Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-06-11
2003-03-11
Nguyen, George (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S057000
Reexamination Certificate
active
06530825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for the production of a glass substrate for magnetic recording mediums and more particularly to a production method capable of producing a glass substrate for magnetic recording mediums, which does not cause edge-sagging, to a substantial extent, at the periphery of the surface of the glass substrate on the side of the magnetic recording layer, which is smooth and uniform even to the outermost peripheral region on the surface of the glass substrate on the side of the magnetic recording layer and which has a substantially small quantity of surface defects.
2. Description of the Prior Art
As the conventional substrates for magnetic recording mediums, there have mainly been used those each prepared by plating an aluminum alloy plate with Ni—P and then polishing the plated main surface of the plate in a multiple step process.
However, the magnetic disk-recording device has recently been adopted even in the portable personal computer such as notebook-sized personal computers and the magnetic recording medium should be rotated at a high speed on the order of not less than 10,000 rpm in order to improve the response speed of the magnetic disk-recording device. For this reason, there has been desired for the development of a substrate for magnetic disk-recording mediums having high strength capable of withstanding such severe conditions. As such a substrate, which can satisfy the foregoing requirements, there has been adopted a glass substrate.
Such a mainly adopted glass substrate for magnetic recording mediums includes, for instance, a chemically strengthened glass substrate whose strength is improved by a chemical strengthening treatment or a crystallized glass substrate prepared by melting and a molding glass material to give a glass substrate, maintaining the glass substrate at a high temperature ranging from 600 to 800° C. over a long period of time to thus partially separate out crystalline phases in the substrate or a vitreous matrix.
The chemically strengthened glass substrate is, for instance, one obtained by melting a glass material and forming the melt into a glass substrate for chemically strengthened glass substrates, then subjecting the glass substrate to grinding and polishing treatments, and immersing it into a molten salt of, for instance, sodium nitrate or potassium nitrate to form a compression stressed layer in the surface layer thereof. The crystallized glass is one, which comprises 40 to 80% of crystalline phases and 20 to 60% of an amorphous glass phase and whose strength is improved by the action of the crystalline phase.
As the storage capacity of the magnetic disk-recording device has increasingly been high, there has been observed such a tendency that a magnetic recording layer is formed on the surface of a glass substrate for magnetic recording mediums even in the region in the proximity of the peripheral edge of the substrate on the side of the magnetic recording layer and the peripheral edge region thus formed is used as the magnetic recording layer, in order to improve the recording capacity per magnetic recording medium. For this reason, there has been desired for the establishment of high smoothness of the magnetic recording medium even in the region in the proximity of the peripheral edge thereof. Moreover, elements for magnetic recording mediums are significantly miniaturized to increase the recording density and therefore, it has likewise been required that defects on the glass substrate for magnetic recording mediums should be smaller and the number thereof should substantially be reduced.
In the polishing step when a glass substrate for magnetic recording mediums is produced by grinding and polishing such a glass material according to a well-known method, however, it is quite difficult to stably produce a glass substrate whose degree of the edge-sagging falls within the required range, by the use of a hard abrasion cloth such as a foamed polyurethane type one or a soft abrasion cloth such as a suede type one and an abrasion liquid containing about several percents of cerium-containing abrasive having an average particle size ranging from about 0.5 to 2 &mgr;m.
When a maker of polishing machines manufactures a both side-polishing device for polishing glass substrates for magnetic recording mediums, the maker in general adjusts the flatness of the surface of the surface table of the device to a level of not more than 50 &mgr;m by finishing through polishing. However, it is impossible to correct the flatness of the surface of the surface table, while fitting the upper and lower surface tables to the both side-polishing device practically used. For this reason, the surface tables whose flatness has been adjusted by the maker of polishing machines are used without any modification or adjustment. In general, the abrasion cloth used in such a both side-polishing device is an elastic material and therefore, the deformation, to some extent, of the surface of the table may be relieved due to the elasticity of the abrasion cloth. If the polishing step is continued while adhering an abrasion cloth to the surface of the surface table, however, the surface of the table undergoes deformation due to the pressure applied thereto during usage thereof and the heat generated by the polishing operations and the deformation reaches a level of not less than 100 &mgr;m in its early stages. In such a condition, the quantity of deformation of the table surface is greater than the quantity of the elasticity of the abrasion cloth and accordingly, the deformation of the table surface cannot be relieved by the elasticity of the abrasion cloth. As a result, the surface condition of the abrasion cloth is greatly influenced by the change or deformation of the surface condition (flatness) of the surface table and the polishing operations are continued while the parallel relation between the surface of the abrasion cloth fitted to the upper table and the surface of that fitted to the lower table falls into disorder. This leads to the extension of the time required for the completion of the polishing to a desired extent (this in turn results in the reduction of the number of glass substrates, which can be polished by an abrasion cloth). This also leads to the generation of surface defects on the glass substrate and becomes a principal cause of the edge-sagging.
SUMMARY OF THE INVENTION
The foregoing problems would easily be able to be solved if the surface of surface tables can be polished to thus improve the flatness of the surface, while the upper and lower surface tables are fitted to a both side-polishing device for polishing a glass substrate for magnetic recording mediums.
Accordingly, it is an object of the present invention to provide a method for the efficient production of a glass substrate for magnetic recording mediums, which does not cause any considerable degree of edge-sagging at the periphery of the surface thereof on the side of the magnetic recording layer, which is smooth even in the surface region near the outermost periphery of the surface on the side of the magnetic recording layer and which does not have surface defects to a substantial degree.
The inventors of this invention have conducted various studies to achieve the foregoing object, have found that the foregoing object of the invention can be accomplished by improving the conventionally well-known method, which comprises the steps of lapping a glass substrate for magnetic recording mediums to a desired thickness and then polishing the glass substrate, such that the surface of the upper and lower surface tables can easily be polished while fitting these surface tables to a both side-polishing device for polishing such a glass substrate, that the flatness precision of the outer surfaces of abrasion cloths can be improved by adhering these abrasion cloths to the surface of the corresponding upper and lower surface tables respectively and that the surface precision of the outer surfaces of abrasion cloths can fu
Fujimura Akio
Hosaka Toshio
Masunaga Junji
Mitsui Mining And Smelting Co., Ltd.
Nguyen Dung Van
Nguyen George
Young & Thompson
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