JP2013135103A - Method of manufacturing cylindrical bonded magnet and manufacturing apparatus for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylindrical bonded magnet that generates magnetic force in an inner peripheral direction.SOLUTION: A method of manufacturing a cylindrical bonded magnet comprises the steps of: filling a cylindrical molding space with a bonded magnet composition including a magnetic material and a resin; and performing magnetic alignment of the magnetic material with an alignment magnet disposed on the inner peripheral side of the molding space and extruding a molten bonded magnet composition in an axial direction of the molding space. The alignment magnet is formed by arranging a second permanent magnet adjacent to a first permanent magnet in an axial direction of the first permanent magnet. The first permanent magnet is configured so that N poles and S poles alternately appear along the inner periphery of the molding space. The second permanent magnet is configured so that N poles and S poles alternately appear, the same poles of the first and second permanent magnets facing each other.

Description

  The present invention relates to a cylindrical anisotropic bonded magnet that is produced by an extrusion method and generates a magnetic force in the inner circumferential direction, and more particularly to a method for manufacturing the anisotropic bonded magnet.

  A bonded magnet composed of a magnetic material and a resin as a binder of the magnetic material can be formed in a complicated shape as compared with a sintered magnet, and has excellent mechanical strength. Therefore, many bonded magnets are employed as electronic parts such as permanent magnet type synchronous motors such as DC motors and stepping motors, and magnet rolls for laser printers.

  By the way, the manufacturing method of such a bond magnet is divided roughly into three types, injection molding, compression molding, and extrusion molding.

  Among these manufacturing methods, the injection molding method is a method in which a bonded magnet composition composed of a magnetic material and a thermoplastic resin is heated in a cylinder of an injection molding machine to be in a molten and fluidized state, and a mold is formed using a plunger. In this method, the inside is filled and formed into a desired shape.

  The compression molding method is a method in which a bonded magnet composition composed of a magnetic material and a thermosetting resin is filled in a press mold and molded while being compressed.

  The processes of the compression molding method and the injection molding method described above have a certain cycle of filling a bonded magnet composition into a mold, molding and taking out a bonded magnet as a molded product, and the production is a so-called batch production. Therefore, its production speed is limited.

  In addition, injection molding and compression molding have a limit for molding a long and narrow molded product, a so-called long product. One reason for this is a problem in mold processing. Although the shape of the molded product is engraved in the mold, high-precision machining in the depth direction of the mold is very difficult. Another reason is a molding problem. In the case of compression molding, even if a long and narrow object is pressed, no pressure is transmitted to the middle of the molded product. Further, when a long product is molded by injection molding, the bonded magnet composition entering from the gate is cooled, resulting in a short shot (molding failure due to unfilled molding material).

  On the other hand, in the extrusion molding method, a bonded magnet composition composed of a magnetic material and a thermoplastic resin or a thermosetting resin is heated in a cylinder to be melted and fluidized. This is a method of forming a bond magnet composition into a desired shape while continuously supplying it to a mold. For this reason, the extrusion molding method is continuous with respect to the batch method of injection molding or compression molding, and thus the productivity is very excellent. Furthermore, since it can shape | mold continuously, the shaping | molding of the long product which was difficult by injection molding and compression molding becomes easy.

  Next, the magnetic material constituting the bonded magnet will be described. First, from the viewpoint of the raw material composition of the magnetic material, it is classified into a ferrite type and a rare earth type magnetic material. Ferrites are most popular because they have a long history and are inexpensive. However, the ferrite type has a lower magnetic force than the rare earth type, and the magnetic force is insufficient when the molded product becomes smaller. Therefore, it is preferable to use a rare earth-based magnetic material for a small molded product.

  Moreover, the magnetic material which comprises a bond magnet is classify | categorized into isotropic and anisotropy from the point of the expression mechanism of magnetism. An isotropic magnetic material exhibits an equivalent magnetic force in any direction. On the other hand, anisotropic magnetic materials can develop a strong magnetic force only in one direction. Therefore, when an anisotropic magnetic material is used as a bonded magnet, the magnetization direction of the particles of the magnetic material must be anisotropic with a certain direction. Such an operation is called orientation. This orientation can be broadly divided into two types: mechanical orientation and magnetic field orientation. “Mechanical orientation” is a method in which when a magnetic material is composed of plate-like particles, the plate-like particles are aligned in the thickness direction when pressure is applied to the plate-like particles from the outside. It is. When the plate-like particles have an easy magnetization axis in the thickness direction, the magnetic material particles can be mechanically oriented by this operation. On the other hand, “magnetic field orientation” means that particles are oriented by applying a magnetic field from the outside during molding. From the relationship between the particle shape and the direction of the easy axis of magnetization, mechanical orientation is possible with ferrite-based magnetic materials, but with rare-earth magnetic materials, it is limited to magnetic field orientation. When an anisotropic magnetic material is used, the orientation process is increased compared to when an isotropic magnetic material is used, so that molding becomes difficult, while magnetic force is higher than when an isotropic magnetic material is used. Become stronger.

