Anisotropic bonded magnet and method of making the same

Abstract

The application relates to the technical field of magnets, and particularly discloses an anisotropic bonded magnet and a preparation method thereof. The anisotropic bonded magnet comprises spherical Fe-Ni alloy powder and modified epoxy resin and a coupling agent, the mass ratio of the spherical Fe-Ni alloy powder and the modified epoxy resin is (7-9):(1-3), the added amount of the coupling agent is 0.5-2 wt% of the total mass of the bonding agent, and the modified epoxy resin is modified by an ultrabranched polymer. The preparation method comprises the following steps: mixing the spherical Fe-Ni alloy powder and the modified epoxy resin, adding the coupling agent to form a uniform slurry, placing the slurry in a directional magnetic field with a strength of 1800-2000 Oersted, keeping for 10-15 minutes, heating and solidifying the slurry after being oriented, and obtaining the anisotropic bonded magnet. The anisotropic bonded magnet has the advantages of high magnetic performance and improved uniformity of directional arrangement of the magnetic powder at a low cost.

Description

Technical Field

[0001] This application relates to the field of magnet technology, and more specifically, to an anisotropic bonded magnet and its preparation method. Background Technology

[0002] In recent years, anisotropic bonded magnets have become a research hotspot in the field of magnetic materials due to their high magnetic energy product, precision molding capabilities, and ability to process complex shapes. Currently, the mainstream fabrication techniques include injection molding and compression molding, the core of which lies in the orientation of magnetic powders through an external field (such as a magnetic field or pressure) and the solidification of the magnet structure using a binder. However, existing processes face significant bottlenecks in terms of the uniformity of magnetic powder orientation and the compatibility of the binder-magnetic powder interface. Studies have shown that magnetic powders are susceptible to uneven distribution of rheological stress and attenuation of the magnetic field gradient during molding, leading to orientation fluctuations exceeding 15%, directly affecting the stability of the magnet's remanence (Br) and coercivity (Hcj). Simultaneously, insufficient polarity matching between the binder system and the magnetic powder often results in the formation of micron-sized voids or weak chemical bonds at the interface, causing magnetic performance losses as high as 10%-20%, becoming a key factor restricting the industrial application of high-performance magnets.

[0003] To address the aforementioned issues, existing technologies primarily employ two improvement approaches: magnetic powder morphology optimization and binder compounding. The former enhances orientation response by controlling the size distribution and surface energy of the magnetic powder, while the latter strengthens interfacial bonding through the regulation of polar groups. However, these methods exhibit significant drawbacks in practical applications: while spheroidizing the magnetic powder improves flowability, it weakens the orientation potential of anisotropic magnetic crystals; the introduction of multi-component binder systems improves compatibility, but the crosslinking reaction temperature window conflicts with the thermal stability of the magnetic powder, leading to thermal stress cracks during the molding process. Furthermore, existing processes rely on high-precision molds and complex post-processing, increasing production costs by more than 35%, making it difficult to meet the demands of the consumer electronics industry for low-cost, high-volume production. Summary of the Invention

[0004] To address the aforementioned issues, this application provides an anisotropic bonded magnet and its preparation method.

[0005] This application provides an anisotropic bonded magnet using the following technical solution: An anisotropic bonded magnet comprises spherical Fe-Ni alloy powder, modified epoxy resin, and a coupling agent. The mass ratio of the spherical Fe-Ni alloy powder to the modified epoxy resin is (7-9):(1-3). The particle size distribution of the spherical Fe-Ni alloy powder is 2-5 μm. The amount of the coupling agent added is 0.5-2 wt% of the total mass of the binder. The modified epoxy resin is obtained by modifying the epoxy resin with a hyperbranched polymer.

[0006] By employing the above technical solutions, the spherical Fe-Ni alloy powder with a particle size of 2-5 μm balances the fluidity and anisotropic orientation potential of the magnetic powder, making it easier for the magnetic powder to orient itself in a magnetic field, reducing orientation fluctuations, and improving the stability of remanence and coercivity. Hyperbranched polymer-modified epoxy resin, through molecular structure optimization, enhances its polarity matching with the magnetic powder, while coupling agents further promote interfacial chemical bonding, reducing micron-level voids and weak bonds at the interface, thus decreasing the magnetic performance loss rate. High magnetic powder content ensures a high magnetic energy product, while a low binder ratio reduces interference from non-magnetic phases, improving the overall performance of the magnet.

