Rare earth bonded magnet

Abstract

The rare earth bonded magnet includes a resin cured product of a rare earth magnet powder and a thermosetting resin, the rare earth magnet powder is an isotropic Nd-Fe-B-based magnet powder, and the thermosetting resin is an epoxy resin. The cured resin is contained in an amount of more than 5% by weight and 6.5% by weight or less in 100% by weight of the rare earth bonded magnet, and the porosity is less than 5%, the ring crush compression strength is 60 MPa or more, and the resistivity is 100 [mu] [Omega] m or more.

Description

Technical Field

[0001] The present invention relates to a rare earth bonded magnet. Background Art

[0002] In recent years, rare earth permanent magnets, due to their excellent magnetic properties, have found application in a wide range of fields, including rotating equipment such as motors, general household appliances, audio equipment, medical devices, and general industrial equipment. In particular, rare earth bonded magnets, made from rare earth magnet powder and a binder (resin) that binds the powder, contribute to the miniaturization and high performance of these devices due to their high degree of shape freedom. One such rare earth bonded magnet has been proposed, comprising Nd-Fe-B-based magnet powder and a thermosetting epoxy resin as the binder (see, for example, Patent Document 1).

[0003] In the rare earth bond magnet of Patent Document 1, Nd—Fe—B-based quenched magnet powder is used as the rare earth magnet powder, and epoxy resin is used as the binder resin, with approximately 2.5 wt% of epoxy resin mixed.

[0004] Furthermore, when rare-earth bonded magnets are incorporated into a high-speed rotating motor, large centrifugal forces act on the rotor to which the rare-earth bonded magnets are mounted, potentially causing the rare-earth bonded magnets to break and scatter. As a means of preventing this scattering, a structure has been proposed in which a reinforced plastic protective cover is provided over the rare-earth bonded magnets (see, for example, Patent Document 2).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 6-314605

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 8-107641 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] When a reinforced plastic protective cover, such as that described in Patent Document 2, is provided on a rare earth bonded magnet, such as that described in Patent Document 1, it is possible to prevent the rare earth bonded magnet from scattering. However, this has the disadvantages of increasing the weight and inertia of the rotor, increasing the number of parts, and increasing the number of assembly steps, thus increasing costs. Therefore, it is necessary to improve the mechanical strength (ring crush strength) of the rare earth bonded magnet.

[0011] Furthermore, rare earth bonded magnets have the advantage of higher electrical resistance compared to rare earth sintered magnets due to the presence of a resin as an insulator between the magnet powders. However, when conventional rare earth bonded magnets, consisting of Nd-Fe-B magnet powder and 2-3 wt% of resin, are assembled into high-speed rotating motors, the electrical resistance is not necessarily high, leading to increased eddy current losses and reduced motor efficiency. Therefore, it is necessary to increase the electrical resistance.

[0012] As described above, in the structure in which rare earth bonded magnets containing thermosetting resin are used in a motor that rotates at high speed, there is room for further improvement in the rare earth bonded magnets.

[0013] Therefore, an object of the present invention is to provide a rare earth bonded magnet having high ring crush strength and electrical resistance without causing a significant deterioration in the magnetic properties of the rare earth bonded magnet.

[0014] Technical means to solve the problem

[0015] In order to solve the above-mentioned problems and achieve the purpose, a rare earth bonded magnet of one embodiment of the present invention is a rare earth bonded magnet comprising rare earth magnet powder and a resin-cured material of a thermosetting resin, wherein the rare earth magnet powder is an isotropic Nd-Fe-B magnet powder, the thermosetting resin is an epoxy resin, and the resin-cured material is contained in 100 weight % of the rare earth bonded magnet in an amount exceeding 5 weight % and less than 6.5 weight %, and the porosity of the rare earth bonded magnet is less than 5%, the ring crush strength is greater than 60 MPa, and the resistivity is greater than 100 μΩ·m.

[0016] Effects of the Invention

[0017] According to one aspect of the present invention, a rare earth bonded magnet having high ring crush strength and electrical resistance can be obtained without significantly degrading the magnetic properties of the rare earth bonded magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] [ Figure 1 ] Figure 1 This is a graph showing the ratio (Vol %) of rare earth magnet powder, cured thermosetting resin, and porosity in a rare earth bond magnet. DETAILED DESCRIPTION

[0019] Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings. In addition, the present invention is not limited to the embodiments described above. In addition, the components in the following embodiments include components that can be easily replaced by those skilled in the art or components that are substantially the same.

