Method for producing granulated powder

Abstract

To provide a method for producing granulated powder in which the surface of each of the multiple magnetic particles contained in the granulated powder can be easily coated with a resin composition. [Solution] The raw materials for the granulated powder (30) are a slurry 9 containing a magnet powder consisting of multiple magnet particles 3, a resin composition 5, and an organic solvent. The magnet powder is an alloy containing Sm, Fe, and N. The resin composition 5 contains a thermosetting resin. By spraying the slurry 9, multiple fine particles 10 made of the slurry 9 are formed. When a magnetic field H is generated by the coil 4, the multiple fine particles 10 are supplied to the inside of the coil 4 by the magnetic field H. Inside the coil 4, the multiple fine particles 10 aggregate due to the magnetic field H, forming multiple aggregates 20. By heating the multiple aggregates 20, the organic solvent is removed from the multiple aggregates 20, and the multiple aggregates 20 become granulated powder (30).

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing granulated powder.

Background Art

[0002] Sm-Fe-N-based permanent magnets (samarium-iron-nitrogen-based permanent magnets) can be manufactured from inexpensive raw materials compared to other rare-earth magnets such as Nd-Fe-B-based permanent magnets (neodymium-iron-boron-based permanent magnets), and have excellent magnetic properties. However, since the crystal structure of Sm-Fe-N-based permanent magnets is liable to deteriorate at high temperatures (about 500°C), it is difficult to manufacture sintered magnets from Sm-Fe-N-based permanent magnets. Therefore, Sm-Fe-N-based permanent magnets are used as raw materials for bonded magnets that can be manufactured by heating at low temperatures (thermosetting of the resin composition mixed with the magnet powder) in which the crystal structure is maintained (see Patent Document 1 below).

[0003] As a raw material for bonded magnets, a compound containing magnet powder (a large number of magnet particles made of a permanent magnet) and a resin composition is used. In the manufacture of bonded magnets, the compound is supplied into a mold. While applying a magnetic field generated by a coil to the compound in the mold, the compound in the mold is heated and compressed. By this molding process, a molded body made of magnet powder and a resin composition is obtained. Each magnet particle (magnetic domain in each magnet particle) in the molded body is magnetized and oriented along the magnetic field.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The resin composition in a bonded magnet functions as a binder, binding multiple magnet particles together. This binding allows the bonded magnet to possess sufficient mechanical strength. To ensure reliable binding of multiple magnet particles within a bonded magnet, it is desirable to cover the surface of each individual magnet particle with the resin composition. However, since magnet powder is made of metal (alloy), it tends to aggregate. Furthermore, the smaller the particle size of the magnet powder, the larger its specific surface area, and the more easily it aggregates. For these reasons, covering the surface of each individual magnet particle with the resin composition is not easy. For example, excessive load on the kneading machine makes it difficult to cover the surface of each individual magnet particle with the resin composition through kneading of the magnet powder and resin composition.

[0006] One aspect of this disclosure is to provide a method for producing granulated powder in which the surface of each of the multiple magnetic particles contained in the granulated powder can be easily covered with a resin composition. [Means for solving the problem]

[0007] For example, one aspect of this disclosure relates to a method for producing granulated powder as described in [1] below.

[0008] [1] A method for producing granulated powder, The raw materials for the granulated powder are a slurry containing a magnet powder consisting of multiple magnet particles, a resin composition, and an organic solvent. The aforementioned magnetic powder is an alloy containing samarium, iron, and nitrogen. The aforementioned resin composition includes a thermosetting resin, By spraying the slurry, a plurality of fine particles made of the slurry are formed. In a state where a magnetic field is generated by the coil, a plurality of the fine particles are supplied to the inside of the coil by the magnetic field. By agglomerating a plurality of the fine particles inside the coil using the magnetic field, a plurality of aggregates are formed from the plurality of fine particles. By heating the multiple aggregates and removing the organic solvent from them, the multiple aggregates become the granulated powder. A method for producing granulated powder. [Effects of the Invention]

[0009] According to one aspect of this disclosure, a method for producing granulated powder is provided, which allows the surface of each of the multiple magnetic particles contained in the granulated powder to be easily covered with a resin composition. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view showing a specific example of a method for producing granulated powder according to this disclosure. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present disclosure will be described below with reference to the drawings. In the drawings, equivalent components are denoted by the same reference numerals. The present disclosure is not limited to the embodiments described below. In Figure 1, X, Y and Z represent three mutually orthogonal coordinate axes. For example, the directions of the X and Y axes may be horizontal, and the direction of the Z axis may be vertical.

