Manufacturing method for bonded magnets

Abstract

To provide a method for manufacturing bonded magnets that includes a demagnetization step that does not use a magnetic field. [Solution] A method for manufacturing a bonded magnet 2B using a manufacturing apparatus (molding apparatus), comprising: a molding step of forming a molded body 2A from a compound by heating and compressing the compound in a mold while applying a first magnetic field H to the compound in the mold; a demagnetization step of demagnetizing the molded body by heating the molded body in the mold without applying a magnetic field to the molded body after the molding step; a removal step of removing the molded body from the mold after the demagnetization step; and a magnetization step of applying a second magnetic field to the molded body after the removal step. The compound comprises magnetic particles (magnetic powder) 3 and a resin composition 5. The magnetic particles (magnetic powder) are an alloy containing samarium, iron, and nitrogen. The resin composition contains a thermosetting resin.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing bonded magnets.

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 (curing of thermosetting resin mixed with magnet powder) at which the crystal structure is maintained.

[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 (see Patent Document 1 below). 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 domains 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] In conventional bond magnet manufacturing, a demagnetization process is performed after the molding process. In the conventional demagnetization process, a magnetic field (reverse magnetic field) with the opposite direction to the magnetic field used in the molding process is applied to the molded body in the mold. The demagnetization process suppresses deformation and damage of the molded body caused by the magnetic force of the molded body itself, and also suppresses adhesion between the molded body and the mold (metal) caused by the magnetic force of the molded body.

[0006] However, conventional demagnetization processes consume a large amount of electricity to generate a reverse magnetic field, thus increasing the energy and cost required for manufacturing bonded magnets. Furthermore, if a reverse magnetic field is applied to the molded body during the demagnetization process, at least some of the magnetized magnet powder in the molded body may rotate due to the reverse magnetic field. In other words, the direction of some of the easy magnetization axes (crystal axes) of the multiple magnetic domains oriented along the magnetic field during the molding process may change due to the reverse magnetic field, potentially resulting in misalignment of the easy magnetization axes of multiple magnetic domains in the molded body. As a result, the residual magnetic flux density of the final bonded magnet may decrease.

[0007] One aspect of this disclosure is to provide a method for manufacturing bonded magnets that includes a demagnetization step that does not use a magnetic field. [Means for solving the problem]

[0008] For example, one aspect of this disclosure relates to a method for manufacturing a bonded magnet as described in [1] below.

[0009] [1] A molding step of forming a molded body from a compound by heating and compressing the compound in the mold while applying a first magnetic field to the compound in the mold, After the molding process, a demagnetization step is performed in which the molded body is demagnetized by heating the molded body in the mold without applying a magnetic field to the molded body in the mold. After the demagnetization step, there is a removal step in which the molded body is removed from the mold, After the extraction step, a magnetization step is performed in which a second magnetic field is applied to the molded body. Includes, The compound comprises magnetic powder and a resin composition. The aforementioned magnetic powder is an alloy containing samarium, iron, and nitrogen. The resin composition includes a thermosetting resin. A method for manufacturing bonded magnets. [Effects of the Invention]

[0010] According to one aspect of this disclosure, a method for manufacturing a bonded magnet is provided, which includes a demagnetization step that does not use a magnetic field. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic cross-sectional view of a specific example of a manufacturing apparatus (molding apparatus) used in the method for manufacturing bonded magnets according to the present disclosure. The cross-section shown in Figure 1 traverses a pair of punches, a die, a compound, and a pair of coils, and is parallel to the direction of pressure exerted by the pair of punches on the compound (pressure direction). [Figure 2] Figure 2 is a schematic cross-sectional view of a specific example of a molded body (or bonded magnet) according to this disclosure. [Modes for carrying out the invention]

[0012] (Overview of compound and bonded magnets) 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. X, Y, and Z shown in Figures 1 and 2 represent three mutually orthogonal coordinate axes. The directions of the X, Y, and Z axes are common to Figures 1 and 2.

