Glass manufacturing – Processes – With chemically reactive treatment of glass preform
Reexamination Certificate
2000-10-02
2003-07-22
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes
With chemically reactive treatment of glass preform
C065S030100, C065S030130, C065S031000, C065S060400, C065S061000
Reexamination Certificate
active
06595028
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a chemical reinforced glass substrate and an information recording medium including the glass substrate and also to a method of manufacturing the chemical reinforced glass substrate and the information medium.
As one of information recording media, a magnetic disk mounted on a hard disk drive (HDD) is known in the art.
Recently, it is strongly required to increase storage capacity of the magnetic disk. As a result, an extension of a recording region on the magnetic disk and a high recording density of the recording become an emergency matter.
The hard disk drive includes a magnetic head that faces a recording surface of the magnetic disk and flies over the recording surface to write/read information to/from the magnetic disk. It is desirable that a flying height or an interval between the magnetic head and the recording surface is lower and lower because the recording density of the magnetic disk can be increased.
Two methods are known as a driving method for driving the hard disk drive. One is a CSS (Contact Start and Stop) method and the other is an LUL (Load/Unload) method. Because the LUL method permits a reduction of the interval between the magnetic head and the recording surface in comparison with the CSS method, the former enables an increase of the recording density in comparison with the CSS method.
On the other hand, the recording surface of the magnetic disk must be flat and smooth to stabilize a flight of the magnetic head. That is, the magnetic disk must have a substrate that has a flat and smooth surface. As the substrate, attention has been directed to a glass substrate for the magnetic disk because its main surface can be made very flat and very smooth.
The main surface of the glass substrate is polished by a soft polisher to even or smooth them. However, polishing by the use of the soft polisher causes a surface down or a surface rise to occur at an outer edge portion and/or an inner edge portion of the glass substrate. In the LUL method, the magnetic head stays at the outside in a radial direction of the magnetic disk when the magnetic disk is not driven. When the magnetic disk is driven, the magnetic head moves toward the center of the magnetic disk to write/read information to/from the magnetic disk and faces the recording surface of the magnetic disk. Accordingly, the surface down and/or the surface rise at the outer edge portion make the flight of the magnetic head unstable. In the worst case, the magnetic head clashes with the surface of the magnetic disk. In addition, the down and/or the rise limits the recording area of the magnetic disk. This is because an extent of the recording area depends on a flat area of the main surface of the glass substrate.
To solve the above-mentioned problems, several proposals have already been made. For example, a technique for reducing the surface down and the surface rise is disclosed in Japanese Unexamined Patent Publication (JP-A) No. H05-89459. The technique provides appropriate polishing conditions (i.e. polishing pressure and polishing time). Moreover, another technique for stabilizing the flight of the magnetic head is disclosed in Japanese Unexamined Patent Publication (JP-A) No. H05-290365. The technique provides an appropriate radius of curvature at the outer edge portion of the glass substrate.
By the way, the glass substrate is often subjected to chemical reinforcement or treatment used by chemical solution after the polishing process to improve mechanical strength and durability. Such a glass substrate will be called a chemical reinforced glass substrate hereinafter. The chemical reinforcement partially replaces specific ions included in the surface of the glass substrate with other ions larger than the specific ions in ionic radii.
According to the inventors' experimental studies, it has been found out that the chemical reinforced glass substrate can not accomplish a stable flight of a magnetic head due to head crashes and the like and therefore makes it impossible to widen a recording area of the magnetic recording medium manufactured from the chemical reinforced glass substrate.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a chemical reinforced glass substrate which is subjected to chemical reinforcement and which has desirable edge shapes or profiles at outer and inner edges.
It is another object of this invention to provide a chemical reinforced glass substrate of the type described having a high mechanical strength and a flat and smooth surface.
It is still another object of this invention to provide a chemical reinforced glass substrate which can widen a recording area formed on its main surface.
It is further still another object of this invention to provide a chemical reinforced glass substrate used for an information recording medium which can be properly clamped by a clamp for an information recording apparatus.
It is yet another object of this invention to provide a chemical reinforced glass substrate used for an information recording medium which enables a writing/reading head to fly stably over its recording surface.
The ski-jump portions at the outer edge portion of the glass substrate make the flight of the magnetic head unstable and limit the recording area. In addition, it is unavoidable to enlarge the interval between the magnetic head and the recording surface of the magnetic disk because the ski-jump portions at the outer edge portion might bring about the head clashes with the magnetic disk.
On the other hand, the ski-jump portions at the inner edge portion of the glass substrate inclines the magnetic disk against a clamp for clamping the magnetic disk. There is a case where the ski-jump portions at the inner edge portion distort or destroy the magnetic disk when it is clamped by the clamp.
Herein, description will be made about principles of this invention for a better understanding of this invention. Heretofore, a chemical reinforced glass substrate is rarely used for manufacturing a magnetic recording medium or has not been investigated about characteristics of the chemical reinforced glass substrate. According to the inventors' experimental studies, it has been found out that the magnetic recording medium which includes a chemical reinforced glass substrate can not accomplish a stable flight of a magnetic head and often causes head crashes to occur during read/write operation. As a result, it is difficult to accomplish a low flight operation of the magnetic head and to expand a recording area of the magnetic recording medium.
Further inventors' research has revealed that the glass substrate is undesirably deformed at inner and outer edge portions of a main surface when the glass substrate is subjected to chemical reinforcement. It has been also found out that deformed portions appear in the form of projections or recesses at the inner and the outer edge portions. In any event, such projections and recesses provide inner and/or outer edge profiles and will be referred to as ski-jump portions and roll-off portions, respectively. The ski-jump portions at the outer edge portion of the glass substrate make the flight of the magnetic head unstable and limit the recording area. In addition, it is unavoidable to enlarge the interval between the magnetic head and the recording surface of the magnetic disk because the ski-jump portions at the outer edge portion might bring about the head clashes with the magnetic disk.
On the other hand, the ski-jump portions at the inner edge portion of the glass substrate inclines the magnetic disk against a clamp for clamping the magnetic disk. This means that the ski-jump portions at the inner edge portion distort or destroy the magnetic disk when it is clamped by a clamp.
The ski-jump portions at the outer edge portion of the glass substrate make the flight of the magnetic head unstable and limit the recording area. In addition, it is unavoidable to enlarge the interval between the magnetic head and the recording surface of the magnetic disk because
Isono Hideki
Miyamoto Takemi
Colaianni Michael
Hoya Corporation
Sughrue & Mion, PLLC
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