High-stability bonded neodymium iron boron magnetic material and preparation method thereof

Abstract

The invention relates to a high-stability bonded neodymium iron boron magnetic material and a preparation method thereof. The preparation method comprises the following steps: 1) grinding and homogenizing: weighing nano neodymium-iron-boron magnetic powder, mixing the nano neodymium-iron-boron magnetic powder with dispersion liquid A, and grinding to obtain a mixture A; weighing nano neodymium-iron-boron magnetic powder, mixing the nano neodymium-iron-boron magnetic powder with the dispersion liquid B, and grinding to obtain a mixture B; uniformly mixing the mixture B with the mixture A to obtain a mixture C; (2) impurity removal and preforming are conducted, specifically, the mixture C is put into a mold, under the vacuum condition, the temperature is increased to 100-105 DEG C at the temperature of 5-10 DEG C, heat preservation is conducted for 10-30 min, meanwhile, in the heating process, the mixture C in the mold is gradually pressurized at the speed of 1-3 MPa / min till heat preservation is conducted, pressurization is stopped, and a blank is obtained; 3) curing and molding: curing the blank to obtain the bonded neodymium-iron-boron magnetic material.The magnetic material obtained by the scheme has higher density, and better impact toughness and magnetic performance stability are ensured.

Description

Technical Field

[0001] This application relates to the field of magnet manufacturing, and more specifically, to a highly stable bonded neodymium iron boron magnetic material and its preparation method. Background Technology

[0002] Bonded NdFeB magnetic materials are a type of composite magnetic material prepared by mixing, molding, curing, or melting and cooling NdFeB permanent magnet powder as the core magnetic energy carrier and supplementing it with a polymer binder. They retain the core magnetic properties of NdFeB permanent magnets, such as high energy product and high coercivity, while also possessing the advantages of bonded materials, such as easy processing, high molding precision, the ability to form complex and irregular structures, and high production efficiency. This effectively compensates for the shortcomings of sintered NdFeB magnetic materials, such as high brittleness, high processing difficulty, limited molding, and high cost. Due to their excellent comprehensive performance, bonded NdFeB magnetic materials have been widely applied in many core fields such as electronics and information technology, automotive industry, new energy, medical devices, and aerospace, becoming an indispensable key functional material in modern high-end manufacturing. In the field of electronic information, it is used in precision components such as micro motors and hard disk drives; in the automotive industry, it is adapted to core components such as drive motors for new energy vehicles; in the field of new energy, it can be used in magnetic circuit structures for wind turbines; and it also has irreplaceable applications in medical devices such as MRI equipment and precision instruments in aerospace.

[0003] In existing technologies, to achieve effective bonding between NdFeB permanent magnet powder particles and with the matrix, a relatively large amount of polymeric binder is typically added, generally accounting for a certain proportion of the total material mass. Commonly used polymeric binders include thermoplastic resins such as epoxy resin, polyethylene, and polypropylene, or thermosetting resins such as polyurethane acrylate. Meanwhile, existing processes mostly employ traditional methods in mixing, molding, and curing. For example, the magnetic powder and binder are directly mixed during mixing; molding uses conventional methods such as compression molding and injection molding; and curing is carried out under conventional temperature and time conditions.

[0004] However, existing bonded NdFeB magnetic materials struggle to achieve good structural stability while maintaining high density. On one hand, the presence of a large amount of binder significantly reduces the overall density of the material, preventing the full utilization of magnetic properties and exacerbating structural instability. On the other hand, most polymer binders lack sufficient toughness and have poor interfacial compatibility with NdFeB permanent magnet powder. The interface between the two easily forms stress concentration points, significantly increasing the brittleness of the material after molding. Under external forces such as vibration and impact, internal cracks easily propagate, powder detaches, and ultimately, the material fractures and cracks.

