JP2005323419A - Process for producing anisotropic bond magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for producing a high performance anisotropic bond magnet of ring shape, especially a small and thin multipolar pole anisotropy bond magnet. <P>SOLUTION: In the process for producing a ring-shape anisotropic bond magnet having a plurality of poles, the anisotropic bond magnet is sectioned into a pole region a corresponding to a pole part and a non-pole region b adjacent to the pole region a. The pole region and the non-pole region are injection molded in two steps into one ring shape. At the time of injection molding, one of the pole region and the non-pole region is oriented in the circumferential direction and the other is oriented in the radial direction. Alternatively, one of the pole region and the non-pole region is oriented in the circumferential direction and the other is non-oriented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a ring-shaped bonded magnet used in a rotating device such as a motor, and more particularly to a method for manufacturing an anisotropic bonded magnet.

  Conventionally, a wide variety of motors have been used for driving white goods such as air conditioners and washing machines, electrical equipment for automobiles, record players, and the like. In recent years, more motors are used for driving magnetic / optical recording devices such as HDDs and DVDs, for controlling OA equipment such as printers, and for cooling personal computers and power supply devices.

  Permanent magnets used in these motors, when focusing on the material, oxide magnets such as Sr ferrite and Ba ferrite, Nd-Fe-B, Sm-Fe-N, Sm-Co And rare earth metal magnets. The oxide-based magnet is inexpensive, but has a feature that the maximum energy product, which is one of magnetic characteristics, is low. On the other hand, although rare earth metal magnets are expensive, the amount of their use is increasing year by year because the maximum energy product is high.

  Permanent magnets can be broadly classified into sintered magnets and bonded magnets. The bonded magnet is formed from a mixture of a magnet material and a resin binder, and has a feature that it can be formed into an arbitrary shape. The sintered magnet is formed by mixing a magnet material and an additive such as a sintering aid and then sintering the mixture. A sintered magnet has a lower degree of freedom in shape than a bonded magnet, but has excellent magnetic properties. However, bond magnets are mainly used as the magnets used in the above-described recording apparatus and OA equipment because they must be thin and precise in shape and cost.

  Such a bonded magnet manufacturing method includes compression molding, injection molding, and extrusion molding.

In injection molding, magnet powder is mixed with a binder made of a thermoplastic resin to form a compound. This compound is melted and given sufficient fluidity, pressure is applied to the molten compound, and it is discharged from a small discharge port into a mold below the solidification temperature of the resin, and sent to a cavity in the mold. This is a method of solidifying the cavity into a bonded magnet. In the injection molding method, the magnetic performance of the magnet molded body is somewhat reduced because the amount of resin component in the magnet composition is larger than that of compression molding in order to give the magnet composition fluidity, but the degree of freedom in shape is Very big.
In the extrusion molding method, as in the case of injection molding, the magnet powder is mixed with a binder made of a thermoplastic resin to form a compound. In this method, the compound is melted and shaped in a mold with sufficient fluidity, and then cooled and solidified to form a predetermined shape. This forming method is suitable for manufacturing a magnet having a long shape.

  Further, when focusing on the magnetic orientation caused by the easy axis of magnetization of the permanent magnet, the permanent magnet can be roughly classified into an isotropic magnet and an anisotropic magnet. In an isotropic magnet, the directions of the easy magnetization axes are not aligned and are not oriented. However, this isotropic magnet is frequently used from the viewpoint of ease of manufacture and low cost. On the other hand, an anisotropic magnet is one in which the direction of the axis of easy magnetization is aligned, that is, oriented at the stage of molding the magnet. Therefore, this anisotropic magnet needs to be applied with an orientation magnetic field in order to align the direction of the easy magnetization axis during molding, but since it is oriented, it has better magnetic properties than an isotropic magnet.

  The isotropic magnet can be magnetized in an arbitrary direction, and must be magnetized before being incorporated in a motor or the like to form an N pole and an S pole corresponding to the direction of the magnetizing magnetic field. Magnetization methods include a rectangular wave magnetization in which the magnetic flux density distribution on the magnet surface is a rectangular wave and a sine wave magnetization in which the sine wave is a sine wave. There are cases where the outer peripheral surface is magnetized. The polarities in the magnet in each magnetization method are shown in FIGS. FIG. 1 shows a case of rectangular wave magnetization, FIG. 2 shows a case of sinusoidal magnetization on the inner peripheral surface, and FIG. 3 shows a case of sinusoidal magnetization on the outer peripheral surface.

  On the other hand, in the anisotropic magnet, an orientation magnetic field is applied at the time of molding, and an N pole and an S pole are formed corresponding to the direction of the easy axis of magnetization. The S pole is magnetized with the same polarity and used as a magnet. The anisotropic magnet includes a radial anisotropic magnet and a polar anisotropic magnet. The polarity in the radial anisotropic magnet is the same as that of a rectangular wave magnetized isotropic magnet (see FIG. 1), and the magnetic flux density distribution on the magnet surface is also a rectangular wave. On the other hand, the polarity in the polar anisotropic magnet is the same as that of an isotropic magnet magnetized with a sine wave (see FIGS. 2 and 3), and the magnetic flux density distribution on the magnet surface is also a sine wave. It becomes. Further, in the case of a polar anisotropic magnet, the NS pole appears along one of the outer peripheral surface and the inner peripheral surface of the magnet, and the magnetic flux hardly appears on the opposite surface. It is the same as a magnetized isotropic magnet.

