JPH0250528B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium effective for preventing counterfeiting of magnetic cards. In recent years, magnetic recording media have become extremely popular, and are used in cash cards and magnetic bankbooks used in banks, as well as magnetic commuter passes, magnetic tickets, and expressway passes used in public transportation. With the spread of such magnetic cards, there has recently been a concern that these magnetic cards may be misused by being counterfeited or duplicated. For example, if the recorded magnetization of a magnetic commuter pass could be duplicated, a single commuter pass could be used by many people, which would be inconvenient. Generally speaking, there are two methods for duplicating magnetic recording. One is recording using a magnetic head, which is a normal magnetic recording and reproducing method. Although this method is the most common and well-known method, it is difficult to actually reproduce it because the mechanical parts, electric circuits, etc. are complicated and requires considerable specialized knowledge. Another method of reproduction is the magnetic transfer method. This can be further divided into two ways. These are the so-called thermomagnetic transfer method and the contact magnetic transfer method. Thermomagnetic transfer involves placing a regular magnetic card (hereinafter referred to as the master) and a magnetic card prepared for duplication (hereinafter referred to as the slave) in close contact with each other with their magnetic surfaces. This method applies a temperature slightly higher than the Curie temperature and then cools it to magnetize the slave. Contact magnetic transfer is a method of magnetizing the slave by bringing the master and slave into close contact with each other and simply applying a bias magnetic field slightly higher than the coercive force of the slave magnetic material. This method requires a master with high coercivity, which is said to be at least 2.5 times that of the slave. Until now, most magnetic cards had a coercive force of less than 700 Oe, but recently magnetic cards have been made to have higher coercive forces, and some have a coercive force of up to 3000 Oe.
This is to prevent data from being demagnetized by permanent magnets and improve reliability.
This trend is expected to continue in the future. With the advent of this type of magnetic card, there is an increasing concern that it can be easily counterfeited because it can be copied by contact magnetic transfer. SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a system that enables easy detection of a copy when it is copied by contact magnetic transfer or thermomagnetic transfer, and that prevents counterfeiting. An object of the present invention is to provide an effective magnetic recording medium. According to the present invention, a high coercivity magnetic layer, a high permeability magnetic layer, and a low coercivity magnetic layer are sequentially laminated on a substrate from the substrate side, and the high permeability magnetic layer is always
It exhibits a magnetic shielding effect against the signal magnetization for forgery prevention recorded in the high coercive force magnetic layer,
The above object is achieved by a magnetic recording medium that is characterized in that it loses the magnetic shielding effect during magnetic transfer. Further, according to the present invention, by forming the high permeability magnetic layer with temperature-sensitive ferrite, a magnetic layer that can easily detect not only contact magnetic transfer but also thermomagnetic transfer duplication is provided. It is considered a record. Next, the present invention will be described in detail with reference to embodiments of the present invention based on the accompanying drawings. FIG. 1 is a longitudinal sectional view of a magnetic card using a magnetic recording medium according to an embodiment of the present invention. A high coercive force magnetic layer 2, a high permeability magnetic layer 3, a low coercive force magnetic layer 4, and a protective layer 5 are sequentially laminated on a magnetic card base 1. Now, an arbitrary signal is recorded on the high coercive force magnetic layer 2 of this magnetic card by a magnetic head. Further, after this, regular data is recorded in the low coercive force magnetic layer 4 by the magnetic head. At this time,
If the recording current applied to the magnetic head is appropriately set, it will hardly affect the signal magnetization recorded on the high coercive force magnetic layer 2. When a magnetic card magnetized in this manner is reproduced by a magnetic head, the signal on the high coercive force magnetic layer 2 is magnetically shielded by the high permeability magnetic layer 3 and hardly appears as an output.
Therefore, data is observed as if it were recorded only on the low coercive force magnetic layer 4. Now, let us consider the case where this magnetic card is reproduced by contact magnetic transfer. A regular magnetic card recorded as described above and a magnetic card prepared for duplication are brought into close contact with each other with their magnetic surfaces facing each other, and a transfer magnetic field is applied. At this time, the high permeability magnetic layer 3 is magnetically saturated by the transfer magnetic field and its magnetic permeability is significantly reduced, so that the magnetic shielding effect is lost. Therefore, the signal magnetic field recorded on the high coercive force magnetic layer 2 reaches the magnetic surface of the magnetic card to be copied and is magnetically transferred. In the end, both the regular signal recorded in the low coercive force magnetic layer 4 and the arbitrary signal recorded in the high coercive force magnetic layer 2 are recorded on the duplicated magnetic card.
Therefore, if this duplicated magnetic card is reproduced by a magnetic head, it will be read as a signal different from that of a regular magnetic card, and it will be easily detected that it is a duplicate. Next, a more specific example of manufacturing a magnetic recording medium according to the present invention and its experimental results will be described. A magnetic paint of the composition A shown below was applied to a 188μ titanium oxide-mixed polyethylene terephthalate base as substrate 1 using a gravure coater to a thickness of 6μ after drying, and after drying, it was left in a constant temperature bath at 60℃ for 48 hours. As a result, a high coercive force magnetic layer 2 is obtained. Composition A Barium ferrite powder (coercive force 3000Oe, average particle size 0.7μ) …100 parts by weight Surfactant …3 Salt vinyl acetate resin …12 Urethane resin …18 Isocyanate resin …3 Methyl ethyl ketone …60 Methyl isobutyl ketone …60 Toluene …60 On top of the coating as described above, a magnetic paint of composition B shown in the table below was applied using a gravure coater to a thickness of 15 μm after drying, and then heated again at 60°C after drying.
The high permeability magnetic layer 3 is obtained by leaving it in a constant temperature bath for 48 hours. Composition B Fe-Al-Si alloy powder (average particle size 7μ)
…100 parts by weight Surfactant …1 Salt vinyl acetate resin …8 Urethane resin …12 Isocyanate resin …2 Methyl ethyl ketone …30 Methyl isobutyl ketone …30 Toluene …30 Further, on the base coated as above, the following composition C was applied. 6μ thickness after drying magnetic paint
Apply with a gravure coater so that
The low coercive force magnetic layer 4 is formed by leaving it in a constant temperature bath at 60° C. for 48 hours. Composition C Barium ferrite powder (coercive force 1700Oe, average particle size 0.7μ) …100 parts by weight Surfactant …3 Salt vinyl acetate resin …12 Urethane resin …18 Isocyanate resin …3 Methyl ethyl ketone …60 Methyl isobutyl ketone …60 Toluene …60 Further, a protective layer 5 is applied thereon to a thickness of 3 μm after drying. The magnetic properties of each magnetic layer thus formed were as shown in the table below.

