JP2649932B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a protection function for preventing information tampering.

<Prior Art> Magnetic cards are increasingly used in so-called security cards, in addition to bank cards and credit cards that have been used in the past. If the information is easily falsified, the reliability of the system is significantly reduced.

For this reason, a magnetic recording medium having a protection function for preventing falsification of information has been demanded, and magnetic recording media having various structures have been proposed and used. Among them, as a magnetic recording medium suitable for providing this kind of protection function, a magnetic recording medium in which a high coercive force layer, a low coercive force layer, and a high magnetic permeability layer are sequentially laminated on a base has been proposed.

However, in this type of conventional magnetic recording medium, in order to further enhance the protection function for preventing information tampering, the material and magnetic properties of the high coercive force layer, low coercive force layer, and high magnetic permeability layer must be determined. There is not enough elucidation as to how to select.

Under such circumstances, the present inventors have proposed a magnetic recording medium in which the information defining the coercive force of the high coercive force layer and the low coercive force layer is difficult to alter (Japanese Patent Application No. 62-43389).

<Problems to be Solved by the Invention> However, in this magnetic recording medium, only the coercive force is specified for the material having a high magnetic permeability layer. Depending on the material or properties of the magnetic powder, a desired magnetic shielding effect cannot be obtained, the recorded information is easily read, and it is not always sufficient to prevent the recorded information from being falsified.

An object of the present invention is to obtain a magnetic recording medium in which it is extremely difficult to falsify recorded information.

<Means for Solving the Problems> Such an object is achieved by the present invention described below.

That is, the present invention provides a magnetic recording medium having a magnetic recording layer on a substrate, and a high magnetic permeability layer laminated on the magnetic recording layer, wherein the high magnetic permeability layer comprises a soft magnetic powder and a binder. The soft magnetic powder is composed of Fe-based amorphous alloy soft magnetic flat particles, and the amorphous alloy soft magnetic flat particles contain Fe, Si and B, and the total amount of Si and B is 15 to 37 at. % Of the magnetic recording medium.

FIG. 1 is a partial cross-sectional view showing one embodiment when the magnetic recording medium of the present invention is used as a magnetic card.

The magnetic recording medium 1 is formed by sequentially laminating a high coercive force layer 3, a low coercive force layer 4, a high magnetic permeability layer 5, and preferably a protective layer 6 on a substrate 2 as a magnetic recording layer.

Although the material of the base 2 is not particularly limited, it is generally preferable to be formed of various known resin materials, for example, PET, and the thickness thereof varies depending on the application.
It is about 0 μm.

The layer thickness of each of the high coercive force layer 3 and the low coercive force layer 4 is usually preferably about 2 to 20 μm.

It is preferable that the magnetic card has flexibility in consideration of the purpose of use and the state of use. In order to maintain such flexibility, the high magnetic permeability layer 5 is formed by dispersing a soft magnetic powder having high magnetic permeability. Must be formed.

The present invention uses an amorphous alloy soft magnetic flat particle as a soft magnetic powder and disperses it in a binder to form a high magnetic permeability layer 5.

The amorphous alloy soft magnetic flat particles used in the present invention have a flat shape, and preferably have an average thickness of 0.01 to 1 μm.

When the average thickness is less than 0.01 μm, the dispersibility in the binder is reduced, the magnetic properties such as the magnetic permeability are deteriorated, and the shield properties are deteriorated.

On the other hand, if it exceeds 1 μm, the thickness of the high magnetic permeability layer 5 becomes 50 μm.
If the thickness is as thin as about m or less, a uniformly dispersed coating film cannot be formed, and the number of particles in the thickness direction of the high magnetic permeability layer 5 decreases, resulting in insufficient shielding characteristics.

The average thickness may be measured with an analytical scanning electron microscope.

Further, such amorphous alloy soft magnetic flat particles preferably have the following physical properties.

Average aspect ratio (average outer diameter / average thickness) is 10 to 1000
It is preferably 0. If the average aspect ratio is less than 10, the effect of the demagnetizing field on the flat particles becomes large, and the effective magnetic properties such as the magnetic permeability are reduced, and the shielding properties are reduced. On the other hand, if it is 10,000 or more, it becomes difficult to produce a powder having a small average outer diameter, so that the moldability is deteriorated.

The average outer diameter A of the case, the particle size when it becomes 50% by total weight from the smaller particle size, which is known as D _50.

The particle size in this case is an average particle size measured by a particle size analyzer using a light scattering method.