  By the way, it is known that when a radial anisotropic magnet is incorporated in a motor, it causes cogging. The rotation unevenness due to the cogging torque is fatal for a spindle motor for a recording medium for which high density is required. However, radial anisotropic magnets have the advantage that they can be easily manufactured compared to polar anisotropic magnets.

  In order to perform radial anisotropic orientation, it is necessary to form an orientation magnetic field by flowing a magnetic field through the ring-shaped cavity from the inner circumference side to the outer circumference side. In a general horizontal magnetic field injection molding machine, an electromagnetic coil is provided in the space before and after the mold, and a magnetic field is generated there and collected by a magnetic yoke. A method of causing a magnetic field to flow from an inner peripheral surface of a ring-shaped cavity toward an outer peripheral surface by colliding in a mold is performed. The magnetic field returns to the original electromagnet coil through the column supporting the mold.

  In contrast, polar anisotropic magnets reduce cogging when incorporated into a motor. Furthermore, the polar anisotropic magnet is advantageous because the peak value of the waveform of the magnetic flux density distribution becomes high. However, there is a problem that polar anisotropic magnets have many manufacturing restrictions. Furthermore, it is difficult to reduce the thickness of the ring magnet. This is because, for example, in the case of inner peripheral surface magnetization, the magnetic flux does not fit in the thickness due to the thinning and leaks to the outside. When the magnetic flux leaks, the surface magnetic flux of the polar anisotropic magnet approaches a rectangular wave and becomes a trapezoidal wave. As a countermeasure, a back yoke made of a magnetic material is attached to the outside of the polar anisotropic magnet. However, a loss corresponding to the amount of magnetic flux escaping to the back yoke is generated. For this reason, the efficiency at the time of incorporating in a motor falls.

The polar anisotropy magnet is manufactured in such a manner that when polar anisotropy is applied to the outer peripheral side, the N pole and the S pole appear on the outer peripheral surface of the ring-shaped cavity provided in the mold. This is performed by using a mold having a configuration in which a permanent magnet or an orientation coil is embedded outside. On the other hand, when polar anisotropy is applied to the inner peripheral side, it is necessary to use a mold having a configuration in which a permanent magnet or an alignment coil is embedded inside the cavity.
In the mold, a polar anisotropic magnetic field is formed in the cavity, and in the case of a bonded magnet, a molten compound composed of magnetic powder and a resin binder is injected and filled into the mold cavity. By taking out from the mold after cooling, the above-mentioned polar anisotropic magnet can be manufactured.

Regarding the magnetic field formation of anisotropic magnets, there are a method using a static magnetic field by an orientation coil (electromagnet method), a method using a pulsed magnetic field by an orientation coil, and a method using a magnetic circuit by a permanent magnet (permanent magnet method). Among these methods, the method using a pulsed magnetic field needs to complete the molding within the generation time of the pulsed magnetic field, but is applied to compression molding but not used for injection molding or extrusion molding.

  Most of the conventional polar anisotropic magnets are manufactured from ferrite injection-molded bonded magnets or sintered ferrite magnets, and none are manufactured from rare earth metal magnets. The reason is that it was difficult to orient the magnetic powder in the cavity of the molding die in the molding process for rare earth bonded magnets and in the green compact molding process before the sintering process for rare earth sintered magnets. is there.

  The larger the magnetic field applied to orient the magnet powder in the mold cavity during magnet molding, the better. For example, in order to orient an anisotropic Nd—Fe—B magnet having a very high coercive force of about 800 kA / m in a magnetic field, an orientation magnetic field of about 1200 kA / m or more, at least 1.5 times that, is required. Is estimated to be necessary. However, to embed the size and number of pole anisotropic magnets to be molded, the material and thickness of the sleeve in contact with the cavity, the material of the permanent magnet or the coil material of the orientation coil or magnetic circuit, and the magnetic circuit The intensity of the magnetic field that can be applied depends on the size of the space that is allowed. In particular, in order to orient the inner peripheral surface of a ring-shaped magnet, it is necessary to incorporate an orientation coil with a copper wire wound on the inner peripheral side of the ring-shaped cavity in the die set. In order to achieve complete orientation, it is necessary to generate a strong magnetic field by increasing the number of turns of the coil or passing a large current. Furthermore, since a die set with a built-in orientation coil is subjected to a large pressing pressure at the time of molding, it needs to have a certain level of strength. In the past, it was impossible to satisfy these conditions.

  In the case of rare earth metal magnets, bond magnets that are currently used are mainly isotropic magnets that have inferior magnetic properties than anisotropic magnets. Furthermore, in the bonded magnet, the volume ratio occupied by the magnetic phase is lowered by the resin binder, so that the energy product showing the magnet characteristics is limited to about 20 to 30% of the sintered magnet and the hot-worked magnet.

