JPH11278865A - Crystallized glass for magnetic disk substrate, magnetic disk substrate, magnetic disk and production of crystallized glass for magnetic disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly decrease the center line average surface roughness Ra of a magnetic disk substrate after the substrate is precisely polished, by increasing the strength and Young's modulus of a crystallized glass for a magnetic disk substrate. SOLUTION: The basic compsn. of the crystallized glass for a magnetic disk substrate consists of 44 to 52 wt.% SiO2 ; 16 to 25 wt.% MgO, 13 to 20 wt.% Al2 O3 ; 10 to 15 wt.% TiO2 , 1 to 8 wt.% ZnO; 0 to 5 wt.% ZrO2 ; 0 to 3 wt % Li2 O; 0 to 3 wt.% B2 O2 ; to 5 wt.% P2 O5 and 0 to 2 wt.% Sb2 O3 . The main crystal phase of the crystallized glass is an enstatite phase, and the crystal grain of the crystallized glass has 0.01 to 0.1 μm particle size. Preferably the center line average surface roughness Ra of the glass after precision polishing is 1 to 6 Å.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to crystallized glass for a magnetic disk substrate, a magnetic disk substrate and a magnetic disk using the same, and a method for manufacturing a magnetic disk substrate.

[0002]

2. Description of the Related Art Recently, a magnetic disk substrate made of crystallized glass has been studied. In crystallized glass, most of the alkali metal ions contained are present in the crystal phase, and only a trace amount is present in the glass matrix, so that the alkali metal components elute and corrode the magnetic film. Does not occur.

[0003] With the progress of multimedia, there has been a strong demand for recording a large amount of information such as image information in a smaller magnetic disk, and further improvement in the recording density of the magnetic disk is required. It has become. As a result, especially in the read / write zone of the magnetic disk, it is required to reduce the center line average surface roughness (Ra) to a region of 10 Å or less.

However, in the case of crystallized glass, the crystal phase and the amorphous phase have different hardnesses. For this reason, even after the polishing process, minute irregularities are inevitably generated between the crystalline phase and the amorphous phase. As a result, it was difficult to suppress the center line average surface roughness of the processed surface to 10 Å or less.

In Japanese Patent Application Laid-Open No. 9-208260, a specific Li ₂ O—Al ₂ O ₃ —SiO ₂ having a specific composition is disclosed.
Using a magnetic disk substrate made of a system crystallized glass,
By precision polishing this, the surface roughness becomes 2-10.
I am trying to get an Angstrom substrate.

[0006]

The present inventors have studied the application of crystallized glass having an enstatite phase as a main crystal phase to a magnetic disk substrate. Such a study has not been conventionally performed. As a result of this study, the present inventor has discovered that there are the following problems when applied to a magnetic disk substrate.

Japanese Patent No. 2,486,733 discloses a highly refractory crystallized glass having enstatite as a main crystal phase. However, since the melting conditions disclosed herein are as high as 1650 ° C. for 16 hours, a general optical glass melting method using platinum on the inner wall of the crucible cannot be used. As a result, striae in the crystallized glass do not disappear, and after polishing the glass, raised surface defects (convex) are easily formed, which is not suitable for magnetic disk applications.
This glass is a crystallized glass used under a high temperature condition of 1200 ° C., particularly 1400 ° C. or higher.

JP-A-7-53238 discloses a transparent crystallized glass having a melting temperature of 1550 to 1600 ° C. and having an enstatite phase as a main crystal phase. The crystallized glass disclosed in this patent is disclosed in Japanese Patent No. 2648.
As in Japanese Patent No. 673, since the melting temperature is high, crystallized glass without striae cannot be obtained. As a result, after the glass is polished, raised surface defects (convex) are easily formed, which is suitable for magnetic disk applications. No Further, since a large amount of elements having a large mass number, such as Zr, Y, and La, are contained, the specific gravity of the crystallized glass becomes large. When this is applied to the material of the magnetic disk substrate, it is necessary to rotate the magnetic disk. It is not suitable for magnetic disk applications because the motor load increases.

