Cylindrical bond magnet, method for manufacturing the same and molding die

Abstract

To provide a cylindrical bond magnet whose magnetic flux density waveform is a sine wave or close to a sine wave, a method for manufacturing the same, and a molding die thereof.SOLUTION: A manufacturing method for a cylindrical bond magnet includes a step of preparing a mold having an inner mold portion 1 and an outer mold portion 2 that include non-magnetic members, a first orientation magnet 3, and a second orientation magnet 4, the first orientation magnet 3 and the second orientation magnet 4 being arranged to interpose the inner mold portion 1 and the outer mold portion 2 therebetween in a predetermined direction, and a molding step of filling and molding a resin composition for a bond magnet between the outer surface of the inner mold portion and the inner surface of the outer mold portion while applying a magnetic field by the first orientation magnet 3 and the second orientation magnet 4, thereby obtaining a cylindrical bond magnet. In a sectional view in a predetermined direction, a distance of a straight line in the magnetic field direction which is tangent to a circle defined by the inner surface of the outer mold portion 2 between the first orientation magnet 3 and the second orientation magnet 4 is shorter than a distance of a straight line in the magnetic field direction which passes through a center of a circle likewise defined by the outer surface of the inner mold portion 1.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present disclosure relates to a cylindrical bonded magnet, a manufacturing method thereof, and a molding die thereof. [Background technology]

[0002] Known cylindrical magnets include one with four magnetic poles and a sine wave magnetic flux density (Patent Document 1) and one with two magnetic poles and a magnetic flux density with a waveform close to a triangular wave (Patent Document 2). However, when manufacturing a cylindrical magnet with a two-pole sine wave, the magnetic field waveform during magnetic field orientation differs from the magnetic flux density waveform of the magnet that is actually obtained. For this reason, even with the methods described in Patent Documents 1 and 2, it is difficult to manufacture a cylindrical magnet with a magnetic flux density close to a sine wave. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-212863 A [Patent Document 2] JP 2019-123126 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a cylindrical bonded magnet whose magnetic flux density has a sine waveform or a waveform close to a sine waveform, a manufacturing method thereof, and a molding die thereof. [Means for solving the problem]

[0005] A method for producing a cylindrical bonded magnet according to one aspect of the present disclosure includes the steps of: (1) preparing a mold having an inner mold part including a non-magnetic member, an outer mold part including a non-magnetic member, a first alignment magnet, and a second alignment magnet; The inner mold portion has an outer surface that is circular in cross section in a predetermined direction, The outer mold part has an inner surface that is positioned away from an outer surface of the inner mold part and has a circular shape when viewed in a cross section in the predetermined direction, preparing a mold in which the first orientation magnet and the second orientation magnet are arranged to sandwich the inner mold part and the outer mold part in the predetermined direction; (2) a molding process for obtaining a cylindrical bonded magnet by filling a resin composition for a bonded magnet into the region between the outer surface of the inner mold part and the inner surface of the outer mold part and molding the resin composition while applying a magnetic field using the first orientation magnet and the second orientation magnet; Including, When viewed in a cross-sectional view in the specified direction, the straight-line distance between the first alignment magnet and the second alignment magnet in the magnetic field application direction tangent to the circle defined by the inner surface of the outer mold part is shorter than the straight-line distance between the first alignment magnet and the second alignment magnet in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part.

[0006] A cylindrical bonded magnet according to one embodiment of the present disclosure comprises anisotropic rare earth magnetic powder and resin, is oriented into two poles in the radial direction, and has a distortion rate of the surface magnetic flux density on the outer periphery relative to a sine wave curve of 15% or less.

[0007] The molding die for a cylindrical bonded magnet according to one embodiment of the present disclosure comprises: A mold for molding a cylindrical bonded magnet, the mold having an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first alignment magnet, and a second alignment magnet, The inner mold portion has an outer surface that is circular in cross section in a predetermined direction, The outer mold part has an inner surface that is positioned away from an outer surface of the inner mold part and has a circular shape when viewed in a cross section in the predetermined direction, The first orientation magnet and the second orientation magnet are arranged to sandwich the inner mold part and the outer mold part so that a magnetic field is applied in the predetermined direction during magnetic field orientation, In a cross-sectional view in the specified direction, the straight-line distance in the magnetic field application direction passing through the tangent point of the circle defined by the inner surface of the outer mold part between the first alignment magnet and the second alignment magnet is shorter than the straight-line distance in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part between the first alignment magnet and the second alignment magnet. Effect of the Invention

[0008] According to the manufacturing method of cylindrical bonded magnets and the molding die for cylindrical bonded magnets of the present disclosure, it is possible to provide cylindrical bonded magnets whose magnetic flux density waveform is a sine wave or close to a sine wave. [Brief description of the drawings]

