JPH11232602A - Magnetic record medium and reproduction method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a fraudulent use of data of a magnetic record medium, which has MnBi magnetic powders in a magnetic layer, caused by copying the data of this magnetic record medium onto the magnetic recording medium in which usual magnetic powders are used as recording elements. SOLUTION: In a magnetic record medium such as a magnetic card 3 provided on a substrate 30 with a magnetic layer 31 having MnBi magnetic powders, a special signal for performing a degaussing operation of a portion at which a data signal is recorded and a conversion operation for converting the data signal into a meaningful data is recorded together with the data signal. At reproduction, the special signal is first read out, and the data signal is then converted into the meaningful data by the special signal by using a residual output after the degaussing operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic layer containing MnB.
The present invention relates to a magnetic recording medium such as a magnetic card containing i-magnetic powder and a reproducing method therefor.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as video tapes, floppy disks, credit cards, prepaid cards, etc. because of their easy recording and reproduction. However, the feature of easy recording / reproduction is that the recorded data is easily erased by mistake, and
There is a problem that data can be easily tampered with. For example, magnetic cards have recently been erased by strong magnetic field magnets that have come to be used in places close to us, such as various doors and handbags, and data on magnetic cards has been rewritten. Accidents and crimes such as unauthorized use occur frequently.

As a countermeasure, for example, an irreversible change is caused in a recording medium by a laser beam, such as an optical card, and the recording medium cannot be rewritten once recorded.
There have been proposed IC cards and the like that have high security and difficult to falsify data. However, the optical card requires a new expensive device dedicated to the optical card for recording and reproducing the optical card, and the IC card requires a high cost due to the use of semiconductors. However, none of them can replace the magnetic card recording / reproducing device which has spread all over the world, and it is not as widespread as expected.

For this reason, various measures have been proposed to prevent tampering of the magnetic card. For example, hologram printing and printing using advanced printing techniques have been performed on the magnetic card. However, while these methods can be effective in preventing the appearance of a card from forgery, tampering can, for example, replace a legitimate credit card obtained by unauthorized means with that of another person. -When writing data read from the
This cannot be prevented because the written data is legitimate.

On the other hand, a magnetic recording medium using MnBi magnetic powder as a recording element has a feature that once a signal is recorded, it cannot be easily erased at room temperature. -19244
Nos. 54-33725, 57-38962, 57-38963, and 59-31764. In particular, today, as magnetic card readers are widely used in all corners of the world, credit cards are frequently used in accidents and crimes such as data being erased by mistake or being intentionally rewritten. Attention is being paid to such things as accidents and unauthorized use in products such as Yahoo!

[0006]

As described above, MnBi
Magnetic recording media using magnetic powders as recording elements can be read only, such as credit cards and cache cards.
Once the signal is recorded, it has strong security for applications that do not require rewriting. However, it is difficult to rewrite this medium, but by reading the data on this medium,
It is possible to copy a normal magnetic powder to a magnetic recording medium using a recording element.

A description will be given using a card as an example. When the data of a card using MnBi magnetic powder is copied to a card using normal magnetic powder, the design is different from that of a regular card, so it is similar to a credit card. When used in public, it is revealed that it is a copy card. In particular, if the design of the card using the MnBi magnetic powder is made using advanced printing technology such as hologram, it can be easily identified as a copy card. However, when the card is used in an unmanned place such as an ATM (automatic teller machine and payout machine), the ATM does not have a function of identifying the design.
Even if the data is copied, if the data is regular, it is processed as a regular card.

In view of such circumstances, the present invention is directed to a magnetic recording medium containing a MnBi magnetic powder in a magnetic layer, wherein the data of the magnetic recording medium is formed by recording an ordinary magnetic powder containing no MnBi magnetic powder. An object of the present invention is to prevent unauthorized use by being copied to a magnetic recording medium used as an element.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above object, and as a result, a magnetic recording medium containing MnBi magnetic powder in a magnetic layer, together with a data signal,
By recording a special signal for performing degaussing processing of the part where the data signal was recorded and conversion processing for converting the data signal to significant data, the data of this magnetic recording medium is recorded. Can be prevented from being copied onto other magnetic recording media.

