Composition for bonded magnets, bonded magnets, and integrally molded parts

Abstract

To provide a composition for a bond magnet which has higher flowability than a conventional composition while maintaining durability against a cold heat impact test and adhesion, a bond magnet which is a molding of the composition for the bond magnet, and an integrally molded component having the bond magnet.SOLUTION: A composition for a bond magnet contains 88.0 mass% or more and 91.0 mass% or less of samarium-iron-nitrogen-based magnet powder having an average particle diameter of 1.7 μm or more and 2.8 μm or less, 3.0 mass% or more and 7.0 mass% or less of a polyamide elastomer having tensile breaking elongation of 400% or more and bending elastic modulus of 70 MPa or more, 0.5 mass% or more and 2.0 mass% or less of carbon fibers having a fiber diameter of 5 μm or more and 12 μm or less, 0.3 mass% or more and 1.0 mass% or less of carboxylate, 1.0 mass% or more and 8.0 mass% or less of a polyamide 12 resin having weight average molecular weight Mw in measurement of a molecular weight distribution of 4,500 or more and 7,500 or less, and has flowability measured using a flow tester under the conditions of 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 of 1.5 cm3 / second or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composition for bonded magnets, bonded magnets, and integrally molded parts. [Background technology]

[0002] Bonded magnets are manufactured by heating and kneading a composition containing magnetic powder and a binder component such as an organic resin in a kneader such as an extruder, then processing it into a pellet or other shape, and finally heating and molding it using methods such as injection molding, compression molding, or extrusion molding.

[0003] Bonded magnets offer advantages over sintered magnets, including higher dimensional accuracy and easier production of complex shapes. They also exhibit high uniformity in quality and performance, good yield, and excellent machinability. In particular, magnets manufactured by injection molding using thermoplastic resins such as polyamide or polyphenylene sulfide as binders have the advantage of high dimensional accuracy and the elimination of the need for post-processing, thus reducing manufacturing costs. Furthermore, bonded magnets containing rare-earth magnet powder exhibit superior magnetic properties (residual magnetic flux density Br, coercivity iHc, and maximum energy product (BH)max), resulting in strong magnetic force. Therefore, they can be miniaturized and have high performance, making them useful for applications such as small motors and sensors.

[0004] Bonded magnets are often used as integrally molded parts combined with metal components. Specifically, bonded magnets are combined with metal components using methods such as adhesive bonding or insert molding to create integrally molded parts, which are then used in this form. However, bonded magnets and metal components have different coefficients of thermal expansion. Therefore, when integrally molded parts are subjected to thermal shock testing, problems such as cracking of the bonded magnet or separation of the bonded magnet from the metal component due to adhesive peeling are likely to occur. To address this, a technology has been proposed to add additives to bonded magnets that do not adversely affect adhesion, such as polyamide elastomers or carbon fibers, to improve their durability against thermal shock testing.

[0005] For example, Patent Document 1 discloses a composition for bonded magnets containing a predetermined samarium-iron-nitrogen-based magnet powder, a polyamide elastomer, carbon fibers, a carboxylic acid ester, and a polyamide resin in predetermined proportions (Claim 1 of Patent Document 1). According to this composition for bonded magnets, the fluidity during molding is good and processing by injection molding, etc. is easy, the bonded magnets obtained from this composition have high durability against thermal shock tests and do not crack, and the bonded magnets are provided with excellent adhesion when bonded to metal parts, etc. via an adhesive (

[0015] of Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5979733 [Overview of the project] [Problems that the invention aims to solve]

[0007] The bonded magnet composition proposed in Patent Document 1 has some effect in terms of fluidity, durability against thermal shock tests, and adhesion, but there was room for further improvement. Specifically, depending on the application of the bonded magnet, the bonded magnet composition may be filled into a narrow cavity, in which case it is desirable to further increase the fluidity of the composition. However, because the bonded magnet composition in Patent Document 1 contains polyamide elastomer and carbon fibers, there were limitations in improving fluidity. Therefore, it was difficult to further increase fluidity while maintaining durability against thermal shock and adhesion.

[0008] In view of these problems, the inventors conducted thorough research. As a result, they found that by blending specific samarium-iron-nitrogen-based magnet powder, carbon fibers, carboxylic acid esters, and polyamide resins in predetermined proportions, and further combining them with a specific polyamide elastomer, it is possible to obtain a bonded magnet composition with improved fluidity while maintaining durability and adhesion to thermal shock tests.

[0009] This invention was completed based on such findings, and aims to provide a bonded magnet composition that has higher fluidity than conventional compositions while maintaining durability and adhesion to thermal shock tests. The invention also aims to provide a bonded magnet, which is a molded body of such a bonded magnet composition, and an integrally molded part equipped with a bonded magnet. [Means for solving the problem]

[0010] The present invention encompasses the following embodiments (1) to (5). In this specification, the expression "~" includes the values ​​at both ends. That is, "X~Y" is synonymous with "X or more and Y or less".

[0011] (1) Samarium-iron-nitrogen-based magnetic powder with an average particle size of 1.7 μm or more and 2.8 μm or less, in an amount of 88.0% to 91.0% by mass, A polyamide elastomer having a tensile elongation of 400% or more and a flexural modulus of 70 MPa or more is used in an amount of 3.0% to 7.0% by mass. Carbon fibers with a fiber diameter of 5 μm or more and 12 μm or less, in an amount of 0.5% to 2.0% by mass, Carboxylic acid ester in an amount of 0.3% by mass or more and 1.0% by mass or less, It contains polyamide 12 resin with a weight-average molecular weight Mw of 4500 or more and 7500 or less in a proportion of 1.0% to 8.0% by mass. Using a flow tester, the fluidity was measured at 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, resulting in a flow rate of 1.5 cm³. 3 A composition for bonded magnets that has a rate of 1 / second or more.

