JP3403957B2 - Glass for information recording medium substrate and glass substrate for information recording medium using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a glass used as a substrate for an information recording medium such as a hard disk, and a glass substrate for an information recording medium using this glass.

[0002]

2. Description of the Related Art In recent years, glass substrates have been used for information recording media such as hard disks.
It is preferable that such a glass substrate for an information recording medium has a smoother surface and a larger Young's modulus. In addition, the alkali metal such as sodium added to increase the melting property of glass adversely affects the magnetic film formed on the substrate surface. For this reason, this type of glass substrate has conventionally been replaced by an alkaline metal having a small atomic radius by an alkaline earth metal (eg, calcium ) having a large atomic radius by ion exchange to remove adverse effects on the magnetic film and chemically strengthen it. ing. For example, as disclosed in Japanese Patent Application Laid-Open No. 8-335315, it is known that glass contains ZrO2 to improve hardness and improve ion exchange performance.

Further, the Young's modulus of a glass substrate generally used at present is about 83 [GPa].

[0004]

[Problems to be Solved by the Invention] The above-mentioned conventional ZrO2
Although the glass containing cerium does improve the ion exchange performance, it has a poor melting property and a high temperature (about 1500 to 1550 ° C) is required to obtain a high-quality glass substrate without bubbles or striae.
In this case, heating and melting must be performed for a long time, which not only requires a large amount of energy but also the production efficiency is poor. Further, since it contains an alkali metal in order to improve the meltability of the glass, an ion exchange treatment was indispensable. Further, in order to make the glass substrate thinner and less likely to be deformed, it is required to further increase the Young's modulus of the glass.

According to the present invention, firstly, the glass does not contain alkali metals such as sodium at all, and therefore does not require an ion exchange step, and secondly, it has excellent meltability even though it does not contain alkali metals at all. Third, it was made to provide high-quality glass and glass substrates having a Young's modulus larger than that of the conventional one.

[0006]

SUMMARY OF THE INVENTION The present invention is based on S, in mol%.
The iO ₂ below 45% exceeds 25%, the a TiO ₂ 25% Yue
For example 45% or less, 35% less than the RO 20% or more (However,
R is an alkaline earth metal), Al ₂ O ₃ is 0% or more 1
0% or less , ZrO ₂ content of 0% or more and 8% or less , and Al
_A glass for an information recording medium substrate, which is an oxide glass in which the total of ₂ O ₃ and ZrO ₂ is 15% or less , and an information recording medium glass substrate made of this glass. Here, R is an alkaline earth metal such as Mg, Ca, Sr, or Ba, and all% are mol%.

SiO ₂ is the main component of glass and is 25
If it is less than 45%, it does not practically become glass, and if it exceeds 45%, the meltability deteriorates. Therefore, the range of more than 25% and less than 45% is suitable.

TiO ₂ has a great effect of increasing Young's modulus. If it is 25% or less, the effect of increasing the Young's modulus is not sufficient, and devitrification (it is likely to be crystallized instead of being in a glass state after once melted). If it exceeds 45%, devitrification tends to occur. A range of more than 25% and 45% or less is a range in which devitrification hardly occurs and Young's modulus is also excellent. Conventional TiO ₂ -containing glass has a TiO ₂ content of 1
It was 0% or less. It has been said that when the content of TiO ₂ exceeds 10, devitrification is likely to occur.
It was confirmed that devitrification is unlikely to occur even in the range of more than 5% and 45% or less .

Al2O3 has the effect of suppressing devitrification and the effect of increasing viscosity to improve moldability, but if it exceeds 10%, the meltability deteriorates. ZrO2 also has an effect of suppressing devitrification and an effect of improving moldability, but if it exceeds 8%, the meltability becomes extremely poor. When both Al2O3 and ZrO2 are used, if the total amount exceeds 15%, the meltability deteriorates, which is not suitable.

