JPH11149632A - Magnetic recording media - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic record medium less liable to reduce output even after storage at a high temp. and under high humidity over a long period of time and excellent in preservability by forming a metallic thin film layer on a magnetic layer contg. MnBi magnetic powder. SOLUTION: An oxide coating film is formed on the surface of MnBi magnetic powder by heating the powder at a prescribed temp. in gaseous nitrogen or argon contg. a prescribed amt. of oxygen to improve the stability of the powder. The stabilized MnBi magnetic powder is mixed with a resin binder, an org. solvent and various additives to prepare a magnetic coating material. This coating material is applied on a substrate and dried to form a magnetic layer and a metallic thin film layer is further formed on the magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium such as a magnetic card having a magnetic layer containing MnBi magnetic powder and a binder resin.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as video tapes, floppy disks, credit cards, prepaid cards, etc. because of their easy recording and reproduction. However, the feature that recording and reproduction are easy is
Conversely, there is a problem that the recorded data is easily erased by mistake and that the data can be easily falsified.
For example, a magnetic card is erased by a strong magnetic field magnet that is used in our daily life, such as various doors and handbags, or the data on the magnetic card is rewritten and misused. Accidents and crimes are occurring frequently.

[0003] As a countermeasure, for example, a recording medium such as an optical card that causes an irreversible change in the recording medium by laser light and cannot be rewritten once recorded,
There has been proposed an IC card which is difficult to falsify and has high security. However, an optical card requires a dedicated and expensive recording and reproducing device, and an IC card.
However, the use of semiconductors has the disadvantage of being expensive, and none of them have been replaced with magnetic card recording / reproducing devices that are widely used all over the world. Not as widespread.

For this reason, various measures have been proposed to prevent tampering of the magnetic card. For example, hologram printing and printing using advanced printing techniques have been performed on the magnetic card. While this method is effective in preventing the appearance of card forgeries, tampering does not include data read from another person's card, for example, into a legitimate credit card obtained through unauthorized means. If the writing is performed by a method such as writing, this cannot be prevented because the written data is regular.

On the other hand, it is known that a magnetic recording medium using MnBi magnetic powder as a recording element has a feature that once a signal is recorded, it is not easily erased at room temperature (Japanese Patent Publication No. 52-1982). 46801, 54
-19244, 54-33725, 57-38
962, 57-38963, 59-31764
No. and other publications). In particular, today, as magnetic card readers are widely used in all corners of the world, credit cards are frequently used in accidents and crimes such as data being erased by mistake or being intentionally rewritten. It has attracted attention as a device that can prevent accidents and unauthorized use in computers and cache cards.

[0006]

As described above, MnBi
According to a magnetic recording medium using a magnetic powder as a recording element, once a signal is recorded, it is extremely difficult to erase or rewrite the signal thereafter. Yes, but M
There has been a problem that the nBi magnetic powder is chemically unstable, and the magnetization tends to decrease particularly when left under a high temperature and high humidity for a long time.

To solve this problem, a method of forming an oxide film having a specific structure on the surface of MnBi magnetic powder,
A method has been proposed in which an additive having an amine group is added to the magnetic layer (JP-A-8-138921). These methods are based on the premise that water vapor penetrates into the magnetic layer, and prevent deterioration of the MnBi magnetic powder as much as possible. On the other hand, JP-A-8-138921
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes that a water-repellent resin layer is formed on the MnBi magnetic layer to prevent water vapor from entering the magnetic layer, thereby preventing the MnBi magnetic powder from deteriorating.

According to the present invention, a magnetic recording medium using MnBi magnetic powder as a recording element is prevented from deteriorating the magnetic characteristics under high temperature and high humidity by means different from those already proposed, and the magnetic characteristics are excellent in storage characteristics. It is intended to provide a recording medium.

[0009]

To achieve the above object, the present inventors first form various protective films on a magnetic layer to prevent the invasion of water vapor. In the case where the proposed resin layer is formed or the layer in which various additives are dispersed in the resin layer, since the resin layer itself has a myriad of fine holes, it is liable to deteriorate under high temperature and high humidity.
It was considered that the effect of preventing invasion of water vapor was not sufficiently obtained for a magnetic recording medium using nBi magnetic powder as a recording element. When the thickness of the resin layer is increased,
Although it is expected that the effect of blocking water vapor is increased, in this case, the gap between the magnetic head and the magnetic layer is increased, and the problem of lowering the output is likely to occur.

