Auxiliary material formula of magnetic powder core and magnetic powder core
By combining silicone resin, active additives, insulation enhancers and lubricants, a dense ceramic composite insulation layer is formed, which solves the problem of insulation failure of magnetic powder cores under high temperature environment and realizes magnetic powder cores with high magnetic permeability, low loss and high thermal conductivity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGXI AITE MAGNETS
- Filing Date
- 2025-12-16
- Publication Date
- 2026-05-01
AI Technical Summary
The insulating coating material of existing magnetic powder cores is prone to decomposition in high-temperature environments, leading to insulation failure and a surge in losses, which limits its application in high-temperature and high-frequency fields. Moreover, the existing processes are complex and costly, and the interface bonding problem is difficult to solve.
A combination of silicone resin, active additives, insulating reinforcing agents, and lubricants is used to form an insulating coating slurry through shear dispersion. After coating with magnetic powder, a step-by-step heat treatment is performed to form a dense ceramic composite insulating layer, which enhances the interfacial bonding and thermal stability.
It achieves stable insulation performance over a long period of time in high-temperature environments, reduces power loss, improves magnetic permeability and thermal conductivity, enhances crush resistance, and ensures product yield and consistency.
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Abstract
Description
A formulation of auxiliary materials for a magnetic powder core and the magnetic powder core itself. Technical Field
[0001] This invention belongs to the field of magnetic core technology, and specifically relates to an auxiliary material formula for magnetic powder cores and magnetic powder cores. Background Technology
[0002] In the manufacturing process of magnetic powder cores, in addition to the magnetic alloy powder as the main component, a variety of auxiliary materials need to be added to optimize its final performance. Magnetic powder cores are made from soft magnetic alloy powder through insulating coating, pressing, and heat treatment; the insulating coating material is one of the most important auxiliary materials, which provides sufficient resistance to the magnetic powder core to reduce high-frequency eddy current losses, while possessing good mechanical properties to withstand pressing stress and remaining stable in subsequent heat treatment and operating temperatures.
[0003] Traditional insulating coating materials mainly include inorganic materials such as phosphates, silica, and forsterite, as well as organic materials such as epoxy resins, polyimides, and ordinary silicone resins. Inorganic coatings typically have high hardness and good temperature resistance, but they are brittle, have weak bonding with magnetic powder, and are prone to cracking during pressing. Organic coatings, on the other hand, have good flexibility and uniform coating, but their heat resistance is generally low (usually below 300℃). During the high-temperature annealing process (500℃~700℃) of magnetic powder cores or in high-temperature working environments, they are prone to decomposition and carbonization, leading to insulation failure and a surge in losses, severely limiting the application of magnetic powder cores in high-temperature and high-frequency fields.
[0004] To balance insulation and temperature resistance, existing technologies employ multilayer coating or organic-inorganic hybrid approaches, such as first forming an inorganic layer on the surface of magnetic powder and then coating it with an organic layer. These methods are complex, costly, and the interfacial bonding between layers is difficult to solve, making them prone to delamination under thermal stress. Additionally, some studies have attempted to add heat-resistant fillers such as alumina and silicon nitride to organic resins; however, these fillers have poor interfacial compatibility with the resin matrix, often existing in a physically mixed form. At high temperatures, they cannot prevent the decomposition of the resin matrix, resulting in limited reinforcing effects and often impairing the material's molding flowability.
[0005] Therefore, there is a need to develop a magnetic powder core coating material that is simple to process, has excellent overall performance, and can maintain stable insulation performance in high-temperature environments for a long time. Summary of the Invention
[0006] Therefore, the present invention aims to provide an auxiliary material formula for magnetic powder cores and magnetic powder cores, in order to solve at least one technical problem in the background art.
[0007] The present invention is implemented as follows: A first aspect of the present invention provides an auxiliary material formulation for a magnetic powder core, wherein the auxiliary material formulation is an insulating coating material for coating magnetic powder; comprising organosilicon resin, active additives, insulating reinforcing agents, lubricants, and solvents; wherein the active additive is aluminum acetylacetonate or zirconium acetylacetonate; wherein the insulating reinforcing agent is hexagonal boron nitride or modified boron nitride; wherein the modified boron nitride is silane coupling agent surface-modified boron nitride; wherein the lubricant is selected from at least one of amide wax, oxidized polyethylene wax, and maleic anhydride grafted polyethylene wax; the preparation method of the auxiliary material formulation for the magnetic powder core includes the following steps: dissolving organosilicon resin in a solvent to form a resin solution; sequentially adding active additives and insulating reinforcing agents to the resin solution, performing shear dispersion to form a uniform slurry; adding lubricant to the slurry, continuing shear dispersion to obtain an insulating coating slurry, which serves as the auxiliary material formulation for the magnetic powder core.