[0013] The compound is a raw material for bonded magnets and comprises magnetic powder and a resin composition. The compound may be described as a mixture containing magnetic powder and a resin composition. The compound may be in the form of a powder, tablet, or paste at room temperature (e.g., 20°C ± 15°C).

[0014] Magnetic powder is an alloy containing samarium (Sm), iron (Fe), and nitrogen (N). Magnetic powder can be described as a large number of magnetic particles made up of an alloy containing samarium, iron, and nitrogen. The 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, which is an Sm-Fe-N permanent magnet, has an easy magnetization axis (crystal axis) extending in one direction.

[0015] The resin composition includes a thermosetting resin. As described later, the resin composition may further include one or more components other than the thermosetting resin. Part or all of the resin composition in the compound may be uncured. Part or all of the resin composition in the compound may be semi-cured (stage B resin composition). Part of the resin composition in the compound may be uncured, and the remainder of the resin composition in the compound may be semi-cured. The resin composition functions as a binder that binds together multiple magnet particles constituting the magnet powder. For example, the resin composition filled between multiple magnet particles binds the magnet particles together. Furthermore, due to the thermosetting of the resin composition, the cured resin composition binds the multiple magnet particles together more firmly. In other words, the resin composition imparts mechanical strength to the molded articles and bonded magnets manufactured from the compound.

[0016] The bonded magnet according to this embodiment is an anisotropic bonded magnet and includes a cured product of a compound. The bonded magnet may consist only of the cured product of the compound. As shown in FIG. 2, the magnetization direction m of each of the plurality of magnet particles 3 constituting the magnet powder contained in the bonded magnet 2B is oriented along a first magnetic field H applied to the compound during the molding process described later. In other words, the magnetization direction m of each magnet particle 3 in the bonded magnet 2B is substantially or completely parallel to the first magnetic field H. The overall magnetization direction M of the bonded magnet 2B is also substantially or completely parallel to the direction of the first magnetic field H applied to the compound during the molding process. The plurality of magnet particles 3 in the bonded magnet 2B are bonded to each other by the cured product of the resin composition 5.

[0017] (Manufacturing Apparatus for Bonded Magnet) FIG. 1 shows a schematic cross-section of a specific example of a manufacturing apparatus 10 (molding apparatus) used in the method for manufacturing a bonded magnet.

[0018] The manufacturing apparatus 10 includes a pair of punches (first punch p1 and second punch p2) facing each other, and a cylindrical die d1 into which the pair of punches are inserted. A first opening is formed in the end face of the die d1 facing the first punch p1, and the first punch p1 is inserted into the first opening. A second opening is formed in the end face of the die d1 facing the second punch p2, and the second punch p2 is inserted into the second opening. A cavity (concave type) is formed by the second punch p2 inserted into the die d1 and the die d1. The first punch p1 functions as a core (convex type). That is, a pair of punches (first punch p1 and second punch p2) facing each other and a cylindrical die d1 into which the pair of punches are inserted constitute a set of molds. The manufacturing apparatus 10 further includes a heating mechanism (heater) for heating the compound 2 in the mold. The heating mechanism is omitted in each figure. For example, the heating mechanism may be an electric heater, an infrared heater, or a high-frequency induction heater. The manufacturing apparatus 10 may further include a thermometer for measuring the temperature of the mold or the compound 2 in the mold. The thermometer is omitted in each figure.

[0019] Compound 2 is supplied into the cavity composed of the second punch p2 and the die d1. Compound 2 in the cavity is sandwiched between the first punch p1 and the second punch p2. In the molding process described later, Compound 2 is pressurized and compressed by the first punch p1 and the second punch p2. The direction of the pressure (pressurization direction) exerted by each of the first punch p1 and the second punch p2 on Compound 2 is parallel to the Z-axis. In the present embodiment, the "pressure acting on the compound in the mold" refers to the pressure exerted by each of the first punch p1 and the second punch p2 on Compound 2. The "pressure acting on the compound in the mold" is expressed as the molding pressure.

