JP2005119963A - Process for preparation of crystallized glass for information recording disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallized glass holding the characteristic of high stiffness (>130 GPa) suitable as a substrate for an information recording medium such as a magnetic recording medium and having excellent characteristics such as high surface smoothness and high surface flatness having a surface roughness Ra suppressed to ≤0.5 nm. <P>SOLUTION: This process for preparing the crystallized glass is a method of preparing the crystallized glass obtained by making a glass containing TiO<SB>2</SB>subjected to a phase splitting step and a crystallization step, where the phase splitting step has heat treatment of the glass at a temperature in the range from the glass transition temperature Tg to the glass transition temperature Tg+60°C. The crystallized glass for the information recording disk is the crystallized glass obtained by this preparation process and has ≤100 nm average particle diameter of the crystal particle or ≥40% transmissivity at 600 nm wave length. The information recording disk is composed of this glass and has a polished surface having 0.1-0.5 nm surface roughness Ra (JIS B0601). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing crystallized glass having high rigidity suitable for an information recording disk such as a magnetic disk substrate and having high surface smoothness and high surface flatness. Furthermore, the present invention relates to a crystallized glass having excellent surface smoothness and surface flatness obtained by the production method of the present invention, an information recording medium substrate made of the crystallized glass, and a magnetic disk using the substrate.

  The main components of a magnetic storage device such as a computer are a magnetic recording medium and a magnetic head for magnetic recording and reproduction. As a magnetic recording medium, a flexible disk and a hard disk are known. Of these, aluminum alloys are mainly used as substrate materials for hard disks. Recently, the flying height of the magnetic head has been remarkably reduced with the increase in the recording density of the PC personal computer and the server hard disk drive (lowering of the magnetic head). Accordingly, extremely high accuracy has been required for the surface smoothness of the magnetic disk substrate. However, in the case of an aluminum alloy, since the hardness is low, even if polishing is performed using a highly accurate abrasive and machine tool, the polished surface is plastically deformed. It is difficult to manufacture. Also, as magnetic disk recording increases in TPI (Track per Inch), BPI (Bit Per Inch) or high-speed rotation, the deflection and amplitude of the magnetic disk substrate during high-speed rotation are greatly suppressed, and data due to vibration and deflection There is also a need to reduce the number of read errors (TMR). However, since the aluminum alloy has low strength and rigidity, it is difficult to maintain a predetermined low level of TMR required from the specifications of the hard disk drive.

Therefore, a crystallized glass substrate for magnetic disks having high rigidity has appeared instead of the aluminum substrate. For example, US Pat. No. 5,472,811 discloses SiO ₂ : 35-60%, Al ₂ O ₃ : 20-35%, MgO: 0-25%, ZnO: 0-25% in terms of weight%, provided that MgO + ZnO _{> 10%, TiO 2: 0-20} %, ZrO 2: 0-10%, Li 2 O: 0-2%, NiO: 0-8%, provided that the oxidation of such _{TiO 2 + ZrO 2 + NiO>} 5% There is disclosed a crystallized glass for a disc containing physical components and containing spinel crystal particles as a main crystal. In addition, in US Pat. No. 5,491,116, SiO ₂ : 35-60%, Al ₂ O ₃ : 10-30%, MgO: 12-30%, ZnO: 0-10%, TiO ₂ : 5- There is disclosed a crystallized glass for a disc containing an oxide component such as 20%, NiO: 0-8% and the like and containing spinel crystal particles and enstatite crystal particles as main crystals.
US Pat. No. 5,472,721 US Patent 5491116

  However, although these crystallized glasses have a high Young's modulus of about 140 GPa, they have a drawback that it is difficult to suppress the surface roughness to 0.5 nm or less with Ra due to the large crystal particles contained. Even if the Young's modulus is as high as about 140 GPa, the flying height of the head cannot be suppressed and the recording density cannot be increased.

  Accordingly, an object of the present invention is a crystallized glass that maintains the characteristics of high rigidity (> 130 GPa) suitable as a substrate for an information recording medium such as a magnetic recording medium, and has performance such as high surface smoothness and high flatness. It is an object of the present invention to provide a crystallized glass that is excellent in surface roughness, that is, the surface roughness of Ra can be suppressed to 0.5 nm or less.

In order to achieve the above-mentioned object, the present inventors have studied based on various experiments. As a result, a glass containing TiO ₂ as a crystal nucleation agent is obtained from a temperature exceeding the Tg of the glass from the Tg of the glass. By heat-treating the glass at a temperature range as high as 60 ° C and then phase-separating the glass homogeneously, it has a high Young's modulus of 140 GPa or higher and a surface roughness of Ra (JIS B0601) of 0.5 nm or lower. The present inventors have found that a crystallized glass suitable for an information recording medium substrate can be obtained, and have reached the present invention.

  Furthermore, the present inventors raised the glass after the above phase separation to a temperature for crystallization (for example, 850 to 1150 ° C., more preferably 900 to 1100 ° C.) at a temperature rising rate of 10 ° C. or less per minute. It is also preferable to provide a crystallized glass suitable for an information recording medium substrate having a high Young's modulus of 140 GPa or more and a surface roughness of Ra (JIS B0601) of 0.5 nm or less. I found it.

