Bonded magnet, method for manufacturing a bonded magnet, compound powder, and method for manufacturing compound powder

Abstract

To provide a novel bonded magnet. [Solution] One aspect of the present disclosure provides a bonded magnet comprising magnetic particles and a binder that binds the magnetic particles together, wherein the binder is a cured product of a polymerizable composition containing a cyanoacrylate compound.

Description

Technical Field

[0001] The present disclosure relates to bonded magnets, a method for manufacturing bonded magnets, compound powder, and a method for manufacturing compound powder.

Background Art

[0002] As a raw material for bonded magnets, a compound containing magnetic particles and a thermosetting resin is used (for example, Patent Document 1). Further, Patent Document 2 discloses a resin particle mixture that can be used as a molding material for bonded magnets and the like and has an excellent pot life. More specifically, a bonded magnet manufactured from a resin particle mixture containing epoxy resin particles and phenolic resin particles containing a curing accelerator and Sm-Fe-N powder is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the manufacture of bonded magnets, a bonded magnet made of a cured product of a compound is manufactured by supplying the compound into a mold and heating and compressing it. If the curing of the molded body formed in the mold is insufficient, the molded body is likely to deform or break as it is taken out of the mold. Therefore, it would be useful to be able to use a compound that can be cured in a shorter time than before.

[0005] An object of the present disclosure is to provide a novel bonded magnet and a novel compound powder.

Means for Solving the Problems

[0006] This disclosure includes the following aspects: [1] Magnetic particles and, The binder includes a binder that binds the magnetic particles together, A bonded magnet wherein the binder is a cured product of a polymerizable composition containing a cyanoacrylate compound. [2] A compound powder used in the manufacture of bonded magnets, Magnetic particles and, A polymerizable composition containing a cyanoacrylate compound, A compound powder in which the magnetic particles are coated with the polymerizable composition. [3] The compound powder according to [2], wherein the cyanoacrylate compound contains at least one selected from the group consisting of methyl cyanoacrylate, ethyl cyanoacrylate, butyl acrylate, octyl cyanoacrylate, and bis(2-cyanoacrylate). [4] The compound powder according to [2] or [3], wherein the content of the cyanoacrylate compound is 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the magnetic particles. [5] The compound powder according to [2] to [4], wherein the polymerizable composition further comprises a compound having a (meth)acryloyl group. [6] A method for producing a compound powder, comprising the steps of dispersing magnetic particles in a solution containing a cyanoacrylate compound and a dehydrating solvent, volatilizing the dehydrating solvent, and coating the magnetic particles with a polymerizable composition containing the cyanoacrylate compound. [7] The method for producing compound powder according to [6], wherein the solution further comprises a compound having a (meth)acryloyl group. [8] A step of supplying a compound powder into a mold under a dry atmosphere, comprising magnetic particles and a polymerizable composition containing a cyanoacrylate compound, wherein the magnetic particles are coated with the polymerizable composition, A method for manufacturing a bonded magnet, comprising the steps of: compressing the compound powder and reacting the cyanoacrylate compound with water to obtain a molded body from the compound powder. [Effects of the Invention]

[0007] This disclosure provides novel bonded magnets and novel compound powders. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a bonded magnet. [Modes for carrying out the invention]

[0009] 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.

[0010] 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.

[0011] In this specification, (meth)acrylate means acrylate or the corresponding methacrylate. The same applies to other similar expressions such as (meth)acryloyl group.

[0012] One embodiment of a bonded magnet includes magnetic particles and a binder that binds the magnetic particles together. In this embodiment, the binder is a cured product of a polymerizable composition containing a cyanoacrylate compound.

[0013] The magnetic particles may be composed of a permanent magnet. The permanent magnet may be a samarium-cobalt (Sm-Co) based permanent magnet, a neodymium-iron-boron (Nd-Fe-B) based permanent magnet, a samarium-iron-nitrogen (Sm-Fe-N) based permanent magnet, an iron-cobalt (Fe-Co) based permanent magnet, or an Al-Ni-Co based permanent magnet (alnico magnet). The magnetic particles preferably contain a samarium-iron-nitrogen (Sm-Fe-N) based permanent magnet.

