JPH02122420A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve so-called security of the medium by depositing a magnetic recording layer on a substrate, a first thermomagnetic transfer layer comprising such a magnetic material having low Curie point and larger coercive force at room temperature than that of the magnetic recording layer, and a second thermomagnetic transfer layer comprising such a magnetic material having smaller coercive force at room temperature than that of the first thermomagnetic transfer layer. CONSTITUTION:The magnetic recording medium 1 is composed of the substrate 2, the magnetic recording layer 3 containing gamma-Fe2O3 particles dispersed in a binder, the second thermomagnetic transfer layer 4 with CrO2 particles dispersed in a binder and the first thermomagnetic transfer layer with Sr ferrite particles dispersed in a binder. Magnetization of the recording layer in which informations are recorded, magnetization of the first thermomagnetic transfer layer 5 and magnetization of the second thermomagnetic transfer layer 4 make closed loops of magnetic flux, so that the magnetic flux does not leak from the recording medium. The informations thermomagnetically transferred into the first thermomagnetic transfer layer 5 can be kept by very large coercive force of the layer at room temperature. Thereby, recorded informations can be stably maintained against magnetic fields from outside generated by magnets such as that used for a handbag lid. Moreover, the recorded informations can be protected from modification by general techniques.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium suitable for use as an ID card, a prepaid card, or the like.

[Prior Art/Problems to be Solved by the Invention] In ID cards, prepaid cards, etc., so-called security is becoming more and more important. In particular, there is a long-awaited measure that can stably hold recorded information against magnetic fields from stopper magnets such as handbags, and can prevent falsification of recorded information. The coercive force of the magnetic material of the magnetic recording layer is 3.0.
A card with an improved level of 0.00 OE has been developed, but since a magnetic field with a value larger than the coercive force is generated from the yoke of the stopper magnet where magnetic flux is concentrated, there is still a risk that the magnetically recorded information on the card will be erased. Remaining. Furthermore, since the card is recorded and reproduced using a general ring-shaped magnetic head,
There was a drawback that magnetic heads could be easily obtained and magnetically recorded information could be tampered with.

An object of the present invention is to provide a magnetic recording medium suitable for ID cards, prepaid cards, etc., which can stably retain recorded information against magnetic fields from stopper magnets in handbags, etc., and can prevent the recorded information from being tampered with using general techniques. The goal is to provide a medium.

[Means to solve the problem]

The magnetic recording medium according to the present invention includes a magnetic recording layer on a substrate, a Curie point as low as possible for thermomagnetic transfer of magnetic recording information in the magnetic recording layer using a heating head, and a coercive force of the magnetic recording layer at room temperature. a first thermomagnetic transfer layer made of a magnetic material with a coercive force larger than the magnetic force, for example, so large that magnetic recording cannot be performed with a general ring-shaped magnetic head; and a coercive force of the first thermomagnetic transfer layer whose coercive force at room temperature is and a second thermomagnetic transfer layer made of a magnetic material having a smaller Curie point lower than that of the first thermomagnetic transfer layer.

[Effect]

In the magnetic recording medium according to the present invention, by heating the first thermomagnetic transfer layer with a heating head to a temperature higher than the Curie point of the magnetic material and then cooling it naturally, the magnetically recorded information on the magnetic recording layer is transferred to the first thermomagnetic transfer layer. Thermomagnetic transfer can be performed on the magnetic transfer layer. Furthermore, during the natural cooling process, excess magnetization of the magnetic recording layer can be magnetically absorbed by the second thermomagnetic transfer layer. In other words, the magnetization of the magnetic recording layer in which information is recorded, the magnetization of the first thermomagnetic transfer layer, and the magnetization of the second thermomagnetic transfer layer create a closed loop of magnetic flux, so that the magnetic flux does not leak out from the magnetic recording medium. . The information thermomagnetically transferred to the first thermomagnetic transfer layer is transferred to the magnetic recording layer and the second thermomagnetic transfer layer using a magnetic field that is less than or equal to the coercive force of the first thermomagnetic transfer layer at room temperature. It can be played back while being saturated. therefore,
The thermomagnetic transferred information of the first thermomagnetic transfer layer is stably retained against the magnetic field from a stopper magnet of a handbag, etc., because the coercive force of the first thermomagnetic transfer layer at room temperature can be made very large. Furthermore, since the magnetic flux generated by magnetization when information is magnetically recorded does not leak out from the magnetic recording medium, it is impossible to falsify or even reproduce information using a general ring-shaped magnetic head.