That is, the invention is a method of converting a glass containing TiO ₂ into a crystallized glass through a phase separation step and a crystallization step, wherein the phase separation step exceeds the glass transition temperature Tg, and the glass The present invention relates to a method for producing crystallized glass, which is performed by heating at a temperature in the range up to a transition temperature Tg + 60 ° C.

Furthermore, the present invention is a crystallized glass obtained by subjecting a raw glass containing TiO ₂ to a phase separation step and a crystallization step, wherein the phase separation step exceeds the glass transition temperature Tg. Further, the present invention relates to a crystallized glass that is formed by heating at a temperature in the range of the glass transition temperature Tg + 60 ° C.

In the present invention, a plate-shaped crystallized glass, particularly a disk-shaped crystallized glass plate can be obtained.
Furthermore, the present invention is a disk-shaped crystallized glass plate, characterized in that the average particle size of the crystal particles is 100 nm or less, the substrate for information recording medium, the disk-shaped crystallized glass plate, An information recording medium substrate having a transmittance at 600 nm of 40% or more, and a disk-shaped crystallized glass plate having a polished surface having a surface roughness Ra (JIS B0601) of 1 nm or less An information recording medium substrate is included.
The present invention also relates to a method for manufacturing a magnetic disk in which at least a magnetic layer as a recording layer is formed on a disk-shaped crystallized glass plate, and a magnetic disk having at least a magnetic layer as a recording layer on the information recording medium substrate.

  According to the manufacturing method of the present invention, a magnetic disk substrate made of crystallized glass having a polished surface having a surface roughness (Ra (JIS B0601)) in the range of 0.1 to 0.5 nm that enables low head flying is provided. A crystallized glass that can be provided can be provided. Furthermore, since the magnetic disk made of crystallized glass produced by the production method of the present invention has excellent surface smoothness, the magnetic head can achieve low flying height, that is, high density recording, Young's modulus and specific elastic modulus. Therefore, it is possible to reduce the thickness and speed of the magnetic disk.

The present invention relates to a method for converting a glass containing TiO ₂ into a crystallized glass through a phase separation step and a crystallization step, and a crystallized glass obtained by this method. TiO ₂ contained in the raw glass is a component that becomes a crystal nucleation agent in the process of producing crystallized glass. The content of TiO ₂ is such that the glass is sufficiently phase-separated in the heat treatment (phase separation step) at a temperature of Tg + 60 ° C. or lower, which is a feature of the present invention, and the crystallized glass crystal particles obtained in the crystallization step are desired From the viewpoint of achieving a relatively small size, it is appropriate to make it 8 mol% or more. In order to precipitate smaller crystal particles from the glass, the content of TiO ₂ is preferably 8.5 mol% or more. The upper limit of the content of TiO ₂ is 15 mol%, and it is 12 mol% or less from the viewpoint that the glass melted in the production process can be molded and stable.
Examples of crystals to be precipitated in the method of the present invention include enstatite and its solid solution, β-quartz and its solid solution, cordierite, titanate, spinel, lithium disilicate, and garnite. Among them, enstatite and its solid solution are suitable as crystallized glass used for an information recording medium substrate in that a high Young's modulus can be obtained even if crystal grains are small.

The raw glass containing TiO ₂ includes, for example, MgO—Al ₂ O ₃ —SiO ₂ glass containing TiO ₂ and the total content of MgO, Al ₂ O ₃ and SiO ₂ being 80 mol% or more. Or MgO—RO—Al ₂ O ₃ —SiO ₂ (R = alkaline earth metal (for example, at least one selected from the group consisting of Ca, Sr and Ba), at least one selected from the group consisting of Zn and Ni) ) Based glass. These MgO-Al ₂ O ₃ —SiO ₂ glass and MgO— (RO) —Al ₂ O ₃ —SiO ₂ glass, which use TiO ₂ as a crystal nucleating agent, are very easily phase-separated in the vicinity of Tg. As in the invention, it is suitable for producing a crystallized glass having a fine crystal structure utilizing a differential phase at a lower temperature. Examples of the raw glass containing TiO ₂ include the glasses described in US Pat. No. 5,476,821 and US Pat. No. 5,491,116. Or SiO ₂ : 35-65 mol%, Al ₂ O ₃ : 5-25 mol%, MgO: 10-40 mol%, SiO ₂ + Al ₂ O ₃ + MgO ≦ 80 mol%, TiO ₂ : 5-15 mol% , RO (R = at least one selected from the group consisting of alkaline earth metals (Ca, Sr, Ba), Zn and Ni): glass containing 0 to 10 mol%.

The raw material glass containing TiO ₂ is an alkali metal oxide (for example, Li ₂ O, Na ₂ O, K ₂ O, etc.) and / or alkaline earth metal oxidation as long as the desired properties of the crystallized glass are not impaired. A component such as a product (for example, CaO, SrO, BaO) may be included. When the raw glass containing TiO ₂ is the above-described MgO—Al ₂ O ₃ —SiO ₂ glass containing TiO ₂ , it can further contain an alkali metal oxide and / or an alkaline earth metal oxide. . Moreover, when the raw material glass containing TiO ₂ is the above-mentioned MgO—RO—Al ₂ O ₃ —SiO ₂ glass containing TiO ₂ , it can further contain an alkali metal oxide. Of course, two or more alkali metal oxides and alkaline earth metal oxides can be used in combination.

