JP2003099913A - Glass base plate for magnetic disk and magnetic disk using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass base plate that can meet the requirement for high density recording and has an appropriate thermal expansion coefficient and Young's modulus with a high mechanical strength and is also excellent in mass production, and provide a magnetic disk that uses it. SOLUTION: This glass base plate for a magnetic disk is a glass plate that contains rare earth oxides of Pr, Nd, Sm, and Eu. This glass plate has a thermal expansion coefficient larger than 61×10<-7> / deg.C but less than 72×10<-7> / deg.C within the range of 30-100 deg.C. Its Young's modulus is 80 GPa or larger but 90 GPa or smaller and its transmissivity is 50% or larger but 80% or smaller to the visible light of the wavelength of 300 nm-700 nm. And also, its magnetization is 3×10<-3> emu/cc or less when a magnetic field of 1 kOe is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass substrate for a magnetic disk, and in particular, a glass substrate for a magnetic disk suitable for high density recording, which is suitable for thermal expansion coefficient and Young's modulus and has good mass productivity. Relates to a magnetic disk using.

[0002]

2. Description of the Related Art At present, magnetic disk devices are used as recording media for general-purpose large-sized computers and personal computers, and also as home servers for temporarily storing images distributed by digital signals. Conventionally, as a substrate for this magnetic disk, an aluminum substrate of 3.5 ″ size is used for general purpose or desktop personal computers, and a glass of 2.5 ″ is mainly used for a portable notebook computer. Substrates have been used.

Since this glass substrate is harder than an aluminum substrate and is less likely to be deformed and has excellent surface smoothness, it can be applied to the general-purpose substrate of 3.5 "or 3" size. Is coming. Furthermore 1.8 "
, 1 ″, such a glass substrate is about to be applied to a recording device for a small mobile terminal.

In addition to such miniaturization, there is an increasing demand for larger capacity of the magnetic disk device, and in recent years, the annual rate is 1
The storage capacity is increasing at a rate of 00%. In order to cope with this, it is necessary to further reduce the flying height of the magnetic head in the recording section, and therefore it is necessary to develop a magnetic disk having a smoother recording surface.

At present, the problem of breakage inherent in glass is overcome by using a chemically strengthened glass substrate or a crystallized glass substrate. However, in the chemically strengthened amorphous glass substrate, the surface is roughened because it is strengthened by the substitution of alkali ions during the chemical strengthening process, and it is difficult to cope with future low head flying height. Furthermore, under the use environment as described above, the surface of the chemically strengthened glass is
Since the substituted alkali ions with a large ionic radius are chemically unstable, this may occur during the cleaning process in the production process, the heating process in the film formation process, or under the environment of long-term use or high temperature and high humidity. There is a concern that alkali ions may move and precipitate on the surface of the substrate, resulting in deterioration of the magnetic properties of the magnetic film, peeling of the film, and adhesion.

On the other hand, in the crystallized glass substrate, crystalline fine particles are formed in amorphous glass. However, the polishing rate varies depending on the hardness difference between the amorphous part and the crystalline part, and thus the magnetic disk is There has been a problem that it is difficult to form a recording surface having sufficient smoothness to meet the demand for higher density.

In order to overcome the above problems, the inventors of the present invention increase the mechanical strength by containing rare earth ions in the glass substrate as described in Japanese Patent Application Laid-Open No. 10-083531. Has been resolved.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In Japanese Patent No. 3531, although a glass substrate having a high mechanical strength can be obtained, it cannot be said that the thermal expansion coefficient and Young's modulus, which are the properties required as a glass substrate for a magnetic disk, are adequately considered. I wanted Therefore, in a thermal environment test such as thermal shock, there is a mismatch between the thermal expansion characteristics of the glass substrate and the magnetic disk drive device member that supports it, or a track shift occurs during high-speed rotation of the drive device due to a defect in Young's modulus. It is possible to do it. This is expected to become a more severe subject as the capacity increases in the future.

In view of the above, the present invention has an object to obtain a glass substrate for a magnetic disk and a magnetic disk using the same, which have suitable thermal expansion coefficient and Young's modulus and are suitable for mass production with good mass productivity. did.

