Composition for bonded magnet, method for producing same, and bonded magnet

Abstract

To provide a composition for a bonded magnet having excellent fluidity and fully exhibiting the effect of terminal treatment of a polyamide 12 resin, and also provide a method for manufacturing the composition for the bonded magnet, and the bonded magnet.SOLUTION: A composition for a bonded magnet includes a rare earth magnet powder and a polyamide 12 resin, and further includes an end treatment agent having a carbodiimide bond in an amount of 0.3 mass % or more, using a flow tester, the fluidity measured under the conditions of the capillary temperature of 250°C, the load of 588 N, the orifice diameter of 1 mm, the orifice diameter of 1 mm, and a preheating time of 300 seconds is 0.7 cm3 / sec or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composition for a bonded magnet, a method for producing the same, and a bonded magnet. [Background technology]

[0002] Bonded magnets are produced by heating and kneading a composition containing magnetic powder, binder components such as organic resin, and additives such as reinforcing agents, plasticizers, and lubricants in a kneading machine such as an extruder, then processing the mixture into pellets or other shapes, followed by hot molding using techniques such as injection molding, compression molding, or extrusion molding. Compared to sintered magnets, these bonded magnets have the advantage of higher dimensional accuracy and easier production of complex shapes. They also have high uniformity in quality and performance, good yield, and excellent machinability. In particular, magnets manufactured by injection molding using thermoplastic resins such as polyamide resin and polyphenylene sulfide resin as binder resins offer high dimensional accuracy and no need for post-processing, thereby reducing magnet manufacturing costs. Furthermore, bonded magnets containing rare earth magnetic powders have excellent magnetic properties (residual magnetic flux density Br, coercive force iHc, and maximum energy product (BH)max) and strong magnetic force. This allows for miniaturization and high performance, making them useful for applications such as small motors and sensors.

[0003] In bonded magnet compositions, polyamide resins, particularly polyamide 12 resins, are often used as binder resins. Polyamide resins contain polar functional amide bonds within their molecules, which facilitate adhesion through interactions with the surface of magnetic powder. This provides a high affinity for magnetic powder, promoting high dispersion and high packing density of the magnetic powder. Furthermore, polyamide resins, particularly polyamide 12 resins, have relatively low melting points. This enhances the fluidity of the composition during kneading and molding processes, which involve heating, thereby further enhancing the dispersibility and packing density of magnetic powder. Polyamide 12 resins also have low water absorption and excellent resistance to cold and thermal shock. This allows for the production of bonded magnets with high mechanical strength and low water absorption. For example, Patent Document 1 (Patent Document 1, paragraph

[0027] ) describes a bonded magnet composed of magnetic powder and resin, stating that polyamide 12 is the preferred resin among polyamides, and that its high polarity allows for high magnetic powder packing. Furthermore, polyamide 12, with its low water absorption, allows for the production of bonded magnets with high magnetic properties and low water absorption.

[0004] However, in bonded magnet compositions, the fluidity of the composition can decrease during kneading or molding, making kneading or molding difficult. This is said to be due to the reaction between the functional groups of the binder resin and the components of the magnet powder, particularly rare earth metals, caused by heating during kneading or molding. In other words, the magnet powder components act as a catalyst, causing a reaction (such as a condensation polymerization reaction) between the terminal functional groups (carboxyl groups, amino groups) of the binder resin. When a reaction occurs between the terminal functional groups, the resin polymerizes, which causes the composition to thicken and reduce its fluidity.

[0005] In order to prevent such reactions of the terminal functional groups of the binder resin and the resulting thickening, a method has been proposed in which the binder resin is treated in advance with a terminal treatment agent, and then the terminal-treated binder resin is kneaded with magnetic powder and molded to produce a bonded magnet. The terminal treatment adjusts (blocks) the functional groups of the binder resin, thereby suppressing reactions with the magnetic powder and thickening, and is said to thereby improve the fluidity of the composition.

[0006] For example, Patent Document 2 teaches that, with regard to a resin composition comprising a polyamide resin and a metal powder, the use of a specific terminal-modified polyamide resin, the terminals of which have been modified with a monocarboxylic hydrocarbon compound, can solve problems such as poor flowability and increased melt viscosity of the molten mixture that occur when the metal powder content is increased (paragraphs

[0004] to

[0008] of Patent Document 2). Patent Document 2 also describes, in its examples, the preparation of a composition comprising 88 parts by weight of ferrite and 12 parts by weight of terminal-modified polyamide resin, and that when the mixture is molded using an injection molding machine, the high fluidity of the molten mixture of metal powder and polyamide resin results in good moldability even when a large amount of metal powder is contained (paragraphs

[0022] and

[0029] of Patent Document 2).