[0009] [Figure 1A] FIG. 2 is a cross-sectional view of the molding die for the cylindrical bonded magnet used in Example 1. [Figure 1B] 2 is a diagram in which the surface magnetic flux density on the outer periphery is plotted against the angle for the cylindrical bonded magnet produced in Example 1. [Figure 1C] FIG. 2 is an image diagram showing the magnetization direction in each specific region of the cylindrical bonded magnet of Example 1. [Figure 1D] FIG. 2 is a cross-sectional view of the molding die for the cylindrical bonded magnet used in Example 1 in an open state when removing the molded product. [Figure 2A] 13 is a diagram in which the aligning magnetic field is plotted against the angle in Example 2. [Figure 2B] FIG. 13 is a plot of the outer periphery surface magnetic flux density versus angle for the cylindrical bonded magnet of Example 2. [Figure 3A] FIG. 11 is a cross-sectional view of the molding die for the cylindrical bonded magnet used in Example 3. [Figure 3B] 13 is a diagram in which the aligning magnetic field is plotted against the angle in Example 3. [Figure 3C] FIG. 13 is a plot of the outer periphery surface magnetic flux density versus angle for the cylindrical bonded magnet of Example 3. [Figure 4A]FIG. 11 is a cross-sectional view of the molding die for the cylindrical bonded magnet used in Example 4. [Figure 4B] 13 is a diagram in which the aligning magnetic field is plotted against the angle in Example 4. [Figure 4C] FIG. 13 is a plot of the outer periphery surface magnetic flux density versus angle for the cylindrical bonded magnet of Example 4. [Figure 4D] FIG. 11 is a cross-sectional view of the molding die for the cylindrical bonded magnet used in Example 4 in an open state when removing the molded product. [Figure 5A] FIG. 11 is a cross-sectional view of the molding die for the cylindrical bonded magnet used in Example 5. [Figure 5B] 13 is a diagram in which the aligning magnetic field is plotted against the angle in Example 5. [Figure 5C] FIG. 13 is a plot of the outer periphery surface magnetic flux density versus angle for the cylindrical bonded magnet of Example 5. [Figure 6A] FIG. 11 is a cross-sectional view of the molding die for the cylindrical bonded magnet used in Example 6. [Figure 6B] FIG. 13 is a plot of the aligning magnetic field against the angle in Example 6. [Figure 6C] FIG. 13 is a plot of the outer periphery surface magnetic flux density versus angle for the cylindrical bonded magnet of Example 6. [Figure 7A] FIG. 2 is a cross-sectional view of a molding die for the cylindrical bonded magnet used in Comparative Example 1. [Figure 7B] 1 is a plot of outer periphery surface magnetic flux density versus angle for the cylindrical bonded magnet of Comparative Example 1. [Figure 7C] 7B is an image diagram showing the magnetization direction in each specific region of the cylindrical bonded magnet of Comparative Example 1. The part surrounded by a square corresponds to the part indicated by the arrow in FIG. [Figure 8A] 13 is a diagram in which the aligning magnetic field is plotted against the angle in Comparative Example 2. FIG. [Figure 8B] FIG. 13 is a plot of outer periphery surface magnetic flux density versus angle for the cylindrical bonded magnet of Comparative Example 2. [Figure 9A]FIG. 11 is a cross-sectional view of a molding die for the cylindrical bonded magnet used in Comparative Example 3. [Figure 9B] 13 is a diagram in which the aligning magnetic field is plotted against the angle in Comparative Example 3. FIG. [Figure 9C] FIG. 13 is a plot of the outer periphery surface magnetic flux density versus angle for the cylindrical bonded magnet of Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present disclosure will be described in detail. However, the embodiments shown below are examples for embodying the technical ideas of the present disclosure, and the present disclosure is not limited to the following. In this specification, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, a numerical range indicated using "~" indicates a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively.

[0011] <<Molding die for cylindrical bonded magnets>> The molding die for the cylindrical bonded magnet of this embodiment is: A mold for molding a cylindrical bonded magnet, the mold having an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first alignment magnet, and a second alignment magnet, The inner mold portion has an outer surface that is circular in cross section in a predetermined direction, The outer mold part has an inner surface that is positioned away from an outer surface of the inner mold part and has a circular shape when viewed in a cross section in the predetermined direction, The first orientation magnet and the second orientation magnet are arranged to sandwich the inner mold part and the outer mold part so that a magnetic field is applied in the predetermined direction during magnetic field orientation, In a cross-sectional view in the specified direction, the straight-line distance in the magnetic field application direction passing through the tangent point of the circle defined by the inner surface of the outer mold part between the first alignment magnet and the second alignment magnet is shorter than the straight-line distance in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part between the first alignment magnet and the second alignment magnet.