By making the composition as described above, it is possible to obtain a glass which does not contain an alkali metal at all, has a Young's modulus of more than 100 [GPa], and is sufficiently meltable at 1450 ° C. and has excellent meltability. . Generally, alkali-free glass having a high Young's modulus has a high melting temperature, and defects such as bubbles and stones (unmelted foreign matters) due to poor melting are likely to occur. In the glass having good meltability, bubbles generated during melting disappear in a short time, so that the glass melting time can be shortened, and energy saving and manufacturing time reduction can be realized. Further, striae and the generation of undissolved foreign matter hardly occur, so that a high quality glass substrate can be obtained. Further, with the above composition, it is possible to obtain a glass substrate having a larger Young's modulus than the conventional one.
As the Young's modulus increases, the amount of deformation decreases even when the substrate rotates at high speed, and information can be recorded and read accurately. Further, the glass substrate can be formed thin. Further, since the glass of the present invention does not contain an alkali metal, ion exchange treatment is unnecessary.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in comparison with comparative examples of glass for substrates which are generally used at present. The examples and comparative examples were manufactured and evaluated as follows. High purity silica sand and reagents are blended to make a batch equivalent to 100 g of glass. Put the batch in a crucible of 95% platinum + 5% gold and melt in an electric furnace at 1450 ° C for 2 hours. After completion of melting, take out from the furnace and cool slowly. Count the number of bubbles remaining in the glass. The above glass is roughly crushed, put in a crucible of 95% platinum + 5% gold, and remelted at 1450 ° C. for 1 hour. The molten glass is poured from the crucible into a casting mold and slowly cooled. The Young's modulus is measured by polishing the glass into a 6 cm × 2 cm × 2 mm sample. The number of bubbles was measured by visually counting the number of bubbles remaining in a given volume under a microscope with a magnification of 40 and converted into the number per cubic cm. The Young's modulus was measured with a high temperature dynamic elastic modulus measuring device YK-1300 manufactured by Nissan Arc.

[0012]

[Examples] Table 1 lists Examples 1 to 6 and Table 2 lists the compositions and measurement results of the glasses of Comparative Examples. The comparative example is a glass for substrates which is generally used at present. When these examples and comparative examples are compared, it is recognized that the examples have almost no residual bubbles and are extremely excellent in meltability. Further, when the Young's modulus is compared, the comparative example has a value of 81.7 [GPa], but all the examples have large values exceeding 100 [GPa]. In addition, since the comparative example contains alkali metals such as lithium and sodium, it is necessary to perform the ion exchange treatment, but the examples do not include the alkali metal at all, and therefore, it is not necessary to perform the ion exchange treatment. In Table 1, the amount of each substance is [mol%], the number of bubbles is [cells / cubic cm], and the Young's modulus is [GPa].

[Table 1]

[Table 2]

The glass substrate of the present invention usually has a disk shape or a donut disk shape, and is manufactured from glass raw materials through various steps such as melting, molding, polishing, cleaning, and forming a magnetic film for recording. Each of these steps is well known.

[0014]

Since the glass for substrates of the present invention does not contain an alkali metal, ion exchange treatment is unnecessary, and the number of steps can be reduced to realize cost reduction. Further, since it has excellent meltability, defects such as bubbles and striae are unlikely to occur, and it can be efficiently produced with a small amount of energy. Furthermore, this glass is
Since the Young's modulus is large, the glass substrate has a small amount of deformation, can be made thinner than the conventional one, and can be expected to have stable operation, and is a high-quality glass substrate for an information recording medium. .

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI G11B 11/10 500 G11B 11/10 500

Claims (2)

(57) [Claims] 1. A mole percentage of SiO ₂ exceeds 25% and 45
%, TiO ₂ more than 25% and 45% or less , RO 2
0% or more and 35% or less (where R is an alkaline earth metal), Al ₂ O ₃ is 0% or more and 10% or less , and ZrO ₂ is 0%
% Or more and 8% or less , and a glass for a substrate of an information recording medium, which is an oxide glass in which the total of Al ₂ O ₃ and ZrO ₂ is 15% or less. 2. A glass substrate for information recording medium, comprising the glass according to claim 1.