystallinity can be obtained.

The heat treated crystallized glass ceramic is lapped by a conventional method and then polished, so that the surface roughness Ra (arithmetic mean roughness) is 1.0 ° or more.
A disk substrate for an information storage medium within a range of 5.0 ° or less is obtained, and a magnetic film and, if necessary, Ni-P plating, or an underlayer, a protective layer, a lubricating film, etc. are formed on the disk substrate. As a result, it is possible to obtain a good information magnetic storage medium disk which has good surface smoothness, has no defects due to alkali elution, and does not cause any problem even in a long-time input / output test.

[0044]

Next, a preferred embodiment of the present invention will be described. Tables 1 to 3 show working composition examples (No. 1 to No. 1) of a glass ceramic substrate for a disc for an information storage medium of the present invention.
7) and the comparative conventional Li ₂ O-SiO ₂ system glass ceramics two as Composition Example (Comparative Example 1: JP 62-72
No. 547, Comparative Example 2: JP-A-9-352
No. 34, the composition (expressed in terms of mass percentage based on oxide), nucleation temperature, crystallization temperature, crystal phase, crystallinity, and crystal particle size (average) are shown in Table 4. 6 to 6 show the thermal expansion of the glass ceramic substrate shown in Tables 1 to 3,
Young's modulus, specific gravity, bending strength, surface roughness Ra polished
It shows the value of (arithmetic average roughness) and the amount of alkali elution.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

[Table 5]

[0050]

[Table 6]

[0051]

[Table 7]

[0052]

[Table 8]

[0053]

[Table 9]

[0054]

[Table 10]

[0055]

[Table 11]

[0056]

[Table 12]

In the glasses of the above embodiments of the present invention, raw materials such as oxides, carbonates, nitrates, etc. are all mixed, and the mixture is melted at a temperature of about 1350 to 1450 ° C. using an ordinary melting apparatus, and the mixture is stirred and homogenized. Then, the mixture was molded into a disk and cooled to obtain a glass molded body. Thereafter, this is heat-treated at 400 to 600 ° C. for about 1 to 7 hours, and after forming crystal nuclei, 700 to 760 ° C.
For about 1 to 7 hours to obtain a desired glass ceramic. Then, the above glass ceramics were
Approximately 5-30 with # ~ 2000 # diamond pellets
Wrapping, then particle size (average) 0.02-3μ
The abrasive was polished for about 30 to 60 minutes with an abrasive oxidized cerium. The external dimensions of this glass ceramic substrate are
Outer diameter 65mmφ, inner diameter 20mmφ, thickness 0.635m
m, chamfering: 0.1 mm at 45 °.

The crystal grain size (average) of each crystal phase was determined by a transmission electron microscope (TEM). For the crystal seed of each crystal phase, an X-ray diffraction (XRD) apparatus was used, and for the degree of crystallinity, Si was prepared as a 100% by mass crystal standard sample and an internal standard sample of each crystal seed.
D) Internal standard method (Internal standard meth
od: determined by the diffraction peak area using the internal standard method in JIS.

Further, the surface roughness Ra (arithmetic mean roughness) was determined by an atomic force microscope (AFM).

The bending strength was calculated from the inner diameter, outer diameter, plate thickness, Poisson's ratio, and maximum load of the disk by a cup-type ring bending test.

The measurement of the alkaline elution component was performed by using ion chromatography. The test conditions were as follows. One glass ceramic substrate obtained above was immersed in pure water at 30 ° C. and 80 ml for 3 hours, and the alkali elution amount of the substrate was calculated from the alkali concentration eluted in the pure water. I asked.

As shown in Tables 1 to 3, the glass-ceramic substrate of the present invention has a main crystal phase of lithium disilicate (Li ₂
Si ₂ O ₅ ) and α-quartz, all of the crystal grains are fine and less than 0.02 μm, and the particle shape is almost spherical, whereas the glass ceramic of Comparative Example 1 has a crystal particle diameter of lithium disilicate ( (Average) is 1.5 μm, and the glass ceramics of Comparative Example 2 have a β-spodumene crystal particle diameter (average) of 0.2 μm, all of which have a relatively large acicular or rice grain shape. This has an effect on the surface roughness and defects obtained by polishing in a situation where more smoothness is required, and the glass ceramics of Comparative Examples 1 and 2 all have a surface roughness Ra (arithmetic average roughness). 11 ° or more indicates that it is difficult to obtain surface characteristics having excellent smoothness.

The average coefficient of linear expansion (× 10 ⁻⁷ / ° C.) of the glass ceramic substrate was less than 50 in both Comparative Examples 1 and 2, and the Young's modulus was 84 GP.
a, the bending strength is 320 MPa or less, and the glass ceramics of Comparative Examples 1 and 2 are low Young's modulus and low strength materials,
For this reason, it is unsuitable as a recent substrate material for a high-density magnetic information storage medium.

Further, a Cr intermediate layer (80 nm), a Co—Cr magnetic layer (50 nm), a Si
A C protective film (10 nm) was formed. Next, a perfluoropolyether-based lubricant (5 nm) was applied to obtain an information storage medium. The information storage medium obtained in this way can reduce the flying height of the head compared to the conventional one due to its good surface roughness, and perform input / output in the state where the head and the medium are in contact by the ramp loading method. Even
Magnetic signals could be input and output without causing head damage and medium damage. Further, the glass ceramic of the present invention is a substrate which shows a stable bump shape even in a laser texture performed by a landing zone method.

