Resin composition for bonded magnet and molded article using the same

Abstract

According to this embodiment, a resin composition for bonding magnets is provided that does not reduce magnetic properties, exhibits excellent physical properties such as heat resistance, flexural strength, and IZOD impact strength, and reduces the generation of corrosive gases. A resin composition for bonding magnets and a molded article thereof are also provided, comprising magnetic powder, polyphenylene sulfide (PPS) resin, and hydrotalcite powder, wherein the content of hydrotalcite powder relative to PPS resin is 0.1 to 25.0% by weight.

Description

Technical Field

[0001] This invention relates to a resin composition for bonding magnets that does not degrade magnetic properties, exhibits excellent physical properties such as heat resistance, flexural strength, and IZOD impact strength, and reduces the generation of corrosive gases. Furthermore, this invention relates to a molded bonded magnet using this resin composition. Prior Technology

[0002] As is well known, bonded magnets have the advantages of being lightweight and having good dimensional accuracy compared to sintered magnets. Furthermore, even complex-shaped bonded magnets are easily mass-produced. Therefore, bonded magnets are widely used in various applications such as toys, office equipment, audio equipment, and motors.

[0003] As magnetic powders used for bonding magnets, rare-earth magnet powders, represented by Nd-Fe-B series, and ferrite particle powders are known. Rare-earth magnet powders possess high magnetic properties, but they are also expensive. Therefore, their applications are limited. On the other hand, ferrite particle powders are slightly inferior in magnetic properties compared to rare-earth magnet powders. However, ferrite particle powders are inexpensive and chemically stable. Therefore, ferrite particle powders are used in a wide range of applications.

[0004] In the manufacture of bonded magnets, generally speaking, the mixed rubber or plastic material is formed with magnetic powder in a magnetic field, or formed by mechanical methods.

[0005] In recent years, there has been a demand for high functionality, incorporating various materials and equipment to improve productivity and reliability during use. This has led to a demand for high-performance bonding magnets used in these materials and equipment, characterized by increased productivity, improved mechanical strength, and enhanced magnetic properties.

[0006] For example, in vehicles, bonded magnets are used as rotors or sensors. Due to the need for long-life and high-speed rotation in these applications, the bonded magnets used require high heat resistance and mechanical strength. Therefore, bonded magnets utilizing PPS resin as the binder resin can be used. These bonded magnets are known to have high heat resistance and can reduce mechanical properties at high temperatures.

[0007] For example, Patent Document 1 proposes to mix PPS resin and polyamide (PA) resin in a specified ratio, while Patent Document 2 proposes to add modified polyolefins and glass fibers to PPS resin, thereby preparing a compound for bonding magnets with high heat resistance, excellent mechanical strength and magnetic properties.

[0008] In addition, Patent Document 3 proposes a resin composition for bonded magnets containing a phosphorus-based antioxidant in order to obtain bonded magnets that can suppress strength reduction even when exposed to high temperature environments.

[0009] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2013-77802 Patent Document 2: Japanese Patent Application Publication No. 4-44304 Patent Document 3: Japanese Patent Application Publication No. 2015-76572 Implementation

[0010] However, in bonded magnets using PPS resin, the corrosive gases (Cl- or SO4 2-) from the PPS resin pose risks such as increased mold maintenance frequency during production, shortened mold life, and deterioration of the bonded magnets. Therefore, it is strongly recommended to reduce the amount of corrosive gases.

[0011] The aforementioned technical issues can be addressed through the implementation method described below.

[0012] That is, the resin composition for bonding magnets in Embodiment 1 includes magnetic powder, PPS resin and hydrotalcite powder, and contains hydrotalcite at a weight of 0.1 to 25.0% relative to PPS resin.

[0013] In addition, the resin composition for bonding magnets in Embodiment 2 is the resin composition for bonding magnets in Embodiment 1 containing 5 to 30% by weight of PPS resin.

[0014] In addition, the resin composition for bonding magnets in Embodiment 3 is the resin composition for bonding magnets in Embodiment 1 or 2 containing 0.01 to 4.0% by weight of hydrotalcite.

