JPH08138921A - Magnetic powder and manufacture thereof, magnetic recording medium by use thereof, and recording/ reproducing method and device thereof - Google Patents

Abstract

PURPOSE: To provide a magnetic recording medium where data that are stored once can not be erased and to provide a recording/reproducing method and a recording/reproducing device using the magnetic recording medium by a method wherein MnBi magnetic powder hardly deteriorating in saturation magnetization and excellent in corrosion resistance is used. CONSTITUTION: MnBi magnetic powder is manufactured through such a method that Mn powder and Bi powder both of grain diameter 50 to 300 mesh are mixed together, wherein the mol ratio of Mn content to Bi content of the mixed powder is previously set to 45:55 to 65:35, the mixture is press-molded, and the molded body is heated at temperatures lower than the fusing point of Bi in a non-oxidizing or a reducing atmosphere, whereby a reaction takes place to produce MnBi magnetic powder. A magnetic recording medium is formed of the manufactured MnBi magnetic powder, and a recording/reproducing method and a recording/reproducing device using the magnetic recording medium are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to MnBi magnetic powder, a method for producing the same, a magnetic recording medium using the magnetic powder obtained by the method, a recording / reproducing method for the magnetic recording medium, and a recording / reproducing apparatus.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as video tapes, floppy disks, credit cards, prepaid cards, etc. because they are easy to record and reproduce. However, the characteristic of easy recording / reproduction is that, on the contrary, the recorded data is easily erased by mistake and the data can be easily tampered with. In the case of a card, it is erased by a magnet with a strong magnetic field that is recently used for various doors and handbags, and the data on the magnetic card is rewritten and is used illegally. Crime is occurring frequently.

As a countermeasure against this, for example, a recording medium such as an optical card which causes an irreversible change in the recording medium by laser light and cannot be rewritten once recording is made, or data tampering is difficult. High security IC card
Although optical cards have been proposed, in the case of optical cards, optical cards
It requires new expensive equipment exclusively for optical cards to record and reproduce data, and IC cards have the drawback of high cost due to the use of semiconductors. Both have become popular all over the world. It has not been possible to replace the existing magnetic card recording / playback device, and has not been widely used as expected.

Therefore, various measures have been proposed to prevent tampering with the magnetic card. For example, the magnetic card is subjected to hologram printing or printing using advanced printing techniques. This method is used. Although it can be effective in preventing the appearance of counterfeit cards, it is a magnetic card.
For tampering with the data written in the magnetic stripe of the card, this tampering is performed by, for example, copying the data read from another person's credit card to a legitimate credit card obtained by unauthorized means. This cannot be prevented because the data written by a method such as writing is legitimate.

On the other hand, it is known that a magnetic recording medium which uses MnBi magnetic powder as a recording element has a feature that once it is recorded, it cannot be easily rewritten at room temperature (Japanese Patent Publication No. 52-46801, Japanese Patent Publication No. 52-46801). Kosho 54
-19244, JP-B-54-33725, JP-B-5
No. 7-38962, Japanese Patent Publication No. 57-38963, Japanese Patent Publication No. 59-31764), and in particular, the readers for magnetic cards have spread to every corner of the world. In credit cards, prepaid cards, and the like, in which accidents and crimes such as being made or intentionally rewritten occur frequently, attention is being paid to prevent accidents and unauthorized use.

[0006]

However, this type of M
The nBi magnetic powder is a magnetic powder that is essentially deliquescent, and has the drawback that when it is kept under high temperature and high humidity for a long time, it is corroded and decomposed to deteriorate the saturation magnetization.
A method (Japanese Patent Publication No. 60-57127, Japanese Patent Publication No. 61-41048) such as wrapping nBi magnetic powder with a dense binder resin or including a volatile anticorrosive agent in the magnetic layer has been tried. However, in these methods, the effect of blocking water vapor which is close to the molecular state is small, and it is not possible to sufficiently prevent the infiltration of water molecules into the magnetic layer, so a sufficient effect is still obtained. Absent.

Further, since MnO ₂ which is an oxide of Mn which is one of the constituent elements of the MnBi magnetic powder is originally a stable oxide, it is possible to improve the corrosion resistance by forming a uniform film of this MnO _2. It is considered that it is usually necessary to heat MnO ₂ to a high temperature in an oxidizing atmosphere to form MnO ₂ , and when the fine magnetic particles for magnetic recording are heated to a high temperature in an oxidizing atmosphere, the saturation magnetization remarkably decreases. I will end up.
Further, when MnBi is oxidized, Bi oxide is naturally generated at the same time as Mn oxide, and while Mn and Bi exist as MnBi which is an intermetallic compound, they are relatively stable under normal environment. In the presence of water, Mn and Bi are decomposed to form oxides of Mn and Bi. When these oxides of Mn and Bi are formed, a local battery is generated and in the presence of water. Further, since decomposition and corrosion are accelerated, it is extremely difficult to apply the stabilization by forming the MnO ₂ film to the MnBi magnetic powder.

The present invention has been made as a result of various investigations in view of the present situation. MnBi magnetic powder is heat-treated at a specific temperature and atmosphere to obtain MnBi.
An MnBi magnetic powder having excellent corrosion resistance is formed by preferentially forming a Mn oxide having a specific structure only in the vicinity of the surface of the magnetic powder, and the deterioration of saturation magnetization is extremely small. A first object is to provide a magnetic powder, and a second object is to provide a method for producing such a MnBi magnetic powder having excellent corrosion resistance. A third object is to provide a magnetic recording medium using a binder resin and an additive suitable for this MnBi magnetic powder, and a fourth object is to record once using this magnetic recording medium. Then, it is to provide a non-rewritable magnetic card. Furthermore, the fifth purpose is to obtain such M
A sixth object of the present invention is to provide a magnetic recording medium having novel characteristics by using a magnetic recording medium using nBi magnetic powder and an ordinary magnetic recording medium in combination. -To provide a recording / reproducing method for a magnetic recording medium having excellent characteristics and an apparatus therefor.

[0009]

The magnetic powder of the present invention comprises:
In the magnetic powder mainly composed of MnBi, the average particle diameter of the magnetic powder is 0.1 μm or more and 20 μm or less, and the coercive force measured by applying a magnetic field of 16 KOe is 300 at 300K.
0 to 15,000 Oe, 50 to 1000 O at 80K
e, the rate of decrease of the amount of magnetization when the amount of magnetization measured by applying a magnetic field of 16 KOe at 300 K is 20 emu / g to 60 emu / g, and left for 7 days in an environment of a temperature of 60 ° C. and a relative humidity of 90%. Is 40% or less, and the amount of metal Bi is represented by the formula: metal Bi / (MnBi + metal Bi) <0.5 (where metal Bi is the peak from the (012) plane in the X-ray diffraction peak of Bi). Area, MnBi is M
It is the peak area from the (101) plane in the X-ray diffraction peak of nBi. ) Is an amount represented by (4), and is an MnBi magnetic powder in which a film of an inorganic material is further formed in the vicinity of the surface of the magnetic particles.

The MnBi magnetic powder is produced in such a manner that the Mn powder having a particle diameter of 50 to 300 mesh or the powder mainly composed of Mn and the powder mainly composed of Bi or Bi are contained in Mn and Bi. Is a molar ratio of 45:
After premixing the mixture to 55 to 65:35, the mixture is press-molded, heated and reacted at a temperature not higher than the melting point of Bi in a non-oxidizing or reducing atmosphere to obtain MnBi, and then the MnBi is non-oxidizing. Magnetic powder obtained by pulverizing in an oxidizing atmosphere into fine particles, and further heat treating the magnetic powder thus obtained in an atmosphere containing oxygen, and further in an atmosphere containing oxygen and a non-oxidizing atmosphere. It is being heat treated.

Further, in the magnetic recording medium of the present invention, the above MnBi magnetic powder is contained in the magnetic layer to obtain 16KO.
The coercive force measured by applying the magnetic field of e is 5000 to 16000 Oe at 300K and 100 to 1 at 80K.
The magnetic flux density measured by applying a magnetic field of 16 KOe at 500 Oe and 300 K is 500 to 2500 G, the rectangular shape in the longitudinal direction is 0.60 to 0.95, and the temperature is 60 ° C. and the relative humidity is 90% for 7 days. A magnetic recording medium having a magnetic flux density reduction rate of 50% or less when left unattended, wherein a magnetic layer further contains a binder resin having a basic functional group and an additive having a basic functional group. It is a medium.
A magnetic recording medium having a water-repellent layer provided on the surface of the magnetic layer or between the magnetic layer and the substrate, and a magnetic recording medium having a magnetic layer using ordinary magnetic powder in addition to the above MnBi magnetic powder. The magnetic recording media are magnetic cards.

Further, in the magnetic recording medium recording / reproducing method of the present invention, the above magnetic recording medium is cooled to a low temperature to be in a demagnetized state, and thereafter, a signal is recorded / reproduced by using a magnetic head. When the magnetic recording medium is cooled to a low temperature to be in the demagnetized state, the magnetic recording medium is cooled to the low temperature, or immediately after cooling, an alternating magnetic field is applied to the magnetic layer to bring the magnetic recording medium into the demagnetized state.

Further, in the magnetic recording medium recording / reproducing apparatus of the present invention, the magnetic layer is provided on the upstream side of the magnetic head of the magnetic recording medium reproducing apparatus for reproducing the signal magnetically recorded on the magnetic recording medium by the magnetic head. And a magnetic recording medium reproducing means provided with a magnetic field applying means for applying a direct current or an alternating magnetic field smaller than the coercive force of the magnetic layer.

[0014]

The magnetic powder of the present invention is a magnetic powder mainly composed of MnBi, in which the average particle diameter of the magnetic powder is 0.1 μm or more and 20 μm or less, and the coercive force measured by applying a magnetic field of 16 KOe is 3000 to 15000 Oe. The amount of magnetization measured by applying a magnetic field of 50 to 1000 Oe at 80 K and 16 KOe at 300 K is 20 em.
u / g to 60 emu / g, the decrease rate of the amount of magnetization is 40% or less when left for 7 days in an environment of a temperature of 60 ° C. and a relative humidity of 90%, and the amount of metal Bi is expressed by the formula metal Bi / ( MnBi + metal Bi) <0.5 (where metal Bi is the peak area from the (012) plane in the X-ray diffraction peak of Bi, and MnBi is M
It is the peak area from the (101) plane in the X-ray diffraction peak of nBi. ) Is MnBi magnetic powder having an amount represented by), and further, a MnBi magnetic powder in which an inorganic film is formed in the vicinity of the surface of the magnetic particles, the manufacturing method of which is Mn powder having a particle diameter of 50 to 300 mesh. Or M
The powder mainly composed of n and the powder mainly composed of Bi or Bi are mixed at a molar ratio of Mn and Bi of 45:55.
To 65:35, and then press-molding this mixture in a non-oxidizing or reducing atmosphere,
MnBi is obtained by heating and reacting at a temperature not higher than the melting point of Bi,
Next, this MnBi is crushed in a non-oxidizing atmosphere to form fine particles, and the magnetic powder thus obtained is heat-treated in an oxygen-containing atmosphere. Since the heat treatment is performed in a non-oxidizing atmosphere, the corrosion resistance is remarkably improved and the saturation magnetization is hardly deteriorated.

Further, such a magnetic powder mainly composed of MnBi is contained in the magnetic layer, and a coercive force measured by applying a magnetic field of 16 KOe is 5000 to 1 at 300K.
100-1500 Oe at 6000 Oe at 80K,
The magnetic flux density measured by applying a magnetic field of 16 KOe at 300 K is 500 to 2500 G, and the rectangular shape in the longitudinal direction is 0.6.
0 to 0.95, the decrease rate of the magnetic flux density is 50 when left for 7 days in an environment of temperature 60 ° C and relative humidity 90%.
% Or less, the magnetic layer further contains a binder resin having a basic functional group in the magnetic layer, and an additive having a basic functional group in the magnetic layer, and the surface of the magnetic layer or the magnetic layer. A water repellent layer is provided between the base and the base, and further,
A magnetic recording medium such as a magnetic card having a magnetic layer using a normal magnetic powder together with the above MnBi magnetic powder has a characteristic that once recorded, it cannot be easily erased at room temperature.
It is possible to prevent tampering, which has been a serious problem in magnetic cards, and the deterioration of saturation magnetization is extremely small even when stored for a long time under high temperature and high humidity.

Further, the magnetic recording medium of the present invention has an extremely high coercive force of about 10,000 Oe or more at room temperature,
Since the magnetic recording medium has a peculiar property that the coercive force is reduced to about 1500 Oe or less at a temperature of about 100 K or less, the magnetic recording medium is cooled to a temperature of about 100 K or less to be in a demagnetized state, and then at room temperature, using a magnetic head The signal can be recorded so that the recorded data cannot be easily rewritten at room temperature. Recording is performed by using a reproducing apparatus for a magnetic recording medium, which is provided on the upstream side of a magnetic head of the reproducing apparatus for a magnetic recording medium, a magnetic field applying means for applying a direct current or an alternating magnetic field smaller than the coercive force of the magnetic layer to the magnetic layer. By reproducing, the data of the falsified magnetic recording medium obtained by copying the data of this magnetic recording medium cannot be reproduced, and only the data of the genuine magnetic recording medium can be reproduced.

The present invention will be described in detail below.
First, MnBi magnetic powder has a high coercive force of about 12000 Oe at room temperature as shown in FIG. 1, which shows the temperature dependence of the coercive force as an example, but decreases as the temperature decreases.
It becomes 1500 Oe or less at 0K. Therefore, this property can be utilized to demagnetize by cooling to a low temperature, and after demagnetization, it can be easily magnetized at room temperature.

Further, as is clear from FIG. 2 showing the initial magnetization curve of the magnetic recording medium using this MnBi magnetic powder, when cooled at a low temperature to be in a demagnetized state, 2000 at room temperature.
It can be easily magnetized in a magnetic field as low as Oe. However, this magnetic recording medium, once magnetized, is 140
It exhibits a high coercive force of about 00 Oe, making it almost impossible to erase or rewrite data thereafter.

FIG. 3 illustrates an erasing characteristic of a magnetic card using such a magnetic recording medium.
When the magnetic field of about 1000 Oe is applied, the magnetic field is almost completely demagnetized and the reproduction output becomes almost zero, which means that the data of the ordinary magnetic card can be easily rewritten. On the other hand, in the magnetic card using MnBi magnetic powder, the output decreases only by about 30% even when a magnetic field of about 5000 Oe is applied, and even when a magnetic field of about 8000 Oe is applied, the output is still 50%. % Remains,
This means that once the data is recorded, it is extremely difficult to rewrite it.

The MnBi magnetic powder of the present invention is produced by pulverizing the MnBi ingot by powder metallurgy, arc furnace melting, high frequency melting, melt quenching, etc.
For example, in the case of manufacturing by the powder metallurgy method, it is manufactured as follows by dividing it into a step of producing an ingot, a step of crushing the ingot, and a stabilization treatment step. The MnBi magnetic powder may be used instead of the pulverization method.

First, the production of an ingot is 50 to 300.
The Mn powder and Bi powder of the mesh are sufficiently mixed, and this is pressed under pressure to form a molded body, and an ingot is produced.
Although this mixing is preferably performed in an inert atmosphere, it may be performed in an oxidizing atmosphere.

When Mn powder and Bi powder are mixed, the molar ratio (Mn / Bi) is 45:55 to 65: 3.
The range of 5 is preferable, and when Mn is larger than that of Bi, MnBi magnetic powder is improved in corrosion resistance by forming Mn oxide or hydroxide on the surface thereof. Good quality magnetic powder can be obtained.
Therefore, it is more preferable to increase Mn as compared with Bi.

As the Mn powder and the Bi powder used here, those having a small content of impurities are preferably used, but when adjusting the magnetic characteristics, Ni, A and
It is used by adding a metal such as 1, Cu, Pt, Zn, or Fe. When such a metal is added, the magnetic properties cannot be well controlled if the added amount is less than 0.6 atomic% with respect to MnBi, and if the added amount is more than 5.0 atomic%, MnBi crystals are added. Since the structure itself is impaired and the original characteristics of MnBi cannot be exhibited, it is preferable to set the content within the range of 0.6 to 5.0 atom%. As a method of adding these, it is preferable to previously make an alloy of Mn and these elements.

As the Mn powder and the Bi powder,
What was crushed in advance may be used, or lumps such as flakes or shots may be crushed into fine powder for use. In the case of synthesizing by a sintering reaction, MnBi is produced by a diffusion reaction through a contact interface between Mn and Bi. Therefore, if Mn powder and Bi powder are pulverized to 50 to 300 mesh, the production reaction is smooth. And the reaction is greatly influenced by the surface property, so Mn powder and Bi
It is preferable to remove the oxide film on the powder surface. For this reason, it is preferable to previously perform surface treatment performed by powder metallurgy such as etching the surfaces of Mn powder and Bi powder with an acid or degreasing with a solvent. The Mn powder and the Bi powder are mixed by an arbitrary means such as an automatic mortar and a ball mill.

When the Mn powder and the Bi powder are pressed to form a molded body, it is preferable that the pressing force is 1 to 8 t / cm ^2. , The sintering reaction is promoted and a uniform ingot is produced. On the other hand, if the applied pressure is too low, the uniformity of the MnBi ingot cannot be obtained. If the applied pressure is too high, the pressurizing device becomes expensive, but the characteristics of the MnBi ingot are not improved.

The obtained molded body is sealed in a glass container or a metal container, and the inside of the container is kept in a vacuum or an inert gas atmosphere to prevent oxidation during heat treatment. Hydrogen, nitrogen, argon or the like is used as the inert gas, but nitrogen gas is most preferably used in terms of cost.
The container in which the molded body is thus sealed is then placed in an electric furnace and heat-treated at 260 to 271 ° C. for 2 to 15 days. If the temperature of this heat treatment is too low, the heat treatment takes time, and the amount of magnetization of the obtained ingot decreases.
On the other hand, if it is too high, Bi melts and flows out, and a uniform ingot cannot be obtained. Therefore, it is preferable to carry out just below the melting point of Bi.

The MnBi ingot thus produced was taken out and coarsely pulverized in advance in an inert gas atmosphere by an automatic mortar or the like to have a particle size of 100 to 500 μm.
adjusted to m. Then, a ball mill, a planetary ball mill, or the like is wet-milled by using the impact of a ball, or a dry mill such as a jet mill to be atomized by the impact of the particles colliding with each other or the wall of the container. It

In the pulverization utilizing the impact of the ball, as the pulverization progresses, the diameter of the ball is gradually reduced to obtain a magnetic powder having a more uniform particle diameter. Originally, since MnBi has a hexagonal crystal structure, it has a property of cleaving, and therefore, it is not necessary to grind it by applying high energy. An organic solvent is preferably used as the liquid in the case of wet pulverization, and a nonpolar solvent such as toluene is preferably used as the organic solvent, and the dissolved water in the solvent is preferably removed in advance. On the other hand, in the case of dry crushing, it is preferable to carry out in a non-oxidizing atmosphere. As the non-oxidizing atmosphere, vacuum or an inert gas atmosphere such as nitrogen gas or argon gas is preferably used.