For example, the production method of the present invention can be applied to the production of crystallized glass as follows.
SiO _2: 35-65 mol%
Al ₂ O ₃ : 5-25 mol%
MgO: 10-40 mol%
TiO _2: 5-15 mol%
Y ₂ O ₃ : 0-10 mol%
ZrO ₂ : 0-10 mol%
R ₂ O: 0-5 mol% (provided that R represents at least one selected from the group consisting of Li, Na, K)
RO: 0-5 mol% (provided that R represents at least one selected from the group consisting of Ca, Sr, and Ba)
As ₂ O ₃ + Sb ₂ O ₃ : 0-2 mol%
SiO ₂ + Al ₂ O ₃ + MgO + TiO ₂ : Crystallized glass containing 92 mol% or more and having a main crystal phase of enstatite and / or a solid solution thereof.

SiO ₂ : 44-52% by weight
MgO: 16-25% by weight
Al ₂ O ₃ : 13-20% by weight
TiO ₂ : 10-15% by weight
ZnO: 1-8% by weight
ZrO ₂ : 0-5% by weight
Li ₂ O: 0-3% by weight
B ₂ O ₃ : 0-3% by weight
P ₂ O ₅ : 0-5% by weight
Sb ₂ O ₃ : 0-2% by weight
And crystallized glass whose main crystal is enstatite.

SiO ₂ : 40-60% by weight
MgO: 10-20% by weight
Al ₂ O ₃ : Less than 10-20% by weight
P ₂ O ₅ : 0-4 wt%
B ₂ O ₃ : 0-4% by weight
CaO: 0.5-4% by weight
BaO: 0-5 wt%
ZrO ₂ : 0-5% by weight
TiO ₂ : 2.5-8% by weight
Sb ₂ O ₃ : 0-1% by weight
As ₂ O ₃ : 0 to 1% by weight
F: 0-3% by weight
SnO ₂ : 0-5% by weight
MoO ₃ : 0-3 wt%
CeO: 0-5% by weight
Fe ₂ O ₃ : 0-5% by weight
A crystallized glass containing at least one selected from the group consisting of cordierite solid solution, spinel crystal, spinel crystal solid solution, enstatite, enstatite solid solution, β-quartz, and β-quartz solid solution.

SiO ₂ : 40-60% by weight
MgO: 10-20% by weight
Al ₂ O ₃ : Less than 10-20% by weight
P ₂ O ₅ : 0.5-2.5% by weight
B ₂ O ₃ : 1 to 4% by weight
Li ₂ O: 0.5-4% by weight
CaO: 0.5-4% by weight
ZrO ₂ : 0.5-5% by weight
TiO ₂ : 2.5-8% by weight
Sb ₂ O ₃ : 0.01-0.5% by weight
As ₂ O ₃ : 0-0.5% by weight
SnO ₂ : 0-5% by weight
MoO ₃ : 0-3 wt%
CeO: 0-5% by weight
Fe ₂ O ₃ : 0-8% by weight
And crystallized glass whose main crystal is at least one selected from β-quartz, β-quartz solid solution, enstatite, enstatite solid solution, forsterite, and forsterite solid solution.

The alkali metal oxide and / or alkaline earth metal oxide can use nitrate as a glass raw material. When Sb ₂ O ₃ is used as a defoaming agent during glass production, it is easy to mix platinum into the glass from the platinum melting crucible for glass melting, and by using nitrate as the glass raw material, the mixing of platinum into the glass is suppressed. Can do. The content of the alkali metal oxide and alkaline earth metal oxide is preferably 0.1 mol% or more from the viewpoint of obtaining the above effect. However, when an alkali metal oxide is contained, the alkali metal oxide tends to lower the Young's modulus, so the content is suitably 5 mol% or less. Further, when the alkaline earth metal oxide is contained, the alkaline earth metal oxide has a tendency to enlarge the crystal particles, so that the content is suitably 5 mol% or less. If it contains alkali metal oxides, in particular, 0.1 to 5 mol%, preferably 0.1 to 2 mol%, more preferably 0.1 to 1 mol% of K ₂ O. When the alkaline earth metal oxide is contained, 0.1 to 5 mol%, preferably 0.1 to 2 mol% of SrO is particularly preferable.
The crystallized glass produced by producing the glass by the method of the present invention contains enstatite or its solid solution and / or quartz solid solution as the main crystal phase.

Each heat treatment process in the method for producing crystallized glass of the present invention will be described below.
MgO- (RO) -Al ₂ O ₃ —SiO ₂ (R = alkaline earth metal (eg, Ca, Sr, Ba, Zn, and Ni)) glass containing a certain amount of TiO ₂ exceeds Tg When heat-treated at a temperature, it is divided into a TiO ₂ rich phase and a SiO ₂ rich glass phase. So-called glass becomes phase separation (phase separation step). Such phase separation of the glass has a great influence on the crystal seed and crystal grain size of the crystallized glass. Usually, the phase rich in TiO ₂ is dispersed in the form of fine particles in the glass matrix phase rich in SiO ₂ . The smaller the size of the fine particles rich in TiO ₂ , the smaller the size of the final crystal particle having the differential phase particle as a nucleus. How to deposit such differential phase particles small is the key to making fine crystallized glass.