Japanese Unexamined Patent Publication (Kokai) No. 64-52632 discloses a crystallized glass capable of melting at 1400 to 1500 ° C. and precipitating an enstatite phase. However, in this crystallized glass, the existence of a rutile phase together with an enstatite phase is disclosed. The presence of the rutile phase deteriorates the surface roughness after precision polishing, and is obviously not suitable for use as a magnetic disk substrate for the above-mentioned reason. The present inventors, as a result of their own research, according to was discovered, the _{SiO 2 -Al 2 O 3 -MgO-} TiO 2 based crystallized glass, when containing an alkaline earth other than MgO, in addition to the enstatite phase It has been found that the rutile phase tends to precipitate. In JP-A-64-52632, since CaO is contained as an essential component,
It is considered that the rutile phase was precipitated.

An object of the present invention is to provide a crystallized glass for a magnetic disk substrate in which the center line average surface roughness Ra after the magnetic disk substrate is precisely polished can be significantly reduced.

[0011]

Means for Solving the Problems The present invention is a crystallized glass for magnetic disk substrates, the basic composition of crystallized glass SiO _2: 44 to 52 wt%, MgO: 16 to 25 wt%, Al ₂ O _3: 13 to 20 wt%, TiO _2: 10
15 wt%, ZnO: 1~ 8 wt%, ZrO _2: 0
5 wt%, Li ₂ O: 0~3 wt%, B ₂ O _2: 0~
3 wt%, P ₂ O _5: 0~5 wt% and Sb ₂ O _3:
0 to 2% by weight, wherein the main crystal phase of the crystallized glass is an enstatite layer, and the crystal particles of the crystallized glass have a particle size of 0.01 μm-0.1 μm.

The present invention is also a magnetic disk substrate made of the above glass.

Further, a magnetic disk according to the present invention is characterized by comprising the above-described magnetic disk substrate, a base film formed thereon, and a metal magnetic layer on the base film.

The present invention also relates to a method for producing crystallized glass for a magnetic disk substrate, wherein the basic composition is Si.
O ₂ : 44 to 52% by weight, MgO: 16 to 25% by weight,
Al ₂ O _3: 13~20 wt%, TiO _2: 10~15
Wt%, ZnO: 1 to 8 wt%, ZrO _2: 0~5 wt%, Li ₂ O: 0~3 wt%, B ₂ O _2: 0~3 wt%, P ₂ O _5: 0~5 wt % And Sb ₂ O ₃ : 0 to 2
(Tg−30) ° C .— (Tg)
C. (Tg is the glass transition temperature of the parent glass) in the range of preferably 1-4 hours for nucleation, and then crystallization at 925-1075C, preferably 2-6 hours. It is characterized by making it.

The melting temperature of the parent glass in the composition range of the present invention can be set to 1400 to 1500 ° C. this is,
It is considered that the composition is limited to a region having a low liquidus temperature in the phase diagram of SiO ₂ —Al ₂ O ₃ —MgO and the effect of containing ZnO. Further, Li ₂ O, B ₂ O ₃ , P
By adding ₂ O ₅ , the melting temperature of the parent glass becomes 1
Can be lowered to 300 ° C.

SiO ₂ —Al ₂ O ₃ —MgO—TiO ₂
It is known that system-crystallized glass has low viscosity at high temperature, high glass transition temperature, and high liquidus temperature.
Therefore, as a method of forming glass for a magnetic disk,
Casting and drawing methods are suitable. But Z
When rO ₂ is contained, the viscosity of the parent glass increases, and it becomes possible to use a direct press molding method. The direct press molding method requires less post-processing and can reduce the processing cost.

The parent glass is heated at 925 ° C. to 1075 ° C.
After crystallization for preferably 2 to 6 hours, MgO.SiO ₂
A crystallized glass having (enstatite phase) as a main crystal phase is obtained. When the crystallized glass was etched with HF and observed with a scanning microscope, it was found that enstatite crystals existed in a size of 0.01 to 0.1 μm.

In particular, rather than crystallization after nucleation at a glass transition temperature Tg + 20 to Tg + 50 ° C., which is generally performed with crystallized glass, the glass transition temperature Tg−30 to Tg ± 0 ° C. By crystallization after nucleation in the range, the crystal grain size is significantly reduced from 0.01 μm to 0.08 μm.

When this crystallized crystallized glass is precisely polished, Ra is 8 Å or less, particularly 1 to 6 Å.
A precision polished body having an angstroms smooth surface is obtained. It is considered that this is because the crystal grain size is fine, the crystallinity is large, and the glass layer filling the space between the crystals is thin.

