Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
2002-02-14
2003-04-15
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S141000, C428S426000, C428S432000, C428S690000, C428S690000, C360S135000
Reexamination Certificate
active
06548139
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a glass substrate for use in a magnetic recording medium, such as, a hard disk, a magnetic recording medium having the glass substrate, and a method of manufacturing the magnetic recording medium and the glass substrate.
An interface between a magnetic head and a magnetic disk has become a key technology for improving recording capacity in a technical field for magnetically recording (writing) and reproducing (reading).
It is necessary to excessively reduce a flying height of the magnetic head which is float over a surface of the magnetic disk to improve recording density.
However, when the record/reproduce (write/read) operation is carried out in the known CSS (Contact Start Stop) method, the magnetic head often sticks to the magnetic disk with a low flying height of the magnetic head. Herein, it is to be noted that this phenomenon is generally called “head stiction”.
Suggestions conventionally have been made about a variety of texture techniques to prevent such stiction of the magnetic head. A representative suggestion has been made about a method of forming a surface of an Al/NiP plating substrate into a rough surface by mechanically polishing (mechanically texturing) the surface in Japanese Unexamined Patent Publication (JP-A) No. Sho. 62-273619.
Further, another suggestion has been made about a method of depositing a thin-film having the rough surface on a glass substrate by the use of the known sputtering process in Japanese Examined Patent Publication (JP-B) No. Hei. 4-62413 or a method of forming the rough surface by the use of the chemical etching process in Japanese Examined Patent Publication (JP-B) No. Hei.7-101507 when the glass substrate is superior in flatness in comparison with an aluminum substrate.
In the meanwhile, a glide height recently has reached 1.2 &mgr;inch or less to improve the recording capacity.
However, the method of forming the texture, which has been conventionally suggested and described above, is the texture technique on the condition that the glide height is equal to about 8 &mgr;inch.
Therefore, even when the conventional texture forming method is applied for the recent magnetic disk which records (writes) and reproduces (reads) with the low flying height, it is difficult to obtain the magnetic disk which simultaneously satisfies sufficient electro-magnetic conversion characteristic and stiction preventing effect of the magnetic head.
In this case, the conventional glide height was equal to about 8 &mgr;inch. Therefore, the surface state (the surface morphology) of the magnetic disk (the substrate) could be sufficiently evaluated by the known thally step. Herein, the surface roughness is measured by scanning a contact needle having radius of several &mgr;m (for example, 2.5 &mgr;m) along the surface.
However, when the flying height becomes 1.2 g inch or less (1 inch =25.4 mm) which is recently required, it is difficult to judge whether or not the surface state of the glass substrate can realize prevention of the stiction of the magnetic head by the use of the conventional thally step.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a magnetic recording medium and a glass substrate for the magnetic recording medium which has a glide height of 1.2 &mgr;inch or less and which is capable of realizing high electro-magnetic characteristic (high memory performance) and high CSS durability characteristic.
Inventors have paid attention to specify the surface state of the glass substrate by the use of the interatomic force microscope (AFM) in order to evaluate the surface state of the glass substrate. This is because it is impossible to identify whether or not the surface state of the glass substrate is suitable, since the resolution is low in the conventional measuring method using the contact needle method.
Based upon the above-mentioned evaluation method, it has been confirmed that height and distribution (namely, variation of the height) of each projection of fine roughness, which are formed on a principle surface of the glass substrate, are important factors to achieve the above purpose.
Further, as a result of various experiments, it has been found out that the glass substrate surface as a target or a goal can not be obtained unless specific polishing condition and surface process condition are properly combined. This invention is performed base upon this analyzed result.
(First Invention)
In the glass substrate for use in the magnetic recording medium according to the first invention, when the surface roughness of at least the principal surface of the glass substrate is measured by the use of the interatomic force microscope (AFM), Ra (center-line mean roughness) falls within the range between 0.2 and 2.5 nm, Rmax (maximum height) falls within the range between 3 and 25 nm, and Rmax/Ra falls within the range between 3 and 35.
(Second Invention)
In the glass substrate according to the first invention, a surface parallel to a virtual principal surface is defined as a contour surface when it is assumed that the principal surface of the glass substrate is completely flattened,
when the roughness formed on the principal surface is cut by the use of the contour surface (a surface which is structured by the same height components), a percentage rate of a total area of the principal surface for sum of areas of the cut cross sectional surface is defined as a bearing ratio,
the contour surface having the bearing ratio of 50% is defined as a referential surface,
each distance from the referential surface to each contour surface having each bearing ratio is specified as a bearing height, the bearing height of the contour surface having the bearing ratio of 2.5% is defined as B.H.(2.5) while the bearing height of the contour surface having the bearing ratio of 5.0% is defined as B.H. (5.0), and
B.H. (2.5)/Rmax fills within the range between 0.1 and 0.5 or B.H. (5.0)/Rmax falls within the range between 0.1 and 0.45.
(Third Invention)
In the glass substrate according to the first invention, the surface roughness of at least the principal surface is measured by the use of the interatomic force microscope (AFM),
Rmax falls within the range between 5 and 25 nm, and
B.H. (2.5)/Rmax falls within the range between 0.1 and 0.5 or B.H. (5.0)/Rmax falls within the range between 0.1 and 0.45.
(Fourth Invention)
In the glass substrate according to any one of the first through the third inventions, the glass substrate contains at least alkali metal oxide and alkali earth oxide, and
the content of alkali earth oxide is not exceeding 3 mol %.
(Fifth Invention)
In the glass substrate according to any one of the first through the fourth inventions, the glass substrate is used for a magnetic disk which has a glide height having 1.2 &mgr;inch or less.
(Sixth Invention)
In a magnetic recording medium according to the fifth invention, at least a magnetic layer is formed on the principal surface of the glass substrate of any one of the first through the fifth inventions.
(Seventh Invention)
A method of manufacturing a glass substrate which is for use in a magnetic recording medium, comprising the steps of:
preparing a glass member in which Ra falls within the range between 0.1 and 1.0 nm when a surface roughness of a principal surface of the glass member is measured by the use of the interatomic force microscope (AFM), and
chemically processing the surface so that Ra falls within the range between 0.2 and 2.5 nm, Rmax falls within the range between 3 and 25 nm, and Rmax/Ra falls within the range between 3 and 35.
(Eighth Invention)
A method of manufacturing a glass substrate which is for use in a magnetic recording medium, comprising the steps of:
preparing a glass member in which Ra falls within the range between 0.1 and 1.0 nm when a surface roughness of a principal surface of said glass member is measured by the use of the interatomic force microscope (AFM), and
processing at least the principle surface by the use of hydrofluosilic acid.
(Ninth Invention)
A method according to the se
Matsuda Syoji
Ono Katsutoshi
Sakai Hiroyuki
Hoya Corporation
Resan Stevan A.
Sughrue & Mion, PLLC
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