Then the relationship between the processing temperature in the phase separation step and the crystal structure of the crystallized glass, an example _{48SiO 2 -11Al 2 O 3 -30MgO-} 1Y 2 O 3 -10TiO 2 glass, will be described below.
48SiO ₂ -11Al ₂ O ₃ -30MgO-1Y ₂ O ₃ -10TiO ₂ glass (a glass of composition 1 in Table 2 in the examples described later. This glass was prepared as described in the examples). After heat treatment for phase separation for 4 hours in a temperature range (730-820 ° C.) around Tg (Tg = 732 ° C.), the temperature was immediately raised to 1000 ° C. at a heating rate of 5 ° C./min. Crystallization was carried out at temperature for 4 hours. The crystallized glass was ground and processed into a disk with a diameter of 95 mm and polished with CeO ₂ or SiO ₂ .

  FIG. 1 shows the relationship between the surface roughness of the crystallized glass obtained and the treatment temperature for phase separation. The surface roughness was measured using an atomic force microscope (AFM). Arithmetic average roughness in a 5 × 5 μm visual field was calculated for 3-5 spots on the sample surface. As shown in FIG. 1, it was found that the surface roughness of the crystallized glass that had been heat-treated for phase separation in the temperature range of Tg temperature (732 ° C.) to Tg + 60 ° C. was 0.5 nm or less. This is because the size of the crystal particles in the glass subjected to the phase separation treatment in the temperature range exceeding Tg and up to Tg + 60 ° C. is reduced. From the viewpoint that a crystallized glass having a small surface roughness can be obtained, the heat treatment for phase separation is performed in a temperature range exceeding Tg to Tg + 60 ° C., preferably Tg + 10 ° C. to Tg + 50 ° C., more preferably Tg + 20 ° C. The temperature range is ~ Tg + 40 ° C.

In order to confirm this point, the relationship between the transmittance of the obtained crystallized glass at a wavelength of 600 nm and the phase separation treatment temperature was determined, and the results are shown in FIG. The results shown in FIG. 2 indicate that the transmittance of the crystallized glass that has undergone phase separation in the temperature range exceeding Tg and up to Tg + 60 ° C. is high. I support small things.
Furthermore, in order to investigate how the microstructure of the crystallized glass obtained when the glass is processed at a temperature near Tg, phase separation between the untreated glass and Tg + 25 ° C. (760 ° C.) using a transmission electron microscope (TEM) is performed. Changes in the structure of the crystallized glass obtained by the treatment were observed. Fig. 3 shows TEM photographs of these glasses. As can be seen from FIG. 3, the differential phase particles are not visible in the untreated glass, but the differential phase particles rich in TiO ₂ are clearly visible in the glass heat-treated at Tg + 25 ° C. (760 ° C.).
Further, these glasses were heated to 1000 ° C. at a heating rate of 5 ° C./min, subjected to crystallization treatment for 4 hours, and then subjected to TEM observation. FIG. 4 shows a TEM photograph of the glass after the heat treatment at 1000 ° C. for 4 hours and the glass without phase separation treatment and the glass subjected to the phase separation treatment at Tg + 25 ° C. (760 ° C.) for 4 hours. It can be seen from the TEM photograph in FIG. 4 that the crystallized glass pretreated at Tg + 25 ° C. (760 ° C.) for 4 hours is smaller than the crystallized glass without phase separation treatment.

  The effect of refining crystal grains by heat treatment for phase separation was also observed in glasses having compositions 2 to 10 shown in Table 2 described later. These glass were heat-treated at a temperature of 800 ° C. (Tg + 65 ° C.) or higher and subjected to crystallization treatment under the same conditions. Experiments have shown that it is about twice as large as that of the crystallized glass.

  Furthermore, it was investigated how such a phase separation treatment affects other characteristics of crystallized glass. The results are summarized in Table 1. As can be seen from Table 1, the Young's modulus and expansion coefficient of the crystallized glass prepared by the method of the present invention are almost the same as those of the crystallized glass pretreated by the conventional heat treatment method and the crystallized glass without pretreatment. I understand that. In short, in the method of the present invention, only the size of the crystal particles can be reduced without changing the mechanical characteristics and thermal characteristics of the crystallized glass.

In the production method of the present invention, it is preferable to raise the temperature of the glass obtained in the phase separation step to the heating temperature in the crystallization step at a temperature rising rate of 10 ° C./min or less. The reason for suppressing the rate of temperature increase from the treatment temperature to the crystallization treatment temperature in the phase separation step to 10 ° C./min or less is to avoid deformation of the glass. Since ordinary crystallized glass is subjected to heat treatment for phase separation at a higher temperature, the glass has already been partially crystallized during the process. Therefore, it was difficult to be deformed even when the heating rate was high. However, the heat-treated glass for phase separation by the method of the present invention does not contain crystal particles, and if the temperature rises quickly, the glass may be deformed. When the temperature is raised at a slow rate of 10 ° C./min or less, crystal particles gradually precipitate during the temperature rise, so that deformation of the glass can be suppressed. The temperature rising rate is preferably in the range of 1 to 7 ° C./min. A lower heating rate is also very advantageous for homogenization of crystal grains.
The heating for crystallization is appropriately determined in consideration of characteristics such as the size, crystallinity, and Young's modulus of glass crystal particles. For example, the heating for crystallization is about 1-10 at a temperature in the range of 850-1100 ° C. Can be done for hours.