[0008] Preferably, the amount of the silicone resin is 0.8% to 1.5% of the magnetic powder mass; the amount of the active additive is 0.2% to 0.8% of the magnetic powder mass; the amount of the insulation reinforcing agent is 0.3% to 1.0% of the magnetic powder mass; and the amount of the lubricant is 0.4% to 1.0% of the magnetic powder mass.
[0009] Preferably, the active additive further includes a mineralizing agent; the mineralizing agent is triethyl borate, boron acetylacetonate, or borosilicate sol, and its amount is 0.05wt%~0.5wt% of the organosilicon resin.
[0010] Preferably, the solvent is toluene or xylene; the amount of solvent used is such that the viscosity of the slurry is 100 mPa·s to 2000 mPa·s.
[0011] Preferably, the silicone resin is a methylphenyl silicone resin.
[0012] Preferably, the hexagonal boron nitride is made of micron-sized powder with a D50 of 1μm to 10μm.
[0013] Preferably, the lubricant is a micronized lubricant with a D50 of 5μm to 20μm and a D90 of ≤30μm.
[0014] The second aspect of the present invention provides a magnetic powder core, wherein the magnetic powder is surface coated, pressed and molded, and heat-treated using the above-mentioned auxiliary material formula for a magnetic powder core to form the magnetic powder core.
[0015] Preferably, the preparation method of the magnetic powder core is as follows: the auxiliary material formula of the magnetic powder core is prepared as a coating slurry; the magnetic powder and the coating slurry are mixed evenly, dried to remove the solvent, and a pre-coated powder is obtained; the pre-coated powder is pressed into shape to obtain a magnetic core green blank; the magnetic core green blank is subjected to a stepped heat treatment in a protective atmosphere, and then cooled in a furnace to obtain the magnetic powder core.
[0016] Preferably, the heat treatment specifically involves heating to 300℃~400℃ at a rate of 2℃ / min~5℃ / min and holding at that temperature for 30min~60min, followed by further heating to 500℃~600℃ and holding at that temperature for 90min~150min.
[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides an auxiliary material formula that has ultra-high permeability, ultra-low loss, excellent DC bias and high temperature stability, which can be used as an insulating coating material for magnetic powder cores; the magnetic powder core prepared by the present invention achieves extremely low power loss while maintaining high permeability.
[0018] 2. This invention achieves a qualitative change from physical mixing to in-situ chemical bonding by combining organosilicon resin with an active additive (aluminum acetylacetonate / zirconium) during heat treatment. The highly active nano-oxides generated by the decomposition of the active additive react in-situ with the resin pyrolysis products at the molecular scale, forming a continuous, dense, and high-strength ceramic composite insulating layer.
[0019] 3. The present invention introduces an insulation reinforcing agent, which not only provides an excellent insulation barrier, but also constructs an efficient heat conduction path, significantly improving thermal conductivity. This allows the magnetic powder core to dissipate heat quickly when subjected to high power density, effectively suppressing temperature rise and improving operational reliability.
[0020] 4. Compared with traditional single inorganic (such as phosphate) or organic coatings, the coating layer of the present invention is firmly bonded to the magnetic powder matrix, has higher crush resistance, and is not easy to crack or peel off during high pressing and post-processing, thus ensuring the yield and consistency of the product.
[0021] 5. By introducing trace amounts of mineralizer, this invention can further reduce the in-situ ceramization reaction temperature, promote a more complete and uniform reaction, further optimize the microstructure of the coating layer, and thus improve performance indicators such as loss. Detailed Implementation
[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0023] A formulation for an auxiliary material of a magnetic powder core, wherein the auxiliary material is an insulating coating material used to coat the magnetic powder; the auxiliary material formulation of the magnetic powder core includes an organosilicon resin, an active additive, an insulating reinforcing agent, a lubricant, and a solvent; the organosilicon resin can be any organosilicon resin permitted in the art, such as methyl silicone resin, hydroxyl-containing silicone resin, organosilicon epoxy resin, polyester organosilicon resin, etc., preferably methylphenyl organosilicon resin. The amount of organosilicon resin is 0.8% to 1.5% of the mass of the magnetic powder. As a basic binder and film-forming substance in the auxiliary material formulation, organosilicon resin has certain thermal stability and oxidation stability, and it is very suitable for providing a skeleton for the insulating coating layer. Among them, methylphenyl organosilicon resin has a high phenyl content, and its thermal stability and oxidation stability are better than those of conventional organosilicon resins, and it can maintain its performance at higher temperatures. However, the preparation of magnetic powder cores requires heat treatment exceeding 500°C. The porous and fragile structure produced by the high-temperature decomposition of organosilicon resin results in poor heat resistance and decreased mechanical properties. Therefore, active additives, insulating reinforcing agents, and other components need to be added to the auxiliary material.