[0010] The present inventors have based on such an idea,
As a result of various studies on what kind of protective film should be provided, if a metal thin film layer is formed on a magnetic layer containing MnBi magnetic powder, for example, although it is considerably thinner than the above-mentioned resin layer or the like, By forming the thin film layer of tin or aluminum to a thickness of 10 to 1,000 nm, the penetration of water vapor can be effectively blocked, whereby deterioration under high temperature and high humidity can be prevented with almost no decrease in output. As a result, the present inventors have found that a magnetic recording medium having remarkably excellent storage characteristics can be obtained, and have completed the present invention.

That is, the present invention provides a magnetic recording medium having a magnetic layer containing MnBi magnetic powder and a binder resin, wherein a metal thin film layer is provided on the magnetic layer. The magnetic recording medium according to claim 1, wherein the metal thin film layer is made of either tin or aluminum (claim 2), wherein the metal thin film layer has a thickness of 10 to 1,000 nm. The present invention can provide a magnetic recording medium having the above configuration (claim 3), and a magnetic recording medium having the above configuration wherein the magnetic layer is provided on the entire or partial surface of the card-like substrate.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The MnBi magnetic powder used in the present invention is produced by making a MnBi ingot by a powder metallurgy method, an arc furnace melting method, a high frequency melting method, a melt quenching method, etc., and pulverizing the MnBi ingot. Is done. For example, in the powder metallurgy method, an ingot is formed into a process, a process for pulverizing the process, and a process for stabilizing the ingot. The MnBi magnetic powder may be manufactured without necessarily using the pulverization method.

In the step of producing an ingot, first, Mn powder and Bi powder of 50 to 300 mesh are sufficiently mixed. Mixing can be performed by any means such as an automatic mortar and a ball mill. At this time, the mixing is preferably performed in an inert atmosphere, but the mixing may be performed in an oxidizing atmosphere.
The mixing ratio (Mn / Bi) of Mn powder and Bi powder is preferably in the range of 45:55 to 65:35 in molar ratio.
When Mn is increased as compared with Bi, when the MnBi magnetic powder is formed, an oxide or hydroxide of Mn is formed on the surface, the corrosion resistance of the MnBi magnetic powder is improved, and a high quality magnetic powder is obtained. For this reason, it is preferable to increase Mn as compared with Bi.

The Mn powder and Bi powder preferably have a low impurity content. Ni, for adjusting magnetic properties
Other metals such as Al, Cu, Pt, Zn, and Fe may be added. When the amount of these other metals is 0.6 atomic% or more with respect to MnBi, the magnetic properties can be controlled well, and when the amount is less than 5.0 atomic%, the crystal structure of MnBi itself can be improved. Can be maintained favorably, and Mn
Bi original characteristics can be exhibited. For this reason, the addition amount of these other metals is 0.6 to 5.0 atomic% with respect to MnBi.
Is preferably within the range. In addition, in order to add these other metals, it is preferable to form an alloy of Mn and these metals in advance.

The Mn powder and Bi powder may be used in advance, or may be used by pulverizing a flake or shot-like lump into fine particles. Mn
When Bi magnetic powder is obtained by a sintering reaction, MnBi is generated by a diffusion reaction at a contact interface between Mn and Bi.
If the powder and the Bi powder are finely divided into 50 to 300 mesh, the above-mentioned formation reaction proceeds smoothly. As described above, since the reaction is greatly affected by the surface properties of the raw material powder, the surface treatment performed by the powder metallurgy method such as etching the surface of the raw material Mn powder and Bi powder or degreased with a solvent. It is preferable to apply

After the Mn powder and the Bi powder are mixed in this way, they are pressed and formed into a molded body. The pressure at that time is preferably in the range of 1 to 8 ton / cm ² . When the molded body is formed under such a pressing force, the sintering reaction is promoted and a uniform ingot can be produced with good productivity. That is, by setting the pressing force to 1 ton / cm ² or more, the MnBi ingot can be manufactured uniformly, and the pressing force is set to 8 ton / cm 2.
By setting it to ² or less, the productivity of MnBi ingot can be improved.

Next, the molded body is sealed in a glass container or a metal container. The inside of the container is set to a vacuum or an inert gas atmosphere to prevent oxidation during the heat treatment. Examples of the inert gas include a hydrogen gas, a nitrogen gas, an argon gas and the like, and a nitrogen gas is most preferable in terms of cost. The sealed container is placed in an electric furnace and heat-treated at 260 to 271 ° C. for 2 to 15 days to produce a MnBi ingot. By setting the heat treatment temperature to 260 ° C. or higher, the heat treatment can be performed in a short time and the magnetization amount of the ingot can be increased.
Further, when the temperature is set to 271 ° C. or lower, the dissolution of Bi is suppressed, and a uniform ingot can be obtained.

