Method for manufacturing rare earth magnet assembly and rare earth magnet assembly

Abstract

SOLUTION: To provide a method for manufacturing a rare earth magnet joint by joining a plurality of rare earth magnets, which includes bringing one surfaces 3a, 3b of rare earth magnets 1a, 1b into contact with each other, forming a coating 2 having an average film thickness of 30 to 90 μm and a film density of 1.15 to 1.21 g / cm3 on at least a portion of adjacent surfaces 4a, 4b of the two rare earth magnets adjacent to each other across the edge of the contact surface 3ab, in which the coating 2 extends across the edge of the contact surface 3ab and continues across both adjacent surfaces 4a, 4b, thereby joining the rare earth magnets 1a, 1b to each other.EFFECT: A rare earth magnet joint can be manufactured by joining a plurality of rare earth magnets with good dimensional accuracy using a low-cost, simple method, and at the same time, and it is also possible to impart corrosion resistance and insulation properties to the rare earth magnets.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a rare earth magnet assembly in which a plurality of rare earth magnets such as Nd-Fe-B sintered magnets are joined, and a rare earth magnet assembly formed by joining a plurality of rare earth magnets.

Background Art

[0002] An Nd-Fe-B sintered magnet is obtained by pressure-molding alloy powder and then sintering it. Applications include electric motors for automobiles. If the rotor core of an electric motor is not insulated between the laminated steel plate and the magnet, the eddy current generated in the magnet may flow through the laminated steel plate to another magnet inserted into an adjacent slot, resulting in a relatively large loop of eddy current. As a result, there has been a problem that the temperature of the magnet rises due to the eddy current, causing heat loss and deterioration of magnetic properties, making it difficult to obtain the desired performance in the electric motor.

[0003] One of the countermeasures against such problems in electric motors is a method of suppressing eddy currents by forming a coating on the surface of the Nd-Fe-B sintered magnet to improve insulation and corrosion resistance (for example, Japanese Patent Application Laid-Open No. 2011-193621 (Patent Document 1)).

[0004] Typical methods for surface treatment to impart insulation to Nd-Fe-B sintered magnets include spray coating and electrodeposition coating of resin. However, in the case of spray coating, since it is spraying, a certain proportion of paint loss that does not adhere to the object to be coated occurs. Also, in the case of thermosetting resins generally used for spray coating and electrodeposition coating, heating by a heater during drying or baking after coating is essential, and the heat treatment furnace generally used in this process consumes a large amount of time and energy for resin curing. Furthermore, since a large space is required for the installation of equipment, the surface treatment cost of magnets has tended to be high with the conventional methods.

[0005] As a means of reducing the cost of the above surface treatment, film formation using an ultraviolet-curable resin can be mentioned. Since the ultraviolet-curable resin cures with ultraviolet light, film formation can be achieved in a short time, at low cost, and in a space-saving manner compared to heat curing in a heat treatment furnace. As a method of applying the ultraviolet-curable resin, there is a method in which the magnet body is immersed and then rotated to remove excess uncured components and cured by ultraviolet irradiation. However, as a method of applying more uniformly, there is a method of applying by an inkjet method. By using this method, a uniform film can be formed in a short time, at low cost, and in a simple manner. As a result, insulation can be easily imparted to the magnet.

[0006] Also, as another countermeasure against the problems of the above electric motor, a method of dividing the magnet can be mentioned. That is, by dividing the Nd-Fe-B sintered magnet in the slot into a plurality of pieces, the transfer of electrons can be physically inhibited and eddy currents can be suppressed. However, there is a problem that the number of magnets to be handled increases due to the division of the magnet, and the workability of the assembly process such as insertion into the slot decreases. In response to this problem, methods such as joining a plurality of magnets with an adhesive and fixing with an insulating tape (for example, Japanese Patent Application Laid-Open No. 2015-61328 (Patent Document 2)) have been devised.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Both the method of joining the above plurality of divided magnets with an adhesive and the method of fixing the divided magnets described in Patent Document 2 have drawbacks such as inability to obtain high dimensional accuracy and an increase in work.

[0009] The present invention has been made in view of such circumstances, and provides a method for manufacturing a rare earth magnet assembly in which a plurality of rare earth magnets can be joined by a simple method, and at the same time, corrosion resistance and insulation can be imparted, and a rare earth magnet assembly manufactured by such a method.

Means for Solving the Problems

[0010] As a result of intensive studies to achieve the above object, the present inventors, when joining a plurality of rare earth magnets to produce a rare earth magnet assembly, brought one surface of each of the rare earth magnets to be joined into contact with each other, and formed a continuous film across the edges of the contact surface and over both adjacent surfaces of the adjacent rare earth magnets on the adjacent surfaces of the two rare earth magnets adjacent to the contact surface (joint surface). By joining the two rare earth magnets, it has been found that a plurality of rare earth magnets can be joined by a relatively low-cost and simple method of film formation to obtain a rare earth magnet assembly, and at the same time, the film formed can impart corrosion resistance and insulation to the rare earth magnets, and the present invention has been completed.

