Mold for Bond Magnet Molding and Method for Manufacturing Bond Magnet

Abstract

To provide a bond magnet molding die capable of easily taking out a bond magnet molded article from the die without breaking the same.SOLUTION: A bond magnet molding die comprises: an outside die 4; an inside die 3 inserted into the outside die 4; and a first punch and a second punch movable along the center axis direction of the hole of the inside die 3, in which the inside die 3 is splittable.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a mold for forming bonded magnets, a method for manufacturing bonded magnets using the mold, and further to bonded magnets produced by the manufacturing method.

Background Art

[0002] Patent Document 1 discloses a method for manufacturing a molded body of SmFeN-based magnetic powder using a Zn alloy as a binder. FIG. 1 discloses a mold composed of an inner mold made of cemented carbide and an outer mold made of a metal material softer than the inner mold. However, the inner mold cannot be divided.

[0003] Patent Documents 2 to 4 describe molds for sintered magnet forming. However, none of the molds having a two-layer structure with an outer mold disclose that the mold itself can be divided, and all are directed to sintered magnets.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a mold for forming bonded magnets that can easily remove a molded bonded magnet from the mold without damage.

Means for Solving the Problems

[0006] The mold for forming a bonded magnet according to one aspect of the present invention is a mold for forming a bonded magnet, comprising an outer mold, an inner mold inserted into the outer mold, and a first punch and a second punch movable along the central axis direction of the hole of the inner mold, wherein the inner mold is divisible.

[0007] A method for manufacturing a bonded magnet according to one aspect of the present invention includes a mixing step of mixing a magnetic powder having an average particle diameter of 10 μm or less and a thermosetting resin to obtain a composition for a bonded magnet, a compression step of filling the composition for a bonded magnet into the mold for forming a bonded magnet and then compressing it to obtain a formed body for a bonded magnet, a heat treatment step of heat-treating the formed body for a bonded magnet. It includes.

[0008] Also, a method for manufacturing a bonded magnet according to one aspect of the present invention includes a first compression step of filling a magnetic powder having an average particle diameter of 10 μm or less into the mold for forming a bonded magnet, compressing it while magnetically orienting it to obtain a first formed body, a second compression step of bringing the first formed body into contact with a thermosetting resin and then compressing it to obtain a second formed body, a heat treatment step of heat-treating the second formed body. It includes.

[0009] Furthermore, a bonded magnet according to one aspect of the present invention is produced by the method for manufacturing a bonded magnet.

Advantages of the Invention

[0010] According to the mold for forming a bonded magnet of the present invention, since the inner mold is divisible, the formed bonded magnet can be easily taken out from the inner mold without being damaged.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments shown below are merely examples for embodying the technical idea of the present invention, and the present invention 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.

[0013] The mold for forming bonded magnets of this embodiment is a mold for forming bonded magnets, which comprises an outer mold, an inner mold inserted into the outer mold, and a first punch and a second punch that are movable along the central axis direction of the holes of the inner mold, characterized in that the inner mold is separable.

[0014] In a non-separable mold, the formed product is pushed out and taken out with a punch. However, at this time, friction and springback occur between the mold and the formed product, and the formed product may be damaged. In particular, in a brittle bonded magnet with a high content of magnetic powder, it is more likely to be damaged. In the mold of the present invention, after taking out the formed product and the inner mold at the same time, the mold can be divided and disassembled, and the formed product can be taken out. Therefore, the friction and springback generated between the mold and the formed product can be significantly reduced, and the damage of the formed product during the taking-out process can be suppressed.

[0015] The splitting direction of the inner mold is not particularly limited, but in terms of the friction between the molded product and the mold and the suppression of springback, it is preferably possible to split in a direction that is not substantially perpendicular to the central axis direction of the hole, and more preferably possible to split in a direction substantially parallel to the central axis direction of the hole. Here, in the case of being substantially perpendicular, the angle from the perpendicular state with respect to the central axis direction of the hole is preferably ±5 degrees or less, and more preferably ±1 degree or less. Also, in the case of being substantially parallel, the inclination of the central axis of the splitting direction with respect to the central axis direction of the hole is preferably 5 degrees or less, and more preferably 1 degree or less.

