Bonded magnet and compound

Abstract

One aspect of the present disclosure provides a bonded magnet comprising magnetic particles and a binder that binds the magnetic particles, wherein the binder contains a biodegradable resin.

Description

Bond magnet and compound

[0001] The present disclosure relates to a bond magnet and a compound.

[0002] A bond magnet containing magnetic particles and a binder is advantageous in terms of a high degree of freedom in shape compared to a sintered magnet. For example, Patent Document 1 discloses a method for manufacturing a bond magnet using magnetic particles and an epoxy resin.

[0003] International Publication No. 2024 / 142174

[0004] Magnetic particles used in bond magnets often contain rare earth elements and are expensive. Therefore, it is desirable to recover and reuse the magnetic particles from the bond magnet.

[0005] On the other hand, when recovering magnetic particles from a bond magnet obtained using a curable resin such as an epoxy resin, there is a problem in separating the binder (the cured product of the curable resin) from the magnetic particles. For example, it is possible to remove the binder by burning it. However, in this case, since the magnetic particles are also exposed to high heat, the magnetic particles deteriorate and cannot withstand reuse. Therefore, a bond magnet that is more easily removable of the binder and can recover the magnetic particles while reducing the impact on the magnetic particles would be useful.

[0006] An object of the present disclosure is to provide a novel bond magnet and a novel compound used for manufacturing the bond magnet.

[0007] This disclosure includes the following aspects: [1] A bonded magnet comprising magnetic particles and a binder that binds the magnetic particles together, wherein the binder comprises a biodegradable resin. [2] The bonded magnet according to [1], wherein the biodegradable resin comprises at least one selected from the group consisting of polyester biodegradable resins, polyamide biodegradable resins, polyaspartic acid biodegradable resins, and polyhydroxyalkanoic acid biodegradable resins. [3] The bonded magnet according to [1] or [2], wherein the biodegradable resin comprises at least one selected from the group consisting of polybutylene succinate, polylactic acid, and polyhydroxyalkanoic acid. [4] The bonded magnet according to [1], wherein the binder further comprises a cured product of a thermosetting resin. [5] A compound used in the manufacture of a bonded magnet, comprising magnetic particles and a biodegradable resin. [6] The compound according to [5], wherein the magnetic particles are coated with the biodegradable resin. [7] The compound according to [5] or [6], wherein the biodegradable resin comprises at least one selected from the group consisting of polyester biodegradable resins, polyamide biodegradable resins, polyaspartic acid biodegradable resins, and polyhydroxyalkano biodegradable resins. [8] The compound according to any one of [5] to [7], further comprising a thermosetting resin. [9] A method for recovering magnetic particles, comprising: biodegrading the binder of a bonded magnet comprising magnetic particles and a binder that binds the magnetic particles together to obtain a mixture containing the decomposition products of the magnetic particles and the binder; and recovering the magnetic particles from the mixture, wherein the binder contains a biodegradable resin.

[0008] This disclosure provides novel bonded magnets and novel compounds for use in the manufacture of bonded magnets.

[0009] Figure 1 is a schematic cross-sectional view showing an example of a bonded magnet.

[0010] Embodiments of the present disclosure are described below. However, the following embodiments are illustrative for the purpose of illustrating the present disclosure and are not intended to limit the present disclosure to the following. In this specification, numerical ranges indicated by the symbol "~" include lower and upper limits. That is, a numerical range indicated by "x~y" means x or greater and y or less.

[0011] Unless otherwise specified, the materials exemplified herein may be used individually or in combination of two or more. The content of each component in a composition means the total amount of any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition.

[0012] One embodiment of a bonded magnet comprises magnetic particles and a binder that binds the magnetic particles together.

[0013] The bonded magnet according to this embodiment contains a biodegradable resin as a binder. This makes it possible to decompose the binder portion by microorganisms. Although the decomposition of the binder by microorganisms also generates heat, it is possible to suppress the temperature rise compared to removing the binder by combustion, and it is possible to reduce the thermal degradation of the magnetic particles recovered after the binder has been removed. Therefore, after use, the magnetic particles of the bonded magnet can be recovered and used as raw materials to manufacture new bonded magnets.