[0020] <Implementation Method 1>

[0021] The rare earth bond magnet of the first embodiment comprises rare earth magnet powder and a cured thermosetting resin. The rare earth magnet powder is isotropic Nd (neodymium)-Fe (iron)-B (boron) magnet powder. Examples of isotropic Nd-Fe-B magnet powder include MQP-14-12 (trade name), MQP-8-5 (trade name), MQP-10-8.5HD (trade name), MQP-11-8 (trade name), and MQP12-8HD (trade name) manufactured by Magnequench.

[0022] Alternatively, for example, Nd-Fe-B magnet powder can be produced by a super-quenching method. Specifically, a Nd-Fe-B alloy is melted by high-frequency induction heating under reduced pressure or in an argon environment. Then, the melted alloy is sprayed onto a copper rotating roller and super-quenched (high-speed cooling) to produce a ribbon-shaped thin ribbon sheet. Then, after the thin ribbon sheet is broken into pieces of several mm to tens of mm, it is crushed using a crusher to obtain a powder. After the crushed powder is classified using a sieve with a specified mesh, it is heat-treated to produce rare earth magnet powder. Since the directions of the easy magnetization axes of each grain are not aligned in one direction, the rare earth magnet powder is isotropic in terms of magnetism.

[0023] The rare earth magnet powder preferably has a particle size within a range of 45 μm to less than 175 μm. Alternatively, the rare earth magnet powder may have a particle size within a range of 45 μm to less than 75 μm, or within a range of 75 μm to less than 175 μm. Adjustment of the particle size range can be achieved by classification using a sieve with a predetermined mesh size.

[0024] The cured thermosetting resin contained in the rare earth bond magnet of the first embodiment is specifically a cured epoxy resin.

[0025] The cured resin is contained in an amount exceeding 5% by weight and below 6.5% by weight within 100% by weight of the rare earth bonded magnet. Furthermore, the rare earth magnet powder is contained in an amount exceeding 93.5% by weight and below 95% by weight. Furthermore, in the rare earth bonded magnet of Embodiment 1, it is preferred that the rare earth magnet powder and the cured resin of the thermosetting resin be uniformly mixed. Furthermore, conventionally, when producing bonded magnets using thermosetting resins, the binder content has been between 2% by weight and 3% by weight.

[0026] The porosity of the rare earth bonded magnet of Embodiment 1 is less than 5%. Thus, since the rare earth bonded magnet of Embodiment 1 contains the cured thermosetting resin in the aforementioned amount, its porosity is low and its ring crush strength is high. Specifically, the ring crush strength of the rare earth bonded magnet of Embodiment 1 is 60 MPa or greater. Furthermore, the low porosity of the rare earth bonded magnet of Embodiment 1 allows for a relatively high volume fraction of the rare earth magnet powder, thereby suppressing any degradation of its magnetic properties.

[0027] Furthermore, the rare earth bond magnet of Embodiment 1 contains the cured thermosetting resin in the aforementioned amount, and therefore has a high electrical resistance. That is, the resistivity of the rare earth bond magnet of Embodiment 1 is 100 μΩ·m or more.

[0028] The rare earth bonded magnet of embodiment 1 can be produced, for example, in the following manner. First, the rare earth magnet powder and the components that constitute the cured resin in the rare earth bonded magnet (the raw material components of the cured resin) are mixed at a predetermined mixing ratio to produce a composite. The mixing ratio of the rare earth magnet powder and the raw material components of the cured resin is considered to be the same as the ratio of the rare earth magnet powder and the cured resin in the rare earth bonded magnet after production. As raw material components of the cured resin, in addition to thermosetting resins (e.g., epoxy resins) serving as binders, curing agents can also be listed. Furthermore, a small amount of lubricant (e.g., calcium stearate) can be added when producing the composite. Specifically, the lubricant can be added in an amount of 0.02% by weight or more and less than 0.5% by weight relative to the total of 100% by weight of the raw material components of the rare earth magnet powder and the cured resin.

[0029] Next, the composite is filled into the mold cavity of the mold and compressed under a specified pressure to produce a green body. Next, the green body removed from the mold is placed in an oven and thermally cured at a specified temperature for a specified time to produce a solidified body (thermosetting body) comprising the rare earth magnet powder and the resin cured product. Furthermore, it is preferred that a rust-proofing method be applied to the surface of the solidified body to prevent oxidation. As rust-proofing methods, known methods such as electroplating and spray coating can be implemented. In this way, the rare earth bonded magnet of embodiment 1 can be obtained.