[0011] Therefore, the present invention provides the following method for manufacturing a rare earth magnet assembly and the following rare earth magnet assembly obtained by the manufacturing method. 1. A method for manufacturing a rare earth magnet assembly by joining a plurality of rare earth magnets, wherein one surface of each of the rare earth magnets to be joined is brought into contact with each other, and at least a part of the adjacent surfaces of the two adjacent rare earth magnets sandwiching the edge of the contact surface is formed by an inkjet method of ejecting droplets from a head. Droplets of the resin composition are ejected from the tip of the head and adhered over both adjacent surfaces of the rare earth magnets to be joined, and the adhered resin composition is cured to form a continuous film having an average film thickness of 30 to 90 across the edge of the contact surface and over both adjacent surfaces. Coating of μm A method for manufacturing a rare earth magnet assembly, characterized by joining adjacent rare earth magnets. 2. A method for manufacturing a rare earth magnet bonded body by bonding a plurality of rare earth magnets, comprising bringing one surface of each of the rare earth magnets to be bonded into contact with each other, and injecting droplets of a resin composition from the tip of a head by an inkjet method in which droplets are ejected from the head, so as to sandwich the edge of such a contact surface and attach the droplets to at least a part of the adjacent surfaces of the two adjacent rare earth magnets on both sides of the contact surface, and curing the attached resin composition to form a continuous coating having a film density of 1.15 to 1.21 g / cm 3 that crosses the edge of the contact surface and extends over the two adjacent surfaces, thereby bonding the adjacent rare earth magnets. A method for manufacturing a rare earth magnet bonded body, characterized by this. 3. The film density of the above coating is 1.15 to 1.21 g / cm 3The method for manufacturing a rare earth magnet bonded body according to Item 1, wherein the film density is as described above. 4. One or both of the rare earth magnets joined to each other is / are a joined body to which a plurality of rare earth magnets have already been joined. 1 Any one of ~3 The method for manufacturing a rare earth magnet joined body according to 1 5. The operation of attaching droplets of the resin composition to the both adjacent surfaces and the operation of curing the attached resin composition are repeated a plurality of times to form the coating film. 1 To any one of ~4 The method for manufacturing a rare earth magnet joined body according to the description. 6. The resin composition is a composition of an ultraviolet curable resin, and the resin composition attached to the both adjacent surfaces is irradiated with ultraviolet rays to cure the resin composition. 1~5 The method for manufacturing a rare earth magnet joined body according to any one of the above. 7. The rare earth magnet joined body is in a rectangular parallelepiped shape, and the coating film is formed on two or more of a plurality of surfaces including the edges of the contact surface. 1~6 The method for manufacturing a rare earth magnet joined body according to any one of the above. 8. After applying a primer to at least a part of the adjacent surface on which the coating film of the rare earth magnet is formed and / or the coating film already formed on the adjacent surface, the coating film is formed. 1~7 The method for manufacturing a rare earth magnet joined body according to any one of the above. 9. In a rare earth magnet joined body in which a plurality of rare earth magnets are joined, for at least a pair of rare earth magnets constituting the rare earth magnet joined body, a cured coating film of a resin composition applied by an inkjet method is formed continuously across the edge of the joined surface on at least a part of the adjacent surfaces of both rare earth magnets adjacent to each other across the edge of the joined surface where one surface contacts and joins with the other surface, and the Film density of the coating is 1.15 to 1.21 g / cm 3 and the rare earth magnets are joined to each other by the coating film. A rare earth magnet joined body characterized by this. 10. The hardness of the coating film is 6H or more in terms of the pencil hardness defined in JIS K 5600. As described in 9 The rare earth magnet joined body of the above.

Advantages of the Invention

[0012] According to the present invention, a plurality of rare earth magnets can be joined with high dimensional accuracy by a low-cost and simple method to produce a rare earth magnet joined body. Moreover, at the same time, it is also possible to impart corrosion resistance and insulation to the rare earth magnets.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in more detail. In the method for manufacturing a rare earth magnet joined body of the present invention, as described above, rare earth sintered magnets to be joined to each other are joined by forming a coating that extends over both magnets, thereby manufacturing a rare earth magnet joined body formed by joining a plurality of rare earth magnets.