When the crystal phase of the crystallized glass is identified by the X-ray diffraction method, MgAl ₂ TiO ₃ O ₁₁ and Mg ₂ Al ₆ Ti ₇ O besides MgSiO ₃ (enstatite phase) are identified.
₂₅ (MAT), (Mg, Al) SiO ₃ (MAS1),
ZnAl ₂ O ₄ (garnite) and the like were sometimes observed.

Incidentally, Mg ₂ Al ₄ Si ₅ O ₁₈ (cordrite phase, indianite), TiO ₂ (rutile phase), MgO
When Al ₂ O ₃ SiO ₂ (MAS2) is present, the surface roughness after precision polishing tends to deteriorate.

In particular, Mg ₂ Al ₄ Si ₅ O ₁₈ (cordierite phase, indite) is recognized when the crystallization temperature is 1100 ° C. or higher. Also, MgOAl ₂
O ₃ SiO ₂ (MAS2) is recognized when the crystallization temperature is 900 ° C. or lower. Therefore, the crystallization temperature is particularly preferably from 925 to 1075 ° C.

TiO ₂ (rutile phase) contains C
When a, Sr, and Ba are contained, they are deposited.
In particular, Ca has a remarkable effect. Therefore, it is particularly preferable not to contain an alkaline earth metal other than Mg.

The chemical formula, name, and JCP of each crystal phase are described below.
Indicates the DS card number and abbreviation (described later in Tables 2 to 6).

[Table 1]

The crystallization ratio of the crystallized glass is preferably 70% or more. In the crystal phase, the expression that the enstatite phase is the main crystal phase means that the peak intensity of the enstatite phase is the largest in the X-ray diffraction method.

The ratio of each component in the parent glass will be described. The amount of SiO ₂ should be at least 44% by weight and 46% by weight.
It is particularly preferable to set the above. Thereby, the particles after crystallization are refined. When the content of SiO ₂ is 52% by weight or less (particularly preferably 50% by weight or less), the melting temperature of the parent glass can be reduced, and the devitrification of the parent glass hardly occurs.

When the amount of MgO is 16% by weight or more (particularly preferably 18% by weight or more), an enstatite phase is obtained, and the melting temperature of the parent glass can be reduced. M
The amount of gO is 25% by weight or less (particularly preferably 22% by weight).
In the following, the melting temperature of the glass can be reduced, and the devitrification of the parent glass can be prevented.

By setting the amount of Al ₂ O ₃ to 13% by weight or more (particularly preferably 16% by weight or more), the melting temperature of glass can be reduced. 20% by weight of Al ₂ O ₃
By setting the content to not more than (particularly preferably not more than 19% by weight), an enstatite phase can be obtained, and the melting temperature of the parent glass can be reduced.

By setting the amount of TiO ₂ to 10% by weight or more (particularly preferably 11% by weight or more), particles after crystallization are easily made fine. By setting the amount of TiO ₂ to 15% by weight or less (particularly preferably 13% by weight or less), the devitrification of the parent glass can be prevented.

By increasing the amount of ZnO by 1% by weight (particularly preferably at least 2% by weight), the melting temperature of the parent glass increases. By setting the amount of ZnO to 8% by weight or less (particularly preferably 5% by weight or less), devitrification of the parent glass can be prevented and Vickers hardness can be increased.

Next, the optional components in the parent glass will be described. The viscosity of the glass can be adjusted by adding ZrO ₂ . The amount of ZrO ₂ is preferably 5% by weight or less, and particularly preferably 4% by weight or less. This can prevent the viscosity of the parent glass from excessively increasing. ZrO ₂
Is preferably added in an amount of 0.5% by weight or more.

The addition of Li ₂ O improves the solubility of the parent glass. By setting the amount of Li ₂ O to 3% by weight or less (particularly preferably 2% by weight or less),
Crystal grains after crystallization are refined. When Li ₂ O is added, the amount is preferably set to 0.1% by weight or more.

By adding B ₂ O ₃ , the solubility of the parent glass is improved. By setting the amount of B ₂ O ₃ to 3% by weight or less (particularly preferably 2% by weight or less),
Crystal grains after crystallization are refined. When B ₂ O ₃ is added, its amount is preferably 0.5% by weight or more.

