Composition for rare earth bonded magnets and rare earth bonded magnets

Abstract

To provide a rare-earth bonded magnet composition that can produce bonded magnets with excellent resistance to water and LLC (Long Life Coolant). Also, to provide a rare-earth bonded magnet that is a molded body of the rare-earth bonded magnet composition. [Solution] A composition for rare earth bonded magnets comprising rare earth iron-based magnet powder and a binder component, wherein the binder component comprises a polyamide resin, a polypropylene resin, and an acid-modified polypropylene resin, the proportion of the polyamide resin in the binder component being 30% by mass or more and 60% by mass or less, and the proportion of the acid-modified polypropylene resin being 10% by mass or more and 20% by mass or less.

Description

[Technical Field]

[0001] This invention relates to compositions for rare earth bonded magnets and rare earth bonded magnets. [Background technology]

[0002] Rare-earth bonded magnets are magnets made from a composite material consisting of rare-earth transition metal magnet powder and a binder component made of resin. They are manufactured by injection molding or compression molding of a composition (composition for rare-earth bonded magnets) obtained by mixing and kneading the rare-earth transition metal magnet powder and the binder component (resin). Rare-earth bonded magnets are small yet have high magnetic force and can be made into complex shapes. For this reason, they are widely used as magnetic force sources for small motors, and are essential in portable devices such as automobiles and power tools.

[0003] Rare-earth iron-based magnetic powder, containing rare earth elements (RE) and iron (Fe), is widely used as the rare-earth transition metal-based magnetic powder in rare-earth bonded magnets. Rare-earth iron-based magnetic powder has the advantage of being relatively inexpensive and possessing excellent magnetic properties. Furthermore, polyamide resin (nylon) is frequently used as the binder component in rare-earth bonded magnets.

[0004] Patent Document 1 contains rare earth magnet powder and polyamide 12 resin, and further contains a carbodiimide bond-containing end treatment agent in an amount of 0.3% by mass or more, and the fluidity measured under predetermined conditions is 0.7 cm³. 3 Regarding a bond magnet composition with a melting point of 2 / second or more, it has been disclosed that the magnetic powder is a samarium (Sm)-iron (Fe)-nitrogen (N) based magnetic powder (claims of Patent Document 1). Furthermore, it has been stated that polyamide resin has high affinity for magnetic powder and a relatively low melting point, which can enhance the dispersion and packing of the magnetic powder (

[0003] of Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-137392 [Overview of the project] [Problems that the invention aims to solve]

[0006] As mentioned above, rare-earth bonded magnets are widely used as magnetic force sources in small motors. On the other hand, one of the major applications of small motors is in pumps (electric pumps) that circulate temperature-controlled liquids such as water or long-life coolant (LLC). Here, LLC is a mixture containing water, diethylene glycol, and rust inhibitors. Magnets used in electric pumps are likely to be exposed to water and LLC, and therefore require excellent resistance to these substances.

[0007] However, polyamide resin (nylon), which is frequently used as a binder component in rare-earth bonded magnets, has high water absorption. In addition, rare-earth iron-based magnet powder is prone to oxidation, which degrades its magnetic properties. Therefore, in rare-earth bonded magnets containing polyamide resin, moisture can accumulate near the rare-earth iron-based magnet powder, potentially causing oxidative degradation.

[0008] Although techniques have been proposed to control the composition of binder components to improve the water resistance of rare-earth bonded magnets, no techniques are known to improve resistance to LLC (Long Life Coolant). Therefore, in reality, there are no rare-earth bonded magnet compositions that are highly resistant to water and LLC.

[0009] In light of these circumstances, the inventors conducted thorough research. As a result, they found that in a composition for rare earth bonded magnets containing rare earth iron-based magnet powder and a binder component, by including polyamide resin, polypropylene resin, and acid-modified polypropylene resin in the binder component, and by controlling the ratio of polyamide resin and acid-modified polypropylene resin in the binder component within a predetermined range, it is possible to obtain a rare earth bonded magnet with excellent resistance to water and LLC (Long Life Coolant).