[0015] Specifically, for example, as shown in FIG. 1, when joining rectangular parallelepiped-shaped rare earth magnets 1a and 1b, first, as shown in FIG. 1(A), one surface 3a and 3b of the rare earth magnets 1a and 1b to be joined are brought into contact with each other. The contact surface 3ab obtained by this contact becomes the joint surface of the joined body 1. Next, as shown in FIG. 1(B), at least a part (in FIG. 1(B), most of the two surfaces) of the adjacent surfaces 4a and 4b of the adjacent rare earth magnets 1a and 1b sandwiching the edge of such a contact surface 3ab (joint surface), continuous coatings 2 and 2 are formed across the edge of the contact surface 3ab (joint surface) and extending over both adjacent surfaces 4a and 4b. The two rare earth magnets 1a and 1b are joined by these coatings 2 and 2 to obtain the rare earth magnet joined body 11 of the present invention.

[0016] Here, when the surface on which the coating 2 is formed is, for example, a rectangular parallelepiped shape of the obtained rare earth magnet bonded body 11, from the viewpoint of bonding strength, it is preferable to form the coatings 2, 2 on two or more surfaces including the edge of the contact surface (bonding surface) 3ab as shown in FIG. 1. Further, the area of the coating 2 is not particularly limited, but it is preferably as large as possible from the viewpoints of bonding strength, corrosion resistance, and imparting insulation.

[0017] In FIG. 1, a pair of rare earth magnets 1a and 1b having the same shape are bonded to form a rare earth magnet bonded body 11. However, the shapes and sizes of the rare earth magnets may be different from each other, and three or more rare earth magnets may be bonded to form a rare earth magnet bonded body. Further, one or both of the rare earth magnets to be bonded to each other may be a bonded body in which a plurality of rare earth magnets are already bonded. In that case, the magnet in which a plurality of rare earth magnets are already bonded may be bonded by forming a coating in the same manner as the present invention, or may be bonded by other methods.

[0018] The rare earth magnet used for the bonding operation is not particularly limited. For example, sintered magnets such as Nd-Fe-B sintered magnets and SmCo sintered magnets are preferably used as the bonding target. The shape of the rare earth magnet is preferably such that the coating formation surface of the rare earth magnet and the bonding surface between the rare earth magnets are flat in order to fix a plurality of rare earth magnets by forming a coating described later. Specifically, a rectangular parallelepiped shape is most suitable.

[0019] The means for forming the coating is not particularly limited, and for example, a known method such as spray coating can be applied. In order to obtain a more preferable effect, for example, an inkjet method in which droplets of a resin composition are ejected from a head can be applied, and more preferably, an ultraviolet curable resin composition can be applied as the resin composition.

[0020] Hereinafter, as an aspect of the coating formation operation in the manufacturing method of the present invention, the case of forming a coating by an inkjet method using an ultraviolet curable resin composition will be described. A method of forming a film by an inkjet method includes: (A) a step of ejecting droplets of an ultraviolet-curable resin composition from the tip of a head onto the surface of a rare-earth magnet by an inkjet method of ejecting droplets from the head; and (B) a step of irradiating the ultraviolet-curable resin composition adhered to the surface of the rare-earth magnet with ultraviolet rays to cure the ultraviolet-curable resin.

[0021] In the above steps (A) and (B), the ultraviolet-curable resin is applied and cured as a film 2 that is continuous across the adjacent surfaces 4a and 4b of both adjacent magnets 1a and 1b across the edge of the contact surface (joint surface) 3ab, sandwiching the contact surface (joint surface) 3ab of the rare-earth magnets 1a and 1b that are joined to each other, as described with reference to FIG. 1 above. The plurality of magnets are connected by the mechanical strength of the ultraviolet-curable resin and the bonding strength to the surface of the rare-earth magnet. At this time, when there are three or more rare-earth magnets to be joined, it may be a film that is continuous across the adjacent surfaces of the three or more magnets.

[0022] The thickness (average film thickness) of such a film is not particularly limited, but is usually 30 μm or more, preferably 40 μm or more, and more preferably 50 μm or more. Also, it is usually 90 μm or less, preferably 80 μm or less, and more preferably 70 μm or less. If the film thickness is within the above range, corrosion resistance and insulation properties are good, and for example, a rare-earth magnet assembly having sufficient electrical resistance as a magnet for motor applications can be obtained.

[0023] In the above step (A), by using an inkjet method of ejecting droplets from a head, droplets of the ultraviolet-curable resin composition are ejected from the tip of the head to adhere the ultraviolet-curable resin composition to the surface of the rare-earth magnet. An apparatus applying the inkjet method is generally known as an inkjet printer, which is an apparatus that atomizes a liquid coating material into fine droplets and ejects them to directly adhere to the surface of an object. In addition to an apparatus for printing ink on paper or the like, there is also a commercially available apparatus that ejects an uncured resin composition instead of ink and directly adheres it to the surface of an object. In this case as well, it is usually called an inkjet printer. There are two types of inkjet methods: a continuous type that constantly ejects a liquid coating material, and an on-demand type that ejects a liquid coating material only when necessary. The on-demand type further has two methods: a piezo method that uses a piezoelectric element to eject a liquid coating material, and a thermal method that uses bubbles generated by heating to eject a liquid coating material. In the present invention, although not particularly limited, the on-demand type, for which it is relatively easy to miniaturize the apparatus, is preferable. Further, since the ultraviolet-curable resin composition may be cured by heat, the piezo method is preferable.