[0012] (2) The fluidity is 2.0 cm 3 / second or more, and the composition for bonded magnet of (1) above.

[0013] (3) The samarium-iron-nitrogen-based magnet powder has a composition represented by Sm2Fe 17 N3, and the composition for bonded magnet of (1) or (2) above.

[0014] (4) A bonded magnet which is a molded body of the composition for bonded magnet of (1) or (2) above.

[0015] (5) An integrally molded part including the bonded magnet of (4) above and a metal part. [Advantages of the Invention]

[0016] According to the present invention, there is provided a composition for bonded magnet having higher fluidity than conventional ones while maintaining durability and adhesiveness against a thermal shock test. Further, there are provided a bonded magnet which is a molded body of such a composition for bonded magnet, and an integrally molded part including the bonded magnet. [Modes for Carrying Out the Invention]

[0017] Specific embodiments 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 embodiments, and various modifications are possible without changing the gist of the present invention.

[0018] [<1. Composition for Bonded Magnet>] The bonded magnet composition of this embodiment contains 88.0% to 91.0% by mass of samarium-iron-nitrogen-based magnet powder with an average particle size of 1.7 μm to 2.8 μm, 3.0% to 7.0% by mass of polyamide elastomer having a tensile elongation of 400% or more and a flexural modulus of 70 MPa or more, 0.5% to 2.0% by mass of carbon fibers with a fiber diameter of 5 μm to 12 μm, 0.3% to 1.0% by mass of carboxylic acid ester, and 1.0% to 8.0% by mass of polyamide 12 resin having a weight-average molecular weight Mw of 4500 to 7500 as measured by molecular weight distribution measurement. Furthermore, the fluidity of this bonded magnet composition, as measured using a flow tester under the conditions of 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, was 1.5 cm³. 3 It is greater than / second.

[0019] A composition for bonded magnets (hereinafter sometimes simply referred to as "the composition") is a precursor for bonded magnets. That is, bonded magnets are manufactured by molding the composition under heating using methods such as injection molding or extrusion molding. Bonded magnets may be anisotropic or isotropic. If a magnetic field is applied to the composition during molding, an anisotropic magnet can be manufactured, and if no magnetic field is applied, an isotropic magnet can be obtained.

[0020] [1] Magnetic powder The bonded magnet composition of this embodiment contains samarium-iron-nitrogen (Sm-Fe-N; SFN)-based magnetic powder (hereinafter sometimes simply referred to as "magnetic powder"). Magnetic powder is the main component responsible for the magnetic properties of bonded magnets. Sm-Fe-N-based magnetic powder is a type of rare-earth transition metal-based magnetic powder and is known as a high-performance and inexpensive magnetic powder. Sm-Fe-N-based magnetic powder is composed of Sm2Fe 17 N x It has a basic composition represented by , and when x=3, that is, Sm2Fe 17 The saturation magnetization is maximized at the N3 composition. Therefore, it is possible to increase the magnetic flux density of the resulting bonded magnet. Consequently, Sm-Fe-N based magnet powder is Sm2Fe 17It is preferable that the composition be represented by N3.

[0021] The average particle size of the Sm-Fe-N magnetic powder is between 1.7 μm and 2.8 μm. Limiting the average particle size to 1.7 μm or larger suppresses the decrease in fluidity and moldability of the composition, and reduces the risk of oxidation of the magnetic powder and the resulting ignition. Furthermore, the Sm-Fe-N magnetic powder has a nucleation-type coercivity generation mechanism. Limiting the average particle size to 2.8 μm or smaller suppresses the decrease in coercivity.

[0022] The average particle size can be determined by observing the magnet powder with a scanning electron microscope (SEM). The magnet powder can be obtained by treating the bonded magnet composition with a solvent such as hexafluoroisopropanol to dissolve and remove the resin, and then removing the reinforcing agent by magnetic separation. Alternatively, the magnet powder used in the manufacture of the bonded magnet composition can be directly subjected to SEM observation. More specifically, the method can be carried out according to the example described later.

[0023] The content of Sm-Fe-N-based magnetic powder in the composition for bonded magnets is 88.0% by mass or more and 91.0% by mass or less. If the content is less than 88.0% by mass, the magnetic properties of the resulting bonded magnet will be lower. Also, because the resin content will be higher, the coefficient of linear expansion of the bonded magnet will be higher, resulting in increased cracking during thermal shock tests. On the other hand, if the content exceeds 91.0% by mass, the fluidity of the bonded magnet will be poor, making it difficult to mold the bonded magnet, or causing defects in the appearance of the molded product (bonded magnet), such as weld lines. The content of Sm-Fe-N-based magnetic powder is preferably 88.0% by mass or more and 90.0% by mass or less.

[0024] Methods for producing Sm-Fe-N magnetic powder include the dissolution method and the reduction-diffusion method. In the dissolution method, metal powders containing iron (Fe) and samarium (Sm) are used as raw materials, and these raw materials are heated and melted at a temperature of 1500°C or higher using a furnace such as a high-frequency furnace or an arc furnace. The resulting product is then pulverized and further heat-treated to homogenize the composition to produce an Sm-Fe master alloy. After that, the resulting master alloy is nitrided to produce magnetic powder.

[0025] In contrast, the reduction-diffusion method involves heating a mixture of samarium oxide (Sm2O3), iron raw materials (Fe, Fe2O3, etc.), and a reducing agent (Ca, etc.) to obtain a master alloy, which is then nitrided to produce magnetic powder. Sm-Fe-N magnetic powder has a nucleation-type coercivity generation mechanism. To obtain high coercivity, it is desirable to finely mill the powder. Therefore, it is desirable to prepare fine Sm-Fe-N magnetic powder by methods such as finely grinding the nitrided master alloy or using fine raw materials.