In the pulverizing step, the MnBi ingot prepared as described above is taken out of the container and coarsely pulverized in an inert gas atmosphere using an automatic mortar or the like to adjust the particle size to 100 to 500 μm. Then, by wet pulverization using the impact of a ball using a ball mill or planetary ball mill, or dry pulverization using a jet mill, etc. Fine particles are formed in a particle size range of 0.1 to 20 μm. This particle size can be controlled by the pulverization conditions. When the particle diameter is larger than 0.1 μm, the saturation magnetization of the MnBi magnetic powder can be increased, and when it is 20 μm or less, the coercive force can be sufficiently increased, and the surface smoothness of the magnetic recording medium becomes good, and sufficient recording can be performed. Can be.

By such a pulverizing step, the coercive force measured by applying a magnetic field of 16 KOe is in the range of 3,000 to 20,000 Oe at 300 K,
The MnBi magnetic powder used in the present invention has a saturation magnetization measured in a range of 50 to 1,000 Oe at K and an applied magnetic field of 16 KOe at 300 K in a range of 20 to 60 emu / g.

In the stabilizing step, the MnBi magnetic powder thus obtained is put in a range of 100 to 10,000.
Heating at a temperature of 20 to 150 ° C. in a nitrogen gas or an argon gas containing about ppm of oxygen to form an oxide film on the surface of the MnBi magnetic powder, thereby improving the stability of the powder. It is.

In the present invention, the above stabilized MnBi magnetic powder is used, mixed with a binder resin or an organic solvent, and a commonly used dispersant, lubricant, antistatic agent is used. A magnetic paint is prepared by adding and mixing various additives such as This magnetic paint is applied on a substrate such as a polyester film and dried to provide a magnetic layer.
At this time, it is preferable to perform magnetic field orientation parallel to the magnetic layer surface, and the magnetic field strength is preferably about 1,000 to 5,000 Oe. The thickness of the magnetic layer is preferably 2 to 30 μm for a magnetic card or the like.

As the binder resin, any resin commonly used for magnetic recording media can be used.
Vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, cellulose resins, fluorine resins, polyurethane resins, isocyanate compounds, radiation-curable resins and the like are used. The inclusion of basic functional groups such as imines, amines, amides, thioureas, thiosols, ammonium salts or phosphonium compounds in these binder resins provides good results in the chemical stabilization of MnBi magnetic powder. Therefore, it is preferable. Further, the same stabilization as described above may be achieved by adding an additive having the same basic functional group as described above to the magnetic paint.

In providing such a magnetic layer, gamma iron oxide magnetic powder,
Magnetite magnetic powder, iron oxide magnetic powder such as gamma iron oxide magnetite intermediate iron oxide magnetic powder, chromium dioxide magnetic powder, cobalt-containing iron oxide magnetic powder containing cobalt, barium ferrite magnetic powder, strontium ferrite magnetic powder, lead Hexagonal ferrite magnetic powder such as ferrite magnetic powder, and metal magnetic powder such as iron-nickel alloy magnetic powder, iron-cobalt alloy magnetic powder,
Various other magnetic powders such as samarium cobalt magnetic powder and neodymium iron boron magnetic powder can also be used in combination.

When these other magnetic powders are used in combination, Mn
Whether they are included together in a magnetic layer containing Bi magnetic powder,
What is necessary is just to laminate the magnetic layer containing the other magnetic powder on the magnetic layer containing only the MnBi magnetic powder. In the latter case,
The magnetic layer containing the other magnetic powder may be the upper layer or the lower layer of the magnetic layer containing only the MnBi magnetic powder.
20 μm, the total thickness of the magnetic layer is usually 2 to 30 μm
What is necessary is just to make it.

The present invention is characterized in that a metal thin film layer is further formed on the magnetic layer provided on the base as described above. There are various methods for forming the metal thin film layer, such as a vacuum evaporation method and a sputter method, but the vacuum evaporation method is preferable because it has excellent productivity. As the metal thin film layer, tin or aluminum is preferable. The thickness of the metal thin film layer is usually 10 to 1,000 nm, preferably 30 to 500 nm. With such a small thickness, a large water vapor cutoff effect can be obtained without lowering the output due to spacing.

