Compositions: ceramic – Ceramic compositions – Devitrified glass-ceramics
Reexamination Certificate
2001-04-02
2003-11-04
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Devitrified glass-ceramics
C501S009000, C501S010000, C428S690000, C065S033100
Reexamination Certificate
active
06642162
ABSTRACT:
RELATED APPLICATION
This application claims priority to Japanese Patent Application No. 2000-100817 filed in Japan on Apr. 3, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a glass composition, and specifically relates to a glass composition suited for crystallized glass. More specifically, the present invention relates to a composition for crystallized glass disk medium. Such disk medium include hard disks, magnetic disks, optical disks and magnetic-optical disks
2. Description of the Prior Art
Aluminum and glass are known materials suitable for use as magnetic disk substrates. Among these substrates, glass substrates have been the focus of most attention due to their superior surface smoothness and mechanical strength. Such glass substrates include chemically reinforced glass substrates strengthened by ion exchange on the surface, and crystallized glass substrates having strengthened bonds by depositing a crystal component on the substrate.
The performance demands of recent substrates have become more severe day by day, and improved performance is particularly sought regarding strength, flex and warp during high-speed rotation. This type of performance can be expressed by the Young's modulus of the substrate material, in which a higher numerical value is desirable.
For example, the composition disclosed in Japanese Laid-Open Patent Application No. 11-322362 attains a Young's modulus value of 130 or greater. However, this prior art requires extremely high thermal processing temperatures which complicate the manufacturing process, that is, this art requires a primary processing temperature of 800° C., and a secondary processing temperature of 1,000° C.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved glass composition.
Another object of the present invention is to provide a glass composition having a high Young's modulus and which is highly suited for mass production.
These objects are attained with a glass composition of the present invention desirably having the main components within the ranges described below:
about 45 wt % or more, but less than about 60 wt % SiO
2
;
about 5 wt % or more, but less than about 20 wt % Al
2
O
3
;
about 9 wt % or more, but less than about 25 wt % MgO;
about 0.1 wt % or more, but less than about 12 wt % TiO
2
;
about 0.1 wt % or more, but less than about 12 wt % Li
2
O; and
about 5 wt % or more, but less than about 22 wt % ZnO.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiments of the present invention are described hereinafter.
These objects are attained with a glass composition of the present invention desirably having the main components within the ranges described below:
about 45 wt % or more, but less than about 60 wt % SiO
2
;
about 5 wt % or more, but less than about 20 wt % Al
2
O
3
;
about 9 wt % or more, but less than about 25 wt % MgO;
about 0.1 wt % or more, but less than about 12 wt % TiO
2
;
about 0.1 wt % or more, but less than about 12 wt % Li
2
O; and
about 5 wt % or more, but less than about 22 wt % ZnO.
When the composition content of SiO
2
used as a glass forming oxide is less than about 45 wt %, melting characteristics are typically adversely affected, and when the percentage exceeds about 60 wt %, a stabilized state of glass is achieved and crystal deposition typically becomes difficult.
Aluminum oxide (Al
2
O
3
) is an intermediate oxide of glass, and is a structural component of the crystal-phase magnesium-aluminum crystals formed during heating. When the composition content is less than about 5 wt %, there are typically few crystals formed, and the desired strength is not obtained, whereas when the percentage exceeds about 20 wt %, the melting temperature is typically raised and devitrification readily occurs.
Magnesium oxide (MgO) is a fluxing agent, which is added to induce the crystal particles to nucleate and form crystal particle clusters. When the composition content is less than about 9 wt %, the working temperature range is typically narrowed, and the chemical durability of the glass matrix phase is not typically improved. When the composition content exceeds about 25 wt %, other crystal phase matter is often deposited and the desired strength is typically difficult to obtain.
Titanium oxide (TiO
2
) is a crystal nucleating agent, which is often an essential component for magnesium silicate crystal deposition. Furthermore, TiO
2
functions as a fluxing agent to improve stability during production. When the composition content is less than about 0.1 wt %, melting characteristics are typically adversely affected, and crystal growth is often difficult. When the content exceeds about 12 wt %, crystallization typically progresses rapidly, the crystallization state often becomes difficult to control, the deposited crystals are typically coarse with heterogeneity of the crystal phase, and a fine homogeneous crystal structure often cannot be obtained, such that the required surface smoothness for use as a disk substrate is difficult to obtain by a polishing process. Furthermore, devitrification readily occurs during fusion molding, and mass production characteristics are reduced.
Stability during manufacture is improved by the addition of Li
2
O, which functions as a fluxing agent. When the composition content is less than about 0.1 wt %, there is inadequate improvement in melting characteristics. When the composition content exceeds about 12 wt %, stability often decreases during the polishing and washing processes.
Zinc oxide (ZnO) functions as a fluxing agent which augments uniform crystal deposition. When the composition content is less than about 5 wt %, there is typically insufficient improvement in crystal homogeneity. When the composition content exceeds about 22 wt %, the glass becomes stable, and crystallization is suppressed, such that the desired strength is often difficult to obtain.
The manufacturing method is described below. The raw materials of the ultimately produced glass substrate are thoroughly mixed in specific proportions, then introduced to a platinum crucible and melted. After melting, the melted material is poured into a mold to form an approximate shape. Then the material is annealed to room temperature. Next, the material is maintained at a primary heating process temperature of about 500 to about 680° C. during a primary process (heating process) to generate crystal nuclei. Then, the material is maintained at a secondary heating process temperature of about 680 to about 800° C. during a secondary process to grow crystal nuclei. Then the material is cooled to obtain the crystallized glass.
This material may be used as a disk substrate by processing such as polishing to attain a desired shape and thickness.
By using the above raw materials and the process described herein, an extremely high Young's modulus and high mass production characteristics are obtainable. Even higher performance is obtained by adding the components described below in a suitable range.
Phosphoric anhydride (P
2
O
5
), which functions as a fluxing agent, is a nucleating agent for depositing silicate crystals, and is an important component for uniform deposition of crystals on the entirety of the glass. When the composition content is less than about 0.1 wt %, sufficient formation of crystal nuclei typically becomes difficult, crystal particles are often coarse, heterogeneous crystal deposition often occurs, the desired fine homogeneous crystal structure may be difficult to obtain, such that the required surface smoothness for use as a disk substrate may be difficult to obtain by a polishing process. When the content exceeds about 5.0 wt %, reactivity to the filter medium increases during melting, and devitrification increases so as to reduce mass production characteristics during fusion molding. Chemical durability typically decreases, there is concern that the magnetic layer may be affected, and stability is often reduced during the polishing and washing processes.
Addin
Ishimaru Kazuhiko
Kawai Hideki
Mori Toshiharu
Nagata Hideki
Yuki Hiroshi
Group Karl
Minolta Co. , Ltd.
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