JPH01245419A - Composite magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease the danger of spontaneous ignition and explosion and to obtain good workability by using flat magnetic powder of pure Ni or flat magnetic powder of an Ni-Cu alloy as magnetic powder for a magnetic film or protection. CONSTITUTION:The magnetic film 3 for protection is constituted of the pure Ni or the Ni alloy contg. <=25wt.% Cu and is constituted by coating the flat magnetic powder having the major diameter of the particles equal to the inter- gap size of a magnetic head or below. The flat powder of the Ni or the powder of the Ni-Cu alloy is used as the flat magnetic powder for the magnetic film for protection. The flat powder of the pure Ni has the ignition temp. extremely higher than the ignition temp. of 'Permalloy(R)' and about the same workability as the workability of the 'Permalloy(R)' is assured with said powder. The com posite magnetic recording medium having the safety to the spontaneous ignition and the good workability in combination is thereby obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a composite magnetic recording medium employed in, for example, telephone cards, prepaid cards, etc., and is particularly concerned with protection for preventing forgery, that is, unauthorized recording and reproduction. This invention relates to improving safety and processability during the production of magnetic powder used in magnetic films.

[Conventional technology]

In recent years, with dramatic advances in electronic technology and data processing technology, magnetic cards (magnetic recording media) such as telephone cards and prepaid cards have come to be used frequently in general corporate life. When using magnetic cards, counterfeit prevention measures are required to ensure authenticity.

Conventionally, as a composite magnetic recording medium having this type of counterfeit prevention function, there is one shown in FIG. 7 or FIG. 9, for example.

In FIG. 7, a recording magnetic film 2 is formed on a plastic base (substrate) 1, and a low coercivity protective magnetic film 3 is formed on the upper and lower surfaces of the recording magnetic 1lQ2.

FIG. 9 is a microscopic photograph of the layer cross section of another magnetic card with anti-counterfeiting function.As shown in the photograph, this card consists of a plastic base 1, a recording magnetic film 2, and a protective magnetic film from the right end. It is configured by arranging 3. Generally, the recording magnetic film 2 has a coercive force of about 18250e, and the magnetic film 3 has a coercive force of about 8308.

Here, the counterfeit prevention function of the composite magnetic recording medium will be briefly explained. FIG. 8 is a diagram showing its principle. In the figure, 1 is a plastic base, 2 is a recording magnetic film, 3 is a protective magnetic film, and 4.5 is a recording head and a reproducing head, respectively.

In magnetic recording, when a normal recording current is applied to the magnetic head 4, the main magnetic flux path is formed under the gap 4a of the recording head 4 for protection of low coercive force, as shown by the broken line in the figure. It only passes through the magnetic film 3 but does not reach the recording magnetic film 2, thus preventing unauthorized recording. If a current equal to the sum of the current that magnetically saturates the protective magnetic film 3 and the recording current is applied, the main magnetic flux path reaches the recording magnetic film 2 as shown by the solid line in the figure, and therefore, of course, recording is not possible. It becomes possible.

On the other hand, during reproduction, even if the gap 5a of the reproduction radar 5 is brought close to the magnetic recording medium and moved relative to each other, the magnetized portion of the recording magnetic film 2 forms a closed magnetic path as shown by the broken line in the figure. Since there is no magnetic flux change in the gap 5a, it cannot be reproduced by normal reproduction means, and therefore unauthorized reproduction can be prevented.

In this case, the magnetic powder constituting the protective magnetic film 3 is
In the case of fine powder (spherical), the magnetic flux easily passes through it, whereas in the case of flat powder, the magnetic flux is blocked, the closed magnetic path is reliably formed, and the function of preventing unauthorized reproduction is increased accordingly.

When manufacturing the protective magnetic film 3, a soft magnetic metal powder with low coercive force, a separating agent 9 binder, and a solvent are mixed to form a paste, which is then applied in a sheet form and dried. I try to do that. Conventionally, the following materials have been used as the soft magnetic metal powder with low coercive force.

■ A14-14wt%, Si: 4-13wt%.

Fe-Al-Si alloy (Sendust® registered trademark) consisting of 5 to 92 wt% Fe N+gold alloy or Ni: 50 to 85 wt%, Fe: 15 to 5
0wt%.

Mn: 0 to Iwt%, Cu: 0 to 15 wt%, M
.

: Fe-Ni-(Mo, consisting of Q~5wt%)
Cu, Mn) alloy (see JP-A-56-51136).

■ Sendust, permalloy flakes (flat powder) (see JP-A-57-6725).

■ Mn-Zn ferrite, Sendust (Japanese Patent Application Laid-Open No. 1983-
(See Publication No. 127623).

■ Fe-33wt%Ni (JP-A-61-2800
(See Publication No. 22).

■ SL: 1 to 11 wt%, AJ: 5 to 7 wt%, and the balance is Fe, and the aspect ratio (major axis/minor axis) is 1.
0 or more sendants (see Japanese Patent Laid-Open No. 62-238305).

