JPH07166201A - Method for heat treatment of flaky soft magnetic powder - Google Patents

Abstract

PURPOSE:To efficiently obtain flaky soft magnetic powder excellent in shape characteristics and magnetic particle properties by mixing high m.p. heat-resistant grains having a large particle size to flaky soft magnetic powder and subjecting this mixed powder to heat treatment at a specified temp. in a hydrogen atmosphere. CONSTITUTION:Flaky soft magnetic powder such as permalloy based alloy powder is mixed with heat-resistant particles such as high m.p. aluminum oxide powder whose average particle diameter is 1 to 5 times of that of the powder and which is not brought into reaction with the powder. In this case, as for the mixing ratio, the heat resistant particle are preferably mixed by 1/2 to 5 times wt. of the flaky soft magnetic powder. Moreover, as for the particles of the flaky soft magnetic powder, preferably, the average particle diameter is regulated to 1mum to 10mm, the ratio of the minor axis/major axis to 1 to 0.3 and the ratio of the thickness/minor axis to <=1/3. The obtd. mixed powder is subjected to heating treatment at 650 to 1300 deg.C in a hydrogen atmosphere. Thus, the surface is reduced without sintering the soft magnetic powder. After that, the heat resistant particles are separated by a magnetic vibrating screen or the like, by which the flake soft magnetic powder of high quality can easily be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for flaky soft magnetic powder. More specifically, it is used for the purpose of protecting electronic devices that are sensitive to magnetism from external magnetic fields such as magnetic fields generated by electronic devices and high voltage wires, or external magnetic fields such as earth magnetism, and for shielding the magnetic fields that leak to the outside from electronic devices The present invention relates to a heat treatment method for flaky soft magnetic powder having a high magnetic permeability and a low coercive force.

[0002]

2. Description of the Related Art Conventionally, as a magnetic shield material,
A resin-based magnetic shield material obtained by adding a magnetic shield filler to a resin is known, and a soft magnetic powder typified by Permalloy is used for the magnetic shield filler.
It is necessary that the soft magnetic powders are in contact with each other as much as possible so that magnetic leakage does not occur. Therefore, it is preferable that the soft magnetic powders are scale-like powders so that the contact area between the powders becomes large. Such scale-like metal powder is generally produced by atomizing a molten metal by an atomizing method or a spray method and flattening the powder by a ball mill or a stamp mill. However, permalloy, which is commonly used as a magnetic shield filler, is apt to cause crystal distortion due to impact, and there is a problem that magnetic properties are greatly deteriorated due to crystal distortion when processed into a scale. This crystal strain is eliminated by heat treating the powder at a high temperature, and the magnetic characteristics are restored. Therefore, in order to exert high magnetic properties as a magnetic shield material, it is necessary to heat the scaled powder at a high temperature, but the scale-like powder used as a magnetic shield filler is fine and has a large surface area. There is a problem that it easily sinters at a high temperature, and if it is heat-treated to remove crystal strain after processing, it will sinter and lose its scaly shape, making it unsuitable as a magnetic shield filler.

In order to prevent such sintering, for example, in JP-A-1-298101, scale-like soft magnetic powder is mixed with fine heat-resistant oxide powder having an average particle size of 0.3 μm or less. A method for annealing is described. Although this method has a temporary effect on prevention of sintering, it is very difficult to separate the fine oxide powder after annealing. This method is intended to be used by mixing it with ink or paint without separating the above oxide powder, but in terms of magnetic shielding, unnecessary powder will be mixed in, so relatively soft magnetic powder It is easy for the shielding effect to become insufficient due to a decrease in the amount used. Further, since the oxide powder is present between the soft magnetic powders, the soft magnetic powders cannot directly contact each other, and the shield effect is reduced from this point as well.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above problems in conventional flaky soft magnetic powders by a heat treatment method for flaky soft magnetic powders having excellent shape characteristics and magnetic properties, that is, high magnetic permeability, and It is an object of the present invention to provide a heat treatment method for flaky soft magnetic powder having a low coercive force. In the present invention, in solving the above problems in the conventional heat treatment method, it was found that the particle size of the particles for sintering prevention greatly affects the effect of preventing sintering and the effect of separating the particles. The present invention is based on such knowledge, and has achieved a heat treatment method which is excellent in both the effect of preventing sintering of soft magnetic powder and the effect of separating added particles.

