Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-06-28
2001-11-06
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S900000, C427S128000, C427S129000, C427S130000
Reexamination Certificate
active
06312841
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate for an information recording medium, to a method of producing the substrate, and to an information recording medium comprising the substrate.
2. Description of the Related Art
As a substrate for an information recording medium, attention is recently directed to a glass substrate and a ceramic substrate which are excellent in various properties as compared with other substrates. For example, an aluminum substrate has been widely used as a substrate for a magnetic disk. With a demand for reduction in size and thickness of the magnetic disk and for a low flying height of a magnetic head, the glass substrate and the ceramic substrate become more and more widely used. This is because the glass substrate and the ceramic substrate can be readily reduced in size and thickness and has an excellent flatness so that the flying height of the magnetic head can easily be lowered as compared with the aluminum substrate.
In the case of using the glass substrates for information recording media, their surface is often subjected to chemical strengthening treatment to increase their strength in order to improve their impact resistance and vibration resistance to thereby prevent them from being broken by shock or vibration.
For the chemical strengthening treatment, for example, an ion-exchanging method is much employed in which the alkali ions in glass are substituted with other alkali ions having a larger ionic radius to thereby increase the volume of the ion-exchanged site in the glass processed. In that method, the increase in the volume of the ion-exchanged site gives strong compression stress to the surface layer of the glass processed whereby the glass surface is strengthened. In the ion-exchanging method for chemical strengthening, the glass substrates to be processed must contain alkali ions because of the principle of the method itself. In some types of glass for substrates for information recording media, containing alkali ions are known which have a predetermined strength even without being subjected to chemical strengthening treatment, for example, high-valence glass.
On the other hand, for ceramic substrates for information recording media, such as crystal glass substrates, in general, they do not require chemical strengthening treatment as their impact resistance and vibration resistance are generally increased through crystallization.
Using glass or ceramic substrates in information recording media is often problematic in that the alkalis existing in the glass or ceramic substrates are extracted out, and it is desirable to minimize the alkali extract from those substrates. Even the ion-exchanged glass substrates give the trouble of alkali extract from them.
As mentioned above, the problem with glass or ceramic substrates for information recording media is the alkali extract from them, but, at present, no high-level technique of preventing the alkali extract is known.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a glass substrate, from which extract alkali and other components is prevented at a high level, and to provide a method for producing it.
It is another object of the present invention to provide a substrate for information recording media and a method for producing it, in which treatment of a substrate for alkali extract retardation is effected continuously and uniformly for a long period of time and the effect of the treatment lasts long.
It is still another object of the present invention to provide an information recording medium comprising the substrate.
According to one aspect of the present invention, there is provided an information recording medium which comprises a substrate containing a glass as a main component, an underlying layer formed on the substrate, a magnetic layer formed on the underlying layer, a protective layer formed on the magnetic layer outside the direction in which the layers are laminated, and a lubricative layer formed on the protective layer. In the information recording medium, the substrate is subjected to treatment for retarding the extract of alkali ions of the glass component from the substrate by contacting it with a molten salt that contains at least one of hydrogensulfates and pyrosulfates and to treatment for retarding the crystallization of the molten salt.
According to another aspect of the present invention, there is provided a substrate for information recording media, which containing a glass as a main element. The substrate is subjected to treatment for retarding the extract of alkali ions of the glass component from the substrate by contacting it with a molten salt that contains at least one of hydrogensulfates and pyrosulfates and to treatment for retarding the crystallization of the molten salt.
According to still another aspect of the present invention, there is provided a method of producing a substrate for information recording media, in which a substrate for information recording media that contains a glass as a main component is subjected to treatment for retarding the extract of the glass component from the substrate by contacting it with a molten salt that contains at least one of hydrogensulfates and pyrosulfates, before, during, or after being subjected to additional treatment for retarding the crystallization of the molten salt.
In the last aspect, preferably, the glass component of which the extract from the substrate is retarded is a group of alkali ions. Also preferably, the treatment for retarding the crystallization of the molten salt is water addition treatment of any one of treatment of supplying water to the molten salt or treatment of compensating for water being away from the molten salt.
Still preferably, the water addition treatment in the last aspect of the invention is effected by any one of a method of introducing steam into the molten salt, a method of putting the molten salt in a-steam atmosphere, or a method of adding a hydrogensulfate to the molten salt.
REFERENCES:
patent: 3583850 (1971-06-01), Bortholou et al.
patent: 3583858 (1971-06-01), Bartholomew
patent: 5874376 (1999-02-01), Taguchi
patent: 6174824 (2001-01-01), Goto
patent: 6187441 (2001-02-01), Takeuchi
patent: 6191058 (2001-02-01), Yamaguchi
patent: 57 129840 (1982-08-01), None
patent: 58 049636 (1983-03-01), None
patent: 11-503403 (1999-03-01), None
Hashimoto Kazuaki
Watanabe Takashi
Hoya Corporation
Kiliman Leszek
Sughrue Mion Zinn Macpeak & Seas, PLLC
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