JP2005251995A - Permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means which can sufficiently control an eddy-current loss and prevent the lowering of a magnet characteristic caused by an insulating material in a permanent magnet in which permanent magnet powder is closely densed where a covering layer formed of the insulating material is formed on the surface. <P>SOLUTION: In the permanent magnet, the permanent magnet powder is closely densed where the covering layer formed of the insulating material is formed on the surface. In the permanent magnet, a relation H≥23,000×d<SP>-1</SP>is satisfied, where covering resistance is H (= t×ρ<SB>r</SB>÷ρ<SB>m</SB>) defined as a value obtained by dividing the product of the thickness t(m) of the covering layer formed of the insulating material and the volume resistance ρ<SB>r</SB>(Ωm) of the permanent magnet powder with a volume resistance coefficient ρ<SB>m</SB>(Ωm) of the permanent magnet powder, and a grain size of the permanent magnet powder is d(mm). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a permanent magnet used for rotating equipment, electronic components, electronic equipment, motors, and the like.

  Permanent magnet rotating machines have mainly used ferrite permanent magnets with high electrical resistance. However, with the recent improvement in the performance of rotating machines, the use frequency of higher performance rare earth permanent magnets has increased. Yes.

  However, since the rare earth permanent magnet is a metal magnet, its electric resistance is low. For this reason, when incorporated in a rotating device or the like, there arises a problem that eddy current loss increases and motor efficiency decreases. In addition, there is a problem that the magnet performance decreases due to the temperature rise.

  In view of the above, attempts have been made to increase the specific electric resistance of rare earth permanent magnets and reduce eddy current loss by coating rare earth magnet powder with an insulating material.

  For example, Patent Document 1 discloses a method in which a bonded magnet is coated with an inorganic binder by a sol-gel method or the like, and then directly energized in a molding die to obtain a full density magnet.

  Patent Document 2 discloses a method for obtaining a rare earth permanent magnet by densifying a mixture of a rare earth magnet powder and an insulating inorganic fluoride or inorganic oxide by sintering or the like.

  Furthermore, in Patent Document 3, a rare earth magnet powder is obtained by mixing rare earth magnet powder, a binder such as paraffinic hydrocarbon, and an insulator such as inorganic fluoride, and performing debinding after molding to obtain a rare earth magnet. A method is disclosed.

  In the rare earth permanent magnets manufactured by the methods described in Patent Documents 1 to 3, the rare earth magnet powder is coated with an insulating material. Thereby, the electrical resistance of the rare earth permanent magnet is increased, and the eddy current loss is reduced.

However, the specific electric resistance of the rare earth permanent magnet obtained by using these methods can vary depending on the thickness of the coating layer made of an insulating material, the particle size of the rare earth magnet powder, and the like. For this reason, it is difficult to produce a magnet having a desired specific electric resistance, and there have been cases in which eddy current loss cannot be reduced sufficiently. On the other hand, when the amount of the insulating material used is increased for the purpose of obtaining a sufficient specific electric resistance, there is a problem that the content of the rare earth magnet powder is relatively lowered and the magnet characteristics are deteriorated.
Japanese Patent Laid-Open No. 5-121220 JP-A-9-186010 JP 10-163055 A

  Accordingly, an object of the present invention is to sufficiently suppress eddy current loss in a permanent magnet formed by densifying a permanent magnet powder having a coating layer made of an insulating material formed on the surface, and to provide an insulating material. It is to provide a means capable of preventing the deterioration of the magnet characteristics due to the above.

The present invention is a permanent magnet formed by densifying a permanent magnet powder having a coating layer made of an insulating material formed on its surface, and a thickness t (mm) of the coating layer made of the insulating material, Covering resistance H (= t × ρ _r ÷ defined as a value obtained by dividing the product of the volume resistivity ρ _r (Ωm) of the insulating material by the volume resistivity ρ _m (Ωm) of the permanent magnet powder. ρ _m ) and the particle size d (mm) of the permanent magnet powder satisfy H ≧ 23000 × d ⁻¹ .

  According to the permanent magnet of the present invention, the eddy current loss is sufficiently suppressed, the deterioration of the magnet characteristics due to the insulating material is prevented, and the high magnet characteristics are maintained.