[0016] The inner mold only needs to be splittable into two or more parts, but it is preferably splittable into four or more parts. FIG. 1 shows an external view of the inner mold 3 and the outer mold 4 that can be split into four parts, and FIG. 2 shows a cross-sectional view in the vertical direction thereof. When using this mold, a rectangular prism bonded magnet can be obtained. While holding one side of the hole with the second punch 2, the bond magnet composition is injected into the cavity 5 in the inner mold, and compressed from the other side with the first punch 1, and the thermosetting resin is cured while heating to produce a molded product. The shapes of the individual parts of the inner mold may be different from each other, but it is preferable that all have the same shape. Examples of the shapes of the individual parts include a rectangular parallelepiped, a cube, and a trapezoidal prism.

[0017] FIG. 3 shows an external view of the inner mold 3 and the outer mold 4 that can be split into eight parts, and FIG. 4 shows a cross-sectional view in the vertical direction thereof. When using this mold, a cylindrical bonded magnet can be obtained, and a cylindrical bonded magnet can be obtained by installing a cylindrical insert 9 in the center. The second punch 2 and the insert 9 are inserted into the inner mold, the bond magnet composition is injected into the formed cavity 5, and compressed from the other side with the first punch 1, and the thermosetting resin is cured while heating to produce a molded product. The shapes of the individual parts of the inner mold may be different from each other, but it is preferable that all have the same shape. Examples of the shapes of the individual parts include an arc column shape.

[0018] The material of the inner mold is preferably a hard alloy. Examples include magnetic steels such as SKD11 and SKD61, and non-magnetic steels and non-magnetic cemented carbides such as silver alloy QS15, QS25, QS35, Q2, Q3, Q5, and Q7. The material can be appropriately selected according to the purpose of forming a magnetic circuit in the mold corresponding to the pattern of the magnetization direction formed on the bonded magnet compact. If two molds facing each other across the cavity are both made of magnetic steel or non-magnetic steel, a pattern of a specific magnetization direction can be imparted to the bonded magnet. For example, when using an inner mold that can be divided into four or more parts, by making the mold facing the orientation magnetic field a magnetic steel and the mold not facing the orientation magnetic field a non-magnetic cemented carbide, the orientation of the magnetic powder can be improved and the residual magnetic flux density can be increased.

[0019] The inner mold preferably has a clearance on at least one or more of the contact surfaces between the divided molds. By having a clearance, the occurrence of springback can be alleviated. When using magnetic powder with an average particle size of 10 μm or less, the clearance is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 60 μm or less.

[0020] The size of the cavity of the inner mold is not particularly limited, but so that the excess thermosetting resin can be easily removed, the volume of the molded product is preferably in the range of 0.1 cm 3 or more and 10 cm 3 or less.

[0021] The outer mold covers and holds the periphery of the inner mold so that the size of the cavity inside the inner mold does not change due to the compression pressure. Therefore, the outer mold can be made non-separable in the splitting direction of the inner mold. In the mold for bonded magnet forming shown in Fig. 1, the outer mold covers the entire side surface of the inner mold, but it may also hold a part of the side surface of the inner mold. The material of the outer mold is preferably a relatively soft metal material, and examples include magnetic steels such as SS400, S45C, S55C, NAK55, NAK80, and non-magnetic steels such as SUS304, HPM75. The material can be appropriately selected according to the purpose of forming a magnetic circuit in the mold corresponding to the pattern of the magnetization direction formed in the bonded magnet formed body. Also, the outer mold in contact with the inner mold can also be a split mold. For example, when using an outer mold that can be split into four or more parts, the mold facing the orientation magnetic field is made of magnetic steel, and the mold not facing the orientation magnetic field is made of non-magnetic steel, so that the orientation of the magnetic powder can be improved and the residual magnetic flux density can be increased. In the case of a split mold, for example, the outer molds can be fastened with screws or the like, the outer molds having concave or convex portions can be fitted together by press-fitting, or a new outer mold that cannot be split further outside the outer mold can be provided to maintain the form of the outer mold.

[0022] The mold can be provided with magnetization means for orienting the magnetic powder in the injected bonded magnet material and heating means for thermosetting the injected thermosetting resin.