[0005]

According to the present invention, there is provided a method for producing flaky soft magnetic powder having the following constitution. (1) The flaky soft magnetic powder is mixed with high melting point heat-resistant particles having an average particle size 1 to 5 times the average particle size of the soft magnetic powder and not reacting with the soft magnetic powder at high temperature. A heat treatment method for scaly soft magnetic powder, which comprises heat-treating the mixed powder at 650 to 1300 ° C. in a hydrogen atmosphere and then separating the heat-resistant particles. (2) The treatment method according to the above (1), in which aluminum oxide powder is mixed with the flaky permalloy-based alloy powder, the mixture is heat treated, and then the powder is separated by a magnetic vibration sieve. (3) The treatment method according to the above (1) or (2), wherein heat-resistant particles are mixed in an amount of ½ to 5 times the weight of the flaky soft magnetic powder and the mixture is heat-treated. (4) Use of a scale-like soft magnetic powder having an average particle diameter of 1 μm to 10 mm, a minor axis / major axis ratio of 1 to 0.3, and a thickness / minor axis ratio of 1/3 or less, (1), The processing method of (2) or (3).

[0006]

DETAILED DESCRIPTION OF THE INVENTION The treatment method of the present invention is, for example, a magnetic shield filler mixed with various magnetic shield materials such as resin-based magnetic shield materials, or scale-like soft particles used as other magnetic shield powders. Targets magnetic powder. As the soft magnetic powder, Ni-F such as Permalloy which is commonly used as a filler of this kind is used.
Mainly composed of e-alloy and Ni-Fe, Mo, Cr, Mn
Ni-Fe based alloys (hereinafter referred to as permalloy based alloys) containing such additional elements as described above are preferably carried out, but the object to be treated is not limited to permalloy based alloys. Flake-shaped powder of soft magnetic metal typified by permalloy-based alloy is conventionally flattened by applying mechanical pressure using a ball mill or a stamp mill after atomizing these molten metals using an atomizing method or a spray method. Obtained. The particle size and flatness can be appropriately selected depending on the processing conditions. In the present invention, the processing method for making the soft magnetic material scale-like is not limited.

The scaly powder has an average particle size of 1 μm to 10 mm, preferably 2 to 100 μm, and the ratio of the minor axis to the major axis of the plane is 1 (minor axis / long axis).
~ 0.3, the ratio of thickness to minor axis (thickness / minor axis)
Is preferably 1/3 or less. Here, the average particle diameter means an average value including the short diameter, the long diameter, and the thickness, and can be measured by a laser scattering method or the like. In addition, the short diameter and the long diameter are the lengths of the planes, the long diameter means the longest diameter and the short diameter means the shortest diameter, and these can be measured by the naked eye or microscopic observation. Similarly, the thickness of the flat surface can be measured by microscopically observing the cross section of the flaky powder oriented in the flat surface. In three-dimensional observation of the plane, the smallest length is the thickness of the plane. If the average particle size is less than 1 μm, the particle size is too small to prevent sintering during heat treatment even if high melting point particles are mixed. Further, if the average particle size exceeds 10 mm, heat-resistant particles having a considerably large particle size are required, which is not practical. Minor axis /
The closer the major axis ratio is to 1, the wider the flat surface is, and if this ratio is less than 0.3, the powder becomes needle-like and is not suitable as a magnetic shield filler. Further, the closer the thickness / minor axis ratio is to 1, the more it becomes rod-shaped or agglomerated, which is not suitable as a magnetic shield filler. Therefore, the thickness / minor axis ratio is preferably 1/3 or less.
If this ratio is larger than 1/3, the degree of flatness is small, which is not preferable.

In the treatment method of the present invention, heat treatment is carried out by mixing heat-resistant particles having a high melting point that do not react with the soft magnetic powder at high temperature and do not melt. As the heat-resistant particles, 650 to 13
A non-magnetic oxide, carbide, or nitride having a melting point equal to or higher than the heat treatment temperature of 00 ° C. is used. Specifically, ceramic powders such as aluminum oxide, zirconium oxide, and zirconium carbide are suitable. By using the non-magnetic powder, it can be easily separated from the flaky soft magnetic powder by a magnetic vibrating screen after the heat treatment.

The particle size of the heat-resistant particles is appropriately 1 to 5 times, preferably 3 to 4 times the average particle size of the soft magnetic powder. If the particle size of the heat-resistant particles is smaller than that of the soft magnetic powder, it becomes difficult to separate the heat-resistant particles, and if added in an amount necessary for preventing sintering, the volume becomes bulky. Also, it is easily scattered and difficult to handle. On the other hand, if the particle size of the heat-resistant particles exceeds 5 times, the soft magnetic powder enters between the particles and a sufficient sintering preventing effect cannot be obtained. The amount of the heat-resistant particles mixed is an amount capable of preventing the soft magnetic powder from sintering during the heat treatment. The same weight as that of the soft magnetic powder, particularly, when aluminum oxide is used at a high temperature, it is preferable to use 3 times the weight of the soft magnetic powder. Usually, if the mixing amount of the heat-resistant particles is less than 1/2 times the weight of the soft magnetic powder, a sufficient effect of preventing sintering cannot be obtained. On the other hand, if the mixing amount exceeds about 5 times the weight, the heat amount at the time of heating is wasted, and the separation of the heat resistant particles becomes troublesome.