[0014] The magnetic particles may be composed of permanent magnets. The permanent magnets may be samarium-cobalt (Sm-Co) permanent magnets, neodymium-iron-boron (Nd-Fe-B) permanent magnets, samarium-iron-nitrogen (Sm-Fe-N) permanent magnets, iron-cobalt (Fe-Co) permanent magnets, or Al-Ni-Co permanent magnets (alnico magnets). Preferably, the magnetic particles include samarium-iron-nitrogen (Sm-Fe-N) permanent magnets.

[0015] The magnetic particles may be composed of a soft magnetic material. The soft magnetic material may contain at least one metal selected from the group consisting of pure iron and iron-containing alloys. The iron-containing alloy may be at least one selected from the group consisting of, for example, Fe-Cr alloys (stainless steel), Fe-Ni-Cr alloys (stainless steel), Fe-Si alloys, Fe-Si-Al alloys (Sendust), Fe-Ni alloys (Permalloy), Fe-Cu-Ni alloys (Permalloy), Fe-Cr-Si alloys (electromagnetic stainless steel), and Fe-Ni-Mn-C alloys (Invar). The soft magnetic material may be amorphous. The soft magnetic material may be an Fe amorphous alloy. The magnetic particles composed of the soft magnetic material may be composed of amorphous iron or carbonyl iron.

[0016] Magnetic particles may contain multiple types of metallic elements. In addition to the above elements, magnetic particles may further contain at least one element selected from the group consisting of base metal elements, noble metal elements, transition metal elements, and rare earth elements. Magnetic particles may further contain at least one element selected from the group consisting of copper (Cu), titanium (Ti), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), tin (Sn), chromium (Cr), barium (Ba), strontium (Sr), lead (Pb), silver (Ag), oxygen (O), beryllium (Be), phosphorus (P), boron (B), and silicon (Si).

[0017] The average particle size of the magnetic particles may be 20 μm or more, 40 μm or more, or 60 μm or more, and may be 300 μm or less, 250 μm or less, or 150 μm or less.

[0018] The average particle size of magnetic particles is defined as the particle size (D50) at which the cumulative volume distribution curve reaches 50% when plotted from the smallest diameter side in the particle size distribution. The average particle size is measured using a laser diffraction particle size analyzer.

[0019] The magnetic particle content may be, for example, 90% by mass or more, or 95% by mass or more, or 98% by mass or less, or 97% by mass or less, based on the total amount of bonded magnets.

[0020] The biodegradable resin may include, for example, at least one selected from the group consisting of polyester-based biodegradable resins, polyamide-based biodegradable resins, polyaspartic acid-based biodegradable resins, and polyhydroxyalkano-based biodegradable resins.

[0021] Examples of polyester-based biodegradable resins include polyglycolic acid, poly(ε-caprolactone), polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, and polylactic acid.

[0022] Examples of polyamide-based biodegradable resins include polyamide 4.

[0023] Examples of polyaspartic acid-based biodegradable resins include polyaspartic acid and sodium polyaspartate.

[0024] Examples of polyhydroxyalkano-based biodegradable resins include poly(3-hydroxybutanoic acid).

[0025] The biodegradable resin may include at least one selected from the group consisting of polybutylene succinate, polylactic acid, and polyhydroxyalkanoic acid, from the viewpoint of having excellent biodegradability among the resins mentioned above.

[0026] The binder described above may further contain a cured product of a thermosetting resin in addition to the biodegradable resin. By including the cured product, the fixation of magnetic particles in the bonded magnet becomes more secure, and the mechanical strength of the bonded magnet itself can be further improved.

[0027] Examples of thermosetting resins include epoxy resins, phenolic resins, bismaleimide resins, polyimide resins, and polyamideimide resins. Preferably, the thermosetting resin contains an epoxy resin.