[0020] The dimensions and shapes of each of the first punch p1, the second punch p2, and the die d1 are not limited. For example, the dimensions and shapes of each of the first punch p1, the second punch p2, and the die d1 may be changed according to the desired dimensions and shapes of the bonded magnet. The composition of each of the first punch p1, the second punch p2, and the die d1 is not limited. For example, each of the first punch p1, the second punch p2, and the die d1 may be a material having sufficient mechanical strength as a mold. For example, the mold (each of the first punch p1, the second punch p2, and the die d1) may be composed of one or more materials selected from the group consisting of soft magnetic metals (such as iron), carbon, ceramics, synthetic resins, and cemented carbides.

[0021] The manufacturing apparatus 10 includes a pair of coils (the first coil c1 and the second coil c2). The die d1 and Compound 2 in the die d1 are disposed between the pair of coils (the first coil c1 and the second coil c2). The first punch p1 and the second punch p2 do not penetrate inside each of the pair of coils (the first coil c1 and the second coil c2).

[0022] The manufacturing apparatus 10 further includes a power supply mechanism. The power supply mechanism is electrically connected to the first coil c1 and the second coil c2, respectively. The direction and absolute value of the first current generated in the first coil c1 and the direction and absolute value of the second current generated in the second coil c2 can be freely controlled by the power supply mechanism. The power supply mechanism is omitted in each figure.

[0023] A first magnetic field H may be generated from the magnetic field generated in the first coil c1 and the magnetic field generated in the second coil c2, and this combined first magnetic field H may be applied to the compound 2 in the die d1. Alternatively, the first magnetic field H generated by only one of the coils, the first coil c1 and the second coil c2, may be applied to the compound 2 in the die d1. Details of the first magnetic field H will be described later.

[0024] The central axes of the first coil c1 and the second coil c2 coincide with each other and are parallel to the X-axis. The first magnetic field H generated by the first coil c1 and the second coil c2 is also parallel to the X-axis. The direction of the first magnetic field H may be perpendicular to the direction of pressure. In other words, a first magnetic field H perpendicular to the direction of pressure may be applied to the compound. However, the direction of the first magnetic field H is not limited. The direction of the first magnetic field H may be changed by changing the arrangement of the first coil c1 and the second coil c2. For example, a first punch p1 may penetrate the inside of the first coil c1, and a second punch p2 may penetrate the inside of the second coil c2, and a die d1 may be placed between the first coil c1 and the second coil c2, and the central axes of the first coil c1 and the second coil c2 may coincide with each other, and the central axes of the first coil c1 and the second coil c2 may be parallel to the direction of pressure. As a result, a first magnetic field H parallel to the direction of pressure may be applied to the compound 2.

[0025] As long as the first coil c1 and the second coil c2 are conductors, their respective compositions are not limited. The first coil c1 and the second coil c2 may each be air-core coils. An iron core (yoke) may be installed inside the first coil c1 and the second coil c2. The inner diameter and number of turns of the first coil c1 and the second coil c2 are not limited. The inner diameters of the first coil c1 and the second coil c2 may be the same. The inner diameters of the first coil c1 and the second coil c2 may be different. The number of turns of the first coil c1 and the second coil c2 may be the same. The number of turns of the first coil c1 and the second coil c2 may be different.

[0026] (Method of manufacturing bonded magnets) The method for manufacturing a bonded magnet according to this embodiment includes at least a molding step, a demagnetization step, a removal step, and a magnetization step. The method for manufacturing a bonded magnet may further include a cooling step and a thermosetting step. Details of each step will be described below.

[0027] <Molding process> Before the start of the molding process, compound 2 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. The compound supplied into the mold may be in the form of a powder, tablet, or paste.

[0028] In the molding process, the compound 2 inside the mold is heated and compressed while a first magnetic field H is applied to it. For example, in the molding process, the compound 2 inside the mold, heated at the molding temperature T, may be compressed while a first magnetic field H is applied to it. By heating and compressing the compound in the first magnetic field H, a molded body 2A is formed from the compound 2 inside the mold.

