Granules for preparing neodymium-iron-boron flexible magnet, neodymium-iron-boron flexible magnet and preparation method and application of neodymium-iron-boron flexible magnet

Abstract

The invention discloses a neodymium iron boron flexible magnet which is prepared from the following raw materials in parts by weight: 93.5-94.6 wt% of neodymium iron boron magnetic powder; 0.2 wt%-0.5 wt% of a magnetic powder surface treating agent; 2.7 wt% to 3.7 wt% of a binder; 0.3 wt% to 1.0 wt% of an antioxidant; 0.5 wt% to 1.8 wt% of a plasticizer; wherein the binder is prepared by compounding an A-type thermoplastic elastomer and a B-type thermoplastic elastomer; the mass ratio of the A-type thermoplastic elastomer to the B-type thermoplastic elastomer is (1: 9)-(4: 6). The A-type thermoplastic elastomer is selected from one or more of a thermoplastic polyamide elastomer and a thermoplastic polyurethane elastomer; the B-type thermoplastic elastomer is selected from one or more of a styrene block copolymer, a dynamic vulcanization thermoplastic elastomer, a thermoplastic polyolefin elastomer and a thermoplastic polyester elastomer. The granule for the injection molding flexible magnet, which is high in magnetic powder filling ratio and high in flowability, is realized by adopting a mode of double-component magnetic powder and double-component resin, and the high-performance injection molding flexible magnet of which the maximum magnetic energy product (BH) max is 7.5-9.0 MGOe is prepared on the basis of the granule.

Description

Technical Field

[0001] The present application relates to the technical field of magnet manufacturing, and in particular to a granular material for preparing a NdFeB flexible magnet, a NdFeB flexible magnet, and a preparation method and application thereof. Background Art

[0002] As a functional material with a wide range of uses, magnetic materials play an important role in the development and progress of human society. Flexible bonded rare earth magnets are a type of bonded rare earth magnet product that is flexible, can be bent freely without cracking, has adjustable product size, and is thin, making it easy to assemble and use. It can meet the requirements of consumer electronics or micro motors that are developing in the direction of small, ultra-thin, high-speed, and high-precision, and has a promising market prospect.

[0003] At present, flexible magnets are mainly prepared by calendering with rubber as a binder. The conventional raw material preparation of rubber magnets requires processes such as open mixing, internal mixing, calendering, and pressing (vulcanization), which is not suitable for preparing flexible magnet products with complex shapes.

[0004] The injection molding process is a processing method in which plastic or rubber is mixed with magnetic powder to form granules. After the obtained granules are plasticized, they are injected into the mold cavity of a closed mold by a plunger or a reciprocating screw to form a product. The injection molding method can process products with complex shapes, precise dimensions or with inserts, but there are currently few studies on the injection molding technology for preparing high magnetic properties flexible magnets. This is mainly because flexible magnets require a higher magnetic powder filling ratio to meet the magnetic property requirements of the magnet, and the injection molding process has higher requirements on the fluidity of the granules. The higher the magnetic powder filling ratio in the granules, the less the amount of binder. The fluidity of the granules will be affected, which will lead to insufficient mold filling and the product will be prone to defects.

[0005] Based on this, CN111667967A discloses a high-fluidity SmFeN flexible bonded permanent magnet for injection molding and a preparation method thereof, wherein a rubber-based binder such as chlorinated polyethylene, polyvinyl chloride, thermoplastic polyurethane elastomer, SmFeN magnetic powder and additives are mixed and kneaded, calendered and pelletized to form a granular material, and the granular material is molded in an injection molding machine to finally prepare a high-performance flexible magnet. However, SmFeN magnetic powder is finer in particle size than NdFeB (neodymium iron boron) magnetic powder and is easily oxidized. In addition, the preparation process in this study is complicated, and the production efficiency is low, which is not conducive to mass production. Summary of the invention

[0006] In order to solve the above-mentioned deficiencies in the art, the present application aims to provide a granular material for preparing NdFeB flexible magnets, a NdFeB flexible magnet and its preparation method and application, provide a reasonable combination of magnetic powder, resin and additives for coordinated use, improve the fluidity of the granular material, and achieve a balance between the magnetic performance requirements and flexibility of the magnet.

[0007] According to one aspect of the present application, there is provided a NdFeB flexible magnet, which is prepared from the following raw materials in parts by weight:

[0008] NdFeB magnetic powder 93.5wt%-94.6wt%;

[0009] Magnetic powder surface treatment agent 0.2wt%-0.5wt%;

[0010] Binder 2.7wt%-3.7wt%;

[0011] Antioxidant 0.3wt%-1.0wt%;

[0012] Plasticizer 0.5wt%-1.8wt%;

[0013] Wherein, the binder is a compound of type A thermoplastic elastomer and type B thermoplastic elastomer;

[0014] The mass ratio of the type A thermoplastic elastomer to the type B thermoplastic elastomer is 1:9-4:6.

[0015] The type A thermoplastic elastomer is selected from one or more of thermoplastic polyamide elastomer and thermoplastic polyurethane elastomer.

[0016] The B-type thermoplastic elastomer is selected from one or more of: styrene block copolymers, dynamically vulcanized thermoplastic elastomers, thermoplastic polyolefin elastomers and thermoplastic polyester elastomers.

[0017] The styrene block copolymers include, but are not limited to, polystyrene-polybutadiene-polystyrene block copolymers, polystyrene-poly(ethylene-butylene)-polystyrene block copolymers, polystyrene-poly(ethylene-propylene)-polystyrene block copolymers, and polystyrene-polyisoprene-polystyrene block copolymers.