Thus, various means for improving the energy product of rare earth bonded magnets have been studied. One of the means includes a flexible magnet (see, for example, Patent Documents 1 and 2). The flexible magnet is a flexible sheet formed by orienting anisotropic magnets. When assembled to a motor, the sheet magnet is rolled into a ring shape. However, a complicated process of rounding the magnet sheet and joining both ends into a ring shape is required. Further, when incorporated in a motor, the joined part may disturb the magnetic field and deteriorate the motor characteristics. There is also the problem of being.
JP 2002-343623 A JP 2003-318052 A

In addition, there is an example in which magnetic powder that is more easily oriented is studied (for example, see Patent Documents 3 and 4). However, there is no suggestion of applying to a polar anisotropic magnet having inner surface magnetization and multiple poles.
JP 2000-195713 A JP 2000-195714 A

Furthermore, it has been devised to use a combination of a magnet ring oriented in polar anisotropy and a magnet ring oriented in radial anisotropy (see, for example, Patent Documents 5 and 6).
Japanese Patent Publication No.7-1726 Japanese Patent Publication No.7-1727

  For driving magnetic / optical recording devices such as HDDs and DVDs, an outer rotor type brushless DC motor is a motor that has been used in recent years. The demand for miniaturization and high performance of these devices is very strong. Therefore, a small, thin and high performance magnet is required. Furthermore, since it is an outer rotor type, the inner peripheral surface of a ring-shaped magnet must be magnetized, and it is required to rotate the motor at high speed and smoothly in order to improve the recording density of the recording apparatus. . Therefore, in addition to being small and thin, it is required to increase the number of poles and to magnetize a sine wave. That is, the most desirable magnet is a small and thin magnet with polar anisotropy having multiple poles.

In addition, examples of the inner rotor type motor include stepping motors that are frequently used for controlling OA equipment such as printers. In the stepping motor, if sinusoidal magnetization is possible, a larger torque can be obtained. Further, the stepping motor has a problem that the cogging is larger than that of the DC motor. However, increasing the number of poles and magnetizing a sine wave are effective. Thus, as in the case of a DC motor, the most desirable is a polar anisotropic magnet having multiple poles.
However, in order to keep the cogging of the motor low, it is necessary that the back electromotive force constant of the motor has a “sine wave shape”. When the magnet is brought closer to the “sinusoidal magnetic flux density distribution”, the motor counter electromotive force constant tends to approach the “sinusoidal shape”, but there is a difference. This is due to the balance between the iron core, winding coil, and magnet that make up the magnetic circuit that is the basic design of the motor. For this reason, it is important not only to realize a polar anisotropic magnet but also to appropriately control the orientation state of the magnet according to the basic design of the motor to be applied.

  The present invention has been made in view of the above problems, and is a method for producing a high-performance ring-shaped anisotropic bonded magnet, in particular, a small-sized and thin polar anisotropic bonded magnet having multiple poles. It aims to provide a method.

The first aspect of the present invention is:
A method of manufacturing a ring-shaped anisotropic bonded magnet having a plurality of poles,
The anisotropic bonded magnet is divided into a polar region corresponding to the pole portion and a non-polar region adjacent to the polar region,
The polar region and the non-polar region are injection-molded in two stages to form one ring shape,
In the injection molding, one of the polar region and the non-polar region is oriented in the circumferential direction, and the other is oriented in the radial direction.
The second aspect of the present invention is:
A method of manufacturing a ring-shaped anisotropic bonded magnet having a plurality of poles,
The anisotropic bonded magnet is divided into a polar region corresponding to the pole portion and a non-polar region adjacent to the polar region,
The polar region and the non-polar region are injection-molded in two stages to form one ring shape,
An anisotropic bonded magnet manufacturing method characterized in that at the time of injection molding, one of the polar region and the non-polar region is oriented in the circumferential direction and the other is non-oriented.
The third aspect of the present invention is:
The method for producing an anisotropic bonded magnet according to the first or second aspect, wherein the non-polar regions are bonded to each other.
The fourth aspect of the present invention is:
The anisotropic bonded magnet manufacturing method according to the first or second aspect, characterized in that the anisotropic bonded magnet is divided into regions having twice the number of the poles.
The fifth aspect of the present invention is:
The anisotropic bonded magnet is a method for producing an anisotropic bonded magnet according to the first or second aspect, characterized in that the anisotropic bonded magnet is divided into a number of the number of the poles + 1.
The sixth aspect of the present invention is:
The cross-sectional ring shape of the anisotropic bonded magnet is not a concentric circle, only the inner periphery, only the outer periphery, or both the inner periphery and the outer periphery are elliptical,
The anisotropic bonded magnet manufacturing method according to any one of the first to fifth aspects.
The seventh aspect of the present invention is:
The magnet powder constituting the anisotropic bonded magnet is one or more rare earth metal magnets of Nd—Fe—B, Sm—Fe—N, and Sm—Co. It is a manufacturing method of the anisotropic bonded magnet as described in any one of the 1st thru | or 6th viewpoint.
The eighth aspect of the present invention provides
Of the first to sixth aspects, the magnet powder constituting the anisotropic bonded magnet is one or two oxide magnets of Ba ferrite and Sr ferrite. It is a manufacturing method of the anisotropic bonded magnet as described in any one.
The ninth aspect of the present invention provides
The magnet powder constituting the anisotropic bonded magnet includes Nd-Fe-B, Sm-Fe-N, or Sm-Co rare earth metal magnets, and Ba-based ferrite or Sr-based ferrite oxide magnets. It is a manufacturing method of the anisotropic bonded magnet as described in any one of the 1st thru | or 6th viewpoint characterized by consisting of a mixture with these.
The tenth aspect of the present invention is:
The method for producing an anisotropic bonded magnet according to any one of the first to ninth aspects, wherein the anisotropic bonded magnet is integrally formed with a back yoke.
The eleventh aspect of the present invention provides
The anisotropic bonded magnet manufacturing method according to any one of the first to ninth aspects, wherein the anisotropic bonded magnet is integrally formed with a rotor or a stator.