A mixture of the flaky soft magnetic powder and the above heat-resistant particles is heat-treated in a hydrogen atmosphere at 650 ° C. to 1300 ° C. to remove the processing strain of the flaky powder and restore the magnetic properties. If the heating temperature is lower than 650 ° C., the processing strain cannot be sufficiently removed, and the magnetic properties of the powder will deteriorate. On the other hand, heat treatment at a high temperature exceeding 1300 ° C. is unsuitable because the permalloy alloy has a melting point of about 1450 ° C. and softens. When the heat treatment atmosphere is oxidizing or inert, the soft magnetic powder surface is not reduced and the magnetic properties are not sufficiently recovered.

After the heat treatment, the heat resistant particles are separated. When non-magnetic particles such as aluminum oxide are used as the heat-resistant particles, the soft magnetic powder and the non-magnetic particles can be easily separated by using a magnetic vibrating screen as the separating means. By separating the heat-resistant particles as described above, these particles do not exist between the flaky soft magnetic powders and the soft magnetic powders are in direct contact with each other, so that the magnetic shield effect is excellent. Further, if the soft magnetic powder is mixed with a resin or the like together with the heat-resistant particles without separating the heat-resistant particles, the amount of the mixture becomes relatively large, so that flexibility tends to be lost when the resin sheet or the like is molded.

[0012]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of the present invention are shown below together with comparative examples. It should be noted that the present embodiment is an example and does not limit the scope of the present invention.

Example 1 Spherical permalloy alloy powder (Ni80wt% -Fe20wt%) 500 which was produced by a water atomizing method and then classified to 50 μm or less
g, 1500 cc of water, and 20 g of stearic acid were charged into a wet ball mill grinder (using steel balls) and operated for 30 hours to obtain scaly permalloy powder. 100 of this powder
It was crushed after being dried at ℃ for 24 hours. When the particle diameter of the obtained powder was measured by a laser scattering method, the average particle diameter was 15 μm. According to the SEM photograph, the minor axis / major axis ratio was 0.6 and the thickness / minor axis ratio was 1/10.
When the coercive force of this powder was measured by a vibrating magnetometer, it was 12 Oe. 20 g of this flaky permalloy powder
Then, 60 g of alumina powder (average particle size 20 μm) passed through a 200-mesh sieve was mixed and uniformly stirred. This mixed powder was heated at 1100 ° C. for 30 minutes in a hydrogen atmosphere.
After heating, the mixed powder was put into a magnetic vibration sieve to separate the permalloy powder and the alumina powder. The coercive force of the scale-like permalloy powder obtained by separation was measured by a vibrating magnetometer and found to be 2 Oe, which was about 1/6 of that before the heat treatment.
It was confirmed that it was extremely small and had excellent soft magnetic properties.

Example 2 Spherical permalloy alloy powder (Ni 78 wt% -Fe 22 wt%) 60 produced by the water atomizing method and then classified to 45 μm or less
0 g of water, 1500 cc of water and 15 g of stearic acid were charged into a wet ball mill crusher (using steel ball balls) and operated for 35 hours to obtain flaky permalloy powder. 10 of this powder
It was crushed after being dried at 0 ° C. for 24 hours. When the particle diameter of the obtained powder was measured by a laser scattering method, the average particle diameter was 14 μm. According to the SEM photograph, the minor axis / major axis ratio was 0.6 and the thickness / minor axis ratio was 1/8.
The coercive force of this powder was measured by a vibrating magnetometer and found to be 10 Oe. 20 g of the flaky permalloy powder was mixed with 60 g of zirconium oxide powder (average particle size: 15 μm) passed through a 235 mesh sieve, and stirred uniformly. This mixed powder was heated in a hydrogen atmosphere at 1000 ° C. for 30 minutes. After heating, the mixed powder was put into a magnetic vibration sieve to separate the permalloy powder and the zirconium oxide powder. The coercive force of the separated permalloy powder was measured by a vibrating magnetometer and found to be 3 Oe.