[0018] The dynamically vulcanized thermoplastic elastomer includes, but is not limited to, a blend of EPDM rubber and polypropylene, a blend of nitrile rubber and polypropylene, and thermoplastic vulcanizates of diene rubber and polyolefin.

[0019] According to some embodiments of the present application, the NdFeB magnetic powder is a large-particle magnetic powder with D50=50-100μm. Optionally, the NdFeB magnetic powder includes: rare earth metal elements R=20-26wt%, M=0-2.5wt%, Co=0-5wt%, B=0.98-1.1, and Fe as a balance; M is a transition metal element other than Fe and Co; Optionally, M is selected from one or more of Cu, Zr, Nb, Ti, Cr, V, Mo, and W.

[0020] According to some embodiments of the present application, it also includes compounding magnetic powder;

[0021] Optionally, the compound magnetic powder is a small-particle magnetic powder with a D50 of 2-20 μm;

[0022] Optionally, the composite magnetic powder is selected from: NdFeB composite magnetic powder, SmFeN composite magnetic powder or ferrite powder, preferably NdFeB composite magnetic powder.

[0023] According to some embodiments of the present application, the mass ratio of the NdFeB magnetic powder to the compound magnetic powder is 9:1-7:3.

[0024] According to some embodiments of the present application, the NdFeB composite magnetic powder includes: rare earth metal elements R = 20-26wt%, M = 0-2.5wt%, Co = 0-5wt%, B = 0.98-1.1, and Fe as a remainder; the M is a transition metal element other than Fe and Co; optionally, the M is selected from one or more of Cu, Zr, Nb, Ti, Cr, V, Mo, and W.

[0025] According to some embodiments of the present application, the type A thermoplastic elastomer is preferably a thermoplastic polyurethane elastomer; and the type B thermoplastic elastomer is preferably a thermoplastic polyester elastomer.

[0026] According to some embodiments of the present application, the magnetic powder surface treatment agent is selected from one or more of a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a phosphate ester, a phosphate and nano-silicon dioxide;

[0027] A silane coupling agent or a titanate coupling agent is preferred.

[0028] According to some embodiments of the present application, the plasticizer is selected from: one or more of natural wax, synthetic wax, fatty acid metal salt, silicon dioxide compound, polysiloxane, fluoroplastic, epoxy soybean oil, silicone oil, phthalate, phosphate, adipate, azelaic acid ester and sebacate, citrate, trimellitate, halogenated hydrocarbon, benzoate, fatty acid ester, pentaerythritol, epoxidized fatty ester, polyester; preferably, the phthalate includes dioctyl phthalate; the adipate includes dioctyl adipate;

[0029] Preferred are artificial synthetic wax, silicone oil, epoxidized soybean oil, dioctyl phthalate and dioctyl adipate.

[0030] According to some embodiments of the present application, the antioxidant is selected from: hindered amine antioxidants, hindered phenol antioxidants, phosphites or thioesters.

[0031] Preferred hindered phenol antioxidants include N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hydrazine and pentaerythritol tetrakis(β(3,5,-di-tert-butyl-4-hydroxyphenyl)propionate).

[0032] According to some embodiments of the present application, the maximum magnetic energy product of the NdFeB flexible magnet is ≥7.5 MGOe, and preferably the maximum magnetic energy product is 8.0-9.0 MGOe.

[0033] According to one aspect of the present application, there is provided a granular material for preparing a NdFeB flexible magnet, comprising:

[0034] NdFeB magnetic powder 93.5wt%-94.6wt%;

[0035] Magnetic powder surface treatment agent 0.2wt%-0.5wt%;

[0036] Binder 2.7wt%-3.7wt%;

[0037] Antioxidant 0.3-1.0wt%;

[0038] Plasticizer 0.5wt%-1.8wt%;

[0039] Wherein, the binder comprises type A thermoplastic elastomer and type B thermoplastic elastomer;

[0040] The mass ratio of the type A thermoplastic elastomer to the type B thermoplastic elastomer is 1:9-4:6;

[0041] The type A thermoplastic elastomer is selected from: one or more of a thermoplastic polyamide elastomer and a thermoplastic polyurethane elastomer;

[0042] The B-type thermoplastic elastomer is selected from one or more of: styrene block copolymers, dynamically vulcanized thermoplastic elastomers, thermoplastic polyolefin elastomers and thermoplastic polyester elastomers.

[0043] The melt index MVR of the pellets tested at 170°C with a load of 10 kg is 15-65 cm 3 / 10min, MFR is 80-350g / 10min; preferably, MVR is 15-55cm 3 / 10min; MFR is 80-300g / 10min.

[0044] The styrene block copolymers include, but are not limited to, polystyrene-polybutadiene-polystyrene block copolymers, polystyrene-poly(ethylene-butylene)-polystyrene block copolymers, polystyrene-poly(ethylene-propylene)-polystyrene block copolymers, and polystyrene-polyisoprene-polystyrene block copolymers; the dynamically vulcanized thermoplastic elastomers include, but are not limited to, blends of EPDM rubber and polypropylene, blends of nitrile rubber and polypropylene, and thermoplastic vulcanizates of diene rubber and polyolefins.

[0045] According to some embodiments of the present application, the NdFeB magnetic powder is a large-particle magnetic powder with D50=50-100μm. Optionally, the NdFeB magnetic powder includes: rare earth metal elements R=20-26wt%, M=0-2.5wt%, Co=0-5wt%, B=0.98-1.1, and Fe as a balance; M is a transition metal element other than Fe and Co; Optionally, M is selected from one or more of Cu, Zr, Nb, Ti, Cr, V, Mo, and W.

