JPH0777003B2 - Magnetic recording / reproducing method and apparatus - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording method and a magnetic recording / reproducing apparatus, and sometimes, payment for goods and services such as cash voucher cards, coupon cards, credit cards and the like. The present invention relates to a magnetic recording method and a magnetic recording / reproducing apparatus suitable for a system that requires high confidentiality such as used as a means.

2. Description of the Related Art Conventionally, a system using a magnetic card has been widely used for payment for finance and distribution. However, the magnetic card has a disadvantage that the recorded information can be read or rewritten by a relatively simple recording / reproducing device, while the medium itself is inexpensive, easy to handle, and easy to rewrite information. .

Magnetic cards used in systems that require high confidentiality cannot read the information written on the recording layer with a magnetic card reader that is relatively easy to obtain, or cannot visualize the magnetization pattern by developing. Is desirable. In order to meet such a demand, a magnetic recording medium and a magnetic recording / reproducing apparatus as described in the specification and drawings of Japanese Patent Application No. 61-178503 have been proposed by the present applicant. In the magnetic recording medium and the magnetic recording / reproducing apparatus, the signal magnetization of the low coercive force magnetic layer is opposite to the signal magnetization of the high coercive force magnetic layer by magnetic transfer utilizing the difference in coercive force of the two-layer magnetic body. It is generated so that the signal magnetizations cancel each other and the signal magnetic field does not leak to the outside.

Further, as disclosed in JP-A-55-93514, a high magnetic permeability material layer is provided on the magnetic layer to shield the magnetic output,
A method for disabling reading in a normal state has also been proposed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above-described magnetic recording medium and magnetic recording / reproducing apparatus, magnetic transfer means for magnetically transferring the residual magnetization of the magnetic recording layer having the highest coercive force to the magnetic recording layer having the lowest coercive force, For example,
A magnetic head for transfer and a transfer bias generator are required, and the structure of the device is complicated and the cost becomes high.

Further, the above-mentioned magnetic layer having the high magnetic permeability material layer has the following problems. That is, suitable as a magnetic shielding material, high permeability ferromagnetic metal material, such as N _i -F _e alloy, on a plastic substrate such as a magnetic card, if it is bonded in a foil shape, the deformation of the base body When stress is generated in the magnetic layer, its magnetic properties are deteriorated, and when it is applied in the form of powder or granular material, it is necessary to take special care so that the material is not chemically deteriorated in the manufacturing process. Moreover, this type of high-permeability ferromagnetic metal material is a magnetic material that is usually used for magnetic tapes, magnetic cards, etc. γF _e2 O ₃
It is very expensive as compared with cobalt-coated γF e ₂ O _{3 and the} like.

An object of the present invention is to provide a magnetic recording method and a magnetic recording / reproducing apparatus which can solve the above-mentioned problems.

According to a feature of the present invention, there is provided a magnetic recording method for recording information on a magnetic recording medium comprising at least two magnetic recording layers having different coercive forces, the magnetic recording method comprising: With respect to the medium, the output level after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers is higher than the output level due to the residual magnetization of at least two magnetic recording layers. Information is recorded with various magnetic head write current values.

According to another feature of the present invention, in a magnetic recording / reproducing method for recording and reproducing information on a magnetic recording medium formed by laminating at least two magnetic recording layers having different coercive forces, the magnetic recording medium is On the other hand, the output level after the residual magnetization of the magnetic recording layer having the lowest coercive force is erased is higher than the output level due to the residual magnetization of at least two magnetic recording layers. When information is recorded with a head write current value and the information recorded on the magnetic recording medium is reproduced, reproduction of the information is performed after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers. Is done.

According to still another feature of the present invention, in a magnetic recording / reproducing apparatus for recording / reproducing information on / from a magnetic recording medium formed by laminating at least two magnetic recording layers having different coercive forces,
For the magnetic recording medium, the output level after the residual magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers is erased is higher than the output level due to the residual magnetization of at least two magnetic recording layers. A magnetic head for recording information with a high write current value, a residual magnetization erasing means for erasing residual magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers, and the magnetic recording medium. And a reproducing means for reproducing the information recorded in.