[0024] By applying an inkjet method to the injection of the ultraviolet-curable resin and the ultraviolet-curable resin composition for film formation, a uniform film can be formed. Thereby, a uniform bonding strength can be obtained, and further, an error in the dimensions of the rare-earth magnet bonded body can be suppressed. Also, by repeating step (A) and step (B), the film thickness can be increased and the bonding strength can be improved.

[0025] The resolution when adhering the ultraviolet-curable resin composition by the inkjet method is preferably 300 dpi or more, particularly 600 dpi or more, and especially 1000 dpi or more. By increasing the resolution and making the droplets finer, uncoated portions such as unevenness and pinholes of the formed film are reduced, and the density of the film increases, so that the bonding strength increases. On the other hand, considering the influence of the internal stress of the film due to an increase in the film density by increasing the resolution, the resolution is usually preferably 1200 dpi or less. Note that only one droplet or two or more droplets of the liquid droplets may be adhered to one dot.

[0026] When using the inkjet method, the liquid volume of the droplets is selected according to the thickness and resolution of the film. Considering the characteristics of the film to be formed and the production efficiency, it is preferably 3 pL or more, particularly 6 pL or more, 20 pL or less, particularly 12 pL or less, and especially 10 pL or less per drop. Further, the viscosity of the ultraviolet curable resin composition for forming the droplets is preferably 17 mPa·s or more and 27 mPa·s or less at 25°C. Here, although not particularly limited, for the purpose of improving the adhesion of the film, a primer layer may be formed on a part or all of the film-forming surface of the rare earth magnet before attaching the ultraviolet curable resin composition. In this case, when one or both of the rare earth magnets to be joined are joined bodies in which a plurality of magnets have already been joined by the joining method of the present invention by film formation, a primer layer can also be formed on the film.

[0027] In the formation of the film by the inkjet method of the present invention, it is possible to increase the film density by controlling the resolution and the liquid volume of the droplets described above. The film density is preferably 1.15 g / cm 3 or more, more preferably 1.17 g / cm 3 or more, and preferably 1.21 g / cm 3 or less, more preferably 1.19 g / cm 3 or less. When the film density is in such a range, it is possible to satisfactorily suppress problems such as film peeling and cracking while ensuring a high bonding strength. Also, when in such a range, the corrosion resistance and insulation properties are good. The film density can be calculated from the film thickness and the film mass when the film is formed on a predetermined area.

[0028] In one embodiment of the present invention, when manufacturing a rare earth magnet joined body, compared with joining by a normal adhesive, there is an advantage that no dimensional adjustment such as surface polishing is required because there is no overhang of the adhesive or the like. Further, there is no process of applying an adhesive, fixing the magnet, and curing by drying or heating, and it is possible to manufacture a rare earth magnet joined body by one coating.

[0029] In this embodiment, the ultraviolet-curable resin used as the resin for forming the film is a resin that undergoes a photochemical reaction by the energy of ultraviolet light and cures from a liquid to a solid within seconds. The ultraviolet-curable resin composition (uncured ultraviolet-curable resin) contains a photopolymerizable compound (monomer or resin precursor) as the main component, a photoinitiator, a colorant, an auxiliary agent, and the like. Examples of the photopolymerizable compound include radical-type acrylic monomers in which double bonds are cleaved and polymerized. In addition to this, cationic epoxy monomers, oxetane monomers, vinyl ether monomers, etc. can be mentioned, but it is not limited to these. In the radical type, the photoinitiator is decomposed by light to generate radicals, and these react with the monomer to generate new radicals, thereby proceeding with the polymerization. Examples of the photoinitiator species in this case include aromatic ketones. On the other hand, in the cationic type, the photoinitiator is decomposed by light to generate an acid, and this reacts with the monomer to generate a new cationic active species, thereby proceeding with the polymerization. Examples of the photoinitiator species in this case include triallylsulfonium cation and hexafluorophosphate. Examples of the colorant include carbon black, etc., and carbon black also contributes to improving the visibility of the rare earth magnet after film formation.