[0026] Preferably, Sm-Fe-N based magnetic powder produced by the reduction-diffusion method is used. The reduction-diffusion method, which uses inexpensive oxide raw materials (such as Sm2O3), has the advantage of keeping raw material costs down. In addition, it is possible to obtain magnetic powder with fewer impurities compared to the dissolution method. In contrast, the dissolution method is extremely complicated. Also, since the product is exposed to the atmosphere between each step, there is a risk that impurities will be generated on the surface of the product due to oxidation. If the surface of the product is oxidized, nitriding will not proceed uniformly, and the properties of the resulting magnetic powder, especially the magnetic properties such as saturation magnetization, coercivity, and / or prismaticity, will decrease, and there is a risk that the maximum energy product of the bonded magnet that is finally obtained will decrease.

[0027] In the reduction-diffusion method, first, a samarium raw material (Sm2O3), an iron raw material (Fe, etc.), and a reducing agent (Ca, etc.) are subjected to a reduction treatment to obtain a reduced product containing a Sm-Fe alloy. Next, this reduced product is subjected to a wet treatment to remove by-products (CaO, Ca(OH)2, etc.) derived from the reducing agent contained in the reduced product. Then, the obtained Sm-Fe alloy is nitrided in a mixed gas stream containing ammonia and hydrogen. By pulverizing and drying the obtained nitride, Sm-Fe-N-based magnet powder can be obtained.

[0028] When the Sm-Fe-N-based magnet powder is composed of a Sm2Fe 17 N3-based alloy, it is desirable to pulverize the coarse powder first. That is, since the magnet alloy coarse powder with an average particle size exceeding 20 μm has low magnetic properties, it is desirable to pulverize it in an organic solvent. During this pulverization or after pulverization, the magnet powder may be put into and stirred in a solution containing a surface treatment agent such as phosphoric acid to provide a coating such as a composite phosphate coating on the surface of the magnet powder. For pulverization, a known pulverization device applicable to magnet powder pulverization may be used. Among these, wet pulverization devices such as a medium stirring mill and a bead mill are particularly suitable because they are likely to obtain a uniform powder composition and particle size. Also, as the pulverization solvent, organic solvents such as isopropyl alcohol, ethanol, toluene, methanol, and hexane are preferable. After pulverization, filtration and drying may be performed using a filter with a predetermined mesh size.

[0029] The Sm-Fe-N-based magnet powder may be surface-treated with a coupling agent. Examples of the coupling agent include a silane-based coupling agent, a titanium-based coupling agent, an aluminum-based coupling agent, etc., and it is particularly preferable to perform surface treatment with a silane-based coupling agent.

[0030] [2] Thermoplastic resin binder The composition for bonded magnets of the present embodiment contains a polyamide elastomer and a polyamide 12 resin as the thermoplastic resin binder. The thermoplastic binder is plasticized when heated during kneading or molding to impart fluidity to the composition. Also, it solidifies when cooled after molding. Therefore, it functions to bind the magnet powder and maintain the shape retention of the bonded magnet.

[0031] (A) Polyamide elastomer As the polyamide elastomer, one having polyamide segments and polyether segments can be used. In addition, in the bonded magnet composition of this embodiment, a polyamide elastomer having a tensile elongation of 400% or more and a flexural modulus of 70 MPa is used. By using a polyamide elastomer with such tensile elongation and flexural modulus, the fluidity of the bonded magnet composition can be improved and cracking during thermal shock tests can be effectively prevented. The tensile elongation is measured according to the method specified in ISO 527, and the flexural modulus is measured according to the method specified in ISO 178.

[0032] The polyamide elastomer content in the bonded magnet composition is 3.0% by mass or more and 7.0% by mass or less. When the polyamide elastomer content is within this range, the fluidity of the bonded magnet composition is improved, and cracking of the resulting bonded magnets during thermal shock tests can be effectively prevented.

[0033] (B) Polyamide 12 resin Polyamide 12 resin is used as the polyamide resin. Generally, various polyamide resins such as polyamide 11 and polyamide 6 are known. However, by using polyamide 12 resin, the fluidity of the bonded magnet composition is improved, and moldability can be enhanced. Furthermore, by using polyamide 12 resin, it is possible to further increase the strength of the resulting bonded magnet.

[0034] In the bonded magnet composition of this embodiment, a polyamide 12 resin is used in which the weight-average molecular weight Mw measured by molecular weight distribution measurement is in the range of 4500 to 7500. If the Mw of the polyamide 12 resin is less than 4500, the mechanical strength of the resulting bonded magnet may decrease. On the other hand, if the Mw exceeds 7500, the fluidity of the bonded magnet composition may decrease significantly, making molding difficult. It is conceivable to mold at high temperatures to increase fluidity, but in that case, the magnet powder may oxidize, making it difficult to obtain a bonded magnet with excellent magnetic properties. By using a polyamide 12 resin with an appropriate Mw, it becomes possible to obtain a bonded magnet composition with high fluidity even at low temperatures. Mw is preferably between 5000 and 6000. The weight-average molecular weight Mw is determined by molecular weight distribution measurement under conditions similar to those in the examples.

[0035] The polyamide 12 resin content in the bonded magnet composition is preferably 1.0% by mass or more and 8.0% by mass or less. If the content is less than 1.0% by mass, the fluidity of the bonded magnet composition will be poor, which may make molding difficult. On the other hand, if the content exceeds 8.0% by mass, the coefficient of linear expansion of the bonded magnet will be large, which may cause cracking in thermal shock tests. The polyamide 12 resin content is more preferably 1.5% by mass or more and 4.0% by mass or less.