In the magnetic recording medium of the present invention, various resin layers or concealing layers for imparting sliding resistance can be formed on the metal thin film layer. When the magnetic recording medium manufactured in this way is a magnetic card or the like, the card
The magnetic layer (and the metal thin film layer thereon) provided on the substrate may be provided on the entire surface of the substrate or partially (including a stripe shape or the like). When the magnetic card is a pre-paid card, a magnetic commuter pass, or the like, the metal thin film layer on the magnetic layer can also function as a thermal printing layer in addition to the water vapor blocking effect.

In addition, credit cards and cache cards
For example, the magnetic tape may be manufactured using a transfer magnetic tape. In this case, a metal thin film layer is formed on a base film for transfer, and the metal thin film layer is formed on this thin film layer directly or through an intermediate layer.
A magnetic layer containing nBi magnetic powder is provided to prepare a transfer magnetic tape. This is heat-pressed on the entire or partial surface of the card-like substrate, and the base film is peeled off. When the magnetic layer and the metal thin film layer thereon are transferred, the desired card is produced. You.

[0028]

EXAMPLES Examples of the present invention will be described below in more detail. In the following, “parts” means “parts by weight”.

Example 1 <Synthesis of MnBi magnetic powder> Mn powder and Bi powder pulverized to a particle size of 200
And Bi were weighed so that the molar ratio became 55:45, and they were sufficiently mixed by a ball mill. This was molded into a cylindrical shape having a diameter of 20 mm and a height of 10 mm at a pressure of 3 ton / cm ^{2 by} a press machine. The molded body was placed in a sealed aluminum container, and after vacuum was drawn, nitrogen gas was introduced at 0.5 atm. The container was placed in an electric furnace and heat-treated at a temperature of 270 ° C. for 10 days. Then, the MnBi ingot was taken out into the air, and lightly pulverized in a mortar to measure magnetic properties. The coercive force measured by applying a maximum magnetic field of 16 KOe at 300 K is 840 O
e, the amount of magnetization was 53.6 emu / g.

Next, the coarsely pulverized MnBi powder is
It was pulverized with a planetary ball mill. Contents 1,000c
The ball mill pot (c) was filled with a zirconia ball having a diameter of 3 mm so as to occupy 1/3 of the inner volume. In this,
500 g of coarsely pulverized MnBi powder and 500 g of toluene as a solvent were added, and pulverized at 150 rpm for 4 hours. After taking out the obtained MnBi magnetic powder and evaporating toluene, the magnetic properties were measured. The coercive force measured by applying a maximum magnetic field of 16 KOe at 300 K is 8,
The amount of magnetization was 600 Oe and the amount of magnetization was 39.2 emu / g.

The MnBi magnetic powder thus obtained is
Stabilization was performed by the following method. The MnBi magnetic powder was taken out in a state of being immersed in toluene, transferred to a heat treatment vessel, and vacuum dried at room temperature for about 2 hours. While in the same container,
One atmosphere of nitrogen gas containing 1,000 ppm of oxygen was introduced, and heat treatment was performed at a temperature of 40 ° C. for 15 hours. Subsequently, as a second stage heat treatment, the oxygen mixed gas filled in the container is evacuated and removed, then nitrogen gas is introduced at 0.5 atm, the temperature is raised to 330 ° C., and heating is performed at this temperature for 2 hours. Processed. MnB after this stabilization treatment
The i-magnetic powder had an average particle diameter of 1.8 μm, a coercive force measured by applying a magnetic field of 300 K and a maximum magnetic field of 16 KOe, and a coercivity of 46.3 emu / g.

<Preparation of Magnetic Card> MnBi magnetic powder (Hc: 8,500 Oe) 100 synthesized by the above method
A composition consisting of 25 parts of VAGH (vinyl chloride-vinyl acetate copolymer manufactured by UCC), 50 parts of methyl isobutyl ketone and 50 parts of toluene was mixed with a ball mill to give 2 parts.
The dispersion was dispersed for 4 hours to prepare a magnetic paint.

Separately, a release layer made of a resin having a thickness of about 1 μm is formed on a base film made of a polyethylene terephthalate film having a thickness of 20 μm by a coating method, and a vacuum deposition is performed thereon. According to the method, the thickness is 100
A metal thin film layer composed of a tin thin film having a thickness of 10 nm was formed. The magnetic paint prepared as described above is coated on this metal thin film layer by 3,000 O so that the thickness of the dried magnetic layer becomes 15 μm.
e was applied while applying a longitudinal orientation magnetic field to prepare a transfer magnetic tape.