[0029] Each magnetic particle 3 (each magnetic domain) in compound 2 is magnetized and oriented along the first magnetic field H during the molding process. For example, as compound 2 is heated during the molding process, the resin composition 5 in compound 2 softens. As the resin composition 5 softens, each magnetic particle 3 in compound 2 becomes easier to rotate due to the first magnetic field H. Each magnetic particle 3 in the compound is magnetized and rotated by the first magnetic field H, and the easy magnetization axis of the magnetic domain in each magnetic particle 3 is oriented along the first magnetic field H. For example, the magnetization direction m of each magnetic particle 3 in compound 2 and the molded body 2A may be approximately or perfectly parallel to the first magnetic field H (see Figure 2). If each magnetic particle 3 is a single crystal grain (single magnetic domain), the magnetization direction m of each magnetic particle 3 may be the same as the direction in which the easy magnetization axis in each magnetic particle 3 extends. The overall magnetization direction M of the molded body 2A may be approximately or perfectly parallel to the direction of the first magnetic field H applied to the compound 2 during the molding process (see Figure 2). Due to the above mechanism, the residual magnetic flux density of the bonded magnet 2B obtained in the end is increased.

[0030] For the reason that each magnetic particle 3 in the compound 2 is easily oriented along the first magnetic field H, the entire compound 2 in the mold may be compressed in a direction perpendicular to the first magnetic field H applied to the compound 2 during the molding process. In other words, the molding pressure may be perpendicular to the first magnetic field H. However, the entire compound 2 in the mold may also be compressed in a direction parallel to the first magnetic field H during the molding process. In other words, the molding pressure may be parallel to the first magnetic field H. The entire compound 2 in the mold may also be compressed in both directions: perpendicular to the first magnetic field H and parallel to the first magnetic field H during the molding process.

[0031] The molding temperature T may be rephrased as the temperature of compound 2 during the molding process. The molding temperature T may change during the molding process. The temperature of compound 2 during the molding process may gradually increase to reach the maximum value of the molding temperature T. For example, the maximum value of the molding temperature T may be equal to or greater than the thermosetting temperature of the resin composition 5. The thermosetting temperature may be rephrased as the temperature at which the thermosetting resin in the resin composition 5 begins to thermoset. The maximum value of the molding temperature T may be less than the thermosetting temperature of the resin composition 5. If the maximum value of the molding temperature T is equal to or greater than the thermosetting temperature of the resin composition 5, the thermosetting of the resin composition 5 during the molding process forms a molded body 2A containing the cured resin composition 5 and the magnetic powder. In other words, if the maximum value of the molding temperature T is equal to or greater than the thermosetting temperature of the resin composition 5, a molded body 2A consisting of the cured compound 2 is formed. If the maximum molding temperature T is less than the thermosetting temperature of the resin composition 5, a molded body 2A containing the uncured resin composition 5 and magnetic powder is formed. In other words, if the maximum molding temperature T is less than the thermosetting temperature of the resin composition 5, a molded body 2A consisting of the uncured compound 2 is formed.

[0032] If the molding temperature T is equal to or greater than the thermosetting temperature of the resin composition 5, the molded body 2A may be a completed bonded magnet 2B. The overall magnetization direction of the bonded magnet 2B may be substantially or perfectly parallel to the direction of the first magnetic field H applied to the compound 2 in the molding process, the overall magnetization direction M of the molded body 2A, and the magnetization direction m of each magnet particle 3 in the bonded magnet 2B. The bonded magnet 2B can have a high residual magnetic flux density due to the excellent orientation of the magnet powder. Furthermore, the mechanical strength and residual magnetic flux density of the bonded magnet increase due to the compression of the compound 2 in the molding process (i.e., an increase in the filling rate of magnet powder in the molded body 2A) and the thermosetting of the resin composition 5.

[0033] 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 2 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, several minutes or more and several hours or less, or several tens of seconds or more and several minutes or less. 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.