[0007] Patent Document 3 discloses a composition for bonded magnets, which is made of rare earth magnet particles containing at least Nd-based magnet particles and a binding resin and is used to manufacture bonded magnets, where the binding resin is made of polyamide 66 (PA66) in which the total amount of terminal groups consisting of carboxyl groups and amino groups is less than a predetermined amount (Claim 1 of Patent Document 3). Patent Document 3 also describes that at least a portion of the carboxyl and / or amino groups at the ends of unmodified PA66 have been replaced with unreactive or low-reactive terminal groups, and as a result, the composition no longer shows a sudden increase in viscosity even when it comes into contact with catalytic rare earth magnet powder particles (paragraph

[0037] of Patent Document 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-72406 [Patent Document 2] Patent No. 3103149 [Patent Document 3] Japanese Patent Application Publication No. 2019-67957 Summary of the Invention [Problem to be solved by the invention]

[0009] Although techniques for improving the fluidity of compositions by using end-treated binder resins have been proposed, the inventors' research has revealed that there is room for improvement in these conventional techniques. Specifically, when attempting to produce bonded magnets using rare earth magnet powder and polyamide 12 resin, even if pre-end-treated polyamide 12 resin (binder resin) is used, thickening may occur, preventing the desired fluidity and making molding difficult.

[0010] As a result of further investigation, the inventors discovered that it is effective to treat the ends of the polyamide 12 resin when kneading it with the rare earth magnet powder, rather than using a polyamide 12 resin that has been end-treated in advance. That is, they discovered that by simultaneously kneading rare earth magnet powder, unend-treated polyamide 12 resin, and an end-treating agent having a carbodiimide bond, the end-treating effect of the polyamide 12 resin can be fully exerted, and as a result, a bonded magnet composition with excellent flowability can be obtained.

[0011] The present invention was completed based on these findings, and its objective is to provide a bonded magnet composition with excellent fluidity in which the effects of the end treatment of polyamide 12 resin are fully realized. Another objective of the present invention is to provide a method for producing the bonded magnet composition, and a bonded magnet. [Means for solving the problem]

[0012] The present invention encompasses the following aspects (1) to (8). In this specification, the expression "to" includes both ends of the symbol. In other words, "X to Y" is synonymous with "at least X and at most Y."

[0013] (1) A magnet containing rare earth magnet powder and polyamide 12 resin, and further containing a terminal treatment agent having a carbodiimide bond in an amount of 0.3% by mass or more, Using a flow tester, the flowability measured under the conditions of a capillary temperature of 250°C, a load of 588N, an orifice diameter of 1mm, an orifice length of 1mm, and a preheating time of 300 seconds was 0.7cm. 3 / sec or more.

[0014] (2) The composition for bonded magnets according to (1) above, containing the end treatment agent in an amount of 0.5% by mass or more and 0.9% by mass or less.

[0015] (3) The fluidity is 2.0 cm 3 / second or more.

[0016] (4) A bonded magnet composition according to any one of (1) to (3) above, wherein the rare earth magnet powder is a samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder having an average particle size of 1.8 μm or more and 2.8 μm or less, and the content of the magnet powder in the bonded magnet composition is 88 mass % or more and 92 mass % or less.

[0017] (5) A bonded magnet composition according to any one of (1) to (4) above, which contains the rare earth magnet powder, the polyamide 12 resin, and the end treatment agent, with the remainder being unavoidable impurities.

[0018] (6) A method for producing a bonded magnet composition, comprising a step of simultaneously kneading rare earth magnet powder, polyamide 12 resin, and a terminal treatment agent having a carbodiimide bond, A method in which the content of the terminal treatment agent in the bonded magnet composition is 0.3 mass % or more.

[0019] (7) The method according to (6) above, wherein the magnet powder is a samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder having an average particle size of 1.8 μm or more and 2.8 μm or less, and the content of the magnet powder in the bonded magnet composition is 88% by mass or more and 92% by mass or less.