By such a method of the present invention, a crystallized glass having an average grain size of 100 nm or less can be obtained.
In the crystallized glass obtained by the method of the present invention, the average particle size of the crystal particles is 100 nm or less, but the average particle size of the crystal particles is preferably in the range of 10 to 70 nm.
The average particle diameter of the crystal particles can be measured using, for example, a transmission electron microscope (TEM).
Further, the crystallized glass obtained by the method of the present invention can have a transmittance at a wavelength of 600 nm of 40% or more, more preferably 50%. That is, since the transmittance increases as the crystal grain becomes smaller, this transmittance can be used as an index for estimating the approximate size of the crystal grain. However, since a component that affects the transmittance may be included depending on the composition of the glass, the relationship between the size of the crystal particles and the transmittance is slightly different depending on the composition of the glass.

  In the production method of the present invention, a plate-shaped crystallized glass can be obtained by using a molded body having a plate-shaped raw material glass. In this case, it is preferable to raise the temperature of the glass obtained in the phase separation step to the heat treatment temperature in the crystallization step at a temperature rising rate of 10 ° C./min or less. The raw material glass which is a plate-shaped molded body can be manufactured using a conventional method. Furthermore, a disk-shaped crystallized glass plate can be obtained by using a disk-shaped raw material glass as the plate-shaped molded body. Alternatively, the raw glass, which is a plate-shaped molded body, can be made into a crystallized glass plate and then processed into a disk shape to obtain a disk-shaped crystallized glass plate. The disc shape can be processed by a polishing method described later.

  The glass after the heat treatment for crystallization is polished into a desired shape, and then the surface is further polished. The polishing method is not particularly limited, and polishing can be performed by a known method using synthetic abrasive grains such as synthetic diamond, silicon carbide, aluminum oxide, and boron carbide, or natural abrasive grains such as natural diamond and cerium oxide. . For example, the surface roughness (Ra (JIS B0601)) of the polished surface can be in the range of 0.1 to 0.5 nm by lapping and polishing with cerium oxide using a normal polishing method and apparatus.

The disk-shaped crystallized glass plate obtained by the production method of the present invention has a crystal particle average particle size in the range of 100 nm or less, and is suitable as an information recording medium substrate.
Further, the disc-shaped crystallized glass plate obtained by the production method of the present invention has, for example, a transmittance of 40% or more at a wavelength of 600 nm, which is also suitable as a substrate for information recording media.
The disc-shaped crystallized glass plate obtained by the production method of the present invention can have a polished surface having a surface roughness Ra (JIS B0601) of 1 nm or less, and is suitable as a substrate for an information recording medium.

  The crystallized glass prepared by the production method of the present invention and having a polished surface with a surface roughness (Ra (JIS B0601)) in the range of 0.1-0.5 nm is necessary for the surface smoothness and flatness required for a magnetic disk substrate. All can be satisfied. In addition, the crystallized glass of the present invention has a Young's modulus that is about twice as high as that of the conventional glass, so that the deflection due to the high-speed rotation of the disk can be suppressed, and a high TPI / high BPI hard disk can be realized. Therefore, it is suitable as a substrate material.

  A magnetic disk can be manufactured by forming at least a magnetic layer as a recording layer on a disc-shaped crystallized glass plate obtained by the manufacturing method of the present invention. A conventional method can be used for forming the magnetic layer on the crystallized glass plate. The present invention includes a magnetic disk having at least a magnetic layer as a recording layer on a substrate obtained by the production method of the present invention.

[Description of magnetic disk]
The information recording medium of the present invention includes the substrate of the present invention and a recording layer formed on the substrate. A magnetic disk (hard disk) in which at least a magnetic layer is formed on the main surface of a substrate made of crystallized glass of the present invention will be described below.
Examples of layers other than the magnetic layer include an underlayer, a protective layer, a lubricating layer, and an unevenness control layer from the functional aspect, and are formed as necessary. Various thin film forming techniques are used to form these layers. The material of the magnetic layer is not particularly limited. Examples of the magnetic layer include a Co-based material, a ferrite-based material, and an iron-rare earth-based material. The magnetic layer may be either a horizontal magnetic recording or a perpendicular magnetic recording magnetic layer.
Specific examples of the magnetic layer include magnetic thin films such as CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiCrPt, CoNiCrTa, CoCrPtTa, and CoCrPtSiO containing Co as a main component. Moreover, it is good also as a multilayer structure which divided | segmented the magnetic layer by the nonmagnetic layer and aimed at noise reduction.

  The underlayer in the magnetic layer is selected according to the magnetic layer. As the underlayer, for example, at least one material selected from non-magnetic metals such as Cr, Mo, Ta, Ti, W, V, B, and Al, or oxides, nitrides, and carbides of these metals For example, an underlying layer. In the case of a magnetic layer containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic properties. The underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Al / Cr / CrMo, Al / Cr / Cr, or the like can be given.

  Further, an unevenness control layer for preventing the magnetic head and the magnetic disk from adsorbing may be provided between the substrate and the magnetic layer or above the magnetic layer. By providing the unevenness control layer, the surface roughness of the magnetic disk is adjusted appropriately, so that the magnetic head and the magnetic disk are not attracted, and a highly reliable magnetic disk can be obtained. Various materials and methods for forming the unevenness control layer are known and are not particularly limited. For example, as the material of the unevenness control layer, at least one metal selected from Al, Ag, Ti, Nb, Ta, Bi, Si, Zr, Cr, Cu, Au, Sn, Pd, Sb, Ge, Mg, etc. Or an alloy thereof, or an underlayer made of an oxide, nitride, carbide, or the like thereof. From the viewpoint of easy formation, it is desirable that the metal is mainly composed of Al, such as Al alone, Al alloy, Al oxide, and Al nitride.

