Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1999-05-18
2001-10-16
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S141000, C428S163000, C428S167000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06303205
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a magnetic disk apparatus and a magnetic disk which is used in the magnetic disk apparatus.
In recent years, a significance of a magnetic disk apparatus as an external memory device of a computer system has been more and more increased and its recording density has remarkably been improved every year.
It is better to reduce a distance between a magnetic head and a magnetic layer of a magnetic disk (hereinafter referred as “spacing”) upon recording/reproduction in order to improve the recording density of the magnetic disk apparatus. To reduce the spacing, a distance between a magnetic head and a surface of a magnetic disk (hereinafter referred as “flying height”) is also reduced. To assure the floating stability of the magnetic head in such a case, it is required that the surface of a magnetic disk is as flat as possible.
On the other hand, upon start and stop of the magnetic disk apparatus, a frictional force which is generated between the magnetic head and the magnetic disk causes an abrasion between them and becomes a cause or deterioration of characteristics such as writing characteristic, reading characteristic, and the like. Further, if a moisture or the like exists between the magnetic head and the magnetic disk in a stop state of the magnetic disk, both of them are strongly adsorbed. If the apparatus is started in such a state, a large frictional force occurs between the magnetic head and the magnetic disk and there is a fear such that the magnetic head and the magnetic disk are damaged. There is a tendency such that the above frictional force increases as the surface of the magnetic disk is flat. Such a tendency is contradictory to the requirement for the floating stability of the magnetic head in association with the improvement of the recording density mentioned above.
There has been known a method whereby micro protrusions are formed on the surface of the magnetic disk in order to reduce such a frictional force.
In JP-A-1-134720, for instance, there has been disclosed a method whereby island-like projections are formed on the surface of a magnetic disk.
In JP-A-1-122028, there has been disclosed a method whereby a metal alkoxide solution is coated onto the surface of a magnetic layer of a magnetic disk and is rapidly heated and a protective layer having projections is formed onto the surface of the magnetic layer.
In JP-A-57-20925, there has been disclosed a method whereby cylindrical projections each having a diameter of 0.03 to 0.1 mm and a height of about 0.05 &mgr;m are formed onto the surface of a magnetic layer or a protective layer.
All of the above conventional techniques intend to reduce a flying height of the magnetic head for the magnetic disk and to prevent that, in such a case, a slider to support the magnetic head is adsorbed to the magnetic disk.
In the above conventional techniques, nothing is considered with respect to a point that the floating stability of the magnetic head is continued for a long time.
Further, nothing is considered with respect to a point that a change of a spacing is caused by a change of flying height of the magnetic head due to a difference of a radial position of the magnetic disk, which limits the recording density.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic disk which can maintain the floating stability of a magnetic head.
Another object of the invention is to provide a magnetic disk which can set a change of a spacing to be smaller than a change of flying height of a magnetic head due to a difference of a radial position of a magnetic disk.
Still another object of the invention is to provide a magnetic disk apparatus having a magnetic disk which can accomplish the above object. Still another object of the invention is to provide a magnetic disk apparatus which can suppress a flying height of a magnetic head to 0.2 &mgr;m or less and can maintain the floating stability for a long time and also to provide a magnetic disk for the above purpose.
A magnetic disk apparatus of the invention comprises: at least one magnetic disk which essentially has a magnetic layer and a surface protective layer on a substrate; a magnetic head which face the rotating magnetic disk with a micro distance and is supported by a slider; rotating means for rotating the magnetic disk; and an actuator for moving and positioning the magnetic head to a predetermined position on the magnetic disk, wherein a plurality of protrusions each having a flat surface are formed in at least a region which can execute a contact start/stop operation on the surface of the magnetic disk, an area ratio of the protrusions is set to 0.1 to 80% per 1 mm
2
a height of the protrusion having the maximum height among the protrusions lies within a range from 5 to 40 nm, and the magnetic layer is formed on the whole surface of the substrate.
The invention is based on the investigation of the fact that the protrusions which satisfy the foregoing requirements are formed in the region which can execute the contact start/stop (CSS) operation on the surface of the magnetic disk and the magnetic layer is formed on the whole surface of the substrate, so that the flying height of the magnetic head is reduced and the floating stability can be maintained.
Thus, the flying height of the magnetic head can be set to a remarkably small value and the flying height of the magnetic head can be held almost constant. Particularly, it is important to control both of the area ratio of the protrusions which are formed on the surface and the protrusion heights to values within predetermined ranges. However, in the conventional techniques, there is no idea such that both of the protrusion area ratio and the maximum protrusion height are controlled to values within specified ranges by paying an attention to them.
The significance of the above technique is particularly remarkable as the flying height of the head is reduced to realize a high recording density of the magnetic disk apparatus, for instance, in the case where the flying height is set to a value within a range from 0.02 to 0.2 &mgr;m.
According to the invention, only the portions of the protrusion surfaces directly face the head and the area ratio of the magnetic disk which is come into contact with the head can be decreased, so that the frictional force with the head can be reduced.
On the other hand, by controlling the maximum protrusion height to a value within a specified range, the fluctuation of the flying height of the head is small, the floating stability of the head can be assured over the whole surface of the magnetic disk, and the fluctuation of the output due to the flying height fluctuation can be prevented.
As mentioned above, the frictional force with the head can be reduced, the output fluctuation can be prevented, and the stable floating of the head can be assured. Therefore, it is possible to obtain a magnetic disk which has a high recording/reproducing accuracy and can cope with a low flying height of the head due to the realization of a high recording density and also to obtain a magnetic recording apparatus using such a magnetic disk.
Further, the protrusions to be formed are arranged so as to rapidly eliminate micro dusts deposited on the head or the magnetic disk, so that a head crush by the micro dusts is difficult to occur and the floating stability of the head can be assured for a long time.
To enable the dusts deposited to the magnetic head or the magnetic disk to be promptly eliminated.
(i) it is desirable that the protrusions of the magnetic disk are separated on the same circumference and the same radius, hollows are formed between the protrusions, and an interval between the closest protrusions on the magnetic disk is set to a value within a range from 0.2 to 50 &mgr;m, and
(ii) it is particularly desirable to arrange the convex portions so as to face the whole surface of the slider when the slider was put at an arbitrary position on the magnetic disk and the magnetic disk was rotated
Gomi Kenichi
Inomata Youichi
Kato Yoshiki
Miyake Yoshihiko
Ohura Masaki
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Rickman Holly C.
Thibodeau Paul
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