[0036] [3] Strengthening agent The bonded magnet composition of this embodiment contains carbon fibers as a reinforcing agent. Generally, various reinforcing agents such as carbon flakes and glass fibers are known. However, by using carbon fibers, the tensile strength of the resulting bonded magnet can be effectively increased. In the bonded magnet composition of this embodiment, carbon fibers with a fiber diameter of 5 μm to 12 μm are used. By including carbon fibers with such a fiber diameter, it is possible to increase the strength of the bonded magnet, increase the fluidity of the composition, and improve moldability. From the viewpoint of increasing strength, a fiber diameter of 5 μm to 8 μm is preferred for the carbon fibers.

[0037] The carbon fiber (reinforcement agent) content in the bonded magnet composition is 0.5% by mass or more and 2.0% by mass or less. If the content is less than 0.5% by mass, the strength of the bonded magnet will be insufficient, and cracking may occur in thermal shock tests. On the other hand, if the content exceeds 2.0% by mass, the fluidity of the bonded magnet composition will deteriorate, and molding of the bonded magnet may become difficult. From the viewpoint of suppressing cracking in thermal shock tests, a carbon fiber content of 0.7% by mass or more is preferable. Furthermore, from the viewpoint of improving fluidity, a carbon fiber content of 1.5% by mass or less is preferable.

[0038] [4] Additives The bonded magnet composition of this embodiment contains a carboxylic acid ester as an additive. Examples of carboxylic acid esters include sebacate ester and / or adibate ester. Generally, additives such as lubricants represented by hydrocarbons or fatty acids, and plasticizers made from various esters are used to improve fluidity during molding. However, by using carboxylic acid esters such as sebacate ester and adibate ester, high adhesive strength can be ensured when the resulting bonded magnet and metal parts are bonded together, for example, via an adhesive such as an epoxy adhesive.

[0039] The content of carboxylic acid ester (additive) in the composition for bonded magnets is 0.3% by mass or more and 1.0% by mass or less. If the content is less than 0.3% by mass, sufficient adhesive strength cannot be obtained between the bonded magnet and metal parts, although the mechanism is not clear. On the other hand, if the content exceeds 1.0% by mass, there is a risk of cracking in the bonded magnet during thermal shock testing. From the viewpoint of improving adhesive strength, a carboxylic acid ester content of 0.5% by mass or more is preferable. From the viewpoint of suppressing cracking during thermal shock testing, a carboxylic acid ester content of 0.8% by mass or less is preferable.

[0040] [5] Other ingredients The bonded magnet composition of this embodiment may contain only magnet powder, polyamide elastomer, polyamide 12 resin, carbon fiber, and carboxylic acid ester, or it may contain other components. Other components include antioxidants, stabilizers, pigments, and / or compatibilizers. The bonded magnet composition may contain these components as needed, to the extent that it does not impair its effect.

[0041] [6] Liquidity The bonded magnet composition of this embodiment has a fluidity of 1.5 cm². 3 The fluidity is 2.0 cm² or more. Here, the fluidity is the value 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°C. The bonded magnet composition of this embodiment has excellent moldability due to its high fluidity. Therefore, thin-shaped and complex-shaped bonded magnets can be easily obtained without post-processing. Furthermore, the amount of magnet powder in the composition can be increased while maintaining a highly dispersed state, and even with the same content, the orientation of the magnet powder can be improved. Moreover, it is not necessary to perform molding at high temperatures to increase fluidity. Low-temperature molding becomes possible, so the deterioration of the magnetic properties of the magnet powder can be suppressed. As a result of the combined action of these factors, it becomes possible to manufacture bonded magnets with excellent magnetic properties, especially anisotropic bonded magnets. Higher fluidity is desirable, 2.0 cm². 3 Preferably 2.5 cm / second or more. 3 A flow rate of 4.0 cm / second or higher is even more preferable. On the other hand, compositions with excessively high fluidity are difficult to manufacture. The typical fluidity is 4.0 cm / second. 3 It is less than / second.

[0042] The composition for bonded magnets in this embodiment is preferably manufactured by combining a predetermined amount of amino-terminated polyamide elastomer (polyamide elastomer without terminal amino groups) and a predetermined amount of unterminated polyamide elastomer (polyamide elastomer with terminal amino groups). Specifically, it is preferable that the product is manufactured by mixing and kneading the following in proportions: 88.0% to 91.0% by mass of samarium-iron-nitrogen-based magnetic powder with an average particle size of 1.7 μm to 2.8 μm; 1.0% to 2.5% by mass of a polyamide elastomer with terminal amino groups having a tensile elongation of 400% or more and a flexural modulus of 100 MPa or more; 2.0% to 4.5% by mass of a polyamide elastomer without terminal amino groups having a tensile elongation of 400% or more and a flexural modulus of 70 MPa or more; 0.5% to 2.0% by mass of carbon fibers with a fiber diameter of 5 μm to 12 μm; 0.3% to 1.0% by mass of carboxylic acid ester; and 1.0% to 8.0% by mass of polyamide 12 resin having a weight-average molecular weight Mw of 4500 to 7500 as measured by molecular weight distribution analysis.

[0043] By combining predetermined amounts of polyamide elastomer without terminal amino groups and polyamide elastomer with terminal amino groups, a bonded magnet composition with excellent fluidity can be obtained while maintaining durability and adhesion to thermal shock tests. In contrast, when using only polyamide elastomer with terminal amino groups, or only polyamide elastomer without terminal amino groups, it is difficult to obtain a bonded magnet composition with excellent fluidity while maintaining durability and adhesion to thermal shock tests.