The addition of P ₂ O ₅ improves the solubility of the parent glass. By controlling the amount of P ₂ O ₅ to 5% by weight or less (particularly preferably 3% by weight or less),
Crystal grains after crystallization are refined. When P ₂ O ₅ is added, its amount is preferably 0.5% by weight or more.

Sb ₂ O ₃ acts as a defoamer for glass. The amount of Sb ₂ O ₃ content _of 2 wt% or less (particularly preferably 0.2-1.5% by weight) have sufficient effect.

In producing the parent glass, the respective raw materials containing the respective metal atoms are mixed so as to correspond to the aforementioned weight ratio, and the mixture is melted. Examples of this raw material include oxides, carbonates, nitrates, sulfates, and hydroxides of each metal atom. The atmosphere for crystallizing the parent glass by heat treatment may be an air atmosphere,
A reducing atmosphere, a steam atmosphere, a pressurized atmosphere, or the like can be selected.

In the step of precision polishing of the above-mentioned crystallized glass material with abrasive grains, a magnetic disk substrate can be manufactured by polishing by a known precision polishing method such as so-called lapping or polishing. On the main surface of the magnetic disk substrate of the present invention, a base treatment layer, a magnetic film, a protective film, and the like can be formed, and a lubricant can be applied on the protective film.

[0038]

EXAMPLES [Experiment 1] (Preparation of parent glass) Compounds containing each metal were mixed so that the weight ratios of various metal oxides shown in Tables 2, 3 and 4 were obtained. 250 g of this mixture was put into a 200 cc platinum crucible, heat-treated at 1430 ° C. for 6 hours, and melted. After lowering the temperature of the furnace to 1300 ° C. and maintaining the temperature at 1300 ° C. for 1 hour, the glass melt was poured into a carbon mold and molded. This was annealed at 700 ° C. for 1 hour and then gradually cooled to obtain a disk-shaped molded body of the parent glass.

From the molded body of the parent glass, a size of 15 mm
× 15mm × thickness 0.85mm, dimensions 22mm × 22m
mx thickness 0.85mm, dimension 5mm x 30mm x thickness 0.85mm, dimension 10mm x 45mm x thickness 1.2m
m of each plate sample was cut out. In addition, thickness 0.85
Both surfaces of the (mm) plate sample and the 1.2 (mm) plate sample were finished with a # 400 whetstone.

(Measurement of glass transition temperature) Dimension 5 mm × 3
From a plate sample of 0mm x 0.85mm thickness, length 20m
m test samples were cut out. The coefficient of thermal expansion of the test sample was measured in the range of room temperature to 900 ° C. with a thermal expansion coefficient measuring device (“TD5000S” manufactured by Max Science). This thermal expansion measuring device has a function of automatically stopping the measurement when the glass is bent. The temperature at which the thermal expansion curve of glass is deflected with respect to temperature is defined as the glass transition temperature (T
g). This value is shown in Table 2 to Table 4.

(Production of Crystallized Glass) Each plate-like sample was crystallized in a nitrogen atmosphere while being sandwiched between carbon plates having a thickness of 5 mm. The crystallization schedule is to raise the nucleation temperature to 720 ° C at 300 ° C / hour,
The temperature was raised from 720 ° C. to 1000 ° C. at 300 ° C./hour, kept at 1000 ° C. for 4 hours, and lowered from 1000 ° C. to room temperature at 200 ° C./hour.

(Identification of Crystal Phase, Calculation of Constituent Ratio of Each Crystal Phase) An X-ray diffractometer (“Geiger-Flex” manufactured by Rigaku Denki Co., Ltd .: tube voltage 30 kV, tube current 20 m) using Kα ray of copper
Using A), the crystallized dimension 15 mm x 15
The crystal phase on the surface of the plate-shaped test sample of mm was identified. At that time, the scanning angle was set at 2θ = 15 to 40 °. The detected crystal phases are shown in Table 2 to Table 4.

Experiment Nos. 1-1 to 1-15 (Examples of the Present Invention)
In any of the samples, an enstatite phase (chemical formula: MgO.SiO ₂ : JC
PDS No. 19-0768: diffraction angle 2θ = 31.1
°) was precipitated. In addition, MAT (2
θ = 25.9 °) and MAS (2θ
= 36.0 °) or garnite phase (2θ = 36.8)
°) was observed.

Experiment Nos. 1-21 to 1 outside the present invention in Table 4
At -28, various crystal phases were confirmed.