  According to the present invention, the link-shaped anisotropic bonded magnet is formed in two steps by dividing into a polar region and a non-polar region, and the orientation and shape of each region are appropriately controlled, thereby reducing the size. A thin and multipolar polar anisotropic bonded magnet can be produced relatively easily and inexpensively.

  The anisotropic bonded magnet manufactured according to the present invention is particularly suitable as a permanent magnet for a permanent magnet type motor because a large number of N poles and S poles are oriented anisotropically in a ring-shaped circumferential direction. It is valid.

The anisotropic bonded magnet formed by the manufacturing method of the present invention can maximize the performance of the magnet material and give the optimum polar anisotropy orientation according to the basic design of the motor. Industrial value is extremely high.

The magnet powder constituting the anisotropic bonded magnet of the present invention includes Nd—Fe—B rare earth magnet, Sm—Fe—N rare earth magnet, Sm—Co rare earth magnet, Ba ferrite ferrite, and Sr ferrite magnet. Any of these may be used, or two or more of these may be used in combination.
Specifically, Nd—Fe—B system includes Nd ₂ Fe ₁₄ B, Nd ₂ Fe ₁₄ B and α-Fe nanocomposite magnets, Nd ₂ Fe ₁₄ B and Fe ₃ B nanocomposites. There is a composite magnet. The Sm—Fe—N system includes Sm ₂ Fe ₁₇ N ₃ and SmFe ₉ N _1.5 . The Sm—Co system includes SmCo ₅ and Sm ₂ Co ₁₇ . Any of these magnets includes those in which Co or Fe is replaced with the same iron group element (Fe, Co, Ni), and those in which Nd or Sm is replaced with the same rare earth metal element (including Y). Among these, Nd—Fe—B magnets exhibit the most excellent magnet characteristics, but are inferior in heat resistance and corrosion resistance. For this reason, Sm—Fe—N and Sm—Co based magnets are often used.
Further, the magnet powder constituting the anisotropic bonded magnet of the present invention may be used by mixing a Ba-based ferrite magnet or an Sr-based ferrite magnet with the rare earth magnet as necessary. Some of these oxide-based magnets have a W-type crystal structure in addition to a commonly used magnetoplumbite (M-type) crystal structure. In the production method of the present invention, the greatest effect can be obtained when a rare earth metal magnet is used. However, even when an oxide magnet is used, the effect of the production method of the present invention can be obtained. In particular, in order to adjust the magnet characteristics of the rare earth metal magnet, it may be partially mixed with an oxide magnet.
Since the magnetic properties and weight of the finally obtained anisotropic bonded magnet can be controlled by the mixing ratio of rare earth metal magnet and oxide magnet, especially ring-shaped magnet is incorporated in the rotor of the motor When used, freedom can be given to the design of the inertia of the rotor.
The production method of the present invention can provide a greater effect when a rare earth metal magnet is used, but the effect of the production method of the present invention can also be obtained when an oxide magnet is used.

  Furthermore, isotropic and anisotropic magnet powders may be combined as needed for the purpose of controlling magnet characteristics, orientation, and the like. For example, anisotropic magnet powder can be used for the region oriented in the circumferential direction, and isotropic magnet powder can be used for the non-oriented region. Therefore, in order to obtain an anisotropic bonded magnet, not all of the magnet powder must be anisotropic. However, in order to obtain an anisotropic bonded magnet, an anisotropic magnet powder must basically be used, and at least one kind of anisotropic magnet powder must be used.

  In the anisotropic bonded magnet of the present invention, so-called two-color molding can be performed in which the polar region and the non-polar region are molded from materials having different magnet characteristics. One of the difficulties in orienting in polar anisotropy is that the magnetic flux easily escapes out of the magnet. For example, by using a material with a high residual magnetic flux density in the region oriented in the circumferential direction, A very high magnetic flux density can be obtained in combination with the effect of characterization. This high magnetic flux density can prevent the magnetic flux from escaping out of the magnet.

The average particle size of the magnet powder used in the present invention is not particularly limited, but is preferably 20 to 50 μm. Coarse grains are preferably cut to reduce the fluidity of the compound. A rough standard is 100 μm or less. When these are satisfied and the particle size distribution is widened to some extent, the fluidity is improved.
The resin binder used in the present invention serves as a binder for magnet powder, and the resin constituting the resin binder is not particularly limited. Examples of the resin include thermoplastic resins such as 6 nylon and 12 nylon. Moreover, you may mix and use 2 or more types of thermoplastic resins as needed.

  The content of the resin binder is 20% or more and 50% or less in a volume ratio with respect to the whole compound including the magnet powder and the resin binder. When the resin binder is filled more than 50%, the magnetic flux density of the anisotropic bonded magnet is remarkably lowered. Conversely, when it is less than 20%, the formability of the anisotropic bonded magnet is remarkably lowered and the desired molded body is obtained. Cannot be obtained.

  Further, when a coupling agent, a lubricant, a stabilizer or the like is added as an additive to the compound, the heat fluidity of the compound is further improved and the moldability and magnetic properties are improved. Examples of commonly used lubricants include metal soaps such as calcium stearate and zinc stearate. Not only the mold filling properties and mold release properties are improved, but also the compressibility is improved and the compact density is increased.

