Composition for bonded magnet and bonded magnet

Abstract

To provide a composition for a bond magnet, capable of obtaining a bond magnet with excellent cold shock resistance and humidity resistance, and having a good fluidity and an excellent formability.SOLUTION: A composition for a bond magnet, contains a magnetic powder and a thermal plasticity binder resin, and contains 0.5 or more mass% of carboxylic acid ester and 0.4 or more mass% of a carbodiimide compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a bonded magnet composition and a bonded magnet. [Background technology]

[0002] Bonded magnets are manufactured by kneading a composition containing magnet powder, binder components such as organic resin, and additives such as reinforcing agents, plasticizers, and lubricants in a kneader such as an extruder, then processing the mixture into pellets or other shapes, and then molding the resulting mixture using techniques such as injection molding, compression molding, or extrusion molding. Compared to sintered magnets, these bonded magnets have the advantage of being more dimensionally accurate and easier to produce in complex shapes. They also have high uniformity in quality and performance, good yield, and excellent machinability. In particular, magnets manufactured using thermoplastic resins such as polyamide resin and polyphenylene sulfide resin as binders and injection molding offer particularly high dimensional accuracy and no need for post-processing, reducing magnet manufacturing costs.

[0003] Furthermore, the properties of bonded magnets are improved depending on the conditions of the materials in which they are used. For example, Patent Documents 1 and 2 propose adding carbon fiber as a reinforcing agent to a bonded magnet composition obtained by kneading magnet powder with an organic resin in order to improve mechanical strength. Patent Document 3 also proposes adding carbon fiber and components such as a plasticizer to improve durability against thermal shock. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-072240 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-251545 [Patent Document 3] Patent No. 5979733 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to improve the magnetic properties of a bonded magnet, it is desirable to increase the proportion of magnetic powder, which is the main component responsible for the expression of these magnetic properties. However, increasing the amount of magnetic powder reduces the fluidity of the composition during injection molding, and this leads to problems such as deterioration of the properties of the bonded magnet obtained by molding, such as resistance to thermal shock. In this regard, Patent Document 3 proposes a method of adding a plasticizer to the bonded magnet composition. However, after investigation by the present inventors, it was found that although adding a plasticizer is effective in improving fluidity and resistance to thermal shock, it also reduces the moisture resistance of the bonded magnet.

[0006] In particular, bonded magnets have high dimensional accuracy and do not require post-processing, which helps reduce manufacturing costs. With the trend toward electrification of automotive components, these features are often utilized to incorporate them into parts. However, automotive parts are susceptible to the effects of the external environment, and they are required to function stably even in high-temperature, high-humidity environments. Therefore, bonded magnets that can be used in automotive parts are also expected to have excellent moisture resistance.

[0007] In light of this situation, the inventors of the present invention have conducted further research. As a result, they have discovered that by adding a carboxylic acid ester, which acts as a plasticizer, to a bonded magnet composition, and also using a carbodiimide compound in a specified ratio, it is possible to prevent the deterioration of the moisture resistance of the bonded magnet. As a result, they have discovered that it is possible to obtain a bonded magnet with excellent resistance to thermal shock and moisture, as well as to realize a bonded magnet composition with good fluidity and excellent moldability.

[0008] The present invention was completed based on these findings, and its objective is to provide a composition for bonded magnets that can produce bonded magnets with excellent resistance to thermal shock and moisture, as well as good fluidity and moldability. [Means for solving the problem]

[0009] The present invention encompasses the following aspects (1) to (5). In this specification, the expression "to" includes the numerical values ​​on both ends. In other words, "X to Y" is synonymous with "at least X and at most Y."

[0010] (1) A composition for bonded magnets, comprising a magnet powder and a thermoplastic binder resin, and further comprising 0.5% by mass or more of a carboxylic acid ester and 0.4% by mass or more of a carbodiimide compound.

[0011] (2) The composition for a bonded magnet according to (1) above, containing the carboxylic acid ester in an amount of 0.5% by mass or more and 1.0% by mass or less and the carbodiimide in an amount of 0.4% by mass or more and 1.0% by mass or less.

[0012] (3) A bonded magnet composition according to (1) or (2) 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.