Such amorphous alloy soft magnetic flat particles are obtained by pulverizing ribbons, scales, sheets and other shapes produced by a rapid quenching method. The amorphous alloy used in the present invention is a Fe-based amorphous alloy mainly composed of Fe. B, Si, C, P, and Ge, particularly B and Si are preferable as the semimetal added for amorphization. Therefore, a preferable amorphous alloy used in the present invention is Fe-B -Si ternary system. Also,
It is preferable to add one or more elements selected from Cr, Mo and Nb to these components in a range of 10 at% or less.

In particular, in the case of Fe-B-Si alloys, those indicated by ○ in FIG. 2 are amorphous soft magnetic alloys, and compositions in regions including these can be used.

FIG. 2 is a (Fe + M) -Si-B3 element composition diagram, and M will be described later.

The alloy composition in this case is represented by the following formula.

Formula Fe _100-xy M _x (Si, B) _{y where} x = 0 to 0
It is 10, especially more than 0 and 10 or less, preferably 1 to 10, and y = 15 to 37.

M is at least one element selected from Cr, Mo and Nb, and among them, it is preferable that only Cr or Cr is essential and contains at least one other element in terms of corrosion resistance.

M is added in order to improve the corrosion resistance and brittleness of the alloy. However, when the content of M, that is, x exceeds 10, the saturation magnetic flux density decreases.

More specifically, when Cr is added, the addition amount is preferably 2 to 10 at%, and when Nb or Mo is added, the addition amount is preferably 1 to 10 at%.

By setting the addition amount in such a range, corrosion resistance and brittleness are improved, and the saturation magnetic flux density does not decrease.

 Further, y = 15 to 37 is an amorphous formation region.

Among such composition ranges, points E, F, and
The portion above the line connecting G and H in this order is a region where a mechanically strong amorphous alloy is generated by the rapid quenching method, so that in applications requiring grinding as in the present invention, grinding costs are high. Become.

The present inventors conducted extensive tests on the ternary alloy and the substitutional alloy as described above, and found that the line connecting points E, F, G, and H outside such a region and the amorphous forming region It was found that the amorphous alloy in a region substantially between the lines connecting points A, B, C, and D at the boundary was brittle and easily crushed.

When this is shown numerically, Fe + M in the ternary composition diagram of FIG.
Preferred ranges represented by the coordinate points of B and Si (Fe + M, B, Si) are A (63, 32, 5), B (62, 23, 15), C (63,
15, 22), D (68, 5, 27), E (80, 5, 15), F
(77, 7, 16), G (75, 13, 12), and H (77, 18,
5). However, the numerical value is at%. It has been found that the magnetic shielding properties of the alloy obtained from this region are excellent.

Further, the alloy obtained from this region is sufficiently brittle. The brittleness is obtained by forming an amorphous ribbon to a constant thickness, and bending the ribbon around a rod having a diameter r.
0m at the line EFGH in FIG.
m and about 5 mm at the line ABCD.

In addition, various additional elements such as W, Mn, Co, and Ni may be contained in small amounts.

Such an amorphous alloy can be produced by any conventionally known rapid quenching method. For example, an ingot of a predetermined alloy composition is melted at a high temperature, sprayed on a rotating steel single roll or the like and cooled at a high speed, and the obtained ribbon or flake is roughly pulverized into coarse particles. . In addition, an amorphous alloy powder produced by a known water atomizing method may be used.

Coarse pulverization may be performed by any known method, and a powdery powder having an average particle size of several μm to about 50 μm in diameter or a powder of the same size produced by a known powder production method such as a water atomization method is used.

 The rapidly quenched alloy is then subjected to a grinding process.

For the pulverization, it is preferable to use a medium stirring mill such as a pin mill (or a bead mill).

When the amorphous alloy is pulverized with a pin mill, the average thickness of the amorphous alloy ribbon can be reduced to about 0.01 to 1 μm by a strong shearing action of the pin mill.
Therefore, the shape of the obtained alloy particles is flat. When these flat particles are viewed from the plane direction, they show a particle shape having a long axis instead of an amorphous shape.

The soft magnetic powder composed of the amorphous alloy soft magnetic flat particles obtained in this way is dispersed in a binder, usually formed into a coating composition using a necessary solvent, and then coated on the low coercive force layer 4. Thus, the high magnetic permeability layer 5 is formed.

The binder is not particularly limited, and a known binder such as a thermoplastic resin, a thermosetting resin, or a reactive resin can be appropriately selected.

The solvent is not particularly limited, and a known solvent may be used.

The volume ratio between the soft magnetic powder and the binder is generally 2: 8 by volume ratio.
About 8: 2.

Further, a known curing agent such as polyisocyanate may be contained in the coating composition.

The high magnetic permeability layer 5 may contain a dispersant, a stabilizer, a coupling agent and the like in addition to the soft magnetic powder and the binder.

