JP2002255585A - Glass substrate for information recording disk and information recording disk using the glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate for information recording disks optimized in the thermal expansion coefficient. SOLUTION: The glass substrate is composed of >=50 to <=70 wt.% SiO2 , >=10 to <=25 wt.% Al2 O3 , 0 to <5 wt.% B2 O3 , >13 to <18 wt.% R2 O (R is an alkali metal) and >=1 to <=8 wt.% Ln2 O3 (Ln represents Pr, Nd, Sm or Eu), wherein the difference between the thermal expansion coefficient of the glass substrate and that of a supporting spindle supporting by fitting to a throughhole 3 is reduced, so as to eliminate a track shifting by keeping the thermal expansion coefficient of the glass substrate in a proper range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a glass substrate for an information recording disk, and more particularly to a glass substrate suitable for a magnetic disk and the like.

[0002]

2. Description of the Related Art At present, magnetic disk devices and portable information are used as information recording media for general-purpose large-sized computers and personal computers, and as home servers for temporarily storing images distributed by digital signals. Magneto-optical disks and optical disks are used as recording media.

For example, in a magnetic disk drive, a 3.5-inch aluminum substrate has conventionally been used as a substrate for general-purpose or desktop personal computers, and mainly a portable notebook-type personal computer has been mainly used. A glass substrate with a size of 0.5 inches has been used. This glass substrate is harder and harder to deform than the aluminum substrate, and has excellent surface smoothness. For this reason, glass substrates have come to be applied to general-purpose 3.5-inch and 3-inch substrates instead of aluminum substrates. Also, glass substrates are being applied to information recording devices for small portable terminals such as 1.8-inch size and 1-inch size.

[0004] Further, demands for increasing the capacity of information recording devices and information recording media have been increasing, and in recent years, the annual rate of 10
The storage capacity is increasing at a rate of 0%. In order to cope with such an increase in the storage capacity, it is necessary to lower the flying height of the head of the recording unit with the increase in the density of information recorded on the disk. Therefore, the application of a glass substrate to the substrate of the information recording disk is expanding because the development of an information recording disk having a smoother recording surface is required.

[0005]

However, it is difficult to say that a conventional glass substrate takes into account the optimization of the coefficient of thermal expansion. For this reason, track misalignment may occur when recording or reading information on an information recording disk due to a mismatch in the coefficient of thermal expansion between a conventional information recording disk using a glass substrate and a spindle supporting the information recording disk. I am concerned. This is considered to be a more serious problem due to the increase in track density due to the increase in capacity in the future. Therefore, it is desired to optimize the thermal expansion coefficient of the glass substrate so that a track shift or the like does not occur when the glass substrate or the spindle thermally expands.

An object of the present invention is to optimize the thermal expansion coefficient of a glass substrate for an information recording disk.

[0007]

According to the present invention, there is provided a glass substrate for an information recording disk according to the present invention, comprising, by weight percentage, 50% or more and 70% or less of SiO ₂ and 10% or more and 25% or less of Al ₂ O ₃ ;
The above object is achieved by employing a structure containing 0% or more and less than 5% of B ₂ O ₃ and more than 13% and less than 18% of R ₂ O (R represents an alkali metal element).

[0008] With such a structure, the glass is made of B ₂ O _{3 of} 0% or more and less than 5% and R ₂ O (R represents an alkali metal element) of more than 13% and less than 18%. The thermal expansion coefficient of the glass substrate for an information recording disk can be optimized so that a track shift or the like does not occur when the substrate or the spindle thermally expands.

Further, ZnO of not more than 10% by weight is used.
, A composition containing 12% or less by weight of ReO (Re represents an alkaline earth metal element), and a composition containing 7% or less by weight of La ₂ O ₃ . It is preferable to increase the coefficient of thermal expansion of the glass substrate because the coefficient of thermal expansion of the glass substrate for an information recording disk can be optimized.

Incidentally, the glass substrate has problems such as easiness of breaking, easy breaking, and easy cracking, which are inherent properties of glass. In order to solve such problems as the easiness of breaking glass, chemical strengthening and crystallization are performed on glass substrates. However, with the chemically strengthened amorphous glass substrate, the surface of the glass substrate is roughened by the replacement of alkali ions in the chemical strengthening process, so the smoothness is lost, and the head flying height will be reduced in the future Difficult to do. Further, on the surface of the chemically strengthened glass substrate, the substituted alkali ions having a large ionic radius are chemically unstable, so that the glass substrate cleaning process and the film forming process on the glass substrate surface during the production process are performed. Alkali ions move to the surface of the substrate and precipitate during heat treatment, etc., and defects such as peeling or adhesion of the film or layer formed on the surface of the glass substrate and magnetic films formed on the surface of the glass substrate etc. There is a concern that the magnetic properties may deteriorate. In addition, even when the information recording disk is used for a long time or stored in a high-temperature and high-humidity environment, defects such as peeling or adhesion of the film or layer may occur, and alkali ions may migrate to the glass substrate surface. It is feared that the magnetic properties of the magnetic film and the like are deteriorated.

On the other hand, the crystallized glass substrate is in a state in which crystalline fine particles are generated in the amorphous glass, and the polishing rate is reduced by the difference in hardness between the amorphous portion and the crystalline portion. Due to the difference, there has been a problem that it is difficult to create a recording surface having sufficient smoothness so as to be able to cope with a high density required for an information recording disk.

In order to solve the problems of such chemically strengthened and crystallized glass substrates, the inventors disclosed in Japanese Patent Laid-Open No.
No. 83531 proposes improving the mechanical strength by incorporating rare earth ions into a glass substrate. As a result, a glass substrate with sufficient strength can be obtained without chemical strengthening or crystallization,
The glass substrate surface is not roughened during the manufacturing or processing process of the information recording disk using the glass substrate, and the glass substrate surface is not roughened due to prolonged use or storage of the information recording disk. Smoothness can be maintained. That is, it is possible to produce a glass substrate having a recording surface with sufficient smoothness so as to be able to cope with the high density required for information recording disks.