[0030] <Implementation Method 2>

[0031] One of the problems of the second embodiment is to prevent a significant decrease in the magnetic properties of the rare earth bond magnet even when the amount of rare earth magnet powder is small.

[0032] To address the aforementioned issues and achieve the objectives, a rare earth bonded magnet according to a second embodiment comprises rare earth magnet powder and a cured resin of a thermosetting resin. The rare earth magnet powder is isotropic Nd—Fe—B magnet powder, the thermosetting resin is an epoxy resin, and the cured resin is included in an amount exceeding 5% by weight and not more than 6.5% by weight of 100% by weight of the rare earth bonded magnet. The particle size of the rare earth magnet powder is 45 μm or less, and the surface of the rare earth magnet powder is coated with a compound containing phosphorus. In the second embodiment, similar to the first embodiment, the rare earth bonded magnet preferably has a porosity of less than 5%, a ring crush strength of 60 MPa or greater, and a resistivity of 100 μΩ·m or greater.

[0033] By subjecting rare earth magnet powder to phosphate treatment after pulverization, oxidative degradation of the magnet powder can be prevented, thereby preventing a significant decrease in the magnetic properties of the rare earth bond magnet.

[0034] Furthermore, even when the particle size of the rare earth magnet powder is set to be greater than 0 μm and 45 μm or less during the phosphate treatment, a rare earth bonded magnet can be provided that prevents a significant decrease in magnetic properties of the rare earth bonded magnet.

[0035] Furthermore, the rare earth magnet powder is not limited to Nd-Fe-B quenched magnetic powder, and may also be isotropic Sm-Fe-N or anisotropic Sm-Fe-N, anisotropic Nd-Fe-B magnetic powder (trade name d-HDDR), or SmCo magnetic powder (magnetic powder obtained by pulverizing anisotropic magnetic powder).

[0036] Furthermore, the thermosetting resin may be a conductive epoxy resin. In this case, during the electrodeposition coating process of applying a conductive epoxy resin to the magnet for rust prevention, the magnet itself is conductive, making electrodeposition coating easier to apply, resulting in excellent film-forming properties. The method for manufacturing the cured product of rare earth magnet powder and thermosetting resin, and the rare earth bonded magnet, is otherwise the same as in Embodiment 1.

[0037] Hereinafter, the present invention will be described in further detail based on examples, but the present invention is not limited to these examples.

[0038] [Example]

[0039] <Production of rare earth bonded magnets>

[0040] Isotropic Nd-Fe-B magnet powder was used as the rare earth magnet powder. MQP-14-12 (trade name) manufactured by Magnequench was prepared as the isotropic Nd-Fe-B magnet powder. The MQP-14-12 particle size was classified into two groups: 75 μm or larger and less than 150 μm, and 45 μm or larger and less than 75 μm. The classification was performed using a sieve with a specified mesh size.

[0041] Next, for each of the two groups, isotropic Nd—Fe—B magnet powder was mixed with a raw material component of a cured resin (Pelnox, Model XW2310) containing an epoxy resin as a binder and a hardener at a predetermined ratio to produce a composite. The ratio of the rare earth magnet powder to the raw material component of the cured resin was such that, with the total weight being 100% by weight, the raw material component of the cured resin accounted for 2.5% by weight, and the rare earth magnet powder accounted for 97.5% by weight. Furthermore, composites were also produced with a cured resin material containing 5% by weight of raw material and 95% by weight of rare earth magnet powder, a cured resin material containing 5.5% by weight of raw material and 94.5% by weight of rare earth magnet powder, a cured resin material containing 6% by weight of raw material and 94% by weight of rare earth magnet powder, a cured resin material containing 6.5% by weight of raw material and 93.5% by weight of rare earth magnet powder, and a cured resin material containing 7.5% by weight of raw material and 92.5% by weight of rare earth magnet powder. Composites were also produced by mixing the cured resin material and rare earth magnet powder dissolved in a solvent, evaporating the solvent, and then crushing and classifying. All composites were produced with the same particle size and the same flowability conditions during filling into the mold cavity.

