Resin composition for bonded magnet and bonded magnet using same

Abstract

According to the present embodiment, a resin composition for a bonded magnet can be provided with the resin composition exhibiting excellent impact resistance and thermal shock resistance without a reduction in magnetic properties.　The provided resin composition for a bonded magnet comprises at least a magnetic powder, a polyphenylene sulfide (PPS) resin, and a polyamide-based thermoplastic elastomer. The polyamide-based thermoplastic elastomer has a melting point of 130-170°C.

Description

Resin composition for bonded magnets and bonded magnets using the same

[0001] The present disclosure relates to a resin composition for bonded magnets and a bonded magnet using the resin composition.

[0002] Bonded magnets have many advantages. For example, they are lighter and have better dimensional accuracy than sintered magnets. Furthermore, bonded magnets can be mass-produced into products with complex shapes more easily than sintered magnets. For this reason, bonded magnets are widely used in a variety of applications, such as toys, office equipment, audio equipment, and motors.

[0003] In the manufacturing process of bonded magnets, rubber or plastic material and magnetic powder are generally mixed together, and the resulting mixture is then molded in a magnetic field. Alternatively, the mixture may be molded by mechanical means.

[0004] In recent years, the productivity and reliability of various materials and devices have improved significantly. As these materials and devices become more sophisticated, the bonded magnets used in them are required to have higher performance. Such higher performance includes improved productivity, mechanical strength, and magnetic properties.

[0005] For example, in vehicles, bonded magnets are used as rotors and sensors. In order to extend the life of the devices and enable use at high rotational speeds, high heat resistance and high mechanical strength are strongly required for rotors and sensors. Therefore, bonded magnets using PPS resin as the binder resin are used. PPS resin is known to have high heat resistance. It is also known that the mechanical properties of PPS resin are not significantly affected even at high temperatures. However, PPS resin has low toughness. Therefore, there is a concern that bonded magnets using PPS resin may crack immediately after injection molding or crack (heat shock) in cold and hot environments. Therefore, high impact resistance and high resistance to cold and thermal shock are strongly required for these bonded magnets.

[0006] For example, Japanese Patent Application Laid-Open Publication No. 2013-253219 proposes a method for producing a compound for bonded magnets with high magnetic force. In this method, PA resin or PPS resin is mixed with a block copolymer containing styrene units and butylene units as constituent components in a predetermined ratio. This allows the production of a compound for bonded magnets with high magnetic force and excellent fluidity and mechanical strength.

[0007] Japanese Patent Application Laid-Open No. 4-44304 proposes a method for producing a compound for bonded magnets with excellent resistance to thermal shocks, in which modified polyolefins and glass fibers are added to PPS resin.

[0008] Japanese Patent Application Laid-Open No. 9-219312 proposes a method for producing a compound for a high-magnetic-strength bonded magnet, in which PPS resin and vinylidene fluoride rubber are mixed in a predetermined ratio.

[0009] This makes it possible to produce a compound for a bonded magnet with excellent flowability and mechanical strength and high magnetic force.

[0010] According to the research of the present inventors, the bonded magnets using PPS resin obtained using the technology of JP 2013-253219 A had issues with heat resistance and mechanical strength. Furthermore, JP 4-44304 A aimed to improve thermal shock resistance. However, this technology inevitably resulted in a decline in magnetic properties. The technology of JP 9-219312 A improved the mechanical strength of molded products. However, there was a concern about the generation of corrosive gases derived from vinylidene fluoride rubber. Therefore, these molded products were not suitable for use in high-temperature environments.

[0011] Therefore, one technical objective of this embodiment is to obtain a resin composition for a bonded magnet that has excellent heat resistance, impact resistance, and thermal shock resistance without deteriorating the magnetic properties.

[0012] The above technical object can be achieved by the present embodiment as follows.

[0013] That is, the resin composition for a bonded magnet according to this embodiment contains at least a magnetic powder, a PPS resin, and a polyamide-based thermoplastic elastomer, the melting point of which is 130°C or higher and 170°C or lower (first embodiment).