[0023] Examples of the magnetization means for orienting the magnetic powder in the injected bonded magnet material include an electromagnetic coil installed outside the mold, a permanent magnet, and an outer mold containing a permanent magnet. The outer mold containing a permanent magnet may be made entirely of non-magnetic steel, but for the permanent magnet contained, it is preferable that the material of the surface facing the orientation magnetic field is magnetic steel, and the material of the surface not facing the orientation magnetic field is non-magnetic steel so that magnetic short-circuiting does not occur.

[0024] Figs. 5 to 7 show top views of molds for forming bonded magnets in the shape of square columns, which are composed of four inner molds and four outer molds in three modes. In each figure, (a) shows a mold magnetized by an electromagnetic coil installed outside the mold, (b) shows a mold magnetized by a permanent magnet installed outside the mold, and (c) shows a mold magnetized using an outer mold containing a permanent magnet. With these molds, a bonded magnet magnetized from the N-pole electromagnetic coil or magnet in the direction of the S-pole electromagnetic coil or magnet can be produced. As shown in (a) and (b), among the four inner molds and four outer molds existing in the magnetization direction, the two molds facing the orientation magnetic field are made of magnetic steel so that the bonded magnet is magnetized, and the two molds not facing the orientation magnetic field are made of non-magnetic steel or non-magnetic cemented carbide so that magnetism does not short-circuit. Also, as shown in (c), among the four inner molds existing in the magnetization direction, the two inner molds facing the orientation magnetic field are made of magnetic steel so that the bonded magnet is magnetized, the two inner molds not facing the orientation magnetic field are made of non-magnetic steel or non-magnetic cemented carbide so that magnetism does not short-circuit, and the two outer molds not facing the orientation magnetic field are made of non-magnetic steel so that magnetism does not short-circuit.

[0025] Figures 8(a) to (c) show top views of a cylindrical or columnar mold for forming a bonded magnet, which is composed of eight inner molds and eight outer molds. Figure 8(d) shows the magnetic poles of a cylindrical bonded magnet produced by the cylindrical bonded magnet forming mold. Note that a cylindrical bonded magnet can be obtained by inserting the nested part 9, and a columnar bonded magnet can be obtained without inserting it. (a) shows a mold magnetized by an electromagnetic coil installed outside the mold, (b) shows a mold magnetized by a permanent magnet installed outside the mold, and (c) shows a mold magnetized using an outer mold containing a permanent magnet. Using these molds, a bonded magnet having magnetic poles as shown in (d), magnetized from the electromagnetic coil or magnet of the N pole in the direction of the electromagnetic coil or magnet of the S pole, can be produced. As shown in (a) and (b), among the eight inner molds and eight outer molds existing in the magnetization direction, the four molds facing the orientation magnetic field are made of magnetic steel so that the bonded magnet is magnetized, and the four molds not facing the orientation magnetic field are made of non-magnetic steel or non-magnetic cemented carbide so that magnetism does not short-circuit. Also, as shown in (c), among the eight inner molds existing in the magnetization direction, the four inner molds facing the orientation magnetic field are made of magnetic steel so that the bonded magnet is magnetized, the four inner molds not facing the orientation magnetic field are made of non-magnetic steel or non-magnetic cemented carbide so that magnetism does not short-circuit, and the four outer molds not facing the orientation magnetic field are made of non-magnetic steel so that magnetism does not short-circuit.

[0026] The method for manufacturing a bonded magnet according to this embodiment includes a mixing step of mixing a magnetic powder having an average particle size of 10 μm or less and a thermosetting resin to obtain a composition for a bonded magnet, a compression step of filling the composition for a bonded magnet into the mold for forming a bonded magnet and then compressing it to obtain a formed body for a bonded magnet, a heat treatment step of heat-treating the formed body for a bonded magnet, and is characterized by including these steps.

[0027] <Mixing step> In the mixing step, a magnetic powder having an average particle size of 10 μm or less and a thermosetting resin are mixed to obtain a composition for a bonded magnet.