According to another feature of the present invention, in a magnetic recording / reproducing apparatus for recording / reproducing information on / from a magnetic recording medium formed by laminating at least two magnetic recording layers having different coercive forces, Write current such that the output level after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers is higher than the output level due to the residual magnetization of at least two magnetic recording layers. A magnetic head for recording information with a value, a remanent magnetization erasing means for erasing remanent magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers, and information recorded on the magnetic recording medium. The difference between the reproducing means for reproducing and the reproducing output level of the magnetic recording medium before and after erasing the residual magnetization by the residual magnetization erasing means after recording the information by the magnetic head is known. And identification means for are provided.

Examples Next, the present invention will be described in more detail with reference to the accompanying drawings with reference to the examples of the present invention.

FIG. 1 is an enlarged sectional view showing a magnetic card as an example of a magnetic recording medium used in the present invention. As shown in FIG. 1, this magnetic card comprises a card base 1 made of vinyl chloride resin, polyester, paper, etc.
The second magnetic layer 3 and the protective layer 4 are laminated. The first magnetic layer 2, coercive force with magnetic properties of 1800O _e, for example, is formed by high-coercivity magnetic material, such as such as barium ferrite. The second magnetic layer 3 has a coercive force of 300 O _e
It is formed of a low coercive force magnetic material such as γF _e2 O ₃ having the magnetic characteristics of The protective layer 4 is made of a non-magnetic material.

A curve 5 in the graph of FIG. 2 shows a saturated recording characteristic when the magnetic card having the structure shown in FIG. 1 is written by a magnetic head having a high saturation magnetic flux density such as Sendust, that is, The relationship between the write current value and the reproduction output level at that time is shown. As can be seen from the curve 5, the saturation recording characteristics of the magnetic card showed a plurality of characteristics having two maximum values and one minimum value. The maximum value on the left side of the curve 5 shows the saturation output of the second magnetic layer 3 which is the low coercive force layer of the magnetic card. Both of the second maximum values appear due to the interaction between the signal magnetizations of the first magnetic layer that is a high coercive force layer and the second magnetic layer 3 that is a low coercive force layer, and this phenomenon is It has been confirmed by experiments that the higher the ratio of the coercive forces of both magnetic layers and the lower the coercive force of the low coercive layer, the more likely it is to occur.

A curve 6 in the graph of FIG. 2 shows the saturation of the second magnetic layer 3 of the magnetic card after the magnetic card having the structure shown in FIG. The reproduction output level after direct current demagnetization at the current value I _S , that is, the saturation recording characteristic of only the first magnetic layer 2 of the magnetic card is shown.

In FIG. 2, the horizontal axes of both curves 5 and 6 indicate the write current I _W to the magnetic card and the saturation current value I _S of the second magnetic layer 3.
The value standardized by I _W / I _S.

From the figure, curve 5 is above curve 6 between I _W / I _S from 0 to 5.5 and from 9 to 11, but I _W / I _S from 5.5 to 9 and above 11 On the contrary, it can be seen that the curve 6 is higher than the curve 5.

In this way, in the range of a certain value of I _W / I _S , curve 5 is curve 6
The reason for lowering is that when the two-layer magnetic card shown in FIG. 1 is written with a write current value higher than a certain value, the reproduction output at that time is the same as that of the second magnetic layer 3 having a low coercive force and the high coercive force. While the signal magnetizations of the first magnetic layer 2 interact with each other, they cancel each other and become lower. However, after the DC demagnetization of only the second magnetic layer 3 having the low coercive force, the interaction between the two magnetic layers is reduced. This is because the signal written in the first magnetic layer disappears and is reproduced as it is. Therefore, curve 5 and curve 6
When a signal is written to the magnetic card with a write current value lower than that, the signal output is hidden by the difference between the curve 6 and the curve 5, and the reproduction output becomes low. Even if the magnetic card reproducing apparatus normally used in this state reproduces the magnetic card, it is difficult to correctly read the contents of the written signal.

At the write current value which is the minimum value of the curve 5 where I _W / I _S is between 7 and 8, the above-mentioned effect is extremely high.

