JPS63273202A - Method and device for magnetic recording and reproduction - Google Patents

Abstract

PURPOSE:To improve a masking effect, by writing with a current value whose output level after erasing the remaining magnetization of a magnetic recording layer with a low coercive force higher than that by the remaining magnetization of two magnetic recording layers with different coercive forces. CONSTITUTION:A magnetic recording medium is formed by laminating a first magnetic layer 2 of a magnetic material with the high coercive force, a second magnetic layer 3 of the magnetic material with the low coercive force, and the protection layer 4 of a non-magnetic material. Write is performed on the recording medium with the current value in which the output value after erasing the remaining magnetization of the layer 3 with the low coercive force is set higher than the output level due to the remaining magnetization of two layers 2 and 3. In such a way, no signal leakage to the output occurs by the mutual function of the magnetization of the layers 2 and 3, and the mutual function of the layers 2 and 3 disappears by de-magnetizing the layer 3 with a saturation current, and the signal of the layer 2 can be read out. In such a way, it is possible to improve the masking effect of the recording medium, and to easily find forgery or alteration.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magnetic recording method and a magnetic recording/reproducing device, and is particularly used for payment of goods and services such as coupon cards, coupon cards, credit cards, etc. The present invention relates to a magnetic recording method and a magnetic recording/reproducing apparatus suitable for systems that require high secrecy, such as when used as a magnetic recording device.

Conventional Technology Conventionally, systems using magnetic cards have been widely used for payment in finance, distribution, etc. However, although the medium itself of magnetic cards is inexpensive, easy to handle, and information can be easily rewritten, the disadvantage is that the recorded information can be read and rewritten using a relatively simple recording/reproducing device. .

Magnetic cards used in systems that require high secrecy cannot read the information written on the recording layer with a relatively easily obtained magnetic card reader, nor can the magnetization pattern be seen visually by developing it. This is desirable. In order to meet such demands, a magnetic recording medium and a magnetic recording/reproducing apparatus have been proposed as described in the specification and drawings of Japanese Patent Application No. 178503/1983 filed by the present applicant. In this magnetic recording medium and magnetic recording/reproducing device, the signal magnetization of the low coercive force magnetic layer is reversed from the signal magnetization of the high coercive force magnetic layer by magnetic transfer by utilizing the difference in coercive force between the two-layered magnetic material. Generate it in the direction,
The respective signal magnetizations cancel each other out to prevent the signal magnetic field from leaking to the outside.

Also, Japanese Patent Publication No. 1986-55. A method disclosed in Japanese Patent No. 93514 has also been proposed in which a layer of high magnetic permeability material is provided on the magnetic layer to shield magnetic output and disable reading under normal conditions.

Problems to be Solved by the Invention The above-described magnetic recording medium and magnetic recording/reproducing device include a magnetic transfer means for magnetically transferring residual magnetization of a magnetic recording layer having a high coercive force to a magnetic recording layer having a lowest coercive force; for example,
On the other hand, a magnetic head for transfer and a transfer bias generating device are required, and the device configuration becomes complicated and expensive.

Further, the above-mentioned device in which a layer of high magnetic permeability material is provided on the magnetic layer has the following problems. In other words, when a high magnetic permeability ferromagnetic metal material such as N, -F, or alloy, which is suitable as a magnetic shielding material, is adhered in the form of a foil onto a plastic substrate such as a magnetic card, it may cause deformation of the substrate. If stress is generated in the magnetic layer, its magnetic properties will deteriorate, and when it is applied in the form of powder or granules, special care must be taken to avoid chemical alteration of the material during the manufacturing process. Moreover, this type of high magnetic permeability ferromagnetic metal material is rF, which is a magnetic material normally used for magnetic tapes, magnetic cards, etc.
, 20s and cobalt-coated type TF-203.

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

Means for Solving the Problems According to one feature of the present invention, in a magnetic recording method for recording information on a magnetic recording medium formed by laminating at least two magnetic recording layers having different coercive forces, the magnetic recording For the medium, the output level after erasing the residual magnetization of the magnetic recording layer with 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 a magnetic head write current value.

