JP2005340290A - Hard magnetic solid material and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hard magnetic solid material for a high resistance magnet having high resistance and high level magnet performance, and a method for producing the same.
A hard magnetic solid material compressed and solidified by applying a shock wave to a hard magnetic powder having an insulating coating, wherein the hard magnetic powder has a volume fraction of 85% or more and a volume resistivity of 300 μΩ. A hard magnetic solid material having a thickness of cm or more, which is produced by compressing and solidifying the hard magnetic powder by applying a shock wave to the hard magnetic powder having an insulating coating through a liquid.
[Selection] Figure 1

Description

  The present invention relates to a hard magnetic solid material for a high-resistance magnet used for a motor or the like in which core loss is a problem when, for example, a hard disk is rotationally driven, and a method for manufacturing the same.

Ferrite magnets and bonded magnets are known as high resistance magnets. In particular, since the bond magnet is solidified by mixing a resin or the like with magnet powder, a high volume resistivity of 10,000 μΩ · cm or more is obtained. Therefore, these high resistance magnets have been used for magnet applications where core loss or the like becomes a problem.
For example, with respect to a magnet used for a motor or the like in which core loss is a problem when rotating a hard disk, increasing the volume resistivity of the magnet is one solution. However, in recent years, under the circumstances where the motor is rotated at a higher speed and the motor is lighter, a magnet having a low core loss and a good magnet performance is being demanded.

However, bond magnets have a magnetic powder volume fraction of less than 85%, and in order to increase the magnet powder volume fraction and increase magnet performance, a very large molding pressure is required. There was a limit. Ferrite magnets have lower magnet performance than bonded magnets and have limited use.
Therefore, an attempt has been made to apply dust core technology used for soft magnetic materials, coat Nd-Fe-B hard magnetic powder with an insulating coating, etc., mold in a magnetic field, and then heat and sinter. (See Patent Document 1). However, the volume fraction of the magnet powder cannot be increased more than that of the bonded magnet, and the magnet powder containing rare earth elements reacts with the insulating coating because of its high chemical reactivity, resulting in volume resistivity. However, the value is at a level of 100 μΩ · cm or less, and further, the magnet performance is deteriorated.

In order to increase the volume fraction of the magnetic powder, the volume fraction of the insulating coating is lowered, and when molding is performed by applying hot press, the volume fraction of the magnetic powder can be increased, but as described above, Magnet powder containing rare earth elements reacts with the insulating coating because of its high chemical reactivity, and as a result, the volume resistivity does not increase and the magnet performance is further reduced.
In addition, it has been tried to reduce the core loss by cutting the sintered magnet into small pieces and then bonding them together. However, if the number of cuts is small, the core loss can hardly be reduced. You need to do more. However, if the Nd—Fe—B based sintered magnet or the like is cut into small pieces, the magnet performance is lowered. Moreover, cutting once solidified, subdividing, and joining with an adhesive again has been a heavy load as a manufacturing method.
JP 2003-86414 A

As described above, when a high-resistance magnet is manufactured using a hard magnetic powder containing a rare earth element, the volume fraction of the magnet powder is reduced, causing a reduction in magnet performance. Moreover, when it tries to improve magnet performance, the fall of volume resistivity will be caused.
An object of the present invention is to solve such problems and to provide a hard magnetic solid material useful as a raw material for a high resistance magnet in which magnet performance and volume resistivity are compatible at a high level and a method for producing the same.

In the case of a conventional magnet, the present inventors consider that the volume fraction of hard magnetic powder is less than 85% and that the volume resistivity is about 100 μΩ · cm at the maximum. Was set as a development goal to be 85% or more and a volume resistivity of 300 μΩ · cm or more.
And as a result of intensive studies to solve the above problems, the magnetic powder has a high volume fraction and high volume resistivity by applying a shock wave to the hard magnetic powder having an insulating coating and solidifying it by compression. The inventors have found that a hard magnetic solid material can be obtained, and have made the present invention.

That is, in the present invention, a hard magnetic solid material compressed and solidified by applying a shock wave to a hard magnetic powder having an insulating coating, the volume fraction of the hard magnetic powder is 85% or more, and the volume resistance A hard magnetic solid material characterized in that the rate is 300 μΩ · cm or more is provided.
The present invention also provides a method for producing a hard magnetic solid material, wherein the hard magnetic powder is compressed and solidified by applying a shock wave to the hard magnetic powder having an insulating coating through a liquid.