[0014] In the resin composition for a bonded magnet of the first embodiment, the polyamide-based thermoplastic elastomer may have a Shore D hardness of 35 to 60 or more (second embodiment).

[0015] In the resin composition for a bonded magnet of the first or second embodiment, the polyamide-based thermoplastic elastomer may have a tensile elongation of 400% or more (third embodiment).

[0016] In addition, in the resin composition for bonded magnets of any of the first to third embodiments, the content of the polyamide-based thermoplastic elastomer relative to the PPS resin may be 3.0 to 20.0% by weight (fourth embodiment).

[0017] In addition, in the resin composition for a bonded magnet of any of the first to fourth embodiments, the content of the PPS resin may be 5 to 30% by weight (fifth embodiment).

[0018] In addition, in the resin composition for a bonded magnet of any of the first to fifth embodiments, the content of the polyamide-based thermoplastic elastomer may be 0.40 to 2.60 wt % (sixth embodiment).

[0019] Furthermore, the bonded magnet according to this embodiment is a bonded magnet molded using the resin composition for a bonded magnet according to any one of the first to sixth embodiments (seventh embodiment).

[0020] In molded articles made using the resin composition for bonded magnets according to this embodiment, magnetic properties such as Br (residual magnetic flux density) do not deteriorate. Furthermore, these molded articles have excellent impact resistance even after exposure to a thermal environment, and also have high resistance to cold and thermal shock. Therefore, these molded articles can be used in harsh environments. For this reason, the resin composition for bonded magnets according to this embodiment is suitable as a material for bonded magnets.

[0021] This embodiment will be described in detail below.

[0022] The resin composition for a bonded magnet according to this embodiment contains at least a magnetic powder, a PPS resin, and a polyamide-based thermoplastic elastomer.

[0023] The magnetic powder used in this embodiment is not particularly limited. Magnetic powders typically used in bonded magnets can be used. Examples of magnetic powders that can be used include ferrite particles, rare earth magnetic powders, and soft ferrite particles.

[0024] The ferrite particles are preferably magnetoplumbite ferrite particles. The magnetoplumbite ferrite particles are represented by the formula AO.nFe ２ O ３ (where A is Ba, Sr, or Ba—Sr, and n=5.0 to 6.5). Examples of ferrite particles represented by this formula include barium ferrite particles, strontium ferrite particles, and barium-strontium ferrite particles. These ferrite particles may contain, as constituent elements, one or more elements selected from Ti, Mn, Al, La, Zn, Bi, and Co. The content of these constituent elements in the ferrite particles is, for example, in the range of 0.1 to 7.0 mol %.

[0025] The average particle size of the ferrite particles is preferably 1.0 to 5.0 μm, more preferably 1.0 to 2.0 μm. The BET specific surface area of ​​the ferrite particles is preferably 1 to 10 m. ２ / g, more preferably 1 to 5 m ２ The ferrite particles preferably have a coercive force iHc of 119 to 557 kA / m (1500 to 7000 Oe), more preferably 119 to 398 kA / m (1500 to 5000 Oe). The ferrite particles preferably have a remanent magnetization of 100 to 300 mT (1000 to 3000 G), more preferably 100 to 200 mT (1000 to 2000 G).

[0026] Rare earth magnetic powder is an intermetallic compound. Intermetallic compounds contain at least one rare earth element and at least one transition metal as constituent elements. Examples of such rare earth magnetic powders include rare earth-cobalt-based, rare earth-iron-boron-based, and rare earth-iron-nitrogen-based magnetic powders. In particular, when rare earth-iron-boron-based magnetic powders and rare earth-iron-nitrogen-based magnetic powders are used, bonded magnets with excellent magnetic properties can be obtained.