[0010]

In order to solve the above problems, the glass substrate for a magnetic disk of the present invention has a weight percentage of SiO ₂ : 55% or more and 70% or less, Al ₂ O ₃ : 10.
% Or more, 17% or less, B ₂ O ₃ : 2% or more, 8% or less, R
₂ O: 10% or more and 16% or less (R represents an alkali metal element), ZnO: 0% or more, 10% or less ReO: 0% or more, 10% or less (Re represents an alkaline earth metal element) It contains an oxide expressed as an oxide and further contains Pr ₂ O ₃ or Nd ₂ O _{3 in an amount} of 1% or more and 7% or less, or Sm ₂ O ₃ of 2.5% in the following oxide conversion weight percentage. or 9% or less, or Eu ₂ O ₃ 2.5% or more, containing 8% or less, a thermal expansion coefficient in a temperature range of 30 ° C. to 100 ° C. is 61 × 10 ^-7 / ℃ or higher, 72 × 1
It is 0 ^-7 / ° C or less.

Further, the glass substrate for a magnetic disk of the present invention has a Young's modulus of 80 GPa or more and 90 GPa or less, a transmittance of visible light of wavelength 300 nm to 700 nm of 50% or more and 85% or less, and a magnetic field of 1 kOe. The magnetization when applied is 3 × 10 ⁻³ emu / cc or less.

The magnetic disk of the present invention is a magnetic disk having a glass substrate for a magnetic disk and a magnetic layer formed on the glass substrate directly or through another layer, wherein the glass substrate is in weight percentage. SiO ₂ : 55% or more, 7
0% or less, Al ₂ O ₃ : 10% or more, 17% or less, B
₂ O ₃ : 2% or more, 8% or less, R ₂ O: 10% or more, 16
% Or less (R represents an alkali metal element), ZnO: 0%
Or more, 10% or less ReO: 0% or more, 10% or less (Re represents an alkaline earth metal element) containing an oxide represented by oxide conversion, and further, Pr _{2 in} the following oxide conversion weight percentage: Contains O ₃ or Nd ₂ O _{3 in an amount} of 1% to 7%, Sm ₂ O _{3 in an amount} of 2.5% to 9%, or Eu ₂ O _{3 in an amount} of 2.5% to 8%. , The coefficient of thermal expansion in the temperature range of 30 ° C. to 100 ° C. is 61 × 10 ⁻⁷ / ° C. or more, 72 × 10
^-7 / ° C or less.

The magnetic disk of the present invention is a magnetic disk having at least a glass substrate and a magnetic film formed on the surface of the glass substrate directly or through another layer, and the surface roughness of the glass substrate is Young. Rate is over 80 GPa, 90
The glass substrate has a wavelength of 300 nm or less
Transmittance in visible light of 700 nm is 50% or more and 85%
And the magnetization when a magnetic field of 1 kOe is applied to this glass substrate is 3 × 10 ⁻³ emu / cc or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail.

(Embodiment 1) FIG. 1 is a plan view of a magnetic disk substrate according to the present invention. In the present invention, a 2.5 ″ type glass substrate having a diameter of 65 mmφ and a thickness of 0.635 mm was produced as the glass substrate 1 for a magnetic disk. In this substrate, a circular hole 2 having a diameter of 20 mmφ for an inner peripheral chuck was formed. A chamfer portion 3 is formed on the inner and outer peripheries of the chamfer.

The production of this glass substrate for magnetic disk is
The procedure was as follows. First, raw material powders in an amount determined so as to have a desired glass composition were weighed and mixed, put into a platinum crucible, and melted at 1600 ° C. in an electric furnace. After the raw materials were sufficiently dissolved, a stirring blade was inserted into the glass melt and stirred for about 4 hours. After that, take out the stirring blade,
After standing still for 30 minutes, the 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. Then, the glass block was reheated to near the glass transition point of this glass and gradually cooled to remove strain.

Next, the strain-relieved glass block was cut out using a core drill with the inner circumference and the outer circumference being concentric circles. Further, chamfering of the chamfer portion was performed on the inner and outer circumferences using a diamond grindstone. Then, both surfaces were roughly polished, then polished, and the substrate was washed with a cleaning agent and pure water to obtain a glass substrate for a magnetic disk. As described above, the glass substrate for a magnetic disk of the present invention is not subjected to any special strengthening treatment such as chemical strengthening treatment.

A magnetic film was formed on this substrate to prepare a magnetic disk. FIG. 2 shows a schematic view of a cross-sectional structure of the magnetic recording medium manufactured by the present invention. In FIG. 2, 1 is a glass substrate produced by the present invention, 4 is a grain size control layer for controlling the grain size of the magnetic film, 5 is an orientation control layer for controlling the orientation of the magnetic film, 6 is a magnetic film, Reference numeral 7 is a protective film, and 8 is a lubricating film. In the present invention, a NiAl alloy film is used as the grain size control layer of 2
A 0 nm film was formed. A CrMo-based alloy thin film having a thickness of 10 nm was used as the orientation control layer 5 and CoCr was used as a magnetic film 6.
A PrB-based magnetic film having a thickness of 20 nm was formed. In addition, the protective film is C
Was deposited to a thickness of 4 nm. All of these thin films were formed by using the sputtering method. Also, the lubricating film is
It was formed by a coating method.