However, in the glass substrate containing rare earth ions proposed in Japanese Patent Application Laid-Open No. 10-083531, the occurrence of defective products during the production of glass substrates and information recording disks, the detection of defective products, and the chemical durability It is difficult to say that the magnetic properties required for processing into a magnetic disk device or a magneto-optical disk are sufficiently considered, and from these viewpoints the quality of the glass substrate for information recording disks has been improved. It has been demanded.

On the other hand, the weight percentage is 50% or more and 7% or more.
0% or less of SiO ₂ and 10% or more and 25% or less of Al ₂ O
_3, and B ₂ O ₃ of 5% or more and less than 0%, greater than 13% 18
% Of R ₂ O (R represents an alkali metal element);
% To 8% Ln ₂ O ₃ (Ln is Pr, Nd, Sm,
Or Eu).

According to this structure, the glass substrate is appropriately colored by Ln ₂ O _{3 of} 1% or more and 8% or less (Ln represents Pr, Nd, Sm, or Eu) and has an appropriate transmission. This makes it easier to visually detect bubbles and other contaminants in the glass substrate. Further, since the glass substrate is easily visible in the processing and cleaning steps of the glass substrate, the processing step of the information recording disk, and the like, processing defects such as damaging the glass substrate can be suppressed. In addition, when the glass substrate is used for a magnetic disk device, a magneto-optical disk, or the like, the amount of magnetization of the glass substrate can be reduced, and variations in magnetic characteristics can be reduced. Therefore, it is possible to suppress the occurrence of defects during the production of the glass substrate and the information recording disk, and furthermore, it is possible to reduce the variation in the magnetic characteristics, so that the quality of the information recording disk glass substrate can be improved. That is, the thermal expansion coefficient of the information recording disk glass substrate can be optimized, and the quality of the information recording disk glass substrate can be improved.

It is preferable that Ln constituting Ln ₂ O ₃ be Pr, because the quality of the glass substrate for the information recording disk can be further improved.

Furthermore, the thermal expansion coefficient, measured at a temperature range of 30 ° C. to 100 ° C. is 73 × 10 ^{- 7} / ℃ least 86 × 1
0 ⁻⁷ / ° C. or less, and transmittance of visible light having a wavelength of 300 nm to 700 nm is 50% or more and 85% or less,
The magnetization when a magnetic field of 1 kOe is applied is 3 × 10 ⁻³ e
A glass substrate for an information recording disk having a value of mu / cc or less. With such an information recording disk glass substrate, the thermal expansion coefficient of the glass substrate can be optimized, and the quality of the glass substrate can be improved.

Further, an information recording disk having the glass substrate for an information recording disk described in any of the above and an information recording layer formed directly or via another layer on the surface of the glass substrate is provided. In addition, since the thermal expansion coefficient of the glass substrate can be optimized, the reliability as an information recording disk can be improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a glass substrate for an information recording disk to which the present invention is applied will be described below with reference to FIGS. FIG. 1 is a plan view showing a schematic configuration of a glass substrate for an information recording disk to which the present invention is applied. FIG. 2 is a sectional view showing a schematic configuration of a magnetic disk using a glass substrate to which the present invention is applied.
FIG. 3 is a perspective view showing a schematic configuration of a magnetic disk drive provided with a magnetic disk using a glass substrate to which the present invention is applied.

As shown in FIG. 1, the glass substrate 1 for an information recording disk of this embodiment has a diameter of 65 mm and a thickness of 0.1 mm.
This is a 635-mm 2.5-inch disk-shaped disk. In the center, when used as an information recording disk, the disk is mounted on a spindle or the like connected to a motor of a device that performs recording, reading, or reproducing. A circular through hole 3 having a diameter of 20 mmφ for fixing by an inner peripheral chuck or the like is formed. The corners of the inner peripheral surface and the outer peripheral surface are cut off and chamfered at 45 degrees to form a chamfer portion 5.

The production of such a glass substrate 1 is performed as follows. A raw material powder in an amount determined to have a desired glass composition is weighed and mixed, put in a platinum crucible, and melted at 1600 ° C. in an electric furnace. After the raw materials are sufficiently dissolved, the stirring blade is inserted into the glass melt in the crucible, and the
Stir for hours. Thereafter, the stirring blade was taken out and allowed to stand for 30 minutes, and then a glass melt was poured into a mold to obtain a glass block having a diameter of about 70 mmφ and a thickness of about 1 mm. The obtained glass block is reheated to the vicinity of the glass transition point of the glass, and is gradually cooled to remove a strain.

The glass block from which the distortion has been removed is cut out using a core drill so that the inner periphery and the outer periphery are concentric. Further, the chamfered portion 5 is formed by chamfering both corners of the inner peripheral surface and the outer peripheral surface with a diamond grindstone. As a result, a disk-shaped glass substrate 1 having the holes 3 is formed. Thereafter, both surfaces of the glass substrate 1 are roughly polished and then polished. After the polishing, the glass substrate 1 is washed with a cleaning agent and pure water to form the glass substrate 1 for an information recording disk. As described above, the glass substrate 1 for an information recording disk of the present invention has not been subjected to a strengthening process such as a chemical strengthening process or a crystallization process.

As an example of an information recording disk formed by using such an information recording disk glass substrate 1, a magnetic disk will be described. The magnetic disk 7 is, as shown in FIG.
A particle size control layer 9 sequentially formed on the surface of the
It is composed of an orientation control layer 11, a magnetic film 13, a protective film 15, a lubricating film 17, and the like. The grain size control layer 9 controls the grain size of the magnetic film 13, and the orientation control layer 11 controls the orientation of the magnetic film 13. In this example, the particle size control layer 9 is made of NiAl
A 20-nm thick alloy film is formed. The orientation control layer 11 is formed of a CrMo-based alloy film with a thickness of 10 nm. The magnetic film 13 serving as the information recording layer is made of CoCrPrB.
A system magnetic film is formed with a thickness of 20 nm. Protective film 15
Has a film thickness of C of 4 nm. All of these layers or films were formed by a sputtering method. The lubricating film 17 was formed by a coating method after the end of the sputtering.