[0042] Next, the compound is filled into the mold cavity and a predetermined pressure is applied (molding pressure: surface pressure 5 ton / cm 2 The green body is cylindrical with a diameter of Φ10 mm and a height of 7 mm.

[0043] The green body removed from the mold was then placed in an oven and heat-cured at a predetermined temperature (150°C) for a predetermined time to produce a cured product (thermocured product). The cured product had a cylindrical shape with a diameter of 10 mm and a height of 7 mm. No dimensional change was observed between the green body and the cured product.

[0044] Next, a rust-proofing method (specifically, electrodeposition coating) is applied to the surface of the cured product to prevent oxidation.

[0045] In this manner, rare earth bonded magnets (Samples 1 to 12) were produced, comprising rare earth magnet powder and a cured thermosetting resin. Samples 3 to 5, and Samples 9 and 11 are examples, while Samples 1, 2, 6, 7, 8, and 12 are comparative examples.

[0046] Evaluation Method

[0047] (Porosity)

[0048] The porosity was calculated from the apparent density relative to the true density. The evaluation criteria are as follows.

[0049] ○: Porosity is less than 5%.

[0050] △: The porosity is 5% or more and less than 15%.

[0051] ×: Porosity is 15% or more.

[0052] (Ring crush strength)

[0053] The ring crush strength was measured based on Japanese Industrial Standards (JIS) Z2507. The evaluation criteria are as follows.

[0054] ◎: Ring crush strength is 100 MPa or more.

[0055] ○: Ring crush strength is 60 MPa or more and less than 100 MPa.

[0056] △: Ring crush strength is 50 MPa or more and less than 60 MPa.

[0057] ×: Ring crush strength is less than 50 MPa.

[0058] (Resistivity)

[0059] Resistivity was measured using a four-probe method. The magnet sample had a diameter of 10 mm and a height of 7 mm. The average resistivity of N5 samples was calculated. The evaluation criteria are as follows.

[0060] ◎: The resistivity is 100 μΩ·m or more.

[0061] ○: The resistivity is 10 μΩ·m or more and less than 100 μΩ·m.

[0062] △: Resistivity is less than 10 μΩ·m.

[0063] (Comprehensive evaluation)

[0064] Comprehensive evaluation was performed on Samples 1 to 12. The evaluation criteria are as follows.

[0065] ○: The evaluation results of the ring crush strength and the resistivity were both ◎.

[0066] ×: Cases other than those described above.

[0067] The evaluation results for Samples 1 to 12 are shown in Tables 1 and 2 below. In Table 1, "45-75" in the "Magnetic Powder Particle Size (μm)" indicates that the particle size of the isotropic Nd—Fe—B magnet powder is within the range of 45 μm or greater and less than 75 μm. Furthermore, in Table 2, "75-150" in the "Magnetic Powder Particle Size (μm)" indicates that the particle size of the isotropic Nd—Fe—B magnet powder is within the range of 75 μm or greater and less than 150 μm.

[0068] [Table 1]

[0069] (Table 1)

[0070]

[0071] Table 1 shows samples 1 to 6, representing the evaluation of rare earth bonded magnets whose isotropic Nd-Fe-B magnet powder had a particle size of 45 μm or greater and less than 75 μm. Sample 1, in which the raw material content of the cured resin was 2.5% by weight, had a porosity of 15% or greater, and both the ring crush strength and electrical resistance (surface resistivity) were rated as △. This is because the raw material content of the cured resin was roughly the same as that of conventional rare earth bonded magnets. Furthermore, in Sample 6, in which the raw material content of the cured resin was 7.5% by weight, some of the binder leaked from the mold cavity, causing a production problem, and was therefore not evaluated. This is because the raw material content of the cured resin was excessive.

[0072] In the evaluation of samples 3 to 5, except for the samples in which the raw material component content of the cured resin was 2.5 wt%, 5 wt%, and 7.5 wt%, all items were rated ◎. Therefore, the comprehensive evaluation of samples 3 to 5 shown in Table 1 was rated ○.

[0073] The results in Table 1 show that as the porosity of the rare earth bonded magnet decreases, the ring crush strength and resistivity increase. In Samples 3 to 5 of the Examples, both the ring crush strength and resistivity are improved.

[0074] In addition, it was confirmed that compared with Sample 1 (Comparative Example) in which the raw material component amount of the resin cured material was 2.5 weight %, Samples 3 to 5 had a slightly lower filling ratio of the magnet powder due to the increased raw material component amount of the resin cured material, and the magnetic properties of the rare earth bonded magnet were slightly lower than those of Sample 1 (Comparative Example), but magnetic properties of a degree that was not inferior could be obtained.

