Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Patent
1996-03-14
1997-07-15
Resan, Stevan A.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
428336, 428403, 428404, 428694BA, 428900, 148105, 148314, 360 2, 235493, 283 82, 283904, G11B 5706
Patent
active
056481608
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a MnBi magnetic powder, a method for producing the same, a magnetic recording medium comprising the magnetic powder produced by said method, and a method and apparatus for recording and reproducing said magnetic recording medium.
DESCRIPTION OF THE PRIOR ART
A magnetic recording medium is widely used as a video tape, a floppy disc, a credit card, a prepaid card, and so on, since it is easily recorded and reproduced.
However, the feature that the recording and reproducing are easy raises problems that recorded data tend to be erased by mistake and data are easily altered. For example, in a case of a magnetic card, accidents or crimes such that data are erased by a magnetic having a strong magnetic field which is used in various doors or handbags, or data are altered to use the magnetic card fraudulently, occur frequently.
As a countermeasure to such accidents or crimes, there is proposed a recording medium in which irreversible change is caused therein by a laser beam and once recorded data cannot be rewritten such as an optical card, or an IC card in which data cannot be altered and which has a high security. However, the optical card requires an expensive apparatus which is exclusively used with the optical card for recording and reproducing data in the optical card, and the IC card is associated with a high cost since it uses a semiconductor. Then, the optical card or the IC card cannot be substituted for the magnetic cards which are spread over the world, and has not been widely used as expected.
Then, various proposals have been made to prevent altering of the magnetic card. For example, a printing is provided on the magnetic card by a hologram printing method or a high level printing method. This method can be effective in preventing forgery in appearance but cannot prevent the altering of the data recorded on a magnetic stripe, if such altering is done by writing data which are read from other credit card on a genuine credit card which is obtained by an illegal way, and therefore, the written data are genuine. Therefore, such altering of the data cannot be prevented.
It is known that data which are once recorded on a magnetic recording medium using a MnBi magnetic powder as a recording element cannot be easily rewritten at room temperature (see Japanese Patent Publication Nos. 46801/1977, 19244/1979, 33725/1979, 38962/1982, 38963/1982 and 31764/1984). In particular, since reading apparatuses for magnetic cards are widely spread over the world, the magnetic recording media utilizing the MnBi magnetic powder attract attentions as media which can prevent accidents or crimes such as erroneous erasing of the data or intentional altering of the date in the field of credit cards or prepaid cards in which such accidents or fraudulent uses occur frequently.
However, the conventional MnBi magnetic powder has a deliquescence property inherently. When it is stored at high temperature and high humidity for a long time, it is corroded and decomposed, and its saturation magnetization is deteriorated. To solve this drawback, it is tried to surround the MnBi magnetic powder by a dense binder resin, or add a volatile rust preventive in the magnetic layer (see Japanese Patent Publication Nos. 57127/1985 and 1048/1986). However, in these methods, a shielding effect against steam which is almost in a molecular state is low, so that they cannot sufficiently prevent gradual penetration of water molecules in the magnetic layer, and does not achieve sufficient effect.
Since MnO.sub.2, an oxide of Mn which is one of the constituent elements of the MnBi magnetic powder is a stable oxide by nature, corrosion resistance of the magnetic powder may be improved, if a uniform coating of MnO.sub.2 can be formed. In general, to form MnO.sub.2, Mn should be heated at high temperature in an oxidizing atmosphere. But, when a finely ground magnetic powder for magnetic recording is heated at high temperature in the oxidizing atmosphere, its saturation magnetization is severely dec
REFERENCES:
patent: 4277806 (1981-07-01), Jeffers et al.
Derwent Publications Ltd., London, GB, Abstract No. AN 77-44523Y, May 1977.
Derwent Publications Ltd., London, GB, Abstract No. AN 77-38926Y, Apr. 1977 .
Kanzaki Hisao
Kishimoto Mikio
Kitahata Shin'ichi
Ohtani Noriaki
Sueyoshi Toshinobu
Hitachi Maxell Ltd.
Resan Stevan A.
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