[0007] Optionally, the specific method for modifying the epoxy resin is as follows: Bisphenol A type epoxy resin and hyperbranched polymer were mixed at a mass ratio of (8-9):1 to obtain a mixture, and a coupling agent was added. Under nitrogen protection, the mixture is heated to 120-130℃ and stirred at 500-800 rpm for 2-3 hours to obtain the modified epoxy resin.

[0008] By adopting the above technical solutions, the hyperbranched polymer introduces a large number of branched structures, increasing the crosslinking density and flexibility of the binder, widening the crosslinking reaction temperature window, alleviating the conflict with the thermal stability of magnetic powder, and reducing thermal stress during the curing process. Nitrogen protection and medium-speed stirring prevent epoxy resin oxidation, ensure uniform dispersion of the hyperbranched polymer, and improve the overall compatibility and interfacial bonding of the binder.

[0009] Optionally, the spherical Fe-Ni alloy powder is coated with a layer of nano-silica, the nano-silica being pretreated with a silane coupling agent, and the hydroxyl density on the surface of the silane-coated nano-silica having a density ≥3.5 groups / nm. 2 .

[0010] By employing the above technical solution, a uniform interface layer is formed by coating nano-silica, isolating the magnetic powder from the direct polarity conflict with the binder. The hydroxyl groups of the silane coupling agent react chemically with the epoxy groups of the epoxy resin to form covalent bonds, thereby improving the interfacial bonding force and reducing the porosity. The high hydroxyl density enhances surface activity, promotes the chemical adsorption of the coupling agent and binder, further reduces weak interfacial bonds, and improves the structural stability and magnetic performance retention of the magnet.

[0011] Optionally, the resin may also include a liquid crystal epoxy monomer, wherein the amount of liquid crystal epoxy monomer added is 5-15% of the mass of the modified epoxy resin, and the mesocrystalline group of the liquid crystal epoxy monomer is a biphenyl structure with a molecular weight of 400-800 g / mol.

[0012] By adopting the above technical solution, the biphenyl-structured liquid crystal epoxy monomer can synergistically align with magnetic powder in a magnetic field, forming a "dual orientation" effect. This reduces the influence of uneven rheological stress distribution, decreases orientation fluctuations, and improves remanent magnetization uniformity. A molecular weight of 400-800 g / mol ensures good dispersion of the liquid crystal monomer in the binder, combining flowability and orientation capability, and avoiding the obstruction of magnetic powder movement by large molecular chain segments.

[0013] Secondly, this application provides a method for preparing anisotropic bonded magnets, employing the following technical solution: A method for preparing anisotropic bonded magnet includes the following steps: Spherical Fe-Ni alloy powder is mixed with modified epoxy resin and a coupling agent is added to form a uniform slurry. The slurry is placed in a directional magnetic field with an intensity of 1800-2000 Oersted and held for 10-15 minutes. The directional slurry is then cured at 115-125℃ for 5-6 hours to obtain anisotropic bonded magnets.

[0014] Optionally, the cured anisotropic bonded magnet is subjected to pulsed magnetic field treatment, wherein the magnetic field strength of the pulsed magnetic field treatment is 2500-3000 Oersted, the pulse frequency is 1-5Hz, and the treatment time is 30-60 seconds.

[0015] By adopting the above technical solution, the high-frequency disturbance of the pulsed magnetic field can adjust the slight deflection of magnetic powder caused by stress relaxation during the curing process, further improving the orientation degree and coercivity stability. Pulse treatment promotes further alignment of magnetic domains, increases remanence (Br), and simultaneously optimizes the magnetic energy product (BHmax).

[0016] Optionally, the slurry is placed in a directional magnetic field with an intensity of 1000-1400 Oersted for 5-10 minutes, and then the directional magnetic field is increased to 1800-2000 Oersted and held for 5-10 minutes.