[0013] (4) A bonded magnet composition according to any one of (1) to (3) above, wherein the thermoplastic binder resin is at least one of polyamide 12 and polyamide elastomer, and the content of the thermoplastic binder resin in the bonded magnet composition is 6.0% by mass or more and 11.2% by mass or less.

[0014] (5) A bonded magnet which is a molded product of the bonded magnet composition according to any one of (1) to (4) above. [Effects of the Invention]

[0015] According to the present invention, a bonded magnet composition can be obtained that has excellent resistance to thermal shock and moisture, and also has good flowability and excellent moldability during molding. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] <<1. Bonded Magnet Composition>> The bonded magnet composition of this embodiment contains magnet powder and a thermoplastic binder resin, and further contains 0.5% by mass or more of a carboxylic acid ester and 0.4% by mass or more of a carbodiimide compound.

[0018] The bonded magnet composition of this embodiment (hereinafter sometimes simply referred to as the "composition") is a precursor to a bonded magnet. That is, the composition is molded 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.

[0019] [Magnetic powder] The bonded magnet composition of this embodiment contains magnet powder. The magnet powder is made of a hard magnetic material and is the powder that mainly expresses the magnetic properties of the bonded magnet. The magnet powder is not particularly limited as long as it is made of a hard magnetic material. It may be rare earth magnet powder or ferrite magnet powder. As the rare earth magnet powder, NdFe 14 Neodymium-iron-boron (Nd-Fe-B) magnet powder with B as the basic composition, Sm2Fe 17 N x Samarium-iron-nitrogen (Sm-Fe-N) magnet powder with the basic composition of SmCo5 or Sm2Co 17 Examples of ferrite powder include samarium-cobalt (Sm-Co) magnet powders with the basic composition BaFe 12 O 19 Barium (Ba) ferrite with the basic composition SrFe 12 O 19 Strontium (Sr) ferrite with the basic composition (Ca, La) (Fe, Co) x O yExamples of suitable rare earth magnet powders include lanthanum-calcium-cobalt (La-Ca-Co) ferrites with a basic composition of the above. Furthermore, some of the elements in these basic compositions may be substituted with other elements. For example, the rare earth magnet powder may be one in which some of the neodymium (Nd) or samarium (Sm) is 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).

[0020] 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.

[0021] Preferably, the average particle size of the 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. Furthermore, the fluidity of the composition may decrease, or the dimensional stability and surface properties of the resulting bonded magnet may deteriorate. 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, if the magnet powder is a rare earth magnet powder, the magnet powder may oxidize, degrading its properties and, in some cases, ignition may occur 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.

[0022] Preferably, the content of magnetic powder in the bonded magnet composition is 80% by mass or more and 95% by mass or less. If the amount of magnetic powder, which is the main component responsible for the 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 weak 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 magnetic powder content 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.

[0023] Particularly preferably, 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 mass % or more and 92 mass % or less. 17 N x Samarium-iron-nitrogen magnets with the basic composition of x=3, i.e., SmFe 17 The 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. It also has a high coercive force, about five times that of neodymium-iron-boron magnet powder. Samarium-iron-nitrogen magnet powder in particular has a nucleation-type coercive force generation mechanism, so by limiting the average particle size to 2.8 μm or less, the coercive force can be further increased. This makes it useful for applications where a strong demagnetizing field is applied, such as in motors.

[0024] 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.

[0025] 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 (Sm2O3, Fe2O3, etc.), 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 bonded magnet.

[0026] In the reduction-diffusion method, a samarium raw material (Sm2O3), an iron raw material (Fe2O3, etc.), and a reducing agent (Ca, etc.) 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 (CaO, Ca(OH)2, etc.) contained in the reduction product. 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.

[0027] Samarium (Sm)-iron (Fe)-nitrogen (N) based magnet powder is Sm2Fe 17 When 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.

[0028] [Thermoplastic binder resin] The bonded magnet composition of this embodiment contains a thermoplastic binder resin. The thermoplastic binder resin acts as a binding agent (binder) that binds the magnetic powder particles together in the bonded magnet. The thermoplastic binder resin also becomes plasticized and fluid when heated during molding, and solidifies and improves strength when cooled after molding. Therefore, by using a thermoplastic binder resin and performing molding that involves heating, such as injection molding or extrusion molding, it is possible to easily obtain bonded magnets that are high in strength and have complex shapes.

