JPH07166202A - Low aspect ratio flat soft magnetic metal powder and production thereof - Google Patents

Abstract

PURPOSE:To produce magnetic powder optimum for the formation of a magnetic bar code having high sensitivity and high in the confidentiality of information by printing. CONSTITUTION:This low aspect ratio magnetic powder is defined as 1.5-4 the average aspect ratio of the particles to 1.5 to 4, <=44mum maximum particle diameter. >=0.7T saturation magnetic flux density and <=1200A/m coercive force. In this method, granular or spherical powder having <=31mum maximum particle diameter is contained in a vessel together with a pulverizing medium, and at least either one of the medium or the vessel is driven in the coexistence with a lubricant, by which the powder is mechanically flattened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft magnetic metal powder used in a recording medium using a magnetic recording system, and particularly to a magnetic bar code which gives identification information depending on the presence or absence of a magnetic substance having a specific magnetism. The present invention relates to a flat soft magnetic metal powder having a low aspect ratio and a method for producing the same.

[0002]

2. Description of the Related Art Cash cards, credit cards,
With the spread of prepaid cards and the like, there is an increasing demand for protection of recorded information. Especially in the magnetic recording method adopted by many of these cards, many methods for protecting recorded information and preventing forgery are proposed.
Has been adopted. For example, JP-A-55-93514
JP-A-59-94188 and JP-A-62-1896.
No. 26, JP-A-62-204430, etc., there is a proposal of a card in which a magnetic shield layer is provided above the recording layer of a magnetic card and information cannot be easily read or written, and a recording / reproducing apparatus therefor. . In addition, Japanese public examination 4
Cards having two recording magnetic layers, such as 0-23745 and JP-A-62-189626, have also been proposed.

On the other hand, a method of providing identification information on each card is also adopted. As one of means for giving this identification information, there is a method of forming a magnetic barcode on a card. Usually, this magnetic barcode is created by printing, and a magnetic barcode in which a desired pattern is formed with magnetic ink containing magnetic powder and a dummy barcode formed with non-magnetic ink containing non-magnetic pigment are arranged arbitrarily. It is used as identification information. In order to read this magnetic bar code, a method is generally used in which an external magnetic field having an appropriate strength is applied, the magnetization of the magnetic bar code is detected by a magnetic sensor, and the change in magnetic resistance is detected.

As the magnetic powder used for the magnetic bar code, spherical carbonyl iron powder, near-spherical permalloy, sendust, etc. have been used as described in JP-A-1-109524.

The respective powder manufacturing methods are different for the recording magnetic layer, the shield layer and the magnetic bar code. The powder for the recording magnetic layer is mainly produced by dehydration and reduction of acicular goethite and the like. On the other hand, as a method for producing the powder for the shield layer, a ball mill, an attritor, or the like is used to store the powder in a container together with a grinding medium,
A method of mechanically crushing and flattening by driving at least one of the medium and the container is widely used. For example, JP-A-63-35701 discloses a method for producing flaky powder using a halogenated hydrocarbon as a grinding aid using a wet ball mill.
No. 8606 describes a method capable of producing a large amount of flat powder by a continuous attritor. Further, the spherical magnetic powder used in the conventional magnetic barcode has been produced by gas atomization or the like.

[0006]

Since the magnetic powder used in the conventional magnetic bar code is substantially spherical, it has a large diamagnetic field coefficient and a small magnetic permeability. For this reason,
The magnetic barcode pattern cannot be read by a simple method such as a viewer, and information can be kept secret. However, conversely, even when reading with a magnetic sensor, the output is small because the leakage magnetic flux is small, and there are cases in which a reading error occurs due to fluctuations in the thickness of the protective layer on the barcode and dirt. In order to prevent this in practical use, a magnetic sensor with higher sensitivity is required, which makes the reading device expensive. Further, since the output is low, it is necessary to frequently replace the sensor even if the sensor performance is deteriorated due to wear of the sensor or the like.