The thickness of the high magnetic permeability layer 5 is preferably 5 to 30 μm.

This is because, in the present invention, the high magnetic permeability layer 5 contains a soft magnetic powder having the above-mentioned thickness, so that the layer has a uniform magnetic shielding effect even at a thickness of 5 μm. This is because the loss increases. Also,
If the thickness is 30 μm or less, it is advantageous in terms of cost.

In the present invention, the high magnetic permeability layer 5 having a highly directional magnetic shield effect can be obtained by applying an orientation magnetic field or mechanically aligning the high magnetic permeability layer 5 when applying the high magnetic permeability layer 5. .

In the case of the structure of two magnetic layers as shown in FIG.
Recording of information on the high coercivity layer and recording of information on the low coercivity layer can be performed using the difference in coercive force, which is more effective. Since this is not possible, this point is also effective in preventing information tampering.

<Example> Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 An amorphous soft magnetic alloy having the composition shown in Table 1 below was roughly pulverized by a vibrating ball mill, and further pulverized by a pin type mill to produce a soft magnetic powder composed of amorphous alloy soft magnetic flat particles.

Table 1 shows the properties of each amorphous alloy soft magnetic flat particle.

The average thickness was measured with an analytical scanning microscope.

These soft magnetic powders were mixed with a binder at a volume ratio of 1: 1 and dissolved in a solvent to prepare a paste for a high magnetic permeability layer.

These pastes were applied on the low coercive force layer of the magnetic recording layer formed of the high coercive force layer of 4000 Oe and the low coercive force layer of 750 Oe, to obtain samples of the present invention (Sample Nos. 1 and 2). Note that the thickness of the high magnetic permeability layer was 12 μm.

For comparison, a high permeability layer was formed using a permalloy alloy soft magnetic powder instead of the amorphous alloy, and a comparative sample was prepared (sample No. 3). In this case, the volume ratio of the soft magnetic powder to the binder was 1: 1.

These samples were recorded at the optimum current value, and the leakage output after recording was measured. Measurement is 50 for each sample
This was performed for 0 pieces, and the variation of the leak output was obtained. The leak output was expressed as a relative value with sample No. 3 as 1.

 Table 1 shows the results.

Next, using an amorphous alloy having the same composition as that of Sample No. 1, soft magnetic particles of various thicknesses were prepared by changing the grinding conditions in a pin mill, and samples were prepared in the same manner as Sample No. 1. (Sample Nos. 4 to 6).

For these samples, the output was measured in the same manner as described above.

 Table 1 shows the results.

From the results shown in Table 1, it is understood that the sample of the present invention using the amorphous alloy soft magnetic flat particles for the high magnetic permeability layer has a high magnetic shielding effect.

On the other hand, when the permalloy alloy is used, the magnetic shielding effect is insufficient.

Further, the thickness of the amorphous alloy soft magnetic flat particles is 1 μm.
It is understood that the shielding effect is higher when the value is less than m.

<Effects of the Invention> In the magnetic recording medium of the present invention, it is extremely difficult to falsify recorded information, and the variation is small. Therefore, the magnetic recording medium of the present invention can be suitably applied to a security card.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing one embodiment of the magnetic recording medium of the present invention, and FIG. 2 is a ternary diagram showing an amorphous alloy composition. DESCRIPTION OF SYMBOLS 1 ... magnetic recording medium, 2 ... substrate, 3 ... high coercive force layer, 4 ... low coercive force layer, 5 ... high magnetic permeability layer, 6 ... protective layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Hosaka 1-5-1, Taito, Taito-ku, Tokyo Inside Tokyo Magnetic Printing Co., Ltd. (72) Inventor Norio Yano 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Ginya Ishiguro 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-60-238405 (JP, A) 57-67251 (JP, U) Actually open 1981-51136 (JP, U)

Claims (3)

(57) [Claims] 1. A magnetic recording medium having a magnetic recording layer on a substrate and a high magnetic permeability layer laminated on the magnetic recording layer, wherein the high magnetic permeability layer comprises a soft magnetic powder, a binder, The soft magnetic powder is composed of Fe-based amorphous alloy soft magnetic flat particles, and the amorphous alloy soft magnetic flat particles contain Fe, Si and B, and the total amount of Si and B is 15 to 37 at%. A magnetic recording medium. 2. The amorphous alloy soft magnetic flat particles according to claim 1,
2. The magnetic recording medium according to claim 1, further comprising 10 at% or less of M (at least one element selected from Cr, Mo and Nb). 3. The magnetic recording medium according to claim 1, wherein the amorphous alloy soft magnetic flat particles have an average thickness of 0.01 to 1 μm.