[Problem that the invention seeks to solve]

In the conventional composite magnetic recording medium described above, the metal powder for the protective magnetic film is Fe-Ni alloy (permalloy) or Fe-A.
Two types of flat metal powders based on l-Si alloy (Sendust) are mainly used, but Permalloy type has the risk of spontaneous ignition of the powder and explosion, while Sendust type has poor workability. There is a problem. In other words, when the powder is flattened, the surface area increases and non-oxidized parts are exposed on the surface, which increases the apparent activity. However, since permalloy-based powders have a low ignition temperature, they easily ignite, and in extreme cases may explode. In order to flatten the powder, mills, attritors, etc. are used, and there are wet and dry types. Now, if it were flattened using a wet mill, it would not catch fire, but it would require a drying process after that, and if it was exposed to the atmosphere after drying, the lower the ignition temperature, the lower the temperature, and the risk of an explosion. Also, since the ignited material is oxidized, it cannot be used as a magnetic material.

Further, processability is evaluated by the time taken to obtain a good flat powder, and in the case of sendust, an extremely long processing time is required to obtain a good flat powder.

In view of these conventional problems, it is an object of the present invention to provide a composite magnetic recording medium that has both safety against spontaneous combustion during manufacturing and good workability.

[Means for solving problems]

Therefore, the present invention provides a recording magnetic film for recording and reproducing information on a substrate, and a protective magnetic film for preventing information forgery on at least the surface of the recording magnetic film opposite to the substrate. In the composite magnetic recording medium provided, the protective magnetic film is made of flat magnetic powder made of pure Ni or an N1 alloy containing 25 wt% or less of Cu, and whose major axis is equal to or less than the gap distance of the magnetic head. It is characterized by being constructed by applying.

The flat magnetic powder for an iI magnetic film according to the present invention includes not only pure Ni flat powder but also a Ni-Cu alloy powder containing 25 wt% or less of Cu in pure Ni, but as described below, Pure Ni powder is effective in that it has a high ignition temperature, and Ni-Cu alloy powder is effective in that it has a high magnetic permeability.

Here, the reason for limiting various conditions such as components will be explained.

First, pure Ni flat powder has a coercive force substantially similar to that of conventional permalloy, and has a low coercive force characteristic necessary for a protective magnetic film of a magnetic recording medium. Further, the ignition temperature is much higher than that of permalloy, and the workability is maintained at the same level as that of permalloy, so that the object of the present invention can be achieved.

Further, the purpose of adding Cu is to improve the magnetic permeability, and as the amount of Cu increases, the magnetic permeability increases.

On the other hand, setting Cu to 25wt% or less means that Cu >25
This is because when using W[%], the ignition temperature becomes lower than that of permalloy, and safety against spontaneous ignition cannot be ensured, and workability also deteriorates.

The components that are unavoidably included are C〈0゜itw
t%, Mn<0.5 wt%, S<0.0
2wt%.

Fe <0.7 wt%, Si <Q, 5w
t%, Co <1°Qwt%. These are contained in molten steel from melted raw materials, crucibles, or refractories, or are essential components for scouring, but these components do not have an adverse effect that substantially changes the gist of the present invention. . Furthermore, in order to make the present invention more effective, Ru<5wt% and Ti<5wt%.

A trace amount of AN<4% and Cr<4% may be added.

In addition, the long axis of the flat magnetic powder is determined by the air gap distance of the magnetic head (the 8th
The reason why the length is set to be less than 4a and 5a) in the figures is because if the gap is longer than that, regeneration becomes impossible. In other words, when the length of the magnetic powder is longer than the space gap distance, the reproducing action is the same as covering the recording magnetic film with one magnetic plate, and the recording magnetic film in the space of the magnetic head The magnetic flux change due to the magnetic flux from the magnetic flux cannot be obtained, and therefore reproduction is impossible. Therefore, the length of the flat magnetic powder must be equal to or less than the space gap of the magnetic head. -Next, the manufacturing method will be explained.

When manufacturing the composite magnetic recording medium of the present invention, as in the conventional method, magnetic powder and a solvent may be mixed to form a paste, and this may be sequentially applied onto a substrate and dried.

Further, in order to flatten the magnetic powder of the protective magnetic film, it may be processed using a mill, an attritor, etc., as in the conventional method, and a wet or dry method can be used for this.

[Effect]

In this invention, since pure Ni flat magnetic powder or Ni-Cu alloy flat magnetic powder is used as the magnetic powder for the protective magnetic film, its ignition temperature is higher than that of the conventional permalloy type. The risk of spontaneous ignition and explosion is significantly reduced. Further, pure Ni and Ni--Cu alloys themselves have better workability than permalloy systems, which have good workability.

〔Example〕

Hereinafter, the present invention will be explained based on Examples.