[0012] FIG. 1A shows a cross-sectional view in a predetermined direction of the molding die of the cylindrical bonded magnet of this embodiment. FIG. 3A, FIG. 4A, FIG. 5A, and FIG. 6A show cross-sectional views in a predetermined direction of the molding die of the present embodiment of another aspect. Also, FIG. 7A and FIG. 9A show cross-sectional views in a predetermined direction of the molding die of the cylindrical bonded magnet of the comparative example. All of the dies have an inner die part 1 containing a non-magnetic member, an outer die part 2 containing a non-magnetic member, a first orientation magnet 3, and a second orientation magnet 4. All of these dies are specific examples of molding dies in which the outer die part 2 is composed of two parts that can be separated in the vertical direction on the paper surface. The outer die part 2 opens while being separated in conjunction with the opening operation of the die of the molding machine, and the molded product can be taken out. Cross-sectional views of the molding dies of FIG. 1A and FIG. 4A when the die is opened are shown in FIG. 1D and FIG. 4D, respectively. In the figures, the die opening direction is indicated by an arrow. Although the outer mold part 2 is shown separated into two parts in the drawing, it may be separable into three or more parts, or may be an integral member that is not separable.

[0013] From the results of various experiments, it is presumed that the magnetic permeability of the resin composition for bonded magnets when it is in a molten state is greater than the magnetic permeability of the bonded magnet at room temperature. That is, at high temperatures during the molding of the bonded magnets, when the resin composition for bonded magnets is in a molten state, the orientation magnetic field is likely to pass through the center of the cylindrical bonded magnet, and it is considered that the magnitude of the orientation magnetic field applied to the resin composition at the center and the outer periphery of the bonded magnet is different. In particular, in a two-pole magnet, unlike a multi-pole magnet, a magnetic field is applied in one direction, so that in order to apply a sine wave magnetic field, it is necessary to consider the change in the magnetic permeability of the resin composition for bonded magnets. In the mold of this embodiment, the linear distance X in the magnetic field application direction between the first orientation magnet and the second orientation magnet, which is tangent to the circle defined by the inner surface of the outer mold part, is made shorter than the linear distance Y in the magnetic field application direction between the first orientation magnet and the second orientation magnet, which is 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 the center of the magnet. As a result, the magnitude of the aligning magnetic field applied to the resin composition for bonded magnets during molding can be made uniform or close to uniform, and a cylindrical magnet can be produced whose magnetic flux density waveform is a sine wave or close to a sine wave.

[0014] The inner mold part 1 includes a non-magnetic member and is located in the center of the mold. Examples of non-magnetic materials constituting the non-magnetic member include non-magnetic steel, specifically SUS304, HPM75, KN20, etc. The inner mold part 1 can be composed of only a non-magnetic member. The inner mold part 1 has an outer surface that is circular in shape when viewed in a cross section in a predetermined direction. Here, the predetermined direction is the magnetic field orientation direction. It is preferable to have a magnetic member 5 inside the inner mold part 1 in terms of distortion rate. By disposing the magnetic member 5 inside the inner mold part 1, the distortion rate of the surface magnetic flux density on the outer periphery side with respect to the sine wave curve can be reduced. The magnetic member 5 is composed of magnetic steel. Examples of magnetic steel constituting the magnetic member 5 include NAK80 and SS400.

[0015] The outer mold portion 2 includes a non-magnetic member and is located away from the outer surface of the inner mold portion 1. The non-magnetic material constituting the non-magnetic member is as described for the inner mold portion 1. The inner mold portion 1 can be composed of only a non-magnetic member. The outer mold portion 2 has an inner surface that is circular in shape when viewed in a cross section in the specified direction. The gap formed between the outer periphery of the inner mold portion 1 and the inner periphery of the outer mold portion 2 becomes a cavity 6, and when used to manufacture a bonded magnet, the cavity 6 is filled with a resin composition for bonded magnets and molded.

[0016] The first orientation magnet 3 and the second orientation magnet 4 are arranged to sandwich the inner mold part 1 and the outer mold part 2 in the predetermined direction. Examples of these orientation magnets include electromagnets and permanent magnets. The orientation magnet is preferably an electromagnet because it can change the magnetic field and orient with a larger orientation magnetic field. Here, the first orientation magnet 3 and the second orientation magnet 4 sandwich the inner mold part 1 and the outer mold part 2 means that the orientation magnets do not need to sandwich the entire outer mold part 2, but only need to sandwich at least the part of the outer mold part 2 that constitutes the cavity. The first orientation magnet 3 and the second orientation magnet 4 sandwich the entire cavity 6. The first orientation magnet 3 and the second orientation magnet 4 sandwich the part of the outer mold part 2 that constitutes the cavity from one end to the other end in a direction perpendicular to the opening and closing direction of the mold. In the molds shown in Figures 1A, 3A, and 6A, the first orientation magnet 3 and the second orientation magnet 4 sandwich the entire outer mold part 2. In the molds shown in Figures 4A and 5A, the first orientation magnet 3 and the second orientation magnet 4 do not sandwich the entire inner mold part 1 and the entire outer mold part 2, but they do sandwich the entire part that forms the cavity of the outer mold part 2.