[0005] On the other hand, the inherent characteristics of commonly used polymeric adhesives further exacerbate this contradiction. For example, epoxy resin adhesives have high viscosity, making it difficult to evenly disperse with NdFeB permanent magnet powder during mixing. This easily leads to localized agglomeration or adhesive-rich areas, and the cross-linked structure after curing is rigid and brittle, further reducing the material's impact resistance. Meanwhile, thermoplastic resins such as polyethylene and polypropylene require melting under heat to mix with the magnetic powder, but their poor interfacial wettability with the powder results in uneven dispersion and weak interfacial bonding after cooling and molding. This leads to microscopic pores or weak areas within the material, significantly reducing the structural stability of bonded NdFeB magnetic materials. These factors cause existing bonded NdFeB magnetic materials to experience a significant decrease in magnetic properties under harsh conditions, such as high temperature and high humidity, severely impacting their service life and reliability. Summary of the Invention

[0006] To further improve density while ensuring better impact toughness and magnetic property stability, a highly stable bonded NdFeB magnetic material and its preparation method are provided.

[0007] Firstly, a method for preparing a highly stable bonded NdFeB magnetic material is provided, which is obtained by the following method: 1) Grinding and homogenization: Weigh out nano-neodymium iron boron magnetic powder and mix it with dispersion A and grind it to obtain mixture A; weigh out nano-neodymium iron boron magnetic powder and mix it with dispersion B and grind it to obtain mixture B; mix mixture B and mixture A evenly to obtain mixture C; 2) Impurity removal and preforming: Place the C mixture into a mold, and under vacuum conditions, heat it from 5-10℃ to 100-105℃ and hold it for 10-30 minutes. At the same time, during the heating process, gradually pressurize the C mixture inside the mold at 1-3MPa / min until the temperature is held, then stop pressurizing to obtain the blank. 3) Curing and molding: The blank is cured to obtain bonded NdFeB magnetic material; Dispersion B comprises: PI adhesive, methyl vinyl silicone hybrid aromatic resin, dispersant, initiator, and first diluent; Dispersion A comprises: multifunctional polyurethane acrylate, a dispersant, and a second diluent; the proportion of nano-neodymium iron boron magnetic powder in the adhesive NdFeB magnetic material is greater than 90%.

[0008] By adopting the above technical solution, this application has the following advantages: At the process level: the magnetic powder is tightly bonded and its density is increased through the processing steps of "grinding and homogenization - impurity removal and pre-forming - curing and forming".

[0009] Specifically, in the grinding and homogenization process: a stepwise dispersion strategy of dispersion liquid A and dispersion liquid B is adopted, and nano-level neodymium iron boron magnetic powder is used to mix with it, which solves the problems of poor interfacial compatibility and easy agglomeration between traditional single binder and magnetic powder, improves the dispersion uniformity of magnetic powder in the final mixture, eliminates structural defects, and lays the foundation for high-density molding. In the impurity removal and preforming process: the gradual heating and pressurization under vacuum facilitates the rapid removal of small molecules, and the interaction between active groups further stabilizes the structure.

[0010] In the final curing and molding process: the material further reacts and solidifies, forming a dense, bonded neodymium iron boron magnetic material.

[0011] At the raw material level: By forming a ternary blend adhesive network of "polyimide-silicon hybrid aromatic yne-polyurethane acrylate" after curing, a synergistic breakthrough in mechanical properties and stability is achieved.

[0012] Specifically, the dispersant contained in dispersions B and A not only promotes the dispersion and compatibility of their raw material systems, but also prevents the agglomeration of nano-neodymium iron boron magnetic powder and ensures the uniformity of dispersion and the stability of compatibility of the entire raw material system.

[0013] Specifically, this application utilizes a "gradual heating and pressurization under vacuum conditions" process, which, together with the hydrophobic composite system of "polyimide-silicon hybrid aromatic yne-polyurethane acrylate" of this application, simultaneously completes "impurity removal-densification-pre-crosslinking" to construct a ternary blend bonding network of "polyimide-silicon hybrid aromatic yne-polyurethane acrylate", eliminates micropores inside the material, increases the material density, forms a "semi-cured-highly dense" preform structure, and improves structural stability.