[0027] The average particle size of the rare earth magnetic powder is preferably 1 to 120 μm, more preferably 1 to 80 μm. The BET specific surface area of ​​the rare earth magnetic powder is preferably 0.5 to 5 m. ２ / g, more preferably 0.5 to 3m ２ / g. The coercive force iHc of the rare earth magnetic powder is preferably 239 to 1591 kA / m (3.0 to 20 kOe), more preferably 318 to 1114 kA / m (4.0 to 15 kOe). The remanent magnetization of the rare earth magnetic powder is preferably 0.3 to 1.8 mT (3.0 to 18 kG), more preferably 0.5 to 1.3 mT (5.0 to 13 kG).

[0028] Examples of soft ferrite particle powders include Mn-Zn ferrite, Ni-Zn ferrite, Ni-Zn-Cu ferrite, Mn-Mg ferrite, carbonyl iron powder, and sendust. Soft ferrites with modified compositions can also be used depending on the frequency of the electromagnetic waves used.

[0029] The average particle size of the soft ferrite powder is preferably 1 to 150 μm, more preferably 1 to 50 μm.

[0030] Desirably, these magnetic powders are subjected to various surface treatments in order to prevent deterioration of magnetic properties due to oxidation, improve compatibility with resins, and increase the strength of molded products.

[0031] Examples of materials that can be used for surface treatment include silane coupling agents, titanium coupling agents, aluminum coupling agents, siloxane polymers, organic phosphoric acid surface treatment agents, and inorganic phosphoric acid surface treatment agents. In particular, by treating the surface of the magnetic powder in advance with a silane coupling agent, the strength of the molded product can be further improved.

[0032] The polyamide-based thermoplastic elastomer used in this embodiment contains polyamide as a hard segment. Examples of soft segments contained in the polyamide-based thermoplastic elastomer include polyether, polyester, polyether ester, polytetramethylene glycol, and polypropylene glycol. One of these exemplified polyamide-based thermoplastic elastomers can be used alone. Alternatively, two or more of the polyamide-based thermoplastic elastomers can be used in combination.

[0033] When a polyamide-based thermoplastic elastomer is mixed with a PPS resin, the elastomer is easily dispersed uniformly in the PPS resin, and therefore, by using the polyamide-based thermoplastic elastomer, molded articles having excellent moldability and excellent physical properties can be obtained.

[0034] The melting point of the polyamide-based thermoplastic elastomer used in this embodiment is, for example, 130°C or higher and 170°C or lower. When the melting point of the polyamide-based thermoplastic elastomer is within this range, a molded product having excellent impact resistance and thermal shock resistance as well as heat resistance can be obtained. The melting point of the polyamide-based thermoplastic elastomer is preferably 150°C or higher and 165°C or lower.

[0035] The Shore D hardness of the polyamide-based thermoplastic elastomer used in this embodiment is preferably 35 to 60. Shore D hardness is an index that represents the hardness of plastic or rubber. This index is measured using a Type D durometer. A high Shore D hardness value indicates high hardness. When the Shore D hardness of the polyamide-based thermoplastic elastomer is in the above range, a molded product with excellent impact resistance and thermal shock resistance can be obtained. The Shore D hardness of the polyamide-based thermoplastic elastomer is more preferably 40 to 58, and even more preferably 45 to 55.

[0036] The tensile elongation of the polyamide-based thermoplastic elastomer is preferably 400% or more. When the tensile elongation of the polyamide-based thermoplastic elastomer is 400% or more, a molded product having excellent resistance to cold and thermal shock can be obtained. The tensile elongation of the polyamide-based thermoplastic elastomer is more preferably 500% or more.

[0037] The PPS resin used in this embodiment is not particularly limited. However, the preferred average molecular weight range of the PPS resin is 10,000 to 100,000. Low-molecular-weight PPS resins have low melt viscosity. Therefore, when low-molecular-weight PPS resins are used, the resin composition for bonded magnets as an injection molding composition has excellent moldability. On the other hand, the physical properties, such as strength, of the resin composition for bonded magnets are inferior. In contrast, high-molecular-weight PPS resins have high viscosity. Therefore, when high-molecular-weight PPS resins are used, the physical properties of the resin composition for bonded magnets are excellent, in contrast to low-molecular-weight PPS resins. On the other hand, when the loading amount of magnetic powder is high, its moldability is inferior. Furthermore, the molecular structure of the PPS resin is not particularly limited. PPS resins with either crosslinked or linear molecular structures can be used.