When needle-shaped or scale-shaped soft magnetic powder having a large aspect ratio of, for example, 40 or more is used, these powder particles are easily magnetized in a needle-shaped direction or a flattened direction having a small demagnetizing field coefficient, and thus, when reading. The magnetic flux leakage is larger than that of spherical powder. Therefore, the output of the sensor is large and stable reading is possible. However, since the remanent magnetization is large, the bar code pattern can be easily read by a magnetic viewer or the like, and confidentiality of information cannot be secured.

An object of the present invention is to obtain a leakage magnetic flux which can be stably read by a magnetic sensor when an external magnetic field is applied in the powder used for the magnetic bar code, and when there is no external magnetic field. To provide a powder having a shape / characteristic in which the pattern of the magnetic barcode cannot be identified by a magnetic viewer or the like and a method for producing the powder.

[0009]

The first aspect of the present invention is a soft magnetic metal powder used in a magnetic bar code for achieving the above object, wherein the average aspect ratio of the particles is 1.5 to.
4, maximum particle size is 44μm or less, saturation magnetic flux density is 0.7T
As described above, the coercive force is 1200 A / m or less.

The second invention of the present application is a method for producing the soft magnetic metal powder, wherein granular or spherical powder having a maximum particle size of 31 μm or less is housed in a container together with a grinding medium to coexist with a lubricant. Below, at least one of the medium and the container is driven to be mechanically deformed to obtain a flat powder having an average aspect ratio of particles of 1.5 to 4 and a maximum particle diameter of 44 μm or less and having a low aspect ratio.

In the second invention, as the raw material powder which is mechanically deformed, a powder produced directly from a molten alloy such as water atomization or gas atomization is used, and the average particle size is 7
It is preferable to use each having a thickness of μm or less. If necessary, it is mechanically deformed and then heat-treated in a non-oxidizing atmosphere to give a coercive force of 1200 A / m.
It is as follows.

[0012]

The present inventors have tested using powders having various magnetic characteristics and shape characteristics, and as a result, have a saturation magnetic flux density of 0.7 T or more, a coercive force of 1200 A / m or less, and an average aspect ratio of particles of 1 The magnetic bar code using the soft magnetic metal powder having a particle size of 0.5 to 4 and a maximum particle size of 44 μm or less cannot identify the bar code pattern by a simple observation method such as a magnetic viewer, and the magnetic sensor is used. When reading, if an external magnetic field of a specific strength is applied,
It has been found that a sufficient leakage magnetic flux for reading can be obtained and a stable reading of the bar code pattern becomes possible.

The saturation magnetic flux density of the soft magnetic alloy powder is 0.7T
The reason for limiting the above is that at a saturation magnetic flux density of less than 0.7 T, the leakage magnetic flux is insufficient with respect to the application of an external magnetic field during reading, and stable reading cannot be performed.

Further, the powder having a coercive force of more than 1200 A / m has a large residual magnetic flux density, and when a magnetic bar code is used, the bar code can be identified by a magnetic viewer, which is unsuitable as a soft magnetic powder for a magnetic bar code. Is.

The powder of the first invention of the present application is characterized by having a low aspect ratio. Average aspect ratio is 1.5
If the soft magnetic powder is less than the same, the output of the sensor is small like the conventional spherical powder described above, and stable reading cannot be performed. Further, the soft magnetic powder having an average aspect ratio of more than 4 is unsuitable as the soft magnetic powder for a magnetic barcode because the barcode pattern can be read by a magnetic viewer.

Regarding the maximum particle size of 44 μm or less,
When screen-printing a magnetic bar code, particles that exceed this size may not pass through the screen, which may hinder printing.In addition, the surface roughness of the printed bar code may become rough, resulting in a sensor output. Variation easily occurs.