The characteristics, productivity, etc. of the glass substrate 1 for information recording disks of various compositions produced by such a method and the magnetic disk 7 in which the magnetic film 13 and the like are formed on the glass substrate 1 were evaluated. The glass composition for improving the quality of glass was studied.

First, attention was paid to the types of rare earth elements to be added, and glasses having various compositions were produced. Table 1 shows the glass compositions and the characteristics of the glass substrate and the magnetic disk with respect to those glass compositions.

[0026]

[Table 1] In Table 1, aluminoborosilicate glass having the same composition and the same amount except for the type of the rare earth element was used. The amount of the rare earth oxide to be contained was kept constant at 2.8% by weight.
As characteristics of the glass substrate, micro Vickers hardness, transmittance of visible light, coloring property, and yield of the glass substrate were evaluated. The micro-Vickers hardness was applied to a glass substrate under the conditions of a load of 500 g and a load application time of 15 seconds,
An average value of 10 points was obtained. The transmittance of visible light was obtained by measuring a transmittance spectrum from a spectral transmittance curve of a wavelength from 300 nm to 700 nm using a spectrophotometer, and calculating the integrated value of the total transmittance of light in this wavelength range. The degree of coloring was visually evaluated to determine the degree of coloring. Colorless ones were evaluated as x, and colored ones were evaluated as ○. Yield is evaluated by using a device that inspects the glass substrate for the number of foreign substances using scattered light from laser light irradiation. Then, evaluation was made based on the ratio of non-defective products.

Further, as characteristics of the magnetic disk, magnetization, standard deviation of magnetization, recording / reproducing characteristics, and yield of the magnetic disk were evaluated. Further, the overall yield from the production of a glass block before processing to a glass substrate to the production of a magnetic disk was evaluated. The magnetization and the standard deviation of the magnetization are
The BH curve was measured by a vibrating sample magnetometer (VSM), and the background component of the hysteresis loop of the magnetic film was regarded as magnetism from the glass substrate, and the magnitude of the background component was evaluated. The magnetization and the standard deviation of the magnetization are the magnitude of the magnetization when 1 kOe is applied as a magnetic field.

In addition, the recording and reproducing characteristics of the magnetic disk were evaluated. Magnetic disk drive 1 used for evaluation of recording and reproduction characteristics
Reference numeral 8 denotes a magnetic disk 7, a spindle 19, a spindle motor (not shown), a magnetic head 21, an arm 23 of the magnetic head, a voice coil motor 25 for driving the head, a housing 27, etc., as shown in FIG. It is configured. A spindle motor (not shown), a voice coil motor 25, and the like are fixed to the housing 27. A spindle 19 is connected to a spindle motor (not shown), and the magnetic disk 7 is fixed to the spindle 19. The magnetic disk 7 has a spindle 19 driven by a spindle motor (not shown).
By the rotation of, the whole is rotated. On the other hand, the arm 23 is attached to the voice coil motor 25,
The magnetic head 21 is attached to the tip of the arm 23. The magnetic head 21 is a voice coil motor 2
The arm 23 is moved by driving the magnetic disk 5 to move on the recording surface of the magnetic disk 7 by a predetermined flying height.

A magnetic disk formed using glass substrates of various compositions was mounted on such a magnetic disk device 18, and a magnetic signal corresponding to ²⁰ Gb / in ² was recorded to evaluate magnetic recording / reproducing characteristics. This evaluation was performed on 150 magnetic disks, and the ratio of magnetic disks having sufficient recording / reproducing characteristics was determined as the magnetic disk yield. further,
The overall yield was evaluated from the yield of the glass substrate and the yield of the magnetic disk. ×, if the overall yield is less than 80%, ○, 90 if the yield is 80% or more and less than 90%
% Or more was evaluated as ◎.

As shown in Table 1, in the characteristics of the glass substrate, the micro Vickers hardness of about 650 or more was obtained with any of the glass substrates containing a rare earth element. The transmittance of visible light was 80% or more in any of the glass substrates containing a rare earth element. Nd, Pr, Sm, Eu, H among rare earth elements
In the glass substrate containing any one of o and Er, sharp absorption due to the ff transition of rare earth was observed in the visible light region. Therefore, the transmittance is slightly lower than that of a glass substrate containing another rare earth element. However, Nd, Pr, Sm,
Because of the sharp absorption of Eu, Ho, and Er, clear coloring was observed on the glass substrate containing any one of Nd, Pr, Sm, Eu, Ho, and Er among the rare earth elements. In the evaluation by visual observation under an incandescent lamp, it was found that Pr was yellowish-green, Nd was purple, and Sm and Eu were very pale but yellow and pink, respectively. Er and Ho were also colored pink. The glass substrate containing another rare earth element was colorless and no coloring was observed.

When the yield of the glass substrates with respect to these substrates was evaluated, Pr, Nd, H
In the cases of o and Er, defects occurring during processing or cleaning, that is, defects due to damage such as scratches were smaller than those not colored, and the yield was 95% or more. This is because the colored glass substrate is easier to check visually than the transparent glass substrate in the processing step and the cleaning step, and is easy to handle. By suppressing the occurrence of damage,
It is considered that the yield has improved.

Further, although not shown in the table, a glass substrate having high coloring properties containing Ni was evaluated as a comparative example, and the substrate containing Ni had a transmittance of 47%.
It is difficult to find bubbles existing in the glass, or the components that make up the crucible when melting the raw materials of the glass substrate, that is, erosion of the furnace material into the glass. Yield was low due to the remaining.