FIG. 3 shows the magnetic card of FIG. 1 with a write current 7.5 times the saturation recording current I _S of the second magnetic layer 3 and a magnetization reversal interval 70.
The oscilloscope waveform of the reproduction output after writing the signal of μm is shown. On the other hand, FIG. 4 shows an oscilloscope of the reproduction output of the first magnetic layer 2 after direct current demagnetization of the second magnetic layer 3 at a current value equal to the saturated recording current value I _S of the second magnetic layer 3 after writing a signal. It is a waveform. The amplitude of the waveform of FIG. 3 is about 1/8 of the amplitude of the waveform of FIG. 4, and the effect of concealing the recorded information content of the magnetic card by the magnetic recording / reproducing method of the present invention was confirmed.

As described above, according to the magnetic recording / reproducing method of the present invention, at least writing of a signal to a magnetic recording medium such as a magnetic card having a low coercive force magnetic layer and a high coercive force magnetic layer is performed on the magnetic recording medium. The write current value is set so that the output level after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force is higher than the output level due to the residual magnetization of the two magnetic recording layers. As a result, in the written state, almost no signal magnetic field is generated outside due to the interaction between the signal magnetizations of the first magnetic layer (high coercive force magnetic layer) and the second magnetic layer (high coercive force magnetic layer). because it is not in a normal magnetic card reader, it can not be read out signal, when DC demagnetization the second magnetic layer in the saturation current value I _S of the second magnetic layer disappears interaction of both magnetic layers It can be read the written signals to a first magnetic layer. It is also possible to determine the authenticity of the magnetic card by comparing the output level at this time with the output level after writing and before DC demagnetization.

Although the magnetic recording medium has only two magnetic layers having different coercive forces in the above-described embodiments, the present invention is not limited to this and is also applicable to a magnetic recording medium having three or more layers. And is effective.

FIG. 5 is a block diagram schematically showing a configuration example of an apparatus for carrying out the magnetic recording / reproducing method of the present invention. The magnetic recording / reproducing apparatus shown in FIG. 5 includes a first magnetic head 7 for writing and reading an information signal on a magnetic recording medium such as the magnetic cards 1, 2, 3 and 4 shown in FIG. And a second magnetic head 8 for demagnetizing the residual magnetization of the second magnetic layer 3 of the magnetic recording medium, and a recording information signal is read from the first magnetic layer 2 after demagnetization by the second magnetic head 8. For the third magnetic head 9 and the first magnetic head 7 for this purpose, the coercive force of the magnetic recording layer is higher than the output level due to the residual magnetization of at least two magnetic recording layers of the magnetic recording medium. Writing and reading for writing with a write current value such that the output level becomes higher after erasing the residual magnetization of the low magnetic recording layer and for performing reading in the state after the writing as it is A circuit 10; a DC degaussing circuit 11 for causing the second magnetic head 8 to perform a DC degaussing for erasing the residual magnetization of the second magnetic layer 3 after writing by the first magnetic head 7; Read circuit 12 for making the magnetic head 9 read the recorded information signal from the first magnetic layer 2 after direct current demagnetization by the second magnetic head 8, and before direct current demagnetization from the writing and reading circuit 10. If the difference between the read output level and the read output level after demagnetization from the reading circuit 12 is not a predetermined value, the magnetic recording medium is forged or falsified and a rejection signal is given. It is provided with a true / false determination circuit 13 for generating. In this device configuration example, three magnetic heads 7,
I used 8 and 9, but if you use an appropriate head switching circuit, you can share either one,
It is possible to reduce the number of magnetic heads used.

Effects of the Invention According to the present invention, the following effects can be obtained.

(1) Since it is difficult to read the written signal with an ordinary magnetic card reader and to visually observe it by developing the magnetization pattern or using a viewer, it is difficult to falsify the magnetic information.

(2) Economical because no special device or energy is required to hide the output of the written signal.

(3) The magnetic material forming the magnetic recording medium may be any of those used in ordinary magnetic cards, etc., and is stable in characteristics and easy to manufacture.