[0010] The present invention was completed based on such findings, and aims to provide a rare-earth bonded magnet composition that can produce bonded magnets with excellent resistance to water and LLC. Furthermore, the present invention also aims to provide a rare-earth bonded magnet that is a molded body of the rare-earth bonded magnet composition. [Means for solving the problem]

[0011] The present invention encompasses the following embodiments (1) to (3). In this specification, the expression "~" includes the numerical values ​​at both ends. That is, "X~Y" is synonymous with "X or more and Y or less".

[0012] (1) A composition for rare earth bonded magnets comprising rare earth iron-based magnet powder and a binder component, The binder component comprises a polyamide resin, a polypropylene resin, and an acid-modified polypropylene resin. A composition for rare earth bond magnets, wherein the proportion of the polyamide resin in the binder component is 30% by mass or more and 60% by mass or less, and the proportion of the acid-modified polypropylene resin is 10% by mass or more and 20% by mass or less.

[0013] (2) The rare earth bond magnet composition according to (1), wherein the proportion of the rare earth iron-based magnet powder in the rare earth bond magnet composition is 80% by mass or more and 93% by mass or less.

[0014] (3) A rare earth bonded magnet, which is a molded body of the rare earth bonded magnet composition of (1) or (2) above. [Effects of the Invention]

[0015] The present invention provides a rare-earth bonded magnet composition that can produce bonded magnets having excellent resistance to water and LLC. The present invention also provides a rare-earth bonded magnet which is a molded body of the rare-earth bonded magnet composition. [Brief explanation of the drawing]

[0016] [Figure 1]Shows the swelling and cracking on the surface of the molded body (bond magnet). [Figure 2] Shows the relationship between the polyamide resin ratio and the properties (fluidity) of the bond magnet composition. [Figure 3] Shows the relationship between the acid-modified polypropylene ratio and the properties (fluidity, demagnetization rate) of the bond magnet composition.

Mode for Carrying Out the Invention

[0017] Specific embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described below. However, the present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention. Also, in this specification, as long as technical consistency can be achieved, any combination of suitable aspects can be adopted. For example, one and the other of suitable numerical ranges can be arbitrarily combined.

[0018] <<1. Composition for Rare Earth Bond Magnet>> The composition for rare earth bond magnet of the present embodiments (hereinafter may be simply referred to as "the composition" or "the composition for bond magnet") contains rare earth iron-based magnet powder and a binder component. The binder component contains polyamide resin, polypropylene resin, and acid-modified polypropylene resin, and the ratio of polyamide resin in the binder component is 30% by mass or more and 60% by mass or less, and the ratio of acid-modified polypropylene resin is 10% by mass or more and 20% by mass or less. Regarding the binder component, it may be composed only of polyamide resin, polypropylene resin, and acid-modified polypropylene resin, or may further contain another component.

[0019] <Rare Earth Iron-Based Magnet Powder> The rare earth iron-based magnet powder (hereinafter may be simply referred to as "magnet powder") is a powder made of an alloy (non-oxide-based compound) containing at least a rare earth element (Re) and iron (Fe), and exhibits magnet properties, that is, hard magnetic properties. Here, the alloy is a concept including not only solid solutions but also eutectics and intermetallic compounds. As intermetallic compounds, CaCu5 type, Th2Zn 17 type, Th2Ni17 type, TbCu7 type, ThMn 12 Type, NaZn 13 Type, Nd2Fe 14 Examples include compounds having crystalline structures such as type B and MgCu2 type. In this specification, powder refers to an aggregate of many particles; that is, many particles aggregate to form powder. The particle size of the particles constituting the rare earth iron-based magnet powder is not particularly limited. However, it is preferable that the particle size distribution is uniform. The average particle diameter (x50) of the powder is preferably 1 μm or more and 10 μm or less. The average particle diameter (x50) is the cumulative 50% diameter obtained by accumulating from the smallest particle size in the particle size distribution curve determined by volume. The average particle diameter (x50) is measured using a known measuring instrument such as a dry particle size distribution analyzer or a wet particle size distribution analyzer.