[0029] The thermoplastic binder resin may be any known thermoplastic resin used in the manufacture of bonded magnets. Examples of such resins include polyamide-based resins, polyamide elastomers, polyethylene-based resins, polyphenylene sulfide (PPS)-based resins, and polyethylene terephthalate (PET)-based resins. Examples of polyamide-based resins include homopolymer polyamides and copolymer polyamides, such as polyamide 6, polyamide 6,6, polyamide 11, polyamide 12, polyamide 6,12, aromatic polyamides, polymerized fatty acid polyamides, and polyamides with modified end groups. These resins may be used alone or in combination. The shape of the binder resin is not particularly limited. Various shapes, such as powder, beads, and pellets, can be used. Among these, powder-like binder resins, which can be uniformly mixed with the magnet powder, are particularly preferred.

[0030] Preferably, the thermoplastic binder resin is at least one of a polyamide resin and a polyamide elastomer, and particularly preferably at least one of polyamide 12 and a polyamide elastomer. Polyamide resins, particularly polyamide 12 and polyamide elastomers, have a high affinity with magnetic powder, especially rare earth magnetic powder. This increases the strength of the bonded magnet. They also increase the fluidity of the composition, making it easier to mold the bonded magnet. They are also characterized by their light weight and high heat resistance. Either a polyamide resin (such as polyamide 12) or a polyamide elastomer may be used alone, or both may be used in combination. In particular, using both polyamide 12 and a polyamide elastomer in combination makes it possible to achieve a balanced increase in the fluidity of the composition and the strength of the bonded magnet.

[0031] Preferably, the binder resin content in the bonded magnet composition is 3.0% by mass or more and 15.0% 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. The binder resin content is more preferably 5.0% by mass or more and 13.0% by mass or less, and even more preferably 6.0% by mass or more and 11.2% by mass or less.

[0032] When polyamide 12 and a polyamide elastomer are used in combination, the mixing ratio of the polyamide 12 and the polyamide elastomer is not particularly limited. However, blending a larger amount of polyamide 12 further increases the fluidity. The proportion of the polyamide elastomer relative to the total amount of polyamide 12 and the polyamide elastomer is preferably 70% by mass or less, more preferably 10% by mass or more and 30% by mass or less.

[0033] [Carboxylic acid esters] The bonded magnet composition of this embodiment contains 0.5% by mass or more of a carboxylic acid ester. The carboxylic acid ester increases the fluidity of the composition and improves the bonded magnet's resistance to thermal shock and adhesive strength. Conventional bonded magnet compositions contain lubricants, typically hydrocarbon or fatty acid lubricants, and various esters to improve fluidity during molding, such as injection molding. However, the use of conventional lubricants and various esters can sometimes reduce the adhesive strength of the bonded magnet. For example, even when a bonded magnet is bonded to an iron yoke using an adhesive such as an epoxy adhesive to produce an integrally molded part, sufficient adhesive strength may not be achieved. In contrast, the use of a carboxylic acid ester can achieve good adhesive strength. The type of carboxylic acid ester is not particularly limited. Examples include sebacate ester and / or adipic acid ester.

[0034] The content of carboxylic acid ester in the bonded magnet composition is limited to 0.5% by mass or more. If the content is less than 0.5% by mass, the effect of improving fluidity and thermal shock resistance will be insufficient. The content may be 0.6% by mass or more, 0.7% by mass or more, 0.8% by mass or more, or 0.9% by mass or more. On the other hand, the content of carboxylic acid ester is preferably 1.0% by mass or less. By appropriately limiting the amount of carboxylic acid ester, the bonded magnet will have better thermal shock resistance.

[0035] [Carbodiimide compounds] The bonded magnet composition of this embodiment contains a carbodiimide compound in an amount of 0.4 mass% or more. A carbodiimide compound is a compound with a carbodiimide bond. Adding a carbodiimide compound has the effect of improving the moisture resistance of the bonded magnet. A carbodiimide compound has a higher reactivity to water than magnet powder. When a bonded magnet contains a carbodiimide compound, water reacts preferentially with the carbodiimide compound to form a urea derivative. It is thought that the reaction between water and magnet powder is inhibited, thereby improving moisture resistance.