Thus, there is a clear correlation between the transmittance and the yield of the glass substrate and the magnetic disk. If the transmittance is less than 50%, bubbles remaining in the glass substrate and mixing of furnace materials are hard to be found, which causes a reduction in yield. Further, when the transmittance of the glass substrate exceeds 85%, the glass substrate becomes difficult to visually recognize, so that it is difficult to handle the glass substrate in processing and cleaning work, and processing defects such as accidental scratching increase. . Therefore,
The transmittance of the glass substrate is colored enough to be seen,
In addition, in order to obtain a glass substrate in which bubbles and furnace materials remaining in the glass substrate can be easily found, that is, defects can be easily found, the content needs to be 50% or more and 85% or less. further,
Rare earth elements added to the glass substrate to achieve such optical characteristics include Pr, Nd, Sm, Eu, and E.
r or Ho was found to be preferred. this house,
Pr, Nd, Er or Ho is more preferable because coloring is remarkable.

On the other hand, as shown in Table 1,
In the characteristics, the magnetization characteristics are Sc, of the rare earth elements,
Formed using a glass substrate containing any one of Y and La
In the magnetic disk, the magnitude of magnetization of the glass substrate is 1
0^-4on the order of emu / cc and other rare earth elements
Compared to magnetic disks formed using glass substrates containing
Thus, the amount of magnetization was extremely small. S as rare earth element
With a magnetic disk formed using a glass substrate containing m
Indicates that the magnetization shows a diamagnetic behavior, and -4 × 10
^-4emu / cc. Pr, N as rare earth elements
Formed using a glass substrate containing either d or Eu
1.0 to 3.0 × 10 ^-3emu
/ Cc.

Gd, Tb, Dy, H as rare earth elements
Glass substrate containing any one of o, Er, Tm, and Yb
In a magnetic disk formed by using^-3~ 2
× 10 ^-2emu / cc and the value of magnetization is other rare earth element
Was larger than the case where The difference in magnetization
When the standard deviation of the magnetization shown was evaluated, the magnitude of the magnetization
The larger the value, the larger the standard deviation of magnetization. This
This is because the larger the magnetization, the more the glass substrate
This indicates that the variation in magnetization is large. In particular,
Magnetization size is 3 × 10^-3G exceeding emu / cc
Any one of d, Tb, Dy, Ho, Er, Tm, and Yb
Magnetic disk using a glass substrate containing
In the disk, the standard deviation of magnetization is 1 × 10^-3emu / cc
As described above, the variation in the magnetic characteristics due to the glass substrate is large.
I got it.

[0036] Looking at the yield of the magnetic disk by the magnetic recording and reproducing characteristics, the magnetization is 3 × ^{10 -} with 3 emu / cc or less, the magnetic disk of a standard deviation of less than 1 × ¹⁰ -3 emu / cc in magnetization, sufficient The magnetic disk from which magnetic properties were obtained was as good as 90% or more. However, the magnetization is 3 ×
Exceeds 10 ⁻³ emu / cc and the standard deviation of magnetization is 1
For a magnetic disk having a capacity of × 10 ⁻³ emu / cc or more,
It was found that the yield was reduced to 80% or less.
This is because the magnetic properties of the glass substrate changed due to a slight solid-state difference of the rare earth element contained in the glass substrate, and the standard deviation became large, resulting in variations in recording when recording with a constant magnetic field. it is conceivable that.

Thus, the magnitude of the magnetization is 3 × 10 ^−3.
If it is less than emu / cc, a magnetic disk having a relatively small variation in magnetic recording / reproduction was obtained. Magnitude of 3
If it exceeds × 10 ⁻³ emu / cc, the dispersion of the magnetic recording / reproducing characteristics among the glass substrates increases, which is not preferable. Therefore, in order to reduce the influence of the glass substrate on the magnetization of the magnetic disk, the magnitude of the magnetization is 3 × 10 ^−3.
It is necessary to be less than emu / cc. Further, in order to obtain such magnetic characteristics, Sc, as a rare earth element,
It is preferable that any one of Y, La, Pr, Nd, Sm, and Eu is contained in the glass substrate.

The total yield was evaluated in consideration of the effect on the yield of the glass substrate and the effect of the magnetic characteristics on the recording and reproducing characteristics of the magnetic disk drive. As a result, both the effect on the yield of the glass substrate and the effect of the magnetic characteristics on the recording / reproducing characteristics showed satisfactory results, and any one of Pr, Nd, Sm, and Eu having an overall yield of 80% or more was obtained. If the glass substrate contains one as a rare earth element, the quality of the glass substrate can be improved. Furthermore, if a glass substrate containing Pr as a rare earth element that provides an overall yield of 90% is used, the quality of the glass substrate can be further improved.

Further, the relationship between the type of rare earth oxide and the amount of rare earth oxide added was examined. For coloring, Table 1
In the glass substrate containing a rare earth element which was transparent in the above, no change was observed in the transmittance of the glass substrate even when the content of the rare earth element was increased or decreased. For this reason, among the rare earth elements that colored the glass substrate, Pr, Er, and Sm were prepared with glass substrates having different contents, and the same examination as in Table 1 was performed. Table 2 shows the results of the study.

[0040]

[Table 2] When the content of Pr was changed, sample No. 1
The glass substrate containing 0.7% by weight of Pr ₂ O ₃ of No. 7 has low micro Vickers hardness and low mechanical strength of the glass, so there are many defects such as polishing scratches and spatters, and the yield of the glass substrate is 82. % Was low. Sample No. 1 containing 1% by weight of Pr ₂ O ₃ . 16, and Pr ₂ O ₃ at 1.5
No. 7% by weight. In Nos. 18 to 21, the micro Vickers hardness showed a high value, and both the coloring and the magnetic properties were sufficient. From this, the sample No. 16,
And sample no. For the glass substrates of Nos. 18 to 21, the total yield exceeded 90%, and good results were obtained.