[0028] The material of the magnetic powder is not particularly limited, and examples include rare earth magnetic materials such as SmFeN-based, NdFeB-based, and SmCo-based. Among them, SmFeN-based magnetic powder is preferable in terms of heat resistance and non-inclusion of rare metals. As the SmFeN-based magnetic powder, it has a Th2Zn 17 type crystal structure, and the general formula is Sm x Fe 100-x-y N y and is a nitride composed of the rare earth metal samarium Sm, iron Fe, and nitrogen N. Here, x is preferably 8.1 atomic% or more and 10 atomic% or less, y is preferably 13.5 atomic% or more and 13.9 atomic% or less, and the balance is mainly Fe.

[0029] The SmFeN-based magnetic powder can be produced by the method disclosed in Japanese Patent Application Laid-Open No. 11-189811. The NdFeB-based magnetic powder can be produced by the HDDR method disclosed in International Publication No. 2003 / 85147. The SmCo-based magnetic powder can be produced by the method disclosed in Japanese Patent Application Laid-Open No. 08-260083. Further, as the magnetic powder, for example, those surface-treated with a silane coupling agent by the method shown in Patent Document 1 can be used.

[0030] The average particle size of the magnetic powder is 10 μm or less, but from the viewpoint of magnetic properties, 6 μm or less is preferable, and 4 μm or less is more preferable. When it exceeds 10 μm, the coercive force of the magnetic powder tends to decrease significantly due to the increase in crystal grain size.

[0031] The thermosetting resin is not particularly limited as long as it can be thermoset, and examples include thermosetting monomers, thermosetting prepolymers, thermosetting polymers, etc. Examples of thermosetting monomers include norbornene-based, dicyclopentadiene, alicyclic epoxy monomers, etc. Examples of thermosetting prepolymers include epoxy resins, phenolic resins, melamine resins, guanamine resins, unsaturated polyesters, vinyl ester resins, diallyl phthalate resins, silicone resins, alkyd resins, furan resins, acrylic resins, urea resins, melamine resins, allyl carbonate resins, etc. Examples of thermosetting polymers include polyurethane resins, polyimide resins, polyester resins, etc.

[0032] Together with the thermosetting resin, an initiator or curing agent for the thermosetting resin can be blended. Examples of initiators include radical initiators such as Grubbs catalyst, RuCl3 / alcohol mixture, dihalogen, azo compounds, and cationic polymerization initiators such as antimony-based and PF6-based. Examples of curing agents include amine-based curing agents, acid anhydride-based curing agents, polyamide-based curing agents, imidazole-based curing agents, phenolic resin-based curing agents, polymercaptan resin-based curing agents, polysulfide resin-based curing agents, organic acid hilalide-based curing agents, etc. Examples of amine-based curing agents include diaminodiphenyl sulfone, metaphenylenediamine, diaminodiphenyl methane, diethylenetriamine, triethylenetetramine, isocyanate, etc.

[0033] The viscosity of the thermosetting resin is not particularly limited, but preferably 100 mPa·S or less, more preferably 50 mPa·S or less, even more preferably 15 mPa·S or less, and most preferably 10 mPa·S or less. When it exceeds 100 mPa·S, impregnation may not be sufficient and there is a tendency to cause molding defects.

[0034] The method of mixing the magnetic powder and the thermosetting resin is not particularly limited, and examples include mixing with various mixers such as an axial mixer and a Henschel mixer, a method of spraying the thermosetting resin and applying it evenly, an impregnation method of bringing a compact into contact with a liquid of the thermosetting resin and absorbing it. The mixing temperature is preferably -40°C or higher and 30°C or lower so that the thermosetting resin does not cure.

[0035] <Compression process> In the compression process, after filling the composition for bonded magnet into the mold for forming a bonded magnet, it is compressed to obtain a formed body for bonded magnet.

[0036] The magnitude of the applied pressure is not particularly limited, but it is preferably 0.5 ton / cm 2 or more and less than 15 ton / cm 2 More preferably, it is 1 ton / cm 2 or more and less than 12 ton / cm 2 If it is less than 0.5 ton / cm, the applied pressure is insufficient and it becomes difficult to highly fill the magnetic powder. If it is 15 ton / cm 2 or more, it is necessary to use a high-hardness steel material such as cemented carbide for the members constituting the mold, and since the members wear quickly, it tends to be a cost-up factor. 2 Here, the compression is preferably performed while magnetically orienting the magnetic powder. The magnitude of the external magnetic field applied for magnetic orientation is not particularly limited, but it is preferably 0.5 T or more, and more preferably 1 T or more. If it is less than 0.5 T, the magnet may not be sufficiently oriented.