The average particle size of the MnBi magnetic powder thus obtained is in the range of 0.1 μm or more and 20 μm or less, and the particle size can be controlled depending on the grinding conditions. If the particle size is smaller than 0.1 μm, the saturation magnetization of the finally obtained magnetic powder will decrease, and if it exceeds 20 μm, the coercive force of the magnetic powder will not be sufficiently large, As a result, the surface smoothness of the magnetic recording medium deteriorates and sufficient recording cannot be performed.

Through the above steps, the coercive force measured by applying a magnetic field of 16 kOe is 3000 to 1 at 300K.
50-1000 at 80K, in the range of 5000 Oe
The saturation magnetization amount measured in the range of Oe and applying a magnetic field of 16 kOe at 300 K is 20 to 60 em.
A MnBi magnetic powder in the u / g range is obtained.

However, the MnBi magnetic powder produced by such a method is chemically unstable,
When it is kept under high humidity for a long time, there is a problem that the corrosion progresses and the saturation magnetization deteriorates. Therefore, the following stabilization treatment is performed.

The stabilization treatment method of the MnBi magnetic powder is roughly divided into MnBi magnetic powder near the surface.
Method of forming oxide or hydroxide film of these metals using Mn or Bi contained in Bi magnetic powder itself, and forming film of nitride or carbide of these metals using Mn or Bi There is a method, such as a method of directly forming a coating film on the MnBi magnetic powder, or a method of further forming a coating film of an inorganic material such as titanium, silicon, aluminum, zirconium or carbon on the magnetic film. All of these methods form an inorganic film on the surface of the MnBi magnetic powder, but it is also effective to form an organic film such as a surfactant on the surface of the MnBi magnetic powder.

In such a stabilizing method, Mn or Bi contained in the MnBi magnetic powder itself is used in the vicinity of the surface of the MnBi magnetic powder to form an inorganic film, and oxides of these metals or water are used. There is a method of forming an oxide film, and as a typical method therefor, a method of forming an oxide film using oxygen will be described below.

First, in the step of forming a coating film of Mn and Bi oxides on the surface of the MnBi magnetic powder in the first stage treatment, heat treatment is performed in an oxygen-containing atmosphere at a temperature in the range of 20 to 150 ° C.

As the heat treatment atmosphere, an inert gas containing a certain amount of oxygen is preferable, and it is preferable to heat in a nitrogen gas or an argon gas containing oxygen of about 100 ppm to 10,000 ppm. Although it is possible to heat in air, it is preferable to perform heat treatment in an inert gas atmosphere containing a trace amount of oxygen gas in order to rapidly progress the oxidation reaction in air and obtain a uniform oxide film. .

The heat treatment time is 0.5 to 40 hours.
It is preferable to perform heat treatment for a longer time as the temperature is lower and the temperature is lower. By this heat treatment, MnOx (1 ≦ x ≦ 3.5) oxide of Mn and BiOx (1.5 ≦ x ≦ 2.5) oxide of Bi were formed on the surface of the MnBi magnetic powder. It is formed.

The MnBi magnetic powder is essentially an intermetallic compound in which Mn and Bi are combined at a molar ratio of 1: 1 and, in common sense, an equimolar amount of Bi oxide is produced simultaneously with Mn. However, when the heat treatment of the present invention is performed, an oxide of Mn is preferentially generated over Bi. The reason for this is not clear, but when the oxidation is performed under the mild oxidation conditions of the present invention, B
Mn having an electrode potential lower than that of i is preferentially oxidized over Bi, and as a result, the metal Mn becomes leaner than the metal Bi near the surface, and the MnBi magnetic powder becomes Mn near the surface.
Is diluted, so that inside the magnetic particles, Mn diffuses from the inside of the particles toward the surface so that the concentration distribution of Mn and Bi becomes as gentle as possible, and the diffused Mn is also preferentially oxidized. As a result, it seems that Mn oxide is preferentially formed near the surface.

On the other hand, when MnBi magnetic powder is rapidly oxidized, Bi oxide is also produced at the same time as Mn. A magnetic powder in which an oxide of Mn is preferentially formed and B simultaneously with Mn.
In the magnetic powder in which the oxide of i was also formed, the corrosion resistance was remarkably different even though there was not much difference in the saturation magnetization in the initial state, and the magnetic powder in which the oxide of Mn was preferentially formed had extremely excellent corrosion resistance. Indicates. Thus, the preferential formation of Mn oxide represented by MnOx near the surface of the magnetic powder is clearly recognized by X-ray photoelectron spectroscopy analysis.

By the above heat treatment, the oxide of Mn is preferentially produced, but at the same time, the oxide of Bi is also produced to some extent. The ratio of the oxide of Mn and Bi is preferably 2 or more in terms of atomic ratio of Mn and Bi (Mn / Bi), and when it is 2 or less, the Mn oxide and Bi oxide form a local battery. It is easy and corrosion resistance is insufficient. On the other hand, Mn
A larger ratio of the oxides of Bi and Bi is preferable from the viewpoint of corrosion resistance, but in order to increase the ratio, the degree of oxidation must be increased, and as a result, the initial value of saturation magnetization tends to decrease. Therefore, normally, the ratio of the oxide of Mn and Bi is preferably about 50 or less in terms of the atomic ratio of Mn and Bi (Mn / Bi).

As described above, as the degree of oxidation increases, the oxide film formed near the surface becomes thicker and corrosion resistance improves, but the initial value of saturation magnetization decreases. The amount of the oxide film is about 1 to 5 with respect to the magnetic particles.
0% by weight. Although it is generally difficult to accurately measure the thickness of the oxide coating, it is preferable to adjust the thickness of the magnetic coating so that it will be in the range of 20 to 60 emu / g at 300K as represented by the saturation magnetization of the magnetic powder. Saturation magnetization is 20em
A magnetic powder having a particle size smaller than u / g has a thick oxide film and thus has good corrosion resistance, but has a too low saturation magnetization and a small reproduction output when used as a magnetic recording medium. 60e again
If it is larger than mu / g, the oxide film is too thin and the corrosion resistance is poor.

By the first stage treatment as described above, MnB
Although the corrosion resistance of the i magnetic powder is remarkably improved, the magnetic powder in this state has an extremely strong catalytic activity, and in the magnetic recording medium, the magnetic powder is usually dispersed in a binder resin which is an organic substance. When the magnetic powder having a strong catalytic activity comes into contact with the binder resin which is an organic substance, the binder resin is decomposed due to its catalytic property, and further, the substance generated from the decomposed binder resin may corrode the magnetic powder.

Then, next, by the first stage treatment, MnB
After forming a film of MnOx near the surface of the i magnetic powder,
As the second stage treatment, heat treatment is further performed in an inert gas to convert this MnOx into MnO ₂ . This MnO ₂
Is a stable oxide, but is not generated unless it is heated to a high temperature in an oxidizing atmosphere, and usually needs to be heated at a high temperature of 500 ° C. or higher. However, such high temperature heating in an oxidizing atmosphere not only significantly reduces the saturation magnetization of the magnetic powder, but also causes the magnetic powder to sinter and agglomerate.

Under these circumstances, the inventors of the present invention have conducted various studies, and as a result, instead of directly forming MnO ₂ on the surface of the magnetic powder, once MnO x is formed, heat treatment is performed in an inert gas. It has been found that it can be efficiently converted to MnO ₂ at a relatively low temperature. That is, instead of being formed directly MnO ₂ metal Mn, if by way of MnOx to generate MnO _2, a relatively dense at low temperatures Mn
It has been discovered that it is possible to form an O ₂ coating.

The heat treatment temperature is preferably higher than the heat treatment temperature in the first stage treatment, and usually 200 to
It is preferably about 400 ° C. If the temperature is lower than 200 ° C, the conversion to MnO ₂ is insufficient, and if the temperature is higher than 400 ° C, MnBi easily decomposes into Mn and Bi. Nitrogen gas or argon gas is usually used as the inert gas, but the same effect can be obtained by heat treatment in vacuum. Further, as the structure of MnO ₂ , α type, β type, and γ
Although the type is known, it is preferable to use β-type, which has the smallest catalytic activity.
It is particularly preferable to set the temperature to about 0 to 400 ° C.

By applying such heat treatment, Mn
An oxide film of Mn mainly represented by MnO ₂ is formed near the surface of the Bi magnetic powder. The fact that such a film is formed is clearly recognized by measuring this magnetic powder by ESCA (X-ray photoelectron spectroscopy), and in the ESCA analysis chart, 2p electrons of Mn tetravalent ion are observed. The peak area based on the atomic ratio is 0.5 to 0.5 when compared with the peak area based on 2p electrons of metal Mn.
It will be 50 times. Further, the Bi oxide film is also formed at the same time, but as a result of the Mn oxide film being preferentially formed, the peak area based on the 2p electron of the Mn ion is 4f of the Bi ion as measured by ESCA. The peak area based on electrons is more than doubled in terms of atomic ratio.

In the above method, in order to improve the corrosion resistance of the MnBi magnetic powder, M is added to the surface of the MnBi magnetic powder.
It describes a basic method for forming an oxide of n. It is also possible to form a hydroxide on the surface of the magnetic powder by subjecting the magnetic powder to a heat treatment in an atmosphere containing a small amount of water. Further, it is also possible to form a mixture of the above Mn oxide and a hydroxide.

As described above, the heat treatment preferentially forms an oxide of Mn mainly represented by MnO ₂ on the surface of the MnBi magnetic powder, and does not deteriorate the properties such as coercive force and orientation, and the magnetic property is excellent in corrosion resistance. A powder can be obtained.

The saturation magnetization of the magnetic powder thus treated shows an initial value of 20 to 60 emu / g, and even after the magnetic powder is kept in an environment of a temperature of 60 ° C. and a relative humidity of 90% for 7 days. The deterioration rate is 40% or less. Further, such excellent corrosion resistance is due to MnBi as described above.
The deliquescent that is inherently suppressed is suppressed and Mn and B due to water content
This is because the decomposition into i is prevented, but the X-ray diffraction analysis of the magnetic powder subjected to this heat treatment reflects that the decomposition into Mn and Bi is prevented, and the temperature is 60 ° C. and the relative humidity is 60 ° C. The amount of metal Bi is 0.5 or less as expressed by metal Bi / (MnBi + metal Bi) even after being kept in a 90% environment for 7 days.

Besides, by forming a dense film of nitride or carbide on the surface of the MnBi magnetic powder, the corrosion resistance is remarkably improved, and in order to form the film of nitride, in a nitrogen or ammonia gas atmosphere, Alternatively, it can be formed by heat treatment in a mixed gas containing hydrogen in these gases as necessary. When forming a carbide film, it is formed by heat treatment in a gas atmosphere containing carbon such as carbon monoxide or methane, or in a mixed gas containing hydrogen as needed for these gases. be able to. Heating temperature is usually 300-4
The temperature is preferably 00 ° C.

Further, a nitride or a carbide such as Mn or Bi is replaced with C.
It is also possible to deposit and form from the gas phase by the VD method or the thermal decomposition method. Further, when a nitride or a carbide such as Mn or Bi is newly deposited and formed on the surface of the MnBi magnetic powder on which the above oxide film is formed, the corrosion resistance is further improved.

Further, Ti, on the surface of the MnBi magnetic powder,
Corrosion resistance is also improved by forming a film of an inorganic material of a metal such as Si, Al, Zr, Mg, Pb, or P, and an oxide is suitable as a stable inorganic material of these metals capable of forming a dense film. There is.

Specifically, there are titanium oxide, silicon oxide, aluminum oxide, zirconium oxide, magnesium oxide, lead oxide and the like, and complex oxides or solid solutions containing two or more kinds of these oxides, such as mullite and titanium. Aluminum oxide, forsterite, cordierite, spinel and the like are also used. Also these oxides,
The composite oxide or the solid solution can be used without distinction in the crystalline state or the amorphous state.

In order to coat the surface of the MnBi magnetic powder with the above-mentioned oxide, complex oxide, or solid solution, a method usually used for surface modification of powder can be applied. That is, a liquid phase method such as a sol-gel method, a precipitation method or a microencapsulation method, a vapor phase method such as a CVD method or a thermal decomposition method, or a mechanochemical method is used.

For example, in the case of forming a film by the liquid phase method, MnBi magnetic powder is dispersed in an organic solvent such as toluene, and then an organic metal such as titanate, silane or silazane is added to this dispersion. Dissolve. Next, a small amount of water is added to this dispersion, or water is adhered to the MnBi magnetic powder in advance, whereby these organic metals are hydrolyzed on the surface of the magnetic powder and adsorbed on the surface of the magnetic powder. . Next, when this magnetic powder is heated in a non-oxidizing gas atmosphere or an atmosphere containing a trace amount of oxygen, the organic metal adsorbed on the surface of the magnetic powder is dehydrated and condensed to form an oxide film such as titanium oxide or silicon oxide. To be done.

As described above, by forming an oxide or hydroxide film of Mn or Bi on the surface of the MnBi magnetic powder, or by forming a nitride or carbide film of Mn or Bi, Ti is further added. , Si, Al, Zr, M
By forming a film of a metal inorganic material such as g, Pb, or P, the corrosion resistance of the MnBi magnetic powder can be significantly improved. Further, it is preferable to form the coating film of these inorganic materials so as to have a weight ratio of 2 to 50% with respect to MnBi. If the amount is too small, the corrosion resistance becomes insufficient, and if it is too large, the saturation magnetization decreases. . By forming the inorganic film in the above range, it is possible to obtain magnetic powder having a good balance of corrosion resistance and magnetic properties.

By such a method, the average particle diameter of the magnetic powder is in the range of 0.1 μm or more and 20 μm or less, and 1
The coercive force measured by applying a magnetic field of 6 kOe is 300 K
In the range of 3000 to 15000 Oe, 80K in the range of 50 to 1000 Oe, and 300K
In this, MnBi magnetic powder having a saturation magnetization measured by applying a magnetic field of 16 kOe in the range of 20 to 60 emu / g can be obtained.

Further, the magnetic powder treated by the above method exhibits excellent corrosion resistance.
Even after being kept in an environment of 90% relative humidity for 7 days, the deterioration rate is 40% or less. Furthermore, Mn and B due to water content
Reflecting that the decomposition into i was prevented, the magnetic powder was analyzed by X-ray diffraction, and the amount of the metal Bi was found to be the same as that of the metal B even after being kept in an environment of a temperature of 60 ° C. and a relative humidity of 90% for 7 days.
It is 0.5 or less when expressed by i / (MnBi + metal Bi).
Furthermore, this magnetic powder not only exhibits excellent corrosion resistance at high temperature and high humidity, but also shows little deterioration in saturation magnetization even when immersed in a corrosive solvent such as sodium chloride aqueous solution or acetic acid aqueous solution, and has extremely excellent corrosion resistance. Show.

A magnetic recording medium using the MnBi magnetic powder manufactured as described above is manufactured according to a conventional method.
For example, MnBi magnetic powder is mixed and dispersed with a binder resin, an organic solvent and the like to prepare a magnetic coating material, which is coated on a substrate and dried to form a magnetic layer.

As the binder resin used here, any of those generally used in magnetic recording media is used. For example, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, fibrin resin. Resins, fluorine-based resins, polyurethane-based resins, isocyanate compounds, radiation-curable resins, etc. are used.

As already described, the MnBi magnetic powder easily corrodes and decomposes in the presence of water, and particularly when the water is acidic, the corrosion and decomposition become remarkable. So MnB
When the i magnetic powder is uniformly dispersed in the magnetic layer, the above-mentioned binder resin is sufficient, but in order to further improve the stability against moisture, the above-mentioned binder resin contains a basic functional group. It is preferable. In particular, MnBi magnetic powder is improved in corrosion resistance by the above-mentioned treatment,
By further containing a basic functional group in the binder resin, the corrosion resistance can be further improved. As the basic functional group, for example, imine, amine, amide, thiourea, thiazole, ammonium salt or phosphonium compound is suitable.

It is also effective to add an additive having a basic functional group as a means for containing a basic functional group in the magnetic layer. As for the basic functional group contained in this additive, imine, amine, amide, thiourea, thiazole, ammonium salt, phosphonium compound or the like is also suitable as in the binder resin.

Specifically, methylamine, ethylamine, propylamine, isopropylamine, butylamine, amylamine, hexylamine, heptylamine,
Octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, cetylamine,
Aliphatic primary amines such as stearylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, aliphatic secondary amines such as diamylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, triamylamine, triamine Aliphatic tertiary amines such as dodecylamine, as well as aliphatic unsaturated amines, cycloaliphatic amines and aromatic amines are preferably used. Furthermore Si
Suitable examples include those obtained by modifying a coupling agent such as Al, Ti, and the like with various amines.

Generally, the larger the amount of such an additive containing a basic functional group added, the greater the effect on improving the corrosion resistance, but if it is too large, the magnetic flux density of the magnetic layer decreases. Therefore, the weight ratio is usually 1 to 1 with respect to the magnetic powder.
It is preferable to add about 5%, but it is particularly preferable to add about 4 to 10% by weight as a range in which the effect of improving the corrosion resistance is large without significantly reducing the magnetic flux density of the magnetic layer.

As the organic solvent, conventionally used organic solvents such as toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran and ethyl acetate may be used alone or in admixture of two or more. Further, for the reasons described above, it is preferable to remove the water dissolved in these organic solvents as much as possible before use, and it is further preferable to use a nonpolar solvent in which water is difficult to dissolve among the organic solvents. preferable.

In the magnetic paint, various kinds of commonly used additives such as dispersants, lubricants and antistatic agents may be optionally added. However, when an acidic substance is present, MnBi is present. The magnetic powder easily deteriorates. Therefore, it is preferable from the viewpoint of corrosion resistance that the amount of the acidic lubricant that is usually used in the magnetic recording medium is as small as possible.

The content ratio of the magnetic powder must be such that the volume ratio of the magnetic powder in the magnetic layer is 5 to 60%. If this ratio is small, the output when used as a magnetic recording medium is low. At the same time, the corrosion resistance is also reduced.
Thus, if the volume ratio of the magnetic powder is too small, the cause of the deterioration in corrosion resistance is unknown, but if the occupancy ratio of the binder resin in the coating film is too large, the water content tends to easily penetrate and the corrosion resistance is improved. Expected to decline. On the other hand, if the volume ratio of the magnetic powder is too large, the dispersibility of the magnetic powder deteriorates and the orientation of the magnetic powder decreases, and at the same time, the effect of embedding the magnetic powder by the binder resin becomes insufficient and corrosion resistance decreases. . As described above, the occupied volume ratio of the MnBi magnetic powder in the coating film affects the magnetic characteristics and the recording characteristics as in the case of the ordinary magnetic recording medium. It also affects the point of corrosion resistance.
Therefore, in order to obtain a coating film excellent in not only magnetic characteristics and recording characteristics but also corrosion resistance, the volume ratio of the magnetic powder is 5 to 60.
%, It is necessary to design the content to be 10%, and if it is 10 to 50%, the effect of improving the corrosion resistance is improved, and it is most preferably 20 to 45%.