[0028] Epoxy resins include biphenyl-type epoxy resins, stilbene-type epoxy resins, diphenylmethane-type epoxy resins, sulfur atom-containing epoxy resins, novolac-type epoxy resins, dicyclopentadiene-type epoxy resins, salicylaldehyde-type epoxy resins, copolymer epoxy resins of naphthols and phenols, epoxidized aralkyl-type phenol resins, bisphenol-type epoxy resins (bisphenol A type epoxy resins and bisphenol F type epoxy resins, etc.), glycidyl ether-type epoxy resins of alcohols, glycidyl ether-type epoxy resins of paraxylylene and / or metaxylylene-modified phenol resins, and terpene-modified phenol Examples include glycidyl ether type epoxy resins of oleic resins, cyclopentadiene type epoxy resins, glycidyl ether type epoxy resins of polycyclic aromatic ring-modified phenolic resins, glycidyl ether type epoxy resins of naphthalene ring-containing phenolic resins, glycidyl ester type epoxy resins, glycidyl type or methylglycidyl type epoxy resins, alicyclic epoxy resins, halogenated phenol novolac type epoxy resins, orthocresol novolac type epoxy resins, hydroquinone type epoxy resins, thioether type epoxy resins, trimethylolpropane type epoxy resins, and linear aliphatic epoxy resins obtained by oxidizing olefin bonds with peracids such as peracetic acid.

[0029] The content of the cured material may be 1% by mass or more, 2% by mass or more, or 3% by mass or more, based on the total amount of the binder, and may be 20% by mass or less, 10% by mass or less, 7% by mass or less, or 5% by mass or less.

[0030] The bonded magnet described above can be obtained, for example, by compression molding of a compound containing magnetic particles and a biodegradable resin. An example of a method for manufacturing a bonded magnet comprises step S1 of supplying a compound containing magnetic particles and a biodegradable resin into a mold, and step S2 of obtaining a molded body from the compound by compressing the compound in the mold.

[0031] The compression of the compound in the mold in step S2 may be accompanied by heating. For example, the compound may be compressed in a mold heated at the molding temperature T. The molding temperature T may be above the softening temperature of the biodegradable resin. In this specification, the softening temperature is (glass transition temperature of the biodegradable resin + 20)°C. The glass transition temperature refers to the value measured by differential scanning calorimetry.

[0032] The molding temperature T in step S2 may be, for example, 80 to 180°C or 100 to 150°C. The heating time in step S2 may be, for example, 15 minutes or less, 0.5 to 15 minutes, or 0.5 to 10 minutes.

[0033] The molding pressure in step S2 may be, for example, 500 to 2000 MPa, 700 to 2000 MPa, or 980 to 2000 MPa.

[0034] The compression of the compound in step S2 may be carried out while applying a magnetic field to the compound. For example, the compound may be compressed in the mold while applying a magnetic field to the compound in the mold heated at the molding temperature T. Each magnetic particle in the compound is magnetized and rotated by the magnetic field H, and the easy magnetization axis of the magnetic domain in each magnetic particle is oriented along the magnetic field. In other words, each magnetic particle 3 in the compound 2 is oriented such that its magnetization direction m is approximately parallel to the magnetic field H (see Figure 1). If each magnetic particle 3 is a single crystal grain (single magnetic domain), the magnetization direction m of each magnetic particle 3 is the same as the direction in which the easy magnetization axis of each magnetic particle 3 extends.

[0035] After compression molding of the compound (for example, compression molding with heating), the binder solidifies, forming a molded body 2A containing a plurality of magnetic particles oriented along the magnetic field H and the binder 5 (see Figure 1). In other words, a molded body 2A made of solidified compound 2 is formed. The magnetization direction M of the entire molded body 2A is substantially or perfectly parallel to the direction of the magnetic field H applied to the compound in this process. If the compound further contains a thermosetting resin, the above solidification may be read as curing.

[0036] In Figure 1, the molded body 2A is shown as an example of an anisotropic bonded magnet 2. The overall magnetization direction of the anisotropic bonded magnet is approximately or perfectly parallel to the direction of the magnetic field H applied to the compound, the overall magnetization direction M of the molded body 2A, and the magnetization direction m of each magnetic particle 3 in the bonded magnet. The anisotropic bonded magnet 2 can have a high residual magnetic flux density due to the excellent orientation of the magnetic powder. Furthermore, the mechanical strength and residual magnetic flux density of the anisotropic bonded magnet are increased by the compression of the compound (i.e., an increase in the filling rate of magnetic powder in the molded body 2A) and the solidification of the compound.