  Since this solid material has a volume fraction of hard magnetic powder of 85% or more, it has excellent magnet performance. In addition, since it is compressed and solidified using a shock wave, the insulating coating of the hard magnetic powder is not destroyed, and the volume resistivity is as high as 300 μΩ · cm or higher. That is, it is a solid material having both excellent magnet performance and high resistance.

The hard magnetic solid material of the present invention is manufactured by applying a shock wave to a hard magnetic powder described later having an insulating coating. First, the hard magnetic powder will be described.
Examples of the hard magnetic powder used here include Nd—Fe—B based hard magnetic powder and Sm—Fe—N based hard magnetic powder. As the Nd-Fe-B type hard magnetic powder, an isotropic magnet powder obtained by the melt spin method, or its powder is anisotropicized by a hot plastic working method such as a hot upset method, and pulverized. Nd-Fe-B magnet powder. However, the Nd-Fe-B magnet powder anisotropicized by the HDDR method has weak mechanical properties, and in the present invention, there is a high probability that the Nd-Fe-B magnet powder will be broken by a shock wave employed when the powder is compressed and solidified. Can not be used because of a drop.

Examples of the Sm—Fe—N hard magnetic powder include magnet powder having a TbCu ₇ type crystal structure or powder having a Th ₂ Zn ₁₇ type crystal structure. If necessary, these hard magnetic powders can be mixed. Further, even if pulverized, the magnet performance does not deteriorate, and rare earth magnet powders that can be used as bonded magnet powders can also be used.
The shape of the hard magnetic powder may be granular or flaky depending on the production method. In the case of granules, the average particle size is 1 mm or less, preferably 500 μm or less, more preferably 300 μm or less. In these cases, it is a powder obtained only by passing through a sieve, and fine powder can be removed in order to suppress performance deterioration due to oxidation of the magnet.

From the viewpoint of the filling rate of the hard magnetic powder, a powder mixing system having a bimodal distribution having two particle size peaks is preferable. In that case, the average particle diameter of the whole is preferably in the above range so that the ratio of the small diameter powder to the large diameter powder is 1/5 or less. The tapping density is confirmed by the composition, and the particle size ratio of the high tapping density is selected.
When powder is made by the melt spin method, it becomes a flake. The thickness is about 10 to 30 μm. The powder is crushed and generally sieved with a sieve having an opening of 500 μm or less. However, in the case of this powder, since the ratio of thickness and width is large, it may be difficult to fill. If there is a disturbance during filling, it may become a defective part when squeezed with a shock wave. In that case, it crushes and uses about 20-100 micrometers. In addition, there is a method for producing powder using an atomizing method.

The hard magnetic powder is coated with an insulating film.
As a coating material, a resin, a coupling agent, insulating ceramics, insulating glass, a mixture obtained by appropriately mixing them, or the like can be used.
In this case, the addition ratio is considered depending on the density of the coating material used, and it is possible to select an amount that makes the volume fraction of the hard magnetic powder 85% or more. For example, when a resin having a density of about 1 is used, 0.1 to 1% by mass is preferable with respect to the total mass of the resin and the hard magnetic powder. More preferably, 0.3-0.7 mass% is good.

Examples of the resin include polyamide, polyimide, polyolefin, silicon resin, epoxy, polyester, and acrylic resin. The coating method is selected depending on the type of resin. For example, a wet microcapsule method, a dry microcapsule method, or the like can be used.
When using a resin, the surface of the hard magnetic powder can be treated in advance with a coupling agent in order to enhance the bonding with the hard magnetic powder. A silane coupling agent, a titanate coupling agent, etc. can be utilized as a coupling material. Further, the insulating coating may be a coupling agent alone.

As the insulating ceramic, for example, particles composed of SiO ₂ , Al ₂ O ₃ , ZrO ₂ or the like and having a size of submicron are preferable.
As the insulating glass, water glass or the like can be used, for example. It is also possible to use water ceramics or organic solvents in combination with insulating ceramics.
In the case of forming an insulating film by a wet method, an organic material is dissolved in a solvent, this and a hard magnetic powder are mixed, and the solvent is removed to perform the film treatment. After coating the hard magnetic powder, it is possible to react on the surface of the powder to polymerize the coating. These methods are for coating an organic material, but when coating an inorganic material by a wet method, a hard magnetic powder is mixed with a solution or suspension containing a metal chloride or a metal hydroxide. Alternatively, a sonochemical method can be used in which the particles are decomposed by ultrasonic waves and deposited on the surface of the hard magnetic powder.