  Cylindrical magnets that generate magnetic force in the inner circumferential direction are widely used in spindle motors incorporated in hard disk drives and optical media. Most of these are cylindrical bonded magnets obtained by compression molding a bonded magnet composition comprising an isotropic Nd—Fe—B based magnetic material and a resin. This is because, as described above, the isotropic Nd—Fe—B based magnetic material does not require a step of orienting the magnetic material at the time of molding. This is because a desired surface magnetic flux waveform can be applied only by this.

  However, in order to increase the surface magnetic flux density of the molded cylindrical bonded magnet, a large amount of Nd—Fe—B magnetic material must be packed per unit volume. As a result, the specific gravity of the molded cylindrical bonded magnet is reduced. The problem is that it grows.

  In order to reduce the size and weight of the spindle motor, the cylindrical bonded magnet is required to be lighter and have a higher magnetic force. Therefore, researches for producing a cylindrical bonded magnet by injection molding or compression molding have been actively conducted.

JP 2005-223233 A

  However, the spread of anisotropic bonded magnets has been delayed compared to bonded magnets using isotropic Nd—Fe—B based magnetic materials. Hereinafter, the reason will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a conventional mold for injection molding a cylindrical bonded magnet. FIG. 2 is a perspective view showing the size of one piece of a small magnet constituting the magnet for orientation.

  Consider a case in which a cylindrical bonded magnet that generates a magnetic force in the inner circumferential direction is formed using a bonded magnet composition containing an anisotropic magnetic material as a material. First, as a configuration of the manufacturing apparatus, as shown in FIG. 1, it is necessary to dispose a permanent magnet for orientation in a mold for molding the inner peripheral surface of a cylindrical bonded magnet that is a molded product.

  Here, as a typical specification of the cylindrical magnet for the spindle motor, there is a specification that the outer shape (Φ) is 19 mm × the inner diameter (Φ) is 17 mm × the height (H) is 3 mm, and the number of poles is twelve. As shown in FIG. 2, the dimensions of one piece of magnet that constitutes an orientation magnet for such a cylindrical magnet are as follows. The side surface is generally center angle (α) 30 degrees, radius (r) 8 mm, and circular. The size (a) is 4.97 mm, and the depth (b) is a wedge shape with 3 mm, which is very small compared to the size of the entire magnet for orientation. At such a small size, even if a strong permanent magnet is used as a material, the generated orientation magnetic field becomes weak. Actually, when such a small-sized magnet is manufactured with the NdFeB sintered magnet N48H manufactured by Shin-Etsu Chemical Co., Ltd. and placed in the mold shown in FIG. 1, the orientation magnetic field is only 4000G.

  In such an orientation magnetic field with a small surface magnetic flux density, the magnetic material contained in the bond magnet composition is difficult to orientate, and as a result, the surface magnetic flux density of the cylindrical bond magnet becomes small. For example, the surface magnetic flux density of a cylindrical bonded magnet by compression molding using an isotropic Nd—Fe—B-based magnetic material is about 2000 G, whereas molding by injection molding in such a small orientation magnetic field. The surface magnetic flux density of the cylindrical bonded magnet as a product is about 1500G.

  In order to solve the problem of decreasing the surface magnetic flux density in this way, for example, as disclosed in Patent Document 1, it is considered to use a magnet arranged so as to repel in the outer circumferential direction as an orientation magnet. Has been. Thus, when it is set as the orientation magnet comprised by arranging a plurality of small magnets so as to repel in the outer peripheral direction, as described in Patent Document 1, the inner peripheral direction of the cylindrical bonded magnet that is a molded product When the measured surface magnetic flux density is represented in a graph, the waveform is tapered.

  In order to solve such a problem, in Patent Document 1, a magnetic yoke is disposed between a plurality of small magnets constituting the magnet for orientation to eliminate the above-described taper problem. A surface magnetic flux density waveform close to a sine wave is obtained.

  However, in order to obtain a cylindrical bonded magnet having a pole number of 12 poles, which is a typical specification of a cylindrical magnet for a spindle motor, by using such an orientation magnet, orientation in the circumferential direction is required. It is necessary to divide the working magnet into 24 parts and arrange the 24 small magnets side by side while repelling them. In order to form a small cylindrical bonded magnet having an inner diameter of 17 mm as described above, it is very difficult to apply such a prior art.

  That is, since one piece of small magnets constituting the magnet for orientation is very small, processing is difficult, the magnetic force of each magnet constituting the magnet for orientation is weak, and assembly of the magnet for orientation is difficult. The reason is that it is difficult.

  The present invention has been made in view of such circumstances, and the object of the present invention is to have a light and strong magnetic force, which is difficult with the conventional molding technology, and the waveform of the surface magnetic flux density is a sine waveform. It is to provide a cylindrical magnet that emits a magnetic force in the inner circumferential direction with a small variation in surface magnetic flux density in the height direction.