(Measurement of thermal expansion coefficient)
Cut a sample with dimensions of 5 mm x 30 mm and cut it to a length of 20 mm.
Was prepared. The coefficient of thermal expansion of the test sample was measured in the range of -75 ° C to 110 ° C with a thermal expansion coefficient measuring device (“TD5030S” manufactured by Mac Science). The coefficient of thermal expansion up to 100 ° C. was calculated based on 25 ° C. This value is shown in Table 2 to Table 4.

(Measurement of Ra on Smooth Surface after Precision Polishing) Dimension 15 mm × 15 mm after Identification of Crystal Phase
Was precision ground using a # 700 grinding wheel until the sample thickness became 0.645 mm. Then, using a high-purity zirconium oxide abrasive with a particle size of 0.3 μm using a double-sided polishing machine, the thickness of the sample was 0.6
Polishing was performed until the thickness became 35 mm. Further, the particle size 5
Using 0 Angstrom colloidal silica abrasive,
Perform the second stage polish processing, thickness 0.635mm
Was obtained.

Silicon cantilever (resonance frequency 3
00 kHz) using an atomic force microscope (PSI “M
In the tapping mode 5)), the center line average surface roughness (Ra) of the surface of the precision polished body was measured. This value is shown in Table 2 to Table 4.

(Microstructure Observation) Each precision polished body was etched with a 5% hydrofluoric acid aqueous solution for 10 minutes, and the size of the crystals was observed with a scanning electron microscope. Tables 2 to 4 show the observed crystal grain sizes.

(Measurement of bending strength) A plate-like sample having a size of 22 mm × 22 mm, which had been crystallized, was placed in a size of 15 mm × 1
Precision polishing was performed in the same procedure as for a 5 mm plate sample. Thereafter, a measurement sample having a size of 2 mm × 20 mm was cut out and subjected to a four-point bending test under the conditions of a lower span of 15 mm, an upper span of 5 mm, and a crosshead speed of 0.5 mm / min, to determine the bending strength.

(Measurement of Young's Modulus) A plate-like sample having a size of 10 mm × 45 mm and having been crystallized is placed in a size of 15 mm × 15
Precision polishing was performed in the same procedure as for the mm-shaped plate sample. afterwards,
A measurement sample having a size of 4 mm × 40 mm was cut out, a strain gauge was attached to the sample, and a lower span of 30 mm, an upper span of 10 mm, and a crosshead speed of 0.5 mm / min.
A four-point bending test was performed under the conditions described above, and the Young's modulus was calculated from the relationship between the load and the displacement.

(Measurement of Vickers Hardness) The Vickers hardness of the sample after precision polishing was measured at an indentation pressure of 1 kgf using a micro Vickers hardness meter.

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

In Experiment No. 1-21, although the amount of TiO ₂ was set to 9.0% by weight, the crystal grain size was about 0.2 μm, and the surface roughness after precision polishing was 10 Å. When the amount of TiO ₂ is increased beyond 10% by weight, the crystal becomes finer, and the surface roughness after precision polishing is remarkably reduced to 5 Å or less. However, this is 1
If the content exceeds 5% by weight, the glass tends to be devitrified. Therefore, the amount of TiO ₂ should be 10 to 15% by weight. Further, as shown in Experiment Nos. 1-2 to 1-15 of the examples of the present invention, the content is particularly preferably 11 to 13% by weight.

In each of Examples 1-3 to 1-9, a particle size of 0.02 to 0.07 μm was obtained in each of the examples, and the surface roughness after precision polishing was 5 Å or less. became. Here, Examples 1-3, 1-4, 1-
7, 1-8, as the amount of SiO ₂ decreases, the crystal grain size once decreases and then increases again. In Example 1-3 (51.8% by weight of SiO ₂ ), the parent glass tended to be slightly devitrified. Therefore, SiO ₂
As regards the amount, it should be between 44 and 52% by weight,
-50% by weight is particularly preferred.

In Experiment Nos. 1-10 to 15, in addition to the essential components, Li ₂ O, K ₂ O, B ₂ O ₃ , P ₂ O ₅ ,
ZrO ₂ was included. In each of these examples, crystallized glass having an enstatite phase as a main crystal phase was obtained. When K ₂ O is contained, the crystal grains tend to be slightly larger. Therefore, the content other than K ₂ O is preferable. Also,
In Experiment Nos. 1-1 to 1-15, no projections or the like caused by striae were observed.