The glass composition for a magnetic disk manufactured as described above and the magnetic disk having a magnetic film formed thereon were evaluated for characteristics and mass productivity, and the glass composition was examined.

First, focusing on the kind of rare earth element to be added, glasses having various compositions were produced. Table 1 shows the composition of the glass produced in the present invention and the characteristics of the glass substrate and the magnetic disk.

[0021]

[Table 1]

In Table 1, the mother glass composition other than the rare earth elements was aluminoborosilicate glass having the same composition.
The amount of rare earth oxide contained was constant at 2.8% by weight. As the characteristics of the glass substrate, the micro Vickers hardness, the visible light transmittance, the coloring property, and the yield of the glass substrate were evaluated. The micro Vickers hardness is 500 g and the load is applied for 15 seconds.
It was determined as an average value of 10 points. The transmittance of visible light was obtained as an integral value of the total transmittance of light in this wavelength range by measuring a transmittance spectrum from a spectral transmittance curve of wavelengths from 300 nm to 700 nm using a spectrophotometer. The colorability was evaluated by visually observing the degree of coloring, and the black ones were marked with X, and the colored ones were marked with ◯. The yield is evaluated by a device that inspects the number of foreign substances on the glass substrate by scattered light from laser light irradiation, and defects such as bubbles, polishing scratches, chips, and surface foreign substances are counted as 20 or more defects on each side of the disk. Then, the ratio of non-defective ones was evaluated.

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

The recording / reproducing characteristics of this magnetic disk were evaluated. FIG. 3 shows a magnetic disk drive manufactured by the present invention for evaluating recording / reproducing characteristics. In FIG. 3, 9 is a magnetic disk, 10 is a spindle, 11 is a magnetic head, 1
Reference numeral 2 is an arm of the magnetic head, 13 is a voice coil motor for driving the head, and 14 is a casing for supporting the whole. Although not shown in this figure, a spindle motor is installed below the magnetic disk 9 to rotate the entire disk. Each magnetic disk was mounted on the magnetic disk drive of FIG. 3, a magnetic signal corresponding to ²⁰ Gb / in ² was recorded, and the magnetic recording / reproducing characteristics were evaluated. This evaluation was performed on 150 disks, and the ratio of those having sufficient recording / reproducing characteristics was expressed as the magnetic disk yield.

Further, the total yield was evaluated from the yield of the glass substrate on the upper part and the yield of the magnetic disk. When the overall yield was less than 80%, it was evaluated as X, when 80% or more and less than 90% was evaluated as ◯, and when 90% or more was evaluated as ◎.

The micro-Vickers hardness of the substrate characteristics shown in Table 1 was 640 or more on any of the substrates, which proved to be good. In addition, the transmittance of visible light was 80% or more on any of the substrates. Of these, Nd and P
r, Sm, Eu, Ho and Er are f-of rare earths in the visible light region.
Sharp absorption due to the f transition was observed. Therefore, the transmittance is slightly lower than that of other elements.
% Or less. However, due to this sharp absorption, clear coloring was seen on the glass substrate. By visual observation under an incandescent lamp, Pr is yellow-green, Nd is purple, Sm, E
u was very light, but it was seen to be colored yellow and pink respectively. Further, Er and Ho were also colored pink.

Substrates containing other rare earth elements were colorless and had a transmittance of more than 85% and no coloring was observed.

When the yields of the glass substrates with respect to these substrates were evaluated, Pr, Nd and S showing clear coloring were observed.
With m, Eu, Ho, and Er, the number of defects due to processing, especially scratches, was smaller than that of the uncolored product, and the yield was 95.
It was over%. It is considered that this is because the substrate is visible in the substrate processing step and the cleaning step, and thus the handling is easy, and thus the yield is improved.

As a comparative example, nickel oxide (NiO)
A glass substrate having a high coloring property containing was evaluated.
Since this substrate has a low transmittance of 47%, it is difficult to find bubbles present in the glass or melting loss of the components that make up the crucible in the glass during melting, and these remain on the substrate surface. The yield was falling. Further, it was found that in the glass substrate in which the NiO content was slightly reduced and the transmittance was 50% or less, light was transmitted through the substrate and the inside of the substrate could be observed. Therefore, defects due to bubbles and the like are reduced, and the yield is improved.