  In the method for producing an anisotropic bonded magnet of the present invention, magnet powder, resin binder, and the like are mixed and kneaded using a kneader such as a Nauter mixer, a Henschel mixer, a kneader, a single screw extruder, or a twin screw extruder. To do. And the compound for anisotropic bonded magnets is obtained by granulating in an appropriate shape, for example, pellet shape, and sizing. For granulation and sizing, a hot cutter method or a strand cutter method can be adopted.

  The anisotropic bonded magnet of the present invention is obtained by injection-molding the compound into a mold capable of applying a magnetic field having a necessary strength to the cavity in the die set on the orientation magnetic field generation side. The strength of the orientation magnetic field required here is determined depending on the characteristics of the magnet powder constituting the injected compound, particularly the coercive force. The strength of the orientation magnetic field may be about 1.5 times the coercive force of the magnet powder. Further, the cylinder temperature at the time of injection molding is set to be equal to or higher than the melting temperature of the bond magnet, and the mold temperature is set to be equal to or lower than the solidification temperature. The cylinder temperature is determined depending on the material of the resin binder, the particle size of the magnet powder, the mixing ratio of the resin binder and the magnet powder, and is generally in the range of 180 to 300 ° C. The mold temperature also affects magnet properties and productivity. When the mold temperature is high, the molding time becomes long. Conversely, when the mold temperature is low, the magnet characteristics are deteriorated. Therefore, the range of room temperature to 120 ° C is generally selected.

  In general, a gate for injection-filling a compound into a cavity in the die set is disposed on an end face of a ring-shaped magnet. Here, the gate of the anisotropic bonded magnet of the present invention is preferably a multipoint gate having a score twice as many as the number of poles finally obtained. However, the number of gates is not necessarily limited to this.

  The method for generating the orientation magnetic field is not particularly limited, and either a permanent magnet method or an electromagnet method using an orientation coil may be used. However, in the method for producing an anisotropic bonded magnet according to the present invention, since the injection molding is divided into two stages and the magnetic field applied at each stage is different, the magnetic field can be switched at each stage. However, when one region is non-oriented, it is not necessary to apply a magnetic field when forming the non-oriented region in the two-stage injection process.

In the anisotropic bonded magnet manufacturing method of the present invention, when a magnet is provided to a motor using a back yoke, the back yoke is previously placed in a cavity of a die set, and the anisotropic bonded magnet is injection-molded therein. There is also a method of integrally molding.
Furthermore, in the method for producing an anisotropic bonded magnet according to the present invention, the rotor or stator is placed in a cavity of a die set, and the anisotropic bonded magnet is injection-molded therein, whereby the rotor or stator is anisotropic. The bond magnet can be integrally formed.
According to these methods, the variation in fitting between the magnet and the back yoke, the magnet and the rotor, or the magnet and the stator is reduced, and the assembling operation and cost can be reduced. By incorporating the back yoke, rotor, or stator and anisotropic bonded magnet integrally formed in this way into the motor, the assembly accuracy of the motor can be improved and the assembly operation and cost can be reduced. For example, in brushless DC motors for recording devices such as HDDs and DVDs, vibration and the like must be eliminated as much as possible in order to increase the recording density. For this purpose, in addition to magnetizing the magnet in multiple poles and magnetizing in polar anisotropy, the dimensional accuracy of the magnet is required. Furthermore, the accuracy and fitting accuracy of individual parts such as magnets, rotors, and shafts are very important. For this reason, it is very significant to integrally mold the magnet and the rotor by injection molding. The same applies to a stepping motor or the like used for control of a printer or the like.

  The anisotropic bonded magnet manufactured according to the present invention may be demagnetized once for the purpose of facilitating handling and preventing adhesion of dust or the like. Then, if necessary, the surface of the magnet is coated and magnetized, and then incorporated into a rotor or a stator and used for a motor or the like.

  Either the coating or the magnetization order may be first. The coating is performed to prevent rusting of the magnet. However, when the amount of the resin binder is large with respect to the magnet powder, the magnet is difficult to rust, and thus the coating process may be omitted. Examples of the coating method include a method of applying a resin by spraying and a method of plating with a metal such as Ni.

  The present invention will now be described in more detail with reference to the drawings, which are not intended to limit the invention to certain specific embodiments.

  FIG. 4 illustrates a ring-shaped anisotropic bonded magnet having four poles. The anisotropic bonded magnet 1 is divided into a polar region a corresponding to the pole portion and a non-polar region b adjacent to the polar region a, and the anisotropic bonded magnet 1 has a number of poles of 2 as a whole. It is divided into a double number, that is, eight regions. In the manufacturing method of the present invention, the polar region a and the nonpolar region b are injection molded in two stages to form one ring shape. For example, after four nonpolar regions b are injection molded, The four polar regions a remaining in the mold are injection molded. The order of injection molding may be reversed.

  FIG. 5 illustrates the magnetic field of an anisotropic bonded magnet in which the nonpolar region b is oriented in the circumferential direction and the polar region a is oriented in the radial direction in the ring-shaped anisotropic bonded magnet illustrated in FIG. . Conventionally, when orienting so that a sinusoidal magnetic flux density distribution is formed on the inner peripheral surface of a ring-shaped magnet, it is necessary to place an orientation coil inside the ring-shaped cavity in the die set. . However, in the present invention, the orientation coil can be arranged outside the cavity, which makes it possible to make the magnet smaller, thinner, and multipolar. Furthermore, the magnet characteristics are remarkably improved by the anisotropy.