[0015] In addition, the resin composition for bonding magnets in Embodiment 4 is the resin composition for bonding magnets described in any one of Embodiments 1 to 3, in which the hydrotalcite powder is Mg-Al based hydrotalcite.

[0016] Furthermore, the resin composition for bonding magnets in Embodiment 5 is a molded body formed using the resin composition for bonding magnets described in any one of Embodiments 1 to 4.

[0017] According to this embodiment, the generation of corrosive gases can be reduced without decreasing Br (residual magnetic flux density). Furthermore, molded articles obtained using the resin composition for bonding magnets according to this embodiment exhibit physical properties such as high flexural strength and high IZOD impact strength. Therefore, this resin composition is suitable for molding bonded magnets. Implementation

[0018] The following describes this embodiment in detail.

[0019] The resin composition for bonding magnets in this embodiment contains at least magnetic powder, PPS resin, and hydrotalcite powder.

[0020] The magnetic powder used in this embodiment is not particularly limited. Magnetic powders used for bonding magnets, such as ferrite particle powder or rare-earth magnetic powder, can generally be used.

[0021] The preferred ferrite particle powder is gypsum-type ferrite particle powder. Here, gypsum-type ferrite particle powder refers to barium ferrite particle powder, strontium ferrite particle powder, barium-strontium ferrite particle powder, and 0.1 to 7.0 mol% of particle powder selected from one or more elements selected from Ti, Mn, Al, La, Zn, Bi, and Co.

[0022] The average particle size of the ferrite powder is preferably 1.0~5.0 μm, more preferably 1.0~2.0 μm. The BET specific surface area is preferably 1~10 m² / g, more preferably 1~5 m² / g. The coercivity iHc is preferably 119~557 kA / m (1500~7000 Oe), more preferably 119~398 kA / m (1500~5000 Oe). The remanence is preferably 100~300 mT (1000~3000 G), more preferably 100~200 mT (1000~2000 G).

[0023] Rare earth magnetic powders are intermetallic compounds whose constituent elements include at least one rare earth element and at least one transition metal. Examples include rare earth cobalt-based, rare earth-iron-boron-based, and rare earth-iron-nitrogen-based magnetic powders. In particular, when using rare earth-iron-boron-based or rare earth-iron-nitrogen-based magnetic powders, bonded magnets with excellent magnetic properties can be obtained.

[0024] The average particle size of the rare-earth magnetic powder is preferably 1~120 μm, more preferably 1~80 μm. The BET specific surface area is preferably 0.5~5 m² / g, more preferably 0.5~3 m² / g. The coercivity iHc is preferably 239~1591 kA / m (3.0~20 kOe), more preferably 318~1114 kA / m (4.0~15 kOe). The remanence is preferably 0.3~1.8 mT (3.0~18 kG), more preferably 0.5~1.3 mT (5.0~13 kG).

[0025] It should be noted that Nd-Fe-B magnetic powders can be directly used for mixing. However, when the Nd-Fe-B magnetic powder is in the form of flakes, it is preferable to pulverize the flakes using a jet mill, atomizer, or ball mill to obtain higher flowability and magnetic properties. This will yield flakes with an average particle size of less than 100 μm.

[0026] Examples of soft ferrite particle powders include Mn-Zn ferrite, Ni-Zn ferrite, Ni-Zn-Cu ferrite, Mn-Mg ferrite, carbonyl iron powder, and iron dust. Furthermore, the composition of the soft ferrite used can be changed according to the frequency of the electromagnetic wave being used.

[0027] The average particle size of the soft ferrite powder is preferably 1~150μm, more preferably 1~50μm.

[0028] Preferably, various surface treatments are performed to suppress the deterioration of the magnetic properties of these magnetic powders due to oxidation, improve their compatibility with the resin, and enhance the strength of the molded articles.

[0029] Examples of materials that can be used for surface treatment include silane coupling agents, titanium coupling agents, aluminum coupling agents, silicone polymers, organic phosphate-based surface treatment agents, and inorganic phosphate-based surface treatment agents. In particular, by pre-treating the surface of magnetic powder with a silane coupling agent, the strength of the molded product can be further improved.