[0014] During the curing and molding stage, precise temperature control enables full cross-linking and structural locking of the ternary bonding network, improving the tensile and impact strength of the bonding skeleton. Ultimately, the product density approaches that of sintered NdFeB, significantly enhancing impact strength and preventing moisture from penetrating into the magnetic material. Under harsh working conditions, the structural integrity and magnetic performance stability are significantly superior to existing products, greatly extending the service life.

[0015] Preferably, the mixture B is mixed with the mixture A at a rotation speed of 100-200 r / min for 10-20 min.

[0016] By adopting the above technical solution, mixing mixture B with mixture A at a rotation speed of 100-200 r / min for 10-20 min helps to make the two mix more uniformly, further improves the dispersion uniformity of nano-neodymium iron boron magnetic powder in the final mixture, eliminates the structural defects of "binder enrichment zone" and "magnetic powder agglomeration zone", and lays a better foundation for the subsequent preparation of high-density and high-stability bonded neodymium iron boron magnetic materials.

[0017] Preferably, the curing conditions in step 3) are as follows: heat up to 180-200℃ at 3-5℃, hold for 10-20 minutes, then continue to heat up to 225-250℃, hold for 30-60 minutes, then continue to heat up to 305-320℃, hold for 10-20 minutes.

[0018] By employing the above technical solution, precise temperature control during the curing and molding stage enables full cross-linking and structural locking of the ternary adhesive network. The pre-curing stage completes solvent removal and initial cross-linking, ensuring no deformation of the preform. The final curing stage promotes complete cyclization of polyimide and deep copolymerization of silicon-hybridized aromatic resin and polyurethane acrylate, forming a three-dimensional cross-linked network, significantly improving the tensile and impact strength of the adhesive skeleton. After high and low temperature cycling, the final product exhibits minimal magnetic degradation and no cracking or powdering. After high-frequency vibration testing, surface wear is slight, and structural integrity remains excellent, completely resolving the pain points of traditional materials being prone to breakage and failure under harsh operating conditions.

[0019] Preferably, the dispersant in dispersion B and dispersion A is composed of multiple components including acryloyloxypropyl-glycidyl etheroxypropyl cage polysilsesquioxane, vinylbenzylaminotrimethoxysilane hydrochloride, and ethylene-acrylate-maleic anhydride terpolymer, with at least one component comprising ethylene-acrylate-maleic anhydride terpolymer.

[0020] By employing the above technical solution, the maleic anhydride groups of the ethylene-acrylate-maleic anhydride terpolymer undergo esterification or amidation reactions with the hydroxyl and amino groups on the surface of the nano-neodymium iron boron magnetic powder, anchoring the dispersant to the magnetic powder surface. Combined with the steric hindrance effect of the acryloyloxypropyl-glycidyl etheroxypropyl cage-type polysilsesquioxane and the electrostatic repulsion effect of the cationic groups of vinylbenzylaminotrimethoxysilane hydrochloride, the nano-neodymium iron boron magnetic powder is uniformly dispersed, preventing agglomeration. Furthermore, the acrylate groups of the ethylene-acrylate-maleic anhydride terpolymer react with the multifunctional polyurethane acrylate in dispersion A and the PI in dispersion B. The active groups in the adhesive form a compatible interface. The silanol groups formed after the hydrolysis of vinylbenzylaminotrimethoxysilane hydrochloride combine with the hydroxyl groups on the surface of the magnetic powder and crosslink with the binder system. The organic functional groups of acryloyloxypropyl-glycidyloxypropyl cage-type polysilsesquioxane enhance the affinity with the organic phase of the binder, improving the interfacial compatibility between the magnetic powder and the binder. The active groups in the dispersant undergo a synergistic crosslinking reaction with the acrylate groups of the multifunctional polyurethane acrylate in dispersion A, the vinyl groups of the methyl vinylsilyl hybrid aromatic acetylenic resin in dispersion B, and the amino groups of the PI adhesive, forming a three-in-one crosslinking network of "magnetic powder-dispersant-binder". This improves the material density and mechanical properties, enhances the stability of mass production, and reduces the decrease in magnetic properties caused by water absorption in bonded NdFeB magnetic materials under long-term high temperature and high humidity conditions, thus improving the durability and safety of bonded NdFeB magnetic materials.