[0012] (Method for producing granulated powder) The method for producing granulated powder according to this embodiment uses a slurry containing a plurality of magnetic particles, a resin composition, and an organic solvent as raw materials for the granulated powder. The slurry may consist only of the magnetic powder, the resin composition, and the organic solvent. The slurry may further contain other components in addition to the magnetic powder, the resin composition, and the organic solvent. The magnetic powder is an alloy containing samarium, iron, and nitrogen. The resin composition contains a thermosetting resin. Part or all of the resin composition may be dissolved in the organic solvent because the surface of each of the plurality of magnetic particles is easily covered uniformly with the resin composition. For the same reason, the magnetic powder, the resin composition, and the organic solvent may be mixed. In other words, the plurality of magnetic particles may be dispersed in the slurry. In this disclosure, the components of the slurry excluding the magnetic powder are referred to as "coating components." In other words, the coating components are components containing the resin composition and the organic solvent. The coating components may consist only of the resin composition and the organic solvent.

[0013] Figure 1 is a cross-sectional view showing an overview of the method for manufacturing granulated powder according to this embodiment. The method for manufacturing granulated powder uses a sprayer, a magnetic field generator, and a heating mechanism. Parts of the sprayer other than the nozzle 2 (for example, the container in which the slurry 9 is contained) are omitted in Figure 1. Parts of the magnetic field generator other than the coil 4 (for example, the power supply mechanism electrically connected to the coil 4) are also omitted in Figure 1. The heating mechanism is also omitted in Figure 1. The cross-section shown in Figure 1 crosses the nozzle 2 (the opening of the nozzle 2) and the coil 4, and includes the central axis of the coil 4. The central axis of the coil 4 is a straight line that penetrates the inside of the coil 4 and whose distance from the inner wall of the coil 4 is 1 / 2 of the inner diameter of the coil 4. For example, the nozzle 2 may be positioned on the central axis of the coil 4, and the opening of the nozzle 2 and the end of the coil 4 may face each other.

[0014] The central axis of the coil 4 may be vertical, and the opening of the nozzle 2 may face the end of the coil 4 in the vertical direction. The central axis of the coil 4 may be horizontal, and the opening of the nozzle 2 may face the end of the coil 4 in the horizontal direction. The central axis of the coil 4 may be inclined with respect to the vertical direction.

[0015] Coil 4 is an air-core coil and a type of electromagnet. The method for manufacturing granulated powder is carried out when a magnetic field H is generated by coil 4. One end of coil 4 is the north pole, and the other end is the south pole, and the opening of nozzle 2 faces the south pole of coil 4. Each of the multiple lines that penetrate the inside of coil 4 shown in Figure 1 is a magnetic field line mf indicating the direction of the magnetic field H. In other words, the direction (arrow) of each magnetic field line mf indicates the direction of the magnetic field H. The direction and strength of the magnetic field H (i.e., the direction of each magnetic field line mf and the density of multiple magnetic field lines mf) can be freely controlled by adjusting the direction and absolute value of the current flowing through coil 4. The direction and absolute value of the current flowing through coil 4 can be freely adjusted by a power supply mechanism (power source) electrically connected to coil 4.

[0016] The direction of the magnetic field H (the direction of each of the multiple magnetic field lines mf) converges from the outside of coil 4 towards the inside of coil 4. In other words, the spacing between the multiple magnetic field lines mf decreases from the outside of coil 4 towards the inside of coil 4, reaching its minimum inside coil 4. Consequently, the strength of the magnetic field H (the density of the multiple magnetic field lines mf) increases from the outside of coil 4 towards the inside of coil 4, reaching its maximum inside coil 4.