[0030] The hydrotalcite powder used in this embodiment has the general formula: 〔M2+ 1-xM3+ x(OH)2〕〔An- x / n‧mH2O〕 (where M2+ represents divalent metal ions such as Mg2+, Co2+, Ni2+, Zn2+; M3+ represents trivalent metal ions such as Al3+, Fe3+, Cr3+; An- represents interlayer anions such as OH-, Cl-, CO3 2-, SO4 2-; X satisfies 0 < x < 1; n is the valence of A; M satisfies 0 m < 1.) and is a layered compound as shown.

[0031] The hydrotalcite powder used in this embodiment is preferably a Mg-Al-based hydrotalcite containing Mg2+ as a divalent metal ion and Al3+ as a trivalent metal ion. Part or all of these metal ions can be replaced by other metal ions.

[0032] [[ID=​​​​​​​​​

[0035] The hydrotalcite powder used in this embodiment can be manufactured by conventional methods. For example, one method involves first mixing a magnesium compound and an aluminum compound, calcining the resulting mixture, and then hydrating the resulting Mg-Al composite oxide with an aqueous solution containing anions. Alternatively, in other examples, a hydrotalcite powder can be obtained by first mixing an alkaline aqueous solution containing anions, an aqueous solution of magnesium salts, and an aqueous solution of aluminum salts, adding an aqueous solution of calcium salts to the resulting mixed aqueous solution, and then heating and aging the aqueous solution containing the obtained calcium salts.

[0036] The PPS resin used in this embodiment is not particularly limited, but the average molecular weight is preferably 10,000 to 100,000. When using a low molecular weight PPS resin, the injection molding composition exhibits excellent moldability due to its low melt viscosity, but physical properties such as strength deteriorate. When using a high molecular weight PPS resin, the physical properties are excellent due to its high melt viscosity, but the filling amount of magnetic powder is high, resulting in deteriorated moldability.

[0037] Furthermore, the melt viscosity of the PPS resin can be appropriately set according to the magnetic powder. A preferred melt viscosity is in the range of 5 to 200 Pa·s at 310°C. If the melt viscosity at 310°C is less than 5 Pa·s, the mechanical strength of the resulting resin composition for bonding magnets may decrease. On the other hand, if the melt viscosity at 310°C exceeds 200 Pa·s, the flowability of the resin composition for bonding magnets decreases significantly. Furthermore, injection molding becomes difficult.

[0038] There are no particular restrictions on the molecular structure of PPS resin. That is, its molecular structure can be either cross-linked or linear. In addition, various elastomers such as rubber or elastic resins can be added to PPS resin as needed.

[0039] In this embodiment, the content of hydrotalcite powder in the resin composition for bonding magnets is 0.1 to 25.0% by weight relative to PPS resin. When the content of hydrotalcite powder relative to PPS resin is less than 0.1% by weight, the effect of reducing corrosive gases is insufficient. When the content of hydrotalcite powder relative to PPS resin exceeds 25.0% by weight, mechanical properties, magnetic properties, and flowability decrease. The content of hydrotalcite powder relative to PPS resin is more preferably 0.5 to 15.0% by weight, and even more preferably 1.0 to 5.0% by weight.

[0040] The resin composition for bonding magnets in this embodiment preferably contains 0.01 to 4.0% by weight of hydrotalcite powder. When the content of hydrotalcite powder is less than 0.01% by weight, the effect of reducing corrosive gases is not sufficient. When the content of hydrotalcite powder exceeds 4.0% by weight, the non-magnetic components increase. As a result, mechanical properties, magnetic properties, and flowability may sometimes decrease. The content of hydrotalcite powder is preferably 0.10 to 2.5% by weight, more preferably 0.20 to 1.0% by weight.

[0041] The resin composition for bonding magnets in this embodiment preferably contains 5 to 30% by weight of PPS resin. When the content of PPS resin is less than 5% by weight, sufficient flowability of the resin composition for bonding magnets is sometimes not obtained. In this case, it is not easy to obtain a good molded article. When the content of PPS resin exceeds 30% by weight, the magnetic properties are sometimes reduced. The content of PPS resin is more preferably 7 to 25% by weight, and even more preferably 10 to 20% by weight.