[0046] According to some embodiments of the present application, the granular material further includes compound magnetic powder;

[0047] Optionally, the composite magnetic powder of the granular material is a small-particle magnetic powder with a D50 of 2-20 μm;

[0048] Optionally, the small-particle magnetic powder is selected from: NdFeB composite magnetic powder, SmFeN composite magnetic powder or ferrite powder, preferably NdFeB composite magnetic powder.

[0049] According to some embodiments of the present application, the mass ratio of the NdFeB magnetic powder to the compound magnetic powder is 9 / 1-7 / 3.

[0050] According to some embodiments of the present application, the NdFeB composite magnetic powder includes: rare earth metal elements R = 20-26wt%, M = 0-2.5wt%, Co = 0-5wt%, B = 0.98-1.1, and Fe as a remainder; the M is a transition metal element other than Fe and Co; optionally, the M is selected from one or more of Cu, Zr, Nb, Ti, Cr, V, Mo, and W.

[0051] According to some embodiments of the present application, the type A thermoplastic elastomer is preferably a thermoplastic polyurethane elastomer; and the type B thermoplastic elastomer is preferably a thermoplastic polyester elastomer.

[0052] According to some embodiments of the present application, the magnetic powder surface treatment agent is selected from one or more of a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a phosphate ester, a phosphate and nano-silicon dioxide;

[0053] A silane coupling agent or a titanate coupling agent is preferred.

[0054] According to some embodiments of the present application, the plasticizer is selected from: one or more of natural wax, synthetic wax, fatty acid metal salt, silicon dioxide compound, polysiloxane, fluoroplastic, epoxy soybean oil, silicone oil, phthalate, phosphate, adipate, azelaic acid ester and sebacate, citrate, trimellitate, halogenated hydrocarbon, benzoate, fatty acid ester, pentaerythritol, epoxidized fatty ester, polyester; preferably, the phthalate includes dioctyl phthalate; the adipate includes dioctyl adipate;

[0055] Preferred are artificial synthetic wax, silicone oil, epoxidized soybean oil, dioctyl phthalate and dioctyl adipate.

[0056] According to some embodiments of the present application, the antioxidant is selected from: hindered amine antioxidants, hindered phenol antioxidants, phosphites or thioesters.

[0057] Preferred hindered phenol antioxidants include N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hydrazine and pentaerythritol tetrakis(β(3,5,-di-tert-butyl-4-hydroxyphenyl)propionate).

[0058] According to another aspect of the present application, a method for preparing the above-mentioned NdFeB flexible magnet is provided, comprising:

[0059] Surface treatment and drying of the NdFeB magnetic powder are performed to obtain dried NdFeB magnetic powder;

[0060] The dried NdFeB magnetic powder is uniformly mixed with a binder, an antioxidant and a plasticizer to obtain a mixed powder;

[0061] The mixed powder is mixed and granulated to obtain a granular material, and then injection molding is performed to obtain a NdFeB flexible magnet;

[0062] Wherein, the binder comprises type A thermoplastic elastomer and type B thermoplastic elastomer;

[0063] The mass ratio of the type A thermoplastic elastomer to the type B thermoplastic elastomer is 1:9-4:6;

[0064] The type A thermoplastic elastomer is selected from: one or more of a thermoplastic polyamide elastomer and a thermoplastic polyurethane elastomer;

[0065] The B-type thermoplastic elastomer is selected from one or more of: styrene block copolymers, dynamically vulcanized thermoplastic elastomers, thermoplastic polyolefin elastomers and thermoplastic polyester elastomers.

[0066] According to some embodiments of the present application, the mixing and granulation is mixing and granulation through a twin-screw extruder;

[0067] The twin-screw extruder has 9 mixing sections, and the mixing temperature is 140-170°C.

[0068] Optionally, the injection molding machine for injection molding has 5 temperature zones, and the injection molding temperature is 170-190°C.

[0069] According to another aspect of the present application, the above-mentioned NdFeB flexible magnet is used in product fields such as 3C, automobiles, drones, aerospace, etc.

[0070] Compared with the prior art, this application has at least the following beneficial effects:

[0071] The present application provides a NdFeB flexible magnet and a granular material for preparing the magnet. The present application adopts a two-component magnetic powder and a two-component resin method to achieve a high magnetic powder filling ratio and high fluidity, and the melt index MVR is 15-65cm 3 / 10min or MFR of 80-350g / 10min (test temperature 170℃ load 10kg) for injection molding flexible magnet particles, and the maximum magnetic energy product (BH) is prepared based on the particles max High performance injection molded flexible magnets with 7.5-9.0MGOe.

[0072] The NdFeB flexible magnet of the present application can achieve the two properties of high magnetic performance requirements and high flexibility. With the composition ratio of each component of the present application, the NdFeB flexible magnet with high filling degree and good flexibility can be prepared by injection molding. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 This is a schematic diagram of the preparation process of NdFeB flexible magnets according to an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0074] The technical solution of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0075] It is particularly important to point out that similar substitutions and modifications made to the present application are obvious to those skilled in the art, and they are all deemed to be included in the present application. Relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present application to implement and apply the technology of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments.

[0076] If no specific conditions are specified in this application, the preparation shall be carried out under conventional conditions or the conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, for which the manufacturers are not specified, are all conventional products that can be obtained commercially.

[0077] The application is described in detail below.