[0021] Preferably, the dispersant is composed of acryloyloxypropyl-glycidyloxypropyl cage-type polysilsesquioxane, vinylbenzylaminotrimethoxysilane hydrochloride, and ethylene-acrylate-maleic anhydride terpolymer.

[0022] By adopting the above technical solutions, the compounded dispersant can achieve "molecular-level" uniform distribution of nano-neodymium iron boron magnetic powder, eliminate local agglomeration, and construct a stable raw material system; it can improve the interfacial compatibility between magnetic powder and binder, eliminating the "inorganic-organic" interface gap; its active groups can deeply crosslink with the active components in the dual dispersion system, constructing a stable adhesive framework, making the internal structure of the material dense and pore-free, and increasing density; it can lead to a leap in the mechanical properties of the material, enhancing its fracture resistance, impact resistance, and wear resistance; it can also enhance the stability of batch production, reduce the performance deviation between different batches of products, and reduce the defect rate.

[0023] Preferably, the content of the dispersant in both dispersion B and dispersion A is ≤3%.

[0024] By adopting the above technical solution, the content of dispersant in both dispersion B and dispersion A is controlled to be ≤3%. This allows for the uniform dispersion of magnetic powder and the improvement of interfacial compatibility and the formation of a stable three-dimensional network through the compound dispersant. It also avoids the influence of excessive dispersant content on the binder performance, further ensuring the formation of a dense structure in the material. This helps to improve the density, mechanical properties and stability of the material, enabling it to maintain good structural integrity and magnetic stability under harsh working conditions.

[0025] Preferably, in dispersion B, the content of PI adhesive and methyl vinyl silicone hybrid aromatic resin is ≤5wt%; and in dispersion A, the content of multifunctional polyurethane acrylate is ≤5wt%.

[0026] By adopting the above technical solution, controlling the content of PI adhesive and methyl vinyl silicone hybrid aromatic resin in dispersion B to be ≤5wt%, and the content of multifunctional polyurethane acrylate in dispersion A to be ≤5wt%, it is possible to ensure the bonding effect while avoiding the problem of reduced overall material density and deteriorated structural stability due to excessive binder content. This helps to improve the density and structural stability of the material, making the material closer to the performance of sintered NdFeB, while ensuring the magnetic energy product retention rate and enhancing the reliability and service life of the material under harsh working conditions.

[0027] Preferably, the second diluent is ethyl acetate and the first diluent is DMF.

[0028] By adopting the above technical solution, using ethyl acetate as the second diluent and DMF as the first diluent, both gradually decompose and volatilize during the process, leaving no residual impurities, ensuring the compactness of the bonded skeleton, significantly improving the volume fraction of magnetic powder and the material density, approaching the level of sintered NdFeB, while ensuring the retention rate of magnetic energy product, thus solving the contradiction of traditional materials where "more binder leads to lower density and less binder leads to instability".

[0029] Preferably, the particle size of the nano-neodymium iron boron magnetic powder is 80-500 nm.

[0030] By adopting the above technical solution, the particle size of the nano-neodymium iron boron magnetic powder is limited to 80-500nm, which allows the magnetic powder to be better dispersed in dispersion A and dispersion B. This helps to form a uniform mixture in the subsequent preparation process, thereby making the internal structure of the final bonded neodymium iron boron magnetic material more uniform and improving the magnetic properties, mechanical properties and structural stability of the material.