[0020] Rare earth elements (Re) are a general term for metals (elements) that make up the group consisting of scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71. The types of rare earth elements (Re) are not particularly limited. Examples include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). From the viewpoint of obtaining a magnetic material with excellent magnetic properties, it is preferable to use one or more elements selected from the group consisting of samarium (Sm), neodymium (Nd), and praseodymium (Pr), and it is particularly preferable to use either samarium (Sm) or neodymium (Nd) or both. The magnetic powder may contain one type of rare earth element alone, or it may contain a combination of multiple types of rare earth elements.

[0021] Rare earth iron-based magnet powder may contain other metallic or nonmetallic elements besides rare earth elements (Re) and iron (Fe). Examples of such alloy powders include samarium iron nitrogen (SmFeN) powder and neodymium iron boron (NdFeB) powder. Samarium iron nitrogen powder is Sm2Fe17 N x is a permanent magnet material having a basic composition, and the neodymium iron boron powder is Nd2Fe 14 is a permanent magnet material having a basic composition of B.

[0022] Preferably, the rare earth iron-based magnet powder is a samarium iron nitride (SmFeN)-based powder. The samarium iron nitride-based powder is excellent in heat resistance and weather resistance and is useful as a magnet powder for bonded magnets. The composition of the samarium iron nitride-based powder is not particularly limited as long as magnet characteristics can be obtained. However, from the viewpoint of magnet characteristics, the samarium (Sm) content in the powder is preferably 14% by mass or more and 27% by mass or less, more preferably 15% by mass or more and 25% by mass or less. Also, in the samarium iron nitride powder, the saturation magnetization becomes maximum when x = 3 in the basic composition (Sm2Fe 17 N x ). Therefore, x is preferably 2.5 or more and 3.5 or less, more preferably 2.8 or more and 3.2. In the samarium iron nitride-based powder, a part of samarium (Sm) may be substituted with other rare earth elements, such as lanthanum (La) or neodymium (Nd). Also, a part of iron (Fe) may be substituted with other transition metal elements, such as manganese (Mn) or cobalt (Co).

[0023] The rare earth iron-based magnet powder may be a powder surface-treated with phosphoric acid or phosphate (hereinafter referred to as "phosphates"). By using a magnet powder surface-treated with phosphates, it becomes possible to further improve the water resistance of the obtained molded body (bonded magnet). At the time of surface treatment, a phosphate treatment agent such as orthophosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, zinc phosphate, and / or calcium phosphate is dissolved in an organic solvent and / or water to prepare a dilution solution, and the magnet powder may be added thereto. Thereby, a phosphate film is formed on the particle surface of the magnet powder. The P quantification value of the magnet powder after surface treatment is preferably 0.1% by mass or more and 2% by mass or less, more preferably 0.3% by mass or more and 0.9% by mass or less. When the P quantification value is within the above-described range, oxidation of the magnet powder can be more effectively suppressed while preventing deterioration of magnet performance.

[0024] The rare-earth iron-based magnet powder may be a powder that has been surface-treated with a coupling agent such as a silane coupling agent or a titanate coupling agent. Magnet powder surface-treated with a coupling agent has high adhesion to the binder component. Surface treatment can be performed by directly surface-treating the magnet powder with the coupling agent. Alternatively, the binder component to which the coupling agent has been added may be kneaded with the magnet powder.

[0025] The proportion of rare earth iron-based magnet powder in the composition is preferably 80% by mass or more and 93% by mass or less. A magnet powder proportion of 80% by mass or more further improves the magnetic properties of the resulting rare earth bonded magnet. A magnet powder proportion of 93% by mass or less improves the melt fluidity during molding, thereby improving moldability. From the viewpoint of achieving both high magnetic properties and high moldability, a magnet powder proportion of 83% by mass or more and 92% by mass or less is preferable.