[0020] (8) A bonded magnet which is a molded product of the bonded magnet composition according to any one of (1) to (5) above. [Effects of the Invention]

[0021] According to the present invention, there is provided a bonded magnet composition with excellent fluidity in which the effects of terminal treatment of polyamide 12 resin are fully exerted. There are also provided a method for producing the bonded magnet composition, and a bonded magnet. DETAILED DESCRIPTION OF THE INVENTION

[0022] A specific embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described. Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

[0023] <<1. Bonded Magnet Composition>> The bonded magnet composition of this embodiment (hereinafter sometimes referred to simply as "composition") contains rare earth magnet powder and polyamide 12 resin, and further contains a terminal treatment agent having a carbodiimide bond in an amount of 0.3 mass % or more. This bonded magnet composition has a flowability of 0.7 cm, as measured using a flow tester under the following conditions: capillary temperature 250°C, load 588 N, orifice diameter 1 mm, orifice length 1 mm, and preheating time 300 seconds. 3 / seconds or more.

[0024] A bonded magnet composition is a precursor to a bonded magnet (hereinafter sometimes referred to simply as a "bonded magnet"). That is, the composition is molded under heat using a method such as injection molding or extrusion molding to produce a bonded magnet. The bonded magnet may be anisotropic or isotropic. If a magnetic field is applied to the composition during molding, an anisotropic magnet can be produced, and if no magnetic field is applied, an isotropic magnet can be obtained.

[0025] [Magnetic powder] The bonded magnet composition of this embodiment contains rare earth magnet powder (hereinafter, sometimes simply referred to as "magnet powder"). The rare earth magnet powder is made of a hard magnetic material and is the powder that is the main source of the magnetic properties of the bonded magnet. There are no particular limitations on the rare earth magnet powder, as long as it is made of a rare earth-based hard magnetic material. For example, NdFe 14 Neodymium (Nd)-iron (Fe)-boron (B) based magnet powder with B as the basic composition, Sm2Fe 17 N x Samarium (Sm)-iron (Fe)-nitrogen (N) based magnet powder, SmCo5 or Sm2Co 17 Examples of suitable magnet powders include samarium (Sm)-cobalt (Co)-based magnet powders having a basic composition of the above. Furthermore, some of the elements in these basic compositions may be substituted with other elements. For example, some of the neodymium (Nd) or samarium (Sm) may be substituted with lanthanum (La), cerium (Ce), praseodymium (Pr), terbium (Tb), and / or dysprosium (Dy). Furthermore, some of the iron (Fe) and cobalt (Co) may be substituted with cobalt (Co), iron (Fe), manganese (Mn), nickel (Ni), copper (Cu), zirconium (Zr), and / or hafnium (Hf).

[0026] The bonded magnet composition may contain only one type of magnetic powder alone, or may contain a combination of multiple types of magnetic powder. The magnetic powder may be magnetic powder alone or may be composite powder with other materials. For example, the magnetic powder may be magnetic powder with a coating layer formed on its surface using a treatment agent such as a phosphoric acid compound, a silica compound, and / or a triazine thiol derivative.

[0027] Preferably, the rare earth magnet powder is a samarium (Sm)-iron (Fe)-nitrogen (N) based magnet powder. 17 N x Samarium-iron-nitrogen magnets with the basic composition of x=3, i.e., SmFe 17The saturation magnetization is at its highest when the composition is N3. This makes it possible to increase the magnetic flux density of the resulting bonded magnet. The coercive force is also high, about five times that of neodymium-iron-boron magnet powder.

[0028] Preferably, the average particle size of the rare earth magnet powder is 0.5 μm or more and 5.0 μm or less. Magnet powder with an excessively large particle size has a low coercive force. It may also reduce the fluidity of the composition or worsen the dimensional stability and surface properties of the resulting bonded magnet. On the other hand, if the particle size of the magnet powder is excessively small, the viscosity of the composition increases and the fluidity deteriorates. Furthermore, the rare earth magnet powder may oxidize, degrading its properties and, in some cases, ignite due to heat generated by oxidation. By appropriately increasing the particle size, it is possible to improve fluidity and prevent heat generation. The average particle size of the magnet powder is more preferably 1.0 μm or more and 3.0 μm or less, and even more preferably 1.8 μm or more and 2.8 μm or less.