[0030] In the above step (B), the ultraviolet-curable resin composition adhered to the surface of the rare earth magnet in step (A) is irradiated with ultraviolet light to cure the ultraviolet-curable resin composition. The ultraviolet light is appropriately selected according to the type of the ultraviolet-curable resin composition used, but usually, ultraviolet light having a wavelength of about 200 to 380 nm can be used. The ultraviolet light can be irradiated, for example, from a mercury lamp, a UV-LED, a xenon lamp, or the like.

[0031] In the film formation method by the above inkjet method, which is an embodiment of film formation in the manufacturing method of the present invention, the above steps (A) and (B) can be carried out, for example, in the following modes (1) or (2).

[0032] Aspect (1): In step (A), while moving the tip of the head near the rare earth magnet, droplets of the ultraviolet curable resin composition are sequentially ejected onto the film-forming surface of the magnet and connected while being lined up one after another, so that the connected droplets of the ultraviolet curable resin composition adhere to part or all of the adjacent surfaces (for example, the adjacent surfaces 4a and 4b in FIG. 1) of the plurality of rare earth magnets, and a continuous thin layer made of the ultraviolet curable resin composition is formed across the contact surface (bonding surface) (for example, the contact surface (bonding surface) 3ab in FIG. 1) between the rare earth magnets. Next, step (B) is carried out to cure the thin layer of the ultraviolet curable resin composition to form a film, and the plurality of rare earth magnets are connected and fixed by this film to be joined. At this time, for the purpose of increasing the film thickness, steps (A) and (B) can be carried out multiple times to stack thin films of the ultraviolet curable resin composition to form a multi-layered film.

[0033] Aspect (2): In step (A), droplets of the ultraviolet curable resin composition are ejected from the tip of the head, and step (B) is carried out sequentially or as needed with respect to the droplets. The tip of the head is moved to the adjacent part of the ultraviolet curable resin in which the droplets have cured, and steps (A) and (B) are further carried out repeatedly. This is carried out while moving the tip of the head near the surface of the rare earth magnet with respect to the planned range of film formation. Thereby, a continuous film made of the ultraviolet curable resin composition is formed across part or all of the adjacent surfaces (for example, the adjacent surfaces 4a and 4b in FIG. 1) of the plurality of rare earth magnets and across the contact surface (bonding surface) (for example, the contact surface (bonding surface) 3ab in FIG. 1) between the rare earth magnets.

[0034] The time (timing) from when the droplets are attached to the surface of the rare earth magnet until ultraviolet irradiation is started (curing is started) is not particularly limited. However, from the viewpoint of preventing inconveniences such as variations in the film thickness of the film formed by the aggregation of the droplets, aspect (2) in which curing occurs substantially simultaneously with the attachment of the droplets (for example, from immediately after the ejection of the droplets to immediately after the attachment) is preferably adopted.

[0035] As in the above aspect (2), when droplets are adhered to the surface of the rare earth magnet and then irradiated with ultraviolet rays substantially simultaneously with the adhesion, it is effective to provide an ultraviolet irradiation unit at the tip of the head that injects the droplets of the ultraviolet curable resin composition or in its vicinity, either as a part of the head or as a separate part from the head. For example, if an ultraviolet curable inkjet printer equipped with an ultraviolet irradiation unit as a part of the head or as a separate part from the head is used at the tip of the head that injects the droplets of the ultraviolet curable resin composition or in its vicinity, the ultraviolet curable resin composition can be cured on the spot where the droplets are ejected from the head. Therefore, there is no need to perform a drying process or a heat treatment process as carried out in the formation of a film by spray coating using a separate device, which is more advantageous. Also, in this case, if the timing of ultraviolet irradiation is controlled, it is possible to irradiate the ultraviolet rays after holding for a certain period of time after the droplets are adhered, and it is possible to irradiate the ultraviolet rays without moving the head or after moving the tip of the head to the adjacent part of the ultraviolet curable resin composition to which the droplets are adhered.

[0036] On the other hand, when droplets are adhered to the surface of the rare earth magnet and then irradiated with ultraviolet rays after holding for a certain period of time, particularly in the case of the above-described aspect (1), an ultraviolet irradiation device such as an ultraviolet lamp is provided separately from the inkjet printer, and after holding for a predetermined period of time as necessary on the droplets of the ultraviolet curable resin composition or the thin layer of the ultraviolet curable resin composition formed by connecting the droplets of the ultraviolet curable resin composition, the step (B) may be carried out by irradiating the ultraviolet rays all at once.

[0037] When performing the steps (A) and (B), from the viewpoint of obtaining good bonding and dimensional accuracy, it is preferable to form the film in a series of processes without moving the rare earth magnet and without taking it out of the apparatus. For example, if an inkjet printer is used, since the steps (A) and (B) can be performed in a series of operations, misalignment of the rare earth magnet is less likely to occur, and furthermore, if jigs or the like are used, dimensional errors can be suppressed.