  The law of electromagnetism shows that the eddy current induced in a magnet placed in a periodic magnetic field increases as the cross-sectional area perpendicular to the magnetic field direction of the magnet increases. Therefore, when the magnetic powder is coated with an insulating material to suppress the eddy current, in order to increase the effect of suppressing the eddy current, the particle size of the magnetic powder and the coating layer made of the insulating material (hereinafter simply referred to as “magnetic powder”) It is expected that the thickness of the “coating layer”) needs to satisfy a predetermined relationship.

In order to investigate the effect of the relationship between the particle size of the magnetic powder and the thickness of the coating layer on the insulating properties of the coating layer, the present inventors obtained the magnetic powder by coating it with a polymer compound or ceramics. Various magnets having coating layers with different thicknesses were prepared by densifying the powder. And about these magnets, the emitted-heat amount in a fixed periodic magnetic field was compared. As a result, the relationship between the particle size of the magnetic powder and the thickness of the coating layer and the insulating properties of the coating layer was found, and the present invention was completed. Specifically, the thickness of the coating layer made of an insulating material is t (mm), the volume resistivity of the insulating material is ρ _r (Ωm), and the volume resistivity of the permanent magnet powder is ρ _m (Ωm). When the coating resistance H expressed by H = t × ρ _r ÷ ρ _m and the particle size d (mm) of the permanent magnet powder are in the range of 0.001 ≦ d ≦ 1, H ≧ 23000 × The permanent magnet is designed so as to satisfy d- ¹ . Preferably, the permanent magnet is designed to satisfy H ≧ 61500 × d ^−1.1 . By designing the permanent magnet so as to satisfy the above relationship, the eddy current loss in the permanent magnet formed by densifying the permanent magnet powder coated with the insulating material is effectively suppressed.

  In the present invention, the particle size of the permanent magnet powder refers to the average particle size of the permanent magnet powder contained in the permanent magnet. In addition, what is necessary is just to measure the particle size of permanent magnet powder by a normal measuring means.

  The particle size of the permanent magnet powder is preferably 0.001 to 1 mm, more preferably 0.005 to 0.7 mm. If this particle size is too small, it will be difficult to control the volume ratio of the insulating material during the manufacture of the magnet, and satisfactory magnetization characteristics may not be obtained. On the other hand, if the particle size of the permanent magnet powder is too large, it may be difficult to densify the magnet powder during the production of the magnet.

The particle diameter d (mm) of the permanent magnet powder and the thickness t (mm) of the coating layer are preferably t <0.16 × d ^0.99 , more preferably t ≦ 0.1 × d, More preferably, t ≦ 0.025 × d is satisfied. By satisfying such a relationship between the particle diameter d of the permanent magnet powder and the thickness t of the coating layer, it is possible to minimize degradation of the magnet characteristics.

  Hereinafter, the permanent magnet of the present invention will be described in detail.

  The permanent magnet of the present invention is made of permanent magnet powder. The permanent magnet powder is a magnet powder constituting a permanent magnet, and a coating layer formed by coating with an insulating material is formed on the surface of the permanent magnet powder. It is densified by the method to constitute a permanent magnet.

  The shape of the permanent magnet and the permanent magnet powder is not particularly limited. The shape of the permanent magnet may be determined according to the part to which the permanent magnet is applied. For example, when applied to a motor of an automobile, the size and shape of the permanent magnet may be determined in accordance with the size and shape of the motor.

  The type of permanent magnet is not particularly limited and can be applied to various metal magnets. Preferably, the permanent magnet powder of the present invention contains a rare earth magnet phase. Since the magnetic force of the magnet is somewhat reduced by the coating layer, the use of magnet powder containing a magnetic phase with a strong magnetic force, such as a rare earth magnet phase, minimizes the deterioration of the magnet properties due to the coating layer. Is possible. However, if there is a special reason, such as when used in applications where magnetic force is not so required, magnet powder containing no rare earth magnet phase may be used, and such an embodiment is also within the technical scope of the present invention. Can be included.

  Examples of the rare earth magnet phase include an R-T-B magnet phase or an RT magnet phase (R is a rare earth element, and T is a transition metal element). Specifically, an Nd—Fe—B based magnet phase and an Sm—Co based magnet phase are exemplified. The main elements constituting the rare earth magnet may be replaced with other elements as necessary. For example, a part of Nd may be substituted with Pr, Dy, Tb, etc., and a part of Fe may be substituted with Co.

  Some of these permanent magnet powders require a liquid phase to be generated under a high temperature condition of 800 ° C. or higher in the densification step in order to ensure sufficient magnet performance. However, depending on the type of insulating material constituting the coating layer, the insulating properties may be reduced due to reaction with the liquid phase, and the effect of providing the coating layer may be reduced.