[0026] <Polyamide resin> The composition of this embodiment contains a polyamide resin as a binder component. Any known polyamide resin can be used as a binder component for bonded magnets. Examples include nylon resins such as nylon 11, nylon 12, nylon 6, nylon 66, and aromatic nylons. Among these, nylon 12, which has a low water absorption rate, is preferred. Furthermore, the weight-average molecular weight Mw of the polyamide resin is not particularly limited. However, increasing Mw appropriately improves the strength of the molded article (bonded magnet). Conversely, decreasing Mw appropriately suppresses the decrease in the fluidity of the composition during molding, thereby improving moldability. The weight-average molecular weight Mw of the polyamide resin is preferably 6,000 or more and 20,000 or less.

[0027] The proportion of polyamide resin in the binder component is 30% by mass or more and 60% by mass or less. If the proportion is less than 30% by mass, the surface of the molded article (bonded magnet) obtained from the composition will be eroded, resulting in appearance defects such as blistering. If the proportion exceeds 60% by mass, the permanent demagnetization rate of the bonded magnet will decrease significantly due to water absorption by the polyamide resin. In this specification, permanent demagnetization rate refers to the percentage by which the magnetic properties (magnetization) of the molded magnet product decrease due to oxidation of the magnet powder. It can also be said to be the percentage of the decrease in magnetic properties due to chemical changes in the magnet powder that will never return to its initial value. In this embodiment, the percentage of decrease in magnetic properties after the molded magnet product has been exposed to an 80°C LLC solution for 1000 hours is evaluated as the permanent demagnetization rate. From the viewpoint of more effectively suppressing the problems of appearance defects and decrease in permanent demagnetization rate, a proportion of polyamide resin of 30% by mass or more and 60% by mass or less is more preferable.

[0028] <Polypropylene resin> The composition of this embodiment contains polypropylene resin (PP) as a binder component. Polyamide resin is commonly used as a binder component in bonded magnet compositions used in injection molding. However, hydrophilic polyamide resins are hygroscopic. Therefore, molded articles (bonded magnets) containing only polyamide resin as a binder component may absorb moisture from the LLC (Long Life Coolant) and cause oxidation of the magnet powder. Unlike hydrophilic polyamide resins, polypropylene resin is hydrophobic. Therefore, by using polypropylene resin as a binder component, oxidation of the magnet powder can be suppressed.

[0029] The weight-average molecular weight Mw of the polypropylene resin is not particularly limited. However, increasing Mw appropriately improves the strength of the molded article (bonded magnet). Conversely, decreasing Mw appropriately suppresses the decrease in the fluidity of the composition during molding, thereby improving moldability. The weight-average molecular weight Mw of the polypropylene resin is preferably between 200,000 and 300,000. Note that the polypropylene resin is an unmodified polypropylene resin that has not undergone modification treatment such as acid modification.

[0030] The proportion of polypropylene resin in the binder component is, for example, 20% by mass or more and 60% by mass or less.

[0031] <Acid-modified polypropylene resin> The composition of this embodiment contains acid-modified polypropylene resin (acid-modified PP) as a binder component. Acid-modified polypropylene resin is obtained by grafting polypropylene resin with an acid component such as maleic anhydride, and the acid component is graft-bonded to the polypropylene main chain.

[0032] As mentioned above, using polypropylene resin as a binder component can suppress the oxidation of magnet powder. However, polypropylene resin is susceptible to damage from diethylene glycol contained in LLC. Therefore, molded articles (bonded magnets) containing only polypropylene resin are prone to surface defects such as blistering due to damage from diethylene glycol. Furthermore, polypropylene resin has low compatibility with polyamide resin, and molded articles containing only these two as binder components suffer from problems such as uncontrolled magnet powder oxidation and low mechanical strength.