In Experiment Nos. 1-22 to 1-25 outside the present invention, the ratio of at least one of SiO ₂ , Al ₂ O ₃ , MgO and TiO ₂ is out of the scope of claim 1 of the present invention. I have. In these experiment numbers, the main crystal phase after crystallization did not become the enstatite phase. Glass having these crystals as main crystals had a large crystal grain size, and could not obtain a surface roughness of 10 Å or less after precision polishing.

FIG. 1 shows a scanning electron micrograph of the ceramic structure of the sample of Experiment Nos. 1-4 in the present invention. FIG. 2 shows a scanning electron micrograph of the ceramic structure of Experiment Nos. 1-7 in the present invention. In each case, extremely fine particles are observed. FIG. 3 shows experiment numbers 1-2 outside the present invention.
1 shows a scanning electron micrograph of a microstructured ceramic structure of Example 1. 1 and 2, coarse particles are observed.

In the present invention, experiment numbers 1-4 and 1-
7. The Vickers hardness of each sample of Experiment No. 1-23 outside the present invention was measured. As a result, it is 910 for 1-4,
It was 975 for 1-7 and 780 for 1-23.

Further, the experiment numbers 1-4, 1-
7. The Young's modulus of each sample of Experiment No. 1-23 outside the present invention was measured. As a result, it is 126 for 1-4, and 1-7
Was 137, and in Comparative Example 1-3, it was 111.

[Experiment 2] A molded body of a parent glass having the composition of Experiment No. 1-7 in Table 2 was produced in the same manner as in Experiment 1, and this parent glass was crystallized in the same manner as in Experiment 1. At this time, the nucleation conditions were 715 ° C. for 2 hours, and the crystallization temperature was changed as shown in Table 5. However, the holding time at each crystallization temperature was all 4 hours. The heating rate and the cooling rate were the same as in Experiment 1.

As in Experiment 1, the crystal phase was identified, Ra was measured, the microstructure was observed, and the coefficient of thermal expansion was measured. Table 5 shows the results.

[0064]

[Table 5]

In Experiment No. 2-1 outside the method of the present invention, the crystallization temperature is 900 ° C. The main crystal phase is an enstatite phase, but “MAS2” having a diffraction peak at 2θ = 24.1 ° appears as a sub-crystal phase. The microstructure photograph at this time is shown in FIG. Particles having a particle size of 0.1 μm or more are found. Therefore, the surface roughness after precision polishing is as large as 9 angstroms.

Experiment Nos. 2-2 and 2- in the method of the present invention
As shown in 3 and 2-4, when the crystallization temperature is 950 ° C. or higher, the crystal phase of MAS2 does not precipitate, extremely fine crystals are obtained, and the surface roughness is improved.

Experiment Nos. 2-5 and 2-6 outside the method of the present invention
In this case, the crystallization temperature is 1100 ° C. or higher, but the crystals of Indialite begin to precipitate. Since these crystals form coarse particles, they deteriorate the surface roughness. Note that, India Light is α cordierite.

Therefore, the crystallization temperature is from 925 ° C. to 107 ° C.
5 ° C., more preferably 950 ° C. to 105
0 ° C.

(Experiment 3) Experiment Nos. 1-4 in Experiment 1
A molded body of a parent glass having a composition of
Crystallized as in experiment 1. At this time, the nucleation conditions were
The values were changed as shown in Table 6. The holding time at the nucleation temperature was 2 hours. Thereafter, crystallization was performed at 1000 ° C. for 4 hours. The heating rate and the cooling rate were the same as in Experiment 1.

As in Experiment 1, the crystal phase was identified, the surface roughness was measured, and the microstructure was observed. Table 6 shows the results.

[0071]

[Table 6]

As the nucleation temperature increases, the ratio of “MAT” phase to enstatite increases. In Experiment No. 3-3 outside of the present invention, nucleation was performed at a glass transition temperature Tg + 26 ° C. in the same manner as in general crystallized glass. FIG. 5 shows a photograph of the microstructured ceramic structure of the sample of Experiment No. 3-3. 0.5 μm coarse particles are seen. For this reason, the surface roughness after honey polishing is poor.