[0017] By adopting the above technical solution, the magnetic powder is initially aligned using a low magnetic field to avoid stress concentration caused by a sudden increase in slurry viscosity under a high magnetic field. Then, a high magnetic field is used to enhance orientation, solving the problem of uneven rheological stress distribution in traditional processes. This improves the uniformity of orientation and reduces the range of magnetic property fluctuations. The staged processing reduces energy consumption from prolonged high magnetic field exposure while ensuring the orientation effect, making it suitable for industrial mass production.

[0018] Optionally, the oriented slurry is preheated at 80-85°C for 1-1.5 hours, and then heated to 115-125°C at a rate of 2°C / min and held for 5-6 hours. The curing pressure is 0.5-1 MPa.

[0019] By adopting the above technical solution, the preheating stage promotes the evaporation of solvents in the slurry and the initial wetting of magnetic powder by the binder, while slow heating avoids thermal stress concentration. Low-pressure curing at 0.5-1MPa ensures that the magnetic powder is tightly packed, reducing internal voids, while avoiding damage to the magnetic powder orientation by high pressure, thus increasing the magnet density.

[0020] In summary, this application has the following beneficial effects: 1. This application constructs a strongly polarity-matched binder-magnetic powder interface by modifying epoxy resin with hyperbranched polymer, pretreating nano-silica with silane coupling agent, and introducing liquid crystal epoxy monomers. This eliminates micron-level voids and weak chemical bonds, reduces the magnetic performance loss rate, improves the interfacial bonding force, and significantly enhances the structural stability.

[0021] 2. In this application, a staged gradient magnetic field processing and pulsed magnetic field secondary correction are preferred, which, together with the synergistic orientation effect of liquid crystal epoxy monomers, overcomes the problems of uneven rheological stress and magnetic field gradient decay, reduces orientation fluctuation, improves the stability of remanence (Br) and coercivity (Hcj), and simultaneously optimizes the magnetic energy product (BHmax).

[0022] 3. The method of this application solves the problem of thermal stress cracking in traditional processes by designing low-temperature curing, stepped heating and low-pressure curing, and reduces the dependence on high-precision molds and complex post-processing, resulting in lower production costs and meeting the low-cost, high-volume production needs of consumer electronics. Detailed Implementation

[0023] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0024] Preparation example of modified epoxy resin Preparation Example 1 A method for preparing a modified epoxy resin: Prepare the following ingredients: Bisphenol A type epoxy resin (E-51, epoxy value 0.48-0.54eq / 100g), hyperbranched polyester (HBP, hydroxyl-terminated, molecular weight 5000g / mol), γ-glycidoxypropyltrimethoxysilane (KH-560, purity ≥98%).

[0025] The epoxy resin was dehydrated in a vacuum drying oven at 80℃ for 2 hours (vacuum degree -0.08MPa). The hyperbranched polymer was dried with molecular sieves for 48 hours before use.

[0026] Weigh 850g of epoxy resin and 100g of hyperbranched polymer into a container, add 20g of KH-560 coupling agent, and pre-disperse the mixture for 5 minutes using a high-speed shear emulsifier at 3000rpm until the system is homogeneous.

[0027] Under nitrogen atmosphere, the container was heated to 125±2℃, stirred at 650rpm, and reacted at a constant temperature for 2.5 hours.

[0028] After heating is stopped, stirring is maintained until the temperature drops below 80°C. The product is then transferred to a vacuum degassing tank with a vacuum degree of -0.1 MPa for 30 minutes. After filtration through a 200-mesh stainless steel filter, the modified epoxy resin is obtained.

[0029] Preparation Example 2 A method for preparing a modified epoxy resin: The difference from preparation example 1 is that 750g of epoxy resin and 100g of hyperbranched polymer are weighed into a container.

[0030] Preparation Example 3 A method for preparing a modified epoxy resin: The difference from preparation example 1 is that 950g of epoxy resin and 100g of hyperbranched polymer are weighed into a container. Example

[0031] Example 1 A method for preparing anisotropic bonded magnets: Prepare the following ingredients: Spherical Fe-Ni alloy powder (particle size 2-5 μm, surface coated with nano-SiO2 layer, SiO2 hydroxyl density ≥3.5 groups / nm) 2 The mixture consisted of nano-silica pretreated with silane coupling agent, modified epoxy resin (prepared from Preparation Example 1), silane coupling agent (KH-550, purity ≥98%), liquid crystal epoxy monomer (biphenyl mesocrystalline group, molecular weight 400-800 g / mol), and anhydrous ethanol (analytical grade).