[0037] Here, the compression is preferably performed while magnetically orienting the magnetic powder. The magnitude of the external magnetic field applied for magnetic orientation is not particularly limited, but it is preferably 0.5 T or more, and more preferably 1 T or more. If it is less than 0.5 T, the magnet may not be sufficiently oriented.

[0038] <Heat treatment process> In the heat treatment process, the formed body for bonded magnet is heat-treated to cure the thermosetting resin and obtain a bonded magnet.

[0039] The heat treatment temperature is not particularly limited, but it is preferably 100°C or higher and 150°C or lower, and more preferably 110°C or higher and 130°C or lower. If it is less than 100°C, the curing of the resin does not proceed sufficiently and the strength becomes insufficient. If it exceeds 150°C, the oxidation of the resin proceeds and the strength tends to become insufficient.

[0040] The heat treatment time is not particularly limited, but is preferably 1 minute or more and 120 minutes or less, and more preferably 3 minutes or more and 60 minutes or less. If it is less than 1 minute, the curing of the resin does not proceed sufficiently and the strength becomes insufficient. If it exceeds 120 minutes, the oxidation of the resin tends to proceed and the strength becomes insufficient.

[0041] In addition, another method for manufacturing a bonded magnet according to the present embodiment includes a first compression step of filling a mold for forming a bonded magnet with magnetic powder having an average particle size of 10 μm or less, compressing while magnetically orienting, and obtaining a first molded body, a second compression step of compressing after bringing the first molded body into contact with a thermosetting resin to obtain a second molded body, a heat treatment step of heat-treating the second molded body, and is characterized by including the above.

[0042] <First Compression Step> In the first compression step, magnetic powder having an average particle size of 10 μm or less is compressed while being magnetically oriented to obtain a first molded body. The first compression step may be performed not only once but also a plurality of times.

[0043] As the magnetic powder to be used, the same magnetic powder as described above can be used.

[0044] The magnitude of the external magnetic field applied for magnetic orientation is not particularly limited, but is preferably 0.5 T or more, and more preferably 1 T or more. If it is less than 0.5 T, the magnet may not be sufficiently oriented.

[0045] The magnitude of the pressure applied is not particularly limited, but is preferably 0.1 ton / cm 2 or more and less than 4 ton / cm 2 and more preferably 0.5 ton / cm 2 or more and less than 2 ton / cm 2 If it is less than 0.1 ton / cm 2 the rearrangement of the magnetic powder does not proceed, and the filling rate of the magnetic powder in the finally obtained second molded body tends to decrease. If it is 4 ton / cm 2In the above, when impregnating the resin into the first molded body described later, it cannot be sufficiently impregnated and tends to result in molding defects.

[0046] <Second Compression Step> In the second compression step, after bringing the first molded body into contact with the thermosetting resin, it is compressed to obtain a second molded body. The magnetic powder used in the present invention has an average particle size of 10 μm or less and is very bulky, so the packing ratio is low. If, after sufficient magnetic orientation in the first compression step, it is brought into contact with the thermosetting resin and compressed, excess thermosetting resin is discharged, the packing ratio and orientation ratio of the magnetic powder increase, and the magnetic properties of the bonded magnet are improved.

[0047] As the thermosetting resin to be used, the same thermosetting resin as described above can be used, and the initiator and curing agent of the above-described thermosetting resin can be blended.

[0048] The method of bringing them into contact is not particularly limited, and for example, a thermosetting resin may be added to the first molded body present in the mold and impregnated. The amount of the thermosetting resin to be brought into contact is not particularly limited, but is preferably 0.25 times or more and 2 times or less the volume of the molded body, and more preferably 0.5 times or more and 1.5 times or less. If it is less than 0.25 times, impregnation cannot be sufficiently performed and molding defects occur, and if it exceeds 2 times, the resin and magnetic powder overflow from the mold, the yield decreases, and at the same time, the overflowed material must be removed.