[0024] The active additive is aluminum acetylacetonate or zirconium acetylacetonate, preferably aluminum acetylacetonate; the amount of the active additive is 0.2% to 0.8% of the magnetic powder mass; it decomposes in the range of 300-500℃ to generate highly active, nanoscale Al2O3 or ZrO2; the highly active nanoparticles can undergo strong interdiffusion and local reaction with SiO2 generated by the pyrolysis of organosilicon resin at higher temperatures to form an extremely thin, chemically bonded aluminum / zirconium silicate transition layer. However, active additives differ from directly added metal oxide powders. If Al2O3 or ZrO2 is added directly, its activity is low. After heat treatment, the resin decomposes into porous SiO2, and Al2O3 or ZrO2 particles are embedded as inert fillers. The two are only physically embedded, and the interface is weak. Not only does it fail to enhance the coating, but it may also become stress concentration points due to interface defects, reducing the overall strength and toughness of the coating layer. It loses the temperature-resistant strengthening effect brought by the in-situ generation of a dense and uniform ceramic phase. The coating layer is still a loose resin pyrolysis product + filler structure, which is prone to further cracking and pulverization at high temperatures. Due to the non-dense structure and many defects, the dielectric loss will actually increase. In practical applications, the transition layer formed by heat treatment of magnetic powder coated with a combination of silicone resin and active additives is a metastable state under confined conditions. In order to further strengthen this interface, this invention adds a trace amount of mineralizer to the active additive, such as triethyl borate, boron acetylacetonate, or borosilicate sol, with an amount of 0.05wt%~0.5wt% of the silicone resin. Trace mineralizers overcome the low-temperature solid-state reaction kinetics barrier at the interface between highly active nanoparticles and SiO2, thereby promoting further solid-state reaction or close composite formation at the interface within the allowable heat treatment temperature window of the magnetic powder core, forming more heat-resistant and denser composite ceramic phases such as mullite, aluminosilicate, or zirconium silicate. Borosilicate sol is preferred; it can be commercially available or prepared in-house. For example, under sealed conditions, tetraethyl orthosilicate and triethyl borate (molar ratio approximately 9:1) are stirred evenly in anhydrous ethanol (solid-liquid ratio approximately 1:5) to obtain a mixed ester solution. At 60°C with continuous stirring, approximately 100 mL of an alcohol-acid mixture (ethanol + water + hydrochloric acid, pH = 2~3) is added dropwise to the 100 mL mixed ester solution. After the addition is complete, stirring is continued at a constant temperature for 24 h to obtain borosilicate sol.
[0025] The insulating reinforcing agent is hexagonal boron nitride or modified boron nitride; the modified boron nitride is silane coupling agent surface-modified boron nitride; the amount of the insulating reinforcing agent is 0.3%~1.0% of the magnetic powder mass. The hexagonal boron nitride uses micron-sized powder with a D50 of 1μm~10μm. In specific implementations, hexagonal boron nitride can be made into micron-sized powder of the corresponding size through methods such as airflow crushing. Silane coupling agent surface-modified boron nitride can be purchased or prepared by oneself. The preparation method is as follows: first, mix γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane with a 90% ethanol solution (liquid-solid ratio of 100~200:1), adjust the pH to 4~5 with acetic acid, and prepare a silane hydrolysis solution; add the dried hexagonal boron nitride hot powder (approximately 60-80°C) to the silane hydrolysis solution (approximately 50°C~60°C); use... The powder is thoroughly wetted and dispersed in the solution by vigorous mechanical stirring or ultrasonic dispersion. The reaction is carried out at a constant temperature for 2-4 hours. After the reaction, the product is washed multiple times by centrifugation with ethanol (e.g., 3-5 times) until the supernatant is clear. After solid-liquid separation, the resulting wet filter cake is vacuum dried at 80-100℃ for 6-12 hours, and finally heat-treated at 110-120℃ for 1-1.5 hours. After natural cooling, the silane coupling agent surface-modified boron nitride is obtained. The insulating reinforcing agent physically blocks the conductive path, forming a double layer of protection with the chemical insulation of the resin. It significantly improves the lateral thermal conductivity of the coating layer and even the entire magnetic core, aiding in heat dissipation, reducing temperature rise at high frequencies, and lowering losses.