[0017] In a cross-sectional view in the predetermined direction, the linear distance X between the first and second orientation magnets in the magnetic field application direction tangent to the circle defined by the inner surface of the outer mold part is shorter than the linear distance Y between the first and second orientation magnets in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part. In FIG. 1A, the linear distances X and Y are shown by dotted lines. The linear distance X being shorter than the linear distance Y means that the distance between the orientation magnets is shorter at the outer periphery than at the center of the mold. The upper limit of the ratio X / Y of the linear distance X to the linear distance Y is preferably 0.9 or less, more preferably 0.8 or less. The lower limit may be 0.2 or more. By having the ratio X / Y of the linear distance X to the linear distance Y within the above range, orientation is also easily achieved at the center of the cavity during bonded magnet molding, and a bonded magnet in which the waveform of the surface magnetic flux density is a sine waveform or close to a sine waveform tends to be obtained.

[0018] In addition, in the comparative molds shown in Figures 7A and 9A, the straight-line distance X in the magnetic field application direction between the first alignment magnet and the second alignment magnet and tangent to the circle defined by the inner surface of the outer mold part is the same length as the straight-line distance Y in the magnetic field application direction between the first alignment magnet and the second alignment magnet and passing through the center of the circle defined by the outer surface of the inner mold part.

[0019] When viewed in a cross section in a predetermined direction, the shape of the outer periphery of the outer mold part 2 is not rectangular, but may be, for example, a perfect circle or an ellipse. An ellipse is preferred in terms of both the ease of manufacturing the mold and the ease of manufacturing a bonded magnet whose surface magnetic flux density has a sine wave or a waveform close to a sine wave. The lower limit of the ratio of the major axis to the minor axis of the ellipse is preferably 1.1 or more, and more preferably 1.3 or more. The upper limit may be 2 or less. When the ratio of the major axis to the minor axis is 2 or less, a sufficient aligning magnetic field is obtained, and when the ratio of the major axis to the minor axis is 1.1 or more, it becomes easier to both easily manufacture the mold and easily manufacture a bonded magnet whose surface magnetic flux density has a sine wave or a waveform close to a sine wave.

[0020] The linear distance Z between the first and second orientation magnets in the magnetic field application direction tangent to the circle defined by the outer surface of the outer mold part may be zero, but from the viewpoint of achieving both mass productivity and a sine waveform, it may be 1 mm or more, and preferably 3 mm or more. Moreover, the linear distance Z is preferably 1% or more, and preferably 80% or less of the linear distance Y. The upper limit of the linear distance Z may be 50% or less.

[0021] <<Manufacturing method of cylindrical bonded magnets>> The manufacturing method of the cylindrical bonded magnet of this embodiment is as follows: (1) preparing a mold having an inner mold part including a non-magnetic member, an outer mold part including a non-magnetic member, a first alignment magnet, and a second alignment magnet; The inner mold portion has an outer surface that is circular in cross section in a predetermined direction, The outer mold part has an inner surface that is positioned away from an outer surface of the inner mold part and has a circular shape when viewed in a cross section in the predetermined direction, preparing a mold in which the first orientation magnet and the second orientation magnet are arranged to sandwich the inner mold part and the outer mold part in the predetermined direction; (2) a molding process for obtaining a cylindrical bonded magnet by filling a resin composition for a bonded magnet into the region between the outer surface of the inner mold part and the inner surface of the outer mold part and molding the resin composition while applying a magnetic field using the first orientation magnet and the second orientation magnet; Including, When viewed in a cross-sectional view in the specified direction, the straight-line distance between the first alignment magnet and the second alignment magnet in the magnetic field application direction tangent to a circle defined by the inner surface of the outer mold part is shorter than the straight-line distance between the first alignment magnet and the second alignment magnet in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part.

[0022] In step (1) of preparing a mold, a mold for molding the cylindrical bonded magnet of this embodiment described above is prepared. In step (2) of molding to obtain a cylindrical bonded magnet, the mold is used to fill and mold the region (cavity) between the outer surface of the inner mold part and the inner surface of the outer mold part with a resin composition for bonded magnets. During molding, the resin composition for bonded magnets is oriented while applying a magnetic field using the first alignment magnet and the second alignment magnet. Molding methods include injection molding.

[0023] <Resin composition for bonded magnets> The resin composition for bonded magnets used in the molding step (2) preferably contains a resin and anisotropic rare earth magnetic powder.

[0024] <Anisotropic rare earth magnetic powder> The material of the anisotropic rare earth magnetic powder is not particularly limited, and examples thereof include rare earth magnetic materials of the SmFeN system, NdFeB system, and SmCo system. Among them, SmFeN system magnetic powder is preferable because of its heat resistance and lack of rare metals. SmFeN system magnetic powder has a stronger magnetic force than ferrite system, and can generate a high magnetic force even with a relatively small amount. In addition, SmFeN system has a smaller particle size than other rare earth systems such as NdFeB system and SmCo system, and is suitable as a filler for base resin and is resistant to rust. Examples of SmFeN system magnetic powder include Th2Zn 17 It has a crystal structure of the type Sm x Fe 100-x-y N y Here, it is preferable 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 is one example.