As described above, the MnBi magnetic powder is mixed and dispersed with the binder resin, the organic solvent and the like to prepare a magnetic paint, and the magnetic paint is applied onto a substrate such as a polyester film by an arbitrary application means and dried. When forming the magnetic layer, it is preferable to apply a magnetic coating on the substrate and then perform magnetic field orientation parallel to the surface of the magnetic layer. The magnetic field strength is preferably about 500 to 3000 Oe.

When the magnetic layer is formed in this way, 1
The coercive force measured by applying a magnetic field of 6 kOe is 300
In the range of 5000 to 16000 Oe at the temperature of K,
In the range of 100 to 1500 Oe at a temperature of 80 K, and the magnetic flux density Bm measured by applying a magnetic field of 16 kOe at 300 K is in the range of 500 to 2500 G,
A magnetic recording medium having a longitudinal Br / Bm of 0.60 to 0.95 can be obtained.

When applied to a magnetic card, it is applied on a substrate on which a release layer has been applied in advance. It should be noted that the release layer is conventionally made of silicone resin or the like.
A synthetic resin material having a poor surface activity, which is used for a peeling layer such as a seal, a seal, and a sheet, can be used. As for thickness
0.1 to 2.0 μm is suitable.

In order to further improve the corrosion resistance and chemical resistance of the magnetic layer containing the MnBi magnetic powder, it is preferable to provide a water repellent layer made of a water repellent resin between the release layer and the magnetic layer. As the water-repellent resin, polyvinylidene chloride resin, ethylene-vinyl alcohol-based polymer,
Fluorine resin, vinylidene fluoride resin, acrylic resin or the like can be used. The thickness of the water-repellent layer is preferably 0.5 to 10 μm. When the thickness is smaller than this, a sufficient water-repellent effect cannot be obtained. Output decreases.

The magnetic recording medium thus manufactured exhibits excellent corrosion resistance, a temperature of 60 ° C. and a relative humidity of 90%.
The rate of decrease in magnetic flux density when left for 7 days in the environment is 50% or less. Even when immersed in a 5% acetic acid aqueous solution, which is an extremely severe corrosion condition, for 24 hours, the reduction rate of the magnetic flux density is 80% or less. Further, this magnetic recording medium was cooled to a low temperature to be demagnetized,
The magnitude of the magnetic flux density when a magnetic field of 500 Oe is applied is 50% or more of the saturation magnetic flux density at 300K.

Of course, such MnBi magnetic powder can be used in combination with other magnetic powders.
By using them in combination, it is possible to provide a magnetic recording medium having unique characteristics which are not available in the conventional magnetic recording medium, which utilizes the characteristics of the MnBi magnetic powder.

In this case, as the magnetic powder to be mixed, gamma iron oxide magnetic powder, cobalt-containing iron oxide magnetic powder, B
An a-ferrite magnetic powder, an Sr-ferrite magnetic powder, a metallic magnetic powder mainly composed of Fe, or the like having a coercive force of about 250 to 3000 Oe at room temperature is preferably used. The advantages of mixing and using these magnetic powders with MnBi magnetic powders are roughly divided into the following four points.

Since these magnetic powders generally have a larger saturation magnetization than MnBi magnetic powders, the magnetic flux density of the magnetic recording medium becomes large and a high output is easily obtained as compared with the case where MnBi magnetic powders are used alone. . When the oxide magnetic powder is mixed, these magnetic powders have no problem of corrosion, so that the corrosion resistance of the magnetic recording medium is further improved. When the MnBi magnetic powder is mixed with another magnetic powder having a low coercive force, it is difficult to falsify the data,
It is possible to lower the write current value of data. As will be described in detail later, when recording data, different data is overwritten on the same rack and a filter is added during playback.
Multiple recording can be performed by separating and reproducing the data through the above.

Even when the MnBi magnetic powder and the above-mentioned magnetic powder are mixed and used, the preparation of the magnetic paint is basically the same as the case where the MnBi magnetic powder is used alone. However, it is preferable to adjust the dispersing means of the magnetic powder, the magnetic field orientation strength, etc. to some extent according to the kind and mixing amount of the magnetic powder to be mixed. The mixing ratio of the MnBi magnetic powder and these magnetic powders is 1: 9 by weight.
7: 3 is preferable, and when the mixing ratio of MnBi magnetic powder and other magnetic powder is higher than this ratio, MnB
When the i magnetic powder is used alone, the above advantages are less likely to be exhibited, and when it is too small, it is easy to record the data once, which is the most important feature of the magnetic recording medium using the MnBi magnetic powder. Features that are not erased are compromised.

Further, as a magnetic recording medium, a magnetic layer using MnBi magnetic powder, gamma iron oxide magnetic powder, Co
Containing iron oxide magnetic powder, Ba-ferrite magnetic powder, Sr
-A magnetic layer using a ferrite magnetic powder or a metallic magnetic powder mainly composed of Fe may be laminated, and the advantage of laminating in this way is basically the above-mentioned MnBi magnetic powder and other magnetic materials. It is similar to the case of using by mixing with powder.

In particular, the magnetic recording medium in which the magnetic layers are laminated in this way can be rewritten on one magnetic recording medium.
There is a feature that two types of data can be written, that is, data and data that is extremely difficult to rewrite once the data is written.

For example, a magnetic layer using MnBi magnetic powder is formed in a stripe shape, and gamma iron oxide magnetic powder, Co-containing iron oxide magnetic powder, Ba-ferrite magnetic powder, Sr-ferrite are formed so as to cover the stripe. When a magnetic layer made of magnetic powder or metallic magnetic powder mainly composed of Fe is applied, the portion where the magnetic layer made of MnBi magnetic powder is not laminated has the same data rewriting as a normal magnetic recording medium. You can However, MnBi
Although data can be easily written in a portion where a magnetic layer using a magnetic powder and a magnetic layer using another magnetic powder are stacked, rewriting becomes extremely difficult. Such characteristics cannot be realized by the conventional magnetic recording medium,
This can be realized for the first time by using MnBi magnetic powder in such a structure.

The thickness of the magnetic layer in the case of stacking in this manner is, for example, 2 to 20 μm for both upper and lower layers when applied to a magnetic card, and the total thickness is 3 to 3
It is preferably about 0 μm. If this thickness is too thin, the output will be small, and the reliability as a card will be low. On the other hand, if it is too thick, it will be difficult to record uniformly on the entire magnetic layer, and the error rate will increase during data reproduction. Also in this case, it is possible to use the above-mentioned various methods in combination, such as forming the water-repellent resin layer on the surface of the magnetic layer or inserting it between two types of laminated magnetic layers. .

When a magnetic card is produced as a magnetic recording medium thus formed, the above magnetic coating material is applied while magnetic field orientation is applied on a base base film on which a release layer is applied in advance. And dry. If necessary, an adhesive layer is applied on the magnetic layer thus produced. As the adhesive layer, usually, a heat-fusion adhesive such as urethane resin or acrylic resin is preferably used.
Adhesives such as isocyanate-curing type and UV-curing type can also be used. It is also possible to use the resin of the magnetic layer to heat-bond to the card substrate without using this adhesive.

When the water repellent layer is provided for the purpose of further improving the corrosion resistance and water resistance of the magnetic layer, a water repellent layer made of a water repellent resin is further provided between the release layer and the magnetic layer.
When this water repellent layer is used, it is generally composed of a base base film, a release layer, a water repellent layer, a magnetic layer and an adhesive layer. Further, it is of course possible to use a combination of methods usually used for magnetic cards, such as forming a concealing layer such as a color layer between the release layer and the magnetic layer.

Further, after the magnetic tape of the magnetic recording medium formed as described above is slit into a predetermined width, the adhesive layer side is superposed on the magnetic card substrate or the like, and the heating roll is placed thereon. It is prepared by temporarily adhering the adhesive layer to the surface of the card substrate by a method such as pressing with a la, and then by peeling the base film, and further by thermocompression bonding with a press plate or the like, the adhesive layer, the magnetic layer, Embed the release layer in the substrate,
It is also manufactured by punching into the shape of a card.

The magnetic recording medium thus manufactured is initialized and recorded / reproduced. First, in the initialization of the magnetic recording medium using the MnBi magnetic powder, the MnBi magnetic powder is extremely large at room temperature. While having a coercive force, 1
This is done by utilizing the property that the coercive force is significantly reduced when cooled to a low temperature of about 00K or less.
The magnetic recording medium has a temperature of 300 to 30 at a temperature below K.
This is a step of applying an alternating magnetic field of 00 Oe to demagnetize the magnetic recording medium. Such initialization may be performed while the tape is running in a magnetic tape state, or may be performed batchwise while being wound on a reel. Further, it is of course possible to use the magnetic card.

The data recording method itself is the same as the ordinary magnetic recording method. For example, when applied to a magnetic card, an encod- ing machine for a magnetic card or a magnetic card is used. Data can be recorded using a card reader / writer. Unlike other magnetic recording media, once the data is recorded in the magnetic recording medium using the MnBi magnetic powder, it becomes extremely difficult to erase or rewrite the data thereafter.

At this time, when the MnBi magnetic powder and other magnetic powder are mixed and used, or when the magnetic layer using MnBi magnetic powder and the magnetic layer using other magnetic powder are laminated and used, In the case of multiple recording, data recording is performed at least twice.

As for the order, first, non-rewritable fixed data (A) is recorded by using a writer. M in this state
The same data (A) is recorded on the nBi magnetic powder and the magnetic powders other than the MnBi magnetic powder. Further, the recording magnetic field at this time depends on the coercive force of other magnetic powder used together with the MnBi magnetic powder, but it is preferable that the recording magnetic field is as high as possible within a range in which magnetic powder other than the MnBi magnetic powder is not demagnetized. This is a phenomenon peculiar to the magnetic recording medium using the MnBi magnetic powder, and is based on the phenomenon that the coercive force of the magnetic recording medium is improved as the recording magnetic field is higher.

Next, rewritable data (B) is overwritten and recorded on the same track. At this time, the fixed data (A) that cannot be rewritten and the rewritable data (B) are recorded with different recording densities. As for the recording density at this time, generally, rewritable data requires a larger recording capacity than fixed data, and therefore fixed data can be rewritten. Recording density of 3 to 100
It is preferable to make it twice as high. Further, in order to prevent the magnetic fields from the signals of (A) and (B) from interfering with each other and separate and reproduce the data by using a filter or the like, the difference in recording density is given in this way. There is a need. From the standpoint of separability, the larger the difference in recording density, the better.
In order to increase the amount of data of (A), it is preferable to make it about 100 times or less.

Generally, it is preferable to form data having a low recording density in the lower layer of the magnetic recording medium and data having a high recording density in the upper layer. This is because the higher the recording density, the greater the influence of the spacing loss between the magnetic head and the magnetic recording medium. Therefore, it is preferable to arrange the data having a higher recording density closer to the magnetic head.

By such multiple recording, first, the data (A) is recorded over the entire magnetic layer, and then the data (B) is overrecorded. Then, another magnetic powder of MnBi magnetic powder or those The magnetic layer using the magnetic powder of
Data (B). On the other hand, the MnBi magnetic powder or the magnetic layer using the MnBi magnetic powder has an extremely large coercive force of 10,000 Oe or more at room temperature once the data is recorded. Therefore, the data (B) recorded later is not recorded, and Only the fixed data (A) recorded in (3) remains recorded.

If a DC magnetic field is applied after recording a non-rewritable (A), this (A) is more stabilized against an external magnetic field. The magnetic field at this time is 3000
It is preferably about 10000 Oe. After that, the data (B)
By recording by the method described above, the fixed data (A) and the rewritable data (B) can be recorded on the same track.

Furthermore, when a magnetic layer using MnBi magnetic powder and a magnetic layer using other ordinary magnetic powder are laminated,
Two types of data can be written on one magnetic recording medium, that is, rewritable data and data that is extremely difficult to rewrite once the data is written.

For example, a magnetic layer using MnBi magnetic powder is partially formed in a stripe shape, and gamma iron oxide magnetic powder, Co-containing iron oxide magnetic powder, and Ba-ferrite magnetic powder are formed so as to cover the magnetic layer. , Sr-ferrite magnetic powder or metallic magnetic powder mainly composed of Fe is applied. The data written in the portion where the magnetic layer using the MnBi magnetic powder and the magnetic layer using another magnetic powder are laminated is extremely difficult to rewrite.
In the non-laminated portion, data can be rewritten in the same manner as a normal magnetic recording medium.

As a data recording method, first, a non-rewritable fixed data (a) is usually formed on a portion where a magnetic layer using MnBi magnetic powder and a magnetic layer using another magnetic powder are laminated. Record by method. Even if the recorded data (a) is rewritten to another data (b) for the purpose of falsification, the data (a) recorded in the magnetic layer using the MnBi magnetic powder is rewritten. Since this is not possible, two types of signals coming from the data of (a) and (b) are mixed at the time of reproduction, the data is destroyed, and it becomes impossible to reproduce with a normal reader. When the fixed data (a) is applied to a magnetic card, for example, the date of issue of the card, the issuer, the ID of the card owner, and other data that cannot be rewritten. To record.

On the other hand, a rewritable data is formed in the portion consisting only of the magnetic layer using magnetic powder other than MnBi magnetic powder.
Record data (c). This data (c) can be arbitrarily rewritten each time it is used, as in a normal magnetic recording medium.

The mixed magnetic layers using the MnBi magnetic powder and other magnetic powders and the magnetic layers obtained by laminating the magnetic layers using these magnetic powders have been described as examples. Of course, various combinations can be used. For example, in the case of applying to a magnetic card, the above-mentioned laminated magnetic layer is formed on one side of the card, and a normal magnetic layer using iron oxide magnetic powder or barium ferrite magnetic powder is formed on the other side. It can also be formed.

Further, the reproduction of data is not particularly different from the reproduction method of an ordinary magnetic recording medium, and can be performed by using an ordinary magnetic head. For example, a magnetic card can be reproduced by using a magnetic card reader.

On the other hand, the reproduction of the above-mentioned multiplex-recorded data will be described in detail in the embodiment, but a signal read by the magnetic head is passed through a bandpass filter and two kinds of data (recording density different from each other are recorded. Separately reproduced into A) and (B). The band width of this band pass filter is +10 centered on the frequency corresponding to the recording density to be reproduced normally.
It is preferable to set the width to about 0% or -50%, but it is possible to change this width according to the required S / N.

The case of applying to a magnetic card has been described above as an example, but it is extremely difficult to rewrite such a data.
Data and a rewritable data like an ordinary magnetic recording medium.
It is needless to say that the application of multiple recording or mixed use on the same magnetic recording medium can be applied not only to magnetic cards but also to all magnetic recording media such as magnetic tapes and floppy disks.

As described above, the magnetic recording medium (for example, a magnetic card) using the MnBi magnetic powder has a property that once data is recorded, it cannot be easily erased at room temperature, that is, the recorded data is easily tampered with. Although it has the feature that it can not be read, the data recorded on this magnetic card can be easily read by the same method as a normal magnetic card.
It is conceivable that the data of this magnetic card is copied to another ordinary magnetic card and this card is illegally used as an authentic card.

Therefore, a reproducing method and an apparatus therefor capable of reproducing the data only from the genuine magnetic recording medium using the MnBi magnetic powder are required.
Data recorded on a magnetic recording medium using nBi magnetic powder
Before reproducing the data, a direct current or an alternating magnetic field smaller than the coercive force of the magnetic layer is applied to the magnetic layer by, for example, a permanent magnet or a magnetic head for applying a magnetic field.

The case of application to a magnetic card will be described as an example. A magnetic card using MnBi magnetic powder cannot be easily erased at room temperature once data is recorded. Even if a magnetic field is applied, the data is hardly affected and can be reproduced. On the other hand, a normal magnetic card
In the magnetic field, the magnetic field erases or destroys the data, making it unreadable. Therefore, even if the card using the MnBi magnetic powder is copied, the data of this copy card cannot be regenerated. Absent.

The strength of this magnetic field must be smaller than the coercive force of the magnetic layer using MnBi magnetic powder and higher than the coercive force of the magnetic layer using ordinary magnetic powder. As for the strength of this magnetic field, for example, for a magnetic layer using gamma iron oxide magnetic powder or Co-containing iron oxide magnetic powder, a magnetic field of 500 to 1000 Oe is applied to copy.
Most of the card data is erased and becomes unreadable. On the other hand, most of the data is erased by applying a magnetic field of about 3000 Oe to the magnetic layer using Ba-ferrite magnetic powder or Sr-ferrite magnetic powder. Therefore, the range of the applied magnetic field is preferably 500 to 5000 Oe. Even if a magnetic field within this range is applied,
Since the data recorded on the magnetic layer using the MnBi magnetic powder is hardly affected, the data can be read accurately.

Further, such a magnetic field may be a DC magnetic field or an alternating magnetic field, and the means is not particularly limited as long as the magnetic field of the above-mentioned intensity is generated. For example, when a DC magnetic field is applied, a permanent magnet may be installed between the magnetic head for data reproduction and the card insertion port. When applying an alternating magnetic field, a reproducing magnetic head and a card are used.
A magnetic head for applying an alternating magnetic field may be installed between the insertion slots. It is also possible to use a reproducing magnetic head to apply a direct current or an alternating magnetic field to the magnetic card and then insert the magnetic card again to read the data with this magnetic head.

On the other hand, when the reproducing method and reproducing apparatus of the present invention are used, not only the magnetic card for the purpose of illegal use but also the data of the ordinary magnetic card may be erroneously erased. . However, this kind of trouble is caused by normal magnetic
Card cannot be inserted, or measures such as ejecting the magnetic card before applying a magnetic field can be added.
This can be prevented by adding identification information to the code.

This identification information can be realized, for example, by providing a cutout or a hole in a part of the magnetic card so that the magnetic card is different in shape from the ordinary magnetic card. When the notch or the pore is detected, for example, optically or mechanically when it is inserted into the reproducing device, the magnetic card having the notch or the pore permits the insertion, and the notch or the pore The missing magnetic card is ejected from the regenerator.

Further, by printing on the card surface with an ink containing a phosphor excited by infrared rays or ultraviolet rays, exciting the phosphors by infrared rays or ultraviolet rays, and detecting the fluorescence emitted from the identification mark. Can also be identified.