[0026] The lubricant is selected from at least one of amide wax, oxidized polyethylene wax, and maleic anhydride-grafted polyethylene wax; the amount of lubricant used is 0.4% to 1.0% of the magnetic powder mass. The lubricant is a micronized lubricant, specifically: D50 = 5μm to 20μm, D90 ≤ 30μm, preferably D50 = 8μm to 12μm, D90 ≤ 25μm. On the one hand, the lubricant can achieve internal lubrication between magnetic powder particles. The lubricant micronized powder is uniformly distributed on the surface of the magnetic powder particles. During pressing, the tiny lubricant wax particles locally melt or soften under huge pressure and frictional heat to form an extremely thin lubricating film, making the particles easier to slide and rearrange, allowing the powder to flow and fill more evenly in the mold, reducing the density gradient, thereby obtaining a green body with lower internal stress and more uniform density, which is beneficial to obtaining low hysteresis loss and high DC bias performance. On the other hand, the lubricant can also achieve external lubrication between the magnetic powder particles and the mold cavity wall. During subsequent pressing and molding, some of the lubricant will migrate to the contact interface between the powder and the steel mold, forming a separation film, which greatly reduces the demolding force and reduces cracking, delamination or powdering at the edge of the green body caused by friction and stress concentration during demolding; it can also reduce mold wear and tear. The micronized modified polyethylene wax or amide wax of this invention has a certain compatibility with organosilicon resin and can be uniformly embedded in the resin coating layer or attached to its surface, and is not easy to fall off; during the mixing process, the presence of lubricant micronized powder helps to physically separate the insulating reinforcing agent, assists its dispersion, and prevents agglomeration; during subsequent heat treatment, the lubricant completely decomposes and volatilizes after the resin has formed sufficient strength and before the ceramization reaction begins, leaving no residual carbon in the final product.
[0027] The solvent used is toluene or xylene. Insufficient solvent results in excessively high slurry viscosity, poor fluidity, and an inability to form a uniform, continuous film on the magnetic powder surface, easily leading to magnetic powder agglomeration. Excessive solvent results in an overly thin slurry with insufficient solid content, leading to a thin coating layer with inadequate performance. Furthermore, it places a heavy burden on solvent evaporation during subsequent drying, easily creating pores and reducing production efficiency. By controlling the viscosity of the final mixed slurry within the range of 100 mPa·s to 2000 mPa·s (preferably 300 mPa·s to 1000 mPa·s), optimal rheological properties can be ensured, allowing for uniform application to the magnetic powder surface through stirring, spraying, or impregnation, while also guaranteeing sufficient solid content to form an effective coating layer.
[0028] The magnetic powder used in this invention can be any soft magnetic metal material permitted in the art, including but not limited to at least one of carbonyl iron powder, Fe-Ni-Mo alloy powder, Fe-Ni alloy powder, Fe-Co alloy powder, Fe-Si alloy powder, Fe-Si-Al alloy powder, Fe-Si-Cr alloy powder, Fe-based amorphous alloy powder, Ni-based amorphous alloy powder, Co-based amorphous alloy powder, and Fe-based nanocrystalline powder, and the particle size of the soft magnetic metal powder is not higher than 200 mesh; the following examples use Fe-Si-Al alloy powder as the magnetic powder, etc., as examples, but are not limited to this material, and other unlisted magnetic powders are also applicable.
[0029] The above-mentioned auxiliary material formula is used to prepare magnetic powder cores by insulating and coating magnetic powder. The preparation method is as follows: S1, the auxiliary material formula is prepared into a coating slurry. Specifically, the organosilicon resin is dissolved in a solvent to form a resin solution; active additives and insulating reinforcing agents are added to the resin solution in sequence, and high-speed shear dispersion is performed to form a uniform slurry. The amount of solvent used makes the viscosity of the slurry 100mPa·s~2000mPa·s; a lubricant is added to the slurry, and dispersion is continued to obtain a composite insulating coating slurry.
[0030] S2. The magnetic powder is mixed evenly with the coating slurry, dried to remove the solvent, and a pre-coated powder is obtained. S3. The pre-coated powder is pressed into a shape to obtain a magnetic core green blank. S4. The magnetic core green blank is subjected to a stepped heat treatment in a protective atmosphere, and then cooled in the furnace to obtain the magnetic powder core. Specifically, the heat treatment involves heating to 300℃~400℃ at a heating rate of 2℃ / min~5℃ / min and holding for 30min~60min, followed by further heating to 500℃~600℃ and holding for 90min~150min.
