Cylindrical bonded magnet, method for manufacturing same, and mold for molding same

Abstract

Provided are a cylindrical bonded magnet having a sinusoidal or approximately sinusoidal waveform of magnetic flux density, a method for manufacturing the same, and a mold for molding the same. A method for manufacturing a cylindrical bonded magnet, the method including: (1) a step for preparing a mold having an inner mold section (1) including a non-magnetic member, an outer mold section (2) including a non-magnetic member, a first orientation magnet (3), and a second orientation magnet (4); and (2) a molding step in which a region between the outer surface of the inner mold part and the inner surface of the outer mold part is filled with a bonded magnet resin composition and molded while applying a magnetic field using the first orientation magnet (3) and the second orientation magnet (4), thereby obtaining a cylindrical bonded magnet.

Description

Technical Field

[0001] The present application relates to a cylindrical bonded magnet, a method for manufacturing the same, and a mold for forming the same. Background Art

[0002] Among cylindrical magnets, there are known cylindrical magnets with four poles and a magnetic flux density of a sinusoidal waveform (Patent Document 1), and cylindrical magnets with two poles and a magnetic flux density of a waveform close to a triangular wave (Patent Document 2). However, in particular, when manufacturing a cylindrical magnet with a sinusoidal waveform of two poles, the waveform of the magnetic field during magnetic field orientation is different from the waveform of the magnetic flux density of the magnet actually obtained. Therefore, it is also difficult to manufacture a cylindrical magnet with a magnetic flux density close to a sinusoidal waveform using the methods described in Patent Documents 1 and 2.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-212863

[0006] Patent Document 2: Japanese Patent Application Publication No. 2019-123126 Summary of the invention

[0007] Problems to be solved by the invention

[0008] The object of the present application is to provide a cylindrical bonded magnet having a magnetic flux density that is a sinusoidal waveform or a near-sinusoidal waveform, a method for producing the same, and a molding die therefor.

[0009] Solutions to the problem

[0010] A method for manufacturing a cylindrical bonded magnet according to one embodiment of the present application includes:

[0011] (1) preparing a mold including an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first orientation magnet, and a second orientation magnet,

[0012] The inner mold portion has an outer surface whose shape is circular in a cross section in a given direction,

[0013] The outer mold portion has an inner surface which is located at a position separated from the outer surface of the inner mold portion and has a circular shape in a cross section in the given direction.

[0014] The mold is arranged so that the first orientation magnet and the second orientation magnet clamp the inner mold portion and the outer mold portion in the given direction; and

[0015] (2) a step of applying a magnetic field using the first orientation magnet and the second orientation magnet while filling and molding the area between the outer surface of the inner mold portion and the inner surface of the outer mold portion with a resin composition for a bonded magnet, thereby obtaining a cylindrical bonded magnet;

[0016] In which, in a cross-section in the above-mentioned given direction, the straight-line distance in the direction of magnetic field application of the above-mentioned first orientation magnet and the above-mentioned second orientation magnet and tangent to the circle defined by the inner surface of the above-mentioned outer mold portion is shorter than the straight-line distance in the direction of magnetic field application of the above-mentioned first orientation magnet and the above-mentioned second orientation magnet and passing through the center of the circle defined by the outer surface of the above-mentioned inner mold portion.

[0017] A cylindrical bonded magnet according to one embodiment of the present application includes anisotropic rare earth magnetic powder and resin, is oriented in two polarities with respect to a radial direction, and has a surface magnetic flux density on the outer peripheral side with a deformation rate of 15% or less with respect to a sine wave curve.

[0018] A cylindrical bonded magnet molding die according to one embodiment of the present application includes an inner die portion including a non-magnetic member, an outer die portion including a non-magnetic member, a first orientation magnet, and a second orientation magnet.

[0019] The inner mold portion has an outer surface whose shape is circular in a cross section in a given direction,

[0020] The outer mold portion has an inner surface which is located at a position separated from the outer surface of the inner mold portion and has a circular shape in a cross section in the given direction.

[0021] The first orientation magnet and the second orientation magnet are arranged so as to sandwich the inner mold portion and the outer mold portion, thereby applying a magnetic field in the given direction during magnetic field orientation.

[0022] In a cross-section in the above-mentioned given direction, the straight-line distance in the direction of magnetic field application of the above-mentioned first orientation magnet and the above-mentioned second orientation magnet passing through the tangent point of the circle defined by the inner surface of the above-mentioned outer mold portion is shorter than the straight-line distance in the direction of magnetic field application of the above-mentioned first orientation magnet and the above-mentioned second orientation magnet passing through the center of the circle defined by the outer surface of the above-mentioned inner mold portion.

[0023] Effects of the Invention

[0024] According to the method for manufacturing a cylindrical bonded magnet and the mold for forming a cylindrical bonded magnet of the present application, a cylindrical bonded magnet having a magnetic flux density waveform that is a sine waveform or a waveform close to a sine waveform can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1AThis is a cross-sectional view of a mold for forming a cylindrical bonded magnet used in Example 1.