[0049] In the second compression step, the magnitude of the pressure applied is not particularly limited, but in terms of producing a magnet with a higher filling, it is preferably equal to or higher than the compression pressure in the first compression step. Specifically, it is preferably 4 tons / cm 2 or more and less than 11 tons / cm 2 and more preferably 6 tons / cm 2 or more and less than 10 tons / cm 2 If it is less than 4 tons / cm 2 , the packing ratio of the magnetic powder cannot be sufficiently increased, and if it exceeds 11 tons / cm 2 , the coercive force tends to decrease.

[0050] Even in the second compression step, magnetic orientation can be performed in the same manner as in the first compression step. When performing magnetic orientation, the magnitude of the externally applied magnetic field is not particularly limited, and the magnitude of the externally applied magnetic field in the first compression step can be directly applied.

[0051] <Heat treatment step> The heat treatment temperature is not particularly limited, but is preferably 100°C or higher and 150°C or lower, and more preferably 110°C or higher and 130°C or lower. If it is less than 100°C, the curing of the resin does not proceed sufficiently and the strength becomes insufficient. If it exceeds 150°C, the oxidation of the resin proceeds and the strength tends to become insufficient.

[0052] The heat treatment time is not particularly limited, but is preferably 1 minute or longer and 120 minutes or shorter, and more preferably 3 minutes or longer and 60 minutes or shorter. If it is less than 1 minute, the curing of the resin does not proceed sufficiently and the strength becomes insufficient. If it exceeds 120 minutes, the oxidation of the resin proceeds and the strength tends to become insufficient.

[0053] After the heat treatment is completed, the inner mold and the punch are pulled out and the inner mold is divided to take out the bonded magnet compact, and magnetization is performed by applying a pulsed magnetic field of 6T in the orientation direction.

[0054] Regarding the magnetization magnetic field, it is preferably 1T or higher and 36T or lower, and more preferably 3T or higher and 12T or lower. If it is less than 1T, the magnet cannot be sufficiently magnetized and a sufficient residual magnetic flux density cannot be obtained. If it exceeds 36T, the heat shock due to the heat generated during magnetization is too large and the magnet may crack.

[0055] The bonded magnet of the present embodiment is produced by the method for manufacturing a bonded magnet of the present invention.

[0056] The impregnation deficiency rate of the bonded magnet refers to the ratio of the area that is not actually occupied by resin in the area that should be occupied by resin. The impregnation deficiency rate is preferably 10% or less, more preferably 1% or less. If it exceeds 10%, the mechanical strength tends to decrease. The impregnation deficiency rate is calculated by binarization analysis of brightness (BMPEdit) of the area of the resin-free part (resin deficiency part area) and the area of the entire cut surface (cut surface area) which is the outline of the image, in an image observed at the lowest magnification that includes the entire cut surface of the bonded magnet using an optical microscope, and is taken as the ratio of the resin deficiency part area to the cut surface area. The cut surface of the bonded magnet is produced by cutting the obtained bonded magnet through the center of the surface in contact with the resin, perpendicular to the surface in contact with the resin, and with the largest cut area.

[0057] The ratio of the magnetic powder contained in the bonded magnet, that is, the filling rate, is not particularly limited, but is preferably 71% by volume or more, more preferably 72% by volume or more. If it is less than 71% by volume, there is a tendency that a sufficient residual magnetic flux density cannot be obtained.

[0058] The coercive force of the bonded magnet is not particularly limited, but is preferably 1020 kA / m or more, more preferably 1150 kA / m or more. If it is less than 1020 kA / m, there is a tendency that demagnetization occurs when used in a powerful motor or the like.

[0059] The residual magnetic flux density of the bonded magnet is not particularly limited, but is preferably 0.75 T or more, more preferably 0.8 T or more. If it is less than 0.75 T, there is a tendency that sufficient torque cannot be obtained when used in a motor or the like.

[0060] The magnetic flux orientation rate of the bonded magnet is preferably 80% or more, more preferably 81% or more. By setting it to 80% or more, the residual magnetic flux density becomes high. Here, the orientation rate is obtained by dividing the residual magnetic flux density of the bonded magnet by the product of the residual magnetic flux density of the magnetic powder and the volume filling rate of the bonded magnet.