[0042] The content of magnetic powder in the resin composition for bonding magnets is preferably 69.65 to 94.53% by weight. When the content of magnetic powder is less than 69.65% by weight, the desired magnetic properties are sometimes not obtained. When the content of magnetic powder exceeds 94.53% by weight, the mechanical strength of the resulting bonded magnet is sometimes reduced, and the formability, such as flowability or loopability, is extremely reduced. The content of magnetic powder is more preferably 74.63 to 92.54% by weight, and even more preferably 79.60 to 89.55% by weight.

[0043] The remanent magnetic flux density Br of the resin composition for bonding magnets in this embodiment is preferably 230 mT (2300 G) or more, and more preferably 245 mT (2450 G) or more, when the above-mentioned ferrite particle powder is used as the magnetic powder. This remanent magnetic flux density Br can be determined by the magnetic measurement method described later. The coercivity iHc is preferably 119~279 kA / m (1500~3500 Oe), and more preferably 127~259 kA / m (1600~3250 Oe). The maximum energy product (BH)max is preferably 10.3 kJ / m3 (1.30 MGOe) or more, and more preferably 10.7 kJ / m3 (1.35 MGOe) or more.

[0044] The remanent magnetic flux density Br of the resin composition for bonding magnets in this embodiment, when using the above-mentioned rare earth magnetic powder as the magnetic powder, is preferably 300 mT (3000 G) or more, and more preferably 350 mT (3500 G) or more. The coercivity iHc is preferably 636~955 kA / m (8000~12000 Oe), and more preferably 676~915 kA / m (8500~11500 Oe). The maximum energy product (BH)max is preferably 15.9 kJ / m3 (2.00 MGOe) or more, and more preferably 19.9 kJ / m3 (2.50 MGOe) or more.

[0045] Next, the method for manufacturing the resin composition for bonding magnets according to this embodiment will be discussed.

[0046] The resin composition for bonding magnets according to this embodiment can be obtained by a known method for manufacturing resin compositions for bonding magnets. For example, magnetic powder, PPS resin component and hydrotalcite powder are first uniformly mixed, and then melt-kneaded using a kneading extruder or the like. Furthermore, by pulverizing or cutting the obtained mixture into granules or pellets, the resin composition for bonding magnets can be obtained.

[0047] In order to achieve improved formability, improved heat resistance, resistance to oxidation and deterioration, and rust prevention, the resin composition for bonding magnets in this embodiment may appropriately contain plastic molding lubricants and various stabilizers.

[0048] Examples of lubricants include saturated and unsaturated fatty acids such as propionic acid, stearic acid, linoleic acid, oleic acid, malonic acid, glutaric acid, adipic acid, maleic acid, and fumaric acid, as well as their derivatives. Examples of derivatives include metal soaps such as calcium stearate, magnesium stearate, and lithium stearate, and fatty acid amides such as hydroxystearamide, ethylene dilaurate amide, and ethylene dioleate amide. Other examples include waxes such as paraffin wax, polysiloxanes such as dimethyl polysiloxane and silicone oil, and fluorinated compounds such as fluorinated oils.

[0049] As a stabilizer, antioxidants are preferably added to inhibit heat-induced degradation. Examples of antioxidants include hindered amine stabilizers. Other examples include hindered / low-hindered phenolic antioxidants such as pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], metal inactivators such as N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionylhydrazine], phosphite antioxidants, and thioether antioxidants. In particular, the combined use of hindered / low-hindered phenolic antioxidants with phosphite antioxidants or metal inactivators is effective.

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

[0051] In addition, known mold release agents such as zinc stearate or calcium stearate can be added to the resin as needed.

[0052] There are no particular limitations on the molding method used to obtain molded articles of the resin composition for bonding magnets using this embodiment. Depending on the material properties of the resin composition for bonding magnets, the molding purpose, and the intended use, any of the known methods such as conveying, injection molding, extrusion, blow molding, rolling, T-die molding, blow molding, vacuum molding, lamination, spraying, foaming, die molding, and SMC molding can be used. Furthermore, multiple methods can be combined. In particular, injection molding or extrusion is a preferred molding method for the resin composition for bonding magnets using thermoplastic resins. These molding methods are used in most industrial parts. Moreover, these molding methods enable continuous, high-speed, and mass production.