[0037] The magnetic field applied to the compound in the mold may be a static magnetic field (a continuous, constant magnetic field). The magnetic field may also be a pulsed magnetic field (a pulsed magnetic field). The strength of the static magnetic field may be, for example, 0.5 to 2.5 T (Tesla), 1.0 to 2.5 T, or 2.0 to 2.5 T. The time for which the static magnetic field is applied to the compound in the mold may be, for example, 0.08 to 4 minutes, 0.5 to 4 minutes, or 1 to 4 minutes. The strength of the pulsed magnetic field may be, for example, 4 to 12 T, or 8 to 12 T. The number of times the pulsed magnetic field is applied to the compound may be one or more times.

[0038] The above manufacturing method may further include a cooling step, a demagnetization step, a thermosetting step, and a magnetization step as steps following step S2.

[0039] If the molded body does not solidify sufficiently when step S2 is performed while applying a magnetic field to the compound, the magnetization directions of the magnetic particles will align, causing each magnetic particle to move in the direction of the magnetic field generated in the molded body, potentially leading to deformation of the molded body. Therefore, from the viewpoint of suppressing this deformation, a demagnetization treatment of the molded body may be performed when removing the molded body from the mold.

[0040] If the binder in the molded body obtained in step S2 contains a cured product of a thermosetting resin, a thermosetting step may be included from the viewpoint of further advancing the curing of the thermosetting resin. In the thermosetting step, the molded body is heated to a temperature above the curing temperature of the thermosetting resin. As a result, the curing of the thermosetting resin in the molded body progresses further, and the bulk density, mechanical strength, and residual magnetic flux density of the molded body tend to increase further.

[0041] When performing a demagnetization process, in order to manufacture an anisotropic bonded magnet, as a subsequent process, a magnetization process may be further provided.

[0042] One embodiment of the compound is a compound used for manufacturing a bonded magnet, and includes magnetic particles and a biodegradable resin. The content described for the bonded magnet can be applied to the magnetic particles and the biodegradable resin.

[0043] The content of the magnetic particles may be, for example, 90% by mass or more, or 95% by mass or more based on the total amount of the compound.

[0044] In addition to the biodegradable resin, the compound may further include a thermosetting resin. The content described for the bonded magnet can be applied to the thermosetting resin.

[0045] The content of the thermosetting resin may be 1% by mass or more, 2% by mass or more, or 3% by mass or more, and may be 20% by mass or less, 10% by mass or less, 7% by mass or less, or 5% by mass or less based on the total amount of the compound.

[0046] The content of the thermosetting resin may be 1 part by mass or more, 2 parts by mass or more, or 3 parts by mass or more, and may be 20 parts by mass or less, 10 parts by mass or less, 7 parts by mass or less, or 5 parts by mass or less with respect to 100 parts by mass of the magnetic particles.

[0047] In addition to the magnetic particles, the biodegradable resin, and the thermosetting resin, the compound may further include an additive. Examples of the additive include a curing agent, a curing accelerator (curing catalyst), a polymerization initiator, a coupling agent (e.g., a silane coupling agent), a wax (lubricant), a flame retardant, and an organic solvent. When the compound includes a thermosetting resin, the compound may further include a curing agent.

[0048] The curing agent may contain an imidazole compound. Examples of the imidazole compound include 2-ethyl-4-methylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole (4-methyl-2-phenylimidazole), 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-aminopropyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, and 1-cyanoethyl-2-phenylimidazole, etc.

[0049] The content of the curing agent may be 0.01% by mass or more, 0.03% by mass or more, or 0.05% by mass or more, and may be 0.5% by mass or less, 0.3% by mass or less, 0.2% by mass or less, or 0.1% by mass or less, based on the total amount of the compound.

[0050] The content of the curing agent may be 1 part by mass or more, 1.5 parts by mass or more, or 1.8 parts by mass or more, and may be 20 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less, per 100 parts by mass of the thermosetting resin.

