Bonded magnet molded body

Abstract

To provide a bond magnet molding that does not use a thermosetting resin, uses a thermoplastic resin and magnetic powder, in a simple process, excellent in moldability, and excellent flexibility.SOLUTION: The above problem can be solved by a bond magnet molding containing magnetic powder and a resin as essential components, where the resin is selected from a polyolefin thermoplastic elastomer, LLDPE, and a mixture of a polyolefin thermoplastic elastomer and EEA, and the tensile strength of the bond magnet molding is 3 MPa or more and 8 MPa or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a bonded magnet molded body and a coated bonded magnet molded body.

Background Art

[0002] There are bonded magnet molded bodies obtained by mixing and kneading magnetic powder, a thermoplastic resin, additives, etc., pelletizing them, and extrusion molding while applying a magnetic field. These bonded magnet molded bodies utilize the high degree of freedom in cross-sectional shape and are used in magnet rolls, motors, sensors, health appliances, etc. (Patent Documents 1, 2)

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, since a kneaded product of a thermosetting resin and magnetic powder, etc. is used as a magnet material, as manufacturing processes, a molding process, a crosslinking reaction process, and a secondary vulcanization process are required, which makes the process very complicated, the difficulty of molding is high, and it also leads to an increase in cost. Furthermore, since the hardness of the molded body is also relatively high, there is a lack of flexibility.

[0005] An object of the present invention is to provide a bonded magnet molded body that does not use a thermosetting resin, uses a thermoplastic resin and magnetic powder, has excellent moldability and flexibility in a simple process.

Means for Solving the Problems

[0006] As a result of intensive studies, the inventors of the present case have found that the above problems can be solved by the following configuration. That is, the present invention has the following configuration.

[0007] 1) A bonded magnet molded body containing magnetic powder and resin as essential components, The resin is selected from polyolefin-based thermoplastic elastomers, LLDPE, and a mixture of polyolefin-based thermoplastic elastomers and EEA. A bonded magnet molded body characterized in that the tensile strength of the bonded magnet molded body is 3 MPa or more and 8 MPa or less.

[0008] 2) The bonded magnet molded body has a weight ratio of magnetic powder to thermoplastic elastomer resin of magnetic powder:thermoplastic elastomer resin = 95:5 to 20:80. The bonded magnet molded body according to 1), characterized in that the magnetic powder consists of anisotropic rare earth magnetic powder, ferrite, or a mixture thereof.

[0009] 3). A bonded magnet molded body characterized by being a magnetized material of the bonded magnet molded body described in 1) or 2).

[0010] 4) A bonded magnet molded body characterized in that the bonded magnet molded body described in any of 1) to 3) is in the shape of a string.

[0011] 5). A coated bonded magnet molded body characterized in that the bonded magnet molded body described in any of 1) to 4) is coated with resin.

[0012] 6) The coated bonded magnet molded body according to 5), characterized in that the resin is selected from silicone polymer, urethane polymer, isobutylene polymer, ethylene propylene copolymer, natural rubber, ethylene propylene copolymer, ethylene propylene diene copolymer, styrene butadiene copolymer, olefin polymer, vinyl chloride resin, urethane resin, and fluororesin. [Effects of the Invention]

[0013] According to the present invention, a bonded magnet molded body with excellent moldability and flexibility can be provided by using a thermoplastic resin and magnetic powder, without using a thermosetting resin, through a simple process. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of an extrusion molding machine according to an embodiment of the present invention. [Modes for carrying out the invention]

[0015] The present invention relates to a bonded magnet molded body containing magnetic powder and resin as essential components. The present invention relates to a bonded magnet molded body characterized in that the resin is selected from polyolefin-based thermoplastic elastomer, LLDPE, and a mixture of polyolefin-based thermoplastic elastomer and EEA, and the tensile strength of the bonded magnet molded body is 3 MPa or more and 8 MPa or less.

[0016] The aforementioned polyolefin-based thermoplastic elastomer is a thermoplastic elastomer having the structure of a polyolefin resin, which is plasticized (becomes fluid) at high temperatures of, for example, 200 degrees Celsius or higher, can be processed like a plastic, and exhibits the properties of a rubber elastic material (elastomer) at room temperature (23°C). Specifically, examples include Mitsui Chemicals' Milastomer(R) 8032NS and Mitsubishi Chemical's Treexprene(TM) A35BWJ.