[0014] 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 alloys containing iron. The alloy containing iron may be, for example, at least one selected from the group consisting of 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 a soft magnetic material may be composed of amorphous iron or carbonyl iron.

[0015] The magnetic particles may contain a plurality of metal elements. In addition to the above elements, the 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. The 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 (О), beryllium (Be), phosphorus (P), boron (B), and silicon (Si).

[0016] The average particle diameter 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.

[0017] The average particle size of the magnetic particles is the particle size (D50) at which the cumulative percentage is 50% when a volume cumulative distribution curve is drawn from the smaller diameter side in the particle size distribution. The average particle size is measured by a laser diffraction particle size distribution measuring device.

[0018] 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 bonded magnet.

[0019] The binder is a cured product of a polymerizable composition containing a cyanoacrylate compound. The bonded magnet may contain a cured product of a compound powder described later and may be composed of a cured product of the compound powder. The compound powder may be composed of magnetic particles and a polymerizable composition.

[0020] The bonded magnet may be an anisotropic bonded magnet. An example of the anisotropic bonded magnet is shown in FIG. 1. The anisotropic bonded magnet 2A shown in FIG. 1 means a bonded magnet in which a plurality of magnetic particles 3 are bonded by a binder 5 and the magnetization directions m of each magnetic particle 3 are aligned along the magnetization direction M.

[0021] One embodiment of the compound powder is a compound powder used for manufacturing a bonded magnet, which includes magnetic particles and a polymerizable composition containing a cyanoacrylate compound. The compound powder may be composed of magnetic particles and a polymerizable composition.

[0022] The compound powder contains a cyanoacrylate compound that cures relatively rapidly by reaction with moisture. Therefore, it is possible to shorten the curing time in the bonded magnet. For this reason, it is possible to shorten the time for retaining the molded body in the mold, and the productivity of the bonded magnet can be improved. Since the compound powder has high reactivity, it is desirable to prepare and store it in an environment with reduced moisture (for example, a dry atmosphere, vacuum, etc.). The compound powder may be stored by accommodating the compound powder in a container and sealing it together with a dry gas, or by degassing or evacuating the inside of the container and then sealing it.

[0023] The magnetic particles contained in the compound powder can be treated according to the above-mentioned principles for bonded magnets.

[0024] The magnetic particle content may be, for example, 90% or more by mass or 95% or more by mass, based on the total amount of compound powder.

[0025] A cyanoacrylate compound is a compound having a cyanoacrylate group. In polymerizable compositions, the cyanoacrylate compound may be, for example, alkyl cyanoacrylate, allyl-2-cyanoacrylate, or aryloxyethyl-2-cyanoacrylate. The number of carbon atoms in the alkyl group in alkyl cyanoacrylate may be, for example, 1 to 10, 1 to 8, 1 to 6, or 1 to 4. The cyanoacrylate compound may contain at least one selected from the group consisting of methyl cyanoacrylate, ethyl cyanoacrylate, butyl acrylate, octyl cyanoacrylate, and bis(2-cyanoacrylate). The bis(2-cyanoacrylate) is a compound represented by the general formula: [H2C=C(CN)-CO-O]2R, where R represents an alkylene group or an arylene group. The number of carbon atoms in the alkylene group may be, for example, 1 to 10, 1 to 8, 1 to 6, or 1 to 4. The above-mentioned arylene group may be, for example, a 1,4-phenylene group.

[0026] The content of the cyanoacrylate compound may be, for example, 0.1 parts by mass or more and 10 parts by mass or less, 1 part by mass or more and 5 parts by mass or less, or 2 parts by mass or more and 3 parts by mass or less, per 100 parts by mass of the magnetic particles.