From the above, a clear correlation was found between the transmittance and the yield of magnetic disks. When the transmittance of the glass substrate was 50% or more and 85% or less, the colorability was good, and a glass substrate with a good yield was obtained. When the transmittance was less than 50%, it was difficult to find bubbles remaining in the substrate and the mixture of furnace materials, which was a factor of lowering the yield. Also, when the transmittance of the substrate exceeds 85%, it becomes difficult to handle the substrate,
Since the number of processing defects such as scratches increased, it was not preferable.

In order to achieve the above optical characteristics,
The element to be added is Pr, Nd, Sm, Eu, Er or Ho.
Was found to be good. Of these, Pr, Nd,
Er or Ho was more preferable because the coloring was remarkable.

Next, the magnetic characteristics of the magnetic disk were evaluated. In the magnetic disk containing Sc, Y, La,
The magnitude of magnetization of the substrate was on the order of 10 ⁻⁴ emu / cc, and the amount of magnetization was extremely small. When Sm is used, the magnetization exhibits diamagnetic behavior, and is −4 × 10 ^−4.
It became emu / cc. For Pr, Nd and Eu, 1.0-
It was on the order of 3.0 × 10 ^-3 emu / cc, but G
5 × 10 for d, Tb, Dy, Ho, Er, Tm, Yb
^The magnetization value was as large as ^{−3 to} 2 × 10 ⁻² emu / cc.

When the standard deviation of the magnetization showing the individual difference in the magnetization was evaluated, it was found that the larger the magnitude of the magnetization was, the larger it was, and the larger the variation due to the substrate was. In particular, the magnitude of magnetization exceeds 3 × 10 ^-3 Gd, Tb, D
For y, Ho, Er, Tm, and Yb, the standard deviation of magnetization is 1
X10 ^-3 emu / cc or more, and the variation in magnetic characteristics depending on the substrate increased.

Looking at the magnetic disk yield due to the magnetic recording / reproducing characteristics, in the case where the magnetization is 3 × 10 ⁻³ emu / cc or less and the standard deviation of the magnetization is less than 1 × 10 ⁻³ emu / cc,
The magnetic disk with good magnetic characteristics was 90% or more, but the magnetization exceeded 3 × 10 ^-3 emu / cc,
Moreover, it was found that the yield of the sample having the standard deviation of magnetization of 1 × 10 ⁻³ emu / cc or more was drastically reduced to 80% or less. This is because the magnetic characteristics of the substrate change due to slight differences in the solids of the rare earth elements contained in the substrate, which increases the standard deviation, resulting in variations in recording when the magnetic field during recording is constant. it is conceivable that.

From the above, Sc, Y, La, Pr, Nd and S are used as rare earth elements which have a small influence on the magnetization of the substrate.
m and Eu were good. Also, the magnitude of magnetization is 3 × 1
When it was 0 ⁻³ emu / cc or less, a magnetic recording medium with small variations in magnetic recording and reproduction was obtained. The magnitude of magnetization is 3 × 1
When it exceeds 0 ⁻³ emu / cc, the magnetic recording / reproducing characteristics vary greatly from substrate to substrate, and therefore it is not preferable.

The overall yield was evaluated in consideration of the influence of the above optical characteristics on the yield of the glass substrate and the influence of the magnetic characteristics on the recording / reproducing characteristics. As a result, in the case of both glass substrates using good Pr, Nd, Sm, and Eu, the overall yield was 80% or more, which was good. On the other hand, when other rare earths are added, the total yield becomes 80% or less,
It wasn't good.

Further, particularly when Pr is used as the rare earth element, the total yield is 90%, and a further excellent result is obtained.

Next, the relationship between the kind of rare earth oxide and the amount added was examined in detail. Regarding the coloring, the transparent ones shown in Table 1 showed no change in transmittance even if the content was increased or decreased. Therefore, among the colored elements,
A glass substrate was prepared in which the contents of Pr, Er, and Sm were changed, and the same examination as in Table 1 was conducted. Table 2
The results of the examination are shown in.

[0039]

[Table 2]

When the Pr content was changed,
The glass substrate containing 0.7 wt% of Pr ₂ O ₃ of Sample No. 17 has a low micro-Vickers hardness, and the mechanical strength of the glass is low, resulting in a glass substrate yield of 8
It was as low as 2%. 1% of sample No. 16 and 1.5% ~
In Examples 18 to 21 with 7%, the micro Vickers hardness also showed a high value, and the coloring and magnetic properties were good. From this fact, the total yield exceeded 80%, which was a good result.