[0017] Furthermore, LLDPE refers to low-density polyethylene and is a general term that includes both conventional chromium or Ziegler-Natta catalyst systems and single-site catalysts such as metallocene (sometimes called "m-LLDPE"), and includes linear, substantially linear, or heterogeneous polyethylene copolymers or homopolymers. Specifically, examples include ZnLLDPE, uLLDPE, and mLLDPE.

[0018] Also, as the resin of the present invention, a mixture of a polyolefin-based thermoplastic elastomer and EEA is also preferable. The polyolefin-based thermoplastic elastomer is the same as the aforementioned polyolefin-based thermoplastic elastomer. Further, EEA is an ethylene-ethyl acrylate copolymer, and specifically, examples thereof include PES-250 and PES-220 manufactured by Dow Chemical Company.

[0019] From the viewpoint of flexibility, the mixing ratio of the polyolefin-based thermoplastic elastomer and EEA is preferably 5:5 to 9:1, more preferably 6.5:3.5 to 8.5:1.5, and still more preferably 7:3 to 8:2.

[0020] As described above, the resin used in the bonded magnet molded body of the present invention is selected from a polyolefin-based thermoplastic elastomer, LLDPE, and a mixture of a polyolefin-based thermoplastic elastomer and EEA. As the resin content other than these, 20% by weight or less in the total resin content is preferable, 10% by weight or less is more preferable, 5% by weight or less is still more preferable, and 0% by weight may also be acceptable. Additives (stabilizers, lubricants, plasticizers, etc.) added as necessary shall not be included in the above resin.

[0021] If the tensile strength of the bonded magnet molded body of the present invention is 3 MPa or more and 8 MPa or less, it can have strength and flexibility that can be used without practical problems, and it is preferably 3 MPa or more and 7.5 MPa or less.

[0022] In order to achieve the above tensile strength, the tensile strength of the bonded magnet molded body can be achieved by selecting a resin serving as a binder from a polyolefin-based thermoplastic elastomer, LLDPE, and a mixture of a polyolefin-based thermoplastic elastomer and EEA.

[0023] The weight ratio of magnetic powder to thermoplastic elastomer resin is preferably magnetic powder:thermoplastic elastomer resin = 95:5 to 20:80, more preferably 83:17 to 95:5, and even more preferably 85:15 to 93:7. From the viewpoint of magnetic flux density, the magnetic powder is preferably anisotropic rare earth magnetic powder, ferrite, or a mixture thereof.

[0024] Examples of anisotropic rare-earth magnetic powders include NdFeB magnetic powder, SmFeN magnetic powder, and SmCo magnetic powder, with NdFeB magnetic powder and SmFeN magnetic powder being particularly preferred among these.

[0025] Examples of ferrites include strontium ferrite magnetic powder and barium ferrite magnetic powder, with strontium ferrite magnetic powder being particularly preferred among these.

[0026] The MFR value (JIS K7210 210℃×10kg) of the bonded magnet material used in the bonded magnet molded body of the present invention is preferably 1.5g / 10min or more and 30.0g / 10min or less, more preferably 2.0g / 10min or more and 25.0g / 10min or less, and even more preferably 2.0g / 10min or more and 23.0g / 10min or less, from the viewpoint of stable moldability.

[0027] The bonded magnet material used in the bonded magnet molded body of the present invention is formed by mixing and kneading magnetic powder with a resin selected from polyolefin-based thermoplastic elastomer, LLDPE, and a mixture of polyolefin-based thermoplastic elastomer and EEA, and adding additives (stabilizers, lubricants, plasticizers, etc.) as needed, and then forming it into pellets.

[0028] An example of a molding method for forming bonded magnets will be explained using Figure 1. Pelleted bonded magnet material (Plamag raw material in the diagram) is fed from hopper 1, melted and heated, extruded by screw 2, and molded into a string shape by mold 5. At this time, mold 5 is equipped with an electromagnet, which generates a parallel magnetic field (1T to 3T) inside the mold. The molten bonded magnet material is passed through the mold and the magnetic field is applied to orient and magnetize the magnetic particles in the molten resin magnet. The magnet molded material that comes out of the mold is cooled and solidified in cooling water tank 7 to form a string-shaped magnetized bonded magnet molded body. The cooled and solidified string-shaped magnetized bonded magnet molded body is pulled out by take-up machine 8 and, if necessary, cut to the desired length by cutting machine 9 or wound up.