On the other hand, as shown in sample No. 22, Pr ₂ O ₃
When the content exceeds 7% by weight, there is no problem with regard to coloring, but the magnetization of the magnetic disk is 3 × 10 ⁻³ em.
The value exceeded u / cc. For this reason, the variation in magnetization became large, and the yield of the magnetic disk was less than 80%, and a sufficient result was not obtained. Further, the sample No.
In a glass substrate having a Pr ₂ O ₃ content of 10.5% by weight, such as 23, rare earth elements in the glass are not uniformly dissolved in the glass, the number of defective products increases, and the yield is as low as 15%. It was not preferable as a glass substrate.

On a glass substrate containing Er as a rare earth element, sample N having an Er ₂ O ₃ content of 0.5% by weight was used.
o. In 25, the micro Vickers hardness is small,
A glass substrate with sufficient strength could not be obtained, and the yield of the glass substrate was poor. At this time, the magnetization value of the magnetic disk was as high as 3.1 × 10 ⁻³ emu / cc, and the yield as the magnetic disk was also low. Er ₂ O ₃ content of 1
When the weight percentage is increased, the micro Vickers hardness increases and the transmittance decreases, so that the yield of the glass substrate increases, but the magnetization is still 3 × 1.
Since more than 0 ^-3 emu / cc, yield of the magnetic disk was bad. As described above, when Er is used as the rare earth element, the hardness and optical characteristics of the glass substrate,
It has been found that there is no composition range that simultaneously satisfies both magnetic properties as a magnetic disk.

In a glass substrate containing Sm as a rare earth element, the optical characteristics of the glass substrate are as follows: Sm ₂
When the O ₃ content is 2.5% by weight or more, the transmittance is 85%.
Below is the appropriate range. Magnetic properties of a magnetic disk, which was also a fair the _Sm 2 _{O 3} is contained 10% by weight, the content of _Sm 2 _{O 3} exceeds 10 wt% P
As in the case of r, the residual raw material remains in the glass, which is not preferable.

Similarly, rare earth elements such as Nd, Eu, H
When a glass substrate containing o was examined, the same results were obtained for Nd and Eu as for Sm, but when the content of Nd or Eu exceeded 8% by weight, the magnetic properties as a magnetic disk were Decreased, which was not preferable. Regarding Ho, as in the case of the glass substrate containing Er as a rare earth element, there was no composition range that satisfied both the optical characteristics of the glass substrate and the magnetic characteristics of the magnetic disk at the same time, so that a favorable result was not obtained.

As described above, Pr and N are rare earth elements.
By containing d, Sm, and Eu, and making the concentration of the rare earth oxide contained 1% by weight or more and 8% by weight or less, the optical characteristics of the glass substrate improve the visibility of the glass substrate and improve the visibility of the glass substrate. It is possible to reduce the occurrence of defects such as scratches and chips generated during processing, and to easily find defects such as bubbles, striae, foreign matter, scratches and chips in the glass substrate in quality inspection and the like. Furthermore, since the magnetization of the glass substrate can be reduced in the magnetic characteristics of a magnetic disk or a magneto-optical disk, the influence of the glass substrate on the magnetic characteristics of the magnetic disk or magneto-optical disk can be reduced. Therefore, the quality of the glass substrate can be improved.

Further, Pr is contained as a rare earth element,
The concentration of the rare earth oxide is 1.5% by weight to 5.2% by weight.
If it is below, the total yield is 90% or more, and the quality of the glass substrate can be further improved.

In the case other than the case where any one of Pr and Nd is contained as the rare earth element, and when the Sm is contained as the rare earth element, the concentration of the rare earth oxide is not less than 2.5% by weight and 9%. Wt% or less, Eu as a rare earth element
Is contained, the concentration of the rare earth oxide is 2.5.
It may be not less than 8% by weight and not more than 8% by weight.

The rare earth elements Pr, Nd, S
If the content of m and Eu is less than 1% by weight, the mechanical strength of the glass substrate, such as the micro-Vickers hardness, decreases, or the transmittance becomes too high, and the yield of the glass substrate decreases. That is, defects due to scratches, sprinkling, etc. of the glass substrate are increased, and the quality of the glass substrate is reduced. On the other hand, when the content of the rare earth element is more than 8% by weight, the magnetization value of the glass substrate increases, and when processed into a magnetic disk or a magneto-optical disk, the variation in the magnetization characteristics of the magnetic disk or the magneto-optical disk is reduced. This is not preferable because it increases the quality of the glass substrate and the quality of a magnetic disk or a magneto-optical disk using the glass substrate. Further, when the content of the rare earth element is more than 8% by weight, the quality of the glass substrate is deteriorated because the raw material may remain in the glass, which is not preferable.

Next, in order to examine a glass composition suitable for a glass substrate for an information recording disk, the results of an examination of glass stability, a coefficient of thermal expansion, micro Vickers hardness of the glass substrate surface, ring strength, and a heat cycle test were conducted. Are shown in Table 3. In each sample shown in Table 3, Pr was used as a rare earth element to be added. In the glass compositions in Table 3, R ₂ O is Li ₂ O, Na ₂ O, and K ₂
Shows the content of all alkali metal oxides including O.

[0050]

[Table 3] Here, with respect to the stability of the glass, those in which bubbles, striae, foreign matter, etc. were remarkably observed after melting the glass were evaluated as x, and clear, homogeneous glass was obtained without bubbles, striae, foreign matter, etc. When it was, it was marked as ○. The coefficient of thermal expansion is such that a glass block corresponding to the composition of each sample is prepared and 4 mm × 4 mm × 15 m
The test piece for measuring thermal expansion of m was cut out and measured using a thermal expansion measuring device. At this time, the measurement temperature range is 30 ° C.
100 ° C. The ring strength is determined by placing an annular member having an outer diameter of 22 mmφ on the upper surface side of a 2.5 ″ glass substrate serving as a sample, and 63 mmφ inner diameter and 65 mm outer diameter on the lower surface side of the glass substrate.
After installing the annular members of mmφ, a load was applied to these annular members, and the breaking strength of the glass substrate was measured.