[0044] Thus, in obtaining the bonded magnet composition of this embodiment, it is important to combine predetermined amounts of polyamide elastomer without terminal amino groups and polyamide elastomer with terminal amino groups. However, in the obtained bonded magnet composition, it is difficult to distinguish between the polyamide elastomer with terminal amino groups and the polyamide elastomer without terminal amino groups and to determine the amount of each by measurement. Therefore, in this embodiment, the bonded magnet is identified using fluidity as an indicator.

[0045] <<2. Method for Manufacturing Compositions for Bonded Magnets>> In the method for producing the bonded magnet composition of this embodiment, predetermined amounts of components such as magnet powder, polyamide elastomer, polyamide 12 resin, carbon fiber, carboxylic acid ester, and optionally antioxidant are weighed out, and these components are mixed in a mixer such as a stirring mixer, and then kneaded using a kneading device.

[0046] Details of the magnetic powder, polyamide 12 resin, carbon fibers, carboxylic acid ester, and other components are as described above. Specifically, samarium-iron-nitrogen (Sm-Fe-N) magnetic powder with an average particle size of 1.7 μm to 2.8 μm is blended in a proportion of 88.0% to 91.0% by mass. Polyamide 12 resin with a weight-average molecular weight Mw of 4500 to 7500 as measured by molecular weight distribution is blended in a proportion of 1.0% to 8.0% by mass. Carbon fibers with a fiber diameter of 5 μm to 12 μm are blended in a proportion of 0.5% to 2.0% by mass. Carboxylic acid ester is blended in a proportion of 0.3% to 1.0% by mass. If necessary, components such as antioxidants, stabilizers, pigments, and compatibilizers may be blended in a range that does not impair the effect of the bonded magnet composition.

[0047] As a polyamide elastomer, a combination of polyamide elastomers having amino groups at the ends (terminal amino group polyamide elastomer) and polyamide elastomers without amino groups at the ends (terminal amino group-free polyamide elastomer) is used. Conventional polyamide elastomers have amino groups at their ends. These terminal groups (amino groups) interact with the magnetic powder in the composition, which can increase the viscosity of the composition (thickening). By using terminal amino group-free polyamide elastomer in part, it is possible to suppress the interaction with the magnetic powder and reduce the effects such as thickening.

[0048] As the terminal amino group polyamide elastomer, one having polyamide segments and polyether segments can be used. Furthermore, it is preferable to use a terminal amino group polyamide elastomer with a tensile elongation of 400% or more and a flexural modulus of 100 MPa or more. By using a polyamide elastomer with such tensile elongation and modulus, it is possible to effectively prevent cracking during thermal shock tests of bonded magnets.

[0049] The amount of polyamide elastomer with terminal amino groups is preferably 1.0% by mass or more and 2.5% by mass or less. If the amount is less than 1.0% by mass, cracking is more likely to occur in thermal shock tests. On the other hand, if the amount exceeds 2.5% by mass, the fluidity of the bonded magnet composition decreases, making it difficult to mold the bonded magnets. Polyamide elastomer with terminal amino groups usually has an amino group concentration of more than 0.2 mgKOH / g.

[0050] As a terminal amino group-free polyamide elastomer, one having polyamide segments and polyether segments can be used. Furthermore, it is preferable to use a terminal amino group-free polyamide elastomer with a tensile elongation of 400% or more and a flexural modulus of 70 MPa or more. By using a polyamide elastomer with such tensile elongation and modulus, it is possible to achieve both the effect of improving the fluidity of the bonded magnet composition and the effect of suppressing crack occurrence in the thermal shock test of the bonded magnet.

[0051] The amount of polyamide elastomer without terminal amino groups is preferably 2.0% by mass or more and 4.5% by mass or less. If the amount is less than 2.0% by mass, the effect of improving fluidity is small, while if the amount exceeds 4.5% by mass, cracking of the bonded magnet is more likely to occur in the thermal shock test. Polyamide elastomer without terminal amino groups can be determined by heating polyamide elastomer with terminal amino groups together with a saturated fatty acid such as stearic acid under an inert gas at about 300°C. Polyamide elastomer without terminal amino groups usually has an amino group concentration of 0.2 mg KOH / g or less.

[0052] The shape of the thermoplastic resin binder (polyamide elastomer and polyamide 12 resin) added during mixing and kneading is not particularly limited. For example, various shapes such as powder, beads, and pellets can be used. Among these, powder form is preferred from the viewpoint of uniform mixing with the magnet powder.

[0053] The mixing and kneading of the raw materials can be carried out by known methods. The kneading apparatus is not particularly limited, and for example, a batch-type kneader or a continuous-type extruder can be used. When kneading, it is preferable to control the shear force applied to the composition during kneading within the kneading apparatus. For example, when using a kneader, the shear force can be controlled by adjusting conditions such as temperature, the amount of raw materials put into the mixing tank, the rotation speed of the kneading blades, or the kneading time. When using a continuous extruder, the shear force can be controlled by adjusting conditions such as temperature distribution, raw material input speed, screw segment shape, screw rotation speed, and die bore diameter.

[0054] <<3. Bonded Magnets>> The bonded magnet of this embodiment is a molded body of the bonded magnet composition described above. That is, the bonded magnet is manufactured by molding the bonded magnet composition. Specifically, the bonded magnet is manufactured by heating and melting the bonded magnet composition at a temperature above the melting point of its constituent resin binder, and then molding the resulting molten material. Molding can be carried out by known methods such as injection molding, extrusion molding, or compression molding. If molded in a magnetic field, an anisotropic bonded magnet can be obtained, and if molded in a non-magnetic field, an isotropic bonded magnet can be obtained. Since polyamide 12 resin is used, the heating and melting temperature is preferably in the range of 200°C to 250°C.