[0038] The coating surfaces of multiple rare earth magnets are usually arranged in a direction perpendicular to the injection direction of the droplets. For example, when the rare earth magnet has a cuboid shape and one surface is coated, only one side is connected and fixed by the coating, and the joint surface is not completely fixed. Therefore, it is difficult to handle multiple rare earth magnets as one joined body. Thus, it is preferable to form coatings on two or more surfaces when forming at least a rare earth magnet joined body, such as the coatings 2, 2 of the rare earth magnet joined body 11 illustrated in FIG. 1(B) described above. In order to form coatings on two surfaces of the rare earth magnet joined body, for example, after coating one surface, it is necessary to rotate the rare earth magnet joined body and perform coating. At this time, if a gap is generated on the coating surfaces of the multiple rare earth magnets to be joined due to warping of the coating or the like, the joining will not succeed well. Therefore, it is preferable that the interval between the coating surfaces is narrow.

[0039] In the present invention, in the method for forming a coating by the above inkjet method, when injecting droplets of the ultraviolet curable resin composition from the tip of the head in the above step (A), and also when irradiating ultraviolet rays in the above step (B), the surface of the rare earth magnet can also be arranged to be inclined from a direction perpendicular to the injection direction of the droplets. When the rare earth magnet has a cuboid shape, for example, by tilting the surface of the rare earth magnet by 45°, two adjacent surfaces can be processed simultaneously. When the surface of the rare earth magnet is arranged to be inclined from a direction perpendicular to the injection direction of the droplets, it is preferable to apply the aspect (2).

[0040] The coating formed in the present invention is not particularly limited, but preferably has a hardness of 6H or more in terms of pencil hardness in JIS K 5600. With such a hardness, the coating is less likely to peel off, and good joining strength can be obtained.

[0041] Also, the joining force between each rare earth magnet in the rare earth magnet joined body obtained by the manufacturing method of the present invention can be evaluated, for example, by measuring the flexural strength by performing a three-point bending test with Shimadzu Corporation AG-I 250kN. Although not particularly limited, it is preferable that the average of the flexural strength is 60 N or more.

Example

[0042] The following are examples to specifically describe the present invention, but the present invention is not limited to the following examples.

[0043] [Example 1] An Nd-Fe-B sintered magnet with a rectangular parallelepiped shape (14.23 mm × 7.06 mm × 5.16 mm) was prepared, fixed in pairs with a jig, and then, using a UV-LED curing flat head inkjet printer UFJ-6042MkII (manufactured by Mimaki Engineering Co., Ltd.), as in the example shown in Fig. 1(B), on both adjacent surfaces (4a, 4b) sandwiching the edge of the contact surface (bonding surface) (3ab) of both magnets (1a, 1b), a film (2) continuous across the edge of the contact surface (bonding surface) (3ab) and extending over both adjacent surfaces (4a, 4b) was formed. The ultraviolet curable resin composition for forming the film was mainly composed of acrylate ester and contained hexamethylene diacrylate as a reactive diluent, a polymerization initiator, and carbon black as a coloring agent. The liquid volume of the droplets of the ultraviolet curable resin composition ejected by the inkjet printer was set to 10 pL, and the resolution was set to 1200 dpi × 1200 dpi. The film formation operation was performed as follows.

[0044] With respect to the entire surface (a total of 14.23 mm × 14.12 mm) composed of two adjacent surfaces (4a, 4b) of the two combined Nd-Fe-B sintered magnets, while moving the tip of the head near the surface of the rare earth magnet, droplets of the ultraviolet curable resin composition were sequentially ejected to form a thin layer of the ultraviolet curable resin composition, and then immediately irradiated with ultraviolet light to form a film of the ultraviolet curable resin. Thereafter, the rare earth magnet was inverted 180 degrees, and a film was formed in the same manner as before to form films on the two opposing surfaces and bond the Nd-Fe-B sintered magnets. This operation was performed on three sets of Nd-Fe-B sintered magnets to obtain three rare earth magnet bonded bodies.

[0045] Regarding the obtained Nd-Fe-B sintered magnet assembly, a three-point bending test was performed with a Shimadzu Corporation AG-I 250 kN, and the bonding strength was evaluated by measuring the flexural strength. The average flexural strength was 114.5 N, and sufficient strength was obtained for use in an electric motor. Also, as a result of measuring the hardness of the coating with a pencil hardness tester conforming to JIS K 5600, it was 6H or higher. Furthermore, when the cross-section of the assembly was observed with a scanning electron microscope (SEM), as shown in Figure 2, a part of the ultraviolet curable resin forming the coating had penetrated into the gap of the bonding surface. In Figure 2, the dark gray portion appearing above the coating is the background and not a part of the assembly.