[0017] In the method for producing granulated powder, a nozzle 2 sprays slurry 9 towards the inside of a coil 4. The spraying of slurry 9 from the nozzle 2 forms a plurality of fine particles 10 consisting of slurry 9 on the outside of the coil 4. The plurality of fine particles 10 consisting of slurry 9 can be rephrased as atomized slurry 9. Each of the plurality of fine particles 10 contains one or more magnetic particles 3 and a coating component 7. That is, each of the plurality of fine particles 10 contains one or more magnetic particles 3, a resin composition, and an organic solvent. Each of the plurality of fine particles 10 may consist only of one or more magnetic particles 3, a resin composition, and an organic solvent. Part or all of the surface of each of the one or more magnetic particles 3 contained in each fine particle 10 is covered with the coating component 7 (resin composition and organic solvent). Since the viscosity of the coating component 7 (a mixture of resin composition and organic solvent) is lower than that of the resin composition itself, the magnet powder (multiple magnet particles 3) and the coating component 7 in the slurry 9 are easily mixed uniformly, and the surface of each magnet particle 3 in the slurry 9 is easily covered with the coating component 7. In other words, due to the low viscosity of the slurry 9 caused by the organic solvent, the magnet powder is easily dispersed in the slurry 9, and aggregation of the magnet powder in the slurry 9 is easily suppressed. Furthermore, the pressure acting on the slurry 9 as it is sprayed from the nozzle 2 easily dissolves the aggregation of the magnet powder in the slurry 9. For these reasons, the surface of one or more magnet particles 3 contained in each fine particle 10 is easily covered uniformly with the coating component 7 (resin composition and organic solvent). Since the viscosity of the resin composition itself is higher than the viscosity of the coating component 7 (a mixture of the resin composition and the organic solvent), the viscosity of the mixture consisting only of the magnet powder and the resin composition (a mixture not containing an organic solvent) is significantly higher than the viscosity of the slurry 9. Therefore, when the mixture consisting only of the magnet powder and the resin composition is used instead of the slurry 9, it is difficult to uniformly mix the magnet powder and the resin composition in the mixture, the magnet powder in the mixture is likely to aggregate, and it is difficult to uniformly cover the surfaces of each of the plurality of magnet particles in the mixture with the resin composition. Furthermore, since the viscosity of the mixture consisting only of the magnet powder and the resin composition is significantly higher than the viscosity of the slurry 9, it is difficult to spray the mixture consisting only of the magnet powder and the resin composition from the nozzle 2 in the first place. The temperature of the slurry 9 sprayed from the nozzle 2 is not limited. The temperature of the slurry 9 may be a temperature at which the thermosetting of the resin composition in the slurry 9 is suppressed and the vaporization of the organic solvent in the slurry 9 is suppressed. For example, the temperature of the slurry 9 may be normal temperature (for example, 20 ° C ± 15 ° C) or lower.

[0018] In a state where a converging magnetic field H is generated from the outside of the coil 4 toward the inside of the coil 4, the plurality of fine particles 10 are supplied from the outside of the coil 4 (the tip of the nozzle 2) to the inside of the coil 4 by the magnetic field H. That is, the plurality of fine particles 10 formed outside the coil 4 move to the inside of the coil 4 through the end (S pole) of the coil 4 by the magnetic force received by one or more magnet particles 3 contained in each fine particle 10 from the magnetic field H. Further, the plurality of fine particles 10 aggregate by the magnetic field H inside the coil 4. As a result, a plurality of aggregates 20 are each formed from the plurality of fine particles 10 inside the coil 4. That is, one aggregate 20 consists of a plurality of fine particles 10. Another aggregate 20 may be formed by further aggregation of the plurality of aggregates 20 inside the coil 4. Another aggregate 20 may be formed by aggregation of one or more fine particles 10 and one or more aggregates 20 inside the coil 4. The plurality of microparticles 10 may move from the outside of the coil 4 to the inside of the coil 4 not only due to the magnetic force received from the magnetic field H but also due to gravity. The moving direction of each microparticle 10 (the direction of the velocity of each microparticle 10) inside the coil 4 does not necessarily coincide with the direction of the magnetic field H inside the coil 4. Since the plurality of microparticles 10 are gathered from the outside of the coil 4 to the inside of the coil 4 by the magnetic field H, the frequency at which the plurality of microparticles 10 contact each other inside the coil 4 is significantly higher than the frequency at which the plurality of microparticles 10 contact each other outside the coil 4. Therefore, it is easy for a plurality of aggregates 20 to be formed from the plurality of microparticles 10 inside the coil 4.

[0019] As described above, a part or the whole of the surface of each of the one or more magnet particles 3 contained in each microparticle 10 is likely to be covered with the coating component 7 (resin composition and organic solvent). Therefore, a part or the whole of the surface of each of the plurality of magnet particles 3 contained in each aggregate 20 formed from the plurality of microparticles 10 is also likely to be covered with the coating component 7 (resin composition and organic solvent).