[0033] Acid-modified polypropylene resin acts as a compatibilizer between polyamide resin and polypropylene resin. Therefore, by adding acid-modified polypropylene resin to polyamide resin and polypropylene resin, the affinity between hydrophilic polyamide resin and hydrophobic polypropylene resin is increased, making it possible to achieve both water resistance and LLC resistance.

[0034] The proportion of acid-modified polypropylene resin in the binder component is between 10% by mass and 20% by mass. If the proportion is less than 10% by mass, the compatibility between the polyamide resin and the polypropylene resin cannot be maintained. As a result, the mechanical strength of the molded product (bonded magnet) decreases. In addition, it is not possible to prevent the intrusion of moisture, leading to a decrease in the demagnetization rate. If the proportion exceeds 20% by mass, the fluidity of the composition during molding decreases, making it difficult to obtain a molded product (bonded magnet).

[0035] The functional groups present in acid-modified polypropylene resins are not limited. Examples of functional groups include carboxylic acid anhydride groups, carboxyl groups, hydroxyl groups, amino groups, and maleic anhydride groups.

[0036] The acid value of the acid-modified polypropylene resin is not particularly limited. However, moderately increasing the acid value further improves the compatibility between the polyamide resin and the polypropylene resin. This makes it possible to significantly improve water resistance and mechanical strength. Moderately lowering the acid value suppresses the decrease in fluidity of the composition during molding, thus improving moldability. The acid value of the acid-modified polypropylene resin is preferably 10 mg KOH / g or more and 50 mg KOH / g or less.

[0037] The weight-average molecular weight (Mw) of the acid-modified polypropylene resin is not particularly limited. However, increasing Mw appropriately further improves the compatibility between the polyamide resin and the polypropylene resin. This makes it possible to significantly improve water resistance and mechanical strength. Increasing Mw appropriately suppresses the decrease in the fluidity of the composition during molding, thereby improving moldability. The Mw of the acid-modified polypropylene resin is preferably between 10,000 and 200,000.

[0038] <Other ingredients> The total proportion of polyamide resin, polypropylene resin, and modified polypropylene resin in the binder component is 100% by mass or less. The binder component may contain only polyamide resin, polypropylene resin, and modified polypropylene resin. In this case, the total proportion is 100% by mass. On the other hand, other resins may be included as long as they do not impair the effects of this embodiment. The proportion of other resins may be, for example, 30% by mass or less, 20% by mass or less, or 10% by mass or less.

[0039] Furthermore, the bonded magnet composition may contain only the magnet powder and binder component, or it may contain other additive components as long as they do not impair the effects of this embodiment. Examples of such additive components include hydrophobic silane coupling agents. The amount of the additive component is preferably 5% by mass or less relative to the amount of the binder component.

[0040] <Liquidity> The bonded magnet composition of this embodiment exhibits good fluidity (Q value). 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 1 mm, an orifice length of 1 mm, and a preheating time of 300 seconds is preferably 0.8 cm³. 3 / sec (cc / sec) or more, more preferably 1.2cm 3 / second or more, more preferably 1.6cm 3 / second or more, particularly preferably 2.0cm 3 The fluidity is greater than / second. Increasing fluidity makes it possible to manufacture bonded magnets with superior magnetic properties, especially anisotropic bonded magnets. There is no particular upper limit on fluidity. However, typically the fluidity is 4.0 cm³. 3 It is less than / second.

[0041] <<2. Manufacturing of compositions for rare earth bonded magnets>> The rare-earth bond magnet composition of this embodiment is manufactured by using rare-earth iron-based magnet powder and binder components (polyamide resin, polypropylene resin, acid-modified polypropylene resin) as raw materials, and mixing and kneading them together.