In the thermal cycle test, a magnetic disk was manufactured using the obtained glass substrate in the same manner as described above, and the manufactured magnetic disk was mounted on a magnetic disk device as shown in FIG. According to the results of the thermal cycle test, the rate of problems such as reading errors due to track deviation is 1%
In the following cases, ○ was shown, and in the case of 1% or more, ×.
At this time, the heat cycle was maintained at 0 ° C. for 4 hours, and then the temperature was raised and maintained at 65 ° C. for 4 hours. Thereafter, the temperature was lowered to 0 ° C. and maintained for 4 hours. This cycle was repeated 10 times, and it was determined whether or not an error occurred during the cycle.

SiO_TwoSamples shown in Table 3 for the content of
No. The study was conducted using glass substrates such as 50 to 55. S
iO_TwoHaving a content of 49.5% by weight. 52 glass substrate
Does not have sufficient micro Vickers hardness and ring strength
With sufficient quality as a glass substrate for information recording discs
There was no. However, the sample No. As shown in FIG.
O_TwoIf the content of
Suitable as a glass substrate because its hardness exceeds 650
Met. In addition, the sample No. SiO like 55 _TwoIncluding
If the content exceeds 70% by weight, bubbles and the like will be generated when the glass is melted.
This was not preferable because the occurrence of blemishes became remarkable. On the other hand, the sample
No. SiO as in 54_TwoContent of 70% by weight
Is free from bubbles, striae, etc.
Thus, a glass substrate having an appropriate strength was obtained.

As described above, SiO 2_TwoContent is 50 weight
% Or more and 70% by weight or less,
Glass with sufficient water resistance and mechanical strength as a glass substrate
Substrate can be obtained. Note that SiO_TwoContent of
If it is less than 50% by weight, it may be difficult to use micro-Vickers strength
It is not preferable because mechanical strength is reduced. In addition, SiO _Two
If the content exceeds 70% by weight, bubbles and striae are generated.
However, it is difficult to obtain a clear and homogeneous glass, which is not preferable.

With respect to the content of Al ₂ O ₃ , 5
The study was conducted using glass substrates such as 6 to 59. Sample No.
In a glass substrate having an Al ₂ O ₃ content of 26% by weight, the melting temperature of the glass is too high,
The melting was not preferable because the glass raw material remained. However, the sample No. 56 having an Al ₂ O ₃ content of 2
With 5% by weight of glass, clear glass could be obtained. At this time, both the micro Vickers hardness and the ring strength showed sufficient values for a glass substrate. On the other hand, Al ₂ O ₃
No. 10 content of 10% by weight. Even with the glass substrate No. 58, both the micro Vickers hardness and the ring strength showed sufficient values as a glass substrate, and a clear glass substrate was obtained. However, when the content of Al ₂ O ₃ was 9.5 wt%,
With the 59 glass substrate, inhomogeneity such as striae occurred in the glass, and clear glass could not be obtained.

As described above, Al_TwoO₃Content of 10
If the amount is from 25% by weight to 25% by weight,
Having sufficient mechanical strength as a glass substrate
A stable glass substrate, that is, a clear and homogeneous glass
A substrate was obtained. In addition, Al _TwoO₃Content of 10 weight
%, A clear and homogeneous glass substrate cannot be obtained
Was. On the other hand, Al_TwoO₃Content exceeded 25% by weight
Sometimes, raw materials remain in the glass and clear glass
I couldn't get it.

Li₂O, Na₂O, K₂All with O
Content of alkali oxide (R in the table) ₂O) and glass substrate
The change in the coefficient of thermal expansion of Sample No. 42-49 etc.
It was examined by. Sample No. 44, 45 glass substrates
In glass with a low alkali metal oxide content,
Errors due to track deviation are confirmed in the thermal cycle test.
It has been certified. Sample No. Alkali metal like 48, 49
Similarly, when the oxide content is large,
A magnetic disk drive that caused an error was identified.

Looking at the thermal expansion coefficients of these glass substrates, Sample No. For the glass substrates 44 and 45, 7
Has a ^{1.0 × 10 -7 /℃,58.3×10 -7 / ℃} , the generally 80 × ^{10 -7} / ℃ a thermal expansion coefficient such as stainless steel used as the material of the spindle It is smaller than that. Sample No. 48, 49
Of glass substrates of 87.4 × 10 ⁻⁷ / ° C. and 95.
It was 1 × 10 ⁻⁷ / ° C., which was larger than the coefficient of thermal expansion of the material forming the spindle. Therefore, such a difference between the thermal expansion coefficient of the glass substrate and the thermal expansion coefficient of the spindle becomes a difference between the thermal expansion of the glass substrate and the thermal expansion of the spindle due to thermal cycling, and as shown in FIG. The thermal expansion of the through hole 3 becomes larger than the thermal expansion of the spindle 19 of the magnetic disk device 18 as shown in FIG. Is considered to have occurred.

As described above, the coefficient of thermal expansion of the glass substrate greatly depends on the contained alkali metal oxide. From the results shown in Table 3, the content of the alkali metal oxide is 13.0.
If the weight percent or less, the thermal expansion coefficient of the glass substrate is too small than the thermal expansion coefficient of the material forming the spindle,
This is not preferable because track deviation occurs in the heat cycle test. On the other hand, if it is 18.0% by weight or more, the coefficient of thermal expansion of the glass substrate becomes too large than the coefficient of thermal expansion of the material forming the spindle, which is also not preferable because a track shift occurs in the thermal cycle test. On the other hand, when the content of the alkali metal oxide is more than 13.0% by weight and less than 18.0% by weight, problems such as track deviation in the heat cycle test hardly occur. In addition, the sample No. Sample No. 43 has a coefficient of thermal expansion of 73.0 × 10 ⁻⁷ / ° C. or more like the glass substrate No. 43. Like the glass substrate of No. 47, the coefficient of thermal expansion is 86.0 × 10 ⁻⁷ /
When the temperature is lower than or equal to ° C., a magnetic disk device which hardly causes a problem such as track deviation in the thermal cycle test was obtained.