[0026] Figure 1B This is a graph in which the surface magnetic flux density at the outer periphery of the cylindrical bonded magnet produced in Example 1 is plotted against the angle.

[0027] Figure 1C This is an image diagram showing the magnetization direction of each specific region of the cylindrical bonded magnet of Example 1.

[0028] Figure 1D This is a cross-sectional view of the mold for molding the cylindrical bonded magnet used in Example 1 in the mold opening state when the molded product is taken out.

[0029] Figure 2A This is a graph obtained by plotting the orientation magnetic field versus angle for Example 2.

[0030] Figure 2B This is a graph in which the surface magnetic flux density at the outer periphery of the cylindrical bonded magnet of Example 2 is plotted against the angle.

[0031] Figure 3A This is a cross-sectional view of a mold for forming a cylindrical bonded magnet used in Example 3.

[0032] Figure 3B This is a graph obtained by plotting the orientation magnetic field versus angle for Example 3.

[0033] Figure 3C This is a graph in which the surface magnetic flux density at the outer circumference of the cylindrical bonded magnet of Example 3 is plotted against the angle.

[0034] Figure 4A This is a cross-sectional view of a mold for forming a cylindrical bonded magnet used in Example 4.

[0035] Figure 4B This is a graph obtained by plotting the orientation magnetic field versus angle for Example 4.

[0036] Figure 4C This is a graph in which the surface magnetic flux density at the outer circumference of the cylindrical bonded magnet of Example 4 is plotted against the angle.

[0037] Figure 4D This is a cross-sectional view of the mold for molding a cylindrical bonded magnet used in Example 4 in the mold opening state when the molded product is taken out.

[0038] Figure 5A This is a cross-sectional view of a mold for forming a cylindrical bonded magnet used in Example 5.

[0039] Figure 5BThis is a graph of Example 5 in which the orientation magnetic field is plotted against the angle.

[0040] Figure 5C This is a graph in which the surface magnetic flux density at the outer periphery of the cylindrical bonded magnet of Example 5 is plotted against the angle.

[0041] Fig. 6A This is a cross-sectional view of a mold for forming a cylindrical bonded magnet used in Example 6.

[0042] Figure 6B This is a graph of Example 6 in which the orientation magnetic field is plotted against the angle.

[0043] Figure 6C This is a graph in which the surface magnetic flux density at the outer periphery of the cylindrical bonded magnet of Example 6 is plotted against the angle.

[0044] Fig. 7A This is a cross-sectional view of a mold for forming a cylindrical bonded magnet used in Comparative Example 1.

[0045] Figure 7B This is a graph in which the surface magnetic flux density at the outer circumference of the cylindrical bonded magnet of Comparative Example 1 is plotted against the angle.

[0046] Figure 7C This is an image diagram showing the magnetization direction of each specific area of ​​the cylindrical bonded magnet of Comparative Example 1. The area surrounded by the quadrilateral corresponds to Figure 7B The parts indicated by arrows.

[0047] Fig. 8A This is a graph in which the orientation magnetic field is plotted against the angle for Comparative Example 2.

[0048] Figure 8B This is a graph in which the surface magnetic flux density at the outer circumference of the cylindrical bonded magnet of Comparative Example 2 is plotted against the angle.

[0049] Fig.9A This is a cross-sectional view of a mold for forming a cylindrical bonded magnet used in Comparative Example 3.

[0050] Fig. 9B This is a graph in which the orientation magnetic field is plotted against the angle for Comparative Example 3.

[0051] Fig. 9C This is a graph in which the surface magnetic flux density at the outer circumference of the cylindrical bonded magnet of Comparative Example 3 is plotted against the angle.

[0052] Explanation of symbols

[0053] 1: Inner mold part

[0054] 2: Outer mold part

[0055] 3: Magnet for the first orientation

[0056] 4: Second orientation magnet

[0057] 5: Magnetic components

[0058] 6: Chamber

[0059] X: Linear distance between the first orientation magnet and the second orientation magnet in the direction of magnetic field application tangent to the circle defined by the inner surface of the outer mold portion

[0060] Y: The straight-line distance between the first orientation magnet and the second orientation magnet in the magnetic field application direction passing through the center of a circle defined by the outer surface of the inner mold portion

[0061] Z: The straight-line distance between the first orientation magnet and the second orientation magnet in the magnetic field application direction tangent to the circle defined by the outer surface of the outer mold portion DETAILED DESCRIPTION

[0062] Hereinafter, the embodiments of the present application will be described in detail. However, the embodiments shown below are examples for concretizing the technical ideas of the present application, and the present application is not limited to the following embodiments. It should be noted that in this specification, the term "process" is not only an independent process, but also is included in this term as long as the intended purpose of the process can be achieved when it cannot be clearly distinguished from other processes. In addition, the numerical range represented by "~" represents the range of the minimum and maximum values ​​recorded before and after the "~" as a whole.