[0036] The type of carbodiimide compound is not particularly limited, and examples thereof include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, bis(2,6-diisopropylphenyl)carbodiimide, di-t-butylcarbodiimide, and / or di-β-naphthylcarbodiimide.

[0037] The content of the carbodiimide compound in the bonded magnet composition is limited to 0.4% by mass or more. If it is less than 0.4% by mass, the effect of improving moisture resistance will be insufficient. The content may be 0.5% by mass or more, 0.6% by mass or more, 0.7% by mass or more, 0.8% by mass or more, or 0.9% by mass or more. On the other hand, the content of the carbodiimide compound is preferably 1.0% by mass or less. By keeping the amount of the carbodiimide compound appropriately, the strength of the bonded magnet will be superior.

[0038] [Other ingredients] The bonded magnet composition of this embodiment may be composed solely of the above-mentioned components (magnet powder, thermoplastic binder resin, carboxylic acid ester, and carbodiimide compound). Alternatively, it may contain components other than those mentioned above as necessary. Such components include, but are not limited to, reinforcing agents, stabilizers, and / or compatibilizers. Among 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.

[0039] As explained above, the bonded magnet composition of this embodiment contains magnet powder and a thermoplastic binder resin, and further contains 0.5% by mass or more of a carboxylic acid ester and 0.4% by mass or more of a carbodiimide compound. By providing this configuration, it is possible to obtain a bonded magnet with excellent resistance to thermal shock and moisture, and also to realize a bonded magnet composition with good fluidity and excellent moldability.

[0040] <<2. Manufacturing Method of Bonded Magnet Composition>> The bonded magnet composition of this embodiment can be produced by mixing and kneading the above-mentioned components (magnet powder, thermoplastic binder resin, carboxylic acid ester, carbodiimide compound, etc.). A batch kneader or a continuous extruder (continuous extruder) can be used as the kneading device. Kneading is carried out 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 put into the mixing tank, the temperature of the composition during kneading, the rotation speed of the kneading blade, and / or the kneading time can be controlled. .Ma When a continuous extruder is used, conditions such as the feed rate of the raw materials, temperature distribution, shape of the screw segments, screw rotation speed, and / or die hole diameter are adjusted.

[0041] <<3. Bonded Magnets>> The bonded magnet of this embodiment is a molded product of a bonded magnet composition. This bonded magnet is manufactured by injection molding or extrusion molding the bonded magnet composition. In other words, the bonded magnet is an injection-molded or extrusion-molded product. 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 then the molten material is molded by injection molding or extrusion molding to obtain a molded product (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.

[0042] 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.

[0043] The bonded magnet of this embodiment has excellent magnetic properties, high resistance to cold and thermal shocks, so it does not crack, and also has excellent mechanical strength. This bonded magnet can be molded into complex shapes and is suitable for mass production. Furthermore, no post-processing is required, so it can be insert molded. Therefore, this bonded magnet is suitable for small, flat, complex-shaped parts such as motor parts for electronic devices.

[0044] 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.

[0045] The bonded magnet of this embodiment has excellent resistance to thermal shock and humidity. For example, when a tensile test is performed on a 0.3 mm thick test piece at -30°C, the elongation is 0.6% or more. Furthermore, after being left in a high-temperature, high-humidity environment at a temperature of 85°C and a humidity of 85% for 1000 hours, the flux (amount of magnetic flux) decreases by less than 2%. Such bonded magnets with excellent resistance to thermal shock and humidity are suitable for use in parts used in high-temperature, high-humidity environments, such as automotive motors. [Example]

[0046] 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.

[0047] (1) Preparation of bonded magnet composition and bonded magnet [Example 1] A samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size of 2.3 μm was prepared as the magnet powder, and a sebacic acid ester was used as the carboxylic acid ester. The raw materials were then mixed using a stirrer mixer to obtain a blend composition of 89.5% by mass of the magnet powder (Sm-Fe-N-based magnet powder), 7.1% by mass of polyamide 12 resin, 2.1% by mass of polyamide elastomer, 0.8% by mass of the carboxylic acid ester (sebacic acid ester), and 0.5% by mass of a carbodiimide compound with a carbodiimide bond. The resulting mixture was then kneaded at 200°C using a continuous extruder to produce a bonded magnet composition. The average particle size was measured using a laser diffraction particle size analyzer (HELOS & RODOS, manufactured by Sympatec GmbH, Germany) as the 50% cumulative diameter (D50) on a volume basis.