[0029] Preferably, the content of magnetic powder in the composition is 80% by mass or more and 95% by mass or less. If the amount of magnetic powder, which is the main component in expressing magnetic properties, is too small, the magnetic properties of the bonded magnet, particularly the magnetic flux density, will be reduced. Furthermore, because the amount of binder resin is large, the linear expansion coefficient of the bonded magnet will increase, which may result in weaker adhesive strength in applications where the bonded magnet is bonded to an iron yoke. On the other hand, if the amount of magnetic powder is too large, the fluidity of the composition will decrease, making molding difficult. The content of magnetic powder is more preferably 85% by mass or more and 93% by mass or less, and even more preferably 88% by mass or more and 92% by mass or less.

[0030] Particularly preferably, the magnet powder is a samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder with an average particle size of 1.8 μm to 2.8 μm, and the content of the magnet powder in the bonded magnet composition is 88% by mass to 92% by mass. Because samarium-iron-nitrogen-based magnet powder has a nucleation-type coercive force generation mechanism, limiting the average particle size to 2.8 μm or less further increases the coercive force. This makes it useful for applications where a strong demagnetizing field is applied, such as motors. Furthermore, limiting the average particle size to 1.8 μm or more further improves the flowability during composition molding and effectively prevents heat generation and fire problems due to oxidation of the magnet powder.

[0031] Known methods for producing samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder include the melting method and the reduction-diffusion method. In the melting method, metal powder containing iron and samarium is used as raw materials. This raw material is heated and melted at temperatures above 1500°C in a furnace such as a high-frequency furnace or an arc furnace. The resulting product is then crushed and heat-treated to homogenize the composition to produce a Sm-Fe master alloy. The resulting master alloy is then nitrided to produce magnet powder. In the reduction-diffusion method, a mixture of samarium oxide (Sm2O3), iron raw materials (Fe, Fe2O3, etc.), and a reducing agent (Ca, etc.) is heated to obtain a master alloy, which is then nitrided to produce magnet powder. Because samarium-iron-nitrogen-based magnet powder has a nucleation-type coercive force generation mechanism, it is desirable to finely grind the powder to achieve high coercive force. Therefore, methods such as finely grinding the nitrided master alloy or using fine raw materials are used.

[0032] Preferably, the samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder is produced by a reduction-diffusion method. The reduction-diffusion method, which uses inexpensive oxide raw materials (such as Sm2O3), has the advantage of reducing raw material costs. It also produces magnet powder with fewer impurities than the melting method. In contrast, the melting method requires extremely complicated processes. Furthermore, because the product is exposed to the air between each process, there is a risk of impurities forming on the product surface due to oxidation. If the product surface is oxidized, nitriding will not proceed uniformly, resulting in a deterioration in the properties of the resulting magnet powder, particularly magnetic properties such as saturation magnetization, coercive force, and / or squareness, which may reduce the maximum energy product of the final bonded magnet.

[0033] In the reduction-diffusion method, a samarium raw material (Sm2O3), an iron raw material (e.g., Fe), and a reducing agent (e.g., Ca) are first reduced to obtain a reduction product containing a Sm-Fe alloy. Next, this reduction product is subjected to a wet process to remove by-products derived from the reducing agent (e.g., CaO, Ca(OH)2), and the resulting Sm-Fe alloy is then nitrided in a mixed gas stream containing ammonia and hydrogen. The resulting nitride is then crushed and dried to obtain a samarium-iron-nitrogen magnet powder.

[0034] Samarium (Sm)-iron (Fe)-nitrogen (N) based magnet powder is Sm2Fe 17When using an N3-based alloy, it is desirable to pulverize the coarse powder. Since magnetic alloy coarse powder with an average particle size exceeding 20 μm has poor magnetic properties, it is desirable to pulverize it in an organic solvent. During or after this pulverization, the magnetic powder may be placed in a solution containing a surface treatment agent such as phosphoric acid and stirred to produce magnetic powder coated with a composite phosphate coating or other coating. Pulverization can be performed using any known pulverizer suitable for pulverizing magnetic powders. Among these, wet pulverizers such as media agitation mills and bead mills are particularly suitable, as they facilitate the production of uniform powder composition and particle size. Organic solvents such as isopropyl alcohol, ethanol, toluene, methanol, and hexane are also preferred as pulverization solvents. After pulverization, the samarium-iron-nitrogen magnetic powder can be filtered and dried using a filter with a specified mesh size. In this manner, samarium-iron-nitrogen magnetic powder can be obtained.