In consideration of head stiction, the surface roughness of the unevenness forming layer is preferably Rmax = 50 to 300 angstroms. A more preferable range is Rmax = 100 to 200 angstroms. When Rmax is less than 50 angstroms, the magnetic disk surface is almost flat, so the magnetic head and the magnetic disk are attracted, the magnetic head and the magnetic disk are attracted, the magnetic head and the magnetic disk are damaged, or the head crashes due to the adsorption. This is not preferable. On the other hand, when Rmax exceeds 300 angstroms, the glide height (glide height) is increased and the recording density is lowered.
In addition, without providing an unevenness control layer, the glass substrate surface may be provided with unevenness by means such as etching treatment or laser light irradiation, and textured.

Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective films can be continuously formed by an in-line type sputtering apparatus or the like together with the underlayer and the magnetic layer. These protective films may be a single layer, or may have a multilayer structure composed of the same or different films.
Another protective layer may be formed on the protective layer or instead of the protective film. For example, colloidal silica fine particles may be dispersed and coated in tetraalkoxylane diluted with an alcohol solvent on the protective layer, and then fired to form a silicon oxide (SiO ₂ ) film. In this case, it functions as both a protective film and an unevenness control layer.
Various proposals have been made for the lubricating layer, but in general, perfluoropolyether, which is a liquid lubricant, is diluted with a solvent such as Freon, and the surface of the medium is dipped, spin-coated, or sprayed. The film is applied by heat treatment as necessary.

Hereinafter, the production method of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Tables 2 to 4 show the glass compositions of Examples 1 to 25 in mol% (or weight%). In addition, although the composition of Tables 2-4 is a composition of a raw material, as a result of analyzing and comparing a raw material composition and a crystallized glass composition about the crystallized glass of Examples 1-15, the difference of both is less than +/- 0.1 mol% Met. Accordingly, the raw glass compositions shown in Tables 2 to 4 are substantially the same as the crystallized glass composition.

As the starting material to be used in dissolving these _{glasses, SiO 2, Al 2 O 3} , Al (OH) 3, MgO, ZnO, NiO, CaCO 3, SrCO 3, BaCO 3, Y 2 O 3, TiO 2, and 2000g weighed in a predetermined ratio shown in Table 2-4 by using a _{ZrO 2, KNO 3, Sr (} NO 3) 2, Sb 2 O 3. Although not shown in the table, all glasses contain 0.03 mol% of Sb ₂ O ₃ . The weighed raw materials were mixed thoroughly to form a preparation batch, which was put into a platinum crucible, and the glass was melted in air for 6 hours or more with stirring at 1570 ° C. After melting, the glass melt was poured into a mold, allowed to cool to the glass transition temperature, immediately placed in an annealing furnace, annealed for about 1 hour in the glass transition temperature range, and allowed to cool to room temperature in the furnace. . The obtained glass did not precipitate crystals that could be observed with a microscope.

  The obtained glass was formed into a rectangular sample of 100 × 10 × 10 mm and a disk of φ100 × 1 mm and further polished. The obtained glass was put into a heat treatment furnace, heated to a heat treatment temperature for phase separation shown in Tables 2 to 4 at a rate of 3-10 ° C./min, and kept at this temperature for about 4 hours. Heat treatment for phase separation was performed. Immediately after finishing this heat treatment, the temperature is raised at a heating rate of 5 ° C./min up to the heat treatment temperature for crystallization shown in Tables 2 to 4 and kept for about 4 hours, and then cooled to room temperature in the furnace. Thus, a crystallized glass was produced. The obtained rectangular crystallized glass was further polished to a length of 90 mm to obtain a sample for measuring Young's modulus and specific gravity. The crystallized glass of a disk of φ100 × 1 mm was further precisely polished into a disk of φ95 × 0.8 mm to obtain a sample for measuring the surface roughness. The Young's modulus was measured by an ultrasonic method using a sample of 90 × 10 × 10 mm. The data obtained by the measurement are shown in Tables 2 to 4 together with the glass composition.

About the crystallized glass of Examples 1-4, when the average particle diameter of the crystal particle was measured using the transmission electron microscope (TEM), the average particle diameter was 20-30 nm. Further, with respect to the crystallized glass of Example 5, when the average particle diameter of the crystal particles was measured using a transmission electron microscope (TEM), the average particle diameter was 50-70 nm.
The surface roughness was measured using an atomic force microscope (AFM). Arithmetic average roughness in a 5 × 5 μm visual field was calculated for 3-5 spots on the sample surface. FIG. 5 shows an AFM photograph after the crystallized glass of Example 4 heat-treated under the heat treatment conditions shown in Table 2 was polished in the optical glass polishing step. The surface roughness of Example 4 is as low as about 0.21 nm in Ra (JIS B0601), and can sufficiently meet the demand for the surface smoothness of the next generation magnetic disk.
Further, the crystallized glass of the present invention had a transmittance of 50% or more at a wavelength of 600 nm when the thickness was 1 mm, and was somewhat transparent. Such transparency can be an indicator of whether a desired crystal seed and crystal grain size are obtained. In the case of the crystallized glass of the present invention, the transmittance can be, for example, 20% or more, further 40 to 90%, and further 60 to 90%.