[0031] Secondly, a highly stable bonded NdFeB magnetic material is obtained by a method for preparing a highly stable bonded NdFeB magnetic material.

[0032] By adopting the above technical solutions, the density of the prepared bonded NdFeB magnetic material is significantly improved, approaching the density level of sintered NdFeB; the impact strength and bending strength are greatly increased, enhancing the resistance to fracture and wear; under harsh working conditions such as vibration, temperature cycling, and impact, the structural integrity and magnetic performance stability are significantly better than existing products, greatly extending the service life; and in mass production, the deviations in density, mechanical properties, and magnetic properties between different batches of products are reduced, product consistency is improved, molding defects are reduced, and the defect rate is lowered.

[0033] In summary, this application includes at least one of the following beneficial technical effects: 1. Through the processing steps of "grinding and homogenization - impurity removal and pre-forming - curing and forming", the magnetic powder is tightly bonded, and the material density is increased; 2. The grinding and homogenization process adopts a stepwise dispersion strategy of dispersion liquid A and dispersion liquid B, which is mixed with nano-neodymium iron boron magnetic powder. This solves the problems of poor interfacial compatibility and easy agglomeration between traditional single binders and magnetic powder, improves the dispersion uniformity of magnetic powder in the final mixture, eliminates structural defects, and lays the foundation for high-density molding. 3. The impurity removal preforming process involves gradually heating and pressurizing under vacuum, which can quickly remove small molecules and allow active groups to react with each other, further stabilizing the material structure; 4. The curing and molding process further reacts and solidifies the material, forming a dense, bonded neodymium iron boron magnetic material; 5. After the raw material system is cured, a ternary blend bonding network of "polyimide-silicon hybrid aromatic yne-polyurethane acrylate" is formed, achieving a synergistic breakthrough in mechanical properties and stability; 6. The dispersants in dispersions B and A can promote the dispersion and compatibility of the raw material system, prevent the agglomeration of nano-neodymium iron boron magnetic powder, and ensure the uniformity of dispersion and compatibility of the raw material system. 7. The process of "gradual heating and pressurization under vacuum conditions" combined with the hydrophobic composite system of "polyimide-silicon hybrid aromatic yne-polyurethane acrylate" can simultaneously complete "impurity removal-densification-pre-crosslinking". Detailed Implementation

[0034] The present application will be further described in detail below with reference to the embodiments.

[0035] Introduction to some raw materials: The particle size of neodymium iron boron magnetic powder is 100-800 nm, and its chemical composition is 29-32% neodymium, 63-69% iron, and 1.1-1.2% boron. Ethylene-acrylate-maleic anhydride terpolymer, with ethylene content of 60-80%, acrylate content of 10-30%, and maleic anhydride content of 5-15%; molecular weight of 10,000-50,000 MW. PI adhesive (polyimide adhesive): solid content 45-48%, polyimide CAS number 62929-02-6; after complete curing, its unnotched impact strength of a simply supported beam (GB / 1043.1-2008) is 250-260 K / m. 2 ; The molecular weight of methyl vinyl silicone hybrid aromatic yne resin is 2000-5000, and its molecular structure is as follows:

[0036] The multifunctional polyurethane acrylate is composed of a difunctional aliphatic polyurethane acrylate, EBECRIL 8215, and a hexafunctional polyurethane acrylate, EBECRIL 8702, in a weight ratio of 1:1. Acryloyloxypropyl-glycidyl etheroxypropyl cage-type polysilsesquioxane, with the following molecular structure: ; Vinylbenzylaminotrimethoxysilane hydrochloride CAS No.: 34937-00-3. Example

[0037] Example 1 A method for preparing a highly stable bonded NdFeB magnetic material, obtained by the following method: 1. Grinding and homogenization: Weigh neodymium iron boron magnetic powder and dispersion A at a weight ratio of 2:1 and mix and grind them in a planetary ball mill at 300 rpm for 2 hours to obtain mixture A; weigh neodymium iron boron magnetic powder and dispersion B at a weight ratio of 2:1 and mix and grind them in another planetary ball mill at 300 rpm for 2 hours to obtain mixture B; put 1 part by weight of mixture B and 1 part by weight of mixture A back into the planetary ball mill and mix them at 200 rpm for 10 minutes to ensure that the materials are fully stirred and homogenized to obtain mixture C.