Therefore, when the content of the alkali metal oxide is more than 13.0% by weight and less than 18.0% by weight, the coefficient of thermal expansion of the glass substrate is in an appropriate range which does not cause a problem such as track deviation, that is, 73%. 0.0 × 10 ⁻⁷ / ℃ or higher 8
6.0 × 10 ⁻⁷ / ° C. or less, and the thermal expansion coefficient of the glass substrate can be optimized.

Regarding the content of B ₂ O ₃ , sample No. 60
It examined from glass substrates, such as -63. Or do not contain B ₂ O _3, samples the content of B 2 _{O 3} is 3 wt% or less No. The glass substrates of 60 to 62 were sufficiently homogeneous with few bubbles and striae, and also exhibited appropriate values of mechanical strength such as thermal expansion coefficient, Vickers hardness and ring strength. On the other hand, sample N having a B ₂ O ₃ content of 5% by weight
o. In the glass substrate of No. 63, the coefficient of thermal expansion was small and deviated from an appropriate range, and a magnetic disk device which caused track deviation in a thermal cycle test was observed.

As described above, if the content of B ₂ O ₃ is 0% by weight or more and less than 5% by weight, the thermal expansion coefficient of the glass substrate can be optimized, and no track shift occurs in the thermal cycle test. Although not shown in Table 3, when the content of B ₂ O ₃ is 5% by weight or more, the thermal expansion coefficient is out of an appropriate range, which is not preferable.

Here, like the glass substrates of Sample Nos. 63 to 72, etc., the composition of the glass substrate described so far includes an alkaline earth metal such as MgO, CaO, or ZnO.
Is effective in increasing the coefficient of thermal expansion of the glass substrate, which is preferable in optimizing the coefficient of thermal expansion of the glass substrate. Alkaline earth metals such as MgO and CaO are not shown in Table 3, but when the content in the glass substrate exceeds 12% by weight, cracks occur, and the micro Vickers hardness is in an appropriate range. Nevertheless, the ring strength decreased. Therefore, when the alkaline earth metal oxide is contained, it has the effect of increasing the coefficient of thermal expansion of the glass substrate, but when it exceeds 12% by weight, the mechanical strength of the glass substrate is reduced. Therefore, if the content of the alkaline earth metal oxides MgO and CaO is 0% by weight or more and 12% by weight or less, the glass substrate has sufficient Vickers hardness and ring strength, that is, mechanical strength. A glass substrate having an optimized thermal expansion coefficient can be obtained.

Sample No. The glass substrates 73 and 74 are made of MgO, CaO, and B as alkaline earth metal oxides.
It contains two types of aO at the same time. Although not shown in Table 3, the precipitation or elution of the alkali metal element or alkaline earth element from the glass substrate is suppressed by simultaneously containing two or more kinds of alkaline earth metals in the glass substrate as in this example. it can. Thereby, the separation of the information recording layer such as the magnetic film formed on the surface of the glass substrate can be suppressed, and the chemical stability can be improved. Even when two kinds of alkaline earth metals are contained in the glass substrate, the content needs to be 12% by weight or less in order to suppress the occurrence of cracks.

On the other hand, for ZnO, sample No. As shown in the glass substrate No. 72, etc., when the content exceeds 10% by weight, crystals are remarkably precipitated in the glass substrate, which is not preferable. At a ZnO content of 10% by weight, no such crystals were precipitated. Therefore, ZnO
Is preferably 0% by weight or more and 10% by weight or less.

The inclusion of La, which is a rare earth element, in the composition of the glass substrate described above also has the effect of increasing the coefficient of thermal expansion of the glass substrate, which is preferable for optimizing the coefficient of thermal expansion of the glass substrate. . Sample No. 75-7
When the content of La ₂ O ₃ was 7% by weight or less as in the glass substrate No. 7, no striae or bubbles were generated in the glass, and good glass was obtained. On the other hand, sample No. With the glass substrate No. 78, although sufficient properties were obtained in terms of the coefficient of thermal expansion, micro Vickers hardness, etc., striae were observed in the glass substrate, and it was difficult to obtain sufficient glass stability.

As described above, when La ₂ O ₃ of 7% by weight or less is contained in the glass substrate, the thermal expansion coefficient of the glass substrate is increased without impairing the mechanical strength, and the thermal expansion coefficient of the glass substrate is optimized. it can. However, L exceeds 7% by weight.
When a ₂ O ₃ is contained in a glass substrate, it is difficult to obtain sufficient glass stability, which is not preferable.

As described above, 50% by weight or more and 70% by weight or more
% By weight of SiO ₂ , 10% by weight to 25% by weight of Al ₂ O ₃ , and 0% by weight to less than 5% by weight of B ₂ O
₃ and a glass substrate for an information recording disk having a configuration containing more than 13% by weight and less than 18% by weight of R ₂ O (R represents an alkali metal element). This reduces the difference between the coefficient of thermal expansion of the information recording disk glass substrate and the coefficient of thermal expansion of the spindle that supports the information recording disk fitted into the through hole of the information recording disk. An appropriate range in which the coefficient of thermal expansion of the substrate does not cause a problem such as track deviation, that is, 73.0 × 10 ⁻⁷ / ° C. or more 8
Since the temperature is not more than 6.0 × 10 ⁻⁷ / ° C., the thermal expansion coefficient of the glass substrate can be optimized.

Further, a composition containing 10% by weight or less of ZnO, a composition containing 12% by weight or less of ReO (Re represents an alkaline earth metal element), and a composition containing 7% or less by weight of La ₂ O ₃ . With such a configuration, the thermal expansion coefficient of the glass substrate can be increased, so that the thermal expansion coefficient of the glass substrate can be optimized. In addition, when a composition containing two or more types of ReO (Re represents an alkaline earth metal element) of 12% or less by weight in total is used, the chemical stability of the glass substrate is improved, and The coefficient of thermal expansion can be optimized.