[0027] The polymerizable composition described above may further contain other components in addition to the cyanoacrylate compound. These other components may include, for example, diluents, reactive diluents, and polymerization initiators. When the polymerizable composition contains diluents and reactive diluents, the concentration of the cyanoacrylate compound in the compound powder can be diluted, improving storage stability. When the polymerizable composition contains polymerization initiators, the polymerization of the cyanoacrylate compound and other polymerizable compounds can be promoted, improving the mechanical strength of the cured product during the manufacture of bonded magnets and making it easier to remove the molded product from the mold.

[0028] The above-mentioned diluent and reactive diluent may be, for example, a polymerizable compound and an organic solvent. The polymerizable compound may be, for example, a compound having a (meth)acryloyl group, a compound having a polymerizable group in its side chain, and the like.

[0029] Polymerizable compositions may contain compounds having (meth)acryloyl groups, as they do not easily inhibit the polymerization reaction when cyanoacrylate compounds react with water. The compounds having (meth)acryloyl groups may be low-molecular-weight compounds or high-molecular-weight compounds. For example, the compounds having (meth)acryloyl groups may be (meth)acrylates, poly(meth)acrylates having (meth)acryloyl groups, etc.

[0030] In compounds having polymerizable groups in their side chains, the polymerizable group may be, for example, an allyl group. Examples of compounds having polymerizable groups in their side chains include poly(allyl-2-cyanoacrylate) and poly(alyloxyethyl-2-cyanoacrylate). When the polymerizable composition contains poly(allyl-2-cyanoacrylate) or poly(alyloxyethyl-2-cyanoacrylate), copolymerization with a cyanoacrylate compound strengthens the bonding between magnetic particles in the molded body (bonded magnet), making it easier to further increase the bulk density, mechanical strength, and residual magnetic flux density of the molded body (bonded magnet).

[0031] If the polymerizable composition contains a compound having a (meth)acryloyl group, the content of the compound having a (meth)acryloyl group may be, for example, 1 to 300 parts by mass, 5 to 100 parts by mass, or 10 to 50 parts by mass, per 100 parts by mass of the cyanoacrylate compound.

[0032] The polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator, and may be a radical polymerization initiator. When the polymerizable composition contains a compound having a (meth)acryloyl group, further inclusion of a polymerization initiator further promotes the curing of the compound having a (meth)acryloyl group in the molded body, making it easier to further increase the bulk density, mechanical strength, and residual magnetic flux density of the molded body (bonded magnet).

[0033] In the compound powder described above, the magnetic particles are coated with a polymerizable composition. In other words, each magnetic particle in the compound powder has a coating layer, and this coating layer contains a polymerizable composition. The coating layer may consist of a polymerizable composition. If the polymerizable composition contains a compound having a (meth)acryloyl group, coating the magnetic particles with the polymerizable composition becomes easier, and the stability of the coating layer made of the polymerizable composition can be improved.

[0034] One embodiment of a method for producing compound powder comprises step S1, in which magnetic particles are dispersed in a solution containing a polymerizable composition containing a cyanoacrylate compound and a dehydrating solvent, the dehydrating solvent is volatilized, and the magnetic particles are coated with the polymerizable composition containing the cyanoacrylate compound. This step makes it possible to produce compound powder in which magnetic particles are coated with a polymerizable composition.

[0035] As the dehydrating solvent, for example, a dehydrated organic solvent can be used. Furthermore, from the viewpoint of easy removal by volatilization, the boiling point (boiling point at atmospheric pressure) of the organic solvent is preferably 150°C or lower, may be 100°C or lower, or 80°C or lower, and may be 50°C or higher, or 60°C or higher. Examples of such organic solvents include ketone solvents such as acetone and methyl ethyl ketone, and tetrahydrofuran.

[0036] In this specification, "dehydrated solvent" means a solvent in which the water content is 0.1% by mass or less. The water content of an organic solvent may be, for example, 0.05% by mass or less, 0.01% by mass or less, or it may not contain any water at all.

[0037] The above solution may further contain, in addition to the cyanoacrylate compound, a compound having a (meth)acryloyl group, a polymerization initiator, and so on. The compounds having a (meth)acryloyl group and the polymerization initiator can be applied as described above for the compound powder.