[0078] A patent application of the applicant, CN111667967A, discloses a method for preparing a flexible bonded rare earth permanent magnet, wherein NdFeB magnetic powder, a thermoplastic elastomer binder having the properties of an engineering plastic, and a processing aid are uniformly mixed, and then the flexible bonded magnet is prepared by injection, calendering or extrusion molding process, and the mixing method includes high-speed mixing method, internal mixing method, open mixing method and twin-screw mixing. Based on this, the applicant found that the magnetic powder filling ratio of the magnet prepared by the injection molding process is lower than the magnetic powder filling ratio of the magnet prepared by the calendering or extrusion molding process. Through multiple groups of experimental verification, it was found that the magnetic powder filling ratio of the conventional injection molding process is up to 92.1wt%, while the magnetic powder filling ratios of the other two processes are up to 95.5wt% and 96.5wt%, respectively.

[0079] Further analysis shows that the higher the filling ratio of magnetic powder, the lower the flexibility (or tensile strength) of the magnet and the lower the fluidity of the granules. Injection molding magnets have strict requirements on the fluidity of granules. If the fluidity is too low, it will cause problems such as mold filling difficulties, mold sticking, and uneven distribution of product performance. Therefore, it is very necessary to improve the fluidity of granules.

[0080] Therefore, it is necessary to further increase the magnetic powder filling ratio of injection molded flexible magnets without reducing the flexibility requirements. It is necessary to explore the reasonable combination and coordinated use of magnetic powder, binders or additives to find a balance between magnetic performance requirements and flexibility performance.

[0081] The present application uses thermoplastic elastomer (hereinafter referred to as TPE) as a binder, and a compound system of type A TPE resin and type B TPE resin can be selected to improve the magnetic powder filling ratio and the fluidity of the granular material.

[0082] Selection of raw material types used for pellets in this application.

[0083] Magnetic powder: 93.5wt%-94.6wt%, ① single main magnetic powder system or ② main magnetic powder and compound magnetic powder combination system. Main magnetic powder (large particle size magnetic powder): isotropic NdFeB and anisotropic NdFeB (including but not limited to HDDR powder) can be selected, the composition of NdFeB is R = 20-26wt%, M = 0-2.5wt%, Co = 0-5wt%, B = 0.98-1.1, Fe balance, average particle size D50 = 50-100μm; Compound magnetic powder (small particle size magnetic powder): one of NdFeB, SmFeN and ferrite, average particle size D50 = 2-10 micron fine powder, wherein the ratio of main magnetic powder / compound magnetic powder is 9:1-7:3.

[0084] TPE (binder): 2.7wt%-3.7wt%, type A TPE + type B TPE are compounded and used, and the mass ratio of type A TPE / type B TPE = 1 / 9-4 / 6.

[0085] Magnetic powder surface treatment agent: 0.2wt%-0.5wt%, surface treatment can be achieved by coupling the surface treatment agent with the magnetic powder, so that the magnetic powder is coated with the surface treatment agent to reduce oxidation of the magnetic powder.

[0086] Plasticizer: 0.5wt%-1.8wt%, to improve the flexibility of magnet and the fluidity of granular materials while ensuring strength. Natural wax, artificial wax, fatty acid metal salt, silicon dioxide compound, polysiloxane, fluoroplastic, epoxy soybean oil, silicone oil, phthalate (especially dioctyl phthalate), phosphate, adipate (especially dioctyl adipate), azelaic acid ester and sebacate, citrate, trimellitate, halogenated hydrocarbon, benzoate, fatty acid ester (including oleate, stearate, ricinoleate, etc.), pentaerythritol, epoxidized fatty ester, polyester and some polycondensates can be selected; preferably, one or more compound systems of artificial synthetic wax, silicone oil, epoxy soybean oil, dioctyl phthalate, dioctyl adipate, etc. are selected.

[0087] Antioxidant: 0.3wt%-1.0wt%, reduces the thermal decomposition of resin and reduces the corrosion of resin thermal decomposition products to magnetic powder. It can be selected from one or more compound systems of hindered amines, hindered phenols (butylated hydroxytoluene (BHT) or 2,6-di-tert-butyl-4-methylphenol, etc., especially N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hydrazine or tetrakis(β(3,5,-di-tert-butyl-4-hydroxyphenyl)propionate)pentaerythritol), phosphites, thioesters, etc.

[0088] Preparation of granular material of the present application.

[0089] Magnetic powder preparation: prepared by rapid quenching process, crushed by double roll crusher;

[0090] Magnetic powder surface treatment: The magnetic powder is surface treated using at least one of a silane coupling agent, a titanate coupling agent and a phosphate coupling agent.

[0091] Premixing: Use a high-speed mixer to premix the magnetic powder, resin (binder), and other additives in a powder state.

[0092] Mixing and granulation: Magnetic powder, resin and additives are mixed and granulated by a twin-screw extruder. The twin-screw extruder has 9 mixing sections. The maximum mixing temperature is 170°C and the minimum mixing temperature is 140°C.

[0093] Injection molding: The granules obtained after mixing and granulation are injection molded. The injection molding machine has 5 temperature zones, with the highest temperature of 190°C and the lowest temperature of 170°C.

[0094] The technical solution of the present application is further described below in conjunction with embodiments.