[0020] Multiple aggregates 20 formed inside coil 4 move through the inside of coil 4 and out of coil 4 due to the magnetic force (and gravity) received from the magnetic field H. In other words, the multiple aggregates 20 formed inside coil 4 move through the end (N pole) of coil 4 and out of coil 4. The multiple aggregates 20 are heated outside coil 4 by a heating mechanism. The heating of the multiple aggregates 20 removes the organic solvent from the multiple aggregates 20. In other words, the organic solvent in the coating component 7 contained in each aggregate 20 vaporizes due to heating. The resin composition 5 in the coating component 7 solidifies as the organic solvent vaporizes and remains on the surface of each of the multiple magnet particles 3 contained in each aggregate 20. As a result, the multiple aggregates 20 become a granulated powder consisting of multiple granulated particles 30. Each of the multiple granulated particles 30 contains multiple magnet particles 3 and a resin composition 5 that covers part or all of the surface of each of the multiple magnet particles 3. In other words, one granulated particle 30 contains multiple magnet particles 3 and a resin composition 5. The resin composition 5 in each granulated particle 30 binds together multiple magnet particles 3 within each granulated particle 30. Each of the multiple granulated particles 30 may consist only of multiple magnet particles 3 and the resin composition 5. A small amount of organic solvent may remain in the granulated powder.

[0021] As described above, part or all of the surface of each of the multiple magnet particles 3 contained in each aggregate 20 is easily covered by the coating component 7 (resin composition and organic solvent). Therefore, part or all of the surface of each of the multiple magnet particles 3 contained in each granulated particle 30 is also easily covered by the resin composition 5 derived from the coating component 7.

[0022] As long as the aggregates 20 are heated after the particle size of each aggregate 20 reaches a desired value, the timing of starting the heating of the aggregates 20 and the location where the aggregates 20 are heated are not limited. The heating mechanism is also not limited. For example, the heating mechanism may be a hot air dryer. That is, the aggregates 20 may be heated by hot air outside the coil 4. For example, the heating mechanism may be a heater that does not use hot air (for example, an electric heater such as an infrared heater). For example, the heating mechanism may be a heating furnace that communicates with the inside of the coil 4, and the aggregates 20 may be heated inside the heating furnace. The temperature of the aggregates 20 heated by the heating mechanism may be above the temperature at which the organic solvent vaporizes and below the thermosetting temperature of the resin composition 5. For example, the temperature of the aggregates 20 heated by the heating mechanism may be 20°C or more and 60°C or less.

[0023] The magnetization direction (the easy magnetization axis of each magnetic domain in each magnetic particle) of the multiple magnetic particles 3 in each aggregate 20 formed inside the coil 4 is easily oriented along the direction of the magnetic field H inside the coil 4. Therefore, the magnetization direction of the multiple magnetic particles 3 in each granulated particle 30 is also easily oriented along one direction. By molding granulated powder containing multiple magnetic particles 3 with oriented magnetization directions in a magnetic field, it is possible to easily manufacture bonded magnets magnetized along the magnetic field. Furthermore, this process makes it easy to increase the residual magnetic flux density of the bonded magnets.

[0024] Bonded magnets manufactured from raw materials containing granulated powder tend to have high bulk density, mechanical strength, and residual magnetic flux density. For this reason, the proportion of the mass of magnet powder (multiple magnet particles) in the total mass of magnet powder and resin composition may be 90.0% to 99.9%, 95.0% to 99.5%, or 96.0% to 98.0%. The bulk density and residual magnetic flux density of the bonded magnet tend to increase with increasing proportion of magnet powder. The mechanical strength of the bonded magnet tends to increase with decreasing proportion of magnet powder. The content of the resin composition in the total mass of magnet powder and resin composition may be 0.1% to 10.0%, 0.5% to 5.0%, or 2.0% to 4.0%. The bulk density and residual magnetic flux density of the bonded magnet tend to increase with decreasing proportion of resin composition. As the mass ratio of the resin composition increases, the resin composition 5 covering the surface of each of the multiple magnet particles 3 in each granulated particle 30 tends to become thicker, and the mechanical strength of the bonded magnet tends to increase.

[0025] The total content of magnet powder and resin composition in slurry 9 may be expressed as M1 by mass%. The content of organic solvent in slurry 9 may be expressed as M2 by mass%. M1 + M2 may be 100% by mass. For example, M1 may be 5% by mass or more and 50% by mass or less, and for example, M2 may be 50% by mass or more and 95% by mass or less. As M1 decreases (M2 increases), the magnet powder becomes easier to disperse in slurry 9, and the surface of each of the multiple magnet particles 3 in each granulated particle 30 becomes easier to uniformly cover with the resin composition 5. As M1 increases (M2 decreases), the particle size of the multiple fine particles 10 tends to increase, and the particle size of the granulated powder also tends to increase.

