Glass manufacturing – Processes – With chemically reactive treatment of glass preform
Reexamination Certificate
2000-05-15
2002-08-06
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
With chemically reactive treatment of glass preform
C065S060530, C065S061000, C065S374120
Reexamination Certificate
active
06427489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing an information recording medium used as a recording medium of an information processing apparatus and also a process for producing a substrate employed for the medium.
2. Description of the Related Art
One of such information recording mediums is a magnetic disk. The magnetic disk is produced by forming a thin film such as a magnetic layer on a substrate and as the substrate for it, an aluminum or glass substrate has been employed. Reflecting the recent pursuit of high recording densification, a glass substrate which makes it possible to decrease a distance between a magnetic head and a magnetic. recording medium has come to be more prevalent compared with an aluminum substrate.
The glass substrate showing such an increasing tendency is, in general, subjected to chemical reinforcement for heightening its strength so that it can endure the impact upon mounting on a magnetic disk driver. The surface of the glass substrate is polished with high accuracy so that the flying height of the magnetic head can be lowered to the utmost, whereby the high recording densification is actualized.
As well as the improvement in the glass substrate, a magnetic head has been changed from a thin-film head to a magnetoresistive type head (MR head) to meet the tendency to high recording densification.
As described above, high evenness on the surface of a magnetic disk is indispensable for the flying height reduction to heighten the recording density. In addition, when an MR head is employed, high flatness on the surface of a magnetic recording medium is also required in order to prevent the generation of TA (thermal asperity). The term “thermal asperity” as used herein means a phenomenon that a projection existing on the surface of a magnetic disk affects an MR head to generate heat, thereby causing fluctuations in the resistance of the head and causing a malfunction in the electromagnetic conversion.
There is an increasing demand for a magnetic disk having high evenness for both the lowering of flying height and prevention of occurrence of thermal asperity. A substrate having a highly even surface is eventually required for a magnetic disk having a surface of high evenness, but the requirement for heightening of the recording density exceeds the level which can be materialized by only polishing the surface of the substrate with high accuracy. In other words, it is impossible to attain high evenness even by polishing with high accuracy if foreign matters adhere onto the substrate. The removal of foreign matters has been carried out conventionally but the conventional tolerance of foreign matters on the substrate is now regarded as inadequate for the recent tendency to heighten the recent densification level.
Examples of such foreign matters include considerably fine iron powders, stainless pieces, glass chips and organic substance which cannot be removed by ordinary washing. When a thin film such as magnetic film is stacked on a glass substrate without removing the particles such as iron powders from the glass substrate, a protrusion is formed on the surface of a magnetic disk, which becomes a cause for disturbing the lowering in the flying height or prevention of thermal asperity.
SUMMARY OF THE INVENTION
An object of the present invention is to prevent the adhesion of particles such as fine iron powders to a glass substrate. Another object of the present invention is to produce an information recording medium in a high yield by using a glass substrate from which foreign matters to be a cause for under-layer defects have been removed.
The present inventors have conducted an extensive investigation on the cause of the adhesion of the particles such as fine iron powders to a glass substrate. As a result, it has been found that a metal such as iron powders or metal oxide generated from manufacturing facilities or buildings is floating in an atmosphere surrounding a chemical reinforcement apparatus and such a floating substance is mixed in a chemical reinforcement solution and adheres to the glass substrate.
In one aspect of the present invention, there is thus provided a process for producing a glass substrate for an information recording medium, which comprises a step of polishing a principal surface of a glass substrate and a step of chemically reinforcing said glass substrate (said step may hereinafter be called “chemical reinforcement step”) by bringing it into contact with a chemical reinforcement liquid to substitute a portion of ions contained in said glass substrate by ions having a diameter larger than the former ions in said chemical reinforcement liquid, wherein at least one of the steps subsequent to a final polishing step, that is, washing step, said chemical reinforcement step, step of washing off said chemical reinforcement liquid, drying step, inspection step, and a step of packing said glass substrate or filling the same in a container is effected in an atmosphere where clean filtered air is circulated so as to prevent the adhesion of particles to said glass substrate.
In a second aspect of the present invention, there is also provided a process for producing a glass substrate for an information recording medium, which comprises a step of polishing a principal surface of a glass substrate; and a step of chemically reinforcing said glass substrate by bringing it into contact with a chemical reinforcement liquid to substitute a portion of ions contained in said glass substrate by ions having a diameter larger than the former ions in said chemical reinforcement liquid, thereby reinforcing said glass substrate, wherein at least one of the steps subsequent to a final polishing step, that is, a washing step, said chemical reinforcement step, a step of washing off said chemical reinforcement liquid, a drying step, an inspection step, and a step of packing said glass substrate or filling the same in a container is effected under an environment whose air cleanliness permits the existence of particles having a size of 0.3 to 100 &mgr;m in an amount not more than 1000 particles per cubic feet-meter of the air.
In a third aspect of the present invention, there is also provided a process for producing a glass substrate for an information recording medium as described in the first aspect, wherein the clean filtered air has cleanliness permitting the existence of particles having a size of 0.3 to 100 &mgr;m in an amount not more than 1000 particles per cubic feet-meter of the air.
In a fourth aspect of the present invention, there is also provided a process for producing a glass substrate for an information recording medium as described in the first or second aspect, wherein the air has cleanliness permitting the existence of particles in an amount not more than 100 particles per cubic feet·meter of the air.
In a fifth aspect of the present invention, there is also provided a process for producing a glass substrate for an information recording medium as described in the first or second aspect, wherein the air has cleanliness permitting the existence of particles in an amount not more than 50 cubic feet·meter of the air.
In a sixth aspect of the present invention, there is also provided a process for producing a glass substrate for an information recording medium as described in the first or second aspect, wherein the washing and chemical reinforcement of the glass substrate subsequent to the final polishing step are effected under an environment whose air cleanliness permits the existence of particles in a prescribed amount in the air.
Examples of the particles to be removed in the present invention include metal pieces such as fine iron powders, metal oxide pieces, glass chips, oil mist, silicon dust, fibers and organic substance. Particles large enough to cause inferiority during the use of an information recording medium or in the production step are removed. The size of the particles to be removed preferably ranges from 0.3 micron to 100 microns, but control to a size within a range of
Eda Shinji
Ozawa Jun
Frishauf Holtz Goodman & Chick P.C.
Hoya Corporation
Vincent Sean
LandOfFree
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