[0065]

As described above, according to the present invention, it is possible to solve the above-mentioned drawbacks of the prior art and to achieve a low flying height or contact of the head corresponding to a high recording density. It has ultra-smoothness, high Young's modulus and low specific gravity corresponding to high-speed rotation corresponding to high information speed, and at the same time has high mechanical strength indispensable for mobile applications It is possible to provide a glass ceramic substrate for an information storage medium in which an alkali component is reduced as much as possible, a method for manufacturing the same, and a magnetic information storage medium in which a coating of a magnetic medium is formed on the glass ceramic substrate.

Continued on the front page F-term (reference) 4G062 AA11 BB01 CC04 CC09 DA07 DA08 DB03 DC01 DD03 DE03 DF01 EA03 EB02 EB03 EC02 EC03 ED03 EE03 EF03 EG03 FA01 FB01 FC03 FD01 FE01 FE02 FE03 FF01 FG01 F03 F01 GA01 GB01 GC01 GD01 GE01 HH01 HH03 HH05 HH07 HH08 HH09 HH11 HH13 HH15 HH17 JJ01 JJ03 JJ04 JJ05 JJ07 KK01 KK03 KK05 KK07 KK10 MM27 NN30 NN33 QQ02 QQ20 5D006 CB04 CB07

Claims (14)

[Claims] 1. The method according to claim 1, wherein lithium disilicate (Li ₂
O.2SiO ₂ ), and the content of Li ₂ O is from 4% by mass to 8% by mass in terms of oxide mass. 2. The crystalline phase of lithium disilicate has a crystallinity of 1
The glass ceramic substrate for an information storage medium according to claim 1, wherein the content is 5 to 40% by mass. 3. The glass ceramic substrate for an information storage medium according to claim 1, wherein the average linear expansion coefficient at −50 to + 70 ° C. is +65 to + 130 × 10 ⁻⁷ / ° C. 4. The glass ceramic substrate for an information storage medium according to claim 1, wherein the Young's modulus (GPa) / specific gravity is 37 or more. 5. The glass-ceramic substrate for an information storage medium according to claim 1, having a bending strength of 400 MPa or more. 6. The main crystal phases (1) lithium disilicate (Li ₂ O.2SiO ₂ ) and (2) α-quartz (α)
-SiO ₂ ) or α-quartz solid solution (α-SiO ₂ solid solution), and the crystal grain size (average) of the entire main crystal phase is 0.05 μm or less. The glass-ceramic substrate for an information storage medium according to any one of the above. 7. The main crystal phases include (1) lithium disilicate (Li ₂ O.2SiO ₂ ) and (2) α-quartz (α).
-SiO ₂ ) or α-quartz solid solution (α-SiO ₂ solid solution), and the crystallinity of the α-quartz or α-quartz solid solution crystal phase is 3 to 35% by mass, and the crystal particle diameter (average) is The glass-ceramic substrate for an information storage medium according to any one of claims 1 to 6, wherein the thickness is 0.10 µm or less. 8. The glass-ceramic substrate for an information storage medium according to claim 1, wherein the crystal grains are all fine and substantially spherical. 9. The glass-ceramic substrate for an information storage medium according to claim 1, wherein the glass-ceramic substrate is substantially free of PbO. 10. The glass for an information storage medium according to claim 1, wherein a surface roughness Ra (arithmetic mean roughness) after polishing is 5.0 ° or less. Ceramic substrate. 11. The composition of glass ceramics is expressed as mass percentage (in terms of oxide) of SiO ₂ 70 to 77% Li ₂ O 4 to 8% K ₂ O 0.5 to 5% MgO + ZnO + SrO + BaO + CaO 1 to 7% Y ₂ O ₃ + WO _{3 + La 2 O 3 + Bi} 2 O 3 + SnO 2 0 ~ 3% P 2 O 5 1.0~ 2.5% ZrO 2 2.0~ 7% Al 2 O 3 5 ~ 10% Na 2 O 0.5~ The composition according to claim 1, further comprising 3% Sb ₂ O ₃ + As ₂ O ₃ 0 to 2% of each component.
11. The glass-ceramic substrate for an information storage medium according to any one of items 10 to 10. 12. The composition of glass ceramics is expressed as mass percentage (in terms of oxide) of SiO ₂ 70 to 77% Li ₂ O 4 to 8% K ₂ O 0.5 to 5% MgO + ZnO + SrO + BaO + CaO 1 to 7% Y ₂ O ₃ + WO ₃ + La ₂ O ₃ + Bi ₂ O ₃ + SnO ₂ 0 to 3% P ₂ O ₅ 1.0 to 2.5% ZrO ₂ 2.0 to 7% Al ₂ O ₃ 5 to 10% Na ₂ O 0 to 1% _{2. The} composition according to claim 1, wherein each component is contained in the range of Sb ₂ O ₃ + As ₂ O ₃ 0 to 2%.
11. The glass-ceramic substrate for an information storage medium according to any one of items 10 to 10. 13. The raw glass is heated at 400.degree.
After heat treatment for 7 hours to form nuclei, heat treatment is performed at 700 ° C. to 760 ° C. for 1 to 7 hours to grow crystals, and the surface roughness Ra (arithmetic mean roughness) after polishing is set to 5 ° or less. The method for producing a glass ceramic substrate for an information storage medium according to claim 11 or 12, wherein 14. A magnetic film and optionally Ni-P plating, or an underlayer, a protective layer, a lubricating film, etc., on the glass-ceramic substrate for an information storage medium according to claim 1. An information storage medium disk formed.