[0048] Next, using an injection molding machine and an injection molding die, JIS K7139A12 test pieces (thickness 3 mm) were made from the obtained bonded magnet composition, and these were used for evaluation of the bonded magnet.

[0049] [Example 2] The amounts of raw materials other than the magnet powder were increased in the composition of Example 1. Specifically, the raw materials were mixed to obtain a composition of 88.0 mass% magnet powder (Sm-Fe-N magnet powder), 8.1 mass% polyamide 12 resin, 2.4 mass% polyamide elastomer, 0.9 mass% carboxylic acid ester (sebacic acid ester), and 0.6 mass% carbodiimide compound having a carbodiimide bond. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0050] [Example 3] The amount of magnet powder was increased in the composition of Example 1. Specifically, the raw materials were mixed to obtain a composition of 91.9 mass% magnet powder (Sm-Fe-N magnet powder), 5.5 mass% polyamide 12 resin, 1.7 mass% polyamide elastomer, 0.5 mass% carboxylic acid ester (sebacic acid ester), and 0.4 mass% carbodiimide compound having a carbodiimide bond. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0051] [Example 4] In the formulation of Example 1, no polyamide elastomer was added, and instead the amount of polyamide 12 resin was increased. Specifically, the raw materials were mixed to obtain a formulation of 89.5 mass% magnet powder (Sm-Fe-N magnet powder), 9.2 mass% polyamide 12 resin, 0.8 mass% carboxylic acid ester (sebacic acid ester), and 0.5 mass% carbodiimide compound with a carbodiimide bond. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0052] [Example 5] In the compounding composition of Example 1, adipic acid ester was used as the carboxylic acid ester instead of sebacate ester. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0053] [Example 6] In the formulation of Example 2, polyamide 12 resin was not added, and instead the amount of polyamide elastomer was increased. Specifically, the raw materials were mixed to obtain a formulation of 88.0 mass% magnet powder (Sm-Fe-N magnet powder), 10.7 mass% polyamide elastomer, 0.8 mass% carboxylic acid ester (sebacic acid ester), and 0.5 mass% carbodiimide compound with carbodiimide bonds. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0054] [Example 7] In the formulation of Example 1, the amount of polyamide 12 resin was reduced and the amount of carbodiimide compound was increased instead. Specifically, the raw materials were mixed to obtain a formulation of 89.5 mass% magnet powder (Sm-Fe-N magnet powder), 6.6 mass% polyamide 12 resin, 2.1 mass% polyamide elastomer, 0.8 mass% carboxylic acid ester (sebacic acid ester), and 1.0 mass% carbodiimide compound with carbodiimide bonds. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0055] [Comparative Example 1] In the formulation of Example 1, the carbodiimide compound was not added, and instead the amount of polyamide 12 resin was increased. Specifically, the raw materials were mixed to obtain a formulation of 89.5 mass% magnet powder (Sm-Fe-N magnet powder), 7.6 mass% polyamide 12 resin, 2.1 mass% polyamide elastomer, and 0.8 mass% carboxylic acid ester (sebacic acid ester). Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0056] Comparative Example 2 In the formulation of Example 3, the amount of carbodiimide compound was reduced and the amount of polyamide 12 resin was increased instead. Specifically, the raw materials were mixed to obtain a formulation of 91.9 mass% magnet powder (Sm-Fe-N magnet powder), 5.7 mass% polyamide 12 resin, 1.7 mass% polyamide elastomer, 0.5 mass% carboxylic acid ester (sebacic acid ester), and 0.3 mass% carbodiimide compound with carbodiimide bonds. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0057] Comparative Example 3 In the formulation of Comparative Example 2, the amount of carboxylic acid ester (sebacic acid ester) was reduced and the amount of polyamide 12 resin was increased instead. Specifically, the raw materials were mixed to obtain a formulation of 91.9 mass% of magnet powder (Sm-Fe-N based magnet powder), 5.9 mass% of polyamide 12 resin, 1.7 mass% of polyamide elastomer, 0.2 mass% of carboxylic acid ester (sebacic acid ester), and 0.3 mass% of a carbodiimide compound 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 4 In the formulation of Comparative Example 3, the amount of magnet powder was reduced and the amounts of polyamide 12 resin and polyamide elastomer were increased instead. Specifically, the raw materials were mixed to obtain a formulation of 88.0 mass% magnet powder (Sm-Fe-N magnet powder), 8.7 mass% polyamide 12 resin, 2.8 mass% polyamide elastomer, 0.2 mass% carboxylic acid ester (sebacic acid ester), and 0.3 mass% carbodiimide compound having a carbodiimide bond. Otherwise, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[0059] (2) Evaluation The bonded magnet compositions and bonded magnets obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were evaluated for various properties as follows.