[0053] Example

[0054] The following are representative examples of this embodiment, but this embodiment is not limited to these examples.

[0055] The average particle size of the ferrite particle powder used in this embodiment was measured using a "Sub-Sieve Sizer Model 95" (made by Fisher Scientific).

[0056] The BET specific surface area of ​​the ferrite particle powder used in this embodiment was measured using a "Macsorb model-1201 fully automatic specific surface area meter" (manufactured by MountTech Co., Ltd.).

[0057] The plate diameter of the hydrotalcite powder was determined by transmission electron microscopy (TEM) images of the observation samples. The average value of the measured values ​​was defined as the average plate diameter of the hydrotalcite powder. The TEM used was a JEM-1200EX II (manufactured by JEOL). A solution containing hydrotalcite powder dispersed in water or alcohol was poured onto a sieve. The observation samples were prepared by drying the particles attached to the sieve. Within the observation samples, particles (200 points) whose plate surfaces were horizontally attached relative to the sieve were selected. The plate diameter of the selected particles was measured.

[0058] The BET specific surface area of ​​the hydrotalcite powder was determined using a Monosorb MS-21 (made by QUANTA CHROME).

[0059] The amount of corrosive gases generated by the resin composition for bonding magnets was determined using the following method. First, as a pretreatment adjustment, 1 g of the resin composition for bonding magnets was heated for 10 minutes at a set temperature of 350°C (atmospheric environment) using a benchtop high-temperature tubular furnace (TSS-430-P, Yamada Denki Co., Ltd.) to generate gas. Only the generated gas was introduced into the tubular furnace set to 1000°C for combustion. The ionized generated gas was then drawn into two absorbent cuvettes (absorbent composition: 20 ml / cuvette of 0.05 M NaOH + 0.06% H₂O₂ aqueous solution). Subsequently, using an absorbent diluted to 100 mL, Cl⁻ and SO₄²⁻ were quantified using a Dionex Integrion HPIC ion chromatograph (Thermo Fisher Scientific).

[0060] The molding density of the resin composition for bonding magnets was determined using an "Electronic Hydrometer EW-120SG" (manufactured by Yasuda Seiki Co., Ltd.). Specifically, the molding density of the core obtained by molding the resin composition for bonding magnets molten in a mold with a diameter of 25 mm and a height of 10.5 mm was measured using the electronic hydrometer.

[0061] The melt mass-flow rate (MFR) of the bonded magnet composition was determined as follows: based on JIS K7210, the melt mass-flow rate of the bonded magnet composition at 330°C was measured with a 10 kg load.

[0062] The magnetic properties (remanent magnetic flux density Br, coercivity iHc, coercivity bHc, and maximum energy product (BH)max) of the resin composition for bonding magnets were determined by the following method. First, the resin composition for bonding magnets was melted in a mold with a diameter of 25 mm and a height of 10.5 mm and then oriented under a magnetic field of 716.2 kA / m (9 kOe). Subsequently, the magnetic properties of the resin composition for bonding magnets were measured using a "DC magnetization characteristic automatic recording device 3257" (manufactured by Yokokawa Hokushin Electric Co., Ltd.) under a magnetic field of 1114.1 kA / m (14 kOe).

[0063] Using a J55AD injection molding machine manufactured by Nippon Steel, the adhesive magnet resin composition was injection molded to obtain a test piece with a total length of 80 mm, a total width of 12.7 mm, and a thickness of 3.2 mm. Based on the injection pressure recorded during the injection molding of the test piece, the injectability of the resin composition for adhesive magnets was determined.

[0064] The flexural strength and IZOD impact strength of molded bodies using a resin composition for bonding magnets were determined based on ASTM D790 and D256 specifications. More specifically, test pieces were obtained using a J55AD injection molding machine manufactured by Nippon Steel Works. Subsequently, the flexural strength and IZOD impact strength of the test molded bodies were determined using a Shimadzu AG-1 computer-controlled precision universal testing machine and a Yasuda Seiki No. 158 machine.