[0025] 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, unevenness, cracks, etc. are less likely to occur on the surface of the product, and the appearance is excellent. Furthermore, cost reduction can be achieved. If the average particle size is larger than 10 μm, there is a risk that unevenness, cracks, etc. may occur on the surface of the product, resulting in inferior appearance. On the other hand, if the average particle size is smaller than 1 μm, the cost of the magnetic powder increases, which is not preferable from the perspective of cost reduction. The average particle size of the anisotropic rare earth magnetic powder is measured as the particle size at which the volume integration value from the small particle size side becomes 50% in the volume-based particle size distribution obtained by the laser scattering method. Also, it is preferable that the ratio D90 / D10 of the 90% particle size D90 to the 10% particle size D10 in the cumulative particle size distribution based on volume is 4.5 or less, more preferably 4 or less, and particularly preferably 3.5 or less. When the particle size distribution D90 / D10 is 4.5 or less, the fluidity is improved even when forming a magnet with a thin wall thickness, resulting in good orientation and making it easier to obtain a bonded magnet with a high orientation rate.

[0026] 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% or more and 65 vol% or less, more preferably 50 vol% or more and 60 vol% or less, still more preferably 50 vol% or more and 59 vol% or less, and particularly preferably 51 vol% or more and 56 vol% or less. By setting it to 65 vol% or less, there is a tendency to suppress a decrease in magnetic flux density even when the cylindrical bonded magnet has a thin wall thickness. 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.

[0027] Examples of the resin include thermoplastic resins such as polyphenylene ether, polypropylene, polyethylene, polyvinyl chloride, polyester, polyamide, polycarbonate, polyphenylene sulfide, and acrylic resin.

[0028] <Manufacturing method of <SmFeN-based anisotropic rare earth magnetic powder>> The SmFeN anisotropic rare earth magnetic powder may be prepared by purchasing or by manufacturing using a known method. For example, it can be manufactured using the following method. 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); A step of calcining the precipitate to obtain an oxide containing metals such as Sm and Fe (oxidation step); A step of heat-treating the oxide in an atmosphere containing a reducing gas to obtain a partial oxide (pretreatment step); A step of reducing the partial oxide (reduction step), and A process of nitriding the alloy particles obtained in the reduction process (nitriding process) In addition, for the manufacturing method of SmFeN-based anisotropic rare earth magnetic powder, reference can be made to the descriptions in, for example, JP-A-11-189811 and WO2022 / 107462 (the entire disclosures of which are incorporated herein by reference).

[0029] The anisotropic rare earth magnetic powder produced by the above-mentioned production method can be used as it is, but may also be further subjected to the following treatment. A phosphoric acid treatment step 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 phosphate-coated surface.

[0030] [Silica treatment process] The anisotropic rare earth magnetic powder after phosphoric acid treatment may be silica-treated as necessary. By forming a silica thin film on the magnetic powder, the oxidation resistance can be improved. The silica thin film can be formed, for example, by mixing an alkyl silicate, a phosphate-coated anisotropic rare earth magnetic powder, and an alkaline solution.

[0031] [Silane coupling treatment process] The magnetic powder after silica treatment may be further treated with a silane coupling agent. By subjecting the magnetic powder on which the silica thin film is formed to the silane coupling treatment, a coupling agent film is formed on the silica thin film, which improves the magnetic properties of the magnetic powder and improves wettability with the resin and strength of the magnet. The silane coupling agent may be selected according to the type of resin, and for example, the silane coupling agent described in JP 2020-109840 A (the entire disclosure of which is incorporated herein by reference) can be appropriately used. The amount of the silane coupling agent added is preferably 0.2 parts by mass or more and 0.8 parts by mass or less, and more preferably 0.25 parts by mass or more and 0.6 parts by mass or less, relative to 100 parts by mass of the magnetic powder. If the amount is less than 0.2 parts by mass, the effect of the silane coupling agent is small, and if the amount is more than 0.8 parts by mass, the magnetic powder tends to aggregate, which tends to reduce the magnetic properties of the magnetic powder and magnet.

[0032] 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.

[0033] <<Cylindrical bonded magnets>> The cylindrical bonded magnet of this embodiment contains anisotropic rare earth magnetic powder and resin, is oriented in two poles in the radial direction, and is characterized in that the distortion rate of the sine wave curve of the surface magnetic flux density on the outer periphery is 15% or less. The cylindrical bonded magnet of this embodiment is divided into two poles in the radial direction. One and the other of the two poles of the cylindrical bonded magnet have different magnetization directions.

[0034] The cylindrical bonded magnet of this embodiment can be manufactured, for example, by the manufacturing method of the cylindrical bonded magnet of this embodiment described above. The anisotropic rare earth magnetic powder and resin, and the amount of each do not change significantly before and after molding, as explained in the resin composition for bonded magnets. The resin is preferably a thermoplastic resin, and the anisotropic rare earth magnetic powder is preferably a SmFeN magnetic powder. The cylindrical bonded magnet may be cut from the one obtained by the manufacturing method described above.