On the other hand, when the Pr ₂ O ₃ content exceeds 7% like sample No. 22, there was no problem in coloring, but the magnetization of the magnetic disk was 3 × 10 ^-3 emu / cc.
The value exceeded. For this reason, the variation in magnetization becomes large, and the magnetic disk yield falls below 80%, which is not a preferable result. Further, in the glass substrate of Example 23, the rare earth elements in the glass were not uniformly dissolved in the glass, the number of defective products was large, and the yield was low at 15%.
Therefore, it is not preferable as a glass substrate material.

Further, looking at the examples in which the rare earth element was changed to Er, sample No. 25 with an Er content of 0.5% was used.
However, the yield was poor because the content was low and the micro Vickers hardness was low. At this time, the magnetization value of the magnetic disk was as high as 3.1 × 10 ⁻³ emu / cc, and the yield of the magnetic disk was also low. Further, when the Er content is increased from 1%, the Micro Vickers hardness is also increased, the transmittance is decreased and the substrate yield is increased, but the magnetization is still 3 × 10 ^−3.
Since it exceeded emu / cc, the yield as a substrate was reduced. From the above, it has been found that when Er is used as the rare earth element, there is no composition range that simultaneously satisfies both the hardness, optical characteristics, and magnetic characteristics of the substrate.

Regarding Sm, regarding the optical characteristics, when the content was 2.5% by weight or more, the transmittance was 85% or less, which was in the proper range. Although the magnetic properties were proper even if contained in 10% by weight, if it exceeds 10% by weight, the residual raw material remains in the glass as in the case of Pr, which is not preferable.

Similarly, when Nd, Eu and Ho were examined, when Nd and Eu exceeded 8% by weight, the magnetic properties were not good, but the same results as Sm were obtained. As for Er, like Er, there was no composition range that simultaneously satisfied both optical characteristics and magnetic characteristics, so favorable results were not obtained.

From the above, as a rare earth element having a preferable composition range in both optical characteristics and magnetic characteristics, Pr, Nd,
It was judged that Sm and Eu were good. Among them, P
When r and Nd were used, a good composition range could be obtained in the composition range of 1% by weight to 7% by weight. Further, good characteristics could be obtained in the case of Sm of 2.5 to 9% by weight and in the case of Eu of 2.5 to 8% by weight. Further, when Pr was contained in an amount of 1.5% by weight to 5.2% by weight, the overall yield was 90% or more, and very good results were obtained.

When the content of these rare earths is small, the mechanical strength such as micro Vickers hardness is low, the transmittance is high, and the yield of the glass substrate is lowered, which is not preferable. Further, when the content of the rare earth element is large, the value of the magnetization of the substrate becomes large, so that the magnetic characteristics are not good. Further, addition of a larger amount is not preferable because the raw material remains in the glass.

Example 2 Next, a glass composition range suitable for a magnetic disk glass substrate was examined. Table 3 shows examples of the glass substrate manufactured according to the present invention. As the rare earth element to be added, Pr which gave good results in Example 1 was used. Among the glass compositions in the table, R ₂ O is Li ₂
The total content of alkali metal oxides of O, Na ₂ O and K ₂ O is shown.

[0048]

[Table 3]

For each sample, the thermal expansion coefficient of the glass substrate material for magnetic disk, the thermal shock test result measured by making the glass substrate for magnetic disk, the stability of the glass at the time of making this substrate, the annular strength, The Young's modulus, the high speed rotation test result and the surface roughness of the substrate are shown.

Here, the coefficient of thermal expansion was measured by making a block of each glass, cutting out a test piece for measuring thermal expansion of 15 mm × 4 mm × 4 mm, and using a thermal expansion measuring device. The measurement temperature range was 30 ° C to 100 ° C.

A magnetic disk was manufactured from the obtained substrate in the same manner as in Example 1, and this was mounted on the magnetic disk drive shown in FIG. 3 to carry out a thermal shock test of the drive.
When the thermal shock test did not cause problems such as cracks and breaks in the glass and reading errors due to track displacement, the mark was ◯, and when the problem occurred, the mark was x. Thermal shock test is -40 ℃
After heating at 80 ° C for 2 hours, heat rapidly to 80 ° C
After holding for a while, it is rapidly cooled to -40 ° C. This was repeated 5 times, and it was determined whether the above-mentioned problems would occur during that time.