[0035] [Polyamide 12 resin] The bonded magnet composition of this embodiment contains polyamide 12 resin as a binder resin. Polyamide 12 resin is a thermoplastic resin. Thermoplastic resins plasticize and become fluid when heated during molding, and solidify and improve strength when cooled after molding. Therefore, by using a thermoplastic resin and performing molding that involves heating, such as injection molding or extrusion molding, it is possible to easily obtain bonded magnets with high strength and complex shapes. In particular, polyamide 12 resin has a low melting point, which further improves the dispersibility and packability of magnetic powder. This improves the moldability of the composition and enables the production of bonded magnets with excellent magnetic properties. Polyamide 12 resin also has the characteristic of low water absorption.

[0036] The form of the binder resin (polyamide 12 resin) is not particularly limited. Various forms such as powder, beads, pellets, etc. can be used. Among these, powder-like binder resin is particularly preferred as it can be mixed uniformly with the magnet powder.

[0037] Preferably, the content of binder resin (polyamide 12 resin) in the bonded magnet composition is 7.1% by mass or more and 11.7% by mass or less. If the amount of binder resin is too small, the fluidity of the composition may decrease, making molding difficult. On the other hand, if the amount of binder resin is too large, the proportion of magnetic powder in the bonded magnet may decrease, which may result in a decrease in the magnetic properties of the bonded magnet. Furthermore, the linear expansion coefficient of the bonded magnet may increase, which may cause cracks to occur in thermal shock tests. It is even more preferable that the content of binder resin is 7.1% by mass or more and 11.5% by mass or less.

[0038] [End treatment agent] The bonded magnet composition of this embodiment contains 0.3% by mass or more of a terminal treatment agent having a carbodiimide bond. The terminal treatment agent prevents the bonded magnet composition from thickening and improves its fluidity. Specifically, the polyamide 12 resin contained in the bonded magnet composition has terminal functional groups such as carboxyl and amino groups. In a composition without a terminal treatment agent, the rare earth magnet powder component contained in the composition tends to cause reactions between functional groups (such as degeneration reactions) to progress, resulting in polymerizing the resin. Polymerizing the resin can lead to thickening of the composition. In contrast, adding a highly dispersed terminal treatment agent suppresses reactions between the resin and the rare earth magnet component and reactions between functional groups, thereby suppressing thickening of the composition and improving its fluidity. This is because the terminal treatment agent adjusts, caps, and deactivates the terminal functional groups (carboxyl and amino groups) of the resin.

[0039] To fully utilize the effects of the terminal treatment agent, it is important to uniformly disperse the terminal treatment agent in the composition. If the terminal treatment agent is not uniformly dispersed, the terminal functional groups will not be adjusted (capping) sufficiently, making it difficult to fully suppress reactions between functional groups and thereby improve flowability. To uniformly disperse the terminal treatment agent, it is effective to perform terminal treatment on the polyamide 12 resin during the kneading stage with the rare earth magnet powder during composition production.

[0040] In this embodiment, a compound having a carbodiimide bond is used as the terminal treatment agent. Because terminal treatment agents having carbodiimide bonds are highly reactive, terminal treatment is possible even at low temperatures. Since treatment at high temperatures is not required, damage to the magnet powder, specifically deterioration of magnetic properties, can be minimized. The type of carbodiimide compound used as the terminal treatment agent is not particularly limited. Examples include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, bis(2,6-diisopropylphenyl)carbodiimide, di-t-butylcarbodiimide, and / or di-β-naphthylcarbodiimide.

[0041] In this embodiment, the content of the terminal treatment agent in the composition is limited to 0.3% by mass or more. If the content is less than 0.3% by mass, the effect of terminal adjustment will be insufficient, and the effects of preventing thickening of the composition and improving fluidity will be insufficient. The content of the terminal treatment agent is preferably 0.5% by mass or more and 0.9% by mass or less.

[0042] [Liquidity] The bonded magnet composition of this embodiment has good fluidity because the viscosity increase phenomenon is suppressed. Specifically, the fluidity measured using a flow tester under the conditions of a capillary temperature of 250°C, a load of 588N, an orifice diameter of 1mm, an orifice length of 1mm, and a preheating time of 300 seconds was 0.7cm. 3 / sec or more. Increasing fluidity improves molding processability. Therefore, thin or complex shaped bonded magnets can be easily obtained without post-processing. It is also possible to increase the amount of magnetic powder in the composition while maintaining a high dispersion state, and even with the same content, the orientation of the magnetic powder can be improved. Furthermore, there is no need to mold at high temperatures to increase fluidity. Low-temperature molding is possible, so deterioration of the magnetic properties of the magnetic powder can be suppressed. These factors work in combination to make it possible to manufacture bonded magnets with excellent magnetic properties, especially anisotropic bonded magnets. High fluidity is desirable, and a flow rate of 2.0 cm is recommended. 3 / g or more is preferable. On the other hand, compositions with excessively high fluidity are difficult to manufacture. 3 / seconds or less.