Examples

[0061] Hereinafter, examples will be described. Unless otherwise specified, “%” is based on mass.

[0062] Example 1 First Compression Step Using the mold for bonded magnet forming shown in Fig. 1 (clearance 30 μm) consisting of an inner mold made of non-magnetic cemented carbide with a 5 mm square cavity and an outer mold made of SUS304, a relatively soft non-magnetic steel, 0.8 g of SmFeN magnetic powder (average particle size 3.4 μm, density 7.55 g / cc) was filled into the inner mold, upper and lower punches were attached, and compression was carried out at a compression pressure of 1 ton / cm 2 in a 1 T orientation magnetic field to obtain a first formed body.

[0063] Second Compression Step Subsequently, the upper punch was removed, and 0.1 g of a 100:1 mixed solution of tetrahydroindene diepoxide (viscosity 20 mPa·s @ 25°C, density 1 g / cc, manufactured by JXTG Energy Corporation, product number THI-DE), an alicyclic epoxy monomer, and dimethyl-p-acetoxyphenylsulfonium = hexafluoroantimonate (manufactured by Sanshin Chemical Co., Ltd., product number SI-150L) as a reaction initiator was dropped onto the first formed body and held for 30 seconds. Again, the upper punch was attached, and compression was carried out at a compression pressure of 8 ton / cm 2 in a 1 T orientation magnetic field to impregnate tetrahydroindene diepoxide and discharge excess mixed solution components, obtaining a second formed body.

[0064] Heat Treatment Step Subsequently, the second formed body was continuously heated at 140°C for 15 minutes while being compressed to cure the thermosetting resin and produce a bonded magnet. Subsequently, after pulling out the bonded magnet together with the inner mold from the outer mold, the inner mold was divided to remove the magnet. The filling rate, yield, magnet breakage, and residual magnetic flux density of the obtained bonded magnet were confirmed by the methods shown below. The results are shown in Table 1.

[0065] <Magnetic Powder Filling Rate> The weight and dimensions of the obtained bonded magnet were measured to obtain the density ρ (g / cm 3) was calculated, and the filling rate F (Vol%) of the magnetic powder was derived from the following formula. F (Vol%) = (100 - 0) ÷ (7.55 - 1) × (ρ - 1)

[0066] <Yield> From the following formula, the theoretical weight (g) of the molded product at a yield of 100% was obtained, and the yield was calculated by dividing the actual weight of the molded product by the theoretical weight. The yield was set to 0% when damage was confirmed in the magnet. The decrease in the yield is caused by some magnetic powder flowing out during the process of discharging the excess mixed liquid component by compression after impregnation. Table 1 shows the average yield when five bonded magnets were produced. Theoretical weight (g) = 0.8 × {7.55F + 1(100 - F)} ÷ 7.55F

[0067] <Magnet damage> The presence or absence of damage to the removed magnet was visually confirmed.

[0068] <Magnetic properties of the magnet> The obtained magnet was installed in an air-core coil and magnetized with an applied magnetic field of 6T. The residual magnetic flux density of the magnet after magnetization was measured using a BH curve tracer.

[0069] Example 2 A bonded magnet was obtained in the same manner as in Example 1 except that the clearance of the mold for molding the bonded magnet was changed to 60 μm. The results are shown in Table 1.

[0070] Example 3 A bonded magnet was obtained in the same manner as in Example 1 except that the mold for molding the bonded magnet shown in Fig. 6(a) (clearance 30 μm) was used, where two of the inner molds with a 5 mm square cavity facing the orientation magnetic field were made of magnetic steel SKD61 and two of the inner molds not facing the orientation magnetic field were made of non-magnetic cemented carbide. The results are shown in Table 1.

[0071] Comparative Example 1 A bonded magnet was obtained in the same manner as in Example 1, except that a mold for forming a bonded magnet shown in Fig. 9, which consists of an inner mold made of non-magnetic cemented carbide provided with a 5-mm corner cavity and an outer mold made of relatively soft non-magnetic steel SUS304, was used. The results are shown in Table 1. When taking out the bonded magnet from the inner mold, all 5 bonded magnets were damaged and dimensional measurement could not be performed, so the magnetic powder filling rate could not be derived.