Regarding the stability of the glass, those in which bubbles, striae, foreign matters, etc., which were found in the glass substrate after melting the glass, were marked were marked with x, and such a thing was not found, and clear glass was obtained. If it was given, it was marked as ○.

The annular strength was determined as follows. A ring with an outer diameter of 22 mmφ is placed on the upper part of the inner circumference of the 2.5 ″ substrate, and a ring with an inner diameter of 63 mmφ and an outer diameter of 65 mmφ is placed on the lower part of the substrate. Was measured.

The Young's modulus was measured using a Young's modulus measuring device by cutting out a block of each glass, cutting out a 10 mm × 2 mm × 55 mm Young's modulus measuring test piece. The measurement is
At room temperature.

Similarly, a magnetic disk was prepared and mounted on a magnetic disk drive to carry out a high speed rotation test of the drive. In the high-speed rotation test, when the rate of occurrence of problems such as reading errors due to track displacement caused by rotational strain or the like was 1% or less, ◯ was given, and when 1% or more, x was given. In the high speed rotation test, the rotation speed was maintained at 7,000 rpm for 5 hours, and it was determined whether an error occurred during that time. Also,
The surface roughness was evaluated using a surface roughness meter.

First, samples in which the total amount of alkali oxides of Li ₂ O, Na ₂ O and K ₂ O (R ₂ O in the table) were changed are shown in Nos. 42 to 49 of Table 3.

When glass having a low alkali metal oxide content of less than 10%, such as No. 44 and No. 45, was used, cracks occurred in the glass in the thermal shock test. Further, since the Young's modulus becomes too large, the surface roughness during substrate processing cannot be reduced, which is not preferable. On the contrary, when the content of alkali metal oxide exceeds 16% by weight like No. 48 and No. 49, an error due to track deviation occurs in the thermal shock test, and rotation occurs in the high speed rotation test. Since distortion is likely to occur, an error due to track deviation occurs, which is not preferable. N
When the total content of alkali metal oxides is 10% by weight or more and 16% by weight or less like glass of o.43,46,47, good results can be obtained in a thermal shock test or a high speed rotation test, and favorable results are obtained. Became.

Focusing on the thermal expansion coefficients of these glasses, Table 3 shows that the glass of No. 44 and No. 45 had a thermal expansion of 55 × 10 ⁻⁷ / ° C. and 59 × 10 ⁻⁷ / ° C., respectively, of the drive device members. 70 × 10 ⁻⁷ / ° C. to 80 × 10 ⁻⁷ which is a coefficient
It was much smaller than / ° C. Also, No. 4
No.8 and No.49 glass are 74 × 10 ^-7 / ° C,
The value was 78 × 10 ⁻⁷ / ° C., which was almost the same as that of the device member. These glasses were not preferable because cracks and track deviations occurred in the thermal shock test due to the difference in thermal expansion with other device members.

As shown in Nos. 43, 46 and 47 glass, the coefficient of thermal expansion is 61 × 10 ⁻⁷ / ° C. or higher, 72 × 10.
Good results were obtained at ^-7 / ° C or lower. From this, it was found that the thermal expansion coefficient of the glass substrate was set to be slightly smaller than the thermal expansion coefficient of the drive device member so that the glass substrate was matched with the thermal shock test and good results were obtained.

From the above, an appropriate coefficient of thermal expansion is 61 × 10.
^{It was -7} / ° C or higher and 72 × 10 ^-7 / ° C or lower. 61 x 1
If it is less than 0 ^-7 / ° C, the coefficient of thermal expansion cannot be matched with that of the material forming the other drive, and cracks are generated in the thermal shock test, which is not preferable. 72 × 10 ^-7
The temperature of / ° C is not preferable because a problem such as track deviation occurs.

Focusing on Young's modulus, No. 4
For No. 4 and No. 45 glass, 91 GPa and 95, respectively
It was GPa. These glasses were not preferable because the Young's modulus was too high, so that the polishing property at the time of processing the substrate was not good and the surface roughness became rough. The glass of Nos. 48 and 49 was as low as 79 GPa and 75 GPa, respectively.
For this reason, rotational strain was generated in the high-speed rotation test, which was not preferable. As shown in Nos. 43, 46, and 47 glass, it is preferable that the substrate has a surface roughness of 80 GPa or more and 90 GPa or less, and that rotational distortion does not occur even in a high-speed rotation test. It was

From the above, the Young's modulus is 80 GPa or more and 90.
It was preferable that it was not more than GPa. Young's modulus is 80
Below GPa, good results cannot be obtained in the high speed rotation test. If it exceeds 90 GPa, the surface roughness of the substrate becomes rough, which is not preferable.

