Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-06-23
2002-08-06
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S336000, C428S402000, C428S425900, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06428884
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic recording particulate medium which comprises a flexible support having provided thereon a magnetic layer comprising a ferromagnetic powder and a binder, and which exhibits a high output and a good C/N ratio under high-density recording and which is suitable for recording and reproducing digital signals at high densities.
2. Description of Related Art
In recent years, a recording wavelength tends to be shorter along with high densification, and if the magnetic layer is thick, the output tends to be lowered, thereby raising problems in a self-demagnetization loss during recording and a thickness loss during reproducing. Therefore, a magnetic layer is tried to be thinner, but the influence of a nonmagnetic support may easily appear on the surface of the magnetic layer when the magnetic layer having a thickness equal to or less than 2 &mgr;m is directly applied to the support, and a deteriorating tendency in electromagnetic characteristics and dropouts are seen.
To solve such problems, there has been proposed a method for forming a thin thickness magnetic layer and a nonmagnetic layer under the magnetic layer, on a nonmagnetic support, by using a simultaneous multilayer coating technique as well as a concentrated coating liquid for the magnetic layer as disclosed in Japanese Unexamined Patent Publication (KOKAI) Showa No. 63-191,315 and Japanese Unexamined Patent Publication (KOKAI) Showa No. 63-187,418, thereby obtaining a magnetic recording medium having an improved electromagnetic characteristics in excellent production yields.
In digital VCR systems for consumer use, magnetic recording film medium (or what is called ME tapes), in which a magnetic recording layer comprises a vacuum deposited cobalt alloy, are used in practice. But, in order to manufacture magnetic recording particulate tapes, what is called MP tapes, applicable to the digital VCR systems for consumer use, an improvement in Over Write erasing property is required while having a high output for data signals and securing an output for tracking signals. The present inventors proposed a magnetic recording particulate tape satisfying the above demands by increasing a filling degree of a magnetic layer while making the magnetic layer thinner (See, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 11-185,240.
In the digital VCR systems for consumer use, an apparatus (amplifier) noise is high, and therefore, a total noise consisting of the apparatus noise and a medium noise is determined by the apparatus noise. Thus, lot of attention has not been paid to the medium noise in practical use. Under the standard of the digital VCR systems for consumer use, however, it is required to make the medium noise within −2 dB with respect to a ME reference tape.
In addition, disc systems or tape systems mounting an MR head (magneto resistive head) have recently been developed, and a demand for reducing medium noises of the magnetic recording media used in those systems becomes higher. In the thin metal film type of magnetic recording medium, a thickness of a magnetic layer is made thinner and a crystal particle is made smaller to increase the number of the magnetic particles per unit volume, thereby reducing the medium noise [“Study of Vapor Deposited Thin Layer Tape for MR head in Helical Scan Systems”, Nihon Ouyo Jiki Kiroku Gakkai Shi (Journal of Applied Magnetic Recording Society of Japan), VOL. 22 Supplement No. S3, 1998, (Seiichi Onodera, et al.)].
On the other hand, reduction of the medium noise in the magnetic recording particulate medium is not enough in comparison with that in the magnetic recording film medium, so, when the magnetic recording particulate medium is used in a system mounting the MR head as a reproduction head, the following problems are raised, in terms of reduction of the medium noise:
(1) A filling degree of a magnetic layer is lower in comparison with that of the film medium, as well as the number of the magnetic particles per unit volume is smaller.
(2) A surface roughness across a wide wavelength area [especially, a pitch roughness from 1 to 20 &mgr;m] is generated during the coating operation of the magnetic layer and the nonmagnetic layer.
(3) Fluctuation of the magnetic layer thickness by coating is generated [this is raised as a problem especially in saturation recording systems].
(4) Keeping uniformity of the magnetic particles is difficult because the nonmagnetic material is added in the magnetic layer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic recording particulate medium capable of reducing a medium noise and exhibiting a high C/N ratio even under high-density magnetic recording such as that employed in the system utilizing an MR head.
The present inventors improved the magnetic recording medium described in the aforementioned Japanese Unexamined Patent Publication (KOKAI) Heisei No. 11-185,240 as a basis so as to respond to the above problems, finding a magnetic recording medium having high output and fully low noise, and therefore the present invention has been accomplished.
The present invention relates to a magnetic recording medium comprising, on a flexible nonmagnetic support, a nonmagnetic layer containing a nonmagnetic powder and a binder, and a magnetic layer containing a ferromagnetic powder and a binder in this order, characterized in that the magnetic layer has an average thickness d from 0.01 to 0.3 &mgr;m and the average particle number m of the ferromagnetic powder existing in a thickness direction of the magnetic layer is in the range of from 1 to 20.
In the magnetic recording medium of the present invention, it is preferable that the particle of the ferromagnetic powder contained in the magnetic layer has an acicular shape where a mean length l of the major axis ranges from 0.02 to 0.15 &mgr;m and a ratio d/l of an average thickness d of the magnetic layer to the mean length of the major axis 1 is equal to or less than 4.
In the magnetic recording medium of the present invention, it is further preferable that the particle of the ferromagnetic powder contained in the magnetic layer has a flat acicular shape and that the flat acicular magnetic powder has an aspect ratio of a cross section in a direction perpendicular to the major axis being more than 1.
MODE FOR CARRYING OUT THE INVENTION
A magnetic recording medium according to the present invention is characterized in that the average thickness d of a magnetic layer ranges from 0.01 to 0.3 &mgr;m and the average particle number m of a ferromagnetic powder existing in a thickness direction of the magnetic layer is in the range of from 1 to 20.
In recording and reproducing with a conventional magnetic induction head, if the magnetic layer is made thin to the extent mentioned above, a magnetization amount becomes smaller, and a reproduction output is lowered. When an MR head is used for reproduction, however, its sensitivity is sufficiently high, thereby a sufficient output and an improvement in a resolution property which is an advantage resulting from the thin magnetic layer can be obtained. In other words, by making the average value d of the thickness of the magnetic layer equal to or higher than 0.01 &mgr;m, desirable magnetism is secured, and by making the average value d equal to or less than 0.3 &mgr;m, the resolution property can be enhanced, thus the C/N ratio in the MR head can be improved. Particularly, the average value d of the thickness of the magnetic layer is preferably in the range of from 0.01 &mgr;m to 0.2 &mgr;m, more preferably from 0.01 &mgr;m to 0.1 &mgr;m, from the viewpoint of securing the resolution property because the magnetic layer is easily saturated with the high sensitive MR head.
Further, in the magnetic recording medium of the present invention, the average particle number m of the ferromagnetic powder existing in the thickness direction of the magnetic layer is in the range of from 1 to 20. As the results of diligent
Ejiri Kiyomi
Naoe Koji
Bernatz Kevin M.
Resan Stevan A.
Stroock & Stroock & Lavan LLP
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