[0095] The characteristic parameters of the NdFeB magnetic powder used in the examples and comparative examples of the present application are shown in Table 1:

[0096] Table 1

[0097] characteristic unit Large particle size NdFeB magnetic powder Small particle size NdFeB magnetic powder Remanence(Br) Gs 9077 8700 Coercivity (Hcb) Oe 7273 6600 Intrinsic coercivity (Hcj) Oe 9955 9800 <![CDATA[Maximum energy product ((BH) max )]]> MGO 17.4 14.8 Average particle size D50 μm 57.79 4.53

[0098] Example 1

[0099] Preparation of the NdFeB flexible magnet of this application:

[0100] Magnetic powder pretreatment: 94.00wt% of large-particle size NdFeB magnetic powder is surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder;

[0101] Mixing: The dried magnetic powder, 2.74wt% of thermoplastic polyester elastomer, 0.68wt% of thermoplastic polyurethane elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate are uniformly mixed at room temperature using a high-speed mixer to obtain a mixed powder;

[0102] Preparation of granular material: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granular material for injection molding. The twin-screw compounding extruder is composed of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0103] Injection molding: The prepared pellets are injection molded using an injection molding machine, which has 5 temperature zones, with the highest temperature being 190°C and the lowest temperature being 170°C.

[0104] Example 2

[0105] Preparation of the NdFeB flexible magnet of this application:

[0106] Magnetic powder pretreatment: 84.60wt% of large-particle size NdFeB magnetic powder and 9.40wt% of small-particle size NdFeB magnetic powder are surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder;

[0107] Mixing: The dried magnetic powder, 2.74wt% of thermoplastic polyester elastomer, 0.68wt% of thermoplastic polyurethane elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate are uniformly mixed at room temperature using a high-speed mixer to obtain a mixed powder;

[0108] Injection molding: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granules for injection molding. The twin-screw compounding extruder consists of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0109] Example 3

[0110] Preparation of the NdFeB flexible magnet of this application:

[0111] Magnetic powder pretreatment: 85.10wt% of large-particle size NdFeB magnetic powder and 9.46wt% of small-particle size NdFeB magnetic powder are surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder;

[0112] Mixing: The dried magnetic powder is mixed evenly with 2.29wt% of thermoplastic polyester elastomer, 0.57wt% of thermoplastic polyurethane elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil and 1.00wt% of dioctyl adipate using a high-speed mixer at room temperature to obtain a mixed powder.

[0113] Injection molding: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granules for injection molding. The twin-screw compounding extruder consists of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0114] Example 4

[0115] Preparation of the NdFeB flexible magnet of this application:

[0116] Magnetic powder pretreatment: 84.5wt% of large-particle size NdFeB magnetic powder and 9.39wt% of small-particle size NdFeB magnetic powder are surface treated with 0.47wt% of titanate coupling agent, and the solvent is dried to obtain dried magnetic powder;

[0117] Mixing: The dried magnetic powder is mixed evenly with 2.67wt% of thermoplastic polyolefin elastomer, 0.67wt% of thermoplastic polyamide elastomer, 1.0wt% of 2,6-di-tert-butyl-4-methylphenol, 0.30wt% of silicone oil, 0.50wt% of epoxy soybean oil and 0.50wt% of dioctyl phthalate using a high-speed mixer at room temperature to obtain a mixed powder.

[0118] Injection molding: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granules for injection molding. The twin-screw compounding extruder consists of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0119] Example 5

[0120] Preparation of the NdFeB flexible magnet of this application:

[0121] Magnetic powder pretreatment: 93.74wt% of large-particle size NdFeB magnetic powder is surface treated with 0.28wt% of phosphate, and the solvent is dried to obtain dried magnetic powder;

[0122] Mixing: The dried magnetic powder, 3.11wt% of polystyrene-poly(ethylene-butylene)-polystyrene block copolymer, 2.07wt% of thermoplastic polyamide elastomer, 0.3wt% of N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hydrazine, and 0.50wt% of dioctyl adipate are mixed uniformly at room temperature using a high-speed mixer to obtain a mixed powder.

[0123] Injection molding: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granules for injection molding. The twin-screw compounding extruder consists of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0124] Example 6

[0125] Preparation of the NdFeB flexible magnet of this application:

[0126] Magnetic powder pretreatment: 65.84wt% of large-particle size NdFeB magnetic powder and 28.22wt% of small-particle size NdFeB magnetic powder are surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder;

[0127] Mixing: The dried magnetic powder, 3.36wt% of thermoplastic polyester elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate are uniformly mixed at room temperature using a high-speed mixer to obtain a mixed powder;

[0128] Preparation of granular material: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granular material for injection molding. The twin-screw compounding extruder is composed of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0129] Injection molding: The prepared pellets are injection molded using an injection molding machine, which has 5 temperature zones, with the highest temperature being 190°C and the lowest temperature being 170°C.

[0130] Example 7

[0131] Preparation of the NdFeB flexible magnet of this application:

[0132] Magnetic powder pretreatment: 84.61wt% of large-particle size NdFeB magnetic powder and 9.4wt% of small-particle size NdFeB magnetic powder are surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder;

[0133] Mixing: The dried magnetic powder, 3.07wt% of thermoplastic polyester elastomer, 0.34wt% of thermoplastic polyurethane elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate are uniformly mixed at room temperature using a high-speed mixer to obtain a mixed powder;

[0134] Preparation of granular material: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granular material for injection molding. The twin-screw compounding extruder is composed of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0135] Injection molding: The prepared pellets are injection molded using an injection molding machine, which has 5 temperature zones, with the highest temperature being 190°C and the lowest temperature being 170°C.

[0136] Example 8

[0137] Preparation of the NdFeB flexible magnet of this application:

[0138] Magnetic powder pretreatment: 75.19wt% of large-particle size NdFeB magnetic powder and 18.8wt% of small-particle size NdFeB magnetic powder are surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder;

[0139] Mixing: The dried magnetic powder, 2.47wt% of thermoplastic polyester elastomer, 0.69wt% of thermoplastic polyurethane elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate are uniformly mixed at room temperature using a high-speed mixer to obtain a mixed powder;

[0140] Preparation of granular material: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granular material for injection molding. The twin-screw compounding extruder is composed of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0141] Injection molding: The prepared pellets are injection molded using an injection molding machine, which has 5 temperature zones, with the highest temperature being 190°C and the lowest temperature being 170°C.

