JPH01245418A - Composite magnetic recording medium - Google Patents

Abstract

PURPOSE:To assure the safety to spontaneous ignition and good workability by constituting flat powder for a magnetic film for protection of an Fe-Ni alloy added with 1 or >=2 kinds of Cr, Ru, Ti, and Nb. CONSTITUTION:The magnetic film 3 for protection is constituted by coating the flat magnetic powder contg. 1 or >=2 kinds among 0.2-4wt.% Cr, 0.1-3wt.% Ru, 0.2-2wt.% Ti, and 0.2-2wt.% Nb, and 35-80wt.% Ni and having the major diameter of the particles equal to the inter-gap length of a magnetic head or below. Since the Fe-Ni alloy is used as the magnetic powder for the magnetic film for protection in such a manner, the good workability is assured and further the flat magnetic powder added with 1 or >=2 kinds among the Cr, Ru, Ti, and Nb is used and, therefore, the ignition temp. rises and the danger of spontaneous ignition and explosion is extremely decreased.

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 (mega-recording media), such as telephone cards and prepaid cards, have come to be used frequently in general corporate life. When using such magnetic cards, counterfeit prevention measures are required to ensure authenticity.

Conventionally, as a composite magnetic recording medium having this type of anti-counterfeiting function, there is one shown in FIG. 1 or 3, for example.

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

In addition, Fig. 3 is a microscopic photograph of the layer cross section of another magnetic card with anti-counterfeiting function.As shown in the same photograph, this card consists of a plastinokhose 1, a recording magnetic film 2, and a protective layer from the right end. [It is constructed by disposing a 53-dimensional membrane 3. Generally, the recording magnetic film 2 has a coercive force of about 18250e, and the protective 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. Figure 2 is a diagram of its principle. In the figure, 1 is a plastic base, 2 is a magnetic film for recording, 3 is a magnetic film for protection, and 4 and 5 are a recording head and a reproducing head, respectively.6 - In magnetic recording When a normal recording current is applied to the magnetic head 4, the main magnetic flux path is formed by a protective magnetic film with a low coercive force under the gap 4a of the recording head 4, as shown by the broken line in the figure. 3, it does not reach the recording magnetic film 2, so that unauthorized recording can be prevented. 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 will reach the recording magnetic film 2 as shown by the solid line in the figure, so of course Recording becomes possible.

On the other hand, during reproduction, even if the gap 5a of the reproduction head 5 is brought close to this magnetic recording medium and moved relative to each other, the magnetized portion of the recording magnetic film 2 forms a closed magnetic path shown by the broken line in the figure, and the gap Since there is no magnetic flux change in the portion 53, it cannot be reproduced by normal reproduction means, and therefore unauthorized reproduction can be prevented.

In this case, if the magnetic powder constituting the protective magnetic film 3 is fine powder (spherical), the &R flux easily passes through it, whereas if it is flat powder, the magnetic flux is blocked and the closed magnetic path is reliably formed. This increases the ability to prevent unauthorized playback.

When manufacturing the protective magnetic film 3, a soft magnetic metal powder with low coercive force is mixed with a separating agent, a binder, and a solvent 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-Al1-Si consisting of 5 to 92 wt% Fe
Alloy, (Sendust registered trademark) Fe-Ni alloy, or Ni: 50 to 85 wt%, Fe: 15 to 50
wt%.

Mn: O~1wL%, Cu: O~15wt% 9M.

:0 to 5 wt% Fe-Ni-(Mo,
Cu, Mn) alloy (see JP-A-56-51136).

■ Sendust, permalloy flakes (flat powder) (
(See Japanese Unexamined Patent Publication No. 57-6725).

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

■ Fe-33wL%Ni (JP-A-61-280022
(see publication).

■ Consisting of Si near to 11wt%, Al: 5 to 7wt%, and the balance 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 powder based on 1-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 in
:0.1~3wt%, Ti;0.2~2WL%,
Nb: o, 2 to 2 wt% of one or more types and Ni
:35 to 80 wL%, and the major axis of the particles is equal to or less than the gap distance of the magnetic head.

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

First, the Fe-Ni alloy was used as a raw material in order to achieve the object of the present invention by increasing the ignition temperature by adding alloying elements while ensuring good workability of the Fe-Ni alloy. It is from.

In addition, as alloying elements, Cr, Ru, Ti, Nb
The reason why one or more elements are added is that these elements can increase the ignition temperature of the Fe-Ni alloy. where Cr <0.2 wt
%, Ru <0.1 wt%, Ti
<0°2 wt%, Nb <0.2 wt%, the ignition temperature of the Fe-Ni alloy cannot be increased, while C
r >4 w[%, Ru >3 wL%, Ti >2
wL%, when Nb >2wt%, the retention force increases,
Since information is also written on the protective magnetic film for the purpose of preventing counterfeiting, which poses a practical problem, Cr: 0.2~
4wj%.

Ru: 0.1~3 wt%, Ti: 0.2~
2 wt%.

Nb: Needs to be 0.2 to 2 wt%.

In addition, as an unavoidable component, C<O.

l wt%, Mn <0.5 wt%,
P<0.02wt%.

S<0.02 wt%, O<0.1 wL%. These are contained in molten raw materials, crucibles, or refractories, and are essential components for scouring, but these components have such an adverse effect that they substantially change the gist of the present invention. It's not a thing.