[Table] The magnetic layer forming base obtained in this way is approximately 85 mm
It was punched out to a size of 54 mm and made into a magnetic card. Evaluation Recording current of 300 mA using Fe-Co alloy amorphous magnetic head with gap length of 30 μ and track width of 6 mm.
All 1s are recorded using the NRZI method and a recording density of 210 BPI. Furthermore, the recording current is
All 1s are recorded using the NRZI method at 200mA and a recording density of 150BPI. Gap this magnetic card by 20μ,
When I read it with a magnetic head with a track width of 2mm, I was able to read only 150BPI, all 1 data. This is thought to be because the signal magnetization recorded in the high coercive force magnetic layer is magnetically shielded by the high permeability magnetic layer, and the output for the signal magnetization is below the slicing level of the reading device. Next, in order to copy this magnetic card by contact magnetic transfer, prepare a magnetic card with a coercive force of 300 Oe and a residual magnetic flux of 1.0 mask well/cm, and place the magnetic surfaces of both magnetic cards in close contact with each other so that they face each other to maximize the magnetic field.
A 500 Oe 250 Hz AC damping magnetic field was applied. The output of the duplicated magnetic card was 4.0V, but the 150BPI all 1 output waveform was modulated by the 210BPI all 1 signal and could not be read. This is because the high permeability magnetic layer is magnetically saturated due to the transfer magnetic field, and the magnetic shielding effect is significantly reduced.
Signals recorded on the high coercive force magnetic layer are magnetically transferred,
It is thought that an error occurred when reading all 1 data at 150 BPI. In the above embodiment, the high coercive force layer is a continuous film, and
Although arbitrary signals were recorded by a magnetic head, this high coercive force magnetic layer does not have to be a continuous film. FIG. 2 is a longitudinal sectional view of a magnetic card using a magnetic recording medium, which is another embodiment of the present invention. Since this is an explanatory drawing, the dimensional ratio is not accurate. On the magnetic card base 1, a high coercive force magnetic layer 6 is printed not as a continuous film but in a predetermined pattern shape, and a high permeability magnetic layer 3, a low coercive force magnetic layer 4, and a protective layer 5 are formed on top of the high coercive force magnetic layer 6. ing. Even with this configuration,
Of course, if the patterned high coercive force magnetic layer 6 is magnetized in advance, the intended effect of the present invention can be achieved in preventing duplication by contact magnetic transfer. In addition, in the above-mentioned example, Fe-Al-Si alloy powder was used as the high permeability magnetic material, but permalloy,
Similar effects can be obtained with metal powders such as amorphous metal and carbonyl iron, and ferrite powders such as Mn-Zn ferrite and Ni-Zn ferrite. Further, the high permeability magnetic layer may be not only a powder dispersed coating but also a vapor deposited film or foil of the above-mentioned materials. The above has described the prevention of duplication by contact magnetic transfer, but if temperature-sensitive ferrite is used as the material for the high permeability magnetic layer 3, the high permeability magnetic layer 3 will be heated even against duplication by thermomagnetic transfer. Since the magnetic permeability is significantly reduced and the magnetic shielding effect is lost, a signal that prevents normal data reading is transferred to the copied magnetic card, thereby preventing copying. That is, it is possible to prevent both duplication by contact magnetic transfer and duplication by thermomagnetic transfer. According to the structure of the magnetic recording medium of the present invention, duplication can be easily detected and prevented using existing reading devices and electric circuits, which is both easy and economical.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a magnetic card using a magnetic recording body which is one embodiment of the present invention, and FIG. 2 is a longitudinal cross-sectional view of a magnetic card using a magnetic recording body which is another embodiment of the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Magnetic card base, 2, 6... High coercive force magnetic layer, 3... High permeability magnetic layer, 4... Low coercive force magnetic layer, 5... Protective layer.

Claims (1)

[Claims] 1. On a substrate, from the substrate side, a high coercive force magnetic layer,
A high permeability magnetic layer and a low coercive force magnetic layer are sequentially laminated, and the high permeability magnetic layer normally exhibits a magnetic shielding effect against the signal magnetization for forgery prevention recorded in the high coercive force magnetic layer. . A magnetic recording body characterized in that the magnetic shielding effect is lost during magnetic transfer. 2. The magnetic recording body according to claim 1, wherein the high coercive force magnetic layer is a continuous film. 3. The magnetic recording body according to claim 1, wherein the coercive force magnetic layer has a predetermined pattern shape. 4. The magnetic recording body according to claim 1, 2, or 3, wherein the high permeability magnetic layer is made of temperature-sensitive ferrite.