[0042] The order in which the raw materials are added during mixing and kneading is not restricted. For example, the magnetic powder and binder components (polyamide resin, polypropylene resin, and acid-modified polypropylene resin) may be mixed and kneaded at the same time. Alternatively, the resin components (binder components) may be mixed and kneaded first, and then the magnetic powder may be added and the whole mixture may be mixed and kneaded. Some of the resin components and the magnetic powder may be mixed and kneaded, and then the remaining resin components may be added and the whole mixture may be mixed and kneaded. The following describes the case in which the magnetic powder and resin components (binder components) are mixed and kneaded at the same time.

[0043] <Raw material mixing process> In the raw material mixing process, magnet powder and various resins are uniformly mixed to obtain a raw material mixture. If the mixture is not uniform, the distribution of magnet powder and resin in the kneaded product (composition for bonded magnets) obtained by melt kneading will be uneven, which may cause fluctuations in magnetic properties. The raw material mixing process is performed using a mixer with an agitation mechanism or by manual stirring. There are no particular restrictions on the agitation mechanism, but a mixer equipped with various types of stirring blades can be used. The mixing time cannot be generalized as it depends on the processing volume, but it is generally between 5 and 30 minutes.

[0044] <Mixing process> In the kneading process, the raw material mixture is kneaded using kneading equipment such as a Banbury mixer, kneader, roll, single-screw extruder, and / or twin-screw extruder to produce a kneaded product. The kneading temperature should be such that the binder components (polyamide resin, polypropylene resin, acid-modified polypropylene resin) melt but do not decompose. Specifically, 170°C to 250°C is preferred. When using a batch-type kneading device, it is preferable to create an inert atmosphere inside the container. It is also preferable to control the rotation speed of the kneading blade and / or the kneading time while controlling the shear heat generated during kneading. When using a continuous-type kneading device, conditions such as the amount of raw material mixture added per time, the temperature of each zone, the shape of the screw segment, the screw rotation speed and / or the die hole diameter can be adjusted. It is also desirable to create an inert atmosphere in the hopper section. After the predetermined kneading is complete, the bond magnet composition is cooled to room temperature. At this time, it may be pelletized to a size that can be fed into a molding machine using equipment such as a plastic crusher or pelletizer.

[0045] <<3. Rare Earth Bonded Magnets>> The rare-earth bonded magnet of this embodiment (hereinafter sometimes simply referred to as "bonded magnet") is a molded body of a rare-earth bonded magnet composition. This bonded magnet is manufactured by injection molding or extrusion molding of the bonded magnet composition under heating. In other words, the bonded magnet is an injection-molded or extruded body. Specifically, the bonded magnet composition is heated and melted at a temperature above the melting point of each resin, which is a binder component contained therein, to form a molten material, and then the molten material is 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 no magnetic field is applied, an isotropic bonded magnet can be obtained.

[0046] Preferably, the bonded magnet is an injection-molded body. That is, the bonded magnet composition is injection-molded to produce the molded body. By employing the injection molding method, the degree of freedom in the shape of the molded bonded magnet can be greatly increased, and dimensional accuracy can be improved. Furthermore, the surface properties and magnetic properties of the bonded magnet become excellent. Therefore, the molded body (bonded magnet) can be incorporated directly into electronic components without any further processing.

[0047] The bonded magnet of this embodiment has excellent magnetic properties because it uses a precursor composition with excellent fluidity and moldability, and can be made thin and in complex shapes. Furthermore, it does not require post-processing and can be inserted into shape. Therefore, this bonded magnet is suitable for small, flat, and complexly shaped parts such as motor components for electronic equipment.

[0048] It is desirable to magnetize bonded magnets before use. Magnetization is performed using magnetization devices such as electromagnets that generate a static magnetic field or capacitor magnetizers that generate a pulsed magnetic field. The strength of the magnetization 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.

[0049] Since the bonded magnet of this embodiment is a molded body of the above-described composition, it has excellent resistance to water and LLC. [Examples]

[0050] The present invention will be described in more detail using the following examples and comparative examples. However, the present invention is not limited to the following examples.