Taking a magnetic card as an example, after the card is cooled to a low temperature and demagnetized (initialized), the above-mentioned special signal is recorded together with the data signal. When playing, the car
The signal recording portion is read by reading the signal recording portion, the special signal is separated and extracted, and the signal recording portion is demagnetized according to the instruction. Even if this treatment is performed, the card containing MnBi magnetic powder does not erase the signal because the coercive force of the magnetic powder is extremely large, but data is stored on the card using ordinary magnetic powder. In the copy, the signal is erased by the degaussing process. Next, Mn
In a card containing Bi magnetic powder, a signal recording portion is read again by a lead head, a data signal is extracted, and this is converted into meaningful data by a special signal.

[0011] Thus, a conventional magnetic powder is used for a car.
In the case where the data is copied to the disk, all the recorded signals are erased by the degaussing process, so that the copy card can be eliminated. Also, even if the data signal and the special signal are separated by some method and only the data signal can be copied without recording the special signal including the degaussing signal, the data signal is encrypted. Therefore, it cannot be converted into significant data unless a special signal is used. In short, the MnBi magnetic powder is contained in the magnetic layer, and at the same time as the data signal, a special signal for demagnetizing the signal recording portion and converting the data signal to meaningful data is used. By recording, it is possible to effectively prevent the card from being copied using ordinary magnetic powder.

The present invention has been completed based on the above findings. That is, in a magnetic recording medium containing a MnBi magnetic powder in a magnetic layer, a demagnetizing process of a portion where the data signal is recorded together with the data signal and a conversion process of converting the data signal into significant data. And a reproducing method for the magnetic recording medium. First, a special signal is read and a data signal is read. A method for reproducing a magnetic recording medium, comprising: performing a degaussing process on a portion on which is recorded, and converting a data signal into meaningful data by a special signal based on a residual output after the degaussing process. Claim 6).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The MnBi magnetic powder used in the present invention has a high coercive force of about 10,000 Oe at room temperature, but decreases as the temperature decreases.
e or less. By utilizing this property, it can be demagnetized by cooling to a low temperature, and can be easily magnetized at room temperature after demagnetization.
FIG. 1 is an initial magnetization curve of (a longitudinal magnetic layer of) a magnetic recording medium using MnBi magnetic powder. From this, it can be seen that when cooled to a low temperature and brought into a demagnetized state, magnetization can be easily performed at room temperature with a low magnetic field of about 2,000 Oe.

Further, once magnetized, the magnetic recording medium exhibits a high coercive force of about 14,000 Oe, and it becomes almost impossible to erase or rewrite data thereafter. FIG. 2 shows the erasure of a magnetic card using MnBi magnetic powder (Example 1 to be described later) and a magnetic card using barium ferrite magnetic powder having a coercive force of 2,750 Oe (Comparative Example 1 to be described later). Show characteristics. Both cards were recorded under the same conditions using the same reader / writer. The magnetic card (curve-2b) using barium ferrite magnetic powder is 100
The reproduction output becomes almost zero at a current value of about mA, whereas the magnetic card using MnBi magnetic powder (curve-2)
In a), it can be seen that the output decrease is extremely small even at a current value of about 300 mA due to a large coercive force.

The MnBi magnetic powder having such characteristics is produced by obtaining a MnBi ingot by a powder metallurgy method, an arc furnace melting method, a high frequency melting method, a melt quenching method, etc., and pulverizing the MnBi ingot. For example, in the case of manufacturing by powder metallurgy, the ingot is manufactured as follows, divided into a manufacturing step, a pulverizing step, and a stabilizing step. In addition, MnBi magnetic powder can also be manufactured by means other than the pulverization method.

In the ingot manufacturing process, 50 to 300
The Mn powder and the Bi powder of the mesh are sufficiently mixed, and this is formed into a molded body by a pressure press to produce an ingot. The mixing is preferably performed in an inert atmosphere, but may be performed in an oxidizing atmosphere. Mixing ratio of Mn powder and Bi powder (M
n / Bi) is preferably in a molar ratio of 45:55 to 65:35. When Mn is increased as compared with Bi, M
By forming an oxide or a hydroxide of Mn on the surface of the nBi magnetic powder, the corrosion resistance of the MnBi magnetic powder can be improved, and a high-quality magnetic powder can be obtained.