[0038] The PPS resin should be selected to have an appropriate melt viscosity depending on the magnetic powder. The preferred melt viscosity range for PPS resin is 5 to 200 Pa·s at 310°C. Having a melt viscosity within this range results in a resin composition for bonded magnets with good fluidity and suitable for injection molding. Furthermore, the resulting resin composition for bonded magnets also has sufficient mechanical strength.

[0039] In the resin composition for bonded magnets according to this embodiment, the content of the polyamide-based thermoplastic elastomer is preferably 3.0 to 20.0% by weight relative to the PPS resin. By having the content of the polyamide-based thermoplastic elastomer relative to the PPS resin within this range, a molded article with good impact resistance and good resistance to cold and thermal shocks can be obtained. This molded article also has excellent flexural strength. If the content of the polyamide-based thermoplastic elastomer relative to the PPS resin exceeds 20.0%, the heat resistance of the molded article may decrease. The content of the polyamide-based thermoplastic elastomer relative to the PPS resin is more preferably 4.0 to 19.0% by weight, and even more preferably 5.0 to 18.0% by weight.

[0040] The resin composition for bonded magnets according to this embodiment preferably contains 0.40 to 2.60% by weight of a polyamide-based thermoplastic elastomer. By having the polyamide-based thermoplastic elastomer content within this range, a molded article with good impact resistance and thermal shock resistance can be obtained. This molded article also has excellent flexural strength. If the polyamide-based thermoplastic elastomer content exceeds 2.60%, the heat resistance of the molded article may decrease. The polyamide-based thermoplastic elastomer content is more preferably 0.60 to 2.45% by weight, and even more preferably 0.70 to 2.40% by weight.

[0041] The resin composition for bonded magnets according to this embodiment preferably contains 5 to 30% by weight of PPS resin. With the PPS resin content in this range, the resin composition for bonded magnets has sufficient fluidity. Therefore, good molded products can be easily obtained. If the PPS resin content exceeds 30% by weight, the magnetic properties will be poor. The PPS resin content is more preferably 7 to 25% by weight, and even more preferably 10 to 20% by weight.

[0042] The magnetic powder content of the resin composition for bonded magnets is preferably 69.6 to 94.5% by weight. By keeping the magnetic powder content within this range, a bonded magnet with excellent magnetic properties can be obtained. If the magnetic powder content exceeds 94.5% by weight, the moldability, such as the fluidity, of the resin composition may decrease. Alternatively, the mechanical strength of the resulting bonded magnet may decrease. The magnetic powder content is more preferably 74.6 to 92.5% by weight, and even more preferably 79.6 to 89.5% by weight.

[0043] When the ferrite particles are used as the magnetic powder, the resin composition for a bonded magnet according to this embodiment has a residual magnetic flux density Br of preferably 230 mT (2300 G) or more, more preferably 245 mT (2450 G) or more. The value of this residual magnetic flux density Br is measured by the magnetic measurement method described below. The resin composition for a bonded magnet has a coercive force iHc of preferably 119 to 279 kA / m (1500 to 3500 Oe), more preferably 127 to 259 kA / m (1600 to 3250 Oe). The resin composition for a bonded magnet has a maximum energy product (BH)max of preferably 10.3 kJ / m. ３ (1.30 MGOe) or more, more preferably 10.7 kJ / m ３ (1.35 MGOe) or more.

[0044] When the rare earth magnetic powder is used as the magnetic powder, the residual magnetic flux density Br of the resin composition for a bonded magnet according to this embodiment is preferably 300 mT (3000 G) or more, more preferably 350 mT (3500 G) or more. The value of this residual magnetic flux density Br is measured by the magnetic measurement method described below. The coercive force iHc of this resin composition for a bonded magnet is preferably 636 to 955 kA / m (8000 to 12000 Oe), more preferably 676 to 915 kA / m (8500 to 11500 Oe). The maximum energy product (BH)max of this resin composition for a bonded magnet is preferably 15.9 kJ / m ３ (2.00 MGOe) or more, more preferably 19.9 kJ / m ３ (2.50 MGOe) or more.