[0034] In the molding process, the application of the first magnetic field H to the compound 2 inside the mold may be started before the mold is heated, or before the temperature of the heated mold reaches the molding temperature T. In the molding process, the application of the first magnetic field H to the compound 2 in the mold may begin simultaneously with the compression of the compound 2 in the mold. Alternatively, the application of the first magnetic field H to the compound 2 in the mold may begin earlier than the compression of the compound 2 in the mold. In the molding process, the application of the first magnetic field H to compound 2 in the mold may be stopped at the same time as the molding pressure reaches its maximum value. The application of the first magnetic field H to compound 2 in the mold may be stopped when the molding pressure begins to decrease. The application of the first magnetic field H to compound 3 in the mold may be stopped at the same time as the compression of compound 2 in the mold ends.

[0035] The first magnetic field H may be a static magnetic field (a continuous, constant magnetic field). The first 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 0.5T (Tesla) and 2.5T, between 1.0T and 2.5T, or between 2.0T and 2.5T. For example, the time for which the static magnetic field is applied to compound 2 in the mold may be between 0.08 minutes and 4 minutes, between 0.5 minutes and 4 minutes, or between 1 minute and 4 minutes. For example, the intensity of the pulsed magnetic field may be between 4T and 12T, or between 8T and 12T. The pulsed magnetic field may be applied to compound 2 once or multiple times.

[0036] <Demagnetization process> After the molding process, a demagnetization process is carried out. The demagnetization process may be carried out immediately after the molding process. For example, after the molding process, the demagnetization process may be started without cooling the molded body 2A in the mold. In the demagnetization process, the molded body 2A is demagnetized by heating the molded body 2A in the mold. As the molded body 2A is heated, thermal vibrations are induced in the atoms in each magnetic particle 3 contained in the molded body 2A. Due to the thermal vibrations of the atoms in each magnetic particle 3, fluctuations and reversals of the spin magnetic moment are induced in each magnetic particle 3 (each magnetic domain). As a result, the direction of the spin magnetic moment becomes uneven throughout the molded body 2A, and the molded body 2A is demagnetized.

[0037] Unlike conventional demagnetization processes, a magnetic field opposite in direction to the first magnetic field H used in the molding process (reverse magnetic field) is not applied to the molded body 2A during the demagnetization process. Therefore, a large amount of power is not consumed to generate a reverse magnetic field during the demagnetization process, reducing the energy and cost required for the manufacture of bonded magnets. Furthermore, since a reverse magnetic field is not applied to the molded body 2A during the demagnetization process, each magnetized magnet particle 3 in the molded body 2A does not rotate during the demagnetization process, and the magnetization direction of the magnet powder in the molded body 2A is not disturbed during the demagnetization process. In other words, since a reverse magnetic field is not applied to the molded body 2A during the demagnetization process, the direction of the easy magnetization axes (crystal axes) of the multiple magnetic domains oriented along the first magnetic field during the molding process does not change during the demagnetization process, and the state in which the easy magnetization axes of the multiple magnetic domains in the molded body 2A are oriented along the first magnetic field H is maintained during the demagnetization process. As a result, the residual magnetic flux density of the bonded magnet that is finally obtained tends to be higher.

[0038] If the demagnetization process is not performed, the following problems are likely to occur. For example, each magnet particle 3 located near the surface of the molded body 2A, accompanied by an uncured or semi-cured resin composition 5, protrudes from the surface of the molded body 2A along the magnetic flux on the surface of the molded body 2A, and one or more protrusions containing the magnet particles 3 and the resin composition 5 are formed on the surface of the molded body. For example, if the mold is made of a material that may be magnetic (e.g., metal), the molded body 2A is likely to adhere firmly to the surface of the mold due to the magnetic force of the molded body 2A itself. As a result, when the molded body 2A is removed from the mold, the portion of the molded body 2A that is firmly adhered to the surface of the mold may separate from the molded body 2A and remain on the surface of the mold. In other words, the molded body 2A may be damaged when it is removed from the mold. Furthermore, when the molded body 2A is removed from the mold, the orientation direction of each magnet particle 3 in the portion of the molded body 2A that is firmly adhered to the surface of the mold may change, potentially reducing the residual magnetic flux density of the bonded magnet that is ultimately obtained. In addition, during the process of removing the molded body 2A that is firmly adhered to the surface of the mold from the mold, part or all of the molded body may be deformed (distorted). The above-mentioned problems can be suppressed by the demagnetization process. In other words, the demagnetization process suppresses deformation and damage to the molded body caused by the magnetic force of the molded body 2A itself.