  In order to solve the above-described problems, the present invention provides the above magnetic material by a step of filling a cylindrical molding space with a bonded magnet composition containing a magnetic material and a resin, and an orientation magnet disposed inside the molding space. And a method of producing a cylindrical bonded magnet having a step of extruding a melted bonded magnet composition in the axial direction of the orientation magnet and forming the orientation bond magnet. For the first permanent magnet configured so that the N pole and the S pole appear alternately in the direction, the N pole and the S pole that face the same pole as the N pole and the S pole of the first permanent magnet appear alternately. It is a manufacturing method of the cylindrical bonded magnet characterized by arrange | positioning the 2nd permanent magnet comprised in this way adjacent to the axial direction of said 1st permanent magnet.

  By arranging a third permanent magnet configured such that N-poles and S-poles appear alternately in the radial direction toward the outer circumference between the first magnet and the second magnet, the orientation magnet It is preferable to constitute.

  In order to solve the above-mentioned problems, the present invention provides a cylindrical molding space filled with a bonded magnet composition containing a magnetic material and a resin, and is disposed inside the molding space, and magnetically disposes the magnetic material. An apparatus for producing a cylindrical bonded magnet, which is formed by extruding a melted bonded magnet composition in the axial direction of the orientation magnet, and the orientation magnet is axially provided. Are arranged adjacent to each other in the axial direction of the first permanent magnet, and are arranged on the N pole and the S pole of the first permanent magnet. An apparatus for producing a cylindrical bonded magnet, comprising: a second permanent magnet configured such that N poles and S poles facing each other are alternately appeared.

  It is preferable that a third permanent magnet configured so that N poles and S poles appear alternately in the radial direction toward the outer periphery is disposed between the first magnet and the second magnet.

  The magnetization directions of the first and second permanent magnets are preferably inclined in the outer circumferential direction at an angle of 0 degree or more and less than 90 degrees with respect to the axial direction. The upper magnetic material is preferably an Sm—Fe—N based magnetic material.

  According to the present invention, a cylinder that emits a magnetic force in the inner circumferential direction is light and has a high surface magnetic flux density, the surface magnetic flux density waveform is close to a sine waveform, and the surface magnetic flux density variation in the height direction is small. A bonded magnet bonded magnet can be provided.

FIG. 1 is a cross-sectional view showing an example of a conventional mold for injection molding a cylindrical bonded magnet. FIG. 2 is a perspective view showing the size of one piece of a small magnet constituting the orientation magnet. FIG. 3 is a cross-sectional view of a manufacturing apparatus for extruding a bonded magnet according to the present invention. FIG. 4 is a perspective view and a cross-sectional view of an orienting magnet in Comparative Example 1 for comparison with the present invention. FIG. 5 is a perspective view and a cross-sectional view of the magnet for orientation in Example 1 of the present invention. FIG. 6 is a perspective view and a sectional view of an orienting magnet in Embodiment 2 of the present invention. FIG. 7 is a perspective view and a sectional view of an orienting magnet in Example 3 of the present invention. FIG. 8 is a perspective view and a sectional view of an orienting magnet in Example 4 of the present invention. FIG. 9 is a diagram showing the results of measuring the surface magnetic flux density in the longitudinal direction of the magnet for orientation in each example and each comparative example. FIG. 10 is a diagram showing the results of measuring the surface magnetic flux density along the circumferential direction of the cylindrical bonded magnet in each example and each comparative example. FIG. 11 is a diagram showing the results of measuring the surface magnetic flux density in the height direction of the cylindrical bonded magnet in each example and each comparative example.

  In order to achieve the above object in a manufacturing method for obtaining a cylindrical bonded magnet that emits a magnetic force in the inner circumferential direction by extrusion molding while aligning a bonded magnet composition comprising a magnetic material and a resin in a magnetic field, the inventors have earnestly As a result of repeated studies, the present invention has been completed by arranging the magnets for orientation by arranging them so that the same poles of a plurality of magnet pieces repel each other at at least one point in the extrusion direction.

  FIG. 3 is a sectional view of a manufacturing apparatus for extruding a cylindrical bonded magnet according to the present invention. The manufacturing apparatus of the cylindrical bonded magnet of this invention is demonstrated using FIG. As shown in FIG. 3, the cylindrical bonded magnet manufacturing apparatus of the present invention includes a plasticizing part 1 that heats and melts a bonded magnet composition composed of a magnetic material and a resin, and is continuous with the plasticizing part 1. And a spider part 2 for flowing the molten bond magnet composition in a cylindrical shape, and a mold part for continuously forming the flowed bond magnet composition in a cylindrical shape. 3 and a molding part 4 which is continuously provided in the mold part 3 and which forms a flowing bonded magnet composition into a cylindrical shape and in which an orientation magnet for orienting a magnetic material is arranged. Hereinafter, the manufacturing method and manufacturing apparatus of the cylindrical bonded magnet of this invention are explained in full detail.

  First, as shown in FIG. 3, a bonded magnet composition composed of a magnetic material and a resin is melted by heating with a screw 5 of the plasticizing part 1 to be in a fluid state.

  Next, the bonded magnet composition melted from the spider part 2 to the mold part 3 through the flow path 8 formed between the spider 6 of the spider part 2 and the inner surface of the outer die 7 by the propulsive force of the screw 5. Send. In the mold part 3, a cylindrical flow path 11 is formed by the inner die 9 and the outer die 10, and the molten bonded magnet composition sent from the spider part 2 through the flow path 11. Is sent to the molding unit 4. At this time, the molten bonded magnet composition is formed into a cylindrical shape that is the shape of the target bonded magnet by passing through the flow path 11.