[0055] Among the molding methods described above, injection molding is particularly preferred for molding bonded magnets. Injection molding allows for a high degree of freedom in the shape of the molded bonded magnet, and also results in a bonded magnet with excellent surface properties and magnetic properties. Therefore, the resulting bonded magnet can be directly incorporated as a component of an electronic device. The bonded magnet composition described above has good fluidity and excellent moldability in injection molding, making it easy to mold bonded magnets. Furthermore, it effectively prevents the occurrence of surface defects such as welds during injection molding.

[0056] The bonded magnets obtained in this way have excellent magnetic properties and high durability against thermal shock tests, making them less prone to cracking. Therefore, they have excellent mechanical strength. These bonded magnets are used, for example, in small, flat, and complexly shaped parts such as motor components for electronic equipment. They also have the advantages of being mass-producible, requiring no post-processing, and being insert-molded. For these reasons, bonded magnets are particularly suitable for integrally molded parts with metal materials.

[0057] It is desirable to magnetize the resulting bonded magnets before use. For magnetization, electromagnets that generate a static magnetic field or capacitor magnetizers that generate a pulsed magnetic field are used. The magnetization magnetic field, i.e., the magnetic field strength during magnetization, varies slightly depending on the type of magnetic powder, so it cannot be determined in general terms. For example, it should be 1200 kA / m (15 kOe) or more, preferably 2400 kA / m (30 kOe) or more.

[0058] <<4. One-piece molded parts>> The integrally molded part of this embodiment comprises the bonded magnet and the metal part described above. The bonded magnet can be integrated with the metal part by bonding via an adhesive or by insert molding, thereby enabling the manufacture of an integrally molded part. The integrally molded part can be manufactured by known methods. For example, it can be manufactured by applying a predetermined adhesive to the bonding surfaces of the bonded magnet and the metal part, pressing them together, and holding them at room temperature for 12 to 24 hours.

[0059] Conventional bonded magnet materials have a coefficient of thermal expansion different from that of metal parts. Therefore, when integrally molded parts are manufactured using these bonded magnet materials and subjected to thermal shock tests, cracks are likely to occur in the bonded magnets. In contrast, the bonded magnet of this embodiment has excellent mechanical strength, so it can effectively prevent cracking of the bonded magnet in integrally molded parts. Furthermore, when the bonded magnet of this embodiment is bonded to an integrally molded part using an adhesive such as an epoxy adhesive, it can provide excellent adhesion to metal parts without weakening the adhesive strength. [Examples]

[0060] 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.

[0061] (1) Preparation of a composition for bonded magnets [Example 1] A composition for bonded magnets was prepared by weighing 90.0% by mass of samarium-iron-nitrogen (Sm-Fe-N;SFN) magnetic powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size of 2.3 μm, 2.2% by mass of polyamide 12 resin with a weight-average molecular weight Mw of 5300, 1.9% by mass of polyamide elastomer with terminal amino groups, 4.3% by mass of polyamide elastomer without terminal amino groups, 0.9% by mass of carbon fiber (C fiber) with a fiber diameter of 6 μm as a reinforcing agent, and 0.7% by mass of sebacate ester as an additive, and then mixing them in a stirring mixer and kneading at 200°C using a continuous extruder. The polyamide elastomer with terminal amino groups had a tensile elongation at break of 530% and a flexural modulus of 130 MPa. Furthermore, the polyamide elastomer without terminal amino groups had a number-average molecular weight of 15,000, an amino group concentration of 0.2 mg KOH / g or less, a tensile elongation at break of 400% or more, and a flexural modulus of 70 MPa or more.

[0062] The average particle size of the magnetic powder was measured as follows. First, the magnetic powder was observed using a scanning electron microscope (JEOL Ltd., JSM-IT200; SEM) to obtain an SEM image. The observation was performed at a magnification of 2000x or higher. Next, image analysis was performed on 1000 particles in the obtained SEM image to determine the volume-based particle size distribution. Then, xd50 was determined as the average particle size from the obtained particle size distribution.

[0063] The tensile elongation at break of the polyamide elastomer was measured according to the method specified in ISO 527, and the flexural modulus was measured according to the method specified in ISO 178. The weight-average molecular weight Mw of the polyamide 12 resin was measured using hexafluoroisopropanol as the eluent and an analyzer: GPC-104 (manufactured by Shoko Scientific Co., Ltd.) with an RI detector, and the weight-average molecular weight is shown converted to polymethyl methacrylate.

[0064] [Example 2] A carbon fiber (C fiber) with a fiber diameter of 11 μm was used as a reinforcing agent. Otherwise, the composition for bonded magnets was prepared in the same manner as in Example 1.

[0065] [Example 3] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 1.1% by mass, and the amount of carbon fiber (C fiber) with a fiber diameter of 6 μm, which is used as a reinforcing agent, was changed to 2.0% by mass. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0066] [Example 4] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 2.6% by mass, and the amount of carbon fiber (C fiber) with a fiber diameter of 6 μm, which is used as a reinforcing agent, was changed to 0.5% by mass. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0067] [Example 5] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 1.9% by mass, and the amount of the additive sebacate ester was changed to 1.0% by mass. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0068] [Example 6] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 2.6% by mass, and the amount of the additive sebacate ester was changed to 0.3% by mass. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0069] [Example 7] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 2.0% by mass, and the amount of polyamide elastomer without terminal amino groups was changed to 4.5% by mass. The polyamide elastomer without terminal amino groups had a number-average molecular weight of 15000, an amino group concentration of 0.2 mgKOH / g or less, a tensile elongation at break of 400% or more, and a flexural modulus of 70 MPa or more. Otherwise, the composition for bonded magnets was prepared in the same manner as in Example 1.