[0035] The distortion rate of the outer peripheral surface magnetic flux density with respect to the sine wave curve is 15% or less, preferably 12% or less, more preferably 10% or less, and even more preferably 8% or less. The distortion rate represents the degree of distortion of the waveform, and is calculated by measuring the surface magnetic flux density using a magnet analyzer or the like, calculating all the harmonic components (E2 to En) contained in the waveform by Fourier transform, and then calculating the ratio of the sum of their effective values ​​to the effective value of the fundamental wave (E1).

[0036] The outer diameter of the obtained cylindrical bonded magnet is not particularly limited, but is preferably 10 mm to 300 mm, more preferably 15 mm to 50 mm. The inner diameter is also not particularly limited, but is preferably 5 mm to 290 mm, more preferably 10 mm to 45 mm. The difference between the outer diameter and the inner diameter is preferably 1 mm to 20 mm, more preferably 2 mm to 10 mm, and even more preferably 2 mm to 6 mm.

[0037] The length of the obtained cylindrical bonded magnet is not particularly limited, but is preferably from 1 mm to 100 mm, and more preferably from 5 mm to 30 mm.

[0038] The disclosure of this specification may include the following aspects. (Aspect 1) (1) preparing a mold having an inner mold part including a non-magnetic member, an outer mold part including a non-magnetic member, a first alignment magnet, and a second alignment magnet; The inner mold portion has an outer surface that is circular in cross section in a predetermined direction, The outer mold part has an inner surface that is positioned away from an outer surface of the inner mold part and has a circular shape when viewed in a cross section in the predetermined direction, preparing a mold in which the first orientation magnet and the second orientation magnet are arranged to sandwich the inner mold part and the outer mold part in the predetermined direction; (2) a molding process for obtaining a cylindrical bonded magnet by filling a resin composition for a bonded magnet into the region between the outer surface of the inner mold part and the inner surface of the outer mold part and molding the resin composition while applying a magnetic field using the first orientation magnet and the second orientation magnet; Including, A method for manufacturing a cylindrical bonded magnet, wherein, when viewed in a cross-sectional view in the specified direction, the straight-line distance between the first alignment magnet and the second alignment magnet in the magnetic field application direction tangent to a circle defined by the inner surface of the outer mold part is shorter than the straight-line distance between the first alignment magnet and the second alignment magnet in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part. (Aspect 2) 2. The method for manufacturing a cylindrical bonded magnet according to claim 1, wherein the outer mold portion has an outer surface that is elliptical in shape when viewed in a cross section in the predetermined direction. (Aspect 3) 3. The method for producing a cylindrical bonded magnet according to embodiment 1 or 2, further comprising the step of: providing an additional magnetic member inside the inner mold portion. (Aspect 4) The method for producing a cylindrical bonded magnet according to any one of aspects 1 to 3, wherein the first orientation magnet and the second orientation magnet are electromagnets. (Aspect 5) A cylindrical bonded magnet that contains anisotropic rare earth magnetic powder and resin, is oriented into two poles in the radial direction, and has a distortion rate of the sine wave curve of the surface magnetic flux density on the outer periphery of 15% or less. (Aspect 6) 6. The cylindrical bonded magnet according to embodiment 5, wherein the resin is a thermoplastic resin. (Aspect 7) 7. The cylindrical bonded magnet according to embodiment 5 or 6, wherein the anisotropic rare earth magnetic powder is SmFeN-based magnetic powder. (Aspect 8) 8. The cylindrical bonded magnet according to any one of aspects 5 to 7, wherein the difference between the outer circumferential diameter and the inner circumferential diameter is 2 mm or more and 10 mm or less. (Aspect 9) 9. The cylindrical bonded magnet according to claim 5, wherein the outer diameter is 15 mm or more and 50 mm or less. (Aspect 10) A mold for molding a cylindrical bonded magnet, the mold having an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first alignment magnet, and a second alignment magnet, The inner mold portion has an outer surface that is circular in cross section in a predetermined direction, The outer mold part has an inner surface that is positioned away from an outer surface of the inner mold part and has a circular shape when viewed in a cross section in the predetermined direction, The first orientation magnet and the second orientation magnet are arranged to sandwich the inner mold part and the outer mold part so that a magnetic field is applied in the predetermined direction during magnetic field orientation, A mold for molding cylindrical bonded magnets, in which, when viewed in a cross-sectional view in the specified direction, the straight-line distance in the magnetic field application direction passing through the tangent point of the circle defined by the inner surface of the outer mold part for the first alignment magnet and the second alignment magnet is shorter than the straight-line distance in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part for the first alignment magnet and the second alignment magnet. (Aspect 11) A mold for molding a cylindrical bonded magnet according to embodiment 10, wherein the outer mold portion has an outer surface that is elliptical in shape when viewed in a cross section in the predetermined direction. (Aspect 12) 12. The mold for molding a cylindrical bonded magnet according to embodiment 10 or 11, further comprising a magnetic member on the inside of the inner mold portion. (Aspect 13) 13. The mold for molding a cylindrical bonded magnet according to claim 10, wherein the first orientation magnet and the second orientation magnet are electromagnets. EXAMPLES

[0039] The present disclosure will be described more specifically with reference to the following examples, but the present disclosure is not limited to these examples in any way.