[0038] 2) Impurity removal and preforming: Place the C mixture into a mold, and under vacuum conditions (-0.095MPa), heat it from 5℃ to 100℃ and hold it for 30 minutes. At the same time, during the heating process, gradually pressurize the C mixture inside the mold at 1MPa / min until the temperature is held, then stop pressurizing to obtain the blank. 3) Curing and molding: The blank is cured by heating it from 3°C to 180°C and holding it for 20 minutes, then heating it to 250°C and holding it for 30 minutes, then heating it to 305°C and holding it for 10 minutes to obtain the bonded neodymium iron boron magnetic material.

[0039] Dispersion B comprises: PI adhesive, methyl vinyl silicone hybrid aromatic acetylenic resin, dispersant, initiator, and first diluent in a weight ratio of 5:3:1.99:0.01:90.

[0040] Dispersion A: is obtained by mixing multifunctional polyurethane acrylate, dispersant, and second diluent (ethyl acetate) in a weight ratio of 7:3:90.

[0041] The dispersant in both dispersion B and dispersion A is composed of acryloyloxypropyl-glycidyloxypropyl cage-type polysilsesquioxane and ethylene-acrylate-maleic anhydride terpolymer in a weight ratio of 1:3.

[0042] Example 2 The difference between Example 2 and Example 1 lies in the process parameters, as detailed below: In step 1), mixture B is mixed with mixture A at a speed of 150 r / min for 15 min.

[0043] In step 2), the temperature is raised from 6°C to 100°C and held for 25 minutes, while the heating process is carried out at 2 MPa / min.

[0044] In step 3), the temperature is increased from 4°C to 190°C and held for 25 minutes, then increased to 240°C and held for 40 minutes, and then increased to 310°C and held for 15 minutes.

[0045] Example 3 The difference between Example 3 and Example 1 lies in the process parameters, as detailed below: In step 1), mixture B is mixed with mixture A at a speed of 150 r / min for 15 min.

[0046] In step 2), the temperature is raised from 6°C to 100°C and held for 25 minutes, while the heating process is carried out at 2 MPa / min.

[0047] In step 3), the temperature is increased from 4°C to 190°C and held for 25 minutes, then increased to 240°C and held for 40 minutes, and then increased to 310°C and held for 15 minutes.

[0048] Example 4 The difference between Example 4 and Example 1 is that the dispersant in both dispersion B and dispersion A is composed of vinylbenzylaminotrimethoxysilane hydrochloride and ethylene-acrylate-maleic anhydride terpolymer in a weight ratio of 1:3.

[0049] Example 5 The difference between Example 5 and Example 1 is that the dispersant in both dispersion B and dispersion A is composed of acryloyloxypropyl-glycidyl oxypropyl cage-type polysilsesquioxane, vinyl benzylaminotrimethoxysilane hydrochloride, and ethylene-acrylate-maleic anhydride terpolymer in a weight ratio of 0.5:0.5:3.

[0050] Comparative Example

[0051] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that mixture A is replaced with an equal amount of mixture B.

[0052] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the methyl vinyl silicone hybrid arylene resin in mixture B is replaced with PI adhesive.