Further, Ln of not less than 1% by weight and not more than 8% by weight
_With a structure containing ₂ O ₃ (Ln represents Pr, Nd, Sm, or Eu), the visibility of the glass substrate is improved, and defects such as scratches and chips generated during processing of the glass substrate are generated. In addition, defects such as air bubbles, striae, foreign matter, scratches, sprinkles, and the like in the glass substrate in quality inspection and the like can be easily found. Further, when used for a magnetic disk or a magneto-optical disk, since the magnetization of the glass substrate can be reduced, the influence of the glass substrate on the magnetization characteristics when processed into a magnetic disk or a magneto-optical disk can be reduced. Therefore, the quality of the glass substrate can be improved, and the thermal expansion coefficient of the glass substrate can be optimized.

Further, if Ln constituting Ln ₂ O ₃ is Pr, the occurrence of defects can be further reduced, defects can be more easily found, and the magnetization when processed into a magnetic disk or a magneto-optical disk can be obtained. Since the influence on the characteristics can be further reduced, the quality of the glass substrate can be further improved.

However, since rare earth elements other than La, ie, Pr, Nd, Sm, or Eu, do not significantly affect the change in the thermal expansion coefficient of the glass substrate, the occurrence of defects can be reduced, defects can be easily found, and When it is not necessary to improve the quality of the glass substrate in terms of reducing the influence on the magnetic characteristics when processed into a magnetic disk or a magneto-optical disk, Pr, Nd, Sm, or Eu may be used as a rare earth element.
Is not contained. Further, in the case where the mechanical strength of the glass substrate is obtained by chemical strengthening or crystallization, a structure in which a rare earth element is not contained in the glass substrate can be employed.

[0072] Furthermore, the thermal expansion coefficient, measured at a temperature range of 30 ° C. to 100 ° C. is 73 × 10 ^{- 7} / ℃ least 86 × 1
0 ⁻⁷ / ° C. or less, and transmittance of visible light having a wavelength of 300 nm to 700 nm is 50% or more and 85% or less,
The magnetization when a magnetic field of 1 kOe is applied is 3 × 10 ⁻³ e
A glass substrate for an information recording disk having a value of mu / cc or less. With such a glass substrate, the quality of the glass substrate can be improved and the coefficient of thermal expansion of the glass substrate can be optimized.

Further, in an information recording disk using a glass substrate for an information recording disk to which the present invention is applied, since the coefficient of thermal expansion of the glass substrate is optimized and track deviation hardly occurs, the information recording disk is used as an information recording disk. Reliability can be improved.

[0074]

According to the present invention, the thermal expansion coefficient of the glass substrate for an information recording disk can be optimized.

[Brief description of the drawings]

FIG. 1 is a plan view of one embodiment of a glass substrate for an information recording disk to which the present invention is applied.

FIG. 2 is a cross-sectional view of one embodiment of a glass substrate for an information recording disk to which the present invention is applied.

FIG. 3 is a perspective view showing a schematic configuration of a magnetic disk device provided with a magnetic disk using a glass substrate for an information recording disk to which the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 glass substrate for information recording disk 3 through hole 5 chamfer part

Continued on the front page (72) Inventor Takashi Naito 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Mitsutoshi Honda 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. F-term in Hitachi Research Laboratory, Hitachi Ltd. (Reference) 4G059 AA09 AC30 DA05 DA07 DB02 EA11 EB04 GA02 GA04 4G062 AA18 BB01 CC01 DA06 DB04 DC01 DC02 DC03 DE01 DE02 DE03 DF01 EA04 EB04 EC04 ED01 ED02 ED03 EE04 EE04 EE04 EE04 EE04 EE04 EE04 EE04 EE04 EE04 EE04 EF03 EF04 EG01 EG02 EG03 EG04 FA01 FB01 FC01 FD01 FE01 FF01 FG01 FH01 FJ01 FK01 FK02 FK03 FL01 GA01 GB01 GC01 GD01 GE01 HH01 HH03 HH05 HH07 HH09 HH11 HH13 HH15 KK NN JJ01 JJ01 JJ01 JJ01 JJ01 JJ01 JJ01 JJ01 JJ01

Claims (8)

[Claims] 1. A weight percentage of 50% or more and 70% or less of SiO ₂ , 10% or more and 25% or less of Al ₂ O ₃ , 0% or more and less than 5% of B ₂ O _3, and more than 13% A glass substrate for an information recording disk, containing less than 18% of R ₂ O (R represents an alkali metal element). 2. A composition in which, by weight percentage, 50% or more and 70% or less of SiO ₂ , 10% or more and 25% or less of Al ₂ O ₃ , 0% or more and less than 5% of B ₂ O _3, and more than 13% Less than 18% of R ₂ O (R represents an alkali metal element) and 1% or more and 8% or less of Ln ₂ O ₃ (Ln is Pr, Nd, S
m or Eu). 3. The glass substrate for an information recording disk according to claim 1, wherein the glass substrate contains ZnO in a weight percentage of 10% or less. 4. The glass substrate for an information recording disk according to claim 1, wherein the glass substrate contains at most 12% by weight of ReO (Re represents an alkaline earth metal element). . 5. The glass substrate for an information recording disk according to claim 1, further comprising La ₂ O ₃ in a weight percentage of 7% or less. 6. The glass substrate for an information recording disk according to claim _2, wherein Ln constituting said Ln ₂ O ₃ is Pr. 7. A thermal expansion coefficient measured in a temperature range of 30 ° C. to 100 ° C. is 73 × 10 ⁻⁷ / ° C. or more and 86 × 10 ^−7.
/ ° C or lower, the transmittance of visible light having a wavelength of 300 nm to 700 nm is 50% or more and 85% or less, and 1 kO
e when the magnetic field is applied is 3 × 10 ⁻³ emu /
A glass substrate for an information recording disk having a size of cc or less. 8. A glass substrate for an information recording disk according to claim 1, and an information recording layer formed directly or via another layer on the surface of the glass substrate. Information recording disc.