  From such a viewpoint, in the present invention, the permanent magnet powder is preferably a magnet powder produced by the HDDR method (hereinafter also referred to as “HDDR powder”). When HDDR powder is used, the restriction of the temperature condition during densification is released, and the magnet powder can be densified efficiently even under a temperature condition of less than 800 ° C. The HDDR method is a method for producing a magnetic powder having the steps of hydrogenation-decomposition / dehydrogenation-recombination (Hydrogenation-Decomposition / Desorption-Recombination).

The shape of the permanent magnet is not particularly limited as described above, but in the present invention, the particle size d (mm) of the permanent magnet powder and the volume resistivity ρ _m (Ωm) of the permanent magnet powder satisfy the relationship described above. Designed as such.

The volume resistivity ρ _m (Ωm) of the permanent magnet powder is an index indicating the difficulty of current flow in the permanent magnet powder, and is defined as an electric resistance value of a material having a unit cross-sectional area. The higher the volume resistivity, the higher the insulation. The volume resistivity can be measured according to a known measurement method such as JIS K6911. Although not particularly limited, the volume resistivity ρ _m of the permanent magnet powder is usually about 0.5 × 10 ^{−4 to} 2.5 × 10 ⁻⁴ μΩm.

  As the insulating material constituting the coating layer for coating the permanent magnet powder, ceramics, polymer resin such as epoxy resin or vinyl resin, inorganic compound, etc. having low electrical conductivity can be used. However, the present invention is not limited to these, and other materials may be used as long as they can insulate between permanent magnet powders and satisfy the conditions specified in the present invention.

The shape of the coating layer is not particularly limited, but at least a coating layer exists between different permanent magnet powders, and the permanent magnet powder is insulated by the coating layer. In the present invention, the thickness t (mm) of the coating layer and the volume resistivity ρ _r (Ωm) of the coating layer are designed to satisfy the above-mentioned definition.

The thickness t (mm) of the coating layer can be controlled by adjusting the mass of the insulating material used. The thickness t of the coating layer can be measured, for example, by analyzing the thickness of a layer lacking a magnet component such as Fe by EPMA (Electron Probe X-ray Micro Analyzer) analysis. The thickness t of the coating layer is preferably uniform in order to develop a stable insulating performance, but may be slightly changed as long as the insulating performance is not affected. When the thickness t is not uniform, an average value is adopted as the thickness t of the coating layer. The average value may be obtained, for example, by measuring the thickness t of each of the 10 coating layers of the sample using an electron microscope, and calculating the average thereof, or calculating the average from the mass of the insulating material used. The thickness may be calculated. Although not particularly limited, the thickness t of the coating layer with respect to the magnet powder is usually about 10 ⁻⁵ to 10 ⁻¹ mm.

Like the volume resistivity ρ _m (Ωm) of the permanent magnet powder, the volume resistivity ρ _r (Ωm) of the coating layer is an index indicating the difficulty of current flow in the coating layer. Defined as a resistance value. The volume resistivity can be measured according to a known measurement method such as JIS K6911. Although not particularly limited, the volume resistivity ρ _m of the insulating film is usually about 10 ⁵ to 10 ¹⁵ Ωm.

  In the permanent magnet of the present invention, the permanent magnet powder coated with an insulating material is not particularly limited, and is densified by various conventionally known methods. Examples of the method for densifying the magnet powder include a hot press method, a discharge plasma sintering method, an explosion pressing method, and a forging method.

  The use of the permanent magnet of the present invention is not particularly limited, but can be applied to a motor. In the permanent magnet of the present invention, generation of eddy current is suppressed, and in addition, it has high magnet performance. For this reason, if the motor manufactured using the permanent magnet of the present invention is used, the continuous output of the motor can be easily increased, and it can be said that it is suitable as a medium to large output motor. Moreover, since the motor using the permanent magnet of the present invention has excellent magnet characteristics, the product can be reduced in size and weight. For example, when applied to automotive parts, fuel efficiency can be improved as the vehicle body becomes lighter. Furthermore, it is particularly effective as a drive motor for electric vehicles and hybrid electric vehicles. Drive motors can be installed in places where it was difficult to secure space so far, which will contribute to the generalization of electric vehicles and hybrid vehicles.