The Mn powder and Bi powder used here are:
It is preferable that the content of impurities is small, but in order to adjust the magnetic properties, Ni, Al, Cu, Pt, Zn, Fe
It may be one to which a metal such as is added. In the case where such a metal is added, if the addition amount is 0.6 atomic% or more with respect to MnBi, the magnetic properties can be controlled well, and if it is less than 5.0 atomic%, the crystal structure itself of MnBi is reduced. It is preferable that the content is in the range of 0.6 to 5.0 atomic% because it can be maintained well and the original characteristics of MnBi can be exhibited. As a method for adding these metals, it is preferable to form an alloy of Mn and these elements in advance.

The Mn powder and Bi powder may be used in advance, or may be used by pulverizing lumps such as flakes and shots and pulverizing them. When synthesizing by a sintering reaction, since MnBi is generated by a diffusion reaction through a contact interface of MnBi, MnBi and Bi powder are 50%.
The use of finely divided powders of up to 300 meshes causes the formation reaction to proceed smoothly, and the reaction greatly depends on the surface properties. For this reason, powder metallurgy such as etching the surfaces of Mn powder and Bi powder or degreasing with a solvent. It is preferable to perform the surface treatment performed by the method. These Mn powder and B
Mixing of the i-powder is performed by any means such as an automatic mortar and a ball mill.

When the Mn powder and the Bi powder are formed into a molded body by a pressure press, the pressing force is preferably set to 1 to 8 ton / cm. By setting the applied pressure to 1 ton / cm or more, the sintering reaction is promoted, and a uniform ingot can be produced.
By setting the diameter to cm or less, productivity can be improved. The molded body obtained in this way is sealed in a glass container or a metal container, and the inside of the container is set to a vacuum or an inert gas atmosphere to prevent oxidation during the heat treatment. As the inert gas, hydrogen, nitrogen, argon, or the like can be used, but from the viewpoint of cost, nitrogen gas is used as the optimum gas.

The container in which the molded body is sealed in this way is then placed in an electric furnace and heated at 260 to 271 ° C. for 2 to 15 minutes.
Heat treated for days. When the heat treatment temperature is 260 ° C. or higher, the heat treatment can be performed in a short time and the magnetization amount of the ingot can be increased. When the heat treatment temperature is 271 ° C. or lower, melting of Bi can be suppressed and a uniform ingot can be obtained. Therefore, the heat treatment is preferably performed just below the melting point of Bi.

In the pulverizing step, the MnBi ingot thus produced is taken out, coarsely pulverized in an inert gas atmosphere using an automatic mortar or the like, and adjusted to a particle size of 100 to 500 μm. Then, ball mill, planetary ball
Wet crushing using the impact of a ball
Alternatively, fine particles are formed by dry pulverization such as a jet mill or the like, by impact due to collision of particles between particles or the wall of a container.

In the wet pulverization utilizing the impact of a ball, as the pulverization proceeds, the diameter of the ball is reduced stepwise to obtain a magnetic powder having a more uniform particle diameter. Mn
Since Bi has a hexagonal structure, it originally exhibits the property of being cleaved, so that it is not necessary to pulverize it by applying high energy. In the case of wet grinding, it is preferable to use an organic solvent as the liquid. In particular, it is preferable to use a non-polar solvent such as toluene and remove dissolved water in the solvent in advance. Dry grinding is preferably performed in a non-oxidizing atmosphere. As the non-oxidizing atmosphere, a vacuum or an inert gas atmosphere such as a nitrogen gas or an argon gas is preferably used.

The MnBi magnetic powder thus obtained can be arbitrarily controlled in particle size depending on pulverization conditions. Generally, the average particle size is 0.1 to 20 μm
It is desirable to be within the range. When the average particle diameter is 0.1 μm or more, the saturation magnetization of the MnBi magnetic powder can be increased, and when the average particle diameter is 20 μm or less, the coercive force of the MnBi magnetic powder can be sufficiently increased, and when the magnetic recording medium is used. The surface smoothness of the magnetic layer is improved, and a favorable result in recording characteristics is obtained.

In the stabilization treatment step, the chemical stability of the MnBi magnetic powder thus obtained is improved. For example, the MnBi magnetic powder is formed on its surface by using Mn or Bi of the powder itself. Chemical stabilization of the powder by forming a coating such as a metal oxide, hydroxide, nitride, or carbide, or by forming a coating similar to the above using Mn or Bi different from the above powder Measure.