[0142] Example 9

[0143] Preparation of the NdFeB flexible magnet of this application:

[0144] Magnetic powder pretreatment: 56.4wt% of large-particle size NdFeB magnetic powder and 37.6wt% of small-particle size NdFeB magnetic powder are surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder;

[0145] Mixing: The dried magnetic powder, 2.74wt% of thermoplastic polyester elastomer, 0.68wt% of thermoplastic polyurethane elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate are uniformly mixed at room temperature using a high-speed mixer to obtain a mixed powder;

[0146] Preparation of granular material: The mixed powder is compounded and granulated in a twin-screw compounding extruder to obtain granular material for injection molding. The twin-screw compounding extruder is composed of 9 mixing sections, with a maximum mixing temperature of 170°C and a minimum mixing temperature of 140°C.

[0147] Injection molding: The prepared pellets are injection molded using an injection molding machine, which has 5 temperature zones, with the highest temperature being 190°C and the lowest temperature being 170°C.

[0148] Comparative Example 1

[0149] Preparation of a comparative example of a NdFeB flexible magnet: The preparation method is the same as that of the example, with the following differences:

[0150] 94.00wt% of large-particle NdFeB magnetic powder is surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder, which is mixed with 3.42wt% of thermoplastic polyester elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate by a high-speed mixer at room temperature to obtain a mixed powder.

[0151] Comparative Example 2

[0152] Preparation of a comparative example of a NdFeB flexible magnet: The preparation method is the same as that of the example, with the following differences:

[0153] 93.7wt% of large-particle NdFeB magnetic powder is surface treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder, which is then mixed with 3.72wt% of thermoplastic polyurethane elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate using a high-speed mixer at room temperature to obtain a mixed powder.

[0154] Comparative Example 3

[0155] Preparation of a comparative example of a NdFeB flexible magnet: The preparation method is the same as that of the example, with the following differences:

[0156] 84.64wt% of large-particle NdFeB magnetic powder and 9.4wt% of small-particle NdFeB magnetic powder are surface treated with 0.28wt% of silane coupling agent, and after drying the solvent, dried magnetic powder is obtained, which is mixed with 3.38wt% of thermoplastic polyester elastomer, 0.50wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate by a high-speed mixer at room temperature to obtain a mixed powder.

[0157] Comparative Example 4

[0158] Preparation of a comparative example of a NdFeB flexible magnet: The preparation method is the same as that of the example, with the following differences:

[0159] 83.5wt% of large-particle NdFeB magnetic powder and 9.28wt% of small-particle NdFeB magnetic powder are surface-treated with 0.28wt% of silane coupling agent, and the solvent is dried to obtain dried magnetic powder, which is then mixed with 4.18wt% of thermoplastic polyester elastomer, 0.46wt% of thermoplastic polyurethane elastomer, 0.5wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate by a high-speed mixer at room temperature to obtain a mixed powder.

[0160] Comparative Example 5

[0161] Preparation of a comparative example of a NdFeB flexible magnet: The preparation method is the same as that of the example, with the following differences:

[0162] 89.19wt% of large-particle NdFeB magnetic powder and 4.69wt% of small-particle NdFeB magnetic powder are surface-treated with 0.28wt% of silane coupling agent, and after drying the solvent, dried magnetic powder is obtained, which is mixed with 1.77wt% of thermoplastic polyester elastomer, 1.77wt% of thermoplastic polyurethane elastomer, 0.5wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate by a high-speed mixer at room temperature to obtain a mixed powder.

[0163] Comparative Example 6

[0164] Preparation of a comparative example of a NdFeB flexible magnet: The preparation method is the same as that of the example, with the following differences:

[0165] 84.6wt% of large-particle NdFeB magnetic powder and 9.4wt% of small-particle NdFeB magnetic powder are surface-treated with 0.28wt% of silane coupling agent, and after drying the solvent, dried magnetic powder is obtained, which is mixed with 3.09wt% of thermoplastic polyester elastomer, 0.33wt% of thermoplastic polyurethane elastomer, 0.5wt% of pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.30wt% of wax liquid, 0.50wt% of epoxy soybean oil, and 1.00wt% of dioctyl adipate by a high-speed mixer at room temperature to obtain a mixed powder.

[0166] Experimental example

[0167] 1. Test the properties of the pellets in the above embodiments and comparative examples. Test conditions: 170°C, load 10kg. The results are shown in Table 2:

[0168] Table 2

[0169]

[0170]

[0171] According to the data in Table 2, it can be seen from the comparison between Example 1 and Comparative Example 1 that the use of the two-component resin (binder) of the present application increases the melt index MVR of the pellets from the original 2.5 cm 3 / 10min increased to 20.1cm 3 / 10min; MFR increased from 14g / 10min to 110g / 10min (test temperature 170℃ load 10kg).

[0172] Compared with Example 1, Example 2 shows that the use of the large and small particle size composite two-component magnetic powder of the present application makes the melt index MVR of the granular material increase from 20cm 3 / 10min increased to 36.5cm 3 / 10min; MFR increased from 110g / 10min to 202g / 10min (test temperature 170℃ load 10kg).

[0173] Compared with Example 2, Example 3 shows that the use of the large and small particle size composite two-component magnetic powder of the present application can increase the magnetic powder filling ratio to 94.56wt%, and still keep the melt index MVR of the granular material at 15.3cm 3 / 10min, MFR remained at 87g / 10min.