[0063] <<Mold for forming cylindrical bonded magnet>>

[0064] The forming die of the cylindrical bonded magnet of this embodiment has:

[0065] an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first orientation magnet, and a second orientation magnet,

[0066] The inner mold portion has an outer surface whose shape is circular in a cross section in a given direction,

[0067] The outer mold portion is located at a position separated from the outer surface of the inner mold portion and has an inner surface whose shape is a circle in a cross section in the given direction.

[0068] The first orientation magnet and the second orientation magnet are arranged so as to sandwich the inner mold portion and the outer mold portion, thereby applying a magnetic field in the given direction during magnetic field orientation.

[0069] In a cross-section in the above-mentioned given direction, the straight-line distance in the direction of magnetic field application of the above-mentioned first orientation magnet and the above-mentioned second orientation magnet passing through the tangent point of the circle defined by the inner surface of the above-mentioned outer mold portion is shorter than the straight-line distance in the direction of magnetic field application of the above-mentioned first orientation magnet and the above-mentioned second orientation magnet passing through the center of the circle defined by the outer surface of the above-mentioned inner mold portion.

[0070] exist Figure 1A , a cross-sectional view in a given direction of a mold for forming a cylindrical bonded magnet according to this embodiment is shown. Figure 3A , Figure 4A , Figure 5A , Fig. 6A , a cross-sectional view of a molding die in a given direction of another embodiment of the present invention is shown in FIG. Fig. 7A and Fig.9A A cross-sectional view in a given direction of a molding die for a cylindrical bonded magnet of a comparative example is shown in FIG. Any mold has an inner mold portion 1 including a non-magnetic member, an outer mold portion 2 including a non-magnetic member, a first orientation magnet 3, and a second orientation magnet 4. These molds are specific examples of molding dies in which the outer mold portion 2 is composed of two parts that can be separated in the upper and lower directions on the paper. The outer mold portion 2 can be opened while separating in conjunction with the opening action of the mold of the molding machine to take out the molded product. Figure 1A and Figure 4A The cross-sectional views of the molding die when the mold is opened are shown in Figure 1D and Figure 4D In the figure, the mold opening direction is indicated by an arrow. The outer mold part 2 is separated into two parts in the figure, but it can also be separated into three or more parts, and can also be an inseparable integral component.

[0071] According to the results of various experiments, it is inferred that the magnetic permeability of the bonded magnet resin composition when it is in a molten state is greater than the magnetic permeability of the bonded magnet at room temperature. That is, it is believed that at the high temperature when the bonded magnet is formed when the bonded magnet resin composition is in a molten state, the orientation magnetic field is easy to pass through the center of the cylindrical bonded magnet, and the size of the orientation magnetic field applied to the resin composition at the center and the periphery of the bonded magnet is different. In particular, the two-pole magnet is different from the multi-pole magnet in that a magnetic field is applied in one direction. Therefore, in order to impart a sinusoidal magnetic field, the change in the magnetic permeability of the bonded magnet resin composition must be considered. In the mold of this embodiment, the straight-line distance X of the magnetic field application direction of the first orientation magnet and the second orientation magnet tangent to the circle defined by the inner surface of the outer mold part is shorter than the straight-line distance Y of the magnetic field application direction of the first orientation magnet and the second orientation magnet passing through the center of the circle defined by the outer surface of the inner mold part, so that the distance between the orientation magnets is shorter on the outside than in the center of the magnet. As a result, the magnitude of the orientation magnetic field applied to the bonded magnet resin composition during molding can be made uniform or nearly uniform, and a cylindrical magnet having a magnetic flux density waveform that is sinusoidal or nearly sinusoidal can be produced.

[0072] The inner mold portion 1 includes a non-magnetic component and is located in the center of the mold. Non-magnetic steels can be cited as non-magnetic materials constituting the non-magnetic component, specifically SUS304, HPM75, KN20, etc. The inner mold portion 1 can be composed only of non-magnetic components. The inner mold portion 1 has an outer surface whose shape is a circle in a cross-section in a given direction. Here, the given direction refers to the magnetic field orientation direction. From the aspect of deformation rate, it is preferred to have a magnetic component 5 inside the inner mold portion 1. By configuring the magnetic component 5 inside the inner mold portion 1, the deformation rate of the surface magnetic flux density on the outer peripheral side relative to the sine wave curve can be reduced. The magnetic component 5 is composed of magnetic steel. As magnetic steel constituting the magnetic component 5, NAK80, SS400, etc. can be cited.

[0073] The outer mold part 2 includes a non-magnetic member and is located at a position separated from the outer surface of the inner mold part 1. As the non-magnetic material constituting the non-magnetic member, as described for the inner mold part 1. The outer mold part 2 can be composed only of non-magnetic members. The outer mold part 2 has an inner surface whose shape is circular in a cross-section in the given direction. The gap formed by the outer periphery of the inner mold part 1 and the inner periphery of the outer mold part 2 becomes a cavity 6. When used for the manufacture of bonded magnets, the resin composition for bonded magnets is filled in the cavity 6 and formed.