  In the molded part 4, the melted bonded magnet composition is oriented with the magnetic material contained therein, and the resin contained therein is cured. In this molding part 4, the flow path 16 formed by the inner die 12 and the outer die 13 is a flow for sending the molten bonded magnet composition sent from the previous mold part 3 to the outside of the manufacturing apparatus. In addition to being a path, it also serves as a molding space for the molten bonded magnet composition. An orientation magnet is embedded in the inner die 12. Therefore, when the bonded magnet composition in the molten state passes through the flow path 16, the magnetic material particles are easily oriented in the magnetization direction. After the magnetic material passes through the orientation magnetic field, the resin is cured to obtain a cylindrical bonded magnet as a molded product.

  5 to 8 show a perspective view of an orienting magnet according to the present invention and a cross-sectional view of a dotted line portion shown in the perspective view, together with an arrow indicating a magnetization direction. As shown in the drawing, the magnet for orientation according to the present invention repels two magnets having the same poles in the longitudinal direction of the magnet for orientation (that is, the extrusion direction of the manufacturing apparatus) with respect to one pole. To extract a strong magnetic field.

  That is, as the configuration of the orientation magnet of the present invention, for example, many forms are possible as described in (1) to (4) described below in detail, but the present invention is not limited to this.

  (1) As shown in FIG. 5, a cylindrical first permanent magnet 51 configured by arranging a plurality of magnet pieces so that N poles and S poles appear alternately in the axial direction, and also in the axial direction Of the cylindrical second permanent magnet 52 formed by arranging a plurality of magnet pieces so that the N pole and the S pole appear alternately on each other, the N pole and the S pole repel each other in parallel to the extrusion direction. Thus, the orientation magnet 50 is configured.

  In addition, the cylindrical first and second permanent magnets may be cylindrical magnets that are hollow to the extent that the magnetic force is not impaired. The same applies to other embodiments described below. Further, the magnets for orientation shown in FIG. 5 may be configured as a set, and a magnet for orientation connected with a plurality of sets by sandwiching a yoke (for example, iron is a material) between the magnets. The same applies to other embodiments described below.

  When the orientation magnet 50 shown in FIG. 5 is cut at a location indicated by a dotted line in the upper diagram of FIG. 5, as shown in the lower diagram of FIG. The permanent magnet 51 and the second permanent magnet 52 face each other at a boundary line connecting them.

  By such an orienting magnet 50, a strong magnetic force is radiated from the surface where the first permanent magnet 51 and the second permanent magnet 52 are connected to the outside (in particular, the flow path 16 in the molded part 4). Can be done. Moreover, the result of having measured the surface magnetic flux density in the longitudinal direction of the magnet 50 for orientation shown by FIG. 5 is shown as Example 1 in FIG. 9, for example.

  (2) As shown in FIG. 6, a cylindrical first permanent magnet 61 configured by arranging a plurality of magnet pieces so that N poles and S poles appear alternately in the axial direction, and also in the axial direction Of the cylindrical second permanent magnet 62 formed by arranging a plurality of magnet pieces so that the N pole and the S pole appear alternately on each other, the N pole and the S pole are oblique to the extrusion direction (see FIG. 6 In the lower diagram, the magnets for orientation are configured so that the magnet pieces are oriented in the diagonal direction of the quadrilateral cross section of the magnet piece and the magnetization directions are directed to the outer peripheral direction and repel each other.

  Here, the “oblique direction” is the direction of the angle θ in the lower diagram of FIG. 6, and the angle is 0 with respect to the extrusion direction of the bonded magnet composition (that is, the axial direction of the orientation magnet). It shall mean a direction of not less than 90 degrees and less than 90 degrees. The same applies to other embodiments described below.

  Further, when the magnet for orientation shown in FIG. 6 is cut at a position indicated by a dotted line in the upper diagram of FIG. 6, as shown in the lower diagram of FIG. The one permanent magnet 61 and the second permanent magnet 62 face each other diagonally toward the boundary where they are connected.

  By such an orientation magnet 60, a strong magnetic force can be radiated from the surface where the first permanent magnet and the second permanent magnet are connected to the outside (in particular, the flow path 16 in the molded part 4). It is like that. Moreover, the result of having measured the surface magnetic flux density in the longitudinal direction of the magnet 60 for orientation shown by FIG. 6 is shown as Example 2 in FIG. 9, for example.

  (3) As shown in FIG. 7, a cylindrical third permanent magnet 73 configured by arranging a plurality of magnet pieces so that N poles and S poles alternately appear in the radial direction is prepared. Cylindrical first and second permanent magnets configured by arranging the third permanent magnet 73 in the middle and arranging a plurality of magnet pieces so that N poles and S poles appear alternately in the axial direction. The orientation magnet 70 is configured by arranging 71 and 72 next to each other on both sides in the axial direction of the third permanent magnet 73. That is, the third permanent magnet 73 is arranged so as to be sandwiched between the first permanent magnet 71 and the second permanent magnet 72 in the axial direction.