[0107]

EXAMPLES Next, examples of the present invention will be shown and described more concretely. << Synthesis of MnBi Magnetic Powder >> First, the synthesis of MnBi magnetic powder will be described. The synthesis method of MnBi magnetic powder is M
The process is divided into a process of producing an nBi ingot, a process of pulverizing the nBi ingot as a raw material to produce MnBi magnetic powder, and a process of heat-treating the pulverized MnBi magnetic powder.

(1) Preparation of MnBi Ingot Mn flakes (manufactured by Furuuchi Chemical Co .; purity 99.9%), B
i-shot (Furuuchi Chemical Co., Ltd .; purity 99.9%) was crushed using a mortar, and the particle size of each of Mn and Bi was 1
Sifting was carried out in the range of 0 to 500 mesh to prepare Mn and Bi powders having different particle sizes. Next, the Mn and Bi powders were weighed so that the molar ratio of Mn and Bi was in the range of 25:75 to 75:25, and thoroughly mixed using a ball mill.

Next, these mixtures were mixed with a pressure press at a pressure of 0.2 to ²⁰ t / cm ² to obtain 6 mmφ × 6 mm.
It was molded into a cylindrical shape. The molded body was placed in a closed aluminum container, evacuated, and then nitrogen gas was introduced at 0.5 atm. Next, this container was put into an electric furnace and heat-treated at a temperature of 250 to 300 ° C. for 1 to 30 days. After the heat treatment, it was taken out in the air and lightly crushed in a mortar to measure the magnetic properties. As the magnetic characteristics, the coercive force when a magnetic field having a maximum magnetic field of 16 kOe was applied and the amount of magnetization at 16 kOe were measured. The coercive force does not depend much on the manufacturing conditions and is 500 to 1000O.
However, the amount of magnetization varied greatly depending on the manufacturing conditions. Therefore, the degree of formation of MnBi in the ingot was evaluated from the value of the amount of magnetization, and the optimum conditions for producing MnBi were obtained.

Examples 1 to 32 The particle size of Mn and Bi powders as raw materials, the mixing ratio of Mn and Bi powders, the molding pressure of the mixture of Mn and Bi powders, the heat treatment temperature and the heat treatment time of the molded body are shown in Table 1 below. The MnBi ingot was produced by changing the MnBi ingot as shown in Table 2, and the magnetization amount of the obtained MnBi ingot was measured. The results are shown in Tables 1 and 2 below.

[0111]

[0112]

From Tables 1 and 2, it is understood that the grain sizes of Mn and Bi as the raw materials influence the magnetization amount of the ingot obtained by the heat treatment. If the particle size is too small, the surface area of the particles will be large, and the reaction will be hindered because the proportion of the oxide film formed on the particle surface will increase.
If the particles are too large, the surface area becomes too small. As a result, the contact area for Mn and Bi to proceed by the diffusion reaction becomes small, the reaction rate becomes slow, and the magnetization amount of the obtained ingot becomes small. Therefore, from Tables 1 and 2, the optimum sizes of the raw material Mn and Bi particles are 50 to 3
It can be seen that it is 00 mesh.

With respect to the mixing ratio of Mn and Bi of the raw materials, the molar ratio of Mn and Bi is 45:55 to 65:
In the range of 35, a high magnetization amount of 40 emu / g or more is obtained, and particularly when this ratio is 55:45 to 50:50 and the mixing ratio of Mn is slightly higher than the mixing ratio of Bi, 5
It can be seen that a large magnetization amount of 0 emu / g or more can be obtained. Further, as the press molding pressure of the mixture of Mn and Bi, there is no particular problem even if it is increased, but it is not preferable to increase it so much in the production, and in order to obtain a sufficiently high magnetization amount, 1 to 8 t / cm ² is preferred.

Further, the heat treatment temperature of this molded product is extremely important for obtaining a high magnetization amount, and it is preferable to perform the heat treatment just below the melting point of Bi. When heat-treated above the melting point of Bi, Bi
Only Mf melts and agglomerates, so the reactivity as MnBi decreases significantly. On the other hand, if this temperature is low, the diffusion reaction speed of Mn and Bi becomes slow, and as a result, a very long heat treatment is required to obtain a high magnetization amount. Considering the productivity, this heat treatment is 260 to 271 ° C just below the melting point of Bi.
It is preferable to carry out.

Regarding the heat treatment time, there is no particular problem because it is too long, but the reaction is almost completed by the heat treatment for 2 to 15 days, and the magnetization amount is 50 emu / g.
The above high values can be obtained.

Examples 33 to 39 (2) Pulverization of MnBi ingot The obtained MnBi ingot was coarsely pulverized in a mortar in an inert (nitrogen) atmosphere using a glove box, and then ball-milled. And pulverized using a jet mill. As the ingot, the one produced by the method shown in Example 3 was used. Regarding ball mill pulverization, a planetary ball mill was used to add 100 parts by weight of solvent to 10 parts by weight of MnBi and pulverize in various solvents. As the pulverizing method, a pulverized zirconia ball having the same diameter is pulverized under the same pulverizing conditions, and a zirconia ball is first used to reduce the number of revolutions (100 rpm), and the pulverizing method is performed in the first stage under a gentle pulverizing condition. After crushing, using a zirconia ball with a smaller ball diameter, the rotation speed (150 r
pm) was increased and the second-stage pulverization was performed for comparison. The jet mill was crushed by changing the atmosphere during crushing. Table 3 shows the Mn thus obtained.
It is the result of having measured the average particle diameter, coercive force, and amount of magnetization of Bi powder.

[0118]

As is clear from Table 3, MnBi fine particles can be produced by any of the ball mill and jet mill methods. Particularly in ball milling, it is preferable to use a nonpolar solvent such as toluene or xylene as the solvent because the reduction in the amount of magnetization due to the milling is small. When the ball diameter is reduced as the pulverization progresses, the particles having a more uniform particle size distribution can be obtained. This is because, as can be seen from Example 35 in Table 3, high saturation magnetization was obtained despite the small particle size, and the generation of fine powder that causes a decrease in the amount of magnetization was small. .

In FIGS. 4 to 7, the average particle size obtained by first performing the first stage pulverization for 2 hours and then performing the second stage pulverization at different times by the two-stage pulverization shown in Example 35. Change in diameter, coercivity at 300K and 80K, and 3
The saturation magnetization at 00K is shown.

FIG. 8 shows the results of examining the change in S ^* due to pulverization. This S ^* is a parameter obtained from the slope of the demagnetization curve of the hysteresis curve as shown in FIG.
The larger this value, the sharper the coercive force distribution of the particles. Each of these measurements was performed by applying a magnetic field of 16 kOe at 300K.

From these figures, as the crushing time becomes longer, the particle size becomes smaller, and the particle size becomes 300 K and 8
The coercive force at 0 K both increases, but the saturation magnetization decreases conversely. Also, as the crushing time increases, S
^* Also increases and the coercive force distribution becomes sharper. From these results, in order to obtain a magnetic powder having a sharp coercive force distribution, the coercive force at 300 K should be 300
It turns out that it is necessary to make it 0 Oe or more.

On the other hand, the coercive force at 300K is 1500.
When it is 0 Oe or more, the tampering prevention function is further enhanced when the magnetic recording medium is used, but as can be seen from FIG. 7, the amount of magnetization is significantly reduced. Therefore, the coercive force at 300K is preferably set in the range of 3000 to 15000 Oe. In addition, the magnetic recording medium of the present invention is recorded at room temperature after being initialized by cooling and demagnetizing at low temperature.
When the coercive force at 0 K is 1000 Oe or more, the demagnetization characteristics at low temperatures deteriorate.

Further, the magnetic powder having a coercive force of 50 Oe or less at 80K has an excessively large particle diameter and is inferior in the orientation of the magnetic powder and the surface property of the magnetic recording medium when it is used as a magnetic recording medium. Therefore, the coercive force at 80K is 5
It is preferable to set it in the range of 0 to 1000 Oe. Although the amount of magnetization decreases as the pulverization progresses, in order to obtain a sufficiently high output when used as a magnetic recording medium, 300 K is required.
In this case, a magnetization amount of 20 emu / g or more is required. Further, the maximum amount of magnetization when the compound having the composition represented by MnBi is generated is approximately 60 emu / g, and therefore the value of the amount of magnetization is preferably set to 20 to 60 emu / g.

As a result of the above examination, the particle size, the coercive force, and the saturation magnetization are related to each other, and the items required for use in the magnetic recording medium of the present invention, that is, the particles suitable for the magnetic recording medium. Diameter Demagnetization property at low temperature High coercive force to prevent tampering at room temperature To satisfy all four requirements of high magnetization to obtain high output, the average particle size should be 0.1 μm or more and 20 μm or less, and 300 K Magnetic force 3000
Coercive force of 5 at 80K in the range of ~ 15000 Oe
It can be seen that it is necessary to set the magnetization amount at 300 K to 20 to 60 emu / g in the range of 0 to 1000 Oe. As described above, when the characteristics of the MnBi magnetic powder satisfy all the above values at the same time, the magnetic powder can be used for the magnetic recording medium of the present invention for the first time.

Examples 40 to 55, Comparative Example 1 << Stabilizing Treatment of MnBi Magnetic Powder >> By the above method,
Although the MnBi magnetic powder having the desired shape and characteristics can be obtained, the MnBi magnetic powder in this state is unstable, and corrosion progresses due to the presence of water, and the magnetization amount decreases. Therefore, stabilization is performed by the heat treatment described below. As the magnetic powder to be heat-treated, an example using a magnetic powder ball-milled by the method shown in Example 35 of Table 3 will be described.

After pulverizing with a ball mill, first, the MnBi magnetic powder was taken out in a state of being immersed in toluene, transferred to a heat treatment container, and vacuum dried at room temperature (25 ° C.) for about 2 hours. Next, in the same container, as the first stage heat treatment, the temperature was variously changed in the range of 20 to 150 ° C. to perform the heat treatment. The heating time is generally long when the heat treatment temperature is low and short when the heat treatment temperature is high, and this example shows an example of heat treatment in the range of 0.5 to 24 hours. Also, as the heat treatment atmosphere, oxygen is 1000 ppm
An example using the contained nitrogen gas is shown.

Further, as a second stage heat treatment,
After removing the oxygen mixed gas filled in the container by evacuation, nitrogen gas or argon gas was introduced at a rate of about 0.3 torr so as not to exceed 1 tor at the time of heating, and the temperature was raised to 15
Various heat treatments were performed between 0 and 450 ° C. Also in this case, it is preferable to adjust the heating time according to the heat treatment temperature as in the case of the first stage heat treatment, but an example in which the heating time is constant at 2 hours will be described.

Tables 4 to 6 show the results of examining the magnetization amount, the coercive force, the deterioration rate of the magnetization amount, and the amount of metal Bi of the magnetic powders which were heat-treated under different heat treatment conditions in the first step and the second step. Shown in. The deterioration rate of the magnetization amount and the amount of metal Bi were measured by the following methods.

<Deterioration Rate of Magnetization Amount> The magnetic powder is heated to a temperature of 60.
The glass substrate was kept in an atmosphere of 90 ° C. and humidity of 90% for 7 days, and the deterioration rate of the saturation magnetization was calculated from the change of the saturation magnetization after the holding magnetization with respect to the saturation magnetization before the holding.

<Amount of Metal Bi> The magnetic powder was added at a temperature of 60 ° C.
The amount of metal Bi was examined using an X-ray diffractometer after holding for 7 days in a glass dish in an atmosphere with a humidity of 90%. The area of the diffraction peak from the (101) plane of MnBi and the area of the diffraction peak from the (012) plane of metal Bi were obtained, and the value obtained from the following formula was used as the amount of metal Bi. Amount of metal Bi = peak area of metal Bi / (peak area of MnBi + peak area of metal Bi)

FIG. 10 shows an example of the amount of metal Bi obtained when the MnBi magnetic powder was held in an environment of a temperature of 60 ° C. and a humidity of 90%, obtained from an X-ray diffraction pattern.

[0133]

[0134]

[0135]

The proportion of Mn and Bi oxides formed near the surface of these magnetic powders, Mn and B
Table 7 shows the results of investigating the atomic ratio of i to oxygen and the ratio of the MnO ₂ component by photoelectron spectroscopy. In addition,
The proportions of Mn and Bi oxides, the atomic proportions of Mn and Bi and oxygen, and the proportions of MnO ₂ components were measured by the following methods.

<Ratio of Mn and Bi Oxides> MnBi
Mn oxide and Bi formed near the surface of the magnetic powder
The proportion of oxides was measured using photoelectron spectroscopy. Mg was used as the radiation source, 2p electrons were measured for the Mn oxide, and 4f electrons were measured for the Bi oxide. As an example, FIG. 11 and FIG. 12 show Mn 2p and Bi 4f spectra, respectively. Both spectra are Mn oxide,
Spectra of metallic Mn and metallic Bi based on MnBi are also observed simultaneously with the Bi oxide. These spectra were separated using a computer, and the area of the spectrum based on Mn oxide and Bi oxide was obtained. Ratio of Mn oxide and Bi oxide was determined from 4f _7/2 area ratio of the electron spectrum of 2p _3/2 electrons of the spectrum and Bi oxide of the oxides of Mn.

<Atomic ratio of Mn and Bi to oxygen and ratio of MnO ₂ component> The oxides of Mn and Bi are composed of several kinds of oxides having different valences. Therefore, the peaks shown in FIGS. 11 and 12 are preliminarily measured, and the peaks are separated by computer fitting using the peaks of standard samples of oxides of Mn and Bi having clear valences. It was From the area of each separated peak, the atomic ratio x of Mn and Bi and oxygen when expressed by MnOx and BiOx, and the ratio of the component of x = 2 in MnOx were obtained.

[0139]

As is clear from Tables 4 to 6, the MnBi magnetic powder which has been subjected to the heat treatment of the present invention has a temperature of 60 ° C.
Even when left for 7 days under high temperature and high humidity with a humidity of 90%, the deterioration rate of saturation magnetization is 40% or less, and the amount of metal Bi is 0.5.
It is found that the corrosion resistance is remarkably improved as below.

Further, from Table 7, it can be seen that an oxide of Mn having a specific structure is preferentially formed in the vicinity of the surface of such MnBi magnetic powder having excellent corrosion resistance. In particular, the ratio of oxides of Mn and Bi depends on the atomic ratio of Mn and Bi (Mn / B
It can be seen that when represented by i), good corrosion resistance is exhibited when it is 2 or more. Furthermore, as the structure of this Mn oxide,
It can be seen that when the component having x of 2 when expressed by MnOx is present in an amount of 50 atomic% or more in all Mn oxides, better corrosion resistance is exhibited.

<< Formation of Oxide Film on MnBi Magnetic Powder >> As a magnetic powder having an oxide film formed on the surface of MnBi magnetic powder, a magnetic powder having a film of TiO ₂ and SiO ₂ will be taken as an example. Explain. Example 56 MnBi magnetic powder (stabilized powder) 100 parts by weight Tetraisopropyl titanate 3 〃 Toluene 1125 〃 The above composition was mixed and dispersed by using ultrasonic waves for 30 minutes at room temperature. Example 4 was used as the MnBi magnetic powder.
The magnetic powder subjected to the stabilization treatment shown in 1 was used. By this operation, tetraisopropyl titanate is hydrolyzed in the air or by the water present on the surface of the MnBi magnetic powder, and is adsorbed on the surface of the MnBi magnetic powder.

Next, the MnBi magnetic powder to which the above tetraisopropyl titanate was adsorbed was heat-treated in nitrogen gas at 350 ° C. for 2 hours. By this heat treatment, MnBi
Tetraisopropyl titanate adsorbed on the magnetic powder was dehydrated and condensed to form a dense TiO ₂ film.

Example 57 In Example 56, as Example 4 as MnBi magnetic powder
The surface of the MnBi magnetic powder was processed in the same manner as in Example 56, except that the magnetic powder that was not subjected to the stabilization treatment shown in Comparative Example 1 was used in place of the magnetic powder that was subjected to the stabilization treatment shown in Example 1. A TiO ₂ coating was formed on.

Example 58 In Example 56, 5 parts by weight of tetramethoxysilane was used in place of 3 parts by weight of tetraisopropyl titanate, and MnBi magnetic powder was further added at a temperature of 60.
Tetramethoxysilane was adsorbed on the surface of the magnetic powder by the same method as in Example 56, except that water was positively adsorbed on the surface of the magnetic powder by keeping the atmosphere at 90 ° C. and humidity of 90% for 10 minutes. Then, heat treatment was performed to form a SiO ₂ film on the surface of the magnetic powder.

Example 59 In Example 58, as Example 4 as MnBi magnetic powder.
The surface of the MnBi magnetic powder was processed in the same manner as in Example 58, except that the magnetic powder which was not subjected to the stabilization treatment shown in Comparative Example 1 was used in place of the magnetic powder which was subjected to the stabilization treatment shown in Example 1. A SiO ₂ coating was formed on the.

For these four types of magnetic powder, 300
Table 8 shows the results of examining the magnetization amount, the coercive force, the deterioration rate of the magnetization amount, and the amount of metal Bi in K.

[0148]

As is clear from Table 8, when the stabilized magnetic powder is used (Examples 56 and 58).
Then, it is understood that the corrosion resistance is further improved by forming the oxide film. It is also understood that even when the magnetic powder which has not been subjected to the stabilization treatment is used (Examples 57 and 59), the corrosion resistance can be improved by forming the oxide film.

<< Preparation of Magnetic Paint and Magnetic Layer >> As a basic method for preparing a magnetic paint, the following compositions were sufficiently dispersed by a ball mill to prepare a magnetic paint. As the magnetic powder, Mn subjected to the heat treatment shown in Example 41 was used.
Bi magnetic powder was used. The average particle size of this magnetic powder is 2.
5 μm, coercive force 9500 Oe, saturation magnetization 50.4 em
u / g.

Example 60 MnBi magnetic powder 100 parts by weight MPR-TAO (manufactured by Nisshin Chemical Co., Ltd .; amine-modified vinyl chloride-vinegar 25 〃 vinyl acid copolymer) cyclohexanone 50 〃 toluene 50 〃 This magnetic paint is used to form a release layer. 30μm thick PET
1 on the film so that the thickness after drying is 15 μm
Application was performed while applying a longitudinal orientation magnetic field of 500 Oe.

Example 61 In the composition of the magnetic coating material in Example 60, MPR-
A magnetic coating material was prepared in the same manner as in Example 60 except that the same amount of S-REC P (manufactured by Sekisui Chemical Co., Ltd .; amine-modified styrene-acrylic copolymer) was used instead of TAO to prepare a magnetic layer.

Example 62 A magnetic coating material was prepared in the same manner as in Example 60 except that 6 parts by weight of dodecylamine was added as an additive to the composition of the magnetic coating material of Example 60 to prepare a magnetic layer.

Example 63 Except that 1 part by weight of stearylamine was further added as an additive in the composition of the magnetic coating material of Example 60.
A magnetic coating material was prepared in the same manner as in Example 60 to prepare a magnetic layer.