As an example of the former film formation, a method of forming an oxide film of Mn and Bi on the surface of a MnBi magnetic powder using oxygen will be described. First, Mn
Bi magnetic powder in nitrogen gas or argon gas containing about 100 to 10,000 ppm of oxygen at 20 to 150 ° C.
Heat at a temperature of The heating time is suitably about 0.5 to 40 hours, and the lower the temperature, the longer the heating time. By such a treatment, a coating of Mn and Bi oxides is formed on the surface of the MnBi magnetic powder, and in particular, Mn oxides that most contribute to chemical stability are preferentially formed.

The MnBi magnetic powder used in the present invention comprises:
The magnetic properties obtained as described above are 16 kO
e in the range of 3,000 to 20,000 Oe at 300 K
The saturation magnetization in K is in the range of 50 to 1,000 Oe, and the saturation magnetization measured by applying a magnetic field of 16 kOe in 300 K is in the range of 20 to 60 emu / g.

The magnetic recording medium of the present invention is characterized in that the magnetic layer contains the above-mentioned MnBi magnetic powder, and together with the MnBi magnetic powder, a gamma iron oxide magnetic powder,
Magnetic powders commonly used in magnetic recording media such as cobalt-containing iron oxide magnetic powder, barium ferrite magnetic powder, strontium ferrite magnetic powder, metal magnetic powder, alloy magnetic powder, and compound magnetic powder may be used in combination. These other magnetic powders may be used together with the MnBi magnetic powder in the magnetic layer, or may be formed by laminating the MnBi magnetic powder and a magnetic layer containing each of these other magnetic powders. Also, non-magnetic powders such as alpha-hematite, alumina, and silica are used without using magnetic powders.
It may be used together with i-magnetic powder.

The addition amount of these other powders other than the MnBi magnetic powder is 7 wt% relative to the MnBi magnetic powder.
It is preferable to set it to about 0% or less. When the addition amount of these other powders is set to 70% or less, a signal due to the residual output from the MnBi magnetic powder can be reproduced with high reliability even after performing the above-described demagnetization treatment.

The magnetic recording medium of the present invention can be prepared by a conventional method.
Can be made. First, the above MnBi magnetic powder, or the above MnBi magnetic powder and another powder, a binder resin,
A magnetic paint is prepared by mixing and dispersing with an organic solvent. Next, this magnetic paint is applied on a substrate such as a polyester film, and is usually 1,000 to
It is manufactured by performing a magnetic field orientation with a magnetic field strength of about 5,000 Oe and then drying it to form a magnetic layer having a thickness of usually about 4 to 20 μm.

In addition, credit cards and cache yuka
In a magnetic card such as a magnetic card, the above-mentioned base is made of a releasable material, and the magnetic layer formed thereon is transferred onto a substrate made of a vinyl chloride resin or the like, and the magnetic layer is formed on one or both surfaces of the substrate. May be provided in the form of a card. At this time, the magnetic layer may be provided on the entire surface of the substrate, or may be provided partially on a stripe or the like.

As the binder resin used for preparing the magnetic coating material, any of those generally used for magnetic recording media can be used. For example, a vinyl chloride-vinyl acetate copolymer, a polyvinyl butyral resin, a cellulose resin, a fluorine resin, a polyurethane resin, an isocyanate compound, a radiation curable resin, and the like are used. M
In order to improve the chemical stability of the nBi magnetic powder, these binder resins have basic functional groups such as imine, amine, amide, thiourea, thiosol, ammonium salt, and phosphonium group in the molecule. Preferably.
Further, in order to further improve the chemical stability of the MnBi magnetic powder, an appropriate additive having the same basic functional group as described above may be added to the magnetic layer.

In manufacturing such a magnetic recording medium,
A shield layer containing permalloy powder or sendust powder may be formed on the surface of the magnetic layer containing MnBi magnetic powder, which makes data reading and rewriting more difficult. Security can be further improved. In the case of the above-mentioned magnetic card, it is preferable to form various kinds of protective layers such as protective layers and color layers on the surface of the magnetic layer.