Cu is 0.0% by weight. 4. Using Ni-Cu atomized powder with an average particle size of approximately 10 μm, which was changed to 0.25%, it was flattened using a wet ball mill, dried in a vacuum oven, and then tape-formed using a doctor blade method to determine the ignition temperature. , various experiments were conducted to evaluate the workability and magnetic properties. The results are shown in FIGS. 1 to 6, respectively. For comparison, FIGS. 1 to 3 also show experimental results for permalloy (Fe-50%Ni) manufactured in the same process.

Here, each evaluation experiment was conducted as follows.

■ Ignition temperature The ignition temperature was determined by placing each powder in the air, increasing the temperature, and measuring the temperature T' at which spontaneous ignition occurred.It goes without saying that it is preferable to set the ignition temperature at this temperature.

■ Workability The index of workability is given by the machining time t. Here, the aspect ratio (major axis/thickness) of the powder is determined by a wet ball mill with a ball filling rate of 65% and a capacity of 2L and a rotation speed of 1500 rpm.
The time t1° at which the value becomes 10 was measured, and the workability was evaluated. Therefore, the shorter the time is, the better the workability is, which is preferable.

■ Magnetic properties The magnetic properties are evaluated by coercive force Hc and magnetic permeability μ.

Regarding the coercive force Hc, the coercive force He was measured after making a paste of metal powder and a solvent to a thickness of 20 μm using a doctor blade method, and applying a magnetic flux density of 25,000 e in the dried and solidified state. This coercive force Hc is better to be small in order to make the magnetic property soft magnetic, and i3 magnetic coefficient μ
A higher value is better in terms of preventing magnetic leakage. Note that in the dry state, the metal powder occupies about 40% of the volume of the protective film.

According to FIG. 1, pure Ni powder (Cu=O%) and Cu
It can be seen that for the Ni-Cu alloy powder in the range of ≦25 WL%, the ignition temperature Tf is 150° C. or higher, which is higher than the ignition temperature 100° C. of Fe-50%Ni, which indicates high safety against spontaneous combustion and explosion.

Moreover, according to FIG. 2, Cu≦25W (in the range of %,
Processing time t1° is within 2.5 hours, Fe-50%
It can be seen that the processing time is shorter than the 2.5 hours for Ni, that flattening is easy, and that excellent workability is exhibited.

Furthermore, according to FIG. 3, in the range of 05011525 wt%, the coercive force Hc is almost the same as that of Fe-50%Ni, and it can be seen that there is no problem as a soft magnetic material.

Also, according to FIG. 4, if the amount of Cu is increased, the magnetic permeability μ
It can be seen that the magnetic field increases, making it easier to prevent magnetic leakage.

Here, FIG. 5 shows changes in the Curie temperature Tc (cited from the Japan Institute of Metals Steel, Metal Data Book). If the temperature exceeds this Curie temperature, the material loses its magnetism, so it can no longer be called a magnetic material and cannot be used. According to the figure, the Curie temperature Tc decreases as the amount of Cu increases, but when the amount of Cu is 25 wt% or less, the Curie temperature Tc1OO°C or higher is ensured.

FIG. 6 shows a microscopic photograph of an example of the shape of the flat powder in the present invention. According to this, it can be seen that a good flat shape is obtained.

〔Effect of the invention〕

As described above, according to the present invention, since the flat magnetic powder for the protective magnetic film is made of pure Ni or a Ni alloy containing 25 wt% or less of Cu, safety against spontaneous ignition can be ensured, and It has the effect of improving workability.

[Brief explanation of the drawing]

1 to 5 are diagrams showing the characteristics of the magnetic powder for the protective magnetic film in the present invention, FIG. 1 is a diagram showing ignition temperature characteristics, FIG. 2 is a diagram showing processing time characteristics, and FIG. 3 is a diagram showing processing time characteristics. Figure 4 shows the coercive force characteristics, Figure 4 shows the magnetic permeability characteristics, Figure 5 shows the Curie temperature characteristics, Figure 6 is a micrograph showing the particle structure of the magnetic powder of the present invention, and Figure 7 is a cross-sectional diagram to explain the configuration of a general composite magnetic recording medium, FIG. 8 is a configuration diagram to explain a general anti-counterfeiting function, and FIG. 9 is a micrograph showing the grain structure of the magnetic recording medium. It is. In the figure, 1 is a plastic base, 2 is a recording magnetic film, and 3 is a protective magnetic film. Patent Applicant Kobe Steel Co., Ltd. Representative Patent Attorney Tsutomu Shimoichi Figure 1 LwW -m-- Figure 3 Figure 5 Cu 輌α片-1〉 Figure 7 1id

Claims (1)

[Claims] (1) A recording magnetic film for recording and reproducing information is provided on the substrate, and a protective magnetic film for preventing information forgery is provided on at least the surface of the recording magnetic film opposite to the substrate. A composite magnetic recording medium comprising: a flat magnetic recording medium in which the protective magnetic film is made of pure Ni or a Ni alloy containing 25% by weight or less of Cu, and the major axis of the particles is equal to or less than the gap distance of the magnetic head; A composite magnetic recording medium characterized in that it is constructed by coating powder.