Example 64 The procedure of Example 60 was repeated except that 6 parts by weight of stearylamine was added as an additive to the composition of the magnetic coating material of Example 60.
A magnetic coating material was prepared in the same manner as in Example 60 to prepare a magnetic layer.

Comparative Example 2 In the composition of the magnetic coating material of Example 60, MPR-
Example 60 except that VAGH (manufactured by UCC; vinyl chloride-vinyl acetate copolymer) was used in the same amount instead of TAO, and 6 parts by weight of stearylamine was added as an additive.
A magnetic coating material was prepared in the same manner as in 1. to prepare a magnetic layer.

Comparative Example 3 In the composition of the magnetic coating material of Example 60, MPR-
A magnetic coating material was prepared and a magnetic layer was prepared in the same manner as in Example 60, except that MR-110 (manufactured by Zeon Corporation; sulfonate-modified styrene-acrylic copolymer) was used in the same amount instead of TAO. did.

Comparative Example 4 In the composition of the magnetic coating material of Example 60, MPR-
A magnetic coating material was prepared in the same manner as in Example 60 except that the same amount of vinyl chloride-vinyl acetate copolymer (in-house synthesized product) modified with phosphoric acid in-house was used instead of TAO to prepare a magnetic layer.

Comparative Example 5 In the composition of the magnetic coating material of Example 60, MPR-
Example 60 except that VAGH (manufactured by UCC; vinyl chloride-vinyl acetate copolymer) was used in the same amount instead of TAO.
A magnetic coating material was prepared in the same manner as in 1. to prepare a magnetic layer.

With respect to the magnetic layer thus manufactured,
The magnetic properties and corrosion resistance were investigated. The magnetic characteristics are 300
The coercive force Hc, the magnetic flux density Bm, and the rectangular shape Br / Bm in the longitudinal direction measured by applying a magnetic field of 16 kOe at K, and as the corrosion resistance, the coating film was left for 7 days in an environment of a temperature of 60 ° C. and a humidity of 90%. The subsequent deterioration rate of the magnetic flux density was measured.
Table 9 shows the result.

[0161]

As is clear from Table 9, in the case where the conventional vinyl chloride-vinyl acetate copolymer is used as the binder resin (Comparative Example 5), the effect of improving the corrosion resistance is not recognized. When using a binder resin containing an acidic functional group for the purpose of further improving dispersibility (Comparative Examples 3 and 4)
In addition, the corrosion resistance is further deteriorated. On the other hand, when a binder resin containing an amine group as a basic functional group is used (Examples 60 and 61), the corrosion resistance is significantly improved.

Further, when an additive having a basic functional group is added as an additive, the corrosion resistance is further improved, and the magnetic flux density tends to decrease as the added amount increases, but the corrosion resistance further improves. The reason why the corrosion resistance is remarkably improved by including a basic functional group in the binder resin or additive is not clear, but it is expected as follows.

On the surface of the MnBi magnetic powder, Mn is mainly
The oxide of Mn is formed, but the oxide of Mn is basic. When the binder resin is adsorbed on the magnetic powder surface,
Usually, the side of the functional group is directed toward the magnetic powder for adsorption. Therefore, when the functional group of the resin is acidic, an acid-alkali reaction occurs on the surface of the magnetic powder, which promotes the decomposition of MnBi magnetic powder into Mn and Bi. In this reaction, when water is present, the property of the functional group as an acid becomes stronger, so that the decomposition is further promoted and the magnetization is deteriorated. On the other hand, when the functional group of the resin or additive is basic, even if the functional group side is adsorbed with the surface of the magnetic powder adsorbed, since the functional group is also basic, Mn and Bi are transferred to the surface of the magnetic powder. The decomposition reaction of does not occur. Therefore,
In this case, the functional group is adsorbed on the MnBi magnetic powder without giving any damage. Furthermore, once these resins or additives having a basic functional group are adsorbed on the MnBi magnetic powder, they prevent the main chain, for example, an alkyl group, from reacting with moisture or the like entering from the outside with the magnetic powder. Therefore, the corrosion resistance is expected to improve.

Examples 65 to 67 In the composition of the magnetic coating material of Example 60, Example 6 is used.
In place of the MnBi magnetic powder used in No. 0, M shown in FIG.
The nBi ingot was crushed in the first step and then crushed in the second step, and the crushing time was changed ^{. Among} the magnetic powders having different S ^* , the crushing time in the second step was 0 hours (S ^* 0.2.
1) 1 hour (S ^* 0.45) and 4 hours (S ^* 0.5)
A magnetic layer was produced in the same manner as in Example 60, except that the same amount of the magnetic powder treated under the same conditions as in Example 41 was used using 1) MnBi.

Comparative Example 6 In the composition of the magnetic coating material of Comparative Example 3, instead of MnBi magnetic powder, Coγ-Fe ₂ O ₃ powder (particle size 0.4 μm) was used.
m, coercive force 650 Oe, S ^* 0.48) was used in the same manner as in Comparative Example 3 except that the same amount was used.

Regarding the magnetic layers obtained in Examples 65 to 67 and Comparative Example 6, these magnetic layers were demagnetized and then 30
Initial magnetization was measured at 0K and is shown in FIG. Further, when these magnetic layers were recorded and reproduced by using a card reader / writer manufactured by Sanwa Newtec Co., Ltd. at a recording current corresponding to a head magnetic field of about 1500 Oe, Coγ-F was obtained.
The magnetic layer using the e ₂ O ₃ powder and the MnBi magnetic powder having a magnetic flux density of 50% or more of the saturation magnetic flux density in FIG. 13 could normally reproduce the recording data. The reason why the magnetic recording medium having a magnetic flux density of 50% or more of the saturation magnetic flux density when a magnetic field of 1500 Oe is applied can be normally reproduced is considered as follows. That is, if the magnetic flux density is 50% or more, a sufficient output can be obtained for reading, but if this value is 50% or less, the magnetic flux density will be low and the output will be reduced.
It is considered that in the magnetic recording medium in which the initial magnetization curve does not have a steep slope as shown in, the recording magnetization becomes unstable in the magnetic layer, and as a result, a read error is likely to occur.

As a result, in the magnetic recording medium using the MnBi magnetic powder, the magnetic recording medium having a steeper rise of the initial magnetization curve after demagnetization can perform saturated recording at a lower current and a magnetic field of 1500 Oe. A magnetic recording medium having a magnetic flux density of 50% or more of a saturation magnetic flux density when applied can read data without causing a read error when recorded and reproduced by a card reader / writer. Recognize.

<Formation of Water-Repellent Layer> By providing a water-repellent layer made of a water-repellent resin on the surface of the magnetic layer, corrosion resistance and acid resistance are further improved. As a forming method, for example, when applied to a magnetic card, it is provided between the peeling layer and the magnetic layer. Examples in which a water repellent layer is provided are shown below.

Example 68 Saran resin F216 (manufactured by Asahi Kasei Corp .; vinylidene chloride resin) 100 parts by weight tetrahydrofuran 200 〃 toluene 100 〃 A paint of this composition was dried on a PET film having a release layer made of an acrylic acid resin. Later thickness is 2.5 μm
To form a water-repellent layer. The magnetic paint shown in Example 64 was applied onto the water-repellent layer in a thickness of 15 after drying.
Application was performed while applying a longitudinal orientation magnetic field of 1500 Oe so that the thickness became μm. Thereafter, this was slit into a 6 mm width to prepare a magnetic tape.

Then, the magnetic tape obtained in this way was used.
The magnetic layer of the magnetic tape was superposed on a vinyl chloride substrate for a magnetic card having a thickness of 0.76 mm, and was pressed by a heating roller from above to be bonded on the vinyl chloride substrate. After the adhesion, the PET film was peeled off, and the resultant was heat-pressed with a press plate to embed the magnetic layer in the vinyl chloride substrate and then punched into a card size to prepare a magnetic card.

Example 69 In the composition of the water-repellent coating composition of Example 68, the same amount of Eval resin F216 (manufactured by Kuraray Co., Ltd .; ethylene vinyl alcohol copolymer) was used in place of the Saran resin F216. In the same manner as in Example 68, a water repellent coating material was prepared to prepare a magnetic card.

Example 70 A magnetic card was produced in the same manner as in Example 68 except that a water repellent layer was further formed on the magnetic layer. That is, a water repellent layer is formed on the release layer, a magnetic layer is formed thereon, and then the magnetic layer is sandwiched between the water repellent layers.
Further, a water repellent layer was formed on the magnetic layer.

Comparative Example 7 A magnetic paint was prepared in the same manner as in Example 68 except that the formation of the water repellent layer between the release layer and the magnetic layer was omitted in the above Example 68 to prepare a magnetic card. It was made.

Magnetic cards obtained in the respective examples and comparative examples
Then, the corrosion resistance and acid resistance of the magnetic layer were investigated. The corrosion resistance was measured as follows. First, a part of the magnetic layer of the card was cut out immediately after the production of the card, and 16 k was cut at 300K.
A magnetic field of Oe was applied to measure the magnetic flux density Bm, and this value was used as an initial value. Next, using the same card, the temperature is 60 ° C and the humidity is 9
After leaving it in an environment of 0% for 7 days, a part of the magnetic layer of the card was cut again to have the same area, and a magnetic field of 16 kOe was applied at 300 K to measure the magnetic flux density. The corrosion resistance was calculated from the deterioration rate of the magnetic flux density with respect to the initial value at this time. The acid resistance was calculated from the deterioration rate of the magnetic flux density by immersing the card in a 5% acetic acid aqueous solution at room temperature (25 ° C.) for 1 day in the same manner as the corrosion resistance. Table 10 shows the result.

[0176]

As is clear from Table 10, by forming the water repellent layer (Example 68), the corrosion resistance is slightly higher than that of the magnetic card without the water repellent layer (Comparative Example 7). It exhibits excellent properties. On the other hand, regarding the acid resistance, in the magnetic card having no water repellent layer (Comparative Example 7), the Bm was 8 by immersing in a 5% acetic acid aqueous solution.
On the other hand, when the water repellent layer was formed between the peeling layer and the magnetic layer (Examples 68 and 69), the deterioration rate of Bm was 2 to 6%, and the acid resistance was remarkable while the decrease was 9.2%. You can see that it will improve. The effect is further enhanced in the magnetic card (Example 70) in which the water repellent layer is formed so as to sandwich the magnetic layer. This is because the water-repellent layer prevents water from entering the magnetic layer of the magnetic card from the outside.

Examples 71 to 87 << Preparation of magnetic card and recording / reproducing characteristics >> Next, magnetic coatings and magnetic layers were prepared using various magnetic powders, and the recording / reproducing characteristics were evaluated using the magnetic card. . As the magnetic powder, various magnetic powders having different characteristics produced by changing the grinding time shown in FIGS. These magnetic powders were pulverized by the two-step pulverization shown in Example 35 using the MnBi ingot produced by the method shown in Example 4. Further, these magnetic powders are stabilized by being subjected to heat treatment by the method shown in Example 41 after pulverization. For the magnetic coating material and the magnetic layer, the magnetic layer in which the volume ratio of the magnetic powder in the magnetic layer was different was prepared by changing the weight part of the magnetic powder relative to the binder resin in the method shown in Example 64. The volume ratio is obtained by calculating the magnetic flux density when the magnetic powder has a specific gravity of 8.0 and the magnetic layer is filled with 100% of the magnetic powder from the saturation magnetization of the magnetic powder. It was calculated from the ratio.

(1) Manufacture of magnetic card The magnetic card was basically manufactured by the method shown in Example 68, but the manufacturing method will be briefly described again as follows. The magnetic coating film prepared by the method of Example 64 was
Slit to a width of mm to make a magnetic tape. Then, the magnetic layer of the magnetic tape obtained in this way is made to have a thickness of 0.76.
It was superposed on a vinyl chloride substrate for a magnetic card having a size of 1 mm, and pressed from above with a heating roller to adhere it onto the vinyl chloride substrate. After adhering, the PET film is peeled off, and the magnetic layer is embedded in a vinyl chloride substrate by heating and pressure bonding with a press plate.
A magnetic card was prepared by punching into a magnetic size. In addition,
In this example, the results of an examination of a magnetic card having no water-repellent layer are shown. However, even if the water-repellent layer is formed, the water-repellent layer is not formed in the magnetic card manufacturing method and recording / reproducing characteristics. It is not essentially different from anything.

(2) Recording / reproduction of data The magnetic card was cooled by immersing it in liquid nitrogen. After this, an AC magnetic field of 1000 Oe was promptly applied for initialization. Data is recorded by a magnetic card reader / writer.
(Manufactured by Sanwa New Tech Co., Ltd .; CRS-700)
With a recording current of 200 milliamps and a recording density of 21
Square waves of 0 FCI and 420 FCI were recorded. De-
The reproduction of the data was also performed using the same magnetic card reader / writer.

Table 11 shows the evaluation results of the magnetic layers produced by using various MnBi magnetic powders, and Table 12 shows various Mn contents.
The evaluation results of a magnetic card produced using Bi magnetic powder are shown below. Regarding the magnetic layer, the coercive force Hc at 300 K and 80 K, the magnetic flux density Bm at 300 K, the square Br / Bm, and the magnetic flux density after leaving this magnetic layer in an atmosphere at a temperature of 60 ° C. and a relative humidity of 90% for 7 days. The reduction rate was measured. For magnetic cards, 210FC
The reproduction output at I and the resolution (the ratio of the reproduction output at 210 FCI to the reproduction output at 420 FCI) were measured.

Among the main recording characteristics of these magnetic cards, the reproduction output, the resolution and the rewriting prevention function, the reproduction output strongly influences the magnetic flux density at 300K, and the resolution and the rewriting prevention function strongly influence the coercive force at 300K. receive.

FIG. 14 shows a coercive force of 10 at 300K.
The results of investigating the relationship between the magnetic flux density and the reproduction output at 210 FCI are shown for a magnetic card in which the magnetic flux density is changed by changing the volume ratio of the magnetic powder in the range of 000 Oe to 15000 Oe. Also, in FIG.
The magnetic flux density of the magnetic recording medium in K is changed from 1200G to 1
The results of investigating the rewriting prevention function of the magnetic card with the coercive force changed at 300K in the range of 800G are shown.
Here, the rewrite prevention function was performed as follows.
That is, after degaussing the magnetic card, 210 FCI signal was saturated recorded at 300 K (DC current 250 mA).
Then, the reproduction output is used as an initial value. Next, using the same magnetic head as the one on which recording was performed, about 700
A direct current (500 mA) corresponding to a magnetic field of 0 Oe was passed to degauss the direct current, and then a signal output of 210 FCI was reproduced.

[0184]

[0185]

As is clear from Table 11 and Table 12,
When the coercive force of the magnetic layer is 300 K and is 5000 Oe or less, the resolution is as low as 80% or less. Further, in the magnetic recording medium having a coercive force of 5000 Oe or less, the characteristic that the magnetic recording medium of the present invention cannot be rewritten once it is recorded cannot be sufficiently exhibited. On the other hand, in a magnetic layer having a coercive force of 1500 Oe or more at 80 K, the degaussing property at low temperature becomes insufficient, so recording at room temperature becomes insufficient, and it is difficult to obtain high output, and particularly the output of 420 FCI with high recording density is low. As a result, the resolution also becomes low. Furthermore, the magnetic flux density is related to the output of 210 FCI,
As can be seen from FIG. 14, a higher output is obtained as the magnetic flux density is larger, and a sufficiently large output cannot be obtained when the magnetic flux density is 500 G or less.

The square shape is closely related to the resolution, and when the square shape becomes 0.60 or less, the resolution remarkably deteriorates. Further, in order to obtain such optimum coercive force, magnetic flux density, and prismatic shape, it is necessary to optimize the volume ratio of the magnetic powder in the magnetic layer, and it is totally excellent in the range of 5 to 60%. It can be seen that the characteristic magnetic layer and magnetic card can be obtained.
Further, in order to obtain a high coercive force at 300K, it is necessary to reduce the particle size of the magnetic powder that is generally used, but when the coercive force at 300K is 16000 Oe or more, the magnetic flux density also decreases and the output decreases. further,
As can be seen from FIG. 15, the rewrite prevention function is 300
It has a close relationship with the coercive force at K, and the coercive force is 500
When it is 0 Oe or more, the prevention function is more exerted.

As a result of the above-mentioned examination, it is sufficiently demagnetized in the initializing step at a low temperature; in data writing at room temperature, it is possible to write at a current value as low as possible; magnetic powder is excellent in dispersibility and orientation; Output and resolution are high enough to prevent reading errors; once data is recorded, which is a characteristic of this magnetic recording medium, it cannot be easily rewritten at room temperature; under high temperature and high humidity In order to obtain a magnetic recording medium that simultaneously satisfies the following characteristics: deterioration of magnetic flux density when left alone; magnetic powder volume ratio, coercive force at 300K and 80K, magnetic flux density at 300K, and rectangular shape in the longitudinal direction are well balanced. It turns out that it needs to be set.

These factors are related to each other, and the range of the volume ratio of MnBi magnetic powder in the magnetic layer is 5 to 5.
60%; coercive force range measured by applying a magnetic field of 16 kOe is 5000 to 16000 Oe at 300K; coercive force range measured by applying a magnetic field of 16 kOe is 100 to 1500 Oe; The range of the magnetic flux density measured at 500K to 2500G at 300K; the rectangular range in the longitudinal direction measured by applying a magnetic field of 16kOe is 0.60 to 0.95; It can be seen that a magnetic recording medium having the above characteristics can be obtained.

<< Preparation of Multi-Layer and Magnetic Powder Mixed Magnetic Card >> A magnetic recording medium using MnBi magnetic powder has a characteristic that it cannot be easily rewritten at room temperature once it is recorded. When used in combination with the magnetic recording medium, a magnetic recording medium having novel features not found in the conventional magnetic recording medium can be obtained.

Taking the case of application to a magnetic card as an example, a magnetic layer using MnBi magnetic powder and a Co-γ-F
When formed at different positions on de surface, once de - - two kinds of magnetic layers of the magnetic layer using a conventional magnetic powder for magnetic recording, such as e ₂ O ₃ months fixed des which can not be rewritten and writing data - Data and data that the user can freely rewrite 2
A magnetic card having different types of data can be obtained.

As fixed data, the rewritable data is recorded by recording the cardholder's ID and password, the card issuing place and the issuing date, which must not be forged or tampered with. Can be used, for example, by recording the usage history of the card each time it is used.

Further, a magnetic layer made of MnBi magnetic powder and a magnetic layer made of another magnetic powder such as Co-γ-Fe ₂ O ₃ are laminated, or MnBi magnetic powder and Co are used.
When mixed with other magnetic powder such as -γ-Fe ₂ O ₃ , two kinds of data, fixed data that cannot be rewritten and data that can be rewritten, can be recorded in multiple layers on the same track. It will be possible.