[0039] For example, the temperature of the molded body 2A inside the mold during the demagnetization process (demagnetization temperature) may be between 100°C and 250°C. For example, the time for maintaining the demagnetization temperature (demagnetization time) may be between 0.5 minutes and 20 minutes. When both the demagnetization temperature and demagnetization time are within the above ranges, the molded body 2A is easily demagnetized, and undesirable alterations of the molded body 2A associated with demagnetization are easily suppressed. For example, undesirable alterations of the molded body 2A may be oxidation or thermal decomposition of the magnet powder and resin composition, respectively.

[0040] <Cooling process> After the demagnetization process, a cooling process may be carried out. In the cooling process, the mold containing the molded body 2A is cooled. For example, in the cooling process, the mold containing the molded body 2A may be cooled to room temperature. For example, the method of cooling the mold containing the molded body 2A may be natural cooling. The molded body 2A in the mold becomes more solidified by the cooling process. As a result, the mechanical strength of the molded body 2A in the mold is increased, deformation and damage of the molded body 2A in each process after the cooling process are suppressed, and the mechanical strength of the bonded magnet obtained in the end tends to be increased.

[0041] <Removal process> After the demagnetization process, the removal process is carried out. The removal process may also be carried out after the cooling process that follows the demagnetization process. In the removal process, the molded body 2A is removed from the mold. As described above, since the demagnetization process is carried out with the molded body 2A housed in the mold, deformation and damage to the molded body that occur when the molded body 2A is removed from the mold are suppressed.

[0042] <Thermosetting process> If the molded body 2A obtained in the molding process contains uncured or semi-cured resin composition 5, a thermosetting process may be performed after the removal process. In the thermosetting process, the molded body 2A is heated to a temperature equal to or higher than the thermosetting temperature of the resin composition 5. As a result, the thermosetting of the resin composition 5 in the molded body progresses further, and the bulk density, mechanical strength, and residual magnetic flux density of the molded body 2A (or bonded magnet) tend to increase further. For example, in the thermosetting process, a large number of molded bodies 2A housed in a heating furnace may be heated simultaneously. As a result, the time, energy, and cost required for the thermosetting process are reduced, and the productivity of bonded magnets is improved. For example, the thermosetting process may be carried out in an inert atmosphere (e.g., argon) or a non-oxidizing atmosphere (e.g., a reduced-pressure atmosphere). If all of the resin composition 5 in the molded body 2A is sufficiently cured during the molding process, the thermosetting process is not a necessary step.

[0043] <Magnetization process> After the extraction process, a magnetization process is carried out. Alternatively, the magnetization process may be carried out after the thermosetting process that follows the extraction process. In the magnetization process, a second magnetic field is applied to the molded body 2A. As a result, the molded body 2A is magnetized and becomes a bonded magnet 2B. The direction of the second magnetic field used in the magnetization process may be the same as or parallel to the direction of the first magnetic field H used in the molding process. The method for generating the second magnetic field in the magnetization process may be substantially the same as the method for generating the first magnetic field H in the molding process. However, in the magnetization process, it is not necessary to heat and compress the molded body to which the second magnetic field is applied using a molding apparatus. For example, the second magnetic field may be applied to the molded body 2A while the molded body 2A is fixed by a jig so that it does not move due to the application of the second magnetic field.

