Magnetic recording disk having a lubicant reservoir on the inner circumferential surface

In a magnetic recording apparatus, a magnetic recording medium has a disk body and a lubricant covering not only the opposite major surfaces but also the inner circumferential edge of the disk body. The medium prevents the lubricant from flying about despite the spinning thereof and, therefore, remains mechanically durable over a long period of time.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic recording medium for use in a 
magnetic disk drive, magnetic drum drive or similar magnetic recording 
apparatus. 
A magnetic recording apparatus having a magnetic head and a magnetic 
recording medium may write and read data out of the medium with a 
conventional contact start/stop (CSS) scheme. In the CSS scheme, at the 
beginning of operation, the head and the surface of the medium are held in 
contact with each other. As the medium is caused to spin at a 
predetermined speed, an air layer or cap is formed between the head and 
the medium. In this condition, the head writes or reads data in or out of 
the medium. As soon as the medium stops spinning at the end of operation, 
the head and medium are again brought into contact. When the head and 
medium are in contact, friction acting therebetween causes them to wear 
and, in the worst case, forms scratches on them. Moreover, even the 
slightest change in the position of the head makes the load distribution 
on the head uneven, again scratching the head and medium. It has been 
customary to apply a lubricant to the surfaces of the medium in order to 
eliminate the wear attributable to the contact and slide of the medium on 
the head. 
However, the problem with the lubricant, which is usually implemented as 
liquid oil, is that it flies about while the medium spins. When the 
lubricant flies about until the thickness thereof decreases below one 
which preserves mechanical durability, the wear of the medium is 
accelerated, resulting in the loss of data. 
Various approaches have been proposed to prevent the lubricant from being 
scattered around. For example, Japanese Patent Laid-Open Publication Nos. 
2-81321, 2-73514, 63-258993, 63-258992 and 63-237216 propose to cover the 
medium with a lubricant having a functional group which coupled with a 
protective film. Japanese Patent Laid-Open Publication Nos. 63-225918 and 
63-225917 contemplate to couple a lubricant to a protective film by use of 
a silane coupling agent. Further, Japanese Patent Laid-Open Publication 
Nos. 61-133029 teaches heating a lubricant in a vacuum atmosphere in order 
to cause it to adhere firmly to a protective film. For the same purpose, 
Japanese Patent Laid-Open Publication No. 1-184723 applies a lubricant 
after vapor rinsing. However, although a lubricant strongly bonded to a 
protective layer in a nearly solid state is prevented from flying about, 
wear resistivity is degraded since the self-repairing function of liquid 
molecules is lost. 
Japanese Patent Laid-Open Publication No. 63-217583 provides a magnetic 
disk with notches inboard of the innermost portion of a data zone and 
infiltrates them with a lubricant. The lubricant infiltrated into the 
notches makes up for the decrease of a lubricant due to the scattering. 
The problem with this kind of approach is that the lubricant once 
infiltrated into the notches remains stable, i.e., sparingly oozes out 
unless a pressure is applied thereto. With such a scheme, it is difficult 
to prevent the lubricant from flying about since a pressure due to the 
movement of a slider does not act and since even a centrifugal force is 
banked by the notches and cannot cause the lubricant to ooze out. 
In addition, Japanese Patent Laid-Open Publication No. 2-81320 proposes a 
structure wherein portions of a magnetic disk contacting a spacer, or jig 
which will be described, are not covered with a lubricant in order to 
prevent liquid drops from flying about. This, however, brings about a 
problem that the mechanical durability of the disk is short due to the 
absence of a lubricant source. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a magnetic 
recording medium for a magnetic recording apparatus which prevents a 
lubricant from flying about despite the spinning thereof and, therefore, 
achieves improved mechanical durability. 
A magnetic recording medium of the present invention comprises a disk body 
made up of a base, a magnetic medium formed on the base, and a protective 
film formed on the magnetic medium, and a lubricant covering the surfaces 
of the disk body including the inner circumferential edge of the disk body 
.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 of the drawings, a magnetic recording medium embodying 
the present invention is shown. As shown, the medium implemented as a 
disk, generally 10a, has a disk body 12 and a lubricant 14 covering the 
disk body 12. The lubricant 14 covers not only opposite major surfaces of 
the medium body 12 but also the inner circumferential edge 12a of the 
same. As shown in FIG. 2, when the disk 10b is clamped by a jig 16, the 
lubricant 14 should preferably exist between the disk body 12 and the jig 
16 also. 
