Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2000-07-17
2004-05-25
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S690000, C428S690000
Reexamination Certificate
active
06740407
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium with high surface recording density, and also to a magnetic recording mode using a large capacity floppy disk providing high reliability for practical use.
In a magnetic recording medium such as magnetic tape, hard disk, etc., a vacuum-deposited tape or a metal thin film type hard disk, etc. are used. Using a ferromagnetic metal thin film prepared by vacuum film forming method, i.e. sputtering method, vacuum evaporation method, etc., this magnetic recording medium is used as a recording layer in practical application. In this type of magnetic recording medium, high magnetic energy can be easily obtained, and flat surface can be easily achieved by smoothening the surface of non-magnetic substrate. In this respect, it is characterized in that spacing loss is low and high electromagnetic transfer characteristics can be attained, and this is suitable for a method to manufacture a high-density recording material. In particular, the sputtering method can increase magnetic energy than the evaporation method, and this is adopted in the magnetic recording medium such as hard disk, which must provide high surface recording density.
On the other hand, compared with the hard disk, a floppy disk type magnetic recording medium has higher impact resistance and can be produced at lower cost, and it is widely used in 2HD class products. Further, in recent years, a high-density magnetic recording medium represented by Zip (Iomega Inc.) based thin layer coating technique has been introduced to practical use. In the magnetic recording medium as described above, recording and reproduction are performed at high speed of about 3000 rpm, and high transfer rate closer to that of hard disk can be achieved. However, its recording density is still less than {fraction (1/20)} of that of the hard disk. This is attributable to the fact that a floppy disk type magnetic recording medium which has the magnetic layer produced by sputtering method as in case of the hard disk is not yet suitable for practical application.
There are various reasons for this. One of the reasons is that, in the magnetic recording mode using such a floppy disk, it is difficult to maintain high running durability and to attain high reliability for practical use.
In the floppy disk with the magnetic layer produced by the sputtering method, it is more difficult to maintain durability than the floppy disk produced by the conventional coating method. The reason is as follows: The floppy disk produced by the coating method contains hard particles and lubricant in the magnetic layer in addition to magnetic particles and has high lubricating property and high wear resistance. On the other hand, in the floppy disk produced by the sputtering method, the magnetic layer is a metal thin film, which is easily worn out.
For this reason, there have been attempts to form a wear-resistant protective layer on the magnetic layer as in the case of hard disk, and to form a lubricating layer on it in order to provide higher lubricating property and wear resistance. However, even when a protective layer and a lubricating layer similar to the case of the hard disk are formed on the floppy disk, running durability can be improved but it is not possible yet to attain high reliability for practical use. In case of hard disk, when the number of revolutions of disk is increased, the head is floated up by floating force applied on the head, and it is used under the condition that the head and the hard disk are not in contact with each other. In case of floppy disk, even when the number of revolutions of the disk is increased, vibration of the disk (surface deviation) is high, and the head cannot be floated up in stable manner. Even at high-speed rotation,-the head and the floppy disk are frequently in contact with each other.
For this reason, with the purpose of increasing the running durability and of maintaining high reliability for practical use in case of the floppy disk, it is necessary to achieve as follows:
(1) Lubricating layer having high lubricating property;
(2) Protective layer with high wear resistance;
(3) Well-controlled surface roughness not to generate high frictional force even when head and disk are in contact with each other; and
(4) Low surface deviation to reduce frequency of contact. In particular, for the lubricating layer and the protective layer must have higher durability in the contact sliding than those used on hard disk.
As the protective layer with high wear resistance, an amorphous carbon film containing carbon and hydrogen and called “diamond-like carbon” (DLC) is most commonly used. It is used as the protective layer for hard disk or for video tape having metal thin film type magnetic layer and formed by vacuum deposition. Diamond-like carbon can be relatively easily produced. It is hard and has low frictional force and is very unlikely to cause seizure. However, it has been found that, when the commonly used diamond-like carbon containing carbon and hydrogen is used as the protective layer for floppy disk, sufficient durability cannot be obtained. The reason for this is that, when diamond-like carbon is used as a protective layer, frictional force is gradually increased as the head and the disk are repeatedly brought into contact with each other. As a result, the diamond-like carbon may be destroyed or the magnetic layer may be destroyed, and scratches may occur.
To reduce the increase of frictional force, various methods for improvement are proposed such as the improvement of structure of lubricant, adsorbing property between lubricant and protective layer, surface treatment of protective layer, property of protective layer, etc. In order to maintain low frictional force even when lubricant or protective layer is consumed or worn out, it seems to be the most effective way to decrease frictional coefficient of the protective layer itself.
For example, as a method to improve the quality of the protective layer of hard disk, there is a method to add a third element in addition to carbon and hydrogen of the diamond-like carbon. Above all, it is reported that a nitrogen-added diamond-like carbon has an effect to decrease the frictional force. For example, JP-A-7-334830, to JP-A-1-320622, etc. describe the use of a DLC film containing nitrogen as the protective layer.
Further, JP-A-6-333231 discloses the use of a protective layer containing hydrogen and nitrogen and a lubricant layer having polar group. U.S. Pat. No. 5,567,512 (JP-A-8-106629) describes a carbon protective layer having a specific ratio of surface density of nitrogen atoms.
Also, JP-A-9-288818 describes a carbon protective layer containing nitrogen and of 10-20 nm in thickness. JP-A-10-143836 discloses that nitrogen concentration in the carbon protective layer is changed in direction of thickness and a material having a specific chemical structure is used as lubricant. Further, U.S. Pat. No. 5,776,602 teaches a nitrogen-containing carbon protective layer having Raman spectrum of a specific range. EP-54720 describes the use of a carbon protective layer containing hydrogen and nitrogen and with thickness of less than 20 nm.
On the other hand, the magnetic head sliding with the floppy disk is mounted on a slider, which generally controls floating and contact conditions. Like the slider used in the hard disk drive, the slider for the floppy disk is made of ceramics such as Al
2
O
3
—TiC. However, carbon protective layer is not formed on the surface of the slider as in the case of the slider for hard disk drive described in JP-A-8-45045. The reason for this may be as follows: When a conventional thin film coating type floppy disk is used as a magnetic recording medium, even in case high hardness carbon protective layer is provided, this protective layer is worn out within short time due to sliding movement with the floppy disk and the effect is very low.
The surface of the slider of hard disk drive is manufactured in such manner that it is floated stably by air flow generated by the rot
Katayama Kazutoshi
Usuki Kazuyuki
LandOfFree
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