Then, the magnetic tape for transfer was superimposed on a 0.76 mm thick vinyl chloride resin substrate for a magnetic card, and pressed from above with a heating roller to form the vinyl tape. Adhered to the substrate. After this bonding, the base film of the magnetic tape for transfer was peeled off and heated and pressed with a press plate.
A magnetic layer and a metal thin film layer thereon were buried in a vinyl chloride resin substrate and punched out in a card size to produce a magnetic card.

Example 2 A magnetic card was manufactured in the same manner as in Example 1 except that the metal thin film layer was changed to an aluminum thin film having a thickness of 100 nm.

Example 3 A magnetic card was manufactured in the same manner as in Example 1 except that the thickness of the metal thin film layer (tin thin film) was changed to 50 nm.

Example 4 The magnetic coating material prepared in Example 1 was placed on a card-like substrate made of polyethylene terephthalate film having a thickness of 188 μm, and dried so that the thickness after drying was reduced to 15 μm.
The coating was performed while applying a longitudinal orientation magnetic field of 0 Oe to form a magnetic layer. On this magnetic layer, a metal thin film layer made of a tin thin film having a thickness of 100 nm is formed by a vacuum evaporation method, and further, an ultraviolet curable resin layer having a thickness of 2 μm is formed thereon, and then punched into a card size. Thus, a magnetic card was manufactured.

Example 5 A magnetic card was manufactured in the same manner as in Example 4 except that the metal thin film layer was changed to an aluminum thin film having a thickness of 100 nm.

Example 6 In preparing a magnetic paint, 50 parts of MnBi magnetic powder and barium ferrite magnetic powder (average particle size 0.9 μm, coercive force 2,
A magnetic card was manufactured in the same manner as in Example 1 except that the amount was changed to 50 parts of 800 Oe and a saturation magnetization of 53.4 emu / g).

Comparative Example 1 A magnetic card was manufactured in the same manner as in Example 1 except that the metal thin film layer composed of the tin thin film was not formed on the magnetic layer.

Comparative Example 2 A magnetic card was manufactured in the same manner as in Example 4, except that the metal thin film layer made of the tin thin film was not formed on the magnetic layer.

Comparative Example 3 A magnetic card was manufactured in the same manner as in Example 6, except that the metal thin film layer made of the tin thin film was not formed on the magnetic layer.

With respect to each of the magnetic cards manufactured in Examples 1 to 6 and Comparative Examples 1 to 3, a storage characteristic test was performed by the following method to examine the degree of deterioration of the reproduction output.
The results were as shown in Table 1.

<Storage Characteristics Test> The magnetic card was immersed in liquid nitrogen for cooling, and was initialized by applying an AC magnetic field of 1,000 Oe. A signal having a recording density of 210 FCI was recorded on the magnetic card by using a magnetic card reader / writer ("CR-700" manufactured by Sanwa Nitec) at a recording current of 200 mA. Immediately after this, the reproduced output was measured by the same magnetic card reader / writer, and this was used as the initial reproduced output A. Next, the magnetic card was stored in an atmosphere at a temperature of 60 ° C. and a relative humidity of 90% for one week, and the reproduction output was measured again. The degree of deterioration of the reproduction output is represented by [(AB)
/ A] × 100 (%).

[0045]

From the results shown in Table 1 above, the magnetic cards of Examples 1 to 6 of the present invention in which a metal thin film layer was formed on a magnetic layer containing MnBi magnetic powder did not have a metal thin film layer. It can be seen that the deterioration of the reproduction output under the atmosphere of the temperature of 60 ° C. and the relative humidity of 90% is clearly smaller than the magnetic cards of Comparative Examples 1 to 3.

[0047]

As described above, according to the present invention, since the metal thin film layer is formed on the magnetic layer containing the MnBi magnetic powder, the output does not decrease much even when stored under high temperature and high humidity for a long period of time. It is possible to provide a magnetic recording medium having remarkably excellent characteristics.

Claims (4)

[Claims] 1. A magnetic recording medium comprising a magnetic layer containing MnBi magnetic powder and a binder resin, wherein a metal thin film layer is provided on the magnetic layer. 2. The magnetic recording medium according to claim 1, wherein the metal thin film layer is made of one of tin and aluminum. 3. The metal thin film layer has a thickness of 10 to 1,000 n.
3. The magnetic recording medium according to claim 1, wherein m is m. 4. The magnetic recording medium according to claim 1, wherein the magnetic layer is provided on the entire surface or a part of the card-like substrate.