  When an insulating coating is formed by a dry method, the surface can be modified by attaching a fine ceramic powder or resin powder having an average particle size of 1 μm or less to the surface of the hard magnetic powder as a base material by a mechanical treatment method. . As the ceramic to be used at this time, it is preferable to use a cleaving hexagonal boron nitride ceramic or the like because the covering property is improved. When cleaving, it may be larger than the average particle size of the ceramic powder. In addition, when it is cleaved, the fluidity of the hard magnetic powder having the insulating coating during shock compression seems to be improved, and resistance breakage between the hard magnetic powders hardly occurs. As an example of this method, a hybridization system (NHS) manufactured by Nara Machinery Co., Ltd. can be applied.

Furthermore, a method of coating the surface of the hard magnetic powder with ceramics after surface treatment with an organic / inorganic hybrid coupling agent can also be used.
Furthermore, it is also possible to apply a metal coating to the hard magnetic powder and then oxidize the coating material to make a ceramic. For example, a method of coating with aluminum followed by oxidation.

Furthermore, the surface of the hard magnetic powder itself can be oxidized to form an insulating film. Depending on the detailed composition and shape, the amount of oxidation affects the magnet performance, so the appropriate range should be determined for each powder. However, as a guide, in the hard magnetic powder having the Nd—Fe—B composition, the oxygen content is preferably about 1000 to 10,000 ppm. Preferably, 2000 to 7000 ppm is good. In the case of hard magnetic powder having a TbCu ₇ type Sm—Fe—N composition, about 500 ppm to 2000 ppm is preferable. In the case of a hard magnetic powder having a Th ₂ Zn ₁₇ type Sm—Fe—N-based composition, about 5000 to 15000 ppm is preferable. Preferably, about 8000-12000 ppm is good.

Further, it is possible to adopt a two-layer treatment method in which treatment is performed with an inorganic coating material and then treatment with an organic coating material.
The hard magnetic solid material of the present invention is produced by compressing and solidifying the above hard magnetic powder with a shock wave.
As a method of compressing and solidifying using a shock wave, a generally used cylindrical convergence method, uniaxial compression method, or the like can be used. If you want to obtain a cylindrical or plate shape, select that method. In particular, in order to obtain an air-core cylindrical compression body, a cylindrical convergence method in which a core material is inserted in the center can be used.

  The source of the shock wave is the explosive, but as the explosive used at that time, a low explosive speed powder explosive (for example, explosive for explosive pressure bonding (trade name PAVEX) manufactured by Asahi Kasei Co., Ltd.), a smelting explosive explosive (ANFO explosive) Commonly used explosives such as hydrous explosives, emulsion explosives, and high-performance explosives can be selected. As the explosion speed, a range of 2,000 to 9,500 m / s can be used, and the explosion speed is appropriately selected depending on the characteristics of the hard magnetic powder.

  In order to suppress the breakdown of the insulating film that coats the surface of the hard magnetic powder and to solidify it by compression, a low explosion speed is preferable. The range is preferably 2,000 to 5,000 m / s, more preferably 2,000 to 4,000 m / s. However, when the insulating coating is formed of ceramics, it is better to make it higher within the preferable explosion speed range. When using a high explosive speed explosive, the shock wave can be controlled by making the thickness of inclusions between the hard magnetic powder and the explosive larger than in the case of a low explosive speed.

  When compressing and solidifying using shock waves, the explosive amount should preferably be selected in the range of 0.5 to 15 in terms of mass ratio with respect to the compression target, which is a bulk body of hard magnetic powder having an insulating coating. Can do. Depending on the type of insulating coating, the mass ratio may change even if the hard magnetic powder material is the same, and the mass ratio also changes depending on the type of hard magnetic powder material. Therefore, it is necessary to make the mass ratio appropriate for the adopted combination. Generally, the above-described mass ratio is 1 to 12, more preferably 1 to 8, but is not limited thereto.

