Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Patent
1983-09-09
1988-11-29
Lesmes, George F.
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
428323, 428329, 428694, 428900, G11B 5714
Patent
active
047880929
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a disc-shaped magnetic recording medium and, more particularly, to a disc-shaped magnetic recording madium for high density recording having particularly a low noise level and a high output power.
BACKGROUND ART
In a magnetic disc device, a magnetic head scans a magnetic surface concentrically in the circumferential direction. For this reason, if magnetic particles are oriented in either a lengthwise or in a widthwise direction as in an elongated magnetic tape, reproduction output differs between the orientation direction and a direction different therefrom, causing a variation in output power. Therefore, magnetic particles of a disc-shaped magnetic recording medium to be used for a magnetic disc device should be oriented at random (unoriented) or in the circumferential direction.
In a so-called electronic camera and the like currently under rapid development which is designed to record still image information and so forth on a magnetic disc, it has also been sought to meet strict requirements for electromagnetic properties of a magnetic layer of the magnetic disc in order to satisfy a demand for high density recording by short wavelength recording. Magnetic particles of the iron oxide type conventionally used heretofore cannot, however, meet such strict requirements.
DISCLOSURE OF INVENTION
Therefore, it is an object of the present invention to provide a disc-shaped magnetic recording medium which in particular can satisfy requirements based on a demand for high density recording by short wavelength recording and has a low noise level and a high output power.
The disc-shaped magnetic recording medium according to the present invention is prepared by dispersing in a binder a magnetic powder having a coercive force of about 1,000 Oe or higher and a BET specific surface area of about 25 to 70 m.sup.2 /g, and then providing a magnetic layer of the resultant material on a non-magnetic substrate so as to orient the dispersed powder particles at random (unoriented) or in the circumferential direction.
The ferromagnetic powder to be used for the present invention may include a ferromagnetic metal or alloy powder. For example, iron oxyhydroxide or iron oxyhydroxide containing cobalt or the like (doped or cladded), or a metal or an alloy composed mainly of iron such as acicular iron obtainable by reduction of iron oxide in a reducible atmosphere, may be enumerated as appropriate powders. In accordance with the present invention, such magnetic powders have a coercive force of about 1,000 Oe or higher and a BET specific surface area of about 25 to 70 m.sup.2 /g. If the coercive force of the magnetic powder to be used is smaller, various performance levels required for high density recording by short wavelength recording cannot be achieved. Even if the coercive force is 1,000 Oe or higher, magnetic powders of the Co-.gamma.-Fe.sub.2 O.sub.3 series have insufficient magnetic properties so that they are inappropriate for unoriented discs for electronic cameras or the like requiring clear pictures, because of their small residual magnetic flux density (Br). It is accordingly desirable that the magnetic disc recording medium according to the present invention has a Br value along the circumferential direction of 1,500 Gauss or higher. If the BET specific surface area of the magnetic powder to be used is larger, a noise level is decreased, but this is not preferred because of a corresponding decrease in dispersibility which causes difficulties in magnetic treatment for random or circumferential orientation, whereby a decrease in Br is caused and consequently an RF-output is decreased or a C/N ratio is deteriorated. If the BET specific surface area is too large, noise levels are undesirably increased.
A binder in which the magnetic powders described hereinabove are dispersed may be any one that is used for conventional magnetic recording media, and is not restricted to any particular one. As such a binder, there may be enumerated a vinylchloride-vinyl acetate copolymer
REFERENCES:
patent: 3865627 (1975-02-01), Roden et al.
patent: 4109046 (1978-08-01), Hammon et al.
patent: 4208447 (1980-06-01), Bate et al.
patent: 4395447 (1983-07-01), Nakamatsu et al.
patent: 4425401 (1984-01-01), Ido et al.
patent: 4439486 (1984-03-01), Yamada et al.
Chubachi Ryoji
Kawamura Yoshihisa
Nihei Nobuyuki
Atkinson William M.
Lesmes George F.
Sony Corporation
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