[0026] The pressure acting on the slurry 9 inside nozzle 2 (spray pressure) is not limited. Spray pressure can be rephrased as the pressure acting on the slurry 9 as it is sprayed from nozzle 2. For example, the spray pressure may be between 0.01 MPa and 1.00 MPa. The higher the spray pressure, the easier it is for the aggregation of the magnetic powder in the slurry 9 to be resolved by spraying the slurry 9 from nozzle 2, and the easier it is for the particle size of the multiple fine particles 10 formed from the slurry 9 to decrease. The diameter of the opening of nozzle 2 is not limited, as long as it is greater than or equal to the particle size of the magnetic powder in the slurry 9. For example, the diameter of the opening of nozzle 2 may be between 5 μm and 1000 μm. As the diameter of the opening of nozzle 2 increases, the particle size of the multiple fine particles 10 tends to increase, and the particle size of the granulated powder also tends to increase. For example, nozzle 2 may be a two-fluid nozzle that sprays slurry 9 mixed with gas. For example, the gas mixed with slurry 9 may be an inert gas that does not react well with slurry 9 (for example, a noble gas such as argon).

[0027] The dimensions and number of turns of coil 4 are not limited. For example, the inner diameter D of coil 4 may be between 1 cm and 10 cm. The distance between the end (south pole) of coil 4 and the opening of nozzle 2 is not limited. For example, the distance between the end (south pole) of coil 4 and the opening of nozzle 2 may be at least 1 times the inner diameter D of coil 4 and no more than 5 times the inner diameter D of coil 4. The length of coil 4 in the direction parallel to the central axis of coil 4 is not limited. For example, the length of coil 4 may be between 1 cm and 10 cm.

[0028] The strength of the magnetic field H inside coil 4 is not limited. For example, the strength of the magnetic field H inside coil 4 may be between 0.01 T (Tesla) and 2.50 T. The higher the strength of the magnetic field H inside coil 4, the easier it is for multiple fine particles 10 to aggregate inside coil 4, the easier it is for the particle size of the multiple aggregates 20 formed inside coil 4 to increase, and the easier it is for the particle size of the granulated powder (multiple granulated particles 30) to increase. In other words, the particle size of the granulated powder can be controlled by the strength of the magnetic field H.

[0029] For example, the average particle size or median diameter D50 of the magnetic powder may be 0.5 μm or more and 100 μm or less, 1 μm or more and 10 μm or less, or 2 μm or more and 3 μm or less. The average particle size or median diameter D50 of the magnetic powder is determined based on the particle size distribution of the magnetic powder. For example, the horizontal axis of the particle size distribution may be the particle size of the magnetic particles, and the vertical axis may be the number, mass, or volume of the magnetic particles. For example, the particle size distribution of the magnetic powder may be measured by a laser diffraction particle size analyzer. The shape of each magnetic particle 3 constituting the magnetic powder is not limited. For example, the shape of each magnetic particle 3 may be approximately spherical or flattened.

[0030] The shape and dimensions of the multiple fine particles 10 formed by spraying the slurry 9 are not limited. The shape and dimensions of the multiple aggregates 20 formed by the aggregation of the multiple fine particles 10 are also not limited. For example, the particle size of the multiple fine particles 10 may be larger than the particle size of the magnetic powder and smaller than the particle size of the multiple aggregates 20. The particle size of the multiple aggregates 20 may be larger than the particle size of the multiple fine particles 10 and may be approximately equal to the particle size of the granulated powder.

[0031] For example, the average particle diameter or median diameter D50 of the granulated powder (multiple granulated particles 30) may be 10 μm to 500 μm, 10 μm to 200 μm, 30 μm to 150 μm, or 80 μm to 120 μm. The larger the particle size of the granulated powder, the easier it is to suppress aggregation of the granulated powder, the easier it is to flow, and the easier it is to process the raw material containing the granulated powder. The smaller the particle size of the granulated powder, the easier it is to fill the mold with the raw material containing the granulated powder without gaps, and the easier it is to finely mold the granulated powder using a mold. The average particle diameter or median diameter D50 of the granulated powder is determined based on the particle size distribution of the granulated powder. For example, the horizontal axis of the particle size distribution may be the particle size of the granulated particles, and the vertical axis may be the number, mass, or volume of the granulated particles. For example, the particle size distribution of the granulated powder may be measured by a laser diffraction particle size analyzer. The shape of each granulated particle 30 constituting the granulated powder is not limited. For example, the shape of each granulated particle 30 may be approximately spherical or flattened.

[0032] The particle size and particle size distribution of the granulated powder may be adjusted by classification. For example, the classification means may be a sieve. The nominal mesh sizes of sieves according to JIS Z8801-1 are 25 μm, 32 μm, 38 μm, 45 μm, 53 μm, 63 μm, 75 μm, 90 μm, 106 μm, 125 μm, 150 μm, 212 μm, 250 μm, 300 μm, 355 μm, 425 μm, 500 μm, 600 μm, 710 μm, 1 mm, 1.18 mm, 1.4 mm, and 1.7 mm, 2 mm, etc. Granulated powder can be classified using sieves with these nominal mesh sizes. By classifying granulated powder using one type of sieve, granulated powder with a particle size below a predetermined value (sieve mesh size) may be recovered. The particle size of the granulated powder may be adjusted to a predetermined range by classifying the granulated powder using two types of sieves with different mesh sizes.