[0074] The first orientation magnet 3 and the second orientation magnet 4 are arranged in such a manner as to clamp the inner mold portion 1 and the outer mold portion 2 in the given direction. Examples of these orientation magnets include electromagnets, permanent magnets, and the like. From the perspective of being able to change the magnetic field and orient with a larger orientation magnetic field, the orientation magnets are preferably electromagnets. Here, the first orientation magnet 3 and the second orientation magnet 4 clamping the inner mold portion 1 and the outer mold portion 2 means that the orientation magnets do not need to clamp the entire outer mold portion 2, but at least clamp the portion of the outer mold portion 2 that constitutes the cavity. The first orientation magnet 3 and the second orientation magnet 4 clamp the entire cavity 6. The first orientation magnet 3 and the second orientation magnet 4 clamp the portion of the cavity that constitutes the outer mold portion 2 in the vertical direction from one end to the other end in the direction of opening and closing of the mold. For Figure 1A , Figure 3A , Fig. 6A In the mold shown in FIG. 1 , the first orientation magnet 3 and the second orientation magnet 4 sandwich the entire outer mold portion 2. Figure 4A , Figure 5A In the mold shown, the first orientation magnet 3 and the second orientation magnet 4 sandwich all of the inner mold section 1 and the outer mold section 2 , and sandwich all of the portion constituting the cavity of the outer mold section 2 .

[0075] In a cross section in the given direction, the straight-line distance X of the magnetic field application direction of the first orientation magnet and the second orientation magnet tangent to the circle defined by the inner surface of the outer mold portion is shorter than the straight-line distance Y of the magnetic field application direction of the first orientation magnet and the second orientation magnet passing through the center of the circle defined by the outer surface of the inner mold portion. Figure 1A In the figure, the straight-line distance X and the straight-line distance Y are represented by dotted lines. The fact that the straight-line distance X is shorter than the straight-line distance Y means that the distance between the orientation magnets in the periphery is shorter than the distance between the orientation magnets in the center of the mold. The upper limit of the ratio X / Y of the straight-line distance X to the straight-line distance Y is preferably less than 0.9, more preferably less than 0.8. The lower limit may be greater than 0.2. By making the ratio X / Y of the straight-line distance X to the straight-line distance Y within the above range, it is easy to orient the bonded magnet in the center of the cavity during the forming of the bonded magnet, and there is a tendency to easily obtain a bonded magnet whose surface magnetic flux density waveform is a sine waveform or a waveform close to a sine waveform.

[0076] It should be noted that in Fig. 7A , Fig.9A In the mold of the comparative example shown, the straight-line distance X in the direction of magnetic field application of the first orientation magnet and the second orientation magnet being tangent to the circle defined by the inner surface of the outer mold portion is the same length as the straight-line distance Y in the direction of magnetic field application of the first orientation magnet and the second orientation magnet passing through the center of the circle defined by the outer surface of the inner mold portion.

[0077] In a cross section in a given direction, the shape of the outer periphery of the outer mold portion 2 is not a rectangle, and for example, a true circle or an ellipse can be cited. From the perspective of taking into account both the ease of mold manufacturing and the ease of manufacturing a bonded magnet with a surface magnetic flux density waveform that is a sine waveform or a waveform close to a sine waveform, an ellipse is preferred. In addition, the lower limit of the ratio of the long radius to the short radius of the ellipse is preferably greater than 1.1, and more preferably greater than 1.3. The upper limit can be less than 2. When the ratio of the long radius to the short radius is less than 2, a sufficient orientation magnetic field can be obtained. In addition, when the ratio of the long radius to the short radius is greater than 1.1, it is easier to take into account both the ease of mold manufacturing and the ease of manufacturing a bonded magnet with a surface magnetic flux density waveform that is a sine waveform or a waveform close to a sine waveform.

[0078] The linear distance Z in the direction of magnetic field application in which the first orientation magnet and the second orientation magnet are tangent to the circle defined by the outer surface of the outer mold portion can be zero, and can be 1 mm or more, preferably 3 mm or more, in consideration of both mass production and sinusoidal waveform. In addition, the linear distance Z is preferably 1% or more of the linear distance Y, preferably 80% or less. The upper limit of the linear distance Z can be 50% or less.

[0079] <<Method for producing cylindrical bonded magnet>>

[0080] The method for manufacturing a cylindrical bonded magnet according to the present embodiment includes:

[0081] (1) preparing a mold including an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first orientation magnet, and a second orientation magnet,

[0082] The inner mold portion has an outer surface whose shape is circular in a cross section in a given direction,

[0083] The outer mold portion is located at a position separated from the outer surface of the inner mold portion and has an inner surface whose shape is a circle in a cross section in the given direction.