[0045] Next, a method for producing the resin composition for a bonded magnet according to this embodiment will be described.

[0046] The resin composition for bonded magnets according to this embodiment can be obtained by a known method for manufacturing resin compositions for bonded magnets. For example, first, the magnetic powder, PPS resin component, and polyamide-based thermoplastic elastomer are uniformly mixed. The resulting mixture is then melt-kneaded using, for example, a kneading extruder. The resulting kneaded product is then crushed or cut into granules or pellets.

[0047] The resin composition for bonded magnets according to this embodiment may contain, as appropriate, for example, plastic molding lubricants or various stabilizers in order to improve moldability, improve heat resistance, prevent oxidation degradation, or obtain anti-rust effects.

[0048] Examples of lubricants that can be used include carboxyl saturated or unsaturated fatty acid-based substances, including propionic acid, stearic acid, linoleic acid, oleic acid, malonic acid, glutaric acid, adipic acid, maleic acid, and fumaric acid, as well as compounds derived from these substances. Examples of compounds derived from these substances include metal soaps, including calcium stearate, magnesium stearate, and lithium stearate, fatty acid amides, including hydroxystearamide, ethylene bislauric acid amide, and ethylene bisoleic acid amide, waxes, such as paraffin wax, polysiloxanes, including dimethylpolysiloxane and silicone oil, and fluorine compounds, such as fluorine-containing oil.

[0049] To inhibit thermal degradation, an antioxidant is preferably added as a stabilizer. Examples of usable antioxidants include metal deactivators and stabilizers. An example of a metal deactivator is N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionylhydrazine]. Examples of stabilizers include hindered amine stabilizers, hindered / less hindered phenol stabilizers such as pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], phosphite stabilizers, and thioether stabilizers. It is particularly effective to use a hindered / less hindered phenol stabilizer in combination with a phosphite stabilizer or a metal deactivator.

[0050] The antioxidant is preferably contained in the range of 0.1 to 1.0 wt %, more preferably 0.2 to 0.8 wt %, based on the total amount of the resin composition.

[0051] If necessary, known mold release agents, such as zinc stearate and calcium stearate, may also be added to the resin.

[0052] The resin composition for a bonded magnet according to this embodiment may contain hydrotalcite powder for the purpose of reducing the generation of corrosive gases.

[0053] The hydrotalcite powder has the general formula: [M ２＋ １－ｘ M ３＋ ｘ (OH) ２ ][A ｎ－ ｘ／ｎ ・mH ２ O] (in the formula, M ２＋ For example, Mg ２＋ , Co ２＋ , Ni ２＋ , and Zn ２＋ It indicates a divalent metal ion including M. ３＋ is, for example, Al ３＋ , Fe ３＋ , and Cr ３＋ A represents a trivalent metal ion including ｎ－ For example, OH － , Cl － , CO ３ ２－ , and S.O. ４ ２－ The interlayer anion includes x, n, and m. The divalent metal ion is preferably Mg. ２＋ Preferably, the trivalent metal ion is Al ３＋ A part or all of these metal ions may be substituted with other metal ions.

[0054] The hydrotalcite powder contains plate-like particles. The average plate surface diameter is 0.01 to 1.0 μm, preferably 0.02 to 0.8 μm, and more preferably 0.03 to 0.7 μm. If the average plate surface diameter is less than 0.01 μm, dispersibility in the resin is insufficient. If the average plate surface diameter exceeds 1.0 μm, it is difficult to industrially produce the plate-like particles.

[0055] The BET specific surface area of ​​the hydrotalcite powder is preferably 1 to 150 m ２ / g, more preferably 5 to 100 m ２ / g, and more preferably 8 to 50 m ２ / g. ２Hydrotalcite particles having a BET specific surface area of ​​less than 150 m / g are difficult to obtain industrially. ２ If the particle size exceeds 1 / g, the particles will aggregate severely, making it difficult to uniformly disperse the particles in the resin.