When compression and solidification is performed using a shock wave, the compression and solidification can be preferably performed with a shock wave using a liquid as a medium. More preferably, water is used as the liquid.
When a shock wave using water as a medium (hereinafter referred to as underwater shock wave) is used, the shock wave pressure itself lasts longer than when air is used as a medium. Hard magnetic powder can be compressed and solidified. Although internal heat generation due to impact compression may affect the properties of the resin and the like, it is extremely easy to keep the temperature lower when using an underwater shock wave than when air is used as a medium.
That is,

(A) The pressure of the underwater shock wave is determined by the Hugoniot function of explosive and water, and the pressure P is approximately expressed by the following equation.
P = 288 (MPa) {(ρ / ρ ₀ ) ^7.25 −1}
From the above equation, when an underwater shock wave is used, the amount of increase in the pressure P is very large with respect to the change in the density ρ of the water with respect to the reference density ρ ₀ , so that an ultrahigh pressure can be easily obtained by adjusting the amount of explosives. In this case, the temperature of the soft magnetic powder material and the insulating coating material is easily maintained at a low temperature as compared with the case of using a conventional shock wave.
(B) The duration of the impact pressure itself is longer than when using conventional shock waves.
(C) The temperature rise of the hard magnetic powder material due to the increase in entropy based on the nonlinear phenomenon of volume compression and shock wave disappears in a very short time.
(D) The temperature of the material of the hard magnetic powder is rarely kept high thereafter and rarely kept for a long time.
(E) Impact pressure is uniformly applied to the object to be compressed.
Due to these excellent characteristics of the underwater shock wave, it can be easily compressed and solidified at a high density without affecting the properties of the soft magnetic powder and the insulating coating.

An example of a method for compressing and solidifying hard magnetic powder using a shock wave will be described with reference to the drawings. The technical scope of the present invention is not limited by these specific examples.
FIG. 1 is a schematic view showing an example of an apparatus for causing a shock wave to act on hard magnetic powder through water by a cylindrical convergence method.
In FIG. 1, a hard magnetic powder 8 is set in a metal pipe 1 for powder filling. Water 7 is placed in the metal pipe 3 for water filling. The explosive 5 is set in the paper tube 4. These are sealed with a metal plug 2. When the explosive 5 is detonated by the detonator 6, the hard magnetic powder 8 is compressed in the radial direction through the water 7 by the shock wave emitted by the explosive 5.

  By this method, a hard magnetic solid material compression-molded into an air-core cylinder can be obtained. That is, it is possible to compress the hard magnetic powder together with the core member with a shock wave and remove at least a part of the core member to form an air core cylindrical shape. For example, a core member is arranged in accordance with the axis of the metal pipe 1 for powder filling, a hard magnetic powder is set around the core member, a shock wave is applied from the outside of the metal pipe 1 for powder filling, and the hard magnetic powder Can be compressed and solidified by shock waves, and at least a part of the core member can be removed to obtain an air-core cylindrical hard magnetic solid material.

  As the core member, materials such as metals, ceramics, and resins can be used, and rod-shaped solid materials can be used. Alternatively, a hollow cylindrical container concentrically arranged as a core member with respect to the powder-filled metal pipe 1 and filled with a powdery, granular, or liquid material may be used. In particular, using an easily-cuttable metal such as pure aluminum as the core member is easy to handle in terms of post-processing.

FIG. 2 is a schematic view showing an example of an apparatus for causing a shock wave to act on hard magnetic powder by uniaxial compression via water.
In FIG. 2, the hard magnetic powder 15 is set in a hard magnetic powder container 16. Water 12 is placed in the water storage unit 13 and sealed with the upper seal 11 and the lower seal 14. The explosive 10 is placed on the upper seal 11. An explosive container may be used. When the explosive 10 is detonated by the detonation unit 9, the hard magnetic powder 15 is compressed downward through the water 12 by the shock wave generated by the explosive 10.

1 and 2 show the case where water is used, but the object of the present invention can also be achieved by a structure in which a layer containing water is removed.
To set the hard magnetic powder, the container is naturally filled with the hard magnetic powder. Pre-compression can be performed if necessary. As a pre-compression, it is filled to a relative density of 40 to 80% and then compressed with a shock wave. Thereby, the relative density of the compressed body can be 85% or more. The relative density can be made 90 to 99% by increasing the shock wave. When obtaining a solid material for an anisotropic magnet, it is necessary to pre-compress in a magnetic field.

Nd-Fe-B-based powder obtained by crushing and pulverizing an anisotropic magnet manufactured by hot plastic working method and passing through a sieve having a mesh size of 300 μm, and insulating silicone resin in toluene Coating was performed by mixing with 5% by mass dissolved resin solution. The coated hard magnetic powder was pre-compressed to a density of 75% in a magnetic field.
Using the apparatus shown in FIG. 2, a pre-compressed preform was placed in a container, and PAVEX was used as the explosive and the mass ratio of explosive / hard magnetic powder was set to 5.12, followed by compression solidification.