[0084] The mold is arranged in such a manner that the first orientation magnet and the second orientation magnet clamp the inner mold portion and the outer mold portion in the given direction;

[0085] (2) a step of applying a magnetic field using the first orientation magnet and the second orientation magnet while filling and molding the area between the outer surface of the inner mold portion and the inner surface of the outer mold portion with a resin composition for a bonded magnet, thereby obtaining a cylindrical bonded magnet;

[0086] In a cross-section in the above-mentioned given direction, the straight-line distance in the direction of magnetic field application of the above-mentioned first orientation magnet and the above-mentioned second orientation magnet and tangent to the circle defined by the inner surface of the above-mentioned outer mold portion is shorter than the straight-line distance in the direction of magnetic field application of the above-mentioned first orientation magnet and the above-mentioned second orientation magnet and passing through the center of the circle defined by the outer surface of the above-mentioned inner mold portion.

[0087] In the step (1) of preparing a mold, a mold for forming the cylindrical bonded magnet of the present embodiment is prepared. In the molding step (2) of obtaining the cylindrical bonded magnet, the above-mentioned mold is used to fill and mold the resin composition for bonded magnet in the area (cavity) between the outer surface of the above-mentioned inner mold part and the inner surface of the above-mentioned outer mold part. During molding, the resin composition for bonded magnet is oriented while applying a magnetic field using the above-mentioned first orientation magnet and the above-mentioned second orientation magnet. As a molding method, injection molding can be mentioned.

[0088] <Resin composition for bonded magnet>

[0089] The bonded magnet resin composition used in the molding step (2) preferably contains a resin and anisotropic rare earth magnetic powder.

[0090] <Anisotropic rare earth magnetic powder>

[0091] The material of the anisotropic rare earth magnetic powder is not particularly limited, and examples thereof include SmFeN-based, NdFeB-based, and SmCo-based rare earth magnetic materials. Among them, SmFeN-based magnetic powder is preferred in terms of heat resistance and the absence of rare metals. The magnetic force of SmFeN-based magnetic powder is stronger than that of ferrite-based powder, and a high magnetic force can be generated even in a relatively small amount. In addition, compared with other rare earth-based powders such as NdFeB-based and SmCo-based powders, SmFeN-based powders have a smaller particle size, are suitable as fillers for base material resins, and are not prone to rust. Examples of SmFeN-based magnetic powders include Th2Zn 17 The crystal structure of the type, the general formula is composed of Sm x Fe 100-x-y N y The nitride represented by is composed of rare earth metal Sm, iron Fe and nitrogen N. Here, it is preferred that x is 8.1 atomic % or more and 10 atomic % or less, y is 13.5 atomic % or more and 13.9 atomic % or less, and the remainder is mainly Fe. For example, Sm2Fe 17 N3.

[0092] The average particle size of the anisotropic rare earth magnetic powder is preferably 10 μm or less, more preferably 1 μm or more and 5 μm or less. If it is 10 μm or less, it is not easy to produce uneven parts, cracks, etc. on the surface of the product, and the appearance is excellent. In addition, low cost can be achieved. If the average particle size is greater than 10 μm, there is a risk of producing uneven parts, cracks, etc. on the surface of the product and poor appearance. On the other hand, if the average particle size is less than 1 μm, the cost of the magnetic powder becomes high, so it is not preferred from the perspective of low cost. For the average particle size of the anisotropic rare earth magnetic powder, in the volume-based particle size distribution obtained by the laser scattering method, the volume cumulative value from the small particle size side becomes 50% of the particle size. In addition, the ratio D90 / D10 of the 10% particle size D10 to the 90% particle size D90 in the cumulative particle size distribution based on the volume basis is preferably 4.5 or less, more preferably 4 or less, and particularly preferably 3.5 or less. By setting the particle size distribution D90 / D10 to 4.5 or less, the flowability is improved even when a thin-walled magnet is formed, thereby making it easy to obtain a bonded magnet with good orientation and a high orientation ratio.

[0093] The filling rate of the anisotropic rare earth magnetic powder (the content of the magnetic powder in the resin composition for bonded magnets) is preferably 50 vol% to 65 vol%, more preferably 50 vol% to 60 vol%, further preferably 50 vol% to 59 vol%, and particularly preferably 51 vol% to 56 vol%. By setting it to 65 vol% or less, there is a tendency to suppress the reduction of the magnetic flux density even in the case of a cylindrical bonded magnet and a thin wall, and by setting it to 50 vol% or more, the proportion of the magnetic powder in the bonded magnet can be increased, and the magnetic flux density can be further improved.

[0094] Examples of the resin include thermoplastic resins such as polyphenylene ether, polypropylene, polyethylene, polyvinyl chloride, polyester, polyamide, polycarbonate, polyphenylene sulfide, and acrylic resin.

[0095] <Method for producing anisotropic rare earth magnetic powder of SmFeN type>

[0096] The SmFeN-based anisotropic rare earth magnetic powder can be purchased or prepared by a known method. For example, it can be produced by the following method.