  6 illustrates the magnetic field of the anisotropic bonded magnet in which the nonpolar region b is oriented in the circumferential direction and the polar region a is not oriented in the ring-shaped anisotropic bonded magnet illustrated in FIG. . Even when magnetized in this way, the orientation coil can be arranged outside the cavity, and the magnet can be made smaller, thinner, multipolar, and improved in magnet characteristics.

  FIG. 8 illustrates another embodiment of a ring-shaped anisotropic bonded magnet having four poles. In this embodiment, the anisotropic bonded magnet 1 is divided into a polar region a corresponding to a pole portion and a non-polar region b adjacent to the polar region a, and the non-polar regions b are coupled to each other to form a single one. There are two areas. Therefore, the anisotropic bonded magnet 1 as a whole is divided into +1 number of poles, that is, five regions.

  FIG. 9 illustrates the magnetic field of the anisotropic bonded magnet in which the nonpolar region b is oriented in the circumferential direction and the polar region a is oriented in the radial direction in the ring-shaped anisotropic bonded magnet illustrated in FIG. . FIG. 10 illustrates the magnetic field of the anisotropic bonded magnet in which the nonpolar region b is oriented in the circumferential direction and the polar region a is not oriented in the ring-shaped anisotropic bonded magnet illustrated in FIG. .

  Here, in the embodiment illustrated in FIGS. 6 and 10, the magnetic flux of the anisotropic bonded magnet 1 becomes a completely closed system by making the polar region a non-oriented. As a result, the magnetic flux of the anisotropic bonded magnet 1 does not leak to the outside, resulting in a “pseudo-isotropic magnet” that is not different from an isotropic magnet in appearance. As a problem of the conventional anisotropic magnet, since it cannot be completely demagnetized, contamination has occurred due to adhesion of dust and the like, but this problem is caused in the anisotropic bonded magnet 1 shown in FIGS. 6 and 10. Can be solved. In consideration of a spindle motor for HDDs that hate contamination so that the entire assembly process is performed in a clean room, it is a significant advantage that contamination can be suppressed as a “pseudo-isotropic magnet”.

6 and 10, the polar region a may be oriented in the radial direction and the non-polar region may be non-oriented. Here, the oriented region and the non-oriented region may be molded with the same compound, or different compounds may be used to perform so-called two-color molding.
As described above, the fact that the injection molding is used in the manufacturing method of the present invention 1 to the present invention 5 has been described with reference to FIGS. However, when it is desired to obtain a long ring-shaped magnet, extrusion molding may be used according to this injection molding.

  The anisotropic bonded magnet 1 of the present invention can be magnetized before use in a motor. In the orientation state illustrated in FIGS. 5 and 9, the polarity inside the anisotropic bonded magnet 1 is an orientation state according to polar anisotropy. This is further magnetized according to the N pole and S pole applied at the time of molding so that a sinusoidal magnetic flux density distribution is formed inside the magnet, for example, as shown in FIGS. A polar anisotropic magnet is obtained by magnetizing.

  Further, in the orientation state shown in FIGS. 6 and 10, since it is a “pseudo-isotropic magnet” as described above, it can be handled so as not to be magnetized. However, the crystal structure inside the magnet is a completely anisotropic magnet, which is further magnetized by a yoke, for example, on the inner side of the magnet, as shown in FIGS. A polar anisotropic magnet is obtained by magnetizing according to the N-pole and S-pole applied at the time of molding so as to be formed.

  Moreover, in the anisotropic bonded magnet 1 of this invention, the ratio of the polar area | region a and the non-polar area | region b can be changed arbitrarily. When four poles are provided, for example, as shown in FIG. 12, the relationship between the angle α of the polar region a and the angle β of the non-polar region b is α + β = 90 °. If within the range satisfying this relationship, the angle α and the angle β are arbitrary, and the ratio between the polar region a and the non-polar region b changes according to the angle.

Further, the angle formed by the surface where the polar region a and the nonpolar region b are in contact with the radial direction of the ring shape formed by the anisotropic bonded magnet 1 can be arbitrarily changed. That is, the surface magnetic flux density can be arbitrarily controlled by changing the angle θ shown in FIG. 13 in the positive and negative directions. For example, as shown in FIG. 14, the result of measuring the inner peripheral surface of a ring-shaped magnet with a magnet analyzer is a waveform that is slightly rounder than the sine wave indicated by the thick line when θ = 0. However, by changing the value of the angle θ in the positive direction by an appropriate amount, a clean sine wave waveform indicated by a broken line can be obtained. Further, when the value of θ is further changed in the positive direction, a sharp waveform indicated by a thin line is obtained. Conversely, by changing the value of θ in the negative direction, it is possible to obtain a waveform that is rounder than the thick line.
In addition to this, there is also a method of controlling the magnetic flux density distribution by making the cross-sectional ring shape of the finally obtained anisotropic bonded magnet not concentric, but only the inner periphery, only the outer periphery, or both the inner periphery and the outer periphery are ellipses. is there.
As described in the “Problems to be Solved by the Invention”, in order to keep the cogging of the motor low, not only a magnet with polar anisotropy is realized, but also according to the basic design of the motor to be applied. The orientation state must be appropriately controlled. For this purpose, the above-described methods can be used.