[0174] The TPE type NdFeB granules prepared in Comparative Example 1 have a melt index MVR of only 2.5 cm 3 / 10min (test temperature 170℃ load 10kg), the TPE NdFeB granules prepared in Comparative Example 2 have a melting index MVR as high as 127.6cm 3 / 10min (test temperature 170℃ load 10kg). However, the high-fluidity TPE-type NdFeB granules have relatively poor strength, toughness and other properties; if the TPE-type NdFeB granules meet the requirements of strength, toughness and other properties, the fluidity is poor and cannot be injection molded.

[0175] 2. The granular materials prepared in the examples and comparative examples were injection molded using an injection molding machine, and the properties of the injection molded samples were tested.

[0176] Characterization methods:

[0177] Bending strength: Injection molded into 80mm×10mm×4mm long strips, the bending strength test is carried out according to standard ISO 178-2019 or GB / T9341-2000, and the bending strength is greater than or equal to 4.5MPa.

[0178] Cylinder winding test: Injection molded into a long strip of 80mm×10mm×1mm, wrap it tightly around a cylinder with a cross-sectional diameter of Φ25mm, Φ18mm, Φ14mm or Φ10mm and a length of 150mm-200mm for one week, and observe whether the spline has cracks. The best is to be able to wrap tightly around a cylinder with a cross-sectional diameter of Φ10mm for one week without breaking or visible cracks.

[0179] Tensile strength ISO 527-1,2: The tensile strength test is carried out in accordance with the standard GB / T 1040.2-2006 (ie ISO 527-2:1993). The dumbbell-shaped tensile specimens are injection molded and tested for tensile strength (unit: MPa) and elongation at break (unit: %) using a universal tensile testing machine.

[0180] High temperature demagnetization under hot and humid conditions: Injection molded into a standard sample column of Φ10mm*(8-10)mm. Treated in a hot and humid oven at 65℃ and 90% humidity for 72 hours, observe the change in magnetic flux of the magnet before and after hot and humid conditions, and observe whether the magnet has rust spots, cracks, powdering, etc.

[0181] The sizes of the molded samples are Φ10mm×10mm, 80mm×10mm×4mm and 80mm×10mm×1mm. The injection molding temperature is 170-190℃. The injection molding conditions are shown in Table 3. The test results of the injection molding sample properties are shown in Table 4.

[0182] Table 3 Injection molding temperature gradient

[0183] One section Second paragraph Three sections Four sections Five sections Mold temperature 190℃ 190℃ 190℃ 180℃ 170℃ 30℃

[0184] Table 4 Properties of injection molded samples in Example

[0185]

[0186] Table 5 Comparative Example Injection Molding Sample Properties

[0187]

[0188] According to the injection molding sample characteristic data in the above table, it can be seen that the granular materials of Comparative Examples 1, 2, and 5 have poor fluidity and cannot be injection molded. Although Comparative Examples 3 and 6 can be injection molded into magnets, the flexibility of the magnets is poor, and the minimum cylindrical diameter that can be wound around is only 18 mm. Although Comparative Example 4 can be injection molded and has good flexibility, the maximum magnetic energy product of the magnet is only 7.241 MGOe.

[0189] Compared with the comparative example, the granular material of the embodiment of the present application has better fluidity, and the magnet prepared therefrom shows excellent performance in terms of filling degree, flexibility, bending strength, tensile strength, etc., especially the maximum magnetic energy product can reach up to 9.002MGOe.

[0190] The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. It should be noted that, for ordinary technicians in this technical field, several improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A NdFeB flexible magnet, characterized in that: It is prepared from the following raw materials in parts by weight: NdFeB magnetic powder 93.5wt%-94.6wt%; Magnetic powder surface treatment agent 0.2wt%-0.5wt%; Binder 2.7wt%-3.7wt%; Antioxidant 0.3wt%-1.0wt%; Plasticizer 0.5wt%-1.8wt%; Wherein, the binder comprises type A thermoplastic elastomer and type B thermoplastic elastomer; The mass ratio of the type A thermoplastic elastomer to the type B thermoplastic elastomer is 1:9-4:6; The type A thermoplastic elastomer is selected from: one or more of a thermoplastic polyamide elastomer and a thermoplastic polyurethane elastomer; The B-type thermoplastic elastomer is selected from one or more of: styrene block copolymers, dynamically vulcanized thermoplastic elastomers, thermoplastic polyolefin elastomers and thermoplastic polyester elastomers.

2. The NdFeB flexible magnet according to claim 1, characterized in that: The D50 of the NdFeB magnetic powder is 50-100 μm; Preferably, the raw material further comprises compound magnetic powder with a D50 of 2-20 μm; Preferably, the composite magnetic powder is selected from: NdFeB composite magnetic powder, SmFeN composite magnetic powder or ferrite powder, preferably NdFeB composite magnetic powder; Preferably, the mass ratio of the NdFeB magnetic powder to the composite magnetic powder is 9:1-7:3; Preferably, the composition of the NdFeB magnetic powder and the NdFeB composite magnetic powder includes: rare earth metal elements R = 20-26wt%, M = 0-2.5wt%, Co = 0-5wt%, B = 0.98-1.1, and Fe as a remainder; the M is a transition metal element other than Fe and Co; preferably, the M is selected from one or more of Cu, Zr, Nb, Ti, Cr, V, Mo, and W.