The magnetic recording medium of the present invention manufactured as described above has a magnetic characteristic of 16k at a temperature of 300K.
When measured by applying an Oe magnetic field, the coercive force is 300
When the magnetic flux density is in the range of
In the range of 000G, the square Br / Bm is 0.60 to 0.9.
It falls within the range of 8.

The recording / reproducing method for a magnetic recording medium according to the present invention will be described. No special operation is required to record the signal. What is necessary is just to record by using the same method as a normal magnetic recording medium using a normal writer. That is, first,
Demagnetizing (initialization) by cooling the magnetic recording medium of the present invention to a low temperature
After that, together with the data signal, a special signal for performing a degaussing process on a portion where the data signal is recorded and a conversion process for converting the data signal into significant data is recorded.

The recording position of the special signal is not particularly limited. The data signal may be recorded on the same track as the data signal, or may be recorded on a different track from the data signal.
For example, in the case of a magnetic card, the data signal may be recorded before or between the data signals with respect to the traveling direction of the card. In this case, the data signal is separated from the special signal. Reproduction becomes easy. On the other hand, instead of recording as described above, data may be dispersed between data signals and recorded by being mixed into the data signals. The means makes it difficult to discriminate the data signal from the special signal, so that the security is further improved.

The reproduction of the recording signal is carried out by the following procedures, taking as an example the case where the above-mentioned special signal is dispersed and mixed into the data signal and recorded. Reading of signal recording part Extraction of special signal Degaussing of signal recording part Re-reading of signal recording part Extraction of data signal Data signal is converted to meaningful data by the special signal read ahead

FIG. 3 shows a lead head 1 as a magnetic head.
And a read-only device having a degaussing head 2 in the forward path when the card is inserted as shown in FIG.
Are performed, and the above-mentioned processes are performed on the return path at the time of card ejection shown in FIG. In the above, the magnetic card 3 having the magnetic layer 31 on the substrate 30 is inserted into the reader,
The recording signal is read by the lead head 1. At this time,
The degaussing head is off. In the above description, since the read signal contains a data signal and a special signal, these signals are separated and only the special signal is separated and extracted.

In the above, the portion where the signal is recorded is demagnetized according to the instruction of the special signal extracted above. At that time, only the data signal may be demagnetized, or both the data signal and the special signal, that is, all the stored signals may be demagnetized. Even if this degaussing treatment is performed, in a card containing MnBi magnetic powder in the magnetic layer, no signal is erased because the coercive force of the MnBi magnetic powder is extremely large. On the other hand, with a card using ordinary magnetic powder, all data is erased. Therefore, M
In the case where data is copied from a regular card using nBi magnetic powder to a card using normal magnetic powder, all data of the copy card is erased by the above processing. And cause a reproduction error.

In the above, the signal recording portion is read again. For a card containing MnBi magnetic powder in the magnetic layer, the data signal and the special signal are read again. This processing is performed at the time of card ejection, so that the number of heads used can be reduced without inconvenience that the processing time is delayed as compared with normal card reading. In the above, the separation of the data signal is extracted from the signal read by the above operation.
In the above, since the data signal extracted as described above is encrypted, the encrypted data signal is decrypted by the special signal read earlier and converted into significant data. .

FIG. 4 is different from the apparatus shown in FIG. 3 in that the two heads 1A and 1B are used as magnetic heads.
This shows an example of a read-only device having a head 2 for degaussing and a degaussing head 2. According to such a device, it is possible to perform all the above processes on the outward path when the card is inserted. In addition to these devices, it is also possible to use a device in which the lead head is a double gap and a lead gap and a degaussing gap are provided without newly providing a degaussing head.

Further, each of the above-described devices is an example of a read-only device, but may be a reader / writer capable of writing a signal. In this case, FIG.
This can be achieved by further providing a write head in the apparatus shown in FIG. 4 or by using a lead / write head as the lead head.