According to the second invention of the present application, a granular or spherical powder having a maximum particle size in anticipation of expansion due to flattening is used for the target powder, and the powder is treated for a relatively short period of time to achieve the target aspect ratio. The treatment is carried out so that the deformation is stopped and the crushing (fine powdering) action is hardly accompanied. This is very different from the conventional method of manufacturing powder for magnetic shield, which deforms the powder largely to make the flatness as high as possible, and grinds (pulverizes) together with the flatness. .

When the maximum particle size of the particles used exceeds 31 μm, there is a high possibility that the target maximum particle size of the powder will be exceeded by the deformation treatment with a predetermined average aspect ratio of 1.5 to 4.

In the production method of the present invention, the process of mechanically deforming the powder is hardly accompanied by the pulverization (pulverization) action, but in order to realize this, a lubricant for reducing the friction between the pulverization medium and the powder particles is used. Is essential.
The addition of the lubricant suppresses the crushing action and promotes the deformation action.

The lubricant may be a liquid or a solid, for example, the well-known stearic acid, oleic acid, lauric acid,
Higher fatty acids such as palmitic acid, zinc stearate, calcium stearate, zinc laurate, metal soaps such as aluminum laurate, higher alcohols such as stearyl alcohol, higher fatty acid alcohols, higher fatty acid amines such as ethanolamine and stearylamine, Polyethylene wax and the like may be added alone or in combination of two or more.

In the present invention, the raw material powder is housed in a container together with a grinding medium, and at least one of the medium and the container is driven in the coexistence with a lubricant to mechanically deform, thereby controlling the aspect ratio. However, if the aspect ratio of the powder used is too high for the target aspect ratio,
Alternatively, if high particles are mixed, this control becomes difficult. Therefore, it is desirable that the aspect ratio of the powder used is 1, and that the particle has a spherical shape at the end, but even if it is granular, there is no practical problem. A granular or spherical raw material powder is easily obtained when a dissolved metal such as water atomized or gas atomized is scattered and solidified in an air stream or in water.
Even if a steel ingot is crushed, a granular material powder with an aspect ratio close to 1 can be obtained with a brittle material, but with a ductile material, flattening occurs in the crushing process, so depending on the material, it is close to a spherical shape. It is difficult to obtain a powder. Therefore, in the method for producing a powder of the present invention using such a material, powder produced directly from a molten alloy such as water atomization and gas atomization is used.

Further, the inside of the powder particles that have been mechanically deformed is distorted, and the target coercive force of 1200 A / m or less cannot be satisfied depending on the material. In such a case, the strain is removed by heat treatment to satisfy this.
However, when the fine powder as in the present invention is heat-treated in air, the magnetic properties may deteriorate due to the oxidation action, and it is desirable to perform the heat-treatment in a non-oxidizing atmosphere.

Further, in the low aspect ratio flat soft magnetic powder of the present invention, it is desirable that the average particle diameter is 10 μm or less from the viewpoint of usability. In order to obtain such powder, the raw material used in the second invention of the present application. The average particle size of the powder is 7μ
It is good to set it as m or less.

[0024]

【Example】

(Example 1) The molten alloy was put into water and rapidly cooled to cause a large number of cracks in a steel ingot, which was pulverized by a dry vibration mill to obtain 7.5S of granular particles.
Using a ball mill, the i-6.6Cr-7.0Al-balance Fe alloy powder was charged with a steel ball having a predetermined diameter and a predetermined weight relative to the powder, and isopropyl alcohol (IPA) in an amount 20 times the weight of the powder as a lubricant. Table 1 shows the measurement results of the average particle size and the maximum particle size before and after processing after each addition for a predetermined time and the average aspect ratio of the obtained powder. Further, the results in the case of the dry method in which stearic acid was added in 3% of the powder weight instead of isopropyl alcohol are also shown in the table.

In each of the examples including this example, the average particle size, maximum particle size and average aspect ratio of the powder were measured by the following methods. The average particle size and the maximum particle size of the powder were measured using a laser dispersion type particle size distribution measuring device. To determine the average aspect ratio, first measure the thickness of the particles. The powder is embedded in a resin or the like in a state where the powder is oriented in a flat direction by a magnet and the cross section is polished. The thickness is measured from the cross section of the particles. An SEM or an optical microscope is used for the measurement. The thickness of some particles is measured, the average thereof is calculated, and this is used as the average thickness. The average aspect ratio is the ratio of the average particle diameter to the average thickness (average particle diameter / average thickness).