[0097] A step of mixing a solution containing metals such as Sm and Fe with a precipitant to obtain a precipitate containing metals such as Sm and Fe (precipitation step);

[0098] a step of calcining the precipitate to obtain an oxide containing metals such as Sm and Fe (oxidation step);

[0099] A step of heat-treating the oxide in an atmosphere containing a reducing gas to obtain a partial oxide (pretreatment step);

[0100] A step of reducing the above-mentioned part of the oxide (reduction step); and

[0101] A step of nitriding the alloy particles obtained in the reduction step (nitriding step)

[0102] In addition, regarding the method for producing the SmFeN-based anisotropic rare earth magnetic powder, for example, reference can be made to the descriptions in Japanese Unexamined Patent Publication No. 11-189811, WO2022 / 107462, and the like.

[0103] The anisotropic rare earth magnetic powder produced by the above-mentioned production method may be used directly, or may be further processed as follows:

[0104] A phosphoric acid treatment step is performed in which an inorganic acid is added to a slurry containing anisotropic rare earth magnetic powder, water, and a phosphoric acid compound to obtain anisotropic rare earth magnetic powder having a surface coated with phosphate.

[0105] [Silicon dioxide treatment process]

[0106] The anisotropic rare earth magnetic powder after phosphoric acid treatment can be treated with silica as needed. By forming a silica film on the magnetic powder, oxidation resistance can be improved. The silica film can be formed by mixing anisotropic rare earth magnetic powder coated with alkyl silicate and phosphate and an alkaline solution.

[0107] [Silane coupling treatment process]

[0108] The magnetic powder after silica treatment can be further treated by a silane coupling agent. By silane coupling treatment of the magnetic powder formed with a silica film, a coupling agent film is formed on the silica film, and the magnetic properties of the magnetic powder are improved, and the wettability with the resin and the strength of the magnet can be improved. The silane coupling agent can be selected accordingly according to the type of resin, for example, the silane coupling agent described in Japanese Patent Publication No. 2020-109840 (introduced into this specification as a whole by reference) can be appropriately used. Relative to 100 parts by mass of magnetic powder, the addition amount of the silane coupling agent is preferably 0.2 parts by mass or more and 0.8 parts by mass or less, more preferably 0.25 parts by mass or more and 0.6 parts by mass or less. When it is less than 0.2 parts by mass, the effect of the silane coupling agent is small, and when it exceeds 0.8 parts by mass, there is a tendency that the magnetic properties of the magnetic powder and the magnet are reduced due to the agglomeration of the magnetic powder.

[0109] The anisotropic rare earth magnetic powder after the phosphoric acid treatment step, the oxidation step, the silica treatment, or the silane coupling treatment can be filtered, dehydrated, and dried by a conventional method.

[0110] <<Cylindrical bonded magnet>>

[0111] The cylindrical bonded magnet of this embodiment includes anisotropic rare earth magnetic powder and resin, and is oriented along the two poles relative to the radial direction, and the deformation rate of the surface magnetic flux density on the outer peripheral side relative to the sine wave curve is less than 15%. The cylindrical bonded magnet of this embodiment is divided into two poles in the radial direction. The magnetization directions of one pole and the other pole of the two poles of the cylindrical bonded magnet are different.

[0112] The cylindrical bonded magnet of the present embodiment can be manufactured, for example, by the manufacturing method of the cylindrical bonded magnet of the present embodiment described above. The anisotropic rare earth magnetic powder and the resin and their blending amounts do not change significantly before and after molding, and therefore, are as described for the resin composition for bonded magnets. As the resin, a thermoplastic resin is preferred, and as the anisotropic rare earth magnetic powder, a SmFeN-based magnetic powder is preferred. For the cylindrical bonded magnet, the cylindrical bonded magnet obtained by the above-mentioned manufacturing method can be cut and used.

[0113] The deformation rate of the surface magnetic flux density on the outer side relative to the sine wave curve is 15% or less, preferably 12% or less, more preferably 10% or less, and further preferably 8% or less. The deformation rate indicates the degree of deformation of the waveform. The surface magnetic flux density is measured using a magnetic analyzer, and all the higher harmonic components (E2 to En) contained in the waveform are calculated by Fourier transform, and are calculated as the ratio of the sum of their effective values ​​to the effective value of the fundamental wave (E1).

[0114] The outer diameter of the obtained cylindrical bonded magnet is not particularly limited, but is preferably 10 mm or more and 300 mm or less, more preferably 15 mm or more and 50 mm or less. The inner diameter is also not particularly limited, but is preferably 5 mm or more and 290 mm or less, more preferably 10 mm or more and 45 mm or less. The difference between the outer diameter and the inner diameter is preferably 1 mm or more and 20 mm or less, more preferably 2 mm or more and 10 mm or less, and further preferably 2 mm or more and 6 mm or less.

[0115] The length of the obtained cylindrical bonded magnet is not particularly limited, but is preferably 1 mm to 100 mm, and more preferably 5 mm to 30 mm.

[0116] Example

[0117] The present application will be described in more detail by the following examples and the like, but the present application is not limited to these examples and the like.