[0056] If necessary, the particle surfaces of the hydrotalcite powder may be coated with at least one surface treatment agent selected from higher fatty acids, anionic surfactants, higher fatty acid phosphate esters, coupling agents, and polyhydric alcohol esters. By coating with a surface coating, the dispersibility of the hydrotalcite powder in the resin is improved.

[0057] The content of hydrotalcite powder in the resin composition for bonded magnets according to this embodiment is preferably 0.1 to 25.0% by weight relative to the PPS resin. When the content of hydrotalcite powder relative to the PPS resin is within this range, the effect of reducing corrosive gases is obtained. If the content of hydrotalcite powder relative to the PPS resin exceeds 25.0% by weight, the amount of non-magnetic components increases. This can result in a decrease in mechanical properties, magnetic properties, or fluidity. The content of hydrotalcite powder relative to the PPS resin is more preferably 0.5 to 15.0% by weight, and even more preferably 1.0 to 5.0% by weight.

[0058] The resin composition for bonded magnets according to this embodiment preferably contains 0.01 to 4.0% by weight of hydrotalcite powder. When the content of hydrotalcite powder is within the above range, the effect of reducing corrosive gases can be obtained. When the content of hydrotalcite powder exceeds 4.0% by weight, the amount of non-magnetic components increases. This can result in a decrease in mechanical properties, magnetic properties, or fluidity. The content of hydrotalcite powder is preferably 0.10 to 2.5% by weight, more preferably 0.20 to 1.0% by weight.

[0059] The molding method for obtaining a molded product using the resin composition for bonded magnets of this embodiment is not particularly limited. As this molding method, for example, a known method can be used alone as appropriate depending on the material properties of the resin composition for bonded magnets, the molding purpose, or the application. Alternatively, a combination of several known methods can be used. Examples of known methods include the transfer method, injection method, extrusion method, inflation method, calendaring method, T-die method, blowing method, vacuum method, lamination method, spray-up method, foaming method, matched die method, and SMC method. In particular, for resin compositions for bonded magnets using thermoplastic resins, the injection method or extrusion method is preferably used. These methods are applied to many industrial parts. These methods allow for continuous, high-speed mass production.

[0060] Representative examples of the present embodiment are shown below, but the present embodiment is not limited to these examples.

[0061] The average particle size of the ferrite particles used in this example was measured using a Sub-Sieve Sizer Model 95 (manufactured by Fisher Scientific).

[0062] The BET specific surface area of ​​the ferrite particles used in the present example was measured using a fully automatic specific surface area meter, Macsorb model-1201 (manufactured by Mountec Co., Ltd.).

[0063] The melting points of the polyamide-based thermoplastic elastomers used in the examples were measured in accordance with ISO 11357.

[0064] The Shore D hardness of the polyamide-based thermoplastic elastomer used in this example was measured in accordance with ISO868.

[0065] The tensile elongation of the polyamide-based thermoplastic elastomer used in this example was measured in accordance with ISO 527.

[0066] The physical properties of the polyamide-based thermoplastic elastomer used in this example are shown in Table 1.

[0067]

[0068] The melt mass flow rate (MFR) of the resin composition for bonded magnets was determined in accordance with JIS K710 by melting at 330°C, followed by measurement under a load of 10 kg.

[0069] The molded density of the bonded magnet was measured as follows. First, a core was molded using a resin composition for bonded magnets in a mold with a diameter of 25 mm and a height of 10.5 mm using an injection molding machine, model J55AD, manufactured by The Japan Steel Works, Ltd. Then, measurements were carried out using an "Electronic Density Meter EW-120SG" (manufactured by Yasuda Seiki Seisakusho, Ltd.). This gave the molded density of the bonded magnet.