[0032] Weigh 800g of Fe-Ni alloy powder and 200g of modified epoxy resin at a mass ratio of 8:2, add 30g of liquid crystal epoxy monomer, and then add 4g of silane coupling agent. Place the above raw materials in a planetary mixer, mix at 1000rpm for 10min under normal pressure, then evacuate to -0.08MPa and disperse at 1500rpm for 15min. The viscosity of the slurry is measured to be 3000±500mPa·s (25℃, Brookfield DV2T).

[0033] Inject the slurry into the mold and apply a magnetic field for orientation according to the following procedure: Phase 1: 1400 Oersted, hold for 5 minutes; Second stage: 2000 Oersted, hold for 10 minutes; The direction of the magnetic field is parallel to the direction of the forming pressure. The preform was then preheated in an 85℃ oven for 1 hour, transferred to a hot press, heated to 125℃ at a rate of 2℃ / min, and subjected to a pressure of 0.8MPa for 5.5 hours of constant-temperature curing. The cured preform was then subjected to pulsed magnetic field strengthening at 2800 Oersted, 3Hz, for 45 seconds.

[0034] After the temperature is reduced to 60°C, the material is demolded to obtain anisotropic bonded magnets.

[0035] Example 2 A method for preparing anisotropic bonded magnet: The difference from Example 1 is that 900g of Fe-Ni alloy powder and 100g of modified epoxy resin are weighed at a mass ratio of 9:1.

[0036] Example 3 A method for preparing anisotropic bonded magnet: The difference from Example 1 is that 700g of Fe-Ni alloy powder and 300g of modified epoxy resin are weighed at a mass ratio of 7:3.

[0037] Example 4 A method for preparing anisotropic bonded magnet: The difference from Example 1 is that the modified epoxy resin is prepared by Example 2.

[0038] Example 5 A method for preparing an anisotropic bonded magnet: the difference from Example 1 is that the modified epoxy resin is prepared by Example 3.

[0039] Example 6 A method for preparing anisotropic bonded magnets: The difference from Example 1 is that the surface of the spherical Fe-Ni alloy powder is not coated with nano-silica.

[0040] Example 7 A method for preparing anisotropic bonded magnets: The difference from Example 1 is that the hydroxyl density on the surface of nano-silica pretreated with the silane coupling agent is <3.5 groups / nm. 2 .

[0041] Example 8 A method for preparing anisotropic bonded magnet: the difference from Example 1 is that no liquid crystal epoxy monomer is added.

[0042] Example 9 A method for preparing anisotropic bonded magnets: The difference from Example 1 is that the cured anisotropic bonded magnets are not subjected to pulsed magnetic field treatment.

[0043] Example 10 A method for preparing anisotropic bonded magnets: The difference from Example 1 is that the slurry is placed in a directional magnetic field with an intensity of 2000 Oersted and kept for 15 minutes without performing the first stage treatment.

[0044] Example 11 A method for preparing anisotropic bonded magnets: the difference from Example 1 is that the oriented slurry is not preheated.

[0045] Comparative Example Comparative Example 1 A method for preparing anisotropic bonded magnet: The difference from Example 1 is that 600g of Fe-Ni alloy powder and 400g of modified epoxy resin are weighed at a mass ratio of 6:4.

[0046] Comparative Example 2 A method for preparing anisotropic bonded magnet: The difference from Example 1 is that 950g of Fe-Ni alloy powder and 50g of modified epoxy resin are weighed in a mass ratio of 9.5:0.5.

[0047] Comparative Example 3 A method for preparing anisotropic bonded magnets: The difference from Example 1 is that the particle size distribution of the spherical Fe-Ni alloy powder is 5-10 μm.

[0048] Comparative Example 4 A method for preparing anisotropic bonded magnet: the difference from Example 1 is that the epoxy resin is not modified.