〔Example〕

FIG. 1 is a partially cutaway perspective view of an embodiment of the magnetic recording medium according to the present invention, where ■ is the magnetic recording medium, 2 is the substrate, and 3 is γ.
-F e= A magnetic recording layer formed by dispersing 03 particles in a binder, 4 a second thermomagnetic transfer layer formed by dispersing Croy particles in a binder, 5 a magnetic recording layer formed by dispersing Sr ferrite particles in a binder. The first thermomagnetic transfer layer is dispersed therein. Here, γ-Fe.

The coercive force of 01 particles is approximately 350 oe, and the Curie point is approximately 59.
At 0℃, the coercive force of Cro particles at room temperature is about 450
oe, Curie point is about 120°C, coercive force of Sr ferrite particles is about 5.000oe, Curie point is about 180°
It is C. The magnetic recording layer 3, the second thermomagnetic transfer layer 4, and the first thermomagnetic transfer layer 5 have approximately the same thickness, but the first thermomagnetic transfer layer 5 uses Sr ferrite particles with a low Curie point. Therefore, its saturation magnetization is ⅓ or less of the saturation magnetization of the magnetic recording layer 3.

Next, information recording and reproduction in an embodiment of the magnetic recording medium according to the present invention will be explained using the drawings. FIG. 2 is a diagram for explaining information recording, and FIG.
A) is a diagram showing the magnetization state when information is recorded on the magnetic recording layer 3 by the ring-shaped magnetic helad 6. At this time, information is also recorded on the second thermomagnetic transfer layer 4, but it is not important.

The solid arrow indicates magnetization, the broken line indicates the main magnetic flux is a loop, and the arrow) indicates the direction of movement of the magnetic recording medium 1 with respect to the head. Second
FIG. 2B is a diagram showing the recording information of the magnetic recording layer 3 being thermomagnetically transferred to the first thermomagnetic transfer layer 5 by the heating head 7. FIG. The Curie point of the magnetic recording layer 3 is approximately 590°C1
Since the Curie point of the first thermomagnetic transfer layer 5 is about 180'C, the heating head 7
The thermomagnetic transfer layer 4 is heated to a temperature of about 200° C., and the magnetic recording medium I is moved in the direction of the arrow with respect to the heating head.

Since the second thermomagnetic transfer layer 4 is non-magnetic until it is naturally cooled to about 120°C, which is the Curie point of the second thermomagnetic transfer layer 4, the magnetically recorded information in the magnetic recording layer 3 is transferred to the first thermomagnetic transfer layer 4. Thermomagnetic transfer can be reliably performed on the transfer layer 5. At this time, since the saturation magnetization of the first thermomagnetic transfer layer 5 is 1/3 or less of the saturation magnetization of the magnetic recording layer 3, a part of the magnetization of the magnetic recording layer 3 due to recording of information is The magnetization of the first thermomagnetic transfer layer 5 due to the thermomagnetic transfer creates a closed loop of magnetic flux. FIG. 2(c) is a diagram showing the state in which excess magnetization of the magnetic recording layer 3 that does not create a closed loop of magnetization and magnetic flux of the first thermomagnetic transfer layer 5 is magnetically absorbed by the second thermomagnetic transfer layer 4. It is. When the second thermomagnetic transfer layer 4 is naturally cooled to about 120° C. or below, it becomes magnetic, and by the time it reaches room temperature, the excess magnetization of the magnetic recording layer 3 is transferred to the second thermomagnetic transfer layer 4. This creates a closed loop of magnetization and magnetic flux in the second thermomagnetic transfer layer 4 due to the thermomagnetic transfer of recorded information. That is, the extra magnetization of the magnetic recording layer 3 is magnetically absorbed by the second thermomagnetic transfer layer 4, and the magnetic flux generated from magnetically recording information does not leak out from the magnetic recording medium 1.