  As a result of compression and solidification by applying a shock wave, a hard magnetic solid material having a relative density of 92% was obtained. The volume resistivity of this solid material was 2130 μΩ · cm. For comparison, the volume resistivity of a hard magnetic solid material formed by hot pressing the isotropic Nd—Fe—B powder produced by the melt spin method used for hot plastic working was 154 μΩ · cm.

  A solid material was produced and evaluated in the same manner as in Example 1 except that the insulating coating was water glass. As a result of compression and solidification by applying a shock wave, a hard magnetic solid material having a relative density of 94.5% was obtained. The volume resistivity of this solid material was 930 μΩ · cm.

A TbCu ₇ type Sm—Fe—N magnet powder produced by the melt spin method and passing through a sieve having an opening of 300 μm was subjected to a surface treatment using 0.3% by mass of a titanium coupling agent.
Using the apparatus shown in FIG. 1, this powder was poured and filled by applying vibration. PAVEX was used as the explosive and the mass ratio of explosive / hard magnetic powder was set to 3.3. As a result, a solid material having a volume fraction of 94.5% by volume and a volume resistivity of 790 μΩ · cm was obtained. In this case, since the magnet powder is a decomposable magnet and a sintered magnet cannot be obtained, the volume resistivity of the ribbon was measured and found to be 155 μΩ · cm.

The anisotropic magnet produced by the hot plastic working method is crushed and pulverized to produce Nd-Fe-B-based powder that passes through a sieve having a mesh size of 300 μm, and its surface is oxidized to 2700 ppm. A powder having an oxygen content was obtained.
Using the powder, using the apparatus shown in FIG. 2, a pre-compressed preform was placed in a container, PAVEX was used as the explosive, and the mass ratio of explosive / hard magnetic powder was set to 5.08 and squeezed. As a result of compression and solidification by applying a shock wave, a hard magnetic solid material having a relative density of 92% was obtained. The volume resistivity of this solid material was 392 μΩ · cm. Incidentally, the volume resistivity of the anisotropic Nd—Fe—B magnet formed by hot plastic working before being powdered and oxidized was 154 μΩ · cm.

  Since this solid material has a volume fraction of hard magnetic powder of 85% or more and a volume resistivity of 300 μΩ · cm or more, it is useful as a material for motors with little core loss. For example, motors for electric vehicles and hybrid vehicles It can be used for hard disk spindle motors, electric tool motors, air conditioner compressor motors, and the like.

It is the schematic which shows the example of the apparatus which makes a shock wave act on hard-magnetic powder by the cylindrical convergence method through water. It is the schematic which shows the example of the apparatus which makes a shock wave act on hard-magnetic powder by the uniaxial compression method through water.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal pipe for powder filling 2 Metal plug 3 Metal pipe for water filling 4 Paper cylinder 5 Explosive 6 Explosion part 7 Water 8 Hard magnetic powder 9 Initiation part 10 Explosive 11 Upper seal 12 Water 13 Water container 14 Lower seal 15 Hard Magnetic powder 16 Hard magnetic powder container

Claims (6)

  A hard magnetic solid material compressed and solidified by applying a shock wave to a hard magnetic powder having an insulating coating, wherein the hard magnetic powder has a volume fraction of 85% or more and a volume resistivity of 300 μΩ · cm or more. There is a hard magnetic solid material.   The hard magnetic solid material according to claim 1, wherein the hard magnetic powder is any one of Sm-Fe-N magnetic powder, Nd-Fe-B magnetic powder, and a mixture thereof. The hard magnetic solid material according to claim 1 or 2, wherein the Sm-Fe-N-based magnetic powder is a magnet powder having a TbCu ₇ type crystal structure or a magnet powder having a Th ₂ Zn ₁₇ type crystal structure.   The Nd-Fe-B-based magnetic powder is obtained by isotropic magnet powder obtained by a melt spin method, or by crystallizing the isotropic magnet powder by hot plastic working and then pulverizing. The hard magnetic solid material according to claim 1, which is an anisotropic magnet powder.   The hard magnetic solid material according to any one of claims 1 to 4, wherein the insulating coating is any one of an organic material, insulating ceramics, insulating glass, or a mixture thereof.   A method for producing a hard magnetic solid material comprising compressing and solidifying the hard magnetic powder by applying a shock wave to the hard magnetic powder having an insulating coating through a liquid.

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