Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2002-04-22
2004-03-09
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S323000, C428S690000, C428S690000, C360S119050
Reexamination Certificate
active
06703106
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to recording and reproducing method of a magnetic recording particulate medium (i.e., a coating-type magnetic recording medium), and a magnetic recording medium for use in the method, in particular, relates to recording and reproducing method of a magnetic recording medium having a thin magnetic layer for high density recording, and a magnetic recording medium for use in the method.
BACKGROUND OF THE INVENTION
Along with the increase in the amount of data to be dealt with, the capacity thereof has become insufficient and the increase of the capacity of the floppy disc has been demanded.
Further, in the field of magnetic tapes, with the spread of office computers, such as minicomputers, personal computers and work stations, magnetic tapes for recording computer data as external storage media (so-called backup tapes) have been eagerly studied in recent years. For the realization of the magnetic tapes for such uses, the improvement of recording capacity has been strongly demanded conjointly with the miniaturization of a computer and the increase of information processing ability (e.g., information throughput).
Magnetic heads working with electromagnetic induction as the principle of operation (an induction type magnetic head) are conventionally used and spread. However, magnetic heads of this type are approaching their limit for use in the field of higher density recording and reproduction. That is, it is necessary to increase the number of winding of the coil of a reproduction head to obtain larger reproduction output, but when the winding number is increased, the inductance increases and the resistance at high frequency heightens, as a result, the reproduction output lowers. In recent years, reproduction heads which work with MR (magneto-resistance) as the principle of operation are proposed and come to be used in hard discs. As compared with the induction type magnetic disc, several times of reproduction output can be obtained with the MR head. Further, an induction coil is not used in the MR head, noises generated from instruments, e.g., impedance noises, are extremely reduced, therefore, it becomes possible to obtain a great S/N ratio by lowering the noise coming from magnetic recording media. In other words, good recording can be done and high density recording property can be drastically improved by lessening the noise of magnetic recording media hiding behind the instruments.
Magnetic recording particulate media (i.e., coating type magnetic recording media excellent in productivity and inexpensive and so far been used are known.
For example, a high capacity magnetic recording medium comprising a nonmagnetic layer having provided thereon a magnetic layer having a thickness of 1.0 &mgr;m or less and containing an abrasive having a Mohs' hardness of 6 or more and an average particle size of larger than the thickness of the magnetic layer is disclosed in JP-A-5-197946 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). Further, a high capacity magnetic recording disc comprising a nonmagnetic layer having provided thereon a magnetic layer having a thickness of 0.5 &mgr;m or less and containing an abrasive having a Mohs' hardness of 6 or more and an average particle size of from 0.8 to 1.4 times larger than the average particle size of the ferromagnetic powder, and an average particle size of from 2 to 4 times larger than the average particle size of the ferromagnetic powder is disclosed in JP-A-6-68453.
The evaluation of these magnetic recording media is in recording and reproducing using an MIG (metal-in-gap) head which is an induction type magnetic head, hence track density is relatively low and when higher density recording is done by further lessening a track width or thinning the magnetic layer thickness, a sufficient S/N ratio cannot be obtained at reproduction. In particular, the influence of the abrasive becomes large when an MR head is used, which causes the degradation of S/N ratio.
A magnetic recording and reproducing method which does not generate a noise and is excellent in a high density characteristic even when a conventionally used coating type magnetic recording medium excellent in productivity and inexpensively commercially available is combined with an MR head, and a magnetic recording medium for use in the method have been desired.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic recording and reproducing method which is excellent in electromagnetic characteristics and optimal for digital recording, and a magnetic recording medium for use in the method.
The present invention has been attained by the following means:
(1) A magnetic recording and reproducing method comprising recording and reproducing a signal in a track width (A) of less than 5 &mgr;m on a magnetic medium comprising a support having provided thereon a magnetic layer containing at least a ferromagnetic powder, an abrasive and a binder with a magnetic head, wherein the average longer size (B) of the abrasive particle(s) on the magnetic layer surface is ⅓ or less of the track width (A).
(2) A magnetic recording medium which is used in the magnetic recording and reproducing method as described in the above item (1), wherein the magnetic recording medium is a magnetic recording medium comprising a support having provided thereon a magnetic layer containing at least a ferromagnetic powder, an abrasive and a binder, and the average longer size (B) of the abrasive particle(s) which are present on the magnetic layer surface is ⅓ or less of the track width (A).
(3) In the magnetic recording and reproducing method and the magnetic recording medium as described in the above item (1) or (2), the magnetic recording medium comprises a support, a substantially nonmagnetic lower layer provided on the support and a magnetic layer containing a ferromagnetic metal powder or a hexagonal ferrite powder dispersed in a binder provided on the nonmagnetic lower layer, and the magnetic layer has a layer thickness of from 0.01 to 0.15 &mgr;m.
(4) In the magnetic recording and reproducing method and the magnetic recording medium as described in the above item (1) or (2), the magnetic recording medium is for MR head reproduction.
DETAILED DESCRIPTION OF THE INVENTION
The magnetic recording and reproducing method of the present invention prescribes the relationship between the average longer size (B) of the abrasive particle(s) which are present on the magnetic layer surface of the magnetic recording medium on which a signal is recorded and reproduced in a track width (A) of less than 5 &mgr;m and the track width (A), and it is necessary that the relationship (B)/(A)≦⅓ should be satisfied, particularly (B)/(A)≦0.20is preferred. The value of (B)/(A) is called ratio &agr;. The lower limit of ratio &agr; is determined by the balance with other characteristics such as the size of the track width (A) and durability, but is generally 0.05 or more.
The present invention is a magnetic recording and reproducing method comprising the step of scanning the magnetic layer surface of a magnetic recording medium having the magnetic layer surface satisfying the above-described ratio &agr; with a magnetic head while ensuring the track width satisfying the ratio &agr;, and the present invention is optimal for reproduction with an MR head.
In the present invention, the average longer size (B) of an abrasive particle(s) is determined by the following method.
The average longer size of an abrasive particle(s) is obtained by subjecting a magnetic layer surface to plasma treatment with Plasma Reactor PR41 (manufactured by Yamato Kagaku K.K.) under the condition of transmitting frequency of 13.56 MHz, output impedance of 50 ohm, output power of 20 W, degree of vacuum of 20 to 30 Pa, oxygen flow rate of 30 ml/min, and treatment time of 20 minutes, after drying, observing the abrasive particle(s) and/or clusters mainly comprising abrasives by an electron microscope of 15,000 magnif
Harasawa Takeshi
Noguchi Hitoshi
Saito Shinji
Fuji Photo Film Co. , Ltd.
Resan Stevan A.
Sughrue & Mion, PLLC
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