[0046] Also, regarding 30 rare earth magnet assemblies fabricated in the same manner, their dimensions were measured with a Mitutoyo Corporation digital caliper, and a comparison before and after bonding was made. As a result, the dimensional variation was within ±0.8%. Since the height with respect to the surface on which the coating was formed includes the film thickness and the surface roughness of the film, the variation is ±0.8%, but the dimensions of the non-coated portions have even smaller variation and are within ±0.5%. Thus, a rare earth magnet assembly with good dimensional accuracy was obtained.

[0047] Next, to examine the heat resistance of the coating, heating was performed in an oven at 160 degrees. After 24 hours had passed, it was taken out of the oven and the surface was observed, but no significant change was seen. Also, when the same rare earth magnet assembly was sandwiched between electrodes and the electrical resistance was measured with a connected resistance meter while under a pressure of 7 MPa, it was 1 MΩ or higher, indicating good electrical resistance.

[0048] Furthermore, to investigate the state of the coating, a 10 mm × 10 mm ultraviolet curable resin coating was formed on a 29 mm × 18 mm × 2 mm Nd-Fe-B sintered magnet under the same conditions as in Example 1. As a result of measuring the average film thickness of the entire formed ultraviolet curable resin coating with a Mitutoyo Corporation digital indicator, it was 81.6 μm. Also, the density of the coating calculated from the area of the surface on which the coating was formed, the film thickness of the coating, and the weight change of the rare earth magnet before and after coating formation was 1.18 g / cm 3 and it was.

[0049] [Example 2] Three rare earth magnet bonded bodies were obtained in the same manner as in Example 1, except that the liquid volume of the droplets of the ultraviolet curable resin composition was 6 pL and the resolution was 600 dpi × 600 dpi.

[0050] Regarding the obtained Nd-Fe-B sintered magnet bonded body, a three-point bending test was carried out with Shimadzu Corporation's AG-I 250 kN, and the bonding strength was evaluated by measuring the flexural strength. The average flexural strength was 66.3 N, and sufficient strength was obtained for use in an electric motor. Also, in the same manner as in Example 1, the hardness of the coating film was measured with a pencil hardness tester, and as a result, it was 6H or higher. Furthermore, when the cross-section of the bonded body was observed by SEM, a part of the ultraviolet curable resin had penetrated into the gap of the bonding surface.

[0051] Also, regarding 30 rare earth magnet bonded bodies produced in the same manner, their dimensions were measured with a Mitutoyo Corporation's digital caliper, and a comparison was made before and after bonding. As a result, the dimensional variation was within ±0.8%. Since the height of the surface on which the coating film was formed includes the film thickness and the surface roughness of the film, the variation is ±0.8%, but the dimensions of the non-coated part have even smaller variation and are within ±0.5%. Thus, a rare earth magnet bonded body with good dimensional accuracy was obtained.

[0052] Next, in order to examine the heat resistance of the coating film, heating was carried out in an oven at 160 degrees. After 24 hours, it was taken out of the oven and the surface was observed, but no significant change was seen. Also, the same rare earth magnet bonded body was sandwiched between electrodes, and the electrical resistance was measured with a connected resistance meter while being pressurized to 7 MPa. As a result, it was 1 MΩ or more, and it had good electrical resistance.

[0053] Furthermore, to investigate the state of the coating, a 10 mm × 10 mm ultraviolet-curable resin coating was formed on a 29 mm × 18 mm × 2 mm Nd-Fe-B sintered magnet under the same conditions as in Example 2. As a result of measuring the average film thickness of the entire formed ultraviolet-curable resin coating with a Mitutoyo digital indicator, it was 42.3 μm. Also, the coating density calculated from the area of the surface on which the coating was formed, the film thickness of the coating, and the weight change of the rare earth magnet before and after coating formation was 1.17 g / cm 3 was obtained.

[0054] [Example 3] Three rare earth magnet joints were obtained in the same manner as in Example 1, except that the liquid volume of the droplets of the ultraviolet-curable resin composition was 8 pL.

[0055] Regarding the obtained Nd-Fe-B sintered magnet joint, a three-point bending test was performed with a Shimadzu Corporation AG-I 250 kN, and the bonding strength was evaluated by measuring the flexural strength. The average flexural strength was 64.1 N, and sufficient strength was obtained for use in an electric motor. Also, in the same manner as in Example 1, as a result of measuring the hardness of the coating with a pencil hardness tester, it was 6H or higher. Furthermore, when the cross-section of the joint was observed with an SEM, a part of the ultraviolet-curable resin had penetrated into the gap of the joint surface.

