Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Patent
1991-06-18
1995-03-07
Resan, Stevan A.
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
428327, 428328, 428329, 428335, 428336, 428337, 428412, 428421, 428422, 4284259, 428694BF, 428900, 235493, 283 82, 283904, 360 2, G11B 500
Patent
active
053956729
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a large-capacity magnetic memory as well as to a method implemented in its manufacture. This card is particularly useful for setting up a system of decentralized portable files.
High density magnetic recording media having information density values of more than 50 kbits/cm.sup.2 are known. However, they can be erased either by external fields or by mechanical effects, and are used only on tapes or disks that can be protected by sleeves, or on cassettes. This is why, up till now, magnetic recording media on cards having an information density of more than 5 kbits/cm.sup.2 have not been commercially available, the usual density of known magnetic cards being in the range of 0.1 to 0.3 kbits/cm.sup.2. Portable cards, in their common uses, are subjected to handling and to environmental stresses that may damage the magnetic layer and the information stored therein, all the more irremediably as the density of the information in the layer is higher. Besides, the magnetic medium should be incapable of being erased by the usual external magnetic fields in order to ensure safety, and it should withstand wear and tear so that the information can be re-read a great many times.
It would be highly desirable to have a magnetic card that is capable of containing a large quantity of data that can be replenished or updated and, at the same time, has appropriate characteristics of safety and permanence.
Such a card could be used for numerous applications such as personal or individual medical files in human and veterinary medicine, machine maintenance sheets, the management of parking lots, stocks, livestock, operations on bank accounts etc.
The manufacturing of such a card, however, raises many difficulties.
It is known that high recording density calls for the smallest possible head/layer spacing, in order to maintain the quality of the signal during the writing and reading operations. However, to protect the magnetic layer during the usual handling operations, a protective overcoat is generally provided. This overcoat contributes to an increase in the head/layer spacing. The two above-named goals, namely signal quality and protection protection, are therefore incompatible a priori.
Furthermore, the card support and the magnetic medium itself must have a certain elasticity, i.e. they should be capable of recovering their initial shape even after repeated bending, and of doing so without causing any cracks in the magnetic medium. Hence, said medium should not be brittle. Nor should it be too soft for it would then be less resistant to wear and an overcoat would be unavoidably necessary. The card should also be thermally stable to withstand the usual environmental temperatures without deformation. These requirements of elasticity and heat stability are particularly important for a high-capacity card that has to contain a large number of tracks/cm. The poly(vinyl chloride) supports commonly used for low-density magnetic cards (bearing ISO tracks for example) tolerate these stresses more easily since they have only a few tracks and are therefore less dependent on an accurate positioning of the head with respect to the layer.
An object of the present invention is a high-capacity magnetic memory card made of a semi-rigid and dimensionally stable support having, on the major part of at least one of its surfaces, a magnetic recording medium containing magnetic particles having a coercive field strength of over 4,000 Oe (320 kA/m) and, preferably, over 5,000 Oe (400 kA/m), a binder and additives, said medium having no overcoat and exhibiting an electrical wear corresponding to a loss of electric signal of less than 5% for 2,000 passes, and preferably for more than 20,000 passes, an average peak-to-valley height of less than 10 nm, an abrasive characteristic of less than 600 .mu.m, scratch resistance of less than 1.5 .mu.m and an information density of at least 5 kbits/cm.sup.2, preferably higher than 50 kbits/cm.sup.2.
The above parameters shall be defined further below in the description of the mea
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Kiota
Resan Stevan A.
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