[0029] By adjusting the extrusion speed (linear velocity) using the screw rotation speed and take-up speed of the extruder, and by adjusting the heating temperature of the extruder, the effective length (L / D) and compression ratio (CR) of the extrusion screw, the desired cross-sectional shape and surface magnetic flux density of the bonded magnet molded body can be obtained.

[0030] Furthermore, from the viewpoint of high magnetic force and magnetic force retention, the magnetic properties of the bonded magnet molded body are preferably such that the Br (residual magnetic flux density) is 40 mT or more and 900 mT or less, more preferably 45 mT or more and 825 mT or less, and even more preferably 50 mT or more and 750 mT or less. In addition, BHmax = 5.6 kJ / m³ or more and 96 kJ / m³ or less is preferred, BHmax = 7.2 kJ / m³ or more and 88 kJ / m³ or more is preferred, and BHmax = 8 kJ / m³ or more and even more preferably 8 kJ / m³ or more and 80 kJ / m³ or less.

[0031] Furthermore, from the perspective of preventing breakage, the molding density of the magnetized bonded magnet molded body is 1.6 g / cm³. 3 More than 6.0g / cm 3 The following is preferable: 1.8 g / cm³ 3 More than 5.4g / cm 3 The following is more preferable: 2.0 g / cm³ 3 More than 4.9g / cm 3 The following is even more preferable.

[0032] Bonded magnet molded bodies are preferable because they are coated with resin, which prevents deterioration such as rusting of the magnetic components.

[0033] The resin used to coat the coated bonded magnet molded body is not particularly limited as long as it can provide coverage, but examples include silicone polymers, urethane polymers, isobutylene polymers, ethylene propylene copolymers, natural rubber, ethylene propylene copolymers, ethylene propylene diene copolymers, styrene butadiene copolymers, olefin polymers, vinyl chloride resins, urethane resins, fluororesins, and the like.

[0034] The thickness of the coating resin is not particularly limited, but it is preferably in a tubular shape of about 0.01 to 1.0 mm, more preferably 0.05 to 0.7 mm, and even more preferably 0.1 to 0.5 mm.

[0035] For example, it is used in health and medical devices such as magnetic necklaces, industrial equipment such as motors and sensors, audio equipment such as CD radio cassette players, information equipment such as CD-ROMs (read-only memory using compact discs) and floppy disks, office automation equipment such as photocopiers, and automotive parts such as car speed sensors, ABS (anti-skid braking system) safety devices, door mirrors, and drive motors. [Examples]

[0036] (Example 1) 99.3 parts by weight of olefin-based thermoplastic elastomer (Milastomer(R) 8032NS, manufactured by Mitsui Chemicals) was used as the main resin. 0.3 parts by weight of lubricant and 0.4 parts by weight of stabilizer were added to this main resin to bring the total resin content to 100 parts by weight. 900 parts by weight of SmFeN magnetic powder (S1, manufactured by Sumitomo Metal Mining Co., Ltd.) was added to achieve a magnetic powder content of 90 wt%, and the mixture was kneaded and pelletized.

[0037] The above pellets were extruded at an extrusion temperature of 140°C, with a magnetic field of 2T applied to the mold (die), and at a linear speed of 5m / min to obtain a string-shaped magnetized bonded magnet molded body with a diameter of Φ3. The extrusion moldability described above was evaluated (good moldability: ◎, acceptable moldability: ○, poor moldability: △, unmoldable: ×), and the tensile strength, surface magnetic flux density, and bending test (no streaks: ◎, some streaks: ○, cracks: △, fracture: ×) of the molded body were also evaluated. Furthermore, the tensile strength, bending resistance, and surface magnetic flux density of the obtained string-shaped magnetized bonded magnet molded body were evaluated according to the following procedure. These results are shown in Table 1.

[0038] (Tensile strength) Using a small desktop testing machine (EZ-SX 500N) manufactured by Shimadzu Corporation, the maximum stress (tensile load) was measured with a sample length of 130 mm to 150 mm, a gripping width of 100 mm, and a speed of 300 mm / min. The tensile strength was then calculated using the formula: tensile strength = (maximum stress) / (cross-sectional area).