[0040] Example 1 (1-1) Production of bonded magnet composition SmFeN magnetic powder (average particle size 3 μm) and 12 nylon resin powder in a volume ratio of about 6:4, and a small amount of lubricant were mixed in a mixer, and the mixed powder was then put into a twin-screw kneader and kneaded at 210° C. to obtain a kneaded product. The kneaded product was cooled and then cut to an appropriate size to obtain a bonded magnet composition.

[0041] (1-2) Molding mold A molding die shown in FIG. 1A was prepared. As shown in FIG. 1A, the die includes an inner die part 1 having a magnetic member 5 at the center, an outer die part 2, a first orientation magnet 3, and a second orientation magnet 4. The distance Y between the first orientation magnet 3 and the second orientation magnet 4 is 31 mm, the linear distance X between the first orientation magnet 3 and the second orientation magnet 4 in the magnetic field application direction tangent to a circle defined by the inner surface of the outer die part 2 is 23 mm, and the distance Z is 10 mm. The inner die part 1 is made of HPM75, and the magnetic member 5 included inside is made of NAK80. The dimensions of the die members used are shown in Table 1.

[0042] (1-3) Injection molding The above mold was placed in an injection molding machine. The bonded magnet composition was melted in a cylinder at 260°C and injection molded into the cavity of the mold, the temperature of which was adjusted to 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.

[0043] Example 2 A simulation of the cylindrical bonded magnet of Example 2 was performed under the same conditions as Example 1, except that the inner mold portion 1 was made of SUS304 and the magnetic member 5 was made of SS400. The simulation was performed on the aligning magnetic field during molding using a molding die, and the surface magnetic flux density of the cylindrical bonded magnet obtained thereby.

[0044] Example 3 A simulation of the cylindrical bonded magnet of Example 3 was carried out under the same conditions as Example 2, except that the solid inner die shown in FIG. 3A was used without including magnetic member 5.

[0045] Example 4 A simulation of the cylindrical bonded magnet of Example 4 was carried out under the same conditions as Example 2, except that the outer mold part shown in FIG. 4A was used.

[0046] Example 5 A simulation of the cylindrical bonded magnet of Example 5 was carried out under the same conditions as Example 4, except that the solid inner die shown in FIG. 5A, which did not include magnetic member 5, was used.

[0047] Example 6 A simulation of the cylindrical bonded magnet of Example 6 was performed under the same conditions as Example 2, except that a solid inner mold part as shown in FIG. 6A, which did not include magnetic member 5, and a perfectly circular outer mold part as shown in FIG. 6A were used.

[0048] Comparative Example 1 A cylindrical bonded magnet was manufactured in the same manner as in Example 1, except that a solid inner mold part as shown in FIG. 7A was used, which did not include magnetic member 5, and a rectangular outer mold part in which distance X and distance Y were the same was used.

[0049] Comparative Example 2 A simulation of the cylindrical bonded magnet of Comparative Example 2 was carried out 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.

[0050] Comparative Example 3 A simulation of the cylindrical bonded magnet of Comparative Example 3 was carried out under the same conditions as Comparative Example 2, except that an inner mold including magnetic member 5 shown in FIG. 9A was used.

[0051] <Distortion Rate Evaluation> 1B and 7B show the surface magnetic flux density of the outer circumference of the cylindrical bonded magnets measured by a magnet analyzer in Example 1 and Comparative Example 1. FIG. 2A, FIG. 3B, FIG. 4B, FIG. 5B, FIG. 6B, FIG. 8A, and FIG. 9B show the simulation results of the oriented magnetic field on the surface of the outer mold part 2 of the cavity outer circumference in Examples 2 to 6 and Comparative Examples 2 to 3. FIG. 2B, FIG. 3C, FIG. 4C, FIG. 5C, FIG. 6C, FIG. 8B, and FIG. 9C show the simulation results of the surface magnetic flux density of the outer circumference of the cylindrical bonded magnets in Examples 2 to 6 and Comparative Examples 2 to 3. Since FIG. 1B and FIG. 2B are almost the same, it can be said that the results of the actually manufactured Example 1 and the results of the simulated Example 2 are almost the same. Since FIG. 7B and FIG. 8B are almost the same, it can be said that the results of the actually manufactured Comparative Example 1 and the results of the simulated Comparative Example 2 are almost the same.

[0052] Fig. 1C is an image diagram showing the magnetization direction, which is the direction of magnetic flux in each specific region, for the cylindrical bonded magnet of Example 1. Fig. 7C is an image diagram showing the magnetization direction in each specific region for the cylindrical bonded magnet of Comparative Example 1. The part surrounded by a square corresponds to the part indicated by the arrow in Fig. 7B. It is believed that the cylindrical bonded magnet of Comparative Example 1 has an oblique magnetization direction in the part surrounded by a square, which resulted in the result shown in Fig. 7B. It is believed that the cylindrical bonded magnet of Example 1 has improved in this respect, which resulted in the result shown in Fig. 1B.