[0051] (1) Composition for rare earth bonded magnets and preparation of rare earth bonded magnets [Example 1] SmFeN powder (manufactured by Sumitomo Metal Mining Co., Ltd., average particle size: 2.0 μm) was prepared as the magnetic powder. In addition, polyamide resin (manufactured by Ube Industries, Ltd., UBESTA P3012U, amine value: 0.96 mg KOH / g), polypropylene resin (manufactured by Nippon Polypropylene Co., Ltd., Novatec PP BC10HRF, Mw: 220,000), and acid-modified polypropylene resin (manufactured by Riken Vitamin Co., Ltd., Rikeaid MG-250P, acid value: 20 mg KOH / g) were prepared as binder components. The polyamide resin, polypropylene resin, and acid-modified polypropylene resin used in this example may be referred to by the abbreviations "PA12," "PP," and "acid-modified PP" below.

[0052] A composition for bonded magnets was prepared by blending and mixing prepared SmFeN powder with polyamide resin (PA12), polypropylene resin (PP), and acid-modified polypropylene resin (acid-modified PP). The resulting raw material mixture was kneaded at 200°C for 20 minutes using a batch-type kneader. The blending was carried out so that the proportion of SmFeN powder in the composition was 87.00% by mass, PA12 was 3.25% by mass, PP was 7.80% by mass, and acid-modified PP was 1.95% by mass. The proportion of PA12 in the binder components was 25% by mass, PP was 60% by mass, and acid-modified PP was 15% by mass.

[0053] Bond magnets were fabricated from the obtained bond magnet compositions. Specifically, the bond magnet compositions were injection-molded using an injection molding machine and an injection mold to produce cylindrical test pieces (bond magnet compacts) with an outer diameter of 20 mm and a thickness of 13 mm in accordance with JIS K7139A.

[0054] [Examples 2 to 27] The blending ratios of SmFeN powder, polyamide resin (PA12), polypropylene resin (PP), and acid-modified polypropylene resin (acid-modified PP) were changed as shown in Table 1 below. Otherwise, bond magnet compositions and bond magnets were produced in the same procedure as in Example 1.

[0055] (2) Evaluation Regarding the bond magnet compositions and bond magnets obtained in Examples 1 to 27, evaluations of various properties were conducted as follows.

[0056] <Flowability> The flowability of the bond magnet composition was measured using a flow tester (Shimadzu Corporation, CFT-100D). The measurement conditions were a capillary temperature of 250°C, a load of 588 N, an orifice diameter of 1 mm, an orifice length of 1 mm, and a preheating time of 300 seconds. If the flowability was 0.8 cc / second or more, it was judged that there was no problem with molding.

[0057] <LLC Resistance> The bond magnet compact (cylindrical test piece) was magnetized, and the total magnetic flux of the test piece was measured by the pull-out method using a search coil, which was designated as the initial magnetic flux A. Next, the test piece was immersed in LLC at 80°C and maintained for 1000 hours. LLC contained 50 mass% ethylene glycol, 47.7 to 50 mass% water, and other trace additives. After 1000 hours, the temperature of LLC was returned to room temperature, and after removing the LLC on the surface of the test piece, the magnetic flux B of the cylindrical test piece was measured. Then, the demagnetization rate C was determined according to the following formula (1) and used as an index for LLC resistance. Specifically, if the demagnetization rate C was greater than -2.00%, it was judged to have LLC resistance.

[0058]

Equation

[0059] <Appearance of the molded product> The appearance of bonded magnet molded bodies after 1000 hours of immersion in LLC was observed under a microscope to check for the presence of irregularities with a diameter of 1 mm or more and cracks. Molded bodies without irregularities or cracks were judged as "○", and those with irregularities or cracks were judged as "×".

[0060] (3) Evaluation results The evaluation results obtained for Examples 1 to 27 are summarized in Table 1 below. Furthermore, Figure 1 shows a microscopic image of the appearance of the bonded magnet molded body in Example 1 after 1000 hours of immersion in LLC.