[0031] The purpose of heat treatment is to guide and complete the transformation of the coating layer from an organic composite coating to a dense inorganic ceramic insulating layer while protecting the intrinsic properties of the magnetic powder, and at the same time completely removing process additives. Specifically: the first stage of low-temperature heat treatment achieves lubricant decomposition and resin pre-curing; the second stage of high-temperature heat treatment completes the resin ceramicization transformation, drives the active additives to react in situ with the resin pyrolysis products, and eliminates the pressing stress of the magnetic powder.
[0032] In the specific preparation of magnetic powder cores, annealing can be performed before furnace cooling. The annealing temperature is 600℃~750℃, and the time is 30min~2h. Specifically, the annealing temperature and time can be adjusted according to the type of soft magnetic powder. The protective atmosphere can be conventional gases such as nitrogen and / or argon to form an oxygen-free environment.
[0033] Example 1: A method for preparing a magnetic powder core, the specific steps of which are as follows: S1: Prepare the auxiliary material formula into a coating slurry. Specifically: Dissolve 8g of organosilicon resin (methyl silicone resin) in 40g of solvent (xylene) to form a resin solution; add 3g of active additive (aluminum acetylacetonate) and 6g of insulating reinforcing agent (micron-sized hexagonal boron nitride, D50=5μm) to the resin solution in sequence, and perform high-speed shear dispersion to form a uniform slurry; add 5g of lubricant (maleic anhydride grafted polyethylene wax, D50=12μm, D90=25μm) to the slurry, and continue dispersion to obtain an insulating coating slurry.
[0034] S2. Take 1000g of magnetic powder (Fe-Si-Al alloy soft magnetic powder) and mix it evenly with the coating slurry prepared in S1. Heat it to about 80℃ and dry it at low temperature for about 1 hour to remove the solvent. After the xylene solvent has completely evaporated, pass it through an 80-mesh sieve to obtain the pre-coated powder.
[0035] S3. Place the pre-coated powder in a mold and press it for several seconds at 2100MPa to form a core blank.
[0036] S4. The green core blank is subjected to a stepped heat treatment in a protective atmosphere (nitrogen). The heat treatment specifically involves: heating to 350℃~360℃ at a heating rate of 2℃ / min~5℃ / min and holding for 40min, then continuing to heat to 550℃~580℃ and holding for 120min; annealing at 700℃ for 30min; and obtaining the magnetic powder core after furnace cooling.
[0037] Example 2: A method for preparing a magnetic powder core, the specific steps of which are as follows: S1: Prepare the auxiliary material formula into a coating slurry. Specifically: Dissolve 8g of organosilicon resin (methyl silicone resin) in 40g of solvent (xylene) to form a resin solution; add 3g of active additive (zirconium acetylacetonate) and 6g of insulating reinforcing agent (silane coupling agent surface-modified boron nitride) to the resin solution in sequence, and perform high-speed shear dispersion to form a uniform slurry; add 5g of lubricant (oxidized polyethylene wax, D50=12μm, D90=25μm) to the slurry, and continue dispersion to obtain an insulating coating slurry.
[0038] S2. Take 1000g of magnetic powder (Fe-Si-Al alloy soft magnetic powder) and mix it evenly with the coating slurry prepared in S1. Heat it to about 80℃ and dry it at low temperature for about 1 hour to remove the solvent. After the xylene solvent has completely evaporated, pass it through an 80-mesh sieve to obtain the pre-coated powder.
[0039] S3. Place the pre-coated powder in a mold and press it for several seconds at 2100MPa to form a core blank.
[0040] S4. The green core blank is subjected to a stepped heat treatment in a protective atmosphere (nitrogen). The heat treatment specifically involves: heating to 350℃~360℃ at a heating rate of 2℃ / min~5℃ / min and holding for 40min, then continuing to heat to 550℃~580℃ and holding for 120min; annealing at 700℃ for 30min; and obtaining the magnetic powder core after furnace cooling.
[0041] Example 3: A method for preparing a magnetic powder core, the specific steps of which are as follows: S1: Prepare the auxiliary material formula into a coating slurry. Specifically: Dissolve 8g of methylphenyl silicone resin in 40g of solvent (toluene) to form a resin solution; add 3g of active additive (zirconium acetylacetonate) and 6g of insulating reinforcing agent (silane coupling agent surface-modified boron nitride) to the resin solution in sequence, and perform high-speed shear dispersion to form a uniform slurry; add 5g of lubricant (amide wax, D50=12μm, D90=25μm) to the slurry, and continue dispersion to obtain an insulating coating slurry.