[0043] [Amine value] In the bonded magnet composition of this embodiment, the amino groups, which are the terminal functional groups of the polyamide 12 resin, are effectively controlled (blocked). Therefore, the amine value of the resin in the composition is relatively low. By reducing the amine value, it is possible to more effectively prevent reactions between functional groups and the resulting thickening, thereby improving the fluidity of the composition. The amine value of the composition is preferably 1.0 or less, and more preferably 0.4 or less.

[0044] [Other ingredients] The bonded magnet composition of this embodiment may be composed solely of the above-mentioned components (magnet powder, polyamide 12 resin, and end treatment agent). For example, it may contain rare earth magnet powder, polyamide 12 resin, and end treatment agent, with the remainder consisting of inevitable impurities. Alternatively, it may contain components other than those mentioned above, as long as it has the desired fluidity. Such components include, but are not limited to, reinforcing agents, stabilizers, and / or compatibilizers. Of these, reinforcing agents are reinforcing components such as carbon fiber, carbon flakes, and / or glass fiber. Adding reinforcing agents can effectively increase the tensile strength of the bonded magnet.

[0045] <<2. Manufacturing Method of Bonded Magnet Composition>> The method for producing a bonded magnet composition of this embodiment includes the step of simultaneously kneading rare earth magnet powder, polyamide 12 resin, and an end treatment agent having a carbodiimide bond. The kneading is performed under heating so that the polyamide 12 resin melts. The content of the end treatment agent in the bonded magnet composition is limited to 0.3 mass% or more.

[0046] The details of the rare earth magnet powder, polyamide 12 resin, and end treatment agent with carbodiimide bonds are as described above. In other words, the rare earth magnet powder is the powder that is the main component responsible for the magnetic properties of the bonded magnet. Furthermore, by using polyamide 12 resin as the binder resin, it is possible to achieve high loading of the magnet powder while maintaining a high dispersion state. Furthermore, the end treatment agent prevents the bonded magnet composition from thickening and improves its flowability.

[0047] In the manufacturing method of this embodiment, it is important to simultaneously heat and knead the above-mentioned raw materials (rare earth magnet powder, polyamide 12 resin), and the end treatment agent. This allows the end treatment agent to be uniformly dispersed in the composition, thereby enabling the composition to fully exhibit its effects of preventing thickening and improving fluidity. It is believed that kneading the end treatment agent together with the magnet powder increases the kneading torque applied to the composition, resulting in uniform dispersion of the end treatment agent. Alternatively, a conceivable method is to pre-knead the binder resin and the end treatment agent to perform end treatment on the binder resin, and then knead the resulting treated binder resin with the magnet powder. This method does not allow the end treatment agent to be uniformly dispersed, limiting its effectiveness in improving the fluidity of the composition.

[0048] As the kneading device, a batch kneader or a continuous extruder (continuous extruder) can be used. Kneading is performed while controlling the shear force applied to the composition in the kneading device. For example, when a kneader is used, the amount of raw materials introduced into the mixing tank, the temperature of the composition during kneading, the rotation speed of the kneading blade, and / or the kneading time are controlled. When a continuous extruder is used, conditions such as the introduction rate of raw materials, temperature distribution, screw segment shape, screw rotation speed, and / or die hole diameter are adjusted. Furthermore, the kneading temperature may be any temperature at which the polyamide 12 resin melts but does not decompose. It is preferably 180°C or higher and 270°C or lower, and more preferably 190°C or higher and 240°C or lower.

[0049] <<3. Bonded Magnets>> The bonded magnet of this embodiment (hereinafter sometimes simply referred to as "bonded magnet") is a molded body of a bonded magnet composition. This bonded magnet is manufactured by injection molding or extrusion molding the bonded magnet composition under heating. In other words, the bonded magnet is an injection molded or extrusion molded body. Specifically, the bonded magnet composition is heated and melted at a temperature equal to or higher than the melting point of the binder resin contained therein to form a molten material, and the molten material is then molded by injection molding or extrusion molding to obtain a molded body (bonded magnet). If a magnetic field is applied to the molten material during molding, an anisotropic bonded magnet can be obtained, and if a magnetic field is not applied, an isotropic bonded magnet can be obtained.