As described above, in the card of the present invention, the signal is not erased even by the demagnetization process, and the card using the ordinary magnetic powder is entirely erased by the above process. A forged card that copies the data of a contained normal card will erase all the data and cause a reading error. Also, the data signal and the special signal are separated, and even if only the data signal is copied without recording the special signal including the degaussing signal, the data signal is encrypted. , If no special signal is used,
Data cannot be combined. However, when the special signal is read, the operation of the degaussing process is performed, so that the data is erased and cannot be reproduced. In short, in the present invention, the magnetic layer contains MnBi magnetic powder, and a special purpose for combining the data signal with the demagnetization of the signal recording portion and the compounding of the data signal into significant data simultaneously with the data signal. By recording the signal, it is possible to effectively prevent the card from being copied using ordinary magnetic powder.

As is apparent from the above description, the magnetic recording medium of the present invention can be used for a credit card, a cache card, and the like.
It is especially effective when applied to various ID cards such as a card and an entry / exit card. However, not limited to these,
It is needless to say that the present invention can be applied to various prepaid cards, magnetic commuter passes, magnetic tickets, and the like.

Generally, in order to spread a new recording medium in the market, it is necessary to newly develop a recording apparatus and a reading apparatus for using the medium, and to spread these apparatuses. However, it is extremely difficult to replace all of these devices in the current situation where recording and reading devices have already spread to every corner of the world, such as magnetic cards.

The magnetic recording medium of the present invention does not require a special device for recording data, and can be easily recorded by using a general-purpose writer. Moreover, in reading signals, it is only necessary to newly provide a demagnetizing magnetic head, and strong security can be exerted by slightly changing the specifications of the device. Therefore, the present invention can provide a magnetic recording medium having extremely high merits from a practical point of view.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention and its reproducing method will be described below with reference to examples. In the following,
"Parts" means parts by weight.

Example 1 <Synthesis of MnBi magnetic powder> Mn powder and Bi powder pulverized to a particle size of 200 mesh
n and Bi were weighed so that the molar ratio was 55:45, and the mixture was sufficiently mixed using a ball mill. This mixture was molded into a columnar shape having a diameter of 20 mm and a height of 10 mm with a pressure press at a pressure of 3 tons / cm. The molded body was placed in a sealed aluminum container, and after vacuum was drawn, nitrogen gas was added to the container for 0.5 minute.
Atmospheric pressure was introduced. Place the container in an electric furnace at 270 ° C for 1
Heat treatment was performed for 0 days. After this heat treatment, the MnBi ingot was taken out into the air, crushed lightly in a mortar, and its magnetic properties were measured. As a result, the coercive force measured by applying a magnetic field having a maximum magnetic field of 16 kOe at 300 k was 840 Oe, and the magnetization amount was 53.6 emu / g.

Next, the coarsely pulverized MnBi powder was finely pulverized using a planetary ball mill as follows. A ball mill pot with an internal volume of 1,000 cc has a diameter of 3
mm zirconia ball was filled so as to occupy 1/3 of the internal volume. Among them, the above coarsely ground MnBi powder 5
00 g and 500 g of toluene as a solvent were added and pulverized at 150 rpm for 4 hours. MnBi obtained
After taking out the magnetic powder and evaporating the toluene, the magnetic properties were measured. As a result, the maximum magnetic field is 16k at 300k.
The coercive force measured by applying an Oe magnetic field is 8,600 Oe
And the magnetization was 39.2 emu / g.

Then, the MnBi magnetic powder was subjected to a stabilizing treatment by the following method. M immersed in toluene
The nBi magnetic powder was taken out, transferred to a heat treatment container, and vacuum dried at room temperature for about 2 weeks. Next, while keeping the same container, a nitrogen gas containing 1,000 ppm of oxygen was introduced at 1 atm, and heat treatment was performed at 40 ° C. for 15 hours. Subsequently, as a second stage heat treatment, the oxygen mixed gas filled in the container is evacuated and removed, and then nitrogen gas is introduced at 0.5 atm and the temperature is raised to 330 ° C. For 2 hours. The obtained MnBi magnetic powder has an average particle size of 1.8 μm and a maximum magnetic field of 16 at 300 k.
The coercive force measured by applying a magnetic field of kOe is 8,500 O
e and the amount of magnetization was 46.3 emu / g.