  Hereinafter, Nd-Fe-B magnet powder or Sm-Co magnet powder as permanent magnet powder is coated with a polymer or ceramics as an insulating material, and the obtained powder is subjected to hot pressing, discharge The correlation between each parameter and magnet characteristics is shown for a permanent magnet obtained by densification by any of the plasma sintering method, the explosive pressing method, or the forging method.

<Example 1>
Nd—Fe—B rare earth magnet powder (volume resistivity ρ _m : 0.000002 Ωm) is sized using a sieve to separate powder having a particle size of 0.2 mm (0.18 mm to 0.23 mm) did. Next, a silicon resin (volume resistivity ρ _r : 1.0 × 10 ⁷ Ωm), which is an insulating polymer material, was sprayed to obtain a magnet powder coated with the silicon resin. At this time, the thickness t of the coating layer was controlled to 2 μm by adjusting the spraying time. The thickness of the coating layer was measured by analyzing the thickness of the Fe component deficient layer, which is a magnet component, by EPMA analysis.

The magnet powder coated with the silicon resin obtained above was densified by a hot press method to produce an Nd—Fe—B rare earth permanent magnet. Hot pressing was performed by maintaining a pressure of 15 ton / cm ² for 120 minutes under a temperature condition of 400 ° C.

  The produced permanent magnet was allowed to stand for 30 minutes in a periodic magnetic field having a magnetic field strength of 0.1 T and a frequency of 1000 Hz, and the temperature change and heat generation at that time were observed. The calorific value was evaluated as a relative calorific value with respect to this calorific value, assuming that the calorific value of a similar permanent magnet without a coating layer was 1. The conditions and evaluation results are shown in Table 1.

Further, the residual magnetization Br and the coercive force iHc of the obtained permanent magnet were measured using a BH tracer. These measurement results are shown in Table 1. Further, the particle size d of the used Nd—Fe—B rare earth magnet powder is multiplied by 0.99, multiplied by 0.16, and divided by the thickness t of the coating layer, that is, 0.16 × d ^0. The value of ^.99 / t is also shown in Table 1.

<Examples 2 to 40 and Comparative Examples 1 to 4>
Type of permanent magnet powder (Nd-Fe-B magnet powder or Sm-Co magnet powder, HDDR powder or sintered powder), particle size, volume resistivity, type of insulating material constituting the coating layer (high Silicon resin or polyimide resin as a molecule, Dy ₂ O ₃ paste as ceramic, MgO paste, or Nd ₂ O ₃ paste, or phosphoric acid compound), coating layer thickness, volume resistivity, coated magnet powder Various permanent magnets were produced by the same procedure as in Example 1 by changing the means for densification (hot pressing method, spark plasma sintering method, explosion pressing method, or forging method) as shown in Table 1. .

FIG. 1 is a graph in which data of a part of a produced permanent magnet is plotted, with the horizontal axis representing the coating resistance H represented by H = t × ρ _r ÷ ρ _m and the vertical axis representing the relative calorific value. As shown in FIG. 1, when the covering resistance H is increased, the calorific value converges to a value determined by the particle size d of the magnet powder. That is, in order to suppress the heat generation due to the generation of eddy current, it is sufficient that the coating resistance H is equal to or greater than a predetermined value determined by the particle diameter d. For example, when the particle size is d = 0.05 mm, it is sufficient that the covering resistance H is about 10 ⁶ to 10 ⁷ (m), and the permanent magnet should be designed so that the covering resistance H is greater than this value. That's fine.

FIG. 2 is a graph in which data of a part of the produced permanent magnet is plotted with the horizontal axis representing the particle diameter d of the magnet powder and the vertical axis representing the covering resistance H. In FIG. 2, “◯” indicates a sample in which “the relative calorific value of the sample = the lower limit value of the relative calorific value of the particle size”, and Δ indicates “the lower limit value of the relative calorific value of the particle size <the relative calorific value of the sample ≦ A sample having a lower limit value of the relative calorific value of the particle size × 2 ”is indicated, and“ x ”indicates a sample of“ lower limit value of the relative calorific value of the particle size × 2 <relative heat value of the sample ”. As shown in FIG. 2, in order to converge the relative calorific value, “H ≧ 23000 × d ⁻¹ ” should be satisfied, and preferably “H ≧ 61500 × d ^−1.1 ”. I know it ’s good.

