Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Patent
1982-11-16
1987-03-31
Robinson, Ellis P.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
252 6254, 427128, 428694, 428900, 4284259, 428522, G11B 570
Patent
active
046542604
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a magnetic recording medium for high density recording in which a short wavelength signal is recorded in, for example, a video tape recorder (VTR) and particularly to a magnetic recording medium in which a magnetic layer containing a ferromagnetic alloy powder is formed on a nonmagnetic substrate.
BACKGROUND ART
In the VTR, a luminance signal is usually recorded in the manner of frequency modulated (FM) signal. In recording the signal, a recording wavelength must be considered which corresponds to a frequency existing at the center of FM carrier having deviation for the luminance signal which occupies the highest band of recorded signal. In the present inventions, the frequency at the center of the FM carrier will be referred to as a center recording frequency and a wavelength corresponding to the center recording frequency will be referred to as a center recording wavelength.
Up to the present, various VTRs have been proposed and put into practice. Recently, it has been a trend to promote the short wavelength recording which aims particularly the high density recording, which requires the center recording wavelength thereof to be 1 .mu.m or below.
While, for a magnetic recording medium for VTR, it has been tried to improve the surface property of the magnetic recording medium whereby to make a spacing loss between a magnetic head and the magnetic recording medium be reduced as much as possible. But, in spite of these previously proposed techniques, the center recording wavelength of those prior art magnetic recording media which utilize chromium dioxide or iron oxide as magnetic powder was generally about 1 .mu.m at best in practice.
While, with a magnetic recording medium which utilizes a ferromagnetic alloy powder (in the specification of this invention, the ferromagnetic alloy powder includes a single substance of Fe), if the playback output therefrom is increased by high coercive force and high residual magnetization thereof and if it is tried to reduce the spacing loss between the magnetic medium and the magnetic head as much as possible, it may be considered that the aforesaid high density recording will relatively easily be made possible. However, as the output increases, a noise is also increased so that a picture with high quality can not be achieved. Therefore, such magnetic recording medium has not yet been practiced.
DISCLOSURE OF THE INVENTION
This invention is to provide a magnetic recording medium having a magnetic layer, which contains the above ferromagnetic alloy powder and is formed on a nonmagnetic substrate, and producing a high output with a low noise level and which is for use in the high density recording.
That is, in accordance with the present invention, it is clarified that a specific surface area measured by BET adsorption method of a ferromagnetic alloy powder such as acicular Fe powder, Fe-Co powder, Fe-Co-Ni powder and the like affects a noise level. On the basis of such clarification, in a magnetic recording medium where a magnetic layer containing the aforesaid ferromagnetic alloy powder is formed on the nonmagnetic substrate, the coercive force of the magnetic layer is made 1000 Oe or more and the specific surface area thereof measured by the BET adsorption method is made 45 m.sup.2 /g or above so that a magnetic recording medium for high density recording can be constructed, of which the center recording wavelength is less than 1 .mu.m.
Here, as the ferromagnetic alloy powder, there can be utilized Fe, Fe-Co, Fe-Co-Ni and so on or an acicular alloy powder containing additional elements such as Al, Cr, Si and the like in fairly small amount, considering, for example, anti-corrosion or the prevention of the sintering upon manufacturing. These acicular alloy powders can be obtained by reducing acicular iron oxide and iron hydroxyoxide and if necessary, iron oxide containing metals such as Ni, Co and so on or iron hydroxyoxide as a starting material in a reducing atmosphere such as H.sub.2 gas and so on. The specific surface a
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Chubachi Ryoji
Kawamura Yoshihisa
Somezawa Masashi
Robinson Ellis P.
Sony Corporation
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