[0065] Example 1

[0066] To 83.57 parts by weight of ferrite particle powder (average particle size 1.20 μm, BET value: 1.75 m² / g, coercivity 226 kA / m (2850 Oe), saturation magnetization 822 Am² / kg (72 emu / g)), 0.42 parts by weight of an aminoalkyl silane coupling agent were added. The resulting mixture was heated and mixed at 120 °C until homogeneous. This yielded surface-treated ferrite particle powder. To this surface-treated ferrite particle powder, 15.80 parts by weight of PPS resin (average molecular weight: 41000, melt viscosity: 60 Pa‧s at 310 °C) and 0.21 parts by weight of Mg-Al based hydrotalcite powder (average plate diameter: 0.24 μm, BET value: 11 m² / g) were added. The mixture obtained by thoroughly mixing using a Henschel mixer yielded a resin composition for bonding magnets.

[0067] The resulting mixture of resin compositions for bonding magnets was quantitatively fed into a biaxial mixer and kneaded at the melting temperature of PPS resin. The mixture was taken out in strips and cut into granules of 2mm diameter × 3mm. This yielded the resin composition for bonding magnets.

[0068] The composition of the obtained resin composition for bonded magnets and the amount of corrosive gases (Cl- and SO4 2-) generated were determined. The results, molding density, MFR, and magnetic properties are shown in Table 2.

[0069] The injection pressure, flexural strength, and IZOD impact strength of the injection-molded test specimens were determined during the injection molding of the resin composition for bonding magnets. The results are shown in Table 3.

[0070] Examples 2-3, Comparative Examples 1-2

[0071] As shown in Table 1, the resin composition for bonding magnets was prepared in the same manner as in Example 1 above, except that the formulation of ferrite magnetic powder, PPS resin and hydrotalcite powder was changed.

[0072] Example 4

[0073] The hydrotalcite powder was changed to Mg-Al hydrotalcite powder with an average plate diameter of 0.06 μm and a BET value of 40 m² / g. Otherwise, the resin composition for bonding magnets was prepared in the same manner as in Example 2.

[0074] It was confirmed that the resin composition for bonding magnets according to this embodiment has superior properties in reducing corrosive gases compared to the resin composition for bonding magnets in Comparative Example 1, which does not contain hydrotalcite powder. It should be noted that the resin composition for bonding magnets in Comparative Example 2 exhibits high injection pressure and reduced flexural strength and IZOD impact strength of the molded body.

[0075] Industrial availability

[0076] By using the resin composition for bonding magnets according to this embodiment, molded articles that maintain high magnetic force and physical properties while reducing the generation of corrosive gases can be obtained. Therefore, the resin composition for bonding magnets according to this embodiment can be suitably used as a material for bonding magnets.

Claims

1. A resin composition for bonding magnets, comprising magnetic powder, PPS resin and hydrotalcite powder, wherein the hydrotalcite content is 0.1 to 25.0% by weight relative to the PPS resin.

2. The resin composition for bonding magnets as claimed in claim 1, wherein, It contains 5-30% by weight of PPS resin.

3. The resin composition for bonding magnets as described in claim 1 or 2, wherein, It contains 0.01 to 4.0% by weight of hydrotalcite.

4. The resin composition for bonding magnets as described in claim 1 or 2, wherein, The hydrotalcite powder is Mg-Al based hydrotalcite.

5. A molded body formed using the resin composition for bonding magnets as described in claim 1 or 2.

6. The resin composition for bonding magnets as described in claim 2, wherein, The average diameter of the hydrotalcite plate is 0.01–1.0 μm.

7. The resin composition for bonding magnets as claimed in claim 6, wherein, The BET specific surface area of ​​the hydrotalcite powder is 1-150 m² / g.

8. The resin composition for bonding magnets as claimed in claim 6 or 7, wherein, It contains 0.01 to 4.0% by weight of hydrotalcite.

9. The resin composition for bonding magnets as claimed in claim 6 or 7, wherein, The hydrotalcite powder is Mg-Al based hydrotalcite.

10. A molded body formed using the resin composition for bonding magnets as described in claim 6 or 7.