[0118] Example 1

[0119] (1-1) Production of bonded magnet composition

[0120] After mixing SmFeN-based magnetic powder (average particle size 3 μm) with 12 nylon resin powder and a small amount of lubricant in a volume ratio of about 6:4 by a mixer, the mixed powder was put into a twin-screw mixer and kneaded at 210° C. to obtain a kneaded product. After cooling the obtained kneaded product, it was cut into appropriate sizes to obtain a bonded magnet composition.

[0121] (1-2) Forming die

[0122] Prepared Figure 1A The forming mold shown. Figure 1A As shown, the mold includes an inner mold part 1 having a magnetic member 5 in the center, an outer mold part 2, a first orientation magnet 3, and a second orientation magnet 4. The following mold is used: the distance Y between the first orientation magnet 3 and the second orientation magnet 4 is 31 mm, the straight-line distance X of the first orientation magnet 3 and the second orientation magnet 4 in the direction of magnetic field application tangent to the circle defined by the inner surface of the outer mold part 2 is 23 mm, and the distance Z is 10 mm. In addition, the inner mold part 1 is made of HPM75, and the magnetic member 5 contained inside uses a magnetic member made of NAK80. The dimensions of the mold components used are shown in Table 1.

[0123] (1-3) Injection molding

[0124] The mold was placed in an injection molding machine, and the bonded magnet composition was melted in a cylinder at 260°C and injection molded in a mold cavity at 60°C to obtain a cylindrical bonded magnet with an outer diameter of 29 mm, an inner diameter of 23 mm, and a height of 11 mm.

[0125] Example 2

[0126] The simulation of the cylindrical bonded magnet of Example 2 was performed under the same conditions as Example 1, except that the inner mold part 1 was made of SUS304 and the magnetic member 5 was made of SS400. The simulation was performed on the orientation magnetic field when the molding was performed using the molding mold and the surface magnetic flux density of the cylindrical bonded magnet obtained thereby.

[0127] Example 3

[0128] Using a device that does not include the magnetic member 5, Figure 3A The simulation of the cylindrical bonded magnet of Example 3 was carried out under the same conditions as in Example 2 except that the solid inner mold described in was used.

[0129] Example 4

[0130] Used Figure 4A The simulation of the cylindrical bonded magnet of Example 4 was carried out under the same conditions as in Example 2 except for the outer mold portion described in .

[0131] Example 5

[0132] Using a device that does not include the magnetic member 5, Figure 5A The simulation of the cylindrical bonded magnet of Example 5 was carried out under the same conditions as in Example 4 except that the solid inner mold described in was used.

[0133] Example 6

[0134] Using a device that does not include the magnetic member 5, Fig. 6A The solid inner mold described in Fig. 6A The simulation of the cylindrical bonded magnet of Example 6 was carried out under the same conditions as in Example 2 except that the outer mold portion was a true circle as described in .

[0135] Comparative Example 1

[0136] Using a device that does not include the magnetic member 5, Fig. 7A A cylindrical bonded magnet was manufactured by the same method as in Example 1 except that the solid inner mold described in and the rectangular outer mold portion were the same as the distance X and the distance Y.

[0137] Comparative Example 2

[0138] The simulation of the cylindrical bonded magnet of Comparative Example 2 was performed under the same conditions as in Example 1 except that the inner mold portion 1 was made of SUS304 and the magnetic member 5 was made of SS400.

[0139] Comparative Example 3

[0140] Used to include Fig.9A The simulation of the cylindrical bonded magnet of Comparative Example 3 was carried out under the same conditions as Comparative Example 2 except that the inner mold of the magnetic member 5 described in was used.

[0141] <Evaluation of deformation rate>

[0142] exist Figure 1B and Figure 7B The surface magnetic flux density of the outer periphery of the cylindrical bonded magnet measured by the magnetic analyzer of Example 1 and Comparative Example 1 is shown in FIG. Figure 2A , Figure 3B , Figure 4B , Figure 5B , Figure 6B , Fig. 8A and Fig. 9B The simulation results of the orientation magnetic field on the surface of the outer mold part 2 at the outer periphery of the cavity of Examples 2 to 6 and Comparative Examples 2 to 3 are shown in FIG. Figure 2B , Figure 3C , Figure 4C , Figure 5C , Figure 6C , Figure 8B and Fig. 9C The simulation results of the surface magnetic flux density on the outer periphery of the cylindrical bonded magnets of Examples 2 to 6 and Comparative Examples 2 to 3 are shown in FIG. Figure 1B and Figure 2B Therefore, it can be considered that the result of the actually produced Example 1 is substantially the same as the result of the simulated Example 2. Figure 7B and Figure 8B Therefore, it can be considered that the result of the actually produced comparative example 1 is substantially the same as the result of the simulated comparative example 2.