[0053] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that step 2 is omitted; the specific process is as follows; 2. Grinding and homogenization: Weigh neodymium iron boron magnetic powder and dispersion A at a weight ratio of 2:1 and mix and grind them in a planetary ball mill at 300 rpm for 2 hours to obtain mixture A; weigh neodymium iron boron magnetic powder and dispersion B at a weight ratio of 2:1 and mix and grind them in another planetary ball mill at 300 rpm for 2 hours to obtain mixture B; put 1 part by weight of mixture B and 1 part by weight of mixture A back into the planetary ball mill and mix them at 200 rpm for 10 minutes to ensure that the materials are fully stirred and homogenized to obtain mixture C.

[0054] 2) Curing and molding: Place the C mixture into a mold, and under vacuum conditions (-0.095MPa), heat it from 3℃ to 180℃ and hold it for 20 minutes. Then, continue to heat it to 250℃ and hold it for 30 minutes. Then, continue to heat it to 305℃ and hold it for 10 minutes to obtain the bonded NdFeB magnetic material.

[0055] Performance testing The samples obtained in Examples 1-5 and Comparative Examples 1-3 were placed in a magnetization device for magnetization. The magnetization magnetic field strength was 3500 kA / m, the magnetization voltage was 2200 V, and the magnetization time was 5 ms. Then, they were used for the following experimental tests.

[0056] I. Density: Tested in accordance with B / T 18149-2017 "NdFeB Permanent Magnets".

[0057] II. Impact toughness: Refer to ASTM E23 "Metallic materials - Notched impact test method".

[0058] III. Magnetic Properties: 1) Remanence Br (mT): Refer to GB / T 3217-2013 "Test Method for Magnetic Properties of Permanent Magnet Materials", when the remanence Br>740 (mT) is considered qualified.

[0059] 2) Coercivity Hcb(mT): GB / T 13560-2017 "Sintered NdFeB Permanent Magnets", the obtained coercivity is denoted as A; when the coercivity Hcb is greater than 450(mT), it is considered qualified.

[0060] 3) Intrinsic coercivity Hcj (KA / m): According to GB / T 13560-2017, intrinsic coercivity Hcj is greater than 800 (KA / m).

[0061] 4) Maximum magnetic energy product: Refer to GB / T 18880-2012 "Bound NdFeB", when the maximum magnetic energy is 9.0-11.5 MGOe, it is considered qualified.

[0062] Only when all of the above 1)-4) are simultaneously qualified can the magnetic properties be considered qualified.

[0063] IV. High stability: Refer to the coercivity test method in section 2) above to cut experimental samples.

[0064] High temperature and high humidity stability test: The experimental sample was placed in an environment with a temperature of 125℃ and a humidity of 95% for 1000h. After being taken out, it was placed in an environment with a temperature of 25℃ and a humidity of 60% for 24h. The coercivity was then tested using the test method in 2), and recorded as B. The coercivity retention rate before and after was calculated as follows: coercivity retention rate = (B / A) * 100%.

[0065] Table 1. Experimental data of Examples 1-5 and Comparative Examples 1-4

[0066] Combining Example 1 and Comparative Examples 1-3 with Table 1, it can be seen that the magnetic properties of Comparative Examples 1-3 all failed the test, and after stability testing, their coercivity retention rate was below 90%, and their density was below 6 g / mm³. 3 The impact strength of the samples was below 5 kJ / m²; however, the magnetic properties of the samples from Example 1 all met the requirements (remanence Br > 740 mT, coercivity Hcb > 450 mT, intrinsic coercivity Hcj > 800 kJ / m, maximum magnetic energy 9.0-11.5 MGOe), and the impact strength reached 5.18 kJ / m², with a density of 6.311 g / mm³. 3The coercivity retention rate reached 96.7%, indicating that the dispersion B used in this application includes: PI adhesive, methyl vinyl silicone hybrid aromatic yne resin, dispersant, initiator, and first diluent; and dispersion A includes: multifunctional polyurethane acrylate, dispersant, and second diluent. Combined with the production process of this application, a high density can be obtained, and it also has better impact performance, magnetic properties, and high stability.