FIG. 3 uses a coordinate system in which the horizontal axis represents the particle diameter d of the magnet powder and the vertical axis represents the coating resistance H, as in FIG. 2, to suppress heat generation due to the generation of eddy currents in the permanent magnet of the present invention. 6 is a graph illustrating a region corresponding to a preferable relationship that the particle diameter d of the magnetic powder and the covering resistance H satisfy. In the permanent magnet of the present invention, it is preferable that the particle diameter d of the magnet powder and the covering resistance H satisfy the relationship represented by the region X shown in FIG. Moreover, it is more preferable to satisfy the relationship represented by the region Y shown in FIG. Here, in region X shown in FIG. 3, H ≧ 23000 × d ⁻¹ , and d is a value in the range of 0.001 ≦ d ≦ 1. In the region Y, a H ≧ 61500 × ^{d -1.1, d} is a value in a range of 0.005 ≦ d ≦ 0.7.

FIG. 4 is a graph in which data of a part of the produced permanent magnet is plotted with the particle diameter d of the magnet powder on the horizontal axis and the thickness t of the coating layer on the vertical axis. In FIG. 4, “◎” indicates a sample where “9 kG <residual magnetization of the sample”, ○ indicates a sample where “8 kG <residual magnetization of the sample ≦ 9 kG”, and Δ indicates “7 kG <residual magnetization of the sample ≦ 8 kG”. And x indicates a sample having “residual magnetization of the sample ≦ 7 kG”. As shown in FIG. 4, in order to improve the value of remanent magnetization, the thickness t of the coating layer and the particle size d of the permanent magnet powder satisfy “t <0.16 × d ^0.99 ”. That is, it is preferable that the value of 0.16 × d ^0.99 / t is larger than 1. More preferably, “t ≦ 0.1 × d” may be satisfied, and more preferably, “t ≦ 0.025 × d” may be satisfied. As shown in Table 1 and FIG. 4, the permanent magnet satisfying t <0.16 × d ^0.99 has a residual magnetization larger than 7 kG and maintains a high magnetic property. Further, the permanent magnet satisfying t ≦ 0.1 × d has a residual magnetization larger than 8 kG, and the permanent magnet satisfying t ≦ 0.025 × d has a residual magnetization larger than 9 kG.

It is the graph which plotted some data of the produced permanent magnet, with the horizontal axis representing the coating resistance H represented by H = t × ρ _r ÷ ρ _m and the vertical axis representing the relative calorific value. It is the graph which plotted the data of a part of the produced permanent magnet by taking the particle diameter d of a magnetic powder on a horizontal axis, and covering resistance H on a vertical axis | shaft. A graph illustrating a region corresponding to a preferable relationship between the particle size d of the magnetic powder and the coating resistance H in the permanent magnet of the present invention, where the horizontal axis represents the particle size d of the magnet powder and the vertical axis represents the coating resistance H. It is. It is the graph which plotted the data of a part of the produced permanent magnet, taking the particle diameter d of the magnet powder on the horizontal axis and the thickness t of the coating layer on the vertical axis.

Claims (9)

A permanent magnet formed by densifying a permanent magnet powder having a coating layer made of an insulating material formed on its surface,
It is defined as a value obtained by dividing the product of the thickness t (mm) of the covering layer and the volume resistivity ρ _r (Ωm) of the insulating material by the volume resistivity ρ _m (Ωm) of the permanent magnet powder. A permanent magnet, wherein a covering resistance H (= t × ρ _r ÷ ρ _m ) and a particle diameter d (mm) of the permanent magnet powder satisfy H ≧ 23000 × d ⁻¹ . The coating resistance H and the particle diameter d of the permanent magnet powder, and satisfies the H ≧ 61500 × d ^-1.1, permanent magnet according to claim 1.   The permanent magnet according to claim 1, wherein a particle diameter d of the permanent magnet powder satisfies 0.001 ≦ d ≦ 1. The thickness t of the coating layer and the particle size d of the permanent magnet powder satisfy t <0.16 × d ^{0.99, according} to any one of claims 1 to 3. permanent magnet.   The permanent magnet according to claim 1, wherein the permanent magnet powder contains a rare earth magnet phase.   6. The rare earth magnet phase is an R-T-B magnet phase or an R-T magnet phase (R is a rare earth element and T is a transition metal element). The permanent magnet described in 1.   The permanent magnet according to claim 1, wherein the permanent magnet powder is a magnet powder manufactured by an HDDR method.   The permanent magnet powder is densified by one or more methods selected from the group consisting of a hot press method, a discharge plasma sintering method, an explosion pressing method, and a forging method. The permanent magnet of any one of these.   The motor using the permanent magnet of any one of Claims 1-8.

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