[0070] The magnetic properties of the bonded magnets (residual magnetic flux density Br, coercive force iHc, coercive force bHc, and maximum energy product (BH)max) were determined as follows. First, using the resin composition for bonded magnets as the material, molding was carried out using an injection molding machine J55AD manufactured by The Japan Steel Works, Ltd., in a mold with a diameter of 25 mm and a height of 10.5 mm, while applying a magnetic field of 318.3 kA / m (4 kOe). Then, using a "DC Magnetization Characteristic Automatic Recorder 3257" (manufactured by Yokogawa Hokushin Electric Co., Ltd.), measurements were carried out on the molded body in a magnetic field of 1114.1 kA / m (14 kOe). This allowed the above magnetic properties to be determined.

[0071] The physical properties of the bonded magnets were measured using test piece A, which was 80 mm long, 12.7 mm wide, and 3.2 mm thick, and cylindrical test piece B, which was 30 mm in outer diameter, 26 mm in inner diameter, and 30 mm in height. These test pieces A and B were obtained by injection molding the resin composition for bonded magnets using a J55AD injection molding machine manufactured by The Japan Steel Works, Ltd.

[0072] The bending strength and IZOD impact strength of the molded body A molded using the resin composition for bonded magnets were measured in accordance with ASTM D790 and D256 standards using a computerized measurement-controlled precision universal testing machine AG-1 manufactured by Shimadzu Corporation and No. 158 manufactured by Yasuda Seiki Seisakusho Co., Ltd.

[0073] In a heat aging test of molded body A molded using a resin composition for bonded magnets, molded body A was exposed to a heat environment of 150°C for 1,000 hours using an oven. Then, molded body A was left at room temperature for 24 hours. Thereafter, the bending strength and IZOD impact strength were measured in the same manner as described above. Furthermore, the strength retention rate (%) was confirmed by comparing the strength before and after exposure to the heat environment.

[0074] In a thermal shock resistance test for molded body B molded using the resin composition for bonded magnets, a thermal shock apparatus TSA-73EL (manufactured by Espec Corporation) was used to carry out 1000 cycles of operation, with one cycle being -20°C to 120°C (holding time for each temperature: 30 minutes). After that, the crack occurrence rate of molded body B was confirmed visually.

[0075] Example 1 Ferrite particles (average particle size: 1.20 μm, BET value: 1.75 m ２ / g, coercive force 226 kA / m (2850 Oe), saturation magnetization 822 Am ２ An aminoalkyl silane coupling agent was added to the resulting mixture (72 emu / g). The resulting mixture was heated and mixed at 120°C until homogeneous. This resulted in a surface-treated ferrite particle powder. To this surface-treated ferrite particle powder, PPS resin (average molecular weight: 30,000, melt viscosity: 30 Pa·s at 310°C) and polyamide-based thermoplastic elastomer 1 (melting point: 135°C, Shore D hardness: 40, tensile elongation: 400% or more) were added. The resulting mixture was thoroughly mixed using a Henschel mixer. The compounding ratios are shown in Table 2. This resulted in a mixture of resin compositions for bonded magnets.

[0076] The resulting bonded magnet resin composition mixture was fed in a fixed amount to a twin-screw kneader. The mixture in the kneader was kneaded at a temperature at which the PPS resin melted. The resulting kneaded product was removed in the form of strands. The removed strands were cut into pellets measuring 2 mm diameter x 3 mm. This yielded a bonded magnet resin composition.

[0077] The resin content of the resulting resin composition for a bonded magnet is shown in Table 3. Table 4 also shows the MFR of the resin composition for a bonded magnet, the molding density of the bonded magnet, and the magnetic properties.

[0078] The results of measuring the bending strength and IZOD impact strength of test piece molded body A obtained by injection molding of the resin composition for bonded magnets before and after the heat aging test, as well as the strength retention rate before and after the heat aging test, are shown in Table 5. Table 5 also shows the yield rate of molded body B in the thermal shock resistance test.

[0079] Examples 2 to 10 Resin compositions for bonded magnets were prepared in the same manner as in Example 1, except that the formulation of ferrite magnetic powder, PPS resin, and polyamide-based thermoplastic elastomer was changed in various ways as shown in Table 2.