According to another feature of the present invention, in addition to the magnetic recording and 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, For the magnetic recording medium, the output level after erasing the residual magnetization of the magnetic recording layer with 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 a magnetic head write current value such that the information recorded on the magnetic recording medium is reproduced after erasing the residual magnetization of the magnetic recording layer having the lowest coercive force among the magnetic recording layers. The information is reproduced.

According to still another feature of the present invention, in a magnetic recording and reproducing apparatus for recording and reproducing information on 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 erasing the residual magnetization of the magnetic recording layer with 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 write current value that increases, a residual magnetization erasing means for erasing residual magnetization of a magnetic recording layer having the lowest coercive force among the magnetic recording layers, and the magnetic recording medium. and reproducing means for reproducing information recorded on the recording medium.

According to another feature of the present invention, in a magnetic recording and reproducing apparatus for recording and reproducing information on 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 with 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 as a value; a residual magnetization erasing means for erasing residual magnetization of a magnetic recording layer having the lowest coercive force among the magnetic recording layers; A reproduction means for reproduction, and an identification means for identifying a difference in reproduction output level of the magnetic recording medium before and after erasing residual magnetization by the residual magnetization erasing means after information is recorded by the magnetic head. It will be done.

Embodiments Next, the present invention will be described in more detail with reference to embodiments of the present invention based on the accompanying 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. As shown in FIG. 1, this magnetic card has a first magnetic layer 2 on a card base l made of vinyl chloride resin, polyester, paper, etc.
, a second magnetic layer 3, and a protective layer 4 are laminated. The first magnetic layer 2 has a coercive force of 18,000. For example, it is made of a high coercive force magnetic material such as barium ferrite, which has magnetic properties of . The second magnetic layer 3 has a coercive force of 3
000. For example, it is made of a low coercive force magnetic material such as TFa203, which has magnetic properties of . The protective layer 4 is
Made of non-magnetic material.

Curve 5 in the graph of FIG. 2 represents the saturation recording characteristic when writing is performed on the magnetic card having the configuration shown in FIG. It shows the relationship between the write current value and the reproduction output level at that time. As seen in curve 5, the saturation recording characteristics of the magnetic card exhibited complex characteristics with two maximum values and one minimum value. Among these, the maximum value on the left side of curve 5 indicates the saturation output of the second magnetic layer 3, which is the low coercive force layer of the magnetic card, but the maximum value on the right side of curve 5 indicates 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 are the first magnetic @2 which is a high coercive force layer.
This phenomenon occurs due to the interaction between the signal magnetizations of the second magnetic layer 3, which is the low coercive force layer, and the larger the ratio of the coercive forces of both magnetic layers, and the lower the coercive force of the low coercive force layer. Experiments have confirmed that the lower the magnetic force, the more likely this occurs.

A curve 6 in the graph of FIG. 2 indicates that after writing is performed on the magnetic card having the configuration shown in FIG. This figure shows the reproduction output level after DC demagnetization with a current value I, that is, the saturation recording characteristic of only the first magnetic layer 2 of the magnetic card.

In FIG. 2, the horizontal axis of both curves 5 and 6 represents the write current (2) to the magnetic card as a value Iw/IS normalized by the saturation current value I of the second magnetic layer 3.

From the same figure, when Iw/Is is between 0 and 5.5 and between 9 and 11, curve 5 is above curve 6, but I
It can be seen that when w/Is is from 5.5 to 9, that is, 11 or more, curve 6 is higher than curve 5.

The reason why curve 5 is lower than curve 6 within a certain value range of Iw/Is is that when the two-layer magnetic card shown in FIG. 1 is written with a write current value above a certain value, The reproduction output at that time is due to the interaction between the signal magnetizations of the second magnetic layer 3 with low coercive force and the first magnetic layer 2 with high coercive force.
However, after DC demagnetization of only the second magnetic layer 3 with low coercive force, the interaction between both magnetic layers disappears, and the signal written in the first magnetic layer is reproduced as is. This is because it will be done. Therefore, when a signal is written to the magnetic card at a write current value such that curve 5 is lower than curve 6, the signal output is hidden by the difference between curve 6 and curve 5, and the reproduced output becomes lower. Even if the magnetic card is reproduced in this state with a commonly used magnetic card reproducing machine, it is difficult to correctly read the contents of the written signals. In particular, at the write current value where Iw/Is is the minimum value of curve 5 between 7 and 8, the above-mentioned effect is extremely high.