[0067] Combining Examples 1 and 5, it can be seen that the retention rate, impact toughness, and density of Example 5 are all greater than those of Example 1. This indicates that the dispersant in both dispersion B and dispersion A used in this application is composed of acryloyloxypropyl-glycidyl etheroxypropyl cage-type polysilsesquioxane, vinylbenzylaminotrimethoxysilane hydrochloride, and ethylene-acrylate-maleic anhydride terpolymer. Their compounding plays a synergistic role, further improving the overall performance.

[0068] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a highly stable bonded NdFeB magnetic material, characterized in that, Obtained by the following method: 1) Grinding and homogenization: Weigh out nano-neodymium iron boron magnetic powder and mix it with dispersion A and grind it to obtain mixture A; weigh out nano-neodymium iron boron magnetic powder and mix it with dispersion B and grind it to obtain mixture B; mix mixture B and mixture A evenly to obtain mixture C; 2) Impurity removal and preforming: Place the C mixture into a mold, and under vacuum conditions, heat it from 5-10℃ to 100-105℃ and hold it for 10-30 minutes. At the same time, during the heating process, gradually pressurize the C mixture inside the mold at 1-3MPa / min until the temperature is held, then stop pressurizing to obtain the blank. 3) Curing and molding: The blank is cured to obtain bonded NdFeB magnetic material; Dispersion B comprises: PI adhesive, methyl vinyl silicone hybrid aromatic resin, dispersant, initiator, and first diluent; Dispersion A comprises: multifunctional polyurethane acrylate, a dispersant, and a second diluent; the proportion of nano-neodymium iron boron magnetic powder in the adhesive NdFeB magnetic material is greater than 90%.

2. The method for preparing a highly stable bonded NdFeB magnetic material according to claim 1, characterized in that: The mixture B is mixed with the mixture A at a speed of 100-200 r / min for 10-20 min.

3. The method for preparing a highly stable bonded NdFeB magnetic material according to claim 1, characterized in that: The curing conditions in step 3) are as follows: heat up to 180-200℃ at 3-5℃, hold for 10-20 minutes, then continue to heat up to 225-250℃, hold for 30-60 minutes, then continue to heat up to 305-320℃, hold for 10-20 minutes.

4. The method for preparing a highly stable bonded NdFeB magnetic material according to claim 3, characterized in that: The dispersants in both dispersion B and dispersion A are multiple components of acryloyloxypropyl-glycidyl etheroxypropyl cage-type polysilsesquioxane, vinylbenzylaminotrimethoxysilane hydrochloride, and ethylene-acrylate-maleic anhydride terpolymer, with at least one component being ethylene-acrylate-maleic anhydride terpolymer.

5. A method for preparing a highly stable bonded NdFeB magnetic material according to any one of claims 4, characterized in that: The dispersant is composed of acryloyloxypropyl-glycidyloxypropyl cage-type polysilsesquioxane, vinylbenzylaminotrimethoxysilane hydrochloride, and ethylene-acrylate-maleic anhydride terpolymer.

6. The method for preparing a highly stable bonded NdFeB magnetic material according to claim 1, characterized in that: The content of the dispersant in both dispersion B and dispersion A is ≤3%.

7. The method for preparing a highly stable bonded NdFeB magnetic material according to claim 1, characterized in that: In dispersion B, the contents of PI adhesive and methyl vinyl silicone hybrid aromatic resin are both ≤5wt%; in dispersion A, the content of multifunctional polyurethane acrylate is ≤5wt%.

8. The method for preparing a highly stable bonded NdFeB magnetic material according to claim 1, characterized in that: The second diluent is ethyl acetate, and the first diluent is DMF.

9. The method for preparing a highly stable bonded NdFeB magnetic material according to claim 1, characterized in that: The particle size of the nano-neodymium iron boron magnetic powder is 80-500 nm.

10. A highly stable bonded neodymium iron boron magnetic material, characterized in that: It is obtained by the preparation method of a highly stable bonded NdFeB magnetic material according to any one of claims 1-9.

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