[0056] Also, regarding 30 rare earth magnet joints produced in the same manner, their dimensions were measured with a Mitutoyo digital caliper and compared before and after bonding. As a result, the dimensional variation was within ±0.8%. Since the height of the surface on which the coating was formed includes the film thickness and the surface roughness of the film, the variation is ±0.8%. However, the dimensions of the uncoated part have even less variation and are within ±0.5%. Thus, a rare earth magnet joint with good dimensional accuracy was obtained.

[0057] Next, to examine the heat resistance of the film, heating was carried out in an oven at 160 degrees. After 24 hours had passed, it was taken out of the oven and the surface was observed, but no significant changes were seen. Also, when the same rare earth magnet assembly was sandwiched between electrodes and the electrical resistance was measured with a connected resistance meter while under a pressure of 7 MPa, it was 1 MΩ or more, indicating that it had good electrical resistance.

[0058] Furthermore, to investigate the state of the film, a 10 mm × 10 mm ultraviolet curable resin film was formed on a 29 mm × 18 mm × 2 mm Nd-Fe-B sintered magnet under the same conditions as in Example 3. As a result of measuring the average film thickness of the entire formed ultraviolet curable resin film with a Mitutoyo Corporation digital indicator, it was 65.8 μm. Also, the film density calculated from the area of the surface on which the film was formed, the film thickness of the film, and the weight change of the rare earth magnet before and after film formation was 1.18 g / cm 3 It was.

Explanation of symbols

[0059] 1a, 1b Rare earth magnets 11 Rare earth magnet assembly 2 Film 3a, 3b One surface of the rare earth magnet 3ab Contact surface (bonding surface) 4a, 4b Adjacent surfaces

Claims

1. A method for manufacturing a rare earth magnet joint by joining a plurality of rare earth magnets, comprising: bringing one surface of the rare earth magnets to be joined into contact with each other; ejecting droplets of a resin composition from the tip of a head using an inkjet method in which droplets are ejected from a head onto at least a portion of the adjacent surfaces of both rare earth magnets adjacent to each other across the edges of the contact surfaces; and hardening the attached resin composition to form a coating having an average thickness of 30 to 90 μm that is continuous across both adjacent surfaces across the edges of the contact surfaces, thereby joining the adjacent rare earth magnets to each other.

2. A method for manufacturing a rare earth magnet joint by joining a plurality of rare earth magnets, comprising the steps of: bringing one surface of the rare earth magnets to be joined into contact with each other; using an inkjet method in which droplets are ejected from a head onto at least a portion of the adjacent surfaces of both adjacent rare earth magnets across the edges of the contact surfaces, ejecting droplets of a resin composition from the tip of a head to adhere to both adjacent surfaces of the rare earth magnets to be joined; hardening the adhered resin composition to form a coating having a film density of 1.15 to 1.21 g / cm 3 that extends across the edges of the contact surfaces and continues across both adjacent surfaces, thereby joining adjacent rare earth magnets together.

3. The method for producing a rare earth magnet joint according to claim 1, wherein the film density of said coating is 1.15 to 1.21 g / cm 3 .

4. 4. The method for producing a rare earth magnet joint according to claim 1, wherein one or both of the rare earth magnets to be joined together is already a joint formed by joining a plurality of rare earth magnets together.

5. The method for producing a rare earth magnet joint according to any one of claims 1 to 4, wherein an operation of depositing droplets of the resin composition on both adjacent surfaces and an operation of curing the deposited resin composition are repeated multiple times to form the coating.

6. The method for producing a rare earth magnet joint according to any one of claims 1 to 5, wherein the resin composition is an ultraviolet curable resin composition, and the resin composition attached to both adjacent surfaces is irradiated with ultraviolet light to cure the resin composition.

7. The method for manufacturing a rare earth magnet assembly according to any one of claims 1 to 6, wherein the rare earth magnet assembly has a rectangular parallelepiped shape, and the coating is formed on two or more of a plurality of surfaces including an edge portion of the contact surface.

8. The method for manufacturing a rare earth magnet joint according to any one of claims 1 to 7, further comprising the steps of: applying a primer to the adjacent surface of the rare earth magnet on which the coating is to be formed and / or to at least a part of the coating already formed on the adjacent surface, and then forming the coating.

9. In a rare earth magnet joint formed by joining a plurality of rare earth magnets, for at least one pair of rare earth magnets constituting the rare earth magnet joint, a cured coating of a resin composition applied by an inkjet method is continuously formed on at least a part of adjacent surfaces of the two rare earth magnets adjacent to each other across an edge of a joining surface where one surface of the rare earth magnets are in contact with each other and joined, across the edge of the joining surface, and the film density of the coating is 1.15 to 1.21 g / cm 3 wherein rare earth magnets are joined together by the coating.

10. 10. The rare earth magnet joint according to claim 9, wherein the coating has a pencil hardness of at least 6H according to JIS K5600.

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