[0072]

Table 1

[0073] From Table 1, it was confirmed that in Examples 1, 2, and 3 using a dividable inner mold, the yield was higher and the breakage of the bonded magnet disappeared compared to Comparative Example 1 using an undividable inner mold. Also, in Examples 1 and 3 where the clearance between the inner molds was reduced, it was confirmed that the yield was higher compared to Example 2. Furthermore, in Example 3 where a part of the inner mold was changed to magnetic steel, it was confirmed that the residual magnetic flux density was higher compared to Example 1 due to the concentration of the orientation magnetic field in the cavity.

Industrial Applicability

[0074] According to the method for manufacturing a bonded magnet of the present invention, since a bonded magnet having a high content of magnetic powder and excellent magnetic properties can be obtained, it can be suitably applied to uses such as motors.

Explanation of Signs

[0075] 1: First punch 2: Second punch 3: Inner mold 4: Outer mold 5: Cavity 6: Magnetic steel 7: Non-magnetic steel or non-magnetic cemented carbide 8: Encapsulated magnet 9: Nest 10: Magnet

Claims

1. A mixing step of mixing magnetic powder with an average particle diameter of 10 μm or less and a thermosetting resin to obtain a composition for bonded magnet; A compression step of filling the composition for bonded magnet into a mold for forming a bonded magnet and then compressing it to obtain a formed body for bonded magnet; A heat treatment step of heat-treating the formed body for bonded magnet; comprising: The mold for forming a bonded magnet comprises an outer mold, an inner mold inserted into the outer mold, and a first punch and a second punch movable along the central axis direction of the hole of the inner mold. The inner mold is divisible, and among the contact surfaces of the divided molds, at least one contact surface has a clearance of 5 μm or more and 100 μm or less. A method for manufacturing a bonded magnet.

2. A first compression step of filling magnetic powder with an average particle diameter of 10 μm or less into a mold for forming a bonded magnet, compressing while magnetically orienting to obtain a first formed body; A second compression step of contacting the first formed body with a thermosetting resin and then compressing to obtain a second formed body; A heat treatment step of heat-treating the second formed body; comprising: The mold for forming a bonded magnet comprises an outer mold, an inner mold inserted into the outer mold, and a first punch and a second punch movable along the central axis direction of the hole of the inner mold. The inner mold is divisible. A method for manufacturing a bonded magnet.

3. The method for manufacturing a bonded magnet according to claim 2, wherein the inner mold has a clearance at at least one of the contact surfaces of the divided molds.

4. The method for manufacturing a bonded magnet according to claim 2 or 3, wherein the compression pressure in the second compression step is equal to or higher than the compression pressure in the first compression step.

5.

6. The method for manufacturing a bonded magnet according to any one of claims 1 to 5, wherein the inner mold is divisible in a direction substantially non-perpendicular to the central axis direction of the hole. The compression pressure in the first compression step is less than 4 tons / cm ２ The method for manufacturing a bonded magnet according to any one of claims 2 to 4, wherein the compression pressure is less than 4 tons / cm

7. The method for manufacturing a bonded magnet according to any one of claims 1 to 6, wherein the inner mold is divisible in a direction substantially parallel to the central axis direction of the hole.

8. The method for manufacturing a bonded magnet according to any one of claims 1 to 7, wherein the inner mold is divisible into four or more parts.

9. The method for manufacturing a bonded magnet according to any one of claims 1 to 8, wherein the viscosity of the thermosetting resin is 100 mPa·S or less.

10. ​ ​ The method for manufacturing a bonded magnet according to any one of claims 1 to 9, wherein the thermosetting resin is a thermosetting monomer, a thermosetting prepolymer or a thermosetting polymer.

11. The method for manufacturing a bonded magnet according to any one of claims 1 to 10, wherein the proportion of the magnetic powder contained in the bonded magnet is 71% by volume or more.

12. The method for manufacturing a bonded magnet according to any one of claims 1 to 11, wherein the magnetic powder is an SmFeN-based magnetic powder.

13. A bonded magnet produced by the method for manufacturing a bonded magnet according to any one of claims 1 to 12.

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