3. The NdFeB flexible magnet according to claim 1, characterized in that: The type A thermoplastic elastomer is a thermoplastic polyurethane elastomer; Preferably, the styrene block copolymer includes but is not limited to: polystyrene-polybutadiene-polystyrene block copolymer, polystyrene-poly(ethylene-butylene)-polystyrene block copolymer, polystyrene-poly(ethylene-propylene)-polystyrene block copolymer, polystyrene-polyisoprene-polystyrene block copolymer; Preferably, the dynamically vulcanized thermoplastic elastomer includes but is not limited to: a blend of EPDM rubber and polypropylene, a blend of nitrile rubber and polypropylene, a thermoplastic vulcanizate of diene rubber and polyolefin; More preferably, the B-type thermoplastic elastomer is a thermoplastic polyester elastomer.

4. The NdFeB flexible magnet according to claim 1, characterized in that: The magnetic powder surface treatment agent is selected from one or more of silane coupling agent, titanate coupling agent, aluminate coupling agent, phosphate ester, phosphate and nano silicon dioxide; preferably, silane coupling agent or titanate coupling agent; Preferably, the plasticizer is selected from: one or more of natural wax, synthetic wax, fatty acid metal salt, silicon dioxide compound, polysiloxane, fluoroplastic, epoxy soybean oil, silicone oil, phthalate, phosphate, adipate, azelaic acid ester, sebacate, citrate, trimellitate, halogenated hydrocarbon, benzoate, fatty acid ester, pentaerythritol, epoxidized fatty ester, polyester; Preferably, the plasticizer is selected from: one or more of artificial synthetic wax, silicone oil, epoxy soybean oil, dioctyl phthalate and dioctyl adipate; Preferably, the antioxidant is selected from: hindered amine antioxidants, hindered phenol antioxidants, phosphites or thioesters; Preferably, the hindered phenol antioxidant includes N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hydrazine and pentaerythritol tetrakis(β(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).

5. The NdFeB flexible magnet according to any one of claims 1 to 4, characterized in that: The maximum magnetic energy product of the NdFeB flexible magnet is ≥7.5 Goe; Preferably, the maximum magnetic energy product of the NdFeB flexible magnet is 8.0-9.0 MGOe.

6. A granular material for preparing NdFeB flexible magnets, characterized in that: It is prepared from the following raw materials in parts by weight: NdFeB magnetic powder 93.5wt%-94.6wt%; Magnetic powder surface treatment agent 0.2wt%-0.5wt%; Binder 2.7wt%-3.7wt%; Antioxidant 0.3-1.0wt%; Plasticizer 0.5wt%-1.8wt%; Wherein, the binder comprises type A thermoplastic elastomer and type B thermoplastic elastomer; The mass ratio of the type A thermoplastic elastomer to the type B thermoplastic elastomer is 1:9-4:6; The type A thermoplastic elastomer is selected from: one or more of a thermoplastic polyamide elastomer and a thermoplastic polyurethane elastomer; The B-type thermoplastic elastomer is selected from: one or more of styrene block copolymers, dynamically vulcanized thermoplastic elastomers, thermoplastic polyolefin elastomers and thermoplastic polyester elastomers; The melt index MVR of the pellets tested at 170°C with a load of 10 kg is 15-65 cm 3 / 10min, or MFR is 80-350g / 10min; Preferably, MVR is 15-55 cm 3 / 10min or MFR is 80-300g / 10min.

7. The granular material according to claim 6, characterized in that: The D50 of the NdFeB magnetic powder is 50-100 μm; Preferably, the granular material further comprises compound magnetic powder with a D50 of 2-20 μm; Preferably, the mass ratio of the NdFeB magnetic powder to the composite magnetic powder is 9:1-7:3; Preferably, the composite magnetic powder is selected from: NdFeB composite magnetic powder, SmFeN composite magnetic powder or ferrite powder, preferably NdFeB composite magnetic powder; Preferably, the composition of the NdFeB magnetic powder and the NdFeB composite magnetic powder includes: rare earth metal elements R = 20-26wt%, M = 0-2.5wt%, Co = 0-5wt%, B = 0.98-1.1, and Fe as a remainder; the M is a transition metal element other than Fe and Co; the M is selected from one or more of Cu, Zr, Nb, Ti, Cr, V, Mo, and W.

8. A method for preparing a NdFeB flexible magnet, characterized in that: include: Surface treatment and drying of NdFeB magnetic powder; The dried NdFeB magnetic powder is mixed evenly with a binder, an antioxidant and a plasticizer to obtain a mixed powder; The granules obtained by mixing and granulating the mixed powder are injection molded to obtain the granules; Wherein, the binder comprises type A thermoplastic elastomer and type B thermoplastic elastomer; The mass ratio of the type A thermoplastic elastomer to the type B thermoplastic elastomer is 1:9-4:6; The type A thermoplastic elastomer is selected from: one or more of a thermoplastic polyamide elastomer and a thermoplastic polyurethane elastomer; The B-type thermoplastic elastomer is selected from one or more of: styrene block copolymers, dynamically vulcanized thermoplastic elastomers, thermoplastic polyolefin elastomers and thermoplastic polyester elastomers.

9. The preparation method according to claim 8, characterized in that: The mixing and granulation is carried out by a twin-screw extruder; The twin-screw extruder has 9 mixing sections, and the mixing temperature is 140-170°C; Preferably, the injection molding machine for injection molding has 5 temperature zones, and the injection molding temperature is 170-190°C.

10. Application of the NdFeB magnet according to any one of claims 1 to 5, and / or the NdFeB magnet prepared by the preparation method according to any one of claims 8 to 9 in the fields of 3C products, automobiles, drones, and aerospace products.

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