[0042] S2. Take 1000g of magnetic powder (Fe-Si-Al alloy soft magnetic powder) and mix it evenly with the coating slurry prepared in S1. Heat it to about 80℃ and dry it at a low temperature for about 1 hour to remove the solvent. After the toluene solvent has completely evaporated, pass it through an 80-mesh sieve to obtain the pre-coated powder.
[0043] S3. Place the pre-coated powder in a mold and press it for several seconds at 2100MPa to form a core blank.
[0044] S4. The green core blank is subjected to a stepped heat treatment in a protective atmosphere (nitrogen). The heat treatment specifically involves: heating to 350℃~360℃ at a heating rate of 2℃ / min~5℃ / min and holding for 40min, then continuing to heat to 550℃~580℃ and holding for 120min; annealing at 700℃ for 30min; and obtaining the magnetic powder core after furnace cooling.
[0045] Example 4: A method for preparing a magnetic powder core, the specific steps of which are as follows: S1: Prepare the auxiliary material formula into a coating slurry. Specifically: Dissolve 8g of organosilicon resin (methyl silicone resin) in 40g of solvent (xylene) to form a resin solution; add 3g of active additive (aluminum acetylacetonate), 0.2g of mineralizer (borosilicate sol) and 6g of insulating reinforcing agent (micron-sized hexagonal boron nitride, D50=5μm) to the resin solution in sequence, and perform high-speed shear dispersion to form a uniform slurry; add 5g of lubricant (maleic anhydride grafted polyethylene wax, D50=12μm, D90=25μm) to the slurry, and continue dispersion to obtain an insulating coating slurry.
[0046] S2. Take 1000g of magnetic powder (Fe-Si-Al alloy soft magnetic powder) and mix it evenly with the coating slurry prepared in S1. Heat it to about 80℃ and dry it at low temperature for about 1 hour to remove the solvent. After the xylene solvent has completely evaporated, pass it through an 80-mesh sieve to obtain the pre-coated powder.
[0047] S3. Place the pre-coated powder in a mold and press it for several seconds at 2100MPa to form a core blank.
[0048] S4. The green core blank is subjected to a stepped heat treatment in a protective atmosphere (nitrogen). The heat treatment specifically involves: heating to 350℃~360℃ at a heating rate of 2℃ / min~5℃ / min and holding for 40min, then continuing to heat to 550℃~580℃ and holding for 120min; annealing at 700℃ for 30min; and obtaining the magnetic powder core after furnace cooling.
[0049] Example 5: A method for preparing a magnetic powder core, the specific steps of which are as follows: S1: Prepare the auxiliary material formula into a coating slurry. Specifically: Dissolve 8g of organosilicon resin (methyl silicone resin) in 40g of solvent (xylene) to form a resin solution; add 3g of active additive (aluminum acetylacetonate), 0.2g of mineralizer (boron acetylacetonate) and 6g of insulating reinforcing agent (micron-sized hexagonal boron nitride, D50=5μm) to the resin solution in sequence, and perform high-speed shear dispersion to form a uniform slurry; add 5g of lubricant (maleic anhydride grafted polyethylene wax, D50=12μm, D90=25μm) to the slurry, and continue dispersion to obtain an insulating coating slurry.
[0050] S2. Take 1000g of magnetic powder (Fe-Si-Al alloy soft magnetic powder) and mix it evenly with the coating slurry prepared in S1. Heat it to about 80℃ and dry it at low temperature for about 1 hour to remove the solvent. After the xylene solvent has completely evaporated, pass it through an 80-mesh sieve to obtain the pre-coated powder.
[0051] S3. Place the pre-coated powder in a mold and press it for several seconds at 2100MPa to form a core blank.
[0052] S4. The green core blank is subjected to a stepped heat treatment in a protective atmosphere (nitrogen). The heat treatment specifically involves: heating to 350℃~360℃ at a heating rate of 2℃ / min~5℃ / min and holding for 40min, then continuing to heat to 550℃~580℃ and holding for 120min; annealing at 700℃ for 30min; and obtaining the magnetic powder core after furnace cooling.