[0070] [Example 8] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 4.5% by mass, and the amount of polyamide elastomer without terminal amino groups was changed to 2.0% by mass. The polyamide elastomer without terminal amino groups had a number-average molecular weight of 15000, an amino group concentration of 0.2 mgKOH / g or less, a tensile elongation at break of 400% or more, and a flexural modulus of 70 MPa or more. Otherwise, the composition for bonded magnets was prepared in the same manner as in Example 1.

[0071] [Example 9] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 1.6% by mass, and the amount of polyamide elastomer with terminal amino groups was changed to 2.5% by mass. The polyamide elastomer with terminal amino groups had a tensile elongation at break of 530% and a flexural modulus of 130 MPa. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0072] [Example 10] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 3.1% by mass, and the amount of polyamide elastomer with terminal amino groups was changed to 1.0% by mass. The polyamide elastomer with terminal amino groups had a tensile elongation at break of 530% and a flexural modulus of 130 MPa. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0073] [Example 11] The amount of samarium-iron-nitrogen (Sm-Fe-N) magnetic powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size of 2.3 μm was changed to 91.0% by mass, the amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 4.4% by mass, the amount of polyamide elastomer with terminal amino groups was changed to 1.0% by mass, and the amount of polyamide elastomer without terminal amino groups was changed to 2.0% by mass. The polyamide elastomer with terminal amino groups had a tensile elongation at break of 530% and a flexural modulus of 130 MPa. The polyamide elastomer without terminal amino groups had a number-average molecular weight of 15000, an amino group concentration of 0.2 mg KOH / g or less, a tensile elongation at break of 400% or more, and a flexural modulus of 70 MPa or more. Otherwise, the composition for bonded magnets was prepared in the same manner as in Example 1.

[0074] [Example 12] The amount of samarium-iron-nitrogen (Sm-Fe-N) magnetic powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size of 2.3 μm was changed to 88.0% by mass, the amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 3.4% by mass, the amount of polyamide elastomer with terminal amino groups was changed to 2.5% by mass, and the amount of polyamide elastomer without terminal amino groups was changed to 4.5% by mass. The polyamide elastomer with terminal amino groups had a tensile elongation at break of 530% and a flexural modulus of 130 MPa. The polyamide elastomer without terminal amino groups had a number-average molecular weight of 15000, an amino group concentration of 0.2 mg KOH / g or less, a tensile elongation at break of 400% or more, and a flexural modulus of 70 MPa or more. Otherwise, the composition for bonded magnets was prepared in the same manner as in Example 1.

[0075] [Example 13] Adipic acid ester was used as an additive. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0076] [Comparative Example 1] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 0.6% by mass, and the amount of carbon fiber with a fiber diameter of 6 μm, which is used as a reinforcing agent, was changed to 2.5% by mass. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0077] [Comparative Example 2] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 2.8% by mass, and the amount of carbon fiber with a fiber diameter of 6 μm, which is used as a reinforcing agent, was changed to 0.3% by mass. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0078] [Comparative Example 3] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 1.7% by mass, and the amount of the additive sebacate ester was changed to 1.2% by mass. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0079] [Comparative Example 4] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 2.7% by mass, and the amount of the additive sebacate ester was changed to 0.2% by mass. Otherwise, a composition for bonded magnets was prepared in the same manner as in Example 1.

[0080] [Comparative Example 5] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 4.7% by mass, and the amount of polyamide elastomer without terminal amino groups was changed to 1.8% by mass. The polyamide elastomer without terminal amino groups had a number-average molecular weight of 15000, an amino group concentration of 0.2 mgKOH / g or less, a tensile elongation at break of 400% or more, and a flexural modulus of 70 MPa or more. Otherwise, the composition for bonded magnets was prepared in the same manner as in Example 1.

[0081] [Comparative Example 6] The amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 1.1% by mass, and the amount of polyamide elastomer with terminal amino groups was changed to 3.0% by mass. The polyamide elastomer with terminal amino groups had a tensile elongation at break of 530% and a flexural modulus of 130 MPa. Otherwise, the composition for bonded magnets was prepared in the same manner as in Example 1.

[0082] [Comparative Example 7] The amount of samarium-iron-nitrogen (Sm-Fe-N) magnetic powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size of 2.3 μm was changed to 91.3% by mass, and the amount of polyamide 12 resin with a weight-average molecular weight Mw of 5300 was changed to 0.9% by mass. Otherwise, a bonded magnet composition was prepared in the same manner as in Example 1.

[0083] [Comparative Example 8] A composition for bonded magnets was obtained by mixing 90.0% by mass of samarium-iron-nitrogen (Sm-Fe-N) magnetic powder with an average particle size of 2.3 μm, manufactured by Sumitomo Metal Mining Co., Ltd., 6.2% by mass of polyamide 12 resin with a weight-average molecular weight Mw of 5300, 2.0% by mass of a polyamide elastomer with terminal amino groups having a tensile elongation at break of 530% and a flexural modulus of 130 MPa, 1.0% by mass of carbon fiber (C fiber) with a fiber diameter of 11 μm as a reinforcing agent, and 0.8% by mass of sebacate ester as an additive, using a stirring mixer, mixing at 200°C with a continuous extruder.

[0084] (2) Evaluation The various properties of the bond magnet compositions obtained in Examples 1 to 13 and Comparative Examples 1 to 8 were evaluated as follows.