In Experiment Nos. 3-1 and 3-2 in the present invention,
In each case, crystals having a particle size of 0.1 μm or less were observed, and Ra after precision polishing was 5 Å or less. Therefore, the nucleation temperature should be Tg-30 to Tg ± 0 ° C., and more preferably Tg-30 to Tg−1.
0 ° C.

[0074]

As described above, according to the present invention, in the crystallized glass for a magnetic disk substrate, the center line average surface roughness Ra after precision polishing of the magnetic disk substrate is obtained.
Surface defects (projections) due to striae in the crystallized glass after precision polishing
Can be prevented from occurring.

[Brief description of the drawings]

FIG. 1 shows a scanning electron micrograph of a ceramic structure of a sample of Experiment Nos. 1-4 in the present invention.

FIG. 2 shows a scanning electron micrograph of the ceramic structure of the sample of Experiment Nos. 1-7 in the present invention.

FIG. 3 shows a scanning electron micrograph of a ceramic structure of a sample of Experiment No. 1-21 outside the present invention.

FIG. 4 shows a scanning electron micrograph of the ceramic structure of the sample of Experiment No. 2-1 outside the method of the present invention.

FIG. 5 shows a photograph of the ceramic structure of the sample of Experiment No. 3-3 outside the method of the present invention.

Claims (8)

[Claims] 1. A crystallized glass for a magnetic disk substrate, wherein the crystallized glass has a basic composition of SiO ₂ : 44-5.
2 wt%, MgO: 16 to 25 wt%, Al ₂ O _3: 1
3 to 20 wt%, TiO _2: 10~15 wt%, Zn
O:. 1 to 8 wt%, ZrO _2: 0~5 wt%, Li ₂
O: 0 to 3 wt%, B ₂ O _2: 0~3 wt%, P
₂ O ₅ : 0 to 5% by weight and Sb ₂ O ₃ : 0 to 2% by weight
The main crystal phase of the crystallized glass is an enstatite phase, and the crystal particles of the crystallized glass have a particle size of 0.0
Crystallized glass for a magnetic disk substrate, having a thickness of 1 μm-0.1 μm. 2. The crystallized glass for a magnetic disk substrate according to claim 1, having a Vickers hardness of 860 to 1100. 3. Center line average surface roughness Ra after precision polishing
3. The crystallized glass for a magnetic disk substrate according to claim 1, wherein is 1 to 6 Å. 4. The thermal expansion coefficient at 25 to 100 ° C. is 60.
2. The method according to claim 1, wherein the ratio is about 85 × 10 ⁻⁷ / k.
3. The crystallized glass for a magnetic disk substrate according to claim 3. 5. The basic composition of the crystallized glass for a magnetic disk substrate is as follows: SiO ₂ : 46 to 50% by weight, MgO:
18 to 22 wt%, Al ₂ O _3: 16~19 wt%, T
iO ₂ : 11 to 13% by weight, ZnO: 2 to 5%, ZrO
_2: 0-4 _{wt%, Li 2 O: 0~2%} , B 2 O 2: 0
2 wt%, P ₂ O _5: 0~3 wt%, Sb ₂ O _3:
The crystallized glass for a magnetic disk substrate according to any one of claims 1 to 4, wherein the content is 0.2 to 1.5% by weight. 6. A magnetic disk substrate comprising the crystallized glass for a magnetic disk substrate according to any one of claims 1 to 5, wherein the substrate is a magnetic disk substrate. 7. A magnetic disk, comprising: the magnetic disk substrate according to claim 6, a base film formed on the magnetic disk substrate, and a metal magnetic layer on the base film. . 8. A method of manufacturing a crystallized glass for magnetic disk substrates, the basic composition of SiO _2: 44 to 52 wt%, MgO: 16 to 25 wt%, Al ₂ O _3: 13~2
0 wt%, TiO _2: 10~15 wt%, ZnO: 1~
8% by weight, ZrO ₂ : 0 to 5% by weight, Li ₂ O: 0 to 0%
3 wt%, B ₂ O _2: 0~3 wt%, P ₂ O _5: 0~5
% By weight and Sb ₂ O ₃ : 0 to 2% by weight of a parent glass in the range of (Tg−30) ° C .− (Tg) ° C. (Tg is the glass transition temperature of the parent glass) A method for producing crystallized glass for a magnetic disk substrate, comprising forming and then crystallizing while holding at 925 ° C to 1075 ° C.