[0053] Additionally, the distortion rate of the surface magnetic flux density on the outer periphery of the cylindrical bonded magnet relative to a sine wave curve is shown in Table 1. The distortion rate indicates the degree of distortion of the waveform, and was calculated by calculating all harmonic components (E2-En) contained in the waveform using a Fourier transform, and then taking the ratio of the sum of their effective values ​​to the effective value of the fundamental wave (E1).

[0054] [Table 1] As can be seen from Table 1, the distortion factors were low for the cylindrical bonded magnets of Examples 1 to 6. On the other hand, the distortion factors of the cylindrical bonded magnets of Comparative Examples 1 to 3 were high. [Industrial Applicability]

[0055] According to the manufacturing method of the bonded magnet disclosed herein, it is possible to produce a cylindrical magnet whose magnetic flux density waveform is a sine wave or close to a sine wave, and this cylindrical bonded magnet can be used for a variety of purposes such as small motors. [Explanation of symbols]

[0056] 1: Inner mold section 2:Outer mold part 3: First alignment magnet 4: Second alignment magnet 5: Magnetic material 6: Cavity X: The linear distance between the first alignment magnet and the second alignment magnet in the direction of magnetic field application, tangent to a circle defined by the inner surface of the outer mold part. Y: Linear distance in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part between the first alignment magnet and the second alignment magnet Z: The linear distance between the first alignment magnet and the second alignment magnet in the direction of magnetic field application, tangent to a circle defined by the outer surface of the outer mold part.

Claims

1. (1) preparing a mold having an inner mold part including a non-magnetic member, an outer mold part including a non-magnetic member, a first orientation magnet, and a second orientation magnet; The inner mold portion has an outer surface that is circular in cross section in a predetermined direction, The outer mold part has an inner surface that is positioned away from an outer surface of the inner mold part and has a circular shape when viewed in a cross section in the predetermined direction, preparing a mold in which the first orientation magnet and the second orientation magnet are arranged to sandwich the inner mold part and the outer mold part in the predetermined direction; (2) a molding process for obtaining a cylindrical bonded magnet by filling a resin composition for a bonded magnet into the region between the outer surface of the inner mold part and the inner surface of the outer mold part and molding the resin composition while applying a magnetic field using the first orientation magnet and the second orientation magnet; Including, A method for manufacturing a cylindrical bonded magnet, wherein, when viewed in a cross-sectional view in the specified direction, the straight-line distance between the first alignment magnet and the second alignment magnet in the magnetic field application direction tangent to a circle defined by the inner surface of the outer mold part is shorter than the straight-line distance between the first alignment magnet and the second alignment magnet in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold part.

2. The method for manufacturing a cylindrical bonded magnet according to claim 1 , wherein the outer mold portion has an outer surface that is elliptical in cross section in the predetermined direction.

3. The method for producing a cylindrical bonded magnet according to claim 1 or 2, further comprising a magnetic member inside the inner mold portion.

4. 3. The method for manufacturing a cylindrical bonded magnet according to claim 1, 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 poles in the radial direction, and having a distortion rate of the surface magnetic flux density on the outer periphery with respect to a sine wave curve of 15% or less.

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

7. 7. The cylindrical bonded magnet according to claim 5, wherein the anisotropic rare earth magnetic powder is a SmFeN magnetic powder.

8. 7. 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. 7. 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 molding a cylindrical bonded magnet, the mold having an inner mold portion including a non-magnetic member, an outer mold portion including a non-magnetic member, a first alignment magnet, and a second alignment magnet, The inner mold portion has an outer surface that is circular in cross section in a predetermined direction, The outer mold part has an inner surface that is positioned away from an outer surface of the inner mold part and has a circular shape when viewed in a cross section in the predetermined direction, The first orientation magnet and the second orientation magnet are arranged to sandwich the inner mold part and the outer mold part so that a magnetic field is applied in the predetermined direction during magnetic field orientation, A mold for molding cylindrical bonded magnets, in which, when viewed in a cross-sectional view in the specified direction, the straight-line distance in the magnetic field application direction passing through the tangent point of the circle defined by the inner surface of the outer mold portion for the first orientation magnet and the second orientation magnet is shorter than the straight-line distance in the magnetic field application direction passing through the center of the circle defined by the outer surface of the inner mold portion for the first orientation magnet and the second orientation magnet.

11. The mold for molding cylindrical bonded magnets according to claim 10 , wherein the outer mold portion has an outer surface that is elliptical in cross section in the predetermined direction.

12. 12. The mold for molding a cylindrical bonded magnet according to claim 10 or 11, further comprising a magnetic member inside the inner mold portion.

13. 12. The mold for molding a cylindrical bonded magnet according to claim 10, wherein the first orientation magnet and the second orientation magnet are electromagnets.

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