[0051] The form of the compound is not particularly limited. In the compound, the magnetic particles may be coated with a biodegradable resin. The compound may be said to include magnetic particles and a coating layer that coats the magnetic particles, and the coating layer contains a biodegradable resin. In this case, the compound may be an aggregate (powder) of coated particles having magnetic particles and a coating layer. In this case, weighing is easy and the handling property is also excellent. The coated particles can be prepared by dissolving the biodegradable resin in a solvent, bringing it into contact with the surface of the magnetic particles, and removing the solvent. As the solvent, for example, a ketone-based solvent such as methyl ethyl ketone can be used. When the compound contains a thermosetting resin or the like, in the compound, the magnetic particles may be coated with a curable composition containing a biodegradable resin and a thermosetting resin or the like.

[0052] One example of a method for recovering magnetic particles is to biodegrade the binder of a bonded magnet, which comprises magnetic particles and a binder that binds the magnetic particles together, thereby obtaining a mixture containing the decomposed magnetic particles and binder, and then recovering the magnetic particles from the mixture. In this recovery method, the binder contains a biodegradable resin.

[0053] In the above recovery method, the binder contains a biodegradable resin, which enables the binder to biodegrade. In this case, it is not necessary to apply high heat to decompose the binder, and magnetic particles with reduced thermal degradation can be recovered. Furthermore, if the binder is made of a biodegradable resin, the environmental pollution and impact on ecosystems can be reduced if the decomposed products are exposed to the environment.

[0054] The binder may be biodegraded using microorganisms, for example. The binder may be biodegraded by placing the bond magnet itself into an environment where microorganisms are present, such as soil or water, or by crushing the bond magnet before placing it into the above environment.

[0055] The means for recovering magnetic particles from the above mixture may be, for example, centrifugation.

[0056] The above recovery method may further include grinding a mixture containing magnetic particles and binder decomposition products. Grinding the mixture makes it easier to recover the magnetic particles.

[0057] Although several embodiments have been described above, this disclosure is not limited in any way to the embodiments described above. Furthermore, the descriptions of the embodiments described above are applicable to each other.

[0058] This disclosure provides novel bonded magnets and novel compounds for manufacturing bonded magnets. Furthermore, bonded magnets containing biodegradable resin as a binder, as described above, allow for binder removal under milder conditions than conventional methods, thereby suppressing thermal degradation of the recovered magnetic particles. Therefore, the magnetic particles can be reused.

[0059] 2... Anisotropic bonded magnet, 2A... Molded body, 3... Magnetic particles, 5... Binder, m... Magnetization direction of magnetic particles, M... Magnetization direction of bonded magnet.

Claims

1. A bonded magnet comprising magnetic particles and a binder that binds the magnetic particles together, wherein the binder contains a biodegradable resin.

2. The bonded magnet according to claim 1, wherein the biodegradable resin comprises at least one selected from the group consisting of polyester-based biodegradable resins, polyamide-based biodegradable resins, polyaspartic acid-based biodegradable resins, and polyhydroxyalkano-based biodegradable resins.

3. The bonded magnet according to claim 1, wherein the biodegradable resin comprises at least one selected from the group consisting of polybutylene succinate, polylactic acid, and polyhydroxyalkanoic acid.

4. The bonded magnet according to claim 1, wherein the binder further comprises a cured product of a thermosetting resin.

5. A compound used in the manufacture of bonded magnets, comprising magnetic particles and a biodegradable resin.

6. The compound according to claim 5, wherein the magnetic particles are coated with the biodegradable resin.

7. The compound according to claim 5, wherein the biodegradable resin comprises at least one selected from the group consisting of polyester-based biodegradable resins, polyamide-based biodegradable resins, polyaspartic acid-based biodegradable resins, and polyhydroxyalkano-based biodegradable resins.

8. The compound according to claim 5, further comprising a thermosetting resin.

9. A method for recovering magnetic particles, comprising: biodegrading the binder of a bonded magnet, which comprises magnetic particles and a binder that binds the magnetic particles together, to obtain a mixture containing the decomposed magnetic particles and the binder; and recovering the magnetic particles from the mixture, wherein the binder contains a biodegradable resin.

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