Manufacturing Method of Magnetic Disk As shown in FIG. 6, the magnetic disk 1 of the present invention is formed on the crystallized glass substrate 2 of Example 1 above, in order, an unevenness control layer 3, an underlayer 4, a magnetic layer 5, and a protective layer. 6. A lubricating layer 7 is formed.
Specifically, each layer is processed on a disk having an outer circle radius of 32.5 mm, an inner circle radius of 10.0 mm, and a thickness of 0.43 mm. Both main surfaces have a surface roughness of Ra. (JIS B0601) = 4 angstroms and Rmax = 40 angstroms are precision polished.
The unevenness control layer is an AlN thin film having an average roughness of 50 angstroms, a surface roughness Rmax of 150 angstroms, and a nitrogen content of 5 to 35%.
The underlayer is a CrV thin film having a thickness of about 600 angstroms, and the composition ratio is Cr: 83 at% and V: 17 at%.
The magnetic layer is a CoPtCr thin film with a thickness of about 300 Å, and the composition ratios are Co: 76 at%, Pt: 6.6 at%, and Cr: 17.4 at%.
The protective layer is a carbon thin film having a thickness of about 100 Å.
The lubricating layer is formed by applying a lubricating layer made of perfluoropolyether on the carbon protective layer by spin coating to a thickness of 8 angstroms.

Next, a method for manufacturing a magnetic disk will be described.
First, the crystallized glass produced in Example 1 was ground on a disk having an outer circle radius of 32.5 mm, an inner circle radius of 10.0 mm, and a thickness of 0.5 mm, and both main surfaces had a surface roughness of Ra (JIS B0601) = 4 angstroms and Rmax = 40 angstroms are precision polished to obtain a crystallized glass substrate for a magnetic disk.
Next, after the glass substrate is set on a substrate holder, the glass substrate is fed into a preparation chamber of an in-line sputtering apparatus. Subsequently, the holder on which the crystallized glass substrate is set is fed into the first chamber in which the Al target is etched, and sputtering is performed in a pressure of 4 mtorr, a substrate temperature of 350 ° C., and an Ar + N ₂ gas (N ₂ = 4%) atmosphere. As a result, an AlN thin film (unevenness forming layer) having a surface roughness Rmax = 150 Å and a film thickness of 50 Å was obtained on the crystallized glass substrate.

Next, the holder on which the crystallized glass substrate on which the AlN film is formed is set in the second chamber in which a CrV (Cr: 83 at%, V: 17 at%) target is installed, CoPtCr (Co: 76 at%, Pt: (6.6 at%, Cr: 17.4 at%) The film is continuously fed into the third chamber in which the target is placed, and a film is formed on the substrate. These films are sputtered in an Ar atmosphere at a pressure of 2 mtorr and a substrate temperature of 350 ° C. to obtain a CrV underlayer having a thickness of about 600 Å and a CoPtCr magnetic layer having a thickness of about 300 Å.
Next, the laminate on which the unevenness control layer, the underlayer, and the magnetic layer are formed is sent to a fourth chamber provided with a heater for heat treatment. At this time, the fourth chamber is placed in an Ar gas (pressure 2 mtorr) atmosphere, and the heat treatment is performed by changing the heat treatment temperature.

Under the same film formation conditions as the CrV underlayer and CoPtCr magnetic layer except that the substrate was fed into a fifth chamber in which a carbon target was installed and was formed in an atmosphere of Ar + H ₂ gas (H ₂ = 6%). A carbon protective layer having a thickness of about 100 Å is obtained.
Finally, the substrate after the formation of the carbon protective layer is taken out from the in-line sputtering apparatus, and a perfluoropolyether is applied to the surface of the carbon protective layer by dipping to form a lubricating layer having a thickness of 8 angstroms. I got a magnetic disk.

The relationship between the surface roughness of crystallized glass and the processing temperature for phase separation is shown. The relationship between the transmittance | permeability in wavelength 600nm of crystallized glass, and the phase separation processing temperature is shown. The transmission electron microscope (TEM) photograph replaced with drawing of the crystallized glass obtained by phase-separating at untreated glass and Tg + 25 degreeC (760 degreeC) is shown. The transmission electron microscope (TEM) photograph replaced with drawing of the glass after heat-processing the glass without a phase separation process and the glass which carried out the phase separation process at Tg + 25 degreeC (760 degreeC) for 4 hours at 1000 degreeC is shown. The AFM photograph replaced with drawing of the surface obtained by grind | polishing the crystallized glass of Example 4 by the grinding | polishing process of optical glass. 1 is a schematic cross-sectional view of a magnetic disk 1 of the present invention in which an unevenness control layer 3, an underlayer 4, a magnetic layer 5, a protective layer 6, and a lubricating layer 7 are sequentially formed on a crystallized glass substrate 2. FIG.