Figure 3 shows the oscilloscope waveform of the reproduced output after writing a signal with a magnetization reversal interval of 70 μm to the magnetic card in Figure 1 with a write current 7.5 times the saturation recording current Is of the second magnetic layer 3. It shows. On the other hand, FIG. 4 shows the oscilloscope waveform of the reproduction output of the first magnetic layer 2 after the second magnetic layer 3 is DC demagnetized with a current value equal to the saturation recording current value Is of the second magnetic layer 3 after writing the signal. It is. The amplitude of the waveform in FIG. 3 is approximately 1/8 of the amplitude of the waveform in FIG.
The effect of concealing the information recorded on the magnetic card by the magnetic recording and reproducing method of the present invention has been confirmed.

As described above, according to the magnetic recording and reproducing method of the present invention, writing 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 can be performed at least on the magnetic recording medium. The writing current is set such that the output level after erasing the residual magnetization of the magnetic recording layer with the lowest coercive force among the magnetic recording layers is higher than the output level due to the residual magnetization of the two magnetic recording layers. Therefore, in the written state, the first magnetic layer (high coercive force magnetic layer) and the second magnetic layer (high coercive force magnetic layer)
Due to the interaction between signal magnetizations, almost no signal magnetic field leaks to the outside, so a normal magnetic card reading device cannot read the signal. When the magnetic layer is demagnetized by direct current, the interaction between both magnetic layers is eliminated, and the signal written in the first magnetic layer can be read. By comparing the output level at this time with the output level before DC demagnetization after writing,
It is also possible to determine the authenticity of the magnetic card.

In the above-mentioned embodiment, the magnetic recording medium had only two magnetic layers with different coercive forces, but the present invention is not limited to this, but can also be applied to magnetic recording media with three or more layers. It is effective.

FIG. 5 is a block diagram schematically showing a configuration example of an apparatus for carrying out the magnetic recording and reproducing method of the present invention. The magnetic recording and reproducing apparatus shown in FIG. 5 includes a first magnetic head 7 for writing and reading information signals to and from a magnetic recording medium such as the magnetic cards 12.3 and 4 shown in FIG. A second magnetic head 8 for demagnetizing the residual magnetization of the second magnetic layer 3 of the magnetic recording medium, and a second magnetic head 8 for reading recorded information signals 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, the magnetic layer having the lowest coercive force among the magnetic recording layers is lower than the output level due to residual magnetization of at least two magnetic recording layers of the magnetic recording medium. a write and read circuit lO for performing writing with a write current value such that the output level is higher after erasing the residual magnetization of the recording layer, and for reading in the same state after the writing; A DC demagnetization circuit 11 for performing DC demagnetization on the second magnetic head 8 to erase the residual magnetization of the second magnetic layer 3 after writing by the first magnetic head 7; and a third magnetic head 9. a read circuit 12 for reading the recorded information signal from the first magnetic layer 2 after DC demagnetization by the second magnetic helad 8; and a read output from the write and read circuit 10 before DC demagnetization. When the level is compared with the read output level after demagnetization from the reading circuit 12 and the difference is not a predetermined value, the magnetic recording medium is considered to be forged or tampered with and a rejection signal is generated. A false determination circuit 13 is also provided.

In this device configuration example, there are three magnetic heads 7.8 and 9.
However, by using an appropriate head switching circuit, it is possible to share one of the heads, thereby reducing the number of magnetic heads used.

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

(1) It is difficult to read the written signal with a normal magnetic card league, or to visually observe it by developing the magnetization pattern or using Pure, making it difficult to tamper with the magnetic information.

(2) It is economical because no special equipment or energy is required to hide the output of the written signal.