[0050] Preferably, the bonded magnet is an injection-molded body. That is, the molded body is produced by injection molding a bonded magnet composition. By employing injection molding, the degree of freedom in the shape of the molded bonded magnet can be increased, and dimensional accuracy can be improved. Furthermore, the surface quality and magnetic properties of the bonded magnet are excellent. Therefore, the molded body (bonded magnet) can be directly incorporated into electronic components without post-processing. In particular, the bonded magnet composition of this embodiment has good fluidity. Therefore, it has excellent moldability during injection molding, and can effectively prevent the occurrence of appearance defects such as welds.

[0051] The bonded magnet of this embodiment uses a precursor composition with excellent fluidity and moldability, so it has excellent magnetic properties and can be made thin and have complex shapes. Furthermore, no post-processing is required, making it suitable for insert molding. Therefore, this bonded magnet is suitable for small, flat, complex-shaped parts, such as motor parts for electronic devices.

[0052] It is desirable to magnetize bonded magnets before use. Magnetization is performed using a magnetizing device such as an electromagnet that generates a static magnetic field or a capacitor magnetizer that generates a pulsed magnetic field. The strength of the magnetizing magnetic field varies depending on the type of magnetic powder, so it cannot be determined in general terms. For example, it may be 1200 kA / m (15 kOe) or more, or 2400 kA / m (30 kOe) or more. [Example]

[0053] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

[0054] (1) Preparation of bonded magnet composition and bonded magnet [Example 1] A samarium (Sm)-iron (Fe)-nitrogen (N) magnet powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size of 2.3 μm was prepared as the rare earth magnet powder, and polyamide 12 resin (P3012U, manufactured by Ube Industries, Ltd., amine value 3.6 mgKOH / g) was prepared as the binder resin. Next, the raw materials were blended to obtain a blend composition of 88.5 mass% magnet powder (Sm-Fe-N magnet powder), 10.8 mass% polyamide 12 resin, and 0.7 mass% end modifier with a carbodiimide bond. The resulting blend was simultaneously kneaded at 200°C for 10 minutes using a batch kneader. This produced a bonded magnet composition.

[0055] The resulting composition was then injection molded using an injection molding machine and an injection mold to produce bonded magnet test pieces (cylindrical, outer diameter 20 mm, thickness 13 mm) conforming to JIS K7139A. The test pieces were molded so that the thickness direction of the test pieces was aligned with the orientation direction of the magnet powder.

[0056] [Example 2] During kneading, a continuous extruder was used instead of a batch kneader, and kneading was carried out under the condition of a barrel temperature of 200° C. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0057] [Example 3] The components were blended to obtain a blend composition of 91.5% by mass of magnet powder (Sm-Fe-N magnet powder), 8.0% by mass of polyamide 12 resin, and 0.5% by mass of an end modifier having a carbodiimide bond. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0058] [Comparative Example 1] In the compounding composition of Example 1, the polyamide 12 resin and the terminal treatment agent were kneaded in advance using a batch kneader at 200°C for 10 minutes, and the resulting kneaded product was pulverized. The resulting kneaded product was then kneaded with magnet powder under the same conditions as in Example 1 to produce a bonded magnet composition. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0059] Comparative Example 2 In the formulation of Example 1, no terminal modifier was added, and the amount of polyamide 12 resin added was increased by its mass (0.7 mass%). Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0060] Comparative Example 3 In the formulation of Example 1, the amount of terminal modifier was reduced by 0.5 mass % and the amount of polyamide 12 resin was increased by the same mass (0.5 mass %). Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0061] Comparative Example 4 In the blend composition of Example 3, no terminal modifier was added and the blend amount of polyamide 12 resin was increased by its mass (0.5 mass%). Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0062] (2) Evaluation The bonded magnet compositions and bonded magnets obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated for various properties as follows.

[0063] <Magnetic properties> The bonded magnets were magnetized using a pulse magnetizer in a magnetizing field of 3000 kA / m or more. The magnetic properties of the magnetized bonded magnets (residual magnetic flux density Br, coercive force iHc, and energy product (BH)max) were measured using a BH tracer.

[0064] <Liquidity> The fluidity of the bonded magnet composition was measured using a flow tester (Shimadzu Corporation, CFT-100D) under the following conditions: capillary temperature 250°C, load 588N, orifice diameter 1mm, orifice length 1mm, and preheating time 300 seconds.