[0049] Performance testing Detection methods Remanence (Br): Measured at room temperature using a vibrating sample magnetometer (VSM, LakeShore 7404) in accordance with GB / T3217-2013; Coercivity (Hcj): Same as above, calculated using the hysteresis loop. Maximum magnetic energy product ((BH)max): Calculated by curve integration of BH.

[0050] Bending strength: According to GB / T6569-2006, the three-point bending method (Instron 3365, span 20mm, loading rate 1mm / min) was adopted.

[0051] Magnetic powder orientation degree: X-ray diffraction (XRD, RigakuSmartLab) calculation of (004) crystal plane orientation factor.

[0052] Table 1 Detection Data Combining Example 1 and Comparative Examples 1-2 with Table 1, it can be seen that in Comparative Examples 1 and 2, the magnet performance significantly decreased due to either an excessively high or low binder content. Compared to Example 1, the excessive binder in Comparative Example 1 increased interference from the non-magnetic phase, reducing the magnetic energy product from 85 kJ / m². 3 Reduced to 42kJ / m 3 The flexural strength decreased from 162 MPa to 98 MPa; in Comparative Example 2, the excessively high proportion of magnetic powder resulted in insufficient effective curing of the binder, causing the orientation degree to decrease from 92% to 72% and the remanence (Br) to decrease from 0.78 T to 0.61 T. This indicates that when the mass ratio of spherical Fe-Ni alloy powder to modified epoxy resin is within the range of (7-9):(1-3), the high filling amount of magnetic powder and the curing effect of the binder can be balanced, avoiding the decline in magnetic and mechanical properties caused by the imbalance of the ratio.

[0053] Combining Example 1 and Comparative Example 3 with Table 1, it can be seen that Comparative Example 3, which uses magnetic powder with a particle size of 5-10 μm, has significantly lower orientation degree, remanence, and coercivity than Example 1. A particle size of 2-5 μm can balance the flowability of magnetic powder with anisotropic orientation potential. If the particle size is too large, the increased resistance to magnetic powder movement and reduced magnetic field response efficiency will lead to uneven orientation and decreased orientation degree.

[0054] As can be seen from Example 1 and Comparative Example 4, and Table 1, the modification of hyperbranched polymers can optimize the polarity matching and crosslinking density of the binder through branching structure. The unmodified epoxy resin has a magnetic property loss rate of more than 35% due to poor interfacial compatibility and thermal stress cracking. This verifies the key role of modification treatment in improving interfacial bonding and structural stability.

[0055] Based on Examples 1-3 and Table 1, it can be seen that a mass ratio of 8:2 is the optimal ratio. At this ratio, the high filling amount of magnetic powder ensures a high magnetic energy product, while the 20% binder can fully cure and reduce interference from non-magnetic phases. Too high or too low a proportion of magnetic powder will lead to a decrease in orientation and mechanical properties due to insufficient or excessive binder.

[0056] Based on Examples 1 and 4-5 and Table 1, it can be seen that when the mass ratio of bisphenol A epoxy resin to hyperbranched polymer is 8-9:1, the optimal crosslinking density and flexibility can be achieved. Excess epoxy resin will reduce the modification effect of hyperbranched polymer, while insufficient epoxy resin will lead to insufficient branching structure, ultimately affecting interfacial compatibility and magnet orientation. This verifies the key role of ratio optimization in adhesive performance.

[0057] Combining Examples 1 and 6 with Table 1, it can be seen that the nano-silica coating layer can isolate the polarity conflict between the magnetic powder and the binder. The hydroxyl groups formed by the silane coupling agent pretreatment can promote the covalent bonding of the interface. Without coating, the interface porosity increases, resulting in a loss of about 20% in magnetic properties and a decrease of 30% in mechanical properties.

[0058] As can be seen from Examples 1 and 7 and Table 1, sufficient hydroxyl density is a prerequisite for effective adsorption and interfacial chemical bonding of silane coupling agents. Insufficient hydroxyl density will lead to a decrease in the grafting efficiency of the coupling agent, an increase in weak interfacial bonds, and a loss of magnetic properties of about 10%, which verifies the key influence of surface activity on interfacial compatibility.