[0026]

[Table 1] From this table, the powder according to the production method of the present invention is a powder having an average particle size of about 4 to 9 μm, a maximum particle size of 22 to 31 μm, and an average aspect ratio of 1.8 to 4, and it is not necessary to classify the barcode. A powder suitable for use is obtained. It was also confirmed that the coercive force of each powder was 1100 A / m or less by the heat treatment in hydrogen or nitrogen, and the saturation magnetic flux density was 0.9 T or more.
Sample No. of the present invention. 1 and No. Comparing No. 4 with each other, it can be seen that the Si-Cr-Al-Fe soft magnetic material can be flattened by suppressing the expansion of the grain size depending on the type of the lubricant.

A magnetic ink was prepared by adding a resin, a solvent and the like to the powder obtained above and screen-printed on a PET (polyethylene terephthalate) substrate to form a magnetic bar code. The formed magnetic bar code could not be identified by a magnetic viewer. In the reading test with the magnetic sensor, the output voltage was improved by about 20% as compared with the magnetic bar code using the spherical carbonyl iron powder.

(Example 2) 1.3Cu-5.6Nb-8.7Si-1.4B- was sprayed by a water atomizing method.
The average particle diameter of the remaining Fe is 6.5 μm, and the maximum particle diameter is 31 μm.
m powder and an average particle size of 5.0 μm and a maximum particle size of 22 μm were obtained. As a result of X-ray diffraction, a halo pattern peculiar to the amorphous alloy was shown. This powder was processed using an attritor using SUJ-2 steel balls as a grinding medium. A steel ball of a predetermined weight ratio to the powder to be processed, isopropyl alcohol of 20 times the weight of the powder as a lubricant, and zinc stearate of 0.6% of the weight of the powder were added in combination, and 3 minutes per minute were added.
It was operated at 00 rpm for a predetermined time. The properties of the powder before and after this processing are shown in Table 2. However, the average aspect ratio is a calculated value of (average particle diameter / average thickness).

For comparison, the same material is used and the average particle size is 9.0.
The case where powder having a particle size of 62 μm and the maximum particle size of 62 μm is processed under the same conditions is shown as Comparative Example 1, and the case where the processing time is extended is shown as Comparative Example 2 in the table.

In the production method according to the present invention, any of the powders used shows the target powder characteristics, but the desirable average grain size limit is 7 μm and the maximum grain size limit is 31 μm.
In Comparative Example 1 in which the raw material powder exceeding m was used, the average aspect ratio was 4.3, and the average particle size was slightly over 11.8 μm, which is desirable 10 μm, but the maximum particle size was 88 μm. It was as large as 2.0 times.

By classifying the powder of Comparative Example 1, a powder satisfying the target could be obtained, but the yield was 55.
It was a remarkably low value of%, and it was found that it was not practical in terms of cost. In Comparative Example 2, the processing time was extended to try to make the particles finer, but the average particle size, the maximum particle size,
It was found that the average aspect ratio was high and a powder having the desired characteristics could not be obtained.

Further, the powder of the present invention was in an amorphous state as it was processed, and the coercive force could not be achieved under the condition of 1200 A / m or less, but the powder was heated at 50 ° C. higher than the crystallization temperature for 1 hour. By performing a heat treatment of cooling after holding, a fine crystalline state was obtained and a coercive force of 790 A / m was obtained, which was a sufficient characteristic. It was confirmed that the saturation magnetic flux density was 1.0 T or more.