[0065] <Amine value> The amine values ​​of the polyamide 12 resin and the bonded magnet composition were measured according to the potentiometric point titration method specified in JIS K 7237. Specifically, the sample was dissolved in m-cresol and titrated with a perchloric acid methanol solution.

[0066] (3) Evaluation results The evaluation results are summarized in Tables 1 and 2.

[0067] The bonded magnet composition of Comparative Example 1 failed to produce a composition with excellent fluidity. It is believed that the pre-blending process resulted in insufficient terminal treatment of the polyamide 12 resin. This caused a reaction between the amide groups at the ends of the polyamide 12 resin and the rare earth magnet powder, resulting in the thickening phenomenon.

[0068] A composition with excellent fluidity could not be obtained with the bonded magnet composition of Comparative Example 2. It is believed that the absence of an end treatment agent caused a reaction between the amide groups at the ends of the polyamide 12 and the rare earth magnet powder, resulting in an increase in viscosity.

[0069] The bonded magnet composition of Comparative Example 3 did not have excellent fluidity. It is believed that the amount of end treatment agent was too small, causing a reaction between the amide groups at the ends of the polyamide 12 and the rare earth magnet powder, resulting in thickening.

[0070] The bonded magnet composition of Comparative Example 4 could not be kneaded, and a composition with excellent filling properties could not be obtained. It also could not be molded, and a bonded magnet could not be produced. It is believed that because no end treatment was performed, the reaction between the amide groups at the ends of the polyamide 12 and the rare earth magnet powder proceeded, resulting in a strong thickening phenomenon.

[0071] In contrast, in Examples 1 to 3, a bonded magnet composition with high fluidity was obtained. In particular, in Example 3, a composition with sufficient fluidity was obtained despite the high proportion of magnetic powder. Furthermore, in Examples 1 and 2, where the proportion of magnetic powder was low, the fluidity was even better. In all Examples, the magnetic properties of the bonded magnet were sufficient.

[0072] The amine values ​​(0.22 to 0.28 mg KOH / g) of the bonded magnet compositions of Examples 1 to 3 were significantly lower than the amine values ​​(1.7 to 1.8 mg KOH / g) of Comparative Examples 1 to 3. It is believed that by kneading the end treatment agent simultaneously with the magnet powder and polyamide 12 resin, the terminal amino groups of the polyamide 12 resin were effectively adjusted (capped).

[0073] [Table 1]

[0074] [Table 2]

Claims

1. A magnet core material comprising a rare earth magnet powder and a polyamide 12 resin, and further comprising a terminal treatment agent having a carbodiimide bond in an amount of 0.3% by mass or more, The flowability measured using a flow tester under the conditions of a capillary temperature of 250°C, a load of 588N, an orifice diameter of 1mm, an orifice length of 1mm, and a preheating time of 300 seconds was 0.7cm ３ / second or more.

2. 2. The bonded magnet composition according to claim 1, comprising the end treatment agent in an amount of 0.5% by mass or more and 0.9% by mass or less.

3. The fluidity is 2.0 cm ３ 3. The bonded magnet composition according to claim 1, wherein the bonded magnet composition has a melting point of 1 / 2 s or more.

4. The bonded magnet composition according to any one of claims 1 to 3, wherein the rare earth magnet powder is a samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder having an average particle size of 1.8 μm or more and 2.8 μm or less, and the content of the magnet powder in the bonded magnet composition is 88 mass% or more and 92 mass% or less.

5. 5. The bonded magnet composition according to claim 1, comprising the rare earth magnet powder, the polyamide 12 resin, and the terminal treatment agent, with the remainder being unavoidable impurities.

6. A method for producing a bonded magnet composition, comprising the steps of simultaneously kneading rare earth magnet powder, polyamide 12 resin, and an end treatment agent having a carbodiimide bond, The method, wherein the content of the terminal treatment agent in the bonded magnet composition is 0.3 mass % or more.

7. The method according to claim 6, wherein the magnetic powder is a samarium (Sm)-iron (Fe)-nitrogen (N)-based magnetic powder having an average particle size of 1.8 μm or more and 2.8 μm or less, and the content of the magnetic powder in the bonded magnet composition is 88 mass % or more and 92 mass % or less.

8. A bonded magnet which is a compact of the bonded magnet composition according to any one of claims 1 to 5.

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