(3) The magnetic materials constituting the magnetic recording medium may be those used in ordinary magnetic cards, etc., and have stable characteristics and are easy to manufacture.

(4) The write current value, which a magnetic recording medium takes to its minimum value when it reaches its saturation recording characteristics, varies depending on the magnetic properties of the medium's low coercive force layer and the material and shape of the write magnetic head. It is easy to detect counterfeit or altered products.

[Brief explanation of the drawing]

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 the saturation recording characteristics when writing is performed using a magnetic write head on the magnetic card having the configuration shown in the diagram, and the readout output characteristics after DC demagnetization of the second magnetic layer of the magnetic card. Figure 4 shows the oscilloscope waveform of the reproduced output after writing a signal with a magnetization reversal interval of 70 μm into the magnetic card of Figure 1 with a write current 7.5 times the saturation recording current I of the second magnetic layer. 5 is a diagram showing the oscilloscope waveform of the reproduction output of the first magnetic layer after the second magnetic layer is DC demagnetized with a current value equal to the saturation recording current value of the second magnetic layer after writing a signal. 1 is a block diagram schematically showing a configuration example of an apparatus for implementing the magnetic recording and reproducing method of the present invention. DESCRIPTION OF SYMBOLS 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, 1
3... Authenticity judgment circuit. Figure 1 Write current (Iw/Is) Figure 4

Claims (8)

[Claims] (1) In a magnetic recording method for recording information on a magnetic recording medium formed by stacking at least two magnetic recording layers with different coercive forces, residual magnetization of at least two magnetic recording layers with respect to the magnetic recording medium Information is recorded at a magnetic head write current value such that the output level after erasing the residual magnetization of the magnetic recording layer with the lowest coercive force among the magnetic recording layers is higher than the output level by the magnetic recording layer. magnetic recording method. (2) The ratio of the coercive forces of the at least two magnetic recording layers of the magnetic recording medium is 5 times or more.
1) The magnetic recording method described in section 1). (3) In a magnetic recording and 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, at least two magnetic recording layers are laminated with respect to 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 with the lowest coercive force among the magnetic recording layers is higher than the output level due to the residual magnetization of the magnetic recording layer. , in reproducing information recorded on the magnetic recording medium, residual magnetization of a magnetic recording layer having the lowest coercive force among the magnetic recording layers is erased before reproducing the information. How to play. (4) The ratio of the coercive forces of the at least two magnetic recording layers of the magnetic recording medium is 5 times or more.
3) The magnetic recording and reproducing method described in section 3). (5) In a magnetic recording and reproducing device for recording and reproducing information on a magnetic recording medium formed by laminating at least two magnetic recording layers having different coercive forces, at least two magnetic recording layers are laminated with respect to the magnetic recording medium. For recording information with a write current value such that the output level after erasing the residual magnetization of the magnetic recording layer with the lowest coercive force among the magnetic recording layers is higher than the output level due to the residual magnetization of the magnetic recording layer. A magnetic head, a residual magnetization erasing means for erasing residual magnetization of a 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 device comprising: (6) The ratio of the coercive forces of the at least two magnetic recording layers of the magnetic recording medium is 5 times or more.
5) The magnetic recording and reproducing device described in item 5). (7) In a magnetic recording and reproducing device for recording and reproducing information on a magnetic recording medium formed by laminating at least two magnetic recording layers having different coercive forces, at least two magnetic recording layers are laminated with respect to the magnetic recording medium. For recording information with a write current value such that the output level after erasing the residual magnetization of the magnetic recording layer with the lowest coercive force among the magnetic recording layers is higher than the output level due to the residual magnetization of the magnetic recording layer. a magnetic head, a residual magnetization erasing means for erasing residual magnetization of a 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 identification means for identifying a difference in reproduction output level of the magnetic recording medium before and after erasing residual magnetization by the residual magnetization erasing means after information is recorded by the magnetic head. Device. (8) The ratio of the coercive forces of the at least two magnetic recording layers of the magnetic recording medium is 5 times or more.
7) The magnetic recording and reproducing device described in item 7).