[0080]

[0081]

[0082]

[0083]

[0084] Comparative Example 1 A resin composition for a bonded magnet was prepared in the same manner as in Example 1, except that the composition of the components was changed as shown in Table 6 so as not to use the polyamide-based thermoplastic elastomer.

[0085] Comparative Example 2 A resin composition for a bonded magnet was prepared in the same manner as in Example 1, except that the polyamide-based thermoplastic elastomer was changed to Polyamide-based thermoplastic elastomer 4 and the component composition was changed as shown in Table 6.

[0086] Comparative Examples 3 to 7 Resin compositions for bonded magnets were prepared in the same manner as in Example 1, except that the thermoplastic elastomer was changed to thermoplastic elastomers 5 to 9 and the component formulation was changed as shown in Table 6.

[0087] The resin content ratios of the resulting resin compositions for bonded magnets are shown in Table 7. The properties of these compositions are shown in Table 8. Furthermore, the test results of the test piece molded bodies obtained by injection molding the resin compositions for bonded magnets are shown in Table 9.

[0088]

[0089]

[0090]

[0091]

[0092] It was confirmed that the bonded magnet resin composition according to this embodiment produces molded articles with better impact resistance and thermal shock resistance than the bonded magnet resin composition of Comparative Example 1, which does not contain a polyamide-based thermoplastic elastomer. It was also confirmed that molded articles using the bonded magnet resin composition of Example 7, which contains a relatively large amount of polyamide-based thermoplastic elastomer, have excellent impact resistance and thermal shock resistance, but have a lower strength retention rate after heat aging tests. Furthermore, the bonded magnet resin composition of Comparative Example 2, which contains a polyamide-based thermoplastic elastomer with a melting point of 172°C, showed a lower yield rate in the thermal shock resistance test.

[0093] In Comparative Examples 3 to 7, resin compositions for bonded magnets containing thermoplastic elastomers other than polyamide-based thermoplastic elastomers were used. The resin compositions for bonded magnets in Comparative Examples 3 and 4 had low fluidity. As a result, molded articles could not be obtained from these resin compositions for bonded magnets. The resin compositions for bonded magnets in Comparative Examples 5 to 7, which contained thermoplastic elastomers other than polyamide-based thermoplastic elastomers, showed a decrease in the yield rate in the thermal shock resistance test. Furthermore, the strength retention rate after the heat aging resistance test was also low.

[0094] Therefore, molded articles obtained using the resin composition for bonded magnets according to this embodiment have excellent magnetic properties and physical properties. At the same time, these molded articles have resistance to cold and thermal shock, allowing them to be used in harsh environments. Furthermore, these molded articles have heat aging resistance and retain excellent physical properties even after exposure to a thermal environment. For this reason, the resin composition for bonded magnets according to this embodiment is suitable as a material for bonded magnets.

Claims

1. A resin composition for bonded magnets, comprising at least magnetic powder, PPS resin, and a polyamide-based thermoplastic elastomer, the polyamide-based thermoplastic elastomer having a melting point of 130°C or higher and 170°C or lower.

2. The resin composition for a bonded magnet according to claim 1, wherein the polyamide thermoplastic elastomer has a Shore D hardness of 35 or more and 60 or less.

3. A resin composition for a bonded magnet according to claim 1 or 2, wherein the polyamide thermoplastic elastomer has a tensile elongation of 400% or more.

4. A resin composition for bonded magnets according to claim 1 or 2, wherein the content of said polyamide thermoplastic elastomer relative to said PPS resin is 3.0 to 20.0% by weight.

5. A resin composition for bonded magnets according to claim 1 or 2, wherein the content of said PPS resin is 5 to 30% by weight.

6. A resin composition for bonded magnets according to claim 1 or 2, wherein the content of said polyamide thermoplastic elastomer is 0.4 to 2.6% by weight.

7. A bonded magnet molded using the resin composition for bonded magnets according to claim 1 or 2.

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