[0033] (Details of magnetic powder) As mentioned above, the magnetic powder (multiple magnetic particles) contained in the slurry is an alloy containing samarium (Sm), iron (Fe), and nitrogen (N). This alloy containing samarium, iron, and nitrogen can be described as an Sm-Fe-N permanent magnet. Sm-Fe-N permanent magnets exhibit magnetic anisotropy. That is, each magnetic particle (magnetic domain within each magnetic particle) constituting the magnetic powder has an easy magnetization axis (crystal axis) extending in one direction.

[0034] For example, a powder containing an Sm-Fe-N permanent magnet (SmFeN powder) has Sm2Fe as the main phase. 17The powder may contain N3 (alloy). For example, at least a portion of the SmFeN powder may be an anisotropic magnetic powder containing Th2Zn type crystals (rhombohedral crystals) as the main phase. An anisotropic magnetic powder is a magnetic powder in which the individual magnetic particles constituting the magnetic powder are single crystals, or a magnetic powder in which the individual magnetic particles constituting the magnetic powder are composed of a large number of fine single crystal grains (magnetic domains), and the direction of the easy magnetization axis of each crystal grain is aligned in a specific direction. For example, at least a portion of the SmFeN powder may be an isotropic magnetic powder containing TbCu7 type crystals (hexagonal crystals) as the main phase. An isotropic magnetic powder is a magnetic powder in which the individual magnetic particles constituting the magnetic powder are composed of a large number of fine single crystal grains (magnetic domains), and the direction of the easy magnetization axis of each crystal grain is disordered. In addition to the SmFeN powder, the magnetic powder may further contain powders made of other permanent magnets.

[0035] The method for producing SmFeN powder is not limited. For example, a method for producing SmFeN powder may include the steps of forming an alloy powder containing Sm and Fe by a mechanical alloying method, and obtaining SmFeN powder by heating the alloy powder in nitrogen gas. SmFeN powder may also be produced by a rapid solidification method. In the rapid solidification method, molten alloy is supplied to the surface of a rotating water-cooled roll. As a result, the molten alloy is rapidly cooled and solidified on the surface of the water-cooled roll. SmFeN powder is obtained by crushing the solidified alloy. SmFeN powder may also be produced by the HDDR (Hydrogenation Disproportion Desorption Recombination) method.

[0036] For example, as the SmFeN powder, unground powder (spherical magnetic powder) obtained by Nichia Corporation's build-up method may be used. The surface of each magnetic particle constituting the SmFeN powder may be covered with an inorganic film by surface treatment. For example, the inorganic film may contain phosphate or silica-based compounds.

[0037] (Details of the resin composition) The resin composition contained in the slurry may be the non-volatile components of the slurry excluding the magnetic powder and organic solvent. As described above, the resin composition contains a thermosetting resin. The thermosetting resin may be the main component of the resin composition. In addition to the thermosetting resin, the resin composition may further contain one or more components selected from the group consisting of curing agents, curing accelerators (curing catalysts), coupling agents, waxes (lubricants), reactive diluents, and flame retardants. Some or all of the resin composition contained in the slurry and granulated powder may be uncured. Some or all of the resin composition contained in the granulated powder may be semi-cured (B-stage resin composition).

[0038] For example, the thermosetting resin may be one or more resins selected from the group consisting of epoxy resins, maleimide compounds (e.g., bismaleimide), polyimides, polyamides, and polyamideimides.

[0039] For example, the curing agent may be one or more compounds selected from the group consisting of phenolic resins, phenol novolac resins, imidazole, dicyandiamide (DICY), aromatic polyamines, acid anhydrides, aliphatic polyamines, polyaminoamides, and polymercaptans. When the resin composition contains a phenolic resin (especially a phenol novolac resin) as a curing agent together with the epoxy resin, the heat resistance (mechanical strength at high temperatures) of the bonded magnet tends to improve. When the resin composition contains an amine (e.g., imidazole) as a curing agent together with the epoxy resin, the resin composition tends to cure quickly during the molding process described later.

[0040] For example, the curing accelerator may be one or more compounds selected from the group consisting of imidazole and tetrasubstituted phosphonium / tetrasubstituted borate.