(4) Since the write current value at which the magnetic recording medium has a minimum value in its saturation recording characteristic differs depending on the magnetic characteristic of the low coercive force layer of the medium and the material and shape of the writing magnetic head, a proper procedure is not taken. A forged or altered product can be easily detected.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view showing a magnetic card as an example of a magnetic recording medium used in the present invention, and FIG.
FIG. 3 is a diagram showing saturation recording characteristics when the magnetic card having the structure shown in FIG. 1 is written by a writing magnetic head and read output characteristics after the second magnetic layer of the magnetic card is degaussed by DC. The magnetic card shown in FIG. 1 was subjected to a magnetization reversal interval of 7 with a write current 7.5 times the saturation recording current I _S of the second magnetic layer.
Fig. 4 shows the oscilloscope waveform of the playback output after writing the 0 µm signal, and Fig. 4 shows the second waveform after writing the signal.
FIG. 5 shows an oscilloscope waveform of the reproduction output of the first magnetic layer after direct current demagnetization of the second magnetic layer at a current value equal to the saturation recording current value of the magnetic layer. FIG. 5 shows the magnetic recording / reproducing method of the present invention. It is a block diagram which shows roughly the structural example of the apparatus for doing. 1 ... Card base, 2 ... First magnetic layer, 3 ... Second magnetic layer, 4 ... Protective layer, 5 ... Saturation recording characteristic curve, 6 ... Reproduction output characteristic curve after demagnetization, 7, 8 , 9 ... Magnetic head, 10 ... Writing and reading circuit, 11 ... DC degaussing circuit, 12 ... Reading circuit, 13 ... Authenticity judging circuit.

Claims (8)

[Claims] 1. A magnetic recording method for recording information on a magnetic recording medium comprising at least two magnetic recording layers having different coercive forces, wherein at least two magnetic recording layers are formed on the magnetic recording medium. Information is recorded with a magnetic head write current value such that the output level after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force is higher than the output level due to the residual magnetization. A magnetic recording method characterized by: 2. The magnetic recording method according to claim 1, wherein a ratio of coercive forces of the at least two magnetic recording layers of the magnetic recording medium is 5 times or more. 3. A magnetic recording / reproducing method for recording / reproducing information on / from a magnetic recording medium comprising at least two magnetic recording layers having different coercive force, wherein at least two magnetic layers are provided for the magnetic recording medium. Information is recorded with a magnetic head write current value such that the output level after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force is higher than the output level due to the residual magnetization of the recording layer. In reproducing the information recorded and recorded on the magnetic recording medium, the information is reproduced after the residual magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers is erased. Magnetic recording / reproducing method. 4. The magnetic recording / reproducing method according to claim 3, wherein a ratio of coercive forces of the at least two magnetic recording layers of the magnetic recording medium is 5 times or more. 5. A magnetic recording / reproducing apparatus for recording / reproducing information on / from a magnetic recording medium having at least two magnetic recording layers having different coercive forces laminated, wherein at least two magnetic layers are provided for the magnetic recording medium. Information is recorded at a write current value such that the output level after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force in the magnetic recording layer is higher than the output level due to the residual magnetization of the recording layer. Magnetic head, a remanent magnetization erasing means for erasing the remanent magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers, and a reproducing means for reproducing information recorded on the magnetic recording medium. A magnetic recording / reproducing apparatus comprising: 6. The magnetic recording / reproducing apparatus according to claim 5, wherein a ratio of coercive forces of the at least two magnetic recording layers of the magnetic recording medium is 5 times or more. 7. A magnetic recording / reproducing apparatus for recording and reproducing information on a magnetic recording medium which is formed by laminating at least two magnetic recording layers having different coercive forces. Information is recorded at a write current value such that the output level after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force in the magnetic recording layer is higher than the output level due to the residual magnetization of the recording layer. Magnetic head, a remanent magnetization erasing means for erasing the remanent magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers, and a reproducing means for reproducing information recorded on the magnetic recording medium. And an identification means for identifying a difference in reproduction output level of the magnetic recording medium after the information is recorded by the magnetic head and before and after the residual magnetization is erased by the residual magnetization erasing means. Magnetic recording and reproducing apparatus comprising: a. 8. The magnetic recording / reproducing apparatus according to claim 7, wherein a ratio of coercive forces of the at least two magnetic recording layers of the magnetic recording medium is 5 times or more.