[0075] [Table 2]

[0076] (Table 2)

[0077]

[0078] Table 2 shows samples 7 to 12, which show the evaluation of rare earth bonded magnets in which the particle size of the isotropic Nd-Fe-B system magnet powder is within the range of 75 μm or more and less than 150 μm. In sample 7, in which the raw material content of the cured resin is 2.5% by weight, the porosity is 15% or more, and the ring crush strength and resistivity are both evaluated as △. This is because the raw material content of the cured resin is roughly the same as that of the previous rare earth bonded magnets. In addition, in sample 12, in which the raw material content of the cured resin is 7.5% by weight, part of the adhesive leaked out of the mold cavity, causing problems in production, so it was not evaluated. This is because the raw material content of the cured resin is too much.

[0079] Samples 9 to 11, except for the samples in which the raw material content of the cured resin was 2.5 wt%, 5 wt%, and 7.5 wt%, all items were rated ⊚. Therefore, the overall evaluation of Samples 9 to 11 shown in Table 2 was ⊚.

[0080] The results in Table 2 show that as the porosity of the rare earth bonded magnet decreases, the ring crush strength and resistivity increase. In Examples 9 to 11, both the ring crush strength and resistivity are improved.

[0081] In addition, it was confirmed that compared with Sample 7 (Comparative Example) in which the raw material component amount of the resin cured material was 2.5 weight%, Samples 9 to 11 had a slightly lower filling ratio of the magnet powder due to the increase in the raw material component amount of the resin cured material, and the magnetic properties of the rare earth bonded magnet were slightly lower than those of Sample 7 (Comparative Example), but magnetic properties of a degree that was no less superior could be obtained.

[0082] in addition, Figure 1 This is a graph showing the ratio (Vol%) of rare earth magnet powder, cured thermosetting resin, and pores in a rare earth bond magnet. Specifically, samples 1 to 6 are shown. It can be seen that in samples 3 to 5, the ratio of pores is reduced and the ring crush strength is increased. In addition, it can be seen that in samples 3 to 5, the ratio of rare earth magnet powder is almost not reduced, and the reduction in magnetic properties is suppressed. In addition, the porosity is calculated as follows. Based on the density of the magnetic powder 7.6 [g / cm 3 ]、resin specific gravity 0.92[g / cm 3] (which contains the organic solvent methyl ethyl ketone (MEK)). Calculate the true density of the prototype magnet. Calculate the volume ratio of the magnetic powder to the resin in the true density, and define the remainder as the porosity.

Claims

1. A rare earth bonded magnet comprising rare earth magnet powder and a cured product of a thermosetting resin, wherein: The rare earth magnet powder is an isotropic Nd-Fe-B magnet powder. The thermosetting resin is an epoxy resin, The cured resin is contained in an amount exceeding 5 wt % and not more than 6.5 wt % in 100 wt % of the rare earth bond magnet. The rare earth bonded magnet has a porosity of less than 5%, a ring crush strength of 60 MPa or more, and a resistivity of 100 μΩ·m or more.

2. A rare earth bonded magnet comprising rare earth magnet powder and a cured product of a thermosetting resin, wherein: The thermosetting resin is an epoxy resin, The cured resin is contained in an amount exceeding 5 wt % and not more than 6.5 wt % in 100 wt % of the rare earth bond magnet. The particle size of the rare earth magnet powder is less than 45 μm. The surface of the rare earth magnet powder is coated with a compound containing phosphorus.

3. The rare earth bond magnet according to claim 2, wherein: The rare earth magnet powder is isotropic Nd-Fe-B magnet powder.

4. The rare earth bond magnet according to claim 2, wherein: The rare earth magnet powder is anisotropic Nd-Fe-B magnet powder.

5. The rare earth bond magnet according to claim 2, wherein: The rare earth magnet powder is an isotropic Sm-Fe-N magnet powder.

6. The rare earth bond magnet according to claim 2, wherein: The rare earth magnet powder is anisotropic Sm-Fe-N magnet powder.

7. The rare earth bond magnet according to claim 2, wherein: The rare earth magnet powder is anisotropic SmCo magnet powder.

8. The rare earth bond magnet according to claim 2, wherein: The epoxy resin has electrical conductivity.

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