[0041] For example, the coupling agent may be any coupling agent that reacts with the glycidyl groups present in the resin composition. When the coupling agent is chemically bonded to the surface of each of the multiple magnet particles in the slurry, the coupling agent promotes the dispersion of the magnet powder in the slurry. As a result, the surface of each of the multiple magnet particles contained in the granulated powder is more easily covered uniformly by the resin composition. Furthermore, the coupling agent improves the adhesion between the magnet particles and the resin composition, thereby improving the mechanical strength of the bonded magnet. The coupling agent that reacts with the glycidyl groups may be, for example, a silane compound (silane coupling agent).

[0042] For example, the wax may be one or more compounds selected from the group consisting of synthetic waxes, saturated fatty acids, saturated fatty acid salts, and saturated fatty acid esters. Due to the lubricating properties of the wax, multiple magnet particles in the granulated powder slide easily against each other, and in the molding process described later, each magnet particle rotates easily due to the magnetic field, and each magnet particle is easily oriented along the magnetic field. As a result, the residual magnetic flux density of the bonded magnet tends to improve.

[0043] For example, the reactive diluent may be at least one of a monoepoxy compound and a diepoxy compound. The reactive diluent may be a monofunctional epoxy resin. For example, the reactive diluent may be at least one selected from the group consisting of alkyl monoglycidyl ethers, alkylphenol monoglycidyl ethers, and alkyl diglycidyl ethers.

[0044] For example, the flame retardant may be one or more compounds selected from the group consisting of brominated flame retardants, phosphorus-based flame retardants, hydrated metal compound-based flame retardants, silicone-based flame retardants, nitrogen-containing compounds, hindered amine compounds, organometallic compounds, and aromatic engineering plastics.

[0045] The resin composition may include other resins, such as thermoplastic resins, in addition to thermosetting resins. For example, the other resins may be one or more resins selected from the group consisting of polyphenylene sulfide resins, acrylic resins, methacrylic resins, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and silicone resins.

[0046] (Details of organic solvents) The organic solvent contained in the slurry is not limited. For example, the organic solvent contained in the slurry may be one or more organic compounds selected from the group consisting of acetone, methyl ethyl ketone (2-butanone), methyl isobutyl ketone (4-methyl-2-pentanone), diisobutyl ketone, diacetone alcohol, cyclohexanone, cyclohexane, benzene, toluene, xylene, N-methyl-2-pyrrolidone (NMP), ethyl acetate, n-butyl acetate, mineral spirits, and propylene glycol monomethyl ether acetate.

[0047] (Analysis method) The dimensions, shape, and structure of each of the granulated particles constituting the granulated powder may be analyzed using an optical microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a scanning transmission electron microscope (STEM). For the analysis and identification of the composition of the granulated powder, the granulated powder may be dissolved in an organic solvent, and the magnetic powder may be separated from the resin composition dissolved in the organic solvent. The separated resin composition and magnetic powder may each be analyzed individually. For example, each component constituting the resin composition may be analyzed and identified by one or more analytical methods selected from the group consisting of infrared spectroscopy (IR), nuclear magnetic resonance (NMR), mass spectrometry (MS), gas chromatography (GC), and high-performance liquid chromatography (HPLC). For example, magnetic powder may be analyzed and identified by one or more analytical methods selected from the group consisting of X-ray fluorescence analysis (XRF), inductively coupled plasma (ICP) emission spectroscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS or EDX), and mass spectrometry.

[0048] (Manufacturing method for bonded magnets) The granulated powder described above is used as a raw material for bonded magnets. The term "compound" as used below refers to the raw material for bonded magnets. The compound may consist only of the granulated powder described above. In addition to the granulated powder, the compound may further contain a resin composition (an uncured resin composition) that is different from the resin composition contained in the granulated powder.

[0049] A method for manufacturing bonded magnets includes at least a molding step. The method for manufacturing bonded magnets may further include a cooling step, a demagnetization step, a thermosetting step, and a magnetization step as steps following the molding step. Details of each step are described below.

[0050] Before the start of the molding process, the compound is supplied and filled into the mold (cavity). The temperature of the compound supplied and filled into the mold may be room temperature or ambient temperature.

[0051] In the molding process, the compound in the mold is heated and compressed. For example, in the molding process, the compound in the mold may be heated at a molding temperature T and then compressed. By heating and compressing the compound, a molded body is formed from the compound in the mold. In the molding process, the compound in the mold may be heated and compressed while a magnetic field is applied to it. When the compound in the mold is heated and compressed while a magnetic field is applied to it, multiple magnetic particles (each magnetic domain) in the compound are magnetized and oriented along the magnetic field, resulting in a molded body that is magnetized along the magnetic field.