[0143] Figure 1C This is an image diagram showing the orientation of the magnetic flux, that is, the magnetization direction, in each specific area of ​​the cylindrical bonded magnet of Example 1. Figure 7C This is an image diagram showing the magnetization direction of each specific area of ​​the cylindrical bonded magnet of Comparative Example 1. The area surrounded by the quadrilateral corresponds to Figure 7B The magnetization direction of the cylindrical bonded magnet of Comparative Example 1 surrounded by the quadrilateral becomes inclined, which is considered to be caused by Figure 7B The cylindrical bonded magnet of Example 1 is considered to have improved this point. Figure 1B Results shown.

[0144] In addition, the deformation rate of the surface magnetic flux density of the outer periphery of the cylindrical bonded magnet relative to the sine wave curve is shown in Table 1. The deformation rate indicates the degree of deformation of the waveform, and all the higher harmonic components (E2 to En) contained in the waveform are calculated by Fourier transform and calculated as the ratio of the sum of their effective values ​​to the effective value of the fundamental wave (E1).

[0145] [Table 1]

[0146]

[0147] According to Table 1, the deformation rates of the cylindrical bonded magnets of Examples 1 to 6 were low. On the other hand, the deformation rates of the cylindrical bonded magnets of Comparative Examples 1 to 3 were high.

[0148] Industrial Applicability

[0149] According to the method for manufacturing a bonded magnet of the present application, a cylindrical magnet having a magnetic flux density waveform that is a sine waveform or a waveform close to a sine waveform can be manufactured, and the cylindrical bonded magnet can be applied to various uses such as small engines.

Claims

1. A method for manufacturing a cylindrical bonded magnet, the method comprising: (1) a mold preparation step: the mold includes an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first orientation magnet, and a second orientation magnet; The inner mold portion has an outer surface whose shape is circular in a cross section in a given direction, The outer mold portion has an inner surface which is located at a position separated from the outer surface of the inner mold portion and has a circular shape in one cross section in the given direction, The mold is arranged so that the first orientation magnet and the second orientation magnet clamp the inner mold portion and the outer mold portion in the given direction; and (2) a molding step of filling a bonded magnet resin composition in a region between an outer surface of the inner mold portion and an inner surface of the outer mold portion while applying a magnetic field using the first orientation magnet and the second orientation magnet, and molding the region, thereby obtaining a cylindrical bonded magnet. Among them, in a cross-section in the given direction, the straight-line distance of the first orientation magnet and the second orientation magnet in the direction of magnetic field application tangent to the circle defined by the inner surface of the outer mold portion is shorter than the straight-line distance of the first orientation magnet and the second orientation magnet in the direction of magnetic field application passing through the center of the circle defined by the outer surface of the inner mold portion.

2. The method for manufacturing a cylindrical bonded magnet according to claim 1, wherein: The outer mold portion has an outer surface whose shape is an ellipse in a cross section in the given direction. 3 . The method for producing a cylindrical bonded magnet according to claim 1 , further comprising a magnetic member inside the inner mold portion.

4. The method for producing a cylindrical bonded magnet according to any one of claims 1 to 3, wherein: The first orientation magnet and the second orientation magnet are electromagnets.

5. A cylindrical bonded magnet comprising anisotropic rare earth magnetic powder and resin, oriented in two polar directions with respect to a radial direction, and having a surface magnetic flux density on the outer peripheral side with a deformation rate of 15% or less with respect to a sine wave curve.

6. The cylindrical bonded magnet according to claim 5, wherein: The resin is a thermoplastic resin.

7. The cylindrical bonded magnet according to claim 5 or 6, wherein: The anisotropic rare earth magnetic powder is SmFeN-based magnetic powder. 8 . The cylindrical bonded magnet according to claim 5 , wherein the difference between the outer diameter and the inner diameter is 2 mm or more and 10 mm or less. 9 . The cylindrical bonded magnet according to claim 5 , wherein the outer diameter is 15 mm or more and 50 mm or less.

10. A mold for forming a cylindrical bonded magnet, comprising an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first orientation magnet, and a second orientation magnet, The inner mold portion has an outer surface whose shape is circular in a cross section in a given direction, The outer mold portion has an inner surface which is located at a position separated from the outer surface of the inner mold portion and has a circular shape in one cross section in the given direction, The first orientation magnet and the second orientation magnet are arranged so as to sandwich the inner mold portion and the outer mold portion, thereby applying a magnetic field in the given direction during magnetic field orientation. In a cross-section in the given direction, a straight-line distance in the direction of magnetic field application of the first orientation magnet and the second orientation magnet passing through the tangent point of the circle defined by the inner surface of the outer mold portion is shorter than a straight-line distance in the direction of magnetic field application of the first orientation magnet and the second orientation magnet passing through the center of the circle defined by the outer surface of the inner mold portion.

11. The mold for forming a cylindrical bonded magnet according to claim 10, wherein: The outer mold portion has an outer surface whose shape is an ellipse in a cross section in the given direction. 12 . The mold for forming a cylindrical bonded magnet according to claim 10 , further comprising a magnetic member inside the inner mold portion.

13. The mold for forming a cylindrical bonded magnet according to any one of claims 10 to 12, wherein: The first orientation magnet and the second orientation magnet are electromagnets.

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