Magnetic inks prepared using these powders according to the invention were printed on polyvinyl chloride substrates to form magnetic bar codes. After a commercially available magnet was brought close to the formed magnetic barcode to magnetize it, an attempt was made to identify it by a magnetic viewer, but it was impossible. In a reading test with a magnetic sensor, it is readable enough, and about 2 times as much as a magnetic bar code using spherical carbonyl iron powder.
It was confirmed that the output voltage was improved by 5%.

[0034]

[Table 2] (Example 3) A molten alloy was put into water and rapidly cooled to produce a large number of cracks in a steel ingot, which was pulverized by a dry vibration mill. The .5Si-5.5Al-balance Fe alloy powder was processed using an attritor by adding steel balls having a predetermined diameter and a predetermined weight relative to the powder, and 0.1% zinc powder stearate as a lubricant. As a comparative example, processing was performed under the same conditions except that no lubricant was added. Table 3 shows processing conditions and powder properties after processing.

The production method according to the present invention makes it possible to obtain a powder having a desired maximum particle size and an average aspect ratio, but in the comparative example in which no lubricant is added, the average aspect ratio after processing is 1.2 to 1. / 3, which is not satisfied with 1.5 or more. In addition, the maximum particle size is far from the limit value of 41 μm, and therefore classification is necessary. This is because, since no lubricant was used, flattening of the powder did not proceed, and a part of the powder particles aggregated, which increased the maximum particle size.

It was confirmed that the coercive force of each powder was 1100 A / m or less and the saturation magnetic flux density was 1.0 T or more by heat treatment in hydrogen or nitrogen.

The magnetic ink prepared using the powder according to the invention described above was printed on a polyvinyl chloride substrate to form a magnetic bar code. The formed magnetic bar code could not be identified by a magnetic viewer as in Examples 1 and 2, and showed a sufficient output voltage in a reading test with a magnetic sensor.

[0038]

[Table 3]

[0039]

As described above, when the low aspect ratio flattened soft magnetic metal powder according to the present invention is used for a magnetic bar code, sufficient leakage that enables more stable reading with a magnetic sensor as compared with the conventional case. Since magnetic flux can be obtained and the pattern of the magnetic barcode cannot be identified by a magnetic viewer or the like, it is an optimum powder for a magnetic barcode with high sensitivity and high confidentiality of information.

In the method for producing soft magnetic metal powder according to the present invention, the particle size of the raw material powder is adjusted by considering an appropriate amount of expansion of the maximum particle size involved in flattening the granular or spherical particles into a predetermined flat shape. This makes it possible to easily produce a powder suitable for a magnetic card having an average aspect ratio of particles of 1.5 to 4 and a maximum particle diameter of 44 μm or less.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Iwata 2107-2 Yasugi-cho, Yasugi-shi, Shimane Prefecture 2 Hitachi Metals Co., Ltd.

Claims (5)

[Claims] 1. The average aspect ratio of the particles is 1.5 to 4,
A low aspect ratio flat soft magnetic metal powder having a maximum particle size of 44 μm or less, a saturation magnetic flux density of 0.7 T or more and a coercive force of 1200 A / m or less. 2. A method for producing a low aspect ratio flat soft magnetic metal powder, which comprises storing granular or spherical powder having a maximum particle size of 31 μm or less in a container together with a pulverizing medium and coexisting with a lubricant. The powder is mechanically deformed into a flat shape by driving at least one of the medium and the container, and the average aspect ratio of the particles is 1.5 to 4 and the maximum particle diameter is 44 μm or less. Aspect ratio flat soft magnetic metal powder manufacturing method. 3. The method for producing a low-aspect ratio flat soft magnetic metal powder according to claim 2, wherein the powder directly produced from the molten alloy by a water atomizing or gas atomizing method is used as a raw material. 4. A method for producing a low aspect ratio flat soft magnetic metal powder according to claim 2, wherein a powder having an average particle size of 7 μm or less is used as a raw material. 5. The soft magnetic metal powder according to claim 2, which is mechanically deformed and then heat-treated in a non-oxidizing atmosphere so that the coercive force is 1200 A / m or less. Manufacturing method.