FIG. 3 is a diagram for explaining reproduction from a magnetic recording medium according to the present invention. FIG. While magnetically saturating the magnetic recording layer 3 and the second thermomagnetic transfer layer 4 by generating a magnetic field larger than the coercive force of the recording layer 3 and the second thermomagnetic transfer layer 4 at room temperature, a magnetic field is applied to the first thermomagnetic transfer layer 5. FIG. 6 is a diagram showing how thermomagnetically transferred information is reproduced by a ring-shaped magnetic head 6'. As is clear from FIG. 3, information cannot be reproduced unless there is a means to magnetically saturate the magnetic recording layer 3 and the second thermomagnetic transfer layer 4. That is, with only a general ring-shaped magnetic head, it is impossible to falsify or even reproduce information. Note that the magnetization of the first thermomagnetic transfer layer 5 due to the thermomagnetic transfer of the recorded information is caused by the heating head 7 shown in FIG. 2(b) after the reproduction.
Erasing can be achieved by heating the first thermomagnetic transfer layer 5 to a temperature of about 200° C. and allowing it to cool naturally.

In the embodiment shown in FIG. 1, the magnetic recording layer 3, the second thermomagnetic transfer layer 4, and the first thermomagnetic transfer layer 5 are laminated in this order. may be in any order as long as the magnetic recording layer 3 is not the top layer.

Furthermore, in the embodiment shown in FIG. 1, the thicknesses of the magnetic recording layer 3, the second thermomagnetic transfer layer 4, and the first thermomagnetic transfer layer 5 are made almost equal. If it becomes thicker, the recording loss when recording information on the magnetic recording layer 3 increases,
This is also to prevent an increase in variations in recording and reproducing output (module rayon) due to deterioration in the flatness of the surface of the magnetic recording medium as the total layer thickness increases.

Although the magnetic material of the second thermomagnetic transfer layer is described as Cro particles, if the magnetic material has a smaller coercive force at room temperature and a lower Curie point than the magnetic material of the first thermomagnetic transfer layer, it can be used at room temperature. Magnetic amorphous particles whose coercive force is too small to be suitable for magnetic recording, such as FeCoCrSi
It is clear that B amorphous particles or the like may be used. Further, the magnetic material of the magnetic recording layer includes those used in general magnetic recording, and other magnetic materials of the first thermomagnetic transfer layer include rare earth alloy particles. In addition,
When rare earth alloy particles are used as the magnetic material of the first thermomagnetic transfer layer, the rare earth alloy particles are expensive, but according to the present invention, the first thermomagnetic transfer layer is made thinner and the second thermomagnetic transfer layer is made thinner. The transfer layer can be made thicker, and a fixed-price magnetic recording medium can be provided accordingly.

〔Effect of the invention〕

As explained above, according to the present invention, recorded information is stably held against magnetic fields from stopper magnets of handbags, etc., and tampering of the recorded information by common techniques can be prevented, that is, so-called security is improved. Can provide high magnetic recording media.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of an embodiment of the magnetic recording medium according to the present invention, and FIGS. 2 (A) to (C) are diagrams for explaining information recording in the embodiment of the magnetic recording medium according to the present invention. , FIG. 3 is a diagram for explaining reproduction of information. ■... Magnetic recording medium, 2... Substrate, 3
. . . Magnetic recording layer, 4 . . . Second thermomagnetic transfer layer, 5 . . . First thermomagnetic transfer layer.

Claims (1)

[Claims] On a substrate, a magnetic recording layer, a first thermomagnetic transfer layer made of a magnetic material whose coercivity at room temperature is larger than that of the magnetic recording layer and whose Curie point is lower than the Curie point of the magnetic recording layer, and and a second thermomagnetic transfer layer made of a magnetic material having a coercive force smaller than that of the first thermomagnetic transfer layer and a Curie point lower than that of the first thermomagnetic transfer layer. magnetic recording media.