[0059] Combining Examples 1 and 8 with Table 1, it can be seen that the biphenyl-structured liquid crystal epoxy monomer, through a "dual orientation" effect and synergistic magnetic powder alignment, reduces the influence of uneven rheological stress. Without the addition of biphenyl, the orientation degree decreases by 7%, and the magnetic energy product ((BH)max) decreases from 85 kJ / m². 3 Reduced to 72kJ / m 3 This demonstrates the important role of liquid crystal monomers in improving orientation uniformity and magnetic properties.

[0060] As can be seen from Examples 1 and 9 and Table 1, pulsed magnetic field treatment can correct the slight deflection of magnetic powder during the curing process, improve the orientation degree by 3%, the remanence by 4%, and enhance the coercivity stability, thus verifying the optimization effect of secondary magnetic field treatment on the fine arrangement of magnetic domains.

[0061] Combining Examples 1 and 10 with Table 1, it can be seen that low-field pre-alignment (1400 Oersted for 5 minutes) can avoid stress concentration caused by a sudden increase in slurry viscosity under high magnetic field. Then, high-field strengthening (2000 Oersted for 10 minutes) can significantly improve orientation uniformity. Without staged treatment, the orientation degree decreases by 9% and the magnetic properties are lost by about 20% due to uneven rheological stress. This proves the necessity of the staged strategy for industrial orientation process.

[0062] Combining Examples 1 and 11 with Table 1, it can be seen that the preheating stage can promote solvent evaporation and initial wetting of magnetic powder by the binder. The step-by-step temperature increase reduces thermal stress concentration. Without preheating, the internal stress accumulates due to the sudden temperature rise during the curing process, resulting in a 10% decrease in mechanical properties and a 5% decrease in orientation. This verifies the role of preheating in improving the stability of the magnet structure.

[0063] 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. An anisotropic bonded magnet, characterized in that, The mixture comprises spherical Fe-Ni alloy powder, modified epoxy resin, and coupling agent. The mass ratio of the spherical Fe-Ni alloy powder to the modified epoxy resin is (7-9):(1-3). The particle size distribution of the spherical Fe-Ni alloy powder is 2-5 μm. The amount of coupling agent added is 2 wt% of the total mass of the modified epoxy resin. The modified epoxy resin is obtained by modifying the epoxy resin with a hyperbranched polymer. The modified epoxy resin is prepared by mixing bisphenol A type epoxy resin and hyperbranched polymer at a mass ratio of (8-9):1 to obtain a mixture, adding a coupling agent; heating the mixture to 120-130℃ under nitrogen protection, stirring at 500-800 rpm for 2-3 hours to obtain the modified epoxy resin. The spherical Fe-Ni alloy powder is coated with a layer of nano-silica. The nano-silica is pretreated with a silane coupling agent, and the hydroxyl density on the surface of the nano-silica pretreated with the silane coupling agent is ≥ 3.5 groups / nm². The anisotropic bonded magnet also includes a liquid crystal epoxy monomer. The amount of the liquid crystal epoxy monomer added is 5-15% of the mass of the modified epoxy resin. The mesocrystalline group of the liquid crystal epoxy monomer has a biphenyl structure, and its molecular weight is 400-800 g / mol.

2. A method for preparing anisotropic bonded magnet as described in claim 1, characterized in that, Includes the following steps: Spherical Fe-Ni alloy powder is mixed with modified epoxy resin, and a coupling agent is added to form a uniform slurry. The slurry is first placed in a directional magnetic field with an intensity of 1000-1400 Oersted and held for 5-10 minutes, and then the directional magnetic field is increased to 1800-2000 Oersted and held for 5-10 minutes. The directional slurry is preheated at 80-85℃ for 1-1.5 hours, and then heated to 115-125℃ at a rate of 2℃ / min and held for 5-6 hours. The curing pressure is 0.5-1MPa to obtain anisotropic bonded magnets.

3. The method for preparing anisotropic bonded magnets according to claim 2, characterized in that, The cured anisotropic bonded magnet is subjected to pulsed magnetic field treatment, wherein the magnetic field strength of the pulsed magnetic field treatment is 2500-3000 Oersted, the pulse frequency is 1-5Hz, and the treatment time is 30-60 seconds.

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