[0044] The strength of the second magnetic field may be the same as the strength of the first magnetic field H. The strength of the second magnetic field may be different from the strength of the first magnetic field H. The second magnetic field may be a static magnetic field. The second magnetic field may be a pulsed magnetic field. For example, the strength of the static magnetic field may be between 0.5T (Tesla) and 2.5T, between 1.0T and 2.5T, or between 2.0T and 2.5T. For example, the time for which the static magnetic field is applied to compound 2 in the mold may be between 0.08 minutes and 4 minutes, between 0.5 minutes and 4 minutes, or between 1 minute and 4 minutes. For example, the intensity of the pulsed magnetic field may be between 4T and 12T, or between 8T and 12T. The pulsed magnetic field may be applied to compound 2 once or multiple times.

[0045] (Compound details) As described above, the compound comprises magnetic powder and a resin composition, the magnetic powder being an Sm-Fe-N permanent magnet, and the resin composition containing a thermosetting resin.

[0046] In this disclosure, the resin composition means the remaining portion of the compound excluding the magnetic powder (non-volatile component). 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. The compound may consist only of the magnetic powder and the resin composition. In addition to the magnetic powder and the resin composition, the compound may further contain other components (e.g., organic solvents).

[0047] 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.

[0048] 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.

[0049] For example, the curing accelerator may be one or more compounds selected from the group consisting of imidazole and tetrasubstituted phosphonium / tetrasubstituted borate.

[0050] For example, the coupling agent may be any coupling agent that reacts with the glycidyl groups present in the resin composition. 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).

[0051] 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, the magnetic particles in the compound slide easily against each other, each magnetic particle rotates easily in the magnetic field during the magnetization and molding processes, and each magnetic particle is easily oriented along the magnetic field. As a result, the residual magnetic flux density of the bonded magnet tends to improve.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] As mentioned above, the magnetic powder is a powder containing Sm-Fe-N permanent magnets (SmFeN powder). For example, SmFeN powder has Sm2Fe as the main phase. 17 The 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 magnetic powder made of Sm-Fe-N permanent magnets, the compound may further contain powder made of other permanent magnets.

[0056] 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 HDG (Hydrogenation Disproportion Desorption Recombination) method.

[0057] As the SmFeN powder, for example, unground powder (spherical magnetic powder) obtained by the build-up method of Nichia Corporation 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.

[0058] d - Average particle size or median diameter of SmFeN powder 50 The average particle size or median diameter d of the SmFeN powder is preferably 0.5 μm or more and 100 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably 2 μm or more and 3 μm or less. 50 This can be measured using a laser diffraction particle size distribution analyzer.

[0059] The mass of the magnetic powder in the compound may be expressed as Mm (unit: g). The total mass of the resin composition in the compound may be expressed as Mr (unit: g). The content of the magnetic powder in the compound (unit: mass%) may be defined as Mm / (Mm+Mr)×100. The content of the resin composition in the compound (unit: mass%) may be defined as Mr / (Mm+Mr)×100. For the reason that bonded magnets manufactured from the compound tend to have high bulk density, mechanical strength, and residual magnetic flux density, the content of the magnetic powder in the compound may be 90.0% by mass or more and 99.9% by mass or less, 95.0% by mass or more and 99.5% by mass or less, or 96.0% by mass or more and 98.0% by mass or less. The bulk density and residual magnetic flux density of bonded magnets tend to increase with increasing magnetic powder content. The mechanical strength of the bonded magnet tends to increase as the content of magnetic powder decreases. The content of the resin composition in the compound may be 0.1% by mass or more and 10.0% by mass or less, 0.5% by mass or more and 5.0% by mass or less, or 2.0% by mass or more and 4.0% by mass or less. The bulk density and residual magnetic flux density of the bonded magnet tend to increase as the content of the resin composition decreases. The mechanical strength of the bonded magnet tends to increase as the content of the resin composition increases.

[0060] (Method of manufacturing compound) A compound can be obtained by mixing magnetic powder and a resin composition. For example, a resin solution can be prepared by uniformly stirring and mixing one or more of the above components constituting the resin composition in an organic solvent. Furthermore, a compound can be obtained by stirring and mixing the resin solution and the magnetic powder. In other words, a mixture (paste) of the resin solution and magnetic powder can be used as the compound.