In addition, the length of the flat magnetic powder is determined by the gap distance of the magnetic head (second
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, magnetic powder and a solvent may be mixed to form a paste, and this may be sequentially applied onto a substrate and dried, as in the conventional method.

Further, in order to flatten the magnetic powder of the protective magnetic film, it can be processed using a mill, an attritor, etc. in the same way as in the past (wet or dry methods can be used for this).

[Effect]

In this invention, as the magnetic powder for the protective magnetic film, F
By using an e-Ni alloy, Fe −
Al! -Good workability is ensured compared to -3i alloys. This Fe-Ni alloy contains Cr, Ru, Ti,
By using flat magnetic powder containing one or more types of Nb, its ignition temperature is higher than that of conventional Fe-Ni alloys, greatly reducing the risk of spontaneous combustion and explosion. be done.

〔Example〕

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

In this example, Cr, Ru, Ti, N
Metal powders containing various amounts of the additive elements b, singly or in combination, are produced, and these various powders are used to adjust the ignition temperature,
The workability and magnetic properties were evaluated.

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 Tf at which spontaneous ignition occurred. It goes without saying that a higher ignition temperature is preferable.

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

■Magnetic properties The magnetic properties are evaluated by the coercive force Hc. Regarding the coercive force Hc, the coercive force Hc was measured after making a paste of metal powder and a solvent to a thickness of 20μ steel using a doctor blade method, and applying a magnetic flux density of 25,000 e in a dry and solidified state. It is better that this coercive force He is small in order to make the magnetic property soft magnetic, and this coercive force He is 2000e
In this case, magnetic recording is also written on the protective magnetic film for the purpose of preventing counterfeiting, which poses a practical problem. In addition, after drying, the metal powder accounts for approximately 40% of the protective film.
occupies a volume of

The above evaluation results are shown in the table. In this table, floors 4 to 6
．． Porcelain 8 to floor 10. 12-14. Dimensions 16 to 18°, width 20 to floor 25 are metal powders within the scope of the present invention, and dimensions 7. Positive 11°+
1i1115. Il&L19 is a comparative metal powder containing elements outside the scope of the present invention, and 11ill-NI13 is a conventional example (Fe-Al-3i, Fe-50%Ni).
, Fe-Ni-Cu-M.

) are the results for metal powder.

According to the table above, Na2 (Fe 5ONi) and Nos. 4 to 7. Na2 and 隘8～11.11h2 and Nn12～1
5. From each comparison between positive 2 and Il&116-19, Fe-
Ni-based alloy with Cr >0.2%, Ru >0.1%, T
By adding one type of i>0.2% and Nb>0.2%, the ignition temperature Tf becomes 150°C or higher, and Fe −
Ignition temperature Tf of 50% Ni (l!12) = 100
℃, which is the main objective of the present invention
It can be seen that the risk of spontaneous ignition and explosion of the alloy powder can be prevented.

Also, from 1 m 20 to 25, Cr, Ru, Ti, Nb
It can be seen that even when two or more of these are added in combination, the ignition temperature Tf becomes 150° C. or higher.

Moreover, regarding processing time t+o, Cr and Ru.

Also by adding one or more of Ti and Nb, F
e-50%Ni (t'h2), Fe-N
i -Cu -Mo (m3), the processing time of Fe -A1-5i (m3) was not much worse than that of
: 8.0 hours or less, indicating that good workability can be obtained.

However, positive 7.11kL11. Magnetic 15. From 19th
Cr >4%, Ru >3%, Ti >2%, Nb
It can be seen that when >2% is added, the coercive force Hr becomes 200θe or more, and in practical terms, the effect of the protective magnetic film applied to prevent counterfeiting is lost.

After all, within the scope of the present invention, the ignition temperature Tf>150
°C, processing time t+o<8 hours, holding force Hc<2000
It was recognized that e can be obtained.

Further, FIG. 4 shows a microscopic photograph of the flat magnetic powder of the protective magnetic film of the present invention. This shows that a good flat shape was obtained.

〔Effect of the invention〕

As described above, according to the present invention, the flat powder for the protective magnetic film is made of a Fe-Ni alloy to which one or more of Cr, Ru, Ti, and Nb are added. This has the effect of guaranteeing safety and ensuring good workability.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the configuration of a general composite magnetic recording medium, Figure 2 is a configuration diagram for explaining a general counterfeit prevention function, and Figure 3 is a diagram for explaining the configuration of a composite magnetic recording medium with another configuration. FIG. 4 is a micrograph showing the particle structure of the flat magnetic powder for protective magnetic film of the present invention. In the figure, I is a plastic base (substrate), 2 is a recording magnetic film, and 3 is a protective magnetic film. Patent distributor Kobe Steel Co., Ltd. Agent Patent attorney Tsutomu Shimoichi Figure 1 2J Figure 3 Figure 4

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: Cr: 0.2-4% by weight, Ru: 0.1-3% by weight,
Ti: 0.2-2% by weight, Nb: 0.2-2% by weight 1
species or two or more species and Ni: 35 to 80% by weight,
1. A composite magnetic recording medium characterized in that it is constructed by applying flat magnetic powder whose major axis is equal to or less than the space gap of a magnetic head.