[0053] Example 6: A method for preparing a magnetic powder core, the specific steps of which are as follows: S1: Prepare the auxiliary material formula into a coating slurry. Specifically: Dissolve 8g of organosilicon resin (methyl silicone resin) in 40g of solvent (xylene) to form a resin solution; add 3g of active additive (aluminum acetylacetonate), 0.2g of mineralizer (triethyl borate), and 6g of insulating reinforcing agent (micron-sized hexagonal boron nitride, D50=5μm) to the resin solution in sequence, and perform high-speed shear dispersion to form a uniform slurry; add 5g of lubricant (maleic anhydride grafted polyethylene wax, D50=12μm, D90=25μm) to the slurry, and continue dispersion to obtain an insulating coating slurry.
[0054] S2. Take 1000g of magnetic powder (Fe-Si-Al alloy soft magnetic powder) and mix it evenly with the coating slurry prepared in S1. Heat it to about 80℃ and dry it at low temperature for about 1 hour to remove the solvent. After the xylene solvent has completely evaporated, pass it through an 80-mesh sieve to obtain the pre-coated powder.
[0055] S3. Place the pre-coated powder in a mold and press it for several seconds at 2100MPa to form a core blank.
[0056] S4. The green core blank is subjected to a stepped heat treatment in a protective atmosphere (nitrogen). The heat treatment specifically involves: heating to 350℃~360℃ at a heating rate of 2℃ / min~5℃ / min and holding for 40min, then continuing to heat to 550℃~580℃ and holding for 120min; annealing at 700℃ for 30min; and obtaining the magnetic powder core after furnace cooling.
[0057] The difference between Comparative Example 1 and Example 1 is that the active additive in S1 is replaced by Al2O3 powder instead of aluminum acetylacetonate. All other reaction conditions and steps are the same as in Example 1.
[0058] The difference between Comparative Example 2 and Example 1 is that the active additive in S1 is removed, while the other reaction conditions and steps are the same as in Example 1.
[0059] The difference between Comparative Example 3 and Example 1 is that the insulating reinforcing agent in S1 is removed, while the other reaction conditions and steps are the same as in Example 1.
[0060] The difference between Comparative Example 4 and Example 1 is that the lubricant in S1 is removed, while the other reaction conditions and steps are the same as in Example 1.
[0061] The difference between Comparative Example 5 and Example 1 is that the heat treatment in S4 is performed at a single temperature, while the other reaction conditions and steps are the same as in Example 1.
[0062] The heat treatment is as follows: heating to 350℃~360℃ at a heating rate of 2℃ / min~5℃ / min and holding for 160min; annealing at 700℃ for 30min; and obtaining the magnetic powder core after furnace cooling.
[0063] The difference between Comparative Example 6 and Example 1 is that the heat treatment in S4 is performed at a single temperature, while the other reaction conditions and steps are the same as in Example 1.
[0064] The heat treatment is as follows: heating to 550℃~580℃ at a heating rate of 2℃ / min~5℃ / min and holding for 160min; annealing at 700℃ for 30min; and obtaining the magnetic powder core after furnace cooling.
[0065] The performance of the magnetic powder cores prepared in Examples 1 to 6 and Comparative Examples 1 to 6 was tested, and the results are shown in Table 1.
[0066] Specifically, it includes: (1) measuring the effective permeability (μe) using an impedance analyzer under the conditions of a test frequency of 100kHz and a test voltage of 1V; (2) DC bias characteristics: the attenuation rate of μe under a test frequency of 100kHz and a DC bias magnetic field of 1000e; (3) measuring the loss under the conditions of 100kHz / 50mT and 100kHz / 100mT using a power analyzer or a dedicated magnetic core loss meter; (4) temperature stability: measuring the rate of change of permeability (Δμ / μ) of the magnetic core in the range of room temperature to 150℃; (5) thermal conductivity: using laser flash test, the magnetic powder core is cut and ground into a disc with a diameter of 12.7mm and a thickness of 2.0mm, and the surface is sprayed with a graphite layer to ensure good laser absorption and infrared emissivity. The thermal conductivity is the thermal conductivity in the thickness direction of the material.
[0067] Table 1
[0068] Table 1 shows that the magnetic core prepared in the embodiments of the present invention has advantages such as high permeability, low loss, good bias, high stability, and high thermal conductivity.
[0069] Compared with Example 1, Comparative Example 1 replaced the agent with Al2O3 powder: the magnetic permeability was artificially high, but the loss soared and the DC bias deteriorated; physical mixing led to a large number of interface defects, severe phonon scattering, and a sharp decrease in thermal conductivity.
[0070] Compared with Example 1, Comparative Example 2 had its insulation effect reduced due to the removal of active additives, resulting in the highest magnetic permeability and extremely high losses; without the ceramic reinforcing phase, the coating layer was loose and porous, leading to a significant reduction in thermal conductivity.