Claims (24)

A method of converting a raw material glass containing TiO ₂ into a crystallized glass through a phase separation step and a crystallization step, wherein the phase separation step exceeds the glass transition temperature Tg, and the glass transition temperature A method for producing crystallized glass, which is carried out by heating at a temperature in the range of Tg + 60 ° C. 2. The production method according to claim 1, wherein the heating is performed so that an average particle diameter of crystal grains contained in the crystallized glass is 100 nm or less. The manufacturing method according to claim 1, wherein the crystallized glass has a TiO ₂ content of 8 mol% or more. The crystallized glass SiO ₂ - Al ₂ O ₃ process according to any one of claims 1 to 3 is -MgO system. The raw material glass contains TiO ₂ , and the total content of MgO, Al ₂ O ₃ and SiO ₂ is 80 mol% or more, or MgO—Al ₂ O ₃ —SiO ₂ glass or MgO—RO—Al ₂ O. ₃ -SiO ₂ prepared as described in claim 1 which is (R = alkaline-earth metals (Ba, Ca, Sr), at least one selected from the group consisting of Zn and Ni) based glass Method. The manufacturing method according to any one of claims 1 to 5, wherein the crystallized glass has a crystal phase containing enstatite. The manufacturing method according to any one of claims 1 to 5, wherein the crystallized glass contains enstatite as a main crystal. The crystallized glass is
SiO _2: 35-65 mol%
Al ₂ O ₃ : 5-25 mol%
MgO: 10-40 mol%
TiO ₂ : 5-15 mol%
Y ₂ O ₃ : 0-10 mol%
ZrO ₂ : 0-10 mol%
R ₂ O: 0-5 mol% (provided that R represents at least one selected from the group consisting of Li, Na, K)
RO: 0-5 mol% (provided that R represents at least one selected from the group consisting of Ca, Sr, and Ba)
As ₂ O ₃ + Sb ₂ O ₃ : 0-2 mol%
_{SiO 2 + Al 2 O 3 +} MgO + TiO 2: containing more than 92 mol%, the main crystals are crystallized glass is enstatite and / or its solid solution according to any one of claims 1 to 7 Manufacturing method. The raw glass is a plate-like molded body, and is a method for obtaining a plate-like crystallized glass, wherein the glass obtained in the phase separation step is subjected to a heat treatment temperature in the crystallization step at a heating rate of 10 ° C./min or less The manufacturing method of any one of Claims 1-8 heated up to. The manufacturing method according to claim 9, wherein the plate-shaped molded body has a disk shape or is processed into a disk shape after the crystallization step to obtain a disk-shaped crystallized glass plate. A crystallized glass obtained by subjecting a raw glass containing TiO ₂ to a phase separation step and a crystallization step, wherein the phase separation step exceeds the glass transition temperature Tg, and the glass transition Crystallized glass made by heating at a temperature in the range of Tg + 60 ° C. The crystallized glass according to claim 11, wherein the heating is performed so that an average particle diameter of crystal grains included in the crystallized glass is 100 nm or less. The crystallized glass according to claim 11 or 12, wherein the TiO ₂ content is 8 mol% or more. The crystallized glass SiO ₂ - crystallized glass according to any one of Al ₂ O ₃ is -MgO system according to claim 11 to 13. MgO—Al ₂ O ₃ —SiO ₂ glass or MgO—RO—Al ₂ O, in which the raw glass contains TiO ₂ and the total content of MgO, Al ₂ O ₃ and SiO ₂ is 80 mol% or more. ₃ -SiO ₂ crystal according to any one of (R = alkaline-earth metals (Ba, Ca, Sr), at least one selected from the group consisting of Zn and Ni) based glass in which claims 11 to 13 Glass. The crystallized glass according to any one of claims 11 to 15, wherein the crystal phase contains enstatite. The crystallized glass according to any one of claims 11 to 15, comprising enstatite as a main crystal. SiO _2: 35-65 mol%
Al ₂ O ₃ : 5-25 mol%
MgO: 10-40 mol%
TiO ₂ : 5-15 mol%
Y ₂ O ₃ : 0-10 mol%
ZrO ₂ : 0-10 mol%
R ₂ O: 0-5 mol% (provided that R represents at least one selected from the group consisting of Li, Na, K)
RO: 0-5 mol% (provided that R represents at least one selected from the group consisting of Ca, Sr, and Ba)
As ₂ O ₃ + Sb ₂ O ₃ : 0-2 mol%
The crystallized glass according to any one of claims 11 to 17, which contains SiO ₂ + Al ₂ O ₃ + MgO + TiO ₂ : 92 mol% or more, and the main crystal is enstatite and / or a solid solution thereof. It is plate shape and disk shape, The crystallized glass of any one of Claims 11-18. A disk-shaped crystallized glass plate obtained by the manufacturing method according to claim 10 or a disk-shaped crystallized glass plate according to claim 19, wherein the average particle diameter of the crystal particles is 100 nm or less. An information recording medium substrate. The disc-shaped crystallized glass plate obtained by the manufacturing method according to claim 10 or the disc-shaped crystallized glass plate according to claim 19, wherein the transmittance at a wavelength of 600 nm is 40% or more. Medium substrate. A disk-shaped crystallized glass plate obtained by the manufacturing method according to claim 10 or a disk-shaped crystallized glass plate according to claim 19, wherein the surface roughness Ra (JIS B0601) is 1 nm or less. An information recording medium substrate having a polished surface. A disk-shaped crystallized glass plate obtained by the manufacturing method according to claim 10 or a magnetic disk manufacturing method in which at least a magnetic layer as a recording layer is formed on the disk-shaped crystallized glass plate according to claim 19. A magnetic disk having at least a magnetic layer as a recording layer on the substrate according to any one of claims 20 to 22.