[0085] <Liquidity> The fluidity of the bond magnet composition was measured using a melt indexer flow tester (Shimadzu Corporation, CTF-100D). The measurement was performed under the following conditions: capillary temperature 250°C, load 588N, orifice diameter 1mm, orifice length 1mm, and preheating time 300 seconds.

[0086] <Heat shock test durability> A bonded magnet composition was injection molded to produce a ring-shaped bonded magnet, and its thermal shock resistance was evaluated. Injection molding was performed at a molding temperature of 240°C with four pinpoint gates. The resulting bonded magnet had an outer diameter of 32 mm, an inner diameter of 30 mm, and a height of 20 mm. Next, the resulting bonded magnet was bonded to the inside of an iron ring with an outer diameter of 34 mm, an inner diameter of 32 mm, and a height of 22 mm using epoxy resin to create a single molded part.

[0087] The resulting integrally molded parts were held at room temperature for 24 hours, and then subjected to a thermal shock test with a cycle of -40°C for 30 minutes to +90°C for 30 minutes. After 300 and 600 cycles, the bonded magnets of the integrally molded parts were observed with a 20x magnification optical microscope to check for any defects such as cracks in the bonded magnets. Ten test samples were evaluated, and the thermal shock test durability was determined according to the following criteria.

[0088] ◎: 0 defects after 600 cycles ○: After 300 cycles, the number of defects is 0, and after 600 cycles, the number of defects is 1 or more. ×: One or more defects after 300 cycles

[0089] <Adhesive strength (adhesion)> For the integrally molded parts evaluated in the thermal shock test (600 cycles) described above, the bond strength was measured by pulling out a bonded magnet attached to an iron ring using an iron shaft with a diameter of 31.5 mm. Measurements were taken for 10 test samples, the average value was calculated, and the adhesion was determined according to the following criteria.

[0090] ◎: Average adhesive strength of 1000N or higher ×: Average adhesive strength is less than 1000N

[0091] (3) Evaluation results The evaluation results obtained for Examples 1-13 and Comparative Examples 1-8 are shown in Tables 1 and 2 below.

[0092] As shown in Table 1, the bond magnet composition of Example 1 has a fluidity of 2.5 cm³. 3 The temperature was extremely high at [number] cycles. Furthermore, in thermal shock tests, zero defects were found even after 600 cycles, demonstrating excellent durability. In addition, the adhesive strength to the iron ring was over 1000N, indicating excellent adhesion to metal parts.

[0093] The bond magnet compositions of Examples 2-13 have a fluidity of 1.5 cm³. 3 The fluidity was high, exceeding 3.0 cm² / g. In particular, the bond magnet composition of Example 10 had a fluidity of 3.0 cm². 3 The value was extremely high at / g. Furthermore, in all cases, zero defects were found even after 300 cycles of thermal shock testing. In addition, the adhesive strength to the iron ring was over 1000N.

[0094] In contrast, as shown in Table 2, the bond magnet compositions of Comparative Examples 1 and 5-8 have a fluidity of 1.4 cm³. 3 The fluidity was low, less than 2.0 cm². Furthermore, the bonded magnet compositions of Comparative Examples 2 and 3 did not sufficiently reinforce the bonded magnets obtained from them, and cracking occurred in the thermal shock test. The bonded magnet composition of Comparative Example 4 had a fluidity of 2.0 cm². 3 Although the bond strength was high at / g, the adhesive strength between the obtained bonded magnets and the iron rings was low, and it was not possible to obtain samples with an adhesive strength of 1000N or more.

[0095] [Table 1]

[0096] [Table 2]

[0097] From the above results, it is understood that the bonded magnet composition of this embodiment has higher fluidity than conventional compositions while maintaining durability and adhesion to thermal shock tests. [Industrial applicability]

[0098] The bonded magnet composition of this embodiment exhibits high fluidity during molding, and the resulting bonded magnets show excellent durability in thermal shock tests. Furthermore, it can impart excellent adhesion to the bonded magnets when bonded to metal parts using an adhesive. Therefore, it is extremely useful as a manufacturing composition for bonded magnets. Bonded magnets obtained from this composition can be used, for example, in small, flat, and complexly shaped parts such as motor components for electronic equipment. These bonded magnets can also be mass-produced. They also have the advantage of requiring no post-processing and being suitable for insert molding. They are particularly suitable for use as molded parts combined with metal components.

Claims

1. Samarium-iron-nitrogen-based magnetic powder with an average particle size of 1.7 μm or more and 2.8 μm or less, in an amount of 88.0% to 91.0% by mass. A polyamide elastomer having a tensile elongation of 400% or more and a flexural modulus of 70 MPa or more, in an amount of 3.0% to 7.0% by mass. Carbon fibers with a fiber diameter of 5 μm or more and 12 μm or less, in an amount of 0.5% to 2.0% by mass, Carboxylic acid ester in an amount of 0.3% by mass or more and 1.0% by mass or less, It contains polyamide 12 resin with a weight-average molecular weight Mw of 4500 or more and 7500 or less in a proportion of 1.0% to 8.0% by mass. Using a flow tester, the fluidity was measured at 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, resulting in a flow rate of 1.5 cm³. ３ A composition for bonded magnets with a frequency of 1 / second or more.

2. The aforementioned fluidity is 2.0 cm ３ The bond magnet composition according to claim 1, wherein the value is 1 / second or more.

3. The samarium-iron-nitrogen-based magnetic powder is Sm ２ Fe １７ N ３ A composition for bonded magnets according to claim 1 or 2, having the composition represented by [the formula shown].

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

5. A one-piece molded part comprising a bonded magnet and a metal part as described in claim 4.

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