<Preparation of Magnetic Card> MnBi magnetic powder (coercive force: 8,500 Oe) 100 synthesized by the above method
Parts, 25 parts of vinyl chloride-vinyl acetate copolymer (“VAGH” manufactured by UCC), 50 parts of methyl isobutyl ketone
And 50 parts of toluene were sufficiently mixed and dispersed by a ball mill to prepare a magnetic coating material. This was applied on a 25 μm thick polyethylene terephthalate film-based base film having a release layer formed thereon, and 3,000 Oe was applied.
, And dried to form a magnetic layer having a thickness of 15 μm. This was slit to a width of 7.3 mm to form a magnetic tape, and then temporarily bonded to a 0.76 mm-thick vinyl chloride resin substrate, and the base film was peeled off.
By heating and pressing, the magnetic layer was buried in the above substrate to produce a magnetic card.

Example 2 The same as Example 1 except that 100 parts of MnBi magnetic powder was changed to 85 parts of MnBi magnetic powder and 15 parts of barium ferrite magnetic powder (average particle size 0.5 μm, coercive force 2,750 Oe). Thus, a magnetic card was manufactured.

Example 3 Same as Example 1 except that 100 parts of MnBi magnetic powder was changed to 70 parts of MnBi magnetic powder and 30 parts of barium ferrite magnetic powder (average particle size 0.5 μm, coercive force 2,750 Oe). Thus, a magnetic card was manufactured.

Example 4 100 parts of MnBi magnetic powder was mixed with 85 parts of MnBi magnetic powder and 15 parts of alpha hematite (α-Fe ₂ O ₃ ) powder.
Except that the magnetic card was changed to
Was prepared.

Example 5 100 parts of MnBi magnetic powder was replaced by 70 parts of MnBi magnetic powder and 30 parts of alpha hematite (α-Fe ₂ O ₃ ) powder.
Except that the magnetic card was changed to
Was prepared.

Example 6 100 parts of MnBi magnetic powder was mixed with 85 parts of MnBi magnetic powder and gamma iron oxide magnetic powder (average particle size 0.4 μm).
m, coercive force 300 Oe) A magnetic card was manufactured in the same manner as in Example 1 except that the amount was changed to 15 parts.

Comparative Example 1 100 parts of MnBi magnetic powder was replaced with barium ferrite magnetic powder (average particle size 0.5 μm, coercive force 2,750O
e) A magnetic card was produced in the same manner as in Example 1 except that the amount was changed to 100 parts.

Comparative Example 2 100 parts of MnBi magnetic powder was mixed with 10 parts of gamma iron oxide magnetic powder (average particle size 0.4 μm, coercive force 300 Oe).
A magnetic card was produced in the same manner as in Example 1 except that the amount was changed to 0.

For each of the magnetic cards of Examples 1 to 6 and Comparative Examples 1 and 2, signal recording and reproduction were performed by the following method, and the performance was evaluated. The results were as shown in Tables 1 and 2 below.

<Recording and Reproduction of Signal> The magnetic card is
First, initialization processing was performed. The signal is recorded on a magnetic card
Darita (CRS-70 manufactured by Sanwa Newtech Co., Ltd.)
0 ") and the recording current is set to 200 mA,
The recording density was set to 210 FCI. The signal was reproduced using the same magnetic card reader / writer as described above, and the degaussing process was performed by passing a 200 mA DC current through the write head.

As a recording signal, first, 10 characters from alphabet a to j were recorded assuming a special signal. Next, the significant data signal is changed to (1, 2,..., 1).
9, 20, A, B,..., S, T), and assuming an encrypted data signal, (1, A, 2, B,.
..., 19, S, 20, T), numerical values from 1 to 20 and 20 letters from A to T in the alphabet are recorded alternately. The flow of such recording and subsequent reproduction processing is as follows.

(I) [Special signal + data signal] (a, b, c,..., I, j, 1, A,
2, B,..., 19, S, 20, T) (II) Reading [special signal + data signal] by read head (III) Reading [special signal] (a, b) , …………,
As a demagnetization process of the signal by (i, j), a direct current is applied to the write head to degauss the signal. (IV) The degaussed signal is read again by the read head.

In the flow of the recording and reproduction processing described above,
Table 1 below shows the results of the signal read processing (II) and the measurement results of the reproduction output of the magnetic card in the same processing state.
Similarly, Table 2 below shows the results of the signal rereading process (IV) and the measurement results of the reproduction output of the magnetic card in the same processing state. The above-mentioned reproduction output is expressed as a ratio (%) to the output at the time of recording in Comparative Example 1.