Particularly, when the multiple recording is performed as described above, not only the data can be recorded without narrowing the print area of the magnetic card, but also it becomes extremely difficult to decode the written data. Thus, a magnetic card with extremely high security can be obtained.

A magnetic layer using MnBi magnetic powder and Co
In the case of forming two kinds of magnetic layers of other magnetic powders such as -γ-Fe ₂ O ₃ at different positions on the card surface, the MnBi magnetic paint prepared by the method already described. And a magnetic paint usually used for magnetic recording media to form magnetic layers at different positions.

Therefore, in this embodiment, a magnetic layer using MnBi magnetic powder and a magnetic layer using other magnetic powder such as Co-γ-Fe ₂ O ₃ are formed at different positions on the card surface. In the case of using, a magnetic layer using MnBi magnetic powder and Co-γ
When stacking a magnetic layer using another magnetic powder such as —Fe ₂ O ₃ and when using MnBi magnetic powder and Co—γ-Fe ₂
The case where other magnetic powders such as O ₃ are mixed and used will be described as an example.

<< Laminate and Single Layer Mixed Card >> A magnetic layer using MnBi magnetic powder is formed in a stripe shape and Co-γ-Fe ₂ O ₃ or barium ferrite magnetic powder is formed so as to cover the magnetic layer. An example of forming a magnetic layer using the usual magnetic powder used for the magnetic recording medium on the entire surface of the card will be described.

Example 88 (1) Preparation of non-rewritable magnetic layer coating material As the non-rewritable magnetic layer coating material, the magnetic coating material using MnBi magnetic powder shown in Example 64 was used.

(2) Preparation of Rewritable Magnetic Layer Coating Material As a rewritable magnetic coating material for ordinary magnetic recording,
Co-γ-Fe ₂ O ₃ magnetic powder having a coercive force of 640 Oe, a saturation magnetization of 74.5 emu / g and an average particle length of 0.3 μm was used.

Co-γ-Fe ₂ O ₃ magnetic powder 80 parts by weight Vinyl chloride-vinyl acetate copolymer (UCC; VAGH) 10 〃 Polyurethane resin (Dainippon Ink and Chemicals; T-5250) 6 〃 Cyclohexanone 75 〃 Toluene 75 〃 This composition was thoroughly kneaded and dispersed by a sand grinder mill, and then 5 parts by weight of a polyfunctional polyisocyanate compound (Nippon Polyurethane Industry Co., Ltd .; Coroneto L) was added to the magnetic paint. And

(3) Preparation of Magnetic Layer First, a magnetic paint using MnBi magnetic powder was applied to a thickness of 190
On a PET base film having a thickness of .mu.m, it was applied in stripes while applying a longitudinal orientation magnetic field of 1500 Oe so that the thickness after drying was 5 .mu.m. This stripe had a width of 5 mm and was formed so that the stripe was parallel to the long side of the magnetic card when formed into a magnetic card. Continue to C
A coating using a magnetic powder of o-γ-Fe ₂ O ₃ was applied to the entire surface of the PET base film so as to cover the stripe, and a longitudinal orientation magnetic field of 1500 Oe was applied so that the thickness after drying was 10 μm. While applying.

(4) Preparation of magnetic card The above-mentioned PET base film having two kinds of magnetic layers formed thereon was punched into a card shape to obtain a magnetic card.

(5) Initialization and recording / reproduction Initialization was performed by the method described above. That is, the card was cooled by immersing it in liquid nitrogen, and immediately thereafter, an AC magnetic field of 1000 Oe was applied to initialize it. The signal was recorded by the following method.

Using a magnetic card reader / writer (manufactured by Sanwa Newtec Co .; CRS-700), a magnetic layer containing MnBi magnetic powder and a magnetic layer containing Co-γ-Fe ₂ O ₃ magnetic powder were used. First, as fixed data that cannot be rewritten, a recording current of 100 mA, (0,
The sequence of numbers 1, 2, 3, 4,) was recorded. Next, as a rewritable signal, the same magnetic card reader / writer was used in a portion where only the magnetic layer using the Co-γ-Fe ₂ O ₃ magnetic powder was formed, with a recording current of 100 mA,
The numerical sequence of (5, 6, 7, 8, 9) was recorded.

Next, the recording data was reproduced by using the same magnetic card reader / writer as at the time of recording. As a result, the same sequence of numbers (0, 1, 2, 3, 4,) as recorded can be reproduced from the laminated portion. Further, from the portion where only the magnetic layer using Co-γ-Fe ₂ O ₃ magnetic powder is formed,
I was able to reproduce the sequence of numbers (5, 6, 7, 8, 9). Next, assuming tampering, at the recording current of 100 mA, the number sequence of (5, 6, 7, 8, 9) is added to the laminated portion by Co-γ-Fe ₂
The number sequence (0, 1, 2, 3, 4,) was overwritten on the portion where only the magnetic layer using the O ₃ magnetic powder was formed.

[0206] As a result of reproducing again using the same cardy writer, from the portion where only the magnetic layer using the Co-γ-Fe ₂ O ₃ magnetic powder is formed, (0, 1, 2,
It was confirmed that the data of 3, 4) was reproduced and the data was rewritten normally.

On the other hand, the laminated portion becomes a reading error,
The data could not be reproduced. This is because the data once written in the magnetic layer using the MnBi magnetic powder cannot be rewritten, so that the data (0,1,2,3,4) first written in the magnetic layer using the MnBi magnetic powder. Data and C
The magnetic layer using the o-γ-Fe ₂ O ₃ magnetic powder was overlaid.
This is because the written data (5, 6, 7, 8, 9) is mixed and, as a result, a read error occurs.

As described above, two kinds of magnetic layers, that is, a magnetic layer using MnBi magnetic powder and a magnetic layer using other magnetic powder such as Co-γ-Fe ₂ O ₃ are provided at different positions on the card surface. By forming the data into a card, it is possible to obtain a card having two kinds of data: fixed data that cannot be rewritten once the data is written, and data that can be freely rewritten by the user. .

Example 89 In Example 88, instead of the Co-γ-Fe ₂ O ₃ magnetic paint, the coercive force was 2800 Oe and the saturation magnetization was 64.5 emu /
g by the same method as in Example 88 except that barium ferrite magnetic powder having an average particle length of 0.6 μm was used.
A magnetic card was produced. With respect to this card, the same data as in Example 88 was recorded and reproduced, except that the recording current was 200 mA. The results are the same as in Example 88.
i The portion where the magnetic layer using the magnetic powder and the magnetic layer using the barium ferrite magnetic powder are laminated becomes a reading error, and the portion where only the magnetic layer using the barium ferrite magnetic powder is formed is normally rewritten. It was confirmed that it was done.

<< Use of mixed magnetic powder and magnetic layer laminated magnetic card >> MnBi magnetic powder and gamma iron oxide magnetic powder,
Co-containing iron oxide magnetic powder, Ba-ferrite magnetic powder,
By mixing with another magnetic powder having a coercive force of 250 to 3000 Oe at room temperature, such as Sr-ferrite magnetic powder or metallic magnetic powder mainly composed of Fe,
Alternatively, by stacking a magnetic layer using MnBi magnetic powder and a magnetic layer using the above magnetic powder, MnB
Like the magnetic layer using only i magnetic powder, it is possible to exhibit the characteristic that it is difficult to tamper with the data. That is MnB
Even if the magnetic powder other than i or the data of the magnetic layer using this magnetic powder is rewritten, the data of the MnBi magnetic powder or the magnetic layer using the MnBi magnetic powder cannot be rewritten. Various types of signals are mixed and cannot be read by an ordinary reader.

As described above, the advantage of the magnetic recording medium having such a structure is that only the MnBi magnetic powder is used because the magnetic powder generally has a larger saturation magnetization than the MnBi magnetic powder. Compared with the case, the magnetic flux density of the magnetic recording medium becomes large, and high output is easily obtained. When an oxide-based magnetic powder is used in combination, these magnetic powders have no problem of corrosion, and therefore the corrosion resistance of the magnetic recording medium is further improved. By using the MnBi magnetic powder in combination with another low coercive force magnetic powder, it is possible to maintain the characteristic that the data cannot be tampered with and to reduce the write current value of the data. Multiple recording is possible by overwriting different data on the same track during data recording and separating and reproducing the data through a filter or the like during reproduction. 4 points.

Among these advantages, the advantages of are MnB
It is basically the same as the characteristic of the magnetic recording medium using the i magnetic powder. However, the advantage of
Bi magnetic powder and other magnetic powder are mixed and used,
Alternatively, it can be realized for the first time by stacking magnetic recording media using these magnetic powders, and two types of data, fixed data that cannot be rewritten and rewritable data, are multi-recorded on the same track. It becomes possible to do. A magnetic recording medium for realizing the advantages there,
The recording and reproducing characteristics thereof will be described.

Example 90 (Preparation of laminated magnetic card) By using a magnetic recording medium using MnBi magnetic powder and a magnetic recording medium using another magnetic powder in a laminated manner, a fixed data which cannot be rewritten is used.
An example of a magnetic card capable of multiple recording of two types of data, that is, rewritable data and rewritable data, will be described.

(1) Preparation of non-rewritable magnetic layer paint As the magnetic paint for the non-rewritable magnetic layer, the paint using MnBi magnetic powder shown in Example 64 was used.

(2) Preparation of Rewritable Magnetic Layer Coating Material As a rewritable magnetic coating material for ordinary magnetic recording,
Co-γ-Fe ₂ O ₃ magnetic powder having a coercive force of 640 Oe, a saturation magnetization of 74.5 emu / g and an average particle length of 0.3 μm was used.

Co-γ-Fe ₂ O ₃ magnetic powder 80 parts by weight Vinyl chloride-vinyl acetate copolymer (UCC; VAGH) 10 〃 Polyurethane resin (Dainippon Ink and Chemicals; T-5250) 6 〃 Cyclohexanone 75 〃 Toluene 75 〃 This composition was thoroughly kneaded and dispersed by a sand grinder mill, and then 5 parts by weight of a polyfunctional polyisocyanate compound (Nippon Polyurethane Industry Co., Ltd .; Coroneto L) was added to the magnetic paint. And

(3) Preparation of Magnetic Layer First, the magnetic coating for the upper layer using Co-γ-Fe ₂ O ₃ magnetic powder was applied onto a PET base film having a thickness of 30 μm and having a release layer formed thereon, and the thickness after drying. Was applied while applying a longitudinal orientation magnetic field of 15000e so that the thickness was 10 μm.
Subsequently, a coating material containing MnBi magnetic powder was applied to the surface of the coating film at 1500 O so that the thickness after drying was 10 μm.
Coating was performed while applying the longitudinal orientation magnetic field of e.

(4) Manufacture of magnetic card By the same method as described in Example 68, the magnetic layer was slit into a magnetic tape shape and then embedded in a vinyl chloride substrate by thermocompression bonding to form a magnetic card. I made it.

(5) Initialization and recording / reproduction Initialization was performed by the same method as described above. The signal was recorded by the following method. First, using a magnetic card reader / writer (manufactured by Sanwa Newtec Co., Ltd .; CRS-700), a sine wave of 400 μm in terms of bit length was recorded as a fixed data that could not be rewritten at a recording current of 200 mA. did. This signal was designated as (A) signal. Next, as a rewritable signal, a sine wave of 100 μm in terms of bit length was recorded at a recording current of 100 mA using the same magnetic card reader / writer.

For reproduction of the signal, the reproduction signal voltage was obtained by using the same magnetic card reader / writer as at the time of recording. The reproduction output was obtained from the amplitude of the reproduction waveform by taking the output from the magnetic head into the oscilloscope via a bandpass filter in order to separate the upper and lower layers signals. As the band pass filter, the frequencies of the low pass filter and the high pass filter were set so that frequencies of + 100% and -50% around the frequency to be measured were passed.

Example 91 In Example 90, the magnetic powder used in the rewritable magnetic layer was Co-γ-Fe ₂ O ₃ magnetic powder, coercive force of 2800 Oe, saturation magnetization of 64.5 emu / g, and average particle length of 0. In the same manner as in Example 90, except that the barium ferrite magnetic powder having a particle size of 0.6 μm was used, a magnetic card having a magnetic layer having an upper layer made of barium ferrite magnetic powder and a magnetic layer having a lower layer made of MnBi magnetic powder was prepared. Example 90
The signal was recorded and reproduced by the same method as in.

Example 92 In Example 90, the magnetic powder used in the rewritable magnetic layer was Co-γ-Fe ₂ O ₃ magnetic powder, coercive force 300 Oe, saturation magnetization 74.3 emu / g, average particle length.
Except that the magnetic powder of 0.5 μm γ-Fe ₂ O ₃ was used.
In the same manner as in Example 90, a magnetic card having a magnetic layer composed of γ-Fe ₂ O ₃ magnetic powder in the upper layer and a magnetic layer composed of MnBi magnetic powder in the lower layer was prepared. The signal was recorded and reproduced by.

Example 93 (Preparation of magnetic card using mixed powder) By mixing MnBi magnetic powder and other magnetic powder for use, two types of fixed data and non-rewritable fixed data can be used. An example of a card capable of multiple recording the same data on the same track will be described.

[0224] In Example 90, in the composition of the magnetic coating material for the rewritable magnetic layer, the magnetic powder was replaced by Co-γ-
Fe ₂ O ₃ magnetic powder varied Co-γ-Fe ₂ O ₃ magnetic powder and MnBi magnetic powder in a weight ratio of 7: the magnetic coating material using the mixed magnetic powder to be 3 was prepared. A PET layer having a thickness of 30 μm and having a release layer formed on this magnetic coating material.
It was applied onto the sputter film while applying a longitudinal orientation magnetic field of 1500 Oe so that the thickness after drying was 20 μm.
After that, the magnetic layer was slit into a magnetic tape in the same manner as in Example 90, and then embedded in a vinyl chloride substrate by thermocompression bonding to obtain a magnetic card. The recording and reproducing of the signal is performed in the 90th embodiment.
The same method was used.

Example 94 In Example 93, the mixing ratio of the Co-γ-Fe ₂ O ₃ magnetic powder and the MnBi magnetic powder was 7: 3 to 5: by weight.
A magnetic paint was prepared in the same manner as in Example 93 except that the number was changed to 5, and a magnetic card was prepared to record and reproduce signals.

Example 95 The magnetic powder to be mixed in Example 93 was Co-γ-F.
γ-Fe ₂ O from e ₂ O ₃ magnetic powder and MnBi magnetic powder
_{3 A} magnetic coating material was prepared in the same manner as in Example 93 except that the magnetic powder and MnBi magnetic powder were changed and the mixing ratio was set to 7: 3 by weight, and a magnetic card was prepared to record signals. Played back.

Comparative Example 8 Only the magnetic coating material using the Co-γ-Fe ₂ O ₃ magnetic powder described in Example 90 was used, and this magnetic coating material was applied onto a PET base film having a thickness of 30 μm and having a release layer formed thereon. , 1500 Oe so that the thickness after drying is 20 μm
Was applied while applying a longitudinal orientation magnetic field to prepare a magnetic card for recording and reproducing signals.

Comparative Example 9 Only the magnetic coating material using the barium ferrite magnetic powder described in Example 91 was used, and this magnetic coating material was applied onto a PET base film having a thickness of 30 μm and having a release layer formed thereon, and then the thickness after drying. To be 20 μm, 3000 Oe
Was applied while applying a longitudinal orientation magnetic field to prepare a magnetic card for recording and reproducing signals.

Comparative Example 10 A coating film was prepared by using the magnetic paint using MnBi magnetic powder shown in Example 64, and the magnetic paint was dried on a PET base film having a thickness of 30 μm and having a release layer formed thereon. After that, coating was performed while applying a longitudinal orientation magnetic field of 1500 Oe so that the thickness became 20 μm, and a magnetic card was produced in the same manner as in Example 91 to record and reproduce signals.

The results of examining the reproduction output of the magnetic cards obtained in Examples 90 to 95 and Comparative Examples 8 to 10 are shown in Table 13.
Shown in At the same time, in order to investigate the stability of the recording data, the results of investigating the change of the reproduction output by applying a direct current magnetic field of 4000 Oe after recording the signal are also shown.

[0231]

As is clear from Table 13, in the magnetic cards of Examples 90 to 92 in which the magnetic layer using the MnBi magnetic powder and the magnetic layer using another magnetic powder were laminated, the fixed signal (A) was applied. Even if the rewritable signal (B) is overwritten,
It can be seen that both the fixed signal (A) and the rewritable signal (B) can be separated and reproduced with high output.

A card prepared by mixing MnBi magnetic powder with another magnetic powder as the magnetic powder (Examples 9 to 9).
Also in 5), it can be seen that both the fixed signal (A) and the rewritable signal (B) can be separated and reproduced with high output. On the other hand, in the card using only Co-γ-Fe ₂ O ₃ magnetic powder and barium ferrite magnetic powder (Comparative Examples 8 and 9), when the (B) signal was overwritten, the (A) signal was erased. , Can not be played.

On the other hand, in the card using only MnBi magnetic powder (Comparative Example 9), even if the (B) signal was overwritten,
It can be seen that the signal (A) remains unerased and cannot be rewritten. This is one of the characteristics of the medium using the MnBi magnetic powder.

Next, regarding the magnetic field stability, all the cards using MnBi magnetic powder (Examples 90 to 95 and Comparative Example 10) were the first recorded signals even after applying a magnetic field of 4000 Oe. It can be seen that (A) remains unerased and functions as fixed data. On the other hand, in the card using only Co-γ-Fe ₂ O ₃ magnetic powder and barium ferrite magnetic powder (Comparative Examples 8 and 9), when the magnetic field of 4000 Oe was applied, not only the signal (A) initially recorded but also It can be seen that the signal (B) recorded later is also erased to a level that cannot be reproduced.

Further, when a mixed magnetic powder of MnBi magnetic powder and another magnetic powder is used, as can be seen from the comparison between Example 93 and Example 94, if the mixing ratio of MnBi magnetic powder is increased, The output rate of the fixed signal (A) to be recorded is larger than that of the rewritable signal (B).

In this example, a magnetic layer made of MnBi magnetic powder was also used as a magnetic recording medium in which magnetic layers were laminated.
An example has been described in which the magnetic layers using magnetic powders other than the Bi magnetic powder also have a thickness of 10 μm. But,
It is of course possible to arbitrarily change the output ratio of the fixed signal (A) and the rewritable signal (B) by changing the thickness of both magnetic layers.

In this example, the basic structure in the case of stacking magnetic layers and in the case of using mixed magnetic powder was described. It is of course possible to form another magnetic layer, a water repellent layer or the like according to the purpose.

As described above, a magnetic layer containing MnBi magnetic powder and a magnetic layer using magnetic powder other than MnBi magnetic powder are laminated, or MnBi magnetic powder and MnBi are laminated.
When a magnetic layer containing a mixed magnetic powder with another magnetic powder other than the magnetic powder is formed into a magnetic card, there are various forms, and as described above, the stripes are provided. -It may be provided on the entire surface.