[0071] Compared with Example 1, Comparative Example 3 showed a significant deterioration in loss and temperature rise stability, and a significant decrease in thermal conductivity after the removal of the insulation reinforcing agent.
[0072] Compared with Example 1, Comparative Example 4 removed the lubricant, and the defects in the magnetic powder blank led to a significant increase in hysteresis loss and poor bias characteristics. The additional interface / pores introduced by the pressing defects also had a certain negative impact on the thermal conductivity.
[0073] Compared with Example 1, Comparative Example 5 uses a single low-temperature heat treatment, which results in the resin not being ceramicized, leading to huge high-frequency eddy current losses and a significant increase in losses; the resin is not ceramicized, forming a porous organic layer with poor thermal conductivity.
[0074] Compared with Example 1, Comparative Example 6 uses a single high-temperature heat treatment, resulting in a severe decrease in magnetic permeability, high loss, and significantly worse temperature stability; although it has some ceramicization, the improvement in thermal conductivity is limited due to numerous structural defects.
[0075] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.
Claims
1. A formulation for auxiliary materials of a magnetic powder core, characterized in that, The auxiliary material formula of the magnetic powder core is an insulating coating material used to coat the magnetic powder; The magnetic powder core comprises silicone resin, active additives, insulating reinforcing agents, lubricants, and solvents; the active additives are aluminum acetylacetonate or zirconium acetylacetonate; the insulating reinforcing agents are hexagonal boron nitride or modified boron nitride; the modified boron nitride is silane coupling agent surface-modified boron nitride; the lubricant is selected from at least one of amide wax, oxidized polyethylene wax, and maleic anhydride grafted polyethylene wax; the preparation method of the auxiliary material formulation of the magnetic powder core includes the following steps: dissolving silicone resin in a solvent to form a resin solution; An active additive and an insulating reinforcing agent are added sequentially to the resin solution, and shear dispersion is performed to form a uniform slurry. A lubricant is added to the slurry, and shear dispersion is continued to obtain an insulating coating slurry, which serves as the auxiliary material formula for the magnetic powder core.
2. The auxiliary material formula for a magnetic powder core according to claim 1, characterized in that, The amount of the silicone resin is 0.8% to 1.5% of the magnetic powder mass; the amount of the active additive is 0.2% to 0.8% of the magnetic powder mass; the amount of the insulation reinforcing agent is 0.3% to 1.0% of the magnetic powder mass; and the amount of the lubricant is 0.4% to 1.0% of the magnetic powder mass.
3. The auxiliary material formula for a magnetic powder core according to claim 2, characterized in that, The active additive also includes a mineralizer; the mineralizer is triethyl borate, boron acetylacetone, or borosilicate sol, and its amount is 0.05wt%~0.5wt% of the organosilicon resin.
4. The auxiliary material formula for a magnetic powder core according to claim 2, characterized in that, The solvent is toluene or xylene; the amount of solvent used is such that the viscosity of the slurry is 100 mPa·s to 2000 mPa·s.
5. The auxiliary material formula for a magnetic powder core according to claim 1, characterized in that, The silicone resin used is methylphenyl silicone resin.
6. The auxiliary material formula for a magnetic powder core according to claim 1, characterized in that, The hexagonal boron nitride is made of micron-sized powder with a D50 of 1μm to 10μm.
7. The auxiliary material formula for a magnetic powder core according to claim 1, characterized in that, The lubricant is a micronized lubricant with a D50 of 5μm to 20μm and a D90 of ≤30μm.
8. A magnetic powder core, characterized in that, The magnetic powder core is formed by surface coating, pressing and heat treatment of magnetic powder using the auxiliary material formula of any one of claims 1 to 7.
9. The magnetic powder core according to claim 8, characterized in that, The preparation method of the magnetic powder core is as follows: the auxiliary material formula of the magnetic powder core is prepared as a coating slurry; the magnetic powder and the coating slurry are mixed evenly, dried to remove the solvent, and a pre-coated powder is obtained; the pre-coated powder is pressed into shape to obtain a magnetic core green blank; the magnetic core green blank is subjected to step heat treatment in a protective atmosphere, and then cooled in a furnace to obtain the magnetic powder core.
10. The magnetic powder core according to claim 9, characterized in that, The heat treatment specifically involves heating to 300℃~400℃ at a rate of 2℃ / min~5℃ / min and holding at that temperature for 30min~60min, followed by further heating to 500℃~600℃ and holding at that temperature for 90min~150min.