[0063]

[0064]

From the results shown in Tables 1 and 2, the magnetic cards of Examples 1 to 6 containing MnBi magnetic powder were read again in the state (II), which is the first read processing. In the state (IV), which is the second re-reading process after performing the degaussing process based on the special signals (a, b,..., I, j), the special signals (a, b,.
.., I, j) and data signals (1, A, 2, B,...)
, 19, S, 20, T) are normally read.

On the other hand, in the magnetic cards of Comparative Examples 1 and 2 containing no MnBi magnetic powder, the special signal and the data signal were normally read in the state (II). It can be seen that in the state (IV) after the execution, all the signals are erased, as in the case where the reproduced output is 0, causing a read error.

As is apparent from the results, the data of a regular magnetic card in which a special signal and a data signal are recorded using MnBi magnetic powder are copied to a normal magnetic card. In this case, the signal is erased, which causes a read error. If the special signal and the data signal are separated and extracted and only the data signal is copied without recording the special signal including the degaussing signal, the content of the read signal is encrypted. (1, A, 2, B, ...
..., 19, S, 20, T). This signal is significant data (1, 2,..., 19, 20, A, B,.
.., S, T) requires a special signal. Therefore, even if only the data signal is copied, no significant data is known.

In the magnetic cards of Examples 1 to 6, the reproduction output shown in Tables 1 and 2 was adjusted by adjusting the thickness of the magnetic layer and the addition ratio of MnBi magnetic powder and other magnetic powder. By doing so, it can be adjusted to an arbitrary value.

[0069]

As described above, according to the present invention, M
In a magnetic recording medium containing nBi magnetic powder,
By recording a special signal for performing a degaussing process on a portion where the data signal is recorded and a conversion process for converting the data signal into significant data, together with the data signal, the MnBi magnetic powder can be obtained. Unauthorized use due to copying data to a normal magnetic recording medium that does not contain it can be effectively prevented.

In order to spread a new medium in the market, it is necessary to newly develop a recording device and a reading device for using the medium, and to spread these devices. However, in the present situation where recording and reading devices have already spread to every corner of the world, such as magnetic cards, it is extremely difficult to replace these devices. According to the present invention, not only strong security but also a general-purpose recording device can be used as it is, and even if the reading device changes the signal processing software or changes the hard part, it is a slight change Therefore, the merits are extremely large in practical use.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing an initial magnetization curve of a magnetic recording medium using MnBi magnetic powder.

FIG. 2 is a characteristic diagram showing erasing characteristics of a magnetic recording medium using MnBi magnetic powder and a magnetic recording medium using barium ferrite magnetic powder.

FIG. 3 is a cross-sectional view showing an example of a device configuration of a magnetic head for reproducing a recording signal of a magnetic recording medium using the MnBi magnetic powder of the present invention.

FIG. 4 is a cross-sectional view showing another example of the configuration of a magnetic head device for reproducing a recording signal of a magnetic recording medium using the MnBi magnetic powder of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 (1A, 1B) Lead head 2 Degaussing head 3 Magnetic card 30 Substrate 31 Magnetic layer 2a Magnetic recording medium of the present invention using MnBi magnetic powder 2b Magnetic recording medium using barium ferrite magnetic powder

Claims (6)

[Claims] 1. In a magnetic recording medium containing MnBi magnetic powder in a magnetic layer, a data signal and a degaussing process of a portion where the data signal is recorded and conversion of the data signal into significant data. A magnetic recording medium on which a special signal for performing a conversion process is recorded. 2. The magnetic recording medium according to claim 1, wherein the data signal and the special signal are recorded on the same track. 3. The magnetic recording medium according to claim 1, wherein the data signal and the special signal are recorded on different tracks. 4. The magnetic recording medium according to claim 1, wherein a magnetic layer is provided on one or both sides of the substrate to form a card. 5. The magnetic recording medium according to claim 4, wherein the magnetic layer is provided on the entire surface of the substrate or partially (including a stripe shape). 6. A reproducing method for a magnetic recording medium according to claim 1, wherein a special signal is read, and a degaussing process is performed on a portion where the data signal is recorded. A method for reproducing a magnetic recording medium, comprising: converting a data signal into significant data by a special signal by using a residual output thereafter.