The kind of the lubricant 14 is open to choice so long as it remains in a 
liquid state over the expected temperature range for use. For example, use 
may be made of perfluoropolyethers represented by the following general 
formulae: 
EQU GCF.sub.2 (OCF.sub.2).sub.p (OC.sub.2 F.sub.4).sub.q OCF.sub.2 G(1) 
(where p and q are integers ranging from 2 to 25, and G is representative 
of a functional group, e.g., --COOH or --OH) 
EQU F(C.sub.3 F.sub.6 O).sub.n C.sub.2 F.sub.4 G (2) 
(where n is an integer ranging from 3 to 25, and G is representative of a 
functional group, e.g., --COOH or --OH) 
EQU F(CF(CF.sub.3)CF.sub.2 O).sub.m CF.sub.2 G (3) 
(where in is an integer ranging from 3 to 25, and G i s representative of a 
functional group, e.g., --COOH or --OH). 
A specific example of the above magnetic disk 10a or 10b is as follows. A 
base was produced by covering an aluminum alloy substrate with a 
nickel-phosphor plating and then mirror-finishing it. A 30 nanometers 
thick cobalt-chromium-platinum layer was formed on the base by sputtering 
as a magnetic medium. A protective layer in the form of an amorphous 
carbon film was formed on the magnetic medium to a thickness of 20 
nanometers, thereby completing the disk body 12. The disk body 12 was 
immersed in a Freon solution of perfluoropolyether having a hydroxyl group 
(HOCF.sub.2 (OCF.sub.2).sub.13 (OC.sub.2 F.sub.4).sub.8 OCF.sub.2 OH), 
which served as the lubricant 14, and then dried. The resulting lubricant 
layer 14 was 3 nanometers thick. Subsequently, the undiluted solution of 
the perfluoropolyether was applied to the inner circumferential edge 12a 
of the disk body 12 by an applicator to a thickness of 1 micron. As a 
result, a magnetic disk 10a having the structure shown in FIG. 1 was 
produced. 
For comparison, a magnetic disk 10b was produced by forming a 2 nanometers 
thick lubricant layer on a disk body, as in the example described above, 
but not covering the inner circumferential edge and the portions 
contacting the jig 16. 
For an accelerated aging test, the disk 10a and the comparative disk 10b 
were each rotated at a speed of 10,000 rpm in an 80.degree. C. atmosphere 
so as to measure the variation of the thickness of the lubricant layer 14. 
On the elapse of 720 hours, the ratio of the difference between the 
initial thickness and the thickness after the test to the initial 
thickness, i.e., reduction ratio was found to be only 1% with the disk 10a 
having the inner edge 12a thereof covered, but it was measured to be as 
great as 50% with the disk 10b whose inner edge 12a and portions 
contacting the jig 16 were not covered. 
Further, after the disk 10a and 10b have undergone the accelerated aging 
test and a magnetic head was repeatedly caused to slide on each other. A 
scratch appeared on the comparative disk 10b after 5,000 times of sliding. 
By contrast, the disk 10a of the embodiment was free from scratches even 
after 20,000 times of sliding. 
In the illustrative embodiment, the lubricant 14 covering the inner edge 
12a of the medium body 12 plays two different roles at the same time, as 
follows. The lubricant 14, of course, serves as a lubricant source. In 
addition, the lubricant 14 links, due to the surface tension thereof, the 
lubricant 14 covering the opposite major surfaces of the disk body 12, 
thereby preventing it from flying about. The surface tension acts even on 
the lubricant intervening between the jig 16 and the disk body 12; the 
lubricant 14 at the inner edge 12a serves to obviate scattering with the 
surface tension thereof, rather than to effect lubricant supply. 
In summary, it will be seen that the present invention provides a magnetic 
recording medium which prevents a lubricant from flying about despite the 
spinning thereof and, therefore, remains mechanically durable over a long 
period of time. 
Various modifications will become possible for those skilled in the art 
after receiving the teachings of the present disclosure without departing 
from the scope thereof.