  By the way, in the anisotropic bonded magnet 1 illustrated in FIGS. 5, 6, 9 and 10, for example, when the polar region a is injection molded after the nonpolar region b is injection molded in an anisotropic magnetic field, There is a concern that the magnetic field formed by the non-polar region b at the time of forming the region a cannot be ignored. However, a magnetic field is applied from the outside so as to cancel the magnetic field generated by the previously formed non-polar region b, and / or the angle θ is set to be different at both ends of the polar region a. This problem can be solved by adjusting. These two methods can be appropriately selected and used according to the magnet, the orientation conditions, the orientation coil, and the like. Conversely, this problem does not occur when the non-oriented region is injection-molded and then the other region is injection-molded in an anisotropic magnetic field.

  The following examples illustrate the invention in more detail, but these examples are not intended to limit the invention to certain embodiments.

Example Anisotropy Nd-Fe-B magnet powder and anisotropic Sm-Fe-N magnet powder 60% by volume, 12 nylon 40% by volume and a very small amount of coupling agent were mixed, and kneading machine Was kneaded and extruded. This was granulated and sized by a strand cutter method to produce a bond magnet pellet (mixture).
Using this pellet, a plate material of 80 × 10 × 5 mm was injection molded by an injection molding machine. Here, the applied anisotropic magnetic field was used as a parameter. Further, the cylinder temperature was 250 ° C., the mold temperature was 100 ° C., and the cooling method for the taken out molded product was air cooling.
The obtained plate material was cut into 10 × 10 × 5 mm to obtain measurement sample 1 to measurement sample 5 (Nd—Fe—B magnet), and measurement sample 6 to measurement sample 10 (Sm—Fe—N magnet). Their magnetic properties were evaluated with a BH curve tracer. Table 1 shows the results of the applied magnetic field, the measured maximum energy product: (BH) max, the residual magnetic flux density: Br, the intrinsic coercivity: iHc, the coercivity: bHc, and the degree of orientation.
When injection molding is performed in a magnetic field of 1200 kA / m, it can be seen that the magnet properties of the bonded magnets (measurement sample 4 and measurement sample 9) using any magnet powder are almost saturated. Compared with the case of injection molding in the absence of a magnetic field, the magnetic properties were remarkably improved and the effect of anisotropy was fully demonstrated.

Of the above, using an anisotropic bonded magnet pellet of Sm—Fe—N magnet powder, the pole of 8 poles on the inner peripheral surface of outer diameter: 20.0 mm, inner diameter: 17.5 mm, height: 2.5 mm An anisotropic bonded magnet was injection molded. The applied magnetic field at this time was 1200 kA / m. Further, the cylinder temperature was 250 ° C., the mold temperature was 100 ° C., and the cooling method for the taken out molded product was air cooling.
The die set had a structure in which two orientation coils were installed on the outer peripheral side of the magnet. Here, since the injection molding is performed in two stages, the area to be injected in the second stage is masked with a sliding member so as to be closed during the injection in the first stage. The region 1 emitted at the first stage was oriented in the radial direction or non-oriented. Moreover, the area | region 2 inject | emitted in the 2nd step | paragraph orientated in the circumferential direction. Then, the present invention 1 to the present invention 5 were obtained using the presence or absence of the orientation of the region 1 and the angles: α, β, and θ as parameters. Details are shown in FIGS. 15 and 16 and Table 2. FIG.
Next, these compacts were once demagnetized with a degaussing coil. And it magnetized using the magnetizing yoke so that it might become polar anisotropy of 8 poles in an inner periphery, and applying a pulse magnetic field. At this time, magnetization was performed so that a sinusoidal magnetic flux density distribution was obtained on the inner circumference in accordance with the polarities of the N pole and S pole at the time of orientation, and the magnets of the present invention 1 to the present invention 5 were obtained.

Similarly, among the above, a radially anisotropic bonded magnet having an outer diameter of 20.0 mm, an inner diameter of 17.5 mm, and a height of 2.5 mm using an anisotropic bonded magnet pellet of Sm—Fe—N magnet powder. Was injection molded. The applied magnetic field at this time was 1200 kA / m. Further, the cylinder temperature was 250 ° C., the mold temperature was 100 ° C., and the cooling method for the taken out molded product was air cooling. At this time, an orientation coil is installed outside the die set, and a magnetic field is applied from the front and back in the axial direction of the mold with a soft iron yoke to cause collision in the mold, and the outer circumference from the inner circumference side of the ring-shaped cavity. A magnetic field toward the side was formed.
A polar anisotropic bonded magnet was not used as a comparative sample because a permanent magnet capable of generating a magnetic field necessary for performing an anisotropic orientation of eight poles on the inner periphery of such a small ring-shaped magnet This is because it was impossible to embed the oriented coil in the ring-shaped cavity in the die set.
Next, the ring-shaped magnet was once demagnetized with a degaussing coil. The magnet of Comparative Example 1 was manufactured by applying a pulsed magnetic field using a magnetizing yoke so as to follow the polarities of the 8-pole radial anisotropy N-pole and S-pole on the inner circumference.
And the surface magnetic flux density of the inner periphery of the magnet of this invention 1 to this invention 5 and the comparative example 1 was measured. Here, a magnet analyzer using a Hall element was used. The results are shown in FIG. In the present invention 1 to the present invention 5, it can be seen that a sine wave having a beautiful magnetization waveform, a shape based on the sine wave, and a round waveform are obtained by varying the angles α, β, and θ.
On the contrary, the magnetization waveform of Comparative Example 1 is a rectangular wave, and the peak value thereof is lower than that of any one of the present invention 1 to the present invention 5.