  When the magnet for orientation shown in FIG. 7 is cut at a location indicated by a dotted line in the upper diagram of FIG. 7, as shown in the lower diagram of FIG. The second permanent magnets 71 and 72 and the third permanent magnet 73 are perpendicular to each other, and the first permanent magnet 71 and the second permanent magnet 72 have a magnetization direction (the tip of the arrow is the N pole). , Towards the third permanent magnet, facing each other parallel to the extrusion direction.

  By such an orienting magnet 70, the first and second permanent magnets 71 and 72 and the third permanent magnet 73 are connected to the outside (in particular, the flow path 16 in the molded portion 4) from the interface between the two locations. Due to the magnetic force and the magnetic force directed from the center of the third permanent magnet 73 to the outside (particularly, the flow path 16 in the molding portion 4), a stronger magnetic force can be emitted from the entire orientation magnet 70. Yes. Moreover, the result of having measured the surface magnetic flux density in the longitudinal direction of the magnet 70 for orientation shown by FIG. 7 is shown as Example 3 in FIG. 9, for example.

  (4) As shown in FIG. 8, a cylindrical third permanent magnet 83 configured by arranging a plurality of magnet pieces so that N and S poles appear alternately in the radial direction is prepared. Cylindrical first and second permanent magnets configured by arranging the third permanent magnet 83 in the middle and arranging a plurality of magnet pieces so that N poles and S poles appear alternately in the axial direction. By aligning 81 and 82 adjacent to each other in the axial direction of the third permanent magnet 83, an orientation magnet 80 is formed. That is, the third permanent magnet 83 is arranged so as to be sandwiched between the first permanent magnet 81 and the second permanent magnet 82 in the axial direction.

  Here, in the first and second permanent magnets 81 and 82, the magnetization direction connecting the N pole and the S pole is oblique to the extrusion direction (in the lower diagram of FIG. 8, the diagonal direction of the quadrilateral cross section of the magnet piece) And the magnet for orientation is comprised so that it may repel with the 3rd magnet 83 in an outer peripheral direction.

  When the orienting magnet 80 shown in FIG. 8 is cut at the position indicated by the dotted line in the upper diagram of FIG. 8, the magnetization direction (the tip of the arrow is N pole) is the first as shown in the lower diagram of FIG. The permanent magnet 81 and the second permanent magnet 82 face each other in an oblique direction on the outer periphery, and the first and second permanent magnets 81 and 82 and the third permanent magnet 83 have a magnetization direction. The third permanent magnet 83 faces diagonally toward the outer periphery. The diagonal directions in the first and second permanent magnets 81 and 82 referred to here are diagonal directions of a quadrangular section of the magnet piece shown in the lower diagram of FIG.

  By such an orienting magnet 80, the first and second permanent magnets 81 and 82 and the third permanent magnet 83 are connected to the outside (particularly, the flow path 16 in the molded part 4) from the interface between the two locations. A stronger magnetic force can be radiated by the magnetic force and the magnetic force directed from the center of the third permanent magnet 83 to the outside (particularly, the flow path 16 in the molded part 4). Moreover, the result of having measured the surface magnetic flux density in the longitudinal direction of the magnet 80 for orientation shown by FIG. 8 is shown as Example 4 in FIG. 9, for example.

  As shown in FIG. 9 showing the surface magnetic flux density in the longitudinal direction of the orientation magnet, generation of magnetic force obtained by the repulsion of the first and second orientation permanent magnets (1) to (4) described above. There is almost one point to do. However, the magnetic force generated at one point is very strong. This is clear even when compared with the magnetic force of a conventional orientation magnet. Extrusion molding according to the present invention is not a batch method such as injection molding or compression molding, but is continuous molding. Therefore, a bonded magnet composition in a molten state is always continuously under only one strong magnetic field. Pass through. For this reason, the molded product of the bonded magnet is uniformly oriented at a high rate in the longitudinal direction, and a high surface magnetic flux density can be obtained.

  Note that it is virtually impossible to apply the magnet for orientation shown in FIGS. 5 to 8 to injection molding or compression molding. Because injection molding or compression molding is not a method in which a bonded magnet composition is continuously filled in a mold as in extrusion molding, it becomes a bonded magnet that emits a strong magnetic force from only one point in the longitudinal direction. This is because a high surface magnetic flux density uniformly oriented at a high rate cannot be obtained.

  In addition, the material of the magnet used for the permanent magnet for orientation is preferably one in which Br is 1T or more. For example, an Nd—Fe—B based sintered magnet or an Sm—Co based sintered magnet can be used. When a magnet with a large magnetic force is used, the orientation magnetic field becomes stronger and the surface magnetic flux density of the bonded magnet can be increased.

  Moreover, the bonded magnet obtained by extrusion molding as described above may be subjected to a magnetizing step if necessary. By performing the magnetization, the surface magnetic flux density becomes higher.

  An anisotropic magnetic material can be applied to the magnetic material used in the present invention. Examples of anisotropic magnetic materials include ferrite, Sm—Co, Nd—Fe—B, and Sm—Fe—N. The above magnetic materials can be used alone or as a mixture of two or more. Moreover, you may perform an oxidation resistance process and a coupling process as needed.