Next, in Nos. 50 to 55, SiO ₂
I would like to examine the content. SiO ₂ content is 54.5
The weight% No. 52 glass was insufficient in Young's modulus and annular strength and was not suitable as a glass substrate for magnetic disks. However, as shown in No. 51, when the amount of SiO ₂ was 55% by weight, the Young's modulus was 80 GPa or more, and it was suitable as a substrate. Further, as in No. 55, when the amount of SiO ₂ exceeds 70% by weight, bubbles and the like are significantly generated when the glass is melted, which is not preferable. On the other hand, when the SiO ₂ content was 70 wt% as in No. 54, a glass substrate excellent in water resistance and mechanical strength was obtained without generation of bubbles and striae.

From the above, good results were obtained as a glass substrate for a magnetic disk when the SiO ₂ content was 55% by weight or more and 70% by weight or less.

Next, the Al ₂ O ₃ content was examined. N
The glass having an Al ₂ O ₃ content of o.57 of 18% by weight was not preferable because the melting temperature of the glass was too high and the raw material of the glass remained in the melting at 1600 ° C. However, the Al ₂ O ₃ content of No. 56 is 17% by weight.
With this glass, clear glass could be obtained. At this time, both Young's modulus and annular strength showed excellent values.

On the other hand, N with an Al ₂ O ₃ content of 10% by weight is used.
With the glass described in o.58, stable glass was obtained and good results were obtained as a glass substrate for magnetic disks, but with No. 59 glass having an Al ₂ O ₃ content of 9.5 wt%. , Nonuniformity such as striae occurred in the glass.

From the above, a good glass was obtained when the Al ₂ O ₃ content was 10% by weight or more and 17% by weight or less.

Further, the B ₂ O ₃ content was examined. N
As shown in o.60, the glass of 9% by weight could not sufficiently satisfy the ring strength and Young's modulus, and could not obtain sufficient characteristics in the high speed rotation test. However, No. 6
In the glass of 8% by weight shown in 1, the annular strength and Young's modulus were excellent, and the high-speed rotation test result was also good.

The No. 62 glass having a B ₂ O ₃ content of 2% by weight was able to stably produce the glass, and the Young's modulus and the mechanical strength also showed appropriate values. On the other hand, B ₂ shown in No. 63
A glass containing 1.5% by weight of O ₃ has a Young's modulus of 9
Since it exceeds 0 GPa, there is a problem in machinability and good surface roughness cannot be obtained.

From the above, the B ₂ O ₃ content is 2% by weight or more,
When the content is 8% by weight or less, good results were obtained in the annular strength and Young's modulus.

Further, as shown in Glass Nos. 63 to 72, when an alkaline earth metal such as MgO or CaO or ZnO is added to the glass composition described above,
All had the effect of increasing the Young's modulus, and were preferable. At the same time, it was possible to obtain a glass having excellent annular strength. However, if any of them is contained too much, various problems occur.

In the case of alkaline earth metal oxides such as MgO and CaO, as shown in No. 68, when the content exceeds 10% by weight, cracking becomes remarkable and the ring strength becomes small, and the mechanical strength is reduced. Was decreased, which was not preferable. When the content of the alkaline earth element was 10% by weight like No. 65 glass, both the annular strength and the Young's modulus were appropriate values. Therefore, the content of the alkaline earth metal oxide is preferably 10% by weight or less.

Regarding ZnO, as shown in No. 72, when the addition amount exceeds 10% by weight, precipitation of crystals becomes remarkable in the glass and it is difficult to obtain a stable glass. At 10% by weight, no such precipitation of crystals was observed. Therefore, the ZnO content was preferably 10% by weight or less.

[0074]

The glass substrate for a magnetic disk of the present invention comprises:
Since the substrate is colored and the magnetization when applying a magnetic field is small,
A glass substrate for a magnetic disk excellent in mass productivity and a magnetic disk using the glass substrate can be manufactured. Further, the glass substrate for a magnetic disk of the present invention has a thermal expansion coefficient of 61 to 72 × 10.
^Since it is ^-7 / ° C, it has good compatibility with the thermal expansion coefficient of the magnetic disk drive device members, so there are few problems such as glass cracking and track shift due to thermal shock tests.
Further, since the Young's modulus is 80 to 90 GPa, there is no problem such as track deviation due to high speed rotation of the disk. Therefore, it is optimal as a substrate material for magnetic disks that have high mechanical strength, high recording density, and high reliability.