[0052] For example, the molding pressure may be between 500 MPa and 2000 MPa, between 700 MPa and 2000 MPa, or between 980 MPa and 2000 MPa.

[0053] The molding temperature T can be rephrased as the temperature of the compound during the molding process. If the maximum value of the molding temperature T is equal to or greater than the thermosetting temperature of the resin composition, the thermosetting of the resin composition during the molding process forms a molded body containing the cured resin composition and magnetic powder. If the maximum molding temperature T is less than the thermosetting temperature of the resin composition, a molded body containing the uncured resin composition and magnetic powder is formed. If the molding temperature T is equal to or greater than the thermosetting temperature of the resin composition, the molded body may be a completed bonded magnet.

[0054] For example, the molding temperature T may be 60°C to 300°C, 60°C to 180°C, 60°C to 150°C, 70°C to 110°C, or 80°C to 100°C. For example, the time during which the compound in the mold is heated at the molding temperature T (molding time) may be several tens of seconds or more and several hours or less.

[0055] The magnetic field applied to the compound inside the mold may be a static magnetic field (a continuous, constant magnetic field). The magnetic field H may also be a pulsed magnetic field (a pulsed magnetic field). For example, the strength of the static magnetic field may be between 0.5 T (Tesla) and 2.5 T. For example, the time for which the static magnetic field is applied to the compound in the mold may be between 0.08 minutes and 4 minutes. For example, the intensity of the pulsed magnetic field may be between 4T and 12T. The pulsed magnetic field may be applied to compound 2 once or multiple times.

[0056] A cooling process may be carried out after the molding process. In the cooling process, the mold containing the molded body (bonded magnet) is cooled. For example, in the cooling process, the mold containing the molded body may be cooled to room temperature. The molded body (bonded magnet) inside the mold becomes more solid due to the cooling process. As a result, the mechanical strength of the molded body inside the mold increases, which suppresses deformation and damage of the molded body in each process after the cooling process, and the mechanical strength of the bonded magnet tends to increase.

[0057] A demagnetization process may be performed after the molding process. The demagnetization process may be performed after the cooling process. The demagnetization process may be performed simultaneously with the cooling process. In the demagnetization process, the molded body is demagnetized by applying a magnetic field (reverse magnetic field) in the opposite direction to the magnetic field used in the molding process. Demagnetization of the molded body suppresses deformation of the molded body caused by the magnetic force of the molded body itself. When a demagnetization process is performed, it is preferable to perform the magnetization process described later.

[0058] If the molded body obtained in the molding process contains an uncured or semi-cured resin composition, a thermosetting process may be further carried out after the molding process, cooling process, or demagnetization process. In the thermosetting process, the molded body is heated to a temperature above the thermosetting temperature of the resin composition. As a result, the thermosetting of the resin composition in the molded body proceeds further.

[0059] A magnetization process may be carried out after the demagnetization process. A magnetization process may also be carried out after the demagnetization process and the subsequent thermosetting process. In the magnetization process, a magnetic field in the same direction as the magnetic field used in the molding process may be applied to the molded body. As a result, the molded body is magnetized and becomes a bonded magnet again.

[0060] This disclosure is not necessarily limited to the embodiments described above. Various modifications to this disclosure are possible and are included in this disclosure, without departing from the spirit of this disclosure. [Industrial applicability]

[0061] For example, granulated powder obtained by a method for producing granulated powder according to one aspect of this disclosure may be used as a raw material for bonded magnets. [Explanation of symbols]

[0062] 2...Nozzle, 3...Magnetic particles, 4...Coil, 5...Resin composition, 7...Coating components (resin composition and organic solvent), 9...Slurry, 10...Fine particles, mf...Magnetic field lines, H...Magnetic field, 20...Agglomerate, 30...Granulated particles (granulated powder).

Claims

[Claim 1] A method for producing granulated powder, The raw materials for the granulated powder are a slurry containing a magnet powder consisting of multiple magnet particles, a resin composition, and an organic solvent. The aforementioned magnetic powder is an alloy containing samarium, iron, and nitrogen. The aforementioned resin composition includes a thermosetting resin, By spraying the slurry, a plurality of fine particles made of the slurry are formed. In a state where a magnetic field is generated by the coil, a plurality of the fine particles are supplied to the inside of the coil by the magnetic field. By agglomerating a plurality of the fine particles inside the coil using the magnetic field, a plurality of aggregates are formed from the plurality of the fine particles. By heating the multiple aggregates and removing the organic solvent from them, the multiple aggregates become the granulated powder. A method for producing granulated powder.

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