[0038] Step S1 may be carried out under a dry atmosphere from the viewpoint of suppressing the polymerization initiation of the cyanoacrylate compound.

[0039] In this specification, "dry atmosphere" refers to an environment with a low moisture content. A dry atmosphere is, for example, one with an absolute humidity of 1 g / cm³ at 25°C. 3 The atmosphere may be a gas atmosphere (e.g., dry air, dry nitrogen gas atmosphere, dry noble gas atmosphere, etc.) or a vacuum atmosphere. The absolute humidity of the gas atmosphere constituting the dry atmosphere at 25°C is, for example, 0.5 g / cm³. 3 The following, or 0.1 g / cm³ 3 The following may apply, and the gas atmosphere constituting the dry atmosphere may not contain any moisture.

[0040] One embodiment of a method for manufacturing bonded magnets comprises: step S2 of supplying a compound powder into a mold under a dry atmosphere, the compound powder comprising magnetic particles and a polymerizable composition containing a cyanoacrylate compound, wherein the magnetic particles are coated with the polymerizable composition; and step S3 of compressing the compound powder and reacting the cyanoacrylate compound with moisture to obtain a molded body from the compound powder.

[0041] In this embodiment, since the compound powder contains a cyanoacrylate compound, it is desirable that the inner wall of the mold into which the compound powder is supplied (the surface in contact with the compound powder) be treated for mold release. The inner wall of the mold may have, for example, a mold release layer made of a fluororesin such as polytetrafluoroethylene. The mold release layer may be coated with a fluororesin, or it may consist of a film made of a fluororesin.

[0042] In this embodiment, the compound powder contains a cyanoacrylate compound, and therefore hardening begins relatively quickly upon reaction with moisture. Consequently, the supply of the compound powder into the mold in step 2 is carried out under a dry atmosphere.

[0043] The dry atmosphere may be, for example, dry air, a dry nitrogen gas atmosphere, a dry noble gas atmosphere, or a vacuum atmosphere.

[0044] In step S3, a molded body is obtained by compressing the compound powder and reacting it with water and a cyanoacrylate compound. The water to be reacted with the cyanoacrylate compound may be supplied, for example, by changing the atmosphere in contact with the compound powder from a dry atmosphere to a moisture-containing atmosphere.

[0045] Step S3 may involve compressing the compound powder and heating it. If the polymerizable composition in the compound powder further contains a compound having a (meth)acryloyl group and a thermal polymerization initiator, heating the compound powder can promote the thermal polymerization (e.g., radical polymerization) of the polymerizable compound, such as the compound having a (meth)acryloyl group, thereby further advancing the curing of the compound powder.

[0046] Step S3 may be, for example, a step of compressing the compound powder in a mold heated at a molding temperature T. The molding temperature T may be above the temperature at which the curing of the polymerizable composition begins. The curing temperature specified herein also varies depending on the components contained in the polymerizable composition, but for example, if a thermal polymerization initiator is included, it is the temperature at which the thermal polymerization initiator cleaves and polymerization initiation species (e.g., radicals) are generated.

[0047] The compression of the compound powder in step S3 may be carried out while applying a magnetic field to the compound powder, or the compound powder in the mold may be compressed while applying a magnetic field to the compound powder in the mold heated at the molding temperature T. Each magnetic particle in the compound powder 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 powder 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.

[0048] In step S3, the curing of the polymerizable composition forms a molded body (bonded magnet 2) containing multiple magnetic particles oriented along the magnetic field H and the cured polymerizable composition. In other words, a molded body (bonded magnet 2) made of cured compound powder is formed. The magnetization direction M of the entire molded body (bonded magnet 2) is approximately or perfectly parallel to the direction of the magnetic field H applied to the compound powder in step S3. In this case, the molded body (bonded magnet 2) can be called an anisotropic bonded magnet 2A.

[0049] The molding temperature T may be, for example, 60 to 180°C or 100 to 150°C. The heating time may be, for example, 15 minutes or less, 0.5 to 15 minutes, or 0.5 to 10 minutes.