[0061] Comparative examples (Examples 1, 5, 6, 8, 11, 13, 14, 16, 18-21, 25-27) that did not satisfy the requirements specified in this embodiment were inferior in terms of the fluidity of the composition, the appearance of the molded body (bonded magnet), or the demagnetization rate.

[0062] For example, in example 26, where only PA12 (polyamide resin) was used as the binder component, the demagnetization rate was low at -4.0%. In example 27, where only PP (polypropylene resin) was used as the binder component, the appearance of the molded product was "X".

[0063] Examples 8, 11, 14, and 18, which contained both PA and PP but had an excessively low amount of acid-modified PP (acid-modified polypropylene resin), had a low demagnetization rate of -2.2% or less. Examples 13, 16, and 24, which had an excessively high amount of acid-modified PP, had a low fluidity of 0.20 cc / second or less.

[0064] Examples 1, 6, and 21, which contained excessively low amounts of PA12, had an undesirable appearance for the molded body. For example, the molded body of Example 1 showed cracks and blistering after immersion in LLC (Figure 1). On the other hand, Examples 5, 19, 20, and 25, which contained excessively high amounts of PA12, had low fluidity of 0.30 cc / second or less. They also had low demagnetization rates of -3.0% or less.

[0065] In contrast, the example samples (Examples 2-4, 7, 9, 10, 12, 15, 17, 22-24) that satisfy the requirements specified in this embodiment were excellent in terms of composition fluidity, appearance of the molded body (bonded magnet), and demagnetization rate.

[0066] In particular, looking at the results of Examples 2-4 or 22-24, it was found that, for the same amount of magnetic powder, the lower the proportion of PA12 and the higher the proportion of PP in the binder component, the higher the fluidity of the molded body, although the appearance and demagnetization rate remained constant.

[0067] Figure 2 shows the relationship between the polyamide resin ratio and the properties (fluidity) of the bonded magnet composition obtained for Examples 6, 7, 12, 17, and 19. This figure shows the change in fluidity of the bonded magnet composition when the ratio of polyamide resin to polypropylene resin is changed while the ratios of magnet powder and acid-modified polypropylene resin are fixed at 89.00% by mass and 1.65% by mass, respectively. From Figure 2, it can be seen that the higher the proportion of polyamide resin, the lower the fluidity.

[0068] Figure 3 shows the relationship between the proportion of acid-modified polypropylene resin and the properties (fluidity, demagnetization rate) of the bonded magnet composition obtained for Examples 11 to 13. This figure shows the changes in fluidity and demagnetization rate of the magnet composition when the proportions of acid-modified polypropylene resin and polypropylene resin are changed, while the proportions of magnet powder and polyamide resin are fixed at 89.00% by mass and 4.95% by mass, respectively. From Figure 3, it can be seen that the higher the proportion of acid-modified polypropylene resin, the lower the fluidity and the higher the demagnetization rate (the smaller the absolute value of the demagnetization rate).

[0069] [Table 1]

[0070] From the above results, it is understood that this embodiment provides a rare-earth bonded magnet and its precursor (composition for rare-earth bonded magnets) that have excellent resistance to water and LLC.

Claims

1. A composition for rare earth bond magnets comprising rare earth iron-based magnet powder and a binder component, The binder component comprises a polyamide resin, a polypropylene resin, and an acid-modified polypropylene resin. A composition for rare earth bond magnets, wherein the proportion of the polyamide resin in the binder component is 30% by mass or more and 60% by mass or less, the proportion of the polypropylene resin is 20% by mass or more and 60% by mass or less, and the proportion of the acid-modified polypropylene resin is 10% by mass or more and 20% by mass or less.

2. The rare earth bond magnet composition according to claim 1, wherein the proportion of the rare earth iron-based magnet powder in the rare earth bond magnet composition is 80% by mass or more and 93% by mass or less.

3. A rare earth bonded magnet, which is a molded article of the rare earth bonded magnet composition according to claim 1 or 2.

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