[0039] (Flexural resistance (bending test)) A test specimen with a diameter of Φ3 and a length of 150 mm (the aforementioned string-shaped magnetized bonded magnet molded body with a diameter of Φ3) was set in a testing machine (YUASA DMX-FS_B08b), and repeated bending tests were performed. The number of bending cycles until a crack occurred in the test specimen was measured.

[0040] (Surface magnetic flux density) An ADS "MODEL HGM 4002A" gaussmeter was used, and an ADS "F-1 type probe" was used as the probe (the position of the Hall element on the probe was d=0.42 mm from the surface). Using the aforementioned gaussmeter and probe, the probe was brought into contact with the surface of a bonded magnet, and the maximum magnetic flux density was measured while rotating the bonded magnet.

[0041] (Bending test) A magnetic molded body (string-like) was wrapped around metal rods (non-magnetic stainless steel) with diameters of 5 mm, 3 mm, and 1 mm at least once, and the surface of the bonded magnet was observed. The evaluation criteria were as follows: ◎: No wrinkles, cracks, or breaks; ○: No cracks or breaks; △: No breaks; ×: Breaks.

[0042] (Examples 2-7, Comparative Examples 1-4) The resin listed in Table 1 was used as the main resin, and the resin was prepared by adding the main resin, lubricant, and stabilizer in the same proportions as in Example 1. To this resin, the magnetic powder listed in Table 1 was added so that the magnetic powder content was 90 wt%, and the mixture was pelletized. These pellets were then molded into string-shaped magnetized bonded magnets in the same manner as in Example 1. The evaluation results for each molded body are shown in Table 1.

[0043] However, EEA in the table refers to NUC-6070 manufactured by ENEOS Corporation, L L The DPE is Novatec™ LL UE320 manufactured by Nippon Polyethylene Co., Ltd., the olefin-based thermoplastic elastomer is Milastomer® 8032NS manufactured by Mitsui Chemicals, and the ferrite is NF-350 manufactured by DOWA F-Tech Co., Ltd. Furthermore, the mixing ratio of the olefin-based thermoplastic elastomer and EEA in Examples 6 and 7 is 50 / 50 by weight.

[0044] (Comparative Example 5) A string-shaped magnetized bonded magnet molded body was formed in the same manner as in Example 1, except that the magnetic powder content was set to 98 wt%. The evaluation results for each molded body are shown in Table 1.

[0045] (Comparative Example 6) A string-shaped magnetized bonded magnet molded body was formed in the same manner as in Example 1, except that the magnetic powder content was set to 5 wt%. The evaluation results for each molded body are shown in Table 1.

[0046] As shown in Examples 1 to 7, materials with a tensile strength of 3 MPa to 8 MPa exhibited good extrusion moldability, and also showed good surface magnetic flux density and bending test results.

[0047] [Table 1] [Explanation of symbols]

[0048] 1. Hopper 2. Screw 3. Heater 4. Electromagnet 5. Mold (die) 6. Heating cylinder 7. Cooling water tank 8. Pickup machine 9.Cutting machine

Claims

1. A bonded magnet molded body containing magnetic powder and resin as essential components, The resin is an LLDPE selected from ZnLLDPE, ULLLDPE, and mLLLDPE. A bonded magnet molded body characterized in that the tensile strength of the bonded magnet molded body is 3 MPa or more and 8 MPa or less.

2. The bonded magnet molded body according to claim 1, characterized in that the magnetic powder consists of anisotropic rare earth magnetic powder, ferrite, or a mixture thereof.

3. A bonded magnet molded body characterized by being a magnetized material of the bonded magnet molded body described in claim 1 or 2.

4. A bonded magnet molded body characterized in that the bonded magnet molded body according to any one of claims 1 to 3 is in the shape of a string.

5. A coated bonded magnet molded body, characterized in that the bonded magnet molded body according to any one of claims 1 to 4 is coated with a resin.

6. The coated bonded magnet molded body according to claim 5, characterized in that the resin is selected from silicone polymers, urethane polymers, isobutylene polymers, ethylene propylene copolymers, natural rubber, ethylene propylene copolymers, ethylene propylene diene copolymers, styrene butadiene copolymers, olefin polymers, vinyl chloride resins, urethane resins, and fluororesins.

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