Also, as shown in FIG. 16, the card substrate 1
A magnetic layer 2 containing a stripe-shaped MnBi magnetic powder is embedded on the top, and a magnetic layer 3 using a magnetic powder other than the MnBi magnetic powder is laminated on the card substrate 1 and the magnetic layer 2 containing the MnBi magnetic powder. Alternatively, as shown in FIG. 17, a magnetic layer 2 containing MnBi magnetic powder in a stripe shape is formed on the card substrate 1, and a magnetic layer 2 other than MnBi magnetic powder is formed so as to cover the magnetic layer 2. Magnetic layer 3 using the magnetic powder of
May be formed on the card substrate 1.

Also, as shown in FIG. 18, the card substrate 1
MnB is formed on the magnetic layer 2 containing MnBi magnetic powder so as to sandwich the magnetic layer 2 containing MnBi magnetic powder in a stripe shape.
The magnetic layer 3 may be formed using a magnetic powder other than the i magnetic powder.

Further, as shown in FIG. 19, a magnetic layer 2 containing stripe-shaped MnBi magnetic powder is embedded and formed on the surface of the card substrate 1, and other than MnBi magnetic powder is formed on the back surface of the card substrate 1. The stripe-shaped magnetic layer 3 using the magnetic powder may be embedded and formed, and as shown in FIG.
A magnetic layer 2 containing a stripe-shaped MnBi magnetic powder and a stripe-shaped magnetic layer 3 using a magnetic powder other than the MnBi magnetic powder may be embedded and formed on the surface of the card substrate 1.

Further, as shown in FIG. 21, a magnetic layer 2 containing MnBi magnetic powder is formed on the entire front surface of the card substrate 1, and a magnetic layer other than MnBi magnetic powder is formed on the entire back surface of the card substrate 1. The magnetic layer 3 using powder may be formed. As shown in FIG. 22, the magnetic layer 2 containing MnBi magnetic powder is formed on the entire front and back surfaces of the card substrate 1, and these magnetic layers 2 are formed. A magnetic layer 3 using a magnetic powder other than the MnBi magnetic powder may be further laminated thereon.

<< Reproducing Device for Magnetic Recording Medium >> As described above, the magnetic recording medium (eg, magnetic card) using MnBi magnetic powder can be easily erased at room temperature once data is recorded. It has the characteristic that there is no property, that is, the recorded data cannot be easily tampered with. On the other hand, the reading of data does not require a special device and one of the major features is that a normal card reader can be used. In this way, it is difficult to tamper with the data written on the card, and the combination with advanced printing technology to prevent counterfeiting of the card itself provides a strong security. Exert.

On the other hand, the data recorded on this magnetic card is used as a general-purpose reader by the same method as that for a normal magnetic card.
The readable feature also allows the data on this magnetic card to be copied to other conventional magnetic cards.
In applications where the card is used without looking through the eyes,
Even if it is a counterfeit card, if the recorded data is correct, the data will be read as an authentic card.

Therefore, a reproducing method and a reproducing apparatus for preventing the reproduction by such a copy card and reproducing the data only by the authentic magnetic card using the MnBi magnetic powder will be described. .

Embodiment 96 A reproducing apparatus is shown in FIG. The reproducing apparatus 10 is provided with a reproducing head 13 for reading the data recorded in the magnetic card 12 inserted from the card insertion port 11, and the reproducing head 13 and the card inserting unit are installed. 5 between mouth 11
A permanent magnet 14 having a magnetic field strength of 00 to 5000 Oe is installed.

The reproducing apparatus 10 shown in FIG. 24 is provided with a magnetic head 15 for applying an alternating magnetic field instead of the permanent magnet 14 of the apparatus shown in FIG. Before reproduction by the reproducing head 13, a magnetic field can be applied to the card by this magnetic head.

The reproducing apparatus shown in FIG. 25 has a structure in which a DC bias power source 16 is connected to the reproducing head 13 of the apparatus shown in FIG. 23 and the reproducing head 13 applies a DC bias magnetic field to reproduce data. Has become.

When the reproducing method and reproducing apparatus of this embodiment are used, not only the magnetic card for the purpose of illegal use but also the data of the ordinary magnetic card may be erroneously erased. However, this kind of trouble is due to the fact that a normal magnetic card cannot be inserted, or the shape of the card is modified so that the magnetic card is ejected before the magnetic field is applied.
This can be prevented by adding identification information other than data.

FIG. 26 shows an example in which the magnetic card 12 is partially provided with a notch 17 or a fine hole so as to be different in shape from the ordinary magnetic card. When the notch 17 or the pore is detected, for example, optically or mechanically when it is inserted into the reproducing apparatus, the magnetic card having the notch 17 or the pore allows the insertion, and the notch 17 or the pore. Cards without pores are immediately discharged from the regenerator.

FIG. 27 shows an example in which an identification mark 18 is attached to the surface of the magnetic card 12 by printing with an ink containing, for example, an infrared or ultraviolet excitation type phosphor, and the identification mark 18 is provided. Since 18 is almost transparent, it does not spoil the appearance of the magnetic card 12. When this magnetic card is inserted into a reproducing device, the identification mark 18 is irradiated with infrared rays or ultraviolet rays to excite the fluorescent substance, and the fluorescence emitted from the identification mark 18 is detected, whereby the identification mark is detected. The magnetic card 12 with the mark 18 is distinguished from the magnetic card 12 not having it.

Next, the results of recording / reproducing on / from a magnetic card using this apparatus will be described. The magnetic cards shown in Comparative Examples 8 to 10 were used for the measurement. The magnetic card of Comparative Example 10 is a card using MnBi magnetic powder, and Comparative Examples 8 and 9 are Co-γ-Fe ₂ O ₃ and barium which are magnetic powders used in ordinary magnetic recording media. A card using ferrite magnetic powder.

First, the card using the MnBi magnetic powder was initialized and the data was recorded. The initialization was performed by immersing the card in liquid nitrogen for cooling as described above, and then immediately applying an alternating magnetic field of 1000 Oe. Then, using a magnetic card reader / writer, a rectangular wave was recorded at a recording current of 200 mA and a recording density of 210 FCI. Regarding the cards using Co-γ-Fe ₂ O ₃ and barium ferrite magnetic powder of Comparative Examples 7 and 8,
Data was recorded in a similar manner, omitting the initialization step.

Regarding the reproduction of data, first, the initial reproduction output was obtained using the reader / writer used for recording the signal. This reader / writer has a gap length of 2 as a magnetic head.
A 0 micron MnZn ferrite head is used.

Next, the reproduction output of each card was measured using the reproducing apparatus having the structure shown in FIG. The magnetic field on the card surface by the permanent magnet 14 of this device is about 2500 Oe. The value of the reproduction output measured by this reproducing device was determined as a relative value to the value of the initial reproduction output measured using the above reader / writer. The value of the reproduction output was obtained from the amplitude of the reproduced waveform observed with an oscilloscope.

Next, the same measurement was performed using the reproducing apparatus shown in FIG. 24, in which a ring type magnetic head having a gap length of 40 μm was attached instead of the permanent magnet 14. A magnetic field was applied to this head by applying a current having a frequency of 1 kHz and a recording current of 100 milliamperes. The value of the magnetic field at this time was about 2000 Oe at the position of the magnetic layer. Table 14 shows the measurement results of the reproduction output using these two types of devices.

[0258]

As is clear from Table 14, a magnetic cover using MnBi magnetic powder before reproducing a signal with the magnetic head.
If a magnetic field smaller than the coercive force of the magnetic field is applied to the magnetic layer, M
It can be seen that in the magnetic card using the nBi magnetic powder, the reproduction output hardly changes, whereas in the card using the magnetic powder for ordinary magnetic recording, the reproduction output is remarkably low.

This means that the data recorded on the authentic magnetic card using MnBi magnetic powder is copied to the card using one ordinary magnetic powder,
It can be seen that the data is erased or destroyed and becomes unreadable. Therefore, only the data of the authentic magnetic card using MnBi magnetic powder cannot be reproduced.
It can be seen that irregular use due to copy card can be prevented.

[0261]

As described above, the magnetic powder of the present invention is a magnetic powder mainly composed of MnBi, in which the average particle size of the magnetic powder is 0.1 μm or more and 20 μm or less, 16 KO.
The coercive force measured by applying the magnetic field of e is 3000 to 15000 Oe at 300K and 50 to 10 at 80K.
Magnetization amount measured by applying a magnetic field of 16 KOe at 00 Oe, 300 K is 20 emu / g to 60 emu / g, and the reduction ratio of the magnetization amount when left for 7 days in an environment of temperature 60 ° C. and relative humidity 90%. Is 40% or less, metal B
The amount of i is represented by the formula: metal Bi / (MnBi + metal Bi) <0.5 (where metal Bi is the peak area from the (012) plane in the X-ray diffraction peak of Bi, and MnBi is , M
It is the peak area from the (101) plane in the X-ray diffraction peak of nBi. ) Is MnBi magnetic powder having an amount represented by), and further, a MnBi magnetic powder in which an inorganic film is formed in the vicinity of the surface of the magnetic particles, the manufacturing method of which is Mn powder having a particle diameter of 50 to 300 mesh. Or M
The powder mainly composed of n and the powder mainly composed of Bi or Bi are mixed at a molar ratio of Mn and Bi of 45:55.
To 65:35, and then press-molding this mixture in a non-oxidizing or reducing atmosphere,
MnBi is obtained by heating and reacting at a temperature not higher than the melting point of Bi,
Next, this MnBi is crushed in a non-oxidizing atmosphere to form fine particles, and the magnetic powder thus obtained is heat-treated in an oxygen-containing atmosphere. Since the heat treatment is performed in a non-oxidizing atmosphere, the corrosion resistance is remarkably improved and the saturation magnetization is hardly deteriorated.

Further, such a magnetic powder containing MnBi as a main component is contained in the magnetic layer and a coercive force measured by applying a magnetic field of 16 KOe is 5000 to 1 at 300K.
100-1500 Oe at 6000 Oe at 80K,
The magnetic flux density measured by applying a magnetic field of 16 KOe at 300 K is 500 to 2500 G, and the rectangular shape in the longitudinal direction is 0.6.
0 to 0.95, the decrease rate of the magnetic flux density is 50 when left for 7 days in an environment of temperature 60 ° C and relative humidity 90%.
% Or less, the magnetic layer further contains a binder resin having a basic functional group in the magnetic layer and a dispersant having a basic functional group in the magnetic layer, and the surface of the magnetic layer or the magnetic layer. A water-repellent layer between the base and the base, and further,
A magnetic recording medium such as a magnetic card having a magnetic layer using a normal magnetic powder together with the above MnBi magnetic powder has a characteristic that once recorded, it cannot be easily erased at room temperature.
It is possible to prevent tampering, which has been a serious problem in magnetic cards, and the deterioration of saturation magnetization is extremely small even when stored for a long time under high temperature and high humidity.

Further, the magnetic recording medium of the present invention has an extremely high coercive force of about 10,000 Oe or more at room temperature,
Since the magnetic recording medium has a peculiar property that the coercive force is reduced to about 1500 Oe or less at a temperature of about 100 K or less, the magnetic recording medium is cooled to a temperature of about 100 K or less to be in a demagnetized state, and then at room temperature, using a magnetic head A direct current or an alternating magnetic field smaller than the coercive force of the magnetic layer is applied to the magnetic layer on the upstream side of the magnetic head of the magnetic recording medium reproducing device so that the recorded data cannot be easily rewritten at room temperature by recording a signal. Recording and reproduction can be performed using a reproducing apparatus for a magnetic recording medium provided with a magnetic field applying means for applying.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of temperature dependence of coercive force of MnBi magnetic powder.

FIG. 2 is a diagram showing an example of an initial magnetization curve and a hysteresis curve of a magnetic recording medium using MnBi magnetic powder.

FIG. 3 MnBi magnetic powder and Co-γ-Fe ₂ O ₃
It is the figure which investigated the magnetic field stability of the reproduction output of the magnetic card using magnetic powder.

FIG. 4 is a graph showing the relationship between the crushing time of MnBi magnetic powder and the particle size.

FIG. 5 is a graph showing the relationship between the pulverization time of MnBi magnetic powder and the coercive force at 300K.

FIG. 6 is a graph showing the relationship between the crushing time of MnBi magnetic powder and the coercive force at 80K.

FIG. 7 is a graph showing the relationship between the pulverization time of MnBi magnetic powder and the amount of magnetization at 300K.

FIG. 8 is a graph showing the relationship between the crushing time of MnBi magnetic powder and S ^* .

FIG. 9 is a diagram illustrating a method of measuring S ^* .

FIG. 10 is a diagram showing an X-ray diffraction result of MnBi magnetic powder when the MnBi magnetic powder was kept in a humid environment.

FIG. 11 is a diagram showing a spectrum of Mn by photoelectron spectroscopy.

FIG. 12 is a diagram showing a spectrum of Bi by photoelectron spectroscopy.

FIG. 13 is a diagram showing the relationship between magnetic field density and magnetic field applied to a magnetic recording medium using MnBi magnetic powder.

FIG. 14 is a relationship diagram between magnetic flux density and output of a magnetic recording medium using MnBi magnetic powder.

FIG. 15 is a relationship diagram between coercive force and tampering prevention function of a magnetic recording medium using MnBi magnetic powder.

FIG. 16 is an enlarged sectional view showing an example of a magnetic card obtained by the present invention.

FIG. 17 is an enlarged cross-sectional view showing another example of the magnetic card obtained by the present invention.

FIG. 18 is an enlarged cross-sectional view showing another example of the magnetic card obtained by the present invention.

FIG. 19 is an enlarged sectional view showing another example of the magnetic card obtained by the present invention.

FIG. 20 is an enlarged cross-sectional view showing another example of the magnetic card obtained by the present invention.

FIG. 21 is an enlarged sectional view showing another example of the magnetic card obtained by the present invention.

FIG. 22 is an enlarged sectional view showing another example of the magnetic card obtained by the present invention.

FIG. 23 is a schematic configuration diagram of a reproducing device according to an embodiment of the present invention.

FIG. 24 is a schematic configuration diagram of a reproducing device according to another embodiment of the present invention.

FIG. 25 is a schematic configuration diagram of a reproducing apparatus according to still another embodiment of the present invention.

FIG. 26 is a plan view of a card-shaped magnetic recording medium according to an example of the present invention.

FIG. 27 is a plan view of a card-shaped magnetic recording medium according to another embodiment of the present invention.

[Explanation of symbols]

 1 Card Substrate 2, 3 Magnetic Layer 10 Reproducing Device 12 Magnetic Card 13 Reproducing Head 14 Permanent Magnet 15 Magnetic Head 16 Bias Power Supply 17 Notch 18 Identification Mark

Continuation of front page (31) Priority claim number Japanese Patent Application No. 6-192902 (32) Priority date Hei 6 (1994) July 25 (33) Priority claim country Japan (JP) (31) Priority claim number Heihei 6-222418 (32) Priority Day Hei 6 (1994) August 24 (33) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application Hei 6-247117 (32) Priority Day Hei 6 (1994) September 14 (33) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application No. 6-247118 (32) Priority Date Hei 6 (1994) September 14 (33) Priority Insistence country Japan (JP) (72) Inventor Toshinobu Sueyoshi 1-88, Torora, Ibaraki-shi, Osaka Within Hitachi Maxell Co., Ltd. (72) Inventor Noriaki Otani 1-88, Torora, Ibaraki-shi, Osaka Hitachi (72) Inventor Hirofumi Tagawa 1-88, Tora, Ibaraki, Osaka Prefecture Hitachi Maxell, Ltd.

Claims (55)