FIG. 1 is a schematic diagram illustrating the polarity in a magnet magnetized with a rectangular wave and the polarity in a radial anisotropic magnet. FIG. 2 is a schematic diagram illustrating the polarity in a magnet whose sine wave is magnetized on the inner peripheral surface and the polarity in a polar anisotropy (inner peripheral side) magnet. FIG. 3 is a schematic diagram illustrating the polarity in a magnet whose sine wave is magnetized on the outer circumferential surface and the polarity in a polar anisotropy (outer circumferential side) magnet. FIG. 4 is a schematic diagram illustrating a ring-shaped anisotropic bonded magnet having four poles. FIG. 5 is a schematic diagram illustrating the polarity in the anisotropic bonded magnet illustrated in FIG. 4 in which the nonpolar region b is oriented in the circumferential direction and the polar region a is oriented in the radial direction. FIG. FIG. 6 is a schematic diagram illustrating the polarity in the anisotropic bonded magnet illustrated in FIG. 4 in which the nonpolar region b is oriented in the circumferential direction and the polar region a is not oriented. It is. FIG. 7 is a schematic diagram illustrating a magnetic field formed by the anisotropic bonded magnet illustrated in FIG. 4. FIG. 8 is a schematic view illustrating another embodiment of a ring-shaped anisotropic bonded magnet having four poles. FIG. 9 is a schematic diagram illustrating the polarity in the anisotropic bonded magnet illustrated in FIG. 8 in which the nonpolar region b is oriented in the circumferential direction and the polar region a is oriented in the radial direction. FIG. FIG. 10 is a schematic diagram illustrating the polarity in the anisotropic bonded magnet illustrated in FIG. 8 in which the nonpolar region b is oriented in the circumferential direction and the polar region a is not oriented. It is. FIG. 11 is a schematic diagram illustrating a magnetic field formed by the anisotropic bonded magnet illustrated in FIG. 8. FIG. 12 is a schematic diagram illustrating the angle α and the angle β that determine the ratio of the polar region a and the non-polar region b. FIG. 13 is a schematic diagram illustrating an angle θ formed by the surface where the polar region a and the nonpolar region b are in contact with the radial direction of the ring shape formed by the anisotropic bonded magnet 1. FIG. 14 is a graph showing changes in the surface magnetic flux density distribution on the inner peripheral surface of the anisotropic bonded magnet due to changes in the angle θ shown in FIG. FIG. 15 is a schematic diagram illustrating the angles α, β, and θ in the embodiment. FIG. 16 is a schematic diagram illustrating regions 1 and 2 in the embodiment. FIG. 17 is a graph showing the results of measuring the surface magnetic flux density distribution on the inner circumferential surface of the magnets of Examples 1 to 5 and Comparative Example 1.

Explanation of symbols

a Polar region b Non-polar region

Claims (11)

A method of manufacturing a ring-shaped anisotropic bonded magnet having a plurality of poles,
The anisotropic bonded magnet is divided into a polar region corresponding to the pole portion and a non-polar region adjacent to the polar region,
The polar region and the non-polar region are injection-molded in two stages to form one ring shape,
A method for producing an anisotropic bonded magnet, wherein one of the polar region and the non-polar region is oriented in the circumferential direction and the other is oriented in the radial direction during injection molding. A method of manufacturing a ring-shaped anisotropic bonded magnet having a plurality of poles,
The anisotropic bonded magnet is divided into a polar region corresponding to the pole portion and a non-polar region adjacent to the polar region,
The polar region and the non-polar region are injection-molded in two stages to form one ring shape,
A method for producing an anisotropic bonded magnet, wherein one of the polar region and the non-polar region is oriented in the circumferential direction and the other is non-oriented during injection molding. The method for manufacturing an anisotropic bonded magnet according to claim 1, wherein the non-polar regions are bonded to each other. 3. The method for manufacturing an anisotropic bonded magnet according to claim 1, wherein the anisotropic bonded magnet is divided into a region whose number is twice the number of the poles. The method for manufacturing an anisotropic bonded magnet according to claim 1, wherein the anisotropic bonded magnet is divided into the number of the poles + 1. The cross-sectional ring shape of the anisotropic bonded magnet is not a concentric circle, but only an inner circumference, only an outer circumference, or an ellipse both at the inner circumference and the outer circumference, according to any one of claims 1 to 5. A method for producing an anisotropic bonded magnet. The magnet powder constituting the anisotropic bonded magnet is one or more rare earth metal magnets of Nd—Fe—B, Sm—Fe—N, and Sm—Co. The manufacturing method of the anisotropic bonded magnet as described in any one of Claims 1 thru | or 6. The magnet powder constituting the anisotropic bonded magnet is any one of Ba-based ferrite and Sr-based ferrite, or two types of oxide-based magnets. A method for producing an anisotropic bonded magnet according to claim 1. The magnet powder constituting the anisotropic bonded magnet includes Nd-Fe-B, Sm-Fe-N, or Sm-Co rare earth metal magnets, and Ba-based ferrite or Sr-based ferrite oxide magnets. The manufacturing method of the anisotropic bonded magnet as described in any one of Claim 1 thru | or 6 characterized by consisting of a mixture with these. The method for producing an anisotropic bonded magnet according to claim 1, wherein the anisotropic bonded magnet is integrally formed with a back yoke. The method for producing an anisotropic bonded magnet according to any one of claims 1 to 9, wherein the anisotropic bonded magnet is integrally formed with a rotor or a stator.

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