[0060] <Liquidity> The fluidity of the bonded magnet composition was measured using a melt indexer (Shimadzu Corporation CFT-100D) to evaluate the fluidity. The measurement conditions were 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. At this time, if the fluidity was 1.0cm 3 / s or more was judged as good (○), and anything else was judged as bad (×).

[0061] <Cold and thermal shock resistance> Using an injection molding machine and an injection molding die, JIS K7139A12 test pieces (3 mm thick) were produced from the bonded magnet composition. Two gates were provided on both sides of the test piece in the longitudinal direction, and the molding temperature was 220 to 250°C, with the die temperature being 115°C. The resulting test pieces were subjected to a tensile test at -30°C, and those that showed an elongation of 0.6% or more were judged to be good (◯), while others were judged to be poor (×). In the tensile test, the test pieces were stretched until they broke, and the elongation immediately before breaking was measured.

[0062] <Moisture resistance> Using a magnetic injection molding machine and an injection mold, cylindrical test pieces with an outer diameter of 20 mm and a thickness of 13 mm were fabricated from the bond magnet composition, with the thickness direction aligned in the orientation direction. The resulting cylindrical test pieces were magnetized using a pulse magnetizer under a magnetic field of 3000 kA / m or higher, and the flux (amount of magnetic flux) was measured using a search coil. The test pieces were then placed in a constant temperature and humidity chamber maintained at a temperature of 85°C and a humidity of 85%, and the flux was measured again after 1000 hours. The flux loss was determined by comparing the flux loss before and after the high-temperature, high-humidity test. A flux loss of less than 2% was evaluated as good (◯), and a flux loss of more than 2% was evaluated as poor (×).

[0063] (3) Evaluation results The evaluation results obtained for Examples 1 to 7 and Comparative Examples 1 to 4 are shown in Table 1.

[0064] The bonded magnet composition of Comparative Example 1 did not have good moisture resistance (water resistance) because it contained no carbodiimide compound. The bonded magnet composition of Comparative Example 2 did not have good moisture resistance because it contained a small amount of carbodiimide compound. The bonded magnet composition of Comparative Example 3 contained a small amount of carboxylic acid ester, so the same amount of carbodiimide compound as in Comparative Example 2 was effective in improving moisture resistance. However, because the amount of carboxylic acid ester was small, the desired fluidity and thermal shock resistance were not achieved. The bonded magnet composition of Comparative Example 4 contained less magnet powder, so it had improved fluidity, but because it contained less carboxylic acid ester, it did not have the desired thermal shock resistance.

[0065] In contrast, the bonded magnet compositions of Examples 1 to 7 exhibited excellent results in terms of fluidity, resistance to thermal shock and moisture resistance.

[0066] [Table 1]

Claims

1. A composition for bonded magnets, comprising 88% by mass or more and 92% by mass or less of magnet powder, 6.0% by mass or more and 11.2% by mass or less of thermoplastic binder resin, 0.5% by mass or more and 1.0% by mass or less of carboxylic acid ester, and 0.4% by mass or more and 1.0% by mass or less of carbodiimide compound, wherein the thermoplastic binder resin is at least one of polyamide 12 and polyamide elastomer.

2. 2. The bonded magnet composition according to claim 1, wherein the magnetic powder is a samarium (Sm)-iron (Fe)-nitrogen (N) magnetic powder having an average particle size of 1.8 μm or more and 2.8 μm or less.

3. A bonded magnet which is a compact of the bonded magnet composition according to claim 1 or 2.

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