[Claims] 1. A magnetic powder mainly composed of MnBi having an average particle diameter of 0.1 μm or more and 20 μm or less and a coercive force of 30 measured by applying a magnetic field of 16 KOe.
The amount of magnetization measured by applying a magnetic field of 3000 to 15000 Oe at 0 K, 50 to 1000 Oe at 80 K, and 16 KOe at 300 K is 20 emu / g to 60.
emu / g, the decrease rate of the magnetization amount is 40% when left for 7 days in an environment of temperature 60 ° C. and relative humidity 90%.
Hereinafter, the amount of the metal Bi is represented by the formula: metal Bi / (MnBi + metal Bi) <0.5 (where the metal Bi is the peak area from the (012) plane in the X-ray diffraction peak of Bi). , MnBi is M
It is the peak area from the (101) plane in the X-ray diffraction peak of nBi. ) Magnetic powder characterized in that the amount is represented by 2. The magnetic powder according to claim 1, wherein the magnetic powder containing MnBi as a main component is a magnetic powder having a coating film of an inorganic substance of 1 to 50% by weight based on the magnetic particles. 3. The inorganic film is an oxide or hydroxide of Mn and Bi, and the ratio of the oxide or hydroxide of Mn and Bi is expressed by the atomic ratio of Mn and Bi (Mn / Bi). The above is the magnetic powder according to claim 2. 4. The Mn oxide is MnO.
When represented by x, the atomic ratio x of Mn and O is 1 ≦ x ≦ 3.5.
4. The magnetic powder according to claim 3, wherein the Bi oxide has an atomic ratio x of Bi and O of 1.5 ≦ x ≦ 2.5 when the Bi oxide is represented by BiOx. 5. When the oxide of Mn is expressed by MnOx, M
The magnetic powder according to claim 4, wherein the content of the component in which the atomic ratio x of n and O is 2 is 50 atomic% or more in the Mn oxide or the Mn hydroxide. 6. When the oxide of Mn is represented by MnOx, M
A component whose atomic ratio x of n and O is 2 is mainly β-Mn.
The magnetic powder according to claim 5, which is O _2. 7. The magnetic powder according to claim 2, wherein the inorganic film is at least one oxide selected from titanium, silicon, aluminum, zirconium, magnesium, lead and phosphorus. 8. The inorganic film is a film composed of an oxide or hydroxide of Mn and Bi and at least one oxide selected from titanium, silicon, aluminum, zirconium, magnesium, lead and phosphorus. The magnetic powder according to claim 2. 9. The content of at least one oxide selected from titanium, silicon, aluminum, zirconium, magnesium, lead and phosphorus is 2 to 50 relative to MnBi.
The magnetic powder according to claim 7 or 8, which has an atomic%. 10. The method according to claim 1 or 2, further comprising at least one element selected from nickel, aluminum, copper, platinum, zinc and iron in an amount of 0.6 to 5.0 atom% with respect to MnBi. Magnetic powder 11. Mn having a particle size of 50 to 300 mesh
Alternatively, the powder containing Mn as the main component and the powder containing Bi or Bi as the main component are used, and the content of Mn and Bi is 4 in molar ratio.
After premixing from 5:55 to 65:35,
A method for producing MnBi, which comprises molding this mixture and heating the mixture in a non-oxidizing or reducing atmosphere at a temperature below the melting point of Bi. 12. A method for producing a magnetic powder containing MnBi as a main component, which comprises further pulverizing the MnBi obtained in claim 11 into a fine particle in a non-oxidizing atmosphere. 13. A method for producing magnetic powder, characterized in that the magnetic powder containing MnBi as a main component obtained in claim 12 is heat-treated in an atmosphere containing oxygen. 14. The method for producing magnetic powder according to claim 12, wherein the heat treatment temperature is 20 to 250 ° C. 15. The magnetic powder mainly composed of MnBi obtained in claim 12 is heat-treated in an atmosphere containing oxygen and in a non-oxidizing atmosphere.
Method for producing magnetic powder containing nBi as a main component 16. The heat treatment temperature in an oxidizing atmosphere is 2
The method for producing magnetic powder according to claim 15, wherein the heat treatment temperature in a non-oxidizing atmosphere is 0 to 250 ° C., and the temperature is 200 to 400 ° C. 17. A magnetic layer containing 5 to 60% by volume of magnetic powder containing MnBi as a main component, and a coercive force measured by applying a magnetic field of 16 KOe is 5,000 to 300 at 300K.
100-1500O at 16000 Oe at 80K
e, the magnetic flux density measured by applying a magnetic field of 16 KOe at 300 K is 500 to 2500 G, and the rectangular shape in the longitudinal direction is
0.60 to 0.95, temperature 60 ° C, relative humidity 90%
Magnetic recording medium characterized in that the rate of decrease in magnetic flux density when left for 7 days under 50% is 50% or less 18. A magnetic layer containing magnetic powder mainly composed of MnBi and having an average particle size of 0.1 to 20 μm.
The coercive force measured by applying a magnetic field of KOe is 5000 to 16000 Oe at 300K and 100 at 80K.
The magnetic flux density measured by applying a magnetic field of 16 KOe at ~ 1500 Oe, 300 K is 500 ~ 2500 G, the rectangular shape in the longitudinal direction is 0.60 ~ 0.95, and the temperature is 60 ° C and the relative humidity is 90%. Magnetic recording medium characterized in that the rate of decrease in magnetic flux density when left for a day is 50% or less 19. After cooling at a low temperature and degaussing, 300K
The magnetic recording medium according to claim 17 or 18, wherein the magnitude of the magnetic flux density when a magnetic field of 1500 Oe is applied is 50% or more of the saturation magnetic flux density at 300K. 20. The magnetic recording medium according to claim 17, wherein the magnetic layer has a thickness of 3 to 30 μm. 21. The magnetic layer further contains, as an additive, an additive having a basic functional group consisting of imine, amine, amide, thiourea, thiazole, ammonium salt or organic phosphonium compound. The magnetic recording medium according to claim 17 or 18. 22. A magnetic layer, wherein the magnetic layer contains magnetic powder containing MnBi as a main component, gamma iron oxide magnetic powder, and Co.
Containing iron oxide magnetic powder, Ba-ferrite magnetic powder, Sr
18. A magnetic layer formed by laminating a ferrite magnetic powder and a magnetic layer containing at least one magnetic powder selected from metallic magnetic powders containing Fe as a main component.
The magnetic recording medium according to claim 18. 23. Mainly composed of MnBi and having an average particle size of 0.
The coercive force measured by applying a magnetic field of 16 KOe from 1 μm to 20 μm is 3000 to 1500 at 300K.
50-1000 Oe, 300K at 0K, 80K
Magnetic layer containing a magnetic powder having a magnetization of 20 emu / g to 60 emu / g measured by applying a magnetic field of 16 KOe, a gamma iron oxide magnetic powder, a Co-containing iron oxide magnetic powder, and a Ba-ferrite magnetic powder, At least one kind of magnetic powder selected from Sr-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component,
A magnetic recording medium characterized in that a magnetic layer containing a magnetic powder having a coercive force measured at 0 K of 250 to 3000 Oe is laminated. 24. The thickness of the laminated magnetic layers as a whole is from 4 to 4.
30 μm, both upper and lower magnetic layers have a thickness of 2 to 20 μm
24. The magnetic recording medium according to claim 22 or 23. 25. The magnetic layer comprises gamma iron oxide magnetic powder, C
O-containing iron oxide magnetic powder, Ba-ferrite magnetic powder, S
19. The magnetic recording according to claim 17 or 18, which is a magnetic layer containing at least one magnetic powder selected from r-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component, and MnBi magnetic powder. Medium 26. A gamma iron oxide magnetic powder in the magnetic layer,
Co-containing iron oxide magnetic powder, Ba-ferrite magnetic powder,
At least one magnetic powder selected from Sr-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component, and having a coercive force of 250 to 300 measured at 300K.
Mainly composed of magnetic powder of 0 Oe and MnBi, average particle diameter of 0.1 μm to 20 μm, coercive force measured by applying magnetic field of 16 KOe is 3000 to 15 at 300K.
50-1000 Oe, 30 at 000 Oe at 80K
A magnetic recording medium containing a magnetic powder having a magnetization amount of 20 emu / g to 60 emu / g measured by applying a magnetic field of 16 KOe at 0 K. 27. Two kinds of different signals are recorded on the same track of the magnetic layer, claim 17, claim 18, claim 19, claim 20, claim 21, claim 22, and claim 23. The magnetic recording medium according to claim 24, claim 25 or claim 26. 28. A water-repellent layer made of a water-repellent resin is further provided on the surface of the magnetic layer or between the magnetic layer and the substrate, claim 17, claim 18, claim 19, claim 20, claim 21. Claim 22, Claim 23, Claim 24, Claim 2
5. The magnetic recording medium according to claim 26 or 27. 29. The magnetic recording medium is a card-shaped magnetic recording medium in which a magnetic layer is provided on one or both sides of a card-shaped substrate, claim 17, claim 18, claim 19, and claim 2.
0, claim 21, claim 22, claim 23, claim 2
4. A magnetic recording medium according to claim 25, claim 26, claim 27 or claim 28. 30. The magnetic recording medium according to claim 29, wherein the magnetic layer is a stripe-shaped magnetic layer. 31. At least one magnetic powder selected from gamma iron oxide magnetic powder, Co-containing iron oxide magnetic powder, Ba-ferrite magnetic powder, Sr-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component. And 3
A magnetic stripe comprising a magnetic layer containing magnetic powder having a coercive force of 250 to 3000 Oe measured at 00K, and Mn
The main particle is Bi, the average particle size is 0.1 μm or more and 20 μm or less, and the coercive force measured by applying a magnetic field of 16 KOe is 30.
The amount of magnetization measured by applying a magnetic field of 3000 to 15000 Oe at 0 K, 50 to 1000 Oe at 80 K, and 16 KOe at 300 K is 20 emu / g to 60.
A magnetic stripe comprising a magnetic layer containing a magnetic powder of emu / g, which is formed on the front surface or both front and back surfaces of a card-shaped substrate. 32. Mainly composed of MnBi and having an average particle size of 0.
The coercive force measured by applying a magnetic field of 16 KOe from 1 μm to 20 μm is 3000 to 1500 at 300K.
50-1000 Oe, 300K at 0K, 80K
In order to cover the magnetic stripe with a larger area than the magnetic stripe, the magnetic stripe is formed on a magnetic layer containing a magnetic powder having a magnetization amount of 20 emu / g to 60 emu / g measured by applying a magnetic field of 16 KOe. Gamma iron oxide magnetic powder, Co-containing iron oxide magnetic powder, Ba
-At least one kind of magnetic powder selected from ferrite magnetic powder, Sr-ferrite magnetic powder, and metallic magnetic powder containing Fe as a main component, the magnetic powder having a coercive force of 250 to 3000 Oe measured at 300K. Magnetic card provided with a magnetic layer 33. At least one magnetic powder selected from gamma iron oxide magnetic powder, Co-containing iron oxide magnetic powder, Ba-ferrite magnetic powder, Sr-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component. And 3
33. The magnetic card according to claim 32, wherein a magnetic layer containing magnetic powder having a coercive force measured at 00K of 250 to 3000 Oe is formed over the entire surface of the card. 34. A magnetic card having a magnetic layer containing magnetic powder mainly composed of MnBi and having a non-rewritable portion and a rewritable portion. 35. Mainly composed of MnBi and having an average particle diameter of 0.
The coercive force measured by applying a magnetic field of 16 KOe from 1 μm to 20 μm is 3000 to 1500 at 300K.
50-1000 Oe, 300K at 0K, 80K
Magnetic layer containing a magnetic powder having a magnetization of 20 emu / g to 60 emu / g measured by applying a magnetic field of 16 KOe, a gamma iron oxide magnetic powder, a Co-containing iron oxide magnetic powder, and a Ba-ferrite magnetic powder, At least one kind of magnetic powder selected from Sr-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component,
Non-rewritable data was recorded in the portion where the magnetic layer containing the magnetic powder having a coercive force measured at 0K of 250 to 3000 Oe was recorded, and gamma iron oxide magnetic powder, Co-containing iron oxide magnetic powder, Ba-ferrite were recorded. Magnetic powder, Sr-
At least one magnetic powder selected from ferrite magnetic powder and metallic magnetic powder containing Fe as a main component, and having a coercive force of 250 to 3000 Oe measured at 300K.
34. The rewritable data is recorded in a portion formed of a magnetic layer containing the magnetic powder according to claim 32 or 33.
Or the magnetic card according to claim 34. 36. A water-repellent layer made of a water-repellent resin is further provided on the surface of the magnetic layer or between the magnetic layer and the base body, claim 31, claim 32, claim 33, claim 34 or claim 35. Magnetic card described 37. The magnetic according to claim 29, claim 30, claim 31, claim 32, claim 33, claim 34, claim 35 or claim 36, wherein one side of the magnetic card is a printing surface. Card 38. On the back surface of the magnetic card, among the gamma iron oxide magnetic powder, the Co-containing iron oxide magnetic powder, the Ba-ferrite magnetic powder, the Sr-ferrite magnetic powder and the metallic magnetic powder containing Fe as a main component. A magnetic layer containing at least one magnetic powder selected from among the magnetic powders having a coercive force measured at 300K of 250 to 3000 Oe, provided in Claim 29, Claim 30, Claim 31, and Claim 3.
2. The magnetic card according to claim 33, claim 34, claim 35 or claim 36. 39. The magnetic layer further has a thickness of 1 to 10 μm.
Claim 29, Claim 30, Claim 31, Claim 32, Claim 33, Claim 34, Claim 3 in which a non-magnetic layer of m is provided.
5. The magnetic card according to claim 36, claim 37 or claim 38. 40. The method according to claim 29, wherein the number of tracks recorded on the magnetic stripe is two or more.
0, claim 31, claim 32, claim 33, claim 3
4, claim 35, claim 36, claim 37, claim 38
Or the magnetic card according to claim 39. 41. Another magnetic card is provided at an appropriate position of the magnetic card.
30. An identifier for distinguishing from the code is attached.
Magnetic card according to claim 30, claim 31, claim 32, claim 33, claim 34, claim 35, claim 36, claim 37, claim 38, claim 39 or claim 40. 42. The identifier is a latent image mark.
Magnetic card described 43. A magnetic layer contains 5 to 60% by volume of magnetic powder mainly composed of MnBi, and a coercive force measured by applying a magnetic field of 16 KOe is 5000 to 300 at 300K.
100-1500O at 16000 Oe at 80K
e, the magnetic flux density measured by applying a magnetic field of 16 KOe at 300 K is 500 to 2500 G, and the rectangular shape in the longitudinal direction is
A method of recording a magnetic recording medium, characterized in that a magnetic recording medium having a density of 0.60 to 0.95 is cooled to a low temperature to be in a demagnetized state, and then a signal is recorded using a magnetic head. 44. A recording method for a magnetic recording medium according to claim 43, wherein the magnetic recording medium is a magnetic card. 45. When the magnetic recording medium is cooled to a low temperature to be in a demagnetized state, the magnetic recording medium is cooled to a low temperature or immediately after cooling, and an alternating magnetic field is further applied to the magnetic layer to bring it into a demagnetized state. 43 or a recording method for a magnetic recording medium according to claim 44. 46. The magnetic layer contains 5 to 60% by volume of magnetic powder mainly composed of MnBi, and the coercive force measured by applying a magnetic field of 16 KOe is 5,000 to 300 at 300K.
100-1500O at 16000 Oe at 80K
e, the magnetic flux density measured by applying a magnetic field of 16 KOe at 300 K is 500 to 2500 G, and the rectangular shape in the longitudinal direction is
Demagnetize the magnetic recording medium of 0.60 to 0.95,
After that, a signal is recorded using a magnetic head, the signal is recorded, an alternating magnetic field is applied to the magnetic layer to stabilize the signal, and then the recording signal is reproduced using the magnetic head. Recording / reproducing method of medium 47. A recording / reproducing method for a magnetic recording medium according to claim 46, wherein the intensity of the alternating magnetic field applied to stabilize the signal is 3000 to 10000 Oe. 48. Mainly containing MnBi and having an average particle size of 0.
The coercive force measured by applying a magnetic field of 16 KOe from 1 μm to 20 μm is 3000 to 1500 at 300K.
50-1000 Oe, 300K at 0K, 80K
Magnetic layer containing a magnetic powder having a magnetization of 20 emu / g to 60 emu / g measured by applying a magnetic field of 16 KOe, a gamma iron oxide magnetic powder, a Co-containing iron oxide magnetic powder, and a Ba-ferrite magnetic powder, At least one kind of magnetic powder selected from Sr-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component,
A first signal is first recorded on the upper and lower magnetic layers of a magnetic recording medium in which a magnetic layer containing a magnetic powder having a coercive force measured at 0 K of 250 to 3000 Oe is laminated, and then a second signal different from the first signal is recorded. Method for recording on a magnetic recording medium, characterized in that the signal is recorded so as to overlap a part or the whole of the track on which the first signal is recorded. 49. Mainly composed of MnBi and having an average particle size of 0.
The coercive force measured by applying a magnetic field of 16 KOe from 1 μm to 20 μm is 3000 to 1500 at 300K.
50-1000 Oe, 300K at 0K, 80K
Magnetic layer containing a magnetic powder having a magnetization of 20 emu / g to 60 emu / g measured by applying a magnetic field of 16 KOe, a gamma iron oxide magnetic powder, a Co-containing iron oxide magnetic powder, and a Ba-ferrite magnetic powder, At least one kind of magnetic powder selected from Sr-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component,
A first signal is first recorded on the upper and lower magnetic layers of a magnetic recording medium in which a magnetic layer containing a magnetic powder having a coercive force measured at 0 K of 250 to 3000 Oe is laminated, and then a second signal different from the first signal is recorded. Signal is recorded so as to overlap a part or the whole of the track on which the first signal is recorded, the first signal is mainly composed of MnBi, and the average particle diameter is 0.1 μm or more 2
The coercive force measured by applying a magnetic field of 0 μm or less and 16 KOe is 80 at 3000 to 15000 Oe at 300K.
50-1000 Oe at K, 16 at 300K
The amount of magnetization measured by applying a magnetic field of KOe is 20 emu /
The second signal was recorded on the magnetic layer containing the magnetic powder of g to 60 emu / g, and the second signal was recorded as gamma iron oxide magnetic powder, Co-containing iron oxide magnetic powder, Ba-ferrite magnetic powder, Sr-ferrite magnetic powder and Fe. At least one kind of magnetic powder selected from metallic magnetic powders as a main component, having a coercive force of 250 to 3000 Oe measured at 300K.
Recording method on a magnetic recording medium, characterized by recording on a magnetic layer containing magnetic powder of 50. A gamma iron oxide magnetic powder in the magnetic layer,
Co-containing iron oxide magnetic powder, Ba-ferrite magnetic powder,
At least one magnetic powder selected from Sr-ferrite magnetic powder and metallic magnetic powder containing Fe as a main component, and having a coercive force of 250 to 300 measured at 300K.
Mainly composed of magnetic powder of 0 Oe and MnBi, average particle diameter of 0.1 μm to 20 μm, coercive force measured by applying magnetic field of 16 KOe is 3000 to 15 at 300K.
50-1000 Oe, 30 at 000 Oe at 80K
First, a first signal is recorded on a magnetic recording medium containing a magnetic powder having a magnetization amount of 20 emu / g to 60 emu / g measured by applying a magnetic field of 16 KOe at 0 K, and then the first signal is recorded. A second signal different from
Recording method for a magnetic recording medium, characterized in that two kinds of signals are recorded so as to overlap a part or the whole of a track on which the above signals are recorded. 51. A magnetic layer contains 5 to 60% by volume of magnetic powder mainly composed of MnBi, and a coercive force measured by applying a magnetic field of 16 KOe is 5000 to 300 at 300K.
100-1500O at 16000 Oe at 80K
e, the magnetic flux density measured by applying a magnetic field of 16 KOe at 300 K is 500 to 2500 G, and the rectangular shape in the longitudinal direction is
When magnetically recording a signal on a magnetic recording medium of 0.60 to 0.95 and reproducing the magnetically recorded signal, it is smaller than the coercive force of the magnetic layer before the magnetically recorded signal is reproduced by the magnetic head. Method of reproducing magnetic recording medium characterized by applying direct current or alternating magnetic field to magnetic layer 52. A reproducing method of a magnetic recording medium according to claim 51, wherein the means for applying a direct current smaller than the coercive force of the magnetic layer to the magnetic layer is a permanent magnet. 53. A magnetic layer contains 5 to 60% by volume of magnetic powder mainly composed of MnBi, and a coercive force measured by applying a magnetic field of 16 KOe is 5000 to 300 at 300K.
100-1500O at 16000 Oe at 80K
e, the magnetic flux density measured by applying a magnetic field of 16 KOe at 300 K is 500 to 2500 G, and the rectangular shape in the longitudinal direction is
Characteristically, when a signal is magnetically recorded on a magnetic recording medium of 0.60 to 0.95 and the magnetically recorded signal is reproduced, a signal is reproduced while applying a bias magnetic field smaller than the coercive force of the magnetic layer. Method for reproducing magnetic recording medium 54. The magnetic layer contains 5 to 60% by volume of magnetic powder mainly composed of MnBi, and the coercive force measured by applying a magnetic field of 16 KOe is 5000 to 300 at 300K.
100-1500O at 16000 Oe at 80K
e, the magnetic flux density measured by applying a magnetic field of 16 KOe at 300 K is 500 to 2500 G, and the rectangular shape in the longitudinal direction is
In a reproducing device of a magnetic recording medium for reproducing a signal magnetically recorded on a magnetic recording medium of 0.60 to 0.95, the coercive force of the magnetic layer is smaller than that of the magnetic layer upstream of the magnetic head. Reproducing apparatus for magnetic recording medium, characterized in that it is provided with magnetic field applying means for applying a direct current or an alternating magnetic field. 55. A reproducing apparatus for a magnetic recording medium according to claim 54, wherein the means for applying a direct current smaller than the coercive force of the magnetic layer to the magnetic layer is a permanent magnet.