  The resin used in the present invention is not particularly limited, and examples thereof include thermoplastic resins such as polypropylene, polyethylene, polyvinyl chloride, polyester, polyamide, polycarbonate, polyphenylene sulfide, and acrylic resin, and esters and polyamides. Thermoplastic elastomer or thermosetting resin such as epoxy or phenol, or natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, chloroprene rubber, nitrile rubber, butyl rubber, ethylene propylene rubber, urethane rubber, silicone rubber Rubber materials such as acrylic rubber, chlorosulfonated polyethylene rubber, fluorine rubber, hydrogenated nitrile rubber, epichlorohydrin rubber, and liquid rubber can be used.

  Although the blending ratio of the magnetic material and the resin depends on the type of the resin, it is desirable that the ratio of the magnetic material to the entire bonded magnet composition is 45 to 65 Vol%. Further, an antioxidant, a lubricant and the like can be further mixed.

  Examples according to the present invention will be described in detail below. Needless to say, the present invention is not limited to the following examples.

<Example 1>
(Preparation of magnetic material)
The magnetic material is an anisotropic Sm—Fe—N-based magnetic material (average particle diameter of 3 μm).
(Preparation of bonded magnet composition)
First, the Sm—Fe—N based magnetic material is surface-treated with ethyl silicate and a silane coupling agent. 9137 g of the Sm—Fe—N magnetic material subjected to the surface treatment and 863 g of 12 nylon (PA12) are mixed with a mixer. The obtained mixed powder is kneaded at 220 ° C. using a biaxial kneader, cooled, and then cut into an appropriate size to obtain a bonded magnet composition.
(Extrusion molding)
FIG. 5 is a diagram showing the orientation magnet 50 used in the first embodiment. Extrusion molding was performed using the magnet for orientation 50 of FIG. The inner diameter of the outer die is 19 mm, and the outer diameter of the inner die is 17 mm. The magnet for orientation is produced by adhering the same poles of the first permanent magnet 51 and the second permanent magnet 51 oriented in the extrusion direction. The magnetization directions of the first permanent magnet 51 and the second permanent magnet 51 are set to 0 ° with respect to the axial direction. The first and second permanent magnets 51 and 52 have a diameter of 16 mm and a length of 10 mm, respectively, and are embedded in the inner die 12. The partition wall separating the orientation magnet and the flow path 11 is 0.5 mm. The mold temperature at the time of extrusion molding is set to 200 ° C., and the outlet temperature is cooled to 165 ° C. In this way, an anisotropic cylindrical bonded magnet having an outer diameter of 19 mm, an inner diameter of 17 mm, a length of 1000 mm, and an inner circumference of 12 poles is obtained. Furthermore, it cut | disconnects in length 20mm using a cutting machine. The obtained molded product is magnetized by a magnetizing yoke. The magnetization conditions are a capacitance of 1000 μF and a voltage of 2.5 kV, and the current flowing at that time is 18.0 kA.

<Example 2>
(Preparation of magnetic material)
The same magnetic material as in Example 1 is used.
(Preparation of bonded magnet composition)
Using the same magnetic material as in Example 1, the same bonded magnet composition as in Example 1 is produced.
(Extrusion molding)
FIG. 6 is a diagram showing the orientation magnet 60 used in the second embodiment. Extrusion molding was performed in the same manner as in Example 1 except that the orientation magnet 50 of Example 1 was changed to the orientation magnet 60 shown in FIG. The magnet for orientation 60 is disposed by adhering the same poles of the first permanent magnet 61 and the second permanent magnet 62 having a magnetization direction oblique toward the outer periphery with respect to the extrusion direction. The magnetization directions of the first permanent magnet 61 and the second permanent magnet 62 are set to 50 ° as an angle (θ) measured from the axial direction toward the outer periphery.

<Example 3>
(Preparation of magnetic material)
The same magnetic material as in Example 1 is used.
(Preparation of bonded magnet composition)
Using the same magnetic material as in Example 1, the same bonded magnet composition as in Example 1 is produced.
(Extrusion molding)
FIG. 7 is a diagram showing the orientation magnet 70 used in the third embodiment. Extrusion molding was performed in the same manner as in Example 1 except that the orientation magnet 50 of Example 1 was changed to the orientation magnet 70 shown in FIG. The orientation magnet 70 has a third permanent magnet 73 having a magnetization direction in a radial direction perpendicular to the extrusion direction in the middle, and has a magnetization direction parallel to the extrusion direction on the left and right sides thereof. The same poles of the two permanent magnets 71 and 72 are disposed on the left and right sides of the third permanent magnet 73. The magnetization directions of the first permanent magnet 71 and the second permanent magnet 72 are 0 ° with respect to the axial direction.