[0050] The molding pressure in process S3 may be 500-2000 MPa, 700-2000 MPa, or 980-2000 MPa.

[0051] The magnetic field applied to the compound powder 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 Tesla, 1.0 to 2.5 Tesla, or 2.0 to 2.5 Tesla. The time for which the static magnetic field is applied to the compound powder 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 Tesla, or 8 to 12 Tesla. The number of times the pulsed magnetic field is applied to the compound powder may be one or more times.

[0052] The above manufacturing method may include a step S1 for preparing the compound powder before step S2, and may further include a cooling step, a demagnetization step, a thermosetting step, and a magnetization step as steps following step S3. The step S1 for preparing the compound powder may be the step S1 described in the above-described method for manufacturing the compound powder.

[0053] If the molded body does not harden sufficiently when step S3 is performed while applying a magnetic field to the compound powder, the magnetic particles may move in a direction that causes them to protrude from the surface of the molded body along the direction of the magnetic field generated in the molded body due to the alignment of the magnetization directions of the magnetic particles, which can lead to deformation of the molded body. Therefore, generally, from the viewpoint of suppressing this deformation, a method is taken to suppress the deformation of the molded body by performing a demagnetization treatment on the molded body when it is removed from the mold. In contrast, in the above manufacturing method, since a compound powder that hardens quickly is used, it is possible to harden the molded body appropriately when it is removed from the mold, and deformation of the molded body is suppressed, so a demagnetization step is not required.

[0054] A thermosetting step may be included to further promote the curing of the polymerizable composition in the molded body obtained in step S3. The thermosetting step is more effective when the polymerizable composition contains a compound having a (meth)acryloyl group. In the thermosetting step, the molded body is heated at a temperature above the curing temperature of the polymerizable composition. As a result, the curing of the polymerizable composition in the molded body progresses further, and the bulk density, mechanical strength, and residual magnetic flux density of the molded body (bonded magnet) tend to increase further.

[0055] When a demagnetization process is performed, a magnetization process may be further included as a subsequent step in order to manufacture an anisotropic bonded magnet.

[0056] 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. [Industrial applicability]

[0057] This disclosure provides novel bonded magnets and novel compound powders. [Explanation of symbols]

[0058] 2...Bonded magnet, 2A...Anisotropic bonded magnet, 3...Magnetic particle, 5...Binder, m...Magnification direction, M...Magnification direction, H...Magnetic field.

Claims

1. Magnetic particles and, The binder includes a binder that binds the magnetic particles together, A bonded magnet wherein the binder is a cured product of a polymerizable composition containing a cyanoacrylate compound.

2. A compound powder used in the manufacture of bonded magnets, Magnetic particles and, A polymerizable composition containing a cyanoacrylate compound, A compound powder in which the magnetic particles are coated with the polymerizable composition.

3. The compound powder according to claim 2, wherein the cyanoacrylate compound contains at least one selected from the group consisting of methyl cyanoacrylate, ethyl cyanoacrylate, butyl acrylate, octyl cyanoacrylate, and bis(2-cyanoacrylate).

4. The compound powder according to claim 2, wherein the content of the cyanoacrylate compound is 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the magnetic particles.

5. The compound powder according to claim 2, wherein the polymerizable composition further comprises a compound having a (meth)acryloyl group.

6. A method for producing a compound powder, comprising the steps of: dispersing magnetic particles in a solution containing a cyanoacrylate compound and a dehydrating solvent; volatilizing the dehydrating solvent; and coating the magnetic particles with a polymerizable composition containing the cyanoacrylate compound.

7. The method for producing compound powder according to claim 6, wherein the solution further comprises a compound having a (meth)acryloyl group.

8. A step of supplying a compound powder into a mold under a dry atmosphere, wherein the compound powder comprises magnetic particles and a polymerizable composition containing a cyanoacrylate compound, and the magnetic particles are coated with the polymerizable composition. A method for manufacturing a bonded magnet, comprising the steps of: compressing the compound powder and reacting the cyanoacrylate compound with water to obtain a molded body from the compound powder.

Images