[Brief description of drawings]

FIG. 1 is a plan view of a glass substrate for a magnetic disk according to the present invention.

FIG. 2 is a cross-sectional view of a magnetic disk using the glass substrate for a magnetic disk of the present invention.

FIG. 3 is a schematic view of a magnetic disk device manufactured according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate for magnetic disks, 2 ... Hole for inner circumference chucks, 3 ... Chamfer part, 4 ... Grain size control layer, 5 ... Orientation control layer, 6 ... Magnetic film, 7 ... Protective film, 8 ... Lubrication film, 9 ... Magnetic disk, 10 ... Spindle, 11 ... Magnetic head, 12
... arm of magnetic head, 13 ... voice coil motor,
14 ... Housing.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Naito             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Mitsutoshi Honda             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. F-term (reference) 4G062 AA01 BB01 DA06 DB04 DC03                       DD01 DE01 DE02 DE03 DF01                       EA01 EA02 EA03 EA04 EA10                       EB01 EB02 EB03 EB04 EC01                       EC02 EC03 EC04 ED01 ED02                       ED03 EE01 EE02 EE03 EF01                       EF02 EF03 EG01 EG02 EG03                       FA01 FA10 FB01 FC01 FD01                       FE01 FF01 FG01 FH01 FJ01                       FK01 FL01 GA01 GA10 GB01                       GC01 GD01 GE01 HH01 HH03                       HH05 HH07 HH09 HH11 HH13                       HH15 HH17 HH20 JJ01 JJ03                       JJ05 JJ07 JJ10 KK02 KK03                       KK04 KK05 KK07 MM27 NN29                       NN33                 5D006 CB04 CB06 CB07

Claims (4)

[Claims] 1. SiO _{2 by} weight percentage: 55% or more, 70
% Or less, Al ₂ O ₃ : 10 or more, 17% or less, B ₂ O ₃ : 2% or more, 8% or less, R ₂ O: 10% or more, 16% or less (R represents an alkali metal element), ZnO : 0% or more and 10% or less ReO: 0% or more and 10% or less (Re represents an alkaline earth metal element) containing an oxide represented by the oxide conversion, and further, the following oxide conversion weight percentages. in Pr ₂ O ₃ or Nd ₂ O ₃ more than 1%, 7% or less, or Sm ₂ O ₃ 2.5% or more, 9% or less, or Eu ₂ O ₃ 2.5% or more, 8% or less And has a thermal expansion coefficient of 61 in the temperature range of 30 ° C to 100 ° C.
A glass substrate for a magnetic disk, which has a temperature of ^{x10 -7} / ° C or higher and 72 x 10 ^-7 / ° C or lower. 2. A Young's modulus of 80 GPa or more and 90 GPa or less, a transmittance of visible light having a wavelength of 300 nm to 700 nm of 50% or more and 85% or less, and a magnetization of 3 × 10 ⁻³ when a magnetic field of 1 kOe is applied. A glass substrate for a magnetic disk, which has an emu / cc or less. 3. A magnetic disk having a glass substrate for a magnetic disk and a magnetic layer formed on the glass substrate directly or through another layer, wherein the glass substrate is S by weight percentage.
iO _2: 55% or more, 70% or less, Al ₂ O _3: 10% or more, 17% or less, B ₂ O _{3: 2%} or more, 8% or less, R ₂ O: 10% or more, 16% or less (R Represents an alkali metal element), ZnO: 0% or more, 10% or less ReO: 0% or more, 10% or less (Re represents an alkaline earth metal element), Further, Pr ₂ O ₃ or Nd ₂ O ₃ is 1% or more and 7% or less, or Sm ₂ O ₃ is 2.5% or more, 9% or less, or Eu ₂ O ₃ in the following oxide-based weight percentage. It contains 2.5% or more and 8% or less and has a thermal expansion coefficient of 61 in the temperature range of 30 ° C to 100 ° C.
A magnetic disk having a temperature of not less than × 10 ^-7 / ° C and not more than 72 × 10 ^-7 / ° C. 4. A magnetic disk having at least a glass substrate and a magnetic film formed on the surface of the glass substrate directly or via another layer, wherein the glass substrate has a surface roughness Young's modulus of 80 GPa or more and 90 GPa. The glass substrate has a transmittance of 50% to 85% in the visible light having a wavelength of 300 nm to 700 nm, and has a magnetization of 3 × 10 ⁻³ when a magnetic field of 1 kOe is applied to the glass substrate.
A magnetic disk characterized by being emu / cc or less.