<Example 4>
(Preparation of magnetic material)
The same magnetic material as in Example 1 is used.
(Preparation of bonded magnet composition)
Using the same magnetic material as in Example 1, the same magnet composition as in Example 1 is produced.
(Extrusion molding)
FIG. 8 is a diagram showing the orientation magnet 80 used in the fourth embodiment. Extrusion molding was performed in the same manner as in Example 1 except that the orientation magnet 50 of Example 1 was changed to the orientation magnet 80 shown in FIG. The orientation magnet 80 has a third permanent magnet 83 having a magnetization direction in a radial direction perpendicular to the extrusion direction in the middle, and has a magnetization direction obliquely toward the outer periphery with respect to the extrusion direction on the left and right sides thereof. The second permanent magnets 81 and 82 are disposed on the left and right sides. The first, second, and third permanent magnets 81, 82, and 83 have the same polarity facing each other in the direction toward the outer periphery. The magnetization directions of the first permanent magnet 81 and the second permanent magnet 82 are set to 50 ° as an angle (θ) measured from the axial direction toward the outer periphery.

<Comparative Example 1>
(Preparation of magnetic material)
The same magnetic material as in Example 1 is used.
(Preparation of bonded magnet composition)
Using the same magnetic material as in Example 1, the same bonded magnet composition as in Example 1 is produced.
(Extrusion molding)
FIG. 4 is a perspective view and a sectional view of an orienting magnet 40 in Comparative Example 1 for comparison with the present invention. 4 is a cross-sectional view of a portion indicated by a dotted line in the upper diagram of FIG. Extrusion molding was performed in the same manner as in Example 1 except that the orientation magnet 50 of Example 1 was changed to the orientation magnet 40 shown in FIG.

<Comparative example 2>
(Preparation of magnetic material)
The same magnetic material as in Example 1 is used.
(Preparation of bonded magnet composition)
Using the same magnetic material as in Example 1, the same bonded magnet composition as in Example 1 is produced.
(injection molding)
The bonded magnet composition is melted in a plasticized portion heated to 200 ° C., and the bonded magnet composition is injected into a mold heated to 90 ° C. to obtain a molded product. The shape of the molding space is outer diameter (Φ) 19 mm × inner diameter (Φ) 17 mm × length (L) 20 mm. The orientation magnet shown in FIG. 5 was placed in the molding space of the mold. The orientation magnet has a diameter (r) of 16 mm and a length (L) of 20 mm. The partition wall that separates the orientation magnet 50 from the molding space is 0.5 mm. The obtained molded product is magnetized by a magnetizing yoke. The magnetization conditions are a capacitance of 1000 μF and a voltage of 2.5 kV, and the current flowing at that time is 18.0 kA.

<Comparative Example 3>
(Preparation of magnetic material)
The same magnetic material as in Example 1 is used.
(Preparation of bonded magnet composition)
Using the same magnetic material as in Example 1, the same bonded magnet composition as in Example 1 is produced.
(Compression molding)
A bonded magnet composition is filled into a mold having a molding space having an outer diameter of (Φ) 19 mm, an inner diameter of (Φ) 17 mm, and a length in the longitudinal direction of 20 mm. A pressure of 500 MPa is applied by a press. The bonded magnet molded product is taken out from the mold, and the resin is cured in an oven at 150 ° C. for 10 hours. In this way, an isotropic bonded magnet molded product having an outer diameter (Φ) of 19 mm, an inner diameter (Φ) of 17 mm, and a height of 20 mm is obtained. The obtained molded product is magnetized by a magnetizing yoke. The magnetization conditions are a capacitance of 1000 μF and a voltage of 2.5 kV, and the current flowing at that time is 18.0 kA.

<Evaluation>
(Measurement of orientation magnetic field)
The orientation magnetic field of the orientation magnets in the above examples and comparative examples was measured with a gauss meter. The measurement was performed by embedding an orientation magnet in a mold and moving the probe in the longitudinal direction of the orientation magnet with respect to one N-pole peak. FIG. 9 is a diagram showing the results of measuring the surface magnetic flux density in the longitudinal direction of the magnet for orientation in each example and each comparative example.

(Measurement of surface magnetic flux density in the radial direction of bonded magnet moldings)
About the cylindrical bond magnet obtained by the said Example and comparative example, the surface magnetic flux density in the inner periphery of a cylindrical bond magnet was measured with the magnet analyzer. The measurement was performed by fixing the cylindrical bonded magnet to the 360 ° rotating stage of the magnet analyzer, bringing the probe into contact with the inner peripheral surface of the cylindrical bonded magnet, and rotating the stage by 360 °. FIG. 10 is a diagram showing the results (30 ° rotation) of the surface magnetic flux density measured along the circumferential direction of the cylindrical bonded magnet in each example and each comparative example.

(Measurement of surface magnetic flux density in the height direction of cylindrical bonded magnets)
The surface magnetic flux density in the height direction of the cylindrical bonded magnet was measured with a gauss meter. With respect to one N-pole peak of a cylindrical bonded magnet having a height of 20 mm, the probe was moved in the height direction from 5 mm to 15 mm from the top. FIG. 11 is a diagram showing the results of measuring the surface magnetic flux density in the height direction of the cylindrical bonded magnet in each example and each comparative example. With respect to the height direction, the surface magnetic flux variation of less than 5% is indicated as “◯”, the case of 5% to 20% as “Δ”, and the case of greater than 20% as “X” Table 1] shows the evaluation results.