[0061] After stirring and mixing the above resin solution and magnet powder, the organic solvent is removed from the resin solution to obtain a powder consisting of magnet powder and resin composition. The powder consisting of magnet powder and resin composition may be used as a compound. The powder obtained by grinding the mixture (lump) consisting of magnet powder and resin composition may also be used as a compound. As the organic solvent is removed from the resin solution, the resin composition adheres to the surface of each magnet particle constituting the magnet powder. The resin composition may adhere to the entire surface of each magnet particle. The resin composition may adhere to only a part of the surface of each magnet particle.

[0062] A compound may be obtained by further mixing a mixture consisting of magnetic powder and a resin composition (excluding wax) with wax.

[0063] Tablets made from a compound may be produced by compression molding of the compound. Tablets made from a compound may be used as raw materials for bonded magnets. The dimensions and shape of the tablets are not particularly limited. For example, the tablets may be cylindrical.

[0064] (Analysis method) To analyze and identify the composition of a bonded magnet, a sample obtained by grinding the bonded magnet may be analyzed. To analyze and identify the composition of the compound itself retrospectively from the bonded magnet, a sample obtained by grinding the bonded magnet may be analyzed. Furthermore, the sample obtained by grinding may be dissolved in an organic solvent, and the magnet powder constituting the sample may be separated from the resin composition dissolved in the organic solvent. The separated resin composition and magnet powder may each be analyzed individually. Even if the composition of the uncured compound is to be analyzed and identified, the compound 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 (such as epoxy resin and imidazole) 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. The residual magnetic flux density Br1 of the bonded magnet and the residual magnetic flux density Br2 of the magnet powder itself may satisfy the following equation 1. Br1 = Br2 × (V2 / V1) × D (1) In Equation 1, V1 is the total volume of the bonded magnet. V2 is the volume of the magnet powder itself contained in the bonded magnet. V2 / V1 corresponds to the packing density of the magnet powder in the bonded magnet. D in Equation 1 is the degree of orientation of the magnet powder in the bonded magnet. Based on Equation 1 above, the degree of orientation D is expressed as Br1 / {Br2×(V2 / V1)}. In other words, the degree of orientation D can be determined based on the measurements of Br1, Br2, V1, and V2. A high degree of orientation means that the easy magnetization axis in each magnet particle constituting the magnet powder contained in the bonded magnet is oriented. In other words, a high degree of orientation means that the magnetization direction of each magnet particle constituting the magnet powder contained in the bonded magnet is oriented. For example, the degree of orientation D (unit: %) of the magnet powder in the bonded magnet may be between 80% and 100%.

[0065] 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]

[0066] For example, a method for manufacturing bonded magnets relating to one aspect of this disclosure may be applied to the manufacture of bonded magnets for motors. [Explanation of Symbols]

[0067] 2...Compound, 2A...Molded body, 2B...Bonded magnet, 3...Magnetic particles (magnetic powder), 5...Resin composition, 10...Manufacturing apparatus (molding apparatus), c1...First coil, c2...Second coil, d1...Die, H...First magnetic field, m...Magnification direction of magnetic particles, M...Magnification direction of molded body or bonded magnet, p1...First punch, p2...Second punch.

Claims

[Claim 1] A molding process in which a molded body is formed from a compound by heating and compressing the compound in the mold while applying a first magnetic field to the compound in the mold, After the molding process, a demagnetization step is performed in which the molded body is demagnetized by heating the molded body in the mold without applying a magnetic field to the molded body in the mold. After the demagnetization step, there is a removal step in which the molded body is removed from the mold, After the extraction step, a magnetization step is performed in which a second magnetic field is applied to the molded body. Equipped with, The compound comprises magnetic powder and a resin composition. The aforementioned magnetic powder is an alloy containing samarium, iron, and nitrogen. The resin composition includes a thermosetting resin. A method for manufacturing bonded magnets.

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