Comparative Example 1 Spherical permalloy alloy powder (Ni 80 wt% -Fe 20 wt%) 50 produced by the water atomizing method and then classified to 50 μm or less
0 g of water, 1500 cc of water and 20 g of stearic acid were charged into a wet ball mill grinder (using steel ball balls) and operated for 28 hours to obtain flaky permalloy powder. 10 of this powder
It was crushed after being dried at 0 ° C. for 24 hours. When the particle diameter of the obtained powder was measured by a laser scattering method, the average particle diameter was 17 μm. According to the SEM photograph, the minor axis / major axis ratio was 0.6 and the thickness / minor axis ratio was 1 / 8.5. The coercive force of this powder was measured by a vibrating magnetometer and found to be 12 Oe. This scale-like permalloy powder 30
g was heated under a hydrogen atmosphere at 600 ° C. for 15 minutes. The powder after heating was sintered into the shape of a container.

Comparative Example 2 Spherical permalloy alloy powder (Ni 80 wt% -Fe 20 wt%) 50 produced by the water atomizing method and then classified to 50 μm or less
0 g of water, 1500 cc of water, and 20 g of stearic acid were charged into a wet ball mill crusher (using steel ball balls) and operated for 24 hours to obtain scaly permalloy powder. 10 of this powder
It was crushed after being dried at 0 ° C. for 24 hours. When the particle diameter of the obtained powder was measured by the laser scattering method, the average particle diameter was 15 μm. According to the SEM photograph, the minor axis / major axis ratio was 0.6 and the thickness / minor axis ratio was 1 / 8.5. The coercive force of this powder was measured by a vibrating magnetometer and found to be 12 Oe. This scale-like permalloy powder 30
g was heated in a hydrogen atmosphere at 300 ° C. for 30 minutes. The coercive force of the powder after heating was measured with a vibrating magnetometer and was found to be 10 Oe, which was almost the same as before the heat treatment.

Comparative Example 3 An average particle diameter of 15 μm obtained in the same manner as in Example 1, a minor axis / major axis ratio of 0.8, a thickness / minor axis ratio of 1/10, and a coercive force of 10.5.
Oe scale flaky permalloy powder 20g, average particle size 3μm
60 g of the alumina powder of was mixed and stirred uniformly. This mixed powder was heated at 1100 ° C. for 30 minutes in a hydrogen atmosphere. After heating, the mixed powder was put into a magnetic vibrating screen to try to separate the permalloy powder and the alumina powder.
About 20 g of g could not be separated. The permalloy powder after the above separation treatment of this comparative example and the heat-separated permalloy powder of Example 1 were kneaded into vinyl chloride resin, respectively, and molded into a sheet shape, and its flexibility was examined. The sample A in which the powder was kneaded maintained the flexibility even when the powder was added up to 75 wt% of the entire molded body, while the sample B in which the powder of this comparative example was kneaded added 40 wt% of the powder in the entire molded body. When it was bent at 90 degrees at the stage, it broke. Further, when the samples A and B were placed between the magnet and the Gauss meter and the magnetic shield performance was simply measured, the shielding effect of the sample B according to this comparative example was 1/10 of that of the sample A according to the first embodiment. It was

[0018]

According to the manufacturing method of the present invention, it is possible to easily obtain a flaky soft magnetic powder having excellent magnetic characteristics, which is optimum as a magnetic shield filler mixed with a resin-based magnetic shield material or the like. The production method of the present invention is a method of mixing heat-resistant particles having a high melting point and separating the particles after heat treatment,
The manufacturing cost is low because it can be easily performed without the need for pretreatment of the soft magnetic powder. Moreover, the obtained powder has excellent soft magnetic properties and can be widely used as a filler for various magnetic shield materials.

Claims (4)

[Claims] 1. A heat-resistant particle having a high melting point, wherein the flaky soft magnetic powder has an average particle diameter 1 to 5 times the average particle diameter of the soft magnetic powder and does not react with the soft magnetic powder at a high temperature. A method for heat-treating flaky soft magnetic powder, which comprises mixing and heat-treating the mixed powder in a hydrogen atmosphere at 650 to 1300 ° C., and then separating the heat-resistant particles. 2. The treatment method according to claim 1, wherein the aluminum oxide powder is mixed with the flaky permalloy-based alloy powder, the mixture is heat-treated, and then the powder is separated by a magnetic vibration sieve. 3. A heat treatment by mixing 1/2 to 5 times the weight of heat-resistant particles with the flaky soft magnetic powder, and subjecting to heat treatment.
Processing method. 4. The average particle size is 1 μm to 10 mm, and the short axis /
The treatment method according to claim 1, 2 or 3, wherein a flaky soft magnetic powder having a major axis ratio of 1 to 0.3 and a thickness / minor axis ratio of 1/3 or less is used.