(Density measurement)
About the bonded magnet obtained by the said Example and comparative example, the density measurement was performed by Archimedes method.

  The above evaluation results are summarized in [Table 1] below.

<Consideration of results>
It can be seen that the embodiment of the present invention has a higher surface magnetic flux in all of the Examples as compared with Comparative Example 1. This shows that the effect of configuring the magnet for orientation by repelling the magnet in the longitudinal direction, which is a feature of the present invention.

  As shown in FIG. 11, in Comparative Example 2 in which a cylindrical bonded magnet was formed by injection molding, the surface magnetic flux density varied in the height direction, and each of the other examples in which the cylindrical bonded magnet was formed by extrusion molding. As described above, the surface magnetic flux density is not uniform in the height direction. That is, the surface magnetic flux density is high at the midpoint of the height. Thereby, it turns out that the structure of the magnet for orientation of this invention exhibits an effect only in combination with extrusion molding.

  Moreover, it turns out that the Example of this invention has a small density compared with the comparative example 3 in all the Examples. That is, it is possible to manufacture a relatively light cylindrical bonded magnet with substantially the same surface magnetic flux density. In short, the present invention can be reduced in weight without reducing the magnetic force as compared with a magnet obtained by compression molding an isotropic Nd—Fe—B magnetic material widely used for spindle motors. I understand.

  Examples 3 and 4 have a high surface magnetic flux density. This shows that a high magnetic field is generated over a wide region in the longitudinal direction as shown in FIG. 9 by configuring the magnet for orientation with three permanent magnets.

  The present invention provides a cylindrical bonded magnet that emits a magnetic force in the inner circumferential direction, which is lightweight, has a high surface magnetic flux density, has a surface magnetic flux density waveform close to a sine waveform, and has a small variation in surface magnetic flux density in the height direction. Can do. Cylindrical bonded magnets that generate magnetic force in the inner circumferential direction can be used for spindle motors such as hard disk drives and optical media.

  DESCRIPTION OF SYMBOLS 1 ... Plasticization part, 2 ... Spider part, 3 ... Mold part, 4 ... Molding part, 5 ... Screw, 6 ... Spider, 8, 11, 16 ... Bond magnet composition flow path, 14, 40, 50, 60, 70, 80 ... orientation magnet, 7, 10, 13 ... outer die, 9, 12 ... inner die, 15 ... Hopper, 51, 61, 71, 81 ... first permanent magnet, 52, 62, 72, 82 ... second permanent magnet, 53, 63, 73, 83 ... third permanent magnet.

Claims (8)

The magnetic material is magnetically oriented and melted by a step of filling a cylindrical molding space with a bonded magnet composition containing a magnetic material and a resin, and an orientation magnet disposed inside the molding space. A method of producing a cylindrical bonded magnet comprising a step of extruding a bonded magnet composition in the axial direction of the orientation magnet and forming the bonded magnet composition,
The orientation magnet is configured so that N poles and S poles alternately appear in the axial direction, and N poles facing the same poles as the N and S poles of the first permanent magnet. A method for producing a cylindrical bonded magnet, comprising: arranging a second permanent magnet configured so that the S pole and the S pole appear alternately adjacent to each other in the axial direction of the first permanent magnet.   By arranging a third permanent magnet configured such that N poles and S poles appear alternately in the radial direction toward the outer circumference between the first magnet and the second magnet, the orientation magnet The manufacturing method of the cylindrical bond magnet of Claim 1 which comprises these.   3. The manufacturing of the cylindrical bonded magnet according to claim 1, wherein the magnetization directions of the first and second permanent magnets are inclined in the outer peripheral direction at an angle of not less than 0 degrees and less than 90 degrees with respect to the axial direction. Method.   The method for manufacturing a cylindrical bonded magnet according to any one of claims 1 to 3, wherein the magnetic material is an Sm-Fe-N-based magnetic material. A cylindrical molding space filled with a bonded magnet composition containing a magnetic material and a resin, and an orientation magnet disposed inside the molding space for magnetically orienting the magnetic material are melted. A cylindrical bonded magnet manufacturing apparatus for extruding and molding the bonded magnet composition in the axial direction of the orientation magnet,
The orientation magnet is disposed adjacent to the first permanent magnet in the axial direction so that N poles and S poles appear alternately in the axial direction, and the first permanent magnet. An apparatus for producing a cylindrical bonded magnet, comprising: a second permanent magnet configured such that N and S poles facing each other on the N and S poles of the magnet alternately appear .   The 3rd permanent magnet comprised so that a north pole and a south pole may appear alternately in the radial direction which goes to the perimeter may be arranged between the 1st magnet and the 2nd magnet. Manufacturing equipment for cylindrical bonded magnets.   The cylindrical bonded magnet according to claim 5 or 6, wherein the magnetization directions of the first and second permanent magnets are inclined in the outer peripheral direction at an angle of 0 degree or more and less than 90 degrees with respect to the axial direction. apparatus.   The apparatus for manufacturing a cylindrical bonded magnet according to any one of claims 5 to 7, wherein the magnetic material is an Sm-Fe-N-based magnetic material.

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